Almond is a medicinal plant commonly infested with mistletoe, and its leaves are consumed as food and/or medicine due to their health-promoting benefits. Mistletoe infestation may interfere with the chemical composition and biological activities of host plants. Therefore, we investigated the influence of mistletoe infestation on polyphenol constituents, antioxidative and hypoglycemic activities of almond leaves in sucrose-rich diet (SRD)-induced diabetic-like phenotypes in the Drosophila

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... aster model. Infested almond leaf (IAL) had higher polyphenol constituents; ellagic acid and isorhamnetin were the most abundant phenolic acid and flavonoid constituents in the almond leaves. However, this study revealed significant (P < 0.05) infestation-induced increase in some phenolic acids (p-hydroxybenzoic, protocatechuic, gallic, and chlorogenic acids) and flavonoids (apigenin and catechin) with known antioxidative, antidiabetic, and neuroprotective properties. Moreover, IAL had higher in vitro antioxidant and inhibition of α-amylase, α-glucosidase, and acetylcholinesterase (AChE) activities. The SRD-fed flies had significant (P < 0.05) decrease in percentage survival and locomotion and increase in weight. In addition, elevated levels of glucose, trehalose, insulin-like peptides and triglycerides coupled with increased oxidative and AChE activities were obtained. However, treatment with the leaves significantly (P < 0.05) lessened the negative alterations caused by SRD with IAL having higher hypoglycemic activities. Hence, we suggest that improved antidiabetic activities of IAL could be related to its higher phenolic constituents.