Measurement Of Whole Body Protein Turnover Research Articles

Measurement duration affects the calculation of whole body protein turnover kinetics but not between-day variability

BackgroundAssessment of whole body protein turnover (WBPT) can provide fundamental information about protein kinetics which underpins the conservation of lean tissue. Reliability and methodology studies on the measurement of WBPT are scarce. This study aimed to assess the effects of urine collection duration (9 versus 12 h) and the reproducibility of WBPT with the end product method calculated from ammonia as the end product. MethodsWBPT was assessed in 21 healthy participants (11M, 10F) on 2 test days. WBPT was assessed using the end product method with a single dose of 15N glycine with ammonia as end product in a postprandial state with 9 and 12-h urine collections. ResultsThe CV for protein flux averaged 10% and 12% for 9 and 12-h urine collections respectively. Protein flux, synthesis and balance were significantly higher and protein breakdown significantly lower with 9-h urine collections compared to 12-h collections (P < 0.01) and there was a trend towards increasingly greater overestimation of 9-h calculated WBPT kinetics with greater overall rates of WBPT. Correlations between the 9 and 12-h values were strong (r > 0.962, P < 0.001 for all variables). ConclusionsThe reproducibility of WBPT with ammonia as the end product was similar to previously reported reproducibility of the gold standard precursor technique. The use of a 12-h urine collection is more effective to achieve full turnover of the ammonia free amino acid (AA) pool.

Measurement of whole-body protein turnover in insulin-dependent (type 1) diabetic patients during insulin withdrawal and infusion: comparison of [13C]leucine and [2H5]phenylalanine methodologies

1. The aims of this study were twofold: (i) to investigate the ability of a recently described [2H5]phenylalanine method for quantifying whole-body protein turnover during acute physiological perturbation; (ii) to determine specifically whether the previously observed increase in protein synthesis on insulin withdrawal in insulin-dependent (type 1) diabetic patients seen when employing the [13C]leucine technique could be corroborated by using [2H5]phenylalanine. 2. Whole-body protein turnover was measured by both the [2H5]phenylalanine and [13C]leucine primed continuous infusion methods applied simultaneously to six type I post-absorptive diabetic patients during insulin withdrawal and infusion. 3. Values were determined by the [13C]leucine method by measuring either [13C]leucine (primary pool) or alpha-[13C] ketoisocaproic acid (reciprocal pool) enrichment in plasma. 4. Values of whole-body protein breakdown during insulin withdrawal derived from the [2H5]phenylalanine and primary and reciprocal pool [13C]leucine models respectively were 3.54 +/- 0.43, 3.85 +/- 0.41 and 4.62 +/- 0.44 g day-1 kg-1 (means +/- SD). Insulin infusion resulted in a significant reduction (P less than 0.02) to 3.07 +/- 0.34, 3.05 +/- 0.26 and 3.82 +/- 0.4 g day-1 kg-1, respectively. Synthesis values fell significantly but by a smaller amount than breakdown, resulting in increased (P less than 0.05) net protein deposition, regardless of the model used. 5. These data demonstrate that the [2H5]phenylalanine and [13C]leucine methods generate similar results both in absolute and relative terms in response to short-term insulin infusion. 6. The confirmation of increased whole-body protein synthesis during insulin withdrawal by two independent methods supports the validity of this observation.

Alteration of Whole‐Body Protein Kinetics According to Severity of Surgical Trauma in Patients Receiving Total Parenteral Nutrition

This study was conducted to clarify the mechanisms of body nitrogen losses according to the severity of surgical trauma. Thirteen male patients who underwent operation for esophageal cancer (group E), and 11 men (who underwent gastric or colorectal surgeries (group GC) were studied. The measurement of whole-body protein turnover, synthesis, and breakdown were made preoperatively on the 3rd and 10th postoperative day with constant infusion of [15N]glycine during isocaloric and isonitrogenous total parenteral nutrition. Significant increases in the rates of whole-body protein turnover (flux) and breakdown were seen in group E on the 3rd postoperative day (p less than 0.01, p less than 0.01, respectively), whereas the increases were not significant in group GC. The rates of whole-body protein flux and breakdown were significantly greater in group E than group GC (p less than 0.01, p less than 0.01, respectively). The rate of protein synthesis significantly increased in group E (p less than 0.05), but did not alter or slightly decreased in group GC. The rates of whole-body protein flux and breakdown in group E were still significantly greater on the 10th postoperative day than preoperatively. It was concluded that unchanged or slightly decreased rates of whole-body protein synthesis with slightly increased breakdown were seen in the group of patients who underwent gastric or colorectal surgery, whereas synthesis increased significantly with a greater increase of breakdown in patients receiving severe surgical procedures, esophagectomy for esophageal cancer.

A model for the measurement of whole-body protein turnover incorporating a protein pool with lifetime kinetics.

The hypothesis is proposed that the body contains a pool of protein turning over by lifetime rather than traditional first-order kinetics. The basis of the hypothesis is the observation of a step in the labelling curve or urinary ammonia during constant infusion of [15N]glycine. A four pool model has been constructed with different values for the rate of uptake of tracer into the lifetime pool; the calculated curves of tracer concentration show a step quite similar to that observed experimentally. It is concluded that it is possible, from an experimental curve, to derive an approximate estimate of the relative flux to the lifetime protein pool. Some suggestions are proposed for the physiological nature of this pool.

Flooding-dose of various amino acids for measurement of whole-body protein synthesis in the rat

These studies were undertaken to investigate the influence of the precursor amino acid on the measurement of whole-body protein turnover by the flooding-dose method. Whole-body protein synthesis rates were estimated in 70 g rats using an intravenous injection of L-(U(14)C) Threonine, L-(U(14)C) Lysine (200µmoles/100g; 0.15µCi/µmol or 1000µmoles/100 g; 0.15µCi/µmol), L-(U(14)C) Phenylalanine, L-(1(14)C) Leucine or L-(U(14)C) Histidine (200µmoles/100 g; 0.15µCi/µmol). Forty two rats were divided into seven groups. Each group received a large dose of one of the labelled amino acids. In each group, one animal was killed every 2 min between 5 and 15 min after the injection. Whole-body protein fractional rate was determined from the slope of the linear regression of Sb(t) (protein specific radioactivity) against Si'(t) ×t, where Si'(t) is the average specific radioactivity of free tissue amino acids between 0 andt. Whole-body protein fractional synthesis rates were 41.4, 25.6, 31.1, 31.4 and 22.8%/day with threonine, lysine, phenylalanine, leucine and histidine respectively. These data suggest that the estimation of whole-body protein synthesis rate varies according to the amino acid used because of the heterogeneity of the protein pool.