Effect of T-2 toxin on in vivo lipid peroxidation and vitamin E status in mice.

The effects of an acute administration of T-2 toxin on vitamin E status and the corresponding degree of lipid peroxidation, as determined by the plasma and organ content of malondialdehyde (MDA), was studied in mice. The effects of T-2 toxin administration on the body weight and weights of liver, spleen and thymus were also assessed. T-2 toxin was administered in doses ranging from 1 to 6.25 mg/kg body weight, depending on the experiment, while the dietary content of vitamin E ranged from near 0 to 5000 IU/kg. There was a significant decrease in vitamin E content of plasma after the administration of the toxin with the concentrations remaining low for periods as long as 48-72 h. MDA content of liver increased significantly after 24-48 h of toxin administration in contrast to the controls. However, MDA levels returned to the control range after 72 h. The concentrations of MDA in liver were inversely related to the vitamin E content of the diet, and were always higher for the toxin-treated animals (significant linear regression between MDA content of liver and the log10 of vitamin E content of the diet). Weights of spleen and thymus decreased after T-2 toxin administration; however, the weight of liver either increased or did not change in the different experiments. In conclusion, T-2 toxin treatment of mice increased lipid peroxidation in the liver as measured by MDA production. This process was maximal after 48 h of T-2 challenge, and decreased thereafter. Plasma alpha-tocopherol levels decreased as soon as 6 h after the toxin challenge, while MDA did not increase until there was a severe depletion of vitamin E. These changes were accompanied by decrease in weight of spleen and thymus.

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

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

Characterization and purification of porcine small intestinal mucus receptor for Escherichia coli K88ac fimbrial adhesin.

The objectives of this study were to investigate the nature of, and to purify K88ac fimbrial adhesin-specific receptors in the mucus from the small intestine of piglet. Adhesion was studied by incubating (3)H-labeled Escherichia coli with mucus that were treated with or without pronase, proteinase, trypsin or sodium metaperiodate. The results indicated that treatment with either proteolytic enzymes or sodium metaperiodate (to oxidize sugars) significantly reduced E. coli K88ac or K88+MB adhesion to the mucus, suggesting that the K88ac and K88+MB specific receptors in this preparation were, at least in part, glycoprotein in nature. The K88+MB fimbriae specific receptor was purified using affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified K88+MB specific receptor together with the above data suggested that the receptor from the mucus of the small intestine of the pig was a 80-kDa glycoprotein.

Cholestyramine protection against ochratoxin A toxicity: role of ochratoxin A sorption by the resin and bile acid enterohepatic circulation.

We have shown that the addition of cholestyramine (CHA, a resin known to bind bile salts in the gastrointestinal tract) to ochratoxin A (OTA)-contaminated rat diets reduced plasma levels of the toxin and prevented OTA-induced nephrotoxicity. To elucidate the mechanism of action of CHA, we carried out in vitro experiments to determine whether the resin may bind the toxin. For comparative purposes, binding of bile salts to the resin was also examined. Results showed that CHA binds both OTA and bile salts (taurodeoxycholate [TDC] and taurocholate [TCA]). Also, CHA showed greater affinity for OTA and TDC than for TCA. At 1 mM concentration, 96% of OTA and 80% of TDC were bound to the resin, while for TCA binding was only 50%. However, saturation of the resin was reached at higher levels with bile acids compared to OTA (3.67 mmol/g resin for TCA and 3.71 mmol/g resin for TDC versus 2.85 mmol/g resin for OTA). To characterize the nature of the binding of the toxin to CHA, NaCl (0 to 200 mM) was added to a fixed amount of OTA or bile acids. As expected, TCA absorption was decreased by the addition of NaCl (<50 mM), indicating electrostatic binding. However, OTA and TDC sorption was decreased only at high concentrations of NaCl (>150 mM), suggesting a stronger binding to the resin than that shown with TCA. Sequential competitive studies demonstrated that CHA binds more OTA than TCA. The results of the in vivo study show the role of bile salts in OTA absorption. The toxin's plasma levels at 1 and 3 h after a single oral dose of OTA were significantly decreased in bile salt-depleted rats compared to the control. Thus, the alteration of the bile salt biliary pool and OTA enterohepatic circulation may be an additional mechanism of action of the resin against mycotoxin toxicity.

Metabolism and excretion of ochratoxin A fed to sheep.

Hydrolysis of the mycotoxin ochratoxin A (OA) to ochratoxin alpha (Oalpha) by microorganisms within the gastrointestinal tract leads to the excretion of OA as the nontoxic alpha form. The Oalpha form is the principal means for the detoxification of OA. In the current experiment, three groups of four sheep were fed diets consisting of 70% concentrates and 30% hay (dry matter basis, energy to supply 1.1 times the requirement for maintenance) for 4 wk with three dietary concentrations of OA (0, 2, or 5 mg/kg of concentrate feed). The OA content did not affect feed intake or nutrient digestibility. In a preliminary experiment, an OA dose of 20 mg/kg of concentrate feed greatly reduced feed intake. After 1, 2, 3, and 4 wk of the trial, significant concentrations of OA were detected in the serum of the animals fed 2 or 5 mg of OA/kg feed. This suggested that even at a dosage of 2 mg of OA/kg of concentrate feed, considerable amounts of OA were not degraded by ruminal and intestinal microorganisms. The analysis of the feces and urine samples reflected these findings; OA and Oalpha were found in significant concentrations, escaping fermentation in the rumen and in the hindgut. The current experiment demonstrates that OA hydrolysis in the gastrointestinal tract of sheep is substantially less than previously described, especially if OA is ingested in combination with concentrate-rich diets.

Passive protective effect of egg-yolk antibodies against enterotoxigenic Escherichia coli K88+ infection in neonatal and early-weaned piglets.

The protective effects of egg-yolk antibodies obtained from hens immunized with fimbrial antigens from a local strain (Escherichia coli K88+ MB, Manitoba, Canada) of K88+ piliated enterotoxigenic E. coli (ETEC) were evaluated in 3- and 21-day-old piglets in which ETEC diarrhea was induced and also in early-weaned piglets in a commercial farm. The results demonstrated that the E. coli K88+ MB-induced diarrhea in 3-day-old piglets was cured 24 h after treating with egg-yolk antibodies while those treated with egg-yolk powder from conventional hens continued to have diarrhea and 62.5% of them died of severe diarrhea. For 21-day-old weaned piglets, those fed egg-yolk antibodies had transient diarrhea, positive body weight gains and 100% survival during the period of the experiment, whereas control piglets that were treated with placebo had severe diarrhea and dehydration and some died within 48 h after infection. In the field trial, the incidence and severity of diarrhea of 14-18-day-old weaned piglets fed egg-yolk antibodies were much lower than in those fed a commercial diet containing an antibiotic. These results indicate that the neonatal and early-weaned piglets that received the egg-yolk antibodies were protected against ETEC infection.

In vitro inhibition of adhesion of enterotoxigenic Escherichia coli K88 to piglet intestinal mucus by egg-yolk antibodies.

The objective of the study was to determine if the adhesion of E. coli K88 to piglet intestinal mucus could be inhibited in vitro by spray-dried egg-yolk anti-K88 antibodies. Binding of E. coli was monitored using a radioactive assay. Four 14+/-2-day-old healthy piglets were used for the preparation of mucus from the small intestine. Competition and displacement phenomena were investigated by incubating (a) egg-yolk antibodies and E. coli together prior to adding to the mucus and (b) E. coli and mucus, followed by egg-yolk antibodies. The results demonstrated that egg-yolk antibodies inhibited the adhesion of 3H-labeled local strain of hemolytic E. coli K88+ (E. coli K88+ MB) to piglet small intestinal mucus by 84.6-97.0% when the egg-yolk antibodies were diluted 10, 20, 40 or 100 times. The adhesion inhibiting effects of egg-yolk antibodies declined dramatically when the antibody dilution was more than 250-fold. A similar adhesion inhibiting effect was observed when egg-yolk antibodies were incubated with E. coli K88+ MB for 15, 30 and 60 min prior to the adhesion test. Egg-yolk antibodies when diluted 50- and 100-fold had a very strong inhibiting ability against E. coli K88+ MB at a concentration of 10(9) colony forming units (cfu) ml(-1) (adhesion was < 6%). However, dilution of 100 times for egg yolk antibodies was insufficient to inhibit the adhesion of E. coli K88+ MB to intestinal mucus when the concentration of E. coli K88+ MB was 10(10) cfu ml(-1). The displacement test indicated that there was no significant reduction in the adhesion of E. coli K88+ MB to the small intestinal mucus when egg-yolk antibodies were added after adhesion of the organism to the mucus. These studies demonstrate that anti-K88+ MB fimbriae antibodies from chicken egg-yolk when added to E. coli K88+ MB prevented their binding to receptors in the mucus isolated from the intestine of piglets.

Dietary cholestyramine reduces ochratoxin A-induced nephrotoxicity in the rat by decreasing plasma levels and enhancing fecal excretion of the toxin.

Ochratoxin A (OTA) is a mycotoxin that may contaminate animal feed (oat, barley, and rye) and food (wheat, rice, coffee, beer, pig meat), leading to major health problems (e.g., nephropathy) in several animal species including humans. Several methods have been tested to reduce the toxicity of OTA in animals but with limited success. In rats, the effect of cholestyramine (CHA), a bile acid-binding resin, was investigated on OTA-induced nephrotoxicity and bioavailability. Animals were fed semisynthetic diets containing two levels of OTA: 1 or 3 ppm. At each level of OTA, the diets were enriched with 0.1, 1, and 5% of CHA. The results showed that CHA decreased the concentration of OTA in plasma. At 1 and 3 ppm of OTA in the diet, CHA is effective at a level of 0.1% and 5%, respectively. The excretion of OTA and its metabolites (ochratoxin alpha and hydroxylated ochratoxin A) in bile and urine was also decreased by addition of 5% CHA in the diet. This was associated with an increase of OTA excretion in feces. Enzymuria and renal morphology revealed that dietary CHA can decrease OTA-induced nephrotoxicity, probably by reducing renal exposure to the toxin. In conclusion, CHA can reduce OTA concentrations in plasma as well as reducing nephrotoxicity, which may be attributed to a decrease of bioavailability and/or enterohepatic circulation of the toxin.

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.

Mycotoxins in fungal contaminated samples of animal feed from western Canada, 1982-1994.

Feed samples from 94 cases involving fungal contamination and suspected mycotoxicosis of farm animals in western Canada were examined during 1982-1994 to assess the incidence of mycotoxins. Samples were analyzed for aflatoxins, ochratoxin A, citrinin, sterigmatocystin, and the fungal estrogen zearalenone. Samples infected with Fusarium fungi were additionally assayed for nivalenol, deoxynivalenol, fusarenone-x, 15-acetyl-deoxynivalenol, diacetoxyscirpenol, HT-2 toxin, and T-2 toxin. Mycotoxins were found in 21 feed samples from 17 cases (18% of the reported cases), generally at levels far below those needed to induce symptoms under laboratory conditions. HT-2 toxin and other type-A trichothecenes were detected in 5 samples, deoxynivalenol and other type-B trichothecenes in 13, ochratoxin A in 5, and citrinin in 2. In 9 cases, symptoms observed in the animals were consistent with the known effects of the mycotoxin(s) found in the particular feed samples.

Toxicity of ochratoxin A, its opened lactone form and several of its analogs: structure-activity relationships.

Ochratoxin A (OA); its three natural analogs, ochratoxin C (OC), B (OB), and alpha (Oalpha); and its six synthetic analogs, the epimere of OA (d-OA), the ethylamide of OA (OE-OA), decarboxylated OA (DC-OA), O-methylated OA (OM-OA), lactone-opened OA (OP-OA), and the methyl ester of Oalpha (M-Oalpha) were assayed for their toxicities in prokaryotic (Bacillus brevis) and eukaryotic (HeLa cell) systems and in animals (mouse and rat). The LC50S (mM) for HeLa cells, were 0.005 (OA), 0.009 (OC), 0.163 (d-OA), 10.1 (OE-OA), 7.6 (DC-OA), 0.83 (OM-OA), 0.054 (OB), and 0.56 Oalpha). The minimum inhibitory doses (nmol/disc) for the growth of B. brevis (pH 6.5) were 8.7 (OA), 2.0 (OC), 5.5 (d-OA), 1.1 (OE-OA), 54 (OB), 390 (Oalpha), and 90 (M-Oalpha) while no inhibition of the bacterial growth was observed for OM-OA, DC-OA, and OP-OA at doses as high as 350 nmol/disc. The results indicate that the toxicities of OA were associated with its isocoumarin moiety but that neither the dissociation of the phenolic hydroxyl group nor the iron-chelating properties of OA were directly related to its toxicities. The lactone carbonyl group of OA, however, appears to be involved in OA toxicity as OP-OA is found in the bile of rats injected with OA and has similar toxicity to that of OA when administered intravenously to the rat. Overall, the structure-activity studies suggest that the toxicity of OA is attributable to its isocoumarin moiety and that the lactone carbonyl group may be involved in its toxicity.

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

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

The incidence and distribution of ochratoxin A in western Canadian swine.

A survey of swine destined for slaughter in Manitoba was conducted to examine the incidence of ochratoxin A (OA) in swine herds from different regions of Manitoba throughout the year 1989-90. Thirty-six percent of the serum samples which were collected from 1600 pigs contained detectable levels of OA. The identity of this toxin was confirmed using liquid chromatography-mass spectrometry and enzymatic hydrolysis. There was a significant effect of the region from which the herds originated, as well as the season in which the samples were collected on both the incidence (p < 0.001) and concentration of OA (p < 0.001). In July, 65% of the samples contained detectable levels of OA, compared with 38, 21 and 17%, in April, October and January respectively. Furthermore, 24% of the samples collected in July contained greater than 15 ng/ml of OA, while only 2, 9, and 1% of the samples collected in April, October and January respectively, contained greater than 15 ng/ml of OA. Based on the six samples collected from each herd, it appears that the presence and concentration of OA within a herd may be estimated from a limited number of animals per herd.

Production of proline-rich proteins by the parotid glands of rats is enhanced by feeding diets containing tannins from faba beans (Vicia faba L.).

Feeding a casein-based diet with either 400 g/kg of tannin-containing faba bean hulls (Vicia faba L.) (1.41% condensed tannins) or 60 g/kg of a tannin-rich hull extract of faba beans (1.99% condensed tannins) to rats over a period of 7 d resulted in a 2.6 and 1.5 fold increase in weight of the parotid glands, respectively, (P < 0.05) and a corresponding 5.5 and 3.7 fold increase in the level of proline-rich proteins in the glands (P < 0.05). In a dose-response experiment, increasing the level of tannin-rich hull extract in the diet (0.0, 3.8, 7.5, 15.0, 30.0 and 60.0 g/kg) resulted in a linear increase in both the relative size of parotid glands (R2 = 0.90; P < 0.05) and the quantity of proline-rich proteins in the glands (R2 = 0.89; P < 0.05). The apparent digestibility of total (R2 = 0.97) and individual amino acids (R2 varied from 0.27 to 0.99) decreased linearly (P < 0.05). The quantity of proline-rich proteins in the cecum of rats was estimated from the decrease in digestibility of proline, glycine and glutamic acid. The estimated secretions of proline-rich proteins, when calculated on the basis of the three respective amino acids, were 3.5, 3.5 and 3.9 mg of proline-rich proteins per 10 mg of additional hull extract (21.8% condensed tannins). The results indicate that tannins from faba beans stimulate the parotid glands to increase the secretion of proline-rich proteins in rats. The proline-rich proteins then interact with dietary condensed tannins to reduce their antinutritional effects.

Comparison of Toxicity of Different Mycotoxins to Several Species of Bacteria and Yeasts: Use of Bacillus brevis in a Disc Diffusion Assay.

Twelve species of bacteria and two species of yeast were tested for sensitivity against 11 different mycotoxins using a disc diffusion assay. Among the bacterial species, Bacillus brevis appeared to be the most sensitive microorganism, being sensitive to eight mycotoxins (AFB1, ochratoxin A [OA], citrinin [CT], patulin [PAT], penicillic acid [PA], cyclopiazonic acid [CPA], penitrem A [PT-A], and zearalenone [ZEE]). This microorganism was not affected by a high concentration (500 µg per disc) of any of the trichothecenes (T-2 toxin, HT-2 toxin, diacetoxyscirpenol, and deoxynivalenol). Kluyveromyces marxianus , a species of yeast, was the only microorganism that was inhibited by all four of the trichothecenes but was not inhibited by the other mycotoxins. The area of the inhibition zone produced by some of the mycotoxins such as OA with the B. brevis assay was dramatically influenced by the pH of the medium, while the toxicity of other mycotoxins such as AFB1 was relatively pH independent. The sensitivity of the B. brevis assay also tended to decrease at agar volumes above 6 ml and as the number of microbes per plate increased. The lowest amounts of the different ochratoxins; OA, OB and OC (OA ethyl ester) that could be detected under optimal conditions were 0.5, 20, and 2 µg per disc, respectively. The lowest amounts of CPA, AFB1 CT, PAT, PA, PT-A, and ZEE that were detectable were 0.5, 1, 1, 1, 1, 1, and 10 µg per disc, respectively. These results demonstrate that B. brevis can be used as a positive indicator organism to detect the presence of several common non-trichothecene mycotoxins. The results demonstrate that, used together, B. brevis and K. marxianus can be used as indicator organisms in a bioassay approach to the detection of several of the most common mycotoxins.

Optimization of Yeast Bioassay for Trichothecene Mycotoxins.

An improved disc diffusion type bioassay was developed for T-2 toxin (T-2), HT-2 toxin (HT-2), diacetoxyscirpenol (DAS), deoxynivalenol (DON), nivalenol (NIV), neosolaniol (NSL), fusarenon-X (FUS-X), trichothecin (TIN), roridin A (RDA) and verrucarin A (VCA) using the yeast, Kluyveromyces marxianus . Factors such as type of medium, agar volume per plate, preincubation time and temperature, incubation temperature, inoculum size and pH had variable, and in some cases a dramatic effect on the sensitivity of the assay. The effect of pH of the assay medium was particularly pronounced. The highest sensitivity was obtained when 6 ml per plate of a tryptic-soy-agar (TSA) medium (pH 7.5) containing 105 CFU inoculum per ml was incubated at 38°C for 18 h. All of the trichothecenes (TNN) were able to inhibit the growth of the yeast with the detection limit being 0.005, 0.01, 0.02, 0.02, 0.1, 0.5, 10, 10, 10 and 50 µg/disc for VCA, RDA, T-2, TTN, DAS, HT-2, DON, NSL, FUS-X and NIV, respectively. The detection limits for corn and wheat spiked with T-2 were 0.1 and 0.2 µg/g, respectively. Non-TNN mycotoxins that did not inhibit yeast at a concentration of 200 µg/disc were aflatoxin B1 (AFB1), ochratoxin A (OA), citrinin (CT), penicillic acid (PA), cyclopiazonic acid (CPA), penitrem-A (PTA) and zearalenone (ZEE). These results indicate that disc diffusion assay using K. marxianus under optimized conditions provides a sensitive method for the detection of low concentrations of several TNN.

Quantification of Ochratoxin A in Swine Kidneys by Enzyme-linked Immunosorbent Assay Using a Simplified Sample Preparation Procedure.

An improved procedure for sample preparation and quantitation of ochratoxin A (OA) in swine kidneys was developed. Kidney samples were homogenized in acidified ethyl acetate, centrifuged, sub-sampled, dried, reconstituted with methanol and directly assayed using an indirect competitive enzyme-linked immunosorbent assay (ELISA). The rabbit antisera used in the development of this assay was found to have a high degree of cross-reaction with ochratoxins A and C but not with ochratoxins B, α, 4-OH-OA and two structurally similar molecules L-phenylalanine and citrinin with the values being 100, 80, 3.33, 10, 1.4, 0 and 0.04%, respectively. Extraction recoveries as determined by high performance liquid chromatography in kidneys spiked with 0.97 to 15.62 ppb OA were determined. The recovery values ranged from 91 to 110% with acceptable inter-assay coefficients of variation (CV) being obtained at the 3.9 ppb spiking concentration or higher. The lowest reproducible OA detection limit for the ELISA in the spiked swine kidney samples was 7.81 ppb with inter-assay CV of 8.85%. The ELISA analysis of the spiked samples correlated highly with conventional high-performance liquid chromatography (HPLC) analysis but was dependent on the conditions of the assay. Standards prepared in methanol or extract prepared from a kidney had correlation coefficients ® of 0.91 ± 0.09 and 0.94 ± 0.07, respectively. The assay is sensitive, specific, simple and sufficiently accurate for routine analysis of swine kidneys.

Effect of neomycin on the hydrolysis and toxicity of vicine and convicine in rats.

This study in the rat established the effects that a broad-spectrum and poorly absorbed antibiotic, neomycin sulfate, had on the in vitro and in vivo hydrolysis of vicine and convicine by the intestinal microflora, and on vicine- and convicine-induced depletion of blood glutathione and the resulting toxicity. The in vitro studies demonstrated that digesta from the caecum and large intestine were highly effective in hydrolysing vicine and convicine, whereas digesta from the same sections of the gastro-intestinal tract of neomycin-treated rats were much less effective (P < 0.0001). The in vivo studies showed that the total amount of vicine and convicine excreted in the urine and faeces was much greater in neomycin-treated rats compared with controls (P < 0.05), indicating the ability of neomycin to increase the amount of glycosides, particularly that of vicine, excreted in the faeces. The ability of glycosides to decrease the concentration of glutathione in blood (P < 0.05) and to increase rat mortality was greatly reduced in rats that were treated with neomycin, particularly in those treated ip with the toxin. Thus, the results demonstrated that neomycin reduced the rate at which vicine and convicine were hydrolysed in the lower section of the gastro-intestinal tract, and that neomycin treatment was associated with a reduced toxicity of the glycosides.

A review of recent advances in understanding ochratoxicosis.

Ochratoxin A (OA) is a toxin that contains an isocoumarin moiety linked by a peptide bond to phenylalanine. It is produced by certain Penicillium (mainly P. verrucosum) and Aspergillus (mainly A. alutaceus) species of storage fungi. Total amounts of OA and other related toxins produced by these fungi are influenced by many factors. Several forms of OA have been discovered, some of which are highly toxic, whereas others have lower toxicity. Ochratoxin A has been detected in foods, feeds, animal tissues, and human blood in both Europe and North America. It has been implicated in the fatal human disease Balkan endemic nephropathy, has been shown to be a powerful carcinogen in rodents, and produces many other adverse effects in animals. It is absorbed passively throughout the gastrointestinal tract and in an active manner in the kidney. It is subjected to intestinal secretion and reabsorption via enterohepatic recycling. Binding of OA in the blood to the albumin fraction and recycling in the bile and kidney contributes to its long half-life in animals. Ochratoxin A is hydrolyzed to its nontoxic alpha form (O alpha) by microorganisms in the rumen, cecum, and large intestine. The toxin is excreted primarily in the urine as O alpha and to a lesser degree as OA; smaller amounts of OA and O alpha are generally excreted in the feces. Three distinct mechanisms of OA toxicity have been proposed; other toxic effects of OA seem to be secondary in nature. Several different strategies can be employed for controlling or neutralizing the effect of OA, including the use of proper storage conditions, the use of specific adsorbents to reduce absorption of OA, and the feeding OA-contaminated feedstuffs to ruminants. Antioxidants such as ascorbic acid have been shown to reduce the toxic effects of OA in laying hens. In summary, OA contamination of cereal food and feed may occur, given appropriate conditions. Implementation of suitable procedures may eliminate or minimize this potentially serious problem.

Hydrolysis of ochratoxin A by the microbial activity of digesta in the gastrointestinal tract of rats.

This study established the influence of dietary neomycin sulphate on the rate of hydrolysis of ochratoxin A (OA) by digesta from the intestine, and its effect on the excretion of OA and its hydrolyzed metabolite, alpha ochratoxin (O alpha), in the urine and feces of the rat. The first in vitro study demonstrated that digesta from the cecum and the large intestine were able to hydrolyze OA whereas digesta from the small intestine and stomach had very low hydrolytic activity against this substrate. Homogenates of the liver had no hydrolytic activity. The second in vivo study demonstrated that digesta from the large intestine and cecum of the neomycin treated rats was much less effective (P < 0.001) in promoting the hydrolysis of OA than digesta from the control rats. Neomycin when added directly to the in vitro system, however, did not affect the rate at which OA was hydrolyzed. In a third study, OA was administered in vivo to control and neomycin-treated rats. Rats fed the neomycin containing diet compared to those fed the control diet had a higher concentration (P < 0.005) of blood OA, and a greater cumulative excretion of OA plus O alpha over the entire 5 day collection period in the feces (P < 0.0001) and a corresponding decrease in the cumulative excretion of OA plus O alpha in the urine (P < 0.0001). Individually, there was a marked increase in cumulative fecal excretion of OA (P < 0.05) and a corresponding decrease in excretion of O alpha (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)