The serotonin uptake-enhancing drug tianeptine suppresses asthmatic symptoms in children: a double-blind, crossover, placebo-controlled study

Role of 5-HT2 receptors family in the allergy-induced increased aorta contractile responses to 5-HT

Asthma poses an increased risk for cardiovascular disorders, suggesting that allergy, which is an underlying process in asthma, causes atypical functioning of organs other than lungs. In a previous study in a guinea pig asthma model, we concluded that allergic sensitization increased aorta contractile responses to 5-HT. To further characterize these responses, here we explored the role of the 5-HT2 receptors family. We found that TCB-2 (5-HT2A agonist) and WAY161503 (5-HT2C agonist) induced aorta contractions resembling those elicited by 5-HT but less intense (~43 % and ~25 %, respectively). In these experiments, aortas from sensitized guinea pigs showed increased contractions to TCB-2, but not to WAY161503. In turn, MDL 100907 (5-HT2A antagonist) and RS-102221 (5-HT2C antagonist) caused a notably and a mild reduction of the 5-HT-induced contractions, respectively, with no differences seen between sensitized and non-sensitized tissues. BW723C86 (5-HT2B agonist) did not induce contractile responses and RS-127445 (5-HT2B antagonist) did not modify the contractile responses to 5-HT. In non-sensitized aortas, the pattern of protein expression of receptors was 5HT2B>5-HT2A=5-HT2C, which did not change in sensitized animals. In conclusion, we found that allergic sensitization increased the aorta contractile responses to 5-HT, partly mediated by enhanced responses of 5-HT2A receptors, which was unrelated to changes in the expression of these receptors.

Exploring the Role of Serotonin as an Immune Modulatory Component in Cardiovascular Diseases

Serotonin, also known as 5-hydroxytryptamine (5-HT) is a well-known neurotransmitter in the central nervous system (CNS), but also plays a significant role in peripheral tissues. There is a growing body of evidence suggesting that serotonin influences immune cell responses and contributes to the development of pathological injury in cardiovascular diseases, such as atherosclerosis, as well as other diseases which occur as a result of immune hyperactivity. In particular, high levels of serotonin are able to activate a multitude of 5-HT receptors found on the surface of immune cells, thereby influencing the process of atherosclerotic plaque formation in arteries. In this review, we will discuss the differences between serotonin production in the CNS and the periphery, and will give a brief outline of the function of serotonin in the periphery. In this context, we will particularly focus on the effects of serotonin on immune cells related to atherosclerosis and identify caveats that are important for future research.

Emerging Roles of Platelets in Allergic Asthma

Allergic asthma is a complex chronic inflammatory disease of the airways, driven by Th2 immune responses and characterized by eosinophilic pulmonary inflammation, airway hyperresponsiveness, excessive mucus production, and airway remodeling. Overwhelming evidence from studies in animal models and allergic asthmatic patients suggests that platelets are aberrantly activated and recruited to the lungs. It has been established that platelets can interact with other immune cells and secrete various biochemical mediators to promote allergic sensitization and airway inflammatory response, and platelet deficiency may alleviate the pathological features and symptoms of allergic asthma. However, the comprehensive roles of platelets in allergic asthma have not been fully clarified, leaving attempts to treat allergic asthma with antiplatelet agents questionable. In this review, we summarize the role of platelet activation and pulmonary accumulation in allergic asthma; emphasis is placed on the different interactions between platelets with crucial immune cell types and the contribution of platelet-derived mediators in this context. Furthermore, clinical antiplatelet approaches to treat allergic asthma are discussed. This review provides a clearer understanding of the roles of platelets in the pathogenesis of allergic asthma and could be informative in the development of novel strategies for the treatment of allergic asthma.

5-HT2A, 5-HT1B/D, 5HT3 and 5-HT7 receptors as mediators of serotonin-induced direct contractile response of bovine airway smooth muscle

Background: Serotonin (5-hydroxytryptamine; 5-HT) performs a variety of functions in the body including the modulation of muscle tone in respiratory airways. Several studies indicate a possible role of 5-HT in the pathophysiology of bronchial hyperresponsiveness. However, the receptors and the molecular mechanisms by which 5-HT acts on airway smooth muscle (ASM) continue to be controversial. Most of the evidence suggests the participation of different subtypes of receptors in an indirect response. This study supports the proposal that 5-HT directly contracts ASM and characterizes pharmacologically the subtypes of serotonergic receptors involved. The characterization was carried out by using selective antagonists in an organ bath model allowing study of the smooth muscle of segments of bovine trachea. Results: The results obtained show that 5-HT_2A receptors are the main mediators of the direct contractile response of bovine ASM, with the cooperation of the 5-HT₇, 5-HT₃ and 5-HT_1B/D receptors. Also, it was observed that the muscle response to serotonin is developed more slowly and to a lesser extent in comparison with the response to cholinergic stimulation. Conclusion: Overall, the receptors that mediate the direct serotonergic contraction of the smooth muscle of the bovine trachea are 5-HT_2A, 5-HT₇, 5-HT₃ and 5-HT_1B/D receptors.

Interleukin-33 Induces the Enzyme Tryptophan Hydroxylase 1 to Promote Inflammatory Group 2 Innate Lymphoid Cell-Mediated Immunity

Group 2 innate lymphoid cells (ILC2s) regulate immunity, inflammation, and tissue homeostasis. Two distinct subsets of ILC2s have been described: steady-state natural ILC2s and inflammatory ILC2s, which are elicited following helminth infection. However, how tissue-specific cues regulate these two subsets of ILC2s and their effector functions remains elusive. Here, we report that interleukin-33 (IL-33) promotes the generation of inflammatory ILC2s (ILC2^INFLAM) via induction of the enzyme tryptophan hydroxylase 1 (Tph1). Tph1 expression was upregulated in ILC2s upon activation with IL-33 or following helminth infection in an IL-33-dependent manner. Conditional deletion of Tph1 in lymphocytes resulted in selective impairment of ILC2^INFLAM responses and increased susceptibility to helminth infection. Further, RNA sequencing analysis revealed altered gene expression in Tph1 deficient ILC2s including inducible T cell co-stimulator (Icos). Collectively, these data reveal a previously unrecognized function for IL-33, Tph1, and ICOS in promoting inflammatory ILC2 responses and type 2 immunity at mucosal barriers.

Stimulatory Effect of 5-Hydroxytryptamine (5-HT) on Rat Capsaicin-Sensitive Lung Vagal Sensory Neurons via Activation of 5-HT3 Receptors

5-hydroxytryptamine (5-HT) is an inflammatory mediator known to be released in lung. Capsaicin-sensitive lung vagal (CSLV) afferents function as a primary sensor for detecting chemical stimuli and produce consequent reflexes during lung inflammation. To characterize the effect of 5-HT on CSLV afferents, responses of cardiorespiratory reflexes and single-unit C-fiber afferents to right-atrial injections of 5-HT were investigated in anesthetized Sprague-Dawley rats. Bolus injection of 5-HT (8 μg/kg) caused an immediate augmented breath and apnea, accompanied by hypotension and bradycardia. These initial responses were then followed by a brief pressor response and a more sustained depressor response. After a perineural treatment of both cervical vagi with capsaicin to block the conduction of C fibers, 5-HT still triggered the augmented breath, but no longer evoked the apnea, bradycardia and hypotension, indicating an involvement of C-fiber activation. The remaining augmented breath induced by 5-HT after perineural capsaicin treatment was totally eliminated by vagotomy. To further study the effect of 5-HT on CSLV afferents, activities arising from these afferents were determined using the single-fiber recording technique. Right-atrial injection of 5-HT evoked an intense discharge in CSLV afferents in a dose-dependent manner. The highest dose of 5-HT (16 μg/kg) activated 79% (19/24) of CSLV afferents which were also sensitive to capsaicin (0.8 μg/kg). The pretreatment of tropisetron, a selective antagonist of the 5-HT₃ receptor, completely blocked CSLV-afferents stimulation induced by 5-HT but did not affect that by capsaicin. Furthermore, a similar afferent response of CSLV afferents was mimicked by phenylbiguanide, a selective agonist of the 5-HT₃ receptor. In isolated rat lung vagal C neurons, 5-HT induced intense calcium transients in a dose-dependent manner. The highest concentration (3 μM) of 5-HT activated 67% (18/27) of the CSLV neurons. The 5-HT-induced response was totally abolished by pretreatment of tropisetron. In conclusion, 5-HT exerts an intense stimulatory effect on lung C-fiber terminals mediated through an activation of the 5-HT₃ receptor, which may contribute to the airway hypersensitivity under lung inflammation.

Autocrine and paracrine regulatory functions of platelet serotonin

Platelets serotonin (5-hydroxytrytamine, 5-HT) uptake and storage in dense granules is tightly regulated by the serotonergic transport system in the blood. Several 5-HT transporters (5-HTTs) have been identified in the vasculature and blood cells, beyond them 5-HTT is the major 5-HT transporter in platelets. Abnormal 5-HT concentrations in the blood plasma or increased platelet 5-HT uptake or abnormal release contribute to the development of various diseases in the vasculature. Consequently, several clinical trials suggested the positive therapeutic effects of 5-HTT blockade in the circulation. Inhibition of 5-HT strongly attenuates autocrine and paracrine functions of platelets, influencing platelet aggregation, vascular contraction, permeability, tissue repair, wound healing, immunity and cancer. Here, we highlight the current state of basic biological research regarding the hemostatic and non-hemostatic functions of platelet-derived 5-HT in normal and disease conditions. We also describe the physiological consequences of targeting platelet 5-HT functions in thrombosis, stroke, inflammation and cancer to overcome common health problems.

Effects of 5-Hydroxytryptamine Class 2 Receptor Antagonists on Bronchoconstriction and Pulmonary Remodeling Processes

Serotonin [5-hydroxytryptamine (5-HT)] is associated with several chronic pulmonary diseases, recognizing 5-HT₂ receptor antagonists as potential inhibitors of tissue remodeling. However, the effects of 5-HT₂ receptors, especially 5-HT_2B receptors on airway function and remodeling, are unclear. We investigated the role of 5-HT_2B receptors on airway smooth muscle contractility and remodeling processes. Murine precision-cut lung slices were pretreated with 5-HT_2B receptor antagonists (EXT5, EXT9, RS 127445, and PRX 08066), as well as ketanserin (5-HT_2A/2C receptor antagonist) (1, 10 μmol/L), before addition of cumulative concentrations of 5-HT to induce bronchoconstriction. Remodeling effects after treatment with 10 μmol/L 5-HT and 5-HT₂ receptor antagonists were further studied in distal lung tissue by examining release of profibrotic transforming growth factor (TGF)-β1 and proliferation of human bronchial smooth muscle cells (HBSMCs). 5-HT-induced bronchoconstriction was significantly reduced by EXT5, EXT9, and ketanserin, but not by RS 127445 or PRX 08066. The 5-HT_2B receptor antagonists significantly reduced TGF-β1 release. 5-HT, in combination with TGF-β1, increased proliferation of HBSMCs, a process reduced by EXT5 and EXT9. Our results indicate that EXT5 and EXT9 may relieve bronchoconstriction in murine airways and serve as an add-on effect in attenuating pulmonary remodeling by improving airway function. The antiproliferative effect on HBSMCs and the inhibition of TGF-β1 release further support a role of 5-HT_2B receptors in pathologic remodeling processes.

Immunomodulatory effects mediated by serotonin

Serotonin (5-HT) induces concentration-dependent metabolic effects in diverse cell types, including neurons, entherochromaffin cells, adipocytes, pancreatic beta-cells, fibroblasts, smooth muscle cells, epithelial cells, and leukocytes. Three classes of genes regulating 5-HT function are constitutively expressed or induced in these cells: (a) membrane proteins that regulate the response to 5-HT, such as SERT, 5HTR-GPCR, and the 5HT₃-ion channels; (b) downstream signaling transduction proteins; and (c) enzymes controlling 5-HT metabolism, such as IDO and MAO, which can generate biologically active catabolites, including melatonin, kynurenines, and kynurenamines. This review covers the clinical and experimental mechanisms involved in 5-HT-induced immunomodulation. These mechanisms are cell-specific and depend on the expression of serotonergic components in immune cells. Consequently, 5-HT can modulate several immunological events, such as chemotaxis, leukocyte activation, proliferation, cytokine secretion, anergy, and apoptosis. The effects of 5-HT on immune cells may be relevant in the clinical outcome of pathologies with an inflammatory component. Major depression, fibromyalgia, Alzheimer disease, psoriasis, arthritis, allergies, and asthma are all associated with changes in the serotonergic system associated with leukocytes. Thus, pharmacological regulation of the serotonergic system may modulate immune function and provide therapeutic alternatives for these diseases.

The role of serotonin and its receptors in activation of immune responses and inflammation

Serotonin or 5-hydroxytryptamine (5-HT) is a neurotransmitter and hormone that contributes to the regulation of various physiological functions by its actions in the central nervous system (CNS) and in the respective organ systems. Peripheral 5-HT is predominantly produced by enterochromaffin (EC) cells of the gastrointestinal (GI) tract. These gut-resident cells produce much more 5-HT than all neuronal and other sources combined, establishing EC cells as the main source of this biogenic amine in the human body. Peripheral 5-HT is also a potent immune modulator and affects various immune cells through its receptors and via the recently identified process of serotonylation. Alterations in 5-HT signalling have been described in inflammatory conditions of the gut, such as inflammatory bowel disease. The association between 5-HT and inflammation, however, is not limited to the gut, as changes in 5-HT levels have also been reported in patients with allergic airway inflammation and rheumatoid arthritis. Based on searches for terms such as '5-HT', 'EC cell', 'immune cells' and 'inflammation' in pubmed.gov as well as by utilizing pertinent reviews, the current review aims to provide an update on the role of 5-HT in biological functions with a particular focus on immune activation and inflammation.

Regulation of serotonin-induced trafficking and migration of eosinophils

Association of the neurotransmitter serotonin (5-HT) with the pathogenesis of allergic asthma is well recognized and its role as a chemoattractant for eosinophils (Eos) in vitro and in vivo has been previously demonstrated. Here we have examined the regulation of 5-HT-induced human and murine Eos trafficking and migration at a cellular and molecular level. Eos from allergic donors and bone marrow-derived murine Eos (BM-Eos) were found to predominantly express the 5-HT2A receptor. Exposure to 5-HT or 2,5-dimethoxy-4-iodoamphetamine (DOI), a 5-HT2A/C selective agonist, induced rolling of human Eos and AML14.3D10 human Eos-like cells on vascular cell adhesion molecule (VCAM)-1 under conditions of flow in vitro coupled with distinct cytoskeletal and cell shape changes as well as phosphorylation of MAPK. Blockade of 5-HT2A or of ROCK MAPK, PI3K, PKC and calmodulin, but not G_αi-proteins, with specific inhibitors inhibited DOI-induced rolling, actin polymerization and changes in morphology of VCAM-1-adherent AML14.3D10 cells. More extensive studies with murine BM-Eos demonstrated the role of 5-HT in promoting rolling in vivo within inflamed post-capillary venules of the mouse cremaster microcirculation and confirmed that down-stream signaling of 5-HT2A activation involves ROCK, MAPK, PI3K, PKC and calmodulin similar to AML14.3D10 cells. DOI-induced migration of BM-Eos is also dependent on these signaling molecules and requires Ca²⁺. Further, activation of 5-HT2A with DOI led to an increase in intracellular Ca²⁺ levels in murine BM-Eos. Overall, these data demonstrate that 5-HT (or DOI)/5-HT2A interaction regulates Eos trafficking and migration by promoting actin polymerization associated with changes in cell shape/morphology that favor cellular trafficking and recruitment via activation of specific intracellular signaling molecules (ROCK, MAPK, PI3K and the PKC-calmodulin pathway).

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.

Psychiatric Factors in Asthma

Emotional factors are an obstacle in the diagnosis and management of asthma. This review discusses three problem patterns: negative emotions in relatively normal patients with asthma; patients presenting possible functional symptoms and; patients presenting asthma in conjunction with psychiatric deviations. Negative emotions influence the symptoms and management of asthma, even in relatively normal patients. Psychogenic symptoms appear normal, but culminate in functional symptoms in a minority of patients. Diagnosing and treating asthma in patients with comorbid asthma and psychiatric symptoms is very difficult. On the one hand, treating asthma may often be just treating the emotions. On the other hand, negative emotions make the treatment of asthma guesswork. Physicians should estimate emotional influences in their patients' symptoms for an optimal evaluation of medication efficacy. Assessment and analysis of emotional factors surrounding exacerbations seems essential, e.g. emotional precipitants of asthma and asthma-evoked negative emotions. Moreover, patients should be informed about stress-induced breathlessness and the consequences of overuse of bronchodilators. When patients present with atypical symptoms, or do not properly respond to asthma medication, functional symptoms should be suspected. Psychiatric analysis may often lead to the conclusion that symptoms have a functional basis. In patients with comorbid asthma and anxiety disorders, asthma should be the focus for treatment since difficult-to-control asthma often causes anxiety problems in the first place. Moreover, panic-like symptoms in asthma are often related to sudden onset asthma exacerbations. However, in patients with comorbid asthma and depression, depression should become the focus of treatment. The reason is that optimal treatment of depressive asthmatics is probably impossible. Special issues include specific problems with children, compliance problems, and physicians' dilemmas regarding the simultaneous treatment of asthma and psychiatric symptoms.

Inhibition of allergic inflammation by supplementation with 5-hydroxytryptophan

Clinical reports indicate that patients with allergy/asthma commonly have associated symptoms of anxiety/depression. Anxiety/depression can be reduced by 5-hydroxytryptophan (5-HTP) supplementation. However, it is not known whether 5-HTP reduces allergic inflammation. Therefore, we determined whether 5-HTP supplementation reduces allergic inflammation. We also determined whether 5-HTP decreases passage of leukocytes through the endothelial barrier by regulating endothelial cell function. For these studies, C57BL/6 mice were supplemented with 5-HTP, treated with ovalbumin fraction V (OVA), house dust mite (HDM) extract, or IL-4, and examined for allergic lung inflammation and OVA-induced airway responsiveness. To determine whether 5-HTP reduces leukocyte or eosinophil transendothelial migration, endothelial cells were pretreated with 5-HTP, washed and then used in an in vitro transendothelial migration assay under laminar flow. Interestingly, 5-HTP reduced allergic lung inflammation by 70-90% and reduced antigen-induced airway responsiveness without affecting body weight, blood eosinophils, cytokines, or chemokines. 5-HTP reduced allergen-induced transglutaminase 2 (TG2) expression and serotonylation (serotonin conjugation to proteins) in lung endothelial cells. Consistent with the regulation of endothelial serotonylation in vivo, in vitro pretreatment of endothelial cells with 5-HTP reduced TNF-α-induced endothelial cell serotonylation and reduced leukocyte transendothelial migration. Furthermore, eosinophil and leukocyte transendothelial migration was reduced by inhibitors of transglutaminase and by inhibition of endothelial cell serotonin synthesis, suggesting that endothelial cell serotonylation is key for leukocyte transendothelial migration. In summary, 5-HTP supplementation inhibits endothelial serotonylation, leukocyte recruitment, and allergic inflammation. These data identify novel potential targets for intervention in allergy/asthma.

Association of 5-hydroxytryptamine (serotonin) receptor 4 (5-HTR4) gene polymorphisms with asthma

BACKGROUND AND OBJECTIVE

The neurotransmitter, 5-hydroxytryptamine, acts as an immunomodulator by stimulating the release of inflammatory cytokines and regulating the function of dendritic cells and monocytes. The 5-hydroxytryptamine receptor 4 (HTR4) gene is located in a region previously linked to an increased risk of asthma and atopy. The aim of this study was to investigate the association between HTR4 and asthma.

METHODS

Thirty-two single nucleotide polymorphisms (SNP) in HTR4 were investigated by direct sequencing of 24 DNA samples from unrelated Korean subjects.

RESULTS

The 32 genetic variants comprised 22 intronic SNP, two SNP in the 3'-untranslated region (exon 7) and eight SNP in the 3'-downstream region. Logistic regression analysis showed that two intronic polymorphisms were significantly associated with the risk of asthma. Two minor HTR4 alleles, +142828G>A and +122769G>A, occurred at significantly higher frequencies in the asthmatic group than in the healthy control group (49.59% vs 42.29%, P=0.003, and 47.99% vs 40.35%, P=0.008, respectively), and these differences remained significant after correction for multiple testing (P=0.05, dominant mode of inheritance; and P=0.03, dominant mode, respectively). Haplotype analysis revealed three haplotype blocks. The frequency of haplotype 1 in block 2 was significantly higher in asthmatics (P=0.003, dominant mode), whereas the frequency of haplotype 4 in block 3 was significantly lower in asthmatics (P=0.0009, dominant mode).

CONCLUSIONS

SNP and haplotypes of the HTR4 gene were associated with the asthma phenotype and genetic variation of HTR4 may affect susceptibility to the development of asthma.

5-hydroxytryptamine modulates migration, cytokine and chemokine release and T-cell priming capacity of dendritic cells in vitro and in vivo

Beside its well described role in the central and peripheral nervous system 5-hydroxytryptamine (5-HT), commonly known as serotonin, is also a potent immuno-modulator. Serotoninergic receptors (5-HTR) are expressed by a broad range of inflammatory cell types, including dendritic cells (DCs). In this study, we aimed to further characterize the immuno-biological properties of serotoninergic receptors on human monocyte-derived DCs. 5-HT was able to induce oriented migration in immature but not in LPS-matured DCs via activation of 5-HTR(1) and 5-HTR(2) receptor subtypes. Accordingly, 5-HT also increased migration of pulmonary DCs to draining lymph nodes in vivo. By binding to 5-HTR(3), 5-HTR(4) and 5-HTR(7) receptors, 5-HT up-regulated production of the pro-inflammatory cytokine IL-6. Additionally, 5-HT influenced chemokine release by human monocyte-derived DCs: production of the potent Th1 chemoattractant IP-10/CXCL10 was inhibited in mature DCs, whereas CCL22/MDC secretion was up-regulated in both immature and mature DCs. Furthermore, DCs matured in the presence of 5-HT switched to a high IL-10 and low IL-12p70 secreting phenotype. Consistently, 5-HT favoured the outcome of a Th2 immune response both in vitro and in vivo. In summary, our study shows that 5-HT is a potent regulator of human dendritic cell function, and that targeting serotoninergic receptors might be a promising approach for the treatment of inflammatory disorders.

Role of the serotonergic system in reduced pulmonary function after exposure to methamphetamine

Although use of methamphetamine (MA) by smoking is the fastest growing method of administration, very limited data are available describing the effects of smoked MA. Using a murine inhalation exposure system, we explored the pulmonary effects of low-dose acute inhalation exposure to MA vapor (smoke). Inhalation of MA vapor resulted in transiently reduced pulmonary function, as measured by transpulmonary resistance, dynamic compliance, and whole-body plethysmography compared with unexposed control animals. These changes were associated with an approximately 34% reduction in serotonin (5-hydroxytryptamine [5-HT]) metabolism/inactivation to 5-hydroxyindolacetic acid, and a nearly 40% reduction in monoamine oxidase (MAO)-A activity in the lung. Pretreatment of mice with a selective 5-HT reuptake inhibitor completely ablated the MA-induced changes in pulmonary function, confirming a key role for the 5-HT transporter (serotonin transporter [SERT]) and the serotonergic system in this effect. Immunofluorescent staining of mouse lung tissue confirmed high expression of SERT in airway epithelial cells. Using mouse airway epithelial cell line, LA-4, and purified human MAO-A, it was demonstrated that MA impedes 5-HT metabolism through direct inhibition of MAO-A activity in vitro. Together, these data demonstrate that low-dose exposure to MA results in reduced pulmonary function mediated via SERT and subsequent perturbation of 5-HT metabolism in the lung. This supports a role for the serotonergic system in MA-mediated pulmonary effects.

Airway smooth muscle relaxation induced by 5-HT(2A) receptors: role of Na(+)/K(+)-ATPase pump and Ca(2+)-activated K(+) channels

AIMS

Although 5-hydroxytryptamine (5-HT) contracts airway smooth muscle in many mammalian species, in guinea pig and human airways 5-HT causes a contraction followed by relaxation. This study explored potential mechanisms involved in the relaxation induced by 5-HT.

MAIN METHODS

Using organ baths, patch clamp, and intracellular Ca(2+) measurement techniques, the effect of 5-HT on guinea pig airway smooth muscle was studied.

KEY FINDINGS

A wide range of 5-HT concentrations caused a biphasic response of tracheal rings. Response to 32 microM 5-HT was notably reduced by either tropisetron or methiothepin, and almost abolished by their combination. Incubation with 10 nM ketanserin significantly prevented the relaxing phase. Likewise, incubation with 100 nM charybdotoxin or 320 nM iberiotoxin and at less extent with 10 microM ouabain caused a significant reduction of the relaxing phase induced by 5-HT. Propranolol, L-NAME and 5-HT(1A), 5-HT(1B)/5-HT(1D) and 5-HT(2B) receptors antagonist did not modify this relaxation. Tracheas from sensitized animals displayed reduced relaxation as compared with controls. In tracheas precontracted with histamine, a concentration response curve to 5-HT (32, 100 and 320 microM) induced relaxation and this effect was abolished by charybdotoxin, iberiotoxin or ketanserin. In single myocytes, 5-HT in the presence of 3 mM 4-AP notably increased the K(+) currents (I(K(Ca))), and they were completely abolished by charybdotoxin, iberiotoxin or ketanserin.

SIGNIFICANCE

During the relaxation induced by 5-HT two major mechanisms seem to be involved: stimulation of the Na(+)/K(+)-ATPase pump, and increasing activity of the high-conductance Ca(2+)-activated K(+) channels, probably via 5-HT(2A) receptors.

Novel uses for anti-platelet agents as anti-inflammatory drugs

An alteration in the character and function of platelets is manifested in patients with inflammatory diseases, and these alterations have been dissociated from the well-characterized involvement of platelets in thrombosis and haemostasis. Recent evidence reveals platelet activation is sometimes critical in the development of inflammation. The mechanisms by which platelets participate in inflammation are diverse, and offer numerous opportunities for future drug intervention. There is now acceptance that platelets act as innate inflammatory cells in immune responses, with roles as sentinel cells undergoing surveillance, responding to microbial invasion, orchestrating leukocyte recruitment, and migrating through tissue, causing damage and influencing repair processes in chronic disease. Some of these processes are targeted by drugs that are being developed to target platelet participation in atherosclerosis. The actions of platelets therefore influence the pathogenesis of diverse inflammatory diseases in various body compartments, encompassing parasitic and bacterial infection, allergic inflammation (especially asthma and rhinitis), and non-atopic inflammatory conditions, for example, chronic obstructive pulmonary disease (COPD), rheumatoid arthritis (RA), inflammatory bowel disease (IBD) and atherosclerosis. This review will first discuss the evidence for platelet activation in these various inflammatory diseases, and secondly discuss the mechanisms by which this pathogenesis occurs and the various anti-platelet agents which have been developed to combat platelet activation in atherosclerosis and their potential future use for the treatment of other inflammatory diseases.

Anti-inflammatory properties of desipramine and fluoxetine

Background

Antidepressants are heavily prescribed drugs and have been shown to affect inflammatory signals. We examined whether these have anti-inflammatory properties in animal models of septic shock and allergic asthma. We also analysed whether antidepressants act directly on peripheral cell types that participate in the inflammatory response in these diseases.

Methods

The antidepressants desipramine and fluoxetine were compared in vivo to the glucocorticoid prednisolone, an anti-inflammatory drug of reference. In a murine model of lipopolysaccharides (LPS)-induced septic shock, animals received the drugs either before or after injection of LPS. Circulating levels of tumour necrosis factor (TNF)-α and mortality rate were measured. In ovalbumin-sensitized rats, the effect of drug treatment on lung inflammation was assessed by counting leukocytes in bronchoalveolar lavages. Bronchial hyperreactivity was measured using barometric plethysmography. In vitro production of TNF-α and Regulated upon Activation, Normal T cell Expressed and presumably Secreted (RANTES) from activated monocytes and lung epithelial cells, respectively, was analysed by immunoassays. Reporter gene assays were used to measure the effect of antidepressants on the activity of nuclear factor-κB and activator protein-1 which are involved in the control of TNF-α and RANTES expression.

Results

In the septic shock model, all three drugs given preventively markedly decreased circulating levels of TNF-α and mortality (50% mortality in fluoxetine treated group, 30% in desipramine and prednisolone treated groups versus 90% in controls). In the curative trial, antidepressants had no statistically significant effect, while prednisolone still decreased mortality (60% mortality versus 95% in controls). In ovalbumin-sensitized rats, the three drugs decreased lung inflammation, albeit to different degrees. Prednisolone and fluoxetine reduced the number of macrophages, lymphocytes, neutrophils and eosinophils, while desipramine diminished only the number of macrophages and lymphocytes. However, antidepressants as opposed to prednisolone did not attenuate bronchial hyperreactivity. In vitro, desipramine and fluoxetine dose-dependently inhibited the release of TNF-α from LPS-treated monocytes. In lung epithelial cells, these compounds decreased TNF-α-induced RANTES expression as well as the activity of nuclear factor-κB and activator protein-1.

Conclusion

Desipramine and fluoxetine reduce the inflammatory reaction in two animal models of human diseases. These antidepressants act directly on relevant peripheral cell types to decrease expression of inflammatory mediators probably by affecting their gene transcription. Clinical implications of these observations are discussed.

Association of depressive symptoms and disease activity in children with asthma: methodological and clinical implications

OBJECTIVE

This study was designed to assess the prevalence of depressive symptoms in children with asthma and the association between depression and asthma activity.

METHOD

Children ages 7 to 17 (n = 129) were recruited from a hospital emergency department after presenting for asthma symptoms. The majority of subjects were from disadvantaged, inner city families. Subjects' asthma disease activity was assessed using the revised National Heart, Lung, and Blood Institute guidelines, and subjects' emotional status was assessed by a combination of self-, parent-, and clinician-reported measures. Parental emotional status was assessed by self-report.

RESULTS

Depressive symptoms within the clinical range were reported in 26% of subjects and 43% of mothers, although symptom severity varied across scales. Self-reported depressive symptoms were more strongly correlated with asthma activity (r = 0.25) than clinician-reported (r = 0.14) or parent-reported symptoms (r = 0.12/0.18). Depressive symptoms in parents were correlated with child's depression scores but not with their asthma activity.

CONCLUSIONS

Depressive symptoms were common and associated with asthma activity in this inner city population of asthmatic children. Self-reported depressive symptoms were more strongly associated with child's asthma activity than either parental depression or parental/clinician ratings of the child's depression.

Serotoninergic receptors on human airway epithelial cells

There is accumulating evidence that points to a role of serotonin (5-hydroxytryptamine [5-HT]) in the pathophysiology of asthma. Therefore, we analyzed the expression of serotoninergic receptors (5-HTR), its linkage to intracellular calcium homeostasis, and its influence on the production and secretion of IL-6, prostaglandin E(2), the CCL-Chemokine CCL5/Rantes, and the CXC-chemokines CXCL8/IL-8, CXCL9/MIG, CXCL10/IP-10, and CXCL11/I-TAC in primary alveolar epithelial cells type II and the human lung cell lines A549 and BEAS-2B. Employing a PCR approach we were able to demonstrate mRNA expression of several 5-HTR, such as the heptahelical receptors 5-HTR1A, 5-HTR1B, 5-HTR1E, 5-HTR1F, 5-HTR2A, 5-HTR4, 5-HTR6, and 5-HTR7, as well as the ligand-gated ion channel 5-HTR3 in alveolar epithelial cells type II (AEC-II), A549, and BEAS-2B cells. To verify functional expression of 5-HTR subtypes, Ca(2+)-transients were analyzed. This enabled us to show that 5-HT induced an increase in intracellular calcium. Further experiments with isotype-selective receptor agonists allowed us to demonstrate that 5-HT induced calcium transients via activation of 5-HTR1, 5-HTR2, and 5-HTR3 in A549 and BEAS-2B cells. Moreover, we revealed that stimulation of 5-HTR1 and 5-HTR2 induced Ca(2+) mobilization from intracellular stores, whereas activation of 5-HTR3 induced Ca(2+) influx from the extracellular space. Functional studies indicated that activation of 5-HTR1B, 5-HTR1E/F, 5-HTR2, 5-HTR3, 5-HTR4, and 5-HTR7 regulated the release of the cytokine IL-6 and the CXC-chemokine CXCL8/IL-8. Our study shows that 5-HT stimulates different signaling pathways and regulates cytokine release in airway epithelial cells. In summary, our data implicate a pathophysiologic role of 5-HT in the asthmatic inflammatory responses in human airway epithelial cells.

Acute effects of tianeptine on circulating neurotransmitters and cardiovascular parameters

Tianeptine is a serotonin-uptake enhancer drug whose antidepressant effectiveness is based on its ability to reduce rather than increase serotonin availability at the synaptic cleft. This paradoxical neuropharmacological mechanism has raised doubt among neuropharmacologists and psychiatrists as to the role of tianeptine as a trusty-reliable antidepressant drug. This controversial issue led us to investigate the acute effects of a single, oral dose (12.5 mg) of this drug on circulating neurotransmitters and cardiovascular parameters in 50 healthy subjects. The drug provoked a striking and significant reduction of plasma noradrenaline (NA) and plasma serotonin (f-5-HT) while it increased plasma dopamine (DA) and platelet serotonin (p-5-HT) concentrations within the 4-h study period. No adrenaline (Ad) changes were registered. The NA/Ad ratio and the f-5-HT/p-5-HT ratio showed significant reduction throughout the test. Finally, although diastolic blood pressure (DBP) showed significant decrease, neither systolic blood pressure (SBP) nor heart rate (HR) showed significant change. These findings are consistent with the postulation that tianeptine reduces both neural sympathetic activity and parasympathetic activity without affecting adrenal sympathetic activity, enabling us to discuss the possible mechanisms involved in the antidepressant effects of tianeptine. The well-known fact that major depressed patients always show raised NA plus lower than normal p-5-HT levels, both disorders which are normalized by tianeptine, gives neurochemical support to the clinical improvement triggered by the drug in these patients. Summarizing, the results presented in this study demonstrate that tianeptine triggers significant reduction of circulating noradrenaline and plasma serotonin while increasing circulating dopamine and platelet serotonin. Other possible neuropharmacological effects are also discussed.

Asthma medication may influence the psychological functioning of children

Asthma is a global health problem with up to 15% of children suffering from the disease. It has been shown by various researchers that symptomatic asthmatic patients have increased levels of free serotonin in plasma when compared with asymptomatic patients. Thus, some researchers suggest that reducing the concentration of free serotonin in plasma might be useful in treating patients with asthma. Low levels of serotonin, has however, been linked to various psychological conditions like depression, oppositional defiant disorder, ADHD and even conduct disorder. Research has indicated that products like methylphenidate (also known by the brand names as e.g., Ritalin, Concerta, Metadate and others) and other stimulants used for these conditions, particularly ADHD, exert their paradoxical calming effects by boosting serotonin levels in the brain. Therefore, the hypothesis suggest that some children using asthma medication that lowers serotonin levels, might present with symptoms of depression ADHD, oppositional defiant disorder and even conduct disorder. They may be using asthma medication that lowers serotonin and additionally use methylphenidate that boosts serotonin levels for e.g., ADHD. The hypothesis therefore suggests that asthmatic children presenting with psychological complaints, be treated holistically and serotonin levels measured before coming to conclusions regarding their psychological functioning.

Venlafaxine and asthma

A 54-year-old man of Asian origin with major depression developed an asthma-like reaction during venlafaxine treatment. Two weeks after therapy was initiated, he experienced gradually worsening dry cough at night and periodically dyspnea during the daytime. After 5 weeks, clinical examination revealed marked signs of pulmonary obstruction and the forced expiratory volume (FEV1) was assessed to only 32% of the expected value. The venlafaxine medication was gradually decreased and eventually discontinued 9 weeks after its initiation, resulting in a successive improvement of the patient's respiratory complaints.

Corticosteroids, depression and the role of serotonin

Patients frequently use medications simultaneously for different complaints, without being aware of the interactions these products may have. An example of this is the simultaneous use of corticosteroids and medications for depression, defiant or aggressive behaviour. Research has also indicated that corticosteroids lower serotonin levels. However, lowered serotonin levels may result in depression, aggression and other psychological conditions. These secondary complaints, caused by the corticosteroids and other products that lower serotonin levels, may then be treated with selective serotonin reuptake inhibitors (SSRIs) or psycho-stimulants (that are known to indirectly increase serotonin levels). The current research takes a look at lowered serotonin levels when using corticosteroids, as well as the interactions with SSRIs and psycho-stimulants. Furthermore, evidence is presented to prove the hypothesis that some individuals with asthma (e.g. children using systemic corticosteroids that lower serotonin levels) might present with symptoms of depression, attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder and even conduct disorder; and that treating these secondary complaints with SSRIs and psycho-stimulants will result in the upregulating of serotonin levels, and that, in turn, will trigger asthma.

Histamine stimulates alveolar macrophages to release neutrophil and monocyte chemotactic activity

Histamine and serotonin are important inflammatory mediators in the pathophysiology of asthma, and asthmatic patients have higher plasma histamine and serotonin levels than non-asthmatic control subjects. Alveolar macrophages (AMs) synthesize and secrete a large number of substances that play a key role in acute and chronic inflammation including asthma. We postulated that AMs might release chemotactic activity for neutrophils and monocytes in response to histamine or serotonin. To test this hypothesis, bovine AMs were cultured, and the supernatant fluids were evaluated for neutrophil chemotactic activity (NCA) and monocyte chemotactic activity (MCA) by a blind well chamber technique. AMs released chemotactic activity in response to histamine and serotonin in a dose- and time-dependent manner (P <.05). Partial characterization and molecular sieve column chromatography revealed that low-molecular-weight lipid-soluble activity was predominant. Lipoxygenase inhibitors significantly blocked the release of chemotactic activity. Leukotriene B(4) receptor antagonists blocked the chemotactic activity. Immunoreactive leukotriene B(4) significantly increased in supernatant fluids in response to histamine and serotonin. The receptor responsible for the release of chemotactic activity in response to histamine was the H2 receptor. These data demonstrate that AMs release NCA and MCA in response to histamine or serotonin (or both) and may modulate the inflammatory cell recruitment into the lung.

Depression in Asthma: Prevalence and Clinical Implications

BACKGROUND: Asthma and depression are both common illnesses. Data suggest that the prevalence of asthma and asthma-related morbidity and mortality has increased in the past 2 decades. Asthma has long been considered an illness in which mood and emotions contribute to symptom exacerbation. Therefore, we reviewed the recent literature on depression in persons with asthma. DATA SOURCES: The MEDLINE (1966-1999) and PSYCHINFO (1967-1999) databases were used to find English-language articles on asthma and depression. Search terms included asthma, depression, dysthymia, and mood. DATA SYNTHESIS: This literature suggests depressive symptoms are more common in asthma patients than in the general population and perhaps even more common than in some other general medical conditions. Depression may be associated with asthma morbidity and mortality. Limited data suggest the older tricyclic antidepressants may improve both depression and asthma symptoms. However, no studies have examined the use of second-generation antidepressants in asthma patients. CONCLUSION: Depressive symptoms are common in asthma patients. However, the prevalence of depressive disorders in this population is not well determined. Future studies should focus on determining the prevalence of major depressive disorder in this population and the effect of antidepressants on mood and asthma symptoms.