Oxidative stress evoked damages leading to attenuated memory and inhibition of NMDAR-CaMKII-ERK/CREB signalling on consumption of aspartame in rat model

J Food Drug Anal. 2018 Apr;26(2):903-916. doi: 10.1016/j.jfda.2017.11.001. Epub 2017 Dec 6.

Abstract

Many controversial reports are available on the use of aspartame as it releases methanol as one of its metabolite during metabolism. The present study proposes to investigate whether long term (90 days) aspartame (40 mg/kg b.wt) administration could induce oxidative stress and alter the memory in Wistar strain male albino rats. To mimic the human methanol metabolism, methotrexate (MTX)-treated rats were included as a model to study the effects of aspartame. Wistar strain albino rats were administered with aspartame (40 mg/kg b.wt) orally and studied along with controls and MTX-treated controls. Aspartame interfered in the body weight and corticosterone levels in the rats. A marked increase in the mRNA and protein expression of neuronal nitric oxide synthase (nNOS) and induced nitric oxide synthase (iNOS) which resulted in the increased nitric oxide radical's level indicating that aspartame is a stressor. These reactive nitrogen species could be responsible for the altered cell membrane integrity and even cause death of neurons by necrosis or apoptosis. The animals showed a marked decrease in learning, spatial working and spatial recognition memory deficit in the Morris water maze and Y-maze performance task which could have resulted due to reduced hippocampal acetylcholine esterase (AChE) activity. The animal brain homogenate also revealed the decrease in the phosphorylation of NMDAR1-CaMKII-ERK/CREB signalling pathway, which well documents the inhibition of phosphorylation leads to the excitotoxicity of the neurons and memory decline. This effect may be due to methanol which may also activate the NOS levels, microglia and astrocytes, inducing neurodegeneration in brain. Neuronal shrinkage of hippocampal layer due to degeneration of pyramidal cells revealed the abnormal neuronal morphology of pyramidal cell layers in the aspartame treated animals. These findings demonstrate that aspartame metabolites could be a contributing factor for the development of oxidative stress in the brain.

Keywords: Aspartame; Folate deficient rat model; Free radical; Memory; Oxidative stress.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Aspartame / adverse effects*
  • Aspartame / metabolism
  • Brain / metabolism
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / genetics
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2 / metabolism*
  • Cyclic AMP Response Element-Binding Protein / genetics
  • Cyclic AMP Response Element-Binding Protein / metabolism*
  • Extracellular Signal-Regulated MAP Kinases / genetics
  • Extracellular Signal-Regulated MAP Kinases / metabolism*
  • Female
  • Male
  • Memory*
  • Methanol / adverse effects
  • Methanol / metabolism
  • Nitric Oxide / metabolism
  • Nitric Oxide Synthase Type I / metabolism
  • Nitric Oxide Synthase Type II / metabolism
  • Oxidative Stress*
  • Rats
  • Rats, Wistar
  • Receptors, N-Methyl-D-Aspartate / genetics
  • Receptors, N-Methyl-D-Aspartate / metabolism*
  • Signal Transduction
  • Sweetening Agents / adverse effects*
  • Sweetening Agents / metabolism

Substances

  • Cyclic AMP Response Element-Binding Protein
  • NMDA receptor A1
  • Receptors, N-Methyl-D-Aspartate
  • Sweetening Agents
  • Nitric Oxide
  • Nitric Oxide Synthase Type I
  • Nitric Oxide Synthase Type II
  • Calcium-Calmodulin-Dependent Protein Kinase Type 2
  • Extracellular Signal-Regulated MAP Kinases
  • Methanol
  • Aspartame

Grants and funding

The financial assistance provided by the Indian Council of Medical Research (ICMR) No. 3/1/2/29/Nut./2012/Dated 29-09-2013 for Senior Research Fellow is gratefully acknowledged.