Protection by thiols of the mitochondrial complexes from 4-hydroxy-2-nonenal

In the present study, the effects of 1-hydroxy-2-nonenal (HNE) on highly pu rified pyruvate dehydrogenase complex (PDC) and its catalytic components in vitro and on PDC, alpha -hetoglutarate dehydrogenase complex (KGDC), and t he branched-chain alpha -keto acid dehydrogenase complex (BCKDC) activities in cultured human HepG2 cells were investigated. Among the PDC components, the activity of the dihydrolipoamide acetyltransferase-E3-binding protein subcomplex (E2-E3BP) only was decreased by HNE. Dihydrolipoamide dehydrogen ase (E3) protected the E3-E3BP subcomplex from HNE inactivation in the abse nce of the substrates. In the presence of E3 and NADH, when lipoyl groups w ere reduced, higher inactivation of the E2-E3BP subcomplex by HNE was obser ved. Purified PDC was protected from HNE-induced inactivation by several th iol compounds including lipoic acid plus [LA-plus: 2-(N,N-dimethylamine)eth ylamidolipoate HCl]. Treatment of cultured HepG2 cella with HNE resulted in a significant reduction of PDC and KGDC activities, whereas BCKDC activity decreased to a lesser extent. Lipoyl compounds afforded protection from HN E-induced inhibition of PDC. This protection was higher in the presence of cysteine and reduced glutathione. Cysteine was able to restore PDC activity to some extent after HNE treatment, These findings show that thiols, inclu ding lipoic acid, provide protection against HNE-induced inactivation of li poyl-containing complexes; in the mitochondria. (C) 2001 Elsevier Science I nc.