Amino acid profiles in adults with growth hormone (GH) deficiency before and during GH replacement therapy

Abstract

Objective GH replacement to growth hormone deficient (GHD) adults improves body composition. In a subset however, lean body mass (LBM) fails to increase despite normalization of IGF-I and amino acid availability could be of importance. We analyzed amino acid (AA) profiles in plasma and erythrocytes (RBC) and associations with LBM, serum IGF-I and IGFBP-1 before and during GH replacement. Design and methods Examinations were performed in 15 GHD patients (six women), aged 34–61 yrs before and after 12 months of GH therapy and in a control group of 20 healthy males aged 31–68 yrs. LBM was measured by dual energy X-ray absorptiometry (DXA), free AAs in plasma and RBC by high performance liquid chromatography and serum IGF-I and IGFBP-1 by in-house RIAs. Setting Tertiary care referral centre. Results At baseline, female GHD patients tended to have lower concentrations of the essential branched – chain AAs isoleucine and leucine, total essential AAs, and of the non-essential AA glutamine than the male patients. Male GHD patients tended to have higher plasma and RBC glutamate than controls. At 12 months, IGF-I had normalized in all but one patient and mean LBM gain was 1.9 ± 0.4 kg. AA levels were unchanged. The change in LBM at 12 months was positively correlated to the ratio between the sum of isoleucine, leucine and valine and baseline LBM kg/m 2 ( r = 0.76, p = 0.001, n = 15). Conclusion Our results suggest that the essential branched-chain amino acids in plasma are important for the LBM response to GH substitution. Our finding has to be confirmed in larger groups of GHD adults before making a proper selection of AAs to be measured in plasma and added as dietary supplement during GH therapy. GH administration did not change AA levels and measurements are not useful for monitoring of GH therapy at the time being.