Activation of genes for spasmolytic peptide, transforming growth factor alpha and for cyclooxygenase (COX)‐1 and COX‐2 during gastric adaptation to aspirin damage in rats

Background: NSAIDs, such as aspirin (ASA), cause widespread mucosal damage, but repeated ASA insults appear to induce mucosal tolerance (adaptation) to this␣injury. The mechanism of the gastric adaptation to the damage induced by ASA has not been fully explained. Aim: To determine the role of the mucosal gene expression for spasmolitic peptide (SP) (a member of trefoil peptides) and transforming growth factor alpha (TGFα) as well as for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to ASA in rats. Methods: Gastric lesions were produced by ASA (100 mg/kg in 1.5 mL of 0.2 M HCl) applied intragastrically (i.g.) as a single dose, every day for 5 days. Control rats were given 1.5 mL of vehicle (0.2 M HCl i.g.) as a single dose, during 5 consecutive days. Gastric blood flow (GBF) was measured by H2-gas clearance technique and gastric mucosal specimens were taken for the assessment of cell␣proliferation rate in gastric mucosa by bromodeoxyuridine (BrdU) uptake, mucosal generation of prostaglandin E2 measured by radioimmunoassay, and for expression of SP, TGFα COX-1 and COX-2 mRNA as determined by RT-PCR. To quantify the relative amounts of mRNA for SP and TGFα, southern blotting analysis of the PCR products was performed and the intensity of PCR products was compared with that of β-actin used as a standard. Results: ASA applied once produced numerous gastric erosions, but with repeated ASA doses the adaptation to this NSAID developed, the area of gastric lesions being reduced by 86% after six consecutive ASA insults. This adaptation to ASA was accompanied by approximately a 90% reduction in prostaglandin E2 biosynthesis, by a significant rise in BrdU uptake by glandular cells predominantly in the neck region of gastric glands and by expression of SP (SP/β-actin ratio; 0.96 ± 0.08 in ASA-adapted mucosa vs. 0.38 ± 0.05 in the control mucosa) and TGFα (TGFα/β-actin ratio: 0.97 ± 0.07 in ASA-adapted mucosa vs. 0.77 ± 0.06 in the control mucosa). COX-1 expression was detected in vehicle-control gastric mucosa and after single exposure to ASA or after six consecutive ASA insults, while COX-2 mRNA was not detected in vehicle-control gastric mucosa, but appeared after single ASA insult and was sustained after subsequent ASA doses. Conclusions: (i) Gastric adaptation to aspirin injury involves enhanced cell proliferation which appears to be mediated by increased expression of SP and TGFα, and (ii) rapid upregulation of COX-2 expression following single and repeated ASA insults may represent a compensatory response to suppression of prostaglandin generation by this NSAID.