Pharmacological and biochemical demonstration of the role of cyclooxygenase 2 in inflammation and pain

Selective neutralization of prostaglandin E2 blocks inflammation, hyperalgesia, and interleukin 6 production in vivo

The role of prostaglandin E2 (PGE2) in the development of inflammatory symptoms and cytokine production was evaluated in vivo using a neutralizing anti-PGE2 monoclonal antibody 2B5. In carrageenan-induced paw inflammation, pretreatment of rats with 2B5 substantially prevented the development of tissue edema and hyperalgesia in affected paws. The antibody was shown to bind the majority of PGE2 produced at the inflammatory site. In adjuvant-induced arthritis, the therapeutic administration of 2B5 to arthritic rats substantially reversed edema in affected paws. Anti-PGE2 treatment also reduced paw levels of IL-6 RNA and serum IL-6 protein without modifying tumor necrosis factor RNA levels in the same tissue. In each model, the antiinflammatory efficacy of 2B5 was indistinguishable from that of the nonsteroidal antiinflammatory drug indomethacin, which blocked the production of all PGs. These results indicate that PGE2 plays a major role in tissue edema, hyperalgesia, and IL-6 production at sites of inflammation, and they suggest that selective pharmacologic modulation of PGE2 synthesis or activity may provide a useful means of mitigating the symptoms of inflammatory disease.

Role of Val509 in time-dependent inhibition of human prostaglandin H synthase-2 cyclooxygenase activity by isoform-selective agents

Prostaglandin H synthase (PGHS), a key enzyme in prostanoid biosynthesis, exists as two isoforms. PGHS-1 is considered a basal enzyme; PGHS-2 is associated with inflammation and cell proliferation. A number of highly selective inhibitors for PGHS-2 cyclooxygenase activity are known. Inhibition by these agents involves an initial reversible binding, followed by a time-dependent transition to a much higher affinity enzyme-inhibitor complex, making these agents potent and poorly reversible PGHS-2 inhibitors. To investigate the PGHS-2 structural features that influence the time-dependent action of the selective inhibitors, we have constructed a three-dimensional model of human PGHS-2 by homologous modeling. Examination of the PGHS-2 model identified Val509 as a cyclooxygenase active site residue, that was not conserved in PGHS-1. Recombinant human PGHS-2 with Val509 mutated to either Ile (the corresponding residue in PGHS-1), Ala, Glu, or Lys was expressed by transient transfection of COS-1 cells to evaluate the effects of the mutations on cyclooxygenase activity and on inhibition by four agents reported to be selective for PGHS-2 (NS398, nimesulide, DuP697, and SC58125). All the recombinant proteins were of the expected mass. The mutants exhibited 45-210% of wild-type cyclooxygenase activity, with Km values for arachidonate of 2.1-7.6 microM (wild-type PGHS-2, 3.8 microM), indicating that changes in position 509 had modest effects on cyclooxygenase catalysis. Each of the agents inhibited wild-type PGHS-2 in a time-dependent fashion, and all but nimesulide did the same for the V509A mutant. In contrast, the V509E and V509I PGHS-2 mutants, like recombinant human PGHS-1, did not show time-dependent inhibition with any of the agents, and the V509K mutant responded in a time-dependent manner only to DuP697. Reversible inhibition was still observed with Val509 mutants that did not show time-dependent inhibition. Thus, the side chain structure at position 509 markedly influenced the ability of PGHS-2 to undergo the time-dependent transition without removing inhibitor or substrate binding. These results indicate that Val509 in PGHS-2 has a major role in the structural transition that underlies time-dependent inhibition by the isoform-selective agents.

Up-regulation of cyclooxygenase-2 mRNA in the rat spinal cord following peripheral inflammation

Prostaglandins (PG) have been described as mediators in spinal nociceptive processing after peripheral inflammation. Enzymes essential for PG biosynthesis, cyclooxygenase isozymes COX-1 and COX-2, have not yet been investigated in the spinal cord. In two studies on rats with adjuvant-induced peripheral inflammation levels of mRNA expression of both COX isoforms were analyzed in the lumbar section of the spinal cord using reverse transcription-polymerase chain reaction (RT-PCR) technique. We could show that mRNA of both COX isoforms is expressed constitutively in the spinal cord with COX-2 as the predominant isoform. Six hours after induction of peripheral inflammation, levels of COX-2 mRNA expression were raised significantly in respect to untreated control rats and returned to baseline within 3 days after induction of inflammation. COX-2 might therefore be regarded as the COX isozyme responsible for spinal PG release in nociceptive processing under a peripheral inflammatory stimulus.

Induction of prostaglandin endoperoxide synthase-2 in human monocytes associated with cyclo-oxygenase-dependent F2-isoprostane formation

1. The isoprostane 8-epi-prostaglandin (PG)F2 alpha is produced by free radical-catalyzed peroxidation of arachidonic acid. It may also be formed as a minor product of the cyclo-oxygenase activity of platelet PGH synthase (PGHS)-1. We investigated 8-epi-PGF2 alpha production associated with induction of the human monocyte PGHS-2 and its pharmacological modulation. 2. Heparinized whole blood samples were drawn from healthy volunteers, 48 h following oral dosing with aspirin 300 mg to suppress platelet cyclo-oxygenase activity. One ml aliquots were incubated with lipopolysaccharide (LPS: 0.1-50 micrograms ml-1) for 0-24 h at 37 degrees C. PGE2 and 8-epi-PGF2 alpha were measured in separated plasma by radioimmunoassay and enzyme immunoassay techniques. 3. Levels of both eicosanoids were undetectable (i.e. < 60 pg ml-1) at time 0. LPS induced the formation of PGE2 and 8-epi-PGF2 alpha in a time- and concentration-dependent fashion, coincident with the induction of PGHS-2 detected by Western blot analysis of monocyte lysates. After 24 h at 10 micrograms ml-1 LPS, immunoreactive PGE2 and 8-epi-PGF2 alpha averaged 10,480 +/- 4,643 and 295 +/- 140 pg ml-1 (mean +/- s.d., n = 6), respectively. 4. Dexamethasone and 5-methanesulphonamido-6-(2,4-difluorothiophenyl)-1-indano ne (L-745,337), a selective inhibitor of the cyclo-oxygenase activity of PGHS-2, reduced PGE2 and 8-epi-PGF2 alpha production in response to LPS. 5. Isolated monocytes produced PGE2 and 8-epi-PGE2 alpha in response to LPS (10 micrograms ml-1) in a time-dependent fashion. Monocyte PGE2 and 8-epi-PGF2 alpha production was largely prevented by dexamethasone (2 microM) and cycloheximide (10 micrograms ml-1) in association with suppression of PGHS-2 but not of PGHS-1 expression. 6. We conclude that the induction of PGHS-2 in human monocytes is associated with cyclo-oxygenase-dependent generation of the vasoconstrictor and platelet-agonist 8-epi-PGF2 alpha.

Nitric oxide: a key mediator in the early and late phase of carrageenan-induced rat paw inflammation

1 The role of nitric oxide (NO) derived from constitutive and inducible nitric oxide synthase (cNOS and iNOS) and its relationship to oxygen-derived free radicals and prostaglandins (PG) was investigated in a carrageenan-induced model of acute hindpaw inflammation. 2 The intraplantar injection of carrageenan elicited an inflammatory response that was characterized by a time-dependent increase in paw oedema, neutrophil infiltration, and increased levels of nitrite/nitrate (NO2-/NO3-) and prostaglandin E2(PGE2) in the paw exudate. 3 Paw oedema was maximal by 6 h and remained elevated for 10 h following carrageenan administration. The non-selective cNOS/iNOS inhibitors, NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME) given intravenously (30-300 mg kg-1) 1 h before or after carrageenan administration, inhibited paw oedema at all time points. 4 The selective iNOS inhibitors, N-iminoethyl-L-lysine (L-NIL) or aminoguanidine (AG), failed to inhibit carrageenan-induced paw oedema during the first 4 h following carrageenan administration, but inhibited paw oedema at subsequent time points (from 5-10 h). iNOS mRNA was detected between 3 to 10 h following carrageenan administration using ribonuclease protection assays. iNOS protein was first detected 6 h and was maximal 10 h following carrageenan administration as shown by Western blot analysis. Administration of the iNOS inhibitors 5 h after carrageenan (a time point where iNOS was expressed) inhibited paw oedema at all subsequent time points. Infiltrating neutrophils were not the source of iNOS since pretreatment with colchicine (2 mg kg-1) suppressed neutrophil infiltration, but did not inhibit the iNOS mRNA expression or the elevated NO2-/NO3- levels in the paw exudate. 5 Inhibition of paw oedema by the NOS inhibitors was associated with attenuation of both the NO2-/NO3- and PGE2 levels in the paw exudate. These inhibitors also reduced the neutrophil infiltration at the site of inflammation. 6 Recombinant human Cu/Zn superoxide dismutase coupled to polyethyleneglycol (PEGrhSOD; 12 x 10(3) u kg-1), administered intravenously either 30 min prior to or 1 h after carrageenan injection, inhibited paw oedema and neutrophil infiltration, but had no effect on NO2-/NO3- or PGE2 production in the paw exudate. The administration of catalase (40 x 10(3) u kg-1), given intraperitoneally 30 min before carrageenan administration, had no effect on paw oedema. Treatment with desferrioxamine (300 mg kg-1), given subcutaneously 1 h before carrageenan, inhibited paw oedema during the first 2 h after carrageenan administration, but not at later times. 7 These results suggest that the NO produced by cNOS is involved in the development of inflammation at early time points following carrageenan administration and that NO produced by iNOS is involved in the maintenance of the inflammatory response at later time points. The potential interactions of NO with superoxide anion and PG is discussed.

Introduction to eicosanoids and the gastroenteric tract

Eicosanoids are produced throughout the gastrointestinal tract and are significant mediators of physiologic and pathophysiologic processes. Understanding the precise role(s) of specific eicosanoid metabolites remains a significant challenge, but has led to the development of new pharmacologic strategies for treating NSAID-induced gastroenteropathy and IBD. Given the complex array of arachidonic acid metabolites, the development of more specific and potent inhibitors of these cyclooxygenase isoforms is important for future studies and possible therapeutic applications. Mice have been prepared that lack expression of COX-1 or COX-2. Once these animals have been carefully evaluated, understanding of the role of various pathways of eicosanoid formation in gastrointestinal function, development, and epithelial growth regulation might be improved. Considerable progress has been made in the understanding of arachidonic acid metabolism and in eicosanoid receptor biology. The identification and characterization of an inducible cyclooxygenase isoform has led to important studies evaluating the role of this enzyme in inflammation, neoplasia, and NSAID-induced gastrointestinal injury. The demonstration that COX-2 overexpression in intestinal epithelial cells leads to specific phenotypic changes, such as increased adhesion and inhibition of apoptosis, indicates that this enzyme may alter the tumorigenic potential of epithelial cells and offers hope for the future development of improved chemopreventive agents.

Stereoselective inhibition of inducible cyclooxygenase by chiral nonsteroidal antiinflammatory drugs

The stereoselective inhibition of inducible cyclooxygenase (COX-2) by chiral nonsteroidal antiinflammatory drugs (NSAIDs)--ketoprofen, flurbiprofen, and ketorolac--has been investigated. The activity and inhibition of COX-2 was assessed in three different in vitro systems: guinea pig whole blood, lipopolysaccharide (LPS)-stimulated human monocytes, and purified preparations of COX-2 from sheep placenta. The results were compared with the inhibition of constitutive cyclooxygenase (COX-1) in three parallel in vitro models: clotting guinea pig blood, human polymorphonuclear leukocytes, and purified COX-1 from ram seminal vesicles. In the whole blood model, both isoenzymes were inhibited by S-enantiomers with equal potency but S-ketoprofen was the most active on COX-2 (IC50 = 0.024 mumol/L). In contrast, both isoenzymes were inhibited less than 40% by all three R-enantiomers at high concentration (> 1 mumol/L). The inhibition of COX by the R-enantiomers may be attributed to contamination with the S-enantiomers (approximately 0.5%). A significant degree of enantioselectivity in COX-2 inhibition was also observed in intact cells. The S-enantiomers inhibited COX-2 from monocytes with IC50 values in the range of 2 to 25 nmol/L, being 100 to 500-fold more potent than the corresponding R-enantiomers. Finally, S-ketoprofen inhibited COX-2 from sheep placenta (IC50 = 5.3 mumol/L) with slightly less potency than S-ketorolac (IC50 = 0.9 mumol/L) and S-flurbiprofen (IC50 = 0.48 mumol/L), whereas the R-enantiomers were found to be essentially inactive (IC50 > or = 80 mumol/L). It is concluded that the chiral NSAIDs studied here inhibit with comparable stereoselectivity both COX-2 and COX-1 isoenzymes, and that the inhibition of COX-2 previously observed for racemic NSAIDs should be attributed almost exclusively to their S-enantiomers.

Selective inhibition of cyclooxygenase (COX)-2 reverses inflammation and expression of COX-2 and interleukin 6 in rat adjuvant arthritis

Prostaglandins formed by the cyclooxygenase (COX) enzymes are important mediators of inflammation in arthritis. The contribution of the inducible COX-2 enzyme to inflammation in rat adjuvant arthritis was evaluated by characterization of COX-2 expression in normal and arthritic paws and by pharmacological inhibition of COX-2 activity. The injection of adjuvant induced a marked edema of the hind footpads with coincident local production of PGE2. PG production was associated with upregulation of COX-2 mRNA and protein in the affected paws. In contrast, the level of COX-1 mRNA was unaffected by adjuvant injection. TNF-alpha and IL-6 mRNAs were also increased in the inflamed paws as was IL-6 protein in the serum. Therapeutic administration of a selective COX-2 inhibitor, SC-58125, rapidly reversed paw edema and reduced the level of PGE2 in paw tissue to baseline. Interestingly, treatment with the COX-2 inhibitor also reduced the expression of COX-2 mRNA and protein in the paw. Serum IL-6 and paw IL-6 mRNA levels were also reduced to near normal levels by SC-58125. Furthermore, inhibition of COX-2 resulted in a reduction of the inflammatory cell infiltrate and decreased inflammation of the synovium. Notably, the antiinflammatory effects of SC-58125 were indistinguishable from the effects observed for indomethacin. These results suggest that COX-2 plays a prominent role in the inflammation associated with adjuvant arthritis and that COX-2 derived PGs upregulate COX-2 and IL-6 expression at inflammatory sites.

Cyclooxygenase-2 inhibitors: a new class of anti-inflammatory agents that spare the gastrointestinal tract

The NSAIDs are potent anti-inflammatory and analgesic agents. It is now believed that the NSAIDs exert their therapeutic activity through the inhibition of COX-2 at the site of inflammation. Unfortunately, these compounds are equally capable of inhibiting constitutively expressed COX-1 in tissues such as the gastrointestinal tract and kidney, which results in serious, mechanism-based toxicities that limit the drug's therapeutic utility. With the identification of selective COX-2 inhibitors, alternatives to traditional NSAID therapy should be available that will provide clinical usefulness with reduced toxicity.

Cyclooxygenase-1 and -2 of endothelial cells utilize exogenous or endogenous arachidonic acid for transcellular production of thromboxane

The presence of prostaglandin (PG) H2 in the supernatant of human umbilical vein endothelial cells (HUVEC) stimulated by thrombin restores the capacity of aspirin-treated platelets to generate thromboxane (TX) B2. Induction of cyclooxygenase-2 (Cox-2) by interleukin (IL)-1alpha or a phorbol ester increases this formation. HUVEC treated with aspirin lost their capacity to generate PGs but recovery occurred after 3- or 6-h induction of Cox-2 with phorbol ester or IL-1alpha. Enzyme activity of the newly synthesized Cox-2 in aspirin-treated cells, evaluated after immunoprecipitation, was similar to untreated cells but after 18 h of cell stimulation only 50-60% recovery of Cox-1 was observed. The use of SC58125, a selective Cox-2 inhibitor, confirmed these findings in intact cells. Cyclooxygenase activity was related to the amount of Cox proteins present in the cells, but after induction of Cox-2, contribution of the latter to PG production was 6-8-fold that of Cox-1. Aspirin-treated or untreated cells were incubated in the absence or presence of SC58125 and stimulated by thrombin, the ionophore A23187, or exogenous arachidonic acid. The production of endogenous (6-keto-PGF1alpha, PGE2, PGF2alpha) versus transcellular (TXB2) metabolites was independent of the inducer, the source of arachidonic acid and the Cox isozyme. However, in acetylsalicylic acid-treated cells, after 6-h stimulation with IL-1alpha, newly synthesized Cox-2 produced less TXB2 than 6-keto-PGF1alpha compared to untreated cells. At later times (>18 h), there was no metabolic difference between the cells. These studies suggest that in HUVEC, Cox compartmentalization occurring after short-term activation may selectively affect transcellular metabolism, but not constitutive production, of PGs.

Elevated interleukin 6 is induced by prostaglandin E2 in a murine model of inflammation: possible role of cyclooxygenase-2

Injection of mineral oils such as pristane into the peritoneal cavities of BALB/c mice results in a chronic peritonitis associated with high tissue levels of interleukin 6 (IL-6). Here we show that increased prostaglandin E2 (PGE2) synthesis causes induction of IL-6 and that expression of an inducible cyclooxygenase, Cox-2, may mediate this process. Levels of both PGE2 and IL-6 are elevated in inflammatory exudates from pristane-treated mice compared with lavage samples from untreated mice. The Cox-2 gene is induced in the peritoneal macrophage fraction isolated from the mice. A cause and effect relationship between increased macrophage PGE2 and IL-6 production is shown in vitro. When peritoneal macrophages are activated with an inflammatory stimulus (polymerized albumin), the Cox-2 gene is induced and secretion of PGE2 and IL-6 increases, with elevated PGE2 appearing before IL-6. Cotreatment with 1 microM indomethacin inhibits PGE2 production by the cells and reduces the induction of IL-6 mRNA but has no effect on Cox-2 mRNA, consistent with the fact that the drug inhibits catalytic activity of the cyclooxygenase but does not affect expression of the gene. Addition of exogenous PGE2 to macrophages induces IL-6 protein and mRNA synthesis, indicating that the eicosanoid stimulates IL-6 production at the level of gene expression. PGE2-stimulated IL-6 production is unaffected by addition of indomethacin. Taken together with the earlier finding that indomethacin diminishes the elevation of IL-6 in pristane-treated mice, the results show that PGE2 can induce IL-6 production in vivo and implicate expression of the Cox-2 gene in the regulation of this cytokine.

Prostaglandin production in cultured cerebral microvascular smooth muscle is serum dependent

To expand the understanding of cerebrovascular eicosanoid metabolism, the ability of smooth muscle isolated from murine cerebral microvessels to produce prostaglandins (PGs) was studied in vitro. Cultures from SJL and BALB/c mice produced primarily prostaglandin E2 (PGE2) and I2 (PGI2) in response to exogenous arachidonate and calcium ionophore as well as the agonists acetylcholine and epinephrine. Subconfluent smooth muscle cultures demonstrated a two- to threefold increased capacity to produce PG compared with confluent cultures. In contrast, serum deprivation of smooth muscle caused an 80-90% diminution in both PGE2 and PGI2 production but had no effect on PG release in cerebromicrovascular endothelium. Reintroduction of serum to smooth muscle restored PG production within 6h, and the restoration was inhibited by 1 microM dexamethasone. Message for both prostaglandin H synthase (PGHS)-1 and -2 was detectable in smooth muscle grown in the presence of serum, but PGHS-2 message was not present in serum-deprived cultures. Furthermore, readdition of serum induced a massive increase in PGHS-2 mRNA with only a small increase in PGHS-1 message. The serum induction of PGHS-2 was corroborated by immunohistochemistry and Western blotting. Thus cerebromicrovascular smooth muscle may contribute significantly to the formation of PG under circumstances likely to be present during central nervous system pathologies. The induction of PGHS, particularly PGHS-2, may play a key role in this process.

Novel terphenyls as selective cyclooxygenase-2 inhibitors and orally active anti-inflammatory agents

A novel series of terphenyl methyl sulfones and sulfonamides have been shown to be highly potent and selective cyclooxygenase-2 (COX-2) inhibitors. The sulfonamide analogs 17 and 21 were found to be much more potent COX-2 inhibitors and orally active anti-inflammatory agents than the corresponding methyl sulfone analogs 16 and 20, respectively, albeit with some decrease in COX-2 selectivity. Structure-activity relationship studies have determined that incorporation of two fluorine atoms in the central phenyl group, as in 20 and 21, is extremely advantageous for both in vitro COX-2 potency and selectivity as well as in vivo activity. Several noticeable examples in the 1,2-diaryl-4,5-difluorobenzenesulfonamide series are 21a-c,k,l,n (COX-2, IC50 = 0.002-0.004 microM), in which all have in vitro COX-1/COX-2 selectivity > 1000. In addition, sulfonamides 21a,b,d,g,j,m,n,q were shown to have greatly enhanced oral activity with more than 90% inhibition of prostaglandin E2 production in the air pouch model of inflammation. Furthermore, sulfonamide 21b was found to be very active in the rat adjuvant-induced arthritis model (ED50 = 0.05 mg/kg) and carrageenan-induced hyperalgesia assay (ED50 = 38.7 mg/kg) with no indication of gastrointestinal toxicity in rats at doses as high as 200 mg/kg.

COX-2, a synaptically induced enzyme, is expressed by excitatory neurons at postsynaptic sites in rat cerebral cortex

Postnatal development and adult function of the central nervous system are dependent on the capacity of neurons to effect long-term changes of specific properties in response to neural activity. This neuronal response has been demonstrated to be tightly correlated with the expression of a set of regulatory genes which include transcription factors as well as molecules that can directly modify cellular signaling. It is hypothesized that these proteins play a role in activity-dependent response. Previously, we described the expression and regulation in brain of an inducible form of prostaglandin synthase/cyclooxygenase, termed COX-2. COX-2 is a rate-limiting enzyme in prostanoid synthesis and its expression is rapidly regulated in developing and adult forebrain by physiological synaptic activity. Here we demonstrate that COX-2 immunoreactivity is selectively expressed in a subpopulation of excitatory neurons in neo-and allocortices, hippocampus, and amygdala and is compartmentalized to dendritic arborizations. Moreover, COX-2 immunoreactivity is present in dendritic spines, which are specialized structures involved in synaptic signaling. The developmental profile of COX-2 expression in dendrites follows well known histogenetic gradients and coincides with the critical period for activity-dependent synaptic remodeling. These results suggest that COX-2, and its diffusible prostanoid products, may play a role in postsynaptic signaling of excitatory neurons in cortex and associated structures.

Pharmacological manipulation of cyclo-oxygenase-2 in the inflamed hydronephrotic kidney

1. Bradykinin (BK, 1 microgram) caused a small (2 fold at 6 h) increase in prostaglandin E2 (PGE2) in the normal rabbit kidney, perfused ex vivo. This was exaggerated (6 fold at 6 h) in the hydronephrotic kidney (HNK). The exaggerated release of PGE2 was attenuated by cycloheximide, an inhibitor of protein synthesis or by dexamethasone, a steroid known to inhibit the induction of cyclo-oxygenase (COX-2). BK (1 microgram) when injected at 6 h of perfusion increased the release of PGE2 from 90 +/- 33 pg ml-1 min-1 to 3069 +/- 946 pg ml-1 min-1. This was reduced to 200 +/- 30 pg ml-1 min-1 in kidneys infused with cycloheximide (1 microM) and to 250 +/- 40 pg ml-1 min-1 in kidneys infused with dexamethasone (n = 8). 2. When tested on human and murine recombinant COX-1 and COX-2 enzymes, DuP-697 was at least 50 fold more selective for COX-2 than for COX-1. 3. DuP-697 reduced the exaggerated release of PGE2 elicited by BK in the HNK (e.g., at 6 h of perfusion BK-evoked PGE2 release decreased from 3069 +/- 946 pg ml-1 min-1 to 187 +/- 22 pg ml-1 min-1 after perfusion with 1 microM DUP-697, n = 8). 4. Cycloheximide, dexamethasone or DuP-697 at doses used to inhibit completely the exaggerated release of PGE2 in the hydronephrotic kidney, failed to inhibit the release of PGE2 elicited by the injection of BK (1 microgram) in the normal contralateral kidney. 5. Indomethacin (1 microM), a non-selective COX-1 and COX-2 inhibitor, completely inhibited PGE2 release in the normal contralateral as well as in the hydronephrotic kidney. 6. We suggest that renal prostaglandin production in the normal kidney is driven by the activity of constitutive COX-1 while at sites of inflammation, such as the hydronephrotic kidney, there is induction of COX-2 that can be blocked selectively by anti-inflammatory glucocorticoids or selective COX-2 inhibitors.

A human whole blood assay for clinical evaluation of biochemical efficacy of cyclooxygenase inhibitors

In this study, PGE2 levels in lipopolysaccharide (LPS)-challenged human whole blood and TxB2 levels following blood coagulation were measured as biochemical index for cyclooxygenase (Cox)-2 and Cox-1 activity respectively. Incubation of human mononuclear cells isolated from whole blood with LPS (100 mu g/mL) induced a time-dependent increase in the expression of Cox-2 protein (>100 fold at 24 hr). This is associated with increases in PGE2 production and free arachidonate release in the plasma. Cox-1 protein was detected in the human mononuclear cells at time zero but was not induced by either LPS or PBS. Most non-steroidal anti-inflammatory drugs (NSAIDs) are more potent at inhibiting Cox-1 than Cox-2. Five experimental compounds CGP-28238, Dup-697, NS-398, SC-58125 and L-745,337, have a greater selectivity for Cox-2. Indomethacin at a single oral dose (25 mg) inhibited approximately 90% the whole blood Cox-2 and Cox-1 activities ex vivo in healthy subjects. These results support the use of this assay to assess the biochemical efficacy of selective Cox-2 inhibitors in clinical trials.

Diarylspiro[2.4]heptenes as orally active, highly selective cyclooxygenase-2 inhibitors: synthesis and structure-activity relationships

A novel series of 5,6-diarylspiro[2.4]hept-5-enes was shown to provide highly potent and selective cyclooxygenase-2 (COX-2) inhibitors. A study of structure-activity relationships in this series suggests that 3,4-disubstituted phenyl analogs are generally more selective than 4-substituted phenyl analogs and that replacement of the methyl sulfone group on the 6-phenyl ring with a sulfonamide moiety results in compounds with superior in vivo pharmacological properties, although with lower COX-2 selectivity. Several compounds have been shown to possess promising pharmacological properties in adjuvant-induced arthritis and edema analgesia models. The absence of gastrointestinal (GI) toxicity at 200 mpk of several selected compounds in rats and mice corresponds well with the weak potency for inhibition of COX-1 observed in the enzyme assay. Methyl sulfone 55 and sulfonamide 24 were shown to have superior in vivo pharmacological profiles, low GI toxicity, and good oral bioavailability and duration of action.

Distinct isoforms (COX-1 and COX-2) of cyclooxygenase: possible physiological and therapeutic implications

The discovery of an inducible isoform of cyclooxygenase (COX-2) requires a refinement of the theory that inhibition of cyclooxygenase activity explains both therapeutic and side effects of non-steroidal anti-inflammatory drugs (NSAIDs). Indeed, new pharmacological results suggest that COX-2 inhibition provides the therapeutic (ie, anti-inflammatory) activity of NSAIDs, whereas inhibition of constitutive COX-1 is responsible for their gastric and renal side effects as well as for their antithrombotic activity. However, a role of COX-1 in inflammation cannot be excluded. Furthermore, the functional relevance of COX-2 expression and induction in various tissues warrants further investigation. These studies should help in predicting potential adverse effects as well as new indications for selective COX-2 inhibitors.

Preclinical and clinical development of dexketoprofen

Dexketoprofen trometamol is a water-soluble salt of the dextrorotatory enantiomer of the nonsteroidal anti-inflammatory drug (NSAID) ketoprofen. Racemic ketoprofen is used as an analgesic and an anti-inflammatory agent, and is one of the most potent in vitro inhibitors of prostaglandin synthesis. This effect is due to the S(+)-enantiomer (dexketoprofen), while the R(-)-enantiomer is devoid of such activity. The pharmacokinetic profile of ketoprofen and its enantiomers was assessed in several animals species and in human volunteers. In humans, the relative bioavailability of oral dexketoprofen trometamol (12.5 and 25 mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50 mg, respectively), as measured in all cases by the area under the concentration-time curve values for S(+)-ketoprofen. Dexketoprofen trometamol, given as a tablet, is rapidly absorbed, with a time to maximum plasma concentration (tmax) of between 0.25 and 0.75 hours, whereas the tmax for the S-enantiomer after the racemic drug, administered as tablets or capsules prepared with the free acid, is between 0.5 and 3 hours. Peak plasma concentrations of 1.4 and 3.1 mg/L are reached after administration of dexketoprofen trometamol 12.5 and 25 mg, respectively. From 70 to 80% of the administered dose is recovered in the urine during the first 12 hours, mainly as the acyl-glucuronoconjugated parent drug. No R(-)-ketoprofen is found in the urine after administration of dexketoprofen [S(+)-ketoprofen], confirming the absence of bioinversion of the S(+)-enantiomer in humans. in animal studies, the anti-inflammatory potency of dexketoprofen was always equivalent to that demonstrated by twice the dose of ketoprofen. Similarly, animal studies showed a high analgesic potency for dexketoprofen trometamol. The R(-)-enantiomer demonstrated a much lower potency, its analgesic action being apparent only in conditions where the metabolic bioinversion to the S(+)-enantiomer was significant. The gastric ulcerogenic effect of dexketoprofen at various oral doses (1.5 to 6 mg/kg) in the rat do not differ from those of the corresponding double doses (3 to 12 mg/kg) of racemic ketoprofen. Repeated (5-day) oral administration of dexketoprofen as the trometamol salt causes less gastric ulceration than was observed after the acid form of both dexketoprofen and the racemate. In addition, single dose dexketoprofen as the free acid at 10 to 20 mg/kg does not show a significant intestinal ulcerogenic effect in rats, while racemic ketoprofen 20 or 40 mg/kg is clearly ulcerogenic to the small intestine. The analgesic efficacy of oral dexketoprofen trometamol 10 to 20 mg is superior to that of placebo and similar to that of ibuprofen 400 mg in patients with moderate to serve pain after third molar extraction. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol than in those treated with ibuprofen 400 mg. Dexketoprofen trometamol was well tolerated, with a reported incidence of adverse events similar to that of placebo.

The mechanisms of action of NSAIDs in analgesia

Traditionally, the analgesic action of nonsteroidal anti-inflammatory drugs (NSAIDs) has been explained on the basis of their inhibition of the enzymes that synthesise prostaglandins. However, it is clear that NSAIDs exert their analgesic effect not only through peripheral inhibition of prostaglandin synthesis but also through a variety of other peripheral and central mechanisms. It is now known that there are 2 structurally distinct forms of the cyclo-oxygenase enzyme (COX-1 and COX-2). COX-1 is a constitutive member of normal cells and COX-2 is induced in inflammatory cells. Inhibition of COX-2 activity represent the most likely mechanism of action for NSAID-mediated analgesia, while the ratio of inhibition of COX-1 to COX-2 by NSAIDs should determine the likelihood of adverse effects. In addition, some NSAIDs inhibit the lipoxygenase pathway, which may itself result in the production of algogenic metabolites. Interference with G-protein-mediated signal transduction by NSAIDs may form the basis of an analgesic mechanism unrelated to inhibition of prostaglandin synthesis. These is increasing evidence that NSAIDs have a central mechanism of action that augments the peripheral mechanism. This effect may be the result of interference with the formation of prostaglandins within the CNS. Alternatively, the central action may be mediated by endogenous opioid peptides or blockade of the release of serotonin (5-hydroxytryptamine; 5-HT). A mechanism involving inhibition of excitatory amino acids of N-methyl-D-aspartate receptor activation has also been proposed.

Mechanism of action of anti-inflammatory drugs

Cyclooxygenase (COX) is the pivotal enzyme in prostaglandin biosynthesis. It exists in two isoforms, constitutive COX-1 (responsible for physiological functions) and inducible COX-2 (involved in inflammation). Inhibition of COX explains both the therapeutic effects (inhibition of COX-2) and side effects (inhibition of COX-1) of non-steroidal anti-inflammatory drugs (NSAIDs). A NSAID which selectively inhibits COX-2 is likely to retain maximal anti-inflammatory efficacy combined with less toxicity. The activity of a number of NSAIDs has been investigated in several test systems, showing that most of those marketed have higher activities against COX-1 or are equipotent against both isoforms. Adverse event data of marketed NSAIDs show a relationship between a poor safety profile and more potent inhibition of COX-1 relative to COX-2. There are several new non-steroidal COX-2 inhibitors in development. The most clinically advanced is meloxicam, which consistently demonstrates higher activity against COX-2 than COX-1 in several test systems.

Calcium-mediated translocation of cytosolic phospholipase A2 to the nuclear envelope and endoplasmic reticulum

Cytosolic phospholipase A2 (cPLA2) is activated by a wide variety of stimuli to release arachidonic acid, the precursor of the potent inflammatory mediators prostaglandin and leukotriene. Specifically, cPLA2 releases arachidonic acid in response to agents that increase intracellular Ca2+. In vitro data have suggested that these agents induce a translocation of cPLA2 from the cytosol to the cell membrane, where its substrate is localized. Here, we use immunofluorescence to visualize the translocation of cPLA2 to distinct cellular membranes. In Chinese hamster ovary cells that stably overexpress cPLA2, this enzyme translocates to the nuclear envelope upon stimulation with the calcium ionophore A23187. The pattern of staining observed in the cytoplasm suggests that cPLA2 also translocates to the endoplasmic reticulum. We find no evidence for cPLA2 localization to the plasma membrane. Translocation of cPLA2 is dependent on the calcium-dependent phospholipid binding domain, as a calcium-dependent phospholipid binding deletion mutant of cPLA2 (delta CII) fails to translocate in response to Ca2+. In contrast, cPLA2 mutated at Ser-505, the site of mitogen-activated protein kinase phosphorylation, translocates normally. This observation, combined with the observed phosphorylation of delta CII, establishes that translocation and phosphorylation function independently to regulate cPLA2. The effect of these mutations on cPLA2 translocation was confirmed by subcellular fractionation. Each of these mutations abolished the ability of cPLA2 to release arachidonic acid, establishing that cPLA2-mediated arachidonic acid release is strongly dependent on both phosphorylation and translocation. These data help to clarify the mechanisms by which cPLA2 is regulated in intact cells and establish the nuclear envelope and endoplasmic reticulum as primary sites for the liberation of arachidonic acid in the cell.

Arginine 120 of prostaglandin G/H synthase-1 is required for the inhibition by nonsteroidal anti-inflammatory drugs containing a carboxylic acid moiety

The therapeutic action of nonsteroidal anti-inflammatory drugs (NSAIDs) is exerted through the inhibition of prostaglandin G/H synthase (PGHS), which is expressed as two isoenzymes, termed PGHS-1 and PGHS-2. From the crystal structure of sheep PGHS-1, it has been proposed that the carboxylic acid group of flurbiprofen is located in a favorable position for interacting with the arginine 120 residue of PGHS-1 (Picot, D., Loll, P. J., and Garavito, R. M. (1994) Nature 367, 243-249). Mutation of this Arg120 residue to Glu was performed and expressed in COS-7 cells using a vaccinia virus expression system. Comparison of microsomal enzyme preparations show that the mutation results in a 20-fold reduction in the specific activity of PGHS-1 and in a 100-fold increase in the apparent Km for arachidonic acid. Indomethacin, flurbiprofen, and ketoprofen, inhibitors of PGHS activity containing a free carboxylic acid group, do not exhibit any inhibitory effects against the activity of PGHS-1(Arg120-->Glu). Diclofenac and meclofenamic acid, other NSAIDs containing a free carboxylic acid group, were 50-100-fold less potent inhibitors of the activity of the mutant as compared with the wild type PGHS. In contrast, the nonacid PGHS inhibitors, 5-bromo-2-(4-fluorophenyl)-3-(4-methylsulfonyl)thiophene (DuP697) and a desbromo-sulfonamide analogue of DuP697 (L-746,483), were both more potent inhibitors of PGHS-1(Arg120-->Glu) than of the wild tyupe PGHS-1. Inhibition of PGHS-1(Arg120-->Glu) was time-dependent for diclofenac and time-independent for DuP697, as observed for the wild type enzyme, indicating that the mutation does not alter the basic mechanism of inhibition. Aspirin is an acid NSAID that inhibits PGHS-1 through a unique covalent acetylation of the enzyme and also showed a reduced rate of inactivation of the mutated enzyme. These data provide biochemical evidence of the importance of the Arg120 residue in PGHS-1 for interaction with arachidonic acid and NSAIDs containing a free carboxylic acid moiety.

Inflammation, reproduction, cancer and all that.... The regulation and role of the inducible prostaglandin synthase

Discovery of a second, inducible prostaglandin synthase provides explanations for many previously puzzling observations, but also raises new questions about prostanoid synthesis. A cis-acting sequence closely related to the cyclic AMP response element has been shown to play a role in both basal and induced prostaglandin synthase 2 gene expression. Aspirin and other currently available non-steroidal anti-inflammatory drugs that inhibit prostaglandin synthase activity do not effectively discriminate between the inducible prostaglandin synthase 2 and constitutive prostaglandin synthase 1 enzymes. Identification of a second prostaglandin synthase, induced by inflammatory stimuli, initiated a search for isoform-specific inhibitors. Use of prostaglandin synthase 2 specific inhibitors and antisense oligonucleotides has led to the suggestion that specific ligands activate alternative pathways of prostanoid production, using one of the prostaglandin synthase isoforms preferentially. The coupling mechanisms by which these pathways are activated in response to alternative stimuli should provide additional routes of intervention in prostanoid production.

Renal abnormalities and an altered inflammatory response in mice lacking cyclooxygenase II

Prostaglandins have wide-ranging effects in the body and are thought to be important mediators of inflammation. Cyclooxygenase (COX) plays a key regulatory role in prostaglandin synthesis, and occurs in both constitutive (COX-1) and inducible (COX-2) isoforms. COX-1 is thought to provide cytoprotective effects, whereas COX-2 is both inducible and the major isoform of inflammatory cells. Reduction of prostaglandin production by inhibition of cyclooxygenases appears to be the main mechanism of action of most non-steroidal anti-inflammatory drugs (NSAIDS). Here we present an animal model of COX-2 deficiency that was generated by gene targeting. Defects in null mice correlating with reduced viability included renal alterations, characteristic of renal dysplasia (100% penetrance), and cardiac fibrosis (50% penetrance). Female Cox-2-/- mice were infertile. COX-2 deficiency failed to alter inflammatory responses in several standard models, but striking mitigation of endotoxin-induced hepatocellular cytotoxicity was observed.

Inhibition of constitutive and inducible cyclooxygenase activity in human platelets and mononuclear cells by NSAIDs and Cox 2 inhibitors

A range of NSAIDs and reported Cox 2 selective compounds were tested in human freshly isolated platelets and LPS-stimulated mononuclear cells to determine their potency and selectivity as inhibitors of constitutive (presumably Cox 1) and inducible (presumably Cox 2) cyclooxygenase respectively. All compounds tested were either equipotent at inhibiting constitutive and inducible cyclooxygenase or were selective for the inducible form. The most selective compound was Dup697 and the least selective, ketoprofen. Several compounds only produced a partial inhibition of constitutive cyclooxygenase as the maximum inhibitor concentration achievable in the assay was limited to 1 mM. With the exception of paracetamol, all compounds were able to produce full inhibition curves against the inducible form. Potency estimates against constitutive Cox compare closely with published data but most compounds were consistently more potent against the inducible isoform than in published data for human cloned, microsomal Cox 2. These data suggest that human mononuclear cells are either exquisitely sensitive to some NSAIDs or they may contain another Cox isoform as yet indistinguishable from Cox 2.