Effects of in vivo carbon disulfide administration on the hepatic monooxygenase systems of microsomes from rats

Loss of 3-methylcholanthrene-inducible form of cytochrome P-450 in liver microsomes following administration of carbon disulfide in C57BL/6 Cr mice

Early after administration of CS2 to untreated, phenobarbital (PB)-and 3-methylcholanthrene (3-MC)-pretreated C57BL/6 Cr mice: (1) the loss of cytochrome P-450 was enhanced by pretreatment with both inducers, but to a greater extent with 3-MC; (2) the decrease in 7-ethoxyresorufin (ER) O-deethylation activity was much greater than that of cytochrome P-450 in untreated and PB-pretreated mice, but both paralleled values in 3-MC-pretreated mice, in which ER O-deethylation activity was induced markedly, (3) the peak of the carbon monoxide-difference spectrum of microsomal reduced cytochrome P-450 (about 448 nm) in 3-MC-pretreated mice shifted toward 450 nm after administration of increasing doses of CS2; (4) similar tendencies were observed in vitro in items (1) to (3); (5) electrophoresis of microsomal proteins revealed a loss of each protein band induced by PB and 3-MC following CS2 administration; (6) in the reconstituted monooxygenase system using partially purified cytochrome P-450 and P-448 forms from PB- and 3-MC-treated rats, CS2 suppressed the drug-metabolizing activities exhibited by the P-448 form but had little or no effect on those by the P-450 form; and (7) in n-octylamine difference spectra of microsomes, loss of the 3-MC-induced high spin form of cytochrome P-450 was evident. These results indicate that the 3-MC-inducible form of cytochrome P-450 was more susceptible to CS2 than the PB-inducible form. The hepato-necrogenic action of CS2 was not enhanced by PB or 3-MC pretreatment in mice.

Early, selective and reversible suppression of cytochrome P-450-dependent monooxygenase of liver microsomes following the administration of low doses of carbon disulfide in mice

The effects of carbon disulfide (CS2) on the liver microsomal drug-metabolizing enzyme system and other enzyme activities were studied 1 hr after the oral administration of 3-300 mg/kg of CS2 in mice. Considerable decreases in drug-metabolizing enzyme activities (such as hydroxylation of aniline, O-dealkylation of p-nitroanisole, 7-ethoxycoumarin and 7-ethoxyresorufin, and N-demethylation of N,N-dimethylaniline), NADPH-cytochrome P-450 reductase (but not NADPH-cytochrome c reductase), and P-450-associated peroxidase activities were already observed at 3 and 30 mg/kg of CS2, dose dependently. At the same dosage levels, the magnitudes of microsomal spectral changes induced by aniline and nicotinamide (type 2 substrates), but not those induced by hexobarbital and SKF-525A (type 1 substrates), were also reduced to a considerable extent. The degrees of these alterations were all greater than that of the measurable loss of P-450 content, i.e. the loss of functional activity of P-450 was much greater than simply expected from the apparent decrease in the hemoprotein content. Cytochrome b5 content and NADH-ferricyanide reductase activity were unchanged at 30 and 300 mg/kg of CS2, although NADH-cytochrome c reductase activity was increased at the latter dose. The following enzyme activities did not change significantly at up to 300 mg/kg of CS2: flavin-containing monooxygenase, UDP-glucuronyl transferase, glucose-6-phosphatase and heme oxygenase in microsomes, and glutathione S-transferases in the soluble fraction. Microsomal conjugated diene levels and liver glutathione content were also unchanged. These observations support the theory that P-450 is a sensitive and selective site for CS2 action, where CS2 itself is bioactivated. It was also shown that the loss of P-450 was reversible after a single, or repeated, administration of CS2.