Altered carnitine homeostasis is associated with decreased mitochondrial function and altered nitric oxide signaling in lambs with pulmonary hypertension

Asymmetric dimethylarginine induces endothelial nitric-oxide synthase mitochondrial redistribution through the nitration-mediated activation of Akt1

We have recently demonstrated that asymmetric dimethylarginine (ADMA) induces the translocation of endothelial nitric-oxide synthase (eNOS) to the mitochondrion via a mechanism that requires protein nitration. Thus, the goal of this study was elucidate how eNOS redistributes to mitochondria and to identify the nitrated protein responsible for this event. Our data indicate that exposure of pulmonary arterial endothelial cells to ADMA enhanced eNOS phosphorylation at the Akt1-dependent phosphorylation sites Ser(617) and Ser(1179). Mutation of these serine residues to alanine (S617A and S1179A) inhibited nitration-mediated eNOS translocation to the mitochondria, whereas the phosphormimic mutations (S617D and S1179D) exhibited increased mitochondrial redistribution in the absence of ADMA. The overexpression of a dominant-negative Akt1 also attenuated ADMA-mediated eNOS mitochondrial translocation. Furthermore, ADMA enhanced Akt1 nitration and increased its activity. Mass spectrometry identified a single nitration site in Akt1 located at the tyrosine residue (Tyr(350)) located within the client-binding domain. Replacement of Tyr(350) with phenylalanine abolished peroxynitrite-mediated eNOS translocation to mitochondria. We also found that in the absence of ADMA, eNOS translocation decreased mitochondrial oxygen consumption and superoxide production without altering cellular ATP level. This suggests that under physiologic conditions, eNOS translocation enhances mitochondria coupling. In conclusion, we have identified a new mechanism by which eNOS translocation to mitochondria is regulated by the phosphorylation of eNOS at Ser(617) and Ser(1179) by Akt1 and that this is enhanced when Akt1 becomes nitrated at Tyr(350).

Chronic inhibition of PPAR-γ signaling induces endothelial dysfunction in the juvenile lamb

We have recently shown that the development of endothelial dysfunction in lambs with increased pulmonary blood flow (PBF) correlates with a decrease in peroxisome proliferator activated receptor-γ (PPAR-γ) signaling. Thus, in this study we determined if the loss of PPAR-γ signaling is necessary and sufficient to induce endothelial dysfunction by exposing lambs with normal PBF to the PPAR-γ antagonist, GW9662. Two-weeks of exposure to GW9662 significantly decreased both PPAR-γ protein and activity. In addition, although eNOS protein and nitric oxide metabolites (NO(x)) were significantly increased, endothelial dependent pulmonary vasodilation in response to acetylcholine was attenuated, indicative of endothelial dysfunction. To elucidate whether downstream mediators of vasodilation were impaired we examined soluble guanylate cyclase (sGC)-α and β subunit protein, cGMP levels, and phosphodiesterase 5 (PDE5) protein and activity, but we found no significant changes. However, we found that peroxynitrite levels were significantly increased in GW9662-treated lambs and this correlated with a significant increase in protein kinase G-1α (PKG-1α) nitration and a reduction in PKG activity. Peroxynitrite is formed by the interaction of NO with superoxide and we found that there was a significant increase in superoxide generation in GW9662-treated lambs. Further, we identified dysfunctional mitochondria as the primary source of the increased superoxide. Finally, we found that the mitochondrial dysfunction was due to a disruption in carnitine metabolism. We conclude that loss of PPAR-γ signaling is sufficient to induce endothelial dysfunction confirming its important role in maintaining a healthy vasculature.

PPAR-γ regulates carnitine homeostasis and mitochondrial function in a lamb model of increased pulmonary blood flow

Objective

Carnitine homeostasis is disrupted in lambs with endothelial dysfunction secondary to increased pulmonary blood flow (Shunt). Our recent studies have also indicated that the disruption in carnitine homeostasis correlates with a decrease in PPAR-γ expression in Shunt lambs. Thus, this study was carried out to determine if there is a causal link between loss of PPAR-γ signaling and carnitine dysfunction, and whether the PPAR-γ agonist, rosiglitazone preserves carnitine homeostasis in Shunt lambs.

Methods and Results

siRNA-mediated PPAR-γ knockdown significantly reduced carnitine palmitoyltransferases 1 and 2 (CPT1 and 2) and carnitine acetyltransferase (CrAT) protein levels. This decrease in carnitine regulatory proteins resulted in a disruption in carnitine homeostasis and induced mitochondrial dysfunction, as determined by a reduction in cellular ATP levels. In turn, the decrease in cellular ATP attenuated NO signaling through a reduction in eNOS/Hsp90 interactions and enhanced eNOS uncoupling. In vivo, rosiglitazone treatment preserved carnitine homeostasis and attenuated the development of mitochondrial dysfunction in Shunt lambs maintaining ATP levels. This in turn preserved eNOS/Hsp90 interactions and NO signaling.

Conclusion

Our study indicates that PPAR-γ signaling plays an important role in maintaining mitochondrial function through the regulation of carnitine homeostasis both in vitro and in vivo. Further, it identifies a new mechanism by which PPAR-γ regulates NO signaling through Hsp90. Thus, PPAR-γ agonists may have therapeutic potential in preventing the endothelial dysfunction in children with increased pulmonary blood flow.

Preserving mitochondrial function prevents the proteasomal degradation of GTP cyclohydrolase I

The development of pulmonary hypertension is a common accompaniment of congenital heart disease (CHD) with increased pulmonary blood flow. Our recent evidence suggests that asymmetric dimethylarginine (ADMA)-induced mitochondrial dysfunction causes endothelial nitric oxide synthase (eNOS) uncoupling secondary to a proteasome-dependent degradation of GTP cyclohydrolase I (GCH1) that results in a decrease in the NOS cofactor tetrahydrobiopterin (BH(4)). Decreases in NO signaling are thought to be an early hallmark of endothelial dysfunction. As l-carnitine plays an important role in maintaining mitochondrial function, in this study we examined the protective mechanisms and the therapeutic potential of l-carnitine on NO signaling in pulmonary arterial endothelial cells and in a lamb model of CHD and increased pulmonary blood flow (Shunt). Acetyl-l-carnitine attenuated the ADMA-mediated proteasomal degradation of GCH1. This preservation was associated with a decrease in the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) and a decrease in its ubiquitination. This in turn prevented the decrease in BH(4) levels induced by ADMA and preserved NO signaling. Treatment of Shunt lambs with l-carnitine also reduced GCH1/CHIP interactions, attenuated the ubiquitination and degradation of GCH1, and increased BH(4) levels compared to vehicle-treated Shunt lambs. The increases in BH(4) were associated with decreased NOS uncoupling and enhanced NO generation. Thus, we conclude that L-carnitine may have a therapeutic potential in the treatment of pulmonary hypertension in children with CHD with increased pulmonary blood flow.

Evaluation of asymmetric dimethylarginine, arginine, and carnitine metabolism in pediatric sepsis

OBJECTIVE

Increased plasma concentrations of the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine, decreased arginine bioavailability, and mitochondrial dysfunction have been reported in adult sepsis. We studied whether asymmetric dimethylarginine, arginine, and carnitine metabolism (a measure of mitochondrial dysfunction) are altered in pediatric sepsis and whether these are clinically useful biomarkers.

DESIGN

: Prospective, observational study.

SETTING

Pediatric intensive care unit at an academic medical center.

PATIENTS

: Ninety patients ≤ 18 yrs old, 30 with severe sepsis or septic shock, compared with 30 age-matched febrile and 30 age-matched healthy control subjects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma asymmetric dimethylarginine and whole blood arginine, citrulline, ornithine, and acylcarnitine:free carnitine ratio were measured daily for septic patients and once for control subjects using tandem mass spectrometry. Plasma asymmetric dimethylarginine concentration (median; interquartile range µmol/L) on day 1 was lower in severe sepsis and septic shock (0.38; 0.30-0.56) compared with febrile (0.45; 0.40-0.59) and healthy (0.60; 0.54-0.67) control subjects (p < .001), although decreased asymmetric dimethylarginine was predominantly found in neutropenic patients. Day 1 arginine was lower in septic (10; interquartile range, 7-20 µmol/L) compared with healthy patients (32; interquartile range, 23-40; p < .001), and the arginine:ornithine ratio was decreased in sepsis, indicating increased arginase activity (an alternative pathway for arginine metabolism). The arginine:asymmetric dimethylarginine and acylcarnitine:free carnitine ratios did not differ between septic and control patients. Asymmetric dimethylarginine was inversely correlated with organ dysfunction by Pediatric Logistic Organ Dysfunction score (r = -0.50, p = .009), interleukin-6 (r = -0.55, p = .01), and interleukin-8 (r = -0.52, p = .03) on admission. Arginine, arginine:asymmetric dimethylarginine, and acylcarnitine:free carnitine were not associated with organ dysfunction or outcomes.

CONCLUSIONS

Asymmetric dimethylarginine was decreased in pediatric sepsis and was inversely associated with inflammation and organ dysfunction. This suggests that inhibition of nitric oxide synthase by asymmetric dimethylarginine accumulation is unlikely to impact sepsis pathophysiology in septic children despite decreased arginine bioavailability. We did not find an association of asymmetric dimethylarginine with altered carnitine metabolism nor were asymmetric dimethylarginine, arginine, and acylcarnitine:free carnitine useful as clinical biomarkers.

Oxidative stress and the development of endothelial dysfunction in congenital heart disease with increased pulmonary blood flow: lessons from the neonatal lamb

Congenital heart diseases associated with increased pulmonary blood flow commonly leads to the development of pulmonary hypertension. However, most patients who undergo histological evaluation have advanced pulmonary hypertension, and therefore it has been difficult to investigate aberrations in signaling cascades that precede the development of overt vascular remodeling. This review discusses the role played by both oxidative and nitrosative stress in the lung and their impact on the signaling pathways that regulate vasodilation, vessel growth, and vascular remodeling in the neonatal lung exposed to increased pulmonary blood flow.

Glutathione supplementation attenuates lipopolysaccharide-induced mitochondrial dysfunction and apoptosis in a mouse model of acute lung injury

Acute lung injury (ALI) is a life threatening condition associated with hypoxemia, diffuse alveolar damage, inflammation, and loss of lung function. Lipopolysaccharide (LPS; endotoxin) from the outer membrane of Gram-negative bacteria is a major virulence factor involved in the development of ALI. The depletion of glutathione (GSH), an essential intra- and extra-cellular protective antioxidant, by LPS is an important event that contributes to the elevation in reactive oxygen species. Whether restoring GSH homeostasis can effectively ameliorate mitochondrial dysfunction and cellular apoptosis in ALI is unknown and therefore, was the focus of this study. In peripheral lung tissue of LPS-treated mice, hydrogen peroxide and protein nitration levels were significantly increased. Pre-treatment with GSH-ethyl ester (GSH-EE) prevented this increase in oxidative stress. LPS also increased the lactate/pyruvate ratio, attenuated SOD2 protein levels, and decreased ATP levels in the mouse lung indicative of mitochondrial dysfunction. Again, GSH-EE treatment preserved the mitochondrial function. Finally, our studies showed that LPS induced an increase in the mitochondrial translocation of Bax, caspase 3 activation, and nuclear DNA fragmentation and these parameters were all prevented with GSH-EE. Thus, this study suggests that GSH-EE supplementation may reduce the mitochondrial dysfunction associated with ALI.

Reactive oxygen and nitrogen species in pulmonary hypertension

Pulmonary vascular disease can be defined as either a disease affecting the pulmonary capillaries and pulmonary arterioles, termed pulmonary arterial hypertension, or a disease affecting the left ventricle, called pulmonary venous hypertension. Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary circulation characterized by endothelial dysfunction, as well as intimal and smooth muscle proliferation. Progressive increases in pulmonary vascular resistance and pressure impair the performance of the right ventricle, resulting in declining cardiac output, reduced exercise capacity, right-heart failure, and ultimately death. While the primary and heritable forms of the disease are thought to affect over 5000 patients in the United States, the disease can occur secondary to congenital heart disease, most advanced lung diseases, and many systemic diseases. Multiple studies implicate oxidative stress in the development of PAH. Further, this oxidative stress has been shown to be associated with alterations in reactive oxygen species (ROS), reactive nitrogen species (RNS), and nitric oxide (NO) signaling pathways, whereby bioavailable NO is decreased and ROS and RNS production are increased. Many canonical ROS and NO signaling pathways are simultaneously disrupted in PAH, with increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and xanthine oxidoreductase, uncoupling of endothelial NO synthase (eNOS), and reduction in mitochondrial number, as well as impaired mitochondrial function. Upstream dysregulation of ROS/NO redox homeostasis impairs vascular tone and contributes to the pathological activation of antiapoptotic and mitogenic pathways, leading to cell proliferation and obliteration of the vasculature. This paper will review the available data regarding the role of oxidative and nitrosative stress and endothelial dysfunction in the pathophysiology of pulmonary hypertension, and provide a description of targeted therapies for this disease.

Attenuated vasodilatation in lambs with endogenous and exogenous activation of cGMP signaling: role of protein kinase G nitration

Pulmonary vasodilation is mediated through the activation of protein kinase G (PKG) via a signaling pathway involving nitric oxide (NO), natriuretic peptides (NP), and cyclic guanosine monophosphate (cGMP). In pulmonary hypertension secondary to congenital heart disease, this pathway is endogenously activated by an early vascular upregulation of NO and increased myocardial B-type NP expression and release. In the treatment of pulmonary hypertension, this pathway is exogenously activated using inhaled NO or other pharmacological agents. Despite this activation of cGMP, vascular dysfunction is present, suggesting that NO-cGMP independent mechanisms are involved and were the focus of this study. Exposure of pulmonary artery endothelial or smooth muscle cells to the NO donor, Spermine NONOate (SpNONOate), increased peroxynitrite (ONOO(-) ) generation and PKG-1α nitration, while PKG-1α activity was decreased. These changes were prevented by superoxide dismutase (SOD) or manganese(III)tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP) and mimicked by the ONOO(-) donor, 3-morpholinosydnonimine N-ethylcarbamide (SIN-1). Peripheral lung extracts from 4-week old lambs with increased pulmonary blood flow and pulmonary hypertension (Shunt lambs with endogenous activation of cGMP) or juvenile lambs treated with inhaled NO for 24 h (with exogenous activation of cGMP) revealed increased ONOO(-) levels, elevated PKG-1α nitration, and decreased kinase activity without changes in PKG-1α protein levels. However, in Shunt lambs treated with L-arginine or lambs administered polyethylene glycol conjugated-SOD (PEG-SOD) during inhaled NO exposure, ONOO(-) and PKG-1α nitration were diminished and kinase activity was preserved. Together our data reveal that vascular dysfunction can occur, despite elevated levels of cGMP, due to PKG-1α nitration and subsequent attenuation of activity.

Therapeutic approaches using nitric oxide in infants and children

Pulmonary hypertension contributes significantly to the morbidity and mortality associated with many pediatric pulmonary and cardiac diseases. Nitric oxide, a gas molecule, is a unique pharmaceutical agent that can be inhaled and thus delivered directly to the lung. Inhaled nitric oxide was approved by the FDA in 1999 as a therapy for infants with persistent pulmonary hypertension. Since then, the use of inhaled nitric oxide has expanded to other neonatal and pediatric conditions, and our knowledge of its properties and mechanisms of action has increased tremendously. This review discusses the physiology of nitric oxide signaling, the most common indications for its clinical use, and promising new investigations that may enhance endogenous production of nitric oxide and/or improve vascular response to it.

Endothelin-1 overexpression restores diastolic function in eNOS knockout mice

BACKGROUND

The cardiac nitric oxide and endothelin-1 (ET-1) systems are closely linked and play a critical role in cardiac physiology. The balance between both systems is often disturbed in cardiovascular diseases. To define the cardiac effect of excessive ET-1 in a status of nitric oxide deficiency, we compared left ventricular function and morphology in wild-type mice, ET-1 transgenic (ET(+/+)) mice, endothelial nitric oxide synthase knockout (eNOS(-/-)) mice, and ET(+/+)eNOS(-/-) mice.

METHODS AND RESULTS

eNOS(-/-) and ET(+/+)eNOS(-/-) mice developed high blood pressure compared with wild-type and ET(+/+) mice. Left ventricular catheterization showed that eNOS(-/-) mice, but not ET(+/+)eNOS(-/-) , developed diastolic dysfunction characterized by increased end-diastolic pressure and relaxation constant tau. To elucidate the causal molecular mechanisms driving the rescue of diastolic function in ET(+/+)eNOS(-/-) mice, the cardiac proteome was analyzed. Two-dimensional gel electrophoresis coupled to mass spectrometry offers an appropriate hypothesis-free approach. ET-1 overexpression on an eNOS(-/-) background led to an elevated abundance and change in posttranslational state of antioxidant enzymes (e.g., peroxiredoxin-6, glutathione S-transferase mu 2, and heat shock protein beta 7). In contrast to ET(+/+)eNOS(-/-) mice, eNOS(-/-) mice showed an elevated abundance of proteins responsible for sarcomere disassembly (e.g., cofilin-1 and cofilin-2). In ET(+/+)eNOS(-/-) mice, glycolysis was favored at the expense of fatty acid oxidation.

CONCLUSION

eNOS(-/-) mice developed diastolic dysfunction; this was rescued by ET-1 transgenic overexpression. This study furthermore suggests that cardiac ET-1 overexpression in case of eNOS deficiency causes specifically the regulation of proteins playing a role in oxidative stress, myocytes contractility, and energy metabolism.

C-terminus of heat shock protein 70-interacting protein-dependent GTP cyclohydrolase I degradation in lambs with increased pulmonary blood flow

We showed that nitric oxide (NO) signaling is decreased in the pulmonary vasculature before the development of endothelial dysfunction in a lamb model of congenital heart disease and increased pulmonary blood flow (Shunt). The elucidation of the molecular mechanism by which this occurs was the purpose of this study. Here, we demonstrate that concentrations of the endogenous NO synthase (NOS) inhibitor, asymmetric dimethylarginine (ADMA), are elevated, whereas the NOS cofactor tetrahydrobiopterin (BH(4)) is decreased in Shunt lambs. Our previous studies demonstrated that ADMA decreases heat shock protein-90 (Hsp90) chaperone activity, whereas other studies suggest that guanosine-5'-triphosphate cyclohydrolase 1 (GCH1), the rate-limiting enzyme in the generation of BH(4), may be a client protein for Hsp90. Thus, we determined whether increases in ADMA could alter GCH1 protein and activity. Our data demonstrate that ADMA decreased GCH1 protein, but not mRNA concentrations, in pulmonary arterial endothelial cells (PAECs) because of the ubiquitination and proteasome-dependent degradation of GCH1. We also found that Hsp90-GCH1 interactions were reduced, whereas the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) increased in ADMA-exposed PAECs. The overexpression of CHIP potentiated, whereas a CHIP U-box domain mutant attenuated, ADMA-induced GCH1 degradation and reductions in cellular BH(4) concentrations. We also found in vivo that Hsp90/GCH1 interactions are decreased, whereas GCH1-Hsp70 and GCH1-CHIP interactions and GCH1 ubiquitination are increased. Finally, we found that supplementation with l-arginine restored Hsp90-GCH1 interactions and increased both BH(4) and NO(x) concentrations in Shunt lambs. In conclusion, increased concentrations of ADMA can indirectly alter NO signaling through decreased cellular BH(4) concentrations, secondary to the disruption of Hsp90-GCH1 interactions and the CHIP-dependent proteasomal degradation of GCH1.

Protein complex formation with heat shock protein 90 in chronic hypoxia-induced pulmonary hypertension in newborn piglets

Aberrant interactions between heat shock protein (Hsp)90 and its client proteins could contribute to pulmonary hypertension. We tested the hypotheses that 1) the interaction between Hsp90 and its known client protein, endothelial nitric oxide synthase (eNOS), is impaired in pulmonary resistance arteries (PRAs) from piglets with pulmonary hypertension caused by exposure to 3 or 10 days of hypoxia and 2) Hsp90 interacts with the prostanoid pathway proteins prostacyclin synthase (PGIS) and/or thromboxane synthase (TXAS). We also determined whether Hsp90 antagonism with geldanamycin alters the agonist-induced synthesis of prostacyclin and thromboxane or alters PRA responses to these prostaglandin metabolites. Compared with normoxic piglets, less eNOS coimmunoprecipitated with Hsp90 in PRAs from hypoxic piglets. Despite reduced Hsp90-eNOS interactions, dilation to ACh was enhanced in geldanamycin-treated PRAs from hypoxic, but not normoxic, piglets. In PRAs from all groups of piglets, PGIS and TXAS coimmunoprecipitated with Hsp90. Geldanamycin reduced the ACh-induced synthesis of prostacyclin and thromboxane and altered responses to the thromboxane mimetic U-46619 in PRAs from all groups. Although geldanamycin enhanced responses to prostacyclin in PRAs from both groups of hypoxic piglets, geldanamycin had no effect on prostacyclin responses in PRAs from either group of normoxic piglets. Our findings indicate that Hsp90 influences both prostanoid and eNOS signaling in the pulmonary circulation of newborn piglets and that the impact of pharmacological inhibition of Hsp90 on these signaling pathways is altered during exposure to chronic hypoxia.

Perinatal changes in superoxide generation in the ovine lung: Alterations associated with increased pulmonary blood flow

Although alterations in ROS generating systems are well described in several vascular disorders, there is very limited information on the perinatal regulation of these systems in the lung both during normal development and in pulmonary hypertension. Thus, this study was undertaken to explore how the two predominant superoxide generating systems, nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase) and xanthine oxidase (XO), are developmentally regulated in control lambs and in our established lamb model of increased pulmonary blood flow (Shunt) over the first 2months of life. We found that the levels of p47(phox), p67(phox), and Rac1 subunits of NADPH oxidase complex were altered. During the first two months of life there was no change in p47(phox) protein levels in either normal or Shunt lambs. However, both p67(phox) and Rac1 protein levels decreased over time. In addition, p47(phox) protein levels were significantly increased in shunt lambs at 2- and 4-, but not 8-weeks of age compared to age-matched controls while levels of the p67(phox) subunit were decreased at 8-weeks of age in the Shunts but unchanged at other time periods. Furthermore, Rac1 protein expression was significantly increased in the Shunts only at 4weeks of age. These data correlated with a significant increase in NADPH oxidase dependent superoxide generation at 2- and 4-, but not 8-weeks of age in the Shunts. During normal development XO levels significantly increased over time in normal lambs but significantly decreased in the Shunts. In addition, XO protein levels were significantly increased in the Shunt at 2- and 4-weeks of age but significantly decreased at 8-weeks. Again this correlated with a significant increase in XO dependent superoxide generation at 2- and 4-, but not 8-weeks of age in the Shunts. Collectively, our findings suggest that NADPH oxidase and XO are major contributors to superoxide generation both during the normal development and during the development of pulmonary hypertension.

Mechanisms of nitric oxide synthase uncoupling in endotoxin-induced acute lung injury: role of asymmetric dimethylarginine

Acute lung injury (ALI) is associated with severe alterations in lung structure and function and is characterized by hypoxemia, pulmonary edema, low lung compliance and widespread capillary leakage. Asymmetric dimethylarginine (ADMA), a known cardiovascular risk factor, has been linked to endothelial dysfunction and the pathogenesis of a number of cardiovascular diseases. However, the role of ADMA in the pathogenesis of ALI is less clear. ADMA is metabolized via hydrolytic degradation to l-citrulline and dimethylamine by the enzyme, dimethylarginine dimethylaminohydrolase (DDAH). Recent studies suggest that lipopolysaccharide (LPS) markedly increases the level of ADMA and decreases DDAH activity in endothelial cells. Thus, the purpose of this study was to determine if alterations in the ADMA/DDAH pathway contribute to the development of ALI initiated by LPS-exposure in mice. Our data demonstrate that LPS exposure significantly increases ADMA levels and this correlates with a decrease in DDAH activity but not protein levels of either DDAH I or DDAH II isoforms. Further, we found that the increase in ADMA levels cause an early decrease in nitric oxide (NO(x)) and a significant increase in both NO synthase (NOS)-derived superoxide and total nitrated lung proteins. Finally, we found that decreasing peroxynitrite levels with either uric acid or Manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTymPyp) significantly attenuated the lung leak associated with LPS-exposure in mice suggesting a key role for protein nitration in the progression of ALI. In conclusion, this is the first study that suggests a role of the ADMA/DDAH pathway during the development of ALI in mice and that ADMA may be a novel therapeutic biomarker to ascertain the risk for development of ALI.

Alterations in lung arginine metabolism in lambs with pulmonary hypertension associated with increased pulmonary blood flow

Previous studies demonstrate impaired nitric oxide (NO) signaling in children and animal models with congenital heart defects and increased pulmonary blood flow. However, the molecular mechanisms underlying these alterations remain incompletely understood. The purpose of this study was to determine if early changes in arginine metabolic pathways could play a role in the reduced NO signaling demonstrated in our lamb model of congenital heart disease with increased pulmonary blood flow (Shunt lambs). The activities of the arginine recycling enzymes, argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) were both decreased in lung tissues of Shunt lambs while arginase activity was increased. Associated with these alterations, lung L-arginine levels were decreased. These changes correlated with an increase in NO synthase-derived reactive oxygen species (ROS) generation. This study provides further insights into the molecular mechanisms leading to decreased NO signaling in Shunt lambs and suggests that altered arginine metabolism may play a role in the development of the endothelial dysfunction associated with pulmonary hypertension secondary to increased pulmonary blood flow.

CARNITINE HOMEOSTASIS, MITOCHONDRIAL FUNCTION, AND CARDIOVASCULAR DISEASE

Carnitines are involved in mitochondrial transport of fatty acids and are of critical importance for maintaining normal mitochondrial function. This review summarizes recent experimental and clinical studies showing that mitochondrial dysfunction secondary to a disruption of carnitine homeostasis may play a role in decreased NO signaling and the development of endothelial dysfunction. Future challenges include development of agents that can positively modulate L-carnitine homeostasis which may have high therapeutic potential.

Progressive dysfunction of nitric oxide synthase in a lamb model of chronically increased pulmonary blood flow: a role for oxidative stress

Cardiac defects associated with increased pulmonary blood flow result in pulmonary vascular dysfunction that may relate to a decrease in bioavailable nitric oxide (NO). An 8-mm graft (shunt) was placed between the aorta and pulmonary artery in 30 late gestation fetal lambs; 27 fetal lambs underwent a sham procedure. Hemodynamic responses to ACh (1 microg/kg) and inhaled NO (40 ppm) were assessed at 2, 4, and 8 wk of age. Lung tissue nitric oxide synthase (NOS) activity, endothelial NOS (eNOS), neuronal NOS (nNOS), inducible NOS (iNOS), and heat shock protein 90 (HSP90), lung tissue and plasma nitrate and nitrite (NO(x)), and lung tissue superoxide anion and nitrated eNOS levels were determined. In shunted lambs, ACh decreased pulmonary artery pressure at 2 wk (P < 0.05) but not at 4 and 8 wk. Inhaled NO decreased pulmonary artery pressure at each age (P < 0.05). In control lambs, ACh and inhaled NO decreased pulmonary artery pressure at each age (P < 0.05). Total NOS activity did not change from 2 to 8 wk in control lambs but increased in shunted lambs (ANOVA, P < 0.05). Conversely, NO(x) levels relative to NOS activity were lower in shunted lambs than controls at 4 and 8 wk (P < 0.05). eNOS protein levels were greater in shunted lambs than controls at 4 wk of age (P < 0.05). Superoxide levels increased from 2 to 8 wk in control and shunted lambs (ANOVA, P < 0.05) and were greater in shunted lambs than controls at all ages (P < 0.05). Nitrated eNOS levels were greater in shunted lambs than controls at each age (P < 0.05). We conclude that increased pulmonary blood flow results in progressive impairment of basal and agonist-induced NOS function, in part secondary to oxidative stress that decreases bioavailable NO.