The new organic nitrate 2-nitrate-1,3-diocthanoxypropan (NDOP) induces nitric oxide production and vasorelaxation via activation of inward-rectifier potassium channels (KIR).

INTRODUCTION: Cardiovascular diseases are coupled to decreased nitric oxide (NO) bioavailability, and there is a constant search for novel and better NO-donors. Here we synthesized and characterized the cardiovascular effects of the new organic nitrate 2-nitrate-1,3-dioctanoxypropan (NDOP). METHODS: A combination of in vitro and in vivo experiments was performed in C57BL/6 mice and Wistar rats. Thus, the ability of NDOP in donating NO in a cell-free system and in vascular smooth muscles cells (VSMC) and its ability to induce vasorelaxation in aortic rings from mice were evaluated. In addition, changes in blood pressure and heart rate to different doses of NDOP were evaluated in conscious rats. Finally, acute pre-clinical toxicity to oral administration of NDOP was assessed in mice. RESULTS: In cell-free system, NDOP increased NO levels, which was dependent on xanthine oxidoreductase (XOR). NDOP also increased NO levels in VSMC, which was not influenced by endothelial NO synthase. Furthermore, incubation with the XOR inhibitor febuxostat blunted the vasorelaxation in aortic ring preparations. In conscious rats, NDOP elicited dose-dependent reduction in blood pressure accompanied with increased heart rate. In vessel preparations, NDOP (10-8-10-3 mol/L) induced endothelium-independent vasorelaxation, which was inhibited by the NO scavengers 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and hydroxocobalamin or by inhibition of soluble guanylyl cyclase using H- [1,2,4] oxadiazolo [4,3-a]quinoxalin-1-one. To investigate if NDOP acts through potassium channels, selective blockers were used. Inhibition of BKCa, Kv or KATP subtypes of potassium channels had no effect, but inhibition of inward-rectifier potassium channels (KIR) significantly reduced NDOP-mediated vasorelaxation. Lastly, NDOP showed low toxicity (LD50 ~5000 mg/kg). CONCLUSION: Bioactivation of NDOP involves functional XOR, and this new organic nitrate elicits vasorelaxation via NO-cGMP-PKG signaling and activation of KIR channels. Future studies should further characterize the underlying mechanism and evaluate the therapeutic benefits of chronic NDOP treatment in relevant cardiovascular disease models.

The novel organic mononitrate NDHP attenuates hypertension and endothelial dysfunction in hypertensive rats.

RATIONALE: Development and progression of cardiovascular diseases, including hypertension, are often associated with impaired nitric oxide synthase (NOS) function and nitric oxide (NO) deficiency. Current treatment strategies to restore NO bioavailability with organic nitrates are hampered by undesirable side effects and development of tolerance. In this study, we evaluated NO release capability and cardiovascular effects of the newly synthesized organic nitrate 1, 3-bis (hexyloxy) propan-2-yl nitrate (NDHP). METHODS: A combination of in vitro and in vivo approaches was utilized to assess acute effects of NDHP on NO release, vascular reactivity and blood pressure. The therapeutic value of chronic NDHP treatment was assessed in an experimental model of angiotensin II-induced hypertension in combination with NOS inhibition. RESULTS: NDHP mediates NO formation in both cell-free system and small resistance arteries, a process which is catalyzed by xanthine oxidoreductase. NDHP-induced vasorelaxation is endothelium independent and mediated by NO release and modulation of potassium channels. Reduction of blood pressure following acute intravenous infusion of NDHP was more pronounced in hypertensive rats (two-kidney-one-clip model) than in normotensive sham-operated rats. Toxicological tests did not reveal any harmful effects following treatment with high doses of NDHP. Finally, chronic treatment with NDHP significantly attenuated the development of hypertension and endothelial dysfunction in rats with chronic NOS inhibition and angiotensin II infusion. CONCLUSION: Acute treatment with the novel organic nitrate NDHP increases NO formation, which is associated with vasorelaxation and a significant reduction of blood pressure in hypertensive animals. Chronic NDHP treatment attenuates the progression of hypertension and endothelial dysfunction, suggesting a potential for therapeutic applications in cardiovascular disease.

Synthesis and characterization of a novel organic nitrate NDHP: Role of xanthine oxidoreductase-mediated nitric oxide formation.

In this report, we describe the synthesis and characterization of 1,3-bis(hexyloxy)propan-2-yl nitrate (NDHP), a novel organic mono nitrate. Using purified xanthine oxidoreductase (XOR), chemiluminescence and electron paramagnetic resonance (EPR) spectroscopy, we found that XOR catalyzes nitric oxide (NO) generation from NDHP under anaerobic conditions, and that thiols are not involved or required in this process. Further mechanistic studies revealed that NDHP could be reduced to NO at both the FAD and the molybdenum sites of XOR, but that the FAD site required an unoccupied molybdenum site. Conversely, the molybdenum site was able to reduce NDHP independently of an active FAD site. Moreover, using isolated vessels in a myograph, we demonstrate that NDHP dilates pre-constricted mesenteric arteries from rats and mice. These effects were diminished when XOR was blocked using the selective inhibitor febuxostat. Finally, we demonstrate that NDHP, in contrast to glyceryl trinitrate (GTN), is not subject to development of tolerance in isolated mesenteric arteries.

Nitric oxide generation by the organic nitrate NDBP attenuates oxidative stress and angiotensin II-mediated hypertension.

BACKGROUND AND PURPOSE: NO deficiency and oxidative stress are crucially involved in the development or progression of cardiovascular disease, including hypertension and stroke. We have previously demonstrated that acute treatment with the newly discovered organic nitrate, 2-nitrate-1,3-dibuthoxypropan (NDBP), is associated with NO-like effects in the vasculature. This study aimed to further characterize the mechanism(s) and to elucidate the therapeutic potential in a model of hypertension and oxidative stress. EXPERIMENTAL APPROACH: A combination of ex vivo, in vitro and in vivo approaches was used to assess the effects of NDBP on vascular reactivity, NO release, NADPH oxidase activity and in a model of hypertension. KEY RESULTS: Ex vivo vascular studies demonstrated NDBP-mediated vasorelaxation in mesenteric resistance arteries, which was devoid of tolerance. In vitro studies using liver and kidney homogenates revealed dose-dependent and sustained NO generation by NDBP, which was attenuated by the xanthine oxidase inhibitor febuxostat. In addition, NDBP reduced NADPH oxidase activity in the liver and prevented angiotensin II-induced activation of NADPH oxidase in the kidney. In vivo studies showed that NDBP halted the progression of hypertension in mice with chronic angiotensin II infusion. This was associated with attenuated cardiac hypertrophy, and reduced NADPH oxidase-derived oxidative stress and fibrosis in the kidney and heart. CONCLUSION AND IMPLICATIONS: The novel organic nitrate NDBP halts the progression of angiotensin II-mediated hypertension. Mechanistically, our findings suggest that NDBP treatment is associated with sustained NO release and attenuated activity of NADPH oxidase, which to some extent requires functional xanthine oxidase.

The new nitric oxide donor cyclohexane nitrate induces vasorelaxation, hypotension, and antihypertensive effects via NO/cGMP/PKG pathway.

We investigated the cardiovascular effects induced by the nitric oxide donor Cyclohexane Nitrate (HEX). Vasodilatation, NO release and the effects of acute or sub-chronic treatment with HEX on cardiovascular parameters were evaluated. HEX induced endothelium-independent vasodilatation (Maximum effect [efficacy, ME] = 100.4 ± 4.1%; potency [pD2] = 5.1 ± 0.1). Relaxation was attenuated by scavenging nitric oxide (ME = 44.9 ± 9.4% vs. 100.4 ± 4.1%) or by inhibiting the soluble guanylyl cyclase (ME = 38.5 ± 9.7% vs. 100.4 ± 4.1%). In addition, pD2 was decreased after non-selective blockade of K(+) channels (pD2 = 3.6 ± 0.1 vs. 5.1 ± 0.1) or by inhibiting KATP channels (pD2 = 4.3 ± 0.1 vs. 5.1 ± 0.1). HEX increased NO levels in mesenteric arteries (33.2 ± 2.3 vs. 10.7 ± 0.2 au, p < 0.0001). Intravenous acute administration of HEX (1-20 mg/kg) induced hypotension and bradycardia in normotensive and hypertensive rats. Furthermore, starting at 6 weeks after the induction of 2K1C hypertension, oral treatment with the HEX (10 mg/Kg/day) for 7 days reduced blood pressure in hypertensive animals (134 ± 6 vs. 170 ± 4 mmHg, respectively). Our data demonstrate that HEX is a NO donor able to produce vasodilatation via NO/cGMP/PKG pathway and activation of the ATP-sensitive K(+) channels. Furthermore, HEX acutely reduces blood pressure and heart rate as well as produces antihypertensive effect in renovascular hypertensive rats.