Different composition of serum amino acids and bile acids in patients with impaired fasting glucose and type 2 diabetes mellitus compared with normal controls

Abstract

Background: Recent advance of metabolomics has made remarkable progress in discovery of novel biomarkers. Among these biomarkers, blood amino acids (AAs) profiles have produced a number of promising results. Elevated blood levels of AAs, especially branched chain amino acids (BCAAs) have been reported in Type 2 DM (T2DM), obesity, and cardiovascular disease. In addition, emerging researches shows the importance of bile acids (BAs) in glucose homoeostasis. Therefore, we performed AAs and BAs profiling in patients with impaired fasting glucose (IFG) and T2DM as well as healthy control to find specific alteration of these profile in patients with IFG and T2DM. Methods: Twenty AAs and fifteen kinds of BAs were analyzed in samples from 72 T2DM patients without diabetic medications, 97 patients with IFG and 75 healthy control subjects using high performance liquid chromatography (HPLC) - tandem mass spectrometry. Serum TNF-α and IL-6 were measured using a commercially available human ELISA kits. The C2C12 mouse myoblast cell lines were used to examine the changes of MAFbx and MuRF1 expressions after development of insulin resistance induced by palmitate treatment. Results: Fasting serum AAs, not only BCAAs but also glutamic acid, lysine, phenylalanine, arginine, alanine, tyrosine, aspartic acid are higher in patients with T2DM and intermediate in patients with IFG compared with normoglycemic controls. These serum AAs concentrations positively correlated with fasting glucose, HOMA-IR, and pro-inflammatory cytokines (TNF-α and IL-6). In addition, HOMA-IR and pro-inflammatory cytokines were two important independent predictor of blood AAs level. 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. Finally, we found that glycine conjugated BAs were decreased in the patients with IFG and T2DM. Conclusion: Fasting blood AAs increase can be early manifestation of insulin resistance. Increased muscle proteolysis by insulin resistance and inflammatory cytokines is possible mechanism of these AAs elevation. Glycine conjugated BAs are decreased in the patients with IFG and T2DM suggesting control of glycine conjugation and deconjugation of BAs could affect glucose homeostasis.