Fasting serum amino acids concentration is associated with insulin resistance and pro-inflammatory cytokines

Aims We evaluated specific alterations in amino acids (AAs) profile in patients with type 2 diabetes mellitus (T2DM) and impaired fasting glucose (IFG) compared with healthy controls. In addition, we tried to find the mechanisms behind these AA alterations. Methods Twenty AAs, TNF-α, and IL-6 were analyzed in fasting serum samples from a total of 198 individuals (56 drug-naive patients with T2DM, 69 patients IFG, and 73 healthy controls). The C2C12 mouse myoblast cell lines were used to examine the changes of MAFbx and MuRF1 expressions, which are muscle specific E3 ligases acting as major mediators of skeletal muscle proteolysis, after development of insulin resistance induced by palmitate treatment. Results In addition to branched chain amino acids BCAAs, fasting serum AAs such as glutamic acid, lysine, phenylalanine, arginine, alanine, tyrosine, aspartic acid, were higher in patients with T2DM and intermediately elevated in patients with IFG compared with normoglycemic controls. These serum AA concentrations positively correlated with fasting glucose, homeostasis model assessment of insulin resistance (HOMA-IR), and pro-inflammatory cytokines. In addition, HOMA-IR and pro-inflammatory cytokines were two important independent predictors of serum AA levels. In vitro experiments showed that palmitate treatment in C2C12 myotubes induced insulin resistance, increased pro-inflammatory cytokine gene expression, and increased MAFbx gene and protein expression. Conclusions The increase in fasting serum AAs can be an early manifestation of insulin resistance. Increased muscle proteolysis induced by insulin resistance and inflammatory cytokines can be a possible mechanism for the rise in serum AA levels.