The administration of
glucocorticoids to patients with
rheumatic diseases often results in
glucocorticoid-induced
myopathy. We previously found that administration of
branched-chain amino acids (BCAA) to such patients improves the loss of skeletal muscle, however, their individual differences were often observed. The present study, therefore, aims to identify specific parameters associated with BCAA-induced increases in skeletal muscle mass. Eighteen patients with
rheumatic diseases treated with
prednisolone were randomly assigned to receive additional BCAAs for 12 wk. Serum biochemistry, plasma
fibroblast growth factor (FGF) 19 and 21, and plasma and urinary
amino acid concentrations were assessed. The relationship between these parameters and the cross-sectional area (CSA) of the biceps femoris (slow-twitch muscle) and rectus femoris (fast-twitch muscle) was assessed using computed tomography. BCAA supplementation increased serum levels of
creatinine and
albumin and decreased
ammonia and urinary
3-methylhistidine levels. With or without BCAA supplementation, each plasma
amino acid concentration decreased during the study period, but the decrease was lower in patients receiving BCAA. Interestingly, a positive correlation was observed between plasma
isoleucine,
aspartate, and
glutamate concentrations and improvement in the biceps femoris
muscle atrophy. Plasma
amino acid concentrations in patients with
rheumatic diseases treated with
glucocorticoids decreased despite tapering the dose of
glucocorticoids, with a smaller decrease in the BCAA-treated group. Plasma BCAA,
aspartic acid, and
glutamate concentrations correlated positively with the rate of improvement in biceps femoris
muscle atrophy, suggesting that these
amino acids are associated with the BCAA-induced increase in muscle mass.