α-Lipoate Can Protect Against Glycation of Serum Albumin, But Not Low-Density Lipoprotein

Abstract

Protein glycation may play a role in the pathogenesis of diabetic complications. α-Lipoate (1,2-dithiolane-3-pentanoate) has been reported to prevent glycation and structural modification of bovine serum albumin (BSA). To elucidate the protective mechanism, we tested the effects of enantiomerism, thiol moiety and hydrophobicity of α-lipoate on glycation of BSA and low density lipoprotein(LDL). When BSA (1 mM) was incubated with 500 mM glucose in the presence of α-lipoate homologues or dihydrolipoate (6,8-dimercaptooctanoate, DHLA) at 37°C for 72 h, both α-lipoate (racemic, R- and S-forms) and DHLA inhibited BSA glycation similarly, but tetranorlipoate (1,2-dithiolane-3-carboxylate) did not. However, under similar conditions, α-lipoate did not inhibit LDL glycation. Scatchard plot analysis demonstrated that 6 mol of α-lipoate bind to 1 mol of BSA with a formation constant of 8.7 × 104 M−1. Therefore, we concluded that α-lipoate protects BSA glycation by hydrophobic binding near the glycation sites of BSA.