Elevation of serum thioredoxin levels in patients with type 2 diabetes

Evaluation of serum thioredoxin as a hepatocellular carcinoma diagnostic marker

Background

Hepatocellular carcinoma (HCC) is one of the most prevalent and fatal malignancies worldwide. Following an increase in reactive oxygen species (ROS), cancer cells enter an oxidative stress state. As a result, these cells experience an increase in antioxidant activity to counteract oxidative stress. The thioredoxin (TRX) system is a ubiquitous mammalian antioxidant system that neutralizes ROS and maintains intracellular reduction oxidation (redox) balance, which is essential for HCC growth. However, the role of TRX protein in HCC remains largely unknown. Hence, we aimed to assess the diagnostic utility of serum TRX in patients with HCC. A total of 50 patients were consecutively recruited in this observational study. They were classified into three groups: an HCC group (25 patients), a cirrhosis group (15 patients with liver cirrhosis on top of chronic HCV infection), and a control group (10 healthy individuals). Serum TRX levels were measured using ELISA.

Results

Higher serum TRX levels were detected in the HCC group than in the cirrhosis and control groups (140.96 ± 12.70 vs 88.33 ± 10.34 vs 73.10 ± 13.22 ng/mL, respectively; P < 0.001). TRX was independently associated with the presence of HCC (P < 0.001). Regarding the detection of HCC, TRX at a cut-off value of 114 ng/mL had superior diagnostic performance to AFP with an AUC of 1.000, sensitivity of 100%, and specificity of 100%, whereas AFP at a cut-off value of 20.5 ng/mL had an AUC of 1.000, sensitivity of 100%, and specificity of 47%.

Conclusion

Thioredoxin has the potential to be an HCC diagnostic marker. The clinical significance of thioredoxin in HCC requires further investigation.

Pancreatic β-cell dysfunction in type 2 diabetes: Implications of inflammation and oxidative stress

Insulin resistance and pancreatic β-cell dysfunction are major pathological mechanisms implicated in the development and progression of type 2 diabetes (T2D). Beyond the detrimental effects of insulin resistance, inflammation and oxidative stress have emerged as critical features of T2D that define β-cell dysfunction. Predominant markers of inflammation such as C-reactive protein, tumor necrosis factor alpha, and interleukin-1β are consistently associated with β-cell failure in preclinical models and in people with T2D. Similarly, important markers of oxidative stress, such as increased reactive oxygen species and depleted intracellular antioxidants, are consistent with pancreatic β-cell damage in conditions of T2D. Such effects illustrate a pathological relationship between an abnormal inflammatory response and generation of oxidative stress during the progression of T2D. The current review explores preclinical and clinical research on the patho-logical implications of inflammation and oxidative stress during the development of β-cell dysfunction in T2D. Moreover, important molecular mechanisms and relevant biomarkers involved in this process are discussed to divulge a pathological link between inflammation and oxidative stress during β-cell failure in T2D. Underpinning the clinical relevance of the review, a systematic analysis of evidence from randomized controlled trials is covered, on the potential therapeutic effects of some commonly used antidiabetic agents in modulating inflammatory makers to improve β-cell function.

An Overview of the TRP-Oxidative Stress Axis in Metabolic Syndrome: Insights for Novel Therapeutic Approaches

Metabolic syndrome (MS) is a complex pathology characterized by visceral adiposity, insulin resistance, arterial hypertension, and dyslipidaemia. It has become a global epidemic associated with increased consumption of high-calorie, low-fibre food and sedentary habits. Some of its underlying mechanisms have been identified, with hypoadiponectinemia, inflammation and oxidative stress as important factors for MS establishment and progression. Alterations in adipokine levels may favour glucotoxicity and lipotoxicity which, in turn, contribute to inflammation and cellular stress responses within the adipose, pancreatic and liver tissues, in addition to hepatic steatosis. The multiple mechanisms of MS make its clinical management difficult, involving both non-pharmacological and pharmacological interventions. Transient receptor potential (TRP) channels are non-selective calcium channels involved in a plethora of physiological events, including energy balance, inflammation and oxidative stress. Evidence from animal models of disease has contributed to identify their specific contributions to MS and may help to tailor clinical trials for the disease. In this context, the oxidative stress sensors TRPV1, TRPA1 and TRPC5, play major roles in regulating inflammatory responses, thermogenesis and energy expenditure. Here, the interplay between these TRP channels and oxidative stress in MS is discussed in the light of novel therapies to treat this syndrome.

Redox Homeostasis in Pancreatic β-Cells: From Development to Failure

Redox status is a key determinant in the fate of β-cell. These cells are not primarily detoxifying and thus do not possess extensive antioxidant defense machinery. However, they show a wide range of redox regulating proteins, such as peroxiredoxins, thioredoxins or thioredoxin reductases, etc., being functionally compartmentalized within the cells. They keep fragile redox homeostasis and serve as messengers and amplifiers of redox signaling. β-cells require proper redox signaling already in cell ontogenesis during the development of mature β-cells from their progenitors. We bring details about redox-regulated signaling pathways and transcription factors being essential for proper differentiation and maturation of functional β-cells and their proliferation and insulin expression/maturation. We briefly highlight the targets of redox signaling in the insulin secretory pathway and focus more on possible targets of extracellular redox signaling through secreted thioredoxin1 and thioredoxin reductase1. Tuned redox homeostasis can switch upon chronic pathological insults towards the dysfunction of β-cells and to glucose intolerance. These are characteristics of type 2 diabetes, which is often linked to chronic nutritional overload being nowadays a pandemic feature of lifestyle. Overcharged β-cell metabolism causes pressure on proteostasis in the endoplasmic reticulum, mainly due to increased demand on insulin synthesis, which establishes unfolded protein response and insulin misfolding along with excessive hydrogen peroxide production. This together with redox dysbalance in cytoplasm and mitochondria due to enhanced nutritional pressure impact β-cell redox homeostasis and establish prooxidative metabolism. This can further affect β-cell communication in pancreatic islets through gap junctions. In parallel, peripheral tissues losing insulin sensitivity and overall impairment of glucose tolerance and gut microbiota establish local proinflammatory signaling and later systemic metainflammation, i.e., low chronic inflammation prooxidative properties, which target β-cells leading to their dedifferentiation, dysfunction and eventually cell death.

The Efficacy of Levocarnitine Treatment in Relieving Fatigue in Patients with Cirrhosis but without Overt Hepatic Encephalopathy

Objective In the present study, we prospectively examined the efficacy of levocarnitine in relieving symptoms of fatigue in patients with cirrhosis but without overt hepatic encephalopathy. Methods Twenty-one cirrhotic patients who were able to undergo fatigue symptom evaluations at our institution were enrolled. A total of 12 cirrhotic patients underwent levocarnitine treatment (1,200-1,800 mg/day), while 9 did not undergo levocarnitine treatment. As primary endpoints, we investigated whether or not levocarnitine treatment exerted any beneficial effects by assessing the symptoms of fatigue [8-item Short-Form Health Survey (SF-8) and Fisk Fatigue Severity Score (FFSS)] at baseline and three months after treatment. Furthermore, as exploratory secondary endpoints, we investigated whether or not levocarnitine treatment exerted ameliorative effects on oxidative stress by assessing the serum thioredoxin (TRX) and urinary 8-hydroxydeoxyguanosine (8-OHdG) levels. Results The median age of the patients was 73 years old. Three men and 18 women were categorized by their Child-Pugh class (A and B in 14 and 7 patients, respectively). There were no significant differences in the clinical laboratory values between the two groups. The FFSS and SF-8 scores were significantly improved in the patients with cirrhosis who underwent levocarnitine treatment (p<0.01) but not in those who did not undergo levocarnitine treatment. Furthermore, three months after levocarnitine treatment, the serum carnitine concentrations were significantly increased, and the serum thioredoxin levels were decreased in the patients with cirrhosis who underwent levocarnitine treatment (p<0.05). Conclusion These results suggest that levocarnitine treatment may relieve symptoms of fatigue in cirrhotic patients by reducing oxidative stress.

Thioredoxin 1 is upregulated in the bone and bone marrow following experimental myocardial infarction: evidence for a remote organ response

Ischemia and reperfusion events, such as myocardial infarction (MI), are reported to induce remote organ damage severely compromising patient outcomes. Tissue survival and functional restoration relies on the activation of endogenous redox regulatory systems such as the oxidoreductases of the thioredoxin (Trx) family. Trxs and peroxiredoxins (Prxs) are essential for the redox regulation of protein thiol groups and for the reduction of hydrogen peroxide, respectively. Here, we determined whether experimental MI induces changes in Trxs and Prxs in the heart as well as in secondary organs. Levels and localization of Trx1, TrxR1, Trx2, Prx1, and Prx2 were analyzed in the femur, vertebrae, and kidneys of rats following MI or sham surgery. Trx1 levels were significantly increased in the heart (P = 0.0017) and femur (P < 0.0001) of MI animals. In the femur and lumbar vertebrae, Trx1 upregulation was detected in bone-lining cells, osteoblasts, megakaryocytes, and other hematopoietic cells. Serum levels of Trx1 increased significantly 2 days after MI compared to sham animals (P = 0.0085). Differential regulation of Trx1 in the bone was also detected by immunohistochemistry 1 month after MI. N-Acetyl-cysteine treatment over a period of 1 month induced a significant reduction of Trx1 levels in the bone of MI rats compared to sham and to MI vehicle. This study provides first evidence that MI induces remote organ upregulation of the redox protein Trx1 in the bone, as a response to ischemia-reperfusion injury in the heart.

Paracrine regulation and improvement of β-cell function by thioredoxin

The failure of insulin-producing β-cells is the underlying cause of hyperglycemia in diabetes mellitus. β-cell decay has been linked to hypoxia, chronic inflammation, and oxidative stress. Thioredoxin (Trx) proteins are major actors in redox signaling and essential for signal transduction and the cellular stress response. We have analyzed the cytosolic, mitochondrial, and extracellular Trx system proteins in hypoxic and cytokine-induced stress using β-cell culture, isolated pancreatic islets, and pancreatic islet transplantation modelling low oxygen supply. Protein levels of cytosolic Trx1 and Trx reductase (TrxR) 1 significantly decreased, while mitochondrial Trx2 and TrxR2 increased upon hypoxia and reoxygenation. Interestingly, Trx1 was secreted by β-cells during hypoxia. Moreover, murine and human pancreatic islet grafts released Trx1 upon glucose stimulation. Survival of transplanted islets was substantially impaired by the TrxR inhibitor auranofin. Since a release was prominent upon hypoxia, putative paracrine effects of Trx1 on β-cells were examined. In fact, exogenously added recombinant hTrx1 mitigated apoptosis and preserved glucose sensitivity in pancreatic islets subjected to hypoxia and inflammatory stimuli, dependent on its redox activity. Human subjects were studied, demonstrating a transient increase in extracellular Trx1 in serum after glucose challenge. This increase correlated with better pancreatic islet function. Moreover, hTrx1 inhibited the migration of primary murine macrophages. In conclusion, our study offers evidence for paracrine functions of extracellular Trx1 that improve the survival and function of pancreatic β-cells.

New insights into serum/extracellular thioredoxin in regulating hepatic insulin receptor activation

BACKGROUND

Serum thioredoxin of type-2 diabetic patients is significantly higher than that of healthy people. Pathophysiological significance is unclear.

METHODS

Effects of serum/extracellular thioredoxin on phosphorylation (activation) of hepatic insulin receptor (IR) were investigated by using methods in biochemistry, cell/molecular biology and mass spectrometry.

RESULTS

In human serum, thioredoxin and insulin may interact. Their mixture contains a mixed disulfide between insulin B-chain and thioredoxin-Cys73, which limits their activities. In contrast, free form of serum/extracellular thioredoxin is active, and can regulate phosphorylation of insulin receptor β-subunits (IRβ) via direct/indirect mechanisms. The direct mechanism associates with positive regulation. Serum/extracellular thioredoxin increases insulin binding to IR, facilitating insulin-induced phosphorylation of IRβ and downstream AKT. The indirect mechanism is involved in negative regulation. Entry of extracellular thioredoxin into hepatic cells via IR enhances the expression and activity of cellular protein-tyrosine phosphatase 1B (PTP1B), which negatively regulates IRβ phosphorylation. After coordination between these two mechanisms, the positive impact of serum/extracellular thioredoxin overwhelms its negative impact on IRβ phosphorylation, which subsequently accelerates hepatic glucose uptake. In hepatic cells with thioredoxin deficiency, insulin-induced IRβ phosphorylation is decreased, which could be restored by extracellular thioredoxin entry. Moreover, the results from assaying 475 serum samples demonstrate a discriminating value of serum thioredoxin activity in diagnosing type-2 diabetes.

CONCLUSION

Serum/extracellular thioredoxin plays a critical role in regulating hepatic IRβ phosphorylation.

GENERAL SIGNIFICANCE

In case of insulin resistance/type-2 diabetes, hepatic IRβ is at low phosphorylation level, thereby the improvement effect of serum/extracellular thioredoxin on insulin-induced IRβ phosphorylation seems particularly important.

The role of the thioredoxin/thioredoxin reductase system in the metabolic syndrome: towards a possible prognostic marker?

Mammalian thioredoxin reductase (TrxR) is a selenoprotein with three existing isoenzymes (TrxR1, TrxR2, and TrxR3), which is found primarily intracellularly but also in extracellular fluids. The main substrate thioredoxin (Trx) is similarly found (as Trx1 and Trx2) in various intracellular compartments, in blood plasma, and is the cell's major disulfide reductase. Thioredoxin reductase is necessary as a NADPH-dependent reducing agent in biochemical reactions involving Trx. Genetic and environmental factors like selenium status influence the activity of TrxR. Research shows that the Trx/TrxR system plays a significant role in the physiology of the adipose tissue, in carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherogenesis. Based on recent research, it has been reported that the modulation of the Trx/TrxR system may be considered as a new target in the management of the metabolic syndrome, insulin resistance, and type 2 diabetes, as well as in the treatment of hypertension and atherosclerosis. In this review evidence about a possible role of this system as a marker of the metabolic syndrome is reported.

Anti-Inflammatory Thioredoxin Family Proteins for Medicare, Healthcare and Aging Care

Human thioredoxin (TRX) is a 12-kDa protein with redox-active dithiol in the active site -Cys-Gly-Pro-Cys-, which is induced by biological stress due to oxidative damage, metabolic dysfunction, chemicals, infection/inflammation, irradiation, or hypoxia/ischemia-reperfusion. Our research has demonstrated that exogenous TRX is effective in a wide variety of inflammatory diseases, including viral pneumonia, acute lung injury, gastric injury, and dermatitis, as well as in the prevention and amelioration of food allergies. Preclinical and clinical studies using recombinant TRX (rhTRX) are now underway. We have also identified substances that induce the expression of TRX in the body, in vegetables and other plant ingredients. Skincare products are being developed that take advantage of the anti-inflammatory and anti-allergic action of TRX. Furthermore, we are currently engaged in the highly efficient production of pure rhTRX in several plants, such as lettuce, grain and rice.

Increased thioredoxin levels are related to insulin resistance in familial combined hyperlipidaemia

BACKGROUND

Thioredoxins (TRX) are major cellular protein disulphide reductases that are critical for redox regulation. Oxidative stress and inflammation play promoting roles in the genesis and progression of atherosclerosis, but until now scarce data are available considering the influence of TRX activity in familial combined hyperlipidaemia (FCH). Since FCH is associated with high risk of cardiovascular disease, the objective of the present study was to assess oxidative stress status in FCH patients, and evaluate the influence of insulin resistance (IR).

MATERIALS AND METHODS

A cohort of 35 control subjects and 35 non-related FCH patients were included, all of them nondiabetic, normotensive and nonsmokers. We measured lipid profile, glucose and insulin levels in plasma, and markers of oxidative stress and inflammation such as oxidized glutathione (GSSG), reduced glutathione (GSH) and TRX.

RESULTS

Familial combined hyperlipidaemia subjects showed significantly higher levels of GSSG, GSSG/GSH ratio and TRX than controls. In addition, FCH individuals with IR showed the worst profile of oxidative stress status compared to controls and FCH patients without IR (P < 0·01). TRX levels correlated with higher insulin resistance.

CONCLUSION

Familial combined hyperlipidaemia patients showed increased TRX levels. TRX was positively correlated with IR. These data could partially explain the increased risk of cardiovascular events in primary dyslipidemic patients.

Serum thioredoxin is a diagnostic marker for hepatocellular carcinoma

Here we found that serum levels of thioredoxin were increased in patients with hepatocellular carcinoma (HCC). The optimum diagnostic cutoff for thioredoxin was 20.5 ng/mL (area under curve [AUC] 0.946 [95% CI 0.923–0.969] in the training cohort; 0.941 [0.918–0.963] in the validation cohort). High serum concentrations of thioredoxin differentiated HCC from chronic liver diseases and cirrhosis (0.901 [0.875–0.923] in the training cohort; 0.906 [0.870–0.925] in the validation cohort). Furthermore, a higher proportion of patients with very early HCC had positive results for thioredoxin than for alpha-Fetoprotein (AFP) (73.7% VS.31.6%; P < 0.0001). Among AFP-negative patients with very early HCC, 18 (69.2%) of 26 had positive thioredoxin results. Our results indicate that serum thioredoxin complements measurement of AFP in the diagnosis of HCC, especially in very early disease. Combined model (thioredoxin and AFP) showed a significantly greater discriminatory ability as compared with those markers alone.

Thioredoxin superfamily and its effects on cardiac physiology and pathology

A precise control of oxidation/reduction of protein thiols is essential for intact cardiac physiology. Irreversible oxidative modifications have been proposed to play a role in the pathogenesis of cardiovascular diseases. An imbalance of redox homeostasis with diminution of antioxidant capacities predisposes the heart to oxidant injury. There is growing interest in endoplasmic reticulum (ER) stress in the cardiovascular field, since perturbation of redox homeostasis in the ER is sufficient to cause ER stress. Because a number of human diseases are related to altered redox homeostasis and defects in protein folding, many research efforts have been devoted in recent years to understanding the structure and enzymatic properties of the thioredoxin superfamily. The thioredoxin superfamily has been well documented as thiol oxidoreductases to exert a role in various cell signaling pathways. The redox properties of the thioredoxin motif account for the different functions of several members of the thioredoxin superfamily. While thioredoxin and glutaredoxin primarily act as antioxidants by reducing protein disulfides and mixed disulfide, another member of the superfamily, protein disulfide isomerase (PDI), can act as an oxidant by forming intrachain disulfide bonds that contribute to proper protein folding. Increasing evidence suggests a pivotal role of PDI in the survival pathway that promotes cardiomyocyte survival and leads to more favorable cardiac remodeling. Thus, the thiol redox state is important for cellular redox signaling and survival pathway in the heart. This review summarizes the key features of major members of the thioredoxin superfamily directly involved in cardiac physiology and pathology.

Thioredoxins in cardiovascular disease

Key thioredoxin (Trx) system components are nicotinamide adenine dinucleotide phosphate (NADPH), Trx reductase (TrxR), and Trx. TrxR catalyzes disulfide reduction in Trx with NADPH as cofactor. Because Trx is an antioxidant, oxidative stress results in an increase in Trx, which has a reduced disulfide component. If Trx is suppressed, oxidative stress in higher. In contrast a decrease in oxidative stress is associated with low Trx levels. Trx is involved in inflammation, apoptosis, embryogenesis, and cardiovascular disease (CVD). This review focuses on the Trx system in CVD. Abnormal Trx binding occurs in mouse familial combined hyperlipidemia; however, this has not been confirmed in humans. Congestive heart failure is a manifestation of many CVDs, which may be improved by attenuating oxidative stress through the suppression of Trx and decreased reactive oxygen species. Angiotensin II is associated with hypertension and other CVDs, and its receptor blockade results in decreased oxidative stress with reduced Trx levels. Inflammation is a major causative factor of CVDs, and myocarditis as an example, is associated with increased Trx levels. Vascular endothelial dysfunction has an association with CVD. This dysfunction is alleviated by hormone replacement therapy, which involves decreased oxidative stress and Trx levels. Diabetes mellitus has a major association with CVDs; increase in Trx levels may reflect insulin resistance. Identification of Trx system abnormalities may lead to innovative approaches to treat multiple CVDs and other pathologies.

High-fat diet-induced changes in liver thioredoxin and thioredoxin reductase as a novel feature of insulin resistance

High-fat diet (HFD) can induce oxidative stress. Thioredoxin (Trx) and thioredoxin reductase (TrxR) are critical antioxidant proteins but how they are affected by HFD remains unclear. Using HFD-induced insulin-resistant mouse model, we show here that liver Trx and TrxR are significantly decreased, but, remarkably, the degree of their S-acylation is increased after consuming HFD. These HFD-induced changes in Trx/TrxR may reflect abnormalities of lipid metabolism and insulin signaling transduction. HFD-driven accumulation of 4-hydroxynonenal is another potential mechanism behind inactivation and decreased expression of Trx/TrxR. Thus, we propose HFD-induced impairment of liver Trx/TrxR as major contributor to oxidative stress and as a novel feature of insulin resistance.

Methodological aspects of ELISA analysis of thioredoxin 1 in human plasma and cerebrospinal fluid

Thioredoxin-1 (Trx1) is a protein antioxidant involved in major cellular processes. Increased plasma levels of Trx1 have been associated with human diseases suggesting that Trx1 is a marker for oxidative stress with putative clinical use. However, the reported mean levels of Trx1 in the control cohorts vary a hundred-fold between studies (0.8-87 ng/ml), possibly due to methodological differences between the capture ELISA used in the different studies. The aim of this study was to investigate methodological aspects related to the ELISA measurement of Trx1. ELISAs utilizing different capture and detection combinations of antibodies to Trx1 and as well as recombinant human (rh) Trx1 standards from two sources were characterized. The different ELISAs were subsequently used to measure Trx1 in human plasma and cerebrospinal fluid samples (CSF) from healthy donors and from patients with various neurological diagnoses. The Trx1 standards differed in their content of monomeric and oligomeric Trx1, which affected the ELISAs composed of different antibody combinations. Thus, the levels of Trx1 determined in human plasma and CSF samples varied depending on the antibody used in the ELISAs and on the rhTrx1 standard. Furthermore, the relevance of preventing interference by heterophilic antibodies (HA) in human plasma and CSF was investigated. The addition of a HA blocking buffer to human samples drastically reduced the ELISA signals in many samples showing that HA are likely to cause false positive results unless they are blocked. In conclusion, the study shows that the design of a Trx1 ELISA in regards to antibodies and standards used has an impact on the measured Trx1 levels. Importantly, analyses of human plasma and CSF without preventing HA interference may obscure the obtained data. Overall, the results of this study are crucial for the improvement of future studies on the association of Trx1 levels with various diseases.

Decreased thioredoxin-1 and increased HSP90 expression in skeletal muscle in subjects with type 2 diabetes or impaired glucose tolerance

In diabetes, the endogenous defence systems are overwhelmed, causing various types of stress in tissues. In this study, newly diagnosed or diet-treated type 2 diabetics (T2D) (n = 10) were compared with subjects with impaired glucose tolerance (IGT) (n = 8). In both groups, at resting conditions, blood samples were drawn for assessing metabolic indices and skeletal muscle samples (m. vastus lateralis) were taken for the measurements of cellular defence markers: thioredoxin-1 (TRX-1) and stress proteins HSP72, HSP90. The protein level of TRX-1 was 36.1% lower (P = 0.031) and HSP90 was 380% higher (P < 0.001) in the T2D than in the IGT subjects, with no significant changes in HSP72. However, after the adjustment of both analyses with HOMA-IR only HSP90 difference remained significant. In conclusion, level of TRX-1 in skeletal muscle tissue was lower while that of HSP90 was higher in T2D than in IGT subjects. This may impair antioxidant defence and lead to disruptions of protein homoeostasis and redox regulation of cellular defences. Because HSP90 may be involved in sustaining functional insulin signalling pathway in type 2 diabetic muscles and higher HSP90 levels can be a consequence of type 2 diabetes, our results are potentially important for the diabetes research.

Thioredoxins, glutaredoxins, and peroxiredoxins--molecular mechanisms and health significance: from cofactors to antioxidants to redox signaling

Thioredoxins (Trxs), glutaredoxins (Grxs), and peroxiredoxins (Prxs) have been characterized as electron donors, guards of the intracellular redox state, and "antioxidants". Today, these redox catalysts are increasingly recognized for their specific role in redox signaling. The number of publications published on the functions of these proteins continues to increase exponentially. The field is experiencing an exciting transformation, from looking at a general redox homeostasis and the pathological oxidative stress model to realizing redox changes as a part of localized, rapid, specific, and reversible redox-regulated signaling events. This review summarizes the almost 50 years of research on these proteins, focusing primarily on data from vertebrates and mammals. The role of Trx fold proteins in redox signaling is discussed by looking at reaction mechanisms, reversible oxidative post-translational modifications of proteins, and characterized interaction partners. On the basis of this analysis, the specific regulatory functions are exemplified for the cellular processes of apoptosis, proliferation, and iron metabolism. The importance of Trxs, Grxs, and Prxs for human health is addressed in the second part of this review, that is, their potential impact and functions in different cell types, tissues, and various pathological conditions.

Thioredoxin interacting protein is a potential regulator of glucose and energy homeostasis in endogenous Cushing's syndrome

Recent studies have described bone as an endocrine organ regulating glucose metabolism, with insulin signaling regulating osteocalcin secretion and osteocalcin regulating β cell function. We have previously demonstrated increased bone expression of TXNIP in patients with endogenous Cushing's syndrome (CS), and we hypothesized that TXNIP could contribute to the dysregulated glucose metabolism in CS. We studied 33 CS patients and 29 matched controls, with bone biopsies from nine patients, before and after surgical treatment. In vitro, the effect of silencing TXNIP (siTXNIP) in osteoblasts, including its effect on human islet cells, was examined. Our major findings were: (i) The high mRNA levels of TXNIP in bone from CS patients were significantly associated with high levels of glucose and insulin, increased insulin resistance, and decreased insulin sensitivity in these patients. (ii) Silencing TXNIP in osteoblasts enhanced their OC response to insulin and glucose and down-regulated interleukin (IL)-8 levels in these cells. (iii) Conditional media from siTXNIP-treated osteoblasts promoted insulin content and anti-inflammatory responses in human islet cells. We recently demonstrated that the thioredoxin/TXNIP axis may mediate some detrimental effects of glucocorticoid excess on bone tissue in CS. Here we show that alterations in this axis also may affect glucose metabolism in these patients.

Effect of glucose ingestion in plasma markers of inflammation and oxidative stress: analysis of 16 plasma markers from oral glucose tolerance test samples of normal and diabetic patients

Sixteen plasma markers of inflammation and oxidative stress were measured during OGTT in 54 subjects. Leptin, RBP4, CRP, OPN, ANG, MDC, and MCSF concentrations significantly decreased during OGTT (P<0.05). IL6, IL8, and MCP3 concentrations significantly increased during OGTT (P<0.05). These results provide evidence that glucose ingestion affects systemic inflammation and oxidative stress.

Methylglyoxal has deleterious effects on thioredoxin in human aortic endothelial cells

Methylglyoxal (MG), a precursor of advanced glycation end products (AGEs), is elevated in diabetic patient's plasma. Some studies have demonstrated that MG induces oxidative stress and apoptosis. Thioredoxin (Trx) is a cytoprotective protein with anti-oxidative and anti-apoptosis functions. In this study, we examined the effects of MG on Trx in human aortic endothelial cells (HAECs). MG increased oxidized-hydroethidine fluorescence intensity, suggesting intracellular accumulation of reactive oxygen species. Flow cytometric analyses with annexin-V/propidium iodide double staining revealed that cells incubated with MG displayed features characteristic of apoptosis. The condensation of chromatin, the release of cytochrome c into cytosol, and the collapse of mitochondrial membrane potential by MG were observed. The exposure to MG decreased Trx protein levels through transcription regulation. MG induced the oxidative damage of peroxiredoxin, a Trx-dependent peroxidase. These results suggest that MG has deleterious effects on Trx in HAECs, which may be contribute to oxidative stress and apoptosis.

TXNIP is highly regulated in bone biopsies from patients with endogenous Cushing's syndrome and related to bone turnover

OBJECTIVE

Patients with endogenous Cushing's Syndrome (CS), as long-time treated patients with exogenous glucocorticoids (GCs), have severe systemic manifestations including secondary osteoporosis and low-energy fractures. The aim of the present study was to investigate the functional role of TXNIP in bone with focus on osteoblast (OB) differentiation and OB-mediated osteoclast activity and function in vitro.

DESIGN AND METHODS

Nine bone biopsies from CS before and after surgical treatment were screened for expressional candidate genes. Microarray analyses revealed that the gene encoding TXNIP ranked among the most upregulated genes. Subsequent in vitro and in vivo studies were performed.

RESULTS

We found that TXNIP gene in bone is downregulated in CS following surgical treatment. Furthermore, our in vivo data indicate novel associations between thioredoxin and TXNIP. Our in vitro studies showed that silencing TXNIP in OBs was followed by increased differentiation and expression and secretion of osteocalcin as well as enhanced activity of alkaline phosphatase. Moreover, treating osteoclasts with silenced TXNIP OB media showed an increased osteoclast activity.

CONCLUSIONS

TXNIP expression in bone is highly regulated during the treatment of active CS, and by GC in bone cells in vitro. Our data indicate that TXNIP may mediate some of the detrimental effects of GC on OB function as well as modulate OB-mediated osteoclastogenesis by regulating the OPG/RANKL ratio.

Reduction of glucose intolerance with high fat feeding is associated with anti-inflammatory effects of thioredoxin 1 overexpression in mice

Aging is associated with reduced ability to maintain normal glucose homeostasis. It has been suggested that an age-associated increase in chronic pro-inflammatory state could drive this reduction in glucoregulatory function. Thioredoxins (Trx) are oxido-reductase enzymes that play an important role in the regulation of oxidative stress and inflammation. In this study, we tested whether overexpression of Trx1 in mice [Tg(TRX1)^+/0] could protect from glucose metabolism dysfunction caused by high fat diet feeding. Body weight and fat mass gains with high fat feeding were similar in Tg(TRX1)^+/0 and wild-type mice; however, high fat diet induced glucose intolerance was reduced in Tg(TRX1)^+/0 mice relative to wild-type mice. In addition, expression of the pro-inflammatory cytokine TNF-α was reduced in adipose tissue of Tg(TRX1)^+/0 mice compared to wild-type mice. These findings suggest that activation of thioredoxins may be a potential therapeutic target for maintenance of glucose metabolism with obesity or aging.

Segment-specific overexpression of redoxins after renal ischemia and reperfusion: protective roles of glutaredoxin 2, peroxiredoxin 3, and peroxiredoxin 6

The disruption of redox control, i.e., oxidative stress, is one of the most destructive causes of ischemia-reperfusion (IR) injury. Thioredoxin (Trx) family proteins play a major role in the cellular response to oxidative stress. Here, we systematically investigated the levels and tissue distribution of 15 members of this family (Trx and TrxR 1 and 2, Nrx, Prx 1-6, and Grx 1-3 and 5) in mouse kidneys after induction of IR by comparing control, clamped, and contralateral organs. After IR, levels of various redoxins were quantified. Immunohistochemical analysis revealed segment-specific alterations induced by the ischemic insult. Grx2, Prx3, and Prx6 were highly expressed in proximal tubule cells. Overexpression of these proteins in HEK293 and HeLa cells subjected to hypoxia and reoxygenation revealed higher survival and proliferation rates and lower oxidative damage compared to controls. Furthermore, we report for the first time the accumulation of Grx1 at the apical side of distal convoluted cells and the specific secretion of Grx1 into the urine after IR. The differences in both the basal equipment and the segment-specific responses of the antioxidant proteins may contribute to the distinct susceptibilities and regeneration processes of the various segments of the nephron to the IR insult.

Treatments with sodium selenate or doxycycline offset diabetes-induced perturbations of thioredoxin-1 levels and antioxidant capacity

Diabetes is associated with increased oxidative stress and impaired antioxidant defenses. Thioredoxin-1 (TRX-1) is a cytosolic thiol antioxidant and redox-active protein which plays a vital role in the maintenance of reduced intracellular redox state. In this study, the authors examined whether 4-week treatments with sodium selenate and doxycycline--a metalloproteinase-2 inhibitor which also has antioxidant-like effects--offset perturbations in oxidative stress and antioxidant protection in rat liver and skeletal muscle in streptozotocin-induced diabetes (SID) model. Experimental diabetes decreased TRX-1 levels in skeletal muscle and liver. On the other hand, SID increased oxidative stress marker protein carbonyl levels and decreased oxygen radical absorbance capacity (ORAC), an indicator of antioxidant capacity, in liver. A 4-week treatment of sodium selenate to diabetic rats decreased blood glucose levels moderately, while doxycycline treatment caused a reduction in weight loss of diabetic rats. Both doxycycline and sodium selenate prevented diabetes-induced decrease of TRX-1 levels in skeletal muscle, whereas only doxyxycline was effectively preventing diabetes-induced decrease of TRX-1 in liver. Furthermore, both treatments prevented diabetes-induced altered levels of protein carbonyls and ORAC in liver, and restored free and total protein thiol levels in both skeletal muscle and liver. In conclusion, the data of this study provides further evidence that sodium selenate and doxycycline treatments may control oxidative stress and improve antioxidant defense in diabetes.

Naturally occurring free thiols within β2-glycoprotein I in vivo: nitrosylation, redox modification by endothelial cells, and regulation of oxidative stress–induced cell injury

β2-Glycoprotein I (β2GPI) is an evolutionary conserved, abundant circulating protein. Although its function remains uncertain, accumulated evidence points toward interactions with endothelial cells and components of the coagulation system, suggesting a regulatory role in vascular biology. Our group has shown that thioredoxin 1 (TRX-1) generates free thiols in β2GPI, a process that may have a regulatory role in platelet adhesion. This report extends these studies and shows for the first time evidence of β2GPI with free thiols in vivo in both multiple human and murine serum samples. To explore how the vascular surface may modulate the redox status of β2GPI, unstimulated human endothelial cells and EAhy926 cells are shown to be capable of amplifying the effect of free thiol generation within β2GPI. Multiple oxidoreductase enzymes, such as endoplasmic reticulum protein 46 (ERp 46) and TRX-1 reductase, in addition to protein disulfide isomerase are secreted on the surface of endothelial cells. Furthermore, one or more of these generated free thiols within β2GPI are also shown to be nitrosylated. Finally, the functional significance of these findings is explored, by showing that free thiol–containing β2GPI has a powerful effect in protecting endothelial cells and EAhy926 cells from oxidative stress–induced cell death.

The roles of thioredoxin and thioredoxin-binding protein-2 in endometriosis

BACKGROUND

Oxidative stress is considered to be involved in the establishment and development of endometriosis. Thioredoxin (TRX) is an endogenous redox regulator that protects cells against oxidative stress, and TRX-binding protein-2 (TBP-2) is a negative regulator of TRX in the biological function and expression. The aim of this study was to investigate the roles of TRX and TBP-2 in the pathophysiology of endometriosis.

METHODS

A total of 35 patients with histologically confirmed endometriosis and 31 patients without endometriosis participated in this study. Real-time polymerase chain reaction was used to quantify TRX and TBP-2 mRNA levels, and immunohistochemistry (IHC) was used to assess TRX and TBP-2 protein localization in the endometrium. Serum and peritoneal fluid levels of TRX and TBP-2 were measured using a specific commercial ELISA.

RESULTS

There were no significant differences in TRX mRNA levels in the endometrium of patients with endometriosis and the control groups. However, TBP-2 mRNA levels in the endometrium were lower, and the TRX to TBP-2 ratio was higher in patients with endometriosis than in the control group. In particular, the TRX to TBP-2 ratio was significantly higher during late secretory and menstrual phase in patients with endometriosis compared with the control group. IHC studies also showed the decreased TBP-2 immunoreactivity in patients with endometriosis compared with the control group. There was no correlation between TRX and TBP-2 mRNA levels in patients with endometriosis, whereas TRX mRNA levels were positively correlated with TBP-2 mRNA levels in the control group. There were no significant differences between the two groups in TRX and TBP-2 levels in serum or peritoneal fluid.

CONCLUSIONS

Aberrant expression of TRX and TBP-2 in the endometrium may be associated with the establishment of endometriosis.

Discovery, identification, and characterization of candidate pharmacodynamic markers of methionine aminopeptidase-2 inhibition

The catalytic activity of methionine aminopeptidase-2 (MetAP2) has been pharmacologically linked to cell growth, angiogenesis, and tumor progression, making this an attractive target for cancer therapy. An assay for monitoring specific protein changes in response to MetAP2 inhibition, allowing pharmacokinetic (PK)/pharmacodynamic (PD) models to be established, could dramatically improve clinical decision-making. Candidate MetAP2-specific protein substrates were discovered from undigested cell culture-derived proteomes by MALDI-/SELDI-MS profiling and a biochemical method using (35)S-Met labeled protein lysates. Substrates were identified either as intact proteins by FT-ICR-MS or applying in-gel protease digestions followed by LC-MS/MS. The combination of these approaches led to the discovery of novel MetAP2-specific substrates including thioredoxin-1 (Trx-1), SH3 binding glutamic acid rich-like protein (SH3BGRL), and eukaryotic elongation factor-2 (eEF2). These studies also confirmed glyceraldehye 3-phosphate dehydrogenase (GAPDH) and cyclophillin A (CypA) as MetAP2 substrates. Additional data in support of these proteins as MetAP2-specific substrates were provided by in vitro MetAP1/MetAP2 enzyme assays with the corresponding N-terminal derived peptides and 1D/2D Western analyses of cellular and tissue lysates. FT-ICR-MS characterization of all intact species of the 18 kDa substrate, CypA, enabled a SELDI-MS cell-based assay to be developed for correlating N-terminal processing and inhibition of proliferation. The MetAP2-specific protein substrates discovered in this study have diverse properties that should facilitate the development of reagents for testing in preclinical and clinical environments.

Thioredoxin and thioredoxin-binding protein-2 in cancer and metabolic syndrome

Thioredoxin (TRX), a small redox-active multifunctional protein, acts as a potent antioxidant and a redox regulator in signal transduction. TRX expression is elevated in various types of human cancer. Overexpression of TRX introduces resistance to anti-cancer drugs or radiation-induced apoptosis; however, there is no evidence that the incidence of cancer is frequent in TRX-transgenic mice or that the administration of recombinant human TRX enhances tumor growth. Plasma/serum level of TRX is a good marker for oxidative stress-induced various disorders, including metabolic syndrome. Thioredoxin-binding protein-2 (TBP-2), which was originally identified as a negative regulator of TRX, acts as a growth suppressor and a regulator in lipid metabolism. TBP-2 expression is downregulated in various types of human cancer. TBP-2 deficiency induces lipid dysfunction and a phenotype resembling Reye syndrome. Thus, TRX and TBP-2 play important roles in the pathophysiology of cancer and metabolic syndrome by direct interaction or by independent mechanisms.

From oxygen sensing to heart failure: role of thioredoxin

Oxidative stress has been widely recognized to be involved in the pathogenesis of cardiopulmonary disorders. In ischemic heart diseases, it is involved not only in the development of atherosclerosis but also in ongoing ischemic injury, especially in the reperfusion process. Cardiomyopathy is another cardiac disorder in which oxidative stress is involved. In diabetic cardiomyopathy, homocysteine, a well-known source of oxidative stress, is believed to play major roles in its development. Thioredoxin (TRX) is a redox-acting protein ubiquitously present in the human body. It also is inducible by a wide variety of oxidative stresses. TRX is a multifunctional protein and has anti-inflammatory and antiapoptotic effects, as well as antioxidative effects. It is therefore feasible to think that TRX is a potential therapy for cardiac disease. Moreover, serum TRX is a well-recognized biomarker of various diseases involving oxidative stress, and this is also the case for cardiac disorders. Here we discuss how TRX is useful as a biomarker of and therapeutic agent for cardiopulmonary disorders, especially focusing on ischemic heart disease, myocarditis and oxygen sensing, and acute respiratory distress syndrome.

Oxygen sensing and redox signaling: the role of thioredoxin in embryonic development and cardiac diseases

It is important to regulate the oxygen concentration and scavenge oxygen radicals throughout the life of animals. In mammalian embryos, proper oxygen concentration gradually increases in utero and excessive oxygen is rather toxic during early embryonic development. Reactive oxygen species (ROS) are generated as by-products in the respiratory system and increased under inflammatory conditions. In the pathogenesis of a variety of adult human diseases such as cancer and cardiovascular disorders, ROS cause an enhancement of tissue injuries. ROS promote not only the development of atherosclerosis but also tissue injury during the reperfusion process. The thioredoxin (TRX) system is one of the most important mechanisms for regulating the redox balance. TRX is a small redox active protein distributed ubiquitously in various mammalian tissues and cells. TRX acts as not only an antioxidant but also an anti-inflammatory and an antiapoptotic protein. TRX is induced by oxidative stress and released from cells in response to oxidative stress. In various human diseases, the serum/plasma level of TRX is a well-recognized biomarker of oxidative stress. Here we discuss the roles of TRX on oxygen stress and redox regulation from different perspectives, in embryogenesis and in adult diseases focusing on cardiac disorders.

Thioredoxin: friend or foe in human disease?

Thioredoxin (Trx), a small, ubiquitous thiol [sulfydryl (-SH)] protein, is one of the most important regulators of reduction-oxidation (redox) balance and, thus, redox-controlled cell functions. Although Trx was discovered 40 years ago in bacteria, the number and diversity of processes that Trx influences in human cells have only been appreciated recently. Processes influenced by Trx include the control of cellular redox balance, the promotion of cell growth, the inhibition of apoptosis and the modulation of inflammation. Not surprisingly, the role of Trx in a wide range of human diseases and conditions, including cancer, viral disease, ischaemia-reperfusion injury, cardiac conditions, aging, premature birth and newborn physiology, is subject to intense investigation. However, whether Trx contributes to or prevents the pathology of a particular condition is not always clear. In this article, we review the role of Trx in human disease and relate this to its redox activity and biological properties, and discuss the development and use of therapies that either inhibit or augment Trx activity.

Increased Gene Expression of Glutathione Peroxidase-3 in Diabetic Mouse Heart

Increased incidence of heart disease is reported in patients with diabetes. To elucidate a molecular profile of expressed genes during the progression of diabetes, a cDNA array was screened in the hearts of mice treated with streptozotocin (200 mg/kg, i.v.). Among the genes investigated, the plasma type glutathione peroxidase, GPX-3, was predominantly up-regulated in diabetic mice compared with control mice. In northern blot analysis, a significant increase in GPX-3 expression was observed as early as 5 d after the induction of hyperglycemia. On day 21, a nearly three-fold induction was demonstrated. Daily administration of insulin (0.2 U/d, s.c.) for 21 d almost completely abolished the increase in GPX-3 mRNA in streptozotocin-treated mice, suggesting that the expression level of the GPX-3 gene was dependent on insulin and serum glucose. Increased GPX-3 may play a significant role in protecting cardiomyocytes from oxidative stress caused by hyperglycemia.

Parameters for Measurement of Oxidative Stress in Diabetes Mellitus: Applicability of Enzyme-Linked Immunosorbent Assay for Clinical Evaluation

Investigations of the mechanisms involved in the onset and progression of diabetes have recently confronted the role of reactive oxygen species (ROS) and oxidative stress. Prolonged exposure to hyperglycemic conditions induces nonenzymatic glycation of protein via the so-called Maillard reaction, resulting in Schiff-base products and Amadori products that engender ROS production. These processes initiate and exacerbate micro- and macrovascular complications in diabetes. Increased oxidative stress is induced by excessive ROS production and inadequate antioxidant defenses. Recently, oxidative stress status markers have been associated directly with the severity and prognosis of diabetes. To examine oxidative stress, reliable and high-throughput methods are needed to examine large numbers of clinical samples. The emerging availability of enzyme-linked immunosorbent assay (ELISA) for oxidative stress status markers allows its application to assessment of various pathophysiologic conditions, including diabetes. This review outlines the recent achievements of ELISA application for clinical studies elucidating oxidative stress. It introduces the potential applicability of ELISA for investigating oxidative stress in diabetes.

Elevation of blood thioredoxin in hemodialysis patients with hepatitis C virus infection

BACKGROUND

Thioredoxin (TRX) is a stress-inducible thiol-containing protein, which has been shown to be an indicator of oxidative stress in a variety of diseases. The association between oxidative stress and hepatitis C virus (HCV) infection, however, remains unknown in hemodialysis patients.

METHODS

We measured serum TRX levels in 85 hemodialysis patients positive for anti-HCV antibodies (age, 60 +/- 1 years old; hemodialysis duration, 17 +/- 1 years; M/F = 57/28) by enzyme-linked immunosorbent assay (ELISA), and examined whether blood TRX may be associated with HCV-related hepatic injury.

RESULTS

Serum TRX was significantly higher in hemodialysis patients with HCV infection (112.3 +/- 3.7 ng/mL, N = 85) than in those without HCV infection (69.7 +/- 3.3 ng/mL, N = 59) (age, 69 +/- 2 years old; hemodialysis duration, 6 +/- 1 years; M/F = 32/27, P < 0.01) or normal subjects (28.0 +/- 5.4 ng/mL, N = 9). TRX was significantly correlated with time on hemodialysis (r = 0.27, P = 0.01) in HCV-positive patients, while it was associated with the patient's age in HCV-negative patients (r = 0.42, P < 0.01). Blood TRX was significantly correlated with asparate aminotransferase in patients with HCV infection (r = 0.34, P < 0.01) and without HCV infection (r = 0.46, P < 0.01). However, serum TRX was not associated with blood alanine aminotransferase, a relatively specific marker of hepatic cellular damage, in HCV-infected hemodialysis patients. A significant relationship was found between serum ferritin and TRX (r = 0.25, P = 0.02) and malondialdehyde (MDA) values (r = 0.25, P = 002) in HCV-positive patients. Serum TRX was also higher in the patients receiving weekly iron supplement with HCV infection (135.3 +/- 10.2 ng/mL vs. 110.2 +/- 3.9 ng/mL, P = 0.06) and without HCV infection (91.8 +/- 12.1 ng/mL vs. 65.2 +/- 2.7 ng/mL, P < 0.01).

CONCLUSION

There was a greater increase in serum TRX in hemodialysis patients with HCV viremia than without HCV viremia. However, there may not be an association between serum TRX and HCV-related hepatic injury. TRX increased with serum ferritin in HCV-infected patients and further increased by iron infusion. These findings indicate that HCV infection and iron loading may aggravate oxidative stress in dialysis patients.