Aims/hypothesis: The aim of the study was to address the importance of mitochondrial function in insulin resistance and type 2 diabetes, and also to identify effective agents for ameliorating insulin resistance in type 2 diabetes. We examined the effect of two mitochondrial nutrients, R-alpha-lipoic acid (LA) and acetyl-L-carnitine (ALC), as well as their combined effect, on mitochondrial biogenesis in 3T3-L1 adipocytes.
Methods: Mitochondrial mass and oxygen consumption were determined in 3T3-L1 adipocytes cultured in the presence of LA and/or ALC for 24 h. Mitochondrial DNA and mRNA from peroxisome proliferator-activated receptor gamma and alpha (Pparg and Ppara) and carnitine palmitoyl transferase 1a (Cpt1a), as well as several transcription factors involved in mitochondrial biogenesis, were evaluated by real-time PCR or electrophoretic mobility shift (EMSA) assay. Mitochondrial complexes proteins were measured by western blot and fatty acid oxidation was measured by quantifying CO2 production from [1-14C]palmitate.
Results: Treatments with the combination of LA and ALC at concentrations of 0.1, 1 and 10 micromol/l for 24 h significantly increased mitochondrial mass, expression of mitochondrial DNA, mitochondrial complexes, oxygen consumption and fatty acid oxidation in 3T3L1 adipocytes. These changes were accompanied by an increase in expression of Pparg, Ppara and Cpt1a mRNA, as well as increased expression of peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1 alpha (Ppargc1a), mitochondrial transcription factor A (Tfam) and nuclear respiratory factors 1 and 2 (Nrf1 and Nrf2). However, the treatments with LA or ALC alone at the same concentrations showed little effect on mitochondrial function and biogenesis.
Conclusions/interpretation: We conclude that the combination of LA and ALC may act as PPARG/A dual ligands to complementarily promote mitochondrial synthesis and adipocyte metabolism.