Experimental Research Of Atherosclerotic Plaque Rupture And Its Intervention With Medications

[Background] The acute coronary syndrome (ACS), which is the major manifestationsof the coronary heart disease, shares common pathophysiology processes that arecharacterized by the disruption of unstable coronary plaque and thrombus formation.However, it is not known the causes of plaque destabilization and mechanism of plaquerupture. Studies have shown that increased matrix metallo-proteinases (MMPs) areinvolved in the process of plaque rupture. Macrophages are the major inflammatory cells inthe plaque and MMPs are produced mainly by macrophages. It has been demonstrated thatMMP-9 plays an important role in plaque rupture and can reflect the condition of plaquestabilization. Clinical studies have demonstrated that angiotensin receptor blockade(ARB)may reduce cardiovascular events and mortality independence of the reduction of bloodpressure, it suggests that ARB may stabilize rupture-prone plaques. However, little isknown about whether Candesartan can stabilize and reduce plaque disrupture bydecreasing the macrophage accumulation and reducing MMP-9 expression in the plaque,moreover, it is not clear about the effect of Telmisartan on AT1/AT2 receptor and MMP-9expression of monocyte-macrophages.[Objectives] 1. The aim of this study is to evaluate the preventional effect ofCandesartan on plaque rupture by using rabbit models with unstable atheroscleroticplaques and explore its mechanisms. 2. To investigate the effect of Telmisartan onAT1/AT2 receptor and MMP-9 expression of monocyte-macrophages and explore theeffect of PKC inhibitor Staurosporine on MMP-9 expression.[Methods] 1. thirty-four New Zealand White male rabbits were randomly divided intothree groups.①The control group (n=10) were fed with normal diets for 12 weeks;②The model group (n=12) were fed with a 1% cholesterol diet for 12 weeks;③Candesartan intervention group (n=12) were also fed with a 1% cholesterol diet added with Candesartan(0.5mg/kg.day) for 12 weeks. Group 2 and 3 rabbits were underwent aortic balloon injuryand afer 12 weeks of the high-cholesterol diet, plaque disrupture was triggered byadministration of China Russel's viper venom and histamine. 2. The MMP-9 staining area,percentages of macrophage area and collagen-staining area of each cross-section of aortawere determined by immunohistochemical technique. 3. The protein expression of MMP-9of each aorta were determined by western-blotting technique. 4. The AT1 and AT2 receptorexpression of THP-1 monocyte cells were measured by flow cytometry,immunofluorscence and lazer scanning confocal microscope. 5. The MMP-9 expression ofTHP-1 macrophage supernate was analyzed by ELISA.[Results] 1. After 12 weeks, the serum lipid and body weight of model and interventiongroups were significantly elevated compared with the baseline levels (p＜0.001), especiallythe levels of total serum cholesterol. Compared with the model group, TG level was muchlower in intervention group (p＜0.001). 2. The pathologic observation of aorticatherosclerotic lesion showed that rabbits in model group had more unstableatherosclerotic plaques compared with the intervention group. In model group, 7 of the 9rabbits in total 12 lesions occurred plaque disruption and thrombosis. In contrast, inintervention group, only 2 of the 10 rabbits in total 3 lesions demonstrated plaquedisruption and thrombosis. 2. Compared with the model group, the percentage area ofMMP-9, the amount of macrophages were significantly decreased in intervention group,however, the content of cllagen was significantly. Compared with the normal group, theexpression level of MMP-9 protein in the aorta vessel of model group was significantlyincreased; compared with the model group, the expression level of MMP-9 protein in theaorta vessel of intervention group was significantly decreased; 3. The AT1 receptorexpression of THP-1 monocyte cells was significantly reduced by Telmisartan measured byflow cytometry, immunofluorscence and lazer scanning confocal microscope, however, theAT2 receptor expression was not significantly changed. 4. In cultured THP-1 macrophagecells, AngⅡ0.1-10μmol/L elicited an increase in MMP-9 expression that was prevented by Telmisartan in a dose-dependent manner. But the AT2 receptor antagonist PD123319had no effect. Telmisartan combined with Atrovastatin had an additional effect on MMP-9expression. 5. The MMP-9 expression of THP-1 macrophage cells was significantlydecreased by the PKC inhibitor Staurosporine.[Conclusions] 1. This study demonstrated that Candesartan could reduce the plaquedisrupture by using rabbit models with unstable atherosclerotic plaques. This may beexplained on the basis that AT1 blockade resulted in a decrease in macrophageaccumulation and MMP-9 expression in the plaque, but an increase in collagen deposition.2. In cultured cells, Telmisartan could reduce AngⅡelicited upregulation of MMP-9expression by decreasing AT1 expression and Telmisartan combined with Atrovastatin hadan additional effect on MMP-9 expression. PKC was involved in the expression ofMMP-9.