A substance need not excel in meeting all these
criteria to be considered a good antioxidant. For example,
vitamin E acts only in the membrane or lipid domains,
its dominant action is to quench lipid peroxyl
radicals, and it has little or no activity against radicals
in the aqueous phase, yet it is considered one of the
central antioxidants of the body. Epidemiological studies
are confirming its role in the prevention of numerous
oxidant-related diseases, such as heart disease. 7"s
An "ideal" antioxidant would fulfill all of the
above criteria. The c~-lipoic acid/dihydrolipoic acid redox
couple approaches the ideal; it has been called
"a universal antioxidant. ''9 a-Lipoic acid is readily
absorbed from the diet. It is probably rapidly converted
to DHLA in many tissues, as recent advances in assay
technique have made evident) °'H One or both of the
components of the redox couple effectively quench a
number of free radicals in both lipid and aqueous domains.
Both DHLA 21'32'33 and a-lipoic acid 13'19"23'24
have metal-chelating activity. DHLA acts synergistically
with other antioxidants, indicating that it is capable
of regenerating other antioxidants from their radical
or inactive forms. Finally, there is evidence that they
may have effects on regulatory proteins and on genes
involved in normal growth and metabolism.
Because of these antioxidant attributes, a number
of experimental and clinical studies have been carried