Doxazosin, an alpha-1 antagonist, prevents further progression of the advanced atherosclerotic lesion in hypercholesterolemic hamsters

Comparison of the cardiac electrophysiological effects between doxazosin and bunazosin

In Langendorff-perfused adult rat heart with constant pressure at 80 mmHg, we found doxazosin, an alpha(1) adrenoceptor blocker, at 10 muM prolonged PR interval and induced occasional arrhythmia followed by complete inhibition of the sinus rhythm, whereas bunazosin, another alpha(1)-blocker, at same concentration did not. The results of voltage-clamp study showed that, at the concentration of 10 muM, doxazosin inhibited I (Na), I ( (Ca,L) ), I (to), and Iss without changing I (k1) but bunazosin only inhibited I ( (Ca,L) ) about 30%. Doxazosin also caused markedly negative shift of the I (Na) inactivation curve. In current-clamp study, doxazosin prolonged action potential duration in association with the decreased action potential amplitude and upstroke velocity, whereas bunazosin did not. We hypothesize that doxazosin-induced arrhythmia may result from the heterogeneous or different level of I ( (Ca,L) ) blockade of AV nodal tissue. In conclusion, the present study suggests that bunazosin is safer than doxazosin for long-term treatment in view of electrophysiological effect. However, the underlying mechanism of doxazosin induced nodal arrhythmia is still needed to be determined.

Comparison of the cardiac effects between quinazoline-based alpha1-adrenoceptor antagonists on occlusion-reperfusion injury

Quinazoline-based compounds such as prazosin and its congeners including doxazosin, bunazosin, and terazosin are widely used as antihypertensive agents. However, there were many clinical observations showing that using these agents may result in higher risk of cardiovascular accidents in recent years. In this study, we compared the effects of four alpha-adrenoceptor antagonists: prazosin, doxazosin, bunazosin, and terazosin on occlusion-reperfusion injury. Langendorff-perfused rat hearts were pretreated with these four antagonists, and then the left main coronary artery was occluded. After 30 min occlusion, the hearts were reperfused for 2 h and the infarct sizes were measured. Two of the compounds studied, prazosin and doxazosin, apparently increased infarct size, CK-MB, and LDH activities after 2 h reperfusion. In contrast, bunazosin decreased infarct size and those biochemical indicators of cellular damage compared to control hearts. Although infarct size after reperfusion was differently changed by these four alpha-adrenoceptor antagonists, TUNEL-positive nuclei and caspase-3 protein expressions of all the groups were not significantly different. We supposed that the different effects of these four agents on infarct size came from the difference in necrosis rather than apoptosis.

ATP-Binding Cassette Transporter A1 Gene Transcription Is Downregulated by Activator Protein 2α

ATP-binding cassette transporter A1 (ABCA1) is a rate-limiting factor for high-density lipoprotein (HDL) biogenesis. The ABCA1 gene expression is known to be upregulated by various transcriptional factors. However, negative regulation factors would be better targets for pharmacological modulation of HDL biogenesis. Doxazosin, an α 1 -adrenoceptor blocker, increased ABCA1 mRNA, its protein, and apolipoprotein A-I–mediated HDL biogenesis in THP-1 macrophages and CHO-K1 cells, independent of α 1 -adrenoceptor blockade. Analysis of the human ABCA1 promoter indicated that the region between the positions −368 and −147 that contains an activator protein (AP)2-binding site responsible for the effects of doxazosin. Overexpression of AP2α inhibited ABCA1 transcription in a dose-dependent fashion. Mutation in the AP2-binding site caused increase of the basal promoter activity and canceling both the transactivation by doxazosin and the trans-repression by AP2α. Doxazosin had no effect on ABCA1 mRNA level in HepG2 cells, which lack endogenous AP2α, and it reversed the inhibitory effect of AP2α expression in this type of cells. Chromatin immunoprecipitation and gel shift assays revealed that doxazosin reduced specific binding of AP2α to the ABCA1 promoter, as it suppressed phosphorylation of AP2α. Finally, doxazosin increased ABCA1 expression and plasma HDL in mice. We thus concluded that AP2α negatively regulates the ABCA1 gene transcription. Doxazosin inhibits AP2α activity independent of α 1 -adrenoceptor blockade and increases the ABCA1 expression and HDL biogenesis. AP2α is a potent pharmacological target for the increase of HDL.