Abstract
Holarrhena mitis (Vahl) R.Br. ex Roem. & Schult. which is an endemic plant growing mainly in the dry regions of the low-country has been used in the treatment of dysentery in Ayurvedic medicine. During the present study, we tested antibacterial, antifungal, antioxidant activities and brine shrimp lethality, as well as the total phenolic content of the dichloromethane, ethyl acetate and methanol extracts of the bark and leaves of H. mitis . The methanol extract of bark produced a measurable zone of inhibition against two Candida species, namely Candida albicans , Candida krusei among all five tested species and against both dermatophytes, Microsporum gypseum and Tricophyton mentagrophytes . In addition, the methanol extract of bark showed very strong antifungal activity against C . krusei (20 mm), which is very close to that of the positive control ketoconazole (22 mm). Both dicholoromethane extracts of bark and leaves and methanol extracts of leaves showed an activity against both tested strains of Staphylococcus aureus but were negative against Escherichia coli and Salmonella enteritidis . However, the rest of the extracts exerted an active against all the tested bacterial strains. In the brine shrimp cytotoxicity assay, the dichloromethane extracts of both leaves and bark showed lower LC 50 values (27.13 ppm and 9.38 ppm, respectively) than that of positive control, K 2 Cr 2 O 7 , (35.74 ppm) indicating cell toxicity. Compared to the positive control, DL-α-tocopherol (IC 50 : 12.2 ppm), the antioxidant activity of the ethyl acetate and methanol extracts of leaves exhibited comparable activity (IC 50 :16.9 ppm and 29.8 ppm, respectively). Antioxidant activity correlated well with the polyphenol content of methanol and ethyl acetate extracts (473.25 and 138.74 mg (GAE) /g, respectively) of leaves, with respect to gallic acid. These empirical results revealed that methanol extract of bark of H. mitis showed strong antifungal activity as well as very low brine shrimp lethality indicating that it would be a potential nontoxic anti-fungal natural product. The dichloromethane extracts exhibited strong brine shrimp lethality and may contain potential natural anticancer lead compounds. Ethyl acetate extracts of both leaves and bark having significant antibacterial activity, would be source of potential antibacterial lead compounds.
Highlights
Natural products from plants and animals have been considered as a rich source of compounds for drug discovery and have continued to be the leading compounds in clinical trials as anticancer and antimicrobial agents (Dias et al, 2012; Harvey, 2008; Harvey et al, 2015; Rishton, 2008)
We evaluated the preliminary pharmaceutical potential of endemic and vulnerable H. mitis which has been used in the treatment of dysentery in Ayurvedic medicine
We focused on the antibacterial, antifungal, antioxidant activities and brine shrimp lethality assay, as well as the total phenolic content of the dichloromethane, ethyl acetate and methanol extracts of the bark and leaves of H. mitis
Summary
Natural products from plants and animals have been considered as a rich source of compounds for drug discovery and have continued to be the leading compounds in clinical trials as anticancer and antimicrobial agents (Dias et al, 2012; Harvey, 2008; Harvey et al, 2015; Rishton, 2008). Biological activity of Sri Lankan lower, non-flowering plants such as lichens have exhibited a great potential as sources for drug leads (Karunaratne et al, 2005; Thadhani et al, 2012). In Sri Lanka, so far it has not been a largescale systematic search for bioactive potential of its plants. The urgency for such an activity is highlighted because out of 3,154 indigenous species evaluated in the Red List (MOE, 2012), 1,386 (44%) are threatened (critically endangered, endangered or vulnerable). Investigating new drug leads from such medicinally important endemic natural sources from Sri Lanka is critically important. Holarrhena mitis (Vahl) R.Br. ex Roem. & Schult. is one
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