Electron microscopic study of intercellular junctions in human gastric mucosa with special reference to their relationship to gastric ulcer

Connexin and pannexin signaling in gastrointestinal and liver disease

Gap junctions, which mediate intercellular communication, are key players in digestive homeostasis. They are also frequently involved in gastrointestinal and liver pathology. This equally holds true for connexin (Cx) hemichannels, the structural precursors of gap junctions, and pannexin (Panx) channels, Cx-like proteins assembled in a hemichannel configuration. Both Cx hemichannels and Panx channels facilitate extracellular communication and drive a number of deteriorative processes, such as cell death and inflammation. Cxs, Panxs, and their channels underlie a wide spectrum of gastrointestinal and liver diseases, including gastritis and peptic ulcer disease, inflammatory intestinal conditions, acute liver failure, cholestasis, hepatitis and steatosis, liver fibrosis and cirrhosis, infectious gastrointestinal pathologies, and gastrointestinal and liver cancer. This could open promising perspectives for the characterization of new targets and biomarkers for therapeutic and diagnostic clinical purposes in the area of gastroenterology and hepatology.

Mucosal barrier defects in gastric intestinal metaplasia: in vivo evaluation by confocal endomicroscopy

BACKGROUND

Helicobacter pylori infection and intestinal metaplasia (IM) are associated with gastric cancer. An impaired gastric mucosal barrier could be involved in this carcinogenesis.

OBJECTIVE

To evaluate laser confocal laser endomicroscopy (CLE) for in vivo functional imaging of mucosal barrier defects in patients with IM.

DESIGN

Prospective, controlled study.

SETTING

A tertiary-care academic center.

PATIENTS

This study involved patients with IM of the gastric mucosa who underwent CLE for surveillance.

INTERVENTIONS

Specific IM mucosa and non-IM mucosa in patients were identified by CLE, and targeted biopsy samples were taken for histopathology and electron microscopy.

MAIN OUTCOME MEASUREMENTS

Post-CLE assessment of paracellular fluorescein leakage was devised and validated by electron microscopy. We also evaluated the effect of H pylori eradication on the mucosal barrier.

RESULTS

Forty-two patients were included. Of non-IM samples, the paracellular permeability was significantly increased in H pylori-positive samples compared with H pylori-negative controls (54 ± 31% vs 3 ± 6%, P < .05). Of IM samples, the permeability was significantly increased in both H pylori-negative and H pylori-positive samples (67 ± 34% and 72 ± 28% vs 3 ± 6%, both P < .05). The results of post-CLE assessment correlated well with the electron microscopy findings (R(2) 0.834, P < .0001). After the eradication of H pylori, the paracellular barrier dysfunction of non-IM mucosa was significantly improved as shown by electron microscopy and CLE (both P < .001). However, there was no significant change in IM mucosa.

LIMITATIONS

Single-center study.

CONCLUSIONS

CLE allows functional imaging of mucosal barrier defects. Gastric IM is associated with an impaired paracellular barrier irrespective of H pylori eradication.

The human gut mobile metagenome: a metazoan perspective

Using the culture independent TRACA system in conjunction with a comparative metagenomic approach, we have recently explored the pool of plasmids associated with the human gut mobile metagenome. This revealed that some plasmids or plasmid families are present in the gut microbiomes of geographically isolated human hosts with a broad global distribution (America, Japan and Europe), and are potentially unique to the human gut microbiome. Functions encoded by the most widely distributed plasmid (pTRACA22) were found to be enriched in the human gut microbiome when compared to microbial communities from other environments, and of particular interest was the increased prevalence of a putative RelBE toxin-antitoxin (TA) addiction module. Subsequent analysis revealed that this was most closely related to putative TA modules from gut associated bacteria belonging to the Firmicutes, but homologues of the RelE toxin were associated with all major bacterial divisions comprising the human gut microbiota. In this addendum, functions of the gut mobile metagenome are considered from the perspective of the human host, and within the context of the hologenome theory of human evolution. In doing so, our original analysis is also extended to include the gut metagenomes of a further 124 individuals comprising the METAHIT dataset. Differences in the incidence and relative abundance of pTRACA22 and associated TA modules between healthy individuals and those with inflammatory bowel diseases are explored, and potential functions of pTRACA22 type RelBE modules in the human gut microbiome are discussed.

Possible involvement of put A gene in Helicobacter pylori colonization in the stomach and motility

H. pylori is a gram-negative bacterium associated with gastric inflammation and peptic ulcer and considered a risk factor for gastric cancer in its natural habitat. However, the energy metabolism of H. pylori in the stomach remains to be clarified. H. pylori shows rather high respiratory activity with L-proline and significantly large amounts of L-proline are present in the gastric juice from H. pylori infected patients. We constructed a disrupted mutant of the put A gene, which encodes the proline utilization A (Put A) flavin-linked enzyme, in order to examine the role of put A in the gastric colonization of H. pylori. The put A disrupted mutant, DeltaputA, was constructed by inserting a chloramphenicol resistant gene into put A. DeltaputA did not show respiratory activity using L-proline and could not incorporate L-proline into cells. DeltaputA also did not show motility in response to amino acids and did not display the swarming activity observed with the wild-type. DeltaputA had lost its ability to colonize the stomach of nude mice, an ability possessed by the wild-type. These findings indicate that put A may play an important role in H. pylori colonization on the gastric mucus layer.

Importance of gap junction in gastric mucosal restitution from acid-induced injury

Evidence is accumulating that gap junctional intercellular communication (GJIC) plays an important role in the gastric mucosal defense system. This study was conducted to determine whether GJIC mediates a restitution process in gastric mucosa. Male Sprague-Dawley rats were fasted and anesthetized. Gastric injury was induced by luminal perfusion with 0.2N HCl for 10 minutes. Mucosal integrity was continuously monitored by measuring the clearance of chromium 51-labeled ethylenediaminetetraacetic acid, which was used for analysis of recovery from the injury. Perfusion with 0.25% octanol (OCT; inhibitor of GJIC) was started after acid injury to assess its effect on restitution. The effect of irsogladine (IG; activator of GJIC) was also tested. Gastric mucosal GJIC was immunohistochemically evaluated with monoclonal antibody gap junction protein (connexin 32). Recovery from acid-induced mucosal injury occurred rapidly when acid perfusion was discontinued (within about 60 minutes). OCT, which didn't cause any injury to normal gastric mucosa, significantly inhibited the restitution. IG reversed this inhibition in a dose-dependent manner. In an immunohistochemical study, OCT-induced damage of gap junction was demonstrated, but not after IG pre-treatment. These findings suggest that GJIC may play a critical role in restitution in rat gastric mucosa and that gap junction function may be one of the important factors for the mucosal defense system.

The effects of water extracts of CagA positive or negative Helicobacter pylori on proliferation, apoptosis and connexin formation in acetic acid-induced gastric ulcer of rats

AIM

To investigate the influence of water extracts of CagA-positive or -negative Helicobacter pylori on healing of chronic gastric ulcers and on connexin formation, proliferation and apoptosis, in acetic acid-induced chronic gastric ulcers in rats.

METHODS

Acetic acid was used to induce chronic gastric ulcers in rats, and a water extract of H. pylori was given by mouth every day. Connexin 32 formation was assessed using Western blotting as previously described. The frequencies of proliferating cell nuclear antigen staining and of TdT-mediated dUTP-biotin nick end labelling were examined.

RESULTS

In untreated rats, acetic acid-induced gastric ulcers healed after 14 days and the electrophoretic band corresponding to connexin 32 appeared 4 days after ulcer induction. Treatment with a water extract of H. pylori delayed ulcer healing, with the ulcers remaining unhealed even on the 14th day; healing was delayed more when treatment was with an extract of CagA-positive rather than CagA-negative H. pylori. Connexin 32 appeared earlier when treatment was with a CagA-negative rather than a CagA-positive extract, but in both cases later than in the untreated control group. Proliferating cell nuclear antigen labelling on the fourth day was seen in 14.5% +/- 1.6% of mucosal cells of control group, but in 35.9% +/- 1.4% and 36.5% +/- 1.4% of mucosal cells treated with either VacA(+)CagA(-) and VacA(+)CagA(+) H. pylori extract, respectively. Furthermore, extracts of both H. pylori strains, especially VacA(+)Cag(+) H. pylori promoted apoptosis.

CONCLUSIONS

A water extract of H. pylori increased both proliferation and apoptosis, which are related to exacerbation and healing of ulcer as well as appearance of connexin 32.

Role of gap junctions in inhibiting ischemia-reperfusion injury of rat gastric mucosa

Gap junctional intercellular communication (GJIC) is known to be important in the maintenance of tissue homeostasis. However, the role of GJIC in gastric mucosa has not been well investigated. We tested the hypothesis that maintenance of GJIC protects rat gastric mucosa against ischemia-reperfusion (I/R) stress by using irsogladine, an activator of GJIC, and octanol, an inhibitor of GJIC. Intragastric perfusion with octanol before ischemia resulted in a significant increase in 51Cr-EDTA clearance after reperfusion. Intraduodenal pretreatment with irsogladine attenuated the increase in 51Cr-EDTA clearance produced by octanol in a dose-dependent manner. Epithelial gap junctions reacted with anticonnexin-32 monoclonal antibodies were not changed after I/R stress alone. Intragastric perfusion with octanol caused a significant reduction in immunoreactive connexin-32 spots, which was completely reversed by irsogladine. These results indicate that inhibition of GJIC weakens the barrier function of gastric mucosa and subsequently causes damage of the barrier function in combination with I/R. Facilitation of GJIC and maintenance of gap junctions protect gastric mucosal barrier functions by potentiating cellular integrity.

Hierarchical and cybernetic nature of biologic systems and their relevance to homeostatic adaptation to low-level exposures to oxidative stress-inducing agents

During evolution in an aerobic environment, multicellular organisms survived by adaptive responses to both the endogenous oxidative metabolism in the cells of the organism and the chemicals and low-level radiation to which they had been exposed. The defense repertoire exists at all levels of the biological hierarchy--from the molecular and biochemical level to the cellular and tissue level to the organ and organ system level. Cells contain preventive antioxidants to suppress oxidative damage to membranes. Cells also contain proteins and DNA; built-in redundancies for damaged molecules and organelles; tightly coupled redox systems; pools of reductants; antioxidants; DNA repair mechanisms and sensitive sensor molecules such as nuclear factor kappa beta; and signal transduction mechanisms affecting both transcription and post-translational modification of proteins needed to cope with oxidative stress. The biologic consequences of the low-level radiation that exceeds the background level of oxidative damage could be necrosis or apoptosis, cell proliferation, or cell differentiation. These effects are triggered by oxidative stress-induced signal transduction mechanisms--an epigenetic, not genotoxic, process. If the end points of cell proliferation, differentiation, or cell death are not seen at frequencies above background levels in an organism, it is unlikely that low-level radiation would play a role in the multistep processes of chronic diseases such as cancer. The mechanism linked to homeostatic regulation of proliferation and adaptive functions in a multicellular organism could provide protection of any one cell receiving deposited energy by the radiation tract through the sharing of reductants and by triggering apoptosis of target stem cells. Examples of the role of gap junctional intercellular communication in the adaptive response of cells and the bystander effect illustrate how the interaction of cells can modulate the effect of radiation on the single cell.

Relationship between healing of acetic acid-induced chronic gastric ulcer and connexin

This study examined the relationship between healing of acetic acid-induced chronic gastric ulcer and connexin formation. In addition, the effect of anti-ulcer drugs on ulcer healing and the presence of connexin was investigated. In a rat model, acetic acid-induced gastric ulcers were healed without administration of drugs after 14 days. Appearance of an electrophoretic connexin 32 band was observed 7 days after ulcer induction. Administration of cimetidine (3 mg/day) promoted ulcer healing, i.e., ulcers were healed 12 days after ulcer induction, 2 days earlier than the control. The appearance of a connexin 32 band in electrophoresis was observed on the fourth day after ulcer induction. Administration of cimetidine at a higher dose further promoted ulcer healing and the connexin 32 band was more strongly visible. After administration of i.p. 2 nM EGF, acetic acid-induced gastric ulcers were healed 12 days after ulcer induction and the appearance of connexin 32 was observed on the fourth day after induction. These results indicate that connexin 32 is related to the healing of acetic acid-induced gastric ulcers.

Restoration of gap junctions in the regenerative process of ethanol-induced gastric mucosal injury

Gap junctions mediate intercellular communication and play an important role in cell proliferation and differentiation. The present study examined the expression of the gap junction protein connexin 32 in rat gastric mucosa during the regenerative process of ethanol-induced gastric mucosal injury. Absolute ethanol (0.5 mL/100 g bodyweight) was administered to rats via gastric intubation. Following the treatment, rats were killed periodically, and gastric tissues were processed for indirect immunofluorescence microscopy using an anti-connexin 32 antibody. Haematoxylin and eosin (H&E), periodic acid Schiff (PAS) and Bromodeoxyuridine (BrdU) staining were also performed in serial sections. Gastric injuries were limited in the mucosal layer. The injury was most severe 1 h after treatment, and was completely resolved by the 4th day after treatment. The number of immunoreactive spots for gap junctions was markedly decreased 1 h after the ethanol treatment. Reappearance of these immunostaining gap junctions occurred with repair of the injury. The reappearance of connexin 32 after injury was delayed in comparison with both the histologic resolution of the injury and the normalization of PAS-stained mucus. In contrast, the time course of reappearance of gap junctions closely paralleled the appearance of BrdU-labelled cells. These results indicate that morphologic repair is different to the recovery of cell maturity and cell proliferation in the regenerative gastric mucosa.

Electron microscopic study of association between Helicobacter pylori and gastric and duodenal mucosa

AIM

To study the ultrastructural appearances of Helicobacter pylori in antral and duodenal biopsy specimens and its relation with the epithelial cells.

METHODS

Endoscopically obtained antral and duodenal biopsy specimens were examined using transmission electron microscopy and freeze fracture analysis.

RESULTS

Most bacteria looked curved, but in the duodenal bulb coccoid bacteria were relatively common. Bacteria were often found around intercellular junctions. freeze fracture examination indicated abnormalities of the tight junction complexes in patients with H pylori infection. In many biopsy specimens bacteria were seen closely attached to the epithelial cell membrane by different forms of adhesion. In addition to what looked like intracytoplasmic penetration by bacteria, several examples of genuine penetration were observed.

CONCLUSION

H pylori is commonly found adhering to epithelial cells. Occasionally, H pylori may also penetrate cells. These features may contribute to the pathogenic action of the organism.