Platelet activating factor (PAF)-induced late asthmatic response in sensitized but not in non-sensitized guinea pigs]

We have recently demonstrated that pretreatment with WEB 2086, a specific PAF antagonist or cyclosporine A (CsA), a potent helper T cell suppressant, resulted in preventing the development of late asthmatic response (LAR) and increase of airway hyperreactivity (AH) in guinea pig experimental models of asthma. We have now examined whether exogenously applied PAF causes LAR in these models in vivo. The respiratory resistance (Rrs) of guinea pigs was measured by an oscillation technique and histological studies of the bronchi were also made. Guinea pigs, actively sensitized by repeated antigen (ovalbumin; OA) inhalation, showed a leftward shift of the inhaled PAF dose response curve of Rrs compared with that in control animals, indicating that the sensitized animals were more sensitive to inhaled, PAF. PC200 PAF, which indicate provocative concentrations of PAF aerosols causing a 200% increase in the baseline Rrs, were 3800 +/- 604.9 micrograms/ml and 780 +/- 94.3 micrograms/ml, in the control and sensitized animals, respectively. The same magnitude of immediate bronchoconstriction after 780 and 3800 micrograms/ml of PAF exposure was observed in the actively sensitized and non-sensitized control animals, respectively. However, LAR developed 4 out of 6 animals only in the sensitized guinea pigs. We conclude that both exogenously applied PAF by inhalation and antigen exposure are capable of inducing LAR in sensitized guinea pigs, and thus the priming effect of immunization and PAF may contribute to the development of LAR observed in asthma.     

Inhibition of antigen-induced late asthmatic response and bronchial hyperresponsiveness by cyclosporin A

We have previously demonstrated that Cyclosporin A (CyA), a T lymphocyte-selective immunosuppressive agent, reduced the delayed-phase bronchial eosinophil infiltration after antigen challenge in a guinea pig model of asthma. In the present study, we studied the effects of CyA on antigen-induced late asthmatic response (LAR) and bronchial hyperresponsiveness following LAR. Guinea pigs immunized by repeated exposure to aerosolized ovalbumin (OA) were intravenously given metopirone, a cortisol synthesis inhibitor, 24 hours before and 30 minutes before antigen challenge, and to prevent death from immediate severe bronchoconstriction, chlorpheniramine maleate was also injected. After antigen challenge with high dose of OA, LAR occurred in twelve of fifteen animals (80%) and the bronchial responsiveness to acetylcholine was significantly increased. However, when guinea pigs were treated with CyA from the beginning of immunization period, the development of LAR was completely inhibited, although similar magnitude of immediate bronchoconstriction was observed, and a subsequent increase in bronchial responsiveness was partially but significantly blocked. Since CyA has been shown to suppress activation of guinea pig T lymphocytes and their production of lymphokines, these results suggest that T cell factor(s) may be important for the elicitation of LAR and the antigen-induced bronchial hyperresponsiveness.     

Procoagulant property of platelet activating factor (PAF)

In this report we demonstrate that ET-2, in addition to its powerful vasoconstrictor properties and its role in hypertension, is capable of creating a hypercoagulable (prothrombotic) state. This study was facilitated by the utilization of a sensitive modified recalcification time (MRT) test that can measure coagulation at all points in the coagulation spectrum. The MRT was determined on aliquots (1 ml) of citrated blood which were added to saline (MRTS), to 10 μg of endotoxin (MRTE), and to 10 pg of ET-2 (MRT ET-2). The mean values of MRTS, MRTE, and MRT ET-2 were 4.3 ±0.8, 3.7 ± 1.0, and 3.9 ± 0.8 min, respectively. There was a statistically significant difference between MRTE vs. MRTS and MRT ET-2 vs. MRTS using the twotailedt-test (p<0.02 andp<0.005, respectively).

     

Effect of tazanolast on platelet activating factor-induced airway hyperresponsiveness in guinea pigs]

To determine whether tazanolast inhibits airway hyperresponsiveness, we studied the effect of this drug on platelet activating factor (PAF)-induced airway hyperresponsiveness in guinea pigs. Inhalation of PAF (1 microgram/ml) caused significant airway hyperresponsiveness to acetylcholine (p < 0.01) or histamine (p < 0.05). Pretreatment with tazanolast (30-300 mg/kg) produced a dose-dependent inhibition of airway hyperresponsiveness induced by PAF inhalation, and significant inhibition (p < 0.05) was obtained with the drug (300 mg/kg). Aspirin also inhibited PAF-induced airway hyperresponsiveness, while tranilast produced hardly any inhibition. From these results, it is suggested that tazanolast is effective in inhibiting airway hyperresponsiveness.     

Effect of disodium cromoglycate on airway mucus secretion during antigen-induced late asthmatic responses in a murine model of asthma

BACKGROUND: Disodium cromoglycate (DSCG) is known to inhibit both immediate and late asthmatic responses (IAR and LAR). However, its effect on mucus hypersecretion is unknown. Using a murine model of asthma, we aimed to determine whether mucus secretion increased during IAR and LAR. We also studied the potency of DSCG in inhibiting mucus secretion and on airway eosinophilia. METHODS: Mice were subjected to initial intraperitoneal sensitization and airway challenge to ovalbumin (OVA) and then provoked by additional exposure to OVA. Some mice were pretreated with aerosolized DSCG (20 mg/ml) 1 h before the provocation with OVA. After serial measurements of enhanced pause (Penh), an indicator of airflow obstruction, serum samples and bronchoalveolar lavage fluids (BALF) were collected. Then, the lungs were excised and a morphometric analysis for mucus hypersecretion was performed. RESULTS: A biphasic increase in Penh (IAR and LAR) was observed in sensitized animals after provocation with OVA. Airway eosinophilia was observed during both responses. Intraluminal mucus significantly increased during LAR, but not during IAR. DSCG significantly attenuated both IAR and LAR, and significantly inhibited the increase in intraluminal mucus during LAR, but had no effect on eosinophilia in BALF. CONCLUSION: Our results suggest that airway hypersecretion may be involved as a component of airflow obstruction during LAR, and that this is unlikely during IAR. DSCG may be effective in reducing excessive airway mucus caused by exposure to allergens.     

The mechanism of airway hyperresponsiveness following immediate bronchial response in ovalbumin (OA)-sensitized guinea pigs]

We have previously demonstrated that airway responsiveness was enhanced following a late bronchial response (LBR) after an allergen challenge in ovalbumin (OA)-sensitized guinea pigs. The purpose of the present studies was to evaluate whether airway responsiveness to methacholine increased after an immediate bronchial response (IBR) and the possible involvement of the beta-adrenoceptor dysfunction in OA-sensitized guinea pigs. Guinea pigs were actively sensitized by aerosolized OA. Following OA exposure, IBR appeared. After IBR when specific airway resistance returned to the base line value, airway responsiveness to methacholine increased significantly. Before OA exposure, propranolol induced bronchoconstriction (PIB) was not provoked, however, after IBR, PIB was provoked and the guinea pigs died because of severe bronchoconstriction. These results suggest that airway responsiveness to methacholine increases significantly after IBR. Furthermore, the dysfunction of the beta-adrenoceptor may be a mechanism of this hyperresponsiveness in OA-sensitized guinea pigs.     

Inhibition of antigen-induced late asthmatic response and bronchial hyperresponsiveness by cyclosporin and FK 506.

Using a guinea pig model of asthma, we have shown that the administration of cyclosporin, a T-lymphocyte-selective immunosuppressive agent, from the beginning of the immunization period inhibits the development of the late asthmatic response and bronchial hyperresponsiveness after antigen challenge. Similar results were obtained with FK 506, a new potent immunosuppressive agent. Since these compounds have been shown to suppress the activation of guinea pig T lymphocytes, the present data suggest that T lymphocytes may be important for the elicitation of the late asthmatic response and bronchial hyperresponsiveness.     

Suppression of late asthmatic response by low-dose oral administration of interferon-beta in the guinea pig model of asthma.

We investigated the anti-asthmatic effects of low-dose oral and subcutaneous administration of interferon-beta (IFN-beta) on an ovalbumin (OVA)-sensitized and challenged guinea pig model of asthma. Subcutaneous administration of IFN-beta suppressed the eosinophil infiltration by 14.2% of the control and the respiratory resistance (Rrs) by 58.2% at 2.0 MIU/kg. Oral administration of IFN-beta inhibited the late asthmatic response (LAR) by suppressing the increase of Rrs by 29% of the control at 1 IU/ml and the eosinophil infiltration into the trachea and lung by 34.6% at the optimum dosage of 10 IU/ml. Both subcutaneous and oral administration could not inhibit the early asthmatic response (EAR). Additionally we found 2',5'-oligoadenylate synthetase (2',5'-OAS) induction by low-dose oral administration (LDOA) of IFN-beta to the same extent as by subcutaneous administration in whole blood in vivo. These data suggest that LDOA of IFN-beta would have some clinical benefit for patients with asthma.     

Blocking action of platelet activating factor (PAF) on atrial fiber calcium currents in frogs and guinea pigs

Bulletin of Experimental Biology and Medicine -     

Effects of platelet activating factor (PAF) and other vasoconstrictors on a model of angiogenesis in the mouse.

The combination of sponge implant and 133Xe washout technique described in this paper provides a model to study neovascularization in mice which can be observed over several days in the same animal. The local blood flow within the ingrowing granulation tissue has been determined by measuring the washout rate of 133Xe injected into the implants. Tissue infiltration of the sponges was assessed by histological examination and by measurement of sponge wet weight, protein and glycosaminoglycans (GAG) content. The newly formed blood vessels, despite having abnormal configuration, responded to platelet activating factor (PAF) and to endothelin-1 (ET-1) similarly to the normal mature vessels in adjacent skin. However, the sponge blood vessels were more sensitive to angiotensin II than the skin blood vessels. Using this model we have also demonstrated an angiogenic activity of PAF substantiated by increased blood flow and biochemical variables in the implanted sponges.     

钙调神经磷酸酶在哮喘豚鼠气道重塑中的作用

目的:观察钙调神经磷酸酶(CaN)在哮喘豚鼠气道重塑中的作用。方法:实验分3组:对照组、哮喘组及CaN抑制剂环孢霉素(CsA)组,测定指标包括:①支气管肺泡灌洗液(BALF)蛋白含量、细胞计数及分类;②大气道平滑肌[³H]-TdR掺入量;③肺组织切片中小气道壁厚度及气道平滑肌厚度;④气管和肺组织CaN活性。结果:①BALF:CsA组蛋白含量、细胞计数及嗜酸粒细胞分别较哮喘组少46%、51%及60%(P＜0.01);②大气道平滑肌[³H]-TdR掺入量:CsA组较哮喘组低22%(P＜0.05);③小气道壁厚度:CsA组较哮喘组少34%(P＜0.01);气道平滑肌厚度:CsA组较哮喘组少37%(P＜0.01);④肺组织CaN活性:CsA组较哮喘组低52%(P＜0.01);气管CaN活性:CsA组较哮喘组低44%(P＜0.01)。结论:CsA可减轻哮喘豚鼠气道重塑,推测CaN参与气道重塑过程。     

氟伐他汀对哮喘气道重塑的抑制作用及机制研究

目的:探讨氟伐他汀对哮喘气道重塑过程的影响及分子机制。方法:以卵蛋白致敏的豚鼠哮喘模型为对象,观察正常对照组、哮喘组及氟伐他汀+哮喘组之间气道平滑肌肌层厚度的差异。氟伐他汀+哮喘组即每次激发哮喘前30min吸入浓度为05g/L的氟伐他汀2mL。同时采用Dot-blot分子杂交法、免疫组化SABC法检测各组气道ras基因的mRNA和蛋白水平变化。结果:哮喘组气道平滑肌层平均厚度为(7427±330)μm,显著高于正常对照组(3857±337)μm(P<001);氟伐他汀+哮喘组的平滑肌层厚度为(5170±413)μm,明显低于哮喘组(P<005)。哮喘组平滑肌细胞的ras基因表达水平明显高于正常对照组,但氟伐他汀+哮喘组未出现该基因的高表达。结论:氟伐他汀在一定程度上能抑制哮喘气道重塑的病理过程,其发挥效应的机制之一是阻断平滑肌细胞rasp21信号转导途径。     

Effects of ozone exposure on experimental asthma in guinea pigs sensitized with ovalbumin through the airway

As ozone (O3) is known to cause airway inflammation and hyperresponsiveness, we examined the effects of O3 exposure (1, 3, or 5 ppm, 2 h) on sensitization and provocation in guinea pigs sensitized with ovalbumin (OA) through the airway. In groups exposed to O3 before sensitization, 5 ppm increased the production of IgG1 antibodies and decreased the OA sensitization threshold from 0.01 to 0.002%. In those exposed before provocation, 1, 3, or 5 ppm of O3 decreased the OA provocation threshold from 0.5 to 0.02%, and this enhancement appeared to depend on airway hyperresponsiveness. We conclude that O3 exposure may play an important role in causing asthmatic attacks rather than enhancing allergic sensitization.     

Study of platelet aggregation induced by platelet activating factor (PAF) after administration of ticlopidine or aspirin

Platelet aggregation induced by platelet activating factor (PAF) was studied in 95 subjects: 39 controls, 23 patients receiving aspirin and 33 receiving ticlopidine. Potentiation of aggregation by concentrations of adrenaline unable to induce aggregation when used alone was also assessed. The 33 patients treated with ticlopidine showed a highly significant fall of platelet aggregation (p<0·001) at the three concentrations of PAF used. The 23 subjects receiving aspirin showed a diminution of platelet aggregation induced by PAF due to inhibition of ADP release. In these last two groups, adrenaline often potentiated platelet aggregation. However, this phenomenon was absent in subjects having taken aspirin in the hours before blood was drawn. This study demonstrates ticlopidine's inhibitory action on PAF-induced aggregation and confirms ticlopidine's role in reducing platelet aggregation by ADP, which has previously been demonstrated.     

Effect of San-Ao-Tang on immediate and late airway response and leukocyte infiltration in asthmatic guinea pigs

San-Ao-Tang (SAT), a traditional Chinese medicines, has been used to treat patients with the bronchial asthma for several centuries. However, the therapeutic mechanisms of this Chinese medicine are still far from clear. To understand the mechanism of antiasthmatic property of SAT, a guinea pig model of allergic asthma was used to investigate the effects of SAT on Dermatophagoides pteronyssinus-induced. immediate and late asthmatic responses and airway inflammation. Our results showed that administration of SAT (10g/kg) extracts singificantly inhibited the antigen induced immediate asthmatic responses (IAR) in actively sensitized guinea pig. Examination of bronchoalveolar lavage fluid (BALF) revealed that SAT significantly inhibited the increase in neutrophil in the airway at 1, 2, 4, 6, 8 hr after antigen challenge. Histopathologic examination showed SAT suppressed the neutrophil infiltration into lung tissue. These results suggest that the antiasthmatic effect of SAT be mainly due to its bronchodilator effect and its ability to inhibit the neutrophil into the airway. The precise mechanism of action of SAT in asthma remains to be elucidated.