Some effects of nipradilol, a beta-antagonist possessing a nitroxy group, on smooth muscle of the pig coronary artery

Effects of beta-adrenergic receptor antagonists on oxidative stress in purified rat retinal ganglion cells

PURPOSE

To investigate the effect of beta-adrenergic receptor antagonists against oxidative stress on purified rat retinal ganglion cells (RGCs), timolol, betaxolol, carteolol and nipradilol were included in the present study.

METHODS

RGCs were purified using a 2 step panning procedure from postnatal days 6-8 using Wistar rats. After 72 h in culture under normal condition, RGCs were exposed to oxidative stress induced by B27 medium without anti-oxidant. To verify whether this stress is apoptotic or necrotic, Annexin V and propidium iodide were used to detect apoptotic and necrotic cells after 2 h stress. The presence of a proinhibitor for intracellular cathepsin B, and an inhibitor for thiol protease (cathepsin B/H/L, calpain), was also assessed to verify necrotic cell death event in oxidative conditions. Next, RGC cultures under oxidative stress were incubated with timolol, betaxolol, carteolol, and nipradilol added, respectively, for 24 h culture. The RGC viability in each condition normalized to that under normal condition was evaluated as live cell percentage based on total experiments of 8-15.

RESULTS

Two h after oxidative stress, Annexin V and propidium iodide positive cells increased. Increased cell death under oxidative stress was significantly reduced by inhibitors for cathepsin or calpain. These data suggest that increased cell death under the current oxidative stress was due to necrosis. Under oxidative stress for 24 h, RGC viability reduced to 52.5-60.2% as compared with normal. With 10 nM and 100 nM timolol, live cell significantly increased to 69.3% and 75.5%, respectively. Both betaxolol and nipradilol enhanced live RGCs significantly in concentration of 100 nM and 1 microM, with viability of 70.5%, 71.6%, and 70.4%, 74.7%, respectively. While with 10 nM, 100 nM and 1 microM addition of carteolol, there was no significant increase in live RGC percentage which ranged from 53.1-55.0%.

CONCLUSIONS

Timolol, betaxolol and nipradilol, but not carteolol, showed neuroprotective effects against oxidative stress induced by B27 without antioxidant on purified rat RGCs at concentrations of 10 nM or higher. Although the neuroprotective mechanism of beta-blockers for oxidative stress is still unknown, this additive effect may deserve future studies.

Nipradilol inhibits atmospheric pressure-induced cell proliferation in human aortic smooth muscle cells

Hypertension is a major risk factor for atherosclerosis and the genesis of cardiovascular and cerebrovascular diseases. Therefore, the protection of atherosclerosis progression is one of the purpose of an anti-hypertensive treatment in vascular system. Nitric oxide (NO)-releasing drugs have been reported to have an inhibitory effect on shear stress-induced extracellular signal-regulated kinase (ERK) activation in endothelial cells. For further understanding of the effects of these drugs, the present study focused on the effects on intracellular signal transduction and cell proliferation in cultured human aortic smooth muscle cells (HASMC) under high atmospheric pressure. Three hours of 160-mmHg atmospheric pressure resulted in an approximately 380% increase in cell proliferation compared to non-pressurized controls. Nipradilol (3,4-dihydro-8-(2-hydroxy-3-isopropylaminoproxy)-3-nitroxy-2H-1-benzopyran) (10(-6)M) demonstrated approximately 40% reduction in cell proliferation compared to that shown by pressurized HASMC as a vehicle control. Three hours of 160-mmHg atmospheric pressure resulted in a 25% increase in the amount of activated ERKs. Nipradilol (10(-6)M) demonstrated approximately a 26% reduction in the amount of activated ERKs. NO(x) concentration under the presence of nipradilol (10microM) with HASMC resulted in a 7.2microM of NO production and was 2.4-fold more than that from no dug control (3.0microM). An administration of L-NAME (10(-4)M) supplemented with Nipradilol (10(-6)M) did not show any significant effect on cell proliferation. From these observations, we concluded that nipradilol has an anti-proliferative effect on HASMC under high atmospheric pressure. Nipradilol may act as a nitric oxide inducer from HASMC and suspected to work as a supplement to mitigate the impaired endothelial cell function caused by hypertension.

Mechanism of an inhibitory effect of nipradilol on rat vascular smooth muscle cell growth

The aim of this study was to clarify the mechanism of an inhibitory effect of nipradilol on cultured rat vascular smooth muscle cell (VSMC) growth. After being starved, cultured VSMCs were stimulated by 5% fetal bovine serum with various concentrations of nipradilol. Nipradilol dose-dependently decreased the values of [(3)H]-thymidine incorporation, cell numbers and total cellular protein content, and the levels of phosphorylated extracellular signal-regulated protein kinase 1/2 and p38. It also suppressed the level of proliferative cell nuclear antigen in a dose-dependent manner. In contrast, nipradilol did not change the level of the phosphorylated value of c-jun NH(2)-terminal protein kinase or cytoplasmic histone-associated DNA fragments in VSMCs. These results indicate that nipradilol suppresses cell growth without apoptosis in rat VSMCs, suggesting that it could be effective for preventing the progression of restenosis after angioplasty.

Nipradilol induces vasodilation of canine isolated posterior ciliary artery via stimulation of the guanylyl cyclase-cGMP pathway

We examined the effect of nipradilol on contraction of the posterior ciliary artery induced by high potassium or norepinephrine and on cyclic GMP (cGMP) levels in the posterior ciliary artery of dogs. Nipradilol caused dose-dependent relaxation of KCl-and norepinephrine-induced contractions of posterior ciliary artery. The relaxant effect of nipradilol on norepinephrine-contracted ciliary artery was significantly greater than that on KCl-contracted ciliary artery. In KCl-contracted ciliary artery, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME, 10(-4) M) did not alter the relaxant effect of nipradilol, whereas 1H-1,2,4-oxadiazolo-4,3-a-quinoxalin-1-one (ODQ, 10(-6) M) significantly inhibited this effect. Ethacrynic acid at 10(-5) M, sulfasalazine at 10(-4) M and S-decylglutathione at 10(-4) M (glutathione S-transferase inhibitors) did not inhibit the relaxant effect of nipradilol. In addition, nipradilol produced dose-dependent increases in cGMP levels in the canine posterior ciliary artery. These findings indicate that nipradilol-induced vasorelaxation in the canine posterior ciliary artery occurs via stimulation of the guanylyl cyclase-cGMP pathway.

Interactions of sildenafil with various coronary vasodilators in isolated porcine coronary artery

There are reports of serious hypotension or circulatory shock when sildenafil citrate, a selective cyclic nucleotide phosphodiesterase type 5 inhibitor, which was developed for the treatment of erectile dysfunction, is given to patients taking certain coronary vasodilators. We thus examined the interaction of sildenafil with various coronary vasodilators including nitric oxide (NO) donors in isolated porcine coronary artery. Sildenafil caused concentration-dependent relaxations of the artery precontracted with U46619 (9,11-dideoxy-9 alpha,11 alpha-methanoepoxy-prostaglandin F(2alpha)). Incubation with the NO synthase inhibitor NG-nitro-L-arginine or the soluble guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one) significantly shifted the concentration-response curve for sildenafil to the right without affecting the maximum response, indicating that some part of the relaxant response to sildenafil may be the result of the inhibition of phosphodiestrase type 5-induced degradation of cyclic GMP (cGMP) that is produced through guanylate cyclase activation by NO released spontaneously. The relaxant effects of the vasodilators with an NO donor property, isosorbide dinitrate, sodium nitroprusside, nicorandil and nipradilol, were significantly enhanced by sildenafil, as shown by a significant leftward shift of their concentration-response curves. In contrast, the relaxant responses to the drugs without a property as an NO donor, diltiazem, celiprolol and pinacidil, were not affected by sildenafil. The cGMP level of the tissue was elevated after adding sildenafil, and the cGMP-generating effect of a combination of sildenafil and sodium nitroprusside was higher than that of each drug alone. The cyclic AMP level determined simultaneously was not changed by sildenafil. These results suggest that sildenafil potentiates specifically the relaxant responses of porcine coronary artery to the drugs which behave as an NO donor, providing basic evidence that the benefit of sildenafil in the treatment of erectile dysfunction can be limited by a risk of marked vasodilation when used together with NO-related coronary vasodilators.

beta-Adrenoceptor blocking activities of nipradilol and its optical isomers in pig coronary artery

1. beta-Adrenoceptor blocking activities of nipradilol, its four optical isomers (RR, RS, SR, SS) and denitro nipradilol were evaluated using pig isolated coronary arteries. 2. (-)-Isoprenaline produced concentration-dependent relaxations of the arteries, which were antagonized by nipradilol, its four optical isomers or denitro nipradilol under KCl-induced contracture. 3. The order of pA2 values for beta-adrenoceptor blocking activities was SR > nipradilol > SS > or = denitro nipradilol > RR > RS. 4. The nitroxy group in nipradilol appears to enhance its beta-adrenoceptor blocking activity, because the beta-adrenoceptor blocking activity of nipradilol was more potent than that of denitro nipradilol. 5. Isomers that have the S configuration (SR, SS) at the 2' position (having a hydroxyl group) in the aryloxypropanolamine showed more potent beta-adrenoceptor blocking activity than isomers that have the R configuration (RR, RS). 6. Isomers that have the R configuration (SR, RR) at the 3 position (having a nitroxy group) in the benzopyran ring showed more potent beta-adrenoceptor blocking activity than those with the S configuration (SS, RS). 7. It is suggested that the difference in configuration of the chemical structure of nipradilol may result in variations of binding affinity for the beta-adrenoceptor.