Abstract 308: Chronic Aspirin Treatment Possibly Poses a Risk to Ischemic Heart via Impairment of Cardiac Proteasome Functions

Background: Impaired cardiac proteasome (CP) has been reported in ischemia and heart failure. Recent data highlighted aspirin as an inhibitor of the ubiquitin-proteasome system, however, it’s unclear whether it affects CP functions. Objective: We investigated the influence of aspirin on CP in the rat model of myocardial infarction (MI). Methods and Results: MI, sham or normal male SD rats were injected intraperitoneally with high (300mg/kg), low (5mg/kg) aspirin or saline (control) once a day for seven weeks. Parallel experiments were performed in the hypoxia/reoxygenated cell model of primary human ventricular myocytes incubated with different concentrations of aspirin. Myocardial hypertrophy, cardiac function, cell viability and the functions of 26S, 20S and 19S, including the β1, β2 and β5 subunits of 20S were determined. The activity of 26S, 20S and 19S declined by about 30%, and β5, β2 and β1 by 40%, 20% and 30%, respectively, in the MI rats compared with the non-MI rats ( P <0.05). Compared with the saline-treated MI rats, 26S and 20S in high or low dose aspirin-treated MI rats further decreased by 30% and 20%, and β5 further decreased by 30% and 12%, and β1 by 40% and 30%, respectively, and their lost activity was correlated with compromised cardiac function in the MI rats. The dose-related and selective inhibition of β5 and β1 by aspirin was comparable to their protein expressions in the MI rats and in the cultured cells. However, the CP in the normal settings, or 19S and β2 in all the groups of animals or cultured cells were less affected by aspirin treatment. The impaired CP, dose-dependently enhanced by aspirin, led to the elevation of oxidative and ubiquitinated proteins in the MI rat hearts or in the hypoxia/reoxygenated cells. These aberrant proteins in turn constituted the ultimate causal factor for the cardiac dysfunction and the loss of cell viability. In vitro experiments confirmed that the purified CP from the MI rats or hypoxic cells, but was more susceptible to aspirin treatment, whereas the complexes in the normal settings appeared less affected by aspirin. Conclusions: Chronic aspirin treatment, via the dose-dependent and selective inhibition of CP, enhanced the ischemic CP dysfunction, which constitutes a potential risk factor for the ischemic heart.