The effect of L-cysteine and glutathione on inhibition of Na⁺, K⁺-ATPase activity by aspartame metabolites in human erythrocyte membrane

Abstract

Background:

Reports have implicated Aspartame (N-L-a-aspartyl-L-phenylalanine methyl ester, ASP) in neurological problems.

Aim:

To evaluate Na⁺, K⁺-ATPase activities in human erythrocyte membranes after incubation with the ASP metabolites, phenylalanine (Phe), methanol (MeOH) and aspartic acid (Asp).

Methods:

Erythrocyte membranes were obtained from 12 healthy individuals and were incubated at 37°C for 1 h with the sum or each of the ASP metabolites separately, which are commonly measured in blood after ASP ingestion. Na⁺, K⁺-ATPase and Mg²⁺-ATPase activities were measured spectrophotometrically.

Results:

Membrane Mg²⁺-ATPase activity was not altered. The sum of ASP metabolite concentrations corresponding to 34, 150 or 200 mg/kg of the sweetener ingestion resulted in an inhibition of the membrane Na⁺, K⁺-ATPase by −30, −40, −48%, respectively. MeOH concentrations of 0.14, 0.60 or 0.80 mM decreased the enzyme activity by −25, −38, −43%, respectively. Asp concentrations of 2.80, 7.60 or 10.0 mM inhibited membrane Na⁺, K⁺-ATPase by −26, −40, −46%, respectively. Phe concentrations of 0.14, 0.35 or 0.50 mM reduced the enzyme activity by −24, −44, −48%, respectively. Preincubation with L-cysteine or reduced glutathione (GSH) completely or partially restored the inhibited membrane Na⁺, K⁺-ATPase activity by high or toxic ASP metabolite concentrations.

Conclusions:

Low concentrations of ASP metabolites had no effect on Na⁺, K⁺-ATPase activity. High or abuse concentrations of ASP hydrolysis products significantly decreased the membrane enzyme activity, which was completely or partially prevented by L-cysteine or reduced GSH.