The effects of 5-HT on cholinergic contraction in human airways in vitro

Alleviation of allergic asthma by rosmarinic acid via gut-lung axis

BACKGROUND

Asthma affects 3% of the global population, leading to over 0.25 million deaths. Due to its complexity, asthma is difficult to cure or prevent, and current therapies have limitations. This has led to a growing demand for alternative asthma treatments. We found rosmarinic acid (RosA) as a potential new drug candidate from natural medicine. However, RosA has poor bioavailability and remains mainly in the gastrointestinal tract after oral administration, suggesting the involvement of gut microbiota in its bioactivity.

PURPOSE

To investigate the mechanism of RosA in alleviating allergic asthma by gut-lung axis.

METHODS

We used 16S rRNA gene sequencing and metabolites analysis to investigate RosA's modulation of gut microbiota. Techniques of molecular biology and metabolomics were employed to study the pharmacological mechanism of RosA. Cohousing was used to confirm the involvement of gut microbiota in RosA-induced improvement of allergic asthma.

RESULTS

RosA decreased cholate levels from spore-forming bacteria, leading to reduced 5-hydroxytryptamine (5-HT) synthesis, bronchoconstriction, vasodilation, and inflammatory cell infiltration. It also increased short-chain fatty acids (SCFAs) levels, facilitating the expression of intestinal tight junction proteins to promote intestinal integrity. SCFAs upregulated intestinal monocarboxylate transporters (MCTs), thereby improving their systemic delivery to reduce Th2/ILC2 mediated inflammatory response and suppress eosinophil influx and mucus production in lung. Additionally, RosA inhibited lipopolysaccharide (LPS) production and translocation, leading to reduced TLR4-NFκB mediated pulmonary inflammation and oxidative stress.

CONCLUSIONS

The anti-asthmatic mechanism of oral RosA is primarily driven by modulation of gut microbiota-derived 5-HT, SCFAs, and LPS, achieving a combined synergistic effect. RosA is a safe, effective, and reliable drug candidate that could potentially replace glucocorticoids for asthma treatment.

5-HT modulates the properties of dendritic cells to interfere with the development of type 1 regulating T cells

BACKGROUND

5-hydroxytryptamine (5-HT, serotonin) is a major mediator in allergic reactions. The number of tolerogenic dendritic cell (tolDC) and regulatory T cell is reduced in allergic disorders. The mechanism is unclear. The objective of this study is to elucidate the role of 5-HT in interfering with tolDC generation and regulatory Type 1 T cell (Tr1 cell).

METHODS

BALB/c mice were treated with 5-HT-containing nasal instillations. The frequency of tolDC and Tr1 cell was evaluated by flow cytometry.

RESULTS

Following treatment with 5-HT nasal instillations for one week, the frequency of tolDC and Tr1 cell was significantly reduced in the respiratory tissues. Higher levels of SOS1 were detected in DCs isolated from the airway tissues of mice treated with 5-HT. A complex of SOS1 and c-Maf was detected in DCs in response to 5-HT stimulation. The expression of IL-10 was suppressed by the presence of 5-HT. The induction of Tr1 cell by DC was substantially compromised by 5-HT.

CONCLUSIONS

5-HT inhibits the expression of IL-10 in DCs. DCs primed with 5-HT lose the ability to induce Tr1 cells.

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.

Caveolin-3 differentially orchestrates cholinergic and serotonergic constriction of murine airways

The mechanisms of controlling airway smooth muscle (ASM) tone are of utmost clinical importance as inappropriate constriction is a hallmark in asthma and chronic obstructive pulmonary disease. Receptors for acetylcholine and serotonin, two relevant mediators in this context, appear to be incorporated in specialized, cholesterol-rich domains of the plasma membrane, termed caveolae due to their invaginated shape. The structural protein caveolin-1 partly accounts for anchoring of these receptors. We here determined the role of the other major caveolar protein, caveolin-3 (cav-3), in orchestrating cholinergic and serotonergic ASM responses, utilizing newly generated cav-3 deficient mice. Cav-3 deficiency fully abrogated serotonin-induced constriction of extrapulmonary airways in organ baths while leaving intrapulmonary airways unaffected, as assessed in precision cut lung slices. The selective expression of cav-3 in tracheal, but not intrapulmonary bronchial epithelial cells, revealed by immunohistochemistry, might explain the differential effects of cav-3 deficiency on serotonergic ASM constriction. The cholinergic response of extrapulmonary airways was not altered, whereas a considerable increase was observed in cav-3^-/- intrapulmonary bronchi. Thus, cav-3 differentially organizes serotonergic and cholinergic signaling in ASM through mechanisms that are specific for airways of certain caliber and anatomical position. This may allow for selective and site-specific intervention in hyperreactive states.

Airway Relaxation Effects of Water-Soluble Sclerotial Extract From Lignosus rhinocerotis

Lignosus rhinocerotis has a long history of use by the indigenous community within East Asia to treat a range of health conditions including asthma and chronic cough. To date, there is limited scientific evidence to support its therapeutic effects in relieving these airways conditions. In this study, we examined the effects of the different molecular weight fractions [high-molecular-weight (HMW), medium-molecular-weight (MMW), and low-molecular-weight (LMW)] obtained from the cold water sclerotial extract (CWE) of L. rhinocerotis on airways patency using airway segments isolated from Sprague Dawley rat in an organ bath set-up. It is demonstrated that the HMW and MMW fractions exhibited higher efficacy in relaxing the pre-contracted airways when compared to the CWE and LMW fraction. In addition, the HMW fraction markedly supressed carbachol-, 5-hydroxytrptamine-, and calcium-induced airway contractions. CWE demonstrated a lower efficacy than the HMW fraction but it also significantly attenuated carbachol- and calcium-induced airway contractions. Results showed that the bronchorelaxation effect of CWE and fractions is mediated via blockade of extracellular Ca²⁺ influx. The composition analysis revealed the following parts of carbohydrate and proteins, respectively: HMW fraction: 71 and 4%; MMW fraction: 35 and 1%; and LMW fraction: 22 and 0.3%. Our results strongly suggest that the polysaccharide–protein complex or proteins found in the HMW and MMW fractions is likely to contribute to the bronchorelaxation effect of CWE.

Tropisetron modulates peripheral and central serotonin/insulin levels via insulin and nuclear factor kappa B/receptor for advanced glycation end products signalling to regulate type-2 diabetes in rats

Despite its known central effect, 5% of serotonin is found centrally, while around 95% is found peripherally. Serotonin is stored and co-released with insulin upon pancreatic islets stimulation by glucose. This fact raises the curiosity regarding its possible role in diabetes. Hence, in this study, we assessed the possible modulatory effects of tropisetron, a 5-HT3 receptor antagonist, on type 2 diabetes mellitus models in rats. The rats were allocated into two groups: normal and diabetic. The latter group was treated with metformin (500 mg kg-1, p.o.), tropisetron (1 and 2 mg kg-1, i.p.), and a combination of metformin and tropisetron (1 mg kg-1). The different treatment regimens corrected glucose and lipid homeostasis manifested by the decrease in serum levels of glucose, fructosamine, homeostasis model of insulin resistance, triglycerides, total cholesterol, free fatty acid, as well as receptor for advanced glycation end products. Additionally, the treatments elevated levels of insulin, serotonin, and homeostasis model of β-cell function. On the molecular level, treatments corrected the altered insulin signaling cascade (phosphorylated insulin receptor substrate 1, phosphorylated protein kinase B, and glucose transporter 4), and inhibited β-catenin and phosphorylated nuclear factor kappa B p65 in the assessed soleus skeletal muscle. A similar pattern was duplicated in the hippocampus. This study provided evidence for the role of tropisetron on type 2 diabetes mellitus via modulating the insulin signaling cascade (insulin, phosphorylated insulin receptor substrate 1, phosphorylated protein kinase B, and glucose transporter 4), improving lipid/glucose profile, decreasing inflammatory markers (receptor for advanced glycation end products, and phosphorylated nuclear factor kappa B p65), as well as increasing 5-HT and reducing β-catenin.

Caveolin-1: Functional Insights into Its Role in Muscarine- and Serotonin-Induced Smooth Muscle Constriction in Murine Airways

An increased bronchoconstrictor response is a hallmark in the progression of obstructive airway diseases. Acetylcholine and 5-hydroxytryptamine (5-HT, serotonin) are the major bronchoconstrictors. There is evidence that both cholinergic and serotonergic signaling in airway smooth muscle (ASM) involve caveolae. We hypothesized that caveolin-1 (cav-1), a structural protein of caveolae, plays an important regulatory role in ASM contraction. We analyzed airway contraction in different tracheal segments and extra- and intrapulmonary bronchi in cav-1 deficient (cav-1−/−) and wild-type mice using organ bath recordings and videomorphometry of methyl-beta-cyclodextrin (MCD) treated and non-treated precision-cut lung slices (PCLS). The presence of caveolae was investigated by electron microscopy. Receptor subtypes driving 5-HT-responses were studied by RT-PCR and videomorphometry after pharmacological inhibition with ketanserin. Cav-1 was present in tracheal epithelium and ASM. Muscarine induced a dose dependent contraction in all airway segments. A significantly higher Emax was observed in the caudal trachea. Although, caveolae abundancy was largely reduced in cav-1−/− mice, muscarine-induced airway contraction was maintained, albeit at diminished potency in the middle trachea, in the caudal trachea and in the bronchus without changes in the maximum efficacy. MCD-treatment of PLCS from cav-1−/− mice reduced cholinergic constriction by about 50%, indicating that cholesterol-rich plasma domains account for a substantial portion of the muscarine-induced bronchoconstriction. Notably, cav-1-deficiency fully abrogated 5-HT-induced contraction of extrapulmonary airways. In contrast, 5-HT-induced bronchoconstriction was fully maintained in cav-1-deficient intrapulmonary bronchi, but desensitization upon repetitive stimulation was enhanced. RT-PCR analysis revealed 5-HT1B, 5-HT2A, 5-HT6, and 5-HT7 receptors as the most prevalent subtypes in the airways. The 5-HT-induced-constriction in PCLS could be antagonized by ketanserin, a 5-HT2A receptor inhibitor. In conclusion, the role of cav-1, caveolae, and cholesterol-rich plasma domains in regulation of airway tone are highly agonist-specific and dependent on airway level. Cav-1 is indispensable for serotonergic contraction of extrapulmonary airways and modulates cholinergic constriction of the trachea and main bronchus. Thus, cav-1/caveolae shall be considered in settings such as bronchial hyperreactivity in common airway diseases and might provide an opportunity for modulation of the constrictor response.

Low-dose oral cadmium increases airway reactivity and lung neuronal gene expression in mice

Inhalation of cadmium (Cd) is associated with lung diseases, but less is known concerning pulmonary effects of Cd found in the diet. Cd has a decades-long half-life in humans and significant bioaccumulation occurs with chronic dietary intake. We exposed mice to low-dose CdCl2 (10 mg/L in drinking water) for 20 weeks, which increased lung Cd to a level similar to that of nonoccupationally exposed adult humans. Cd-treated mice had increased airway hyperresponsiveness to methacholine challenge, and gene expression array showed that Cd altered the abundance of 443 mRNA transcripts in mouse lung. In contrast to higher doses, low-dose Cd did not elicit increased metallothionein transcripts in lung. To identify pathways most affected by Cd, gene set enrichment of transcripts was analyzed. Results showed that major inducible targets of low-dose Cd were neuronal receptors represented by enriched olfactory, glutamatergic, cholinergic, and serotonergic gene sets. Olfactory receptors regulate chemosensory function and airway hypersensitivity, and these gene sets were the most enriched. Targeted metabolomics analysis showed that Cd treatment also increased metabolites in pathways of glutamatergic (glutamate), serotonergic (tryptophan), cholinergic (choline), and catecholaminergic (tyrosine) receptors in the lung tissue. Protein abundance measurements showed that the glutamate receptor GRIN2A was increased in mouse lung tissue. Together, these results show that in mice, oral low-dose Cd increased lung Cd to levels comparable to humans, increased airway hyperresponsiveness and disrupted neuronal pathways regulating bronchial tone. Therefore, dietary Cd may promote or worsen airway hyperresponsiveness in multiple lung diseases including asthma.

Persistence of serotonergic enhancement of airway response in a model of childhood asthma

The persistence of airway hyperresponsiveness (AHR) and serotonergic enhancement of airway smooth muscle (ASM) contraction induced by ozone (O3) plus allergen has not been evaluated. If this mechanism persists after a prolonged recovery, it would indicate that early-life exposure to O3 plus allergen induces functional changes predisposing allergic individuals to asthma-related symptoms throughout life, even in the absence of environmental insult. A persistent serotonergic mechanism in asthma exacerbations may offer a novel therapeutic target, widening treatment options for patients with asthma. The objective of this study was to determine if previously documented AHR and serotonin-enhanced ASM contraction in allergic monkeys exposed to O3 plus house dust mite allergen (HDMA) persist after prolonged recovery. Infant rhesus monkeys sensitized to HDMA were exposed to filtered air (FA) (n = 6) or HDMA plus O3 (n = 6) for 5 months. Monkeys were then housed in a FA environment for 30 months. At 3 years, airway responsiveness was assessed. Airway rings were then harvested, and ASM contraction was evaluated using electrical field stimulation with and without exogenous serotonin and serotonin-subtype receptor antagonists. Animals exposed to O3 plus HDMA exhibited persistent AHR. Serotonin exacerbated the ASM contraction in the exposure group but not in the FA group. Serotonin subtype receptors 2, 3, and 4 appear to drive the response. Our study shows that AHR and serotonin-dependent exacerbation of cholinergic-mediated ASM contraction induced by early-life exposure to O3 plus allergen persist for at least 2.5 years and may contribute to a persistent asthma phenotype.

Cerebral anatomical changes in female asthma patients with and without depression compared to healthy controls and patients with depression

BACKGROUND

Population-based studies have demonstrated that asthma patients with depression symptoms are more likely to have poor asthma control and worse asthma outcomes. However, the underlying mechanism of the relationship between asthma and depression is still unclear. The present study aimed to examine the cerebral anatomical changes in female asthma patients with and without depression.

METHODS

Using structural magnetic resonance imaging (MRI) and a voxel-based morphometry technique, the primary effects of and the interaction between asthma and depression were analyzed. The cerebral gray matter volume (GMV) was compared between the groups. Correlation analyses between the GMV value of the brain regions and the clinical parameters were completed.

RESULTS

The interaction effect of asthma and depression was found on the right superior temporal gyrus (STG) and the left middle temporal gyrus. Patients with both asthma and depression showed less GMV in the right STG, the bilateral precuneus, and the right superior frontal gyrus compared to patients with asthma only. The GMV of the right STG showed a decrement form among the asthma only group, healthy controls and asthma plus depression group. In patients with asthma and depression, the volume of the right STG was positively correlated with PD20 (r = 0.714, p = 0.047) and negatively correlated with the nocturnal awakening score in the Asthma Control Test (r = -0.061, p = 0.038).

CONCLUSION

Current findings provided convergent evidence to support the critical role of the right STG in the brain mechanism that mediates asthma and depression.

Chemosensory functions for pulmonary neuroendocrine cells

The mammalian airways are sensitive to inhaled stimuli, and airway diseases are characterized by hypersensitivity to volatile stimuli, such as perfumes, industrial solvents, and others. However, the identity and function of the cells in the airway that can sense volatile chemicals remain uncertain, particularly in humans. Here, we show that solitary pulmonary neuroendocrine cells (PNECs), which are morphologically distinct and physiologically undefined, might serve as chemosensory cells in human airways. This conclusion is based on our finding that some human PNECs expressed members of the olfactory receptor (OR) family in vivo and in primary cell culture, and are anatomically positioned in the airway epithelium to respond to inhaled volatile chemicals. Furthermore, apical exposure of primary-culture human airway epithelial cells to volatile chemicals decreased levels of serotonin in PNECs, and the led to the release of the neuropeptide calcitonin gene-related peptide (CGRP) to the basal medium. These data suggest that volatile stimulation of PNECs can lead to the secretion of factors that are capable of stimulating the corresponding receptors in the lung epithelium. We also found that the distribution of serotonin and neuropeptide receptors may change in chronic obstructive pulmonary disease, suggesting that increased PNEC-dependent chemoresponsiveness might contribute to the altered sensitivity to volatile stimuli in this disease. Together, these data indicate that human airway epithelia harbor specialized cells that respond to volatile chemical stimuli, and may help to explain clinical observations of odorant-induced airway reactions.

HTR4 gene structure and altered expression in the developing lung

BACKGROUND

Meta-analyses of genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) spanning the 5-hydroxytryptamine receptor 4 (5-HT₄R) gene (HTR4) associated with lung function. The aims of this study were to i) investigate the expression profile of HTR4 in adult and fetal lung tissue and cultured airway cells, ii) further define HTR4 gene structure and iii) explore the potential functional implications of key SNPs using a bioinformatic approach.

METHODS

Following reverse transcription (RT)-PCR in human brain, 5' rapid amplification of cDNA ends (5' RACE) was used to examine the exonic structure of HTR4 at the 5' end. Quantitative (Q)-PCR was used to quantify HTR4 mRNA expression in total RNA from cultured airway cells and whole lung tissue. Publically available gene microarray data on fetal samples of estimated gestational age 7-22 weeks were mined for HTR4 expression. Immunohistochemistry (IHC; in adult and fetal lung tissue) and a radioligand binding assay (in cultured airway cells) were used to analyze 5-HT₄R protein expression.

RESULTS

IHC in adult lung, irrespective of the presence of chronic obstructive pulmonary disease (COPD), suggested low level expression of 5-HT₄R protein, which was most prominent in alveolar pneumocytes. There was evidence of differential 5-HT₄R protein levels during gestation in fetal lung, which was also evident in gene expression microarray data. HTR4 mRNA expression, assessed by Q-PCR, was <0.5% relative to brain in total adult lung tissue and in human airway smooth muscle (HASM) and bronchial epithelial cells (HBEC) derived from adult donors. Radioligand binding experiments also indicated that HBEC and HASM cells did not express a significant 5-HT₄R population. 5' RACE in brain identified a novel N-terminal variant, containing an extended N-terminal sequence. The functional significance of key HTR4 SNPs was investigated using the encyclopedia of DNA elements consortium (ENCODE) dataset. These analyses identified multiple alterations in regulatory motifs for transcription factors implicated in lung development, including Foxp1.

CONCLUSIONS

Taken together, these data suggest a role for HTR4 in lung development, which may at least in part explain the genetic association with lung function.

Modifications of plasma 5-HT concentrations during the allergic bronchoconstriction in guinea pigs

Several contractile mediators involved in the antigen-induced airway obstruction have been identified, but the role of 5-HT (5-hydroxytryptamine or serotonin) has been scantily investigated. In this work, the potential role of 5-HT in the allergic bronchoconstriction was evaluated through a pharmacological approach and plasma 5-HT measurement in blood samples from the right and left ventricles of anesthetized guinea-pigs. Intravenous 5-HT caused a dose-dependent increase of the lung resistance in anesthetized, nonsensitized guinea pigs. Likewise, in sensitized animals the antigenic challenge with ovalbumin also caused a transient bronchoconstriction (356 ± 60% the basal value), which was largely inhibited by the blockade of serotonergic receptors with methiothepin plus tropisetron (134 ± 10%, P = .007). Sensitized animals tended to have plasma 5-HT concentrations higher than nonsensitized controls, and shortly after the peak of the allergic bronchoconstriction the 5-HT levels in the left ventricle (blood flowing out from lungs) tended to be higher than in the right ventricle (blood entering the lungs), although data dispersion precluded the obtaining of statistical significance. Interestingly, the degree of bronchoconstriction highly correlated with the concentrations of 5-HT found in the left ventricle and measured either in platelet-rich plasma (r = 0.97 P = .007) or platelet-poor plasma (r = 0.97, P = .006). After the obstructive response subsided these correlations were lost, but now the degree of bronchoconstriction turned to be correlated with 5-HT concentration in platelet concentrate (r = 0.76, P = .03). In conclusion, our results suggested that 5-HT is actively released from lungs during the antigenic challenge and that this autacoid is involved in the generation of the airway obstruction.

Neurally mediated airway constriction in human and other species: a comparative study using precision-cut lung slices (PCLS)

The peripheral airway innervation of the lower respiratory tract of mammals is not completely functionally characterized. Recently, we have shown in rats that precision-cut lung slices (PCLS) respond to electric field stimulation (EFS) and provide a useful model to study neural airway responses in distal airways. Since airway responses are known to exhibit considerable species differences, here we examined the neural responses of PCLS prepared from mice, rats, guinea pigs, sheep, marmosets and humans. Peripheral neurons were activated either by EFS or by capsaicin. Bronchoconstriction in response to identical EFS conditions varied between species in magnitude. Frequency response curves did reveal further species-dependent differences of nerve activation in PCLS. Atropine antagonized the EFS-induced bronchoconstriction in human, guinea pig, sheep, rat and marmoset PCLS, showing cholinergic responses. Capsaicin (10 µM) caused bronchoconstriction in human (4 from 7) and guinea pig lungs only, indicating excitatory non-adrenergic non-cholinergic responses (eNANC). However, this effect was notably smaller in human responder (30 ± 7.1%) than in guinea pig (79 ± 5.1%) PCLS. The transient receptor potential (TRP) channel blockers SKF96365 and ruthenium red antagonized airway contractions after exposure to EFS or capsaicin in guinea pigs. In conclusion, the different species show distinct patterns of nerve-mediated bronchoconstriction. In the most common experimental animals, i.e. in mice and rats, these responses differ considerably from those in humans. On the other hand, guinea pig and marmoset monkey mimic human responses well and may thus serve as clinically relevant models to study neural airway responses.

Allergen and ozone exacerbate serotonin-induced increases in airway smooth muscle contraction in a model of childhood asthma

BACKGROUND

Serotonin (5-HT) modulates cholinergic neurotransmission and exacerbates airway smooth muscle (ASM) contraction in normal animal and nonasthmatic human tissue. Exposure to house dust mite allergen (HDMA) and ozone (O(3)) leads to airway hyperreactivity and 5-HT-positive cells in the airway epithelium of infant rhesus monkeys. Research shows that concomitant exposure in allergic animals has an additive effect on airway hyperreactivity.

OBJECTIVES

In this study, the hypothesis is that the exposure of allergic infant rhesus monkeys to HDMA, O(3) and in combination, acting through 5-HT receptors, enhances 5-HT modulation of postganglionic cholinergic ASM contraction.

METHODS

Twenty-four HDMA-sensitized infant monkeys were split into 4 groups at the age of 1 month, and were exposed to filtered air (FA), HDMA, O(3) or in combination (HDMA+O(3)). At the age of 6 months, airway rings were harvested and postganglionic, and parasympathetic-mediated ASM contraction was evaluated using electrical-field stimulation (EFS).

RESULTS

5-HT exacerbated the EFS response within all exposure groups, but had no effect in the FA group. 5-HT(2), 5-HT(3) and 5-HT(4) receptor agonists exacerbated the response. 5-HT concentration-response curves performed after incubation with specific receptor antagonists confirmed the involvement of 5-HT(2), 5-HT(3) and 5-HT(4) receptors. Conversely, a 5-HT(1) receptor agonist attenuated the tension across all groups during EFS, and in ASM contracted via exogenous acetylcholine.

CONCLUSIONS

HDMA, O(3) and HDMA+O(3) exposure in a model of childhood allergic asthma enhances 5-HT exacerbation of EFS-induced ASM contraction through 5-HT(2), 5-HT(3) and 5-HT(4) receptors. A nonneurogenic inhibitory pathway exists, unaffected by exposure, mediated by 5-HT(1) receptors located on ASM.

Impact of 5-HT₃ receptor antagonists on peripheral and central diseases

In this article we discuss the novel pharmacological aspects of 5-HT(3) receptor antagonists. Commonly used to counteract chemotherapy-induced emesis, these agents now appear to be reaching out for newer indications. Studies have reported neuroprotective and anti-inflammatory properties in vitro and in vivo. 5-HT(3) receptor antagonists can modulate the immune-inflammatory axis through blockade of 5-HT(3) receptors present on immune cells. We review evidence addressing the effects of these drugs on peripheral inflammatory diseases, including asthma, rheumatoid diseases, inflammatory bowel disease and sepsis in addition to diabetes and CNS disorders, including Alzheimer's disease (AD), seizure and stroke.

Airway responses to desflurane during maintenance of anesthesia and recovery in children with laryngeal mask airways

BACKGROUND

We sought to characterize the airway responses to desflurane during maintenance of and emergence from anesthesia in children whose airways were supported with laryngeal mask airways (LMAs).

METHODS/MATERIALS

Four hundred healthy children were randomized in a 3 : 1 ratio to either desflurane or isoflurane (reference group) during anesthetic maintenance. After induction of anesthesia, anesthesia was maintained with the designated anesthetic. The investigator chose the airway (LMA and facemask), ventilation strategy and when to remove the LMA. The incidence of airway events during maintenance, emergence and recovery was recorded.

RESULTS

Ninety percent of children received LMAs. The frequency of major airway events after desflurane (9%) was similar to that after isoflurane (4%) (number needed to harm [NNH] 20), although the frequency of major events after the LMA was removed during deep desflurane anesthesia (15%) was greater than during awake removal (5%) (NNH 10) (P < 0.006) and during deep isoflurane removal (2%) (NNH 8) (P < 0.03). The frequency of airway events of any severity after desflurane was greater than that after isoflurane (39% vs 27%) (P < 0.05). The frequencies of laryngospasm and coughing of any severity after desflurane were greater than those after isoflurane (13% vs 5% and 26% vs 14%, respectively) (P < 0.05).

CONCLUSIONS

When an LMA is used during desflurane anesthesia in children, fewer airway events occur when it is removed when the child is awake. Although the time to discharge from recovery was not delayed and no child required overnight admission, caution should be exercised when using an LMA in children who are anesthetized with desflurane.

Effects of an oral dose of l-glutamic acid on circulating neurotransmitters: Possible roles of the C1(Ad) and the A5(NA) pontomedullary nuclei

Objective

Investigation of the effects of an oral administration of a small dose of l-glutamic acid on the two peripheral sympathetic branches (neural and adrenal) of the autonomic nervous system.

Research design and methods

Circulating neurotransmitters and cardiovascular parameters were assessed in 28 healthy volunteers before and after the administration of 500 mg of l-glutamic acid or placebo.

Results

The drug triggered a significant and sustained enhancement of the noradrenaline and dopamine circulating levels which were paralleled and positively correlated with the diastolic blood pressure increases. Conversely, both platelet and plasma serotonin showed significant falls throughout the test. Significant positive correlations were registered between noradrenaline, dopamine, and noradrenaline/dopamine ratio versus diastolic blood pressure but not versus systolic blood pressure or heart rate.

Conclusion

The above results allowed us to postulate that the drug provoked a significant enhancement of peripheral neural sympathetic activity and the reduction of adrenal sympathetic and parasympathetic drives. Both sympathetic branches are positively correlated with the A₅ noradrenergic and the C₁ adrenergic pontomedullary nuclei, which interchange inhibitory axons that act at post-synaptic α₂ inhibitory autoreceptors. In addition, we discussed the mechanisms able to explain why the drug acted preferentially at the A₅ noradrenergic rather than the C₁ adrenergic nuclei.

Genome-wide association study identifies five loci associated with lung function

Pulmonary function measures are heritable traits that predict morbidity and mortality and define chronic obstructive pulmonary disease (COPD). We tested genome-wide association with forced expiratory volume in 1 s (FEV(1)) and the ratio of FEV(1) to forced vital capacity (FVC) in the SpiroMeta consortium (n = 20,288 individuals of European ancestry). We conducted a meta-analysis of top signals with data from direct genotyping (n < or = 32,184 additional individuals) and in silico summary association data from the CHARGE Consortium (n = 21,209) and the Health 2000 survey (n < or = 883). We confirmed the reported locus at 4q31 and identified associations with FEV(1) or FEV(1)/FVC and common variants at five additional loci: 2q35 in TNS1 (P = 1.11 x 10(-12)), 4q24 in GSTCD (2.18 x 10(-23)), 5q33 in HTR4 (P = 4.29 x 10(-9)), 6p21 in AGER (P = 3.07 x 10(-15)) and 15q23 in THSD4 (P = 7.24 x 10(-15)). mRNA analyses showed expression of TNS1, GSTCD, AGER, HTR4 and THSD4 in human lung tissue. These associations offer mechanistic insight into pulmonary function regulation and indicate potential targets for interventions to alleviate respiratory disease.

Meta-analyses of genome-wide association studies identify multiple loci associated with pulmonary function

Spirometric measures of lung function are heritable traits that reflect respiratory health and predict morbidity and mortality. We meta-analyzed genome-wide association studies for two clinically important lung-function measures: forced expiratory volume in the first second (FEV(1)) and its ratio to forced vital capacity (FEV(1)/FVC), an indicator of airflow obstruction. This meta-analysis included 20,890 participants of European ancestry from four CHARGE Consortium studies: Atherosclerosis Risk in Communities, Cardiovascular Health Study, Framingham Heart Study and Rotterdam Study. We identified eight loci associated with FEV(1)/FVC (HHIP, GPR126, ADAM19, AGER-PPT2, FAM13A, PTCH1, PID1 and HTR4) and one locus associated with FEV(1) (INTS12-GSTCD-NPNT) at or near genome-wide significance (P < 5 x 10(-8)) in the CHARGE Consortium dataset. Our findings may offer insights into pulmonary function and pathogenesis of chronic lung disease.

Role of 5-HT2A, 5-HT4 and 5-HT7 receptors in the antigen-induced airway hyperresponsiveness in guinea-pigs

BACKGROUND

A possible role of 5-hydroxytryptamine (5-HT) in the origin of antigen-induced airway hyperresponsiveness (AI-AHR) has been scarcely investigated.

OBJECTIVE

To explore the participation of different 5-HT receptors in the development of AI-AHR in guinea-pigs.

METHODS

Lung resistance was measured in anaesthetized guinea-pigs sensitized to ovalbumin (OVA). Dose-response curves to intravenous (i.v.) acetylcholine (ACh) were performed before and 1 h after antigenic challenge and expressed as the 200% provocative dose (PD(200)). Organ bath experiments, confocal microscopy and RT-PCR were additionally used. The 5-HT content in lung homogenates was measured by HPLC.

RESULTS

Antigenic challenge significantly decreased PD(200), indicating the development of AI-AHR. This hyperresponsiveness was abolished by a combination of methiothepin (5-HT(1)/5-HT(2)/5-HT(5)/5-HT(6)/5-HT(7) receptors antagonist) and tropisetron (5-HT(3)/5-HT(4) antagonist). Other 5-HT receptor antagonists showed three different patterns of response. Firstly, WAY100135 (5-HT(1A) antagonist) and ondansetron (5-HT(3) antagonist) did not modify the AI-AHR. Secondly, SB269970 (5-HT(7) antagonist), GR113808 (5-HT(4) antagonist), tropisetron or methiothepin abolished the AI-AHR. Thirdly, ketanserin (5-HT(2A) antagonist) produced airway hyporresponsiveness. Animals with bilateral vagotomy did not develop AI-AHR. Experiments in tracheal rings showed that pre-incubation with LP44 or cisapride (agonists of 5-HT(7) and 5-HT(4) receptors, respectively) induced a significant increase of the cholinergic contractile response to the electrical field stimulation. In sensitized lung parenchyma strips, ketanserin diminished the contractile responses to ACh. Sensitization was associated with a ninefold increase in the 5-HT content of lung homogenates. Confocal microscopy showed that sensitization enhanced the immunolabelling and co-localization of nicotinic receptor and 5-HT in airway epithelium, probably located in pulmonary neuroendocrine cells (PNECs). RT-PCR demonstrated that neither sensitization nor antigen challenge modified the 5-HT(2A) receptor mRNA levels.

CONCLUSIONS

Our results suggested that 5-HT was involved in the development of AI-AHR to ACh in guinea-pigs. Specifically, 5-HT(2A), 5-HT(4) and 5-HT(7) receptors seem to be particularly involved in this phenomenon. Participation of 5-HT might probably be favoured by the enhancement of the PNECs 5-HT content observed after sensitization.

A multi-hit endocrine model of intrinsic adult-onset asthma

Epidemiological studies indicate that adult-onset asthma is initiated by stress (anxiety and depression), obesity and menopause. Ironically, despite our understanding of the various stressors that promote chronic adult-onset asthma, most of which are known to elevate cortisol production via the hypothalamic-pituitary-adrenal (HPA) axis, inhaled and systemic corticosteroids are the mainstay for the treatment of chronic asthma. This implicates other endocrine or cellular changes independent of cortisol synthesis in non-allergic adult-onset asthma. The mechanism by which corticosteroids are thought to modulate bronchial tone in relieving asthma is via corticosteroid-responsive genes that increase PGE(2) and cAMP production which promote muscle relaxation. Therefore, any physiological condition that suppresses intracellular PGE(2) and cAMP production would counter cortisol-induced muscle relaxation and potentially trigger non-allergic adult-onset asthma. Stress, obesity and menopause act on three interrelated endocrine pathways, the serotonergic, leptinergic and hypothalamic pathways, all of which operate through receptors to modulate cAMP and Ca(2+) metabolism in smooth muscle cells (SMCs). We propose that the level of SMC cAMP, as determined by overall signaling through corticosteroid receptors, leptin receptors and the GPCRs of the HPG and serotonergic pathways, will regulate bronchial tone (i.e. the 'Multi-Hit Endocrine Model of Adult-Onset Asthma'). Thus, decreases in HPG (menopause) and serotonergic (depression) signaling and increases in leptinergic (obesity) signaling relative to HPA signaling would decrease cellular SMC cAMP and promote muscle contraction. This model can explain the discrepant epidemiological data associating stress, obesity, depression and menopause with adult-onset asthma and is supported by basic and clinical data. Treatment of depressed or menopausal asthmatics with selective serotonin reuptake inhibitors or hormone replacement therapy, respectively, alleviates bronchoconstriction. Future therapeutic strategies might therefore target the serotonergic, leptinergic and hypothalamic pathways in regulating cellular cAMP production and bronchoconstriction for the treatment of adult-onset asthma.

Activation of 5-HT4 receptors inhibits secretion of β-amyloid peptides and increases neuronal survival

Activation of 5-HT4 receptors has been shown to improve memory processes in preclinical cognition models, suggesting potential utility of 5-HT4 agonists for the symptomatic treatment of Alzheimer's disease (AD). Recent studies have shown that 5-HT4 agonists also increase the secretion of the non-amyloidogenic soluble amyloid precursor protein-alpha (sAPPalpha). In the present study, we demonstrated that a selective 5-HT4 partial agonist, RS67333, inhibited the generation of beta-amyloid peptide (Abeta) in primary cortical cultures of Tg2576 transgenic mice expressing human APP(K670N/M671L). Furthermore, treatments with RS67333 selectively increased the survival of transgenic neurons in a dose-dependent manner, which was inhibited by 5-HT4 antagonists. These and previous data collectively suggest that the 5-HT4 receptor may be an effective therapeutic target for AD, providing both symptomatic improvements and neuroprotection.

Propofol attenuates ovalbumin-induced smooth muscle contraction of the sensitized rat trachea: inhibition of serotonergic and cholinergic signaling

Propofol is considered suitable for induction of anesthesia in patients with bronchial asthma. However, the mechanisms of its action on bronchi are not fully understood. We examined the effects of propofol on ovalbumin (OA)-induced contraction of OA-sensitized rat trachea. Male Wistar rats were sensitized by a single intraperitoneal injection of OA 10 microg mixed with aluminum hydroxide, 10 mg, as adjuvant. Fourteen days later, the experiment was performed using the tracheal rings. We observed the effects of ketanserin, a 5-HT2 receptor antagonist, and atropine on OA-induced contraction. Next, the effects of propofol on OA-, serotonin (5-HT)-, acetylcholine-, or electrical field stimulation-induced contractions were observed. OA-induced contraction was 90% attenuated by the combination of ketanserin and atropine. Propofol significantly attenuated OA-induced contraction in a dose-dependent manner. Propofol abolished 5-HT-induced contraction, attenuated acetylcholine-induced contraction, and also almost completely attenuated the enhancement by 5-HT of electrical field stimulation-induced contraction. These results suggest that the mechanism involved in the attenuation by propofol of OA-induced contraction is inhibition of the actions of 5-HT. Propofol should be a useful anesthetic in patients with immunoglobulin E-related asthma.

The frequency of calcium oscillations induced by 5-HT, ACH, and KCl determine the contraction of smooth muscle cells of intrapulmonary bronchioles

Increased resistance of airways or blood vessels within the lung is associated with asthma or pulmonary hypertension and results from contraction of smooth muscle cells (SMCs). To study the mechanisms regulating these contractions, we developed a mouse lung slice preparation containing bronchioles and arterioles and used phase-contrast and confocal microscopy to correlate the contractile responses with changes in [Ca²⁺]_i of the SMCs. The airways are the focus of this study. The agonists, 5-hydroxytrypamine (5-HT) and acetylcholine (ACH) induced a concentration-dependent contraction of the airways. High concentrations of KCl induced twitching of the airway SMCs but had little effect on airway size. 5-HT and ACH induced asynchronous oscillations in [Ca²⁺]_i that propagated as Ca²⁺ waves within the airway SMCs. The frequency of the Ca²⁺ oscillations was dependent on the agonist concentration and correlated with the extent of sustained airway contraction. In the absence of extracellular Ca²⁺ or in the presence of Ni²⁺, the frequency of the Ca²⁺ oscillations declined and the airway relaxed. By contrast, KCl induced low frequency Ca²⁺ oscillations that were associated with SMC twitching. Each KCl-induced Ca²⁺ oscillation consisted of a large Ca²⁺ wave that was preceded by multiple localized Ca²⁺ transients. KCl-induced responses were resistant to neurotransmitter blockers but were abolished by Ni²⁺ or nifedipine and the absence of extracellular Ca²⁺. Caffeine abolished the contractile effects of 5-HT, ACH, and KCl. These results indicate that (a) 5-HT and ACH induce airway SMC contraction by initiating Ca²⁺ oscillations, (b) KCl induces Ca²⁺ transients and twitching by overloading and releasing Ca²⁺ from intracellular stores, (c) a sustained, Ni²⁺-sensitive, influx of Ca²⁺ mediates the refilling of stores to maintain Ca²⁺ oscillations and, in turn, SMC contraction, and (d) the magnitude of sustained airway SMC contraction is regulated by the frequency of Ca²⁺ oscillations.