Isolation and characterisation of compounds from Helichrysum odoratissimum (L.) Sweet and their activity on oral bacteria.

Abstract

Dental caries (DC) and Periodontal diseases (PD) are the most common oral diseases in the world today. Conventional treatment of these diseases relies on approaches that are not easily accessible to most rural populations, hence the search for viable complementary alternative products is of paramount importance. Plant-based medicines have been traditionally used and are considered as effective complementary alternatives. Helichrysum odoratissimum is used for traditional oral care and its crude extracts previously demonstrated activity against bacteria that cause DC and PD. However, there is little information about the phytochemical compounds in the plant. This study aimed at isolating and characterising phytochemicals from the extracts and essential oil of H. odoratissimum and testing the antibacterial activity of the isolated compounds. The essential oil was extracted by hydrodistillation of fresh areal parts of H. odoratissimum and its chemical composition was analysed using Gas Chromatography-Mass Spectrometry (GC-MS). Crude extracts were obtained from dried, ground aerial plant parts (stems, leaves and flowers) by sequential extraction using hexane, dichloromentane (DCM), and methanol. Compounds were isolated from DCM and methanol extracts using chromatographic methods and characterised using Nuclear Magnetic resonance spectroscopy (NMR) and Mass Spectrometry MS. By using Broth micro-dilution method, the minimum inhibitory concentration (MIC) of the isolated compounds was carried out on Streptococcus mutans and Staphylococcus aureus. 3,5-dihydroxy-6,7,8-trimethoxyflavone (1) was isolated from DCM extract while 3-O-methylquercetin (2), β-sitosterol (3), and stigmasterol (4) were isolated from the methanol extract. This is the first time compounds 3 and 4 were isolated from H. odoratissimum and were identified as white needle-like crystals. Essential oil was found dominated by sesquiterpene hydrocarbons especially α-caryophyllene (17.5 %) and trans-β-caryophyllene (16.8 %). The compounds showed higher activity on S. mutans than on S. aureus. MIC of compound 2 on S. mutans was 0.96 μg/ml and that of compound 3 & 4 on S. mutans was 0.98 μg/ml. In conclusion, DCM and methanol extracts of H. odoratissimum contain phytochemicals that are active on oral bacteria which justify the usage of this plant as traditional medicine for the management of oral conditions.