Appraisal of fluorimetric assay of aryl hydrocarbon (benzo(alpha)pyrene) hydroxylase in cultured human lymphocytes

Detection of specific binding of [1,6-3H]2,3,7,8-tetrachlordibenzo-p- dioxin ([3H]TCDD) in human leukocytes using electrofocusing in polyacrylamide gel

The binding of [1,6-3H]2,3,7,8-tetrachlorodibenzo-p-dioxin ([3H]TCDD) in human leukocyte cytosol has been studied using electrofocusing in polyacrylamide gel. One single peak of bound [3H]TCDD is found after completed focusing with an isoelectric point of 6.0. The binding capacity for 1.5 nM [3H]TCDD in the leukocyte cytosol was completely saturated by incubation in the presence of 150 nM unlabelled 2,3,7,8-tetrachlorodibenzofuran. [3H]TCDD also binds to a single binding species in human serum and plasma which focuses at pH 5.2 and which is not saturated by the addition of a 100-fold excess of unlabelled 2,3,7,8-tetrachlorodibenzofuran to the incubation. The levels of specific binding of [3H]TCDD in leukocytes from healthy blood donors ranged from 0 to 50 fmol/mg cytosolic protein.

Kinetics of uptake and biliary excretion of benzo(alpha)pyrene and mutagenic metabolites in isolated perfused rat liver

An isolated liver perfusion system was used as a simplifying tool to study the metabolism and excretion of benzo(alpha)pyrene (BP) as a prototype carcinogen/mutagen. Phenobarbital (PB) was used to induce liver microsomal enzymes in Sprague-Dawley male rats prior to isolated liver perfusion. Control livers were run simultaneously using generally tritiated (G-3H)BP/BP as substrate in the perfusion medium. Both biliary excretion and liver weight were increased in the induced compared to control liver, but biliary flow when corrected for liver weight is statistically the same for both control and PB-induced livers. The excretion rat of radioactivity in the bile is always higher for PB-induced than for control liver (maximum radioactive excretion at 1 hr). There is a more rapid radioactivity removal in the liver perfusion medium for PB-induced than for control livers. Data are explained by increased metabolism of BP in induced liver leading to the presence of more polar metabolites undergoing preferential biliary excretion than in the control liver. Results support in vivo experimental data. Extracts from liver and bile were tested for microbial mutagenicity by the Ames test (TA 100) after TLC separation. The control liver shows virtually no mutagenicity in bile, only in TLC fractions from the liver. The PB-induced liver shows significant mutagenicity in several TLC fractions in both bile and liver. The net effect of induction is to produce more mutagenic metabolites of BP, excreted in the bile, and presenting a significant exposure of carcinogens/mutagens, and consequent hazard to man.

The metabolism of 7-ethoxycoumarin in primary maintenance cultures of adult rat hepatocytes

7-Ethoxycoumarin is metabolized to 7-hydroxycoumarin in short-term (1-4 days) maintenance cultures of adult rat hepatocytes. The 7-hydroxycoumarin is predominantly found as the sulphate and glucuronic acid conjugates. This pattern of metabolism is very similar to that observed with freshly-isolated rat hepatocytes and suggests that the culture system may be of value in studying the metabolism of novel chemicals designed for human therapeutic use. The specific activity of microsomal monooxygenase activity falls by 50-60% during 4 days in culture. This is not reflected by the sulphate and glucuronic acid conjugation pathways which are retained at normal levels throughout the entire 4-day culture period.