白三烯C_4对人气道结构细胞内皮素1基因表达及分泌水平的影响

目的 :探讨白三烯C4 (LTC4 )对体外培养人气道上皮细胞和平滑肌细胞内皮素 1(ET 1)基因表达及分泌水平的影响。方法 :在离体培养人气道上皮细胞株 (16 HBE)及气道平滑肌细胞 (ASMC)培养液中加入不同浓度LTC4 ,采用酶联免疫吸附 (ELISA)法测定培养液ET 1水平 ,用逆转录多聚酶链反应 (RT PCR)方法检测ET 1mR NA表达水平。结果 :LTC4 能使离体培养的 16 HBE及ASMC两种细胞ET 1mRNA的表达水平显著上调 ,并刺激ET 1释放 ,当LTC4 浓度≥ 10 -8mol/L时 ,两种细胞ET 1分泌水平均显著高于对照组。结论 :LTC4 能上调 16 HBE及ASMC两种细胞ET 1mRNA的表达并刺激ET 1释放 ,这可能是白三烯致哮喘气道炎症及重塑的重要机制之一。     

Protection Against Exercise-Induced Bronchoconstriction Two Hours After a Single Oral Dose of Montelukast

The objective of this double-blind cross-over study was to evaluate montelukast for the prevention of exercise-induced bronchoconstriction (EIB). Sixty-two patients with EIB (post-exercise decrease in forced expiratory volume in 1 second (FEV₁) ≥ 20% at pre-randomization) were randomized to montelukast 10 mg or placebo, followed by exercise-challenge 2, 12, and 24 hours postdose. The primary endpoint was the maximum percent-fall in FEV₁ (from pre-exercise FEV₁) during 60 minutes after exercise-challenge at 2 hours postdose. This endpoint was improved after montelukast (mean ± SD = 11.7% ± 10.8) versus placebo (17.5% ± 13.8) (p ≤ 0.001); numerically greater improvements were seen at 12 hours and 24 hours. A quicker time to recovery after challenge (p ≤ 0.001) and a smaller area under the curve for percent-fall in FEV₁ during 60 minutes after challenge (p ≤ 0.01) were seen with montelukast at 2 hours. At this timepoint, more patients taking montelukast (45/54) than taking placebo (37/54) were protected against EIB (p = 0.039). We concluded that montelukast provided significant protection against EIB at 2 hours after a single dose.     

Microvascular actions of histamine: synergism with leukotriene B4 and role in allergic leucocyte recruitment

Background Previous studies have shown that antihistamities provide little or no protection against the recruitment of leucocytes in allergic inflammation. Objective We wanted to examine if threshold doses of histamine can potentiate chemoattractant-induced leukocyte adhesion and if complete inhibition of histamine-induced microvascular effects is necessary to reduce allergic leucocyte recruitment. Methods The role of histamine in allergic leucocyte recruitment was examined by use of intravital microscopy of the hamster cheek pouch microcirculation. Results We found that topical administration of histamine caused a concentration-dependent increase in microvascular permeability in the cheek pouch; i.e. 0.3 μM histamine caused no detectable plasma leakage, while 1 μM and 10 μM histamine resulted in 29 ± 9.3 and 356 ± 47 leakage sites/cm² cheek pouch area, respectively. The percentage of postcapillary venules with more than five adherent leucocytes (an index of early leucocyte recruitment) was 1.1 ± 0.51% in the control situation, and did not increase significantly after stimulation with histamine alone (0.3–10μM) or with 1 nM ieukotriene B₄ (LTB₄). On the other hand, coapplication of 10μM histamine and 1 nM LTB₄ increased leucocyte adhesion 24-fold. In fact, the 10 times lower dose of histamine (1 μM) together with 1 nM LTB₄ increased leucocyte adhesion to a similar extent (20 fold). The increase in vascular permeabihty evoked by exogenous 10μM histamine (with or without LTB₄), or by histamine released from activated mast cells (antigen challenge), was completely reversed by local pretreatment with the H₁-receptor antagonist mepyramine. This mepyramine treatment also abohshed the enhanced leucocyte adhesion in response to coapplication of histamine and LTB₄. Moreover, mepyramine, which had no effect on leucocyte recruitment evoked by 3 nM LTB₄per se, reduced antigen-induced recruitment of leucocytes to the extravascular tissue by 79.5 ± 14.8%. Conclusion We conclude that threshold concentrations of histamine can strikingly potentiate chemoattractant-induced leucocyte responses, and that in order to reduce allergic leucocyte recruitment it may be necessary to use antihistamines in doses high enough to abolish the microvascular actions of histamine.     

Cysteinyl leukotrienes as mediators of staphylococcal enterotoxin B in the monkey

The role of cysteinyl leukotrienes (LTs) in the action of staphylococcal enterotoxin B (SEB) was investigated in unsensitized monkeys using inhibitors of prostanoid synthesis and LT action and by measuring generation of LT in vivo. LY 171883, a selective LTD4/LTE4 receptor antagonist, proved highly efficient in inhibiting immediate-type hypersensitivity reactions in the skin and protecting against the emetic response provoked by SEB in a concentration-dependent manner. Inhibition of prostanoid formation by pretreatment of monkeys with indomethacin or aspirin did not influence SEB responses. Based on chromatographic and radioimmunologic analysis, the generation of endogenous cysteinyl LTs was demonstrated in vivo. The concentration of LTE4, the major biliary cysteinyl LT detected, increased ten-fold and a novel cysteinyl LT metabolite in urine indicated strongly enhanced LT generation upon challenge with SEB. Cysteinyl LTs are important mediators in the pathophysiology of SEB-induced enteric intoxication. Therefore, cysteinyl LT antagonists may be of therapeutic value in the treatment of this intestinal disorder.     

The role of leukotriene B4 in Clostridium difficile toxin A-induced ileitis in rats

BACKGROUND & AIMS: Clostridium difficile toxin A is a potent intestinal inflammatory agent that has been shown to act at least partially by neurogenic mechanisms involving activation of the transient receptor potential vanilloid 1 (TRPV1) (capsaicin) receptor. We tested the hypothesis that leukotriene B4 (LTB4) mediates the effects of toxin A via activation of the TRPV1 receptor. METHODS: Isolated rat ileal segments were pretreated with pharmacologic agents before intraluminal injection of toxin A or LTB4. After 3 hours, the treated segments were removed and inflammation was assessed by luminal fluid accumulation, myeloperoxidase activity, and histology. RESULTS: LTB4 caused ileitis similar to that caused by toxin A and antagonism of TRPV1 receptors but not LTB4 receptors inhibited LTB4-induced inflammation. LTB4 also stimulated TRPV1-mediated substance P release and pretreatment with a specific substance P-receptor antagonist blocked LTB4-induced substance P action and ileitis. Inhibition of the LTB4 biosynthetic enzyme 5-lipoxygenase inhibited toxin A-induced increases in ileal LTB4 levels and toxin A- but not LTB4-induced ileitis. CONCLUSIONS: LTB4 mediates the inflammatory effects of toxin A via activation of TRPV1 receptors.     

Cysteinyl leukotriene metabolism of human eosinophils in allergic disease

Eosinophils are multifaceted immune cells with diverse functions that enhance allergic inflammation. Cysteinyl leukotrienes (cys-LTs), mainly synthesized in eosinophils, are a class of inflammatory lipid mediators produced via multiple enzymatic reactions from arachidonic acid. Multiple clinical studies have reported dysregulated fatty acid metabolism in severe asthma and aspirin-exacerbated respiratory diseases. Therefore, understanding the mechanism responsible for this metabolic abnormality has attracted a lot of attention. In eosinophils, various stimuli (including cytokines, chemokines, and pathogen-derived factors) prime and/or induce leukotriene generation and secretion. Cell–cell interactions with component cells (endothelial cells, epithelial cells, fibroblasts) also enhance this machinery to augment allergic responses. Nasal polyp-derived eosinophils from patients with eosinophilic rhinosinusitis present a characteristic fatty acid metabolism with selectively higher production of leukotriene D₄. Interestingly, type 2 cytokines and microbiome components might be responsible for this metabolic change with altered enzyme expression. Here, we review the regulation of fatty acid metabolism, especially cys-LT metabolism, in human eosinophils toward allergic inflammatory status.     

Alterations in rat peripheral blood neutrophil function as a consequence of colitis

Altered peripheral neutrophil function is a feature of IBD that may contribute to the chronicity and extragastrointestinal manifestations of this disease, but clinical evidence for such alterations is confounded by variations in patient characteristics, disease onset, and use of therapeutics that can influence neutrophil function. The use of a rat model of colitis has permitted us to characterize, in a controlled manner, the causal relationship between colitis and altered peripheral neutrophil function. At various times after induction of colitis with trinitrobenzene sulfonic acid (TNBS), peripheral neutrophils were isolated and assays of phagocytosis, chemotaxis, leukotriene B₄ (LTB₄) synthesis, and superoxide production were performed using a variety of stimuli. Circulating neutrophil numbers increased about fourfold within 12 hr of TNBS administration and returned to normal levels over the following two weeks. LTB₄ synthesis in response to calcium ionophore decreased at 12 hr after induction of colitis, then returned to control levels. The chemotactic responses of peripheral neutrophils to LTB₄ and FMLPin vitro and to LTB₄ and IL-8in vivo were profoundly suppressed through the two-week study period. Phagocytosis of nitroblue tetrazolium was significantly enhanced (ca. threefold) at 12 hr after induction of colitis and remained elevated throughout the study period. Superoxide production was also significantly elevated in the early phase of colitis (by ca. fourfold), but was not different from control levels at seven and 14 days. These results demonstrate that colonic inflammation profoundly influences peripheral blood neutrophil function, although the direction and magnitude of the alteration varied among the various functions assessed. The prolonged depression of chemotactic activity may represent a physiological reaction to limit the inflammatory response.     

Eicosanoid Lipid Mediators in Fibrotic Lung Diseases: Ready for Prime Time?

Recognition of a pivotal role for eicosanoids in both normal and pathologic fibroproliferation is long overdue. These lipid mediators have the ability to regulate all cell types and nearly all pathways relevant to fibrotic lung disorders. Abnormal fibroproliferation is characterized by an excess of profibrotic leukotrienes and a deficiency of antifibrotic prostaglandins. The relevance of an eicosanoid imbalance is pertinent to diseases involving the parenchymal, airway, and vascular compartments of the lung, and is supported by studies conducted both in humans and animal models. Given the lack of effective alternatives, and the existing and emerging options for therapeutic targeting of eicosanoids, such treatments are ready for prime time.     

Cysteinyl leukotrienes are secretagogues in atrophic coeliac and in normal duodenal mucosa of children

Objective The pathophysiology of intestinal inflammation and diarrhoea is complex and involves the arachidonic acid cascade. Prostaglandins induce chloride secretion in healthy subjects and in patients with coeliac disease. Leukotrienes (LTs) are also known inflammatory mediators which have been shown to stimulate ion secretion in ileum and colon of rats and rabbits. The aim of this study was to determine the effects of leukotrienes C₄ (LTC₄) and D₄ (LTD₄) in normal and atrophic intestinal mucosa in children.

Material and methods Routine paediatric intestinal biopsies were obtained from 109 children. Sixty-seven control biopsies and 42 biopsies from children with different stages of coeliac disease were mounted in a modified Ussing chamber. Potential difference (Pd) was measured continuously and tissue resistance (R_t) and the generated current (I_m) were calculated.

Results In morphologically normal mucosa of duodenum, LTC₄ and LTD₄ increased Pd and I_m in a dose-dependent manner. The increase was more pronounced in the distal than in the proximal part, similar to the response to prostaglandin E₂. The induced current was chloride-mediated, since replacement of Cl^? with SO₄^2? in the bathing solution eliminated the response to the LTs. The LTC₄-induced secretion was significantly decreased in atrophic mucosa, but the response was partially restored after preincubation with the cyclooxygenase inhibitor indomethacin.

Conclusions The results showed that LTC₄ and LTD₄ are secretagogues in the duodenal mucosa from healthy children by inducing a net chloride secretion. Restoration of the response in coeliac disease by cyclooxygenase inhibition suggests interactions between the different pathways of the arachidonic cascade in the intestinal mucosa.