Lipoamide or lipoic acid stimulates mitochondrial biogenesis in 3T3‐L1 adipocytes via the endothelial NO synthase‐cGMP‐protein kinase G signalling pathway

Abstract

Metabolic dysfunction due to loss of mitochondria plays an important role in diabetes, and stimulation of mitochondrial biogenesis by anti-diabetic drugs improves mitochondrial function. In a search for potent stimulators of mitochondrial biogenesis, we examined the effects and mechanisms of lipoamide and α-lipoic acid (LA) in adipocytes. Differentiated 3T3-L1 adipocytes were treated with lipoamide or LA. Mitochondrial biogenesis and possible signalling pathways were examined. Exposure of 3T3-L1 cells to lipoamide or LA for 24 h increased the number and mitochondrial mass per cell. Such treatment also increased mitochondrial DNA copy number, protein levels and expression of transcription factors involved in mitochondrial biogenesis, including PGC-1α, mitochondrial transcription factor A and nuclear respiratory factor 1. Lipoamide produced these effects at concentrations of 1 and 10 µmol·L⁻¹, whereas LA was most effective at 100 µmol·L⁻¹. At 10 µmol·L⁻¹, lipoamide, but not LA, stimulated mRNA expressions of PPAR-γ, PPAR-α and CPT-1α. The potency of lipoamide was 10-100-fold greater than that of LA. Lipoamide dose-dependently stimulated expression of endothelial nitric oxide synthase (eNOS) and formation of cGMP. Knockdown of eNOS (with small interfering RNA) prevented lipoamide-induced mitochondrial biogenesis, which was also blocked by the soluble guanylate cyclase inhibitor, ODQ and the protein kinase G (PKG) inhibitor, KT5823. Thus, stimulation of mitochondrial biogenesis by lipoamide involved signalling via the eNOS-cGMP-PKG pathway. Our data suggest that lipoamide is a potent stimulator of mitochondrial biogenesis in adipocyte, and may have potential therapeutic application in obesity and diabetes.