Lipoic Acid as a Possible Pharmacological Source of Hydrogen Sulfide/Sulfane Sulfur

The aim of the present study was to verify whether lipoic acid (LA) itself is a source of H(2)S and sulfane sulfur. It was investigated in vitro non-enzymatically and enzymatically (in the presence of rat tissue homogenate). The results indicate that both H(2)S and sulfane sulfur are formed from LA non-enzymatically in the presence of environmental light. These results suggest that H(2)S is the first product of non-enzymatic light-dependent decomposition of LA that is, probably, next oxidized to sulfane sulfur-containing compound(s). The study performed in the presence of rat liver and kidney homogenate revealed an increase of H(2)S level in samples containing LA and its reduced form dihydrolipoic acid (DHLA). It was accompanied by a decrease in sulfane sulfur level. It seems that, in these conditions, DHLA acts as a reducing agent that releases H(2)S from an endogenous pool of sulfane sulfur compounds present in tissues. Simultaneously, it means that exogenous LA cannot be a direct donor of H(2)S/sulfane sulfur in animal tissues. The present study is an initial approach to the question whether LA itself is a donor of H(2)S/sulfane sulfur.