Renato S.B. Cordeiro

Cyclooxygenase-2-Derived Prostaglandin E2 and Lipoxin A4 Accelerate Resolution of Allergic Edema in Angiostrongylus costaricensis-Infected Rats: Relationship with Concurrent Eosinophilia

In noninfected rats, challenge with allergen following local IgE sensitization induced a pleurisy marked by intense protein exudation that plateaued from 30 min to 4 h after challenge, reducing thereafter. Infection of rats with Angiostrongylus costaricensis induced a 5-fold increase in blood eosinophil numbers by 25 days postinfection, whereas the numbers of eosinophils in the pleural cavity ranged from normal to a weak increase. In infected rats, identically sensitized, challenge with Ag induced a much shorter duration of pleural edema with complete resolution by 4 h, but no change in the early edema response. In parallel, infection increased the number of eosinophils recovered from the pleural cavity at 4 h, but not at 30 min, following allergen challenge. Pretreatment with IL-5 (100 IU/kg, i.v.) also increased eosinophil numbers in blood and, after allergen challenge, shortened the duration of the pleural edema and increased pleural eosinophil numbers. There were increases in the levels of both PGE2 and lipoxin A4 (LXA4) in pleural exudate. Selective cyclooxygenase (COX)-2 inhibitors, NS-398, meloxicam, and SC-236, did not alter pleural eosinophilia, but reversed the curtailment of the edema in either infected or IL-5-pretreated rats. Pretreatment of noninfected animals with the PGE analogue, misoprostol, or two stable LXA4 analogues did not alter the magnitude of pleural exudation response, but clearly shortened its duration. These results indicate that the early resolution of allergic pleural edema observed during A. costaricensis infection coincided with a selective local eosinophilia and seemed to be mediated by COX-2-derived PGE2 and LXA4.

Cutting Edge: Lipoxin (LX) A4 and Aspirin-Triggered 15-Epi-LXA4 Block Allergen-Induced Eosinophil Trafficking

Tissue eosinophilia prevention represents one of the primary targets to new anti-allergic therapies. As lipoxin A4 (LXA4) and aspirin-triggered 15-epi-LXA4 (ATL) are emerging as endogenous “stop signals” produced in distinct pathologies including some eosinophil-related pulmonary disorders, we evaluated the impact of in situ LXA4/ATL metabolically stable analogues on allergen-induced eosinophilic pleurisy in sensitized rats. LXA4/ATL analogues dramatically blocked allergic pleural eosinophil influx, while concurrently increasing circulating eosinophilia, inhibiting the earlier edema and neutrophilia associated with allergic reaction. The mechanisms underlying this LXA4/ATL-driven allergic eosinophilia blockade was independent of mast cell degranulation and involved LXA4/ATL inhibition of both IL-5 and eotaxin generation, as well as platelet activating factor action. These findings reveal LXA4/ATL as a novel class of endogenous anti-allergic mediators, capable of preventing local eosinophilia.

Differential inhibition by two hetrazepine PAF antagonists of acute inflammation in the mouse

1 The injection of 100 or 300 μg of carrageenin into the mouse paw or pleural cavity produced a delayed inflammatory reaction at 48 h while platelet activating factor (PAF)‐induced paw oedema and pleurisy were maximal 30 min after its injection. 2 The PAF antagonist, WEB 2086, failed to inhibit mouse paw oedema and pleurisy induced by PAF, but reduced the first phase of oedema (1–4 h) induced by carrageenin without interfering with the second one (48–72 h). In contrast, another structurally‐related PAF antagonist, WEB 2170, inhibited dose‐dependently both oedema and pleurisy induced by PAF and by carrageenin (48 h). 3 Repeated injections of PAF into the mouse paw or pleural cavity led to significant auto‐desensitization. The animals desensitized to PAF and injected with carrageenin also displayed a significantly reduced oedema. 4 Our results suggest that PAF may be involved in the inflammatory response to carrageenin in mice. Furthermore, because the different receptor antagonists displayed distinct effects against PAF itself, different sites for in vivo interaction of PAF are available and are species‐ and drug‐dependent.

Alloxan Diabetes Reduces Pleural Mast Cell Numbers and the Subsequent Eosinophil Influx Induced by Allergen in Sensitized Rats

Alloxan damages insulin-producing cells and has been used as an inducer of experimental diabetes in several animal species. In this study, administration of alloxan (40 mg/kg, i.v.) to rats was followed by a selective and time-dependent reduction in the number of pleural mast cells (50 +/- 2.2%, p < 0.01; mean +/- SEM), while mononuclear cell and eosinophil counts were not altered. As compared to naive rats, the reduction in mast cell numbers was first noted 48 h following alloxan administration and remained unaltered for at least 60 days. It is noteworthy, that the depletion in the mast cell population was not accompanied by alterations in the total amount of histamine stored per cell. Sensitized rats turned diabetic by alloxan treatment performed 72 h before challenge showed a less pronounced antigen-induced mast cell degranulation compared to nondiabetic rats. Moreover, rats injected with alloxan 72 and 48 but not 24 h before challenge, reacted to allergenic challenge with 50% reduction in the number of eosinophils recruited to the pleural cavity within 24 h. We found that the less pronounced eosinophil accumulation did not relate to an intrinsic cell locomotor abnormality since eosinophils from diabetic rats presented similar chemotactic responses to LTB4 and PAF in vitro as compared to matching controls. Insulin (3 IU/rat) restored basal levels of mast cells and reversed the subsequent inhibition of allergen-induced pleural eosinophilia, suggesting a causative relationship between these phenomena. Treatment with insulin also significantly increased the number of mast cells in the pleural cavity of naive rats (from 637 +/- 57 to 978 +/- 79 x 10(3) cells/cavity, p < 0.001). Consistently, previous depletion of mast cells by means of local treatment with compound 48/80 significantly reduced the antigen-induced eosinophil recruitment in sensitized animals. We conclude that the reduction in the pleural mast cell population noted in alloxan-treated rats could be directly implicated in the diminished pleural eosinophil influx following allergen challenge. This hyporesponsiveness is independent of an intrinsic abnormality of cell chemotaxis, but can be imitated by local mast cell depletion.

Pharmacological modulation of Paf‐induced rat pleurisy and its role in inflammation by zymosan

1 The intrapleural injection of Paf‐acether into rats caused, at 30 min, a marked exudation accompanied by a reduction in the pleural leucocyte count. At 6 h, the exudate volume had decreased and a significant increase in the total leucocyte count, particularly eosinophils was noted. 2 Two Paf‐acether antagonists, WEB 2086 and 48740 RP abrogated the pleural leucopenia observed 30 min after Paf‐acether administration, whereas the exudation was inhibited only by the former. Pleurisy was also reduced by about 60% with dexamethasone, by about 45% with BW 755C or LY 171883, a mixed cyclo‐oxygenase/lipoxygenase inhibitor and a peptido‐leukotriene antagonist respectively, and by about 30% with indomethacin, flurbiprofen or piroxicam. 3 Repeated daily intrapleural injections of Paf‐acether led to a state of progressive desensitization to Paf‐acether itself, whereas responsiveness to 5‐hydroxytryptamine was maintained. In addition, the Paf‐induced auto‐desensitization was largely inhibited by WEB 2086. 4 Pleurisy induced by zymosan, but not by carrageenin, was significantly reduced in Paf‐acether‐desensitized animals. These results were consistent with those obtained with WEB 2086 which supressed zymosan‐induced but not carrageenin‐induced pleurisy. 5 This study suggests that Paf‐acether‐induced pleurisy in the rat may be mediated by lipoxygenase arachidonic acid metabolites and that pleurisy induced by zymosan, but not by carrageenin, is largely dependent upon Paf‐acether.

Neutrophil infiltration is implicated in the sustained thermal hyperalgesic response evoked by allergen provocation in actively sensitized rats

&NA; It has been proposed that allergen provocation induces hyperalgesia but the involvement of immunoglobulin E and leukocytes remains poorly understood. Here, we have compared the profile of allergen‐evoked thermal hyperalgesic response in both passively and actively sensitized rats, and investigated the role of leukocytes in allergen‐evoked nociception. Wistar rats were passively sensitized with an intraplantar injection of immunoglobulin E anti‐dinitrophenylated bovine serum albumin monoclonal antibody (0.5 &mgr;g/paw), and challenged with dinitrophenylated bovine serum albumin (0.5 &mgr;g/paw) 24 h later. Alternatively, the animals were actively sensitized with a mixture of Al(OH)3 and ovalbumin and challenged intraplantarly with ovalbumin (12 &mgr;g/paw) 14 days later. We found that the thermal hyperalgesic responses set in very rapidly and with comparable intensity in both passively and actively sensitized rats. However, while in the former group the response was shorter, peaking within 1 h and reducing thereafter, a marked plateau was observed from 1 to 6 h post‐challenge in the latter group. Actively sensitized rats also had higher neutrophil influx in the plantar tissue, as attested by both myeloperoxidase activity and histological analysis. Treatment of actively sensitized rats with either fucoidin (10 mg/kg, i.v) or anti‐rat neutrophil antiserum (i.p.) reduced neutrophil accumulation and the late hyperalgesic response noted from 3 to 6 h post‐challenge. Thus, we conclude that though immunoglobulin E‐mediated mechanisms can cause thermal hyperalgesia, components of the cellular immune reaction are crucial in order to amplify and sustain the immediate hyperalgesic response triggered by allergen, in a process dependent on neutrophil recruitment.

Suppressive effect of distinct bradykinin B2 receptor antagonist on allergen-evoked exudation and leukocyte infiltration in sensitized rats

Bradykinin is suggested to play a role in the pathophysiology of several acute and chronic diseases, including allergic disorders such as asthma. In the present study, we have investigated the importance of bradykinin in mediating allergic inflammation in rats. To this end we have tested the effects of the B2 receptor antagonists Hoe 140, FR173657 or FR172357 on the pleural inflammatory response triggered by intrapleural (i.pl.) injection of allergen (ovalbumin, 12 μg cavity−1) in 14 day‐actively sensitized Wistar rats. Analysis of the pleural fluid effluent revealed a sequence of mast cell‐dependent inflammatory events, including early protein exudation and neutrophilia and late pleural eosinophil influx. Local treatment with Hoe 140 (0.1 and 1 μg cavity−1), FR173657 (1 and 10 μg cavity−1) or FR172357 (1 and 10 μg cavity−1) inhibited dose‐dependently allergen‐induced mast cell activation with impairment of pleural plasma leakage, neutrophil accumulation and late eosinophil influx. Moreover, the B2 receptor antagonists also dose‐dependently inhibited the allergic like inflammatory pleurisy triggered by bradykinin (50 μg cavity−1), which is characterized by acute mast cell degranulation, protein leakage and pleural eosinophil infiltration. Taken together, our findings provide substantial evidence to suggest that bradykinin acting on its B2 receptors play a critical role in mediating allergic mast cell‐dependent inflammation in rats, and suggest that B2 receptor antagonists may be useful therapeutically to control allergic dysfunction.

Effects of inhibitors of inflammatory mediators and cytokines on eosinophil and neutrophil accumulation induced by Mycobacterium bovis bacillus Calmette-Guérin in mouse pleurisy.

In this work we characterize the Mycobacterium bovis bacillus Calmette‐Guérin(BCC) ‐induced pleurisy and investigate the role of chemical mediators and cytokines in BCG‐induced granulocyte accumulation at 24 h. Intrathoracic injection of BCG in C57B1/6 mice induces a biphasic inflammatory reaction with intense leukocyte accumulation at 24 h and 15 days. Neutrophils were observed in the pleural cavity at 4‐24 h, mononuclear cells and eosinophils after 24 h. A new wave of mononuclear cells and neutrophils were observed after 15 days. Pretreatments with dexamethasone, BW 755C, BW A4C, WEB 2170, L‐NAME, and monoclonal antibody (mAb) anti‐interleukin‐5 (IL‐5; TRFK‐5) had inhibited the eosinophil accumulation. On the other hand, only the pretreatments with dexamethasone, L‐NAME, or mAb antitumor necrosis factor a (TNF‐α; MP6‐XT3) had inhibited the neutrophil influx. These results suggest the involvement of leukotrienes, platelet‐activating factor, nitric oxide, and IL‐5 in the eosinophil accumulation, and a role for nitric oxide and TNF‐α in the neutrophil influx induced by BCG. J. Leukoc. Biol. 62: 778–785; 1997.

Endothelin-1 inhibits PAF-induced paw oedema and pleurisy in the mouse

1 The current study analyses the effects of endothelin‐1 (ET‐1) on paw oedema and pleurisy induced by platelet activating factor (PAF) and other inflammatory agents in the mouse. 2 Combined subplantar injection of ET‐1 (0.5 pmol/paw) did not modify oedema caused by histamine (1 to 100 μmol/paw), 5‐hydroxytryptamine (1 to 100 μmol/paw) or bradykinin (1 to 100 nmol/paw) but markedly inhibited the response to PAF (0.95 to 3.8 nmol/paw). The selective action of ET‐1 against PAF‐induced (1.9 nmol/paw) oedema was dose‐dependent, reaching a maximum at 0.5 pmol/paw and lasted up to 2 h. 3 ET‐1 (0.5 pmol/paw) also inhibited paw oedema (3–4 h) caused by zymosan (500 μg/paw). In contrast, it did not modify either the early (1–4h) or late (48–72 h) phases of the oedematogenic response to carrageenin (300 μg/paw), when given either together with or 24 h after the carrageenin. 4 Intrathoracic injection of PAF (1.9 nmol/cavity) induced pleurisy characterized by an increase in pleural exudate volume, and in accumulation of Evans Blue which was maximal at 30 min and lasted up to 4h. When injected together with PAF, ET‐1 (0.5 pmol/cavity) virtually abolished PAF‐induced pleurisy. 5 It is concluded that ET‐1 is a potent inhibitor of PAF‐induced inflammation in the mouse. Its mechanism of anti‐inflammatory action in this species, in contrast to what has been found in other species, does not appear to derive from its potent vasoconstrictor properties as ET‐1, at the doses used, failed to affect oedematogenic responses to other inflammatory mediators.

EFFECT OF AZELASTINE ON PLATELET-ACTIVATING FACTOR AND ANTIGEN-INDUCED PLEURISY IN RATS

The interference of azelastine with pleurisy induced by antigen was investigated in actively sensitized rats. The antigenic challenge (ovalbumin, 12 micrograms/cavity) caused early plasma leakage, which peaked within 4 h, accompanied by intense neutrophil infiltration. Pleural exudate decayed 24 h after antigen provocation, when a long-lasting increase in the number of resident eosinophils was observed. Oral pretreatment with azelastine (1-10 mg/kg) dose dependently inhibited the vasopermeation (ED50 = 4.2 mg/kg) and reduced the pleural exudate (ED50 = 6.8 mg/kg) induced by the antigen. In contrast, azelastine (10 mg/kg) failed to modify the neutrophil influx observed at 4 h and the eosinophil accumulation detected at 24 h. Azelastine was also effective against rat pleurisy induced by either platelet-activating factor (PAF-acether), histamine or serotonin. It reduced exudation and the increase in the number of mononuclear cells, neutrophils and eosinophils observed 6 h after PAF-acether. Nevertheless, antagonism of PAF-acether may not be relevant to the inhibition observed in the present model of allergic pleurisy, as the inhibition was refractory to three distinct PAF-acether receptor antagonists. In contrast, like azelastine, the histamine H1 receptor antagonist meclizine and the dual histamine and serotonin receptor antagonist cyproheptadine blocked antigen-induced exudation and failed to interfere with cell influx. We conclude that the anti-exudatory activity of oral azelastine on antigen-induced pleurisy is consistent with it exerting direct effects against vasoactive amines, but is not related to an effect against leucocyte infiltration nor to its ability to inhibit PAF-acether.