Seasonal variation in the cyclooxygenase inhibitory activities of four South African medicinal bulbs

Abstract

Due to the critical role of cyclooxygenase (COX) enzymes in the complex process of inflammation, their inhibition has formed part of the basic therapeutics used in the treatment of inflammation in humans. Medicinal plants have been widely explored in the search for remedies for pain-related ailments. The bulb/corm and leaf extracts of four medicinal bulbs, Tulbaghia violacea, Hypoxis hemerocallidea, Drimia elata and Merwilla plumbea, commonly used in the treatment of pain-related ailments in South African traditional medicine, were evaluated for their ability to inhibit cyclooxygenase (COX-1 and COX-2) enzymes. The plant materials were collected in spring, summer, autumn and winter seasons, with a view of assessing the dynamics of their medicinal properties in different seasons. The dried plant materials were extracted with petroleum ether (PE), dichloromethane (DCM), 80% ethanol (EtOH) and water. All the PE and DCM extracts (at final concentrations of 0.25 mg/ml) in all the tested plant samples recorded between moderate (40–70%) and high (> 70%) COX-1 and COX-2 inhibition levels across all seasons. The ethanol extracts of corms of H. hemerocallidea also demonstrated moderate to high inhibitory activity against COX-1 enzyme across all seasons. The ethanol extracts of bulb and leaf samples of T. violacea showed selective inhibitory activity for COX-2 enzyme in all the seasons. The highest COX inhibitory levels were recorded against COX-2 from the PE leaf (spring) and bulb (autumn) extracts of T. violacea, with both recording 100% inhibitory activity. Thus the material collected in any season can be considered to be similarly effective.