The Effect Of Losartan On Expression Of Matrix Metalloproteinase-2 And Its Inhibitor After Endothelia Injury Of The Abdominal Artery In Rabbits

Backgroud and objective: Coronary heart disease is the main cause of population death in the developed country. In China, its incidence also inceases rapidly and does harm to the body health of people severely. Atherosclersis is the basic pathologic foundation of coronary heart disease. Its formation is a complicated pathological process. Its occurrence and development is one of main diseases threatening human beings'health which is subjected to various factor influence accompanied with other complications.It is shown that under the function of various stimulative factor and multi-cell factor such as hyperlipemia ,the component of extracellular matrix accumulated and sinked in arterial intima and intimal hyperplasia and smooth muscle cells transferred from middle membrane to intima and proliferated result in atherosclerosis finally. Many experts thinks that neointimal hyperplasia or the formation of plaque and the reconstruction of blood vessel after blood vessel is injuried are the main determinate factor of the narrow lumen after atherosclerosis.Excesssive repair after blood vessel is injured, hyperplasia and migration of the smooth muscle cell and subsequently a great deal of extracellular matrix accumulated and vessel remodeling are the key to stenosis formation. Not only the degradation of extracellular matrix is related closely to the transference of smooth muscle cell from middle membrane to intima and hyperplasia inside blood vessel but also the content and the change of constitute of ECM also are important cause of vessel remodeling while hypertension, atherosclerosis and restenosis after PTCA. Therefore,the disturbance of balance between synthesis and degradation of ECM plays animportant role in the occurrence and development of restenosis of blood vessel.Matrix metalloproteinases(MMP) as main degradation enzyme of ECM is increasingly attached importance to in the course of atherosclerosis and acute coronary syndrome. MMP-2 is the most important matrix metalloproteinases expressed and secreted by cell in the blood vessel wall which may degrade the main component of basement membrane efficiently—IV collagen. Study shows that MMP-2 is a kind of indispensable substance to the migration and hyperplasia of smooth muscle cell and through intra-elastic lamina ,basement membrane and so on ,which plays a key role in the reaction of intimal injury and the course of atherosclerosis and affects the development of course of diseases and the occurrence of complications. It is shown that RAS is located in blood vessel whose activity increases in many pathologi -cal states. Angiotensin II created by RAS acts on cell in blood vessel wall and ECM and changes the expression of inflammatory cytokine> chemotactic factor > adhesiv -e factor and leads to the disturbance of endothelia function and promote the deposi -tion of lipid and inflammate reaction and at last results in the formatin of atherosclerosis. It has been proven that angiotensin II takes part in the forma -tion of the stenosis of atherosclerosis with the help of its receptor. In short,the formation of atherosclerosis is a result acted by multi-factors together.Many factors such as rennin-angiotensin system(RAS^ hyperlipemia all have something to do with the occurrence of atherosclerosis, but the detail mechanism of atherosclerosis is still not quite clear. At present, its treatment has no valid medicine. Because the occurrence and development of atherosclerosis are chronic > latent and progressively aggravated and no any clinic syndrome in the early stage of fatty streak formed by atherosclerosis,they are always neglected easily. Until fribrolipid plaque and complex pathologic lesion are formed and the syndrome appear as the stenosis of blood vessel results in the lack of blood supplied by coronary artery, has the sclerosis of blood vessel been not evident and this pathological changes have difficulty in reversion. So it is very important to explore effective medication actively and treat early in order to reverse or block the pathological course.Wilensky RL reviews the relevant contents that the angiotensin receptor antagonist prevents the stenosis of atherosclerosis in 2003. He thinks controlling RAS may become the latent purpose of preventing the stenosis of atherosclerosis. Angiotensin II I receptor antagonist inhibits the biologic effect of angiotensin II through combining angiotensin II I (ATl)receptorand strengthens indirectly biologic effect of angiotensin II II (AT2) receptor to inhibit the content of collagen and intimal hyperplasia while may enhance angiotensin II through the mechanism of negative feedback for inhibiting ATI receptor.The purpose of this experiment is that through the atherosclerotic stenosis model after endothelia injury of the abdominal artery in rabbits it is studied that the mechanism of stenosis and restenosis of atherosclerosis and the function of interference factors and observed the effect of losartan on intimal hyperplasia of blood vessel and MMP-2 and its inhibitor after balloon injury and explored the mechanism that losartan prevents atherosclerosis further,thereby may provide new path looking for treating restenosis.Materials and methods Choosing 24 male New Zealand rabbits , whose weights were about 2.5-3.0 kg.The rabbits were randomly divided into three groups. The groups are as follows: ? ordinary feeding rabbits(Gl);(2) cholesterol feeding + abdominal artery injury rabbits (G2) ;(3) cholesterol feeding + abdominal artery injury rabbits + losartan (G3)The rabbits of Gl group were gived by ordinary feedstuff and the rabbits of G2 and G3 group were undergone intimal denudation in the abdominal artery after a two-week 1.5% cholesterol diet. The rabbit balloon catheter denudation model was made depending on Block et.'s method and modified it. The rabbits of G2 group were fed contantly for 6 weeks after operation and losartan (10 mg/kg) was used in the rabbits of G3 group. The serum total cholesterol(TC) and triglyceride(TG) were measured by taking 2ml blood from marginal vein of ears in rabbits at the end of 0, 2n 4^ 6> 8 weeks. The animals were killed 6 weeks after balloon injury,taken out abdominal artery,replaced the blood in the abdominal artery with normal saline,perfused 15 minutes with 10% formalin under 100 mmHg constant pressure. Abdominal artery was separated and wiped off fatty tissue in the adventitia and intercepted the specimen of shaped part in blood vessel. The specimen was fixed conventionally for 24 hour and dehydrated by degree and embede in paraffin and done 3^111 slice constantly. The slices were done haematoxylin-eosin staining and histomorphology examination. And respective indexes of stenosis were measured by computerized morphometry instrument. MMP-2 and TIMP-2 were measured through immunohistochemical method. Results It is shown that TC and TG were significantly higher than those of pre-experiment inthe blood serum of rabbits of G2 and G3 group after 8 weeks hyperlipid feeding through the measuration of blood-lipid (P < 0.01) . By pathological morphological examination in the specimens of blood vessel,the plaques were formed in rabbits of G2 group by nake eyes and light microscope. And respective stenosis indexes of G2 group were significantly increased such as intimal thick(IT)[(1.28±0.20)vs(0.33±0.06)mm] ^ intimal thick/media thick(IT/MT) [(0.64±0.12)vs(0.25±0.04)]> intimal area(IA)[(5.19±0.33)vs(2.76±0.32)mm2]s intimal area/media area(IA/MA)[(0.88±0.13)vs(0.39±0.05)] and stenosis indexes of G3 group were significantly reduced than those of G2 group such as IT [(0.48±0.06)vs(1.28±0.20)mm] ^ IT/MT [(0.45±0.12)vs(0.64±0.12)] , IA[(3.53±0.54)vs(5.19±0.33)mm2] , IA/MA [(0.56±0.09) vs(0.88±0.13)] through computerized morphometry instrument. Immunohistochemistric alanalysis showed that there were no significant changes in the expression of MMP-2 after losartan treatment [(22.25±3.45)vs(20.00±3.70)], while the expression of TIMP-2 significantly inreased [(37.62±2.67)vs(27.13±5.25)], and the ratio of MMP-2 / TIMP-2 significantly lowered as the result of losartan treatment [(0.42±0.14)vs(1.95±0.08)]( P < 0.01). Conclusion1. Eight weeks high-fat diet and intimal denudation operation in the abdominal artery cansucceededly perform atherosclerotic stenosis model.2. Giving high-cholesterol diet can make blood lipid high ,and then promote the formation ofatherosclerosis.3. Losartan can inhibit intimal hyperplasia and atherosclerosis.4. The mechanism of losartan in preventing atherosclerosis has little to do with lipid.5. Losartan could significantly inhibit intimal proliferation and improve vessel remodeling afterballoon injury .The mechanism of anti-atherosclerosis by losartan may be related to elevation of TIMP-2 and the revertion of balance of MMP-2 / TIMP-2.