Helicobacter pylori causes DNA damage in gastric epithelial cells

Helicobacter pylori infection has been considered as a risk factor for gastric carcinoma. Strong evidence exists that reactive oxygen species (ROS) play an important role in carcinogenesis, and in vivo investigations have shown increased synthesis of ROS in the gastric mucosa of H.pylori-infected patients. In the present study the direct effects of H.pylori on ROS and DNA synthesis, induction of apoptosis and DNA repair were investigated in the gastric epithelial cell lines AGS and HM02. Incubation of gastric cells with H.pylori extract induced the synthesis of ROS, diminished the levels of reduced glutathione (GSH), induced DNA fragmentation and increased DNA synthesis in gastric cells. Poly(ADP-ribose) formation was increased in gastric cells exposed to H.pylori extract. FACS analysis of gastric cells exposed to H.pylori extract did not reveal any change in the percentage of cells in the G(2)/M phase of the cell cycle. The radical scavengers MnTBAP (a cell permeable superoxide dismutase mimic), ebselen (a GSH peroxidase mimic) and high doses of catalase completely blocked H.pylori extract-induced elevation in DNA synthesis. Our results indicate that H.pylori extract directly induces the synthesis of ROS in gastric epithelial cells and causes DNA damage.

Helicobacter pylori causes DNA damage in gastric epithelial cells

Helicobacter pylori infection has been considered as a risk factor for gastric carcinoma. Strong evidence exists that reactive oxygen species (ROS) play an important role in carcinogenesis, and in vivo investigations have shown increased synthesis of ROS in the gastric mucosa of H.pylori-infected patients. In the present study the direct effects of H.pylori on ROS and DNA synthesis, induction of apoptosis and DNA repair were investigated in the gastric epithelial cell lines AGS and HM02. Incubation of gastric cells with H.pylori extract induced the synthesis of ROS, diminished the levels of reduced glutathione (GSH), induced DNA fragmentation and increased DNA synthesis in gastric cells. Poly(ADP-ribose) formation was increased in gastric cells exposed to H.pylori extract. FACS analysis of gastric cells exposed to H.pylori extract did not reveal any change in the percentage of cells in the G(2)/M phase of the cell cycle. The radical scavengers MnTBAP (a cell permeable superoxide dismutase mimic), ebselen (a GSH peroxidase mimic) and high doses of catalase completely blocked H.pylori extract-induced elevation in DNA synthesis. Our results indicate that H.pylori extract directly induces the synthesis of ROS in gastric epithelial cells and causes DNA damage.

Simocyclinones, novel cytostatic angucyclinone antibiotics produced by Streptomyces antibioticus Tü 6040. I. Taxonomy, fermentation, isolation and biological activities

Two novel angucyclinone-type antibiotics, simocyclinones D4 and D8, were detected in the mycelium extract of Streptomyces antibioticus Tü 6040 by HPLC-diode-array and HPLC-electrospray-mass-spectrometry screening. The compounds show antibiotic activities against Gram-positive bacteria and cytostatic effects on various tumor cell lines.

Role of vacA and cagA in Helicobacter pylori inhibition of mucin synthesis in gastric mucous cells

The aim of this study was to investigate the effect of Helicobacter pylori on the function of gastric mucous cells. H. pylori (10(4) to 10(7) CFU/well) was incubated with the mucin-producing gastric cell line HM02 for 12 and 24 h. Mucin synthesis and secretion were determined by the incorporation of D-N-[acetyl-(14)C]glucosamine into intracellular and released high-molecular-weight glycoproteins. cagA-positive, cytotoxin-producing and non-cytotoxin-producing H. pylori strains impaired the incorporation of D-N-[acetyl-(14)C]glucosamine into intracellular glycoproteins. Significant inhibition of mucin synthesis was noted after 12 and 24 h of cocultivation with a bacterial load of >/=10(5) bacteria (bacterium/cell ratio = 0.25). The cagA-positive, cytotoxin-producing strains (HP64, HP57, and HP87) caused significantly stronger inhibition of intracellular mucin synthesis than the cagA-positive, non-cytotoxin-producing strains (HP05, HP83, and HP84). The cagA-negative, non-cytotoxin-producing strains (HP01, HP04, and HP85) did not affect intracellular mucin synthesis. The results indicate that H. pylori directly impairs mucin synthesis in gastric mucous cells and that cytotoxic cagA-positive strains cause more profound inhibition of mucin synthesis. We suggest that the increased inhibitory effect of cagA-positive, cytotoxin-producing strains on mucin synthesis can be considered one possible factor responsible for the increased risk of developing peptic ulceration with these H. pylori strains.

Proinflammatory cytokines trigger MUC gene expression and mucin release in the intestinal cancer cell line LS180

OBJECTIVES AND DESIGN

Proinflammatory cytokines and a defective mucus layer are involved in the pathogenesis of colitis. Therefore, we determined cytokine effects on MUC gene expression and mucin secretion.

MATERIALS AND METHODS

LS180 cells were characterized by light and electron microscopy and subsequently exposed to interleukin 1 (IL-1, 1 ng/ml), interleukin 6 (IL-6, 10 ng/ml), or tumor necrosis factor-alpha (TNFalpha, 10 ng/ml). MUC gene (MUC2, MUC5AC, MUC5B, MUC6) mRNA expression was assessed by RT-PCR, the encoded proteins were identified by immunocytochemistry and Western blotting, and the released mucins were isolated and chromatographically characterized.

RESULTS

Thirty to 40% of the cells contained intracellular mucin granules. Incubation with IL-1 transiently stimulated the mRNA expression of MUC2 and MUC5AC, whereas IL-6 induced an early response of MUC2, MUC5B and MUC6. TNFalpha upregulated the expression of MUC2 and MUC5B for 3 hours, and had no effect on the expression of MUC 5AC and MUC6. Immunocytochemistry and Western blotting confirmed TNFalpha effects on MUC2 and MUC5AC on the protein levels. All cytokines stimulated the release of less glycosylated mucins and considerably modulated their carbohydrate composition.

CONCLUSION

Our data demonstrate differential cytokine effects on mucin synthesis, secretion and composition. These alterations may contribute to the defective mucus layer in colitis.

New biologically active rubiginones from Streptomyces sp

Four new polyketides, named rubiginone D2 (2), 4-O-acetyl-rubiginone D2 (3), rubiginone H (6) and rubiginone I (7) were isolated from the cultures of Streptomyces sp. (strain Gö N1/5). Their structures were established by a detailed spectroscopic analysis. The absolute configuration of 3 was determined by derivatization with chiral acids (Helmchen's method). The rubiginones inhibit the growth of some Gram-positive bacteria and are cytostatically active against different tumor cell lines.

Variation of human mucin gene expression in gastric cancer cell lines and gastric mucous cell primary cultures

Human gastric mucous cells - gastric cancer cell lines mucin gene expression - TNFalpha - RT-PCR immunocytochemistry Little is known on the expression pattern of mucin genes in human gastric cancer cell lines in relation to mucin expression in normal gastric epithelial cells. Thus, the aim of this study was to compare gastric cancer cell lines and non-transformed epithelial cells in their expression of the different mucin genes, in order to use these cells as models for physiological MUC expression in human stomach. Human gastric mucous cell primary cultures which were obtained from surgical specimen by collagenase/pronase treatment and a panel of six human gastric cancer cells were screened for mRNA expression of the mucin genes MUC1, MUC2, MUC5AC, MUC5B, and MUC6. Mucin gene expression was analyzed by semi-quantitative RT-PCR, and by Western blotting and immunocytochemistry. Primary cultured human gastric mucous cells retained the stomach-specific pattern of mRNA expression found in gastric mucosal biopsies (MUC1, MUC5AC, MUC6), whereas any gastric cancer cell line exhibited an aberrant mucin gene expression. Mucin gene expression showed large variations in levels and patterns from cell line to cell line, but MUC2 was aberrantly expressed in all cancer cells. Immunocytochemistry confirmed aberrant MUC2 protein expression in cancer cells. The expression of the secretory mucin genes MUC2 and MUC5AC varied in relation to the length of cultivation of the cancer cell lines. Treatment of the gastric cancer cells with TNFalpha resulted in an enhanced mRNA expression of MUC1, MUC2, and MUC5AC (2-fold increase within 3 hours; p <0.05). In contrast, immunocytochemistry disclosed a decrease in MUC2 and MUC5AC staining intensity. Our results indicate that primary cultured human gastric mucous cells provide a physiological in vitro system for investigations of gastric mucin gene regulation. In gastric cancer cells marked changes in the mucin gene expression pattern are found with coexpression of non-gastric type mucins. Gastric mucin gene expression may be regulated by proinflammatory cytokines which could have implications in gastritis.

Basic aspects of selectivity of pantoprazole and its pharmacological actions

Pantoprazole sodium is a substituted benzimidazole derivative which controls acid secretion by inhibition of gastric H(+)/K(+)-ATPase. The prodrug pantoprazole accumulates in the acidic space of the parietal cell where it is converted to the pharmacologically active principle, a thiophilic cyclic sulfenamide. The pH-dependent activation profile, i.e., activation at pH 1 versus activation at pH 4-6, is more favorable for pantoprazole than for the other proton pump inhibitors (PPIs) currently available. In vitro, pantoprazole interferes less potently than omeprazole with biological targets not related to gastric acid secretion. The gastric target sites for the pantoprazole sulfenamide are the cysteines 813 and 822 of the catalytic subunit of the H(+)/K(+)-ATPase. In contrast to omeprazole, the two binding sites are located right at the proton channel. In rats, dogs and humans, pantoprazole produces marked and prolonged inhibition of both basal and stimulated acid secretion. Overall, its antisecretory potency is equal to that of omeprazole. Antiulcer activity has been demonstrated for pantoprazole in two rat models. As seen with H(2)-receptor antagonists and other PPIs, pantoprazole causes an increase in serum gastrin concentration which reflects the degree of gastric acid inhibition. Pantoprazole is mainly metabolized by CYP3A4 and 2C19, but displays a lower affinity for these phase I cytochrome P450 enzymes than omeprazole. In contrast to the latter, pantoprazole is further conjugated with sulfate by the hepatic phase II metabolism. These two differences may explain why pantoprazole does not interfere with the metabolism of any other drug thus far tested in humans.

Growth characteristics and influence of antibiotics on rough/smooth phenotypic variants of Helicobacter pylori

Helicobacter pylori shows a rather high variability of several biochemical markers including lipopolysaccharide structures. This study aimed to determine whether Helicobacter pylori has a potential for phenotypic variability and to describe its effects on bacterial pathogenesis. From colonies of three clinical strains of Helicobacter pylori with rough (R) colony morphology, spontaneous phenotypic variants with smooth (S) colony morphology were isolated that occurred with a frequency of 10(-2) to 10(-3), irrespective of growth conditions. R-variant bacteria produced exclusively low-molecular-mass lipopolysaccharide. They exhibited increased lysis in the presence of plain air. In contrast, the S variants produced low- and high-molecular-mass lipopolysaccharide and did not exhibit increased lysis in the presence of plain air. Cocultivation of bacterial cells with AGS stomach cancer cells revealed that R-variant bacteria but not S-variant bacteria effected an inhibition of high molecular-weight glycoprotein biosynthesis and secretion by the host cells. Skirrow supplement added as selective agent to liquid and/or solid media was tolerated to a similar extent among R- and S-variant bacteria, while all variants proved sensitive to metronidazole, amoxicillin and clarithromycin except for the R and S isolates of strain Hp57, which showed resistance to the latter compound. It was concluded that R- and S-variants of Helicobacter pylori may have distinct roles in pathogenesis; nevertheless, these bacteria may be isolated by traditional methods and eradicated by conventional anti-infective therapy.

Connecting and becoming culturally competent: a Lakota example

Addressing how nurses become culturally competent is essential for knowledge development beyond why sociocultural understandings are important. This article reports participatory research conducted during intercultural immersion learning experiences of non-native nurses on an Indian reservation. Emphasizing collaborative relationships within unfamiliar social, political, and economic circumstances, and using Diekelmann's "concernful practices" as an organizing scheme, prompted participants to explicate practices that promote intercultural connecting. Suggesting integral shifts in value orientations with changes in cultural competence, the findings argue for attending to associations between those dynamics and potential for developing co-responsibility (with consumer groups) for advocating improved health and health care.

Morphological and molecular characterization of human gastric mucous cells in long-term primary culture

A primary cell culture of human gastric mucous cells was developed using enzymatic treatment of surgically obtained gastric mucosal specimens. Preferential attachment of gastric mucous cells during a preincubation step resulted in the enrichment of mucous cells [over 90% stained with periodic acid-Schiff (PAS) and mucin-type lectins] in the primary cell culture. Gastric mucous cells could be maintained in culture for 10 days. DNA synthesis peaked during the first 2 days in culture (8+/-1% bromodeoxyuridine-positive cells). During the entire culture period gastric mucous cells released high-molecular-weight glycoproteins into the medium, as determined by gel chromatography on a Sepharose CL-4B column and by metabolic labelling with [14C]-N-acetylglucosamine. Gastric mucin was verified by gas chromatographic analysis of the carbohydrate composition and fractionation of the void-volume fraction by density gradient centrifugation. Determination of the terminal glycosylation of the secreted glycoproteins by a lectin-ELISA revealed that there was a high quantity of alpha-l-fucose. Prostaglandin E2 significantly stimulated glycoprotein secretion during the entire cultivation period by 29-60%. Analysis of mucin-encoding MUC mRNA expression by reverse transcriptase polymerase chain reaction revealed that gastric mucous cells predominantly express MUC1 and MUC5AC, and to a lesser extent MUC6, which reflects the expression pattern obtained following analysis of biopsied samples of gastric mucosa. This primary cell culture model enables the regulation of mucin secretion and mucin gene expression in man to be investigated.

Stimulation of pepsinogen release from chief cells by Helicobacter pylori: evidence for a role of calcium and calmodulin

To define the mechanisms by which Helicobacter pylori stimulates pepsinogen secretion, the in vitro release of pepsinogen was studied using a preparation of pig chief cell monolayers. Helicobacter pylori induced a time- and concentration-dependent release of pepsinogen into the medium, with about a three-fold increase in pepsinogen secretion over controls found after 45 min of incubation. 3x10(7) H. pylori produced 50% of the maximal response found at a H. pylori count of 2x10(8). The action of H. pylori did not depend on the presence of the vacuolating toxin (vacA) and the cytotoxin-associated protein (cagA). Dibutyryl-cAMP and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate also markedly stimulated pepsinogen secretion and enhanced the stimulatory effect of H. pylori. Helicobacter pylori-stimulated pepsinogen release was inhibited by lanthanum and the calmodulin antagonist W-7, but not by the L-type Ca2+ channel blocker nifedipine, TMB-8, an agent that blocks the release of Ca2+ from intracellular stores, the protein kinase C inhibitor staurosporine and the protein kinase A inhibitor H-8. It is suggested that H. pylori directly stimulates pepsinogen release from gastric chief cells and that this effect is mediated via the calcium/calmodulin messenger branch.

Helicobacter pylori fatty acid cis 9,10-methyleneoctadecanoic acid increases [Ca2+]i, activates protein kinase C and stimulates acid secretion in parietal cells

The effect of the Helicobacter pylori (H. pylori) fatty acid cis 9,10-methyleneoctadecanoic acid (MOA) on gastric acid secretion was studied in isolated guinea-pig parietal cells. MOA (1 and 3 micromol/l) stimulated basal and enhanced histamine- and dibutyryl cyclic AMP-stimulated acid secretion in parietal cells. MOA increased intracellular free [Ca2+]i concentration in a concentration-dependent manner. The source of [Ca2+]i was extracellular as demonstrated by depletion of [Ca2+]i with EGTA. Furthermore, MOA caused activation of parietal cell protein kinase C (PKC). The effect of MOA upon PKC activation was [Ca2+]i-dependent but did not require phosphatidylserine as phospholipid co-factor. Similarly to the effect of diolein, MOA increased the stimulatory effect of phosphatidylserine at low [Ca2+]i concentrations. Treatment of parietal cells with MOA caused translocation of PKC from the cytosol to the membrane-associated cell fraction. We propose that MOA stimulates parietal cell acid secretion presumably by an increase of cytosolic free [Ca2+]i concentrations and PKC activation.

Effects of PGE2 and of different synthetic PGE derivatives on the glycosylation of pig gastric mucins

The glycosylation of pig gastric mucins, discharged in response to prostaglandin (PG) E2 and to three synthetic PGE-derivatives (misoprostol, nocloprost, rioprostil) was compared. After a 20 h culture period in the absence or presence of 1 micromol/l of one of the PGs, mucins were isolated by gel chromatography and their glycosylation characterized by their linkage to a panel of lectins. For all tested PGs, a significantly increased lectin linkage to mucin glycoproteins of high molecular weight was detected; no significant effects were observed for low molecular weight glycoproteins. Within the stimulatory pattern, major effects were found for the linkage of peanut agglutinin and soybean agglutinin, suggesting predominant effects on the expression of galactose and N-acetyl-galactosamine. Only minor effects were found for sialic acid, mannose, N-acetyl-glucosamine and fucose expression, as evidenced by the linkage of Sambucus nigra agglutinin, Concanavalin A, Datura stramonium agglutinin and Ulex europaeus I agglutinin. All PGs exerted a similar stimulatory pattern. However, at the indicated concentration, misoprostol (281 +/- 36% of control) rendered a significantly higher overall effect than PGE2 (208 +/- 31%), whereas the increases induced by nocloprost (237 +/- 35%) and rioprostil (202 +/- 35%) were not significantly different from the PGE2 effects. These results, suggesting similar stimulatory effects of PGE2 and of the tested synthetic PGs on glycosylation of mucin oligosaccharides, discharged from mucous cells during an in vitro culture, may, at least in part, explain clinical findings that during an impairment of the endogenous PG synthesis, the tested synthetic PGs are effective exogenous substitutes for endogenous E-type prostaglandins and act as anti-ulcer drugs.

Pharmacokinetics of recombinant human interleukin-2 in advanced renal cell carcinoma patients following subcutaneous application

AIMS

The aim of the study was to investigate the pharmacokinetics of recombinant human interleukin-2 (rhIL-2) in patients with metastatic renal cell carcinoma following different subcutaneous (s.c.) administration regimens.

METHODS

RhIL-2 was administered subcutaneously to 10 patients according to two different dosing regimens: group A received 20 x 10(6) IU m(-2) once daily and group B 10 x 10(6) IU m(-2) twice daily (every 12 h). Additionally, in all patients the influence of soluble interleukin-2 receptor (sIL-2R) on the pharmacokinetics of rhIL-2 was investigated.

RESULTS

The mean area under the serum concentration-time curve to 24 h (AUC(0,24 h)) was 627 IU ml(-1) h in treatment group A and 1130 IU ml(-1) h (P=0.029) in treatment group B. In both study groups Cmax and AUC(0,12 h) were not significantly different. Seventy-two hours after the beginning of s.c. rhIL-2 therapy the sIL-2R increased significantly (P=0.016), and sIL-2R levels over 1200 pmol l(-1) seemed to reduce the AUC.

CONCLUSIONS

In patients with metastatic renal cell cancer administration of 20 x 10(6) IU m(-2) of rhIL-2 s.c. in two daily doses (10 x 10(6) IU m(-2) every 12 h) provides better bioavailability and is preferable to the single dose administration.

The Helicobacter pylori fatty acid cis-9,10-methyleneoctadecanoic acid stimulates protein kinase C and increases DNA synthesis of gastric HM02 cells

Protein kinase C (PKC) has been implicated in the control of epithelial proliferative activity and in the process of malignant transformation. Helicobacter pylori (H.p.) infection is associated with increased gastric epithelial cell proliferation and has been linked with gastric carcinoma. In the present study, we report that the H.p. fatty acid cis-9,10-methyleneoctadecanoic acid (MOA) directly activates PKC (Ka 3.3 microM). The effect of MOA upon PKC activation was Ca2+ dependent but did not require phosphatidylserine as phospholipid cofactor. MOA increased the stimulatory effect of phosphatidylserine at low Ca2+ (1 microM) concentrations. These findings indicate that MOA interacts at the phospholipid- and the diacylglycerol-binding domain to elicit PKC activation. Treatment of gastric mucous cells HM02 caused translocation of PKC from the cytosol to the nuclear, mitochondrial and membrane fraction. Furthermore, MOA stimulated [3H]thymidine incorporation into the DNA of HM02 cells. Our results show that the H.p. fatty acid MOA activates PKC and increases DNA synthesis in gastric epithelial cells.

Regulation of gastric epithelial cell growth by Helicobacter pylori: offdence for a major role of apoptosis

BACKGROUND & AIMS

Helicobacter pylori may affect the normal balance between gastric epithelial cell proliferation and epithelial cell death, thus interfering with the maintenance of gastric mucosal integrity. The aim of this study was to investigate the effect of H. pylori on cell growth, DNA synthesis, induction of apoptosis, and viability of human gastric epithelial cells in vitro.

METHODS

H. pylori was incubated with a differentiated human gastric cancer cell line for up to 72 hours, and the effects on cell numbers (cell counts and WST-1 assay), DNA synthesis (5-bromo-2'-deoxyuridine assay and [3H]thymidine incorporation), and DNA fragmentation (DNA fluorochrome staining, transmission electron microscopy, and histone enzyme-linked immunosorbent assay) were assessed.

RESULTS

Incubation of gastric epithelial cells with H. pylori led to a time- and concentration-dependent reduction of epithelial cell growth and a concomitant induction of DNA fragmentation. At high bacteria-cell ratios (> 100), inhibition of cell growth was associated with a reduction in DNA synthesis. Treatment of gastric cells with tumor necrosis factor alpha, a receptor-activating CD95/APO-1/Fas antibody, and interferon gamma markedly potentiated H. pylori-induced DNA fragmentation.

CONCLUSIONS

H. pylori affects gastric epithelial cell growth by direct induction of apoptosis and inhibition of DNA synthesis and indirectly by sensitization of epithelial cells for apoptosis induced by proinflammatory stimuli.

Effects of extracellular Mg2+ concentration on intracellular signalling and acid secretion in rat gastric parietal cells

In the present study, the effects of extracellular magnesium concentration ([Mg2+]ex) on stimulus-secretion coupling processes were investigated in rat gastric parietal cells in vitro. Extracellular magnesium reduction resulted in (1) an increase of basal intracellular free calcium concentration ([Ca2+]in), (2) an enhancement of both carbachol and thapsigargin-induced calcium responses, (3) an improved filling state of intracellular calcium stores, (4) an increase of both basal and carbachol-induced acid secretion, whereas intracellular adenosine 3',5'-cyclic monophosphate (cyclicAMP) levels and histamine stimulated acid secretion were not affected. The effects of high [Mg2+]ex were opposite to the described results, except that high [Mg2+]ex was able to decrease significantly histamine-stimulated cyclicAMP levels and acid secretion. These findings indicate a modulatory role of [Mg2+]ex on the intracellular signalling processes and acid secretory properties in rat parietal cells. These effects seemed to be mediated by regulating (1) calcium loading capacity of intracellular stores, (2) the permeability of the calcium influx pathway, and (3) the formation of cyclicAMP.

Effects of PGE2 on amount and composition of high molecular weight glycoproteins released by human gastric mucous cells in primary culture

The aim of this study was to determine effects of prostaglandin E2 (PGE2) on amount and composition of high molecular weight glycoproteins (HMG), released by human gastric mucous cells in primary culture. PGE2 stimulated the release of HMG, as evidenced by measurement of total carbohydrate and protein content, in a concentration-dependent manner. At the maximally tested concentration of 10(-5) mol/l, the increase amounted to 53% and 85%, over controls, for carbohydrate and protein, respectively. The stimulated release was accompanied by alterations of HMG glycosylation. As detected by lectin-ELISA, there was a relative decrease in N-acetyl glucosamine and an increase in mannose and galactose content. The sialic acid content increased in parallel to the total carbohydrate content. These results suggest that PGE2 plays a regulatory role in the synthesis and secretion of HMG by human gastric mucous cells.

Role of protein kinase C in duodenal mucosal bicarbonate secretion in the guinea pig

Since duodenal bicarbonate secretion (DBS) is increased by m-cholinoceptor agonists, it was postulated that protein kinase C (PKC) has a role in this secretion. This premise was examined in guinea pigs, using 12-O-tetradecanoyl-phorbol 13-acetate (TPA) to stimulate bicarbonate production in the perfused duodenum in vivo, and to activate PKC in isolated duodenal enterocytes. TPA (10(-7) mol.kg-1) infused intravenously stimulated active DBS from basal values of 3.64 +/- 0.66 to 8.73 +/- 1.59 mumol.cm-1.10 min-1. This effect was completely blocked by verapamil (4 x 10(-7) mol.kg-1). PKC activity in duodenal enterocytes in the basal state was most abundant in the cytosolic fraction (2,221 +/- 444 U/mg protein) and very low in the particulate fraction (227 +/- 51 U/mg protein). TPA (10(-7) mol.kg-1) caused a time-dependent translocation of the cytosolic, lipid-dependent activity of PKC into the particulate fraction. The effect was maximal at 5 min incubation and was reversed by 30 min. In the particulate fraction, this activity was no longer lipid-dependent, but could be stimulated by Ca2+ alone. These data support the hypothesis that translocation of PKC may contribute to DBS.

Bicarbonate secretion in the guinea pig duodenum: functional characterization of peptide hormone receptors in duodenal enterocytes

To get information about the peptide hormone receptors involved in duodenal bicarbonate secretion (DBS) and their cellular location, we determined DBS and adenylate cyclase (AC) activity in response to hormones of the vasoactive intestinal polypeptide (VIP)/secretin family of peptides. DBS was determined in an isolated, perfused (24 mmol/1 NaHCO3) loop of the proximal duodenum in urethane- and indometacin-treated guinea pigs. AC stimulation was measured in isolated, homogenized duodenal enterocytes, the histological evaluation of which revealed their villous origin. VIP (10(-9) to 10(-7) mol x kg-1) dose-dependently increased DBS 3.5-fold (p < 0.01); this effect was completely inhibited by the VIP antagonist [D-p-Cl-Phe6,Leu17]VIP (10(-6) mol x kg-1). Glucagon (10(-8) to 10(-6) mol x kg-1) increased DBS 2.1-fold, while secretin (10(-9) to 10(-6) mol x kg-1) had no effect on DBS, but stimulated pancreatic bicarbonate secretion. VIP concentration-dependently increased AC activity 5.6-fold with an EC50 of 1.3 x 10(-9) mol/l. [D-p-Cl-Phe6,Leu17]VIP caused a rightward shift of the VIP concentration-response curve. A Schild plot analysis yielded a slope of 0.85 +/- 0.11, indicating competitive inhibition. While secretin also stimulated AC activity, although 1,000-fold less potent than VIP, glucagon was ineffective. These data indicate that specific VIP receptors, which mediate VIP-stimulated bicarbonate secretion, are present on villous enterocytes. Stimulation of AC by secretin seems to be of pharmacological relevance only and is consistent with the lack of effect of this hormone on DBS. Glucagon likely activates a second transmitter of bicarbonate secretion, or works independently of AC.

Extracellular nucleotides increase cytosolic free calcium by activating P2u-receptors in single human gastric mucous cells

In single human gastric mucous cells extracellular ATP, ATP-gamma-S, ADP and UTP at micromolar concentrations caused a biphasic increase in [Ca2+]i. Consistent with a P2u-receptor the rank-order of potency was ATP > or = UTP > ATP-gamma-S > ADP, and cross-desensitization of the Ca2+ responses occurred between ATP and UTP. The initial transient peak in [Ca2+]i was resistant to extracellular Ca2+ depletion which demonstrates mobilization of internal Ca2+. By contrast, the sustained plateau phase required influx of external Ca2+. Ca2+ influx occurs most likely through a capacitative Ca2+ entry mechanism, which was shown to exist in these cells by experiments performed with thapsigargin. Thus, extracellular ATP and UTP activate a common P2u-receptor most likely coupled to the Ca(2+)-phosphatidylinositol signalling cascade. Extracellular nucleotides from various sources might be an important factor in the regulation of human gastric mucous cells.

Effects of flavonoids on parietal cell acid secretion, gastric mucosal prostaglandin production and Helicobacter pylori growth

The effect of the flavonoids flavone, flavanone and quercetin on parietal cell acid production, H+/K(+)-ATPase activity, gastric mucosal prostaglandin E2 biosynthesis and Helicobacter pylori growth was studied. All flavonoids inhibited acid production in isolated parietal cells in response to histamine and dibutyryl-cAMP stimulation (IC50 values between 26 and 139 mumol/l) and inhibited H+/K(+)-ATPase activity. Inhibition of H+/K(+)-ATPase activity was dependent on the ATP concentration. Fluorescence measurements showed that flavanone reacts with ATP. These findings indicate that the inhibitory action of flavonoids on H+/K(+)-ATPase activity is related to their ability to complex ATP. Flavone and flavanone (10 and 100 mumol/l) stimulated prostaglandin E2 production in isolated gastric mucosal cells. Furthermore, the compounds inhibited Helicobacter pylori growth in a concentration-dependent manner. From these finding it appears that flavonoids are a group of compounds which could have a therapeutic potential for treatment of gastrointestinal diseases associated with Helicobacter pylori infection.

Bismuth subcitrate and omeprazole inhibit Helicobacter pyloriF1-ATPase

The effects of various types of antiulcer agents against Helicobacter pylori F1-ATPase were studied. ATPase was released into the aqueous phase (i.e., solubilized) by sonication. The enzyme activity depended on Mg2+, but not Ca2+. The maximum activity occurred at an ATP/Mg2+ ratio of 1/5 and at pH 7.5. Mg(2+)-dependent ATPase activity was inhibited by sodium azide and the monovalent cations K+ and Na+, but not by oligomycin, dicyclohexylcarbodiimide, ouabain, or SCH 28080. The antiulcer agents ranitidine, pirenzepine, aluminum hydroxide, and sucralfate failed to influence H. pylori F1-ATPase. In contrast, bismuth subcitrate and the H+/K(+)-ATPase inhibitor omeprazole inhibited the enzyme. Inhibition was prevented and reversed by the mercaptan glutathione, indicating that both drugs interfere with sulfhydryl groups of the enzyme. The data suggest that bismuth subcitrate and omeprazole owe their antibacterial activity against H. pylori, at least in part, to inhibition of F1-ATPase, an enzyme involved in bacterial energy metabolism.