... Ochratoxin A is hydrolyzed by the intestinal microflora into nontoxic compounds (7-carboxy-5-chloro-8-hydroxy-3,4-dihydro-3R-methylisocoumarin (Ochratoxin alpha) and phenylalanine). It is excreted as either ochratoxin A, hydroxylated ochratoxin A or Ochratoxin alpha in both the urine and feces. ...
Hydroxyochratoxin A was isolated & identified from urine of rats after injection with ochratoxin A. By incubating ochratoxin A with rat liver microsomes & NADPH, 1 major (90%) & 2 minor metabolites, more polar than ochratoxin A, were formed.
Single oral or iv dose (2.5 mg/kg) ochratoxin A admin to healthy adult rats. Ochratoxin alpha only metabolite recovered from cecum & large intestine. Ochratoxin A excreted via urine & feces, both as free drug & ochratoxin alpha. Unidentified metabolites in urine.
Ochratoxin A is cleaved into phenylalanine and a less toxic iso-coumarin derivative (ochratoxin alpha) by the microbial flora of the colon ... and by carboxypeptidase A and alpha-chymotrypsin ... .
Ochratoxin A is cleaved into phenylalanine and a less toxic iso-coumarin derivative (ochratoxin alpha) by the microbial flora of the colon, and by carboxypeptidase A and alpha-chymotrypsim. This is is the major metabolic pathway. 4-Hydroxyochratoxin A is the main hepatic metabolite and its formation appears to be via a polymorphic-like debrisoquine 4-hydroxylation. Some cytochrome P-450 enzymes, such as CYP2C9, and known to metabolize ochratoxin A into more cytotoxic compounds. (T35, A2870, A3099)
Ochratoxin A has been shown to be weakly mutagenic, possibly by induction of oxidative DNA damage. The nephrotoxin ochratoxin A (OTA) causes a reduction of glomerular filtration rate (GFR) and of para-aminohippuric acid (PAH) clearance. It is a nephrotoxin which blocks plasma membrane anion conductance in Madin-Darby canine kidney (MDCK) cells. Some cytochrome P-450 enzymes, such as CYP2C9, are known to metabolize ochratoxin A into more cytotoxic compounds capable of forming DNA adducts. (A2869, A3099)
Evaluation: There is inadequate evidence in humans for the carcinogenicity of ochratoxin A. There is sufficient evidence in experimental animals for the carcinogenicity of ochratoxin A. Overall evaluation: Ochratoxin A is possibly carcinogenic to humans (Group 2B).
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.
... Ochratoxin A is rapidly absorbed throughout the entire gastrointestinal tract and distributes itself in the body as a two compartment open model and has a particular high affinity for serum albumin. Ochratoxin A is hydrolyzed by the intestinal microflora into nontoxic compounds (7-carboxy-5-chloro-8-hydroxy-3,4-dihydro-3R-methylisocoumarin (Ochratoxin alpha) and phenylalanine). It is excreted as either ochratoxin A, hydroxylated ochratoxin A or Ochratoxin alpha in both the urine and feces. Ochratoxin A appears to exert its toxic effect by promoting an increased level of lipid peroxidation by inhibition of an amino acylation reaction and possibly by conversion into metabolites that are capable of binding DNA. These in turn cause other secondary effects associated with ochratoxin A. It would appear that this compound presents a true potential hazard for humans as its occurrence is wide spread and it is highly carcinogenic.
Rats intubated daily with 500 ug ochratoxin A or fed 250 ug daily in barley. There was little accumulation of cmpd in liver or kidneys. Avg total amount excreted daily in urine & feces was just over 10% of administered dose. Small amount of hydrolysis product also excreted.
Rats given single ip injection of 1 mg ochratoxin A labelled with (14)C. Reached highest levels in serum (90%), liver (4.5%), & kidney (4.4%) 30 min later. Ochratoxin A was excreted primarily in urine as unchanged toxin or metabolites. Excretion in feces less significant.
