Utilizing olive leaves as a rich source of multifunctional bioactive compounds to fight oxidative stress, Alzheimer’s disease, diabetes, and cancer using <i>in vitro</i> , <i>in silico</i> , and bioinformatics techniques

Olive leaves are of significant interest in traditional medicine and in the development of functional nutraceuticals. In this study, the leaves of four olive varieties (Halhali, arbequina, gemlik, karamani) were utilized to examine and compare the chemical composition and biological activities, particularly their role in enzyme inhibition, cancer prevention, and apoptosis induction. Results showed that among the tested varieties analyzed, Gemlik (77.79 mg gallic acid equivalent (GAE)/g) and halhali (76.03 mg GAE/g) exhibited the phenolic contents while arbequina had the highest flavonoid content (36.51 mg rutin equivalent (RE)/g). Similarly, these two varieties of extracts recorded strong antioxidant activity in several assays. Gemlik (2.70 mg galantamine equivalent (GALAE)/g) and arbequina (2.59 mg GALAE/g) demonstrated the highest acetylcholinesterase (AChE) inhibition. The results of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)) assay showed arbequina provided the highest cytotoxic effect against HeLa cells (IC₅₀ value: 60.59 μg/ml) and annexin-V/PI staining confirmed the inducing of apoptosis by arbequina in HeLa cells. In conclusion, the studied olive varieties of leaf extracts appeared to have more potential as a health supplement rich in natural antioxidants and merit further intensive study.