Antioxidant Properties Of Lipoic Acid

The strained-ring conformation of lipoic acid enables the molecule to readily undergo oxidation and reduction, and indeed this is reflected in the high negative redox potential of the oxidized and reduced form ( — 0.32 V), which makes the reduced form (dihydrolipoate) a very powerful reduc-tant. Such properties enable the lipoate couple to interact with a number of reactive oxygen species.

Various cellular pathways like those involved in the electron transport pathways of cell respiration and drug detoxification or activation of neutrophils and macrophages result in the formation of reactive oxygen and nitrogen species. If overproduced and not scavenged or converted to a nonreactive form, they can be potentially damaging to the cell. These include superoxide (0^~ ), hydrogen peroxide (H202), hyperchlorous acid (HOC1), hy-droxyl (OH') and peroxyl (ROO') radicals as well as nitric oxide (NO") and peroxynitrite(ONOO). a-Lipoic acid and dihydrolipoic acid can scavenge both hydrogen peroxide and HOC1 (9), while dihydrolipoic acid can also scavenge superoxide (9). Both «-lipoic and dihydrolipoic acid have been shown to scavenge hydroxyl radicals in a metal-catalysis system and in a metal-free reaction of ultraviolet irradiation induced by decomposition of the aromatic hydroperoxide model compound NP-III (9). Dihydrolipoic acid can also scavenge peroxyl radicals, formed from both lipophilic and hydrophilic peroxyl radical generators (9). Therefore, the lipoate couple represents a potent radical scavenging unit.

When antioxidants react with reactive oxygen species, the antioxidant is converted to a form that is no longer able to function and is said to be consumed. Therefore, this oxidized product needs to be recycled to this native form in order to function again. A number of antioxidants, including vitamin C, ubiquinols, and glutathione, can recycle vitamin E, the major chain-breaking antioxidant that protects biological membranes from lipid peroxidation. Dihydrolipoic acid has only a weak interaction with the tocopheroxyl radical, so the major recycling of vitamin E by dihydrolipoic acid occurs via the intermediary recycling of the ascorbyl radical by dihydrolipoic acid, which, in turn, recycles the vitamin E radical produced by oxidation. There is now evidence that lipoate supplementation increases tissue ubiquinol content, and ubiquinol can also recycle vitamin E. Therefore, there exists a network of antioxidants in which dihydrolipoic acid can interact and replenish in order to maintain both lipid and aqueous phase antioxidant status. This recycling by lipoate was shown as early as 1959 by Rosenberg and Culik (10), who demonstrated that lipoic acid supplementation could prevent the symptoms of both vitamin E and C deficiencies in guinea pigs. This work has since been repeated in vitamin-E-deficient mice (8).

Glutathione is a major intracellular antioxidant that acts as a sulfhydryl buffer, protecting cysteine residues in proteins from oxidation, the modulation of which has been discussed as a potential therapeutic strategy (11). a-Lipoate can interact with glutathione (GSH) both directly and indirectly. Dihydrolipoic acid (DHLA) can reduce oxidized glutathione (GSSG) to GSH, but GSH is incapable of reducing a-lipoate to DHLA (12). DHLA may also recycle vitamin E by reducing GSSG directly; the reduced GSH can then recycle vitamin E (13). Administration of a-lipoate to cells has been shown to cause an increase in intracellular GSH in vitro (14) and in vivo (15). This increase has been shown to be a consequence of increased GSH synthesis due to an improvement in cystine utilization (14).

Homemade Pet Food Secrets

Homemade Pet Food Secrets

It is a well known fact that homemade food is always a healthier option for pets when compared to the market packed food. The increasing hazards to the health of the pets have made pet owners stick to containment of commercial pet food. The basic fundamentals of health for human beings are applicable for pets also.

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