Determination of the epigenetic effects of ochratoxin in a human kidney and a rat liver epithelial cell line

Membrane Receptor-Mediated Disruption of Cellular Homeostasis: Changes in Intracellular Signaling Pathways Increase the Toxicity of Ochratoxin A

Organisms maintain their cellular homeostatic balance by interacting with their environment through the use of their cell surface receptors. Membrane based receptors such as the transforming growth factor β receptor (TGFR), the prolactin receptor (PRLR), and hepatocyte growth factor receptor (HGFR), along with their associated signaling cascade, play significant roles in retaining cellular homeostasis. While these receptors and related signaling pathways are essential for health of cell and organism, their dysregulation can lead to imbalance in cell function with severe pathological conditions such as cell death or cancer. Ochratoxin A (OTA) can disrupt cellular homeostasis by altering expression levels of these receptors and/or receptor-associated intracellular downstream signaling modulators and/or pattern and levels of their phosphorylation/dephosphorylation. Recent studies have shown that the activity of the TGFR, the PRLR, and HGFR and their associated signaling cascades change upon OTA exposure. A critical evaluation of these findings suggests that while increased activity of the HGFR and TGFR signaling pathways leads to an increase in cell survival and fibrosis, decreased activity of the PRLR signaling pathway leads to tissue damage. This review explores the roles of these receptors in OTA-related pathologies and effects on cellular homeostasis.

Applicability of Scrape Loading-Dye Transfer Assay for Non-Genotoxic Carcinogen Testing

Dysregulation of gap junction intercellular communication (GJIC) is recognized as one of the key hallmarks for identifying non-genotoxic carcinogens (NGTxC). Currently, there is a demand for in vitro assays addressing the gap junction hallmark, which would have the potential to eventually become an integral part of an integrated approach to the testing and assessment (IATA) of NGTxC. The scrape loading-dye transfer (SL-DT) technique is a simple assay for the functional evaluation of GJIC in various in vitro cultured mammalian cells and represents an interesting candidate assay. Out of the various techniques for evaluating GJIC, the SL-DT assay has been used frequently to assess the effects of various chemicals on GJIC in toxicological and tumor promotion research. In this review, we systematically searched the existing literature to gather papers assessing GJIC using the SL-DT assay in a rat liver epithelial cell line, WB-F344, after treating with chemicals, especially environmental and food toxicants, drugs, reproductive-, cardio- and neuro-toxicants and chemical tumor promoters. We discuss findings derived from the SL-DT assay with the known knowledge about the tumor-promoting activity and carcinogenicity of the assessed chemicals to evaluate the predictive capacity of the SL-DT assay in terms of its sensitivity, specificity and accuracy for identifying carcinogens. These data represent important information with respect to the applicability of the SL-DT assay for the testing of NGTxC within the IATA framework.

Transcriptome Analysis of Ochratoxin A-Induced Apoptosis in Differentiated Caco-2 Cells

Ochratoxin A (OTA), an important mycotoxin that occurs in food and animal feed, has aroused widespread concern in recent years. Previous studies have indicated that OTA causes nephrotoxicity, hepatotoxicity, genotoxicity, immunotoxicity, cytotoxicity, and neurotoxicity. The intestinal toxicity of OTA has gradually become a focus of research, but the mechanisms underlying this toxicity have not been described. Here, differentiated Caco-2 cells were incubated for 48 h with different concentrations of OTA and transcriptome analysis was used to estimate damage to the intestinal barrier. Gene expression profiling was used to compare the characteristics of differentially expressed genes (DEGs). There were altogether 10,090 DEGs, mainly clustered into two downregulation patterns. The Search Tool for Retrieval of Interacting Genes (STRING), which was used to analyze the protein-protein interaction network, indicated that 24 key enzymes were mostly responsible for regulating cell apoptosis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis was used to validate eight genes, three of which were key genes (CASP3, CDC25B, and EGR1). The results indicated that OTA dose-dependently induces apoptosis in differentiated Caco-2 cells. Transcriptome analysis showed that the impairment of intestinal function caused by OTA might be partly attributed to apoptosis, which is probably associated with downregulation of murine double minute 2 (MDM2) expression and upregulation of Noxa and caspase 3 (CASP3) expression. This study has highlighted the intestinal toxicity of OTA and provided a genome-wide view of biological responses, which provides a theoretical basis for enterotoxicity and should be useful in establishing a maximum residue limit for OTA.

A fluorometric aptamer-based assay for ochratoxin A by using exonuclease III-assisted recycling amplification

A fluorometric assay is described for ochratoxin A (OTA) using an aptamer. The method is based on exonuclease-assisted recycling amplification. The OTA-binding aptamer partially hybridizes with complementary DNA (cDNA) that is released when the aptamer recognizes OTA. Then, cDNA hybridizes with a specifically designed hairpin DNA. Next, short ssDNA and cDNA are, respectively, released by exonuclease III catalyzed hydrolysis of the dsDNA. The cDNA induces the next ring opening and digestion. The short ssDNA captures the sDNA that is labeled with fluorescent FAM and is absorbed on graphene oxide (GO). The green fluorescence of the sDNA/GO system is quenched but is recovered if the sDNA is released from GO. This assay is high sensitive, works in the 5 nM to 200 nM OTA concentration range and has a 0.96 nM lower detection limit. It was applied to the quantitation of OTA in spiked wine and coffee samples. Graphical abstractSchematic of a fluorometric assay based on exonuclease-assisted recycling amplification for quantitative monitoring of OTA without the need of sample separation and multiple washing steps.

Combination of Selenomethionine and N-Acetylcysteine Alleviates the Joint Toxicities of Aflatoxin B1 and Ochratoxin A by ERK MAPK Signal Pathway in Porcine Alveolar Macrophages

Our previous studies showed that aflatoxin B1 (AFB1) and ochratoxin A (OTA) could trigger joint immune toxicity. Little is known about the combined effects of selenomethionine (SeMet) and N-acetylcysteine (NAC) on the joint toxicities of the two toxins. In this study, results showed that SeMet or NAC alone or in combination significantly alleviated the downswing of cell viability, glutathione production, and phagorytosis induced by AFB1 and OTA in porcine alveolar macrophages. The uptrend of lactate dehydrogenase activities, apoptosis, reactive oxygen species levels, and the relative mRNA of inflammatory cytokines triggered by the two toxins was decreased. Combination of them was more effective than single application. Knockdown of p38, c-JUN N-terminal kinase (JNK), or extracellular signal-regulated kinase (ERK) via use of the corresponding specific siRNA could alleviate the joint toxicities of AFB1 and OTA. However, the ERK but not p38 or JNK pathway was involved in the protection of SeMet and NAC against the immunotoxicity. In conclusion, combination of SeMet and NAC might be a new therapeutic orientation for preventing the joint toxicities induced by AFB1 and OTA.

Effects of ochratoxin A on ER stress, MAPK signaling pathway and autophagy of kidney and spleen in pigs

Ochratoxin A (OTA), a worldwide mycotoxin found in food and feeds, is a potent nephrotoxin and immunotoxin in animals and humans. This research was conducted to evaluate whether endoplasmic reticulum (ER) stress, MAPK signaling pathway and autophagy were induced by OTA in kidney and spleen of pigs. Twenty-seven crossbred pigs randomly allocated to 3 groups were fed for 42 days ad libitum a basal diet without (Con group, 0.00 μg OTA/kg) and with supplementation of OTA at 400 (OTA-L group) and 800 μg/kg (OTA-H group). From each group, 6 pigs were randomly selected for blood collection on days 0, 21, and 42 and 3 pigs were randomly selected for tissue collection on day 42. The results showed that OTA at 400 and 800 μg/kg diets significantly increased OTA concentrations in serum and kidney and spleen induced the histopathological lesions of kidney and spleen, decreased TCR-stimulated T lymphocyte viabilities and IL-2 concentration, increased TNF-α concentration, and decreased T-AOC levels. OTA increased glucose regulated protein 78, p38, and ERK1/2 phosphorylation, and LC3 II and Atg5 protein expression in kidney and spleen of pigs. These results provide new insights into the relationship between OTA and ER stress, p38 and ERK1/2 MAPK signaling pathway and autophagy in pigs.

Ochratoxin A induces nephrotoxicity and immunotoxicity through different MAPK signaling pathways in PK15 cells and porcine primary splenocytes

Ochratoxin A (OTA) is reported to be a potent nephrotoxin and immunotoxin in animals and humans. However, the mechanisms underlying OTA toxicity have not been clearly determined until now. Toxicity of OTA and its mechanism was investigated in PK15 cells and in porcine primary splenocytes. The results showed that OTA at 2.0-8.0 μg/mL for 24 h induced cytotoxicity and apoptosis in a dose-dependent manner in PK 15 cells. OTA at 0.5-4.0 μg/mL for 24 h induced cytotoxicity and apoptosis in a dose-dependent manner in porcine primary splenocytes. In addition, OTA induced p38 and ERK1/2 phosphorylation both in PK15 cells and porcine primary splenocytes. Knock-down of p38 instead of ERK by their specific siRNA significantly eliminated the nephrotoxicity induced by OTA. Contrary, knock-down of ERK1/2 instead of p38 by their specific siRNA significantly eliminated the immunotoxicity induced by OTA. The observed effects indicate that OTA induced nephrotoxicity by p38 signaling pathway in PK15 cells and immunotoxicity by ERK signaling pathway in porcine primary splenocytes.

Ochratoxin A: Molecular Interactions, Mechanisms of Toxicity and Prevention at the Molecular Level

Ochratoxin A (OTA) is a widely-spread mycotoxin all over the world causing major health risks. The focus of the present review is on the molecular and cellular interactions of OTA. In order to get better insight into the mechanism of its toxicity and on the several attempts made for prevention or attenuation of its toxic action, a detailed description is given on chemistry and toxicokinetics of this mycotoxin. The mode of action of OTA is not clearly understood yet, and seems to be very complex. Inhibition of protein synthesis and energy production, induction of oxidative stress, DNA adduct formation, as well as apoptosis/necrosis and cell cycle arrest are possibly involved in its toxic action. Since OTA binds very strongly to human and animal albumin, a major emphasis is done regarding OTA-albumin interaction. Displacement of OTA from albumin by drugs and by natural flavonoids are discussed in detail, hypothesizing their potentially beneficial effect in order to prevent or attenuate the OTA-induced toxic consequences.

Ochratoxin A and T-2 Toxin Induce Clonogenicity and Cell Migration in Human Colon Carcinoma and Fetal Lung Fibroblast Cell Lines

T-2 toxin and Ochratoxin A (OTA) are toxic secondary metabolites produced by various fungi, and together they contaminate feedstuffs worldwide. T-2 toxin and OTA may exert carcinogenic action in rodent. Despite the various in vivo experiments, carcinogenicity of these two mycotoxins has not yet been proven for human. In this current study, we proposed to investigate, in Human colon carcinoma cells and fetal lung fibroblast-like cells transfected with MYC, the effect of T-2 toxin and OTA on cell clonogenicity and cell migration. Results of the present investigation showed that T2-toxin as well as OTA has an important clonogenic effect in all cell lines, suggesting that these mycotoxins could promote the transcription of c-myc gene. Furthermore, T-2 toxin and OTA enhanced the migration effect of HCT116 cells at very low concentrations, proposing that these mycotoxins may exhibit carcinogenesis-like properties in the studied cells.

Modulation of the xenobiotic transformation system and inflammatory response by ochratoxin A exposure using a co-culture system of Caco-2 and HepG2 cells

Cytotoxicity of ochratoxin A (OTA) was evaluated using the MTS assay, and membrane integrity was measured using transepithelial electrical resistance (TEER). A transwell system was used to investigate the effect of OTA on the expression of the CYP450 (1A1, 2A6, 2B6, 3A4 and 3A5), NAT2, COX-2, LOX-5, and MRP2 genes in Caco-2 and HepG2 cells. TEER decreased by a mean of 63.2% after 24 h in Caco-2 differentiated cells without inducing cell detachment; revealing damage to the intestinal epithelial cell tight junction proteins and an increase in cell permeability. Gene expression analysis showed that modulation of gene expression by OTA was higher in Caco-2 cells than in HepG2 cells, and generally, the duration of exposure to OTA had a more significant effect than the OTA dose. A general OTA down-regulation effect was observed in Caco-2 cells, in contrast with the down- and up-regulation observed in HepG2 cells. In Caco-2 cells, CYP1A1 was the gene with the highest regulation, followed by CYP3A4 and CYP3A5. Conversely, in HepG2 cells, CYP2B6 was highly regulated at 3 and 12 h compared to the other cytochromes; CYP1A1 was slightly modulated during the first 12 h, but an overexpression was observed at 24 h. Our data support the involvement of the COX-2 and 5-LOX genes in liver metabolism of OTA. On the basis of the gene expression analysis, the results suggest a possible impairment in OTA secretion at the intestinal and hepatic level due to MRP2 repression. In addition, we provide evidence of the effect of OTA on NAT2 gene expression, which had not been reported before.

Modulation by aspirin and naproxen of nucleotide alterations and tumors in the lung of mice exposed to environmental cigarette smoke since birth

Chemoprevention provides an important strategy for cancer control in passive smokers. Due to the crucial role played by smoke-related chronic inflammation in lung carcinogenesis, of special interest are extensively used pharmacological agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs). We evaluated the ability of aspirin and naproxen, inhibitors of both cyclooxygenase-1 and cyclooxygenase -2, to modulate environmental cigarette smoke (ECS)-induced lung carcinogenesis in A/J mice of both genders. Based on a subchronic toxicity study in 180 postweaning mice, we used 1600 mg/kg diet aspirin and 320 mg/kg diet naproxen. In the tumor chemoprevention study, using 320 mice, exposure to ECS started soon after birth and administration of NSAIDs started after weaning. At 10 weeks of life, the NSAIDs did not affect the presence of occult blood in feces. As assessed in a subset of 40 mice, bulky DNA adducts and 8-hydroxy-2'-deoxyguanosine levels were considerably increased in ECS-exposed mice and, irrespective of gender, both NSAIDs remarkably inhibited these nucleotide alterations. After exposure for 4 months followed by 5 months in filtered air, ECS induced a significant increase in the yield of surface lung tumors, the 43.7% of which were adenomas and the 56.3% were adenocarcinomas. Oct-4 (octamer-binding transcription factor 4), a marker of cell stemness, was detected in some adenocarcinoma cells. The NAIDs attenuated the yield of lung tumors, but prevention of ECS-induced lung adenomas was statistically significant only in female mice treated with aspirin, which supports a role for estrogens in ECS-related lung carcinogenesis and highlights the antiestrogenic properties of NSAIDs.

Mechanisms of environmental chemicals that enable the cancer hallmark of evasion of growth suppression

As part of the Halifax Project, this review brings attention to the potential effects of environmental chemicals on important molecular and cellular regulators of the cancer hallmark of evading growth suppression. Specifically, we review the mechanisms by which cancer cells escape the growth-inhibitory signals of p53, retinoblastoma protein, transforming growth factor-beta, gap junctions and contact inhibition. We discuss the effects of selected environmental chemicals on these mechanisms of growth inhibition and cross-reference the effects of these chemicals in other classical cancer hallmarks.

Ochratoxin A activates opposing c-MET/PI3K/Akt and MAPK/ERK 1-2 pathways in human proximal tubule HK-2 cells

Ochratoxin A (OTA) is a mycotoxin produced as a secondary metabolite by filamentous fungi, such as Aspergillus and Penicillium. Because OTA is a common contaminant of food and feeds, humans and animals are frequently exposed to OTA in daily life. It has been classified as a carcinogen in rodents and a possible carcinogen in humans. OTA has been shown to deregulate a variety of different signal transduction pathways in a cell type- and dosage-depending manner resulting in contrasting physiological effects, such as survival or cell death. While the ERK1-2 and JNK/SAPK MAPK pathways are major targets, knowledge about their role in OTA-mediated cell survival and death is fragmented. Similarly, the contribution of the PI3K/Akt pathway to the carcinogenic effect of OTA in proximal tubule cells has not been elucidated in detail. In this study, we demonstrated that OTA induced sustained activation of the PI3K/Akt and MEK/ERK1-2 signaling pathways in a dose- and time-dependent manner in HK-2 cells. Chemical inhibition of ERK1-2 activation or overexpression of dominant-negative and kinase-dead MEK1 leads to increased cell viability and decreased apoptosis in OTA-treated cells. Blockage of PI3K/Akt with Wortmannin aggravated the negative effect of OTA on cell viability and increased the levels of apoptosis. Moreover, we identified the c-MET proto-oncogene as an upstream receptor tyrosine kinase responsible for OTA-induced activation of PI3K/Akt signaling in HK-2 cells. Our data suggest that OTA may potentiate carcinogenesis by sustained activation of c-MET/PI3K/Akt signaling through suppression of apoptosis induced by MEK/ERK1-2 activation in damaged renal proximal tubule epithelial cells.

Case report evidence of relationships between hepatocellular carcinoma and ochratoxicosis

Purpose

The incidence of Hepatocellular carcinoma (HCC) is on the rise, but what is causing that trend has remained a mystery. Mycotoxins are almost entirely ignored health problems, and sometimes actually naively belittled in advanced medical care. Ochratoxin A (OTA) is one of the most abundant food contaminating mycotoxins worldwide that is carcinogenic, but no studies have evaluated its levels in HCC patients. Therefore, this study was designed to monitor the presence of OTA in the serum of HCC patients and to quantify the strength of the association between OTA and HCC.

Methods

We conducted a case control-based study on 61 participants. Thirty-nine were HCC cases identified between 2010 and 2012 and individually matched by age, sex, residence and date of recruitment to 22 healthy controls. Serum OTA and alpha-fetoprotein levels were measured by using high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay, respectively.

Results

HPLC analysis of 61 serum samples indicated that the highest incidence of elevated OTA was found in the HCC group and was 5-fold higher than in the control group. The concentration of OTA in the HCC group ranged between 0.129 and 10.93 ng/mL with a mean value±SD of 1.1±0.3 ng/mL, while in the normal group it ranged between 0.005 and 0.50 ng/mL with a mean value±SD of 0.201±0.02 ng/mL. The odds ratio for HCC patients presenting OTA levels above the cut-off of 0.207 (calculated by the receiver operating characteristic curve) was 9.78 (95% confidence interval = 2.9095–32.9816, P = 0.0002) with respect to normal controls, suggesting that HCC is 9.8 times as frequent in the exposed group to OTA.

Conclusion

Our results reveal a strong association between the presence of OTA and HCC, which may offer a coherent explanation for much of the descriptive epidemiology of HCC and suggest new avenues for analytical research.

Ochratoxin A causes oxidative stress and cell death in rat liver

The effect of ochratoxin A (OTA) on oxidant/antioxidant status and on histopathological changes and apoptotic cell death in livers of male Sprague-Dawley rats has been investigated. OTA (0.5 mg/kg body weight/day) was administered by oral route for 14 days. Plasma biochemical parameters, activities of liver selenoenzymes (glutathione peroxidase-1, thioredoxin reductase) and antioxidant enzymes (catalase, superoxide dismutase, glutathione S-transferase), and levels of total glutathione and thiobarbituric acid reactive substance in hepatic tissue were measured. In addition, histopathological examinations were performed and apoptotic cell death of hepatocytes was evaluated by the TdT-mediated dUTP nick-end labelling (TUNEL) assay. OTA exposure was found to induce focal necrosis of hepatocytes and mononuclear cell infiltration. Besides, exposure to OTA caused an imbalance in oxidant and antioxidant parameters in the rat liver, as evidenced by significant decreases in glutathione S-transferase activity and glutathione levels, and marked increases in concentrations of thiobarbituric acid reactive substances. Furthermore, TUNEL analysis revealed a significant ~2.7-fold increase in the number of TUNEL-positive liver cells of rats exposed to OTA compared to the control group. The results of this study showed that oxidative stress is at least one of the mechanisms underlying the hepatic toxicity of OTA, and that both necrosis and apoptosis are types of cell death in the hepatic toxicity of this mycotoxin.

Ochratoxin a and mitotic disruption: mode of action analysis of renal tumor formation by ochratoxin A

The mycotoxin and food contaminant ochratoxin A (OTA) is a potent renal carcinogen in rodents, but its mode of action (MoA) is still poorly defined. In 2006, the European Food Safety Authority concluded that there is a "lack of evidence for the existence of OTA-DNA adducts" and thus insufficient evidence to establish DNA reactivity as a MoA for tumor formation by OTA. In reviewing the available database on OTA toxicity, a MoA for renal carcinogenicity of OTA is developed that involves a combination of genetic instability and increased proliferative drive as consequences of OTA-mediated disruption of mitosis, whereby the organ- and site-specificity of tumor formation by OTA is determined by selective renal uptake of OTA into the proximal tubule epithelium. The proposed MoA is critically assessed with respect to concordance of dose-response of the suggested key events and tumor formation, their temporal association, consistency, and biological plausibility. Uncertainties, data gaps and needs for further research are highlighted.

Evidence for a role of oxidative stress in the carcinogenicity of ochratoxin a

The in vitro and in vivo evidence compatible with a role for oxidative stress in OTA carcinogenicity has been collected and described. Several potential oxido-reduction mechanisms have been identified in the past. More recently, the possibility of a reduction of cellular antioxidant defense has been raised as an indirect source of oxidative stress. Consequences resulting from the production of oxidative stress are observed at different levels. First, OTA exposure has been associated with increased levels of oxidative DNA, lipid, and protein damage. Second, various biological processes known to be mobilized under oxidative stress were shown to be altered by OTA. These effects have been observed in both in vitro and in vivo test systems. In vivo, active doses were often within doses documented to induce renal tumors in rats. In conclusion, the evidence for the induction of an oxidative stress response resulting from OTA exposure can be considered strong. Because the contribution of the oxidative stress response in the development of cancers is well established, a role in OTA carcinogenicity is plausible. Altogether, the data reviewed above support the application of a threshold-based approach to establish safe level of dietary human exposure to OTA.

A Journey Through Mitogen-Activated Protein Kinase and Ochratoxin A Interactions

Ochratoxin A (OTA) is a ubiquitous mycotoxin with potential nephrotoxic, carcinogenic, and cytotoxic action. It has been proposed that OTA might be involved in the development of Balkan endemic nephropathy, which is associated with an increased risk of urinary tract tumours, and of other forms of interstitial nephritis. Cell susceptibility to OTA mainly depends on mycotoxin concentrations, duration of exposure, and intracellular molecular and genetic context. OTA can affect a cell by stimulating or inhibiting certain signalling pathways such as mitogen-activated protein kinase (MAPK). Three major mammalian MAPKs have been described: extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. All MAPKs regulate diverse cellular programmes, but in most cases ERKs have been linked to cell survival, while JNKs, and p38 MAPKs have been implicated in cell death by apoptosis. This review looks into OTA-mediated MAPK activation and its effects.

Gap junctional intercellular communication as a target for liver toxicity and carcinogenicity

Direct communication between hepatocytes, mediated by gap junctions, constitutes a major regulatory platform in the control of liver homeostasis, ranging from hepatocellular proliferation to hepatocyte cell death. Inherent to this pivotal task, gap junction functionality is frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity and carcinogenicity. In the present paper, the deleterious effects of a number of chemical and biological toxic compounds on hepatic gap junctions are discussed, including environmental pollutants, biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. Particular attention is paid to the molecular mechanisms that underlie the abrogation of gap junction functionality. Since hepatic gap junctions are specifically targeted by tumor promoters and epigenetic carcinogens, both in vivo and in vitro, inhibition of gap junction functionality is considered as a suitable indicator for the detection of nongenotoxic hepatocarcinogenicity.

The mycotoxin ochratoxin A inhibits DNA topoisomerase II and induces polyploidy in cultured CHO cells

Ochratoxin A (OTA), a known nephrotoxin and carcinogenic mycotoxin, was investigated to examine its effectiveness to induce cytotoxicity and DNA damage (Comet assay), as well as its possible inhibition of topoisomerase II (topo II) catalytic activity in cultured Chinese hamster ovary (CHO) cells. The analysis of OTA-induced DNA strand breaks as well as the flow cytometric assessment of polyploidy has provided evidence that is consistent with the idea of a mixed mode of action of the mycotoxin: in addition to its genotoxic activity, OTA may also interfere with chromosome distribution during cell division.

Ochratoxin A: The Continuing Enigma

The mycotoxin ochratoxin A (OTA) has been linked to the genesis of several disease states in both animals and humans. It has been described as nephrotoxic, carcinogenic, teratogenic, immunotoxic, and hepatotoxic in laboratory and domestic animals, as well as being thought to be the probable causal agent in the development of nephropathies (Balkan Endemic Nephropathy, BEN and Chronic Interstitial Nephropathy, CIN) and urothelial tumors in humans. As a result, several international agencies are currently attempting to define safe legal limits for OTA concentration in foodstuffs (e.g., grain, meat, wine, and coffee), in processed foods, and in animal fodder. In order to achieve this goal, an accurate risk assessment of OTA toxicity including mechanistic and epidemiological studies must be carried out. Ochratoxin has been suggested by various researchers to mediate its toxic effects via induction of apoptosis, disruption of mitochondrial respiration and/or the cytoskeleton, or, indeed, via the generation of DNA adducts. Thus, it is still unclear if the predominant mechanism is of a genotoxic or an epigenetic nature. One aspect that is clear, however, is that the toxicity of OTA is subject to and characterized by large species- and sex-specific differences, as well as an apparently strict structure-activity relationship. These considerations could be crucial in the investigation of OTA-mediated toxicity. Furthermore, the use of appropriate in vivo and in vitro model systems appears to be vital in the generation of relevant experimental data. The intention of this review is to collate and discuss the currently available data on OTA-mediated toxicity with particular focus on their relevance for the in vivo situation, and also to suggest possible future strategies for unlocking the secrets of ochratoxin A.

Carcinogen-specific gene expression profiles in short-term treated Eker and wild-type rats indicative of pathways involved in renal tumorigenesis

Eker rats heterozygous for a dominant germline mutation in the tuberous sclerosis 2 (Tsc2) tumor suppressor gene were used as a model to study renal carcinogenesis. Eker and corresponding wild-type rats were exposed to genotoxic aristolochic acid (AA) or non-genotoxic ochratoxin A (OTA) to elucidate early carcinogen-specific gene expression changes and to test whether Eker rats are more sensitive to carcinogen-induced changes in gene expression. Male Eker and wild-type rats were gavaged daily with AA (10 mg/kg body weight) or OTA (210 microg/kg body weight). After 1, 3, 7, and 14 days of exposure, renal histopathology, tubular cell proliferation, and Affymetrix gene expression profiles from renal cortex/outer medulla were analyzed. AA-treated Eker and wild-type rats were qualitatively comparable in all variables assessed, suggesting a Tsc2-independent mechanism of action. OTA treatment resulted in slightly increased cortical pathology and significantly elevated cell proliferation in both strains, although Eker rats were more sensitive. Deregulated genes involved in the phosphatidylinositol 3-kinase-AKT-Tsc2-mammalian target of rapamycin signaling, among other important genes prominent in tumorigenesis, in conjunction with the enhanced cell proliferation and presence of preneoplastic lesions suggested involvement of Tsc2 in OTA-mediated toxicity and carcinogenicity, especially as deregulation of genes involved in this pathway was more prominent in the Tsc2 mutant Eker rat.

Ochratoxin A-induced mutagenesis in mammalian cells is consistent with the production of oxidative stress

Ochratoxin A (OTA) is a widespread mycotoxin in food and a powerful nephrocarcinogen in rats. The mutagenicity of OTA has been extensively investigated but with conflicting results, thus leaving open the mechanistic question for OTA carcinogenicity. Here, we examined the mutagenicity of OTA by using well-standardized mutation assays such as the hypoxanthine-guanine phosphoribosyltransferase (HPRT) assay in Chinese hamster V79 cells and the thymidine kinase assay in mouse lymphoma LY5178 cells. OTA-induced HPRT mutations were characterized at the molecular level. In V79 cells, OTA produced a dose- and time-related decrease in cell number as a consequence of the transitory cytostatic effect mediated by G2/M cell cycle arrest. In both mutation assays, OTA was weakly mutagenic and this effect was independent of biotransformation. OTA-induced mutations were characterized by point mutations (48%) and a lack of a detectable reverse-transcription polymerase chain reaction product (52%). The pattern of OTA-induced point mutations was similar to that of spontaneous mutants, suggesting that OTA induced an increase of the endogenous oxidative metabolism but not covalent DNA adducts. Our data support a model where OTA is mutagenic via oxidative DNA damage induction.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.

Early cytotoxic effects of ochratoxin A in rat liver: a morphological, biochemical and molecular study

We characterized the overall early effect of chronic ochratoxin A (OTA) treatment on rat liver, analyzing different aspects related to: (i) fibrosis, by measuring collagen content and turnover, and alpha-smooth muscle actin (alphaSMA); (ii) oxidative stress and stress response, by analyzing protein carbonylation, superoxide dismutase (SOD) and heat shock protein (HSP70) gene expression; (iii) the possible tumor promoter effect, evaluating cadherin and connexin (CX) mRNA levels. Light microscopy analysis showed no histological differences in OTA-treated and control (CT) rats. Collagen content, determined by computer analysis of Sirius red-stained liver sections, was similar in both groups. In liver homogenates COL-I, COL-III, TIMP-1 and TGF-beta1 mRNA levels and alphaSMA were unaffected by OTA. Matrix metalloproteinase (MMP)-1, MMP-2 and MMP-9 protein levels were also similar in the two groups. Protein carbonylation, a marker of severe oxidative stress, was not evident in the homogenates of OTA-treated livers; superoxide dismutase (SOD) mRNA tended to be lower and HSP70 was strongly down-regulated. OTA reduced E-cadherin and DSC-2 transcription, and down-regulated liver CX26, CX32 and CX43. In conclusion, these in vivo results show that OTA-induced liver injury involves a reduction in the ability to counterbalance oxidative stress, maybe leading to altered gap junction intercellular communication and loss of cell adhesion and polarity. This suggests that mild oxidative damage might be a key factor, in combination with other cytotoxic effects, in triggering the promotion of liver tumors after exposure to OTA.

Ochratoxin A alters cell adhesion and gap junction intercellular communication in MDCK cells

Ochratoxin A (OTA) is one of the most potent renal carcinogens studied to date, but the mechanism of tumor formation by ochratoxin A remains largely unknown. Cell adhesion and cell-cell communication participate in the regulation of signaling pathways involved in cell proliferation and growth control and it is therefore not surprising that modulation of cell-cell signaling has been implicated in cancer development. Several nephrotoxicants and renal carcinogens have been shown to alter cell-cell signaling by interference with gap junction intercell communication (GJIC) and/or cell adhesion, and the aim of this study was to determine if disruption of cell-cell interactions occurs in kidney epithelial cells in response to OTA treatment. MDCK cells were treated with OTA (0-50 microM) for up to 24h and gap junction function was analyzed using the scrape-load/dye transfer assay. In addition, expression and intracellular localization of C x 43, E-cadherin and beta-catenin were determined by immunoblot and immunofluorescence analysis. A clear decrease in the distance of dye transfer was evident following treatment with OTA at concentrations/incubation times which did not affect cell viability. Consistent with the functional inhibition of GJIC, treatment with OTA resulted in a dose-dependent decrease in C x 43 expression. In contrast to C x 43, OTA did not alter total amount of the adherens junction proteins E-cadherin and beta-catenin. Moreover, Western blot analysis of Triton X-100 soluble and insoluble protein fractions did not indicate translocation of cell adhesion molecules from the membrane to the cytoplasm. However, a approximately 78 kDa fragment of beta-catenin was detected in the detergent soluble fraction, indicating proteolytic cleavage of beta-catenin. Immunofluorescence analysis also revealed changes in the pattern of both beta-catenin and E-cadherin labeling, suggesting that OTA may alter cell-adhesion. Taken together, these data support the hypothesis that disruption of cell-cell signaling may contribute to OTA toxicity and carcinogenicity.

Ochratoxin A: Apoptosis and Aberrant Exit from Mitosis due to Perturbation of Microtubule Dynamics?

Ochratoxin A (OTA) is a potent nephrotoxin and causes high incidences of renal tumors in rodents. The molecular events leading to tumor formation by OTA are not well defined. Early pathological changes observed in kidneys of rats treated with OTA in vivo include frequent mitotic and abnormally enlarged cells, detachment of tubule cells, and apoptosis within the S3 segment of the proximal tubule, suggesting that OTA may interfere with molecules involved in the regulation of cell division and apoptosis. In this study, treatment of immortalized human kidney epithelial (IHKE) cells with OTA (0-50 microM) resulted in a time- and dose-dependent increase in apoptosis and activation of c-Jun N-terminal kinase. At the same time, OTA blocked metaphase/anaphase transition and led to the formation of aberrant mitotic figures and giant cells with abnormally enlarged and/or multiple nuclei, sometimes still connected by chromatin bridges. Immunostaining of the mitotic apparatus using an alpha-tubulin antibody revealed defects in spindle formation. In addition, OTA inhibited microtubule assembly in a concentration-dependent manner in a cell-free, in vitro assay. Interestingly, treatment with OTA also resulted in activation of the transcription factor nuclear factor kappa B (NFkappaB), which has recently been shown to promote cell survival during mitotic cell cycle arrest. Based on these observations, we hypothesize that the mechanism by which OTA promotes tumor formation involves interference with microtubuli dynamics and mitotic spindle formation, resulting in apoptosis or-in the presence of survival signals such as stimulation of the NFkappaB pathway-premature exit from mitosis. Aberrant exit from mitosis resulting in blocked or asymmetric cell division may favor the occurrence of cytogenetic abnormalities and may therefore play a critical role in renal tumor formation by OTA.

Toxicokinetics and toxicodynamics of ochratoxin A, an update

Ochratoxin A (OTA) is a mycotoxin produced by fungi of two genera: Penicillium and Aspergillus. OTA has been shown to be nephrotoxic, hepatotoxic, teratogenic and immunotoxic to several species of animals and to cause kidney and liver tumours in mice and rats. Because of differences in the physiology of animal species, wide variations are seen in the toxicokinetic patterns of absorption, distribution and elimination of the toxin. Biotransformation of OTA has not been entirely elucidated. At present, data regarding OTA metabolism are controversial. Several metabolites have been characterized in vitro and/or in vivo, whereas other metabolites remain to be characterized. Several major mechanisms have been shown as involved in the toxicity of OTA: inhibition of protein synthesis, promotion of membrane peroxidation, disruption of calcium homeostasis, inhibition of mitochondrial respiration and DNA damage. The contribution of metabolites in OTA genotoxicity and carcinogenicity is still unclear. The genotoxic status of OTA is still controversial because contradictory results were obtained in various microbial and mammalian tests, notably regarding the formation of DNA adducts. More recent studies are focused on the OTA ability to disturb cellular signalling and regulation, to modulate physiological signals and thereby to influence cells viability and proliferation. The present paper offers an update on these different issues. In addition since humans and animals are likely to be simultaneously exposed to several mycotoxins, especially through their diet, the little information available on the combined effects of OTA and other mycotoxins has also been reviewed.

How much should we involve genetic and environmental factors in the risk assessment of mycotoxins in humans?

Despite consented efforts in prevention, mycotoxins remain a problem of human health concern in several parts of the world including developed countries. Within the same range of toxins concentrations in the blood some people develop a disease while others do not. Could this inequality in front of mycotoxins effects be explained by environment factors and/or genetic predisposition? Among recent advances in environmental health research Correlation between chronic diseases and mycotoxins in humans deserves attention through several questions: Are genetic factors involved in disease causation of mycotoxins? How much are these factors currently taken into account for mycotoxins risk assessment and how much should we involve them? Answers are still to come. Genetic and environment factors deserve therefore more attention when dealing with regulatory limits, since among the general population, those who are at risk and will develop specific diseases are likely those bearing genetic predispositions. We have addressed these questions for the specific case of ochratoxin A in humans by investigating in Tunisia, county of Jelma, in four rural families forming a household of 21 persons all exposed to ochratoxin A in diet. Our results confirm that ochratoxin A induces chronic tubular nephropathy in humans and mainly point at those having the HLA haplotype A3, B27/35, DR7 to be more sensitive to the disease for quantitatively similar or lower exposure. Persons with such haplotype were found to bear chronic interstitial nephropathy with tubular karyomegalic cells while others were apparently healthy. Godin et al. (1996) in France have also found in sibling (a sister and her brother from urban area) that have similar HLA haplotype B35-patern, OTA-related renal tubulopathy with mild proteinuria including beta2-microglobulinuria. Several mechanisms are discussed that could be put ahead to explain how the HLA haplotype could lead to tubular cells lyses and renal failure. In the mean time it is urgent to search for mass screening biomarkers for mycotoxins in humans and related genetic factors to set-up more appropriate regulation.

The Nephrotoxin Ochratoxin A Induces Key Parameters of Chronic Interstitial Nephropathy in Renal Proximal Tubular Cells

Ochratoxin A (OTA) is a nephrotoxic and cancerogenic mycotoxin. There is epidemiological evidence that OTA exposition leads to cortical interstitial nephropathies in humans. However, virtually no data are available investigating the effect of OTA on renal cortical cells with respect to induction of nephropathy. Thus, we investigated whether OTA is able to induce changes of cellular properties potentially leading to interstitial nephropathy, using proximal tubular cell lines (OK, NRK-52E). OTA decreased cell number and cell protein time and dose dependently. Accordingly we investigated the effect of 100 nM or 1000 nM OTA. The decline of cell number after OTA exposure is due to necrosis and apoptosis, as measured by LDH release or DNA ladder formation and caspase-3 activation, respectively. OTA incubation of proximal tubular cells also resulted in a loss of epithelial tightness as determined by diffusion of FITC labeled inulin. Inflammation, fibrosis and epithelial-to-mesenchymal transition are described in chronic interstitial renal disease. Therefore, we also investigated the effect of OTA on NFkappaB activity, collagen secretion and generation of alpha smooth muscle actin. OTA alone was sufficient to induce the latter parameters in proximal tubular cells. Finally, OTA is a nephrotoxcic substance and elevated activity of mitogen activated protein kinases (MAPK) is described in nephropathies. As we investigated the effect of OTA on activity of ERK, JNK and p38 by ELISA, we found that OTA activates the MAPK measured dose dependently. In summary, OTA induced phenomena typical for chronic interstitial nephropathy, like loss of cells and epithelial tightness, necrosis and apoptosis as well as markers of inflammation, fibrosis and epithelial-to-mesenchymal transition in proximal tubular cells. Thus, we could show for the first time that OTA is able to induce key parameters of nephropathy in proximal tubular cells in culture. Moreover OTA interacts with MAPK and thus may exert its specific toxic actions.

Proximal Tubular Toxicity of Ochratoxin A Is Amplified by Simultaneous Inhibition of the Extracellular Signal-Regulated Kinases 1/2

Ochratoxin A (OTA) is a mycotoxin involved in the development of chronic nephropathies and a known carcinogen. As we have shown previously, OTA activates mitogen-activated protein kinases [extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-jun amino-terminal kinase (JNK), and extracellular-regulated protein kinase 38 (p38)] in proximal tubular cells (opossum kidney and normal rat kidney epithelial). ERK1/2, JNK, or p38 are thought to mediate opposite action on apoptosis, fibrosis, and inflammation. As we have already shown, OTA activates the latter processes. Here, we investigated the effect of OTA in the absence or presence of the ERK1/2 inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4bis(2-aminophenylthio)-butadiene] to test whether OTA then will exert increased toxicity. In the presence of ERK1/2 inhibition, OTA decreased cell number and protein to a significantly larger extent compared with OTA alone. The same was true for epithelial tightness, apoptosis (caspase-3 activity), and necrosis (lactate dehydrogenase release). Furthermore, simultaneous inhibition of ERK1/2 amplified the effect of OTA on markers of inflammation (nuclear factor of the kappa-enhancer in B cells activity), fibrosis (collagen secretion), and epithelial mesenchymal transition (alpha smooth muscle actin). OTA induces phenomena typical for chronic interstitial nephropathy and activates ERK1/2, JNK, and p38 in proximal tubular cells. Inhibition of ERK1/2 aggravates the effects of OTA or even induces toxicity at normally nontoxic concentrations. This is highly likely due to activation of JNK and p38. Our data indicate a new mechanistic explanation for the toxic actions induced by OTA, and they are notable with respect to a possible coexposition of the kidney to OTA and naturally occurring ERK1/2 inhibitors. Finally, our data give rise to an attractive hypothesis on the coincidence of increased OTA exposition and urinary tract tumors in humans.

Molecular aspects of the transport and toxicity of ochratoxin a

Ochratoxins are a class of naturally occurring compounds produced by several fungi. The most toxic is ochratoxin A (OTA), and occurrence of some human nephropathies and tumors correlate with enhanced OTA exposure. In this Account, the following areas are examined: molecular details of the binding of OTA to human serum albumin (HSA), the influences of binding to HSA on the trans-port of OTA across epithelial cell membranes by organic anion transport proteins, the oxidative activation of OTA, and the formation of OTA adducts with biological molecules. These studies are beginning to provide a detailed chemical model for the trans-port, accumulation, and genotoxic and carcinogenic effects of OTA.

Metabolism-mediated cytotoxicity of ochratoxin A

Ochratoxin A (OTA) is produced by various strains of Aspergillus and Penicillium and is a common contaminant of food commodities. OTA is metabolised by cytochrome P450 (CYP450) enzymes resulting in hydroxylated metabolites, 4R-OH-OTA and 4S-OH-OTA, and possibly in other minor metabolites including OTA-quinones. However, until now conflicting data have been presented regarding the role of biotransformation products in the adverse effects of OTA. Hence, the aim of this study was to further assess the metabolism-mediated cytotoxicity of OTA in an in vitro model encompassing NIH/3T3 cells, stably expressing the human CYP450 enzymes CYP2C9 and CYP3A4, respectively. In addition, modulation of the cellular glutathione (GSH) content was used to identify a role of GSH in OTA-induced cytotoxicity. Following exposure to OTA, cells expressing CYP2C9 showed a significant reduction in neutral red (NR) uptake but not in Alamar blue (AB) reduction, as compared to the control LNCX cells which do not express CYP450 enzymes. CYP3A4-expressing cells showed no difference in viability from control LNCX cells. When pre-treated with l-buthionine S,R-sulphoximine (BSO) to deplete GSH, CYP2C9-expressing cells showed also a loss of cell viability as compared to LNCX cells, although to a lesser extent as compared to non-depleted CYP2C9-expressing cells. Data presented in this study support previous findings, indicating that different biotransformation pathways contribute to the cytotoxicity induced by OTA.

Ochratoxin A and zearalenone: a comparative study on genotoxic effects and cell death induced in bovine lymphocytes

Ochratoxin A (OTA) and zearalenone (ZEA), two naturally occurring contaminants of animal feed, have been implicated in several mycotoxicoses in farm livestock but there is little information on their genotoxicity and toxicity in these species. Therefore, we investigated on the cytogenetic and cytotoxic effects of both OTA and ZEA in in vitro cultures of bovine lymphocytes. We determined chromosome aberrations (CAs) and sister chromatid exchanges (SCEs) as well as the mitotic index (MI) and cell viability following OTA and ZEA treatment. This report is the first to provide evidence of a statistically significant increase of structural CAs and of SCEs/cell associated with a reduction of the MI in all OTA- and ZEA-treated bovine lymphocyte cultures and a clear reproducible reducing effect of OTA on cell viability mediated by enhanced apoptosis. OTA-induced programmed cell death was not limited to bovine lymphocytes, as comparable data were demonstrated in the human leukemic T-cell line Jurkat.

Apoptosis and oxidative stress induced by ochratoxin A in rat kidney

Ochratoxin A (OTA) is a widespread mycotoxin produced by several species of fungi. OTA induces a tubular-interstitial nephropathy in humans and in animals. It has been implicated as one of the aetiological agents involved in the development of endemic nephropathy. OTA-induced oxidative stress and apoptosis may play key roles in the development of chronic tubulointerstitial nephritis connected to the long-term exposure to this food contaminant. We studied the effects of low doses of OTA on kidney cells. Wistar rats were treated with 120 microg OTA/kg bodyweight daily, for 10, 30 or 60 days. Toxin concentration in kidney was proportional to the time of exposure, and amounted to 547.2, 752.5 and 930.3 ng OTA/g kidney tissue after 10, 30 and 60 days, respectively. OTA treatment caused an increased number of cells undergoing apoptosis in both proximal and distal epithelial kidney cells. The apoptotic cells were visualised using the TUNEL assay and staining with haematoxylin and eosin in situ. The number of apoptotic cells in rats treated for 10, 30 and 60 days increased by 5-, 6.4- and 12.7-fold, respectively, compared with the control cells. However, DNA electrophoresis did not show characteristic fragmentation (DNA laddering). The oxidative stress was evident via increased malondialdehyde formation. The concentration of lipid peroxides showed an increase (36%), but the activity of superoxide dismutase decreased (26%) in 60-day treated rats. In spite of the observed biochemical and morphological changes in the kidney cells, renal functional status was preserved to the end of experiment. This study demonstrates that a combination of morphologic and biochemical markers can be used to monitor early cell death in OTA-induced renal injury. We have shown that the exposure to the relatively low OTA concentrations has activated apoptotic processes and oxidative damage in kidney cells.

The role of oxidative stress in the ochratoxin A-mediated toxicity in proximal tubular cells

Balkan endemic nephropathy (BEN), a disease characterized by progressive renal fibrosis in human patients, has been associated with exposure to ochratoxin A (OTA). This mycotoxin is a frequent contaminant of human and animal food products, and is toxic to all animal species tested. OTA predominantly affects the kidney and is known to accumulate in the proximal tubule (PT). The induction of oxidative stress is implicated in the toxicity of this mycotoxin. In the present study, primary rat PT cells and LLC-PK(1) cells, which express characteristics of the PT, were used to investigate the OTA-mediated oxidative stress response. OTA exposure of these cells resulted in a concentration-dependent elevation of reactive oxygen species (ROS) levels, depletion of cellular glutathione (GSH) levels and an increase in the formation of 8-oxoguanine. The OTA-induced ROS response was significantly reduced following treatment with alpha-tocopherol (TOCO). However, this chain-braking anti-oxidant did not reduce the cytotoxicity of OTA and was unable to prevent the depletion of total GSH levels in OTA-exposed cells. In contrast, pre-incubation of the cell with N-acetyl-L-cysteine (NAC) completely prevented the OTA-induced increase in ROS levels as well as the formation of 8-oxoguanine and completely protected against the cytotoxicity of OTA. In addition, NAC treatment also limited the GSH depletion in OTA-exposed PT- and LLC-PK(1) cells. From these data, we conclude that oxidative stress contributes to the tubular toxicity of OTA. Subsequently, cellular GSH levels play a pivotal role in limiting the short-term toxicity of this mycotoxin in renal tubular cells.