Effect of an abuse dose of aspartame upon plasma and erythrocyte levels of amino acids in phenylketonuric heterozygous and normal adults.

Plasma and erythrocyte levels of free amino acids were measured in five female subjects known to be heterozygous for phenylketonuria and six subjects assumed to be normal (three male, three female) who were administered an abuse dose of aspartame (100 mg/kg) in orange juice. Small increases in plasma aspartate levels were noted 30 minutes after aspartame loading in both groups, with mean (+/- SD) levels increasing from 0.15 +/- 0.05 mumoles/100 ml to 0.43 +/- 0.23 mumoles/100 ml in normal subjects (P = 0.02), and from 0.49 +/- 0.23 mumoles/100 ml to 0.80 +/- 0.56 mumoles/100 ml in heterozygous subjects (P > 0.05). However, plasma aspartate levels remained within normal postprandial levels in each case. Erythrocyte aspartate levels were unchanged in both groups. In normal subjects, plasma phenylalanine levels (mean +/- SD) increased from fasting levels (5.40 +/- 1.05 mumoles/100 ml) to mean peak values of 20.2 +/- 6.77 mumoles/100 ml. In heterozygous subjects, mean peak plasma phenylalanine levels were approximately twice as high (41.7 +/- 2.33 mumoles/100 ml), and the area under the plasma concentration-time curve twice as large. Peak plasma phenylalanine levels, however, were below those associated with toxic effects. The data indicate slower, but adequate metabolism and clearance of an abuse dose of aspartame by the phenylketonuric heterozygote.