Body cells and tissues are threatened continuously bydamage caused by toxic free radicals and reactiveoxygen species (e.g., peroxides) which are producedduring normal oxygen metabolism, by other chemicalreactions, and by toxic agents in the environment. Freeradicals are capable of disrupting metabolic activityand cell structure. When this occurs, additional freeradicals are produced which, in turn, can result in moreextensive damage to cells and tissues. Theuncontrolled production of free radicals is thought tobe a major contributing factor to many degenerativeprocesses seen during aging.
Glutathione is a naturally-occurring tripeptide of Lcysteine,L-glutamate and L-glycine. Glutathione is theessential cosubstrate for two major antioxidantenzymes in the body; glutathione peroxidase andglutathione reductase. As such, glutathione offers onemechanism for scavenging toxic free radicals.Glutathione is well absorbed in the intestine, andenters the blood and other extracellular compartmentswhere it exerts much of its beneficial antioxidanteffects. However, it can not effectively enter the cell.
N-Acetylcysteine (NAC) is a precursor for the sulfuramino acid cysteine, and cysteine is used by the bodyto synthesize glutathione. In contrast to glutathione,NAC is efficiently transported into the cell where it isreadily converted to L-cysteine for glutathionesynthesis. NAC is well absorbed, and unlikeL-cysteine, is virtually non-toxic. NAC is recognizedas a safe, highly effective means of increasingintracellular glutathione stores. Aside from providingcysteine as a glutathione precursor, NAC also appearsto have antioxidant properties by itself, and is avaluable sulfur donor for various metabolic needs.
Alpha-lipoic acid is unique among biologicalantioxidants, because it is soluble in both water andlipids. This allows it to neutralize free radicals justabout everywhere in the body, inside and outside thecells. Due to its unique sulfur-containing structure,alpha-lipoic acid can scavenge several types of freeradicals, such as the highly reactive hydroxyl, andsinglet oxygen free radicals. It is also capable ofsuppressing the generation of free radicals in the firstplace, since alpha-lipoic acid chelates transitionmetals, such as iron and copper. Because alpha-lipoicacid is involved in so many different antioxidantfunctions in virtually all body tissues, it has beencalled the universal antioxidant. Besides being auniversal free radical scavenger, alpha-lipoic acid canalso recharge other antioxidant systems throughout thebody. It can extend the activity of vitamins C and E.and can also regenerate glutathione.
Selenium is a cofactor to about 10 selenoproteins inthe body; the most important of these appears to beglutathione peroxidase (GPX). GPX uses glutathioneto reduce hydrogen peroxide and thus protect cells andplasma against free radical injury. GPX activitydepends on an adequate supply of dietary selenium.