Oxidative stress and vascular smooth muscle cell function in liver disease

Dysregulation of murine long noncoding single-cell transcriptome in nonalcoholic steatohepatitis and liver fibrosis

LncRNAs comprise a heterogeneous class of RNA-encoding genes typified by low expression, nuclear enrichment, high tissue-specificity, and functional diversity, but the vast majority remain uncharacterized. Here, we assembled the mouse liver noncoding transcriptome from >2000 bulk RNA-seq samples and discovered 48,261 liver-expressed lncRNAs, a majority novel. Using these lncRNAs as a single-cell transcriptomic reference set, we elucidated lncRNA dysregulation in mouse models of high fat diet-induced nonalcoholic steatohepatitis and carbon tetrachloride-induced liver fibrosis. Trajectory inference analysis revealed lncRNA zonation patterns across the liver lobule in each major liver cell population. Perturbations in lncRNA expression and zonation were common in several disease-associated liver cell types, including nonalcoholic steatohepatitis-associated macrophages, a hallmark of fatty liver disease progression, and collagen-producing myofibroblasts, a central feature of liver fibrosis. Single-cell-based gene regulatory network analysis using bigSCale2 linked individual lncRNAs to specific biological pathways, and network-essential regulatory lncRNAs with disease-associated functions were identified by their high network centrality metrics. For a subset of these lncRNAs, promoter sequences of the network-defined lncRNA target genes were significantly enriched for lncRNA triplex formation, providing independent mechanistic support for the lncRNA-target gene linkages predicted by the gene regulatory networks. These findings elucidate liver lncRNA cell-type specificities, spatial zonation patterns, associated regulatory networks, and temporal patterns of dysregulation during hepatic disease progression. A subset of the liver disease-associated regulatory lncRNAs identified have human orthologs and are promising candidates for biomarkers and therapeutic targets.

Adrenergic Response of Splanchnic Arteries from Cirrhotic Patients: Role of Nitric Oxide, Prostanoids, and Reactive Oxygen Species

Peripheral and splanchnic vasodilatation in cirrhotic patients has been related to hyporesponsiveness to vasoconstrictors, but studies to examine the vascular adrenergic response provide contradictory results. Hepatic arteries from cirrhotic patients undergoing liver transplantation and mesenteric arteries from liver donors were obtained. Segments 3 mm long from these arteries were mounted in organ baths for testing isometric adrenergic response. The concentration-dependent contraction to noradrenaline (10−8 to 10−4 M) was similar in hepatic and mesenteric arteries, and prazosin (α 1-adrenergic antagonist, 10−6 M), but not yohimbine (α 2-adrenergic antagonist, 10−6 M), produced a rightward parallel displacement of this contraction in both types of arteries. Phenylephrine (α 1-adrenergic agonist, 10−8 to 10−4 M) and clonidine (α 2-adrenergic agonist, 10−8 to 10−4 M) also produced concentration-dependent contractions that were comparable in hepatic and mesenteric arteries. The inhibitor of cyclooxygenase meclofenamate (10−5 M), but not the inhibitor of nitric oxide synthesis Nw-nitro-l-arginine methyl ester (l-NAME, 10−4 M), potentiated the response to noradrenaline in hepatic arteries; neither inhibitor affected the response to noradrenaline in mesenteric arteries. Diphenyleneiodonium (DPI; 5 × 10−6 M), but neither catalase (1000 U/ml) nor tiron (10−4 M), decreased the maximal contraction for noradrenaline similarly in hepatic and mesenteric arteries. Therefore, it is suggested that, in splanchnic arteries from cirrhotic patients, the adrenergic response and the relative contribution of α 1- and α 2-adrenoceptors in this response is preserved, and prostanoids, but not nitric oxide, may blunt that response. Products dependent on NAD(P)H oxidase might contribute to the adrenergic response in splanchnic arteries from control and cirrhotic patients.

Procoagulant changes in fibrin clot structure in patients with cirrhosis are associated with oxidative modifications of fibrinogen

Essentials Patients with cirrhosis have hemostatic changes, which may contribute to a risk of thrombosis. This in vitro study compares clot formation and structure between patients and healthy subjects. Clot formation is delayed in patients; ultimately, however, clot permeability is decreased. The thrombogenic structure of fibrin clots may contribute to the thrombotic risk in cirrhosis.

ABSTRACT

Background and Objectives Patients with cirrhosis can be at risk of thrombotic complications due to an imbalance between hemostatic components. However, little is known on how the disease affects clot generation or how alterations in the structure of fibrin clots may affect the hemostatic function of these patients. Methods We investigated the formation and structure of clots generated with plasma and purified fibrinogen of 42 patients with cirrhosis. Clots generated with plasma and fibrinogen of 29 healthy volunteers were studied for comparison. Clot formation and structure were assessed by turbidity, permeation studies, confocal laser and scanning electron microscopy (SEM). The extent of fibrinogen oxidation was assessed by measuring the carbonyl content of purified fibrinogen samples. Results Tissue factor and thrombin-induced clotting of plasma was delayed in patients. The clotting rate was also decreased, but change in turbidity, fibrin density and fiber thickness were largely comparable to healthy volunteers. Conversely, clot permeability was significantly decreased in patients. When clots were generated with purified fibrinogen, differences in clot formation and structure similar to those in plasma were found. The carbonyl content was increased in patient fibrinogen and correlated with disease severity and clot permeability. Conclusions Delayed clot formation in cirrhosis ultimately results in decreased clot permeability. Similar alterations in clots generated with purified fibrinogen suggest that modifications of the molecule are (partly) responsible. Taken together, these findings are indicative of hypercoagulable features of clots of patients with cirrhosis, which may explain the increased risk of thrombosis associated with this condition.

Survival benefits of terlipressin and non-responder state in hepatorenal syndrome: a meta-analysis

Objectives:

Terlipressin improves renal function in hepatorenal syndrome (HRS) is a known fact. However the reason for lack of its long-term survival benefits despite improvement in renal function remains unclear. The aim of this study was to analyze the survival benefits of terlipressin in HRS and to address the issue of non-responder state to terlipressin.

Materials and Methods:

Electronic databases and relevant articles were searched for all types of studies related to HRS and use of terlipressin in HRS. Reduction in all-cause mortality rate was the primary outcome measure. Reduction in mortality rate due to HRS and other causes of death were also analyzed.

Results:

With total 377 patients analyzed from eight eligible studies; terlipressin reduced all-cause mortality rate by 15% (Risk Difference: -0.15%, 95% CI:-0.26 to -0.03). Reduction in the mortality rate due to HRS at three months was 9% (Risk Difference:-0.09%, 95% CI:-0.18 to 0.00).

Conclusion:

Terlipressin has long term survival benefits perhaps at least up to three months but only with HRS as a cause of death not for other causes of death. Benefits and role of antioxidants like N- Acetylcysteine (NAC) in non-responder patients’ needs to be studied further. Long-term use of low dose terlipressin (<4mg/d) plus albumin and addition of antioxidant NAC to this regimen may help in improving both HRS reversal rate and survival rate in non-responders to terlipressin.

Persistent fibrosis in the liver of choline-deficient and iron-supplemented L-amino acid-defined diet-induced nonalcoholic steatohepatitis rat due to continuing oxidative stress after choline supplementation

Nonalcoholic steatohepatitis (NASH) is characterized by combined pathology of steatosis, lobular inflammation, fibrosis, and hepatocellular degeneration, with systemic symptoms of diabetes or hyperlipidemia, all in the absence of alcohol abuse. Given the therapeutic importance and conflicting findings regarding the potential for healing the histopathologic features of NASH in humans, particularly fibrosis, we investigated the reversibility of NASH-related findings in Wistar rats fed a choline-deficient and iron-supplemented l-amino acid-defined (CDAA) diet for 12weeks, with a recovery period of 7weeks, during which the diets were switched to a choline-sufficient and iron-supplemented l-amino acid-defined (CSAA) one. Analysis showed that steatosis and inflammation were significantly resolved by the end of the recovery period, along with decreases in AST and ALT activities within 4weeks. In contrast, fibrosis remained even after the recovery period, to an extent similar to that in continuously CDAA-fed animals. Real-time reverse transcriptase-polymerase chain reaction, Western blot, and immunohistochemical investigations revealed that expression of some factors indicating oxidative stress (CYP2E1, 4-HNE, and iNOS) were elevated, whereas catalase and SOD1 were decreased, and a hypoxic state and CD34-positive neovascularization were evident even after the recovery period, although the fibrogenesis pathway by activated α-SMA-positive hepatic stellate cells via TGF-β and TIMPs decreased to the CSAA group level. In conclusion, persistent fibrosis was noted after the recovery period of 7weeks, possibly due to sustained hypoxia and oxidative stress supposedly caused by capillarization. Otherwise, histopathological features of steatosis and inflammation, as well as serum AST and ALT activities, were recovered.

Liver impairment after portacaval shunt in the rat: the loss of protective role of mast cells?

Mast cells are involved in various liver diseases and appear to play a broader pathogenic role than originally thought. They may participate in the splanchnic alterations related to a porto-systemic shunt. To verify this hypothesis we studied the serum and hepatic histological changes in rats four weeks after an end-to-side portacaval shunt. In this experimental model of chronic liver insufficiency we also assessed the mucosal mast cells (MMC) and connective tissue mast cells (CTMC) in the liver, mesenteric lymph nodes and small intestine, as well as the serum levels of rat mast cell protease-II (RMCP-II). The results show liver and testes atrophy, with hypoalbuminemia (p=0.0001), hyperbilirubinemia (p=0.0001) and increase in aspartate aminotransferase (p=0.004) and alanine aminotransferase (p=0.0001). Hepatic histopathology demonstrates hepatocytic necrosis and apoptosis, portal inflammation, biliary proliferation, steatosis and fibrosis. There is a decrease of MMCs and CTMCs in the liver, while in the ileum CTMCs increase and MMCs decrease. These results suggest the involvement of mast cells in the pathophysiological splanchnic impairments in this experimental model. In particular, the decreased number of liver mast cells may be associated with the hepatic atrophy. If this is the case, we propose that the disruption of the hepato-intestinal axis after a portocaval shunt in the rat could inhibit the ability of the liver to developing an appropriate repair response mediated by mast cells.

Chronic immobilization in the malpar1 knockout mice increases oxidative stress in the hippocampus

The lysophosphatidic acid LPA₁ receptor has recently been involved in the adaptation of the hippocampus to chronic stress. The absence of LPA₁ receptor aggravates the chronic stress-induced impairment of both hippocampal neurogenesis and apoptosis that were accompanied with hippocampus-dependent memory deficits. Apoptotic death and neurogenesis in the hippocampus are regulated by oxidative stress. In the present work, we studied the involvement of LPA₁ receptor signaling pathway in the regulation of the hippocampal redox after chronic stress. To this end, we used malpar1 knockout (KO) and wild-type mice assigned to either chronic stress (21 days of restraint, 3 h/day) or control conditions. Lipid peroxidation, the activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX), as well as mitochondrial function stimulation, monitored through the activity of cytochrome c oxidase (COX), were studied in the hippocampus. Our results showed that chronic immobilization stress enhanced lipid peroxidation as well as the activity of the antioxidant enzymes studied (CAT, SOD, and GPX). This effect was only observed in absence of LPA₁ receptor. Furthermore, only malpar1 KO mice submitted to chronic stress exhibited a severe downregulation of the COX activity, suggesting the presence of mitochondrial damage. Altogether, these results suggest that malpar1 KO mice display enhanced oxidative stress in the hippocampus after chronic stress. This may be involved in the hippocampal abnormalities observed in this genotype after chronic immobilization, including memory, neurogenesis, and apoptosis.

Simultaneous inhibition of TXA(2) and PGI(2) synthesis increases NO release in mesenteric resistance arteries from cirrhotic rats

Our present study examines, in mesenteric resistance arteries, possible vasodilation alterations, and the role of NO and COX (cyclo-oxygenase) derivatives, in cirrhosis. The vasodilator response to acetylcholine was analysed in segments from control and cirrhotic rats. The effects of the non-specific COX inhibitor indomethacin, the specific COX-1 inhibitor SC-560 and the specific COX-2 inhibitor NS-398 were analysed in segments from both groups of rats. NO release was measured, and eNOS [endothelial NOS (NO synthase)], phospho-eNOS, iNOS (inducible NOS), COX-1 and COX-2 protein expression was also analysed. The effects of the TP receptor [TXA2 (thromboxane A(2)) receptor] antagonist SQ 29548, the TXA(2) synthesis inhibitor furegrelate, the PGI(2) (prostaglandin I(2)) synthesis inhibitor TCP (tranylcypromine) or TCP+furegrelate were only determined in segments from cirrhotic rats. The vasodilator response to acetylcholine was higher in segments from cirrhotic rats. Indomethacin, SC-560 and NS-398 did not modify the vasodilator response in control rats; however, indomethacin, NS-398 and TCP+furegrelate increased, whereas SC-560 did not modify and SQ 29548, furegrelate or TCP decreased, the vasodilator response to acetylcholine in cirrhotic rats. NO release was higher in cirrhotic rats. Furegrelate decreased, whereas TCP+furegrelate increased, the NO release in segments from cirrhotic rats. eNOS and COX-1 protein expression was not modified, whereas phosho-eNOS, iNOS and COX-2 protein expression was higher in cirrhotic rats. Therefore the increase in iNOS expression and eNOS activity may mediate increases in endothelial NO release. The COX-2 derivatives TXA(2) and PGI(2) may act simultaneously, producing a compensatory effect that reduces NO release and may limit the hyperdynamic circulation.

Long-term portal hypertension increases the vasodilator response to acetylcholine in rat aorta: role of prostaglandin I2

In the present study, we have analysed both the effect of long-term portal hypertension on the vasomotor response to acetylcholine in rat aorta and the mechanism involved in this response. For this purpose, sham-operated rats and rats with pre-hepatic PH (portal hypertension; triple partial portal vein ligation) were used at 21 months after surgery. The participation of NO and COX (cyclo-oxygenase) derivatives in the vasodilator response elicited by acetylcholine after incubation with L-NAME (NG-nitro-L-arginine methyl ester), indomethacin, SC-560, NS-398, tranylcypromine and furegrelate, was analysed. NO, TXB2 (thromboxane B2) and 6-keto PGF1alpha (prostaglandin F1alpha) release were measured. In addition, SNP (sodium nitroprusside), U-46619, PGI2 and forskolin vasomotor responses were analysed. COX-1 and COX-2 expression was also determined. The acetylcholine-induced vasodilating response was higher in rats with PH. TXA2 and NO release, and SNP and U-46619 sensitivity were similar in both groups. PGI2 release was not modified by portal hypertension, but vasodilator responses to this prostanoid and to forskolin were higher in rats with PH. COX-1 and COX-2 expression remained unmodified by surgery. In conclusion, increased vasodilation to acetylcholine is maintained in long-term PH. Although the participation of endothelial NO remained unmodified, the COX-2 derivative PGI2 does participate through an increased vasodilator response.

Blood as a reactive species generator and redox status regulator during exercise

The exact origin of reactive species and oxidative damage detected in blood is largely unknown. Blood interacts with all organs and tissues and, consequently, with many possible sources of reactive species. In addition, a multitude of oxidizable substrates are already in blood. A muscle-centric approach is frequently adopted to explain reactive species generation, which obscures the possibility that sources of reactive species and oxidative damage other than skeletal muscle may be also at work during exercise. Plasma and blood cells can autonomously produce significant amounts of reactive species at rest and during exercise. The major reactive species generators located in blood during exercise may be erythrocytes (mainly due to their quantity) and leukocytes (mainly due to their drastic activation during exercise). Therefore, it is plausible to assume that oxidative stress/damage measured frequently in blood after exercise or any other experimental intervention derives, at least in part, from the blood.

Chronic administration of ursodeoxycholic acid decreases portal pressure in rats with biliary cirrhosis

Liver cirrhosis is characterized by increased IHR (intrahepatic resistance) and lipid peroxidation, and decreased antioxidative defence. The present study investigates the effects of administration for 1 month of the antioxidant UDCA (ursodeoxycholic acid) in BDL (bile-duct-ligated) cirrhotic rats. Splanchnic haemodynamics, IHR, hepatic levels of TBARS (thiobarbituric acid-reacting substances), GSH (glutathione), SOD (superoxide dismutase) activity, nitrite, PIIINP (N-terminal propeptide of type III procollagen) and collagen deposition, histological examination of liver, mRNA expression of PIIIP-alpha1 (type III procollagen) and TGF-beta1 (transforming growth factor-beta1), protein expression of TXS (thromboxane synthase) and iNOS (inducible NO synthase), and TXA2 (thromboxane A2) production in liver perfusates were measured. The results showed that portal pressure and IHR, hepatic levels of PIIINP, hepatic collagen deposition, mRNA expression of PIIIP-alpha1 and TGF-beta1, protein expression of iNOS and TXS, and production of TXA2 in liver perfusates were significantly decreased in UDCA-treated BDL rats. The increased levels of hepatic GSH and SOD activity and decreased levels of TBARS and nitrite were also observed in UDCA-treated BDL rats. In UDCA-treated BDL rats, the reduction in portal pressure resulted from a decrease in IHR, which mostly acted through the suppression of hepatic TXA2 production and lipid peroxidation, and an increase in antioxidative defence, leading to the prevention of hepatic fibrosis.

Effects of chronic L-NAME on nitrotyrosine expression and renal vascular reactivity in rats with chronic bile-duct ligation

In liver cirrhosis, elevated levels of NO and ROS (reactive oxygen species) might greatly favour the generation of peroxynitrite. Peroxynitrite is a highly reactive oxidant and it can potentially alter the vascular reactivity and the function of different organs. In the present study, we evaluated whether peroxynitrite levels are related to the progression of renal vascular and excretory dysfunction during experimental cirrhosis induced by chronic BDL (bile-duct ligation) in rats. Experiments were performed at 7, 15 and 21 days after BDL in rats and in rats 21 days post-BDL chronically treated with L-NAME (NG-nitro-L-arginine methyl ester). Sodium balance, BP (blood pressure), basal RPP (renal perfusion pressure) and the renal vascular response to PHE (phenylephrine) and ACh (acetylcholine) in isolated perfused kidneys were measured. NO levels were calculated as 24-h urinary excretion of nitrites, ROS as TBARS (thiobarbituric acid-reacting substances), and peroxynitrite formation as the renal expression of nitrotyrosine. BDL rats had progressive sodium retention, and decreased BP, RPP and renal vascular responses to PHE and ACh in the time following BDL. They also had increasing levels of NO and ROS, and renal nitrotyrosine accumulation, especially in the medulla. All of these changes were either prevented or significantly decreased by chronic L-NAME administration. In conclusion, these results suggest that the increasing levels of peroxynitrite might contribute to the altered renal vascular response and sodium retention in the development of the experimental biliary cirrhosis. Moreover, the beneficial effects of decreasing NO synthesis are, at least in part, mediated by anti-peroxinitrite-related effects.

Increased oxidative stress in cirrhotic rat livers: A potential mechanism contributing to reduced nitric oxide bioavailability

In cirrhotic livers, decreased nitric oxide (NO) bioavailability is a major factor increasing intrahepatic vascular tone. In several vascular disorders, an increase in superoxide (O(2) (-)) has been shown to contribute to reduced NO bioavailability through its reaction with NO to form peroxynitrite. This study was aimed to test the hypothesis that, in cirrhotic livers, increased O(2) (-), by reacting with NO, reduces NO bioavailability. In control and cirrhotic rat livers, NO bioavailability was evaluated by the measurement of cyclic guanosine monophosphate in liver tissue and by 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM-DA) fluorescence in isolated sinusoidal endothelial cells (SEC); the O(2) (-) content was determined by dihydroethidium staining in fresh liver sections. In addition, the role of endothelial nitric oxide synthase (eNOS), xanthine oxidase (XO), and cyclooxygenase (COX) as possible sources of O(2) (-) and the role of superoxide dismutase (SOD) enzymatic activity as an O(2) (-) scavenger were determined in liver homogenates. Protein-nitrotyrosination, a marker of the NO-O(2) (-) reaction, was evaluated in liver homogenates. Furthermore, in control SEC and bovine aortic endothelial cells, NO modulation by O(2) (-) was evaluated. Cirrhotic livers exhibited increased O(2) (-) levels. This was due, at least in part, to increased production by COX and XO but not eNOS and to reduced scavenging by SOD. Increased O(2) (-) was associated with a significant reduction in NO bioavailability and increased nitrotyrosinated proteins. In endothelial cells, an inverse relationship between O(2) (-) levels and NO bioavailability was observed.

CONCLUSION

Our data show that oxidative stress may contribute to reduced NO bioavailability in cirrhotic livers, supporting the evaluation of O(2) (-) reduction as a potential mechanism to restore NO content.

Effects of sodium selenite on some biochemical and hematological parameters of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) exposed to Pb2+ and Cu2+

This study was carried out to understand the preventive effect of selenium (Se4+) on heavy metal stress induced by lead and copper in rainbow trout (Oncorhynchus mykiss). Variation in glutathione peroxidase (Se-GSH-Px) and superoxide dismutase (SOD) activity, and in malondialdehyde (MDA) levels in liver, spleen, heart, and brain tissues of rainbow trout after 72 h of exposure to Pb2+ and Cu2+ were investigated in the presence and absence of Se4+. In the presence of Se4+, Se-GSH-Px activity and SOD activity were found to be higher and MDA levels were lower compared with in its absence. Hematological parameters were also determined and it has been observed that total leukocyte count (WBC), mean cell volume (MCV), and mean cell hemoglobin (MCH) were increased and erythrocyte number (RBC), hemoglobin (Hb), and hematocrit value (Hct; P < 0.05) were decreased in fish exposed to heavy metals in the absence of selenium. Selenium presence recovered hematological parameters to normal levels. In the light of our findings, it could be stated that Pb2+ and Cu2+ lead to dramatic changes in biochemical and hematological parameters and selenium caused these parameters to converge to control levels when it was administered concurrently with these heavy metals.

Plasma redox status is impaired in the portacaval shunted rat--the risk of the reduced antioxidant ability

Background

Portacaval shunting in rats produces a reduction of hepatic oxidant scavenging ability. Since this imbalance in hepatic oxidant/antioxidant homeostasis could coexist with systemic changes of oxidant stress/antioxidant status, plasma oxidants and antioxidant redox status in plasma of portacaval shunted-rats were determined.

Results

Male Wistar male: Control (n = 11) and with portacaval shunt (PCS; n = 11) were used. Plasma levels of the oxidant serum advanced oxidation protein products (AOPP), lipid hydroperoxides (LOOH), the antioxidant total thiol (GSH) and total antioxidant status (TAX) were measured. Albumin, ammonia, Aspartate-aminotransferase (AST), Alanine-aminotransferase (ALT), thiostatin and alpha-1-acid glycoprotein (α₁-AGP) were also assayed 4 weeks after the operation. AOPPs were significantly higher (50.51 ± 17.87 vs. 36.25 ± 7.21 μM; p = 0.02) and TAX was significantly lower (0.65 ± 0.03 vs. 0.73 ± 0.06 mM; p = 0.007) in PCS compared to control rats. Also, there was hypoalbuminemia (2.54 ± 0.08 vs. 2.89 ± 0.18 g/dl; p = 0.0001) and hyperammonemia (274.00 ± 92.25 vs. 104.00 ± 48.05 μM; p = 0.0001) and an increase of thiostatin (0.23 ± 0.04 vs. 0.09 ± 0.01 mg/ml; p = 0.001) in rats with a portacaval shunt. The serum concentration of ammonia is correlated with albumin levels (r = 0.624; p = 0.04) and TAX correlates with liver weight (r = 0.729; p = 0.017) and albumin levels (r = 0.79; p = 0.007)

Conclusion

These findings suggest that in rats with a portacaval shunt a systemic reduction of oxidant scavenging ability, correlated with hyperammonemia, is principally produced. It could be hypothesized, therefore, that the reduced antioxidant defences would mediate a systemic inflammation.

Endothelium-dependent relaxation of isolated splanchnic arteries from cirrhotic patients: Role of reactive oxygen species

AIM

To examine the endothelium-dependent relaxation of splanchnic arteries during cirrhosis as well as the role of reactive oxygen species in this relaxation using hepatic arteries from cirrhotic patients undergoing liver transplantation and mesenteric arteries from liver donors.

METHODS

Arterial segments 3 mm long were mounted in organ baths for isometric tension recording and precontracted with the thromboxane A(2) analog U46619 (10(-7)-10(-6) M).

RESULTS

The relaxation to acetylcholine (10(-8)-10(-4) M), but not to sodium nitroprusside (10(-8)-10(-4) M) was lower in hepatic arteries. The inhibitor of nitric oxide synthesis, N(omega)-nitro-l-arginine methyl ester (l-NAME, 10(-4) M), the inhibitor of cyclooxygenase, meclofenamate (10(-5) M), or l-NAME (10(-4) M) + meclofenamate (10(-5) M) diminished the relaxation to acetylcholine only in mesenteric arteries. l-NAME (10(-4) M) + meclofenamate (10(-5) M) combined with charybdotoxin (10(-7) M) + apamine (10(-6) M) inhibited the relaxation toacetylcholine in both types of arteries, and this inhibition was greater than with l-NAME + meclofenamate. The scavenger of hydrogen peroxide, catalase (1000 U/mL), the superoxide dismutase mimetic, tiron (10(-2) M) or the inhibitor of NAD(P)H oxidase, diphenyleneiodonium (5 x 10(-6) M), but not the inhibitor of superoxide dismutase, diethyldithiocarbamate (10(-3) M) potentiated the acetylcholine-induced relaxation only in hepatic arteries. l-NAME did inhibit the relaxation to acetylcholine in hepatic arteries pretreated with catalase or tiron.

CONCLUSIONS

Cirrhosis may decrease endothelial release and/or bioavailability of nitric oxide and prostacyclin in splanchnic arteries, which might be caused partly by increased production of reactive oxygen species.

Vitamin E supplementation reverses renal altered vascular reactivity in chronic bile duct-ligated rats

An altered vascular reactivity is an important manifestation of the hemodynamic and renal dysfunction during liver cirrhosis. Oxidative stress-derived substances and nitric oxide (NO) have been shown to be involved in those alterations. In fact, both can affect vascular contractile function, directly or by influencing intracellular signaling pathways. Nevertheless, it is unknown whether oxidative stress contributes to the impaired systemic and renal vascular reactivity observed in cirrhosis. To test this, we evaluated the effect of vitamin E supplementation (5,000 IU/kg diet) on the vasoconstrictor and vasodilator responses of isolated perfused kidneys and aortic rings of rats with cirrhosis induced by bile duct ligation (BDL), and on the expression of renal and aortic phospho-extracellular regulated kinase 1/2 (p-ERK1/2). BDL induced a blunted renal vascular response to phenylephrine and ACh, while BDL aortic rings responded less to phenylephrine but normally to ACh. Cirrhotic rats had higher levels of oxidative stress-derived substances [measured as thiobarbituric acid-reactive substances (TBARS)] and NO (measured as urinary nitrite excretion) than controls. Vitamin E supplementation normalized the renal hyporesponse to phenylephrine and ACh in BDL, although failed to modify it in aortic rings. Furthermore, vitamin E decreased levels of TBARS, increased levels of NO, and normalized the increased kidney expression of p-ERK1/2 of the BDL rats. In conclusion, BDL rats showed a blunted vascular reactivity to phenylephrine and ACh, more pronounced in the kidney and reversed by vitamin E pretreatment, suggesting a role for oxidative stress in those abnormalities.

Effects of copper and its ethylenediaminetetraacetate complex on the antioxidant defenses of the goldfish, Carassius auratus

Copper bioavailability in the tissues of goldfish and antioxidant defenses in the liver of fish were investigated in vivo following 40 days of exposure to different species of copper solutions at different concentrations. Copper seemed to be more concentrated in the gill than in the liver after Cu(2+) and copper-ethylenediaminetetraacetate (Cu-EDTA) exposure. The addition of EDTA markedly affected copper adsorption in the gill but had no significant effects in the liver. We also found that in the fish exposed to the concentration of Cu(2+) below the Chinese national fishery water quality standard of 0.01 mg/L, superoxide dismutase (SOD) and glutathione S-transferase (GST) activities in liver were stimulated and catalase (CAT) and Se-dependent glutathione peroxidase (Se-GPx) activities were inhibited after 40 days of exposure. Compared to copper exposure, the addition of EDTA did not affect SOD and GST significantly. However, CAT and GPx activity with Cu(2+) exposure were significantly different from those with Cu-EDTA exposure.

Vasoconstrictor hyporeactivity can be reversed by antioxidants in patients with advanced alcoholic cirrhosis of the liver and ascites

OBJECTIVE

Hyperdynamic circulation and systemic vasodilation complicate cirrhosis of the liver and are related to vasoconstrictor hyporeactivity. We investigated whether impaired vasoconstrictor responsiveness may be overcome by antioxidants in patients with decompensated alcoholic cirrhosis.

DESIGN

Controlled clinical study.

SETTING

University setting.

PATIENTS

Nine patients with liver cirrhosis Child-Pugh grade C and nine healthy age-matched volunteers.

INTERVENTIONS

Forearm blood flow responses to intra-arterial norepinephrine, angiotensin II, and the nitric oxide synthase inhibitor N-monomethyl-l-arginine were measured by strain-gauge plethysmography and compared between groups of patients. To assess the role of oxidative stress, the antioxidant vitamin C (24 mg/min) was administered locally into the brachial artery, and forearm blood flow responses were reassessed.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of vitamin C were lower in patients with cirrhosis (p < .05). In patients with cirrhosis, the reactivity to norepinephrine and angiotensin II was markedly reduced (p < .05 vs. controls). Coadministration of vitamin C completely restored the potency of vasoconstrictors to that in controls but had no effect in healthy subjects. No changes were observed in time-control experiments in cirrhosis patients (n = 3) employing vehicle coinfusion. The response to N-monomethyl-L-arginine was comparable between groups and not affected by vitamin C.

CONCLUSIONS

Oxidative stress with consumption of antioxidants seems to play an important role in the development of vasoconstrictor hyporeactivity in patients with cirrhosis. Antioxidant therapy may be a promising clinical approach to restore vasoconstrictor hyporeactivity in these patients.

Oxidative stress in portal hypertension-induced rats with particular emphasis on nitric oxide and trace metals

AIM: To investigate the oxidative-stress-related changes in rats with portal hypertension with particular emphasis on nitric oxide (NO) and trace metals.

METHODS: Cirrhosis was induced by partial portal vein ligation (PVL) in Wistar rats. The lipid peroxidation marker (malondialdehyde, MDA), antioxidant defense enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and agents known to have antioxidant features including nitric oxide (NO), zinc (Zn), copper (Cu) were determined both in serum and in liver tissue at 4 wk after surgery in PVL and sham-operated rats. Portal pressure of all experimental animals was measured. MDA was detected by thiobarbituric acid reactivity assay. SOD activity was determined by inhibition of nitroblue tetrazolium reduction with xanthine/xanthine oxidase used as a superoxide generator. CAT activity was determined by the breakdown of hydrogen peroxide. GSH concentrations were measured by using metaphosphoric acid for protein precipitation and 5’-5’-dithio-bis-2-nitrobenzoic acid for color development. NO was detected by the Griess method after reduction of nitrate to nitrite with nitrate reductase, and the concentrations of Zn and Cu were measured by a Shimadzu 680 AA atomic absorption spectrometer. Histopathological confirmation was done under light microscope. Statistical analyses were done by Student’s t-test, and significance of the difference was tested by the unpaired Mann-Whitney test. P<0.05 was considered statistically significant.

RESULTS: Histopathological studies confirmed PVL-induced cirrhotic changes. There was a statistically significant difference in portal pressure between PVL and control groups (P<0.001). The results showed significant increases in the levels of MDA and NO in both tissue and serum (P<0.05 and P<0.001, respectively in tissue; P<0.001 for each in serum), and Zn only in tissue (P<0.001) in rats with PVL compared with sham-operated rats. Besides, PVL rats exhibited reduced plasma and tissue GSH, CAT, SOD (P<0.001 for each). Serum and tissue Cu concentration did not change.

CONCLUSION: Our findings suggest that PVL in rats induces important biochemical and molecular changes related to oxidative stress in the liver.

Evaluation of the influence of S-adenosylmethionine on systemic and hepatic effects of prednisolone in dogs

OBJECTIVE

To evaluate the influence of a 1,4-butanedisulfonate stable salt of S-adenosylmethionine (SAMe) administered orally on clinicopathologic and hepatic effects induced by long-term administration of prednisolone in dogs.

ANIMALS

12 healthy dogs.

PROCEDURE

Following a pilot study (4 dogs), 2 groups of 4 dogs received prednisolone (2.2 mg/kg) orally once daily (84-day trial). One group received SAMe (20 mg/kg/d divided in 2 doses) for 42 days and then a placebo for 42 days; the other group received treatments in the reverse order. Before and during the trial, numerous variables were monitored, including serum total alkaline phosphatase (ALP) and glucocorticoid-induced ALP (G-ALP) activities, serum haptoglobin concentration, and total and oxidized glutathione (TGSH and GSSG) and thiobarbiturate-reacting substances (TBARS) concentrations in erythrocytes and liver tissue (days 0, 42, and 84). Hepatic specimens also were examined microscopically.

RESULTS

The stable salt of SAMe was biologically available; plasma concentrations of SAMe or prednisolone were not affected by coadministration. Compared with baseline values, serum ALP and G-ALP activities and haptoglobin concentrations increased and erythrocyte GSSG and TBARS concentrations decreased with both treatments. Erythrocyte TGSH concentration decreased with the prednisolone-placebo treatment. Administration of SAMe appeared to conserve erythrocyte TGSH values and did not inhibit hepatocyte glycogen vacuolation but increased hepatic TGSH concentration and improved the hepatic tissue GSSG:TGSH ratio.

CONCLUSIONS AND CLINICAL RELEVANCE

In dogs, administration of 20 mg of SAMe/kg/d may mitigate the apparent pro-oxidant influences of prednisolone but did not block development of classic clinicopathologic or histologic features of vacuolar hepatopathy.

Protective effect of taurine on hypochlorous acid toxicity to nuclear nucleoside triphosphatase in isolated nuclei from rat liver

AIM: Taurine has been shown to be an effective scavenger of hypochlorous acid (HOCl). The role of HOCl is well established in tissue damage associated with inflammation and injury. In the present study, the effect of HOCl on nuclear nucleoside triphosphatase of hepatocytes and the ability of taurine to prevent this effect were investigated.

METHODS: Isolated hepatic nuclei from rat liver were exposed to HOCl with or without taurine. The NTPase activity on nuclear envelope was assayed using ATP and GTP as substrates, respectively.

RESULTS: The first series of experiments evaluated the toxicity of HOCl and the efficacy of taurine to protect NTPase. HOCl at 10^-9-5 × 10^-6 mol/L reduced nuclear NTPase activities in a concentration dependent manner (ATP and GTP as substrates) (P < 0.01). HOCl at 10^-6 mol/L reduced the NTPase activity by 65% (ATP as substrate) and 76% (GTP as substrate). Taurine (10^-7 to 10^-4 mol/L) was tested for protection against HOCl at 10^-6 mol/L and the nuclei treated with 5 × 10^{- 4} mol/L taurine exhibited only 20% and 12% reduction in NTPase activities compared to untreated controls. A second study was performed comparing taurine to glutathione (GSH). GSH and HOCl at 10^-6 mol/L exhibited 46% and 67.4% reduction in NTPase activities compared with control. GSH (10^-4 mol/L) which was incubated with the nuclei and HOCl still exhibited 44.2% and 44.8% reduction in NTPase activities of untreated control. Taurine with HOCl only exhibited 15.2% and 17.1% reduction in NTPase activities, which provided more powerful protection against HOCl than GSH. The third experiment was undertaken to evaluate the specificity of taurine against HOCl. Incubation of rat hepatic nuclei with Fe³⁺/H₂O₂ (1 mmol/L vs 5 µmol/L) resulted in a decrease in nuclear NTPase activities (P < 0.01). When hepatic nuclei were incubated with Tau (10^-4 mol/L) and Fe³⁺/H₂O₂ (1mmol/L vs 5 µmol/L), nuclear NTPase activities were only slightly increased as compared with that of incubation with Fe³⁺/H₂O₂ alone. However, GSH failed to alter the NTPase activities induced by Fe³⁺/H₂O₂.

CONCLUSION: The present findings indicate that HOCl can act as an inhibitor of nuclear NTPase. Taurine can antagonistically reduce the toxicity of HOCl to NTPase.

3,4-dichloroaniline-induced oxidative stress in liver of crucian carp (Carassius auratus)

3,4-dichloroaniline (DCA) and its analogs are widely used as chemical intermediates in the synthesis of herbicides, azo dyes, and pharmaceuticals. They bring danger to growth, development, and propagation of aquatic organisms. The purpose of this study was to show DCA-induced oxidative stress response in liver of crucian carp (Carassius auratus). Superoxide dismutase (SOD), malondialdehyde (MDA), glutathione (GSH), nitric oxide (NO), and NO synthase (NOS) in liver were measured in crucian carp after exposure to DCA solution (0.2, 0.4, and 0.8 mg/L, respectively) for 15 days and compared with the control. DCA significantly induced SOD activity and enhanced MDA concentration in liver of crucian carp. Compared with the control, GSH and NO concentrations decreased and NOS activity was inhibited in crucian carp liver 15 days after DCA treatment. The data suggested that DCA-induced free radical generation and antioxidant depletion, and caused oxidative stress and lipid peroxidation in liver of crucian carp.

Tyrphostins protect neuronal cells from oxidative stress

Tyrphostins are a family of tyrosine kinase inhibitors originally synthesized as potential anticarcinogenic compounds. Because tyrphostins have chemical structures similar to those of the phenolic antioxidants, we decided to test the protective efficacy of tyrphostins against oxidative stress-induced nerve cell death (oxytosis). Many commercially available tyrphostins, at concentrations ranging from 0.5 to 200 microm, protect both HT-22 hippocampal cells and rat primary neurons from oxytosis brought about by treatment with glutamate, as well as by treatment with homocysteic acid and buthionine sulfoximine. The tyrphostins protect nerve cells by three distinct mechanisms. Some tyrphostins, such as A25, act as antioxidants and eliminate the reactive oxygen species that accumulate as a result of glutamate treatment. These tyrphostins also protect cells from hydrogen peroxide and act as antioxidants in an in vitro assay. In contrast, tyrphostins A9 and AG126 act as mitochondrial uncouplers, collapsing the mitochondrial membrane potential and thereby reducing the generation of reactive oxygen species from mitochondria during glutamate toxicity. Finally, the third group of tyrphostins does not appear to be effective as antioxidants but rather protects cells by increasing the basal level of cellular glutathione. Therefore, the effects of tyrphostins on cells are not limited to their ability to inhibit tyrosine kinases.