Discovery of the novel and potent histamine H1 receptor antagonists for treatment of allergic diseases.

Desloratadine, a second-generation histamine H1 receptor antagonist, has established itself as a first-line drug for the treatment of allergic diseases. Despite its effectiveness, desloratadine exhibits an antagonistic effect on muscarinic M3 receptor, which can cause side effects such as dry mouth and urinary retention, ultimately limiting its clinical application. Herein, we describe the discovery of compound Ⅲ-4, a novel H1 receptor antagonist with significant H1 receptor antagonistic activity (IC50 = 24.12 nM) and enhanced selectivity towards peripheral H1 receptor. In particular, Ⅲ-4 exhibits reduced M3 receptor inhibitory potency (IC50 > 10,000 nM) and acceptable hERG inhibitory activity (17.6 ± 2.1 µM) compare with desloratadine. Additionally, Ⅲ-4 exhibits favorable pharmacokinetic properties, as well as in vivo efficacy and safety profiles. All of these reveal that Ⅲ-4 has potential to emerge as a novel H1 receptor antagonist for the treatment of allergic diseases. More importantly, the compound Ⅲ-4 (HY-078020) has recently been granted clinical approval.

Molecular mechanism of antihistamines recognition and regulation of the histamine H1 receptor.

Histamine receptors are a group of G protein-coupled receptors (GPCRs) that play important roles in various physiological and pathophysiological conditions. Antihistamines that target the histamine H1 receptor (H1R) have been widely used to relieve the symptoms of allergy and inflammation. Here, to uncover the details of the regulation of H1R by the known second-generation antihistamines, thereby providing clues for the rational design of newer antihistamines, we determine the cryo-EM structure of H1R in the apo form and bound to different antihistamines. In addition to the deep hydrophobic cavity, we identify a secondary ligand-binding site in H1R, which potentially may support the introduction of new derivative groups to generate newer antihistamines. Furthermore, these structures show that antihistamines exert inverse regulation by utilizing a shared phenyl group that inserts into the deep cavity and block the movement of the toggle switch residue W4286.48. Together, these results enrich our understanding of GPCR modulation and facilitate the structure-based design of novel antihistamines.

The Added-on of Ziziphus jujube Syrup in the Treatment of Chronic Spontaneous Urticaria Resistant to Standard-Dose of Secondary-generation H1 Antihistamine: A Double-Blind Randomized Clinical Trial.

Background: Although antihistamines are the first-line treatment for chronic spontaneous urticaria (CSU), 50% of patients don't respond to standard doses. In this study, the effectiveness of Ziziphus jujube fruit syrup in combination with antihistamines was assessed in patients with CSU. Methods: This double-blind randomized clinical trial was conducted in Shiraz between December 2019 and December 2020. 64 patients with CSU who had experienced hives for at least six weeks and did not respond to the usual treatments were enrolled in the study. They were randomly assigned to intervention and control groups using permuted block random allocation. For four weeks, the intervention group received 7.5 mL Ziziphus jujube syrup twice a day, while the control group received 7.5 mL simple jujube syrup twice a day. Both groups received cetirizine 10 mg every night. Urticaria activity score (UAS) and CU-Q2oL questionnaires were used to assess urticaria state and sleep quality before and after each week for four consecutive weeks. Data were analyzed using SPSS software version 18, and P<0.05 was considered statistically significant. Results: Before the intervention, there was no statistically significant difference between the two groups' mean of UAS (P=0.490) and sleep quality (P=0.423). During the follow-up, UAS in the intervention group was significantly lower (P=0.001). Moreover, this difference was significant on the day 28 (P=0.046). During the follow-up, the quality of sleep in both groups improved significantly, and this improvement was more significant in the intervention group. Conclusion: Ziziphus jujube syrup could be an effective adjuvant treatment for CSU.Trial Registration Number: IRCT20190304042916N1.

Acute Inhibition of the Human Kv1.5 Channel by H1 Receptor Antagonist Dimenhydrinate: Mode of Action.

Dimenhydrinate, an H1 receptor antagonist, is generally used for the prevention and treatment of nausea and vomiting. However, cardiac arrhythmias have been reported to be associated with the overdose of histamine H1 receptor antagonists, indicating the probable effect of antihistamines on ion channels. By using a two-microelectrode voltage clamp, we have herein studied the electrophysiological effects of dimenhydrinate on the human Kv1.5 channel in the Xenopus oocyte expression system. Dimenhydrinate acutely and reversibly suppressed the amplitudes of the peak and the steady-state current, within 6 min. The inhibitory effect of dimenhydrinate on the peak and the steady-state Kv1.5 currents increased progressively from -10 to +50 mV. At each test voltage, the drug suppressed both the peak and the steady-state currents to a similar extent. When the oocytes were stimulated at the rates of 5- and 30-s intervals, dimenhydrinate-induced a use-dependent blockade of the human Kv1.5 channel. Dimenhydrinate expedited the timecourse of the Kv1.5 channel activation more effectively than the timecourse of its inactivation. However, the activation and inactivation curves of the channel were not altered by the H1 receptor antagonist. In conclusion, we found that dimenhydrinate inhibits the human Kv1.5 channel by changing the channel's activation mode, thereby possibly increasing the possibility of triggering cardiac arrhythmias and affecting atrial fibrillation.

Novel H2S-Releasing Bifunctional Antihistamine Molecules with Improved Antipruritic and Reduced Sedative Actions.

Hydrogen sulfide (H2S) is an endogenous gasotransmitter with anti-inflammatory actions that also reduces itching. To test whether a combination of an antihistamine with a H2S donor has improved antipruritic efficacy, bifunctional molecules with antihistamine and H2S-releasing pharmacophores were synthesized and tested in vitro and in vivo. H2S release from the hybrid molecules was evaluated with the methylene blue and lead acetate methods, and H1-blocking activity was assessed by determining tissue factor expression inhibition. All new compounds released H2S in a dose-dependent manner and retained histamine blocking activity. Two compounds with the highest potency were evaluated in vivo for their antipruritic as well as sedative action; they proved to possess higher efficacy in inhibiting histamine-induced pruritus and decreased sedative effects compared to the parent compounds (hydroxyzine and cetirizine), suggesting that they exhibit superior antipruritic action and limited side effects that likely arise from the H2S-releasing moiety.

Exploring the interactions of antihistamine with retinoic acid receptor beta (RARB) by molecular dynamics simulations and genome-wide meta-analysis.

Kaposi sarcoma (KS) is one of the most common AIDS-related malignant neoplasms, which can leave lesions on the skin among HIV patients. These lesions can be treated with 9-cis-retinoic acid (9-cis-RA), an endogenous ligand of retinoic acid receptors that has been FDA-approved for treatment of KS. However, topical application of 9-cis-RA can induce several unpleasant side effects, like headache, hyperlipidemia, and nausea. Hence, alternative therapeutics with less side effects are desirable. There are case reports associating over-the-counter antihistamine usage with regression of KS. Antihistamines competitively bind to H1 receptor and block the action of histamine, best known for being released in response to allergens. Furthermore, there are already dozens of antihistamines that are FDA-approved with less side effects than 9-cis-RA. This led our team to conduct a series of in-silico assays to determine whether antihistamines can activate retinoic acid receptors. First, we utilized high-throughput virtual screening and molecular dynamics simulations to model high-affinity interactions between antihistamines and retinoic acid receptor beta (RARß). We then performed systems genetics analysis to identify a genetic association between H1 receptor itself and molecular pathways involved in KS. Together, these findings advocate for exploration of antihistamines against KS, starting with our two promising hit compounds, bepotastine and hydroxyzine, for experimental validation study in the future.

P19-derived neuronal cells express H1, H2, and H3 histamine receptors: a biopharmaceutical approach to evaluate antihistamine agents.

Histamine is a biogenic amine implicated in various biological and pathological processes. Convenient cellular models are needed to screen and develop new antihistamine agents. This report aimed to characterize the response of neurons differentiated from mouse P19 embryonal carcinoma cells to histamine treatment, and to investigate the modulation of this response by antihistamine drugs, vegetal diamine oxidase, and catalase. The exposure of P19 neurons to histamine reduced cell viability to 65% maximally. This effect involves specific histamine receptors, since it was prevented by treatment with desloratadine and cimetidine, respectively, H1 and H2 antagonists, but not by the H3 antagonist ciproxifan. RT-PCR analysis showed that P19 neurons express H1 and H2 receptors, and the H3 receptor, although it seemed not involved in the histamine effect on these cells. The H4 receptor was not expressed. H1 and H2 antagonists as well as vegetal diamine oxidase diminished the intracellular Ca2+ mobilization triggered by histamine. The treatment with vegetal diamine oxidase or catalase protected against mortality and a significant reduction of H2O2 level, generated from the cells under the histamine action, was found upon treatments with desloratadine, cimetidine, vegetal diamine oxidase, or catalase. Overall, the results indicate the expression of functional histamine receptors and open the possibility of using P19 neurons as model system to study the roles of histamine and related drugs in neuronal pathogenesis. This model is less expensive to operate and can be easily implemented by current laboratories of analysis and by Contract Research Organizations.

Anti-chlamydial effects of azelastine hydrochloride and the impact of the histamine H1 receptor on chlamydial development.

Introduction. Azelastine hydrochloride, a second-generation histamine H1 receptor (H1R) antagonist, exhibits anti-chlamydial effects against Chlamydia trachomatis (CT) in HeLa cells (genital infection model).Hypothesis/Gap Statement. Non-antibiotic pharmaceutical interactions with CT are an understudied field and the anti-chlamydial effects of azelastine are a potential interaction requiring further elucidation.Aim. To explore the underlying anti-chlamydial mechanisms of azelastine.Methodology. We assessed the specificity of azelastine for the chlamydial species and host cell type, the timing of azelastine application and whether the anti-chlamydial effects could be reproduced with different H1R-modulating compounds.Results. We observed similar anti-chlamydial azelastine effects for Chlamydia muridarum as well as for an ocular CT strain in human conjunctival epithelial cells (ocular infection model). Pre-incubating host cells with azelastine before infection mildly reduced chlamydial inclusion numbers and infectivity. Incubation of cells with azelastine initiated concomitantly with the chlamydial infection, or initiated several hours post-infection, reduced inclusion size, number and infectivity, and altered chlamydial morphology. These effects were strongest when azelastine was added shortly after or with the infection. Azelastine effects were not alleviated by increased concentrations of culture medium nutrients. Additionally, we did not observe anti-chlamydial effects when incubating cultures either with a different H1R antagonist or agonist, indicating that azelastine effects are probably H1R-independent.Conclusion. Accordingly, we conclude that azelastine anti-chlamydial effects are not restricted to a specific chlamydial species, strain or culture model, and are probably not mediated by H1R antagonism. Thus, it appears likely that off-target mechanisms of azelastine may explain our observations.

Effects of histamine and antihistamine on the hard tick Haemaphysalis longicornis during blood sucking.

At the time of host attachment, ticks are very sensitive to histamine, but during rapid blood sucking they paradoxically require histamine. Using a rabbit model, we studied the effects of histamine and antihistamine during attachment and fast-feeding in different life stages of Haemaphysalis longicorns. We examined how they responded to histamine and antihistamine by analyzing the detachment rate, histology of feeding lesions, and post-feeding behavior. A significant difference (P<0.01) was found in the detachment rate between experimental and control treatments throughout the observation period. Ticks exhibited a higher detachment rate (30.1%) at 12 h after histamine application during attachment time and on antihistamine-treated skin (25.4%) at 96 h during fast-feeding. After feeding on histamine-treated rabbits, the fully engorged body weights of larvae and nymphs were 0.7±0.36 mg and 3.5±0.65 mg, respectively. An average increase in body weight of 0.6±0.05 mg and 3.2±0.30 mg was observed for larvae and nymphs compared to the respective control weights. Nymphs and adults engorged after antihistamine treatment had an average body weight of 1.3±0.54 mg and 54±0.81 mg, respectively. An average decrease in body weight was observed in antihistamine-treated H. longicornis compared with control nymphs (3.3±0.42 mg) and adults (174±1.78 mg). Skin biopsies were collected after treatment, and differential histopathological characteristics were found between the treatment and control groups. Tick-infested skin collected from rabbits in the antihistamine-treated group lacked erythrocytes in the feeding pool, indicating that antihistamine impaired tick fast-feeding stage.

Histamine H1 receptor antagonist attenuates catecholamine surge and organ injury after severe burns.

Severe burns induce a catecholamine surge, causing severe damage to the organism and raising the possibility of multisystem organ failure. Few strategies are generally acceptable to reduce catecholamine surge and organ injury post-burn. We have previously shown that histamine can amplify the catecholamine surge. In addition, promethazine, a first-generation histamine H1 receptor antagonist, alleviates catecholamine surge and organ injury after severe burns in rats. However, evidence is lacking on whether promethazine benefits patients after severe burns. Currently, sedation and analgesia (such as midazolam and fentanyl) are commonly required for patients after severe burns. It remains unclear if patients after severe burns derive clinical benefit from histamine H1 receptor antagonists combined with sedation and analgesia. This study investigates the therapeutic effect of promethazine on patients after severe burns. Moreover, we test the therapeutic effect of cetirizine, a second-generation histamine H1 receptor antagonist, combined with sedation and analgesia in rats after severe burns. We find that promethazine-pethidine treatment shows a tendency for a lower level of total bilirubin than midazolam-fentanyl in patients 7-day after severe burn. Our study confirms that cetirizine combined with midazolam and fentanyl reduces catecholamine surge and liver and lung damage after severe burns in rats; the effects are better than midazolam and fentanyl treatment. In summary, for the first time, we suggest that histamine H1 receptor antagonist has the potential clinical value of reducing liver injury in patients after severe burns. In addition, we reveal that cetirizine combined with midazolam and fentanyl may be an ideal strategy for treating severe burns.

Ebastine exerts antitumor activity and induces autophagy by activating AMPK/ULK1 signaling in an IPMK-dependent manner in osteosarcoma.

Numerous studies have confirmed that in addition to interfering with the tumor inflammatory environment, anti-inflammatory agents can directly increase apoptosis and sensitivity to conventional therapies and decrease invasion and metastasis, making them useful candidates for cancer therapy. Here, we first used high-throughput screening and had screened one compound candidate, ebastine (a H1-histamine receptor antagonist), for osteosarcoma therapy. Cell viability assays, colony formation assays, wound healing assays, and Transwell assays demonstrated that ebastine elicited antitumor effects in osteosarcoma cells. In addition, ebastine treatment exerted obvious effects on cell cycle arrest, metastasis inhibition, apoptosis and autophagy induction both in vitro and in vivo. Mechanistically, we observed that ebastine treatment triggered proapoptotic autophagy by activating AMPK/ULK1 signaling in osteosarcoma cells. Treatment with the AMPK inhibitor dorsomorphin reversed ebastine-induced apoptosis and autophagy. More importantly, we found that IPMK interacted with AMPK and functioned as a positive regulator of AMPK protein in osteosarcoma cells. A rescue study showed that the induction of autophagy and activation of the AMPK/ULK1 signaling pathway by ebastine treatment were reversed by IPMK knockdown, indicating that the activity of ebastine was IPMK dependent. We provide experimental evidence demonstrating that ebastine has antitumor activity in osteosarcoma and promotes autophagy by activating the AMPK/ULK1 signaling pathway, which is IPMK dependent. Our results provide insight into the clinical application potential of ebastine, which may represent a new potential therapeutic candidate for the treatment of osteosarcoma.

Re-evaluation of over-the-counter histamine H1-receptor antagonists based on their effects on murine models of allergen-induced nasal hyperresponsiveness.

T cells play an essential role in the development of allergen-induced nasal hyperresponsiveness (NHR), a pathophysiological response in allergic rhinitis. The effects of histamine H1-receptor antagonists (antihistamines) on murine NHR models were investigated. Intragastric epinastine, fexofenadine, and loratadine administration suppressed allergen-induced immediate nasal response but not NHR in immunized mice. Regardless of the alleviation of stimulation-induced Th2 cytokine expression by loratadine and desloratadine in vitro, allergen-induced NHR and nasal eosinophil infiltration in Th2 cell-transferred mice were unaffected by loratadine in vivo. This influence on T cell-mediated NHR was excluded from the pharmacological effects of antihistamines.

Histamine induced high mobility group box-1 release from vascular endothelial cells through H1 receptor.

Background: Systemic allergic reaction is characterized by vasodilation and vascular leakage, which causes a rapid, precipitous and sustained decrease in arterial blood pressure with a concomitant decrease of cardiac output. Histamine is a major mediator released by mast cells in allergic inflammation and response. It causes a cascade of inflammation and strongly increases vascular permeability within minutes through its four G-protein-coupled receptors (GPCRs) on endothelial cells. High mobility group box-1 (HMGB1), a nonhistone chromatin-binding nuclear protein, can be actively secreted into the extracellular space by endothelial cells. HMGB1 has been reported to exert pro-inflammatory effects on endothelial cells and to increase vascular endothelial permeability. However, the relationship between histamine and HMGB1-mediated signaling in vascular endothelial cells and the role of HMGB1 in anaphylactic-induced hypotension have never been studied. Methods and results: EA.hy 926 cells were treated with different concentrations of histamine for the indicated periods. The results showed that histamine induced HMGB1 translocation and release from the endothelial cells in a concentration- and time-dependent manner. These effects of histamine were concentration-dependently inhibited by d-chlorpheniramine, a specific H1 receptor antagonist, but not by H2 or H3/4 receptor antagonists. Moreover, an H1-specific agonist, 2-pyridylethylamine, mimicked the effects of histamine, whereas an H2-receptor agonist, 4-methylhistamine, did not. Adrenaline and noradrenaline, which are commonly used in the clinical treatment of anaphylactic shock, also inhibited the histamine-induced HMGB1 translocation in endothelial cells. We therefore established a rat model of allergic shock by i.v. injection of compound 48/80, a potent histamine-releasing agent. The plasma HMGB1 levels in compound 48/80-injected rats were higher than those in controls. Moreover, the treatment with anti-HMGB1 antibody successfully facilitated the recovery from compound 48/80-induced hypotension. Conclusion: Histamine induces HMGB1 release from vascular endothelial cells solely through H1 receptor stimulation. Anti-HMGB1 therapy may provide a novel treatment for life-threatening systemic anaphylaxis.

Disruption of histamine/H1R-STAT3-SLC7A11 axis exacerbates doxorubicin-induced cardiac ferroptosis.

Doxorubicin (DOX) is widely used in the treatment of various cancers, increasing the great risk of adverse cardiovascular events, while the clinical intervention effect is not ideal. Histamine has been documented to participate in pathophysiological processes of cardiovascular diseases and inflammation-associated carcinogenesis. However, the potential roles of histamine in antitumor-related cardiotoxicity have not been fully elucidated. In this study, cardiomyocytes (hiPSC-CMs, HL-1 cells) and mice were treated with DOX to establish DOX-induced cardiotoxicity (DIC) models. Histidine decarboxylase knockout mice (HDC-/-) mice and histamine 1 receptor (H1R) antagonist were used to explore the effect of histamine/H1R signaling on DIC. Our results demonstrated that histamine deficiency or pharmaceutical inhibition of H1R accelerated myocardial ferroptosis, which is responsible for the aggravated DIC both in vivo and in vitro, while the supplementation of exogenous histamine reversed these changes. Our data revealed that the dysfunction of histamine/H1R signaling repressed the activation of transducer and activator of transcription 3 (STAT3), accompanying with decreased expression of solute carrier family7member11 (SLC7A11), a major modulator of ferroptosis. Conclusively, the disruption of histamine/H1R axis triggered ferroptosis and exacerbated DIC possibly by modulating STAT3-SLC7A11 pathway. Our findings point to a potential therapeutic target for DIC and provide more consideration on the usage of antihistamine drugs.

Plasma-Derived Exosomes in Chronic Spontaneous Urticaria Induce the Production of Mediators by Human Mast Cells.

Mast cell activation and inflammatory mediators play central roles in the pathogenesis of chronic spontaneous urticaria (CSU). The factors that induce mast cell activation in CSU are still largely unknown. Exosomes (EXs) are extracellular vesicles that activate mast cells. In this study, we enriched the EXs derived from the plasma of healthy volunteers and that of patients with CSU without antihistamine sensitivity (i.e., CSU-derived EXs with antihistamine sensitivity) or resistance (i.e., CSU-derived EXs with antihistamine resistance) using ultracentrifugation. We then incubated these EXs with HMC-1 human mast cells. Notably, CSU-derived EXs with antihistamine sensitivity and CSU-derived EXs with antihistamine resistance increased tryptase-1 expression; histamine production; inflammatory mediator production; and toll-like receptor (TLR) 2, TLR4, and phosphorylated MAPK levels in HMC-1 cells. These effects were more significant in the group with CSU-derived EXs with antihistamine resistance than in the group with CSU-derived EXs with antihistamine sensitivity. TLR2, TLR4, and MAPK inhibitors (CC-401, TAK-715, and SCH772984, respectively) reduced CSU-derived EXs-Stimulated production of inflammatory mediators in HMC-1 cells. Overall, EXs in the plasma of patients with CSU were found to activate mast cells and elicit the production of multiple inflammatory mediators, partly through the TLR2, TLR4, and MAPK pathways. In addition, CSU-derived EXs with antihistamine resistance had more powerful mast cell‒activating and histamine-release abilities. Thus, these EXs may be involved in the pathogenesis of CSU with antihistamine resistance.

Brain Mast Cells in Sleep and Behavioral Regulation.

The function of mast cells in the brain for the mediation of neurobehavior is largely unknown. Mast cells are a heterogeneous population of granulocytic cells in the immune system. Mast cells contain numerous mediators, such as histamine, serotonin, cytokines, chemokines, and lipid-derived factors. Mast cells localize not only in the periphery but are also resident in the brain of mammalians. Mast cells in the brain are constitutively active, releasing their contents gradually or rapidly by anaphylactic degranulation. Their activity is also increased by a wide range of stimuli including both immune and non-immune signals. Brain mast cell neuromodulation may thus be involved in various neurobehavior in health and diseases.Using Kit mutant mast cell deficient mice (KitW/KitW-v), we obtained results indicating that brain mast cells regulate sleep/wake and other behavioral phenotypes and that histamine from brain mast cells promotes wakefulness. These findings were also confirmed using a newer inducible and Kit-independent mast cell deficient Mas-TRECK (toxin receptor knockout) mouse. Injections of diphtheria toxin (DT) selectively deplete mast cells and reduce wakefulness during the periods of mast cell depletion.We recently introduced a mouse model for chronic sleep loss associated with diabetes. The mice reared on the wire net for 3 weeks (i.e., mild stress [MS]) showed decreased amount of non-rapid eye movement (NREM) sleep, increased sleep fragmentation, and abnormal glucose tolerance test [GTT] and insulin tolerance test [ITT], phenotypes which mirror human chronic insomnia. Interestingly, these mice with insomnia showed an increased number of mast cells in both the brain and adipose tissue. Mast cell deficient mice (KitW/KitW-v) and inhibition of mast cell functions with cromolyn or a histamine H1 receptor antagonist administration ameliorated both insomnia and abnormal glycometabolism. Mast cells may therefore represent an important pathophysiological mediator in sleep impairments and abnormal glycometabolism associated with chronic insomnia.

Histamine receptors rapidly desensitize without altering nerve-evoked contractions in murine urinary bladder smooth muscle.

Histamine has been implicated in urinary bladder dysfunction as an inflammatory mediator driving sensory nerve hypersensitivity. However, the direct influence of histamine on smooth muscle has not been thoroughly investigated. We hypothesized that histamine directly contracts urinary bladder smooth muscle (UBSM) independent of effects on nerves. Single cell quantitative RT-PCR determined that only histamine H1 and H2 receptors were expressed on UBSM cells. In isolated tissue bath experiments, histamine (200 µM) caused a highly variable and rapidly desensitizing contraction that was completely abolished by the H1 receptor antagonist fexofenadine (5 µM) and the Gq/11 inhibitor YM254890 (1 µM). Neither the muscarinic receptor antagonist atropine (1 µM), the Na+ channel blocker tetrodotoxin (1 µM), nor the transient receptor potential vanilloid type 1 antagonist capsazepine (10 µM) altered responses to histamine, suggesting that nerve activation was not involved. UBSM desensitization to histamine was not due to receptor internalization, as neither the cholesterol-depleting agent methyl-ß-cyclodextrin (10 mM), the dynamin-mediated endocytosis inhibitor dynasore (100 µM), nor the clathrin-mediated endocytosis inhibitor pitstop2 (15 µM) augmented or prolonged histamine contractions. Buffer from desensitized tissues still contracted histamine-naïve tissues, revealing that histamine was not metabolized. Prolonged exposure to histamine also had no effect on contractions due to electrical field stimulation, suggesting that both efferent nerve and UBSM excitability were unchanged. Together, these data suggest that histamine, although able to transiently contract UBSM, does not have a lasting effect on UBSM excitability or responses to efferent nerve input. Thus, any acute effects of histamine directly on UBSM contractility are unlikely to alter urinary bladder function.NEW & NOTEWORTHY Histamine is commonly associated with inflammatory bladder pathologies. We sought to investigate the role of histamine on urinary bladder contractility. Histamine contracts the bladder, but this response is highly variable and desensitizes completely in minutes. This desensitization is not due to internalization of the receptor or metabolism of histamine. Because nerve-evoked contractions are also not increased in the presence of histamine, our findings suggest that histamine is not directly acting to change contractility.

Carbopol emulgel loaded with ebastine for urticaria: development, characterization, in vitro and in vivo evaluation.

Urticaria affects all age groups of a population. It is triggered by allergens in foods, insect bites, medications, and environmental conditions. Urticaria is characterized by itching, a burning sensation, wheals and flares, erythema, and localized edema. The aim of this study was to develop a polymeric dosage form of ebastine using Carbopol 940 and mixture of span and tween. The emulsion was prepared, the gelling agent was added and the desired emulgel loaded with active drug was formulated. The formulations were subjected to physical stability, pH, viscosity, spreadability, drug content analysis, thermal analysis, in vitro drug release, and in vivo anti-allergic activity in animal model. The formulated emulgel exhibited good physical stability. The pH of the formulation was in the range of 5.2 ± 0.17 to 5.5 ± 0.20 which is suitable for topical application. Insignificant changes (p > .05) were observed in viscosity and spreadability of stored emulgels. The drug content was in the official limit of Pharmacopeia (i.e. 100 ± 10%). DSC measurements predicted that there is no interaction between the active moiety and excipients in emulgel formulation. The optimized formulation (ES3) released 74.25 ± 1.8% of ebastine after 12 h. The ebastine emulgel showed significant (p < .05; ANOVA) in vivo anti-allergic activity as compared to commercial product Benadryl® in histamine-induced allergy in rabbits. This study concluded that a topical drug delivery of ebastine-loaded emulgel could be well tolerated and safe for the treatment of urticaria/hives.

Histamine as an Alert Signal in the Brain.

Sleep-wake behavior is a well-studied physiology in central histamine studies. Classical histamine H1 receptor antagonists, such as diphenhydramine and chlorpheniramine, promote sleep in animals and humans. Further, neuronal histamine release shows a clear circadian rhythm in parallel with wake behavior. However, the early stages of histamine-associated knockout mouse studies showed relatively small defects in normal sleep-wake control. To reassess the role of histamine in behavioral state control, this review summarizes the progress in sleep-wake studies of histamine-associated genetic mouse models and discusses the significance of histamine for characteristic aspects of wake behavior. Based on analysis of recent mouse models, we propose that neuronal histamine may serve as an alert signal in the brain, when high attention or a strong wake-drive is needed, such as during exploration, self-defense, learning, or to counteract hypersomnolent diseases. Enhanced histaminergic neurotransmission may help performance or sense of signals concerning internal or environmental dangers, like peripheral histamine from mast cells in response to allergic stimuli and inflammatory signals.

Application of capillary zone electrophoresis to determine second-generation H1 antihistaminic drugs, loratadine and rupatadine

Abstract The second generation of H1 antihistamines from the piperidine group are often used for treating allergic diseases due to their action on histaminic receptors, the primary mediator of allergy. Moreover, the antihistamines have anti-inflammatory action, mediated through platelet-activating factor blocking activity. A simple and rapid capillary zone electrophoresis method was developed and validated for the determination of loratadine (LOR) and rupatadine (RUP) in tablets. The analyses were carried out using a fused silica capillary of 50.2 cm (40 cm effective length), 75 µm i.d. The background electrolyte was composed of boric acid 35 mmol/L, pH 2.5. Voltage of 20 kV, hydrodynamic injection of 3447.3 Pa for 3s, temperature at 25 ºC, and UV detection at 205 nm were applied. Electrophoretic separation was achieved at 1.8 and 2.8 min for RUP and LOR, respectively. The method was linear for both drugs in a range of 50.0 to 400.0 µg/mL (r>0.99). The limits of detection and quantification were 46.37 and 140.52 µg/mL, for LOR and 29.60 and 89.69 µg/mL for RUP respectively. The precision was less than 5.0 % for both drugs. The average recovery was approximately 100 %. The proposed novel method can significantly contribute to the rapid detection of counterfeit products and in quality control of drug products containing antihistamines