Abstract
α-Lipoic acid (LA) has the specific absorption band at 330 nm and is quite vulnerable to UV irradiation, affording a variety of compounds including polymeric materials and hydrogen sulfide. A better understanding of the photochemical reaction of LA has already been carried out focusing mainly on the reaction product analysis derived from LA. We re-investigated the photochemical reaction of LA focusing our attention on the fate of hydrogen sulfide (H2S) produced in the photochemical reaction procedure. The photoirradiation of LA in the presence of oxidized glutathione (GSSG) formed glutathione trisulfide (GSSSG) and a reduced form of glutathione (GSH). Similar results were obtained in the co-presence of cystine and dimethyl disulfide. The concentration of H2S was reaching the maximum concentration, which was gradually decreasing within 10 min after photoirradiation, while the concentration of GSSSG was increasing with the decrease of H2S concentration. The structural confirmation of GSSSG and the plausible mechanism for the formation of GSSSG are proposed based on the time-dependent and pH-dependent profile of the photoirradiation.
Highlights
Faculty of Biological Science and Technology, Institute of Science and Engineering, Kanazawa University, Abstract: α-Lipoic acid (LA) has the specific absorption band at 330 nm and is quite vulnerable to UV irradiation, affording a variety of compounds including polymeric materials and hydrogen sulfide
The ultra-violet light (UVL)-irradiation of LA in the presence of GSSG afforded many reaction products, which were analyzed by high-performance liquid chromatography (HPLC)
By UVL-irradiation, the peak intensity of LA significantly decreased by 20%, which coincided with the appearance of numerous other peaks in the chromatogram (Figure 1B)
Summary
The administration of lipoic acid to cultured cells increases the amount of glutathione which can regenerate various antioxidants such as ascorbic acid, ubiquinone, and vitamin E present in our cells [2,3,4,5]. This antioxidant recycling system is recognized as an antioxidant network [6]. LA and DHLA are converted in the cell with the help of the NADH-NAD system In this procedure DHLA is oxidized to LA, which makes it possible to regenerate other oxidized antioxidants to their reduced states
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