Isolation and receptor profiling of ileal enterochromaffin cells

AIM AND METHODS

Enterochromaffin (EC) cells, interspersed throughout the gastrointestinal mucosa, provide most of the serotonin of the body and control intestinal motility, secretion and absorption. We purified EC cells from the rat ileum by a combination of elutriation and density gradient centrifugation in order to characterize the function of this important cell type.

RESULTS

Immunostaining showed that there were 84% serotonin-positive cells in the highly enriched EC fraction as compared with 12% in unfractionated cells, yielding a approximately sevenfold enrichment. Serotonin measurements in the cell suspensions indicated a seven to 14-fold enrichment. Presence of alpha- and beta-adrenoreceptor isoforms, muscarinic M3 and gama-aminobutyric acid (GABA)-A receptors was confirmed by RT-PCR and cytochemistry. Increased expression of VMAT-1 and GABA-A mRNA was also shown by quantitative TaqMan PCR using EC cell RNA. Serotonin release in isolated EC cells was stimulated by noradrenaline, and to a smaller extent, by carbachol, while GABA addition was without effect.

CONCLUSION

Our data provide a basis for a new approach to characterize receptors on this unique cell type.

Evidence for histamine as a transmitter in rat carotid body sensor cells

Carotid bodies harboring sensor cells for oxygen have a strategic location at the bifurcation of the carotid artery, which supplies the brain. Upon arterial hypoxia they transmit signals to the respiratory center, which increases the frequency of breathing. Dopamine is considered as the predominant transmitter of the rat carotid body sensor cells. Here we show that the rat carotid body sensor cells are the first cell type known to have the complete apparatus to synthesize, store and release both dopamine and histamine. The tyrosine hydroxylase positive dopaminergic sensor cells of juvenile rats express the histamine biosynthesis enzyme, histidine decarboxylase. Moreover, the sensor cells have not only vesicular monoamine transporter 1 (VMAT1) transporting catecholamines but also VMAT2, which is highly specific for histamine. Additionally, we found that these cells possess components of the neuroendocrine exocytosis apparatus, synaptosome-associated protein of 25 kDa (SNAP 25) and syntaxin1. The amount of histamine determined in the rat carotid body (164 pmol/carotid body) is more than 10-fold higher compared with that of dopamine. As a main effect, hypoxia significantly increased histamine release from isolated rat carotid bodies as it has been shown for dopamine. Finally, RT-PCR experiments indicate the presence of histamine receptors H1, H2 and H3 in the carotid body. Our data suggest that histamine is synthesized, stored and released upon hypoxia by dopaminergic sensor cells of the rat carotid body.

Cytokine gene polymorphisms influence mucosal cytokine expression, gastric inflammation, and host specific colonisation during Helicobacter pylori infection

BACKGROUND AND AIMS

Recent studies linked cytokine gene polymorphisms to H pylori related gastric cancer development. The current study evaluated the role of cytokine gene polymorphisms for mucosal cytokine expression, the gastric inflammatory response, and bacterial colonisation during H pylori infection.

PATIENTS AND METHODS

In 207 H pylori infected patients with chronic gastritis, polymorphisms at different loci of the interleukin (IL)-10, IL-1B, IL-1 receptor antagonist (IL-1RN), tumour necrosis factor (TNF)-A, and interferon (IFN)-G genes were genotyped by polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP) analysis, and allelic discriminating TaqMan PCR. Mucosal cytokine mRNA copy numbers were determined by real time quantitative PCR. Presence of bacterial virulence factors was investigated by cagA, vacAs1/2, and babA2 PCR. Biopsies were assessed with regard to the degrees of granulocytic/lymphocytic infiltration and the presence of intestinal metaplasia (IM) and atrophic gastritis (AG).

RESULTS

Proinflammatory IL-1 polymorphisms (IL-1RN*2(+)/IL-1B-511T/-31C(+)) were associated with increased IL-1beta expression, more severe degrees of inflammation, and an increased prevalence of IM and AG. Carriers of the IL-10-1082G/-819C/-592C alleles (GCC haplotype) had higher mucosal IL-10 mRNA levels than ATA haplotype carriers and were associated with colonisation by more virulent cagA(+), vacAs1(+), and babA2(+) H pylori strains. The TNF-A-307(G/A) and IFN-G+874(A/T) polymorphisms did not influence mucosal cytokine expression or the inflammatory response to H pylori.

CONCLUSIONS

Cytokine gene polymorphisms influence mucosal cytokine expression, gastric inflammation, and the long term development of precancerous lesions in H pylori infection. Host polymorphisms are associated with certain bacterial strain types, suggesting host specific colonisation or adaptation. These findings contribute to the understanding of the complex interplay between host and bacterial factors involved in the development of gastric pathology.

Human Dendritic Cells Respond toHelicobacter pylori, Promoting NK Cell and Th1-Effector Responses In Vitro

Helicobacter pylori infection leads to chronic gastric inflammation. The current study determined the response of human APCs, NK cells, and T cells toward the bacteria in vitro. Human monocyte-derived dendritic cells (DC) were incubated with bacteria for 48 h. Intact H. pylori at a multitude of infection 5 stimulated the expression of MHC class II (4- to 7-fold), CD80, and CD86 B7 molecules (10- to 12-fold) and the CD83 costimulatory molecule (>30-fold) as well as IL-12 secretion (>50-fold) in DCs, and thereby, strongly induced their maturation and activation. CD56(+)/CD4(-) NK cells, as well as CD4(+)/CD45RA(+) naive T cells, were isolated and incubated with DCs pulsed with intact bacteria or different cellular fractions. Coculture of H. pylori-pulsed DCs with NK cells strongly potentiated the secretion of TNF-alpha and IFN-gamma. Coculture of naive T cells with H. pylori-pulsed DCs significantly enhanced TNF-alpha, IFN-gamma, and IL-2 secretion as well as T-bet mRNA levels, while GATA-3 mRNA was lowered. However, the effect appeared attenuated compared with coculture with Escherichia coli. A greater stimulation was seen with naive T cells and DCs pulsed with H. pylori membrane preparations. Intact H. pylori potently induced the maturation and activation of human monocyte-derived DC and thereby promote NK and Th1 effector responses. The strong activation of NK cells may be important for the innate immune response. Th1-polarized T cells were induced especially by incubation with membrane preparations of H. pylori, suggesting that membrane proteins may account for the specific adaptive immune response.

Die intraoperative laparoskopische Cholangiografie - Wann ist sie sinnvoll?

Since the introduction of laparoscopic cholecystectomy (LC), a decrease in the practice of intraoperative cholangiography (IOC) has been reported. Are there actually reasons for carrying on IOC during LC? Depending on the management of common bile duct (CBD) stones treatment a different IOC regime is recommended. If the single-stage laparoscopic extraction of ductal calculi during LC is preferred, routine IOC is generally necessary to detect all CBD stones for desobstruction via ductus cysticus or choledochotomy. When therapeutic splitting is favoured, including two-stage management with endoscopic desobstruction and later LC, routine IOC can be foregone. However, selective practice of IOC can help to reduce the rates of unnecessary preoperative investigations from 40-60 % to 20 % when postoperative endoscopic desobstruction demonstrates similar success rates of about 95 %. Regarding the preventive character of laparoscopic IOC to CBD injuries, a routine investigation should be adopted by institutions with injury rates > 0.4 % and in the learning phase of young surgeons. For all other institutions a selective practice should be recommended when difficult intraoperative conditions render recognition of the anatomical situation more difficult or for identification of dissected non-bleeding ducts near the triangle of Calot.

Mechanisms of storage and exocytosis in neuroendocrine tumors

Excitatory and inhibitory neurotransmitters and biogenic amines are important signaling molecules stored by and released from endocrine cells. They are either synthesized or taken up by endocrine cells and subsequently stored in secretory vesicles. Analysis of these storage mechanisms and of the receptors of these paracrine signaling molecules revealed important cross-talk within endocrine glands which add to storage and release of peptide hormones. Components of the exocytosis apparatus are shared by the release of transmitters and hormones. They, as other classical markers, can serve as broad spectrum markers for neuroendocrine tumors. Novel specific markers arise from studies of the synthesis, uptake, and targets of transmitters identified as an additional paracrine signaling system in endocrine systems.

LMO2-associated clonal T cell proliferation in two patients after gene therapy for SCID-X1

We have previously shown correction of X-linked severe combined immunodeficiency [SCID-X1, also known as gamma chain (gamma(c)) deficiency] in 9 out of 10 patients by retrovirus-mediated gamma(c) gene transfer into autologous CD34 bone marrow cells. However, almost 3 years after gene therapy, uncontrolled exponential clonal proliferation of mature T cells (with gammadelta+ or alphabeta+ T cell receptors) has occurred in the two youngest patients. Both patients' clones showed retrovirus vector integration in proximity to the LMO2 proto-oncogene promoter, leading to aberrant transcription and expression of LMO2. Thus, retrovirus vector insertion can trigger deregulated premalignant cell proliferation with unexpected frequency, most likely driven by retrovirus enhancer activity on the LMO2 gene promoter.

Synergistic effect of Helicobacter pylori virulence factors and interleukin-1 polymorphisms for the development of severe histological changes in the gastric mucosa

Polymorphisms of the IL-1B and IL-1RN genes (which encode interleukin [IL]-1beta and IL-1 receptor antagonist, respectively) have been associated with hypochlorhydria and gastric cancer. We investigated the influence of bacterial virulence factors and host IL-1 polymorphisms on the development of histologic abnormalities in 210 Helicobacter pylori-infected patients with chronic gastritis. cagA(+)/vacAs1(+) H. pylori strains were associated with intestinal metaplasia (IM), atrophic gastritis (AG), and severe inflammation. Carriers of the proinflammatory IL-1B -511T/-31C and IL-1RN*2 alleles had an increased risk for the development of AG, IM, and severe inflammation, with odds ratios (ORs) of 1.7 (95% confidence interval [CI], 0.8-3.4) to 4.4 (95% CI, 1.5-12.9). The highest prevalence of severe gastric abnormalities was found in patients with both host and bacterial high-risk genotypes (cagA(+)/vacAs1(+)/IL-1B -511T/IL-1RN*2), with ORs of 24.8 (95% CI, 5.2-117.3) for severe lymphocytic infiltration, 9.5 (95% CI, 2.8-32.1) for severe granulocytic infiltration, 6.0 (95% CI, 2.4-15.5) for IM, and 2.4 (95% CI, 0.93-6.2) for AG. Combined bacterial/host genotyping thus may provide a clinical tool to identify patients at high risk of developing cancer.

Antigenic properties of HpaA and Omp18, two outer membrane proteins of Helicobacter pylori

Outer membrane proteins (OMPs) are incorporated into the outer plasma membrane of Helicobacter pylori and are important for, e.g., ion transport, adherence, structural and osmotic stability, and bacterial virulence but may also be antigenic due to their surface exposure. Previous proteome-based approaches with H. pylori lysates determined a strong serological reaction towards two H. pylori OMPs, HpaA (TIGR HP0797) and Omp18 (TIGR HP1125). PCR was used to detect DNA encoding the two proteins, and a positive signal was found in all H. pylori strains tested. Proteins were cloned and expressed in the human kidney cell line HK293 with the QiaExpressionist system with a C-terminal His tag. Only sera from infected persons showed a positive reaction with the recombinant proteins. Recombinant HpaA (rHpaA) and rOmp18 were incubated with human peripheral blood mononuclear cells and induced secretion of interleukin-12 (IL-12) and IL-10 from these cells. To determine the effect on antigen-presenting cells, human blood monocytic and dendritic cells (DCs) were isolated by magnetic cell separation. rOmp18 and rHpaA strongly stimulated major histocompatibility class II and CD83 expression 7- to 10-fold on isolated DCs. rHpaA and rOmp18 failed to stimulate IL-8 secretion from monocytes but increased secretion of IL-12 and IL-10 from DCs significantly. In summary, HpaA and Omp18 are recognized by human dendritic cells and induce their maturation as well as antigen presentation. HpaA and Omp18 of H. pylori thereby appear to have a specific antigenic potential in humans.

Physiology of gastric enterochromaffin-like cells

Enterochromaffin-like (ECL) cells are neuroendocrine cells in the gastric mucosa that control acid secretion by releasing histamine as a paracrine stimulant. The antral hormone gastrin and the neural messenger pituitary adenylyl cyclase-activating peptide (PACAP) potently stimulate histamine synthesis, storage, and secretion by ECL cells. Histamine is stored in secretory vesicles via V-type ATPases and vesicular monoamine transporters of subtype 2 (VMAT-2). Plasmalemmal calcium entry occurs via L-type calcium channels upon stimulation with secretagogues. K(+) and Cl(-) channels maintain the membrane potential. Calcium-triggered exocytosis of histamine is mediated by interacting SNARE proteins, especially by synaptobrevin and SNAP-25. Dynamins and amphiphysins appear to play a key role in endocytosis. ECL cells are under transcriptional control of various hormones. Gastrin stimulates transcriptional activity of the histidine decarboxylase (HDC), VMAT-2, and chromogranin A promoter by activation of Sp1 elements and CREB. During chronic Helicobacter pylori infection, pro-inflammatory cytokines are released that can also affect ECL cells, thus impairing their secretory function and viability, which can predispose to hypochlorhydria and gastric carcinogenesis.

TNF-alpha induces apoptosis of parietal cells

Helicobacter pylori infection can be associated with chronic gastric inflammation and hypochlorhydria with increased levels of the proinflammatory cytokines. The current study investigated the effects of TNF-alpha on programmed death of gastric parietal cells. TNF-alpha induced apoptosis of parietal cells in isolated perfused rat stomachs at 10ng/mL. In isolated and highly enriched rat parietal cells, 10ng/mL TNF-alpha induced a 2.6-fold increase in the apoptotic rate. The 55kDa protein of TNFR-1 but not the 75kDa of TNFR-2 was detected by Western blot analysis. TNF-alpha-induced apoptosis of isolated parietal cells was inhibited by pretreatment with different NF-kappaB-inhibitors, nitric oxide synthase inhibitors and with antisense-oligodeoxynucleotides against the p65 subunit of NF-kappaB. Investigation of downstream signaling pathways of apoptosis revealed that TNF-alpha induced the expression of iNOS, but failed to stimulate the activity of caspase 3. The TNF-alpha effect on gastric parietal cells may contribute to the atrophy and hypochlorhydria of the gastric mucosa observed during chronic H. pylori infection.

Helicobacter pylori virulence factors and the host immune response: implications for therapeutic vaccination

Helicobacter pylori colonizes the human gastric mucosa and is associated with specific gastric disease. Virulence factors, such as urease, the vacuolating toxin (VacA), the cytotoxin-associated antigen CagA or blood-group-antigen-binding adhesin (BabA), an adherence factor, might account for the development of different diseases. Vaccination trials exploiting the antigenic properties of some of these proteins have not been successful in preventing infection in humans. A more in-depth understanding of the immune response to H. pylori infection as well as additional information on suitable epitopes and adjuvants will be required before a successful vaccine can be developed.

Tumor necrosis factor-alpha effects on rat gastric enterochromaffin-like cells

Gastric enterochromaffin-like (ECL) cells are histamine-producing cells in the gastric epithelium which are responsible for the peripheral regulation of acid secretion. The gastric mucosa is frequently infected with Helicobacter pylori, leading to increased levels of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). The aim of our current study was to identify the effect of TNF-alpha on programmed cell death. ECL cells were isolated from the rat corpus mucosa to a purity >90%. TNF receptor and adapter protein presence were determined using RT-PCR, Western blot and immunocytochemistry. Apoptosis was measured by Tdt-mediated dUTP nick end labeling reaction and by DNA fragmentation based ELISA. Isolated ECL cells were found to express the TNF receptor p55 and IFN-gamma receptor, but not the TNF receptor p75 or CD95. TNF-alpha (25 ng/ml) increased apoptosis in ECL cells approximately 4-fold, IFN-gamma had no effect. Western blot analysis revealed that TNF-alpha caused degradation of I kappa B alpha within 10 min. EMSA demonstrated that TNF-alpha led to increased DNA-binding activity of NF kappa B and that proteasome inhibitors counteracted NF kappa B activation. Proteasome inhibitors, specific antisense oligodeoxynucleotides against the p65 subunit of the NF kappa B complex and the NO synthase inhibitor N(G)-monomethyl-L-arginine completely prevented TNF-alpha-induced apoptosis. Our data suggest that TNF-alpha induces apoptosis of isolated gastric ECL cells via activation of NF kappa B and the generation of NO.

Interactions among the seven Helicobacter pylori proteins encoded by the urease gene cluster

Survival of Helicobacter pylori in acid depends on intrabacterial urease. This urease is a Ni(2+)-containing oligomeric heterodimer. Regulation of its activity and assembly is important for gastric habitation by this neutralophile. The gene complex encodes catalytic subunits (ureA/B), an acid-gated urea channel (ureI), and accessory assembly proteins (ureE-H). With the use of yeast two-hybrid analysis for determining protein-protein interactions, UreF as bait identified four interacting sequences encoding UreH, whereas UreG as bait detected five UreE sequences. These results were confirmed by coimmunoprecipitation and beta-galactosidase assays. Native PAGE immunoblotting of H. pylori inner membranes showed interaction of UreA/B with UreI, whereas UreI deletion mutants lacked this protein interaction. Deletion of ureE-H did not affect this interaction with UreI. Hence, the accessory proteins UreE/G and UreF/H form dimeric complexes and UreA/B form a membrane complex with UreI, perhaps enabling assembly of the urease apoenzyme at the membrane surface and immediate urea access to intrabacterial urease to allow rapid periplasmic neutralization.

Pathogenesis of Helicobacter pylori infection

Five years after publication of the complete genome sequence of Helicobacter pylori, research interest is shifting from the descriptive association of virulence factors with clinical outcome in infected patients to the molecular mechanisms of virulence factor action. This is particularly noticeable for VacA and CagA, for both of which detailed understanding of the interaction with host signalling pathways has accumulated over the last year. The role of H. pylori Lewis antigens for clinical outcome was further substantiated. Various strategies of H. pylori to fool or evade the human immune system are described, which all lead to the dysfunction of specific compartments of the host cellular immune system. Finally, a number of animal models indicate that inflammation is a key factor for gastric carcinogenesis, which is finally supported by a large prospective study identifying corpus atrophy and intestinal metaplasia as precancerous conditions.

Circle of life of secretory vesicles in gastric enterochromaffin-like cells

Enterochromaffin-like (ECL) cells are neuroendocrine cells in the gastric epithelium characterized by numerous electron-empty, histamine-containing secretory vesicles. The antral hormone gastrin is the key stimulus of histamine secretion from this cell type, thereby controling acid secretion. Following receptor binding, gastrin activates a biphasic calcium signal in ECL cells that involves activation of inositol triphosphate receptors and calcium entry across the plasma membrane. Dihydropyridines block gastrin-induced histamine secretion. However, no depolarization was observed following stimulation with gastrin. Elevation of intracellular calcium by gastrin is an important prerequisite for exocytosis. In permeabilized ECL cells, addition of calcium results in histamine release, which can be inhibited by tetanus toxin and botulinum neurotoxin A, underlining the functional importance of the synaptosome-associated protein of 25 kDa (SNAP-25) and synaptobrevin. Immunocytochemistry also confirmed the presence of these SNAP receptor (SNARE) proteins, as well as synaptophysin, synaptotagmin, and syntaxin. Following 3-6 h of incubation in isolated cells, several transcription factors are induced by gastrin, such as ERK1/2, Sp1, and CRE. Gastrin thereby directly stimulates transcription of the vesicular monoamine transporter subtype 2 (VMAT-2) and chromogranins. Gene expression of histidine decarboxylase (HDC) appears to be stimulated by a putative "gastrin-responsive" element adjacent to the HDC exon 1 gene. ECL cells thereby share several similarities with adrenal chromaffin cells and neurons, but have their own functional properties. Gastrin coordinates secretion, synthesis, and storage by activating diverging signal transducers, leading to a functional synergy in this cell type.

Helicobacter pylori induces apoptosis of rat gastric parietal cells

Gastric Helicobacter pylori infection may lead to multifocal atrophic corpus gastritis associated with loss of epithelial cells as well as glandular structures. The current work investigated H. pylori effects on cell death of isolated, nontransformed rat parietal cells (PC). Highly enriched rat PC (>97%) were isolated from gastric mucosa and cultured in serum-free medium over 24 h. The cells were cocultured over 8 h with cytotoxin-associated immunodominant protein (cagA)(+)/vacuolating toxin (vacA)(+) or with cagA(-)/vacA(-) H. pylori laboratory strains and also with H. pylori mutants deleted in several genes of the cag pathogenicity island. Staphylococcus aureus or Campylobacter jejuni were used as controls. Apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and electron microscopy. Interleukin (IL)-8 and cytokine-induced neutrophil chemoattractant (CINC)-1 secretion was measured by ELISA. Activation of nuclear factor-kappaB (NF-kappaB) was studied in nuclear extracts of PC by electrophoretic mobility shift assay. Apoptosis of PC was induced in a concentration- and time-dependent manner by cagA(+)/vacA(+) H. pylori strains but not by cagA(-)/vacA(-) negative strains or by the cagE knockout mutant. S. aureus and C. jejuni had no effect. PC showed no IL-8 or CINC-1 secretion on exposure to cagA(+)/vacA(+) H. pylori. cagA(+)/vacA(+) strains induced activation of NF-kappaB complexes in nuclear extracts of PC, which were composed of p65 and p50 subunits. No significant stimulation of NF-kappaB activation was detected by incubation of PC with the cagE knockout mutant. Preincubation of PC with antisense but not missense oligodeoxynucleotides against the p65 subunit significantly reduced DNA binding to the kappaB recognition sequence. The p65 oligonucleotides as well as the proteasome inhibitor N-CBZ-isoleucin-glutamin-(o-t-butyl-)-alanin-leucin and the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine completely prevented PC apoptosis induced by cagA(+)/vacA(+) strains. In summary, cagE presence appears to be essential for H. pylori-induced apoptosis of gastric parietal cells, and this effect is dependent on the activation of NF-kappaB and production of nitric oxide.

Expression of histidine decarboxylase and synthesis of histamine by human small cell lung carcinoma

We recently found that human small cell lung carcinomas (SCLCs) express, in addition to other neuroendocrine markers, vesicular monoamine transporters. Our present results indicate that SCLCs are histaminergic. We detected the biosynthetic enzyme histidine decarboxylase by immunohistochemistry in paraffin sections of 12 biopsies of SCLC tumors. This finding was supported by immunoblotting and reverse transcription-polymerase chain reaction experiments using established SCLC cell lines, frozen and paraffin-embedded SCLC tumors. Moreover, we found histamine to be synthesized, stored, and released by cultured SCLC cells. Our novel observations may be useful for developing new diagnostic tools for this frequent and highly malignant tumor.

The Helicobacter pylori blood group antigen-binding adhesin facilitates bacterial colonization and augments a nonspecific immune response

Presence of the Helicobacter pylori adherence factor blood group Ag-binding adhesin (BabA; binding to Lewis(b) (Le(b))) is associated with ulcer disease, adenocarcinoma, and precancerous lesions. The importance of BabA for bacterial colonization and the inflammatory response is unknown. A total of 141 antral biopsies from H. pylori-infected patients were assessed in regard to the degree of granulocytic (G0 degrees--G3 degrees) and lymphocytic (L1 degrees--L3 degrees) infiltration. DNA genotypes of babA2 (the transcriptionally active gene of BabA), cagA, and vacAs1/2 were determined by PCR. Colonization density and Le(b) status on gastric epithelial cells were determined by immunohistochemistry. Real-time quantitative (TaqMan) RT-PCR determined mRNA expression of IL-8, TNF -alpha, and the Th1 markers IFN-gamma and the IL-12R beta2 chain. A total of 91% of infected patients were Le(b) positive. The vacAs1(+)/cagA(+) strains harboring babA2 showed significantly higher levels of granulocytic infiltration, bacterial colonization, and IL-8 mRNA than vacAs1(+)/cagA(+) strains lacking babA2. IL-8 mRNA and protein production by KATO III cells in vitro increased dose dependently with addition of different numbers of type 1 strains (G27 and 2808 strains, 0.1--20 bacteria/cell). The mRNA expression of TNF-alpha, IFN-gamma, and IL-12R beta2 was higher in H. pylori-positive patients than in controls, but it did not differ significantly between patients infected with different strain types. These data suggest that BabA facilitates colonization of H. pylori and thereby increases IL-8 response, resulting in enhanced mucosal inflammation. Infection with strains harboring BabA thereby augment a nonspecific immune response, whereas the Th1 response toward H. pylori appears to be independent of BabA, cytotoxin-associated gene A, or vacuolating cytotoxin.

Specific identification of three low molecular weight membrane-associated antigens of Helicobacter pylori

BACKGROUND

A large number of Helicobacter pylori proteins are antigenic, but antibodies to these proteins persist in spite of the eradication of the infection.

METHODS AND RESULTS

The analysis of sera from H. pylori-infected and non-infected patients, before and 3 and 5 months after eradication, showed that the antibody response against unknown H. pylori antigens at 32, 30, 22 and 14 kDa in sodium dodecylsulphate polyacrylamide gel electrophoresis decreased by > or = 60% at 3 months and > or = 70% at 5 months after treatment. Two-dimensional gel electrophoresis and mass spectrometry allowed the identification of eight proteins at these positions: neuraminyl-lactose-binding haemagglutinin precursor, 3-oxoadipate CoA-transferase subunit A, elongation factor P, peptidoglycan-associated lipoprotein precursor, hypothetical protein HP0596, adhesin-thiol peroxidase, 50S ribosomal protein L7/L12 and subunit b' of the F(0) ATP synthase. Three of these eight, expressed as recombinant proteins (32 kDa neuraminyl-lactose-binding haemagglutinin precursor, 30 kDa peptidoglycan-associated lipoprotein precursor and 22 kDa hypothetical protein HP0596), reacted specifically with sera from infected patients, while the 14 kDa 50S ribosomal protein L7/L12 cross-reacted with one out of five sera from H. pylori-negative patients. The other recombinant proteins did not show significant immunoreactivity.

CONCLUSIONS

Four low molecular weight antigens were identified by these methods, three of which were specific. Immunoreaction with these three proteins (neuraminyl-lactose-binding haemagglutinin precursor, peptidoglycan-associated lipoprotein precursor and hypothetical protein HP0596) could provide a serological assessment not only of H. pylori infection, but also of eradication.

Intracellular signal transduction during gastrin-induced histamine secretion in rat gastric ECL cells

Activation of G(q) protein-coupled receptors usually causes a biphasic increase in intracellular calcium concentration ([Ca(2+)](i)) that is crucial for secretion in nonexcitable cells. In gastric enterochromaffin-like (ECL) cells, stimulation with gastrin leads to a prompt biphasic calcium response followed by histamine secretion. This study investigates the underlying signaling events in this neuroendocrine cell type. In ECL cells, RT-PCR suggested the presence of inositol 1,4,5-trisphosphate receptor (IP(3)R) subtypes 1-3. The IP(3)R antagonist 2-aminoethoxydiphenyl borate abolished both gastrin-induced elevation of [Ca(2+)](i) and histamine release. Thapsigargin increased [Ca(2+)](i), however, without inducing histamine secretion. In thapsigargin-pretreated cells, gastrin increased [Ca(2+)](i) through calcium influx across the plasma membrane. Both nimodipine and SKF-96365 inhibited gastrin-induced histamine release. The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate induced histamine secretion, an effect that was prevented by nimodipine. In summary, gastrin-stimulated histamine release depends on IP(3)R activation and plasmalemmal calcium entry. Gastrin-induced calcium influx was mediated by dihydropyridine-sensitive calcium channels that appear to be L-type channels activated through a pathway involving activation of PKC.

Gastrin induces expression and promoter activity of the vesicular monoamine transporter subtype 2

Gastric enterochromaffin-like cells produce histamine in response to the antral hormone gastrin and accumulate the biogenic amine in secretory organelles via vesicular monoamine transporter subtype 2. The putative effects of gastrin on vesicular monoamine transporter subtype 2 expression and promoter activity are poorly understood. In the present study we used highly enriched rat enterochromaffin-like cells (purity, >90%) and rat pheochromocytoma cells stably transfected with a gastrin/cholecystokinin B receptor to investigate the expression and transcriptional regulation of vesicular monoamine transporter subtype 2. Stimulation of vesicular monoamine transporter subtype 2 mRNA and protein expression was observed in isolated enterochromaffin-like cells after 3- to 7-h incubation with gastrin (10(-7) M), forskolin (10(-5) M), or ionomycin (10(-5) M). Deletion analysis of the rat vesicular monoamine transporter subtype 2 promoter defined the minimal promoter sequence necessary for full basal activity as a -121 bp segment upstream of exon 1 containing two Sp1 sites (-97 to -88 bp and -68 to -59 bp) and a cAMP-responsive element (-44 to -35 bp). Gastrin (10(-7) M) stimulated extracellular signal related kinase1/2 phosphorylation, activated Sp1 and cAMP-responsive element-binding protein, and further induced activity of the complete rat vesicular monoamine transporter subtype 2 promoter (-800 bp) in gastrin/cholecystokinin B receptor cells. The -121-bp fragment was able to confer full gastrin responsiveness, and site-directed mutagenesis of the Sp1 and cAMP-responsive element motifs demonstrated their crucial importance for basal and inducible activities. Comparison of promoter activity of histidine decarboxylase, chromogranin A, or vesicular monoamine transporter subtype 2 in transfected cell lines revealed significant differences in basal and gastrin-stimulated activities. Our current study provides the first evidence that gastrin directly stimulates the expression and promoter activity of vesicular monoamine transporter subtype 2. Sp1 and cAMP-responsive element-binding protein recognition motifs located within 121 bp upstream of exon 1 appear to be indispensable for full basal and inducible promoter activities. Diverging effects of gastrin on histidine decarboxylase, chromogranin A, and vesicular monoamine transporter subtype 2 promoter may account for the coordinated synthesis and storage of histamine in this neuroendocrine cell type.

Key importance of the Helicobacter pylori adherence factor blood group antigen binding adhesin during chronic gastric inflammation

Helicobacter pylori has been assigned as a class I carcinogen because of its relation to gastric adenocarcinoma. Chronic H. pylori infection may lead to severe gastritis, glandular atrophy (AT), and intestinal metaplasia (IM). Strains secreting the vacuolating toxin VacA and producing the cytotoxin-associated antigen CagA (type 1 strains), as well as the blood group antigen binding adhesin (BabA) targeting Lewis(b) antigens, have been associated previously with distal gastric adenocarcinoma (M. Gerhard et al., Proc. Natl. Acad. Sci. USA, 96: 12778-12783, 1999) and may therefore also be related to lesions preceding gastric cancer. Antral and corpus biopsies were collected from 451 patients; 151 were H. pylori positive, as determined by PCR. Gastric biopsies were histologically evaluated for activity of gastritis (G0-G3, granulocyte infiltration), chronicity of gastritis (L1-L3, lymphocyte infiltration), and the presence of IM and/or AT according to the Sydney classification. Simultaneously, the presence of bacterial genes encoding virulence and adherence factors (racAs1/s2, cagA, and babA2) was determined by PCR. The presence of cagA+ and vacAs1 (alone or combined) both correlated with activity and chronicity of gastritis (P < 0.05); however, the overall prevalence of these genes was 60 or 72%, respectively, and was thus relatively frequent. The babA2 gene, encoding the adhesin BabA, was detected in 38% of infected patients and was correlated with the activity of gastritis in antrum and corpus (P < 0.005). cagA+/vacAs1+ strains (suggesting the presence of type 1 strains) that were also babA2 positive were detected more frequently in patients with severe histological alterations (such as G3, IM, or AT) compared with subjects without these changes (P < 0.01). cagA+/vacAs1+ strains that were babA2 negative, however, lacked a significant correlation with severe histological changes, activity, or chronicity of gastritis in antrum and corpus. Adherence of H. pylori via BabA appears to be of importance for efficient delivery of VacA and CagA and may play a special role in the pathogenesis of severe histological changes.

Biophysical and lipofection studies of DOTAP analogs

In order to investigate the relationship between lipid structure and liposome-mediated gene transfer, we have studied biophysical parameters and transfection properties of monocationic DOTAP analogs, systematically modified in their non-polar hydrocarbon chains. Stability, size and (by means of anisotropy profiles) membrane fluidity of liposomes and lipoplexes were determined, and lipofection efficiency was tested in a luciferase reporter gene assay. DOTAP analogs were used as single components or combined with a helper lipid, either DOPE or cholesterol. Stability of liposomes was a precondition for formation of temporarily stable lipoplexes. Addition of DOPE or cholesterol improved liposome and lipoplex stability. Transfection efficiencies of lipoplexes based on pure DOTAP analogs could be correlated with stability data and membrane fluidity at transfection temperature. Inclusion of DOPE led to rather uniform transfection and anisotropy profiles, corresponding to lipoplex stability. Cholesterol-containing lipoplexes were generally stable, showing high transfection efficiency at low relative fluidity. Our results demonstrate that the efficiency of gene transfer mediated by monocationic lipids is greatly influenced by lipoplex biophysics due to lipid composition. The measurement of fluorescence anisotropy is an appropriate method to characterize membrane fluidity within a defined system of liposomes or lipoplexes and may be helpful to elucidate structure-activity relationships.