Activation of macrophage peroxisome proliferator-activated receptor-gamma by diclofenac results in the induction of cyclooxygenase-2 protein and the synthesis of anti-inflammatory cytokines

Effect of the Non-steroidal Anti-inflammatory Drug Diclofenac on Ischemia-Reperfusion Injury in Rat Liver: A Nitric Oxide-Dependent Mechanism

Ischemia/reperfusion injury (IRI) is an inevitable complication of liver surgery and transplantation. The purpose of this study was to examine the beneficial effects of diclofenac on hepatic IRI and the mechanism behind it. Wistar rats' livers were subjected to warm ischemia for 60 min followed by 24 h of reperfusion. Diclofenac was administered intravenously 15 min before ischemia at 10, 20, and 40 mg/kg body weight. To determine the mechanism of diclofenac protection, the NOS inhibitor L-Nitro-arginine methyl ester (L-NAME) was administered intravenously 10 min after diclofenac injection (40 mg/kg). Liver injury was evaluated by aminotransferases (ALT and AST) activities and histopathological analysis. Oxidative stress parameters (SOD, GPX, MPO, GSH, MDA, and PSH) were also determined. Then, eNOS gene transcription and p-eNOS and iNOS protein expressions were evaluated. The transcription factors PPAR-γ and NF-κB in addition to the regulatory protein IκBα were also investigated. Finally, the gene expression levels of inflammatory (COX-2, IL-6, IL-1β, IL-18, TNF-α, HMGB-1, and TLR-4) and apoptosis (Bcl-2 and Bax) markers were measured. Diclofenac, at the optimal dose of 40 mg/kg, decreased liver injury and maintained histological integrity. It also reduced oxidative stress, inflammation, and apoptosis. Its mechanism of action essentially depended on eNOS activation rather than COX-2 inhibition, since pre-treatment with L-NAME abolished all the protective effects of diclofenac. To our knowledge, this is the first study demonstrating that diclofenac protects rat liver against warm IRI through the induction of NO-dependent pathway. Diclofenac reduced oxidative balance, attenuated the activation of the subsequent pro-inflammatory response and decreased cellular and tissue damage. Therefore, diclofenac could be a promising molecule for the prevention of liver IRI.

Linking chemical exposure to lipid homeostasis: A municipal waste water treatment plant influent is obesogenic for zebrafish larvae

Obesity, a risk factor for the development of type-2 diabetes, hypertension, cardiovascular disease, hepatic steatosis and some cancers, has been ranked in the top 10 health risk in the world by the World Health Organization. Despite the growing body of literature evidencing an association between the obesity epidemic and specific chemical exposure across a wide range of animal taxa, very few studies assessed the effects of chemical mixtures and environmental samples on lipid homeostasis. Additionally, the mode of action of several chemicals reported to alter lipid homeostasis is still poorly understood. Aiming to fill some of these gaps, we combined an in vivo assay with the model species zebrafish (Danio rerio) to screen lipid accumulation and evaluate expression changes of key genes involved in lipid homeostasis, alongside with an in vitro transactivation assay using human and zebrafish nuclear receptors, retinoid X receptor α and peroxisome proliferator-activated receptor γ. Zebrafish larvae were exposed from 4 th day post-fertilization until the end of the experiment (day 18), to six different treatments: experimental control, solvent control, tributyltin at 100 ng/L Sn and 200 ng/L Sn (positive control), and wastewater treatment plant influent at 1.25% and 2.5%. Exposure to tributyltin and to 2.5% influent led to a significant accumulation of lipids, with white adipose tissue deposits concentrating in the perivisceral area. The highest in vitro tested influent concentration (10%) was able to significantly transactivate the human heterodimer PPARγ/RXRα, thus suggesting the presence in the influent of HsPPARγ/RXRα agonists. Our results demonstrate, for the first time, the ability of complex environmental samples from a municipal waste water treatment plant influent to induce lipid accumulation in zebrafish larvae.

Exopolysaccharide from Paecilomyces lilacinus modulates macrophage activities through the TLR4/NF‑κB/MAPK pathway

Multiple exopolysaccharides (EPSs) have been isolated from various organisms in extreme environments and have yielded a variety of activities. The present study evaluated the immunomodulatory capabilities of an EPS (termed PH‑EPS) derived from the fungus Paecilomyces lilacinus PH0016, which was isolated from a tropical and hyperhaline environment in southern China. The macrophage RAW 264.7 cell line was used to investigate the mechanism of PH‑EPS‑induced macrophage activation. The results indicated that RAW 264.7 macrophages were activated by PH‑EPS, in an effect slightly inferior to lipopolysaccharide (LPS), as evidenced by secretion of interleukin (IL)‑1β, tumor necrosis factor (TNF)‑α and nitric oxide (NO), and by significantly increased phagocytosis in the cells treated with PH‑EPS. Nuclear factor (NF)‑κB p65 was significantly translocated into the nucleus in the PH‑EPS‑treated cells. In addition, expression of inducible NO synthase (iNOS) and IκB‑α degradation were enhanced in PH‑EPS‑treated cells. The phosphorylation levels of p38, JNK and ERK were also significantly increased in the PH‑EPS‑treated cells. Furthermore, IL‑1β and TNF‑α production was markedly decreased in PH‑EPS‑treated cells when the mitogen‑activated protein kinase (MAPK) pathways were blocked by the inhibitor Dectin‑1 and by antibodies against Toll‑like receptor 4 (TLR4). The present results indicated that PH‑EPS from Paecilomyces lilacinus possessed the capability of activating RAW 264.7 cells via the TLR4/NF‑κB/MAPKs signaling pathway.

Self-regulation of the inflammatory response by peroxisome proliferator-activated receptors

The peroxisome proliferator-activated receptor (PPAR) family includes three transcription factors: PPARα, PPARβ/δ, and PPARγ. PPAR are nuclear receptors activated by oxidised and nitrated fatty acid derivatives as well as by cyclopentenone prostaglandins (PGA₂ and 15d-PGJ₂) during the inflammatory response. This results in the modulation of the pro-inflammatory response, preventing it from being excessively activated. Other activators of these receptors are nonsteroidal anti-inflammatory drug (NSAID) and fatty acids, especially polyunsaturated fatty acid (PUFA) (arachidonic acid, ALA, EPA, and DHA). The main function of PPAR during the inflammatory reaction is to promote the inactivation of NF-κB. Possible mechanisms of inactivation include direct binding and thus inactivation of p65 NF-κB or ubiquitination leading to proteolytic degradation of p65 NF-κB. PPAR also exert indirect effects on NF-κB. They promote the expression of antioxidant enzymes, such as catalase, superoxide dismutase, or heme oxygenase-1, resulting in a reduction in the concentration of reactive oxygen species (ROS), i.e., secondary transmitters in inflammatory reactions. PPAR also cause an increase in the expression of IκBα, SIRT1, and PTEN, which interferes with the activation and function of NF-κB in inflammatory reactions.

A Review of Chronic Musculoskeletal Pain: Central and Peripheral Effects of Diclofenac

Diclofenac is widely used to manage chronic inflammatory and degenerative joint diseases such as osteoarthritis (OA), rheumatoid arthritis (RA), ankylosing spondylitis, and extra-articular rheumatism. Its various mechanisms of action make it particularly effective in treating nociceptive pain, but it is also an alternative for treating spinal and chronic central pain. Osteoarthritis and rheumatoid arthritis are the most frequently encountered arthritic conditions in adults. The management of nociceptive pain requires a sequential hierarchical approach, with the initial NSAID treatment being characterized by the replacement of one drug with another, or complete discontinuation usually because of insufficient pain control. OA- and RA-related pain is complex and multifactorial, and due to physiological interactions between the signaling of the central and peripheral nervous systems. The mechanisms of action of diclofenac make it particularly effective in treating both nociceptive pain and chronic central pain. This review underlines the mechanisms of diclofenac involved in chronic and acute joint pain, the most relevant adverse events.

Exploration of Antifungal and Immunomodulatory Potentials of a Furanone Derivative to Rescue Disseminated Cryptococosis in Mice

Cryptococcus neoformans infection is quite complex with both host-pathogen interaction and host immune profile determining disease progress and therapeutic outcome. Hence in the present study, the potential utility of (E)-5-benzylidenedihydrofuran-2(3 H)-one (compound-6) was explored as an effective anticryptococcal compound with immunomodulatory potential. The efficacy of compound-6 in pulmonary cryptococosis model using H99 strain was investigated. The effective dose was found to provide 100% survival, with a significant reduction of yeast burden in lungs and brain. The biodistribution analysis provided evidence for the presence of higher concentration of compound-6 in major organs including lungs and brain. In addition, compound-6 treated mice had significantly higher expression of IL-6, IL-4 and IFN-γ in lung and brain. Similarly, elevated expression of TNF-α, IL-β1 and IL-12 were observed in lungs, suggesting the protective host response against C. neoformans. The reduction and clearance of fungal load in systemic organs and mouse survival are notable results to confirm the ability of compound-6 to treat cryptococcosis. In conclusion, the low molecular weight (174 Da), lipophilicity, its ability to cross blood brain barrier, and facilitating modulation of cytokine expression are the added advantages of compound-6 to combat against disseminated cryptococosis.

Neuroprotectin/protectin D1: endogenous biosynthesis and actions on diabetic macrophages in promoting wound healing and innervation impaired by diabetes

Dysfunction of macrophages (MΦs) in diabetic wounds impairs the healing. MΦs produce anti-inflammatory and pro-resolving neuroprotectin/protectin D1 (NPD1/PD1, 10R,17S-dihydroxy-docosa-4Z,7Z,11E,13E,15Z,19Z-hexaenoic acid); however, little is known about endogenous NPD1 biosynthesis by MΦs and the actions of NPD1 on diabetic MΦ functions in diabetic wound healing. We used an excisional skin wound model of diabetic mice, MΦ depletion, MΦs isolated from diabetic mice, and mass spectrometry-based targeted lipidomics to study the time course progression of NPD1 levels in wounds, the roles of MΦs in NPD1 biosynthesis, and NPD1 action on diabetic MΦ inflammatory activities. We also investigated the healing, innervation, chronic inflammation, and oxidative stress in diabetic wounds treated with NPD1 or NPD1-modulated MΦs from diabetic mice. Injury induced endogenous NPD1 biosynthesis in wounds, but diabetes impeded NPD1 formation. NPD1 was mainly produced by MΦs. NPD1 enhanced wound healing and innervation in diabetic mice and promoted MΦs functions that accelerated these processes. The underlying mechanisms for these actions of NPD1 or NPD1-modulated MΦs involved 1) attenuating MΦ inflammatory activities and chronic inflammation and oxidative stress after acute inflammation in diabetic wound, and 2) increasing MΦ production of IL10 and hepatocyte growth factor. Taken together, NPD1 appears to be a MΦs-produced factor that accelerates diabetic wound healing and promotes MΦ pro-healing functions in diabetic wounds. Decreased NPD1 production in diabetic wound is associated with impaired healing. This study identifies a new molecular target that might be useful in development of more effective therapeutics based on NPD1 and syngeneic diabetic MΦs for treatment of diabetic wounds.

Induction but not inhibition of COX-2 confers human lung cancer cell apoptosis by celecoxib

The antitumorigenic mechanism of the selective cyclooxygenase-2 (COX-2) inhibitor celecoxib is still a matter of debate. Among different structurally related COX-2 inhibitors, only celecoxib was found to cause apoptosis and cell death of human lung cancer cells (IC₅₀ values of 19.96 µM [A549], 12.48 µM [H460], and 41.39 µM [H358]) that was paralleled by a time- and concentration-dependent upregulation of COX-2 and peroxisome proliferator-activated receptor γ (PPARγ) at mRNA and protein levels. Apoptotic death of celecoxib-treated cancer cells was suppressed by the PPARγ antagonist GW9662 and by siRNA targeting PPARγ and, surprisingly, also by the selective COX-2 inhibitor NS-398 and siRNA targeting COX-2. NS-398 (1 µM) was shown to suppress celecoxib-induced COX-2 activity. Among the COX-2-dependent prostaglandins (PG) induced upon celecoxib treatment, PGD₂ and 15-deoxy-Δ¹²,¹⁴-PGJ₂ were found to induce a cytosol-to-nucleus translocation of PPARγ as well as a PPARγ-dependent apoptosis. Celecoxib-elicited PPARγ translocation was inhibited by NS-398. Finally, a COX-2- and PPARγ-dependent cytotoxic action of celecoxib was proven for primary human lung tumor cells. Together, our data demonstrate a proapoptotic mechanism of celecoxib involving initial upregulation of COX-2 and PPARγ and a subsequent nuclear translocation of PPARγ by COX-2-dependent PGs.

Role of PPARγ in COX-2 activation in mycobacterial pulmonary inflammation

Preliminary studies show that intranasal (i.n.) administration of BCG in mice induces M1 activation of alveolar macrophages (M∅) that increase TNF-α production and cyclooxygenase-2 (COX-2) expression but reduce constitutive peroxisome proliferator-activated receptor gamma (PPARγ) expression. However, COX-2 is catalytically inactive for prostaglandin E(2) release, unlike COX-2 that is active in M1 activation in vitro by BCG. In this study, we determined the role of PPARγ for BCG-induced M1 activation in vivo and in vitro. We found that treatment of mice with GW9662, a PPARγ antagonist, prior to i.n. BCG, partially restored PPARγ expression, and decreased TNF-α production and COX-2 expression. But COX-2 was still inactive. The decreased effects on TNF-α and COX-2 were also observed when alveolar M∅ were treated in vitro with GW9662/BCG, but COX-2 was still active. Our results indicate that PPARγ upregulates M1 activation of alveolar M∅, but inactive COX-2 formation is independent of PPARγ in mycobacterial pulmonary inflammation.

Inhibition of the diclofenac-induced cyclooxygenase-2 activity by paracetamol in cultured macrophages is not related to the intracellular lipid hydroperoxide tone

Paracetamol, a weak inhibitor of cyclooxygenase COX-1 and COX-2 activities, has been reported to inhibit the activity of COX-2 induced by diclofenac in J774.2 macrophage cell line. The lack of inhibition of COX-2 by paracetamol in inflamed tissues and thereby the lack of anti-inflammatory activity has been attributed to high lipid hydroperoxide (LHP) tone. In this study, we demonstrate that the inhibition of the diclofenac-induced COX-2 activity in J774.2 cells by paracetamol is not related to the intracellular LHP tone as paracetamol inhibited this activity in the absence and presence of T-butyl hydroperoxide, which is an LHP donor, to the same extents. In fact, treatment of the cells with diclofenac resulted in an increase in the LHP tone. Stimulation of the cells with lipopolysaccharide (LPS) results in the induction of a COX-2 activity, which was not inhibited by paracetamol. This represents the classical induction pathway for COX-2. LPS stimulation did not alter the LHP tone. These results suggest that the enzymatic activity of the diclofenac-induced COX-2 protein does not depend on the supply of hydroperoxides to its peroxidase active site.

Inflammatory pain signals an increase in functional expression of organic anion transporting polypeptide 1a4 at the blood-brain barrier

Pain is a dominant symptom associated with inflammatory conditions. Pharmacotherapy with opioids may be limited by poor blood-brain barrier (BBB) permeability. One approach that may improve central nervous system (CNS) delivery is to target endogenous BBB transporters such as organic anion-transporting polypeptide 1a4 (Oatp1a4). It is critical to identify and characterize biological mechanisms that enable peripheral pain/inflammation to "transmit" upstream signals and alter CNS drug transport processes. Our goal was to investigate, in vivo, BBB functional expression of Oatp1a4 in animals subjected to peripheral inflammatory pain. Inflammatory pain was induced in female Sprague-Dawley rats (200-250 g) by subcutaneous injection of 3% λ-carrageenan into the right hind paw; control animals were injected with 0.9% saline. In rat brain microvessels, Oatp1a4 expression was increased during acute pain/inflammation. Uptake of taurocholate and [d-penicillamine(2,5)]-enkephalin, two established Oatp substrates, was increased in animals subjected to peripheral pain, suggesting increased Oatp1a4-mediated transport. Inhibition of inflammatory pain with the anti-inflammatory drug diclofenac attenuated these changes in Oatp1a4 functional expression, suggesting that inflammation in the periphery can modulate BBB transporters. In addition, diclofenac prevented changes in the peripheral signaling cytokine transforming growth factor-β1 (TGF-β1) levels and brain microvascular TGF-β receptor expression induced by inflammatory pain. Pretreatment with the pharmacological TGF-β receptor inhibitor 4-[4-(1,3-benzodioxol-5-yl)-5-(2-pyridinyl)-1H-imidazol-2-yl]benzamide (SB431542) increased Oatp1a4 functional expression in λ-carrageenan-treated animals and saline controls, suggesting that TGF-β signaling is involved in Oatp1a4 regulation at the BBB. Our findings indicate that BBB transporters (i.e., Oatp1a4) can be targeted during drug development to improve CNS delivery of highly promising therapeutics.

Xanthine oxidoreductase promotes the inflammatory state of mononuclear phagocytes through effects on chemokine expression, peroxisome proliferator-activated receptor-{gamma} sumoylation, and HIF-1{alpha}

The protective effects of pharmacological inhibitors of xanthine oxidoreductase (XOR) have implicated XOR in many inflammatory diseases. Nonetheless, the role played by XOR during inflammation is poorly understood. We previously observed that inhibition of XOR within the inflammatory mononuclear phagocytes (MNP) prevented neutrophil recruitment during adoptive transfer demonstrating the role of XOR in MNP-mediated neutrophil recruitment. To further explore the role of XOR in the inflammatory state of MNP, we studied MNP isolated from inflammatory lungs combined with analyses of MNP cell lines. We demonstrated that XOR activity was increased in inflammatory MNP following insufflation of Th-1 cytokines in vivo and that activity was specifically increased by MNP differentiation. Inhibition of XOR reduced levels of CINC-1 secreted by MNP. Expression of peroxisome proliferator-activated receptor γ (PPARγ) in purified rat lung MNP and MNP cell lines reflected both the presence of PPARγ isoforms and PPARγ SUMOylation, and XOR inhibitors increased levels of SUMO-PPARγ in MNP cell lines. Both ectopic overexpression of XOR cDNA and uric acid supplementation reduced SUMO-PPARγ in MNP cells. Levels of the M2 markers CD36, CD206, and arginase-1 were modulated by uric acid and oxonic acid, whereas siRNA to SUMO-1 or PIAS-1 also reduced arginase-1 in RAW264.7 cells. We also observed that HIF-1α was increased by XOR inhibitors in inflammatory MNP and in MNP cell lines. These data demonstrate that XOR promotes the inflammatory state of MNP through effects on chemokine expression, PPARγ SUMOylation, and HIF-1α and suggest that strategies for inhibiting XOR may be valuable in modulating lung inflammatory disorders.

Diclofenac: an update on its mechanism of action and safety profile

BACKGROUND

Diclofenac is a proven, commonly prescribed nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-inflammatory, and antipyretic properties, and has been shown to be effective in treating a variety of acute and chronic pain and inflammatory conditions. As with all NSAIDs, diclofenac exerts its action via inhibition of prostaglandin synthesis by inhibiting cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) with relative equipotency. However, extensive research shows the pharmacologic activity of diclofenac goes beyond COX inhibition, and includes multimodal and, in some instances, novel mechanisms of action (MOA).

DATA SOURCES

Literature retrieval was performed through PubMed/MEDLINE (through May 2009) using combinations of the terms diclofenac, NSAID, mechanism of action, COX-1, COX-2, and pharmacology. Reference citations resulting from publications identified in the literature search were reviewed when appropriate.

METHODS

This article reviews the established, putative, and emerging MOAs of diclofenac; compares the drug's pharmacologic and pharmacodynamic properties with other NSAIDs to delineate its potentially unique qualities; hypothesizes why it has been chosen for further recent formulation enhancement; and evaluates the potential effect of its MOA characteristics on safety.

DISCUSSION

Research suggests diclofenac can inhibit the thromboxane-prostanoid receptor, affect arachidonic acid release and uptake, inhibit lipoxygenase enzymes, and activate the nitric oxide-cGMP antinociceptive pathway. Other novel MOAs may include the inhibition of substrate P, inhibition of peroxisome proliferator activated receptor gamma (PPARgamma), blockage of acid-sensing ion channels, alteration of interleukin-6 production, and inhibition of N-methyl-D-aspartate (NMDA) receptor hyperalgesia. The review was not designed to compare MOAs of diclofenac with other NSAIDs. Additionally, as the highlighted putative and emerging MOAs do not have clinical data to demonstrate that these models are correct, further research is necessary to ascertain if the proposed pathways will translate into clinical benefits. The diversity in diclofenac's MOA may suggest the potential for a relatively more favorable profile compared with other NSAIDs.