Leucine disposal rate for assessment of amino acid metabolism in maintenance hemodialysis patients

Abstract

Background Protein energy wasting (PEW) is common in patients undergoing maintenance hemodialysis (MHD) and closely associated with poor outcomes. Insulin resistance and associated alterations in amino acid metabolism are potential pathways leading to PEW. We hypothesized that the measurement of leucine disposal during a hyperinsulinemic- euglycemic-euaminoacidemic clamp (HEAC) procedure would accurately measure the sensitivity to insulin for its actions on concomitant carbohydrate and protein metabolism in MHD patients. Methods We examined 35 MHD patients and 17 control subjects with normal kidney function by hyperinsulinemic-euglycemic clamp (HEGC) followed by HEAC clamp procedure to obtain leucine disposal rate (LDR) along with isotope tracer methodology to assess whole body protein turnover. Results The glucose disposal rate (GDR) by HEGC was 5.1 ± 2.1 mg/kg/min for the MHD patients compared to 6.3 ± 3.9 mg/kg/min for the controls (p = 0.38). The LDR during HEAC was 0.09 ± 0.03 mg/kg/min for the MHD patients compared to 0.11 ± 0.05 mg/kg/min for the controls (p = 0.009). The LDR level was correlated with whole body protein synthesis (r = 0.25; p = 0.08), with whole body protein breakdown (r = −0.38 p = 0.01) and net protein balance (r = 0.85; p < 0.001) in the overall study population. Correlations remained significant in subgroup analysis. The GDR derived by HEGC and LDR correlated well in the controls (r = 0.79, p < 0.001), but less so in the MHD patients (r = 0.58, p < 0.001). Conclusions Leucine disposal rate reliably measures amino acid utilization in MHD patients and controls in response to high dose insulin.

Tissue sodium accumulation and peripheral insulin sensitivity in maintenance hemodialysis patients

“…LDR used in this study is based on the same principal but directly assesses insulin sensitivity in terms of amino acid metabolism. We have reported that there is excellent correlation between LDR and whole body protein metabolism estimated by stable isotope studies in both healthy individuals and patients on MHD . The data reported herein suggest that the mechanisms by which insulin sensitivity is altered due to muscle tissue Na + accumulation share a common signaling pathway for both carbohydrate and amino acid metabolism, which occurs predominantly when skeletal muscle is excessively Na + overloaded.…”

“…While earlier studies have reported significant differences in GDR between MHD patients compared with healthy controls, recent data by our group and others suggest that resistance to glycogenic effects of insulin is determined by mechanisms besides the uremic milieu in CKD patients, including ones on maintenance dialysis . On the other hand, we have shown that resistance to anabolic actions of insulin is a direct consequence of underlying CKD, unlike insulin's glycogenic actions . These observations are based on methodology that is considered to be the gold standard for assessment of insulin sensitivity.…”

“…This served as an index of in vivo insulin sensitivity. For reasons of comparison, the value was normalized to body weight …”

“…When the steady‐state condition for leucine was achieved, the leucine infusion rate was assumed to be equal to the leucine incorporation rate into protein because endogenous leucine release from protein is assumed to be zero under steady‐state conditions. Leucine disposal rate (LDR) was obtained by taking the leucine infusion rate (mg/min) during the final 30 min of the steady‐state period and then normalizing by body weight (kg) …”

“…For reasons of comparison, the value was normalized to body weight. 7 Hyperinsulinemic-euglycemic-euaminoacidemic (HEAC) clamp protocol Once the HEGC was achieved, a continuous infusion of a balanced amino acid solution (Freeamine III 10%, B. Braun Medical, Inc. Irvine, CA; amino acid concentrations: leucine, 910 mg; isoleucine, 690 mg; lysine, 730 mg; valine, 660 mg; phenylalanine, 560 mg; threonine, 400 mg; methionine, 530 mg; tryptophan, 150 mg; alanine, 710 mg; arginine, 950 mg; glycine, 1400 mg; proline, 1120 mg; serine, 590 mg; histidine, 280 mg; cysteine, <16 mg; phosphoric acid NF, 120 mg; sodium bisulfite, <100 mg) was administered at variable dose to achieve and maintain the leucine concentration similar to baseline state. The formula for computing the periodically adjusted leucine infusion rate for every 10 min is…”