Increased levels of cytosolic thioredoxin reductase activity and mRNA in rat liver nodules

A new gold(I) phosphine complex induces apoptosis in prostate cancer cells by increasing reactive oxygen species

Thioredoxin reductase (TrxR) is a pivotal regulator of redox homeostasis. It is frequently overexpressed in various cancer cells, including prostate cancer, making it a promising target for the development of anti-cancer drugs. In this study, we screened a series of newly designed complexes of gold(I) phosphine. Specifically, Compound 5 exhibited the highest cytotoxicity against prostate cancer cells and demonstrated stronger antitumor effects than commonly used drugs, such as cisplatin and auranofin. Importantly, our mechanistic study revealed that Compound 5 effectively inhibits the TrxR system in vitro. Additionally, Compound 5 promoted intracellular accumulation of reactive oxygen species (ROS), leading to mitochondrial dysfunction and irreversible apoptosis in prostate cancer cells. Our in vivo xenograft study further demonstrated that Compound 5 has excellent antitumor activity against prostate cancer cells, but does not cause severe side effects. These findings provide a promising lead Compound for the development of novel antitumor agents targeting prostate cancer and offer a valuable tool for investigating biological pathways involving TrxR and ROS modulation.

A new rhodium(I) NHC complex inhibits TrxR: In vitro cytotoxicity and in vivo hepatocellular carcinoma suppression

Thioredoxin reductase (TrxR) is often overexpressed in different types of cancer cells including hepatocellular carcinoma (HCC) cells and regarded as a target with great promise for anticancer drug research and development. Here, we have synthesized and characterized nine new designed rhodium(I) N-heterocyclic carbene (NHC) complexes. All of them were effective towards cancer cells, especially complex 1e was more active than cisplatin and manifested strong antiproliferative activity against HCC cells. In vivo anticancer studies showed that 1e significantly repressed tumor growth in an HCC nude mouse model and ameliorated liver lesions in a chronic HCC model caused by CCl₄. Notably, a mechanistic study revealed that 1e can strongly inhibit TrxR system both in vitro and in vivo. Furthermore, 1e promoted intracellular ROS accumulation, damaged mitochondrial membrane potential, promoted cancer cell apoptosis and blocked the cells in the G1 phase.

Butaselen prevents hepatocarcinogenesis and progression through inhibiting thioredoxin reductase activity

Hepatocellular carcinoma (HCC) accounts for most of primary liver cancer, of which five-year survival rate remains low and chemoprevention has become a strategy to reduce disease burden of HCC. We aim to explore the in vivo chemopreventive effect of an organoselenium-containing compound butaselen (BS) against hepatocarcinogenesis and its underlying mechanisms. Pre- and sustained BS treatment (9, 18 and 36mg/Kg BS) could dose-dependently inhibit chronic hepatic inflammation, fibrosis, cirrhosis and HCC on murine models with 24 weeks treatment scheme. The thioredoxin reductase (TrxR), NF-κB pathway and pro-inflammatory factors were activated during hepatocarcinogenesis, while their expression were decreased by BS treatment. BS treatment could also significantly reduce tumor volume in H22-bearing models and remarkably slow tumor growth. HCC cell lines HepG2, Bel7402 and Huh7 were time- and dose-dependently inhibited by BS treatment. G2/M arrest and apoptosis were observed in HepG2 cells after BS treatment, which were mediated by TrxR/Ref-1 and NF-κB pathways inhibition. BS generated reactive oxygen species (ROS), which could be reduced by antioxidant N-acetyl-L-cysteine (NAC) and NADPH oxidase inhibitor DPI. NAC could markedly increase HepG2 cells viability. TrxR activity of HepG2 cells treated with BS were significantly decreased in parallel with proliferative inhibition. The TrxR1-knockdown HepG2 cells also exhibited low TrxR1 activity, high ROS level, relatively low proliferation rate and increased resistance to BS treatment. In conclusion, BS can prevent hepatocarcinogenesis through inhibiting chronic inflammation, cirrhosis and tumor progression. The underlying mechanisms may include TrxR activity inhibition, leading to ROS elevation, G2/M arrest and apoptosis.

Prenatal expression of thioredoxin reductase 1 (TRXR1) and microsomal glutathione transferase 1 (MGST1) in humans

Thioredoxin reductase 1 (TRXR1) and microsomal glutathione transferase 1 (MGST1) are important redox and detoxifying enzymes in adult life. The aim of this study was to investigate the expression of these enzymes during fetal life. In addition, the role of gene methylation was studied since this might play an important role in the on-and-off switch of gene expression between fetal and adult life. To this end, the expression of the TRXR1-encoding gene TXNRD1 and the MGST1-encoding gene MGST1 was studied in fetal tissues. The mean mRNA expression of TXNRD1 in fetal livers were seven times higher compared to the mean expression in adult livers (p < 0.001). Of the six studied splice variants of TXNRD1, four had a significantly higher expression in the fetal livers as compared to adult livers. The mean expression of MGST1 was twofold higher in adult compared to fetal liver tissue (p = 0.01). For MGST1 the alternative first exon 1B was the predominant splice variant in both fetal and adult liver samples. The highest mRNA expression of both TXNRD1 and MGST1 was found in fetal adrenals, whereas expression was lower in fetal liver, lungs and kidneys. There was a significant correlation between the hepatic expression of TXNRD1 and MGST1. Treatment with the demethylating agent 5-AZA resulted in decreased levels of TXNRD1 in human liver HepG2 cells but did not affect the expression of MGST1. In conclusion, the expression of TXNRD1 is higher in fetuses than in adults and might be of importance during fetal life. Hepatic TXNRD1 and MGST1 are co-expressed in both fetuses and adults suggesting common regulatory mechanisms.

Statin treatment reduces the risk of hepatocellular carcinoma but not colon cancer-results from a nationwide case-control study in Sweden

BACKGROUND

Several studies have indicated that statins may have anticarcinogenic effects. The aim of the present study was to investigate if statin treatment was associated with a reduced risk of hepatocellular carcinoma (HCC) or colon cancer.

METHODS

A nationwide case-control study was carried out in which all cases of HCC and colon cancer in the Swedish population above 40 years of age between 1 July 2006 and 31 December 2010 were identified in the Swedish Cancer Register. For every case, five controls were selected and matched on age and sex. Data on statin use was extracted from the Swedish Prescribed Drug Register. We estimated risks using conditional logistic regression and adjusted for educational level, concomitant medications and comorbidity.

RESULTS

Identified were 3994 cases of HCC and matched with 19.970 controls, and 21.143 cases of colon cancer were identified and matched with 105.715 controls. In the adjusted analysis, the odds ratio (OR) for HCC among statin users was 0.88 (95% confidence interval (CI) 0.81-0.96), and the OR for colon cancer was 1.04 (95%CI 1.00-1.08) compared with non-users.

CONCLUSION

Statin use was associated with a modest decreased risk of HCC but did not influence the risk of colon cancer. Future randomized placebo-controlled trials in HCC high-risk patients are warranted to further investigate the possible prophylactic effect of statins in HCC.

Impact of zinc, selenium and lycopene on capsaicin induced mutagenicity and oxidative damage in mice

Capsaicin is employed as a condiment and colorant in the cosmetic and pharmaceutical industries. Metabolism of capsaicin produces reactive phenoxy radicals, which inflict damage to DNA. Micronutrients such as zinc and selenium facilitate the expression of tissue repair factors, and lycopene has natural antioxidant action. The current study investigated the possible protective role of zinc, selenium and lycopene singly and in combination in ameliorating capsaicin induced mutagenicity. Fifty four Swiss albino mice received the vehicle, zinc (10 mg/kg), selenium (2 mg/kg), lycopene (2 mg/kg) alone, capsaicin alone (2 mg/kg), and capsaicin along with zinc (10mg/kg), selenium (2 mg/kg) and lycopene (2 mg/kg) in combination by the oral route for 32 days. Animals were killed 24 h after the last treatment, and micronuclei formation in bone marrow and peripheral blood were assessed. Antioxidant status in plasma, the total protein, nucleic acids, and DNA fragmentation was assessed in the liver homogenate. Capsaicin substantially damaged nuclear material and increased oxidative stress. Individual therapy with lycopene was most effective in reducing micronuclei formation, lipid peroxidation, and in augmenting ferric reducing ability of plasma. This was closely followed by zinc and selenium. Zinc protected against DNA fragmentation followed by lycopene and selenium. The combination therapy was effective over individual treatment against DNA fragmentation, micronuclei and malondialdehyde formation. The combination did not exert a substantial benefit over individual therapy in enhancing the total antioxidant ability of plasma. The risk of capsaicin induced mutagenicity was lowered with the combination by reducing the generation of free radicals and by enhancing tissue repair.

Selenium homeostasis and induction of thioredoxin reductase during long term selenite supplementation in the rat

Selenium is a candidate treatment for liver tumour prevention in chronic liver disease. In this study, we have studied selenium uptake, distribution and accumulation in rats provided with water containing tumour-preventive doses of sodium selenite for 10 weeks. Male Fischer 344 rats were given drinking water containing 1 μg/mL or 5 μg/mL sodium selenite. Selenium levels were monitored in serum and liver tissue over the 10-week period, and the kinetics of induction of the redox-active cytosolic selenoenzyme thioredoxin reductase were followed. Selenite exposure via drinking water caused a dose-dependent increase in blood and liver selenium levels, with plateaus at 6 and 8 weeks, respectively. These plateaus were reached at the same level of selenium regardless of dose, and no further accumulation was observed. A selenium-dependent increase in the activity of TrxR1 in parallel with the increase in liver selenium levels was also seen, and the induction of TrxR1 mRNA was seen only during the first three days of treatment, when the levels of selenium in the liver were increasing. Sodium selenite at 1 and 5 μg/mL did not affect body weight or relative liver mass. We concluded that long-term treatment with selenite did not cause accumulation of selenium and that the activity of TrxR1 in the liver rose with the selenium levels. We therefore suggest that sodium selenite at doses up to 5 μg/mL could be used for long-term tumour prevention.

Selenite induces posttranscriptional blockade of HLA-E expression and sensitizes tumor cells to CD94/NKG2A-positive NK cells

CD94/NKG2A is an inhibitory receptor that controls the activity of a large proportion of human NK cells following interactions with the nonclassical HLA class Ib molecule HLA-E expressed on target cells. In this study, we show that selenite (SeO(3)(2-)), an inorganic selenium compound, induces an almost complete loss of cell surface expression of HLA-E on tumor cells of various origins. Selenite abrogated the HLA-E expression at a posttranscriptional level, since selenite exposure led to a dose-dependent decrease in cellular HLA-E protein expression whereas the mRNA levels remained intact. The loss of HLA-E expression following selenite treatment was associated with decreased levels of intracellular free thiols in the tumor cells, suggesting that the reduced HLA-E protein synthesis was caused by oxidative stress. Indeed, HLA-E expression and the level of free thiols remained intact following treatment with selenomethionine, a selenium compound that does not generate oxidative stress. Loss of HLA-E expression, but not of total HLA class I expression, on tumor cells resulted in increased susceptibility to CD94/NK group 2A-positive NK cells. Our results suggest that selenite may be used to potentiate the anti-tumor cytotoxicity in settings of NK cell-based immunotherapies.

Selenium and the selenoprotein thioredoxin reductase in the prevention, treatment and diagnostics of cancer

Selenium is an essential element that is specifically incorporated as selenocystein into selenoproteins. It is a potent modulator of eukaryotic cell growth with strictly concentration-dependant effects. Lower concentrations are necessary for cell survival and growth, whereas higher concentrations inhibit growth and induce cell death. It is well established that selenium has cancer preventive effects, and several studies also have shown that it has strong anticancer effects with a selective cytotoxicity on malignant drug-resistant cells while only exerting marginal effects on normal and benign cells. This cancer-specific cytotoxicity is likely explained by high affinity selenium uptake dependent on proteins connected to multidrug resistance. One of the most studied selenoproteins in cancer is thioredoxin reductase (TrxR) that has important functions in neoplastic growth and is an important component of the resistant phenotype. Several reports have shown that TrxR is induced in tumor cells and pre-neoplastic cells, and several commonly used drugs interact with the protein. In this review, we summarize the current knowledge of selenium as a potent preventive and tumor selective anticancer drug, and we also discuss the potential of using the expression and modulation of the selenoprotein TrxR in the diagnostics and treatment of cancer.

Part of the Series: From dietary antioxidants to regulators in cellular signaling and gene regulation

The association of decreased cancer risk with intake of cruciferous vegetables and selenium is stronger than that reported for fruits and vegetables in general. An active constituent in cruciferae is sulforaphane. Chemopreventive effects of both, sulforaphane and selenium have been attributed to an antioxidant action which certainly is too simplicistic. Sulforaphane induces via activation of the Nrf2/Keap1 system phase 2 enzymes that protect against carcinogens and oxidants. Induced enzymes comprise the selenoproteins thioredoxin reductase-1 (TrxR1) and gastrointestinal glutathione peroxidase (GI-GPx, GPx2), which contain antioxidant response elements (ARE) in their promoter regions. Translational realisation of the enhanced transcripts depends on adequate selenium supply, which explains the synergism of Nrf2 activators and selenium. Regarding tumorigenesis the role of TrxR1 is ambiguous: it is essential for fast tumor cell growth but also diminishes vascularisation of tumors. The anticarcinogenic role of GI-GPx is evident from enhanced gastrointestinal tumor formation in gpx2/gpx1 double KO mice.

Hemolysate thioredoxin reductase and glutathione peroxidase activities correlate with serum selenium in a group of New Zealand men at high prostate cancer risk

The study provides data relating serum selenium concentration to activities of 2 key selenoenzymes, hemolysate thioredoxin reductase (TR) and glutathione peroxidase (GPx), measured by spectrophotometry, in a group of men at high risk for prostate cancer. This trial enrolled 43 patients with elevated prostate-specific antigen but negative biopsy for prostate cancer. Such individuals have a high risk of developing prostate cancer in the succeeding 5 y. In the men with baseline serum selenium concentrations ranging from 0.74-1.62 micromol/L (59-128 microg/L), hemolysate TR (r = 0.359, P < 0.05) and GPx (r = 0.341, P < 0.05) activities increased with increasing serum selenium. Furthermore, after a run-in period of 1 mo, men participated in a randomized, double-blind, placebo-controlled selenium supplementation trial for 6 mo and received a placebo, or 200 or 400 microg of Se per day, in the form of a seleno yeast. This study is a subsidiary of an ongoing Phase III cancer chemoprevention trial and, as such, randomization groups have not yet been revealed. After 6 mo of being on trial and with an estimated 66% of the group being supplemented with seleno yeast, the TR activity of the group increased by 80% relative to baseline. In contrast, 6 mo of selenium supplementation did not affect GPx activity. This study presents, to our knowledge for the first time, both measurements of human hemolysate TR activity and its relation to serum selenium.

Liver pathology and hepatocarcinogenesis in a long-term mouse model of erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is an inherited disease of haem synthesis caused by a mutation in one of the alleles of the enzyme ferrochelatase. This mutation leads to partial deficiency of the enzyme, resulting in increased concentrations of protoporphyrin (PP) in blood, liver, and faeces. Five to ten per cent of patients with EPP develop severe liver disease characterized by the presence of PP deposits. This study used histochemistry and immunohistochemistry to investigate the histopathological features present in the livers of 44 mice with a heterozygous or homozygous point mutation in the ferrochelatase gene (fch/+ and fch/fch mice, respectively). Some fch/+ mouse livers showed mixed steatosis and large cell dysplasia. The livers of fch/fch mice showed periportal or septal fibrosis accompanied by an atypical ductular reaction. These findings suggest that the obstruction and damage of a proportion of large and small bile ducts by PP deposits cause an accumulation of PP in the parenchyma, which leads to damage and loss of hepatocytes due to the toxic effects of PP. The classical stages of hepatocarcinogenesis were observed and hepatic progenitor cells appear to be involved in this process. PP acts as the promoting agent and is probably also the initiating agent.

The mammalian cytosolic selenoenzyme thioredoxin reductase reduces ubiquinone. A novel mechanism for defense against oxidative stress

The selenoprotein thioredoxin reductase (TrxR1) is an essential antioxidant enzyme known to reduce many compounds in addition to thioredoxin, its principle protein substrate. Here we found that TrxR1 reduced ubiquinone-10 and thereby regenerated the antioxidant ubiquinol-10 (Q10), which is important for protection against lipid and protein peroxidation. The reduction was time- and dose-dependent, with an apparent K(m) of 22 microm and a maximal rate of about 12 nmol of reduced Q10 per milligram of TrxR1 per minute. TrxR1 reduced ubiquinone maximally at a physiological pH of 7.5 at similar rates using either NADPH or NADH as cofactors. The reduction of Q10 by mammalian TrxR1 was selenium dependent as revealed by comparison with Escherichia coli TrxR or selenium-deprived mutant and truncated mammalian TrxR forms. In addition, the rate of reduction of ubiquinone was significantly higher in homogenates from human embryo kidney 293 cells stably overexpressing thioredoxin reductase and was induced along with increasing cytosolic TrxR activity after the addition of selenite to the culture medium. These data demonstrate that the selenoenzyme thioredoxin reductase is an important selenium-dependent ubiquinone reductase and can explain how selenium and ubiquinone, by a combined action, may protect the cell from oxidative damage.

The thioredoxin system?From science to clinic

The thioredoxin system-formed by thioredoxin reductase and its characteristic substrate thioredoxin-is an important constituent of the intracellular redox milieu. Interactions with many different metabolic pathways such as DNA-synthesis, selenium metabolism, and the antioxidative network as well as significant species differences render this system an attractive target for chemotherapeutic approaches in many fields of medicine-ranging from infectious diseases to cancer therapy. In this review we will present and evaluate the preclinical and clinical results available today. Current trends in drug development are emphasized.

Drug-resistant human lung cancer cells are more sensitive to selenium cytotoxicity. Effects on thioredoxin reductase and glutathione reductase

The human U-1285 and GLC(4) cell lines, both derived from small cell carcinoma of the lung, are present in doxorubicin-sensitive (U-1285 and GLC(4)) and doxorubicin-resistant MRP-expressing (U-1285dox and GLC(4)/ADR) variants. These sublines were examined here with respect to their susceptibilities to the toxic effects of selenite and compared to the toxic effects of selenite on the promyelocytic leukemia cell line HL-60 and its doxorubicin-resistant P-glycoprotein expressing variant. The drug-resistant U-1285dox and GLC(4)/ADR sublines proved to be 3- and 4-fold, respectively, more sensitive to the cytotoxicity of selenite than the drug-sensitive U-1285 and GLC(4) sublines, whereas no difference was observed between the HL-60 sublines. The presence of doxorubicin at a concentration equal to the IC(10) did not significantly potentiate the toxic effects of selenite. The presence of selenite did not significantly affect the expression of the multi-drug resistant proteins (MRP1, LRP and topoisomerase IIalpha) in the drug-resistant cells. The activities of thioredoxin reductase (TrxR) were higher (50 and 25%, respectively) in the drug resistant cell sublines U-1285dox and GLC(4)/ADR compared to the drug-sensitive parental lines. The activity of glutathione reductase (GR) was essentially the same in the drug-sensitive and -resistant cell lines. Exposure to selenite resulted in a 4-fold increase in both TrxR and GR activities in U-1285 cells, an effect, which was less pronounced in the presence of doxorubicin. Under similar conditions the increase in the TrxR activity in the resistant U-1285dox cell line, was only 30% and the activity of GR was unaltered. Different responses in the activity of the key enzymes in selenium metabolism are one possible mechanism explaining the differential cytotoxicity of selenium in these cells.