Expression of endothelial cell-derived nitric oxide synthase (eNOS) is increased during gastric adaptation to chronic aspirin intake in humans

Long-term use of aspirin and the risk of gastrointestinal bleeding

BACKGROUND

In short-term trials, aspirin is associated with gastrointestinal bleeding. However, the effect of dose and duration of aspirin use on risk remains unclear.

METHODS

We conducted a prospective study of 87,680 women enrolled in the Nurses' Health Study in 1990 who provided biennial data on aspirin use. We examined the relative risk (RR) of major gastrointestinal bleeding requiring hospitalization or blood transfusion.

RESULTS

During a 24-year follow-up, 1537 women reported a major gastrointestinal bleeding. Among women who used aspirin regularly (≥2 standard [325 mg] tablets/week), the multivariate RR of gastrointestinal bleeding was 1.43 (95% confidence interval [CI], 1.29-1.59) when compared with nonregular users. Compared with women who denied any aspirin use, the multivariate RRs of gastrointestinal bleeding were 1.03 (95% CI, 0.85-1.24) for women who used 0.5 to 1.5 standard aspirin tablets/week, 1.30 (95% CI, 1.07-1.58) for women who used 2 to 5 tablets/week, 1.77 (95% CI, 1.44-2.18) for women who used 6 to 14 tablets/week, and 2.24 (95% CI, 1.66-3.03) for women who used more than 14 tablets/week (P(trend)<.001). Similar dose-response relationships were observed among short-term users (≤5 years; P(trend)<.001) and long-term users (>5 years; P(trend)<.001). In contrast, after adjustments were made for dose, increasing duration of use did not confer a greater risk of bleeding (P(trend) = .28).

CONCLUSION

Regular aspirin use is associated with gastrointestinal bleeding. Risk seems more strongly related to dose than duration of aspirin use. Efforts to minimize adverse effects of aspirin therapy should emphasize using the lowest effective dose among both short- and long-term users.

Endothelial nitric oxide synthase (eNOS) is not upregulated in gastric mucosa of Helicobacter pylori (H. pylori)-positive patients with type 2 diabetes mellitus

AIM

To evaluate the expression of eNOS and CD34 in gastric mucosa of Helicobacter pylori (H. pylori) positive diabetic patients, in correlation with glycaemic control and diabetic autonomic neuropathy (DAN).

METHODS

We prospectively studied 49 diabetic type 2 patients (29 women, mean age 65.32+/-8.56 years) and 30 control subjects (15 women, mean age 58.47+/-12.40) that underwent endoscopy. Biopsies from the body and antrum were evaluated for H. pylori-gastritis, eNOS and angiogenic marker CD34 expression. Statistical analysis in correlation with mean glycosylated haemoglobin (HbA1c) of the last 3 years, and DAN was performed.

RESULTS

The two groups were matched for age (p=0.144), sex (p=0.335), H. pylori-infection (p=0.617) and degree of gastritis (p=0.78). eNOS and CD34 attenuated expression correlated with diabetes mellitus (DM) in the corpus (p=0.009 and 0.02, respectively). eNOS and CD34 expression was upregulated in H. pylori-positive controls but not in H. pylori-positive diabetic patients (p=0.010 and 0.007 for the corpus and p=0.036 and 0.047 for the antrum, respectively). eNOS expression correlated with good glycaemic control (GGC) in the gastric corpus (p<0.001) and antrum (p=0.0037) and with absence of DAN (p=0.009 and 0.036, respectively for the corpus and antrum).

CONCLUSION

Chronic glycaemic control affects eNOS expression and angiogenesis in the gastric mucosa of patients with type 2 DM. eNOS expression is not upregulated in H. pylori-positive diabetic patients.

The role of prostaglandins in triggering the liver regeneration cascade

Following injury or surgical resection, the liver has the remarkable ability to regenerate. Despite over 100 years of research, the trigger of the liver regeneration cascade has only recently been identified. Shear stress-induced nitric oxide (NO), released secondary to a hemodynamic event following partial hepatectomy (PHX), has been implicated as the trigger of the liver regeneration cascade. However, it is also known that prostaglandins (PGs) are released following PHX, and in response to shear stress. Therefore, it is hypothesized that PGs, released secondary to an increase in the blood flow-to-liver mass ratio following PHX, trigger the liver regeneration cascade, and that NO and PGs interact during the triggering event. An index of initiation of the liver regeneration cascade, c-fos mRNA expression 15 min after PHX, has been employed. As expected, c-fos mRNA expression increased 15 min after PHX and this increase was inhibited by the NO synthase antagonist, l-NAME. This inhibition was reversed by the NO donors, SIN-1 and SNAP, and by the PGs, PGE2 and PGI2. Also, the increase in c-fos mRNA expression was inhibited by indomethacin, a cyclooxygenase antagonist. This inhibition was also reversed by the NO donors, SIN-1 and SNAP, and by the PGs, PGE2 and PGI2. These results suggest that there is interaction between NO and PGs in triggering the liver regeneration cascade, and that in a situation where either NO or COX is inhibited, provision of excess exogenous NO or PGs can reverse the inhibition. This suggests that exogenous NO and/or PGs may play a role in potentiation of the liver regeneration cascade.

Current approaches to prevent NSAID-induced gastropathy--COX selectivity and beyond

Gastrointestinal (GI) toxicity associated with nonsteroidal anti-inflammatory drugs (NSAIDs) is still an important medical and socio-economic problem--despite recent pharmaceutical advances. To prevent NSAID-induced gastropathy, three strategies are followed in clinical routine: (i) coprescription of a gastroprotective drug, (ii) use of selective COX-2 inhibitors, and (iii) eradication of Helicobacter pylori. Proton pump inhibitors are the comedication of choice as they effectively reduce gastrointestinal adverse events of NSAIDs and are safe even in long-term use. Co-medication with vitamin C has only been little studied in the prevention of NSAID-induced gastropathy. Apart from scavenging free radicals it is able to induce haeme-oxgenase 1 in gastric cells, a protective enzyme with antioxidant and vasodilative properties. Final results of the celecoxib outcome study (CLASS study) attenuated the initial enthusiasm about the GI safety of selective COX-2 inhibitors, especially in patients concomitantly taking aspirin for cardiovascular prophylaxis. Helicobacter pylori increases the risk for ulcers particularly in NSAID-naive patients and therefore eradication is recommended prior to long-term NSAID therapy at least in patients at high risk. New classes of COX-inhibitors are currently evaluated in clinical studies with very promising results: NSAIDs combined with a nitric oxide releasing moiety (NO-NSAID) and dual inhibitors of COX and 5-LOX. These drugs offer extended anti-inflammatory potency while sparing gastric mucosa.

Morphological features of rat gastric mucosa after acute and chronic treatment with amtolmetin guacyl: comparison with non-selective and COX-2-selective NSAIDs

BACKGROUND/AIMS

The compound amtolmetin guacyl (AMG) has been characterized in both animal and human studies as a novel non-selective non-steroidal anti-inflammatory drug (NSAID) endowed with lower ulcerogenicity in comparison with traditional NSAIDs due to a unique mechanism of action, namely the increase in endogenous production of gastric nitric oxide.

METHODS

Conscious rats were treated either acutely (4 h) or chronically (3 and 14 days) with intragastric AMG (50 and 150 mg/kg), the non-selective NSAID tolmetin (TOL, 30 and 100 mg/kg) or the COX-2-selective NSAID celecoxib (CXIB, 20 and 60 mg/kg). Macroscopically visible and histologic lesions were evaluated. The ultrastructure of mucosal microvasculature was assessed.

RESULTS

(1) TOL and CXIB caused quantitatively greater endothelial damage and inflammatory cell infiltration than that induced by AMG; (2) AMG and CXIB, unlike TOL, did not cause epithelial damage after acute or chronic treatment, and (3) gastric lesions induced by TOL underwent adaptation during chronic treatment.

CONCLUSION

Endothelial cell damage in the gastric microvasculature is an early event following both non-selective and COX-2-selective inhibitors. The low gastric mucosal toxicity of AMG is confirmed after acute and chronic treatment.

Physiopathologie des lésions gastro-duodénales induites par les anti-inflammatoires non stéroïdiens

The pathogenesis of the gastroduodenal lesions induced by non-steroidal anti-inflammatory drugs and aspirin is primarily caused by a reduction in mucosal blood flow, which is the consequence of inhibition of cyclooxygenase-producing vasodilator prostaglandins. The subsequent phase is adherence of leukocytes to the endothelium, which may depend on cyclooxygenase-2. Endothelial lesions accentuate the fall of mucosal blood flow and promote the inflammatory process in the gastric mucosa. The inflammatory process is amplified by expression of TNFalpha in polymorphonuclears induced by non-steroidal anti-inflammatory drugs. A few days after starting treatment, epithelial proliferation and increased mucosal blood flow, partly dependent on cyclooxygenase-2 and nitric oxide expression, compensates for the damaging process. Selective inhibitors of inducible cyclooxygenase-2 have reduced gastrointestinal toxicity, which could partially be explained by the protection effect of cyclooxygenase-2 on the gastrointestinal mucosa during inflammation or epithelial repair. Selective inhibitors may worsen inflammatory bowel disease. Non-steroidal inflammatory drugs and aspirin, but perhaps not selective inhibitors, increase the mucosal lesions associated with Helicobacter pylori-induced gastritis. Co-administration of selective inhibitors and aspirin leads to gastrointestinal toxicity equivalent to that of non-specific anti-inflammatory drugs.

Nitric oxide: relation to integrity, injury, and healing of the gastric mucosa

Nitric oxide (NO) plays a multifaceted role in mucosal integrity. The numerous functions of NO and the double-edged role played by NO in most of them provide a great complexity to the NO action. The three enzymatic sources of NO, neuronal NO-synthase (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), have been characterised in the gastrointestinal tract. The protective properties of the NO derived from constitutive NO-synthases (eNOS and nNOS) have already been well established. Less clear is the role assigned to iNOS. The simplistic initial view of low levels of NO synthesised by constitutive NOS being protective while exaggerated NO levels after iNOS induction leading irremediably to cytotoxicity is being questioned by new evidence. As initially reported for constitutive NOS, iNOS activity may be associated to reduced leukocyte-endothelium interaction and platelet aggregation as well as protection of mucosal microcirculation. Moreover, iNOS activity may be important to resolve inflammation by increasing apoptosis in inflammatory cells. It is entirely possible that a low level of expression of iNOS will reflect a positive host-defense response to challenge, but that exaggerated or uncontrolled expression of iNOS itself becomes detrimental. There is no doubt about the protective role of NO in physiological conditions. However, when the mucosa is threatened, the role of NO becomes multiple and the final effect will probably depend on the nature of the insult, the environment involved, and the interaction with other mediators.

Nonsteroidal anti-inflammatory drug gastropathy

By inhibiting prostaglandin synthesis, nonsteroidal anti-inflammatory drugs (NSAIDs) compromise gastroduodenal defense mechanism including blood flow and mucus/bicarbonate secretion. This has led to NSAIDs being the most widely reported drug cause of adverse events. While NSAIDs also cause dyspepsia, inhibition of prostaglandin synthesis may reduce this from even higher levels that would otherwise prevail and mask ulcer-related dyspepsia, making anticipatory management difficult. On average, the risk of ulcer complications increases 4-fold, resulting in 1.25 additional hospitalizations per 100 patient-years according to one estimate. Older patients, those with a past history, and those taking anticoagulants or corticosteroids are at higher risk. Risk is dose dependent and is lower with ibuprofen at low doses than with other NSAIDs. It is unlikely that Helicobacter pylori increases the risk, and under some circumstances it may be protective. Selective inhibitors of the inducible cyclooxygenase 2 spare gastric mucosal prostaglandin synthesis and do not damage the gastric mucosa. Their place in therapy, compared with use of misoprostol or proton pump inhibitors, is currently emerging. Future competitors may include nitric oxide-donating, zwitterionic, or R-enantiomer NSAIDs.

Effect of naproxen on the hamster gastric antrum: ulceration, adaptation and efficacy of anti-ulcer drugs

BACKGROUND

Various animal models of non-steroidal anti-inflammatory drug (NSAID)-induced gastric ulceration exist. These models have limitations, which make them less relevant to the human situation.

AIM

: To develop a more simple and more relevant model of NSAID-induced gastric ulceration and adaptation.

METHODS

Gastric ulceration was evaluated following the orogastric administration of naproxen (80 mg/kg b.d.) to hamsters. The effects of misoprostol and famotidine on gastric acid secretion and ulceration were also determined. Gastric adaptation was evaluated by proliferating cell nuclear antigen (PCNA) immunohistochemistry, in hamsters given naproxen for 3 weeks. Antral resistance to acute injury by NSAIDs and ethanol was also determined in these animals.

RESULTS

Naproxen caused primarily gastric antral ulceration, which decreased from day 3 to day 21. This gastric adaptation was accompanied by an increase in PCNA positive cells, particularly on days 7 and 14. The adapted gastric antral mucosa was resistant to acute damage by various agents. Misoprostol (1 or 100 microg/kg) prevented antral ulceration, without affecting gastric acid secretion. Despite decreasing acid output by> 90%, famotidine (30 mg/kg) failed to prevent ulceration.

CONCLUSION

The administration of naproxen (80 mg/kg b.d.) to hamsters is a simple, reliable and relevant method for evaluating NSAID-induced gastric antral ulceration and adaptation.