Susan N. Elliott

A nitric oxide-releasing nonsteroidal anti-inflammatory drug accelerates gastric ulcer healing in rats

BACKGROUND & AIMS Nonsteroidal anti-inflammatory drugs (NSAIDs) have well-characterized inhibitory effects on gastric ulcer healing. A new class of gastrointestinal-sparing, nitric oxide-releasing NSAID derivatives has been recently described. This study was performed to determine if one of these compounds (nitrofenac) would influence healing of a preexisting ulcer. METHODS Seven days after induction of gastric ulcer with serosal acetic acid, daily oral treatment with antiinflammatory doses of diclofenac, nitrofenac, or vehicle was started. After 7 days of treatment, the ulcer area was measured. The effects of misoprostol and two drugs that show in vitro selectivity for inhibiting cyclooxygenase 2 (nabumetone and L745,337) were also assessed. RESULTS Diclofenac, nabumetone, and L745,337 had no effect on ulcer healing when compared with vehicle. Only diclofenac significantly decreased hematocrit and weight gain. On the other hand, nitrofenac significantly accelerated healing. Glyceryl trinitrate also significantly and dose dependently accelerated healing. Nitrofenac suppressed cyclooxygenase 1 activity to a similar extent as diclofenac. CONCLUSIONS These results show that an NO-releasing NSAID derivative and an NO donor could accelerate ulcer healing, whereas a standard NSAID, misoprostol, and two inhibitors of cyclooxygenase 2 had no effect. In addition to sparing the gastrointestinal tract, NO-releasing NSAIDs, despite suppressing cyclooxygenase activity, are capable of accelerating tissue repair.

Platelets modulate gastric ulcer healing: Role of endostatin and vascular endothelial growth factor release

Bleeding and delayed healing of ulcers are well recognized clinical problems associated with the use of aspirin and other nonsteroidal antiinflammatory drugs, which have been attributed to their antiaggregatory effects on platelets. We hypothesized that antiplatelet drugs might interfere with gastric ulcer healing by suppressing the release of growth factors, such as vascular endothelial growth factor (VEGF), from platelets. Gastric ulcers were induced in rats by serosal application of acetic acid. Daily oral treatment with vehicle, aspirin, or ticlopidine (an ADP receptor antagonist) was started 3 days later and continued for 1 week. Ulcer induction resulted in a significant increase in serum levels of VEGF and a significant decrease in serum levels of endostatin (an antiangiogenic factor). Although both aspirin and ticlopidine markedly suppressed platelet aggregation, only ticlopidine impaired gastric ulcer healing and angiogenesis as well as reversing the ulcer-associated changes in serum levels of VEGF and endostatin. The effects of ticlopidine on ulcer healing and angiogenesis were mimicked by immunodepletion of circulating platelets, and ticlopidine did not influence ulcer healing when given to thrombocytopenic rats. Incubation of human umbilical vein endothelial cells with serum from ticlopidine-treated rats significantly reduced proliferation and increased apoptosis, effects reversed by an antibody directed against endostatin. Ticlopidine treatment resulted in increased platelet endostatin content and release. These results demonstrate a previously unrecognized contribution of platelets to the regulation of gastric ulcer healing. Such effects likely are mediated through the release from platelets of endostatin and possibly VEGF. As shown with ticlopidine, drugs that influence gastric ulcer healing may do so in part through altering the ability of platelets to release growth factors.

Selective cyclo-oxygenase-2 inhibition with celecoxib elevates blood pressure and promotes leukocyte adherence

Selective inhibitors of cyclo‐oxygenase‐2 have been shown to be effective anti‐inflammatory drugs with reduced gastrointestinal toxicity relative to conventional nonsteroidal anti‐inflammatory drugs (NSAIDs). In the present study, we examined the possibility that selective COX‐2 inhibition, by blocking prostacyclin synthesis, would increase blood pressure and cause leukocyte adherence and platelet aggregation. Normal rats and rats with hypertension induced by chronic administration of Nω‐nitro‐L‐arginine methylester were given celecoxib (10 mg kg−1) daily for 3 weeks. Celecoxib significantly elevated of blood pressure in both the normal and hypertensive rats (mean increase of >33 mm Hg after 3 weeks). In normal rats, celecoxib had no effect on serum 6‐keto prostaglandin (PG)F1α levels. Hypertensive rats exhibited a significant increase (82%) in serum 6‐keto PGF1α levels, and this was reduced to the levels of normal rats by treatment with celecoxib. Rats treated with celecoxib exhibited significant increases in weight gain (20%), plasma arginine‐vasopressin levels (148%) and plasma urea (69%) relative to vehicle‐treated controls. Plasma creatinine levels were unaffected by treatment with celecoxib, while plasma renin levels were significantly decreased (30%) relative to controls. Superfusion of mesenteric venules with celecoxib (3 μM) in vivo resulted in significant increases in leukocyte adherence to the endothelium in both normal and hypertensive rats. These studies suggest that suppression of COX‐2 significantly influences vascular and/or renal function, leading to elevated blood pressure and leukocyte adherence.

Bacteria rapidly colonize and modulate healing of gastric ulcers in rats

The stomach is generally regarded as an environment that is not conducive to bacterial colonization. In this study, we examined the possibility that this changes significantly when an ulcer has formed and that colonization of ulcers interferes with the normal healing process. Gastric ulcers were induced by serosal application of acetic acid. The relationship between ulcer healing and bacterial colonization was examined. The effects of antibiotics, induction of Lactobacilluscolonization, and selective colonization with an antibiotic resistant strain of Escherichia coli on ulcer healing were examined. Within 6-12 h of their induction, gastric ulcers were colonized by a variety of bacteria, with gram-negative bacteria predominating. Suppression of colonization with antibiotics resulted in marked acceleration of healing. Induction of Lactobacillus colonization also accelerated ulcer healing. The beneficial effects of antibiotics were reversed through selective colonization with antibiotic-resistant E. coli. Bacterial colonization occurred irrespective of the method used to induce the ulcer. This study demonstrates that colonization of gastric ulcers in rats occurs rapidly and significantly impairs ulcer healing. This effect appeared to be primarily attributable to gram-negative bacteria.The stomach is generally regarded as an environment that is not conducive to bacterial colonization. In this study, we examined the possibility that this changes significantly when an ulcer has formed and that colonization of ulcers interferes with the normal healing process. Gastric ulcers were induced by serosal application of acetic acid. The relationship between ulcer healing and bacterial colonization was examined. The effects of antibiotics, induction of Lactobacillus colonization, and selective colonization with an antibiotic resistant strain of Escherichia coli on ulcer healing were examined. Within 6-12 h of their induction, gastric ulcers were colonized by a variety of bacteria, with gram-negative bacteria predominating. Suppression of colonization with antibiotics resulted in marked acceleration of healing. Induction of Lactobacillus colonization also accelerated ulcer healing. The beneficial effects of antibiotics were reversed through selective colonization with antibiotic-resistant E. coli. Bacterial colonization occurred irrespective of the method used to induce the ulcer. This study demonstrates that colonization of gastric ulcers in rats occurs rapidly and significantly impairs ulcer healing. This effect appeared to be primarily attributable to gram-negative bacteria.

NITRIC OXIDE : A REGULATOR OF MUCOSAL DEFENSE AND INJURY

Abstract: There is an abundance of evidence that nitric oxide plays a critical role in regulating several components of gastrointestinal mucosal defense. Suppression of nitric oxide synthesis increases susceptibility to injury, while administration of nitric oxide donors increases resistance to injury. On the other hand, nitric oxide has been implicated as a mediator of tissue injury in the gastrointestinal tract during inflammatory reactions. In these cases, the nitric oxide is generally believed to be derived from an inducible isoform of nitric oxide synthase. In this review, we provide an overview of the evidence for and against these dual roles of nitric oxide in modulating gastrointestinal mucosal defense and injury. We also highlight the potential therapeutic benefits that may be realized through modulation of tissue nitric oxide levels.

Alendronate induces gastric injury and delays ulcer healing in rodents

Gastric ulceration associated with the use of NSAIDs is most frequently observed in elderly women, the same sector of society most likely to be receiving therapy for osteoporosis. As some anti-osteoporosis medications have been suggested to irritate the upper gastrointestinal mucosa, we evaluated the ability of one such drug, alendronate, to damage the gastric mucosa and to influence the severity and healing of gastric ulcers in rodents. The effects of alendronate on indomethacin-induced antral ulceration was evaluated in the rabbit, while effects on ulcer healing and on the formation of gastric erosions was evaluated in the rat. Effects of alendronate on gastric acid secretion, blood flow and prostaglandin synthesis were also evaluated. Alendronate caused erosions in the rabbit stomach, but not antral ulceration. However, at the highest doses tested (80 mg) alendronate increased the incidence and size of indomethacin-induced antral ulcers. Alendronate also enhanced indomethacin-induced gastric damage in the rat, and delayed gastric ulcer healing. These effects of alendronate were not attributable to changes in gastric acid secretion, blood flow, prostaglandin synthesis or the pharmacokinetics of indomethacin. The damaging effects of alendronate on the stomach were due to topical irritant effects and could be observed at concentrations as low as 4 mg/ml within 30 min of oral administration or topical superfusion. These results support preliminary clinical evidence that alendronate can damage the gastric mucosa. While gastric injury may be a rare occurrence in patients taking this drug, concomitant use of alendronate and NSAIDs may increase the incidence or severity of ulceration.

Neutrophil-Mediated Gastrointestinal Injury

Inflammatory diseases of the gastrointestinal tract are frequently characterized by a dense infiltration of neutrophils in the lamina propria and the subsequent transepithelial migration of these cells into the lumen. While the neutrophil plays an essential role in defending against bacterial infection, it can also cause significant injury to the host tissue. The evidence for a role of neutrophils in producing significant tissue injury in a number of gastrointestinal disorders and the mechanisms through which neutrophils produce tissue injury are reviewed. Furthermore, the evidence that some commonly used anti-inflammatory drugs produce beneficial effects through modulation of neutrophil extravasation or activation is reviewed.

Reduction of gastrointestinal injury in acute endotoxic shock by flurbiprofen nitroxybutylester

Nitric oxide has been reported to have paradoxical effects in experimental endotoxic shock, contributing to the hemodynamic consequences of endotoxin administration, but apparently protecting the gastrointestinal mucosa. A novel class of nitric oxide-releasing nonsteroidal anti-inflammatory drug (NSAID) derivatives has recently been described which exert anti-inflammatory activities but produce significantly less gastrointestinal injury than the parent nonsteroidal anti-inflammatory drugs from which they are derived. Thus, the present study was performed to determine the effects of one of these derivatives, flurbiprofen 4-nitroxybutylester, compared to the native nonsteroidal anti-inflammatory drug, flurbiprofen, in an experimental model of endotoxic shock. Intravenous administration of endotoxin from Salmonella typhosa to rats pretreated with flurbiprofen produced a profound decrease in systemic arterial blood pressure, an increase in hematocrit and extensive gastric and small intestinal damage. In rats pretreated with flurbiprofen 4-nitroxybutylester, endotoxin produced comparable changes in blood pressure and hematocrit to those seen in rats treated with flurbiprofen; however, the severity of gastrointestinal damage was significantly reduced. Gastric blood flow was profoundly decreased following endotoxin administration, but was significantly higher in rats pretreated with flurbiprofen 4-nitroxybutylester than in rats pretreated with flurbiprofen. These results demonstrate that despite not affecting the acute systemic effects of endotoxin administration, flurbiprofen 4-nitroxybutylester is capable of protecting the gastrointestinal mucosa from injury, possibly through preservation of mucosal blood flow.

Gastrointestinal-sparing anti-inflammatory drugs: The development of nitric oxide-releasing NSAIDs

Nonsteroidal anti‐inflammatory drugs (NSAIDs) are among the most widely prescribed medications, but their use continues to be limited by significant toxicity, particularly in the gastrointestinal tract and kidney. Better understanding of the pathogenesis of these adverse effects has led to the development of a series of derivatives of standard NSAIDs that are not only less toxic but more efficacious. The coupling of a nitric oxide‐releasing moiety to a range of NSAIDs greatly reduces their ability to induce gastrointestinal damage, and greatly increases their tolerability in situations in which there is preexisting gastrointestinal inflammation. There is also evidence that these compounds are much better tolerated by the kidney. On the other hand, the analgesic and anti‐thrombotic properties of NO‐releasing NSAIDs significantly exceed those of the parent drugs. These compounds appear to represent a significant advance in the treatment of inflammation and pain and for prophylaxis of thrombotic conditions. Drug Dev. Res. 42:144–149, 1997.