Metabolism of ochratoxin A by rats.

Albino rats were given ochratoxin A (6.6 mg/kg body weight) intraperitoneally or per os. Independent of route administration, 6% of a given dose was excreted as the toxin, 1 to 1.5% as (4R)-4-hydroxyochratoxin A, and 25 to 27% as ochratoxin alpha in the urine. The metabolite (4S)-4-hydroxyochratoxin A, which is formed by rat liver microsomes in the presence of NADPH, was not detected. Only traces of ochratoxins A and alpha were found in feces. Identical experiments were carried out with brown rats, since the Km value for the formation of the 4S epimer was considerably lower when brown rat microsomes were used. About the same ratios of metabolites and metabolite recoveries as those found for albino rats were found for brown rats. Brown rats were also given the two hydroxylated metabolites and ochratoxin alpha (0.66 mg/kg body weight) intraperitoneally. The three compounds were excreted in the urine; within 48 h, 90% recovery of ochratoxin alpha and 54 and 35%, respectively, of the 4R and 4S isomers were observed.     

Metabolism of ochratoxin B and its possible effects upon the metabolism and toxicity of ochratoxin A in rats

A metabolic product was formed from ochratoxin B by rat liver microsomal fractions in the presence of NADPH. It was isolated from the incubation mixture by extraction, thin-layer chromatography, high-pressure liquid chromatography, and crystallization. On the basis of mass and nuclear magnetic resonance spectroscopy, the structure is suggested to be 4-hydroxyochratoxin B. The Km for the formation of 4-hydroxyochratoxin B was determined, and the hydroxylation of ochratoxin A was not altered by the presence of ochratoxin B. Rats were given ochratoxin A or B, or a mixture of both intraperitoneally. The ratios of the three metabolites, ochratoxin A, (4R)-4-hydroxyochratoxin A, and ochratoxin alpha, excreted in the urine did not change in the presence of ochratoxin B. Ochratoxin B was metabolized to 4-hydroxyochratoxin B and ochratoxin beta, but in a different ratio than for the ochratoxin A metabolites. When given intraperitoneally, ochratoxin beta was excreted within 24 h. In rats treated with ochratoxin A alone, the food intake was reduced by 50%, and histologically severe lesions, degeneration, and necrosis were observed in the proximal tubules. When ochratoxin A and B given in combination, the animals were clinically unaffected and histologically there was only slight damage of proximal tubules. These observations indicate that ochratoxin B considerably reduces the toxic effects of ochratoxin A.     

Metabolism and toxicokinetics of the mycotoxin ochratoxin A in F344 rats

Male (n=18) and female (n=18) F344 rats were administered a single dose of OTA (0.5 mg/kg b.w.) in corn oil by gavage. Animals (n=3) were sacrificed 24, 48, 72, 96, 672 and 1,344 hours after OTA administration and concentrations of OTA and OTA-metabolites in urine, feces, blood, liver and kidney were determined by HPLC with fluorescence detection and/or by LC-MS/MS. Recovery of unchanged OTA in urine amounted to 2.1% of dose in males and 5.2% in females within 96 h. In feces, only 5.5% resp. 1.5% of dose were recovered. The major metabolite detected was OTalpha, low concentrations of OTA-glucosides were also present in urine. Other postulated metabolites were not observed. The maximal blood levels of OTA were observed between 24 and 48h after administration and were app. 4.6 µmol/l in males and 6.0 µmol/l in females. Elimination of OTA from blood followed first-order kinetics with a half-life of app. 230h calculated from 48h to 1344h. In liver of both male and female rats OTA-concentrations were less than 12 pmol/g tissue, with a maximum at 24h after administration. In contrast, OTA accumulated in the kidneys, reaching a concentration of 480 pmol/g tissue in males 24h after OTA-administration. In general, tissue concentrations in males were higher than in females. OTalpha was not detected in liver and kidney tissue of rats administered OTA and OTalpha concentrations in blood were low (10–15 nmol/1). The high concentrations of OTA in kidneys of male rats may explain the organ- and gender-specific toxicity of OTA.     

Inhibition of renal gluconeogenesis in rats by ochratoxin.

In kidney-cortex slices from rats fed on 2.0 mg of ochratoxin A/kg per day for 2 days, gluconeogenesis from pyruvate is decreased by 26%, and renal phosphoenolpyruvate carboxykinase activity is lowered by about 55%. Gluconeogenesis from 10 mM-lactate or 20 mM-malate or -glutamine is also significantly decreased. Hepatic phosphoenolpyruvate carboxykinase is unchanged or increased, and hexokinase activity in kidney and liver remains unaffected. We conclude that ochratoxin A in vivo is an inhibitor of renal phosphoenolpyruvate carboxykinase activity, which is responsible, at least in part, for the block in renal gluconeogenesis.     

Metabolism of daidzein by fecal bacteria in rats

Daidzein (4',7-dihydroxyisoflavone), a soy phytoestrogen, is a weakly estrogenic compound that may have potential health benefits. Biotransformation of daidzein by the human gut microflora after ingestion converts it to either the highly estrogenic metabolite equol or to nonestrogenic metabolites. We investigated the metabolism of daidzein by colonic microflora of rats. Fecal samples, obtained before and after rats were exposed to daidzein at 250 or 1000 parts per million, were incubated in brain-heart infusion (BHI) broth with daidzein under anaerobic conditions. Samples were removed from the cultures daily and analyzed by high-performance liquid chromatography (HPLC) and mass spectrometry. The fecal bacteria of all rats, regardless of prior daidzein exposure, metabolized the added daidzein to dihydrodaidzein. Both compounds disappeared rapidly from BHI cultures incubated for more than 24 h, but no other daidzein metabolites were detected. Only daidzein and dihydrodaidzein were found in a direct analysis of the feces of rats that had consumed daidzein in their diets. Unlike the fecal bacteria of humans and monkeys, the rat flora rapidly metabolized daidzein to aliphatic compounds that could not be detected by HPLC or mass spectral analysis.     

Metabolism of Imidazole by a Pseudomonad

Intermediates formed during the microbial degradation of imidazole, namely 4(5)-imidazolone, formiminoglycine, and possibly glycine, are similar to those formed during metabolism of imidazole derivatives.     

Metabolism of beta-methylaspartate by a pseudomonad

A bacterium was isolated from soil which utilizes threo-beta-methyl-l-aspartate, certain other amino acids, and a variety of organic substances as single energy sources. It is, or closely resembles, Pseudomonas putida biotype B. The ability of this organism to rapidly decompose such amino acids is dependent on inducible enzyme systems. Dialyzed cell-free extracts of this bacterium metabolize beta-methylaspartate only when catalytic amounts of alpha-ketoglutarate, or pyruvate, and pyridoxal phosphate are also present. The main products formed from beta-methylaspartate under these conditions are alpha-aminobutyrate, carbon dioxide, and alpha-ketobutyrate. When l-aspartate is substituted for beta-methylaspartate in this system, it is converted mainly to alanine and carbon dioxide. beta-Methyloxalacetate is decarboxylated, and the resulting alpha-ketobutyrate is converted enzymatically in the presence of glutamate to alpha-aminobutyrate which accumulates. The added keto acids are converted, in part, to the corresponding amino acids probably by transamination. The data indicate that beta-methylaspartate is converted to alpha-aminobutyrate, and aspartate to alanine, by a circuitous transamination-beta-decarboxylation-transamination sequence rather than by a direct beta-decarboxylation.     

Metabolism of oestradiol-17beta by intestinal bacteria in rats.

In vitro experiments were carried out in which [4-14C]oestradiol-17beta was incubated with a culture from caecal content from adult male rats at 37 degrees C in an atmosphere of nitrogen. Oestrone was identified as the only certain metabolite. Other metabolites, if present, were quantitatively unimportant. The conversion of oestradiol-17beta to oestrone was estimated to be 22-42%.     

Metabolism of leucine in protein-caloriedeficient rats

1. Protein-calorie-depleted rats exhibit a decreased ability to oxidize leucine as compared with control animals. 2. The block in degradation of l-leucine is due to decreased activities of l-leucine transaminase and d-amino acid oxidase associated with liver mitochondria. 3. Cytoplasmic l-leucine transaminase in liver is not affected by the protein depletion. 4. The specific activities of the mitochondrial enzymes can be increased by a single oral dose of 1g. of Bacto-Peptone (meat hydrolysate). The effect of Bacto-Peptone can be inhibited by prior administration of dosages of 10mg. of puromycin/100g. body wt., suggesting that the increased enzyme specific activities may be due to new synthesis of enzyme protein.     

Metabolism of verruculogen in rats.

Radiolabeled verruculogen was detected in a wide range of body tissues 6 min after intravenous administration, but after a further 20 min it was mainly being excreted via the biliary route. In isolated liver perfusion, [14C]verruculogen was rapidly taken up by the liver and metabolized completely, principally to the related tremorgen TR-2 but also to a desoxy derivative of verruculogen. In addition, a smaller amount of an isomer of TR-2 was detected. These metabolic products were excreted in the bile.     

Metabolism of dietary procyanidins in rats

Procyanidins are major dietary polyphenols made of elementary flavan-3-ol (epi)catechin units. They have antioxidant properties and may contribute to health benefits in humans, but little is known about their metabolic fate. We compared here the metabolism of procyanidin dimer B3, trimer C2, and polymer isolated from willow tree catkins to that of catechin monomer in rats. These compounds were administered in the rat diet (0.1%, w/w) for 5 d and their metabolites estimated in 24 h urine. In rats fed procyanidins, neither parent compound nor catechin derivatives could be detected in contrast to animals fed catechin monomer, which excreted large amounts of catechin and its 3'-O-methylated form (25.7 +/- 0.6%). On the other hand, 16 metabolites of microbial origin were detected and identified as phenylvaleric, phenylpropionic, phenylacetic, and benzoic acid derivatives. Their total yields significantly decreased from the catechin monomer (10.6 +/- 1.1%) to the procyanidin dimer (6.5 +/- 0.2%), trimer (0.7 +/- 0.1%), and polymer (0.5 +/- 0.1%). Therefore, the degree of procyanidin polymerization has a major impact on their fate in the body characterized by a poor absorption through the gut barrier and a limited metabolism by the intestinal microflora as compared to catechin. This will have to be considered to explain the health effects of procyanidins. The contribution of their microbial metabolites should also be further investigated.