Effects Of 3-methylcholanthrene Pretreatment Research Articles

Effect of 3-Methylcholanthrene Pretreatment on Aflatoxin B1Metabolism in Hamster Liver

AbstractThe effects of 3-methylcholanthrene (MC) pretreatment of hamsters on the hepatic metabolism of aflatoxin B1 (AFB1) have been investigated in studies with subcellular, isolated hepatocytes and in vivo. Pretreatment of hamsters with MC (2.5 mg/100 g body wt.) 24 hr. before sacrifice not only increased microsomal cytochrome P-450 content by 70% but also increased the specific activity of cytochrome P-450 dependent metabolic activation of AFB1 as judged by AFB1-DNA binding by 65%. Even in isolated hepatocytes, AFB1-DNA binding was elevated by 65% in MC-treated hepatocytes. The ratios of AFB1-glutathione (AFB1-SG) to AFB1-DNA were about the same in both hepatocyte system. Hepatic AFB1-DNA binding was also increased by 85% in intact animals after MC treatment. It appears that the increased hepatic AFB1-DNA binding after MC treatment of hamsters is a result of higher specific activity and higher levels of cytochrome P-450 species involved in the activation of AFB1.

Effect of 3-methylcholanthrene pretreatment on 2-acetylaminofluorene n- and ring-hydroxylation by rat and hamster liver microsomes

The N- and ring-hydroxylation of 2-acetylaminofluorene (AAF) are studied with microsomal fractions of livers from both control and 3-methylcholanthrene (MC)-pretreated rats and hamsters. The profiles of hydroxylations are similar in the presence of either low (2.3 μM) or high (100 μM) substrate concentrations. Pretreatment of rats gives a severalfold increase both in N- and ring-hydroxylation, whereas m hamsters, such a pretreatment induces a specific and large increase in N- hydroxylation only.

Metabolism of benzo[ a]pyrene : Effect of 3-methylcholanthrene pretreatment on metabolism by microsomes from lungs of genetically “responsive” and ”nonresponsive” mice

The metabolism of [ 14C]benzo[ a]pyrene by microsomes from the lungs of normal and 3-methylcholanthrene-treated DBA/2J, C57BL/6J, and A/HeJ mouse strains was quantitatively analyzed by high-pressure liquid chromatography. The ratio of dihydrodiols of benzo[ a]pyrene to total metabolites formed was greater with lung microsomes than with liver microsomes in all three strains. The ratio of epoxide hydrase to monooxygenase activity in mouse lung was shown to be considerably higher than in mouse liver. Benzo[ a]pyrene metabolism by control lung microsomes showed some strain differences. C57BL/6J and A/HeJ mice formed twice as much dihydrodiols as a percentage of total metabolism compared to DBA/2J mice. DBA/2J mice produced somewhat less phenol 2 fraction and considerably more quinone 1 and 2 fractions than the other two mouse strains as a percentage of total metabolism. Treatment of C57BL/6J and DBA/2J mice with 3-methylcholanthrene resulted in a 20-fold increase in the metabolism of benzo[ a]pyrene, while A/HeJ mice were induced more than 50-fold. The profiles of metabolites from the 3-methylcholanthrene-induced animals were nearly identical in all three mouse strains.

Some effects of selenium deficiency on the hepatic microsomal cytochrome P-450 system in the rat

The hepatic microsomal cytochrome P-450 system was investigated in male rats fed a selenium-deficient Torula yeast diet for 3 mo after weaning and in control rats fed the same diet with 0.5 μg selenium as Na 2SeO 3 added per gram of diet. Cytochrome P-450 and b 5 contents, NADPH-cytochrome c reductase, ethylmorphine demethylase, 2- and 4-biphenyl hydroxylase activities, and pentobarbital sleeping time were measured and the effect of phenobarbital pretreatment on these parameters was determined. The effect of 3-methylcholanthrene pretreatment on all parameters except sleeping time was studied. Selenium deficiency caused no alterations in any of the above activities in untreated or 3-methylcholanthrene-treated rats. However, phenobarbital treatment in seleniumdeficient rats produced an increase in cytochrome P-450 content of only 70% as compared to 150% in the similarly treated controls. The induction of ethylmorphine demethylase activity by phenobarbital was also impaired in selenium-deficient rats. No such impairment in the induction of cytochrome b 5 content, NADPH-cytochrome c reductase activity, biphenyl hydroxylase activity, or pentobarbital sleeping time occurred. The percentage of the carbon monoxide-reactive cytochrome P-450 which bound metyrapone was the same in phenobarbital-treated selenium-deficient rats and in phenobarbital-treated controls. Also the cytochrome P-450 ethyl isocyanide binding spectra were similar in phenobarbital-treated selenium-deficient rats and in phenobarbital-treated control rats. These data indicate a specific effect of selenium in the hepatic microsomal cytochrome P-450 system. The biochemical function of selenium giving rise to this effect is unknown.

Effects of 3-methylcholanthrene pretreatment on microsomal hydroxylation of 2-acetamidofluorene by various rat hepatomas.

1. The effects of 3-methylcholanthrene pretreatment on both N- and ring hydroxylation of 2-acetamidofluorene by microsomal preparations from various well-differentiated and poorly differentiated hepatomas, primary tumours and their host livers and kidneys were studied. 2. Well-differentiated Morris hepatomas 5123C, 5123D, 5123CTC and 7800 and their host livers had low hydroxylating activity. Pretreatment with 3-methylcholanthrene caused a several-fold increase in both N- and ring hydroxylation in the host livers whereas in all tumours except 5123CTC it caused a many-fold increase only in ring hydroxylation. 5123CTC tumour in addition showed a fourfold increase in N-hydroxylating activity. 3. Hydroxylating activities of poorly differentiated Morris hepatoma 7288CTC and Novikoff hepatoma were low and they could not be altered by 3-methylcholanthrene pretreatment. 4. Primary hepatomas produced by administration of 4-dimethylamino-3'-methylazobenzene could be stimulated to some extent on 3-methylcholanthrene pretreatment; however, primary mammary tumour produced by administration of 3-methylcholanthrene was not responsive to 3-methycholanthrene pretreatment. 5. Like host livers, kidneys of tumour-bearing animals could also be stimulated to some extent by 3-methylcholanthrene pretreatment.

Species variations in the N- and ring-hydroxylation of 2-acetylaminofluorene and effects of 3-methylcholanthrene pretreatment.

Summary1. Assays for N- and ring-hydroxylation of 2-acetylaminorluorene (AAF) by hepatic microsomes from normal and 3-methylchloranthrene (MC) -treated rats, hamsters, mice, rabbits, and guinea pigs showed marked differences in these enzyme activities in normal animals of the different species and in the effects of MC-treatment. The microsomes of all species, except the guinea pig in which A′-hydroxylation could not be detected, showed increases in N-hy-droxylation on MC-treatment; the largest increase was observed with hamster liver microsomes. Only rat and mouse liver microsomes showed large increases in ring-hydroxylation activity on MC-treatment. Increases in N-hy-droxylation activity of hamster liver microsomes and in ring-hydroxylation activity by rat liver microsomes after MC treatment were inhibited by administration of actinomycin D or puromycin. 2. MC-treatment of rats or hamsters did not affect the reduction of N-hy-droxy-AAF by liver homogenates. 3. MC administration caused a decrease in urina...