Alpha-lipoic acid is a nutritional coenzyme thatparticipates in the energy metabolism of proteins,carbohydrates and fats, with a particular role in bloodglucose disposal. It is also able to scavenge a numberof free radicals.
As both a fat and water-soluble, sulfur-containingcoenzyme, alpha-lipoic acid functions in the body aspart of several multi-enzyme complexes located inthe mitochondria. Alpha-lipoic acid is essential formetabolizing carbohydrates, proteins and fats, for theconversion of their energy into ATP. Two of theseenzyme complexes, pyruvate dehydrogenase (PDH)and alpha-ketoglutarate dehydrogenase (KGDH) arepart of the citric acid cycle (Krebs cycle) and as suchassume a central role for general energy production.Another lipoic acid containing enzyme complex,branched-chain keto-acid dehydrogenase(BCKADH), is involved in deriving energy from thebranched chain amino acids, leucine, isoleucine andvaline.
A related metabolic function of alpha-lipoic acid isits role in blood glucose disposal. This importantcoenzyme appears to be necessary for the normaltransport of blood glucose into the cell. This may beexplained by its functions in the glucosemetabolizingenzymes, PDH and alpha-KGDH, butsome researchers suspect a more direct role incellular glucose uptake at the cell membrane.As early as 1959, alpha-lipoic acid was suggested tobe an antioxidant, since it could extend the actions ofvitamin C in guinea pigs and those of vitamin E inrats. It is only recently, however, that the specificactions of alpha-lipoic acid in free radical quenching,metal chelation and antioxidant regeneration havebeen investigated.
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 and by toxicagents in the environment. Free radicals, onceformed, are capable of disrupting metabolic functionand cell structure. When this occurs, additional freeradicals are produced which, in turn, can result inmore extensive damage to cellular structure andfunction.
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 alphalipoicacid is involved in so many differentantioxidant functions in virtually all body tissues, ithas been called the universal antioxidant.Besides being a universal free radical scavenger,alpha-lipoic acid can also recharge other antioxidantsystems throughout the body. As mentioned earlier,it can extend the activity of vitamins C and E. Inaddition, alpha-lipoic acid can also regenerateglutathione.