In vivo and in vitro evaluation of anti-inflammatory activity and cytotoxicity of extracts of seven Plectranthus species

Plectranthus (Lamiaceae) is a genus of economic and medicinal interest distributed in tropical regions throughout the world [1]. The first phytochemical review of Plectranthus [2] showed that the main constituents of the genus are diterpenoids (abietane, kaurane and labdane) and essential oils [2]. As part of an ongoing search for novel therapeutic agents from plants, seven species of Plectranthus; P. ornatus, P. amboinicus, P. argentatus, P. cilatus, P. hadiensis, P. zuluenesis and P. fructicosus are currently under investigation in our laboratories. Anti-inflammatory activity of the acetone extracts of the tested species has been assessed using in vivo and in vitro assays. The in vivo arachidonic acid mouse ear assay showed P.ciliatus as the most anti-inflammatory species demonstrating dose-dependent behaviour. In the in vitro assay using RBL-2H3 cells we have shown that several species inhibit release of β-hexosaminidase which in this cell line occurs in parallel with histamine release. Several Plectranthus species were inactive and others appear to be pro-inflammatory. Potential anti-cancer activity of the test species has been evaluated in an in vitro screen using the RBL-2H3 cell line. This assay is based on the alteration of plasma membrane permeability by cytotoxic substrates and subsequent quantification of L-lactate dehydrogenase (LDH) released from damaged cells. Our results show that out of the seven species P. ciliatus has the greatest cytotoxicity. P. ciliatus has been successfully transferred into liquid cell suspension culture, extracts appear to be inactive.

References: [1] Lukhoba, C. et al. (2006) J. Ethnopharmacol. 103: 1–24. [2] Abdel-Mogib, M. et al. (2002) Molecules 7: 271–301