Experimental Research Of Atherosclerotic Plaque Vulnerability And Its Intervention With Medications

Experimental research of atherosclerotic plaque vulnerability and itsintervention with medications[Backgroud] The acute coronary syndromes (ACS), which include unstable angina,non-ST-segment and ST-segment elevation acute myocardial infarction, all sharecommon pathophysiology processes that are characterized by coronary plaque ruptureand thrombus formation, leading to myocardial ischemia. However, the underlyingmolecular mechanism about plaque destabilization has not yet been investigated.Activated matrix metalloproteinases (MMPs) and increased cells apoptosis maycontribute to plaque destabilization. Several clinical trials have demonstrated thatStatins (hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors) andARB (direct angiotensinⅡreceptor blockade) therapy can reduce cardiovascularevents and mortality independence of the reduction of blood pressure and serum lipid, itsuggested that Statins and ARB may stabilize vulnerable atheromatous plaques. Thereare increasing clinical and experimental evidences that Tongxinluo, a traditionalChinese drug, achieved significant effect in term of coronary heart disease and anginapectoris therapy, but little is known about its plaque stabilization effect. Moreover thereis no definite conclusion that the mechanism of these drugs' plaque stabilization effectrelated with inhibition of cyclooxygenase-2 (COX-2) and MMP-1 expression andmodulation of apoptosis related genes.[Objective] This study is to evaluate the plaque stabilization effect ofSimvastatin, Irbesartan, Simvastatin plus Irbesartan and Tongxinluo on rabbit model ofatherosclerosis, and explores the molecular mechanism furthermore.[Methods] Fifty-two male white rabbits were randomly divided into six groups. The control rabbits (n=6) were fed with normal diets, other rabbits (n=46), whichunderwent aortic balloon injury followed by a 1.5% cholesterol diet for 16 weeks,were divided no drug therapy (HC group n=10), Simvastatin (2mg/kg/day, n=10),Irbesartan (10mg/kg/day, n=10), Combination (Simvastatin 2mg/kg/day+Irbesartan10mg/kg/day n=8) and Tongxinluo (1g/kg/day, n=8).At the end of the study, forty-three rabbits were available to evaluate. The serumET and NO were measured and the degree of atherosclerosis of aortas was determinedby the ratios of intima to media and lesion to intima each cross-section of aorta. Thepercentages of macrophage area, collagen-staining area, MMP-1 staining area andCOX-2 staining area of each cross-section of aorta were determined byimmunohistochemical technique. The protein expression of MMP-1 and COX-2 ofeach aorta were determined by western-blotting technique. The mRNA expression ofFasL and bcl-2 of each aorta were determined by RT-PCR technique.[Results] After 16 weeks, the serum lipid and body weight of five interventiongroups (HC, Simvastatin, Irbesartan, Simvastatin plus Irbesartan and Tongxinluogroup) were significantly elevated compared with the baseline levels (P＜0.05～0.001),especially the levels of total serum cholesterol which were significantly increased by20-40 folds (P＜0.05～0.001). Compared with HC group, the levels of serum totalcholesterol in Simvastatin and Simvastatin plus Irbesartan group were significantlylower (P＜0.05～0.01), no difference in Irbesartan group (P＞0.05), and slightly lowerin Tongxinluo group (P=0.054). There was no difference in body weight between thefive experiment groups (P＞0.05).Compared with the control group, the level of serum ET in the HC group wassignificantly increased (p＜0.001), the level of serum NO was significantly decreased(p＜0.01). Compared with the HC group, the levels of serum ET in the four interventiongroups were significantly decreased (all p＜0.01), the levels of serum NO were significantly increased (p＜0.01～0.05). There were no difference in levels of ET andNO among the four intervention groups (P＞0.05).The pathologic observation of aotic atherosclerotic lesion showed that rabbits inHC group had thicker intima, thinner media, much vulnerable plaque and morethrombi compared with the intervention groups. The quantified observation of aoticatherosclerotic lesion with computed morphometry showed that:①There was nosignificant difference in lesion of intima area ratio among five experiment groups(P＞0.05).②Compared with the control group, the intima thickness in HC group wassignificantly increased; compared with the HC group, the intima to media thicknessratios in four intervention groups were significantly decreased (all p＜0.05); there wasno difference among the four intervention groups (p＞0.05).③Compared with thecontrol group, The amount of macrophages in HC group was significantly increased;compared with the HC group, the amounts of macrophages in the four interventiongroups were significantly decreased (P＜0.01～0.05), there was no difference amongthe four intervention groups (p＞0.05).④Compared with the control group, Thecontent of collagen in HC group was significantly decreased; compared with the HCgroup, the contents of collagen in the four intervention groups were significantlyincreased (P＜0.01～0.05); There was no difference amnong the four interventiongroups (p＞0.05).⑤Compared with the control group, The percentage area ofMMP-1 in HC group was significantly increased; compared with the HC group, thepercentage areas of MMP-1 in the four intervention groups were significantlydecreased (all P＜0.05), there was no difference among the four intervention groups(p＞0.05).⑥Compared with the control group, The percentage area of COX-2 in HCgroup was significantly increased; compared with the HC group, the percentage areasof COX-2 in the four intervention groups were significantly decreased (P＜0.01～0.05);there was no difference among the four intervention groups (p＞0.05).⑦There was significantly correlation between the percentage area of COX-2 and MMP-1.The expression levels of COX-2 and MMP-1 protein: compared with the controlgroup, the expression levels of COX-2 and MMP-1 protein in the aorta vessel of HCgroup were significantly increased; compared with the HC group, the levels of COX-2and MMP-1 protein in the four intervention groups were significantly decreased(P＜0.05～0.001); there was no difference among the four intervention groups (p＞0.05). There was significantly correlation between the level of COX-2 and MMP-1protein in expression.The expression level of FasL and bcl-2 mRNA: compared with the control group,the expression level of FasL mRNA in the aorta vessel of HC group was significantlyincreased (P＜0.001); the level of bcl-2 mRNA was significantly decreased(P＜0.01);compared with the HC group, the levels of FasL mRNA among the four interventiongroups were significantly decreased (P＜0.05～0.001) and the bcl-2 mRNA wereincreased (P＜0.05～0.01) among the four intervention groups. Except that the level ofFasL mRNA in the Simvastatin group was lower than other three intervention groups(P＜0.05～0.01), there was no difference among other three groups (P＞0.05). therewas no difference in the level of bcl-2 mRNA among the four intervention groups60＞0.05)[Conelusions] This study demonstrates that Simvastatin may decrease serumlipid, also Tongxinluo decrease serum lipid slightly, and Irbesartan has no effect onserum lipid. All these drugs may significantly improve endothelial function.All Simvastatin, Irbesartan, Simvastatin plus Irbesartan and Tongxinluo candecrease the intima thickness and macrophage accumulation, increase the content ofcollagen, showing antiatherosclerosis and stabilizing vulnerable plaques effect,furthermore, Simvastatin and Irbesartan have potential collaboration effect.We presumed that the plaque stabilization effect of these drugs may related with inhibition of expression of COX-2 and MMP and modulation of apoptosis genes.