Antiplasmodial Compounds from Clerodendrum rotundifolium Oliv. and Oral Toxicity Assessment of the Leaf Extracts.

ETHNOPHARMACOLOGICAL RELEVANCE: The growing resistance of Plasmodium strains to known conventional antimalarial drugs has increased challenges of malarial treatment in some parts of the world. Although plants are traditionally used to treat malaria, the antiplasmodial phytochemicals of many species remain uncharacterized. This study aimed to scientifically validate the traditional use of Clerodendrum rotundifolium Oliv. (Lamiaceae) in treating malaria by the herbalists of Prometra-Uganda. The antiplasmodial activity and toxicity of its leaf extracts were evaluated and the chemical structures of the active compounds were characterized to assess the plant's safety and efficacy.

MATERIALS AND METHODS: The plant species was identified from an ethnobotanical survey in Buhija-Prometra, Mpigi district for further phytochemical analysis according to frequency of mention and known scientific work. The antiplasmodial activity of isolated compounds was evaluated in vitro using the SYBR Green I assay. For toxicity assessment, acute oral toxicity studies were conducted on ethyl acetate, methanol, and aqueous extracts in Wistar mice, while sub-acute toxicity was evaluated specifically for the aqueous extract in Albino rats over 21 days. The chemical constituents were isolated through a series of chromatographic techniques, and the structures of the pure compounds were elucidated using spectroscopic analysis and comparison with literature data.

RESULTS: Three known compounds were isolated and identified from C. rotundifolium: 1-octacosanol (A), isoquercitrin (B), and verbascoside (C). In antiplasmodial assays, verbascoside demonstrated moderate activity against both chloroquine-sensitive (3D7, IC50 27.2 μM) and chloroquine-resistant (Dd2, IC50 38.1 μM) strains. Isoquercitrin exhibited weak activity against the 3D7 strain (IC50 92.0 μM) and moderate activity (58.1 μM) for the Dd2 strain. Furthermore, acute toxicity studies on the ethyl acetate, methanol and aqueous extracts showed no mortality up to 5000 mg/kg under the conditions of this preliminary study and an aqueous extract dose of 200 mg/kg showed no observable adverse effects in this preliminary 21-day rodent study while higher doses (400 mg/kg) were associated with observable effects that warrant further investigation.

CONCLUSION: These findings provide preliminary scientific observations that contribute to the knowledge base supporting the traditional use of C. rotundifolium by Prometra-Uganda Herbalists with the aqueous extract showing no observable adverse effects at 200 mg/kg under the conditions tested, while higher doses may pose safety risks requiring confirmation in larger studies. The isolated compounds isoquercitrin and verbascoside represent moderate-activity phytochemical markers that may contribute to the antiplasmodial efficacy of the crude extract and could serve as chemical markers for standardizing herbal formulations derived from this plant.