Nitrate tolerance in angina pectoris

Oxidative stress impairs vasorelaxation induced by the soluble guanylyl cyclase activator BAY 41-2272 in spontaneously hypertensive rats

BACKGROUND

BAY 41-2272 (5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine) relaxes mesenteric arteries (MA) in a synergistic fashion with nitric oxide (NO). We hypothesized that the relaxation to BAY 41-2272 is decreased in spontaneously hypertensive rats (SHR) because of the reduced NO bioavailability in this strain and that relaxation would be improved by inhibiting the oxidative stress. We aimed to evaluate the influence of oxidative stress in BAY 41-2272-induced vasorelaxation in isolated MA from SHR.

METHODS

MA function was evaluated by concentration-response curves to BAY 41-2272. We measured protein expression of endothelial NO synthase (eNOS), soluble guanylyl cyclase (sGC) and human-antigen R (HuR) (sGC mRNA-stabilizing protein), sGC activity and plasma levels of superoxide dismutase (SOD), and total antioxidant status (TAS).

RESULTS

Cyclic guanosine monophosphate (cGMP)-dependent and -independent relaxation induced by BAY 41-2272 (0.0001-1 micromol/l) was impaired in SHR compared with Wistar-Kyoto (WKY). We observed reduced expression of eNOS, sGC and HuR, and decreased sGC activity in SHR. Plasma levels of SOD and TAS were also diminished in SHR. Incubation with SOD or indomethacin increased relaxation to BAY 41-2272 in SHR. Furthermore, acetylcholine (ACh)-induced relaxation was increased in the presence of BAY 41-2272 or SOD, apocynin, or indomethacin.

CONCLUSION

Augmented oxidative stress in SHR impaired cGMP-dependent and -independent relaxation induced by BAY 41-2272, by decreasing NO bioavailability and sGC expression and by increasing contractile activity. Inhibiton of oxidative stress improved the relaxation of BAY 41-2272 in SHR. BAY 41-2272 might be an alternative therapeutic tool for hypertension if administrated with antioxidant compounds.

Vasorelaxing effect of BAY 41-2272 in rat basilar artery: involvement of cGMP-dependent and independent mechanisms

Decreases in intrinsic NO cause cerebral vasospasms because of the dysregulation of cGMP formation by NO-mediated pathways. Because 5-cyclopropyl-2-{1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl}pyrimidin-4-ylamine (BAY 41-2272) is a potent soluble guanylyl cyclase (sGC) stimulator in an NO-independent manner, this study aimed to investigate the mechanisms underlying the relaxant effects of BAY 41-2272 in the rat basilar artery. BAY 41-2272 (0.0001 to 1 micromol/L) induced relaxations in a concentration-dependent manner, with pEC50 values of 8.13+/-0.03 and 7.63+/-0.05 in intact and denuded rings, respectively. The sGC inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one (ODQ) markedly displaced the curve for BAY 41-2272 to the right in intact or denuded rings (&10-fold). The NO synthesis inhibitor NG-nitro-L-arginine methyl ester caused a rightward shift in the curve for BAY 41-2272 (4-fold), whereas the phosphodiesterase type 5 inhibitor sildenafil enhanced BAY 41-2272-induced relaxations (3- to 4-fold). The Na+-K+-ATPase inhibitor ouabain caused 3-fold rightward shifts in the curves for BAY 41-2272. Ca2+-induced contractions in K+ depolarized rings were significantly attenuated by BAY 41-2272 in an ODQ-insensitive manner. The NO donor glyceryl trinitrate and BAY 41-2272 caused rightward shifts in the contractile responses to serotonin. Their coincubation caused a synergistic inhibition of serotonin-induced contractions. BAY 41-2272 and glyceryl trinitrate increased cGMP levels (but not cAMP) by 10-fold and 4-fold above baseline, respectively, in an ODQ-sensitive manner. cGMP levels increased by 50-fold after coincubation. BAY 41-2272 potently relaxes the rat basilar artery in a synergistic fashion with NO. Targeting the sGC with selective activators, such as BAY 41-2272, may represent a new therapy to treat cerebrovascular disease.

Molecular Mechanisms Underlying Rat Mesenteric Artery Vasorelaxation Induced by the Nitric Oxide-Independent Soluble Guanylyl Cyclase Stimulators BAY 41-2272 [5-Cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]pyrimidin-4-ylamine] and YC-1 [3-(5′-Hydroxymethyl-2′-furyl)-1-benzyl Indazole]

The aim of this study was to investigate the mechanisms of relaxation to the nitric oxide (NO)-independent soluble guanylyl cyclase (sGC) stimulators 5-cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]pyrimidin-4-ylamine (BAY 41-2272) and 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) in the rat mesenteric artery. In endothelium-intact rings, BAY 41-2272 (0.0001-1 microM) and YC-1 (0.001-30 microM) caused concentration-dependent relaxations (pEC(50) values of 8.21 +/- 0.05 and 6.75 +/- 0.06, respectively), which were shifted to the right by 6-fold in denuded rings. The sGC inhibitor H-[1,2,4]oxadiazolo [4,3,-a]quinoxalin-1-one (ODQ) (10 microM) partially attenuated the maximal responses to BAY 41-2272 and YC-1 and displaced their curves to the right by 9- to 10-fold in intact and 3-fold in denuded vessels. The NO synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (100 microM) and the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (100 microM) reduced BAY 41-2272 and YC-1 relaxations, whereas the phosphodiesterase type 5 inhibitor sildenafil (0.1 microM) potentiated these responses. The phosphatase inhibitor calyculin A (50 nM) reduced the relaxant responses, and high concentrations of BAY 41-2272 (1 micorM) and YC-1 (10 microM) inhibited Ca(2+)-induced contractions in K(+)-depolarized rings. BAY 41-2272 (0.1 microM) and YC-1 (1 microM) markedly elevated cGMP levels in an ODQ-sensitive manner. Coincubation of BAY 41-2272 or YC-1 with a NO donor resulted in a synergistic inhibition of phenylephrine-induced contractions paralleled by marked increases in cGMP levels. In conclusion, BAY 41-2272 and YC-1 relax the mesenteric artery through cGMP-dependent and -independent mechanisms, including blockade of Ca(2+) influx. The synergistic responses probably reflect the direct effects of NO and NO-independent sGC stimulators on the enzyme, thus representing a potential therapeutic effect by permitting reductions of nitrovasodilator dose.

BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyrimidin-4-ylamine]-induced dilation in ovine pulmonary artery: role of sodium pump

The mechanisms of relaxation to nitric oxide (NO)-independent soluble guanylyl cyclase (sGC) activator BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyrimidin-4-ylamine] were investigated in isolated ovine pulmonary artery. BAY 41-2272 (1 nM-10 microM) produced concentration-dependent relaxation of endothelium-denuded pulmonary artery rings (pD2 = 6.82 +/- 0.16; Emax = 92.30 +/- 2.31%; n = 8), precontracted with 1 microM 5-hydroxytryptamine (serotonin). 1-H-[1,2,4]Oxadiazole[4,3-a]quinoxalin-1-one (ODQ; 10 microM), an inhibitor of sGC, partially inhibited (Emax = 57.10 +/- 3.10%; n = 6) the relaxation response of BAY 41-2272. In comparison with ODQ, sodium pump inhibitor ouabain (1 microM) produced a greater decrease in the vasodilator response of BAY 41-2272 (Emax = 20.17 +/- 4.55%; n = 6). K+-free solution also attenuated (Emax = 39.97 +/- 3.52%; n = 6) BAY 41-2272-induced relaxation. ODQ (10 microM) plus 1 microM ouabain abolished the relaxant response of BAY 41-2272 (Emax = 12.09 +/- 3.76%, n = 6 versus vehicle control dimethyl sulfoxide; Emax = 15.83 +/- 1.72%, n = 6). KT-5823 [1-oxo-9.12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-I][1,6]benzodiazocine-10-carboxylic acid methyl ester (2 microM), a specific inhibitor of protein kinase G had no effect on 10 microM ODQ-insensitive relaxation evoked by BAY 41-2272. BAY 41-2272 (10 microM) inhibited Ca2+-induced contractions in K+-depolarized preparations. BAY 41-2272 (10 microM) caused about a 14-fold increase in the intracellular cGMP over the basal level, which was completely inhibited by 10 microM ODQ. BAY 41-2272 (0.1, 1.0, and 10 microM) significantly (P < 0.05) increased ouabain-sensitive 86Rb uptake in a concentration-dependent manner. BAY 41-2272 (10 microM) also stimulated sarcolemmal Na+-K+-ATPase activity. However, 10 microM ODQ had no significant effect on either basal or BAY 41-2272-stimulated 86Rb uptake/Na+-K+-ATPase activities. In conclusion, this study provides the first evidence of sodium pump stimulation by BAY 41-2272 independent of cGMP as an additional mechanism to sGC activation in relaxation of ovine pulmonary artery.

Reasons for overprescription of mononitrates: the paradigm of stable angina pectoris treatment

BACKGROUND

Oral nitrates, beta-blockers, and calcium channel blockers are used to treat stable angina pectoris (SAP). The 2 therapeutic subtypes of oral nitrates are mononitrates and dinitrates, with no evidence that 1 subtype is more efficacious than the other. Although practice guidelines in Great Britain and Israel recommend dinitrates as the first-line drug for SAP, in practice, many physicians in those 2 countries prescribe mononitrates.

OBJECTIVE

The aim of this study was to identify factors that influence specialist physicians (family practitioners, internists, and cardiologists) in Israel when prescribing nitrates for the prevention of SAP symptoms.

METHODS

A group of specialists was given a self-administered questionnaire regarding their treatment of choice for a patient with SAP described in a hypothetical case vignette. End points for prescribing preferences were evidence-based information, cost, and the influence of pharmaceutical company representatives.

RESULTS

One hundred ten specialists were given the questionnaire. Eighty-nine specialists (45 men, 44 women; mean age, 50.4 years; range, 34-67 years; response rate, 80.9%) completed it (39 family practitioners, 29 internists, and 21 cardiologists). Seventy-eight respondents (87.6%) chose to prescribe nitrates for the case vignette, and among those, 54 (69.2%) chose mononitrates and 24 (30.8%) chose dinitrates (P = 0.034). The choice of mononitrates over dinitrates was mainly affected by habit (25/54 [46.3%]) and the belief that mononitrates are more effective, safer, and/or less expensive than dinitrates (21/54 [38.9%]). Drug costs for the patient significantly influenced more family practitioners than hospital specialists (P<0.05).

CONCLUSIONS

In contrast to guideline recommendations, the paradigm of SAP treatment with nitrates in this study was characterized by significantly more prescriptions for mononitrates than dinitrates. This situation contributes to the erosion of the scarce resources of the health care system in Israel. Further efforts are needed to increase physicians' awareness of quality, cost, and choices when prescribing drugs.

Nitroglycerin inhibits the development of morphine tolerance and dependence in rats

The development of tolerance to and physical dependence on opioids remains a significant barrier to their clinical use. N-Methyl-D-aspartate (NMDA) receptor antagonists inhibit tolerance and dependence. However, many NMDA antagonists have undesirable side effects. It has been shown that nitroglycerin (NTG) can antagonize NMDA receptor activity. This study was designed to determine whether NTG could inhibit the development of morphine tolerance and dependence. Rats were anesthetized and implanted with either morphine or placebo pellets, and pumps infusing vehicle or NTG (doses from 0.1 microg/kg/day to 10 mg/kg/day). Tolerance development was assessed by tail-flick latency (TFL). After 6 days, withdrawal was precipitated by subcutaneous injection of 2 mg/kg naloxone. Withdrawal signs were observed for 15 min. Placebo-pelleted rats showed no changes in TFL over the course of the study and no withdrawal signs. Morphine-pelleted rats developed tolerance. The 0.1 mg/kg/day NTG dose significantly attenuated tolerance development, while the other doses had no significant effect. The 0.1 mg/kg/day dose also attenuated some withdrawal signs. Higher or lower doses were not effective, possibly because of competing biochemical effects.

Cardiovascular actions of a novel NO-independent guanylyl cyclase stimulator, BAY 41-8543: in vivo studies

BAY 41-8543 is a novel non-NO-based stimulator of sGC. This study investigates the acute effects of BAY 41-8543 on haemodynamics in anaesthetized rats and dogs, its long-term effects in conscious hypertension rat models and its antiplatelet effects. In anaesthetized dogs, intravenous injections of BAY 41-8543 (3 - 100 microg kg(-1)) caused a dose-dependent decrease in blood pressure and cardiac oxygen consumption as well as an increase in coronary blood flow and heart rate. In anaesthetized normotensive rats, BAY 41-8543 produced a dose-dependent and long-lasting blood pressure lowering effect after intravenous (3 - 300 microg kg(-1)) and oral (0.1 - 1 mg kg(-1)) administration. A dose-dependent and long-lasting decrease in blood pressure was also observed in conscious spontaneously hypertensive rats with a threshold dose of 0.1 mg kg(-1) p.o. After 3 mg kg(-1) the antihypertensive effect lasted for nearly 24 h. After multiple dosages, BAY 41-8543 did not develop tachyphylaxis in SHR. BAY 41-8543 prolonged the rat tail bleeding time and reduced thrombosis in the FeCl(3) thrombosis model after oral administration. In a low NO, high renin rat model of hypertension, BAY 41-8543 prevented the increase in blood pressure evoked by L-NAME and reveals a kidney protective effect. In this model, the overall beneficial effects of BAY 41-8543 manifested as both antiplatelet effect and vasodilatation were reflected in a significant reduction in mortality. The pharmacological profile of BAY 41-8543 suggests therefore that this compound has the potential to be an important research tool for in vivo investigations in the sGC/cGMP field and it also has the potential of being a unique clinical utility for treatment of cardiovascular diseases.

Pharmacological actions of a novel NO-independent guanylyl cyclase stimulator, BAY 41-8543: in vitro studies

BAY 41-8543 is a novel, highly specific and so far the most potent NO-independent stimulator of sGC. Here we report the effects of BAY 41-8543 on the isolated enzyme, endothelial cells, platelets, isolated vessels and Langendorff heart preparation. BAY 41-8543 stimulates the recombinant sGC concentration-dependently from 0.0001 microM to 100 microM up to 92-fold. In combination, BAY 41-8543 and NO have synergistic effects over a wide range of concentrations. Similar results are shown in implying that BAY 41-8543 stimulates the sGC directly and furthermore makes the enzyme more sensitive to its endogenous activator NO. In vitro, BAY 41-8543 is a potent relaxing agent of aortas, saphenous arteries, coronary arteries and veins with IC(50)-values in the nM range. In the rat heart Langendorff preparation, BAY 41-8543 potently reduces coronary perfusion pressure from 10(-9) to 10(-6) g ml(-1) without any effect on left ventricular pressure and heart rate. BAY 41-8543 is effective even under nitrate tolerance conditions proved by the same vasorelaxing effect on aortic rings taken either from normal or nitrate-tolerant rats. BAY 41-8543 is a potent inhibitor of collagen-mediated aggregation in washed human platelets (IC(50)=0.09 microM). In plasma, BAY 41-8543 inhibits collagen-mediated aggregation better than ADP-induced aggregation, but has no effect on the thrombin pathway. BAY 41-8543 is also a potent direct stimulator of the cyclic GMP/PKG/VASP pathway in platelets and synergizes with NO over a wide range of concentrations. These results suggest that BAY 41-8543 is on the one hand an invaluable tool for studying sGC signaling in vitro and on the other hand its unique profile may offer a novel approach for treating cardiovascular diseases.

[Nicorandil: acute hemodynamic effects of 2 different oral doses of a potassium channel opener in patients with coronary heart disease]

BACKGROUND

In medical treatment of angina pectoris the 3 major groups of antianginal agents are nitrates, beta blockers and calcium antagonists. Now a new class of drugs is introduced in the therapy: the potassium channel openers. One of the first potassium channel openers is nicorandil. We examined the acute hemodynamic effects of 2 different oral nicorandil doses in patients with coronary heart disease.

PATIENTS AND METHODS

Twenty patients with angiographic proven coronary heart disease and stable angina pectoris were treated with a dose of 2 x 10 mg Nicorandil on day 1 and 2 x 20 mg Nicorandil on day 2, while being hemodynamically monitored on an intensive care unit with a pulmonary artery catheter.

RESULTS

Through the hemodynamic monitoring a dose dependent, significant reduction of systolic blood pressure was found (6%/9%), while the heart rate increased dose dependently (6%/11%). The rate pressure product as a marker of myocardial oxygen demand did not increase significantly.

CONCLUSION

The oral application of nicorandil causes an acute, dose dependent, significant decrease in systolic blood pressure and induces a reflextachycardia.

KATP channel activation mediates nicorandil-induced relaxation of nitrate-tolerant coronary arteries

We compared the tolerance-inducing effects of nitroglycerin (NTG) and nicorandil (NIC) in porcine isolated coronary arteries and assessed the role of KATP channels in the response to NIC in nitrate-tolerant and nontolerant preparations. In coronary arteries contracted with U46619 (1-3 x 10(-9) M), NTG, NIC, sodium nitroprusside (SNP), and cromakalim produced concentration-dependent relaxations. The rank order of potency was NTG > or = SNP > cromakalim > nicorandil. Exposure of the rings to NTG (10(-4) M) for 90 min, followed by repeated rinsing for 1 h, produced a parallel, rightward shift of the subsequent concentration-response curves to NTG and SNP; a slight but significant reduction in the maximal response to NTG was also observed. Previous exposure to NTG had no effect on the NIC or cromakalim concentration-response curves. When the tissues were exposed to NIC (3 x 10(-4) M) for 90 min, followed by repeated rinsing for 1 h, there was no effect on the subsequent concentration-response curves to NTG, NIC, SNP, or cromakalim. In both nitrate-tolerant and nontolerant coronary arteries, glibenclamide (GLI 10(-6) M), a selective KATP channel blocker, caused a parallel rightward shift in the concentration-response curve to cromakalim, but had no effect on responses to NTG or SNP. In nontolerant coronary arteries, GLI had no effect on NIC-induced relaxation, but in nitrate-tolerant preparations, GLI produced a significant rightward shift in the NIC concentration-response curve. The results demonstrate that prolonged exposure to NTG, but not NIC, causes tolerance in isolated porcine coronary arteries and that the response to NIC is not affected by nitrate tolerance. The data also suggest that NIC-induced relaxation of nitratetolerant, but not nontolerant, coronary arteries is mediated by activation of KATP channels.

Evidence for a role of endothelin 1 and protein kinase C in nitroglycerin tolerance

We sought to examine mechanisms responsible for increased vasoconstriction that occurs during development of nitroglycerin tolerance. Rabbits were treated for 3 days with nitroglycerin patches (0.4 mg/hr), and their aortic segments were studied in organ chambers. This treatment resulted in attenuated in vitro relaxations to nitroglycerin and increased contractile sensitivity to angiotensin II, serotonin, phenylephrine, KCl, and a direct activator of protein kinase C, the phorbol ester phorbol 12,13-dibutyrate. The protein kinase C antagonists calphostin C (100 nM) and staurosporine (10 nM) corrected the hypersensitivity to constrictors in tolerant vessels, yet had minimal effects on constrictions in control vessels. Paradoxically, constrictions caused by endothelin 1 were decreased in nitrate-tolerant vessels. Immunocytochemical analysis revealed intense endothelin 1-like and big endothelin 1-like immunoreactivity in the media of nitroglycerin-tolerant but not of control aortas. The enhanced vasoconstriction to angiotensin II, serotonin, KCl, and phenylephrine could be mimicked in normal vessels by addition of subthreshold concentrations of endothelin 1, and this effect was prevented by calphostin C. We propose that increased autocrine production of endothelin 1 in nitrate tolerance sensitizes vascular smooth muscle to a variety of vasoconstrictors through a protein kinase C-mediated mechanism.

Compliance as a factor in the development of nitrate tolerance: a patient investigation

Telephone interviews were conducted to establish the prescribing instructions given by experienced physicians to patients with angina pectoris treated with long-acting nitrates. In addition, the times of day when doses were taken were recorded. The aim of the study was to determine whether or not an asymmetric dosing regimen was being followed by the patients. The majority (62.7%) of patients were being treated with 5-isosorbide mononitrate taken orally twice daily. All but two took the correct number of tablets, but more than 50% of these patients were not taking the second tablet at the correct time to achieve the recommended 6-8-h period during which the plasma nitrate concentration was sufficiently low to avoid nitrate tolerance. Possible explanations for the incorrect use of the prescribed drug may be that the patients did not understand the physician's instructions and did not appreciate the importance of rigidly adhering to these instructions. A more satisfactory approach, with improved patient compliance, may be a once-daily dosing regimen.