title: 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.
  
  
  OBJECTIVE
  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 degrees 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 Mg(2+)-ATPase activities were measured spectrophotometrically.
  
  
  RESULTS
  Membrane Mg(2+)-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.
authors.affiliation: Institute of Child Health, Research Center, Aghia Sophia Children's Hospital, Athens, Greece.
authors.forename: K H
authors.initials: KH
authors.lastname: Schulpis
authors.forename: I
authors.initials: I
authors.lastname: Papassotiriou
authors.forename: T
authors.initials: T
authors.lastname: Parthimos
authors.forename: T
authors.initials: T
authors.lastname: Tsakiris
authors.forename: S
authors.initials: S
authors.lastname: Tsakiris
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001218:Aspartame / Q000378:metabolism / Q000494:pharmacology*; D002478:Cells, Cultured; D003545:Cysteine / Q000378:metabolism* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004910:Erythrocyte Membrane / Q000201:enzymology; D005978:Glutathione / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D013053:Spectrophotometry; D013549:Sweetening Agents / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D013549:Sweetening Agents; D000254:Sodium-Potassium-Exchanging ATPase; D005978:Glutathione; D003545:Cysteine; D001218:Aspartame