Puerarin decreases serum total cholesterol and enhances thoracic aorta endothelial nitric oxide synthase expression in diet-induced hypercholesterolemic rats

Abstract

Hypercholesterolemia is a dominant risk factor for the development and progression of atherosclerosis and cardiovascular diseases. Natural compounds have been proved to be useful in lowering serum cholesterol to slow down the progression of cardiovascular diseases. Pueraria lobata is employed clinically to treat cardiovascular diseases in China. In the present study, the atheroscleroprotective potential of the herb's major active compound, puerarin, was investigated by monitoring serum lipid profile and major enzyme expressions on cholesterol homeostasis in Sprague–Dawley rats fed with control diet, hypercholesterolmic diet or hypercholesterolmic diet plus administration of puerarin (300 mg/kg/day, p.o.) for 4 weeks. Puerarin markedly attenuated the increased total cholesterol induced by hypercholesterolmic diet in both serum and liver. It caused a significant reduction in the atherogenic index. Expression of mRNA for hepatic 7α-hydroxylase (CYP7A1) was significantly enhanced but not for those of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and lanosterol 14α-demethylase (CYP51). To further explore the atheroscleroprotective potential of puerarin, acetylcholine induced endothelium-dependent vasorelaxation and endothelial nitric oxide synthase (eNOS) expression on isolated thoracic aortas were analyzed. Animals administered with puerarin suppressed the hypercholesterolemic diet induced impairment of eNOS expression, whereas there was no significant difference in the endothelium-dependent vasorelaxation among various groups of animals. These data indicated that puerarin reduced the atherogenic properties of dietary cholesterol in rats. Its hypocholesterolemic function may be due to the promotion of cholesterol and bile acids excretion in liver. Whether puerarin targets directly on cholesterol homeostasis or both cholesterol homeostasis and endothelial function remains to be determined.

Introduction

The etiology of atherosclerosis is multifactorial with numerous known and unknown genetic and environmental factors influencing lipoprotein metabolism and inflammation (Ross, 1993). Hypercholesterolemia is a dominant risk factor for the development and progression of atherosclerosis and related cardiovascular diseases (Prasad and Kalra, 1993, Farmer and Gotto, 1997, Deepa and Varalakshmi, 2005). A diet high in cholesterol content is a major environmental contributor to an unbalanced lipoprotein metabolism and associates with an increased prevalence of atherosclerosis.

In hypercholesterolemia and atherosclerosis, the physiological activity of nitric oxide (NO) is reduced and results in endothelium-dependent vasodilation impair, platelet aggregation enhancement and increased endothelial adhesiveness for monocytes (for review see Böger et al., 1996). Endothelial dysfunction is recognized as the basic mechanism for initiation and maintenance of atherosclerosis (Sessa et al., 1992, Kuchan and Frangos, 1994). Therefore, the protection of endothelial integrity by elimination of certain risk factors via lipid lowering agent has been proven to be effective in restoring endothelial function and in slowing the progress of the disease (Rosenson, 2001).

Puerarin, 4H-1-benzopyran-4-one,8-β-d-glueopyranosyl-7-hydroxy-3-(4-hydroxy-phenyl) (C₁₂H₂₀C₉), is one of the major isoflavonoid compounds isolated from the root of a wild leguminous creeper, Pueraria lobata (Willd.) Ohwi (Chueh et al., 2004). This medicinal herb has been demonstrated to have effects on treatment of fever (Zhou et al., 1995, Chueh et al., 2004), liver diseases (Keung and Vallee, 1993, Overstreet et al., 1996) and cardiovascular diseases (Fang, 1980, Chai et al., 1985, Song et al., 1988, Fan et al., 1992, Wang et al., 1994). In China, P. lobata is also used as a health supplement for reducing risk factors of cardiovascular diseases. Despite the wide application of P. lobata in clinical prescriptions and dietary supplements (Jiang et al., 2005), no study on the effects on the lipid lowering and vascular protection of puerarin was reported.

An investigation was, therefore, made of the effects of high cholesterol diet in rats with or without treatment with puerarin, on the serum lipid profile [triglycerides, total cholesterol, high density lipoprotein (HDL), low density lipoprotein (LDL)], the liver total cholesterol level and the changes in the gene expression of the key enzymes responsible for cholesterol homeostasis. Further investigations were done on the endothelium-dependent vasorelaxation and endothelial nitric oxide synthase (eNOS) expression of isolated thoracic aortas from rats with or without treatment with puerarin.