Hypocholesterolemic and antioxidant effects of aqueous extracts from the dried calyx of Hibiscus sabdariffa L. in hypercholesterolemic rats
Introduction
Hibiscus sabdariffa L. (roselle) is widely cultivated in Thailand where it is known as Krachiap daeng. Its red persistent calyx is the major component which has a sour taste and is used as beverage and food colorant. It is claimed as a Thai traditional medicine for kidney stones. It is also used as an antibacterial, antifungal, hypocholesterolemic, diuretic, uricosuric, mild laxative and antihypertensive substance (Farnworth and Bunyapraphatsara, 1992). However, only few studies have been reported (El-Saadany et al., 1991) with regard to the hypocholesterolemic effect of these extracts. Currently, the dried calyx extracts of these plants are commercially prepared as health food products available in the form of granules and as tea, and are claimed to be diuretic, hypocholesterolemic and antihypertensive. Since the scientific data on the hypolipidemic efficacy of these extracts are scarce, this was examined in the current study using a rat model.
Atherosclerosis is one of the major risk factors for coronary heart disease and it is widely recognized that the oxidative modification of human low density lipoprotein (Ox-LDL) may play an important role (Steinberg and Witztum, 1990, Witztum and Steinberg, 1991, De Zwart et al., 1999). Excess LDL in the artery wall due to hypercholesterolemia can undergo oxidative modifications. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that Ox-LDL contributes to atherogenesis. The oxidation of lipids in human atheromata lesions and production of excess reactive oxygen species (ROS) including superoxide anion (O2−), hydrogen peroxide (H2O2), and peroxynitrite (ONOO−), are the evidences for the presence of Ox-LDL in vivo (Griendling and FitzGerald, 2003). Ox-LDL has a number of potentially pro-atherogenic activities contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption (Iuliano, 2001). Antioxidative substances are believed to suppress the onset and development of atherosclerosis; compounds such as probucol has been shown to reduce the progression of atherosclerosis lesions in Watanabe heritable hyperlipidemic rabbits (WHHR) in vivo (Carew et al., 1987). In addition, flavonoids and phenolic compounds have also been shown to have antioxidant effects (Di Carlo et al., 1999). Thus, substances which combine antioxidant and hypocholesterolemic activities are expected to be effective in preventing the formation and progression of atherosclerosis (Anderson et al., 1995, Diaz et al., 1997, Chrysselis, 2000).
Various antioxidant constituents are found in the calyx of roselle, such as hibiscus anthocyanin, quercetin, l-ascorbic acid and protocatechuic acid. Antioxidant effects of these extracts have been investigated in many experimental models. We previously demonstrated that the dried calyx extract of roselle exerts an antioxidant effect on LDL oxidation induced by CuSO4 in vitro (Hirunpanich et al., 2005). However, the exact concentrations of roselle required to protect against LDL oxidation have as yet not been directly evaluated in vivo. The present study was designed to investigate the hypolipidemic effects as well as the antioxidant effects of roselle on LDL oxidation in vivo and ex vivo.
Section snippets
Plant material and extracts
The plant was identified by Prof. Dr. Nuntavan Bunyapraphatsara, Department of Pharmacognosy, Faculty of Pharmacy, Mahidol University by comparing with the voucher specimen deposited in the herbarium of Faculty of Pharmacy, Mahidol University, serial number (PBM) W. Chuakul 00087.
The dried calyces of roselle were blended to a fine powder. One kilogram of powder was extracted with 1 l of water and filtered through filter paper. The filtrates were pooled and concentrated using a rotary evaporator
In vivo hypolipidemic effects of the dried calyx extracts of roselle
In the period of induction of hypercholesterolemia through feeding cholesterol to male Sprague-Dawley rats, the increase of body weight and amount of food intake were not significantly different among all groups of the study. Feeding with corn oil in the control II group slightly increased serum cholesterol level compared to the control I group but without significant difference at corresponding times (Fig. 1). Serum cholesterol level increased over the time period in all groups due to the
Discussion
Roselle has been reported to have a variety of biological effects including diuresis, antihypertension and hypocholesterolemia. For the hypocholesterolemic effect, scientific data on its efficacy is scarce. Recently, a number of clinical studies suggest dyslipidemia as one of the major risk factors for coronary disease, and preclinical observations demonstrate that hypercholesterolemia promotes accumulation of oxidatively modified low-density lipoprotein (Ox-LDL) in the arterial wall, promoting
Acknowledgement
This study was supported in part by a grant of Medicinal Plant Research Institute, Department of Medical Sciences, Ministry of Public Health, Thailand.
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