Medicinal uses of Galenia africana: A study of the antimicrobial, antifungal and anticancer properties

Abstract

Over the years, microorganisms have become resistant to commonly used antimicrobial agents leading to multidrug resistance. This is believed to occur even with new classes of therapeutic agents thus creating a challenge on the global healthcare system. The study of medicinal plants allows for their possible use as alternative therapeutic agents. Galenia africana (G. africana) is a South African medicinal plant with numerous health benefits. The purpose of this study was to evaluate the potential antimicrobial, antifungal and anticancer properties of the ethanolic extract of G. africana. Prior to evaluating these properties, in vitro and in vivo acute toxicity studies were conducted to assess the toxicity profile of G. africana. The toxicity profile of the G. africana extract was evaluated using acute toxicity studies conducted in animal and reconstituted human epidermis skin models. The results of the acute oral and dermal toxicity studies revealed that the median lethal dosage (LD50) for G. africana extract in Sprague-Dawley rats was considered to exceed 2000 mg/kg. In the dermal sensitization study, the stimulation index (SI) values for the mice treated with the G. africana extract at concentrations of 25% (50 mg/ml), 50% (100 mg/ml), and 100% (200 mg/ml), when compared to the control group, were 1.3, 0.9 and 1.3, respectively which did not result in an SI value of ≥ 3 in any group. Hence, it did not elicit a hypersensitivity response. In the irritation test, the G. africana (concentrate) and G. africana (in-use dilution) extracts were non-irritant on the reconstituted human epidermis. The antimicrobial activity of G. africana was evaluated against two Staphylococcus aureus strains namely methicillin-resistant (MRSA: ATCC 33591) and methicillin-sensitive/susceptibile (MSSA: ATCC 25923). Results of the broth microdilution assay showed that G. africana exerted good antimicrobial activity against the two strains with a minimum inhibitory concentration (MIC) of 3.12 mg/ml for both strains. Results of the minimum bactericidal concentration (MBC) determination showed that G. africana was bactericidal against both strains (MBCs of 3.125 and 6.25 mg/ml for MSSA and MRSA, respectively). In addition, the checkerboard assay demonstrated that the combination of G. africana and ampicillin had an additive effect against MSSA and an indifference result against MRSA (fractional inhibitory concentration indices (FICI) of 0.64 against MSSA and 1.002 against MRSA). The combination of G. africana with several antimicrobial agents in the Sensititre susceptibility test also showed a reduction in the MICs of a number of the antimicrobial agents. Investigation of the antifungal activity of G. africana was done by evaluating its activity against Candida species (Candida albicans and Candida glabrata, ATCC 90028 and ATCC 26512, respectively). Results of the broth microdilution assay showed that G. africana possessed antifungal activity against the two Candida strains (MIC of 6.25 mg/ml for both Candida strains). Minimum fungicidal concentration (MFC) determination revealed that G. africana was fungicidal against both Candida strains (6.25 and 12.5 mg/ml for C. albicans and C. glabrata, respectively). Results of the checkerboard assay revealed that the combination of G. africana and fluconazole had a strong synergistic effect against C. albicans and an indifference result against C. glabrata when interpreted by the FICI (0.36 and 1.002 for C. albicans and C. glabrata, respectively). Results of the Sensititre susceptibility test also showed a reduction in the MICs of the antifungal agents when combined with G. africana. Microscopic analysis, using scanning electron microscopy, showed that there was cell damage including a decrease in cell size after G. africana treatment for both Candida species. Evaluation of the anticancer properties of G. africana was done by investigating its cytotoxic potential in human breast cancer (MCF-7) and normal fibroblast (KMST-6) cell lines. The ability of G. africana to affect gene expression, apoptosis and cell cycle processes was also evaluated in MCF-7 cell lines. It was observed that G. africana had a greater anticancer effect against the MCF-7 than the KMST-6 cells as determined by the IC50 values. Results of the effect of G. africana on the gene expression, apoptosis and cell cycle of MCF-7 cells showed that genes, such as BCL2L11, CASP2 and CASP7/9, that are involved in apoptosis were up-regulated. It was also observed that genes involved in angiogenesis such as ANGPT1 and ANGPT2 were downregulated. In addition, genes involved in cell cycle processes, such as ACLY, ACSL4 and PFKL, were down-regulated. Collectively, these results suggested that G. africana possessed antimicrobial, antifungal and anticancer activities against medically important microorganisms as well as breast cancer. Furthermore, toxicity analysis results revealed that G. africana was not toxic when tested using animal and human skin models. This provides important information for the development of new therapeutic agents.