Neonatal Fc receptor for IgG (FcRn) expressed in the gastric epithelium regulates bacterial infection in mice.

Neonatal Fc receptors for immunoglobulin (Ig)G (FcRn) assume a central role in regulating host IgG levels and IgG transport across polarized epithelial barriers. We have attempted to elucidate the contribution of FcRn in controlling Helicobacter infection in the stomach. C57BL/6J wild-type or FcRn(-/-) mice were infected with Helicobacter heilmannii, and gastric lesions, bacterial load and the levels of antigen-specific IgG in serum and gastric juice were analyzed. The elevated levels of anti-H. heimannii IgG in gastric juice were observed exclusively in wild-type mice but not in FcRn(-/-) mice. In contrast, an increase in lymphoid follicles and bacterial loads along with deeper gastric epithelium invasion were noted in FcRn(-/-) mice. C57BL/6J wild-type or FcRn(-/-) mice were also infected with Helicobacter pylori SS1, and the results of the bacterial load in stomachs of these mice and the anti-H. pylori IgG levels in serum and gastric juice were similar to those from H. heilmannii infection. Our data suggest that FcRn can be functionally expressed in the stomach, which is involved in transcytosis of IgG, and prevent colonization by H. heilmannii and the associated pathological consequences of infection.

Blockade of macrophage migration inhibitory factor (MIF) prevents the antigen-induced response in a murine model of allergic airway inflammation.

OBJECTIVE AND DESIGN: The role of macrophage migration inhibitory factor (MIF), a proinflammatory cytokine, was tested using a mouse asthma model. MATERIALS: One hundred and four male BALB/c mice were used in this study. TREATMENT: Mice were actively sensitized with an intraperitoneal injection of ovalbumin (OVA) and challenged with repeated nebulization of 1 w/v% OVA. Polyclonal anti-MIF antibody was intraperitoneally injected at 10 mg/kg during the antigen challenge period. METHODS: Bronchoalveolar lavage (BAL) was performed 8 h after the last challenge. Airway hyperresponsiveness to inhaled methacholine was measured 24 h after the last challenge. RESULTS: Antigen challenge to immunized mice induced increase in inflammatory cells and concentration of Th2 cytokines in BAL fluid (BALF), and caused the development of airway hyperresponsiveness. Anti-MIF antibody significantly decreased the numbers of inflammatory cells including macrophages, eosinophils, lymphocytes and neutrophils in BALF from OVA-challenged mice. Prednisolone decreased the numbers of eosinophils, lymphocytes and neutrophils but not macrophages. Anti-MIF antibody reduced airway hyperresponsiveness. Anti-MIF antibody affected neither the cytokine levels in BALF nor the IgE levels in serum. CONCLUSION: MIF was involved in the antigen-induced inflammatory cell accumulation in the lung and airway hyperresponsiveness without affecting immune responses.

No significant difference in neutrophil activation found among three H2RAs.

BACKGROUND: Even with the most effective treatment, Helicobacter pylori eradication is difficult in some patients. Therefore, patients sometimes require acid-suppressive therapy without H. pylori eradication. It has been reported that ranitidine inhibits neutrophil activation, whereas famotidine does not. However, few studies have been published concerning the activation of neutrophils before and after treatment using clinical doses of histamine-2 receptor antagonists in patients with H. pylori infection. AIM: To examine the effects of neutrophil activation after treatment with three different histamine-2 receptor antagonists. PATIENTS: This prospective, open-label, randomised, parallel-group study was conducted. Thirty patients with H. pylori infection were enrolled. These subjects were randomly assigned to receive one of the following treatments: (a) 150 mg ranitidine, (b) 20mg famotidine, or (c) 10 mg lafutidine b.d., for 4 weeks. Before and after histamine-2 receptor antagonist treatment, histological findings, myeloperoxidase activity, and interleukin-8 in the gastric mucosa were evaluated. RESULTS: On the basis of the histological findings between before and after histamine-2 receptor antagonist treatment, no significant differences were found in any groups. Similarly, there were no significant differences in myeloperoxidase activity or interleukin-8 levels. CONCLUSION: In patients with H. pylori, when used at clinical doses, any histamine-2 receptor antagonists can be used without concerning about inhibition of neutrophil activation.

Cytokine production profile of splenocytes derived from zymosan A-treated SKG mice developing arthritis.

OBJECTIVE: SKG mice have a point mutation of the zeta-associated protein of 70 kD (ZAP-70) and spontaneously develop a severe polyarthritis in the conventional condition, whereas they are healthy under the specific pathogen free (SPF) condition. The purpose of this study was to investigate the cytokine production from splenocytes in SKG mice developing arthritis under the SPF condition. MATERIAL: SKG and BALB/c mice were intraperitoneally injected with zymosan A under the SPF condition. Spleen was isolated 1, 2 or 8 weeks after the intraperitoneal injection of saline or zymosan A. Splenocytes were cultured with concanavalin A. Cytokine production and proliferation were measured 48 and 72 h after the culture. RESULTS: An intraperitoneal injection of zymosan A induced severe polyarthritis with increased levels of rheumatoid factor and interleukin 6 (IL-6) only in SKG mice. Splenocytes from SKG mice did not proliferate well maybe because of less productivity of IL-2. The IL-4 production from splenocytes of SKG mice was higher, while interferon-gamma production was lower than those of BALB/c mice. An injection of zymosan A reduced the IL-4 production only in SKG mice. CONCLUSIONS: SKG mice do not develop arthritis under the SPF condition possibly because of a low proliferative activity of T cells and Th2-predominance.

Levofloxacin- versus metronidazole-based rescue therapy for H. pylori infection in Japan.

BACKGROUND: The ideal second-line treatment regimens for Helicobacter pylori infection may differ between the areas, countries and races. AIM: The aim was to confirm which was the better regimen for second-line therapy after treatment failure with a standard triple therapy in Japan, a high dosage of levofloxacin- or metronidazole-based therapy. PATIENTS: Sixty outpatients with persistent H. pylori infection after a standard triple therapy were enrolled in this prospective, open-label and randomised trial. METHODS: The subjects were randomly administered levofloxacin (300 mg b.d.)- or metronidazole (500 mg b.d.)-based therapy with lansoprazole (30 mg b.d.) and amoxicillin (1000 mg b.d.) for 7 days, and the cure rates and side effects were analysed. Antimicrobial susceptibility was also examined before second-line therapy using the E-test. RESULTS: Good compliance was obtained without severe side effects in both the groups except for two patients. The cure rates, expressed as intention-to-treat and per-protocol analyses, respectively, were 70.0 and 72.4% in the levofloxacin group, and 96.7 and 100% in the metronidazole group. Each regimen often overcame even clarithromycin-resistant strains. CONCLUSION: Metronidazole-based triple therapy is recommended as second-line therapy in Japan, and levofloxacin-based therapy can be an alternative treatment option.

Cell kinetic balance in gastric mucosa with intestinal metaplasia after Helicobacter pylori eradication: 2-year follow-up study.

BACKGROUND: Proliferation and apoptosis events are altered in Helicobacter pylori infection. However, whether H. pylori eradication has an effect on the disturbed kinetics in metaplastic mucosa has not been well elucidated. AIM: To investigate the effect of eradication on the gastric cell kinetics. SUBJECTS AND METHODS: Initially, biopsies were obtained from 74 H. pylori-infected subjects and repeated 12 and 24 months after eradication. Biopsies were immunohistochemically stained for apoptosis by single-stranded DNA, for proliferation by Ki-67 antibodies and for intestinal metaplasia MUC2, MUC5AC, MUC6 and CD10. RESULTS: While antral apoptosis in intestinal metaplasia was significantly lower than in non-intestinal metaplasia, proliferation was significantly higher (greater and lesser curvatures, P < 0.05, respectively). This resulted in a significantly lower apoptosis/proliferation ratio in intestinal metaplasia than in non-intestinal metaplasia (antrum greater and lesser curvatures and corpus greater curvature, P < 0.05). After successful eradication, apoptosis and proliferation decreased in both intestinal metaplasia and non-intestinal metaplasia. The pattern of reduction of apoptosis and proliferation differed in these two groups. However, in the corpus, the reduction resulted in a significant increase in the apoptosis/proliferation ratio in both. CONCLUSION: Proliferation and apoptosis are unevenly and disproportionately altered in H. pylori infection leading to an imbalance in cell kinetics. Eradication of the organism improves the balance and may possibly play a role in the prevention of malignancy transformation in the metaplastic mucosa.

Levofloxacin based triple therapy as a second-line treatment after failure of helicobacter pylori eradication with standard triple therapy.

BACKGROUND: Successful eradication of Helicobacter pylori infection after failure of standard triple therapy is difficult. The efficacy and safety of levofloxacin based triple therapy as a first-line therapy has-been studied. AIMS: The aim was to evaluate the efficacy and tolerability of levofloxacin based therapy after a failed standard triple therapy. PATIENTS: We conducted a prospective, uncontrolled study of a consecutive series of 33 patients who failed eradication with 1 week of lansoprazole-amoxicillin-clarithromycin triple therapy. METHODS: The subjects were retreated with 1 week of LA-LVFX triple therapy (lansoprazole, 30 mg twice daily; amoxicillin, 1000 mg twice daily: levofloxacin, 200 mg twice daily). Cure of infection was defined as negative results from culture, histology and a urea breath test 4 to 8 weeks after the second-line therapy. RESULTS: The eradication rate was 69.7% (23/33) by both intention-to-treat and per-protocol analyses (95% confidence interval=61-79%). Seven (21.2%) patients experienced mild side-effects, such as soft stools and taste disturbance. No patient stopped the medication on account of adverse effects. CONCLUSIONS: Levofloxacin based triple therapy is an effective second-line treatment after a failed standard triple therapy.

Two patients with severe alcoholic hepatitis accompanied by hypercytokinemia and granulocytic hyperelastasemia, successfully treated by intravenous infusion of urinastarine (Miraclid).

Severe alcoholic hepatitis (SAH) is not simply a disease of the liver, but it also causes infection and multiple organ failure, and therefore carries an extremely poor prognosis. We report the successful treatment of two patients with SAH. Case 1: The patient was a 55-year-old man. He was a heavy drinker whose alcohol intake had increased for some 3 years to 1.8 L sake a day. Slight clouding of consciousness, fever, and jaundice were evident on his admission to our hospital. Laboratory data showed leukocytosis with a predominance of polymorphonuclear leukocytes, and a decline in coagulability. He tested negative for various hepatitis virus markers. With the diagnosis of SAH made, steroid pulse therapy and bilirubin adsorption therapy were administered. The jaundice improved and the interleukin-8 (IL-8) level decreased. Continuous intravenous infusion of urinastarine (Miraclid) normalized the granulocyte elastase level. Improvement was also seen in coagulability, ascites, icterus and consciousness. Case 2: The patient was a 49-year-old man. He was a heavy drinker whose alcohol intake had increased for 1 month. Fever, jaundice, ascites, and mild disturbance of consciousness were evident at the time of admission. Examination on admission diagnosed SAH. Bilirubin adsorption and continuous intravenous infusion of urinastarine were initiated. As a result, circulating IL-8 level was decreased and coagulability was improved. Therapy for granulocytic hyperelastasemia and hypercytokinemia supervening on SAH is a new effective approach on improvement in the disease.

Anti-arthritic effects of KF20444, a new immunosuppressive compound inhibiting dihydroorotate dehydrogenase, on rat collagen-induced arthritis.

OBJECTIVE AND DESIGN: A newly synthesized inhibitor of pyrimidine de novo biosynthesis, KF20444 (6,7-dihydro-10-fluoro-3-(2-fluorophenyl)-5H-benzo [6,7] cyclohepta [1,2-b] quinoline-8-carboxylic acid), was evaluated as an inhibitor of dihydroorotate dehydrogenase (DHO-DHase) and tested in the rat collagen-induced arthritis (CIA) model. MATERIAL AND METHODS: Female Sprague Dawley rats, 5 weeks-old, were used for evaluation of KF20444 in the CIA model. Arthritis was evaluated by arthritis score, serum anti-type II collagen antibody titer, body weight loss, radiographical and histological changes. TREATMENT: KF20444 was orally administered 5 times per week (0.3, 1, 3 mg/kg/day). RESULTS: KF20444 inhibited rat liver dihydroorotate dehydrogenase in vitro with Ki = 8.5 +/- 3.2 nM, which was a comparable effect to that of brequinar sodium (Ki = 25.3 +/- 5.3 nM). The anti-proliferative effect of KF20444 was caused by cell cycle arrest at the S-phase. Treatment with 3 mg/kg/day of KF20444 completely prevented the development of CIA based on reduction of the arthritis score. The 50% effective dose (ED50) of KF20444 on arthritis score was 0.64 mg/kg. KF20444 ameliorated body weight loss associated with disease onset. The compound also inhibited the increase in serum anti-type II collagen antibody level, and reduced both pannus formation and bone erosion. Importantly, KF20444 suppressed the development of arthritis, even when it was administered after booster immunization of collagen. CONCLUSIONS: KF20444 is a novel immunosuppressant which inhibits DHO-DHase and its effects in CIA suggest that it could be useful in the treatment of rheumatoid arthritis.

Inhibition of P-selectin specific cell adhesion by a low molecular weight, non-carbohydrate compound, KF38789.

OBJECTIVE AND DESIGN: P-selectin is a cell adhesion molecule of the selectin family. This study evaluated the effects of novel, low molecular weight P-selectin inhibitors in a cell adhesion assay and a murine model of peritonitis. MATERIALS: U937 or HL60 was used for cell adhesion assay. Human polymorphonuclear cells were studied for the production of superoxide. BALB/c mice were used for the in vivo study. TREATMENT: The thioglycollate (TG)-induced accumulation of leukocytes in mice was measured 6 h after the treatment. KF38789 or antibody (1 mg/kg) was injected intravenously prior to TG injection and at 3 h following initial injection. RESULTS: Low molecular weight, non-carbohydrate inhibitors against P-selectin- mediated cell adhesion were tested. One of the most potent inhibitors, KF38789, inhibited the binding of U937 cells to immobilized P-selectin immunoglobulin G chimeric protein (P-selectin-Ig) with an IC50 value of 1.97 microM. Cell adhesion to both E-selectin-Ig and L-selectin-Ig were not affected even by 100 microM of KF38789. Moreover, KF38789 inhibited P-selectin-induced superoxide production from human polymorphonuclear cells. Intravenously injected KF38789 significantly inhibited the TG-induced accumulation of leukocytes in the mouse peritoneal cavity (p<0.01). CONCLUSION: A novel low molecular weight compound, KF38789, specifically inhibited P-selectin-dependent cell adhesion and the leukocyte recruitment in mouse peritonitis.

Pharmacological properties of pteleprenine, a quinoline alkaloid extracted from Orixa japonica, on guinea-pig ileum and canine left atrium.

We have investigated the pharmacological properties of pteleprenine, a quinoline alkaloid, on contractile responses of the guinea-pig ileum and on inotropic responses of the canine left atrium. Although pteleprenine (0.1-1 microM) had no effect on the contraction of the ileum induced by acetylcholine at 10 microM it significantly inhibited acetylcholine-induced contraction of the ileum. Pteleprenine (0.1-10 microM) reduced nicotine induced-contraction of the ileum in a concentration-dependent manner yet had no maximum relaxant effect even at a concentration of 10 microM. From Schild analysis the pA2 of pteleprenine on the guinea-pig ileum was found to be 6.6. The contraction of the ileum induced by 10 microM 1,1-dimethyl-4-phenylpiperazinium, a specific agonist of nicotinic acetylcholine receptors, was concentration-dependently suppressed by 10 nM-10 microM pteleprenine. In contrast, 0.1-10 microM pteleprenine did not antagonize the acetylcholine- and nicotine-induced negative inotropic contractile responses of the canine left atrium. These results show that pteleprenine has inhibitory action against nicotinic acetylcholine receptors in the guinea-pig ileum but not in the canine left atrium. Our findings also suggest that pteleprenine might be a novel lead compound as a nicotinic receptor antagonist.

[Pharmacological properties of pteleprenine, a quinoline alkaloid from Orixa japonica (Rutaceae), in guinea pig ileum and canine left atrium].

We investigated the pharmacological properties of pteleprenine, a quinoline alkaloid contained in the Rutaceous plant, Orixa japonica, on the contractile responses of the guinea pig ileum and on the inotropic responses of the canine left atrium. Contractile responses of the ileum to acetylcholine and histamine were not inhibited by less than 10(-6) M of pteleprenine. Meanwhile, the nicotine induced-contraction of the ileum was dose-dependently diminished by pteleprenine, but the contractile response to nicotine did not reach the maximum value in the presence of 10(-5) M of pteleprenine. The pA2 value of pteleprenine was 6.6 as determined from the Schild plot, which slope was nearly unity. Furthermore, the contraction of the ileum by 10(-5) M of 1,1-dimethyl-4-phenylpiperazinium (DMPP), a specific agonist of nicotinic acetylcholine receptors, was also dose-dependently suppressed by pteleprenine. On the other hand, 10(-5) M of pteleprenine did not have considerable inhibitory effects on acetylcholine- and nicotine-induced negative inotropic effects in the canine left atrium. From these results, it is suggested that pteleprenine has a specific inhibitory effect on nicotinic acetylcholine receptors in the guinea pig ileum.

Histamine enhanced the TNF-alpha-induced expression of E-selectin and ICAM-1 on vascular endothelial cells.

Cell adhesion molecules are expressed on endothelial cells by various proinflammatory cytokines. Tumor necrosis factor-alpha (TNF-alpha) induces the expression of E-selectin and intercellular adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cells (HUVEC). Although histamine is a potent vasoactive mediator, it does not induce the expression of E-selectin and ICAM-1. In this report, we show that histamine concentration-dependently enhances the TNF-alpha-induced expression of E-selectin and ICAM-1 on HUVEC. The histamine-enhanced expression of E-selectin and ICAM-1 was inhibited by the histamine H1 receptor antagonists, mepyramine and diphenhydramine. KW-4679 and ketotifen, antiallergic drugs with histamine H1 receptor antagonistic activity, potently inhibit the expression of E-selectin and ICAM-1. A histamine H2 receptor antagonist, ranitidine, did not affect the histamine-induced expression of cell adhesion molecules. These data indicate that histamine induces the expression of E-selectin and ICAM-1 synergistically with TNF-alpha through histamine H1 receptors.

KW-4679, an antiallergic drug, inhibits the production of inflammatory lipids in human polymorphonuclear leukocytes and guinea pig eosinophils.

The effects of (Z)-11-[(3-dimethylamino)propylidene]-6,11-dihydrodibenz [b.e.]oxepin-2-acetic acid monohydrochloride (KW-4679), an orally active antiallergic drug, on the production of platelet-activating factor (PAF), leukotriene (LT) and thromboxane (TX) induced by Ca2+ ionophore A23187 were examined. KW-4679 at 10 microM reduced the amount of cell-associated PAF by 52.8% in human polymorphonuclear leukocytes (PMNs). KW-4679 (1-100 microM) also inhibited the release of both LTB4 and TXB2, a stable metabolite of TXA2, by human PMNs in a concentration-dependent manner, but did not influence the release of beta-glucuronidase. The 50% inhibitory concentration (IC50) values for LTB4 and TXB2 release were 5.9 and 6.0 microM, respectively. In guinea pig eosinophils, KW-4679 inhibited the release of peptide LTs at a concentration higher than 10 microM (IC50 = 66.9 microM). KW-4679 failed to inhibit PAF acetyltransferase, 5-lipoxygenase and TX synthase, but inhibited the arachidonic acid release by human PMNs in a concentration-dependent manner in a similar concentration as that inhibiting production or release of lipid mediators (IC50 = 19.5 microM). These results indicate that KW-4679 suppresses LTs and TX release and PAF formation by reducing arachidonic acid release from phospholipids, probably through interference with phospholipase A2. The inhibitory action of KW-4679 on PAF, LT and TX production is a beneficial effect of an antiallergic drug.

A novel pyridobenzazepinone derivative with long lasting thromboxane synthase inhibition.

A novel pyridobenzazepinone derivative (Z)-11-(5-carboxypentylidene)-6-methyl-5, 11-dihydropyrido +ad4,3-C] [1] benzazepin-5 (6H)-one (CAS 127654-03-9, KF 13218), inhibited human and bovine platelet thromboxane synthase with IC50 values of 27 +/- 5.8 nmol/l (mean +/- S.E.M.) and 36 +/- 6.9 nmol/l, respectively. The compound did not inhibit cyclooxygenase or 5-lipoxygenase up to a dose of 100 mumol/l and did not antagonize thromboxane A2/prostaglandin H2 receptors. KF13218 inhibited arachidonic acid-induced thromboxane B2 production by human intact platelets with an IC50 value of 5.3 +/- 1.3 nmol/l. The IC50 value of KF13218 for the intact platelets was about 5 times lower than that for the microsomal enzyme. The inhibition of thromboxane synthase in platelets by KF13218 was sustained after removal of the extracellular compound. After oral dosing in rat from 0.03 mg/kg to 3 mg/kg, KF13218 dose-dependently inhibited the thromboxane B2 production in serum, and the inhibition was retained for 72 h. KF13218, at a dose of 0.1 mg/kg p.o. prevented mortality induced by sodium arachidonate in rabbit. It is concluded that KF13218 is a potent, selective and long lasting thromboxane synthase inhibitor.

Gold sodium thiomalate down-regulates intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression on vascular endothelial cells.

We examined whether antirheumatic drugs alter cytokine- or lipopolysaccharide-induced expression of adhesion molecules on vascular endothelial cells. Human umbilical cord vein endothelial cells were co-cultured with various antirheumatic drugs in the presence of inflammatory cytokines, and adhesion molecule expression was measured by cell enzyme-linked immunosorbent assay and Northern blot analysis. Among these antirheumatic drugs, gold sodium thiomalate significantly inhibited intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression on vascular endothelial cells and suppressed cellular binding between human monocytic cell lines, including U937 and HL-60 cells, and interleukin-1 beta-stimulated vascular endothelial cells. It is speculated that down-regulation of adhesion molecules might be one of the novel mechanisms of action of gold sodium thiomalate.

Simple colorimetric cell-cell adhesion assay using MTT-stained leukemia cells.

A new and simple method for quantitating adhesion of leukemia cells, HL60, to endothelial cells was developed. HL60 cells were incubated with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) which forms a blue dye of formazan in the cells. MTT did not inhibit shape change of HL60 cells induced on activated endothelial cells at 90 min. The expression of a cell adhesion molecule, LFA-1, in HL60 cells at 21 h was not inhibited by MTT. After incubation of the MTT-labeled cells and endothelial cells, non-adhered cells were washed out. Adhered cells were lysed with dimethylsulfoxide, and quantitated by measuring absorbance at 540 nm. The absorbance was well correlated with the adherent cell numbers measured by direct counting or by 51Cr-labeling method. U937 and Ramos cells were also quantitatively labeled by MTT. The method has the advantage of being easy, simple and applicable to various cell-cell adhesion assays.

Dibenzoxepin derivatives: thromboxane A2 synthase inhibition and thromboxane A2 receptor antagonism combined in one molecule.

A new series of 6,11-dihydrodibenz[b,e]oxepin derivatives exerting both thromboxane synthase inhibitory (TXS-I) and thromboxane receptor antagonist (TXRA) activities is described. (-)-11-[(3-Pyridylmethyl)thio]-6,11-dihydrodibenz[b,e]oxepin -2- carboxylic acid [(-)-3] and (E)-11-[2-(3-pyridyl)ethylidene]-6,11-dihydrodibenz[b,e]oxepin+ ++-2- carboxylic acid methanesulfonate (11E) exhibited potent inhibitory effects on bovine platelet thromboxane synthase with IC50 values of 4.0 and 14 nM, respectively, and these derivatives also antagonized guinea pig platelet TXA2/PGH2 receptors with Ki values of 85 and 180 nM, respectively. Compound 11E exhibited the dual inhibitory activity in ex vivo experiments and demonstrated a significant protective effect in a rat acute renal failure model.

5-HT3 receptor antagonists. 2. 4-Hydroxy-3-quinolinecarboxylic acid derivatives.

A series of 4-hydroxy-3-quinolinecarboxylic acid derivatives (6) and 4-hydroxy-2-oxo-1,2-dihydro-3-quinolinecarboxylic acid derivatives (7) were designed and synthesized as 5-HT3 receptor antagonists. Molecular modeling studies suggested that the 3-carbonyl moiety in 6 was almost coplanar to the plane of an aromatic ring, but in 7 there was a 30 degrees deviation. 4-Hydroxy substitution in quinoline derivatives enhanced affinity for the 5-HT3 receptors, and endo-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-4-hydroxy-3- quinolinecarboxamide (6f) exhibited the most potent activity in the Bezold-Jarisch (B-J) reflex test (ED50 = 0.1 micrograms/kg, iv) among quinoline derivatives 6. Although 4-hydroxy-2-oxo-1,2-dihydro-3-quinolinecarboxamide derivatives (7a) exhibited higher affinity (e.g., 7d: Ki = 0.48 nM) for the 5-HT3 receptors than ondansetron (Ki = 7.6 nM) or granisetron (Ki = 2.1 nM), these amides showed less potent activity in the B-J reflex test than the reference compounds. Interestingly, the ester derivatives 7c, 7f, and 7h eliminated affinity for the 5-HT3 receptors. These unusual structure-activity relationships and the deviation of the 3-carbonyl moiety from the plane of an aromatic ring suggest that the active conformation of 7a might be different from the proposed one for the preceding 5-HT3 antagonists. Thus, 6f was chosen for further studies. No receptor binding for a variety of ligands was significantly antagonized by 6f. Comparing the ratios of the ED50 value in the B-J reflex test (rat, iv) with the LD50 value in acute lethal toxicity (mouse, iv), 6f was proved to have a 600-fold wider margin of safety than ondansetron. Compound 6f dose-dependently attenuated both the incidence and frequency of emetic episodes induced by cisplatin in the dog (ED50 = 14 micrograms/kg, iv) more potently than ondansetron (ED50 = 210 micrograms/kg, iv). Compound 6f (KF-20170) is now under further investigation as a drug for treating gastrointestinal disorder.