Significance of serum branched-chain amino acid to tyrosine ratio measurement in athletes with high skeletal muscle mass.

BACKGROUND: Few nutritional markers reflect the hypermetabolic state of athletes with high levels of skeletal muscle. Although branched-chain amino acids (BCAA) play crucial roles in protein metabolism in skeletal muscle, the relationship between skeletal muscle mass and amino acid imbalances caused by the metabolism of BCAA and aromatic amino acids remains unclear. The aim of this study is to test the hypothesis that athletes with high levels of skeletal muscle mass have plasma amino acid imbalances, assessed by serum BCAA to tyrosine ratio (BTR) which can be measured conveniently. METHODS: The study enrolled 111 young Japanese men: 70 wrestling athletes and 41 controls. None of them were under any medications, extreme dietary restrictions or intense exercise regimens. Each participant's body composition, serum concentrations of albumin and rapid turnover proteins including transthyretin and transferrin, BTR, and thyroid function were assessed. RESULTS: Compared to the controls, the athletes had significantly higher skeletal muscle index (SMI) (p < 0.001), and lower serum albumin concentration (p < 0.001) and BTR (p < 0.001). Kruskal-Wallis tests showed that serum albumin concentration and BTR were significantly lower in the participants with higher SMI. Serum albumin concentration and BTR were inversely correlated with SMI by multiple regression analysis (logarithmic albumin, ß = - 0.358, p < 0.001; BTR, ß = - 0.299, p = 0.001). SMI was inversely and transthyretin was positively correlated with serum albumin (SMI, ß = - 0.554, p < 0.001; transthyretin, ß = 0.379, p < 0.001). Serum concentration of free 3,5,3'-triiodothyronine (FT3) was inversely correlated with BTR, and, along with SMI and albumin, was independent predictor of BTR (SMI, ß = - 0.321, p < 0.001; FT3, ß = - 0.253, p = 0.001; logarithmic albumin, ß = 0.261, p = 0.003). However, FT3 was not correlated with SMI or serum albumin. Serum concentrations of rapid turnover proteins were not correlated with BTR. CONCLUSIONS: Increased skeletal muscle mass enhances the circulating amino acid imbalances, and is independently facilitated by thyroid hormones. Serum BTR may be a useful biomarker to assess the hypermetabolic state of wrestling athletes with high levels of skeletal muscle.

Tyrosine levels are associated with insulin resistance in patients with nonalcoholic fatty liver disease.

OBJECTIVE: Amino acid imbalance is often found in patients with cirrhosis, and this imbalance is associated with insulin resistance. However, the mechanism underlying the relationship between amino acid imbalance and insulin resistance remains unclear. We evaluated serum amino acid concentrations in patients with nonalcoholic fatty liver disease to determine if any of the levels of amino acids were associated with the biochemical markers and fibrosis stage of nonalcoholic steatohepatitis (NASH). METHODS: In 137 patients with nonalcoholic fatty liver disease who underwent liver biopsy, plasma levels of branched-chain amino acid (BCAA), tyrosine (Tyr), and the BCAA-to-Tyr ratio values were determined using mass spectroscopy. These values were then assessed for associations with fibrosis stage, anthropometric markers (age, sex, and body mass index), biochemical markers (alanine aminotransferase, aspartate aminotransferase, γ-glutamyl transpeptidase, albumin, platelet count, total cholesterol, triglycerides, low-density lipoprotein cholesterol, and glycosylated hemoglobin), and relevant disease-specific biomarkers (homeostasis model assessment of insulin resistance [HOMA-IR], serum iron, ferritin, leptin, adiponectin, high-sensitivity C-reactive protein, and hyaluronic acid). RESULTS: Serum albumin levels, plasma BCAA levels, and BCAA-to-Tyr ratio values were negatively associated with the fibrosis stage. In contrast, Tyr levels increased with increasing fibrotic staging. Tyr levels were also correlated with HOMA-IR results. CONCLUSION: Plasma BCAA levels in patients with NASH decreased with increasing liver fibrosis, while Tyr levels increased with increasing fibrotic stage. These results suggest that amino acid imbalance and insulin resistance are intimately involved in a complex pathogenic mechanism for NASH.