Feeding Experiments with Ochratoxin a Contaminated Barley for Bacon Pigs

A review of the diagnosis and treatment of Ochratoxin A inhalational exposure associated with human illness and kidney disease including focal segmental glomerulosclerosis

Ochratoxin A (OTA) exposure via ingestion and inhalation has been described in the literature to cause kidney disease in both animals and humans. This paper reviews Ochratoxin A and its relationship to human health and kidney disease with a focus on a possible association with focal segmental glomerulosclerosis (FSGS) in humans. Prevention and treatment strategies for OTA-induced illness are also discussed, including cholestyramine, a bile-acid-binding resin used as a sequestrant to reduce the enterohepatic recirculation of OTA.

Enzyme-assisted extraction for the HPLC determination of ochratoxin A in pork and dry-cured ham

The extraction of ochratoxin A from meat products is generally carried out using chlorinated organic solvents, such as chloroform or methyl chloride, acidified with hydrochloric or o-phosphoric acid. In this study, an innovative method was developed to extract ochratoxin A from pork and dry-cured ham samples. The method was based on an enzyme-assisted extraction with pancreatin in phosphate buffer pH 7.5. Pancreatin hydrolyses the proteins, so that ochratoxin A, kept in the ionised form, is easily extracted by the aqueous solution. After purification through an immunoaffinity column, ochratoxin A is determined by HPLC with fluorescence detection. The average recovery values were higher than 90.0% and the relative standard deviations were below 5.5%. The limits of detection and of quantification were 0.06 and 0.12 µg kg(-1), respectively. A comparison between the new enzyme-assisted extraction and an established chloroform method was carried out on six naturally contaminated samples of pork and on 40 samples of dry-cured ham. Significantly higher (p<0.001) values of ochratoxin A were obtained on dry-cured ham samples by the enzyme-assisted method.

Ochratoxin A in ruminants−A review on its degradation by gut microbes and effects on animals

Ruminants are much less sensitive to ochratoxin A (OTA) than non-ruminants. The ruminal microbes, with protozoa being a central group, degrade the mycotoxin extensively, with disappearance half lives of 0.6–3.8 h. However, in some studies OTA was detected systemically when using sensitive analytical methods, probably due to some rumen bypass at proportions of estimated 2–6.5% of dosage (maximum 10%). High concentrate proportions and high feeding levels are dietary factors promoting the likeliness of systemic occurrence due to factors like shifts in microbial population and higher contamination potential. Among risk scenarios for ruminants, chronic intoxication represents the most relevant.

Occurrence of ochratoxin A and heavy metals in tissues associated with porcine nephropathy in Serbia

In order to find information on the occurrence of mycotoxic porcine nephropathy in Serbia, during a six month period (2006/2007) samples of blood, kidney and liver from individual animals were collected from healthy slaughtered pigs (n=90) and analysed by HPLC for ochratoxin A (OTA). In addition, the presence of nephrotoxic heavy metals such as cadmium, lead, mercury and arsenic were measured and the kidneys pathohistologically examined. Of the 90 liver samples, 26.6% contained OTA in the range of 0.22-14.5 ng/g. The incidence of OTA in serum and kidney were very similar (30 and 31.1%), but varied between 0.24-220.8 ng/ml and 0.17-52.5 ng/g, respectively. The presence of mercury was confirmed in 33.3% of kidney samples and concentrations ranged between 0.005-0.055 mg/kg, while cadmium was found less frequently (27.7% positive samples) but at higher levels (0.05-1.23 mg/kg). The presence of arsenic was found in only one sample, while lead was not detected in any sample. Histopathological examination of kidneys confirmed tubulopathies with oedema and cell vacuolisation. In addition, haemorrhages and necrosis of proximal kidney tubules' cells were found. These findings indicate that it is likely that most of the kidney injury is related to OTA and other nephrotoxic compounds which enhance the toxicity of OTA.

Screening and confirmatory methods for the analysis of macrocyclic lactone mycotoxins by CE with amperometric detection

A simple analytical scheme for the screening and quantification of zearalenone and its metabolites, alpha-zearalenol and beta-zearalenol, is reported. Extracts from maize flour samples were collected by supercritical fluid extraction and afterwards, they were analyzed by CE with amperometric detection. This scheme allowed a rapid and reliable identification of contaminated flour samples according to the reference value established for zearalenone by directive 2005/38/EC (200 microg/kg). The sample screening method was carried out by CZE using 25 mM borate separation buffer at pH 9.2 and 25.0 kV as separation voltage, monitoring the amperometric signal at +700 mV with a carbon paste electrode. In this way, total amount of mycotoxins was determined and samples were processed in 4 min with a detection limit of 12 microg/L, enough to discriminate between positive (more than 200 microg/L total mycotoxins) and negative samples (less than 200 microg/L total mycotoxins). Positive samples were then subjected to CZE separation and quantification of each analyte was done with 50 mM borate running buffer modified with 30% methanol at pH 9.7 and 17.5 kV as separation voltage. Under these conditions, separation was achieved in 15 min with detection limits from 20 to 35 microg/L for each analyte.

Ochratoxin A: The Continuing Enigma

The mycotoxin ochratoxin A (OTA) has been linked to the genesis of several disease states in both animals and humans. It has been described as nephrotoxic, carcinogenic, teratogenic, immunotoxic, and hepatotoxic in laboratory and domestic animals, as well as being thought to be the probable causal agent in the development of nephropathies (Balkan Endemic Nephropathy, BEN and Chronic Interstitial Nephropathy, CIN) and urothelial tumors in humans. As a result, several international agencies are currently attempting to define safe legal limits for OTA concentration in foodstuffs (e.g., grain, meat, wine, and coffee), in processed foods, and in animal fodder. In order to achieve this goal, an accurate risk assessment of OTA toxicity including mechanistic and epidemiological studies must be carried out. Ochratoxin has been suggested by various researchers to mediate its toxic effects via induction of apoptosis, disruption of mitochondrial respiration and/or the cytoskeleton, or, indeed, via the generation of DNA adducts. Thus, it is still unclear if the predominant mechanism is of a genotoxic or an epigenetic nature. One aspect that is clear, however, is that the toxicity of OTA is subject to and characterized by large species- and sex-specific differences, as well as an apparently strict structure-activity relationship. These considerations could be crucial in the investigation of OTA-mediated toxicity. Furthermore, the use of appropriate in vivo and in vitro model systems appears to be vital in the generation of relevant experimental data. The intention of this review is to collate and discuss the currently available data on OTA-mediated toxicity with particular focus on their relevance for the in vivo situation, and also to suggest possible future strategies for unlocking the secrets of ochratoxin A.

Isolation of Bacillus spp. from Thai fermented soybean (Thua-nao): screening for aflatoxin B1 and ochratoxin A detoxification

AIMS

To study the interaction between Bacillus spp. and contaminating Aspergillus flavus isolated strains from Thai fermented soybean in order to limit aflatoxin production. To study the detoxification of aflatoxin B(1) (AFB(1)) and ochratoxin A (OTA) by Bacillus spp. in order to find an efficient strain to remove these toxins.

METHODS AND RESULTS

One A. flavus aflatoxin-producing strain and 23 isolates of Bacillus spp. were isolated from soybean and fresh Thua-nao collected from the north of Thailand. Inhibition studies of A. flavus and A. westerdijkiae NRRL 3174 (reference strain) growth by all isolates of Bacillus spp. were conducted by dual culture technique on agar plates. These isolates were also tested for AFB(1) and OTA detoxification ability on both solid and liquid media. Most of the strains were able to detoxify aflatoxin but only some of them could detoxify OTA.

CONCLUSIONS

One Bacillus strain was able to inhibit growth of both Aspergillus strains and to remove both mycotoxins (decrease of 74% of AFB(1) and 92.5% of OTA). It was identified by ITS sequencing as Bacillus licheniformis. The OTA decrease was due to degradation in OTalpha. Another Bacillus strain inhibiting both Aspergillus growth and detoxifying 85% of AFB(1) was identified as B. subtilis. AFB(1) decrease has not been correlated to appearance of a degradation product.

SIGNIFICANCE AND IMPACT OF THE STUDY

The possibility to reduce AFB(1) level by a strain from the natural flora is of great interest for the control of the quality of fermented soybean. Moreover, the same strain could be a source of efficient enzyme for OTA degradation in other food or feeds.

Supercritical fluid extraction of macrocyclic lactone mycotoxins in maize flour samples for rapid amperometric screening and alternative liquid chromatographic method for confirmation

A rapid and simple method for the direct screening of macrocyclic lactone mycotoxins (zearalenone, ZON; alpha-zearalenol, alpha-ZOL; and beta-zearalenol, beta-ZOL) in maize flour samples is proposed. The sample screening method comprises supercritical fluid extraction (SFE) and clean-up on Florisil adsorption cartridge of the selected toxic compounds, followed by continuous flow electrochemical detection. Those samples for which the total concentration is close to or above the threshold limit established by legislation (0.200 mg kg(-1)) are subjected to preconcentration on C18 chromatographic material and liquid chromatographic separation for confirmation purposes. This confirmation method allows the determination of ZON, alpha-ZOL and beta-ZOL in the range between 30 and 300 microg kg(-1), with a average relative standard deviation lower than 5.2 in all cases.

Occurrence of pathogenic fungal species in Tunisian vineyards

Mycotoxins are secondary metabolites produced by filamentous fungi detected in food, such are grapes. OTA was evaluated in ten handle musts from different Tunisian vineyard. This mycotoxin was found at levels 1.1 mug/L to 4.3 mug/L. A survey was conducted to assess the contamination of the Tunisian vineyard with pathogenic fungal species, in particular those responsible of the OTA production. The results were evaluated for the first time in parcels cultivated in the North, in the Centre and in the South of the country. Italia Muscate and Superior Seedless varieties were concerned at three developmental stages of the berry, setting, veraison and maturity. Carigon variety was used as positive control for musts contaminating by OTA. The main fungal species isolated were Aspergillus spp. (33.32%), Botrytis cinerea (23.32%), Alternaria spp. (12.80%), Cladosporium spp. (10.59%) and Penicillium spp. (8.3%). The isolates of the Aspergillus genus were identified as Aspergillus niger aggregate (77%), Aspergillus carbonarius (15%) and Aspergillus flavus (8%). Their presence was characterized by a significant decrease in the Centre during the veraison and a slight increase in the North and the South during the maturity stage. Furthermore, when comparing Superior Seedless and Italia Muscate cultivated in the same area, the aspergilli were particularly less abundant at the setting stage in the case of Superior Seedless. There is no correlation between the OTA amount in musts and the contamination by Aspergillus species in different vineyards and for grape varieties studied.

Black aspergilli and ochratoxin A production in French vineyards

A survey on the occurrence on grape of black Aspergillus species and their capability to produce ochratoxin A (OTA) was conducted in France over three years (2001-2003) in 10 vineyards from four winemaking regions with different geographical locations and climatic conditions. During 2001 and 2002, from setting to harvest, the total numbers of fungal isolates were respectively 721 and 711 increasing in 2003 to reach 1035. The Aspergillus genus was essentially represented by Section Nigri (99%) and it was predominant (80%+/-4.6) when compared to Penicillium (20%+/-4.6). Regardless of sampling year, 32.5% (+/-sigma=1.26) of the fungal isolates were OTA producers and 93% (+/-sigma=2.65) belonging to black aspergilli. The ochratoxigenic potential of the isolates and their occurrence on grapes revealed that Aspergillus carbonarius was the main OTA producer (up to 37.5 mug/g). At harvest time, the fungal population was maximal and this was the most critical period influencing OTA contamination. Grapes from Languedoc-Roussillon region were most infested with ochratoxigenic fungi and had the highest concentrations of OTA (up to 2.8 ng/g).

Investigation of the teratogenic potential of ochratoxin A and B using the FETAX system

BACKGROUND

Ochratoxin A (OTA) is a mycotoxin produced by certain Aspergillus and Penicillium species. It has been observed to be teratogenic in a number of animal models including rat, mouse, hamster, and chick, with reduced birth weight and craniofacial abnormalities being the most commonly observed malformations. Neither the potential of OTA to cause malformations in humans nor its teratogenic mode of action is known. The FETAX system is an embryotoxicity assay system, with a high correlation to animal models and epidemiological data. Analysis of OTA-mediated teratogenesis using this system could provide a useful tool for the generation of high numbers of samples for mechanistic studies.

METHODS

Using the standard ASTM 96-hr exposure protocol, the effect of OTA and its structural analogue OTB on the development of Xenopus laevis embryos in vitro was assessed. The accumulation of both substances in Xenopus embryos was also examined using tritiated OTA and OTB.

RESULTS

Both OTA and OTB caused craniofacial malformations, while OTA also caused reduced embryo growth. As expected, OTA was far more potent in inducing these effects than OTB. This could at least in part be due to greater levels of OTA being accumulated within the embryos.

CONCLUSIONS

The ability of FETAX to differentiate between close structural analogues indicates the assay has great potential for the elucidation of the embryotoxic and teratogenic mechanisms of action. Hence, the model could provide a suitable system for the investigation of other known teratogens or for the pre-screening of new agents for teratogenic potential.

Safety assessment of DHA-rich microalgae from Schizochytrium sp. Part V: target animal safety/toxicity study in growing swine

The purpose of this study was to determine the potential toxicity of docosahexaenoic acid (DHA)-rich microalgae (DRM) from Schizochytrium sp., administered in the diet of growing swine. DRM was administered in the diet to groups of castrated male growing pigs (mixed commercial breeds, Landrace & Large White) reared from early weaned (weighing approximately 20 lbs) to approximately 250-270 lbs. Over the course of the 120 day study, animals were fed ad libitum four DRM treatment diets, each designed to optimize weight gain over the growing cycle, and a control diet. DRM was incorporated into the diet of the first treatment group at a level delivering 2.680 kg DRM per pig over the course of 120 days (a constant, whole-life exposure) equating to 598 g DHA per pig. DRM was incorporated into finisher diets only (administered over the last 42 days of the growing cycle) to treatment groups 2, 3, and 4 delivering 1.169, 3.391, and 5.746 kg DRM per pig (261, 756, and 1281 g DHA per pig). These levels represent approximately 1, 3, and 5 times the anticipated commercial dose and were delivered in a feeding strategy designed to mimic commercial use. Vitamin E was added to all diet groups to provide supplementary dietary antioxidant given the high content of polyunsaturated fat in DRM. There were no statistically significant treatment-related effects in clinical observations, body weights, food consumption, mortality, hematologic values, gross necropsy findings, organ weights or histopathology. The only DRM treatment-related changes were higher weight gain and feed conversion efficiency, anticipated results based on the increased fat content in the experimental DRM treatments. This study demonstrates that administration of DRM (at up to five times the anticipated commercial dose) did not produce any treatment-related adverse effects in commercial strains of swine.

Species- and sex-specific variations in binding of ochratoxin A by renal proteins in vitro

The mycotoxin ochratoxin A (OTA) is a potent renal carcinogen in rodents and induces renal fibrosis in pigs. Furthermore, OTA has been associated with the development of renal tumors and nephropathies in humans. Large species- and sex-differences are observed in sensitivity toward OTA-mediated toxicity and carcinogenicity, yet neither the mechanism(s) resulting in OTA toxicity nor the reasons for the observed species- and sex-specificities are known. This paper investigated variations in OTA handling viz binding to renal proteins which could possibly explain the observed differences in OTA susceptibility in vivo and in vitro. The results obtained via a modification of a standard receptor-binding assay demonstrated the presence of at least one homogeneous binding component in renal cortical homogenates from pig, mouse, rat and humans. This component was shown to bind OTA in a specific and saturable manner. A range of compounds selected for their affinity for steroid receptors and/or for various known organic anion transporters were employed in a competition assay to answer the question whether this homogenous OTA binding component represents a steroid-like receptor component or one of the known organic anion transporters of the kidney. Although many of the compounds were able to compete with OTA for protein-binding, the competition patterns displayed a distinct species specificity and did not correspond to the competition patterns associated with presently known organic anion transporters of the kidney in the mouse, rat or human. The data thus suggests the presence of a new organic anion transporter or more likely, a cytosolic binding component of unknown function with high affinity and capacity for OTA binding in humans, rats, mice and possibly pigs.

Content of ochratoxin A in paired kidney and meat samples from healthy Danish slaughter pigs

In 1999, paired samples of kidney and meat were taken from 300 healthy Danish pigs and analysed for ochratoxin A. The concentrations of ochratoxin A in kidney ranged from 0 to 15 microg kg(-1) (mean 0.50 microg kg(-1), median 0.18 microg kg(-1)) and in meat from 0 to 2.9 microg kg(-1) (mean 0.12 microg kg(-1), median 0.03 microg kg(-1)). The data together with the Danish control data show that today the pig industry in Denmark has no problem keeping the content of ochratoxin A in pig at very low levels even in years with wet harvest conditions. The mean ratio 'content in meat/content in kidney' for paired samples was 39%. For kidney samples >1.0 microg kg(-1), the mean ratio was 22%. The Danish control system for ochratoxin A in pig kidney established in 1978 can be regarded as a success because the levels in pig have been reduced substantially, and hence for the consumer the contribution from pig products to the total intake of ochratoxin A is very small compared with other sources.

On ochratoxin A and fungal flora in Polish cereals from conventional and ecological farms - Part 1: occurrence of ochratoxin A and fungi in cereals in 1997

Over 200 samples of Polish cereal grain from the 1997 harvest obtained from conventional and ecological farms were tested for the presence of ochratoxin A as well as for contamination by microscopic fungi. Ochratoxin A contamination of rye from ecological farms was over six times more frequent than that from conventional cultivation. The ochratoxin A content in wheat and barley samples from ecological farms was also higher. No wheat sample from conventional farms contained the mycotoxin. In the group of ecological farms, there were differences in the percentage of cereal samples containing ochratoxin A. The ochratoxin A levels ranged from 0.2 to 57 microg kg(-1). The mean concentration of ochratoxin A in investigated cereal grain was 5.7 microg kg(-1). From samples containing detectable amounts of ochratoxin A, fungi producing ochratoxin A under laboratory conditions were isolated. They were classified as belonging to the species Penicillium cyclopium, P. viridicatum, P. chrysogenum and also Aspergillus alliaceus, A. versicolor, A. glaucus and A. flavus. Penicillium strains - producers of ochratoxin A - were isolated from 93% of the samples; in 7% of samples, only Aspergillus strains producing this mycotoxin were noted. Rye samples mainly from one farm with an ecological type of cultivation and from one conventional farm were contaminated with both Aspergillus and Penicillium mycotoxigenic strains.

A simple HPLC method for the determination of the mycotoxins ochratoxin A and B in blood serum of swine

This paper presents a simple method for the determination of ochratoxins A (OTA) and B (OTB) in pig blood serum. The method includes serum acidification (pH < 1.6) and precipitation of protein with 15% trichloroacetic acid, liquid partitioning with dichloromethane and fluorescence detection. The estimated detection limits were 0.1 ng OTA/ml and 0.2 ng OTB/ml. The mean recoveries from artificially contaminated samples (n = 6 replicates/mycotoxin) spiked at 0.3, 1 and 3ng OTA and OTB/ml, respectively, were 86.8% (s.d. = 8.4) for OTA and 90.0% (s.d. = 9.8) for OTB. Forty-nine Romanian pig blood serum samples (94% of 52 analysed) were found to be naturally contaminated with OTA in the range 0.1-13.4 ng/ml. No sample was found positive for OTB. The method is technically simple, specific, cost effective, suitable for large sample throughput and requires small amount of sample and reagents. It fulfils the criteria for a routine method and could be a suitable toolfor surveying OTA in pig herds and in slaughtered pigs.

Species- and sex-specific renal cytotoxicity of ochratoxin A and B in vitro

Four different cell models were chosen for comparison of OTA and OTB toxicity: primary porcine (PKC), rat (RPTC) and human renal proximal epithelial cells (HKC) from both sexes and a porcine renal cell line: LLC-PK1. Culture conditions were tested and optimized for each respective cell type (species/sex and origin). All cell types were characterized for epithelial origin and growth patterns and following optimization of dosing strategies and assay procedures, a strict study design was implemented to avoid systemic variations. Due to possible sensitivity differences, three simple endpoints were chosen to provide basic data for interspecies comparison: neutral red uptake, MTT reduction and cell number. Of the endpoints tested neutral red appeared the most sensitive, although all three parameters yielded comparable EC50's. Sex-differences were observed between male and female HKC cells following 96 h exposure to OTA, with HKC(m) being more sensitive than HKC(f). No sex-difference was observed in PKC cells, however, the PKC were approximately 3 and 10 times more sensitive than HKC(m) and HKC(f), respectively, to OTA and OTB. Interestingly, the CI95 of the EC50 values obtained for OTA (15.5-16.5 microM) and OTB (17.0-2 1.0 microM) were comparable in the PKC cells. In contrast, OTB had lower cytotoxicity than OTA in HKC and LLC-PK1 (approx. 2-fold) and no effects in RPTC. Overall, HKC(m) were nearly as sensitive as PKC towards OTA, followed by RPTC, LLC-PK1 and HKC(f), thus suggesting a sex specific sensitivity in humans towards OTA induced cytotoxicity.

Determination of zearalenone and its metabolites alpha- and beta-zearalenol in beer samples by high-performance liquid chromatography-tandem mass spectrometry

A fast, robust and sensitive LC-MS-MS method for the determination of zearalenone (ZON) and its metabolites alpha-zearalenol (alpha-ZOL) and beta-zearalenol (beta-ZOL) in beer samples is described. Sample preparation was performed by direct RP-18 solid-phase extraction of undiluted beer samples followed by selective determination of analytes by LC-MS-MS applying an atmospheric pressure chemical ionization (APCI) interface. Using the negative ion mode limits of determination of 0.03-0.06 microg l(-1) beer and limits of quantification of 0.07-0.15 microg l(-1) beer were achieved, which was distinctly more sensitive than in the positive ion mode. Twenty-three beer samples from different countries, produced from different grains and under different brewing conditions, were investigated by this method, but only in one sample could beta-ZOL and ZON be detected. Independently of the type of beer, relative standard deviations between 2.1% and 3.3%, a linear working range of 0.15 microg l(-1) to 500 microg l(-1) beer and recovery rates around 100% could be achieved when zearalanone (ZAN) was used as internal standard.

Studies of the influence of ochratoxin A on immune and defence reactions in weaners

Even in subtoxic amounts, the mycotoxin, ochratoxin A, produced immunomodulation in weaner pigs in a dose-dependent mode. In addition to increased counts of total leukocytes and neutrophils in the blood, reduced lymphocyte levels were observed. There was a striking increase in the counts of eosinophils and of apoptotic phagocytes. Functionally, there was a predominance of the production of reactive oxygen radicals in whole blood, reduced phagocytosis performance and reduced expression of a swine-specific surface marker (SWC1) on lymphocytes. In a few single experiments, clinical manifestations could be demonstrated. Lung clearance and the degree of severity of experimental pneumonia as well as cutaneous hypersensitization may be influenced by ochratoxin A.

Determination of zearalenone in grains by high-performance liquid chromatography-tandem mass spectrometry after solid-phase extraction with RP-18 columns or immunoaffinity columns

In this paper a robust, sensitive and selective LC-MS-MS method for the determination of zearalenone (ZON) in several cereals is described. Sample preparation was performed by extraction of the commodities with a mixture of acetonitrile and water followed by solid-phase extraction with RP-18 columns or immunoaffinity columns. The selective determination of ZON was achieved with an atmospheric pressure chemical ionization interface. Using the negative ion mode a detection limit of 0.5 microg/kg and a determination limit of 1 microg/kg grain was achieved, which is by a factor of 100 more sensitive than the positive ion mode. Zearalanone (ZAN), which does not occur in nature, was used as internal standard for quantification. A linear working range from 1.0 microg/kg to 1000 microg/kg could be achieved in grains with a standard deviation of 4% and recovery rates around 100%. All these results were independent from the grain matrices (maize, barley, oats, wheat) when ZAN was used as internal standard. Sample preparation with RP-18 and immunoaffinity materials gave comparable results. In addition, the method was successfully used for the investigation of naturally contaminated maize samples in the course of an interlaboratory comparison test.

Mycotoxicosis in food producing animals

Mycotoxins are toxic secondary metabolites of fungi. Diseases caused by mycotoxins are collectively referred to as mycotoxicosis. Disease is usually initiated after ingestion of feeds containing toxic doses of mycotoxins. Signs and symptoms vary and depend on the animal, the organ system involved, and on the dose and type of mycotoxins ingested. The symptoms can range from acute death, immunosuppression to skin lesions or to signs of hepatotoxicity, nephrotoxicity, neurotoxicity, or genotoxicity. In addition to concerns over adverse effects of mycotoxins on food animals consuming mycotoxin-contaminated feeds, there is also a public health concern over the potential for human beings to consume animal-derived food products such as meat, milk, or eggs, containing residues of those mycotoxins or their metabolites.

Haematological, biochemical and toxicological investigations in spontaneous cases with different frequency of porcine nephropathy in Bulgaria

Haematological, biochemical and toxicological investigations of blood and urine of normally slaughtered pigs exhibiting different frequency (1-2%, 10-20% and 50-60%) of changes characterized as "enlarged mottled kidneys", at the slaughtering meat inspection were carried out to elucidate the nature of nephropathies encountered in Bulgaria. A content of ochratoxin A, higher in the spring than the autumn, was found in the serum and urine samples. The mean contamination levels of ochratoxin A in consumed feeds ranged from 114 +/- 36 ppb for 1994 to 207 +/- 65 ppb for 1993. The renal changes were characterized by impairment of proximal tubular function (indicated by an increased urinary excretion of glucose and protein) as well as by decreased specific gravity and increased pH in the urine mainly in pigs with 50-60% frequency of nephropathy. The concentration of urea, creatinine and glucose in the blood was increased, whereas the serum protein and cholesterol were decreased in pigs with 10-20% and 50-60% frequency of nephropathy. The mean enzyme levels of gamma-glutamyl transpeptidase and leucine aminopeptidase were significantly increased in the urine. The presence of granular casts and necrotic renal tubular cells were established in the sediment.

Pharmacokinetics of ochratoxin A and its metabolites in rats

Ochratoxin A (OA) is a mycotoxin that is produced on moist grain. It is commonly found in the blood of swine in western Canada and is a potent nephrotoxic, carcinogen, and immunosuppressive agent. The pharmacokinetic characteristics of six analogs of OA including OA, OB (OA without chloride), OC (OA ethyl ester), and some metabolites, such as O alpha (OA without phenylalanine), OA-OH (hydroxylated OA), and a newly discovered form of OA, OP-OA (lactone opened ring of OA), were investigated in rats after a single intravenous administration of the compounds. All of the ochratoxin analogs were distributed following a two compartment open model. The elimination half-lives of OA, OP-OA, O alpha, OA-OH, OB, and OC were 103+/-16, 50.5+/-2.8, 9.6+/-2.3, 6+/-0.9, 4.2+/-1.2, and 0.6+/-0.2 hr, respectively. Total body clearance of OA, OP-OA, O alpha, OA-OH, and OB via the bile, urine, and metabolic routes were 3.1, 3.6, 40, 65, and 43 ml/hr kg, respectively. OA, OB, and O alpha were mainly cleared in the urine (> or = 48%), OA-OH in the bile (41%), and OP-OA as metabolites (43%). Metabolism accounted for 43, 44, 33, and 29% of the total clearance of OA, O alpha, OA-OH, and OB, respectively. It is concluded that OA has a long half-life and is very slowly cleared from the body and that its metabolites are cleared at a much faster rate with much shorter half-lives. Procedures should be devised to enhance the conversion in the body of OA to O alpha, OA-OH, or other metabolites as this would shorten its half-life and therefore its toxicity.

Toxicity and metabolism of ochratoxin A

The frequent occurrence of ochratoxin A (OA) in food and feed commodities and the high incidence of human exposure, as confirmed by different surveillance studies initiated several investigations devoted to elucidating the molecular mechanisms underlying OA toxicity. Previous studies indicated that the primary effects of OA are the inhibition of tRNA synthetase, the inhibition of mitochondrial respiration, and a disturbance of intracellular calcium homeostasis inherent to lipid peroxidation processes. We here report the effect of OA on a number of toxicological endpoints including cytotoxicity in different cell lines and effects on macromolecular synthesis and cell proliferation in primary cultures of hepatocytes at concentrations corresponding to overall exposure levels. These studies provide evidence that prominent toxicological effects might be linked to biotransformation processes. Analysis of hepatic biotransformation resulted in the detection of a number of distinct stable OA-metabolites. As metabolic activation has also been identified as an essential step in OA mutagenicity, the biological relevance on this mechanistic data is discussed.

Ochratoxin A in cereals and the BCR-M&T-projects

Reliable analytical procedures and certified reference materials are essential for the establishment and enforcement of tolerance levels for ochratoxin A in foods. The inadequacy of analytical procedures, together with the need for certified reference materials, led the Commission of the European Communities Community Bureau of Reference (BCR) to undertake a project to prepare suitable reference materials for ochratoxin A in wheat, in order to improve methodology and to harmonise agreement of results between member states. The first intercomparison study indicated problems in the analysis due to the influence of co-extractives in the matrix, and demonstrated that further work was necessary to improve recovery, clean-up and reproducibility. The second intercomparison study, in the EC Measurements and Testing Programme, correlated the performance of the different methods for ochratoxin A measurement in a separate batch of contaminated wheat, and compared novel immunoaffinity column methods with the standard laboratory methods. Results were obtained from 26 laboratories within 11 European countries, which therefore gives a good representation of the scope of methods currently used in Europe. Considerable improvements in the determination of ochratoxin A were noted compared with the first intercomparison study.

Ochratoxin A in plasma of Norwegian swine determined by an HPLC column-switching method

A method well suited for screening large numbers of plasma samples for ochratoxin A is presented. Proteins were precipitated with methanol and the supernatant diluted with 0.01 M phosphoric acid before 1 ml extract was injected into a high-performance liquid chromatograph (HPLC). The extract was further cleaned up and pre-concentrated on a polystyrene-divinylbenzene precolumn. After column-switching, the sample was chromatographed on a C18 analytical column, and ochratoxin A was detected with a fluorescence spectrophotometer, either directly or after postcolumn pH shift. The detection limit was 0.10 ng ochratoxin A/ml plasma. The method was used to determine the ochratoxin A concentration in 216 samples of swine plasma. They were collected from different herds in June 1991 from ten slaughterhouses, located in different parts of Norway. Eighty-two percent of the samples contained > or = 0.10 ng ochratoxin A/ml plasma while 0.9% contained > or = 5.0 ng/ml.

Role of ochratoxin in disease causation

Under experimental conditions renal damage has been induced by alimentary exposure to ochratoxin A in all single-stomach animals tested so far, including rodents, dogs, pigs and birds, and even in young ruminants still functioning as single-stomach animals. Most information on ochratoxin-induced nephropathy has been obtained in pigs during experimental studies comprising structural as well as functional changes. The renal damage is characterized morphologically by atrophy of the proximal tubules, interstitial cortical fibrosis and sclerotized glomeruli, and functionally by impairment of tubular function indicated by a decrease in TmPAH/Cin and reduced ability to produce concentrated urine. The renal effect has been observed using exposure levels of ochratoxin A in the range 200 to 4000 micrograms/kg feed. Field cases of ochratoxin-induced nephropathy in pigs have been encountered in many countries, and the disease mycotoxic porcine nephropathy (MPN) is recognized as an endemic disease entity in several northern and central European countries. Epidemics of MPN have been reported, closely related to excessive climatic conditions in periods preceding harvest. Ochratoxin A is a recognized renal carcinogen in the mouse. In female pigs exposed to alimentary ochratoxin A for 2 years, no renal cancer was observed. Ochratoxin A is metabolized and excreted relatively fast in animals, with an RL50 (residue elimination) in the pig of a few days for various tissues. Past exposure data is a requirement in retrospective epidemiological studies, but because of the short RL50 values tissue analysis for ochratoxin A is unlikely to provide that kind of data, in animals or in humans. In order to meet this demand a procedure has been developed, using renal biopsy material for activity analysis of two renal tubular enzymes, phosphoenolpyruvate carboxykinase and gamma-glutamyl transpeptidase. In pigs exposed to ochratoxin A for 1 week a 40% reduction of the enzyme activity was observed. The dose-related activity decrease of the two enzymes was accompanied by a dose-related aggravation of renal impairment, as measured by a reduction of TmPAH/Cin, suggesting that these enzymes are sensitive indicators of ochratoxin A-induced nephropathy.

Ochratoxin A in blood and its pharmacokinetic properties

Since there are pathomorphological similarities between porcine mycotoxic nephropathy caused by ochratoxin A and Balkan endemic nephropathy (BEN), it has been suggested that the same aetiological agent has a role in BEN. Based on the results from several field and experimental studies carried out on pigs, an appropriate analytical method of monitoring possible human exposure to ochratoxin A was developed. The toxicokinetic properties of the toxin were species specific, although in all the animal species studied (with the exception of fish), as well as in humans, two binding proteins were found in the plasma. The monkey had the longest elimination half-life of the toxin, 510 hr, in contrast to the fish whose elimination half-life was only 0.68 hr. The fish kidney displayed a specific pattern of distribution. In the laying quail the most prominent observation was the accumulation of labelled ochratoxin A in egg yolk. Generally, [14C]ochratoxin A was eliminated rapidly from the quail body, but had a long retention time in the circulating blood in the mouse. Although the elimination of ochratoxin A from the body depending on its binding to plasma constituents, the existence of enterohepatic circulation might have been partially responsible for its prolonged retention and elimination from the body of mammals. The toxicokinetic profile of ochratoxin A did not contradict the mycotoxic hypothesis in the aetiology of BEN.

Renal enzyme activities in experimental ochratoxin A-induced porcine nephropathy: diagnostic potential of phosphoenolpyruvate carboxykinase and gamma-glutamyl transpeptidase activity

Enzyme activities have been measured in needle biopsies from kidneys of pigs fed 1 ppm or 0.2 ppm of ochratoxin A for 1-5 wks. After feeding 1 ppm toxin for 1 wk, the activity of cytosolic phosphoenolpyruvate carboxykinase (PEPCK) was decreased by 40% and remained inhibited until the termination of the experiment (5 wk). The activity of gamma-glutamyl transpeptidase, a brush-border enzyme found in the proximal tubules, was reduced to a similar degree and remained inhibited. The activities of hexokinase, a cytosolic enzyme of general distribution in the nephron, and phosphate-dependent glutaminase, a distal tubule enzyme, were not affected. The biopsy results were confirmed by measurements in renal slices taken at the termination of the experiment, except that biopsy samples showed more variation in enzyme activity and a lower PEPCK activity. A guinea pig antibody against the cytosolic form of PEPCK was used to demonstrate that the mitochondrial form of the enzyme, which accounts for a considerable part of the total cellular activity, was not affected by ochratoxin A. When mitochondrial PEPCK activity present in the cytosolic fraction was accounted for, ochratoxin A was found to reduce PEPCK activity by 70-80%. The increase of ochratoxin A exposure from zero through 0.2 ppm to 1 ppm, which resulted in dose-dependent activity decrease of PEPCK and gamma-glutamyl transpeptidase, was accompanied by dose-dependent decrease of renal function, as measured by a reduction of maximal tubular excretion of para-aminohippurate per clearance of inulin (TmPAH/CIn) and an increase in glucose excretion. This suggest that these enzymes are sensitive indicators of ochratoxin A-induced porcine nephropathy. Assuming that porcine nephropathy represents a valid model of endemic (Balkan) nephropathy in humans, the measurement of cytosolic PEPCK and gamma-glutamyl transpeptidase activity in the kidney could be a sensitive test for ochratoxin A-induced disease in humans.