Prostaglandin modulation of the gastric vasculature and mucosal integrity in cirrhotic rats

Hydrogen sulfide chemical biology: pathophysiological roles and detection

Hydrogen sulfide (H2S) is the most recent endogenous gasotransmitter that has been reported to serve many physiological and pathological functions in different tissues. Studies over the past decade have revealed that H2S can be synthesized through numerous pathways and its bioavailability regulated through its conversion into different biochemical forms. H2S exerts its biological effects in various manners including redox regulation of protein and small molecular weight thiols, polysulfides, thiosulfate/sulfite, iron-sulfur cluster proteins, and anti-oxidant properties that affect multiple cellular and molecular responses. However, precise measurement of H2S bioavailability and its associated biochemical and pathophysiological roles remains less well understood. In this review, we discuss recent understanding of H2S chemical biology, its relationship to tissue pathophysiological responses and possible therapeutic uses.

The diminished expression of proangiogenic growth factors and their receptors in gastric ulcers of cirrhotic patients

Objectives

The pathogenesis of the higher occurrence of peptic ulcer disease in cirrhotic patients is complex. Platelets can stimulate angiogenesis and promote gastric ulcer healing. We compared the expressions of proangiogenic growth factors and their receptors in the gastric ulcer margin between cirrhotic patients with thrombocytopenia and those of non-cirrhotic patients to elucidate possible mechanisms.

Methods

Eligible cirrhotic patients (n = 55) and non-cirrhotic patients (n = 55) who had gastric ulcers were enrolled. Mucosa from the gastric ulcer margin and non-ulcer areas were sampled and the mRNA expressions of the proangiogenic growth factors (vascular endothelial growth factor [VEGF], platelet derived growth factor [PDGF], basic fibroblast growth factor [bFGF]) and their receptors (VEGFR1, VEGFR2, PDGFRA, PDGFRB, FGFR1, FGFR2) were measured and compared. Platelet count and the expressions of these growth factors and their receptors were correlated with each other.

Results

The two groups were comparable in terms of gender, ulcer size and infection rate of Helicobacter pylori. However, the cirrhotic group were younger in age, had a lower platelet count than those in the non-cirrhotic group (p<0.05). The cirrhotic patients had diminished mRNA expressions of PDGFB, VEGFR2, FGFR1, and FGFR2 in gastric ulcer margin when compared with those of the non-cirrhotic patients (p<0.05). Diminished expressions of PDGFB and VEGFR2, FGFR1, and FGFR2 were well correlated with the degree of thrombocytopenia in these cirrhotic patients (ρ>0.5, p<0.001).

Conclusions

Our findings implied that diminished activity of proangiogenic factors and their receptors may contribute to the pathogenesis of gastric ulcers in cirrhotic patients.

Pathogenesis of portal hypertensive gastropathy: translating basic research into clinical practice

Portal hypertensive gastropathy (PHG) is often seen in patients with portal hypertension, and can lead to transfusion-dependent anemia as well as acute, life-threatening bleeding episodes. This Review focuses on the mechanisms that underlie the pathogenesis of PHG that provide reasonable grounds for the treatment of this condition, and ultimately enable translation of basic research into clinical practice. Increased portal pressure associated with cirrhosis and liver dysfunction is critical for the development of clinically significant PHG, and leads to impaired gastric mucosal defense mechanisms that render the stomach susceptible to mucosal injury. The use of pharmacological agents such as beta-blockers reduces the frequency of bleeding episodes in PHG. As a last resort, surgical decompression of the portal system, transjugular intrahepatic stent placement and liver transplantation can resolve this condition. Elimination of known risk factors for gastric injury such as alcohol, aspirin and traditional NSAIDs is critical. The role of Helicobacter pylori colonization of the gastric mucosa in PHG is not clear. Careful and critical interpretation of human and experimental data can be helpful to establish a rationale for the medical management of this important condition.

Prostaglandins, NSAIDs, and gastric mucosal protection: why doesn't the stomach digest itself?

Except in rare cases, the stomach can withstand exposure to highly concentrated hydrochloric acid, refluxed bile salts, alcohol, and foodstuffs with a wide range of temperatures and osmolarity. This is attributed to a number of physiological responses by the mucosal lining to potentially harmful luminal agents, and to an ability to rapidly repair damage when it does occur. Since the discovery in 1971 that prostaglandin synthesis could be blocked by aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs), there has been great interest in the contribution of prostaglandins to gastric mucosal defense. Prostaglandins modulate virtually every aspect of mucosal defense, and the importance of this contribution is evident by the increased susceptibility of the stomach to injury following ingestion of an NSAID. With chronic ingestion of these drugs, the development of ulcers in the stomach is a significant clinical concern. Research over the past two decades has helped to identify some of the key events triggered by NSAIDs that contribute to ulcer formation and/or impair ulcer healing. Recent research has also highlighted the fact that the protective functions of prostaglandins in the stomach can be carried out by other mediators, in particular the gaseous mediators nitric oxide and hydrogen sulfide. Better understanding of the mechanisms through which the stomach is able to resist injury in the presence of luminal irritants is helping to drive the development of safer anti-inflammatory drugs, and therapies to accelerate and improve the quality of ulcer healing.

Cytoprotective activity in the gastric mucosa of rats exposed to carbon tetrachloride-induced liver injury

The present study was undertaken to evaluate the cytoprotective activity in the gastric mucosa of rats subjected to CCl4-induced liver injury. Response of gastric mucosa to absolute ethanol insult or acid (pylorus ligation) after CCl4 challenge was analyzed. Intraperitoneal administration of CCl4 increased plasma AST and ALT, but liver protein and glycogen levels were decreased; in addition, gastric acid secretion was significantly increased with respect to control animals (1541 +/- 266 vs. 629 +/- 25 mu eq H+; p < 0.001). Microscopical gastric erosions were observed in 3/10 animals after CCl4 challenge. Pylorus-ligated as well as CCl4-challenged rats developed increased susceptibility to gastric lesions, compared to control (lesion indices: 4.6 +/- 0.20 vs 2.8 +/- 0.13; p < 0.05), while showing increased resistance to absolute ethanol-induced gastric damage (30.4 +/- 11.2 vs 89.7 +/- 9.7 mm, p < 0.01). PGE2 levels in the gastric mucosa were not influenced by exposure to CCl4. Ultrastructural studies revealed the presence of continuous ethanol-resistant and apparently more adherent layer of mucus in CCl4-challenged animals. Morphological evaluation revealed an increase in Alcian blue-stained mucus. A dual condition of enhanced sensitivity to HCl with increased tolerance to ethanol was observed in gastric mucosa of CCl4-treated animals. These observations could be explained by the amount and/or composition of protective mucus layer in the gastric mucosa.

Weakness of mucosal barrier in portal hypertensive gastropathy of alcoholic cirrhosis. Effects of propranolol and enprostil

BACKGROUND/AIMS

It has been suggested that the vulnerability of gastric mucosa is increased in patients with cirrhosis as a result of a PGE2 deficiency. Therefore, we evaluated whether PGE2 mucosal generation, and gastric potential difference - a reflection of the gastric mucosal barrier - were correlated to endoscopic features and whether these alterations could be alleviated.

METHODS

The potential difference was measured before (basal) and after a stimulation test by aspirin. The serum levels of gastrin and glucagon were also determined. Finally, the effects of a 1-week administration of propranolol or enprostil were tested on potential difference. The endoscopic grade of portal hypertensive gastropathy was assessed according to McCormack et al. The results are presented respectively for controls, patients with mild gastropathy, and patients with severe gastropathy. Comparisons were made using variance or covariance analysis after adjustment with age.

RESULTS

Basal potential difference was significantly different between the three groups: -30.6, -28.8, -24.9 mV, p <0.05, respectively. The effects of aspirin administration on potential difference parameters were significantly different between the three groups (irritability index: 35 +/- 25, 92 +/- 98, 114 +/- 74 mV2.min, p <0.05, respectively) when non-responders to aspirin were excluded. PGE2 mucosal generation was significantly increased in both the antrum (9.8, 19.5, 19.7 ng/mg proteins, p<0.05, respectively) and in the corpus (8.1, 14.0, 20.2 ng/mg proteins, p<0.05, respectively). PGE2 generation was not related to potential difference. Glucagon serum levels were related to the grade of gastropathy. A 1-week administration of 160 mg/d long-acting propranolol, 35 micro g/d enprostil or placebo did not significantly modify basal potential difference.

CONCLUSIONS

Portal hypertensive gastropathy is characterized by a decreased potential difference proportional to the endoscopic severity. The gastric mucosa of patients with cirrhosis seems to be more susceptible to aspirin than that of healthy subjects. It appears that the role of PGE2 is controversial in portal hypertensive gastropathy. Propranolol and enprostil do not improve this decreased potential difference.