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

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.

The role of mycotoxins in neurodegenerative diseases: current state of the art and future perspectives of research

Mycotoxins are fungal metabolites that can cause various diseases in humans and animals. The adverse health effects of mycotoxins such as liver failure, immune deficiency, and cancer are well-described. However, growing evidence suggests an additional link between these fungal metabolites and neurodegenerative diseases. Despite the wealth of these initial reports, reliable conclusions are still constrained by limited access to human patients and availability of suitable cell or animal model systems. This review summarizes knowledge on mycotoxins associated with neurodegenerative diseases and the assumed underlying pathophysiological mechanisms. The limitations of the common in vivo and in vitro experiments to identify the role of mycotoxins in neurotoxicity and thereby in neurodegenerative diseases are elucidated and possible future perspectives to further evolve this research field are presented.

Antioxidant Activity of Royal Jelly Hydrolysates Obtained by Enzymatic Treatment

Recently, research on the processing of raw functional materials with the aim of improving various physiological activities has been conducted. In this study, we investigated the antioxidant activity of royal jelly (RJ) hydrolysates obtained from three commercial proteases. Enzyme-treated royal jelly (ERJ), in which the RJ hydrolysates were converted into easy-to-absorb shorter chain monomers through the removal of two known allergen proteins, showed no difference in the content of (E)-10-hydroxydec-2-enoicacid (10-HDA) or the freshness parameter and showed a significant increase in total free amino acid content. The antioxidant activity of ERJ was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and chemical assays. The ERJ showed about 80% DPPH-radical scavenging activity at same concentration of ascorbic acid. The antioxidant effect of ERJ was confirmed to be due to reduction of intracellular reactive oxidative species (ROS) and nitric oxide (NO) production in LPS-treated macrophages. Moreover, ERJ significantly increased the activity of the antioxidant enzyme superoxide dismutase (SOD) and the level of the antioxidant glutathione (GSH) in a dose-dependent manner. Interestingly, these antioxidant activities of ERJ were stronger than those of non-treated RJ. These findings indicate that ERJ has high potential as an antioxidant agent for use in human and animal diets.

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.

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.

Aoyap1 regulates OTA synthesis by controlling cell redox balance in Aspergillus ochraceus

Among the various factors correlated with toxin production in fungi, oxidative stress is a crucial one. In relation to this, an important role is played by oxidative stress-related receptors. These receptors can transduce the "oxidative message" to the nucleus and promote a transcriptional change targeted at restoring the correct redox balance in the cell. In Aspergillus parasiticus, the knockout of the ApyapA gene, a homologue of the yeast Yap-1, disables the fungus's capacity to restore the correct redox balance in the cell. As a consequence, the onset of secondary metabolism and aflatoxins synthesis is triggered. Some clues as to the involvement of oxidative stress in the regulation of ochratoxin A (OTA) synthesis in Aspergillus ochraceus have already been provided by the disruption of the oxylipin-producer AoloxA gene. In this paper, we add further evidence that oxidative stress is also involved in the regulation of OTA biosynthesis in A. ochraceus. In fact, the use of certain oxidants and, especially, the deletion of the yap1-homologue Aoyap1 further emphasize the role played by this stress in controlling metabolic and morphological changes in A. ochraceus.

Mechanisms of mycotoxin-induced neurotoxicity through oxidative stress-associated pathways

Among many mycotoxins, T-2 toxin, macrocyclic trichothecenes, fumonisin B(1) (FB(1)) and ochratochin A (OTA) are known to have the potential to induce neurotoxicity in rodent models. T-2 toxin induces neuronal cell apoptosis in the fetal and adult brain. Macrocyclic trichothecenes bring about neuronal cell apoptosis and inflammation in the olfactory epithelium and olfactory bulb. FB(1) induces neuronal degeneration in the cerebral cortex, concurrent with disruption of de novo ceramide synthesis. OTA causes acute depletion of striatal dopamine and its metabolites, accompanying evidence of neuronal cell apoptosis in the substantia nigra, striatum and hippocampus. This paper reviews the mechanisms of neurotoxicity induced by these mycotoxins especially from the viewpoint of oxidative stress-associated pathways.

Lipoperoxidation affects ochratoxin A biosynthesis in Aspergillus ochraceus and its interaction with wheat seeds

In Aspergillus nidulans, Aspergillus flavus, and Aspergillus parasiticus, lipoperoxidative signalling is crucial for the regulation of mycotoxin biosynthesis, conidiogenesis, and sclerotia formation. Resveratrol, which is a lipoxygenase (LOX) and cyclooxygenase inhibitor, downmodulates the biosynthesis of ochratoxin A (OTA) in Aspergillus ochraceus. In the genome of A. ochraceus, a lox-like sequence (AoloxA; National Center for Biotechnology Information (NCBI) accession number: DQ087531) for a lipoxygenase-like enzyme has been found, which presents high homology (100 identities, 100 positives %, score 555) with a lox gene of Aspergillus fumigatus (NCBI accession number: XM741370). To study how inhibition of oxylipins formation may affect the A. ochraceus metabolism, we have used a DeltaAoloxA strain. This mutant displays a different colony morphology, a delayed conidia formation, and a high sclerotia production. When compared to the wild type, the DeltaAoloxA strain showed a lower basal activity of LOX and diminished levels of 13-hydroperoxylinoleic acid (HPODE) and other oxylipins derived from linoleic acid. The limited oxylipins formation corresponded to a remarkable inhibition of OTA biosynthesis in the DeltaAoloxA strain. Also, wheat seeds (Triticum durum cv Ciccio) inoculated with the DeltaAoloxA mutant did not accumulate 9-HPODE, which is a crucial element in the host defence system. Similarly, the expression of the pathogenesis-related protein 1 (PR1) gene in wheat seeds was not enhanced. The results obtained contribute to the current knowledge on the role of lipid peroxidation governed by the AoloxA gene in the morphogenesis, OTA biosynthesis, and in host-pathogen interaction between wheat seeds and A. ochraceus.

Complex etiology, prophylaxis and hygiene control in mycotoxic nephropathies in farm animals and humans

Various etiological factors contributing to the development of mycotoxic nephropathy in farm animals and humans are reviewed. The possible synergistic effect between ochratoxin A (OTA) and other mycotoxins, as penicillic acid (PA) and fumonisin B(1) (FB(1)), contributing to this nephropathy is also considered and discussed. The most convenient ways of prophylaxis and various preventive measures against OTA contamination of feeds or foods are reviewed. A reference is made concerning the most successful methods of veterinary hygiene control in the slaughterhouses in order to prevent the entering of OTA in commercial channels with a view to human health. The economic efficacy of these prophylactic procedures is also considered. An evaluation of human exposure to OTA is made.

Suppression of ochratoxin biosynthesis by naturally occurring alkaloids

The effects of four alkaloids on the biosynthesis of ochratoxin A (OTA), ochratoxin B (OTB) and citrinin were examined on four OTA-producing aspergilli: Aspergillus auricomus, A. sclerotiorum and two isolates of A. alliaceus. Piperine and piperlongumine, natural alkaloids of Piper longum, significantly inhibited OTA production at 0.001% (w/v) for all aspergilli examined. Piperine and piperlongumine affected the polyketide synthesis step of OTA production and inhibited production of citrinin. Curcumin, a constituent of tumeric, completely inhibited mycelial growth of A. alliaceus isolate 791 at 0.1% (w/v) and decreased OTA production by approximately 70% at 0.01% (w/v). Sesamin, a constituent of sesame oil, inhibited OTA and OTB production by 60 and 45%, respectively, at 0.1% (w/v), showing its effect was on chloroperoxidase and polyketide synthase activity. The potential advantage of these natural products to reduce ochratoxin contamination of agricultural commodities is discussed.

Can low level exposure to ochratoxin-A cause parkinsonism?

Mycotoxins are fungal metabolites with pharmacological activities that have been utilized in the production of antibiotics, growth promoters, and other classes of drugs. Some mycotoxins have been developed as biological and chemical warfare agents. Bombs and ballistic missiles loaded with aflatoxin were stockpiled and may have been deployed by Iraq during the first Gulf War. In light of the excess incidence of amyotrophic lateral sclerosis (ALS) in veterans from Operation Desert Storm, the potential for delayed neurotoxic effects of low doses of mycotoxins should not be overlooked. Ochratoxin-A (OTA) is a common mycotoxin with complex mechanisms of action, similar to that of the aflatoxins. Acute administration of OTA at non-lethal doses (10% of the LD(50)) have been shown to increase oxidative DNA damage in brain up to 72 h, with peak effects noted at 24 h in midbrain (MB), caudate/putamen (CP) and hippocampus (HP). Levels of dopamine (DA) and its metabolites in the striatum (e.g., CP) were shown to be decreased in a dose-dependent manner. The present study focused on the effects of chronic low dose OTA exposure on regional brain oxidative stress and striatal DA metabolism. Continuous administration of low doses of OTA with implanted subcutaneous Alzet minipumps caused a small but significant decrease in striatal DA levels and an upregulation of anti-oxidative systems and DNA repair. It is possible that low dose exposure to OTA will result in an earlier onset of parkinsonism when normal age-dependent decline in striatal DA levels are superimposed on the mycotoxin-induced lesion.

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.

Unusual astrocyte reactivity caused by the food mycotoxin ochratoxin A in aggregating rat brain cell cultures

Ochratoxin A (OTA), a mycotoxin and widespread food contaminant, is known for its patent nephrotoxicity and potential neurotoxicity. Previous observations in vitro showed that in the CNS, glial cells were particularly sensitive to OTA. In the search for the molecular mechanisms underlying OTA neurotoxicity, we investigated the relationship between OTA toxicity and glial reactivity, in serum-free aggregating brain cell cultures. Using quantitative reverse transcriptase-polymerase chain reaction to analyze changes in gene expression, we found that in astrocytes, non cytotoxic concentrations of OTA down-regulated glial fibrillary acidic protein, while it up-regulated vimentin and the peroxisome proliferator-activated receptor-gamma expression. OTA also up-regulated the inducible nitric oxide synthase and the heme oxygenase-1. These OTA-induced alterations in gene expression were more pronounced in cultures at an advanced stage of maturation. The natural peroxisome proliferator-activated receptor-gamma ligand, 15-deoxy-delta(12,14) prostaglandin J2, and the cyclic AMP analog, bromo cyclic AMP, significantly attenuated the strong induction of peroxisome proliferator-activated receptor-gamma and inducible nitric oxide synthase, while they partially reversed the inhibitory effect of OTA on glial fibrillary acidic protein. The present results show that OTA affects the cytoskeletal integrity of astrocytes as well as the expression of genes pertaining to the brain inflammatory response system, and suggest that a relationship exists between the inflammatory events and the cytoskeletal changes induced by OTA. Furthermore, these results suggest that, by inducing an atypical glial reactivity, OTA may severely affect the neuroprotective capacity of glial cells.

Lack of the effect of mycotoxins-aflatoxin B1 and ochratoxin A on some functions of rat adipocytes

Mycotoxins-aflatoxin B1 (AFB1) and ochratoxin A (OTA)-compounds which are strong carcinogenic, mutagenic and cytotoxic factors-are also known to evoke a decrease of food intake and body weight gains. The purpose of our study was to determine the direct influence of AFB1 and OTA incubated with isolated rat fat cells on the lipogenesis, lipolysis and leptin secretion. Adipocytes were isolated from the epididymal fat tissue by the collagenase digestion. Toxins used at concentrations 1, 10 and 100 microM were incubated for 90 min with adipocytes. Basal and insulin-stimulated lipogenesis-determined by the measure of [U-14C]glucose conversion to total lipids-was abated by AFB1 only at the highest concentration. At two lower ones, AFB1 did not affect the process. OTA at all used concentrations decreased insulin-stimulated lipogenesis but the effect was not dose-dependent. The lipolysis was determined by the measure of glycerol release from adipocytes. The basal lipolysis was unchanged by both toxins. The epinephrine-stimulated lipolysis was intensified by AFB1 only at the highest concentration, however, the process was not altered by OTA. The antilipolytic action of insulin was unaffected by both compounds (10 microM). To determine the influence of the tested toxins on leptin secretion, adipocytes were incubated for 120 min in the presence of glucose and insulin as stimulators of hormone secretion. AFB1 and OTA added to the incubation medium (1, 10 and 100 microM) had no significant influence on the leptin release. The results obtained in this experiment demonstrate that adipocytes are susceptible to the direct action of AFB1 and OTA. This susceptibility is, however, rather weak and is exhibited by a slight restriction of the lipogenesis (in the case of both toxins) and by a slight increase of the lipolysis (in the case of AFB1).

Protective role of melatonin in ochratoxin a toxicity in rat heart and lung

Ochratoxin A (OTA) is a mycotoxin produced by different fungi. The most pronounced adverse effect of OTA is hepatonephrotoxicity. Melatonin (MEL) has an antioxidant effect and has free-radical scavenger properties. The effects of OTA on heart and lung tissue and possible ameliorating effects of MEL were investigated in rats. Twenty-four rats were allocated to three groups (each with eight rats): control; OTA-treated group (OTA dose 289 microg kg(-1) per day); and OTA + MEL-treated group (MEL dose 10 mg kg(-1) per day). After 30 days of treatment, the histopathological changes in the heart and lung of all groups were examined. Compared with the control rats, myocardial tissue of rats treated with OTA showed extensive cytoplasmic vacuole formation, necrosis of the myocytes, dissolution of the nucleus, clumped fibres, fibrillolysis, swollen myocardial fibres, small haemorrhagic areas and hyperaemic vessels (P <0.05). In addition, lungs of rats treated with OTA showed alveolar congestion, alveolar cell hyperplasia, prominent alveolar septal vessels, variable intensity loss of alveolar architecture, intraparenchymal inflammatory infiltration, intraparenchymal hyperaemic vessels, respiratory epithelial proliferation, perivascular and peribronchial inflammation, pneumonic infiltration, distorted appearance of lung parenchyma and emphysematous areas (P <0.05). In comparison with the OTA groups, the ameliorating effects of MEL in the lung damage parameters were on alveolar cell hyperplasia, prominent alveolar septal vessels, variable intensity loss of alveolar architecture, intraparenchymal inflammatory infiltration, perivascular inflammatory inflammation, distorted appearance of lung parenchyma and focal emphysematous areas in lung (P <0.05). Melatonin also significantly reduced myocardial damage in most of the parameters: extensive cytoplasmic vacuole formation, necrosis of the myocytes, clumped fibres, fibrillolysis, small haemorrhagic areas and hypaeremic vessels in heart (P <0.05). On the other hand, MEL did not lower the degree of damage in lung and heart to the level of the control rats, except for the parameters of the interstitial oedema and small haemorrhagic areas only in myocardial tissue. Histopathological findings showed that OTA induced damage in heart and lung and MEL treatment significantly reduced the degree of damage.

Studies of ochratoxin A-induced inhibition of phenylalanine hydroxylase and its reversal by phenylalanine

Ochratoxin A (OTA) is a nephrotoxic, hepatotoxic, and teratogenic mycotoxin produced by storage molds on a variety of foodstuffs. Its chemical structure is composed of an isocumarin part linked to l-phenylalanine. Inhibition of phenylalanine hydroxylase and other enzymes that use phenylalanine as substrate is based on this structural homology. We have examined the effects of low doses of ochratoxin A on the activity of phenylalanine hydroxylase in kidney and in liver of experimental animals. Daily administration of ochratoxin A (50 microg/kg body wt, for 10 and 35 days, respectively) caused a significant reduction in the phenylalanine hydroxylase activity. Inhibition was more pronounced in liver than in kidney, although actual ochratoxin A concentration was higher in the kidney tissue. We observed an apparent increase in the affinity of phenylalanine hydroxylase for substrate following OTA administration to animals. However, simple competitive inhibition was observed for both tissues in vitro (K(i liver) = 0.0119 +/- 0.002 mM and K(i kidney) = 0.13 +/- 0.026 mM). Simultaneous application of ochratoxin A with phenylalanine could reduce inhibition of phenylalanine hydroxylase, in particular in liver. Enzyme activity was almost completely preserved after 35 days of combined treatment. The results obtained suggest that daily administration of ochratoxin A in low doses produced an inhibitory effect that could be diminished by competitive action of l-phenylalanine.

Ochratoxin binding to phenylalanyl-tRNA synthetase: computational approach to the mechanism of ochratoxicosis and its antagonism

Ochratoxin A (OA) is a toxic isocoumarin derivative released by various species of mold which grow on grain, coffee, and nuts, representing a serious worldwide health problem. Among other mechanisms of toxicity, it has been suggested that OA inhibits phenylalanyl-tRNA synthetase (PheRS), thereby reducing protein synthesis. Using the crystal structure of PheRS from Thermusthermophilus, we have modeled its interactions with OA as well as with phenylalanyl adenylate (FAMP), the high-affinity intermediate substrate of PheRS. Our results indicate that while OA may be capable of weakly inhibiting PheRS, the OA-PheRS complex cannot adopt the same conformation as does FAMP-PheRS, contrary to previous assumptions. Relative to FAMP, the phenylalanyl moiety is found to bind more shallowly and in a different overall conformation. Free-energy perturbation calculations of the relative free energies of binding of OA with the phenolic moiety protonated versus deprotonated suggest that the protonated form binds significantly more strongly. Two alternative binding modes were also identified which cannot be discounted on the basis of these calculations. Our results, however, do not suggest binding stronger than millimolar for any of the binding modes, a conclusion which is in agreement with more recent experimental findings. This, in turn, suggests that the previously observed antagonistic effects of aspartame and piroxicam are more likely due to their prevention of OA binding to human serum albumin than to PheRS, which is in agreement with binding studies as well as with preliminary simulations performed in our laboratory.

Kinetic profiles of ochratoxin A and ochratoxin alpha during in vitro incubation in buffered forestomach and abomasal contents from cows

Pure ochratoxin A (OA) was added to buffered rumen fluid collected from fistulated cows and incubated under anaerobic conditions. The kinetic pattern of the disappearance of OA and the appearance of ochratoxin alpha (Oalpha) was principally the same with four diets fed to donor animals and with three donor animals. The concentration of OA declined to a very low or non-detectable level with half-lives at 0.17-1.84 h; its rate of disappearance was first order throughout. The concentration of Oalpha increased to a constant level under all conditions examined. The average amounts of Oalpha formed relative to the disappearance of OA were not different (p > 0.05) and ranged between 94 +/- 8 and 98 +/- 8 %. The rate of disappearance of OA differed (p < 0.001) between diets and animals. It was accelerated by increasing the content of concentrate in the diet. Ochratoxin alpha was not metabolized when added in pure form to buffered rumen fluid and incubated under the same conditions as OA. Pure OA was also added to buffered fluids from the forestomach and abomasum of a slaughtered cow. It disappeared exponentially in a mixture of fluids from the rumen and reticulum and in fluid from the omasum, with the average amounts of Oalpha formed relative to OA disappearance being 107 and 109 %, respectively. Ochratoxin A also was not metabolized in fluid from the abomasum. These studies demonstrate that OA is hydrolysed in the rumen via first order kinetics, diet and animal affect the rate of hydrolysis, OA is quantitatively converted to Oalpha and Oalpha is not degraded.

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.

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.

Subchronic effects of ochratoxin A on young adult rat brain and partial prevention by aspartame, a sweetener

1. Ochratoxin A (OTA) is a mycotoxin produced by several fungi, especially Aspergillus and Penicillium species. Many food and foodstuffs can be contaminated by ochratoxin A, which is consequently found in blood of animals and humans. 2. The distribution into the brain of young adult rats fed OTA for 1 to 6 weeks and some consequences have been investigated in the present study. 3. Our results on rats given OTA (289 microg/kg/48 h) indicated that OTA accumulated in the whole brain as function of time according to a regression curve, Y=-8.723 a+16.72 with a correlation coefficient of r=0.989, where Y-axis is the OTA concentration in ng/g of brain and X-axis is the duration of the treatment in weeks. The brain OTA contents was 11.95 +/- 2.2, 23.89 +/- 4.4, 39.9 +/- 4.5, 50.3 +/- 7.3, 78.8 +/- 6.3, 94 +/- 16 ng/g of brain in the mycotoxin-treated animals for respectively 1, 2, 3, 4, 5 and 6-weeks treatment. OTA induced modifications of free amino-acid concentrations in the brain, mainly, Tyrosine (Tyr) and phenylalanine (Phe). Tyr decreased significantly as compared to control (p < 0.05). Phe increased significantly as compared to control (p < 0.05). 4. Aspartame, (25 mg/kg/48 h) a structural analogue of OTA largely modified the distribution and prevented the accumulation of OTA in the brain since the respective brain OTA contents decreased respectively to 9.6 +/- 7.9, 19.2 +/- 3.0, 26.8 +/- 4.2, 19.7 +/- 1.9, 13.7 /- 5.6 and 11.0 +/- 6.0 ng/g of tissue, for the same duration of treatment. It also prevented the modifications of Tyr and Phe levels. 5. The histological investigations showed several necrotic cells with pyknotic nucleus, detected in OTA treated animals with higher frequency as compared to the controls and Aspartame treated ones. Aspartame appeared to significantly prevent this nuclear effect as well, the meaning of which is discussed.

The neurotoxic effects of ochratoxin-A are reduced by protein binding but are not affected by l-phenylalanine

Recent in vivo investigations indicate that the mycotoxin ochratoxin A (OTA) is a neurotoxicant during prenatal stages. In line with in vivo data, in our embryonic chick brain and neural retina cell cultures the markers for neuritic outgrowth and differentiation (NF68 and 160 kDa, MAP2 and MAP5) were especially negatively affected. In vivo OTA is nearly completely bound to serum constituents. In our culture system binding of OTA to BSA evoked a significant shift of the concentration-effect relationships in meningeal and brain cell cultures. As a result of the albumin binding the OTA IC5 and IC50 values of all parameters increased by nearly the same value (about 15-fold in brain and 32-fold in meningeal cell cultures). One of the mechanisms responsible for OTA toxicity is thought to be the competitive inhibition versus Phe of Phe-dependent enzymes. Therefore, in addition, we investigated the effects of l-phenylalanine (Phe) and its influence on OTA toxicity in brain and neural retina cell cultures. Phe itself was found to differently affect brain and neural retina cell cultures. However, in both cultures OTA toxicity is not diminished by Phe. Therefore, our data indicate that at least in our cultures competition with Phe-dependent processes does not play a role in OTA toxicity.

Renal transepithelial secretion of ochratoxin A in the non-filtering toad kidney

Renal excretion is an important way of elimination for the nephrotoxin ochratoxin A (OTA). Because binding to proteins hinders filtration, excretion is mainly due to proximal tubular secretion. The goal of this study was to investigate the kinetics of secretion as well as the extent of urine and tissue accumulation in situ using the non-filtering amphibian kidney model. Transepithelial secretion is a saturable process (K(m) = 0.63.10(-6) mol/l) and leads to a concentration-dependent accumulation of OTA in the tubular lumen and in renal tissue. Maximum accumulation achieved is approximately 14-fold as compared to the perfusate concentration. There was no accumulation in the tubular lumen as compared to renal tissue (lumen-to-tissue concentration ratio approximately 1). Tissue and tubular lumen accumulation were reduced to approximately 40% of control in the presence of 10(-3) mol/l p-aminohippurate (PAH). Addition of 10(-3) mol/l alpha-ketoglutarate (KG) to PAH-containing perfusate did not lead to a further reduction of secretion. By contrast, addition of 10(-2) mol/l L-phenylalanine (L-Phe) reduced secretion further to approximately 25% of control. In the presence of 10(-3) mol/l probenecid tissue accumulation was reduced to 7% and tubular lumen accumulation to 1% of control. Lumen-to-tissue concentration ratio decreased to 0.15 in the presence of probenecid, indicating an inhibitory action at the luminal membrane. Addition of albumin to the perfusate, reduced secretion to only 50% of control, whereas the concentration of free OTA was reduced below 1% as compared to control. The results of this study show that transepithelial secretion is an effective way for accumulation of OTA in the tubular lumen and thus its urinary excretion. Transport via the basolateral organic anion and a basolateral amino acid carrier are the active steps in transepithelial secretion. Luminal exit of OTA is a passive process. Furthermore, tissue accumulation by the active transport across the basolateral membrane supports the toxic action of OTA on proximal tubular cells. Due to the qualitative similarity of organic anion transport our findings should also apply for the mammalian kidney.

Apical-to-basolateral transepithelial transport of Ochratoxin A by two subtypes of Madin-Darby canine kidney cells

In this study we investigated the transepithelial transport of Ochratoxin A (OTA), a potent nephrotoxin, across monolayers of two collecting duct-derived cells clones (Madin-Darby canine kidney cells (MDCK)-C7 and MDCK-C11 cells, resembling principal and intercalated cells, respectively) either from the apical to the basolateral side or vice versa. We cultured cells on permeable supports and compared the transport rates of OTA, p-aminohippuric acid (PAH) and fluorescein-labelled inulin. Monolayers of both cell clones translocated OTA from the apical to the basolateral side but not in the opposite direction. Transport rate across MDCK-C11 cell monolayers was 2.9-fold the transport rate across MDCK-C7 cell monolayers. OTA transport was temperature-dependent being reduced from 77.5 pmol/cm2 per h to 10.1 pmol/cm2 per h in MDCK-C11 and from 27.0 pmol/cm2 per h to 7.6 pmol/cm2 per h in MDCK-C7 cells when temperature was decreased from 37 degrees C to 4 degrees C. In both cell clones, the dipeptides carnosine and glycylsarcosine but not the amino acids glycine or phenylalanine had an inhibitory effect on OTA transport. In both cell clones, transepithelial transport of OTA was dependent on the apical pH (pK(a) of OTA = 7.1). In an environment mimicking the transepithelial in vivo pH gradient to some extent with more acidic pH on the apical side than on the basolateral side, transport was 4-fold higher in both cell clones as compared to conditions when pH was 7.4 in both bath solutions. In the absence of a pH gradient, transport rates were similar to that at 4 degrees C. Apical uptake of [3H]OTA was inhibited by carnosine and by glycylsarcosine and the uptake of [3H]carnosine was inhibited by OTA. Our results indicate that OTA is transported across the apical membrane of MDCK cells by both non-ionic diffusion and by a H+-dipeptide cotransporter. Thus, reabsorption of OTA in the collecting duct contributes to the observed long half life of OTA in the mammalian body.

Influence of ochratoxin A treatment on the activity of membrane bound enzymes in rat brain regions

Ochratoxin A is a mycotoxin produced by Aspergillus ochraceus and is a natural contaminant of mouldy food. We examined the neuroactive potential of ochratoxin A by measuring the changes in the activities of several membrane bound, cytoplasmic and lysosomal enzymes in the brain of adult female rats, following subchronic application of ochratoxin A. The activities of both soluble and membrane bound fractions of ecto-5'nucleotidase, ecto-Ca2+/Mg2+ATPase, alanine aminopeptidase, gamma-glutamyl transferase, as well as activities of lactate dehydrogenase and of N-acetyl-beta-D-glucosaminidase were followed. Biochemical effects were examined in cerebral cortex, cerebellum and hippocampus. The results obtained showed physiologically significant alterations in the activity of enzymes tested. The changes were found to be time-dependent and regionally selective. Compared to controls, statistically significant increases in gamma-glutamyl transferase were observed in all three brain regions, while in the case of alanine aminopeptidase activities differed with regard to region, the highest increase being observed in hippocampus. Ecto-Ca2+/Mg2+ATPase and ecto-5'nucleotidase showed distinct changes lasting for 20 days of treatment, while increase in the activities of N-acetyl-beta-D-glucosaminidase and lactate dehydrogenase were visible only at the beginning of the treatment. By the end of the trial the activities of almost all enzymes returned back to normal values.

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.

Ochratoxin A impairs activity of the membrane bound enzymes in rat pancreas

Ochratoxin A is a mycotoxin produced by Aspergillus ochraceus and is a natural contaminant of moldly food. Ochratoxin A has a number of toxic effects, some of which may be related to the changes in the cell membrane. We measured the activities of 5 pancreatic, membrane bound enzymes in female Fisher rats that were given low oral doses of ochratoxin A (120 micrograms/kg body weight per day) during 20-35 days. The amount of toxin corresponds to 1.5 mg/kg in the feed, daily. These doses are in the range of natural contamination found in feed. The enzymes studied were alanine aminopeptidase, alkaline phosphatase, ecto-Ca2+/Mg(2+)-ATPase, gamma-glutamyl transferase and ecto-5'-nucleotidase. Treatment lasting 20 days caused a strong decrease in the activity of alanine aminopeptidase, Ca2+/Mg(2+)-ATPase and alkaline phosphatase to 0.76 +/- 0.04, 0.53 +/- 0.03 and 0.30 +/- 0.02 of the control values, respectively (p < 0.05). No significant changes in the activity of gamma-glutamyl transferase and 5'-nucleotidase were observed. However, activity of alanine aminopeptidase returned to normal values after 35 days of treatment, suggesting an adaptation of the organism, or a substitution of a released enzyme. Activities of alkaline phosphatase and Ca2+/Mg(2+)-ATPase remained significantly reduced to 0.42 +/- 0.03 and 0.52 +/- 0.04, respectively (p < 0.01). We conclude that treatment of rats with low doses of ochratoxin A resulted in reduction of the activities of the membrane bound enzymes, most probably by inducing their release, as a result of the impairment of the functional integrity of cell membranes.

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.

Sister chromatid exchange frequency in cultured isolated porcine urinary bladder epithelial cells (PUBEC) treated with ochratoxin A and alpha

The mycotoxin ochratoxin A (OTA) and its metabolite ochratoxin alpha (OT-alpha) were investigated, to examine their potency to induce sister chromatid exchanges (SCE) in cultured porcine urinary bladder epithelial cells (PUBEC) (primary culture). Serum-free cultured PUBEC were incubated for 5 h with either OTA or OT-alpha, respectively, and subsequently cultured in the presence of 5-bromo-2-deoxyuridine (BrdU). After two cell cycles, mitosis was inhibited by the colchicine derivative Colcemid, cells were fixed and chromosomes were prepared for SCE analysis. For OTA, a dose-dependent increase in SCE frequency was measured in concentrations between 100 pM and 100 nM OTA. At 100 nM OTA, SCE frequency increased by about 41%, compared to the base SCE level (7.27 SCEs per chromosome set, solvent control). Higher concentrations of OTA were cytotoxic. The metabolite OT-alpha also increased SCE frequency, but at higher concentrations. At a concentration of 10 microM OT-alpha, an increase of about 55% was detected. OT-alpha showed no cytotoxic effect. These results indicate that OTA is genotoxic in this in vitro system, which represents the urinary bladder epithelium, a target organ of OTA in vivo. It could also be shown that OT-alpha, which is said to be non-toxic, is genotoxic in this assay at higher concentrations.

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.