Evaluation of Neuroprotective Activity of DNA Polymerase Inhibtor Against Scopolamine Induced Amnesia Model in Rats

Abstract

AIM: To evaluate neuroprotective activity of DNA Polymerase Inhibitor against scopolamine induced amnesia model in rats. INTRODUCTION: Alzheimer’s disease stands as the primary contributor to dementia cases, which is characterized by a progressive loss of cognitive ability. The pathogenic hallmarks of this condition include the development of amyloid beta plaques outside of brain cells, accumulation of tau proteins forming neurofibrillary tangles within cells, reduced acetylcholine levels in the brain, oxidative stress, and neuroinflammation. The signs of AD include anterograde amnesia, aphagia, agnosia and anomia. Scopolamine is an anti-muscarinic agent which causes short-term memory loss. The investigational drug, a DNA Polymerase Inhibitor (DPI) used in many viral infections, according to the literature, can reduce cognitive impairment by inhibiting the AChE enzyme. OBJECTIVES: To evaluate the neuroprotective action of DNA Polymerase Inhibitor and to investigate the mechanism of action of drug against scopolamine induced amnesia model in rats. METHODOLOGY: Healthy Sprague Dawley female rats were utilized in the experimental study. Rats were divided into 6 groups: Normal Control; Disease Control (Scopolamine 2mg/kg I.P); Standard Treatment group (Disease treated with Donepezil 5mg/kg PO); DPI-1 treatment: Disease treated with DNA Polymerase Inhibitor at the dose of 87mg/kg PO; DPI-2 treatment: Disease treated with DNA Polymerase Inhibitor at the dose of 130mg/kg PO; DPI-3 treatment: Disease treated with DNA Polymerase Inhibitor at the dose of 173mg/kg PO. The rats were initially (Day -7 to -1) trained for neurobehavioral paradigms i.e., Morris Water Maze, and Novel Object Recognition. The disease was induced from Day 0 to Day 15 by administering scopolamine 2 mg/kg intraperitoneally (I.P) which was followed by 28 days treatment with standard treatment (donepezil) and test drug (DNA polymerase inhibitor) orally along with scopolamine IP. At the end of the protocol, the neurobehavioral paradigms were evaluated and finally, the rats were sacrificed and brain samples were isolated for biochemical estimations, histopathology, and immunohistochemistry. RESULTS: In neurobehavioral paradigms, animals in Morris water maze test showed a decrease in escape latency in DNA Polymerase Inhibitor groups, but no significant changes were seen in the discrimination index of novel object recognition test. In biochemical assays, acetylcholinesterase level was reduced in treatment groups, but the difference was not significant. A significant increase in the levels of glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) were observed in the treatment groups in comparison to the disease control group. Decreased malondialdehyde (MDA) level was observed in the treatment groups in comparison to the disease control group. Histopathological studies revealed that the treatment ameliorated neuronal degeneration and increased neuronal density in the hippocampus. The immunohistochemistry studies showed that scopolamine administration increased glial fibrillary acidic protein (GFAP) immunoreactivity and decreased synaptophysin immunoreactivity in the CA1 region of the hippocampus which was reversed by the DPI treatments. CONCLUSION: The results of the present study showed that the DNA polymerase inhibitor drug inhibited acetylcholinesterase enzyme and thus in-turn increased the available stores of acetylcholine and thus improved memory and cognitive functions. It decreased oxidative stress by increasing GSH, SOD and CAT levels and decreasing the MDA levels. Further it reduced neuroinflammation in the brain as observed from GFAP immunohistochemistry and enhanced synaptic plasticity as shown by increased immunoreactivity to synaptophysin. The results showed that DNA Polymerase Inhibitor drug conferred neuroprotection by decreasing neuroinflammation and oxidative stress and improved synaptic plasticity. Further studies to elucidate the mechanistic pathway in advanced animal models are warranted