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.

Alzheimer’s disease (AD) is a degenerative disorder typified by progressive deterioration of memory and the appearance of β-amyloid peptide (Aβ)-rich senile plaques. Recently we have identified a novel function of a patented formulation of modified Huanglian-Jie-Tu-Tang (HLJDT-M), a Chinese herbal medicine, in treating AD in in vitro studies (US patent No. 9,375,457). HLJDT-M is a formulation composed of Rhizoma Coptitis, Cortex Phellodendri and Fructus Gardeniae without Radix Scutellariae. Here, we assessed the efficacy of HLJDT-M on a triple transgenic mouse model of AD (3XTg-AD). Oral administration of HLJDT-M ameliorated the cognitive dysfunction of 3XTg-AD mice and lessened the plaque burden. In addition, biochemical assays revealed a significant decrease in levels of detergent-soluble and acid-soluble Aβ via decreasing the levels of full length amyloid-β precursor protein (FL-APP) and C-terminal fragments of APP (CTFs) in brain lysates of HLJDT-M-treated mice. HLJDT-M treatment also significantly reduced the levels of FL-APP and CTFs in N2a/SweAPP cells. In contrast, treatment using the classical formula HLJDT did not reduce the memory impairment of 3XTg-AD mice and, rather, increased the Aβ/Fl-APP/CTFs in both animal and cell culture studies. Altogether, our study indicates that HLJDT-M is a promising herbal formulation to prevent and/or cure AD.

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