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The lipid composition of rat liver microsomes was not altered in response to a single acute dose of ethanol relative to isocaloric glycerol-treated controls. Microsomal cytochrome P-450 was transiently elevated, the elevation paralleling blood ethanol levels. Microsomal NADPH oxidase was transiently elevated relative to the activity in isocaloric glycerol-treated controls.
It was demonstrated that endogenous lipid peroxidation (LPO) is an effective mechanism of disassembly of endoplasmic reticulum membranes and cytochrome P-450 (P-448) in the liver. The rate of cytochrome P-450 (P-448) degradation in vivo can be regulated by free radical scavengers. The constitutive forms of cytochrome P-450 (P-448) are less sensitive to LPO induced in vivo or in vitro than the inducible ones.
It was shown that benz (alpha) pyrene inhibits the NADPH-dependent lipid peroxidation (LPO) in rat liver microsomes in vitro. The degree of LPO inhibition is correlated with the accumulation of hydroxylated derivatives of benz (alpha) pyrene in the presence of NADPH. Benz (alpha) pyrene protects cytochrome P-450 against conversion into its inactive form, P-420, induced by LPO. Another inhibitor of the NADPH-dependent LPO in rat liver microsomes is chlorpromazine. Inhibition of LPO is due to the antioxidant effect of hydroxylated derivatives of chlorpromazine formed in the course of its metabolism by NADPH-dependent microsomal oxygenase. NADPH-dependent formation of hydroxylated metabolites of chlorpromazine, possessing antioxidant properties, was also estimated in brain cortex microsomes from rats and men. It is shown that chlorpromazine when preliminarily injected to rats, protects against LPO activation in brain tissue in vivo induced by exposure of the animals to hyperbaric oxygenation.
Previous Benznidazole (Bz) administration to rats (30 mg/kg, i.p.) significantly prolongs their pentobarbital sleeping time. This prolonging effect of Bz administration correlates with the inhibitory action of Bz on the liver aminopyrine or ethylmorphine N-demethylase activities. Inhibition of these enzyme systems by Bz is non-competitive and would not be related to changes in liver microsomal cytochrome P-450 (P-450) content or in cytochrome c-reductase activity or to interactions of Bz with P-450 leading to spectral changes. Covalent interactions of Bz reactive metabolites with microsomal proteins or phospholipids might be involved instead.
1. MFO enzyme activities were measured in microsomes from whole mussels (Mytilus galloprovincialis) comber livers (Serranus cabrilla), or Posidonia oceanica etiolated tissues, and PAH contents were determined in sediments collected in coastal locations of the French Riviera and Corsica during 3 oceanographic cruises in 1987-1988. 2. BaP activities in mussel and EROD activities measured in fish were strongly correlated to the log of PAH content in sediments. The first results for CA4H in Posidonia showed significant differences related to PAH pollution levels. The increase in MFO activities measured in Corsica in summer 1988 indicated a recent petroleum contamination.
1. 3,3',4,4'-tetrachlorobiphenyl (PCB 77), but not hexachlorobenzene, induced liver microsomal cytochrome P-450 (Cyt P-450), ethoxycoumarin-O-deethylase (ECOD) and ethoxyresorufin-O-deethylase (EROD) in rainbow trout. Maximum induction was observed in a PCB 77 injected group of fish (1.0 mg/kg, i.p. injection) 13 days after the injections being 2, 10 and 50 times the value of non-induced fish, respectively. 2. The apparent Km value of ethoxyresorufin of this induced group of fish differed only slightly from that of non-induced fish. The apparent Vmax value (EROD) was 50 times higher. 3. Freezing small pieces of liver in liquid nitrogen did not produce cytochrome P-420. 4. Fluorimetric and spectrophotometric measurements of EROD correlated.
The degradation of cytochrome P-450 as a result of proteolytic action of trypsin is a biphasic process. Lipid peroxidation (LPO) increases the rate of the fast phase of cytochrome P-450 degradation and its accessibility to protease. The efficiency of this process depends on the mode of LPO induction and decreases in the following order: NADPH----NADH----ascorbate-dependent LPO. The induction of the monooxygenase system increases the efficiency of proteolysis. LPO and proteolysis seem to be mutually enhancing processes which provide for a high efficiency of cytochrome P-450 degradation. LPO can be regarded as a triggering mechanism which makes various forms of cytochrome P-450 accessible to endogenous proteases.