HMF causes anaphylactic symptoms by acting as a H1 receptor agonist.

5-Hydroxymethylfurfural (HMF) can readily form by acid-catalyzed transformations of various sugars such as fructose, sucrose and to a lesser degree glucose, and is known to widely exist in various sugar-containing consumer products. Thus the potential health effect of HMF has been a subject of intensive studies. There have been earlier reports of HMF's undesirable effects at or above high micromolar concentrations. In this study, HMF is found to stimulate the H1 receptor in vivo and in vitro. When assessed in cell culture and animal models, HMF was found to cause deformation of in cell culture studies of HUVECs at 50 µM, to increase the vascular permeability of paw skin at 1.0 mg/mL, and trigger symptoms of anaphylaxis in animal models at 32.5 µg/kg. At the molecular level, HMF was found to induce the release of NO and related cytokines, and trigger H1 receptor-mediated inflammatory responses. Mutation studies also suggest the binding sites for HMF on the H1 receptor. The findings described suggest the need for close monitoring of HMF contents in consumer products and their related side effects.

Different perception levels of histamine-induced itch sensation in young adult mice.

Itch is an unpleasant sensation that evokes behavioral responses such as scratching the skin. Interestingly, it is conceived that the perception of itch sensation is influenced by age. Indeed, accumulating evidence supports the idea that even children or younger adults show distinctive itch sensation depending on age. This evidence implies the presence of a mechanism that regulates the perception of itch sensation in an age-dependent fashion. Therefore, the purpose of the present study was to investigate a putative mechanism for the age-dependent perception of itch sensation by comparing histamine-induced scratching behaviors in 45-day old (D45) and 75-day old male "young adult" mice. The results indicated that, following histamine administration, the D75 mice spent a longer time scratching than D45 mice. However, the intensity of the calcium influx induced by histamine in primary culture of dorsal root ganglia (DRG) neurons was not different between D45 and D75 mice. Moreover, no apparent difference was observed in mRNA levels of a characteristic His-related receptor and ion channel. In contrast, the mRNA levels of Toll-Like Receptor 4 (TLR4) were increased approximately by two-fold in D75 DRG compared with D45 DRG. Additionally, D75-derived DRG neurons exhibited enhanced intracellular calcium increase by lipopolysaccharide (LPS, a TLR4 agonist) than those of D45 mice. Furthermore, intensities of calcium influx induced by histamine were significantly potentiated when co-treated with LPS in D75 DRG neurons, but not in those of D45 mice. Thus, it appears that D75 mice showed enhanced histamine-induced scratching behaviors not by increased expression levels of histamine-related genes, but probably due to augmented TLR4 expression in DRG neurons. Consequently, the current study found that different perception levels of histamine-induced itch sensation are present in different age groups of young adult mice.

A novel zebrafish-based model of nociception.

Chronic pain affects the lives of millions yearly, but few new treatments are available. Due to decreasing budgets and increasing costs of preclinical research, alternatives are sought with high translatability and low cost. Here we demonstrate the utility of a zebrafish-based model of nociception to serve as a novel screening tool for analgesic drugs. Zebrafish swimming behavior was measured following administration of various algogens including histamine, cinnamaldehyde, mustard oil, acetic acid and complete Freund's adjuvant. All compounds reduce distance traveled, thought to be an expression of nociception. Additionally, the suppression of swimming was attenuated by administration of the common analgesic, morphine. Together these data provide support for the use of zebrafish as a cost-effective and translatable model of nociception.

Histamine induces microglia activation and dopaminergic neuronal toxicity via H1 receptor activation.

BACKGROUND: Histamine is an amine widely known as a peripheral inflammatory mediator and as a neurotransmitter in the central nervous system. Recently, it has been suggested that histamine acts as an innate modulator of microglial activity. Herein, we aimed to disclose the role of histamine in microglial phagocytic activity and reactive oxygen species (ROS) production and to explore the consequences of histamine-induced neuroinflammation in dopaminergic (DA) neuronal survival. METHODS: The effect of histamine on phagocytosis was assessed both in vitro by using a murine N9 microglial cell line and primary microglial cell cultures and in vivo. Cells were exposed to IgG-opsonized latex beads or phosphatidylserine (PS) liposomes to evaluate Fcγ or PS receptor-mediated microglial phagocytosis, respectively. ROS production and protein levels of NADPH oxidases and Rac1 were assessed as a measure of oxidative stress. DA neuronal survival was evaluated in vivo by counting the number of tyrosine hydroxylase-positive neurons in the substantia nigra (SN) of mice. RESULTS: We found that histamine triggers microglial phagocytosis via histamine receptor 1 (H1R) activation and ROS production via H1R and H4R activation. By using apocynin, a broad NADPH oxidase (Nox) inhibitor, and Nox1 knockout mice, we found that the Nox1 signaling pathway is involved in both phagocytosis and ROS production induced by histamine in vitro. Interestingly, both apocynin and annexin V (used as inhibitor of PS-induced phagocytosis) fully abolished the DA neurotoxicity induced by the injection of histamine in the SN of adult mice in vivo. Blockade of H1R protected against histamine-induced Nox1 expression and death of DA neurons in vivo. CONCLUSIONS: Overall, our results highlight the relevance of histamine in the modulation of microglial activity that ultimately may interfere with neuronal survival in the context of Parkinson's disease (PD) and, eventually, other neurodegenerative diseases which are accompanied by microglia-induced neuroinflammation. Importantly, our results also open promising new perspectives for the therapeutic use of H1R antagonists to treat or ameliorate neurodegenerative processes.

Activity-dependent silencing reveals functionally distinct itch-generating sensory neurons.

The peripheral terminals of primary sensory neurons detect histamine and non-histamine itch-provoking ligands through molecularly distinct transduction mechanisms. It remains unclear, however, whether these distinct pruritogens activate the same or different afferent fibers. Using a strategy of reversibly silencing specific subsets of murine pruritogen-sensitive sensory axons by targeted delivery of a charged sodium-channel blocker, we found that functional blockade of histamine itch did not affect the itch evoked by chloroquine or SLIGRL-NH2, and vice versa. Notably, blocking itch-generating fibers did not reduce pain-associated behavior. However, silencing TRPV1(+) or TRPA1(+) neurons allowed allyl isothiocyanate or capsaicin, respectively, to evoke itch, implying that certain peripheral afferents may normally indirectly inhibit algogens from eliciting itch. These findings support the presence of functionally distinct sets of itch-generating neurons and suggest that targeted silencing of activated sensory fibers may represent a clinically useful anti-pruritic therapeutic approach for histaminergic and non-histaminergic pruritus.

Biochemical and histopathological evaluation of histamine receptors (H1R, H2R, H3R and H4R)-agonist in rabbits.

The present study was designed to investigate the biochemical and histopathological changes in the livers of rabbits treated with histamine and histamine receptors (H1R-H4R)-agonist. The cohort comprised of six groups containing five rabbits each. Control group received sterile distilled water (1 mL/kg × b.i.d.) and treated groups received subcutaneous histamine (100 µg/kg × b.i.d.) and H1R-H4R-agonist (histamine trifluoro-methyl toluidide, amthamine, R-[-]-α-methylhistamine, clobenpropit, respectively) each in a dose of 10 µg/kg × b.i.d. (12 h [8 am and 8 pm]) for 30 days. Hepatotoxicity due to these agonists was analyzed using biochemical and histopathological methods. Histamine and H1R-H3R-agonist were found to be hepatotoxic as shown by statistically significant (p < 0.05) elevated levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), most marked in the H3R-agonist group. However, their levels in H4R-agonist group remained very similar to the control group. The entire drug treated groups as compared to control showed significant elevated levels of alkaline phosphatase (ALP). Histopathological examination revealed obvious changes in histamine, H2R- and H3R-agonist groups in terms of alteration of hepatic microstructure, congestion, focal necrosis and increased incidence of multinucleate hepatocytes while H1R and H4R groups showed minimal changes. From the findings of the present study it may be concluded that on repeated administration, histamine and HR-agonists-induced hepatotoxicity which is most pronounced with H3R-agonist though not severe enough to jeopardize the vital functions of liver and warrants further long-term studies.

Overdose of the histamine H3 inverse agonist pitolisant increases thermal pain thresholds.

OBJECTIVE AND DESIGN: Pitolisant (BF2.649) is a selective inverse agonist for the histamine H(3) receptor and was developed for the treatment of excessive daytime sleepiness in Parkinson disease, narcolepsy, and schizophrenia. Since H(3)-ligands can decrease inflammatory pain, we tested Pitolisant in inflammatory and neuropathic pain models. MATERIALS AND TREATMENTS: Behavioral effects of pitolisant and the structural different H(3) receptor inverse agonists ciproxifan and ST-889 were tested in zymosan-induced inflammation and the spared nerve injury model for neuropathic pain. METHODS: Responses to mechanical and thermal stimuli were determined. Calcium imaging was performed with primary neuronal cultures of dorsal root ganglions. RESULTS: Clinically relevant doses of pitolisant (10 mg/kg) had no relevant effect on mechanical or thermal pain thresholds in all animal models. Higher doses (50 mg/kg) dramatically increased thermal but not mechanical pain thresholds. Neither ciproxifan nor ST-889 altered thermal pain thresholds. In peripheral sensory neurons high concentrations of pitolisant (30-500 µM), but not ciproxifan, partially inhibited calcium increases induced by capsaicin, a selective activator of transient receptor potential vanilloid receptor 1 (TRPV1). High doses of pitolisant induced a strong hypothermia. CONCLUSION: The data show a dramatic effect of high dosages of pitolisant on the thermosensory system, which appears to be H(3) receptor-independent.

Dose-dependent effect of histamine on liver function markers in immunized rabbits.

OBJECTIVE: The present study was designed to delineate the hepatotoxicological roles of histamine dose-dependently in immunized rabbits. METHODS: The cohort comprised of three groups (II, III and IV), containing 18 rabbits each, and received subcutaneous histamine 50 µg/kg, 100 µg/kg and 200 µg/kg, respectively for 10 days (b.i.d., starting from 3 days prior to immunization until 7 days after immunization). Group I (control, n=18) received subcutaneous sterile distilled water for 10 days. They were subsequently immunized at day 3 with intravenous injection of SRBC (1×10(9) cells/ml). Blood samples were collected on pre-immunization (pre-I) day 0, as well as on days 7-, 14-, 21-, 28- and 58-post-immunization (post-I). Biochemical parameters aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and bilirubin [total bilirubin (TB), direct bilirubin (DB) and indirect bilirubin (IB)] were determined. RESULTS: Groups II and IV revealed a significant decrease (on day 0-pre-I) and a significant increase (on days 7-, 14-, 21-, 28- and 58-post-I) in ALT and AST levels, when compared with the corresponding values of groups I and III while group II showed a significant increase in ALT and AST levels as compared to group IV. ALP levels in groups II, III and IV showed a significant enhancement when compared with group I. Moreover, results of TB, DB and IB demonstrated increased levels in group III when compared with groups I, II and IV. The results were found statistically significant (p<0.05). CONCLUSION: Short-term treatment of histamine produces dose-dependent differential patterns of hepatic dysfunctions suggestive mild liver degeneration warranting further long-term studies.

Role of histamine H(4) receptor in allergic conjunctivitis in mice.

We investigated the character of histamine H(1) receptor and H(4) receptor in allergic conjunctivitis. Histamine is the most important mediator in allergic conjunctivitis. We measured eye scratching behavior and allergic-like symptoms score, that is, hyperemia and edema in ICR mice, and examined which receptors intimately involved in allergic conjunctivitis. Histamine caused a dose-dependent eye scratching behavior and allergic-like symptoms. Histamine H(1) receptor antagonist (levocabastine) and H(4) receptor antagonist (JNJ7777120) inhibited eye scratching behavior and histamine H(1) receptor antagonist inhibited allergic-like symptoms induced by histamine. Additionally, combination of levocabastine and JNJ7777120 caused more potent inhibition in allergic conjunctivitis. On the other hand, both selective histamine H(1) receptor agonist (HTMT) and selective H(4) receptor agonist (4-methylhistamine) induced a dose-dependent eye scratching behavior and allergic-like symptoms. JNJ7777120 inhibited the effect of HTMT. However, levocabastine caused no inhibition on the response of 4-methylhistamine. H(4) receptor was closely related with allergic conjunctivitis. H(4) receptor antagonists may be effective in allergic conjunctivitis which showed no inhibition by histamine H(1) receptor antagonists.

Investigation of the pruritogenic effects of histamine, serotonin, tryptase, substance P and interleukin-2 in healthy dogs.

There are numerous studies of the pruritus-producing effects of histamine, serotonin, tryptase, substance P and interleukin-2 in humans and mice, but very little reported in dogs even though a common reason dogs are presented to veterinarians is pruritus. The aim of this study was to determine whether substances known to cause pruritus in humans also cause pruritus in dogs. Twenty-five clinically healthy research beagle dogs were included in the study. All dogs first received an intradermal injection of 0.05 mL saline as a control substance and were video-recorded for 20 min before and after the injection. Twenty-four hours later the dogs were randomly divided into five groups of five dogs each and randomly assigned to receive histamine, serotonin, tryptase, substance P or interleukin-2 injected intradermally each at the volume of 0.05 mL. On subsequent days, increasing concentrations of each substance were used. Before (baseline) and after the injection of each concentration of the substances, the dogs were video-recorded for 20 min. The frequency and character of pruritus episodes (scratching, licking, chewing, rubbing or rolling) were noted and these data were used for statistical analysis. The number of pruritus episodes was compared among baseline, saline and the different concentrations of each substance. The results showed that dogs did not have a significant increase in pruritic behaviour above baseline or saline after injection of any of the investigated substances (generalized linear model; P = 0.23).

Receptor-independent, vacuolar ATPase-mediated cellular uptake of histamine receptor-1 ligands: possible origin of pharmacological distortions and side effects.

The aims of this study were to investigate whether several histamine receptor agonists and antagonists are subjected to receptor-independent ion trapping into acidic organelles, and whether this sequestration influences their pharmacological or toxicological properties. Vacuolar (V)-ATPase-dependent intracellular sequestration of agonists was recognized as morphological alterations (large fluid-filled vacuoles for betahistine and 1-methylhistamine, granular uptake for fluorescent BODIPY FL histamine) prevented by the specific V-ATPase inhibitor bafilomycin A1 in rabbit vascular smooth muscle cells. Lipophilicity was the major determinant of these cellular effects (order of potency: BODIPY FL histamine>betahistine>1-methylhistamine>histamine) that occurred at high concentrations. This ranking was dissociable from the potency order for H(1) receptor-mediated contraction of the rabbit aorta, a response uninfluenced by bafilomycin. Antihistamines are inherently more lipophilic and caused vacuolization of a proportion of cells at 5-500 microM. Agonist or antagonist-induced vacuoles were of macroautophagic nature (labeled with GFP-conjugated LC3, Rab7 and CD63; detection of LC3 II). Further, the 2 most lipophilic antihistamines tested, astemizole and terfenadine, were potentiated by V-ATPase blockade in the aortic contractility assay (13- and 3.6-fold more potent, respectively, pA(2) scale), suggesting that V-ATPase-mediated cation trapping sequesters these antagonists from the vicinity of H(1) receptors in the therapeutic concentration range. This potentiation did not apply to less lipophilic antagonists (pyrilamine, diphenhydramine). While some agonists and all tested antagonists of the histamine H(1) receptors induce the V-ATPase-dependent vacuolar and autophagic cytopathology, sequestration affects the pharmacology of only the most lipophilic antagonists, the ones prone to off-target arrhythmogenic side effects.

Involvement of histamine H4 and H1 receptors in scratching induced by histamine receptor agonists in Balb C mice.

The role of histamine H(1), H(2), H(3) and H(4) receptors in acute itch induced by histamine was investigated in female BalbC mice. Scratching was induced by intradermal injections of pruritogen into the back of the neck and "itch" assessed by quantifying the scratching evoked. Histamine (0.03-80 micromol), histamine-trifluoromethyl-toluidine (HTMT, H(1) agonist, 0.002-2 micromol), clobenpropit (H(4) agonist, H(3) antagonist, 0.002-0.6 micromol) and to a lesser extent imetit (H(3)/H(4) agonist, 0.03-3 micromol) all induced dose-dependent scratching. Dimaprit (H(2) agonist, 0.04-40 micromol) did not cause scratching. Mepyramine (H(1) antagonist, 20 mg kg(-1), i.p.) reduced scratching evoked by histamine and HTMT, but not that caused by H(3) or H(4) agonists. Thioperamide (H(3)/H(4) antagonist, 20 mg kg(-1), i.p.) reduced scratching induced by histamine, H(3) and H(4) agonists, but not that caused by HTMT. The non-sedating H(1) antagonist, terfenadine, also significantly reduced the scratching induced by the H(1) agonist, HTMT. Cimetidine (H(2) antagonist, 20 mg kg(-1), i.p.) did not affect histamine-induced scratching. These results indicate that activation of histamine H(4) receptors causes itch in mice, in addition to the previously recognised role for H(1) receptors in evoking itch. Histamine H(4) receptor antagonists therefore merit investigation as antipruritic agents.

Aggravation of ischemic neuronal damage in the rat hippocampus by impairment of histaminergic neurotransmission.

Delayed damage to hippocampal CA1 pyramidal cells was observed in rats subjected to cerebral ischemia caused by 10 min of 4-vessel occlusion. Animals pretreated with alpha-fluoromethylhistidine, a suicide inhibitor of histidine decarboxylase, showed significantly more necrotic cells than did control animals. Mepyramine (H1-antagonist) and (R) alpha-methylhistamine (H3-agonist), but not zolantidine (H2-antagonist), significantly aggravated the delayed neuronal death. These results suggest that histaminergic neurons have a protective role, probably via H1-receptors, in the development of delayed neuronal death caused by cerebral ischemia.