Phytochemical, Antiplasmodial, Cytotoxicity, Antioxidant and Antityrosinase Studies of the Stem Fractions of Parquetina nigrescens (Afzel.) Bullock

Parquetina nigrescens (Afzel.) Bullock is a medicinal plant from Western Africa and ethnopharmacologically used for conditions such as fever, sickness, disease, wound healing, and malaria. The present study assessed the chemical composition, antioxidant property, tyrosinase inhibition, safety profile, and antiplasmodial activity of its n-hexane, ethyl acetate, and aqueous fractions. GC-MS analysis showed that the n-hexane fraction is rich in triterpenoids, specifically lupeol and β-amyrin, as well as fatty acid esters. The ethyl acetate fraction has lipid profile, including phytol, whereas the aqueous fraction was predominantly constituted of sterols, such as ergost-5-en-3-ol, stigmasterol, and polyols. All fractions demonstrated concentration-dependent antioxidant activity the n-hexane fraction exhibited the strongest nitric oxide reducing activity (IC₅₀ = 60.77±0.27 μg/mL) compared to rutin (IC₅₀ = 73.19±0.85 μg/mL). In tyrosinase inhibition, all three fractions demonstrated significantly greater efficacy than kojic acid (IC₅₀ = 78.10±2.52 μg/mL), as indicated by their IC₅₀ (54 to 58 μg/mL). Based on the antiplasmodial activity against Plasmodium falciparum n-hexane fraction (IC₅₀ = 2.305 μg/mL) has the highest antiplasmodial activity across all the fractions. Its selectivity index (SI ≈ 40) was excellent, which indicates that it can inhibit malaria parasites with much less harm to mammalian HeLa cells (IC₅₀ = 92.08 μg/mL). This is the first report on antiplasmodial activity for P. nigrescens against human malaria parasites, as well as its tyrosinase inhibition potential. Our findings validate the traditional use of this plant and highlight its n-hexane fraction as a promising source of a safe, plant-based antimalarial candidate.