Increased plasma serotonin in primary pulmonary hypertension

[Pulmonary hypertension in pediatric and neonatal intensive care unit. Part I: Physiopathology]

Pulmonary hypertension may be encountered in the pediatric and neonatal intensive care unit. Managing these patients in the intensive care unit can prove extremely challenging, particularly when they become hemodynamically unstable. Pulmonary hypertension in pediatric patients is frequently associated with critical illnesses such as congenital heart disease, acute respiratory disease, and left heart failure. In neonates, pulmonary hypertension is idiopathic or related to respiratory distress or congenital heart failure. This review discusses the pathogenesis and physiology of pulmonary hypertension, the cardiopulmonary interactions in this pathology, and the adaptation to extra-uterine life.

Key role of the RhoA/Rho kinase system in pulmonary hypertension

Pulmonary hypertension (PH) is a general term comprising a spectrum of pulmonary hypertensive disorders which have in common an elevation of mean pulmonary arterial pressure (mPAP). The prototypical form of the disease, termed pulmonary arterial hypertension (PAH), is a rare but lethal syndrome with a complex aetiology characterised by increased pulmonary vascular resistance (PVR) and progressive elevation of mPAP; patients generally die from heart failure. Current therapies are inadequate and median survival is less than three years. PH due to chronic hypoxia (CH) is a condition separate from PAH and is strongly associated with chronic obstructive pulmonary disease (COPD). An early event in the pathogenesis of this form of PH is hypoxic pulmonary vasoconstriction (HPV), an acute homeostatic process that maintains the ventilation-perfusion ratio during alveolar hypoxia. The mechanisms underlying HPV remain controversial, but RhoA/Rho kinase (ROK)-mediated Ca²+-sensitisation is considered important. Increasing evidence also implicates RhoA/ROK in PASMC proliferation, inflammatory cell recruitment and the regulation of cell motility, all of which are involved in the pulmonary vascular remodelling occurring in all forms of PH. ROK is therefore a potential therapeutic target in treating PH of various aetiologies. Here, we examine current concepts regarding the aetiology of PAH and also PH due to CH, focusing on the contribution that RhoA/ROK-mediated processes may make to their development and on ROK inhibitors as potential therapies.

Contribution of gene-modified mice and rats to our understanding of the cardiovascular pharmacology of serotonin

This review focuses on new insights provided by gene-modified animals into the cardiovascular pharmacology of serotonin. During their development, mice mutant for tryptophan hydroxylase 1 and lacking peripheral serotonin, or mutant for 5-HT(2B) receptors, display cardiac defects and dilated cardiomyopathy. The 5-HT(4) receptor is important for the maturation of cardiac conduction. In fact, transgenic approaches have revealed that adult cardiac status is strongly influenced by maternal serotonin. Serotonin has long been known to be a vasoconstrictor in adult physiology. Analysis of animals knocked-out for the serotonin transporter suggested a role in blood pressure control and revealed an effect of 5-HT(2B) receptor antagonists in hypertension. In the lung vasculature, mice lacking the 5-HT(2B) receptor gene that are exposed to chronic hypoxia are resistant to pulmonary hypertension, while 5-HT(1B) receptor and serotonin transporter mutant animals show partial resistance. In platelets, mutant mice revealed that serotonin transporter regulates not only the mechanisms by which serotonin is packaged and secreted but also platelet aggregation. Studies looking at adult cardiac remodeling showed that mice lacking the 5-HT(2B) receptor gene were protected from cardiac hypertrophy. Their fibroblasts were unable to secrete cytokines. Crossing these animals with mice overexpressing the receptor in cardiomyocytes revealed the contribution of cardiac fibroblasts and 5-HT(2B) receptors to cardiac hypertrophy. In mice lacking the monoamine oxidase-A gene, the role of serotonin degradation in cardiac hypertrophy was confirmed. Works with gene-modified animals has contributed strongly to the re-evaluation of the influence of serotonin on cardiovascular regulation, though several unknowns remain to be investigated.

Involvement of tryptophan hydroxylase 2 (TPH2) gene polymorphisms in susceptibility to coronary artery lesions in Korean children with Kawasaki disease

Kawasaki disease (KD) is an acute vasculitis of childhood that predominantly affects the coronary arteries. We investigated single nucleotide polymorphisms (SNPs) of the tryptophan hydroxylase 2 (TPH2) gene as risk factors for KD with coronary artery lesions (CALs) in Korean children. We genotyped two SNPs [rs7305115 (exon 7) and rs4290270 (exon 9)] using direct sequencing in 101 KD and 256 control subjects. To analyze the genetic data, SNPStats, SNPAnalyzer, and Helixtree programs were used. The genotype analysis of rs7305115 and rs4290270 showed no significant differences between KD and control groups. However, we found a statistically significant association between the two SNPs and the development of CALs in KD (p < 0.05). The minor homozygous genotype (rs7305115, AA genotype and rs42901270, AA genotype) of each SNP showed increased susceptibility to risk of CALs in KD patients. These results suggest that TPH2 may be associated with the development of KD with CALs in Korean children.

Nitric oxide, oxidative stress and inflammation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a chronic and progressive disease characterized by a persistent elevation of pulmonary artery pressure accompanied by right ventricular hypertrophy (RVH). The current treatment for pulmonary hypertension is limited and only provides symptomatic relief due to unknown cause and pathogenesis of the disease. Both vasoconstriction and structural remodeling (enhanced proliferation of vascular smooth muscle cell) of the pulmonary arteries contribute to the progressive course of PAH, irrespective of different underlying causes. The exact molecular mechanism of PAH, however, is not fully understood. The purpose of this review is to provide recent advances in the mechanistic investigation of PAH. Specifically, this review focuses on nitric oxide, oxidative stress and inflammation and how these factors contribute to the development and progression of PAH. This review also discusses recent and potential therapeutic advancements for the treatment of PAH.

Cell signaling by protein carbonylation and decarbonylation

Reactive oxygen species (ROS) serve as mediators of signal transduction. However, mechanisms of how ROS influence the target molecules to elicit signaling event have not been defined. Our laboratory recently accumulated evidence for the role of protein carbonylation in the mechanism of ROS signaling. This concept originated from experiments in which pulmonary artery smooth muscle cells were treated with endothelin-1 to understand the mechanism of cell growth. Endothelin-1 was found to promote protein carbonylation in an endothelin receptor- and Fenton reaction-dependent manner. Mass spectrometry identified proteins that are carbonylated in response to endothelin-1, including annexin A1. Our experiments generated a hypothesis that endothelin-1-mediated carbonylation and subsequent degradation of annexin A1 promote cell growth. This mechanism was found also to occur in response to other signaling activators such as serotonin and platelet-derived growth factor in smooth muscle cells of pulmonary circulation, systemic circulation, and the airway, as well as in cardiac muscle cells, suggesting the universal role of this pathway. We also discovered a process of decarbonylation that defines transient kinetics of carbonylation signals in certain conditions. We propose that protein carbonylation and decarbonylation serve as a mechanism of signal transduction.

Pharmacological targets for pulmonary vascular disease: vasodilation versus anti-remodelling

Two gross mechanisms of pathology are central to pulmonary arterial hypertension - increased pulmonary vascular tone and remodelling of the pulmonary arteries. These pathologies can be caused by a variety of aberrant processes, and combine to cause an increase in pulmonary vascular resistance and consequent right ventricular hypertrophy, eventually leading to dysfunction and death. Current therapeutic strategies have focused on altering the vasoconstrictive elements of the disease. Whilst improvements in life expectancy have been observed, current therapies have not managed to halt or reverse progression of the disease. Here we discuss said unmet medical need and postulate as to the impact on disease anti-remodelling therapy might provide. The mechanisms of remodelling in pulmonary arterial hypertension are reviewed, and leading examples of potential targets within such mechanisms are discussed.

Increased concentrations of serotonin and 5-hydroxyindoleacetic acid in blood plasma from patients with pulmonary hypertension due to mitral valve disease

Serotonin content in the plasma and platelets and 5-hydroxyindoleacetic acid concentration in the plasma were shown to increase in patients with pulmonary arterial hypertension due to mitral valve disease. A positive correlation was found between the severity of pulmonary arterial hypertension and concentrations of serotonin (r=0.48) and 5-hydroxyindoleacetic acid in the plasma (r=0.9).

Mechanisms involved in the regulation of bovine pulmonary vascular tone by the 5-HT1B receptor

BACKGROUND AND PURPOSE

5-HT(1B) receptors may have a role in pulmonary hypertension. Their relationship with the activity of BK(Ca,) a T-type voltage-operated calcium channel (VOCC) and cyclic nucleotide-mediated relaxation was examined.

EXPERIMENTAL APPROACH

Ring segments of bovine pulmonary arteries were mounted in organ baths in modified Krebs-Henseleit buffer (37 degrees C) under a tension of 20 mN and gassed with 95% O(2)/5% CO(2). Isometric recordings were made using Chart 5 software.

KEY RESULTS

Contractile responses to 5-HT (10 nM-300 microM) were inhibited similarly by the 5-HT(1B) receptor antagonist SB216641 (100 nM) and the T-type VOCC blockers mibefradil (10 microM) and NNC550396 (10 microM) with no additive effect between SB216641 and mibefradil. Inhibition by SB216641 was prevented by the potassium channel blocker, charybdotoxin (100 nM). 5-HT(1B) receptor activation and charybdotoxin produced a mibefradil-sensitive potentiation of responses to U46619. Bradykinin (0.1 nM-30 microM), sodium nitroprusside (0.01 nM-3 microM), zaprinast (1 nM-3 microM), isoprenaline (0.1 nM-10 microM) and rolipram (1 nM-3 microM) produced 50% relaxation of arteries constricted with 5-HT (1-3 microM) or U46619 (30-50 nM) in the presence of 5-HT(1B) receptor activation, but full relaxation of arteries constricted with U46619, the 5-HT(2A) receptor agonist 2,5 dimethoxy-4 iodoamphetamine (1 microM) or 5-HT in the presence of 5-HT(1B) receptor antagonism. Enhanced relaxation of 5-HT-constricted arteries by cGMP-dependent pathways, seen in the presence of the 5-HT(1B) receptor antagonist, was reversed by charybdotoxin whereas cAMP-dependent relaxation was only partly reversed by charybdotoxin.

CONCLUSIONS AND IMPLICATIONS

5-HT(1B) receptors couple to inhibition of BK(Ca), thus increasing tissue sensitivity to contractile agonists by activating a T-type VOCC and impairing cGMP-mediated relaxation. Impaired cAMP-mediated relaxation was only partly mediated by inhibition of BK(Ca).

The angiopietin-1-Tie2 pathway prevents rather than promotes pulmonary arterial hypertension in transgenic mice

The role of the angiopoietin-1 (Ang1)-Tie2 pathway in the pathogenesis of pulmonary arterial hypertension (PAH) is controversial. Although Ang1 is well known to prevent endothelial activation and injury in systemic vascular beds, this pathway has been suggested to mediate pulmonary vascular remodeling in PAH. Therefore, we used transgenic models to determine the effect of increased or decreased Tie2 activity on the development of PAH. We now report modest spontaneous elevation in right ventricular systolic pressure in Tie2-deficient mice (Tie2(+/-)) compared with wild-type (WT) littermate controls, which was exacerbated upon chronic exposure to the clinically relevant PAH triggers, serotonin (5-HT) or interleukin-6 (IL-6). Moreover, overexpression of Ang1 in transgenic mice had no deleterious effect on pulmonary hemodynamics and, if anything, blunted the response to 5-HT. Exposure to 5-HT or IL-6 also decreased lung Ang1 expression, further reducing Tie2 activity and inducing pulmonary apoptosis in the Tie2(+/-) group only. Similarly, cultured pulmonary artery endothelial cells subjected to Tie2 silencing demonstrated increased susceptibility to apoptosis after 5-HT treatment. Finally, treatment of Tie2-deficient mice with Z-VAD, a pan-caspase inhibitor, prevented the pulmonary hypertensive response to 5-HT. Thus, these findings firmly establish that endothelial survival signaling via the Ang1-Tie2 pathway is protective in PAH.

Genetics of pulmonary arterial hypertension

Tremendous progress has been made in understanding the genetics of hereditable pulmonary arterial hypertension (HPAH) since its description in the 1950s. Germline mutations in the gene coding bone morphogenetic receptor type 2 ( BMPR2) are detectable in the majority of cases of HPAH, and in a small proportion of cases of idiopathic pulmonary arterial hypertension (IPAH). HPAH is an autosomal dominant disease characterized by reduced penetrance, variable expressivity, female predominance, and genetic anticipation. These characteristics suggest that endogenous and exogenous factors modify disease expression and areas of emphasis for future investigation. The variable clinical expression makes genetic counseling complex because the majority of carriers of a BMPR2 mutation will not be diagnosed with the disease. This issue will become increasingly important, as clinical testing for BMPR2 mutations is now available for the evaluation of patients and family members with HPAH and IPAH.

Cellular and molecular basis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is caused by functional and structural changes in the pulmonary vasculature, leading to increased pulmonary vascular resistance. The process of pulmonary vascular remodeling is accompanied by endothelial dysfunction, activation of fibroblasts and smooth muscle cells, crosstalk between cells within the vascular wall, and recruitment of circulating progenitor cells. Recent findings have reestablished the role of chronic vasoconstriction in the remodeling process. Although the pathology of PAH in the lung is well known, this article is concerned with the cellular and molecular processes involved. In particular, we focus on the role of the Rho family guanosine triphosphatases in endothelial function and vasoconstriction. The crosstalk between endothelium and vascular smooth muscle is explored in the context of mutations in the bone morphogenetic protein type II receptor, alterations in angiopoietin-1/TIE2 signaling, and the serotonin pathway. We also review the role of voltage-gated K(+) channels and transient receptor potential channels in the regulation of cytosolic [Ca(2+)] and [K(+)], vasoconstriction, proliferation, and cell survival. We highlight the importance of the extracellular matrix as an active regulator of cell behavior and phenotype and evaluate the contribution of the glycoprotein tenascin-c as a key mediator of smooth muscle cell growth and survival. Finally, we discuss the origins of a cell type critical to the process of pulmonary vascular remodeling, the myofibroblast, and review the evidence supporting a contribution for the involvement of endothelial-mesenchymal transition and recruitment of circulating mesenchymal progenitor cells.

Inhaled iloprost for the control of pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by an elevated pulmonary arterial pressure and vascular resistance with a poor prognosis. Various pulmonary and extrapulmonary causes are now recognized to exist separately from the idiopathic form of pulmonary hypertension. An imbalance in the presence of vasoconstrictors and vasodilators plays an important role in the pathophysiology of the disease, one example being the lack of prostacyclin. Prostacyclin and its analogues are potent vasodilators with antithrombotic, antiproliferative and anti-inflammatory qualities, all of which are important factors in the pathogenesis of precapillary pulmonary hypertension. Iloprost is a stable prostacyclin analogue available for intravenous and aerosolized application. Due to the severe side effects of intravenous administration, the use of inhaled iloprost has become a mainstay in PAH therapy. However, owing to the necessity for 6 to 9 inhalations a day, oral treatment is often preferred as a first-line therapy. Numerous studies proving the efficacy and safety of inhaled iloprost have been performed. It is therefore available for a first-line therapy for PAH. The combination with endothelin-receptor antagonists or sildenafil has shown encouraging effects. Further studies with larger patient populations will have to demonstrate the use of combination therapy for long-term treatment of pulmonary hypertension.

Treatment of pediatric pulmonary hypertension

Pulmonary hypertension was once thought to be a rare condition and only managed in specialized centers. Now however, with the advent of echocardiography, it is found in many clinical scenarios, in the neonate with chronic lung disease, in the acute setting in the intensive care unit, in connective tissue disease and in cardiology pre- and postoperatively. We have a better understanding of the pathological process and have a range of medication which is starting to be able to palliate this previously fatal condition. This review describes the areas that are known in this condition and those that are less familiar. The basic physiology behind pulmonary hypertension and pulmonary vascular disease is explained. The histopathologic process and the various diagnostic tools are described and are followed by the current and future therapy at our disposal.

Selective serotonin reuptake inhibitors and the incidence and outcome of pulmonary hypertension

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) prevent the development of and reverse pulmonary hypertension (PH) in animal models. We sought to determine whether SSRIs are associated with a decreased incidence of PH in at-risk patients and whether SSRIs are associated with decreased mortality in patients with established PH.

METHODS

In a case-control study of patients enrolled in the Surveillance of Pulmonary Hypertension in America (SOPHIA) registry, we tested whether patients without PH (no-PH group; n = 155) were more likely to be receiving SSRIs when compared to those with confirmed PH (n = 1,180). In a separate cohort study of adults with documented PH in the referral-based Pulmonary Hypertension Connection (PHC) registry (n = 542), we classified patients into categories by SSRI use, and we examined whether SSRI use was associated with decreased mortality.

RESULTS

In SOPHIA, the confirmed PH group was less likely to be receiving SSRIs compared with the no-PH group (univariate odds ratio [OR], 0.56 [95% confidence interval (CI), 0.39 to 0.82]; p = 0.003; multivariate OR, 0.71l [95% CI, 0.48 to 1.06]; p = 0.09). In the PHC, 69 of 542 patients (13%) were receiving SSRIs at the time of referral. During a mean (+/- SD) follow-up period of 4.0 +/- 3.1 years, 12% of patients receiving SSRIs vs 23% of patients not receiving SSRIs died (hazard ratio [HR], 0.35; 95% CI, 0.14 to 0.87; p = 0.023). The association between SSRI use and decreased mortality persisted after adjusting for age, gender, etiology of PH, and obesity (HR, 0.35; 95% CI, 0.14 to 0.88; p = 0.026).

CONCLUSIONS

SSRIs appear to be associated with a decreased development of PH and a decreased mortality in PH. These findings provide a rationale for clinical trials of SSRIs in PH.

Review paper: Current strategies in the development of anti-obesity drugs and their safety concerns

Obesity is a well-established risk factor for hypertension, hyperlipidemia, type II diabetes, coronary heart disease, stroke, obstructive sleep apnea, asthma, orthopedic disorders, and certain cancers. Despite this risk, the prevalence of obesity continues to increase worldwide, and there is a growing demand for safe and effective antiobesity drugs. Previous antiobesity drugs or anorexigens, particularly centrally acting agents, have poor safety records. Life-threatening safety issues led to the withdrawal of aminorex in 1968, fenfluramine and dexfenfluramine in 1997, and phenylpropanolamine in 2000. Many of the safety issues, such as valvulopathy with fenfluramine and pulmonary arterial hypertension with aminorex, were initially not predicted by routine preclinical toxicology studies. To date, there are no validated animal models or preclinical and/or toxicologic screens to accurately predict anorexigen-induced valvulopathy and pulmonary arterial hypertension in humans. This review covers the current state of antiobesity drugs and their safety concerns, and highlights new therapeutic targets and scientific advances toward the development of appropriate animal models by using novel techniques that will aid in understanding pathogenesis and pathophysiology of anorexigen-related safety issues.

Continuous fluoxetine administration prevents recurrence of pulmonary arterial hypertension and prolongs survival in rats

1. The serotonin transporter (SERT) is strongly implicated in the pathogenesis of pulmonary arterial hypertension (PAH) in patients and animal models. Inhibitors of SERT have been reported to attenuate or reverse experimental PAH, which makes them potential therapeutic options for the treatment of PAH in humans. However, little is known about pathophysiological features after reversal or attenuation of PAH; moreover, the long-term therapeutic effects of SERT inhibitors on PAH remain undetermined. Thus, the aim of the present study was to investigate the short- and long-term effects of fluoxetine on monocrotaline (MCT)-induced PAH and associated pathophysiological changes in PAH models. 2. Rats were randomly divided into four groups as follows: (i) an M + F group, in which rats received a single injection of MCT (60 mg/kg, s.c.) and then after 3 weeks were given fluoxetine (10 mg/kg) once daily by gavage from Week 4 to Week 12; (ii) an M/F group, in which 3 weeks after a single MCT (60 mg/kg, s.c.) injection, rats were given fluoxetine (10 mg/kg) by daily gavage from Week 4 to Week 6 and were then given an equivalent volume of saline once daily by gavage from Week 7 to Week 12; (iii) an MCT group, in which 3 weeks after a single MCT (60 mg/kg, s.c.) injection rats were given an equivalent volume of saline by gavage from Week 4 to Week 12; and (iv) a saline group, in which rats received an equivalent volume of saline injection or gavage over the 12 week treatment period. Morphometric changes, pulmonary arterial pressure, percentage wall thickness, right ventricular hypertrophy index and SERT expression were detected at various times during the 12 week treatment period. Survival analysis was performed in each group. 3. After 12 weeks treatment, it was found that even through fluoxetine treatment resulted in complete reversal of PAH, PAH recurred after fluoxetine withdrawal. In contrast, continuous administration of fluoxetine prevented the recurrence of PAH and prolonged survival. Analysis of SERT protein levels in rat lung indicated that, compared with values obtained at Week 0, SERT protein increased significantly after discontinuation of fluoxetine but continuous fluoxetine administration inhibited this increase. 4. In conclusion, SERT overexpression correlates with the recurrence of PAH after withdrawal of fluoxetine in rats. Continuous fluoxetine administration prevents recurrence of PAH and prolongs survival.

The right ventricle in sepsis

Right ventricular dysfunction is common in sepsis and septic shock because of decreased myocardial contractility and elevated pulmonary vascular resistance despite a concomitant decrease in systemic vascular resistance. The mainstay of treatment for acute right heart failure includes treating the underlying cause of sepsis and reversing circulatory shock to maintain tissue perfusion and oxygen delivery. Decreasing pulmonary vascular resistance with selective pulmonary vasodilators is a reasonable approach to improving cardiac output in septic patients with right ventricular dysfunction. Treatment for right ventricular dysfunction in the setting of sepsis should concentrate on fluid repletion, monitoring for signs of RV overload, and correction of reversible causes of elevated pulmonary vascular resistance, such as hypoxia, acidosis, and lung hyperinflation.

RhoA and Rho kinase activation in human pulmonary hypertension: role of 5-HT signaling

RATIONALE

The complex and multifactorial pathogenesis of pulmonary hypertension (PH) involves constriction, remodeling, and in situ thrombosis of pulmonary vessels. Both serotonin (5-HT) and Rho kinase signaling may contribute to these alterations.

OBJECTIVES

To investigate possible links between the 5-HT transporter (5-HTT) and RhoA/Rho kinase pathways, as well as their involvement in the progression of human and experimental PH.

METHODS

Biochemical and functional analyses of lungs, platelets, and pulmonary artery smooth muscle cells (PA-SMCs) from patients with idiopathic PH (iPH) and 5-HTT overexpressing mice.

MEASUREMENTS AND MAIN RESULTS

Lungs, platelets, and PA-SMCs from patients with iPH were characterized by marked elevation in RhoA and Rho kinase activities and a strong increase in 5-HT binding to RhoA indicating RhoA serotonylation. The 5-HTT inhibitor fluoxetine and the type 2 transglutaminase inhibitor monodansylcadaverin prevented 5-HT-induced RhoA serotonylation and RhoA/Rho kinase activation, as well as 5-HT-induced proliferation of PA-SMCs from iPH patients that was also inhibited by the Rho kinase inhibitor fasudil. Increased Rho kinase activity, RhoA activation, and RhoA serotonylation were also observed in lungs from SM22-5-HTT(+)mice, which overexpress 5-HTT in smooth muscle and spontaneously develop PH. Treatment of SM22-5-HTT(+) mice with either fasudil or fluoxetine limited PH progression and RhoA/Rho kinase activation.

CONCLUSIONS

RhoA and Rho kinase activities are increased in iPH, in association with enhanced RhoA serotonylation. Direct involvement of the 5-HTT/RhoA/Rho kinase signaling pathway in 5-HT-mediated PA-SMC proliferation and platelet activation during PH progression identify RhoA/Rho kinase signaling as a promising target for new treatments against PH.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Molecular mechanisms of pulmonary hypertension

The pathogenesis of pulmonary arterial hypertension (PAH) is complex, involving multiple modulating genes and environmental factors. Multifactorial impairment of the physiologic balance can lead to vasoconstriction, vascular smooth muscle cell and endothelial cell proliferation/fibrosis, inflammation, remodeling and in-situ thrombosis. These are the likely mechanisms that lead to narrowing of the vessel followed by progressive increase in pulmonary vascular resistance and the clinical manifestations of pulmonary hypertension. Subsequently, major goal of the therapy is to avoid acute pulmonary vasoconstriction, halt the progression of vascular remodeling, and reverse the early vascular remodeling if possible. Recently published data addressing certain molecular mechanisms for pathogenesis of PAH have led to the successful therapeutic interventions. This review will focus on the common and critical molecular pathways including genetic basis of the development of PAH that on the whole may be new targets for therapeutic interventions.

Serotonin transporter polymorphisms in patients with portopulmonary hypertension

BACKGROUND

The long allele of a functional promoter polymorphism in the serotonin transporter (SERT) is associated with an increased risk of some forms of pulmonary arterial hypertension. We hypothesized that the long allele or other polymorphisms in SERT would be associated with an increased risk of portopulmonary hypertension (PPHTN) in patients with advanced liver disease.

METHODS

We performed a multicenter case-control study. Subjects undergoing liver transplant evaluation at seven centers were prospectively screened for the presence of PPHTN using transthoracic echocardiography. PPHTN was confirmed by right heart catheterization using standard criteria.

RESULTS

The study sample included 30 case patients with PPHTN and 109 control subjects with advanced liver disease. There was no significant association between the long allele and case status in an adjusted additive model (odds ratio, 0.63; 95% confidence interval, 0.33 to 1.21; p = 0.17). If anything, LL genotype tended to be associated with a lower risk of PPHTN. There were no associations between other SERT polymorphisms and PPHTN.

CONCLUSIONS

SERT polymorphisms are not associated with the risk of PPHTN in patients with advanced liver disease. Other clinical or genetic risk factors may play a role in this complication of portal hypertension.

Serotonin (5-HT) transporter ligands affect plasma 5-HT in rats

Dual dopamine (DA)/serotonin (5-HT)-releasing agents are promising candidate medications for stimulant addiction and other disorders. However, certain 5-HT transporter (SERT) substrates are associated with development of idiopathic pulmonary arterial hypertension (IPAH) and valvular heart disease (VHD). According to the "5-HT hypothesis," SERT substrates increase the risk for developing IPAH and VHD by increasing plasma 5-HT. To test this hypothesis directly, we determined the effects of acute and chronic fenfluramine, and other SERT ligands, on plasma 5-HT in male rats. For acute treatments, rats received i.v. vehicle or test drug (0.3 and 1.0 mg/kg), and serial blood samples were withdrawn. For chronic treatments, vehicle or test drug was infused via osmotic minipump (3 and 10 mg/kg/d) for 2 weeks. On the last day of infusion, rats received i.v. fenfluramine challenge (1 mg/kg), and serial blood samples were withdrawn. Plasma 5-HT was measured using ex vivo microdialysis in whole-blood samples. Baseline plasma 5-HT was <1.0 nM. Acute injection of fenfluramine or other SERT substrates caused large (up to 24-fold) dose-dependent increases in plasma 5-HT. Chronic fenfluramine at 3 and 10 mg/kg/d produced 1.7- and 3.5-fold increases in baseline plasma 5-HT, while chronic fluoxetine had no effect. Chronic infusions of fenfluramine or fluoxetine diminished the ability of acute fenfluramine to elevate dialysate 5-HT, and both drugs markedly reduced whole-blood 5-HT. Acute fenfluramine increases plasma 5-HT to concentrations that are below the micromolar levels necessary to produce adverse cardiovascular effects. Chronic fenfluramine and fluoxetine have minimal effects on plasma 5-HT, suggesting that the increased risk for IPAH associated with fenfluramine does not depend upon elevations in plasma 5-HT.

Dual dopamine/serotonin releasers: potential treatment agents for stimulant addiction

"Agonist therapy" for cocaine and methamphetamine addiction involves administration of stimulant-like medications (e.g., monoamine releasers) to reduce withdrawal symptoms and prevent relapse. A significant problem with this strategy is that many candidate medications possess abuse liability because of activation of mesolimbic dopamine (DA) neurons in the brain. One way to reduce DA-mediated abuse liability of candidate drugs is to add in serotonin (5-HT) releasing properties, since substantial evidence shows that 5-HT neurons provide an inhibitory influence over mesolimbic DA neurons. This article addresses several key issues related to the development of dual DA/5-HT releasers for the treatment of substance use disorders. First, the authors briefly summarize the evidence supporting a dual deficit in DA and 5-HT function during withdrawal from chronic cocaine or alcohol abuse. Second, the authors discuss data demonstrating that 5HT release can dampen DA-mediated stimulant effects, and the "antistimulant" role of 5-HT-sub(2C) receptors is considered. Next, the mechanisms underlying potential adverse effects of 5-HT releasers are described. Finally, the authors discuss recently published data with PAL-287, a novel nonamphetamine DA/5-HT releasing agent that suppresses cocaine self-administration but lacks positive reinforcing properties. It is concluded that DA/5-HT releasers could be useful therapeutic adjuncts for the treatment of cocaine and alcohol addictions, as well as for obesity, attention-deficit disorder, and depression.

Serotonin-mediated protein carbonylation in the right heart

Pulmonary hypertension is a devastating disease, which leads to right heart failure. Serotonin (5-HT) plays important roles in the pathogenesis of pulmonary hypertension and pulmonary vascular remodeling. The role of 5-HT in right heart failure, however, is unknown. Since oxidative stress may mediate heart failure, the present study examined the effects of 5-HT on protein oxidation in the adult rat right heart ventricle. Treatment of perfused isolated hearts with 5-HT resulted in the promotion of protein carbonylation, specifically in the right ventricle, but not in the left. While no differences between right and left ventricular antioxidant enzymes and 5-HT receptors/transporter were detected, monoamine oxidase A (MAO-A) expression and activity were found to be lower in the right ventricle compared to the left. These results indicate that differences in neither the reactive oxygen species (ROS) scavenging ability, 5-HT membrane signaling capacity, nor MAO-dependent production of hydrogen peroxide are responsible for varied 5-HT-mediated protein carbonylation in right and left ventricles. Rather, lower MAO-A in the right heart might preserve cytosolic 5-HT which triggers other mechanisms for ROS production. Consistently, inhibition of MAO-A resulted in the promotion of protein carbonylation. We propose that low MAO-A, thus reduced degradation of 5-HT, increases the intracellular 5-HT activity in the right ventricle, leading to the promotion of protein carbonylation.

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.

Phospholipase D signaling in serotonin-induced mitogenesis of pulmonary artery smooth muscle cells

We have previously reported the participation of mitogen-activated protein, Rho, and phosphoinositide-3 (PI3) kinases in separate pathways in serotonin (5-HT)-induced proliferation of pulmonary artery smooth muscle cells (SMCs). In this study, we investigated the possible participation of phospholipase D (PLD) and phosphatidic acid (PA) in this growth process. 5-HT stimulated a time-dependent increase in [(3)H]phosphatidylbutanol and PA generation. Exposure of SMCs to 1-butanol or overexpression of an inactive mutant of human PLD1R898R blocked 5-HT-induced proliferation. Furthermore, 1-butanol inhibited 5-HT activation of S6K1 and S6 protein, downstream effectors of mammalian target of rapamycin (mTOR), by 80 and 72%, respectively, and partially blocked activation of extracellular signal-regulated kinase (ERK) by 30% but had no effect on other associated signaling pathways. Exogenous PA caused cellular proliferation and revitalized cyclin D1 expression by 5-HT of the 1-butanol-treated cells. PA also reproduced activations by 5-HT of mTOR, S6K1, and ERK. Transfection with inactive human PLD1 reduced 5-HT-induced activation of S6K1 by approximately 50%. Inhibition of 5-HT receptor 2A (R 2A) with ketaserin blocked PLD activation by 5-HT. Inhibition with PI3-kinase inhibitor failed to block either activation of PLD by 5-HT or PA-dependent S6K1 phosphorylation. Taken together, these results indicate that ligation of the 5-HTR 2A by 5-HT initiates PLD activation in SMCs, and that its product, PA, is an early signaling molecule in 5-HT-induced pulmonary artery SMC proliferation. Signaling by PA produces its downstream effects primarily through the mTOR/S6K1 pathway and to a lesser extent through the ERK pathway. Hydrolysis of cell membrane lipid may be important in vascular effects of 5-HT.

Review: Therapeutic advances in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by vasoconstriction, in situ thrombosis, and vascular remodeling of small pulmonary arteries inducing increased pulmonary arterial resistance. Conventional treatment is based on life style modification and nonspecific treatment (warfarine, diuretics, oxygen). Calcium channel blockers are vasodilatators that have been shown to be of great efficacy in a very specific subpopulation of patients with PAH. For the majority of patients, specific PAH therapies are still lacking. Numerous studies evaluating prostacyclin agonists, endothelin-receptor antagonists, and phosphodiesterase type 5 inhibitors are now available to guide therapeutic choices. Despite those important advances there is still no cure for PAH. Fortunately, research is ongoing and many drugs show promises.

Serotonin induces vasoconstriction of smooth muscle cell-rich neointima through 5-hydroxytryptamine2A receptor in rabbit femoral arteries

BACKGROUND

Smooth muscle cell (SMC)-rich intima is a morphological feature of atherosclerotic lesions that is observed in eroded plaque and spastic arteries. Arteries with SMC-rich intima are susceptible to vasoconstriction or vasospasm against some vasoactive agents.

OBJECTIVE

The present study evaluates the contribution of SMC-rich intima to thrombogenic vasoconstriction.

METHODS

We established SMC-rich neointima by damaging rabbit femoral arteries using balloons and then measured the isometric tension of the femoral strips against 5-hydroxytryptamine (5-HT), adenosine diphosphate, adenosine triphosphate and thrombin.

RESULTS

Among these agents, only 5-HT induced a hypercontractile response of the injured arteries with SMC-rich neointima, compared with non-injured arteries. Smooth muscle cells of both the neointima and media expressed 5-HT(2A) receptor, and sarpogrelate, a selective 5-HT(2A) receptor antagonist significantly inhibited the hypercontraction. Furthermore, 5-HT induced contraction of separated neointima and hypercontraction of separated media compared with non-injured media. Sarpogrelate and fasudil, a specific Rho-kinase inhibitor, significantly suppressed such contraction of both the neointima and media of injured arteries.

CONCLUSIONS

These results suggest that 5-HT plays a crucial role in thrombogenic vasoconstriction, and that SMC-rich intima as well as media directly contributes to the hypercontractile response of atherosclerotic vessels through the 5-HT(2A) receptor and the Rho-kinase pathway.

Pulmonary hypertension: therapeutic targets within the serotonin system

Pulmonary arterial hypertension (PAH) is characterized by a sustained and progressive elevation in pulmonary arterial pressure and pulmonary vascular remodelling leading to right heart failure and death. Prognosis is poor and novel therapeutic approaches are needed. The serotonin hypothesis of PAH originated in the 1960s after an outbreak of the disease was reported among patients taking the anorexigenic drugs aminorex and fenfluramine. These are indirect serotonergic agonists and serotonin transporter substrates. Since then many advances have been made in our understanding of the role of serotonin in the pathobiology of PAH. The rate-limiting enzyme in the synthesis of serotonin is tryptophan hydroxylase (Tph). Serotonin is synthesized, through Tph1, in the endothelial cells of the pulmonary artery and can then act on underlying pulmonary arterial smooth muscle cells and pulmonary arterial fibroblasts in a paracrine fashion causing constriction and remodelling. These effects of serotonin can be mediated through both the serotonin transporter and serotonin receptors. This review will discuss our current understanding of 'the serotonin hypothesis' of PAH and highlight possible therapeutic targets within the serotonin system.

Recent advances in understanding serotonin regulation of cardiovascular function

Serotonin is an important neurohormonal factor that has been implicated in cardiovascular function. It can regulate vascular tone, act directly on cardiomyocytes and stimulate chemosensitive nerves in the heart. Cardiovascular dysfunction is observed when serotonin signaling is altered or when variation in serotonin concentration occurs. Recent studies have provided evidence that, in the absence of peripheral serotonin synthesis, blood serotonin (which is almost exclusively stored in platelets) is markedly reduced, and that this drop leads to heart failure. This implies that the level of circulating serotonin is a key factor in maintaining normal cardiovascular activity. These findings offer new prospects for the use of serotonin in therapies for cardiovascular diseases.

Pulmonary hypertension and the serotonin hypothesis: where are we now?

In the 1960s, serotonin (5HT) was associated with pulmonary arterial hypertension (PAH) caused by certain diet pills, but has recently been the subject of renewed interest in the field of PAH. Serotonin can be synthesised in the pulmonary endothelium with the rate-limiting step being the activity of tryptophan hydroxylase1 (Tph1). The serotonin is released and can then: (i) pass into the underlying pulmonary smooth muscle cells through the serotonin transporter (SERT) to initiate proliferation and/or (ii) activate serotonin receptors on pulmonary smooth muscle cells to evoke proliferation and/or contraction. Serotonin may also mediate pulmonary fibroblast proliferation via the SERT and/or serotonin receptors. Here we will unravel, discuss and update the 'serotonin hypothesis' of PAH in light of recent advances in the field. In conclusion, the activity of serotonin receptors, the SERT and Tph1 can all be elevated in clinical and experimental PAH and each offers a potentially unique therapeutic target.

Serotonin-induced activation of TRPV4-like current in rat intrapulmonary arterial smooth muscle cells

In the present study, we investigated the implication of transient receptor potential vanilloid (TRPV)-related channels in the 5-hydroxytryptamine (5-HT)-induced both intracellular calcium response and mitogenic effect in rat pulmonary arterial smooth muscle cells (PASMC). Using microspectrofluorimetry (indo-1 as Ca(2+) fluorescent probe) and the patch-clamp technique (in whole-cell configuration), we found that 5-HT (10 microM) induced a transient intracellular calcium mobilization followed by a sustained calcium entry. This latter was partly blocked by an inhibitor of cytochrome P450 epoxygenase (17-ODYA) and insensitive to cyclo-oxygenase and lipoxygenase inhibitors (indomethacin and CDC), suggesting the involvement of arachidonic acid metabolization by cytochrome P450 epoxygenase. This calcium influx was also sensitive to Ni(2+) and to ruthenium red, a TRPV channel blocker, and mimicked by 4alpha-phorbol-12,13-didecanoate (4alpha-PDD), a TRPV4 channel agonist. In patched PASMC, 5-HT and 4alpha-PDD-activated TRPV4-like ruthenium red sensitive currents with typical characteristics. Furthermore, 5-HT induced a ruthenium red sensitive increase in BrdU incorporation levels in PASMC. The present study provides evidence that 5-HT activates a TRPV4-like current, potentially involved in PASMC proliferation. The signalling pathway between proliferation and ion channel activation remains to be determined and may represent a molecular target for the treatment of vascular diseases such as pulmonary hypertension.

Analysis of plasma serotonin levels and hemodynamic responses following chronic serotonin infusion in broilers challenged with bacterial lipopolysaccharide and microparticles

There has been extensive interest in the role of serotonin (5-hydoxytryptamine, 5-HT) in the pathogenesis of pulmonary hypertension because episodes of pulmonary arterial hypertension in humans have been linked to serotoninergic appetite-suppressant drugs. In this study, we investigated the role of serotonin in the development of pulmonary hypertension induced by intravenously injecting bacterial lipopolysaccharide (LPS, endotoxin) and cellulose microparticles. In experiment 1, we used a 5-HT ELISA kit for the in vitro quantitative determination of 5-HT in plasma during the development of pulmonary hypertension induced by injecting LPS and cellulose microparticles i.v. in broilers. In experiment 2, broilers were either chronically infused with 5-HT via surgically implanted osmotic pumps or received sham surgery as a control. After a period of 10 d, the pulmonary arterial pressure was recorded during challenge with injected LPS or microparticles. Microparticles elicited 5-HT plasma levels more than 2-fold greater than those elicited by LPS from 15 to 45 min postinjection. This indicates that 5-HT is an important mediator in the pulmonary hypertensive response of broilers to microparticles, but may not play a prominent role in the pulmonary hypertensive response to LPS. Furthermore, chronic 5-HT infusion via osmotic pumps caused an increase in the duration of the pulmonary hypertensive response of broilers to microparticles, indicating that the infused 5-HT was sequestered by circulating thrombocytes and then released upon microparticle-mediated thrombocyte activation. Serotonin appears to play a less prominent role in the pulmonary hypertensive response of broilers to LPS, indicating that other mediators within the innate response to inflammatory stimuli may also be involved. These results are consistent with our hypothesis that pulmonary arterial hypertension ensues when vasoconstrictors such as 5-HT overwhelm the dilatory affects of vasodilators such as nitric oxide, thereby effectively reducing the pulmonary vascular capacity of pulmonary arterial hypertension-susceptible broilers.