Circulating peroxiredoxin 4 and type 2 diabetes risk: the Prevention of Renal and Vascular Endstage Disease (PREVEND) study

A comprehensive review of peroxiredoxin 4, a redox protein evolved in oxidative protein folding coupled with hydrogen peroxide detoxification

Peroxiredoxin (PRDX) primarily employs electrons from thioredoxin in order to reduce peroxides. PRDX4 mainly resides either in the endoplasmic reticulum (ER) lumen or in extracellular spaces. Due to the usage of alternative promoters, a first exon is transcribed from different regions of the Prdx4 gene, which results in two types of mRNAs. The first type is designated as Prdx4. It is translated with a cleavable, hydrophobic signal sequence and is expressed in most cells throughout the body. The second type is designated as Prdx4t. The peroxidase activity of PRDX4 is involved in both the reduction of hydrogen peroxides and in the oxidative folding of nascent proteins in the ER. Prdx4 appears to have evolved from an ancestral gene in Eutherians simultaneously with the evolution of sperm protamine to cysteine-rich peptides, and, therefore, the testis-specific PRDX4t is likely involved in spermatogenesis through the oxidative folding of protamine. The dysfunction of PRDX4 leads to oxidative damage and ER stress, and is related to various diseases including diabetes and cancer. In this review article we refer to the results of biological and medical research in order to unveil the functional consequences of this unique member of the PRDX family.

Relevant Serum Endoplasmic Reticulum Stress Biomarkers in Type 2 Diabetes and Its Complications: A Systematic Review and Meta-Analysis

Endoplasmic reticulum stress (ERS) is activated in all cells by stressors such as hyperglycemia. However, it remains unclear which specific serum biomarkers of ERS are consistently altered in type 2 diabetes (T2D). We aimed to identify serum ERS biomarkers that are consistently altered in T2D and its complications, and their correlation with metabolic and anthropometric variables. We performed a systematic review and meta-analysis following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Meta-Analyses and Systematic Reviews of Observational Studies (MOOSE). The risk of bias was assessed using the Newcastle-Ottawa scale. Random-effects models weighted by the inverse variance were employed to estimate the standardized mean difference and correlations as effect size measures. Indicators of heterogeneity and meta-regressions were evaluated. Of the 1206 identified studies, 22 were finally included, representing 11,953 subjects (2224 with T2D and 9992 non-diabetic controls). Most studies were of high quality. Compared with controls, subjects with T2D had higher circulating levels of heat shock protein 70 (HSP70; SMD: 2.30, 95% CI 1.13-3.46; p < 0.001) and secretagogin (SMD: 0.60, 95%CI 0.19-1.01; p < 0.001). They also had higher serum levels of peroxiredoxin-1, -2, -4, and -6. Secretagogin inversely correlated with HOMA-IR, yet positively correlated with HOMA-B, HbA1c, and FPG. PRX4 negatively correlated with HbA1c and FPG, while HSP70 positively correlated with HbA1c. In conclusion, six ERS biomarkers are consistently elevated in human T2D and correlate with glycemic control, insulin resistance, and β-cell function. Emerging evidence links serum ERS biomarkers to diabetes complications, but further research should evaluate their prognostic implications.

Serum peroxiredoxin-4, a biomarker of oxidative stress, associates with new-onset chronic kidney disease: A population-based cohort study

BACKGROUND

Chronic Kidney Disease (CKD), is often detected late due to its asymptomatic nature in the early stage of the disease. Overproduction of reactive oxygen species contributes to various pathological processes through oxidative stress (OS), impacting on cellular structures and functions with previous studies suggesting a link between OS and CKD progression. This study investigated the association between serum peroxiredoxin-4 (Prx4), a biomarker of oxidative stress, and the development of CKD in the general population.

METHODS

This study featured data from the Prevention of REnal and Vascular ENd-stage Disease (PREVEND) cohort, involving 5341 participants without CKD at baseline who underwent extensive prospective health evaluations. Serum Prx4 levels were quantified using an immunoluminometric assay. The primary outcome was new-onset CKD as defined by the composite of urinary albumin excretion (UAE) > 30 mg/24-h, an estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2, or both.

RESULTS

Baseline median Prx4 level was 0.65 [interquartile range (IQR): 0.42-1.04] U/L, median eGFR was 98 [IQR: 87-108] mL/min/1.73 m2, and median UAE was 8.1 [IQR: 6.0-12.1] mg/L. During a median follow-up of 10.4 [IQR: 6.3-11.4] years, 867 (16.2 %) patients developed new-onset CKD. Higher Prx4 levels were significantly associated with an increased risk of CKD (hazard ratio (HR) per doubling: 1.29 [95 % confidence interval (CI): 1.21-1.37], p < 0.001), also after adjustment for risk factors including sex, smoking status, systolic blood pressure, high-sensitive C-reactive protein, chronic heart failure, diabetes mellitus and dyslipidemia (HR per doubling: 1.16 [1.06-1.24], p < 0.001). Sensitivity analyses confirmed the robustness of these findings.

CONCLUSIONS

This study supports the hypothesis that systemic oxidative stress, reflected by higher serum Prx4 levels, is significantly associated with the risk of developing CKD in the general population. These findings suggest that Prx4 could be a valuable biomarker for early risk stratification and prevention strategies in CKD management.

Assessing anti oxidant, antidiabetic potential and GCMS profiling of ethanolic root bark extract of Zanthoxylum rhetsa (Roxb.) DC: Supported by in vitro, in vivo and in silico molecular modeling

Zanthoxylum rhetsa (ZR) is used traditionally to manage a variety of ailments, including diabetes. Oxidative stress may accelerate the diabetic condition. The available antidiabetic and antioxidant drugs have many shortcomings including resistance, inefficiency, higher dose, side effects and costs. The goal of the current investigation was to assess the antioxidant capacity and antidiabetic activity of an ethanolic extract of Zanthoxylum rhetsa root bark (ZRRB) through in vitro, in vivo, and in silico methods. The antioxidant capacity of the ZRRB extract was measured using both the DPPH radical assay and the total antioxidant activity test. The oral glucose tolerance test (OGTT) and alloxan-induced diabetic mice model were also used to examine in vivo antidiabetic efficacy. Phytochemicals identification was done by GCMS analysis. Additionally, computational methods such as molecular docking, ADMET analysis, and molecular dynamics (MD) modeling were performed to determine the above pharmacological effects. The extract demonstrated significant DPPH scavenging activity (IC50 = 42.65 μg/mL). In the OGTT test and alloxan-induced diabetes mice model, the extract effectively lowered blood glucose levels. Furthermore, in vitro inhibition of pancreatic α-amylase studies demonstrated the ZRRB extract as a good antidiabetic crude drug (IC50 = 81.45 μg/mL). GCMS investigation confirmed that the crude extract contains 16 major phytoconstituents, which were docked with human peroxiredoxin-5, α-amylase, and sulfonylurea receptor 1. Docking and pharmacokinetic studies demonstrated that among 16 phytoconstituents, 6H-indolo[3,2,1-de] [1,5]naphthyridin-6-one (CID: 97176) showed the highest binding affinity to targeted enzymes, and imitated Lipinski's rule of five. Furthermore, MD simulation data confirmed that the aforementioned compound is very steady to the binding site of α-amylase and sulfonylurea receptor 1 receptors. Findings from in vitro, in vivo and in silico investigation suggest that ZRRB extract contains a lead compound that could be a potent source of antidiabetic drug candidate.

Endothelial peroxiredoxin-4 is indispensable for blood-brain barrier integrity and long-term functional recovery after ischemic stroke

The endothelial lining of cerebral microvessels is damaged relatively early after cerebral ischemia/reperfusion (I/R) injury and mediates blood-brain barrier (BBB) disruption, neurovascular injury, and long-term neurological deficits. I/R induces BBB leakage within 1 h due to subtle structural alterations in endothelial cells (ECs), including reorganization of the actin cytoskeleton and subcellular redistribution of junctional proteins. Herein, we show that the protein peroxiredoxin-4 (Prx4) is an endogenous protectant against endothelial dysfunction and BBB damage in a murine I/R model. We observed a transient upregulation of Prx4 in brain ECs 6 h after I/R in wild-type (WT) mice, whereas tamoxifen-induced, selective knockout of Prx4 from endothelial cells (eKO) mice dramatically raised vulnerability to I/R. Specifically, eKO mice displayed more BBB damage than WT mice within 1 to 24 h after I/R and worse long-term neurological deficits and focal brain atrophy by 35 d. Conversely, endothelium-targeted transgenic (eTG) mice overexpressing Prx4 were resistant to I/R-induced early BBB damage and had better long-term functional outcomes. As demonstrated in cultures of human brain endothelial cells and in animal models of I/R, Prx4 suppresses actin polymerization and stress fiber formation in brain ECs, at least in part by inhibiting phosphorylation/activation of myosin light chain. The latter cascade prevents redistribution of junctional proteins and BBB leakage under conditions of Prx4 repletion. Prx4 also tempers microvascular inflammation and infiltration of destructive neutrophils and proinflammatory macrophages into the brain parenchyma after I/R. Thus, the evidence supports an indispensable role for endothelial Prx4 in safeguarding the BBB and promoting functional recovery after I/R brain injury.

Serum peroxiredoxin-4, a biomarker of oxidative stress, is associated with the development of nephropathy in patients with type 2 diabetes (Zodiac-65)

Oxidative stress is implicated in the development and progression of type 2 diabetes (T2D). Peroxiredoxin-4 is an antioxidant protein, which may serve as biomarker of oxidative stress, and has previously been associated with new-onset T2D. In this study, we investigated associations between circulating peroxiredoxin-4 and the risk of developing new-onset microvascular complications in T2D patients. Serum peroxiredoxin-4 was measured in 536 patients with T2D with (n = 257) and without (n = 279) baseline microvascular complications who participated in a primary-care based cohort study (Zwolle Outpatient Diabetes project Integrating Available Care [ZODIAC] study). Over a median follow-up of 3.4 years, 38 (13.6%) developed nephropathy, defined as albuminuria in two consecutive urine samples. In multivariable Cox proportional hazards regression analyses, peroxiredoxin-4 was associated with new-onset nephropathy (hazard ratio [HR] per doubling 1.78 [95% CI: 1.27-2.49], P < 0.001) after adjustment for potential confounding factors, including age, sex, disease duration, HbA1c levels, macrovascular complications, systolic blood pressure, and even high-sensitive C-reactive protein. There was no interaction of peroxiredoxin-4 with hs-CRP impacting on new-onset nephropathy. No significant associations were found with new-onset retinopathy or neuropathy. In conclusion, circulating peroxiredoxin-4 associates positively with an increased risk of developing nephropathy in T2D independent and irrespective of low-grade inflammation.

Comparative Efficacy of Rosuvastatin Monotherapy and Rosuvastatin/Ezetimibe Combination Therapy on Insulin Sensitivity and Vascular Inflammatory Response in Patients with Type 2 Diabetes Mellitus

BACKGRUOUND

Type 2 diabetes mellitus (T2DM) induces endothelial dysfunction and inflammation, which are the main factors for atherosclerosis and cardiovascular disease. The present study aimed to compare the effects of rosuvastatin monotherapy and rosuvastatin/ezetimibe combination therapy on lipid profile, insulin sensitivity, and vascular inflammatory response in patients with T2DM.

METHODS

A total of 101 patients with T2DM and dyslipidemia were randomized to either rosuvastatin monotherapy (5 mg/day, n=47) or rosuvastatin/ezetimibe combination therapy (5 mg/10 mg/day, n=45) and treated for 12 weeks. Serum lipids, glucose, insulin, soluble intercellular adhesion molecule-1 (sICAM-1), and peroxiredoxin 4 (PRDX4) levels were determined before and after 12 weeks of treatment.

RESULTS

The reduction in low density lipoprotein cholesterol (LDL-C) by more than 50% from baseline after treatment was more in the combination therapy group. The serum sICAM-1 levels increased significantly in both groups, but there was no difference between the two groups. The significant changes in homeostasis model assessment of insulin resistance (HOMA-IR) and PRDX4 were confirmed only in the subgroup in which LDL-C was reduced by 50% or more in the combination therapy group. However, after adjusting for diabetes mellitus duration and hypertension, the changes in HOMA-IR and PRDX4 were not significant between the two groups.

CONCLUSION

Although rosuvastatin/ezetimibe combination therapy had a greater LDL-C reduction effect than rosuvastatin monotherapy, it had no additional effects on insulin sensitivity and vascular inflammatory response. Further studies are needed on the effect of long-term treatment with ezetimibe on insulin sensitivity and vascular inflammatory response.

Reactive oxygen species, toxicity, oxidative stress, and antioxidants: chronic diseases and aging

A physiological level of oxygen/nitrogen free radicals and non-radical reactive species (collectively known as ROS/RNS) is termed oxidative eustress or "good stress" and is characterized by low to mild levels of oxidants involved in the regulation of various biochemical transformations such as carboxylation, hydroxylation, peroxidation, or modulation of signal transduction pathways such as Nuclear factor-κB (NF-κB), Mitogen-activated protein kinase (MAPK) cascade, phosphoinositide-3-kinase, nuclear factor erythroid 2-related factor 2 (Nrf2) and other processes. Increased levels of ROS/RNS, generated from both endogenous (mitochondria, NADPH oxidases) and/or exogenous sources (radiation, certain drugs, foods, cigarette smoking, pollution) result in a harmful condition termed oxidative stress ("bad stress"). Although it is widely accepted, that many chronic diseases are multifactorial in origin, they share oxidative stress as a common denominator. Here we review the importance of oxidative stress and the mechanisms through which oxidative stress contributes to the pathological states of an organism. Attention is focused on the chemistry of ROS and RNS (e.g. superoxide radical, hydrogen peroxide, hydroxyl radicals, peroxyl radicals, nitric oxide, peroxynitrite), and their role in oxidative damage of DNA, proteins, and membrane lipids. Quantitative and qualitative assessment of oxidative stress biomarkers is also discussed. Oxidative stress contributes to the pathology of cancer, cardiovascular diseases, diabetes, neurological disorders (Alzheimer's and Parkinson's diseases, Down syndrome), psychiatric diseases (depression, schizophrenia, bipolar disorder), renal disease, lung disease (chronic pulmonary obstruction, lung cancer), and aging. The concerted action of antioxidants to ameliorate the harmful effect of oxidative stress is achieved by antioxidant enzymes (Superoxide dismutases-SODs, catalase, glutathione peroxidase-GPx), and small molecular weight antioxidants (vitamins C and E, flavonoids, carotenoids, melatonin, ergothioneine, and others). Perhaps one of the most effective low molecular weight antioxidants is vitamin E, the first line of defense against the peroxidation of lipids. A promising approach appears to be the use of certain antioxidants (e.g. flavonoids), showing weak prooxidant properties that may boost cellular antioxidant systems and thus act as preventive anticancer agents. Redox metal-based enzyme mimetic compounds as potential pharmaceutical interventions and sirtuins as promising therapeutic targets for age-related diseases and anti-aging strategies are discussed.

A Sex-Specific Comparative Analysis of Oxidative Stress Biomarkers Predicting the Risk of Cardiovascular Events and All-Cause Mortality in the General Population: A Prospective Cohort Study

Oxidative stress plays a pivotal role in cardiovascular (CV) disease, but current biomarkers used to predict CV events are still insufficient. In this study, we comparatively assessed the utility of redox-related biomarkers in predicting the risk of CV events and all-cause mortality in male and female subjects from the general population. Subjects (n = 5955) of the Prevention of REnal and Vascular ENd-stage Disease (PREVEND) population-based cohort study were included. Blood homocysteine, gamma-GT, HDL cholesterol, bilirubin and protein-adjusted free thiol (R-SH, sulfhydryl groups) levels were quantified at baseline and were prospectively analyzed in association with the risk of CV events and all-cause mortality. After adjustment for potentially confounding factors, protein-adjusted R-SH and homocysteine levels were significantly associated with the risk of CV events in men (HR 0.63 [0.40–0.99], p = 0.045 and HR 1.58 [1.20–2.08], p = 0.001, respectively). Protein-adjusted R-SH and HDL cholesterol levels were significantly associated with the risk of all-cause mortality in men (HR 0.52 [0.32–0.85], p = 0.009 and HR 0.90 [0.85–0.94], p < 0.001, respectively), while the same was observed for bilirubin and homocysteine levels in women (HR 0.68 [0.48–0.98], p = 0.040 and HR 2.30 [1.14–3.76], p < 0.001, respectively). Lower levels of protein-adjusted R-SH were robustly associated with an increased risk of CV events and all-cause mortality in men. Our results highlight the value of R-SH levels in cardiovascular risk assessment and their potential significance as being amenable to therapeutic intervention, while reaffirming the importance of other oxidative stress-related biomarkers, such as homocysteine, HDL cholesterol and bilirubin.

Preoperative circulating peroxiredoxin 1 levels as a predictor of non-alcoholic fatty liver disease remission after laparoscopic bariatric surgery

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is associated with obesity and insulin resistance and can be improved after bariatric surgery. Circulating Peroxiredoxin 1 (Prdx1) protein was reported to regulate energy metabolism and inflammation. This study aimed to investigate the roles of serum prdx1 in NAFLD patients with obesity undergoing LSG and to develop a prognostic model to predict the remission of severe NAFLD.

METHODS

The data of 93 participants from a tertiary hospital were assessed. Before laparoscopic sleeve gastrectomy (LSG) and three months after LSG, anthropometric parameters, laboratory biochemical data, and abdominal B-ultrasound results were collected, and their hepatic steatosis index (HSI) and triglyceride-glucose index (TyG) were calculated. A NAFLD improvement (NAFLD-I) nomogram prediction model was constructed using the least absolute shrinkage and selection operator (LASSO) regression and multiple regression, and its predictive ability was verified in a validation cohort.

RESULTS

The baseline Prdx1 (OR: 0.887, 95% CI: 0.816-0.963, p=0.004), preoperative TyG (OR: 8.207, 95% CI: 1.903-35.394, p=0.005) and HSI (OR: 0.861, 95% CI: 0.765-0.969, p=0.013) levels were independently associated with NAFLD-I at three months after LSG in NAFLD patients with obesity. In the primary and validation cohorts, the area under the receiver operating characteristic (AUC) of the developed nomogram model was 0.891 and 0.878, respectively. The preoperative circulating Prdx1 levels of NAFLD patients with obesity were significantly reduced after LSG (25.32 [18.99-30.88] vs. 23.34 [15.86-26.42], p=0.001). Prdx1 was related to obesity and hepatic steatosis based on correlation analysis.

CONCLUSION

The nomogram based on preoperative serum prdx1, HSI and TyG could be an effective tool for predicting remission of severe NAFLD after LSG.

Association of Prx4, Total Oxidant Status, and Inflammatory Factors with Insulin Resistance in Polycystic Ovary Syndrome

INTRODUCTION

Chronic inflammation and oxidative stress conditions have been reported in women with polycystic ovary syndrome (PCOS). Peroxiredoxin 4 (Prx4) is a related antioxidant in insulin synthesis. We hypothesized that insulin resistance in these women is associated with total oxidant status (TOS) and inflammatory factors.

MATERIALS AND METHODS

Two hundred three people including 104 PCOS patients and 99 healthy women, who were matched for age and body mass index (BMI), entered the study. Waist circumference of the participants was measured; serum glucose, lipid profile, insulin, Prx4, TOS, hs-CRP, and TNF-α were also evaluated.

RESULTS

The Prx4 level was significantly lower in PCOS than in the control group. In addition, marked increase was observed in the concentration of TOS, hs-CRP, and TNF-α in PCOS, compared to the healthy women. There was a positive correlation of TOS with hs-CRP, TNF-α, and HOMA-IR. The risk of PCOS for subjects with high hs-CRP was 60 times greater than those who had low serum hs-CRP concentration; after performing multiple logistic regression analyses with the backward method, TNF-α was considered as an effective biomarker to predict PCOS β = 49.087 (all p < 0.05).

CONCLUSION

This study identified increased oxidative stress and inflammation in PCOS; this may be due to decrease in the antioxidants, such as Prx4.

Unfolding Nrf2 in diabetes mellitus

In spite of much awareness, diabetes mellitus continues to remain one of major reasons for mortality and morbidity rate all over the globe. Free radicals cause oxidative stress which is responsible for causing diabetes. The recent advancements in elucidation of ARE/keap1/Nrf2 pathway can help in better understanding of diabetes mellitus. Various clinical trials and animal studies have shown the promising effect of Nrf2 pathway in reversing diabetes by counteracting with the oxidative stress produced. The gene is known to dissociate from Keap1 on coming in contact with such stresses to show preventive and prognosis effect. The Nrf2 gene has been marked as a molecular player in dealing with wide intracellular as well as extracellular cellular interactions in different diseases. The regulation of this gene gives some transcription factor that contain antioxidant response elements (ARE) in their promoter region and thus are responsible for encoding certain proteins involved in regulation of metabolic and detoxifying enzymes.

Peri/Epicellular Thiol Oxidoreductases as Mediators of Extracellular Redox Signaling

Significance: Supracellular redox networks regulating cell-extracellular matrix (ECM) and organ system architecture merge with structural and functional (catalytic or allosteric) properties of disulfide bonds. This review addresses emerging evidence that exported thiol oxidoreductases (TORs), such as thioredoxin, protein disulfide isomerases (PDIs), quiescin sulfhydryl oxidases (QSOX)1, and peroxiredoxins, composing a peri/epicellular (pec)TOR pool, mediate relevant signaling. pecTOR functions depend mainly on kinetic and spatial regulation of thiol-disulfide exchange reactions governed by redox potentials, which are modulated by exported intracellular low-molecular-weight thiols, together conferring signal specificity. Recent Advances: pecTOR redox-modulates several targets including integrins, ECM proteins, surface molecules, and plasma components, although clear-cut documentation of direct effects is lacking in many cases. TOR catalytic pathways, displaying common patterns, culminate in substrate thiol reduction, oxidation, or isomerization. Peroxiredoxins act as redox/peroxide sensors, contrary to PDIs, which are likely substrate-targeted redox modulators. Emerging evidence suggests important pecTOR roles in patho(physio)logical processes, including blood coagulation, vascular remodeling, mechanosensing, endothelial function, immune responses, and inflammation. Critical Issues: Effects of pecPDIs supporting thrombosis/platelet activation have been well documented and reached the clinical arena. Roles of pecPDIA1 in vascular remodeling/mechanosensing are also emerging. Extracellular thioredoxin and pecPDIs redox-regulate immunoinflammation. Routes of TOR externalization remain elusive and appear to involve Golgi-independent routes. pecTORs are particularly accessible drug targets. Future Directions: Further understanding mechanisms of thiol redox reactions and developing assays for assessing pecTOR redox activities remain important research avenues. Also, addressing pecTORs as disease markers and achieving more efficient/specific drugs for pecTOR modulation are major perspectives for diagnostic/therapeutic improvements.

Peroxiredoxin 4 levels in patients with PCOS and/or obesity

BACKGROUND

Peroxiredoxin 4 is a part of endogen antioxidant system and its levels are elevated in increased oxidative stress conditions. It is found to be positively associated with cardiovascular risk. The aim of the study was to investigate peroxiredoxin 4 levels in women with polycystic ovarian syndrome (PCOS) and/or obesity.

METHODS

In this cros-sesctional study were included 80 patients. Anthropometric measurements and biochemical tests, including peroxiredoxin 4 measurement, were performed.

RESULTS

There was a tendency towards lower peroxiredoxin 4 levels in non-obese PCOS subjects (5674.8 ± 3822.4 pg/ml), higher in obese PCOS (6588.9 ± 3731.0 pg/ml) and even higher in obese patients without PCOS (7724.6 ± 4840.4 pg/ml). Patients with abdominal obesity according to waist circumference and waist-to-hip ratio had significantly higher levels of peroxiredoxin compared to those without (7108.2 ± 4568.0 vs. 5079.8 ± 2555.4 pg/ml; p = 0.015 and 7310.6 ± 2646.2 vs. 4785.0 ± 2646.2 pg/ml; p = 0.013). There was no difference in peroxiredoxin 4 levels in patients with and without insulin resistance, hypertension, dislipidemia, hyperandrogenemia, metabolic syndrome. Peroxiredoxin 4 showed weak positive correlation to weight (r = 0.228; p = 0.044) and visceral adiposity index (r = 0.278; p = 0.031) and higher to erythrocyte sedimentation rate (r = 0.4; p < 0.01), but not to hormonal parameters and insulin sensitivity indexes.

CONCLUSIONS

Non-obese patients with PCOS have a tendency towards lower peroxiredoxin 4 levels compared to obese patients with and without PCOS. Patients with abdominal obesity have significantly higher peroxiredoxin 4 levels than those without. We were not able to prove correlation between peroxiredoxin 4 levels and hormonal and carbohydrate status of the PCOS patients.

Role of protein carbonylation in diabetes

Diabetes mellitus is a metabolic disease characterized by, among others, elevated blood glucose levels. Hyperglycaemia as well as enhanced levels of glucose-derived reactive metabolites contribute to the development of diabetic complications partly via increased generation of reactive oxygen species (ROS). ROS are not only part of signaling pathways themselves but also lead to carbonylation of particular amino acid side chains by direct metal-catalyzed oxidation. In addition, carbonyl groups can be introduced into proteins indirectly by non-oxidative covalent adduction of reactive carbonyl species generated by the oxidation of lipids or carbohydrates. Both direct and indirect carbonylation mechanisms may affect protein conformation, activity, and function. Herein we introduce the different mechanisms of the carbonylation reaction, discuss degradation mechanisms, and the fate of proteins modified this way and how the overall degree of carbonylation affects protein homeostasis and function differently. The role of protein carbonylation in metabolic control systems and cell signaling are also summarized. Finally, current diagnostic and antioxidant therapeutic options in diabetes are discussed.

Redox Regulation of Inflammatory Processes Is Enzymatically Controlled

Redox regulation depends on the enzymatically controlled production and decay of redox active molecules. NADPH oxidases, superoxide dismutases, nitric oxide synthases, and others produce the redox active molecules superoxide, hydrogen peroxide, nitric oxide, and hydrogen sulfide. These react with target proteins inducing spatiotemporal modifications of cysteine residues within different signaling cascades. Thioredoxin family proteins are key regulators of the redox state of proteins. They regulate the formation and removal of oxidative modifications by specific thiol reduction and oxidation. All of these redox enzymes affect inflammatory processes and the innate and adaptive immune response. Interestingly, this regulation involves different mechanisms in different biological compartments and specialized cell types. The localization and activity of distinct proteins including, for instance, the transcription factor NFκB and the immune mediator HMGB1 are redox-regulated. The transmembrane protein ADAM17 releases proinflammatory mediators, such as TNFα, and is itself regulated by a thiol switch. Moreover, extracellular redox enzymes were shown to modulate the activity and migration behavior of various types of immune cells by acting as cytokines and/or chemokines. Within this review article, we will address the concept of redox signaling and the functions of both redox enzymes and redox active molecules in innate and adaptive immune responses.

The Nrf2/Keap1/ARE Pathway and Oxidative Stress as a Therapeutic Target in Type II Diabetes Mellitus

Despite improvements in awareness and treatment of type II diabetes mellitus (TIIDM), this disease remains a major source of morbidity and mortality worldwide, and prevalence continues to rise. Oxidative damage caused by free radicals has long been known to contribute to the pathogenesis and progression of TIIDM and its complications. Only recently, however, has the role of the Nrf2/Keap1/ARE master antioxidant pathway in diabetic dysfunction begun to be elucidated. There is accumulating evidence that this pathway is implicated in diabetic damage to the pancreas, heart, and skin, among other cell types and tissues. Animal studies and clinical trials have shown promising results suggesting that activation of this pathway can delay or reverse some of these impairments in TIIDM. In this review, we outline the role of oxidative damage and the Nrf2/Keap1/ARE pathway in TIIDM, focusing on current and future efforts to utilize this relationship as a therapeutic target for prevention, prognosis, and treatment of TIID.

Increased peroxiredoxin 4 levels in patients with prediabetes compared to normal glucose tolerance subjects

BACKGROUND

Peroxiredoxin 4 is a part of endogen antioxidant system and its levels are elevated in oxidative stress conditions. Its levels are positively associated with cardiovascular risk. The aim of this study was to compare serum peroxiredoxin 4 levels between obese subjects with prediabetes and with normal glucose tolerance.

METHODS

In this study, we included 80 patients with mean age 50·4 ± 10·6 years and divided them into two age and BMI-matched groups - group 1 with obesity without glycaemic disturbances (n = 41) and group 2 with obesity and prediabetes (n = 39). Oral glucose tolerance test with measurement of immunoreactive insulin was performed in all participants, and the levels of peroxiredoxin 4 were measured using ELISA method.

RESULTS

We found significantly higher levels of peroxiredoxin 4 in patients with prediabetes compared to controls (2851·2 ± 4576·6 pg/ml vs 1088·0 ± 753·3 pg/ml; P = 0·022). There was a mild but statistically significant correlation between peroxiredoxin 4 and weight (r = 0·232; P = 0·038), waist circumference (r = 0·239; P = 0·044), creatinine (r = 0·264; P = 0·019), liver enzymes (ASAT - r = 0·289; P = 0·019 and ALAT - r = 0·305; P = 0·07) and white blood cells count (r = 0·317; P = 0·005). There was no difference in peroxiredoxin 4 levels in patients with and without insulin resistance, as well as with and without metabolic syndrome (MetS), although the levels of peroxiredoxin 4 increased with the number of components of MetS.

CONCLUSIONS

The levels of peroxiredoxin 4 are higher in patients with prediabetes, but are similar in subjects with and without insulin resistance, which suggests that the main factor for its increased levels is hyperglycaemia and not insulin sensitivity state.

Crystal Structure of the ERp44-Peroxiredoxin 4 Complex Reveals the Molecular Mechanisms of Thiol-Mediated Protein Retention

ERp44 controls the localization and transport of diverse proteins in the early secretory pathway. The mechanisms that allow client recognition and the source of the oxidative power for forming intermolecular disulfides are as yet unknown. Here we present the structure of ERp44 bound to a client, peroxiredoxin 4. Our data reveal that ERp44 binds the oxidized form of peroxiredoxin 4 via thiol-disulfide interchange reactions. The structure explains the redox-dependent recognition and characterizes the essential non-covalent interactions at the interface. The ERp44-Prx4 covalent complexes can be reduced by glutathione and protein disulfide isomerase family members in the ER, allowing the two components to recycle. This work provides insights into the mechanisms of thiol-mediated protein retention and indicates the key roles of ERp44 in this biochemical cycle to optimize oxidative folding and redox homeostasis.

Molecular cloning, characterization and mRNA expression of six peroxiredoxins from Black carp Mylopharyngodon piceus in response to lipopolysaccharide challenge or dietary carbohydrate

Peroxiredoxin (Prx) belongs to a cellular antioxidant protein family that plays important roles in innate immune function and anti-oxidative capability. In the present study, six Prxs were cloned from Black carp Mylopharyngodon piceus (MpPrx) by homology cloning and rapid amplification of cDNA ends (RACE) techniques. There were 199, 197, 250, 260, 189 and 222 amino acids in six MpPrxs, respectively. BLAST analysis reveals that MpPrxs shares high identities and similar characteristics with other known Prxs from animals. The phylogenetic analysis evidenced three major subclasses corresponding to one-Cys-Prx (MpPrx6), typical two-Cys-Prx (MpPrx1-4) and atypical 2-Cys-Prx (MpPrx5) that reflected the present hierarchy of vertebrates and invertebrates. Although six MpPrxs are constitutively expressed in all tissues, relatively higher-level mRNA expression levels of six MpPrxs can be detected in liver, eyes, heart and adipose tissues by real-time PCR assays. The transcriptional patterns of six MpPrxs mRNA in liver were detected by real-time PCR in Black carp after lipopolysaccharide (LPS) challenge and treated with graded levels of dietary carbohydrate (CHO) (106.5, 194.3, 288.4 and 379.1 g kg(-1)), respectively. These results showed that stimulation with LPS could induce up-expression of six MpPrxs mRNA, and the variations of MpPrx4 were more sensitive than these of other MpPrxs in the liver of Black carp. Compared with those in group with 106.5 g kg(-1) dietary CHO, the expression levels of MpPrx2, MpPrx3 and MpPrx6 were significantly down-regulated while MpPrx5 were significantly induced in liver of Black carp fed with adequate dietary CHO (194.3 g kg(-1)). In addition, significant up-regulations of MpPrx2, MpPrx3 and MpPrx6 were observed in Black carp fed with excessive dietary CHO (379.1 g kg(-1)). And MpPrx4 could be constantly induced with increasing dietary CHO contents in this study. These results indicated that MpPrxs were constitutive and inducible proteins and might play important roles in innate immune function after LPS challenge and regulating redox homeostasis in the metabolism of dietary CHO.

The Roles of Peroxiredoxin and Thioredoxin in Hydrogen Peroxide Sensing and in Signal Transduction

A challenge in the redox field is the elucidation of the molecular mechanisms, by which H2O2 mediates signal transduction in cells. This is relevant since redox pathways are disturbed in some pathologies. The transcription factor OxyR is the H2O2 sensor in bacteria, whereas Cys-based peroxidases are involved in the perception of this oxidant in eukaryotic cells. Three possible mechanisms may be involved in H2O2 signaling that are not mutually exclusive. In the simplest pathway, H2O2 signals through direct oxidation of the signaling protein, such as a phosphatase or a transcription factor. Although signaling proteins are frequently observed in the oxidized state in biological systems, in most cases their direct oxidation by H2O2 is too slow (10(1) M(-1)s(-1) range) to outcompete Cys-based peroxidases and glutathione. In some particular cellular compartments (such as vicinity of NADPH oxidases), it is possible that a signaling protein faces extremely high H2O2 concentrations, making the direct oxidation feasible. Alternatively, high H2O2 levels can hyperoxidize peroxiredoxins leading to local building up of H2O2 that then could oxidize a signaling protein (floodgate hypothesis). In a second model, H2O2 oxidizes Cys-based peroxidases that then through thiol-disulfide reshuffling would transmit the oxidized equivalents to the signaling protein. The third model of signaling is centered on the reducing substrate of Cys-based peroxidases that in most cases is thioredoxin. Is this model, peroxiredoxins would signal by modulating the thioredoxin redox status. More kinetic data is required to allow the identification of the complex network of thiol switches.

Clinical Relevance of Biomarkers of Oxidative Stress

SIGNIFICANCE

Oxidative stress is considered to be an important component of various diseases. A vast number of methods have been developed and used in virtually all diseases to measure the extent and nature of oxidative stress, ranging from oxidation of DNA to proteins, lipids, and free amino acids.

RECENT ADVANCES

An increased understanding of the biology behind diseases and redox biology has led to more specific and sensitive tools to measure oxidative stress markers, which are very diverse and sometimes very low in abundance.

CRITICAL ISSUES

The literature is very heterogeneous. It is often difficult to draw general conclusions on the significance of oxidative stress biomarkers, as only in a limited proportion of diseases have a range of different biomarkers been used, and different biomarkers have been used to study different diseases. In addition, biomarkers are often measured using nonspecific methods, while specific methodologies are often too sophisticated or laborious for routine clinical use.

FUTURE DIRECTIONS

Several markers of oxidative stress still represent a viable biomarker opportunity for clinical use. However, positive findings with currently used biomarkers still need to be validated in larger sample sizes and compared with current clinical standards to establish them as clinical diagnostics. It is important to realize that oxidative stress is a nuanced phenomenon that is difficult to characterize, and one biomarker is not necessarily better than others. The vast diversity in oxidative stress between diseases and conditions has to be taken into account when selecting the most appropriate biomarker.

Physiological and pathological views of peroxiredoxin 4

Peroxiredoxins (PRDXs) form an enzyme family that exhibits peroxidase activity using electrons from thioredoxin and other donor molecules. As the signaling roles of hydrogen peroxide in response to extracellular stimuli have emerged, the involvement of PRDX in the hydrogen peroxide-mediated signaling has become evident. Among six PRDX members in mammalian cells, PRDX4 uniquely possesses a hydrophobic signal peptide at the amino terminus, and, hence, it undergoes either secretion or retention by the endoplasmic reticulum (ER) lumen. The role of PRDX4 as a sulfoxidase in ER is now attracting much attention regarding the oxidative protein folding of nascent proteins. Contrary to this role in the ER, the functional significance of PRDX4 in the extracellular milieu is virtually unknown despite its implications as a biomarker under pathological conditions in some diseases. Other than its systemically expressed form, a variant form of PRDX4 is transcribed from the upstream promoter/exon 1 of the systemic promoter/exon 1 and is uniquely expressed in sexually matured testes. Circumstantial evidence, together with deduced functions from the systemic form, suggests that there are potential roles for testicular PRDX4 in the reproductive processes such as the regulation of hormonal signals and the oxidative packaging of sperm chromatin. Elucidation of these PRDX4 functions under in vivo situations is expected to show the whole picture of how PRDX4 has evolved in multicellular organisms.