Accumulation of leukotriene C4 and histamine in human allergic skin reactions

The CysLT2R receptor mediates leukotriene C4-driven acute and chronic itch

Interactions between the nervous system and immune system are central regulators of chronic itch, a key feature of pathologies like atopic dermatitis and allergic contact dermatitis. Cysteinyl leukotrienes (LTC₄, LTD₄, and LTE₄) are eicosanoid lipids known for mediating inflammation, bronchoconstriction, and vascular leakage. We demonstrate here that CysLTs are potent itch inducers and that this effect depends on the specific coupling of LTC₄ with its receptor CysLT₂R, which is expressed in a population of peripheral sensory neurons in the mouse and in human. We show that the LTC₄/CysLT₂R pathway contributes to a model of chronic itch, suggesting that CysLT₂R could be a new therapeutic target for intractable chronic itch.

Acute and chronic itch are burdensome manifestations of skin pathologies including allergic skin diseases and atopic dermatitis, but the underlying molecular mechanisms are not well understood. Cysteinyl leukotrienes (CysLTs), comprising LTC₄, LTD₄, and LTE₄, are produced by immune cells during type 2 inflammation. Here, we uncover a role for LTC₄ and its signaling through the CysLT receptor 2 (CysLT₂R) in itch. Cysltr2 transcript is highly expressed in dorsal root ganglia (DRG) neurons linked to itch in mice. We also detected CYSLTR2 in a broad population of human DRG neurons. Injection of leukotriene C₄ (LTC₄) or its nonhydrolyzable form NMLTC₄, but neither LTD₄ nor LTE₄, induced dose-dependent itch but not pain behaviors in mice. LTC₄-mediated itch differed in bout duration and kinetics from pruritogens histamine, compound 48/80, and chloroquine. NMLTC₄-induced itch was abrogated in mice deficient for Cysltr2 or when deficiency was restricted to radioresistant cells. Itch was unaffected in mice deficient for Cysltr1, Trpv1, or mast cells (W^Sh mice). CysLT₂R played a role in itch in the MC903 mouse model of chronic itch and dermatitis, but not in models of dry skin or compound 48/80- or Alternaria-induced itch. In MC903-treated mice, CysLT levels increased in skin over time, and Cysltr2^−/− mice showed decreased itch in the chronic phase of inflammation. Collectively, our study reveals that LTC₄ acts through CysLT₂R as its physiological receptor to induce itch, and CysLT₂R contributes to itch in a model of dermatitis. Therefore, targeting CysLT signaling may be a promising approach to treat inflammatory itch.

The employment of leukotriene antagonists in cutaneous diseases belonging to allergological field

Leukotrienes (LTs) are potent biological proinflammatory mediators. LTC4, LTD4, and LTE4 are more frequently involved in chronic inflammatory responses and exert their actions binding to a cysteinyl-LT 1 (CysLT1) receptor and a cysteinyl-LT 2 (CysLT2) receptor. LTs receptor antagonists available for clinical use demonstrate high-affinity binding to the CysLT1 receptor. In this paper the employment of anti-LTs in allergic cutaneous diseases is analyzed showing that several studies have recently reported a beneficial effects of these agents (montelukast and zafirlukast as well as zileuton) for the treatment of some allergic cutaneous related diseases-like chronic urticaria and atopic eczema although their proper application remains to be established.

A double-blind, placebo-controlled trial of montelukast in adult atopic eczema

BACKGROUND

Montelukast is an antagonist of cys-leukotriene receptors used mainly in the treatment of asthma- and seasonal-allergic rhinitis. Initial reports concerning the use of montelukast in atopic dermatitis (AD) have been encouraging, although not consistent.

OBJECTIVES

We have undertaken a randomized, double-blind, parallel-group, placebo-controlled trial to investigate further the efficacy of montelukast in the treatment of atopic eczema.

METHODS

Following a screening visit, subjects received placebo treatment for 2 weeks in a single-blind phase, followed after visit 2 by an 8-week, double-blind period of treatment with montelukast 10 mg daily or placebo. Subjects were patients aged 16-60 years under our care for treatment of AD of moderate severity, defined by a six-area, six-sign atopic dermatitis (SASSAD) score in the range 12-50. Response to treatment was assessed by investigators and by subjects using a seven-point scale, with response defined as marked improvement or better. In addition, the SASSAD score was used to monitor the severity of clinical signs. The proportion of skin involved was estimated and visual analogue scales were used to record the severity of pruritus and sleep disturbance. Topical corticosteroid usage was recorded using a five-point scale. Adverse events were recorded.

RESULTS

Sixty subjects were recruited and 54 completed the study. The treatment groups were well matched for disease severity at baseline (SASSAD scores were 25 and 29 in the montelukast and placebo groups, respectively). There were no significant differences between the treatment groups in any of the parameters used to assess treatment response. The improvement in mean SASSAD score from baseline (visit 2) to the end of treatment was marginally superior in the placebo group, 1.41 points on montelukast vs. 1.76 on placebo, a difference of 0.35 (95% confidence interval -6.1 to 6.8). Adverse events were generally of a mild nature except for a brief septicaemic illness in one subject receiving montelukast.

CONCLUSIONS

The data do not support previous reports of efficacy of montelukast in treatment of AD.

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.

Regulating leukotriene synthesis: the role of nuclear 5-lipoxygenase

Leukotrienes are lipid messengers involved in autocrine and paracrine cellular signaling. They are synthesized from arachidonic acid by the 5-lipoxygenase pathway. Current models of this enzymatic pathway recognize that a key step in initiating leukotriene synthesis is the calcium-mediated movement of enzymes, including 5-lipoxygenase, to intracellular membranes. However, 5-lipoxygenase can be imported into or exported from the nucleus before calcium activation. As a result, its subcellular localization will affect its ability to be activated by calcium, as well as the membrane to which it binds and its interaction with other enzymes. This commentary focuses on the role of 5-lipoxygenase compartmentation in determining its regulation and, ultimately, leukotriene synthesis.

The effect of montelukast (10mg daily) and loratadine (10mg daily) on wheal, flare and itching reactions in skin prick tests

Antileukotriene agents are widely used for the treatment of allergic conditions including bronchial asthma and allergic rhinitis. The influence of montelukast on skin reactivity has not been clearly evaluated. The aim of this study was to determine the effect of montelukast on wheal, flare and itching in skin prick tests (SPTs).

METHODS

Fifteen atopic patients (5 women and 10 men) with average age 28.04 (SD+/-8.24) were tested with histamine, codeine, negative control solution and allergen extract (grasses). Montelukast (10mg), loratadine (10mg) or placebo were given to the volunteers for 5 days in a double-blind manner, followed by SPT, with 14 days of wash-out period.

RESULTS

There was no differences in wheal, flare and itching (p=0.205; 0.086 and 0.069, respectively, Wilcoxon rank-sum test) between SPT performed after placebo and wash-out period. The analysis revealed a statistically significant suppression of wheal and flare by loratadine (p<0.05 for all tested solutions). Pre-treatment with montelukast did not influence wheal size (p=0.099, 0.21, 0.066 for histamine, codeine and allergens, respectively), but significantly reduced flare (p=0.005; 0.003; 0.02 for histamine, codeine and allergens, respectively). We found a significant suppression of itching produced by montelukast (p=0.02) and loratadine (p=0.03) as compared to placebo (p=0.068 vs. wash out).

CONCLUSIONS

Our data show a tendency to suppressive effect of montelukast on flare and itching but not on wheal which is basic for SPT interpretation. We conclude that found suppression have little impact on clinical effectiveness of SPT as a diagnostic tool.

Differential modulation of cell recruitment and acute edema in a model of Polybia paulista venom-induced inflammation

Hymenoptera stings are quite common and can cause inflammatory reactions (in nonallergic individuals) or serious reactions (in allergic individuals). Hymenoptera venom contains histamine, vasoactive kinins, serotonin, phospholipase A, phospholipase B, hyaluronidase, antigen 5 and mastoparans. Some of these substances are responsible for local pain, as well as for activation of complement and endothelial cells. Polybia paulista is a wasp typically found in the state of São Paulo, Brazil. In the present study, we evaluated inflammatory reactions in the peritoneal cavities of rats injected with P. paulista venom (PPV). We evaluated leukocyte recruitment and edema formation at the site of inflammation. After i.p. inoculation with PPV, there was dose-dependent and time-dependent recruitment of neutrophils, eosinophils and mononuclear cells. At 4 to 48 h after stimulus, administration of MK 886, a leukotriene synthesis inhibitor, completely abolished granulocyte recruitment to the peritoneal cavity. Therefore, leukotrienes seem to be the primary mediators of PPV-induced neutrophil and eosinophil recruitment. Inoculation with PPV also induced protein extravasation into the peritoneal cavity. This phenomenon was not inhibited by treatment with MK 886 or indomethacin (a prostaglandin synthesis inhibitor), demonstrating that neither leukotrienes nor prostaglandins are involved in this inflammatory reaction. However, edema formation was significantly inhibited by treatment with pyrilamine, indicating that the histamine H1 receptor plays a critical role in PPV-induced formation of acute edema.

Brief case series: montelukast, at doses recommended for asthma treatment, reduces disease severity and increases soluble CD14 in children with atopic dermatitis

BACKGROUND

The choice of oral therapeutic agents for the treatment of atopic dermatitis (AD) in children is limited. Montelukast, a specific cysteinyl leukotriene (LT) receptor antagonist, may be useful in alleviating AD symptoms.

OBJECTIVE

To evaluate the clinical and immunological effects of montelukast in children with AD.

METHODS

After a 2-week run-in, children with AD were started on oral montelukast 5 mg once-daily for children < 12 years of age and 10 mg for older children. The clinical severity of AD as indicated by the SCORing Atopic Dermatitis (SCORAD) score, and serum soluble CD14 and urinary leukotriene E4 (LTE4) concentrations were evaluated at baseline and the end of a 3-month treatment period.

RESULTS

Four boys and three girls, with a median (range) age of 12 (3-16) years, participated in the study. The total SCORAD was reduced in five patients (by 30-84%) and remained similar in two patients. Their median (range) SCORAD scores before and after treatment were 34.7 (16.5-54.8) and 17.0 (6.9-36.9) (p = 0.046). The intensity component of SCORAD also decreased from 5 (2-10) to 3 (1-7) (p = 0.042). Serum sCD14 levels increased significantly from 5533 (4575-6452) ng/ml to 6259 (5617-8988) ng/ml (p = 0.028), whereas urinary LTE4 levels remained the same (p = 0.735).

CONCLUSIONS

Montelukast, at doses recommended for asthma treatment, resulted in over 30% reduction in the total SCORAD in some children. Treatment with montelukast may also be associated with deviation of the immune system towards the Th1-specific pathway.

Inflammation in allergic asthma: initiating events, immunological response and risk factors

Allergic asthma affects 155 million people worldwide. Currently, it is a disease that can be controlled by diverse therapeutic approaches but that cannot be cured. This means that asthma is one of the most expensive diseases for healthcare systems in developed countries. Efficient prevention strategies are therefore greatly needed to reduce both individual morbidity and national economic burdens. This requires a detailed knowledge of the immunological and physiological mechanisms involved in asthma. This review synthesizes current understanding about the immunobiology of IgE-mediated asthma. It discusses the initiating events, the main immunological and inflammatory processes, and addresses the importance of risk factors in the development and maintenance of allergic diseases. Finally, it integrates these concepts in a theoretical causal model for atopic asthma.

The effects of montelukast on intradermal wheal and flare

OBJECTIVE

We sought to determine the effect of montelukast, a leukotriene receptor antagonist, on intradermal skin testing. Study design and setting We conducted a prospective, randomized, double-blind, placebo-controlled study in a university setting.

METHODS

After a 1-week washout of allergy pharmacotherapy, intradermal skin testing was performed on 23 atopic subjects. Whealing size was measured 20 minutes after injection. Subjects then began a 1-week regimen of daily loratadine, montelukast, or placebo. At 1 week, subjects again underwent intradermal skin testing. The change in wheal size was then calculated from baseline.

RESULTS

A significant difference (P < 0.05) between the montelukast and loratadine groups in suppression of intradermal whealing at 1 week was observed. No significant difference was noted between the montelukast and placebo subjects.

CONCLUSIONS

Montelukast demonstrated no significant suppression of skin whealing after antigen challenge over placebo.

SIGNIFICANCE

Montelukast does not need to be discontinued before intradermal allergy testing.

Carboxypeptidase A-catalyzed direct conversion of leukotriene C4 to leukotriene F4

Leukotrienes (LTs) are 5-lipoxygenase (5-LO)-derived arachidonic metabolites that constitute a potent set of lipid mediators produced by inflammatory cells. Leukotriene A(4), a labile allylic epoxide formed from arachidonic acid by dual 5-LO activity, is the precursor for LTB(4) and LTC(4) synthesis. LTC(4) is further transformed enzymatically by the sequential action of gamma-glutamyltranspeptidase and dipeptidase to LTD(4) and LTE(4), respectively. In this report, we present evidence that bovine pancreatic carboxypeptidase A (CPA), which shares significant sequence homology with CPA in mast cell granules, catalyzes the conversion of LTC(4) to LTF(4) via the hydrolysis of an amide bond. The identity of CPA-catalyzed LTC(4) hydrolysis product as LTF(4) was confirmed by several analytical criteria, including enzymatic conversion to conjugated tetraene by soybean LO, conversion to LTE(4) by gamma-glutamyltranspeptidase, cochromatography with the standard LTF(4) and positive-ion fast-atom bombardment mass spectral analysis. Thus, it appears that the physiological significance of this single-step transformation may point toward a major cellular homeostatic mechanism of metabolizing LTC(4), a potent bronco- and vasoconstrictor, to a less potent form of cysteinyl LTs.

Ex-vivo regulation of endotoxin-induced tissue factor in whole blood by eicosanoids

The influence of several eicosanoids of the lipoxygenase pathway was examined in an ex vivo system of human whole blood subjected to stimulation by lipopolysaccharide (LPS). Exogenously added leukotriene B4 [5(S),12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid (LTB4)] or 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) significantly (P<0.05) enhanced LPS-evoked expression of monocyte tissue factor (TF) activity in a concentration-dependent manner. 15(S)-HETE, on the other hand, exerted such activity only when added at certain concentrations, whereas 5(S)-HETE was devoid of any apparent activity. LPS-induced TF activity was inhibited by the lipoxygenase inhibitors nordihydroguaiaretic acid, CGS 23885 and ZM 230487, by 59, 32 and 88%, respectively. Furthermore, the production of LTB4 in LPS-stimulated whole blood was investigated, in the absence or presence of either tumor necrosis factor alpha (TNFalpha) or phorbol-12-myristate-13-acetate (PMA). LPS alone induced a moderate time-dependent and concentration-dependent release of LTB4, reaching the maximum concentration (1260 +/- 202 pg/ml) within 90 min at 5 ng/ml LPS. The prior and concurrent presence of PMA (5 ng/ml) or TNFalpha (10 ng/ml) further enhanced the LTB4 production approximately twofold (P < 0.05). TNFalpha added alone evoked approximately twice the LTB4 production seen when LPS (2200 +/- 243 versus 1260 +/- 203 pg/ml) was added alone. Considering these results, LPS and TNFalpha emerge as important agonists of LTB4 production in whole blood. LTB4 in turn appears to be of importance for the expression of TF in monocytes, potentially amplifying the thrombogenic potential of these cells.

Are cysteinyl leukotrienes involved in allergic responses in human skin?

BACKGROUND

Cysteinyl leukotrienes have been suggested to be involved in producing the symptoms of both the early and late phases of the allergic response in the lung and other tissues.

OBJECTIVE

To use scanning laser Doppler imaging, microdialysis and immunocytochemistry to explore the mediator and cellular mechanisms of the dermal allergic response.

METHODS

Thirteen atopic volunteers received intradermal injections into the forearm of grass pollen or D. pteronyssinus extract. Changes in dermal blood flow up to 8 h were monitored by scanning laser Doppler imaging. The release of histamine, PGD2 and LTC4/D4/E4 was assessed by dermal microdialysis. Skin biopsies were taken at 6 h to determine numbers of mast cells, eosinophils, basophils, Langerhans' cells, and monocytes/macrophages, and the expression of COX-1, COX-2, 5-LO and FLAP.

RESULTS

Allergen provocation produced an immediate weal and flare response followed by an erythematous induration peaking at 6 h. During the first hour, c. 84 pmoles of histamine and c. 0.3 pmoles of PGD2 were recovered by microdialysis (both P < 0.001) but LTC4/D4/E4 was undetectable. No histamine, PGD2 or LTC4/D4/E4 was detectable at later times. Immunocytochemical examination of biopsies taken at 8 h showed increased numbers of eosinophils and basophils and in COX-2, 5-LO and FLAP, but not COX-1. Expression of 5-LO and FLAP was associated primarily with eosinophils.

CONCLUSIONS

These findings suggest that inflammatory cells recruited to the site of allergen injection are not activated to release detectable amounts of cysteinyl leukotrienes. Hence, it is unlikely that the late-phase erythematous induration is mediated by this autocoid.

Hemodialysis-activated granulocytes at the site of interstitial inflammation

It is not known to what extent intravascular phenotypic alterations in adhesion molecule expression induced by hemodialysis influence the recruitment of granulocytes and their ability to up-regulate CD11b at the local site of inflammation in the interstitium. We used a skin suction chamber technique to address this issue. Two skin blisters were raised on the forearm of eight hemodialysis patients and eight healthy subjects, and blister exudate was collected (time 0). The two blisters were stimulated with buffer (intermediate inflammation) or autologous serum (intense inflammation). Then the patients underwent cuprophane hemodialysis for 4 hours. Ten hours after start of dialysis, the exudate was aspirated from each chamber. Granulocyte count and surface expression of CD11b and CD62L were analyzed in samples from peripheral blood and blister exudate by flow cytometry. Granulocytes from healthy blood donors were incubated in blister fluid from patients and healthy subjects to determine the local chemotactic activity in terms of CD11b up-regulation. The expression of CD11b increased fourfold and CD62L decreased simultaneously in patients and healthy subjects when cells transmigrated to the unstimulated blister at time 0. At the site of intermediate inflammation, granulocytes from patients had a significantly lower capacity to mobilize CD11b compared with cells from healthy subjects (P < 0.001). At the site of intense interstitial inflammation, granulocytes from patients had the capacity to mobilize the receptor and reached values close to those obtained in healthy subjects (P = 0.079). The blister exudate from patients had a similar (at time 0 and intermediate inflammation) or higher (intense inflammation; P < 0.05) capacity to up-regulate CD11b on granulocytes in vitro compared with blister exudate from healthy subjects. Granulocytes from hemodialysis patients seem to require a more intense chemotactic stimulus to up-regulate CD11b at the local site of inflammation in the interstitium compared with corresponding cells from healthy subjects despite the fact that cells transmigrate in a milieu that contains chemotactic factors with an equal or higher capacity to up-regulate CD11b. Granulocytes in hemodialysis patients seem to be more refractory to inflammatory stimuli in the interstitium.

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.

A role for leukotriene antagonists in atopic dermatitis?

Atopic dermatitis is a chronic, relapsing skin condition that affects over 2% of the population. The pathophysiology of this disease is not completely understood, but immunologic abnormalities and the subsequent release of inflammatory mediators play a central role. Treatment with glucocorticoids has long been the standard of care, but their use is limited by their adverse effect profile. Leukotrienes (LTB4, LTC4, LTD4, and LTE4) are metabolites of arachidonic acid produced through the 5-lipoxygenase pathway. They play an important role in inflammatory and atopic conditions. LT modulating agents have been used with success in asthma. Recently, there has been increased interest in the potential utility of LT antagonists in atopic dermatitis. In vitro and in vivo data have demonstrated that LTs may play a key role in atopic dermatitis. The 2 different types of LT-modulating agents are 5-lipoxygenase inhibitors and LT receptor antagonists. Since the 5-lipoxygenase inhibitor acts at an earlier step in the LT synthetic pathway, it has the ability to alter the production of all the LTs, including LTB4, while the receptor antagonists target only the cysteinyl LTs, LTC4, LTD4, and LTE4. This reduction of LTB4 activity may point to a therapeutic advantage in using LT synthesis inhibitors as opposed to LT receptor antagonists for atopic dermatitis. Clinical evidence of the use of LT agents in atopic dermatitis is limited, but initial results have been promising and these agents may one day serve as corticosteroid-sparing treatments for atopic dermatitis.

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.

Staphylococcus aureus enterotoxins induce histamine and leukotriene release in patients with atopic eczema

BACKGROUND

Chronic skin colonization with Staphylococcus aureus is a characteristic feature of atopic eczema (AE), and about 60% of S. aureus strains isolated from the skin of patients with AE secrete enterotoxins. Furthermore, IgE antibodies to S. aureus enterotoxins have been identified in 78% of patients with AE.

OBJECTIVES

To examine the S. aureus enterotoxin-induced histamine and leukotriene release of basophils from patients with AE.

METHODS

Peripheral blood basophils from patients with AE were stimulated with the staphylococcal enterotoxins A, B, D, E and toxic shock syndrome toxin-1. Additionally, priming experiments were performed with interleukin (IL)-3, IL-8 and granulocyte/macrophage colony-stimulating factor followed by stimulation with S. aureus enterotoxins.

RESULTS

In patients with AE, basophils secreted significantly higher amounts of histamine and leukotriene C4 (LTC4) than in healthy controls. The priming experiments showed additional histamine and LTC4 release in the group of AE patients.

CONCLUSIONS

Histamine and leukotriene generation from atopic basophils stimulated with staphylococcal enterotoxins may indicate a role for these toxins as possible allergens in at least a subgroup of patients with AE.

Evidence of 5-lipoxygenase overexpression in the skin of patients with systemic sclerosis: a newly identified pathway to skin inflammation in systemic sclerosis

OBJECTIVE

Leukotrienes are a family of arachidonic acid derivatives with potent proinflammatory and profibrotic properties, and 5-lipoxygenase (5-LOX) catalyzes two key steps in the leukotriene biosynthetic pathway. Since inflammatory cell infiltrates and excessive fibrosis are hallmarks of systemic sclerosis (SSc) skin lesions, we undertook the present study to investigate the expression of 5-LOX in skin biopsy specimens from patients with SSc.

METHODS

Expression of 5-LOX in skin sections from 10 SSc patients and 8 healthy controls was examined by in situ hybridization with specific riboprobes and by immunohistochemistry analysis with 5-LOX monoclonal antibodies. Synthesis of 5-LOX by cultured dermal fibroblasts from 7 patients with SSc and 4 controls was measured by fluorescence-activated cell sorter analysis. In addition, concentrations of leukotriene B4 (LTB4) and LTE4 in fibroblast supernatants after stimulation were determined using enzyme immunoassays.

RESULTS

Expression of 5-LOX was found in all skin sections from SSc patients as well as from controls. However, the number and percentage of 5-LOX-positive cells were significantly higher in SSc skin sections compared with control sections. Expression of 5-LOX was seen in cells within perivascular inflammatory infiltrates as well as in fibroblasts throughout the skin. The experiments with cultured skin fibroblasts revealed that 5-LOX was constitutively expressed in these cells, which resulted in the production of leukotrienes after cell stimulation. Whereas no difference was found for LTE4, SSc fibroblasts produced significantly higher amounts of LTB4 after stimulation, compared with healthy control fibroblasts.

CONCLUSION

The results of this study suggest that the 5-LOX pathway may be of significance in the pathogenesis of SSc and may represent a target for new treatment strategies.

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.

Sulphido-leukotriene production from peripheral leukocytes and skin in clinically normal dogs and house dust mite positive atopic dogs

Pathogenesis of canine atopy has not been completely elucidated. In humans, sulphido-leukotrienes (s-LT) play a role in atopy, and increased production of s-LT occurs in the skin and peripheral leukocytes after allergen challenge. The study population included 16 clinically normal and 13 atopic dogs. All atopic dogs had in common a positive reaction (4+) to the intradermal injection of house dust mite (allergen of reference). Blood samples and skin biopsies were collected. Sulphido-LT synthesis by peripheral leukocytes after stimulation was measured, and no statistically significant difference was found between clinically normal and atopic dogs. Sulphido-LT concentrations in skin samples from stimulated and unstimulated sites were measured, and no statistically significant difference was detected between clinically normal and atopic dogs or between lesional and nonlesional skin within the atopic group. Clinical signs of atopic dogs were graded by owners and no correlation was found between their severity and cutaneous concentrations of s-LT. In this study there was no increase in s-LT synthesis in atopic dogs.

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.

Suppression of the early and late cutaneous allergic responses using fexofenadine and montelukast

BACKGROUND

The relative contribution of histamine and the cysteinyl leukotrienes to the early and late cutaneous allergic responses (ECAR and LCAR) can be studied using antagonists of these mediators.

OBJECTIVE

To determine the relative suppression of the ECARs and LCARs using standard doses of an H1-receptor antagonist, a cysteinyl leukotriene1-receptor antagonist, and the two antagonists administered concurrently.

METHODS

We carried out a prospective, randomized, double-blind, placebo-controlled, four-way crossover study in 12 highly allergic participants. Intradermal tests with standardized allergen, and with histamine phosphate, LTD4, and saline controls were performed on 5 different test days as follows: pretreatment baseline and at steady state immediately after the seventh and last dose of a 1-week course of treatment with once-daily fexofenadine, 120 mg; montelukast, 10 mg; fexofenadine and montelukast administered concurrently; or placebo. On each test day, the skin test results were read at intervals from 0.25 to 24 hours after the intradermal injections were performed.

RESULTS

After allergen injection, compared with baseline, all treatment regimens significantly decreased the ECAR and LCAR. After allergen injection, compared with placebo, fexofenadine significantly decreased the ECAR and the LCAR from 0.25 to 2 hours and at 8 hours. Montelukast did not significantly decrease the ECAR or LCAR. Fexofenadine and montelukast administered concurrently were not more effective than fexofenadine alone at any time. In the control skin tests, compared with placebo, fexofenadine, but not montelukast, significantly decreased the histamine-induced response, and montelukast, but not fexofenadine, significantly decreased the LTD4-induced response.

CONCLUSIONS

Fexofenadine and montelukast administered concurrently were not significantly more effective than fexofenadine alone in decreasing the ECAR and LCAR. Montelukast does not need to be discontinued before allergen skin testing. Further studies of the effect of concurrent treatment with higher doses of a histamine antagonist and a leukotriene modifier on the allergic response in the skin are needed.

Humoral and cellular responses to histamine and pollen allergen in a skin chamber model: effect of mizolastine

BACKGROUND

Mizolastine is a new non-sedative antihistamine and antiallergic drug proven to be effective and safe in the treatment of allergic rhinitis and urticaria.

OBJECTIVE

To quantitatively explore the time course of mediator release and cell recruitment during allergen challenge and the effects of mizolastine on the event, using the skin chamber model.

METHODS

Twelve pollen-sensitive patients (23+/-6 years) were included in a double-blind crossover study. Patients received 10 mg mizolastine or placebo once daily in the first 4-day period and, after a 3-week washout period, vice-versa in the crossover period. On day 4 of each period, a non-invasive in vivo skin chamber technique was used to determine the alteration of vascular permeability, mast cell mediator release, the release of soluble intercellular adhesion molecule -1(sICAM-1) in skin sites challenged with exogenous histamine or grass pollen allergen extract, over an 8-hour period.

RESULTS

Challenge with allergen-induced significant mast cell activation, as indicated by the release of histamine, tryptase and LTC4, in chamber fluids 2 hours after initiation of the allergic reaction and during the following 6 hours. Both exogenous histamine and allergen induced significant vasodilatation, which was sustained during the 8-hour challenge, as indicated by the accumulation of protein in the chamber fluids. Likewise, both histamine and allergen induced the release of significant amounts of ICAM-1 throughout the 8-hour period. Mizolastine significantly inhibited the histamine- and allergen-induced extravasation (after 2 hours, P = .003; after 8 hours, P = .009; after 2 hours, P = .044; after 8 hours, P = .003 respectively) and the histamine- and allergen-induced--ICAM-1 release (after 2 hours, P = .004; after 8 hours, P = .05; after 2 hours, P = .03 respectively).

CONCLUSION

Mizolastine strongly inhibited the local response to histamine in this skin chamber model with, of interest, inhibition of the release of the soluble adhesion-molecule ICAM-1.

Temporal patterns of mediator release during developing cutaneous late-phase reactions

BACKGROUND

Several inflammatory mediators have been found released in sites of cutaneous late phase reactions (LPR). However, the temporal pattern of their release during LPR development has not been characterized.

OBJECTIVE

Determine hourly accumulation of mediator release in comparison with gross and inflammatory cell responses during developing LPR.

METHODS

Skin chamber appended to sites of allergen and diluent control challenge with hourly collections. Then, study of exuding leucocytes in chamber bases.

RESULTS

In the allergen-challenged sites, histamine release peaked in the first hour, then low level release over the next 5 h. Lactoferrin release from neutrophils started by the second hour, likely associated with released IL-8. Eosinophil cationic protein levels started increasing slightly later. The percentage of exuding leucocytes which were activated was significantly higher in the allergen challenge sites than in the control challenge sites

CONCLUSIONS

Both gross LPR and local inflammatory cell responses in the skin start soon after the immediate mast cell activation in IgE-mediated responses. Such inflammatory responses include leucocyte activation and mediator release.

Psoriasis and the arachidonic acid cascade

Arachidonic acid (5.8,11,14-eicosatetraenoic acid C20:4, n-6) is released from the cell membrane by the action of phospholipases on membrane phospholipids. Metabolites of arachidonic acid, which are generically termed eicosanoids, including prostaglandins, thromboxane, leukotrienes and hydroxyeicosatetraenoic acids, have been implicated as mediators or modulators of a number of physiological functions and pathological conditions in both normal and diseased human skin. Particularly, eicosanoids have been suspected to play an important role in the pathogenesis of psoriasis, because a number of phenomena observed in psoriasis can be explained, at least in part, by the action of eicosanoids. This review will focus on recent progress regarding the significance of eicosanoids in the pathogenesis of psoriasis. Recent developments in the molecular biology in the eicosanoids have renewed interest in the role of eicosanoids in psoriasis. New understanding of the etiology of psoriasis and advances in its treatment due to recent progress in eicosanoid biology will also be presented.

Comparison of inflammatory events during developing immunoglobulin E-mediated late-phase reactions and delayed-hypersensitivity reactions

To compare cellular and mediator responses in early developing late-phase skin reactions (LPR) and delayed-hypersensitivity (DH) reactions in the same subjects, responses in skin chambers overlying sites of challenge with pollen antigen and Candida albicans antigens were compared in six humans with demonstrated prominent LPR and DH responses. Histamine levels in overlying chamber fluids at 1 h were much higher at LPR than at DH sites (P = 0.002). After the next 4 h, leukocyte exudation was higher at LPR than at DH sites (P = 0.005). Most leukocytes were activated neutrophils with greater frequency of superoxide-secreting cells and released lactoferrin at LPR than at DH sites (P = 0.01 and P = 0.02, respectively). The frequency of exuding eosinophils was higher, but not significantly so (P = 0.5), at LPR sites. Although significantly more eosinophils at LPR sites were activated (P = 0.02), the levels of released eosinophilic cationic protein were not significantly higher at LPR sites (P = 0.09). The levels of interleukin-8 (IL-8), but not IL-6, were greater at LPR than at DH sites. During the first 5 h of challenge there was greater mast cell activation and subsequent exudation of activated neutrophils at sites of developing LPR than at DH sites, possibly related to greater local IL-8 levels. The frequency of activated eosinophils was also greater at LPR sites. These different initial inflammatory responses could play a role in determining expression of LPR or DH reactions.

Comparison of inflammatory events in skin sites with and without cutaneous late-phase reactions after prominent immediate IgE-mediated responses

BACKGROUND

A number of inflammatory events have been detected in skin chambers overlying sites of developing late-phase reactions (LPR) to pollen antigens in sensitive subjects. However, the pathogenic significance of such events is still unclear.

OBJECTIVE

We sought to compare inflammatory responses and cytokine levels in skin chambers that overlie sites of antigen challenge in individuals with and individuals without LPRs after immediate wheal responses of similar intensity.

RESULTS

Early histamine releases at antigen sites were similar in eight subjects with LPR (+/+ group) and eight subjects without LPR (+/- group). However, histamine releases during hours 2 through 5 of antigen challenge were significantly greater in the +/+ subjects than in the +/- subjects. Total exuding leukocytes; percent eosinophils; and levels of eosinophil cationic protein, lactoferrin, and IL-8 were significantly greater at antigen versus buffer control challenge sites in both the +/+ and +/- groups, with no significant differences between the groups. IL-1 and IL-6 levels were not greater at antigen sites than at buffer sites.

CONCLUSIONS

The only significantly greater antigen-induced response detected in +/+ subjects than in +/- subjects was in later histamine release, which is possibly a marker of other inflammatory responses because histamine itself does not induce LPRs. Other inflammatory events assessed may be somewhat greater in +/+ subjects, but not significantly so.

Involvement of leukotrienes in allergic pleurisy in actively sensitized rats: inhibition by the lipoxygenase inhibitor T-0757 of the increase in vascular permeability and leukotriene E4 production

The relative contributions of inflammatory mediators to the increase in vascular permeability in antigen-induced pleurisy were examined in rats actively sensitized with ovalbumin. The effects of various inhibitors were assessed on the exudate volume and plasma exudation rate in the pleural cavity. Two peaks were observed in plasma exudation rate at 0.5 and 3 h after antigen challenge. At 0.5 h, there was a marked decrease in the histamine content of the pleural cells and also a sharp increase in the LTE4 level in the exudate, which was inhibited dose-dependently by the lipoxygenase inhibitor T-0757. Indomethacin and cyproheptadine both depressed exudate volume and exudation rate, whereas T-0757 only reduced the exudation rate. At 3 h, a substantial LTE4 concentration was still detected in the exudate, and the exudation rate was depressed by T-0757 and indomethacin, but not by cyproheptadine. These results suggest that histamine is involved mainly in the early phase, and leukotrienes predominantly contribute to the later phase of exudation. Prostaglandins appear to be involved in both phases. Allergic pleurisy of rats, therefore, may be a suitable model to examine the roles of these inflammatory mediators.

Simplified method for measuring urinary leukotriene E4

The conventional method for measuring urinary leukotriene E4 (LTE4) is by reversed-phase high-performance liquid chromatography (RP-HPLC), followed by radioimmunoassay (RIA) or enzyme immunoassay (EIA). We measured urinary LTE4 levels by two methods, HPLC with EIA and EIA alone after initial crude extraction of urine using an octadecyl reversed-phase extraction cartridge (Sep-Pak). Ninety-three urine samples from normal subjects and patients with bronchial asthma and adult respiratory distress syndrome were tested. The results showed that urinary LTE4 levels measured by EIA significantly correlated with those measured by HPLC plus EIA in the three groups (r = 0.88, 0.85, 0.68). The absolute values of urinary LTE4 measured by EIA without HPLC purification were higher than by EIA with HPLC purification. This suggests that HPLC may not be necessary for routine urinary LTE4 quantitation in different clinical situations.

Involvement of leukotrienes in allergic inflammation in mice

The involvement of leukotrienes in the anaphylactic paw edema was investigated in sensitized boosted or unboosted mice. No difference was noted in the intensity of the antigen-induced paw edema between boosted and unboosted animals. Since the non-steroidal anti-inflammatory agents, indomethacin and aspirin, were inactive, cyclooxygenase products are not involved in the anaphylactic reaction in boosted or unboosted mice. In contrast, the mixed lipoxygenase/cyclooxygenase inhibitor, BW 755C (3-amino-1-m-(trifluoroethyl)phenyl-2-pyrazoline), and the LTD4 (leukotriene D4) receptor antagonist, LY 171883 (1-(2-hydroxy-3-propyl-4-(4-(1H-tetrazol-5-yl)butoxy)phenyl)eth anone, reduced the edema in boosted but not unboosted mice, suggesting the involvement of lipoxygenase metabolites in the allergic edema in boosted mice. Dexamethasone was only effective in inhibiting allergic edema in boosted mice when administered 12 h before provocation, but failed to reduce the edema in unboosted mice. Our results suggest that the booster injection during immunization shifts the anaphylactic mouse paw edema from a leukotriene-independent to a leukotriene-dependent reaction.

The effect of immunotherapy on the cutaneous late phase response to antigen

BACKGROUND

This study used the skin chamber model to evaluate prospectively the effect of immunotherapy (IT) on the cutaneous early and late phase response (LPR) to epicutaneous antigen challenge.

METHODS

Nine subjects with allergic rhinitis were studied at three time points: before starting IT, after 3 months of IT, and after 6 months of IT. Skin chamber histamine content was measured hourly for 12 hours, and cell counts performed hourly during hours 6 to 12. An intradermal skin test was placed, and the reaction was measured hourly for 12 hours. Skin biopsy specimens were obtained 8 hours after intradermal placement and evaluated for cellular infiltrate and major basic protein deposition. Serum antigen-specific IgG and IgE levels were measured at each time point to confirm physiologic effect of IT.

RESULTS

Six months of IT significantly (p < 0.05) decreased both early and LPR skin test reactivity and skin chamber histamine for hours 1 to 3, 4 to 6, and 9 to 12. Skin chamber LPR cellular influx decreased significantly (p < 0.05) for neutrophils only. Decrease in LPR histamine after 6 months of IT was significantly correlated with both decrease in mononuclear cells (R2 = 0.817, p = 0.002) and decrease in neutrophils (R2 = 0.813, p = 0.009). Also significantly correlated were decrease in LPR skin test reactivity, with percent change in skin chamber mononuclear cells (R2 = 0.800, p = 0.009) and decrease in early skin test reactivity (R2 = 0.675, p = 0.01). Biopsy specimens showed no consistent change in either dermal cellular infiltrate or deposition of major basic protein.

CONCLUSION

IT significantly attenuates cutaneous histamine release and skin test reactivity and is accompanied by a decrease in skin chamber LPR neutrophil influx without significantly altering the dermal infiltrate at 8 hours.