Histamine receptors in human skin: indirect evidence

Radioiodine therapy induced sialadenitis versus chronic idiopathic sialadenitis-Presentation and outcomes

BACKGROUND

This study explores the unique characters of high dose radioactive iodine (RAI) induced chronic sialadenitis.

METHODS

A retrospective study of patients having received salivary endoscopy and followed in our outpatient clinic.

RESULTS

A total of 100 patients met the inclusion criteria, 75 were diagnosed with chronic idiopathic sialoadenitis and 25 with radio-iodine induced sialoadenitis (RIS). The main complaint in both groups was swelling of the parotid gland. Pain, dysphagia, and xerostomia were observed considerably more in the RIS group. During sialo-endoscopy, fibrosis of the Stensen's duct was more common in the RIS group (p = 0.003). RIS patients group generally managed better with interventional endoscopic treatment alone (80% vs. 46%).

CONCLUSION

RIS patients have distinct clinical characteristics. There may be a collateral muscular damage to the masticatory muscles. Fibrosis and parenchymal damage are major findings during sialendoscopy. Sialendoscopy is a safe and efficient treatment for RAI induced sialadenitis.

Biochemical characterization of AeD7L2 and its physiological relevance in blood feeding in the dengue mosquito vector, Aedes aegypti

Aedes aegypti saliva facilitates blood meal acquisition through pharmacologically active compounds that prevent host hemostasis. Among these salivary proteins are the D7s, which are highly abundant and have been shown to act as scavengers of biogenic amines and eicosanoids. In this work, we performed comparative structural modeling, characterized the binding capabilities, and assessed the physiological functions of the Ae. aegypti salivary protein AeD7L2 compared to the well-characterized AeD7L1. AeD7L1 and AeD7L2 show different binding affinities to several biogenic amines and biolipids involved in host hemostasis. Interestingly, AeD7L2 tightly binds U-46619, the stable analog of thromboxane A₂ (K_D  = 69.4 nm), which is an important platelet aggregation mediator, while AeD7L1 shows no binding. We tested the ability of these proteins to interfere with the three branches of hemostasis: vasoconstriction, platelet aggregation, and blood coagulation. Pressure myography experiments showed these two proteins reversed isolated resistance artery vasoconstriction induced by either norepinephrine or U-46619. These proteins also inhibited platelet aggregation induced by low doses of collagen or U-46619. However, D7 long proteins did not affect blood coagulation. The different ligand specificity and affinities of AeD7L1 and AeD7L2 matched our experimental observations from studying their effects on vasoconstriction and platelet aggregation, which confirm their role in preventing host hemostasis. This work highlights the complex yet highly specific biological activities of mosquito salivary proteins and serves as another example of the sophisticated biology underlying arthropod blood feeding.

Trp channels and itch

Itch is a unique sensation associated with the scratch reflex. Although the scratch reflex plays a protective role in daily life by removing irritants, chronic itch remains a clinical challenge. Despite urgent clinical need, itch has received relatively little research attention and its mechanisms have remained poorly understood until recently. The goal of the present review is to summarize our current understanding of the mechanisms of acute as well as chronic itch and classifications of the primary itch populations in relationship to transient receptor potential (Trp) channels, which play pivotal roles in multiple somatosensations. The convergent involvement of Trp channels in diverse itch signaling pathways suggests that Trp channels may serve as promising targets for chronic itch treatments.

Targeting TRP ion channels for itch relief

Acute itch (pruritus) is unpleasant and acts as an alerting mechanism for removing irritants. However, severe chronic itch is debilitating and impairs the quality of life. Rapid progress has been made in recent years in our understanding of the fundamental neurobiology of itch. Notably, several temperature-sensitive transient receptor potential (thermo-TRP) ion channels have emerged as critical players in many types of itch, in addition to pain. They serve as markers that define the itch neural pathway. Thermo-TRP ion channels are thus becoming attractive targets for developing effective anti-pruritic therapies.

Histamine H2-receptor antagonists for urticaria

BACKGROUND

Urticaria is a common skin disease characterised by itching weals or hives, which can occur almost anywhere on the body. There are a number of different subtypes and a range of available treatment options. There is lack of agreement on the efficacy of H2-receptor antagonists used in the treatment of urticaria.

OBJECTIVES

To assess the safety and effectiveness of H2-receptor antagonists in the treatment of urticaria.

SEARCH METHODS

We searched the following databases up to 7 October 2011: the Cochrane Skin Group Specialised Register, CENTRAL in The Cochrane Library (2011, Issue 4), MEDLINE (from 2005), EMBASE (from 2007), and LILACS (from 1982). We also searched online trials registries for ongoing trials.

SELECTION CRITERIA

Randomised controlled trials of H2-receptor antagonists in people with a clinical diagnosis of urticaria of any duration or of any subtype. Studies including H1-antihistamines for chronic urticaria are the topic of a separate Cochrane review; thus, they were not included in this review.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted and analysed data.

MAIN RESULTS

Four studies of a relatively small size, involving 144 participants, were included in this review. A combination of ranitidine with diphenhydramine was more effective at improving the resolution of urticaria than diphenhydramine administered alone (risk ratio (RR) 1.59, 95% confidence interval (CI) 1.07 to 2.36). Although there was a similar improvement in itching, weal size, and intensity, cimetidine provided no statistically significant greater overall improvement in symptoms of urticaria when compared to diphenhydramine. However, a combination of these medications was more effective than diphenhydramine alone (RR 2.02, 95% CI 1.03 to 3.94). Adverse events were reported with several of the interventions, i.e. ranitidine and diphenhydramine, causing drowsiness and sedation, but there was no significant difference in the level of sedation from baseline with either famotidine or diphenhydramine.

AUTHORS' CONCLUSIONS

The very limited evidence provided by this review was based on a few old studies of a relatively small size, which we categorised as having high to unclear risk of bias. Thus, at present, the review does not allow confident decision-making about the use of H2-receptor antagonists for urticaria. Although some of these studies have reported a measure of relief of symptoms of urticaria and rather minimal clinical improvement in some of the participants, the evidence was weak and unreliable. We have emphasised the lack of precision and limitations in the reported data where appropriate in this review.

Role of spinal neurotransmitter receptors in itch: new insights into therapies and drug development

Targets for antipruritic therapies are now expanding from the skin to the central nervous system. Recent studies demonstrate that various neuronal receptors in the spinal cord are involved in pruritus. The spinal opioid receptor is one of the best-known examples. Spinal administration of morphine is frequently accompanied by segmental pruritus. In addition to μ-opioid receptor antagonists, κ-opioid receptor agonists have recently come into usage as novel antipruritic drugs, and are expected to suppress certain subtypes of itch such as hemodialysis- and cholestasis-associated itch that are difficult to treat with antihistamines. The gastrin-releasing peptide receptor in the superficial dorsal horn of the spinal cord has also received recent attention as a novel pathway of itch-selective neural transmission. The NMDA glutamate receptor appears to be another potential target for the treatment of itch, especially in terms of central sensitization. The development of NMDA receptor antagonists with less undesirable side effects on the central nervous system might be beneficial for antipruritic therapies. Drugs suppressing presynaptic glutamate-release such as gabapentin and pregabalin also reportedly inhibit certain subtypes of itch such as brachioradial pruritus. Spinal receptors of other neuromediators such as bradykinin, substance P, serotonin, and histamine may also be potential targets for antipruritic therapies, given that most of these molecules interfere not only with pain, but also with itch transmission or regulation. Thus, the identification of itch-specific receptors and understanding itch-related circuits in the spinal cord may be innovative strategies for the development of novel antipruritic drugs.

Anatomy and neurophysiology of pruritus

Itch has been described for many years as an unpleasant sensation that evokes the urgent desire to scratch. Studies of the neurobiology, neurophysiology, and cellular biology of itch have gradually been clarifying the mechanism of itch both peripherally and centrally. The discussion has been focused on which nerves and neuroreceptors play major roles in itch induction. The "intensity theory" hypothesizes that signal transduction on the same nerves leads to either pain (high intensity) or itch (low intensity), depending on the signal intensity. The "labeled-line coding theory" hypothesizes the complete separation of pain and itch pathways. Itch sensitization must also be considered in discussions of itch. This review highlights anatomical and functional properties of itch pathways and their relation to understanding itch perception and pruritic diseases.

Itch, pain, and metaesthetic sensation

Itch is one of the alarm sensations that human beings have phylogenetically evolved for a defense purpose. Many theories and evidences regarding the biological, pathophysiological, and clinical aspects have been given, but an update on the neuroanatomy paths and consequent treatments is required. Some chemicals that are released after skin injury and facilitate the inflammatory process can induce itch or pain or basically lead to a sensitization of the nociceptor response. In clinical practice, the present authors note a continuum of sensations from touch to pain, among which many metaesthetic sensations can be described, even if the patients themselves cannot precisely define them. The specificity of itch neurons is therefore based on their spinal connections to the itch pathway rather than on unique peripheral receptors. The ambiguity of "itch unit" discharge to pruritics and algogens may be solved by the central inhibition of itch by pain: it is common knowledge that scratching relieves itching. Conversely, centrally acting pain-inhibiting opioids enhance itch by disinhibition. The relation between itch and pain is interesting in its clinical and physiopathological aspects in order to select appropriate treatment.

H1 but not H2 histamine receptor activation contributes to the rise in skin blood flow during whole body heating in humans

Recent evidence suggests a role for vasoactive intestinal polypeptide (VIP) in active vasodilatation and it has been shown that VIP-mediated vasodilatation includes a nitric oxide (NO) and histamine component. Thus, the purpose of this study was to determine the role of H1 and H2 histamine receptors and to examine a potential interaction between NO and histamine receptors in cutaneous active vasodilatation. Eleven subjects were instrumented with four microdialysis fibres. Site 1 served as a control and site 2 was perfused with l-NAME to inhibit nitric oxide synthase. Site 3 was perfused with either the H1 antagonist pyrilamine maleate or the H2 antagonist cimetidine. Site 4 was perfused with l-NAME plus pyrilamine maleate or l-NAME plus cimetidine. Laser-Doppler flowmetry (LDF) was used as an index of skin blood flow and cutaneous vascular conductance (CVC) was calculated as LDF/mean arterial pressure and normalized to maximal vasodilatation achieved via 28 mm sodium nitroprusside infusion. During whole body heating, subjects' sublingual temperature increased a minimum of 0.8 degrees C. In the H1 antagonist studies, CVC in l-NAME, pyrilamine, and combined l-NAME plus pyrilamine sites was significantly reduced compared with control (P < 0.001). The l-NAME and combined l-NAME plus pyrilamine sites were significantly reduced compared with pyrilamine only sites (P < 0.05) but no significant differences were observed between sites. In the H2 receptor antagonist studies, CVC in control sites was not significantly different from cimetidine sites. There was no difference between the l-NAME and combined l-NAME plus cimetidine sites but these sites were significantly attenuated compared with control and cimetidine only sites (P < 0.05). These data suggest the rise in skin blood flow during whole body heating contains an H1 histamine receptor component but do not support an H2 histamine receptor component. Furthermore, part of the NO-dependent component of active vasodilatation can be explained by H1 receptor activation.

H1 and H2 histamine receptors are absent on Langerhans cells and present on dermal dendritic cells

Human monocyte-derived dendritic cells (MoDC) have both histamine H1 and H2 receptors and can induce CD86 expression by histamine. Nevertheless, it has not been reported whether human epidermal Langerhans cells (LC) have histamine receptors or not. In this study, using RT-PCR, we investigated the expression of H1 and H2 receptor mRNA on DC with the features of LC (LC-like DC) that were generated in vitro from peripheral blood monocytes, LC derived from CD34+ hematopoietic progenitor cells, and LC obtained from human epidermis. We compared the histamine-induced CD86 expression among these cells. In contrast to MoDC, LC and LC-like DC did not express H1 or H2 receptors. In addition, they could not augment the CD86 expression by histamine. Interestingly, when transforming growth factor-beta1 (TGF-beta1) was added to the culture of MoDC, the expression of H1 and H2 receptors and the histamine-induced CD86 expression were abrogated in a concentration-dependent fashion. Finally, in the assessment of the cell surface expression of histamine receptors using fluorescence-labeled histamine, histamine could bind to MoDC and dermal dendritic cells obtained from the skin, whereas there was no specific binding of histamine to LC-like DC or LC obtained from the skin. These data suggest that LC do not express either H1 or H2 receptors, mainly because of the effect of TGF-beta1. This made a striking contrast with the expression of the functional H1 and H2 receptors on MoDC and dermal dendritic cells.

Dry environment increases mast cell number and histamine content in dermis in hairless mice

BACKGROUND

A variety of skin diseases, such as atopic dermatitis, senile xerosis or psoriasis tends to worsen during the dry winter season. These skin diseases are also characterized by itch sensation.

OBJECTIVES

To evaluate the generation of histamine in the dermis of hairless mice kept under various conditions of environmental humidity.

MATERIALS AND METHODS

We carried out the quantification of mast cell population and evaluated the histamine content in the epidermis, dermis and serum of the mice kept under various conditions of environmental humidity.

RESULTS

Histamine content in the dermis of the mice kept in a low environmental humidity (relative humidity < 10%) for 3 and 5 days was significantly higher than that of the mice kept in a high environmental humidity (relative humidity > 80%) for the same period of time. No significant difference was observed on the histamine content in the epidermis between the two humidity groups. The number of mast cells in the dermis of the mice kept in the low environmental humidity was significantly higher than that of the mice kept in the high environmental humidity. Topical application of petrolatum reduced the level of histamine in the dermis of the mice under the low environmental humidity.

CONCLUSIONS

These results suggest that a low environmental humidity increases mast cell number and dermal histamine content.

Chronic urticaria: impact of allergic inflammation

Urticaria is defined by weals (hives), with or without angioedema, that appear and peak in minutes to hours, usually disappear within 24 h, and are accompanied by pruritus that worsens during the night. Urticaria is caused by cutaneous mast cell degranulation, attributed to immunological, nonimmunological, and idiopathic causes. Chronic idiopathic urticaria (CIU) is the diagnosis when the pathophysiological mechanism of persistent urticaria remains unclear; up to half of patients with CIU have functional autoantibodies directed against the high-affinity receptor for IgE (FcepsilonRI) or against IgE itself, which appear to induce mast cell degranulation. Systemic histamine H1-receptor antagonists, such as desloratadine, are central to the management of CIU. The efficacy and safety of desloratadine, 5 mg once daily, was studied in a double-blind, randomized, placebo-controlled, multicentre trial that included 190 patients, ages 12 and above, with at least a 6-week history of CIU and experiencing a flare of at least moderate severity. Desloratadine was superior to placebo in controlling pruritus and total symptoms after the first dose, and its superiority was maintained throughout the full 6 weeks of the study. Measures of sleep, daily activity, therapeutic response, and global CIU status were also significantly improved with desloratadine after the first dose and maintained throughout the study.

Histamine H1 and H2 receptor antagonists accelerate skin barrier repair and prevent epidermal hyperplasia induced by barrier disruption in a dry environment

Keratinocytes have histamine H1 and H2 receptors, but their functions are poorly understood. To clarify the role of histamine receptors in the epidermis, we examined the effects of histamine receptor antagonists and agonists applied epicutaneously on the recovery of skin barrier function disrupted by tape stripping in hairless mice. Histamine H2 receptor antagonists famotidine and cimetidine accelerated the recovery of skin barrier function, but histamine and histamine H2 receptor agonist dimaprit delayed the barrier repair. Application of compound 48/80, a histamine releaser, also delayed the recovery. Imidazole, an analog of histamine, had no effect. The histamine H1 receptor antagonists diphenhydramine and tripelennamine accelerated the recovery. Histamine H3 receptor agonist Nalpha-methylhistamine and antagonist thioperamide had no effect. In addition, topical application of famotidine or diphenhydramine prevented epidermal hyperplasia in mice with skin barrier disrupted by acetone treatment in a dry environment (humidity < 10%) for 4 d. In conclusion, both the histamine H1 and H2 receptors in the epidermis are involved in skin barrier function and the cutaneous condition of epidermal hyperplasia.

Antihistamines

In the 1990s, major improvements occurred in the therapeutic index of H1 antihistamines. The third-generation compounds promise to be more effective and nontoxic. The future major advances are likely to result from development and exploitation of non-H1 receptor-mediated antiallergic actions of these drugs.

Histamine response and local cooling in the human skin: involvement of H1- and H2-receptors

AIMS

Histamine may contribute locally to cutaneous blood flow control under normal and pathologic conditions. The objective of this study was to observe the influence of skin temperature on histamine vasodilation, and the roles of H1-and H2-receptors using novel noninvasive methods.

METHODS

Eleven healthy subjects received, double-blind, single doses of the H1-receptor antagonist cetirizine (10 mg), cetirizine (10 mg) plus the H2-receptor antagonist cimetidine (400 mg), or placebo on separate occasions. Histamine was dosed cumulatively by iontophoresis to the forearm skin at 34 degrees C and 14 degrees C. Laser-Doppler flux (LDF) was measured at the same sites using customised probeholder/iontophoretic chambers with Peltier cooling elements. Finger mean arterial pressure (MAP) was measured and cutaneous vascular conductance calculated as LDF/MAP.

RESULTS

Histamine vasodilation was reduced in cold skin. Cetirizine shifted the histamine dose-response at both temperatures: statistically significantly at 14 degrees C only. Combined H1- and H2-receptor antagonism shifted the response significantly at both temperatures.

CONCLUSIONS

H1- and H2-receptors mediate histamine-induced skin vasodilation. The sensitivity of these receptors, particularly the H1- receptor, is attenuated at low skin temperature. Whether the reduced effect in cold skin represents specific receptor or postreceptor desensitization, or nonspecific attenuation of cutaneous vasodilation remains to be elucidated.

Nervous control of blood flow in the orofacial region

The blood vessels of orofacial tissues are innervated by cranial parasympathetic, superior cervical sympathetic, and trigeminal nerves, a situation somewhat different from that seen in body skin. This review summarizes our current knowledge of the nervous control of blood flow in the orofacial region, and focuses on what we know of the respective roles of sympathetic, parasympathetic, and trigeminal sensory nerves in the regulation of blood flow in this region, with particular attention being paid to the mutual interaction between them.

The physiology of itch

The perception of itch is associated with many parasites and their vectors, especially following penetration of the skin by the parasites themselves, as in cercarial dermatitis of schistosome infections, or penetration of arthropod mouthparts during blood feeding. Many ectoparasites such as scabies, lice and fleas, provoke sensations of itch - even when the insects are no longer (or have never been) present, giving rise to the phenomenon of delusory parasitosis. Itch, and the host 'grooming' responses with which it is associated, is increasingly recognized as an important factor in modulating vector feeding behaviour, which can have profound effects on the transmission dynamics of vector borne parasites. As a background to future reviews of this developing subject, we asked John Alexander, author of the classic Arthropods and Human Skin (Springer-Verlag, 1984), to explain what is itch, and to discuss what is known about its underlying Physiology.

Histamine-induced microvascular permeability increases in hamster skin: a response predominantly mediated by H2-receptors

The pharmacology of histamine-induced increases in cutaneous microvascular permeability was investigated in the hamster by examining the effects of cimetidine and pyrilamine on the increase in microvascular permeability evoked by graded doses of intradermally-injected histamine, and comparing the cutaneous microvascular permeability responses to graded doses of impromidine (0.1-100 micrograms), dimaprit (1-100 micrograms) and beta-histine (0.1-100 micrograms). Pretreatment with pyrilamine (0.1 mg/kg i.v. bolus injection) did not reduce the increase in microvascular permeability produced by any dose of histamine. In contrast, cimetidine (0.5 mg/kg/min i.v. infusion) significantly inhibited the microvascular permeability responses to 10 and 100 micrograms histamine. Although neither cimetidine nor pyrilamine significantly altered the microvascular permeability response to 0.1 and 1 micrograms histamine, inhibition was afforded by a cimetidine-pyrilamine combination. These results suggest a predominantly H2-receptor mediated phenomenon with a minor H1-receptor mediated component. Studies with the H2-receptor agonists impromidine and dimaprit and the H1-receptor agonist beta-histine provide further support for this contention. Dimaprit and impromidine caused a dose-dependent increase in cutaneous microvascular permeability, but betahistine produced only a relatively modest response. In other laboratory species, increased cutaneous microvascular permeability appears to be mediated solely by H1-receptors. Therefore, the hamster skin appears unique with respect to the pronounced H2-receptor involvement in histamine-induced microvascular permeability changes.

A review of pruritus

This article reviews the neurophysiology of pruritus and presents evidence that itch is a separate modality from pain, rather than a submodality of pain. The numerous suggested pruritogens are reviewed, and evidence supporting each one is critically examined. The systemic causes of generalized pruritus are reviewed, with detailed review of the literature on uremic pruritus, cholestatic pruritus, and the pruritus associated with polycythemia vera. The specific treatments used for each of these conditions are reviewed, as well as the use of antihistamines in generalized pruritus. An approach to the workup of a patient with pruritus is suggested.