Expression of ectopic trypsin in atherosclerotic plaques and the effects of aprotinin on plaque stability

Our previous research revealed that trypsin is abundantly expressed in atherosclerotic plaques and its distribution overlaps with that of matrix metalloproteinase-9 (MMP-9). This study was performed to explore the possible roles of trypsin in vulnerable atherosclerotic plaque formation.

Twenty-four rabbits were randomly assigned to a normal (control) group, an atherosclerosis (experimental) group and a trypsin inhibitor (aprotinin) group. In the 13th feeding week, the aprotinin group was treated with 5 mg/kg/day aprotinin via ear vein for 4 weeks. At the end of the 16th week, coronary arterial and aortic expression of trypsin, proteinase-activated receptor-2 (PAR-2), activated MMP-9, and pro-inflammatory cytokines were significantly greater in the experimental group than in the control group. Aprotinin decreased trypsin expression and activation in plaques, blocked PAR-2 and MMP-9 activation, and decreased cytokine expression; it also increased fibrous cap thickness, decreased the intima-media thickness and intimal/medial ratio, thus significantly ameliorating plaque vulnerability. Upregulated trypsin, MMP-9 and PAR-2 were also found in coronary intimal atherosclerotic plaques of patients undergoing coronary artery bypass grafting.

Ectopic trypsin was significantly upregulated in atherosclerotic plaques, which increased pro-inflammatory cytokine levels by activating PAR-2 and promoted plaque instability by activating proMMP-9, thereby promoting atherosclerosis and plaque vulnerability. In addition, the high trypsin expression in human coronary intimal atherosclerotic plaques suggests that targeting trypsin may be a new strategy for acute coronary syndrome prevention.