Metabolism. 1991 Jun;40(6):612-8.

Metabolism of aspartame and its L-phenylalanine methyl ester decomposition product by the porcine gut.

Burgert SL, Andersen DW, Stegink LD, Takeuchi H, Schedl HP.

Department of Medicine, University of Iowa, Iowa City.

The intestinal metabolism of aspartame (N-L-alpha-aspartyl-L-phenylalanine methyl ester; APM) and its L-phenylalanine methyl ester (PME) decomposition product was evaluated in six young pigs. Equimolar doses (2.5 mmol/kg body weight) of APM, PME, and L-phenylalanine (PHE) administered to the proximal jejunum produced similar increases in portal blood PHE concentrations. Methanol, nondetectable in portal blood after PHE ingestion, increased markedly after administration of either APM or PME. Portal blood aspartate concentrations were unchanged after PME and PHE administration, but increased significantly after APM administration. Increases in portal blood PHE concentrations were significantly greater than were increases in aspartate concentrations following APM administration. Neither APM, PME, nor aspartyl-phenylalanine (AspPhe) were detected in portal or vena caval blood following administration of any test compound. Steady-state perfusion of the small intestine with APM showed a net intraluminal appearance rate of AspPhe at 36% of the disappearance rate of APM. During steady-state PME perfusion, PHE had a significantly greater net appearance rate than during APM perfusion. Methanol appearance rates were slightly, but not significantly, higher during PME than during APM perfusions. The data suggest that (1) APM is hydrolyzed to AspPhe and both APM and PME are hydrolyzed to their constituent amino acids and and methanol prior to entering the portal circulation; (2) AspPhe is an important intraluminal intermediate in aspartame metabolism; and (3) aspartate is rapidly metabolized by the enterocyte.