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Biomedical subjects

W Beil

Publications and source records attributed to W Beil.

At least 55 records · Page 3Linked to original sources
PubMed1994

Interaction of Helicobacter pylori and its fatty acids with parietal cells and gastric H+/K(+)-ATPase.

Helicobacter pylori and the fatty acids produced by this organism were compared for their acid inhibitory activity in isolated parietal cells and their interaction with gastric H+/K(+)-ATPase. H pylori (intact organisms, sonicates, methanolic extracts, and extracts from culture medium) and the fatty acids cis 9,10-methyleneoctadecanoic acid and tetradecanoic acid inhibited at fairly high concentrations histamine- and dibutyryl cyclic adenosine monophosphate stimulated acid production in isolated parietal cells, dissipated (with a slow onset) the H+/K(+)-ATPase created H+ gradient in gastric membrane vesicles, and inhibited H+/K(+)-ATPase activity in a concentration dependent manner. The inhibitory potency of H pylori and the fatty acids in relation to H+/K(+)-ATPase depended on the amount of membrane protein. Bovine serum albumin prevented enzyme inhibition and proton dissipation from gastric vesicles. The data indicate that H pylori establishes its antisecretory action in parietal cells by blocking H+/K(+)-ATPase activity and also by a detergent action at the apical parietal cell membrane. The fatty acids cis 9,10-methyleneoctadecanoic acid and tetradecanoic acid are probably the acid inhibitory factors secreted by H pylori.

Animals↗
PubMed1994

Interaction between Helicobacter pylori and human gastric epithelial cells in culture: effect of antiulcer drugs.

A human in vitro model to study the interaction between Helicobacter pylori and gastric epithelial cells was developed using primary cultures of gastric mucosal cells (isolated from gastric biopsies or operative specimen and maintained in culture for 2 weeks) as well as the well-differentiated human gastric carcinoma cell line HM02, the undifferentiated gastric tumour cell line HM51, and the laryngeal epithelial cell line HEp-2. Primary cultures and all cell lines were exposed to seven isolates of H. pylori isolated from gastritis and duodenal ulcer patients. Microbial adherence was assessed by microscopical evaluation of Giemsa-stained preparations and by culturing the viable bacteria attached to the epithelial cells. All H. pylori isolates adhered to the gastric cells in primary culture, to HM02 cells, and to HEp-2 cells with the greatest binding affinity found in primary gastric cells. No adherence was detected in HM51 cells. H. pylori adherence was dependent on bacterial load, incubation time, and temperature. There was no difference in microbial binding between H. pylori isolates derived from gastritis and duodenal ulcer patients. The effect of antiulcer drugs on H. pylori adherence was investigated by pre-incubating isolates of H. pylori with omeprazole, cimetidine, and bismuth subcitrate. Omeprazole and cimetidine failed to significantly influence microbial adherence. In contrast, bismuth subcitrate already in concentrations below the MIC range decreased H. pylori adherence in gastric epithelial cells and in HEp-2 cells substantially. Our study shows that primary cultured human gastric mucosal cells and the human gastric carcinoma cell line HM02 provide suitable in vitro models for the study of the interactions between H. pylori and the gastric epithelium. This gastric cell model is characterized by a high affinity for H. pylori binding.

Anti-Ulcer Agents↗
PubMed1994

Comparative activities of agonists of active duodenal bicarbonate secretion in the guinea pig.

The comparative activity of agonists of duodenal bicarbonate secretion was studied in the anesthetized guinea pig, where the duodenal lumen was perfused with 24 mmol/l NaHCO3 to ensure active secretion of bicarbonate. Agonists were infused alone and in combination. Dibutyryl 3',5'-cyclic adenosine monophosphate, vasoactive intestinal polypeptide (VIP) and prostaglandin E2 (PGE2) were strong stimulants of bicarbonate secretion. Theophylline, dibutyryl 3',5'-cyclic guanosine monophosphate, glucagon and prostaglandin F2 alpha (PGF2 alpha) were weaker agonists, and secretin had no effect. Combinations of any two of VIP, PGE2 and glucagon depressed bicarbonate secretion, whereas combinations of PGE2 and PGF2 alpha, VIP and PGE2, and glucagon and PGF2 alpha increased bicarbonate secretion. The data indicate that cAMP and other secondary messengers may mediate duodenal bicarbonate secretion.

Adenosine Monophosphate↗
PubMed1994

Cyclic adenosine monophosphate is the second messenger of prostaglandin E2- and vasoactive intestinal polypeptide-stimulated active bicarbonate secretion by guinea-pig duodenum.

In a guinea-pig model we determined the intracellular events mediating the response of duodenal epithelial cells to vasoactive intestinal polypeptide (VIP) and prostaglandin (PG) E2. Intravenous administration of VIP (10(-9) to 10(-7) mol/kg) and PGE2 (10(-9) to 10(-6) mol/kg) dose-dependently increased duodenal epithelial bicarbonate secretion against an HCO3- concentration gradient, measured by a luminal perfusion technique, in anaesthetized guinea-pigs up to 4.5-fold. This secretion could be mimicked by intraduodenal dibutyryl cyclic adenosine monophosphate (dBcAMP; 10(-9) to 10(-7) mol/kg). Secretin (10(-9) mol/kg) and PGF 2 alpha (10(-9) to 10(-7) mol/kg), both given intravenously, were without effect or considerably less efficient. For VIP and PGE2, specific receptors coupled to adenylate cyclase could be demonstrated in homogenates of isolated duodenal epithelial cells. VIP and PGE2 stimulated adenylate cyclase activity up to sixfold, whereas PGF2 alpha and secretin were considerably less potent and efficient. VIP and PGE2 increased intracellular cyclic AMP levels up to fivefold and ninefold, respectively. This was followed by an increase in cytosolic protein kinase A activity. Bicarbonate secretion was maximal at 30 min. Examination of the subcellular distribution of protein kinase A showed a predominant cytosolic location. These data support the notion the PGE2 and VIP cause bicarbonate secretion by the serial activation of adenylate cyclase and protein kinase A in duodenal epithelial cells.

Adenylyl Cyclases↗
PubMed1994

Effects of prostaglandins on [Ca2+]i and adenylate cyclase activity in isolated porcine gastric mucous cells.

In porcine gastric mucous cells, isolated enzymatically from the fundic mucosa and enriched by counterflow centrifugation, PGE2 (1 microM) increased adenylate cyclase activity to 225% and, distinct from that documented for other species, also [Ca2+]i, measured fluorimetrically with Fura2/AM, in Ca(2+)-containing and Ca(2+)-free incubation medium to 182% and 165% of control values, respectively. PGF2 alpha, PGD2, the stable prostacyclin analogue iloprost and the thromboxane-mimetic U46619 had no significant effects on adenylate cyclase activity and [Ca2+]i. Histamine (10 microM) stimulated adenylate cyclase activity to 236% of control value, an effect which could be blocked by the H2-receptor antagonist ranitidine. However, histamine and the activators of the cAMP system forskolin and dibutyryl cAMP had no significant effect on [Ca2+]i, indicating that an activation of the adenylate cyclase/cAMP system per se does not result in an increase in [Ca2+]i. These data suggest that prostanoids stimulate adenylate cyclase activity and [Ca2+]i in gastric mucous cells via activation of EP-receptors linked to both second messenger systems.

Adenylyl Cyclases↗
PubMed1993

Cholinergic regulation of guinea pig duodenal bicarbonate secretion.

Although it is well known that vagal stimulation induces duodenal HCO3- secretion, there is presently no information about the nature of the cholinoceptor and the intracellular signals involved. In a series of experiments performed in a guinea pig duodenal loop model in situ, intravenous carbachol, atropine, pirenzepine, and hexamethonium were used to determine the extent of cholinergic stimulation and the types of cholinoceptors. Carbachol (2 micrograms.kg-1.5 min-1) stimulated HCO3- secretion threefold, and atropine (0.1 mg.kg-1.5 min-1) and pirenzepine (1 mg.kg-1.5 min-1) both abolished this effect. In addition, hexamethonium (0.3 mg.kg-1.5 min-1) inhibited carbachol-stimulated duodenal HCO3- secretion. Vasoactive intestinal peptide (VIP, 5 micrograms.kg-1.5 min-1) stimulated duodenal HCO3- secretion, and this action was partly inhibited by atropine (0.1 mg.kg-1.5 min-1) but not by pirenzepine (1 mg.kg-1.5 min-1). [4Cl-D-Phe6,Leu17]VIP (3.3 mg/kg), an antagonist to VIP, reduced basal, VIP-stimulated, and carbachol-stimulated HCO3- secretion. To examine the role of Ca2+ in this process, Ca2+ ionophore A23187, verapamil, and nifedipine were employed. A23187 (5, 50, 500 micrograms.kg-1.5 min-1) stimulated duodenal HCO3- secretion, an effect blocked by the VIP antagonist, and modestly augmented the effect of carbachol. Verapamil (0.2 mg.kg-1.5 min-1) and nifedipine (1.7 mg.kg-1.5 min-1) stopped the effect of carbachol on duodenal HCO3- secretion. These results suggest, that in cholinergic regulation of duodenal HCO3- secretion, the M-cholinoceptor pathway, Ca2+, and VIP are involved.

Animals↗
PubMed1993

Studies on the mechanism of action of colloidal bismuth subcitrate. I. Interaction with sulfhydryls.

The present study was designed to examine the reaction pathway of colloidal bismuth subcitrate (CBS) with thiols. Studies were performed using the monothiol glutathione (GSH), the dithiol dithiothreitol (DTT) and the thiol enzymes papain and H+/K(+)-ATPase. UV-vis spectra showed that CBS forms complexes with GSH and DTT. The GSH/CBS complex but not the DTT/CBS complex was cleared by 5,5'-dithiobis-(2-nitrobenzoic acid). CBS inhibited H+/K(+)-ATPase (IC50: 23 +/- 6.5 mumol/l) but failed to inhibit papain activity. The inhibitory action of CBS on H+/K(+)-ATPase-mediated proton transport was prevented by the dithiol dithioerythritol but not by GSH. These results indicate that CBS forms stable complexes with dithiols and instable complexes with monothiols. We suggest that some of the effects of CBS (i.e., stimulation of prostaglandin production, antibacterial action against Helicobacter pylori) are mediated via the blockade of SH-groups.

Animals↗
PubMed1993

Studies on the mechanism of action of colloidal bismuth subcitrate. II. Interaction with pepsin.

The effects of colloidal bismuth subcitrate (CBS) on porcine pepsin have been studied in vitro. CBS inhibited pepsin activity in a pH-dependent manner. CBS was not active at pH 4.0 but inhibited pepsin activity at pH 1.0 (IC50: 2.3 +/- 0.09 mmol/l) and pH 2.0 (IC50: 8.9 +/- 0.7 mmol/l). This inhibition was reversible. In the presence of the sulfhydryl ligand mercaptoethanol, which prevents precipitation of CBS, the inhibitory potency of CBS increased. CBS bound to both positively (Amberlite) and negatively charged (Dowex) ion exchangers in a pH-dependent manner. With increasing acidity, binding to Amberlite increased, whereas binding to Dowex decreased. From these data we conclude that negatively charged bismuth salts derived from CBS bind at pH 2.0 and 1.0 via an ionic interaction to positively charged groups of pepsin, thereby inactivating the enzyme.

Animals↗
PubMed1993

[Effects of the histamine H2 receptor antagonist roxatidine acetate on stomach and liver alcohol dehydrogenase and serum alcohol level].

Some histamine-H2-receptor antagonists block gastric first-pass metabolism of ethanol and lead to increased blood alcohol concentrations after ingestion of a low dose (0.15 and 0.3 g/kg) of alcohol. To investigate whether the histamine-H2-receptor antagonist roxatidine acetate has a similar effect, we administered a low dose (0.3 g/kg) of ethanol to eleven volunteers before and after seven days treatment with roxatidine acetate (150 mg once daily). No effect of the drug on mean peak serum alcohol concentrations or on areas under the serum alcohol curves was found. In vitro, roxatidine acetate and its active metabolite roxatidine had almost no effect on guinea-pig gastric alcohol dehydrogenase activity. We conclude that roxatidine acetate does not block gastric first-pass metabolism of ethanol and can be considered as a safe histamine-H2-receptor antagonist in individuals who do not refrain from alcohol consumption under treatment for gastric or duodenal ulcer disease.

Adult↗
PubMed1992

Pantoprazole: a novel H+/K(+)-ATPase inhibitor with an improved pH stability.

The action of the H+/K(+)-ATPase inhibitors pantoprazole and omeprazole was compared in different in vitro test systems. In gastric membrane vesicles under conditions shown to result in acidification of the vesicle interior, pantoprazole and omeprazole inhibited H+/K(+)-ATPase activity with IC50 values of 6.8 and 2.4 microM, respectively. When intravesicular acidification was reduced by inclusion of imidazole (5 mM), a membrane permeable weak base, the inhibitory action of omeprazole was partially lost (IC50 30 microM) and that of pantoprazole almost completely lost. After incubation for 40 min with pumping membrane vesicles, a half-maximal reduction in intravesicular H+ concentration occurred at pantoprazole and omeprazole concentrations of 1.1 and 0.6 microM, respectively. Again, when the intravesicular H+ concentration was reduced by inclusion of imidazole (2.5 mM), pantoprazole (20 and 60 microM) did not reduce the remaining intravesicular proton concentration, whereas omeprazole (10 and 30 microM) did. Both drugs inhibited, with similar potency, papain activity at pH 3.0 and inactivated the enzyme in a similar time-dependent manner; at pH 5.0 omeprazole (IC50 17 microM) was more potent than pantoprazole (IC50 37 microM) and enzyme inhibition was faster than with pantoprazole. These results indicate that pantoprazole is a potent inhibitor of H+/K(+)-ATPase under highly acidic conditions and that it is more stable than omeprazole at a slightly acidic pH such as pH 5.0.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1992

Interaction of the non-steroidal anti-inflammatory drug flufenamic acid with gastric acid secretion and H+/K(+)-ATPase.

1. The effects of the non-steroidal anti-inflammatory drug (NSAID) flufenamic acid on H+ production in isolated and enriched guinea-pig parietal cells and on H+/K(+)-ATPase activity in ion-tight inside-out membrane vesicles from pig gastric mucosa were studied. 2. At low concentrations (0.1 and 1.0 mumol/L), flufenamic acid increased the secretory response of parietal cells to dibutyryl cyclic AMP (dbcAMP). At higher concentrations (10 and 100 mumol/L) it progressively inhibited basal and dbcAMP-stimulated acid production. 3. Flufenamic acid (10 mumol/L) increased K+ (0.5-10.0 mmol/L) and K+ (0.5-1.0 mmol/L) plus gramicidin-stimulated ATPase activity in gastric membrane vesicles. The Km value for K+ (1.6 and 1.0 mmol/L in the absence and presence of gramicidin, respectively) was decreased to 0.8 and 0.5 mmol/L, respectively. At higher concentrations (greater than or equal to 50 mumol/L), flufenamic acid inhibited K+ plus gramicidin-stimulated ATPase activity (inhibited concentration at 50% [IC50] = 186 mumol/L) and reduced the proton concentration (IC50 = 50 mumol/L). 4. It is concluded that flufenamic acid-induced enhancement of dibutyryl cyclic AMP-stimulated H+ production in the parietal cell reflects the stimulation of H+/K(+)-ATPase. We suggest that activation of the enzyme involves increased affinity of K+ towards the K(+)-binding site of the enzyme and/or increased KCl permeability at the vesicle membrane. The inhibitory action of the drug on H+ production in parietal cells results from a detergent and/or protonophoric-like action at the apical parietal cell membrane, and from inhibition of H+/K(+)-ATPase activity.

Adenosine Triphosphatases↗
PubMed1991

Cellular events associated with inflammatory angiogenesis in the mouse cornea.

The aim of this study was to establish an angiogenesis model in the mouse and to define immunohistochemically the cellular events that precede angiogenesis. After chemical cauterization of the murine cornea, neovascularization was observed within 36 hours. The cellular infiltrate was analyzed by using antibodies on cryostat and paraffin sections and by histochemical staining for mast cells. It was found that neither T lymphocytes nor mast cells nor macrophages in a more mature stage of development were part of the infiltrate that preceded the ingrowth of new blood vessels. Instead, the infiltrating cells appearing from 3 hours on were granulocytes and inflammatory monocytes, as detected by an antibody against the calcium-binding protein MRP14. The authors conclude that the induction of angiogenesis during nonspecific inflammation is associated with the early influx of myelomonocytic cells, but not with the infiltration of mature macrophages, T lymphocytes, or mast cells. This study shows that immunohistochemical analysis of cauterized murine corneas presents a useful tool for further studies on cells and cell products involved in the angiogenic process.

Animals↗
PubMed1991

Signal transduction pathway in gastric mucous cells.

In isolated and enriched guinea-pig gastric mucous cells the effects of carbachol, prostaglandin E2 (PG E2), prostaglandin F2 alpha (PG F2 alpha) and histamine on adenylate cyclase (AC) and cytosolic free Ca2+ were investigated, in order to study the biochemical mechanisms involved in secretagogue-mediated mucus release. Histamine and both prostaglandins stimulated AC in partially purified membranes of mucous cells. Histamine was most efficacious, followed by PG E2 and PG F2 alpha. The histamine effect was blocked by the H2-receptor antagonist ranitidine, but not by the H1-receptor antagonist mepyramine. Carbachol raised the resting [Ca2+]i in mucous cells from 120 to 306 nM. This carbachol effect was blocked by atropine. Histamine and PG E2 stimulation of AC was inhibited in a concentration-dependent manner by Ca2+ (IC50:31 microM). In the presence of TPA and phosphatidylserine, conditions which activate protein kinase C, the inhibitory action of Ca2+ on AC was significantly increased. These data indicate that there exists a negative feedback control mechanism between protein kinase C and histamine/prostaglandin E2-induced AC activation. From the finding that TPA and phosphatidylserine increased the inhibitory action of Ca2+ on cholera toxin-, but not on forskolin-stimulated AC we assume that the point, where protein kinase C exerts its inhibitory effect at the AC, is the guanine nucleotide regulatory protein.

Adenylyl Cyclases↗
PubMed1990

Interaction of the anti-inflammatory seleno-organic compound ebselen with acid secretion in isolated parietal cells and gastric H+/K(+)-ATPase.

The effects of the anti-inflammatory seleno-organic compound ebselen on gastric H+/K(+)-ATPase, H+/K(+)-ATPase-mediated proton transport and on parietal cell HCl production was studied. Ebselen inhibited K(+)-stimulated ATPase activity in leaky gastric membranes (IC50:0.15 microM) and H+/K(+)-ATPase-mediated proton transport in intact gastric membrane vesicles (IC50:0.7 microM). Histamine- and dibutyryl-cAMP-stimulated HCl production in isolated and enriched guinea-pig parietal cells was inhibited with an IC50 value of 12 microM. The mercaptan dithioerythritol and the nucleotide ATP prevents the H+/K(+)-ATPase against inactivation and dithioerythritol was found to restore already inhibited enzyme activity and ATPase mediated H+ transport. Furthermore, dithioerythritol could prevent ebselen-induced inhibition of HCl production in the parietal cell preparation. It is concluded that ebselen inhibits acid secretion in the parietal cell by interference with SH groups of the gastric proton pump, the H+/K(+)-ATPase. Therefore ebselen can be regarded as an anti-inflammatory drug for which in vitro anti-secretory properties can be demonstrated.

Adenosine Triphosphatases↗
PubMed1990

Substituted thieno[3,4-d]imidazoles, a novel group of H+/K(+)-ATPase inhibitors. Differentiation of their inhibition characteristics from those of omeprazole.

The action of the H+/K(+)-ATPase inhibitors, Hoe 731 and S 4216, both thieno-imidazole derivatives, was compared with that of the benzimidazole derivative, omeprazole. In intact, gastric membrane vesicles under conditions shown to result in acidification of the vesicle interior. Hoe 731 and S 4216 inhibited H+/K(+)-ATPase activity with an IC50 value of about 1.0 microM. In the absence of a generated pH gradient the respective IC50 values were 5.5 and 2.1 microM. In contrast, omeprazole inhibited the enzyme only in the presence of proton accumulation (IC50: 0.7 microM). The inhibitory action of omeprazole on H+/K(+)-ATPase-mediated proton transport was prevented by the membrane permeable mercaptane, dithioerythritol, but not by the membrane impermeable, mercaptane glutathione, whereas both mercaptanes were able to prevent the effect of Hoe 731 and S 4216. These results indicate that the thienoimidazoles react with intravesicular (luminal) and extravesicular (cytosolic) SH groups of the H+/K(+)-ATPase, whereas omeprazole interacts uniquely with luminal SH groups of the enzyme. In isolated parietal cells all drugs caused a concentration-dependent inhibition of HCl production, as measured by [14C]aminopyrine uptake, during histamine and dibutyryl-cAMP stimulation. The IC50 value was 0.1 microM for Hoe 731 and omeprazole and 0.4 microM for S 4216 after 30-min incubation. The inhibitory action of Hoe 731 and S 4216 faded with increasing incubation time, whereas omeprazole caused an unchanged inhibition over the entire 120-min incubation period. We suggest that several factors, e.g. weaker chemical stability of the drugs or perturbation of cellular glutathione levels, may be responsible for the fading inhibitory action of thienoimidazoles in the parietal cell.

Adenosine Triphosphatases↗
PubMed1990

Interaction of calcium channel antagonists with parietal cell acid production, adenylate cyclase, intracellular-free Ca2+ and H+/K+-ATPase.

The calcium channel antagonists verapamil, gallopamil and nifedipine were tested for their effects on acid secretion stimulated by histamine and dibutyryl-cyclic AMP in isolated and enriched guinea pig parietal cells, on adenylate cyclase activity mediated by histamine H2 receptors, on histamine-stimulated increase in cytosolic-free Ca2+ concentration [Ca2+], on gastric H+/K(+)-ATPase activity and on H+/K(+)-ATPase-mediated proton uptake in intact gastric membrane vesicles. Verapamil and gallopamil impaired all cellular and enzymatic test systems studied. Both drugs affected with highest potency the acid secretion in the parietal cell preparation (IC50: 1-2 mumol/l) and the H+/K(+)-ATPase-mediated H+ uptake in gastric membrane vesicles, whereas their inhibitory action was less pronounced on adenylate cyclase and on histamine-induced increase in cytosolic-free [Ca2+]. The type of interaction found in the gastric membrane vesicle preparation indicates that both drugs act as protonophores. Nifedipine was less effective as an inhibitor of acid secretion in the parietal cell preparation and in reducing proton concentration in isolated gastric membrane vesicles. The drug failed to block adenylate cyclase and H+/K+-ATPase activity. Since nifedipine is a more effective calcium channel blocking agent but a less lipophilic drug than verapamil and gallopamil, we conclude that the antisecretory activity of calcium channel antagonists in vitro is mediated by a nonspecific, i.e. a protonophoric, action. We suggest that verapamil exhibits its antisecretory activity in vivo partially by its protonophoric action at the secretory membrane of the parietal cell, whereas the decrease in acid secretion by nifedipine is not mediated by this mechanism.

Adenosine Triphosphatases↗
PubMed1990

[Secondary messengers in the hormonal regulation of the functional activity of the main and mucoid cells in the stomach].

The messenger role of Ca+2, cyclic nucleotides and inositol triphosphates in the stimulation of pepsinogen and mucous secretion were studied using isolated pig [correction of nug] gastric chief cells and guinea pig mucous cells, resp. Pepsinogen secretion was stimulated by agents either working at the postreceptor adenylate cyclase (AC) level (db-cAMP, forskolin) or after 12-o-tetradecanoyl-phorbol-13-acetate (TPA) stimulation of protein kinase C (PK C). Similar secretory effects were observed with histamine (H), carbachol (C) and cholecystokinin (CCK). [Ca-2] in was elevated by C and by CCK, but not by H in both types of cells. Like TPA, both C and CCK, but not H, stimulated the Ca+2-sensitive particulate PK C. H increased the activity of cAMP-dependent PK A. PGE2, C and CCK were found to increase inositol-1,4,5-triphosphate content in mucous cells. The findings indicate that two pathways of the regulation of pepsinogen and mucous secretion (AC-cAMP-PK C and phosphoinositol breakdown cascade) can act synergistically.

Adenylyl Cyclases↗