Diamine oxidase knockout mice are not hypersensitive to orally or subcutaneously administered histamine.

OBJECTIVE: To evaluate the contribution of endogenous diamine oxidase (DAO) in the inactivation of exogenous histamine, to find a mouse strain with increased histamine sensitivity and to test the efficacy of rhDAO in a histamine challenge model. METHODS: Diamine oxidase knockout (KO) mice were challenged with orally and subcutaneously administered histamine in combination with the ß-adrenergic blocker propranolol, with the two histamine-N-methyltransferase (HNMT) inhibitors metoprine and tacrine, with folic acid to mimic acute kidney injury and treated with recombinant human DAO. Core body temperature was measured using a subcutaneously implanted microchip and histamine plasma levels were quantified using a homogeneous time resolved fluorescence assay. RESULTS: Core body temperature and plasma histamine levels were not significantly different between wild type (WT) and DAO KO mice after oral and subcutaneous histamine challenge with and without acute kidney injury or administration of HNMT inhibitors. Treatment with recombinant human DAO reduced the mean area under the curve (AUC) for core body temperature loss by 63% (p = 0.002) and the clinical score by 88% (p < 0.001). The AUC of the histamine concentration was reduced by 81%. CONCLUSIONS: Inactivation of exogenous histamine is not driven by enzymatic degradation and kidney filtration. Treatment with recombinant human DAO strongly reduced histamine-induced core body temperature loss, histamine concentrations and prevented the development of severe clinical symptoms.

TRPV1 and TRPA1 Channels Are Both Involved Downstream of Histamine-Induced Itch.

Two histamine receptor subtypes (HR), namely H1R and H4R, are involved in the transmission of histamine-induced itch as key components. Although exact downstream signaling mechanisms are still elusive, transient receptor potential (TRP) ion channels play important roles in the sensation of histaminergic and non-histaminergic itch. The aim of this study was to investigate the involvement of TRPV1 and TRPA1 channels in the transmission of histaminergic itch. The potential of TRPV1 and TRPA1 inhibitors to modulate H1R- and H4R-induced signal transmission was tested in a scratching assay in mice in vivo as well as via Ca2+ imaging of murine sensory dorsal root ganglia (DRG) neurons in vitro. TRPV1 inhibition led to a reduction of H1R- and H4R- induced itch, whereas TRPA1 inhibition reduced H4R- but not H1R-induced itch. TRPV1 and TRPA1 inhibition resulted in a reduced Ca2+ influx into sensory neurons in vitro. In conclusion, these results indicate that both channels, TRPV1 and TRPA1, are involved in the transmission of histamine-induced pruritus.

Histamine Ingestion by Anopheles stephensi Alters Important Vector Transmission Behaviors and Infection Success with Diverse Plasmodium Species.

An estimated 229 million people worldwide were impacted by malaria in 2019. The vectors of malaria parasites (Plasmodium spp.) are Anopheles mosquitoes, making their behavior, infection success, and ultimately transmission of great importance. Individuals with severe malaria can exhibit significantly increased blood concentrations of histamine, an allergic mediator in humans and an important insect neuromodulator, potentially delivered to mosquitoes during blood-feeding. To determine whether ingested histamine could alter Anopheles stephensi biology, we provisioned histamine at normal blood levels and at levels consistent with severe malaria and monitored blood-feeding behavior, flight activity, antennal and retinal responses to host stimuli and lifespan of adult female Anopheles stephensi. To determine the effects of ingested histamine on parasite infection success, we quantified midgut oocysts and salivary gland sporozoites in mosquitoes infected with Plasmodium yoelii and Plasmodium falciparum. Our data show that provisioning An. stephensi with histamine at levels consistent with severe malaria can enhance mosquito behaviors and parasite infection success in a manner that would be expected to amplify parasite transmission to and from human hosts. Such knowledge could be used to connect clinical interventions by reducing elevated histamine to mitigate human disease pathology with the delivery of novel lures for improved malaria control.

Identifying bronchoconstriction from the ratio of diaphragm EMG to tidal volume.

BACKGROUND: A fall of ≥ 20 % in forced expiratory volume in the first second (FEV1) with a cumulative dose of histamine ≤ 7.8 µmol is considered to indicate bronchial hyperactivity, but no method exists for patients who cannot perform spirometry properly. Here we hypothesized that increases in respiratory central output measured by chest wall electromyography of the diaphragm (EMGdi-c) expressed as a function of tidal volume (EMGdi-c/VT) would have discriminative power to detect a 'positive' challenge test. METHODS: In a physiological study EMGdi was recorded from esophageal electrode (EMGdi-e) in 16 asthma patients and 16 healthy subjects during a histamine challenge test. In a second study, EMGdi from chest wall surface electrodes (EMGdi-c) was measured during a histamine challenge in 44 asthma patients and 51 healthy subjects. VT was recorded from a digital flowmeter during both studies. RESULTS: With histamine challenge test the change in EMGdi-e/VT in patients with asthma was significantly higher than that in healthy subjects (104.2 % ± 48.6 % vs 0.03 % ± 17.1 %, p < 0.001). Similarly there was a significant difference in the change of EMGdi-c/VT between patients with asthma and healthy subjects (90.5 % ± 75.5 % vs 2.4 % ± 21.7 %, p < 0.001). At the optimal cut-off point (29 % increase in EMGdi-c/VT), the area under the ROC curve (AUC) for detection of a positive test was 0.91 (p < 0.001) with sensitivity 86 % and specificity 92 %. CONCLUSIONS: We conclude that EMGdi-c/VT may be used as an alternative for the assessment of bronchial hypersensitivity and airway reversibility to differentiate patients with asthma from healthy subjects.

Pruriception and neuronal coding in nociceptor subtypes in human and nonhuman primates.

In humans, intradermal administration of ß-alanine (ALA) and bovine adrenal medulla peptide 8-22 (BAM8-22) evokes the sensation of itch. Currently, it is unknown which human dorsal root ganglion (DRG) neurons express the receptors of these pruritogens, MRGPRD and MRGPRX1, respectively, and which cutaneous afferents these pruritogens activate in primate. In situ hybridization studies revealed that MRGPRD and MRGPRX1 are co-expressed in a subpopulation of TRPV1+ human DRG neurons. In electrophysiological recordings in nonhuman primates (Macaca nemestrina), subtypes of polymodal C-fiber nociceptors are preferentially activated by ALA and BAM8-22, with significant overlap. When pruritogens ALA, BAM8-22, and histamine, which activate different subclasses of C-fiber afferents, are administered in combination, human volunteers report itch and nociceptive sensations similar to those induced by a single pruritogen. Our results provide evidence for differences in pruriceptive processing between primates and rodents, and do not support the spatial contrast theory of coding of itch and pain.

Demystifying Excess Immune Response in COVID-19 to Reposition an Orphan Drug for Down-Regulation of NF-κB: A Systematic Review.

The immunological findings from autopsies, biopsies, and various studies in COVID-19 patients show that the major cause of morbidity and mortality in COVID-19 is excess immune response resulting in hyper-inflammation. With the objective to review various mechanisms of excess immune response in adult COVID-19 patients, Pubmed was searched for free full articles not related to therapeutics or co-morbid sub-groups, published in English until 27.10.2020, irrespective of type of article, country, or region. Joanna Briggs Institute's design-specific checklists were used to assess the risk of bias. Out of 122 records screened for eligibility, 42 articles were included in the final review. The review found that eventually, most mechanisms result in cytokine excess and up-regulation of Nuclear Factor-κB (NF-κB) signaling as a common pathway of excess immune response. Molecules blocking NF-κB or targeting downstream effectors like Tumour Necrosis Factor α (TNFα) are either undergoing clinical trials or lack specificity and cause unwanted side effects. Neutralization of upstream histamine by histamine-conjugated normal human immunoglobulin has been demonstrated to inhibit the nuclear translocation of NF-κB, thereby preventing the release of pro-inflammatory cytokines Interleukin (IL) 1ß, TNF-α, and IL-6 and IL-10 in a safer manner. The authors recommend repositioning it in COVID-19.

Amitriptyline functionally antagonizes cardiac H2 histamine receptors in transgenic mice and human atria.

We have previously shown that histamine (2-(1H-imidazol-4-yl)ethanamine) exerted concentration-dependent positive inotropic effects (PIE) or positive chronotropic effects (PCE) on isolated left and right atria, respectively, of transgenic (H2R-TG) mice that overexpress the human H2 histamine receptor (H2R) in the heart; however, the effects were not seen in their wild-type (WT) littermates. Amitriptyline, which is still a highly prescribed antidepressant drug, was reported to act as antagonist on H2Rs. Here, we wanted to determine whether the histamine effects in H2R-TG were antagonized by amitriptyline. Contractile studies were performed on isolated left and right atrial preparations, isolated perfused hearts from H2R-TG and WT mice and human atrial preparations. Amitriptyline shifted the concentration-dependent PIE of histamine (1 nM-10 µM) to higher concentrations (rightward shift) in left atrial preparations from H2R-TG. Similarly, in isolated perfused hearts from H2R-TG and WT mice, histamine increased the contractile parameters and the phosphorylation state of phospholamban (PLB) at serine 16 in the H2R-TG mice, but not in the WT mice. However, the increases in contractility and PLB phosphorylation were attenuated by the addition of amitriptyline in perfused hearts from H2R-TG. In isolated electrically stimulated human atria, the PIE of histamine that was applied in increasing concentrations from 1 nM to 10 µM was reduced by 10-µM amitriptyline. In summary, we present functional evidence that amitriptyline also acts as an antagonist of contractility at H2Rs in H2R-TG mouse hearts and in the human heart which might in part explain the side effects of amitriptyline.

[Effects of Histamine and Related Compounds on the Central Nervous System].

There has been little information about the role of histamine on the central nervous system (CNS), different from dopamine and serotonin. In the present study, therefore, the effects of histamine and related compounds on the CNS were studied using rats. Intracerebroventricular (i.c.v.) injection of histamine and 2-methylhistamine ameliorated memory deficit after long interrution of learning in active avoidance response. First generation H1-antagonists inhibited active avoidance response, whereas newly develpoed H1-antagonists showed little effect. α-Fluoromethylhistidine, an histidine decarboxylase inhibitor, also inhibited active avoidance response. In radial maze performance, almost the same findings were obtained. I.c.v. injection of histamine and H1-agonists inhibited amygdaloid kindled seizures. First generation H1-antagonists attenuated histamine-induced inhibition of amygdaloid kindled seizures. Both i.c.v. and intraperitoneal injections of H3-antagonist, thioperamide, resulted in a dose-related inhibition of amygdaloid kindled seizures. The effect of thioperamide was inhibited by an H3-agonists and H1-antagonists. Similar to nitrazepam, diphenhydramine and chlorpheniramine caused a shortening of sleep latency. On the other hand, no significant effects were observed with second generation H1-antagonists. These findings suggest that histamine plays an important role in learning and memory via H1-receptors, an inhibition of amygdaloid kindled seizures induced by histamine occurred through not only H1-receptors but also H3-receptors, and that classic H1-antagonists can be useful as a effective hypnotic for difficulty in falling asleep.

Direct evidence that the brain reward system is involved in the control of scratching behaviors induced by acute and chronic itch.

In the present study, we demonstrated that there is a direct relationship between scratching behaviors induced by itch and functional changes in the brain reward system. Using a conditional place preference test, the rewarding effect was clearly evoked by scratching under both acute and chronic itch stimuli. The induction of ΔFosB, a member of the Fos family of transcription factors, was observed in dopamine transporter (DAT)-positive dopamine neurons in the ventral tegmental area (VTA) of mice suffering from a chronic itch sensation. Based on a cellular analysis of scratching-activated neurons, these neurons highly expressed tyrosine hydroxylase (TH) and DAT genes in the VTA. Furthermore, in an in vivo microdialysis study, the levels of extracellular dopamine in the nucleus accumbens (NAcc) were significantly increased by transient scratching behaviors. To specifically suppress the mesolimbic dopaminergic pathway using pharmacogenetics, we used the TH-cre/hM4Di mice. Pharmacogenetic suppression of mesolimbic dopaminergic neurons significantly decreased scratching behaviors. Under the itch condition with scratching behaviors restricted by an Elizabethan collar, the induction of ΔFosB was found mostly in corticotropin-releasing hormone (CRH)-containing neurons of the hypothalamic paraventricular nucleus (PVN). These findings suggest that repetitive abnormal scratching behaviors under acute and chronic itch stimuli may activate mesolimbic dopamine neurons along with pleasant emotions, while the restriction of such scratching behaviors may initially induce the activation of PVN-CRH neurons associated with stress.

Flare Size but Not Intensity Reflects Histamine-Induced Itch.

INTRODUCTION: Flare reactions arise due to the release of vasodilators from sensory nerves caused by antidromic transmission of action potentials after the induction of itch. OBJECTIVE: We investigated the link between flare and itch using 3 models of itch. METHODS: Skin provocations with histamine, capsaicin, and cowhage were performed in 31 subjects. Itch was quantified using the visual analog scale. Flare was assessed using laser speckle contrast imaging (LSCI) and digital photography. RESULTS: The duration, intensity, and area under the curve of histamine-induced itch correlated with the area of increased blood flow measured with LSCI (r = 0.545, p = 0.002; r = 0.575, p = 0.001; and r = 0.649, p < 0.001, respectively). Itch and skin blood flow in response to capsaicin or cowhage did not correlate. CONCLUSION: In histamine-induced skin inflammation, itch and increased blood flow are linked. Thus, the area of histamine-induced flare may be used as a surrogate marker for histamine-induced itch.

Involvement of the tuberomammillary nucleus of the hypothalamus in the modulation of nociception and joint edema in a model of monoarthritis.

AIMS: Investigate the involvement of the histaminergic projections from tuberomammillary nucleus (TMN) to the spinal cord in the modulation of nociception and peripheral edema in a model of monoarthritis. MAIN METHODS: Subacute monoarthritis was induced by an intraarticular injection of carrageenan followed by LPS 72 h later. Disability and joint edema were assessed at the 3rd hour after LPS and at every hour up to 6 h. KEY FINDINGS: Intrathecal administration of histamine potentiated joint incapacitation and edema, while the H1R antagonist cetirizine decreased both. The H3R agonist immepip decreased both incapacitation and edema, while the H3R antagonist thioperamide had the opposite effect. The microinjection of glutamate into the ventral TMN (vTMN) caused an increase of incapacitation and articular edema, whereas the blockade of this nucleus by cobalt chloride inhibited both parameters. Intrathecal administration of cetirizine prevented the increase of incapacitation and joint edema caused by glutamate microinjection into the vTMN. Similarly, an intrathecal injection of the NKCC1 cotransporter inhibitor bumetanide prevented the effects of glutamate microinjection into the vTMN, whereas coadministration of histamine with bumetanide only inhibited the potentiation of joint edema. A microinjection of orexin B into the vTMN potentiated incapacitation and joint edema, while coadministration of the OX1/2 receptor antagonist almorexant with orexin B did not. SIGNIFICANCE: These data support the notion that TMN participates in the modulation of a peripheral inflammatory process by means of histaminergic projections to the spinal cord, and the hypothalamus may trigger TMN activation by means of glutamate and orexin.

Histaminergic Control of Corticostriatal Synaptic Plasticity during Early Postnatal Development.

A reduction in the synthesis of the neuromodulator histamine has been associated with Tourette's syndrome and obsessive-compulsive disorder. Symptoms of these disorders are thought to arise from a dysfunction or aberrant development ofcorticostriatal circuits. Here, we investigated how histamine affects developing corticostriatal circuits, both acutely and longer-term, during the first postnatal weeks, using patch-clamp and field recordings in mouse brain slices (C57Bl/6, male and female). Immunohistochemistry for histamine-containing axons reveals striatal histaminergic innervation by the second postnatal week, and qRT-PCR shows transcripts for H1, H2, and H3 histamine receptors in striatum from the first postnatal week onwards, with pronounced developmental increases in H3 receptor expression. Whole-cell patch-clamp recordings of striatal spiny projection neurons and histamine superfusion demonstrates expression of functional histamine receptors from the first postnatal week onwards, with histamine having diverse effects on their electrical properties, including depolarization of the membrane potential while simultaneously decreasing action potential output. Striatal field recordings and electrical stimulation of corticostriatal afferents revealed that histamine, acting at H3 receptors, negatively modulates corticostriatal synaptic transmission from the first postnatal week onwards. Last, we investigated effects of histamine on longer-term changes at developing corticostriatal synapses and show that histamine facilitates NMDA receptor-dependent LTP via H3 receptors during the second postnatal week, but inhibits synaptic plasticity at later developmental stages. Together, these results show that histamine acutely modulates developing striatal neurons and synapses and controls longer-term changes in developing corticostriatal circuits, thus providing insight into the possible etiology underlying neurodevelopmental disorders resulting from histamine dysregulation.SIGNIFICANCE STATEMENT Monogenic causes of neurologic disorders, although rare, can provide opportunities to both study and understand the brain. For example, a nonsense mutation in the coding gene for the histamine-synthesizing enzyme has been associated with Tourette's syndrome and obsessive-compulsive disorder, and dysfunction of corticostriatal circuits. Nevertheless, the etiology of these neurodevelopmental disorders and histamine's role in the development of corticostriatal circuits have remained understudied. Here we show that histamine is an active neuromodulator during the earliest periods of postnatal life and acts at developing striatal neurons and synapses. Crucially, we show that histamine permits NMDA receptor-dependent corticostriatal synaptic plasticity during an early critical period of postnatal development, which suggests that genetic or environmental perturbations of histamine levels can impact striatal development.

Measurement of bronchial hyperreactivity: comparison of three Nordic dosimetric methods.

Clinical testing of bronchial hyperreactivity (BHR) provides valuable information in asthma diagnostics. Nevertheless, the test results depend to a great extent on the testing procedure: test substance, apparatus and protocol. In Nordic countries, three protocols predominate in the testing field: Per Malmberg, Nieminen and Sovijärvi methods. However, knowledge of their equivalence is limited. We aimed to find equivalent provocative doses (PD) to obtain similar bronchoconstrictive responses for the three protocols. We recruited 31 patients with suspected asthma and health care workers and performed BHR testing with methacholine according to Malmberg and Nieminen methods, and with histamine according to Sovijärvi. We obtained the individual response-dose slopes for each method and predicted equivalent PD values. Applying a mixed-model, we found significant differences in the mean (standard error of mean) response-dose (forced expiratory volume in one second (FEV1)%/mg): Sovijärvi 7.2 (1.5), Nieminen 13.8 (4.2) and Malmberg 26 (7.3). We found that the earlier reported cut-point values for moderate BHR and marked BHR between the Sovijärvi (PD15) and Nieminen (PD20) methods were similar, but with the Malmberg method a significant bronchoconstrictive reaction was measured with lower PD20 values. We obtained a relationship between slope values and PD (mg) between different methods, useful in epidemiological research and clinical practice.

Hippocalcin-like 4, a neural calcium sensor, has a limited contribution to pain and itch processing.

Calcium binding proteins are expressed throughout the central and peripheral nervous system and disruption of their activity has major consequences in a wide array of cellular processes, including transmission of nociceptive signals that are processed at the level of the spinal cord. We previously reported that the calcium binding protein, hippocalcin-like 4 (Hpcal4), is heavily expressed in interneurons of the superficial dorsal horn, and that its expression is significantly downregulated in a TR4 mutant mouse model that exhibits major pain and itch deficits due to loss of a subpopulation of excitatory interneurons. That finding suggested that Hpcal4 may be a contributor to the behavioral phenotype of the TR4 mutant mouse. To address this question, here we investigated the behavioral consequences of global deletion of Hpcal4 in a battery of acute and persistent pain and itch tests. Unexpectedly, with the exception of a mild reduction in acute baseline thermal responses, Hpcal4-deficient mice exhibit no major deficits in pain or itch responses, under normal conditions or in the setting of tissue or nerve injury. Taken together, our results indicate that the neural calcium sensor Hpcal4 likely makes a limited contribution to pain and itch processing.

Effect of diphenhydramine and cetirizine on immediate and late-phase cutaneous allergic reactions in healthy dogs: a randomized, double-blinded crossover study.

BACKGROUND: Currently, there is insufficient evidence to confirm oral diphenhydramine (DPH) efficacy to prevent mast cell degranulation and histamine release in dogs. HYPOTHESIS/OBJECTIVE: To determine and compare the effects oral of DPH and cetirizine on the immediate- and late-phase cutaneous allergic reactions in healthy dogs. ANIMALS: Twelve healthy laboratory beagle dogs. METHODS AND MATERIALS: The study was designed as a randomized, double-blinded crossover study in which each dog served as its own control; twice-daily oral DPH (2.2 mg/kg) or cetirizine (2 mg/kg) were given for six days with a two week washout period. Intradermal injections of histamine, compound 48/80 (positive control) and saline (negative control) were performed on the right thorax 10 days before drug administration (baseline), during oral antihistamine administration on Day 6 and 10 days after last medication dosage. Global wheal scores (GWS) at 20 min and late-phase reactions (LPR) at 6 h post-injection were evaluated by an investigator blinded to the drug and the interventions. RESULTS: Treatment with cetirizine significantly reduced histamine and compound 48/80 GWS and LPR compared to baseline; there was no significant difference for DPH. In all dogs, oral DPH and cetirizine reached plasma concentrations considered therapeutic in people. No adverse effect or behavioural changes were observed during the study. CONCLUSION AND CLINICAL SIGNIFICANCE: In conclusion, oral cetirizine was effective in preventing cutaneous allergic reactions without any obvious adverse effects in dogs. Oral DPH failed to show an inhibitory effect despite attaining plasma drug concentrations that are considered effective in people.

Quantification of Trigeminovascular Hypersensitivity Using Laser Speckle Contrast Analysis in a Patient With Chronic Migraine.

BACKGROUND: Activation of peripheral and/or central trigeminovascular pain pathways are implicated in the pathogenesis of migraine. Small fibers mediate pain, thermal sensation, and autonomic functions. Axon flare response is correlated with local C-fiber activation and calcitonin gene-related peptide release. Laser speckle contrast analysis (LASCA) detects very subtle microcirculatory changes that are not visible to the naked eye. CASE: Axon flare response was elicited by 0.01 mL intradermal (i.d.) histamine introduced to the left forehead, trigeminal nerve ophthalmic branch (V1) skin area. Skin microvascular blood flow data were recorded using a LASCA real-time microcirculation imaging system. In the healthy control, prick stimulus slightly elevated focal skin microcirculation only at the stimulated focal area. However, in our patient with chronic migraine, the unilateral prick stimulation transiently (over 10 to 12 seconds) increased ipsilateral skin microcirculation at all 3 branches of the trigeminal nerve, with a slight expansion across the midline. Left V1 stimulation by i.d. histamine induced not only prominent but also long-lasting (10 to 15 minutes of recording time) axon flare response at the ipsilateral V1, V2, and V3 areas, with an expansion to the contralateral V1 area and without any report of allodynia or hyperalgesia. The treatment decreased axon flare characteristics probably by inhibiting neurogenic inflammation. DISCUSSION: The clinical characteristics and individual response to treatment vary widely across patients with pain. Here, we demonstrated the presence of transient spread of increased microcirculation at the ipsilateral trigeminal nerve, and also across the midline after prick stimulus, whereas a more prominent, widespread, and long-lasting histamine-induced axon flare response occurred in a rare subclass of patient who had chronic migraine with autonomic symptoms. The modulatory effect of the pharmacological intervention has also been objectively quantified by LASCA.

A porcine model of ureteral contractile activity: Influences of age, tissue orientation, region, urothelium, COX and NO.

INTRODUCTION: We aimed to investigate factors contributing to ureteral responses and establish a reliable porcine model for studying ureteral contractility. METHODS: Isolated ureteral strips from young (6-month old) and older (3-year old) pigs were mounted in organ baths and subjected to phenylephrine, 5-HT, carbachol and histamine. Ureteral strips developed bursts of contractile activity which was measured as area under the curve (AUC) and frequency. Phenylephrine and 5-HT-induced responses of proximal and distal ureters were obtained, in the presence and absence of indomethacin (10 µM) and L-NNA (100 µM), and the influence of an intact mucosa was examined. RESULTS: Phenylephrine and 5-HT-induced contractile responses were greater than those to carbachol in the porcine ureter. In fact, responses to carbachol were only present in ureters from older animals. Ureters suspended longitudinally had increased phenylephrine-induced contractions compared to those suspended circularly (p < .05). A greater amount of tissue strips developed spontaneous contractions from the proximal region compared to distal (83% vs 25%). There was an increase in maximum phenylephrine-induced responses in the distal ureter when compared to the proximal ureter (p < .05). In the presence of indomethacin, only 5-HT-induced contractions in the young animals were depressed (p < .05) while L-NNA did not affect any ureteral responses. The intact mucosa significantly decreased contractile responses to phenylephrine and 5-HT in the porcine ureter. DISCUSSION: The complexity of ureteral contractions depicting bursts of phasic activity requires AUC assessment. Porcine ureteral contractile properties, such as regional differences, influence of mucosa and lack of response to carbachol, are similar to those reported in the literature for human ureter.

Histamine induces peripheral and central hypersensitivity to bladder distension via the histamine H1 receptor and TRPV1.

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a common chronic pelvic disorder with sensory symptoms of urinary urgency, frequency, and pain, indicating a key role for hypersensitivity of bladder-innervating sensory neurons. The inflammatory mast cell mediator histamine has long been implicated in IC/BPS, yet the direct interactions between histamine and bladder afferents remain unclear. In the present study, we show, using a mouse ex vivo bladder afferent preparation, that intravesical histamine enhanced the mechanosensitivity of subpopulations of afferents to bladder distension. Histamine also recruited "silent afferents" that were previously unresponsive to bladder distension. Furthermore, in vivo intravesical histamine enhanced activation of dorsal horn neurons within the lumbosacral spinal cord, indicating increased afferent signaling in the central nervous system. Quantitative RT-PCR revealed significant expression of histamine receptor subtypes (Hrh1-Hrh3) in mouse lumbosacral dorsal root ganglia (DRG), bladder detrusor smooth muscle, mucosa, and isolated urothelial cells. In DRG, Hrh1 was the most abundantly expressed. Acute histamine exposure evoked Ca2+ influx in select populations of DRG neurons but did not elicit calcium transients in isolated primary urothelial cells. Histamine-induced mechanical hypersensitivity ex vivo was abolished in the presence of the histamine H1 receptor antagonist pyrilamine and was not present in preparations from mice lacking transient receptor potential vanilloid 1 (TRPV1). Together, these results indicate that histamine enhances the sensitivity of bladder afferents to distension via interactions with histamine H1 receptor and TRPV1. This hypersensitivity translates to increased sensory input and activation in the spinal cord, which may underlie the symptoms of bladder hypersensitivity and pain experienced in IC/BPS.

IL-33 mediated amplification of allergic response in human mast cells.

Context: IL-33 is a pro-inflammatory cytokine that is involved in the development of chronic inflammatory diseases and the initiation of allergic inflammation in response to pathogens and acts an alarmin.Objective: Present study aims to explore the IL-33 mediated effects of histamine induced allergic inflammation in human mast cells.Materials and methods: In this study, cord blood derived CD34+ mast cells and HMC-1 cells were primed with IL-33 followed by the stimulation with histamine. We investigated the functional activation of mast cell by intracellular calcium release using calcium mobilization assay, release of granular content using degranulation assay, profiling of various inflammatory and regulatory cytokines as well as chemokines by Luminex Bioplex assay and its signaling mechanisms involved using western blot analysis.Results: In our study, we found that the IL-33 acts as a mediator in the allergic inflammation induced by the histamine. IL-33 potentiates the release of intracellular calcium and degranulation content in human mast cells. Also, it enhances the production of Th2, Th1 cytokines and chemokines and down-regulates the production of regulatory cytokine. Furthermore, it enhanced the phosphorylation of the signaling molecules such as ERK, Akt, and NFκB in activated mast cells. Therefore, IL-33 acts as a potent activator of mast cells and it can elicit inflammatory response synergistically with histamine.Conclusions: Taken together, IL-33 acts as a potent mediator by inducing the inflammatory response in activated mast cells, hence increasing their responsiveness to antigens and amplifying the allergic response.

Safety, pharmacokinetics and pharmacodynamics of a novel anti-asthmatic drug, XC8, in healthy probands.

INTRODUCTION: XC8 (histamine glutarimide) is a novel agent which targets eosinophilic migration and mast cell degranulation and has shown anti-asthmatic effects in animal studies. OBJECTIVE: The objective of this placebo-controlled phase 1 study was to assess the safety of oral XC8 and to evaluate its pharmacokinetic and pharmacodynamic properties. METHODS: 32 healthy volunteers in three dose-escalation treatment groups (10 mg [n = 8], 50 mg [n = 8] and 200 mg [n = 16]) were randomized in a 3:1 ratio to XC8 or placebo respectively. The subjects received a single dose of the drug at Day 1 and then once-daily for 14 days (Days 8-21). RESULTS: No severe adverse events occurred. The number of adverse events was similar in the treatment arms compared to placebo and all subjects completed the study as planned. No clinically significant changes occurred in hematologic and biochemical blood tests in subjects receiving XC8. The pharmacokinetic data showed similar dose and time dependent mean plasma XC8 concentrations after single (Day 1) and multiple (Day 21) dosing. The mean maximum concentrations were 114-1993 ng/mL after single and 115-2089 ng/mL after multiple dosing. The mean times to maximum concentration were 0.68-1.01 and 0.67-0.98 h, respectively. There was no evidence for accumulation of XC8 after multiple dosing. CONCLUSION: XC8 was safe and well tolerated. A phase 2 study is being performed to further evaluate the potential role of XC8 in asthma treatment. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02882217.