Inhibitory effect of phospholipid hydroperoxide glutathione peroxidase on the activity of lipoxygenases and cyclooxygenases

Regulation of Ferroptosis in Cancer and Immune Cells

Ferroptosis, an iron-dependent form of regulated cell death, is driven by lipid peroxidation and shaped by metabolic and antioxidant pathways. In immune cells, ferroptosis susceptibility varies by cell types, lipid composition, and metabolic demands, influencing immune responses in cancer, infections, and autoimmune diseases. Therapeutically, targeting ferroptosis holds promise in cancer immunotherapy by enhancing antitumor immunity or inhibiting immunosuppressive cells. This review highlights the metabolic pathways underlying ferroptosis, its regulation in immune cells, its dual role in tumor progression and antitumor immunity, and its context-dependent therapeutic implications for optimizing cancer treatment.

Ferroptosis in colorectal cancer: a future target?

Colorectal cancer (CRC) is the third leading cause of cancer deaths worldwide and is characterised by frequently mutated genes, such as APC, TP53, KRAS and BRAF. The current treatment options of chemotherapy, radiation therapy and surgery are met with challenges such as cancer recurrence, drug resistance, and overt toxicity. CRC therapies exert their efficacy against cancer cells by activating biological pathways that contribute to various forms of regulated cell death (RCD). In 2012, ferroptosis was discovered as an iron-dependent and lipid peroxide-driven form of RCD. Recent studies suggest that therapies which target ferroptosis are promising treatment strategies for CRC. However, a greater understanding of the mechanisms of ferroptosis initiation, propagation, and resistance in CRC is needed. This review provides an overview of recent research in ferroptosis and its potential role as a therapeutic target in CRC. We also propose future research directions that could help to enhance our understanding of ferroptosis in CRC.

Regulatory mechanism and research progress of ferroptosis in obstetrical and gynecological diseases

Ferroptosis is a novel type of regulated cell death driven by iron-dependent lipid peroxidation, which is distinguished from traditional types of programmed cell death, such as apoptosis, proptosis and necrosis et al. Impaired iron homeostasis, lipid peroxidation and antioxidants depletion are three hallmarks of ferroptosis. Over the past years, emerging studies support the notion that ferroptosis might be involved in the pathology of obstetrical and gynecological diseases, including preeclampsia (PE), endometriosis (EMs) and polycystic ovarian syndrome (PCOS). In the PE condition, the high sensitivity of trophoblasts towards ferroptosis has been found to potentially link to inflammation, suboptimal vascular remodeling and aberrant hemodynamics, which are three prominent pathophysiological features of PE. As for EMs, compromised ferroptosis of endometrial cells was associated with the formation ectopic lesions, whereas in the nearby lesions, the presence of ferroptosis was suggested to promote the progression of EMs, contributing to the relative clinical manifestations. Ferroptosis has been implicated a crucial role in the initiation of ovarian follicular atresia, which might help to manage ovulation in PCOS patients. Taken together, this review explored the basis of ferroptosis mechanisms and comprehensively summarized the latest discovery of roles of ferroptosis on PE, EMs and PCOS, gaining a deeper insight into the pathogenesis of these obstetrical and gynecological diseases and investigation of novel therapeutic interventions.

The Emerging Role of Ferroptosis in Cardiovascular Diseases

Ferroptosis is one type of programmed cell death discovered in recent years, which is characterized by iron-dependent lipid peroxidation and participating in iron, lipid and antioxidant metabolism. Ferroptosis is different from the traditional cell death types such as apoptosis, necroptosis and autophagy in morphology, biochemistry and genetics. Cardiovascular diseases are considered as an important cause of death from non-communicable diseases in the global population and poses a serious threat to human health. Apoptosis has long been thought to be the major type of cardiomyocyte death, but now ferroptosis has been shown to play a major role in cardiovascular diseases as well. This review will discuss related issues such as the mechanisms of ferroptosis and its effects on the occurrence and development of cardiovascular diseases, aiming to provide a novel target for the prevention and treatment of cardiovascular diseases.

Ferroptosis: A Trigger of Proinflammatory State Progression to Immunogenicity in Necroinflammatory Disease

Until recently, necrosis is generally regarded as traumatic cell death due to mechanical shear stress or other physicochemical factors, while apoptosis is commonly thought to be programmed cell death, which is silent to immunological response. Actually, multiple modalities of cell death are programmed to maintain systematic immunity. Programmed necrosis, such as necrosis, pyroptosis, and ferroptosis, are inherently more immunogenic than apoptosis. Programmed necrosis leads to the release of inflammatory cytokines, defined as danger-associated molecular patterns (DAMPs), resulting in a necroinflammatory response, which can drive the proinflammatory state under certain biological circumstances. Ferroptosis as a newly discovered non-apoptotic form of cell death, is characterized by excessive lipid peroxidation and overload iron, which occurs in cancer, neurodegeneration, immune and inflammatory diseases, as well as ischemia/reperfusion (I/R) injury. It is triggered by a surplus of reactive oxygen species (ROS) induced in an imbalanced redox reaction due to the decrease in glutathione synthesis and inaction of enzyme glutathione peroxidase 4 (GPX4). Ferroptosis is considered as a potential therapeutic and molecular target for the treatment of necroinflammatory disease, and further investigation into the underlying pathophysiological characteristics and molecular mechanisms implicated may lay the foundations for an interventional therapeutic strategy. This review aims to demonstrate the key roles of ferroptosis in the development of necroinflammatory diseases, the major regulatory mechanisms involved, and its potential as a therapeutic target.

Arachidonate 12S-lipoxygenase of platelet-type in hepatic stellate cells of methionine and choline-deficient diet-fed mice

A role of 12-lipoxygenase in the progression of non-alcoholic steatohepatitis (NASH) is suggested, although the underlying mechanism is not entirely understood. The catalytic activity of 12S-lipoxygenase that was hardly observed in liver cytosol of normal chow-fed mice was clearly detectable in that of NASH model mice prepared by feeding a methionine and choline-deficient (MCD) diet. The product profile, substrate specificity and immunogenicity indicated that the enzyme was the platelet-type isoform. The expression levels of mRNA and protein of platelet-type 12S-lipoxygenase in the liver of MCD diet-fed mice were significantly increased compared with those of normal chow-fed mice. Immunohistochemical analysis showed that platelet-type 12S-lipoxygenase colocalized with α-smooth muscle actin as well as vitamin A in the cells distributing along liver sinusoids. These results indicate that the expression level of platelet-type 12S-lipoxygenase in hepatic stellate cells was increased during the cell activation in MCD diet-fed mice, suggesting a possible role of the enzyme in pathophysiology of liver fibrosis.

Ferroptosis at the crossroads of cancer-acquired drug resistance and immune evasion

Ferroptosis is a recently recognized cell death modality that is morphologically, biochemically and genetically distinct from other forms of cell death and that has emerged to play an important role in cancer biology. Recent discoveries have highlighted the metabolic plasticity of cancer cells and have provided intriguing insights into how metabolic rewiring is a critical event for the persistence, dedifferentiation and expansion of cancer cells. In some cases, this metabolic reprogramming has been linked to an acquired sensitivity to ferroptosis, thus opening up new opportunities to treat therapy-insensitive tumours. However, it is not yet clear what metabolic determinants are critical for therapeutic resistance and evasion of immune surveillance. Therefore, a better understanding of the processes that regulate ferroptosis sensitivity should ultimately aid in the discovery of novel therapeutic strategies to improve cancer treatment. In this Perspectives article, we provide an overview of the known mechanisms that regulate sensitivity to ferroptosis in cancer cells and how the modulation of metabolic pathways controlling ferroptosis might reshape the tumour niche, leading to an immunosuppressive microenvironment that promotes tumour growth and progression.

Ferroptosis and necroinflammation, a yet poorly explored link

Ferroptosis is a non-apoptotic form of cell death characterized by overwhelming iron-dependent lipid peroxidation, which contributes to a number of pathologies, most notably tissue ischemia/reperfusion injury, neurodegeneration and cancer. Cysteine availability, glutathione biosynthesis, polyunsaturated fatty acid metabolism and modulation of the phospholipidome are the key events of this necrotic cell death pathway. Non-enzymatic and enzymatic lipoxygenase (LOX)-mediated lipid peroxidation of lipid bilayers is efficiently counteracted by the glutathione (GSH)/glutathione peroxidase 4 (GPX4) axis. Preliminary studies suggest that bursting ferroptotic cells release pro-inflammatory damage-associated molecular patterns (DAMPs) that trigger the innate immune system as exemplified by diseased kidney and brain tissues where ferroptosis contributes to organ demise in a predominant manner. The GSH/GPX4 node is known to control the activities of LOX and prostaglandin-endoperoxide synthase (PTGS) via the so-called peroxide tone. Since LOX and PTGS products do have pro- and anti-inflammatory effects, one may speculate that these enzymes contribute to the ferroptotic process on several levels in cell-autonomous and non-autonomous ways. Hence, this review provides the reader with an outline on what is currently known about the link between ferroptosis and necroinflammation and discusses critical events that may alert the innate immune system in early phases when cells become sensitized towards ferroptosis.

The oxido-reductase enzyme glutathione peroxidase 4 (GPX4) governs Salmonella Typhimurium-induced neutrophil transepithelial migration

Neutrophil (polymorphonuclear leucocytes; PMN) transmigration across mucosal surfaces contributes to dysfunction of epithelial barrier properties, a characteristic underlying many mucosal inflammatory diseases. Using Salmonella enterica serovar Typhimurium (S. Typhimurium) as a prototypic proinflammatory insult, we have previously reported that the eicosanoid hepoxilin A₃ (HXA₃), an endogenous product of 12-lipoxygenase (12-LOX) activity, is secreted from the apical surface of the intestinal epithelium to establish a chemotactic gradient that guides PMN across the epithelial surface. Since little is known regarding the molecular mechanisms that regulate 12-LOX during S. Typhimurium infection, we investigated this pathway. We found that expression of phospholipid glutathione peroxidase (GPX4), which is known to have an inhibitory effect on 12-LOX activity, is significantly decreased at both the mRNA and protein level during infection with S. Typhimurium. Moreover, employing intestinal epithelial cell monolayers expressing siRNA against GPX4 mRNA, S. Typhimurium-induced PMN migration was significantly increased compared with the non-specific siRNA control cells. Conversely, in cells engineered to overexpress GPX4, S. Typhimurium-induced PMN migration was significantly decreased, which is consistent with the finding that partial depletion of GPX4 by RNAi resulted in a significant increase in HXA₃ secretion during S. Typhimurium infection. Mechanistically, although we found Salmonella entry not to be required for the induced decrease in GPX4, the secreted effector, SipA, which is known to induce epithelial responses leading to stimulation of HXA₃, governed the decrease in GPX4 in a process that does not lead to an overall increase in the levels of ROS. Taken together, these results suggest that S. Typhimurium induces apical secretion of HXA₃ by decreasing the expression of phospholipid GPX, which in turn leads to an increase in 12-LOX activity, and hence HXA₃ synthesis.

Lipoxygenase: an emerging target for stroke therapy

Neuroprotection as approach to stroke therapy has recently seen a revival of sorts, fueled in part by the continuing necessity to improve acute stroke care, and in part by the identification of novel drug targets. 12/15- Lipoxygenase (12/15-LOX), one of the key enzymes of the arachidonic acid cascade, contributes to both neuronal cell death and vascular injury. Inhibition of 12/15-LOX may thus provide multifactorial protection against ischemic injury. Targeting 12/15-LOX and related eicosanoid pathways is the subject of this brief review.

Targeted disruption of glutathione peroxidase 4 in mouse skin epithelial cells impairs postnatal hair follicle morphogenesis that is partially rescued through inhibition of COX-2

Selenoproteins are essential molecules for the mammalian antioxidant network. We previously demonstrated that targeted loss of all selenoproteins in mouse epidermis disrupted skin and hair development and caused premature death. In the current study we targeted specific selenoproteins for epidermal deletion to determine whether similar phenotypes developed. Keratinocyte-specific knockout mice lacking either the glutathione peroxidase 4 (GPx4) or thioredoxin reductase 1 (TR1) gene were generated by cre-lox technology using K14-cre. TR1 knockout mice had a normal phenotype in resting skin while GPx4 loss in epidermis caused epidermal hyperplasia, dermal inflammatory infiltrate, dysmorphic hair follicles and alopecia in perinatal mice. Unlike epidermal ablation of all selenoproteins, mice ablated for GPx4 recovered after 5 weeks and had a normal lifespan. GPx1 and TR1 were upregulated in the skin and keratinocytes of GPx4 knockout mice. GPx4 deletion reduces keratinocyte adhesion in culture and increases lipid peroxidation and COX-2 levels in cultured keratinocytes and whole skin. Feeding a COX-2 inhibitor to nursing mothers partially prevents development of the abnormal skin phenotype in knockout pups. These data link the activity of cutaneous GPx4 to the regulation of COX-2 and hair follicle morphogenesis and provide insight into the function of individual selenoprotein activity in maintaining cutaneous homeostasis.

Characterization of phospholipid hydroperoxide glutathione metabolizing peroxidase (gpx4) isoforms in Coho salmon olfactory and liver tissues and their modulation by cadmium

Exposure to environmental contaminants, including various pesticides and trace metals, can disrupt critical olfactory-driven behaviors of fish such as homing to natal streams, mate selection, and an ability to detect predators and prey. These neurobehavioral injuries have been linked to reduced survival and population declines. Despite the importance of maintaining proper olfactory signaling processes in the presence of chemical exposures, little is known regarding chemical detoxification in the salmon olfactory system, and in particular, the antioxidant defenses that maintain olfactory function. An understudied, yet critical component of cellular antioxidant defense is phospholipid hydroperoxide glutathione peroxidase (PHGPx/GPx4), an isoform within the family of selenium-dependent glutathione peroxidase (GPx) enzymes that can directly reduce lipid peroxides and other membrane-bound complex hydroperoxides. In this study, we cloned two gpx4 isoforms (gpx4a and gpx4b) from Coho salmon olfactory tissues and compared their modulation in olfactory and liver tissues by cadmium, an environmental pollutant and olfactory toxicant that cause oxidative damage as a mechanism of toxicity. Amino acid sequence comparisons of the two gpx4 isoforms shared 71% identity, and also relatively high sequence identities when compared with other fish GPx4 isoforms. Sequence comparisons with human GPx4 indicated conservation of three important active sites at selenocysteine (U46), glutamine (Q81), and tryptophan (W136), suggesting similar catalytic activity between fish and mammalian GPx4 isoforms. Tissue profiling confirmed the expression of gpx4a and gpx4b in all ten Coho tissues examined. The expression of gpx4 mRNAs in the Coho olfactory system was accompanied by comparably high initial rates of GPx4 enzymatic activity in mitochondrial and cytosolic fractions. Exposure to low (3.7 ppb) and high (347 ppb) environmental Cd concentrations for 24-48 h significantly decreased gpx4a expression in Coho olfactory rosettes, whereas olfactory gpx4b mRNA expression was not modulated by exposures at these concentrations. In summary, Coho salmon express two paralogs of gpx4, a key enzyme in the maintenance of signal transduction processes that protect against cellular oxidative damage. The Cd-associated downregulation of salmon olfactory gpx4a expression in particular, may be associated with the loss of olfactory signal transduction that accompanies metal-associated loss of olfaction in salmonids.

Animal products, diseases and drugs: a plea for better integration between agricultural sciences, human nutrition and human pharmacology

Eicosanoids are major players in the pathogenesis of several common diseases, with either overproduction or imbalance (e.g. between thromboxanes and prostacyclins) often leading to worsening of disease symptoms. Both the total rate of eicosanoid production and the balance between eicosanoids with opposite effects are strongly dependent on dietary factors, such as the daily intakes of various eicosanoid precursor fatty acids, and also on the intakes of several antioxidant nutrients including selenium and sulphur amino acids. Even though the underlying biochemical mechanisms have been thoroughly studied for more than 30 years, neither the agricultural sector nor medical practitioners have shown much interest in making practical use of the abundant high-quality research data now available. In this article, we discuss some specific examples of the interactions between diet and drugs in the pathogenesis and therapy of various common diseases. We also discuss, using common pain conditions and cancer as specific examples, how a better integration between agricultural science, nutrition and pharmacology could lead to improved treatment for important diseases (with improved overall therapeutic effect at the same time as negative side effects and therapy costs can be strongly reduced). It is shown how an unnaturally high omega-6/omega-3 fatty acid concentration ratio in meat, offal and eggs (because the omega-6/omega-3 ratio of the animal diet is unnaturally high) directly leads to exacerbation of pain conditions, cardiovascular disease and probably most cancers. It should be technologically easy and fairly inexpensive to produce poultry and pork meat with much more long-chain omega-3 fatty acids and less arachidonic acid than now, at the same time as they could also have a similar selenium concentration as is common in marine fish. The health economic benefits of such products for society as a whole must be expected vastly to outweigh the direct costs for the farming sector.

Selenoprotein P protects cells from lipid hydroperoxides generated by 15-LOX-1

Reactive lipid hydroperoxides formed by lipoxygenases and cyclooxygenases can contribute to disease through cellular oxidative damage. Several selenoproteins have lipid hydroperoxidase activity, including glutathione peroxidase 4, thioredoxin reductase, and selenoprotein P (SelP). SelP is an extracellular glycoprotein that functions both in selenium distribution and has an antioxidant activity. The major objective of this study was to determine if an SelP, at physiological concentrations and in selenium replete media, possessed hydroperoxidase activity directed at lipid hydroperoxides generated from the metabolism of arachidonic acid by 15-lipoxygenase-1 (15-LOX-1). An SelP displayed in vitro lipid hydroperoxidase activity of 15-hydroperoxyeicosatetraenoic acid (15-HpETE), attenuated 15-HpETE oxidation in cellular assays, and in transcellular assay when 15-LOX-1 is metabolically active. These results suggest that an SelP can function as an antioxidant enzyme against reactive lipid intermediates formed during inflammation, but an SelP has modest activity. Nevertheless, this effect may help protect cells against the oxidative damage induced by these lipid metabolites.

Effect of maternal exposure of fluoride on biometals and oxidative stress parameters in developing CNS of rat

Excessive intake of essential elements agitates elemental homeostasis resulting in their heterogeneous distribution. Distraction of these elements in central nervous system (CNS) have been demonstrated in many neurological disorders, which are vital in generating free radicals, causing oxidative stress, and contributing to neuronal maladies. The developing CNS is highly vulnerable to environmental agents, including fluoride. Fluorosis is one such disorder ensued from excessive consumption of fluoride containing water and/or foods that poses a greater threat to the life. Present study offers perturbations caused by fluoride toxicity on the level of biometal and antioxidant homeostasis and their interactions. Pregnant Wistar rats were exposed to 100- and 200-ppm fluoride (F(-)) in drinking water and controls with tap water. The pups born to them were used for the study. On 21st postnatal day, the concentration of fluoride, biometals, and oxidative stress markers were determined in discrete regions of CNS. The levels of fluoride, copper, and iron increased whereas manganese and zinc were decreased considerably. Among antioxidant enzymes, catalase, superoxide dismutase, and glutathione peroxidase were decreased and lipid peroxidation was increased with regional alterations. The correlation coefficient values among oxidative stress markers and biometals were either positive or negative and showed less significance during correlation. The results confirm that the fluoride provoked oxidative stress and biometal deformations are synergistic that successively governs the neuronal damage and developing CNS no longer prevents exacerbations of fluoride.

Protecting against cerebrovascular injury: contributions of 12/15-lipoxygenase to edema formation after transient focal ischemia

BACKGROUND AND PURPOSE

The concept of the neurovascular unit suggests that effects on brain vasculature must be considered if neuroprotection is to be achieved in stroke. We previously reported that 12/15-lipoxygenase (12/15-LOX) is upregulated in the peri-infarct area after middle cerebral artery occlusion in mice, and 12/15-LOX contributes to brain damage after ischemia-reperfusion. The current study was designed to investigate 12/15-LOX involvement in vascular injury in the ischemic brain.

METHODS

In cell culture, a human brain microvascular endothelial cell line was subjected to either hypoxia or H(2)O(2)-induced oxidative stress with or without lipoxygenase inhibitors. For in vivo studies, mice were subjected to 90 minutes middle cerebral artery occlusion, and the effects of either 12/15-LOX gene knockout or treatment with lipoxygenase inhibitors were compared. Expression of 12/15-LOX and claudin-5 as well as extravasation of immunoglobulin G were detected by immunohistochemistry. Edema was measured as water content of brain hemispheres according to the wet-dry weight method.

RESULTS

Brain endothelial cells were protected against hypoxia and H(2)O(2) by the lipoxygenase inhibitor baicalein. After focal ischemia, 12/15-LOX was increased in neurons and endothelial cells. The vascular tight junction protein claudin-5 underwent extensive degradation in the peri-infarct area, which was partially prevented by the lipoxygenase inhibitor baicalein. Leakage of immunoglobulin G into the brain parenchyma was significantly reduced in 12/15-LOX knockout mice as well as wild-type mice treated with baicalein. Likewise, brain edema was significantly ameliorated.

CONCLUSIONS

12/15-LOX may contribute to ischemic brain damage not just by causing neuronal cell death, but also by detrimental effects on the brain microvasculature. 12/15-LOX inhibitors may thus be effective as both neuroprotectants and vasculoprotectants.

FcepsilonRI- and Fcgamma receptor-mediated production of reactive oxygen species by mast cells is lipoxygenase- and cyclooxygenase-dependent and NADPH oxidase-independent

We investigated the enzymes responsible for FcepsilonRI-dependent production of reactive oxygen species (ROS) and the influence of ROS on mast cell secretory responses. 5-Lipoxygenase (5-LO) was the primary enzyme involved in ROS production by human mast cells (huMC) and mouse bone marrow-derived mast cells (mBMMC) following FcepsilonRI aggregation because incubation with 5-LO inhibitors (AA861, nordihydroguaiaretic acid, zileuton) but not a flavoenzyme inhibitor (diphenyleneiodonium) completely abrogated Ag-induced dichlorodihydrofluorescein (DCF) fluorescence. Furthermore, 5-LO-deficient mBMMC had greatly reduced FcepsilonRI-dependent DCF fluorescence compared with wild type mBMMC or those lacking a functional NADPH oxidase (i.e., gp91(phox)- or p47(phox)-deficient cells). A minor role for cyclooxygenase (COX)-1 in FcepsilonRI-dependent ROS production was demonstrated by inhibition of Ag-mediated DCF fluorescence by a COX-1 inhibitor (FR122047) and reduced DCF fluorescence in COX-1-deficient mBMMC. Complete abrogation of FcepsilonRI-dependent ROS production in mast cells had no effect on degranulation or cytokine secretion. In response to the NADPH oxidase-stimulating agents including PMA, mBMMC and huMC produced negligible ROS. IgG-coated latex beads did stimulate ROS production in huMC, and in this experiment 5-LO and COX again appeared to be the enzymatic sources of ROS. In contrast, IgG-coated latex bead-induced ROS production in human polymorphonuclear leukocytes occurred by the NADPH oxidase pathway. Thus mBMMC and huMC generate ROS by 5-LO and COX-1 in response to FcepsilonRI aggregation; huMC generate ROS upon exposure to IgG-coated latex beads by 5-LO and COX; and ROS appear to have no significant role in FcepsilonRI-dependent degranulation and cytokine production.

Chronic inflammation and oxidative stress in human carcinogenesis

A wide array of chronic inflammatory conditions predispose susceptible cells to neoplastic transformation. In general, the longer the inflammation persists, the higher the risk of cancer. A mutated cell is a sine qua non for carcinogenesis. Inflammatory processes may induce DNA mutations in cells via oxidative/nitrosative stress. This condition occurs when the generation of free radicals and active intermediates in a system exceeds the system's ability to neutralize and eliminate them. Inflammatory cells and cancer cells themselves produce free radicals and soluble mediators such as metabolites of arachidonic acid, cytokines and chemokines, which act by further producing reactive species. These, in turn, strongly recruit inflammatory cells in a vicious circle. Reactive intermediates of oxygen and nitrogen may directly oxidize DNA, or may interfere with mechanisms of DNA repair. These reactive substances may also rapidly react with proteins, carbohydrates and lipids, and the derivative products may induce a high perturbation in the intracellular and intercellular homeostasis, until DNA mutation. The main substances that link inflammation to cancer via oxidative/nitrosative stress are prostaglandins and cytokines. The effectors are represented by an imbalance between pro-oxidant and antioxidant enzyme activities (lipoxygenase, cyclooxygenase and phospholipid hydroperoxide glutathione-peroxidase), hydroperoxides and lipoperoxides, aldehydes and peroxinitrite. This review focalizes some of these intricate events by discussing the relationships occurring among oxidative/nitrosative/metabolic stress, inflammation and cancer.

Thioredoxin reductase regulates the induction of haem oxygenase-1 expression in aortic endothelial cells

Certain selenoproteins such as GPX-1 (glutathione peroxidase-1) and TrxR1 (thioredoxin reductase-1) possess important antioxidant defence functions in vascular endothelial cells. Reduced selenoprotein activity during dietary selenium (Se) deficiency can result in a compensatory increase of other non-Se-dependent antioxidants, such as HO-1 (haem oxygenase-1) that may help to counteract the damaging effects of oxidant stress. However, the role of individual selenoproteins in regulating vascular-derived protective gene responses such as HO-1 is less understood. Using an oxidant stress model based on Se deficiency in BAECs (bovine aortic endothelial cells), we sought to determine whether TrxR1 activity may contribute to the differential regulation of HO-1 expression as a function of altered redox environment. Se-sufficient BAECs up-regulated HO-1 expression following stimulation with the pro-oxidant, 15-HPETE (15-hydroperoxyeicosatetraenoic acid), and levels of this antioxidant inversely correlated with EC apoptosis. While Se-deficient BAECs exhibited higher basal levels of HO-1, it was not up-regulated upon 15-HPETE treatment, which resulted in significantly higher levels of pro-apoptotic markers. Subsequent results showed that HO-1 induction depended on the activity of TrxR1, as proved with chemical inhibitor studies and direct inhibition with TrxR1 siRNA. Finally, restoring intracellular levels of the reduced substrate Trx (thioredoxin) in Sedeficient BAECs was sufficient to increase HO-1 activation following 15-HPETE stimulation. These data provide evidence for the involvement of the Trx/TrxR system, in the regulation of HO-1 expression in BAECs during pro-oxidant challenge.

Blocking tumor cell eicosanoid synthesis by GP x 4 impedes tumor growth and malignancy

Using tumor cell-restricted overexpression of glutathione peroxidase 4 (GP x 4), we investigated the contribution of tumor cell eicosanoids to solid tumor growth and malignant progression in two tumor models differing in tumorigenic potential. By lowering cellular lipid hydroperoxide levels, GP x 4 inhibits cyclooxygenase (COX) and lipoxygenase (LOX) activities. GP x 4 overexpression drastically impeded solid tumor growth of weakly tumorigenic L929 fibrosarcoma cells, whereas B16BL6 melanoma solid tumor growth was unaffected. Yet, GP x 4 overexpression did markedly increase the sensitivity of B16BL6 tumors to angio-destructive TNF-alpha therapy and abolished the metastatic lung colonizing capacity of B16BL6 cells. Furthermore, the GP x 4-mediated suppression of tumor cell prostaglandin E(2) (PGE(2)) production impeded the induction of COX-2 expression by the tumor stress conditions hypoxia and inflammation. Thus, our results reflect a PGE(2)-driven positive feedback loop for COX-2 expression in tumor cells. This was further supported by the restoration of COX-2 induction capacity of GP x 4-overexpressing L929 tumor cells when cultured in the presence of exogenous PGE(2). Thus, although COX-2 expression and eicosanoid production may be enabled by PGE(2) from the tumor microenvironment, our results demonstrate the predominant tumor cell origin of protumoral eicosanoids, promoting solid tumor growth of weakly tumorigenic tumors and malignant progression of strongly tumorigenic tumors.

Effects of gpx4 haploid insufficiency on GPx4 activity, selenium concentration, and paraquat-induced protein oxidation in murine tissues

Selenium-dependent glutathione peroxidase-4 (GPx4) catalyzes the reduction of phospholipid hydroperoxides. Because a full gpx4 knockout is embryonic lethal, we examined the effect of deletion of one copy of gpx4 on the activities of three selenoperoxidases (GPx1, GPx3, and GPx4), selenium concentrations, and pro-oxidant-induced protein oxidation in various tissues of mice. A total of 32 gpx4 hemizygous (GPx4+/-) and wild-type (WT) mice (8- to 10-weeks old; 16 males and 16 females) were fed a selenium-adequate diet and given an intraperitoneal injection of paraquat (PQ; 24 mg/kg body wt) or phosphate-buffered saline (PBS). All mice were euthanized 4 hrs after injection to collect tissues for analyses. In PBS-treated mice, GPx4 activities in lung, liver, kidney, and testes of GPx4+/- mice were 24-39% lower (P < 0.05) than in WT mice. Among PQ-treated mice, only testis GPx4 activity in GPx4+/- mice was significantly lower (54% P < 0.05) than WT mice. Selenium concentration in testes, but not in other tissues, was reduced (34% P < 0.05) in GPx4+/- mice compared with WT mice, irrespective of treatment. Tissue GPx1 activities and plasma GPx3 and alanine aminotransferase (ALT) activities were unaffected by PQ treatment or gpx4 hemizygosity. Total protein carbonyl was elevated (73% P < 0.05) by PQ only in lung, and this effect of PQ was independent of genotypes. In conclusion, gpx4 haploid insufficiency reduced GPx4 activities and/or selenium concentrations, but had no effect on pro-oxidant-induced protein oxidation in various tissues of mice.

Regulation of cyclooxygenase catalysis by hydroperoxides

Activation of cyclooxygenase catalysis in prostaglandin H synthase-1 and -2 by peroxide-dependent formation of a tyrosyl radical is emerging as an important part of regulating cellular production of bioactive prostanoids. This review discusses the mechanism of tyrosyl radical formation and the influence of peroxide, fatty acid, peroxidase cosubstrate, and protein structure on the activation process and cyclooxygenase catalysis.

[Biological significance of lipid hydroperoxide and its reducing enzyme, phospholipid hydroperoxide glutathione peroxidase, in mammalian cells]

Excessive production of reactive oxygen species (ROS) may lead to oxidative stress, loss of cell function, and cell death by apoptosis or necrosis. Recently, ROS have gained attention as important second messengers. ROS lifetimes can be very short, and many types of ROS cannot penetrate organelle membranes. It is therefore thought that only ROS signal molecules that are generated locally in an organelle are transduced when cells are stimulated. Lipid hydroperoxides are one type of ROS of which the biological function has not yet been clarified. The phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) is a unique antioxidant enzyme and separately distributed to the mitochondria, nucleus, nucleoli, and cytosol, where it regulates phospholipid hydroperoxide and fatty acid hydroperoxide as signal molecules. This review focuses on the structure and biological functions of PHGPx in mammalian cells. Overexpression of different types of PHGPx in the RBL2H3 cell line provides a useful model system with which to clarify the ability of different types of PHGPx to modulate cellular function and the importance of lipid hydroperoxides as signal molecules. Transformant studies show that lipid hydroperoxide is an activator of lipoxygenase and cyclooxygenase and participates in inflammation, cardiolipin hydroperoxide is the signal molecule for the release of cytochrome c during apoptotic cell death, and PHGPx is a signal regulator in the IgE receptor-mediated signaling pathway. It is becoming clear that PHGPx has an important role in spermatogenesis, sperm function, and embryonic development, and its deficiency is implicated in human infertility and in embryonic lethality of PHGPx knockout mice.

Depletion of phospholipid hydroperoxide glutathione peroxidase up-regulates arachidonate metabolism by 12S-lipoxygenase and cyclooxygenase 1 in human epidermoid carcinoma A431 cells

Phospholipid hydroperoxide glutathione peroxidase (PHGPx), a selenium-dependent glutathione peroxidase, can interact with lipophilic substrates, including the phospholipid hydroperoxides, fatty-acid hydroperoxides, and cholesteryl ester hydroperoxides, and reduce them to hydroxide compounds. We studied the functional role of endogenous PHGPx in regulation of 12(S)-lipoxygenase and cyclooxygenase 1 activities in human epidermoid carcinoma A431 cells by using a cell system overexpressing anti-PHGPx mRNA. A retroviral expression vector designated as L1-3, wherein cDNA of PHGPx was reversely inserted into pFB-ERV in antisense orientation, was constructed. A number of stable transfectants of A431 cells with PHGPx depletion were generated from virions containing plasmid L1-3. In an intact cell assay system, the metabolism of arachidonic acid to prostaglandin E2 and 12(S)-hydroxyeicosatetraenoic acid was significantly enhanced in stable L1-3 transfectants compared with that in vector-control cells. Flow cytometric analysis revealed a significant elevated level of intracellular hydroperoxides in stable L1-3 transfectants. Treatment of stable L1-3 transfectants with 50 microM arsenite induced more significant formation of intracellular hydroperoxides than that of vector-control cells. Taken together, these results support the notion that the endogenous PHGPx plays a pivotal role in the regulation of 12(S)-lipoxygenase and cyclooxygenase 1 activities by reducing the level of intracellular lipid hydroperoxides in arachidonate metabolism in A431 cells.

Comparison of the properties of prostaglandin H synthase-1 and -2

Biosynthesis of prostanoid lipid signaling agents from arachidonic acid begins with prostaglandin H synthase (PGHS), a hemoprotein in the myeloperoxidase family. Vertebrates from humans to fish have two principal isoforms of PGHS, termed PGHS-1 and-2. These two isoforms are structurally quite similar, but they have very different pathophysiological roles and are regulated very differently at the level of catalysis. The focus of this review is on the structural and biochemical distinctions between PGHS-1 and-2, and how these differences relate to the functional divergence between the two isoforms.

Activation of NAD(P)H oxidase by lipid hydroperoxides: mechanism of oxidant-mediated smooth muscle cytotoxicity

Oxidized lipids, such as 13-hydroperoxyoctadecadienoic acid (13-HPODE), have been implicated in the pathogenesis of atherosclerosis. 13-HPODE, a constituent of oxidized low-density lipoproteins, can induce cytotoxicity of vascular smooth muscle cells (SMC), which may facilitate plaque destabilization and/or rupture. 13-HPODE-induced cytotoxicity has been linked to oxidative stress, although the mechanisms by which this occurs are unknown. In the present study, we show that 13-HPODE and 9-HPODE (10-30 microM) increased superoxide (O2*-) production and induced cytotoxicity in SMC. The 13-HPODE-induced increase in O2*- was blocked by transfecting the cells with antisense oligonucleotides against p22phox, suggesting that the O2*- was produced by NAD(P)H oxidase. Similar concentrations of the corresponding HPODE reduction products, 13-hydroxyoctadecadienoic acid (13-HODE) and 9-HODE, neither increased O2*- production nor induced cytotoxicity, while 4-hydroxy nonenal (4-HNE), an unsaturated aldehyde lipid peroxidation product, induced cytotoxicity without increasing O2*- production. Treatment with superoxide dismutase or Tiron to scavenge O2*-, or transfection with p22phox antisense oligonucleotides to inhibit O2*- production, attenuated 13-HPODE-induced cytotoxicity, but not that induced by 4-HNE. These findings suggest that activation of NAD(P)H oxidase, and production of O2*-, play an important role in lipid hydroperoxide-induced smooth muscle cytotoxicity.

Biological significance of phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) in mammalian cells

Reactive oxygen species (ROS) are known mediators of intracellular signal cascades. Excessive production of ROS may lead to oxidative stress, loss of cell function, and cell death by apoptosis or necrosis. Lipid hydroperoxides are one type of ROS whose biological function has not yet been clarified. Phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) is a unique antioxidant enzyme that can directly reduce phospholipid hydroperoxide in mammalian cells. This contrasts with most antioxidant enzymes, which cannot reduce intracellular phospholipid hydroperoxides directly. In this review, we focus on the structure and biological functions of PHGPx in mammalian cells. Recently, molecular techniques have allowed overexpression of PHGPx in mammalian cell lines, from which it has become clear that lipid hydroperoxides also have an important function as activators of lipoxygenase and cyclooxygenase, participate in inflammation, and act as signal molecules for apoptotic cell death and receptor-mediated signal transduction at the cellular level.

Involvement of reactive oxygen species in arsenite-induced downregulation of phospholipid hydroperoxide glutathione peroxidase in human epidermoid carcinoma A431 cells

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is unique in the substrate specificity among the glutathione peroxidase family because it can interact with lipophilic substrates, including the peroxidized phospholipids and cholesterol, and reduce these hydroperoxide to hydroxide compounds. However, what kinds of ligand can regulate the PHGPx expression is still unknown. In the present study, we found that sodium arsenite induced downregulation of mRNA, protein expression, and enzyme activity of PHGPx in time- and dose-dependent manners. At the same time, it upregulated mRNA and protein expression of p21(WAF1/CIP1). With the aid of agarose gel electrophoresis, and propidium iodide and annexin-V staining, we found that treatment of 30 microM sodium arsenite for 24 h induced apoptosis in human epidermoid carcinoma A431 cells and EA.hy926 cells. An increase of intracellular peroxide levels was measured by flow cytometry using 2',7'-dichlorofluorescin diacetate (DCFH-DA) after treatment of arsenite. Overexpression of PHGPx prevented arsenite-induced increase of intracellular peroxide levels, downregulation of PHGPx, upregulation of p21(WAF1/CIP1), and apoptosis in A431 cells. N-Acetyl-L-cysteine also significantly prevented arsenite-induced effects in A431 cells. Therefore, we concluded that reactive oxygen species were involved in arsenite-induced downregulation of PHGPx, upregulation of p21(WAF1/CIP1), and apoptosis in A431 cells.

Regulation of enzymatic lipid peroxidation: the interplay of peroxidizing and peroxide reducing enzymes

For a long time lipid peroxidation has only been considered a deleterious process leading to disruption of biomembranes and thus, to cellular dysfunction. However, when restricted to a certain cellular compartment and tightly regulated, lipid peroxidation may have beneficial effects. Early on during evolution of living organisms special lipid peroxidizing enzymes, called lipoxygenases, appeared and they have been conserved during phylogenesis of plants and animals. In fact, a diverse family of lipoxygenase isoforms has evolved starting from a putative ancient precursor. As with other enzymes, lipoxygenases are regulated on various levels of gene expression and there are endogenous antagonists controlling their cellular activity. Among the currently known mammalian lipoxygenase isoforms only 12/15-lipoxygenases are capable of directly oxygenating ester lipids even when they are bound to membranes and lipoproteins. Thus, these enzymes represent the pro-oxidative part in the cellular metabolism of complex hydroperoxy ester lipids. Its metabolic counterplayer, representing the antioxidative part, appears to be the phospholipid hydroperoxide glutathione peroxidase. This enzyme is unique among glutathione peroxidases because of its capability of reducing ester lipid hydroperoxides. Thus, 12/15-lipoxygenase and phospholipid hydroperoxide glutathione peroxidase constitute a pair of antagonizing enzymes in the metabolism of hydroperoxy ester lipids, and a balanced regulation of the two proteins appears to be of major cell physiological importance. This review is aimed at summarizing the recent developments in the enzymology and molecular biology of 12/15-lipoxygenase and phospholipid hydroperoxide glutathione peroxidase, with emphasis on cytokine-dependent regulation and their regulatory interplay.

Unsaturated fatty acids selectively induce an inflammatory environment in human endothelial cells

BACKGROUND

Activation of the vascular endothelium by dietary fatty acids may be among the most critical early events in the development of atherosclerosis. However, the specific effects of fatty acids on inflammatory responses in endothelial cells are not fully understood.

OBJECTIVE

The present study focused on the induction of inflammatory genes in human endothelial cells exposed to individual dietary fatty acids. Because of the significance of nuclear factor kappaB (NF-kappaB) and activator protein 1 (AP-1) in the regulation of inflammatory gene expression, we also determined the effects of fatty acids on NF-kappaB and AP-1 transcriptional activation.

DESIGN

Human umbilical vein endothelial cells were exposed to dietary mono- and polyunsaturated 18-carbon fatty acids. Transcriptional activation of NF-kappaB and AP-1 was determined in human umbilical vein endothelial cells transfected with reporter constructs regulated by these transcription factors. Induction of the inflammatory genes was studied by use of reverse transcriptase-polymerase chain reaction.

RESULTS

Of the fatty acids studied, linoleic acid stimulated NF-kappaB and AP-1 transcriptional activation the most. In addition, treatment with this fatty acid markedly enhanced messenger RNA levels of tumor necrosis factor alpha, monocyte chemoattractant protein 1, vascular cell adhesion molecule 1, and intercellular adhesion molecule 1. Treatment with linolenic acid stimulated only a moderate induction of the genes encoding for these inflammatory mediators, and exposure to oleic acid either had no effect or resulted in decreased inflammatory gene messenger RNA. In addition, exposure to both linoleic and linolenic acids strongly stimulated induction of the phospholipid hydroperoxide glutathione peroxidase gene.

CONCLUSION

Specific unsaturated dietary fatty acids, particularly linoleic acid, can selectively stimulate the development of a proinflammatory environment within the vascular endothelium.

PKA and arachidonic acid activation of human recombinant ClC-2 chloride channels

An HEK-293 cell line stably expressing the human recombinant ClC-2 Cl(-) channel was used in patch-clamp studies to study its regulation. The relative permeability P(x)/P(Cl) calculated from reversal potentials was I(-) > Cl(-) = NO(3)(-) = SCN(-)>/=Br(-). The absolute permeability calculated from conductance ratios was Cl(-) = Br(-) = NO(3)(-) >/= SCN(-) > I(-). The channel was activated by cAMP-dependent protein kinase (PKA), reduced extracellular pH, oleic acid (C:18 cisDelta9), elaidic acid (C:18 transDelta9), arachidonic acid (AA; C:20 cisDelta5,8,11,14), and by inhibitors of AA metabolism, 5,8,11,14-eicosatetraynoic acid (ETYA; C:20 transDelta5,8,11,14), alpha-methyl-4-(2-methylpropyl)benzeneacetic acid (ibuprofen), and 2-phenyl-1,2-benzisoselenazol-3-[2H]-one (PZ51, ebselen). ClC-2 Cl(-) channels were activated by a combination of forskolin plus IBMX and were inhibited by the cell-permeant myristoylated PKA inhibitor (mPKI). Channel activation by reduction of bath pH was increased by PKA and prevented by mPKI. AA activation of the ClC-2 Cl(-) channel was not inhibited by mPKI or staurosporine and was therefore independent of PKA or protein kinase C activation.