Pharmacological evaluation of hydro-ethanol and hot water leaf extracts of Bauhinia galpinii (Fabaceae): A South African ethnomedicinal plant

Abstract

Bauhinia galpinii is one of several plant species native to South Africa that has been reported to be used traditionally to manage ailments including gastrointestinal disorders, infectious diseases and inflammation. This study was designed to evaluate the in vitro antibacterial, antifungal, antioxidant, cytotoxicity and anti-inflammatory activities of the hydro-ethanol (70% ethanol) and hot water extracts of Bauhinia galpinii leaves. The antibacterial and antifungal activities of the extracts were determined using the serial microplate dilution technique. The minimum inhibitory concentrations (MIC) of seven bacterial strains (Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Salmonella enterica serovar Typhimurium (S. Typhimurium), Salmonella enterica Serotype Dublin (S. Dublin), Pseudomonas aeruginosa and Klebsiella pneumoniae) and three clinical fungal isolates (Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans) were determined. The extraction yield and MIC values were used to determine the total activity (TA) of the extracts. Radical scavenging potential of the extracts was determined using the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay while the lipoxygenase (LOX) enzyme inhibitory assay was used to ascertain the anti-inflammatory activity. The safety of the extracts was determined using the colorimetric mitochondrial viability assay against Vero, Caco-2 and C3A cells. UPLC-MS analysis was also conducted to detect and identify the compounds present in the plant. Results from the study showed that the extracts had inhibitory activities against the growth of all tested pathogens with MIC values ranging from 0.04 to 1.25 mg/ml. Both extracts were most active against S. Typhimurium with MIC = 0.16 mg/ml, while the hot water extract was very active at 48 h incubation against Candida albicans with MIC = 0.04 mg/ml. The hydro-ethanol and hot water extracts had high total antibacterial activity (TAA) of 1000 and 937 ml/g against Salmonella Typhimurium respectively. The highest total antifungal activity of 3750 ml/g was recorded against Candida albicans by the hot water extract. The extracts showed strong DPPH radical scavenging activity with the hydro-ethanol extract displaying higher scavenging activity (IC50 = 3.72 mg/ml) than the hot water extract (IC50 = 10.82 mg/ml). Both extracts had moderate lipoxygenase inhibitory activity. The extracts had relatively low cytotoxic to non-cytotoxic effects with LC50 values of 0.094 to ˃1.000 mg/ml and selectivity index values of 0.075 to 22.698. Three compounds with known biological activity (2′'-O-rhamnosylvitexin, myricetin 3-O-galactopyranoside and quercetin 3-O-galactopyranoside) were tentatively identified from UPLC-MS analysis. Therefore, this study supports the folkloric use of the plant in treating gastrointestinal disorders, inflammation and infectious diseases.