Biological role of hepoxilins: upregulation of phospholipid hydroperoxide glutathione peroxidase as a cellular response to oxidative stress?

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.

Exploring the molecular approach of COX and LOX in Alzheimer's and Parkinson's disorder

Neuroinflammation is well established biomarker for the major neurodegenerative like Alzheimer's disease (AD) and Parkinson's disease (PD). Cytokines/chemokines excite phospholipase A2 and cyclooxygenases (COX), facilitating the release of arachidonic acid (AA) and docosahexaenoic acid (DHA) from membrane glycerophospholipids, in which the former is oxidized to produce pro-inflammatory eicosanoids (prostaglandins, leukotrienes and thromboxane's), which intensify the neuroinflammatory events in the brain. Similarly, resolvins and neuroprotectins are the metabolized products of docosahexaenoic acid, which exert an inhibitory effect on the production of eicosanoids. Furthermore, an oxidized product of arachidonic acid, lipoxin, is generated via 5-lipoxygenase (5-LOX) pathway, and contributes to the resolution of inflammation, along with anti-inflammatory actions. Moreover, DHA and its lipid mediators inhibit neuroinflammatory responses by blocking NF-κB, inhibiting eicosanoid production, preventing cytokine secretion and regulating leukocyte trafficking. Various epidemiological studies reported, elevated levels of COX-2 enzyme in patients with AD and PD, indicating its role in progression of the disease. Similarly, enhanced levels of 5-LOX and 12/15-LOX in PD models represent their role brain disorders, where the former is expressed in AD patients and the latter exhibits it involvement in PD. The present review elaborates the role of AA, DHA, eicosanoids and docosanoids, along with COX and LOX pathway which provides an opportunity to the researchers to understand the role of these lipid mediators in neurological disorders (AD and PD). The information gathered from the review will aid in facilitating the development of appropriate therapeutic options targeting COX and LOX pathway.

The Lipoxygenases: Their Regulation and Implication in Alzheimer's Disease

Inflammatory processes and alterations of lipid metabolism play a crucial role in Alzheimer’s disease (AD) and other neurodegenerative disorders. Polyunsaturated fatty acids (PUFA) metabolism impaired by cyclooxygenases (COX-1, COX-2), which are responsible for formation of several eicosanoids, and by lipoxygenases (LOXs) that catalyze the addition of oxygen to linolenic, arachidonic (AA), and docosahexaenoic acids (DHA) and other PUFA leading to formation of bioactive lipids, significantly affects the course of neurodegenerative diseases. Among several isoforms, 5-LOX and 12/15-LOX are especially important in neuroinflammation/neurodegeneration. These two LOXs are regulated by substrate concentration and availability, and by phosphorylation/dephosphorylation through protein kinases PKA, PKC and MAP-kinases, including ERK1/ERK2 and p38. The protein/protein interaction also is involved in the mechanism of 5-LOX regulation through FLAP protein and coactosin-like protein. Moreover, non-heme iron and calcium ions are potent regulators of LOXs. The enzyme activity significantly depends on the cell redox state and is differently regulated by various signaling pathways. 5-LOX and 12/15-LOX convert linolenic acid, AA, and DHA into several bioactive compounds e.g. hydroperoxyeicosatetraenoic acids (5-HPETE, 12S-HPETE, 15S-HPETE), which are reduced to corresponding HETE compounds. These enzymes synthesize several bioactive lipids, e.g. leucotrienes, lipoxins, hepoxilins and docosahexaenoids. 15-LOX is responsible for DHA metabolism into neuroprotectin D1 (NPD1) with significant antiapoptotic properties which is down-regulated in AD. In this review, the regulation and impact of 5-LOX and 12/15-LOX in the pathomechanism of AD is discussed. Moreover, we describe the role of several products of LOXs, which may have significant pro- or anti-inflammatory activity in AD, and the cytoprotective effects of LOX inhibitors.

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.

Following experimental stroke, the recovering brain is vulnerable to lipoxygenase-dependent semaphorin signaling

Recovery from stroke is limited, in part, by an inhibitory environment in the postischemic brain, but factors preventing successful remodeling are not well known. Using cultured cortical neurons from mice, brain endothelial cells, and a mouse model of ischemic stroke, we show that signaling from the axon guidance molecule Sema3A via eicosanoid second messengers can contribute to this inhibitory environment. Either 90 nM recombinant Sema3A, or the 12/15-lipoxygenase (12/15-LOX) metabolites 12-HETE and 12-HPETE at 300 nM, block axon extension in neurons compared to solvent controls, and decrease tube formation in endothelial cells. The Sema3A effect is reversed by inhibiting 12/15-LOX, and neurons derived from 12/15-LOX-knockout mice are insensitive to Sema3A. Following middle cerebral artery occlusion to induce stroke in mice, immunohistochemistry shows both Sema3A and 12/15-LOX are increased in the cortex up to 2 wk. To determine whether a Sema3A-dependent damage pathway is activated following ischemia, we injected recombinant Sema3A into the striatum. Sema3A alone did not cause injury in normal brains. But when injected into postischemic brains, Sema3A increased cortical damage by 79%, and again, this effect was reversed by 12/15-LOX inhibition. Our findings suggest that blocking the semaphorin pathway should be investigated as a therapeutic strategy to improve stroke recovery.

Investigations of human platelet-type 12-lipoxygenase: role of lipoxygenase products in platelet activation

Human platelet-type 12-lipoxygenase (12-LOX) has recently been shown to play an important role in regulation of human platelet function by reacting with arachidonic acid (AA). However, a number of other fatty acids are present on the platelet surface that, when cleaved from the phospholipid, can be oxidized by 12-LOX. We sought to characterize the substrate specificity of 12-LOX against six essential fatty acids: AA, dihomo-γ-linolenic acid (DGLA), eicosapentaenoic acid (EPA), α-linolenic acid (ALA), eicosadienoic acid (EDA), and linoleic acid (LA). Three fatty acids were comparable substrates (AA, DGLA, and EPA), one was 5-fold slower (ALA), and two showed no reactivity with 12-LOX (EDA and LA). The bioactive lipid products resulting from 12-LOX oxidation of DGLA, 12-(S)-hydroperoxy-8Z,10E,14Z-eicosatrienoic acid [12(S)-HPETrE], and its reduced product, 12(S)-HETrE, resulted in significant attenuation of agonist-mediated platelet aggregation, granule secretion, αIIbβ3 activation, Rap1 activation, and clot retraction. Treatment with DGLA similarly inhibited PAR1-mediated platelet activation as well as platelet clot retraction. These observations are in surprising contrast to our recent work showing 12(S)-HETE is a prothrombotic bioactive lipid and support our hypothesis that the overall effect of 12-LOX oxidation of fatty acids in the platelet is dependent on the fatty acid substrates available at the platelet membrane.

Influence of nutrient intake on antioxidant capacity, muscle damage and white blood cell count in female soccer players

Background

Soccer is a form of exercise that induces inflammatory response, as well as an increase in free radicals potentially leading to muscle injury. Balanced nutritional intake provides important antioxidant vitamins, including vitamins A, C and E, which may assist in preventing exercise-related muscle damage. The purpose of the present study was to determine the effect of macro/micronutrient intake on markers of oxidative stress, muscle damage, inflammatory and immune response in female soccer players.

Methods

Twenty-eight female players belonging to two soccer teams of the same professional soccer club participated in this study after being informed about the aims and procedures and after delivering written consent. Each team completed an 8-day dietary record and played one competition match the same week. Participants were divided into two groups: the REC group (who complied with recommended intakes) and the NO-REC group (who were not compliant). Laboratory blood tests were carried out to determine hematological, electrolytic and hormonal variables, as well as to monitor markers of cell damage and oxidative stress. Blood samples were obtained 24 h before, immediately after and 18 h after official soccer matches. Student t-test or Mann–Whitney U-test was used to compare both groups throughout the match.

Results

At rest, we observed that the REC group had higher levels of total antioxidant status (TAS), glutathione peroxidase (GPx), and lower levels of creatine kinase (CK) and lactate dehydrogenase (LDH) in comparison to the NO-REC group. Immediately after the match, levels of TAS, GPx, superoxide dismutase (SOD), LDH and % lymphocytes were higher and the % of neutrophils were lower in the REC group compared to the NO-REC group. These differences were also maintained 18 h post-match, only for TAS and GPx.

Conclusions

Our data reveal an association between nutritional intake and muscle damage, oxidative stress, immunity and inflammation markers. The benefit of the intake of specific nutrients may contribute to preventing the undesirable physiological effects provoked by soccer matches.

Could a vegetarian diet reduce exercise-induced oxidative stress? A review of the literature

Oxidative stress is a natural physiological process that describes an imbalance between free radical production and the ability of the antioxidant defence system of the body to neutralize free radicals. Free radicals can be beneficial as they may promote wound healing and contribute to a healthy immune response. However, free radicals can have a detrimental impact when they interfere with the regulation of apoptosis and thus play a role in the promotion of some cancers and conditions such as cardiovascular disease. Antioxidants are molecules that reduce the damage associated with oxidative stress by counteracting free radicals. Regular exercise is a vital component of a healthy lifestyle, although it can increase oxidative stress. As a typical vegetarian diet comprises a wide range of antioxidant-rich foods, it is plausible that the consumption of these foods will result in an enhanced antioxidant system capable of reducing exercise-induced oxidative stress. In addition, a relationship between a vegetarian diet and lower risks of cardiovascular disease and some cancers has been established. This review explores the current available evidence linking exercise, vegetarians, antioxidants, and oxidative stress.

Membrane redox state and apoptosis: death by peroxide

Membrane redox state is governed by the complex interplay between oxidation of unsaturated fatty acids and lipophilic antioxidants. In this issue of Cell Metabolism, Seiler et al. (2008) show that a lipid oxidase, 12/15-lipoxygenase, and a membrane antioxidant enzyme, glutathione peroxidase-4, interact to regulate a novel redox-dependent cell death pathway.