Free amino acid formula: nitrogen utilization and metabolic effects in normal subjects

Sex effects of dietary protein source and acid load on renal and bone status in the Pahenu2 mouse model of phenylketonuria

The low‐phenylalanine (Phe) diet with amino acid (AA) medical foods is associated with low bone mineral density (BMD) and renal dysfunction in human phenylketonuria (PKU). Our objective was to determine if diets differing in dietary protein source and acid load alter bone and renal outcomes in Pah^−/− and wild‐type (WT) mice. Female and male Pah^−/− (Pah^enu2/enu2) and WT littermates (C57BL/6 background) were fed high‐acid AA, buffered AA (BAA), glycomacropeptide (GMP), or high‐Phe casein diets from 3 to 24 weeks of age. The BAA diet significantly reduced the excretion of renal net acid and ammonium compared with the AA diet. Interestingly, the BAA diet did not improve renal dilation in hematoxylin and eosin (H&E) stained renal sections, femoral biomechanical parameters, or femoral bone mineral content (BMC). Significantly lower femoral BMC and strength occurred in Pah^−/− versus WT mice, with greater decline in female Pah^−/− mice. Polyuria and mild vacuolation in the proximal convoluted tubules were observed in male Pah^−/− and WT mice fed the high‐acid AA diet versus absent/minimal cortical vacuolation in males fed the GMP, BAA, or casein diets. Vacuole contents in male mice were proteinaceous. Cortical vacuolation was absent in female mice. Dilated medullary tubules were observed in all Pah^−/− mice, except for male Pah^−/− mice fed the GMP diet. In summary, the PKU genotype and diet showed differential effects on renal and bone status in male and female mice. Renal status improved in male Pah^−/− mice fed the GMP diet.

Effects of three liquid diets on nutrition-sensitive plasma proteins of tube-fed elderly men

The effects on three nutrition-sensitive plasma proteins of isocaloric feedings with three enteral formulas were compared in 10 tube-fed male nursing home residents. The enteral products were Isocal (based on whole protein), Peptamen (based on a mixture of oligopeptides), and Vivonex T.E.N. (based on free amino acids). The nutrition-sensitive plasma proteins were albumin, transferrin, and retinol-binding protein. After observation during four weeks of feeding with Isocal, each subject was then monitored during four weeks of Peptamen and four weeks of Vivonex T.E.N. The latter two products were alternated in a crossover design. The shift of Isocal to Peptamen did not significantly (P greater than .05) influence the serum level of albumin, transferrin, or retinol-binding protein. In contrast, the shift of Isocal to Vivonex T.E.N. or of Peptamen to Vivonex caused a significant (P less than .05) decline in all three plasma proteins, the kinetics of their reductions corresponding to their known half-lives. The behavior of the three nutrition-sensitive plasma proteins suggests that in elderly nursing home men without gastrointestinal disease the nutritional value of the protein component of the three formulas follows the order Isocal = Peptamen greater than Vivonex T.E.N. However, this conclusion will require confirmation by nitrogen balance studies.