Inhibition of glutathione synthesis eliminates the adaptive response of ascitic hepatoma 22 cells to nedaplatin that targets thioredoxin reductase

Buthionine sulfoximine and chemoresistance in cancer treatments: a systematic review with meta-analysis of preclinical studies

Buthionine sulfoximine (BSO) is a synthetic amino acid that blocks the biosynthesis of reduced glutathione (GSH), an endogenous antioxidant cellular component present in tumor cells. GSH levels have been associated with tumor cell resistance to chemotherapeutic drugs and platinum compounds. Consequently, by depleting GSH, BSO enhances the cytotoxicity of chemotherapeutic agents in drug-resistant tumors. Therefore, the aim of this study was to conduct a systematic review with meta-analysis of preclinical studies utilizing BSO in cancer treatments. The systematic search was carried out using the following databases: PubMed, Web of Science, Scopus, and EMBASE up until March 20, 2023, in order to collect preclinical studies that evaluated BSO, alone or in association, as a strategy for antineoplastic therapy. One hundred nine investigations were found to assess the cytotoxic potential of BSO alone or in combination with other compounds. Twenty-one of these met the criteria for performing the meta-analysis. The evidence gathered indicated that BSO alone exhibits cytotoxic activity. However, this compound is generally used in combination with other antineoplastic strategies, mainly chemotherapy ones, to improve cytotoxicity to carcinogenic cells and treatment efficacy. Finally, this review provides important considerations regarding BSO use in cancer treatment conditions, which might optimize future studies as a potential adjuvant antineoplastic therapeutic tool.

The Role of Selenium Nanoparticles in the Treatment of Liver Pathologies of Various Natures

The liver is the body's largest gland, and regulates a wide variety of physiological processes. The work of the liver can be disrupted in a variety of pathologies, the number of which is several hundred. It is extremely important to monitor the health of the liver and develop approaches to combat liver diseases. In recent decades, nanomedicine has become increasingly popular in the treatment of various liver pathologies, in which nanosized biomaterials, which are inorganic, polymeric, liposomal, albumin, and other nanoparticles, play an important role. Given the need to develop environmentally safe, inexpensive, simple, and high-performance biomedical agents for theragnostic purposes and showing few side effects, special attention is being paid to nanoparticles based on the important trace element selenium (Se). It is known that the metabolism of the microelement Se occurs in the liver, and its deficiency leads to the development of several serious diseases in this organ. In addition, the liver is the depot for most selenoproteins, which can reduce oxidative stress, inhibit tumor growth, and prevent other liver damage. This review is devoted to the description of the results of recent years, revealing the important role of selenium nanoparticles in the therapy and diagnosis of several liver pathologies, depending on the dose and physicochemical properties. The possibilities of selenium nanoparticles in the treatment of liver diseases, disclosed in the review, will not only reveal the advantages of their hepatoprotective properties but also significantly supplement the data on the role of the trace element selenium in the regulation of these diseases.

(-)-Epigallocatechin-3-Gallate Attenuates the Adverse Reactions Triggered by Selenium Nanoparticles without Compromising Their Suppressing Effect on Peritoneal Carcinomatosis in Mice Bearing Hepatocarcinoma 22 Cells

Increasing evidence shows that selenium and polyphenols are two types of the most reported compounds in tumor chemoprevention due to their remarkable antitumor activity and high safety profile. The cross-talk between polyphenols and selenium is a hot research topic, and the combination of polyphenols and selenium is a valuable strategy for fighting cancer. The current work investigated the combination anti-peritoneal carcinomatosis (PC) effect of selenium nanoparticles (SeNPs) and green tea (Camellia sinensis) polyphenol (-)-epigallocatechin-3-gallate (EGCG) in mice bearing murine hepatocarcinoma 22 (H22) cells. Results showed that SeNPs alone significantly inhibited cancer cell proliferation and extended the survival time of mice bearing H22 cells. Still, the potential therapeutic efficacy is accompanied by an approximately eighty percent diarrhea rate. When EGCG was combined with SeNPs, EGCG did not affect the tumor proliferation inhibition effect but eliminated diarrhea triggered by SeNPs. In addition, both the intracellular selectively accumulated EGCG without killing effect on cancer cells and the enhanced antioxidant enzyme levels in ascites after EGCG was delivered alone by intraperitoneal injection indicated that H22 cells were insensitive to EGCG. Moreover, EGCG could prevent SeNP-caused systemic oxidative damage by enhancing serum superoxide dismutase, glutathione, and glutathione peroxidase levels in healthy mice. Overall, we found that H22 cells are insensitive to EGCG, but combining EGCG with SeNPs could protect against SeNP-triggered diarrhea without compromising the suppressing efficacy of SeNPs on PC in mice bearing H22 cells and attenuate SeNP-caused systemic toxicity in healthy mice. These results suggest that EGCG could be employed as a promising candidate for preventing the adverse reactions of chemotherapy including chemotherapy-induced diarrhea and systemic toxicity in cancer individuals.

Olean-28,13b-olide 2 plays a role in cisplatin-mediated apoptosis and reverses cisplatin resistance in human lung cancer through multiple signaling pathways

Lung cancer, similar to other chronic diseases, occurs due to perturbations in multiple signaling pathways. Mono-targeted therapies are not ideal since they are not likely to be effective for the treatment and prevention of lung cancer, and are often associated with drug resistance. Therefore, the development of multi-targeted agents is required for novel lung cancer therapies. Thioredoxin reductase (TrxR or TXNRD1) is a pivotal component of the thioredoxin (Trx) system. Various types of tumor cells are able to overexpress TrxR/Trx proteins in order to maintain tumor survival, and this overexpression has been shown to be associated with clinical outcomes, including irradiation and drug resistance. Emerging evidence has indicated that oleanolic acid (OA) and its derivatives exhibit potent anticancer activity, and are able to overcome drug resistance in cancer cell lines. In the present study, it was demonstrated that a novel synthesized OA family compound, olean-28,13b-olide 2 (OLO-2), synergistically enhanced cisplatin (CDDP)-mediated apoptosis, led to the activation of caspase-3 and the generation of reactive oxygen species (ROS), induced DNA damage, and inhibited the activation of the extracellular-signal-regulated kinase (ERK), signal transducer and activator of transcription 3 (STAT3), AKT and nuclear factor-κB (NF-κB) pathways in human multidrug-resistant A549/CDDP lung adenocarcinoma cells. Subsequent analyses revealed that OLO-2 inhibited P-glycoprotein (P-gp or ABCB1) and TrxR by reducing their expression at the protein and mRNA levels, and by suppressing P-gp ATPase and TrxR activities. Further biological evaluation indicated that OLO-2 significantly reduced Trx and excision repair cross-complementary1 (ERCC1) protein expression and significantly inhibited the proliferation of drug-sensitive (A549) and multidrug-resistant (A549/CDDP) non-small cell lung cancer (NSCLC) cells, but had no effect on non-tumor lung epithelial-like cells. In addition, the present study demonstrated, for the first time, to the best of our knowledge, that overexpressing or knocking down TrxR in NSCLC cells enhanced or attenuated, respectively, the resistance of NSCLC cells against CDDP, which indicated that TrxR plays an important role in CDDP resistance and functions as a protector of NSCLC against chemotherapeutic drugs. OLO-2 treatment also exhibited up to 4.6-fold selectivity against human lung adenocarcinoma cells. Taken together, the results of the present study shed light on the drug resistance-reversing effects of OLO-2 in lung cancer cells.

Glutathione de novo synthesis but not recycling process coordinates with glutamine catabolism to control redox homeostasis and directs murine T cell differentiation

Upon antigen stimulation, T lymphocytes undergo dramatic changes in metabolism to fulfill the bioenergetic, biosynthetic and redox demands of proliferation and differentiation. Glutathione (GSH) plays an essential role in controlling redox balance and cell fate. While GSH can be recycled from Glutathione disulfide (GSSG), the inhibition of this recycling pathway does not impact GSH content and murine T cell fate. By contrast, the inhibition of the de novo synthesis of GSH, by deleting either the catalytic (Gclc) or the modifier (Gclm) subunit of glutamate-cysteine ligase (Gcl), dampens intracellular GSH, increases ROS, and impact T cell differentiation. Moreover, the inhibition of GSH de novo synthesis dampened the pathological progression of experimental autoimmune encephalomyelitis (EAE). We further reveal that glutamine provides essential precursors for GSH biosynthesis. Our findings suggest that glutamine catabolism fuels de novo synthesis of GSH and directs the lineage choice in T cells.

Metabolic Reprogramming in Modulating T Cell Reactive Oxygen Species Generation and Antioxidant Capacity

A robust adaptive immune response requires a phase of proliferative burst which is followed by the polarization of T cells into relevant functional subsets. Both processes are associated with dramatically increased bioenergetics demands, biosynthetic demands, and redox demands. T cells meet these demands by rewiring their central metabolic pathways that generate energy and biosynthetic precursors by catabolizing and oxidizing nutrients into carbon dioxide. Simultaneously, oxidative metabolism also produces reactive oxygen species (ROS), which are tightly controlled by antioxidants and plays important role in regulating T cell functions. In this review, we discuss how metabolic rewiring during T cell activation influence ROS production and antioxidant capacity.

Flavored black ginseng exhibited antitumor activity via improving immune function and inducing apoptosis

Flavored black ginseng rich in ginsenoside F2, Rg5 and protopanaxadiol exhibited antitumor activity via improving immune function and inducing apoptosis.

Epigallocatechin-3-gallate enhances key enzymatic activities of hepatic thioredoxin and glutathione systems in selenium-optimal mice but activates hepatic Nrf2 responses in selenium-deficient mice

Selenium participates in the antioxidant defense mainly through a class of selenoproteins, including thioredoxin reductase. Epigallocatechin-3-gallate (EGCG) is the most abundant and biologically active catechin in green tea. Depending upon the dose and biological systems, EGCG may function either as an antioxidant or as an inducer of antioxidant defense via its pro-oxidant action or other unidentified mechanisms. By manipulating the selenium status, the present study investigated the interactions of EGCG with antioxidant defense systems including the thioredoxin system comprising of thioredoxin and thioredoxin reductase, the glutathione system comprising of glutathione and glutathione reductase coupled with glutaredoxin, and the Nrf2 system. In selenium-optimal mice, EGCG increased hepatic activities of thioredoxin reductase, glutathione reductase and glutaredoxin. These effects of EGCG appeared to be not due to overt pro-oxidant action because melatonin, a powerful antioxidant, did not influence the increase. However, in selenium-deficient mice, with low basal levels of thioredoxin reductase 1, the same dose of EGCG did not elevate the above-mentioned enzymes; intriguingly EGCG in turn activated hepatic Nrf2 response, leading to increased heme oxygenase 1 and NAD(P)H:quinone oxidoreductase 1 protein levels and thioredoxin activity. Overall, the present work reveals that EGCG is a robust inducer of the Nrf2 system only in selenium-deficient conditions. Under normal physiological conditions, in selenium-optimal mice, thioredoxin and glutathione systems serve as the first line defense systems against the stress induced by high doses of EGCG, sparing the activation of the Nrf2 system.

•

EGCG increases hepatic activities of TrxR, GR and Grx in selenium-optimal mice.

•

EGCG fails to manipulate the above-mentioned enzymes in selenium-deficient mice.

•

EGCG in turn activates hepatic Nrf2 response in selenium-deficient mice.

•

Selenium deficiency does not increase EGCG toxicity due to potent Nrf2 response.

Serum thioredoxin reductase is highly increased in mice with hepatocellular carcinoma and its activity is restrained by several mechanisms

Increased thioredoxin reductase (TrxR) levels in serum were recently identified as possible prognostic markers for human prostate cancer or hepatocellular carcinoma. We had earlier shown that serum levels of TrxR protein are very low in healthy mice, but can in close correlation to alanine aminotransferase (ALT) increase more than 200-fold upon chemically induced liver damage. We also found that enzymatic TrxR activity in serum is counteracted by a yet unidentified oxidase activity in serum. In the present study we found that mice carrying H22 hepatocellular carcinoma tumors present highly increased levels of TrxR in serum, similarly to that reported in human patients. In this case ALT levels did not parallel those of TrxR. We also discovered here that the TrxR-antagonistic oxidase activity in serum is due to the presence of quiescin Q6 sulfhydryl oxidase 1 (QSOX1). We furthermore found that the chemotherapeutic agents cisplatin or auranofin, when given systemically to H22 tumor bearing mice, can further inhibit TrxR activities in serum. The TrxR serum activity was also inhibited by endogenous electrophilic inhibitors, found to increase in tumor-bearing mice and to include protoporphyrin IX (PpIX) and 4-hydroxynonenal (HNE). Thus, hepatocellular carcinoma triggers high levels of serum TrxR that are not paralleled by ALT, and TrxR enzyme activity in serum is counteracted by several different mechanisms. The physiological role of TrxR in serum, if any, as well as its potential value as a prognostic marker for tumor progression, needs to be studied further.

TrxR1 as a potent regulator of the Nrf2-Keap1 response system

SIGNIFICANCE

All cells must maintain a balance between oxidants and reductants, while allowing for fluctuations in redox states triggered by signaling, altered metabolic flow, or extracellular stimuli. Furthermore, they must be able to rapidly sense and react to various challenges that would disrupt the redox homeostasis.

RECENT ADVANCES

Many studies have identified Keap1 as a key sensor for oxidative or electrophilic stress, with modification of Keap1 by oxidation or electrophiles triggering Nrf2-mediated transcriptional induction of enzymes supporting reductive and detoxification pathways. However, additional mechanisms for Nrf2 regulation are likely to exist upstream of, or in parallel with, Keap1.

CRITICAL ISSUES

Here, we propose that the mammalian selenoprotein thioredoxin reductase 1 (TrxR1) is a potent regulator of Nrf2. A high chemical reactivity of TrxR1 and its vital role for the thioredoxin (Trx) system distinguishes TrxR1 as a prime target for electrophilic challenges. Chemical modification of the selenocysteine (Sec) in TrxR1 by electrophiles leads to rapid inhibition of thioredoxin disulfide reductase activity, often combined with induction of NADPH oxidase activity of the derivatized enzyme, thereby affecting many downstream redox pathways. The notion of TrxR1 as a regulator of Nrf2 is supported by many publications on effects in human cells of selenium deficiency, oxidative stress or electrophile exposure, as well as the phenotypes of genetic mouse models.

FUTURE DIRECTIONS

Investigation of the role of TrxR1 as a regulator of Nrf2 activation will facilitate further studies of redox control in diverse cells and tissues of mammals, and possibly also in animals of other classes.

Polyphenols as mitochondria-targeted anticancer drugs

Mitochondria are the respiratory and energetic centers of the cell where multiple intra- and extracellular signal transduction pathways converge leading to dysfunction of those organelles and, consequently, apoptotic or/and necrotic cell death. Mitochondria-targeted anticancer drugs are referred to as mitocans; they have recently been classified by Neuzil et al. (2013) according to their molecular mode of action into: hexokinase inhibitors; mimickers of the Bcl-2 homology-3 (BH3) domains; thiol redox inhibitors; deregulators of voltage-dependent anionic channel (VDAC)/adenine nucleotide translocase (ANT) complex; electron redox chain-targeting agents; lipophilic cations targeting the mitochondrial inner membrane; tricarboxylic acid cycle-targeting agents; and mitochondrial DNA-targeting agents. Polyphenols of plant origin and their synthetic or semisynthetic derivatives exhibit pleiotropic biological activities, including the above-mentioned modes of action characteristic of mitocans. Some of them have already been tested in clinical trials. Gossypol has served as a lead compound for developing more efficient BH3 mimetics such as ABT-737 and its orally available structural analog ABT-263 (Navitoclax). Furthermore, mitochondriotropic derivatives of phenolic compounds such as quercetin and resveratrol have been synthesized and reported to efficiently induce cancer cell death in vitro.

Green tea polyphenol (-)-epigallocatechin-3-gallate triggered hepatotoxicity in mice: responses of major antioxidant enzymes and the Nrf2 rescue pathway

(-)-Epigallocatechin-3-gallate (EGCG), a constituent of green tea, has been suggested to have numerous health-promoting effects. On the other hand, high-dose EGCG is able to evoke hepatotoxicity. In the present study, we elucidated the responses of hepatic major antioxidant enzymes and nuclear factor erythroid 2-related factor 2 (Nrf2) rescue pathway to high-dose levels of EGCG in Kunming mice. At a non-lethal toxic dose (75mg/kg, i.p.), repeated EGCG treatments markedly decreased the levels of superoxide dismutase, catalase, and glutathione peroxidase. As a rescue response, the nuclear distribution of Nrf2 was significantly increased; a battery of Nrf2-target genes, including heme oxygenase 1 (HO1), NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione S-transferase (GST), and those involved in glutathione and thioredoxin systems, were all up-regulated. At the maximum tolerated dose (45mg/kg, i.p.), repeated EGCG treatments did not disturb the major antioxidant defense. Among the above-mentioned genes, only HO1, NQO1, and GST genes were significantly but modestly up-regulated, suggesting a comprehensive and extensive activation of Nrf2-target genes principally occurs at toxic levels of EGCG. At a lethal dose (200mg/kg, i.p.), a single EGCG treatment dramatically decreased not only the major antioxidant defense but also the Nrf2-target genes, demonstrating that toxic levels of EGCG are able to cause a biphasic response of Nrf2. Overall, the mechanism of EGCG-triggered hepatotoxicity involves suppression of major antioxidant enzymes, and the Nrf2 rescue pathway plays a vital role for counteracting EGCG toxicity.

Selenoproteins and selenium status in bone physiology and pathology

BACKGROUND

Emerging evidence supports the view that selenoproteins are essential for maintaining bone health.

SCOPE OF REVIEW

The current state of knowledge concerning selenoproteins and Se status in bone physiology and pathology is summarized.

MAJOR CONCLUSIONS

Antioxidant selenoproteins including glutathione peroxidase (GPx) and thioredoxin reductase (TrxR), as a whole, play a pivotal role in maintaining bone homeostasis and protecting against bone loss. GPx1, a major antioxidant enzyme in osteoclasts, is up-regulated by estrogen, an endogenous inhibitor of osteoclastogenesis. TrxR1 is an immediate early gene in response to 1α,25-dihydroxyvitamin D3, an osteoblastic differentiation agent. The combination of 1α,25-dihydroxyvitamin D3 and Se generates a synergistic elevation of TrxR activity in Se-deficient osteoblasts. Of particular concern, pleiotropic TrxR1 is implicated in promoting NFκB activation. Coincidentally, TrxR inhibitors such as curcumin and gold compounds exhibit potent osteoclastogenesis inhibitory activity. Studies in patients with the mutations of selenocysteine insertion sequence-binding protein 2, a key trans-acting factor for the co-translational insertion of selenocysteine into selenoproteins have clearly established a causal link of selenoproteins in bone development. Se transport to bone relies on selenoprotein P. Plasma selenoprotein P concentrations have been found to be positively correlated with bone mineral density in elderly women.

GENERAL SIGNIFICANCE

A full understanding of the role and function of selenoproteins and Se status on bone physiology and pathology may lead to effectively prevent against or modify bone diseases by using Se.

The thioredoxin antioxidant system

The thioredoxin (Trx) system, which is composed of NADPH, thioredoxin reductase (TrxR), and thioredoxin, is a key antioxidant system in defense against oxidative stress through its disulfide reductase activity regulating protein dithiol/disulfide balance. The Trx system provides the electrons to thiol-dependent peroxidases (peroxiredoxins) to remove reactive oxygen and nitrogen species with a fast reaction rate. Trx antioxidant functions are also shown by involvement in DNA and protein repair by reducing ribonucleotide reductase, methionine sulfoxide reductases, and regulating the activity of many redox-sensitive transcription factors. Moreover, Trx systems play critical roles in the immune response, virus infection, and cell death via interaction with thioredoxin-interacting protein. In mammalian cells, the cytosolic and mitochondrial Trx systems, in which TrxRs are high molecular weight selenoenzymes, together with the glutathione-glutaredoxin (Grx) system (NADPH, glutathione reductase, GSH, and Grx) control the cellular redox environment. Recently mammalian thioredoxin and glutathione systems have been found to be able to provide the electrons crossly and to serve as a backup system for each other. In contrast, bacteria TrxRs are low molecular weight enzymes with a structure and reaction mechanism distinct from mammalian TrxR. Many bacterial species possess specific thiol-dependent antioxidant systems, and the significance of the Trx system in the defense against oxidative stress is different. Particularly, the absence of a GSH-Grx system in some pathogenic bacteria such as Helicobacter pylori, Mycobacterium tuberculosis, and Staphylococcus aureus makes the bacterial Trx system essential for survival under oxidative stress. This provides an opportunity to kill these bacteria by targeting the TrxR-Trx system.

PX-12-induced HeLa cell death is associated with oxidative stress and GSH depletion

PX-12, as an inhibitor of thioredoxin (Trx), has antitumor activity. However, little is known about the toxicological effect of PX-12 on cervical cancer cells. In the present study, the growth inhibitory effects of PX-12 on HeLa cervical cancer cells in association with reactive oxygen species (ROS) and glutathione (GSH) levels were investigated. Based on MTT assays, PX-12 inhibited the growth of HeLa cells with an IC₅₀ value of ~7 μM at 72 h. DNA flow cytometry analysis indicated that 5 and 10 μM PX-12 significantly induced a G2/M phase arrest of the cell cycle. PX-12 also increased the number of dead cells and annexin V-fluorescein isothiocyanate-positive cells, which was accompanied by the loss of mitochondrial membrane potential. All the investigated caspase inhibitors significantly rescued certain cells from PX-12-induced HeLa cell death. With respect to ROS and GSH levels, PX-12 increased ROS levels (including O₂^•-) in HeLa cells and induced GSH depletion. N-acetyl cysteine markedly reduced the levels of O₂^•- in PX-12-treated HeLa cells, and prevented apoptotic cell death and GSH depletion in these cells. By contrast, L-buthionine sulfoximine intensified cell death and GSH depletion in PX-12-treated HeLa cells. To conclude, this is the first study to demonstrate that PX-12 inhibits the growth of HeLa cells via G2/M phase arrest, as well as inhibiting apoptosis; the effect was associated with intracellular increases in ROS levels and GSH depletion.