Marta López-Parra

The selective cyclooxygenase-2 inhibitor SC-236 reduces liver fibrosis by mechanisms involving non-parenchymal cell apoptosis and PPARγ activation

The importance of inflammation in initiating the sequence of events that lead to liver fibrosis is increasingly recognized. In this study, we tested the effects of SC‐236, a selective cyclooxygenase (COX)‐2 inhibitor, in rats with carbon tetrachloride (CCl4)‐induced liver fibrosis. Livers from CCl4‐treated rats showed increased COX‐2 expression and 15‐deoxy‐prostaglandin (PG)J2 (15d‐PGJ2) formation, as well as decreased peroxisome proliferator‐activated receptor (PPAR)γ expression. In these animals, SC‐236 reduced liver fibrosis as revealed by histological analysis and by a reduction in hepatic hydroxyproline levels, metalloproteinase‐2 activity, and α‐smooth muscle actin expression. Interestingly, SC‐236 normalized 15d‐PGJ2 levels and restored PPARγ expression in the liver of CCl4‐treated rats. In isolated hepatic stellate cells (HSCs)—the major player in liver fibrogenesis—and Kupffer cells—the cell type primarily responsible for increased hepatic COX‐2—SC‐236 exhibited remarkable pro‐apoptotic and growth inhibitory properties. Of interest, SC‐236 decreased HSC viability to a similar extent than the PPARγ ligand rosiglitazone. Moreover, SC‐236 significantly induced PPARγ expression in HSCs and acted as a potent PPARγ agonist in a luciferase‐reporter trans‐activation assay. These data indicate that, by mechanisms involving non‐parenchymal cell apoptosis and PPARγ activation, the selective COX‐2 inhibitor SC‐236 might have therapeutic potential for prevention of liver fibrosis.

Obesity-induced insulin resistance and hepatic steatosis are alleviated by ω-3 fatty acids: a role for resolvins and protectins

Omega‐3‐polyunsaturated fatty acids (w‐3‐PUFAs) have well‐documented protective effects that are attributed not only to eicosanoid inhibition but also to the formation of novel biologically active lipid mediators (i.e., resolvins and protectins). In this study, we examined their effects on ob/ob mice, an obesity model of insulin resistance and fatty liver disease. Dietary intake ofw‐3‐PUFAs had insulin‐sensitizing actions in adipose tissue and liver and improved insulin tolerance in obese mice. Genes involved in insulin sensitivity (PPAR/γ), glucose transport (GLUT‐2/GLUT–4), and insulin receptor signaling (IRS‐1/IRS–2) were up‐regulated byw‐3‐PUFAs. Moreover,w‐3‐PUFAs increased adiponectin, an anti‐inflammatory and insulin‐sensitizing adipokine, and induced AMPK phosphorylation, a fuel‐sensing enzyme and a gatekeeper of the energy balance. Concomitantly, hepatic steatosis was alleviated byw‐3‐PUFAs. A lipidomic analysis with liquid chromatography/mass spectrome‐try/mass spectrometry revealed that w‐3‐PUFAs inhibited the formation of w‐6‐PUFA‐derived eicosanoids, while triggering the formation of w‐3‐PUFA‐derived resolvins and protectins. Moreover, representative members of these lipid mediators, namely resolvin E1 and protectin D1, mimicked the insulin‐sensitizing and antisteatotic effects of w‐3‐PUFAs and induced adiponectin expression to a similar extent that of rosigli‐tazone, a member of the thiazolidinedione family of antidiabetic drugs. Taken together, these findings uncover beneficial actions of w‐3‐PUFAs and their bioactive lipid autacoids in preventing obesity‐induced insulin resistance and hepatic steatosis.—Gonzalez‐Periz, A.,Horrillo, R., Ferre, N., Gronert, K., Dong, B., Moran‐Salvador, E.,Titos, E., Martinez‐Clemente, M.,Lopez‐Parra, M.,Arroyo, V., Claria, J. Obesity‐induced insulin resistance and hepatic steatosis are alleviated byw‐3 fatty acids: a role for resolvins and protectins. FASEB J. 23, 1946–1957 (2009)

Role for PPARγ in obesity-induced hepatic steatosis as determined by hepatocyte- and macrophage-specific conditional knockouts

Peroxisome proliferator‐activated receptor (PPAR) γ is a nuclear receptor central to glucose and lipid homeostasis. PPARγ role in nonalcoholic fatty liver disease is controversial because PPARγ over‐expression is a general property of steatotic livers, but its activation by thiazolidinediones reduces hepatic steatosis. Here, we investigated hepatic PPARγ function by using Cre‐loxP technology to generate hepatocyte (PPARγΔhep)‐ and macrophage (PPARγΔmac)‐specific PPARγ‐knockout mice. Targeted deletion of PPARγ in hepatocytes, and to a lesser extent in macrophages, protected mice against high‐fat diet‐induced hepatic steatosis. Down‐regulated expression of genes involved in lipogenesis (SCD1, SREBP‐1c, and ACC), lipid transport (CD36/FAT, L‐FABP, and MTP), and β‐oxidation (PPARα and ACO) was observed in PPARγΔhep mice. Moreover, PPARγΔhep mice showed improved glucose tolerance and reduced PEPCK expression without changes in Pcx, Fbp1, and G6Pc expression and CREB and JNK phosphorylation. In precision‐cut liver slices (PCLSs) and hepatocytes, rosiglitazone either alone or in combination with oleic acid increased triglyceride accumulation, an effect that was blocked by the PPARγ antagonist biphenol A diglycidyl ether (BADGE). PCLSs and hepatocytes from PPARγΔhep mice showed blunted responses to rosiglitazone and oleic acid, whereas the response to these compounds remained intact in PCLSs from PPARγΔmac mice. Collectively, these findings establish PPARγ expression in hepatocytes as a prosteatotic factor in fatty liver disease.—Morán‐Salvador, E., López‐Parra, M., García‐Alonso, V., Titos, E., Martínez‐Clemente, M., González‐Périz, A., López‐Vicario, C., Barak, Y., Arroyo, V., Clària, J. Role for PPARγ in obesity‐induced hepatic steatosis as determined by hepatocyte‐ and macrophage‐specific conditional knockouts. FASEB J. 25, 2538–2550 (2011). www.fasebj.org

Docosahexaenoic acid (DHA) blunts liver injury by conversion to protective lipid mediators: protectin D1 and 17S-hydroxy-DHA

Docosahexaenoic acid (DHA) is a ω‐3 essential fatty acid that reduces the incidence and severity of a number of diseases. Recently, a novel series of DHA‐derived lipid mediators with potent protective actions has been identified. In this study we demonstrate that dietary amplification of these DHA‐derived products protects the liver from necroinflammatory injury. In vitro, supplementation of hepatocytes with DHA significantly reduced hydrogen peroxide‐induced DNA damage, evaluated by the “comet assay,” and oxidative stress, determined by measurement of malondialdehyde levels. In vivo, dietary supplementation of mice with DHA ameliorated carbon tetrachloride‐induced necroinflammatory damage. In addition, hepatic cyclooxygenase‐2 expression and PGE2 levels were significantly reduced in mice fed DHA‐enriched diets. In these animals, increased hepatic formation of DHA‐derived lipid mediators (i.e., 17S‐hydroxy‐DHA (17S‐HDHA) and protectin D1) was detected by HPLC‐gas chromatography/mass spectrometry analysis. Consistent with these findings, synthetic 17‐HDHA abrogated genotoxic and oxidative damage in hepatocytes and decreased TNF‐α release and 5‐lipoxygenase expression in macrophages. In a transactivation assay, 17‐ HDHA acted in a concentration‐dependent manner as a PPARγ agonist. Taken together, these findings identify a potential role for DHA‐derived products, specifically 17S‐HDHA and protectin D1, in mediating the protective effects of dietary DHA in necroinflammatory liver injury.—González‐Périz, A., Planagumà, A., Gronert, K., Miquel, R., López‐Parra, M., Titos, E., Horrillo, R., Ferré, N., Deulofeu, R., Arroyo, V., Rodés, J., Clària, J. Docosahexaenoic acid (DHA) blunts liver injury by conversion to protective lipid mediators: protectin D1 and 17S‐hydroxy‐DHA. FASEB J. 20, E1844–E1855 (2006)

5-Lipoxygenase Activating Protein Signals Adipose Tissue Inflammation and Lipid Dysfunction in Experimental Obesity

The presence of the so-called low-grade inflammatory state is recognized as a critical event in adipose tissue dysfunction, leading to altered secretion of adipokines and free fatty acids (FFAs), insulin resistance, and development of hepatic complications associated with obesity. This study was designed to investigate the potential contribution of the proinflammatory 5-lipoxygenase (5-LO) pathway to adipose tissue inflammation and lipid dysfunction in experimental obesity. Constitutive expression of key components of the 5-LO pathway, as well as leukotriene (LT) receptors, was detected in adipose tissue as well as in adipocyte and stromal vascular fractions. Adipose tissue from obese mice, compared with that from lean mice, exhibited increased 5-LO activating protein (FLAP) expression and LTB4 levels. Incubation of adipose tissue with 5-LO products resulted in NF-κB activation and augmented secretion of proinflammatory adipokines such as MCP-1, IL-6, and TNF-α. In addition, LTB4, but not LTD4, reduced FFA uptake in primary adipocytes, whereas 5-LO inhibition suppressed isoproterenol-induced adipose tissue lipolysis. In mice with dietary obesity, elevated FLAP expression in adipose tissue was paralleled with macrophage infiltration, increased circulating FFA levels, and hepatic steatosis, phenomena that were reversed by FLAP inhibition with Bay-X-1005. Interestingly, FLAP inhibition induced AMP-activated protein kinase phosphorylation in parallel with decreases in hormone-sensitive lipase activity and the expression and secretion of TNF-α and IL-6. Similar effects were observed in differentiated 3T3-L1 adipocytes incubated with either Bay-X-1005 or the selective LTB4 receptor antagonist U-75302. Taken together, these findings indicate that the 5-LO pathway signals the adipose tissue low-grade inflammatory state and steatogenic potential in experimental obesity.

Effects of celecoxib and naproxen on renal function in nonazotemic patients with cirrhosis and ascites

Nonselective inhibition of cyclooxygenase (COX) by nonsteroidal anti‐inflammatory drugs frequently induces renal failure in decompensated cirrhosis. Studies in experimental cirrhosis suggest that selective inhibitors of the inducible isoform COX‐2 do not adversely affect renal function. However, very limited information is available on the effects of these compounds on renal function in human cirrhosis. This investigation consists of a double‐blind, randomized, placebo‐controlled trial aimed at comparing the effects of the selective COX‐2 inhibitor celecoxib (200 mg every 12 hours for a total of 5 doses) on platelet and renal function and the renal response to furosemide (40 mg intravenously) with those of naproxen (500 mg every 12 hours for a total of 5 doses) and placebo in 28 patients with cirrhosis and ascites. A significant reduction (P < .05) in glomerular filtration rate (113 ± 27 to 84 ± 22 mL/min), renal plasma flow (592 ± 158 to 429 ± 106 mL/min) and urinary prostaglandin E2 excretion (3430 ± 430 to 2068 ± 549 pg/min) and suppression of the diuretic (urine volume: 561 ± 128 to 414 ± 107 mL/h) and natriuretic (urine sodium: 53 ± 13 to 34 ± 10 mEq/h) responses to furosemide were observed in the group of patients treated with naproxen but not in the other two groups. Naproxen, but not celecoxib or placebo, significantly inhibited platelet aggregation (72% ± 8% to 47% ± 8%, P < .05) and thromboxane B2 production (41 ± 12 to 14 ± 5 pg/mL, P < .05). In conclusion, our results indicate that short‐term administration of celecoxib does not impair platelet and renal function and the response to diuretics in decompensated cirrhosis. Further studies are needed to evaluate the long‐term safety of this drug in cirrhosis. (HEPATOLOGY 2005;41:579–587.)

Aspirin (ASA) regulates 5-lipoxygenase activity and peroxisome proliferator-activated receptor α-mediated CINC-1 release in rat liver cells: novel actions of lipoxin A4 (LXA4) and ASA-triggered 15-epi-LXA4

The mechanism of action of aspirin (ASA) is related to cyclooxygenase (COX) inhibition, but additional actions cannot be excluded for their antiinflammatory properties and antithrombotic activity. In the current investigation, we examined the effects of ASA on COX and 5‐lipoxygenase (5‐LO) pathways and its impact on peroxisome proliferator‐activated receptor α (PPARα) and cytokine‐induced neutrophil chemoattractant‐1 (CINC‐1) levels in rat liver cells. In Kupffer cells, the liver resident macrophages, ASA switched eicosanoid biosynthesis from prostaglandin E2 (PGE2) to leukotriene B4 (LTB4) and 15‐epi‐lipoxin A4 (15‐epi‐LXA4) formation. In hepatocytes, ASA significantly inhibited PPARα protein expression and CINC‐1 secretion, effects that were also observed in hepatocytes exposed to the selective PPARα agonist Wy‐14643. In contrast, treatment of hepatocytes with PGE2 in association with LTB4 had no significant effect on PPARα but stimulated CINC‐1 release. Interestingly, the endogenous antiinflammatory eicosanoids LXA4 and ASA‐triggered 15‐epi‐LXA4, in addition to inhibiting macrophage 5‐LO activity to a similar extent as PGE2, significantly reduced PPARα and CINC‐1 levels in hepatocytes. Taken together and because arachidonic acid‐derived products, PPARα levels, and CINC‐1 secretion are involved in the extent and duration of an inflammatory response, these findings provide additional molecular mechanisms for the pharmacological properties of ASA.

5‐lipoxygenase deficiency reduces hepatic inflammation and tumor necrosis factor α–induced hepatocyte damage in hyperlipidemia‐prone ApoE‐null mice

The actual risk factors that drive hepatic inflammation during the transition from steatosis to steatohepatitis are unknown. We recently demonstrated that hyperlipidemia‐prone apolipoprotein E–deficient (ApoE−/−) mice exhibit hepatic steatosis and increased susceptibility to hepatic inflammation and advanced fibrosis. Because the proinflammatory 5‐lipoxygenase (5‐LO) pathway was found to be up‐regulated in these mice and given that 5‐LO deficiency confers cardiovascular protection to ApoE−/− mice, we determined the extent to which the absence of 5‐LO would alter liver injury in these mice. Compared with ApoE−/− mice, which showed expected hepatic steatosis and inflammation, ApoE/5‐LO double‐deficient (ApoE−/−/5‐LO−/−) mice exhibited reduced hepatic inflammation, macrophage infiltration, tumor necrosis factor α (TNF‐α), monocyte chemoattractant protein‐1 (MCP‐1) and interleukin (IL)‐18 expression, caspase‐3 and nuclear factor‐κB (NF‐κB) activities, and serum alanine aminotransferase levels in the absence of changes in hepatic steatosis. The lack of 5‐LO produced a remarkable insulin‐sensitizing effect in the adipose tissue because peroxisome proliferator‐activated receptor γ, insulin receptor substrate‐1, and adiponectin were up‐regulated, whereas c‐Jun amino‐terminal kinase phosphorylation and MCP‐1 and IL‐6 expression were down‐regulated. On the other hand, hepatocytes isolated from ApoE−/−/5‐LO−/− mice were more resistant to TNF‐α–induced apoptosis. The 5‐LO products leukotriene (LT) B4, LTD4, and 5‐HETE consistently triggered TNF‐α–induced apoptosis and compromised hepatocyte survival by suppressing NF‐κB activity in the presence of actinomycin D. Moreover, ApoE−/−/5‐LO−/− mice were protected against sustained high‐fat diet (HFD)‐induced liver injury and hepatic inflammation, macrophage infiltration and insulin resistance were significantly milder than those of ApoE−/− mice. Finally, pharmacological inhibition of 5‐LO significantly reduced hepatic inflammatory infiltrate in the HFD and ob/ob models of fatty liver disease. Conclusion: These combined data indicate that hyperlipidemic mice lacking 5‐LO are protected against hepatic inflammatory injury, suggesting that 5‐LO is involved in mounting hepatic inflammation in metabolic disease. (HEPATOLOGY 2010.)

Inhibition of 5-lipoxygenase induces cell growth arrest and apoptosis in rat Kupffer cells: implications for liver fibrosis

The existence of an increased number of Kupffer cells is recognized as critical in the initiation of the inflammatory cascade leading to liver fibrosis. Because 5‐lipoxygenase (5‐LO) is a key regulator of cell growth and survival, in the current investigation we assessed whether inhibition of the 5‐LO pathway would reduce the excessive number of Kupffer cells and attenuate inflammation and fibrosis in experimental liver disease. Kupffer cells were the only liver cell type endowed with a metabolically active 5‐LO pathway (i.e., expressed mRNAs for 5‐LO, 5‐LO‐activating protein [FLAP], and leukotriene [LT] C4 synthase and generated LTB4 and cysteinyl‐LTs). Both the selective 5‐LO inhibitor AA861 and the FLAP inhibitor BAY‐X‐1005 markedly reduced the number of Kupffer cells in culture. The antiproliferative properties of AA861 and BAY‐X‐1005 were associated with the occurrence of condensed nuclei, fragmented DNA, and changes in DNA content and cell cycle frequency distribution consistent with an apoptotic process. In vivo, in carbon tetrachloride‐treated rats, BAY‐X‐1005 had a significant antifibrotic effect and reduced liver damage and the hepatic content of hydroxyproline. Together, these findings indicate a novel mechanism by which inactivation of the 5‐LO pathway could disrupt the sequence of events leading to liver inflammation and fibrosis.

Increased susceptibility to exacerbated liver injury in hypercholesterolemic ApoE-deficient mice: potential involvement of oxysterols

The contribution of metabolic factors to the severity of liver disease is not completely understood. In this study, apolipoprotein E-deficient (ApoE-/-) mice were evaluated to define potential effects of hypercholesterolemia on the severity of carbon tetrachloride (CCl4)-induced liver injury. Under baseline conditions, hypercholesterolemic ApoE-/- mice showed increased hepatic oxidative stress (SOD activity/4-hydroxy-2-nonenal immunostaining) and higher hepatic TGF-beta1, MCP-1, and TIMP-1 expression than wild-type control mice. After CCl4 challenge, ApoE-/- mice exhibited exacerbated steatosis (Oil Red O staining), necroinflammation (hematoxylin-eosin staining), macrophage infiltration (F4/80 immunohistochemistry), and fibrosis (Sirius red staining and alpha-smooth muscle actin immunohistochemistry) and more severe liver injury [alanine aminotransferase (ALT) and aspartate aminotransferase] than wild-type controls. Direct correlations were identified between serum cholesterol and hepatic steatosis, fibrosis, and ALT levels. These changes did not reflect the usual progression of the disease in ApoE-/- mice, since exacerbated liver injury was not present in untreated age-paired ApoE-/- mice. Moreover, hepatic cytochrome P-450 expression was unchanged in ApoE-/- mice. To explore potential mechanisms, cell types relevant to liver pathophysiology were exposed to selected cholesterol-oxidized products. Incubation of hepatocytes with a mixture of oxysterols representative of those detected by GC-MS in livers from ApoE-/- mice resulted in a concentration-dependent increase in total lipoperoxides and SOD activity. In hepatic stellate cells, oxysterols increased IL-8 secretion through a NF-kappaB-independent mechanism and upregulated TIMP-1 expression. In macrophages, oxysterols increased TGF-beta1 secretion and MCP-1 expression in a concentration-dependent manner. Oxysterols did not compromise cell viability. Taken together, these findings demonstrate that hypercholesterolemic mice are sensitized to liver injury and that cholesterol-derived products (i.e., oxysterols) are able to induce proinflammatory and profibrogenic mechanisms in liver cells.