Basic principles and emerging concepts in the redox control of transcription factors

Cyclic Peptides in Neurological Disorders: The Case of Cyclo(His-Pro)

Communication between and within communities of cells or independent organisms is a crucial prerequisite for species survival. In response to variations in the extracellular environment, the collective behavior of cell populations can be coordinated by regulating community-level gene expression. This mechanism is strongly conserved during evolution, being shared both by bacterial communities and central nervous system cells. Notably, cyclic dipeptides (CDPs) are molecules that are implicated in these quorum sensing behaviors in both settings. Bacteria coordinate their collective behavior by producing CDPs (quorum sensing inducers) that enhance the capacity of individual members of the community to detect these signals and thus amplify the community-level response. In this review, we highlight recent data indicating that strikingly similar molecular mechanisms control communications between glial and neuronal cells to maintain homeostasis in the central nervous system, with a specific focus on the role of the thyrotropin-releasing hormone—derived CDP cyclo(His-Pro) in the protection against neurotoxic insults.

Sex differences in subcutaneous adipose tissue redox homeostasis and inflammation markers in control and high-fat diet fed rats

The development of obesity-related metabolic disorders is more evident in male in comparison with female subjects, but the mechanisms are unknown. Several studies have shown that oxidative stress is involved in the pathophysiology of obesity, but the majority of these studies were performed with male animals. The aim of this study was to evaluate the sex-related differences in subcutaneous adipose tissue redox homeostasis and inflammation of rats chronically fed a high-fat diet. NADPH oxidase (NOX), glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase activities were evaluated in the subcutaneous adipose tissue (SC) of adult male and female rats fed either a standard chow (SCD) or a high-fat diet (HFD) for 11 weeks. NOX2 and NOX4 messenger RNA (mRNA) levels, total reduced thiols, interleukin (IL)-1β, tumor necrosis factor α (TNF-α), and IL-6 were also determined. Higher antioxidant enzyme activities and total reduced thiol levels were detected in SC of control male compared with female rats. Chronic HFD administration increased NOX activity and NOX2 and NOX4 mRNA levels and decreased SOD and GPx activities only in male animals. IL-1β, TNF-α, and IL-6 levels, as well as Adgre1, CD11b, and CD68 mRNA levels, were also higher in SC of males after HFD feeding. In SC of females, catalase activity was higher after HFD feeding. Taken together, our results show that redox homeostasis and inflammation of SC is sexually dimorphic. Furthermore, males show higher oxidative stress in SC after 11 weeks of HFD feeding owing to both increased reactive oxygen species (ROS) production through NOX2 and NOX4 and decreased ROS detoxification.

Nucleoredoxin-Dependent Targets and Processes in Neuronal Cells

Nucleoredoxin (Nrx) is an oxidoreductase of the thioredoxin family of proteins. It was shown to act as a signal transducer in some pathways; however, so far, no comprehensive analysis of its regulated substrates and functions was available. Here, we used a combination of two different strategies to fill this gap. First, we analyzed the thiol-redox state of the proteome of SH-SY5Y neuroblastoma cells depleted of Nrx compared to control cells using a differential thiol-labeling technique and quantitative mass spectrometry. 171 proteins were identified with an altered redox state; 161 of these were more reduced in the absence of Nrx. This suggests functions of Nrx in the oxidation of protein thiols. Second, we utilized the active site mutant Cys208Ser of Nrx, which stabilizes a mixed disulfide intermediate with its substrates and therefore trapped interacting proteins from the mouse brain (identifying 1710 proteins) and neuronal cell culture extracts (identifying 609 proteins). Profiling of the affected biological processes and molecular functions in cells of neuronal origin suggests numerous functions of Nrx in the redox regulation of metabolic pathways, cellular morphology, and signal transduction. These results characterize Nrx as a cellular oxidase that itself may be oxidized by the formation of disulfide relays with peroxiredoxins.

Acute HIIE elicits similar changes in human skeletal muscle mitochondrial H2O2 release, respiration, and cell signaling as endurance exercise even with less work

It remains unclear whether high-intensity interval exercise (HIIE) elicits distinct molecular responses to traditional endurance exercise relative to the total work performed. We aimed to investigate the influence of exercise intensity on acute perturbations to skeletal muscle mitochondrial function (respiration and reactive oxygen species) and metabolic and redox signaling responses. In a randomized, repeated measures crossover design, eight recreationally active individuals (24 ± 5 yr; V̇o2peak: 48 ± 11 ml·kg−1·min−1) undertook continuous moderate-intensity [CMIE: 30 min, 50% peak power output (PPO)], high-intensity interval (HIIE: 5 × 4 min, 75% PPO, work matched to CMIE), and low-volume sprint interval (SIE: 4 × 30 s) exercise, ≥7 days apart. Each session included muscle biopsies at baseline, immediately, and 3 h postexercise for high-resolution mitochondrial respirometry ( Jo2) and H2O2 emission ( Jh2o2) and gene and protein expression analysis. Immediately postexercise and irrespective of protocol, Jo2 increased during complex I + II leak/state 4 respiration but Jh2o2 decreased ( P < 0.05). AMP-activated protein kinase and acetyl co-A carboxylase phosphorylation increased ~1.5 and 2.5-fold respectively, while thioredoxin-reductase-1 protein abundance was ~35% lower after CMIE vs. SIE ( P < 0.05). At 3 h postexercise, regardless of protocol, Jo2 was lower during both ADP-stimulated state 3 OXPHOS and uncoupled respiration ( P < 0.05) but Jh2o2 trended higher ( P < 0.08) and PPARGC1A mRNA increased ~13-fold, and peroxiredoxin-1 protein decreased ~35%. In conclusion, intermittent exercise performed at high intensities has similar dynamic effects on muscle mitochondrial function compared with endurance exercise, irrespective of whether total workload is matched. This suggests exercise prescription can accommodate individual preferences while generating comparable molecular signals known to promote beneficial metabolic adaptations.

Clair WH, St. Clair DK. Redox Paradox: A Novel Approach to Therapeutics-Resistant Cancer

SIGNIFICANCE

Cancer cells that are resistant to radiation and chemotherapy are a major problem limiting the success of cancer therapy. Aggressive cancer cells depend on elevated intracellular levels of reactive oxygen species (ROS) to proliferate, self-renew, and metastasize. As a result, these aggressive cancers maintain high basal levels of ROS compared with normal cells. The prominence of the redox state in cancer cells led us to consider whether increasing the redox state to the condition of oxidative stress could be used as a successful adjuvant therapy for aggressive cancers. Recent Advances: Past attempts using antioxidant compounds to inhibit ROS levels in cancers as redox-based therapy have met with very limited success. However, recent clinical trials using pro-oxidant compounds reveal noteworthy results, which could have a significant impact on the development of strategies for redox-based therapies.

CRITICAL ISSUES

The major objective of this review is to discuss the role of the redox state in aggressive cancers and how to utilize the shift in redox state to improve cancer therapy. We also discuss the paradox of redox state parameters; that is, hydrogen peroxide (H2O2) as the driver molecule for cancer progression as well as a target for cancer treatment.

FUTURE DIRECTIONS

Based on the biological significance of the redox state, we postulate that this system could potentially be used to create a new avenue for targeted therapy, including the potential to incorporate personalized redox therapy for cancer treatment.

Significance of the mitochondrial thioredoxin reductase in cancer cells: An update on role, targets and inhibitors

Thioredoxin reductase 2 (TrxR2) is a key component of the mitochondrial thioredoxin system able to transfer electrons to peroxiredoxin 3 (Prx3) in a reaction mediated by thioredoxin 2 (Trx2). In this way, both the level of hydrogen peroxide and thiol redox state are modulated. TrxR2 is often overexpressed in cancer cells conferring apoptosis resistance. Due to their exposed flexible arm containing selenocysteine, both cytosolic and mitochondrial TrxRs are inhibited by a large number of molecules. The various classes of inhibitors are listed and the molecules acting specifically on TrxR2 are extensively described. Particular emphasis is given to gold(I/III) complexes with phosphine, carbene or other ligands and to tamoxifen-like metallocifens. Also chemically unrelated organic molecules, including natural compounds and their derivatives, are taken into account. An important feature of many TrxR2 inhibitors is provided by their nature of delocalized lipophilic cations that allows their accumulation in mitochondria exploiting the organelle membrane potential. The consequences of TrxR2 inhibition are presented focusing especially on the impact on mitochondrial pathophysiology. Inhibition of TrxR2, by hindering the activity of Trx2 and Prx3, increases the mitochondrial concentration of reactive oxygen species and shifts the thiol redox state toward a more oxidized condition. This is reflected by alterations of specific targets involved in the release of pro-apoptotic factors such as cyclophilin D which acts as a regulator of the mitochondrial permeability transition pore. Therefore, the selective inhibition of TrxR2 could be utilized to induce cancer cell apoptosis.

Antioxidants in Personalized Nutrition and Exercise

The present review highlights the idea that antioxidant supplementation can be optimized when tailored to the precise antioxidant status of each individual. A novel methodologic approach involving personalized nutrition, the mechanisms by which antioxidant status regulates human metabolism and performance, and similarities between antioxidants and other nutritional supplements are described. The usefulness of higher-level phenotypes for data-driven personalized treatments is also explained. We conclude that personally tailored antioxidant interventions based on specific antioxidant inadequacies or deficiencies could result in improved exercise performance accompanied by consistent alterations in redox profile.

Redox Homeostasis and Natural Dietary Compounds: Focusing on Antioxidants of Rice (Oryza sativa L.)

Redox homeostasis may be defined as the dynamic equilibrium between electrophiles and nucleophiles to maintain the optimum redox steady state. This mechanism involves complex reactions, including nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, activated by oxidative stress in order to restore the redox balance. The ability to maintain the optimal redox homeostasis is fundamental for preserving physiological functions and preventing phenotypic shift toward pathological conditions. Here, we reviewed mechanisms involved in redox homeostasis and how certain natural compounds regulate the nucleophilic tone. In addition, we focused on the antioxidant properties of rice and particularly on its bioactive compound, γ-oryzanol. It is well known that γ-oryzanol exerts a variety of beneficial effects mediated by its antioxidant properties. Recently, γ-oryzanol was also found as a Nrf2 inducer, resulting in nucleophilic tone regulation and making rice a para-hormetic food.

Thioredoxin-related protein of 14 kDa as a modulator of redox signalling pathways

Thioredoxin-related protein of 14 kDa (TRP14; also named TXNDC17 for thioredoxin domain-containing protein 17) is a highly conserved and ubiquitously expressed oxidoreductase. It is expressed in parallel with thioredoxin 1 (Trx1, TXN; TXN1), an efficient substrate for the mammalian cytosolic selenoprotein thioredoxin reductase 1 (TrxR1; TXNRD1). However, TRP14, in sharp contrast to Trx1, cannot support the activities of ribonucleotide reductase, peroxiredoxins or methionine sulfoxide reductases, thus is unable to directly support cell proliferation or antioxidant defence through these pathways. However, TRP14 has been shown to efficiently reduce l-cystine, which thereby indirectly supports glutathione synthesis. TRP14 can also suppress NF-κB signalling, is functionally linked to STAT3 signalling, and can directly reactivate oxidized protein-tyrosine phosphatase PTP1B. Furthermore, TRP14 can efficiently reduce persulfidated or nitrosylated cysteine residues in many proteins, thereby having the capacity to modulate signalling through hydrogen sulfide or NO. Additional bioinformatics analyses and observations suggest further roles for TRP14; therefore, further studies of its functions are warranted. Collectively, the results available suggest that TRP14 is a member of the thioredoxin system dedicated to the control of cellular redox signalling pathways. LINKED ARTICLES: This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Sensors and signals: the role of reactive oxygen species in hypoxic pulmonary vasoconstriction

When lung cells experience hypoxia, the functional response, termed hypoxic pulmonary vasoconstriction, activates a multitude of pathways with the goal of optimizing gas exchange. While previously controversial, overwhelming evidence now suggests that increased reactive oxygen species - produced at complex III of the mitochondrial electron transport chain and released into the intermembrane space - is the cellular oxygen signal responsible for triggering hypoxic pulmonary vasoconstriction. The increased reactive oxygen species (ROS) activate many downstream targets that ultimately lead to increased intracellular ionized calcium concentration and contraction of pulmonary arterial smooth muscle cells. While the specific targets of ROS signals are not completely understood, it is clear that this signalling pathway is critical for development and for normal lung function in newborns and adults.

Redox regulation in regenerative medicine and tissue engineering: The paradox of oxygen

One of the biggest challenges in tissue engineering and regenerative medicine is to incorporate a functioning vasculature to overcome the consequences of a lack of oxygen and nutrients in the tissue construct. Otherwise, decreased oxygen tension leads to incomplete metabolism and the formation of the so‐called reactive oxygen species (ROS). Cells have many endogenous antioxidant systems to ensure a balance between ROS and antioxidants, but if this balance is disrupted by factors such as high levels of ROS due to long‐term hypoxia, there will be tissue damage and dysfunction. Current attempts to solve the oxygen problem in the field rarely take into account the importance of the redox balance and are instead centred on releasing or generating oxygen. The first problem with this approach is that although oxygen is necessary for life, it is paradoxically also a highly toxic molecule. Furthermore, although some oxygen‐generating biomaterials produce oxygen, they also generate hydrogen peroxide, a ROS, as an intermediate product. In this review, we discuss why it would be a superior strategy to supplement oxygen delivery with molecules to safeguard the important redox balance. Redox sensor proteins that can stimulate the anaerobic metabolism, angiogenesis, and enhancement of endogenous antioxidant systems are discussed as promising targets. We propose that redox regulating biomaterials have the potential to tackle some of the challenges related to angiogenesis and that the knowledge in this review will help scientists in tissue engineering and regenerative medicine realize this aim.

Mechanisms and Applications of Redox-Sensitive Green Fluorescent Protein-Based Hydrogen Peroxide Probes

SIGNIFICANCE

Genetically encoded hydrogen peroxide (H₂O₂) sensors, based on fusions between thiol peroxidases and redox-sensitive green fluorescent protein 2 (roGFP2), have dramatically broadened the available "toolbox" for monitoring cellular H₂O₂ changes. Recent Advances: Recently developed peroxiredoxin-based probes such as roGFP2-Tsa2ΔC_R offer considerably improved H₂O₂ sensitivity compared with previously available genetically encoded sensors and now permit dynamic, real-time, monitoring of changes in endogenous H₂O₂ levels.

CRITICAL ISSUES

The correct understanding and interpretation of probe read-outs is crucial for their meaningful use. We discuss probe mechanisms, potential pitfalls, and best practices for application and interpretation of probe responses and highlight where gaps in our knowledge remain.

FUTURE DIRECTIONS

The full potential of the newly available sensors remains far from being fully realized and exploited. We discuss how the ability to monitor basal H₂O₂ levels in real time now allows us to re-visit long-held ideas in redox biology such as the response to ischemia-reperfusion and hypoxia-induced reactive oxygen species production. Further, recently proposed circadian cycles of peroxiredoxin hyperoxidation might now be rigorously tested. Beyond their application as H₂O₂ probes, roGFP2-based H₂O₂ sensors hold exciting potential for studying thiol peroxidase mechanisms, inactivation properties, and the impact of post-translational modifications, in vivo. Antioxid. Redox Signal. 29, 552-568.

Pyrethroid bifenthrin induces oxidative stress, neuroinflammation, and neuronal damage, associated with cognitive and memory impairment in murine hippocampus

Exposure to synthetic pyrethroid (SPs) pesticides such as bifenthrin (BF) has been associated with adverse neurodevelopmental outcomes and cognitive impairments, but the underlying neurobiological mechanism is poorly understood so far. The present study has been designed to evaluate changes in behavior and in biomarkers of oxidative stress and neuroinflammation in the hippocampus of rats subchronically treated with BF. Rats exposed daily to BF at doses of 0.6 and 2.1 mg/kg b. w. for 60 days exhibited spatial and cognitive impairments as well as memory dysfunction after 60 days. This repeated BF treatment also significantly increased mRNA expression of pro-inflammatory cytokines tumor necrosis factor (TNF-α), interleukin (IL-1β), (IL-6), nuclear factor erythroid-2 (Nrf2), cyclooxygenase-2 (COX-2), nuclear factor-kappaB pathway (NF-kappaB), and prostaglandin E₂ (PGE₂) in the hippocampus. It further resulted in a significant increase in protein levels of Nrf2, COX-2, microsomal prostaglandin synthase-1 (mPGES-1) and NF-kappaB. This was accompanied by oxidative/nitrosative stress in the hippocampus of treated rats, as shown by increased levels of malondialdehyde (MDA), protein carbonyls (PCO), and nitric oxide (NO), and reduced levels of enzymatic (catalase, superoxide dismutase, and glutathione peroxidase) and non-enzymatic (reduced glutathione) antioxidants. The data are in line with those obtained in organotypic hippocampal slice cultures (OHSCs) isolated from mouse brain and exposed to BF for 72 h, showing neuronal death only at the high dose of 20 μM when compared to controls. These findings suggest that exposure to BF induces neuronal damage, alters redox state, and causes neuroinflammation in the hippocampus, which might lead to cognitive and memory impairment.

Tyrosine substitution of a conserved active-site histidine residue activates Plasmodium falciparum peroxiredoxin 6

Peroxiredoxins efficiently remove hydroperoxides and peroxynitrite in pro- and eukaryotes. However, isoforms of one subfamily of peroxiredoxins, the so-called Prx6-type enzymes, usually have very low activities in standard peroxidase assays in vitro. In contrast to other peroxiredoxins, Prx6 homologues share a conserved histidyl residue at the bottom of the active site. Here we addressed the role of this histidyl residue for redox catalysis using the Plasmodium falciparum homologue PfPrx6 as a model enzyme. Steady-state kinetics with tert-butyl hydroperoxide (tBuOOH) revealed that the histidyl residue is nonessential for Prx6 catalysis and that a replacement with tyrosine can even increase the enzyme activity four- to six-fold in vitro. Stopped-flow kinetics with reduced PfPrx6^WT , PfPrx6^C128A , and PfPrx6^H39Y revealed a preference for H₂ O₂ as an oxidant with second order rate constants for H₂ O₂ and tBuOOH around 2.5 × 10⁷ M^-1 s^-1 and 3 × 10⁶ M^-1 s^-1 , respectively. Differences between the oxidation kinetics of PfPrx6^WT , PfPrx6^C128A , and PfPrx6^H39Y were observed during a slower second-reaction phase. Our kinetic data support the interpretation that the reductive half-reaction is the rate-limiting step for PfPrx6 catalysis in steady-state measurements. Whether the increased activity of PfPrx6^H39Y is caused by a facilitated enzyme reduction because of a destabilization of the fully folded enzyme conformation remains to be analyzed. In summary, the conserved histidyl residue of Prx6-type enzymes is non-essential for catalysis, PfPrx6 is rapidly oxidized by hydroperoxides, and the gain-of-function mutant PfPrx6^H39Y might provide a valuable tool to address the influence of conformational changes on the reactivity of Prx6 homologues.

Prostate cancer tends to metastasize in the bone-mimicking microenvironment via activating NF-κB signaling

Prostate cancer preferentially metastasizes to the bone. However, the underlying molecular mechanisms are still unclear. To explore the effects of a bone-mimicking microenvironment on PC3 prostate cancer cell growth and metastasis, we used osteoblast differentiation medium (ODM; minimal essential medium alpha supplemented with L-ascorbic acid) to mimic the bone microenvironment. PC3 cells grown in ODM underwent epithelial-mesenchymal transition and showed enhanced colony formation, migration, and invasion abilities compared to the cells grown in normal medium. PC3 cells grown in ODM showed enhanced metastasis when injected in mice. A screening of signaling pathways related to invasion and metastasis revealed that the NF-κB pathway was activated, which could be reversed by Bay 11-7082, a NF-κB pathway inhibitor. These results indicate that the cells in different culture conditions manifested significantly different biological behaviors and the NF-κB pathway is a potential therapeutic target for prostate cancer bone metastasis.

Models of intermittent hypoxia and obstructive sleep apnea: molecular pathways and their contribution to cancer

Obstructive sleep apnea (OSA) is common and linked to a variety of poor health outcomes. A key modulator of this disease is nocturnal intermittent hypoxia. There is striking epidemiological evidence that patients with OSA have higher rates of cancer and cancer mortality. Small-animal models demonstrate an important role for systemic intermittent hypoxia in tumor growth and metastasis, yet the underlying mechanisms are poorly understood. Emerging data indicate that intermittent hypoxia activates the hypoxic response and inflammatory pathways in a manner distinct from chronic hypoxia. However, there is significant heterogeneity in published methods for modeling hypoxic conditions, which are often lacking in physiological relevance. This is particularly important for studying key transcriptional mediators of the hypoxic and inflammatory responses such as hypoxia-inducible factor (HIF) and NF-κB. The relationship between HIF, the molecular clock, and circadian rhythm may also contribute to cancer risk in OSA. Building accurate in vitro models of intermittent hypoxia reflective of OSA is challenging but necessary to better elucidate underlying molecular pathways.

p47phox-Dependent Reactive Oxygen Species Stimulate Nuclear Translocation of the FoxO1 Transcription Factor During Metabolic Inhibition in Cardiomyoblasts

Reactive oxygen species (ROS) control forkhead box O (FOXO) transcription factor activity by influencing their nuclear translocation. However, knowledge of the ROS cellular source(s) involved herein remains scarce. Recently, we have shown p47^phox-dependent activation of ROS-producing NADPH oxidase (NOX) at the nuclear pore in H9c2 rat cardiomyoblasts in response to ischemia. This localizes NOX perfectly to affect protein nuclear translocation, including that of transcription factors. In the current study, involvement of p47^phox-dependent production of ROS in the nuclear translocation of FOXO1 was analyzed in H9c2 cells following 4 h of metabolic inhibition (MI), which mimics the effects of ischemia. Nuclear translocation of FOXO1 was determined by quantitative digital-imaging fluorescence and western blot analysis. Subsequently, the effect of inhibiting p47^phox-dependent ROS production by short hairpin RNA (shRNA) transfection on FOXO1 translocation was analyzed by digital-imaging microscopy. MI induced a significant translocation of FOXO1 into the nucleus. Transfection with p47^phox-shRNA successfully knocked-down p47^phox expression, reduced nuclear nitrotyrosine production, an indirect marker for ROS production, and inhibited the nuclear translocation of FOXO1 following MI. With these results, we show for the first time that nuclear import of FOXO1 induced by MI in H9c2 depends critically on p47^phox-mediated ROS production.

Redox properties of Cys2His2 and Cys4 zinc fingers determined by electrospray ionization mass spectrometry

Zinc finger (ZF) protein motifs, stabilized by binding of Zn(II), typically function as interaction modules that bind nucleic acids, proteins and other molecules. The elucidation of the redox states of ZF proteins in cellular conditions, which depend on their midpoint redox potentials, is important for understanding of ZF functioning. In the present study we determined the midpoint redox potentials for representatives of Cys₂His₂ and Cys₄ types of ZF proteins in apo and Zn(II)-bound forms using electrospray ionization mass spectrometry. The midpoint redox potentials of the apo forms of Cys₂His₂ and Cys₄ ZF proteins were -326 and -365 mV (pH 7.5), respectively. These values are close to the cytosolic redox potential of approx. -350 mV (pH 7.5) and thus we can conclude that the apo form of Cys₂His₂-type ZF proteins is predominantly reduced but apo forms of Cys₄-type ZF proteins should be substantially oxidized in the cytoplasm. As expected, Zn(II) binding stabilized the reduced forms of both ZF proteins: the corresponding redox potential values were -284 and -301 mV, respectively. Consequently, binding of Zn(II) ions to ZF motifs can act as a sensitive switch that activates the functioning of the ZF motifs within the cell, and also protects them from oxidation and can function as part of a redox-sensitive regulation mechanism of cellular functions.

Inflammatory and cytotoxic effects of bifenthrin in primary microglia and organotypic hippocampal slice cultures

BACKGROUND

Pyrethroids, such as bifenthrin (BF), are among the most widely used class of insecticides that pose serious risks to human and wildlife health. Pyrethroids are proposed to affect astrocytic functions and to cause neuron injury in the central nervous system (CNS). Microglia are key cells involved in innate immune responses in the CNS, and microglia activation has been linked to inflammation and neurotoxicity. However, little information is known about the effects of BF-induced toxicity in primary microglial cells as well as in organotypic hippocampal slice cultures (OHSCs).

METHODS

Oxidative stress and inflammatory responses induced by BF were evaluated in primary microglial cells and OHSCs incubated with different concentrations of BF (1-20 μM) for 4 and 24 h. mRNA and protein synthesis of cyclooxygenase-2 (COX-2), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), nuclear erythroid-2 like factor-2 (Nrf-2), and microsomal prostaglandin synthase-1 (mPGES-1) was also studied by qPCR and Western blot. Cell viability was analyzed by MTT-tetrazolio (MTT) and lactate dehydrogenase (LDH) assays. Neurotoxicity in OHSCs was analyzed by propidium iodide (PI) staining and confocal microscopy.

RESULTS

Exposure of microglial cells to BF for 24 h resulted in a dose-dependent reduction in the number of viable cells. At sub-cytotoxic concentrations, BF increased reactive oxygen species (ROS), TNF-alpha synthesis, and prostaglandin E2 (PGE2) production, at both 4- and 24-h time points, respectively. Furthermore, BF incubation decreased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities and increased lipid peroxidation, protein oxidation, and H2O2 formation. In addition, BF significantly induced protein synthesis and mRNA expression of oxidative and inflammatory mediators after 4 and 24 h, including Nrf-2, COX-2, mPGES-1, and nuclear factor kappaB (NF-kappaB). A 24-h exposure of OHSCs to BF also increased neuronal death compared to untreated controls. Furthermore, depletion of microglia from OHSCs potently enhanced neuronal death induced by BF.

CONCLUSIONS

Overall, BF exhibited cytotoxic effects in primary microglial cells, accompanied by the induction of various inflammatory and oxidative stress markers including the Nrf-2/COX-2/mPGES-1/NF-kappaB pathways. Moreover, the study provided evidence that BF induced neuronal death in OHSCs and suggests that microglia exert a protective function against BF toxicity.

Antioxidative properties and structural features of atypical 2-Cys peroxiredoxin from Sebastes schlegelii

Atypical 2-Cys peroxiredoxin (Prx5) is an antioxidant protein that exerts its antioxidant function by detoxifying different reactive oxygen species (ROS). Here, we identified mitochondrial Prx5 from rockfish (SsPrx5) and described its specific structural and functional characteristics. The open reading frame (ORF) of SsPrx5 (570 bp) was translated into a 190-amino acid polypeptide that contained a mitochondrial targeting sequence (MTS), thioredoxin 2 domain, two Prx-specific signature motifs, and three conserved cysteine residues. Sequence comparison indicated that the SsPrx5 protein sequence shared greatest identity with teleost orthologs, where the phylogenetic results showed an evolutionary position within the fish Prx5. The coding sequence of SsPrx5 was scattered in six exons as found in other vertebrates. Additionally, the potent antioxidant functions of recombinantly expressed SsPrx5 protein was demonstrated by insulin reduction and extracellular H₂O₂ scavenging both in vitro and in vivo. Quantitative real time PCR (qPCR) detected ubiquitous mRNA expression of SsPrx5 in healthy rockfish tissues, with remarkable expression observed in gill, liver, and reproductive tissues. Prompt transcription of SsPrx5 was shown in the immune-stimulated gill and liver tissues against Streptococcus iniae and lipopolysaccharide injection. Taken together, present results suggest the indispensable role of SsPrx5 in the rockfish antioxidant defense system against oxidative stresses and its role in maintaining redox balance upon pathogen invasion.

Antioxidant effects of Lycium barbarum polysaccharides on photoreceptor degeneration in the light-exposed mouse retina

We assessed the neuroprotective effects of Lycium barbarum Polysaccharides (LBP) on photoreceptor degeneration and the mechanisms involved in oxidative stress in light-exposed mouse retinas. Mice were given a gavage of LBP (150 mg/kg or 300 mg/kg) or phosphate buffered saline (PBS) for 7 days before exposure to light (5000 lx for 24 h). We found that LBP significantly improved the electroretinography (ERG) amplitudes of the a- and b-waves that had been attenuated by light exposure. In addition, changes caused by light exposure including photoreceptor cell loss, nuclear condensation, an increased number of mitochondria vacuoles, outer membrane disc swelling and cristae fractures were distinctly ameliorated by LBP. LBP treatment also significantly prevented the generation of reactive oxygen species (ROS) compared with PBS treatment. The levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and thioredoxin reductase (TrxR1) mRNA were decreased in PBS-treated mice compared with controls but increased remarkably in LBP-treated mice. The mRNA levels of the DNA repair gene Poly (ADP-ribose) polymerase (PARP14) was increased in PBS-treated mice but decreased significantly in the LBP-treated mice. Our findings indicate that pretreatment with LBP effectively protected photoreceptor cells against light-induced retinal damage probably through the up-regulation of the antioxidative genes Nrf2 and TrxR1, the elimination of oxygen free radicals, and the subsequent reduction in the mitochondrial reaction to oxidative stress and enhancement in antioxidant capacity. In addition, the decreased level of PARP14 mRNA in LBP-treated mice also indicated a protective effect of LBP on delaying photoreceptor in the light-damaged retina.

Glutathionylation: a regulatory role of glutathione in physiological processes

Glutathione (γ-glutamyl-cysteinyl-glycine) is an intracellular thiol molecule and a potent antioxidant that participates in the toxic metabolism phase II biotransformation of xenobiotics. It can bind to a variety of proteins in a process known as glutathionylation. Protein glutathionylation is now recognised as one of important posttranslational regulatory mechanisms in cell and tissue physiology. Direct and indirect regulatory roles in physiological processes include glutathionylation of major transcriptional factors, eicosanoids, cytokines, and nitric oxide (NO). This review looks into these regulatory mechanisms through examples of glutathione regulation in apoptosis, vascularisation, metabolic processes, mitochondrial integrity, immune system, and neural physiology. The focus is on the physiological roles of glutathione beyond biotransformational metabolism.

The other myeloperoxidase: Emerging functions

Myeloperoxidase (MPO) is a member of the mammalian peroxidase family. It is mainly expressed in neutrophils, monocytes and macrophages. As a catalyzer of reactive oxidative species and radical species formation, it contributes to neutrophil bactericidal activity. Nevertheless MPO invalidation does not seem to have major health consequences in affected individuals. This suggests that MPO might have alternative functions supporting its conservation during evolution. We will review the available data supporting these non-canonical functions in terms of tissue specific expression, function and enzymatic activity. Thus, we discuss its cell type specific expression. We review in between others its roles in angiogenesis, endothelial (dys-) function, immune reaction, and inflammation. We summarize its pathological actions in clinical conditions such as cardiovascular disease and cancer.

6'-O-Galloylpaeoniflorin Attenuates Cerebral Ischemia Reperfusion-Induced Neuroinflammation and Oxidative Stress via PI3K/Akt/Nrf2 Activation

6'-O-galloylpaeoniflorin (GPF), a galloylated derivative of paeoniflorin isolated from peony root, has been proven to possess antioxidant potential. In this present study, we revealed that GPF treatment exerted significant neuroprotection of PC12 cells following OGD, as evidenced by a reduction of oxidative stress, inflammatory response, cellular injury, and apoptosis in vitro. Furthermore, treatment with GPF increased the levels of phosphorylated Akt (p-Akt) and nuclear factor-erythroid 2-related factor 2 (Nrf2), as well as promoted Nrf2 translocation in PC12 cells, which could be inhibited by Ly294002, an inhibitor of phosphoinositide 3-kinase (PI3K). In addition, Nrf2 knockdown or Ly294002 treatment significantly attenuated the antioxidant, anti-inflammatory, and antiapoptotic activities of GPF in vitro. In vivo studies indicated that GPF treatment significantly reduced infarct volume and improved neurological deficits in rats subjected to CIRI, as well as decreased oxidative stress, inflammation, and apoptosis, which could be inhibited by administration of Ly294002. In conclusion, these results revealed that GPF possesses neuroprotective effects against oxidative stress, inflammation, and apoptosis after ischemia-reperfusion insult via activation of the PI3K/Akt/Nrf2 pathway.

The Conundrum of Hydrogen Peroxide Signaling and the Emerging Role of Peroxiredoxins as Redox Relay Hubs

SIGNIFICANCE

Hydrogen peroxide (H₂O₂) is known to act as a messenger in signal transduction. How H₂O₂ leads to selective and efficient oxidation of specific thiols on specific signaling proteins remains one of the most important open questions in redox biology. Recent Advances: Increasing evidence implicates thiol peroxidases as mediators of protein thiol oxidation. Recently, this evidence has been extended to include the peroxiredoxins (Prxs). Prxs are exceptionally sensitive to H₂O₂, abundantly expressed and capture most of the H₂O₂ that is generated inside cells.

CRITICAL ISSUES

The overall prevalence and importance of Prx-based redox signaling relays are still unknown. The same is true for alternative mechanisms of redox signaling.

FUTURE DIRECTIONS

It will be important to clarify the relative contributions of Prx-mediated and direct thiol oxidation to H₂O₂ signaling. Many questions relating to Prx-based redox relays remain to be answered, including their mechanism, structural organization, and the potential role of adaptor proteins. Antioxid. Redox Signal. 28, 558-573.

Nrf2-Keap1 signaling in oxidative and reductive stress

Nrf2 and its endogenous inhibitor, Keap1, function as a ubiquitous, evolutionarily conserved intracellular defense mechanism to counteract oxidative stress. Sequestered by cytoplasmic Keap1 and targeted to proteasomal degradation in basal conditions, in case of oxidative stress Nrf2 detaches from Keap1 and translocates to the nucleus, where it heterodimerizes with one of the small Maf proteins. The heterodimers recognize the AREs, that are enhancer sequences present in the regulatory regions of Nrf2 target genes, essential for the recruitment of key factors for transcription. In the present review we briefly introduce the Nrf2-Keap1 system and describe Nrf2 functions, illustrate the Nrf2-NF-κB cross-talk, and highlight the effects of the Nrf2-Keap1 system in the physiology and pathophysiology of striated muscle tissue taking into account its role(s) in oxidative stress and reductive stress.

Characteristic single glucosinolates from Moringa oleifera: Induction of detoxifying enzymes and lack of genotoxic activity in various model systems

Leaves of Moringa oleifera are used by tribes as biological cancer medicine. Scientific investigations with M. oleifera conducted so far have almost exclusively used total plant extracts. Studies on the activity of single compounds are missing. Therefore, the biological effects of the two main aromatic multi-glycosylated glucosinolates of M. oleifera were investigated in the present study. The cytotoxic effects of M. oleifera glucosinolates were identified for HepG2 cells (NRU assay), for V79-MZ cells (HPRT assay, SCE assay), and for two Salmonella typhimurium strains (Ames test). Genotoxic effects of these glucosinolates were not observed (Ames test, HPRT assay, and SCE assay). Reporter gene assays revealed a significant increase in the ARE-dependent promoter activity of NQO1 and GPx2 indicating an activation of the Nrf2 pathway by M. oleifera glucosinolates. Since both enzymes can also be induced via activation of the AhR, plasmids containing promoters of both enzymes mutated in the respective binding sites (pGL3enh-hNQO1-ARE, pGL3enh-hNQO1-XRE, pGL3bas-hGPX2-mutARE, pGL3bas-hGPX2-mutXRE) were transfected. Analyses revealed that the majority of the stimulating effects was mediated by the ARE motif, whereas the XRE motif played only a minor role. The stimulating effects of M. oleifera glucosinolates could be demonstrated both at the transcriptional (reporter gene assay, real time-PCR) and translational levels (enzyme activity) making them interesting compounds for further investigation.

The A to Z of modulated cell patterning by mammalian thioredoxin reductases

Mammalian thioredoxin reductases (TrxRs) are selenocysteine-containing proteins (selenoproteins) that propel a large number of functions through reduction of several substrates including the active site disulfide of thioredoxins (Trxs). Well-known enzymatic systems that in turn are supported by Trxs and TrxRs include deoxyribonucleotide synthesis through ribonucleotide reductase, antioxidant defense through peroxiredoxins and methionine sulfoxide reductases, and redox modulation of a number of transcription factors. Although these functions may be essential for cells due to crucial roles in maintenance of cell viability and proliferation, findings during the last decade reveal that mammals have major redundancy in their cellular reductive systems. The synthesis of glutathione (GSH) and reductive functions of GSH-dependent pathways typically act in parallel with Trx-dependent pathways, with only one of these systems often being sufficient to support viability. Importantly, this does not imply that a modulation of the Trx system will remain without consequences, even when GSH-dependent pathways remain functional. As suggested by several recent findings, the Trx system in general and the TrxRs in particular, function as key regulators of signaling pathways. In this review article we will discuss findings that collectively suggest that modulation in mammalian systems of cytosolic TrxR1 (TXNRD1) or mitochondrial TrxR2 (TXNRD2) influence cell patterning and cellular stress responses. Effects of lower activities include increased adipogenesis, insulin responsiveness, glycogen accumulation, hyperproliferation, and distorted embryonic development, while increased activities correlate with decreased proliferation and extended lifespan, as well as worse cancer prognosis. The molecular mechanisms that underlie these diverse effects, involving regulation of protein phosphorylation cascades and of key transcription factors that guide cellular differentiation pathways, will be discussed. We conclude that the selenium-dependent oxidoreductases TrxR1 and TrxR2 should be considered as key components of signaling pathways that control cell differentiation and cellular stress responses.

GFZF, a Glutathione S-Transferase Protein Implicated in Cell Cycle Regulation and Hybrid Inviability, Is a Transcriptional Coactivator

The core promoters of protein-encoding genes play a central role in regulating transcription. M1BP is a transcriptional activator that associates with a core promoter element known as Motif 1 that resides at thousands of genes in Drosophila To gain insight into how M1BP functions, we identified an interacting protein called GFZF. GFZF had been previously identified in genetic screens for factors involved in maintenance of hybrid inviability, the G₂-M DNA damage checkpoint, and RAS/mitogen-activated protein kinase (MAPK) signaling, but its contribution to these processes was unknown. Here, we show that GFZF resides in the nucleus and functions as a transcriptional coactivator. In addition, we show that GFZF is a glutathione S-transferase (GST). Thus, GFZF is the first transcriptional coactivator with intrinsic GST activity, and its identification as a transcriptional coactivator provides an explanation for its role in numerous biological processes.

Leishmania LABCG2 transporter is involved in ATP-dependent transport of thiols

The Leishmania LABCG2 transporter has a key role in the redox metabolism of these protozoan parasites. Recently, the involvement of LABCG2 in virulence, autophagy and oxidative stress has been described. Null mutant parasites for LABCG2 present an increase in the intracellular levels of glutathione (GSH) and trypanothione [T(SH)₂]. On the other hand, parasites overexpressing LABCG2 transporter export non-protein thiols to the extracellular medium. To explore if LABCG2 may mediate an active transport of non-protein thiols, the effect of these molecules on ATPase activity of LABCG2 as well as the ability of LABCG2 to transport them was determined using a baculovirus-Sf9 insect cell system. Our results indicate that all thiols tested [GSH, T(SH)₂] as well as their oxidized forms GSSG and TS₂ (trypanothione disulfide) stimulate LABCG2-ATPase basal activity. We have measured the transport of [³H]-GSH in inside-out Sf9 cell membrane vesicles expressing LABCG2-GFP (green fluorescence protein), finding that LABCG2 was able to mediate a rapid and concentration-dependent uptake of [³H]-GSH in the presence of ATP. Finally, we have analyzed the ability of different thiol species to compete for this uptake, T(SH)₂ and TS₂ being the best competitors. The IC₅₀ value for [³H]-GSH uptake in the presence of increasing concentrations of T(SH)₂ was less than 100 μM, highlighting the affinity of this thiol for LABCG2. These results provide the first direct evidence that LABCG2 is an ABC transporter of reduced and oxidized non-protein thiols in Leishmania, suggesting that this transporter can play a role in the redox metabolism and related processes in this protozoan parasite.

Anti-aging potential of tree nuts with a focus on the phytochemical composition, molecular mechanisms and thermal stability of major bioactive compounds

Tree nuts, complete functional foods, contain macro- and micronutrients of high biological value.

Effects of Glucagon-Like Peptide-1 on Oxidative Stress and Nrf2 Signaling

Oxidative cellular damage caused by free radicals is known to contribute to the pathogenesis of various diseases such as cancer, diabetes, and neurodegenerative diseases, as well as to aging. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and Kelch-like ECH-associated protein1 (Keap1) signaling pathways play an important role in preventing stresses including oxidative and inflammatory stresses. Nrf2 is a master regulator of cellular stress responses, induces the expression of antioxidant and detoxification enzymes, and protects against oxidative stress-induced cell damage. Glucagon-like peptide-1 (GLP-1) is an incretin hormone, which was originally found to increase insulin synthesis and secretion. It is now widely accepted that GLP-1 has multiple functions beyond glucose control in various tissues and organs including brain, kidney, and heart. GLP-1 and GLP-1 receptor agonists are known to be effective in many chronic diseases, including diabetes, via antioxidative mechanisms. In this review, we summarize the current knowledge regarding the role of GLP-1 in the protection against oxidative damage and the activation of the Nrf2 signaling pathway.

Nrf2, the Master Regulator of Anti-Oxidative Responses

Tight regulation of inflammation is very important to guarantee a balanced immune response without developing chronic inflammation. One of the major mediators of the resolution of inflammation is the transcription factor: the nuclear factor erythroid 2-like 2 (Nrf2). Stabilized following oxidative stress, Nrf2 induces the expression of antioxidants as well as cytoprotective genes, which provoke an anti-inflammatory expression profile, and is crucial for the initiation of healing. In view of this fundamental modulatory role, it is clear that both hyper- or hypoactivation of Nrf2 contribute to the onset of chronic diseases. Understanding the tight regulation of Nrf2 expression/activation and its interaction with signaling pathways, known to affect inflammatory processes, will facilitate development of therapeutic approaches to prevent Nrf2 dysregulation and ameliorate chronic inflammatory diseases. We discuss in this review the principle mechanisms of Nrf2 regulation with a focus on inflammation and autophagy, extending the role of dysregulated Nrf2 to chronic diseases and tumor development.

A role for 2-Cys peroxiredoxins in facilitating cytosolic protein thiol oxidation

Hydrogen peroxide (H₂O₂) acts as a signaling messenger by triggering the reversible oxidation of redox-regulated proteins. It remains unclear how proteins can be oxidized by signaling levels of H₂O₂ in the presence of peroxiredoxins, which are highly efficient peroxide scavengers. Here we show that the rapid formation of disulfide bonds in cytosolic proteins is enabled, rather than competed, by cytosolic 2-Cys peroxiredoxins. Under the conditions tested, the combined deletion or depletion of cytosolic peroxiredoxins broadly frustrated H₂O₂-dependent protein thiol oxidation, which is the exact opposite of what would be predicted based on the assumption that H₂O₂ oxidizes proteins directly. We find that peroxiredoxins enable rapid and sensitive protein thiol oxidation by relaying H₂O₂-derived oxidizing equivalents to other proteins. Although these findings do not rule out the existence of Prx-independent H₂O₂ signaling mechanisms, they suggest a broader role for peroxiredoxins as sensors and transmitters of H₂O₂ signals than hitherto recognized.

Mitochondrial Ca2+ transport in the endothelium: regulation by ions, redox signalling and mechanical forces

Calcium (Ca²⁺) transport by mitochondria is an important component of the cell Ca²⁺ homeostasis machinery in metazoans. Ca²⁺ uptake by mitochondria is a major determinant of bioenergetics and cell fate. Mitochondrial Ca²⁺ uptake occurs via the mitochondrial Ca²⁺ uniporter (MCU) complex, an inner mitochondrial membrane protein assembly consisting of the MCU Ca²⁺ channel, as its core component, and the MCU complex regulatory/auxiliary proteins. In this review, we summarize the current knowledge on the molecular nature of the MCU complex and its regulation by intra- and extramitochondrial levels of divalent ions and reactive oxygen species (ROS). Intracellular Ca²⁺ concentration ([Ca²⁺]_i), mitochondrial Ca²⁺ concentration ([Ca²⁺]_m) and mitochondrial ROS (mROS) are intricately coupled in regulating MCU activity. Here, we highlight the contribution of MCU activity to vascular endothelial cell (EC) function. Besides the ionic and oxidant regulation, ECs are continuously exposed to haemodynamic forces (either pulsatile or oscillatory fluid mechanical shear stresses, depending on the precise EC location within the arteries). Thus, we also propose an EC mechanotransduction-mediated regulation of MCU activity in the context of vascular physiology and atherosclerotic vascular disease.

The Incomplete Glutathione Puzzle: Just Guessing at Numbers and Figures?

SIGNIFICANCE

Glutathione metabolism is comparable to a jigsaw puzzle with too many pieces. It is supposed to comprise (i) the reduction of disulfides, hydroperoxides, sulfenic acids, and nitrosothiols, (ii) the detoxification of aldehydes, xenobiotics, and heavy metals, and (iii) the synthesis of eicosanoids, steroids, and iron-sulfur clusters. In addition, glutathione affects oxidative protein folding and redox signaling. Here, I try to provide an overview on the relevance of glutathione-dependent pathways with an emphasis on quantitative data. Recent Advances: Intracellular redox measurements reveal that the cytosol, the nucleus, and mitochondria contain very little glutathione disulfide and that oxidative challenges are rapidly counterbalanced. Genetic approaches suggest that iron metabolism is the centerpiece of the glutathione puzzle in yeast. Furthermore, recent biochemical studies provide novel insights on glutathione transport processes and uncoupling mechanisms.

CRITICAL ISSUES

Which parts of the glutathione puzzle are most relevant? Does this explain the high intracellular concentrations of reduced glutathione? How can iron-sulfur cluster biogenesis, oxidative protein folding, or redox signaling occur at high glutathione concentrations? Answers to these questions not only seem to depend on the organism, cell type, and subcellular compartment but also on different ideologies among researchers.

FUTURE DIRECTIONS

A rational approach to compare the relevance of glutathione-dependent pathways is to combine genetic and quantitative kinetic data. However, there are still many missing pieces and too little is known about the compartment-specific repertoire and concentration of numerous metabolites, substrates, enzymes, and transporters as well as rate constants and enzyme kinetic patterns. Gathering this information might require the development of novel tools but is crucial to address potential kinetic competitions and to decipher uncoupling mechanisms to solve the glutathione puzzle. Antioxid. Redox Signal. 27, 1130-1161.

Antiobesity potential of Piperonal: promising modulation of body composition, lipid profiles and obesogenic marker expression in HFD-induced obese rats

Background

Black pepper or Piper nigrum is a well-known spice, rich in a variety of bioactive compounds, and widely used in many cuisines across the world. In the Indian traditional systems of medicine, it is used to treat gastric and respiratory ailments. The purpose of this investigation is to study the antihyperlipidemic and antiobesity effects of piperonal in high-fat diet (HFD)-induced obese rats.

Methods

Piperonal, an active constituent of Piper nigrum seeds, was isolated and confirmed by HPLC, ¹H and ¹³C NMR spectroscopy. Male SD rats were fed on HFD for 22 weeks; Piperonal was supplemented from the 16th week as mentioned in the experimental design. Changes in body weight and body composition were measured by TOBEC, bone mineral composition and density were measured by DXA, and adipose tissue distribution was measured by 7 T–MRI. Plasma levels of glucose, insulin, insulin resistance and lipid profiles of plasma, liver and kidney, adipocyte hormones and liver antioxidants were evaluated using standard kit methods. Expression levels of adipogenic and lipogenic genes, such as PPAR-γ, FAS, Fab-4, UCP-2, SREBP-1c, ACC, HMG-COA and TNF-α were measured by RT-PCR. Histopathological examination of adipose and liver tissues was also carried out in experimental rats.

Results

HFD substantially induced body weight, fat%, adipocyte size, circulatory and tissue lipid profiles. It elevated the plasma levels of insulin, insulin resistance and leptin but decreased the levels of adiponectin, BMC and BMD. Increased expression of PPAR-γ, FAS, Fab-4, UCP-2, SREBP-1c, ACC, and TNF-α was noticed in HFD-fed rats. However, supplementation of piperonal (20, 30 and 40 mg/kg b.wt) for 42 days considerably and dose-dependently attenuated the HFD-induced alterations, with the maximum therapeutic activity being noticed at 40 mg/kg b.wt.

Conclusions

Piperonal significantly attenuated HFD-induced body weight and biochemical changes through modulation of key lipid metabolizing and obesogenic genes. Our findings demonstrate the efficacy of piperonal as a potent antiobesity agent, provide scientific evidence for its traditional use and suggest the possible mechanism of action.

Extracellular superoxide dismutase and its role in cancer

Reactive oxygen species (ROS) are increasingly recognized as critical determinants of cellular signaling and a strict balance of ROS levels must be maintained to ensure proper cellular function and survival. Notably, ROS is increased in cancer cells. The superoxide dismutase family plays an essential physiological role in mitigating deleterious effects of ROS. Due to the compartmentalization of ROS signaling, EcSOD, the only superoxide dismutase in the extracellular space, has unique characteristics and functions in cellular signal transduction. In comparison to the other two intracellular SODs, EcSOD is a relatively new comer in terms of its tumor suppressive role in cancer and the mechanisms involved are less well understood. Nevertheless, the degree of differential expression of this extracellular antioxidant in cancer versus normal cells/tissues is more pronounced and prevalent than the other SODs. A significant association of low EcSOD expression with reduced cancer patient survival further suggests that loss of extracellular redox regulation promotes a conducive microenvironment that favors cancer progression. The vast array of mechanisms reported in mediating deregulation of EcSOD expression, function, and cellular distribution also supports that loss of this extracellular antioxidant provides a selective advantage to cancer cells. Moreover, overexpression of EcSOD inhibits tumor growth and metastasis, indicating a role as a tumor suppressor. This review focuses on the current understanding of the mechanisms of deregulation and tumor suppressive function of EcSOD in cancer.

Discovery of a head-to-tail cyclic peptide as the Keap1-Nrf2 protein-protein interaction inhibitor with high cell potency

Directly disrupting Keap1-Nrf2 protein-protein interaction (PPI) has emerged as a novel way to activate Nrf2. Peptide Keap1-Nrf2 PPI inhibitors have been reported with high Keap1 binding affinity. However, these peptide inhibitors show weak activity in cells. In this study, the head-to-tail cyclic strategy was applied in the development of peptide inhibitors. The privileged residue sequence with minimal acidic residues was used as the template for the cyclic peptide, and the appropriate conjugation method was designed based on the peptide-Keap1 binding mode. The glycine was introduced as the linker to connect both sides, which can avoid the terminal charge, enhance the peptide stability and constrain the binding conformation simultaneously. The obtained novel cyclic peptide 3 showed high binding affinity with Keap1 and possessed high potency in Nrf2 activation at cellular level. We also showed that peptide 3 exhibited effective anti-inflammatory effects in mouse RAW 264.7 cells by activating the Nrf2-regulated defense system and enhancing the antioxidant capacity. This study proved that the head-to-tail cyclic strategy is quite useful in improving the cell potency of peptide Keap1-Nrf2 inhibitors and provided a possible way to develop drug-like peptides as therapeutic Nrf2 activators.

The exceptionally high reactivity of Cys 621 is critical for electrophilic activation of the sensory nerve ion channel TRPA1

Electrophiles produced during oxidative stress trigger pain responses by reacting with TRPA1 ion channels on sensory nerves. Bahia et al. show that residue C621 on TRPA1 has remarkable reactivity with electrophiles—more than cellular antioxidants—and is crucial for this sensory response.

Activation of the sensory nerve ion channel TRPA1 by electrophiles is the key mechanism that initiates nociceptive signaling, and leads to defensive reflexes and avoidance behaviors, during oxidative stress in mammals. TRPA1 is rapidly activated by subtoxic levels of electrophiles, but it is unclear how TRPA1 outcompetes cellular antioxidants that protect cytosolic proteins from electrophiles. Here, using physiologically relevant exposures, we demonstrate that electrophiles react with cysteine residues on mammalian TRPA1 at rates that exceed the reactivity of typical cysteines by 6,000-fold and that also exceed the reactivity of antioxidant enzymes. We show that TRPA1 possesses a complex reactive cysteine profile in which C621 is necessary for electrophile-induced binding and activation. Modeling of deprotonation energies suggests that K620 contributes to C621 reactivity and mutation of K620 alone greatly reduces the effect of electrophiles on TRPA1. Nevertheless, binding of electrophiles to C621 is not sufficient for activation, which also depends on the function of another reactive cysteine (C665). Together, our results demonstrate that TRPA1 acts as an effective electrophilic sensor because of the exceptionally high reactivity of C621.

Nrf2-Inducers Counteract Neurodegeneration in Frataxin-Silenced Motor Neurons: Disclosing New Therapeutic Targets for Friedreich's Ataxia

Oxidative stress is actively involved in Friedreich's Ataxia (FA), thus pharmacological targeting of the antioxidant machinery may have therapeutic value. Here, we analyzed the relevance of the antioxidant phase II response mediated by the transcription factor Nrf2 on frataxin-deficient cultured motor neurons and on fibroblasts of patients. The in vitro treatment of the potent Nrf2 activator sulforaphane increased Nrf2 protein levels and led to the upregulation of phase II antioxidant enzymes. The neuroprotective effects were accompanied by an increase in neurites' number and extension. Sulforaphane (SFN) is a natural compound of many diets and is now being used in clinical trials for other pathologies. Our results provide morphological and biochemical evidence to endorse a neuroprotective strategy that may have therapeutic relevance for FA. The findings of this work reinforce the crucial importance of Nrf2 in FA and provide a rationale for using Nrf2-inducers as pharmacological agents.

Ozone therapy: an overview of pharmacodynamics, current research, and clinical utility

The use of ozone (O₃) gas as a therapy in alternative medicine has attracted skepticism due to its unstable molecular structure. However, copious volumes of research have provided evidence that O₃'s dynamic resonance structures facilitate physiological interactions useful in treating a myriad of pathologies. Specifically, O₃ therapy induces moderate oxidative stress when interacting with lipids. This interaction increases endogenous production of antioxidants, local perfusion, and oxygen delivery, as well as enhances immune responses. We have conducted a comprehensive review of O₃ therapy, investigating its contraindications, routes and concentrations of administration, mechanisms of action, disinfectant properties in various microorganisms, and its medicinal use in different pathologies. We explore the therapeutic value of O₃ in pathologies of the cardiovascular system, gastrointestinal tract, genitourinary system, central nervous system, head and neck, musculoskeletal, subcutaneous tissue, and peripheral vascular disease. Despite compelling evidence, further studies are essential to mark it as a viable and quintessential treatment option in medicine.