MMP9 and medical procedure: To sum up, exogenous CO liberated from CORM-2 has protective activities against PM-induced aorta inflammation through the inhibition of the TLR2 and TLR4/NADPH oxidase/ROS/IL-6 signaling pathway, thereby reducing the expression of ICAM-1 and VCAM-1 as well as MMP-2 and MMP-9 that was followed by monocyte adherence and aortic smooth muscle cell migration.