Abstract: The effect of ethanolic stembark extract of Mammea africana Sabine on total cholesterol, triglyceride and lipoproteins levels was studied on normal rats. The extract (30-90 mg kg-1) was orally administered to rats for 21 days after which they were sacrificed and blood taken for analysis. The extract produced a significant (p<0.05) dose-dependent decrease in the levels of total cholesterol, triglyceride, LDL-cholesterol and VLDL cholesterol, with a significant (p<0.05) increase in the level of HDL-cholesterol. The stembark extract has the potential to produce hypolipidaemia as well as preventing the development of atherosclerosis.
INTRODUCTION
Heart diseases have been implicated as leading causes of death for both men and women of all racial and ethnic groups (Smith, 2004). The elevation of serum total cholesterol and low density lipoprotein (LDL) cholesterol have been implicated as a primary risk factor for cardiovascular disease (Edijala et al., 2005). A number of plants have been used traditionally in the treatment of various cardiovascular diseases of which Mammea africana is one of them.
Mammea africana Sabine (syn. Ochrocarpus africana Oliv.) (Guttiferae) is a large forest tree of 50-100 feet high with bark often yellow with pale scales and resinous yellow sap (Daziel, 1956). The plant is widely distributed in Tropical Africa. The stem bark of the plant is used traditionally by the Ibibios of Niger Delta region of Nigeria in the treatment of hypercholesterolemia, internal heat and microbial infections. It is reported by Adjanohoun et al. (1996) to be used in the treatment of rheumatic pains, cough and hypertension. The antimalarial (Okokon et al., 2006), antidiabetic (Okokon et al., 2007) and vasorelaxant (Dongmo et al., 2006) properties of the plant have been reported. The chloroformic and ether stembark extracts are reported to possess cytotoxic activity on cell culture (Chapius et al., 1988). Ouahouo et al. (2004) reported cytotoxic coumarins with antimicrobial activity against Staphylococcus aureus from the plant stembark. The stembark has also been reported to contain 5-7-dihydroxy-8-(12-methyl-butryl)-4-N-pentyl coumarins (Carpenter et al., 1971; Crichton and Waterman, 1978; Carpenter et al., 1970) and Mesuxanthane B (Carpenter et al., 1971). The heartwood has been reported to contain xanthone (Carpenter et al., 1969), friedelin (triterpene) (Crichton and Waterman, 1978) and flavonoids (Carpenter et al., 1970). Alkaloids have been reported to be absent in the entire plants parts (Garflans et al., 1980). The present study was aimed at assessing the effect of the stembark extract on total cholesterol, triglyceride and lipoproteins levels of rats so as to evaluate its cardioprotective potentials.
MATERIALS AND METHODS
Plant Material
Fresh stembark of M. africana were collected in November, 2004, from
Anwa forest in Uruan area of Akwa Ibom State and authenticated by Dr. (Mrs.)
Margaret Bassey, a taxonomist in Botany Department, University of Uyo, Uyo-Nigeria.
Hebarium specimen was deposited at Faculty of Pharmacy, University of Uyo, Uyo
with voucher No. FPHU 381.
The fresh stembark (4 kg) of the plant was dried on a laboratory table for 2 weeks and reduced to powder. The powder (300 g) was macerated in ethanol (500 mL) for 72 h. The liquid extract obtained was concentrated in vacuo at 40°C. The yield was 3.51%. The extract was stored in a refrigerator at 4°C until used for experiment reported in this study.
Animals
The animals used in the study were adult male and female albino wistar rats
(150-220 g) obtained from University of Uyo animal house, Uyo, Nigeria. The
animals were used after acclimatization period of 10 days to room temperature
and relative humidity of 28±5°C and 50%, respectively. They were
housed in standard cages and maintained on standard animal pellets (Pfizer livestock
feeds, Aba, Nigeria) and water ad libitum. The study was approved by
University of Uyo College of Health Sciences Animal Ethics Committee.
Experimental
The rats were weighed and randomly assigned on the basis of weight into
4 groups of 5 animals each. Animals in Groups A, B and C were orally administered
with 30, 60 and 90 mg kg-1 of the extract respectively, while animals
in group D were orally given normal saline 5 mL kg-1 and served as
control. Administration of the extract continued for 21 days between 08:00 and
09:00 h each day. Twenty four hours after the last administration, the animals
were anaesthesized with chloroform vapour and dissected. Whole blood was obtained
by cardiac puncture from each rats and collected into sample bottles. Serum
total cholesterol, triglyceride and High Density Lipo-protein (HDL) levels were
measured by enzymatic colorimetric method using Randox kits. The concentration
of Low Density Lipoprotein (LDL) cholesterol and Very Low Density Lipoprotein
(VLDL) were calculated by the formula of Friedwald et al. (1972).
Statistical Analysis
All Data obtained were statistically analysed using one way ANOVA followed
by Tukey-Kramer post test.
RESULTS AND DISCUSSION
The ethanolic stembark extract of M. africana produced a significant (p<0.05) decrease in the levels of total cholesterol, triglyceride, LDL-cholesterol and VLDL-cholesterol of the extract treated group compared to control after 21 days of administration of the extract in a dose dependent fashion. The reduction was more pronounced at the highest dose of the extract (Table 1). However, there was a significant (p<0.05) increase in the levels of HDL-cholesterol in a dose dependent fashion when compared to control.
Hyperlipidaemia has been implicated in the development of atherosclerosis (Kaplan, 1989). Accumulation of lipids in the arterial wall plays a crucial role in the development of atherosclerosis by impairing the endothelial function which can subsequently result in vasoregulation, platelet and monocyte adhesion, vascular smooth muscle cell growth and oxidization of LDL (Vogel, 1997; Shaila et al., 1995).
| Table 1: | Effect of ethanolic stembark extract of Mammea africana on serum total cholesterol, triglyceride, hdl-cholesterol, ldl-cholesterol and VLDL-cholesterol |
| Data are expressed as Mean±SEM, n = 5 *: p<0.05, **: p<0.01 | |
Lowering of the lipid levels could reduce the risk of Cardiac Heart Disease (CHD) by regression of atherosclerosis. Oxidation of LDL has been known to play a crucial role in atherogenesis or formation of atheroma. In the result of this study, there was a significant reduction in the levels of total cholesterol, triglycerides, LDL and VLDL-cholesterol of the extract treated rats which could have resulted from the antioxidant properties of the extract especially in the case of LDL and VLDL. This finding corroborates that of Okokon et al. (2007), who reported similar reduction in diabetic rats. Lowering of cholesterol levels in rats have been reported to be due to antioxidant activity of phytochemical compounds such as flavonoids (Igarashi and Onhuruma, 1995). HDL functions in the transport of cholesterol away from the peripheral tissues to the liver, thus preventing the genesis of atheroselerosis. The observed significant increase in the level of HDL, further points to the cardiac protective activity of the stembark extract.
CONCLUSIONS
In this study, it is evident that ethanolic stembark extract of M. africana possesses anticholesterolaemic and antihyperlipidaemic properties. Thus, the stembark maybe use in the prevention and management of cardiovascular disorders. However, further studies should be carried out to determine the active principles and the exact mechanism of hypolipidaemic effects.
ACKNOWLEDGMENT
The authors are grateful to Mr. Efiong Bassey of Pathology Department, University of Uyo Teaching Hospital for his technical assistance.