Study On Aneurysmal Remodeling And Mechanisms Of The Basilar Artery Induced By Hemodynamics

Part oneAneurysmal remodeling and mechanisms of the basilar arteryterminus induced by hemodynamics in rabbitsObjective: Intracranial aneurysm is a cerebrovascular disease with significant risk，while the detailed pathological mechanisms of formation have not been elucidated. Thisstudy tried to survey aneurysmal remodeling and investigate potential mechanisms in thebasilar artery terminus induced by hemodynamics in rabbits.Methods: Thirty six adult New Zealand white rabbits were subjected to sham surgery(12animals), or bilateral common carotid artery ligation (12animals in1week afterligation,12animals in2weeks after ligation). TOF MRA was performed and carried outthree-dimensional before the operation, and1,2weeks after ligation and hemodynamicswas calculated. Immediately after rabbit euthanasia at1,2weeks after ligation, the arterieswere perfused. The basilar bifurcations were dissected, sectioned longitudinally, andstained with EVG and Masson for smooth muscle cells and internal elastic laminarespectively. Sections were then stained with mouse monoclonal antibodies (anti-RAM-11for macrophages, anti-eNOS for endothelial cells, anti-iNOS, anti-NK-κB p65and anti-TNF-α for proinflammatory factor) for immunohistochemistry analysis. And anti-α-SMAfor α-smooth muscle actin, anti-MMP-2and anti-MMP-9for extracellular matrix-degrading enzymes carried out immunofluorescence analysis. Relative content of proteinof NF-κB and TNF-α were detected by ELISA in the tissue of the basilar artery terminus.Relative expression of CD68, eNOS, iNOS, α-SMA, MMP-2and MMP-9mRNA wereexamined by Quantitative real time-polymerase chain reaction (RT-PCR) analysis.Results: Wall shear stress of the basilar terminus increased after the bilateral carotidartery ligation.83.3%(10/12) basilar terminus presented with absent, disrupted or thinnedinternal elastic lamina and thinning media and a bulge induced by hemodynamics. It was aneurysmal remodeling. However, wall shear stress of the basilar terminus in one rabbit intwo experimental groups respectively (16.7%,2/12) lower than that of other animals, andthey didn’t show the aneurysmal remodeling. There were significant differences in thelength of internal elastic lamina loss, length of thinned media and percent of mediathinning in aneurysmal remodeling among the three groups (P <0.001, P <0.001, P<0.001). No macrophage infiltration was found in the aneurysmal remodeling region of thebasilar terminus. Hemodynamic resulted in endothelial dysfunction, and vascularprotective factor (eNOS) secretion decreased, while iNOS secretion increased which hadvascular toxicity. eNOS mRNA and iNOS mRNA expression were significant differencesamong the three groups (P=0.003, P=0.019). Hemodynamics and cytokines led tovascular smooth muscle cell phenotypic modulation characterized by decreased expressionof SMC contractile genes and increased expression of pro-inflammatory,pro-matrix-remodeling genes. There was significant difference in the α-SMA mRNAexpression among the three groups (P <0.001). Synthetic smooth muscle cells couldsecrete MMPs, activate NF-κB, and increased TNF-α expression, which degradedextracellular matrix, damaged the vessel wall, thinned the wall, and bulged outward. Therewere significant difference in the NF-κB, TNF-α, MMPs expression among the threegroups (P <0.001, P <0.001, P <0.001).Conclusion: Modification of hemodynamics alone led to wall shear stress of thebasilar terminus increased, subsequently aneurysmal remodeling, which didn’t appear inthe basilar terminus of the lower wall shear stress. These aneurysmal remodeling was notcaused by inflammation of immunological cells. But hemodynamic resulted in endothelialdysfunction, and vascular protective factor (eNOS) secretion decreased, while iNOSsecretion increased. And vascular smooth muscle cell phenotypic modulation was initiated,proinflammatory cytokine was secreted largely and extracellular matrix was degradated.So aneurysmal remodeling involved a series of biomechanical reactions. Part twoVascular remodeling and its effect of the rabbitbasilar artery induced by hemodynamicsObjective: Vascular remodeling plays an important role in vascular disease. Thisstudy tried to survey pathological remodeling and its effect on basilar terminus followingbilateral common carotid artery ligation in New Zealand white rabbits.Methods: Eighteen adult New Zealand white rabbits were subjected to sham surgery(6animals), or bilateral common carotid artery ligation (6animals in1week after ligation,6animals in2weeks after ligation) to produce the basilar artery flow increase. Basilarartery flow velocity was monitored by transcranial Doppler before the operation,1day,1and2weeks after surgery. TOF MRA was performed and carried out three-dimensionalbefore the operation, and1,2weeks after ligation and hemodynamics was calculated.Cerebral angiography was performed1and2weeks after surgery. Diameter, bending angle,tortuosity index and wall shear stress were measured and analysed respectively. The basilarartery in the each group was removed1,2weeks after ligation, sectioned cross-sectionally,and stained with Masson, EVG and immunohistochemistry. HE staining was performed onthe longitudinal section of the basilar bifurcations whose wall shear stress was lower thanany others.Results: Subsequent to bilateral common carotid artery ligation, basilar artery flowvelocity increased obviously compared with the sham group at each predestinate time.Analysis of flow rate demonstrated significant differences between sham and experimentalgroups (P <0.001). Wall shear stress increased significantly from the vertebrobasilarjunction, and declined in the middle of the basilar artery, but was still higher than that inthe sham group. However, wall shear stress of the basilar artery in one rabbit in twoexperimental groups respectively was lower than that of other animals. A tortuosityappeared in the middle of the basilar artery in the experimental group, and outwardexpansion of the basilar artery and more obvious bending angle showed up2weeks afterligation. But the more obvious tortuosity is, the lower wall shear stress of the basilarterminus is. Cerebral angiography demonstrated the outward expansion and tortuosity ofthe basilar artery. There were statistically significant differences in the diameter, bendingangle and tortuosity index among sham group and experimental groups (P <0.001, P= 0.008, P <0.001). And the larger basilar artery diameter is, the lower wall shear stress is.Histological staining indicated that lumen dilation of the basilar artery in the experimentalgroup compared with that in the sham. And Internal elastic lamina was intact and jaggedfolds evenly distributed in the sham group, while jagged folds of the internal elastic laminawere stretched and flatten, and the part smooth muscle layer migrated into the internalelastic lamina in the experimental group. Smooth muscle layer was slight proliferation inthe experimental group compared with the sham group1week after operation, and thinner2weeks after operation. Aneurysmal remodeling didn’t appear in basilar terminus with HEstaining in16.7%(2/12) rabbits whose wall shear stress were lower in the middle of thebasilar artery. eNOS was all presented in the three groups and iNOS wasn’t presented inthe sham in immunohistochemical staining. The expression of eNOS and iNOS increasedin the experimental group, and the expression of MMP-2and MMP-9increased1weekafter ligation, but declined2weeks after operation.Conclusion: After bilateral common carotid artery ligation, flow velocity of thebasilar artery increased obviously, subsequently83.3%(10/12) wall shear stress increased,which resulted in pathological remodeling charactered by outward expansion and tortuosityin rabbit basilar artery.16.7%basilar artery dilated and curved significantly, thereby wallshear stress reduced and there weren’t aneurysmal remodeling in the basilar terminus. Andjagged folds of the internal elastic lamina were stretched and flatten and part of smoothmuscle layer migrated into the internal elastic lamina on histopathological staining in theexperimental group. NO signaling pathway and MMP-2, MMP-9involved in vascularremodeling of the basilar artery.