Accumulation of nitrotyrosine correlates with endothelial NO synthase in pulmonary resistance arteries during chronic hypoxia in the rat

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Pulmonary hypertension and vascular oxidative damage in cigarette smoke exposed eNOS(-/-) mice and human smokers

CONTEXT

Cigarette smoke is known to be associated with pulmonary hypertension in humans and in animal models. Although the etiology of pulmonary hypertension in smokers is not understood, recent work has suggested a role for inducible nitric oxide synthase (iNOS) in inducing oxidative stress.

OBJECTIVE AND METHODS

To further evaluate this question, we assessed eNOS-/- mice exposed to air or cigarette smoke for the presence of pulmonary hypertension and examined vascular remodeling and expression of nitrotyrosine, a marker of reactive nitrogen species-induced oxidative damage, using immunohistochemistry. To ascertain whether oxidants may play a role in humans, we also examined lung tissue from nonsmokers, and patients with chronic obstructive pulmonary disease (COPD) with and without pulmonary hypertension.

RESULTS

We found that eNOS(-/-) mice developed increased pulmonary arterial pressure after six months cigarette smoke exposure, and this was associated with vascular remodeling and increased vascular nitrotyrosine staining. iNOS gene expression was decreased in the pulmonary arteries of the smoke exposed animals, and no protein was detectable by immunohistochemistry. In humans, vascular nitrotyrosine staining intensity was increased in smokers with COPD compared to nonsmokers, and further increased in smokers with combined COPD and pulmonary hypertension.

CONCLUSIONS

We conclude that cigarette smoke-induced pulmonary hypertension is associated with evidence of oxidative vascular damage by reactive nitrogen species, but that iNOS does not appear to be the major contributor to such damage. Most likely the source of reactive nitrogen species is the cigarette smoke itself.

Tissue localization of nanoparticles is altered due to hypoxia resulting in poor efficacy of curcumin nanoparticles in pulmonary hypertension

The present study is an attempt to leverage therapeutic benefits of curcumin in pulmonary hypertension by encapsulating it in biodegradable poly(lactide-co-glycolic) acid nanoparticles. Pulmonary hypertension is induced in experimental animals by subjecting them to chronic hypoxic conditions. The ability of curcumin encapsulated nanoparticles to manage pulmonary hypertension is measured by right ventricular hypertrophy, haematocrit, vascular remodelling and target tissue levels of curcumin. Further, single oral dose tissue distribution of the nanoparticulate curcumin was also assessed under normoxic and hypoxic conditions. Orally administered nanoparticulate curcumin failed to offer any protection against hypoxia induced pulmonary hypertension as indicated by insignificant changes in right ventricular hypertrophy and vascular remodelling that are similar to untreated groups. A significant difference in the target tissue levels was observed between normoxic vs. hypoxic rats. The study suggests that hypoxia has a major role in the particle localization in lungs probably due to the altered blood flow, increased barrier properties of the lung vasculature and decreased endocytosis. The target tissue levels of curcumin under hypoxia are much lower to that achieved in normoxic rats probably due to difference in particle dynamics, resulting in the failure of treatment.

Acute hypoxia stimulates intracellular peroxynitrite formation associated with pulmonary artery smooth muscle cell proliferation

There is separate evidence for peroxynitrite formation and hypoxia-induced cell proliferation in several models of hypoxic pulmonary hypertension. We therefore hypothesized that the stimulation of pulmonary artery smooth muscle cells (PASMCs) proliferation by hypoxia is due to peroxynitrite formation. The effect of hypoxia alone and in combination with ≤ 0.2 μM peroxynitrite on PASMCs was investigated in explants from bovine lungs grown in 1%, 5%, or 10% oxygen for 24 hours with or without peroxynitrite. At 0.1% fetal bovine serum, DNA synthesis of PASMCs (assessed by 3H thymidine incorporation) was increased by transient exposure to 0.2 μM peroxynitrite (by 158% ± 14%, P < 0.01) or to 24 hours of hypoxia (5% oxygen) (by 221% ± 17%, P < 0.01). Results were similar at 2.5% fetal bovine serum. Treatment of PASMCs with 0.2 μM peroxynitrite or 5% O2 hypoxia caused a significant increase in nitrotyrosine formation to a similar extent and intensity. The proliferative response to 0.2 μM peroxynitrite or to the combination of peroxynitrite plus 5% O2 was similar to the effect of 5% O2 alone and was abolished by simultaneous treatment with peroxynitrite scavenger-ebselen (5 μM). Our present data indicate that hypoxia can initiate peroxynitrite-induced proliferative events and suggest a mechanism for the vascular hypertrophy associated with pulmonary hypertension.

Endothelial NOS-derived nitric oxide prevents injury resulting from reoxygenation in the hypoxic lung

To date, the role that NO derived from endothelial NO synthase (eNOS) plays in the development of the injuries occurring under hypoxia/reoxygenation (H/R) in the lung remains unknown and thus constitutes the subject of the present work. A follow-up study was conducted in Wistar rats submitted to H/R (hypoxia for 30 min; reoxygenation of 0 h, 48 h and 5 days), with or without prior treatment using the eNOS inhibitor L-NIO (20 mg/kg). Lipid peroxidation, apoptosis, protein nitration and NO production (NOx) were analysed. The results showed that L-NIO administration lowered NOx levels in all the experimental groups. Contrarily, the lipid peroxidation level and the percentage of apoptotic cells rose, implying that eNOS-derived NO may have a protective effect against the injuries occurring during H/R in the lung. These findings could open the possibility of future studies to design new therapies for this type of hypoxia based on NO-pharmacology.

Tetrahydrobiopterin analogues with NO-dependent pulmonary vasodilator properties

Reduced NO levels due to the deficiency of tetrahydrobiopterin (BH(4)) contribute to impaired vasodilation in pulmonary hypertension. Due to the chemically unstable nature of BH(4), it was hypothesised that oxidatively stable analogues of BH(4) would be able to support NO synthesis to improve endothelial dysfunction in pulmonary hypertension. Two analogues of BH(4), namely 6-hydroxymethyl pterin (HMP) and 6-acetyl-7,7-dimethyl-7,8-dihydropterin (ADDP), were evaluated for vasodilator activity on precontracted rat pulmonary artery rings. ADDP was administered to pulmonary hypertensive rats, followed by measurement of pulmonary vascular resistance in perfused lungs and eNOS expression by immunohistochemistry. ADDP and HMP caused significant relaxation in vitro in rat pulmonary arteries depleted of BH(4) with a maximum relaxation at 0.3μM (both P<0.05). Vasodilator activity of ADDP and HMP was completely abolished following preincubation with the NO synthase inhibitor, L-NAME. ADDP and HMP did not alter relaxation induced by carbachol or spermine NONOate. BH(4) itself did not produce relaxation. In rats receiving ADDP 14.1mg/kg/day, pulmonary vasodilation induced by calcium ionophore A23187 was augmented and eNOS immunoreactivity was increased. In conclusion, ADDP and HMP are two analogues of BH(4), which can act as oxidatively stable alternatives to BH(4) in causing NO-mediated vasorelaxation. Chronic treatment with ADDP resulted in improvement of NO-mediated pulmonary artery dilation and enhanced expression of eNOS in the pulmonary vascular endothelium. Chemically stable analogues of BH(4) may be able to limit endothelial dysfunction in the pulmonary vasculature.

Peroxynitrite stimulates pulmonary artery endothelial and smooth muscle cell proliferation: involvement of ERK and PKC

BACKGROUND

There is evidence that peroxynitrite is generated in pulmonary hypertension and we have therefore investigated whether peroxynitrite can cause proliferation of pulmonary artery cells.

METHODS

Bovine pulmonary artery endothelial (PAEC) and smooth muscle cells (PASMC) were exposed to peroxynitrite solution or to the peroxynitrite generating compound, 3-morpholinosydnonimine (SIN-1). Vascular cell proliferation was determined by cell count and (3)H-thymidine incorporation. Protein biochemistry was by western blot analysis.

RESULTS

Transient exposure to peroxynitrite stimulated the proliferation of PASMC (peroxynitrite 0.2 nM-2 μM) and PAEC (peroxynitrite 0.2 μM). Peroxynitrite 0.2 μM stimulated DNA synthesis in PASMC cell by 200 ± 22% and in PAEC by 137 ± 4%. DNA synthesis in PAEC and PASMC was also stimulated by the peroxynitrite generator SIN-1 2 μM. Cell proliferation was accompanied by activation of ERK, which peaked at 15 min and remained elevated for 12 h in PASMC. However peroxynitrite at the concentrations used in this study did not activate the stress pathways p38 mitogen activated protein kinase (MAPK) or Jun N-terminal kinase (JNK). Peroxynitrite-induced proliferation and ERK phosphorylation in PASMC were abolished by the peroxynitrite scavenger ebselen 5 μM. Peroxynitrite-induced proliferation and extracellular signal-regulated kinase (ERK) phosphorylation in PASMC was prevented by selective inhibitors of MAP kinase kinase (MEK) (U0126 5 μM, PD98059 50 μM), Raf-1 (Raf-1 kinase inhibitor 10 μM), Ras (FPT II and FPT III 10 μM) and protein kinase C (PKC) (GF109203X 10 μM). Inhibition of EGF or PDGF receptor signaling using AG-1296, AG-1478 or imatinib prevented peroxynitrite-induced cell proliferation and ERK phosphorylation in PASMC.

CONCLUSION

Peroxynitrite can stimulate proliferation of pulmonary artery cells, involving ERK, PKC and EGF or PDGF receptors.

Nitric oxide synthases in infants and children with pulmonary hypertension and congenital heart disease

Rationale

Nitric oxide is an important regulator of vascular tone in the pulmonary circulation. Surgical correction of congenital heart disease limits pulmonary hypertension to a brief period.

Objectives

The study has measured expression of endothelial (eNOS), inducible (iNOS), and neuronal nitric oxide synthase (nNOS) in the lungs from biopsies of infants with pulmonary hypertension secondary to cardiac abnormalities (n = 26), compared to a control group who did not have pulmonary or cardiac disease (n = 8).

Methods

eNOS, iNOS and nNOS were identified by immunohistochemistry and quantified in specific cell types.

Measurements and main results

Significant increases of eNOS and iNOS staining were found in pulmonary vascular endothelial cells of patients with congenital heart disease compared to control infants. These changes were confined to endothelial cells and not present in other cell types. Patients who strongly expressed eNOS also had strong expression of iNOS.

Conclusion

Upregulation of eNOS and iNOS occurs at an early stage of pulmonary hypertension, and may be a compensatory mechanism limiting the rise in pulmonary artery pressure.

Inhibition of p38 MAPK reverses hypoxia-induced pulmonary artery endothelial dysfunction

Hypoxia-induced endothelial dysfunction plays a crucial role in the pathogenesis of hypoxic pulmonary hypertension. p38 MAPK expression is increased in the pulmonary artery following hypoxic exposure. Recent evidence suggests that increased p38 MAPK activity is associated with endothelial dysfunction. However, the role of p38 MAPK activation in pulmonary artery endothelial dysfunction is not known. Sprague-Dawley rats were exposed to 2 wk hypobaric hypoxia, which resulted in the development of pulmonary hypertension and vascular remodeling. Endothelium-dependent relaxation of intrapulmonary vessels from hypoxic animals was impaired due to a reduced nitric oxide (NO) generation. This was despite increased endothelial NO synthase immunostaining and protein expression. Hypoxia exposure increased superoxide generation and p38 MAPK expression. The inhibition of p38 MAPK restored endothelium-dependent relaxation, increased bioavailable NO, and reduced superoxide production. In conclusion, the pharmacological inhibition of p38 MAPK was effective in increasing NO generation, reducing superoxide burden, and restoring hypoxia-induced endothelial dysfunction in rats with hypoxia-induced pulmonary hypertension. p38 MAPK may be a novel target for the treatment of pulmonary hypertension.

Endothelial dysfunction: from molecular mechanisms to measurement, clinical implications, and therapeutic opportunities

Endothelial dysfunction has been implicated as a key factor in the development of a wide range of cardiovascular diseases, but its definition and mechanisms vary greatly between different disease processes. This review combines evidence from cell-culture experiments, in vitro and in vivo animal models, and clinical studies to identify the variety of mechanisms involved in endothelial dysfunction in its broadest sense. Several prominent disease states, including hypertension, heart failure, and atherosclerosis, are used to illustrate the different manifestations of endothelial dysfunction and to establish its clinical implications in the context of the range of mechanisms involved in its development. The size of the literature relating to this subject precludes a comprehensive survey; this review aims to cover the key elements of endothelial dysfunction in cardiovascular disease and to highlight the importance of the process across many different conditions.

Sildenafil in hypoxic pulmonary hypertension potentiates a compensatory up‐regulation of NO‐cGMP signaling

The availability of inhibitors of cGMP-specific phosphodiesterase 5 (PDE 5), such as sildenafil, has revolutionized the treatment of pulmonary hypertension (PH). Sildenafil may exert its protective effects in a mechanism-based fashion by targeting a pathophysiologically attenuated NO-cGMP signaling pathway. To elucidate this, we analyzed changes in the pulmonary expression and activity of key enzymes of NO-cGMP signaling as well as the functional pulmonary responses to sildenafil in the 5 or 21 day hypoxia mouse model of PH. Surprisingly, we found doubled NO synthase (NOS) II and III levels, no evidence for attenuated NO bioavailability as evidenced by the nitrosative/oxidative stress marker protein nitro tyrosine, and no changes in the expression and activity of the NO receptor, soluble guanylyl cyclase (sGC). PDE 5 was either unchanged at day 5 or, after 21 days of hypoxia, even significantly decreased along with unchanged activity. Biochemically, these changes were mirrored by increased cGMP spillover into the lung perfusate and cGMP-dependent phosphorylation of the vasodilator-stimulated phosphoprotein, VASP. Sildenafil further augmented cGMP and phospho-VASP levels in lungs of mice exposed for 5 or 21 days and decreased pulmonary arterial pressure in mice after 5 days but not 21 days of hypoxia. In conclusion, NO-cGMP signaling is compensatorily up-regulated in the hypoxic mouse model of PH, and sildenafil further augments this pathway to functionally alleviate pulmonary vasoconstriction.

Adrenomedullin acts via nitric oxide and peroxynitrite to protect against myocardial ischaemia-induced arrhythmias in anaesthetized rats

1. The overall aim of this study was to determine if adrenomedullin (AM) protects against myocardial ischaemia (MI)-induced arrhythmias via nitric oxide (NO) and peroxynitrite. 2. In sham-operated rats, the effects of in vivo administration of a bolus dose of AM (1 nmol kg-1) was assessed on arterial blood pressure (BP), ex vivo leukocyte reactive oxygen species generation and nitrotyrosine deposition (a marker for peroxynitrite formation) in the coronary endothelium. 3. In pentobarbitone-anaesthetized rats subjected to ligation of the left main coronary artery for 30 min, the effects of a bolus dose of AM (1 nmol kg-1, i.v.; n=19) or saline (n=18) given 5 min pre-occlusion were assessed on the number and incidence of cardiac arrhythmias. In a further series of experiments, some animals received infusions of the NO synthase inhibitor N(G)-nitro-L-arginine (LNNA) (0.5 mg kg-1 min-1) or the peroxynitrite scavenger N-mercaptopropionyl-glycine (MPG) (20 mg kg-1 h-1) before AM. 4. AM treatment significantly reduced mean arterial blood pressure (MABP) and increased ex vivo chemiluminescence (CL) generation from leukocytes in sham-operated animals. AM also enhanced the staining for nitrotyrosine in the endothelium of coronary arteries. 5. AM significantly reduced the number of total ventricular ectopic beats that occurred during ischaemia (from 1185+/-101 to 520+/-74; P<0.05) and the incidences of ventricular fibrillation (from 61 to 26%; P<0.05). AM also induced a significant fall in MABP prior to occlusion. AM-induced cardioprotection was abrogated in animals treated with the NO synthase inhibitor LNNA and the peroxynitrite scavenger MPG. 6. This study has shown that AM exhibits an antiarrhythmic effect through a mechanism that may involve generation of NO and peroxynitrite.

Transforming growth factor-beta receptors localize to caveolae and regulate endothelial nitric oxide synthase in normal human endothelial cells

Caveolae (sphingolipid- and cholesterol-rich, 100 nm flask-shaped invaginations of the cell membrane) serve as a nexus of cell signalling. In the present study caveolin-rich lipid raft domains were extracted from HUVEC (human umbilical-vein endothelial cells) using both density gradient and immunoprecipitation techniques, and demonstrated localization of the TGF-beta (transforming growth factor-beta) receptors TbetaRI and TbetaRII to the Cav-1 (caveolin-1)-enriched raft fractions of these normal, human endothelial cells. Immunoprecipitation demonstrated an association between TbetaRI and TbetaRII, as well as an association of the TbetaRs receptors with Cav-1 and eNOS (endothelial nitric oxide synthase), suggesting a mutual co-localization to caveolae; after treatment of HUVEC with 5 ng/ml TGF-beta1 for 15 min, however, co-precipitation of eNOS with TbetaRI, TbetaRII and Cav-1 was diminished. The loss of immunoprecipitable eNOS from Cav-1-enriched fractions was accompanied by a decrease both in phosphorylation of eNOS and in enzymatic activity (conversion of arginine into citrulline). No change in the localization of eNOS to morphologically distinct caveolae could be detected by electron microscopy after treatment of HUVEC with TGF-beta1 for 20 min. The results of these investigations provide evidence that TbetaRI interacts with eNOS in the caveolae of normal, human endothelial cells and has a regulatory function on basal eNOS enzymatic activity.

Nitric oxide mediates hypoxia-induced changes in paracellular permeability of cerebral microvasculature

Ischemic stroke from a reduction in blood flow to the brain microvasculature results in a subsequent decreased delivery of oxygen (i.e., hypoxia) and vital nutrients to endothelial, neuronal, and glial cells. Hypoxia associated with stroke has been shown to increase paracellular permeability of the blood-brain barrier, leading to the release of cellular mediators and brain tissue injury. Whereas reperfusion does not occur in all ischemic strokes, increased permeability has been seen in posthypoxic reoxygenation. Currently, it is unknown whether these deleterious effects result from cellular mechanisms stimulated by decreased oxygen during stroke or posthypoxic reoxygenation stress. This study used primary bovine brain microvessel endothelial cells (BBMECs) to examine the involvement of nitric oxide (NO) as a mediator in hypoxia-induced permeability changes. Hypoxia-induced increased transport of [14C]sucrose across BBMEC monolayers compared with normoxia was attenuated by either posthypoxic reoxygenation or inhibition of NO synthase (NOS). The hypoxia-induced permeability effect was further reduced when NOS inhibition was combined with posthypoxic reoxygenation. Additionally, a significant increase in total NO was seen in BBMECs after hypoxic exposure. This correlation was supported by the increased [14C]sucrose permeability observed when BBMECs were exposed to the NO donor diethylenetriaamine NONOate. Western blot analyses of NOS isoforms showed a significant increase in the inducible isoform after hypoxic exposure with a subsequent reduction in expression on reoxygenation. Results from this study suggest that hypoxia-induced blood-brain barrier breakdown can be diminished by inhibition of NO synthesis, decreased concentration of NO metabolites, and/or reoxygenation.

Effect of a potent iNOS inhibitor (ONO-1714) on acetaminophen-induced hepatotoxicity in the rat

Overproduction of nitric oxide (NO) in the liver has been implicated as an important event in endotoxin shock and in other models of hepatic inflammation and injury. The present study was undertaken to evaluate the effect of ONO-1714, a potent and specific inhibitor of inducible NO synthase (iNOS), on acetaminophen-induced hepatotoxicity in the rats. Oral administration of ONO-1714 dose-dependently inhibited NOx (NO2- and NO3-) accumulation in rat plasma after lipopolysaccharide (LPS) treatment. Intraperitoneal acetaminophen at 1 g/kg caused damage to the centrilobular regions of the liver and increase in serum alanine and aspartate transaminase (ALT and AST, respectively) levels accompanied by elevated plasma NOx levels after 24 h. Oral administration of ONO-1714 at 10 and 100 microg/kg dose-dependently reduced the acetaminophen-induced hepatic tissue damage and the increases in serum ALT and AST levels. ONO-1714 also blocked the increase in plasma NOx concentrations. These findings demonstrate that oral ONO-1714, an iNOS inhibitor, protects against acetaminophen-evoked hepatic inflammation/injury, strongly suggesting that NO produced by iNOS plays a key role in the pathogenesis of this drug-induced hepatotoxicity.

Endothelial nitric oxide synthase (NOS) is upregulated in rapid progressive pulmonary hypertension of the newborn

OBJECTIVE

To provide evidence for the upregulation of endothelial nitric oxide synthase (eNOS) or inducible nitric oxide synthase (iNOS) in the assumed imbalance in the pathophysiology of rapid progressive pulmonary hypertension of the newborn (RPPHN), which is characterized by abnormal hypertrophy of the pulmonary arterioles and arteries leading to increased pulmonary vascular resistance. Furthermore, to determine the cellular source and topographic distribution of eNOS and iNOS.

MATERIAL AND METHODS

Lung biopsies were taken from two term neonates with clinical and echocardiographic evidence of RPPH and of three controls. Biopsies were obtained at an early stage of the disease as well as at post mortem and examined immunohistochemically for the presence of eNOS, iNOS and nitrotyrosine.

RESULTS

The endothelial cells of pulmonary arterioles stained significantly for eNOS protein in RPPHN patients. This was not the case in the control infants. There were no differences for nitrotyrosine or iNOS between RPPHN patients and controls.

CONCLUSION

Rapid progressive pulmonary hypertension of the newborn leads to compensatory induction of eNOS synthesis specifically in endothelial cells of the pulmonary arterioles. This mechanism of compensation can lead to delayed presentation of RPPHN during the late neonatal period. Exogenous inhaled nitric oxide therapy does not lead to suppression of the endogenous synthesis of nitric oxide.

Hyperoxia causes inducible nitric oxide synthase-mediated cellular damage to the immature rat brain

Relative hyperoxia is a condition frequently encountered in premature infants, either spontaneously or during treatment in the Neonatal Intensive Care Unit. The effects of high inspiratory oxygen concentrations on immature brain cells and their signaling cascades are largely unknown. The aim of the study was to investigate the effect of hyperoxia on the amount and topographic distribution of iNOS-expression (inducible nitric oxide synthase) in the immature rat brain, and to localize hyperoxia-induced formation of peroxynitrite as a potential marker of cellular damage to immature cerebral structures. Seven-day-old Wistar rat pups were exposed to >80% oxygen for 24 h and were then transcardially perfused. Following paraformaldehyde fixation, brains were paraffin-embedded and immunohistochemically stained for iNOS and nitrotyrosine. iNOS protein was quantified by Western blot; iNOS mRNA expression was studied by RT-PCR. Total brain iNOS mRNA was up-regulated, demonstrating a peak at 6 h following the onset of hyperoxia. Immunohistochemical staining was predominantly observed in microglial cells of hippocampus and frontal cortex with some iNOS reactivity in endothelial and perivascular cells. Nitrotyrosine staining was positive in apical dendrites of neurons in the frontal cortex. There was no positive staining for iNOS or nitrotyrosine in control animals. Hyperoxia causes iNOS mRNA and protein up-regulation in microglial cells of the immature rat brain. Positive neuronal nitrotyrosine staining indicates formation of peroxynitrite with potential deleterious effects for immature cellular structures in the neonatal brain.

Chronic hypoxia opposes pregnancy-induced increase in uterine artery vasodilator response to flow

We tested the hypotheses that pregnancy increases the uterine artery (UA) vasodilator response to flow and that this increase is impaired under conditions of chronic hypoxia (30 days, simulated elevation 3,960 m). UA were isolated from 24 normoxic or chronically hypoxic midpregnant guinea pigs and studied with the use of pressure myography. Normoxic pregnancy increased UA flow vasodilator response and protected against a rise in wall shear stress (WSS). Chronic hypoxia opposed these effects, prompting vasoconstriction at high flow and increasing WSS above levels seen in normoxic pregnant UA. The nitric oxide synthase inhibitor N(G)-nitro-l-arginine (l-NNA) eliminated the pregnancy-associated increase in flow vasodilation in normoxic UA, suggesting that increased nitric oxide production was responsible. The considerable residual vasodilation after nitric oxide synthase and cyclooxygenase inhibition implicated endothelial-derived hyperpolarizing factor (EDHF) as an additional contributor to flow vasodilation. l-NNA increased flow vasodilation in UA from chronically hypoxic animals, suggesting that chronic hypoxia may have lowered EDHF or elevated peroxynitrite production. In conclusion, flow is an important physiological vasodilator for the acute and more chronic UA dimensional changes required to increase uteroplacental blood flow during normal pregnancy. Chronic hypoxia may be a mechanism that opposes the pregnancy-associated rise in UA flow vasodilation, thereby increasing the incidence of preeclampsia and intrauterine growth restriction at a high altitude.

Regulation of endothelial-type NO synthase expression in pathophysiology and in response to drugs

In many types of cardiovascular pathophysiology such as hypercholesterolemia and atherosclerosis, diabetes, cigarette smoking, or hypertension (with its sequelae stroke and heart failure) the expression of endothelial NO synthase (eNOS) is altered. Both up- and downregulation of eNOS have been observed, depending on the underlying disease. When eNOS is upregulated, the upregulation is often futile and goes along with a reduction in bioactive NO. This is due to an increased production of superoxide generated by NAD(P)H oxidase and by an uncoupled eNOS. A number of drugs with favorable effects on cardiovascular disease upregulate eNOS expression. The resulting increase in vascular NO production may contribute to their beneficial effects. These compounds include statins, angiotensin-converting enzyme inhibitors, AT1 receptor antagonists, calcium channel blockers, and some antioxidants. Other drugs such as glucocorticoids, whose administration is associated with cardiovascular side effects, downregulate eNOS expression. Stills others such as the immunosuppressants cyclosporine A and FK506/tacrolimus or erythropoietin have inconsistent effects on eNOS. Thus regulation of eNOS expression and activity contributes to the overall action of several classes of drugs, and the development of compounds that specifically upregulate this protective enzyme appears as a desirable target for drug development.

A novel inhibitor of inducible nitric oxide synthase (ONO-1714) prevents critical warm ischemia-reperfusion injury in the pig liver

BACKGROUND

Recently, a novel inhibitor of inducible nitric oxide synthase, ONO-1714, was developed. We evaluated the effect of ONO-1714 on a critical warm I/R model of the pig liver.

METHODS

Pigs were subjected to 180 min of hepatic warm I/R under the extracorporeal circulation. We investigated the time course of changes in the serum NO2- + NO3- (NOx), the cellular distribution of endothelial and inducible nitric oxide synthase, thrombocyte-thrombi, and nitrotyrosine by immunohistochemistry. The hepatic tissue blood flow (HTBF) was measured continuously using a laser-Doppler blood flowmeter.

RESULTS

ONO-1714 at 0.05 mg/kg improved the survival rate from 54 (control group) to 100%. The serum NOx levels in the ONO-1714 group were significantly lower than those in the control group at 1, 1.5, 2, 3, and 6 hr after reperfusion. The serum aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels of the ONO-1714 group were significantly lower than the control group, and the HTBF of the ONO-1714 group was significantly higher than the control group. The formation of thrombocyte-thrombi and nitrotyrosine after reperfusion was significantly lower in the ONO-1714 group.

CONCLUSIONS

These results indicated that ONO-1714 improved the survival rates and attenuated I/R injury in a critical hepatic warm I/R model of the pig. ONO-1714 will be beneficial for hepatectomy or liver transplantation in the clinical field.

Discrepant distribution of big endothelin (ET)-1 and ET receptors in the pulmonary artery

Since pulmonary vasculature is complex in terms of regional difference in structure and function, it is important to understand the site of endothelin (ET) synthesis and the distribution of the ET system along the axial pathways of pulmonary artery. The expression of big ET-1, ET converting enzyme (ECE) and ET(A) receptors were examined in rat pulmonary arteries under normal and hypoxic conditions using an immunohistochemical method and Northern blot analysis. In normal conditions, big ET-1 was expressed in the intima and media of pulmonary arteries with a predominant distribution in the distal segments and a preferential localization in the media, while ETA receptors were dominantly expressed in the proximal segments. ECE was constitutively expressed in the intima and media. Following exposure to hypoxia, messenger ribonucleic acid (mRNA) expression of ET-1 and ET(A) receptors were up-regulated by two-fold and immunoreactivities for big ET-1, ECE, and ET(A) receptors significantly increased by two to five-fold in the distal segments. Smooth muscle cells are an important source of endothelin-1 in the pulmonary artery. The distribution of big endothelin-1 and endothelin A receptors in pulmonary arteries was discrepant in normal conditions while their expression concomitantly increased in the distal segments in hypoxic conditions. This heterogeneity may play an important role in the regulation of pulmonary vascular tone.