| BackgroundAtherosclerosis is the common pathological basis to generate many serious cardiovascular and cerebrovascular diseases, such as myocardial infarction, stroke. With the continuous progress of the society, the changes of dietary structure and lifestyle, the persistent acceleration of work pace, the incidence of atherosclerosis is increasing year by year, which is one of common and frequently-occurring diseases endangering to human health, so it is called the number one killer. Atherosclerosis mainly involves main artery and medium sized artery, especially happening in heart, brain and kidney, and its basic lesion is lipid deposition in the arterial intima, intimal focal fibrosis and atheromatous plaque formation, which leads to vessel wall hardening and vascular stenosis, then causes a range of secondary and ischemic changes. There are multiple risk factors in the chronic and evolutionary process of atherosclerosis, thus its pathogenesis has not been fully elucidated so far. A large number of studies have shown that dyslipidemia and oxidative stress plays an important role in the process of atherosclerosis occurrence and development.Apolipoprotein E is an important component of chylomicron, very low density lipoprotein and high density lipoprotein as well as Apolipoprotein E could scavenge serum lipid through low density lipoprotein receptor pathway or non-low density lipoprotein receptor pathway. Therefore, knocking out the Apolipoprotein E gene can result in elevated blood lipid levels, arterial intimal injury and lipid deposition which easily causes atherosclerosis onset. Apolipoprotein E-deficient(ApoE-/-) mice were cultivated successfully by the biochemical genetics and metabolism laboratory of Rockefeller University USA and the pathological genetics laboratory of North Carolina Central University in1992. Obvious hyperlipemia and atherosclerosis lesions can be detected in ApoE-/-mice whether high-fat diet or not. For this reason, ApoE-/-mice which are given high-fat diet and perivascular constrictive collar placement around the carotid artery generally are recognized as reliable animal models for exploring the process of atherosclerosis occurrence and development.Silymarin, a new type of flavonolignans isolated from the seeds of the milk thistle plant silybum marianum, is a bioactive mixture condensated from dihydroflavonol and phenylpropanoid derivatives. Silymarin consists of a mixture of four bioactive bioflavonoids found in the plant:silybin, isosilybin, silychristin and silydianin. Silybin is the main component and is believed to have the most biological activity. A lot of studies have demonstrated that silymarin exhibits scavenging reactive oxygen species, preventing lipid peroxidation, decreasing hepatic fibrosis and protecting hepatocyte membrane effects. So silymarin is widely used as a hepatoprotectant drug in the clinical treatment of acute or chronic hepatitis, hepatic cirrhosis and hepatic injury, and so on. Silymarin has been shown to have anti-atherosclerosis utility, such as lowering serum lipid and inhibiting vascular intimal hyperplasia in recent years. However, the report regard to its effect on existing atherosclerotic lesions is rare.ObjectiveTo examine the effect of silymarin on atherosclerosis in ApoE-/-mice, and explore the potential mechanisms.Methods 1. Animal ProtocolAfter two weeks of high-fat feeding, all mice were placed peri vascular constrictive collars (3mm×0.3mm) on the left common carotid arteries so as to establish an atherosclerosis model. Four weeks after surgery, six ApoE-/-mice were randomly selected so as to identify the atherosclerosis model formation, whose left common carotid arteries were dissected for histopathological observation. All other ApoE-/-mice were randomly allocated into three groups (n=42):control group (group A), low-dose silymarin group(group B) and high-dose silymarin group(group C)(n=14in each group). Mice in group A received a high-fat diet as before, while those in group B were given a high-fat diet plus50mg/(kg-d) silymarin feeding at the same time those in group C were given a high-fat diet plus200mg/(kg-d) silymarin feeding until killed four weeks later.2. Histological and Morphometric AnalysesAt the end of the study, left common carotid arteries were removed to produce specimens which stained with hematoxylin and eosin and oil red O. Plaque area, cap thickness and lipid were determined by Image-Pro Plus5.0image analysis system.3. Serological AnalysesAt the end of the experiment, blood serum were collected from the retro-orbital plexus. Serum total cholesterol, triglyceride, high density lipoprotein cholesterol as well as low density lipoprotein cholesterol were measured by automatic biochemical analyzer P-800. Serum malondialdehyde was assayed by thiobarbituric acid chromatometry in the meanwhile superoxide dismutase was assayed by xanthine oxidase method.Results1. Before medicine intervention, significant atherosclerotic plaques were detected in0.5mm area proximal to the collar of ApoE-/-mice.2. Compared with group A, plaque area and lipid were decreased in group B and C (P<0.05) while cap thickness increased (P<0.05). Furthermore the changes of group C were more significant (P<0.05). 3. There were no significant differences in serum lipid between group A and B. Compared with other groups, group C had a lower level of serum lipid (P<0.05).4. Serum malondialdehyde was lower in group B and C than that in group A(P<0.05), in the meanwhile superoxide dismutase was higher (P<0.05). In addition the changes of group C were more significant (P<0.05).ConclusionSilymarin can evidently inhibit the progress of existing atherosclerotic lesions in ApoE-/-mice. The possible mechanisms may be associated with lowering serum lipid levels and inhibiting oxidative stress. |
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