Formation of ochratoxin A metabolites and DNA-adducts in monkey kidney cells

Optimised Fermentation Production of Radiolabelled Ochratoxin A by Aspergillus ochraceus with Maximum 14C in the Pentaketide Moiety for Exploring Its Rat Renal Toxicology

In the context of the mysterious Balkan endemic nephropathy of the 1900s, and the discovery in the 1960s of the potent mycotoxin ochratoxin A, experimental research projects sought to explore any inter-relationship. Experimental lifetime administration of the toxin to male rats had revealed renal DNA adducts with the toxin, correlated with renal tumours, confirmation of which required molecular evidence. Consequently, production of 14C-ochratoxin A of a high specific radioactivity was required, practical biosynthetic detail of which had not previously been published. A fermentation study of Aspergillus ochraceous was carried out during 2002 for a European project, to select for the production of high-quality 14C-ochratoxin A, necessarily exploring for the maximum diversion of 14C-sodium acetate into the pentaketide portion of mycotoxin. Experimentation necessarily had to optimise the competitive context of fungal growth dynamics and addition of the biosynthetic precursor in the early days of shaken-flask fermentation before adding the radiolabelled precursor. From optimal fermentation, 50 mg of the 14C ochratoxin A was supplied within a European project for DNA adduct experimentation, but that proved negative as subsequently published. Experimental description of the radiolabelled ochratoxin A production was later made in a doctoral thesis, but is first publicised here. Further review of the literature reveals an explanation for the published failure to confirm rat DNA/ochratoxin A adduct formation, for which further experimentation is now recommended.

Risk assessment of ochratoxin A in food

The European Commission asked EFSA to update their 2006 opinion on ochratoxin A (OTA) in food. OTA is produced by fungi of the genus Aspergillus and Penicillium and found as a contaminant in various foods. OTA causes kidney toxicity in different animal species and kidney tumours in rodents. OTA is genotoxic both in vitro and in vivo; however, the mechanisms of genotoxicity are unclear. Direct and indirect genotoxic and non-genotoxic modes of action might each contribute to tumour formation. Since recent studies have raised uncertainty regarding the mode of action for kidney carcinogenicity, it is inappropriate to establish a health-based guidance value (HBGV) and a margin of exposure (MOE) approach was applied. For the characterisation of non-neoplastic effects, a BMDL 10 of 4.73 μg/kg body weight (bw) per day was calculated from kidney lesions observed in pigs. For characterisation of neoplastic effects, a BMDL 10 of 14.5 μg/kg bw per day was calculated from kidney tumours seen in rats. The estimation of chronic dietary exposure resulted in mean and 95th percentile levels ranging from 0.6 to 17.8 and from 2.4 to 51.7 ng/kg bw per day, respectively. Median OTA exposures in breastfed infants ranged from 1.7 to 2.6 ng/kg bw per day, 95th percentile exposures from 5.6 to 8.5 ng/kg bw per day in average/high breast milk consuming infants, respectively. Comparison of exposures with the BMDL 10 based on the non-neoplastic endpoint resulted in MOEs of more than 200 in most consumer groups, indicating a low health concern with the exception of MOEs for high consumers in the younger age groups, indicating a possible health concern. When compared with the BMDL 10 based on the neoplastic endpoint, MOEs were lower than 10,000 for almost all exposure scenarios, including breastfed infants. This would indicate a possible health concern if genotoxicity is direct. Uncertainty in this assessment is high and risk may be overestimated.

UPLC-MS/MS analysis of ochratoxin A metabolites produced by Caco-2 and HepG2 cells in a co-culture system

Ochatoxin A (OTA) is one of the most important mycotoxins based on its toxicity. The oral route is the main gateway of entry of OTA into the human body, and specialized epithelial cells constitute the first barrier. The present study investigated the in vitro cytotoxic effect of OTA (5, 15 and 45 μM) and production of OTA metabolities in Caco-2 and HepG2 cells using a co-culture Transwell System to mimic the passage through the intestinal epithelium and hepatic metabolism. The results derived from MTS cell viability assays and transepithelial electrical resistance measurements showed that OTA was slightly cytotoxic at the lowest concentration at 3 h, but significant toxicity was observed at all concentrations at 24 h. OTA metabolites generated in this co-culture were ochratoxin B (OTB), OTA methyl ester, OTA ethyl ester and the OTA glutathione conjugate (OTA-GSH). OTA methyl ester was the major metabolite found in both Caco-2 and HepG2 cells after all treatments. Our results showed that OTA can cause cell damage through several mechanisms and that the OTA exposure time is more important that the dosage in in vitro studies. OTA methyl ester is proposed as an OTA exposure biomarker, although future studies should be conducted.

A Review: Epigenetic Mechanism in Ochratoxin A Toxicity Studies

Ochratoxin A (OTA) is a natural contaminant that has displayed nephrotoxicity and hepatotoxicity in mammals. It contaminates a great variety of foodstuffs and threatens people's lives. The molecular mechanism of OTA-induced toxicity has been studied since 1965. Moreover, epigenetic mechanisms are also studied in OTA-induced toxicity. Additionally, the mode of OTA epigenetic research has been advanced in research hotspots. However, there is still no epigenetic study of OTA-induced toxicity. In this review, we discuss the relationship between these epigenetic mechanisms and OTA-induced toxicity. We found that studies on the epigenetic mechanisms of OTA-induced toxicity all chose the whole kidney or liver as the model, which cannot reveal the real change in DNA methylation or miRNAs or histone in the target sites of OTA. Our recommendations are as follows: (1) the specific target site of OTA should be detected by advanced technologies; and (2) competing endogenous RNAs (ceRNA) should be explored with OTA.

Evaluation of renal in vitro models used in ochratoxin research

Ochratoxin A (OTA) induces renal carcinomas in rodents with a specific localisation in the S3 segment of proximal tubules and distinct early severe tissue alterations, which have been observed also in other species. Pronounced species- and sex-specific differences in toxicity occur and similar effects cannot be excluded in humans, however precise mechanism(s) remain elusive until today. In such cases, the use of in vitro models for mechanistic investigations can be very useful; in particular if a non-genotoxic mechanism of cancer formation is assumed which include cytotoxic effects. However, potential genotoxic mechanisms can also be investigated in vitro. A crucial issue of in vitro research is the choice of the appropriate cell model. Apparently, the cellular target of OTA is the renal proximal tubular cell; therefore cells from this tissue area are the most reasonable model. Furthermore, cells from affected species should be used and can be compared to cells of human origin. Another important parameter is whether to use primary cultures or to choose a cell line from the huge variety of cell lines available. In any case, important characteristics and quality controls need to be verified beforehand. Therefore, this review discusses the renal in vitro models that have been used for the investigation of renal ochratoxin toxicity. In particular, we discuss the choice of the models and the essential parameters making them suitable models for ochratoxin research together with exemplary results from this research. Furthermore, new promising models such as hTERT-immortalised cells and 3D-cultures are briefly discussed.

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.

Toxicity of the mycotoxin citrinin and its metabolite dihydrocitrinone and of mixtures of citrinin and ochratoxin A in vitro

Citrinin (CIT) and ochratoxin A (OTA) are mycotoxins produced by several species of the genera Aspergillus, Penicillium and Monascus. Both can be present as contaminants in various food commodities and in animal feed. The occurrence and toxicity of OTA and human exposure have been intensively studied, but for CIT such data are scarce by comparison. Recently, dihydrocitrinone (DH-CIT) was detected as main metabolite of CIT in human urine, and co-occurrence of CIT and OTA was shown in human blood plasma (Blaszkewicz et al. in Arch Toxicol 87:1087-1094, 2013). In light of these new findings, we have now investigated the toxicity of the metabolite DH-CIT in comparison with CIT and analysed the effects of mixtures of CIT and OTA in vitro. The cytotoxic potency of DH-CIT (IC50 of 320/200 μM) was distinctly lower compared with CIT (IC50 of 70/62 μM) after treatment of V79 cells for 24 and 48 h. Whereas CIT induced a concentration-dependent increase in micronucleus frequencies at concentrations ≥30 μM, DH-CIT showed no genotoxic effect up to 300 μM. Thus, conversion of CIT to DH-CIT in humans can be regarded as a detoxification step. Mixtures of CIT and OTA exerted additive effects in cytotoxicity assays. The effect of CIT and OTA mixtures on induction of micronuclei varied dependent on the used concentrations between additive for low μM concentrations and more-than-additive for high μM concentrations. Effects on cell cycle were mostly triggered by OTA when both mycotoxins were used in combination. The implications of our and related in vitro studies are discussed with respect to in vivo concentrations of CIT and OTA, which are found in animals and in humans.

Multi-mycotoxin determination in baby foods and in vitro combined cytotoxic effects of aflatoxin M1 and ochratoxin A

The co-occurrence of mycotoxins in baby foods, including aflatoxin M1 (AFM1) and ochratoxin A (OTA), has been reported in previous studies, but data on their potential combined toxic effects are still missing. The present work aimed at (1) validating an in-house multi-mycotoxin high performance liquid chromatography with fluorescence detection (HPLC-FLD) method for AFM1, total aflatoxins (aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1), aflatoxin G2 (AFG2)) and OTA in infant formulae (milk powders) and cereal baby foods (flours), and (2) assessing the combined cytotoxic effects of AFM1 and OTA in an intestine-derived cell line. The HPLC-FLD method, which included a chloroform extraction, liquid-liquid extraction, immunoaffinity column clean-up and fluorescence detection after post-column derivatisation with electrochemically generated bromine, was adequate for the analysis of baby foods and met the requirements of validation and quality control for the studied working ranges. The limits of quantification for AFM1, AFB1, AFB2, AFG1, AFG2 and OTA were 0.069, 0.032, 0.020, 0.047, 0.020 and 0.244 μg/kg, respectively. The mean recovery values were 96, 114, 112, 107, 101 and 87%, respectively. A dose-dependent cytotoxicity was observed for individual and combined AFM1 and OTA using the Caco-2 cell line, which represents a site of contact of both mycotoxins in the body, after oral exposure. Interactions between both mycotoxins were disclosed by application of the concentration addition (CA) and independent action (IA) models, revealing the predominance of an antagonistic pattern. In conclusion, this study proposes a HPLC-FLD method for multi-mycotoxin monitoring in baby foods and provides evidence for the interaction between AFM1 and OTA, and for the applicability of CA/IA models to predict the effect of mycotoxins mixtures, further contributing to the prevention of mycotoxins-associated adverse health effects.

Toxicity of ochratoxin a and its modulation by antioxidants: a review

Ochratoxin A (OTA) is a mycotoxin involved in the development of different types of cancers in rats, mice and humans. A growing number of in vitro and in vivo studies has been collected and has described evidence compatible with a role for oxidative stress in OTA toxicity and carcinogenicity. Because the contribution of the oxidative stress response in the development of cancers is well established, a role in OTA carcinogenicity is plausible. Several studies have been performed to try to counteract the adverse effects of oxygen radicals generated under OTA-exposure. A number of molecules with various antioxidant properties were tested, using in vivo or in vitro models. Protection against OTA-induced DNA damage, lipid peroxidation, as well as cytotoxicity were observed, further confirming the link between OTA toxicity and oxidative damage. These studies demonstrated that antioxidants are able to counteract the deleterious effects of chronic consumption or exposure to OTA and confirmed the potential effectiveness of dietary strategies to counteract OTA toxicity.

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.

A reassessment of risk associated with dietary intake of ochratoxin A based on a lifetime exposure model

Mycotoxins, such as ochratoxin A (OTA), can occur from fungal growth on foods. OTA is considered a possible risk factor for adverse renal effects in humans based on renal tumors in male rats. For risk mitigation, Health Canada proposed maximum limits (MLs) for OTA based largely on a comparative risk assessment conducted by Health Canada (Kuiper-Goodman et al., 2010), in which analytical data of OTA in foods were used to determine the possible impact adopting MLs may have on OTA risks. The EU MLs were used for comparison and resultant risk was determined based on age-sex strata groups. These data were reevaluated here to determine comparative risk on a lifetime basis instead of age strata. Also, as there is scientific disagreement over the mechanism of OTA-induced renal tumors, mechanistic data were revisited. On a lifetime basis, risks associated with dietary exposure were found to be negligible, even without MLs, with dietary exposures to OTA three to four orders of magnitude below the pivotal animal LOAEL and the TD(05). Our review of the mechanistic data supported a threshold-based mechanism as the most plausible. In particular, OTA was negative in genotoxicity assays with the highest specificity and levels of DNA adducts were very low and not typical of genotoxic carcinogens. In conclusion, OTA exposures from Canadian foods do not present a significant cancer risk.

Structure-activity relationships imply different mechanisms of action for ochratoxin A-mediated cytotoxicity and genotoxicity

Ochratoxin A (OTA) is a fungal toxin that is classified as a possible human carcinogen based on sufficient evidence for carcinogenicity in animal studies. The toxin is known to promote oxidative DNA damage through production of reactive oxygen species (ROS). The toxin also generates covalent DNA adducts, and it has been difficult to separate the biological effects caused by DNA adduction from that of ROS generation. In the current study, we have derived structure-activity relationships (SAR) for the role of the C5 substituent of OTA (C5-X = Cl) by first comparing the ability of OTA, OTBr (C5-X = Br), OTB (C5-X = H), and OTHQ (C5-X = OH) to photochemically react with GSH and 2'-deoxyguanosine (dG). OTA, OTBr, and OTHQ react covalently with GSH and dG following photoirradiation, while the nonchlorinated OTB does not react photochemically with GSH and dG. These findings correlate with their ability to generate covalent DNA adducts (direct genotoxicity) in human bronchial epithelial cells (WI26) and human kidney (HK2) cells, as evidenced by the (32)P-postlabeling technique. OTB lacks direct genotoxicity, while OTA, OTBr, and OTHQ act as direct genotoxins. In contrast, their cytotoxicity in opossum kidney epithelial cells (OK) and WI26 cells did not show a correlation with photoreactivity. In OK and WI26 cells, OTA, OTBr, and OTB are cytotoxic, while the hydroquinone OTHQ failed to exhibit cytotoxicity. Overall, our data show that the C5-Cl atom of OTA is critical for direct genotoxicity but plays a lesser role in OTA-mediated cytotoxicity. These SARs suggest different mechanisms of action (MOA) for OTA genotoxicity and cytotoxicity and are consistent with recent findings showing OTA mutagenicity to stem from direct genotoxicity, while cytotoxicity is derived from oxidative DNA damage.

An update on direct genotoxicity as a molecular mechanism of ochratoxin a carcinogenicity

Ochratoxin A (OTA) is a naturally occurring chlorophenolic fungal toxin that contaminates a wide range of food products and poses a cancer threat to humans. The mechanism of action (MOA) for OTA renal carcinogenicity is a controversial issue. In 2005, direct genotoxicity (covalent DNA adduct formation) was proposed as a MOA for OTA-mediated carcinogenicity [ Manderville , R. A. ( 2005 ) Chem. Res. Toxicol. 18 , 1091 - 1097 ]. At that time, inconsistent results had been published on OTA genotoxicity/mutagenicity, and conclusive evidence for OTA-mediated DNA adduction had been lacking. In this update, published data from the past 6-7 years are presented that provide new hypotheses for the MOA of OTA-mediated carcinogenicity. While direct genotoxicity remains a controversial issue for OTA, new findings from the Umemura and Nohmi laboratories provide definitive results for the mutagenicity of OTA in the target tissue (outer medulla) of male rat kidney that rules out oxidative DNA damage. These findings, coupled with our own efforts that provide new structural evidence for DNA adduction by OTA, has strengthened the argument for involvement of direct genotoxicity in OTA-mediated renal carcinogenesis. This MOA should be taken into consideration for OTA human risk assessment.

Ochratoxin A induces CYP3A4, 2B6, 3A5, 2C9, 1A1, and CYP1A2 gene expression in primary cultured human hepatocytes: a possible activation of nuclear receptors

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 tumors in mice and rats. Biotransformation of OTA has not been entirely elucidated. Several metabolites have been characterized in vitro and/or in vivo, whereas other metabolites remain to be characterized. At present, data available regarding OTA metabolism and cytochrome inductions concern only rodents or in vitro systems. The aim of the present study was to explore the effect of OTA on mRNA expression of some cytochromes known to be regulated by pregnane X receptor (PXR), constitutive androstane receptor (CAR), and aryl hydrocarbon receptor (AhR), using primary cultures of human hepatocytes. Our results showed that OTA reduced hepatocyte viability in a dose-dependent manner. Using quantitative real-time reverse-transcription polymerase chain reaction, our study showed that treatment of primary cultured human hepatocytes with noncytotoxic increasing concentrations of OTA for 24 hours caused a significant upregulation of CYP3A4, CYP2B6, and, to a lesser extent, CYP3A5 and CYP2C9. PXR mRNA expression increased in only 1 treated liver, whereas CAR mRNA expression was not affected. OTA was found also to induce an overexpression of CYP1A1 and CYP1A2 genes accompanied by an increase in AhR mRNA expression. These findings suggest that OTA could activate PXR and AhR; however, further investigations are needed to confirm nuclear-receptor activation by OTA.

Human ochratoxin a biomarkers--from exposure to effect

Ochratoxin A (OTA) is a nephrotoxic mycotoxin that has received particular attention because of the toxic effects, widespread occurrence in contaminated food and feed chain, suspected causal effect on nephropathies, and, more recently, possibility of exposure by inhalation in domicile and occupational settings. Biomarkers have been used not only to ascertain the role of OTA in inducing chronic renal failure diseases, but also as a means to portray general populations' risk to the mycotoxin. Biomonitoring can thus be used to assess internal OTA exposure, with no need to recognize the main source of exposure. And so it presents undeniable advantages over the monitoring of external dose. With a just right understanding of biomarkers, it is possible to follow the trail from exposure right to effect, and so contribute both to surveillance plans and etiological studies. In recognition of the long serum half-life and the renal elimination of OTA, most of the studies present serum/plasma and/or urine analyses as markers of exposure. In this review and for each of these main matrices, a comparison over the advantages and disadvantages is offered. Although currently limited, an overview of the current knowledge on OTA biomarkers and the influential role of the individual characteristics, namely gender and age, along with season and geographical location is given. Attention is also given to the ongoing debate over the existence of OTA-DNA adducts, a biomarker of effective dose regarded as an alternative to biomarkers of internal dose. Although unspecific, OTA effect biomarkers are also reviewed.

Absence of 2'-deoxyguanosine-carbon 8-bound ochratoxin A adduct in rat kidney DNA monitored by isotope dilution LC-MS/MS

The contribution of DNA adduct formation in the carcinogenic action of the mycotoxin ochratoxin A (OTA) has been subject to much debate. Recently, a carbon-bonded ochratoxin A-2'-deoxyguanosine adduct (dGuoOTA) formed by photochemical reaction in vitro has been shown by 32P-postlabeling/TLC to comigrate with a spot detected in DNA isolated from rat and pig kidney following exposure to OTA. Considering the large body of evidence arguing against covalent DNA binding of OTA and the poor resolution and specificity of postlabeling analysis, we developed a stable isotope dilution LC-MS/MS method to analyze dGuoOTA in kidney DNA isolated from rats treated with OTA. dGuoOTA and nitrogen-15-labeled dGuoOTA (15N(5)-dGuoOTA) were prepared by photoirradiation of OTA in the presence of dGuo or nitrogen-15-labeled dGuo. Conditions for DNA hydrolysis were optimized using a synthetic oligonucleotide containing dGuoOTA to ensure complete release of dGuoOTA. The LOD of the method (S/N > 3) was 10 fmol dGuoOTA on-column. However, dGuoOTA was not detected in DNA samples isolated from male F344 rats treated with OTA for up to 90 days at doses known to cause renal tumor formation. Detection limits, calculated for each individual sample based on the absolute LOD and the amount of DNA injected, were as low as 3.5 dGuoOTA/10(9) nucleotides. These data are consistent with previous results showing lack of DNA adduct formation by OTA and demonstrate that dGuoOTA is not formed in biologically relevant amounts under physiological conditions in vivo.

Inula crithmoides extract protects against ochratoxin A-induced oxidative stress, clastogenic and mutagenic alterations in male rats

Ochratoxin A (OTA) is a mycotoxin often found in cereals and agricultural products. There is unequivocal evidence of renal carcinogenicity of OTA in male rats, although the mechanism of action is unknown. Several reports suggest that exposure to OTA resulted in oxidative stress, genotoxicity and DNA damage. Therefore, the aim of the current study was to evaluate the protective effects of aqueous extract of Inula crithmoides growing in Egypt against OTA-induced mutagenicity and oxidative stress. Forty male Sprague-Dawley rats were divided into four groups and treated for 15 days as follows: control group and the groups treated with OTA (3 mg/kg b.w), I. crithmoides extract alone (370 mg/kg b.w) and OTA+I. crithmoides extract. Blood and tissue samples were collected for different biochemical analyses. Bone marrow micronucleus test and blood for random amplified polymorphism DNA-PCR (RAPD-PCR) method were performed to assess the antigenotoxic effect of the extract. The results indicated that OTA induced toxicological effects typical to those reported in the literature and increased the frequencies of MnPCEs in bone marrow. The RAPD-PCR analysis revealed the appearance of new bands in DNA resulting from genetic alteration. The extract alone was safe and succeeded in counteracting the oxidative stress and protect against the cytotoxicity resulting from OTA.

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.

Ochratoxin A: An overview on toxicity and carcinogenicity in animals and humans

Ochratoxin A (OTA) is a ubiquitous mycotoxin produced by fungi of improperly stored food products. OTA is nephrotoxic and is suspected of being the main etiological agent responsible for human Balkan endemic nephropathy (BEN) and associated urinary tract tumours. Striking similarities between OTA-induced porcine nephropathy in pigs and BEN in humans are observed. International Agency for Research on Cancer (IARC) has classified OTA as a possible human carcinogen (group 2B). Currently, the mode of carcinogenic action by OTA is unknown. OTA is genotoxic following oxidative metabolism. This activity is thought to play a central role in OTA-mediated carcinogenesis and may be divided into direct (covalent DNA adduction) and indirect (oxidative DNA damage) mechanisms of action. Evidence for a direct mode of genotoxicity has been derived from the sensitive 32P-postlabelling assay. OTA facilitates guanine-specific DNA adducts in vitro and in rat and pig kidney orally dosed, one adduct comigrates with a synthetic carbon (C)-bonded C8-dG OTA adduct standard. In this paper, our current understanding of OTA toxicity and carcinogenicity are reviewed. The available evidence suggests that OTA is a genotoxic carcinogen by induction of oxidative DNA lesions coupled with direct DNA adducts via quinone formation. This mechanism of action should be used to establish acceptable intake levels of OTA from human food sources.

In vitro approaches to develop weight of evidence (WoE) and mode of action (MoA) discussions with positive in vitro genotoxicity results

A recent analysis by Kirkland et al. [Kirkland, D., Aardema, M., Henderson, L. and Müller, L. (2005) Evaluation of the ability of a battery of 3 in vitro genotoxicity tests to discriminate rodent carcinogens and non-carcinogens. I. Sensitivity, specificity and relative predictivity. Mutat. Res. 584, 1-256] demonstrated an extremely high false positive rate for in vitro genotoxicity tests when compared with carcinogenicity in rodents. In many industries, decisions have to be made on the safety of new substances, and health risk to humans, without rodent carcinogenicity data being available. In such cases, the usual way to determine whether a positive in vitro genotoxicity result is relevant (i.e. indicates a hazard) for humans is to develop weight of evidence (WoE) or mode of action (MoA) arguments. These are based partly on further in vitro investigations, but usually rely heavily on tests for genotoxicity in one or more in vivo assays. However, for certain product types in the European Union, the use of animals for genotoxicity testing (as well as for other endpoints) will be prohibited within the next few years. Many different examples have been described that indicate DNA damage and genotoxic responses in vitro can arise through non-relevant in vitro events that are a result of the test systems and conditions used. The majority of these non-relevant in vitro events can be grouped under a category of 'overload of normal physiology' that would not be expected to occur in exposed humans. However, obtaining evidence in support of such MoAs is not easy, particularly for those industries prohibited from carrying out in vivo testing. It will become necessary to focus on in vitro studies to provide evidence of non-DNA, threshold or in vitro-specific processes and to discuss the potential for such genotoxic effects to occur in exposed humans. Toward this end, we surveyed the published literature for in vitro approaches that may be followed to determine whether a genotoxic effect observed in vitro will occur in humans. Unfortunately, many of the approaches we found are based on only a few published examples and validated approaches with consensus recommendations often do not exist. This analysis highlights the urgent need for developing consensus approaches that do not rely on animal studies for dealing with in vitro genotoxins.

Comparison of ELISA and capillary electrophoresis with laser-induced fluorescence detection in the analysis of Ochratoxin A in low volumes of human blood serum

In this paper the determination of Ochratoxin A (OTA) in low volumes of human blood serum by enzyme-linked immunosorbent assay (ELISA) is compared with an appropriate capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) method. In order to use ELISA for high-throughput analysis in epidemiological studies no sample cleanup was performed. Both methods showed a limit of detection (LOD) of 0.5 ng/mL. Comparing the precisions of both methods, the data show that the quantified concentrations in ELISA are higher than the corresponding concentrations in the CE-LIF method. Using a matrix calibration curve instead of a standard calibration curve the reproducibilities of both methods are comparable. No additional matrix effect could be observed by adding phenylalanine as probable matrix compound to the serum.

DNA adduct formation by ochratoxin A: review of the available evidence

The mycotoxin ochratoxin A (OTA) is a potent nephrotoxin and renal carcinogen in rodents. However, the mechanism of OTA-induced tumour formation is unknown and conflicting results regarding the potential of OTA to react with DNA have been obtained. While experiments using radiolabelled ((3)H or (14)C) OTA and liquid scintillation counting or accelerator mass spectrometry indicate lack of formation of covalent DNA-adducts, spots detected by (32)P-postlabelling have been attributed to treatment with OTA. However, these putative DNA-adducts have not been shown to contain OTA or part of the OTA molecule and so far no structural information has been provided. Consistent with the absence of DNA-binding of radiolabelled OTA, studies on biotransformation in vivo and in vitro indicate that OTA is poorly metabolized and does not form reactive intermediates capable of interacting with DNA. Recently however, the structures of a carbon- and an oxygen-bonded OTA-deoxyguanosine adduct which is formed by photoirradiation of OTA in the presence of deoxyguanosine have been reported and suggested to be involved in OTA carcinogenicity. The aim of this manuscript is to provide an overview of the available literature regarding DNA adduct 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.

Ochratoxin A-induced DNA damage in human fibroblast: protective effect of cyanidin 3-O-β-d-glucoside

Ochratoxin A (OTA), a mycotoxin produced by Aspergillus ochraceus and other moulds, has recently received growing attention because of its carcinogenic, teratogenic and nephrotoxic properties in both humans and farm animals. Nevertheless, with regard to the mechanism of toxicity, the data in the literature are inconclusive. The aim of our work was to verify in human fibroblasts treated with different OTA dosages the involvement of oxidative pathway in the damage mechanism of this mycotoxin and the possible protective effect exerted by cyanidin 3-O-beta-D-glucoside (C3G), an anthocyanin present in pigmented oranges, red wines, fruits and vegetables. The addition of OTA at 25 and 50 microM concentrations for 48 h determined only a slight but significant (P<.05) increase in radical oxygen species, whereas a substantial increase in their production was observed at longer exposure, in particular, when the fibroblasts were treated with 50 microM OTA for 72 h. Under the same experimental conditions, our data showed a significant (P<.05) increase in the rupture of cellular membrane and high damage to genomic DNA, evaluated by single-cell gel electrophoresis (comet assay), thus confirming the involvement of oxidative stress in the OTA genotoxicity in agreement with other studies. Diversely, mitochondrial functionality does not appear influenced by OTA treatment. C3G (0.125, 0.250 mM) added to the cells treated with 50 microM OTA significantly reduced free radical species production and prevented genomic DNA damage.

Chemically induced renal tubule tumors in the laboratory rat and mouse: review of the NCI/NTP database and categorization of renal carcinogens based on mechanistic information

The incidence of renal tubule carcinogenesis in male and female rats or mice with 69 chemicals from the 513 bioassays conducted to date by the NCI/NTP has been collated, the chemicals categorized, and the relationship between carcinogenesis and renal tubule hyperplasia and exacerbation of the spontaneous, age-related rodent disease chronic progressive nephropathy (CPN) examined. Where information on mechanism or mode of action exists, the chemicals have been categorized based on their ability to directly or indirectly interact with renal DNA, or on their activity via epigenetic pathways involving either direct or indirect cytotoxicity with regenerative hyperplasia, or exacerbation of CPN. Nine chemicals were identified as directly interacting with DNA, with six of these producing renal tubule tumors at high incidence in rats of both sexes, and in some cases also in mice. Ochratoxin A was the most potent compound in this group, producing a high tumor incidence at very low doses, often with metastasis. Three chemicals were discussed in the context of indirect DNA damage mediated by an oxidative free radical mechanism, one of these being from the NTP database. A third category included four chemicals that had the potential to cause DNA damage following conjugation with glutathione and subsequent enzymatic activation to a reactive species, usually a thiol-containing entity. Two chemicals were allocated into the category involving a direct cytotoxic action on the renal tubule followed by sustained compensatory cell proliferation, while nine were included in a group where the cell loss and sustained increase in renal tubule cell turnover were dependent on lysosomal accumulation of the male rat-specific protein, alpha2mu-globulin. In a sixth category, morphologic evidence on two chemicals indicated that the renal tumors were a consequence of exacerbated CPN. For the remaining chemicals, there were no pertinent data enabling assignment to a mechanistic category. Accordingly, these chemicals, acting through an as yet unknown mechanism, were grouped as either being associated with an enhancement of CPN (category 7, 16 chemicals), or not associated with enhanced CPN (category 8, 4 chemicals). A ninth category dealt with 11 chemicals that were regarded as producing increases in renal tubule tumors that did not reach statistical significance. A 10th category discussed 6 chemicals that induced renal tumors in mice but not in rats, plus 8 chemicals that produced a low incidence of renal tubule tumors in mice that did not reach statistical significance. As more mechanistic data are generated, some chemicals will inevitably be placed in different groups, particularly those from categories 7 and 8. A large number of chemicals in the series exacerbated CPN, but those in category 7 especially may be candidates for inclusion in category 6 when further information is gleaned from the relevant NTP studies. Also, new data on specific chemicals will probably expand category 5 as cytotoxicity and cell regeneration are identified as obligatory steps in renal carcinogenesis in more cases. Additional confirmatory outcomes arising from this review are that metastases from renal tubule tumors, while encountered with chemicals causing DNA damage, are rare with those acting through an epigenetic pathway, with the exception being fumonisin B1; that male rats and mice are generally more susceptible than female rats and mice to chemical induction of renal tubule tumors; and that a background of atypical tubule hyperplasia is a useful indicator reflecting a chemically associated renal tubule tumor response. With respect to renal tubule tumors and human risk assessment, chemicals in categories 1 and 2, and possibly 3, would currently be judged by linear default methods; chemicals in category 4 (and probably some in category 3) as exhibiting a threshold of activity warranting the benchmark approach; and those in categories 5 and 6 as representing mechanisms that have no relevance for extrapolation to humans.

Determination of Ochratoxin A in small volumes of human blood serum

A new simple and rapid method for analysing Ochratoxin A (OTA) in small volumes of human blood serum using capillary zone electrophoresis coupled to laser-induced fluorescence is described. The clean-up procedure solely consists of a double extraction step. To improve the reproducibility of migration times and quantification, two internal standards were used. The limit of detection was 0.55 ng/ml, with a linear range of 1-100 ng/ml of OTA in spiked human blood serum. The method is used to rapidly screen suspected patients.

Immunotoxic effects of Ochratoxin A in wistar rats after oral administration

Ochratoxin A (OTA) is a mycotoxin produced by species of the genus Aspergillus and Penicillium. Human exposure has been demonstrated worldwide and its origin seems to be the intake of contaminated foods. The kidneys are the target organ of this mycotoxin. Immunotoxic and genotoxic effects of OTA were investigated in Wistar male rats (aged 12 weeks), treated by gavage with 50, 150 or 450 microg OTA/kg body weight for 28 days, in the context of a general toxicity study, which was designed following the recommendations of OECD guideline 407. At the end of the study, the mean plasma concentration of the mycotoxin was determined, several immune function assays were performed and bone marrow smears were obtained and stained in order to analyse micronuclei in polychromatic erytrocytes. Mean plasma concentration was found to be 187, 600 and 807 microg/L, respectively. At the highest dose, a decrease in body weight gain was observed. Histopathological investigations revealed tubulonephrosis and acute tubular necrosis in the kidneys of the animals treated with OTA. The frequency and severity of the lesions increased with the dose. The response of splenocytes to sheep red blood cells was decreased in a dose-dependent manner; however, nonstatistically significant differences were obtained. The natural killer cell activity was strongly affected by OTA treatment. Cytotoxic T lymphocyte activity was lower in the animals exposed to 50 microg OTA/kg b.w. but was not modified in the groups exposed to 150 and 450 microg OTA/ kg b.w. The bacteriolytic capability of macrophages was significantly reduced in groups exposed to 50 and 450 microg OTA/ kg b.w. The number of micronuclei in bone marrow polychromatic erytrocytes did not vary significantly with respect to the control at any dose, but a false negative result can not be ruled out because the exposure doses were much lower than those recommended in OECD guideline 474.

Failure of the standard battery of short-term tests in detecting some rodent and human genotoxic carcinogens

Theoretical reasons and experimental evidence indicate that a no-effect level generally cannot be expected for genotoxic carcinogens; as a consequence, in quantitative risk assessment the capability of distinguishing genotoxic from non-genotoxic carcinogens is of fundamental importance in order to identify relevant levels of human exposure. According to generally accepted guidelines, the standard three-test battery for the detection of genotoxic compounds consists of: (i) an in vitro test for gene mutation in bacteria; (ii) an in vitro test in mammalian cells with cytogenetic evaluation of chromosomal damage and/or a test that detects gene mutations; (iii) an in vivo test for chromosomal damage using rodent hematopoietic cells. This test battery is designed to avoid the risk of false negative results for compounds with genotoxic potential, but it cannot be taken for granted that the risk is completely eliminated. As a matter of fact there are some chemicals, classified by the International Agency for Research on Cancer (IARC) as probably or possibly carcinogenic to humans, which gave consistent negative results in this test battery, and in contrast provided positive results in other not routinely employed genotoxicity assays. The failure of the standard test battery in detecting some genotoxic carcinogens is attributable to several causes, but the principal of them are the following ones: in vitro, the artificial metabolic activity of the liver S9-mix, and the different biotransformation of chemicals in cells of different type and from different animal species; in vivo, the pharmacokinetic behaviour of the test compound, and its possible species-, sex- and tissue-specificity.

Effects of the mycotoxin ochratoxin A in a bacterial and a mammalian in vitro mutagenicity test system

Ochratoxin A (OTA), a mycotoxin produced by several Aspergillus and Penicillium species, is a worldwide contaminant of food and feedstuffs. It is nephrotoxic, immunosuppressive and carcinogenic in several animal species. The mechanism by which OTA acts is not fully understood up to now. Here, OTA was evaluated for mutagenicity in the Salmonella typhimurium assay (Ames assay) and in the HPRT assay with V79 hamster fibroblasts. In the bacterial assay using the strains TA 98, TA 100, TA 1535, TA 1538, TA 102 and TA 104, OTA was not mutagenic at a concentration range from 0.01 to 500 micro M in the presence and absence of an external metabolising enzyme system (rat liver S9 enzyme mix). In V79 fibroblasts, cytotoxicity of OTA was estimated with the neutral red uptake assay. An IC(50) of 11.6 micro M was found in the absence and an IC(50) of 6.4 micro M in the presence of S9 mix. In the subsequent HPRT (hypoxanthine-guanine-phosphoribosyl-transferase) assay with V79 cells the negative result of the bacterial assay was confirmed using OTA in concentrations from 0.1 to 100 micro M. In order to obtain converted OTA metabolites from viable, metabolically competent cells, a preincubation of primary cultured rat hepatocytes with 0.016 to 0.8 micro M OTA was performed. The resulting culture medium, which contained OTA metabolites, was tested in both mutagenicity assays. Again, no mutagenic effect was detected either in the bacterial or in the mammalian test assay. In accordance with several literature data, the present results imply that OTA does not act as direct mutagen. Additionally, the OTA metabolites derived from cultured rat hepatocytes or rat liver S9 mix, also, do not have a mutagenic potency in the test systems used.

Balkan endemic nephropathy and associated urinary tract tumours: a review on aetiological causes and the potential role of mycotoxins

A series of publications in the 1950s described a kidney disease in Bulgaria, the former Yugoslavia and Romania that became known as Balkan endemic nephropathy (BEN). The disease was qualified by World Health Organisation (WHO) experts as 'progressive and very gradually developing renal failure with insidious onset.... The last stage shows marked fibrosis...'. BEN is characterized by tubular degeneration, interstitial fibrosis and hyalinization of glomeruli accompanied by enzymuria and impaired renal function without nephrotic syndrome. Later, an association between BEN and tumours of the kidney pelvis and ureter was recognized, so that the problem of BEN became not only nephrological, but also oncological. There may also be an association with increased urinary bladder cancer incidence, although many confounding factors may interfere in the analysis of data for this organ. In view of the very intimate association between BEN and the urinary tract tumours (UTT), the term 'endemic uropathy' has been proposed. Several hypothesis concerning the aetiology of these diseases has been investigated, which include: predisposing genes factors, environmental factors (heavy metals, minerals, bacteria, leptospira, viruses, fungal toxins and, most recently, pliocene lignites). This paper reviews the different hypotheses about the aetiology of endemic uropathy and pays particular attention to the role of fungal toxins.

Metabolism and lack of DNA reactivity of the mycotoxin ochratoxin a in cultured rat and human primary hepatocytes

It is still unclear whether the carcinogenic mycotoxin ochratoxin A (OTA) is bioactivated to DNA-binding metabolites in rodents and humans. Therefore, we have incubated cultured rat and human primary hepatocytes with noncytotoxic concentrations of (3)H-OTA ranging from 10(-7) to 10(-5) M for 8 h and determined its metabolism and covalent DNA binding. In rat hepatocytes, OTA was metabolized to small amounts of three products, which were further studied by electrospray ionization (ESI)-MS/MS techniques. In addition to 4-hydroxy-OTA, which is a known product of OTA biotransformation, two novel metabolites were detected and tentatively identified as hexose and pentose conjugates of OTA. The in vitro induction with 3-methylcholanthrene (3MC) increased the formation of 4-hydroxy-OTA but did not alter the formation of the conjugated metabolites. No covalent binding of (3)H-OTA or its metabolites to DNA was observed in rat hepatocytes with or without 3MC induction with a limit of detection of 2 adducts per 10(9) nucleotides. However, the cellular ratio of reduced glutathione to oxidized glutathione was significantly decreased by treatment with OTA. In cultured human hepatocytes, (3)H-OTA was only very poorly metabolized, and no covalent DNA binding was observed. In conclusion, the results of this in vitro study do not support the notion that OTA has the potential to undergo metabolic activation and form covalent DNA adducts in rodents and humans.

The mycotoxin ochratoxin A alters intestinal barrier and absorption functions but has no effect on chloride secretion

Ochratoxin A (OTA) is a mycotoxin that contaminates cereals and animal feed and causes nephropathy to a variety of animal species. OTA is also known as a potent immunotoxic, teratogenic, and carcinogenic mycotoxin. In addition, OTA ingestion induces intestinal injuries, including inflammation and diarrhea. With the aim to study the cellular mechanisms associated with the intestinal toxicity of OTA, two human epithelial intestinal cell lines (HT-29-D4 and Caco-2-14 cells), widely used as in vitro models for the intestinal epithelium, were incubated with OTA. The main effects of the mycotoxin were an inhibition of cellular growth and a dramatic decrease of transepithelial resistance in both cell lines. Since transepithelial resistance reflects the organization of tight junctions over the cell monolayer, these data may suggest that OTA could potentiate its own absorption through paracellular pathways. OTA induced a 60% decrease of sodium-dependent glucose absorption but increased the absorption of fructose and L-serine in HT-29-D4 cells. Moreover, the mycotoxin did not inhibit the cAMP-dependent chloride secretion through the cystic fibrosis transmembrane conductance regulator channel. The inhibitory effect of OTA on active glucose transport was partially antagonized by L-phenylalanine, but not by alpha-tocopherol, suggesting that the toxicity of OTA could result from an inhibition of protein synthesis, rather than an induction of lipid peroxidation. In particular, OTA affected the protein content of plasma membrane microdomains, which are known to regulate tight junction assembly and intestinal transport activity. Taken together, these data showed that OTA alters both barrier and absorption functions of the intestinal epithelium.

In vitro DNA and dGMP adducts formation caused by ochratoxin A

Ochratoxin A (OTA), a nephrotoxic and nephrocarcinogenic mycotoxin, leads to the formation of DNA adducts after administration to animals. This could be due to an epigenetic effect. In vitro assays can exclude an indirect effect, where the xenobiotic can generate, in vivo, endogenous reactive compounds which give adducts on DNA. Microsomes prepared from mice or rabbit kidney and liver, used as metabolic activators, were incubated in the presence of commercial salmon testes DNA and OTA, with NADPH or arachidonic acid used as cofactors. Upto 126 DNA adducts for 10(9) nucleotides were detected using the 32P postlabeling method after incubation with the mouse kidney system. Similar results were obtained with rabbit kidney microsomes. Using liver microsomes, the number of DNA adducts detected was much lower. When NADPH was used as a cosubstrate (to explore the cytochrome P450 metabolic pathways), with mice kidney microsomes, the adduct level was only 44% of the one obtained with arachidonic acid. These results lend support to the hypothesis of the preferential activation of OTA by the peroxidase activity of prostaglandin synthases and/or lipoxygenases to direct genotoxic metabolites, and are in agreement with the previously obtained results after in vivo treatment of mice. In order to identify the nucleotides of DNA modified by the OTA metabolites, dAMP, dGMP, dTMP and dCMP were used as substrates under the same conditions as with DNA. The adducts were found only on dGMP. The total adduct level was of 344 adducts per 10(9) nucleotides with the appearance of three major adducts in the presence of arachidonic acid. With NADPH, 271 adducts were obtained per 10(9) nucleotides, with again three major adducts, but only two of them were similar to two adducts obtained in the presence of arachidonic acid. Desferal (desferrioxamine B methanesulphonate), at a 50 microM concentration, did not reduce the adduct level. Adducts were also obtained when polydG, polydC and dG-p-dG were used as alternative substrates, whereas no adducts were obtained with polydA, polydT and polydC. The major adduct obtained after incubation of DNA with OTA, comigrated with the major adduct obtained with dGMP, in two chromatographic solvents. These results show that OTA is metabolized to genotoxic metabolite(s) which interact with the guanine residues of DNA.

Genotoxicity of ochratoxin A by Salmonella mutagenicity test after bioactivation by mouse kidney microsomes

Ochratoxin A (OTA) was, up to now, believed to be non-mutagenic in the classical Salmonella typhimurium reverse mutation test. This was confirmed using rat liver microsomal fractions with the strains, TA1535, TA1538 and TA98, and up to 1210 micrograms/plate, utilizing an Ames microtest. However, using mice kidney microsomal fractions as metabolic activators, reverse mutations were obtained with the three strains used, in the presence of either NADP or arachidonic acid as cofactors. The mutagenicity was higher with arachidonic acid than with NADP using the TA1535 strain. This lends support to the results concerning the DNA or dGMP adducts obtained in vitro which were also higher in the presence of arachidonic acid, and indicate that several metabolic pathways of OTA can lead to genotoxic compounds. In addition, both base pair substitutions and frameshift mutations can be caused by OTA after metabolic activation.

Induction of genotoxic effects and modulation of the intracellular calcium level in syrian hamster embryo (SHE) fibroblasts caused by ochratoxin A

The mycotoxin ochratoxin A (OTA) is a naturally occuring contaminant of food. The genotoxic status of OTA is still controversial because contradictory results were obtained in various microbial and mammalian gene mutation assays. In this study, OTA was investigated to examine its potency to induce micronuclei (MN) in SHE cells. The SHE-micronucleus assay revealed that OTA induces MN in a dose- and time-dependent manner. The results of kinetochore analysis revealed that mainly clastogenic events are involved in OTA genotoxicity. Induction of mitotic disturbances can be closely related to changes of the intracellular calcium concentration ([Ca2+]i). The investigated time course of OTA-induced [Ca2+]i changes revealed that the obtained signal is a short spike signal resembling physiological responses. In the absence of extracellular calcium, a long-lasting signal indicates possible damage to intracellular calcium stores or channels. Our data show that the OTA-induced [Ca2+]i rise is caused by Ca2+ -release from intracellular stores as well as Ca2+ influx from extracellular area. Finally, the influence of the changed intracellular calcium level on the actin cytoskeleton was investigated. Visualization of the actin filaments revealed time- and concentration-dependent effects. Cell shrinkage and depolymerized filaments were observed. We conclude that OTA disrupts actin filaments by a direct irreversible binding to actin.

Ochratoxin A-binding proteins in rat organs and plasma and in different cell lines of the kidney

In order to detect cellular proteins which bind the mycotoxin ochratoxin A (OTA) we coupled OTA covalently to horseradish peroxidase (HRP). The peroxidase activity of the conjugate was used to detect these proteins in Western (ligand) blot analysis. Only signals caused by OTA binding to proteins were viewable. HRP alone detected no proteins and OTA-HRP binding could be inhibited by free OTA. Several proteins from the rat intestine, liver, spleen, and kidney were detected by OTA. Also rat plasma proteins bind OTA which confirms previous findings. In all renal cell lines investigated (MDCK-C11, OK, LLC-PK1, IHKE, and SKPT) there are several proteins which bind OTA. Comparison of the PonceauS stain on the nitrocellulose sheet with the signal obtained from OTA-HRP unveiled proteins with high specific OTA binding. Especially, proteins with molecular masses between 55 and 60 kDa, 40 and 45 kDa and 25 and 30 kDa showed OTA binding in all samples. OTA was partially displaced by aspartame and phenylalanine from some but not all proteins. Binding to cytosolic and organellar proteins was comparable in all investigated cell lines. In the OK cell organellar compartment a 62 kDa protein is preferentially detected by OTA-HRP although virtually no protein band is detectable. In conclusion we have found a method to clearly detect proteins which bind OTA. With this new method we proved that OTA has the potential to bind to several proteins yet specific binding differs dramatically. Thus, highly specific binding of OTA possibly makes certain proteins a preferential target of OTA toxicity. Furthermore, binding contributes to intracellular accumulation of OTA, thus leading to a prolonged half life in the mammalian body and emphasises the toxic potential of this fungal metabolite.

Roles of cyclooxygenase and lipoxygenases in ochratoxin A genotoxicity in human epithelial lung cells

The roles of constitutive prostaglandin-H-synthetase (PGHS) and lipoxygenases in ochratoxin A (OTA) genotoxicity, as reflected by DNA adduct formation, have been investigated in vitro: (1) in culture of human epithelial cells and (2) by incubation in presence of pig seminal vesicle microsomes. Indomethacin (0.1 μM), which inhibits PGHS and significantly increases leukotriene C(4) production by enhancement of lipoxygenases, enhanced formation of OTA-DNA adducts tenfold. At highest dose of 10 μM, indomethacin inhibited all pathways (PGHS and lipoxygenases) and thus prevented OTA-DNA adduct formation. Nordihydroguaiaretic acid, which inhibits lipoxygenases, suppressed OTA-DNA adduct formation. The OTA metabolites formed were analysed by HPLC. OTα, 4[R]- and 4[S]-hydroxy-OTA and a unidentified derivative were formed in control cells. After pre-incubation with indomethacin (0.1 μM), further unidentified metabolites were obtained. They were similar to those obtained in presence of pig seminal vesicle microsomes. These data demonstrate that OTA is biotransformed into genotoxic metabolites via a lipoxygenase, whereas PGHS decreases OTA genotoxicity.