Purification and characterization of thioredoxin reductase enzyme from commercial Spirulina platensis tablets by affinity chromatography and investigation of the effects of some chemicals and drugs on enzyme activity.

Thioredoxin reductase (TrxR, enzyme code [E.C.] 1.6.4.5) is a widely distributed flavoenzyme that catalyzes nicotinamide adenine dinucleotide phosphate (NADPH)-dependent reduction of thioredoxin and many other physiologically important substrates. Spirulina platensis is a blue-green algae that is often used as a dietary supplement. S. platensis is rich in protein, lipid, polysaccharide, pigment, carotenoid, enzyme, vitamins and many other chemicals and exhibits a variety of pharmacological functions. In the present study, a simple and efficient method to purify TrxR from S. platensis tablets is reported. The extractions were carried out using two different methods: heat denaturation and 2',5'-adenosine diphosphate Sepharose 4B affinity chromatography. The enzyme was purified by 415.04-fold over the crude extract, with a 19% yield, and specific activity of 0.7640 U/mg protein. Optimum pH, temperature and ionic strength of the enzyme activity, as well as the Michaelis constant (Km ) and maximum velocity of enzyme (Vmax ) values for NADPH and 5,5'-dithiobis(2-nitrobenzoic acid) were determined. Tested metal ions, vitamins, and drugs showed inhibition effects, except Se4+ ion, cefazolin sodium, teicoplanin, and tobramycin that increased the enzyme activity in vitro. Ag+ , Cu2+ , Mg2+ , Ni2+ , Pb2+ , Zn2+ , Al3+ , Cr3+ , Fe3+ , and V4+ ions; vitamin B3 , vitamin B6 , vitamin C, and vitamin U and aciclovir, azithromycin, benzyladenine, ceftriaxone sodium, clarithromycin, diclofenac, gibberellic acid, glurenorm, indole-3-butyric acid, ketorolac, metformin, mupirocin, mupirocin calcium, paracetamol, and tenofovir had inhibitory effects on TrxR. Ag+ exhibited stronger inhibition than 1-chloro-2,4-dinitrobenzene (a positive control).

Redox regulation of the NLRP3-mediated inflammation and pyroptosis.

The review considers modern data on the mechanisms of activation and redox regulation of the NLRP3 inflammasome and gasdermins, as well as the role of selenium in these processes. Activation of the inflammasome and pyroptosis represent an evolutionarily conserved mechanism of the defense against pathogens, described for various types of cells and tissues (macrophages and monocytes, microglial cells and astrocytes, podocytes and parenchymal cells of the kidneys, periodontal tissues, osteoclasts and osteoblasts, as well as cells of the digestive and urogenital systems, etc.). Depending on the characteristics of redox regulation, the participants of NLRP3 inflammation and pyroptosis can be subdivided into 2 groups. Members of the first group block the mitochondrial electron transport chain, promote the formation of reactive oxygen species and the development of oxidative stress. This group includes granzymes, the mitochondrial antiviral signaling protein MAVS, and others. The second group includes thioredoxin interacting protein (TXNIP), erythroid-derived nuclear factor-2 (NRF2), Kelch-like ECH-associated protein 1 (Keap1), ninjurin (Ninj1), scramblase (TMEM16), inflammasome regulatory protein kinase NLRP3 (NEK7), caspase-1, gasdermins GSDM B, D and others. They have redox-sensitive domains and/or cysteine residues subjected to redox regulation, glutathionylation/deglutathionylation or other types of regulation. Suppression of oxidative stress and redox regulation of participants in NLRP3 inflammation and pyroptosis depends on the activity of the antioxidant enzymes glutathione peroxidase (GPX) and thioredoxin reductase (TRXR), containing a selenocysteine residue Sec in the active site. The expression of GPX and TRXR is regulated by NRF2 and depends on the concentration of selenium in the blood. Selenium deficiency causes ineffective translation of the Sec UGA codon, translation termination, and, consequently, synthesis of inactive selenoproteins, which can cause various types of programmed cell death: apoptosis of nerve cells and sperm, necroptosis of erythrocyte precursors, pyroptosis of infected myeloid cells, ferroptosis of T- and B-lymphocytes, kidney and pancreatic cells. In addition, suboptimal selenium concentrations in the blood (0.86 µM or 68 µg/l or less) have a significant impact on expression of more than two hundred and fifty genes as compared to the optimal selenium concentration (1.43 µM or 113 µg/l). Based on the above, we propose to consider blood selenium concentrations as an important parameter of redox homeostasis in the cell. Suboptimal blood selenium concentrations (or selenium deficiency states) should be used for assessment of the risk of developing inflammatory processes.

Recent Advances in the Synthesis and Antioxidant Activity of Low Molecular Mass Organoselenium Molecules.

Selenium is an essential trace element in living organisms, and is present in selenoenzymes with antioxidant activity, like glutathione peroxidase (GPx) and thioredoxin reductase (TrxR). The search for small selenium-containing molecules that mimic selenoenzymes is a strong field of research in organic and medicinal chemistry. In this review, we review the synthesis and bioassays of new and known organoselenium compounds with antioxidant activity, covering the last five years. A detailed description of the synthetic procedures and the performed in vitro and in vivo bioassays is presented, highlighting the most active compounds in each series.

Modeling Selenoprotein Se-Nitrosation: Synthesis of a Se-Nitrososelenocysteine with Persistent Stability.

The Se-nitrosation in selenoproteins such as glutathione peroxidase and thioredoxin reductase to produce Se-nitrososelenocysteines (Sec-SeNOs) has been proposed to play crucial roles in signaling processes mediated by reactive nitrogen species and nitrosative-stress responses, although chemical evidence for the formation of Sec-SeNOs has been elusive not only in proteins but also in small-molecule systems. Herein, we report the first synthesis of a Sec-SeNO by employing a selenocysteine model system that bears a protective molecular cradle. The Sec-SeNO was characterized using 1H and 77Se nuclear magnetic resonance as well as ultraviolet/visible spectroscopy and found to have persistent stability at room temperature in solution. The reaction processes involving the Sec-SeNO provide experimental information that serves as a chemical basis for elucidating the reaction mechanisms involving the SeNO species in biological functions, as well as in selenol-catalyzed NO generation from S-nitrosothiols.

Design, Synthesis and Antitumor Activity of Novel Selenium-Containing Tepotinib Derivatives as Dual Inhibitors of c-Met and TrxR.

Cellular mesenchymal-epithelial transition factor (c-Met), an oncogenic transmembrane receptor tyrosine kinase (RTK), plays an essential role in cell proliferation during embryo development and liver regeneration. Thioredoxin reductase (TrxR) is overexpressed and constitutively active in most tumors closely related to cancer recurrence. Multi-target-directed ligands (MTDLs) strategy provides a logical approach to drug combinations and would adequately address the pathological complexity of cancer. In this work, we designed and synthesized a series of selenium-containing tepotinib derivatives by means of selenium-based bioisosteric modifications and evaluated their antiproliferative activity. Most of these selenium-containing hybrids exhibited potent dual inhibitory activity toward c-Met and TrxR. Among them, compound 8b was the most active, with an IC50 value of 10 nM against MHCC97H cells. Studies on the mechanism of action revealed that compound 8b triggered cell cycle arrest at the G1 phase and caused ROS accumulations by targeting TrxR, and these effects eventually led to cell apoptosis. These findings strongly suggest that compound 8b serves as a dual inhibitor of c-Met and TrxR, warranting further exploitation for cancer therapy.

Deodorized Garlic Decreases Oxidative Stress Caused by Lipopolysaccharide in Rat Heart through Hydrogen Sulfide: Preliminary Findings.

Deodorized garlic (DG) may favor the activity of the antioxidant enzymes and promote the synthesis of hydrogen sulfide (H2S). The objective was to test if DG favors an increase in H2S and if it decreases the oxidative stress caused by lipopolysaccharide (LPS) in rat hearts. A total of 24 rats were divided into 4 groups: Group 1 control (C), Group 2 LPS, Group 3 DG, and Group 4 LPS plus DG. The cardiac mechanical performance (CMP), coronary vascular resistance (CVR), and oxidative stress markers, such as total antioxidant capacity (TAC), glutathione (GSH), selenium (Se), lipid peroxidation (LPO), thiols, hydrogen sulfide (H2S), and the activities and expressions of thioredoxin reductase (TrxR), glutathione peroxidase (GPx), and glutathione-S-transferase (GST), cystathionine synthetase (CBS), cystathionine γ-lyase (CTH), iNOS, and eNOS-p, were analyzed in the heart. Infarct zones in the cardiac tissue were present (p = 0.01). The CMP and CVR decreased and increased (p ≤ 0.05), TAC, GSH, H2S, NO, thiols, and GST activity (p ≤ 0.01) decreased, and LPO and iNOS increased (p ≤ 0.05). The activities and expressions of TrxR, GPx, eNOS-p, CTH, and CBS (p ≤ 0.05) decreased with the LPS treatment; however, DG normalized this effect. DG treatment decreases heart damage caused by LPS through the cross-talk between the H2S and NO systems.

The emerging role of selenium metabolic pathways in cancer: New therapeutic targets for cancer.

Selenium (Se) is incorporated into the body via the selenocysteine (Sec) biosynthesis pathway, which is critical in the synthesis of selenoproteins, such as glutathione peroxidases and thioredoxin reductases. Selenoproteins, which play a key role in several biological processes, including ferroptosis, drug resistance, endoplasmic reticulum stress, and epigenetic processes, are guided by Se uptake. In this review, we critically analyze the molecular mechanisms of Se metabolism and its potential as a therapeutic target for cancer. Sec insertion sequence binding protein 2 (SECISBP2), which is a positive regulator for the expression of selenoproteins, would be a novel prognostic predictor and an alternate target for cancer. We highlight strategies that attempt to develop a novel Se metabolism-based approach to uncover a new metabolic drug target for cancer therapy. Moreover, we expect extensive clinical use of SECISBP2 as a specific biomarker in cancer therapy in the near future. Of note, scientists face additional challenges in conducting successful research, including investigations on anticancer peptides to target SECISBP2 intracellular protein.

Self-delivery nanomedicine for chemotherapy sensitized photodynamic therapy.

A chlorine e6 (Ce6) and curcumin (Cur) based self-delivery nanomedicine (CeCu) is prepared for chemotherapy sensitized photodynamic therapy (PDT). The chemotherapeutic agent of Cur could inhibit the TrxR activity to destroy the cellular ROS-defence system for enhanced PDT, which provides synergistic effects for tumor precision therapy in consideration of the unfavorable tumor microenvironments.

Anti-oxidant, anti-inflammatory and anti-fibrosis effects of ganoderic acid A on carbon tetrachloride induced nephrotoxicity by regulating the Trx/TrxR and JAK/ROCK pathway.

Ganoderic acid A (GAA), one of the major triterpenoid components extracted from Ganoderma mushroom has been shown to possess numerous important pharmacological activities. The present study was aimed to investigate the mechanisms of GAA on carbon tetrachloride (CCl4)-induced kidney inflammation, fibrosis and oxidative stress in mice. The male mice were treated with 25 and 50 mg/mg GAA after stimulated with CCl4. Our results showed that GAA improved renal damage by decreasing the serum levels of creatinine, urea, uric acid and alleviating kidney fibrosis. GAA ameliorated CCl4-induced indices of inflammation. GAA suppressed oxidative stress by regulating the glutathione antioxidant system and the thioredoxin antioxidant system. GAA increased the activations of thioredoxin reductase (TrxR), Trx, GSH, SOD, GPx. Furthermore, GAA supplementation inhibited the JAK and STAT3 pathway. GAA inhibited the activations of RhoA, ROCK, NF-κB, TGF-ß and Smad3. Thus, this study demonstrated that GAA possesses immune-protective properties through regulating the Trx/TrxR, JAK2/STAT3 and RhoA/ROCK pathways.

Selenium Status in Diet Affects Acetaminophen-Induced Hepatotoxicity via Interruption of Redox Environment.

Aims: Drug-induced liver injury, especially acetaminophen (APAP)-induced liver injury, is a leading cause of liver failure worldwide. Mouse models were used to evaluate the effect of microelement selenium levels on the cellular redox environment and consequent hepatotoxicity of APAP. Results: APAP treatment affected mouse liver selenoprotein thioredoxin reductase (TrxR) activity and glutathione (GSH) level in a dose- and time-dependent manner. Decrease of mouse liver TrxR activity and glutathione level was an early event, and occurred concurrently with liver damage. The decreases in the GSH/glutathione disulfide form (GSSG) ratio and TrxR activity, and the increase of protein S-glutathionylation were correlated with the APAP-induced hepatotoxicity. Moreover, in APAP-treated mice both mild deprivation and excess supplementation with selenium increased the severity of liver injury compared with those observed in mice with normal dietary selenium levels. An increase in the oxidation state of the TrxR-mediated system, including cytosolic thioredoxin1 (Trx1) and peroxiredoxin1/2 (Prx1/2), and mitochondrial Trx2 and Prx3, was found in the livers from mice reared on selenium-deficient and excess selenium-supplemented diets upon APAP treatment. Innovation: This work demonstrates that both Trx and GSH systems are susceptible to APAP toxicity in vivo, and that the thiol-dependent redox environment is a key factor in determining the extent of APAP-induced hepatotoxicity. Dietary selenium and selenoproteins play critical roles in protecting mice against APAP overdose. Conclusion: APAP treatment in mice interrupts the function of the Trx and GSH systems, which are the main enzymatic antioxidant systems, in both the cytosol and mitochondria. Dietary selenium deficiency and excess supplementation both increase the risk of APAP-induced hepatotoxicity.

Structure-based identification of natural compound inhibitor against M. tuberculosis thioredoxin reductase: insight from molecular docking and dynamics simulation.

Antioxidant systems of M. tuberculosis (Mtb) play an important role in providing resistance in the hostile environment of mononuclear phagocytes. Thioredoxin system is a known antioxidant system that consists of three copies of thioredoxins (Trxs) and a single copy of thioredoxin reductase (TrxR). TrxR has been validated as an essential gene known to be involved in the reduction of peroxides, dinitrobenzenes and hydroperoxides, and is crucial in maintaining the survival of Mtb in macrophages. Recently, it has been demonstrated to be a druggable target. In this study, molecular docking was applied to screen more than 20,000 natural compounds from the Traditional Chinese Medicine database. Theoretical calculation of ΔGbinding by the Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) methods indicated two top-hit compounds that bind with a high affinity to the allosteric site, consisting of a hinge region, of TrxR. Further, stability and binding analysis of both compounds were carried out with molecular dynamics simulation. An analysis of conformational variation by principal component analysis (PCA) and protein contact network (PCN) uncovered the conformational changes in the compound-bound forms of protein. The NADPH domain formed many new interactions with the FAD domain in the compound-bound form, signifying that the binding may render an effect on the protein structure and function. Our results suggest that these two compounds could potentially be used for structure-based lead inhibitors against TrxR. The inhibitor selected as lead compound will be used further as a scaffold to optimize as novel anti-tuberculosis therapeutic.Communicated by Ramaswamy H. Sarma.

Selenium-independent antioxidant and anti-inflammatory effects of thioredoxin reductase inhibition in alveolar macrophages.

AIMS: Interleukin-1ß (IL-1ß) contributes to the development of bronchopulmonary dysplasia (BPD). Thioredoxin reductase-1 (Txnrd1) inhibition activates nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent responses. Txnrd1 activity is selenium (Se) dependent and Se deficiency is common in prematurity. Auranofin (AFN), a Txnrd1 inhibitor, decreases IL-1ß levels and increases Nrf2 activation in lipopolysaccharide (LPS) treated alveolar macrophages. In lung epithelia, AFN-induced Nrf2 activation is Se dependent. We tested the hypothesis that the effects of Txnrd1 inhibition in alveolar macrophages are Se dependent. MAIN METHODS: To establish Se sufficient (Se+) and deficient (Se-) conditions, alveolar (MH-S) macrophages were cultured in 2.5% fetal bovine serum (FBS) ± 25 nM Na2SeO3. Se- (2.5% FBS) and Se+ (2.5% FBS + 25 nM Na2SeO3) cells were cultured in the presence or absence of 0.05 µg/mL LPS and/or 0.5 µM AFN. Nrf2 activation was determined by measuring NADPH quinone oxidoreductase-1 (Nqo1) and glutathione levels. IL-1ß mRNA (Il1b) and protein levels were measured using qRT-PCR and ELISA. Data were analyzed by ANOVA followed by Tukey's post-hoc. KEY FINDINGS: We detected an independent effect of AFN, but not LPS, on Nqo1 expression and GSH levels in Se+ and Se- cells. LPS significantly increased Il1b and IL-1ß levels in both groups. AFN-mediated attenuation of this effect was not impacted by Se status. SIGNIFICANCE: The beneficial effects of Txnrd1 inhibition in alveolar macrophages are Se-independent and therefore unlikely to be diminished by clinical Se deficiency.

Synergistic therapeutic efficacy of ebselen and silver ions against multidrug-resistant Acinetobacter baumannii-induced urinary tract infections.

Ebselen (EbSe), an organo-selenium compound with well-characterized toxicology and pharmacology, exhibited potent antibacterial activity against glutathione (GSH)-positive bacteria when combined with silver ions (Ag+). In this paper, the strong bactericidal activity of EbSe-Ag+ against multidrug-resistant (MDR) Acinetobacter baumannii has been confirmed, and its efficacy was mainly based on the inhibition of thioredoxin reductase (TrxR) activity and the depletion of the total GSH amount. Moreover, the therapeutic effect of EbSe-Ag+ on urinary tract infection was assessed in a mouse model induced with A. baumannii 0361# strain. The treatment with EbSe-Ag+ significantly reduced the bacterial load and expression levels of the pro-inflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) in bladder lesions; meanwhile, the pathological experiment showed that A. baumannii-induced changes in EbSe-Ag+ treated mice were much attenuated than that in the control group. Thus, all the results obtained here may lay the foundation for further analysis and development of EbSe-Ag+ as potential antibacterial agents for MDR A. baumannii-induced urinary tract infection treatment.

[Selenium compounds in redox regulation of inflammation and apoptosis]. / Soedineniia selena v redoks-reguliatsii vospaleniia i apoptoza.

Monocytes and macrophages play a key role in the development of inflammation: under the action of lipopolysaccharides (LPS), absorbed from the intestine, monocytes and macrophages form reactive oxygen species (ROS) and cytokines, this leads to the development of oxidative stress, inflammation and/or apoptosis in all types of tissues. In the cells LPS induce an "internal" TLR4-mediated MAP-kinase inflammatory signaling pathway and cytokines through the superfamily of tumor necrosis factor receptor (TNFR) and the "death domain" (DD) initiate an "external" caspase apoptosis cascade or necrosis activation that causes necroptosis. Many of the proteins involved in intracellular signaling cascades (MYD88, ASK1, IKKa/b, NF-kB, AP-1) are redox-sensitive and their activity is regulated by antioxidants thioredoxin, glutaredoxin, nitroredoxin, and glutathione. Oxidation of these signaling proteins induced by ROS enhances the development of inflammation and apoptosis, and their reduction with antioxidants, on the contrary, stabilizes the signaling cascades speed, preventing the vicious circle of oxidative stress, inflammation and apoptosis that follows it. Antioxidant (AO) enzymes thioredoxin reductase (TRXR), glutaredoxin reductase (GLRXR), glutathione reductase (GR) are required for reduction of non-enzymatic antioxidants (thioredoxin, glutaredoxin, nitroredoxin, glutathione), and AO enzymes (SOD, catalase, GPX) are required for ROS deactivation. The key AO enzymes (TRXR and GPX) are selenium-dependent; therefore selenium deficiency leads to a decrease in the body's antioxidant defense, the development of oxidative stress, inflammation, and/or apoptosis in various cell types. Nrf2-Keap1 signaling pathway activated by selenium deficiency and/or oxidative stress is necessary to restore redox homeostasis in the cell. In addition, expression of some genes is changed with selenium deficiency. Consequently, growth and proliferation of cells, their movement, development, death, and survival, as well as the interaction between cells, the redox regulation of intracellular signaling cascades of inflammation and apoptosis, depend on the selenium status of the body. Prophylactic administration of selenium-containing preparations (natural and synthetic (organic and inorganic)) is able to normalize the activity of AO enzymes and the general status of the body. Organic selenium compounds have a high bioavailability and, depending on their concentration, can act both as selenium donors to prevent selenium deficiency and as antitumor drugs due to their toxicity and participation in the regulation of signaling pathways of apoptosis. Known selenorganic compounds diphenyldiselenide and ethaselen share similarity with the Russian organo selenium compound, diacetophenonylselenide (DAPS-25), which serves as a source of bioavailable selenium, exhibits a wide range of biological activity, including antioxidant activity, that governs cell redox balance, inflammation and apoptosis regulation.

Quantitative Proteomics Analysis of Barley-Based Liquid Feed and the Effect of Protease Inhibitors and NADPH-Dependent Thioredoxin Reductase/Thioredoxin (NTR/Trx) System.

Liquid feeding strategies have been devised with the aim of enhancing grain nutrient availability for livestock. It is characterized by a steeping/soaking period that softens the grains and initiates mobilization of seed storage reserves. The present study uses 2D gel-based proteomics to investigate the role of proteolysis and reduction by thioredoxins over a 48 h steeping period by monitoring protein abundance dynamics in barley-based liquid feed samples supplemented with either protease inhibitors or NADPH-dependent thioredoxin reductase/thioredoxin (NTR/Trx). Several full-length storage proteins were only identified in the water-extractable fraction of feed containing protease inhibitors, illustrating significant inhibition of proteolytic activities arising during the steeping period. Application of functional NTR/Trx to liquid feed reductively increased the solubility of known and potentially new Trx-target proteins, e.g., outer membrane protein X, and their susceptibility to proteolysis. Thus, the NTR/Trx system exhibits important potential as a feed additive to enhance nutrient digestibility in monogastric animals.

Targeting the Thioredoxin System as a Strategy for Cancer Therapy.

Thioredoxin reductase (TrxR) participates in the regulation of redox reactions in organisms. It works mainly via its substrate molecule, thioredoxin, to maintain the redox balance and regulate signal transduction, which controls cell proliferation, differentiation, death, and other important physiological processes. In recent years, increasing evidence has shown that the overactivation of TrxR is related to the development of tumors. The exploration of TrxR-targeted antitumor drugs has attracted wide attention and is expected to provide new therapies for cancer treatment. In this perspective, we highlight the specific relationship between TrxR and apoptotic signaling pathways. The cytoplasm and mitochondria both contain TrxR, resulting in the activation of apoptosis. TrxR activity influences reactive oxygen species (ROS) and further regulates the inflammatory signaling pathway. In addition, we discuss representative TrxR inhibitors with anticancer activity and analyze the challenges in developing TrxR inhibitors as anticancer drugs.

Thimerosal inhibits Drosophila melanogaster tyrosine hydroxylase (DmTyrH) leading to changes in dopamine levels and impaired motor behavior: implications for neurotoxicity.

Thimerosal (THIM) is a well-established antifungal and antiseptic agent widely used as a preservative in vaccines. Recent studies identified the neurotoxic effects of THIM, including malfunction of the monoaminergic system. However, the underlying cytotoxic mechanisms are not well understood. Here we used the fruit fly Drosophila melanogaster to investigate the mechanisms of THIM-induced neurotoxicity. We focused on the dopaminergic system, and the rate-limiting enzyme tyrosine hydroxylase (DmTyrH), to test the hypothesis that THIM can impair dopamine (DA) homeostasis and subsequently cause dysfunction. We studied the effect of THIM by feeding 1-2 day old flies (both sexes) food supplemented with 25 µM THIM for 4 days and determined THIM-induced effects on survival, oxidative stress, and metabolic activity based on MTT assay and acetylcholinesterase (AChE) activity. Our results demonstrate that D. melanogaster exposed to THIM present changes in DmTyrH expression and activity, together with altered DA levels that led to impaired motor behavior. These phenotypes were accompanied by an increase in oxidative stress, with a decrease in MTT reduction, in AChE activity, and also in survival rate. These findings suggest an initiating and primary role for THIM-mediated DmTyrH dysfunction that leads to impaired DA function and behavioral abnormalities, ultimately causing oxidative stress-related neurotoxicity.

Expression of Selenoprotein Genes and Association with Selenium Status in Colorectal Adenoma and Colorectal Cancer.

Dietary selenium (Se) intake is essential for synthesizing selenoproteins that are important in countering oxidative and inflammatory processes linked to colorectal carcinogenesis. However, there is limited knowledge on the selenoprotein expression in colorectal adenoma (CRA) and colorectal cancer (CRC) patients, or the interaction with Se status levels. We studied the expression of seventeen Se pathway genes (including fifteen of the twenty-five human selenoproteins) in RNA extracted from disease-normal colorectal tissue pairs, in the discovery phase of sixty-two CRA/CRC patients from Ireland and a validation cohort of a hundred and five CRC patients from the Czech Republic. Differences in transcript levels between the disease and paired control mucosa were assessed by the Mann-Whitney U-test. GPX2 and TXNRD3 showed a higher expression and GPX3, SELENOP, SELENOS, and SEPHS2 exhibited a lower expression in the disease tissue from adenomas and both cancer groups (p-values from 0.023 to <0.001). In the Czech cohort, up-regulation of GPX1, SELENOH, and SOD2 and down-regulation of SELENBP1, SELENON, and SELENOK (p-values 0.036 to <0.001) was also observed. We further examined the correlation of gene expression with serum Se status (assessed by Se and selenoprotein P, SELENOP) in the Irish patients. While there were no significant correlations with both Se status markers, SELENOF, SELENOK, and TXNRD1 tumor tissue expression positively correlated with Se, while TXNRD2 and TXNRD3 negatively correlated with SELENOP. In an analysis restricted to the larger Czech CRC patient cohort, Cox regression showed no major association of transcript levels with patient survival, except for an association of higher SELENOF gene expression with both a lower disease-free and overall survival. Several selenoproteins were differentially expressed in the disease tissue compared to the normal tissue of both CRA and CRC patients. Altered selenoprotein expression may serve as a marker of functional Se status and colorectal adenoma to cancer progression.

Xanthatin Promotes Apoptosis via Inhibiting Thioredoxin Reductase and Eliciting Oxidative Stress.

Xanthatin (XT), a naturally occurring sesquiterpene lactone presented in cocklebur ( Xanthium strumarium L.), is under development as a potential anticancer agent. Despite the promising anticancer effect of XT, the molecular mechanism underlying its cellular action has not been well elucidated. The mammalian thioredoxin reductase (TrxR) enzymes, the essential seleno-flavoproteins containing a penultimate selenocysteine (Sec) residue at the C-terminus, represent a promising target for cancer chemotherapeutic agents. In this study, XT inhibits both the purified TrxR and the enzyme in cells. The possible binding mode of XT with the TrxR protein is predicted by the covalent docking method. Mechanism studies reveal that XT targets the Sec residue of TrxR and inhibits the enzyme activity irreversibly. Simultaneously, the inhibition of TrxR by XT promotes the oxidative stress-mediated apoptosis of HeLa cells. Importantly, the knockdown of the enzyme sensitizes the cells to XT treatment. Targeting TrxR thus discloses a novel molecular mechanism in accounting for the cellular action of XT and provides insights into the development of XT as an anticancer agent.

Neuroprotective mechanisms of sildenafil and selenium in PTZ-kindling model: Implications in epilepsy.

Epilepsy is one of the furthermost common neurodegenerative diseases affecting above 50 million individuals worldwide. The pathogenesis of epileptic seizures is not satisfactorily explored, and hence more effective anti-convulsive therapies are indispensable. Current study aimed to investigate the mechanisms of the potential neuroprotective effects of sildenafil/selenium on chemically-induced convulsions in mice. Kindling model was induced using pentylenetetrazol (PTZ; 35 mg/Kg, 11 doses, intraperitoneally, every other day). PTZ-insulted groups were treated intraperitoneally with sildenafil (20 mg/Kg), selenium (0.2 mg/Kg) or their combination; 30 min before PTZ administration. PTZ-kindled model showed a significant loss of neuronal cells concurrently with nitrative/oxidative stress and lipid peroxidation. This was associated with enhanced expression of inducible nitric oxide synthase (iNOS), hemeoxygenase-1 (HO-1) and vascular endothelial growth factor (VEGF) along with increased activity of thioredoxin reductase (TrxR) in hippocampal tissue. Individual treatment with sildenafil or selenium showed partial neuroprotection, simultaneously with lower hippocampal expression of 4-hydroneonenal (4-HNE), nitrotyrosine, iNOS and HO-1, yet without reaching normal levels. Sildenafil, but not selenium, enhanced the expression of VEGF and the endothelial cell marker CD34. The joint treatment with sildenafil and selenium preserved hippocampal neuronal count, improved kindling score, blunted lipid peroxides and nitrotyrosine levels, concomitantly with iNOS inhibition, normalization of TrxR activity and HO-1 expression, and evident neo-angiogenesis. Current study demonstrated the roles of several central signalling cascades in the sildenafil/selenium-evoked neuroprotection represented in, at least in part, amelioration of nitrative/oxidative stress alongside modulation of angiogenesis. Thus, sildenafil combined with selenium could be repurposed as a potential therapeutic regimen for delaying epilepsy progression.