5-Lipoxygenase and endotoxin-induced microvascular albumin exchanges and leucocyte recruitment in guinea-pig lungs

In vitro and in vivo activities of leukotriene B4-loaded biodegradable microspheres

Leukotriene B(4) (LTB(4)) is a potent inflammatory mediator and stimulates the immune response. In addition, LTB(4) promotes leukocyte functions such as phagocytosis, chemotaxis and chemokinesis of polymorphonuclear leukocytes, as well as modulates cytokine release. However, some physicochemical characteristics of leukotrienes, such as poor solubility in water and chemical instability, make them difficult to administer in vivo. The aim of this study was to develop LTB(4)-loaded microspheres (MS) that prolong and sustain the in vivo release of this mediator. An oil-in-water emulsion solvent extraction-evaporation method was chosen to prepare the lipid-loaded MS. We determined their diameters, evaluated the in vitro release of LTB(4), using enzyme immunoassay and evaluated in vitro MS uptake by peritoneal macrophages. To assess the preservation of neutrophil chemoattractant activity, LTB(4)-loaded MS were tested in vitro (in a modified Boyden microchamber) and in vivo, after intratracheal administration.

Intrapulmonary application of a 5-lipoxygenase inhibitor using surfactant as a carrier reduces lung edema in a piglet model of airway lavage

Leukotriene-generated effects on microvascular integrity and polymorphonuclear leukocytes (PMNL) play a key role in the inflammatory process of the alveolar-capillary unit in neonatal acute respiratory distress syndrome. We asked if intrapulmonary application of MK886, a 5-lipoxygenase inhibitor, and the use of a porcine surfactant preparation (Curosurftrade mark) as a carrier substance would improve lung function in a neonatal piglet model of airway lavage. Anesthetized, mechanically ventilated newborn piglets (n = 19) underwent repeated airway lavage to induce acute lung injury. Piglets then received either surfactant alone (S, n = 6), or MK886 admixed with surfactant (S + MK, n = 7), or an air-bolus injection as control (C, n = 6). Measurements of gas exchange, lung function, extravascular lung water (EVLW), cell counts, and leukotriene B(4) (LTB(4)) concentrations in bronchoalveolar lavage fluid (BAL) were performed during 6 hr of mechanical ventilation. Arterial oxygen partial pressure (PaO(2)) (S, 13.8 +/- 4.2 kPa, vs. S + MK, 20 +/- 6.6; P < 0.05), functional residual capacity (S, 15.1 +/- 6.8 ml/kg, vs. S + MK, 18.8 +/- 3.7 ml/kg; P < 0.05), and EVLW (S, 29 +/- 14 ml/kg, vs. S + MK 24 +/- 4 ml/kg; P < 0.05) were significantly improved in the MK886 group. This clinical effect was linked with a decrease in LTB(4) concentration in BAL (S, 3.5 (1.9-5.4) pg/ml, vs. S + MK, 1.6 (0.7-4.7) pg/ml; P < 0.05) and an increase in IL-8 (S, 2,103 (852-4,243) pg/ml, vs. S + MK, 3,815 (940-26,187) pg/ml; P < 0.05). PMNL counts in BAL were reduced (S, 570 +/- 42 cells/ml, vs. 275 +/- 35 cells/ml; P < 0.05). In conclusion, intrapulmonary application of the 5-lipoxygenase inhibitor MK886 with surfactant as a carrier improves lung function by decreasing EVLW as the main response to LTB(4) reduction.

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.

Effect of a BLT receptor antagonist in a model of severe ischemia and reperfusion injury in the rat

Pharmacological strategies which limit neutrophil recruitment may also limit the damage induced by the reperfusion of an ischemic vascular territory. In the present study, we have investigated the effects of the BLT receptor antagonist, CP-105,696 ((+)-1-(3S,4R)-[3-(4-phenyl-benzyl)-4-hydroxy-chroman-7-yl]-cyclopentane carboxylic acid), on the local, remote and systemic inflammatory changes observed during severe intestinal ischemia (120 min) and reperfusion (120 min) injury. The post-ischemic treatment with CP-105,696 (3 mg/kg) virtually abolished the increase in vascular permeability, but not neutrophil accumulation, in the intestine and lungs. CP-105,696 partially inhibited the reperfusion-induced neutropenia, but failed to affect intestinal haemorrhage or lethality. CP-105,696 had no inhibitory effect on the local and systemic increases in the concentrations of tumour necrosis factor (TNF-alpha), interleukin-1 beta and interleukin-10, but markedly suppressed interleukin-6. Overall, our results show that activation of BLT receptor plays a minor role in the local, remote and systemic injuries following severe ischemia and reperfusion in rats.

Leukotrienes are involved in leukocyte recruitment induced by live Histoplasma capsulatum or by the beta-glucan present in their cell wall

1. The inflammatory cell influx towards the peritoneal cavity in mice inoculated i.p. with live or dead Histoplasma capsulatum or with its subcellular preparations was studied. We also evaluated the effects of dexamethasone (Dexa) or MK886, an inhibitor of leukotriene (LT) biosynthesis, on the recruitment of leukocytes. 2. Live yeast form of fungus (LYH) induced an increase in neutrophils (NE) which was highest 4 to 24 h after inoculation. Mononuclear cell (MN) migration beginning at 24 h with a gradual increase over 48 and 168 h, and an eosinophil (EO) recruitment occurs between 24 and 48 h. 3. NE and EO recruitment induced by dead mycelial form of fungus (DMH) was greater than that observed for dead yeast form of fungus (DYH). A similar leukocyte migration pattern was seen after i.p. injection of the alkali-insoluble fraction (F1) from DYH (F1Y) and F1 from DMH (F1M) this being more active than former. The difference in concentration of beta-glucan in DYH and DMH could explain the different inflammatory capacity exhibited by the two forms of H. capsulatum. 4. LT seems to be the principal mediator of leukocyte migration in response to LYH, DYH or DMH or to beta-glucan. However, other mediators appear to contribute to NE and EO migration since the treatment with Dexa was more effective in inhibiting cell migration than MK886. Complement dependent leukocyte migration may participate in this recruitment. Treatment with MK886 completely abolished MN cell migration, indicating its dependence on the presence of LT.