Nitric oxide-releasing aspirin but not conventional aspirin improves healing of experimental colitis

AIM:To determine the effect of non-selective cyclooxygenase (COX) inhibitors,selective COX-2 inhibitors and nitric oxide (NO)-releasing aspirin in the healing of ulcerative colitis.METHODS:Rats with 2,4,6 trinitrobenzenesulfonic acid (TNBS)-induced colitis received intragastric (ig) treatment with vehicle,aspirin (ASA) (a nonselective COX inhibitor),celecoxib (a selective COX-2 inhibitor) or NO-releasing ASA for a period of ten days.The area of colonic lesions,colonic blood flow (CBF),myeloperoxidase (MPO) activity and expression of proinflammatory markers COX-2,inducible form of nitric oxide synthase (iNOS),IL-1β and tumor necrosis factor (TNF)-α were assessed.The effects of glyceryl trinitrate (GTN),a NO donor,and 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxy-3-oxide,onopotassium salt (carboxy-PTIO),a NO scavenger,administered without and with ASA or NO-ASA,and the involvement of capsaicin-sensitive afferent nerves in the mechanism of healing the experimental colitis was also determined.RESULTS:Rats with colitis developed macroscopic and microscopic colonic lesions accompanied by a significant decrease in the CBF,a significant rise in colonic weight,MPO activity and plasma IL-1β and TNF-α levels.These effects were aggravated by ASA and 5-(4-chlorophenyl)-1-(4-methoxyphenyl)3-(trifluoromethyl)-1H-pyrazole (SC-560),but not celecoxib and counteracted by concurrent treatment with a synthetic prostaglandin E 2 (PGE 2) analog.Treatment with NO-ASA dose-dependently accelerated colonic healing followed by a rise in plasma NO x content and CBF,suppression of MPO and downregulation of COX-2,iNOS,IL-1β and TNF-α mRNAs.Treatment with GTN,the NO donor,significantly inhibited the ASA-induced colonic lesions and increased CBF,while carboxy-PTIO or capsaicin-denervation counteracted the NO-ASAinduced improvement of colonic healing and the accompanying increase in the CBF.These effects were restored by co-treatment with calcitonin gene related peptide (CGRP) and NO-ASA in capsaicin-denervated animals.CONCLUSION:NO-releasing ASA,in contrast to ASA,COX-1 inhibitors,and SC-560,accelerated the healing of colitis via a mechanism involving NO mediated improvement of microcirculation and activation of sensory nerves releasing CGRP.

Grapefruit-seed extract attenuates ethanol-and stress-induced gastric lesions via activation of prostaglandin, nitric oxide and sensory nerve pathways

AIM: Grapefruit-seed extract (GSE) containing flavonoids, possesses antibacterial and antioxidative properties but whether it influences the gastric defense mechanism and gastroprotection against ethanol- and stress-induced gastric lesions remains unknown. METHODS: We compared the effects of GSE on gastric mucosal lesions induced in rats by topical application of 100% ethanol or 3.5 h of water immersion and restraint stress (WRS) with or without (A) inhibition of cyclooxygenase (COX)-1 activity by indomethacin and rofecoxib, the selective COX-2 inhibitor, (B) suppression of NO-synthase with L-NNA (20 mg/kg ip), and (C) inactivation by capsaicin (125 mg/kg sc) of sensory nerves with or without intragastric (ig) pretreatment with GSE applied 30 min prior to ethanol or WRS. One hour after ethanol and 3.5 h after the end of WRS, the number and area of gastric lesions were measured by planimetry, the gastric blood flow (GBF) was assessed by H2-gas clearance technique and plasma gastrin levels and the gastric mucosal generation of PGE2, superoxide dismutase (SOD) activity and malonyldialdehyde (MDA) concentration, as an index of lipid peroxidation were determined. RESULTS: Ethanol and WRS caused gastric lesions accompanied by the significant fall in the GBF and SOD activity and the rise in the mucosal MDA content. Pretreatment with GSE (8-64 mg/kg i g) dose-dependently attenuated gastric lesions induced by 100% ethanol and WRS; the dose reducing these lesions by 50% (ID50) was 25 and 36 mg/kg, respectively, and this protective effect was similar to that obtained with methyl PGE2 analog (5 μg/kg i g). GSE significantly raised the GBF, mucosal generation of PGE2, SOD activity and plasma gastrin levels while attenuating MDA content. Inhibition of PGE2 generation with indomethacin or rofecoxib and suppression of NO synthase by L-NNA or capsaicin denervation reversed the GSE-induced protection and the accompanying hyperemia. Co-treatment of exogenous calcitonine gene-related peptide (CGRP) with GSE restored the protection and accompanying hyperemic effects of GSE in rats with capsaicin denervation. CONCLUSION: GSE exerts a potent gastroprotective activity against ethanol and WRS-induced gastric lesions via an increase in endogenous PG generation, suppression of lipid peroxidation and hyperemia possibly mediated by NO and CGRP released from sensory nerves.