Local upregulation of interleukin-1 beta in aortic dissecting aneurysm: correlation with matrix metalloproteinase-2, 9 expression and biomechanical decrease.

Our goal was to examine whether interleukin-1 beta (IL-1β) originates locally and its possible relationship with matrix metalloproteinases (MMPs), apoptosis, elastin fibres and biomechanics in aortic dissecting aneurysms (DAs). Aortic DAs were induced in 24 rats with β-aminopropionitrile (BAPN); another 12 rats without BAPN were designated as controls. Then IL-1β levels were measured both in the circulation and in local aortic specimens. The expression of MMP-2 and MMP-9 and Victoria blue and TUNEL staining were also detected. Biomechanical parameters such as the elasticity modulus were used to detect the biomechanical changes in the aortic wall. The correlation of IL-1β, MMP-2, MMP-9, apoptosis and biomechanical properties was analysed. Seventeen rats (17/24, 71%) in the BAPN-treated group died of DA rupture. IL-1β levels were dramatically increased in the DA specimens but not in the circulation. Victoria blue staining confirmed the formation of the DA and the reduction of elastin content after induction by BAPN. The extent of apoptosis in the aortic media was dramatically higher in rats with BAPN-induced DA than that in the control group and that in rats treated with BAPN but without DA. MMP-2 and MMP-9 levels were significantly increased in BAPN-treated rats compared to the controls, but no statistical significance was found between rats with and without DA. There were significant differences in biomechanical parameters, such as the elasticity modulus. Among the 3 groups, IL-1β was positively correlated with MMP-2 and MMP-9 levels and with the elasticity modulus but not with apoptosis. Local IL-1β might participate in the formation of aortic DA through the upregulation of MMP-2 and MMP-9 and the breakage of elastin fibres, which finally weakens the biomechanical properties of the aortic wall.