Formation of (4R)- and (4S)-4-hydroxyochratoxin A and 10-hydroxyochratoxin A from Ochratoxin A by rabbit liver microsomes

Role of albumin in the metabolism and excretion of ochratoxin A

Ochratoxin A (OTA) is known to be strongly bound to serum albumin, but it remains unknown how albumin affects its metabolism and kinetics. To close this gap, we used a mouse model, where heterozygous albumin deletion reduces serum albumin to concentrations similar to hypoalbuminemic patients and completely eliminates albumin by a homozygous knockout. OTA and its potential metabolites (OTα, 4-OH-OTA, 7'-OH-OTA, OTHQ, OP-OTA, OTB-GSH, OTB-NAC, OTB) were time-dependently analyzed in plasma, bile, and urine by LC-MS/MS and were compared to previously published hepatotoxicity and nephrotoxicity data. Homozygous albumin deletion strongly accelerated plasma clearance as well as biliary and urinary excretion of the parent compound and its hydroxylation products. Decreasing albumin in mice by the heterozygous and even more by the homozygous knockout leads to an increase in the parent compound in urine which corresponded to increased nephrotoxicity. The role of albumin in OTA-induced hepatotoxicity is more complex, since heterozygous but not homozygous nor wild-type mice showed a strong biliary increase in the toxic open lactone OP-OTA. Correspondingly, OTA-induced hepatotoxicity was higher in heterozygous than in wild-type and homozygous animals. We present evidence that albumin-mediated retention of OTA in hepatocytes is required for formation of the toxic OP-OTA, while complete albumin elimination leads to rapid biliary clearance of OTA from hepatocytes with less formation of OP-OTA. In conclusion, albumin has a strong influence on metabolism and toxicity of OTA. In hypoalbuminemia, the parent OTA is associated with increased nephrotoxicity and the open lactone with increased hepatotoxicity.

Risks for animal health related to the presence of ochratoxin A (OTA) in feed

In 2004, the EFSA Panel on Contaminants in the Food Chain (CONTAM) adopted a Scientific Opinion on the risks to animal health and transfer from feed to food of animal origin related to the presence of ochratoxin A (OTA) in feed. The European Commission requested EFSA to assess newly available scientific information and to update the 2004 Scientific Opinion. OTA is produced by several fungi of the genera Aspergillus and Penicillium. In most animal species it is rapidly and extensively absorbed in the gastro-intestinal tract, binds strongly to plasma albumins and is mainly detoxified to ochratoxin alpha (OTalpha) by ruminal microbiota. In pigs, OTA has been found mainly in liver and kidney. Transfer of OTA from feed to milk in ruminants and donkeys as well as to eggs from poultry is confirmed but low. Overall, OTA impairs function and structure of kidneys and liver, causes immunosuppression and affects the zootechnical performance (e.g. body weight gain, feed/gain ratio, etc.), with monogastric species being more susceptible than ruminants because of limited detoxification to OTalpha. The CONTAM Panel considered as reference point (RP) for adverse animal health effects: for pigs and rabbits 0.01 mg OTA/kg feed, for chickens for fattening and hens 0.03 mg OTA/kg feed. A total of 9,184 analytical results on OTA in feed, expressed in dry matter, were available. Dietary exposure was assessed using different scenarios based on either model diets or compound feed (complete feed or complementary feed plus forage). Risk characterisation was made for the animals for which an RP could be identified. The CONTAM Panel considers that the risk related to OTA in feed for adverse health effects for pigs, chickens for fattening, hens and rabbits is low.

Ochratoxin A-The Current Knowledge Concerning Hepatotoxicity, Mode of Action and Possible Prevention

Ochratoxin A (OTA) is considered as the most toxic of the other ochratoxins synthesized by various fungal species belonging to the Aspergillus and Penicillium families. OTA commonly contaminates food and beverages, resulting in animal and human health issues. The toxicity of OTA is known to cause liver damage and is still being researched. However, current findings do not provide clear insights into the toxin mechanism of action. The current studies focusing on the use of potentially protective compounds against the effects of the toxin are insufficient as they are mainly conducted on animals. Further research is required to fill the existing gaps in both fields (namely the exact OTA molecular mechanism and the prevention of its toxicity in the human liver). This review article is a summary of the so far obtained results of studies focusing on the OTA hepatotoxicity, its mode of action, and the known approaches of liver cells protection, which may be the base for expanding other research in near future.

The Secondary Metabolites and Biosynthetic Diversity From Aspergillus ochraceus

Aspergillus ochraceus, generally known as a food spoilage fungus, is the representative species in Aspergillus section Circumdati. A. ochraceus strains are widely distributed in nature, and usually isolated from cereal, coffee, fruit, and beverage. Increasing cases suggest A. ochraceus acts as human and animal pathogens due to producing the mycotoxins. However, in terms of benefits to mankind, A. ochraceus is the potential source of industrial enzymes, and has excellent capability to produce diverse structural products, including polyketides, nonribosomal peptides, diketopiperazine alkaloids, benzodiazepine alkaloids, pyrazines, bis-indolyl benzenoids, nitrobenzoyl sesquiterpenoids, and steroids. This review outlines recent discovery, chemical structure, biosynthetic pathway, and bio-activity of the natural compounds from A. ochraceus.

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.

Recent Advances in Ochratoxin A Electrochemical Biosensors: Recognition Elements, Sensitization Technologies, and Their Applications

Ochratoxin A (OTA) is a class of mycotoxin that are mainly produced by Aspergillus and Penicillium and widely found in plant origin food. OTA-contaminated foods can cause serious harm to animals and humans, while high stability of OTA makes it difficult to remove in conventional food processing. Thus, sensitive and rapid detection of OTA undoubtedly plays an important role in OTA prevention and control. In this paper, the conventional and novel methods of OTA at home and abroad are summarized and compared. The latest research progress and related applications of novel OTA electrochemical biosensors are mainly described with a new perspective. We innovatively divided the recognition element into single and combined recognition elements. Specifically, signal amplification technologies applied to the OTA electrochemical aptasensor are proposed. Furthermore, summary of the current limitations and future challenges in OTA analysis is included, which provide reference for the further research and applications.

Detoxification of Mycotoxins through Biotransformation

Mycotoxins are toxic fungal secondary metabolites that pose a major threat to the safety of food and feed. Mycotoxins are usually converted into less toxic or non-toxic metabolites through biotransformation that are often made by living organisms as well as the isolated enzymes. The conversions mainly include hydroxylation, oxidation, hydrogenation, de-epoxidation, methylation, glycosylation and glucuronidation, esterification, hydrolysis, sulfation, demethylation and deamination. Biotransformations of some notorious mycotoxins such as alfatoxins, alternariol, citrinin, fomannoxin, ochratoxins, patulin, trichothecenes and zearalenone analogues are reviewed in detail. The recent development and applications of mycotoxins detoxification through biotransformation are also discussed.

Ochratoxin A: 50 Years of Research

Since ochratoxin A (OTA) was discovered, it has been ubiquitous as a natural contaminant of moldy food and feed. The multiple toxic effects of OTA are a real threat for human beings and animal health. For example, OTA can cause porcine nephropathy but can also damage poultries. Humans exposed to OTA can develop (notably by inhalation in the development of acute renal failure within 24 h) a range of chronic disorders such as upper urothelial carcinoma. OTA plays the main role in the pathogenesis of some renal diseases including Balkan endemic nephropathy, kidney tumors occurring in certain endemic regions of the Balkan Peninsula, and chronic interstitial nephropathy occurring in Northern African countries and likely in other parts of the world. OTA leads to DNA adduct formation, which is known for its genotoxicity and carcinogenicity. The present article discusses how renal carcinogenicity and nephrotoxicity cause both oxidative stress and direct genotoxicity. Careful analyses of the data show that OTA carcinogenic effects are due to combined direct and indirect mechanisms (e.g., genotoxicity, oxidative stress, epigenetic factors). Altogether this provides strong evidence that OTA carcinogenicity can also occur in humans.

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.

Comparative Ochratoxin Toxicity: A Review of the Available Data

Ochratoxins are a group of mycotoxins produced by a variety of moulds. Ochratoxin A (OTA), the most prominent member of this toxin family, was first described by van der Merwe et al. in Nature in 1965. Dietary exposure to OTA represents a serious health issue and has been associated with several human and animal diseases including poultry ochratoxicosis, porcine nephropathy, human endemic nephropathies and urinary tract tumours in humans. More than 30 years ago, OTA was shown to be carcinogenic in rodents and since then extensive research has been performed in order to investigate its mode of action, however, this is still under debate. OTA is regarded as the most toxic family member, however, other ochratoxins or their metabolites and, in particular, ochratoxin mixtures or combinations with other mycotoxins may represent serious threats to human and animal health. This review summarises and evaluates current knowledge about the differential and comparative toxicity of the ochratoxin group.

Efeitos in vitro de ocratoxina A, deoxinivalenol e zearalenona sobre a viabilidade celular e atividade de E-ADA em linfócitos de frangos de corte

Micotoxinas representam um vasto grupo de contaminantes químicos naturais originados a partir do metabolismo secundário de fungos filamentosos patogênicos. Elas são produzidas, principalmente, pelos gêneros Fusarium, Alternaria, Aspergillus e Penicillium, os quais podem contaminar grãos e cereais, como trigo, milho e soja. Conforme sua natureza e níveis de concentração, micotoxinas podem induzir efeitos tóxicos em animais de produção e humanos. Um estudo in vitro foi realizado para avaliar a susceptibilidade das células linfocitárias de frangos de corte a diferentes concentrações de ocratoxina A, deoxinivalenol e zearalenona. Cada micotoxina foi adicionada ao meio celular em diferentes concentrações (0,001; 0,01; 0,1 e 1μg/mL). A viabilidade celular e atividade de ecto-adenosina desaminase foram analisadas em 24, 48 e 72 horas através de ensaios colorimétricos. Para isso, foram utilizados 0,7x10(5) linfócitos/mL em meio RPMI 1640, suplementado com 10% de soro fetal bovino e 2,5 UI de penicilina/estreptomicina por mL, incubados em atmosfera de 5% de CO2 a 37 °C. Todos os experimentos foram realizados em triplicata e os resultados foram expressos como média e erro padrão da média. Os resultados obtidos demonstraram que tanto ocratoxina A como deoxinivalenol induziram proliferação linfocitária e baixa atividade enzimática in vitro (P<0,05), enquanto zearalenona também induziu proliferação (P<0,05), mas nenhuma alteração na atividade enzimática (P>0,05). Foi possível correlacionar os dados referentes à viabilidade celular e atividade de ecto-adenosina desaminase, sugerindo que, em concentrações mínimas, as micotoxinas testadas não estimularam a atividade da enzima, que possui ação pró-inflamatória e contribui para o processo de imunossupressão e, portanto, evitando um decréscimo na viabilidade celular. Este é o primeiro estudo feito com OCRA, DON e ZEA sobre linfócitos de frangos de corte em cultivos in vitro na avaliação desses parâmetros.

Transformation of the mycotoxin ochratoxin A in artificially contaminated vegetables and cereals

The metabolism of the mycotoxin ochratoxin A (OTA) in intact vegetables and germinating cereals is described and compared with metabolism studies in cell suspension cultures. The metabolites formed in intact, OTA spiked vegetables were ochratoxin a and 4- hydroxyochratoxin A (dI) and II), which are also known from studies with plant cell suspension cultures.

Mutagenicity of ochratoxin A and its hydroquinone metabolite in the SupF gene of the mutation reporter plasmid Ps189

Ochratoxin A (OTA) is a mycotoxin that enhances renal tumor formation in the outer medulla of male rat kidney. Direct DNA damage and subsequent mutagenicity may contribute to these processes. In this study we have determined whether OTA in the absence or presence of activated rat liver microsomes (RLM) or redox-active transition metals (Fe(III) or Cu(II)) causes promutagenic DNA damage in the supF gene of the mutation reporter plasmid pS189 replicating in human Ad293 cells. In addition, we have assessed the mutagenicity of the hydroquinone metabolite (OTHQ) of OTA in the absence or presence of cysteine without added cofactors. Our results show that oxidation of OTA, either by RLM or by transition metal ions, activates OTA to a directly genotoxic mutagen(s). The Fe(III)/OTA system was the most potent mutagen in our experimental system, causing a 32-fold increase in mutant fraction (MF) above the spontaneous control MF. The Cu(II)/OTA system caused a 9-fold increase in MF, while a 6-10-fold increase in MF was observed for OTA in the presence of RLM. The OTHQ metabolite is also mutagenic, especially in the presence of cysteine, in which a 6-fold increase in MF was observed. Our data provide further insight into OTA bioactivation that may account for its in vivo mutagenicity in male rat kidney.

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.

Chemical, physical and biological approaches to prevent ochratoxin induced toxicoses in humans and animals

Ochratoxins are polyketide derived fungal secondary metabolites with nephrotoxic, immunosuppressive, teratogenic, and carcinogenic properties. Ochratoxin-producing fungi may contaminate agricultural products in the field (preharvest spoilage), during storage (postharvest spoilage), or during processing. Ochratoxin contamination of foods and feeds poses a serious health hazard to animals and humans. Several strategies have been investigated for lowering the ochratoxin content in agricultural products. These strategies can be classified into three main categories: prevention of ochratoxin contamination, decontamination or detoxification of foods contaminated with ochratoxins, and inhibition of the absorption of consumed ochratoxins in the gastrointestinal tract. This paper gives an overview of the strategies that are promising with regard to lowering the ochratoxin burden of animals and humans.

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.

Evidence of a new dechlorinated ochratoxin A derivative formed in opossum kidney cell cultures after pretreatment by modulators of glutathione pathways: correlation with DNA-adduct formation

Ochratoxin A (OTA), a nephrotoxic mycotoxin probably implicated in human Balkan endemic nephropathy and associated urothelial tumors, induces renal carcinomas in rodents and nephrotoxicity in pigs. OTA induces DNA-adduct formation, but the structure of the adducts and their role in nephrotoxicity and carcinogenicity have only partly been elucidated. In vivo, 2-mercaptoethane sulfonate (MESNA) protects rats against OTA-induced nephrotoxicity but not against carcinogenicity, indicating two different mechanisms leading to nephrotoxicity or carcinogenicity. To better understand how DNA-adduct could be generated, opossum kidney cells (OK) have been treated by OTA alone or in presence of several compounds such as MESNA or N-acetylcysteine (another agent that, like MESNA, reduces oxidative stress by increasing of free thiols in kidney), buthionine sulfoximine (BSO) (an inhibitor of glutathione-synthase), and alpha amino-3-chloro-4,5-dihydro-5-isoxazole acetic acid (ACIVICIN) (an inhibitor of gamma glutamyl transpeptidase). Cytotoxicity of OTA on OK cells was evaluated by applying the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. None of the listed agents diminished OTA cytotoxicity significantly; ACIVICIN even increases OTA cytotoxicity. In contrast, analysis of the HPLC profiles of OTA metabolites produced during these incubations indicated that the pattern, the quantity of metabolites, and the nature of the derivatives were modulated by these agents. Ochratoxin B (OTB), open-ring ochratoxin A (OP-OA), 4 hydroxylated OTA, 10 hydroxylated OTA, OTA without phenylalanine, OTB without phenylalanine, and a dechlorinated OTA metabolite could be identified by nano-ESI-IT-MS.

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.

Alterations induced in vitro by ochratoxin A in rat lymphoid cells

Ochratoxin A (OTA) is a nephrotoxic mycotoxin produced by species of the genus Penicillium and Aspergillus that is present in food and feed as a natural contaminant. It modifies the immune function in animals and inhibits the proliferative response of lymphocytes in vitro. The toxic effect of OTA (0.5, 2, 20 microM) in lympho-proliferative response, natural killer (NK) cell activity, cytotoxic T lymphocytes (CTL) activity and macrophages' bacteriolytic capability was studied in vitro after 1 hour of treatment. The proliferative response of lymphocytes to concanavalin A and lipopolysaccharide was not affected by OTA; the cytotoxic activity of NK cells was dose-dependent decreased; the CTL activity was significantly decreased at the lowest concentration; the bacteriolytic activity of macrophages varied only slightly. These in vitro results reproduced, at least in part, some effects detected previously in vivo. The protein synthesis inhibition and the oxidative metabolism of OTA coupled to the prostaglandin synthesis are probably implicated in NK cells' toxicity, because the effects were reverted by the addition of phenylalanine or piroxicam to the culture medium. The induction of apoptosis seems to be the principal mechanism of action in the CTL effect. The intracellular concentration of OTA after 1 hour was analysed by HPLC and was found to be proportional to the quantity of OTA added to the culture medium for the three cell types; the presence of phenylalanine and piroxicam on the culture medium did not change the intracellular OTA concentration.

Ochratoxin A at nanomolar concentrations: A signal modulator in renal cells

Ochratoxin A (OTA) is a ubiquitous fungal metabolite with nephrotoxic, carcinogenic, and apoptotic potential. Toxicokinetics make the kidney the primary target organ for OTA. Due to its widespread occurrence in improperly stored foodstuff the complete and safe avoidance of OTA for humans is impossible. There are several reports showing a significant correlation between OTA exposure and certain forms of nephropathies. At nanomolar concentrations OTA leads to specific changes of function and phenotype in renal cells. The toxin interacts with certain cellular "key-molecules" (e. g., mitogen-activated protein (MAP) kinases, Ca2+), thereby disturbing cellular signalling and regulation events as well as mitochondrial function. Moreover, OTA has the ability to modulate physiological signals (e. g., angiotensin II or TNFalpha) and thereby influences cell function and cell growth and may even stable re-program the cells (e. g., altered distribution of chromosomes). This review concentrates on the effects of OTA in the nanomolar range and its interactions with cellular signalling networks in different renal cells proposing OTA to act as a signal modulator.

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.

Stoichiometric preference in copper-promoted oxidative DNA damage by ochratoxin A

The ability of the fungal carcinogen, ochratoxin A (OTA, 1), to facilitate copper-promoted oxidative DNA damage has been assessed using supercoiled plasmid DNA (Form I)-agarose gel electrophoresis and gas chromatography-mass spectrometry with selected-ion monitoring (GC-MS-SIM). OTA is shown to promote oxidative cleavage of Form I DNA with optimal cleavage efficiency occurring under excess Cu(II) conditions. As the concentration of OTA was increased and present in excess of Cu(II) the cleavage was less effective. Parallel findings were found for the ability of the OTA-Cu mixture to facilitate oxidative base damage. Yields (lesions per 10(6) DNA bases) of modified bases upon exposure of calf-thymus DNA (CT-DNA) to OTA-H(2)O(2)-Cu(II) were diminished when the OTA:Cu ratio was increased to 5:1. Electrochemical studies carried out in methanol implicate a ligand-centered 2e oxidation of OTA in the presence of excess Cu(II), while product analyses utilizing electrospray mass spectrometry support the intermediacy of the quinone, OTQ (3), in Cu-promoted oxidation of OTA. The implications of these findings with regard to the mutagenicity of OTA are discussed.

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.

Identification of ochratoxins and some of their metabolites in bile and urine of rats

The objectives of this study were to develop and evaluate procedures for the confirmation of ochratoxin A (OA), lactone opened OA (OP-OA), ochratoxin B (OB), hydroxy OA (OA-OH) and ochratoxin alpha (Oalpha) and metabolites formed in the rats from these toxins, and to demonstrate that many ochratoxin metabolites can be identified in the bile and urine of rats injected with the different ochratoxins. An esterification procedure in acidified methanol and a lactone hydrolysis procedure in strong base yielded two additional forms of most of the different ochratoxins. The esterification procedure provided a simple, fast and reliable method for the confirmation of the ochratoxins. A total of 20 different metabolites of OA, OP-OA, OB, OA-OH and Oalpha were detected in the urine and the bile of rats of which several were identified. Among these, OA and the recently discovered and toxic form of OA (OP-OA) were readily formed in vivo when either were injected. Procedures developed in this study can be used to confirm and isolate ochratoxins in biological samples and have shown that a new form of OA (OP-OA) along with many other metabolites are formed from OA and related ochratoxins in vivo.

The role of alpha2u-globulin in ochratoxin A induced renal toxicity and tumors in F344 rats

The mycotoxin ochratoxin A (OTA) was shown to be a potent kidney carcinogen in rats demonstrating a marked sex difference in the response. Compared to female rats, male rats had a 10-fold higher incidence of kidney carcinomas. The objective of this study was to investigate whether this sex difference in tumor response is due to an exacerbation of effect resulting from the interaction of the male rat specific urinary protein alpha2u-globulin (alpha2u) with OTA. Male and female rats were treated by oral gavage with OTA (1 mg/kg per day), D-limonene (dL; 1650 mg/kg per day) as a positive control or corn oil for 7 consecutive days. OTA induced severe renal lesions predominantly in the P3 region of the proximal tubules. The lesions consisted of necrotic cells and cell exfoliations. No hyaline droplets were found in the P2 segment following OTA treatment, whereas dL induced the expected accumulation of droplets. The results suggest that OTA induced kidney lesions are in all characteristic points different from the known alpha2u-nephropathy induced by dL. Based on these experiments the male rat specific protein alpha2u does not seem to be involved in the mechanism(s) leading to the high tumor incidence observed in OTA exposed male rats.

Chromatographic methods for the determination of ochratoxin A in animal and human tissues and fluids

This paper gives a review of chromatographic methods used for the determination of ochratoxin A (OA) in animal and human tissues and fluids. These methods are needed for example for monitoring studies of OA occurrence in the food chain and for studies dealing with the OA carry-over. In this survey, emphasis was given to HPLC methods. The review includes sampling, sample storage, extraction, spiking procedures, clean-up, detection and determination, and confirmation procedures. Emphasis is laid on special problems associated with the analysis of animal tissues and fluids.

Effect of cytochrome P450 induction on the metabolism and toxicity of ochratoxin A

Liver microsomes from rats treated with various P450 inducers were examined for their ability to metabolize the mycotoxin ochratoxin A (OTA) to 4(R)-4-hydroxyochratoxin A (4R), the major metabolite, and 4(S)-4-hydroxyochratoxin A (4S), the minor metabolite. Pretreatment of rats with phenobarbital (PB), dexamethasone (DXM), 3-methylcolcanthrene (3MC) and isosafrole (ISF) greatly induced 4R formation. PB, DXM, 3MC, clofibrate (CLF) and ISF treatments also induced 4S formation. Isoniazid (INH) pretreatment primarily induced 4S formation. The pH optimum for 4R formation was found to be 6.0 with 3MC microsomes, and 6.5 with PB and DXM microsomes. For 4S formation, the pH optimum was 7.0. At the optimum pH (compared with pH 7.4), 4R formation increased 40-50% with PB and DXM microsomes but 8.0-fold with 3MC microsomes. Studies using the inhibitors metyrapone and alpha-naphthoflavone as well as monoclonal antibodies against various P450s suggested that at least the P450 isoforms IA1/IA2, IIB1 and IIIA1/IIIA2 are involved in 4R formation. Using urinary excretion of the enzymes alkaline phosphatase and gamma-glutamyl transferase as an index of renal damage, we observed that pretreatment of rats with PB, which induced hepatic P450 (P450II2B1), protected against OTA nephrotoxicity, whereas cobalt-protoporphyrin IX pretreatment, which decreased P450 levels, exacerbated OTA nephrotoxicity. Our results suggest that at least P450IIB1-dependent metabolism of OTA leads to its detoxication and that OTA itself may be toxic in some circumstances or that other pathways are responsible for its activation.

Metabolites of ochratoxins in rat urine and in a culture of Aspergillus ochraceus

We studied the metabolic profile of ochratoxin A (OA) in rats and in a culture of OA-producing Aspergillus ochraceus. Ochratoxin alpha (O alpha), ochratoxin beta (O beta), 4-R-hydroxyochratoxin A (4-R-OH OA), 4-R-hydroxyochratoxin B (4-R-OH OB), and 10-hydroxyochratoxin A (10-OH OA) were isolated from a culture of A. ochraceus and structurally characterized by 1H nuclear magnetic resonance spectroscopy, mass spectrometry and high-pressure liquid chromatography. 4-R-OH OA and O alpha were consistently produced and were the dominant biotransformed metabolites in the fungal culture and in rats treated with OA and ochratoxin C (OC), while the formation of 10-OH OA was conditional in the fungal system. Green fluorescent biomacromolecules were isolated by detergent extraction of the fungal culture followed by cold-acetone precipitation and gel filtration. Acid hydrolysis of the fluorescent macromolecules resulted in the release of several ochratoxins, including O alpha (80%), OA (2%), and OC (5%), and other unidentified fluorescent compounds but not OB and O beta. Cross-reactivity studies of the natural macromolecule conjugates of OA with anti-OA polyclonal antibodies indicated that they were covalently linked to the macromolecules via a group other than the carboxyl group. These studies demonstrated that a fungus can produce some of the same metabolites of OA as the rat and that O alpha, OA, and OC may be covalently linked to fungal macromolecules.

Transformation of the mycotoxin ochratoxin A in plants. 2. Time course and rates of degradation and metabolite production in cell-suspension cultures of different crop plants

Ochratoxin A, one of the most toxic mycotoxins, can be metabolized nearly completely by suspension cultures of various plant cells. The transformation products identified in this study were almost the same in the cell-suspension cultures of maize, carrot, tomato, potato, soybean, wheat and barley, but the quantitative distribution differed strongly depending on incubation time and species of plant-cell culture. The compounds were extracted with ethyl acetate and detected by reversed-phase HPLC with gradient elution. From the result it is supposed that besides ochratoxin A also ochratoxin derivatives may occur in food and feedstuff of plant origin.

Prevention of nephrotoxicity of ochratoxin A, a food contaminant

Ochratoxin A (OTA) is a mycotoxin produced by ubiquitous Aspergilli, mainly by Aspergillus ochraceus and also by Penicilium verrucosum. It was found all over the world in feed and human food and blood as well as in animal blood and tissues. The most threatening effects of OTA are its nephrotoxicity and carcinogenicity, since this mycotoxin is nephrotoxic to all animal species studied so far and is increasingly involved in the Balkan endemic nephropathy (BEN), a human chronic interstitial nephropathy which is most of the time associated to urinary tract tumours. Since it seems impossible to avoid contamination of foodstuffs by toxigenic fungi, detoxification and detoxication for OTA are needed. To reduce or abolish the OTA-induced toxic effects, several mechanisms were investigated. The results of these investigations showed that some of the potential antidotes were efficient in preventing the main OTA toxic effects whereas some others were not. Promising compounds are structural analogues of OTA, and/or compounds having a high binding affinity for plasma proteins such as piroxicam, a non-steroidal anti-inflammatory drug (NSAID). Some enzymes such as superoxide dismutase (SOD) and catalase, radical scavengers, vitamins, prostaglandin (PG) synthesis inhibitors, (such as piroxicam), pH modificators, adsorbant resin such as cholestyramine etc. are efficient in vivo. Some of the results obtained in vivo were already confirmed in vitro and gave useful information on how to safely use these antidotes. The most generally acting compound seems to be A19 (Aspartame), a structural analogue of OTA and phenylalanine. When given to rats A19 (25 mg/kg/48 h) combined to OTA (289 micrograms/kg/48 h) for several weeks largely prevented OTA nephrotoxicity and genotoxicity. When given after intoxication of animals with OTA it washes out the toxin efficiently from the body. In vitro, A19 (10 micrograms/ml) prevents OTA (20-500 micrograms/ml) binding to plasma proteins. Its general action without any known side effect in humans and in animals, points at A19 to be the best candidate for preventing the OTA-induced subchronic effects.

Foodstuffs and human blood contamination by the mycotoxin ochratoxin A: correlation with chronic interstitial nephropathy in Tunisia

Ochratoxin A (OTA) has been detected in high amounts in human blood samples collected in nephrology departments in Tunisia from nephropathy patients under dialysis, especially those categorised as having a chronic interstitial nephropathy of unknown aetiology. These represent 12-26.1% of all chronic renal failure patients. To clarify the situation, food and blood samples were collected from nephropathy patients and controls, (with no familial case of nephropathy). The OTA assay showed very different scales of OTA food and blood contamination from 0.1 to 16.6 micrograms/kg and 0.1-2.3 ng/ml, respectively, in controls and healthy individuals and 0.3-46 830 micrograms/kg for food and 0.7-1136 ng/ml for blood in nephropathy patients. The disease seems related to OTA blood levels and food contaminations, since the control group was significantly different from the nephropathy group (p < 0.005) for both food and blood ochratoxin A contamination. Combined with data published already, the results emphasize the likely endemic aspect of this OTA-related nephropathy occurring in Tunisia and possibly in other countries of northern Africa. This nephropathy is very similar to Balkan endemic nephropathy.

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

Monkey kidney cells (named Vero cells) were incubated with increasing doses of ochratoxin A (10-100 microM). The inhibiting concentration 50% (IC50) on protein synthesis was about 14 microM in the presence of 5% fetal calf serum and 37 microM in the presence of 10% fetal calf serum. Some metabolites of ochratoxin A, including the chlorinated dihydroisocoumarin moiety of OTA (OT alpha), 4-[S]-hydroxy-OTA and 4-[R]-hydroxy-OTA were detected by HPLC in the mixture of cell homogenate after a 24 h incubation with 10 and 25 microM of OTA. Using the 32P-postlabelling method, several DNA-adducts, similar to those formed in mouse kidney after OTA treatment, were detected in monkey kidney cells. Thus, Vero cells are suitable for genotoxic and cytotoxic studies in relation to the metabolism of nephrotoxic xenobiotics such as OTA.

Ochratoxin-A production in Brazilian dry beans (Phaseolus vulgaris L.)

Ochratoxin A was produced, at concentrations of about 200 mg kg1 of dry beans (Phaseolus vulgaris L.) of each of five Brazilian commercial varieties. Both intact and decorticated kernels of the varieties Preto, Branco, Rosinha, Roxo and Carioca (22% moisture) were inoculated withAspergillus alutaceous and incubated at 25°C for 28 days. Results from thin-layer and column chromatography, mass, infrared, 1H-nuclear magnetic resonance and UV-spectrometry showed that 1) the common bean is a highly stimulatory substrate for the bioproduction of ochratoxin A and 2) the putative toxin extracted by the method of Soares & Rodriguez-Amaya was in fact ochratoxin A. Removal of the seed coat resulted in increased OTA production for all varieties, particularly for the Rosinha, Roxo and Carioca.

Effect of piroxicam on the nephrotoxicity induced by ochratoxin A in rats

Ochratoxin A (OTA) is a mycotoxin which contaminates animal feed and human food and is nephrotoxic for all animal species studied so far. It binds to plasma proteins and is transported into target organs, especially the kidney. An attempt to prevent its toxic effects has been made using piroxicam, a non-steroidal anti-inflammatory drug (NSAID). Piroxicam also binds strongly to plasma proteins and our hypothesis is that this drug could stop OTA-binding and transport into target organs, thereby preventing its nephrotoxicity. Our experiments on rats given OTA (289 micrograms/kg/48 h for 2 weeks) show that piroxicam prevents the enzymuria induced by OTA and increases renal elimination of OTA. In vivo, piroxicam could prove useful in preventing the chronic effects of ochratoxin A, mainly nephrotoxicity, at doses 5 mg/kg/48 h, which were not found to be nephrotoxic in experimental animals.

Differential DNA adduct formation and disappearance in three mouse tissues after treatment with the mycotoxin ochratoxin A

Ochratoxin A (OTA) is a mycotoxin which has been implicated in Balkan endemic nephropathy, a disease characterized by a high incidence of urinary tract tumors. It induces DNA single-strand breaks and has been shown to be carcinogenic in two rodent species. For a better understanding of the OTA genotoxic effect, OTA-DNA adduct formation and disappearance has been measured using the 32P-post-labelling method after oral administration of 2.5 mg/kg of OTA to mice. In kidney, liver and spleen, several modified nucleotides were clearly detected in DNA, 24 h after administration of OTA, but their level varied significantly in a tissue and time dependent manner over a 16-day period. Total DNA adducts reached a maximum at 48 h when 103, 42 and 2.2 adducts per 10(9) nucleotides were found respectively in kidney, liver and spleen, indicating that kidney is the main target of the genotoxicity and likely carcinogenicity of OTA. The major adduct differed between kidney and liver. All adducts disappeared in liver and spleen 5 days after compound administration, whereas some adducts persisted for at least 16 days in the kidney. Some adducts were organ specific. The finding that the adducts are not quantitatively and qualitatively the same in the three organs examined is likely due to differences of metabolism in these organs, leading to different ultimate carcinogens and may also result from differences in the efficiency of repair processes.

Characterization of pig liver purified cytochrome P-450 isoenzymes for ochratoxin A metabolism studies

In this paper, we report the characterization of 4 isolated, constitutive cytochrome P-450 fractions from pig liver microsomes. The two predominant forms, A2 and A3, exhibit several similarities: a Mr of 54 kDa, a lambda max CO-Fe++ at 448 nm, a relatively high ratio of the high-spin form and an immunological cross-reaction with polyclonal antibodies against rat liver P-450 IIB1. It is shown that these forms and the minor form Ba, which are active as benzphetamine N-demethylase, play an important metabolic role in ochratoxin A oxidation. This mycotoxin was oxidized by at least 3 different pig liver cytochrome P-450 fractions, each producing different metabolites, namely (4R)-, (4S)-hydroxyochratoxin A, and a new lipophilic metabolite. Since the pig is particularly susceptible to ochratoxin A toxicity, it represents a good animal model for in vitro studies of the metabolism of such a xenobiotic.

Induction of characteristic chromosomal aberrations, particularly X-trisomy, in cultured human lymphocytes treated by ochratoxin A, a mycotoxin implicated in Balkan endemic nephropathy

Ochratoxin A (OA), a mycotoxin which induces nephropathy and kidney tumours in rats and mice, is a contaminant of food consumed by a population with a high incidence of endemic nephropathy (EN). It was therefore tested in vitro for its ability to induce chromosomal aberrations in human peripheral lymphocytes in a small number of subjects, in the presence or absence of a kidney microsomal metabolic activation system. OA was found to induce aberrations on X chromosomes of similar types to those previously detected in lymphocytes from patients suffering from endemic nephropathy.

The myocotoxin ochratoxin A is a substrate for phenylalanine hydroxylase in isolated rat hepatocytes and in vivo

Ochratoxin A (OTA), is a myocotoxin contaminating food and feed stuffs, consisting of a chlorinated dihydroisocoumarin linked through a 7-carboxyl group to L-phenylalanine by an amide bond. When OTA (0.12-1.4 mM) is incubated with freshly isolated rat hepatocytes, it inhibits both the hydroxylation of phenylalanine (0.05 mM) to tyrosine, catalyzed by phenylalanine hydroxylase and the subsequent metabolism of tyrosine as measured by homogentisate oxidation. The IC50 of OTA for phenylalanine hydroxylation is 0.43 mM. OT alpha, (0.5-1.0 mM), the dihydroisocoumarin moiety of OTA, does not inhibit phenylalanine hydroxylase activity under these conditions. During incubations of hepatocytes with uniformly labelled [3H]-OTA and unlabelled phenylalanine, tyrosine-ochratoxin A is formed (up to 6% of the total mycotoxin added), indicating that ochratoxin can act as a substrate for phenylalanine hydroxylase. In vivo tyrosine-OTA is also found in liver of poisoned animals.

Mechanism of ochratoxin A-induced immunosuppression

Ochratoxin A (OA) has been reported to affect immune function both at the level of antibody synthesis and natural killer (NK) cell activity. In the present study we demonstrate that exposure of purified human lymphocyte populations and subpopulations to the toxin will abrogate the cells' ability to respond to activating stimuli in vitro. Thus, both IL-2 production and IL-2 receptor expression of activated T lymphocytes are severely impaired. When the cells are preincubated with the analogue ochratoxin B (OB) prior to OA exposure, the inhibitory effect of OA is reversed. Furthermore, the inhibitory effect of OA on antibody production is not only due to blocking of T helper cell function. Highly purified B lymphocytes will not respond to polyclonal activators in vitro after a brief pulse with OA. The results strongly suggest that the toxin causes its immunosuppression through interference with essential processes in cell metabolism irrespective of lymphocyte population or subpopulation.

Perturbation of liver microsomal calcium homeostasis by ochratoxin A

The effect of ochratoxin A on hepatic microsomal calcium sequestration was studied both in vivo and in vitro. The rate of ATP-dependent calcium uptake was inhibited by 42-45% in ochratoxin A intoxicated rats as compared to controls. In the presence of NADPH, addition of ochratoxin A (2.5 to 100 microM) caused a concentration-dependent inhibition of calcium uptake (28-94%) by untreated rat liver microsomes. The rate of NADPH-dependent lipid peroxidation, measured as malondialdehyde formed, was also greatly enhanced by ochratoxin A. Various agents that inhibited ochratoxin A enhanced lipid peroxidation were also able to block the destruction of calcium uptake activity. Lipid peroxidation enhanced by ochratoxin A was also accompanied by leakage of calcium from calcium-loaded microsomes. These results suggest that ochratoxin A disrupts microsomal calcium homeostasis by an impairment of the endoplasmic reticulum membrane probably via enhanced lipid peroxidation.

Lipid peroxidation as a possible cause of ochratoxin A toxicity

Addition of the mycotoxin ochratoxin A (OA), a nephrotoxic carcinogen, to rat liver microsomes greatly enhanced the rate of NADPH or ascorbate-dependent lipid peroxidation as measured by malondialdehyde formation. NADPH-dependent lipid peroxidation in kidney microsomes was similarly enhanced by OA. The process required the presence of trace amounts of iron but cytochrome P-450 and free active oxygen species appeared not to be involved. The efficiency of several ochratoxins (ochratoxins A, B, C, alpha and O-methyl-ochratoxin C) to enhance lipid peroxidation was related to the presence and reactivity of the phenolic hydroxyl group. Furthermore, the ability of these ochratoxins to enhance lipid peroxidation in microsomes correlated precisely with their known toxicities in chicks. Administration of ochratoxin A to rats also resulted in enhanced lipid peroxidation in vivo as evidenced by a seven-fold increase in the rate of ethane exhalation. These results suggest that lipid peroxidation may play a role in the observed toxicity of ochratoxin A in animals; a mechanism is proposed. (Formula: see text). Ochratoxin A: X = Cl; R1 = R2 = R3 = R4 = H Ochratoxin B: X = H; R1 = R2 = R3 = R4 = H Ochratoxin C: X = Cl; R1 = R2 = R3 = H; = R4 = CH3 O-Methyl-ochratoxin C: X = Cl; R2 = R3 = H; R1 = R4 = CH3 (4R)-4-hydroxyochratoxin A: X = Cl; R1 = R3 = R4 = H; R2 = OH (4S)-4-hydroxyochratoxin A: X = Cl; R1 = R2 = R4 = H; R3 = OH Fig. 1. Chemical structures of the various ochratoxins.