The role of nitric oxide in hepatic metabolism

Selective gene expression profiling contributes to a better understanding of the molecular pathways underlying the histological changes observed after RHMVL

Background

In previous studies, five vasoactive drugs were investigated for their effect on the recovery process after extended liver resection without observing relevant improvements. We hypothesized that an analysis of gene expression could help to identify potentially druggable pathways and could support the selection of promising drug candidates.

Methods

Liver samples obtained from rats after combined 70% partial hepatectomy and right median hepatic vein ligation (n = 6/group) sacrificed at 0 h, 24 h, 48 h, and 7days were selected for this study. Liver samples were collected from differentially perfused regions of the median lobe (obstruction-zone, border-zone, normal-zone). Gene expression profiling of marker genes regulating hepatic hemodynamics, vascular remodeling, and liver regeneration was performed with microfluidic chips. We used 3 technical replicates from each sample. Raw data were normalized using LEMming and differentially expressed genes were identified using LIMMA.

Results

The strongest differences were found in obstruction-zone at 24 h and 48 h postoperatively compared to all other groups. mRNA expression of marker genes from hepatic hemodynamics pathways (iNOS,Ptgs2,Edn1) was most upregulated.

Conclusion

These upregulated genes suggest a strong vasoconstrictive effect promoting arterial hypoperfusion in the obstruction-zone. Reducing iNOS expression using selective iNOS inhibitors seems to be a promising approach to promote vasodilation and liver regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-022-01364-z.

Engineering Modular 3D Liver Culture Microenvironments In Vitro to Parse the Interplay between Biophysical and Biochemical Microenvironment Cues on Hepatic Phenotypes

In vitro models of human liver functions are used across a diverse range of applications in preclinical drug development and disease modeling, with particular increasing interest in models that capture facets of liver inflammatory status. This study investigates how the interplay between biophysical and biochemical microenvironment cues influence phenotypic responses, including inflammation signatures, of primary human hepatocytes (PHH) cultured in a commercially available perfused bioreactor. A 3D printing-based alginate microwell system was designed to form thousands of hepatic spheroids in a scalable manner as a comparator 3D culture modality to the bioreactor. Soft, synthetic extracellular matrix (ECM) hydrogel scaffolds with biophysical properties mimicking features of liver were engineered to replace polystyrene scaffolds, and the biochemical microenvironment was modulated with a defined set of growth factors and signaling modulators. The supplemented media significantly increased tissue density, albumin secretion, and CYP3A4 activity but also upregulated inflammatory markers. Basal inflammatory markers were lower for cells maintained in ECM hydrogel scaffolds or spheroid formats than polystyrene scaffolds, while hydrogel scaffolds exhibited the most sensitive response to inflammation as assessed by multiplexed cytokine and RNA-seq analyses. Together, these engineered 3D liver microenvironments provide insights for probing human liver functions and inflammatory response in vitro.

Pathophysiological Changes During Ischemia-reperfusion Injury in Rodent Hepatic Steatosis

BACKGROUND/AIM

Ischemia and reperfusion injuries may produce deleterious effects on hepatic tissue after liver surgery and transplantation. The impact of ischemia-reperfusion injury (IRI) on the liver depends on its substrate, the percentage of liver ischemic tissue subjected to IRI and the ischemia time. The consequences of IRI are more evident in pathologic liver substrates, such as steatotic livers. This review is the result of an extended bibliographic PubMed search focused on the last 20 years. It highlights basic differences encountered during IRI in lean and steatotic livers based on studies using rodent experimental models.

CONCLUSION

The main difference in cell death between lean and steatotic livers is the prevalence of apoptosis in the former and necrosis in the latter. There are also major changes in the effect of intracellular mediators, such as TNFα and IL-1β. Further experimental studies are needed in order to increase current knowledge of IRI effects and relevant mechanisms in both lean and steatotic livers, so that new preventive and therapeutic strategies maybe developed.

An Immunohistochemical Study on the Presence of Nitric Oxide Synthase Isoforms (nNOS, iNOS, eNOS) in the Spinal Cord and Nodose Ganglion of Rats Receiving Ionising Gamma Radiation to their Liver

INTRODUCTION

This study determined the presence of nitric oxide synthesis isoforms (nNOS, iNOS, and eNOS) in thoracic spinal cord segments and nodose ganglia of rats with gamma-irradiated livers.

MATERIAL AND METHODS

Male rats (n = 32) were divided into equal groups A, B, C, and D. In group A, the controls, no radiation was applied, while groups B, C, and D received 10 Gy of ionising gamma radiation. The rats of group B were euthanized at the end of the first day (d1), those of group C on the second day (d2), and those of group D on the third day (d3). The liver, spinal cord segments, and nodose ganglion tissues were dissected and fixed, and the liver sections were examined histopathologically. The other tissues were observed through a light microscope.

RESULTS

Regeneration occurred at the end of d3 in hepatocytes which were radiation-damaged at the end of d1 and d2. On d1, some nNOS-positive staining was found in the neuronal cells of laminae I-III of the spinal cord and in neurons of the nodose ganglion, and on d3, some staining was observed in lamina X of the spinal cord, while none of note was in the nodose ganglion. Dense iNOS-positive staining was seen on d1 in the ependymal cells of the spinal cord and in the glial cells of the nodose ganglion, and on d3, there was still considerable iNOS staining in both tissues. There was clear eNOS-positive staining in the capillary endothelial cells of the spinal cord and light diffuse cytoplasmic staining in the neurons of the nodose ganglion on d1, and on d3, intense eNOS-positive staining was visible in several endothelial cells of the spinal cord, while light nuclear staining was recognised in the neurons of the nodose ganglion.

CONCLUSION

The nNOS, iNOS, and eNOS isoforms are activated in the spinal cord and nodose ganglion of rats after ionising radiation insult to the liver.

Hepatic Cytochrome P450 Activity and Nitric Oxide Production During Multiple Ovalbumin Challenges

BACKGROUND AND OBJECTIVES

Mast cell-mediated allergic diseases are a significant global health problem. Nitric oxide (NO) produced by acute type 1 allergies greatly suppresses hepatic cytochrome P450 (CYP) metabolism. A recent in vitro study demonstrated that repeated FcεRI-mediated activation intrinsically modulates mast cell function. We investigated the effect of ovalbumin (OVA) challenges on CYP activity and NO production under real immune responses.

METHODS

After repeated sensitization with OVA once a week, serum nitrate plus nitrite (NOx) and total plasma immunoglobulin E concentrations were measured using commercially available kits. Hepatic microsomal CYP-specific activities and protein expression were determined using typical substrates and by western blot, respectively. In the liver, the levels of inducible NO synthase (iNOS), F4/80, and c-kit mRNA were determined by real-time polymerase chain reaction. Hepatic total NOS activity was measured using a colorimetric assay kit.

RESULTS

When mice received multiple OVA challenges, the 11th sensitization elevated NOx concentrations in serum and suppressed the activities of five major CYPs without altering protein expression levels. After the 7th, 11th, and 15th sensitizations, F4/80-positive Kupffer cell and hepatic c-kit-dependent mast cell mRNA levels were similar to those of the control. The 7th and 11th sensitizations increased hepatic iNOS mRNA expression to 15-fold and threefold above control levels, respectively, but did not enhance the total NOS activity in the liver.

CONCLUSIONS

Multiple OVA challenges, unlike acute sensitization, greatly reduced serum NOx levels. The challenge-suppressed hepatic CYP metabolism was likely related to the increased serum NOx. Serum NOx may be an endogenous marker for CYP metabolism inhibition in type 1 allergic diseases.

Regulation of Mitochondria-Associated Membranes (MAMs) by NO/sGC/PKG Participates in the Control of Hepatic Insulin Response

Under physiological conditions, nitric oxide (NO) produced by the endothelial NO synthase (eNOS) upregulates hepatic insulin sensitivity. Recently, contact sites between the endoplasmic reticulum and mitochondria named mitochondria-associated membranes (MAMs) emerged as a crucial hub for insulin signaling in the liver. As mitochondria are targets of NO, we explored whether NO regulates hepatic insulin sensitivity by targeting MAMs. In Huh7 cells, primary rat hepatocytes and mouse livers, enhancing NO concentration increased MAMs, whereas inhibiting eNOS decreased them. In vitro, those effects were prevented by inhibiting protein kinase G (PKG) and mimicked by activating soluble guanylate cyclase (sGC) and PKG. In agreement with the regulation of MAMs, increasing NO concentration improved insulin signaling, both in vitro and in vivo, while eNOS inhibition disrupted this response. Finally, inhibition of insulin signaling by wortmannin did not affect the impact of NO on MAMs, while experimental MAM disruption, using either targeted silencing of cyclophilin D or the overexpression of the organelle spacer fetal and adult testis-expressed 1 (FATE-1), significantly blunted the effects of NO on both MAMs and insulin response. Therefore, under physiological conditions, NO participates to the regulation of MAM integrity through the sGC/PKG pathway and concomitantly improves hepatic insulin sensitivity. Altogether, our data suggest that the induction of MAMs participate in the impact of NO on hepatocyte insulin response.

Postoperative renal impairment is associated with increased length of stay for incisional hernia repair after liver transplantation

Background

Incisional hernia repair is the most common procedure after orthotopic liver transplantation. Although enhanced recovery protocols are increasingly employed, the post–orthotopic liver transplantation patient may not benefit from all aspects of these models. The aim of the present study is to assess which perioperative interventions and patient factors affect hospital length of stay in a cohort of post–orthotopic liver transplantation patients undergoing incisional hernia repair.

Methods

We conducted a retrospective review of a series of adult patients undergoing incisional hernia repair after orthotopic liver transplantation. The primary endpoint was length of stay. Results were stratified by demographic, intraoperative, and postoperative variables.

Results

Eleven percent (172/1523) of patients who received orthotopic liver transplantation during the study period underwent subsequent incisional hernia repair. Median length of stay was 5 days (range 2–50). The strongest predictor of length of stay was postoperative renal function. Despite liberal intraoperative administration of volume (median 642 mL/h) and brisk intraoperative urine output (median 72 mL/h), postoperative acute kidney injury occurred in 48% of patients. Those that developed acute kidney injury received less intraoperative volume (6 vs 8.5 mL/kg/h; P = .031) and the severity of postoperative renal injury was inversely related to the amount intraoperative volume given.

Conclusions

In patients undergoing incisional hernia repair after orthotopic liver transplantation, postoperative renal function is frequently impaired. Although many aspects of current ERAS protocols may be applied to post-transplant patients, restrictive intraoperative fluid administration strategies should be employed with caution given a high propensity for the development of post-operative acute kidney injury in this complex population.

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Eleven percent (172/1523) of patients who received OLT during the years 2005 to 2016 underwent subsequent IHR.

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The strongest predictor of length of stay in this population was postoperative renal function.

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Despite liberal intraoperative administration of volume (median 642 mL/h; 7 mL/kg/h) and brisk intraoperative urine output (median 72 mL/h), postoperative acute kidney injury (AKI) occurred in 48% of patients.

•

Those that developed AKI received less intraoperative volume (6 vs 8.5 mL/kg/h; P = .031) and the severity of postoperative renal injury was inversely related to intraoperative volume

Paroxysmal Permeability Disorders: Development of a Microfluidic Device to Assess Endothelial Barrier Function

Background: Paroxysmal Permeability Disorders (PPDs) are pathological conditions caused by periodic short lasting increase of endothelial permeability, in the absence of inflammatory, degenerative, ischemic vascular injury. PPDs include primary angioedema, idiopathic systemic capillary leak syndrome and some rare forms of localized retroperitoneal-mediastinal edema.

Aim: to validate a microfluidic device to study endothelial permeability in flow conditions.

Materials and Methods: we designed a microchannel network (the smallest channel is 30μm square section). Human Umbilical Vein Endothelial Cells (HUVECs) were cultured under constant shear stress in the networks. Endothelial permeability assessment was based on interaction of biotinylated fibronectin used as a matrix for HUVECs and FITC-conjugated avidin. The increase in endothelial permeability was identified as changes in fluorescence intensity detected by confocal fluorescent microscopy.

Results: The microchannels were constantly perfused with a steady flow of culture medium, ensuring a physiologically relevant level of shear stress at the wall of ~0.2 Pa. Our preliminary results demonstrated that circulation of culture medium or plasma from healthy volunteers was associated with low fluorescence of fibronectin matrix. When bradykinin diluted in culture medium was perfused, an increase in average fluorescence was detected.

Conclusion: Our microvasculature model is suitable to study endothelial functions in physiological flow conditions and in the presence of factors like bradykinin known as mediator of several PPDs. Therefore, it can be a promising tool to better understand the mechanisms underlying disorders of endothelial permeability.

Evaluation of a Flat Membrane Hepatocyte Bioreactor for Pharmacotoxicological Applications: Evidence that Inhibition of Spontaneously Produced Nitric Oxide Improves Cell Functionality

A laboratory-scale bioreactor was re-evaluated, with the aim of improving its use for the perfused culture of rat hepatocytes. In contrast to conventional culture systems, the flat membrane bioreactor (FMB) showed good functionality and biochemical competence during 2-3 days. Hepatocytes cultured in the FMB, specifically in a "sandwich" configuration, were functionally stable, as shown by a high rate of urea biosynthesis after challenge with NH4Cl, a low alanine-aminotransferase leakage and suppressed spontaneous nitric oxide (NO) production. Moreover, the time-course of the disappearance of cyclosporin A (CsA) from the perfusate demonstrated the high biotransformation capacity of cells in the FMB. The effect of CsA on the modulation of urea and spontaneous NO production demonstrated flexibility, in that minor changes could be observed at diverse time intervals and in a non-destructive way. The monitoring of nitrite levels during various steps of isolation and culture suggested that spontaneously produced NO has a negative impact on hepatocyte metabolic and functional integrity. In spite of the sophisticated techniques that are being used for the preparation of bioreactors, with hepatocytes surviving for longer periods, our data have shed light on some factors that could be important for the successful use of similar models for pharmacotoxicological and other biomedical applications.

Protective effect of Spirulina platensis against cell damage and apoptosis in hepatic tissue caused by high fat diet

Spirulina platensis is a microalga that may be a source of antioxidants that can reduce body fat deposition. Consumption of a high fat diet produces elevated blood lipid levels, inflammation and apoptosis. We investigated the possible effects of S. platensis on the blood lipid profile, and liver inflammation and apoptosis in rats fed a high fat diet. Sixty-four young male rats were divided into eight equal groups. The control group was fed a basic diet. The experimental groups were fed a diet for 60 days that was prepared by mixing variable amounts of 43% vegetable oil and 10% cholesterol with or without 3% S. platensis mixed with the basal diet. Blood and liver tissue samples were collected from each animal. Serum samples were used to analyze lipid parameters, total antioxidant status and total oxidant status. iNOS and eNOS were determined by immunohistochemistry. TUNEL staining was used to detect apoptosis to investigate a possible connection between inflammation and apoptosis in the liver tissue. The relations between fat deposition and liver degeneration were assessed by Sirius red staining and alpha-smooth muscle actin immunostaining. S. platensis reduced serum HDL-C, LDL-C and triglyceride, increased HDL-C levels in rats fed a high fat diet to near control levels, and reduced iNOS levels and increased eNOS levels in the liver tissue compared to vegetable oil and cholesterol treated groups. The apoptotic index was reduced in the groups that were fed a high fat or a basic diet when supplemented with S. platensis.

Adenovirus-mediated eNOS expression augments liver injury after ischemia/reperfusion in mice

Hepatic ischemia/reperfusion (l/R) injury continues to be a critical problem. The role of nitric oxide in liver I/R injury is still controversial. This study examines the effect of endothelial nitric oxide synthase (eNOS) over-expression on hepatic function following I/R. Adenovirus expressing human eNOS (Ad-eNOS) was administered by tail vein injection into C57BL/6 mice. Control mice received either adenovirus expressing LacZ or vehicle only. Sixty minutes of total hepatic ischemia was performed 3 days after adenovirus treatment, and mice were sacrificed after 6 or 24 hrs of reperfusion to assess hepatic injury. eNOS over expression caused increased liver injury as evidenced by elevated AST and ALT levels and decreased hepatic ATP content. While necrosis was not pervasive in any group, TUNEL demonstrated significantly increased apoptosis in Ad-eNOS infected livers. Western blotting demonstrated increased levels of protein nitration and upregulation of the pro-apoptotic proteins bax and p53. Our data suggest that over-expression of eNOS is detrimental in the setting of hepatic I/R.

A novel upregulation of glutathione peroxidase 1 by knockout of liver-regenerating protein Reg3β aggravates acetaminophen-induced hepatic protein nitration

Murine regenerating islet-derived 3β (Reg3β) represents a homologue of human hepatocarcinoma-intestine-pancreas/pancreatic-associated protein and enhances mouse susceptibility to acetaminophen (APAP)-induced hepatotoxicity. Our objective was to determine if and how knockout of Reg3β (KO) affects APAP (300 mg/kg, ip)-mediated protein nitration in mouse liver. APAP injection produced greater levels of hepatic protein nitration in the KO than in the wild-type mice. Their elevated protein nitration was alleviated by a prior injection of recombinant mouse Reg3β protein and was associated with an accelerated depletion of the peroxynitrite (ONOO(-)) scavenger glutathione by an upregulated hepatic glutathione peroxidase-1 (GPX1) activity. The enhanced GPX1 production in the KO mice was mediated by an 85% rise (p<0.05) in the activity of selenocysteine lyase (Scly), a key enzyme that mobilizes Se for selenoprotein biosynthesis. Knockout of Reg3β enhanced AP-1 protein and its binding activity to the Scly gene promoter, upregulating its gene transcription. However, knockout of Reg3β did not affect gene expression of other key factors for selenoprotein biosynthesis. In conclusion, our findings unveil a new metabolic role for Reg3β in protein nitration and a new biosynthesis control of GPX1 by a completely "unrelated" regenerating protein, Reg3β, via transcriptional activation of Scly in coping with hepatic protein nitration. Linking selenoproteins to tissue regeneration will have profound implications in understanding the mechanism of Se functions and physiological coordination of tissue regeneration with intracellular redox control.

Cross-activating invariant NKT cells and kupffer cells suppress cholestatic liver injury in a mouse model of biliary obstruction

Both Kupffer cells and invariant natural killer T (iNKT) cells suppress neutrophil-dependent liver injury in a mouse model of biliary obstruction. We hypothesize that these roles are interdependent and require iNKT cell-Kupffer cell cross-activation. Female, wild-type and iNKT cell-deficient C57Bl/6 mice were injected with magnetic beads 3 days prior to bile duct ligation (BDL) in order to facilitate subsequent Kupffer cell isolation. On day three post-BDL, the animals were euthanized and the livers dissected. Necrosis was scored; Kupffer cells were isolated and cell surface marker expression (flow cytometry), mRNA expression (qtPCR), nitric oxide (NO^.) production (Griess reaction), and protein secretion (cytometric bead-array or ELISAs) were determined. To address the potential role of NO^. in suppressing neutrophil accumulation, a group of WT mice received 1400W, a specific inducible nitric oxide synthase (iNOS) inhibitor, prior to BDL. To clarify the mechanisms underlying Kupffer cell-iNKT cell cross-activation, WT animals were administered anti-IFN-γ or anti-lymphocyte function-associated antigen (LFA)-1 antibody prior to BDL. Compared to their WT counterparts, Kupffer cells obtained from BDL iNKT cell-deficient mice expressed lower iNOS mRNA levels, produced less NO^., and secreted more neutrophil chemoattractants. Both iNOS inhibition and IFN-γ neutralization increased neutrophil accumulation in the livers of BDL WT mice. Anti-LFA-1 pre-treatment reduced iNKT cell accumulation in these same animals. These data indicate that the LFA-1-dependent cross-activation of iNKT cells and Kupffer cells inhibits neutrophil accumulation and cholestatic liver injury.

Protective effect of sildenafil on liver injury induced by intestinal ischemia/reperfusion

BACKGROUND

This study evaluated the protective effect of sildenafil on liver injury induced by intestinal ischemia-reperfusion.

METHODS

Forty female Sprague Dawley rats were divided into 4 groups: sham-control (SC), ischemia (I), ischemia-reperfusion (IR), and ischemia-reperfusion+sildenafil (SIL; sildenafil gavaged at 50mg/kg before operating). A 2-h ischemia-reperfusion was performed by clamping the superior mesenteric artery. Liver function, plasma alanine (ALT) and aspartate (AST) aminotransferase, and intestinal and liver malondialdehyde (MDA) were measured at the end of the experiment. Intestinal and liver tissue damage was examined by histology. Liver samples were immunologically stained for endothelial nitric oxide synthase (eNOS) and proliferating cell nuclear antigen (PCNA).

RESULTS

The ALT and AST levels were highest in the IR group and were lower in the SIL group (p<0.05). Intestinal MDA levels were statistically higher in the IR group than in the SC, I and SIL groups. Liver MDA levels were significantly higher in the IR group than in the I and SC groups (p<0.05) and higher than in the SIL group (p>0.05). Intestinal damage based on Chiu scoring was more severe in the IR than in the SIL group (p<0.05). Sildenafil reduced damage and also increased eNOS and PCNA immunoreactivity in liver tissue.

CONCLUSIONS

Sildenafil shows a protective effect on intestinal ischemia-reperfusion-induced liver injury, possibly by decreasing vascular resistance through increased nitric oxide levels.

Biochanin A protects against acute carbon tetrachloride-induced hepatotoxicity in rats

Biochanin A (BCA) is an isoflavone found in red clover possessing multiple pharmacological activities including antimicrobial, antioxidant, and anticancer ones. The present study aimed to assess its hepatoprotective potential at different doses in a carbon tetrachloride (CCl4)-induced hepatotoxicity model in rats. The effects on hepatic injury were explored by measuring serum levels of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. Furthermore, the serum levels of glucose, urea, creatinine, total bilirubin, total proteins, triglycerides, and total cholesterol were determined. The metabolic capacity of the liver was assessed by measuring changes in cytochrome P450 2E1 activity. The underlying mechanisms were substantiated by measuring oxidative stress markers as catalase, superoxide dismutase, glutathione peroxidase, glutathione transferase, glutathione reductase, reduced glutathione, total antioxidant capacity, and lipid peroxidation, as well as inflammation markers such as nitric oxide, inducible nitric oxide synthase, cyclooxygenase2, tumor necrosis factor-α, and leukocyte-common antigen. The results were confirmed by histopathological examination, and the median lethal dose was determined to confirm the safety of the drug. BCA successively protected against CCl4-induced damage, normalizing many parameters to that of the control group. The study indicates that BCA possesses multimechanistic hepatoprotective activity that can be attributed to its antioxidant, anti-inflammatory, and immunomodulatory actions.

Ferric citrate CYP2E1-independently promotes alcohol-induced apoptosis in HepG2 cells via oxidative/nitrative stress which is attenuated by pretreatment with baicalin

In the case of alcoholic liver injury, an iron overload is always present. Both alcohol and iron can individually induce oxidative stress in liver. However, the combined effect of physiological concentrations of alcohol and iron on oxidative stress in hepatocytes remains unknown. Baicalin has been demonstrated to be an antioxidant or iron chelator in animal experiments. In this study, we investigated the injury to hepatocytes CYP2E1-independently induced by the combination of alcohol and iron and the protective effect of baicalin. Compared with cells treated with ethanol alone, ferric citrate enhanced the accumulation of reactive oxygen and nitrogen species, increased the occurrence of protein carbonylation/nitration and the levels of 4-hydroxy-2-nonenal, changed the distribution of iNOS, and eventually resulted in apoptosis. However, pretreatment with baicalin inhibited the oxidative stress induced by the combination of alcohol and iron, mainly by chelating iron. Our findings therefore suggest that iron could CPY2E1-independently enhance the oxidative stress induced by alcohol, which probably contributes to the pathogenesis of alcoholic liver disease. Baicalin is a promising phytomedicine for preventing alcoholic liver disease.

Nitric oxide mimics transcriptional and post-translational regulation during α-tocopherol cytoprotection against glycochenodeoxycholate-induced cell death in hepatocytes

BACKGROUND & AIMS

Reactive oxygen species (ROS) and nitric oxide (NO) exert a relevant role during bile acid-induced hepatotoxicity. Whether α-Tocopherol regulates oxidative and nitrosative stress, bile acid transporter expression and their NO-dependent post-translational modifications, and cell death were assessed in vitro and in vivo.

METHODS

α-Tocopherol and/or NO donors (DETA-NONOate or CSNO, and V-PYRRO/NO) were administered to glycochenodeoxycholic acid (GCDCA)-treated cultured human hepatocytes or to bile duct obstructed rats. Cell injury, superoxide anion (O⁻₂) production, as well as inducible nitric oxide synthase (NOS-2), cytochrome P4507A1 (CYP7A1), heme oxygenase-1, (HO-1) and bile acid transporter expression were determined. Cysteine S-nitrosylation and tyrosine nitration of Na(+)-taurocholate co-transporting polypeptide (NTCP), as well as taurocholic acid (TC) uptake were also evaluated.

RESULTS

GCDCA-induced cell death was associated with increased (O⁻₂) production, NTCP and HO-1 expression, and with a reduction of CYP7A1 and NOS-2 expression. α-Tocopherol reduced cell death, (O⁻₂) production, CYP7A1, NTCP, and HO-1 expression, as well as increased NOS-2 expression and NO production in GCDCA-treated hepatocytes. α-Tocopherol and NO donors increased NTCP cysteine S-nitrosylation and tyrosine nitration, and reduced TC uptake in hepatocytes. α-Tocopherol and V-PYRRO/NO reduced liver injury and NTCP expression in obstructed rats.

CONCLUSIONS

The regulation of CYP7A1, NTCP, and HO-1 expression may be relevant for the cytoprotective properties of α-Tocopherol and NO against mitochondrial dysfunction, oxidative stress and cell death in GCDCA-treated hepatocytes. The regulation of NO-dependent post-translational modifications of NTCP by α-Tocopherol and NO donors reduces the uptake of toxic bile acids by hepatocytes.

Obstructive jaundice activates nitroxidergic neurons of the vago-vagal neural circuit that regulates the hepatobiliary system in rabbits

In this study, we investigated the expression of neuronal nitric oxide synthase (nNOS) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), two specific enzymes for nitric oxide (NO) synthesis, in the development of liver fibrosis induced by chronic bile duct ligation (BDL) in the rabbit. We specifically studied the liver-innervated nitroxidergic neurons that originate in the nodose ganglion (NG), nucleus of the solitary tract (NTS) and dorsal motor vagal nucleus (DMV). Our data showed that BDL resulted in overexpression of NADPH-d/nNOS in the NG, NTS and DMV neurons. Using densitometric analysis, we found a significant increase in NADPH-d expression as a result of BDL in the NG, NTS and DMV (72.6, 79.4 and 57.4% increase, respectively). These findings were corroborated by serum biochemistry and hepatic histopathological examination, which were influenced by NADPH-d/nNOS-generated NO in the liver following BDL. Upregulation of NADPH-d/nNOS expression may have important implications, including (1) facilitation of extrahepatic biliary parasympathetic tone that promotes gallbladder emptying of excess stagnant bile; (2) relaxation of smooth muscles of bile canaliculi thus participating in the pathogenesis of cholestasis; (3) dilation of hepatic sinusoids to counter BDL-induced intrahepatic portal hypertension in which endothelia may be damaged, and (4) alterations in hepatic metabolism, such as glycogenesis, bile formation and secretion, and bilirubin clearance.

Pathophysiological roles of peroxynitrite in circulatory shock

Peroxynitrite is a reactive oxidant produced from nitric oxide and superoxide, which reacts with proteins, lipids, and DNA, and promotes cytotoxic and proinflammatory responses. Here, we overview the role of peroxynitrite in various forms of circulatory shock. Immunohistochemical and biochemical evidences demonstrate the production of peroxynitrite in various experimental models of endotoxic and hemorrhagic shock both in rodents and in large animals. In addition, biological markers of peroxynitrite have been identified in human tissues after circulatory shock. Peroxynitrite can initiate toxic oxidative reactions in vitro and in vivo. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na+/K+ ATPase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of peroxynitrite. In addition, peroxynitrite is a potent trigger of DNA strand breakage, with subsequent activation of the nuclear enzyme poly(ADP-ribose) polymerase, which promotes cellular energetic collapse and cellular necrosis. Additional actions of peroxynitrite that contribute to the pathogenesis of shock include inactivation of catecholamines and catecholamine receptors (leading to vascular failure) and endothelial and epithelial injury (leading to endothelial and epithelial hyperpermeability and barrier dysfunction), as well as myocyte injury (contributing to loss of cardiac contractile function). Neutralization of peroxynitrite with potent peroxynitrite decomposition catalysts provides cytoprotective and beneficial effects in rodent and large-animal models of circulatory shock.

A soluble guanylate cyclase-dependent mechanism is involved in the regulation of net hepatic glucose uptake by nitric oxide in vivo

OBJECTIVE

We previously showed that elevating hepatic nitric oxide (NO) levels reduced net hepatic glucose uptake (NHGU) in the presence of portal glucose delivery, hyperglycemia, and hyperinsulinemia. The aim of the present study was to determine the role of a downstream signal, soluble guanylate cyclase (sGC), in the regulation of NHGU by NO.

RESEARCH DESIGN AND METHODS

Studies were performed on 42-h-fasted conscious dogs fitted with vascular catheters. At 0 min, somatostatin was given peripherally along with 4× basal insulin and basal glucagon intraportally. Glucose was delivered at a variable rate via a leg vein to double the blood glucose level and hepatic glucose load throughout the study. From 90 to 270 min, an intraportal infusion of the sGC inhibitor 1H-[1,2,4] oxadiazolo[4,3-a] quinoxalin-1-one (ODQ) was given in -sGC (n = 10) and -sGC/+NO (n = 6), whereas saline was given in saline infusion (SAL) (n = 10). The -sGC/+NO group also received intraportal SIN-1 (NO donor) to elevate hepatic NO from 180 to 270 min.

RESULTS

In the presence of 4× basal insulin, basal glucagon, and hyperglycemia (2× basal ), inhibition of sGC in the liver enhanced NHGU (mg/kg/min; 210-270 min) by ∼55% (2.9 ± 0.2 in SAL vs. 4.6 ± 0.5 in -sGC). Further elevating hepatic NO failed to reduce NHGU (4.5 ± 0.7 in -sGC/+NO). Net hepatic carbon retention (i.e., glycogen synthesis; mg glucose equivalents/kg/min) increased to 3.8 ± 0.2 in -sGC and 3.8 ± 0.4 in -sGC/+NO vs. 2.4 ± 0.2 in SAL (P < 0.05).

CONCLUSIONS

NO regulates liver glucose uptake through a sGC-dependent pathway. The latter could be a target for pharmacologic intervention to increase meal-associated hepatic glucose uptake in individuals with type 2 diabetes.

Mitochondrial-driven ubiquinone enhances extracellular calcium-dependent nitric oxide production and reduces glycochenodeoxycholic acid-induced cell death in hepatocytes

Ca(2+) mobilization, nitric oxide (NO), and oxidative stress have been involved in cell death induced by hydrophobic bile acid in hepatocytes. The aim of the study was the elucidation of the effect of the antioxidant mitochondrial-driven ubiquinone (Mito Q) on the intracellular Ca(2+) concentration, NO production, and cell death in glycochenodeoxycholic acid (GCDCA)-treated HepG2 cells. The role of the regulation of the intracellular Ca(2+) concentration by Ca(2+) chelators (EGTA or BAPTA-AM), agonist of Ca(2+) entrance (A23187) or NO (L-NAME or NO donor), was assessed during Mito Q cytoprotection in GCDCA-treated HepG2 cells. Cell death, NO synthase (NOS)-1, -2, and -3 expression, Ca(2+) mobilization, and NO production were evaluated. GCDCA reduced the intracellular Ca(2+) concentration and NOS-3 expression and enhanced cell death in HepG2. NO donor prevented and L-NAME enhanced GCDCA-induced cell death. The reduction of Ca(2+) entry by EGTA, but not its release from intracellular stores by BAPTA-AM, reduced the expression of NOS-3 and enhanced cell death in control and GCDCA-treated cells. Mito Q prevented the reduction of intracellular Ca(2+) concentration, NOS-3 expression, NO production, and cell death in GCDCA-treated HepG2 cells. The conclusion is that the recovery of Ca(2+)-dependent NOS-3 expression by Mito Q may be considered an additional cytoprotective property of an antioxidant.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Reaction of Mycobacterium tuberculosis cytochrome P450 enzymes with nitric oxide

During the initial growth infection stage of Mycobacterium tuberculosis (Mtb), (*)NO produced by host macrophages inhibits heme-containing terminal cytochrome oxidases, inactivates iron/sulfur proteins, and promotes entry into latency. Here we evaluate the potential of (*)NO as an inhibitor of Mtb cytochrome P450 enzymes, as represented by CYP130, CYP51, and the two previously uncharacterized enzymes CYP125 and CYP142. Using UV-visible absorption, resonance Raman, and stopped-flow spectroscopy, we investigated the reactions of (*)NO with these heme proteins in their ferric resting form. (*)NO coordinates tightly to CYP125 and CYP142 (submicromolar) and with a lower affinity (micromolar) to CYP130 and CYP51. Anaerobic reduction of the ferric-NO species with sodium dithionite led to the formation of two spectrally distinct classes of five-coordinate ferrous-NO complexes. Exposure of these species to O(2) revealed that the ferrous-NO forms of CYP125 and CYP142 are labile and convert back to the ferric state within a few minutes, whereas ferrous CYP130 and CYP51 bind (*)NO almost irreversibly. This work clearly indicates that, at physiological concentrations (approximately 1 microM), (*)NO would impair the activity of CYP130 and CYP51, whereas CYP125 and CYP142 are more resistant. Selective P450 inhibition may contribute to the inhibitory effects of (*)NO on Mtb growth.

Kupffer cell products and interleukin 1beta directly promote VLDL secretion and apoB mRNA up-regulation in rodent hepatocytes

Plasma VLDL accumulation in Gram-negative sepsis is partly ascribed to an increased hepatic VLDL production driven by pro-inflammatory cytokines. We previously showed that hepatocytes of the Kupffer cell (KC)-rich periportal area are major contributors to enhanced VLDL production in lipopolysaccharide (LPS)-injected rats. However, it remains to be established whether KC generated products directly affect the number (apoB) and composition of secreted VLDL. Using rat primary cells, we show here that hepatocytes respond to stimulation by soluble mediators released by LPS-stimulated Kupffer cells with enhanced secretion of apoB and triglycerides in phospholipid-rich VLDL particles. Unstimulated KC products also augmented the secretion of normal VLDL, doubling apoB mRNA abundance. IL-1beta treatment resulted in concentration-dependent increases of hepatocyte apoB mRNA and protein secretion, increases that were greater, but not additive, when combined with IL-6 and TNF-alpha. Lipid secretion and MTP mRNA levels were unaffected by cytokines. In summary: (i) enhanced secretion of phospholipid-rich VLDL particles is a net hepatocyte response to LPS-stimulated KC products, which gives a clue about the local role of Kupffer cells in septic dyslipidemia induction; and (ii) pro-inflammatory cytokines act redundantly to enhance apoB secretion involving translational apoB up-regulation, but other humoral components or KC mediators are necessary to accomplish increased lipid association.

Role of N-acetylcysteine on fibrosis and oxidative stress in cirrhotic rats

BACKGROUND: Hepatic cirrhosis is the final stage of liver dysfunction, characterized by diffuse fibrosis which is the main response to the liver injury. The inhalatory carbon tetrachloride is an effective experimental model that triggers cirrhosis and allows to obtain histological and physiological modifications similar to the one seen in humans. AIM: To investigate the effects of N-acetylcysteine (NAC) on the fibrosis and oxidative stress in the liver of cirrhotic rats, analyzing liver function tests, lipoperoxidation, activity of glutathione peroxidase enzyme, collagen quantification, histopathology, as well as the nitric oxide role. METHODS: The animals were randomly in three experimentals groups: control (CO); cirrhotic (CCl4) and CCl4 + NAC. Evaluate the lipid peroxidation, the glutathione peroxidase enzyme, the collagen and the expression of inducible nitric oxide synthase (iNOS). RESULTS: The cirrhotic group treated with N-acetylcysteine showed trough the histological analysis and collagen quantification lower degrees of fibrosis. This group has also shown less damage to the cellular membranes, less decrease on the glutathione peroxidase levels and less expression of inducible nitric oxide synthase when matched with the cirrhotic group without treatment. CONCLUSION: N-acetylcysteine seams to offer protection against hepatic fibrosis and oxidative stress in cirrhotic rat livers.

Inhibition of nitric oxide release pre-slaughter increases post-mortem glycolysis and improves tenderness in ovine muscles

The aim of this experiment was to determine the effect of inhibiting the release of nitric oxide (NO) pre-slaughter in lambs on post-slaughter muscle metabolism and meat quality. Exercise was used as a positive control as NO is known to be released in skeletal muscle during exercise. Forty Border Leicester×Merino lambs were assigned to the treatments L-NAME (NO synthase inhibitor) infusion (0mg/kg vs. 30mg/kg, 135min pre-slaughter) and exercise (none vs. 15min immediately pre-slaughter). The inhibition of NO release using L-NAME reduced Warner-Bratzler shear force (WBSF) in the longissimus thoracis et lumborum (LTL) after 3days of ageing, while the Semimembranosous (SM) was unaffected. Inhibition of NO release with L-NAME resulted in altered glucose metabolism as indicated by reduced plasma glucose pre-slaughter particularly in exercised lambs, reduced LTL and SM glycogen of non-exercised lambs post-slaughter and increased SM lactate in exercised lambs post-slaughter. In conclusion, inhibition of NO Synthase with L-NAME pre-slaughter increases post-mortem glycolysis and improves tenderness in the loin muscle.

Effects of the nitric oxide donor SIN-1 on net hepatic glucose uptake in the conscious dog

To determine the role of nitric oxide in regulating net hepatic glucose uptake (NHGU) in vivo, studies were performed on three groups of 42-h-fasted conscious dogs using a nitric oxide donor [3-morpholinosydnonimine (SIN-1)]. The experimental period was divided into period 1 (0-90 min) and period 2 (P2; 90-240 min). At 0 min, somatostatin was infused peripherally, and insulin (4-fold basal) and glucagon (basal) were given intraportally. Glucose was delivered intraportally (22.2 mumol.kg(-1).min(-1)) and peripherally (as needed) to increase the hepatic glucose load twofold basal. At 90 min, an infusion of SIN-1 (4 mug.kg(-1).min(-1)) was started in a peripheral vein (PeSin-1, n = 10) or the portal vein (PoSin-1, n = 12) while the control group received saline (SAL, n = 8). Both peripheral and portal infusion of SIN-1, unlike saline, significantly reduced systolic and diastolic blood pressure. Heart rate rose in PeSin-1 and PoSin-1 (96 +/- 5 to 120 +/- 10 and 88 +/- 6 to 107 +/- 5 beats/min, respectively, P < 0.05) but did not change in response to saline. NHGU during P2 was 31.0 +/- 2.4 and 29.9 +/- 2.0 mumol.kg(-1).min(-1) in SAL and PeSin-1, respectively but was 23.7 +/- 1.7 in PoSin-1 (P < 0.05). Net hepatic carbon retention during P2 was significantly lower in PoSin-1 than SAL or PeSin-1 (21.4 +/- 1.2 vs. 27.1 +/- 1.5 and 26.1 +/- 1.0 mumol.kg(-1).min(-1)). Nonhepatic glucose uptake did not change in response to saline or SIN-1 infusion. In conclusion, portal but not peripheral infusion of the nitric oxide donor SIN-1 inhibited NHGU.

Simultaneous determination of L-arginine and 12 molecules participating in its metabolic cycle by gradient RP-HPLC method: application to human urine samples

We have developed and described a highly sensitive, accurate and precise reversed-phase high-performance liquid chromatography (RP-HPLC) method for the simultaneous determination of L-arginine and 12 molecules participating in its metabolic cycle in human urine samples. After pre-column derivatization with ortho-phthaldialdehyde (OPA) reagent containing 3-mercaptopropionic acid (3MPA), the fluorescent derivatives were separated by a gradient elution and detected by fluorescence measurement at 338 nm (excitation) and 455 nm (emission). L-Arginine (ARG) and its metabolites: L-glutamine (GLN), N(G)-hydroxy-L-arginine (NOHA), L-citrulline (CIT), N(G)-monomethyl-L-arginine (NMMA), L-homoarginine (HARG), asymmetric N(G),N(G)-dimethyl-L-arginine (ADMA), symmetric N(G),N(G')-dimethyl-L-arginine (SDMA), L-ornithine (ORN), putrescine (PUT), agmatine (AGM), spermidine (SPERMD) and spermine (SPERM) were extracted in a cation-exchange solid-phase extraction (SPE) column and after derivatization separated in a Purospher STAR RP-18e analytical column. The calibration curves of analysed compounds are linear within the range of concentration: 45-825, 0.2-15, 16-225, 12-285, 0.1-32, 15-235, 0.1-12, 0.1-12, 10-205, 0.02-12, 0.1-24, 0.01-10 and 0.01-8 nmol mL(-1) for GLN, NOHA, CIT, ARG, NMMA, HARG, ADMA, SDMA, ORN, PUT, AGM, SPERMD and SPERM, respectively. The correlation coefficients are greater than 0.9980. Coefficients of variation are not higher than 6.0% for inter-day precision. The method has been determined or tested for limits of detection and quantification, linearity, precision, accuracy and recovery. All detection parameters of the method demonstrate that it is a reliable and efficient means of the comprehensive determination of ARG and its 12 main metabolites, making this approach suitable for routine clinical applications. The levels of analysed compounds in human urine can be successfully determined using this developed method with no matrix effect.

Interaction of L-Arginine-methyl ester and Sonic hedgehog in liver ischemia-reperfusion injury in the rats

AIM: To investigate the role of Sonic hedgehog (Shh) on the course of liver ischemia and reperfusion (I/R) in rats, and the interaction between treatment with nitric oxide donor L-Arginine-methyl ester (L-Arg) and up-regulation of Shh expression.

METHODS: A total of 30 male Sprague-Dawley rats weighing 220-240 g were used in this study. Sham-control group (G1, n = 10): a sham operation was performed (except for liver I/R). I/R-untreated group (G2, n = 10): rats underwent liver ischemia for 1 h followed by reperfusion for 45 min. I/R-L-Arg group (G3, n = 10): after performing the same surgical procedure as in group 2, animals were treated with L-Arg. Liver tissues were taken for determination of malondialdehyde (MDA) levels, and biochemical and histological evaluations were made.

RESULTS: Plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and γ-glutamyltranspeptidase (GGT) activities were higher in group 2 than in group 3. MDA values and the hepatic injury score decreased in the L-Arg treated group compared to the I/R-untreated group. In group 2, the hepatocytes were swollen with marked vacuolization. Group 3 rats showed well-preserved liver parenchyma, with hepatocytes extending from the central vein. The morphology of the hepatocytes and the sinusoidal structures was normal, without any signs of congestion. Mild Shh positive immunostaining was detected in group 2 animals. The expression of immunoreactive cells was increased markedly in liver tissue from I/R-L-Arg rats.

CONCLUSION: Our findings suggest that Shh molecules are critical factors in the pathophysiology of inflammatory liver injury induced by I/R. In addition, NO plays an important role in the immunohistochemical expression of these molecules.

Dietary supplementation with laminarin, a fermentable marine beta (1-3) glucan, protects against hepatotoxicity induced by LPS in rat by modulating immune response in the hepatic tissue

We tested the hypothesis that laminarin (LAM), a beta (1-3) polysaccharide extracted from brown algae, can modulate the response to a systemic inflammation. Male Wistar rats (n=7 per group) were fed a standard diet (control) or a diet supplemented with LAM for 25 days (5% during 4 days followed by 10% during 21 days). Thereafter, Escherichia coli lipopolysaccharides (LPS; 10 mg/kg i.p.) were injected and the animals were sacrificed 24 h after LPS challenge. The hypothermia, hyperglycemia and hypertriglyceridemia occurring early after LPS administration were less pronounced in LAM-treated rats than in controls. The increase in serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) activities - reflecting hepatic alterations - was lessened after LPS injection in LAM-treated rats compared to control rats. LAM treatment decreased serum monocytes number, nitrite (NO2) and tumor necrosis factor-alpha (TNF-alpha). LAM also modulated intra-hepatic immune cells: it lowered the occurrence of peroxidase-positive cells (corresponding to monocytes/neutrophils) and, in contrast, it increased the number of ED2-positive cells, corresponding to resident hepatic macrophages, i.e. Kupffer cells. In conclusion, the hepatoprotective effect of marine beta (1-3) glucan during endotoxic shock may be linked to its immunomodulatory properties. We propose that both lower recruitment of inflammatory cells inside the liver tissue and lower secretion of inflammatory mediators play a role in the tissue protective effect of LAM. These effects could be due to a direct effect of beta-glucan on immune cells, or to an indirect effect through their dietary fibre properties (fermentation in the gut).

Hepatic morphological alterations, glycogen content and cytochrome P450 activities in rats treated chronically with N(omega)-nitro-L-arginine methyl ester (L-NAME)

Chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension mediated partly by enhanced angiotensin-I-converting enzyme (ACE) activity. We examined the influence of L-NAME on rat liver morphology, on hepatic glycogen, cholesterol, and triglyceride content, and on the activities of the cytochrome P450 isoforms CYP1A1/2, CYP2B1/2, CYP2C11, and CYP2E1. Male Wistar rats were treated with L-NAME (20 mg/rat per day via drinking water) for 2, 4, and 8 weeks, and their livers were then removed for analysis. Enzymatic induction was produced by treating rats with phenobarbital (to induce CYP2B1/2), beta-naphthoflavone (to induce CYP1A1/2), or pyrazole (to induce CYP2E1). L-NAME significantly elevated blood pressure; this was reversed by concomitant treatment with enalapril (ACE inhibitor) or losartan (angiotensin II AT(1) receptor antagonist). L-NAME caused vascular hypertrophy in hepatic arteries, with perivascular and interstitial fibrosis involving collagen deposition. Hepatic glycogen content also significantly increased. L-NAME did not affect fasting glucose levels but significantly reduced insulin levels and increased the insulin sensitivity of rats, based on an intraperitoneal glucose tolerance test. Immunoblotting experiments indicated enhanced phosphorylation of protein kinase B and of glycogen synthase kinase 3. All these changes were reversed by concomitant treatment with enalapril or losartan. L-NAME had no effect on hepatic cholesterol or triglyceride content or on the basal or drug-induced activities and protein expression of the cytochrome P450 isoforms. Thus, the chronic inhibition of NO biosynthesis produced hepatic morphological alterations and changes in glycogen metabolism mediated by the renin-angiotensin system. The increase in hepatic glycogen content probably resulted from enhanced glycogen synthase activity following the inhibition of glycogen synthase kinase 3 by phosphorylation.

Hydrogen sulfide potentiates interleukin-1beta-induced nitric oxide production via enhancement of extracellular signal-regulated kinase activation in rat vascular smooth muscle cells

Hydrogen sulfide (H(2)S) and nitric oxide (NO) are endogenously synthesized from l-cysteine and l-arginine, respectively. They might constitute a cooperative network to regulate their effects. In this study, we investigated whether H(2)S could affect NO production in rat vascular smooth muscle cells (VSMCs) stimulated with interleukin-1beta (IL-1beta). Although H(2)S by itself showed no effect on NO production, it augmented IL-beta-induced NO production and this effect was associated with increased expression of inducible NO synthase (iNOS) and activation of nuclear factor (NF)-kappaB. IL-1Beta activated the extracellular signal-regulated kinase 1/2 (ERK1/2), and this activation was also enhanced by H(2)S. Inhibition of ERK1/2 activation by the selective inhibitor U0126 inhibited IL-1beta-induced NF-kappaB activation, iNOS expression, and NO production either in the absence or presence of H(2)S. Our findings suggest that H(2)S enhances NO production and iNOS expression by potentiating IL-1beta-induced NF-kappaB activation through a mechanism involving ERK1/2 signaling cascade in rat VSMCs.

Inhibition of endothelin-1-mediated up-regulation of iNOS by bosentan ameliorates endotoxin-induced liver injury in cirrhosis

Endothelin-1 (ET-1) has been shown to regulate the expression of various genes in addition to its vasoconstrictor role in the liver. Elevated levels of ET-1 during cirrhosis play an important role in the observed microcirculatory dysfunction; however, its role as a transcription regulator remains unclear. This study aimed to determine the role of ET-1 in the hepatic gene expression of vasomediators after cirrhosis in response to LPS. Cirrhosis was induced by bile duct ligation (BDL) for 1 or 3 weeks in male Sprague-Dawley rats. Following 1 or 3 weeks of BDL or sham operation (sham), rats received an intravenous (i.v.) injection of bosentan, a dual-selective ETA/B receptor antagonist (30 mg/kg bw) or saline, and an intraperitoneal (i.p.) injection of LPS (1 mg/kg bw). Plasma alanine aminotransferase (ALT) levels were significantly elevated in 1- and 3-week BDL animals. Six hours following LPS, the elevated ALT levels were markedly exacerbated in 3-week BDL animals, which were significantly ameliorated with bosentan treatment. LPS resulted in increased ET-1, inducible nitric oxide synthase (iNOS), and cyclooxygenase (COX)-2 mRNA expressions in both sham and BDL rats. Bosentan significantly inhibited the up-regulations of ET-1, iNOS, and COX-2 mRNA. Our data strongly suggest that ET-1 plays an important role in up-regulating the expression of iNOS, COX-2, and ET-1 itself in hepatic tissue following LPS challenge, which may contribute to the observed hepatocellular injury during endotoxemia in cirrhosis. Thus, due to significant increases in ET-1 levels during cirrhosis, ET-1 receptor blockade may prove to be of great therapeutic value in the treatment of cirrhotic patients exposed to secondary injuries such as endotoxemia.

Impaired Progression of Cerebral Aneurysms in Interleukin-1β–Deficient Mice

BACKGROUND AND PURPOSE

Subarachnoid hemorrhage caused by cerebral aneurysm rupture remains a life-threatening emergency despite advances in treatment. However, the mechanisms underlying aneurysm initiation, progression, and rupture remain unclear. We developed a method to induce experimental cerebral aneurysms in rats, monkeys, and mice. Interleukin-1beta (IL-1beta) is a key inflammatory mediator, and it is thought to be a promising target for the treatment of inflammatory diseases. In the present study, we examined the role of IL-1beta in cerebral aneurysm development.

METHODS

Cerebral aneurysms were experimentally induced in 5-week-old male C57BL/6 mice, IL-1beta gene-deficient (IL-1beta-/-) mice, and age-matched control B10 mice (wild-type). Their cerebral arteries were dissected and examined histologically and immunohistochemically.

RESULTS

IL-1beta was expressed in vascular media in mice at an early stage of aneurysmal models' cerebral arteries. No differences were seen in the rate of aneurysm development between IL-1beta-/- and wild-type mice, but the percentage of advanced aneurysm change was significantly larger in wild-type animals. Furthermore, in IL-1beta-/- mice, increased caspase-1 expression was seen compared with wild-type animals. Additionally, the number of apoptotic cells assessed by single-stranded DNA immunoreactivity and TUNEL was significantly reduced in IL-1beta-/- mice compared with wild-type animals.

CONCLUSIONS

IL-1beta is important for the progression of cerebral aneurysms in a mouse model. Disruption of the IL-1beta gene results in the reduced incidence of mature experimental cerebral aneurysms.

Heme oxygenase 1 expression in postischemic reperfusion liver damage: effect of L-Arginine

Ischemia/reperfusion (I/R) injury is a multifactorial process that affects liver function after transplantation and resectional surgery. Alterations in hepatic microcirculation and decreased hepatic flow can cause local hypoxia and consequently liver damage, which is worsened by reperfusion. The aim of this study was to evaluate if treatment with L-arginine improved hepatic function in rats with I/R injury. Animals were treated with L-arginine, ischemized for 30 min, and reperfused for 3 h. Plasmatic levels of GOT, GPT, lipid hydroperoxides (LOOH), and total thiol groups (RSH) were evaluated. In addition, we analyzed hepatic LOOH and RSH levels, DNA fragmentation, heme oxygenase 1 (HO-1) expression, and histological modifications. Our results demonstrate a significant improvement in hepatic function of I/R rats compared to the control group. Treatment with L-arginine increased the expression of HO-1. These data suggest that L-arginine could be useful in preventing oxidative damage during hepatic surgery.

Dual effects of 8-Br-cAMP on differentiation and apoptosis of human esophageal cancer cell line Eca-109

AIM: To investigate the effects of 8-Br-cAMP on differentiation and apoptosis of human esophageal cancer cell line Eca-109, and the related gene expression.

METHODS: The cultured Eca-109 cells were divided into four groups: E1 group (co-cultured with 8-Br-cAMP for 24 h); E2 group (co-cultured with 8-Br-cAMP for 48 h); C1 group (treated without 8-Br-cAMP for 24 h); and C2 group (treated without 8-Br-cAMP for 48 h). The same concentration of cell suspension of each group was dropped separately onto the slides and nitrocellulose membranes (NCM). The biotin-labeled cDNA probes for c-myc, wild-type (wt) p53, bcl-2 and iNOS were prepared for in situ hybridization. The expressions of epidermal growth factor receptor (EGFR), p38 kinase, FAS, FasL and caspase-3 were detected using immunocytochemistry, and the NOS activity and the ratio of differentiated cells/proliferating cells were examined by cytochemistry. Immunocytochemistry, cytochemistry, and in situ hybridization were separately carried out on both slides and NCM specimens for each group. In addition, TUNEL was used to detect the cell apoptosis rate in each group.

RESULTS: The apoptotic rate of E2 group was significantly higher compared to E1 group, while there was no difference in the ratio of differentiated cells/proliferating cells between E1 and E2 groups. The signals of wt p53 and iNOS were markedly stronger, while the signals of c-myc and EGFR were obviously weaker in E1 group than those in C1 group (P<0.05). Moreover, the signals of wt p53, iNOS, p38 kinase, caspase-3 and NOS activity were significantly stronger, whereas, the signals of bcl-2, c-myc and Fas/FasL were markedly weaker in E2 group than those in C2 group (P<0.05).

CONCLUSION: The differentiation and apoptosis of human esophageal cancer cell Eca-109 can be induced after 24- and 48-h treatment with 8-Br-cAMP, respectively. Upregulation of wt p53, iNOS and downregulation of c-myc may be associated with differentiation and apoptosis of Eca-109 cells. Furthermore, upregulation of FasL, p38 kinase and caspase-3 as well as downregulation of bcl-2, and Fas may be involved in the apoptosis of Eca-109 cells.

Protective effect of resveratrol against oxidative stress in cholestasis

BACKGROUND

We investigated the protective role of resveratrol in rat liver injuries induced by chronic biliary obstruction.

MATERIALS AND METHODS

Secondary biliary cirrhosis was induced by bile duct ligation for 28 days. Swiss albino rats were divided into the three following groups: group 1: sham (n = 7); group 2: bile duct ligation (n = 7); group 3: bile duct ligation plus resveratrol (n = 7). Bile duct ligation plus resveratrol group received 10 mg/kg dose of resveratrol intraperitoneally daily for 28 days. Liver damage and cholestasis were determined by the biochemical and the pathologic examination.

RESULTS

The present data showed a decrease in both plasma bilirubin levels and aspartate aminotransferase and alanine aminotransferase levels in the resveratrol-treated rats, when compared with bile duct ligation group (P < 0.05). In the resveratrol-treated rats, tissue levels of malondialdehyde and nitric oxide were significantly lower than that of the bile duct ligation (P < 0.002). The levels of glutathione in resveratrol-treated rats were significantly higher than that in bile duct ligation group (P < 0.004). The levels of interleukin-1alpha, interleukin-6, and tumor necrosis factor-alpha in resveratrol group were significantly lower than that in bile duct ligation group (P < 0.004, P < 0.001, P < 0.001, respectively). Administration of resveratrol in the rats with biliary obstruction resulted in inhibition of ductular proliferation and lymphocytic inflammation.

CONCLUSION

The present study demonstrates that intraperitoneal administration of resveratrol in bile duct ligated rats maintained antioxidant defenses and reduces liver oxidative damage and ductular proliferation. This effect of resveratrol may be useful in the preservation of liver function in cholestasis.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Nonspecific phosphodiesterase inhibition attenuates liver injury in acute endotoxemia

BACKGROUND

Endotoxemia is accompanied by pro-inflammatory cytokine production, generation of reactive oxygen species, and end-organ injury. Pentoxifylline (PTX), a methylxanthine derivative and phosphodiesterase inhibitor, is known for its anti-inflammatory properties, including down-regulation of interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha synthesis. Its effects on liver function and hepatic histology following acute endotoxemia have not been investigated fully. We hypothesized that PTX would preserve liver architecture and function after intravenous lipopolysaccharide (LPS) injection.

METHODS

Anesthetized Sprague-Dawley rats received an i.v. bolus injection of LPS (5 mg/kg), LPS + PTX (25 mg/kg), or saline (sham). Plasma concentrations of alanine aminotransferase (ALT), aspartate aminotransferase (AST), TNF-alpha, IL-6, and nitrite were measured at different time points after LPS injection. Liver injury was graded according to a scoring system in a blinded fashion from 0 (normal) to 4 (severe) for hepatocellular necrosis, hemorrhage, and parenchymal and sinusoidal inflammatory infiltrates. Neutrophil infiltration was measured by counting myeloperoxidase (MPO)-positive stained cells. Nuclear factor (NF)-kappaB p-65 was measured by counting positive stained nuclei of hepatocytes and Kupffer cells (KC). Inducible nitric oxide synthase (iNOS) was evaluated by positively stained KC. Data are presented as mean +/- SEM. Analysis of variance with p < 0.05 was considered statistically significant.

RESULTS

Animals treated with PTX showed a significant reduction in liver injury score and neutrophil infiltration. Treatment with PTX significantly decreased TNF-alpha, IL-6, and the concentrations of AST and ALT when compared to LPS alone. In addition, a significant decrease in NF-kappaB-positive staining in hepatocytes and KC, as well as in KC iNOS immunostaining was observed in PTX-treated animals compared to the LPS group.

CONCLUSIONS

Pentoxifylline downregulates the inflammatory response significantly and decreases liver injury in acute endotoxemia.

Does dietary ornithine α-ketoglutarate supplementation protect the liver against ischemia–reperfusion injury?

Nutritional supplementation with glutamine, arginine and their precursors has been proposed to contribute to the protection against ischemia-reperfusion-related injuries. The aim of this study was to evaluate in an isolated perfused rat liver model the preventive effect of a 4-day oral ornithine alpha-ketoglutarate (OKG) supplementation against warm ischemia-reperfusion (I-R) injury, and the involvement of nitric oxide synthesis. Rats were fed a controlled regimen supplemented with either OKG (5 g kg(-1); n=15) or an isonitrogenous mixture of non-essential amino acids (Control; n=6) for 4 days. Livers were subsequently prepared for isolated perfusion experiments, including a 45 min no-flow ischemic period. The OKG-treated group was divided into two groups according to the absence (OKG; n=8) or presence of a NO-synthase inhibitor, L-N(omega)-nitro-arginine methyl ester (OKG L-NAME; n=7) during liver perfusion. Liver cytolysis after ischemia was demonstrated by an elevated alanine aminotransferase release during the last 15 min of reperfusion that was significantly higher in the OKG-L-NAME group. Tumor necrosis factor alpha (TNF(alpha)) production was transiently increased only in the control group just after ischemia. At the end of the reperfusion period, liver superoxide dismutase activity was significantly lower in the OKG-L-NAME group compared to control animals. Dietary OKG administration had only a limited effect in this model of mild hepatic I-R, leading mainly to reduced TNF(alpha) production. As the content of lipid peroxidation products was not modified, it seems that OKG acts on the inflammatory response rather than on oxidative reactions. This action can tentatively be attributed to the role of OKG as a glutamine precursor rather than to the synthesis of arginine and nitric oxide.

Effects of renal diseases on the regulation and expression of renal and hepatic drug-metabolizing enzymes: a review

1. The activity of drug-metabolizing enzymes (DMEs) in extrahepatic organs is highest in the kidneys. Generally, the kidneys contain most, if not all, of the DMEs found in the liver. Surprisingly, some of these DMEs show higher activity in the kidneys than in the liver. 2. Most of the renal DMEs are localized in the cortex of the kidneys, especially in the proximal tubules. DMEs are also found in the distal tubules and collecting ducts. 3. Renal diseases such as acute and chronic renal failure and renal cell carcinoma alter the regulation of both hepatic and extrahepatic phase I and II DMEs. Changes in the expression of these DMEs seem to be tissue and species specific. 4. Generally, there is significant down-regulation of most of the phase I and a few of phase II DMEs at the protein, mRNA and activity levels. Unfortunately, the mechanisms leading to the alteration in DMEs in renal diseases remain unclear, although many theories have been made. 5. The presence of some circulating factors such as cytokines, nitric oxide, parathyroid hormones and increased intracellular calcium play a role in the regulation of DMEs in renal diseases.

Effect of bradykinin on nitric oxide production, urea synthesis and viability of rat hepatocyte cultures

BACKGROUND

It is well known that cytotoxic factors, such as lipopolysaccharides, derange nitrogen metabolism in hepatocytes and nitric oxide (NO) is involved among the other factors regulating this metabolic pathway. Hepatocytes have been shown to express large levels of NO following exposure to endotoxins, such as bacterial lipopolysaccharide and/or cytokines, such as tumour necrosis factor-alpha (TNFalpha), interleukin-1. The control role of arginine in both urea and NO biosynthesis is well known, when NO is synthesized from arginine, by the NOS reaction, citrulline is produced. Thus, the urea cycle is bypassed by the NOS reaction. Many authors demonstrated in other cellular types, like cardiomyocytes, that bradykinin caused the increase in reactive oxygen species (ROS) generation. The simultaneous increase of NO and ROS levels could cause peroxynitrite synthesis, inducing damage and reducing cell viability. The aim of this research is to study the effect of bradykinin, a proinflammatory mediator, on cell viability and on urea production in cultures of rat hepatocytes.

RESULTS

Hepatocytes were treated with bradykinin, that stimulates nitric oxide synthase (NOS). NO release was determined using 4,5 diaminofluorescein diacetate (DAF-2DA), as fluorescent indicator of NO. Addition of the NOS inhibitor, Ng-nitro-L-arginine methyl ester (L-NAME), to the culture medium inhibited the increase of NO production. Exposure of hepatocytes to bradykinin 0,1 mM for 2 hours resulted in a significant decrease of urea synthesis. Cell viability, instead, showed a significant decrease 24 hours after the end of bradykinin treatment as determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5diphenyl-2H-tetrazolium (MTT) assay. L-NAME addition recovered urea production and cell viability at control values.

CONCLUSION

The findings suggest that the cell toxicity, after bradykinin treatment, effectively depends upon exposure to increased NO levels and the effects are prevented by L-NAME. The results show also that the increased NO synthesis induces a reduced urea production, that is another index of cell damage.

Direct evidence that induced nitric oxide production in hepatocytes prevents liver damage during lipopolysaccharide tolerance in rats

BACKGROUND

The role of nitric oxide (NO) in lipopolysaccharide (LPS) tolerance in the liver has been investigated in a number of previous studies, but it is still not clear whether NO is cytotoxic or cytoprotective. The aims of this study were to investigate whether low-dose LPS (LLPS)-induced hepatic production of NO is beneficial and to clarify the origins of cytoprotective NO-producing cells in the liver during LPS tolerance.

MATERIALS AND METHODS

Male Wistar rats received saline or LLPS intraperitoneally (i.p.; 0.01-1000 microg/kg) followed by a high dose of LPS (HLPS, 5 mg/kg) at various time intervals (4-16 h). NG-nitro-L-arginine methyl ester (L-NAME) was used to investigate the effects of inhibition of NOS. 4,5-Diaminofluorescein (DAF-2) was used to identify NO-producing cells in isolated liver cells in vitro. At various time points (4-16 h) after saline or LLPS (1 microg/kg, i.p.) injection, hepatocytes and Kupffer cells were isolated, incubated in 7 microm DAF-2 diacetate, and perfused with Krebs solution. Illumination at 495 nm revealed DAF-fluorescence (515 nm) in isolated cells under confocal laser fluorescence microscopy. The NO production in hepatocytes and Kupffer cells was assessed by the number of labeled cells per 1000 cells or per 100 cells, respectively.

RESULTS

Pretreatment with LLPS (0.1-100 microg/kg) resulted in a significant reduction (maximal at 8 h) of the HLPS-induced liver damage. L-NAME abolished the LLPS-induced protection. The NO production in hepatocytes was significantly increased and reached a maximum of 84% of all cells 8 h after LLPS administration. By contrast, the NO production in Kupffer cells remained constant at 95%, even following preinjection of LLPS.

CONCLUSION

LLPS-induced NO in hepatocytes, but not in Kupffer cells, exhibits cytoprotective effects on HLPS-induced liver damage, suggesting that NO has a beneficial role in the induction of the early phase of LPS tolerance.

As bases experimentais da lesão por isquemia e reperfusão do fígado: revisão

O transplante hepático tornou-se o procedimento de escolha para o tratamento da doença hepática terminal. Não obstante o sucesso da cirurgia, a disfunção pós-operatória do fígado enxertado ainda representa importante causa de morbidade e mortalidade. O restabelecimento do fluxo sangüíneo ao fígado recém transplantado impõe a ele nova agressão, agravando a lesão causada pelo período de isquemia. Este fenômeno pouco compreendido é conhecido como lesão por isquemia e reperfusão e envolve disfunção endotelial, seqüestro de leucócitos e agregação de plaquetas, lesão por radicais livre de oxigênio, e distúrbios da microcirculação hepática. Essa revisão discute os vários aspectos fisiopatológicos que estão envolvidos na lesão por isquemia e reperfusão do fígado.

The role of nitric oxide in systemic and hepatic haemodynamics in the rat in vivo

The physiological role of nitric oxide (NO) in portal venous and hepatic arterial haemodynamics in the rat in vivo during healthy and diseased conditions remains unclear. The present study determined the physiological role of nitric oxide in hepatic haemodynamics in the rat in vivo during healthy conditions as a basis for future pharmacological work. Male Wistar rats (300-350 g) were anaesthetised with fentany/fluanisone (0.3 mg/kg s.c.) and midazolam (0.3 mg/kg s.c.) and heparinised (30 U/100 g i.v.) via a cannulated left carotid artery for measurement of heart rate, mean arterial pressure, and the difference between systolic and diastolic blood pressures (P(S-D)). Following laparotomy, two distal ileocolic veins were cannulated, one catheter introduced to a distance of 1 cm and used for intraportal drug injections and the other to the main trunk of the portal vein for continuous measurement of portal venous pressure. The portal venous trunk and hepatic artery were carefully isolated and electromagnetic probes placed around each of them for measurement of portal venous flow and hepatic arterial flow. Augmentation of NO production was achieved by intraportal injection of 0.2, 0.4, 0.6 and 0.8 g/kg L-arginine and the NO donor, 3-morpholinosydnonimine (SIN-1), was injected intraportally at 0.2, 0.4, 0.6 and 0.8 mg/kg. L-NAME, the non-selective NOS inhibitor, was injected intraportally in increasing doses of 5, 10, 15 and 20 mg/kg in the absence or presence of L-arginine in doses of 0.2 and 0.5 g/kg. L-arginine increased portal blood flow by 25% without significant changes in systemic haemodynamics. SIN-1 decreased mean arterial pressure by 33% with no effect on portal blood flow. Both L-arginine and SIN-1 reduced portal venous pressure by 25% in a dose-dependent manner. L-NAME had no effect on portal haemodynamics despite a significant increase in systemic arterial pressure of 60% that was reduced dose-dependently by L-arginine. Hepatic arterial flow increased by 88% and 49% at the second and third doses of L-arginine and by 68% and 27% at the first two doses of L-NAME. No significant changes in hepatic arterial flow were found when L-NAME and L-arginine were given together. It is concluded that augmented endogenous NO production increased portal flow. Inhibition of endogenous NO had no effect on portal haemodynamics. Endogenous NO may not play a major role in regulation of portal haemodynamics in the rat in vivo.