Anti-mycobacterium ulcerans activity and pharmacognostic standardisation of Pycnanthus angolensis (Welw) Warb

Abstract

Buruli ulcer disease, a necrotising skin and subcutaneous tissue disease, is endemic to tropical Africa. People in endemic communities’ resort to topical and oral consumption of plant extracts which have not been validated. The present study focused on validating the antimycobacterial properties and toxicity of different solvent extracts of the stem bark of P. angolensis and establish pharmacognostic standards for quality control purposes. In vitro antimycobacterial activity of the aqueous, 70% hydro-ethanol and ethyl acetate stem bark extracts of P. angolensis against M. ulcerans (NM 203 strain) was done using the Resazurin Microtiter Assay and their cytotoxicity assessed on normal Chang liver cells via the Alamar Blue assay. Pharmacognostic parameters were also evaluated according to standard methods. The ethyl acetate extract of the stem bark showed considerable activity against the M. ulcerans (MIC = 256 µg/mL) but was less active than the reference drugs streptomycin (MIC = 0.25 µg/mL) and rifampicin (MIC = 0.125 µg/mL). The aqueous and hydroethanolic extracts showed no activity. The active ethyl acetate extract was not cytotoxic (CC50=383.9 ± 69.7 µg/mL). Micromorphological analysis of the leaf surface revealed stellate trichomes and schizogenous cavities. Stem bark powder microscopy showed abundant starch grains, prismatic calcium oxalate crystals and large striated stone cells with a wide lumen. Morphological features, physicochemical, chromatographic, and spectroscopic standards have been established to guarantee consistency in the quality of herbal products containing P. angolensis. The activity of P. angolensis extract against M. ulcerans substantiates the traditional use of P. angolensis stem bark for Buruli ulcer management and as a potential source of antimycobacterial agents.