Bioactivity-guided Studies on the Crude Extract and Fractions of Hibiscus Asper Hook F. (Malvaceae) Leaf.
ABSTRACT
The antibacterial and anti-inflammatory activities of the leaf extract of Hibiscus asper Hook F. (Malvaceae) were investigated. Solvent extraction of the leaves yielded the crude methanol extract (CME), while solvent-guided fractionation of CME yielded a n-hexane fraction (HF),
chloroform fraction (CF), ethyl acetate fraction (EF), acetone fraction (AF), butanol fraction (BF), methanol fraction (MF) and water fraction (WF).
TheCME and the solvent fractions were subjected to phytochemical analysis using standard procedures. The acute toxicity test (LD50) of oral doses of CME was conducted using mice.
CME and the solvent fractions were screened for antibacterial activity using agar well diffusion method against Gram-positive bacteria: Staphylococcus aureus, Bacillus subtilis and Gram-negative bacteria Pseudomonas aeruginosa, Escherichia coli and Klebsiellapneumoniae (clinical strains).
The crude extract, CME was also screened for antiinflammatory activities using egg albumen-induced rat paw oedema as a model for acute inflammation, while formaldehyde-induced rat paw oedema was used as a model for chronic inflammatory states.
Results of the phytochemical analysis of CME revealed the presence of various substances including alkaloids, tannins, flavonoids, saponins, sterols, terpenoids, carotenoids and glycosides.
The solvent fraction HF contains mainly steroids, terpenoids and carotenoids, CF contains alkaloids, carotenoids, flavonoids, terpenoids and glycosides, EF contains flavonoids and glycosides,
AF contains tannins and glycosides,while BF, MF and WF contains saponins and glycosides. The acute toxicity test for CME revealed that it has a high safety profile (LD50>5000 mg/kg) as the extract was well tolerated by the animals.
INTRODUCTION
Nature has been a continuous source of pharmacologically active molecules and medicinal plants which have been used by human generations (Iriti et al, 2010). Plants have also been one of the important sources of medicine since the dawn of civilization. Of the250,000-500,000 known plant species on earth, more than 80,000 are medicinal (Increase-Coker, 2005).
The tropics are naturally endowed with about 150,000 seed plants, with 120,000 found in the tropical rain forests alone; an indication of the rich ethnomedicinal attributes of the rain forest plants (Increase Coker, 2005; Lewis, 2001).
In Brazil alone, about 80,000 species of plants were described, which offer enormous prospects for discovery of new compounds with therapeutic property (Adebolu and Oladimeji, 2005).
In spite of a rapidly expanding literature on phytochemistry, only a small percentage of the total plant species have been examined chemically and it is still a vast field for research (Gyang, 2001).
The plant genome, paradoxically is much larger than other natural sources (Bacteria: 1000 genes, fungi: 10,000 genes, plants: more than 100,000 genes) and this offers a broader biochemical network for the generation of unique and novel chemical structures.
A prime example of this scenario is the natural product anticancer drugs paclitaxel. Paclitaxel produced by Taxus brevifolia is a cytotoxic agent that is most likely produced to prevent organisms from feeding on the plant.
Thus, for this and other reasons, drug discovery from plant, and hence research in the area has gotten better appreciation and concern, nowadays (Silverman, 2008).
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