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2024 Volume 4
Article Contents
Abstract
Introduction
Materials and methods
Cell lines and cell culture
In vivo mouse models
Generation of modified gastric cancer cell lines
Cell counting Kit-8 assay
Colony formation assay
RNA pull-down assay
Extracellular acidification rate assay
Single-cell RNA-seq data analysis
RNA-seq data analysis
Cell-cell communication analysis
Statistical analysis
Results
Glycolysis was upregulated in trastuzumab-resistant gastric cancer cells
ENO1 was upregulated in trastuzumab-resistant gastric cancer cells
ENO1 was associated with cell survival, colony formation, and tumor growth in gastric cancer
Overexpressed ENO1 inhibited the expression of TCA-related gene IRP1
Elevated IRP1 impaired cell survival, colony formation, and tumor growth in gastric cancer
IRP1 regulated ferroptosis in gastric cancer cells
Gastric cancer epithelial cells expressing ENO1 enhanced the interaction with other components of the tumor microenvironment
Discussion
Ethical statements
Author contributions
Data availability
Acknowledgments
Conflict of interest
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References
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REVIEW   Open Access    

Application of modified zeolite in the remediation of heavy metal in contaminated soil: a short review

  • 1.

    Faculty of Natural Resources and Environment, TNU-University of Sciences, Tan Thinh ward, Thai Nguyen City, 250000, Vietnam

  • 2.

    Center for Advanced Technology Development, Thai Nguyen University, Tan Thinh ward, Thai Nguyen City, 250000, Vietnam

More Information
  • This paper explores the significant potential of modified zeolites in various industries, emphasizing their role in promoting environmental sustainability. The study highlights the applications of modified zeolites in heavy metals in contaminated soil, showcasing their ability to address environmental pollution and enhance resource utilization. The research underscores the importance of fine-tuning zeolite modification techniques to achieve precise structural control and stability. Challenges related to the impact of even minor modifications on performance and the long-term stability of modified zeolites are acknowledged. Despite these challenges, the paper anticipates a promising future for modified zeolites, with advancements in materials science and nanotechnology expected to pave the way for innovative solutions in contaminated soil.

  • Introduction

    Gastric cancer is a prevalent malignancy and a leading cause of cancer-related mortality in China[1]. Current treatment approaches, including surgery, chemotherapy, targeted therapy, and immunotherapy, are often combined to enhance patient outcomes. Neoadjuvant chemotherapy, administered before surgery, aims to shrink tumors and increase resection success[2], while adjuvant chemotherapy after surgery targets residual cancer cells to reduce recurrence risk. Advances in targeted therapies and immunotherapies, particularly for advanced stages, represent significant progress in gastric cancer management.

    Cell metabolism is essential for the initiation and progression of gastric cancer. Gastric cancer cells undergo metabolic reprogramming, predominantly adopting glycolysis to enhance survival and metastasis — a phenomenon known as the Warburg effect. This common metabolic phenotype in cancer is strongly linked to drug resistance[3,4]. The Warburg effect involves increased glucose uptake and lactate production, leading to elevated levels of metabolites such as fumaric acid and alpha-ketoglutaric acid in cancer tissues[5]. Similarly, higher concentrations of 3-hydroxypropionic acid and pyruvic acid are detected in the blood of gastric cancer patients[6]. These metabolic alterations support cancer cell growth and confer resistance to chemotherapy[7]. Key proto-oncogenes, such as Myc, drive this glycolytic shift by upregulating enzymes like glucose transporter 1 (GLUT1), lactate dehydrogenase A (LDHA), and pyruvate kinase M2 (PKM2)[8−11]. Additionally, the inactivation of the tumor suppressor gene p53 further promotes glycolysis[11]. Unlike normal cells, which primarily rely on oxidative phosphorylation (OXPHOS) for energy, cancer cells favor glycolysis to generate intermediates that support rapid proliferation[12]. Beyond glycolysis, lipid metabolism is crucial for cancer cell growth and metastasis. Enhanced lipid synthesis and uptake facilitate membrane biosynthesis and energy storage[13,14]. Amino acid metabolism also plays a pivotal role, particularly in one-carbon metabolism, which is essential for DNA and RNA synthesis and promoting cell proliferation. Moreover, gastric cancer cells experience heightened oxidative stress, resulting in DNA damage and mutations that drive cancer progression[15]. Accumulated reactive oxygen species (ROS) further exacerbate metabolic dysregulation, creating a feedback loop that fuels malignancy. Understanding these metabolic adaptations highlights potential therapeutic targets, underscoring the importance of metabolic pathways in gastric cancer biology.

    Trastuzumab, a recombinant humanized monoclonal antibody, specifically targets the human epidermal growth factor receptor 2 (HER2) and is the only approved first-line targeted therapy for HER2-positive advanced gastric cancer[16,17]. Combination of trastuzumab with platinum-fluoropyrimidine chemotherapy has been shown to significantly improve survival in patients with HER2-positive gastric cancer[16]. However, the overall response rate remains below 50%, indicating that many HER2-positive cases have developed resistance to HER2 inhibition[18]. Identifying patient subgroups likely to benefit from trastuzumab and optimizing HER2-targeted treatment regimens are therefore critical. While trastuzumab is highly effective against HER2-positive tumors, particularly in breast cancer, resistance mechanisms in gastric cancer are less well-characterized compared to breast cancer. Addressing this gap is essential to improve therapeutic outcomes in HER2-positive gastric cancer patients.

    Emerging evidence highlights the significant role of glycolysis in influencing trastuzumab efficacy in gastric cancer. Activation of 6-phosphofructo-2-kinase (PFKFB3) within the glycolytic pathway induces trastuzumab resistance and promotes vascular instability in HER2-positive gastric cancer. In contrast, PFKFB3 inhibition reduces tumor growth and normalizes vasculature[19]. Similarly, GATA6 knockout re-sensitizes gastric cancer cells to trastuzumab by regulating metabolic pathways such as the TCA cycle and glycolysis[20]. Various glycolysis inhibitors, including MTCI, PDK, LDHA, and hexokinase inhibitors, have been explored to counteract resistance to cancer therapies[21−23]. These agents disrupt cancer metabolism, enhancing therapeutic efficacy. Notably, 2-deoxy-D-glucose (2-DG)[24], and Oxamate[25] have shown promise in clinical trials. 2-DG, when combined with docetaxel, exhibits efficacy with manageable side effects, while Oxamate selectively targets cancer cells, sparing normal tissues. Combining glycolysis inhibitors with anti-tumor therapies offers a potential strategy to overcome drug resistance and improve treatment outcomes. Future research should prioritize optimizing these inhibitors for clinical application.

    Through a combination of in vivo and in vitro experiments alongside bioinformatics analyses, we identified a significant upregulation of the glycolytic enzyme ENO1 in trastuzumab-resistant gastric cancer cell lines. Elevated ENO1 expression levels were shown to suppress ACO1 expression, thereby inhibiting cellular ferroptosis. These findings highlight the potential of targeting ENO1 or modulating ACO1 expression to overcome trastuzumab resistance, offering new avenues for novel personalized treatment strategies in gastric cancer.

    Materials and methods

    Cell lines and cell culture

    Trastuzumab-sensitive (NCI-N87, MKN45) and trastuzumab-resistant (NCI-N87R, MKN45R) gastric cancer cell lines (Genelily Biotech Co., LTD, China) were cultured in DMEM medium supplemented with 10% fetal bovine serum (FBS) (Gibco, USA) and 1% antibiotics (100 U/mL penicillin G and 100 μg/mL streptomycin). The cells were maintained at 37 °C in an atmosphere containing 5% CO2.

    In vivo mouse models

    The Balb/c Nude mice were housed under specific pathogen-free conditions following the guidelines of Changzhou Cavens Laboratory Animal Co., Ltd (Changzhou, China). Animals aged 6 to 8 weeks, with age- and gender-matched controls, were used for all in vivo experiments. Detailed sample sizes for each study are provided in the figure legends.

    The dorsal skin of Balb/c Nu mice was sterilized with alcohol. A total of 1 × 107 tumor cells were injected subcutaneously, and housed under standard conditions. Trastuzumab was administered intraperitoneally at a dose of 30 mg/kg every 5 d. Tumor size was measured at 5-d intervals up to day 30. After the final measurement, the tumors were photographed, excised, and fixed in formalin. Tumor volume was calculated using the formula V = a × b2/2, where a is the length and b is the width of the tumor.

    Generation of modified gastric cancer cell lines

    All shRNA (pLVX-shRNA) and overexpression (pLVX-IRES-puro-RNA) vectors were synthesized by Genelily Biotech Co., LTD (Shanghai, China). These vectors were subsequently packaged into lentiviruses for the establishment of stably transfected cell lines. Cells were seeded in 6-well plates at a density of 5 × 105 cells per well, followed by the addition of distinct lentiviruses (pLVX-IRES-puro and pLVX-IRES-puro-ENO1) at a multiplicity of infection (MOI) of 50. The medium was replaced 24 h post-infection. After 48 h, the medium was completely switched to one containing 2 μg/mL puromycin. The medium was refreshed every 2 d. Once stable cell growth was observed, cells were passaged. After two passages, puromycin was no longer required in the culture medium, indicating the successful establishment of the cell lines. A portion of the cells was preserved for future use, while another portion was utilized for RNA and protein extraction to validate ENO1 expression via Real-time PCR and Western blotting, respectively.

    Cell counting Kit-8 assay

    In a 96-well plate, 100 μL of a cell suspension at a density of 2 × 104 cells/mL was dispensed into each well and incubated at 37 °C with 5% CO2 for 24 h. Following the pre-incubation period, the cells were treated with varying concentrations of trastuzumab (0.1, 0.3, 1, 3, 10, 30, 100, 300, and 1,000 μg/mL) and further incubated for an additional 24 h. At predetermined time points (0, 12, 24, 48, and 72 h), the plate was removed, and 10 μL of CCK-8 solution was added to each well, ensuring the avoidance of bubble formation to prevent interference with OD values. The plate was incubated for 1 h, and absorbance was measured at 450 nm using a microplate reader to assess cell viability. The data were analyzed, and the IC50 curve was generated using Prism 9 software.

    Colony formation assay

    Cells in the logarithmic growth phase were treated with 0.25% trypsin to dissociate them into single cells, which were subsequently suspended in DMEM medium supplemented with 10% FBS. The cell suspension was serially diluted, and 100 cells per dish were seeded into 10 mL of pre-warmed culture medium at 37 °C. The dishes were gently rotated to ensure even cell distribution and incubated at 37 °C in a cell culture incubator with 5% CO2 and saturated humidity for 2 to 3 weeks. Regular observations were made, and upon the appearance of visible colonies, the culture was terminated. The supernatant was removed, and the cells were washed twice with PBS. The cells were then fixed with 5 mL of 4% paraformaldehyde for 15 min, after which the fixative was discarded. The cells were stained with crystal violet solution for 10 to 30 min, followed by gentle washing with running water, and the dishes were air-dried. Finally, the colony plates were scanned for imaging, and the number of colonies was quantified using ImageJ software.

    RNA pull-down assay

    Firstly, the cell protein was extracted from a sample containing 1 × 107 cells and set aside. Next, 50 μL of resuspended streptavidin magnetic beads were added to each 1.5 mL EP tube, and the beads were washed twice with 500 μL of Wash Buffer to remove impurities. The beads were then resuspended in 500 μL of Wash Buffer. Subsequently, 2 μg of biotin-labeled IRP1 mRNA was introduced and incubated at 4 °C for 6−8 h to facilitate binding. Following the binding process, 100 μL of pre-lysed cell lysate and 5 μL of RNase inhibitor were added to prevent RNA degradation, followed by overnight incubation at 4 °C. Ten μL of the lysate was taken as an input sample and stored at −20 °C for subsequent analysis. The beads-RNA-protein complex was centrifuged at low speed and washed six times with 500 μL of Wash Buffer II to remove unbound proteins, ensuring complete removal of the supernatant after each wash. Finally, 40 μL of Wash Buffer and 10 μL of 5 × SDS loading buffer were added to the beads and heated at 95 °C for 10 min to release the proteins. The resulting samples were then subjected to SDS-PAGE gel electrophoresis and Western blotting to detect the ENO1 protein in the IRP1 mRNA-enriched fraction, thereby analyzing the binding efficiency of IRP1 mRNA to ENO1 protein.

    Extracellular acidification rate assay

    A total of 175 μL of the original growth medium was aspirated from each well, followed by two rinses with 600 μL of hippocampal testing medium. Subsequently, 450 to 525 μL of hippocampal testing medium was added to each well. Microscopic examination confirmed that the cell monolayer in each well remained continuous and undamaged. The culture plate was then incubated in a non-CO2 incubator for 1 h. Post-incubation, cells were treated with specified drug concentrations according to the manufacturer's operating procedures. Following drug treatment, the culture plate was transferred to the Seahorse XF Analyzer, where baseline ECAR values were recorded. Sequential injections of glucose, oligomycin, and 2-DG were performed, with ECAR changes recorded at each step to assess cellular glycolytic capacity. All ECAR data were collected for statistical analysis, and comparisons of ECAR values across different treatment groups were conducted to evaluate the drugs' impact on cellular glycolytic metabolism.

    Single-cell RNA-seq data analysis

    scRNA-seq data for gastric cancer were obtained from the GEO database (GSE183904)[26] and processed using the standard workflow provided by the Seurat package. Initially, Seurat objects were created for each dataset, and the percentages of mitochondrial and ribosomal RNA were calculated and added to the metadata. These datasets were then merged into a single Seurat object and normalized using the LogNormalize method. Variable features were identified using DUBStepR, and cell cycle scoring was performed based on these features to mitigate cell cycle effects. Data standardization and Principal Component Analysis (PCA) were conducted for preliminary dimensionality reduction. Batch effects were corrected with the Harmony algorithm. The resulting principal components were utilized for clustering analysis, and Uniform Manifold Approximation and Projection (UMAP) visualizations were generated. Clusters were annotated based on marker gene expression, and multiple plots were produced to provide a comprehensive visualization of the data.

    RNA-seq data analysis

    RNA-seq data for trastuzumab-sensitive and -resistant gastric cancer cells were sourced from GEO database (GSE77346)[27], and gene sets associated with trastuzumab resistance were identified. The AddModuleScore function was applied to the scRNA-seq data to compute scores, categorizing epithelial cells into resistance high and resistance low groups based on the median score. Differential expression genes (DEGs) between these groups were calculated using the FindMarkers function. Metabolic pathway scores were calculated using gene sets from the hallmark database. All visualizations were generated using functions from the Seurat package.

    Cell-cell communication analysis

    After data preprocessing, we used the CellPhoneDB tool to analyze receptor-ligand interactions between different cell populations. CellPhoneDB leveraged a comprehensive receptor-ligand interaction database and integrated single-cell transcriptomic data to identify potential intercellular communication networks by calculating interaction scores between cell types. The workflow involved inputting the processed single-cell expression matrix into CellPhoneDB, defining the cell types, and running the analysis to generate receptor-ligand interaction scores and their statistical significance across cell populations.

    Following the initial analysis, further filtering of the interaction data was conducted, focusing on the interactions between epithelial cells and various components of the tumor microenvironment. The selection criteria included the significance of receptor-ligand pairs, their expression levels, and their potential biological functions. Finally, the filtered receptor-ligand interaction network was visualized using the ktplots package for clearer interpretation and presentation.

    Statistical analysis

    All bioinformatics analyses were conducted using R-4.2.3, RStudio, and GraphPad Prism 9. No new algorithms were generated during these bioinformatics analyses. All figures were created using Adobe Illustrator 2023 for scientific visualization. scRNA-seq data were analyzed using the Seurat package. For specific details on statistical tests, please refer to the legends associated with the figures.

    Results

    Glycolysis was upregulated in trastuzumab-resistant gastric cancer cells

    To explore the association between HER2 expression and key metabolic pathways, we applied the GSVA method to calculate scores for seven metabolic pathways from the Hallmark database. Correlation analysis revealed a strong positive relationship between ERBB2 expression and both the cholesterol homeostasis and glycolysis pathways (Fig. 1a). This finding prompted further investigation into the link between ERBB2 expression and glycolysis. Using data from both the TCGA and GEO (GEO: GSE220917) databases, Pearson correlation analysis confirmed a significant association between ERBB2 expression and glycolysis in both datasets (Fig. 1b & c).

    Figure 1.  Elevated glycolysis in trastuzumab-resistant gastric cancer cells. (a) Heat map showing the correlation between ERBB2 expression and metabolic pathways in TCGA-STAD. (b) Dot plot showing the correlation between ERBB2 expression and glycolysis in the TCGA-STAD. (c) Dot plot showing the correlation between ERBB2 expression and glycolysis in the GEO database. (d) UMAP visualized the clustering of gastric cancer cells based on the trastuzumab-resistant score. (e) Heat map showing the DEGs between 'resistance low' and 'resistance high' groups. (f) Scores of metabolism-related pathways between 'resistance low' and 'resistance high' groups. (g) ECAR assay results of trastuzumab-resistant gastric cancer cell line NCI-N87R and trastuzumab-sensitive gastric cancer cell line NCI-N87. The experiment was performed with three biological replicates (N = 3). (h) Box plots displaying the basal glycolysis level (glycolysis), glycolytic capacity (glycolytic capacity), glycolytic reserve (glycolytic reserve), and non-glycolytic acidification (non-glycolytic acidification) of two gastric cancer cell lines according to (g). Pearson correlation analysis was used to calculate the correlation in (a)−(c). The 'resistance low' and 'resistance high' groups are defined by the median value of the trastuzumab-resistant score. Statistical analyses in (h) were performed using an unpaired, two-tailed Student's t-test. * p < 0.05, ** p < 0.01, *** p < 0.001.
    DownLoad: Full-Size Img PowerPoint

    To investigate the mechanisms underlying trastuzumab resistance in gastric cancer, we utilized previously published gene sets associated with trastuzumab resistance[27]. By scoring the trastuzumab resistance-related gene set in scRNA-seq data[26] (GEO: GSE183904) of gastric cancer epithelial cells, the cells were classified into two groups: low resistance and high resistance (Fig. 1d). Differential expression genes analysis revealed marked differences in gene expression profiles between these two groups (Fig. 1e).

    Given the critical role of metabolic pathways in influencing trastuzumab treatment outcomes, we evaluated the activity of metabolism-related pathways using Hallmark gene sets. The analysis showed significant enrichment of oxidative phosphorylation, fatty acid metabolism, and glycolysis pathways in the resistant high group (Fig. 1f). These results suggest that metabolic reprogramming may contribute substantially to trastuzumab resistance.

    Since glycolysis has been implicated in immune suppression across various cancers, we further assessed glycolysis activity in trastuzumab-sensitive and trastuzumab-resistant gastric cancer cell lines. Extracellular acidification rate (ECAR) assays revealed significantly reduction glycolysis activity in the trastuzumab-resistant gastric cancer cell line NCI-N87R (Fig. 1g & h). These findings indicate that glycolysis inhibition may contribute to trastuzumab resistance and highlight the glycolysis pathway as a promising target for overcoming therapeutic resistance.

    ENO1 was upregulated in trastuzumab-resistant gastric cancer cells

    To further investigate the role of glycolysis in trastuzumab resistance, we conducted a comparative analysis of glycolysis-related genes between the resistant-low and resistant-high groups. This analysis revealed significant upregulation of several key glycolytic genes, including ENO1, PGK1, PGAM1, TPI1, PKM, and ALDOA, in the resistant-high group (Fig. 2a). Among these, ENO1 demonstrated consistent upregulation in four gastric cancer cell lines (GEO: GSE77346), aligning with the scRNA-seq findings (Fig. 2b).

    Figure 2.  Increased ENO1 expression in trastuzumab-resistant gastric cancer cells. (a) Violin plots showing upregulated glycolysis-related genes in Fig. 1a. (b) Bar plots displaying upregulated glycolysis-related genes in gastric cancer cell lines. (c) RT-PCR analysis of ENO1 expression in trastuzumab-resistant and trastuzumab-sensitive gastric cancer cell lines. The experiment was performed with three biological replicates (N = 3). (d) and (e) Western blot analysis of ENO1 protein levels in trastuzumab-resistant and trastuzumab-sensitive gastric cancer cell lines. The experiment was performed with three biological replicates (N = 3). Statistical analyses in (a), (c), and (e) were performed using an unpaired, two-tailed Student's t-test. * p < 0.05, ** p < 0.01, *** p < 0.001.
    DownLoad: Full-Size Img PowerPoint

    ENO1 encodes a pivotal enzyme in glycolysis that catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate, a critical step in the glycolytic pathway. As glycolysis is a major metabolic process that supports cancer cells' energy demands and proliferation, the elevated expression of ENO1 suggests its role as a metabolic adaptation mechanism promoting trastuzumab resistance. To validate the involvement of ENO1 in glycolysis and trastuzumab resistance, we performed RT-PCR (Fig. 2c), and Western blotting (Fig. 2d & e) analyses on trastuzumab-sensitive (NCI-N87 and MKN45) and resistant (NCI-N87R and MKN45R) gastric cancer cell lines. The results demonstrated significant upregulation of ENO1 at both mRNA and protein levels in resistant cell lines compared to their sensitive counterparts (Fig. 2c−e).

    In summary, our findings underscore the upregulation of ENO1 and other glycolysis-related genes in trastuzumab-resistant gastric cancer cell lines. These results suggest that ENO1 plays a central role in glycolysis-mediated mechanisms contributing to trastuzumab resistance, highlighting it as a potential target for therapeutic intervention.

    ENO1 was associated with cell survival, colony formation, and tumor growth in gastric cancer

    To further investigate the functional role of ENO1 in gastric cancer, we established ENO1 overexpression models in the trastuzumab-sensitive cell lines NCI-N87 and MKN45, and ENO1 knockdown models in the trastuzumab-resistant cell lines NCI-N87R and MKN45R (Fig. 3a−c). ENO1 knockdown significantly reduced glycolysis activity, as demonstrated by decreased lactate production and extracellular acidification rate (Fig. 3d & e). Conversely, overexpression of ENO1 in trastuzumab-sensitive cells significantly enhanced their resistance to trastuzumab treatment, while knockdown of ENO1 in resistant cells notably reduced their resistance (Fig. 3f). Colony formation assays demonstrated that elevated ENO1 expression significantly increased the clonogenic capacity of gastric cancer cells (Fig. 3g & h). Specifically, ENO1 overexpression resulted in a substantial rise in both colony number and size, indicating a pronounced enhancement in tumorigenic potential.

    Figure 3.  ENO1 linked to enhanced cell survival and colony formation in gastric cancer cells. (a) RT-PCR analysis of ENO1 expression in modified gastric cancer cell lines. (b) and (c) Western blot analysis of ENO1 protein levels in modified gastric cancer cell lines. (c) ECAR assay results of ENO1-knockdown gastric cancer cell lines. (d) Box plots displaying the basal glycolysis level (glycolysis), glycolytic capacity (glycolytic capacity), glycolytic reserve (glycolytic reserve) and non-glycolytic acidification (non-glycolytic acidification) of two gastric cancer cell lines according to (c). (f) Curves of cell viability assay for modified gastric cancer cell lines. (g) and (h) Colony formation assay results for modified gastric cancer cell lines. The experiment was performed with three biological replicates (N = 3). Statistical analyses in (a), (c), (e), and (h) were performed using an unpaired, two-tailed Student's t-test. * p < 0.05, ** p < 0.01, *** p < 0.001.
    DownLoad: Full-Size Img PowerPoint

    To explore the impact of ENO1 expression on tumor growth in gastric cancer, we constructed an in vivo mouse xenograft model. ENO1 knockdown was performed in the trastuzumab-resistant NCI-N87R cell line, and the modified cells were injected into mice to establish stable tumor models. Mice were subsequently treated with trastuzumab to evaluate its efficacy under conditions of reduced ENO1 expression (Fig. 4a & b). The results revealed that ENO1 knockdown significantly suppressed tumor growth in mice bearing trastuzumab-resistant gastric cancer cells (Fig. 4c−e). These findings indicate that elevated ENO1 expression is linked to accelerated tumor progression while reducing ENO1 expression can mitigate tumor growth, suggesting its potential as a therapeutic target in gastric cancer treatment.

    Figure 4.  ENO1 was associated with tumor growth in gastric cancer. (a) Balb/c Nu mice were injected subcutaneously with 1 × 107 tumor cells and housed under standard conditions. Trastuzumab (30 mg/kg) was administered intraperitoneally every 5 d. Tumor size was measured every 5 d until day 30, after which the tumors were photographed, excised, and fixed in formalin. Tumor volume diagram with five biological replicates (N = 5). (b) Representative IHC staining results from (a). (c) Tumor growth curves corresponding to (a). (d) Box plots illustrated tumor weight in (a). (e) Levels of ENO1 protein based on IHC results in (b). Statistical analyses in (c)−(e) were performed using an unpaired, two-tailed Student's t-test. ** p < 0.01, *** p < 0.001.
    DownLoad: Full-Size Img PowerPoint

    Collectively, our results underscore the pivotal role of ENO1 in driving trastuzumab resistance and promoting tumor clonogenicity in gastric cancer cells. Targeting ENO1 offers a promising therapeutic strategy to overcome resistance and inhibit tumor progression, paving the way for improved treatments for gastric cancer.

    Overexpressed ENO1 inhibited the expression of TCA-related gene IRP1

    Previous studies have shown that ENO1 suppresses the expression of the TCA cycle-related gene IRP1[28]. IRP1 functions as a cytoplasmic isomer of aconitase, an iron-sulfur protein requiring a 4Fe-4S cluster for its enzymatic activity, which catalyzes the conversion of citrate to isocitrate[29]. To investigate this relationship, we analyzed IRP1 mRNA and protein levels in NCI-N87 and MKN45 gastric cancer cell lines using RT-PCR and Western blotting. The results demonstrated that elevated ENO1 expression significantly downregulates IRP1 mRNA and protein levels (Fig. 5a−c). Additionally, RNA pull-down assays revealed that ENO1 can bind to IRP1 mRNA, thereby regulating its expression (Fig. 5d). These findings underscore ENO1's critical role in metabolic reprogramming by suppressing IRP1, thereby influencing TCA cycle activity and cellular metabolism.

    Figure 5.  ENO1 overexpression suppressed TCA-related gene IRP1 expression. (a) RT-PCR analysis of IRP1 expression in ENO1-overexpressed gastric cancer cell lines. (b) and (c) Western blot analysis of IRP1 protein levels in ENO1-overexpressed gastric cancer cell lines. (d) RNA pull-down assay of trastuzumab-resistant gastric cancer cell line NCI-N87R. (e) RT-PCR analysis of IRP1 expression in ENO1-knockdown gastric cancer cell lines. (f) and (g) Western blot analysis of IRP1 protein levels in ENO1-knockdown gastric cancer cell lines. The experiment was performed with three biological replicates (N = 3). (h)−(k) The curves represent IRP1 expression at various time points (0, 1, 3, 6 h). (h) OE-ENO1 NCI-N87R. (i) OE-ENO1 MKN45R. (j) sh-ENO1 NCI-N87R. (k) sh-ENO1 MKN45R. All statistical analyses were performed using an unpaired, two-tailed Student's t-test. * p < 0.05, ** p < 0.01, *** p < 0.001.
    DownLoad: Full-Size Img PowerPoint

    To further validate these mechanisms in trastuzumab-resistant gastric cancer, we examined IRP1 expression in NCI-N87R and MKN45R cell lines. Knocking down ENO1 expression markedly increased IRP1 mRNA and protein levels (Fig. 5e−g). Additionally, RNA stability assays revealed that high ENO1 expression decreases IRP1 mRNA stability, whereas ENO1 knockdown enhances its stability (Fig. 5h−k).

    These results suggest that ENO1 modulates IRP1 expression and mRNA stability through multiple mechanisms, leading to potential disruptions in the TCA cycle. This regulatory axis highlights ENO1's pivotal role in the metabolic reprogramming of gastric cancer cells and provides insights into its contribution to tumor progression and therapeutic resistance.

    Elevated IRP1 impaired cell survival, colony formation, and tumor growth in gastric cancer

    To further investigate the role of IRP1 in gastric cancer, we conducted both in vitro and in vivo experiments. Using the trastuzumab-resistant NCI-N87R cell line, we established IRP1 knockdown models (Fig. 6a & b). In vitro analysis demonstrated that IRP1 downregulation significantly increased trastuzumab resistance. Colony formation assays further revealed that reduced IRP1 expression enhanced the clonogenic potential of gastric cancer cells, as evidenced by a notable increase in colony number and size (Fig. 6c & d), indicating greater tumorigenic capacity.

    Figure 6.  IRP1 impaired cell survival, colony formation and tumor growth in gastric cancer. (a) and (b) Curves of cell viability assay for modified gastric cancer cell lines. (a) NCI-N87R. (b) MKN45R. (c) and (d) Colony formation assay results for modified gastric cancer cell lines. The experiment was performed with three biological replicates (N = 3). (e) Balb/c Nu mice were injected subcutaneously with 1 × 107 tumor cells and housed under standard conditions. Trastuzumab (30 mg/kg) was administered intraperitoneally every 5 d. Tumor size was measured every 5 d until day 30, after which the tumors were photographed, excised, and fixed in formalin. Tumor volume diagram with five biological replicates (N = 5). (f) Tumor growth curves corresponding to (e). (g) Representative IHC staining results from (e). (h) Box plots illustrated tumor weight in (e). All statistical analyses were performed using the Tukey's multiple-comparison test. *** p < 0.001.
    DownLoad: Full-Size Img PowerPoint

    To examine the impact of IRP1 expression on tumor growth, we constructed an in vivo mouse xenograft model. Mice were subsequently treated with trastuzumab to evaluate its efficacy under conditions of reduced IRP1 and ENO1 expression (Fig. 6e). The results showed that IRP1 downregulation significantly accelerated tumor growth in mice bearing trastuzumab-resistant gastric cancer cells (Fig. 6f−h). These findings suggest that high IRP1 expression is associated with reduced tumorigenicity and slower tumor progression, while its suppression promotes tumor growth.

    In summary, our study highlights IRP1 as a key regulator of trastuzumab resistance and tumor progression in gastric cancer. Targeting IRP1 may offer a novel therapeutic strategy to mitigate tumor progression and improve treatment outcomes in trastuzumab-resistant gastric cancer.

    IRP1 regulated ferroptosis in gastric cancer cells

    In trastuzumab-resistant gastric cancer cells, ferroptosis levels are typically reduced[30]. Analysis of scRNA-seq data revealed upregulation of the ferritin-encoding genes FTL and FTH1 in these resistant cells (Fig. 7a & b). This upregulation might be linked to mechanisms that enable gastric cancer cells to evade ferroptosis. In contrast, trastuzumab-sensitive cells showed elevated expression of IRP1, a key regulator of cellular ferroptosis (Fig. 7c). Additionally, the transferrin receptor gene (TFRC), involved in iron ion transport, was also upregulated in sensitive cells (Fig. 7c). These findings indicate that trastuzumab-sensitive cells may increase intracellular iron levels by upregulating iron regulatory and transport proteins, thereby promoting ferroptosis and enhancing trastuzumab sensitivity.

    Figure 7.  IRP1 regulated ferroptosis in gastric cancer cells. (a) and (b) Violin and UMAP plots visualizing expression of ferritin-encoding genes FTL and FTH1 in Fig. 1a. (c) UMAP plots visualizing expression of ferritin-encoding genes ACO1 and TRRC in Fig. 1a. (d) Ferrous iron levels in modified gastric cancer cell lines. (e) and (f) Western blotting analysis of ferritin levels in modified gastric cancer cell lines. The experiment was performed with three biological replicates (N = 3). Statistical analyses in (a) were performed using an unpaired, two-tailed Student's t-test, (d) and (f) were performed using the Tukey's multiple-comparison test. ** p < 0.01, *** p < 0.001.
    DownLoad: Full-Size Img PowerPoint

    Further analysis of ferrous ion levels across various gastric cancer cell lines revealed a significant decrease in ferrous ion levels in trastuzumab-resistant lines following ENO1 knockdown. However, this reduction was reversed by IRP1 loss (Fig. 7c & d). Western blot analysis showed that ferritin levels, encoded by FTL and FTH1, were markedly reduced in ENO1-knockout cells, while IRP1 deficiency led to a significantly increased ferritin level (Fig. 7e). These findings indicate that ENO1 suppresses IRP1 expression, thereby impairing its critical role in regulating ferroptosis. By modulating iron homeostasis and ferroptosis, ENO1 contributes to the resistance mechanisms in trastuzumab-resistant gastric cancer cells.

    Gastric cancer epithelial cells expressing ENO1 enhanced the interaction with other components of the tumor microenvironment

    CellPhoneDB analysis revealed that ENO1-overexpressing epithelial cells exhibited significantly enhanced interactions with stromal, endothelial, and myeloid cells, indicating robust intercellular communication (Supplementary Fig. S1). In contrast, their interactions with immune cells, including T cells, B cells, plasma cells, and mast cells, were notably weaker. This suggests that immune cell engagement with ENO1-overexpressing epithelial cells may occur indirectly, mediated by signaling from stromal and endothelial cells.

    Further analysis of the Wnt and Notch signaling pathways identified strong ligand-receptor interactions in the ENO1-overexpressing group. Stromal cells secreted ligands such as WNT2B, WNT4, and WNT5A, which interacted prominently with receptors on ENO1-overexpressing epithelial cells (Fig. 8a & b). Similarly, endothelial cell-derived ligands, including DLL1, DLL4, JAG1, and JAG2, exhibited significant interactions with receptors on these epithelial cells (Fig. 8c & d), underscoring the importance of the Wnt and Notch pathways in regulating cell communication, potentially contributing to tumor aggressiveness and therapy resistance.

    Figure 8.  ENO1 expression levels regulated ligand-receptor interactions of Wnt and Notch signaling pathways in different cell types. (a) Dot plot showing the interactions of the Wnt signaling pathways across different cell types. The color of the dots represents the number of receptor-ligand pairs involved in the interactions, while the size of the dots indicates the percentage of interacting cells. The black circles around the dots denote statistically significant interactions. (b) The expression of the corresponding genes in different cell populations from (a). The size of the circles represent the percentage of cells expressing the genes, and the color of the circles indicate the average expression levels. (c) Dot plot showing the interactions of the Notch signaling pathways across different cell types. (d) The expression of the corresponding genes in different cell populations from (c).
    DownLoad: Full-Size Img PowerPoint

    TGF-β signaling also played a major role, with strong ligand-receptor interactions between TGF-β ligands and ENO1-overexpressing epithelial cells, suggesting its involvement in promoting tumor progression and immune evasion (Supplementary Fig. S2a & b). Additionally, EGF signaling was implicated, as interactions between ENO1-overexpressing epithelial cells and EGFR on stromal cells, mediated by TGF-α, further suggested a role in driving tumor aggressiveness. Gene expression analysis reinforced these findings, with high expression of TGFB2 and TGFB3 in stromal cells and elevated TGFA in ENO1-overexpressing epithelial cells. Moreover, TNF and chemokine signaling pathways provided further insights into the complex communication within the ENO1-overexpressing tumor microenvironment (Supplementary Fig. S2c & d). TNFSF10 from myeloid cells interacted strongly with ENO1-overexpressing epithelial cells, emphasizing the role of TNF signaling in immune regulation. Chemokines such as CXCL1, secreted by ENO1-overexpressing cells, and CCL11, secreted by stromal cells, showed significant interactions with their respective receptors, highlighting their roles in immune cell recruitment and activation (Supplementary Fig. S2e & f).

    In conclusion, the Wnt, Notch, TGF-β, EGF, TNF, and chemokine pathways create a highly integrated communication network in ENO1-overexpressing tumors, regulating tumor growth, immune modulation, and progression.

    Discussion

    The present study provides critical insights into the metabolic alterations underlying trastuzumab resistance in HER2-positive gastric cancer. Through scRNA-seq data analysis, we classified gastric cancer cells and observed a significant upregulation of glycolysis-related genes in trastuzumab-resistant cells, particularly ENO1. Subsequent validation using RT-PCR and Western blot confirmed the overexpression of ENO1, identifying it as a key driver of metabolic reprogramming. Elevated ENO1 expression enhanced glycolysis, contributing to increased cell survival, colony formation, and tumor growth in trastuzumab-resistant gastric cancer.

    Beyond its role in glycolysis, ENO1 has emerged as a multifunctional target in cancer therapy. Elevated ENO1 levels are linked to disease progression and poor survival outcomes across various cancers, including colorectal, breast, and gastric cancers, glioblastoma, head and neck cancers, and leukemia. ENO1 contributes to tumor growth by promoting angiogenesis, evading immune detection, and resisting apoptosis. ENO1 inhibitors have shown promise in suppressing cancer cell proliferation[31−33]. For example, the selective ENO1 inhibitor POMHEX has demonstrated effectiveness in reducing glioblastoma progression in vivo by inducing apoptosis, with a favorable safety profile in non-human primates[34]. Similarly, macrosphelide A, another potent ENO1 inhibitor, has exhibited anticancer activity by targeting ENO1 alongside aldolase and fumarase[35].

    The glycolytic shift was associated with a significant downregulation of the TCA cycle-related gene IRP1, as identified through RNA immunoprecipitation assays. IRP1 suppression disrupted cellular metabolism, contributing to the resistance mechanism. Additionally, our analysis revealed that ENO1 plays a dual role in regulating ferroptosis, a form of regulated cell death linked to iron metabolism and oxidative stress. In trastuzumab-resistant cells, the inhibition of ferroptosis-related genes highlighted the complex interplay between glycolysis and ferroptosis mediated by ENO1. This dual regulatory function underscores ENO1's pivotal role in the metabolic alterations driving trastuzumab resistance.

    Recent advances in targeting glycolysis in HER2-positive advanced gastric cancer has yielded significant insights. HER2-positive gastric cancer cells undergo metabolic reprogramming by regulating key glycolytic enzymes, including hexokinase 2 (HK2), phosphofructokinase 1 (PFK1), and pyruvate kinase M2 (PKM2), as well as the transcription factor HIF-1α[36−38]. This reprogramming facilitates cancer cell proliferation and survival. Furthermore, lactate produced during glycolysis suppresses immune function by inhibiting T cells and NK cells while promoting regulatory T cell (Treg) survival, thereby contributing to immune evasion[39,40]. In clinical settings, combining HER2-targeted therapies, such as pembrolizumab, trastuzumab, and chemotherapy, has improved progression-free survival (PFS) and overall survival (OS) in patients[41]. Additionally, novel agents like trastuzumab deruxtecan (ENHERTU®)[42] have shown promising response and disease control rates, even in patients with low to intermediate HER2 expression. These findings enhance our understanding of metabolic reprogramming in gastric cancer and provide a foundation for developing innovative diagnostic and therapeutic strategies.

    In conclusion, our findings underscore the pivotal role of ENO1-mediated metabolic reprogramming in driving trastuzumab resistance. Targeting glycolysis and ENO1, alongside further investigation into the regulatory mechanisms involving IRP1 and ferroptosis, offers promising therapeutic avenues to overcome resistance in trastuzumab in HER2-positive gastric cancer. These insights provide a foundation for developing more effective strategies aimed at disrupting the metabolic dependencies of resistant gastric cancer cells, potentially improving treatment outcomes.

  • All mouse experiments were approved by the Ethics Committee of the Third Affiliated Hospital of Soochow University.

  • The authors confirm contribution to the paper as follows: conception and design: Jiang Y, Yuan M; administrative support: Jiang Y, Yuan M; collection and assembly of data: Wang L, Fang Z; data analysis and interpretation: Wang L, Ding X, Yang J; manuscript writing: all authors. All authors reviewed the results and approved the final version of the manuscript.

  • All sequencing data in this study were obtained from publicly available articles, and no additional data were generated during the course of this research.

    • Acknowledgments

    The present study was supported by the Supported by Changzhou Sci & Tech program (CJ20230053, CJ20200050, and CJ20241101).

  • The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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  • Cite this article

    Nguyen TBH, Van HT. 2024. Application of modified zeolite in the remediation of heavy metal in contaminated soil: a short review. Technology in Agronomy 4: e002 doi: 10.48130/tia-0023-0021
    Nguyen TBH, Van HT. 2024. Application of modified zeolite in the remediation of heavy metal in contaminated soil: a short review. Technology in Agronomy 4: e002 doi: 10.48130/tia-0023-0021
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Application of modified zeolite in the remediation of heavy metal in contaminated soil: a short review

  • 1.

    Faculty of Natural Resources and Environment, TNU-University of Sciences, Tan Thinh ward, Thai Nguyen City, 250000, Vietnam

  • 2.

    Center for Advanced Technology Development, Thai Nguyen University, Tan Thinh ward, Thai Nguyen City, 250000, Vietnam

  • Received: 19 September 2023
  • Revised: 20 November 2023
  • Accepted: 26 December 2023
  • Published online: 31 January 2024
Technology in Agronomy  4,  Article number: e002  (2024)  |  Cite this article

Abstract: This paper explores the significant potential of modified zeolites in various industries, emphasizing their role in promoting environmental sustainability. The study highlights the applications of modified zeolites in heavy metals in contaminated soil, showcasing their ability to address environmental pollution and enhance resource utilization. The research underscores the importance of fine-tuning zeolite modification techniques to achieve precise structural control and stability. Challenges related to the impact of even minor modifications on performance and the long-term stability of modified zeolites are acknowledged. Despite these challenges, the paper anticipates a promising future for modified zeolites, with advancements in materials science and nanotechnology expected to pave the way for innovative solutions in contaminated soil.

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    Introduction

    • Contaminated soil with heavy metals represents a significant environmental concern that has garnered increasing public attention due to its potential impact on agricultural product safety and human well-being[1−3]. Heavy metals, natural elements with the potential for toxicity upon accumulation in soil, are commonly characterized as metallic and metalloid elements with atomic mass greater than 20 and specific gravity exceeding 5, including Cd, Hg, Cu, As, Pb, Cr, Ni, and Zn. From a biological perspective, the term 'heavy' encompasses an array of metals, and in certain cases metalloids, which even at low concentrations, can pose toxicity to plants and animals[4]. The primary sources of heavy metal pollution in soil are predominantly attributed to human activities such as mining, metallurgical processes, agricultural practices (including fertilizer and pesticide usage), improper electronic waste disposal, battery waste, sludge, and mismanagement of materials containing heavy metals[5]. Common heavy metals of concern include Pb, Cd, Hg, As, Cr and Ni. Among these, As, Cd, Cr(VI), Hg, and Pb are classified as non-threshold toxicants capable of inducing toxicity at remarkably low concentrations[6]. Numerous researchers underscore the ecological and human health consequences of heavy metal contamination in soil[7−9]. These metals can disrupt the natural equilibrium of ecosystems by impairing soil microorganisms, diminishing soil fertility, and inhibiting plant growth. Furthermore, they can enter the food chain through plant uptake, resulting in bioaccumulation in animals and posing latent threats to human health. Prolonged exposure to heavy metals can lead to various health issues, including respiratory disorders, cardiovascular diseases, renal impairment, and neurological disorders[10]. Therefore, addressing heavy metal pollution in soil is paramount for safeguarding ecosystems and human health.

      Zeolites are naturally occurring aluminosilicate hydrates that exhibit more than 50 distinct forms[11,12] and find a plethora of applications. They serve as soil conditioners, nutrient supplements for both animals and aquatic life, and additionally function as heat storage materials. Moreover, zeolites possess the capacity to serve as adsorbents, ion exchangers, molecular sieves, and catalytic agents in various chemical reactions[13,14]. These applications are mainly based on their ion exchange properties[15].

      According to Johnson et al., the structure of zeolites consists of three-dimensional frameworks composed of alumina and silicate tetrahedral units linked together by oxygen atoms. This framework contains interconnected channels and pores, imparting zeolites with distinctive properties such as selective adsorption and molecular sieving[16]. The composition of zeolites can vary, with different ratios of aluminum and silicon determining the framework charge and the type of cations present within the channels. These voids provide zeolites with a large surface area, enabling high adsorption capacity. Furthermore, properties of zeolites, such as thermal stability, acidity, and ion exchange capability, can be tuned by controlling the framework composition and the choice of cations. Additionally, natural zeolites are regarded as beneficial soil amendments, possessing water and nutrient retention abilities. They enhance permeability, saturated hydraulic conductivity, cation exchange capacity, and mitigate deep percolation losses[17−21].

      Despite its many advantages, natural zeolite has little or no affinity for anions due to its negative surface charge[22−25]. In the study conducted by Misaelides[26], the author provided a comprehensive analysis of various research efforts involving the use of natural zeolites in soil remediation. Misaelides emphasized that the modification of zeolites through different techniques, such as ion exchange, acid treatment, and surface modification, enhances their ability to remove pollutants from soil. The author further argued that the application of modified zeolites in soil remediation has shown promising results in removing heavy metals, organic pollutants, and various types of contaminants from polluted soils. Therefore, modifying zeolite to treat heavy metal pollution in the environment is extremely important. Modified zeolites refer to zeolite materials that have undergone intentional physical or chemical transformations to alter their properties, enhance their performance, or tailor them for specific applications.

      The objective of this work is to present a brief overview of the use of modified zeolite as a remediation technique for heavy metal contamination in soil environments. This work aims to explore different methods of zeolite modification to enhance their properties, allowing effective immobilization, adsorption or reduction of heavy metal contaminants in soil. The scope of the article focuses on: current knowledge related to the application of modified zeolite as a possible solution to overcome heavy metal pollution in soil through adsorption mechanism, advantages and limitations of them through case studies. In addition, the article also highlights factors affecting the adsorption capacity of heavy metals and future research prospects of modified zeolite.

    Modified zeolite materials and their applications for heavy metal remediation in contaminated soil

      Method of modifying zeolite with organic and inorganic compounds

    • Methods of modifying natural zeolites can be categorized into two major groups: modification using organic and inorganic compounds. Firstly, the modification of zeolites using inorganic compounds is executed through: ion exchange; wherein zeolites are converted into their monocation forms (e.g., H+, K+, Cu2+, NH4+, etc.) via treatment with salt or acid solutions. The outcome of this modification alters ion exchange selectivity, molecular sieving, and adsorption properties of zeolites. Treatment with inorganic solutions, in the presence or absence of an oxidizing agent, can also modify the surface properties of zeolites[27,28].

      Secondly, the modification of zeolites using organic compounds involves: treatment with simple organic cations (e.g., tetramethylammonium, tetraethylammonium, etc.) to impart hydrophobicity to the zeolite surface[29−31]. Such an adsorbent begins to effectively hold organic compounds. Treatment with more complex organic compounds (e.g., water-soluble polyamines). In this case, the surface of zeolite becomes hydrophobic and zeolites acquire anion exchange properties[31−33]. However, information regarding the extent of preservation of the initial cation exchange characteristics of zeolites is not found in the referenced literature[34].

      For more environmentally friendly applications, zeolite was modified using metal cations or metal oxides through straightforward, effective, and relatively cost-efficient processes[35,36]. The charge characteristics of modified zeolites depend on the type of modifying agent and preparation conditions[37].

      The techniques for zeolite modification aim to enhance adsorption capacity

    • There exist a multitude of techniques for zeolite modification. Modifications encompass alterations in the chemical surface, structure, or incorporation of supplementary functional groups into the zeolite framework[8, 27−33, 38−40]. These modifications are often tailored to specific requirements of intended applications, aiming to optimize material performance and efficacy. Modified zeolites find applications across diverse fields including environmental remediation, water filtration, gas separation, catalysis, and more. Several common modification methods are presented in Table 1.

      Table 1.  Some zeolite modification techniques.

      Zeolite modification techniqueProceedEffective
      Ion exchangeDetermined ions are delivered to the zeolite surface through ion exchange processesEnhances the selectivity of the material towards specific ions or molecules
      Surface functionalizationAdding functional groups to the surfaceIncreases the material's affinity for specific pollutants or molecules, making it more effective in adsorption or catalytic reactions
      Chemical treatmentZeolites are treated with acids, bases or other chemicals to change their surface properties or expand their porous structure.Increase the adsorption capacity or interaction of the material with various substances, including light treatment, silanization, grafting
      ImpregnatioAdditional materials are introduced or impregnated onto the zeolite surfaceEnhances the properties of modified materials or provides additional functions.
      NanostructureCreate nano-sized particles or structures from zeoliteAmplify their surface area, thereby enhancing their performance in various applications
      Mixture formationZeolite is combined with different materials, such as polymers or nanoparticles, leading to the development of composite materials with complex propertiesImprove the adsorption capacity of the material
      Steam treatment and calcinationSteam treatment can change the surface properties of zeolite.The calcination process can remove organic matter and regenerate the zeolite structure. Improve the adsorption capacity of the material.

      Exemplary studies on the application of modified zeolite for remediation of heavy metal from contaminated soil

    • The application of modified zeolites for pollution treatment in water has been extensively researched and diversified. However, studies on the application of these materials for heavy metal adsorption in soil remain limited. Presented below are some exemplary studies and outcomes regarding the application of modified zeolites for heavy metal remediation in soil.

      In a recent study by Ma et al.[41], the authors investigated the potential of modified zeolites for the remediation of heavy metal contamination in soil. This enhancement could be attributed to the introduction of functional groups or nano-particles on the surface of zeolites, thereby augmenting their adsorption capacity. Reeve & Fallowfield devised a remediation scheme for As and Cd contaminated agricultural soils proximate to metal mining and refining activities in China. They employed modified zeolite, specifically hexadecyltrimethylammonium (HDTMA)-modified zeolite, to amend the soil within the mining area and assessed the efficacy of immobilization. Sequential extraction results indicated that the incorporation of HDTMA-modified zeolite not only increased the residual fraction of As (2.7%–5.9%) but also reduced its toxicity-related fraction (2.3%–2.7%) in comparison to unmodified zeolite and blank samples[42]. In 2012, Ioannou et al.[43] employed modified zeolite for the sorption of Cu in soil environments. They crafted altered zeolite systems (I and II) by utilizing a zeolite precursor and goethite. The outcomes demonstrated that the combination of System II with sandy loam soil yielded the most favorable morphological attributes in lettuce with minimal uptake of Cu[43].

      In a study by Gao et al.[44], zeolite 4A synthesized from fly ash was modified through a simple ammonia inorganic impregnation method, enabling the incorporation of various types of inorganic amine functional groups into the zeolite structure. This modification enhances the ability of the modified zeolite to remove Hg2+ ions. The modification mechanisms involving impregnation with NH3·H2O, KH792, and NH4Cl on zeolite 4A, as well as the effectiveness in removing Hg2+ ions, were investigated and compared. During the process of soil filtration contaminated with mercury, NH3·H2O-modified zeolite 4A can effectively remove Hg2+ ions and mitigate the risk of additional soil pollution. Li et al.[45] conducted a study on the synthesis of nanoscale zero-valent iron supported by zeolite (Z-NZVI) and its application for simultaneous adsorption of As(III), Cd(II), and Pb(II) from aqueous solutions and soils. These research highlight the significant potential of Z-NZVI for treating water and soils contaminated with multiple heavy metals. Yang et al.[46] implemented a 'waste transformation for soil remediation' strategy by recycling alkali waste red mud and treating heavy metal-contaminated soil. This work primarily converted alkali waste into Fe2O3-ANA for soil treatment, showcasing its value in resource recycling and environmental preservation.

      Additionally, experiments conducted by various researchers have aimed to explore the effects of mixing soil with nano-zeolite for the purpose of adsorbing heavy metals in the soil. Most of the results indicate that the nano-material will lead to an increase in the soil's pH efficiency and significantly reduce the concentration of heavy metals in the soil. Notably, this material has no discernible impact on the main flow, which is why nano-zeolite does not participate in the chemical reactions of the soil and water[27, 47−50]. Therefore, future studies might examine the influence of various forms of nano-zeolite and the effective adsorption capabilities of each type on different soil types contaminated with heavy metals.

      Dang et al.[51] utilized zeolite and Mg/Al LDH-zeolite to immobilize Cd and Pb ions in artificial soil. The results revealed that the optimal soil pH, adsorbent mass ratio, incubation time, and soil moisture content for immobilizing Cd and Pb ions were 7.0, 3%, 30 d, and 70%, respectively. Precipitation, coprecipitation, and electrostatic attraction were the primary mechanisms of Cd and Pb immobilization on Mg/Al LDH-zeolite, leading to the formation of metal carbonates (CdCO3 and PbCO3). This was attributed to the surface functional groups of the adsorbent and the presence of Fe and Al oxyhydroxides, Mn oxides, as well as Si and O elements in the composition of Mg/Al LDH-zeolite. The Cd and Pb immobilization efficiency with Mg/Al LDH-zeolite was 1.5 to 1.6 times higher than with zeolite. Mg/Al LDH-zeolite exhibited an enhanced capability for immobilizing Cd and Pb ions in a contaminated environment.

      Advantages and limitations of current studies

    • In the field of soil remediation, the use of modified zeolite has shown promising results in addressing soil pollution issues. Firstly, studies have demonstrated that modified zeolite exhibits higher adsorption capacity and selectivity for heavy metals compared to natural zeolite. This enhancement could be attributed to the introduction of functional groups or nano-sized particles onto the zeolite surface, thereby enhancing its adsorption properties. Moreover, research has shown significant improvements in the ion exchange capacity, surface area, and number of adsorption sites of modified zeolite. These improvements render it more efficient in sequestering heavy metals within the soil. Additionally, studies have highlighted the stability, recyclability, and cost-effectiveness of modified zeolite, positioning it as a sustainable solution for soil remediation. In conclusion, the findings from these studies contribute valuable insights into the potential of modified zeolite as a promising tool for addressing heavy metal pollution in soil.

      However, there are potential challenges that need to be considered for optimizing its application. One such challenge is selecting an appropriate technique for modifying zeolite. According to Usman et al., there are various methods available for zeolite modification, including ion exchange, impregnation, and surface modification. Each technique comes with its own advantages and limitations, and the choice of method must be based on the specific pollutants present in the soil and their chemical characteristics[52]. Furthermore, the effectiveness of modified zeolite in soil remediation is influenced by factors such as pH, temperature, and moisture content. Proper understanding and control of these environmental factors are crucial to ensure the optimal performance of modified zeolite in soil treatment processes. Additionally, the long-term stability and durability of modified zeolite in soil need to be studied. It's essential to assess the filtering capacity of modified zeolite and its potential impact on the surrounding environment. Future research directions should focus on investigating the transport of modified zeolite in soil, as well as its potential effects on soil microorganisms and plant development. By addressing these challenges and exploring future research avenues, the application of modified zeolite for soil treatment could be further enhanced. Furthermore, these studies have mainly concentrated on specific heavy metals. Hence, further research is needed to explore the efficacy of modified zeolite for different soil types and varied environmental conditions, thereby enhancing its practical applicability.

    Factors influencing the heavy metal adsorption of modified zeolite

      Factors related to the mechanisms of heavy metal adsorption in soil by modified zeolite

    • The mechanisms of heavy metal adsorption on modified zeolite encompass three primary processes (Fig. 1): precipitation, ion exchange and surface complexation[41, 43, 51, 53−55]. Zeolites exhibit a high capacity for cation exchange, enabling efficient removal of heavy metal ions from solutions. Exchange occurs when cations on the zeolite surface are replaced by heavy metal cations present in the solution. This process is driven by differences in charge and ion size between zeolite cations and heavy metal cations. On the other hand, surface complexation involves the formation of complex compounds between heavy metal ions and functional groups on the zeolite surface. Functional groups such as hydroxyl (-OH) and carboxyl (-COOH) can serve as binding sites for heavy metal ions. These binding sites create stable complexes due to the coordination between functional groups and heavy metal ions, leading to the adsorption of heavy metals on the zeolite surface. This mechanism of heavy metal adsorption on modified zeolite through ion exchange and surface complexation plays a crucial role in the removal of heavy metals from aqueous solutions[53, 56−58]. The effectiveness of these mechanisms for heavy metal removal in soil has also been demonstrated[41, 51, 55, 59].

      Figure 1. 

      Mechanisms for heavy metals by precipitation (I), ion exchange (II) and surface complexation (III)[60].

      Factors influencing the process of heavy metal adsorption in contaminated soil by modified zeolite

    • The adsorption of heavy metals onto modified zeolite is influenced by several factors, including pH, temperature, moisture, and contact time[25, 51]. According to Ören & Kaya, pH plays a crucial role in the process of heavy metal adsorption on zeolite[25]. The pH of the solution affects the surface charge of zeolite, thereby influencing its adsorption capacity. For instance, at low pH values, the surface of zeolite becomes positively charged, leading to an increased affinity for heavy metal ions. Conversely, at high pH values, the surface charge becomes negative, reducing the adsorption capacity. Temperature is another significant factor affecting the adsorption of heavy metals. It has been observed that increasing the temperature accelerates the adsorption rate due to the enhanced mobility of metal ions and the higher energy level of the zeolite surface. Additionally, contact time, the duration of interaction between zeolite and the solution, also plays a crucial role in the adsorption efficiency. Longer contact times usually lead to higher adsorption capacity as more metal ions have the opportunity to interact with the zeolite surface. In conclusion, understanding and applying these factors are essential in optimizing the process of heavy metal adsorption onto modified zeolite.

      The process of heavy metal adsorption in soil can be influenced by various factors, including the characteristics of the adsorbent material, such as zeolite, and the properties of the heavy metal ions themselves. One significant factor affecting the selective adsorption of heavy metal ions by zeolite is the pore size of the zeolite. Synthesized zeolites with larger pore sizes have been found to exhibit higher adsorption capacities for heavy metal ions[61]. This is because the larger pore size allows hydrated ions to enter the zeolite channels, creating favorable conditions for their adsorption process. Conversely, if the diameter of the hydrated ions exceeds the zeolite's pore size, the metal ions may be excluded from the adsorption process. The dehydration of ions can also enhance their movement into the zeolite channels.

      The negative charge and hydration energy of heavy metal ions also play a role in the selective adsorption process by zeolite[62]. It has been observed that heavy metal ions with higher electronegativity, such as Pb2+ and Cu2+, exhibit stronger affinity for the electron clouds of oxygen atoms in the zeolite structure[61]. This is because the electronegative oxygen atoms in the zeolite structure can interact with positively charged heavy metal ions, leading to their selective adsorption. The hydration energy of heavy metal ions also affects their adsorption capacity, with ions possessing higher hydration energy demonstrating greater adsorption ability.

      In addition to the characteristics of zeolite, modifying zeolite can also influence the adsorption of heavy metal ions in the soil. For instance, modifying zeolite with calcium or ammonium ions has been found to enhance the adsorption capacity for heavy metal ions[63]. The modified ions promote the ion exchange surface normalization process of zeolite, leading to a higher adsorption capacity for heavy metal ions. The type and concentration of zeolite modifications can also impact the accumulation of heavy metal ions in crops grown in the soil. It has been observed that crops grown on modified zeolite-based substrates exhibit lower transport coefficients for heavy metal ions compared to crops grown on natural zeolite-based substrates.

      In summary the adsorption process of heavy metals in soil by modified zeolite is affected by factors such as the pore size of the zeolite, the negative charge and hydration energy of the metal ions and the transformation of the zeolite. Understanding these factors can aid in developing effective strategies for the remediation of heavy metal-contaminated soil.

    Future prospects

    • Future prospects in this field are promising, with ongoing research focusing on further enhancing the application of zeolite-based remediation methods. As we continue to deepen our understanding of the mechanisms behind heavy metal adsorption on modified zeolites, we can anticipate the development of more efficient and sustainable techniques for soil remediation. Investigating the interactions between zeolites and various types of heavy metals, as well as their effects on soil microorganisms and plant growth, will be essential for expanding the practical applications of zeolite-based approaches. Moreover, exploring innovative modifications of zeolites and optimizing their performance under different environmental conditions will contribute to the continuous advancement of this field. As we address these challenges and delve into future research directions, the utilization of modified zeolites for soil remediation is likely to see further enhancements and widespread implementation

      Modified zeolites have demonstrated significant potential across various industries due to their contribution to environmental sustainability. The utilization of modified zeolites in industries such as catalysis, wastewater treatment, and gas separation can offer substantial environmental benefits[64]. The process of zeolite modification has been shown to reduce the release of harmful elements, making modified zeolites more environmentally friendly[65]. In the future, efforts will continue to develop effective methods for regenerating and reusing modified zeolites, aiding in the reduction of environmental pollution. Concurrently, the use of modified zeolites requires careful assessment to minimize any potential negative impacts on the environment (such as the release of hazardous chemicals during zeolite modification, its long-term stability in different environments, etc.). By addressing these concerns and challenges, modified zeolites have the potential to play a key role in sustainable environmental management.

      The development of modified zeolites holds significant potential for diverse applications in various fields. In recent years, researchers have made significant advancements in modifying the structure and properties of zeolites to enhance their catalytic activity and selectivity. According to Khan et al. one of the key challenges in the development of modified zeolites is achieving a high level of control over their structure and composition[66]. This is because even minor changes in the modification process can have a significant impact on their performance. Furthermore, the stability and durability of modified zeolites are crucial factors that need to be addressed to ensure their long-term effectiveness. Additionally, the development of more effective modification methods for large-scale production is essential. Despite these challenges, the prospects for the future of modified zeolites are promising. With further advancements in materials science and nanotechnology, it is anticipated that researchers will overcome these challenges and unlock the full potential of modified zeolites in various applications such as catalysis, gas separation, and environmental treatment.

    Conclusions

    • The utilization of modified zeolites presents a substantial potential across diverse industries, offering solutions that contribute to environmental sustainability. The application of modified zeolites in treatment of contaminated soil has demonstrated promising results, showcasing their ability to mitigate environmental pollution and enhance resource efficiency. The optimization of zeolite modification processes, encompassing factors like structure control, stability, and large-scale production, remains a crucial area of research. Overcoming challenges associated with minor alterations impacting performance and ensuring the long-term stability of modified zeolites are paramount for their successful implementation. As scientific progress continues, particularly in materials science and nanotechnology, researchers are poised to address these challenges and harness the full potential of modified zeolites, unlocking innovative solutions for sustainable environmental management.

    Author contributions

    • The authors confirm contribution to the paper as follows: reference collection, analysis and review of data: Nguyen TBH; draft manuscript preparation: Van HT. Both authors reviewed and approved the final version of the manuscript.

    Data availability

    • The data used in this study is free from any conflict of interest. The data is available from the corresponding author upon reasonable request.

      Acknowledgments

      • This work was financially supported by the Vietnam Ministry of Education and Training under project number: B2023-TNA-32.

      Conflict of interest

      • The authors declare that they have no conflict of interest.

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      • Copyright: © 2024 by the author(s). Published by Maximum Academic Press, Fayetteville, GA. This article is an open access article distributed under Creative Commons Attribution License (CC BY 4.0), visit https://creativecommons.org/licenses/by/4.0/.
    Figure (1)  Table (1) References (66)
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    Nguyen TBH, Van HT. 2024. Application of modified zeolite in the remediation of heavy metal in contaminated soil: a short review. Technology in Agronomy 4: e002 doi: 10.48130/tia-0023-0021
    Nguyen TBH, Van HT. 2024. Application of modified zeolite in the remediation of heavy metal in contaminated soil: a short review. Technology in Agronomy 4: e002 doi: 10.48130/tia-0023-0021
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  • Introduction
  • Modified zeolite materials and their applications for heavy metal remediation in contaminated soil

  • Method of modifying zeolite with organic and inorganic compounds

  • The techniques for zeolite modification aim to enhance adsorption capacity

  • Exemplary studies on the application of modified zeolite for remediation of heavy metal from contaminated soil

  • Advantages and limitations of current studies

  • Factors influencing the heavy metal adsorption of modified zeolite

  • Factors related to the mechanisms of heavy metal adsorption in soil by modified zeolite

  • Factors influencing the process of heavy metal adsorption in contaminated soil by modified zeolite

  • Future prospects
  • Conclusions
  • Author contributions
  • Data availability
  • Acknowledgments
  • Conflict of interest
  • Rights and permissions
  • About this article
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