Enhanced leukotriene synthesis in leukocytes of atopic and asthmatic subjects.

1. We have investigated the capacities of peripheral leukocytes from atopic asthmatic (AA) (n = 7), atopic non-asthmatic (AN) (n = 7), and normal (N) (n = 7) subjects to generate the bronchoconstrictor and proinflammatory mediators leukotrienes (LTs) B4 and C4. 2. Mixed leukocyte preparations containing 61-84% neutrophils, 2.4-15% eosinophils, and 13-29% mononuclear cells were incubated in vitro at 37 degrees C in the presence of calcium ionophore A23187. Synthesis of LTB4 and LTC4 was quantitated by radioimmunoassay. 3. Both in dose-response experiments (0-10 microM A23187 for 5 min), and in time-course investigations (2 microM A23187 for 0-30 min), the mixed leukocytes of the AA and AN subjects generated on average 4- to 5-fold more LTB4 and 3- to 5-fold more LTC4 than the normal leukocytes (P less than 0.01 in all cases; ANOVA). 4. This enhanced LT synthesis by the AN and AA leukocytes was not due to differences in the counts of leukocyte sub-types, or to altered rates of LT catabolism between the subject groups. 5. LTB4 synthesis correlated significantly with LTC4 synthesis in the leukocytes of the AN and AA subjects (r = 0.81, n = 14, P less than 0.01), but not in those of the normal subjects (r = 0.19, n = 7, P greater than 0.05). 6. Our results demonstrate an up-regulation of the leukotriene synthetic pathway in the circulating leukocytes of atopic non-asthmatic and atopic asthmatic subjects, which may have important implications in the pathophysiology of asthma and allergy.     

R2D(2) for C(4)Eo: an 'alliance' of PGD(2) receptors is required for LTC(4) production by human eosinophils

Eosinophils play important roles in limiting parasitic infection and in allergic inflammation in the asthmatic airways. Activation of eosinophils by diverse stimuli, including prostaglandin D(2) (PD(2) ), leads to leukotriene C(4) (LTC(4) ) synthesis that contributes to the expulsion of parasites and to epithelial injury in allergic inflammation. Mesquita-Santos et al. in this issue of the journal describe a collaboration between the two PGD(2) receptors, DP(1) and DP(2) [also known as CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 lymphocytes)] that is required to trigger LTC(4) synthesis. DP(1) receptors coupled to G(αs) increase adenylate cyclase activity and cAMP/ protein kinase A-dependent formation of lipid bodies, and DP(2) receptors coupled to G(αi) increase calcium. Each of these signals is required for LTC(4) production. These observations lead to consideration of the effects of other stimuli for eosinophil cAMP, such as the β(2) -adrenoceptor agonists, which inhibit rather than enhance LTC(4) production.     

Effects of theophylline and rolipram on antigen-induced airway responses in neonatally immunized rabbits.

1. The effects of the xanthine, theophylline, a non-selective phosphodiesterase (PDE) inhibitor, and the phosphodiesterase type 4 (PDE 4) inhibitor, rolipram, were evaluated in a model of antigen-induced airway responses in the allergic rabbit. 2. Adult litter-matched NZW rabbits (2.5-3.9 kg), immunized within 24 h of birth with Alternaria tenuis antigen, were pretreated twice daily for 3 days with theophylline (3 mg kg-1, i.p) or rolipram (1 mg kg-1, i.p) prior to antigen challenge (Alternaria tenuis). For each drug-treated group, a parallel group of rabbits were pretreated with the appropriate vehicle. In all groups airway responsiveness to inhaled histamine and bronchoalveolar lavage (BAL) was performed 24 h before and after antigen-challenge. 3. Basal lung function in terms of resistance (RL, cmH2O 1(-1)s-1) and dynamic compliance (Cdyn, ml cmH2O-1) were unaltered by pretreatment with theophylline or rolipram compared to their respective vehicles 24 h prior to or post antigen challenge. 4. The acute bronchoconstriction induced by inhaled Alternaria tenuis aerosol was unaffected by pretreatment with theophylline or rolipram. 5. Airway hyperresponsiveness to inhaled histamine was indicated by reduced RL PC50 (2.4-3.5 fold) and Cdyn PC35 (2.5-2.6 fold) values 24 h after antigen challenge. Treatment with rolipram, but not theophylline, prevented the increase in responsiveness to inhaled histamine 24 h after antigen challenge. 6. Total cells per ml of BAL fluid increased 24 h after antigen challenge due to the recruitment of neutrophils and eosinophils. Antigen-induced increases in pulmonary neutrophils were unaffected; however, eosinophils were reduced 57.5% in theophylline and 82% in rolipram-treated rabbits. 7. Inhalation of Alternaria tenuis aerosol elicits an acute bronchoconstriction, followed 24 h later by an increased responsiveness to inhaled histamine and pulmonary neutrophil and eosinophil recruitment in the immunized rabbit. With the dosing regimes used, both rolipram and theophylline inhibited eosinophil recruitment, whilst only rolipram prevented the development of airway hyperresponsiveness. Neither agent inhibited the acute bronchoconstriction due to inhaled antigen.     

Co-operative signalling through DP(1) and DP(2) prostanoid receptors is required to enhance leukotriene C(4) synthesis induced by prostaglandin D(2) in eosinophils

BACKGROUND AND PURPOSE

Prostaglandin (PG) D₂ has emerged as a key mediator of allergic inflammatory pathologies and, particularly, PGD₂ induces leukotriene (LT) C₄ secretion from eosinophils. Here, we have characterized how PGD₂ signals to induce LTC₄ synthesis in eosinophils.

EXPERIMENTAL APPROACH

Antagonists and agonists of DP₁ and DP₂ prostanoid receptors were used in a model of PGD₂-induced eosinophilic inflammation in vivo and with PGD₂-stimulated human eosinophils in vitro, to identify PGD₂ receptor(s) mediating LTC₄ secretion. The signalling pathways involved were also investigated.

KEY RESULTS

In vivo and in vitro assays with receptor antagonists showed that PGD₂-triggered cysteinyl-LT (cysLT) secretion depends on the activation of both DP₁ and DP₂ receptors. DP₁ and DP₂ receptor agonists elicited cysLTs production only after simultaneous activation of both receptors. In eosinophils, LTC₄ synthesis, but not LTC₄ transport/export, was activated by PGD₂ receptor stimulation, and lipid bodies (lipid droplets) were the intracellular compartments of DP₁/DP₂ receptor-driven LTC₄ synthesis. Although not sufficient to trigger LTC₄ synthesis by itself, DP₁ receptor activation, signalling through protein kinase A, did activate the biogenesis of eosinophil lipid bodies, a process crucial for PGD₂-induced LTC₄ synthesis. Similarly, concurrent DP₂ receptor activation used Pertussis toxin-sensitive and calcium-dependent signalling pathways to achieve effective PGD₂-induced LTC₄ synthesis.

CONCLUSIONS AND IMPLICATIONS

Based on pivotal roles of cysLTs in allergic inflammatory pathogenesis and the collaborative interaction between PGD₂ receptors described here, our data suggest that both DP₁ and DP₂ receptor antagonists might be attractive candidates for anti-allergic therapies.

LINKED ARTICLE

This article is commented on by Mackay and Stewart, pp. 1671–1673 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2011.01236.x     

The effect of age on theophylline clearance in normal subjects.

Dose-interval AUC and clearance of theophylline at steady-state were determined in healthy male subjects in each of three age groups (18-35, 36-54 and 55-70 years old). Mean AUC in the oldest group was significantly higher than in the youngest and clearance in both the middle and oldest groups was significantly lower than in the youngest. Though clearance was significantly correlated with age, age alone accounted for only 31% of the variability in clearance.     

Autocrine enhancement of leukotriene synthesis by endogenous leukotriene B4 and platelet-activating factor in human neutrophils.

1. Platelet-activating factor (PAF) and leukotriene B4 (LTB4), two potent lipid mediators synthesized by activated neutrophils, are known to stimulate several neutrophil functional responses. In this study, we have determined that endogenous LTB4 and PAF exert autocrine effects on LT synthesis, as well as the underlying mechanism involved. 2. Pretreatment of neutrophils with either pertussis toxin (PT), or with receptor antagonists for LTB4 and PAF, resulted in an inhibition of LT synthesis induced by calcium ionophore, A23187. This inhibition was most marked at submaximal (100-300 nM) A23187 concentrations, whilst it was least at ionophore concentrations which induce maximal LT synthesis (1-3 microM). Thus newly-synthesized PAF and LTB4 can enhance LT synthesis induced by A23187 under conditions where the LT-generating system is not fully activated. 3. In recombinant human (rh) granulocyte-macrophage colony-stimulating factor (GM-CSF)-primed neutrophils, LT synthesis in response to chemoattractants (fMet-Leu-Phe or rhC5a) was also significantly inhibited by the LTB4 receptor antagonist, and to a lesser extent by PAF receptor antagonists. 4. Further investigation revealed that LTB4 and/or PAF exert their effects on LT synthesis via an effect on arachidonic acid (AA) availability, as opposed to 5-lipoxygenase (5-LO) activation. Indeed, the receptor antagonists, as well as PT, inhibited LT synthesis and AA release to a similar extent, whereas 5-LO activation (assessed with an exogenous 5-LO substrate) was virtually unaffected under the same conditions. Accordingly, we showed that addition of exogenous LTB4 could enhance AA availability in response to chemoattractant challenge in rhGM-CSF-primed cells, without significantly affecting the 5-LO activation status.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential inhibitory effects of auranofin on leukotriene B4 and leukotriene C4 formation by human polymorphonuclear leukocytes

Auranofin (AF) is a newly introduced oral gold compound having antirheumatic properties, and its efficacy in the treatment of bronchial asthma is now under investigation. In this study, we examined the effects of AF on leukotriene (LT) formation by human polymorphonuclear leukocytes (PMNs) stimulated with the calcium ionophore A23187. AF inhibited LTC4 formation in a dose-dependent manner with an IC50 (concentration required to produce 50% inhibition of control) of 3.2 microM. In contrast, LTB4 formation was not prevented by AF at concentrations up to 6 microM, but it was reduced to 59 +/- 4% (mean +/- SE, N = 3) of control by an 8 microM concentration. As a next step, we explored the mechanisms of the differential inhibitory effects of AF using cell-free systems. When arachidonic acid (AA) and reduced glutathione (GSH) were used as substrates, AF inhibited LTC4 synthesis more effectively (IC50 = 14 microM) than LTB4 synthesis (IC50 = 100 microM). However, LTB4 and LTC4 syntheses from LTA4 were affected only slightly by AF within the concentrations tested (3-100 microM). These results in the cell-free systems indicate that the inhibition of LT formation was caused by a reduction of LTA4 synthesis and that the differential inhibitory effects can be ascribed to the higher Km value of glutathione S-transferase for LTA4 than that of LTA4 hydrolase in PMNs. In accordance with this hypothesis, LTC4 synthesis was more dependent than LTB4 synthesis on LTA4 concentrations within 25-100 microM, and AA-861, a 5-lipoxygenase inhibitor, caused similar differential inhibitory effects on the formation of LTs by intact PMNs. The inhibitory effect of AF on LT formation at physiological concentrations may play some role in the efficacy of this drug.     

Inhibitory effects of helenalin and related compounds on 5-lipoxygenase and leukotriene C(4) synthase in human blood cells.

The sesquiterpene lactone helenalin, which can be isolated from several plant species of the Asteraceae family, is a potent anti-inflammatory and antineoplastic agent. In agreement, alcohol extracts of these plants are used for local external treatment of inflammatory conditions. Since leukotrienes are important mediators in inflammatory processes, the inhibitory effects of helenalin and some derivatives on leukotriene (LT) biosynthesis were studied. Treatment of human platelets with helenalin provoked irreversible inhibition of LTC(4) synthase in a concentration- and time-dependent manner with an IC(50) of 12 microM after a 60 min preincubation. 11alpha,13-Dihydrohelenalin acetate was less potent. Interestingly, individual donors could be divided into two distinct groups with respect to the efficacy of helenalin to suppress platelet LTC(4) synthase. In human granulocytes, helenalin inhibited both the 5-lipoxygenase (IC(50) 9 microM after 60 min preincubation) and LTC(4) synthase in a concentration- and time-dependent fashion. In contrast, the drug was without effect on LTA(4) hydrolase. The GSH-containing adducts (2beta-(S-glutathionyl)-2,3-dihydrohelenalin and 2beta-(S-glutathionyl)-2,3,11alpha,13-tetra hydrohelenalin acetate) did not significantly inhibit LTC(4) synthase. The present results indicate a mechanism for the anti-inflammatory effect of helenalin and related compounds.     

Effects of antirheumatic drugs on leukotriene B4 and prostanoid synthesis in human polymorphonuclear leukocytes in vitro

The effects of D-penicillamine, sodium aurothiomalate, indomethacin, timegadine and tolfenamic acid on the lipoxygenase and cyclo-oxygenase pathways of arachidonic acid metabolism were studied in human polymorphonuclear leukocytes (PMNs) in vitro. In short-term incubations, D-penicillamine and aurothiomalate did not affect leukotriene B4 (LTB4), prostaglandin E2 (PGE2) or thromboxane B2 (TXB2) production. Each of the three non-steroidal anti-inflammatory drugs (NSAIDs) used were potent inhibitors of prostanoid synthesis. In higher concentrations they also reduced LTB4 production; timegadine and tolfenamic acid were effective in concentrations comparable to those measured in plasma during drug therapy, whereas indomethacin was needed in ten times higher concentrations. The different effects of NSAIDs on 5-lipoxygenase activity may be of importance in their therapeutic actions as well as in the appearance of some side-effects, e.g. gastric irritation and "aspirin-induced" asthma.     

砒石对哮喘小鼠肺组织白三烯含量的影响

目的探讨砒石对哮喘小鼠的治疗作用及对肺组织LTB4、LTC4水平的影响。方法建立小鼠卵蛋白哮喘模型,灌胃给予砒石等药,对肺泡灌洗液进行白细胞分类计数,肺组织切片HE染色观察病理变化,用ELISA法检测肺组织匀浆LTB4、LTC4含量。结果哮喘组小鼠肺组织匀浆中LTB4、LTC4含量较生理盐水对照组升高。砒石1.25mg/kg能降低哮喘小鼠肺组织LTB4的含量;砒石0.625mg/kg可降低哮喘小鼠肺组织中LTC4水平至正常。砒石不能影响哮喘小鼠肺泡灌洗液中白细胞分类百分比。结论肺组织中LTB4、LTC4水平的增高可能在哮喘的发病中起作用。砒石能减轻哮喘小鼠肺的病理损害,降低哮喘小鼠肺组织LTB4、LTC4水平,从而表现出抗哮喘的活性。     

Lack of effect of terfenadine on theophylline pharmacokinetics and metabolism in normal subjects.

The pharmacokinetics of oral theophylline (250 mg) and the production of its metabolites (3-methylxanthine, 1-methyluric acid, 1,3-dimethyluric acid) were studied before and after the administration of oral terfenadine (120 mg twice daily for 16 days) in 10 healthy volunteers. Comparison of volumes of distribution, elimination half-lives, areas under the plasma concentration-time curves, plasma clearance of theophylline and elimination of theophylline metabolites indicated that terfenadine had no significant effect on theophylline pharmacokinetics and metabolism.     

Concentration-dependent activity of mometasone furoate and dexamethasone on blood eosinophils isolated from atopic children: modulation of Mac-1 expression and chemotaxis

Treatment of asthma with corticosteroids results in downregulation of eosinophilic airway inflammation. We evaluated in vitro the activity of an "inhaled" corticosteroid, mometasone furoate (MF), and of a "systemic" corticosteroid, dexamethasone (DEX), on eosinophil functions, i.e. adhesion molecule expression and cell chemotaxis. Partially purified blood eosinophils were obtained from 18 asthmatic subjects sensitized to house dust mites. The expression of the macrophage antigen (Mac)-1 (CD11b/CD18) was measured by specific monoclonal antibody (mAb) staining and flow cytometry analysis at baseline or after stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) or with recombinant human (rh) granulocyte macrophage-colony stimulating factor (GM-CSF) plus a mAb anti-human (ah) IgE low affinity receptor [FcepsilonRII or CD23]. Cell chemotaxis toward the complement fragment 5a (C5a) or rh interleukin (IL)-5 was evaluated in Boyden microchambers by light microscopy. Eosinophils showed a significant increase in Mac-1 expression after activation with fMLP or with rh GM-CSF plus ah CD23 mAbs (p<0.05, each comparison) and a remarkable chemotactic response to both C5a or rh IL-5 (p<0.001, each comparison). To test the inhibitory activity of MF and DEX on eosinophil functions, the cells were preincubated for 3 h with four concentrations (0.1, 1, 10 and 100 nM) of each of the two drugs, before being activated by fMLP or by rh GM-CSF plus ah CD23 mAbs or tested with C5a or with rh IL-5. Independently of the stimulus used, both Mac-1 expression and eosinophil migration were effectively downregulated by preincubation with MF or DEX at 1, 10 and 100 nM (p<0.05). The inhibitory activity on cell chemotaxis in response to both C5a or with rh IL-5 was higher for MF than DEX, but only at the highest concentration tested (p<0.05, each comparison). These data demonstrate that concentrations of MF similar to those obtained in vivo are highly effective in inhibiting eosinophil functions involved in airway inflammation.     

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and opsonization synergistically enhance leukotriene B4 (LTB4) synthesis induced by phagocytosis in human neutrophils

Normal human blood neutrophils were studied for their capacity to synthesize leukotriene B4 (LTB4) and its omega-oxidized metabolites after phagocytosis of zymosan. Phagocytosis of serum-opsonized particles led to a higher release of LTs than did unopsonized zymosan. The most striking effect of phagocytosis was observed when neutrophils were primed with granulocyte-macrophage colony-stimulating factor (GM-CSF): opsonization and GM-CSF synergistically increased LTB4 synthesis by neutrophils.     

Identification of specific binding sites for leukotriene C4 in membranes from human lung

Leukotriene C4 (LTC4), one of the major components of the slow-reacting substance of anaphylaxis (SRS-A), is a potent constrictor of bronchial smooth muscle in many species including humans. Here we report the identification and characterization of specific binding sites for LTC4 in membranes from human lung parenchyma. At 4 degrees, 3H-LTC4 binding is specific, saturable (Bmax = 32-41 pmoles/mg prot.), rapid (equilibrium being attained within 15 min), reversible and of high affinity (Kd = 3.6-7 X 10(-8) M). The binding sites are sensitive to heat and probably possess a protein moiety, being inactivated upon trypsinization. CaCl2 affects both the association and the dissociation rate and dose-dependently enhances the binding of 3H-LTC4 at equilibrium; maximal enhancement (4-fold) occurred at 10(-2)M CaCl2. Unlabelled LTC4 is able to complete with 3H-LTC4 for its binding sites with an IC50 of 7.8 X 10(-8) M. The addition of 10(-2) M CaCl2 increases the potency of LTC4 in inhibiting the binding (2.2-fold); both the competition curves are monophasic, indicating the existence of a homogeneous class of binding sites. In the presence of CaCl2, LTD4, LTE4 and the SRS-A antagonist FPL 55712 can inhibit 3H-LTC4 specific binding, being, however, less potent than LTC4 (IC50 S = 2.2 X 10(-6), 2.4 X 10(-5) M, for LTD4, LTE4 and FPL 55712, respectively). FPL 55712 displayed a competitive mechanism; its affinity, however, was lower if absorption to glass was not prevented. The present studies indicate that specific binding sites for 3H-LTC4 exist in human lung parenchyma, and that a receptor-mediated process might be involved in the bronchoconstriction induced by LTC4.     

Inhibition of human neutrophil leukotriene B4 synthesis by combination auranofin and eicosapentaenoic acid.

It has been demonstrated that both auranofin and eicosapentaenoic acid (EPA) have anti-inflammatory properties and both inhibit neutrophil leukotriene B4 (LTB4) synthesis. In the present study, we examined interactions between auranofin and EPA with regard to inhibition of human neutrophil LTB4 synthesis. Auranofin inhibited A23187-stimulated LTB4 synthesis, but the dose required for inhibition of LTB4 was greater than that required for inhibition of other 5-lipoxygenase metabolites; namely, the all-trans isomers of LTB4 and 5-hydroxyeicosatetraenoic acid. These results were explained after a comparison of the rates of synthesis of these 5-lipoxygenase metabolites in the presence and absence of added arachidonic acid which led to the conclusion that leukotriene A hydrolase, the enzyme catalysing the formation of LTB4, was saturated with substrate and rate-limiting for LTB4 synthesis during A23187 stimulation. In combination, auranofin and EPA had a simple additive effect on inhibition of the 5-lipoxygenase pathway. Favorable drug/EPA combinations have the potential to provide a beneficial anti-inflammatory effect with lower levels of each component than are required when used individually.     

茶碱、咯利普兰和acetamide—45对GL62酵母细胞表达的人磷酸二酯酶4A的抑制作用

目的:研究GL62 酵母细胞中磷酸二酯酶4A(PDE4A)的诱导表达和茶碱、咯利普兰、N-对氟苄基-3-[(N-4-吡啶)-乙酰胺]-吲哚45(acetamide-45)对GL62酵母细胞诱导提取物中PDE4A活性的抑制作用.方法:克隆了人PDE4A基因的GL62酵母细胞在CuSO_4 150μmol/L条件下诱导表达PDE4A并提取,用高效液相色谱法测定PDE4A的活性.结果:GL62酵母细胞在CuSO_4诱导下的表达产物蛋白分子在62 kDa和83 kDa之间,表达产物的PDE4A的活性在3 h达到最大为(188±23)μmol·g~(-1)·min~(-1),其米氏常数 K_m为(17.7±2.6)μmol·L~(-1).茶碱,咯利普兰和acetamide-45对诱导提取物PDE4A活性的IC_(50)(95 ％可信限)分别为1642(989-2727),4.58(3.45-6.08)和275(170-444)μmol·L~(-1).结论:GL62酵母细胞经CuSO_4诱导可表达PDE4A,茶碱、咯利普兰和 acetamide-45能抑制其活性,GL62酵母细胞的诱导表达提取物可用来研究PDE4A及其抑制剂.     

Effects of nifedipine and indomethacin on leukotriene C4- and D4-induced coronary constriction at normal and reduced coronary perfusion in dogs

The effects of intracoronary leukotriene C4 (LTC4) and D4 (LTD4) (both 0.1 microgram/kg) were studied in 23 anesthetized open-chest dogs at normal (= mean aortic pressure) and reduced (51 +/- 2 and 32 +/- 2 mm Hg) coronary perfusion pressures. The left anterior descending coronary artery was cannulated and blood flow measured. Subendocardial fiber segment length was obtained with ultrasonic crystals. At normal coronary perfusion pressure, LTC4 and LTD4 reduced coronary blood flow from 81 +/- 6 and 78 +/- 7 ml/min per 100 g by 41 +/- 4% and 41 +/- 4% (both p less than 0.0005), respectively. However, segment length shortening was not depressed by LTC4 or LTD4. At reduced coronary perfusion pressure, LTC4 and LTD4 diminished coronary blood flow from 35 +/- 5 and 32 +/- 3 ml/min per 100 g, by 28 +/- 5% (p less than 0.0025) and 30 +/- 5% (p less than 0.005). Thus, reduction of coronary blood flow was less by both LTC4 (p less than 0.01) and LTD4 (p less than 0.05) at reduced rather than at normal coronary perfusion pressure. Segment length shortening was depressed by LTC4 from 6.5 +/- 1.2% to 2.4 +/- 1.6% (p less than 0.05) and by LTD4 from 5.6 +/- 1.4% to 3.1 +/- 0.9% (p less than 0.05), respectively. Indomethacin (5 mg/kg, i.v.) and nifedipine (10 micrograms/kg, i.v.) did not abolish the LT-induced coronary artery constriction. However, in animals pretreated with indomethacin or nifedipine, reduction of coronary blood flow by LTs was not attenuated at reduced coronary perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of L-serine borate on antagonism of leukotriene C4-induced contractions of guinea-pig trachea.

The antagonist activity of three leukotriene D4 (LTD4) receptor antagonists and a number of bronchodilators was determined against LTC4-induced contractions of guinea-pig isolated tracheal chains in the absence and presence of the gamma-glutamyltranspeptidase inhibitor, L-serine borate (SB). The LTD4 receptor antagonists FPL-55712, L-649,923 and L-648,051 effectively antagonized LTC4 responses in the absence of SB but were ineffective in the presence of 15 and/or 45 mM SB. Salbutamol greater than isobutylmethylxanthine (IBMX) greater than dibutyryl cyclic AMP greater than aminophylline greater than nifedipine antagonized contractions to LTC4 in the absence of SB. In contrast, in the presence of SB the antagonist activity of all of these agents except nifedipine was significantly reduced. The antagonist activity of the Ca2+ entry blocker, nifedipine, was similar in the absence and presence of SB. Salbutamol and IBMX were potent functional antagonists of LTE4-induced contractions both in the absence and presence of SB. These results are consistent with the hypothesis that there are contractile LTC4 receptor mechanisms in guinea-pig trachea which are unmasked by SB and are not blocked by LTD4 receptor antagonists and which are less effectively down modulated by cyclic AMP-dependent bronchodilators.     

Effects of saiboku-to on the survival of human eosinophils.

In recent years, bronchial asthma has come to be regarded as a chronic inflammatory disease of the respiratory tract, with mast cells, lymphocytes and eosinophils playing important roles in its pathogenesis. Proteins contained in eosinophil granules, especially major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN) and eosinophil peroxidase (EPO), can cause tissue injury. When stimulated, eosinophils release mediators such as leukotriene C4 (LTC4) and platelet activating factors (PAF). Thus, they are recognized as effector cells that are actively involved in the development of allergic inflammation. In this study, eosinophils from healthy volunteers were used to investigate the effects of Saiboku-to on eosinophils whose survival had been prolonged through stimulation with eosinophil-activating cytokines such as interleukin (IL)-3, IL-5 and granulocyte macrophage colony stimulating factors (GM-CSF). As a result, the cytokine-enhanced survival of eosinophils was significantly shortened by the addition of Saiboku-to. These findings suggest that Saiboku-to has the potential to inhibit allergic responses by directly affecting eosinophils which are related to allergic inflammation.