l-Arginine Synthesis from Enteral Proline

The importance of l-arginine synthesis in humans throughout the life cycle is clear. The experiments of Young et al. with an l-arginine- and precursor-free diet for 4 weeks in healthy adults demonstrate that these amino acids are truly non-essential in the diet (Tharakan et al. Clin Nutr 27(4):513–522, 2008). Thus, efficient l-arginine synthesis is implied. In newborn humans, the amount of l-arginine in breast milk is inadequate to meet the needs of growth and metabolism, again implying effective mechanisms of l-arginine synthesis (Carcillo. Crit Care Med. 31(2):657–659, 2003; Zello et al. Pediatr Res 53(2):338–344, 2003). Yet in both adults and newborns, l-arginine may become essential under certain conditions where rates of synthesis are inadequate. The most significant example is that of parenteral nutrition where an l-arginine-free parenteral diet leads to life-threatening hyperammonemia (Batshaw et al. J Pediatr 105(1):86–91, 1984; Heird et al. J Pediatr 81(1):162–165, 1972).