Potential of acetone leaf extract and fractions of Psychotria capensis (Rubiaceae) to manage co-morbidities of tuberculosis and helminthiasis

Co-infection of tuberculosis (TB) and helminths (worms) is an emerging global public health concern with both affecting about one-third of the global population. Studies shows that worm infected individuals have a high risk of contracting tuberculosis and failure of therapy or vaccination against TB during co- or pre-infection with helminths has an immunological basis. Plants are potential sources of antimycobacterial and anthelminthic compounds. In this study the antimycobacterial and anthelminthic activity as well as cellular toxicity of a crude acetone extract and fractions of Psychotria capensis were determined. The antimycobacterial activity of the extract and fractions were determined against three non-tuberculous mycobacteria (M. smegmatis, M. fortuitum, M. aurum) and M. bovis BCG using a two-fold serial microdilution assay. The Egg Hatch Assay (EHA) was used to determine anthelminthic activity on eggs of Haemonchus contortus. Cytotoxicity was determined using a tetrazolium-based colorimetric assay against Vero kidney cells.

The minimum inhibitory concentration (MIC) values of the crude extract and fractions ranged from 0.039 mg/mL to 1.25 mg/mL with the crude having the best (0.039 mg/mL) compared to Isoniazid acid (> 100 µg/ml).

In the EHA, the hexane fraction had the best inhibitory concentration (IC50) of 0.16 mg/mL, while the crude extract, n-butanol and chloroform fractions had IC50 of 0.23, 0.63 and 0.63 mg/mL respectively compared to 0.02 µg/ml of albendazole.

The hexane and chloroform fractions had low toxicity with LC50 values of 0.290 and 0.248 mg/mL respectively. The crude extract (0.064 mg/mL) and n-butanol fraction (0.071 mg/mL) were moderately toxic. The SI values (LC50/MIC) ranged from 0.1 to 6.3. The hexane fraction had the highest SI.

The hexane fraction had the best dual activity and was the least cytotoxic. Compounds responsible for activity may be present in this fraction. Further work is in progress to isolate compound(s) and determine their anti-TB and anthelminthic activities.