Background: The alpha1-adrenoceptor-blocking antihypertensive doxazosin has been associated with increased risk of heart failure and is known to induce prostate cell apoptosis. We hypothesized that it might also induce apoptosis in cardiomyocytes.
Methods and results: Hoechst dye vital staining and flow cytometry provided evidence that doxazosin induced apoptosis time- and dose-dependently in cardiomyocytes of the HL-1 cell line. TUNEL assays and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) viability test confirmed that doxazosin induced DNA damage and cell death in these cells. MTT tests showed that doxazosin treatment decreased cell viability in primary cultures of neonatal rat cardiomyocytes, and Hoechst dye vital staining demonstrated doxazosin-induced apoptosis in primary cultures of human adult cardiomyocytes. The proapoptotic effect of doxazosin on cardiomyocytes seems not to depend on alpha1 blockade, because it was not modified by cotreatment with alpha- or beta-adrenergic agonists or with the irreversible alpha1-blocker phenoxybenzamine and because doxazosin also decreased the viability of NIH 3T3 cells, which lack alpha1-adrenoceptors. It also does not involve calcineurin, being unaffected by the presence of the calcineurin inhibitors cyclosporin A and FK506. Three other alpha1-blockers were also investigated; prazosin was proapoptotic, like doxazosin, but 5-methylurapidil and terazosin were not.
Conclusions: The alpha1-blockers doxazosin and prazosin induce the apoptosis of cardiomyocytes cultured in vitro by a mechanism that is independent of alpha1 blockade and calcineurin.