Chemical mediators in atopic dermatitis: involvement of leukotriene B4 released by a type I allergic reaction in the pathogenesis of atopic dermatitis

Crisaborole Inhibits Itch and Pain by Preventing Neutrophil Infiltration in a Mouse Model of Atopic Dermatitis

Crisaborole, a phosphodiesterase 4 (PDE4) inhibitor, has been approved for the treatment of mild to moderate atopic dermatitis. Atopic dermatitis is often associated with increased pain. Using a mouse model, this study investigated whether crisaborole suppresses pain associated with atopic dermatitis and the potential mechanisms underlying it. The mouse model for atopic dermatitis was developed by repeatedly applying MC903. MC903-treated mice had increased spontaneous scratching (itch-related behaviour) and wiping behaviour (pain-related behaviour). Crisaborole was topically applied to the cheek skin of MC903-treated mice, and it reduced both itch- and pain-related behaviours in these mice. Immunofluorescence staining revealed that crisaborole reduced neutrophil infiltration and interaction of neutrophils with sensory neurones. Intradermal injection of S100A8/A9, proinflammatory neutrophil mediator, enhanced not only itch-related behaviours evoked by histamine or chloroquine, but also pain-related behaviours evoked by capsaicin. Calcium imaging of mouse dorsal root ganglion neurones revealed that pretreatment with S100A8/A9 significantly increased calcium responses to histamine and capsaicin, and the proportion of chloroquine-sensitive neurones. These findings suggest that the PDE4 inhibitor reduces itch and pain, in part by inhibiting infiltration of S100A8/A9-containing neutrophils in a mouse model of MC903-induced atopic dermatitis.

Clinical and histological characterization of transient dermal pain triggered by sweating stimuli

BACKGROUND

Tingling dermal pain triggered by sweating impairs the lives of patients with cholinergic urticaria and generalized anhidrosis. However, dermal pain evoked by sweating stimuli has been under investigated.

METHODS

To clarify characteristics of tingling dermal pain on sweating, we retrospectively evaluated clinical and histopathological manifestations in 30 patients having the main problem of dermal pain on sweating, and the efficacy of treatments.

RESULTS

Dermal pain upon sweating affected mostly young males. It accompanied eruptions upon sweating and/or hypohidrosis in 24 patients, while 6 patients had dermal pain independently of hypohidrosis or eruptions. Dermal pain appeared immediately upon exposure to sweating stimuli, and disappeared within mostly 30 or 10 min. Hypohidrosis was not necessarily generalized but localized or absent. Histological analysis revealed that dermal pain could occur even without morphological changes and inflammation of sweat glands. Hypersensitivity to sweat contents was found only in 26% of patients. Sweat histamine and increase of plasma histamine after thermal induction in patients were significantly higher than those in healthy subjects. Effectiveness of steroid pulse therapy was demonstrated for dermal pain with hypohidrosis. Medications acting on nervous systems and regular sweat-inducing activities for promoting perspiration were also effective.

CONCLUSIONS

Short-lasting tingling dermal pain appears immediately upon exposure to sweating stimuli, regardless of developing eruptions and/or presence of hypohidrosis, but possibly in association with sweat and plasma histamine.

Pathogenic Mechanism of Der p 38 as a Novel Allergen Homologous to RipA and RipB Proteins in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic relapsing pruritic disease encompassing skin inflammation and barrier dysfunction. House dust mites are key allergens that augment the development of atopic dermatitis. We aimed to investigate the pathogenic mechanism of AD due to Der p 38, recently identified by us. The frequency of IgE reactivity to Der p 38 in AD subjects was 52.6% (10/19) in the skin prick test and 57.9% (11/19) in the dot blot assay. In human keratinocyte HaCaT cells, Der p 38 triggered the impairment of filaggrin expression and induced pro-inflammatory cytokines such as IL-6, IL-8 and MCP-1 through TLR4, PI3K, AKT, c-Jun N-terminal kinase (JNK) and NF-κB pathway. Supernatants from Der p 38-treated cells blocked filaggrin expression and neutrophil apoptosis. The anti-apoptotic effect of the Der p 38-released molecules on neutrophils was accomplished by inhibition of the caspase 9/3 pathway, and by increased MCL-1 expression and BCL-2/BAX expression ratio. In C57BL/6 wild type (WT) mice, Der p 38 induced a dose-dependent increase of AD-like skin lesions, with enhanced expressions of total and Der p 38-specific IgE. Der p 38 also diminished the expressions of skin barrier proteins and induced JNK activation. However, the AD-like features following cutaneous Der p 38 exposure were observed to be reduced in the TLR4 knockout (KO) group, as compared to the WT group. Skin infiltration of neutrophils, eosinophils and mast cells was increased in the WT mice, but was not portrayed in the TLR4 KO mice. These findings indicate that Der p 38 is a novel mite allergen that triggers AD by lowering skin barrier proteins and increasing inflammatory cells. Results of this study have thereby paved the way to unveil the pathogenic mechanisms of AD.

Current perspective on eicosanoids in asthma and allergic diseases: EAACI Task Force consensus report, part I

Eicosanoids are biologically active lipid mediators, comprising prostaglandins, leukotrienes, thromboxanes, and lipoxins, involved in several pathophysiological processes relevant to asthma, allergies, and allied diseases. Prostaglandins and leukotrienes are the most studied eicosanoids and established inducers of airway pathophysiology including bronchoconstriction and airway inflammation. Drugs inhibiting the synthesis of lipid mediators or their effects, such as leukotriene synthesis inhibitors, leukotriene receptors antagonists, and more recently prostaglandin D₂ receptor antagonists, have been shown to modulate features of asthma and allergic diseases. This review, produced by an European Academy of Allergy and Clinical Immunology (EAACI) task force, highlights our current understanding of eicosanoid biology and its role in mediating human pathology, with a focus on new findings relevant for clinical practice, development of novel therapeutics, and future research opportunities.

Decreased intracellular histamine concentration and basophil activation in anaphylaxis

BACKGROUND

Histamine is a crucial mediator in the development of anaphylaxis. Although histamine is promptly degraded because of its short half-life in plasma, basophils, which release histamine, remain in the blood for days. To explore basophils as a potential marker and their involvement in the pathogenesis of anaphylaxis, we evaluated the intracellular histamine concentration and the degree of basophil activation in anaphylaxis patients.

METHODS

We conducted a case-control study enrolling anaphylaxis patients and healthy controls. Basophil activation was evaluated by flow cytometry using up-regulation of CD203c expression.

RESULTS

We enrolled 23 patients and measured their blood histamine concentration. Basophil activation was analyzed in seven of 23 patients. The median intracellular histamine concentrations at admission were significantly lower in patients compared with controls (16.4 ng/mL [interquartile range {IQR}, 2.70 to 34.0] vs. 62.3 ng/mL [IQR, 46.0 to 85.1]; p < 0.0001). The median basophil number at admission was also significantly lower in patients compared with controls (2.21 cell/μL [IQR, 0.75 to 12.3] vs. 21.0 cell/μL [IQR, 19.5 to 28.9]; p = 0.027). CD203c expression was not up-regulated in any of the seven patients in vitro, but it was up-regulated in response to anti-IgE stimulation in vitro in two patients at admission and four patients at follow-up.

CONCLUSIONS

Anaphylaxis is associated with a decrease in intracellular histamine, and a reduced number and reactivity of peripheral basophils. Impaired basophil function and a decrease in their number and intracellular histamine levels in the circulation may reflect the underlying mechanism, suggesting that basophils may be a marker of anaphylaxis.

Neutrophils promote CXCR3-dependent itch in the development of atopic dermatitis

Chronic itch remains a highly prevalent disorder with limited treatment options. Most chronic itch diseases are thought to be driven by both the nervous and immune systems, but the fundamental molecular and cellular interactions that trigger the development of itch and the acute-to-chronic itch transition remain unknown. Here, we show that skin-infiltrating neutrophils are key initiators of itch in atopic dermatitis, the most prevalent chronic itch disorder. Neutrophil depletion significantly attenuated itch-evoked scratching in a mouse model of atopic dermatitis. Neutrophils were also required for several key hallmarks of chronic itch, including skin hyperinnervation, enhanced expression of itch signaling molecules, and upregulation of inflammatory cytokines, activity-induced genes, and markers of neuropathic itch. Finally, we demonstrate that neutrophils are required for induction of CXCL10, a ligand of the CXCR3 receptor that promotes itch via activation of sensory neurons, and we find that that CXCR3 antagonism attenuates chronic itch.

Chronic itch is a debilitating disorder that can last for months or years. Eczema, or atopic dermatitis, is the most common cause for chronic itch, affecting one in ten people worldwide. Many treatments for the condition are ineffective, and the exact cause of the disease is unknown, but many different types of cells are likely involved. These include skin cells and inflammation-promoting immune cells, as well as nerve cells that detect inflammation, relay itch and pain information to the brain, and regulate the immune system.

Learning more about how these cells interact in eczema may help scientists find better treatments for the condition. So far, a lot of research has focused on static ‘snapshots’ of mature eczema lesions from human skin or animal models. These studies have identified abnormalities in genes or cells, but have not revealed how these genes and cells interact over time to cause chronic itch and inflammation.

Now, Walsh et al. reveal that immune cells called neutrophils trigger chronic itch in eczema. The experiments involved mice with a condition that mimics eczema, and showed that removing the neutrophils in these mice alleviated their itching. They also showed that dramatic and rapid changes occur in the nervous system of mice suffering from the eczema-like condition. For example, excess nerves grow in the animals’ damaged skin, genes in the nerves that detect sensations become hyperactive, and changes occur in the spinal cord that have been linked to nerve pain. When neutrophils are absent, these changes do not take place.

These findings show that neutrophils play a key role in chronic itch and inflammation in eczema. Drugs that target neutrophils, which are already used to treat other diseases, might help with chronic itch, but they would need to be tested before they can be used on people with eczema.

Arachidonic Acid-Derived Bioactive Lipids: Their Role and the Role for Their Inhibitors in Dermatology

Background:

In addition to corticosteroids, there are increasing numbers of anti-inflammatory agents that specifically target bioactive lipids generated from arachidonic acid. Knowledge of the diverse mechanisms of action of these different bioactive lipids holds promise in the therapy of a wide spectrum of cutaneous and systemic disorders.

Objective:

Therapeutic manipulations of these lipid molecules through inhibition, stimulation, or direct replacement have broad physiologic effects. These therapeutic strategies not only modulate inflammation, pain, and hemostatic parameters, they also play a role in cardiac, respiratory, renal, and gastrointestinal function and disease, as well as in angiogenesis and in factors that control cell growth and apoptosis important in carcinogenesis.

Conclusion:

Newer drug discovery methods, including combinatorial chemistry with molecular modeling, have made it possible to develop inhibitors and analogs with increasing specificity and bioactivity and decreasing toxicity. Although the application of these analogs and inhibitors for cutaneous disease is limited today, either as primary agents or adjuvant therapy, these drugs will have a place in our therapeutic regimes of the future. We present a review of the therapeutic agents now available from manipulation of these bioactive lipids, and their role and future in dermatology.

The role of leukotrienes in allergic diseases

Leukotrienes (LTs), both LTB4 and the cysteinyl LTs (CysLTs) LTC4, LTD4 and LTE4, are implicated in a wide variety of inflammatory disorders. These lipid mediators are generated from arachidonic acid via multistep enzymatic reactions through which arachidonic acid is liberated from membrane phospholipids through the action of phospholipase A2. LTB4 and CysLTs exert their biological effects by binding to cognate receptors, which belong to the G protein-coupled receptor superfamily. LTB4 is widely considered to be a potent chemoattractant for most subsets of leukocytes, whereas CysLTs are potent bronchoconstrictors that have effects on airway remodeling. LTs play a central role in the pathogenesis of asthma and many other inflammatory diseases. This review will provide an update on the synthesis, biological function, and relevance of LTs to the pathobiology of allergic diseases, and examine the current and future therapeutic prospects of LT modifiers.

Establishment of a mast cell line, NCL-2, without Kit mutation, derived from NC mouse bone marrow

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We established an immortal mast cell line without Kit mutation, NCL-2.

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NCL-2 cells could be maintained without additional growth factors.

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NCL-2 cells expressed FcεRI and released histamine and LTB₄ in response to antigens.

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NCL-2 cells were tumorigenic but much less aggressive than P815 mastocytoma.

Immortal mast cell lines, such as RBL-2H3 and HMC-1 cells, are commonly utilized to investigate the function of mast cells. However, they are tumor cells carrying a gain-of-function mutation of Kit. We established an immortal mast cell line without Kit mutation, NCL-2, derived from NC mouse bone marrow. NCL-2 cells could be maintained without additional growth factors and thus could respond to exogenous growth signals. Moreover, NCL-2 cells expressed FcεRI and KIT, and release histamine and LTB₄ in response to antigen stimulation. This cell line could be a useful tool to analyze proliferation, differentiation, and function of normal mast cells.

Leukotriene B4-driven neutrophil recruitment to the skin is essential for allergic skin inflammation

Scratching triggers skin flares in atopic dermatitis. We demonstrate that scratching of human skin and tape stripping of mouse skin cause neutrophil influx. In mice, this influx was largely dependent on the generation of leukotriene B4 (LTB4) by neutrophils and their expression of the LTB4 receptor BLT1. Allergic skin inflammation in response to epicutaneous (EC) application of ovalbumin to tape-stripped skin was severely impaired in Ltb4r1(-/-) mice and required expression of BLT1 on both T cells and non-T cells. Cotransfer of wild-type (WT) neutrophils, but not neutrophils deficient in BLT1 or the LTB4-synthesizing enzyme LTA4H, restored the ability of WT CD4(+) effector T cells to transfer allergic skin inflammation to Ltb4r1(-/-) recipients. Pharmacologic blockade of LTB4 synthesis inhibited allergic skin inflammation elicited by cutaneous antigen challenge in previously EC-sensitized mice. Our results demonstrate that a neutrophil-T cell axis reliant on LTB4-BLT1 interaction is required for allergic skin inflammation.

Leukotriene inhibition in small animal medicine

Leukotrienes are important mediators of inflammatory and allergic conditions in people and are suspected to play an important role in tumorigenesis and tumor growth of several different tumor types. Based on this, researchers are making great progress in identifying novel pharmacologic targets for several human diseases. Leukotriene inhibition has resulted in therapeutic benefit in clinical trials involving people with osteoarthritis, allergic asthma, and atopic dermatitis. Despite this progress and the possibility that leukotriene inhibition may also play an important therapeutic role in veterinary patients, parallel advances have not yet been made in veterinary medicine. This article summarizes leukotriene function and synthesis. It also reviews the published literature regarding potential therapeutic applications of leukotriene inhibition in both human and veterinary medicine, focusing primarily on osteoarthritis, NSAID induced gastrointestinal mucosal damage, allergic asthma, atopic dermatitis, and cancer.

Fatty acid composition of serum lipid classes in mice following allergic sensitisation with or without dietary docosahexaenoic acid-enriched fish oil substitution

Dietary fatty acids have been shown to influence allergic sensitisation. Bothn-3 andn-6 PUFA are involved in targeted mediation of inflammatory responses during allergic sensitisation and manifestation of atopic diseases. In the present experiments we investigated whether supplementation of DHA-enriched fish oil partly substituting dietary sunflower-seed oil, in comparison with sunflower-seed oil, supplemented to mice influences fatty acid composition of serum lipid classes. The effects of the two different diets were also investigated depending on allergic sensitisation. Supplementation of DHA and EPA in doses of 2 and 0·12 % (w/w) to non-sensitised and sensitised mice resulted in significantly increased percentile contributions of DHA to all lipid classes. In contrast, serum values of then-6 PUFA arachidonic acid (AA) were significantly lower, both in non-sensitised and sensitised mice fed the DHA-enriched diet. The fatty acid composition of serum lipids also reflected allergic sensitisation: the EPA:AA ratio in TAG, cholesteryl esters and phospholipids in non-supplemented animals fell to 23, 29 and 29 % respectively of the original value after allergic sensitisation, whereas it decreased to 70, 80 and 76 % respectively only in the animals supplemented with DHA. In summary, allergic sensitisation alone decreased significantly the EPA:AA ratios in serum TAG, while concomitant supplementation of DHA-enriched fish oil ameliorated this decrease. We postulate from the present results that the amelioration of the severity of allergic sensitisation after DHA supplementation may be linked to altered ratios of the eicosanoid precursors EPA and AA as well as DHA needed for further metabolic activation to pro- or anti-inflammatory bioactive lipids.

Living cell positioning on the surface of gold film for SPR analysis

Living cell reactions are detected as changes of the angle of resonance (AR) for surface plasmon resonance (SPR). Since SPR reflects the events in the field of evanescence, cells need to be fixed on the sensor chip. In this study, we developed methods to fix living cells on a gold surface and to recover adherent cells from the culture dish, preserving their functions to be analyzed by SPR. Human basophils and B cells were fixed to the sensor chip by a biocompatible anchor for cell membranes (alpha-succinimidyloxysuccinyl omega-oleyloxy polyoxyethylene), aminoalkanethiol (cyteamine, 8-amino octanethiol) or an amino-reactive cross-linker (dithiobis [succinimidylpropionate]). They showed an increase of AR in response to various stimuli. RBL-2H3 cells, which firmly adhered to the culture dish, were cultured/recovered with HydroCell/simple pipetting, with RepCell/pipetting at 4 degrees C, or on normal plastic culture dishes with trypsinization or by scraping at 4 degrees C, respectively. The exocytosis of RBL-2H3 cells was largely impaired by scraping, but only slightly by the treatment with pipetting on HydroCell, on RepCell, or with trypsin. The membrane ruffling of the cells prepared by the last three treatments induced by antigens appeared the same. However, the change of AR with cells prepared by trypsin and those by scraping at 4 degrees C were lower than those by HydroCell or RepCell, suggesting that trypsin may harm molecules involved in cellular reactions. Thus, the methods of cell fixation and removal with HydroCell or RepCell should enable us to analyze various reactions in either adherent or non-adherent cells by SPR.

Pharmacotherapy of diseases mediated by 5-lipoxygenase pathway eicosanoids

Inflammatory eicosanoids generated by the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism are now known to have at least 6 receptors: OXE, which recognizes 5-HETE and 5-oxo-ETE; a putative receptor recognizing a potent 5-oxo-ETE metabolite, FOG(7); the LTB(4) receptors, BLT1 and BLT2; the cysteinyl leukotriene receptors, CysLT(1) and CysLT(2), which recognize leukotrienes LTC(4), LTD(4), LTE(4) and LTF(4). The 5-LO pathway is activated in many diseases and invokes inflammatory responses not affected by glucocorticoids, but therapy with selective BLT1 or CysLT(1) antagonists in asthma has met with variable success. Studies show that 5-LO pathway eicosanoids are not primary mediators in all cases of asthma, but may be especially important in severe persistent asthma, aspirin- and exercise-induced asthma, allergic rhinitis, COPD, idiopathic pulmonary fibrosis, atherosclerosis, atopic dermatitis, acne and ischemia-related organ injury. These disorders appear to involve multiple 5-LO pathway eicosanoids and receptor subtypes, suggesting that inhibition of the pathway at the level of 5-LO may be necessary for maximal efficacy.

Bone marrow derived mast cell acquire responsiveness to substance P with Ca(2+) signals and release of leukotriene B(4) via mitogen-activated protein kinase

Substance P (SP) selectively activates mast cells that reside in connective tissues. We studied the reactions of bone marrow-derived mast cells (BMMC) of three mouse strains, cultured with or without fibroblasts. BMMC co-cultured with fibroblasts, but not those cultured alone, increased intracellular Ca(2+), released LTB(4) and histamine in response to SP. PD098059 significantly inhibited the release of LTB(4), but not histamine in all strains. SB203580 failed to reduce or slightly impaired the release of LTB(4). These results suggest that mast cells undergo maturation under the influence of fibroblasts, acquiring the responsiveness to SP with Ca(2+) signals and predominantly ERK-MAP kinase.

Cytochrome P450 4F subfamily: at the crossroads of eicosanoid and drug metabolism

The cytochrome P450 4F (CYP4F) subfamily has over the last few years come to be recognized for its dual role in modulating the concentrations of eicosanoids during inflammation as well as in the metabolism of clinically significant drugs. The first CYP4F was identified because it catalyzed the hydroxylation of leukotriene B(4) (LTB(4)) and since then many additional members of this subfamily have been documented for their distinct catalytic roles and functional significance. Recent evidence emerging in relation to the temporal change of CYP4F expression in response to injury and infection supports an important function for these isozymes in curtailing inflammation. Their tissue-dependent expression, isoform-based catalytic competence and unique response to the external stimuli imply a critical role for them to regulate organ-specific functions. From this standpoint variations in relative CYP4F levels in humans may have direct influence on the metabolic outcome through their ability to generate and/or degrade bioactive eicosanoids or therapeutic agents. This review covers the enzymatic characteristics and regulatory properties of human and rodent CYP4F isoforms and their physiological relevance to major pathways in eicosanoid and drug metabolism.

Increased leukotriene B4 production, complement C3 conversion and acid hydrolase enzyme concentrations in different leucocyte sub-populations of dogs with atopic dermatitis

Various markers of the inflammatory response were measured in peripheral blood mononuclear cells (PBMCs) and polymorphonuclear neutrophils (PMNs) from 31 dogs with atopic dermatitis (AD). The variables assayed included chemiluminescence, acid hydrolase enzyme concentrations, leukotriene B(4) (LTB(4)) production and complement C3 conversion. The results were compared to those derived from a population of clinically healthy dogs. Dogs with AD exhibited a significant increase in median LTB(4) production in PMNs compared to controls (0.94 versus 0.00 ng/10(6) cells; P<0.01). Significant increases in the median concentrations of intracellular beta-galactosidase (PBMC fraction - 0.42 versus 0.25 mU/10(6) cells; P<0.05) (PMN fraction - 0.47 versus 0.12 mU/10(6) cells; P<0.01) and beta-glucuronidase (PBMC fraction - 0.52 versus 0.27 mU/10(6) cells; P<0.05) were also evident in the AD group. Although median maximum chemiluminescence values for both leucocyte sub-populations were higher in controls, the differences recorded were not significant (P>0.05). However, the median time taken to reach maximum chemiluminescence was significantly shorter in the PMN fraction of dogs with AD (7.00 versus 10.00 min; P<0.01). Atopic dogs had a significant increase in the median percentage conversion of complement C3 to C3b (66.0 versus 57.3%; P<0.01). The results of this study indicate a priming of the inflammatory response in dogs with AD. The role of LTB(4) in the pathogenesis of canine AD and the potential efficacy of leukotriene antagonists in the treatment of this disorder warrant further investigation.

Induction of allergic inflammation by interleukin-18 in experimental animal models

Interleukin-18 (IL-18) has been regarded as a proinflammatory cytokine because of its potent interferon-gamma-inducing activity. However, mutant mice that release excess amounts of IL-18 spontaneously develop pruritic chronic dermatitis-like atopic dermatitis (AD), suggesting the importance of IL-18 for the development of AD. Intriguingly, depletion of il-18 but not stat6, an essential transcriptional factor for IL-4 signaling, rescues the mice from AD, indicating IL-18-dependent, T-helper 2 (Th2) cell-independent AD. This type of AD is classified as innate-type allergy in contrast to Th2 cell-dependent ordinary allergy. Consistent with the previous studies, mice transferred with antigen-specific Th1 cells exhibit no airway hyperresponsiveness and respiratory eosinophilic inflammation after challenge with antigen alone. However, they suffer from asthma upon challenge with antigen plus IL-18, with comparable levels of both the alterations as in those transferred with Th2 cells following challenge with antigen. The former type of asthma is categorized as Th1-associated allergy. Therefore, it is definitely necessary to evaluate whether individual allergic disorders involve either of these IL-18-mediated pathways or a Th2-mediated one.

Increased levels of urinary leukotriene E4 in children with severe atopic eczema/dermatitis syndrome

BACKGROUND

Leukotrienes are thought to play a role in the pathogenesis of atopic eczema/dermatitis syndrome (AEDS). Urinary leukotriene E4 (U-LTE4) is a marker of whole-body cysteinyl-leukotriene production.

AIMS OF THE STUDY

To evaluate the role of leukotrienes in children with AEDS by measuring levels of U-LTE4, and to evaluate whether levels of U-LTE4 may reflect disease activity and allergic sensitization in AEDS.

METHODS

U-LTE4 was measured by enzyme-linked immunosorbent assay in 87 children with mild (n=32), moderate (n=34) and severe (n=21) AEDS, as well as in 72 nonatopic healthy controls. Fifty-eight of the children with AEDS were sensitized to common allergens, and 29 were not.

RESULTS

Levels of U-LTE4 were higher in children with severe AEDS (140; 66-166 microg/mmol creatinine, median; quartiles) than in controls (52; 30-90, P <0.05), whereas levels of U-LTE4 in moderate and mild disease were similar to controls. U-LTE4 levels were similar in children with or without sensitization to common allergens, but severe AEDS children with sensitization had higher levels of U-LTE4 than those without sensitization.

CONCLUSION

The results suggest a role for leukotrienes in the pathogenesis of severe AEDS, and may support a role for leukotriene-antagonists in the treatment of this disorder. Levels of U-LTE4 may reflect the disease severity and sensitization to allergens in AEDS.

Synthesis of eosinophil infiltration inhibitors with antihistaminic activity

A series of [1, 2, 4]triazolo[1, 5-b]pyridazines (5) and imidazo[1, 2-b]pyridazines (6) having cyclic amines was synthesized and evaluated for antihistaminic activity and inhibitory effect on eosinophil infiltration. When a piperidine or a piperazine containing a benzhydryl group and a suitable spacer was incorporated at the 6-position, the fused pyridazines were found to exhibit both antihistaminic activity and an inhibitory effect on eosinophil chemotaxis. Above all, 6a showed potent antihistaminic activity, but little blockade of central H(1) receptors in contrast with its complete blockade of peripheral H(1) receptors as determined by an ex vivo binding assay. Furthermore, 6a inhibited eosinophil infiltration of the skin caused by a topical antigen challenge in sensitized guinea pigs, while an antihistamine terfenadine was not effective. After the pharmacokinetic study, 6a was found to be rapidly hydrolyzed to 6o, which was also orally active. Compound 6o, 2-[6-[[3-[4-(diphenylmethoxy)piperidino]propyl]amino]imidazo[1, 2-b]pyridazin-2-yl]-2-methylpropionic acid dihydrate (TAK-427), having both antihistaminic and antiinflammatory activity, is currently undergoing clinical trials as a therapeutic agent for atopic dermatitis and allergic rhinitis.

Urinary leukotriene levels are increased during exacerbation of atopic eczema/dermatitis syndrome. Relation to clinical status

BACKGROUND

Leukotrienes are potent mediators of allergic inflammation and their role in the pathogenesis of allergic disorders, particularly asthma, is well established. Their importance in the pathogenesis of atopic eczema/dermatitis syndrome (AEDS) is still unclear. We aimed to compare urinary cysteinyl leukotriene (Cys-LT) levels during exacerbation and remission of AEDS in relation to clinical status, IgE levels, and eosinophil counts.

METHODS

Urinary Cys-LTs were measured by direct enzyme immunoassay in 17 adult patients with AEDS and in 17 healthy controls in whom atopy had been excluded. Cys-LTs were compared during exacerbation and remission of AEDS in relation to the clinical status measured by SCORAD. Total IgE levels were measured by enzyme-linked immunoassay (ELISA).

RESULTS

Mean clinical score during the exacerbation was 64.3 +/- 3.1 and during remission 22.4 +/- 4 (P < 0.01). Cys-LTs levels were significantly higher during the exacerbation of AEDS than in the control group (230.9 +/- 20.8 vs 123.2 +/- 9.9 pg/mg creatinine; P < 0.005). During the remission, the difference between AEDS patients and the control group was not significant (96.3 +/- 8.7 vs 123.2 +/- 9.9 pg/mg creatinine; P = 0.8). During AEDS exacerbation Cys-LTs levels were significantly correlated with the clinical status (rS = 0.73, P < 0.01) and with eosinophil counts (r = 0.86; P < 0.01) but not with the duration of the disease, age of patients, or IgE levels.

CONCLUSIONS

Our results point to enhanced biosynthesis of Cys-LTs during the AEDS exacerbations. Inflammatory cells, e.g. eosinophils are the most probable source of Cys-LTs. A strong correlation between Cys-LT levels and clinical status may in part explain preliminary clinical observations of efficacy of leukotriene antagonists in alleviating symptoms of AEDS.

Pathophysiological role of leukotrienes in dermatological diseases: potential therapeutic implications

In vitro and in vivo data have demonstrated that leukotrienes play a key role not only in allergic airway diseases but also in inflammatory reactions of the skin. Antileukotriene drugs, i.e. leukotriene receptor antagonists and synthesis inhibitors, are a new class of anti-inflammatory drugs that have shown clinical efficacy in the management of asthma, allergic rhinitis and inflammatory bowel disease. To address the question of the validity and applicability of published evidence of the use of antileukotriene drugs in dermatological diseases, we reviewed data concerning the pathophysiological effect of leukotrienes in the skin and in skin diseases, and the experience with antileukotriene treatment that has been published. In vivo and in vitro data suggest that antileukotriene treatment may have efficacy in atopic dermatitis, different types of urticaria or psoriasis and other skin diseases such as bullous skin diseases, collagenoses, Sjogren-Larsson syndrome or Kawasaki disease. Nevertheless, published evidence is very limited and before any conclusions can be drawn, additional basic research needs to be performed with regard to the role of different leukotrienes and leukotriene receptors in skin diseases. On the basis of these data, randomised and placebo-controlled clinical trials with leukotriene antagonists and synthesis inhibitors should be performed. Moreover, future studies investigating the additive benefit of antileukotriene drugs are warranted, e.g. in combination with antihistamines, corticosteroids or other anti-inflammatory drugs.

Pathophysiologic mechanisms in atopic dermatitis

Atopic dermatitis is a common, chronic inflammatory skin disease that frequently predates the development of asthma and/or allergic rhinoconjunctivitis. Recent studies have provided new insights into how the complex interrelationship of genetic, environmental, and immunologic factors may contribute to the development of atopic dermatitis. This article examines some of the factors involved in chronic cutaneous inflammation in this disease. Greater understanding of the mechanisms that underlie the pathophysiology of atopic dermatitis may lead to improved treatment strategies for this increasingly common skin disease.

The ACVD task force on canine atopic dermatitis (XXII): nonsteroidal anti-inflammatory pharmacotherapy

The pharmacotherapy of canine atopic dermatitis has relied primarily on the use of glucocorticoids and anti-histamines. During the last decade, other anti-inflammatory drugs have been investigated in clinical trials. This paper will review the studies using misoprostol, cyclosporine, tacrolimus, phosphodiesterase inhibitors, capsaicin, leukotriene inhibitors and serotonin-reuptake inhibitors for treatment of dogs with atopic dermatitis. For each drug the mechanism of action, the rationale for use in atopic dermatitis, the clinical efficacy, reported adverse effects and strength of recommendation for treatment of canine atopic dermatitis are described. At the time of this writing, there is fair evidence to support the recommendation for using cyclosporine, misoprostol and pentoxifylline for treatment of canine atopic dermatitis. This recommendation can be strengthened by the performance of additional blinded randomized controlled trials with larger number of dogs. In contrast, there is insufficient evidence to recommend for or against treatment with tacrolimus, leukotriene inhibitors, serotonin-reuptake antagonists and capsaicin.

The ACVD task force on canine atopic dermatitis (VII): mediators of cutaneous inflammation

Controversy still exists on the role of various inflammatory mediators in the pathogenesis of canine atopic dermatitis. The objective of this article is to review the most recent information available on the inflammatory mediators that have been implicated in the pathogenesis of this disease. Studies on the role of histamine, serotonin, leukotrienes and various cytokines are presented in a comparative manner reviewing the experimental evidence for a role in the pathogenesis and the arguments against it.

Anti-inflammatory activities of LDP-392, a dual PAF receptor antagonist and 5-lipoxygenase inhibitor

Leukotrienes (LTs) and platelet-activating factor (PAF) are important mediators of inflammation and allergy. LDP-392, a novel dual PAF receptor antagonist and 5-lipoxygenase (5-LO) inhibitor, has been identified. LDP-392 is 17.9-fold more potent than zileuton (5-LO inhibitor) in the RBL cytosolic 5-LO assay, and equally potent as MK 287 (PAF receptor antagonist) in the human platelet PAF receptor binding assay. The in vivo dual activities of LDP-392 were confirmed by measuring the inhibition of ex vivo LTB(4)production in rats and PAF-induced hemoconcentration in mice. Intravenous administration of LDP-392 demonstrated greater inhibition than zileuton, BN 50739 or MK 287 on arachidonic acid-induced ear edema and protected mice from LPS-induced lethality. Topical administration of LDP-392, in a dose-dependent manner, inhibited TPA-induced ear edema in mice and UVB-induced erythema in guinea-pigs. These data suggest that LDP-392, as a dual PAF receptor antagonist and 5-LO inhibitor, may be of greater clinical effectiveness.

Double-blinded, placebo-controlled, cross-over pilot study on the efficacy of zileuton for canine atopic dermatitis

Nine dogs meeting the diagnostic criteria for canine atopic dermatitis were enrolled in a double-blind, placebo-controlled, cross-over clinical trial. In this pilot study, zileuton (a 5-lipoxygenase inhibitor) given orally at 2 mg kg(-1) three times daily for 4 weeks significantly decreased erythema in dogs with atopic dermatitis but had no effect on pruritus. Zileuton was well tolerated and no adverse clinical signs were noted. However, one dog developed mild alanine aminotransaminase elevation, which resolved within 1 week of discontinuation of therapy. Monitoring of alanine aminotransaminase may be necessary in dogs receiving zileuton. Further studies with larger number of dogs are needed to evaluate the efficacy of zileuton as treatment for canine atopic dermatitis.

The release of leukotriene B4 from human skin in response to substance P: evidence for the functional heterogeneity of human skin mast cells among individuals

Substance P is located in cutaneous nerve fibres and induces wheal and flare responses, accompanied by granulocyte infiltration, upon intradermal injection. Studies with animal skin and rat peritoneal mast cells have suggested that substance P induces the release of histamine and leukotriene B4 (LTB4), a potent chemoattractant for granulocytes, from skin mast cells. However, the release of LTB4 has not been detected from mast cells enzymatically isolated from human skin. In order to investigate the mechanism of granulocyte infiltration induced by substance P in human skin, we studied the release of LTB4 and histamine in response to substance P, and the effect of dexamethasone using human skin obtained from 22 nonallergic individuals. Histamine was released from all skin tissue samples in a dose-dependent manner. However, the amount of LTB4 release, both constitutive and inducible, was variable among skin preparations. Substance P induced a large release of LTB4 from the skin of eight donors (twice to six times that of the spontaneous release), but no or only negligible release from the skin of 14 donors. The amount of constitutive release of LTB4 correlated with the amount of tissue histamine. Dexamethasone selectively abolished the inducible release of LTB4, without an effect on histamine release and the constitutive release of LTB4. These results suggest that substance P induces the release of LTB4 in a certain population of human individuals by a glucocorticosteroid-dependent mechanism, and plays an important role in neurogenic inflammation with granulocyte infiltration.

Update on the role of leukotrienes in the pathogenesis of atopy: a comparative review

The pathogenesis of atopic disease (AD) is controversial in humans and dogs. In humans, leukotrienes (LT) are thought to play an important role in this disease and LT inhibitors are commonly used as treatment for AD. Leukotrienes are a heterogeneous group of biologically active compounds that mediate many aspects of inflammatory and allergic reactions. This paper will review the role of LT in atopic disease in a comparative manner. Leukotriene inhibitors and their therapeutic use in the management of atopic disease in humans and dogs are discussed.

What are the most promising strategies for the therapeutic immunomodulation of allergic diseases?

Specific immunotherapy and other immunomodulatory strategies have long been a stronghold in the management of allergic diseases. In particular, "immunodeviation-therapy" or "vaccination for allergies", i.e. the redirection of Th2-type immune responses towards a Th1-response pattern, has become an ever more popular concept. The present feature of CONTROVERSIES complements our previous discussion of atopy (Röcken et al., Exp Dermatol 7: 97--104, 1998), and is dedicated to a critical analysis of the general problems and limitations one faces with the main immunomodulatory strategies traditionally considered in this context. We also explore alternative approaches that appear promising in order to achieve both a more effective and/or a more specific immunotherapy of allergic diseases. Given that the mast cell remains a key protagonist in the pathogenesis of allergic diseases finally, this feature examines how innovative, more selectively mast cell-targeted strategies may be developed for the management of allergic diseases.

Increased urinary leukotriene E4 excretion in patients with atopic dermatitis

BACKGROUND

Synthesis of cysteinyl leukotrienes (LTs) is known to play a part in the pathogenesis of inflammatory diseases.

OBJECTIVES

To define the involvement of cysteinyl LTs in atopic dermatitis (AD).

METHODS

Synthesis of cysteinyl LTs was assessed in patients with AD and healthy volunteers by measuring urinary LTE4, a useful index of systemic cysteinyl LT synthesis, using liquid chromatography/tandem mass spectrometry.

RESULTS

Mean +/- SD urinary LTE4 levels in patients with AD (125 +/- 69 pg mg(-1) creatinine, n = 20) were significantly higher (P < 0.01) than in healthy volunteers (60 +/- 19 pg mg(-1) creatinine, n = 17). A significant correlation between urinary LTE4 and total serum IgE levels in patients with AD was observed (r = 0.643, P < 0.05).

CONCLUSIONS

Our findings demonstrate an enhanced synthesis of cysteinyl LTs in patients with AD and suggest that cysteinyl LTs are involved in the pathophysiology of AD.

Substance P induces tumor necrosis factor-alpha release from human skin via mitogen-activated protein kinase

Substance P plays an important role in neurogenic inflammation with granulocyte infiltration. To investigate cytokines involved in the substance P-induced inflammation and the mechanism of cell activation, we studied the release of TNF (tumor necrosis factor)-alpha and histamine from human skin slices in response to substance P and antigen. Substance P induced the release of histamine and TNF-alpha in a dose-dependent manner at concentrations from 0.8 to 100 microM. PD 098059 (2'-amino-3'-methoxyflavone) selectively inhibited the release of TNF-alpha, but not the release of histamine induced by either substance P or antigen. SB 203580 ([4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-++ +imida zole]) slightly inhibited TNF-alpha release induced by antigen, but not that induced by substance P, and slightly enhanced histamine release induced by either stimulation. The release of TNF-alpha in response to either stimulation was inhibited by 1 nM-1 microM dexamethasone, but histamine release was not affected. These results suggest that substance P, in addition to antigen, induced TNF-alpha release from human skin by a mitogen-activated protein (MAP) kinase, predominantly extracellular signaling-regulated protein kinase (ERK)-dependent, and dexamethasone-sensitive pathway, which is separate from that for histamine release from mast cells.

Promoter activity and regulation of the CYP4F2 leukotriene B(4) omega-hydroxylase gene by peroxisomal proliferators and retinoic acid in HepG2 cells

The human liver CYP4F2 gene (Accession No. AF221943) encodes a leukotriene B(4) omega-hydroxylase that metabolizes leukotriene B(4) (LTB(4)) to a less potent proinflammatory eicosanoid, 20-OH-LTB(4). We sequenced a 6.7-kb genomic fragment of the human CYP4F2 gene that has the first five exons and 500 bp of the 5'-flanking region. The major transcription start site was found to be 49 bp upstream of the 3' end of exon 1 and the ATG translation initiation codon was located in exon 2. Besides the TATA box at -39 bp and basal transcription factor binding sites, the promoter region and 412-bp intron 1 have several putative binding sites for nuclear factors that may mediate the inflammatory response and lipid homeostasis. We found two DR1 elements in the 5' promoter, a DR2 element in intron 1, and RXR/RAR binding sites in both intron 1 and the 5' promoter. DNase I footprinting revealed three protected sequences, with the region containing two CAATT boxes at -71 and -111 bp important in CYP4F2 gene expression. Luciferase reporter assays showed that the 500-bp upstream sequence has strong promoter activity. Transient transfection experiments identified two sites in the 5' promoter and intron 1 that cooperate in gene transcription while exon 1 and a GC-rich region flanking exon 1 inhibit transcription. trans-Retinoic acid and 9-cis-retinoic acid stimulate promoter activity 3- and 6-fold, respectively, while cotransfection with RXRalpha or RAR/RXRalpha further enhanced activity. Peroxisome proliferators inhibit CYP4F2 gene promoter activity and cotransfection with PPARalpha or PPARalpha/RXRalpha can slightly attenuate this inhibition. Both saturated fatty acids and 12-hydroxydodecanoic acid (12-OH-C(12)) can stimulate CYP4F2 gene promoter activity. Therefore, the CYP4F2 gene is repressed by peroxisomal proliferators and induced by retinoic acid, with RAR/RXRalpha mediating the induction while PPARalpha/RXR functions neither in the repression nor in the induction by peroxisomal proliferators or retinoic acid.

Atopic dermatitis: new insights and opportunities for therapeutic intervention

Atopic dermatitis (AD) is a chronic inflammatory skin disease that frequently predates the development of allergic rhinitis or asthma. It is an important skin condition with significant costs and morbidity to patients and their families; the disease affects more than 10% of children. Recent studies have demonstrated the complex interrelationship of genetic, environmental, skin barrier, pharmacologic, psychologic, and immunologic factors that contribute to the development and severity of AD. The current review will examine the cellular and molecular mechanisms that contribute to AD as well as the immunologic triggers involved in its pathogenesis. These insights provide new opportunities for therapeutic intervention in this common skin condition.

Correlation between deposition of immuno-components and infiltration pattern of polymorphonuclear leukocytes in the lesions of chronic urticaria

Urticaria is often associated with perivascular infiltration of leukocytes into the lesions. Although mast cell-derived chemical mediators are considered to play crucial roles in the infiltration of leukocytes as well as in the dermal edema, other mechanisms for the leukocyte infiltration have not been well defined. This study revealed that approximately 25% of the cases of chronic idiopathic urticaria in whom wheals had continued for more than 12 h had deposition of immuno-components in the lesions, although histological examination of the lesions did not show leukocytoclastic vasculitis. In these lesions with deposition of immuno-components, both neutrophils and eosinophils had infiltrated at a constant ratio (approximately 2:1), whereas, in the lesions without deposition, a variable population of leukocytes was seen. This result suggests that activation of complements occurs in the lesions of a considerable percentage of patients with chronic idiopathic urticaria and that the complement fragments influence the infiltration patterns of polymorphonuclear leukocytes.