Regulatory effect of histamine H1 receptor antagonist on the expression of messenger RNA encoding CC chemokines in the human nasal mucosa.

BACKGROUND: Allergic rhinitis is characterized by tissue accumulation of inflammatory cells. CC chemokines, including monocyte chemotactic protein (MCP) 1, MCP-3, RANTES, and eotaxin, are thought to play an important role in inducing selective recruitment of these cells to the allergic inflammatory site. Furthermore, MCPs have been indicated as histamine-releasing factors. Histamine is an important mediator in the pathogenesis of nasal allergy. The regulation of histamine may have a role in the management of allergic inflammation. OBJECTIVE: The objectives of this study were to investigate the expression of MCP-1, MCP-3, RANTES, and eotaxin in the nasal mucosa of patients with allergic rhinitis and to clarify the effect of histamine and antihistamine on the regulation of the expression of these CC chemokines. METHODS: By using a semiquantitative reverse transcriptase PCR technique, the numbers of copies of messenger RNA encoding MCP-1, MCP-3, RANTES, and eotaxin were measured in explant cultures of human nasal mucosa. In culture medium, specific antigen or histamine was added. Furthermore, the effect of preincubation with the antihistamine carebastine was estimated. RESULTS: Mite antigen (1:2 x 10(4) dilution) and histamine (10(-4) to 10(-3) mol/L) upregulated the messenger RNA expression of these CC chemokines at 3- to 10-fold increases. Carebastine (10(-7) to 10(-6) mol/L) inhibited this upregulation. CONCLUSION: Our results suggest that histamine may induce CC chemokine production in the nasal mucosa of patients with allergic rhinitis. This indicates that there may be a prolonged inflammatory cycle in the histamine-MCP axis in allergic rhinitis. The regulation of histamine-CC chemokine interaction could lead to new therapeutic approaches in the treatment of nasal allergy.

Preclinical comparison of ebastine and other second generation H1-antihistamines.

The present study was performed to compare the properties of ebastine--the long duration of antiallergic effect and less penetration to the CNS--with those of other H1-antihistamines. Passive cutaneous anaphylactic reaction was induced and the dye leakage from the skin measured after oral administration of the various H1-antihistamines in guinea pigs. The H1-antihistamines examined inhibited passive cutaneous anaphylactic reactions, with ED50 values of 1.55-5.77 mg/kg administered orally. Evaluation at doses close to the ED50 values determined that the rank order of the various H1-antihistamines for the duration of antiallergic effects, calculated from the AUC, was as follows: ebastine>cetirizine> or =oxatomide=loratadine=epinastine. The inhibition of [3H]-mepyramine binding to the cortical membrane was examined ex vivo after oral administration of the drugs in rats. Ketotifen as a positive control of sedative antihistamine, oxatomide, cetirizine, ebastine and epinastine dose-dependently inhibited the [3H]-mepyramine binding to rat cortical membranes. However, ebastine and epinastine did not show 50% [3H]-mepyramine binding inhibition even at 100 mg/kg orally In conclusion, ebastine was shown to be a potent and long-lasting H1-antihistamine with less effect to the CNS. Consequently, in conjunction the two experimental models used in this study--passive cutaneous anaphylactic reaction in guinea pigs and ex vivo [3H]-mepyramine binding to rat cortical membrane--may be important to estimate the duration of antiallergic effects of drugs and to detect their sedative effects, which are important indicators in the development of new antiallergic drugs.

The equivalent bronchodilator effects of salbutamol formulated in chlorofluorocarbon and hydrofluoroalkane-134a metered dose inhalers on the histamine-induced pulmonary response in dogs.

PURPOSE: The bronchodilator effect of salbutamol formulated in hydrofluoroalkane-134a (HFA-134a), a chlorofluorocarbon (CFC)-free propellant for metered dose inhalation (MDI) devices, was compared with that of salbutamol formulated in CFC in anesthetized dogs. METHODS: Bronchospasms were induced by the intravenous injection of histamine, and bronchial resistance was measured by the method of Konzett and Rossler. RESULTS: While the placebo vehicles (HFA-134a and CFC propellants) had no significant effect on histamine-induced bronchospasms, the salbutamol/HFA-134a and salbutamol/CFC MDI formulations had equivalent dose-related inhibitory effects. CONCLUSIONS: These data indicated that salbutamol formulated in HFA-134a and that in CFC propellant are bioequivalent.

Antinociceptive and antidepressant-like profiles of BL-2401, a novel enkephalinase inhibitor, in mice and rats.

To clarify the properties of BL-2401 ((+/-)-3-[2-benzyl-3-(propionylthio) propionyl]amino-5-methylbenzoic acid), a novel enkephalinase inhibitor, we examined its antinociceptive and antidepressant-like activities after oral administration, along with their association with endogenous opioid systems. BL-2401 produced an antinociceptive effect after oral administration in the mouse phenylbenzoquinone writhing test (ED50: 12.4 mg/kg) and the rat acetic acid writhing test (ED50: 55.8 mg/kg), the antinociceptive effect being antagonized by naloxone hydrochloride. BL-2401 also relieved arthritis-induced hyperalgesia in rats. In the mouse hot-plate and tail pressure tests, BL-2401 showed significant but modest antinociception at higher doses (200 and 400 mg/kg). In addition, BL-2401 (100 mg/kg) produced a naloxone-reversible antidepressant-like effect in the mouse forced swimming test. As for the mechanism of the action, the active metabolite of BL-2401, BL-2240 ((+/-)-3-(2-benzyl-3-mercaptopropionyl) amino-5-methylbenzoic acid), selectively inhibited enkephalinase in vitro (IC50: 5.2 nM). Oral administration of BL-2401 to mice significantly inhibited the enkephalinase activity in the striatum and also potentiated the antinociceptive effect of (D-Ala2,Met5)-enkephalin given intracisternally. These findings indicate that BL-2401 is an orally active enkephalinase inhibitor and may produce antinociceptive and antidepressant-like effects in association with endogenous opioid systems.

Inhibitory effect of AL-3264, a new antiallergic agent, on the Prausnitz-Küstner reaction and leukotriene production in monkeys.

To clarify the antiallergic effect and antiallergic mechanism of AL-3264 (N-[4-[4-(diphenylmethyl)-1-piperazinyl]butyl]-3-(6-methyl-3- pyridyl)acrylamide) in monkeys, its effects on the Prausnitz-Küstner (P-K) reaction, the histamine skin reaction and leukotriene production were examined. In contrast to ketotifen and mepyramine, AL-3264 inhibited the P-K reaction, which is mainly mediated by leukotriene and histamine, more clearly than the skin reaction evoked by histamine alone. AL-3264 also inhibited the leukotriene (LT) production in the broncho-alveolar cells, suggesting that the inhibition of LT production actually contributes to the antiallergic effect of AL-3264.

Inhibition of leukotriene production by N-[4-[4-(diphenylmethyl)-1- piperazinyl]butyl]-3-(6-methyl-3-pyridyl) acrylamide (AL-3264), a new antiallergic agent.

The effects of AL-3264, which exhibits a 5-lipoxygenase (5-LO) inhibiting property by blocking histamine H1-receptors and inhibition of histamine release, were examined on leukotriene (LT) production and LT-mediated responses. AL-3264 (1-30 microM) inhibited the A23,187-induced LT production from human leukocytes with almost the same potency as that of nordihydroguaiaretic acid. AL-3264 (30-100 mg/kg, p.o.) inhibited the antigen-induced LT production in the abdominal cavity of passively sensitized rats; its effect was as potent as that of AA-861, a 5-LO inhibitor. AL-3264 (30 microM) suppressed both the initial and sustained phases of the antigen-induced contractions in isolated trachea from actively sensitized guinea pig. Phenidone (3 microM), a dual inhibitor of 5-LO and cyclooxygenase (CO), suppressed the sustained phase, while indomethacin was without effect on either phase. AL-3264 (40-160 mg/kg, p.o.) suppressed the arachidonic acid-induced ear edema in mice, for which 5-LO inhibitors were effective but antihistamines were not. The anti-edematous effect of AL-3264 (160 mg/kg) was reduced by intradermal administration of LTC4 (0.1 microgram). These results suggest that AL-3264 suppresses LT production in vivo and in vitro by inhibiting 5-LO activity, and this property may contribute to the antiallergic effect of AL-3264.

[Pharmacological study of ebastine, a novel histamine H1-receptor antagonist].

The anti-allergic activity of ebastine, a novel antihistamine, was assessed in comparison with several antihistamines. 1) Orally administered ebastine dose-dependently inhibited 7-day homologous passive cutaneous anaphylaxis (PCA), experimental allergic rhinitis and experimental asthma in guinea pigs or rats (ED50-values were 2.17, 0.29 and 0.35 mg/kg, respectively); and its anti-allergic activity was more potent than those of terfenadine and mequitazine. Moreover, its PCA-inhibitory activity was still observed 24 hr after the administration. 2) Orally administered ebastine also inhibited histamine-induced skin reaction in rats (ED50: 1.10 mg/kg). 3) In isolated guinea pig trachea, ebastine had no effect on histamine-induced contraction, but carebastine, a main metabolite of ebastine, inhibited this contraction (IC50: 0.12 microM). 4) Carebastine (30-100 microM) suppressed the histamine release from rat peritoneal mast cells and human basophils. 5) Ebastine at a high oral dose showed slight inhibition of the specific binding of 3H-mepyramine to the histamine H1-receptor in rat brain. This binding-inhibitory activity of ebastine was little more potent than that of terfenadine, but much less potent than those of mequitazine and ketotifen. These results indicated that ebastine has potent and long acting anti-allergic activity with few side effects based on the antihistaminic activity in the central nervous system. Furthermore, it was suggested that these effects of ebastine are due to the action of a main metabolite, carebastine.

Dissociation between central and peripheral antihistamine activities of the new antiallergic agent N-[4-[4-(diphenylmethyl)-1-piperazinyl]-butyl]-3-(6-methyl-3-pyridyl) acrylamide in rats and monkeys.

In order to examine the penetration of N-[4-[4-(diphenylmethyl)-1-piperazinyl]-butyl]-3-(6-methyl-3-pyrid yl) acrylamide (AL-3264, CAS 118420-47-6), a new antiallergic agent, into the brain, the antihistamine activities in the central and peripheral tissues from the rats and monkeys orally treated with AL-3264 were measured in comparison with those of ketotifen, oxatomide, mequitazine and terfenadine. These 5 drugs dose-relatedly suppressed the histamine-induced dye leakage in the rat skin and, except terfenadine, inhibited the binding of 3H-mepyramine to brain homogenates obtained from the rats treated orally with the drugs. The ratio (0.07) of AL-3264 for the central (3H-mepyramine binding) to peripheral (dye leakage) antihistamine activities was lower than that of ketotifen, oxatomide and mequitazine, and higher than that of terfenadine. The serum and cerebrospinal fluid (CSF) samples, which were collected from the monkeys treated with 80 mg/kg p.o. of AL-3264, terfenadine or oxatomide, inhibited the histamine-induced contractions in isolated guinea pig trachea. The ratio (0.003) of AL-3264 for the central (CSF) to peripheral (serum) antihistamine activities was lower than that of terfenadine and oxatomide. These results suggest that AL-3264 is poorly accessible to the brain, and may be regarded as a non-sedative antiallergic agent.

Inhibition of passive sensitization of human peripheral basophils by synthetic human immunoglobulin E peptide fragments.

To delineate the binding site in the human immunoglobulin E (IgE) molecule to the Fc epsilon receptor on basophils and mast cells, we chemically synthesized a total of 71 peptide fragments within the sequence Ser300-Lys547 in the human IgE molecule. The synthetic peptides were tested for their capacity to inhibit passive sensitization of human peripheral basophils with atopic patient's serum containing the specific IgE against dust mites in vitro. It was found that a peptide fragment, Pro345-Ile356, potently inhibited the passive sensitization. To clarify the minimal active core, various analogues, such as shortened, substituted (by Gly or Ala residue), omission and retro-sequence peptides, were synthesized and assayed. The results suggested that the sequence Pro345-Lys352 in the human IgE molecule would be an IgE binding site, and that a synthetic octapeptide, Pro345-Phe-Asp-Leu-Phe-Ile-Arg-Lys352, inhibited the passive sensitization, probably by occupying the Fc epsilon receptor sites on the cells.

Antiallergic activity and mode of action of N-[4-[4-(diphenylmethyl)-1-piperazinyl]butyl]-3-(6-methyl-3- pyridyl)acrylamide in experimental animals.

Antiallergic effects of AL-3264 (N-[4-[4-(diphenylmethyl)-1-piperazinyl]butyl]-3-(6-methyl-3- pyridyl)acrylamide, CAS 118420-47-6) were compared with those of ketotifen, oxatomide, azelastine and tranilast in experimental animals. AL-3264 inhibited passive cutaneous anaphylaxis (PCA) in rats with an ED50 value of 6.1 mg/kg p.o. In inhibiting PCA, AL-3264 was the most potent among the antiallergic drugs examined. The anti-PCA effect of AL-3264 was long-lasting. Tolerance was not produced by repeated administration of AL-3264. AL-3264 inhibited antigen-induced bronchoconstriction in actively sensitized rats and in passively sensitized guinea pigs, with ED50 values of 14.5 and 0.44 mg/kg p.o., respectively. In the in vitro experiments, AL-3264 inhibited 5-lipoxygenase activity of guinea pig leukocytes with an IC50 value of 4.9 mumol/l, being the most potent among antiallergic drugs examined, and suppressed the antigen-induced histamine release from rat peritoneal mast cells with an IC50 value of 12.2 mumol/l. AL-3264 antagonized histamine-induced contractions in isolated guinea pig trachea with an IC50 value of 0.16 mumol/l. These results suggest that AL-3264 is an orally active, potent and long-lasting antiallergic compound which inhibits 5-lipoxygenase activity, histamine release and histamine H1 receptors at the similar concentrations.

Role of peptide-leukotrienes in liver injury in mice.

The role of peptide leukotrienes (p-LTs), especially LTC4 and LTD4 in liver disease, was investigated in mice experimental liver injury models. The liver injury was induced by the injection of bacterial lipopolysaccharide (LPS) into Corynebacterium parvum pretreated mice. Carbon tetrachloride (CCl4)-induced liver injury in mice was used as a standard model. In both injury models, extensive liver parenchymal cell damage was observed by the elevation of glutamate transaminase (GOT and GPT) activity and confirmed by significant histopathological changes in the liver. Moreover, significant elevation of LTC4 in the liver was observed in both models 1 and 6 h after the onset of disease. Administration of AA-861, a selective 5-lipoxygenase inhibitor (0.5, 1, and 2 mg/kg) and LY-171883, a p-LT receptor antagonist (50 and 200 mg/kg) suppressed the elevation of serum GOT and GPT levels and histopathological changes in both experimental liver injury models. In addition, when authentic LTC4 or LTD4 was injected into the mouse, clear elevation of serum GOT and GPT and histopathological changes of the liver were observed. These results suggest that p-LTs play a role in the onset of liver diseases in mice.

Effect of OKY-046 and ONO-3708 on liver injury in mice.

The effects of OKY-046, a selective thromboxane A2 (TXA2) synthetase inhibitor, and ONO-3708, a novel TXA2 receptor antagonist, on liver disease were investigated in mice. The liver injury was induced by either an injection of antibasic liver protein (BLP) antibody into DBA/2 mice that had been previously immunized with rabbit IgG or by an injection of bacterial lipopolysaccharide (LPS) into Corynebacterium parvum (C. parvum) pretreated DDY mice. 1) In both injury models, clear elevation of glutamate transaminase (GOT and GPT) activity due to extensive liver parenchymal cell damage was observed; this was confirmed by significant histopathological changes in the liver. 2) Typical histopathological changes in the liver were submassive hepatocellular necrosis in the anti-BLP antibody-induced injury model and focal necrosis in the LPS-induced model. Inflammation and increased cell infiltration in portal connective tissue were observed in both cases. 3) Administration of OKY-046 (50 mg/kg) and ONO-3708 (0.5, 1.0 and 2.0 mg/kg) suppressed the elevation of serum GOT and GPT levels and histopathological changes in both experimental liver injury models. 4) Indomethacin inhibited the development of liver disease caused by anti-BLP antibody but not by bacterial LPS. Prostaglandin I2 inhibited the elevation of serum GOT and GPT levels and histopathological changes of the liver in the mice treated with anti-BLP antibody and showed the tendency to inhibit the development of liver injury caused by bacterial LPS.

The role of thromboxane A2 [TxA2] in liver injury in mice.

The role of thromboxane A2 (TxA2) in CCl4-induced liver disease was investigated in mice. Significant elevation of TxB2 in the liver was observed 6 hours after the injection of CCl4. Administration of OKY-046, a selective TxA2 synthetase inhibitor (10 and 50 mg/kg) and ONO-3708, a TxA2 receptor antagonist, (0.5, 1 and 2 mg/Kg) suppressed the elevation of serum GOT and GPT levels and histopathological changes of the liver. In addition, OKY-046 inhibited the elevation of TxB2 in the liver. When U-46619, a stable TxA2 mimetic was injected i.v. into the mice, clear elevation of serum GOT and GPT levels and histopathological score of the liver were observed. These results suggest that TxA2 play a role for the onset of CCl4-induced liver injury in mice.

Pathological studies on nephrotoxic serum nephritis accelerated with rabbit gamma-globulin in mice.

In order to characterize nephrotoxic serum nephritis accelerated with rabbit gamma-globulin in mice, histopathological studies were carried out 15 days after NTS injection, the time when increases in urinary protein and serum cholesterol and a decrease in serum albumin were apparent. Characteristic changes were widespread thickening of glomerular capillary walls and widening of mesangial areas, owing to deposits of mesangial matrixlike substances. The mesangial interposition into subendothelial areas and the resultant narrowing of the capillary lumen were shown ultrastructurally. In severely affected glomeruli, a hyaline nodular lesion was observed. Visceral epithelial cells demonstrated fusion of the foot processes, microvilli formation, occasional proliferation, and enlargement. Parietal epithelial cells proliferated, forming a cellular crescent. Based on these characteristics, it appears this nephritic model shares a common pathology with human membranoproliferative glomerulonephritis type 1 and crescentic glomerulonephritis and can be considered an appropriate model for producing severe nephritis for short periods.

Evaluation of anti-allergic effects of 1-substituted 2-n-butyl-methylenedioxy indenes.

The effects of ten 1-substituted 2-n-butyl-5,6-methylenedioxyindenes on mice and guinea pigs were investigated for their allergic reactions in the development of a new anti-allergic drug. Anti-allergic effects were determined by testing the effect of agents on passive cutaneous anaphylaxis (PCA) in mice and Schultz-Dale reaction in guinea pig tracheal muscle. 2-Butyl-1-[N-methyl-N-[2-(N',N'-dimethylamino) ethyl]amino]5,6- methylenedioxyindene (1) indicated the most potent anti-allergic activity. Since our previous experiments indicated that 2-n-butyl 3-dimethyl amino-5,6-methylenedioxyindene (MDI-A) and its derivatives showed a potent anti-allergic effect by interfering with the calcium (Ca) movement in the allergic reaction in guinea pigs, the effect of 1 and MDI-A on allergic reaction and Ca-induced contraction of tracheal muscle in these animals were compared. The present data indicate the superiority of 1 in both reactions.

The role of thromboxane A2 (TxA2) in allergic cutaneous reactions and the effect of (E)-3-[p-(1H-imidazol-1-ylmethyl) phenyl]-2-propenoic acid hydrochloride (OKY-046), a TxA2 synthetase inhibitor.

To study the role of thromboxane A2 (TxA2) in cutaneous allergic reactions, the effect of (E)-3-[p-(1H-Imidazol-1-ylmethyl)phenyl]-2-propenoic acid hydrochloride (OKY-046), a selective TxA2 synthetase inhibitor, on cutaneous reactions in rats and mice was studied. Simultaneously, the effect of 9,11-methanoepoxy-prostaglandin H2 (U-46619), a stable analogue of TxA2, on capillary permeability in mouse and rat skin was investigated. Passive cutaneous anaphylaxis (PCA) in mouse ear was clearly inhibited by OKY-046 but not by indomethacin. The inhibitory action of OKY-046 was not influenced by pretreatment with indomethacin. Moreover, prostaglandin I2, which accumulated as a result of the inhibition of TxA2 synthetase, did not affect the PCA. But, the dye leakages caused by histamine, serotonin and leukotriene C4 in mouse ear were clearly inhibited by OKY-046. In addition, OKY-046 inhibited rat reversed cutaneous anaphylaxis, but its inhibitory action was not affected by pretreatment with indomethacin. Contrary to the above results, rat footpad passive Arthus reaction and mouse footpad tuberculin delayed hypersensitivity reaction were not affected by OKY-046. Additionally, U-46619 did not cause an increase of capillary permeability in either mouse and rat skin. These results suggest a slight role of TxA2 in cutaneous allergic reactions in mice and rats and the efficacy of OKY-046 on Type I and II reactions regardless of the inhibition of TxA2 synthetase activity.

The effect of gomisin A on immunologic liver injury in mice.

The hepatoprotective effect of Gomisin A (TJN-101), which is a lignan compound isolated from Schizandra fruits, was studied on three immunologic liver injury models in mice. The first liver injury model was produced by the injection of anti-basic liver protein (BLP) antibody into DBA/2 mice which had been previously immunized with rabbit IgG (RGG). Other models were effected by injection of anti-liver specific protein (LSP) antibody into DBA/2 mice or by the injection of bacterial lipopolysaccharide (LPS) into ddY mice pretreated with Corynebacterium parvum (C. parvum). TJN-101 inhibited the elevation of transaminase (GOT and GPT) activities and showed the tendency to inhibit the histopathological changes of the liver in all models. Moreover, TJN-101 inhibited deoxycholic acid-induced release of transaminase from cultured rat hepatocytes in vitro, but did not affect the formation of hemolytic plaque forming cells in immunized mice spleens and hemolytic activity of guinea pig complement in immunohemolysis reaction. These results, therefore, suggested that the hepatoprotective effect of TJN-101 could be related to the protecting effect of hepatocyte plasma membrane rather than the inhibiting effects of the antibody formation and complement activity.

Anti-asthmatic activity of newly synthesized calcium antagonists: 2-n-butyl-1 (N-methyl-n-[2-(N',N'-dimethylamino)ethyl]amino) -5,6-methylenedioxy-indene and -indane.

The anti-asthmatic activity of the newly synthesized methylenedioxyindene (MDI) derivatives, 2-n-butyl-1 (N-methyl-N-[2-(N', N' -dimethylamino)ethyl]amino)-5, 6-methylenedioxy-indene (MDI-C) and -indane (MDI-D), were investigated in vitro and in vivo in guinea pigs. The in vitro pharmacological activity of both derivatives was compared to that of 8-(diethylamino)octyl-3,4, 5-trimethyoxybezoate hydrochloride. All three agents caused a concentration-dependent inhibition of the antigen-induced contraction of sensitized guinea pig tracheal smooth muscle. In histamine and leukotriene D4-induced contractions of guinea pig tracheal smooth muscle, each agent showed clear antagonistic actions. Additionally, all three agents demonstrated potent calcium antagonistic actions via inhibition of guinea pig tracheal smooth muscle contractions caused by CaCl2 in a high potassium and Ca-free medium and by compound 48/80 in a solution of ethylene glycol bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid in a contained Ca-free medium. MDI-C and MDI-D inhibited the antigen-induced release of histamine and slow reacting substance of anaphylaxis from sensitized guinea pig lung tissue. Lastly, both MDI is clearly inhibited asthmatic respiratory disorders without affecting blood pressure in guinea pigs.

Liver injury model in mice for immunopharmacological study.

Experimental liver injury was produced in mice by the immunological technique. The utility of these models as an immunopharmacological method was investigated. The first model was produced by the injection of anti-basic liver protein (BLP) rabbit antibody into DBA/2 mice that had been previously immunized with rabbit IgG. The second liver injury was caused by injection of anti-liver specific protein (LSP) rabbit antibody into DBA/2 mice. The third model was produced by the injection of bacterial lipopolysaccharide (LPS) into Corynebacterium parvum pretreated ddY mice. In all injury models, extensive liver parenchymal cell damage was estimated by elevation of glutamate transaminase (GOT and GPT) activity. These were confirmed by histopathological studies of the liver. Typical histopathological changes in the liver from injured mice were submassive hepatocellular necrosis and infiltration of granulocytes and lymphocytes into the portal tract and sinusoid in the necrotic lesion. Administration of prednisolone and cyclophosphamide for 10 days prior to injection of eliciting antibodies or LPS suppressed the elevation of serum transaminase levels in all experimental liver injury models. Cianidanol and sylibin inhibited the elevation of GOT and GPT in anti-BLP induced liver injured mice. These evidences suggest that the above models are suitable for investigating the remedy for liver diseases.

Effect of OKY-046, a new thromboxane A2 synthetase inhibitor, on experimental asthma in guinea pigs.

The effect of OKY-046, a newly synthetized thromboxane A2 (TxA2) synthetase inhibitor, on IgE mediated experimental asthma in guinea pigs was investigated. Indomethacin, a cyclooxygenase inhibitor, and tranilast (N-5'), a potent anti-allergic agent, were used as comparative drugs. OKY-046 clearly improved asthmatic respiratory disorders in guinea pigs. Whereas indomethacin had no effect on the changes of asthmatic respiration, tranilast significantly inhibited the changes. OKY-046 inhibited the in vitro antigen-induced contraction of sensitized guinea pig lung parenchyma. This antigen-induced contraction was also inhibited by tranilast, but not by indomethacin. OKY-046 inhibited the contractions of lung parenchyma caused by leukotriene C4, D4 and E4 (LTC4, LTD4 and LTE4), but not by histamine. Indomethacin showed a biphasic action on the contractile responses caused by histamine and LTD4 Consequently, contractions due to either agonist at low concentrations were inhibited by indomethacin, but those at high concentrations were enhanced. Tranilast inhibited the contraction of lung parenchyma induced by a low concentration of LTD4 but not that produced by histamine. Moreover, OKY-046 inhibited an elevation of concentration of thromboxane B2 (TxB2) in guinea pig lung perfusate after infusion of LTC4 but did not affect the elevation of 6-keto-PGF1 alpha. OKY-046 had no effect on the antigen-induced release of histamine but it inhibited the release of the slow reacting substance of anaphylaxis (SRS-A) from sensitized chopped lung tissues. Indomethacin at a high concentration inhibited the release of histamine but did not affect the release of SRS-A. Tranilast clearly inhibited the release of both mediators. These results suggest that OKY-046 inhibits IgE mediated experimental asthma in guinea pigs and that its main mechanism is related to the inhibition of LT induced contraction of airway smooth muscle and the release of SRS-A from lung tissues.