Modulation of acid secretion in common bile duct ligation-related gastropathy in Wistar rats

The use of the Cre/loxP system to study oxidative stress in tissue-specific manganese superoxide dismutase knockout models

SIGNIFICANCE

Respiring mitochondria are a significant site for reactions involving reactive oxygen and nitrogen species that contribute to irreversible cellular, structural, and functional damage leading to multiple pathological conditions. Manganese superoxide dismutase (MnSOD) is a critical component of the antioxidant system tasked with protecting the oxidant-sensitive mitochondrial compartment from oxidative stress. Since global knockout of MnSOD results in significant cardiac and neuronal damage leading to early postnatal lethality, this approach has limited use for studying the mechanisms of oxidant stress and the development of disease in specific tissues lacking MnSOD. To circumvent this problem, a number of investigators have employed the Cre/loxP system to precisely knockout MnSOD in individual tissues.

RECENT ADVANCES

Multiple tissue and organ-specific Cre-expressing mice have been generated, which greatly enhance the specificity of MnSOD knockout in tissues and organ systems that were once difficult, if not impossible to study.

CRITICAL ISSUES

Evaluating the contribution of MnSOD deficiency to oxidant-mediated mitochondrial damage requires careful consideration of the promoter system used for creating the tissue-specific knockout animal, in addition to the collection and interpretation of multiple indices of oxidative stress and damage.

FUTURE DIRECTIONS

Expanded use of well-characterized tissue-specific promoter elements and inducible systems to drive the Cre/loxP recombinational events will lead to a spectrum of MnSOD tissue knockout models, and a clearer understanding of the role of MnSOD in preventing mitochondrial dysfunction in human disease.

Loss of parietal cell superoxide dismutase leads to gastric oxidative stress and increased injury susceptibility in mice

Mitochondrial superoxide dismutase (SOD2) prevents accumulation of the superoxide that arises as a consequence of oxidative phosphorylation. However, SOD2 is a target of oxidative/nitrosative inactivation, and reduced SOD2 activity has been demonstrated to contribute to portal hypertensive gastropathy. We investigated the consequences of gastric parietal cell-specific SOD2 deficiency on mitochondrial function and gastric injury susceptibility. Mice expressing Cre recombinase under control of the parietal cell Atpase4b gene promoter were crossed with mice harboring loxP sequences flanking the sod2 gene (SOD2 floxed mice). Cre-positive mice and Cre-negative littermates (controls) were used in studies of SOD2 expression, parietal cell function (ATP synthesis, acid secretion, and mitochondrial enzymatic activity), increased oxidative/nitrosative stress, and gastric susceptibility to acute injury. Parietal cell SOD2 deficiency was accompanied by a 20% (P < 0.05) reduction in total gastric SOD activity and a 93% (P < 0.001) reduction in gastric SOD2 activity. In SOD2-deficient mice, mitochondrial aconitase and ATP synthase activities were impaired by 36% (P < 0.0001) and 44% (P < 0.005), respectively. Gastric tissue ATP content was reduced by 34% (P < 0.002). Basal acid secretion and peak secretagogue (histamine)-induced acid secretion were reduced by 43% (P < 0.0001) and 40% (P < 0.0005), respectively. There was a fourfold (P < 0.02) increase in gastric mucosal apoptosis and 41% (P < 0.001) greater alcohol-induced gastric damage in the parietal cell SOD2-deficient mice. Our findings indicate that loss of parietal cell SOD2 leads to mitochondrial dysfunction, resulting in perturbed energy metabolism, impaired parietal cell function, and increased gastric mucosal oxidative stress. These alterations render the gastric mucosa significantly more susceptible to acute injury.

Divergent effects of irritants on the gastric mucosa in rats during various stages after bile duct ligation

BACKGROUND AND AIM

Controversy exists as to whether rats after bile duct ligation (BDL) are more susceptible to gastric mucosal damage (GMD) induced by irritants. In the present study we characterize GMD after intragastric instillation of either ethanol or hydrochloric acid (HCL), 3 and 21 days after the surgical procedure.

METHODS

Bile duct ligation and sham operated (SO) rats were studied.

RESULTS

Three days after surgery, BDL rats exhibited a reduction in gastric mucosal nitric oxide synthase (NOS) activity but an increase in ethanol-induced GMD. Twenty-one days after surgery gastric mucosal prostaglandin (PG) E(2) generation in BDL rats was increased while NOS activity in both groups was similar. Ethanol-induced GMD in SO rats was higher. Pretreatment with NG-nitro-L-arginine methyl ester, prior to ethanol administration was associated with an increase in gastric mucosal PGE(2) generation: (147% in SO and 104% in BDL rats) and in GMD (176% in SO and 303% in BDL rats). HCL induced GMD was of similar magnitude in both groups in both time periods.

CONCLUSIONS

The gastric resistance to damage by irritants in rats with BDL is not a static phenomenon. This may result from sequential changes that occur in the gastric mucosal defense mechanisms during the evolution of liver disease.

Avoiding pitfalls: what an endoscopist should know in liver transplantation--part II

Over the last decade the number of patients undergoing transplantation has increased. At the same time, effective peri- and postoperative care and better surgical techniques have resulted in greater numbers of recipients achieving long-term survival. Identification and effective management in the form of adequate treatment is essential, since any delay in diagnosis or treatment may result in graft loss or serious threat to patient's life. Various aspects of endoscopic findings that can be commonly encountered among liver transplant recipients are discussed herein. Topics include: persistent and/or recurrent esophageal varices, reflux, Candida or cytomegalovirus (CMV) esophagitis, esophageal neoplasms, posttransplant peptic ulcer, biliary complications, posttransplant lymphoproliferative disorder (PTLD), Kaposi's sarcoma, CMV colitis and inflammatory bowel disease, colonic neoplasms, Clostridium difficile infection, and graft versus host disease (GVHD).

Proton pump inhibitors in cirrhosis: tradition or evidence based practice?

Proton pump inhibitors (PPI) are very effective in inhibiting acid secretion and are extensively used in many acid related diseases. They are also often used in patients with cirrhosis sometimes in the absence of a specific acid related disease, with the aim of preventing peptic complications in patients with variceal or hypertensive gastropathic bleeding receiving multidrug treatment. Contradicting reports support their use in cirrhosis and evidence of their efficacy in this condition is poor. Moreover there are convincing papers suggesting that acid secretion is reduced in patients with liver cirrhosis. With regard to Helicobacter pylori (H pylori) infection, its prevalence in patients with cirrhosis is largely variable among different studies, and it seems that H pylori eradication does not prevent gastro-duodenal ulcer formation and bleeding. With regard to the prevention and treatment of oesophageal complications after banding or sclerotherapy of oesophageal varices, there is little evidence for a protective role of PPI. Moreover, due to liver metabolism of PPI, the dose of most available PPIs should be reduced in cirrhotics. In conclusion, the use of this class of drugs seems more habit related than evidence-based eventually leading to an increase in health costs.

Consequences of living-donor liver transplantation for upper gastrointestinal lesions: high incidence of reflux esophagitis

There is little information available regarding the consequences of living-donor liver transplantation (LDLT) for upper gastrointestinal lesions. We retrospectively compared the pre- and posttransplant incidences of noninfectious reflux esophagitis, portal hypertensive gastropathy (PHG), esophageal varix, gastroduodenal ulcer, Helicobacter pylori infection, and abnormal gastroesophageal valve in 29 adult patients (16 males, 13 females) who underwent LDLT for end-stage liver disease. Here we present four findings from this study. First, the posttransplant incidence of noninfectious esophagitis was significantly higher than the pretransplant incidence (27.6% vs. 3.4%; P < 0.001), irrespective of postoperative use of standard-dose H2RA. Second, PHG and esophageal varix, which were noted in 65.5% and 96.6% of pretransplant recipients, respectively, spontaneously resolved postoperatively in all cases. Third, H. pylori infection, which was observed in 50.0% of preoperative recipients, decreased to 5.6% postoperatively, although no significant difference was observed between the pre- and the posttransplant incidences of gastroduodenal ulcer (6.9% vs. 6.9%). Finally, the incidence of abnormal gastroesophageal valve did not change following LDLT (34.5% vs. 34.5%). In conclusion, this study suggests that noninfectious reflux esophagitis occurs more frequently following LDLT. Although the disease is the results of a very complex interaction of various factors, spontaneous resolution of PHG and serendipitous H. pylori eradication might have contributed to increased incidence of postoperative esophagitis, possibly through gastric acid hypersecretion. In contrast, morphological change of the gastroesophageal valve was not considered to be the cause of this disease. Because this study was a retrospective analysis of a small population of LDLT recipients, prospective randomized controlled studies of a sufficient number of cases are required to substantiate these conclusions.