Neurobehavioral changes and activation of neurodegenerative apoptosis on long-term consumption of aspartame in the rat brain

Though several studies on toxic effect of aspartame metabolite have been studied, there are scanty data on whether aspartame exposure administration could release formate, a methanol metabolite thereby inducing oxidative stress and neurodegeneration in brain discrete region. To mimic the human methanol metabolism, the methotrexate (MTX) treated folate deficient rats were used. Aspartame was administered orally to the MTX treated animals and was studied along with controls and MTX treated controls. Oral intubations of FDA approved 40 mg/kg b.wt aspartame were given daily for 90 days. The loco–motor activity and emotionality behavior in the aspartame treated animals showed a marked increase in the immobilization, fecal bolus with a marked decrease in ambulation, rearing, grooming. The anxiety behavior in the aspartame treated animals showed a marked decrease in percentage of open arm entry, percentage of time spent in open arm and number of head dips. It is appropriate to point out, formaldehyde and formate could have led to an increased formation of free radical in the aspartame treated animals resulting in altered neurobehavioral changes owing to neuronal oxidative damage. Aspartame induced ROS may be also linked to increased neuronal apoptosis. In this study the aspartame treated animals showed an up regulation in the apoptotic gene expression along with protein expression in the respective brain region indicating the enhancement of neuronal cell death. This study intends to corroborate that chronic aspartame consumption can alter the behavior and neurodegeneration in brain discrete regions

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

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, Memory, Folate deficient rat model, Oxidative stress, Free radica

Disruption of redox homeostasis in liver function and activation of apoptosis on consumption of aspartame in folate deficient rat model

This study assesses the effect of long-term intake of aspartame on liver function and apoptosis signaling pathway in the Wistar albino rats. Several reports have suggested that methanol is one of the major metabolites of Aspartame. Non-primate animals are usually resistant to methanol-induced metabolic acidosis due to high levels of hepatic folate content; hence a folate deficiency model was induced by treating animals with methotrexate (MTX) prior to aspartame exposure. The aspartame treated MTX animals exhibited a marked significant increase in hepatic alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP) and lactic acid dehydrogenase (LDH) activity compared to controls. Aspartame treated MTX animals additionally exhibited down-regulation of genes namely B-cell lymphoma 2 (Bcl2) expression and up-regulation of Bcl-2-associated X protein (Bax), Fas-associated protein with death domain (FADD) and Caspase 3, 9 genes and apoptotic protein expression, indicating the augmentation of hepatic apoptosis. Nuclear condensation, micro vacuole formation in the cytoplasm and necrosis were observed in the liver of the aspartame treated animals on histopathology evaluation. Additionally, Immunohistochemical analysis revealed a significant increase in positive cells expressing Fas, FADD, Bax and Caspase 9 protein, indicating an increase in apoptotic protein expression in the liver. Thus, Aspartame may act as a chemical stressor which alters the functional status of liver, leading to hepatotoxicity