Evaluation of Methanol-Dichloromethane Extract of Stemonocoleus micranthus Harms (Fabaceae) Stem Bark for Anti-Inflammatory and Immunomodulatory Activities

Background: The stem bark decoction of Stemonocoleus micranthus Harms (Fabaceae) is most widely used traditionally as a remedy for various diseases such as malaria and boil. In this study, the anti-inflammatory and immunomodulatory activities of the methanol-dichloromethane extract (MDE) from the stem bark of the plant in rodents were evaluated.

Methods: The carrageenan-induced rat paw oedema, cotton pellet-induced granuloma in rat, and xylene-induced ear oedema in mice were used to study the anti-inflammatory activity of methanol-dichloromethane extract of Stemonocoleus micranthus (MDESm) (100, 200, and 400 mg/kg). The effects of MDESm (100, 200, and 400 mg/kg) on cyclophosphamide-induced immunosuppression, neutrophil adhesion, carbon clearance, and haematological and biochemical parameters were carried out to study its immunomodulatory activity in mice.

Result: MDESm (100 mg/kg, p.o.) significantly (p < 0.05) inhibited carrageenan-induced oedema by 57.1% at 5^th h posttreatment compared with control. At 100 mg/kg, p.o., MDESm significantly (p < 0.05) reduced cotton pellet-induced granuloma by 39.28% and nonsignificantly reduced xylene-induced ear oedema by 34.1%. Treatment with MDESm (100 and 400 mg/kg) nonsignificantly abolished the neutropenia caused by cyclophosphamide with a percentage neutrophil reduction of 0 and -14.86%, respectively, while MDESm (200 mg/kg) and levamisole (50 mg/kg) had a nonsignificant reduction in neutrophil count (10.16 and 31.40%), respectively, all compared to the distilled water-treated group with a neutrophil count of -9.82%. MDESm at doses of 100 and 200 mg/kg increased phagocytic index by 0.0447 ± 0.00762 and 0.0466 ± 0.00703, respectively, although not significantly when compared to the control group with a value of 0.0226 ± 0.02117. There was a decrease in WBC and lymphocyte counts in MDESm- (200 mg/kg) treated group, suggesting immunosuppressive potential at this dose. MDESm caused a dose-dependent decrease in ALT and core liver enzymes, suggesting a hepatoprotective effect. The acute toxicity test revealed that MDESm is safe in mice with an oral lethal dose (LD₅₀) of >5 g/kg.

Conclusion: The methanol-dichloromethane extract of Stemonocoleus micranthus Harms possesses mild anti-inflammatory and immunomodulatory activities which may be more pronounced upon fractionation and purification. Therefore, more investigations are needed to explore these activities further.