Cyclooxygenases (COX) -1 and -2 are key mediators of the inflammatory response in the central nervous system. Since COX-2 is inducible by inflammatory stimuli, it has been traditionally considered as ...the most appropriate target for anti-inflammatory drugs. However, the specific roles of COX-1 and COX-2 in modulating a neuroinflammatory response are unclear. Recently, we demonstrated that COX-1 deficient mice show decreased neuroinflammatory response and neuronal damage in response to lipopolysaccharide (LPS).
In this study, we investigated the role of COX-2 in the neuroinflammatory response to intracerebroventricular-injected LPS (5 mug), a model of direct activation of innate immunity, using COX-2 deficient (COX-2-/-) and wild type (COX-2+/+) mice, as well as COX-2+/+ mice pretreated for 6 weeks with celecoxib, a COX-2 selective inhibitor.
Twenty-four hours after LPS injection, COX-2-/- mice showed increased neuronal damage, glial cell activation, mRNA and protein expression of markers of inflammation and oxidative stress, such as cytokines, chemokines, iNOS and NADPH oxidase. Brain protein levels of IL-1beta, NADPH oxidase subunit p67phox, and phosphorylated-signal transducer and activator of transcription 3 (STAT3) were higher in COX-2-/- and in celecoxib-treated mice, compared to COX-2+/+ mice. The increased neuroinflammatory response in COX-2-/- mice was likely mediated by the upregulation of STAT3 and suppressor of cytokine signaling 3 (SOCS3).
These results show that inhibiting COX-2 activity can exacerbate the inflammatory response to LPS, possibly by increasing glial cells activation and upregulating the STAT3 and SOCS3 pathways in the brain.
Cyclooxygenase (COX) -1 and -2 metabolize arachidonic acid to prostanoids and reactive oxygen species, major players in the neuroinflammatory process. While most reports have focused on the inducible ...isoform, COX-2, the contribution of COX-1 to the inflammatory response is unclear. In the present study, the contribution of COX-1 in the neuroinflammatory response to intracerebroventricular lipopolysaccharide (LPS) was investigated using COX-1 deficient (COX-1⁻/⁻) mice or wild-type (COX-1⁺/⁺) mice pretreated with SC-560, a selective COX-1 inhibitor. Twenty-four hours after lipopolysaccharide (LPS) injection, COX-1⁻/⁻ mice showed decreased protein oxidation and LPS-induced neuronal damage in the hippocampus compared with COX-1⁺/⁺ mice. COX-1⁻/⁻ mice showed a significant reduction of microglial activation, proinflammatory mediators, and expression of COX-2, inducible NOS, and NADPH oxidase. The transcriptional down-regulation of cytokines and other inflammatory markers in COX-1⁻/⁻ mice was mediated by a reduced activation of NF-κB and signal transducer and activator of transcription 3. Administration of SC-560 prior to LPS injection also attenuated the neuroinflammatory response by decreasing brain levels of prostaglandin (PG)E₂, PGD₂, PGF₂α, and thromboxane B₂, as well as the expression of proinflammatory cytokines and chemokine. These findings suggest that COX-1 plays a previously unrecognized role in neuroinflammatory damage.--Choi, S-H., Langenbach, R., Bosetti, F. Genetic deletion or pharmacological inhibition of cyclooxygenase-1 attenuate lipopolysaccharide-induced inflammatory response and brain injury.
Therapeutic use of cyclooxygenase-inhibiting (COX-inhibiting) nonsteroidal antiinflammatory drugs (NSAIDs) is often complicated by renal side effects including hypertension and edema. The present ...studies were undertaken to elucidate the roles of COX1 and COX2 in regulating blood pressure and renal function. COX2 inhibitors or gene knockout dramatically augment the pressor effect of angiotensin II (Ang II). Unexpectedly, after a brief increase, the pressor effect of Ang II was abolished by COX1 deficiency (either inhibitor or knockout). Ang II infusion also reduced medullary blood flow in COX2-deficient but not in control or COX1-deficient animals, suggesting synthesis of COX2-dependent vasodilators in the renal medulla. Consistent with this, Ang II failed to stimulate renal medullary prostaglandin E(2) and prostaglandin I(2) production in COX2-deficient animals. Ang II infusion normally promotes natriuresis and diuresis, but COX2 deficiency blocked this effect. Thus, COX1 and COX2 exert opposite effects on systemic blood pressure and renal function. COX2 inhibitors reduce renal medullary blood flow, decrease urine flow, and enhance the pressor effect of Ang II. In contrast, the pressor effect of Ang II is blunted by COX1 inhibition. These results suggest that, rather than having similar cardiovascular effects, the activities of COX1 and COX2 are functionally antagonistic.
Carbon nanotubes (CNTs) are engineered graphene cylinders with numerous applications in engineering, electronics and medicine. However, CNTs cause inflammation and fibrosis in the rodent lung, ...suggesting a potential human health risk. We hypothesized that multi-walled CNTs (MWCNTs) induce two key inflammatory enzymes in macrophages, cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), through activation of extracellular signal-regulated kinases (ERK1,2).
RAW264.7 macrophages were exposed to MWCNTs or carbon black nanoparticles (CBNPs) over a range of doses and time course. Uptake and subcellular localization of MWCNTs was visualized by transmission electron microscopy (TEM). Protein levels of COX-2, iNOS, and ERK1,2 (total ERK and phosphorylated ERK) were measured by Western blot analysis. Prostaglandin-E(2) (PGE(2)) and nitric oxide (NO) levels in cell supernatants were measured by ELISA and Greiss assay, respectively.
MWCNTs, but not CBNPs, induced COX-2 and iNOS in a time- and dose-dependent manner. COX-2 and iNOS induction by MWCNTs correlated with increased PGE(2) and NO production, respectively. MWCNTs caused ERK1,2 activation and inhibition of ERK1,2 (U0126) blocked MWCNT induction of COX-2 and PGE2 production, but did not reduce the induction of iNOS. Inhibition of iNOS (L-NAME) did not affect ERK1,2 activation, nor did L-NAME significantly decrease COX-2 induction by MWCNT. Nickel nanoparticles (NiNPs), which are present in MWCNTs as a residual catalyst, also induced COX-2 via ERK-1,2. However, a comparison of COX-2 induction by MWCNTs containing 4.5 and 1.8% Ni did not show a significant difference in ability to induce COX-2, indicating that characteristics of MWCNTs in addition to Ni content contribute to COX-2 induction.
This study identifies COX-2 and subsequent PGE(2) production, along with iNOS induction and NO production, as inflammatory mediators involved in the macrophage response to MWCNTs. Furthermore, our work demonstrates that COX-2 induction by MWCNTs in RAW264.7 macrophages is ERK1,2-dependent, while iNOS induction by MWCNTs is ERK1,2-independent. Our data also suggest contributory physicochemical factors other than residual Ni catalyst play a role in COX-2 induction to MWCNT.
Studies of the molecular and cellular mechanisms of concanavalin A (ConA)‐induced liver injury have provided important knowledge on the pathogenesis of many liver diseases involving hepatic ...inflammation. However, studies identifying hepato‐protective factors based on the mechanistic understanding of this model are lacking. Evidence suggests that certain prostaglandin (PG) products of cyclooxygenase (COX)‐1 and COX‐2 provide important anti‐inflammatory and cytoprotective functions in some pathophysiological states. In the present study, we demonstrate a protective role of COX‐2 derived PGs in ConA‐induced liver injury. COX‐2−/− mice developed much more severe liver damage upon ConA treatment compared with wild‐type and COX‐1−/− mice. Treatment of COX‐2−/− mice with misoprostol (a PGE1/2 analog) or beraprost (a PGI2 analog) significantly decreased ConA‐induced liver injury. Data from both in vivo and in vitro experiments demonstrated that misoprostol and beraprost acted directly on hepatic leukocytes, including natural killer (NK)T and T cells, and down‐regulated their production of interferon (IFN)‐γ, which are critical in mediating ConA‐induced tissue damage. Collectively, the results provide strong evidence that the protective effects of COX‐2 within the liver are mediated through the production of PGE2 and PGI2, which exert anti‐inflammatory functions. These findings suggest that COX‐2‐derived PGs may have great therapeutic potentials in treating patients with inflammatory liver diseases. (HEPATOLOGY 2007;45:159–169.)
We determined the roles of reactive oxygen species (ROS) in the expression of cyclooxygenase‐2 (COX‐2) and the production of prostaglandin E2 (PGE2) in lipopolysaccharide (LPS)‐activated microglia. ...LPS treatment increased intracellular ROS in rat microglia dose‐dependently. Pre‐treatment with superoxide dismutase (SOD)/catalase, or SOD/catalase mimetics that can scavenge intracellular ROS, significantly attenuated LPS‐induced release in PGE2. Diphenylene iodonium (DPI), a non‐specific NADPH oxidase inhibitor, decreased LPS‐induced PGE2 production. In addition, microglia from NADPH oxidase‐deficient mice produced less PGE2 than those from wild‐type mice following LPS treatment. Furthermore, LPS‐stimulated expression of COX‐2 (determined by RT‐PCR analysis of COX‐2 mRNA and western blot for its protein) was significantly reduced by pre‐treatment with SOD/catalase or SOD/catalase mimetics. SOD/catalase mimetics were more potent than SOD/catalase in reducing COX‐2 expression and PGE2 production. As a comparison, scavenging ROS had no effect on LPS‐induced nitric oxide production in microglia. These results suggest that ROS play a regulatory role in the expression of COX‐2 and the subsequent production of PGE2 during the activation process of microglia. Thus, inhibiting NADPH oxidase activity and subsequent ROS generation in microglia can reduce COX‐2 expression and PGE2 production. These findings suggest a potential therapeutic intervention strategy for the treatment of inflammation‐mediated neurodegenerative diseases.
Influenza is a significant cause of morbidity and mortality worldwide despite extensive research and vaccine availability. The cyclooxygenase (COX) pathway is important in modulating immune responses ...and is also a major target of nonsteroidal anti-inflammatory drugs (NSAIDs) and the newer COX-2 inhibitors. The purpose of the present study was to examine the effect of deficiency of COX-1 or COX-2 on the host response to influenza. We used an influenza A viral infection model in wild type (WT), COX-1-/-, and COX-2-/- mice. Infection induced less severe illness in COX-2-/- mice in comparison to WT and COX-1-/- mice as evidenced by body weight and body temperature changes. Mortality was significantly reduced in COX-2-/- mice. COX-1-/- mice had enhanced inflammation and earlier appearance of proinflammatory cytokines in the BAL fluid, whereas the inflammatory and cytokine responses were blunted in COX-2-/- mice. However, lung viral titers were markedly elevated in COX-2-/- mice relative to WT and COX-1-/- mice on day 4 of infection. Levels of PGE2 were reduced in COX-1-/- airways whereas cysteinyl leukotrienes were elevated in COX-2-/- airways following infection. Thus, deficiency of COX-1 and COX-2 leads to contrasting effects in the host response to influenza infection, and these differences are associated with altered production of prostaglandins and leukotrienes following infection. COX-1 deficiency is detrimental whereas COX-2 deficiency is beneficial to the host during influenza viral infection.
Microglial activation has been implicated in many astrogliosis-related pathological conditions including astroglioma; however, the detailed mechanism is not clear. In this study, we used primary ...enriched microglia and astrocyte cultures to determine the role of microglial prostaglandin E
2 (PGE
2) in the proliferation of astrocytes. The proliferation of astrocytes was measured by BrdU incorporation. The level of PGE
2 was measured by ELISA method. Pharmacological inhibition or genetic ablation of COX-2 in microglia were also applied in this study. We found that proliferation of astrocytes increased following lipopolysaccharide (LPS) treatment in the presence of microglia. Furthermore, increased proliferation of astrocytes was observed in the presence of conditioned media from LPS-treated microglia. The potential involvement of microglial PGE
2 in enhanced astrocyte proliferation was suggested by the findings that PGE
2 production and COX-2 expression in microglia were increased by LPS treatment. In addition, activated microglia-induced increases in astrocyte proliferation were blocked by the PGE
2 antagonist AH6809, COX-2 selective inhibitor DuP-697 or by genetic knockout of microglial COX-2. These findings were further supported by the finding that addition of PGE
2 to the media significantly induced astrocyte proliferation. These results indicate that microglial PGE
2 plays an important role in astrocyte proliferation, identifying PGE
2 as a key neuroinflammatory molecule that triggers the pathological response related to uncontrollable astrocyte proliferation. These findings are important in elucidating the role of activated microglia and PGE
2 in astrocyte proliferation and in suggesting a potential avenue in the use of anti-inflammatory agents for the therapy of astroglioma.
ABSTRACTThe importance of cyclooxygenase‐2 (COX‐2) in mediating Parkinson's disease (PD) was suggested in reports, indicating that COX‐2 selective inhibitors or genetic knockout reduce ...1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced dopaminergic (DA) neurotoxicity in a mouse model of PD. However, cell types and mechanisms underlying the activation of COX‐2 have not been clearly elucidated in these animal studies. Using primary neuron‐glia cultures, we aimed to determine 1) whether microglia participate in 1‐methyl‐4‐phenylpryridinium (MPP+)‐induced COX‐2 activation and 2) whether the activation of COX‐2 contributes to subsequent neurotoxicity. MPP+, in a concentration‐dependent manner, increased prostaglandin E2 (PGE2) production in mixed neuron‐microglia cultures but not in enriched neuron, microglia, or astroglia cultures nor in mixed neuron‐astroglia cultures. MPP+‐induced PGE2 increase was completely abolished by treatment with DuP697, a COX‐2 selective inhibitor. DuP697 also significantly reduced MPP+‐induced DA neurotoxicity as determined by DA uptake assay. Immunocytochemistry and confocal microscopy studies showed enhanced COX‐2 expression in both microglia and neurons after MPP+ treatment. However, neuronal increase in COX‐2 expression was not totally dependent on the production of PGE2 from microglia, since microglia deficient in COX‐2 only attenuated, but did not completely block, MPP+‐increased PGE2 production in mixed neuron‐microglia cultures, suggesting that part of PGE2 production was originated from neurons. Together, these results indicate that MPP+‐induced COX‐2 expression and subsequent PGE2 production depend on interactions between neurons and microglia. Microgliosis may also be responsible for the COX‐2 activation in neurons, leading to the enhanced DA neurotoxicity, which, in turn, reinforces microgliosis. Thus inhibition of microgliosis and COX‐2 activity may stop this vicious circle and be valuable strategies in PD therapy.
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