Spermacocestachydea DC. (Rubiaceae), a traditionally used antimalarial plant: Phytochemical profiling, antioxidant and antiplasmodial activities, host-protective effects, and preclinical safety assessment.

ETHNOPHARMACOLOGICAL RELEVANCE: Spermacoce stachydea (Rubiaceae) is traditionally used for malaria treatment across West Africa, yet its phytochemical composition, antioxidant properties, antiplasmodial activity, and safety profile remain insufficiently characterised. This study aimed to provide a comprehensive preclinical characterisation for its ethnomedicinal use in malaria management.

METHODS: The whole-plant methanolic extract was profiled by ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) and gas chromatography-mass spectrometry (GC-MS). Total phenolic (TPC), flavonoid (TFC), and condensed tannin (CTC) contents were quantified, and antioxidant capacity was assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and oxygen radical absorbance capacity (ORAC) assays. Antiplasmodial activity was evaluated in vitro against Plasmodium falciparum 3D7 using a growth inhibition assay and in vivo in Plasmodium berghei ANKA-mice using a four-day suppressive test at 125, 250, and 500 mg/kg b.wt., and curative and prophylactic models at 250 mg/kg b.wt. Host-protective effects defined as the capacity of the extract to attenuate malaria-induced physiological disturbances including anaemia, organ enlargement, and hepatic and renal dysfunction were evaluated at 250 mg/kg b.wt. through restorative and protective assays encompassing physiological, haematological, biochemical analyses. Safety was assessed following single oral administration at 2000 and 5000 mg/kg b.wt. and repeated oral administration at 20, 200, and 2000 mg/kg b.wt./day in accordance with Organisation for Economic Co-operation and Development (OECD) guidelines 423 and 407, respectively.

RESULTS: Phytochemical profiling revealed a diverse array of bioactive metabolites including flavonoids, terpenoids, coumarins, iridoids, alkaloids, and polyphenols. The extract exhibited a flavonoid-dominant phenolic profile (TPC: 33.99 ± 0.07 mg GAE/100 mg; TFC: 7.57 ± 0.03 mg QE/100 mg) and strong DPPH radical-scavenging activity reached 774 ± 3.9 μmol AAE/g, compared with 647 ± 3.5 and 766 ± 2.9 μmol AAE/g for Trolox and quercetin, respectively. In vitro antiplasmodial activity was significant (IC50 = 6.30 ± 0.13 μg/mL) with negligible haemolysis (<1%). In vivo, parasitaemia suppression reached 88.10 ± 6% at 500 mg/kg (suppressive model), with good curative (58.40 ± 14.70%) and moderate prophylactic (35.70 ± 5.60%) activities at 250 mg/kg b.wt. The extract attenuated malaria-associated physiological disturbances including anaemia, organ enlargement, and hepatic and renal dysfunction while demonstrated hepatoprotective effects. No mortality or consistent treatment-related toxicological alterations were observed after a single oral dose up to 5000 mg/kg b.wt. or repeated administration up to 2000 mg/kg b.wt./day. The median lethal dose exceeded 5000 mg/kg b.wt., and the no-observed-adverse-effect level was 2000 mg/kg b.wt./day under the study conditions.

CONCLUSION: S. stachydea demonstrated significant antiplasmodial, antioxidant, and host-protective activities with a favourable safety profile, providing preliminary scientific support for its traditional use in malaria management and identifying it as a promising candidate for bioassay-guided investigation of its active constituents.