Table 1 Effects of leucine supplementation on animal e human studies related to skeletal muscle protein turnover
From: Potential antiproteolytic effects of L-leucine: observations of in vitro and in vivo studies
Study | Duration | Dose | Methods | Results |
|---|---|---|---|---|
Human | ||||
4 | 180 min | L-leucine: 1.09 and or 1.74 μmol/kg/min with insulin (plasma: 208 and 207 μmol/L) (infusion) | Leucine + KIC rates of appearance; KIC oxidation; Leucine-carbon flux | Leucine 1.09 μmol/kg/min stimulated leucine deposition into body protein in 37.7% but did not suppress endogenous proteolysis; Leucine 1.74 μmol/kg/min with insulin had a cumulative effect of 49.9% on net leucine deposition into body protein. |
5 | 7 h | L-leucine: 154 ± 1 mmol/kg-1/h-1 (infusion) | Whole-body valine and phenylalanine (tracers) flux | Inhibition of protein degradation without causing an increase in protein synthesis. |
6 | 16 h | BCAA: 1.66 μmol/kg/min (infusion) | Whole-body (arterial and venous) leucine and phenylalanine (tracers) flux rates | Suppressed rate of whole-body (-37%) and forearm (-43%) muscle proteolysis. |
Rat | ||||
8†| 105 min | BCAA: 246 mg/kg-1/h-1 (infusion) | - | Neither muscle protein synthesis nor breakdown affected. |
9 | NR | L-leucine: 0.1, 0.2, 0.25 and/or 0.5 mM (muscle incubation) | Rate of 14CO2 and KIC production | Protein synthesis was stimulated in: 10% (0.1 mM), 19% (0.2 mM) and 42% (0.5 mM); Protein degradation was inhibited in: 0% (0.1 mM), 6% (0.2 mM), 15% (0.25 mM) and 26% (0.5 mM). |
1 | 2 h | L-leucine: 0.5 mM (muscle incubation) | Incorporation of tyrosine (tracer) into proteins | Leucine increased the specific activity of the proteins by 25% and incorporated tissue proteins by 11.5%. |
27 | 2 h | L-leucine: 0.5 mM (muscle incubation) | Rate of tyrosine (tracer) incorporated and released | Protein synthesis was stimulated in the soleus muscles by 69% and in EDL muscles by 38%. No effects on protein degradation were observed. |
12 | NR | L-leucine: 5 mM (muscle incubation) | Release of acid-soluble 3H-tyrosine (tracer) | Leucine caused a significantly reduction in proteolysis of -8 to 12%. |
11 | NR | L-leucine: 10 mM (muscle incubation) | Rate of tyrosine (tracer) released | Decreased whole-body proteolytic rate in 25%. |
14 | 10 d | L-leucine: ~0,7 g/kg/day* (ingestion) | Rate of tyrosine (tracer) released | Suppressed postprandial proteolysis in old rats in 40% (measured by proteasome-dependent proteolysis). |
17 | 12–15 d | BCAA: 1 g/kg/day* (ingestion) | Incorporation of L- [2,6-3H]phenylalanine and release of tyrosine (tracers) | Suppression on the loss of body weight (-1.5 vs. -4.5 g of control group); increase in rate of protein synthesis in gastrocnemius muscle (~50–60%) and in weight of the soleus muscle (~0.007 g); decrease of protein degradation in soleus muscle (-1500 g/2 h measured by fluorescence). |
Mice | ||||
16 | 20 d | L-leucine: ~4.2 g/day* (ingestion) | Rate of incorporation of [3H]-phenylalanine and release of tyrosine (tracers) | Protein synthesis was higher around 23.4% and degradation reduced in by around 11% with leucine supplementation. |
Calves | ||||
18 | 5 d | L-leucine: 239.6 μmol/L (infusion) | Urea creatinine, urea nitrogen and urea 3-methyl-histidine levels | Improvement on nitrogen balance without effect on protein degradation |