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Glutathione peroxidase 2 (GPx2) is one of the five selenoprotein GPxs having a selenocysteine in the active center. GPx2 is strongly expressed in the gastrointestinal epithelium, as is another isoform, GPx1, though with a different localization pattern. Both GPxs are redox-active enzymes that are important for the reduction of hydroperoxides. Studies on GPx2-deficient mice and human HT-29 cells with a stable knockdown (kd) of GPx2 revealed higher basal and IL-1β-induced expression of NF-κB target genes in vivo and in vitro. The activation of the IKK–IκBα–NF-κB pathway was increased in cultured GPx2 kd cells. Basal signaling was only restored by re-expressing active GPx2 in GPx2 kd cells but not by redox-inactive GPx2. As it is still not clear if the two isoforms GPx1 and GPx2 have different functions, kd cell lines for either GPx1 or GPx2 were studied in parallel. The inhibitory effect of GPx2 on NF-κB signaling and its target gene expression was stronger than that of GPx1, whereas cyclooxygenase (COX)- and lipoxygenase (LOX)-derived lipid mediator levels increased more strongly in GPx1 kd than in GPx2 kd cells. Under unstimulated conditions, the levels of the COX-derived prostaglandins PGE2 and PGD2 were enhanced in GPx2 as well as in GPx1 kd compared to control cells. Specifically, in GPx1 kd cells IL-1β stimulation led to a dramatic shift of the PGE2/PGD2 ratio towards pro-inflammatory PGE2. Taken together, GPx2 and GPx1 have overlapping functions in controlling inflammatory lipid mediator synthesis and, most probably, exert their anti-inflammatory effects by preventing excessive PGE2 production. In view of the high activity of COX and LOX pathways during inflammatory bowel disease our data therefore provide new insights into the mechanisms of the protective function of GPx1 and GPx2 during colitis as well as inflammation-driven carcinogenesis., Graphical abstract Image 1, Highlights • Loss of GPx2 results in higher basal and IL-1β-induced NF-κB activation. • Suppressive effects of GPx2 on NF-κB are mediated in a redox-dependent manner. • Both GPx isoforms modulate the lipid mediator profile in response to IL-1β. • COX-derived prostaglandins increase more strongly in GPx1 than in GPx2 kd cells.

Redox regulation has been proposed to control various aspects of carcinogenesis, cancer cell growth, metabolism, migration, invasion, metastasis and cancer vascularization. As cancer has many faces, the role of redox control in different cancers and in the numerous cancer-related processes often point in different directions. In this review, we focus on the redox control mechanisms of tumor cell destruction. The review covers the tumor-intrinsic role of oxidants derived from the reduction of oxygen and nitrogen in the control of tumor cell proliferation as well as the roles of oxidants and antioxidant systems in cancer cell death caused by traditional anticancer weapons (chemotherapeutic agents, radiotherapy, photodynamic therapy). Emphasis is also put on the role of oxidants and redox status in the outcome following interactions between cancer cells, cytotoxic lymphocytes and tumor infiltrating macrophages. Keywords: Cancer, Redox regulation, Natural killer cells, Cytotoxic lymphocytes, Chemotherapeutics, Free radicals, Antioxidants

Non-alcoholic fatty liver disease (NAFLD) represents the most common chronic liver disease in industrialized countries. NAFLD progresses through the inflammatory phase of non-alcoholic steatohepatitis (NASH) to fibrosis and cirrhosis, with some cases developing liver failure or hepatocellular carcinoma (HCC). Liver biopsy remains the gold standard approach to a definitive diagnosis of NAFLD and the distinction between simple steatosis and NASH. The pathogenesis of NASH is still not clear. Several theories have been proposed ranging from the "Two Hit Theory" to the "Multiple Hit Theory". However, the general consensus is that the gut microbiota, oxidative stress, and mitochondrial damage play key roles in the pathogenesis of NASH. The interaction between the gut epithelia and some commensal bacteria induces the rapid generation of reactive oxygen species (ROS). The main goal of any therapy addressing NASH is to reverse or prevent progression to liver fibrosis/cirrhosis. This problem represents the first "Achilles' heel" of the new molecules being evaluated in most ongoing clinical trials. The second is the inability of these molecules to reach the mitochondria, the primary sites of energy production and ROS generation. Recently, a variety of non-pharmacological and pharmacological treatment approaches for NASH have been evaluated including vitamin E, the thiazolidinediones, and novel molecules related to NASH pathogenesis (including obeticholic acid and elafibranor). Recently, a new isoform of human manganese superoxide dismutase (MnSOD) was isolated and obtained in a synthetic recombinant form designated rMnSOD. This protein has been shown to be a powerful antioxidant capable of mediating ROS dismutation, penetrating biological barriers via its uncleaved leader peptide, and reducing portal hypertension and fibrosis in rats affected by liver cirrhosis. Based on these distinctive characteristics, it can be hypothesized that this novel recombinant protein (rMnSOD) potentially represents a new and highly efficient adjuvant therapy to counteract the progression from NASH to HCC.

The complete mechanism accounting for the progression from simple steatosis to steatohepatitis in nonalcoholic fatty liver disease (NAFLD) has not been elucidated. Lipotoxicity refers to cellular injury caused by hepatic free fatty acids (FFAs) and cholesterol accumulation. Excess cholesterol autoxidizes to oxysterols during oxidative stress conditions. We hypothesize that interaction of FAs and cholesterol derivatives may primarily impair mitochondrial function and affect biogenesis adaptation during NAFLD progression. We demonstrated that the accumulation of specific non-enzymatic oxysterols in the liver of animals fed high-fat+high-cholesterol diet induces mitochondrial damage and depletion of proteins of the respiratory chain complexes. When tested in vitro, 5α-cholestane-3β,5,6β-triol (triol) combined to FFAs was able to reduce respiration in isolated liver mitochondria, induced apoptosis in primary hepatocytes, and down-regulated transcription factors involved in mitochondrial biogenesis. Finally, a lower protein content in the mitochondrial respiratory chain complexes was observed in human non-alcoholic steatohepatitis. In conclusion, hepatic accumulation of FFAs and non-enzymatic oxysterols synergistically facilitates development and progression of NAFLD by impairing mitochondrial function, energy balance and biogenesis adaptation to chronic injury., Graphical abstract fx1, Highlights • Mitochondrial adaptation in NAFLD is lost in fatty acids + cholesterol-induced NASH. • Fatty acids + oxysterols alter mitochondria function/biogenesis inducing cell death. • Mitochondria respiratory proteins and biogenesis regulators are lower in human NASH. • Fatty acids and oxysterols interaction may explain mitochondria dysfunction in NASH.

Therapeutic potential of metformin in obese/diabetic patients has been associated to its ability to combat insulin resistance. However, it remains largely unknown the signaling pathways involved and whether some cell types are particularly relevant for its beneficial effects. M1-activation of macrophages by bacterial lipopolysaccharide (LPS) promotes a paracrine activation of hypoxia-inducible factor-1α (HIF1α) in brown adipocytes which reduces insulin signaling and glucose uptake, as well as β-adrenergic sensitivity. Addition of metformin to M1-polarized macrophages blunted these signs of brown adipocyte dysfunction. At the molecular level, metformin inhibits an inflammatory program executed by HIF1α in macrophages by inducing its degradation through the inhibition of mitochondrial complex I activity, thereby reducing oxygen consumption in a reactive oxygen species (ROS)-independent manner. In obese mice, metformin reduced inflammatory features in brown adipose tissue (BAT) such as macrophage infiltration, proinflammatory signaling and gene expression, and restored the response to cold exposure. In conclusion, the impact of metformin on macrophages by suppressing a HIF1α-dependent proinflammatory program is likely responsible for a secondary beneficial effect on insulin-mediated glucose uptake and β-adrenergic responses in brown adipocytes., Graphical abstract Image 1, Highlights • Macrophage-mediated inflammation in brown adipocytes stabilizes HIF1α. • Stabilization of HIF1α reduces brown adipocyte hormonal responses. • Metformin attenuates inflammation and BAT dysfunction in obese mice. • Mitochondrial complex I inhibition by metformin reduces HIF1α in macrophages. • Targeting macrophages HIF1α by metformin alleviates brown adipocyte inflammation.

Alcohol use disorders are common both in the United States and globally, and are associated with a variety of co-morbid, inflammation-linked diseases. The pathogenesis of many of these ailments are driven by the activation of the NLRP3 inflammasome, a multi-protein intracellular pattern recognition receptor complex that facilitates the cleavage and secretion of the pro-inflammatory cytokines IL-1β and IL-18. We hypothesized that protracted exposure of leukocytes to ethanol would amplify inflammasome activation, which would help to implicate mechanisms involved in diseases associated with both alcoholism and aberrant NLRP3 inflammasome activation. Here we show that long-term ethanol exposure of human peripheral blood mononuclear cells and a mouse macrophage cell line (J774) amplifies IL-1β secretion following stimulation with NLRP3 agonists, but not with AIM2 or NLRP1b agonists. The augmented NRLP3 activation was mediated by increases in iNOS expression and NO production, in conjunction with increases in mitochondrial membrane depolarization, oxygen consumption rate, and ROS generation in J774 cells chronically exposed to ethanol (CE cells), effects that could be inhibited by the iNOS inhibitor SEITU, the NO scavenger carboxy-PTIO, and the mitochondrial ROS scavenger MitoQ. Chronic ethanol exposure did not alter K+ efflux or Zn2+ homeostasis in CE cells, although it did result in a lower intracellular concentration of NAD+. Prolonged administration of acetaldehyde, the product of alcohol dehydrogenase (ADH) mediated metabolism of ethanol, mimicked chronic ethanol exposure, whereas ADH inhibition prevented ethanol-induced IL-1β hypersecretion. Together, these results indicate that increases in iNOS and mitochondrial ROS production are critical for chronic ethanol-induced IL-1β hypersecretion, and that protracted exposure to the products of ethanol metabolism are probable mediators of NLRP3 inflammasome hyperactivation., Graphical abstract fx1, Highlights • Chronic ethanol exposure amplifies NLRP3 inflammasome-induced IL-1β secretion. • NO and mitochondrial ROS mediate chronic ethanol-augmented IL-1β secretion. • Alcohol dehydrogenase-generated metabolites cause NLRP3 inflammasome over-activation.

Reactive oxygen species (ROS) are integral components of multiple cellular pathways even though excessive or inappropriately localized ROS damage cells. ROS function as anti-microbial effector molecules and as signaling molecules that regulate such processes as NF-kB transcriptional activity, the production of DNA-based neutrophil extracellular traps (NETs), and autophagy. The main sources of cellular ROS are mitochondria and NADPH oxidases (NOXs). In contrast to NOX-generated ROS, ROS produced in the mitochondria (mtROS) were initially considered to be unwanted by-products of oxidative metabolism. Increasing evidence indicates that mtROS have been incorporated into signaling pathways including those regulating immune responses and autophagy. As metabolic hubs, mitochondria facilitate crosstalk between the metabolic state of the cell with these pathways. Mitochondria and ROS are thus a nexus of multiple pathways that determine the response of cells to disruptions in cellular homeostasis such as infection, sterile damage, and metabolic imbalance. In this review, we discuss the roles of mitochondria in the generation of ROS-derived anti-microbial effectors, the interplay of mitochondria and ROS with autophagy and the formation of DNA extracellular traps, and activation of the NLRP3 inflammasome by ROS and mitochondria., Graphical abstract fx1, Highlights • Mitochondrial ROS production is regulated by and incorporated into immunity pathways. • ROS regulate mitophagy and xenophagy and neutrophil extracellular trap formation. • Mitochondria and mitochondrial ROS regulate NLRP3 inflammasome activation.

© 2014 The Authors. Alcoholic liver disease (ALD) is a major cause of chronic liver disease and a growing health concern in theworld. While the pathogenesis of ALD is poorly characterized key players identified in experimental models and patients, such as perturbations in mitochondrial structure and function, selective loss of antioxidant defense and susceptibility to inflammatory cytokines, contribute to ALD progression. Both oxidative stress and mitochondrial dysfunction compromise essential cellular functions and energy generation and hence are important pathogenic mechanisms of ALD. An important process mediating the mitochondrial disruption induced by alcohol intake is the trafficking of cholesterol to mitochondria, mediated by acid sphingomyelinase-induced endoplasmic reticulum stress, which contributes to increased cholesterol synthesis and StARD1upregulation. Mitochondrial cholesterol accumulation not only sensitizes to oxidative stress but it can contribute to the metabolic reprogramming in ALD, manifested by activation of the hypoxia inducible transcription factor 1 and stimulation of glycolysis and lactate secretion. Thus, a better understanding of the mechanisms underlying alcohol-mediated mitochondrial impairment and oxidative stress may lead to the identification of novel treatments for ALD. The present review briefly summarizes current knowledge on the cellular and molecular mechanisms contributing to alcohol-induced mitochondrial dysfunction and cholesterol accumulation and provides insights for potential therapeutic targets in ALD., The work was supported by CIBEREHD, Fundació la Marató de TV3 and Grants PI11/0325 (META) and PI10/02114, PI12/00110, PI13/00374 from the Instituto de Salud Carlos III and Grants SAF2011-23031, SAF2012-34831 from Plan Nacional de I+D, Spain; and the Center Grant P50-AA-11999 (Research Center for Liver and Pancreatic Diseases, NIAAA/NIH (Grant no. P50-AA-11999)

The generation of excessive amounts of reactive oxygen species (ROS) leads to cellular oxidative stress that underlies a variety of forms of hepatocyte injury and death including that from alcohol. Although ROS can induce cell damage through direct effects on cellular macromolecules, the injurious effects of ROS are mediated largely through changes in signal transduction pathways such as the mitogen-activated protein kinase c-Jun N-terminal kinase (JNK). In response to alcohol, hepatocytes have increased levels of the enzyme cytochrome P450 2E1 (CYP2E1) which generates an oxidant stress that promotes the development of alcoholic steatosis and liver injury. These effects are mediated in large part through overactivation of JNK that alters cell death pathways. Targeting the JNK pathway or its downstream effectors may be a useful therapeutic approach to the oxidative stress generated by CYP2E1 in alcoholic liver disease., Graphical abstract, Highlights • c-Jun N-terminal kinase (JNK) activation regulates metabolic signaling and cell death pathways in hepatocytes. • Cytochrome P450 2E1 (CYP2E1) overexpression in fatty liver disease increases levels of reactive oxygen species (ROS) triggering oxidative stress. • CYP2E1-generated ROS cause JNK overactivation which is a mechanism for the development of alcoholic fatty liver disease. • The CYP2E1-ROS-JNK injury cascade is a therapeutic target in alcoholic liver disease.

Objective Measurements of oxidative stress biomarkers in patients with heart failure (HF) have yielded controversial results. This study aimed at testing the hypothesis that circulating levels of the lipid peroxidation product 4-hydroxynonenal bound to thiol proteins (4HNE-P) are strongly associated with those of its potential precursors, namely n-6 polyunsaturated fatty acids (PUFA). Methods and results Circulating levels of 4HNE-P were evaluated by gas chromatography-mass spectrometry in 71 control subjects and 61 ambulatory symptomatic HF patients along with various other clinically- and biochemically-relevant parameters, including other oxidative stress markers, and total levels of fatty acids from all classes, which reflect both free and bound to cholesterol, phospholipids and triglycerides. All HF patients had severe systolic functional impairment despite receiving optimal evidence-based therapies. Compared to controls, HF patients displayed markedly lower circulating levels of HDL- and LDL-cholesterol, which are major PUFA carriers, as well as of PUFA of the n-6 series, specifically linoleic acid (LA; P=0.001). Circulating 4HNE-P in HF patients was similar to controls, albeit multiple regression analysis revealed that LA was the only factor that was significantly associated with circulating 4HNE-P in the entire population (R2=0.086; P=0.02). In HF patients only, 4HNE-P was even more strongly associated with LA (P=0.003) and HDL-cholesterol (p, Graphical abstract, Highlights • Peroxidation of n-6 polyunsaturated fatty acids (PUFA) forms 4-hydroxynonenal (4HNE). • Heart failure (HF) patients have lower plasma levels of n-6 PUFA linoleic acid (LA). • Blood levels of 4HNE bound to proteins (4HNE-P) in HF patients are similar to controls. • 4HNE-P levels are associated with those of LA in the entire population (p