The apparent volumes of distribution of H1 receptor antagonists

ABSTRACT: The apparent volume of distribution (V_D) of a drug estimates its distribution into the body. Referring to the volume of exchangeable water (0.6 L/kg body weight), it indicates if tissue distribution is extensive when V_D is greater than 0.6 L/kg or poor if V_D is less than 0.6 L/kg. Its interest in the selection of an appropriate drug is found after comparing the map of selected targets (mainly receptors) to be reached by the drug, the accessibility of these targets by the drug, and the V_D necessary and sufficient to reach them. This analysis is here applied to H₁ receptor antagonists, a pharmacologic class, where target cells, endothelial cells such as eosinophils, mastocytes, basophils, and smooth fibers have receptors on the external side of cell membranes and thus are more readily accessible from blood than toxic sites located inside cells (heart, brain, liver). Of the H₁ receptor antagonists marketed today, cetirizine has the lowest V_D, 0.4 L/kg, enough to reach selected targets without extensive distribution in organs where it would be useless. These characteristics are related to its chemical amphoteric structure.     

The effect of H1 and H2 histamine antagonists on symptomatic dermographism

In ten patients suffering from symptomatic dermographism the combined administration of chlorpheniramine + cimetidine produced a greater reduction in the weal and flare response provoked by a standardized scratch than the administration of chlorpheniramine alone. There was a statistically significant improvement in the overall assessment of the patient's skin condition with the combined administration of chlorpheniramine + cimetidine. Chlorpheniramine given alone produced no significant benefit whilst cimetidine alone produced a marked exacerbation in itching in nearly half the patients who initially entered the study and was sufficient to require withdrawal.     

Suppression of alcohol-induced flushing by a combination of H1 and H2 histamine antagonists

Alcohol-induced flushing of the face and neck regions is a well recognized condition, probably genetically determined and due to individual differences in alcohol metabolism. We have shown that the flushing appears only after a threshold level of blood alcohol (20–35 mg per 100 ml) is exceeded. The rate of alcohol absorption and peak blood levels were reduced by a combination of H₁ and H₂ antagonists. This reduction was accompanied by abolition of flushing in sensitive individuals.     

In dermographic urticaria H2 receptor antagonists have a small but therapeutically irrelevant additional effect compared with H1 antagonists alone

Two studies of the additional effect of an H₂ receptor antagonist when given in combination with an H₁ antagonist were undertaken in dermographic urticaria. Using a randomized, double-blind, crossover design in 19 patients, a combination of cetirizine (10 mg at night) and ranitidine (150 mg twice daily) was compared with a combination of cetirizine (10 mg at night) and placebo. The addition of ranitidine did not produce any significant difference in linear analogue scores for weal, Itch or sleep disturbance. There was a significant depression of the frictional force/wealing response curve with an increase in wealing threshold (P<0.0001) following the addition of H₂ blockade. The wealing threshold was 54.7 ± 4.4 (mean ± SEM) g/mm² for the H₁ antagonist alone, and 73.2 ± 5.7 for the combination of H₁ and H₂ antagonists. In a second similar study involving nine different patients, comparing terfenadine (120 mg twice daily) with a combination of terfenadine and ranitidine (150 mg twice daily), the weal threshold was 59.8 ± 6.6 for the H₁ antagonist alone, and 73.0 ± 6.4 for the combination of H₁ and H₂ antagonists. Thus, in dermographic urticaria, adding an H₂ antagonist to treatment with a potent H₁ antagonist gives a small, significant reduction in wealing response, but no symptomatic benefit. We conclude that involvement of the H₂ receptor in this urticarial disease is minimal, and does not justify the use of H₂ receptor antagonists.     

Effects of H1 antagonists on the cutaneous vascular response to histamine and bradykinin: a study using scanning laser Doppler imaging

Histamine plays an important part in the cutaneous weal and flare response which underlies many allergic skin conditions. It has a direct effect on the local vasculature to promote vasodilatation and increase microvascular permeability and may also initiate the more widely spread neurogenic flare. Quantification of these responses and studies of the mediator mechanisms underlying them have been limited by the lack of appropriate techniques to investigate them. To address this we have used two relatively new techniques, scanning laser Doppler imaging (LDI) and dermal microdialysis to measure changes in skin blood flow and the release of histamine within the weal and flare, following intradermal injection of histamine or bradykinin. These measurements have been made both in the absence and presence of the H₁ receptor blockers cetirizine and loratadine. Scanning LDI of the inflammatory response revealed marked differences in both the development and steady state responses to the intradermal injection of histamine (1–3 μmol/L) and bradykinin (1 μmol/L). The development of the flare and the weal response to both histamine and bradykinin was significantly reduced by cetirizine but not by loratadine. The histamine-induced flare area fell by 57 ± 4% (mean ± SEM, n = 10, P < 0.001) after cetirizine and the area of the weal fell by 73 ± 11% (P < 0.009). Bradykinin-induced inflammatory responses were similarly reduced by cetirizine, the weal by 60 ± 16% (P < 0.02) and the flare by 61 ± 4% (P < 0.005). Measurement of histamine concentration in skin using microdialysis, in six subjects, confirmed that histamine levels rose in the dialysate collected from the weal to 310 ± 16 nmol/L following injection of histamine. Histamine levels also rose following bradykinin injection in some subjects (mean 147 ± 46 nmol/L, range 18–336). Little increase in histamine concentration was seen in the dialysate from the flare following injection of either histamine or bradykinin. The histamine concentration in dialysate from unprovoked skin was 4.19 ± 0.75 nmol/L. These data reveal differences in the dermal responses to different mediators when assessed using scanning LDI. They confirm that histamine is released within the weal but not the flare response to the intradermal injection of both histamine and bradykinin and that its effects on the local vasculature to cause the oedematous weal and the axon reflex-mediated flare are significantly attenuated by the H₁ antagonist cetirizine and to a lesser extent by the H₁ antagonist loratadine.     

The intradermal effects of the H3 receptor agonist R α methylhistamine in human skin

We have investigated the possible existence of the H₃ histamine receptor in human skin with the highly selective ligands R α methylhistamine (RAMHA) (H₃ agonist) and thioperamide (H₃ antagonist). We compared the intradermal effects of RAMHA with histamine, and studied their potential modulation by the H₁ antagonist terfenadine, and H₂ antagonist cimetidine. The effects of RAMHA and thioperamide on codeine phosphate-, substance P- and histamine-induced weal and flare responses were also studied. RAMHA produced dose-related weal and flare responses that were approximately 10- and fivefold less, respectively, than responses to histamine. Flare responses to RAMHA were significantly inhibited by oral terfenadine ( P  < 0.05). Weal and flare responses to histamine after oral cimetidine showed much intersubject variation, and cimetidine did not significantly alter either RAMHA- or histamine-induced weal and flare responses. Codeine phosphate-, substance P- and histamine-induced responses were not significantly affected by concurrent administration of RAMHA. Thioperamide was not found to influence codeine phosphate-, substance P-, RAMHA- or histamine-induced effects. RAMHA induces vascular (weal and flare) responses in human skin, and these responses are partially inhibited by terfenadine. There is a trend for RAMHA to have an additive effect to the weal induced by substance P and histamine, although our results largely do not reach statistical significance. Thioperamide does not affect the vascular responses to RAMHA, codeine phosphate, histamine or substance P. We cannot conclude that the effects of RAMHA are induced by H₃ receptors on cutaneous endothelial or mast cells.     

Effects of prostaglandin E1 on human keratinocytes and dermal fibroblasts: A possible mechanism for the healing of skin ulcers

Abstract The effects of prostaglandin E, (PGE) on cell growth, cytokine production and interaction of cultured normal human keratinocytes (NHKs) and human dermal fibroblasts (HDFs) were investigated. When NHKs were treated with PGE, directly, only a slight increase in cell growth and a transient decrease in interleukin 1 alpha (IL-lα) secretion were observed. No IL-6 was detected either before or after PGE, treatment. In addition, IL-8 and transforming growth factor alpha (TGFα) production were uninfluenced by PGE. The response of HDFs to PGE, differed from that of NHKs. Following PGE₁, treatment, IL-lα and TGFα. from HDFs remained undetectable while IL-6 production was enhanced markedly. IL-8 production was also slightly enhanced. Exposure of HDFs to PGE, for 96 hours significantly promoted cell proliferation. Two kinds of conditioned media (CM) were prepared by a brief feeding of HDFs with keratinocyte basic medium or Dulbecco's modified Eagle's medium supplemented with 5% PCS with or without PGE. NHKs proliferated more rapidly in CM than in corresponding basic medium. Moreover, CM prepared with PGE, treatment showed a stronger effect in promoting NHK proliferation than CM without PGE, treatment. This promoting effect was inhibited by anti-human IL-6 monoclonal antibody dose-dependently. These results indicate that fibroblasts are more sensitive than keratinocytes in response to PGE, and that, upon PGE, stimulation. HDF-derived IL-6 may play an essential role in NHK cell proliferation which may at least partly account for the beneficial effects of PGE, in the treatment of cutaneous liberations.     

Pharmacological modulation of IL-6 and IL-8 secretion by the H1-antagonist decarboethoxy-loratadine and dexamethasone by human mast and basophilic cell lines

Abstract Mast cells and basophils are central effector cells of allergic reactions and are involved in inflammatory diseases. These cell types produce an array of mediators including a broad spectrum of cytokines. In order to examine whether antiallergic drugs modulate the release of these mediators, we have investigated the influence of dexamethasone and decarboethoxy-loratadine (DEL), the active metabolite of the H₁-blocking agent loratadine, on the release of IL-6 and IL-8 by the human mast cell line HMC-1 and the human basophilic cell line KU812 by ELISA. Dexamethasone (10^?6-10^?11 M) or Del (10^?5-10^?14 M) were added to the cells either 1 h prior to or simultaneously with PMA and Ca-ionophore A23187. When preincubated with the cells, DEL dose-dependently suppressed IL-6 release by up to 40% and IL-8 release by up to 50%. Dexamethasone potently suppressed secretion of both cytokines if simultaneously added to the cells with the stimuli by up to 60% and after preincubalion by up to 80%. Since both antihistamines and glucocorticoids are used for treatment of allergic diseases, the findings reported here indicate that these drugs may modulate allergic reactions via inhibition of cytokine release from mast cells and basophils.     

Lack of intrinsic polarity in the ligandbinding ability of keratinocyte β1 integrins

Abstract: Within the basal layer of the epidermis the β1 integrins have a pericellular distribution. Two monoclonal antibodies, 15/7 and 12G10, that detect a conformation of the β1 integrin subunit that is induced following cation or ligand occupancy selectively recognized β1 integrins at the basement membrane zone in vivo and in focal adhesions of cultured keratinocytes; they did not recognize integrins on the apical and upper lateral membranes of basal keratinocytes nor integrins on the suprabasal keratinocytes of hyperproliferative epidermis. Inhibition of intercellular adhesion did not induce the 15/7 epitope on the lateral and apical membrane domains. The surface distribution of the epitopes was consistent with the antibodies acting as reporters of ligand-binding; in addition, the 15/7 epitope was exposed on unglycosylated, immature β1 integrins. Although the apical membrane of basal keratinocytes is not normally in contact with extracellular matrix proteins, we found that it was capable of binding fibronectin-coated beads and that the 15/7 epitope was exposed on plasma membrane in contact with the beads. When a chimeric molecule consisting of the extracellular domain of CD8 and the cytoplasmic domain of the β1 integrin subunit, used to mimic a constitutively active β1 heterodimer, was introduced into keratinocytes it localized to the basal, lateral and apical membrane domains. We conclude that although the conformation of the keratinocyte β1 integrins differs between the basal and the lateral/apical membrane domains there is no intrinsic polarity in the ligand binding potential of the receptors.     

Divalent cations (Mg2+, Ca2+) differentially influence the β1 integrin-mediated migration of human fibroblasts and keratinocytes to different extracellular matrix proteins

Abstract Directed migration of keratinocytes and fibroblasts is a fundamental prerequisite in wound healing. Cation-dependent affinity changes of integrins are responsible for cell adhesion to and deadhesion from extracellular matrix proteins and have been implicated in driving cell migration. The specific requirements for divalent cations in the integrin-dependent migration of human dermal fibroblasts and human epidermal keratinocytes to various extracellular matrix proteins have been studied in vitro using blindwell Boyden chambers. The migration of the tested cells to collagen type I was mediated by the α₂β₂ integrins, to fibronectin by the combined action of the α₃β₂ and the α₅β₁ integrin, and the migration of fibroblasts to laminin dependent both on the α₂β₁ and the α₆β₁ integrins. No migration of keratinocytes to laminin was detected. Mg²⁺ alone induced cell migration with an optimum at 2 mM for fibroblasts and at 10 mM for keratinocytes. Ca²⁺ alone at 2 mM only marginally enhanced fibroblast and keratinocyte migration. At higher concentrations Ca²⁺ suppressed the stimulatory Mg²⁺ effect. 2 mM Ca²⁺ combined with 2 mM Mg²⁺ showed an additive stimulatory effect on the migration of fibroblasts to fibronectin. These data suggest that extracellular divalent cations differentially influence the integrin-mediated cell migration. A concentration gradient of Mg²⁺/Ca²⁺, as reported in tissue injury, thus may play a regulatory role in cell migration required for tissue remodelling.     

All-trans retinoic acid inhibits binding of 1,25-dihydroxy-vitamin D3 to the vitamin D receptor in cultured human keratinocytes

Abstract Psoriasis is characterized by hyperproliferation and impared differentiation of epidermal keratinocytes (KCs). Psoriasis can be treated with derivatives of relinoic acid (RA) and vitamin D₃. Analogues of vitamin D₃ are able to inhibit proliferation and stimulate differentiation of KCs. In contrast, RA inhibits terminal differentiation of KCs. Interactions are known to occur between RA and vitamin D₃ signalling pathways. The purpose of the present study was to determine the effect of all-trans RA on the binding of 1,25-dihydroxy-vitamin D₃ (1,25 (OH)₂D₃) to the vitamin D₃, receptor (VDR) of cultured human KCs. Cultured KCs from normal adults were incubated with or without RA (10^?9–10^?7 M) for 4-24 h. Cells were then harvested, homogenized and ultrasonicated. The extracted protein was incubated with 3H-1,25 (OH)₂D₃ (0.015-1.0 nM) with or without 250-fold excess nonradioactive 1,25 (OH)₂D₃ for 24 h and specific binding was determined by use of the dextran coated charcoal binding assay. Western blot analysis utilizing the monoclonal antibody 9A7γ to VDR was performed on protein extracted from the KCs. The bands resulting from Western blot analysis were visualized by enhanced chemiluminescence. From Scatchard analysis it was found that KCs bind 1,25 (OH)₂D₃ with high affinity (Kd = 0.175 nM). This binding was dose and time dependently inhibited by RA (60% inhibition at 10^?7 M after 24 h of incubation). By Western blot analysis, RA had no effect on the amount of protein extracted from KCs at any of the RA concentrations tested. In conclusion, these results show that binding of vitamin D₃ to its receptor of human KCs can be inhibited markedly by RA without effecting the amount of protein. These results are in contrast to results with other cell types in which RA upregulates binding of 1,25 (OH)₂D₃ to the VDR. Because interaction between retinoids and vitamin D₃ may occur at different levels during signal trans-duction, it is not possible to predict from our results whether RA will inhibit the effects of vitamin D₃, in vivo.     

Transdermal application of prostaglandin E1 ethyl ester for the treatment of trophic acral skin lesions in a patient with systemic scleroderma

An early dinical symptom in scleroderma patients is Raynaud's phenomenon. Later cutaneous manifestations of the disease include oedematous swelling in the extremities and in more extreme cases often very painful, refractory acral necroses. We report on a 56-year-old female patient who participated in a prospective, double-blind, multicentre comparative pilot study because of her severe Raynaud symptoms, with dystrophic skin lesions on both hands. The goal of the study was to evaluate the efficacy and safety of prostaglandin E1 ethyl ester in a transdermal drug delivery system compared with placebo in patients with secondary Raynaud's phenomenon associated with systemic scleroderma or mixed connective tissue disease. After 2 weeks of verum treatment the patient experienced a marked improvement of Raynaud's attacks, with increased capillary flow velocity, reduced blood stasis and dinical healing of the acral trophic lesions. For this patient the transdermal application of prostaglandin E1 ethyl ester in the form of a medicated patch proved to be a simple and effective therapy for the acral trophic skin lesions associated with systemic scleroderma.     

Pretreatment of the test area with 1-day occlusion improves the response rate to NiSO4 5% pet. Patch tests in subjects with a positive history of nickel allergy

A group of 58 women, aged 18 to 51 years, with a clinical history of nickel allergy, who exhibited equivocal or negative reactions to nickel sulfate 5% pet, patch tests performed on the skin of the back, were recruited consecutively from the patch test clinic from September 1993 to June 19944. In order to improve the response rate to NiSO₄ 5% pet, patch tests, a testing procedure utilizing pretreatment of the test area by 1-day (24-h) occlusion was introduced. Patients underwent 2 patch tests on adjacent sites of the volar surface of both forearms. 3 of the patch tests were performed with 40 mg nickel sulfate 5% pet., whereas a control test was carried out by occluding with an empty chamber. 2 of the nickel sulfate test sites were pretreated with 1-day occlusion performed with an empty chamber. A visual grading system and echographic measurement were used to quantify the responses 30–40 min after patch test removal. Echographic evaluations were carried out using a 20 MHz B-scanner. Measurement of skin thickness and determination of the hypoechogenic dermal area, both considered to be parameters of inflammation, were used to evaluate the intensity of the allergic reaction. At the 3-day (72-h) evaluation. 19 subjects out of 58 clearly showed positive reactions to nickel sulfate 5% pet, at pre-occluded skin sites. Moreover, values of skin thickness and of 0–30 areas at positive pre-occluded nickel test areas were higher in respect to control test areas, confirming clinical evidence of increased response to NiSO₄, after occlusion.     

Decreased Interleukin-7 and transforming growth factor-beta1 levels in blister fluids as compared to the respective serum levels in patients with bullous pemphigoid: Opposite behavior of TNF-alpha, Interleukin-4 and Interleukin-10

Abstract: This study analyzes both the blister fluid (BF) and serum levels of IL-7 and TGF-beta₁ in samples from 18 patients affected with bullous pemphigoid (BP). These cytokines clearly present lower concentrations ( P <0.001) in BFs than in the sera (1/20 and 1/2, respectively). In contrast, TNF-alpha, IL-10 and IL-4 present increased amounts in BFs that were 12, 12 and 17-fold, respectively. Eighteen sera (and 10 suction BF) from normal individuals were also employed as control. Normal sera presented significantly lower serum IL-7 concentrations than BP, while no significant TGF-beta₁ variations were observed between normal and pathologic serum samples. In addition, the serum levels detected in BP patients were significantly correlated with disease intensity ( r =0.64, P =0.003, evaluated as the number of blisters/erosions for each patient) as well as with the peripheral B-lymphocyte counts ( r =0.80, P <0.001) and antibodies directed against the basement membrane zone ( r =0.65, P <0.005). Although a clear explanation of this phenomenon is lacking, the data presented in this report agree with a strong decrease of IL-7 production at the local level (keratinocyte is known to produce IL-7 and the latter is known to be down-regulated by IL-10, and in other models also by TGF-beta₁ and IL-4, whose levels are elevated in BP BFs) as opposed to an increased peripheral release of the same modulator. The IL-7 reduction may have a biological relevance in controlling a chronic, progressive disease.