Liver DNA adducts in methyl-deficient rats administered a single dose of aflatoxin B1

Retrospective evaluation of serum ornithine carbamyltransferase activity as an index of hepatotoxicity in toxicological studies with rats

The sensitivity of elevated serum ornithine carbamyltransferase (OCT) as an index of hepatotoxicity in rats was assessed in different studies conducted over a number of years and originally designed to examine the toxicity or carcinogenicity of a variety of test chemicals and diets. Changes in serum OCT activities were compared with the more widely used clinical endpoints, alanine aminotranserase (ALT) and aspartate aminotransferase (AST). In the first study, rats received a single oral dose of the hepatotoxic and hepatocarcinogenic fungal toxin aflatoxin B(1) (AFB(1)). The increase in enzyme levels between control and AFB(1)-treated rats was greater for serum OCT than for ALT or AST. This response was similar to the changes in serum enzyme levels in studies where rats ingested a hepatotoxic and hepatocarcinogenic choline deficient (CD) diet. When rats were exposed to the hepatotoxic and nephrotoxic fungal toxin fumonisin B(1) (FB(1)) by intraperitoneal injection for 6 days, serum AST and ALT were significantly elevated above control levels while OCT was unaffected. The peroxisome proliferator ciprofibrate caused elevated ALT and AST but not OCT at week 52 of dietary exposure, after the development of liver nodules and tumours. Of the two liver-specific enzymes examined in all of the studies, ALT was more consistently predictive of hepatotoxicity than OCT.

Acute hepatic response to aflatoxin B1 in rats fed a methyl-deficient, amino acid-defined diet

In order to evaluate the relative contribution of aflatoxin B1 (AFB1)-induced toxicity towards a methyl-deficient diet influenced AFB1 carcinogenesis, a no-observed-effect-level (NOEL) for AFB1, with reference to liver damage, was determined in rats fed a nutritionally complete amino acid-defined basal (CMS) diet or a choline-methionine-deficient (CMD) diet. After 3 weeks of dietary treatment, male Fischer 344 rats received a single, oral dose of AFB1 in the range of 100-600 pg/kg body weight. At 24, 48 and 72 h after AFB1 treatment, six serum biochemical parameters were analysed in parallel with histological examination of liver sections. In rats fed the CMS diet and receiving 250-600 micrograms/kg AFB1, serum levels of glutamyl oxalo-transaminase (SGOT), glutamyl pyruvic transaminase (SGPT), alkaline phosphatase (ALP) and total bilirubin increased, glucose levels decreased and gamma glutamyl transpeptidase (GGT) levels remained unchanged over the 72-h period following mycotoxin treatment. However, at 100 micrograms/kg AFB1, these serum parameters remained at control levels. Pathological examination of liver sections indicated no significant lesions at 100 micrograms/kg AFB1 confirming this as the non-necrogenic dose or NOEL in CMS diet group rats. In contrast, in CMD diet fed rats, serum or pathology data showed no obvious time- or dose-response to mycotoxin treatment, extensive hepatic lipidosis in response to dietary treatment being the only predominant lesion in this diet group. The milder response of CMD rat livers to a single dose of AFB1 suggest a possible reduction in the susceptibility of these livers to AFB1 toxicity.