Acetylcholinesterase Activity in the Brain of Rats: Presence of an Inhibitor of Enzymatic Activity in Heliotropium eichwaldi L. Induced Silver/Gold Allied Bimetallic Nanoparticles

A simple green method for the production of silver/gold bimetallic nanoparticles (Ag/Au BNPs) using a Heliotropium eichwaldi L. (HE) extract was designed in this study. The reduction of Ag/Au metals to stable Ag/Au BNPs within 24 h at pH 5 using 1 mL of HE at 40 °C signifies a greater rate of reaction compared with chemically elaborated synthesis. The confirmation of the synthesis and the examination of the size, shape, and elemental composition of these BNPs were performed using visible absorption spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Stable, irregular-rod-shaped, and crystalline Ag/Au BNPs with a well-defined 6-nm diameter and a blue shift λ_max of 532 nm were synthesized using the HE extract. Moreover, the anti-cholinesterase (anti-AChE) potential of the Ag/Au BNPs was tested as a treatment for Alzheimer’s disease (AD). An excellent anti-AChE activity (IC₅₀, 71.2 ± 0.22 μg/mL) was observed for these biogenic-synthesized NPs. A statistical analysis revealed that Ag/Au BNPs inhibited AChE competitively, according to a Lineweaver–Burk plot, with K_m increasing from 0.019 to 0.063 (288%–1185.7%) and V_max remaining constant. The Ag/Au BNPs also caused an increase in K_Iapp, from 128 to 1184 (236%–828%), whereas they did not affect V_maxiapp. The K_m, K_I, and K_i values were also calculated to be 0.0053 mmol/L, 595.25 µg, and 80 µg, respectively. Therefore, it is concluded that small-size, stable, and potent Ag/Au BNPs were synthesized successfully from HE extracts that exhibited anti-AChE activity, which renders them a significant remedy for AD.