Concerted action of sulfiredoxin and peroxiredoxin I protects against alcohol-induced oxidative injury in mouse liver

Cisplatin induces kidney damage through the down-regulation of Prx I by autophagic degradation

In this study, we investigated the potential role of PrxI in cis-diamminedichloroplatinum (cisplatin)-induced renal damage in mice. The anticancer drug cisplatin is a chemotherapeutic agent that is widely used to treat solid tumors. Cisplatin-induced nephrotoxicity is a serious dose-limiting side effect, primarily caused by oxidative stress. The oxidative stress further damages DNA, membranes, and mitochondria, and increases endoplasmic reticulum (ER) stress. Cisplatin produces reactive oxygen species (ROS) through Cytochrome P450 2E1 (CYP2E1) and localizes to the surface of the ER, where CYP2E1 is located. Among the six Prx isoforms, Prx I was selectively degraded in cisplatin-treated kidneys during severe renal function damage. Prx I degradation is blocked in mouse proximal tubular cells treated with 3-methyladenine, an autophagy inhibitor, and in MEF lacking ATG7. Moreover, increased ROS levels on the ER surface due to CYP2E1 overexpression further accelerated Prx I degradation. These results suggest that Prx I degradation is largely mediated through autophagy, which is promoted by cisplatin-induced ER stress. Ablation of Prx I exacerbated cisplatin-induced nephrotoxicity and significantly increased the abundance of oxidative stress, ER stress, and inflammatory markers in the kidney, indicating that Prx I plays a protective role against cisplatin-induced nephrotoxicity.

The desert woodrat (Neotoma lepida) induces a diversity of biotransformation genes in response to creosote bush resin

Liver biotransformation enzymes have long been thought to enable animals to feed on diets rich in xenobiotic compounds. However, despite decades of pharmacological research in humans and rodents, little is known about hepatic gene expression in specialized mammalian herbivores feeding on toxic diets. Leveraging a recently identified population of the desert woodrat (Neotoma lepida) found to be highly tolerant to toxic creosote bush (Larrea tridentata), we explored the expression changes of suites of biotransformation genes in response to diets enriched with varying amounts of creosote resin. Analysis of hepatic RNA-seq data indicated a dose-dependent response to these compounds, including the upregulation of several genes encoding transcription factors and numerous phase I, II, and III biotransformation families. Notably, elevated expression of five biotransformation families - carboxylesterases, cytochromes P450, aldo-keto reductases, epoxide hydrolases, and UDP-glucuronosyltransferases - corresponded to species-specific duplication events in the genome, suggesting that these genes play a prominent role in N. lepida's adaptation to creosote bush. Building on pharmaceutical studies in model rodents, we propose a hypothesis for how the differentially expressed genes are involved in the biotransformation of creosote xenobiotics. Our results provide some of the first details about how these processes likely operate in the liver of a specialized mammalian herbivore.

The micro-743a-3p-GSTM1 pathway is an endogenous protective mechanism against alcohol-related liver disease in mice

BACKGROUND AND AIMS

Epidemiological evidence suggests that the phenotype of glutathione S-transferase mu 1 (GSTM1), a hepatic high-expressed phase II detoxification enzyme, is closely associated with the incidence of alcohol-related liver disease (ALD). However, whether and how hepatic GSTM1 determines the development of ALD is largely unclear. This study was designed to elucidate the role and potential mechanism(s) of hepatic GSTM1 in the pathological process of ALD.

METHODS

GSTM1 was detected in the liver of various ALD mice models and cultured hepatocytes. Liver-specific GSTM1 or/and micro (miR)-743a-3p deficiency mice were generated by adenoassociated virus-8 delivered shRNA, respectively. The potential signal pathways involving in alcohol-regulated GSTM1 and GSTM1-associated ALD were explored via both genetic manipulation and pharmacological approaches.

RESULTS

GSTM1 was significantly upregulated in both chronic alcohol-induced mice liver and ethanol-exposed murine primary hepatocytes. Alcohol-reduced miR-743a-3p directly contributed to the upregulation of GSTM1, since liver specific silencing miR-743a-3p enhanced GSTM1 and miR-743a-3p loss protected alcohol-induced liver dysfunctions, which was significantly blocked by GSTM1 knockdown. GSTM1 loss robustly aggravated alcohol-induced hepatic steatosis, oxidative stress, inflammation, and early fibrotic-like changes, which was associated with the activation of apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase (JNK), and p38. GSTM1 antagonized ASK1 phosphorylation and its downstream JNK/p38 signaling pathway upon chronic alcohol consumption via binding with ASK1. ASK1 blockage significantly rescued hepatic GSTM1 loss-enhanced disorders in alcohol-fed mice liver.

CONCLUSIONS

Chronic alcohol consumption-induced upregulation of GSTM1 in the liver provides a feedback protection against hepatic steatosis and liver injury by counteracting ASK1 activation. Down-regulation of miR-743a-3p improves alcohol intake-induced hepatic steatosis and liver injury via direct targeting on GSTM1. The miR-743a-3p-GSTM1 axis functions as an innate protective pathway to defend the early stage of ALD.

Insights of mitochondrial involvement in alcoholic fatty liver disease

Alcoholic liver disease (ALD) is a global concern affecting most of the population and leading to the development of end-stage liver disease. Metabolic alterations due to increased alcohol consumption surge the hepatic accumulation of lipids and develop into a severe form of alcoholic steatohepatitis (ASH), depending on age and the consumption rate. The mitochondria in the hepatocyte actively regulate metabolic homeostasis and are disrupted in ALD pathogenesis. The increased NADH upon ethanol metabolism inhibits the mitochondrial oxidation of fatty acids, alters oxidative phosphorylation, and favors de novo lipogenesis. The higher mitochondrial respiration in early ALD increases free radical generation, whereas mitochondrial respiration is uncoupled in chronic ALD, affecting the cellular energy status. The defective glutathione importer due to excessive cholesterol loading and low adenosine triphosphate accounts for additional oxidative stress leading to hepatocyte apoptosis. The defective mitochondrial transcription machinery and sirtuins function in ALD affect mitochondrial function and biogenesis. The metabolites of ethanol metabolism epigenetically alter the gene expression profile of hepatic cell populations by modulating the promoters and sirtuins, aiding hepatic fibrosis and inflammation. The defect in mitophagy increases the accumulation of megamitochondria in hepatocytes and attracts immune cells by releasing mitochondrial damage-associated molecular patterns to initiate hepatic inflammation and ASH progression. Thus, maintaining mitochondrial lipid homeostasis and antioxidant capacity pharmacologically could provide a better outcome for ALD management.

PRDX1 Cys52Ser variant alleviates nonalcoholic steatohepatitis by reducing inflammation in mice

OBJECTIVE

Peroxiredoxin 1 (PRDX1) is a peroxidase and guards against oxidative stress by scavenging intracellular peroxides, whereas it also has been shown to stimulate inflammatory response by functioning as a chaperone protein. The potential in vivo link between PRDX1's peroxidase activity and its pro-inflammatory activity remains elusive.

METHODS

We generated peroxidase-dead PRDX1 variant mice by mutating its peroxidatic cysteine at 52 (Cys52) to serine, here referred to as PRDX1Cys52Ser. Trx-TrxR-NADPH coupled activity assay was applied to evaluate the peroxidase activity of global PRDX in PRDX1Cys52Ser variant mice. PRDX1Cys52Ser mice and their wild-type littermates were subjected to western diet or methionine and choline deficient diet feeding. NASH phenotypes were assessed through different analyses including physiological measurements, immunohistochemical staining, and quantitative PCR (qPCR). RNA sequencing, qPCR and western blotting were used to reveal and validate any changes in the signaling pathways responsible for the altered NASH phenotypes observed between WT and PRDX1Cys52Ser variant mice.

RESULTS

PRDX1Cys52Ser variant mice showed impaired global PRDX peroxidase activity and reduced susceptibility to diet-induced NASH and liver fibrosis. Mechanistically, PRDX1 Cys52Ser variant suppressed NF-κB signaling and STAT1 signaling pathways that are known to promote inflammation and NASH.

CONCLUSION

The peroxidatic Cys52 of PRDX1 is required for its pro-inflammatory activity in vivo. This study further suggests that PRDX1 may play dual but opposing roles in NASH.

Echinacoside from Cistanche tubulosa ameliorates alcohol-induced liver injury and oxidative stress by targeting Nrf2

Cistanche tubulosa (Schrenk) Wight, named Guan hua Rou Cong-Rong in Chinese, is a traditional plant with liver, kidney, and intestine protective effects. Echinacoside (ECH) is its active constituent and has been found to have various biological effects, including antioxidative stress and anti-inflammatory effects. Liver injury caused by acetaminophen or CCL₄ has been proven to benefit from ECH; however, the effects of ECH against alcoholic liver disease (ALD) remain unclear. This study was used to estimate the effect of echinacoside on nuclear factor erythroid 2-related factor 2 (Nrf2), which ameliorates ALD by inhibiting oxidative stress and cell apoptosis through affecting Nrf2.A mouse model of ALD was established with ethanol using hematoxylin and eosin (HE) staining, oiled staining, and biochemical indices. Alpha Mouse Liver 12 (AML-12) cells were induced with ethanol in vitro and analyzed using western blotting, flow cytometry, and biochemical assays. In the animal model of ALD, ECH dramatically reduced liver damage, as proven by the downregulation of aspartate aminotransferase (AST) and HE staining. In vitro, ECH distinctly reduced the damage caused by ethanol through the decreased expression of cleaved caspase-3 measured by western blotting. ECH significantly increased the activity of Nrf2 in vivo and in vitro. Nrf2 knockout may diminish the influence of ECH on ALD. Meanwhile, ECH also increased the expression of haem oxygenase-1 (HO-1) and glutamate-cysteine ligase catalytic subunit (GCLC), while it inhibited levels of oxidative stress and cell apoptosis. Our findings suggest that ECH protects against ethanol-induced liver injuries by alleviating oxidative stress and cell apoptosis by increasing the activity of Nrf2. Therefore, ECH is promising for the treatment of ALD.

Nrf2 Activation: Involvement in Central Nervous System Traumatic Injuries. A Promising Therapeutic Target of Natural Compounds

Central nervous system (CNS) trauma, such as traumatic brain injury (TBI) and spinal cord injury (SCI), represents an increasingly important health burden in view of the preventability of most injuries and the complex and expensive medical care that they necessitate. These injuries are characterized by different signs of neurodegeneration, such as oxidative stress, mitochondrial dysfunction, and neuronal apoptosis. Cumulative evidence suggests that the transcriptional factor nuclear factor erythroid 2-related factor 2 (Nrf2) plays a crucial defensive role in regulating the antioxidant response. It has been demonstrated that several natural compounds are able to activate Nrf2, mediating its antioxidant response. Some of these compounds have been tested in experimental models of SCI and TBI, showing different neuroprotective properties. In this review, an overview of the preclinical studies that highlight the positive effects of natural bioactive compounds in SCI and TBI experimental models through the activation of the Nrf2 pathway has been provided. Interestingly, several natural compounds can activate Nrf2 through multiple pathways, inducing a strong antioxidant response against CNS trauma. Therefore, some of these compounds could represent promising therapeutic strategies for these pathological conditions.

Mitochondrial Peroxiredoxin III Protects against Non-Alcoholic Fatty Liver Disease Caused by a Methionine-Choline Deficient Diet

Non-alcoholic fatty liver disease (NAFLD) is emerging as the most common chronic liver disease worldwide. In addition, NAFLD may increase the risk of cardiovascular and liver-related diseases, and displays features of metabolic syndrome. In NAFLD, oxidative stress is primarily caused by excessive free fatty acids. The oxidation of fatty acids is usually caused by β-oxidation of mitochondria under normal conditions, resulting in the production of energy. However, when the inflow of fatty acids in NAFLD becomes excessive, the β-oxidation of mitochondria becomes saturated and the oxidation process increases at sites including peroxisomes and microsomes, thereby increasing production of reactive oxygen species (ROS). Thus, hepatic mitochondrial ROS play an important role in the pathogenesis of NAFLD. Eliminating mitochondrial ROS may improve NAFLD, but the underlying mechanism remains unclear. We examined the effect of mitochondrial ROS on NAFLD by focusing on peroxiredoxin (Prx), an antioxidant protein that can remove hydrogen peroxide. The protective effect and pathological phenomenon of mitochondrial peroxiredoxin in methionine-choline deficient diet (MCD)-induced liver injury was assessed in a mouse model of NAFLD. In these mice, mitochondrial peroxiredoxin deficiency significantly increased hepatic steatosis and fibrosis. In addition, ablation of Prx III enhances susceptibility to MCD diet-induced oxidative stress and exacerbates NAFLD progression by promoting inflammation. The binding assay results also showed that Prx III-deficient mice had more severe liver damage than Prx III-abundant mice in MCD diet liver injury models. The present data suggest that mitochondrial peroxiredoxin III could be a therapeutic target for preventing and suppressing diet-induced NAFLD.

Antioxidant effects of Se-glutathione peroxidase in alcoholic liver disease

Oxidative damage induced by ethanol and its metabolites is one of the factors that fuels the development of alcoholic liver disease (ALD). Selenium (Se) is an effective cofactor for glutathione peroxidase (GPx), and has antioxidant effects that improve ALD. In patients with ALD, ethanol-induced oxidative damage inhibits the synthesis of related Se-containing proteins such as: selenoprotein P (Sepp1), albumin (ALB), and GPx in the liver, thus decreasing the overall Se level in patients. Both Se deficiency and excess can affect the expression of GPx, resulting in damage to the antioxidant defense system. This damage enhances oxidative stress by increasing the levels of reactive oxygen species (ROS) in the body, which aggravates the inflammatory response, lipid metabolism disorder, and lipid peroxidation and worsens ALD symptoms. A cascade of oxidative damages caused by ALD will deplete selenium deposition in the body, stimulate the expression of Gpx1, Sepp1, and Gpx4, and thus mobilize systemic selenoproteins, which can restore GPx activity in the hepatocytes of ALD patients, reduce the levels of reactive oxygen species and alleviate oxidative stress, the inflammatory response, lipid metabolism disorder, and lipid peroxidation, thus helping to mitigate ALD. This review provides a reference for future ALD studies that evaluate the regulation of Se levels and contributes to studies on the potential pathological mechanisms of Se imbalance in ALD.

Alcohol-Related Liver Disease: An Overview on Pathophysiology, Diagnosis and Therapeutic Perspectives

Alcohol-related liver disease (ALD) refers to a spectrum of liver manifestations ranging from fatty liver diseases, steatohepatitis, and fibrosis/cirrhosis with chronic inflammation primarily due to excessive alcohol use. Currently, ALD is considered as one of the most prevalent causes of liver disease-associated mortality worldwide. Although the pathogenesis of ALD has been intensively investigated, the present understanding of its biomarkers in the context of early clinical diagnosis is not complete, and novel therapeutic targets that can significantly alleviate advanced forms of ALD are limited. While alcohol abstinence remains the primary therapeutic intervention for managing ALD, there are currently no approved medications for treating ALD. Furthermore, given the similarities and the differences between ALD and non-alcoholic fatty liver disease in terms of disease progression and underlying molecular mechanisms, numerous studies have demonstrated that many therapeutic interventions targeting several signaling pathways, including oxidative stress, inflammatory response, hormonal regulation, and hepatocyte death play a significant role in ALD treatment. Therefore, in this review, we summarized several key molecular targets and their modes of action in ALD progression. We also described the updated therapeutic options for ALD management with a particular emphasis on potentially novel signaling pathways.

Accurate and Precise Protocol to Estimate the Activity of Peroxiredoxin Enzyme

BACKGROUND

Accurate estimation of Prx activity poses many complications and interferences. The present protocol is free of interference and provides an effective alternative for the assessment of peroxide with high sensitivity. The assay can be used in clinical pathology laboratories since it is simple, rapid, and inexpensive. The systematic reagent consisted of AFS/ASA which acted as a sensitive probe for peroxide.

METHODS

Prx activity was estimated by incubating samples in suitable concentrations of 1,4-dithio-DL-threitol (DTT) and hydrogen peroxide (H2O2) or t-Butyl hydroperoxide (t-BOOH), as the substrates. The enzymatic reaction was inhibited after incubation with a working reagent containing ammonium ferrous sulfate (AFS) and aminosalicylic acid (ASA).

RESULTS

Residual peroxide reacted with the working solution to form a brown-colored ferriaminosalicylate (FAS) complex with a maximum absorbance (λmax) of 425 nm. This protocol used sodium azide (NaN3) to eliminate catalase interference and avoided using high concentrations of strong acid to inhibit the Prx reaction.

CONCLUSION

We concluded that the new protocol produced the same efficacy as the reference method since a strong correlation coefficient of comparison (r> 0.99) was found between both the FAS and ferrithiocyanate method.

Hyperoxidation of Peroxiredoxins and Effects on Physiology of Drosophila

The catalytic activity of peroxiredoxins (Prx) is determined by the conserved peroxidatic cysteine (Cys_P), which reacts with peroxides to form sulfenic acid (Cys-SOH). Under conditions of oxidative stress, Cys_P is oxidized to catalytically inactive sulfinic (Cys-SO₂) and sulfonic (Cys-SO₃) forms. The Cys-SO₂ form can be reduced in a reaction catalyzed by sulfiredoxin (Srx). To explore the physiological significance of peroxiredoxin overoxidation, we investigated daily variations in the oxidation state of 2-Cys peroxiredoxins in flies of different ages, or under conditions when the pro-oxidative load is high. We found no statistically significant changes in the 2-Cys Prxs monomer:dimer ratio, which indirectly reflects changes in the Prx catalytic activity. However, we found daily variations in Prx-SO_2/3 that were more pronounced in older flies as well as in flies lacking Srx. Unexpectedly, the srx mutant flies did not exhibit a diminished survivorship under normal or oxidative stress conditions. Moreover, the srx mutant was characterized by a higher physiological activity. In conclusion, catalytically inactive forms of Prx-SO_2/3 serve not only as a marker of cellular oxidative burden, but may also play a role in an adaptive response, leading to a positive effect on the physiology of Drosophila melanogaster.

The critical role of redox regulation of PTEN and peroxiredoxin III in alcoholic fatty liver

Hepatic steatosis and subsequent fatty liver disease are developed in response to alcohol consumption. Reactive oxygen species (ROS) are thought to play an important role in the alcoholic fatty liver disease (AFLD). However, the molecular targets of ROS and the underlying cellular mechanisms are unknown. Here, we investigate roles of peroxiredoxin III and redox regulation of phosphatase and tension homolog deleted on chromosome 10 (PTEN) in the alcoholic fatty liver. Alcohol-induced mitochondrial oxidative stress was found to contribute to reversible oxidation of PTEN, which results in Akt and MAPK hyperactivation with elevated levels of the lipogenesis regulators SREBP1c and PPARγ. Moreover, mitochondrial peroxiredoxin III was found to have antagonistic effects on lipogenesis via the redox regulation of PTEN by removing ROS, upon alcohol exposure. This study demonstrated that redox regulation of PTEN and peroxiredoxin III play crucial roles in the development of AFLD.

An Overview of Nrf2 Signaling Pathway and Its Role in Inflammation

Inflammation is a key driver in many pathological conditions such as allergy, cancer, Alzheimer’s disease, and many others, and the current state of available drugs prompted researchers to explore new therapeutic targets. In this context, accumulating evidence indicates that the transcription factor Nrf2 plays a pivotal role controlling the expression of antioxidant genes that ultimately exert anti-inflammatory functions. Nrf2 and its principal negative regulator, the E3 ligase adaptor Kelch-like ECH- associated protein 1 (Keap1), play a central role in the maintenance of intracellular redox homeostasis and regulation of inflammation. Interestingly, Nrf2 is proved to contribute to the regulation of the heme oxygenase-1 (HO-1) axis, which is a potent anti-inflammatory target. Recent studies showed a connection between the Nrf2/antioxidant response element (ARE) system and the expression of inflammatory mediators, NF-κB pathway and macrophage metabolism. This suggests a new strategy for designing chemical agents as modulators of Nrf2 dependent pathways to target the immune response. Therefore, the present review will examine the relationship between Nrf2 signaling and the inflammation as well as possible approaches for the therapeutic modulation of this pathway.

2-Cys peroxiredoxin oxidation in response to hydrogen peroxide and contractile activity in skeletal muscle: A novel insight into exercise-induced redox signalling?

Skeletal muscle generates superoxide during contractions which is rapidly converted to H2O2. This molecule has been proposed to activate signalling pathways and transcription factors that regulate key adaptive responses to exercise but the concentration of H2O2 required to oxidise and activate key signalling proteins in vitro is much higher than the intracellular concentration in muscle fibers following exercise. We hypothesised that Peroxiredoxins (Prx), which reacts with H2O2 at the low intracellular concentrations found in muscle, would be rapidly oxidised in contracting muscle and hence potentially transmit oxidising equivalents to downstream signalling proteins as a method for their oxidation and activation. The aim of this study was to characterise the effects of muscle contractile activity on the oxidation of Prx1, 2 and 3 and determine if these were affected by aging. Prx1, 2 and 3 were all rapidly and reversibly oxidised following treatment with low micromolar concentrations of H2O2 in C2C12 myotubes and also in isolated mature flexor digitalis brevis fibers from adult mice following a protocol of repeated isometric contractions. Significant oxidation of Prx2 was seen within 1 min (i.e. after 12 contractions), whereas significant oxidation was seen after 2 min for Prx1 and 3. In muscle fibers from old mice, Prx2 oxidation was significantly attenuated following contractile activity. Thus we show for the first time that Prx are rapidly and reversibly oxidised in response to contractile activity in skeletal muscle and hypothesise that these proteins act as effectors of muscle redox signalling pathways which are key to adaptations to exercise that are attenuated during aging.

Sulfiredoxin-1 is a promising novel prognostic biomarker for hepatocellular carcinoma

Identifying novel prognostic biomarkers for hepatocellular carcinoma (HCC) and then, develop an effective individualized treatment strategy remain extremely warranted. The prognostic role of sulfiredoxin-1(SRXN1), an antioxidant enzyme, remains unknown in HCC. This study aimed to explore the prognostic implications of SRXN1 in HCC patients after partial hepatectomy. The expression of SRXN1 in HCC and normal tissue were analyzed using the patients from the public databases and Zhongshan Hospital. The Cox regression, Kaplan-Meier survival analysis, and time-dependent receiver operating characteristic curves were performed to identify the predictive role of SRXN1 expression on HCC patients. A prognostic nomogram based on SRXN1 expression was constructed and validated to further confirm the predictive power of SRXN1 as a prognostic biomarker. Finally, functional enrichment analysis and protein-protein interaction network analysis of SRXN1 and its associated genes were conducted. The results showed that SRXN1 was upregulated in HCC samples compared with the normal liver tissues. Patients with SRXN1 upregulation had shorter survival time. SRXN1 overexpression was significantly correlated with advanced clinicopathological parameters. The prognostic nomogram based on SRXN1 expression was proved to be more accurate than routine staging systems for the prediction of overall survival. Protein-protein interaction network analysis demonstrated the first neighbor genes of SRXN1 mainly participated in response to oxidative stress. In brief, SRXN1 could be a prognostic biomarker for the management of HCC.

Ablation of Peroxiredoxin V Exacerbates Ischemia/Reperfusion-Induced Kidney Injury in Mice

Ischemia/reperfusion (I/R) is one of the major causes of acute kidney injury (AKI) and associated with increased mortality and progression to chronic kidney injury (CKI). Molecular mechanisms underlying I/R injury involve the production and excessive accumulation of reactive oxygen species (ROS). Peroxiredoxin (Prx) V, a cysteine-dependent peroxidase, is located in the cytosol, mitochondria, and peroxisome and has an intensive ROS scavenging activity. Therefore, we focused on the role of Prx V during I/R-induced AKI using Prx V knockout (KO) mice. Ablation of Prx V augmented tubular damage, apoptosis, and declined renal function. Prx V deletion also showed higher susceptibility to I/R injury with increased markers for oxidative stress, ER stress, and inflammation in the kidney. Overall, these results demonstrate that Prx V protects the kidneys against I/R-induced injury.

Bacteroides fragilis Enterotoxin Induces Sulfiredoxin-1 Expression in Intestinal Epithelial Cell Lines Through a Mitogen-Activated Protein Kinases- and Nrf2-Dependent Pathway, Leading to the Suppression of Apoptosis

Enterotoxigenic Bacteroides fragilis is a causative agent of colitis and secrets enterotoxin (BFT), leading to the disease. Sulfiredoxin (Srx)-1 serves to protect from oxidative damages. Although BFT can generate reactive oxygen species in intestinal epithelial cells (IECs), no Srx-1 expression has been reported in ETBF infection. In this study, we explored the effects of ETBF-produced BFT on Srx-1 induction in IECs. Treatment of IECs with BFT resulted in increased expression of Srx-1 in a time-dependent manner. BFT treatment also activated transcriptional signals including Nrf2, AP-1 and NF-κB, and the Srx-1 induction was dependent on the activation of Nrf2 signals. Nrf2 activation was assessed using immunoblot and Nrf2-DNA binding activity and the specificity was confirmed by supershift and competition assays. Suppression of NF-κB or AP-1 signals did not affect the upregulation of Srx-1 expression. Nrf2-dependent Srx-1 expression was associated with the activation of p38 mitogen-activated protein kinases (MAPKs) in IECs. Furthermore, suppression of Srx-1 significantly enhanced apoptosis while overexpression of Srx-1 significantly attenuated apoptosis during exposure to BFT. These results imply that a signaling cascade involving p38 and Nrf2 is essential for Srx-1 upregulation in IECs stimulated with BFT. Following this upregulation, Srx-1 may control the apoptosis in BFT-exposed IECs.

The Role of Hydrogen Peroxide and Peroxiredoxins throughout the Cell Cycle

Hydrogen peroxide (H₂O₂) is an oxidizing agent that induces cellular damage at inappropriate concentrations and gives rise to an arrest during cell cycle progression, causing cell death. Recent evidence indicates that H₂O₂ also acts as a promoter for cell cycle progression by oxidizing specific thiol proteins. The intracellular concentration of H₂O₂ is regulated tightly, enabling its use as a cellular signaling molecule while minimizing its potential to cause cellular damage. Peroxiredoxins (Prxs) have peroxidase activity toward H₂O₂, organic hydroperoxides, and peroxynitrite for protecting cells from oxidative stress. They are suggested to work as signaling mediators, allowing the local accumulation of H₂O₂ by inactivating their peroxidase activity uniquely compared with other antioxidant proteins such as catalase and glutathione peroxidase. Given that Prxs are highly sensitive to oxidation by H₂O₂, they act as sensors and transducers of H₂O₂ signaling via transferring their oxidation state to effector proteins. The concentrations of intracellular H₂O₂ increase as the cell cycle progresses from G₁ to mitosis. Here, we summarize the roles of Prxs with regard to the regulation of cell cycle-dependent kinase activity and anaphase-promoting complex/cyclosome in terms of changes in H₂O₂ levels. Protection of the cell from unwanted progression of the cell cycle is suggested to be a role of Prx. We discuss the possible roles of Prxs to control H₂O₂ levels.

Relevance of reactive oxygen species in liver disease observed in transgenic mice expressing the hepatitis B virus X protein

The hepatitis B virus (HBV) infects approximately 240 million people worldwide, causing chronic liver disease (CLD) and liver cancer. Although numerous studies have been performed to date, unfortunately there is no conclusive drug or treatment for HBV induced liver disease. The hepatitis B virus X (HBx) is considered a key player in inducing CLD and hepatocellular carcinoma (HCC). We generated transgenic (Tg) mice expressing HBx protein, inducing HCC at the age of 11–18 months. The incidence of histological phenotype, including liver tumor, differed depending on the genetic background of HBx Tg mice. Fatty change and tumor generation were observed much earlier in livers of HBx Tg hybrid (C57BL/6 and CBA) (HBx-Tg hybrid) mice than in HBx Tg C57BL/6 (HBx-Tg B6) mice. Inflammation was also enhanced in the HBx-Tg B6 mice as compared to HBx-Tg hybrid mice. HBx may be involved in inducing and promoting hepatic steatosis, glycemia, hepatic fibrosis, and liver cancer. Reactive oxygen species (ROS) generation was remarkably increased in livers of HBx Tg young mice compared to young wild type control mice. Previous studies on HBx Tg mice indicate that the HBx-induced ROS plays a role in inducing and promoting CLD and HCC.

Free radicals, antioxidants, nuclear factor-E2-related factor-2 and liver damage

Oxidative/nitrosative stress is proposed to be a critical factor in various diseases, including liver pathologies. Antioxidants derived from medicinal plants have been studied extensively and are relevant to many illnesses, including liver diseases. Several hepatic disorders, such as viral hepatitis and alcoholic or nonalcoholic steatohepatitis, involve free radicals/oxidative stress as agents that cause or at least exacerbate liver injury, which can result in chronic liver diseases, such as liver fibrosis, cirrhosis and end-stage hepatocellular carcinoma. In this scenario, nuclear factor-E2-related factor-2 (Nrf2) appears to be an essential factor to counteract or attenuate oxidative or nitrosative stress in hepatic cells. In fact, a growing body of evidence indicates that Nrf2 plays complex and multicellular roles in hepatic inflammation, fibrosis, hepatocarcinogenesis and regeneration via the induction of its target genes. Inflammation is the most common feature of chronic liver diseases, triggering fibrosis, cirrhosis and hepatocellular carcinoma. Increasing evidence indicates that Nrf2 counteracts the proinflammatory process by modulating the recruitment of inflammatory cells and inducing the endogenous antioxidant response of the cell. In this review, the interactions between antioxidant and inflammatory molecular pathways are analyzed.

Pathogenesis, Early Diagnosis, and Therapeutic Management of Alcoholic Liver Disease

Alcoholic liver disease (ALD) refers to the damages to the liver and its functions due to alcohol overconsumption. It consists of fatty liver/steatosis, alcoholic hepatitis, steatohepatitis, chronic hepatitis with liver fibrosis or cirrhosis, and hepatocellular carcinoma. However, the mechanisms behind the pathogenesis of alcoholic liver disease are extremely complicated due to the involvement of immune cells, adipose tissues, and genetic diversity. Clinically, the diagnosis of ALD is not yet well developed. Therefore, the number of patients in advanced stages has increased due to the failure of proper early detection and treatment. At present, abstinence and nutritional therapy remain the conventional therapeutic interventions for ALD. Moreover, the therapies which target the TNF receptor superfamily, hormones, antioxidant signals, and MicroRNAs are used as treatments for ALD. In particular, mesenchymal stem cells (MSCs) are gaining attention as a potential therapeutic target of ALD. Therefore, in this review, we have summarized the current understandings of the pathogenesis and diagnosis of ALD. Moreover, we also discuss the various existing treatment strategies while focusing on promising therapeutic approaches for ALD.

Peroxiredoxin-mediated disulfide bond formation is required for nucleocytoplasmic translocation and secretion of HMGB1 in response to inflammatory stimuli

The nuclear protein HMGB1 (high mobility group box 1) is secreted by monocytes-macrophages in response to inflammatory stimuli and serves as a danger-associated molecular pattern. Acetylation and phosphorylation of HMGB1 are implicated in the regulation of its nucleocytoplasmic translocation for secretion, although inflammatory stimuli are known to induce H₂O₂ production. Here we show that H₂O₂-induced oxidation of HMGB1, which results in the formation of an intramolecular disulfide bond between Cys²³ and Cys⁴⁵, is necessary and sufficient for its nucleocytoplasmic translocation and secretion. The oxidation is catalyzed by peroxiredoxin I (PrxI) and PrxII, which are first oxidized by H₂O₂ and then transfer their disulfide oxidation state to HMGB1. The disulfide form of HMGB1 showed higher affinity for nuclear exportin CRM1 compared with the reduced form. Lipopolysaccharide (LPS)–induced HMGB1 secretion was greatly attenuated in macrophages derived from PrxI or PrxII knockout mice, as was the LPS-induced increase in serum HMGB1 levels.

Inactivation of the PtdIns(4)P phosphatase Sac1 at the Golgi by H2O2 produced via Ca2+-dependent Duox in EGF-stimulated cells

Binding of epidermal growth factor (EGF) to its cell surface receptor induces production of H₂O₂, which serves as an intracellular messenger. We have shown that exogenous H₂O₂ reversibly inactivates the phosphatidylinositol 4-phosphate [PtdIns(4)P] phosphatase Sac1 (suppressor of actin 1) at the Golgi complex of mammalian cells by oxidizing its catalytic cysteine residue and thereby increases both the amount of Golgi PtdIns(4)P and the rate of protein secretion. Here we investigated the effects of EGF on Sac1 oxidation and PtdIns(4)P abundance at the Golgi in A431 cells. EGF induced a transient increase in Golgi PtdIns(4)P as well as a transient oxidation of Sac1 in a manner dependent on elevation of the intracellular Ca²⁺ concentration and on H₂O₂. Oxidation of Sac1 occurred at the Golgi, as revealed with the use of the Golgi-confined Sac1-K2A mutant. Knockdown of Duox enzymes implicated these Ca²⁺-dependent members of the NADPH oxidase family as the major source of H₂O₂ for Sac1 oxidation. Expression of a Golgi-targeted H₂O₂ probe revealed transient EGF-induced H₂O₂ production at this organelle. Our findings have thus uncovered a previously unrecognized EGF signaling pathway that links intracellular Ca²⁺ mobilization to events at the Golgi including Duox activation, H₂O₂ production, Sac1 oxidation, and PtdIns(4)P accumulation.

The Role of Nrf2 in Liver Disease: Novel Molecular Mechanisms and Therapeutic Approaches

Oxidative stress and inflammation are the most important pathogenic events in the development and progression of liver diseases. Nuclear erythroid 2-related factor 2 (Nrf2) is the master regulator of the cellular protection via induction of anti-inflammatory, antioxidant, and cyto-protective genes expression. Multiple studies have shown that activation or suppression of this transcriptional factor significantly affect progression of liver diseases. Comprehensive understanding the roles of Nrf2 activation/expression and the outcomes of its activators/inhibitors are indispensable for defining the mechanisms and therapeutic strategies against liver diseases. In this current review, we discussed recent advances in the function and principal mechanisms by regulating Nrf2 in liver diseases, including acute liver failure, hepatic ischemia-reperfusion injury (IRI), alcoholic liver disease (ALD), viral hepatitis, non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma (HCC).

Ginseng (Panax ginseng Meyer) Oligopeptides Protect Against Binge Drinking-Induced Liver Damage through Inhibiting Oxidative Stress and Inflammation in Rats

Panax ginseng C.A. Meyer (ginseng) is an edible and traditional medicinal herb, which is reported to have a wide range of biological activity and pharmaceutical properties. There were more studies on ginsenoside and polysaccharides, but fewer on ginseng oligopeptides (GOPs), which are small molecule oligopeptides extracted from ginseng. The present study was designed to investigate the effects and underlying mechanism of ginseng oligopeptide (GOPs) on binge drinking-induced alcohol damage in rats. Sprague Dawley rats were randomly assigned to six groups (n = 10), rats in normal control group and alcohol model group was administered distilled water; rats in four GOPs intervention groups (at a dose of 0.0625, 0.125, 0.25, 0.5 g/kg of body weight, respectively) were administered GOPs once a day for 30 days. Experiment rats were intragastrically administered ethanol at a one-time dose of 7 g/kg of body weight after 30 days. The liver injury was measured through traditional liver enzymes, inflammatory cytokines, expression of oxidative stress markers, and histopathological examination. We found that the GOPs treatment could significantly improve serum alanine aminotransferase and aspartate aminotransferase, plasma lipopolysaccharide, and inflammatory cytokine levels, as well as the oxidative stress markers that were altered by alcohol. Moreover, GOPs treatment inhibited the protein expression of toll-like receptor 4, and repressed the inhibitor kappa Bα and nuclear factor-κB p65 in the liver. These findings suggested that GOPs have a significant protective effect on binge drinking-induced liver injury, and the mechanism possibly mediated by the partial inhibition of lipopolysaccharide-toll-like receptor 4-nuclear factor-κB p65 signaling in the liver.

The Multifaceted Impact of Peroxiredoxins on Aging and Disease

SIGNIFICANCE

Peroxiredoxins (Prxs), a family of thiol-associated peroxidases, are purported to play a major role in sensing and managing hydrogen peroxide concentrations and transducing peroxide-derived signals. Recent Advances: Prxs can act as detoxifying factors and impart effects to cells that can be either sparing or suicidal. Advances have been made to address the qualitative changes in Prx function in response to quantitative changes in the signal level and to understand how Prx activity could be affected by their own substrates. Here we rationalize the basis for both positive and negative effects on signaling pathways and cell physiology, summarizing data from model organisms, including invertebrates.

CRITICAL ISSUES

Resolving the relationship between the promiscuous behavior of reactive oxygen species and the specificity of Prxs toward different targets in redox-sensitive signaling pathways is a key area of research. Attempts to understand Prx function and underlying mechanisms were conducted in vitro or in vivo under nonphysiological conditions, leaving the physiological relevance yet to be defined. Other issues: Why despite the high degree of homology and similarities in subcellular and tissue distribution between Prxs do they display differential effects on signaling? How is the specificity of post-translational protein modifications determined? Other than chaperone-like activity, how do hyperoxidized Prxs function?

FUTURE DIRECTIONS

Genetic models with mutated catalytic and resolving cysteines should be further exploited to dissect the functional significance of individual Prxs in their different states together with their alternative reducing partners. Such an analysis may then be extended to help identify Prx-specific targets.

Lipid peroxidation derived reactive aldehydes in alcoholic liver disease

Lipid peroxidation is a known consequence of oxidative stress and is thought to play a key role in numerous disease pathologies, including alcoholic liver disease (ALD). The overaccumulation of lipid peroxidation products during chronic alcohol consumption results in pathogenic lesions on protein, DNA, and lipids throughout the cell. Molecular adducts due to secondary end products of lipid peroxidation impact a host of biochemical processes, including inflammation, antioxidant defense, and metabolism. The aggregate burden of lipid peroxidation which occurs due to chronic alcohol metabolism, including downstream signaling events, contributes to the development and progression of ALD. In this current opinion we highlight recent studies and approaches relating cellular mechanisms of lipid peroxidation to the pathogenesis of alcoholic liver disease.

Nrf2 in alcoholic liver disease

Alcoholic liver disease (ALD) is a leading cause of morbidity and mortality of liver disorders and a major health issue globally. ALD refers to a spectrum of liver pathologies ranging from steatosis, steatohepatitis, fibrosis, cirrhosis and even hepatocellular carcinoma. Various mechanisms, including oxidative stress, protein and DNA modification, inflammation and impaired lipid metabolism, have been implicated in the pathogenesis of ALD. Further, reactive oxygen species (ROS) in particular, have been identified as a key component in the initiation and progression of ALD. Nuclear factor erythroid 2 like 2 (Nrf2) is a master regulator of the intracellular adaptive antioxidant response to oxidative stress, and aids in the detoxification of a variety of toxicants. Given its cytoprotective role, Nrf2 has been extensively studied as a therapeutic target for ALD. Paradoxically, however, emerging evidence have revealed that Nrf2 may be implicated in the progression of ALD. In this review, we summarize the role of Nrf2 in the development of ALD and discuss the underlying mechanisms. Clearly, more comprehensive studies with proper animal and cell models and in human are needed to verify the potential therapeutic role of Nrf2 in ALD.

Dynamic imaging of adaptive stress response pathway activation for prediction of drug induced liver injury

Drug-induced liver injury remains a concern during drug treatment and development. There is an urgent need for improved mechanistic understanding and prediction of DILI liabilities using in vitro approaches. We have established and characterized a panel of liver cell models containing mechanism-based fluorescent protein toxicity pathway reporters to quantitatively assess the dynamics of cellular stress response pathway activation at the single cell level using automated live cell imaging. We have systematically evaluated the application of four key adaptive stress pathway reporters for the prediction of DILI liability: SRXN1-GFP (oxidative stress), CHOP-GFP (ER stress/UPR response), p21 (p53-mediated DNA damage-related response) and ICAM1 (NF-κB-mediated inflammatory signaling). 118 FDA-labeled drugs in five human exposure relevant concentrations were evaluated for reporter activation using live cell confocal imaging. Quantitative data analysis revealed activation of single or multiple reporters by most drugs in a concentration and time dependent manner. Hierarchical clustering of time course dynamics and refined single cell analysis allowed the allusion of key events in DILI liability. Concentration response modeling was performed to calculate benchmark concentrations (BMCs). Extracted temporal dynamic parameters and BMCs were used to assess the predictive power of sub-lethal adaptive stress pathway activation. Although cellular adaptive responses were activated by non-DILI and severe-DILI compounds alike, dynamic behavior and lower BMCs of pathway activation were sufficiently distinct between these compound classes. The high-level detailed temporal- and concentration-dependent evaluation of the dynamics of adaptive stress pathway activation adds to the overall understanding and prediction of drug-induced liver liabilities.

Peroxiredoxins in inflammatory liver diseases and ischemic/reperfusion injury in liver transplantation

Peroxiredoxins (Prxs) belong to the superfamily of thiol-dependent peroxidases, and remove reactive oxygen species (ROS) and other oxidative stress products. The expression and activity of Prxs can be substantially affected by stimuli from the microenvironment, and in turn regulate cytokine secretion in the context of inflammation in both peroxidase-dependent and -independent pathways. Prxs translocate to mitochondria and are hyperoxidized during acute liver damage, and attenuate intracellular ROS accumulation through their peroxidase activity. In particularly, Prx1 modulates the microenvironment in liver injuries by reducing adhesion molecule expression in vascular endothelial cells and inhibiting the inflammatory response and adhesion of macrophages. Prxs have potent prosurvival effects against ROS in ischemic/reperfusion (I/R) injury, but Prxs released from necrotic cells increase secretion of inflammatory cytokines by macrophages through TLR2 and 4 activation, which promotes cell death. Prxs can be used as biomarkers to evaluate I/R injury and predict graft survival in liver transplantation. Prxs are modulated in various types of chronic hepatitis and hepatosteatosis, and mediate disease progression. Alcohol administration increases oxidization and inactivation of Prxs in mice because of oxidative stress. In conclusion, Prxs are essential mediators and biomarkers in inflammatory liver diseases and I/R injury.

Prdx1 (peroxiredoxin 1) deficiency reduces cholesterol efflux via impaired macrophage lipophagic flux

Oxidative stress activates macroautophagy/autophagy and contributes to atherogenesis via lipophagic flux, a form of lipid removal by autophagy. However, it is not known exactly how endogenous antioxidant enzymes are involved in lipophagic flux. Here, we demonstrate that the antioxidant PRDX1 (peroxiredoxin 1) has a crucial role in the maintenance of lipophagic flux in macrophages. PRDX1 is more highly expressed than other antioxidant enzymes in monocytes and macrophages. We determined that Prdx1 deficiency induced excessive oxidative stress and impaired maintenance of autophagic flux in macrophages. Prdx1-deficient macrophages had higher intracellular cholesterol mass and lower cholesterol efflux compared with wild type. This perturbation in cholesterol homeostasis was due to impaired lipophagic cholesterol hydrolysis caused by excessive oxidative stress, resulting in the inhibition of free cholesterol formation and the reduction of NR1H3 (nuclear receptor subfamily 1, group H, member 3) activity. Notably, impairment of both lipophagic flux and cholesterol efflux was restored by the 2-Cys PRDX-mimics ebselen and gliotoxin. Consistent with this observation, apoe ^−/− mice transplanted with bone marrow from prdx1^−/−apoe^−/− mice had increased plaque formation compared with apoe^−/− BM-transplanted recipients. This study reveals that PRDX1 is crucial to regulating lipophagic flux and maintaining macrophage cholesterol homeostasis against oxidative stress. We suggest that PRDX1-dependent control of oxidative stress may provide a strategy for treating atherosclerosis and autophagy-related human diseases.

Fortilin: A Potential Target for the Prevention and Treatment of Human Diseases

Fortilin is a highly conserved 172-amino-acid polypeptide found in the cytosol, nucleus, mitochondria, extracellular space, and circulating blood. It is a multifunctional protein that protects cells against apoptosis, promotes cell growth and cell cycle progression, binds calcium (Ca²⁺) and has antipathogen activities. Its role in the pathogenesis of human and animal diseases is also diverse. Fortilin facilitates the development of atherosclerosis, contributes to both systemic and pulmonary arterial hypertension, participates in the development of cancers, and worsens diabetic nephropathy. It is important for the adaptive expansion of pancreatic β-cells in response to obesity and increased insulin requirement, for the regeneration of liver after hepatectomy, and for protection of the liver against alcohol- and ER stress-induced injury. Fortilin is a viable surrogate marker for in vivo apoptosis, and it plays a key role in embryo and organ development in vertebrates. In fish and shrimp, fortilin participates in host defense against bacterial and viral pathogens. Further translational research could prove fortilin to be a viable molecular target for treatment of various human diseases including and not limited to atherosclerosis, hypertension, certain tumors, diabetes mellitus, diabetic nephropathy, hepatic injury, and aberrant immunity and host defense.

Multiple Functions and Regulation of Mammalian Peroxiredoxins

Peroxiredoxins (Prxs) constitute a major family of peroxidases, with mammalian cells expressing six Prx isoforms (PrxI to PrxVI). Cells produce hydrogen peroxide (H₂O₂) at various intracellular locations where it can serve as a signaling molecule. Given that Prxs are abundant and possess a structure that renders the cysteine (Cys) residue at the active site highly sensitive to oxidation by H₂O₂, the signaling function of this oxidant requires extensive and highly localized regulation. Recent findings on the reversible regulation of PrxI through phosphorylation at the centrosome and on the hyperoxidation of the Cys at the active site of PrxIII in mitochondria are described in this review as examples of such local regulation of H₂O₂ signaling. Moreover, their high affinity for and sensitivity to oxidation by H₂O₂ confer on Prxs the ability to serve as sensors and transducers of H₂O₂ signaling through transfer of their oxidation state to bound effector proteins.

Activation of the Nrf2-Keap 1 Pathway in Short-Term Iodide Excess in Thyroid in Rats

Wistar rats were randomly divided into groups of varying iodide intake: normal iodide; 10 times high iodide; and 100 times high iodide on Days 7, 14, and 28. Insignificant changes were observed in thyroid hormone levels (p > 0.05). Urinary iodine concentration and iodine content in the thyroid glands increased after high consumption of iodide from NI to 100 HI (p < 0.05). The urinary iodine concentration of the 100 HI group on Days 7, 14, and 28 was 60–80 times that of the NI group. The mitochondrial superoxide production and expressions of Nrf2, Srx, and Prx 3 all significantly increased, while Keap 1 significantly decreased in the 100 HI group when compared to the NI or 10 HI group on Days 7, 14, and 28 (p < 0.05). Immunofluorescence staining results showed that Nrf2 was localized in the cytoplasm in NI group. Although Nrf2 was detected in both cytoplasm and nucleus in 10 HI and 100 HI groups, a stronger positive staining was found in the nucleus. We conclude that the activation of the Nrf2-Keap 1 antioxidative defense mechanism may play a crucial role in protecting thyroid function from short-term iodide excess in rats.

Redox proteomics screening cellular factors associated with oxidative stress in hepatocarcinogenesis

Liver cancer is a major global health problem being the sixth most common cancer and the third cause of cancer-related death, with hepatocellular carcinoma (HCC) representing more than 90% of primary liver cancers. Mounting evidence suggests that, compared with their normal counterparts, many types of cancer cell have increased levels of ROS. Therefore, cancer cells need to combat high levels of ROS, especially at early stages of tumor development. Recent studies have revealed that ROS-mediated regulation of redox-sensitive proteins (redox sensors) is involved in the pathogenesis and/or progression of many human diseases, including cancer. Unraveling the altered functions of redox sensors and the underlying mechanisms in hepatocarcinogenesis is critical for the development of novel cancer therapeutics. For this reason, redox proteomics has been developed for the high-throughput screening of redox sensors, which will benefit the development of novel therapeutic strategies for the treatment of HCC. In this review, we will briefly introduce several novel redox proteomics techniques that are currently available to study various oxidative modifications in hepatocarcinogenesis and summarize the most important discoveries in the study of redox processes related to the development and progression of HCC.

Mitochondrial H2O2 signaling is controlled by the concerted action of peroxiredoxin III and sulfiredoxin: Linking mitochondrial function to circadian rhythm

Mitochondria produce hydrogen peroxide (H₂O₂) during energy metabolism in most mammalian cells as well as during the oxidation of cholesterol associated with the synthesis of steroid hormones in steroidogenic cells. Some of the H₂O₂ produced in mitochondria is released into the cytosol, where it serves as a key regulator of various signaling pathways. Given that mitochondria are equipped with several H₂O₂-eliminating enzymes, however, it had not been clear how mitochondrial H₂O₂ can escape destruction by these enzymes for such release. Peroxiredoxin III (PrxIII) is the most abundant and efficient H₂O₂-eliminating enzyme in mitochondria of most cell types. We found that PrxIII undergoes reversible inactivation through hyperoxidation of its catalytic cysteine residue to cysteine sulfinic acid, and that release of mitochondrial H₂O₂ likely occurs as a result of such PrxIII inactivation. The hyperoxidized form of PrxIII (PrxIII-SO₂H) is reduced and reactivated by sulfiredoxin (Srx). We also found that the amounts of PrxIII-SO₂H and Srx undergo antiphasic circadian oscillation in mitochondria of the adrenal gland, heart, and brown adipose tissue of mice maintained under normal conditions. Cytosolic Srx was found to be imported into mitochondria via a mechanism that requires formation of a disulfide-linked complex with heat shock protein 90, which is likely promoted by H₂O₂ released from mitochondria. The imported Srx was found to be degraded by Lon protease in a manner dependent on PrxIII hyperoxidation state. The coordinated import and degradation of Srx underlie Srx oscillation and consequent PrxIII-SO₂H oscillation in mitochondria. The rhythmic change in the amount of PrxIII-SO₂H suggests that mitochondrial release of H₂O₂ is also likely a circadian event that conveys temporal information on steroidogenesis in the adrenal gland and on energy metabolism in heart and brown adipose tissue to cytosolic signaling pathways.

Mitochondrial H2O2 signaling is controlled by the concerted action of peroxiredoxin III and sulfiredoxin: Linking mitochondrial function to circadian rhythm

Mitochondria produce hydrogen peroxide (H₂O₂) during energy metabolism in most mammalian cells as well as during the oxidation of cholesterol associated with the synthesis of steroid hormones in steroidogenic cells. Some of the H₂O₂ produced in mitochondria is released into the cytosol, where it serves as a key regulator of various signaling pathways. Given that mitochondria are equipped with several H₂O₂-eliminating enzymes, however, it had not been clear how mitochondrial H₂O₂ can escape destruction by these enzymes for such release. Peroxiredoxin III (PrxIII) is the most abundant and efficient H₂O₂-eliminating enzyme in mitochondria of most cell types. We found that PrxIII undergoes reversible inactivation through hyperoxidation of its catalytic cysteine residue to cysteine sulfinic acid, and that release of mitochondrial H₂O₂ likely occurs as a result of such PrxIII inactivation. The hyperoxidized form of PrxIII (PrxIII-SO₂H) is reduced and reactivated by sulfiredoxin (Srx). We also found that the amounts of PrxIII-SO₂H and Srx undergo antiphasic circadian oscillation in mitochondria of the adrenal gland, heart, and brown adipose tissue of mice maintained under normal conditions. Cytosolic Srx was found to be imported into mitochondria via a mechanism that requires formation of a disulfide-linked complex with heat shock protein 90, which is likely promoted by H₂O₂ released from mitochondria. The imported Srx was found to be degraded by Lon protease in a manner dependent on PrxIII hyperoxidation state. The coordinated import and degradation of Srx underlie Srx oscillation and consequent PrxIII-SO₂H oscillation in mitochondria. The rhythmic change in the amount of PrxIII-SO₂H suggests that mitochondrial release of H₂O₂ is also likely a circadian event that conveys temporal information on steroidogenesis in the adrenal gland and on energy metabolism in heart and brown adipose tissue to cytosolic signaling pathways.

Chronic Glutathione Depletion Confers Protection against Alcohol-induced Steatosis: Implication for Redox Activation of AMP-activated Protein Kinase Pathway

The pathogenesis of alcoholic liver disease (ALD) is not well established. However, oxidative stress and associated decreases in levels of glutathione (GSH) are known to play a central role in ALD. The present study examines the effect of GSH deficiency on alcohol-induced liver steatosis in Gclm knockout (KO) mice that constitutively have ≈15% normal hepatic levels of GSH. Following chronic (6 week) feeding with an ethanol-containing liquid diet, the Gclm KO mice were unexpectedly found to be protected against steatosis despite showing increased oxidative stress (as reflected in elevated levels of CYP2E1 and protein carbonyls). Gclm KO mice also exhibit constitutive activation of liver AMP-activated protein kinase (AMPK) pathway and nuclear factor-erythroid 2–related factor 2 target genes, and show enhanced ethanol clearance, altered hepatic lipid profiles in favor of increased levels of polyunsaturated fatty acids and concordant changes in expression of genes associated with lipogenesis and fatty acid oxidation. In summary, our data implicate a novel mechanism protecting against liver steatosis via an oxidative stress adaptive response that activates the AMPK pathway. We propose redox activation of the AMPK may represent a new therapeutic strategy for preventing ALD.

SPARC gene deletion protects against toxic liver injury and is associated to an enhanced proliferative capacity and reduced oxidative stress response

SPARC, also known as osteonectin and BM-40, is a matricellular protein with a number of biological functions. Hepatic SPARC expression is induced in response to thioacetamide, bile-duct ligation, and acute injuries such as concanavalin A and lipopolysacharide (LPS)/D-galactosamine. We have previously demonstrated that the therapeutic inhibition of SPARC or SPARC gene deletion protected mice against liver injury. We investigated the mechanisms involved in the protective effect of SPARC inhibition in mice. We performed a proteome analysis of livers from SPARC^+/+ and SPARC^−/− mice chronically treated with thioacetamide. Catalase activity, carbonylation levels, oxidative stress response, and mitochondrial function were studied. Genomic analysis revealed that SPARC^−/− mice had an increased expression of cell proliferation genes. Proteins involved in detoxification of reactive oxygen species such as catalase, peroxirredoxine-1, and glutathione-S-transferase P1 and Mu1 were highly expressed as evidenced by proteome analysis; hepatic catalase activity was increased in SPARC^−/− mice. Oxidative stress response and carbonylation levels were lower in livers from SPARC^−/− mice. Hepatic mitochondria showed lower levels of nitrogen reactive species in the SPARC^−/− concanavalin A-treated mice. Mitochondrial morphology was preserved, and its complex activity reduced in SPARC^−/− mice. In conclusion, our data suggest that the protection associated with SPARC gene deletion may be partially due to a higher proliferative capacity of hepatocytes and an enhanced oxidative stress defense in SPARC^−/− mice after liver injury.

Fortilin potentiates the peroxidase activity of Peroxiredoxin-1 and protects against alcohol-induced liver damage in mice

Fortilin, a pro-survival molecule, inhibits p53-induced apoptosis by binding to the sequence-specific DNA-binding domain of the tumor suppressor protein and preventing it from transcriptionally activating Bax. Intriguingly, fortilin protects cells against ROS-induced cell death, independent of p53. The signaling pathway through which fortilin protects cells against ROS-induced cell death, however, is unknown. Here we report that fortilin physically interacts with the antioxidant enzyme peroxiredoxin-1 (PRX1), protects it from proteasome-mediated degradation, and keeps it enzymatically active by blocking its deactivating phosphorylation by Mst1, a serine/threonine kinase. At the whole animal level, the liver-specific overexpression of fortilin reduced PRX1 phosphorylation in the liver, enhanced PRX1 activity, and protected the transgenic animals against alcohol-induced, ROS-mediated, liver damage. These data suggest the presence of a novel oxidative-stress-handling pathway where the anti-p53 molecule fortilin augments the peroxidase PRX1 by protecting it against degradation and inactivation of the enzyme. Fortilin-PRX1 interaction in the liver could be clinically exploited further to prevent acute alcohol-induced liver damage in humans.

Mitochondrial dysfunction and tissue injury by alcohol, high fat, nonalcoholic substances and pathological conditions through post-translational protein modifications

Mitochondria are critically important in providing cellular energy ATP as well as their involvement in anti-oxidant defense, fat oxidation, intermediary metabolism and cell death processes. It is well-established that mitochondrial functions are suppressed when living cells or organisms are exposed to potentially toxic agents including alcohol, high fat diets, smoking and certain drugs or in many pathophysiological states through increased levels of oxidative/nitrative stress. Under elevated nitroxidative stress, cellular macromolecules proteins, DNA, and lipids can undergo different oxidative modifications, leading to disruption of their normal, sometimes critical, physiological functions. Recent reports also indicated that many mitochondrial proteins are modified via various post-translation modifications (PTMs) and primarily inactivated. Because of the recently-emerging information, in this review, we specifically focus on the mechanisms and roles of five major PTMs (namely oxidation, nitration, phosphorylation, acetylation, and adduct formation with lipid-peroxides, reactive metabolites, or advanced glycation end products) in experimental models of alcoholic and nonalcoholic fatty liver disease as well as acute hepatic injury caused by toxic compounds. We also highlight the role of the ethanol-inducible cytochrome P450-2E1 (CYP2E1) in some of these PTM changes. Finally, we discuss translational research opportunities with natural and/or synthetic anti-oxidants, which can prevent or delay the onset of mitochondrial dysfunction, fat accumulation and tissue injury.

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Hepatotoxic agents including alcohol and high fat elevate nitroxidative stress.

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Increased nitroxidative stress promotes post-translational protein modifications.

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Post-translational protein modifications of many proteins lead to their inactivation.

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Inactivation of mitochondrial proteins contributes to mitochondrial dysfunction.

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Mitochondrial dysfunction contributes to necrotic or apoptotic tissue injury.

Circadian Oscillation of Sulfiredoxin in the Mitochondria

Hydrogen peroxide (H2O2) released from mitochondria regulates various cell signaling pathways. Given that H2O2-eliminating enzymes such as peroxiredoxin III (PrxIII) are abundant in mitochondria, however, it has remained unknown how such release can occur. Active PrxIII-SH undergoes reversible inactivation via hyperoxidation to PrxIII-SO2, which is then reduced by sulfiredoxin. We now show that the amounts of PrxIII-SO2 and sulfiredoxin undergo antiphasic circadian oscillation in the mitochondria of specific tissues of mice maintained under normal conditions. Cytosolic sulfiredoxin was found to be imported into the mitochondria via a mechanism that requires formation of a disulfide-linked complex with heat shock protein 90, which is promoted by H2O2 released from mitochondria. The imported sulfiredoxin is degraded by Lon in a manner dependent on PrxIII hyperoxidation state. The coordinated import and degradation of sulfiredoxin provide the basis for sulfiredoxin oscillation and consequent PrxIII-SO2 oscillation in mitochondria and likely result in an oscillatory H2O2 release.

Calcium signaling and secretion in cholangiocytes

Alcoholic hepatitis affects up to one-third of individuals who abuse alcohol and can be associated with high mortality. Although this disorder is characterized by hepatocellular damage, steatosis and neutrophil infiltration, recent evidence suggests that cholestasis or impaired bile secretion may be a frequent occurrence as well. Bile secretion results from the concerted activity of hepatocytes and cholangiocytes, the epithelial cells that line the bile ducts. Hepatocytes secrete bile acids and conjugated products into the bile canaliculi, which then are modified by cholangiocytes through secretion of bicarbonate and water to give rise to the final secreted bile. Here the molecular mechanisms regulating bile secretion in cholangiocytes are reviewed. Moreover, we discuss how the expression of intracellular Ca(2+) channels might be regulated in cholangiocytes, plus evidence that components of the Ca(2+) signaling machinery are altered in a range of cholestatic diseases of the bile ducts.

Proteomic analysis of mice fed methionine and choline deficient diet reveals marker proteins associated with steatohepatitis

The mechanisms underlying the progression of simple steatosis to steatohepatitis are yet to be elucidated. To identify the proteins involved in the development of liver tissue inflammation, we performed comparative proteomic analysis of non-alcoholic steatohepatitis (NASH). Mice fed a methionine and choline deficient diet (MCD) developed hepatic steatosis characterized by increased free fatty acid (FFA) and triglyceride levels as well as alpha-SMA. Two-dimensional proteomic analysis revealed that the change from the normal diet to the MCD diet affected the expressions of 50 proteins. The most-pronounced changes were observed in the expression of proteins involved in Met metabolism and oxidative stress, most of which were significantly downregulated in NASH model animals. Peroxiredoxin (Prx) is the most interesting among the modulated proteins identified in this study. In particular, cross-regulated Prx1 and Prx6 are likely to participate in cellular defense against the development of hepatitis. Thus, these Prx isoforms may be a useful new marker for early stage steatohepatitis. Moreover, curcumin treatment results in alleviation of the severity of hepatic inflammation in steatohepatitis. Notably, curcumin administration in MCD-fed mice dramatically reduced CYP2E1 as well as Prx1 expression, while upregulating Prx6 expression. These findings suggest that curcumin may have a protective role against MCD fed-induced oxidative stress.

Role of Nrf2 in chronic liver disease

Nuclear erythroid 2-related factor 2 (Nrf2) is a central regulator of antioxidative response elements-mediated gene expression. It has a significant role in adaptive responses to oxidative stress by interacting with the antioxidant response element, which induces the expression of a variety of downstream targets aimed at cytoprotection. Previous studies suggested oxidative stress and associated damage could represent a common link between different forms of diseases. Oxidative stress has been implicated in various liver diseases, including viral hepatitis, nonalcoholic fatty liver disease/steatohepatitis, alcoholic liver disease and drug-induced liver injury. Nrf2 activation is initiated by oxidative or electrophilic stress, and aids in the detoxification and elimination of potentially harmful exogenous chemicals and their metabolites. The expression of Nrf2 has been observed throughout human tissue, with high expression in detoxification organs, especially the liver. Thus, Nrf2 may serve as a major regulator of several cellular defense associated pathways by which hepatic cells combat oxidative stress. We review the relevant literature concerning the crucial role of Nrf2 and its signaling pathways against oxidative stress to protect hepatic cell from oxidative damage during development of common chronic liver diseases. We also review the use of Nrf2 as a therapeutic target to prevent and treat liver diseases.

Role of sulfiredoxin in systemic diseases influenced by oxidative stress

Sulfiredoxin is a recently discovered member of the oxidoreductases family which plays a crucial role in thiol homoeostasis when under oxidative stress. A myriad of systemic disorders have oxidative stress and reactive oxygen species as the key components in their etiopathogenesis. Recent studies have evaluated the role of this enzyme in oxidative stress mediated diseases such as atherosclerosis, chronic obstructive pulmonary disease and a wide array of carcinomas. Its action is responsible for the normal functioning of cells under oxidative stress and the promotion of cell survival in cancerous cells. This review will highlight the cumulative effects of sulfiredoxin in various systemic disorders with a strong emphasis on its target activity and the factors influencing its expression in such conditions.

Peroxiredoxin post-translational modifications by redox messengers

Peroxiredoxins (Prxs) are a family of thiol peroxidases that participate in hydroperoxide detoxification and regulates H₂O₂ signaling. In mammals, the four typical 2-Cys Prxs (Prxs 1, 2, 3 and 4) are known to regulate H₂O₂-mediated intracellular signaling. The 2 catalytic cysteines of 2-Cys Prxs, the so-called peroxidatic and resolving cysteines, are regulatory switches that are prone to react with redox signaling molecules. We investigated the respective modifications induced by H₂O₂, NO and H₂S in the murine macrophage cell line RAW264.7 by mass spectrometry and immunoblotting after separating 2-Cys Prxs by one-dimensional or two-dimensional PAGE. We found that H₂S, unlike NO, does not prevent H₂O₂-mediated sulfinylation of 2-Cys Prxs and that Prx2 is more sensitive to NO-mediated protection against sulfinylation by peroxides. We also observed that cells exposed to exogenous NO, released by Cys-SNO or DETA-NO, or producing NO upon stimulation by IFN-γ and LPS, present an acidic form of Prx1 whose modification is consistent with S-homocysteinylation of its peroxidatic cysteine.

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NO and H₂O₂ differently modify 2-Cys peroxiredoxins.

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Prx1 is more prone to modifications by NO than the other 2-Cys Prxs.

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NO promotes S-homocysteinylation of Prx1 peroxidatic cysteine.