Spin-trapping studies on the free-radical products formed by metabolic activation of carbon tetrachloride in rat liver microsomal fractions isolated hepatocytes and in vivo in the rat

Abstract

1. The metabolic activation of carbon tetrachloride to free-radical intermediates is an important step in the sequence of disturbances leading to the acute liver injury produced by this toxic agent. Electron-spin-resonance (e.s.r.) spin-trapping techniques were used to characterize the free-radical species involved. 2. Spin trapping was applied to the activation of carbon tetrachloride by liver microsomal fractions in the presence of NADPH, and by isolated intact rat hepatocytes. The results obtained with the spin trap N-benzylidene-2-methylpropylamine N-oxide ('phenyl t-butyl nitrone') (PBN) and [13Clcarbon tetrachloride provide unequivocal evidence for the formation and trapping of the trichloromethyl free radical in these systems. 3. With the spin trap 2-methyl-2-nitrosopropane, however, the major free-radical species trapped are unsaturated lipid radicals produced by the initiating reaction of lipid peroxidation. 4. Although pulse radiolysis and other evidence support the very rapid formation of the trichloromethyl peroxy radical from the trichloromethyl radical and oxygen, no clear evidence for the trapping of the peroxy radical was obtainable. 5. The effects of a number of free-radical scavengers and metabolic inhibitors on the formation of the PBN-trichloromethyl radical adduct were studied, as were the influences of changing the concentration of PBN and incubation time. 6. High concentrations of the spin traps used were found to have significant effects on cytochrome P-450-mediated reactions; this requires caution in interpreting results of experiments done in the presence of PBN at concentrations greater than 50mM.

Chemistry and biology of spin-trapping radicals associated with halocarbon metabolism in vitro and in vivo.

“…These results have now been confirmed by other laboratories (39,40). It was also demonstrated that the trichloromethyl radicals apparently are generated in rat liver microsomes by only one form of cytochrome P-450 (41,42 rapidly and essentially disappears within 1 hr.…”

“…2(CH3)3COO-(CH3)3COOOOC(CH3)3 (38) (CH3)3COOOOC(CH3)3 --2(CH3)3CO + 02 (39) 0 (CH3)3CO -> CH3-+ CH3-C-CH3 (40) Superoxide can be made electrochemically by reduction of oxygen and subsequently reacted with the halocarbon (19,25,26). Sawyer and co-workers (5,25,26) have published some studies on compounds with the trichloromethyl group performed in this manner.…”

Antioxidant and hepatoprotective activities of Egyptian moraceous plants against carbon tetrachloride-induced oxidative stress and liver damage in rats

“…Also, kaempferol is a very good scavenger, even though it only has one hydroxyl group on the B ring (4′-OH), possibly due to the combination of other characteristics such as, a C2-C3 double bond, 3-OH group, and 4-keto group on ring C (Van Acker et al, 1996. The mechanism of antiradical action of quercetin and its glycoside was evaluated by Afanas'ev et al (1989) and Albano et al (1982) who referred the inhibitory effects of both quercetin and rutin to their ability to ameliorated the damage occurred by CCl 4 -dependent lipid peroxidation in rat liver microsomes. Therefore, the data reported herein reveal a protective potential of quercetin and kaempferol glycosides, the main constituents of F. carica leaf, against the acute hepatotoxicity induced by CCl 4 in rats.…”

Antioxidant and drug detoxification potential of aqueous extract ofAnnona senegalensisleaves in carbon tetrachloride-induced hepatocellular damage

“…Hepatocellular toxicity of CCl 4 requires activation by the liver microsomal mixed function oxidase (CYP 2E1) to produce trichloromethyl radical (CCl 3 . ) (Albano et al, 1982). In the presence of oxygen, however, CCl 3…”