Protein turnover in critically ill children

Protein quantity, not protein quality, accelerates whole-body leucine kinetics and the acute-phase response during acute infection in marasmic Malawian children

The present study compared leucine kinetics and acute-phase-protein concentrations in three groups of marasmic, acutely infected Malawian children fed one of three isoenergetic diets. These were: an enhanced-protein-quality diet (egg-white+tryptophan, providing 1.2 g protein/kg per d; n 14); an increased-protein-content diet (egg-white+tryptophan, providing 1·8 g protein/kg per d; n 14); a standard-protein diet (1·2 g milk protein/kg per d; n 25). The hypotheses tested were that children receiving a diet with more protein would have greater rates of non-oxidative leucine disposal and that children receiving an isonitrogenous diet with a higher protein quality would have lower rates of leucine oxidation. The children were studied after 24 h of therapy using standard [13C]leucine stable-isotope tracer techniques. The children receiving the higher-protein-content diet had greater leucine kinetic rates than those receiving the standard-protein-content diet; non-oxidative leucine disposal was 170 (SD 52) v. 122 (SD 30) μmol leucine/kg per h (P<0·01). Leucine oxidation was less in the children receiving the enhanced-protein-quality diet than in those receiving the standard-protein-quality diet; 34 (SD 12) v. 45 (SD 13) μmol leucine/kg per h (P<0·05). The children receiving the high-protein-content diet increased their serum concentration for five of six acute-phase proteins 24 h after starting therapy, while those receiving the standard-protein-content diet did not. These data suggest that there was greater whole-body protein synthesis, and a more vigorous acute-phase response associated with the higher-protein-content diet. The clinical benefits associated with a higher protein intake in marasmic, acutely infected children need further study.

Whole-body leucine kinetics and the acute phase response during acute infection in marasmic Malawian children

This study compared leucine kinetics and acute-phase protein and cytokine concentrations in three groups of Malawian children who were fed an isoenergetic, isonitrogenous diet: children with marasmus with (n = 25) and without (n = 17) infection and well-nourished children with infection (n =13). The hypotheses tested were that whole-body leucine kinetics will be less in marasmic acutely infected children than in well-nourished acutely infected children but greater than in marasmic uninfected children. Children were studied after 24 h of therapy using standard (13)C-leucine stable isotope tracer techniques. Well-nourished children with acute infection had greater leucine kinetic rates than did marasmic children with acute infection; nonoxidative leucine disposal was 153 +/- 31 versus 118 +/- 43 micromol leucine. kg(-1). h(-1), leucine derived from whole-body proteolysis was 196 +/- 34 versus 121 +/- 47, and leucine oxidation was 85 +/- 31 versus 45 +/- 13 (p < 0.01 for all comparisons). Leucine kinetic rates were similar in marasmic children with and without acute infection. Well-nourished children with acute infection increased their serum concentration of five of six acute-phase proteins during the first 24 h, whereas marasmic children with infection did not have any increases. The serum concentrations of IL-6 were elevated in well-nourished and marasmic children with infection. These data suggest that the cytokine stimulus for the acute-phase protein kinetic response to acute infection is present in marasmic children but that the acute-phase protein metabolic response is blunted by malnutrition.

Plasma urea appearance rate is lower when children with kwashiorkor and infection are fed egg white-tryptophan rather than milk protein

In kwashiorkor, there is less endogenous proteolysis in response to acute infection than in a well-nourished state. Thus the amino acid composition of dietary protein may be more important in facilitating the acute phase response in kwashiorkor. This study tested the hypothesis that during the treatment of kwashiorkor with infection, there is a lower rate of urea appearance when the dietary intake of amino acids more closely resembles the amino acid composition of acute phase proteins. Thirty children in Malawi with kwashiorkor and acute infection were fed isoenergetic, isonitrogenous meals containing either egg white-tryptophan or milk as a protein source. After 24 h, the rates of urea appearance and whole-body protein breakdown and synthesis were measured with the use of 1-13C-leucine and 15N2-urea tracers. Plasma concentrations of seven acute phase proteins, interleukin 6 and tumor necrosis factor-alpha were measured on admission, and at 24 and 48 h. The 16 children who received egg white-tryptophan had lower rates of urea appearance than those who received milk [57+/-30 vs. 87+/-36 micromol/(kg x h), mean +/- SD, P<0.02]. No significant differences were found in the rates of whole-body protein turnover or in the concentration of any of the acute phase proteins or cytokines. The concentration of interleukin 6 was consistent with an appropriate proinflammatory response and correlated directly with the concentrations of C-reactive protein (r = 0.67, P<0.01) and alpha1-antitrypsin (r = 0.40, P<0.05). The findings suggest that egg white-tryptophan is associated with less amino acid oxidation in kwashiorkor and acute infection than is milk.