High plasma serotonin levels in primary pulmonary hypertension. Effect of long-term epoprostenol (prostacyclin) therapy

Relationship between Urine Serotonin and Persistent Pulmonary Hypertension of the Newborn

Urine serotonin (5-HT)/creatinine was lower at day of life 3 in newborns with pulmonary hypertension compared with controls, while the percent change in the 5-HT metabolite, 5-hydroxyindoleacetic acid (5-HIAA)/creatinine increased. We speculate that the changes in 5-HT and 5-HIAA reflect enhanced pulmonary 5-HT uptake and/or metabolism.

Strain in the Midbrain: Impact of Traumatic Brain Injury on the Central Serotonin System

Traumatic brain injury (TBI) is a pervasive public health crisis that severely impacts the quality of life of affected individuals. Like peripheral forms of trauma, TBI results from extraordinarily heterogeneous environmental forces being imparted on the cranial space, resulting in heterogeneous disease pathologies. This has made therapies for TBI notoriously difficult to develop, and currently, there are no FDA-approved pharmacotherapies specifically for the acute or chronic treatment of TBI. TBI is associated with changes in cognition and can precipitate the onset of debilitating psychiatric disorders like major depressive disorder (MDD), generalized anxiety disorder (GAD), and post-traumatic stress disorder (PTSD). Complicating these effects of TBI, FDA-approved pharmacotherapies utilized to treat these disorders often fail to reach the desired level of efficacy in the context of neurotrauma. Although a complicated association, decades of work have linked central serotonin (5-HT) neurotransmission as being involved in the etiology of a myriad of neuropsychiatric disorders, including MDD and GAD. 5-HT is a biogenic monoamine neurotransmitter that is highly conserved across scales of biology. Though the majority of 5-HT is isolated to peripheral sites such as the gastrointestinal (GI) tract, 5-HT neurotransmission within the CNS exerts exquisite control over diverse biological functions, including sleep, appetite and respiration, while simultaneously establishing normal mood, perception, and attention. Although several key studies have begun to elucidate how various forms of neurotrauma impact central 5-HT neurotransmission, a full determination of precisely how TBI disrupts the highly regulated dynamics of 5-HT neuron function and/or 5-HT neurotransmission has yet to be conceptually or experimentally resolved. The purpose of the current review is, therefore, to integrate the disparate bodies of 5-HT and TBI research and synthesize insight into how new combinatorial research regarding 5-HT neurotransmission and TBI may offer an informed perspective into the nature of TBI-induced neuropsychiatric complications.

Applications of flexible electronics related to cardiocerebral vascular system

Ensuring accessible and high-quality healthcare worldwide requires field-deployable and affordable clinical diagnostic tools with high performance. In recent years, flexible electronics with wearable and implantable capabilities have garnered significant attention from researchers, which functioned as vital clinical diagnostic-assisted tools by real-time signal transmission from interested targets in vivo. As the most crucial and complex system of human body, cardiocerebral vascular system together with heart-brain network attracts researchers inputting profuse and indefatigable efforts on proper flexible electronics design and materials selection, trying to overcome the impassable gulf between vivid organisms and rigid inorganic units. This article reviews recent breakthroughs in flexible electronics specifically applied to cardiocerebral vascular system and heart-brain network. Relevant sensor types and working principles, electronics materials selection and treatment methods are expounded. Applications of flexible electronics related to these interested organs and systems are specially highlighted. Through precedent great working studies, we conclude their merits and point out some limitations in this emerging field, thus will help to pave the way for revolutionary flexible electronics and diagnosis assisted tools development.

A Review of Serotonin in the Developing Lung and Neonatal Pulmonary Hypertension

Serotonin (5-HT) is a bioamine that has been implicated in the pathogenesis of pulmonary hypertension (PH). The lung serves as an important site of 5-HT synthesis, uptake, and metabolism with signaling primarily regulated by tryptophan hydroxylase (TPH), the 5-HT transporter (SERT), and numerous unique 5-HT receptors. The 5-HT hypothesis of PH was first proposed in the 1960s and, since that time, preclinical and clinical studies have worked to elucidate the role of 5-HT in adult PH. Over the past several decades, accumulating evidence from both clinical and preclinical studies has suggested that the 5-HT signaling pathway may play an important role in neonatal cardiopulmonary transition and the development of PH in newborns. The expression of TPH, SERT, and the 5-HT receptors is developmentally regulated, with alterations resulting in pulmonary vasoconstriction and pulmonary vascular remodeling. However, much remains unknown about the role of 5-HT in the developing and newborn lung. The purpose of this review is to discuss the implications of 5-HT on fetal and neonatal pulmonary circulation and summarize the existing preclinical and clinical literature on 5-HT in neonatal PH.

OP2113, a new drug for chronic hypoxia-induced pulmonary hypertension treatment in rat

BACKGROUND AND PURPOSE

Pulmonary hypertension (PH) is a cardiovascular disease characterised by an increase in pulmonary arterial (PA) resistance leading to right ventricular (RV) failure. Reactive oxygen species (ROS) play a major role in PH. OP2113 is a drug with beneficial effects on cardiac injuries that targets mitochondrial ROS. The aim of the study was to address the in vivo therapeutic effect of OP2113 in PH.

EXPERIMENTAL APPROACH

PH was induced by 3 weeks of chronic hypoxia (CH-PH) in rats treated with OP2113 or its vehicle via subcutaneous osmotic mini-pumps. Haemodynamic parameters and both PA and heart remodelling were assessed. Reactivity was quantified in PA rings and in RV or left ventricular (LV) cardiomyocytes. Oxidative stress was detected by electron paramagnetic resonance and western blotting. Mitochondrial mass and respiration were measured by western blotting and oxygraphy, respectively.

KEY RESULTS

In CH-PH rats, OP2113 reduced the mean PA pressure, PA remodelling, PA hyperreactivity in response to 5-HT, the contraction slowdown in RV and LV and increased the mitochondrial mass in RV. Interestingly, OP2113 had no effect on haemodynamic parameters, both PA and RV wall thickness and PA reactivity, in control rats. Whereas oxidative stress was evidenced by an increase in protein carbonylation in CH-PH, this was not affected by OP2113.

CONCLUSION AND IMPLICATIONS

Our study provides evidence for a selective protective effect of OP2113 in vivo on alterations in both PA and RV from CH-PH rats without side effects in control rats.

When Pulmonary Arterial Hypertension may be Associated with Portal Hypertension: A Case Report of Two Different Hepatic Disorders in One Patient with Pulmonary Hypertension

BACKGROUND

pulmonary arterial hypertension (PAH) is a rare complication of hepatic diseases with portal hypertension that, however, has a significant influence on prognosis. We present a mini-review of how to diagnose and treat it based on a clinical case.

CASE PRESENTATION

in early childhood, a patient had portal hypertension associated with cavernous transformation of the portal vein. It was successfully treated by reno-splenic surgery. At the age of 20 years, this patient experienced increased dyspnea at minimal physical activity after the hepatic biopsy due to a hepatocellular adenoma. The examination in the specialized unit showed PAH, which was evaluated as associated with portal hypertension (PAH-PoH). The specific two-drug combination therapy was started with prominent improvement in patient's state. Successful surgical tumor treatment was provided some months later. The practical and clinical approaches to the diagnosis and treatment of PAH-PoH are discussed. It was emphasized that not all patients with portal hypertension have pulmonary hypertension, which needs to be treated. A lot of evidence gaps exist in management of these patients.

CONCLUSION

all patients, even with past history of portal hypertension, should be monitored closely and screened for PAH earlier, for better results of treatment.

Cardiac Roles of Serotonin (5-HT) and 5-HT-Receptors in Health and Disease

Serotonin acts solely via 5-HT4-receptors to control human cardiac contractile function. The effects of serotonin via 5-HT4-receptors lead to positive inotropic and chronotropic effects, as well as arrhythmias, in the human heart. In addition, 5-HT4-receptors may play a role in sepsis, ischaemia, and reperfusion. These presumptive effects of 5-HT4-receptors are the focus of the present review. We also discuss the formation and inactivation of serotonin in the body, namely, in the heart. We identify cardiovascular diseases where serotonin might play a causative or additional role. We address the mechanisms which 5-HT4-receptors can use for cardiac signal transduction and their possible roles in cardiac diseases. We define areas where further research in this regard should be directed in the future, and identify animal models that might be generated to this end. Finally, we discuss in what regard 5-HT4-receptor agonists or antagonists might be useful drugs that could enter clinical practice. Serotonin has been the target of many studies for decades; thus, we found it timely to summarise our current knowledge here.

Recognition and Management of Serotonin Toxidrome in the Emergency Department-Case Based Review

Serotonin syndrome (SS) is a clinical toxidrome with high variability in clinical practice. It develops due to increased serotonin levels in the central nervous system. With an underestimated frequency, SS can develop following an overdose, a therapeutic dose increase, or drug to drug interaction of at least one serotonergic agent. It can present with autonomic signs, neuromuscular changes and an altered mental status. However, history and clinical examination are key features to formulate the diagnosis. Treatment options consist of supportive measures, discontinuation of the offending agent and certain therapeutic agents previously reported to improve outcomes. Physicians have limited experience with SS, partially due to the lack of its identification in clinical practice. Therefore, we have integrated, in a narrative review, the case of a young male with SS following an atypical antipsychotic overdose superimposed on chronic treatment with agents previously known to produce SS.

Uptake and Metabolization of Serotonin by Granulosa Cells Form a Functional Barrier in the Mouse Ovary

Serotonin (5-HT) plays an essential role in regulating female reproductive function in many animals. 5-HT accumulates in the mammalian ovary with the involvement of membrane serotonin transporter SERT and is functionally active in the oocytes of growing follicles, but shows almost no activity in follicular cells. In this study, we clarified the interplay between 5-HT membrane transport and its degradation by monoamine oxidase (MAO) in the mammalian ovary. Using pharmacologic agents and immunohistochemical staining of the cryosections of ovaries after serotonin administration in vitro, we demonstrated the activity of transport and degradation systems in ovarian follicles. The MAO inhibitor pargyline increased serotonin accumulation in the granulosa cells of growing follicles, indicating the activity of both serotonin uptake and degradation by MAO in these cells. The activity of MAO and the specificity of the membrane transport of serotonin was confirmed in primary granulosa cell culture treated with pargyline and fluoxetine. Moreover, the accumulation of serotonin is more effective in the denuded oocytes and occurs at lower concentrations than in the oocytes within the follicles. This confirms that the activity of SERT and MAO in the granulosa cells surrounding the oocytes impedes the accumulation of serotonin in the oocytes and forms a functional barrier to serotonin.

Serotonin-deficient neonatal mice are not protected against the development of experimental bronchopulmonary dysplasia or pulmonary hypertension

Serotonin (5-hydroxytryptamine, 5-HT) is a potent pulmonary vasoconstrictor and contributes to high pulmonary vascular resistance in the developing ovine lung. In experimental pulmonary hypertension (PH), pulmonary expression of tryptophan hydroxylase-1 (TPH1), the rate limiting enzyme in 5-HT synthesis, and plasma 5-HT are increased. 5-HT blockade increases pulmonary blood flow and prevents pulmonary vascular remodeling and PH in neonatal models of PH with bronchopulmonary dysplasia (BPD). We hypothesized that neonatal tph1 knock-out (KO) mice would be protected from hypoxia-induced alveolar simplification, decreased vessel density, and PH. Newborn wild-type (WT) and tph1 KO mice were exposed to normoxia or hypoxia for 2 weeks. Normoxic WT and KO mice exhibited similar alveolar development, pulmonary vascular density, right ventricular systolic pressures (RVSPs), and right heart size. Circulating (plasma and platelet) 5-HT decreased in both hypoxia-exposed WT and KO mice. Tph1 KO mice were not protected from hypoxia-induced alveolar simplification, decreased pulmonary vascular density, or right ventricular hypertrophy, but displayed attenuation to hypoxia-induced RVSP elevation compared with WT mice. Tph1 KO neonatal mice are not protected against hypoxia-induced alveolar simplification, reduction in pulmonary vessel density, or RVH. While genetic and pharmacologic inhibition of tph1 has protective effects in adult models of PH, our results suggest that tph1 inhibition would not be beneficial in neonates with PH associated with BPD.

An Overview of Circulating Pulmonary Arterial Hypertension Biomarkers

Pulmonary arterial hypertension (PAH), also known as Group 1 Pulmonary Hypertension (PH), is a PH subset characterized by pulmonary vascular remodeling and pulmonary arterial obstruction. PAH has an estimated incidence of 15-50 people per million in the United States and Europe, and is associated with high mortality and morbidity, with patients' survival time after diagnosis being only 2.8 years. According to current guidelines, right heart catheterization is the gold standard for diagnostic and prognostic evaluation of PAH patients. However, this technique is highly invasive, so it is not used in routine clinical practice or patient follow-up. Thereby, it is essential to find new non-invasive strategies for evaluating disease progression. Biomarkers can be an effective solution for determining PAH patient prognosis and response to therapy, and aiding in diagnostic efforts, so long as their detection is non-invasive, easy, and objective. This review aims to clarify and describe some of the potential new candidates as circulating biomarkers of PAH.

A Systematic Review with Meta-analysis of Biomarkers for detection of Pulmonary Arterial Hypertension

Rationale

The blood is a rich source of potential biomarkers for the diagnosis of idiopathic and hereditary pulmonary arterial hypertension (iPAH and hPAH, referred to as “PAH”). While a lot of biomarkers have been identified for PAH, the clinical utility of these biomarkers often remains unclear. Here, we performed an unbiased meta-analysis of published biomarkers to identify biomarkers with the highest performance for detection of PAH.

Methods

A literature search (in PubMed, Embase.com, Clarivate Analytics/Web of Science Core Collection and Wiley/Cochrane Library) was performed up to 28 January 2021. Primary end points were blood biomarker levels in PAH versus asymptomatic controls or patients suspected of pulmonary hypertension (PH) with proven normal haemodynamic profiles.

Results

149 articles were identified by the literature search. Meta-analysis of 26 biomarkers yielded 17 biomarkers that were differentially expressed in PAH and non-PH control subjects. Red cell distribution width, low density lipid-cholesterol, d-dimer, N-terminal prohormone of brain natriuretic protein (NT-proBNP), interleukin-6 (IL-6) and uric acid were biomarkers with the largest observed differences, largest sample sizes and a low risk of publication bias. Receiver operating characteristic curves and sensitivity/specificity analyses demonstrated that NT-proBNP had a high sensitivity, but low specificity for PAH. For the other biomarkers, insufficient data on diagnostic accuracy with receiver operating characteristic curves were available for meta-analysis.

Conclusion

This meta-analysis validates NT-proBNP as a biomarker with high sensitivity for PAH, albeit with low specificity. The majority of biomarkers evaluated in this meta-analysis lacked either external validation or data on diagnostic accuracy. Further validation studies are required as well as studies that test combinations of biomarkers to improve specificity.

Meta-analysis of 26 biomarkers yielded 17 differentially expressed biomarkers in PAH. NT-proBNP had the highest diagnostic accuracy but had a low specificity for PAH. Other markers, including IL-6, RDW, LDL-c, D-dimer and UA, lacked clinical validation.https://bit.ly/3J4YAyC

The roles of serotonin in cell adhesion and migration, and cytoskeletal remodeling

Serotonin is well known as a neurotransmitter. Its roles in neuronal processes such as learning, memory or cognition are well established, and also in disorders such as depression, schizophrenia, bipolar disorder, and dementia. However, its effects on adhesion and cytoskeletal remodelling which are strongly affected by 5-HT receptors, are not as well studied with some exceptions for e.g. platelet aggregation. Neuronal function is strongly dependent on cell-cell contacts and adhesion-related processes. Therefore the role played by serotonin in psychiatric illness, as well as in the positive and negative effects of neuropsychiatric drugs through cell-related adhesion can be of great significance. In this review, we explore the role of serotonin in some of these aspects based on recent findings.

Increased intracellular Cl- concentration in pulmonary arterial myocytes is associated with chronic hypoxic pulmonary hypertension

Chloride channels play an important role in regulating smooth muscle contraction and proliferation, and contribute to the enhanced constriction of pulmonary arteries (PAs) in pulmonary hypertension (PH). The intracellular Cl^- concentration ([Cl^-]_i), tightly regulated by various Cl^- transporters, determines the driving force for Cl^- conductance, thereby the functional outcome of Cl^- channel activation. This study characterizes for the first time the expression profile of Cl^- transporters/exchangers in PA smooth muscle and provides the first evidence that the intracellular Cl^- homeostasis is altered in PA smooth muscle cells (PASMCs) associated with chronic hypoxic PH (CHPH). Quantitative RT-PCR revealed that the endothelium-denuded intralobar PA of rats expressed Slc12a gene family-encoded Na-K-2Cl cotransporter 1 (NKCC1), K-Cl cotransporters (KCC) 1, 3, and 4, and Slc4a gene family-encoded Na⁺-independent and Na⁺-dependent Cl^-/HCO₃^- exchangers. Exposure of rats to chronic hypoxia (10% O₂, 3 wk) caused CHPH and selectively increased the expression of Cl^--accumulating NKCC1 and reduced the Cl^--extruding KCC4. The intracellular Cl^- concentration ([Cl^-]_i) averaged at 45 mM and 47 mM in normoxic PASMCs as determined by fluorescent indicator MEQ and by gramicidin-perforated patch-clamp technique, respectively. The ([Cl^-]_i was increased by ∼10 mM in PASMCs of rats with CHPH. Future studies are warranted to further establish the hypothesis that the altered intracellular Cl^- homeostasis contributes to the pathogenesis of CHPH.

Assessment of Platelet and Plasma Serotonin in Canine Pulmonary Hypertension Secondary to Degenerative Mitral Valve Disease

Background: Pulmonary hypertension (PH) is a common complication of degenerative mitral valve disease (DMVD), the most common cardiovascular disease in dogs. Serotonin has been suspected to play a role in the pathogenesis of PH, so this study aimed to investigate the differences in platelet and plasma serotonin between normal, DMVD and DMVD with PH (DMVD+PH) dogs. Materials and Methods: Sixty-two small-breed dogs were enrolled to the study and divided into the normal (n = 22), DMVD (n = 20), and DMVD+PH (n = 20) groups. The platelet and plasma serotonin concentrations were measured by the competitive ELISA. Results: The Kruskal-Wallis revealed the difference among the four groups of normal (179.73 [102.37-352.24] ng/10⁹ platelets), DMVD (325.99 [96.84-407.66] ng/10⁹ platelets), DMVD with intermediate probability of PH (291.11 [106.69-400.84] ng/10⁹ platelets) and DMVD with high probability of PH (35.82 [2.69-126.35] ng/10⁹ platelets) (p = 0.014). The Dunn's post-hoc test showed a decrease in the platelet serotonin concentration of the DMVD dogs with high probability of PH compared to the DMVD group (p = 0.008). The plasma serotonin concentration was not different between normal, DMVD, and DMVD+PH dogs. Conclusion: In conclusion, a decrease in platelet serotonin concentration, which is associated with a degree of PH probability was found in DMVD dogs with PH. Further studies investigating roles of platelet serotonin in PH secondary to DMVD should be performed.

Increased MAO-A Activity Promotes Progression of Pulmonary Arterial Hypertension

Monoamine oxidases (MAOs), a class of enzymes bound to the outer mitochondrial membrane, are important sources of reactive oxygen species. Increased MAO-A activity in endothelial cells and cardiomyocytes contributes to vascular dysfunction and progression of left heart failure. We hypothesized that inhibition of MAO-A can be used to treat pulmonary arterial hypertension (PAH) and right ventricular (RV) failure. MAO-A levels in lung and RV samples from patients with PAH were compared with levels in samples from donors without PAH. Experimental PAH was induced in male Sprague-Dawley rats by using Sugen 5416 and hypoxia (SuHx), and RV failure was induced in male Wistar rats by using pulmonary trunk banding (PTB). Animals were randomized to receive either saline or the MAO-A inhibitor clorgyline at 10 mg/kg. Echocardiography and RV catheterization were performed, and heart and lung tissues were collected for further analysis. We found increased MAO-A expression in the pulmonary vasculature of patients with PAH and in experimental experimental PAH induced by SuHx. Cardiac MAO-A expression and activity was increased in SuHx- and PTB-induced RV failure. Clorgyline treatment reduced RV afterload and pulmonary vascular remodeling in SuHx rats through reduced pulmonary vascular proliferation and oxidative stress. Moreover, clorgyline improved RV stiffness and relaxation and reversed RV hypertrophy in SuHx rats. In PTB rats, clorgyline had no direct clorgyline had no direct effect on the right ventricle effect. Our study reveals the role of MAO-A in the progression of PAH. Collectively, these findings indicated that MAO-A may be involved in pulmonary vascular remodeling and consecutive RV failure.

Serum Serotonin Differentiates Between Disease Activity States in Crohn's Patients

BACKGROUND

Diagnosis and monitoring of inflammatory bowel diseases (IBDs) utilize invasive methods including endoscopy and tissue biopsy, with blood tests being less specific for IBDs. Substantial evidence has implicated involvement of the neurohormone serotonin (5-hydroxytryptamine, 5-HT) in the pathophysiology of IBDs. The current study investigated whether serum 5-HT is elevated in patients with active ulcerative colitis (UC) or Crohn's disease (CD).

METHODS

Serum samples were obtained from a German cohort of 96 CD and UC patients with active disease, refractory disease, or remission of disease based upon their disease activity index (DAI) and disease history. High pressure liquid chromatography with tandemmass spectrometry was used to measure 5-HT, tryptophan (TRP), and kynurenine (KYN) levels in the serum samples, and Luminex Multiplex ELISA was used to measure cytokine levels. Intestinal mucosal biopsies were obtained from a separate cohort of healthy and CD patients, and the immunoreactivity of the serotonin transporter (SERT) was determined.

RESULTS

There was no statistically significant difference in TRP or KYN levels between disease categories in either UC or CD. Interestingly, 5-HT levels were significantly elevated in patients with active CD but not active UC when compared with the levels in remission or refractory disease. Serum 5-HT was superior to C-reactive protein and circulating cytokines in differentiating between disease categories in CD. Additionally, SERT immunoreactivity was decreased in the ileum and colon of patients with CD compared to healthy controls.

CONCLUSION

We have shown that the serum 5-HT can differentiate between active disease and refractory disease or remission among CD patients, emphasizing the potential suitability of serum 5-HT as an auxiliary measure in diagnosing active CD.

Plasma Serotonin is Elevated in Adult Patients with Sudden Sensorineural Hearing Loss

Background The roles of thrombophilia and cardiovascular risk factors in sudden sensorineural hearing loss (SSNHL) remain controversial. Cochlear microthrombosis and vasospasm have been hypothesized as possible pathogenic mechanisms of SSNHL. This article investigates the circulating serotonin and homocysteine levels besides thrombophilia screening in patients with idiopathic SSNHL.

Methods A total of 133 SSNHL patients and age- and sex-matched controls were investigated (discovery cohort). Measurement included common inherited natural coagulation inhibitors, factor VIII, von Willebrand factor (VWF), antiphospholipid antibodies, homocysteine, and serotonin (whole blood, platelet, and plasma) levels, along with frequent relevant genetic variants. A validation cohort (128 SSNHL patients) was studied for homocysteine and serotonin levels.

Results and Conclusion In the discovery cohort, 58.6% of patients exhibited thrombophilia, of which most had a low to moderate titers of antiphospholipid antibodies and high levels of factor VIII/VWF. Twenty-seven patients (20%) had mild-to-moderate hyperhomocysteinemia or were homozygous for the methylenetetrahydrofolate reductase (MTHFR) C677T mutation. Regarding serotonin, SSNHL patients had elevated whole blood levels that remained within the normal range and normal platelet content. However, approximately 90% patients of both cohorts had elevated plasma serotonin. Elevated plasma serotoninemia was accompanied by serotonylation of platelet rhoA protein. This study shows that increased plasma serotonin appears as a biomarker of SSNHL (specificity: ∼96%, sensitivity: ∼90%) and could participate in the pathophysiology of SSNHL.

Connexin-43 is a promising target for pulmonary hypertension due to hypoxaemic lung disease

The mechanisms underlying pulmonary hypertension (PH) are complex and multifactorial, and involve different cell types that are interconnected through gap junctional channels. Although connexin (Cx)-43 is the most abundant gap junction protein in the heart and lungs, and critically governs intercellular signalling communication, its contribution to PH remains unknown. The focus of the present study is thus to evaluate Cx43 as a potential new target in PH.Expressions of Cx37, Cx40 and Cx43 were studied in lung specimens from patients with idiopathic pulmonary arterial hypertension (IPAH) or PH associated with chronic hypoxaemic lung diseases (chronic hypoxia-induced pulmonary hypertension (CH-PH)). Heterozygous Cx43 knockdown CD1 (Cx43^+/-) and wild-type littermate (Cx43^+/+) mice at 12 weeks of age were randomly divided into two groups, one of which was maintained in room air and the other exposed to hypoxia (10% oxygen) for 3 weeks. We evaluated pulmonary haemodynamics, remodelling processes in cardiac tissues and pulmonary arteries (PAs), lung inflammation and PA vasoreactivity.Cx43 levels were increased in PAs from CH-PH patients and decreased in PAs from IPAH patients; however, no difference in Cx37 or Cx40 levels was noted. Upon hypoxia treatment, the Cx43^+/- mice were partially protected against CH-PH when compared to Cx43^+/+ mice, with reduced pulmonary arterial muscularisation and inflammatory infiltration. Interestingly, the adaptive changes in cardiac remodelling in Cx43^+/- mice were not affected. PA contraction due to endothelin-1 (ET-1) was increased in Cx43^+/- mice under normoxic and hypoxic conditions.Taken together, these results indicate that targeting Cx43 may have beneficial therapeutic effects in PH without affecting compensatory cardiac hypertrophy.

Platelet activation in experimental murine neonatal pulmonary hypertension

Serotonin (5-HT) contributes to the pathogenesis of experimental neonatal pulmonary hypertension (PH) associated with bronchopulmonary dysplasia (BPD). Platelets are the primary source of circulating 5-HT and is released upon platelet activation. Platelet transfusions are associated with neonatal mortality and increased rates of BPD. As BPD is often complicated by PH, we tested the hypothesis that circulating platelets are activated and also increased in the lungs of neonatal mice with bleomycin-induced PH associated with BPD. Newborn wild-type mice received intraperitoneal bleomycin (3 units/kg) three times weekly for 3 weeks. Platelets from mice with experimental PH exhibited increased adhesion to collagen under flow (at 300 s-1 and 1,500 s-1 ) and increased expression of the αIIbβ3 integrin and phosphatidylserine, markers of platelet activation. Platelet-derived factors 5-HT and platelet factor 4 were increased in plasma from mice with experimental PH. Pharmacologic blockade of the 5-HT 2A receptor (5-HT 2A R) prevents bleomycin-induced PH and pulmonary vascular remodeling. Here, platelets from mice with bleomycin-induced PH demonstrate increased 5-HT 2A R expression providing further evidence of both platelet activation and increased 5-HT signaling in this model. In addition, bleomycin treatment increased lung platelet accumulation. In summary, platelets are activated, granule factors are released, and are increased in numbers in the lungs of mice with experimental neonatal PH. These results suggest platelet activation and release of platelet-derived factors may increase vascular tone, promote aberrant angiogenesis, and contribute to the development of neonatal PH.

Serotonin Transporter Deficiency is Associated with Dysbiosis and Changes in Metabolic Function of the Mouse Intestinal Microbiome

Serotonin transporter (SERT) plays a critical role in regulating extracellular availability of serotonin (5-HT) in the gut and brain. Mice with deletion of SERT develop metabolic syndrome as they age. Changes in the gut microbiota are being increasingly implicated in Metabolic Syndrome and Diabetes. To investigate the relationship between the gut microbiome and SERT, this study assessed the fecal and cecal microbiome profile of 11 to 12 week-old SERT+/+ and SERT-/- mice. Microbial DNA was isolated, processed for metagenomics shotgun sequencing, and taxonomic and functional profiles were assessed. 34 differentially abundant bacterial species were identified between SERT+/+ and SERT-/-. SERT-/- mice displayed higher abundances of Bacilli species including genera Lactobacillus, Streptococcus, Enterococcus, and Listeria. Furthermore, SERT-/- mice exhibited significantly lower abundances of Bifidobacterium species and Akkermansia muciniphilia. Bacterial community structure was altered in SERT-/- mice. Differential abundance of bacteria was correlated with changes in host gene expression. Bifidobacterium and Bacilli species exhibited significant associations with host genes involved in lipid metabolism pathways. Our results show that SERT deletion is associated with dysbiosis similar to that observed in obesity. This study contributes to the understanding as to how changes in gut microbiota are associated with metabolic phenotype seen in SERT deficiency.

Nanomaterial based electrochemical sensing of the biomarker serotonin: a comprehensive review

This review (with 131 references) summarizes the progress made in the past years in the field of nanomaterial based sensing of serotonin (5-HT). An introduction summarizes the significant role of 5-HT as a biomarker for several major diseases, methods for its determination and the various kinds of nanomaterials for use in electrochemical sensing process relies principally on a precise choice of electrodes. The next main section covers nanomaterial based methods for sensing 5-HT, with subsections on electrodes modified with carbon nanotubes, graphene related materials, gold nanomaterials, and by other nanomaterials. A concluding section discusses future perspectives and current challenges of 5-HT determination. Graphical abstract Conceptual design of electrochemical sensing process of the biomarker serotonin by using nanomaterials and the role of 5-HTas biomarker in the body from preclinical to clincal.

Hierarchical Au nanoclusters electrodeposited on amine-terminated ITO glass as a SERS-active substrate for the reliable and sensitive detection of serotonin in a Tris-HCl buffer solution

In this study, a SERS-active substrate was fabricated by electrodepositing hierarchical Au nanostructures on amine-terminated ITO (indium tin oxide) glass to achieve an enhanced Raman signal of 5-HT.

The Role of G Protein-Coupled Receptors in the Right Ventricle in Pulmonary Hypertension

Pressure overload of the right ventricle (RV) in pulmonary arterial hypertension (PAH) leads to RV remodeling and failure, an important determinant of outcome in patients with PAH. Several G protein-coupled receptors (GPCRs) are differentially regulated in the RV myocardium, contributing to the pathogenesis of RV adverse remodeling and dysfunction. Many pharmacological agents that target GPCRs have been demonstrated to result in beneficial effects on left ventricular (LV) failure, such as beta-adrenergic receptor and angiotensin receptor antagonists. However, the role of such drugs on RV remodeling and performance is not known at this time. Moreover, many of these same receptors are also expressed in the pulmonary vasculature, which could result in complex effects in PAH. This manuscript reviews the role of GPCRs in the RV remodeling and dysfunction and discusses activating and blocking GPCR signaling to potentially attenuate remodeling while promoting improvements of RV function in PAH.

Fast and Selective Plasmonic Serotonin Detection with Aptamer-Gold Nanoparticle Conjugates

Neurotransmitters detection is critical to understanding communication between the brain and peripheral tissue. Serotonin is a key neurotransmitter linked to a number of conditions, but a full understanding of its role in disease is still lacking. The development of fast and selective serotonin detection platforms will provide researchers with tools to monitor serotonin in individuals before and after treatment for the condition of interest. Aptamer-gold nanoparticles conjugates that responded colorimetrically to serotonin with minimal response to its metabolite and other neurotransmitters were designed by simply adsorbing the DNA on the surface of AuNPs. A plasmonic assay for serotonin detection was designed with a response to biologically relevant serotonin levels. Importantly, the assay performance was not compromised when tested in filtered spiked fetal bovine serum as a mimic of biofluids. This work shows that these simple and stable Apt-AuNP conjugates are promising tools to develop fast assays for point-of-care and personalized diagnostics applications.

Signaling Pathways Linked to Serotonin-Induced Superoxide Anion Production: A Physiological Role for Mitochondria in Pulmonary Arteries

Serotonin (5-HT) is a potent vasoconstrictor agonist and contributes to several vascular diseases including systemic or pulmonary hypertension and atherosclerosis. Although superoxide anion (O2•_) is commonly associated to cellular damages due to O2•_ overproduction, we previously demonstrated that, in physiological conditions, O2•_ also participates to the 5-HT contraction in intrapulmonary arteries (IPA). Here, we focused on the signaling pathways leading to O2•_ production in response to 5-HT in rat IPA. Using electron paramagnetic resonance on rat IPA, we showed that 5-HT (100 μM)-induced O2•_ production was inhibited by ketanserin (1 μM—an inhibitor of the 5-HT₂ receptor), absence of extracellular calcium, two blockers of voltage-independent calcium permeable channels (RHC80267 50 μM and LOE-908 10 μM) and a blocker of the mitochondrial complex I (rotenone—100 nM). Depletion of calcium from the sarcoplasmic reticulum or nicardipine (1 μM—an inhibitor of the L-type voltage-dependent calcium channel) had no effect on the 5-HT-induced O2•_ production. O2•_ levels were also increased by α-methyl-5-HT (10 μM—a 5-HT₂ receptors agonist) whereas GR127935 (1 μM—an antagonist of the 5-HT_1B/D receptor) and citalopram (1 μM—a 5-HT transporter inhibitor) had no effect on the 5-HT-induced O2•_ production. Peroxynitrites were increased in response to 5-HT (100 μM). In isolated pulmonary arterial smooth muscle cells loaded with rhod-2 or mitosox probes, we respectively showed that 5-HT increased both mitochondrial calcium and O2•_ levels, which were both abrogated in absence of extracellular calcium. Mitochondrial O2•_ levels were also abolished in the presence of rotenone (100 nM). In pulmonary arterial smooth muscle cells loaded with TMRM, we showed that 5-HT transiently depolarized the mitochondrial membrane whereas in the absence of extracellular calcium the mitochondrial membrane depolarisation was delayed and sustained in response to 5-HT. 5-HT decreased the mitochondrial respiratory rate measured with a Clark oxygen electrode. Altogether, in physiological conditions, 5-HT acts on 5-HT₂ receptors and induces an O2•_ production dependent on extracellular calcium and mitochondria.

[Pulmonary arterial hypertension, bone marrow, endothelial cell precursors and serotonin]

Serotonin and bone-marrow-derived stem cells participate together in triggering pulmonary hypertension. Our work has shown that the absence of 5-HT2B receptors generates permanent changes in the composition of the blood and bone-marrow in the myeloid lineages, particularly in endothelial cell progenitors. The initial functions of 5-HT2B receptors in pulmonary arterial hypertension (PAH) are restricted to bone-marrow cells. They contribute to the differentiation/proliferation/mobilization of endothelial progenitor cells from the bone-marrow. Those bone-marrow-derived cells have a critical role in the development of pulmonary hypertension and pulmonary vascular remodeling. These data indicate that bone-marrow derived endothelial progenitors play a key role in the pathogenesis of PAH and suggest that interactions involving serotonin and bone morphogenic protein type 2 receptor (BMPR2) could take place at the level of the bone-marrow.

Increased Tyrosine Phosphorylation of Platelet Proteins Including pp125FAK Suggests Endogenous Activation and Aggregation in Pulmonary Hypertension

Despite of several lines of evidence indicating a pathophysiologic role of platelets in pulmonary hypertension, the occurrence of chronic endogenous platelet activation has been a matter of debate. It was hypothesized that the pattern of tyrosine phosphorylation of platelet proteins examined ex vivo could provide information on the state of platelet activation. This was examined in 10 patients with pulmonary arterial hypertension aged 18 to 53 years. Phosphotyrosine density and the amounts of specific proteins were analyzed in resting platelets after reaction with anti-phosphotyrosine, anti-pp60c-src, anti-pp125FAK, and anti-αIIbβ3 antibodies. There was a 79% increase in protein-associated phosphotyrosine in patients in comparison to levels in controls (p<0.05). In particular, phosphorylation on tyrosine residues of pp120 and pp125FAK increased 24% and 57%, respectively (p<0.05). Although pp60c-src-associated phosphotyrosine was not altered in the patient group as a whole, it was clearly decreased in three subjects. Platelet content of β3 integrin, pp60c-src, and pp125FAK, was not altered. This pattern of phosphorylation suggests an ongoing process of platelet activation. Because phosphorylation of pp125FAK is a late, integrin-dependent event, results suggest that platelet activation and aggregation occur in vivo in these patients.

Clopidogrel treatment may associate with worsening of endothelial function and development of new digital ulcers in patients with systemic sclerosis: results from an open label, proof of concept study

Background

Activated platelets release serotonin that binds 5-HT_2B receptor on fibroblasts leading to fibroblast activation. Clopidogrel, an inhibitor of ADP-dependent platelet activation prevents fibrosis in animal models of systemic sclerosis (SSc). We aimed at assessing whether i) ADP-dependent platelet activation is increased in patients with SSc compared to healthy subjects and patients with rheumatoid arthritis (RA) and ii) whether clopidogrel can effectively suppress ADP-dependent activation, reduce circulating serotonin levels and hence, favorably affect fibrosis or vasculopathy in patients with systemic sclerosis.

Methods

Thirteen patients with SSc were recruited. Platelet activation was assessed by aggregometry prior to and following 14 days of clopidogrel treatment. At the same time points serotonin and soluble vascular cell adhesion molecule 1 (s-VCAM1), a marker of endothelial dysfunction, were measured.

Results

ADP-dependent platelet activation was similar between patients with SSc (n = 13), patients with RA (n = 28) and healthy subjects (n = 22) (mean ± SEM AU*min: 392.1 ± 58.4, 535.5 ± 61.33 and 570.9 ± 42.9 in patients with SSc, patients with RA and healthy subjects respectively, p = 0.14). Clopidogrel treatment significantly reduced platelet activation in patients with SSc (mean ± SEM AU*min: 392.1 ± 58.4 vs 163.8 ± 51.7, p = 0.014). Clopidogrel treatment did not affect serotonin levels but led to a significant increase in s-VCAM1 (p = 0.03). Three patients developed new digital ulcers during the study. The potential association of the study drug with the development of new digital ulcers led to early termination of the study.

Conclusion

Clopidogrel may worsen markers of endothelial function and associate with development of new digital ulcers in patients with SSc.

Clinical trial registration

ISRCTN63206606. Registered 02/Dec/2014.

Biocompatibility Assessment of the CentriMag-Novalung Adult ECMO Circuit in a Model of Acute Pulmonary Hypertension

Extracorporeal membrane oxygenation (ECMO) is rarely used in patients with severe pulmonary hypertension (PH) as a bridge to lung transplantation. In this study, we assess the blood biocompatibility of the integrated CentriMag-Novalung ECMO system (venoarterial) in an acute model of PH. Severe PH (≥2/3 systemic) was induced in eight sheep through progressive ligation of the main pulmonary artery. System performance, platelet activation, thromboelastography (TEG) parameters, fibrinogen, plasma-free hemoglobin, and total plasma protein were measured at initiation, 3, and 6 hr of support in the ECMO (N = 4) and sham (N = 4) groups. A stable ECMO flow (2.2 ± 0.1 L/min), low transmembrane pressure gradient, and steady blood O2 and CO2 levels were maintained. Platelet activation was low (<4%) in both the groups, whereas platelet responsiveness to agonist (platelet activating factor) was reduced in the sham group when compared with the ECMO group. There were no differences in the TEG parameters, fibrinogen concentration, plasma-free hemoglobin (<10 mg/dl), and plasma total protein between the two groups. The findings of low levels of platelet activation and plfHb suggest adequate blood biocompatibility of the integrated CentriMag-Novalung circuit use for short-term support in a model of PH.

Platelet serotonin modulates immune functions

This short review addresses immune functions of platelet serotonin. Platelets transport serotonin at a high concentration in dense granules and release it upon activation. Besides haemostatic, vasotonic and developmental modulation, serotonin also influences a variety of immune functions (mediated by different serotonin receptors). First, platelet serotonergic effects are directed against invading pathogens via activation and proliferation of lymphocytes, modulation of cytokine release, and recruitment of neutrophils to sites of acute inflammation by induction of selectin expression on endothelial cells. Second, serotonin levels are elevated in autoimmune diseases, such as asthma or rheumatoid arthritis, and during tissue regeneration after ischemia of myocardium or brain. Specific antagonism of serotonin receptors appears to improve survival after myocardial infarction or sepsis and to attenuate asthmatic attacks in animal models. It will be of great clinical relevance if these findings can be translated into human applications. In conclusion, targeting immune modulatory effects of platelet serotonin may provide novel therapeutic options for common health problems.

5-HT2B receptor antagonists inhibit fibrosis and protect from RV heart failure

Objective. The serotonin (5-HT) pathway was shown to play a role in pulmonary hypertension (PH), but its functions in right ventricular failure (RVF) remain poorly understood. The aim of the current study was to investigate the effects of Terguride (5-HT2A and 2B receptor antagonist) or SB204741 (5-HT2B receptor antagonist) on right heart function and structure upon pulmonary artery banding (PAB) in mice. Methods. Seven days after PAB, mice were treated for 14 days with Terguride (0.2 mg/kg bid) or SB204741 (5 mg/kg day). Right heart function and remodeling were assessed by right heart catheterization, magnetic resonance imaging (MRI), and histomorphometric methods. Total secreted collagen content was determined in mouse cardiac fibroblasts isolated from RV tissues. Results. Chronic treatment with Terguride or SB204741 reduced right ventricular fibrosis and showed improved heart function in mice after PAB. Moreover, 5-HT2B receptor antagonists diminished TGF-beta1 induced collagen synthesis of RV cardiac fibroblasts in vitro. Conclusion. 5-HT2B receptor antagonists reduce collagen deposition, thereby inhibiting right ventricular fibrosis. Chronic treatment prevented the development and progression of pressure overload-induced RVF in mice. Thus, 5-HT2B receptor antagonists represent a valuable novel therapeutic approach for RVF.

Tumor necrosis factor alpha induces a serotonin dependent early increase in ciliary beat frequency and epithelial transport velocity in murine tracheae

The tracheal epithelium prevents via its highly effective clearance mechanism the contamination of the lower airways by pathogens. This mechanism is driven by ciliary bearing cells which are not only in contact with the gas phase; in addition they are also influenced by inflammatory mediators. These mediators can alter the protective function of the epithelium. Since the pro-inflammatoric cytokine tumor necrosis factor-α (TNF-α) plays a pivotal role within the inflammatory cascade, we investigated its effect onto the tracheal epithelium measured by its ciliary beat frequency and the particle transport velocity. In organ explant experiments the ciliary beat frequency and the particle transport velocity were measured under the application of TNF-α using tracheae from male C57BL6J mice. We observed a dose dependent TNF-α induced increase of both particle transport velocity and ciliary beat frequency. Knock out mice experiments made evident that the increase was depended on the expression of tumor necrosis factor receptor 1 (TNF-R1). The increases in ciliary beat frequency as well as the accelerated particle transport velocity were either inhibited by the unspecific serotonin antagonist methysergide or by cyproheptadine a specific 5-HT2 receptor antagonist. Thus, acetylcholine antagonists or nitric oxide synthase (NOS) inhibitors failed to inhibit the TNF-α induced activation. In conclusion, TNF-α may play a pivotal role in the protection of lower airways by inducing ciliary activity and increase in particle transport velocity via TNF-R1 and 5-HT2 receptor.

Venous plasma serotonin is not a proper biomarker for pulmonary arterial hypertension

OBJECTIVES

Serotonin (5-HT) most likely plays an important role in the pathogenesis of pulmonary arterial hypertension (PAH). We aimed to test if venous plasma 5-HT is a potential biomarker of PAH. We also measured venous blood β-thromboglobulin (β-TG) in all participants to ensure that any increase in serotonin levels measured is due to platelet release.

DESIGN

Blood samples from patients (n = 9) with pulmonary arterial hypertension (Group 1 of the World Health Organization classification of pulmonary hypertension) as well as healthy volunteers (n = 9) were analyzed. We used enzyme-linked immunosorbent assay (ELISA) to measure venous platelet-poor plasma 5-HT and β-TG in patients with pulmonary arterial hypertension (PAH) and in age-matched normal controls.

RESULTS

Venous platelet-free plasma 5-HT and β-TG were almost similar in patients with PAH and healthy controls with only a slight trend toward increased 5-HT levels in patients with PAH. No correlation was found between venous platelet-poor plasma 5-HT and disease severity. There was no association between venous plasma 5-HT and the mean pulmonary artery pressure.

CONCLUSIONS

Our data suggest that 5-HT is not significantly elevated in venous platelet-free plasma in patients with PAH and may accordingly not be a useful biomarker in this condition.

Elevated transglutaminase 2 activity is associated with hypoxia-induced experimental pulmonary hypertension in mice

Previous studies in human patients and animal models have suggested that transglutaminase 2 (TG2) is upregulated in pulmonary hypertension (PH), a phenomenon that appears to be associated with the effects of serotonin (5-hydroxytryptamine; 5-HT) in this disease. Using chemical tools to interrogate and inhibit TG2 activity in vivo, we have shown that pulmonary TG2 undergoes marked post-translational activation in a mouse model of hypoxia-induced PH. We have also identified irreversible fluorinated TG2 inhibitors that may find use as non-invasive positron emission tomography probes for diagnosis and management of this debilitating, lifelong disorder. Pharmacological inhibition of TG2 attenuated the elevated right ventricular pressure but had no effect on hypertrophy of the right ventricle of the heart. A longitudinal study of pulmonary TG2 activity in PH patients is warranted.

Transglutaminase 2-mediated serotonylation in pulmonary hypertension

The monoamine serotonin (5-HT) has been previously implicated in pulmonary arterial remodeling and is considered a potential therapeutic target for the disease pulmonary arterial hypertension (PAH). More recently, it has been recognized that the enzyme tissue transglutaminase (TG2) mediates cross-linking of proteins with 5-HT, a posttranslational process of monoaminylation known as "serotonylation." TG2 activity and serotonylation of protein participate in both smooth muscle proliferation and contraction produced by 5-HT. Indeed, markedly increased TG2 activity has now been identified in lung tissue of an experimental rodent model of pulmonary hypertension, and elevated serotonylation of fibronectin and the signaling molecule Rho, downstream products of transglutamidation, have been found in blood of patients with PAH. The basic mechanism by which TG2 is activated and the potential role(s) of serotonylated proteins in pulmonary hypertension remain a mystery. In the present review we have tried to address the current understanding of 5-HT metabolism in pulmonary hypertension and relate it to what is currently known about the evolving cellular process of serotonylation.

Standard nonspecific therapies in the management of pulmonary arterial hypertension

Recent advances in pulmonary arterial hypertension (PAH) research have created a new era of PAH-specific therapies. Although these therapeutics have revolutionized PAH therapy, their innovation was predated by supportive but nonspecific medical therapies adapted from their use in more common cardiopulmonary diseases. These therapies include oxygen therapy, diuretics, digoxin, anticoagulation, and high-dose calcium channel blockers. Expert opinion continues to support the use of adjunct therapies based on current pathologic understandings of PAH combined with some evidence extrapolated from small studies. This article discusses why these therapies continue to play an important role in the treatment of patients with PAH.

Assessment of the serotonin pathway as a therapeutic target for pulmonary hypertension

Blockade of the serotonin reuptake transporter (5-HTT), using fluoxetine, has been identified as a potential therapeutic target for preventing and, importantly, reversing pulmonary hypertension (PH). This study utilized synchrotron radiation microangiography to determine whether fluoxetine could prevent or reverse endothelial dysfunction and vessel rarefaction, which underpin PH. PH was induced by a single injection of monocrotaline (MCT; 60 mg kg(-1)). Following MCT administration, rats received daily injections of either saline or fluoxetine (MCT+Fluox; 10 mg kg(-1)) for three weeks. A third group of rats also received the fluoxetine regime, but only three weeks after MCT (MCT+FluoxDelay). Control rats received daily injections of saline. Pulmonary microangiography was performed to assess vessel branching density and visualize dynamic changes in vessel diameter following (i) acute fluoxetine or (ii) acetylcholine, sodium nitroprusside, BQ-123 (ET-1A receptor blocker) and L-NAME (NOS inhibitor). Monocrotaline induced PH that was inevitably terminal. `Delayed' treatment of fluoxetine (MCT+FluoxDelay) was unable to reverse the progression of PH. Early fluoxetine treatment pre-PH (i.e. MCT+Fluox) attenuated but did not completely prevent vascular remodeling, vessel rarefaction and an increase in pulmonary pressure, and it did not prevent pulmonary endothelial dysfunction. Interestingly, fluoxetine treatment did counter-intuitively prevent the onset of right ventricular hypertrophy. Using synchrotron radiation microangiography, selective blockade of the serotonin reuptake transporter alone is highlighted as not being sufficient to prevent pulmonary endothelial dysfunction, which is the primary instigator for the inevitable onset of vascular remodeling and vessel rarefaction. Accordingly, potential therapeutic strategies should aim to target multiple pathways to ensure an optimal outcome.

Serum serotonin concentration is associated with severity of myxomatous mitral valve disease in dogs

BACKGROUND

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) has recently been suggested to play a role in the development of naturally acquired myxomatous mitral valve disease (MMVD) in dogs.

AIM

To investigate the association between serum 5-HT concentration and MMVD severity in dogs, and to assess potential associations between serum 5-HT concentrations and dog characteristics, echocardiographic variables, heart rate, systolic blood pressure, presence of macrothrombocytosis, and plateletcrit.

ANIMALS

A total of 120 client-owned dogs.

MATERIAL AND METHODS

Dogs were prospectively recruited and were classified by standard echocardiography into healthy (dogs of breeds predisposed to MMVD, but without echocardiographic evidence of the disease), mild, moderate, or severe MMVD groups. Serum 5-HT concentrations were analyzed using an ELISA.

RESULTS

Dogs with severe MMVD had lower serum 5-HT concentrations than healthy dogs (P = .0025) and dogs with mild MMVD (P = .0011). Unilinear and multiple regression analyses showed that serum 5-HT concentrations decreased with increasing left atrial to aortic root ratio (LA/Ao), were higher in Cavalier King Charles Spaniel (CKCS) dogs compared to dogs of other breeds, and were higher in female dogs than in male dogs. The LA/Ao was the variable most strongly associated with serum 5-HT concentration.

CONCLUSIONS AND CLINICAL IMPORTANCE

The finding of higher serum 5-HT concentrations in dogs of breeds predisposed to the early onset of MMVD (CKCS) and dogs with mild MMVD suggests that alterations in 5-HT signaling might play a role in progression of early stages of MMVD.

Serotonin contributes to high pulmonary vascular tone in a sheep model of persistent pulmonary hypertension of the newborn

Although past studies demonstrate that altered serotonin (5-HT) signaling is present in adults with idiopathic pulmonary arterial hypertension, whether serotonin contributes to the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN) is unknown. We hypothesized that 5-HT contributes to increased pulmonary vascular resistance (PVR) in a sheep model of PPHN and that selective 5-HT reuptake inhibitor (SSRI) treatment increases PVR in this model. We studied the hemodynamic effects of 5-HT, ketanserin (5-HT2A receptor antagonist), and sertraline, an SSRI, on pulmonary hemodynamics of the late gestation fetal sheep with PPHN caused by prolonged constriction of the ductus arteriosis. Brief intrapulmonary infusions of 5-HT increased PVR from 1.0 ± 0.07 (baseline) to 1.4 ± 0.22 mmHg/ml per minute of treatment (P < 0.05). Ketanserin decreased PVR from 1.1 ± 0.15 (baseline) to 0.82 ± 0.09 mmHg/ml per minute of treatment (P < 0.05). Sertraline increased PVR from 1.1 ± 0.17 (baseline) to 1.4 ± 0.17 mmHg/ml per minute of treatment (P = 0.01). In addition, we studied 5-HT production and activity in vitro in experimental PPHN. Compared with controls, pulmonary artery endothelial cells from fetal sheep with PPHN exhibited increased expression of tryptophan hydroxylase 1 and 5-HT production by twofold and 56%, respectively. Compared with controls, 5-HT2A R expression was increased in lung homogenates and pulmonary artery smooth muscle cell lysates by 35% and 32%, respectively. We concluded that increased 5-HT contributes to high PVR in experimental PPHN through activation of the 5-HT2A receptor and that SSRI infusion further increases PVR in this model.

Production of serotonin by tryptophan hydroxylase 1 and release via platelets contribute to allergic airway inflammation

RATIONALE

5-Hydroxytryptamine (5-HT) is involved in the pathogenesis of allergic airway inflammation (AAI). It is unclear, however, how 5-HT contributes to AAI and whether this depends on tryptophan hydroxylase (TPH) 1, the critical enzyme for peripheral 5-HT synthesis.

OBJECTIVES

To elucidate the role of TPH1 and the peripheral source of 5-HT in asthma pathogenesis.

METHODS

TPH1-deficient and TPH1-inhibitor-treated animals were challenged in ovalbumin and house dust mite models of AAI. Experiments with bone marrow chimera, mast cell-deficient animals, platelets transfusion, and bone marrow dendritic cells (BMDC) driven model of AAI were performed. 5-HT levels were measured in bronchoalveolar lavage fluid or serum of animals with AAI and in human asthma.

MEASUREMENTS AND MAIN RESULTS

5-HT levels are increased in bronchoalveolar lavage fluid of mice and people with asthma after allergen provocation. TPH1 deficiency and TPH1 inhibition reduced all cardinal features of AAI. Administration of exogenous 5-HT restored AAI in TPH1-deficient mice. The pivotal role of 5-HT production by structural cells was corroborated by bone marrow chimera experiments. Experiments in mast cell-deficient mice revealed that mast cells are not a source of 5-HT, whereas transfusion of platelets from wild-type and TPH1-deficient mice revealed that only platelets containing 5-HT enhanced AAI. Lack of endogenous 5-HT in vitro and in vivo was associated with an impaired Th2-priming capacity of BMDC.

CONCLUSIONS

In summary, TPH1 deficiency or inhibition reduces AAI. Platelet- and not mast cell-derived 5-HT is pivotal in AAI, and lack of 5-HT leads to an impaired Th2-priming capacity of BMDC. Thus, targeting TPH1 could offer novel therapeutic options for asthma.

Pulmonary hypertension: biomarkers

Physicians look to biomarkers to inform the management of pulmonary hypertension (PH) at all stages, from assessing susceptibility through screening, diagnosis, and risk stratification to drug selection and monitoring. PH is a heterogeneous disorder and currently there are no accepted blood biomarkers specific to any manifestation of the condition. Brain natriuretic peptide and its N-terminal peptide have been most widely studied. Other candidate prognostic biomarkers in patients with pulmonary arterial hypertension (PAH) include growth and differentiation factor-15, red cell distribution width, uric acid, creatinine, inflammatory markers such as interleukin-6, angiopoietins, and microRNAs. Combining the measurement of biomarkers reflecting different components of the pathology with other modalities may enable better molecular characterisation of PH subtypes and permit improved targeting of therapeutic strategies and disease monitoring.

Molecular determinants of platelet delta storage pool deficiencies: an update

Delta storage pool deficiency (δ-SPD) is a rare heterogeneous group of platelet disorders characterized by a reduction in the number or content of dense granules. δ-SPD causes a mild to moderate bleeding diathesis characterized mainly by mucocutaneous bleeding. Currently, no specific treatment is available and the therapeutic approach is based on prevention of excessive bleeding. However, during the last few years, important insights into the pathophysiology of δ-SPD have been achieved using mouse models and dense granule deficiency-associated congenital diseases, such as Hermansky-Pudlak syndrome and Chediak-Higashi syndrome. It thus appears that δ-SPD represents a genetically heterogeneous group of intracellular vesicle biogenesis and/or trafficking disorders. This review summarizes recent data regarding the molecular mechanisms together with clinical features of the different types of δ-SPD. Although the molecular basis of isolated inherited δ-SPD remains currently unknown, next-generation sequencing strategies should enable researchers to identify the causative genes. Identification of those genes should contribute to our understanding of the pathophysiology, represent useful tools for genetic diagnosis, and eventually lead to new specific therapeutic approaches.