Comparative effect of phenobarbital and 3-methylcholanthrene on azo dye metabolism in rat liver. II. In vivo binding of metabolites to cellular macromolecules

The binding of 4-dimethylaminoazobenzene (DAB) metabolites to liver total protein and nuclear DNA was studied in rats pretreated with phenobarbital (PB) or 3-methylcholanthrene (3-MC), then fed with a (-14C)DAB diet (0.06%) for 3 days. Three consecutive injections of PB (80mg-kg) led to a 50% decrease of DAB metabolites bound to total protein and nuclear DNA. A single injection of 3-MC(20 mg-kg) roughly doubled the amount of metabolites bound to nuclear DNA but did not modify those bound to protein. When given in the diet (0.005%) for 8 days before the (-14C)-DAB diet, 3-MC did not change the amount of DAB metabolites bound either to protein, or to DNA. The opposite effect of PB and 3-MC injections on azodye binding to cellular constituents might be relevant to the action of these drugs on carcinogenesis. Moreover the route of 3-MC administration might be meaningful since DAB metabolite binding to DNA was only increased by intraperitoneal injection.

Comparative effect of phenobarbital and 3-methyl-cholanthrene on azodye metabolism in rat liver. I. In vitro studies on detoxication and activation processes

The effect of phenobarbital (PB) and 3-methylcholanthrene (3-MC) administration on detoxication and activation of the carcinogenic azodye 4-dimethyl-aminoazobenzene (DAB) was studies in rat liver microsomes. Azoreductase activity and in vitro DAB metabolite binding to calf thymus DNA and microsomal protein were simultaneously determined. Pretreatment of rats with 3 daily injections of PB (80 mg/kg) did not significantly modify azoreductase activity by increased DAB metabolite binding to DNA (+ 67%) and to protein (+ 123%). The effect of 3-MC differed according to the route of administration. When it was given intraperitoneally (1 times 20 mg/kg)azoreductase was not modified and DAB metabolite binding to DNA and to protein was eight-fold enhance. After continuous administration of 3-MC in the diet (3.0 MG/KG/DAY)AZOREDUCTASE ACTIVITY WAS DECREASED (MINUS 40%), DAB metabolite binding to DNA was unchanged and DAB metabolite binding to protein tripled. Thus the balance between the formation of DAB metabolites bound to DNA and azoreduction led to an increased activation/reduction ratio only by 3-MC injection. In every case, the formation of DAB metabolites bound to protein was significantly increased as compared with detoxication. Different effects of PB and 3-MC were discussed with reference to the synthesis of distinct cytochromes.

[Metabolism and in vitro binding of several organochlorine and organophosphate pesticides to calf thymus DNA and rat liver microsomal proteins]

The organophosphorus insecticide ethyl-parathion was transformed by rat liver microsomes into metabolites which were bound to calf thymus DNA, in large amount. When the rats were treated by phenobarbital or 3-methylcholanthrene, the metabolite binding to DNA was increased two-fold. By contrast, in the same conditions, the organochlorine insecticides, aldrin, dieldrin and gamma hexachlorocyclohexane (lindane), did not yield metabolites able to bind to DNA and to proteins.

Differential solubilization of proteins, phospholipids, free and esterified cholesterol of rat liver cellular membranes by sodium deoxycholate

1. Smooth microsomes, Golgi-rich fractions, and light and heavy plasmalemmal subfractions from rat liver were isolated and their purity assessed using enzymic, chemical and morphological criteria. 2. Membranes were prepared by Tris-EDTA washing combined with sonication treatment of the different subcellular fractions. 3. Washed membranes were submitted to differential solubilization with 0.26% sodium deoxycholate. When the deoxycholate/phospholipid molar ratio (R) is raised, all the membranes showed a maximum protein solubilization occurring at R approximately equal TO 2. The higher the membrane neutral lipid to phospholipid molar ratio is, the lower the solubilized protein plateau lies. 4. Phospholipids are solubilized in slightly greater amounts than proteins and their solubilization is complete at R equals 14-16. 5. For R smaller than 2, sterols are solubilized in slightly greater amounts than phospholipids. At maximum protein solubilization, cholesterol and cholesterol esters completely differ in their behaviour. The whole membrane cholesterol goes into solution for R equals 14-16 while the solubilization of esterified cholesterol is never complete. The higher the protein plateau is, the lower the cholesterol esters solubilization curve asymptote lies.