Anti-inflammatory activity of myricetin-3-O-beta-D-glucuronide and related compounds

OBJECTIVE AND DESIGN: The anti-inflammatory effect of myricetinglucuronide (MGL) was investigated and structurally-related compounds were compared to examine the structure/activity-relationship in carrageenan-induced rat paw edema. MATERIALS AND SUBJECTS: In vitro studies were performed using rat basophilic leukemia (RBL-1) cells, human polymorphonuclear leukocytes (PMNL), COX-1 from ram seminal vesicle, COX-2 from sheep placenta and human venous blood. For the in vivo tests male Wistar rats were used, for the ex vivo test perfused rabbit ears. TREATMENT: 1-300 microg/kg MGL or myricetinmethylglucuronate and 0.1-5 mg/kg other related compounds administered p.o. (carrageenan edema). 5, 50 and 150 microg/kg MGL p.o. for 14 days (Freund's adjuvant arthritis), 5 and 50 microg/kg p.o. for 6 days (ulceration). METHODS: Anti-inflammatory effects were measured in carrageenan edema and in adjuvant arthritis. Incidence of gastric lesions was tested in an ulcerogenicity model in vivo. Influence on COX was determined in the perfused rabbit ear, in PMNL and in a test assay using COX-1 and COX-2. 5-LOX activity was studied using PMNL and RBL-1. The influence on platelet aggregation was evaluated measuring light transmission. RESULTS: MGL exerted a marked and dose-dependent anti-inflammatory effect in acute (carrageenan edema, ED50 15 microg/kg, indomethacin ED50 10 mg/kg) and chronic (adjuvant arthritis, inhibition at 150 microg/kg 18.1 % left paw, 20.6% right paw, indomethacin 3 mg/kg 18.0% and 19.4%)) models of inflammation. In the perfused rabbit ear 1 microg MGL inhibited the release of PGI2, PGD2 and PGE2 to the same extent as 1 microg indomethacin. The inhibition of COX-1 in the intact cell system was IC50 = 0.5 microM, that of indomethacin 0.0038 microM. In the isolated enzyme preparations of COX-1 and COX-2 the IC50 was 10 microM and 8 microM, that of indomethacin 9.2 mM and 2.4 microM. In the RBL-1 and PMNL test assay the inhibition of 5-LOX was 0.1 microM and 2.2 microM. An orally administered dose of 50 microg/kg/day induced no gastric ulcers in rats treated for 6 days. The investigations on carrageenan edema showed a close relationship between the structure of MGL and the anti-inflammatory effect. CONCLUSIONS: MGL is a COX-1, COX-2 and 5-LOX inhibitor. In view of the moderate in vitro activity and the very potent in vivo activity an additive mechanism must be involved. Small changes in the molecular structure lead to the loss or reduction of the anti-inflammatory activity.     

Effects of meloxicam, compared with other NSAIDs, on cartilage proteoglycan metabolism, synovial prostaglandin E2, and production of interleukins 1, 6 and 8, in human and porcine explants in organ culture

Some non-steroidal anti-inflammatory drugs (NSAIDs) can accelerate joint damage in osteoarthritis by enhancing the production of pro-inflammatory cytokines or inhibiting cartilage proteoglycan synthesis. Meloxicam, a new NSAID, was compared with standard NSAIDs for its effect on proteoglycan synthesis and degradation in human and porcine cartilage explants, as well as the production of prostaglandin E2 (PGE2) and interleukins 1 and 6 by human synovial tissue explants in-vitro. Meloxicam at submicromolar concentrations inhibited synovial PGE2 production but, up to therapeutic drug concentrations (< or = 4 microM), did not affect synovial production of the pro-inflammatory cytokine IL-1. In contrast, hydrocortisone, 10 microM, a positive control, inhibited release of this cytokine, and indomethacin, 100 microM, increased its production. The lack of effects of meloxicam were evident irrespective of intrinsic IL-1 bioactivity of the synovia, production of IL-1 inhibitors or time of incubation. Production of the part anti-inflammatory cytokine IL-6, was significantly increased by therapeutic concentrations of meloxicam, as well as by indomethacin. Another major pro-inflammatory cytokine, IL-8, was unaffected by therapeutic concentrations of meloxicam. Meloxicam, 0.1-4.0 microM, did not affect cartilage proteoglycan production whereas indomethacin, 100 microM, significantly reduced synthesis of these macromolecules. Thus meloxicam, at concentrations within the therapeutic range and at which pronounced inhibition of prostaglandin production is evident, affects neither cartilage proteoglycan production nor the production of those cytokines likely to be important in cartilage destruction.     

Meloxicam in acute UV dermatitis--a pilot study

The non-steroidal anti-inflammatory drug (NSAID) meloxicam is a preferential cyclooxygenase-2 (COX-2) antagonist. The UV protective potential of this drug was studied to compare it with the reported beneficial effects of such preferentially COX-1 specific NSAIDs as indomethacin and acetylsalicylic acid in the literature. In a pilot study (open-label, non-randomized, non-controlled, unblinded), 10 patients received UV irradiation with the minimal erythema dose (MED), first with meloxicam (7.5 mg/die) to reduce post-operative pain and second without ingestion of meloxicam. The factor of UV protection was evaluated. In six of ten patients meloxicam showed no benefit, whereas four of ten patients had a 1.3- up to 3-fold UV protection. In this study, the benefit in UV protection of meloxicam as a preferential COX-2 antagonist was not above the reported benefit of the "old" COX-1 inhibiting NSAIDS.     

Selective inhibition of cyclooxygenase-2 by NS-398 in endotoxin shock rats in vivo

OBJECTIVE AND DESIGN: The role of cyclooxygenase (COX)-2 was examined using a rat endotoxin shock model and the potency and selectivity of NS-398, a COX-2 selective inhibitor in vitro, for COX-2 activity was examined in vivo. MATERIAL: Male Wistar rats (weighing 140-180 g) were used. METHODS: Lipopolysaccharide (LPS, 1 mg/kg, i.v.) was administered to rats (LPS-treated rats) and expression of COX-1 mRNA and COX-2 mRNA in the aorta and peripheral blood leukocytes was examined by RT-PCR. COX activity was assessed by measuring the plasma 6-keto prostaglandin (PG) F1 alpha, PGE2 and thromboxane (TX)B2 30s after administration of arachidonic acid (AA, 3 mg/kg, i.v.), NS-398 (0.3-100 mg/kg, p.o.) or indomethacin (0.3-3 mg/kg, p.o.) was administered 1 h before the AA injection. RESULTS: COX-2 mRNA was detectable in the aorta and peripheral blood leukocytes at least from 3 to 9 h after the LPS injection but not in non-LPS-treated rats. Plasma 6-keto PGF1 alpha, PGE2 and TXB2 levels after AA injection into LPS-treated rats were significantly enhanced compared to findings in non-LPS-treated rats. NS-398 showed significant inhibition of the increase in PGs in LPS-treated rats, the ED50 values being 0.35 mg/kg for 6-keto PGF1 alpha, 1.5 mg/kg for PGE2 and < 0.3 mg/kg for TXB2. NS-398 even at 100 mg/kg did not significantly suppress the increased PGs levels in non-LPS-treated rats. In contrast, indomethacin significantly inhibited plasma PGs levels after AA injection into LPS-treated rats and non-LPS-treated rats. The ED50 values in LPS-treated rats, determined by 6-keto PGF1 alpha, PGE2 and TXB2 production, were 1.0, 1.3 and 2.3 mg/kg and those in non-LPS-treated rats were 0.42, 0.24 and 0.93 mg/kg, respectively. CONCLUSIONS: In a rat endotoxin shock model, expression of COX-2 plays a role in an increase in COX activity. NS-398 showed preferential inhibitory effects on COX-2 activity in vivo. This approach is useful to directly analyze the inhibitory activity of NSAIDs for COX-1 and COX-2 in vivo.     

Role of spinal cyclooxygenase (COX)-2 on thermal hyperalgesia evoked by carageenan injection in the rat

Prostaglandins, which are known to play an important role in the nociceptive transmission in the spinal cord, are produced by cyclooxygenase (COX). Two forms of COX have been identified, COX-1 (constitutive form) and COX-2 (a form highly inducible in response to inflammatory stimuli). COX-2 mRNA was reported to be expressed in the brain in normal rats in the absence of inflammation. We investigated the role of spinal COX-2 in the maintenance of thermal hyperalgesia induced by paw carageenan injection in the rat using NS-398, a selective COX-2 inhibitor. Intrathecally administered NS-398 attenuated the level of thermal hyperalgesia in a dose-dependent manner. This suggested that spinal COX-2 plays an important role in the maintenance of thermal hyperalgesia induced by paw carageenan injection.     

Gastrointestinal tolerability of meloxicam compared to diclofenac in osteoarthritis patients. International MELISSA Study Group. Meloxicam Large-scale International Study Safety Assessment

Although widely used, non-steroidal anti-inflammatory drugs (NSAIDs) are associated with a high incidence of gastrointestinal (GI) side-effects. Inhibition of the cyclooxygenase (COX) enzyme is the basis for both the efficacy and toxicity of NSAIDs. The discovery of two COX isoforms, constitutive COX-1 and inducible COX-2, has led to the hypothesis that selective inhibition of COX-2 will minimize the potential for GI toxicity without compromising efficacy. The Meloxicam Large-scale International Study Safety Assessment (MELISSA) trial reported here was therefore set up to investigate the tolerability of meloxicam, a preferential inhibitor of COX-2, compared to diclofenac. MELISSA was a large-scale, double-blind, randomized, international, prospective trial, conducted over 28 days in patients with symptomatic osteoarthritis. Patients received either meloxicam 7.5 mg or diclofenac 100 mg slow release, the recommended doses for the treatment of osteoarthritis. Evaluation of the profile of adverse events was the main aim of the trial, together with assessment of efficacy. A total of 9323 patients received treatment (4635 and 4688 in the meloxicam and diclofenac groups, respectively). Significantly fewer adverse events were reported by patients receiving meloxicam. This was attributable to fewer GI adverse events (13%) compared to diclofenac (19%; P < 0.001). Of the most common GI adverse events, there was significantly less dyspepsia (P < 0.001), nausea and vomiting (P < 0.05), abdominal pain (P < 0.001) and diarrhoea (P < 0.001) with meloxicam compared to diclofenac. Five patients on meloxicam experienced a perforation, ulcer or bleed vs seven on diclofenac (not significant). No endoscopically verified ulcer complication was detected in the meloxicam group compared to four with diclofenac. There were five patient days of hospitalization in patients on meloxicam compared to 121 with diclofenac. Adverse events caused withdrawal from the study in 254 patients receiving meloxicam (5.48%) compared to 373 (7.96%) on diclofenac (P < 0.001). These differences were attributable to differences in reported GI adverse events (3.02% on meloxicam vs 6.14% on diclofenac; P < 0.001). Differences in efficacy, as assessed by visual analogue scales, consistently favoured diclofenac. In all instances, 95% confidence intervals did not cross zero, suggesting a statistically significant effect. However, differences were small (4.5-9.01% difference) and did not reach pre-determined levels of clinical significance. Nevertheless, significantly more patients discontinued meloxicam because of lack of efficacy (80 out of 4635 vs 49 out of 4688; P < 0.01). The MELISSA trial confirms earlier studies suggesting that meloxicam has a significantly improved GI tolerability profile in comparison with other NSAIDs, including diclofenac. These results may in part reflect the preferential COX-2 selectivity of meloxicam, although the dose and other aspects of tolerability may be important. These results may provide support for the hypothesis that selective inhibition of COX-2 relative to COX-1 might be an effective approach towards improved NSAID therapy.     

Tumor necrosis factor-alpha promotes sustained cyclooxygenase-2 expression: attenuation by dexamethasone and NSAIDs

Prostaglandin (PG) release is characteristic of most inflammatory diseases. The committed step in the formation of free arachidonic acid into PG products is catalyzed by cyclooxygenase (COX, prostaglandin H2 synthase, PGHS), which exists as two genetically distinct isoforms. COX-1 is constitutively expressed and produces PGs and thromboxane A2 during normal physiologic activities, while COX-2 is an inducible enzyme stimulated by growth factors, lipopolysaccharide, and cytokines during inflammation or cell injury. Proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) released into the amniotic fluid in the setting of infection have been proposed to signal amnion and decidual cells to produce PGs that may culminate in preterm labor. However, since the molecular control of this phenomenon has not been established, this study used amnion-derived WISH cells to determine if TNF-alpha promoted the formation of PGs through COX-2 activity. Treatment of WISH cells with TNF-alpha (0.1 ng/mL-100 ng/mL) caused a dose-dependent increase in COX-2 expression and the subsequent biosynthesis of PGE2 that persisted for at least 48 hrs. In contrast, COX-1 mRNA and protein levels were unaltered by TNF-alpha treatment as determined by RT-PCR and immunoblot analysis, respectively. TNF-alpha-stimulated COX-2 expression and the subsequent formation of PGE2 were inhibited by dexamethasone (0.1 microM). In addition, indomethacin (1 microM) and the novel COX-2-selective inhibitor, NS-398 (IC50 approximately 1.1 x 10(-9) M), attenuated TNF-alpha-elicited PGE2 production. Results presented here demonstrate that TNF-alpha elicits prolonged and regulatable induction of COX-2 in WISH cells, while COX-1 is constitutively expressed and unchanged in response to TNF-alpha stimulation.     

Effects of cyclooxygenase-2 selective and nitric oxide-releasing nonsteroidal antiinflammatory drugs on mucosal ulcerogenic and healing responses of the stomach

Effects of selective cyclooxygenase-2 (COX-2) inhibitors (NS-398) and nitric oxide (NO) -releasing aspirin (NO-ASA) on gastric ulcerogenic and healing responses were examined in comparison with nonselective COX inhibitors such as indomethacin and aspirin (ASA). Hypothermic stress (28-30 degrees C, 4 hr) induced gastric lesions in anesthetized rats with an increase of acid secretion. The lesions induced by hypothermic stress were markedly worsened by subcutaneous administration of both indomethacin and ASA but were not affected by either NS-398 or NO-ASA, although the increased acid secretion during hypothermia was not affected by any of the drugs. On the other hand, the healing of gastric ulcers induced in mice by thermal cauterization (70 degrees C, 15 sec) was significantly delayed by daily subcutaneous administration of indomethacin and ASA as well as NS-398, but not by NO-ASA. COX-2 mRNA was not detected in the intact mucosa but was positively expressed in the ulcerated mucosa, most potently on day 3 after ulceration. Prostaglandin contents in the intact mouse stomach were reduced by indomethacin, ASA, and NO-ASA, while the increased prostaglandin generation in the ulcerated mucosa was inhibited by all drugs including NS-398. After subcutaneous administration of NO-ASA to pylorus-ligated rats and mice, high amounts of NOx were detected in both the gastric contents and serum. In addition, both NS-398 and NO-ASA showed an equipotent antiinflammatory effect against carrageenan-induced paw edema in rats as compared with indomethacin and ASA. These results suggest that both indomethacin and ASA not only increased the mucosal ulcerogenic response to stress but impaired the healing response of gastric ulcers as well. The former action was due to inhibition of COX-1, while the latter effect was accounted for by inhibition of COX-2 and was mimicked by the COX-2-selective inhibitor NS-398. NO-ASA, although it inhibited both COX-1 and COX-2 activity, had no deleterious effects on gastric ulcerogenic and healing responses.     

Measurement of cyclooxygenase inhibition in vivo: a study of two non-steroidal anti-inflammatory drugs in sheep

The anti-inflammatory effects of the non-steroidal anti-inflammatory drugs phenylbutazone (PBZ) and flunixin meglumine (FM) and the relationship between the effects and drug concentration in vivo were studied using a subcutaneous tissue-cage model in sheep. Intracaveal injection of carrageenan induced prostaglandin (PG) E2 production in tissue-cage exudate (maximal concentration, 101 nM) with significant increases in white blood cell (WBC) numbers, skin temperature over the inflamed cage and exudate leukotriene B4 (LTB4) concentration (P < 0.05). Intravenous PBZ, 4.4 mg kg-1 produced mild inhibition of exudate PGE2 generation (10%), but greater inhibition of serum TXB2 (75.3%). The IC50 for TXB2 was 36.0 microM. Phenylbutazone did not alter effects on skin temperature, WBC numbers or exudate LTB4 concentrations. Intravenous FM, 1.1 mg kg-1, significantly inhibited carrageenan-induced exudate PGE2 formation (Emax, 100%, IC50, < 0.4 nM) and serum TXB2 generation (Emax, 100%, IC50, 17 nM) for up to 32 h. Flunixin meglumine significantly inhibited the rise in skin temperature but had a limited effect on exudate WBC. Phenylbutazone and FM have distinct effects on carrageenan-induced cyclooxygenase (COX-2) and platelet COX (COX-1). Flunixin meglumine was a more potent COX inhibitor than PBZ and was more selective for the inducible form of COX in vivo.     

The foot in hereditary motor and sensory neuropathies in children

We investigated the regulation of COX-2 expression and activity by adenosine receptors in rat microglial cells. The selective adenosine A2a-receptor agonist CGS21680 and the non-selective adenosine A1- and A2-receptor agonist 5'-N-ethylcarboxiamidoadenosine (NECA) induced an increase in COX-2 mRNA levels and the synthesis of prostaglandin E2 (PGE2). The adenosine A1-receptor agonist cyclopentyladenosine (CPA) was less potent, and the adenosine A1-receptor-specific agonist N6-2-(-aminophenylo)ethyladenosine (APNEA) showed only marginal effects. Microglia expressed adenosine A1-, A2a-, and A3-, but not A2b-receptor mRNAs, whereas astroglial cells expressed adenosine A2b- but not A2a-receptor mRNA. The adenosine A2a-receptor selective antagonist (E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxanthine (KF17837) inhibited both CGS21680-induced COX-2 expression and PGE2 release. CGS21680-increased PGE2 levels were inhibited by dexamethasone, by the nonsteroidal antiinflammatory drug meloxicam, and by the adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536). CGS21680 and NECA both increased intracellular cAMP levels in microglial cells. Dibutyryl cAMP as well as forskolin induced the release of PGE2. The results strongly suggest that adenosine A2a-receptor-induced intracellular signaling events cause an up-regulation of the COX-2 gene and the release of PGE2. Apparently, the cAMP second messenger system plays a crucial role in COX-2 gene regulation in rat microglial cells. The results are discussed with respect to neurodegenerative disorders of the CNS such as Alzheimer's disease, in which activated microglia are critically involved and COX inhibitors may be of therapeutic benefit.     

Effects of indomethacin and iloprost on contraction of the afferent arterioles by endothelin-1 in juxtamedullary nephron preparations from normotensive Wistar-Kyoto and spontaneously hypertensive rats

The contractile effects of endothelin-1 on the afferent arterioles of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) and the modulation of these responses by cyclooxygenase blockade or by the prostacyclin analog iloprost were investigated. For this, the preglomerular vasculature was visualized by using the juxtamedullary nephron preparation. Endothelin-1 (100 pM-1 microM) induced concentration-dependent reduction of afferent diameters either in WKY and SHR kidneys, which were inhibited by 1 microM nifedipine, indicating its dependence on extracellular calcium. After incubation with 20 microM indomethacin, the endothelin-1-induced contractions were potentiated in WKY but abolished in SHR vessels. These results could be explained if endothelin-1 is releasing vasodilator prostanoids in WKY, whereas in SHR preparations, vasoconstrictor prostanoids predominate. The prostacyclin analog iloprost (1 nM-1 microM) did not modify basal diameters of the WKY afferent arterioles, whereas a weak vasodilatatory effect was observed in the SHR afferent vasculature. Both in WKY and SHR preparations, iloprost (10 nM-1 microM) abolished the afferent contractility by endothelin-1, this effect being more prominent in SHR. We conclude that a defective production of vasodilator prostanoids or an enhanced release of vasoconstrictor cyclooxygenase derivatives may determine the renovascular effects of endothelins in SHR kidneys.     

Inhibition of cyclooxygenase-2 rapidly reverses inflammatory hyperalgesia and prostaglandin E2 production

PGs derived from cyclooxygenase-2 (COX-2), in particular PGE2, play important roles in the initiation of inflammation and pain. In the present study, we evaluated the role of COX-2-derived PGE2 in an animal model of established hyperalgesia. Inflammation and hyperalgesia were first induced by injection of carrageenan into rat footpads. Then we investigated the effects of subsequent therapeutic treatment with a selective COX inhibitor, with a nonsteroidal anti-inflammatory drug and with anti-PGE2 antibody. Test compounds were administered 1 to 3 hr after carrageenan challenge, and inhibition of pain (hyperalgesia, measured by withdrawal from a thermal stimulus), and changes in paw edema and PG levels were evaluated. The i.v. administration of a nonselective COX inhibitor, ketorolac, caused a rapid reduction in hyperalgesia in the inflamed footpad, returning it to near-normal values within 1 hr. Normal (control) paw response times were not affected. Therapeutic administration of ketorolac prevented most further swelling caused by carrageenan but did not reverse edema already present at the time of dosing. Administered p.o., a selective COX-2 inhibitor (SC-58635) was as efficacious as ketorolac in reducing inflammatory hyperalgesia. Footpad PG levels returned to base line or below within 5 min of dosing with ketorolac, which suggests rapid turnover of PG in the inflamed tissue. Therapeutic treatment with a monoclonal anti-PGE2 antibody also fully reversed the hyperalgesia response. These studies suggest that continuous production of PGE2 by the COX-2 enzyme is a critical element in sustaining the hyperalgesic response at sites of tissue inflammation.     

Involvement of calcitonin gene-related peptide (CGRP) receptors in insulin-induced vasodilatation in mesenteric resistance blood vessels of rats

1. The vascular effect of insulin in the mesenteric resistance blood vessel and the role of calcitonin generelated peptide (CGRP)-receptor in insulin-induced vascular responsiveness were investigated in rats. 2. The mesenteric vascular beds isolated from Wistar rats were perfused with Krebs solution, and perfusion pressure was measured with a pressure transducer. In preparations contracted by perfusion with Krebs solution containing methoxamine in the presence of guanethidine, the perfusion of insulin (from 0.1 to 3000 nM) caused a concentration-dependent decrease in perfusion pressure due to vasodilatation. The pD2 value and maximum relaxation (%) were 6.94+/-0.22 and 43.9+/-5.2, respectively. 3. This vasodilator response to insulin was unaffected by 100 nM propranolol (beta-adrenoceptor antagonist) plus 100 nM atropine (muscarinic cholinoceptor antagonist), 100 microM L-NG-nitroarginine (nitric oxide synthase inhibitor), 1 microM ouabain (Na+-K+ ATPase inhibitor), or 1 microM glibenclamide (ATP sensitive K+-channel inhibitor). 4. In preparations without endothelium, perfusion of insulin produced a marked vasodilatation. The pD2 value and maximum relaxation (%) were 7.62+/-0.21 and 81.0+/-4.6, respectively, significantly greater than in preparations with intact endothelium. 5. The vasodilator responses to insulin in the preparations without endothelium were significantly inhibited by CGRP[8 37], a CGRP receptor antagonist, whereas pretreatment with capsaisin, a toxin for CGRP-containing nerves, did not affect insulin-induced vasodilatation. 6. These results suggest that insulin induces non-adrenergic, non-cholinergic and endothelium-independent vasodilatation, which is partially mediated by CGRP receptors.     

Meloxicam inhibits the growth of colorectal cancer cells

Cyclooxygenase-2 has been reported to play an important role in colorectal carcinogenesis. The effects of meloxicam (a COX-2 inhibitor) on the growth of two colon cancer cell lines that express COX-2 (HCA-7 and Moser-S) and a COX-2 negative cell line (HCT-116) were evaluated. The growth rate of these cells was measured following treatment with meloxicam. HCA-7 and Moser-S colony size were significantly reduced following treatment with meloxicam; however, there was no significant change in HCT-116 colony size with treatment. In vivo studies were performed to evaluate the effect of meloxicam on the growth of HCA-7 cells when xenografted into nude mice. We observed a 51% reduction in tumor size after 4 weeks of treatment. Analysis of COX-1 and COX-2 protein levels in HCA-7 tumor lysates revealed a slight decrease in COX-2 expression levels in tumors taken from mice treated with meloxicam and no detectable COX-1 expression. Here we report that meloxicam significantly inhibited HCA-7 colony and tumor growth but had no effect on the growth of the COX-2 negative HCT-116 cells.     

Structural basis for selective inhibition of cyclooxygenase-2 by anti-inflammatory agents

Prostaglandins and glucocorticoids are potent mediators of inflammation. Non-steroidal anti-inflammatory drugs (NSAIDs) exert their effects by inhibition of prostaglandin production. The pharmacological target of NSAIDs is cyclooxygenase (COX, also known as PGH synthase), which catalyses the first committed step in arachidonic-acid metabolism. Two isoforms of the membrane protein COX are known: COX-1, which is constitutively expressed in most tissues, is responsible for the physiological production of prostaglandins; and COX-2, which is induced by cytokines, mitogens and endotoxins in inflammatory cells, is responsible for the elevated production of prostaglandins during inflammation. The structure of ovine COX-1 complexed with several NSAIDs has been determined. Here we report the structures of unliganded murine COX-2 and complexes with flurbiprofen, indomethacin and SC-558, a selective COX-2 inhibitor, determined at 3.0 to 2.5 A resolution. These structures explain the structural basis for the selective inhibition of COX-2, and demonstrate some of the conformational changes associated with time-dependent inhibition.