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We have compared the biokinetics of deuterated natural (RRR) and synthetic (all rac) alpha-tocopherol in male apoE4-carrying smokers and nonsmokers. In a randomized, crossover study subjects underwent two 4-week treatments (400 mg/day) with undeuterated RRR- and all rac-alpha-tocopheryl acetate around a 12-week washout. Before and after each supplementation period subjects underwent a biokinetic protocol (48 h) with 150 mg deuterated RRR- or all rac-alpha-tocopheryl acetate. During the biokinetic protocols, the elimination of endogenous plasma alpha-tocopherol was significantly faster in smokers (P < 0.05). However, smokers had a lower uptake of deuterated RRR than nonsmokers, but there was no difference in uptake of deuterated all rac. The supplementation regimes significantly raised plasma alpha-tocopherol (P < 0.001) with no differences in response between smokers and nonsmokers or between alpha-tocopherol forms. Smokers had significantly lower excretion of alpha-carboxyethyl-hydroxychroman than nonsmokers following supplementation (P < 0.05). Nonsmokers excreted more alpha-carboxyethyl-hydroxychroman following RRR than all rac; however, smokers did not differ in excretion between forms. At baseline, smokers had significantly lower ascorbate (P < 0.01) and higher F(2)-isoprostanes (P < 0.05). F(2)-isoprostanes in smokers remained unchanged during the study, but increased in nonsmokers following alpha-tocopherol supplementation. These data suggest that apoE4-carrying smokers and nonsmokers differ in their handling of natural and synthetic alpha-tocopherol.

Exposure of the human skin to ultraviolet radiation (UVR) leads to depletion of cutaneous antioxidants, regulation of gene expression and ultimately to the development of skin diseases. Although exogenous supplementation of antioxidants prevents UVR-induced photooxidative damage, their effects on components of cell signalling pathways leading to gene expression has not been clearly established. In the present study, the effects of the antioxidants alpha-lipoic acid, N-acetyl-L-cysteine (NAC) and the flavonoid extract silymarin were investigated for their ability to modulate the activation of the transcription factors nuclear factor kappa B (NF-kappaB) and activator protein-1 (AP-1) in HaCaT keratinocytes after exposure to a solar UV simulator. The activation of NF-kappaB and AP-1 showed a similar temporal pattern: activation was detected 2 h after UV exposure and maintained for up to 8 h. To determine the capacity of activated NF-kappaB to stimulate transcription, NF-kappaB-dependent gene expression was measured using a reporter gene assay. The effects of the antioxidants on NF-kappaB and AP-1 activation were evaluated 3 h after exposure. While a high concentration of NAC could achieve a complete inhibition, low concentrations of alpha-lipoic acid and silymarin were shown to significantly inhibit NF-kappaB activation. In contrast, AP-1 activation was only partially inhibited by NAC, and not at all by alpha-lipoic acid or silymarin. These results indicate that antioxidants such as alpha-lipoic acid and silymarin can efficiently modulate the cellular response to UVR through their selective action on NF-kappaB activation.

Mono-thiols can act either as pro- or anti-oxidants during metal-catalyzed low density lipoprotein (LDL) peroxidation, however investigation of the role of vicinal thiols has been neglected. Therefore dihydrolipoic acid (DHLA), a vicinal dithiol, and lipoic acid, its oxidized form, were used to investigate Cu2+-mediated LDL peroxidation. We demonstrate here that DHLA inhibited Cu2+-dependent LDL peroxidation by chelating copper. DHLA (0-20 microM) increased lag-times of conjugated diene formation in LDL (100 microg/ml) oxidized with 5 microM Cu2+ in a concentration dependent manner, and this effect was saturated after 5 microM DHLA; enough to chelate all of the added Cu2+. In a similar fashion DHLA prevented LDL-mediated reduction of Cu2+ to Cu+. Lipoic acid had no effect in these systems. DHLA alone also reduced Cu2+, however this was inhibited when DHLA was in excess of the copper concentration. Hence there is complex formation between the two species. Copper:DHLA complex formation was further investigated and found to be dependent upon pH and the presence of oxygen. At low pH (<6), or in the absence of oxygen, the complex is stable, presumably due to vicinal thiol chelation. As the pH is increased, the carboxylate group also participates in copper chelation, this results in a less stable complex which is susceptible to oxidation, and copper is eventually released. Electron spin resonance studies demonstrate the formation of hydroxyl, but not superoxide, radicals during Cu2+-catalyzed DHLA oxidation. Thus in our LDL experiments at physiological pH, DHLA is able to either reductively inactivate Cu2+ when Cu2+ is in excess, or effectively chelate Cu2+ when DHLA is in excess. The Cu2+:DHLA complex eventually undergoes copper-catalyzed oxidation, copper is released and LDL peroxidation proceeds. DHLA, thus, has both pro- and antioxidant properties depending upon the ratio of Cu2+:DHLA and the pH. These results provide an additional mechanism of thiol-mediated formation of radicals and metal chelation.

R-alpha-Lipoic acid is found naturally occurring as a prosthetic group in alpha-keto acid dehydrogenase complexes of the mitochondria, and as such plays a fundamental role in metabolism. Although this has been known for decades, only recently has free supplemented alpha-lipoic acid been found to affect cellular metabolic processes in vitro, as it has the ability to alter the redox status of cells and interact with thiols and other antioxidants. Therefore, it appears that this compound has important therapeutic potential in conditions where oxidative stress is involved. Early case studies with alpha-lipoic acid were performed with little knowledge of the action of alpha-lipoic acid at a cellular level, but with the rationale that because the naturally occurring protein bound form of alpha-lipoic acid has a pivotal role in metabolism, that supplementation may have some beneficial effect. Such studies sought to evaluate the effect of supplemented alpha-lipoic acid, using low doses, on lipid or carbohydrate metabolism, but little or no effect was observed. A common response in these trials was an increase in glucose uptake, but increased plasma levels of pyruvate and lactate were also observed, suggesting that an inhibitory effect on the pyruvate dehydrogenase complex was occurring. During the same period, alpha-lipoic acid was also used as a therapeutic agent in a number of conditions relating to liver disease, including alcohol-induced damage, mushroom poisoning, metal intoxification, and CCl4 poisoning. Alpha-Lipoic acid supplementation was successful in the treatment for these conditions in many cases. Experimental studies and clinical trials in the last 5 years using high doses of alpha-lipoic acid (600 mg in humans) have provided new and consistent evidence for the therapeutic role of antioxidant alpha-lipoic acid in the treatment of insulin resistance and diabetic polyneuropathy. This new insight should encourage clinicians to use alpha-lipoic acid in diseases affecting liver in which oxidative stress is involved.