Isolation of Secondary Metabolites from Protea venus and Evaluation of Their Antioxidant Activity and Effects Under Glucolipotoxic Stress: In Silico and In Vitro Studies.

Protea venus, a hybrid of Protea repens and Protea aristata, is a commonly found flower in the South African market. To date, there are no reported chemical or biological studies on this hybrid. This study presents the first investigation of the chemical composition and preliminary biological activity of the methanolic extract of P. venus. Phytochemical analysis of the methanolic extract led to the isolation of nine known phenolic compounds (2-10) and one new compound, p-coumaroyl calleryanin (1). The identified known constituents include calleryanin derivatives (2-4), lacticolorin (5), quercetin derivatives (6-8), protocatechuic acid (9), and p-hydroxybenzoic acid (10). Notably, calleryanin (2), protocatechuoyl calleryanin (3), kaempferol-3-O-rhamnoside (6), and quercetin-3-O-rhamnoside (7) are reported for the first time in the genus Protea. Compounds 3 and 9 exhibited strong antioxidant activity in the ferric reducing antioxidant power (FRAP) assay, with 9 exceeding vitamin C. Molecular docking studies suggest that the isolated compounds may interact with Kelch-like ECH-associated protein 1 (KEAP1). In H9c2 cardiomyocytes exposed to high glucose (40 mM) and palmitate (0.15 mM), the extract and compound 6 were non-cytotoxic (≤100 µg/mL) and produced a moderate restoration of ATP levels under glucolipotoxic conditions. These findings expand the phytochemical profile of P. venus and provide preliminary insight into its biological activity under metabolic stress.