Mechanism of selective inhibition of human prostaglandin G/H synthase-1 and -2 in intact cells

Lipid composition differentiates ferroptosis sensitivity between in vitro and in vivo systems

Ferroptosis is a regulated non-apoptotic cell death process characterized by iron-dependent lipid peroxidation. This process has recently emerged as a promising approach for cancer therapy. Peroxidation of polyunsaturated fatty acid-containing phospholipids (PUFA-PLs) is necessary for the execution of ferroptosis. Ferroptosis is normally suppressed by glutathione peroxidase 4 (GPX4), which reduces lipid hydroperoxides to lipid alcohols. Some evidence indicates that GPX4 may be a useful target for drug development, yet factors that govern GPX4 inhibitor sensitivity in vivo are poorly understood. We find that pharmacological and genetic loss of GPX4 function was sufficient to induce ferroptosis in multiple adherent ("2D") cancer cell cultures. However, reducing GPX4 protein levels did not affect tumor xenograft growth when these cells were implanted in mice. Furthermore, sensitivity to GPX4 inhibition was markedly reduced when cells were cultured as spheroids ("3D"). Mechanistically, growth in 3D versus 2D conditions reduced the abundance of PUFA-PLs. 3D culture conditions upregulated the monounsaturated fatty acid (MUFA) biosynthetic gene stearoyl-CoA desaturase (SCD). SCD-derived MUFAs appear to protect against ferroptosis in 3D conditions by displacing PUFAs from phospholipids. Various structurally related long chain MUFAs can inhibit ferroptosis through this PUFA-displacement mechanism. These findings suggest that growth-condition-dependent lipidome remodeling is an important mechanism governing GPX4 inhibitor effects. This resistance mechanism may specifically limit GPX4 inhibitor effectiveness in vivo .

New neuroprotective derivatives of cinnamic acid by biotransformation

Microbial transformation is extensively utilized to generate new metabolites in bulk amounts with more specificity and improved activity. As cinnamic acid was reported to exhibit several important pharmacological properties, microbial transformation was used to obtain its new derivatives with enhanced biological activities. By manipulating the 2-stage fermentation protocol of biotransformation, five metabolites were produced from cinnamic acid. Two of them were new derivatives; N-propyl cinnamamide 2̲ and 2-methyl heptyl benzoate 3̲ produced by Alternaria alternata. The other 3 metabolites, p-hydroxy benzoic acid 4̲, cinnamyl alcohol 5̲ and methyl cinnamate 6̲, were produced by Rhodotorula rubra, Rhizopus species and Penicillium chrysogeneum, respectively. Cinnamic acid and its metabolites were evaluated for their cyclooxygenase (COX) and acetylcholinesterase (AChE) inhibitory activities. Protection against H2O2 and Aβ1-42 induced-neurotoxicity in human neuroblastoma (SH-SY5Y) cells was also monitored. Metabolite 4̲ was more potent as a COX-2 inhibitor than the parent compound with an IC50 value of 1.85 ± 0.07 μM. Out of the tested compounds, only metabolite 2̲ showed AChE inhibitory activity with an IC50 value of 8.27 μM. These results were further correlated with an in silico study of the binding interactions of the active metabolites with the active sites of the studied enzymes. Metabolite 3̲ was more potent as a neuroprotective agent against H2O2 and Aβ1-42 induced-neurotoxicity than catechin and epigallocatechin-3-gallate as positive controls. This study suggested the two new metabolites 2̲ and 3̲ along with metabolite 4̲ as potential leads for neurodegenerative diseases associated with cholinergic deficiency, neurotoxicity or neuroinflammation.

Microbial Transformation of the Sesquiterpene Lactone, Vulgarin, by Aspergillus niger

The biotransformation of vulgarin (1), an eudesmanolides-type sesquiterpene lactone obtained from Artemisia judaica, by the microorganism, Aspergillus niger, was carried out to give three more polar metabolites; 1-epi-tetrahydrovulgarin (1α,4α-dihydroxy-5αH,6,11βH-eudesman-6,12-olide (2), 20% yield, 1α,4α-dihydroxyeudesm-2-en-5αH,6,11βH-6,12-olide (3a), 10% yield, and C-1 epimeric mixture (3a, b), 4% yield, in a ratio of 4:1, 3a/3b. The structures of vulgarin and its metabolites were elucidated by 1 and 2D NMR spectroscopy in conjunction with HRESIMS. Metabolites (3a) and (3b) are epimers, and they are reported here for the first time as new metabolites obtained by biotransformation by selective reduction at C-1. Vulgarin and its metabolites were evaluated as anti-inflammatory agents using the human cyclooxygenase (COX) inhibitory assay. The obtained data showed that (1) exhibited a good preferential inhibitory activity towards COX-2 (IC50 = 07.21 ± 0.10) and had a moderate effect on COX-1 (IC50 = 11.32 ± 0.24). Meanwhile, its metabolite (3a) retained a selective inhibitory activity against COX-1 (IC50 = 15.70 ± 0.51). In conclusion, the results of this study revealed the necessity of the presence α, β unsaturated carbonyl group in (1) for better COX-2 inhibitory activity. On the other hand, the selectivity of (1) as COX-1 inhibitor may be enhanced via the reduction of C-1 carbonyl group.

Discovery of pyrazole N-aryl sulfonate: A novel and highly potent cyclooxygenase-2 (COX-2) selective inhibitors

Based on a new pyrazole sulfonate synthetic method, a novel class of molecules with a basic structure of pyrazole N-aryl sulfonate have been designed and synthesized. The interest in conducting intensive research stems from quite evident anti-inflammatory effects exhibited by the compounds in preliminary animal experiments. A series of compounds were synthesized by different substitutions of the R¹, R², and R³ groups. Within the series, 4-iodophenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate and phenyl 5-methyl-3-(4-(trifluoromethyl) phenyl)-1H-pyrazole-1-sulfonate exhibited excellent anti-inflammatory activity (% inhibition of auricular edemas = 27.0 and 35.9, respectively); the in vivo analgesic activity of phenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate and 2-chlorophenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate was confirmed to be effective (inhibition ratio of writhing = 50.7% and 48.5% separately), and compounds phenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate , 4-iodophenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate and 2-chlorophenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate were identified as selective COX-2 inhibitors (SI = 455, 10,497 and >189 severally). In Acute Oral Toxicity assays conducted in vivo, the lethal dose 50 (LD₅₀) of 4-iodophenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate and 2-chlorophenyl 5-methyl-3-(p-tolyl)-1H-pyrazole-1-sulfonate to mice was >2000 mg/kg BW.

The effective interplay of (non-) selective NSAIDs with neostigmine in animal models of analgesia and inflammation

BACKGROUND

Surgical procedures cause perioperative immunosuppression and neuroendocrine stress, exerted by activation of the autonomic nervous system and the hypothalamic-pituitary-adrenal axis. The acetylcholinesterase inhibitor (ACHEI); neostigmine, is known clinically for its analgesic effect in the perioperative phases proving high efficacy; besides possessing anti-inflammatory properties controlling immune cells and cytokine level. Hence, this study evaluated and compared the analgesic and anti-inflammatory activities of the combination of selective Cox-2 inhibitor; celecoxib, with neostigmine versus a combination of the non-selective Cox inhibitor; diclofenac, with neostigmine; in different experimental models of analgesia and inflammation in rats.

METHODS

Analgesic activity of neostigmine with/without diclofenac or celecoxib was assessed in female Sprague-Dawely rats using the tail clip model and acetic acid induced writhing. Serum level of β-endorphin was assessed after the tail clip test. The anti-inflammatory activity was evaluated using acute and sub-chronic formalin induced paw edema. At the end of the sub-chronic formalin test, blood samples were collected for analysis of anti-inflammatory, liver and kidney function markers. Livers, kidneys and hind paws were also examined histopathologically.

RESULTS

Addition of neostigmine to selective or non-selective NSAIDs (celecoxib or diclofenac) causes an increased level of analgesia of NSAIDs with rapid onset of action and short duration, while causing potentiation of the anti-inflammatory effect of neostigmine as seen in the tail clip, writhing, formalin test, Cox-1 and Cox-2 activities, serum β-endorphin, TNF-α, NF-кB and HS-CRP. All combinations of this study disturb some kidney and liver functions, however with normal histopathological appearances, while hind paws reveal improved inflammatory infiltration in all treated groups.

CONCLUSIONS

Selective and non-selective NSAIDs examined in this study could be good adjunct options to general anesthetic agents and neostigmine in perioperative stages, an outcome that needs further clinical investigations.

Deep sequencing of prostaglandin-endoperoxide synthase (PTGE) genes reveals genetic susceptibility for cross-reactive hypersensitivity to NSAID

BACKGROUND AND PURPOSE

Cross-reactive hypersensitivity to nonsteroidal anti-inflammatory drugs (NSAIDs) is a relatively common adverse drug event caused by two or more chemically unrelated drugs and that is attributed to inhibition of the COX activity, particularly COX-1. Several studies investigated variations in the genes coding for COX enzymes as potential risk factors. However, these studies only interrogated a few single nucleotide variations (SNVs), leaving untested most of the gene sequence.

EXPERIMENTAL APPROACH

In this study, we analysed the whole sequence of the prostaglandin-endoperoxide synthase genes, PTGS1 and PTGS2, including all exons, exon-intron boundaries and both the 5' and 3' flanking regions in patients with cross-reactive hypersensitivity to NSAIDs and healthy controls. After sequencing analysis in 100 case-control pairs, we replicated the findings in 540 case-control pairs. Also, we analysed copy number variations for both PTGS genes.

KEY RESULTS

The most salient finding was the presence of two PTGS1 single nucleotide variations, which are significantly more frequent in patients than in control subjects. Patients carrying these single nucleotide variations displayed a significantly and markedly lower COX-1 activity as compared to non-carriers for both heterozygous and homozygous patients.

CONCLUSION AND IMPLICATIONS

Although the risk single nucleotide variations are present in a small proportion of patients, the strong association observed and the functional effect of these single nucleotide variations raise the hypothesis of genetic susceptibility to develop cross-reactive NSAID hypersensitivity in individuals with an impairment in COX-1 enzyme activity.

A network integration approach for drug-target interaction prediction and computational drug repositioning from heterogeneous information

The emergence of large-scale genomic, chemical and pharmacological data provides new opportunities for drug discovery and repositioning. In this work, we develop a computational pipeline, called DTINet, to predict novel drug-target interactions from a constructed heterogeneous network, which integrates diverse drug-related information. DTINet focuses on learning a low-dimensional vector representation of features, which accurately explains the topological properties of individual nodes in the heterogeneous network, and then makes prediction based on these representations via a vector space projection scheme. DTINet achieves substantial performance improvement over other state-of-the-art methods for drug-target interaction prediction. Moreover, we experimentally validate the novel interactions between three drugs and the cyclooxygenase proteins predicted by DTINet, and demonstrate the new potential applications of these identified cyclooxygenase inhibitors in preventing inflammatory diseases. These results indicate that DTINet can provide a practically useful tool for integrating heterogeneous information to predict new drug-target interactions and repurpose existing drugs.Network-based data integration for drug-target prediction is a promising avenue for drug repositioning, but performance is wanting. Here, the authors introduce DTINet, whose performance is enhanced in the face of noisy, incomplete and high-dimensional biological data by learning low-dimensional vector representations.

Rutin as a Mediator of Lipid Metabolism and Cellular Signaling Pathways Interactions in Fibroblasts Altered by UVA and UVB Radiation

Background. Rutin is a natural nutraceutical that is a promising compound for the prevention of UV-induced metabolic changes in skin cells. The aim of this study was to examine the effects of rutin on redox and endocannabinoid systems, as well as proinflammatory and proapoptotic processes, in UV-irradiated fibroblasts. Methods. Fibroblasts exposed to UVA and UVB radiation were treated with rutin. The activities and levels of oxidants/antioxidants and endocannabinoid system components, as well as lipid, DNA, and protein oxidation products, and the proinflammatory and pro/antiapoptotic proteins expression were measured. Results. Rutin reduced UV-induced proinflammatory response and ROS generation and enhanced the activity/levels of antioxidants (SOD, GSH-Px, vitamin E, GSH, and Trx). Rutin also normalized UV-induced Nrf2 expression. Its biological activity prevented changes in the levels of the lipid mediators: MDA, 4-HNE, and endocannabinoids, as well as the endocannabinoid receptors CB1/2, VR1, and GPR55 expression. Furthermore, rutin prevented the protein modifications (tyrosine derivatives formation in particular) and decreased the levels of the proapoptotic markers—caspase-3 and cytochrome c. Conclusion. Rutin prevents UV-induced inflammation and redox imbalance at protein and transcriptional level which favors lipid, protein, and DNA protection. In consequence rutin regulates endocannabinoid system and apoptotic balance.

Maternal diabetes impairs oxidative and inflammatory response in murine placenta

Placenta is the major exchange surface between mother and fetus and plays a pivotal role in fetal development. A better understanding of the mechanisms by which diabetes alters placental function may allow better management of diabetes pregnancies. In this study, we attempt to investigate the effect of diabetic milieu with and without malformation on placental function. In order to investigate the impact of diabetic pregnancy on oxidative stress, endothelial and vascular functions of placental tissue, we mated diabetic and non-diabetic female rats with normal male rats. At gestational day 17, we terminated pregnancy, assessed fetuses for malformations and isolated placenta for measurement of various parameters of placental function. Our results show that maternal diabetes induced a state of oxidative stress in placenta, which disrupts normal signaling, activating apoptosis, as well as perturbing endothelial and vascular placental functions. The coalescence of these insults on various levels of placental function could contribute to the pleiotropic nature of diabetes-induced placental stress.

Effects of Lipoic Acid Supplementation on Activities of Cyclooxygenases and Levels of Prostaglandins E2 and F2α Metabolites, in the Offspring of Rats with Streptozotocin-Induced Diabetes

Background. Our aim was to evaluate the protective effect of lipoic acid (LA) on fetal outcome of diabetic mothers. Methods. Diabetes was induced in female rats using streptozotocin and rats were made pregnant. Pregnant control (group 1; n = 9; and group 2; n = 7) or pregnant diabetic (group 3; n = 10; and group 4; n = 8) rats were treated daily with either LA (groups 2 and 4) or vehicle (groups 1 and 3) between gestational days 0 and 15. On day 15 of gestation, the fetuses, placentas, and membranes were dissected, examined morphologically, and then homogenized, to measure cyclooxygenase (COX) activities and metabolisms of prostaglandin (PG) E₂ (PGEM) and PGF₂α (PGFM) levels. The level of total glutathione was measured in the maternal liver and plasma and in all fetuses. Results. Supplementation of diabetic rats with LA was found to significantly (p < 0.05) reduce resorption rates in diabetic rats and led to a significant (p < 0.05) increase in liver, plasma, and fetuses total glutathione from LA-TD rats as compared to those from V-TD. Decreased levels of PGEM and elevated levels of PGFM in the fetuses, placentas, and membranes were characteristic of experimental diabetic gestation associated with malformation. The levels of PGEM in malformed fetuses from LA-TD mothers was significantly (p < 0.05) higher than those in malformed fetuses from V-TD rats. Conclusions. LA treatment did not completely prevent the occurrence of malformations. Thus, other factors may be involved in the pathogenesis of the diabetes-induced congenital malformations.

D-amino acids boost the selectivity and confer supramolecular hydrogels of a nonsteroidal anti-inflammatory drug (NSAID)

As systemically used therapeutics for treating acute or chronic pains or inflammations, nonsteroidal anti-inflammatory drugs (NSAIDs) also associate with the adverse gastrointestinal and renal effects and cardiovascular risks. Thus, it is beneficial to develop topical gels that selectively inhibit cyclooxygenase-2 (COX-2) for the management of local inflammation. In this work, we demonstrate that the covalent conjugation of d-amino acids to naproxen (i.e., a NSAID) not only affords supramolecular hydrogelators for the topical gels but also unexpectedly and significantly elevates the selectivity toward COX-2 about 20× at little expense of the activity of naproxen. This work illustrates a previously unexplored approach that employs d-amino acids for the development of functional molecules that have dual or multiple roles and exceptional biostability, which offers a new class of molecular hydrogels of therapeutic agents.

Design, synthesis, characterization and biological evaluation of novel pyrazole integrated benzophenones

A series of novel pyrazole integrated benzophenones (9a-j) have been designed, synthesized from 1-methyl-5-(2,4,6-trimethoxy-phenyl)-1H-pyrazole 6. The structures of the regioisomers 6 and 7 were determined by 2D (1)H-(1)H COSY, (1)H-(13)C HSQC and (1)H-(13)C HMBC experiments. The newly synthesized compounds (9a-j) were evaluated for in vivo anti-inflammatory activity by carrageenan paw edema in rats and in vitro COX-1/COX-2 inhibition and antioxidant potential. Among the synthesized compounds, compounds 9b, 9d and 9f, were found to be active anti-inflammatory agents in addition to having potent antioxidant activity.

Human prostaglandin H synthase (hPHS)-1- and hPHS-2-dependent bioactivation, oxidative macromolecular damage, and cytotoxicity of dopamine, its precursor, and its metabolites

The dopamine (DA) precursor l-dihydroxyphenylalanine (L-DOPA) and metabolites dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxytyramine may serve as substrates for prostaglandin H synthase (PHS)-catalyzed bioactivation to free radical intermediates. We used CHO-K1 cells expressing human (h) PHS-1 or hPHS-2 to investigate hPHS isozyme-dependent oxidative damage and cytotoxicity. hPHS-1- and hPHS-2-expressing cells incubated with DA, L-DOPA, DOPAC, or HVA exhibited increased cytotoxicity compared to untransfected cells, and cytotoxicity was increased further by exogenous arachidonic acid (AA), which increased hPHS activity. Preincubation with catalase, which detoxifies reactive oxygen species, or acetylsalicylic acid, an inhibitor of hPHS-1 and -2, reduced the cytotoxicity caused by DA, L-DOPA, DOPAC, and HVA in hPHS-1 and -2 cells both with and without AA. Protein oxidation was increased in hPHS-1 and -2 cells exposed to DA or L-DOPA and further increased by AA addition. DNA oxidation was enhanced earlier and at lower substrate concentrations than protein oxidation in both hPHS-1 and -2 cells by DA, L-DOPA, DOPAC, and HVA and further enhanced by AA addition. hPHS-2 cells seemed more susceptible than hPHS-1 cells, whereas untransfected CHO-K1 cells were less susceptible. Thus, isozyme-specific, hPHS-dependent oxidative damage and cytotoxicity caused by neurotransmitters, their precursors, and their metabolites may contribute to neurodegeneration associated with aging.

Human prostaglandin H synthase (hPHS)-1 and hPHS-2 in amphetamine analog bioactivation, DNA oxidation, and cytotoxicity

Neurotoxicity of the amphetamine analogs methamphetamine (METH) and 3,4-methylenedioxyamphetamine (MDA) (the active metabolite of ecstasy) may involve their prostaglandin H synthase (PHS)-dependent bioactivation to free radical intermediates that generate reactive oxygen species and oxidatively damage cellular macromolecules. We used Chinese hamster ovary-K1 (CHO-K1) cell lines either untransfected or stably expressing human PHS-1 (hPHS-1) or hPHS-2 to investigate hPHS isozyme-dependent oxidative damage and cytotoxicity. Both METH and MDA (250-1000 μM) caused concentration-independent cytotoxicity in hPHS-1 cells, suggesting maximal bioactivation at the lowest concentration. In hPHS-2 cells, with half the activity of hPHS-1 cells, METH (250-1000 μM) cytotoxicity was less than that for hPHS-1 cells but was concentration dependent and increased by exogenous arachidonic acid (AA), which increased hPHS activity. Whereas 10 μM MDA and METH were not cytotoxic, at 100 μM both analogs caused AA-dependent and concentration-dependent increases in cytotoxicity and DNA oxidation in both hPHS-1/2 cells. The hPHS-2 isozyme appeared to provide more efficacious bioactivation of these amphetamine analogs. Acetylsalicylic acid, an irreversible inhibitor of both hPHS-1 and hPHS-2, blocked cytotoxicity and DNA oxidation in both cell lines and untransfected CHO-K1 cells lacking PHS activity were similarly resistant. Accordingly, isozyme-dependent hPHS-catalyzed bioactivation of METH and MDA can cause oxidative macromolecular damage and cytotoxicity, which may contribute to their neurotoxicity.

In Silico Screening of Nonsteroidal Anti-Inflammatory Drugs and Their Combined Action on Prostaglandin H Synthase-1

The detailed kinetic model of Prostaglandin H Synthase-1 (PGHS-1) was applied to in silico screening of dose-dependencies for the different types of nonsteroidal anti-inflammatory drugs (NSAIDs), such as: reversible/irreversible, nonselective/selective to PGHS-1/PGHS-2 and time dependent/independent inhibitors (aspirin, ibuprofen, celecoxib, etc.) The computational screening has shown a significant variability in the IC50s of the same drug, depending on different in vitro and in vivo experimental conditions. To study this high heterogeneity in the inhibitory effects of NSAIDs, we have developed an in silico approach to evaluate NSAID action on targets under different PGHS-1 microenvironmental conditions, such as arachidonic acid, reducing cofactor, and peroxide concentrations. The designed technique permits translating the drug IC₅₀, obtained in one experimental setting to another, and predicts in vivo inhibitory effects based on the relevant in vitro data. For the aspirin case, we elucidated the mechanism underlying the enhancement and reduction (aspirin resistance) of its efficacy, depending on PGHS-1 microenvironment in in vitro/in vivo experimental settings. We also present the results of the in silico screening of the combined action of sets of two NSAIDs (aspirin with ibuprofen, aspirin with celecoxib), and study the mechanism of the experimentally observed effect of the suppression of aspirin-mediated PGHS-1 inhibition by selective and nonselective NSAIDs. Furthermore, we discuss the applications of the obtained results to the problems of standardization of NSAID test assay, dependence of the NSAID efficacy on cellular environment of PGHS-1, drug resistance, and NSAID combination therapy.

Activities of cyclooxygenases, and levels of prostaglandins E2 and F2alpha, in fetopathy associated with experimental diabetic gestation

AIM

The present study investigated the cyclooxygenase (COX) pathway to elucidate any changes that may be involved in the mechanism(s) underlying diabetic fetopathy.

METHODS

Diabetes was induced in female rats (n=12) by two successive daily injections of 55 mg/kg streptozotocin, while control animals (n=10) were injected with a buffer solution; hyperglycaemia was confirmed by blood glucose levels greater than 11 mmol/L. The study female rats were made pregnant and, on day 15 of gestation, the rats were sacrificed, and the fetuses, placentas and membranes dissected out of the uterine horns. Following morphological examination, the fetuses, placentas and membranes were homogenized, and used to measure COX activities and prostaglandin (PG) E(2) and PGF(2alpha) levels.

RESULTS

Fetuses from diabetic mothers exhibited significantly (P<0.05) shorter crown-to-rump lengths, lower body weights and heavier placental weights. The activity of COX-1 in the fetuses, placentas and membranes from diabetic mothers represented a small percentage of total COX activity compared with that of COX-2. The presence of a COX-1 inhibitor in the control and diabetic rats was investigated and found to be negative. The activity of COX-2 in malformed fetuses from diabetic mothers was significantly lower (P<0.05) compared with non-malformed fetuses from control and diabetic mothers. The mean level of PGE(2) in fetuses from diabetic mothers was significantly (P<0.05) lower than that in controls. In contrast, the biggest increases in PGF(2alpha) were observed in the malformed diabetic fetuses, placentas and membranes.

CONCLUSION

The increased production of PGF(2alpha) probably proceeds, at least in part, independently of the COX pathway and via the isoprostane route. However, it is unclear whether the relatively high levels of PGF(2alpha) are causally related to, or simply coincidental with, fetal malformation.

Kinetic modelling of NSAID action on COX-1: focus on in vitro/in vivo aspects and drug combinations

The detailed kinetic model of Prostaglandin H Synthase-1 (COX-1) was developed to in silico test and predict inhibition effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on target. The model takes into account key features of the complex catalytic mechanism of cyclooxygenase-1, converting arachidonic acid to prostaglandin PGH(2), and includes the description of the enzyme interaction with various types of NSAIDs (reversible/irreversible, non-selective and selective to COX-1/COX-2). Two different versions of the model were designed to simulate the inhibition of COX-1 by NSAIDs in two most popular experimental settings - in vitro studies with purified enzyme, and the experiments with platelets. The developed models were applied to calculate the dose-dependence of aspirin and celecoxib action on COX- 1 in vitro and in vivo conditions. The mechanism of the enhancement of aspirin efficiency in platelet as compared to its action on purified COX-1 was elucidated. The dose-dependence of celecoxib simulated with the use of the "in vivo" version of the model predicted potentially strong inhibitory effect of celecoxib on thromboxan production in platelets. Simulation of the combined effect of two NSAIDs, aspirin and celecoxib, on COX-1 allowed us to reveal the mechanism underlying the suppression of aspirin-mediated COX-1 inhibition by celecoxib. We discuss our modelling results in the context of the on-going debates on the potential cardio-vascular risks associated with co-administration of various types of NSAIDs.

CD36 deficiency leads to choroidal involution via COX2 down-regulation in rodents

BACKGROUND

In the Western world, a major cause of blindness is age-related macular degeneration (AMD). Recent research in angiogenesis has furthered the understanding of choroidal neovascularization, which occurs in the "wet" form of AMD. In contrast, very little is known about the mechanisms of the predominant, "dry" form of AMD, which is characterized by retinal atrophy and choroidal involution. The aim of this study is to elucidate the possible implication of the scavenger receptor CD36 in retinal degeneration and choroidal involution, the cardinal features of the dry form of AMD.

METHODS AND FINDINGS

We here show that deficiency of CD36, which participates in outer segment (OS) phagocytosis by the retinal pigment epithelium (RPE) in vitro, leads to significant progressive age-related photoreceptor degeneration evaluated histologically at different ages in two rodent models of CD36 invalidation in vivo (Spontaneous hypertensive rats (SHR) and CD36-/- mice). Furthermore, these animals developed significant age related choroidal involution reflected in a 100%-300% increase in the avascular area of the choriocapillaries measured on vascular corrosion casts of aged animals. We also show that proangiogenic COX2 expression in RPE is stimulated by CD36 activating antibody and that CD36-deficient RPE cells from SHR rats fail to induce COX2 and subsequent vascular endothelial growth factor (VEGF) expression upon OS or antibody stimulation in vitro. CD36-/- mice express reduced levels of COX2 and VEGF in vivo, and COX2-/- mice develop progressive choroidal degeneration similar to what is seen in CD36 deficiency.

CONCLUSIONS

CD36 deficiency leads to choroidal involution via COX2 down-regulation in the RPE. These results show a novel molecular mechanism of choroidal degeneration, a key feature of dry AMD. These findings unveil a pathogenic process, to our knowledge previously undescribed, with important implications for the development of new therapies.

Therapeutic hypothermia in acute ischemic stroke

Increased body temperatures are common in the acute phase of stroke. Experimental and clinical studies have suggested that increased body temperatures are related to poor outcome. In animal studies of focal cerebral ischemia, early hypothermia consistently reduced infarct volume. Based on these findings, several Phase II clinical trials have been performed to study physical methods to reduce body temperature in patients with acute stroke. The feasibility and safety of these methods have not yet been established with sufficient certainty. Pharmacological lowering of body temperature may be an attractive alternative approach. In guidelines for the treatment of acute stroke, antipyretics are generally recommended to reduce fever, although their effect on functional outcome is unknown. There is currently no evidence from randomized trials to support routine use of physical or pharmacological cooling in acute stroke. Large randomized clinical trials are needed to study the effect of both physical and medical cooling on functional outcome after stroke.

Role for prostaglandins in the regulation of type 1 11beta-hydroxysteroid dehydrogenase in human granulosa-lutein cells

11beta-hydroxysteroid dehydrogenase (11betaHSD) enzymes regulate glucocorticoid availability in target tissues. 11betaHSD1 is the predominant isoenzyme expressed and active in human granulosa-lutein (hGL) cells. This study investigated the effects of pharmacological inhibitors of prostaglandin (PG) synthesis on 11betaHSD1 activities and expression in hGL cells. The consequences for 11betaHSD1 of increasing exposure of hGL cells to PGs, either by treatment with exogenous PGs or by challenging cells with IL-1beta, were also assessed. Suppression of basal PG synthesis using four different inhibitors of PG H synthase enzymes [indomethacin, niflumic acid, meclofenamic acid (MA) and N-(2-cyclohexyloxy-4-nitorophenyl) methane sulfonamide (NS-398)] each resulted in significant decreases in both cortisol oxidation and cortisone reduction. Both activities of 11betaHSD1 were suppressed by up to 64+/-6% (P<0.05). Over 4 and 24 h, neither MA nor NS-398 affected the expression of 11betaHSD1 protein, suggesting enzyme regulation by PGs at the posttranslational level. When cells were cotreated for 4 h with PGHS inhibitors plus 30 nm PGD2, PGF2alpha, or PGE2, each PG overcame the suppression of cortisol oxidation by indomethacin or MA. Treatment of hGL cells with IL-1beta increased the concentrations of both PGE2 and PGF2alpha, accompanied by a 70+/-25% increase in net cortisol oxidation. All three responses to IL-1beta were abolished when cells were cotreated with MA. These findings suggest a role for PGs in the posttranslational regulation of 11betaHSD1 activities in hGL cells.

Contributions of cyclooxygenase-2 to neuroplasticity and neuropathology of the central nervous system

Cyclooxygenase (COX) enzymes, or prostaglandin-endoperoxide synthases (PTGS), are heme-containing bis-oxygenases that catalyze the first committed reaction in metabolism of arachidonic acid (AA) to the potent lipid mediators, prostanoids and thromboxanes. Two isozymes of COX enzymes (COX-1 and COX-2) have been identified to date. This review will focus specifically on the neurobiological and neuropathological consequences of AA metabolism via the COX-2 pathway and discuss the potential therapeutic benefit of COX-2 inhibition in the setting of neurological disease. However, given the controversy surrounding the use of COX-2 selective inhibitors with respect to cardiovascular health, it will be important to move beyond COX to identify which down-stream effectors are responsible for the deleterious and/or potentially protective effects of COX-2 activation in the setting of neurological disease. Important advances toward this goal are highlighted herein. Identification of unique effectors in AA metabolism could direct the development of new therapeutics holding significant promise for the prevention and treatment of neurological disorders.

Biphasic role of nuclear factor-kappa B on cell survival and COX-2 expression in SOD1 Tg astrocytes after oxygen glucose deprivation

In cytoplasm, nuclear factor-kappaB (NF-kappaB) is associated with the inhibitory protein, IkappaBalpha. On activation by H2O2, IkappaBalpha is phosphorylated and degraded, exposing the nuclear localization signals on the NF-kappaB heterodimer. Cyclooxygenase-2 (COX-2), which mediates prostaglandin synthesis during inflammation, is induced by oxidative stress mediated by NF-kappaB. We investigated whether the NF-kappaB signaling pathway affected cell death and COX-2 expression after hypoxia-induced oxidative stress in wild-type (WT) and copper/zinc-superoxide dismutase transgenic (SOD1 Tg) astrocytes. In WT astrocytes, phospho-IkappaBalpha was highly expressed after oxygen-glucose deprivation (OGD) and 2 h of reperfusion, concomitant with the decrease in IkappaBalpha. The NF-kappaB p50 level increased similarly in WT and SOD1 Tg astrocytes (1.2-/1.4-fold) after OGD. Electrophoretic mobility shift assay showed higher DNA-binding activity of NF-kappaB p50 in WT than in SOD1 Tg astrocytes 6 h after 4 h of OGD. The COX-2 level was induced by 2.7- and 1.3-fold after OGD in WT and SOD1 Tg astrocytes, and an antioxidant protected both groups against OGD injury. Superoxide dismutase transgenic cells were 23% more protective against OGD injury than WTs when assessed by lactate dehydrogenase release. However, transfection of NF-kappaB small interfering RNAs in SOD1 Tg astrocytes aggravated cell death and increased COX-2 expression. These results suggest that the NF-kappaB signaling pathway induced COX-2 expression and promoted cell death in WTs after OGD injury; however, NF-kappaB activation protected cells and decreased COX-2 expression in SOD1 Tg astrocytes. This biphasic role of NF-kappaB might be coordinately regulated by reactive oxygen species levels in astrocytes, thereby functioning as a regulator of cell death/survival.

Cyclo-oxygenase-2 contributes to constitutive prostanoid production in rat kidney and brain

Cyclo-oxygenases (COXs) catalyse the synthesis of PGH2 (prostaglandin H2), which serves as the common substrate for the production of PGE2, PGD2, PGF(2alpha), prostacyclin (or PGI2) and TXs (thromboxanes). While COX-1 is the major isoform responsible for prostanoid synthesis in healthy tissues, little information is available on the contribution of constitutive COX-2 to the various prostanoid synthetic pathways under non-inflammatory conditions. To evaluate further the role of COX-2 in prostanoid biosynthesis, rats were acutely treated with the selective COX-1 inhibitor SC-560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole] or the selective COX-2 inhibitors MF tricyclic [3-(3,4-difluorophenyl)-4-(4-(methylsulphonyl)phenyl)-2-(5H)-furanone] and DFU [5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2-(5H)-furanone]. Selected tissues were then processed for a complete analysis of their prostanoid content by liquid chromatography MS. Whereas the treatment with SC-560 caused a 60-70% inhibition in the total prostanoid content of most tissues examined, a significant decrease (35-50%) in total prostanoid content following selective COX-2 inhibition was solely detected for kidney and brain tissues. Analysis of the individual prostanoids reveals significant inhibition of 6-oxo-PGF(1alpha), PGE2, PGD2, PGF(2alpha) and TXB2 in the kidney and inhibition of all these prostanoids with the exception of PGD2 in the forebrain. These results demonstrate that constitutively expressed COX-2 contributes to the production of prostanoids in kidney and brain for each of the PGE2, PGI2 and TXB2 pathways under non-inflammatory conditions. Approaches to modulate inflammation through specific inhibition of terminal synthases, such as mPGES-1 (microsomal PGE2 synthase-1), thus have the potential to differ from COX-2 inhibitors and non-selective non-steroidal anti-inflammatory drugs with regard to effects on constitutive prostanoid synthesis and on renal function.

TNF alpha reduces tachykinin, PGE2-dependent, relaxation of the cultured mouse trachea by increasing the activity of COX-2

1. Chronic inflammation is a central feature of asthma. The inflammatory cytokine tumour necrosis factor alpha (TNFalpha) has been implicated in this disease, and is known to alter airway smooth muscle functionally. 2. The aim of this study was to investigate the influence of TNFalpha on tachykinin-induced airway relaxation. Mouse tracheae were cultured in the absence and presence of TNFalpha for 1 or 4 days. 3. In the absence of TNFalpha, substance P (SP) and neurokinin A (NKA) induced comparable levels of relaxation in fresh and cultured segments. Functional studies with selective antagonists/inhibitors indicated that the relaxation was mediated by the NK(1) receptor coupled to cyclooxygenase (COX)-2 activation and subsequent release of prostaglandin E(2) (PGE(2)). TNFalpha attenuated SP- and NKA-induced relaxation in a time- and concentration-dependent manner, decreasing the ability of PGE(2) to relax tissues. 4. Further studies indicated that TNFalpha elevated COX-2 activity and that concomitant inhibition of COX-2 reversed TNFalpha-attenuated PGE(2) relaxation. Culture with PGE(2) decreased SP- and PGE(2)-mediated relaxation, further implicating the activity of COX-2 in the attenuation of tachykinin signalling. 5. Gene expression analysis demonstrated that TNFalpha increased the expression of smooth muscle COX-2, PGE(2) synthase and EP(2) receptor mRNA, and decreased the expression of the EP(4) receptor. 6. Overall, these results show that NK(1) receptor-mediated relaxation induced by PGE(2) is attenuated by prolonged TNFalpha stimulation. Increased COX-2 activity induced by TNFalpha appears to be central to this process.

N-Benzyl-2-chloroindole-3-carboxylic acids as potential anti-inflammatory agents. Synthesis and screening for the effects on human neutrophil functions and on COX1/COX2 activity

The synthesis of N-benzyl-2-chloroindole-3-carboxylic acids related to indomethacin is reported. These compounds were tested on in vitro human neutrophil activation. Some of them, more soluble in water, were tested to define the influence on prostaglandin biosynthesis via inhibition of cyclooxygenases (COX1 and COX2) by a chemiluminescent method suitable for fast screening. Several derivatives showed inhibitory effects and in some cases were more active than the parent compound.

Effect of flavonoids and vitamin E on cyclooxygenase-2 (COX-2) transcription

Cyclooxygenase-2 (COX-2)-catalysed synthesis of prostaglandin E2 plays a key role in inflammation and its associated diseases, such as cancer and cardiovascular disease. There are numerous reports demonstrating that flavonoids inhibit COX-2 activity. However, transcriptional regulation of COX-2 can also be important. Nobiletin, amentoflavone, quercetin, quercetin penta-acetate, flavone, resveratrol, apigenin, chrysin, kaempferol, galangin, and genistein have been reported to modulate COX-2 transcription in a wide variety of systems. Here, we briefly review the literature on regulation of COX-2 transcription by flavonoids, and report some new preliminary data on Vitamin E and quercetin conjugates. Quercetin, quercetin 3-glucuronide, quercetin 3'-sulfate and 3'methylquercetin 3-glucuronide reduced COX-2 mRNA expression in both unstimulated and interleukin-1beta stimulated colon cancer (Caco2) cells. Quercetin and quercetin 3'-sulfate, unlike quercetin 3-glucuronide and 3'methylquercetin 3-glucuronide, also inhibited COX-2 activity. In contrast, tocopherols (alpha-tocopherol, alpha-tocopherol acetate, and gamma-tocopherol at 10microM) did not affect COX-2 mRNA expression in unstimulated Caco2 cells. However, the tocopherols inhibited COX-2 activity showing that the tocopherols act post-transcriptionally on activity, whereas quercetin and some quercetin conjugates affect both the transcription and activity of COX-2. Flavonoid modulation of COX-2 transcription may therefore be an important mechanism in anti-carcinogenesis.

Adiponectin, a fat cell product, influences the earliest lymphocyte precursors in bone marrow cultures by activation of the cyclooxygenase-prostaglandin pathway in stromal cells

Adiponectin, an adipocyte-derived hormone, is attracting considerable interest as a potential drug for diabetes and obesity. Originally cloned from human s.c. fat, the protein is also found in bone marrow fat cells and has an inhibitory effect on adipocyte differentiation. The aim of the present study is to explore possible influences on lymphohematopoiesis. Recombinant adiponectin strongly inhibited B lymphopoiesis in long-term bone marrow cultures, but only when stromal cells were present and only when cultures were initiated with the earliest category of lymphocyte precursors. Cyclooxygenase inhibitors abrogated the response of early lymphoid progenitors to adiponectin in stromal cell-containing cultures. Furthermore, PGE(2), a major product of cyclooxygenase-2 activity, had a direct inhibitory influence on purified hematopoietic cells, suggesting a possible mechanism of adiponectin action in culture. In contrast to lymphopoiesis, myelopoiesis was slightly enhanced in adiponectin-treated bone marrow cultures, and even when cultures were initiated with single lymphomyeloid progenitors. Finally, human B lymphopoiesis was also sensitive to adiponectin in stromal cell cocultures. These results suggest that adiponectin can negatively and selectively influence lymphopoiesis through induction of PG synthesis. They also indicate ways that adipocytes in bone marrow can contribute to regulation of blood cell formation.

Arachidonic acid metabolites contribute to the irreversible depolarization induced by in vitro ischemia

Intracellular recordings were made from hippocampal CA1 neurons in rat slice preparations. Superfusion with oxygen- and glucose-deprived medium (in vitro ischemia) produced a rapid depolarization approximately 5 min after the onset of the superfusion. Even when oxygen and glucose were reintroduced immediately after rapid depolarization, the membrane depolarized further (persistent depolarization) and reached 0 mV (irreversible depolarization) after 5 min from the reintroduction. The pretreatment of the slice preparation with a phospholipase A2 (PLA2) inhibitor, para-bromophenacyl bromide, or a cytochrome p-450 inhibitor, 17-octadecynoic acid, significantly restored the membrane to the preexposure potential level after the reintroduction of oxygen and glucose. The administration of 14,15-epoxyeicosatrienoic acid or 20-hydroxyeicosatetraenoic acid did not change the latency of the rapid depolarization and did not allow the membrane potential to recover after the ischemic exposure. In contrast, after pretreatment with cyclooxygenase or lipoxygenase inhibitors, such as indomethacin, resveratrol, Dup-697, nordihydroguaiaretic acid, and 3,4-dihydrophenyl ethanol, a minority of neurons tested showed postischemic recovery from the persistent depolarization. Improved recovery was also seen after treatment with the free radical scavengers, edaravone and alpha-tocopherol. These results suggest that the activation of the arachidonic acid cascade via PLA2 and the free radicals produced by arachidonic acid metabolism contribute to the irreversible depolarization produced by in vitro ischemia.

Cyclooxygenase expression is elevated in retinoic acid-differentiated U937 cells

Cyclooxygenase (COX) is the rate-limiting enzyme for the biosynthesis of prostaglandins in monocytes/macrophages. The COX-1 is constitutively expressed in most tissues and may be involved in cellular homeostasis, whereas the COX-2 is an inducible enzyme that may play an important role in inflammation and mitogenesis. When U937 monocytic cells were incubated with retinoic acid (RA) for 48 h, cell differentiation took place with concomitant increases in prostaglandin E2 (PGE2) production and COX activity. In this study, the mechanism of RA (all-trans- or 9-cis-RA)-induced enhancement of PGE2 biosynthesis in U937 cells was examined. Treatment of cells with all-trans- or 9-cis-RA up to 48 h caused an increase in PGE2 production in a time- and dose-dependent manner. Both RA isomers caused the enhancement of PGE2 production and the up-regulation of COX-1 expression at the protein and mRNA levels. The increase in COX-1 mRNA was found to precede the increase in COX-1 protein expression. Interestingly, the COX-2 protein and COX-2 mRNA were not detected in U937 cells, and their levels remained undetectable during the entire course of RA treatment. We conclude that treatment of U937 cells by RA for 48 h caused the initiation of cell differentiation, which was found to be concomitant with a significant increase in PGE2 production mediated via the up-regulation of COX-1 mRNA and protein expression.

Variation in cyclooxygenase expression levels within the colorectum

The positive association of decreased risk of colorectal cancer with nonsteroidal antiinflammatory drug (NSAID) use, combined with the observation that cyclooxygenase(COX)-2 is present in a majority of colorectal tumors, has led to the proposed use of isozyme-specific COX inhibitors as preventive agents in polyp and tumor formation in the colon. However, the exact biochemical mechanisms and disease stage at which reduced risk is mediated remain somewhat controversial, in part because of the complex biochemical changes that occur during the progression from aberrant crypt to polyp to tumor. In this study, COX-1 and COX-2 protein expression levels were determined in sets of tumor and normal colon tissue. Changes were characterized in COX-1 and COX-2 expression within individuals, in relation to such factors as sex, tumor grade, and location in the colorectum. COX-1 expression levels were found to be significantly reduced in tumors compared to matched normal tissues (Dunn's method, P < 0.05). Additionally, COX-1 expression was decreased in stage T3 tumors as compared to stage T2 tumors (Student's t-test, P = 0.009). Similar to previous reports, COX-2 protein expression was present in 73% of the tumors studied and appeared to be independent of tumor grade and sex. Interestingly, decreased COX-2 expression correlated with tumor occurrence in rectal mucosa (Wilcoxon two-sample test, P < 0.05). These results warrant further investigation, especially the identification of determinants that would predict which populations would be most responsive to COX-2 inhibition as a means of colorectal cancer chemoprevention.

3,4-Diaryl-5-hydroxyfuranones: highly selective inhibitors of cyclooxygenase-2 with aqueous solubility

The introduction of a hydroxyl group into the 5-position of the diaryl furanone system provides highly selective inhibitors of cyclooxygenase-2. These molecules can be converted into their sodium salts which are water soluble, facilitating intravenous formulation. These salts show excellent potency in rat models of pain, fever and inflammation.

Pyridazinones as selective cyclooxygenase-2 inhibitors

Pyridazinone was found to be an excellent core template for selective COX-2 inhibitors. Two potent, selective and orally active COX-2 inhibitors, which were highly efficacious in rat paw edema and rat pyresis models, have been obtained.

Continuous spectrophotometric assay amenable to 96-well plate format for prostaglandin E synthase activity

The measurement of prostaglandin E synthase (PGES) activity is cumbersome because the product of the reaction, PGE(2), is not readily quantitated by spectral means. The activity of isolated PGES is typically determined by PGE(2) immunoassay or by high-performance liquid chromatography using radiolabeled substrate. A relatively rapid continuous spectrophotometric assay which uses 15-hydroxyprostaglandin dehydrogenase (PGDH) to couple the oxidation of the 15-hydroxy group of PGE(2) to the formation of NADH was developed. PGDH is relatively specific for PGE(2) over the substrate for the PGES reaction, PGH(2), allowing a highly reproducible assay of PGES activity to be obtained.

The role of spinal neuropeptides and prostaglandins in opioid physical dependence

This study examined the role of spinal calcitonin gene-related peptide (CGRP), substance P, and prostaglandins in the development and expression of opioid physical dependence. Administration of escalating doses (5 - 100 mg kg-1, i.p.) of morphine for 7 days markedly elevated CGRP and substance P- immunoreactivity in the dorsal horn of the rat spinal cord. Naloxone (2 mg kg-1, i.p.) challenge decreased both CGRP and substance P immunoreactivity and precipitated a robust withdrawal syndrome. Acute intrathecal pre-treatment with a CGRP receptor antagonist, CGRP(8 - 37) (4, 8 microg), a substance P receptor antagonist, SR 140333 (1.4, 2.8 microg), a cyclo-oxygenase (COX) inhibitor, ketorolac (30, 45 microg), and COX-2 selective inhibitors, DuP 697 (10, 30 microg) and nimesulide (30 microg), 30 min before naloxone challenge, partially attenuated the symptoms of morphine withdrawal. CGRP(8 - 37) (8 microg), but no other agents, inhibited the decrease in CGRP immunoreactivity. Chronic intrathecal treatment with CGRP(8 - 37) (4, 8 microg), SR 140333 (1.4 microg), ketorolac (15, 30 microg), DuP 697 (10, 30micro g), and nimesulide (30 microg), delivered with daily morphine injection significantly attenuated both the symptoms of withdrawal and the decrease in CGRP but not substance P immunoreactivity. The results of this study suggest that activation of CGRP and substance P receptors, at the spinal level, contributes to the induction and expression of opioid physical dependence and that this activity may be partially expressed through the intermediary actions of prostaglandins.

Potential adverse effects of cyclooxygenase-2 inhibition: evidence from animal models of inflammation

Cyclooxygenase (COX; prostaglandin H synthase, prostaglandin endoperoxidase) is the key enzyme in the synthesis of the prostaglandin and thromboxane families of eicosanoid mediators, and is the target for the nonsteroidal anti-inflammatory drugs (NSAIDs). The identification of an inducible COX isoform, COX-2, and the demonstration of its specific expression at sites of inflammation suggested that it may provide a useful therapeutic target for novel anti-inflammatory drugs. Inhibition of an enzyme that is not expressed in most healthy tissues would potentially avoid most of the adverse effects associated with NSAIDs, which target a constitutively expressed isoform, COX-1. The development of novel 'super aspirins' with high selectivity towards the inhibition of COX-2 showed that this hypothesis was well-founded and that high levels of these drugs could be tolerated without these serious adverse effects. The first two of these new generation NSAIDs, celecoxib and rofecoxib, are now in clinical use. More recently, however, concern has been expressed that COX-2 inhibition may in fact have a number of potential, previously hidden, pitfalls. These have arisen from the demonstration that COX-2 induction is not exclusively associated with the onset of an inflammatory reaction, with expression limited to inflammatory sites. In fact, COX-2 is expressed more chronically, and is also seen during the resolution of inflammation and in areas of wound-healing. The application of COX-2-selective inhibitors during these periods has been shown to be deleterious in that resolution of inflammation is delayed, gastric ulcer healing is delayed and, in some patients, ulcers have been shown to progress further to perforation. The suggestion has now been made that, in these situations, COX-2 may help resolve the pathology, perhaps by generating alternative series of prostaglandins such as the cyclopentenone prostaglandins. The finding that these prostaglandins can affect proteins by direct chemical modifications as well as having their own receptor families has rekindled debate on the deleterious and beneficial effects of prostanoids, and the implications of inhibiting the production of these mediators, in the body. Therefore, in this review we discuss the role of COX-2 in inflammation and the potential adverse effects of its inhibition.

Mechanism of acetaminophen inhibition of cyclooxygenase isoforms

Acetaminophen has similar analgesic and antipyretic properties to nonsteroidal antiinflammatory drugs (NSAIDs), which act via inhibition of cyclooxygenase enzymes. However, unlike NSAIDs, acetaminophen is at best weakly antiinflammatory. The mechanism by which acetaminophen exerts its therapeutic action has yet to be fully determined, as under most circumstances, acetaminophen is a very weak cyclooxygenase inhibitor. The potency of acetaminophen against both purified ovine cyclooxygenase-1 (oCOX-1) and human cyclooxygenase-2 (hCOX-2) was increased approximately 30-fold by the presence of glutathione peroxidase and glutathione to give IC50 values of 33 microM and 980 microM, respectively. Acetaminophen was found to be a good reducing agent of both oCOX-1 and hCOX-2. The results are consistent with a mechanism of inhibition of acetaminophen in which it acts to reduce the active oxidized form of COX to the resting form. Inhibition would therefore be more effective under conditions of low peroxide concentration, consistent with the known tissue selectivity of acetaminophen.

Non-steroidal anti-inflammatory drugs with activity against either cyclooxygenase 1 or cyclooxygenase 2 inhibit colorectal cancer in a DMH rodent model by inducing apoptosis and inhibiting cell proliferation

BACKGROUND

Standard non-steroidal anti-inflammatory drugs (NSAIDs) reduce the risk of colorectal cancer by 40-60% but the mechanism by which this occurs is uncertain. Selective cyclooxygenase 2 inhibitors are potentially ideal chemopreventive agents as they are less toxic than standard NSAIDs. No study has compared the efficacy of these drugs at clinically relevant doses in a tumour model.

AIMS

To assess the efficacy of a range of NSAIDs with varying activity against the two cyclooxygenase isoforms in a rodent colorectal carcinogen model at anti-inflammatory doses and to explore the effect of NSAIDs on the rate of tumour apoptosis and proliferation.

METHODS

Colorectal tumours were induced in six week old Sprague-Dawley rats with five weekly doses of 1,2 dimethylhydrazine. Test agents were: indomethacin 2 mg/kg/day, meloxicam 0.6 mg/kg/day, celecoxib 6 mg/kg/day, and sulindac sulphone 40 mg/kg/day. Sulindac was tested at its chemoprotective dose of 20 mg/kg/day. After 23 weeks the number and volume of tumours per animal were recorded. Histology was performed. Tumour apoptosis was quantified on haematoxylin-eosin sections. Tumour proliferation was quantified using an immunohistochemical stain for bromodexoyuridine incorporation.

RESULTS

Test agents effectively reduced the number and volume of tumours developing in the treatment period. In all groups there was an increase in the rate of tumour apoptosis and a reduced rate of proliferation.

CONCLUSIONS

These data suggest that the chemopreventive effect of NSAIDs is independent of their cyclooxygenase inhibitory profile. One potential mechanism for their action may be through induction of apoptosis and inhibition of proliferation.

The optimal analgesic dose of rofecoxib: Overview of six randomized controlled trials

BACKGROUND

Rofecoxib, which specifically inhibits cyclooxygenase-2, is indicated for relief of the signs and symptoms of osteoarthritis and for the management of acute pain in adults. The authors present an overview of six placebo-controlled trials designed to evaluate the single-dose analgesic efficacy of a range of doses of rofecoxib in the treatment of postoperative dental pain.

METHODS

The six studies included doses of rofecoxib ranging from 7.5 to 500 milligrams. Maximal analgesic doses of a nonsteroidal anti-inflammatory drug, or NSAID, either naproxen sodium (550 mg) or ibuprofen (400 mg), were used as active comparators in each study. Analgesic efficacy was assessed with the use of validated self-administered questionnaires. The primary endpoint in each study was the total pain relief over the eight-hour postdose period. Additional endpoints were used to characterize the onset of analgesia and peak analgesic effect.

RESULTS

The results of these studies demonstrated that the efficacy of rofecoxib was dose-related, with 50 mg being consistently more effective than placebo for all measures of analgesic efficacy. Moreover, 50 mg was the lowest dose that reproducibly demonstrated an analgesic effect comparable to the effect of maximum single analgesic doses of NSAIDs.

CONCLUSION

The results of these studies support the recommended dose of 50 mg of rofecoxib once daily for the management of pain.

CLINICAL IMPLICATIONS

Rofecoxib, at a dose of 50 mg, is effective in the management of postoperative dental pain.

Non-steroidal anti-inflammatory drugs with different cyclooxygenase inhibitory profiles that prevent aberrant crypt foci formation but vary in acute gastrotoxicity in a rat model

BACKGROUND

Standard non-steroidal anti-inflammatory drugs (NSAIDs) reduce the risk of colorectal cancer; however, their use as preventive agents is limited by their inherent toxicity. Drugs that selectively inhibit cyclooxygenase-2 (COX-2) may be useful in this setting as they are supposedly less toxic. No study has directly compared the ability of standard NSAIDs and selective COX-2 inhibitors to inhibit colorectal cancer at clinically relevant doses.

METHODS

Aberrant crypt foci (ACF) were induced in Sprague-Dawley rats by using 1,2-dimethylhydrazine (DMH). Test agents or vehicle were then administered for 3 weeks, twice daily through orogastric gavage. At the end of this period, the number and multiplicity of ACF were determined. The agents tested at equivalent anti-inflammatory doses were: sulindac and indomethacin (standard NSAIDs), meloxicam (selective COX-2 inhibitor), celecoxib (specific COX-2 inhibitor) and sulindac sulfone (no known COX activity). Acute gastrotoxicity of NSAID in rats was compared by using quantitative histology.

RESULTS

All test agents reduced the number of ACF. There was a 42% reduction with indomethacin, 46% with sulindac, 46% with meloxicam, 22% with celecoxib and 36% with sulindac sulfone. Only the COX-2 inhibitors caused no significant gastrotoxicity in rats.

CONCLUSIONS

Cyclooxygenase-2 inhibitors are potentially ideal chemopreventive agents as they inhibit ACF and are not gastrotoxic.

Preferential inhibition of cyclooxygenase-2 by meloxicam in human rheumatoid synoviocytes

The aim of this study was to evaluate the anti-inflammatory effect of 4-hydroxy-2-methyl-N-[5-methyl-2-thiazolyl]-2H-1, 2-benzothiazine-3-carboxamide-1,1-dioxide (meloxicam) using cultured rheumatoid synovial fibroblast-like cells (synoviocytes). Synoviocytes were treated with meloxicam in the presence or absence of interleukin-1beta. Meloxicam had no effect on both cyclooxygenase-1 and -2 expression as determined by Western blot analysis, immunohistochemical staining, and reverse transcription polymerase chain reaction (RT-PCR). Even the lower doses of meloxicam inhibited cyclooxygenase-2 activity, but only the higher doses of meloxicam inhibited cyclooxygenase-1 activity as determined by prostaglandin E(2) synthesis assay. So meloxicam had a preferential inhibitory effect of cyclooxygenase-2 relative to cyclooxygenase-1 on cultured rheumatoid synoviocytes without affecting cyclooxygenase expression. On the other hand, indomethacin had no selectivity and dexamethasone inhibited the expression of cyclooxygenase-2. Our data indicate that clinical efficacy and safety of meloxicam for rheumatoid arthritis may result from its preferential inhibition of cyclooxygenase-2 activity relative to cyclooxygenase-1 on rheumatoid synoviocytes.

Synthesis and biological evaluation of 3-heteroaryloxy-4-phenyl-2(5H)-furanones as selective COX-2 inhibitors

A series of 3-heteroaryloxy4-phenyl-2-5H)-furanones were prepared and evaluated for their potency and selectivity as COX-2 inhibitors. This led to the identification of L-778,736 as a potent, orally active and selective inhibitor of the COX-2 enzyme.

A new structural variation on the methanesulfonylphenyl class of selective cyclooxygenase-2 inhibitors

By inserting an oxygen link between the 3-fluorophenyl and the lactone ring of 5,5-dimethyl-3-(3fluorophenyl)-4-(4-methanesulfonylphenyl)-2 (5H)-furanone 1 (DFU), analogs with enhanced in vitro COX-2 inhibitory potency as well as in vivo potency in models of inflammation were obtained.

The discovery of rofecoxib, [MK 966, Vioxx, 4-(4'-methylsulfonylphenyl)-3-phenyl-2(5H)-furanone], an orally active cyclooxygenase-2-inhibitor

The development of a COX-2 inhibitor rofecoxib (MK 966, Vioxx) is described. It is essentially equipotent to indomethacin both in vitro and in vivo but without the ulcerogenic side effect due to COX-1 inhibition.