Induction of cyclooxygenase-2 expression by peroxisome proliferators and non-tetradecanoylphorbol 12,13-myristate-type tumor promoters in immortalized mouse liver cells

Impact of fenofibrate therapy on serum uric acid concentrations: a review and meta-analysis

Fenofibrate is a marketed fibric acid derivative for lipid-lowering in patients with lipid disorders. Numerous studies have proven fenofibrate had a certain effect on serum uric acid, here we conducted this study to quantitatively assess the effect of fenofibrate intervention in modulating serum uric acid concentration and the influence on serum creatinine. The PubMed, Embase and Cochrane were systematically searched for randomized controlled trials update to January, 2020. Primary endpoints focused on serum uric acid concentration and serum creatinine concentration. The pooled effects were calculated as weighted mean difference (WMD) by a random-effects model. Finally, 9 studies representing 487 patients were included in the meta-analysis. The meta-analysis demonstrated that fenofibrate significantly reduced serum uric acid levels (WMD -1.32 mg/dL, 95%CI -1.61 to -1.03, p < 0.001) and an elevated level in serum creatinine (WMD 0.09 mg/dL, 95%CI 0.02 to 0.15, p < 0.001) following fenofibrate therapy compared with placebo. The present study provided strong evidence that fenofibrate intervention exerted a significant reduction on serum uric acid and a mild increase on serum creatinine. Meta-analysis suggested that there were no significant association between the serum uric acid lowering effect with either dose or treatment duration. Overall, our meta-analysis ascertained that fenofibrate have potential therapeutic effects in patients with lipid metabolic abnormalities but with mid nephrotoxicity. There is strong evidence to provide future direction of practical application and clinical researches of fenofibrate.

Treatment With Gemfibrozil Prevents the Progression of Chronic Kidney Disease in Obese Dahl Salt-Sensitive Rats

Recently, we reported that Dahl salt-sensitive leptin receptor mutant (SS^LepRmutant) rats exhibit dyslipidemia and renal lipid accumulation independent of hyperglycemia that progresses to chronic kidney disease (CKD). Therefore, in the current study, we examined the effects of gemfibrozil, a lipid-lowering drug (200 mg/kg/day, orally), on the progression of renal injury in SS and SS^LepRmutant rats for 4 weeks starting at 12 weeks of age. Plasma triglyceride levels were markedly elevated in the SS^LepRmutant strain compared to SS rats (1193 ± 243 and 98 ± 16 mg/day, respectively). Gemfibrozil treatment only reduced plasma triglycerides in the SS^LepRmutant strain (410 ± 79 mg/dL). MAP was significantly higher in the SS^LepRmutant strain vs. SS rats at the end of the study (198 ± 7 vs. 165 ± 7 mmHg, respectively). Administration of gemfibrozil only lowered MAP in SS^LepRmutant rats (163 ± 8 mmHg). During the course of the study, proteinuria increased to 125 ± 22 mg/day in SS rats. However, proteinuria did not change in the SS^LepRmutant strain and remained near baseline (693 ± 58 mg/day). Interestingly, treatment with gemfibrozil increased the progression of proteinuria by 77% in the SS^LepRmutant strain without affecting proteinuria in SS rats. The renal injury in the SS^LepRmutant strain progressed to CKD. Moreover, the kidneys from SS^LepRmutant rats displayed significant glomerular injury with mesangial expansion and increased renal lipid accumulation and fibrosis compared to SS rats. Treatment with gemfibrozil significantly reduced glomerular injury and lipid accumulation and improved renal function. These data indicate that reducing plasma triglyceride levels with gemfibrozil inhibits hypertension and CKD associated with obesity in SS^LepRmutant rats.

Blastocyst-induced ATP release from luminal epithelial cells initiates decidualization through the P2Y2 receptor in mice

Embryo implantation involves a sterile inflammatory reaction that is required for the invasion of the blastocyst into the decidua. Adenosine triphosphate (ATP) released from stressed or injured cells acts as an important signaling molecule to regulate many key physiological events, including sterile inflammation. We found that the amount of ATP in the uterine luminal fluid of mice increased during the peri-implantation period, and this depended on the presence of an embryo. We further showed that the release of ATP from receptive epithelial cells was likely stimulated by lactate released from the blastocyst through connexin hemichannels. The ATP receptor P2y2 was present on uterine epithelial cells during the preimplantation period and increased in the stromal cells during the time at which decidualization began. Pharmacological inhibition of P2y2 compromised decidualization and implantation. ATP-P2y2 signaling stimulated the phosphorylation of Stat3 in uterine luminal epithelial cells and the expression of early growth response 1 (Egr1) and prostaglandin-endoperoxide synthase 2 (Ptgs2, also known as Cox-2), all of which are required for decidualization and/or implantation, in stromal cells. Short exposure to high concentrations of ATP promoted decidualization of primary stromal cells, but longer exposures or lower ATP concentrations did not. The expression of genes encoding ATP-degrading ectonucleotidases increased in the decidua during the peri-implantation period, suggesting that they may limit the duration of the ATP signal. Together, our results indicate that the blastocyst-induced release of ATP from uterine epithelial cells during the peri-implantation period may be important for the initiation of stromal cell decidualization.

Investigating the potential protective effects of natural product quercetin against imidacloprid-induced biochemical toxicity and DNA damage in adults rats

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Imidacloprid insecticide causes hepatotoxicity, renal damage and DNA damage.

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Quercetin revealed a significant protective action against the toxic effects of Imidacloprid.

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Quercetin counteracts the imidacloprid effects on liver, Kidney and DNA damage to the normal level.

Quercetin (QT) is a natural antioxidant materials that’s possesses different type of pharmacological activities. In the current study, the protective effect QT against imidacloprid (IMD)-induced toxicity in rats was studied. The experiment included thirty-six adult male rats groups treated with QT, IMD (two different doses), their combinations and control non-treated group for 21 consecutive days. Different biochemical analysis (serum liver and kidney enzymes level, cholesterol and Glucose levels) were evaluated. DNA damage using comet assay and histopathological examination of different body organs were also screened. Treatment with IMD increased ALT, AST, serum urea, creatinine, cholesterol and Glucose levels but decreased the levels of serum total protein, albumin and body weight with induction in triacylglycerol and cholesterol levels. Animals treated with QT prior to IMD administration showed normal enzymatic levels which indicating a protective effect of QT. In addition, QT protected the different body organs from the histological changes and DNA damages induced by IMD toxicity. The present results showed the protective effect of QT as a natural material against the IMD induced toxicity at different doses.

Cyclooxygenase-1 and -2 Play Contrasting Roles in Listeria-Stimulated Immunity

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit cyclooxygenase (COX) activity and are commonly used for pain relief and fever reduction. NSAIDs are used following childhood vaccinations and cancer immunotherapies; however, how NSAIDs influence the development of immunity following these therapies is unknown. We hypothesized that NSAIDs would modulate the development of an immune response to Listeria monocytogenes-based immunotherapy. Treatment of mice with the nonspecific COX inhibitor indomethacin impaired the generation of cell-mediated immunity. This phenotype was due to inhibition of the inducible COX-2 enzyme, as treatment with the COX-2-selective inhibitor celecoxib similarly inhibited the development of immunity. In contrast, loss of COX-1 activity improved immunity to L. monocytogenes Impairments in immunity were independent of bacterial burden, dendritic cell costimulation, or innate immune cell infiltrate. Instead, we observed that PGE₂ production following L. monocytogenes is critical for the formation of an Ag-specific CD8⁺ T cell response. Use of the alternative analgesic acetaminophen did not impair immunity. Taken together, our results suggest that COX-2 is necessary for optimal CD8⁺ T cell responses to L. monocytogenes, whereas COX-1 is detrimental. Use of pharmacotherapies that spare COX-2 activity and the production of PGE₂ like acetaminophen will be critical for the generation of optimal antitumor responses using L. monocytogenes.

Regulation of MicroRNA 183 by Cyclooxygenase 2 in Liver Is DEAD-Box Helicase p68 (DDX5) Dependent: Role in Insulin Signaling

Cyclooxygenase (COX) catalyzes the first step in prostanoid biosynthesis and exists as two isoforms. COX-1 is a constitutive enzyme involved in physiological processes, whereas COX-2 is induced by a variety of stimuli. MicroRNAs (miRNAs) are noncoding RNAs that function as key posttranscriptional regulators of gene expression. Although it is known that COX-2 expression is regulated by miRNAs, there are no data regarding COX-2 involvement in miRNA regulation. Considering our previous results showing that COX-2 expression in hepatocytes protects against insulin resistance, we evaluated the role of COX-2 in the regulation of a specific set of miRNAs implicated in insulin signaling in liver cells. Our results provide evidence of the molecular basis for a novel function of COX-2 in miRNA processing. COX-2 represses miRNA 23b (miR-23b), miR-146b, and miR-183 expression in liver cells by increasing the level of DEAD-box helicase p68 (DDX5) through phosphatidylinositol 3-kinase (PI3K)/p300 signaling and by modulating the enzymatic function of the Drosha (RNase type III) complex through its physical association with DDX5. The decrease of miR-183 expression promotes protection against insulin resistance by increasing insulin receptor substrate 1 (IRS1) levels. These results indicate that the modulation of miRNA processing by COX-2 is a key event in insulin signaling in liver and has potential clinical implications for the management of various hepatic dysfunctions.

Mono-ethylhexyl phthalate stimulates prostaglandin secretion in human placental macrophages and THP-1 cells

BACKGROUND

Diethylhexyl phthalate (DEHP) is widely used as a plasticizer in polyvinyl chloride products. DEHP exposure, which is widespread in the US, increases preterm birth risk; however, the mechanisms driving this relationship are unclear. Because cyclooxygenase-2 (COX-2) dependent prostaglandin synthesis is implicated in preterm birth, we evaluated effects of mono-2-ethylhexyl phthalate (MEHP), the active metabolite of DEHP, on prostaglandin E2 (PGE2) synthesis and COX expression in human placental macrophages (PM). In addition, responses in PM were compared to those in a human macrophage-like cell line, THP-1.

METHODS

PM and THP-1 cells were treated for 2, 4, 8, or 24 h with MEHP concentrations ranging from 10 to 180 micromolar. PGE2 concentrations were assessed in culture medium using ELISA, and COX expression was determined by western blot.

RESULTS

Treatment of PM and THP-1 cells with 180 micromolar MEHP for 24 h significantly increased PGE2 release. Co-treatment of PMs or THP-1 cells with 180 micromolar MEHP and the non-selective COX inhibitor indomethacin reduced MEHP-stimulated PGE2 production. Similarly, co-treatment of PM and THP-1 cells with the COX-2 selective inhibitor NS-398 resulted in a significant decrease in PGE2, suggesting that MEHP-stimulated PGE2 is dependent specifically on increased COX-2 expression. Western blot analysis revealed a significant increase in COX-2 expression in PM and THP-1 cells treated with 180 micromolar MEHP, and no changes in COX-1 expression, supporting the role of COX-2 in MEHP-stimulated PGE2 synthesis.

CONCLUSIONS

The findings from this study are the first to demonstrate phthalate-stimulated PGE2 synthesis in PM and warrant future studies into COX-2-dependent prostaglandin synthesis as a mechanism of toxicant-associated preterm birth.

Withaferin A induces apoptosis through the generation of thiol oxidation in human head and neck cancer cells

Withaferin A is a steroidal lactone purified from the Indian medicinal plant, Withania somnifera. Withaferin A has been shown to inhibit the proliferation, metastasis, invasion and angiogenesis of cancer cells. In the present study, we investigated whether withaferin A induces apoptosis in the human head and neck cancer cells, AMC-HN4. Withaferin A markedly increased the sub-G1 cell population and the cleavage of poly(ADP-ribose) polymerase (PARP), which are markers of apoptosis. Pan-caspase inhibitor, z-VAD-fmk (z-VAD), markedly inhibited the withaferin A-induced apoptosis. However, the withaferin A-induced increase in the expression of COX-2 was not affected by treatment with z-VAD. Furthermore, withaferin A upregulated cyclooxygenase-2 (COX-2) expression. The COX-2 inhibitor, NS-398, reduced the withaferin A-induced production of prostaglandin E2. However, treatment with NS-398 did not affect the sub-G1 population and the cleavage of PARP. In addition, the withaferin A-induced apoptosis was independent of reactive oxygen species production. Thiol donors [N-acetylcysteine (NAC) and dithiothreitol (DTT)] reversed withaferin A-induced apoptosis. Therefore, our data suggest that withaferin A induces apoptosis through the mechanism of thiol oxidation in head and neck carcinoma cells.

Influence of fenofibrate treatment on triacylglycerides, diacylglycerides and fatty acids in fructose fed rats

Fenofibrate (FF) lowers plasma triglycerides via PPARα activation. Here, we analyzed lipidomic changes upon FF treatment of fructose fed rats. Three groups with 6 animals each were defined as control, fructose-fed and fructose-fed/FF treated. Male Wistar Unilever Rats were subjected to 10% fructose-feeding for 20 days. On day 14, fenofibrate treatment (100 mg/kg p.o.) was initiated and maintained for 7 days. Lipid species in serum were analyzed using mass spectrometry (ESI-MS/MS; LC-FT-MS, GC-MS) on days 0, 14 and 20 in all three groups. In addition, lipid levels in liver and intestine were determined. Short-chain TAGs increased in serum and liver upon fructose-feeding, while almost all TAG-species decreased under FF treatment. Long-chain unsaturated DAG-levels (36:1, 36:2, 36:4, 38:3, 38:4, 38:5) increased upon FF treatment in rat liver and decreased in rat serum. FAs, especially short-chain FAs (12:0, 14:0, 16:0) increased during fructose-challenge. VLDL secretion increased upon fructose-feeding and together with FA-levels decreased to control levels during FF treatment. Fructose challenge of de novo fatty acid synthesis through fatty acid synthase (FAS) may enhance the release of FAs ≤ 16:0 chain length, a process reversed by FF-mediated PPARα-activation.

Obesity, metabolic syndrome and diabetes mellitus after renal transplantation: prevention and treatment

The prevalence of the metabolic syndrome in dialysis patients is high and further increases after transplantation due to weight gain and the detrimental metabolic effects of immunosuppressive drugs. Corticosteroids cause insulin resistance, hyperlipidemia, abnormal glucose metabolism and arterial hypertension. The calcineurin inhibitor tacrolimus is diabetogenic by inhibiting insulin secretion, whereas cyclosporine causes hypertension and increases cholesterol levels. Mtor antagonists are responsible for hyperlipidemia and abnormal glucose metabolism by mechanisms that also implicate insulin resistance. The metabolic syndrome in transplant recipients has numerous detrimental effects such as increasing the risk of new onset diabetes, cardiovascular disease events and patient death. In addition, it has also been linked with accelerated loss of graft function, proteinuria and ultimately graft loss. Prevention and management of the metabolic syndrome are based on increasing physical activity, promotion of weight loss and control of cardiovascular risk factors. Bariatric surgery before or after renal transplantation in patients with body mass index >35 kg/m(2) is an option but its long term effects on graft and patient survival have not been investigated. Steroid withdrawal and replacement of tacrolimus with cyclosporine facilitate control of diabetes, whereas replacement of cyclosporine and mtor antagonists can improve hyperlipidemia. The new costimulation inhibitor belatacept has potent immunosuppressive properties without metabolic adverse effects and will be an important component of immunosuppressive regimens with better metabolic risk profile. Medical treatment of cardiovascular risk factors has to take potential drug interactions with immunosuppressive medication and drug accumulation due to renal insufficiency into account.

The involvement of peroxisome proliferator activated receptors (PPARs) in prostaglandin F2α production by porcine endometrium

In the present study, we investigated the in vitro effects of peroxisome proliferator activated receptor (PPAR) ligands on PGF2α secretion and mRNA expression of prostaglandin F synthase (PGFS) in porcine endometrial explants collected on days 10-12 and 14-16 of the estrous cycle or pregnancy. The explants were incubated for 6h with: PPARα ligands - WY-14643 (agonist) and MK 886 (antagonist); PPARβ ligands - l-165,041 (agonist) and GW 9662 (antagonist); PPARγ ligands - 15d-prostaglandin J2 (PGJ2, agonist), rosiglitazone (agonist) and T0070907 (antagonist). The expression of PGFS mRNA in the endometrium and the concentration of PGF2α in culture media were determined by real time RT-PCR and radioimmunoassay, respectively. During the estrous cycle (days 10-12 and 14-16), the agonists - WY-14643 (PPARα), l-165,041 (PPARβ), PGJ2 and rosiglitazone (PPARγ) - increased PGF2α secretion but did not affect PGFS mRNA abundance. During pregnancy (days 10-12 and 14-16), PPARα and PPARγ ligands did not change PGF2α release, whereas PPARβ agonist augmented PGF2α release on days 14-16 of pregnancy. In addition, WY-14643 and l-165,041 increased PGFS mRNA level in both examined periods of pregnancy. PPARγ agonist (PGJ2) and antagonist (T0070907) enhanced PGFS mRNA abundance in the endometrium on days 10-12 and 14-16 of pregnancy, respectively. The results indicate that PPARs are involved in the production of PGF2α by porcine endometrium, and that the sensitivity of the endometrium to PPAR ligands depends on reproductive status of animals.

Progression of liver oncogenesis in the double transgenic mice c-myc/TGF α is not enhanced by cyclooxygenase-2 expression

Cyclooxygenase-2 (COX-2) has been associated with cell growth regulation, tissue remodeling and carcinogenesis. Overexpression of COX-2 in hepatocytes constitutes an ideal condition to evaluate the role of prostaglandins (PGs) in liver pathogenesis. The effect of COX-2-dependent PGs in genetic hepatocarcinogenesis has been investigated in triple c-myc/transforming growth factor α (TGF-α) transgenic mice that express human COX-2 in hepatocytes on a B6CBAxCD1xB6DBA2 background. Analysis of the contribution of COX-2-dependent PGs to the development of hepatocarcinogenesis, evaluated in this model, suggested a minor role of COX-2-dependent prostaglandins to liver oncogenesis as indicated by liver histopathology, morphometric analysis and specific markers of tumor progression. This allows concluding that COX-2 is insufficient for modifying the hepatocarcinogenesis course mediated by c-myc/TGF-α.

Fenofibrate and the kidney: an overview

BACKGROUND

Fenofibrate has been used for the management of atherogenic dyslipidaemia for many years. Reports of fenofibrate-associated increases in serum creatinine (SCr) levels raised concerns regarding deleterious effects on renal function.

DESIGN

In this narrative review, we discuss available literature on the effect of fenofibrate on the kidney.

RESULTS

Most clinical studies showed a rapid (within weeks) raising effect of fenofibrate on SCr levels. This was often accompanied by declined estimated glomerular filtration rate. Risk predictors of this adverse effect might include increased age, impaired renal function and high-dose treatment. Also, the concomitant use of medications affecting renal hemodynamics (e.g. angiotensin-converting enzyme-inhibitors (ACEi) and angiotensin receptor blockers) may predispose to fenofibrate-associated increased SCr levels. Interestingly, SCr increases by fenofibrate were transient and reversible even without treatment discontinuation. Furthermore, fenofibrate was associated with a slower progression of renal function impairment and albuminuria in a long-term basis. Also, fenofibrate might be protective against pathological changes in diabetic nephropathy and hypertensive glomerulosclerosis. In this context, it is uncertain whether fenofibrate-associated increase in SCr levels mirrors true renal function deterioration. Several theories have been expressed. The most dominant one involved the inhibition of renal vasodilatory prostaglandins reducing renal plasma flow and glomerular pressure. Increased creatinine secretion or reduced creatinine clearance by fenofibrate was also suggested. These hypotheses should be settled by further studies.

CONCLUSIONS

Fenofibrate may not be a nephrotoxic drug. However, a close monitoring of SCr levels is relevant especially in high-risk patients. Increases in SCr levels ≥30% can impose treatment discontinuation.

Mono-2-ethylhexyl phthalate induces oxidative stress responses in human placental cells in vitro

Di-2-ethylhexyl phthalate (DEHP) is an environmental contaminant commonly used as a plasticizer in polyvinyl chloride products. Exposure to DEHP has been linked to adverse pregnancy outcomes in humans including preterm birth, low birth-weight, and pregnancy loss. Although oxidative stress is linked to the pathology of adverse pregnancy outcomes, effects of DEHP metabolites, including the active metabolite, mono-2-ethylhexyl phthalate (MEHP), on oxidative stress responses in placental cells have not been previously evaluated. The objective of the current study is to identify MEHP-stimulated oxidative stress responses in human placental cells. We treated a human placental cell line, HTR-8/SVneo, with MEHP and then measured reactive oxygen species (ROS) generation using the dichlorofluorescein assay, oxidized thymine with mass-spectrometry, redox-sensitive gene expression with qRT-PCR, and apoptosis using a luminescence assay for caspase 3/7 activity. Treatment of HTR-8 cells with 180μM MEHP increased ROS generation, oxidative DNA damage, and caspase 3/7 activity, and resulted in differential expression of redox-sensitive genes. Notably, 90 and 180μM MEHP significantly induced mRNA expression of prostaglandin-endoperoxide synthase 2 (PTGS2), an enzyme important for synthesis of prostaglandins implicated in initiation of labor. The results from the present study are the first to demonstrate that MEHP stimulates oxidative stress responses in placental cells. Furthermore, the MEHP concentrations used were within an order of magnitude of the highest concentrations measured previously in human umbilical cord or maternal serum. The findings from the current study warrant future mechanistic studies of oxidative stress, apoptosis, and prostaglandins as molecular mediators of DEHP/MEHP-associated adverse pregnancy outcomes.

Evaluation of epigenetic modulation of cyclooxygenase-2 as a prognostic marker for hepatocellular carcinoma

Cyclooxygenases (COX-1 and 2) catalyze the first step in prostanoid biosynthesis. They are implicated in homeostatic processes with an important role in inflammation and carcinogenesis. In the liver, COX-2 expression is restricted to proliferation or dedifferentiation situations. The COX-2 promoter contains numerous CpG islands that, when hypermethylated, result in transcriptionally silencing thus regulating the growth of carcinoma cells. In this work, we investigated whether a correlation exists between COX-2 expression and methylation signatures at the 5'region of the gene in hepatoma cell lines and human hepatocellular carcinoma (HCC). We also examined the acetylation status of the COX-2 promoter and the effects of histone deacetylase (HDAC) inhibitors on COX-2 expression. Our results suggest a significant association between reduced COX-2 expression and promoter hypermethylation of COX-2 and histone deacetylation in some hepatoma cell lines and in HCC. Treatment with demethylating agents or HDAC inhibitors restored the expression of COX-2. Moreover, in an HCC cohort, a statistically significant inverse association was observed between COX-2 mRNA levels and promoter methylation. In agreement with these data, a reduction of overall survival of the patients was observed after decreased COX-2 expression by promoter hypermethylation and histone H3 hypoacetylation.

Cyclooxygenase-2 is a target of microRNA-16 in human hepatoma cells

Cyclooxygenase-2 (COX-2) expression has been detected in human hepatoma cell lines and in human hepatocellular carcinoma (HCC); however, the contribution of COX-2 to the development of HCC remains controversial. COX-2 expression is higher in the non-tumoral tissue and inversely correlates with the differentiation grade of the tumor. COX-2 expression depends on the interplay between different cellular pathways involving both transcriptional and post-transcriptional regulation. The aim of this work was to assess whether COX-2 could be regulated by microRNAs in human hepatoma cell lines and in human HCC specimens since these molecules contribute to the regulation of genes implicated in cell growth and differentiation. Our results show that miR-16 silences COX-2 expression in hepatoma cells by two mechanisms: a) by binding directly to the microRNA response element (MRE) in the COX-2 3'-UTR promoting translational suppression of COX-2 mRNA; b) by decreasing the levels of the RNA-binding protein Human Antigen R (HuR). Furthermore, ectopic expression of miR-16 inhibits cell proliferation, promotes cell apoptosis and suppresses the ability of hepatoma cells to develop tumors in nude mice, partially through targeting COX-2. Moreover a reduced miR-16 expression tends to correlate to high levels of COX-2 protein in liver from patients affected by HCC. Our data show an important role for miR-16 as a post-transcriptional regulator of COX-2 in HCC and suggest the potential therapeutic application of miR-16 in those HCC with a high COX-2 expression.

Transgenic mice expressing cyclooxygenase-2 in hepatocytes reveal a minor contribution of this enzyme to chemical hepatocarcinogenesis

Cyclooxygenase-2 (COX-2) has been associated with cell growth regulation, tissue remodeling, and carcinogenesis. Ectopic expression of COX-2 in hepatocytes constitutes a nonphysiological condition ideal for evaluating the role of prostaglandins (PGs) in liver pathogenesis. The effect of COX-2-dependent PGs in chronic liver disease, hepatitis, fibrosis, and chemical hepatocarcinogenesis, has been investigated in transgenic (Tg) mice that express human COX-2 in hepatocytes and in Tg hepatic human cell lines. We have used three different complementary approaches: i) diethylnitrosamine (DEN)-induced chemical hepatocarcinogenesis in COX-2 Tg mice, ii) DEN/phenobarbital treatment of human COX-2 Tg hepatocyte-like cells, and iii) COX-2 Tg hepatocyte-like cells implants in nude mice. The data suggest that PGs produced by COX-2 in hepatocytes promoted mild hepatitis in 60-week-old mice, as assessed by histological examination, but failed to contribute to the development of liver fibrogenesis after methionine- and choline-deficient diet treatment. Moreover, liver injury, collagen content, and hepatic stellate cell activation were equally severe in wild-type and COX-2 Tg mice. The contribution of COX-2-dependent PGs to the development of DEN-induced hepatocarcinogenesis was evaluated in Tg mice, Tg hepatocyte-like cells, and nude mice and the analysis revealed that COX-2 expression favors the development of preneoplastic foci without affecting malignant transformation. Endogenous COX-2 expression in wild-type mice is a late event in the development of hepatocellular carcinoma.

Effects of high dose aleglitazar on renal function in patients with type 2 diabetes

BACKGROUND

Aleglitazar is a new, balanced dual peroxisome proliferator-activated receptor (PPAR)α/γ agonist designed to optimize lipid and glycemic benefits and minimize PPAR-related adverse effects.

METHODS

SESTA R was a 26-week, randomized, double-blind, multicenter study comparing the effects of a supratherapeutic dosage of aleglitazar (600 μg/day) with pioglitazone (45 mg/day) on change in measured GFR (mGFR) in 174 patients with type 2 diabetes and normal to mildly impaired renal function (estimated GFR [eGFR] 60 to 120 ml/min/1.73 m(2)).

RESULTS

In 118 patients with evaluable GFR measurements, baseline mean (± SD) mGFR was 97.6 ± 17.5 ml/min/1.73 m(2) in the aleglitazar group and 101.9±21.6ml/min/1.73m(2) in the pioglitazone group. Mean percent change from baseline mGFR was -16.9% (90% confidence interval -22.0 to -11.5) with aleglitazar and -4.6% (-10.15 to 1.35) with pioglitazone, a mean treatment difference of -13.0% (-19.0 to -6.5). The 17% decrease from baseline in mGFR was consistent with the 19% decrease in eGFR Modification of Diet in Renal Disease (MDRD) observed with aleglitazar, which reached a plateau after 4weeks, with no further progression until treatment discontinuation. Following aleglitazar withdrawal, eGFR values returned to pretreatment levels within the 4-8-week follow-up, which suggests reversible hemodynamic changes in renal function.

CONCLUSIONS

Despite the increased incidence of expected, dose-dependent PPAR class side effects (e.g., peripheral edema, weight gain, and congestive heart failure) limiting further development of this supratherapeutic dosage of aleglitazar (600 μg/day), these data, together with the data from the dose-ranging SYNCHRONY study, suggest aleglitazar may be a potential new treatment for cardiovascular risk reduction in post-acute coronary syndrome patients at the therapeutic 150 μg daily dose.

PPARalpha: an emerging therapeutic target in diabetic microvascular damage

The global pandemic of diabetes mellitus portends an alarming rise in the prevalence of microvascular complications, despite advanced therapies for hyperglycemia, hypertension and dyslipidemia. Peroxisome proliferator-activated receptor alpha (PPARalpha) is expressed in organs affected by diabetic microvascular disease (retina, kidney and nerves), and its expression is regulated specifically in these tissues. Experimental evidence suggests that PPARalpha activation attenuates or inhibits several mediators of vascular damage, including lipotoxicity, inflammation, reactive oxygen species generation, endothelial dysfunction, angiogenesis and thrombosis, and thus might influence intracellular signaling pathways that lead to microvascular complications. PPARalpha has emerged as a novel target to prevent microvascular disease, via both its lipid-related and lipid-unrelated actions. Despite strong experimental evidence of the potential benefits of PPARalpha agonists in the prevention of vascular damage, the evidence from clinical studies in patients with diabetes mellitus remains limited. Promising findings from the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study on microvascular outcomes are countered by elevations in participants' homocysteine and creatinine levels that might potentially attenuate the benefits of PPARalpha activation. This Review focuses on the role of PPARalpha activation in diabetic microvascular disease and highlights the available experimental and clinical evidence from studies of PPARalpha agonists.

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.

Mono(2-ethylhexyl) phthalate induces both pro- and anti-inflammatory responses in rat alveolar macrophages through crosstalk between p38, the lipoxygenase pathway and PPARalpha

Airway inflammation is important in asthma pathogenesis. Recent epidemiological data have indicated an association between asthma symptoms in children and exposure to di(2-ethylhexyl) phthalate (DEHP). Thus, we have studied inflammatory responses in primary rat alveolar macrophages (AMs) after exposure to mono(2-ethylhexyl) phthalate (MEHP), the major primary metabolite of DEHP. First, we show that MEHP induces a dose-dependent release of the pro-inflammatory tumour necrosis factor-alpha (TNF-alpha) in AMs, giving a maximal (5-fold) increase at 0.7 mM. This concentration also induced some cell death. MEHP also induced phosphorylation of MAPK p38, while the p38 inhibitor SB 202190 reduced MEHP-induced TNF-alpha, suggesting a p38-dependent cytokine production. Next, we elucidated possible effects of MEHP on the 5-lipoxygenase (5-LO) pathway and found that MEHP caused increased leukotriene (LTB(4)) release. Further, we found that the 5-LO inhibitor nordihydrogualaretic acid (NDGA) significantly reduced both MEHP-induced TNF-alpha release and MEHP-induced formation of reactive oxygen species (ROS), supporting an involvement of the 5-LO pathway in MEHP induced inflammatory reactions. Last, we found that MK-886, a known inhibitor of peroxisome proliferator-activated receptor alpha (PPARalpha), increased the MEHP-induced TNF-alpha response. This indicates that MEPH-PPARalpha binding mediates an anti-inflammatory signal.

Urinary phthalate metabolites in relation to preterm birth in Mexico city

BACKGROUND

Rates of preterm birth have been rising over the past several decades. Factors contributing to this trend remain largely unclear, and exposure to environmental contaminants may play a role.

OBJECTIVE

We investigated the relationship between phthalate exposure and preterm birth.

METHODS

Within a large Mexican birth cohort study, we compared third-trimester urinary phthalate metabolite concentrations in 30 women who delivered preterm (< 37 weeks of gestation) with those of 30 controls (> or = 37 weeks of gestation).

RESULTS

Concentrations of most of the metabolites were similar to those reported among U.S. females, although in the present study mono-n-butyl phthalate (MBP) concentrations were higher and monobenzyl phthalate (MBzP) concentrations lower. In a crude comparison before correcting for urinary dilution, geometric mean urinary concentrations were higher for the phthalate metabolites MBP, MBzP, mono(3-carboxylpropyl) phthalate, and four metabolites of di(2-ethyl-hexyl) phthalate among women who subsequently delivered preterm. These differences remained, but were somewhat lessened, after correction by specific gravity or creatinine. In multivariate logistic regression analysis adjusted for potential confounders, elevated odds of having phthalate metabolite concentrations above the median level were found.

CONCLUSIONS

We found that phthalate exposure is prevalent among this group of pregnant women in Mexico and that some phthalates may be associated with preterm birth.

The role of endogenous and exogenous ligands for the peroxisome proliferator-activated receptor alpha (PPAR-alpha) in the regulation of inflammation in macrophages

The aim of the present study was to evaluate the role of endogenous and exogenous peroxisome proliferator-activated receptor alpha (PPAR-alpha), a nuclear receptor, on the regulation of inflammation in macrophages. To address this question, we have stimulated peritoneal macrophages from PPAR-alpha wild-type mice and PPAR-alpha knockout mice (PPAR-alpha) with 10 microg/mL LPS and 100 U/mL IFN-gamma. We report here that the absence of a functional PPAR-alpha gene in PPAR-alpha knockout mice resulted in a significant augmentation of various inflammatory parameters in peritoneal macrophages. In particular, we have clearly demonstrated that PPAR-alpha gene deletion increases (1) the mitogen-activated protein kinase phosphorylation (extracellular signal-regulated kinase, c-Jun NH2-terminal kinase, and p38), (2) nuclear factor-kappaB activation, (3) IkappaB-alpha degradation, (4) iNOS expression and NO formation, and (5) cyclooxygenase 2 expression and prostaglandin E2 formation caused by LPS/IFN-gamma stimulation. On the contrary, the incubation of peritoneal macrophages from PPAR-alpha wild type with clofibrate (2 mM) at 2 h before the LPS and IFN-gamma stimulation significantly reduced the expression and the release of the proinflammatory mediators. To elucidate whether the protective effects of clofibrate is related to activation of the PPAR-alpha receptor, we also investigated the effect of clofibrate treatment on PPAR-alpha-deficient mice. The absence of the PPAR-alpha receptor significantly abolished the protective effect of the PPAR-alpha agonist against LPS/IFN-gamma-induced macrophage inflammation. In conclusion, our study demonstrates that the endogenous and exogenous PPAR-alpha ligands reduce the degree of macrophage inflammation caused by LPS/IFN-gamma stimulation.

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

Cyclooxygenase-2 (COX-2) is an inducible isoform of the COX family of enzymes central to the synthesis of pro-inflammatory prostaglandins. Induction of COX-2 is mediated by many endogenous and exogenous molecules that include pro-inflammatory cytokines and bacterial lipopolysaccharide (LPS). It has been demonstrated that COX-2 can also be induced by diclofenac in cultured J774.2 macrophages. This induction was delayed compared to COX-2 induced by LPS and paracetamol selectively inhibited activity of this protein. The aim of the present study was to determine the transcription factor involved in the production of COX-2 after treatment of J774.2 cells with 500 microM diclofenac. Pre-treatment of cells with the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) antagonists GW9662 (0.1-1 microM) or biphenol A Diglycidyl Ether (100-200 microM) resulted in reduction of the induction of COX-2 by diclofenac, but not by LPS. Induction of COX-2 by the PPAR-gamma agonist 15deoxyDelta(12,14)prostaglandin J(2) was also reduced when the cells were pre-treated with the PPAR-gamma antagonists BADGE or GW9662. On the other hand, pre-treatment of cells with the nuclear factor-kappa-B (NF-kappaB) Super-repressor IkappaBalpha (150-600 nM) reduced the induction of COX-2 by LPS, but not by diclofenac. We, therefore, have identified that PPAR-gamma activation is a requirement for COX-2 induction after diclofenac stimulation of J774.2 cells. These results along with the finding that treatment of J774.2 macrophages with diclofenac resulted in the release of the anti-inflammatory cytokines, interleukin-10 and transforming growth factor-beta suggest that the diclofenac-induced COX-2 protein may possess anti-inflammatory actions.

Constitutive expression of cyclo-oxygenase 2 transgene in hepatocytes protects against liver injury

The effect of COX (cyclo-oxygenase)-2-dependent PGs (prostaglandins) in acute liver injury has been investigated in transgenic mice that express human COX-2 in hepatocytes. We have used three well-established models of liver injury: in LPS (lipopolysaccharide) injury in D-GalN (D-galactosamine)-preconditioned mice; in the hepatitis induced by ConA (concanavalin A); and in the proliferation of hepatocytes in regenerating liver after PH (partial hepatectomy). The results from the present study demonstrate that PG synthesis in hepatocytes decreases the susceptibility to LPS/D-GalN or ConA-induced liver injury as deduced by significantly lower levels of the pro-inflammatory profile and plasmatic aminotransferases in transgenic mice, an effect suppressed by COX-2-selective inhibitors. These Tg (transgenic) animals express higher levels of anti-apoptotic proteins and exhibit activation of proteins implicated in cell survival, such as Akt and AMP kinase after injury. The resistance to LPS/D-GalN-induced liver apoptosis involves an impairment of procaspase 3 and 8 activation. Protection against ConA-induced injury implies a significant reduction in necrosis. Moreover, hepatocyte commitment to start replication is anticipated in Tg mice after PH, due to the expression of PCNA (proliferating cell nuclear antigen), cyclin D1 and E. These results show, in a genetic model, that tissue-specific COX-2-dependent PGs exert an efficient protection against acute liver injury by an antiapoptotic/antinecrotic effect and by accelerated early hepatocyte proliferation.

Peroxisome-proliferator-activated receptors and the control of levels of prostaglandin-endoperoxide synthase 2 by arachidonic acid in the bovine uterus

Arachidonic acid is a potential paracrine agent released by the uterine endometrial epithelium to induce PTGS2 [PG (prostaglandin)-endoperoxide synthase 2] in the stroma. In the present study, bovine endometrial stromal cells were used to determine whether PTGS2 is induced by arachidonic acid in stromal cells, and to investigate the potential role of PPARs (peroxisome-proliferator-activated receptors) in this effect. Arachidonic acid increased PTGS2 levels up to 7.5-fold within 6 h. The cells expressed PPARalpha and PPARdelta (also known as PPARbeta) (but not PPARgamma). PTGS2 protein level was increased by PPAR agonists, including polyunsaturated fatty acids, synthetic PPAR ligands, PGA1 and NSAIDs (non-steroidal anti-inflammatory drugs) with a time course resembling that of arachidonic acid. Use of agonists and antagonists indicated PPARalpha (but not PPARdelta or PPARgamma) was responsible for PTGS2 induction. PTGS2 induction by arachidonic acid did not require PG synthesis. PTGS2 levels were increased by the PKC (protein kinase C) activators 4beta-PMA and PGF(2alpha), and the effects of arachidonic acid, NSAIDs, synthetic PPAR ligands and 4beta-PMA were blocked by PKC inhibitors. This is consistent with PPAR phosphorylation by PKC. Induction of PTGS2 protein by 4beta-PMA in the absence of a PPAR ligand was decreased by the NF-kappaB (nuclear factor kappaB) inhibitors MG132 and parthenolide, suggesting that PKC acted through NF-kappaB in addition to PPAR phosphorylation. Use of NF-kappaB inhibitors allowed the action of arachidonic acid as a PPAR agonist to be dissociated from an effect through PKC. The results are consistent with the hypothesis that arachidonic acid acts via PPARalpha to increase PTGS2 levels in bovine endometrial stromal cells.

The peroxisome proliferator-activated receptor alpha activator, Wy14,643, is anti-inflammatory in vivo

The peroxisome proliferator-activated receptor system is exciting much interest as a novel point of therapeutic intervention in inflammation. Here, the effect of a peroxisome proliferator-activated receptor alpha agonist, [4-chloro-6-(2,3-xylidine)-pyrimidinylthio]acetic acid (Wy14,643), was examined in arachidonic acid-induced murine ear inflammation. 3-[1-(4-Chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2-dimethylpropanoic acid (MK886, a 5-lipoxygenase inhibitor) and indomethacin (a cyclo-oxygenase inhibitor) were used as reference compounds. Wy14,643 dose dependently inhibited ear swelling and polymorphonuclear leukocyte influx, as did MK886, associated with reduced tissue leukotriene B4 but not prostaglandin E2 levels. Unlike MK886, Wy14,643 did not inhibit ex vivo leukotriene B4 production. However, Wy14,643, but not MK886, induced peroxisomal enzyme activity. Indomethacin was less effective, though tissue prostaglandin E2 but not leukotriene B4 levels were reduced. Again, unlike indomethacin, Wy14,643 did not reduce ex vivo prostaglandin E2 production. However, indomethacin did increase peroxisomal enzyme activity but to a lesser extent than Wy14,643. This study demonstrates that peroxisome proliferator-activated receptor alpha activation can inhibit arachidonic acid-induced inflammation in part by enhancing degradation of leukotriene B4.

n-3 and n-6 polyunsaturated fatty acids induce the expression of COX-2 via PPARgamma activation in human keratinocyte HaCaT cells

Polyunsaturated fatty acids (PUFA) n-3 inhibit inflammation, in vivo and in vitro in keratinocytes. We examined in HaCaT keratinocyte cell line whether eicosapentaenoic acid (EPA) a n-3 PUFA, gamma-linoleic acid (GLA) a n-6 PUFA, and arachidic acid a saturated fatty acid, modulate expression of cyclooxygenase-2 (COX-2), an enzyme pivotal to skin inflammation and reparation. We demonstrate that only treatment of HaCaT with GLA and EPA or a PPARgamma ligand (roziglitazone), induced COX-2 expression (protein and mRNA). Moreover stimulation of COX-2 promoter activity was increased by those PUFAs or rosiglitazone. The inhibitory effects of GW9662 and T0070907 (PPARgamma antagonists), on COX-2 expression and on stimulation of COX-2 promoter activity by EPA and GLA suggest that PPARgamma is implicated in COX-2 induction. Finally, PLA2 inhibitor methyl arachidonyl fluorophosphonate blocked the PUFA effects on COX-2 induction, promoter activity and arachidonic acid mobilization suggesting involvement of AA metabolites in PPAR activation. These findings demonstrate that n-3 and n-6 PUFA increased PPARgamma activity is necessary for the COX-2 induction in HaCaT human keratinocyte cells. Given the anti-inflammatory properties of EPA, we suggest that induction of COX-2 in keratinocytes may be important in the anti-inflammatory and protective mechanism of action of PUFAs n-3 or n-6.

Protection against Fas-induced liver apoptosis in transgenic mice expressing cyclooxygenase 2 in hepatocytes

Cyclooxygenase-2 (COX-2) is upregulated in many cancers, and the prostanoids synthesized increase proliferation, improve angiogenesis, and inhibit apoptosis in several tissues. To explore the function of COX-2 in liver, transgenic (Tg) mice were generated containing a fusion gene (LIVhCOX-2) consisting of human COX-2 cDNA under the control of the human ApoE promoter. Six lines were developed; all of them expressed the LIVhCOX-2 transgene selectively in hepatocytes. The Tg mice exhibited a normal phenotype, and the increased levels of PGE2 found were due to the constitutively expressed COX-2. Histological analysis of different tissues and macroscopic examination of the liver showed no differences between wild-type (Wt) and Tg animals. However, Tg animals were resistant to Fas-mediated liver injury, as demonstrated by low levels of plasmatic aminotransferases, a lesser caspase-3 activation, and Bax levels and an increase in Bcl-2, Mcl-1, and xIAP proteins, when compared with the Wt animals. Moreover, the resistance to Fas-mediated apoptosis is suppressed in the presence of COX-2-selective inhibitors, which prevented prostaglandin accumulation in the liver of Tg mice.

CONCLUSION

These results demonstrate that expression of COX-2-dependent prostaglandins exerted a protection against liver apoptosis.

Effect of fenofibrate in combination with urate lowering agents in patients with gout

BACKGROUND

To assess the efficacy of fenofibrate treatment in combination with urate lowering agents in patients with gout.

METHODS

Fourteen male patients with chronic tophaceous or recurrent acute attacks of gout were evaluated in an open-label pilot study of the hypolipidemic agent, fenofibrate (Lipidil Supra 160 mg/d). Patients were stable on urate lowering agents (allopurinol or benzbromarone) for > or = three months without acute attack for the most recent one month before participating. All patients were being treated with established doses of urate lowering agents without modification throughout the study. Clinical and biochemical assessments including serum uric acid, creatinine, liver function test and fasting serum lipid were measured at (1) baseline (2) after two months of fenofibrate treatment and (3) two months after fenofibrate was withdrawn.

RESULTS

Serum uric acid was lowered by 23% after two months of fenofibrate treatment (6.93 +/- 2.16 vs. 5.22 +/- 1.16 mg/dL; p = 0.016). Triglyceride levels were also reduced after fenofibrate treatment (p = 0.001). However, this effect was reversed after the withdrawal (p = 0.002) of the drug. Alkaline phosphatase was reduced after fenofibrate treatment (p = 0.006), but increased 21% after the withdrawal of the drug (p = 0.002). By contrast, serum levels of high density lipoprotein and creatinine were increased 9% (p = 0.018) and 12% (p = 0.006), respectively; however, both levels were significantly decreased to the baseline levels upon withdrawal of fenofibrate.

CONCLUSIONS

Fenofibrate can effectively reduce uric acid levels in addition to its known hypolipidemic effect. Fenofibrate may be used as a potential urate lowering agent in patients with gout, especially in those with coexisting hyperlipidemia.

The effect of benzo(a)pyrene on porcine urinary bladder epithelial cells analyzed for the expression of selected genes and cellular toxicological endpoints

Consumption of tobacco products is the most relevant risk factor for the development of bladder cancer beside occupational contributions. In order to investigate mechanisms of tobacco smoke components in bladder carcinogenesis we have introduced a primary epithelial cell culture system derived from porcine urinary bladder as a suitable representative for the corresponding human tissue under physiological conditions. Two independent readouts were selected as markers for genotoxic events. Changes in the expression level of several toxicologically relevant genes should serve as indicators for early response, while classical genotoxic endpoints monitored manifested damages. Here, we present the first results of our study with benzo(a)pyrene (BaP) as a member of polycyclic aromatic hydrocarbons (PAHs) found in tobacco smoke. Cells treated with BaP show a dramatic increase in the expression of CYP1A1 that appears to be both indicator of and contributor for BaP toxicity. Genes coding for other proteins relevant in xenobiotic metabolism, signal transduction or tumor suppression show moderate effects or no enhancement of their expression levels. Comet assay and micronucleus test did show a significant, dose-dependent increase in DNA damages or aberrations after cell division. While these effects are conforming to the response at the mRNA expression level, they are less pronounced and require rather higher dosages of the chemical.

Transcriptome analysis of endometrial cancer identifies peroxisome proliferator-activated receptors as potential therapeutic targets

Endometrial cancer is the most common gynecologic malignancy, frequently arising in association with obesity and diabetes mellitus. To identify gene pathways contributing to endometrial cancer development, we studied the transcriptome of 20 endometrial cancers and 11 benign endometrial tissues using cDNA microarrays. Among the transcript changes identified in endometrial cancer were up-regulation of the nuclear hormone receptors peroxisome proliferator-activated receptors (PPAR) α and γ, whereas retinoid X receptor β was down-regulated. To clarify the contribution of PPARα to endometrial carcinogenesis, we did experiments on cultured endometrial carcinoma cells expressing this transcript. Treatment with fenofibrate, an activating ligand for PPARα, significantly reduced proliferation and increased cell death, suggesting that altered expression of nuclear hormone receptors involved with fatty acid metabolism leads to deregulated cellular proliferation and apoptosis. These results support further investigation of members of the PPAR/retinoid X receptor pathway as novel therapeutic targets in endometrial cancer.

Cyclooxygenase-2 and prostaglandins in articular tissues

OBJECTIVES

To provide an overview on: 1) the expression of cyclooxygenase (COX)-2 in articular tissues; 2) the role of prostaglandin E2 (PGE2) in these tissue functions; and 3) clinical trials with COX-2-selective nonsteroidal anti-inflammatory drugs (NSAIDs) (coxibs).

METHODS

MEDLINE search was performed using the key words "cyclooxygenase," "prostaglandin," "osteoarthritis" (OA), and "rheumatoid arthritis" (RA). Selected publications related to clinical trials with coxibs also are included.

RESULTS

COX-2 is upregulated in inflamed joint tissues and is responsible for elevated PGE2 production. The overexpression of COX-2 is likely induced by proinflammatory mediators such as interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF) alpha. However, the exact molecular mechanisms through which the expression of COX-2 is regulated remain to be elucidated. Several studies suggest that PGE2 is involved in inflammation, apoptosis, angiogenesis, and possibly structural changes that characterize arthritic diseases. NSAIDs are prescribed for the treatment of OA and RA and provide effective relief from symptoms; however, serious gastrointestinal complications occur with their use. The clinical efficacy of NSAIDs is primarily related to the inhibition of COX-2, whereas much of the toxicity is related to COX-1 inhibition. Selective COX-2 inhibitors (coxibs) that spare COX-1 at therapeutic doses are more effective than placebo and as effective as other NSAIDs for relief of symptoms of OA and RA, and have significantly improved gastrointestinal safety and tolerability. However, some studies showed that COX-2-selective inhibitors still have classic NSAID complications.

CONCLUSIONS

Overexpression of COX-2 protein in articular tissues is a characteristic feature of arthritic diseases. However, the molecular mechanisms involved in the regulation of COX-2 expression and activity are still unclear. Elucidating the mechanisms of COX-2 expression and PGE2 production and action will help identify novel and more selective potential drug targets in the treatment of arthritic diseases.

Alterations of Activities of Cytosolic Phospholipase A2 and Arachidonic Acid-Metabolizing Enzymes in Di-(2-Ethylhexyl)Phthalate-Induced Testicular Atrophy

Di-(2-ethylhexyl) phthalate (DEHP), a peroxisome proliferator-activated receptor alpha (PPARalpha) ligand, alters the lipid composition of rat testis, yet the mechanism is unclear. In this study, we investigated the effect of DEHP on the synthesis and metabolism of arachidonic acid (AA), a precursor of eicosanoids, in the testis of prepubertal rats. DEHP (100 and 1,000 mg/kg, 5 days) administration caused a significant reduction in activity of cytosolic phospholipase A2 (cPLA2), the rate-limiting enzyme in the AA and eicosanoid synthesis pathways. DEHP increased the expression of 12-lipoxygenase (12-LOX) in rat testis, whereas cyclooxygenase-2 (COX-2) expression was not altered. Cytochrome P450 4A1 (CYP4A1), a product of a PPARalpha-regulated gene, was markedly increased in the testis by DEHP administration. Taken together, DEHP suppresses cPLA2 activity and induces the AA metabolizing enzymes such as 12-LOX and CYP4A1, resulting in the reduction of AA level. These data suggest that altered AA metabolic cascades may be related to the decrease of testosterone concentration in DEHP-induced testicular atrophy.

PPARdelta activation induces COX-2 gene expression and cell proliferation in human hepatocellular carcinoma cells

Cyclooxygenase-2 (COX-2) has been suggested to be associated with carcinogenesis. Recently, many studies have shown increased expression of COX-2 in a variety of human malignancies, including hepatocellular carcinoma (HCC). Therefore, it becomes important to know more about what determines COX-2 expression. In this work, we have studied the effect of PPARdelta activation on COX-2 expression using a selective agonist (GW501516) in human hepatocellular carcinoma (HepG2) cells. Activation of PPARdelta resulted in increased COX-2 mRNA and protein expression. The mechanism behind the induction seems to be increased activity of the proximal promoter of the COX-2 gene, spanning nucleotides -327 to +59. The increased COX-2 protein expression and promoter activity induced by the GW501516 was also confirmed in the monocytic cell line THP-1. Induced levels of COX-2 have previously been associated with resistance to apoptosis and increased cell proliferation in many cell types. In HepG2 cells, we observed a dose-dependent increase in cell number by GW501516 treatment for 72h. The levels of PCNA, used as an indicator of cell division were induced, and the cell survival promoting complex p65 (NF-kappaB) was phosphorylated under GW501516 treatment. We conclude that PPARdelta activation in HepG2 cells results in induced COX-2 expression and increased cellular proliferation. These results may suggest that PPARdelta plays an important role in the development of HCC by modulating expression of COX-2.

Enhancement of carcinogen-induced malignant cell transformation by prostaglandin F(2 alpha)

The enhancement of carcinogen-induced malignant transformation of C3H/M2 mouse fibroblasts by the tumor promoters 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with the induction of cyclooxygenase expression and the stimulation of prostaglandin (PG) formation. Therefore, the potential of PGs, i.e., PGF(2alpha) and PGE(2), for tumor promotion was studied in the two-step C3H/M2 cell transformation assay, a model of the multi-step process of carcinogenesis. The transformation of fibroblasts was clearly enhanced by the addition of PGF(2alpha) in the promotion phase after pretreatment with a subthreshold dose of a carcinogen (3-methylcholanthrene or N-methyl-N'-nitro-N-nitrosoguanidine). No enhancement of cell transformation was observed in cells without carcinogen-pretreatment, i.e., PGF(2alpha) had no tumor initiating potential. The promotional effect was dose-dependent with a maximum at 16 nM PGF(2alpha). PGE(2) had no significant effect in this assay. Furthermore, PGF(2alpha) (but not PGE(2)) clearly reduced the inhibition of TPA-induced promotion by NS-398, an isozyme-specific inhibitor of cyclooxygenase-2. The inhibition of TPA- or TCDD-induced promotion by the non-specific cyclooxygenase inhibitor indomethacin was not affected by co-treatment with PGF(2alpha) and PGE(2). Our data suggest that PGF(2alpha) acts as an endogenous promoter of cell transformation implying that it may also be critically involved in tumor promoter-induced signalling transfer cascades ultimately triggering the process of carcinogenesis.

Advances in understanding the regulation of apoptosis and mitosis by peroxisome-proliferator activated receptors in pre-clinical models: relevance for human health and disease

Peroxisome proliferator activated receptors (PPARs) are a family of related receptors implicated in a diverse array of biological processes. There are 3 main isotypes of PPARs known as PPARalpha, PPARbeta and PPARgamma and each is organized into domains associated with a function such as ligand binding, activation and DNA binding. PPARs are activated by ligands, which can be both endogenous such as fatty acids or their derivatives, or synthetic, such as peroxisome proliferators, hypolipidaemic drugs, anti-inflammatory or insulin-sensitizing drugs. Once activated, PPARs bind to DNA and regulate gene transcription. The different isotypes differ in their expression patterns, lending clues on their function. PPARalpha is expressed mainly in liver whereas PPARgamma is expressed in fat and in some macrophages. Activation of PPARalpha in rodent liver is associated with peroxisome proliferation and with suppression of apoptosis and induction of cell proliferation. The mechanism by which activation of PPARalpha regulates apoptosis and proliferation is unclear but is likely to involve target gene transcription. Similarly, PPARgamma is involved in the induction of cell growth arrest occurring during the differentiation process of fibroblasts to adipocytes. However, it has been implicated in the regulation of cell cycle and cell proliferation in colon cancer models. Less in known concerning PPARbeta but it was identified as a downstream target gene for APC/beta-catenin/T cell factor-4 tumor suppressor pathway, which is involved in the regulation of growth promoting genes such as c-myc and cyclin D1. Marked species and tissue differences in the expression of PPARs complicate the extrapolation of pre-clinical data to humans. For example, PPARalpha ligands such as the hypolipidaemic fibrates have been used extensively in the clinic over the past 20 years to treat cardiovascular disease and side effects of clinical fibrate use are rare, despite the observation that these compounds are rodent carcinogens. Similarly, adverse clinical responses have been seen with PPARgamma ligands that were not predicted by pre-clinical models. Here, we consider the response to PPAR ligands seen in pre-clinical models of efficacy and safety in the context of human health and disease.

Cyclooxygenase-2 expression by nonsteroidal anti-inflammatory drugs in human airway smooth muscle cells: role of peroxisome proliferator-activated receptors

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to modulate cyclooxygenase (COX)-2 expression, but the mechanisms involved are controversial and may be cell specific. We show in this study that indomethacin (Indo), flurbiprofen (Flur), and the selective COX-2 inhibitor NS-398 induced COX-2 expression and markedly enhanced IL-1beta-induced COX-2 expression in human airway smooth muscle (HASM) cells. These effects were not reversed by exogenous PGE(2), suggesting that they are prostanoid-independent. Indeed, PGE(2) also induced and enhanced IL-1beta-induced COX-2 expression. Peroxisome proliferator-activated receptor (PPAR) alpha and PPARgamma (not PPARbeta) were expressed in HASM cells. PPARgamma activators ciglitizone (Cig) and 15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), but not the PPARalpha activator WY-14643, mimicked the effect of NSAIDs on COX-2 expression. Treatment with Flur, NS-398, Cig, and 15d-PGJ(2) alone, but not Indo and WY-14643, elevated COX activity; however, neither enhanced IL-1beta-induced COX activity. Pretreatment with dexamethasone suppressed COX-2 expression, PGE(2) release, and COX activity induced by NS-398, Cig, IL-1beta, alone or in combination. Unlike IL-1beta, NS-398 and Cig did not cause NF-kappaB (p65) nuclear translocation, nor did they further enhance IL-1beta-induced NF-kappaB translocation, but they stimulated PPARgamma translocation. Indo, NS-398, Flur, and 15d-PGJ(2), but not WY-14643, induced transcriptional activity of a COX-2 reporter construct containing the peroxisome proliferator response element (PPRE) on their own and enhanced the effect of IL-1beta, but had no effect on a COX-2 reporter construct lacking the PPRE. The results suggest that COX-2 expression by NSAIDs is biologically functional, prostanoid-independent, and involves PPARgamma activation, and provide the first direct evidence that the PPRE in the promoter is required for NSAID-induced COX-2 expression.

P53-mediated induction of Cox-2 counteracts p53- or genotoxic stress-induced apoptosis

The identification of transcriptional targets of the tumor suppressor p53 is crucial in understanding mechanisms by which it affects cellular outcomes. Through expression array analysis, we identified cyclooxygenase 2 (Cox-2), whose expression was inducible by wild-type p53 and DNA damage. We also found that p53-induced Cox-2 expression results from p53-mediated activation of the Ras/Raf/MAPK cascade, as demonstrated by suppression of Cox-2 induction in response to p53 by dominant-negative Ras or Raf1 mutants. Furthermore, heparin-binding epidermal growth factor-like growth factor (HB- EGF), a p53 downstream target gene, induced Cox-2 expression, implying that Cox-2 is an ultimate effector in the p53-->HB-EGF-->Ras/Raf/MAPK-->Cox-2 pathway. p53-induced apoptosis was enhanced greatly in Cox-2 knock-out cells as compared with wild-type cells, suggesting that Cox-2 has an abrogating effect on p53-induced apoptosis. Also, a selective Cox-2 inhibitor, NS-398, significantly enhanced genotoxic stress-induced apoptosis in several types of p53+/+ normal human cells, through a caspase-dependent pathway. Together, these results demonstrate that Cox-2 is induced by p53-mediated activation of the Ras/Raf/ERK cascade, counteracting p53-mediated apoptosis. This anti-apoptosis effect may be a mechanism to abate cellular stresses associated with p53 induction.

Cyclooxygenase-2 is induced in monocytes by peroxisome proliferator activated receptor gamma and oxidized alkyl phospholipids from oxidized low density lipoprotein

Low density lipoprotein (LDL) oxidation and monocyte infiltration of the vessel wall underlie atherogenesis. These cells express cyclooxygenase-2, but the way oxidized LDL stimulates cyclooxygenase-2 transcription is unknown. Oxidized LDL, oxidatively fragmented phospholipids isolated from oxidized LDL, a synthetic oxidized alkylphospholipid (azPC) that is a potent peroxisome proliferator activated receptor (PPAR) gamma agonist, or the PPARgamma agonist rosiglitazone all induced cyclooxygenase-2 expression and enhanced prostaglandin E(2) (PGE(2)) secretion in primary human monocytes. The cyclooxygenase-2 inhibitor NS398 blocked PPARgamma-induced PGE(2) secretion. Phospholipase A(1) and A(2) digestion shows that oxidized alkylphospholipids, and not oxidized fatty acids, were the relevant agonists. The upstream PPAR-responsive element (PPRE) of cyclooxygenase-2 was required for induction of a luciferase reporter by oxidized phospholipids, azPC, and rosiglitazone, and a (COX-2 PPRE)(3)-luciferase reporter was responsive to these PPARgamma agonists. Circulating human monocytes do not contain PPARgamma, but PPARgamma was induced rapidly (<4 h) in monocytes upon ligation of surface ICAM-3, but not P-selectin glycoprotein-1 even though both interactions prime cytokine secretion. Cyclooxygenase-2 induction by oxidized phospholipids only occurred in monocytes containing PPARgamma. Thus PPARgamma was induced rapidly in primary monocytes by appropriate outside-in signaling, sensitizing them to previously undetectable agonists in oxidized LDL. Cyclooxygenase-2 and PGE(2) secretion are induced, not inhibited, by selective PPARgamma agonists that include oxidatively fragmented phospholipids in oxidized LDL.

Early cell signaling by the cytotoxic enterotoxin of Aeromonas hydrophila in macrophages

A cytotoxic enterotoxin (Act) of Aeromonas hydrophila is an important virulence factor with hemolytic, cytotoxic and enterotoxic activities. In this report, we demonstrated Act rapidly mobilized calcium from intracellular stores and evoked influx of calcium from the extracellular milieu in macrophages. A direct role of calcium in Act-induced prostaglandin (e.g. PGE(2)) and tumor necrosis factor alpha (TNF alpha) production was demonstrated in macrophages using a cell-permeable calcium chelator BAPTA-AM, which also down-regulated activation of transcription factor NF-kappa B. We showed that Act's capacity to increase PGE(2) and TNF alpha production could be blocked by inhibitors of tyrosine kinases and protein kinase A. In addition, Act caused up-regulation of the DNA repair enzyme redox factor-1 (Ref-1), which potentially could promote DNA binding of the transcription factors allowing modulation of various genes involved in the inflammatory response. Taken together, a link between Act-induced calcium release, regulation of downstream kinase cascades and Ref-1, and activation of NF-kappa B leading to PGE(2) and TNF alpha production was established. Since Act also caused extensive tissue damage, we showed that Act increased reactive oxygen species, and the antioxidant N-acetyl cysteine, blocked Act-induced PGE(2) and TNF alpha production, as well as NF-kappa B nuclear translocation in macrophages. We have demonstrated for the first time early cell signaling initiated in eukaryotic cells by Act, which leads to various biological effects associated with this toxin.

Regulation of prostaglandin endoperoxide synthase-2 and IL-6 expression in mouse bone marrow-derived mast cells by exogenous but not endogenous prostanoids

Mouse bone marrow-derived mast cells (BMMC), stimulated with stem cell factor, IL-1beta, and IL-10, secrete IL-6 and demonstrate a delayed phase of PGD(2) generation that is dependent upon the induced expression of PG endoperoxide synthase (PGHS)-2. We have examined the potential for exogenous prostanoids, acting in a paracrine fashion, and endogenous prostanoids, acting in an autocrine fashion, to regulate PGHS-2 induction and IL-6 secretion in mouse BMMC. Exogenous PGE(2), which acts through G protein-coupled receptors, and 15-deoxy-Delta(12,14)-PGJ(2), which is a ligand for peroxisome proliferator-activated receptor (PPAR)gamma, elicited a 2- to 3-fold amplification of PGHS-2 induction, delayed-phase PGD(2) generation, and IL-6 secretion in response to stem cell factor, IL-1beta, and IL-10. The effect of PGE(2) was reproduced by the E prostanoid (EP)1 receptor agonist 17-trinor-PGE(2), and the EP1/EP3 agonist, sulprostone, but not the EP2 receptor agonist, butaprost. Although BMMC express PPARgamma, the effects of 15-deoxy-Delta(12,14)-PGJ(2) were not reproduced by the PPARgamma agonists, troglitazone and ciglitazone. PGHS-2 induction, but not IL-6 secretion, was impaired in cPLA(2)-deficient BMMC. However, there was no impairment of PGHS-2 induction in BMMC deficient in hematopoietic PGD synthase or PGHS-1 in the presence or absence of the PGHS-2 inhibitor, NS-398. Thus, although exogenous prostanoids may contribute to amplification of the inflammatory response by augmenting PGD(2) generation and IL-6 secretion from mast cells, endogenous prostanoids do not play a role.

Increased expression of cyclooxygenase-2 protein during rat hepatocarcinogenesis caused by a choline-deficient, L-amino acid-defined diet and chemopreventive efficacy of a specific inhibitor, nimesulide

Expression of cyclooxygenase (COX)-2 protein during rat hepatocarcinogenesis associated with fatty change, fibrosis, cirrhosis and oxidative DNA damage, caused by a choline-deficient, L-amino acid-defined (CDAA) diet were investigated in F344 male rats, along with the chemopreventive efficacy of the specific COX-2 inhibitor, nimesulide (NIM). Nimesulide, which was administered in the diet at concentrations of 200, 400, 600 and 800 p.p.m. for 12 weeks, decreased the number and size of preneoplastic enzyme-altered liver foci, levels of oxidative DNA damage, and the grade and incidence of fibrosis in a dose-dependent manner. A preliminary long-term study of 65 weeks also revealed that 800 p.p.m. NIM decreased the multiplicity of neoplastic nodules and hepatocellular carcinomas and prevented the development of cirrhosis. Western blot analysis revealed that COX-2 protein was barely expressed in control livers and increased approximately 2.9-fold in the livers of rats fed on a CDAA diet for 12 weeks and approximately 4.5-5.4-fold in tumors, with a diameter larger than 5 mm, at 80 weeks. Immunohistochemically, COX-2 protein was positive in sinusoidal and stromal cells in fibrotic septa, which were identified by immunoelectron microscopy as Kupffer cells, macrophages, either activated Ito cells or fibroblasts, after exposure to the CDAA diet for 12 weeks, whereas it was only occasionally weakly positive in sinusoidal, probably Kupffer, cells in control livers. In neoplastic nodules in rats fed on a CDAA diet for 30 and 80 weeks, sinusoidal cells and cells with relatively large round nuclei and scanty cytoplasm were strongly positive for COX-2 protein, with the neoplastic hepatocytes in the minority of the nodules, but not the cancer cells, being moderately positive. These results clearly indicate that rat hepatocarcinogenesis, along with fatty change, fibrosis and cirrhosis, is associated with increased expression of COX-2 protein, and point to the chemopreventive efficacy of a selective COX-2 inhibitor against, at least, the early stages of hepatocarcinogenesis.

Contribution of cyclooxygenase 2 to liver regeneration after partial hepatectomy

Partial hepatectomy (PH) triggers a rapid regenerative response in the remaining tissue to reinstate the organ function and the cell numbers. Among the molecules that change in the course of regeneration is an accumulation of prostaglandin E2 in the sera of rats with PH. Analysis of the cyclooxygenase (COX) isoenzymes in the remnant liver showed the preferential expression of COX-2 in hepatocytes. Cultured regenerating hepatocytes expressed significant levels of COX-2, a process that was not observed in the sham counterparts. Maximal expression of COX-2 was detected 16 h after PH with increased levels present even at 96 h. Pharmacological inhibition of COX-2 activity with NS398 shunted the up-regulation of cell proliferation after PH, which suggests a positive interaction of prostaglandins with the progression of the cell cycle. Similar results were obtained after PH of mice lacking the COX-2 gene. The expression of COX-2 in regenerating liver was concomitant with a decrease in CCAAT-enhancer binding protein (C/EBP-a) level and an increase in the expression of C/EBP-b and C/EBP-d. These results suggest a contribution of the enhanced synthesis of prostaglandins to liver regeneration observed after PH.