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

The Emerging Role of the Double-Edged Impact of Arachidonic Acid- Derived Eicosanoids in the Neuroinflammatory Background of Depression

Eicosanoids are arachidonic acid (AA) derivatives belonging to a family of lipid signalling mediators that are engaged in both physiological and pathological processes in the brain. Recently, their implication in the prolonged inflammatory response has become a focus of particular interest because, in contrast to acute inflammation, chronic inflammatory processes within the central nervous system (CNS) are crucial for the development of brain pathologies including depression. The synthesis of eicosanoids is catalysed primarily by cyclooxygenases (COX), which are involved in the production of pro-inflammatory AA metabolites, including prostaglandins and thromboxanes. Moreover, eicosanoid synthesis is catalysed by lipoxygenases (LOXs), which generate both leukotrienes and anti-inflammatory derivatives such as lipoxins. Thus, AA metabolites have double- edged pro-inflammatory and anti-inflammatory, pro-resolving properties, and an imbalance between these metabolites has been proposed as a contributor or even the basis for chronic neuroinflammatory effects. This review focuses on important evidence regarding eicosanoid-related pathways (with special emphasis on prostaglandins and lipoxins) that has added a new layer of complexity to the idea of targeting the double-edged AA-derivative pathways for therapeutic benefits in depression. We also sought to explore future research directions that can support a pro-resolving response to control the balance between eicosanoids and thus to reduce the chronic neuroinflammation that underlies at least a portion of depressive disorders.

Resolution of inflammation as a novel chemopreventive strategy

Acute inflammation, a physiologic response to protect cells from microbial infection and other noxious stimuli, is automatically terminated by endogenous anti-inflammatory and pro-resolving mediators to restore homeostatic conditions. However, if timely resolution of inflammation is failed, inflammation persists and can progress to a chronic inflammation which has long been thought as a predisposing factor to carcinogenesis. Excessive and pathologic inflammation causes DNA damage, genomic instability, epigenetic dysregulation, and alteration of intracellular signaling, all of which are involved in neoplastic transformation. To prevent chronic inflammation and resulting inflammation-promoted cancer development, understanding the process that resolves inflammation is essential. Resolution of inflammation is an active coordinated process regulated by distinct anti-inflammatory and pro-resolving endogenous lipid mediators, such as resolvins and lipoxins. The role of pro-inflammatory signaling in carcinogenesis has become more and more evident and well characterized, but the potential role of pro-resolving mediators in cancer prevention remains still elusive. In searching for an efficacious way to prevent chronic inflammation-associated cancer, the pro-resolving signal transduction pathways and their regulators should be unraveled.

Screening New Drugs for Immunotoxic Potential: I. Assessment of the Effects of Conventional Nonsteroidal Anti-Inflammatory Drugs and Selective COX-2 Inhibitors on In Vitro and In Vivo Phagocytic Activity

Although both experimental and clinical literature contain reports suggestive of associations between enhanced susceptibility to soft tissue infections and nonsteroidal anti-inflammatory drug (NSAID) use, the immunotoxicological potential of this class of therapeutic agents has not been thoroughly investigated. In consideration of the widespread clinical use of these agents, we have initiated studies of the interaction between NSAIDs (both nonselective and selective COX-2 inhibitors) and the immune system. This communication describes the conduct and results of assessments of the effects of NSAIDs on the in vitro phagocytic activity of rat macrophages and canine neutrophils and on the functional activity of the intact murine mononuclear phagocytic system. During in vitro experiments 0.1 to 10 muM concentrations of naproxen, indomethacin, and experimental selective COX-2 inhibitors, SC-236, SC-245 and SC-791, caused marginal, but statistically significant, reductions in phagocytic activity of resident rat peritoneal macrophages. The effects were consistently small and there was no evidence of concentration-response relationships. An in vitro concentration of 10 muM of either SC-236 or SC-791 was required to decrease phagocytosis by dog neutrophils. Repeated oral doses of either naproxen or SC-236 (3, 10, or 30 mg/kg twice daily for 3 days) were without effect on the intact phagocytic system of the mouse. A potential immunotoxicologic effect based on direct impairment of phagocytic processes seems an unlikely explanation for drug-induced susceptibility to infection reported earlier. However, the results of these experiments do not support an unequivocal conclusion relative to immunotoxicological potential of either conventional NSAIDs or selective COX-2 inhibitors. Further studies on other components of the immune system are needed to fully explore possible immunomodulatory effects of NSAIDs.

Cyclooxygenase and neuroinflammation in Parkinson's disease neurodegeneration

Cyclooxygenase (COX) expression in the brain is associated with pro-inflammatory activities, which are instrumental in neurodegenerative processes such as Parkinson’s disease (PD). It is discussed that drugs with the capacity to rescue dopaminergic neurons from microglia toxicity and neuroinflammatory processes may result in an amelioration of parkinsonian symptoms by delaying the onset or slowing progression. This article reviews the involvement of COX in neuroinflammation, specifically focussing at the role of selective COX-2 inhibition in neuroinflammation and neurodegeneration in Parkinson’s disease.

Flavocoxid, a dual inhibitor of cyclooxygenase-2 and 5-lipoxygenase, reduces pancreatic damage in an experimental model of acute pancreatitis

BACKGROUND AND PURPOSE

Acute pancreatitis is an autodigestive process resulting in acute inflammation of the pancreas. Accumulating evidence indicates the essential contribution of cyclooxygenase (COX)-2 and 5-lipoxygenase (5-LOX) to acute pancreatitis. We studied the effects of flavocoxid, a plant-derived dual inhibitor of COX-2 and 5-LOX, in a model of caerulein (CER)-induced acute pancreatitis.

EXPERIMENTAL APPROACH

Rats were given CER (80 µg·kg⁻¹ for each of four injections at hourly intervals) or vehicle (Sham-CER). Animals were then randomized to receive flavocoxid (20 mg·kg⁻¹ i.p.) or vehicle, 30 min after the first CER injection. Two hours after the last CER injection, we evaluated damage to the pancreas by histological methods; serum levels of amylase, lipase, leukotriene (LT)B₄ and prostaglandin (PG)E₂ ; pancreatic expression of COX-2 and 5-LOX and tumour necrosis factor-α (TNF-α) gene expression by real-time polymerase chain reaction.

KEY RESULTS

Caerulein induced inflammatory changes in the pancreas and raised values of the other variables measured. In CER-treated animals, but not in those given saline, flavocoxid inhibited COX-2 and 5-LOX expression, reduced serum levels of lipase and amylase and the degree of pancreatic oedema. Treatment with flavocoxid blunted the increased pancreatic TNF-α mRNA expression, serum leukotriene B₄ and prostaglandin E₂ levels, and protected against histological damage in terms of vacuolization and leukocyte infiltration.

CONCLUSIONS AND IMPLICATIONS

Our results confirm the key role of both COX-2 and 5-LOX in the inflammatory response to acute pancreatitis. Flavocoxid may provide a potential therapeutic approach to the treatment of patients at high risk of developing this life-threatening condition.

[11C]-PK11195 PET: quantification of neuroinflammation and a monitor of anti-inflammatory treatment in Parkinson's disease?

[(11)C]-PK11195 PET has been used for in vivo brain imaging of microglia activation in Parkinson's disease (PD) patients. COX-2 inhibition has been shown to reduce neuroinflammation and neurodegeneration in animal models of PD. This pilot study assessed the use of [(11)C]-PK11195 PET to quantify neuroinflammation and evaluate the ability of COX-2 inhibition to reduce neuroinflammation in PD patients.

METHODS

Fourteen PD patients and eight healthy, age matched controls underwent a [(11)C]-PK11195 PET and MRI scan. Five PD patients were scanned before and after one month of celecoxib treatment 200 mg/day. Arterial plasma sampling and metabolite analysis were performed to create plasma input curves. A 2-compartment model and Logan analysis were applied and parametric DV images were compared using t-test in SPM2. In addition a simplified reference region model (SRTM) was applied, with both the cerebellum and a reference region derived from cluster analysis.

RESULTS

Using the cluster analysis, PD patients showed higher contralateral putamen BP and midbrain BP compared to controls, although considerable overlap was seen and differences were not statistically significant. Unexpectedly, BP and DV after celecoxib were slightly higher. Cerebellum as reference region resulted in lower BP values and k(3)/k(4) gave 10-fold higher BP values. Linearization of the data did not show differences between PD patients and controls.

CONCLUSIONS

In current practice, [(11)C]-PK11195 seems an unsuitable tracer for accurate or reliable quantification of neuroinflammation. Refinement of [(11)C]-PK11195 uptake analysis and, more importantly, further development of better tracers is necessary to enable accurate measurement of neuroinflammation and effects of anti-inflammatory treatment in patients.

Cyclooxygenase expression and prostanoid production in pyloric and duodenal mucosae in dogs after administration of nonsteroidal anti-inflammatory drugs

OBJECTIVE

To assess cyclooxygenase (COX) expression and prostanoid concentrations in pyloric and duodenal mucosae of dogs after administration of nonsteroidal anti-inflammatory drugs (NSAIDs).

ANIMALS

8 healthy dogs.

PROCEDURES

Each dog received carprofen (4.4 mg/kg, q 24 h), deracoxib (2 mg/kg, q 24 h), aspirin (10 mg/kg, q 12 h), and placebo (1 dog treat, q 24 h) orally for 3 days (4-week interval between treatments). Before study commencement (baseline) and on day 3 of each treatment, pyloric and duodenal mucosal appearance was assessed endoscopically and biopsy specimens were obtained for histologic examination. Cyclooxygenase-1 and COX-2 protein expressions were assessed via western blotting, and prostanoid concentrations were measured via ELISAs. An ANOVA was used to analyze data.

RESULTS

Treatments had no effect on mucosal appearance and ulceration was not evident histologically. In pyloric and duodenal mucosae, COX-1 expression was unaffected by treatments. Cyclooxygenase-2 expression remained unchanged in pyloric mucosa; in duodenal mucosa, aspirin significantly increased COX-2 expression, compared with effects of deracoxib and carprofen. At baseline, total prostaglandin and thromboxane B2 concentrations in pyloric mucosa were significantly greater than those in duodenal mucosa. Aspirin significantly decreased both prostanoid concentrations in both mucosal tissues, compared with other treatments. In pyloric mucosa, carprofen administration significantly decreased total prostaglandin and thromboxane B2 concentrations, compared with deracoxib administration.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, prostanoid synthesis was greater in pyloric mucosa than it was in duodenal mucosa. Nonselective NSAIDs significantly decreased prostanoid concentrations in these mucosae, compared with the effects of a selective COX-2 NSAID.

The effects of COX-1 and COX-2 inhibitors on prostaglandin synthesis and the formation of heterotopic bone in a rat model

INTRODUCTION

Traumatic heterotopic ossification (HO) is a common clinical condition associated with various orthopedic procedures that involve injury to soft tissues near bone. In this study, we tested the hypothesis that the prophylactic effects of NSAID's in the treatment of HO are mediated via inhibition of the COX-2 enzyme. Here we describe a rat model that simulates HO in the human that was used to test the above hypothesis.

MATERIALS AND METHODS

Heterotopic ossification was surgically induced in the quadriceps by injury to the muscle and femoral periosteum and transplantation of donor bone marrow cells containing osteoprogenitors into the site of injury. HO was imaged and quantified by micro-CT scanning of femurs removed from sacrificed animals at 6 weeks post-injury, three-dimensional computer reconstructions of the scanned bones and computer-assisted morphometric analysis. Prostaglandin E(2) (PGE(2)) synthesis was quantified using an enzyme immunoassay system. The effects of a nonselective COX inhibitor or specific inhibitors of COX-1 or COX-2 following oral administration on the content of ectopic bone and PGE(2) were also measured.

RESULTS

Micro-CT and histological analyses demonstrated that all of the femurs in operated limbs developed HO in the vastus lateralis muscle belly of the quadriceps close to the anterior femur. Only the COX-1,2 nonselective and COX-2 inhibitors significantly decreased HO formation (by about one-third in each case; P < 0.05). PGE(2) synthesis at the site of injury was increased 50- and 100-fold (to 25 ng/g tissue) within 1 and 7 days, respectively, post-injury with the levels declining to near baseline within 2 weeks of surgery. Both the COX-1,2 nonselective and COX-2 inhibitors significantly decreased PGE(2) levels to 25% of control HO levels within 24 h of the first administration, even at low dosages. The COX-1 inhibitor only produced the same effect after 1 week of administration.

CONCLUSION

These findings suggest that although inhibitors of COX-2 or COX-1 reduced PGE(2) synthesis, only the COX-2 enzyme plays a role in the mechanism of traumatic HO.

Inhibition of cyclooxygenase-2 in experimental severe acute pancreatitis

BACKGROUND

The standard treatment for acute pancreatitis (AP) is still based on supportive care. The search for a new drug that could change the natural history of the disease is a continuing challenge for many researchers. The aim of this study is to evaluate the effect of a cyclooxygenase-2 (COX-2) inhibitor on experimental AP in rats.

METHODS

The animals were divided into 2 groups: Group 1 (n = 30)-animals with taurocholate-induced AP treated with parecoxib (40 mg/kg). Group 2 (n = 30)-animals with taurocholate-induced AP that received saline. The COX-2 inhibitor (parecoxib) was injected immediately after AP induction, through the penis dorsal vein. The parameters evaluated were histology, serum levels of amylase, IL-6 and IL-10, and mortality rate.

RESULTS

The serum levels of IL-6 and IL-10 in the parecoxib-treated group were lower than the control group. The amylase serum levels and the mortality rate remained unchanged in the treated animals. Histologic morphology also was unaltered, except for fat necrosis, which was higher in parecoxib-treated rats.

CONCLUSION

Inhibition of Cox-2 decreases the systemic release of inflammatory cytokines, but has a poor effect on the direct pancreas injury caused by taurocholate.

Is COX-2 a perpetrator or a protector? Selective COX-2 inhibitors remain controversial

COX-2(cyclooxygenase-2) has sparked a surge in pharmaceutical interest since its discovery at the beginning of the 1990s. Several COX-2 selective inhibitors that avoid gastrointestinal side effects have been successfully launched into the market in recent years. The first selective COX-2 inhibitor, celecoxib, entered the market in December 1998 [corrected] However, there are a few organs that physiologically and functionally express COX-2, particularly the glomeruli of the kidney and the cortex of the brain. Inhibition of COX-2 expression in these organs possibly causes heart attack and stroke in long-term COX-2 inhibitor users. Recently, a USA Food and Drug Agency (FDA) advisory panel re-evaluated COX-2 inhibitors and unanimously concluded that the entire class of COX-2 inhibitors increase the risk of cardiovascular problems. Thus the use of COX-2 inhibitors is still controversial, and there is a challenge for not only pharmacologists, but also the pharmaceutical industry, to develop improved painkilling and anti-inflammatory drugs. This may involve exploring a new generation of COX-2 inhibitors with different inhibitory mechanisms through computer-aided design, screening different sources of inhibitors with lower selectivity, or seeking completely new targets. Synthetic COX-2 inhibitors have high selectivity and the advantage of irreversible inhibition, whereas naturally derived COX-2 inhibitors have lower selectivity and fewer side effects, with the medical effects in general not being as striking as those achieved using synthetic inhibitors. This review discusses the mechanism of COX-2 inhibitor therapy and a possible new way of exploration in the development of anti-inflammatory, analgetic, and antipyretic drugs.

Treatment costs to prevent or treat upper gastrointestinal adverse events associated with NSAIDs

The widespread use of nonselective NSAIDs and cyclo-oxygenase (COX)-2 inhibitors has a substantial impact on healthcare budgets worldwide. The cost of their gastrointestinal (GI) adverse effects is a major component of their direct cost and has received much attention in the literature. Published studies have often differed in their methodologies and results. It is important for decision makers to understand the reasons for these differences in order to make informed decisions. We conducted a literature review to summarise data that evaluate the direct costs of NSAID-related GI adverse effects worldwide. This resulted in 789 articles from which 29 studies met the inclusion criteria and were fully reviewed. Of these 29, the 9 studies that assessed the cost of COX-2 inhibitors were all based on decision economic models, compared with only 7 of the remaining 20 studies, which assessed the cost of nonselective NSAIDs. In most studies, the perspective was that of the healthcare payer and the costs assessed were reimbursement costs. Costs of GI events almost doubled between regular users and non-users of nonselective NSAIDs and were much higher in high-dose versus low-dose users. The ratio of the total cost of nonselective NSAIDs to their acquisition cost reported in all studies varied from 1.36 to 2.12. Both of these numbers were reported in one single study assessing several different NSAIDs in France. Thus, the GI adverse events attributable to nonselective NSAIDs are substantial, and their costs often exceed the cost of the nonselective NSAID itself.The acquisition cost of the COX-2 inhibitors was the main driver of their total cost. The GI adverse effects with the COX-2 inhibitors added 10-20% to their acquisition cost in North America, while this increase was about 50% in some European countries. Decision analysis models showed that the direct costs of COX-2 inhibitors were lower than those of nonselective NSAIDs in patients at risk of NSAID gastropathy but higher in patients at no to low risk of gastropathy. Thus, from an economic perspective, the healthcare system would benefit from treating patients at risk of NSAID gastropathy with COX-2 inhibitors, but not those at no to low risk.

Expression of cyclooxygenase-2 in corneal cells after photorefractive keratectomy and laser in situ keratomileusis in rabbits

PURPOSE

To compare the expression pattern of cyclooxygenase-2 (COX-2) in rabbit corneal cells after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) with the same refractive correction.

SETTING

Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan.

METHODS

Thirty adult albino rabbits were used in the study. Photorefractive keratectomy or LASIK was performed in 1 eye of each animal for the same refractive correction. Each animal was killed after healing intervals up to 6 months. Paraffin sections of the cornea were processed for immunohistochemistry for COX-2 and NFkappaB (p65).

RESULTS

After PRK, the central and peripheral corneal epithelia up-regulated COX-2 at 3 days; the central epithelium was positive at 4 weeks. Central and peripheral epithelia returned to negative 3 months later. After LASIK, the central epithelium on the corneal flap up-regulated COX-2 at 1 and 2 weeks; it returned to negative at 4 weeks. The peripheral epithelium was labeled with the antibody. Keratocytes around the stromal incision between the flap and the stromal bed up-regulated COX-2 and returned to negative at 3 months. COX-1 was not detected immunohistochemically in corneal tissue during the healing intervals after both procedures. Nuclear factor kappaB was detected in the cytoplasm and nuclei of migrating corneal epithelial cells 1 day after PRK, was positive in the cytoplasm at 3 days and negative in cytoplasm and nuclei at week and later.

CONCLUSIONS

Migrating injured epithelium expressed COX-2 until week 4 during post-PRK healing. Central uninjured epithelium as well as stromal keratocytes expressed COX-2 from 3 days to 2 weeks after LASIK. Uninjured peripheral epithelium also expressed COX-2 at 4 weeks. Activation of stromal keratocytes may induce expression of COX-2 in overlying uninjured epithelium via the inflammatory cytokine(s)/NFkappaB pathway.

Lipoxins inhibit Akt/PKB activation and cell cycle progression in human mesangial cells

Lipoxins (LX) are endogenously produced eicosanoids with a spectrum of bioactions that suggest anti-inflammatory, pro-resolution roles for these agents. Mesangial cell (MC) proliferation plays a pivotal role in the pathophysiology of glomerular inflammation and is coupled to sclerosis and tubulointerstitial fibrosis. We have previously reported that LXA4 acts through a specific G-protein-coupled-receptor (GPCR) to modulate MC proliferation in response to the proinflammatory mediators LTD4 and platelet-derived growth factor (PDGF). Further investigations revealed that these effects were mediated by modulation of receptor tyrosine kinase activity. Here we have explored the underlying mechanisms and report inhibition of growth factor (PDGF; epithelial growth factor) activation of Akt/PKB by LXA4. LXA4 (10 nmol/L) modulates PDGF-induced (10 ng/ml, 24 hours) decrements in the levels of cyclin kinase inhibitors p21Cip1 and p27Kip1. PDGF-induced increases in CDK2-cyclin E complex formation are also inhibited by LXA4. The potential of LXA4 as an anti-inflammatory therapeutic is compromised by its degradation; this has been circumvented by synthesis of stable analogs. We report that 15-(R/S)-methyl-LXA4 and 16-phenoxy-LXA4 mimic the native compound with respect to modulation of cell proliferation and PDGF-induced changes in cell cycle proteins. In vivo, MC proliferation in response to PDGF is associated with TGFbeta1 production and the subsequent development of renal fibrosis. Here we demonstrate that prolonged (24 to 48 hours) exposure to PDGF is associated with autocrine TGFbeta1 production, which is significantly reduced by LXA4. In aggregate these data demonstrate that LX inhibit PDGF stimulated proliferation via modulation of the PI-3-kinase pathway preventing mitogen-elicited G1-S phase progression and suggest the therapeutic potential of LX as anti-fibrotic agents.

Influence of nonsteroidal anti-inflammatory drug treatment duration and time of onset on recovery from exercise-induced muscle damage in rats

OBJECTIVE

To determine if duration and time of onset of treatment with diclofenac sodium influence force recovery after exercise-induced muscle damage in rats.

DESIGN

Randomized placebo-controlled trial.

SETTING

Animal laboratory.

ANIMALS

A total of 217 female adult Wistar rats.

INTERVENTION

Rats were submitted to a protocol consisting of 450 eccentric contractions of the ankle dorsiflexors. Treatment by gavage with diclofenac sodium (1 mg/kg, twice daily) was started at different times pre- and postprotocol or for various treatment durations.

MAIN OUTCOME MEASURES

In vitro contractile properties.

RESULTS

When treatment was initiated shortly postprotocol, force recovery was roughly proportional to treatment duration during the first 3 days but not at 7 and 28 days postprotocol. A 7-day treatment was no more effective than 1- or 2-day treatments when force was measured at 7 and 28 days; however, such prolonged treatment had no deleterious effect on muscle force at either time. A single-dose prophylactic treatment was as effective as a 2-day treatment initiated soon after the protocol when force was assessed 2 days postprotocol; on the other end, a treatment delayed for 3 days had no effect when force was measured at 7 days.

CONCLUSIONS

Treatment with diclofenac sodium extending past the acute inflammatory phase was no more effective than short and timely treatment in this model of skeletal muscle damage.

Cyclooxygenase-2 expression in early gastric cancer, intestinal metaplasia and Helicobacter pylori infection

Cyclooxygenase (COX) is the crucial enzyme for synthesis of prostaglandins and occurs in two isoforms COX-1 and COX-2. Whilst COX-1 is constantly expressed in the gastrointestinal tract in large quantities and probably maintains mucosal integrity through constant generation of prostaglandins, COX-2 is induced principally during inflammation. In early gastric cancer and in intestinal metaplasia the expression of COX-2 in patients infected by Helicobacter pylori is increased in intestinal type compared to diffuse type gastric cancer and in intestinal metaplasia. In tumours of mixed type, COX-2 is also increased in the intestinal component compared to the diffuse component. Whilst there has been success of COX-2 inhibition for chemoprevention in colon cancer, a similar role in gastric cancer needs to be carefully assessed in the light of reported adverse effects and whether the precancerous condition, intestinal metaplasia, can truly regress.