Webb McKnight

Cyclooxygenase 1 contributes to inflammatory responses in rats and mice: Implications for gastrointestinal toxicity

BACKGROUND & AIMS Selective inhibitors of cyclooxygenase (COX)-2 are being developed as gastrointestinal-sparing anti-inflammatory drugs based on the premise that this isoform is solely responsible for prostaglandin synthesis at sites of inflammation, whereas COX-1 produces prostaglandins important for maintenance of mucosal integrity. We investigated the relationship between suppression of inflammation by COX-2 inhibitors (NS-398, nimesulide, DuP697, and etodolac) and their effects on gastric prostaglandin synthesis. METHODS Effects of pretreatment of rats with drugs with a range of in vitro selectivity for COX-2 vs. COX-1 on carrageenan-induced paw inflammation were assessed, along with extent of suppression of COX-1 and COX-2. The role of COX-1 in inflammation was also assessed in COX-2-deficient mice. RESULTS Significant anti-inflammatory effects were only observed at doses of the drugs that inhibited COX-1. At these doses, the drugs also significantly suppressed gastric prostaglandin synthesis and elicited gastric mucosal erosions. The degree of suppression of prostaglandin synthesis at the site of inflammation correlated significantly with inhibition of COX-1 but not COX-2. CONCLUSIONS COX-1 makes an important contribution to inflammatory responses. To achieve desirable anti-inflammatory effects, COX-2 inhibitors needed to be given at doses in which selectivity was lost, leading to suppression of gastric prostaglandin synthesis and to mucosal injury.

Novel nonsterodial anti-inflammatory drug derivatives with markedly reduced ulcerogenic properties in the rat

BACKGROUND/AIMS The use of nonsteroidal anti-inflammatory drugs (NSAIDs) is limited by their ability to induce gastrointestinal injury. Two NSAIDs were modified by incorporation of an nitroxybutyl moiety. The short-term ulcerogenic and anti-inflammatory properties of these derivatives were compared with the native NSAIDs. METHODS Rats were given flurbiprofen, ketoprofen, or their respective derivatives, and the extent of gastric damage and effect on gastric prostaglandin E2 synthesis was assessed. The damage-promoting effects of these compounds were also compared following twice-daily administration for 1 week. Anti-inflammatory properties were examined using a carrageenan-induced paw edema model. RESULTS The derivatives of flurbiprofen and ketoprofen caused significantly less short-term gastric mucosal injury at all doses tested, despite producing comparable suppression of prostaglandin synthesis. The NSAID derivatives also showed comparable anti-inflammatory activity to the native compounds. The flurbiprofen derivative inhibited collagen-induced platelet aggregation significantly more than the native NSAID. Plasma nitrate/nitrite levels increased significantly following administration of the flurbiprofen derivative, consistent with release of a nitrogen oxide. CONCLUSIONS Addition of a nitroxybutyl moiety to two NSAIDs markedly reduced the ability of these agents to induce short-term gastric injury but did not interfere with their ability to suppress inflammatory processes, inhibit prostaglandin synthesis, or inhibit platelet aggregation. These NSAID derivatives may therefore represent a novel class of anti-inflammatory drugs with markedly less ulcerogenic effects on the stomach.

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.

Proton Pump Inhibitors Exacerbate NSAID-Induced Small Intestinal Injury by Inducing Dysbiosis

BACKGROUND & AIMS Proton pump inhibitors (PPIs) and nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used classes of drugs, with the former frequently coprescribed to reduce gastroduodenal injury caused by the latter. However, suppression of gastric acid secretion by PPIs is unlikely to provide any protection against the damage caused by NSAIDs in the more distal small intestine. METHODS Rats were treated with antisecretory doses of omeprazole or lanzoprazole for 9 days, with concomitant treatment with anti-inflammatory doses of naproxen or celecoxib on the final 4 days. Small intestinal damage was blindly scored, and changes in hematocrit were measured. Changes in small intestinal microflora were evaluated by denaturing gradient gel electrophoresis and reverse-transcription polymerase chain reaction. RESULTS Both PPIs significantly exacerbated naproxen- and celecoxib-induced intestinal ulceration and bleeding in the rat. Omeprazole treatment did not result in mucosal injury or inflammation; however, there were marked shifts in numbers and types of enteric bacteria, including a significant reduction (∼80%) of jejunal Actinobacteria and Bifidobacteria spp. Restoration of small intestinal Actinobacteria numbers through administration of selected (Bifidobacteria enriched) commensal bacteria during treatment with omeprazole and naproxen prevented intestinal ulceration/bleeding. Colonization of germ-free mice with jejunal bacteria from PPI-treated rats increased the severity of NSAID-induced intestinal injury, as compared with mice colonized with bacteria from vehicle-treated rats. CONCLUSIONS PPIs exacerbate NSAID-induced intestinal damage at least in part because of significant shifts in enteric microbial populations. Prevention or reversal of this dysbiosis may be a viable option for reducing the incidence and severity of NSAID enteropathy.

Endogenous and exogenous hydrogen sulfide promotes resolution of colitis in rats.

BACKGROUND & AIMS Hydrogen sulfide (H(2)S) is an endogenous gaseous mediator of mucosal defense with antiinflammatory effects that promote ulcer healing. The effects of H(2)S during the pathogenesis of colitis have not been established. We analyzed the contribution of H(2)S to inflammation and ulceration of the colon in a rat model of colitis. METHODS Colitis was induced by intracolonic administration of trinitrobenzene sulfonic acid. The ability of the colon to synthesize H(2)S was studied over the course of the resolution of the colitis. Expression of 2 enzymes involved in the synthesis of H(2)S and the effects of inhibitors of these enzymes were examined. We also examined the effects of H(2)S donors on the resolution of colitis. RESULTS The capacity for the colon to produce H(2)S increased markedly over the first days after induction of colitis and then declined toward control levels as the colitis was resolved. Inhibition of colonic H(2)S synthesis markedly exacerbated the colitis, resulting in significant mortality. Inhibition of H(2)S synthesis in healthy rats resulted in inflammation and mucosal injury in the small intestine and colon along with down-regulation of cyclooxygenase-2 messenger RNA expression and prostaglandin synthesis. Intracolonic administration of H(2)S donors significantly reduced the severity of colitis and reduced colonic expression of messenger RNA for the proinflammatory cytokine tumor necrosis factor alpha. CONCLUSIONS In rats, H(2)S modulates physiological inflammation and contributes to the resolution of colitis.

NO-naproxen vs. naproxen: ulcerogenic, analgesic and anti-inflammatory effects

Background: A novel class of nitric oxide‐releasing nonsteroidal anti‐inflammatory drug (NO‐NSAID) derivatives has recently been described which exert anti‐inflammatory activities but produce significantly less gastrointestinal injury than the parent NSAID from which they are derived. The present studies were performed to determine if a nitroxybutylester derivative of naproxen was less ulcerogenic to the gastrointestinal tract than its parent NSAID, and if it exerted comparable analgesic and anti‐inflammatory properties to the parent NSAID.

Hydrogen sulfide enhances ulcer healing in rats

Hydrogen sulfide is an endogenous mediator that relaxes vascular smooth muscle, exhibits several antiinflammatory activities, and contributes to gastric mu‐cosal defense. This study was performed to examine the role of hydrogen sulfide in the resolution of injury; specifically, the healing of gastric ulcers. Ulcers were induced in rats by serosal application of acetic acid. This elicited a marked increase in gastric expression of the two key enzymes in hydrogen sulfide synthesis (cystathionine‐β‐synthase and cystathionine‐γ‐lyase) and in hydrogen sulfide synthesis. Twice‐daily treatment for a week with hydrogen sulfide donors significantly increased the extent of healing of gastric ulcers as compared to vehicle‐treatment. Similar treatment with L‐cysteine, a precursor for hydrogen sulfide, also accelerated healing of the ulcers, and the effect was abolished by cotreatment with an inhibitor of cystathionine‐γ‐lyase. The beneficial effects of hydrogen sulfide on ulcer healing were not dependent on nitric oxide synthesis, nor did they appear to occur through activation of ATP‐sensitive K+ channels. These results suggest that hydrogen sulfide is produced in the gastric mucosa in response to injury and acts to promote healing. The results further suggest that drugs releasing hydrogen sulfide could be employed to accelerate healing of gastric ulcers, and possibly of other wounds.— Wallace J. L., Dicay, M., McKnight, W., Martin G. R. Hydrogen sulfide enhances ulcer healing in rats. FASEB J. 21, 4070–4076 (2007)

Anti-thrombotic effects of a nitric oxide-releasing, gastric-sparing aspirin derivative.

Effects of a nitroxybutylester derivative of aspirin (NCX 4215) on platelet aggregation and prostanoid synthesis were compared to the effects of aspirin. NCX 4215 was approximately seven times more potent than aspirin as an inhibitor of thrombin-induced human platelet aggregation in vitro, but did not inhibit platelet thromboxane synthesis or gastric prostaglandin synthesis. NCX 4215 released nitric oxide when incubated in the presence of platelets and increased platelet levels of cGMP within 10 min of exposure, while aspirin did not. The anti-aggregatory effects of NCX 4215 in vitro were significantly attenuated by 10 microM hemoglobin. In ex vivo studies of ADP- or collagen- or thrombin-induced rat platelet aggregation, aspirin and NCX 4215 had comparable inhibitory effects 3 h after administration. Aspirin (10-120 mg/kg) caused extensive hemorrhagic erosion formation in the stomach of the rat within 3 h of oral administration, while NCX 4215 did not produce significant damage at doses of up to 300 mg/kg, nor when given daily for two weeks at 166 mg/kg. NCX 4215 did not alter systemic arterial blood pressure when administered intravenously to the rat. These studies demonstrate that NCX 4215 has comparable or enhanced anti-thrombotic activity to that of aspirin, but does not cause gastric damage or alter systemic blood pressure. The anti-thrombotic actions of NCX 4215 are, at least in part, due to generation of nitric oxide.

Limited anti-inflammatory efficacy of cyclo-oxygenase-2 inhibition in carrageenan-airpouch inflammation

Cyclo‐oxygenase‐2 (COX‐2) is expressed at sites of inflammation and is believed to be the major source of inflammation‐associated prostaglandin synthesis. Selective inhibition of COX‐2 has been suggested to produce anti‐inflammatory effects with reduced toxicity in the gastrointestinal tract. We examined the extent to which suppression of COX‐2 led to inhibition of various components of inflammation in the carrageenan‐airpouch model in the rat. Indomethacin (0.3 mg kg−1), nimesulide (3 mg kg−1) and the selective COX‐2 inhibitor, SC‐58125 (0.3 mg kg−1), significantly suppressed the production of prostaglandin E2 at the site of inflammation. At higher doses, indomethacin (1 mg kg−1) and nimesulide (30 mg kg−1), but not SC‐58125 (up to 10 mg kg−1), significantly inhibited COX‐1 activity (as measured by whole blood thromboxane synthesis). All three test drugs significantly reduced the volume of exudate in the airpouch, but only at doses greater than those required for substantial (>90%) suppression of COX‐2 activity. Similarly, reduction of leukocyte infiltration was only observed with the doses of indomethacin and nimesulide that caused significant suppression of COX‐1 activity. SC‐58125 did not significantly affect leukocyte infiltration into the airpouch at any dose tested (up to 10 mg kg−1). A second selective COX‐2 inhibitor, Dup‐697, was also found to suppress exudate PGE2 levels without significant effects on leukocyte infiltration. These results indicate that selective inhibition of COX‐2 results in profound suppression of PGE2 synthesis in the carrageenan‐airpouch, but does not affect leukocyte infiltration. Exudate volume was only reduced with the highly selective COX‐2 inhibitor when a dose far above that necessary for suppression of COX‐2 activity was used. Inhibition of leukocyte infiltration was observed with indomethacin and nimesulide, but only at doses that inhibited both COX‐1 and COX‐2.

Wound collagen deposition in rats: effects of an NO-NSAID and a selective COX-2 inhibitor

Selective cyclo‐oxygenase (COX)‐2 inhibitors and nitric oxide‐releasing nonsteroidal anti‐inflammatory drugs (NSAIDs) exhibit reduced toxicity in the gastrointestinal tract, but may affect wound healing in other tissues. In this study, we have compared the effects of a selective COX‐2 inhibitor (celecoxib), a nitric‐oxide releasing derivative of naproxen (HCT‐3012) and naproxen in a model of wound collagen deposition in the rat. Polyvinyl alcohol sponges were implanted subcutaneously in rats. The rats were treated daily for 5 days with the test drugs at equieffective anti‐inflammatory doses. Naproxen (10 mg kg−1) significantly decreased (45%) collagen deposition at the wound site relative to the vehicle‐treated control group. In contrast, HCT‐3012 (14.5 mg kg−1) significantly increased (62%) collagen deposition, while celecoxib (10 mg kg−1) had no effect. Naproxen and HCT‐3012 suppressed prostaglandin (PG) E2 levels at the wound site and whole blood thromboxane synthesis to similar degrees. Celecoxib had no significant effect on wound fluid PGE2 levels, but slightly reduced whole blood thromboxane synthesis (by 17%). COX‐1 mRNA and protein were expressed in the wound exudate, the skin surrounding the wound and in normal skin. In contrast, COX‐2 mRNA, but not protein, was expressed in wound and normal skin. These results demonstrate that HCT‐3012 can significantly enhance collagen deposition at a wound site, despite inhibiting prostaglandin synthesis to the same extent as the parent drug. Nitric oxide‐releasing NSAIDs may represent a safer alternative to standard NSAIDs for use as anti‐inflammatory and analgesic agents by post‐surgery patients.