Anti-NO action of carvedilol in cell-free system and in vascular endothelial cells

1. Carvedilol, an adrenoceptor blocker with antioxidant activity, was studied for its ability to interact with NO in a cell-free condition and in an endothelial cell line (ECV304). 2. In a cell-free system, carvedilol attenuated NO-dependent reduction of carboxy-2-phenyl-4,4, 5,5-tetramethyl-imidazoline-1-oxyl-3-oxide induced by a NO donor, 1-hydroxy-2-oxo-3-(aminopropyl)-3-isopropyl-1-triazene (NOC5), which was determined by electron paramagnetic resonance (EPR) spectrometry. The EPR study also showed that nitrosylhaemoglobin formation in rat red blood cells by the addition of NO-saturated solution was attenuated by prior incubation with 0.1 - 10 microM carvedilol. 3. NO-induced fluorescence in 4,5-diaminofluorescein-2 diacethyl (DAF-2DA)-loaded ECV304 cells was attenuated by carvedilol but not by labetalol. The IC(50) of carvedilol for NOC5 or sodium nitroprusside-induced fluorescence of DAF-2DA in ECV304 cells was 1. 0x10(-7) M, which was similar to the reported IC(50) of carvedilol for the antioxidant effect. 4. Cell toxicity induced by a NO donor determined by the number of viable cells after 24 h treatment with 2-2'(hydroxynitrosohydrazino)bis-ethanamine was significantly attenuated by pretreatment with 1 microM carvedilol. 5. Both free and cell-associated carvedilol quenched NO. Because NO mediates both physiological and pathophysiological processes, NO quenching by the drug may have diverse clinical implications depending upon specific functions of local NO in tissues where carvedilol is distributed.