The potential value of capsaicin in modulating cognitive functions in a rat model of streptozotocin-induced Alzheimer’s disease

Abstract

Background: Alzheimer’s disease (AD) is a progressive neurodegenerative disorder. Objectives: This study aimed to examine the role of capsaicin dietary exposure in ameliorating cognitive functions in experimental rat model of streptozotocin-induced Alzheimer’s disease (STZ-induced AD). Methods: Thirty adult albino male rats were distributed randomly into three equal groups. Ten rats, served as negative controls, were treated once with intracerebroventricular (icv) injection and intragastric infusion of saline for 47 days. Twenty rats were treated with a single icv-STZ (3 mg/kg) injection for induction of AD. Behavioral tests were done after 2 weeks to evaluate the development of Alzheimer’s model. Rats with retention latency less than 300 s in the passive avoidance test were further subdivided into 2 groups; one group was treated with intragastric infusion of capsaicin (10 mg/kg) for 47 days and the other group was treated similarly with saline as positive controls. Then, behavioral tests were repeated at the end of the experiment. The expression level of β-amyloid 1-42 peptide (Aβ1-42) and tau proteins was measured using ELISA test. Results: The behavioral impairments had been ameliorated by capsaicin treatment. Furthermore, there was improvement in the estimated biochemical parameters as revealed by the significant decline in the mean values of β-amyloid 1-42 peptide (Aβ1-42) and tau proteins in hippocampal homogenate in capsaicin-treated group as compared to the positive controls (p < 0.001 and p = 0.004, respectively). Chorioallantoic membrane (CAM) assay showed inhibition of angiogenesis in chick embryo by 5 μg capsaicin. Conclusions: Our study suggests that capsaicin is a promising agent for food additives and drugs which ameliorates AD through improvement of the behavioral and biochemical alterations detected in STZ-induced AD.