Ethnopharmacological relevance: Ptaeroxylon obliquum (Thunb.) Radlk, sneezewood, is a commonly used medicinal plant in South Africa for the treatment of parasitic infections in animals, tuberculosis (TB) and related symptoms, and other microbial infections.
Aim of the study: In this study anthelmintic, antifungal, antimycobacterial, larvicidal and cytotoxic activities of the acetone leaf extract of P. obliquum, solvent-solvent derived fractions of the extract and isolated compounds (obliquumol and a mixture of lupeol and β-amyrin) were determined.
Materials and methods: The in vitro anthelmintic activity was tested against Haemonchus contortus ova and larvae using the egg hatch inhibition and larval development assays. The antifungal activity was investigated using a serial microplate dilution method against Aspergillus fumigatus, Cryptococcus neoformans and Candida albicans. Antimycobacterial activity was evaluated by a tetrazolium violet-based broth microdilution method against pathogenic Mycobacterium tuberculosis and Mycobacterium bovis. The larvicidal activity was evaluated against Aedes aegypti. Cytotoxicity was determined using human liver (C3A) and Vero African green monkey kidney cell lines.
Results: Obliquumol (ptaeroxylinol acetate) was more effective than the crude acetone extract against H. contortus ova and larvae with an LC50 of 95 μg/mL against the larvae. Obliquumol had very good antifungal activity with minimal inhibitory concentrations (MIC) values from 2 to 16 μg/mL. Lupeol and β-amyrin mixture also had good activity against C. neoformans and C. albicans with an MIC of 16 μg/mL against both fungi. The crude extract and fractions had average to weak antimycobacterial activity against the two pathogenic mycobacteria with MICs of 313-625 μg/mL for the extract and fractions tested. Obliquumol had good activity with an MIC of 63 μg/mL against pathogenic M. tuberculosis ATCC 27115. The acetone crude extract was toxic against Vero cells with an CC50 of 14.2 μg/mL. Obliquumol and the mixture of lupeol and β-amyrin were not toxic against both Vero and C3A cells at the highest concentration tested of 200 μg/mL and had good selectivity index values against the opportunistic fungal pathogens. No tested samples had any larvicidal activity against A. aegypti at the concentrations tested.
Conclusion: The activity noted against H. contortus may support the ethnoveterinary use of this plant against animal parasites in South Africa although aqueous extracts were not active. The activity of obliquumol against opportunistic fungal pathogens was also promising. The cytotoxicity of the acetone leaf extract, however, raises concerns about the traditional use of P. obliquum to treat a wide range of diseases although if an aqueous extract is used the toxicity concern may not be relevant.
Keywords: Cytotoxicity; Fungi; Haemonchus contortus; Obliquumol; Ptaeroxylon obliquum; Tuberculosis.
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