Bioactivity of extracts and components of Pteleopsis myrtifolia

Abstract

Combretaceae contain several species with bioactive properties - especially the genera Combretum and Terminalia. Pteleopsis myrtifolia and Quisqualis littorea belong to this family and have not previously been thoroughly investigated for their bioactivity. Leaf and fruit extracts of P. myrtifolia and leaf extracts of Q. littorea were separated by three different thin layer chromatography eluent systems. For all leaf and fruit material, the largest amount of acetone soluble material was extracted with extractants of intermediate polarity. Antibacterial activity of 30 extracts was investigated using a microplate serial dilution method and bioautography. The four most important nosocomial pathogens that are used worldwide namely two Gram-positive: Staphylococcus aureus and Enterococcus faecalis, and two Gram-negative bacteria: Pseudomonas aeruginosa and Escherichia coli were used as test organisms. Areas of growth inhibition were best defined after an eluent system that separates compounds of intermediate polarity had been used. The Gram-positive bacteria were most sensitive to some extracts of P. myrtifolia leaves. Fruit extracts exhibited minimum inhibitory concentrations (MIC) values as low as 0.04 mg/ml, less than that of the allopathic antibiotics, ampicillin and chloramphenicol. Q.littorea leaf extracts had an average MIC value of 0.32 mg/ml for Gram-negative bacteria. The average antibacterial activity expressed as total activity for each bacterium was higher in the leaves than in the fruit of P. myrtifolia. After considering the amount of antibacterial compounds extracted, toxicity of extractants to test organisms and miscibility of several extractants, acetone was eventually chosen as the best extractant for future extractions. Results obtained in this investigation showed clearly that P. myrtifolia leaves, fruit, and Q. littorea leaves contain several antibacterial compounds. Five different extracts of P. myrtifolia leaves were tested for growth inhibitory effects on different human cell lines (MCF-12, MCF-7, H157, WHCO3, HeLa). The non-cancerous MCF-12A cell line’s growth was not inhibited extensively, and the cancer cell lines - MCF-7, H157, WHCO3 and HeLa, differed in their sensitivity to the plant extracts. This indicated that the plant extracts’ effects were selective and not due to general toxicity. The effect of some extracts on certain cell lines, especially WHCO3, was growth inhibitory but not lethal. This is the desired effect – to inhibit growth of cancer cells, but not to be toxic to cells in general. The presence of tannin in extracts either promoted or inhibited growth inhibition of different cell lines. The same extractants that were used for cytotoxic tests were investigated for their antioxidant activity. All extracts gave positive scavenging capacity with the 1,2-diphenyl-2-picrylhydrazyl assay. The cold water, methanol and hot water extracts had vitamin C equivalents of 0.34, 0.20 and 0.147 mg/g respectively, all more than that of black tea. The solvent-solvent separation of P. myrtifolia leaves was started with acetone as an initial extractant. Separation was undertaken with immiscible solvents of different polarities. All fractions had antibacterial activity against the Gram-positive bacteria. The chloroform fraction was antibacterial to all bacteria tested, and had the largest amount of antibacterial compounds. Pure compounds were isolated from the chloroform fraction by column chromatography. One pure compound’s structure was elucidated as a pentacyclic triterpenoid, taraxerol (C30H50O). Taraxerol had MIC values of 0.04, 0.016, 0.63 and 0.31 mg/ml for the bacteria S. aureus, E. faecalis, P. aeruginosa and E. coli respectively. It significantly inhibited growth of the human lung cancer cell line H157 and did not display free radical scavenger activity. This is the first report of the antibacterial activity of several extracts from P. myrtifolia and Q. littorea, growth inhibition effects of several P. myrtifolia leaf extracts on the human cell lines MCF-12, MCF-7, H157 and WHCO3, the isolation of taraxerol from P. myrtifolia leaves, taraxerol’s antibacterial activity for above-mentioned test organisms, and growth inhibition effects on human cancer cell lines MCF-7, H157, WHCO3 and HeLa.