Skeletal Protein Breakdown Research Articles

A rapid MEKC method for the simultaneous determination of creatinine, 1‐ and 3‐methylhistidine in human urine

The present report describes the use of MEKC in the presence of 35 mM sodium tetraborate, pH 9.0, containing 60 mM SDS for the complete separation and identification of creatinine, 1-methylhistidine (1-MeH) and 3-MeH in human urine. Their simultaneous quantification in urine of healthy controls and subjects submitted to elective surgery to their lower limbs allowed to use 3-MeH as a reliable measure of skeletal protein breakdown. Simplicity, sensitivity and low running costs are the main advantages of this method that is suitable for the routine analysis in clinical laboratories of a large number of samples per day.

Whole body protein turnover, studied with 15N-glycine, and muscle protein breakdown in mildly obese subjects during a protein-sparing diet and a brief total fast

A modification of the Picou and Taylor-Roberts Model was used to estimate rates of total body protein synthesis (S), breakdown (C), and amino nitrogen (N) flux (Q) in the metabolic N pool of five obese females. The subjects were fed egg white albumin at 1.5/kg ideal body weight (IBW) and total calories at 1.2 times the basal energy expenditure (fat:carbohydrate = 30%:50%) as a formula diet (period 1, 1 wk). This was followed by 3 wk during which the nonprotein calories were omitted (period 2, protein-sparing modified fast [PSMF]) and a 1-wk total fast (period 3). Estimates of body protein turnover and skeletal protein breakdown were made during the last 60 and 48 hr, respectively, of each period. Q, S, and C were 223 ± 22, 154 ± 22, and 150 ± 22 g protein 24 hr , respectively, for period 1. These values were unchanged at the end of period 2. Total fasting decreased Q and S by 36% and 27%, respectively ( p < 0.001), but C remained unchanged. Skeletal protein breakdown, as estimated by urinary Nτ-methylhistidine excretion, was 108 ± 47 μmole in period 1, 79 ± 51 μmole in period 2 ( p < 0.01), and 100 ± 49 μmole in period 3, representing 16 ± 5%, 12 ± 5% ( p < 0.01), and 16 ± 4% of whole body breakdown. N balance was unchanged in period 1 (−0.4 ± 1.2 g N) and the final week of period 2 (−0.4 ± 1.5 g N), but was −5.8 ± 0.6 g N in period 3. These data indicate that weight reduction with a PSMF is associated with a maintenance of total body protein turnover parameters and N balance but a reduction in skeletal protein breakdown, whereas a total fast causes a marked reduction in whole body protein synthesis and amino N flux with little change in the rate of total body and skeletal protein breakdown, resulting in a negative N balance. The minimization of N losses that develops after prolonged starvation is achieved at rates of whole body and skeletal protein breakdown similar to those found when the diet is adequate, suggesting that endogenous fat-derived fuels are as effective as exogenous energy in limiting protein catabolism. However, protein intake is necessary to maintain whole body protein synthesis under these conditions.