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 þ , K þ -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 371C for 1 h with the sum or each of the ASP metabolites separately, which are commonly measured in blood after ASP ingestion. Na þ , K þ -ATPase and Mg 2 þ -ATPase activities were measured spectrophotometrically. Results: Membrane Mg 2 þ -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 þ , K þ -ATPase by À30, À40, À48%, respectively. MeOH concentrations of 0.14, 0.60 or 0.80 mM decreased the enzyme activity by À25, À38, À43%, respectively. Asp concentrations of 2.80, 7.60 or 10.0 mM inhibited membrane Na þ , K þ -ATPase by À26, À40, À46%, respectively. Phe concentrations of 0.14, 0.35 or 0.50 mM reduced the enzyme activity by À24, À44, À48%, respectively. Preincubation with L-cysteine or reduced glutathione (GSH) completely or partially restored the inhibited membrane Na þ , K þ -ATPase activity by high or toxic ASP metabolite concentrations. Conclusions: Low concentrations of ASP metabolites had no effect on Na þ , K þ -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.

Effect of hydrogen peroxide on Na+,K+-ATPase activity in spermatozoa of infertile men

“…This suggests that GSH partially protects the Na + ,K + -ATPase from inhibition under experimental oxidative stress. Similar results which show protective effects of GSH on Na + ,K + -ATPase against oxidation were demonstrated earlier (Schulpis et al, 2006). However, administration of GSH only after H 2 O 2 treatment does not reverse Na + ,K + -ATPase inhibition.…”

Self-Assembly of Artificial Sweetener Aspartame Yields Amyloid-like Cytotoxic Nanostructures

“…1,40,71,72 Furthermore, membrane-damaging effects of aspartame on RBCs have been reported. 73,74 The presence of both a hydrophobic exterior and inner hydrophilic core regions in the amyloid structures has been proposed to intervene in the RBC bilayer, 75 inducing ion-leakage-mediated cellular damage. 76 Time-dependent structural evolution during aspartame selfassembly (as observed between 10 and 100 ns) showed preferable minor readjustment of aspartame's molecular orientation, facilitating precise distribution of its charged and aromatic moieties that eventually contribute to the surface hydrophobicity (Figures 1l, S3−S5).…”

Chronic Effect of Aspartame on Ionic Homeostasis and Monoamine Neurotransmitters in the Rat Brain

“…Consecutively, the properties of membrane-bound enzymes could be altered. It is suggested that phenylalanine, an important metabolite of aspartame, could induce reactive species production 13 and oxidative stress in experimental models. 38,39 Further, it has been found that high phenylalanine concentrations reduced Na + -K + -ATPase activity in rat brain.…”

“…[9][10][11] Ionic involvement has been suggested to play a role in spatial learning and memory. 12 In an earlier in vitro study, Schulpis et al 13 have reported that aspartame significantly decreased the Na þ -K þ -ATPase activity in the erythrocyte membrane. Na þ -K þ -ATPase is crucial for maintaining ionic homeostasis and cell volume in neurons.…”