Synergistic effects of pranlukast and leukotriene B4 receptor antagonist on antigen-induced pulmonary reaction

Desflurane induces airway contraction mainly by activating transient receptor potential A1 of sensory C-fibers

We previously reported that desflurane induced airway contraction via antidromic tachykinin release from sensory C-fibers. Here, we investigated the effect of desflurane on airway lung resistance (R(L)) using specific receptor antagonists in C-fibers. Young guinea pigs were anesthetized and their tracheas were cannulated with an endotracheal tube via a tracheotomy. A Fleisch pneumotachograph and a differential transducer were used to monitor respiratory flow rate, intrapleural pressure, and airway pressure, and R(L) was calculated and recorded. A transient receptor potential A1 (TRPA1) or a transient receptor potential V1 (TRPV1) selective antagonist of sensory C-fibers, i.e., HC030031 or BCTC, was administered before the exposure to desflurane. In an additional experiment, tachykinin receptor of airway smooth muscles was antagonized only by the neurokinin-2 receptor antagonist MEN-10376 before the exposure to desflurane. HC030031 completely inhibited both the first and the second contractile responses induced by desflurane, whereas BCTC had little effect. MEN-10376 also significantly and substantially diminished the contractile response. Desflurane contracts the airway in untreated guinea pigs mainly by activating irritant gas receptor TRPA1 of afferent C-fibers, resulting in the release of contractile tachykinins such as neurokinin A.

CD8+ T cells in asthma: friend or foe?

While it is well established that CD4(+) T lymphocytes play a crucial role in the initiation, progression and persistence of asthma, the role of CD8(+) T cells is less understood. CD8(+) T cells form functionally similar subsets which exhibit similar cytokine profiles as Th1 and Th2 cells, known as Tc1 and Tc2. Evidence from animal studies suggest that CD8(+) T cells are capable of regulating IgE production through the induction of IL-12 and IL-18 production in dendritic cells, and that CD8(+) T cells may act to moderate Th2 polarisation within the localised lymph nodes during allergic sensitisation. Such findings have led to the suggestion that Th1 polarising, CD8(+) T cell-inducing vaccines would inhibit the development of airway hyperresponsiveness (AHR) and Th2 cell infiltration. Despite these positive findings, the role of CD8(+) T cells within the lung remains poorly understood. While CD8(+) T cells, particularly those expressing the Tc1 phenotype, are capable of moderating inflammation and suppressing AHR, it has been postulated that Tc2 CD8(+) T cells predominate within established asthma and may act to amplify the inappropriate immune response which defines the condition. Within the clinic, the association between CD8(+) T cells and asthma is almost universally defined as injurious, further suggesting a prejudicial role for these cells within the established disease. CD8(+) T cells may be a valuable potential target for therapeutic intervention, either by potentiating their regulatory effects prior to the development of sensitisation, or through suppressing their pro-inflammatory properties within established atopy.

Inhibitory effects of the alpha-2 adrenergic agonists clonidine and dexmedetomidine on enhanced airway tone in ovalbumin-sensitized guinea pigs

BACKGROUND AND OBJECTIVE

The alpha-2 adrenergic agonists clonidine and dexmedetomidine are used as an antihypertensive and a sedative, respectively. The aim of this study was to determine the effects of these agonists on ovalbumin-sensitized airway tone in guinea pigs.

METHODS

The animals were divided into two groups: control and sensitized. The sensitized group received ovalbumin intraperitoneally and was boosted by exposure to aerosolized ovalbumin. The effects of the alpha-2 agonists were investigated by measuring (1) total lung resistance and (2) smooth muscle tension using a tracheal ring preparation.

RESULTS

In the control group, acetylcholine significantly increased total lung resistance in a dose-dependent manner. In the sensitized animals, total lung resistance was significantly higher (by 95%) at 6 mug kg-1 acetylcholine than that in the control group. Both clonidine and dexmedetomidine had a slight but significant inhibitory effect on the response curve of lung resistance at higher concentrations of carbachol, a potent muscarinic receptor agonist. Similar to the data obtained in the control group, both clonidine and dexmedetomidine significantly decreased total lung resistance and the inhibitory effects of these alpha-2 agonists on lung resistance were significantly distinguishable. Similar direct inhibitory effects of the alpha-2 agonists on carbachol-induced muscle contraction were observed in both the control and sensitized groups, the inhibitory effects in the sensitized group being significantly greater.

CONCLUSION

Both clonidine and dexmedetomidine can relax the airway even in the hyper-reactive state.

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.

The leukotriene B4 receptor (BLT1) is required for effector CD8+ T cell-mediated, mast cell-dependent airway hyperresponsiveness

Studies in both humans and rodents have suggested that CD8+ T cells contribute to the development of airway hyperresponsiveness (AHR) and that leukotriene B4 (LTB4) is involved in the chemotaxis of effector CD8+ T cells (T(EFF)) to the lung by virtue of their expression of BLT1, the receptor for LTB4. In the present study, we used a mast cell-CD8-dependent model of AHR to further define the role of BLT1 in CD8+ T cell-mediated AHR. C57BL/6+/+ and CD8-deficient (CD8-/-) mice were passively sensitized with anti-OVA IgE and exposed to OVA via the airways. Following passive sensitization and allergen exposure, C57BL/6+/+ mice developed altered airway function, whereas passively sensitized and allergen-exposed CD8-/- mice failed to do so. CD8-/- mice reconstituted with CD8+ T(EFF) developed AHR in response to challenge. In contrast, CD8-/- mice reconstituted with BLT1-deficient effector CD8+ T cells did not develop AHR. The induction of increased airway responsiveness following transfer of CD8+ T(EFF) or in wild-type mice could be blocked by administration of an LTB4 receptor antagonist confirming the role of BLT1 in CD8+ T cell-mediated AHR. Together, these data define the important role for mast cells and the LTB4-BLT1 pathway in the development of CD8+ T cell-mediated allergic responses in the lung.

Optimization of imidazole 5-lipoxygenase inhibitors and selection and synthesis of a development candidate

Structural modification of imidazole 5-lipoxygenase (5-LO) inhibitors for optimizing inhibitory potency, pharmacokinetic behavior and toxicity (ocular) profile led to 4-{3-[4-(2-methyl-1H-imidazol-1-yl)phenylthio]}phenyl-3,4,5,6-tetrahydro-2H-pyran-4-carboxamide (6) with no observable ocular toxicity. The orally active and safe imidazole 5-LO inhibitor 6 was selected as a clinical candidate and advanced to clinical studies. An improved synthesis of 6 is also discussed.

[Leukotriene-lipoxygenase pathway and drug discovery]

The first drugs affecting the leukotriene-lipoxygenase pathway, which have been introduced in clinical application, inhibit effects of slow reacting substance of anaphylaxis (SRS-A). Although, a 5-lipoxygenase inhibitor was first used in clinical practice as an anti-asthma drug, cysteinyl-leukotriene type 1 receptor (cysLT(1)R) antagonists are preferred as anti-asthma and anti-rhinitis drugs because they are almost as effective as the 5-lipoxygenase inhibitors but have fewer side effects. The cloning of genes related to lipoxygenase-leukotriene metabolism prompted us to try to elucidate the role of leukotrienes in various inflammations. There are at least two types of cysLTRs known: cysLT(1)R and cysLT(2)R. CysLT(1)R plays an important role in the pathophysiology of asthma; however, the role of the cysLT(2)R remains unknown. The abundant distribution of cysLT(2)R in heart and brain tissues suggests that cysLTs play an important role in the pathophysiology of ischemic heart diseases or arrhythmias and through this receptor (cysLT(2)R), psychoneurological disorders. The use of a selective cysLT(2)R antagonist may clarify these questions. Since the 5-lipoxygenase pathway is abundantly expressed in atherosclerotic lesions, and 12/15-lipoxygenase is able to oxygenate polyunsaturated fatty acid esterified in the membranous phospholipids, 5-lipoxygenase or 12/15-lipoxygenase inhibitors may prevent progression of atherosclerosis. In addition, it has been reported that 15-lipoxygenase participates in suppression of prostate cancer. In conclusion, the leukotriene-lipoxygenase metabolism may be involved in the pathophysiology of acute inflammatory to chronic progressive disorders. We think that more drugs modifying leukotriene-lipoxygenase metabolism will be introduced into clinical practice in the future.

Contribution of anaphylatoxin C5a to late airway responses after repeated exposure of antigen to allergic rats

We attempted to elucidate the contribution of complement to allergic asthma. Rat sensitized to OVA received repeated intratracheal exposures to OVA for up to 3 consecutive days, and pulmonary resistance was then estimated for up to 6 h after the last exposure. Whereas the immediate airway response (IAR) in terms of R(L) tended to decrease in proportion to the number of OVA exposures, late airway response (LAR) became prominent only after three. Although premedication with two kinds of complement inhibitors, soluble complement receptor type 1 (sCR1) or nafamostat mesylate, resulted in inhibition of the IAR after either a single or a double exposure, the LAR was inhibited after the triple. Premedication with a C5a receptor antagonist (C5aRA) before every exposure to OVA also inhibited the LAR after three. Repeated OVA exposure resulted in eosinophil and neutrophil infiltration into the bronchial submucosa which was suppressed by premedication with sCR1 or C5aRA. Up-regulation of C5aR mRNA was shown in lungs after triple OVA exposure, but almost no up-regulation of C3aR. Pretreatment with sCR1 or C5aRA suppressed the up-regulation of C5aR expression as well as cytokine messages in the lungs. The suppression of LAR by pretreatment with sCR1 was reversed by intratracheal instillation of rat C5a desArg the action of which was inhibited by C5aRA. In contrast, rat C3a desArg or cytokine-induced neutrophil chemoattractant-1 induced cellular infiltration into the bronchial submucosa by costimulation with OVA, but these had no influence on the LAR. These differences might be explained by the fact that costimulation with OVA and C5a synergistically potentiated IAR, whereas that with OVA and either C3a or cytokine-induced neutrophil chemoattractant-1 did not. C5a generated by Ag-Ab complexes helps in the production of cytokines and contributes to the LAR after repeated exposure to Ag.

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.

Intratracheal administration of anaphylatoxin C5a potentiates antigen-induced pulmonary reactions through the prolonged production of cysteinyl-leukotrienes

The effects of intratracheal administration of anaphylatoxin C5a on airway inflammation have been studied using two sources of material, zymosan activated serum (ZAS) and purified rat C5a des Arg, in order to determine the influence of complement activation on allergic airway disorders.The intratracheal administration of ovalbumin (OA) to OA-sensitized rats generated two phases of airway response, an immediate airway response (IAR) occurring within 15 min and a late airway response (LAR) beginning 4-6 h after the allergen challenge. The simultaneous administration of ZAS and OA into the trachea generated a sustained elevation of airway resistance (Raw) following IAR, while that of OA or ZAS alone resulted in Raw returning nearly to the baseline just after the IAR. The elevation of Raw after the combined challenge of OA and ZAS was significantly inhibited by pretreatment with a CysLT(1) receptor antagonist, pranlukast 30 mg/kg, but after that OA or ZAS alone was not significantly inhibited by pranlukast. The intratracheal administration of purified C5a produced an airway response that was similar to, but higher than, that evoked by ZAS. Namely, the challenge with OA plus C5a resulted in a higher IAR than OA plus ZAS, and also caused an early animal death up to 6 h, which was prevented by a combined pretreatment with pranlukast and the H(1) receptor antagonist, diphenhydramine.A histological examination at 6 h after the OA challenge identified an infiltration of inflammatory cells into the bronchial submucosal tissue, with a predominance of neutrophils and fewer eosinophils. On the other hand, a histological examination after the OA and ZAS challenge showed more severe infiltration of granulocytes into the bronchial submucosal tissue than that with OA or ZAS alone. The challenge with OA plus C5a was associated with severe perivascular leakage in the lungs and the combined pretreatment with both the antagonists led to a marked reduction in perivascular leakage. The quantitation of N-acetyl-leukotriene E(4) (N-Ac-LTE(4)), a major metabolite of cysteinyl-leukotrienes (cysLTs), in the bile indicated a significantly greater and longer excretion of cysLTs, from 1 to 6 h after the combined challenge, than that after either OA or ZAS alone. This suggested a prolonged generation of cysLTs in the lung by the combined challenge.In conclusion, our findings suggest that anaphylatoxin C5a may mediate the airway inflammatory response induced by a specific antigen challenge partly through a prolonged production of cysLTs and the release of histamine.