The effect of aspartame metabolites on human erythrocyte membrane acetylcholinesterase activity

Studies have implicated aspartame (ASP) with neurological problems. The aim of this study was to evaluate acetylcholinesterase (AChE) activity in human erythrocyte membranes after incubation with the sum of ASP metabolites, phenylalanine (Phe), methanol (met) and aspartic acid (aspt), or with each one separately. Erythrocyte membranes were obtained from 12 healthy individuals and were incubated with ASP hydrolysis products for 1 h at 37°C. AChE was measured spectrophotometrically. Incubation of membranes with ASP metabolites corresponding with 34 mg/kg, 150 mg/kg or 200 mg/kg of ASP consumption resulted in an enzyme activity reduction by -33%, -41%, and -57%, respectively. Met concentrations 0.14 mM, 0.60 mM, and 0.80 mM decreased the enzyme activity by -20%, -32% or -40%, respectively. Aspt concentrations 2.80 mM, 7.60 mM or 10.0 mM inhibited membrane AChE acitivity by -20%, -35%, and -47%, respectively. Phe concentrations 0.14 mM, 0.35 mM or 0.50 mM reduced the enzyme activity by -11%, -33%, and -35%, respectively. Aspt or Phe concentrations 0.82 mM or 0.07 mM, respectively, did not alter the membrane AChE activity. It is concluded that low concentrations of ASP metabolites had no effect on the membrane enzyme activity, whereas high or toxic concentrations partially or remarkably decreased the membrane AChE activity, respectively. Additionally, neurological symptoms, including learning and memory processes, may be related to the high or toxic concentrations of the sweetener metabolites. © 2005 Elsevier Ltd. All rights reserved

l-Cysteine and glutathione restore the modulation of rat frontal cortex Na+, K+-ATPase activity induced by aspartame metabolites

Background: Studies have suggested that aspartame (ASP) ingestion is implicated in neurological problems. Aim: The aim of this study was to evaluate rat frontal cortex Na+, K+-ATPase and Mg2+-ATPase activities after incubation with ASP or each of its metabolites, phenylalanine (Phe), methanol (MeOH) and aspartic acid (asp) separately. Method: Suckling rat frontal cortex homogenates or pure Na+, K+-ATPase were incubated with ASP metabolites. Na+, K+-ATPase and Mg2+-ATPase activities were measured spectrophotometrically. Results: Incubation of frontal cortex homogenate or pure Na+, K+-ATPase with various ASP concentrations as expected in the cerebrospinal fluid (CSF) after ASP consumption of 34, 150 or 200 mg/kg, decreased the frontal cortex enzyme activity by 33%, 53% or 57%, respectively, whereas pure enzyme was remarkably stimulated. Moreover, incubation of frontal cortex homogenate with each one of the expected ASP metabolites in the CSF, except MeOH, which are related to the intake of the above mentioned doses of the sweetener, resulted in an activation of the membrane Na+, K+-ATPase, as well as pure enzyme. Frontal cortex Mg2+-ATPase remained unaltered. Addition of l-cysteine (cys) or reduced glutathione (GSH) to ASP metabolites mixtures, corresponding to 150 or 200 mg/kg doses of the sweetener, completely or partially restored to normal the modulated membrane and pure Na+, K+-ATPase activities. Conclusion: CSF concentrations of the sum of ASP metabolites corresponding to the intake of common, abuse or toxic doses (34 or 150 or 200 mg/kg, respectively) of the additive significantly increased rat frontal cortex Na+, K+-ATPase and pure enzyme activities. Cys or GSH completely or partially restored to normal both enzyme activities, possibly due to amelioration of the cellular GSH reduction from the action of MeOH, a metabolite of the sweetener and/or by their scavenging effect. © 2008 Elsevier Ltd. All rights reserved

The effect of aspartame metabolites on the suckling rat frontal cortex acetylcholinesterase. An in vitro study

Aspartame (ASP) consumption is suggested to be implicated with muscarinic dysfunction. The aim of this work was to evaluate the effect of ASP and its metabolites on acetylcholinesterase (AChE) activity in rat frontal cortex and pure enzyme. Rat frontal cortex homogenate or pure enzyme AChE (eel E. Electricus) were incubated with ASP and each of ASP components, phenylalanine (Phe), aspartic acid (asp), and methanol (MeOH) for 1 h at 37 °C. AChE was measured spectrophotometrically. The results showed that incubation of rat tissue or pure enzyme with the sum of ASP metabolites, as reported to be found in the CSF after 150 or 200 mg/kg ASP consumption, inhibited frontal cortex and pure AChE about -11% to -29% (p < 0.001). Asp, Phe or MeOH concentrations related to their CSF levels after ingestion of abuse or toxic ASP doses, when separately incubated with frontal cortex or pure AChE, resulted in a significant decrease of the enzyme activities. In conclusion:. ASP compounds may directly and/or indirectly act on the frontal cortex AChE. High or toxic doses of the sweetener remarkably decreased the enzyme activity. If this in vitro finding comes into human reality, it may be suggested that cholinergic symptoms are related to the consumption of the above ASP doses. © 2007 Elsevier Ltd. All rights reserved

The effect of aspartame on acetylcholinesterase activity in hippocampal homogenates of suckling rats

Background: Neurological disturbances have been implicated with aspartame (ASP) consumption and the cholinergic system with acetylcholinesterase (AChE) seems actively involved. Aim: To evaluate the effect of ASP and its metabolites on rat hippocampal AChE activity. Methods: Hippocampal homogenate or pure enzyme AChE (eel E. electricus) was incubated with the sum or each of ASP components, phenylalanine (Phe), aspartic acid (asp) and methanol (MeOH) for 1 h at 37 °C. AChE activity was measured spectrophotometrically. Results: Incubation of rat tissue or pure enzyme with the sum of ASP metabolites in concentrations in CSF (the concentrations were calculated according to the CSF/plasma concentration ratios) following 150 or 200 mg kg-1 of ASP consumption, resulted in significant enzyme activity reductions of 25 and 31% for hippocampal AChE and 11% (p < 0.01) and 19% for pure enzyme, respectively. Aspartic acid concentrations of 0.42 or 0.56 mM significantly reduced the enzyme activities by 13 and 20% for hippocampal AChE and 15 and 18% for pure enzyme, respectively. Phe concentrations of 0.042 or 0.083 mM decreased the enzyme activity by 12% (p < 0.01) and 20% (p < 0.001) for hippocampal AChE and 15 and 18% (p < 0.001) for pure enzyme, respectively. Methanol concentrations of 0.60 or 0.80 mM remarkably inhibited hippocampal AChE by about 18 and 22% and pure enzyme by about 14 and 20%, respectively. Conclusions: Low concentrations of ASP components had no effect on hippocampal and pure AChE activity, whereas high or toxic concentrations remarkably decreased both enzyme activities. Muscarinic symptoms may be related to the latter concentrations of ASP metabolites. © 2007 Elsevier Ltd. All rights reserved

l-Cysteine and glutathione restore the reduction of rat hippocampal Na+, K+-ATPase activity induced by aspartame metabolites

Studies have implicated aspartame (ASP) ingestion in neurological problems. The aim of this study was to evaluate hippocampal Na+,K+-ATPase and Mg2+-ATPase activities after incubation with ASP or each of ASP metabolites, phenylalanine (Phe), methanol (MeOH) and aspartic acid (asp) separately. Suckling rat hippocampal homogenates or pure Na+,K+-ATPase were incubated with ASP metabolites. Na+,K+-ATPase and Mg2+-ATPase activities were measured spectrophotometrically. Incubation of hippocampal or pure Na+,K+-ATPase with ASP concentrations (expected in the cerebrospinal fluid (CSF)) after ASP consumption of 34, 150 or 200 mg/kg resulted in hippocampal enzyme activity reduction of 26%, 50% or 59%, respectively, whereas pure enzyme was remarkably stimulated. Moreover, incubation with hippocampal homogenate of each one of the corresponding in the CSF ASP metabolites related to the intake of common, high/abuse doses of the sweetener, inhibited Na+,K+-ATPase, while pure enzyme was activated. Hippocampal Mg2+-ATPase remained unaltered. Addition of l-cysteine (cys) or reduced glutathione (GSH) in ASP mixtures, related with high/toxic doses of the sweetener, completely or partially restored the inactivated membrane Na+,K+-ATPase, whereas the activated pure enzyme activity returned to normal. CSF concentrations of ASP metabolites related to common, abuse/toxic doses of the additive significantly reduced rat hippocampal Na+,K+-ATPase activity, whereas pure enzyme was activated. Cys or GSH completely or partially restored both enzyme activities. © 2007 Elsevier Ireland Ltd. All rights reserved

Clinical and subclinical autonomic dysfunction in chronic inflammatory demyelinating polyradiculoneuropathy

Autonomic neuropathy, although common in Guillain-Barré syndrome, is considered rare in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and has not been systematically investigated in that disorder. The present study was aimed at determining the prevalence of autonomic dysfunction and investigating the integrity of autonomic nervous system (ANS) reflexes in CIDP. We studied 17 patients with idiopathic CIDP and 20 healthy controls. Six quantitative autonomic function tests (AFTs) were used: Valsalva ratio, 30/15 ratio, and inspiration-expiration difference for parasympathetic function; and tilt test, handgrip test, and sympathetic skin response for sympathetic function. Eleven patients had symptoms of autonomic dysfunction. AFTs were abnormal in 13 patients. Parasympathetic and sympathetic systems were affected with equal frequency. The tilt test was abnormal most frequently, followed by the 30/15 ratio. Three patients developed postural hypotension with loss of consciousness during the tilt test. Abnormality of AFTs did not correlate with the presence of dysautonomic symptoms; duration, severity, and clinical course of the disease; or with age or gender of patients. Our study suggests a higher frequency of clinical and subclinical involvement of the ANS in CIDP than previously estimated. Dysautonomic symptoms are frequent but are mild. However, upon prolonged passive standing, autonomic failure can lead to loss of consciousness. The subclinical involvement of the ANS affects mainly the sympathetic vasomotor and parasympathetic cardiovascular fibers. © 2005 Wiley Periodicals, Inc

Evaluating the suitability of postnuclear supernatants as in vitro models for assessing cadmium- and other xenobiotic-induced neurotoxicity on crucial enzymatic parameters

No abstract available