Polymorphisms and genetic linkage of histamine receptors

Histamine receptors in heart failure

The biogenic amine, histamine, is found predominantly in mast cells, as well as specific histaminergic neurons. Histamine exerts its many and varied actions via four G-protein-coupled receptors numbered one through four. Histamine has multiple effects on cardiac physiology, mainly via the histamine 1 and 2 receptors, which on a simplified level have opposing effects on heart rate, force of contraction, and coronary vasculature function. In heart failure, the actions of the histamine receptors are complex, the histamine 1 receptor appears to have detrimental actions predominantly in the coronary vasculature, while the histamine 2 receptor mediates adverse effects on cardiac remodeling via actions on cardiomyocytes, fibroblasts, and even endothelial cells. Conversely, there is growing evidence that the histamine 3 receptor exerts protective actions when activated. Little is known about the histamine 4 receptor in heart failure. Targeting histamine receptors as a therapeutic approach for heart failure is an important area of investigation given the over-the-counter access to many compounds targeting these receptors, and thus the relatively straight forward possibility of drug repurposing. In this review, we briefly describe histamine receptor signaling and the actions of each histamine receptor in normal cardiac physiology, before describing in more detail the known role of each histamine receptor in adverse cardiac remodeling and heart failure. This includes information from both clinical studies and experimental animal models. It is the goal of this review article to bring more focus to the possibility of targeting histamine receptors as therapy for heart failure.

Label-Free Investigations on the G Protein Dependent Signaling Pathways of Histamine Receptors

G protein activation represents an early key event in the complex GPCR signal transduction process and is usually studied by label-dependent methods targeting specific molecular events. However, the constrained environment of such "invasive" techniques could interfere with biological processes. Although histamine receptors (HRs) represent (evolving) drug targets, their signal transduction is not fully understood. To address this issue, we established a non-invasive dynamic mass redistribution (DMR) assay for the human H1-4Rs expressed in HEK cells, showing excellent signal-to-background ratios above 100 for histamine (HIS) and higher than 24 for inverse agonists with pEC50 values consistent with literature. Taking advantage of the integrative nature of the DMR assay, the involvement of endogenous Gαq/11, Gαs, Gα12/13 and Gβγ proteins was explored, pursuing a two-pronged approach, namely that of classical pharmacology (G protein modulators) and that of molecular biology (Gα knock-out HEK cells). We showed that signal transduction of hH1-4Rs occurred mainly, but not exclusively, via their canonical Gα proteins. For example, in addition to Gαi/o, the Gαq/11 protein was proven to contribute to the DMR response of hH3,4Rs. Moreover, the Gα12/13 was identified to be involved in the hH2R mediated signaling pathway. These results are considered as a basis for future investigations on the (patho)physiological role and the pharmacological potential of H1-4Rs.

Histamine H3 receptor gene variants associated with drug abuse in patients with cocaine use disorder

BACKGROUND

Preclinical work revealed significant interactions between ligands of the histamine H₃ receptor and different drugs of abuse. In the case of psychostimulants, the results reported are somewhat controversial and human data are still scarce, despite the fact that an inverse agonist of the H₃ receptor (pitolisant) has reached the market after approval for the treatment of narcolepsy.

AIMS

We have studied associations between histamine H₃ receptor gene variants and cocaine use disorder to increase the knowledge of the possible involvement of histamine H₃ receptor in drug abuse.

METHODS

Seven single nucleotide polymorphisms of the histamine H3 receptor gene were genotyped by using a multiplexing assay in 248 samples of subjects with cocaine use disorder and 500 randomized samples of subjects representative of the Spanish population.

RESULTS

The study of the epidemiological information associated to the samples revealed that subjects with cocaine use disorder broadly abused alcohol, tobacco and cannabinoids. Two single nucleotide polymorphisms (rs3787430 and rs74627870) were found significantly associated with the occurrence of addiction and one more (rs13042865) was specifically related to the severity of cocaine dependence within drug abusers.

CONCLUSIONS

The associations found in this study further extend the hypothesis that histamine H₃ receptor function could be relevant in drug abuse in general and cocaine addiction in particular.

The role of the histamine H4 receptor in atopic dermatitis and psoriasis

Atopic dermatitis (AD) and psoriasis are common skin diseases with a high negative impact on patients' quality of life. Both diseases are mediated by a pro-inflammatory infiltrate consisting of several cell types, such as T-cells, antigen-presenting cells and granulocytes and display disturbed keratinocyte differentiation. Given the fact that histamine levels are also highly elevated in inflamed skin, it is likely that histamine plays a relevant role in disease pathology. However, antagonists blocking histamine H1 receptor or H2 receptors are largely ineffective in reducing chronic symptoms in AD and psoriasis. Over the last years, much research has been undertaken to shed light into the mode of action of the most recently discovered histamine H4 receptor. This research has shown that H4 receptor antagonists display antipruritic and anti-inflammatory effects not only in mouse models but also in first human clinical trials, and therefore, H4 receptors might present a novel therapeutic target. In this review, we summarize the effects of the H4 receptors on different cell types, mouse models and clinical studies in regard to AD and psoriasis respectively. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

pH-induced conformational changes in histamine in the solid state

Histamine is one of the most basic biogenic amino-compounds, which is composed of imidazole and a flexible ethylamine side chain moiety. Histamine is known to take the form of various types of cations, free base, monocation and dication form, where its conformational change is highly sensitively to the pH conditions. The details of these changes are still controversial due to a lack of detailed information on its crystal structures. Thus, in this study, the molecular packing structures of histidine at various pH were analyzed via X-ray diffraction in combination with vibrational spectroscopy and energy calculations. A variety of molecular conformations including the tautomeric phenomenon was found to be intimately related with intra- and intermolecular hydrogen bonds. The role of the hydrogen bonds was studied also to check the possibility of high proton conductivity of histamine, as predicted by computer simulation. Consequently, the thus-predicted proton conductivity was confirmed for the first time experimentally. During the heating process, the conductivity showed the relatively high maximum value of 10-4 S cm-1 at around 60 °C, which is related to the effective proton transfer between the amino NH group of one histamine unit and the imidazole ring of another.

Pathophysiological Role of Histamine H4 Receptor in Cancer: Therapeutic Implications

Cancer is a leading cause of death in both developed and developing countries. Although advances in cancer research lead to improved anti-neoplastic therapies, they continue to have unfavorable outcomes, including poor response and severe toxicity. Thus, the challenge for the new therapeutic approaches is to increase anti-tumor efficacy by targeting different molecules encompassed in the tumor and its microenvironment, as well as their specific interactions. The histamine H4 receptor (H4R) is the last discovered histamine receptor subtype and it modulates important immune functions in innate and in adaptive immune responses. Several ligands have been developed and some of them are being used in clinical trials for immune disorders with promising results. When searched in The Cancer Genome Atlas (TCGA) database, human H4R gene was found to be expressed in bladder cancer, kidney cancer, breast cancer, gastrointestinal cancers, lung cancer, endometrial cancer, and skin cancer. In the present work, we aimed to briefly summarize current knowledge in H4R's pharmacology and in the clinical use of H4R ligands before focusing on recent data reporting the expression of H4R and its pathophysiological role in cancer, representing a potential molecular target for cancer therapeutics. H4R gene and protein expression in different types of cancers compared with normal tissue as well as its relationship with patient prognosis in terms of survival will be described.

Topical Application of TAT-Superoxide Dismutase in Acupoints LI 20 on Allergic Rhinitis

Reactive oxygen species are products of cellular metabolism and assigned important roles in biomedical science as deleterious factors in pathologies. In fact, some studies have shown that the therapeutic benefits of taking antioxidants were limited and the potential for therapeutic intervention remains unclear. New evidences showed that ROS have some ability of intercellular transportation. For treating allergic rhinitis, as a novel intracellular superoxide quencher, TAT-SOD applied to acupoints LI 20 instead of directly to nasal cavity can be used to test that. TTA group apply TAT-SOD cream prepared by adding purified TAT-SOD to the vehicle cream to acupoints LI 20, while placebo group used the vehicle cream instead. TTN group applied the same TAT-SOD cream directly to nasal cavity three times daily. Symptom scores were recorded at baseline and days 8 and 15. For the overall efficacy rate, TTA group was 81.0%, while placebo group was 5.9% and TTN was 0%. Malondialdehyde levels decreased observably in TTA group, and superoxide dismutase, catalase, and glutathione peroxidase levels remained basically unaffected. Enzymatic scavenging of the intracellular superoxide at acupoints LI 20 proved to be effective in treating allergic rhinitis, while no improvement was observed with the placebo group and TTN group.

Genetic variations within the promotor region of the human histamine H4 receptor gene in psoriasis patients

Environmental triggers and genetic factors are supposed to lead to complex gene expression changes in psoriasis and interact in the manifestation of the disease. The histamine H4 receptor (HRH4) is functionally expressed on Th17 cells and plasmacytoid dendritic cells (pDCs) which play a prominent role in the pathogenesis of psoriasis. On pDCs a higher basal expression level of the HRH4 in psoriasis patients compared to healthy controls has been detected. The functional relationship between predisposing genetic variations in the HRH4 gene and psoriasis is yet not known. The aim of the study was to evaluate a possible association between single nucleotide polymorphisms (SNPs) in the HRH4 gene primarily in the promotor region and incidence, severity as well as special clinical features (nail involvement, arthritis, palmoplantar location) of psoriasis. For this approach genomic DNA from 206 patients with psoriasis and 213 healthy controls of Caucasian origin was extracted and three SNPs in the promotor region and one SNP located in an intron of the HRH4 gene were analysed by PCR and pyrophosphate DNA-sequencing. The genotype distributions and allele frequencies between the different groups were compared by chi-square test. The analysis of association between HRH4 polymorphisms and psoriasis was assessed by odds ratio with 95% confidence interval. The genotype distributions and allele frequencies of the four SNPs in the HRH4 gene did not show obvious differences between the whole group of psoriasis patients and healthy controls. However, there were differences by trend in subgroup analysis: The mutant genotypes (A/G) of rs17203314 and (G/A) of rs615283 were more frequent in patients with severe psoriasis PASI≥30 (34.8% and 34.8%) when compared to the control groups (23.5% and 27.2%), respectively. The mutant G/A genotype of rs615283 was significantly more frequent in patients with moderate-to-severe psoriasis PASI≥10 when compared to mild psoriasis PASI<10 (33.3% vs 21.7%, p=0.022). For rs524149 and rs17797945 the wildtype CC genotype was more frequent by trend in moderately-to-severely affected patients with PASI≥10 (85.2% and 63.0%) when compared to the group with mild psoriasis PASI<10 (77.0% and 49.4%), respectively. Furthermore, a significant association of rs615283 with psoriasis palmoplantaris was detected. In conclusion our study suggests that genetic variations within the HRH4 gene might be associated with special clinical features of psoriasis. Further studies are needed in larger study populations to confirm the reported associations and investigate the functional relevance of the identified SNPs.

Histamine H3 receptor as a potential target for cognitive symptoms in neuropsychiatric diseases

The potential contributions of the brain histaminergic system in neurodegenerative diseases, and the possiblity of histamine-targeting treatments is attracting considerable interests. The histamine H3 receptor (H3R) is expressed mainly in the central nervous system, and is, consequently, an attractive pharmacological target. Although recently described clinical trials have been disappointing in attention deficit hyperactivity disorder (ADHD) and schizophrenia (SCH), numerous H3R antagonists, including pitolisant, demonstrate potential in the treatment of narcolepsy, excessive daytime sleepiness associated with cognitive impairment, epilepsy, and Alzheimer's disease (AD). This review focuses on the recent preclinical as well as clinical results that support the relevance of H3R antagonists for the treatment of cognitive symptoms in neuropsychiatric diseases, namely AD, epilepsy and SCH. The review summarizes the role of histaminergic neurotransmission with focus on these brain disorders, as well as the effects of numerous H3R antagonists on animal models and humans.

Characterisation of non-coding genetic variation in histamine receptors using AnNCR-SNP

Almost 90 % of disease-associated genetic variants found using genome wide association studies (GWAS) are located in non-coding regions of the genome. Such variants can affect phenotype by altering important regulatory elements such as promoters, enhancers or repressors, leading to changes in gene expression and consequently disease, such as thyroid cancer and allergic diseases. A number of allergy and atopy related diseases such as asthma and atopic dermatitis are related to histamine receptors; however, these diseases are not fully characterized at the molecular level. Moreover, candidate gene based studies of common variants known as single nucleotide polymorphism (SNPs) located in the coding regions of these receptors have given mixed results. It is important to complement these approaches by identifying and characterising non-coding variants in order to further elucidate the role of these receptors in disease. Here we present an analysis of histamine receptor genes using the tool AnNCR-SNP to characterise variants in non-coding genomic regions. AnNCR-SNP combines bioinformatics and experimental data sets from various sources to predict the effects of genetic variation on gene expression regulation. We find many SNPs located in areas of open chromatin, overlapping with transcription factor binding sites and associated with changes in gene expression in expression quantitative trait loci (eQTL) experiments. Here we present the results as a catalogue of non-coding variation in histamine receptor genes to aid histamine researchers in identifying putative functional SNPs found in GWAS for further validation, and to help select variants for candidate gene studies.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.