A novel mechanism for pulmonary arterial hypertension?

Evaluation of Asymmetric Dimethylarginine Levels in Patients With Chronic Thromboembolic Pulmonary Hypertension Undergoing Pulmonary Endarterectomy

BACKGROUND

Chronic thromboembolic pulmonary hypertension (CTEPH) is a form of pulmonary embolism, and pulmonary endarterectomy (PEA) is the surgical treatment. Asymmetric dimethylarginine (ADMA) levels are increased in pulmonary hypertension. This study aimed to investigate serum ADMA levels in patients with CTEPH, the effect of PEA on ADMA, and its prognostic value in long-term mortality.

METHOD

Eighty (80) patients with CTEPH and 32 healthy controls were included. Preoperative serum ADMA levels, determined using an enzyme-linked immunosorbent assay, were compared between patients with CTEPH and controls. Of 80 patients, 64 had PEA. Pre- and 6-month postoperative serum ADMA levels, 6-minute walk distance (6MWD), and haemodynamic parameters were collected from patients undergoing PEA. Patients were followed-up for survival analysis.

RESULTS

Mean ± standard deviation serum ADMA levels were significantly higher in patients with CTEPH compared with controls (0.79±0.32 μmol/L vs 0.52±0.12 μmol/L; p=0.0001). Statistically significant differences were observed between preoperative and postoperative serum ADMA levels (0.78±0.30 μmol/L vs 0.62±0.22 μmol/L; p=0.0001), 6MWD (p=0.0001), and pulmonary vascular resistance (p=0.0001) in 60 patients who underwent and survived PEA. The decrease in serum ADMA levels and increase in 6MWD were significantly correlated (r=-0.286, p=0.027). No other correlation was found. Perioperative mortality was 6.3%, and the survival rate with a mean follow-up of 34.57±8.20 months was 93.3%. Patients with serum ADMA levels >0.8 μmol/L had a significantly lower survival rate (logrank: 5.86; p=0.015).

CONCLUSIONS

Levels of circulating ADMA might add diagnostic and prognostic information in CTEPH. Pulmonary endarterectomy is associated with an improvement in serum ADMA levels. Preoperative serum ADMA levels may be useful for estimating the outcome of PEA.

Effect of Ambrisentan Therapy on the Expression of Endothelin Receptor, Endothelial Nitric Oxide Synthase and NADPH Oxidase 4 in Monocrotaline-induced Pulmonary Arterial Hypertension Rat Model

Background and Objectives

Elevated endothelin (ET)-1 level is strongly correlated with the pathogenesis of pulmonary arterial hypertension (PAH). Expression level of nicotinamide adenine dinucleotide phosphate oxidase (NOX) 4 is increased in the PAH patients. Ambrisentan, a selective endothelin receptor A (ERA) antagonist, is widely used in PAH therapy. The current study was undertaken to evaluate the effects of ambrisentan treatment in the monocrotaline (MCT)-induced PAH rat model.

Methods

Rats were categorized into control group (C), monocrotaline group (M) and ambrisentan group (Am). The M and Am were subcutaneously injected 60 mg/kg MCT at day 0, and in Am, ambrisentan was orally administered the day after MCT injection for 4 weeks. The right ventricle (RV) pressure was measured and pathological changes of the lung tissues were observed by Victoria blue staining. Protein expressions of ET-1, ERA, endothelial nitric oxide synthase (eNOS) and NOX4 were confirmed by western blot analysis.

Results

Ambrisentan treatment resulted in a recovery of the body weight and RV/left ventricle+septum at week 4. The RV pressure was lowered at weeks 2 and 4 after ambrisentan administration. Medial wall thickening of pulmonary arterioles and the number of intra-acinar arteries were also attenuated by ambrisentan at week 4. Protein expression levels of ET-1 and eNOS were recovered at weeks 2 and 4, and ERA levels recovered at week 4.

Conclusions

Ambrisentan administration resulted in the recovery of ET-1, ERA and eNOS protein expression levels in the PAH model. However, the expression level of NOX4 remained unaffected after ambrisentan treatment.

Long-Term Chronic Intermittent Hypobaric Hypoxia in Rats Causes an Imbalance in the Asymmetric Dimethylarginine/Nitric Oxide Pathway and ROS Activity: A Possible Synergistic Mechanism for Altitude Pulmonary Hypertension?

Chronic intermittent hypoxia (CIH) and chronic hypoxia (CH) are associated with high-altitude pulmonary hypertension (HAPH). Asymmetric dimethylarginine (ADMA), a NO synthase (NOS) inhibitor, may contribute to HAPH. This study assessed changes in the ADMA/NO pathway and the underlying mechanisms in rat lungs following exposure to CIH or CH simulated in a hypobaric chamber at 428 Torr. Twenty-four adult Wistar rats were randomly assigned to three groups: CIH2x2 (2 days of hypoxia/2 days of normoxia), CH, and NX (permanent normoxia), for 30 days. All analyses were performed in whole lung tissue. L-Arginine and ADMA were analyzed using LC-MS/MS. Under both hypoxic conditions right ventricular hypertrophy was observed (p < 0.01) and endothelial NOS mRNA increased (p < 0.001), but the phosphorylated/nonphosphorylated vasodilator-stimulated phosphoprotein (VASP) ratio was unchanged. ADMA increased (p < 0.001), whereas dimethylarginine dimethylaminohydrolase (DDAH) activity decreased only under CH (p < 0.05). Although arginase activity increased (p < 0.001) and L-arginine exhibited no changes, the L-arginine/ADMA ratio decreased significantly (p < 0.001). Moreover, NOX4 expression increased only under CH (p < 0.01), but malondialdehyde (MDA) increased (up to 2-fold) equally in CIH2x2 and CH (p < 0.001). Our results suggest that ADMA and oxidative stress likely reduce NO bioavailability under altitude hypoxia, which implies greater pulmonary vascular reactivity and tone, despite the more subdued effects observed under CIH.

The endothelial ADMA/NO pathway in hypoxia-related chronic respiratory diseases

Since its discovery, many adhere to the view that asymmetric dimethylarginine (ADMA), as an inhibitor of the synthesis of nitric oxide (NO), contributes to the pathogenesis of various diseases. Particularly, this is evident in disease of the cardiovascular system, in which endothelial dysfunction results in an imbalance between vasoconstriction and vasodilatation. Even if increased ADMA concentrations are closely related to an endothelial dysfunction, several studies pointed to a potential beneficial effect of ADMA, mainly in the context of angioproliferative disease such as cancer and fibrosis. Antiproliferative properties of ADMA independent of NO have been identified in this context. In particular, the regulation of ADMA by its degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH) is the object of many studies. DDAH is discussed as a promising therapeutic target for the indirect regulation of NO. In hypoxia-related chronic respiratory diseases, this controversy discussion of ADMA and DDAH is particularly evident and is therefore subject of this review.

Serum asymmetric dimethylarginine, nitrate, vitamin B(12), and homocysteine levels in individuals with pulmonary embolism

We aimed to analyze the pre- and posttreatment serum asymmetric dimethylarginine (ADMA), nitrate (NO₃), vitamin B₁₂ and homocysteine levels in pulmonary embolism (PTE) patients and to determine the prognostic value of these variables in predicting chronic thromboembolic pulmonary hypertension (CTEPH). This study was conducted in 64 patients. The patients were classified into the two groups: patients with normal pulmonary artery pressure (PAP) (group I) and patients with high PAP with persistent lung perfusion defects or who died at the end of 3 months of therapy (group II). We found statistically significant differences between two groups with respect to the partial oxygen pressure, the oxygen saturation, and the PAP, but there was no difference between the two groups with respect to the pretreatment ADMA, NO₃, or homocysteine levels. The vitamin B₁₂ levels were higher in group II. The NO₃ levels increased and the ADMA and vitamin B₁₂ levels decreased with treatment in both groups. These results suggest that these parameters are not predictive of the development of CTEPH.

Nitric oxide and nursing: a review

AIMS AND OBJECTIVES

This paper, therefore, aimed to review published literature in this area of pharmacological exploitation, to look at the therapeutic applications and clinical relevance and, by so doing, provide an accessible source for nurses to gain insight into the role of nitric oxide in the clinical setting.

BACKGROUND

Nitric oxide is a chemical mediator fundamental in the maintenance of adequate tissue perfusion and effective cardiovascular function; a major endogenous regulator of vascular tone. The use of nitrates are well established as pharmacological agents but it is only recently that it has been recognized that they act as a source of nitric oxide. Although widely addressed within the medical literature, there appears to be a paucity of nursing literature that explores either its physiological action, or its relevance to nursing practice.

CONCLUSIONS

This literature review provides an overview of the use of nitric oxide and its implications for nursing practice and patient outcomes.

RELEVANCE TO CLINICAL PRACTICE

Knowledge of nitric oxide and its action is pertinent to nurses across diverse specialities. It helps in understanding the principles of many nitrogen-derived medications which nurses administer to their patients on a daily basis. In terms of oral medication, this is demonstrated by greater insights into the action of nitrates, the appreciation of surprising developments in medications such as sildenafil and the development of new drug opportunities such as nitric oxide-non-steroidal anti-inflammatory drugs. Equally, the use of inhaled nitric oxide therapy in adult and neonatal critical care units appears to be an increasingly valuable source of treatment. A particular research challenge is found in the attempt at nitric oxide inhibition in the management of septic shock. The authors argue that understanding such esoteric areas of therapeutic developments is increasingly to be part of the repertoire of knowledge and skills for nurses in the 21st century.

NOS2 polymorphisms associated with the susceptibility to pulmonary arterial hypertension with systemic sclerosis: contribution to the transcriptional activity

Systemic sclerosis (SSc) is a connective tissue disease characterized by tissue fibrosis. One of several complications of SSc, pulmonary arterial hypertension (PAH) can be refractory to treatment, both novel and established. In the present study we investigated the ratio of circulating nitric oxide to endothelin-1 in patients with both SSc and PAH, and determined whether polymorphisms in NOS2 (the nitric oxide synthase 2 gene) are associated with susceptibility to PAH. Endothelin-1 in plasma and nitric oxide metabolites (nitrate and nitrite) in serum were measured. The nitric oxide/endothelin-1 ratio was significantly lower in patients with both SSc and PAH than in patients with SSc only or in healthy control individuals. We confirmed the presence of two single nucleotide polymorphisms at positions -1,026 and -277 and a pentanucleotide repeat (CCTTT) at -2.5 kilobases. There were significant differences in single nucleotide polymorphisms between patients with SSc who had PAH and those who did not, and between patients with both SSc and PAH and healthy control individuals. The CCTTT repeat was significantly shorter in patients with both SSc and PAH than in patients with SSc only or in healthy control individuals. Transcriptional activity were analyzed using the luciferase reporter assay. The transcriptional activity of NOS2 was much greater in fibroblasts transfected by a vector with a long allele of the CCTTT repeat than in those transfected by a vector with a short allele. Polymorphisms in the NOS2 gene are associated with transcriptional activity of the NOS2 gene and with susceptibility to SSc-related PAH.

Involvement of endothelial NO in the dilator effect of VIP on rat isolated pulmonary artery

The endothelium and its interaction with smooth muscle play a central role in the local control of the pulmonary vasculature, and endothelial dysfunction is thought to contribute to pulmonary hypertension and chronic obstructive pulmonary disease. Vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide, relaxes the rat pulmonary artery, but there is controversy as to whether or not this action of VIP depends on the endothelium. The aim of this study, therefore, was to investigate the role of the endothelium and nitric oxide (NO), the major endothelium-derived relaxing factor, in the dilator action of VIP on the rat isolated pulmonary artery. Pulmonary artery preparations pre-contracted by the alpha(1)-adrenoceptor agonist L-phenylephrine were relaxed by VIP (0.003-1 microM) and acetylcholine (0.003-10 microM) in a concentration-dependent manner. Mechanical removal of the endothelium reduced the maximal response to VIP by about 50% and practically abolished the response to acetylcholine. Inhibition of NO synthesis by N(omega)-nitro-L-arginine methyl ester (0.5 mM) had a similar effect, abolishing the vasorelaxation caused by acetylcholine and attenuating the vasorelaxation caused by VIP by about 50%. From these data it is concluded that the relaxant action of VIP on the rat isolated pulmonary artery depends in part on the presence of the endothelium and that this part is mediated by endothelial NO.

Oral sildenafil citrate lacks genotoxicity and cytotoxicity in a primate model: Callithrix jacchus

OBJECTIVE

To determine sildenafil citrate (SC) genotoxicity and cytotoxicity in the Callithrix jacchus.

STUDY DESIGN

Fifteen organisms were assigned to one of three groups as follows: experimental (25 mg/kg of SC); negative control (glucose solution 5%); and positive control (3 mg/kg of cytocine arabinoside). Systemic hemodynamic changes were monitored in each animal before and after each treatment. A drop of blood was obtained before and after the treatment at 24-120 h. Smears were made and the frequency of micronucleated erythrocytes (MNE), micronucleated polychromatic erythrocytes (MNPCE) and polychromatic erythrocytes (PCE) was counted.

RESULTS

No significant differences in MNE, MNPCE and PCE were found in the group that received sildenafil and negative control. A significant increase in genotoxicity and cytotoxicity was observed in the positive control group. No changes were observed in systemic hemodynamic changes.

CONCLUSION

The macro-dose of SC lacks genotoxic, cytotoxic or systemic hemodynamic changes effects in this species.

Advances in the Medical Treatment of Pulmonary Hypertension

Increased pulmonary precapillary vascular resistance due to vasoconstriction and vasoproliferative processes is the basic pathophysiological mechanism in the development of pulmonary hypertension (PH). With the exception of pulmonary venous hypertension, where the primary cause of PH is left ventricular failure or mitral valvular disease, all the other PH categories will benefit to a greater or lesser extent from pulmonary vasodilator and antivasoproliferative therapy. Today, for this purpose, in addition to intravenous prostacyclin (epoprostenol), which is restricted to severe pulmonary arterial hypertension (NYHA class IV and late class III), other therapeutic options such as treatment with more stable prostacyclin analogs (oral beraprost, aerosolized iloprost), endothelin-receptor antagonists (bosentan) or phosphodiesterase inhibitors (sildenafil) are also available and these are especially useful for the treatment of the early stages of the disease. The recent progress in medical therapy has markedly increased the life expectancy in patients with pulmonary arterial hypertension and substantially improved their quality of life. Chronic hemodialysis (HD) patients show higher endothelin-1 (ET-1) activity in comparison to healthy individuals and there is evidence that the increase of pulmonary vascular resistance in these patients is at least in part mediated by ET-1. Recent data show good results after PH therapy with the endothelin-receptor antagonist bosentan in HD patients. Also prostacyclin and its analogs, as well as phosphodiesterase inhibitors, can be useful for the treatment of pulmonary hypertension in patients with chronic renal failure.

Asymmetrical dimethylarginine in idiopathic pulmonary arterial hypertension

OBJECTIVE

We explored the potential role of the endogenous NO synthase inhibitor asymmetrical dimethylarginine (ADMA) in patients with idiopathic pulmonary arterial hypertension (IPAH). Method and Results- We correlated plasma ADMA levels and cardiovascular indices from right heart catheterization in 57 patients with IPAH. Predictors of survival in patients with IPAH were studied. Furthermore, the effect of systemic ADMA infusion on pulmonary ventricular resistance and stroke volume was investigated in healthy volunteers using right heart catheterization. Mean plasma ADMA concentrations were significantly higher in patients with IPAH than in control subjects (0.53+/-0.15 versus 0.36+/-0.05 micromol/L; P<0.001). ADMA plasma concentrations correlated significantly with indices of right ventricular function, such as mixed-venous oxygen saturation (r=-0.49; P<0.0001), right atrial pressure (r=0.39; P<0.003), cardiac index (r=-0.35; P<0.008), as well as survival (r=-0.47; P<0.0001). Multiple regression analysis revealed that right atrial pressure (r=0.31; P<0.026) and ADMA (r=0.29; P<0.039) were independent predictors of mortality. Moreover, patients with supra-median plasma ADMA levels had significantly (P<0.021) worse survival than patients with infra-median ADMA values. ADMA infusion in healthy volunteers increased pulmonary vascular resistance (68.9+/-7.6 versus 95.6+/-6.3 dyne x s x cm(-5); P<0.05) and decreased stroke volume (101.1+/-6.7 mL versus 95.6+/-6.3 mL; P<0.05).

CONCLUSIONS

Increased ADMA plasma levels are associated with unfavorable pulmonary hemodynamics and worse outcome in patients with IPAH.