Lipoic acid-mediated signal transduction

We found, in NIH/3T3 cells, that α-lipoic acid (ALA), a thiol antioxidant as well as a co-factor for mitochondrial dehydrogenases, activated p44/42 MAP kinase. Cells were serum-starved for 2 h with or without ALA, cell lysates prepared, and activation of MAP kinase determined by Western blot analysis using antibody for phosphorylated MAP kinase (Tyr204). Treatment of cells with ALA (20nM - 20μm) resulted in concentration- and time-dependent, increase in phosphorylated MAP kinase with maximal activation reached at 1-2 h. Slow activation of MAP kinase by ALA may reflect the involvement of glutathione synthesis since N-acetylcysteine also activated MAP kinase although mM concentrations were needed. Activation of MAP kinase by these thiols was blocked by dominant negative mutant of p21^ras, suggesting the involvement of Ras GTPase. ALA-induction of p21^ras-signaling for MAP kinase phosphorylation is independent of Ca²⁺-signaling since neither BAPTA-AM nor W-7 had inhibitory effects. Activation of Ras-MAP kinase pathways may be the mechanism of ALA-dependent cell growth which we have previously observed in vascular smooth muscle cells.