Evaluation of the medicinal potentials of the methanol extracts of the leaves and stems of Halleria lucida

Abstract

The medicinal potentials of the methanol extracts of the leaves and stems of Halleria lucida (Scrophulariaceae) were evaluated by assessing their antibacterial and antioxidant properties in vitro using standard procedures. The antioxidant activities of methanol extract of the leaves as determined by the ABTS, DPPH, proanthocyanidins and total flavonoids were higher than that of the stem. On the other hand, the total phenols, the flavonoids and the FRAP contents of the stem were higher than that of the leaves. The extracts however showed poor activity against both Gram-positive and Gram-negative bacteria. The methanol extract of the stem showed activities against Bacillus cereus and Staphylococcus epidermidis at MIC of 1.0 mg/ml. The methanol extract of the leaves did not show activity against any of the organisms used in this study. This study has to some extent validated the medicinal potential of the leaves and stems of H. lucida.

Introduction

Halleria lucida L. (Scrophulariaceae) is a shrub or small to medium-sized evergreen tree, single or usually multistemmed; crown rounded, with or without branchlets; leaves opposite, simple, drooping, ovate, thinly leathery, shiny bright green above, hairless; base very broadly tapering to square, often asymmetrical; margin finely toothed to scalloped; fruit fleshy, ovoid, black when ripe and crowned by the dry remains of the style (Van Wyk et al., 2000). H. lucida is found in coastal and karroid scrub, deep evergreen forest, forest margins, near rivers and on stream banks from the Cape peninsula in the south in a strip up the eastern coast of South Africa, through the Eastern Cape to Lesotho, the eastern Free State, KwaZulu-Natal and Swaziland where it turns inland and roughly follows the escarpment into Mpumalanga, Guateng and the Northern and North West Province. It also occurs in isolated pockets in Zimbabwe (Jackson, 1990, Pooley, 1993, Van Wyk and Van Wyk, 1997).

H. lucida is used by the Zulus to treat skin and ear complaints. Dry leaves are soaked in water and squeezed into the ear to relieve ear ache. This tree is also considered a charm against evil (Messana et al., 1984, Pooley, 1993, Van Wyk et al., 2000). The leaves are also utilized by livestock and game. Two compounds: hallerone and halleridone were isolated from the leaves of this plant (Messana et al., 1984). The presence of these cyclohexanones and related quinols in the metabolism of plants of different families (Cornaceae, Scrophulariaceae, Bignoniaceae, Compositae) indicates that these products may not be specific secondary metabolites but may represent an aspect of primary metabolism connected with the prephenic–shikimic–chorismic acids route as evidenced by the close structural similarity of these products with prephenic acid (Messana et al., 1984). Abdullahi et al. (1986) also reported the isolation of cyclohexandiol from the stems of this plant.

Recent developments in biomedicals point to the involvement of free radicals in many diseases (Behera et al., 2006). Free radicals attack the unsaturated fatty acids in the biomembranes resulting in membrane fluidity (Dean and David, 1993). For these reasons antioxidants are of interest for the treatment of many kinds of cellular degeneration (Behera et al., 2006). Synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are very effective but they may possess mutagenic activity (Namiki, 1990, Hettiarachchy et al., 1996, Park et al., 2001, Tripathi et al., 2007). For this reason the desire for natural food has led to the search for naturally-occurring antioxidants. Antioxidants can act by the following mechanisms in lipid peroxidation: (i) decreasing localized oxygen concentrations; (ii) preventing chain initiation by scavenging initiating radicals; (iii) binding catalysts, such as metal ions, to prevent initiating radical generation; (iv) decomposing peroxides so they cannot be reconverted to initiating radicals; and (v) chain-breaking to prevent continued abstraction by active radicals (Dorman et al., 2003, Tepe et al., 2006). Free radicals have been implicated in the causation of several diseases such as liver chirrhosis, atherosclerosis, cancer, diabetes, etc. and compounds that can scavenge free radicals have great potential in ameliorating these disease processes (Wilson, 1998, Gerber et al., 2002, Kris-Etherton et al., 2002, Serafini et al., 2002, Di Matteo and Esposito, 2003, Behera et al., 2006). Antioxidants thus play an important role to protect the human body against damage by reactive oxygen species (Tutour, 1990). Plants containing flavonoids have been reported to possess strong antioxidant properties (Raj and Shalini, 1999, Badami et al., 2003).

The problem of microbial resistance is growing, therefore, actions must be taken to reduce this problem. One such way is carrying out research aiming at the development of synthetic or natural new drugs. The ultimate goal is to offer appropriate and efficient antimicrobial drugs to patient (Kumar et al., 2005).

In the present study, methanol extracts of the leaves and stem of H. lucida were screened for antioxidant and antibacterial properties using standard procedures. The findings from this work may add to the overall value of the medicinal potential of the plant.