Factors involved in upregulation of inducible nitric oxide synthase in rat small intestine following administration of nonsteroidal anti-inflammatory drugs

Pain killers: the interplay between nonsteroidal anti-inflammatory drugs and Clostridioides difficile infection

Clostridioides difficile is one of the leading causes of nosocomial infections worldwide. Increases in incidence, severity, and healthcare cost associated with C. difficile infection (CDI) have made this pathogen an urgent public health threat worldwide. The factors shaping the evolving epidemiology of CDI and impacting clinical outcomes of infection are not well understood, but involve tripartite interactions between the host, microbiota, and C. difficile. In addition to this, emerging data suggests an underappreciated role for environmental factors, such as diet and pharmaceutical drugs, in CDI. In this review, we discuss the role of nonsteroidal anti-inflammatory drugs (NSAIDs) and eicosanoids in CDI.

Research progress of non-steroidal anti-inflammatory drug-induced small intestinal injury

Non-steroidal anti-inflammatory drugs (NSAIDs) are used widely around the world because of their anti-inflammatory, analgesic, and antiplatelet activity. However, long-term application of NSAIDs can lead to complications. Previously, the clinical attention was dedicated to the NSAID-induced upper gastrointestinal complications. Recently, the detection rate of small intestinal damage related to NSAIDs has increased due to the wide use of endoscopes such as capsule endoscopy and double-balloon colonoscopy. Although the majority of patients have no significant symptoms, there are still a small percentage of patients who develop obvious symptoms or complicated ulcers that require therapeutic intervention. Despite significant advances in our understanding of NSAIDs, the treatment modality and regimen for NSAID-induced small intestinal damage have remained relatively unclear. This article will provide a comprehensive overview of NSAID-induced small intestinal damage with regard to the epidemiology, clinical manifestations, diagnosis, risk factors, pathogenesis, and treatment, in order to provide informative evidence for clinical practice.

Loxoprofen enhances intestinal barrier function via generation of its active metabolite by carbonyl reductase 1 in differentiated Caco-2 cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used worldwide as antipyretic analgesics and agents for rheumatoid arthritis and osteoarthritis, but known to cause damage to the gastrointestinal mucosae as their serious adverse effects. Few studies showed the impairment of intestinal epithelial barrier function (EBF) by high concentrations (0.5-1 mM) of NSAIDs, but the underlying mechanism is not fully understood. This study is aimed at clarifying effects at a low concentration (50 μM) of three NSAIDs, loxoprofen (Lox), ibuprofen and indomethacin, on intestinal EBF using human intestinal epithelial-like Caco-2 cells. Among those NSAIDs, Lox increased the transepithelial electric resistance (TER) value, decreased the paracellular Lucifer yellow CH (LYCH) permeability, and upregulated claudin (CLDN)-1, -3 and -5, indicating that low doses of Lox enhanced EBF through increasing expression of CLDNs. Lox is known to be metabolized to a pharmacologically active metabolite, (2S,1'R,2'S)-loxoprofen alcohol (Lox-RS), by carbonyl reductase 1 (CBR1), which is highly expressed in human intestine. CBR1 was expressed in the Caco-2 cells, and the pretreatment with a CBR1 inhibitor suppressed both the Lox-evoked CLDN upregulation and EBF enhancement. In addition, the treatment of the cells with Lox-RS resulted in higher TER value and lower LYCH permeability than those with Lox. Thus, Lox-RS synthesized by CBR1 may greatly contribute to the improving efficacy of Lox on the barrier function. Since EBF is decreased in inflammatory bowel disease, we finally examined the effect of Lox on EBF using the Caco-2/THP-1 co-culture system, which is used as an in vitro inflammatory bowel disease model. Lox significantly recovered EBF which was impaired by inflammatory cytokines secreted from THP-1 macrophages. These in vitro observations suggest that Lox enhances intestinal EBF, for which the metabolism of Lox to Lox-RS by CBR1 has an important role.

Chymase inhibitor prevents the development and progression of non-alcoholic steatohepatitis in rats fed a high-fat and high-cholesterol diet

The effect of the chymase inhibitor TY-51469 on the development and progression of non-alcoholic steatohepatitis (NASH) was evaluated in rats fed a high-fat and high-cholesterol (HFC) diet. To evaluate the preventive effect of TY-51469 on the development of NASH, stroke-prone spontaneously hypertensive rat 5 (SHRSP5)/Dmcr rats were fed either a normal or HFC diet for 8 weeks, and concurrently administered either placebo or TY-51469 (1 mg/kg per day). To evaluate the effect of TY-51469 on the survival rate, TY-51469 was administered either concurrently with HFC diet (pretreated group) or 8 weeks after HFC diet at which point NASH had developed (posttreated group). Eight weeks after HFC diet, significant increases of steatosis, fibrosis and chymase-positive cells were observed in liver from the placebo-treated rats. Significant increases of myeloperoxidase, transforming growth factor-β, matrix metalloproteinase-9, and collagen I mRNA levels were also observed. However, all parameters were significantly attenuated in the TY-51469-treated group. A survival rate of the placebo-treated group fed the HFC diet was 0% at 14 weeks. In comparison, the rates of TY-51469-pretreated and TY-51469-posttreated groups were 100% and 50% at 14 weeks, respectively. Chymase inhibitor may be applicable to preventing the development and progression of NASH.

Influence of Adrenalectomy on Protective Effects of Urocortin I, a Corticotropin-Releasing Factor, Against Indomethacin-Induced Enteropathy in Rats

We examined the influence of adrenalectomy on NSAID-induced small intestinal damage in rats and investigated the possible involvement of adrenal glucocorticoids in the protective effects of urocortin I, a corticotropin-releasing factor (CRF) agonist. Male SD rats without fasting were administered indomethacin s.c. and killed 24 h later in order to examine the hemorrhagic lesions that developed in the small intestine. Urocortin I (20 µg/kg) was given i.v. 10 min before the administration of indomethacin. Bilateral adrenalectomy was performed a week before the experiment. Indomethacin (10 mg/kg) caused multiple hemorrhagic lesions in the small intestine, which were accompanied by a decrease in mucus secretion and increases in intestinal motility, enterobacterial invasion, and iNOS expression. Adrenalectomy markedly increased the ulcerogenic and motility responses caused by indomethacin, with further enhancements in bacterial invasion and iNOS expression; severe lesions occurred at 3 mg/kg, a dose that did not induce any damage in sham-operated rats. This worsening effect was also observed by the pretreatment with mifepristone (a glucocorticoid receptor antagonist). Urocortin I prevented indomethacin-induced enteropathy, and this effect was completely abrogated by the pretreatment with astressin 2B, a CRF2 receptor antagonist, but was not significantly affected by either adrenalectomy or the mifepristone pretreatment. These results suggested that adrenalectomy aggravated the intestinal ulcerogenic response to indomethacin, the intestinal hypermotility response may be a key element in the mechanism for this aggravation, and endogenous glucocorticoids played a role in intestinal mucosal defense against indomethacin-induced enteropathy, but did not account for the protective effects of urocortin I, which were mediated by the activation of peripheral CRF2 receptors

Small bowel protection against NSAID-injury in rats: Effect of rifaximin, a poorly absorbed, GI targeted, antibiotic

Nonsteroidal anti-inflammatory drugs, besides exerting detrimental effects on the upper digestive tract, can also damage the small and large intestine. Although the underlying mechanisms remain unclear, there is evidence that enteric bacteria play a pivotal role. The present study examined the enteroprotective effects of a delayed-release formulation of rifaximin-EIR (R-EIR, 50mg/kg BID, i.g.), a poorly absorbed antibiotic with a broad spectrum of antibacterial activity, in a rat model of enteropathy induced by indomethacin (IND, 1.5mg/kg BID for 14 days) administration. R-EIR was administered starting 7 days before or in concomitance with IND administration. At the end of treatments, blood samples were collected to evaluate hemoglobin (Hb) concentration (as an index of digestive bleeding). Small intestine was processed for: (1) histological assessment of intestinal damage (percentage length of lesions over the total length examined); (2) assay of tissue myeloperoxidase (MPO) and TNF levels, as markers of inflammation; (3) assay of tissue malondialdehyde (MDA) and protein carbonyl concentrations, as an index of lipid and protein peroxidation, respectively; (4) evaluation of the major bacterial phyla. IND significantly decreased Hb levels, this effect being significantly blunted by R-EIR. IND also induced the occurrence of lesions in the jejunum and ileum. In both intestinal regions, R-EIR significantly reduced the percentage of lesions, as compared with rats receiving IND alone. Either the markers of inflammation and tissue peroxidation were significantly increased in jejunum and ileum from IND-treated rats. However, in rats treated with R-EIR, these parameters were not significantly different from those observed in controls. R-EIR was also able to counterbalance the increase in Proteobacteria and Firmicutes abundance induced by INDO. To summarize, R-EIR treatment significantly prevents IND-induced intestinal damage, this enteroprotective effect being associated with a decrease in tissue inflammation, oxidative stress and digestive bleeding as well as reversal of NSAID-induced alterations in bacterial population.

NSAID-induced small intestinal damage--roles of various pathogenic factors

BACKGROUND/AIMS

NSAID-induced enteropathy has been the focus of recent basic and clinical research subsequent to the development of the capsule endoscope and double-balloon endoscope. We review the possible pathogenic mechanisms underlying NSAID-induced enteropathy and discuss the role of the inhibition of COX-1/COX-2 and the influences of food as well as various prophylactic treatments on these lesions.

METHODS

Studies were performed in experimental animals.

RESULTS

Multiple factors, such as intestinal hypermotility, decreased mucus secretion, enterobacteria, and upregulation of iNOS/NO expression, are involved in the pathogenesis of NSAID-induced enteropathy, in addition to the decreased production of PGs due to the inhibition of COX. Enterobacterial invasion is the most important pathogenic event, and intestinal hypermotility, which was associated with this event, is essential for the development of these lesions. NSAIDs also upregulate the expression of COX-2, and the inhibition of both COX-1 and COX-2 is required for the intestinal ulcerogenic properties of NSAIDs to manifest. NSAID-induced enteropathy is prevented by PGE2, atropine, ampicillin, and aminoguanidine as well as soluble dietary fiber, and exacerbated by antisecretory drugs such as proton pump inhibitors.

CONCLUSION

These findings on the pathogenesis of NSAID-induced enteropathy will be useful for the future development of intestinal-sparing alternatives to standard NSAIDs.

[Glutamate as a potential protective drug in the gastrointestinal mucosa]

Monosodium glutamate (MSG) is known to provide the umami taste in the food. We have recently reported that glutamate has the potential to protect the small intestine against non-steroidal anti-inflammatory drugs (NSAIDs)-induced lesions in rats. In this paper, we examined this protective effect using sodium loxoprofen, one of the NSAIDs frequently used in Asian countries, to determine whether MSG accelerates the healing of loxoprofen-induced small intestinal lesions in rats. Loxoprofen at 60 mg/kg caused hemorrhagic lesions in the small intestine, mainly in the jejunum and ileum. These lesions spontaneously healed within 7 days, but this healing process was delayed by repeated administration of loxoprofen at low doses (10, 30 mg/kg) for 5 d after lesion induction. The healing-impairment action of loxoprofen was accompanied by the down-regulation of vascular endothelium-derived growth factor (VEGF) expression and an angiogenic response. The impaired healing caused by loxoprofen was significantly restored by co-treatment with a diet containing 5% MSG for 5 d, accompanied by the enhancement of VEGF expression and angiogenesis. We suggest that daily intake of MSG not only protects the small intestine against NSAIDs-induced damage but also exerts healing-promoting effects on these lesions.

Prophylactic effects of prostaglandin E2 on NSAID-induced enteropathy-role of EP4 receptors in its protective and healing-promoting effects

Prostaglandin E2 not only prevents NSAID-generated small intestinal lesions, but also promotes their healing. The protective effects of prostaglandin E2 are mediated by the activation of EP4 receptors and functionally associated with the stimulation of mucus/fluid secretions and inhibition of intestinal hypermotility, resulting in the suppression of enterobacterial invasion and iNOS up-regulation, which consequently prevents intestinal lesions. Prostaglandin E2 also promotes the healing of intestinal damage by stimulating angiogenesis through the up-regulation of VEGF expression via the activation of EP4 receptors. These findings have contributed to a further understanding of the mechanisms responsible for 'protective' and 'healing-promoting' effects of prostaglandin E2 and the development of new strategies for the prophylactic treatment of NSAID-induced enteropathy.

Therapeutic effect and mechanism of electroacupuncture at Zusanli on plasticity of interstitial cells of Cajal: a study of rat ileum

Background

Electroacupuncture (EA) is one of the techniques of acupuncture and is believed to be an effective alternative and complementary treatment in many disorders. The aims of this study were to investigate the effects and mechanisms of EA at acupoint Zusanli (ST36) on the plasticity of interstitial cells of Cajal (ICCs) in partial bowel obstruction.

Methods

A Sprague Dawley rat model of partial bowel obstruction was established and EA was conducted at Zusanli (ST36) and Yinglingquan (SP9) in test and control groups, respectively. Experiments were performed to study the effects and mechanisms of EA at Zusanli on intestinal myoelectric activity, distribution and alteration of ICCs, expression of inflammatory mediators, and c-Kit expression.

Results

1) EA at Zusanli somewhat improved slow wave amplitude and frequency in the partial obstruction rats. 2) EA at Zusanli significantly stimulated the recovery of ICC networks and numbers. 3) the pro-inflammatory mediator TNF-α and NO activity were significantly reduced after EA at Zusanli, However, no significant changes were observed in the anti-inflammatory mediator IL-10 activity. 4) EA at Zusanli re-expressed c-Kit protein. However, EA at the control acupoint, SP9, significantly improved slow wave frequency and amplitude, but had no effect on ICC or inflammatory mediators.

Conclusions

We concluded that EA at Zusanli might have a therapeutic effect on ICC plasticity, and that this effect might be mediated via a decrease in pro-inflammatory mediators and through the c-Kit signaling pathway, but that the relationship between EA at different acupoints and myoelectric activity needs further study.

Lubiprostone prevents nonsteroidal anti-inflammatory drug-induced small intestinal damage by suppressing the expression of inflammatory mediators via EP4 receptors

Lubiprostone, a bicyclic fatty acid derived from prostaglandin E1, has been used to treat chronic constipation and irritable bowel syndrome, and its mechanism of action has been attributed to the stimulation of intestinal fluid secretion via the activation of the chloride channel protein 2/cystic fibrosis transmembrane regulator (ClC-2/CFTR) chloride channels. We examined the effects of lubiprostone on indomethacin-induced enteropathy and investigated the functional mechanisms involved, including its relationship with the EP4 receptor subtype. Male Sprague-Dawley rats were administered indomethacin (10 mg/kg p.o.) and killed 24 hours later to examine the hemorrhagic lesions that developed in the small intestine. Lubiprostone (0.01-1 mg/kg) was administered orally twice 30 minutes before and 9 h after the indomethacin treatment. Indomethacin markedly damaged the small intestine, accompanied by intestinal hypermotility, a decrease in mucus and fluid secretion, and an increase in enterobacterial invasion as well as the up-regulation of inducible nitric-oxide synthase (iNOS) and tumor necrosis factor α (TNFα) mRNAs. Lubiprostone significantly reduced the severity of these lesions, with the concomitant suppression of the functional changes. The effects of lubiprostone on the intestinal lesions and functional alterations were significantly abrogated by the coadministration of AE3-208 [4-(4-cyano-2-(2-(4-fluoronaphthalen-1-yl)propionylamino)phenyl)butyric acid], a selective EP4 antagonist, but not by CFTR(inh)-172, a CFTR inhibitor. These results suggest that lubiprostone may prevent indomethacin-induced enteropathy via an EP4 receptor-dependent mechanism. This effect may be functionally associated with the inhibition of intestinal hypermotility and increase in mucus/fluid secretion, resulting in the suppression of bacterial invasion and iNOS/TNFα expression, which are major pathogenic events in enteropathy. The direct activation of CFTR/ClC-2 chloride channels is not likely to have contributed to the protective effects of lubiprostone.

New therapeutic strategy for amino acid medicine: prophylactic and healing promoting effect of monosodium glutamate against NSAID-induced enteropathy

We reviewed the effect of monosodium glutamate (MSG) on the development and healing of nonsteroidal anti-inflammatory drug (NSAID)-induced small intestinal lesions in rats. Loxoprofen (60 mg/kg, p.o.) induced lesions in the small intestine within 24 h, accompanied by a decrease of Muc2 expression and an increase in enterobacterial invasion and inducible nitric oxide synthase (iNOS) expression. These lesions were prevented when MSG was given as a mixture of powdered food for 5 days before the loxoprofen treatment. This effect of MSG was accompanied by an increase in Muc2 expression / mucus secretion as well as the suppression of bacterial invasion and iNOS expression. These intestinal lesions healed spontaneously within 6 days, but the process was impaired by the repeated administration of low-dose loxoprofen (30 mg/kg) for 5 days after the ulceration, with the decrease of vascular endothelial derived growth factor (VEGF) expression and angiogenesis. The healing-impairing effect of loxoprofen was prevented by feeding 5% MSG for 5 days after the ulceration. These results suggest that MSG not only prevents loxoprofen-induced small intestinal damage but also promotes a healing of these lesions; the former is functionally associated with the increase in Muc2 expression / mucus secretion and the suppression of bacterial invasion and iNOS expression, while the latter is associated with the stimulation of VEGF expression/angiogenesis.

Measurement of small intestinal damage

Many animal models have been devised for investigating the pathogenesis of intestinal lesions and for screening drugs for the treatment of intestinal ulcers in humans. Recently, particular attention has been focused on NSAID-induced intestinal lesions as a result of the development of the capsule endoscope and double-balloon endoscope. Ischemic enteritis, one of the most dramatic abdominal emergencies, is known to cause severe damage to the small intestine by a significant decrease of arterial blood flow in the small intestine. In this unit, two animal models for small intestinal damage induced by NSAIDs or intestinal ischemia are described. Also included are methods for lesion induction and evaluation of the damage as well as the measurement of pathogenic functional and biochemical changes.

Urocortin prevents indomethacin-induced small intestinal lesions in rats through activation of CRF2 receptors

PURPOSE

The role of corticotropin-releasing factor (CRF) in the pathogenesis of indomethacin-induced small intestinal lesions was examined in rats.

METHODS

Animals were given indomethacin (10 mg/kg) subcutaneously and killed 24 h later. Urocortin I [a nonselective CRF receptor (CRFR) agonist], astressin (a nonselective CRFR antagonist), NBI-27914 (a CRFR1 antagonist), or astressin-2B (a CRFR2 antagonist) was given intravenously 10 min before the administration of indomethacin.

RESULTS

Indomethacin caused hemorrhagic lesions in the small intestine, accompanied by intestinal hypermotility, mucosal invasion of enterobacteria, up-regulation of inducible nitric oxide synthase (iNOS) expression, and an increase of mucosal myeloperoxidase (MPO) activity. Pretreatment of the animals with astressin, a non-selective CRFR antagonist, aggravated the lesions in a dose-dependent manner. Likewise, astressin-2B also exacerbated the intestinal ulcerogenic response induced by indomethacin, while NBI-27914 did not. Urocortin I prevented indomethacin-induced intestinal lesions, together with the suppression of bacterial invasion and an increase in mucosal MPO activity and iNOS expression; these effects were significantly reversed by co-administration of astressin-2B but not NBI-27914. Urocortin I suppressed the hypermotility response to indomethacin, and this effect was also abrogated by astressin-2B but not NBI-27914.

CONCLUSIONS

These results suggest that urocortin 1 prevents indomethacin-induced small intestinal lesions, and that this action is mediated by the activation of CRFR2 and is functionally associated with the suppression of the intestinal hypermotility response caused by indomethacin. It is assumed that endogenous CRF contributes to the maintenance of the mucosal defensive ability of the small intestine against indomethacin through the activation of CRFR2.

Protective effect of lafutidine, a histamine H2 receptor antagonist, against loxoprofen-induced small intestinal lesions in rats

BACKGROUND AND AIMS

We examined the effect of lafutidine, a histamine H(2) receptor antagonist with a mucosal protective action mediated by capsaicin-sensitive sensory neurons (CSN), on intestinal lesions produced by loxoprofen administration in rats.

METHODS

Animals were given loxoprofen (10-100 mg/kg p.o.) and killed 24 h later. Lafutidine (10 and 30 mg/kg), cimetidine (100 mg/kg) or famotidine (30 mg/kg) was given twice p.o. at 0.5 h before and 6 h after loxoprofen. Omeprazole (100 mg/kg) was given p.o. once 0.5 h before. Ampicillin (800 mg/kg) was given p.o. twice at 24 h and 0.5 h before loxoprofen, while 16,16-dimethyl prostaglandin E(2) (dmPGE(2); 0.01 mg/kg) was given i.v. twice at 5 min before and 6 h after.

RESULTS

Loxoprofen dose-dependently produced hemorrhagic lesions in the small intestine, accompanied by invasion of enterobacteria and increased inducible nitric oxide synthase (iNOS) expression as well as myeloperoxidase activity in the mucosa. The ulcerogenic response to loxoprofen (60 mg/kg) was significantly prevented by lafutidine (30 mg/kg), similar to dmPGE(2) and ampicillin, and the effect of lafutidine was totally attenuated by ablation of CSN. Neither cimetidine, famotidine nor omeprazole had a significant effect against these lesions. Lafutidine alone increased mucus secretion and reverted the decreased mucus response to loxoprofen, resulting in suppression of bacterial invasion and iNOS expression. In addition, loxoprofen downregulated Muc2 expression, and this response was totally reversed by lafutidine mediated by CSN.

CONCLUSION

Lafutidine protects the small intestine against loxoprofen-induced lesions, essentially mediated by the CSN, and this effect may be functionally associated with increased Muc2 expression/mucus secretion, an important factor in the suppression of bacterial invasion.

High-dose naproxen aggravates pancreatic fibrosis in a rat model of chronic pancreatitis

OBJECTIVES

: Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely prescribed for the treatment of pain in chronic pancreatitis (CP). This study aimed to investigate the effect of NSAIDs on the inflammation and fibrosis progression in trinitrobenzene sulfonic acid-induced CP rats.

METHODS

Chronic pancreatitis was induced by trinitrobenzene sulfonic acid infusion into rat pancreatic ducts. Naproxen treatment (20 and 40 mg/kg per os [PO] and intraperitoneally) started 2 weeks after the induction of CP for 3 weeks. Histological analysis of the pancreas, Van Gieson staining, and contents of hydroxyproline were used to evaluate pancreatic damage and fibrosis. Furthermore, the effect of naproxen on nociceptive reflective behaviors and serum tumor necrosis factor alpha concentration were studied, and immunohistochemical analysis of alpha-smooth muscle actin in the pancreas was performed.

RESULTS

Pancreatic collagen content and alpha-smooth muscle actin expression were higher in the CP group treated with high-dose (40 mg/kg PO) naproxen (P < 0.05). High-dose naproxen administered orally aggravated pancreatic fibrosis and inflammation (P < 0.05). Instead of playing an analgesic role, high-dose naproxen decreased the thermal withdrawal latencies in CP rats (P < 0.05).

CONCLUSIONS

High-dose naproxen treatment (40 mg/kg PO) aggravated pancreatic fibrosis in CP rats and played an algogenic role that suggests the potential risk of long-term use of NSAIDs as analgesic in clinical practice with CP.

Significance of chymase-dependent matrix metalloproteinase-9 activation on indomethacin-induced small intestinal damages in rats

The side effects of nonsteroidal anti-inflammatory drugs (NSAIDs) include gastrointestinal damage not only in the stomach but also in the small intestine. Chymase converts promatrix metalloproteinase-9 to matrix metalloproteinase (MMP)-9, which plays an important role in NSAID-induced gastric damage, but it has been unclear whether chymase-dependent MMP-9 activation is involved in the NSAID-induced small intestinal damage. To clarify the involvement of chymase-dependent MMP-9 activation on NSAID-induced small intestinal damage, the effect of a chymase inhibitor, 2-[4-(5-fluoro-3-methylbenzo[b]thiophen-2-yl)sulfonamido-3-methanesulfonylphenyl] thiazole-4-carboxylic acid (TY-51469), on indomethacin-induced small intestinal damage in rats was evaluated. Until 6 h after oral administration of indomethacin in rats, intestinal MMP-9 activity was unchanged compared with normal rats, but significant increases in MMP-9 activity were observed 12 and 24 h after indomethacin administration. Significant increases in the small intestinal damage score were also observed 12 and 24 h after indomethacin administration. In the extract from the small intestine 24 h after indomethacin administration, the MMP-9 activation was significantly attenuated by TY-51469. Intraperitoneal injection of TY-51469 (10 mg/kg) 3 h before indomethacin administration significantly attenuated the MMP-9 activity in the small intestine compared with placebo treatment. Myeloperoxidase activity, which indicates accumulation of neutrophils, was significantly increased in the small intestine in the placebo-treated rats, but its activity was significantly attenuated by TY-51469 treatment. The area of small intestinal damage was also significantly ameliorated by TY-51469 treatment. These findings suggest that chymase-dependent MMP-9 activation has a significant role in indomethacin-induced small intestinal damage in rats.

Roles of COX inhibition in pathogenesis of NSAID-induced small intestinal damage

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin decrease mucosal PGE(2) content by inhibiting cyclooxygenase (COX) activity and produce damage in the small intestine. The development of intestinal lesions induced by indomethacin was accompanied by increases in intestinal motility, enterobacterial invasion, and myeloperoxidase (MPO) as well as inducible nitric oxide synthase (iNOS) activity, together with the up-regulation of COX-2 and iNOS mRNA expression. Neither SC-560, a selective COX-1 inhibitor, nor rofecoxib, a selective COX-2 inhibitor, alone caused intestinal damage, but their combined administration provoked lesions in the small intestine. SC-560, but not rofecoxib, caused intestinal hypermotility, bacterial invasion and the expression of COX-2 as well as iNOS mRNA, yet the iNOS and MPO activity was increased only when rofecoxib was administered together with SC-560. Although SC-560 inhibited PG production, the level of PGE(2) recovered in a rofecoxib-dependent manner. The intestinal hypermotility in response to indomethacin was prevented by both 16,16-dimethyl PGE(2) and atropine but not by ampicillin, yet all these agents inhibited not only the bacterial invasion but also the expression of COX-2 as well as the iNOS activity in the intestinal mucosa following indomethacin treatment, thereby preventing the intestinal damage. These results suggest that inhibition of COX-1, despite causing intestinal hypermotility, bacterial invasion and iNOS expression, up-regulates the expression of COX-2, and the PGE(2) derived from COX-2 counteracts the deleterious events caused by COX-1 inhibition and maintains mucosal integrity. These sequences of events explain why intestinal damage occurs when both COX-1 and COX-2 are inhibited.

Sildenafil, an inhibitor of phosphodiesterase subtype 5, prevents indomethacin-induced small-intestinal ulceration in rats via a NO/cGMP-dependent mechanism

We examined the effect of sildenafil, an inhibitor of phosphodiesterase subtype 5, that catalyzes hydrolysis of 3',5'-cyclic guanosine monophosphate (cGMP), on indomethacin-induced small-intestinal ulceration in rats and investigated the mechanism of this action, especially in relation to endogenous nitric oxide (NO). Animals without fasting were given indomethacin (10 mg/kg) s.c. and then killed 24 h later. Indomethacin produced hemorrhagic lesions in the small intestine, accompanied by a promotion of enterobacterial invasion and the expression of inducible NO synthase (iNOS) as well as myeloperoxidase (MPO) activity in the mucosa. Sildenafil (3-20 mg/kg), given p.o. 30 min before indomethacin, dose-dependently reduced the severity of these lesions, with concomitant suppression of the increase in MPO activity, iNOS expression and bacterial invasion. These effects were attenuated by the prior administration of the nonselective NOS inhibitor, N (G)-nitro-L-arginine methyl ester, in an L-arginine-reversible manner. Indomethacin also decreased the secretion of mucus and fluid (enteropooling) and enhanced intestinal motility, but these responses were all prevented by the prior administration of sildenafil. Likewise, pretreatment of the animals with NOR-3, a NO donor, also reversed the functional changes caused by indomethacin, followed by suppression of bacterial invasion and iNOS expression, and prevented the development of intestinal lesions. These results suggest that sildenafil prevents indomethacin-induced small-intestinal ulceration in rats, via a NO/cGMP-dependent mechanism, and this effect is functionally associated with an increase in the secretion of mucus/fluid and a decrease of hypermotility, resulting in the suppression of bacterial invasion and iNOS expression following indomethacin treatment.

TNF-alpha modulates iNOS expression in an experimental rat model of indomethacin-induced jejunoileitis

Multiple mucosal immune factors, such as TNF-alpha and IL-1beta, are thought to be key mediators involved in inflammatory bowel disease. We evaluated the role of the pro-inflammatory cytokine TNF-alpha on nitric oxide synthase (NOS) expression in indomethacin-induced jejunoileitis in rats. Jejunoileitis was induced in rats with subcutaneous injections of indomethacin (7.5 mg/kg) 24 h apart for two consecutive days, and animals were randomized into four groups. Group 1 received only indomethacin. Group 2 was treated with a daily dose of phosphodiesterase (PDE) inhibitor (theophylline or pentoxifylline) by oral gavage for 2 days before and 4 days after indomethacin. Group 3 received a single dose of anti-TNF-alpha monoclonal antibody (TNF-Ab, IP) 30 min before indomethacin. Group 4 was treated with 1 h hyperbaric oxygenation (HBO(2)) for 5 days after indomethacin. Rats were sacrificed at 12 h or 4 days after final indomethacin injection. PDE inhibitor, TNF-Ab, or HBO(2) treatment significantly decreased indomethacin-induced ulceration, myeloperoxidase activity, and disease activity index. Although indomethacin significantly increased serum TNF-alpha and nitrate/nitrite (NOx) concentrations above control values at 12 h, inducible NOS (iNOS) expression was detected only at day 4. Serum IL-1beta levels did not change at 12 h but increased 4-fold after 4 days. Indomethacin had no effect on constitutive NOS. Treatment with PDE inhibitor, TNF-Ab, or HBO(2) significantly reduced serum/tissue TNF-alpha, IL-1beta, NOx, and iNOS expression. Our data show TNF-alpha plays an early pro-inflammatory role in indomethacin-induced jejunoileitis. Additionally, down-regulation of NOx by PDE inhibitors, TNF-Ab, or HBO(2) suggests that TNF-alpha modulates iNOS expression.

Visceral pain hypersensitivity in functional gastrointestinal disorders

INTRODUCTION

Functional gastrointestinal disorders (FGIDs) are a highly prevalent group of heterogeneous disorders whose diagnostic criteria are symptom based in the absence of a demonstrable structural or biochemical abnormality. Chronic abdominal pain or discomfort is a defining characteristic of these disorders and a proportion of patients may display heightened pain sensitivity to experimental visceral stimulation, termed visceral pain hypersensitivity (VPH).

SOURCES OF DATA

We examined the most recent literature in order to concisely review the evidence for some of the most important recent advances in the putative mechanisms concerned in the pathophysiology of VPH.

AREAS OF AGREEMENT

VPH may occur due to anomalies at any level of the visceral nociceptive neuraxis. Important peripheral and central mechanisms of sensitization that have been postulated include a wide range of ion channels, neurotransmitter receptors and trophic factors. Data from functional brain imaging studies have also provided evidence for aberrant central pain processing in cortical and subcortical regions. In addition, descending modulation of visceral nociceptive pathways by the autonomic nervous system, hypothalamo-pituitary-adrenal axis and psychological factors have all been implicated in the generation of VPH.

AREAS OF CONTROVERSY

Particular areas of controversy have included the development of efficacious treatment of VPH. Therapies have been slow to emerge, mainly due to concerns regarding safety.

GROWING POINTS

The burgeoning field of genome wide association studies may provide further evidence for the pleiotropic genetic basis of VPH development.

AREAS TIMELY FOR DEVELOPING RESEARCH

Tangible progress will only be made in the treatment of VPH when we begin to individually characterize patients with FGIDs based on their clinical phenotype, genetics and visceral nociceptive physiology.

Role of nitric oxide in the gastrointestinal tract

Worldwide osteoarthritis (OA) affects more than 9.6% of men and 18% of women older that 60 years. Treatment for OA often requires chronic use of selective or nonselective nonsteroidal anti-inflammatory drugs (NSAIDs), which have been associated with gastrointestinal and cardiovascular complications. An increased risk for upper gastrointestinal bleeding with NSAIDs alone and when combined with low-dose aspirin has been described in numerous studies. Although cyclo-oxygenase-2 inhibitors have been shown to carry a lower risk for gastrointestinal injury than nonselective NSAIDs, research continues to identify new treatments that not only are effective but also provide an improved benefit/risk profile, including better gastrointestinal tolerability. Nitric oxide (NO) is known to have a protective effect on the gastrointestinal tract. In preclinical studies NO was shown to help maintain gastric mucosal integrity, to inhibit leukocyte adherence to the endothelium, and to repair NSAID-induced damage. In addition, epidemiologic studies have shown that the use of NO-donating agents with NSAIDs or aspirin resulted in reduced risk for gastrointestinal bleeding. Recent studies have shown that cyclo-oxygenase inhibiting NO-donating drugs (CINODs), in which a NO molecule is chemically linked to an NSAID, are effective anti-inflammatory agents and may result in less gastrointestinal damage than is associated with NSAID use. Therefore, these agents provide a potential therapeutic option for patients with arthritis who require long-term NSAID therapy.

Prophylactic effect of irsogladine maleate against indomethacin-induced small intestinal lesions in rats

The effect of irsogladine maleate, a widely used antiulcer drug in Japan, on indomethacin-induced small intestinal lesions was examined in rats. Animals without fasting were given indomethacin (10 mg/kg, s.c.) and sacrificed 24 h later. Irsogladine (1-10 mg/kg) or 16,16-dimethyl prostaglandin E2 (dmPGE2 0.03 mg/kg) was given p.o. twice, 0.5 before and 6 h after indomethacin, while ampicillin (800 mg/kg) was given twice, 18 and 0.5 h before. Indomethacin caused severe lesions in the small intestine, mainly the jejunum and ileum, accompanied by intestinal hypermotility, the up-regulation of inducible nitric oxide synthase (iNOS) expression, and an increase of myeloperoxidase (MPO) activity as well as enterobacterial invasion in the mucosa. These events were all prevented by both dmPGE2 and ampicillin, except the intestinal hypermotility which was only prevented by dmPGE2. Likewise, irsogladine also significantly and dose-dependently prevented these lesions at > 1 mg/kg. This agent alone increased mucus secretion and significantly suppressed the decreased mucus response to indomethacin, resulting in a suppression of the bacterial invasion as well as the increase in MPO activity and iNOS expression. The protective effect of irsogladine was mimicked by isobutylmethylxanthine, a nonselective inhibitor of phosphodiesterase (PDE), as well as rolipram, a selective PDE4 inhibitor. These results suggest that irsogladine protects the small intestine against indomethacin-induced lesions, and this effect may be associated with the increased mucus secretion, probably due to the inhibitory actions of PDE, resulting in suppression of enterobacterial invasion and iNOS expression.

5-aminosalicylic acid improves indomethacin-induced enteropathy by inhibiting iNOS transcription in rats

Nitric oxide has been implicated in the pathogenic mechanism of inflammatory bowel disease states. We evaluated indomethacin-induced enteropathy in rats, in relation to the expression of the inducible isoform of NO synthase (iNOS) using aminosalicylic acid (5-ASA), its isomer 4-ASA (10 or 50 mg/kg/day, po), and dexamethasone, an iNOS transcription inhibitor (3 mg/kg/day, sc). Enteropathy was induced by indomethacin (7.5 mg/kg/day, sc) for two days and the small intestine was examined for lesions over the next 14 days. Indomethacin-induced small-intestinal ulcer size, mucosal myeloperoxidase activity, iNOS expression and serum nitrite/nitrate levels were maximally increased by day 4 and gradually decreased by day 14. Treatment with 5-ASA, but not 4-ASA, decreased indomethacin-induced ulcer length, myeloperoxidase activity, serum nitrite/nitrate levels and iNOS expression at day 4. Dexamethasone had a greater effect than 5-ASA in reducing myeloperoxidase activity and ulcer length by 26 and 32%, respectively. Dexamethasone also reduced serum nitrate/nitrite and iNOS expression to their basal levels. In conclusion, inhibition of iNOS expression by 5-ASA appears to be associated with diminished intestinal ulceration in indomethacin-induced enteropathy.