Reduced glutathione effects on alpha-tocopherol concentration of rat liver microsomes undergoing NADPH-dependent lipid peroxidation.
Factors involved in reduced glutathione (GSH) and vitamin E-mediated inhibition of NADPH-dependent rat liver microsomal lipid peroxidation were examined. Lipid peroxidation was monitored over a time-course of 180 min by thiobarbituric acid reactive product formation. The addition of 5 mM GSH to the reaction system containing microsomes from rats fed a diet supplemented with 150 IU/kg of alpha-tocopherol acetate for eight weeks produced a lag in peroxidation of greater than 30 min. This effect was not observed for microsomes prepared from rats fed a diet deficient in vitamin E. Indeed, a prooxidant effect of 5 mM GSH was observed in assays containing microsomes from rats fed a diet deficient in vitamin E. The inhibition by GSH of lipid peroxidation in microsomes prepared from livers of vitamin E supplemented rats was not restricted by its availability, for it was found that approximately 92% of the GSH remained in the reduced form after 60 min. Additional experiments revealed that the alpha-tocopherol content of peroxidizing microsomes decreased rapidly in the absence of GSH. The addition of 5 mM GSH to the assay system markedly depressed the loss of microsomal alpha-tocopherol. The results of in vivo labeling of liver microsomes with [14C]alpha-tocopherol demonstrated that i) GSH addition to the in vitro peroxidizing medium reduced the disappearance of alpha-tocopherol, and ii) a compound that interfered with the determination of alpha-tocopherol was separated by HPLC and was not an oxidation product of alpha-tocopherol. A portion of the microsomal 14C-labeled alpha-tocopherol was converted to an unidentified product with HPLC retention characteristics that was similar, but not identical, to alpha-tocopherol quinone.
Graham
K S
KS
Environmental Resources Research Institute, Penn State University, University Park 16802.
Reddy
C C
CC
Scholz
R W
RW
D000818:Animals; D005978:Glutathione / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D019803:Glutathione Disulfide; D066298:In Vitro Techniques; D007700:Kinetics; D015227:Lipid Peroxidation / Q000187:drug effects*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D051381:Rats; D014810:Vitamin E / Q000378:metabolism*
D014810:Vitamin E; D009249:NADP; D005978:Glutathione; D019803:Glutathione Disulfide