Inflammatory mediator changes in cotton-top tamarins (CTT) after SC-41930 anti-colitic therapy

Use of the CTT model provides insight into the inflammatory mediator contribution in the pathogenesis of idiopathic colitis. To evaluate anti-colitic efficacy, the leukotriene B₄ receptor antagonist and anti-inflammatory agent, SC-41930, was administered (10 mg/kg BW by gavage BID) for 8 weeks to CTTs with histologically confirmed persistent and defined active colitis. The inflammatory mediators LTB₄, PGE₂, TXB₂, and PAF were assayed in colonic dialysate that was collected after 11/2 h from four CTTs pre-, mid-, and post-treatment, frozen at −70°C, and analyzed by RIA after HPLC purification. LTB₄ levels were lower at mid- and post-treatment and had little inter-animal variation post-treatment. PGE₂ and PAF levels were elevated during SC-41930 treatment, but there was a trend towards lower thromboxane B₂ levels. Reduced LTB₄ (PMN degranulation and chemotaxis) and increased PGE₂ (mucosal-protective effect) may, in part, explain the observed efficacy of SC-41930 in active tamarin colitis.

     

The design and synthesis of second generation leukotriene B4 (LTB4) receptor antagonists related to SC-41930

SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid, is a selective, orally active, LTB₄ receptor antagonist currently in clinical trials for psoriasis and ulcerative colitis. Exhaustive SAR studies found a potential backup compound, SC-50605, which was 7–16 times more potent than SC-41930 in LTB₄ receptor binding, chemotaxis and degranulation assays. SC-50605 also inhibited LTB₄-induced intradermal chemotaxis in cavine skin at an oral dose of 0.10 mg/kg and displayed good activity in animal models of colitis and epidermal inflammation both orally and topically.     

The effect of leukotriene-B4 receptor antagonist,SC-41930, on acetic acid-induced colonic inflammation

SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid, is a potentin vitro leukotriene-B₄ (LTB₄) receptor antagonist. LTB₄ levels are elevated in colonic tissue of inflammatory bowel disease (IBD) patients which may account for the high degree of neutrophil (PMN) infiltration. The guinea pig acetic acid-induced colonic inflammation model has characteristics of IBD including PMN infiltration, edema, ulceration and necrosis. The model was used to evaluate the effect of SC-41930. SC-41930 was given orally, 30 min before and after intrarectal administration of 3% acetic acid. The PMN marker enzyme, myeloperoxidase, was measured along with histological evaluation to assess inflammation. Both parameters showed significantly less inflammation in SC-41930 treated animals with an oral ED₅₀ of 20 mg/kg. These study results with an LTB₄ receptor antagonist indicate a role for LTB₄ in colonic inflammation and that an LTB₄ receptor antagonist may be beneficial for treatment of IBD.     

Effects of SC-41930 on leukocyte adherence and emigration in rat mesenteric venules

This study demonstrates that SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid, an orally active LTB₄ receptor antagonist, reduces LTB₄-induced leukocyte adhesion and emigration in rat mesenteric venules. The mesentery of Sprague-Dawley rats was prepared for intravital microscopic examination and venules of 25–35 m were chosen for evaluation. In control animals, LTB₄ (20nM) was superfused over the mesentery for 30 min. In the treatment group SC-41930 (5 M) was superfused for 30 min, followed by a 30 min superfusion with SC-41930 and LTB₄. The LTB₄-induced increase in leukocyte adherence and emigration in postcapillary venules was significantly attenuated by pretreatment with SC-41930. Other experiments demonstrated that platelet-activating-factor-induced leukocyte adherence was not affected by SC-41930. These results indicate that SC-41930 is a potent inhibitor of LTB₄-induced leukocyte-endothelial cell adhesive interactions in postcapillary venules.     

Leukotriene B4-induced granulocyte trafficking in guinea pig dermis

Leukotriene B₄ (LTB₄) is a proinflammatory product of arachidonic acid metabolism that has teen implicated as a mediator in a number of inflammatory diseases. When injected intradermally into the guinea pig, LTB₄ elicits a dose-dependent migration (chemotaxis) of neutrophils (PMNs) into the injection sites as assessed by the presence of a neutrophil marker enzyme myeloperoxidase. SC-41930 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8-propyl-2H-1 -benzopyran-2-carboxylic acid, a first-generation LTB₄ receptor antagonist inhibitedthe chemotactic actions of LTB₄ when coadministered into the dermal site and when given orally with ED₅₀ values of 340 ng and 1.7 mg/kg, respectively. The secondgeneration LTB₄ receptor antagonists SC-50605 7-[3-[2(cyclopropylmethyl)-3-methoxy-4-(4-thiazolyl)phenoxy] propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid and SC-51146 7-[3-[2(cyclopropylmethyl)-3-methoxy-4-[(methylamino)carbonyl]phenoxy]propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran2-propanoic acid inhibited LTB₄-induced chemotaxis when coadministered with ED₅₀ values of 70 ng and 32 ng, respectively, and when given intragastrically with ED₅₀ values of 0.10 and 0.09 mg/kg, respectively. SC-41930, SC-50605, and SC-51146 had oral durations of action of 5.5, 15, and 21 h, respectively. These potent, LTB₄ receptor antagonists may well have application in the medical management of disease states such as asthma, rheumatoid arthritis, inflammatory bowel disease, contact dermatitis, and psoriasis, where LTB₄ is implicated as an inflammatory mediator.     

SC-41930, a leukotriene B4 receptor antagonist,inhibits 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) binding to epidermal cells

SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxyl]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid, a potent leukotriene-B₄ (LTB₄) receptor antagonist, inhibitsin vivo 12-hydroxyei-cosatetraenoic acid (12-HETE)-induced neutrophil infiltration, suggesting a potential 12-HETE receptor antagonist effect, as well. Since 12-HETE is assumed to have a pathophysiological role in inflammatory skin diseases, and epidermal cells possess high affinity binding sites for 12(S)-HETE, we studied the effect of SC-41930 on 12(S)-HETE binding to the human epidermal cell line, SCL-II. SC-41930 antagonized the 12(S)-HETE binding to SCL-II cells with a Ki of 480 nM. This Ki value is similar to that obtained for the inhibition of LTB₄ binding to human neutrophils. Our results show that SC-41930, in addition to its LTB₄ receptor antagonist effect, exhibits 12-HETE receptor antagonist effect as well, and therefore may be of benefit in skin diseases with elevated 12-HETE levels.Dr. Kemény is on leave from the Department of Dermatology, Albert Szent-Györgyi Medical University, Szeged, Hungary, as a recipient of the Humboldt Fellowship, and his work was supported by the Alexander von Humboldt Foundation.     

Effect of the leukotriene B4 receptor antagonist,SC-41930, on experimental allergic encephalomyelitis (EAE) in the guinea pig

The accepted model for the human demyelinating disease, multiple sclerosis (MS), is experimental allergic encephalomyelitis (EAE). We assessed the ability of SC-41930(7-[3(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxyl acid), to modulate the symptoms of acute EAE generated in guinea pigs. Animals were pretreated with SC-41930 (20 mg/kg, i.p.) for two days followed by thrice-weekly maintenance. At day 52, a significant number of the SC-41930-treated animals were alive as compared to EAE alone. Control animals had an increase in body weight while EAE animals lost over 20% (p<0.5) of their body weight by day 18. SC-41930-treatment significantly reduced, but did not completely inhibit the cachectic response. The results indirectly implicate LTB₄ in the pathogenesis of EAE. Agents that modify this model be useful in the treatment of human MS.     

Inflammation of guinea pig dermis

Neutrophil (PMNL) infiltration is a prominent feature of human psoriasis. Psoriatic skin lesions contain abnormally high amounts of leukotriene B₄ (LTB₄), itself a potent PMNL chemoattractant both in vivo and in vitro. SC-41930 {7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8-propyl-2H-1-benzo-pyran-2-carboxylic acid}, an orally active LTB₄ receptor antagonist, was tested topically in models of skin inflammation induced by 200 nmol of the calcium ionophore A23187 or 200g phorbol-12-myristate-13-acetate (PMA) applied topically to the guinea pig ear as assessed by ear weight, levels of the PMNL marker enzyme myeloperoxidase (MPO), and histological examination (PMA model) at 4 and 18 h respectively. When coapplied topically with A23187 or PMA, SC-41930 significantly inhibited epidermal inflammation with ED₅₀ values of 0.6 and 4 mg, respectively. SC-41930 treatment also was associated with lowered dermal LTB₄ levels in both models. The PMA-induced skin inflammation model also was assessed histologically and revealed acanthosis, edema, PMNL infiltration, and rete ridge prominence as long as 96 h after a single application that was completely inhibited by SC-41930 topical coapplication. Furthermore, oral treatment (40 mg/kg) significantly reduced edema and inflammatory cell infiltration in both models. These models possess many of the characteristics of human psoriasis, and agents such as SC-41930 that demonstrate activity in these models may well have therapeutic utility in the treatment of human psoriasis.     

Antiinflammatory effects of second-generation leukotriene B4 receptor antagonist,SC-53228: Impact upon Leukotriene B4- and 12(R)-HETE- mediated events

Leukotriene B₄ (LTB₄) and 12(R)-hydroxyeicosatetraenoic acid [12(R)-HETE] are proinflammatory products of arachidonic acid metabolism that have been implicated as mediators in a number of inflammatory diseases. When injected intradermally into the guinea pig, LTB₄ and 12(R)-HETE elicit a dose-dependent migration (chemotaxis) of neutrophils (PMNs) into the injection sites as assessed by the presence of a neutrophil marker enzyme myeloperoxidase. SC-41930 {7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxyl]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid}, a first-generation LTB₄ receptor antagonist, inhibited the chemotactic actions of LTB₄ when given orally with an ED₅₀ value of 1.7 mg/kg. The second-generation LTB₄ receptor antagonist, SC-53228 [(+)-(S)-7-(3-{2-(cyclopropylmethyl)-3-methoxy-4-[(methylamino)carbonyl]phenoxy} propoxy)-3,4-dihydro-8-propyl-2H-1-benzopyran-2-propanoic acid], inhibited LTB₄-induced chemotaxis when given intragastrically with an ED₅₀ value of 0.07 mg/kg. Furthermore, SC-53228 inhibited 12(R)-HETE-induced granulocyte chemotaxis with an oral ED₅₀ value of 5.8 mg/kg. When dosed orally over a range of 0.03–100 mg/kg, SC-53228 gaveC _max plasma concentrations of 0.015–41.1g/ml. SC-53228 inhibited LTB₄-primed membrane depolarization of human neutrophils with an IC₅₀ value of 34 nM. As a potent LTB₄ receptor antagonist, SC-53228 may well have application in the medical management of disease states such as asthma, rheumatoid arthritis, inflammatory bowel disease, contact dermatitis, and psoriasis, in which LTB₄ and/or 12(R)-HETE are implicated as inflammatory mediators.     

Effect of a leukotriene B4 receptor antagonist on leukotriene B4-induced neutrophil chemotaxis in cavine dermis

Leukotriene B₄ (LTB₄) is a proinflammatory product of arachidonic acid metabolism that has been implicated as a mediator in a number of inflammatory diseases. When injected intradermally into the cavine, LTB₄ elicits a dose-dependent immigration (chemotaxis) of neutrophils (PMNs) into the injection sites as assessed by the presence of a neutrophil marker enzyme myeloperoxidase. SC-41930 {7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8-propyl-2H-l-benzopyran-2-carboxylic acid, a potent LTB₄ receptor antagonist inhibited the chemotactic actions of LTB₄ when coadministered into the dermal site and when given intravenously or orally with ED₅₀ values of 200 ng, 0.5 mg/kg, and 0.6 mg/ kg respectively. This compound may well have application in disease states, such as inflammatory bowel disease and psoriasis, where LTB₄ is implicated as a proinflammatory mediator.     

15-HETE is the main eicosanoid formed by human colonic mucosa

Eicosanoids were measured in colonic biopsies from eleven patients with active ulcerative colitis and from thirteen controls. Eicosanoid formation was measured after the addition of arachidonic acid and stimulation with calcium ionophore A23187. The 15-lipoxygenase derivative 15-hydroxy-eicosatetraenoic acid (15-HETE) was the predominant product formed in all biopsies. The amount of 15-HETE formed was dependent on the site of biopsy and decreased in the controls in biopsies taken in an aboral direction in the colon. The formation of 15-HETE and that of prostaglandin E₂ (PGE₂) and PGF_2α was proportional to the histologically obtained inflammation score. The role of 15-H(P)ETE as a mediator in ulcerative colitis should, therefore, be considered in addition to the effects of known modulators such as leukotriene B₄ (LTB₄) and PGE₂.     

15-HETE is the main eicosanoid formed by human colonic mucosa

Eicosanoids were measured in colonic biopsies from eleven patients with active ulcerative colitis and from thirteen controls. Eicosanoid formation was measured after the addition of arachidonic acid and stimulation with calcium ionophore A23187. The 15-lipoxygenase derivative 15-hydroxy-eicosatetraenoic acid (15-HETE) was the predominant product formed in all biopsies. The amount of 15-HETE formed was dependent on the site of biopsy and decreased in the controls in biopsies taken in an aboral direction in the colon. The formation of 15-HETE and that of prostaglandin E₂ (PGE₂) and PGF₂ was proportional to the histologically obtained inflammation score. The role of 15-H(P)ETE as a mediator in ulcerative colitis should, therefore, be considered in addition to the effects of known modulators such as leukotriene B₄ (LTB₄) and PGE₂.     

Eicosanoid production in rheumatoid synovitis

Leukotriene B₄ (LTB₄) synthesis in rheumatoid synovitis was studied using peripheral and synovial fluid polymorphonuclear leukocytes (PMNs) and rheumatic synovial lining cells. No differences were found in LTB₄ synthesis between peripheral PMNs from healthy volunteers and rheumatoid arthritis patients. When peripheral and synovial PMNs from the same RA patient were compared, arachidonic acidinduced LTB₄ synthesis in synovial fluid PMNs was increased 1.7–7.2 fold, whereas the response to Ca ionophore A23187 stimulation was similar. This suggests 5-lipoxygenase stimulating factor(s) in inflamed joints. Rheumatic synovial lining cells in a primary cell culture produced small amounts of LTB₄, the concentrations being less than 0.1 per cent of those of prostaglandin E₂ (PGE₂). PGE₂ synthesis in synovial cells was increased when arachidonic acid or interleukin-1 was added to the culture, whereas LTB₄ production remained unaltered. The present results suggest that in inflamed joints LTB₄ originates mainly from PMNs whereas synovial lining cells are the source for PGE₂.     

Are leukotrienes or PAF involved in hyperbaric oxygen toxicity?

Several very selective leukotriene inhibitors, and a PAF inhibitor, suitable forin vivo use, have been tested for their effects on hyperbaric oxygen toxicity.The leukotriene D₄ inhibitor, L660 771, and the 5-lipoxygenase pathway inhibitor L663 563, failed to affect convulsions or lung damage induced by hyperbaric oxygen (pressure range 515–615 kPa) in either rats or mice. The specific PAF antagonist L659 989 showed marginal protection against hyperoxic convulsions and did not alter pulmonary damage. The specific LTB₄ antagonist SC-41930 was very effective in inhibiting hyperbaric oxygen-induced convulsions in both rats and mice. SC-41930 also very significantly protected rats against pulmonary oxygen toxicity, but had only marginally significant effects on pulmonary protection in mice.     

Comparative evaluation of arachidonic acid (AA)- and tetradecanoylphorbol acetate (TPA)-induced dermal inflammation

The effects of topical application of arachidonic acid (AA) or phorbol ester, tetradecanoylphorbol 13-acetate (TPA), on edema response, vascular permeability, MPO, NAG, and generation of eicosanoids were studied in two murine models of cutaneous inflammation. AA produced a short-lived edema response with a rapid onset that was associated with marked increases in levels of prostaglandins (PGE₂, 6-keto-PGF₁, PGF₂), thromboxane B₂ (TxB₂) and leukotriene B₄ (LTB₄), with smaller increases in levels of LTC₄. TPA produced a longer-lasting edema that was associated with marked influx of neutrophils and predominant formation of LTB₄ along with significant changes in levels of TxB₂. Circulating T lymphocytes have no apparent role in the acute inflammatory responses induced by either agent. Arachidonic acid-induced vascular permeability preceded the edema response and neutrophil influx, whereas TPA-induced vascular permeability paralleled the edema response and influx of neutrophils. Mast cells appear to be important in the complete expression of inflammatory response, i.e., edema, cellular influx, and vascular permeability induced by either AA or TPA, as these responses were blunted in mast cell-deficient mice. Inhibitors of CO or 5-LO attenuated inflammatory responses in both models. The LTB₄ receptor antagonist, SC-41930, inhibited the inflammatory response to TPA but had little effect on that initiated by AA. This suggests that LTB₄ is an important mediator in the phorbol ester-induced inflammatory response, whereas peptidoleukotrienes and prostaglandins regulate vascular permeability responses in the arachidonate model.     

Efficacy of recombinant granulocyte colony-stimulating factor (rhG-CSF) in experimental colitis

Inflammatory bowel disease is associated with mucosal neutrophil recruitment and activatation, mediated in part by arachidonic acid metabolites. G-CSF attenuates the immune response to sepsis and ameliorates glycogen storage disease Ib-related colitis. These actions may be effected through the shedding of neutrophil adhesion molecules, or inhibition of proinflammatory mediator synthesis. Immune complex colitis was used to evaluate the effect of rhG-CSF on colonic mucosal inflammation, neutrophil recruitment and the generation of eicosanoids. Immune complex colitis was induced in White New Zealand rabbits. Animals were pretreated with rhG-CSF either 24 h before induction, or at induction, with dosages of 50 and 200 μg/kg. rhG-CSF caused a time- and dose-dependent neutrophilia in all animals. Pretreatment with rhG-CSF resulted in increased tissue myeloperoxidase levels, despite a histologically similar mucosal polymorphonuclear cell infiltrate between treated and control colitis groups. Leukotriene B₄ (LTB₄) and thromboxane B₂ (TXB₂) dialysis fluid levels were lower in treated animals, in particular in the groups receiving two doses (LTB₄: both P < 0.01; TXB₂: both P < 0.01. Prostaglandin E₂ (PGE₂) levels in dialysis fluid of the rhG-CSF-treated animals showed no difference from controls. In this model of experimental colitis, high-dose therapy with G-CSF resulted in a marked decrease of proinflammatory mediators, but mucosal generation of the protective PGE₂ was preserved. These results suggest that prolonged high-dose therapy with G-CSF may have anti-inflammatory effects in colitis.     

Inhibitory Effects of Panduratin A on Allergy-Related Mediator Production in Rat Basophilic Leukemia Mast Cells

Immediate-type hypersensitivity is characterized by elevated levels of immunoglobulin E (IgE) and activated mast cell plays a crucial role by releasing granule contents, lipid-derived mediators, cytokines, and chemokines. To evaluate the antiallergic effects of panduratin A isolated from Boesenbergia pandurata Roxb., we determined its effects on calcium (Ca²⁺) influx, degranulation, and inflammatory mediators in calcium ionophore A23187 and phorbol 12-myristate 13-acetate (PMA)-stimulated rat basophilic leukemia (RBL-2H3) cells. Panduratin A (20???M) inhibited secretion of ??-hexosaminidase (46.69?±?9.6?%), histamine (34.32?±?2.1?%), and Ca²⁺ influx (43.84?%). Panduratin A reduced the production of prostaglandin E₂ (PGE₂, 47.58?±?3.4?%), leukotriene B₄ (LTB₄, 98.15?±?1.6?%), and the mRNA expression of cyclooxygenase-2, 5-lipoxygenase, interleukin (IL)-4, IL-13, and tumor necrosis factor-??. Furthermore, panduarin A attenuated phosphorylation of Akt, the mitogen-activated protein kinases (MAPK) extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK) expression. These results indicate that panduratin A might be useful as an agent against immediate-type hypersensitivity.     

Comparison of PGE2, 6-keto PGF1α and renin release from dog kidneys

Several renal cell types synthesize prostaglandin E₂ (PGE₂) and prostacyclin (PGI₂). To examine whether the release of these prostaglandins varies in proportion, prostaglandin synthesis was stimulated in anaesthetized dogs by renal arterial constriction, ureteral occlusion, intrarenal angiotensin II infusion and infusion of arachidonic acid, the precursor of PG synthesis. PGI₂ was measured as its stable hydrolysed product, 6-keto PGF_1α. The two former procedures raised PGE₂ release to 13 ± 2 pmol min^-1, 6-keto PGF_1α release to 5 ± 2 pmol min^-1 and renin release to 23 ± 5 μg AI min^-1, Angiotensin II infusion, reducing the renal blood flow by 30%, increased PGE₂ and 6-keto PGF_1α release only half as much as ureteral and renal arterial constriction, and exerted no significant effect on renin release. By increasing the infusion rate of angiotensin II up to 10 times, the renal blood flow remained unaltered in four dogs and fell to 50% of control in two dogs, but PGE₂ and 6-keto PGF_1α release did not increase further in any of the experiments. Arachidonic acid, infused at 40 and 160 μg kg^-1 min^-1, increased prostaglandin release in proportion to the infusion rate. At the highest infusion rate, PGE₂ release averaged 166± 37 pmol min^-1 and 6-keto PGF_1α release 98 ± 28 pmol min^-1. All procedures increased PGE₂ and 6-keto PGF_1α release in a fixed proportion of about 2.5:1, whereas renin release increased only during autoregulatory vasodilation.     

Modulation of the chemotactic properties of complement fragments C5a and C3 by the anti-inflammatory agent,SC-41930

Cleavage of the fifth component of complement yields C5a, a potent neutrophil (PMN) and eosinophil chemoattractant, and modulator of microvascular permeability. Similarly, but to a lesser degree, C3 increases vascular permeability and histamine release. SC-41930 (7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxy]-3,4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid), an orally-active antiinflammatory agent was tested in anin vivo model of dermal PMN chemotaxis induced by r-hu-C5a and hu-C3. Intradermal injection of C5a in the guinea pig resulted in a significant dose-dependent influx of PMNs at 4 hours as assessed by the dermal levels of myeloperoxidase (MPO). SC-41930 (20 mg/kg) given orally to guinea pigs with intradermal injections of 1 μg C5a significantly (p<0.001) reduced dermal MPO content. SC-41930 was less potent against C3, requiring 40 mg/kg to significantly reduce dermal MPO levels. Agents such as SC-41930, which nullify complement's proinflammatory properties, may well have therapeutic potential.     

The COX-2 inhibitor, rofecoxib, ameliorates dextran sulphate sodium induced colitis in mice

Objective: We have evaluated the efficacy of the selective cyclo-oxygenase (COX)-2 inhibitor, rofecoxib, for the prevention of experimental colitis.Material and methods: To induce colitis BALB/c mice received 5% dextran sulphate sodium (DSS) in their drinking water continuously for 7 days. Rofecoxib (2.5–10 mg/kg body weight, p.o.) was administered throughout the treatment period with DSS. Colitis was quantified by a clinical damage score, colon length, weight loss, stool consistency and rectal bleeding. Inflammatory response was assessed by neutrophil infiltration, determined by histology and myeloperoxidase (MPO) activity. Interleukin (IL)-1, prostaglandin (PG)E₂ and PGD₂ levels in colon mucosa and the immunohistochemical expression of COX-1 and –2 were also studied.Results: The COX-2 inhibitor ameliorated severe colitis, reduced the degree of inflammation through reduction of neutrophil infiltration and IL-1 levels. PGE₂, and PGD₂ synthesis were significantly reduced in DSS-treated groups. Indeed, treatment with rofecoxib diminished the lost of COX-1 caused by DSS in the crypt epithelium whereas expression of COX-2 remained unaffected.Conclusions: Rofecoxib is protective in acute DSS – induced colitis, probably by reducing neutrophil infiltration, inhibiting up-regulation of IL-1 and returning to normal COX-1 expression in the inflamed colonic mucosa.Received 19 April 2004; returned for revision 17 June 2004; accepted by I. Ahnfelt-Rønne 23 November 2004