Mutual changes of thioredoxin and nitrosothiols during biliary cirrhosis: results from humans and cholestatic rats

DDIT4 S-Nitrosylation Aids p38-MAPK Signaling Complex Assembly to Promote Hepatic Reactive Oxygen Species Production

Mitogen-activated protein kinase (MAPK) signaling plays a significant role in reactive oxygen species (ROS) production. The authors have previously shown that Brahma-related gene 1 (BRG1), a chromatin remodeling protein, contributes to hepatic ROS accumulation in multiple animal and cellular models of liver injury. Here it is reported that DNA damage-induced transcript 4 (DDIT4) is identified as a direct transcriptional target for BRG1. DDIT4 overexpression overcomes BRG1 deficiency to restore ROS production whereas DDIT4 knockdown phenocopies BRG1 deficiency in suppressing ROS production in vitro and in vivo. Mechanistically, DDIT4 coordinates the assembly of the p38-MAPK signaling complex to drive ROS production in an S-nitrosylation dependent manner. Molecular docking identifies several bioactive DDIT4-inteacting compounds including imatinib, nilotinib, and nateglinide, all of which are confirmed to attenuate hepatic ROS production, dampen p38-MAPK signaling, and ameliorate liver injury by influencing DDIT4 S-nitrosylation. Importantly, positive correlation between ROS levels and BRG1/DDIT4/S-nitrosylated DDIT4 levels is detected in human liver biopsy specimens. In conclusion, the data reveal a transcription-based signaling cascade that contributes to ROS production in liver injury.

S100 calcium binding protein A6 and associated long noncoding ribonucleic acids as biomarkers in the diagnosis and staging of primary biliary cholangitis

BACKGROUND

Primary biliary cholangitis (PBC) is a chronic and slowly progressing cholestatic disease, which causes damage to the small intrahepatic bile duct by immuno-regulation, and may lead to cholestasis, liver fibrosis, cirrhosis and, eventually, liver failure.

AIM

To explore the potential diagnosis and staging value of plasma S100 calcium binding protein A6 (S100A6) messenger ribonucleic acid (mRNA), LINC00312, LINC00472, and LINC01257 in primary biliary cholangitis.

METHODS

A total of 145 PBC patients and 110 healthy controls (HCs) were enrolled. Among them, 80 PBC patients and 60 HCs were used as the training set, and 65 PBC patients and 50 HCs were used as the validation set. The relative expression levels of plasma S100A6 mRNA, long noncoding ribonucleic acids LINC00312, LINC00472 and LINC01257 were analyzed using quantitative reverse transcription-polymerase chain reaction. The bile duct ligation (BDL) mouse model was used to simulate PBC. Then double immunofluorescence was conducted to verify the overexpression of S100A6 protein in intrahepatic bile duct cells of BDL mice. Human intrahepatic biliary epithelial cells were treated with glycochenodeoxycholate to simulate the cholestatic environment of intrahepatic biliary epithelial cells in PBC.

RESULTS

The expression of S100A6 protein in intrahepatic bile duct cells was up-regulated in the BDL mouse model compared with sham mice. The relative expression levels of plasma S100A6 mRNA, log10 LINC00472 and LINC01257 were up-regulated while LINC00312 was down-regulated in plasma of PBC patients compared with HCs (3.01 ± 1.04 vs 2.09 ± 0.87, P < 0.0001; 2.46 ± 1.03 vs 1.77 ± 0.84, P < 0.0001; 3.49 ± 1.64 vs 2.37 ± 0.96, P < 0.0001; 1.70 ± 0.33 vs 2.07 ± 0.53, P < 0.0001, respectively). The relative expression levels of S100A6 mRNA, LINC00472 and LINC01257 were up-regulated and LINC00312 was down-regulated in human intrahepatic biliary epithelial cells treated with glycochenodeoxycholate compared with control (2.97 ± 0.43 vs 1.09 ± 0.08, P = 0.0018; 2.70 ± 0.26 vs 1.10 ± 0.10, P = 0.0006; 2.23 ± 0.21 vs 1.10 ± 0.10, P = 0.0011; 1.20 ± 0.04 vs 3.03 ± 0.15, P < 0.0001, respectively). The mean expression of S100A6 in the advanced stage (III and IV) of PBC was up-regulated compared to that in HCs and the early stage (II) (3.38 ± 0.71 vs 2.09 ± 0.87, P < 0.0001; 3.38 ± 0.71 vs 2.57 ± 1.21, P = 0.0003, respectively); and in the early stage (II), it was higher than that in HCs (2.57 ± 1.21 vs 2.09 ± 0.87, P = 0.03). The mean expression of LINC00312 in the advanced stage was lower than that in the early stage and HCs (1.39 ± 0.29 vs 1.56 ± 0.33, P = 0.01; 1.39 ± 0.29 vs 2.07 ± 0.53, P < 0.0001, respectively); in addition, the mean expression of LINC00312 in the early stage was lower than that in HCs (1.56 ± 0.33 vs 2.07 ± 0.53, P < 0.0001). The mean expression of log10 LINC00472 in the advanced stage was higher than those in the early stage and HCs (2.99 ± 0.87 vs 1.81 ± 0.83, P < 0.0001; 2.99 ± 0.87 vs 1.77 ± 0.84, P < 0.0001, respectively). The mean expression of LINC01257 in both the early stage and advanced stage were up-regulated compared with HCs (3.88 ± 1.55 vs 2.37 ± 0.96, P < 0.0001; 3.57 ± 1.79 vs 2.37 ± 0.96, P < 0.0001, respectively). The areas under the curves (AUC) for S100A6, LINC00312, log10 LINC00472 and LINC01257 in PBC diagnosis were 0.759, 0.7292, 0.6942 and 0.7158, respectively. Furthermore, the AUC for these four genes in PBC staging were 0.666, 0.661, 0.839 and 0.5549, respectively. The expression levels of S100A6 mRNA, log10 LINC00472, and LINC01257 in plasma of PBC patients were decreased (2.35 ± 1.02 vs 3.06 ± 1.04, P = 0.0018; 1.99 ± 0.83 vs 2.33 ± 0.96, P = 0.036; 2.84 ± 0.92 vs 3.69 ± 1.54, P = 0.0006), and the expression level of LINC00312 was increased (1.95 ± 0.35 vs 1.73 ± 0.32, P = 0.0007) after treatment compared with before treatment using the paired t-test. Relative expression of S100A6 mRNA was positively correlated with log10 LINC00472 (r = 0.683, P < 0.0001); serum level of collagen type IV was positively correlated with the relative expression of log10 LINC00472 (r = 0.482, P < 0.0001); relative expression of S100A6 mRNA was positively correlated with the serum level of collagen type IV (r = 0.732, P < 0.0001). The AUC for the four biomarkers obtained in the validation set were close to the training set.

CONCLUSION

These four genes may potentially act as novel biomarkers for the diagnosis of PBC. Moreover, LINC00472 acts as a potential biomarker for staging in PBC.

Hepatoprotective effect of the hydroalcoholic extract of Cichorium intybus in a rat model of obstructive cholestasis

BACKGROUND AND STUDY AIMS

Obstructive cholestasis increases the levels of oxidants and inflammatory mediators, leading to liver damage. Previous studies have found that Cichorium intybus possesses anti-inflammatory effects. In the present study, the effects of the hydroalcoholic extract of C. intybus leaves were assessed in a rat model of obstructive cholestasis.

MATERIAL AND METHODS

Male Wistar rats were randomly divided into five groups (n = 6 rats per group): sham-operated, control [bile duct ligation (BDL) + vehicle)] and BDL + extract treatment (100, 200 and 400 mg/kg/day, i.p.) groups. Rats received treatments for 7 consecutive days. On the eighth day, prothrombin time (PT); serum albumin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase and total and direct bilirubin levels and total antioxidant and paraoxonase activities were measured using colorimetric methods. In addition, tumour necrosis factor-α and nitric oxide (NO) levels were measured using enzyme-linked immunosorbent assay.

RESULTS

The hydroalcoholic extract of C. intybus significantly decreased PT and the serum levels of AST, ALT, TNF-α and NO compared with the control group (p < 0.05). On the other hand, the serum albumin levels were increased in the extract-treated groups compared with the control group (p < 0.05).

CONCLUSION

The hydroalcoholic extract of C. intybus protects the liver against injury induced by obstructive cholestasis.

Aberrant expression of redox regulatory proteins in patients with concomitant primary Sclerosing cholangitis/inflammatory bowel disease

OBJECTIVE

Primary Sclerosing Cholangitis (PSC) is a severe cholestatic liver disease characterized by progressive peri-biliary tract inflammation, elevated oxidative stress and hepatocellular injury. A hallmark of PSC patients is the concurrent diagnosis of Inflammatory Bowel Disease occurring in approximately 70%-80% of PSC patients (PSC/IBD). We previously reported dysregulation of key anti-oxidant pathways in PSC/IBD. The objective of this study was to expand previous data by examining the abundance of thioredoxins (Trx) in PSC/IBD.

METHODS

Using hepatic tissue and whole cell extracts isolated from age-matched healthy humans and patients diagnosed with end stage PSC/IBD, the protein abundance of thioredoxin, thioredoxin reductase (TrxR1), and their downstream substrates peroxiredoxins was assessed.

RESULTS

Western blot analyses of thioredoxin and peroxiredoxin abundance revealed significant increases in abundance of Trx1 and TrxR1 whereas expression of thioredoxin-interacting protein was significantly decreased in PSC/IBD. Concurrently, abundance of cytosolic peroxiredoxins was not significantly impacted. The abundance of mitochondrial Trx2, along with peroxiredoxins 3, 5 and 6 were significantly decreased by concurrent PSC/IBD. Histological staining of Trx1/TrxR1 revealed elevated nuclear Trx1 and TrxR1 staining within cholangiocytes as well as an overall periportal increase in expression in PSC/IBD. An examination of additional anti-oxidant responses reveal suppression of gamma-glutamylcysteine synthetase and heme oxygenase (HO-1) whereas expression of the protein chaperone glucose regulated protein 78 increased suggesting elevated cellular stress in PSC/IBD.

CONCLUSIONS

Results herein suggest that in addition to severe dysregulation of anti-oxidant responses, cholestasis impacts both cytosolic/nuclear (Trx1) as well as mitochondrial (Trx2) redox signaling and control pathways.

Txn1, Ctsd and Cdk4 are key proteins of combination therapy with taurine, epigallocatechin gallate and genistein against liver fibrosis in rats

The anti-fibrotic mechanism of combination therapy with taurine, epigallocatechin gallate and genistein was studied from the perspective of serum proteomics in our previous work. In order to further investigate and systematically analyse other possible therapeutic mechanism of combination therapy against liver fibrosis, isobaric tags for relative and absolute quantification (iTRAQ) proteomic analysis was applied to study the protein profile changes in liver tissue of carbon tetrachloride-induced liver fibrosis rats after combination therapy. A total of 115 differentially expressed proteins containing 84 up-regulated and 31 down-regulated proteins in response to combination therapy were identified. Three differentially expressed proteins (Txn1, Ctsd and Cdk4) involved in antioxidant defense system and the activation and proliferation of hepatic stellate cell were selected for further validation by western blot and real-time PCR analysis. Our study highlight the importance of differentially expressed proteins Txn1, Ctsd and Cdk4 against liver fibrosis, which may provide a more precise and comprehensive perspective for clarifying the roles of combination therapy as a potential agent for treatment of liver fibrosis.

Nature and Implications of Oxidative and Nitrosative Stresses in Autoimmune Hepatitis

Oxidative and nitrosative stresses can damage cellular membranes, disrupt mitochondrial function, alter gene expression, promote the apoptosis and necrosis of hepatocytes, and increase fibrosis in diverse acute and chronic liver diseases, including autoimmune hepatitis. The objectives of this review are to describe the mechanisms of oxidative and nitrosative stresses in inflammatory liver disease, indicate the pathogenic implications of these stresses in autoimmune hepatitis, and suggest investigational opportunities to develop interventions that counter them. The principal antioxidant defenses, including glutathione production, the activities of antioxidant enzymes, and the release of the nuclear factor erythroid 2-related factor 2, may be inadequate or suppressed by transforming growth factor beta. The generation of reactive oxygen species can intensify nitrosative stress, and this stress may not be adequately modulated by the thioredoxin-thioredoxin reductase system and induce post-translational modifications of proteins that further disrupt hepatocyte function. The unfolded protein response and autophagy may be unable to restore redox stability, meet metabolic demands, and maintain hepatocyte survival. Emerging interventions with highly selective site- and organelle-specific actions may improve outcomes, and they include inhibitors of nicotinamide adenine dinucleotide phosphate oxidase, nitric oxide synthase, and transforming growth factor beta. Pharmacological manipulation of nuclear transcription factors may favor expression of antioxidant genes, and stimulation of chaperone proteins within the endoplasmic reticulum and modulation of autophagy may prevent hepatic fibrosis and enhance cell survival. These interventions constitute investigational opportunities to improve the management of autoimmune hepatitis.

Can Chronic Nitric Oxide Inhibition Improve Liver and Renal Dysfunction in Bile Duct Ligated Rats?

The aims of the present work were to study the effects of chronic NO inhibition on liver cirrhosis and to analyze its relationship with liver and kidney damage markers. Two inhibitors of NO synthesis (inducible NO synthase (iNOS) inhibitor, aminoguanidine (AG), and nonselective NOS inhibitor, L-nitroarginine methyl ester (L-NAME)) were administered for 6 weeks to bile duct ligated (BDL) rats 3 days after surgery. The present study showed that BDL was associated with liver injury and renal impairment. BDL increased liver NO content and myeloperoxidase (MPO) activity. This was corroborated by increased oxidative stress, TNF-α, TGF-1β, and MMP-13 genes overexpression. Although both drugs reduced NO synthesis and TNF-α gene overexpression, only AG improved renal dysfunction and liver damage and reduced liver oxidative stress. However, L-NAME exacerbated liver and renal dysfunction. Both drugs failed to modulate TGF-1β and MMP-13 genes overexpression. In conclusion, inhibition of NO production by constitutive nitric oxide synthase (cNOS) plays a crucial role in liver injury and renal dysfunction while inhibition of iNOS by AG has beneficial effect. TNF-α is not the main cytokine responsible for liver injury in BDL model. Nitric oxide inhibition did not stop the progression of cholestatic liver damage.

Cysteine 96 of Ntcp is responsible for NO-mediated inhibition of taurocholate uptake

The Na(+) taurocholate (TC) cotransporting polypeptide Ntcp/NTCP mediates TC uptake across the sinusoidal membrane of hepatocytes. Previously, we demonstrated that nitric oxide (NO) inhibits TC uptake through S-nitrosylation of a cysteine residue. Our current aim was to determine which of the eight cysteine residues of Ntcp is responsible for NO-mediated S-nitrosylation and inhibition of TC uptake. Thus, we tested the effect of NO on TC uptake in HuH-7 cells transiently transfected with cysteine-to-alanine mutant Ntcp constructs. Of the eight mutants tested, only C44A Ntcp displayed decreased total and plasma membrane (PM) levels that were also reflected in decreased TC uptake. C266A Ntcp showed a decrease in TC uptake that was not explained by a decrease in total expression or PM localization, indicating that C266 is required for optimal uptake. We speculated that NO would target C266 since a previous report had shown the thiol reactive compound [2-(trimethylammonium) ethyl] methanethiosulfonate bromide (MTSET) inhibits TC uptake by wild-type NTCP but not by C266A NTCP. We confirmed that MTSET targets C266 of Ntcp, but, surprisingly, we found that C266 was not responsible for NO-mediated inhibition of TC uptake. Instead, we found that C96 was targeted by NO since C96A Ntcp was insensitive to NO-mediated inhibition of TC uptake. We also found that wild-type but not C96A Ntcp is S-nitrosylated by NO, suggesting that C96 is important in regulating Ntcp function in response to elevated levels of NO.

Oxidized LDL receptor 1 gene polymorphism in patients with metabolic syndrome

AIMS

The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), encoded by the OLR1 gene, has been implicated in the pathogenesis of atherosclerosis. We therefore evaluated the genotyping of OLR1 gene in a sample of 55 patients with Metabolic Syndrome, a clinical condition characterized by a high cardiovascular risk.

METHODS AND PATIENTS

The genotyping of the LOX-1 was performed by polymerase chain reaction (PCR) analysis of the IVS4-14 A>G OLR1 polymorphism embedded within the OLR1 Linkage Disequilibrium block. Patients were assessed for routine serum parameters, microalbuminuria, insulin resistance (HOMA) and oxidative stress (thiobarbituric acid reactive substances, TBARs and thioredoxin).

RESULTS

The allele or genotype distribution of the OLR1 IVS4-14 A>G was not statistically different between MS and controls subjects. A positive association was found between IVS4-14 GG genotype, microalbuminuria and fasting glycaemia as well as a higher frequency of type 2 diabetes, elevated microalbuminuria, fasting serum glucose and HOMA index in the same subjects. Thioredoxin values were higher in patients with MS but did not differ in relation to OLR1 IVS4-14 A>G genotype. The TBARs/Cholesterol ratio was higher in MS both in IVS4-14 GG and in IVS4-14 AG.

CONCLUSION

IVS4-14 GG genotype seems to be related to glucose metabolism disturbance, elevated insulin level and lipid peroxidation in patients with MS.

Antioxidant and antigenotoxic effects of lycopene in obstructive jaundice

BACKGROUND

Obstructive jaundice, a frequently observed condition caused by obstruction of the common bile duct or its flow and seen in many clinical situations, may end up with serious complications like sepsis, immune depression, coagulopathy, wound breakdown, gastrointestinal hemorrhage, and hepatic and renal failures. Intrahepatic accumulation of reactive oxygen species is thought to be an important cause for the possible mechanisms of the pathogenesis of cholestatic tissue injury from jaundice. Carotenoids have been well described that are able to scavenge reactive oxygen species. Lycopene, a carotenoid present in tomatoes, tomato products, and several fruits and vegetables, have been suggested to have antioxidant activity, so may play a role in certain diseases related to the oxidative stress. The aim of the present study was to determine the effects of lycopene on oxidative stress and DNA damage induced by experimental biliary obstruction in Wistar albino rats.

MATERIALS AND METHODS

Daily doses of 100 mg/kg lycopene were given to the bile duct-ligation (BDL) rats orally for 14 days. DNA damage was evaluated by an alkaline comet assay. The levels of aspartate transferase, amino alanine transferase, gamma glutamyl transferase, alkaline phosphatase, and direct bilirubin were analyzed in plasma for the determination of liver functions. The levels of malondialdehyde, reduced glutathione, nitric oxide, catalase, superoxide dismutase, and glutathione S transferase were determined in the liver and kidney tissues. Pro-inflammatory cytokine tumor necrosis factor-alpha level was determined in the liver tissues. Histologic examinations of the liver and kidney tissues were also performed.

RESULTS

According to this study, lycopene significantly recovered the parameters of liver functions in plasma, reduced malondialdehyde and nitric oxide levels, enhanced reduced glutathione levels, as well as enhancing all antioxidant enzyme activity in all tissues obtained from the BDL group. Moreover, the parameters of DNA damage in the liver and kidney tissue cells, whole blood cells, and lymphocytes were significantly lower in the lycopene-treated BDL group, compared with the BDL group.

CONCLUSIONS

Lycopene significantly reduced the DNA damage, and markedly recovered the liver and kidney tissue injuries seen in rats with obstructive jaundice.

Role of mitochondria in nonalcoholic fatty liver disease--from origin to propagation

OBJECTIVES

Mitochondria play a major role in cell energy-generating processes and integrate several signalling pathways to control cellular life and death.

DESIGN AND METHODS

Several liver diseases are characterized by mitochondrial alterations which are directly or indirectly dependent on the activation of intracellular stress cascades or receptor-mediated pathways. This article examines the role of mitochondrial dysfunction in critical initiating or propagating events in fatty liver infiltration and nonalcoholic fatty liver disease (NAFLD). Genetic variants and the role of drug-induced toxicity have been considered.

RESULTS

Key alterations of mitochondrial physiology associated with hepatocyte fatty changes are described. The value of novel non-invasive diagnostic methods to detect mitochondrial metabolic alterations is also discussed.

CONCLUSIONS

Mitochondrial metabolic remodeling is a predominant factor in the appearance and perpetuation of hepatocyte fat accumulation. Non-invasive techniques to identify mitochondrial dysfunction and proper mitochondria protection are two necessary clinical steps for an efficient management of NAFLD.

Long-term ursodeoxycholate improves circulating redox changes in primary biliary cirrhotic patients

BACKGROUND AND AIMS

Cholestasis is associated with systemic and hepatic oxidative and nitrosative stress; in this scenario, the conjugated hydrophilic bile salt ursodeoxycholate (UDCA) might play a protective role.

METHODS

Circulating oxidative and nitrosative stress markers were assessed in patients with primary biliary cirrhosis (PBC) before and during UDCA (15-20mg/kg/day) therapy.

RESULTS

In patients with stage I-II PBC, UDCA improved ALT and alkaline phosphatase levels and near normalized serum thioredoxin (1.97 ± 0.37 vs 2.41 ± 0.39 nmol/L), nitrotyrosine (15 ± 4 vs 22 ± 7 nmol/L), nitrosothiols (144 ± 28 vs 205 ± 84 nmol/L) and K-18 levels (162 ± 21 vs 228 ± 33 U/L). Conversely, less marked changes were noted in patients with stages III-IV who showed lower thioredoxin (1.01 ± 0.31 nmol/L), higher nitrosothiols (605 ± 64 nmol/L), nitrotyrosine (62 ± 13 nmol/L) and K-18 levels (521 ± 57 U/L). Overall, thioredoxin was inversely related with nitrotyrosine (r=-0.838, P<0.001) and K-18 (r=-0.838, P<0.001) levels. Nitrosothiols and K-18 were linearly and significantly related with nitrotyrosine (r=0.862, P<0.001; r=0.894, P<0.001, respectively).

CONCLUSIONS

Oxidative and nitrosative changes in patients with PBC are effectively counteracted by UDCA. The protective effect of UDCA, however, are limited to early disease stages and progressively diminishes with ongoing cholestasis.

Thioredoxin, thioredoxin-interacting protein and digestive diseases

The thioredoxin system is an antioxidative and redox-regulating system that consists of several small proteins, including thioredoxin (TRX), reduced coenzyme II (NADPH) and thioredoxin reductase (TRX-R). It can function to regulate oxidation-reduction state of cells, resist oxidative stress, activate transcription factors NF-κB and AP-1 to promote the growth and proliferation of cells, and interact with ASK-1 to inhibit apoptosis. Thioredoxin-interacting protein (TXNIP) is a member of the thioredoxin-binding protein family and plays a role in mediating oxidative stress, resisting cell proliferation and inducing apoptosis, acting as a negative regulator of the TRX system. Since oxidative stress and apoptosis are often involved in the pathogenesis of digestive diseases, TRX and TXNIP may play roles in the pathogenesis of digestive diseases. This paper gives an overview of the structure and functions of TRX and TXNIP and reviews the recent advances in understanding the relationship between the two proteins and digestive diseases.

Participation of nuclear factor (erythroid 2-related), factor 2 in ameliorating lithocholic acid-induced cholestatic liver injury in mice

BACKGROUND AND PURPOSE

Lithocholic acid (LCA), the most toxic bile acid, induces cholestatic liver injury in rodents. We previously showed that LCA activates the oxidative stress-responsive nuclear factor (erythroid-2 like), factor 2 (Nrf2) in cultured liver cells, triggering adaptive responses that reduce cell injury. In this study, we determined whether Nrf2 protects the liver against LCA-induced toxicity in vivo.

EXPERIMENTAL APPROACH

Nrf2 disrupted (Nrf2(-/-) ) and wild-type mice were treated with LCA (125 mg·kg(-1) body weight) to induce liver injury. Levels of mRNA, protein and function of important Nrf2 target genes coupled with liver histology and injury biomarkers of mice were examined.

KEY RESULTS

In 4 day LCA treatments, we observed a significantly higher hepatic induction of Nrf2 target, cytoprotective genes including thioredoxin reductase 1, glutamate cysteine ligase subunits, glutathione S-transferases, haeme oxygenase-1 and multidrug resistance-associated proteins 3 and 4 in the wild type as compared with the Nrf2(-/-) mice. Moreover, basal and LCA-induced hepatic glutathione and activities of glutathione S-transferases and thioredoxin reductases were higher in wild-type than in Nrf2(-/-) mice. This reduced production of cytoprotective genes against LCA toxicity rendered Nrf2(-/-) mice more susceptible to severe liver damage with the presence of multifocal liver necrosis, inflamed bile ducts and elevation of lipid peroxidation and liver injury biomarkers, such as alanine aminotransferase and alkaline phosphatase.

CONCLUSIONS AND IMPLICATIONS

Nrf2 plays a crucial cytoprotective role against LCA-induced liver injury by orchestrating adaptive responses. The pharmacological potential of targeting liver Nrf2 in the management of cholestatic liver diseases is proposed.

Enhanced hepatic Nrf2 activation after ursodeoxycholic acid treatment in patients with primary biliary cirrhosis

The cytoprotective mechanisms of ursodeoxycholic acid (UDCA) in primary biliary cirrhosis (PBC) have not been fully clarified. UDCA has some antioxidant properties. Nuclear factor-E2-related factor-2 (Nrf2) plays a critical role in protecting a variety of tissues against oxidative stress. Therefore, to investigate the potential antioxidant effects of UDCA in PBC, we determined the intracellular status of both oxidant stress and antioxidant defenses in paired pre- and posttreatment liver biopsies from 13 PBC patients by immunodetection of 8-hydroxydeoxyguanosine (8-OHdG), Nrf2-, and Nrf2-mediated antioxidant proteins. After UDCA treatment, the number of 8-OHdG-positive hepatocytes or bile duct cells decreased with improvement of hepatic injury. The hepatic levels of both total and phosphorylated Nrf2 protein were increased, along with upregulation of nuclear phosphorylated Nrf2 expression in bile duct cells. In addition, the levels of both thioredoxin (TRX) and thioredoxin reductase 1 (TrxR1) protein were increased in the liver after UDCA. The upregulation of hepatic TRX or TrxR1 protein expression positively correlated with that of total Nrf2 protein expression. In conclusion, UDCA treatment can enhance hepatic Nrf2 activation and upregulate hepatic TRX and TrxR1 protein expression. Hepatic Nrf2 activation may play a role in the therapeutic response to UDCA in PBC.

Inhibition of nitric oxide synthesis during induced cholestasis ameliorates hepatocellular injury by facilitating S-nitrosothiol homeostasis

Cholestatic liver injury following extra- or intrahepatic bile duct obstruction causes nonparenchymal cell proliferation and matrix deposition leading to end-stage liver disease and cirrhosis. In cholestatic conditions, nitric oxide (NO) is mainly produced by a hepatocyte-inducible NO synthase (iNOS) as a result of enhanced inflow of endotoxins to the liver and also by accumulation of bile salts in hepatocytes and subsequent hepatocellular injury. This study was aimed to investigate the role of NO and S-nitrosothiol (SNO) homeostasis in the development of hepatocellular injury during cholestasis induced by bile duct ligation (BDL) in rats. Male Wistar rats (200-250 g) were divided into four groups (n=10 each), including sham-operated (SO), bile duct-ligated (BDL), tauroursodeoxycholic acid (TUDCA, 50 mg/kg) and S-methylisothiourea (SMT, 25 mg/kg) treated. After 7 days, BDL rats showed elevated serum levels of gamma-glutamiltranspeptidase, aspartate aminotransferase, alanine aminotransferase, LDH, and bilirubin, bile duct proliferation and fibrosis, compared with the SO group. TUDCA treatment did not significantly alter these parameters, but the iNOS inhibitor SMT ameliorated hepatocellular injury, as shown by lower levels of circulating hepatic enzymes and bilirubin, and a decreased grade of bile duct proliferation and fibrosis. Both TUDCA and SMT treatments reversed Mrp2 canalicular pump expression to control levels. However, only SMT treatment significantly lowered the increased levels of plasma NO and S-nitrosation (S-nitrosylation) of liver proteins in BDL rats. Moreover, BDL resulted in a reduction of the S-nitrosoglutathione reductase (GSNOR/Adh5) enzymatic activity and a downregulation of the GSNOR/Adh5 mRNA expression that was reverted by SMT, but not TUDCA, treatment. A total of 25 liver proteins, including S-adenosyl methionine synthetase, betaine-homocysteine S-methyltransferase, Hsp90 and protein disulfide isomerase, were found to be S-nitrosated in BDL rats. In conclusion, the inhibition of NO production during induced cholestasis ameliorates hepatocellular injury. This effect is in part mediated by the improvement of cell proficiency in maintaining SNO homeostasis.

Nitric oxide and dihydrolipoic acid modulate the activity of caspase 3 in HepG2 cells

Herein, we report that dihydrolipoic acid and lipoic acid (LA) plus lipoamide dehydrogenase and NADH denitrosate S-nitrosocaspase 3 (CASP-SNO). In HepG2 cells, S-nitroso-L-cysteine ethyl ester (SNCEE) impeded the activity of caspase 3 (CASP-SH), while a subsequent incubation of the cells in SNCEE-free medium resulted in endogenous denitrosation and reactivation of CASP-SH. The latter process was inhibited in thioredoxin reductase-deficient HepG2 cells, in which, however, LA markedly reactivated CASP-SH. The data obtained are discussed with focus on low molecular mass dithiols that mimic the activity of thioredoxin in reactions of protein S-denitrosation.