Stimulation of the proliferation of human normal esophageal epithelial cells by fumonisin B1 and its mechanism

Fumonisin distorts the cellular membrane lipid profile: A mechanistic insight

Monitoring modifications in membrane lipids in association with external stimuli/agents, including fumonisins (FUMs), is a widely employed approach to assess cellular metabolic response/status. FUMs are prevalent fusariotoxins worldwide that have diverse structures with varying toxicity across species; nevertheless, they can induce metabolic disturbances and disease, including cancer. The capacity of FUMs to disrupt membrane lipids, demonstrated across numerous species and organs/tissues, is ascribed to a multitude of factors/events, which range from direct to indirect effects. Certain events are well established, whereas the potential consequences of others remain speculative. The most notable effect is their resemblance to sphingoid bases, which impacts the synthesis of ceramides leading to numerous changes in lipids' composition that are not limited to sphingolipids' composition of the membranes. The next plausible scenario involves the induction of oxidative stress, which is considered an indirect/secondary effect of FUMs. Additional modes of action include modifications of enzyme activities and nuclear signals related to lipid metabolism, although these are likely not yet fully comprehended. This review provides in-depth insight into the current state of these events and their potential mechanistic actions in modifying membrane lipids, with a focus on long-chain fatty acids. This paper also presents a detailed description of the reported modifications to membrane lipids by FUMs.

Autophagy Contributes to Homeostasis in Esophageal Epithelium Where High Autophagic Vesicle Level Marks Basal Cells With Limited Proliferation and Enhanced Self-Renewal Potential

BACKGROUND & AIMS

Autophagy plays roles in esophageal pathologies both benign and malignant. Here, we aim to define the role of autophagy in esophageal epithelial homeostasis.

METHODS

We generated tamoxifen-inducible, squamous epithelial-specific Atg7 (autophagy related 7) conditional knockout mice to evaluate effects on esophageal homeostasis and response to the carcinogen 4-nitroquinoline 1-oxide (4NQO) using histologic and biochemical analyses. We fluorescence-activated cell sorted esophageal basal cells based on fluorescence of the autophagic vesicle (AV)-identifying dye Cyto-ID and then subjected these cells to transmission electron microscopy, image flow cytometry, three-dimensional organoid assays, RNA sequencing, and cell cycle analysis. Three-dimensional organoids were subjected to passaging, single-cell RNA sequencing, cell cycle analysis, and immunostaining.

RESULTS

Genetic autophagy inhibition in squamous epithelium resulted in increased proliferation of esophageal basal cells under homeostatic conditions and also was associated with significant weight loss in mice treated with 4NQO that further displayed perturbed epithelial tissue architecture. Esophageal basal cells with high AV level (Cyto-IDHigh) displayed limited organoid formation capability on initial plating but passaged more efficiently than their counterparts with low AV level (Cyto-IDLow). RNA sequencing suggested increased autophagy in Cyto-IDHigh esophageal basal cells along with decreased cell cycle progression, the latter of which was confirmed by cell cycle analysis. Single-cell RNA sequencing of three-dimensional organoids generated by Cyto-IDLow and Cyto-IDHigh cells identified expansion of 3 cell populations and enrichment of G2/M-associated genes in the Cyto-IDHigh group. Ki67 expression was also increased in organoids generated by Cyto-IDHigh cells, including in basal cells localized beyond the outermost cell layer.

CONCLUSIONS

Autophagy contributes to maintenance of the esophageal proliferation-differentiation gradient. Esophageal basal cells with high AV level exhibit limited proliferation and generate three-dimensional organoids with enhanced self-renewal capacity.

Autophagy contributes to homeostasis in esophageal epithelium where high autophagic vesicle content marks basal cells with limited proliferation and enhanced self-renewal potential

Background & Aims

Autophagy has been demonstrated to play roles in esophageal pathologies both benign and malignant. Here, we aim to define the role of autophagy in esophageal epithelium under homeostatic conditions.

Methods

We generated tamoxifen-inducible, squamous epithelial-specific Atg7 (autophagy related 7) conditional knockout mice to evaluate effects on esophageal homeostasis and response to the carcinogen 4-nitroquinoline 1-oxide (4NQO) using histological and biochemical analyses. We FACS sorted esophageal basal cells based upon fluorescence of the autophagic vesicle (AV)-identifying dye Cyto-ID, then subjected these cells to transmission electron microscopy, image flow cytometry, 3D organoid assays, RNA-Sequencing (RNA-Seq), and cell cycle analysis. 3D organoids were subjected to passaging, single cell (sc) RNA-Seq, cell cycle analysis, and immunostaining.

Results

Genetic autophagy inhibition in squamous epithelium resulted in increased proliferation of esophageal basal cells. Esophageal basal cells with high AV level (Cyto-ID High ) displayed limited organoid formation capability upon initial plating but passaged more efficiently than their counterparts with low AV level (Cyto-ID Low ). RNA-Seq suggested increased autophagy in Cyto- ID High esophageal basal cells along with decreased cell cycle progression, the latter of which was confirmed by cell cycle analysis. scRNA-Seq of 3D organoids generated by Cyto-ID Low and Cyto- ID High cells identified expansion of 3 cell populations, enrichment of G2/M-associated genes, and aberrant localization of cell cycle-associated genes beyond basal cell populations in the Cyto- ID High group. Ki67 expression was also increased in organoids generated by Cyto-ID High cells, including in cells beyond the basal cell layer. Squamous epithelial-specific autophagy inhibition induced significant weight loss in mice treated with 4NQO that further displayed perturbed epithelial tissue architecture.

Conclusions

High AV level identifies esophageal epithelium with limited proliferation and enhanced self-renewal capacity that contributes to maintenance of the esophageal proliferation- differentiation gradient in vivo .

Fumonisin B1 induces hepatotoxicity in mice through the activation of oxidative stress, apoptosis and fibrosis

Fumonisin B1 (FB1) is a harmful environmental pollutant that induces hepatotoxicity, but the mechanism is still poorly understood. Therefore, the aim of this work was to investigate the effects of FB1 on the liver of mice and discover the underlying molecular mechanisms. A total of 40 male mice were exposed to 0 or 5 mg/kg FB1 for 42 days, and then, they were sacrificed, and the liver and blood were collected. Besides, AML12 cells were exposed to FB1. Biochemical and liver related indexes as well morphological changes, redox, apoptosis and fibrosis related markers were measured in liver and AML12 cells. The results showed that the liver function and biochemical indexes in the blood were changes, and the histopathological analysis indicated that FB1 exposure caused hepatic sinusoid atrophy, hemosiderosis, hepatocyte steatosis and fibrosis, finally inducing liver injury. Notably, a significant increase in the intracellular antioxidant enzymes SOD1, SOD2, NF-κB (p65), H₂O₂ and NO was found in FB1 exposed AML12 cells and liver tissues. In addition, TUNEL staining showed many apoptotic cells, and western blotting revealed a significant increase in the pro-apoptosis proteins. FB1 also induced liver fibrosis by triggering TGF-β1/α-SMA/collagen/MMP signaling in the hepatocytes. Our results provide a novel explanation of the toxicological mechanism of action of FB1, which provoked oxidative stress, apoptosis and fibrosis in mice liver.

Alginate oligosaccharides protect against fumonisin B1-induced intestinal damage via promoting gut microbiota homeostasis

Fumonisin B1 (FB1), one of the most common mycotoxins contaminating feed and food, has been shown to induce intestinal barrier degradation. However, its role on gut microbiota in this process is still unclear. Alginate oligosaccharides (AOS) have been reported to exert their anti-inflammatory and anti-apoptotic function partially via modulation the gut microbiota. However, little is known about the beneficial effect of AOS on gut microbiota upon FB1 exposure. Results show that FB1 degraded intestinal epithelial barrier function as evidenced by increased pathological epithelial cell shedding, reduced the number of goblet cells, and promoted intestinal cell apoptosis. Markedly, FB1 disturbed the cecal and fecal microbiota composition. FB1 increased the level of Lactobacillus and decreased the relative abundance of beneficial microbes. FB1 largely inhibited the production of short chain fatty acids (SCFAs). AOS greatly ameliorated FB1-induced intestinal damage, inflammation, and oxidative stress (eg., T-SOD and MDA). AOS alleviated gut microbial dysbiosis by promoting the growth of beneficial microbes such as Roseburia, Bifidobacterium, and Akkermansia, and increasing SCFAs production upon FB1 exposure. Moreover, the correlation analysis showed that FB1- and AOS-treated gut microbiota alteration is closely associated with the change of intestinal phenotype. We have thus provided a novel insight into the protective role of AOS on FB1-induced gut microbial dysbiosis.

Fumonisin B1 triggers carcinogenesis via HDAC/PI3K/Akt signalling pathway in human esophageal epithelial cells

Fumonisin B1 (FB1) is a contaminant that commonly present in the global environment, especially in food and feed. Epidemiologic studies have shown that esophageal cancer is associated with fumonisin toxicity. However, the molecular mechanism of FB1-induced esophageal cancer is unclear. In this research, the molecular mechanism of FB1-induced cell carcinogenesis in human esophageal epithelial cells line (HEEC) was explored. We found that FB1 (0.3125-5 μM) could promote cell proliferation, and the same phenomenon was found in a 3D cell model. FB1 could also accelerate cell migration. The expression levels of DNA damage markers were significantly increased after FB1 exposure. Meanwhile, the expression levels of cell cycle-regulated proteins and cancer-related genes were abnormal. Furthermore, FB1 significantly upregulated the histone deacetylase (HDAC) expression and activated the phosphoinositide 3 kinase (PI3K)/protein kinase B (Akt) signalling pathway. The HDAC inhibitor trichostatin A (TSA) could repressed FB1-promoted cell proliferation and abnormal phenomenon induced by FB1. Moreover, myriocin (ISP-1) could relieve FB1-enhanced HDAC expression and cell proliferation, which implied that ISP-1 may be used to block the fumonisin toxicity in the future. Our findings suggested that the HDAC/PI3K/Akt signalling pathway is a novel mechanism for FB1-induced cell carcinogenesis in HEEC and provided new ideas for the prevention and control of fumonisin toxicity, subsequently avoiding adverse effects on the ecosystem and human health.

Research Progress on Fumonisin B1 Contamination and Toxicity: A Review

Fumonisin B1 (FB1), belonging to the member of fumonisins, is one of the most toxic mycotoxins produced mainly by Fusarium proliferatum and Fusarium verticillioide. FB1 has caused extensive contamination worldwide, mainly in corn, rice, wheat, and their products, while it also poses a health risk and is toxic to animals and human. It has been shown to cause oxidative stress, endoplasmic reticulum stress, cellular autophagy, and apoptosis. This review focuses on the current stage of FB1 contamination, its toxic effects of acute toxicity, immunotoxicity, organ toxicity, and reproductive toxicity on animals and humans. The potential toxic mechanisms of FB1 are discussed. One of the main aims of the work is to provide a reliable reference strategy for understanding the occurrence and toxicity of FB1.

Metabolic Depletion of Sphingolipids Does Not Alter Cell Cycle Progression in Chinese Hamster Ovary Cells

The cell cycle is a sequential multi-step process essential for growth and proliferation of cells comprising multicellular organisms. Although a number of proteins are known to modulate the cell cycle, the role of lipids in regulation of cell cycle is still emerging. In our previous work, we monitored the role of cholesterol in cell cycle progression in CHO-K1 cells. Since sphingolipids enjoy a functionally synergistic relationship with membrane cholesterol, in this work, we explored whether sphingolipids could modulate the eukaryotic cell cycle using CHO-K1 cells. Sphingolipids are essential components of eukaryotic cell membranes and are involved in a number of important cellular functions. To comprehensively monitor the role of sphingolipids on cell cycle progression, we carried out metabolic depletion of sphingolipids in CHO-K1 cells using inhibitors (fumonisin B₁, myriocin, and PDMP) that block specific steps of the sphingolipid biosynthetic pathway and examined their effect on individual cell cycle phases. Our results show that metabolic inhibitors led to significant reduction in specific sphingolipids, yet such inhibition in sphingolipid biosynthesis did not show any effect on cell cycle progression in CHO-K1 cells. We speculate that any role of sphingolipids on cell cycle progression could be context and cell-type dependent, and cancer cells could be a better choice for monitoring such regulation, since sphingolipids are differentially modulated in these cells.

Safety of Corn and Corn-Based Products Intended for Human Consumption Concerning Fumonisins from a Brazilian Processing Plant

Brazil is one of the world's largest corn producers and is a leader in exportation. Due to intense globalization, corn may be commercialized worldwide and the issue concerning the safety of corn-based products has become a topic of widespread international interest. Dietary exposure evaluation is a relevant criterion for mycotoxin risk assessment. Thus, human exposure to fumonisins were assessed for corn grain and its derivatives (endosperm, cornmeal, and grits; n = 320) sampled from one of the large-scale corn processing plants in Brazil. The total probable daily intake (PDI) for fumonisins in Brazil was 96.9 ng kg-1 body weight day-1, which corresponds to 5% of the provisional maximum tolerable daily intake (PMTDI) of 2000 ng kg-1 b.w. day-1 for fumonisins. In countries that import Brazilian corn, the total PDI is lower in European countries (from 35.7 to 177 ng kg-1 b.w. day-1) and higher in Angola (1553 ng kg-1 b.w. day-1). Taking into account that dietary exposure in populations in Brazil and importing countries was low, the corn-based products were safe for human consumption regarding fumonisins, even for regions with high corn consumption.

Detection of Fusarium verticillioides by PCR-ELISA based on FUM21 gene

Fusarium verticillioides is a primary corn pathogen and fumonisin producer which is associated with toxic effects in humans and animals. The traditional methods for detection of fungal contamination based on morphological characteristics are time-consuming and show low sensitivity and specificity. Therefore, the objective of this study was to develop a PCR-ELISA based on the FUM21 gene for F. verticillioides detection. The DNA of the F. verticillioides, Fusarium sp., Aspergillus sp. and Penicillium sp. isolates was analyzed by conventional PCR and PCR-ELISA to determine the specificity. The PCR-ELISA was specific to F. verticillioides isolates, showed a 2.5 pg detection limit and was 100-fold more sensitive than conventional PCR. In corn samples inoculated with F. verticillioides conidia, the detection limit of the PCR-ELISA was 1 × 10⁴ conidia/g and was also 100-fold more sensitive than conventional PCR. Naturally contaminated corn samples were analyzed by PCR-ELISA based on the FUM21 gene and PCR-ELISA absorbance values correlated positively (p < 0.05) with Fusarium sp. counts (CFU/g). These results suggest that the PCR-ELISA developed in this study can be useful for F. verticillioides detection in corn samples.

Fumonisin B1 induces oxidative stress in oesophageal (SNO) cancer cells

Fumonisin B₁ (FB₁) is a ubiquitous contaminant of maize that is epidemiologically linked to oesophageal cancer (OC) in South Africa. FB₁-induced oxidative stress mediates toxicity in animals and human cell lines, but the effects relating to OC are limited. Given the species-specific effects of FB₁, this study investigated FB₁-mediated toxicity and oxidative stress in spindle-shaped N-cadherin (+) CD45 (-) osteoblastic (SNO) cells. Following exposure to FB₁ (0-20 μM) for 48 h, mitochondrial membrane potential and intracellular reactive oxygen species (iROS) were measured (flow cytometry). Malondialdehyde concentration (lipid peroxidation) was determined spectrophotometrically. ATP and reduced glutathione (GSH) concentrations were quantified using luminometry, gene expression of SOD2 by qPCR and protein expression of SOD2, GPx1, Nrf2 and HSP70 by western blotting. Mitochondrial depolarization increased at 10 μM and 20 μM FB₁, with a concomitant reduction in ATP, iROS and GSH at both concentrations. Lipid peroxidation increased at 10 μM FB₁ exposure. While transcript levels of SOD2 were significantly increased, protein levels decreased. Protein expression of GPx1, Nrf2 and HSP70 increased. In contrast to the 10 μM and 20 μM FB₁ treatment, mitochondrial depolarization decreased at 1.25 μM FB₁. Intracellular ROS and ATP were decreased and lipid peroxidation increased. Decreased GSH was accompanied by a decrease in GPx1 protein levels, and increased HSP70 and Nrf2. SOD2 expression and protein levels were significantly increased. Overall these results indicate that FB₁ caused increased ROS that were counteracted by engaging the antioxidant defense. Furthermore, the peculiar response at 1.25 μM FB₁ is noteworthy, as compared to the other two concentrations tested.

Concentration-dependent effect of fumonisin B1 on apoptosis in oesophageal cancer cells

The geographical distribution of oesophageal cancer is linked to the exposure of fumonisin B1 (FB1), a mycotoxin produced by fungi that contaminates staple food worldwide. Non-genotoxic carcinogens like FB1 disturb homeostasis through increased cell proliferation or suppression of apoptosis. This study investigated the involvement of FB1 (0–20 μM) in spindle-shaped N-cadherin (+) CD45 (−) osteoblastic (SNO) cell death. Cell viability and death were assessed using the MTS and Annexin V-Fluos assays, respectively. Caspase activities were determined luminometrically and the comet assay assessed DNA damage. Induction of oxoguanine glycosylase 1 (OGG1) was measured using quantitative Polymerase Chain Reaction (qPCR), while cleaved poly (ADP-ribose) polymerase 1 (PARP-1) and Bax were determined by western blotting. Cell viability and PARP-1 cleavage were not affected by 1.25 μM FB1, but phosphatidylserine externalization, Bax protein expression, caspase activity, comet tail length and OGG1 transcripts were increased. The reduced cell viability in 10 μM FB1-treated cells was accompanied by corresponding increases in externalized phosphatidylserine, Bax, caspase-3/7 activity and cleaved PARP-1. The OGG1 transcripts were not significantly increased, but comet tails were increased. Bax, caspase-3/7 activities and cleaved PARP-1 were inhibited at 20 μM FB1. In addition, the OGG1 transcript levels were decreased ( p < 0.0001) along with comet lengths ( p < 0.0001). This study showed that FB1-induced apoptosis in SNO cells may be caspase-dependent or caspase-independent; the pathway used depends on the exposure concentration.

Differential modulation of the lipid metabolism as a model for cellular resistance to fumonisin B1-induced cytotoxic effects in vitro

Differential sensitivity of primary hepatocytes and Chang cells to the cancer promoter fumonisin B1 (FB1)-induced cytotoxic effects were investigated in relation to changes in membrane lipid distribution. In contrast to primary hepatocytes, Chang cells were resistant to FB1-induced cytotoxic effects. This was associated with a high cholesterol (Chol) and sphingomyelin (SM) and low phosphatidylcholine (PC) content, resulting in a significant (P<0.05) decrease in phosphatidylethanolamine (PE)/PC ratio, increased Chol/total phosphoglyceride (TPG) ratios and low total polyunsaturated fatty acids (PUFA) content in PC and PE, suggesting a more rigid membrane structure. High levels of C18:1 and reduced polyunsaturated fatty acid (PUFA) levels are likely to provide selective resistance to FB1-induced oxidative stress. FB1-associated lipid changes included decreases in SM and Chol, increases in sphinganine (Sa) and PE with the increases in key saturated, monounsaturated, and PUFAs in PE as key role players in the differential responses to FB1-induced cell growth responses in cells.

The antagonistic effects of Candida parapsilosis on the growth of Fusarium species and fumonisin production

Background and Purpose:

Fusarium species are avid producers of secondary toxic and carcinogenic metabolites such as fumonisin. Contamination of food and feed products with fumonisin can be hazardous to the health of humans and animals and may lead to agricultural loss. Accordingly, in this study, we aimed to evaluate the effects of Candida parapsilosis on the growth and fumonisin production of Fusarium species.

Materials and Methods:

Mycelial growth rate of 26 Fusarium isolates, including F. verticillioides (n=6), F. proliferatum (n=18), F. solani (n=1), and F. oxysporum (n=1), in the presence of 42 C. parapsilosis strains was investigated by pour-plate method. The decline in fumonisin production was measured in co-cultured fungi in coarsely ground maize after four weeks of incubation in the dark at 22°C, using ELISA technique. For data analysis, paired t-test was performed, using SPSS version 20.

Results:

The mycelial growth and fumonisin production of Fusarium isolates significantly decreased in the presence of C. parapsilosis in comparison with the control cultures (P<0.05). The percentage of mycelial growth inhibition ranged from 56.36% to 74.54%. The minimum and maximum decline in total fumonisin production was 12% and 78%, respectively. F. oxysporum and F. solani were found to be minor fumonisin producers among the studied Fusarium species. On the other hand, a decline was reported in the growth of Fusarium species and fumonisin production in the presence of C. parapsilosis.

Conclusion:

C. parapsilosis showed notable inhibitory activities against Fusarium isolates. Therefore, this fungal species could be considered as a biocontrol agent against the growth and fumonisin production of toxigenic Fusarium species in the future.