Experimental ochratoxicosis A in pigs

New Evidences about the Carcinogenic Effects of Ochratoxin A and Possible Prevention by Target Feed Additives

A review of the carcinogenic effects of ochratoxin A (OTA) on various tissues and internal organs in laboratory and farm animals is made. Suggestions are made regarding how to recognize and differentiate the common spontaneous neoplastic changes characteristic for advanced age and the characteristic neoplasia in different tissues and organs in laboratory animals/poultry exposed to OTA. The synergistic effects of OTA together with its natural combination of penicillic acid are also investigated regarding possible carcinogenic effects. The malignancy and the target location of OTA-induced neoplasia is studied. The sex-differences of such neoplasia are investigated in the available literature. The time of appearance of the first neoplasia is investigated in long-term carcinogenic studies with OTA-treated animals. The possibility of target feed additives or herbs to counteract the toxic and carcinogenic effects of OTA is studied in the available literature. Some effective manners of prophylaxis and/or prevention against OTA contamination of feedstuffs/foods or animal production are suggested. The suitability of various laboratory animals to serve as experimental model for humans with regard to OTA-induced tumorigenesis is investigated.

Follow up long term preliminary studies on carcinogenic and toxic effects of ochratoxin A in rats and the putative protection of phenylalanine

Carcinogenic effects of ochratoxin A (OTA) on liver, kidneys, intestine, lung and eyes of Wistar rats exposed to 10 ppm or 5 ppm OTA in the diet and additionally supplemented or not with phenylalanine (PHE) were examined during 24-months experimental period. OTA was seen to provoke strong degenerative changes and slight pericapillary oedema in most internal organs, e.g. kidneys, liver, intestine, spleen and brain. Six of total nine neoplasms were identified as malignant and three as benign. Five of total six malignant neoplasms and two of total three benign neoplasms were seen in male rats. The pathological finding in rats after two weeks feeding with OTA-contaminated feed was dominated by degenerative changes in various internal organs, which were weaker in the group additionally supplemented with PHE. The protective effect of PHE was evident with respect to OTA-induced decrease of serum glucose and serum protein, but this protection was not singnificant with respect to serum enzymes activity. The number of neoplasms in PHE-supplemented group exposed to 10 ppm OTA was similar to that in the group exposed to twice lower feed levels of OTA alone, suggesting about a possible protective effect of PHE. The rats would not be able to serve as experimental model for humans with regard to OTA-induced tumorigenesis, because the target organ of OTA-toxicity in humans and pigs is mainly the kidney as opposed to the significant damages and carcinogenic effects seen in various organs in rats exposed to OTA.

Mass spectrometry-based abundance atlas of ABC transporters in human liver, gut, kidney, brain and skin

ABC transporters (ATP-binding cassette transporter) traffic drugs and their metabolites across membranes, making ABC transporter expression levels a key factor regulating local drug concentrations in different tissues and individuals. Yet, quantification of ABC transporters remains challenging because they are large and low-abundance transmembrane proteins. Here, we analysed 200 samples of crude and membrane-enriched fractions from human liver, kidney, intestine, brain microvessels and skin, by label-free quantitative mass spectrometry. We identified 32 (out of 48) ABC transporters: ABCD3 was the most abundant in liver, whereas ABCA8, ABCB2/TAP1 and ABCE1 were detected in all tissues. Interestingly, this atlas unveiled that ABCB2/TAP1 may have TAP2-independent functions in the brain and that biliary atresia (BA) and control livers have quite different ABC transporter profiles. We propose that meaningful biological information can be derived from a direct comparison of these data sets.

Selected herbal feed additives showing protective effects against ochratoxin A toxicosis in broiler chicks

The protective effects of herbal feed additives Silybum marianum, Withania somnifera and Centella asiatica against the toxic effects of ochratoxin A (OTA) were studied in 70 broiler chicks aged from 11 to 42 days. OTA was given with the feed at levels 5 mg/kg, whereas S. marianum, W. somnifera and C. asiatica were given at levels of 1,100, 4,000 and 4,600 mg/kg, respectively. All chicks were immunised at the age of 14 days against Newcastle disease. A protective effect of all studied herbal additives against the immunosuppressive effect of OTA and associated biochemical or pathomorphological changes was seen. The intensity of macroscopical and histopathological changes, the deviations in relative organs’ weight or body weight, the biochemical changes and the decrease of antibody titer were strongest in the OTA-exposed chicks without herbal supplementation; followed by chicks treated additionally with C. asiatica, whereas the same changes were significantly slighter or not seen in chicks additionally treated with the herbal additives W. somnifera or S. marianum. The slight increase in the serum levels of uric acid and the enzyme activity of aspartate transaminase and alanine transaminase also supported the protective effects of both herbs on the kidneys and/or liver. The strong immunosuppressive effect of OTA on humoral immune response against Newcastle disease was completely prevented in the chicks taking the herbal additives W. somnifera or S. marianum, which was supported by the higher relative weight of immunocompetent (lymphoid) organs in the same chicks. A hepatoprotective effect was found in OTA-exposed chicks treated additionally with W. somnifera and S. marianum, whereas a nephroprotective effect was only found in the chicks additionally treated with S. marianum as observed from the biochemical and pathomorphological findings. The same herbs could be used as a practical approach for safely utilising of OTA-contaminated feed.

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

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

Xenobiotic transporters and kidney injury

Renal proximal tubules are targets for toxicity due in part to the expression of transporters that mediate the secretion and reabsorption of xenobiotics. Alterations in transporter expression and/or function can enhance the accumulation of toxicants and sensitize the kidneys to injury. This can be observed when xenobiotic uptake by carrier proteins is increased or efflux of toxicants and their metabolites is reduced. Nephrotoxic chemicals include environmental contaminants (halogenated hydrocarbon solvents, the herbicide paraquat, the fungal toxin ochratoxin, and heavy metals) as well as pharmaceuticals (certain beta-lactam antibiotics, antiviral drugs, and chemotherapeutic drugs). This review explores the mechanisms by which transporters mediate the entry and exit of toxicants from renal tubule cells and influence the degree of kidney injury. Delineating how transport proteins regulate the renal accumulation of toxicants is critical for understanding the likelihood of nephrotoxicity resulting from competition for excretion or genetic polymorphisms that affect transporter function.

The effects of orchidectomy on toxicological responses to dietary ochratoxin A in Wistar rats

Ochratoxin A (OTA) causes pathological lesions in the organs of animals. Males are more sensitive to OTA exposure than females but the reasons for this are unknown. The objective of this study was to explore the role of testosterone in male rats with OTA-related pathogenesis. To test the effect of testosterone on OTA toxicity, the testes of a group of rats were surgically removed. Male and female rats (approximately 300 and 200 g) were fed with OTA-contaminated feed (initially approximately 300 μg kg(-1) b.w. per day) for 24 weeks. The organs of all the animals were collected and their organ lesion pathology, caspase-3 expression, OTA plasma and organ concentrations and total plasma testosterone concentrations were evaluated. OTA treatment created serious lesions in the kidney, liver and testes of rats. The major histopathological changes in the kidney and liver were karyomegaly, hemorrhages and vacuolization. In the testes, there was a marked decrease in the amount of spermatozoon. The degrees of organ lesion were evaluated and the castrated males had the lowest kidney and liver lesion scores, indicating that testosterone reduction in males dramatically reduces OTA-related organ damage. The plasma OTA levels for the intact males, the castrated and the females were 6.34, 8.42 and 12.5 μg ml(-1), respectively. In conclusion, despite the similar plasma OTA levels of the intact and castrated males, OTA is less toxic in the castrated males. Therefore, the well-known gender specific toxicity of OTA seems to be related to the testosterone levels of rats.

Effects of ochratoxin a on livestock production

Ochratoxin A (OTA) contamination often causes large economic losses on livestock production. The intake of feed contaminated by OTA also represents a potential risk for animal health and a food safety issue due to the transfer of the toxin through the food chain to humans. The aim of this paper is to review the available literature on: (1) the frequency and degree of occurrence of OTA in different feedstuffs; (2) the toxicological effects of OTA intake on the performance of the main livestock (i.e., poultry, swine, cattle, goats and sheep); and (3) the transfer of OTA, or its metabolites, from animal feed into animal products such as milk, meat and eggs.

Studies on carcinogenic and toxic effects of ochratoxin A in chicks

Carcinogenic/toxic effects of ochratoxin A (OTA) in various internal organs of Plymouth Rock chicks were determined. The number of OTA-induced neoplasms was similar in chicks given 25 ppm L-β-phenylalanine (PHE) in addition to 5 ppm OTA compared to chicks given only 5 ppm OTA, which showed that PHE cannot be used as a real protector against the carcinogenic or toxic effects of OTA in chicks. OTA was found to provoke strong degenerative changes in liver and kidneys, degenerative changes and depletion of cells in lymphoid organs, oedematous and degenerative changes in the brain, muscular haemorrhages and fatty changes in the bone marrow. The target organs for carcinogenic effect of OTA in chicks were found to be kidneys and liver.

Nutritive value and non-toxicity of Botryosphaeria zeae-infected wheat for weaner pigs

A novel fungal infection of wheat by Botryosphaeria zeae was identified on the Darling Downs of Queensland, Australia and called 'white grain' because of its bleached appearance. The only nutritional changes in the wheat grain infected with B. zeae were decreases in nitrogen and total amino acids (approximately 5%), and slight increases in the lysine, fibre and fat content, with starch unaffected. Nutrient digestibility and potential toxicity were assessed in weaner pigs housed in metabolism crates and fed this grain over a 4-week period, as they grew from 15 to 35 kg. Digestibility of energy and nitrogen in white grain was not different from that of normal wheat. The piglets were then bled for biochemical and haematological testing, slaughtered and the entire viscera subjected to gross pathological inspection, followed by histological examination of the liver, kidney, pancreas, spleen, heart, lung, muscle and intestine. White grain did not affect palatability of diets, pig growth rates; no abnormalities were detected in tissues, while biochemical and haematological parameters did not suggest any toxic effect. Hence, wheat with white grain appears suitable for use in pig diets, but the use of this wheat for human food should be restricted until additional longer term studies are conducted.

Studies on some feed additives and materials giving partial protection against the suppressive effect of ochratoxin A on egg production of laying hens

The protective effects of various feed supplements against the harmful effect of ochratoxin A on egg production and sexual maturation of two-weeks old Plymouth Rock female chicks designed for laying hens were studied. A significant protective effect of the feed additives or materials: water extract of artichoke (WEA), sesame seed (SS), Roxazyme-G (RG) and l-beta phenylalanine (PHE) against the suppressive effect of ochratoxin A (OTA) on egg production of laying hens was found. A similar protection was also seen on the toxic effect of OTA on various internal organs of the same hens. A significant protection was found against the decrease of the weight or the quantity of eggs as well as against the delay of the beginning of the laying period of chicks, both of which were provoked by ochratoxin A. These protective effects were strongest in chicks treated with SS or WEA, but were slightest in chicks treated with l-beta PHE.

Effectiveness of mycotoxin sequestration activity of micronized wheat fibres on distribution of ochratoxin A in plasma, liver and kidney of piglets fed a naturally contaminated diet

A study was carried out to determine the ability of dietary micronized wheat fibres (MWF) to decrease the levels of ochratoxin A (OTA) in plasma, kidney and liver of piglets fed a naturally contaminated diet. A total of 96 piglets (weighting 11.4+/-1.5 kg) were fed one of four different diets for 28 days. Diets included (1) control diet, (2) control diet with MWF (1%), (3) OTA naturally contaminated diet (117.45+/-4.74 ng/g), (4) OTA naturally contaminated diet (118.13+/-2.85 ng/g) with MWF (1%). No difference in feed efficiency (P>0.05) could be observed between the different diets. The absolute weight of kidneys and liver were significantly higher in pigs fed the OTA-contaminated diet (diet 3) as compared to the control diet (diet 1) or to the control diet amended with MWF (diet 2) (P<0.05). However the use of MWF (diet 4) significantly protected against these weight changes. A significant protective effect of MWF was also observed in terms of OTA concentration in plasma (45.6% decrease), kidney (40.8% decrease) and liver (26.5% decrease). These results suggest that the addition of MWF is effective in decreasing the bioavailability of OTA from contaminated diets in piglets.

Experimental coccidiosis provoked by Eimeria acervulina in chicks simultaneously fed on ochratoxin A contaminated diet

The progression of coccidiosis provoked by Eimeria acervulina was followed in chicks fed on OTA-contaminated as well as on OTA-free diets. More heavy progress of duodenal coccidiosis, including mortality, occurred in OTA-treated chicks as can be seen from the higher value of lesion (3.50) and oocyst (31.65) indices. A stronger decrease of serum total protein was found in OTA-treated chicks (22.80 g/l) than in chicks infected with E. acervulina(24.20 g/l), but that decrease was strongest in chicks treated with OTA and simultaneously infected with E. acervulina (19.71 g/l). The serum concentration of uric acid was significantly increased in all chicks exposed to OTA, most notably in those additionally infected with E. acervulina (1020.6 (micro mol/L), whereas the serum enzyme activity of AST was increased only in chicks infected with E. acervulina and highest in those fed OTA contaminated diet (122.2 U/L). OTA induced degenerative changes in kidneys, liver and heart as well as a depletion of lymphoid tissue in the lymphoid organs and a decrease of body weight. Coccidiosis induced only a slight growth depression and duodenal hemorrhages in addition to characteristic duodenal damages. The impairment of kidney function, histopathological changes and general growth depression were stronger when chicks infected with E. acervulina were also given OTA.

Alkalinization of urinary pH accelerates renal excretion of ochratoxin A in pigs

The mycotoxin ochratoxin A (OA) is a cause of endemic nephropathy in farm animals and humans. Reabsorption of OA along the nephron results from nonionic diffusion and by carrier-mediated mechanisms, indicating that urine alkalinization may help to accelerate OA excretion and thus reduce its toxicity. The aim of the present study was to investigate the effect of a dietary sodium bicarbonate supplementation as a means of increasing urinary pH on the systemic availability and excretion of OA in pigs. Dietary supplementation of 2% sodium bicarbonate significantly increased urinary pH (5.7 +/- 0.2 to 8.3 +/- 0.1) and daily urine volume (1108 +/- 276 to 2479 +/- 912 mL). The systemic availability of OA and its dechloro-analog, Ochratoxin B (OB), calculated as the area under the curve (AUC) was reduced to 75 and 68%, respectively, of the control group (P < 0.05). This effect was due mainly to an accelerated elimination of OA and OB in the urine. The faster renal elimination may be due to reduced reabsorption of the ochratoxins by nonionic diffusion, and other H(+)-dependent mechanisms. Thus, urinary alkalinization may be an efficient means to partially reduce the toxic effects of OA in pigs.

Studies on some feed additives giving partial protection against ochratoxin A toxicity in chicks

Significant protective effects of the feed additives: water extract of artichoke, sesame seed, Roxazyme-G and L-beta phenylalanine against the growth inhibitory effect of ochratoxin A (OTA) and associated pathomorphological changes were seen. Similarly, there was less OTA-induced decrease in serum total protein and increase of serum creatinine and urea in the chicks. Whereas OTA induced strong degenerative changes and an increase in weight of kidneys and liver as well as a decrease of the weight of lymphoid organs the additives variously gave protection against these changes. The protection of Roxazyme-G and sesame seed was better expressed in kidneys and liver, whereas the phenylalanine better protected the weight changes in gizzard, heart and the changes in differential WBC count. Notably, sesame seed gave strong protection against 5 ppm OTA-induced suppression of humoral immune response, for which artichoke also had some beneficial effect, whereas phenylalanine had hardly any effect.

Clinicomorphological studies in chicks fed ochratoxin A while simultaneously developing coccidiosis

The progression of coccidiosis and the resultant mortality were followed in chicks fed a OTA-contaminated diet. More complex and rapid progress of coccidiosis occurred in OTA-treated chicks than in chicks fed a OTA-free diet. The concentration of total protein in the serum was significantly decreased in the chicks in the OTA-treated group, whereas this was significantly increased in chicks infected with Eimeria tenella, irrespective of additional treatment with OTA. The serum glucose concentration was significantly increased in all the chicks exposed to OTA and/or suffering from coccidiosis, as was serum retention of uric acid in all groups, most notably in those consuming OTA. OTA induced degenerative changes in, and an increase in the weight of the kidneys, liver, heart and ventriculum; there was depletion of lymphoid tissue and a decrease in the lymphoid organs' weight and body weight. Coccidiosis induced only a slight growth depression and a slight increase in the relative weight of the kidneys and liver. The intensity of the clinical signs, the impairment of kidney function, macroscopic and histopathological changes, deviations in the weight of some organs and general depression in growth were greater when chicks infected with E. tenella were also given OTA.

Experimental one year ochratoxin A toxicosis in pigs

Mild mycotoxic nephropathy was induced in 6 pigs by a diet containing ochratoxin A at 800 ppb, several times higher than that naturally encountered in some feed for pig production in Bulgaria. The nephropathy was expressed only as slightly hypertrophied kidneys with a faintly mottled surface, discernible at the end of the experiment to a skilled observer but probably not recognisable in routine slaughterhouse processing. Histological examination showed two types of changes: degenerative - affecting epithelial cells in some proximal tubules of pigs after 6 months, and proliferative changes in the interstitium which predominated after 1 year of exposure to ochratoxin A. Telangiectasis and lymph stasis were rarely seen. The renal lesions were similar to those described for classical mycotoxic porcine nephropathy formerly encountered in Denmark, but they were rather different from the porcine nephropathy which occurs spontaneously in Bulgaria. Measurement of ochratoxin A in serum provided analytical values complementary to feed intake and with similar concentration values. It also showed both accumulation with time, from 3 months to 6 months (approximately 1 ppm), and a 2-fold range of values within a group eating from a common feed source, as in commercial pig production. Mild symptomatology in this long, single-mycotoxin experiment serves to lessen somewhat the current perception of the direct renal toxicity of ochratoxin A alone, though a role in multi-toxin contexts is unquestioned.

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.

Biosynthesis of diaporthin and orthosporin by Aspergillus ochraceus

Diaporthin and orthosporin were characterised from the fungus Aspergillus ochraceus D2306. Diaporthin was identified by high-resolution electron impact mass spectrometry and 1H and 13C NMR spectroscopy, from which new spectroscopic assignments were made. Orthosporin was also identified by mass spectrometry and both fungal metabolites are reported for the first time as co-metabolites and also as products of A. ochraceus. The methylation inhibitor ethionine affected production of both diaporthin and orthosporin in spite of no obvious methylation step in the biosynthesis of orthosporin, implying that extracellular orthosporin may arise by de-O-methylation of diaporthin. The biosynthetic origin of diaporthin was demonstrated by incorporation of [1-14C]acetate and [methyl-14C]methionine administered in early idiophase.

Susceptibility to secondary bacterial infections in growing pigs as an early response in ochratoxicosis

Mycotoxic nephropathy was induced in twelve 14 kg pigs fed a dietary component, moulded by Aspergillus ochraceus and contributing ochratoxin A at 1 or 3 ppm for up to 3 weeks. Concurrently, salmonellosis arose spontaneously in all six animals treated at 3 ppm and all died between days 15 and 17. Two of the six pigs in the 1 ppm group died similarly but the rest, and all of six control animals, were unaffected. Clinical biochemistry and histology revealed changes typical of renal ochratoxicosis in all ochratoxin-treated pigs. Clinical and pathomorphological changes typical of salmonellosis were evident in all those that died and Salmonella choleraesuis was consistently isolated from their faeces and liver. In a further experiment at 1 ppm ochratoxin A in animals immunised against S. choleraesuis haemorrhagic diarrhoea resulted instead, associated with Serpulina hyodysenteriae and Campylobacter coli. There was concomitant evidence of immunosuppression and delayed response to immunization. For the first time, susceptibility to natural infectious disease has been demonstrated in pigs exposed to the immunotoxicity of ochratoxin A. Differentiation of biochemical and histological changes attributable to ochratoxicosis or to secondary disease may require reinterpretation of a classical description of experimental porcine ochratoxicosis.

Ochratoxin formation in Aspergillus ochraceus with particular reference to spoilage of coffee

Production of ochratoxin on media by eight isolates of Aspergillus ochraceus from coffee or its processing environment in India, Indonesia, Kenya, and Brazil, and seven Brazilian isolates from other commodities, has been compared with yields in shaken fermentation on shredded wheat and coffee (Coffea arabica). Shredded wheat most consistently allowed expression of biosynthesis of ochratoxins A and B in yields up to 3.5% of the dry product. Culture on artificial media was an unreliable predictor of ochratoxin yield on both shredded wheat and coffee. Coffee was a relatively poor substrate for ochratoxin production particularly when sterilised. Notably, two Asian coffee isolates produced 400 mg kg(-1) ochratoxin A on unsterilised ground green coffee, showing this to be a preferred substrate for further experimentation. The study focused on isolates of A. ochraceus, which from evidence of culture on media would not be expected to be suitable fungi for future studies to establish both the fact of spoilage of coffee by A. ochraceus and the dynamics of ochratoxin formation by isolates of this species.

Influence of halogen salts on the production of the ochratoxins by Aspergillus ochraceus Wilh

The first report of the biological production of bromo ochratoxin B by Aspergillus ochraceus Wilh. is presented as well as a study of the influence of potassium bromide, potassium iodide, potassium fluoride, and potassium chloride on the production of ochratoxin A and ochratoxin B. Potassium fluoride and potassium iodide inhibited the growth of the fungus, whereas potassium chloride substantially stimulated the production of ochratoxin A in shaken solid substrate fermentation on whole wheat or shredded wheat, generally giving a high yield of ochratoxins. Increasing levels of potassium bromide led to a decline in ochratoxin A production and an increase in bromo-ochratoxin B, ochratoxin B, and 4-hydroxy ochratoxin B. Nevertheless, A. ochraceus was much less versatile in the bromo analogues than other fungi, which produce metabolites containing chlorine. Analysis included aminopropyl solid-phase extraction column cleanup followed by quantitative analysis on reversed-phase HPLC using fluorescence detection and employing N-(5-chloro-2-hydroxybenzoyl)phenylalanine as an internal standard.

Ochratoxin A secretion in primary cultures of rabbit renal proximal tubule cells

Primary cultures of rabbit renal proximal tubule cells grown under improved culture conditions were used to study the transepithelial transport of the nephrotoxic mycotoxin ochratoxin A. The basal-to-apical transepithelial flux, i.e., secretion, of this fluorescence organic acid was measured in primary cultures of rabbit renal proximal tubule cells. The basal-to-apical flux of ochratoxin A increased with time and reached a steady state after 12 h. On the other hand, the apical-to-basal flux, i.e., reabsorption, of ochratoxin A was minimal over time. The secretory flux of ochratoxin A was as much as eightfold greater than the reabsorptive flux, indicating that net secretion is the primary mechanism for ochratoxin A clearance by the proximal tubule. The kinetic analysis of ochratoxin A flux revealed secretion to be a saturable and very high-affinity process with an apparent K50 of 0.33 +/- 0.21 mM. A saturating concentration of the prototypical organic anion substrate para-aminohippurate (PAH) reduced ochratoxin A secretion by approximately 75%. The kinetic analysis of PAH inhibition of ochratoxin A secretion revealed an IC50 of 195 mM, which is similar to the IC50 for PAH inhibition of peritubular ochratoxin A uptake in tubule suspensions and the Km, values for peritubular PAH uptake. The organic anions probenecid, octanoate, and alpha-ketoglutarate reduced ochratoxin A excretion to the same degree as PAH, whereas the amino acid phenylalanine had a minimal effect on ochratoxin A secretion. Thus, collectively, these observations indicate that the secretion of ochratoxin A in primary cultures of rabbit renal proximal tubules is limited to the organic anion secretory pathway. The high affinity measured for the basal-to-apical flux of ochratoxin A suggests that at concentrations typical of naturally occurring exposures, transepithelial secretion by the organic anion transport pathway represents a significant avenue for excretion of this mycotoxin by the renal proximal tubule.

Porcine nephropathy in Bulgaria: a progressive syndrome of complex or uncertain (mycotoxin) aetiology

Macroscopic nephropathy was observed in 506 pigs at slaughter in Bulgaria in 1993/94. Histopathological changes were mainly degenerative and proliferative, and were linked with kidney hypertrophy similar to that of the classical Danish Syndrome. Retention cysts formed by dilated tubules, activation or proliferation of capillary and vascular endothelium, and the development of neoplastic tissue were also observed. The most advanced pathology took the form of extensive interstitial fibrosis. Traces of ochratoxin A were found in the kidneys of the majority of 96 cases examined, and in some feed samples taken retrospectively from farms or commercial sources. The dietary ochratoxin concentration (100 micrograms/kg), calculated from serum analyses, closely matched the average of individually analysed feeds. In other feeds no ochratoxin A was detected and the cosmopolitan mycobiota isolated did not include the ochratoxinogenic Penicillium verrucosum that caused the Danish syndrome. Aspergillus ochraceus was rare and the isolates did not synthesise ochratoxin in laboratory culture. The unconfirmed diagnosis of ochratoxicosis suggests a complex or multi-toxin aetiology for this rather common chronic disease in Bulgaria.

Ochratoxin A impairs "postproximal" nephron function in vivo and blocks plasma membrane anion conductance in Madin-Darby canine kidney cells in vitro

Ochratoxin A (OTA) is a widespread nephrotoxin which causes porcine nephropathy and is supposed to have caused the human Balkan endemic nephropathy. We performed experiments in vivo and in vitro to elucidate the mechanism of OTA action in renal epithelium. Application of OTA to male Wistar rats [1.25 mumol/(kg.day)] for 6 days led to a reduction of glomerular filtration rate (to 63% of control), an increased fractional water (194% of control), Na+ (199% of control), K+ (147% of control) and Cl- (270% of control) excretion and an increased dependence of the osmole clearance on urine flow. Acute application of OTA to rats (3 mumol/kg) increased urinary pH from 6.0 +/- 0.2 to 6.6 +/- 0.1 and urinary NaCl excretion, but decreased titratable acid excretion to 47% of control. As these in vivo findings may be the result of an action of OTA beyond the proximal tubule ("postproximal") we investigated the effect of OTA on cultured Madin-Darby canine kidney (MDCK) cells, regarded as a model of collecting duct epithelium. In confluent monolayers formed by MDCK cells OTA reduced the number of domes in a dose-dependent manner and impaired the formation of a transepithelial Cl- gradient. Electrophysiological measurements in giant MDCK cells revealed that OTA blocks fractional anion conductance of the plasma membrane with an IC50 value of 30 +/- 5 nmol/l, unmasking OTA as a naturally occurring anion conductance blocker about 20-times more effective than the most potent synthetic blocker 5-nitro-2-(3-phenylpropyl-amino) benzoic acid (NPPB) (IC50 = 600 +/- 50 nmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunosuppression due to chronic ochratoxicosis in broiler chicks

Crystalline ochratoxin A (OA) was added to the feed of broiler chicks at 0.5 ppm and 2.0 ppm, and humoral and cell-mediated immunity (CMI) were studied. CMI was assessed by skin sensitivity testing, graft versus host (GVH) reaction and T lymphocyte count. Humoral immunity was examined by measuring the haemagglutinin (HA) response to sheep RBC (SRBC). In addition, total lymphocyte counts, total serum protein, albumin and globulin were determined and the phagocytic activity of splenic macrophages was measured in the nitroblue tetrazolium test (NBT). The weights of lymphoid organs were also recorded at post-mortem examination of the birds. Highly significant reductions in CMI were indicated by diminished skin sensitivity, GVH reactions and T lymphocyte counts. On the other hand, only the overall HA titres differed significantly between the various treatment groups. Total lymphocyte counts, total serum protein, serum albumin and serum globulin were significantly depressed on the 21st day of intoxication. The number of NBT-positive cells was drastically reduced in both the intoxicated groups compared with controls (P less than 0.05) and the weights of thymus, bursa of Fabricius and spleen of intoxicated birds were significantly reduced. The study illustrated the immunosuppressive effects of ochratoxicosis in broiler chicks.

Ochratoxinogenicity of Aspergillus ochraceus strains from nephropathic and non-nephropathic areas in Yugoslavia

Mycological analyses of 855 samples of stored grains and dried meat collected in period 1980-1987 from individual households in the nephropathic and wider non-nephropathic area in SR Croatia in Yugoslavia showed 10% of samples to be contaminated with Aspergillus ochraceus. Ability to produce ochratoxin A (OA) was tested in 70 samples (27 from nephropathic areas and 43 from non-nephropathic areas). The detection was carried out under UV-light (365 nm) (light blue fluorescence) and 6 OA-producers were found. A biosynthetic procedure on liquid nutritional substrate with saccharose and yeast extract as well as a method using wet crushed wheat revealed that 37% of the samples from a nephropathic area, and 35% of the samples from a non-nephropathic area produce OA. In the nephropathic area 1/10 strains was a strong producer of OA (concentration crushed wheat 135 mg/kg, and 240 mg/l on YES liquid substrate), 1/10 strains was a moderate producer (concentration 16.6 mg/l and 0.07-7.0 mg/l and 0.1-10.4 mg/kg). Among the strains isolated from a wider non-nephropathic area no strong producers of OA were found, but 2/15 strains were moderate producers of OA (concentration of OA 20.4-27.0 mg/l and 15.0-33.7 mg/kg). The other strains, 8/10 on the crushed wheat and 13/15 on the liquid substrate, were weak producers of OA with concentrations of OA between 0.2-9.0 mg/l and 0.2-10.0 mg/kg with the two methods respectively.

Experimental combined aflatoxin B1 and ochratoxin A intoxication in pigs

Twenty-one pigs weighing approximately 18 kg were placed in 7 groups of 3 and given diets containing respectively aflatoxin B1 alone at 0.375 and 0.0750 mg/kg, ochratoxin A alone at 1 and 2 mg/kg, 0.375 mg/kg of aflatoxin B1 plus 1 mg/kg of ochratoxin A and 0.750 mg/kg aflatoxin B1 and 2 mg/kg of ochratoxin A. The remaining group served as untreated control. At the respective dose levels, pigs receiving similar doses of ochratoxin A alone or in combination with aflatoxin B1, were similarly affected, the clinical effects of aflatoxin having been mostly obscured by those due to ochratoxin A. Mild degenerative hepatic changes typical of aflatoxicosis were observed in pigs fed this toxin alone or in combination with ochratoxin A. In kidneys of pigs fed diet containing 1 and 2 mg of ochratoxin A alone changes included interstitial fibrosis of the vortex and dystrophy and degeneration of the tubular epithelium. Similar lesions but less pronounced fibrosis were found in kidneys of pigs receiving both toxins. The respective lower dose levels of mycotoxins selected were judged to be about the no-effect levels for each dosed separately under the conditions of the trial. Such levels have been found not infrequently on mould affected grain and stock foods. The result highlights the difficulties that may be experienced in the recognition of such multimycotoxicoses as they are likely to occur in the field and indicate the need for toxicological analysis as well as pathological investigation in establishing a diagnosis.