Bioproduction of [14C]ochratoxin A in submerged culture

Porcine/chicken or human nephropathy as the result of joint mycotoxins interaction

A survey was made of the literature concerning the occurrence and incidence of mycotoxic nephropathy in pigs and chicks in different countries. Various etiological factors contributing to the development of the disease were considered. The main nephrotoxic fungi as well as the specific conditions for their growth and toxins production were briefly described. A survey was made about the most frequent nephrotoxic fungal contaminants in various feedstuffs from plant origin. In addition, their natural quantities and importance for development of mycotoxic porcine/chick nephropathy (MPN/MCN) are also explored. In addition, a survey was made of the feedstuffs representing the most favorable environment for nephrotoxic fungal growth as well as the most favorable storehouse conditions for this fungal growth were shortly described. The significance of some underestimated fungal species, which can provoke kidney damage, was studied. The importance of joint mycotoxin interaction and newly identified fungal metabolites in the complex etiology of mycotoxic nephropathy ranged in some countries is deeply investigated. The toxicity of the low contamination levels of some combinations of mycotoxins often administered by pigs and chicks in the practice was carefully studied.

Production of(14)C-ochratoxin A byPenicillium verrucosum sp. 1761 in liquid culture

The synthesis of(14)C-labelled ochratoxin A was carried out by biosynthesis withPénicillium verrucosum sp. 1761 in liquid culture using 2-(14)C-Na-acetate and 2-(14)C-malonic acid as precursor. The largest amount of ochratoxin A produced byPénicillium verrucosum was detected in a minimal medium after an incubation period of 28 days. By addition of citric acid and 2,4-dichlorophenoxy acetic acid larger ochratoxin A contents could be measured. For transformation studies of ochratoxin A, a molecule which is exclusively labelled in the isocoumarin moiety is best suitable. This labelling could be obtained by using labelled malonic acid as precursor, whereas with 2-(14)C-Na-acetate as precursor the whole molecule was labelled. Incorporation rates of radioactivity into the molecule were from 0.04% to 0.11%, specific radioactivities from 0.02 μCi/mg to 0.07 μCi/mg.

Ochratoxin A biosynthetic genes in Aspergillus ochraceus are differentially regulated by pH and nutritional stimuli

Expression of the polyketide synthase (pks) gene which is involved in ochratoxin A (OTA) biosynthesis in Aspergillus ochraceus is linked to production of the mycotoxin, with high levels of pks mRNA accumulation occurring in cultures producing OTA, as assessed by real-time reverse transcription (RT)-PCR. OTA production is regulated by nutrient availability, with supplementation of OTA restrictive potato dextrose broth with yeast extract resulting in a 39-fold increase in production of the mycotoxin. This effect appears to be mediated at the level of gene transcription as there is a concomitant increase in pks mRNA accumulation. OTA production is also strongly influenced by culture pH with large amounts of OTA being produced at pH values <7.0 with reduced amounts being produced at higher pH values. pks transcript levels again mirrored the OTA production profile observed at the different pH values. The transcription of two putative p450 type monooxygenase genes, namely p450-H11 and p450-B03 genes closely mirrored that of the pks gene under all growth conditions tested, suggesting their involvement together with the pks in OTA biosynthesis. The expression profile of the p450-B03 gene in particular is very similar to that of the pks gene, indicating that this gene may be clustered with the pks as part of the OTA biosynthetic gene cluster.

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.

Biosynthesis of ochratoxins by Aspergillus ochraceus

Shaken liquid fermentation of an isolate of Aspergillus ochraceus showed growth-associated production of ochratoxins A and B, followed by production of a related polyketide diaporthin. Later, between 150 and 250 h, mellein accumulated transitorily. In contrast, shaken solid substrate (shredded wheat) fermentation over 14 days produced mainly ochratoxins A and B (ratio ca. 5:1) in very high yield (up to 10 mg/g). In these systems experiments with 14C-labelled precursors and putative intermediates revealed temporal separation of early and late stages of the ochratoxin biosynthetic pathway, but did not support an intermediary role for mellein. The pentaketide intermediate ochratoxin beta was biotransformed very efficiently into both ochratoxins A and B, 14 and 19%, respectively. The already chlorinated ochratoxin alpha was only biotransformed significantly (4.85%) into ochratoxin A, indicating that chlorination is mainly a penultimate biosynthetic step in the biosynthesis of ochratoxin A. This was supported by poor (1.5%) conversion of radiolabelled ochratoxin B into ochratoxin A. Experiments implied that some ochratoxin B may arise by dechlorination of ochratoxin A.

Tissue distribution of radioactivity from ochratoxin A-14C in rats

Examination of the distribution of radioactivity in rat tissues during the first 24 hr after administration of ochratoxin A-14C demonstrated maximum accumulation in stomach and kidney. The highest counts were observed in stomach, lung, kidney, thymus, spleen and heart during the first 6 hr after treatment, whereas the brain, liver muscle, duodenum, jejunum, ileum, and cecum exhibited the greatest counts at 18 hr after toxin exposure.