Inhibition potential against acetylcholinesterase of commercial and extracts of capsaicin and dihydrocapsaicin by in vitro and in silico studies

Abstract

The present research investigates the amount of capsaicin and dihydrocapsaicin in three parts of chili extracts (pericarp, seeds, and placenta). Moreover, inhibition potential of capsaicin and dihydrocapsaicin, and chili extracts against AChE were also investigated in vitro and in silico study. The results show that placenta extract had more capsaicin (3818.72 mg/kg DW) and dihydrocapsaicin (2788.37 mg/kg DW) than other extracts. The inhibition potential of dihydrocapsaicin against AChE was higher than that of capsaicin and chili extracts. Which corresponded to the Ki value of dihydrocapsaicin (0.85 mM) higher inhibition potential than that of capsaicin (1.20 mM). The stronger interaction of dihydrocapsaicin than capsaicin at the active site of AChE was also supported by the binding affinity value (−7.8 kcal/mol for dihydrocapsaicin and −7.3 kcal/mol for capsaicin). However, the inhibition modes of dihydrocapsaicin and capsaicin were mixed-type inhibition against AChE. Besides, dihydrocapsaicin and capsaicin were surrounded by aromatic amino acids in the active site of AChE, which caused an increase in fluorescence intensity (FI). A similar increase in FI was also observed in the chili extracts (pericarp, seeds, and placenta). Our results show that capsaicinoids (capsaicin and dihydrocapsaicin) from chili extracts are natural inhibitors of AChE and may be applied to therapeutic Alzheimer's disease.