Phytochemical evaluation, in vitro-in vivo antioxidant and cytotoxicity activities of various layers of watermelon fruit Citrullus lanatus (Cucurbitaceae) Matsum. Nakai

Citrullus lanatus (watermelon) is a popular plant whose fruits are use in all parts of Nigeria as remedy for various diseases. In this present study, the phytochemical contents, antioxidant and cytotoxicity activities of extracts from the various layers (peel, rind, pulp and seeds), of watermelon fruit were evaluated. The phytochemical contents were evaluated qualitatively while NMR and GC-MS used to identify phytoconstituents present. Antioxidant activities were examined by DPPH, H2O2 radical scavenging, ORAC, FRAP, and ABTS assays. In vitro cytotoxic activity was examined by MTT assay while apoptosis was detected by flow cytometry as well as fluorescence microscopy. Phytochemical evaluation showed the presence of various metabolites in the pulp and seed extracts. GC-MS and NMR elucidations of compound revealed the presence of methyl stearate ester. Antioxidant evaluations by various radical scavenging showed that the pulp (PP) had IC50 value of 8-22 μg/mL, indicating potential antioxidant effect. In vivo evaluation of superoxide dismutase, catalase activities and total proteins in serum of rats further confirmed the in vitro studies. Antiproliferative study showed that the pulp and the seeds significantly displayed concentration-dependent effects. These results were further replicated in the cytotoxicity effect against MCF-7 and HMVII cells with much reduced IC50 on MCF-7, as well as early and late apoptosis after 72 h caused by exposure of pulp extract in vitro. Our study showed that the pulp and seed layers of watermelon contain phytochemicals which were responsible for its antioxidant and cytotoxicity effects