Pharmacological Evaluation of Sunitinib for the Treatment of Alzheimer's Disease

Abstract

Introduction: Alzheimer’s disease (AD) is the most prevalent cause of dementia. AD leads to the development of cognitive impairment that progresses over time. The pathology includes the extracellular plaques formation of amyloid beta (Aβ), intracellular deposition of tau known as, neurofibrillary tangles, a decrease in the neurotransmitter level of acetylcholine, oxidative stress, and neuroinflammation. These pathologies cause cerebral atrophy and result in memory loss. AD has symptoms such as anterograde amnesia, aphasia, agnosia, apraxia, and anomia. Streptozotocin (STZ) intracerebroventricular (ICV) injection is a model for examining the pathogenic processes related to sporadic AD (sAD). STZ administration causes typical agingassociated changes, such as telomere instability, mitochondrial dysfunction, genomic instability, metabolic dysfunction, and cellular senescence. STZ-ICV administered rats develop an insulin-resistant brain state that acts as an animal model for sAD. Sunitinib is a tyrosine kinase inhibitor that as per literature can improve cognitive impairment by the inhibition of acetylcholinesterase enzyme and thus increases the available stores of acetylcholine. The present study aims to evaluate the efficacy of sunitinib for the treatment of AD. Methodology: Healthy Wistar female rats 2-3 months were utilized in the present study. Rats were divided into 7 groups: Normal Control; Sham Control; Disease Control administered ICV streptozotocin 3mg/kg bilaterally; Disease treated with Donepezil 5mg/kg PO; Disease treated with sunitinib 2.2mg/kg PO; Disease treated with sunitinib 3.4mg/kg PO; Disease treated with sunitinib 4.5mg/kg PO. The rats were initially (Day -7 to -1) trained for neurobehavioral paradigms i.e., modified Y-maze, Morris Water Maze, and Novel Object Recognition. On day 0, the disease was induced surgically by administration of ICV STZ (3mg/kg) bilaterally in the brain. One month resting period was followed for the development of sAD. The treatments as per the respective groups were administered from day 31 for a period of 28 days. At the end of the treatment phase, the neurobehavioral paradigms were evaluated (Day 52 to 58) and finally, on Day 59 the rats were sacrificed and brain samples were isolated for biochemical estimations, histopathology, and immunohistochemistry. Results: Neurobehavioral paradigms: Modified Y-Maze results showed the number of entries in the novel arm was significantly increased in the SUN2 group (p<0.01) when compared with the DC group. The percentage time spent in the novel arm was found to be increased in the treatment groups as compared to the DC group. In the novel objection recognition test, the treatment groups showed slight improvement in the percentage discrimination index. The Morris Water Maze test showed that after training, animals could easily locate the hidden platform and the escape latency was found to be decreased in treatment groups. Biochemical parameters: The treatment decreased the levels of acetylcholinesterase enzyme with DPZ (p<0.01) and SUN2 (p<0.01) showing significant results. The treatments also reduced the MDA levels with SUN2 group showing a significant reduction (p<0.05) in comparison to the DC group. Further, the treatments showed improvement in the levels of reduced glutathione with SUN1 and SUN3 groups showing comparable levels to the NC group. Histopathology: The histopathological evaluation showed that the administration of ICV STZ caused degeneration of the pyramidal neurons which was ameliorated by the treatment as witnessed by the images of DPZ and SUN2. Immunohistochemistry: The treatment improved the expression of synaptophysin with SUN1 (p<0.05), SUN2 (p<0.01), and SUN3 (p<0.001) showing significant improvement in the percentage of GFAP-positive area (p<0.001). The treatment with sunitinib showed a decrease in the GFAP expression. Conclusion: Our results show that sunitinib has significant efficacy in inhibiting the acetylcholinesterase enzyme which can be beneficial as it increases the stores of acetylcholine and thus improves cognitive function and memory which is evident from the neurobehavioral paradigms. Sunitinib also decreases oxidative stress by increasing the levels of MDA and decreasing the levels of reduced glutathione and thus effectively ameliorates. AD pathology by reversing the degeneration of the pyramidal neurons in the hippocampus. The immunohistochemistry data shows that sunitinib improves synaptophysin expression which is essential for synaptic plasticity and synaptic transmission at the synapses. It also decreases GFAP expression which is a marker of astrogliosis and is involved in neuroinflammation. Thus, it can be inferred that sunitinib effectively reduces the acetylcholinesterase enzyme levels, decreases neuroinflammation, increases synaptic plasticity and decreases oxidative stress and thus can be further evaluated for repurposing for the treatment of AD.