Fumito Ichinose

Inhaled Nitric Oxide A Selective Pulmonary Vasodilator: Current Uses and Therapeutic Potential

Since the recognition of nitric oxide (NO) as a key endothelial-derived vasodilator molecule in 1987, the field of NO research has expanded to encompass many areas of biomedical research. It is now well established that NO is an important signaling molecule throughout the body. The therapeutic potential of inhaled NO as a selective pulmonary vasodilator was suggested in a lamb model of pulmonary hypertension and in patients with pulmonary hypertension in 1991.1,2 Because NO is scavenged by hemoglobin (Hb) on diffusing into the blood and is thereby rapidly inactivated, the vasodilatory effect of inhaled NO is limited largely to the lung. This is in contrast to intravenously infused vasodilators that can cause systemic vasodilation and severe systemic arterial hypotension. Recent data indicate that inhaled NO can be applied in various diseases. For example, studies suggest that inhaled NO is a safe and effective agent to determine the vasodilatory capacity of the pulmonary vascular bed. This article summarizes the pharmacology and physiology of inhaled NO and reviews the current uses of inhaled NO for the treatment, evaluation, and prevention of cardiovascular and respiratory diseases. ### Chemistry of NO Gas NO is a colorless, odorless gas that is only slightly soluble in water.3 NO and its oxidative byproducts (eg, NO2 and N2O4) are produced by the partial oxidation of atmospheric nitrogen in internal combustion engines, in the burning cinder cones of cigarettes, and in lightning storms. Medical-grade NO gas is produced under carefully controlled conditions, diluted with pure nitrogen, and stored in the absence of oxygen. The recent article by Williams4 provides a review of the chemistry of NO. ### Therapeutic Versus Endogenous NO Concentrations in the Airway Although early studies of inhaled NO in the treatment of pulmonary hypertension used concentrations of 5 to 80 ppm, it has since been realized that concentrations >20 ppm provide little additional …

Pulmonary Vasoconstriction and Hypertension in Mice With Targeted Disruption of the Endothelial Nitric Oxide Synthase (NOS 3) Gene

NO, synthesized in endothelial cells by endothelial NO synthase (NOS 3), is believed to be an important endogenous pulmonary vasodilator substance that contributes to the normal low pulmonary vascular resistance. To selectively investigate the role of NOS 3 in the pulmonary circulation, mice with targeted disruption of the NOS 3 gene were studied. Pulmonary hemodynamics were studied by measuring pulmonary artery pressure, left ventricular end-diastolic pressure, and lower thoracic aortic flow by using a novel open-chest technique. Transient partial occlusion of the inferior vena cava was used to assess the pulmonary artery pressure-flow relationship. Tension developed by isolated pulmonary artery segments after acetylcholine stimulation was measured in vitro. The histological appearance of NOS 3-deficient and wild-type murine lungs was compared. NOS 3-deficient mice (n = 27), when compared with wild-type mice (n = 32), had pulmonary hypertension (pulmonary artery pressure, 19.0 +/- 0.8 versus 16.4 +/- 0.6 mm Hg [mean +/- SE]; P < .05) that was due to an increased total pulmonary resistance (62 +/- 6 versus 33 +/- 2 mm Hg.min.g.mL-1; P < .001). In vitro, acetylcholine induced vasodilation in the main pulmonary arteries of wild-type but not NOS 3-deficient mice. The morphology of the lungs of NOS 3-deficient mice did not differ from that of wild-type mice. We conclude that NOS 3 is a key enzyme responsible for providing basal pulmonary NO release. Congenital NOS 3 deficiency produces mild pulmonary hypertension in mice.

Emergence agitation after sevoflurane versus propofol in pediatric patients

UNLABELLED Sevoflurane may be associated with a high incidence of emergence agitation in preschool children. We tested the hypothesis that maintenance of anesthesia with propofol after sevoflurane induction would reduce the incidence of this excitatory behavior compared with continuing sevoflurane for maintenance. We conducted a randomized, single-blinded, two-period, cross-over study in 16 preschool age children undergoing repeated brief general anesthetics for eye examination. After sevoflurane induction, patients were randomly assigned to receive either sevoflurane or propofol anesthesia for maintenance. The alternative anesthetic was used for the maintenance of anesthesia on the second occasion. We compared the speed and quality of recovery characteristics of these anesthetics, as well as, overall parent satisfaction with anesthesia. Eight patients first received sevoflurane and the remaining eight patients first received propofol. Of the patients who received sevoflurane for the maintenance of anesthesia, 38% developed emergence agitation. In contrast, none developed emergence agitation when propofol was administered for maintenance of anesthesia. Despite emergence agitation, sevoflurane provided a shorter postanesthesia care unit stay than propofol. Parent satisfaction with anesthesia was greater with propofol than with sevoflurane. IMPLICATIONS In this cross-over study, we observed the incidence of emergence agitation with sevoflurane (38%) was significantly greater than with propofol (0%) in premedicated, preschool-aged children undergoing minor noninvasive surgery.

Nebulized sildenafil is a selective pulmonary vasodilator in lambs with acute pulmonary hypertension

ObjectiveTo determine whether inhalation of aerosolized sildenafil with and without inhaled nitric oxide (NO) causes selective pulmonary vasodilation in a sheep model of pulmonary hypertension. DesignA controlled laboratory study in instrumented, awake, spontaneously breathing lambs. SettingAnimal research laboratory affiliated with a university hospital. SubjectTwenty Suffolk lambs. InterventionsLambs were instrumented with a carotid artery catheter, a pulmonary artery catheter, and a tracheostomy tube and studied awake. After baseline measurements, pulmonary hypertension was induced by the continuous infusion of U46619, a thromboxane A2 analog. After breathing three concentrations of inhaled NO (2, 5, and 20 ppm), lambs were divided into two groups. Group 1 (n = 7) breathed aerosols containing 1, 10, and 30 mg of sildenafil alone, and group 2 (n = 4) simultaneously breathed NO (2 and 5 ppm) and aerosols containing 10 mg of sildenafil. Hemodynamic measurements were obtained before and at the end of each drug administration. Venous admixture was calculated, and plasma cyclic guanosine monophosphate and sildenafil concentrations were measured. Measurements and Main Results Aerosols containing 10 mg and 30 mg of sildenafil selectively decreased the pulmonary artery pressure by 21% ± 3% and 26% ± 3%, respectively (p < .05 vs. baseline pulmonary hypertension). When 10 mg of sildenafil was inhaled while simultaneously breathing 2 ppm and 5 ppm NO, the pulmonary artery pressure decreased by 35% ± 3% and 43% ± 2% (p < .05 vs. baseline pulmonary hypertension). Inhaled sildenafil did not impair systemic oxygenation, increase right-to-left intrapulmonary shunting, or impair the ability of inhaled NO to reduce right-to-left shunting. ConclusionsNebulized sildenafil is a selective pulmonary vasodilator that can potentiate the pulmonary vasodilating effects of inhaled NO.

Hydrogen Sulfide Improves Survival After Cardiac Arrest and Cardiopulmonary Resuscitation via a Nitric Oxide Synthase 3–Dependent Mechanism in Mice

Background— Sudden cardiac arrest (CA) is one of the leading causes of death worldwide. We sought to evaluate the impact of hydrogen sulfide (H2S) on the outcome after CA and cardiopulmonary resuscitation (CPR) in mouse. Methods and Results— Mice were subjected to 8 minutes of normothermic CA and resuscitated with chest compression and mechanical ventilation. Seven minutes after the onset of CA (1 minute before CPR), mice received sodium sulfide (Na2S) (0.55 mg/kg IV) or vehicle 1 minute before CPR. There was no difference in the rate of return of spontaneous circulation, CPR time to return of spontaneous circulation, and left ventricular function at return of spontaneous circulation between groups. Administration of Na2S 1 minute before CPR markedly improved survival rate at 24 hours after CPR (15/15) compared with vehicle (10/26; P=0.0001 versus Na2S). Administration of Na2S prevented CA/CPR-induced oxidative stress and ameliorated left ventricular and neurological dysfunction 24 hours after CPR. Delayed administration of Na2S at 10 minutes after CPR did not improve outcomes after CA/CPR. Cardioprotective effects of Na2S were confirmed in isolated-perfused mouse hearts subjected to global ischemia and reperfusion. Cardiomyocyte-specific overexpression of cystathionine γ-lyase (an enzyme that produces H2S) markedly improved outcomes of CA/CPR. Na2S increased phosphorylation of nitric oxide synthase 3 in left ventricle and brain cortex, increased serum nitrite/nitrate levels, and attenuated CA-induced mitochondrial injury and cell death. Nitric oxide synthase 3 deficiency abrogated the protective effects of Na2S on the outcome of CA/CPR. Conclusions— These results suggest that administration of Na2S at the time of CPR improves outcome after CA possibly via a nitric oxide synthase 3–dependent signaling pathway.

Congenital Deficiency of Nitric Oxide Synthase 2 Protects Against Endotoxin-Induced Myocardial Dysfunction in Mice

BackgroundSepsis can be complicated by severe myocardial dysfunction and is associated with increased nitric oxide (NO) production by inducible NO synthase (NOS2). To investigate the role of NOS2 in endotoxin-induced myocardial dysfunction in vivo, we studied wild-type and NOS2-deficient mice. Methods and ResultsSerial echocardiographic parameters of myocardial function were measured before and at 4, 7, 16, and 24 hours after an endotoxin challenge. Seven hours after challenge with either endotoxin or saline, systemic and left ventricular pressures were measured, and the first derivative of left ventricular developed pressure (dP/dt), slope of the end-systolic pressure–dimension relationship (SlopeLVESPD), and time constant of isovolumic relaxation (&tgr;) were calculated. Endotoxin challenge in wild-type mice decreased left ventricular fractional shortening, velocity of circumferential shortening, dP/dtmax, SlopeLVESPD, and dP/dtmin and increased time constant &tgr;. Endotoxin-induced myocardial dysfunction was associated with increased ventricular NOS2 gene expression and cGMP concentrations. Seven hours after endotoxin challenge, NOS2-deficient mice had greater fractional shortening, dP/dtmax, and SlopeLVESPD than did endotoxin-challenged wild-type mice. Measures of diastolic function, dP/dtmin and time constant &tgr;, were preserved in endotoxin-challenged NOS2-deficient mice. After endotoxin challenge in wild-type mice, early (3-hour) inhibition of NOS2 with l-N6-(1-iminoethyl)lysine hydrochloride prevented, whereas later (7-hour) inhibition could not reverse, endotoxin-induced myocardial dysfunction. ConclusionsThese results suggest that NOS2 is required for the development of systolic and diastolic dysfunction in murine sepsis.

Mitochondrial dysfunction remodels one-carbon metabolism in human cells

Mitochondrial dysfunction is associated with a spectrum of human disorders, ranging from rare, inborn errors of metabolism to common, age-associated diseases such as neurodegeneration. How these lesions give rise to diverse pathology is not well understood, partly because their proximal consequences have not been well-studied in mammalian cells. Here we provide two lines of evidence that mitochondrial respiratory chain dysfunction leads to alterations in one-carbon metabolism pathways. First, using hypothesis-generating metabolic, proteomic, and transcriptional profiling, followed by confirmatory experiments, we report that mitochondrial DNA depletion leads to an ATF4-mediated increase in serine biosynthesis and transsulfuration. Second, we show that lesioning the respiratory chain impairs mitochondrial production of formate from serine, and that in some cells, respiratory chain inhibition leads to growth defects upon serine withdrawal that are rescuable with purine or formate supplementation. Our work underscores the connection between the respiratory chain and one-carbon metabolism with implications for understanding mitochondrial pathogenesis. DOI: http://dx.doi.org/10.7554/eLife.10575.001

Inhaled Hydrogen Sulfide: A Rapidly Reversible Inhibitor of Cardiac and Metabolic Function in the Mouse

Background:Breathing hydrogen sulfide (H2S) has been reported to induce a suspended animation–like state with hypothermia and a concomitant metabolic reduction in rodents. However, the impact of H2S breathing on cardiovascular function remains incompletely understood. In this study, the authors investigated the cardiovascular and metabolic effects of inhaled H2S in a murine model. Methods:The impact of breathing H2S on cardiovascular function was examined using telemetry and echocardiography in awake mice. The effects of breathing H2S on carbon dioxide production and oxygen consumption were measured at room temperature and in a warmed environment. Results:Breathing H2S at 80 parts per million by volume at 27°C ambient temperature for 6 h markedly reduced heart rate, core body temperature, respiratory rate, and physical activity, whereas blood pressure remained unchanged. Echocardiography demonstrated that H2S exposure decreased both heart rate and cardiac output but preserved stroke volume. Breathing H2S for 6 h at 35°C ambient temperature (to prevent hypothermia) decreased heart rate, physical activity, respiratory rate, and cardiac output without altering stroke volume or body temperature. H2S breathing seems to induce bradycardia by depressing sinus node activity. Breathing H2S for 30 min decreased whole body oxygen consumption and carbon dioxide production at either 27° or 35°C ambient temperature. Both parameters returned to baseline levels within 10 min after the cessation of H2S breathing. Conclusions:Inhalation of H2S at either 27° or 35°C reversibly depresses cardiovascular function without changing blood pressure in mice. Breathing H2S also induces a rapidly reversible reduction of metabolic rate at either body temperature.

Xenon Provides Faster Emergence from Anesthesia than Does Nitrous Oxide-sevoflurane or Nitrous Oxide-isoflurane

Background: Xenon, an inert gas with anesthetic properties (minimum alveolar concentration [MAC] = 71%), has an extremely low blood:gas partition coefficient (0.14). Therefore, we predicted that xenon would provide more rapid emergence from anesthesia than does N2 O + isoflurane or N2 O + sevoflurane of equivalent MAC. Methods: Thirty American Society of Anesthsiologists class I or II patients undergoing total abdominal hysterectomy were randomly assigned to receive 60% xenon, 60% N2 O + 0.5% isoflurane, or 60% N2 O + 0.7% sevoflurane (all concentrations are end‐tidal: n = 10 per group). After placement of an epidural catheter, anesthesia was induced with standardized doses of midazolam, thiopental, and fentanyl. Thirty minutes later, xenon, N2 O + isoflurane, or N2 O + sevoflurane was started as previously assigned. These regimens were supplemented with epidural anesthesia with mepivacaine so that the mean arterial pressure and heart rate were controlled within 20% of the preoperative values. At the end of operation lasting approximately 2 h, all inhalational anesthetics were discontinued, and the patients were allowed to awaken while breathing spontaneously on an 8 l/min inflow of oxygen. A blinded investigator recorded the time until the patient opened her eyes on command (T1), was judged ready for extubation (T2), could correctly state her name, her date of birth, and the name of the hospital (T3), and could count backward from 10 to 1 in less than 15 s (T4). Results: Emergence times from xenon anesthesia were: T1, 3.4 +/‐ 0.9 min; T2, 3.6 +/‐ 1 min; T3, 5.2 +/‐ 1.4 min; and T4, 6.0 +/‐ 1.6 min (mean +/‐ SD). These were one half to one third of those from N2 O + sevoflurane (T1, 6.0 +/‐ 1.7 min; T4, 10.5 +/‐ 2.5 min) or N2 O + isoflurane (T1, 7.0 +/‐ 1.9 min; T4, 14.3 +/‐ 2.8 min) anesthesia. The three groups did not differ in terms of patient demographics, the duration of anesthesia, the amount of epidural mepivacaine administered, or the postoperative pain rating. No patient could recalls intraoperative events. Conclusions: Emergence from xenon anesthesia is two or three times faster than that from equal‐MAC N2 O + isoflurane or N2 O + sevoflurane anesthesia.

Inhaled Nitric Oxide Enables Artificial Blood Transfusion Without Hypertension

Background— One of the major obstacles hindering the clinical development of a cell-free, hemoglobin-based oxygen carrier (HBOC) is systemic vasoconstriction. Methods and Results— Experiments were performed in healthy mice and lambs by infusion of either murine tetrameric hemoglobin (0.48 g/kg) or glutaraldehyde-polymerized bovine hemoglobin (HBOC-201, 1.44 g/kg). We observed that intravenous infusion of either murine tetrameric hemoglobin or HBOC-201 induced prolonged systemic vasoconstriction in wild-type mice but not in mice congenitally deficient in endothelial nitric oxide (NO) synthase (NOS3). Treatment of wild-type mice by breathing NO at 80 ppm in air for 15 or 60 minutes or with 200 ppm NO for 7 minutes prevented the systemic hypertension induced by subsequent intravenous administration of murine tetrameric hemoglobin or HBOC-201 and did not result in conversion of plasma hemoglobin to methemoglobin. Intravenous administration of sodium nitrite (48 nmol) 5 minutes before infusion of murine tetrameric hemoglobin also prevented the development of systemic hypertension. In awake lambs, breathing NO at 80 ppm for 1 hour prevented the systemic hypertension caused by subsequent infusion of HBOC-201. Conclusions— These findings demonstrate that HBOC can cause systemic vasoconstriction by scavenging NO produced by NOS3. Moreover, in 2 species, inhaled NO administered before the intravenous infusion of HBOC can prevent systemic vasoconstriction without causing methemoglobinemia.