Absorption, utilization, and safety of aspartic acid.

The dicarboxylic amino acids, asparate and glutamate, occupy unique positions in intermediary metabolism, particularly in the mitochondria, where they play important roles in nitrogen and energy metabolism. Administration of large quantities of glutamate and asparate to the newborn mouse produces a variety of neurotoxic effects, the most marked of which is neuronal necrosis. Neurotoxic effects of glutamate and aspartate in animal species other than the rodent are highly controversial. In the most critical animal species, the infant subhuman primate, at least four research groups have failed to duplicate the original report of glutamate-induced neuronal necrosis. Marked elevations in plasma glutamate or aspartate must occur for development of neuronal necrosis. In the highly sensitive neonatal mouse, plasma glutamate plus plasma aspartate levels must reach 60-80 mumol/dl to produce even minimal neuronal necrosis. In the healthy neonatal primate, loads producing plasma glutamate levels ranging from 50 to 1,600 mumol/dl failed to produce neuronal necrosis in our studies. Thus, it is clear that (1) marked elevations in plasma glutamate and aspartate must occur for neuronal necrosis, and (2) threshold levels required to produce neuronal necrosis vary greatly with species. The available data indicate little danger to the healthy primate and humans from ingestion of the dicarboxylic amino acids under anything resembling a reasonable intake. However, there is no doubt that these amino acids are toxic to the neonatal mouse at high dose levels.