NW-nitro L-arginine benzyl ester, a potent irreversible inhibitor of endothelium dependent relaxation

Significance of nitric oxide derived from the nitric oxide synthases system in cardiovascular interorgan crosstalk

Interorgan crosstalk contributes to the pathogenesis of various disorders, and drug development based on interorgan crosstalk is attracting attention. The roles of nitric oxide (NO) derived from the NO synthases system (NOSs) in interorgan crosstalk remain unclear. We have investigated this issue by using our mice deficient in all 3 NOSs (triple n/i/eNOSs-/- mice). We reported that 2/3 nephrectomized triple n/i/eNOSs-/- mice die suddenly because of the early onset of myocardial infarction, suggesting the protective role of NO derived from NOSs in the crosstalk between the kidney and the heart. We studied the role of NO derived from NOSs expressed in the bone marrow in vascular lesion formation. Constrictive arterial remodeling and neointimal formation following unilateral carotid artery ligation were prominently aggravated in wild-type mice transplanted with triple n/i/eNOSs-/- bone marrow cells as compared with those with wild-type bone marrow cells, suggesting the protective role of NO derived from NOSs in the crosstalk between the bone marrow and the blood vessel. We further investigated the role of NO derived from NOSs expressed in the bone marrow in pulmonary hypertension. The extent of pulmonary hypertension after chronic hypoxic exposure was markedly exacerbated in wild-type mice that underwent triple n/i/eNOSs-/- bone marrow transplantation as compared with those that underwent wild-type bone marrow transplantation, suggesting the protective role of NO derived from NOSs in the crosstalk between the bone marrow and the lung. These lines of evidence demonstrate that systemic and myelocytic NOSs could be novel therapeutic targets for myocardial infarction, vascular disease, and pulmonary hypertension. SIGNIFICANCE STATEMENT: This study demonstrated partial nephrectomy accelerates the occurrence of myocardial infarction induced by systemic NOSs deficiency in triple n/i/eNOSs-/- mice, that myelocytic NOSs deficiency aggravates vascular lesion formation after unilateral carotid artery ligation, and that myelocytic NOSs deficiency exacerbates chronic hypoxia-induced pulmonary hypertension. These results suggest that NO derived from NOSs plays a protective role in cardiovascular interorgan crosstalk, indicating that systemic and myelocytic NOSs could be important therapeutic targets for myocardial infarction, vascular disease, and pulmonary hypertension.

Role of Nitric Oxide Synthases in Respiratory Health and Disease: Insights from Triple Nitric Oxide Synthases Knockout Mice

The system of nitric oxide synthases (NOSs) is comprised of three isoforms: nNOS, iNOS, and eNOS. The roles of NOSs in respiratory diseases in vivo have been studied by using inhibitors of NOSs and NOS-knockout mice. Their exact roles remain uncertain, however, because of the non-specificity of inhibitors of NOSs and compensatory up-regulation of other NOSs in NOS-KO mice. We addressed this point in our triple-n/i/eNOSs-KO mice. Triple-n/i/eNOSs-KO mice spontaneously developed pulmonary emphysema and displayed exacerbation of bleomycin-induced pulmonary fibrosis as compared with wild-type (WT) mice. Triple-n/i/eNOSs-KO mice exhibited worsening of hypoxic pulmonary hypertension (PH), which was reversed by treatment with sodium nitrate, and WT mice that underwent triple-n/i/eNOSs-KO bone marrow transplantation (BMT) also showed aggravation of hypoxic PH compared with those that underwent WT BMT. Conversely, ovalbumin-evoked asthma was milder in triple-n/i/eNOSs-KO than WT mice. These results suggest that the roles of NOSs are different in different pathologic states, even in the same respiratory diseases, indicating the diversity of the roles of NOSs. In this review, we describe these previous studies and discuss the roles of NOSs in respiratory health and disease. We also explain the current state of development of inorganic nitrate as a new drug for respiratory diseases.

Urinary dysfunction in transgenic sickle cell mice: model of idiopathic overactive bladder syndrome

Voiding abnormalities are common among the sickle cell disease (SCD) population, among which overactive bladder (OAB) syndrome is observed at rates as high as 39%. Although detrusor overactivity is the most common cause of OAB, its molecular pathophysiology is not well elucidated. The nitric oxide (NO) signaling pathway has been implicated in the regulation of lower genitourinary tract function. In the present study, we evaluated the role of the NO signaling pathway in voiding function of transgenic SCD mice compared with combined endothelial and neuronal NO synthase gene-deficient mice, both serving as models of NO deficiency. Mice underwent void spot assay and cystometry, and bladder and urethral specimens were studied using in vitro tissue myography. Both mouse models exhibited increased void volumes; increased nonvoiding and voiding contraction frequencies; decreased bladder compliance; increased detrusor smooth muscle contraction responses to electrical field stimulation, KCl, and carbachol; and increased urethral smooth muscle relaxation responses to sodium nitroprusside compared with WT mice. In conclusion, our comprehensive behavioral and functional study of the SCD mouse lower genitourinary tract, in correlation with that of the NO-deficient mouse, reveals NO effector actions in voiding function and suggests that NO signaling derangements are associated with an OAB phenotype. These findings may allow further study of molecular targets for the characterization and evaluation of OAB.

Significance of nitric oxide synthases: Lessons from triple nitric oxide synthases null mice

Nitric oxide (NO) is synthesized by three distinct NO synthases (neuronal, inducible, and endothelial NOSs), all of which are expressed in almost all tissues and organs in humans. The regulatory roles of NOSs in vivo have been investigated in pharmacological studies with non-selective NOS inhibitors. However, the specificity of the inhibitors continues to be an issue of debate, and the authentic significance of NOSs is still poorly understood. To address this issue, we generated mice in which all three NOS genes are completely disrupted. The triple NOSs null mice exhibited cardiovascular abnormalities, including hypertension, arteriosclerosis, myocardial infarction, cardiac hypertrophy, diastolic heart failure, and reduced EDHF responses, with a shorter survival. The triple NOSs null mice also displayed metabolic abnormalities, including metabolic syndrome and high-fat diet-induced severe dyslipidemia. Furthermore, the triple NOSs null mice showed renal abnormalities (nephrogenic diabetes insipidus and pathological renal remodeling), lung abnormalities (accelerated pulmonary fibrosis), and bone abnormalities (increased bone mineral density and bone turnover). These results provide evidence that NOSs play pivotal roles in the pathogenesis of a wide variety of disorders. This review summarizes the latest knowledge on the significance of NOSs in vivo, based on lessons learned from experiments with our triple mutant model.

Severe dyslipidaemia, atherosclerosis, and sudden cardiac death in mice lacking all NO synthases fed a high-fat diet

AIMS

The precise role of the nitric oxide synthase (NOS) system in lipid metabolism remains to be elucidated. We addressed this point in mice that we have recently developed and that lack all three NOS isoforms.

METHODS AND RESULTS

Wild-type (WT), singly, doubly, and triply NOS(-/-) mice were fed either a regular or high-cholesterol diet for 3-5 months. The high-cholesterol diet significantly increased serum low-density lipoprotein (LDL) cholesterol levels in all the genotypes when compared with the regular diet. Importantly, when compared with the WT genotype, the serum LDL cholesterol levels in the high-cholesterol diet were significantly and markedly elevated only in the triply NOS(-/-) genotype, but not in any singly or doubly NOS(-/-) genotypes, and this was associated with remarkable atherosclerosis and sudden cardiac death, which occurred mainly in the 4-5 months after the high-cholesterol diet. Finally, hepatic LDL receptor expression was markedly reduced only in the triply NOS(-/-) genotype, accounting for the diet-induced dyslipidaemia in the genotype.

CONCLUSION

These results provide the first direct evidence that complete disruption of all NOS genes causes severe dyslipidaemia, atherosclerosis, and sudden cardiac death in response to a high-fat diet in mice in vivo through the down-regulation of the hepatic LDL receptor, demonstrating the critical role of the whole endogenous NOS system in maintaining lipid homeostasis.

Spontaneous myocardial infarction in mice lacking all nitric oxide synthase isoforms

BACKGROUND

The roles of nitric oxide (NO) in the cardiovascular system have been investigated extensively in pharmacological studies with NO synthase (NOS) inhibitors and in studies with NOS isoform-deficient mice. However, because of the nonspecificity of the NOS inhibitors and the compensatory interactions among NOS isoforms (nNOS, iNOS, and eNOS), the ultimate roles of endogenous NO derived from the entire NOS system are still poorly understood. In this study, we examined this point in mice deficient in all 3 NOS isoforms (triply n/i/eNOS(-/-) mice) that we have recently developed.

METHODS AND RESULTS

The triply n/i/eNOS(-/-) mice, but not singly eNOS(-/-) mice, exhibited markedly reduced survival, possibly due to spontaneous myocardial infarction accompanied by severe coronary arteriosclerotic lesions. Furthermore, the triply n/i/eNOS(-/-) mice manifested phenotypes that resembled metabolic syndrome in humans, including visceral obesity, hypertension, hypertriglyceridemia, and impaired glucose tolerance. Importantly, activation of the renin-angiotensin system was noted in the triply n/i/eNOS(-/-) mice, and long-term oral treatment with an angiotensin II type 1 receptor blocker significantly suppressed coronary arteriosclerotic lesion formation and the occurrence of spontaneous myocardial infarction and improved the prognosis of those mice, along with ameliorating the metabolic abnormalities.

CONCLUSIONS

These results provide the first direct evidence that genetic disruption of the whole NOS system causes spontaneous myocardial infarction associated with multiple cardiovascular risk factors of metabolic origin in mice in vivo through the angiotensin II type 1 receptor pathway, demonstrating the critical role of the endogenous NOS system in maintaining cardiovascular and metabolic homeostasis.

Asymmetric dimethylarginine (ADMA) induces vascular endothelium impairment and aggravates post-ischemic ventricular dysfunction in rats

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) inhibitor recognized as an independent risk factor for endothelial dysfunction and coronary heart diseases. This study investigated whether ADMA (10 mg/kg day for 14 days) affected endothelial function and aggravated post-ischemic ventricular dysfunction in the perfused rat heart. Systolic blood pressure and heart rate, plasma levels of ADMA and nitrite/nitrate were measured in vehicle- and ADMA-treated rats. Perfused hearts were submitted to global ischemia-reperfusion and vascular endothelial dysfunction was examined with angiotensin II in coronary vessels and aortic rings. Endothelial NO synthase (eNOS) and angiotensin-converting enzyme (ACE) mRNA expression in aortic and cardiac tissues were measured. ADMA-treated rats had higher systolic blood pressure (1.3-fold, P<0.01) and slower heart rate (16%, P<0.05) than controls. Plasma ADMA rose (1.9-fold, P<0.01) and nitrite/nitrate concentration decreased 59% (P<0.001). Ventricular contraction (stiffness) increased significantly, with worsening of post-ischemic ventricular dysfunction. In preparations from ADMA-treated rats the coronary vasculature's response to angiotensin II was almost doubled (P<0.01) and the maximal vasorelaxant effect of acetylcholine in aortic rings was significantly lower than in preparations from vehicle-treated rats. In cardiac and aortic tissues eNOS mRNA and ACE mRNA levels were similar in controls and ADMA-treated rats. The increased plasma levels of ADMA presumably cause endothelial dysfunction because of a deficiency in NO production, which also appears involved in the aggravation of myocardial ischemia-reperfusion injury.

Asymmetric dimethylarginine produces vascular lesions in endothelial nitric oxide synthase-deficient mice: involvement of renin-angiotensin system and oxidative stress

OBJECTIVE

Asymmetric dimethylarginine (ADMA) is widely believed to be an endogenous nitric oxide synthase (eNOS) inhibitor. However, in this study, we examined our hypothesis that the long-term vascular effects of ADMA are not mediated by inhibition of endothelial NO synthesis.

METHODS AND RESULTS

ADMA was infused in wild-type and eNOS-knockout (KO) mice by osmotic minipump for 4 weeks. In wild-type mice, long-term treatment with ADMA caused significant coronary microvascular lesions. Importantly, in eNOS-KO mice, treatment with ADMA also caused an extent of coronary microvascular lesions that was comparable to that in wild-type mice. These vascular effects of ADMA were not prevented by supplementation of l-arginine, and vascular NO production was not reduced by ADMA treatment. Treatment with ADMA caused upregulation of angiotensin-converting enzyme (ACE) and an increase in superoxide production that were comparable in both strains and that were abolished by simultaneous treatment with temocapril (ACE inhibitor) or olmesartan (AT(1) receptor antagonist), which simultaneously suppressed vascular lesion formation.

CONCLUSIONS

These results provide the first direct evidence that the long-term vascular effects of ADMA are not solely mediated by simple inhibition of endothelial NO synthesis. Direct upregulation of ACE and increased oxidative stress through AT(1) receptor appear to be involved in the long-term vascular effects of ADMA in vivo. This study demonstrates that asymmetrical dimethylarginine (ADMA) causes arteriosclerotic coronary lesions in mice in vivo through mechanisms other than simple inhibition of endothelial NO synthesis. Our findings should contribute to a better understanding of the pathophysiological role of ADMA in arteriosclerosis.

Vasculoprotective roles of neuronal nitric oxide synthase

Nitric oxide (NO) has multiple important actions that contribute to the maintenance of vascular homeostasis. NO is synthesized by three different isoforms of NO synthase (NOS), all of which have been reported to be expressed in human atherosclerotic vascular lesions. Although the regulatory roles of endothelial NOS (eNOS) and inducible NOS (iNOS) on the development of atherosclerosis have been described, little is known about the role of neuronal NOS (nNOS). Here, we show that nNOS also exerts important vasculoprotective effects in vivo. In a carotid artery ligation model, nNOS gene-deficient (nNOS-KO) mice exhibited accelerated neointimal formation and constrictive vascular remodeling caused by blood flow disruption. In a rat balloon injury model, the selective inhibition of nNOS activity potently enhanced vasoconstrictor responses to a variety of calcium-mobilizing stimuli, suppressed tissue cGMP concentrations, a marker of vascular NO production, and exacerbated neointimal formation. In both models, nNOS was absent before injury and was up-regulated only after the injury, and was predominantly expressed in the neointima and medial smooth muscle cells. These results provide the first direct evidence that nNOS plays important roles in suppressing arteriosclerotic vascular lesion formation in vivo.

Long-term treatment with N(omega)-nitro-L-arginine methyl ester causes arteriosclerotic coronary lesions in endothelial nitric oxide synthase-deficient mice

BACKGROUND

N(omega)-nitro-L-arginine methyl ester (l-NAME) is widely used to inhibit endothelial synthesis of NO in vivo. However, it is controversial whether the long-term vascular effects of l-NAME are mediated primarily by inhibition of endothelial NO synthesis. We addressed this point in mice that are deficient in the endothelial NO synthase gene (eNOS-KO mice).

METHODS AND RESULTS

Wild-type and eNOS-KO mice received l-NAME in drinking water for 8 weeks. In wild-type mice, long-term treatment with l-NAME caused significant medial thickening and perivascular fibrosis in coronary microvessels but not in large coronary arteries. Importantly, in eNOS-KO mice, treatment with l-NAME also caused an extent of medial thickening and perivascular fibrosis in coronary microvessels that was comparable to that in wild-type mice and that was not prevented by supplementation of L-arginine. Vascular NO and cGMP levels were not significantly reduced by l-NAME treatment, and no expression of inducible or neuronal NO synthase was noted in microvessels of eNOS-KO mice, suggesting an involvement of NO-independent mechanisms. Treatment with l-NAME caused an upregulation of vascular ACE and an increase in cardiac lucigenin chemiluminescence that were comparable in both strains and that were abolished by simultaneous treatment with temocapril (ACE inhibitor) or CS866 (angiotensin II type 1 receptor antagonist) along with the suppression of vascular lesion formation.

CONCLUSIONS

These results provide the first direct evidence that the long-term vascular effects of l-NAME are not mediated by simple inhibition of endothelial NO synthesis. Direct upregulation of local ACE and increased oxidative stress appear to be involved in the long-term vascular effects of l-NAME in vivo.

Long-term vascular effects of Nomega-nitro-L-arginine methyl ester are not soley mediated by inhibition of endothelial nitric oxide synthesis in the rat mesenteric artery

Nomega-nitro-L-arginine methyl ester (L-NAME), one of the synthetic L-arginine analogues with inhibitory effects of nitric oxide (NO) synthesis, is now widely used to examine the role of NO in various organs. We and others demonstrated that long-term treatment with L-NAME causes hypertension and cardiovascular lesions (perivascular fibrosis and medial thickening), especially at microvascular levels. However, convincing evidence is still lacking that these long-term cardiovascular effects of L-NAME are solely mediated by the inhibition of the synthesis of endothelium-derived NO (EDNO). This study was thus designed to better understand the effects of long-term treatment with L-NAME with special reference to EDNO synthesis. Male Wister-Kyoto rats were orally administered L-NAME for 8 weeks. Blood pressure significantly increased at 3 days and 1 and 8 weeks of the treatment. Endothelium-dependent relaxations to acetylcholine (ACh) of the aorta were reduced 3 days after the treatment, recovered at 1 week, and again reduced at 8 weeks, whereas the relaxations of the small mesenteric artery were unaltered throughout the experimental periods. At 8 weeks, indomethacin-sensitive, endothelium-dependent contractions to ACh were noted. The relative contributions of NO and endothelium-derived hyperpolarizing factor also were unchanged. Citrulline assay demonstrated that substantial levels of constitutive NO synthase activity remained in the aorta during the experiments. The long-term treatment with L-NAME caused perivascular fibrosis and medial thickening, not only in the aorta but also in the mesenteric artery. These results suggest that mechanism(s) other than simple inhibition of EDNO synthesis is involved in the long-term cardiovascular effects of L-NAME in the rat mesenteric artery.

Endothelium-dependent relaxation resistant to NG-nitro-L-arginine in rat aorta

Experiments were designed to determine whether cyclic GMP-independent relaxation is involved in the endothelium-dependent vascular relaxation response of rat aortic strip to acetylcholine. The relaxation response to acetylcholine in the presence of 3 x 10(-4) M NG-nitro-L-arginine was apparent when the precontraction was induced by norepinephrine at 5 x 10(-9) M or 10(-8) M. The relaxation response to acetylcholine resistant to NG-nitro-L-arginine was abolished by 10(-6) M atropine, 10 mM tetraethylammonium, or endothelium removal, but was not inhibited by 10(-5) M indomethacin, 3 x 10(-6) M oxyhemoglobin or 10(-5) M glibenclamide. The response was virtually abolished when the vascular strips had been preconstricted with 20 mM KCl. The increase in vascular cyclic GMP levels induced by 10(-5) M acetylcholine was completely abolished by 3 x 10(-4) M NG-nitro-L-arginine. These results suggest that acetylcholine-induced endothelium-dependent relaxation resistant to NG-nitro-L-arginine in rat aorta is unmasked when the precontractile force is caused by lower concentrations of norepinephrine and the relaxation is mediated by a cyclic GMP-independent mechanism, possibly an endothelium-derived hyperpolarizing factor.

Identification of guanidino succinate as a putative endogenous source of the endothelium derived relaxing factor

Using a specific HPLC analysis for guanidines, we find that rat aorta contains guanidino succinate (GS), guanidino acetate (GA), guanidino propionate (GP), guanidino butyrate (GB), methyl guanidine (MG) and guanidine. The concentration of L-arginine (0.05 nmol/mg tissue) is significantly lower than the other guanidines. GS is found to be the most potent vasodilator-guanidine in the rat aorta preparation and this vasodilation depends predominantly on the presence of the endothelium. This effect of GS is antagonized by NG-monomethyl L-arginine (L-NMMA), NW-nitro L-arginine benzyl ester (L-NABA), hemoglobin and by methylene blue, all of which are known to block or attenuate endothelium dependent relaxation. Further, the relaxation mediated by GS is accompanied by the formation of cGMP in the rat aorta. From these results we suggest that GS may be a major endogenous source of EDRF.