A bioactivity guided study on the anti-gonococcal and anti-inflammatory activity of Ficus abutilifolia stem bark extracts

Abstract

Background: With high annual infection rates and rapidly increasing antimicrobial resistance (AMR), Neisseria gonorrhoea has become a major global public health concern, especially because delayed treatment often results in severe reproductive complications, and increases the risk of contracting the human immunodeficiency virus (HIV). Aims of the Study: In South Africa, traditional healers use the stem bark of Ficus abutilifolia (Miq.) Miq. to manage gonorrhoea and to treat associated inflammatory conditions. Therefore, this study aimed to evaluate the anti-gonococcal and anti-inflammatory potential of extracts obtained from the stem bark of F. abutilifolia. Materials and Methods: The chemical constituents of the stem bark were extracted in dichloromethane, absolute methanol, 50% methanol (methanol: water, 1:1, v/v) and water, to yield four crude extracts. The anti-gonococcal potential of the crude extracts was determined using the in vitro broth microdilution assay, whilst the anti-inflammatory potential was determined by screening for inhibitory activity against 15-lipoxygenase (15-LOX). Active extracts were subjected to bioassay-guided fractionation and phytochemical analysis using proton nuclear magnetic resonance (1H-NMR) spectroscopy and gas chromatography time-of-flight mass spectrometry (GC-ToF-MS), to determine the compounds or classes of compounds responsible for the observed bioactivity. Results: The polar crude extracts (absolute methanol, 50% methanol, water) all displayed good anti-gonococcal activity, with a minimum inhibitory concentration (MIC) value of 0.20 mg/mL. Low IC50 values comparable to that of quercetin (15.13 ± 0.19 μg/mL) were also reported for these extracts (absolute v methanol: 18.33 ± 0.70 μg/mL; 50% methanol: 23.82 ± 0.90 μg/mL; decoction: 25.58 ± 0.41 μg/mL), thus indicating significant anti-inflammatory potential. 1H-NMR-based metabolomics revealed distinct chemical differences between the active and non-active fractions on the PCA, OPLS-DA and contribution plots, with bioactivity attributable to prominent peaks in the alcohol, vinylic, aromatic, phenolic and amide regions. GC-ToF-MS analysis was also used to tentatively identify compounds present in the active fractions, however, due to the low mass spectral similarity caused by the polar nature of these fractions, the identity of these compounds could not be established with certainty. Conclusion: The results obtained in this study support the traditional use of F. abutilifolia. As this is the first report of anti-gonococcal activity in F. abutilifolia, the results may also help to discover new classes of compounds for the treatment of gonorrhoea and/or associated inflammatory conditions.