Metabolomic analysis on anti-HIV activity of selected Helichrysum species

Abstract

Since the beginning of human civilization, medicinal plants have been used to treat a variety of infectious and non-infectious diseases. The therapeutic properties of phytochemicals have been recognized since ancient human history. The genus Helichrysum Mill. with its attractive flowers consist of an estimated 500‒600 species in the Asteraceae family. In South Africa and Namibia there are about 244‒250 species with tremendous morphological diversity. Several Helichrysum species are widely used by the indigenous population to treat various disorders such as wounds, infections, respiratory conditions, headaches, coughs, colds and fevers. Several of the Helichrysum species exhibit antiviral activity with the most relevant to this study being the discovery of anti-human immunodeficiency virus (anti-HIV) and anti-reverse transcriptase (anti-RT) activity of some species. Drug discovery and development, from the early stages of a promising compound to the final medication, is an intensive, expensive and incremental process. The ultimate goal is to identify a molecule with the desired effect in the human body and to establish its quality, safety and efficacy for treating patients. The ability to combine high-throughput analytical techniques like metabolomic and other experimental approaches with drug discovery will speed up the development of safer, more effective and better-targeted therapeutic agents. The rapidly emerging field of metabolomics and molecular docking analysis provides valuable information on drug activity, toxicity, customized drug treatments and can predict therapeutic outcomes. Extraction of the aerial parts of 32 Helichrysum species was done using polar [methanol (MeOH) 50%: distilled water (dH2O) 50%] and non-polar [hexane (Hex), dichloromethane (DCM) and acetone (Ace)] solvent systems. Anti-human immunodeficiency virus bioassays on the live HI virus revealed that polar extracts of H. mimetes and H. chrysargyrum at 2.5 μg/mL and 25 μg/mL, polar and non-polar extracts of H. infuscum at 25 μg/mL and polar and non-polar extracts of H. zeyheri, H. setosum, H. platypterum and H. kraussii at 2.5 and 25 μg/mL, had higher than 90% inhibitory activity. The polar extract of H. mimetes also exhibited reverse transcriptase (RT) inhibition as a possible indication of the mechanism of action. Proton nuclear magnetic resonance (1H NMR) spectra of the polar extracts exhibited the presence of aromatic compounds and carbohydrate moieties. Principal component analysis (PCA) of the polar extracts showed clustering related to the activity of the extracts with good predictability scores (Q2 > 0.5). However, orthogonal projections to latent structures discriminant analysis (OPLS-DA) predictability of the model was low based on the Q2 at approximately 0.25. Quinic acid (QA), isolated from H. mimetes showed promising anti-RT activity [50% inhibition concentration (IC50) = 53.82 μg/mL] which was comparable to the positive drug control, doxorubicin (IC50 = 40.31 μg/mL). The molecular docking study revealed the probable binding site and conformation of QA within cavity 4, with a docking score of -8.03. The docking score of doxorubicin within cavity 4 was -7.87. With this study, it was shown that metabolomic analysis as a tool to predict anti-HIV activity in Helichrysum species can be valuable to shorten the process. Moreover, the study of molecular docking revealed the mechanism action of quinic acid and doxorubicin against RT.