Lipoic acid glutathione

All reduced thiols contain very active SH groups and therefore, are potentially efficient antioxidants. There are numerous endogenous and synthetic thiols, which have already been studied and applied as antioxidative drugs and food supplements, but the most important antioxidant thiols are undoubtedly lipoic acid and glutathione. 

As in the case of other cardiovascular diseases, the possibility of antioxidant treatment of diabetes mellitus has been studied in both animal models and diabetic patients. The treatment of streptozotocin-induced diabetic rats with a-lipoic acid reduced superoxide production by aorta and superoxide and peroxynitrite formation by arterioles providing circulation to the region of the sciatic nerve, suppressed lipid peroxidation in serum, and improved lens glutathione level [131]. In contrast, hydroxyethyl starch desferrioxamine had no effect on the markers of oxidative stress in diabetic rats. Lipoic acid also suppressed hyperglycemia and mitochondrial superoxide generation in hearts of glucose-treated rats [132],... 

Direct evidence of the reaction of PAN with sulfhydryl compounds has since been obtained (PAN at 115 ppm for 1-10 min). - In the reaction with glutathione, the major products are oxidized glutathione (disulfide) and 5-acetylglutathione. Other sulfhydryl compounds (e.g., coenzyme A, lipoic acid, and cysteine) yield only oxidation products, with no evidence of 5-acetylation. However, acetylation reactions have been observed with alcohols and amines. Sulfur compounds other than thiols can undergo oxidation by PAN methionine is converted to methionine sulfoxide, and oxidized lipoic acid (disulfide) is converted to sulfoxide. 

In lipoic acid (6), an intramolecular disulfide bond functions as a redox-active structure. As a result of reduction, it is converted into the corresponding dithiol. As a prosthetic group, lipoic acid is usually covalently bound to a lysine residue (R) of the enzyme, and it is then referred to as lipoamide. Lipoamide is mainly involved in oxidative decarboxylation of 2-0X0 acids (see p. 134). The peptide coenzyme glutathione is a similar disulfide/ dithiol system (not shown see p. 284). 

CS causes alkylation of sulfhydryl-containing enzymes and inhibits lactic dehydrogenase, glutamic dehydrogenase, pyruvic decarboxy-. lase, and alpha-glycerophosphate dehydrogenase.24,40 it reacts with a number of nucleophilic compounds, such as glutathione, plasma protein, and lipoic acid.24... 

The body s natural defenses against overenthusiastic oxidation include a-lipoic acid, reduced glutathione, ascorbic acid, the tocopherols, the carotenoids, and a number of enzymes such as epoxide hydrolase and the like. Very efficient DNA repair systems also operate defensively. These various means are remarkably effective, but DNA assault is continuous, cumulative, and implacable. Thus, many degenerative diseases are associated with aging because of the gradual slippage in functional fidelity of cellular machinery which occurs with age. 

The reaction catalyzed by the first of these is illustrated in Table 15-2 (reaction type F). The other two enzymes usually promote the reverse type of reaction, the reduction of a disulfide to two SH groups by NADPH (Eq. 15-22). Glutathione reductase splits its substrate into two halves while reduction of the small 12-kDa protein thioredoxin (Box 15-C) simply opens a loop in its peptide chain. The reduction of lipoic acid opens the small disulfide-containing 5-membered ring in that molecule. Each of these flavoproteins also contains within its structure a reducible disulfide group that participates in catalysis. 

Heme oxidase Glutathione Lipoic acid Vitamin C Vitamin E Melatonin Coenzyme Qio Plasmalogens... 

Fig. 9.5 Chemical structures of low molecular weight antioxidants Melatonin (a) ascorbic acid (Vitamin C) (b) glutathione (c) lipoic acid (d) a-tocopherol (Vitamin E) (e) and a-tocotrienol (f)...

Fucassi F et al (2007) a-Lipoic acid and glutathione protect against the prooxidant activity of SOD/catalase mimetic salen Mn(III) derivatives. J Inorg Biochem 101 225-232... 

The RSH/RSSR interconversion is well known in organic chemistry due to its biological importance in systems like cysteine-cystine, glutathione and the corresponding disulfide, and Q -lipoic acid and related dithiol. 

Coenzyme A, lipoic acid and the tripeptide glutathione (y-glutamylcysteinylglycine) frequently feature in biological systems as coenzymes. These coenzymes catalyse a wide... 

Lipoic acid is a vitally important antioxidant that also aids in the recycling of other antioxidants, especially vitamins C and E, coenzyme QIO, and glutathione. While it is found in meats and potatoes, adequate amounts are unlikely to be provided via food sources. Lipoic acid as a supplement helps to prevent oxidative damage associated with aging, disease, and metabolism. 

---