Neuroprotective Potential of Green-Synthesized Silver Nanoparticles from Psidium guajava in a Scopolamine-Induced Rat Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a chronic neurodegenerative condition marked by progressive memory decline and cognitive dysfunction, and oxidative stress, with no definitive cure currently available. The present study aimed to develop a plant-based nanotherapeutic approach for AD by synthesizing silver nanoparticles (AgNPs) using the ethanolic leaf extract of Psidium guajava (PG) via a green synthesis method. Formation of PG-AgNPs was confirmed by a characteristic surface plasmon resonance (SPR) peak observed in UV-Visible spectroscopy and a visible colour change to dark brown. The synthesized nanoparticles exhibited a mean particle size of 107 ± 4 nm, a polydispersity index (PDI) of 0.364 ± 0.08, and a zeta potential of -30.7 ± 2.3 mV, indicating good colloidal stability. Energy-dispersive X-ray diffraction (E-XRD) confirmed the crystalline nature and elemental composition of silver. In a scopolamine-induced rat model of AD, treatment with PG-AgNPs significantly improved cognitive performance. Rats treated with PG-AgNPs showed a statistically significant increase (p < 0.001) in spontaneous alternation behaviour, prolonged step-through latency in the passive avoidance test (p < 0.001), and a significant reduction in escape latency time in the Morris Water Maze test (p < 0.001) compared to the disease control group. Biochemical analyses revealed that PG-AgNPs significantly reduced lipid peroxidation (LPO) levels (p < 0.001) and significantly increased catalase (CAT) activity (p < 0.001), indicating strong antioxidant potential. In conclusion, Psidium guajava leaf extract and its green-synthesized silver nanoparticles demonstrated statistically significant neuroprotective, antioxidant, and cognitive-enhancing effects, supporting their potential as a novel therapeutic strategy for the treatment of Alzheimer's disease. Further research is needed to explore and conform their clinical applicability.