Bromosulfophthalein abolishes glutathione-dependent protection against lipid peroxidation in rat liver mitochondria

Effect of clofibrate, a peroxisome proliferator, in sea bass (Dicentrarchus labrax), a marine fish

The effects of 35 or 70 mg/kg clofibrate on some peroxisomal, mitochondrial, and microsomal enzymes (markers of peroxisome proliferation) in liver, gill, and kidney of sea bass following 2 weeks i.p. treatment have been studied. Induction of lauric acid hydroxylase, UDP-glucuronyl transferase, palmitoyl-CoA oxidase, carnitine-palmitoyl-transferase, p-nitrophenylacetate hydrolase, and benzaldehyde and propionaldehyde dehydrogenase activities was not observed in any case. The clofibrate administration at the dose of 70 mg/kg induced in the liver the glutathione S-tranferase and reduced epoxide hydrolase activities. These results demonstrate that a marine fish species, such as sea bass, is refractory to peroxisome proliferation.

The effect of dietary supplements on gene expression in mice tissues

Exposure of living organisms to various environmental stresses induces the synthesis of so-called shock/stress proteins; many of them can provide either immediate stress protection or participate in cellular repair processes. In the present study we focused our attention on the potential effect of dietary vitamins and microelements with antioxidant properties on stress protein gene expression. The analysis of gene expression in tissues of antioxidant-fed mice shows hsp-70 gene overexpression in liver and brain, but not in spleen and lung. Heat shock significantly induces gene expression that is less pronounced in antioxidant-fed animals in all analyzed tissues. Under conditions of oxidative stress, accumulation of lipid peroxidation products in liver homogenates is partially suppressed in mice subjected to heat shock, and significantly inhibited in antioxidant-fed mice and in antioxidant-fed mice subjected to heat shock. The glutathione content in liver homogenates of antioxidant-fed mice is higher than in the control group. Heat shock decreases the level of endogenous glutathione in both groups of animals, but it is still higher in the liver homogenate of antioxidant-fed mice. Thus, dietary supplements can modify gene expression induced by heat shock in vivo and protect rat tissues against oxidative stress by enhancing the level of endogenous antioxidants and inducing hsp-70 gene expression.

The role of metabolism in the antioxidant function of vitamin E

Vitamin E (alpha-tocopherol), the principal chain-breaking antioxidant in biological membranes, prevents toxicant- and carcinogen-induced oxidative damage by trapping reactive oxyradicals. Although alpha-tocopherol antioxidant reactions appear to be not under direct metabolic control, alpha-tocopherol may function through redox cycles, which deliver reducing equivalents for antioxidant reactions and link antioxidant function to cellular metabolism. This review describes the antioxidant chemistry of alpha-tocopherol and evaluates the experimental evidence for the linkage of alpha-tocopherol turnover to cellular metabolism through redox cycles. Numerous in vitro experiments demonstrate antioxidant synergism between alpha-tocopherol and ascorbate, reduced glutathione, NADPH, and cellular electron transport proteins. Nevertheless, evidence that a one-electron redox cycle regenerates alpha-tocopherol from the tocopheroxyl radical is inconclusive. The difficulty of separating tocopheroxyl recycling from direct antioxidant actions of other antioxidants has complicated interpretation of the available data. A two-electron redox cycle involving alpha-tocopherol oxidation to 8a-substituted tocopherones followed by tocopherone reduction to alpha-tocopherol may occur, but would require enzymatic catalysis in vivo. Metabolism of antioxidant-inactive alpha-tocopheryl esters releases alpha-tocopherol, whereas reductive metabolism of alpha-tocopherylquinone, an alpha-tocopherol oxidation product, yields alpha-tocopherylhydroquinone, which also may provide antioxidant protection.

Ascorbate and phenolic antioxidant interactions in prevention of liposomal oxidation

Efficient prevention of membrane lipid peroxidation by vitamin E (alpha-tocopherol) may involve its regeneration by vitamin C (ascorbate). Conceivably, the efficacy of antioxidants designed as therapeutic agents could be enhanced if a similar regeneration were favorable; thus, a model membrane system was developed which allowed assessment of interaction of phenolic antioxidants with ascorbate and ascorbyl-6-palmitate. Ascorbate alone (50-200 microM) potentiated oxidation of soybean phosphatidylcholine liposomes by Fe2+/histidine-Fe3+, an effect which was temporally related to reduction of Fe3+ generated during oxidation. Addition of 200 microM ascorbate to alpha-tocopherol-containing liposomes (0.1 mol%) resulted in marked, synergistic protection. Accordingly, in the presence but not absence of ascorbate, alpha-tocopherol levels were maintained relatively constant during Fe2+/histidine-Fe3+ exposure. Probucol (4,4'-[(1-methylethylidine)bis(thio)]bis[2,6-bis(1,1- dimethylethyl)]phenol), an antioxidant which prevents oxidation of low density lipoproteins, and its analogues MDL 27,968 (4,4'-[(1-methylethylidene)bis(thio)]bis[2,6- dimethyl]phenol) and MDL 28,881 (2,6-bis(1,1-dimethylethyl)-4-[(3,7,11- trimethyldodecyl)thio]phenol) prevented oxidation but exhibited no synergy with ascorbate. Ascorbyl-6-palmitate itself was an effective antioxidant but did not interact synergistically with any of the phenolic antioxidants. Differential scanning calorimetry revealed significant differences among the antioxidants in their effect on the liquid-crystalline phase transition of dipalmitoyl phosphatidylcholine (DPPC) liposomes. Both alpha-tocopherol and MDL 27,968 significantly reduced the phase transition temperature and the enthalpy of the transition. MDL 28,881 had no effect while probucol was intermediate. The potential for ascorbate or its analogues to interact with phenolic antioxidants to provide a more effective antioxidant system appears to be dictated by structural features and by the location of the antioxidants in the membrane.

Vitamin E and glutathione are required for preservation of microsomal glutathione S-transferase from oxidative stress in microsomes

Glutathione (GSH) inhibited lipid peroxidation induced by NADPH-BrCCl3 in vitamin E sufficient microsomes, but did not in phenobarbital (PB)-treated microsomes (containing about 60% of normal vitamin E) or in vitamin E-deficient microsomes (containing about 30% of normal vitamin E). There was a good correlation between the increased formation of CHCl3 from BrCCl3 in the presence of GSH under anaerobic conditions and the vitamin E level in the microsomes. A normal level of vitamin E in microsomes was thus very important for GSH-dependent inhibition of lipid peroxidation and for the efficient formation of CHCl3 from BrCCl3. Bromosulfophthalein (BSP) eliminated the effects of GSH on lipid peroxidation and CHCl3 formation. The apparent Km and Vmax of substrates for GSH S-transferase were changed by in vivo depletion of vitamin E in microsomes, and the Vmax/Km values were significantly reduced. The enzyme activity in microsomes was inactivated following the loss of vitamin E during in vitro lipid peroxidation, and GSH prevented the loss of vitamin E and protected the enzyme from attack by free radicals. GSH inhibited lipid peroxidation induced by NADPH-Fe2+ and the loss of GSH S-transferase activity during the peroxidation in PB-treated microsomes, but did not in the case of induction by NADPH-BrCCl3. A possible relation between the microsomal GSH S-transferase activity and defense by GSH against lipid peroxidation in microsomes is discussed.

Activity of rat liver microsomal glutathione transferase toward products of lipid peroxidation and studies of the effect of inhibitors on glutathione-dependent protection against lipid peroxidation

Rat liver microsomal glutathione transferase displays glutathione peroxidase activity with linoleic acid hydroperoxide, linoleic acid ethyl ester hydroperoxide, and dilinoleoyl phosphatidylcholine hydroperoxide, with rates of 0.2, 0.3, and 0.3 mumol/min/mg, respectively. The activities are increased between three- and fourfold when the enzyme is activated with N-ethylmaleimide. Microsomal glutathione transferase can also conjugate 4-hydroxynon-2-enal with a specific activity of 0.5 mumol/min/mg. These findings show that the enzyme can remove harmful products of lipid peroxidation and thereby possibly protect intracellular membranes against oxidative stress. A set of glutathione transferase inhibitors (rose bengal, tributyltin acetate, S-hexylglutathione, indomethacin, cibacron blue, and bromosulfophtalein) which abolish the glutathione-dependent protection against lipid peroxidation in liver microsomes have been characterized. These inhibitors were found to be effective in the micromolar range and could prove valuable in studying the factor responsible for glutathione-dependent protection against lipid peroxidation.