Inhibition of inducible nitric oxide synthase activity prevents liver recovery in rat thioacetamide-induced fibrosis reversal

Cellular stress in the pathogenesis of nonalcoholic steatohepatitis and liver fibrosis

The burden of chronic liver disease is rising substantially worldwide. Fibrosis, characterized by excessive deposition of extracellular matrix proteins, is the common pathway leading to cirrhosis, and limited treatment options are available. There is increasing evidence suggesting the role of cellular stress responses contributing to fibrogenesis. This Review provides an overview of studies that analyse the role of cellular stress in different cell types involved in fibrogenesis, including hepatocytes, hepatic stellate cells, liver sinusoidal endothelial cells and macrophages.

Rotavirus Reassortant-Induced Murine Model of Liver Fibrosis Parallels Human Biliary Atresia

BACKGROUND AND AIMS

Biliary atresia (BA) is a devastating neonatal cholangiopathy that progresses to fibrosis and end-stage liver disease by 2 years of age. Portoenterostomy may reestablish biliary drainage, but, despite drainage, virtually all afflicted patients develop fibrosis and progress to end-stage liver disease requiring liver transplantation for survival.

APPROACH AND RESULTS

In the murine model of BA, rhesus rotavirus (RRV) infection of newborn pups results in a cholangiopathy paralleling human BA and has been used to study mechanistic aspects of the disease. Unfortunately, nearly all RRV-infected pups succumb by day of life 14. Thus, in this study we generated an RRV-TUCH rotavirus reassortant (designated as T^R(VP2,VP4) ) that when injected into newborn mice causes an obstructive jaundice phenotype with lower mortality rates. Of the mice that survived, 63% developed Ishak stage 3-5 fibrosis with histopathological signs of inflammation/fibrosis and bile duct obstruction.

CONCLUSIONS

This model of rotavirus-induced neonatal fibrosis will provide an opportunity to study disease pathogenesis and has potential to be used in preclinical studies with an objective to identify therapeutic targets that may alter the course of BA.

The effects of concurrent treatment of silymarin and lactulose on memory changes in cirrhotic male rats

Introduction: Chronic liver disease frequently accompanied by hepatic encephalopathy (HE). Changes in the permeability of the blood-brain barrier in HE, make an easier entrance of ammonia among other substances to the brain, which leads to neurotransmitter disturbances. Lactulose (LAC), causes better defecation and makes ammonia outreach of blood. Silymarin (SM) is a known standard drug for liver illnesses. The purpose of this research was to determine the results of LAC and SM combined treatment, on the changes in memory of cirrhotic male rats. Methods: The cirrhotic model established by treatment with thioacetamide (TAA) for 18 weeks. Cirrhotic rats randomized to four groups (n = 7): TAA group (received drinking water), LAC group (2 g/kg/d LAC in drinking water), SM group (50 mg/kg/d SM by food), SM+ LAC group (similar combined doses of both compounds) for 8 weeks. The control group received drinking water. The behavior examined by wire hanging (WH), passive avoidance (PA), and open field (OF) tests.

Results: Our findings showed that treatment with SM+LAC effectively increased PA latency, compared with the control group. The results showed that the administration of LAC and SM+LAC affected the number of lines crossed, the total distance moved and velocity in the OF tests.

Conclusion: SM and LAC have anti-inflammatory effects that are memory changing. It may be due to their useful effects. These results indicated that SM+LAC restored memory disturbance and irritated mood in the cirrhotic rats. Comparable neuroprotection was never previously informed. Such outcomes are extremely promising and indicate the further study of SM+LAC.

AdipoRs- a potential therapeutic target for fibrotic disorders

Introduction: Fibrotic disorders are a leading cause of morbidity and mortality; hence effective treatments are still vigorously sought. AdipoRs (AdipoR1 and Adipo2) are responsible for the antifibrotic effects of adiponectin (APN). APN exerts antifibrotic effects by binding to its receptors. APN concentration and AdipoR expression are closely associated with fibrotic disorders. Decreased AdipoR expression may reduce APN-AdipoR signaling, while the upregulation of AdipoR expression may restore the anti-fibrotic effects of APN. Loss of APN signaling exacerbates fibrosis in vivo and in vitro. Areas covered: We assess the relationship between APN and fibrotic disorders, the structure of receptors for APN and the pathways accounting for APN or its analogs blocking fibrotic disorders. This article also discusses designed APN products and their therapeutic prospects for fibrotic disorders. Expert opinion: AdipoRs have a critical role in blocking fibrosis. The development of small-molecule agonists toward this target represents a valid drug development pathway.

Antifibrotic effects of gallic acid on hepatic stellate cells: In vitro and in vivo mechanistic study

Few studies reported the antifibrotic effects of gallic acid (GA) despite its known hepatoprotective and antioxidant activities. Accordingly, this study investigated the antifibrotic effects of GA through clarifying its mechanisms on hepatic stellate cells' (HSCs) activation, proliferation and/or apoptosis. In vitro effects of GA on HSC-T6 activation/proliferation, morphology and safety on hepatocytes were assessed. In vivo, hepatic fibrosis was induced via chronic thioacetamide (TAA)-intoxication. TAA-intoxicated rats were treated with silyamrin or GA. At end of experiment, liver functions, hepatic MDA, GSH, PDGF-BB, TGF-β1, TIMP-1 and hydroxyproline were determined. Histological analysis and Sirius red staining of hepatic sections, expressions of alpha-smooth muscle actin (α-SMA), proliferating cellular nuclear antigen (PCNA) and caspase-3 were examined. In vitro, GA resulted in a concentration and time-dependent inhibition in HSCs activation, proliferation (IC₅₀= 45 and 19 μg/mL at 24 and 48 h respectively); restored the quiescent morphology of some activated HSCs plus its safety on hepatocytes. In vivo, GA reduced ALT, AST, MDA, PDGF-BB levels, collagen deposition and fibrosis score (S1 vs S4); increased caspase-3 expression and restored GSH stores, TGF-β1 level, α-SMA and PCNA expressions. In conclusion, GA counteracted the progression of hepatic fibrosis through reduction of HSCs proliferation/activation mutually with their apoptosis induction.

Role and regulation of autophagy and apoptosis by nitric oxide in hepatic stellate cells during acute liver failure

BACKGROUND & AIMS

We previously found that hepatic stellate cell activation induced by autophagy maintains the liver architecture to prevent collapse during acute liver failure. Nitric oxide has shown to induce hepatic stellate cell apoptosis. Whether and how nitric oxide is involved in acute liver failure and autophagy remains unclear.

METHODS

Acute liver failure patients were recruited to investigate the correlation between plasma nitric oxide levels and clinical features. Liver tissues were collected from chronic hepatitis patients by biopsy and from acute liver failure patients who had undergone liver transplantation. The expression of nitric oxide synthases and hepatic stellate cell activation (alpha-SMA), and autophagic activity (LC3) were investigated by immunohistochemistry. Autophagy and apoptosis were investigated by immunoblot analysis, confocal microscopy, and flow cytometry in hepatic stellate cells treated with nitric oxide donors.

RESULTS

Plasma nitric oxide level was significantly increased in patients with acute liver failure compared to those with cirrhosis (53.60±19.74 μM vs 19.40±9.03 μM, Z=-7.384, P<.001) and positively correlated with MELD-Na score (r=.539, P<.001), implicating nitric oxide in acute liver failure. At least some Nitric oxide was produced by overexpression of inducible nitric oxide synthases and endothelial nitric oxide synthases, but not neuronal nitric oxide synthases in the liver tissue. In vivo observation revealed that autophagy was inhibited in hepatic stellate cells based on decreased LC3 immunostaining, and in vitro experiments demonstrated that Nitric oxide can inhibit autophagy. Moreover, nitric oxide promoted hepatic stellate cell apoptosis, which was rescued by an autophagy inducer.

CONCLUSIONS

Increased nitric oxide synthases/ nitric oxide promotes apoptosis through autophagy inhibition in hepatic stellate cells during acute liver failure, providing a novel strategy for the treatment of patients with acute liver failure.

Rosmarinic acid attenuates hepatic fibrogenesis via suppression of hepatic stellate cell activation/proliferation and induction of apoptosis

OBJECTIVE

To investigate the antifibrotic role of rosmarinic acid (RA), a natural polyphenolic compound, on HSCs activation/proliferation and apoptosis in vitro and in vivo.

METHODS

The impact of RA on stellate cell line (HSC-T6) proliferation, activation and apoptosis was assessed along with its safety on primary hepatocytes. In vivo, rats were divided into: (i) normal; (ii) thioacetamide (TAA)-intoxicated rats for 12 weeks; (iii) TAA + silymarin or (iv) TAA + RA. At the end of experiment, liver functions, oxidative stress, inflammatory and profibrogenic markers, tissue inhibitor metalloproteinases type-1 (TIMP-1) and hydroxyproline (HP) levels were evaluated. Additionally, liver histopathology and immunohistochemical examinations of alpha-smooth muscle actin (α-SMA), caspase-3 and proliferation cellular nuclear antigen (PCNA) were determined.

RESULTS

RA exhibited anti-proliferative effects on cultured HSCs in a time and concentration dependent manner showing an IC₅₀ of 276 μg/mL and 171 μg/mL for 24 h and 48 h, respectively, with morphological reversion of activated stellate cell morphology to quiescent form. It significantly improved ALT, AST, oxidative stress markers and reduced TIMP-1, HP levels, inflammatory markers and fibrosis score (S1 vs S4). Furthermore, reduction in α-SMA plus elevation in caspase-3 expressions of HSCs in vitro and in vivo associated with an inhibition in proliferation of damaged hepatocytes were recorded.

CONCLUSIONS

RA impeded the progression of liver fibrosis through inhibition of HSCs activation/proliferation and induction of apoptosis with preservation of hepatic architecture.

Hybrid inhibitor of peripheral cannabinoid-1 receptors and inducible nitric oxide synthase mitigates liver fibrosis

Liver fibrosis, a consequence of chronic liver injury and a way station to cirrhosis and hepatocellular carcinoma, lacks effective treatment. Endocannabinoids acting via cannabinoid-1 receptors (CB₁R) induce profibrotic gene expression and promote pathologies that predispose to liver fibrosis. CB₁R antagonists produce opposite effects, but their therapeutic development was halted due to neuropsychiatric side effects. Inducible nitric oxide synthase (iNOS) also promotes liver fibrosis and its underlying pathologies, but iNOS inhibitors tested to date showed limited therapeutic efficacy in inflammatory diseases. Here, we introduce a peripherally restricted, orally bioavailable CB₁R antagonist, which accumulates in liver to release an iNOS inhibitory leaving group. In mouse models of fibrosis induced by CCl₄ or bile duct ligation, the hybrid CB₁R/iNOS antagonist surpassed the antifibrotic efficacy of the CB₁R antagonist rimonabant or the iNOS inhibitor 1400W, without inducing anxiety-like behaviors or CB₁R occupancy in the CNS. The hybrid inhibitor also targeted CB₁R-independent, iNOS-mediated profibrotic pathways, including increased PDGF, Nlrp3/Asc3, and integrin αvβ6 signaling, as judged by its ability to inhibit these pathways in cnr1^-/- but not in nos2^-/- mice. Additionally, it was able to slow fibrosis progression and to attenuate established fibrosis. Thus, dual-target peripheral CB₁R/iNOS antagonists have therapeutic potential in liver fibrosis.

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

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

Curcumin, Silybin Phytosome(®) and α-R-Lipoic Acid Mitigate Chronic Hepatitis in Rat by Inhibiting Oxidative Stress and Inflammatory Cytokines Production

Chronic hepatitis is recognized as a worldwide health problem that gradually progresses towards cirrhosis and hepatocellular carcinoma. Despite the large number of experiments using animal models for allergic hepatitis, it is still difficult to produce a picture of chronic hepatitis. Therefore, this study was conducted to introduce an animal model approximating to the mechanism of chronicity in human hepatitis. The study also aimed to examine the hepatoprotective effects of curcumin, silybin phytosome(®) and α-R-lipoic acid against thioacetamide (TAA)-induced chronic hepatitis in rat model. TAA was administered intraperitoneally at a dose of 200 mg/kg three times weekly for 4 weeks. At the end of this period, a group of rats was killed to assess the development of chronic hepatitis in comparison with their respective control group. TAA administration was then discontinued, and the remaining animals were subsequently allocated into four groups. Group 1 was left untreated, whereas groups 2-4 were allowed to receive daily oral doses of curcumin, silybin phytosome(®) or α-R-lipoic acid, respectively, for 7 weeks. Increases in hepatic levels of malondialdehyde associated with TAA administration were inhibited in groups receiving supplements. Furthermore, glutathione depletion, collagen deposition, macrophage activation and nuclear factor κappa-B expression as well as tumour necrosis factor-α and interleukin-6 levels were significantly decreased in response to supplements administration. Serological analysis of liver function and liver histopathological examination reinforced the results. The above evidence collectively indicates that the antioxidant and anti-inflammatory activities of curcumin, silybin phytosome(®) and α-R-lipoic acid may confer therapeutic efficacy against chronic hepatitis.

The role of iNOS in cholesterol-induced liver fibrosis

Accumulation of cholesterol in the liver is associated with the development of non-alcoholic steatohepatitis-related fibrosis. However, underlying mechanisms are not well understood. The present study investigated the role of inducible nitric oxide synthase (iNOS) in cholesterol-induced liver fibrosis by feeding wild-type (WT) and iNOS-deficient mice with control or high-cholesterol diet (HCD) for 6 weeks. WT mice fed with HCD developed greater liver fibrosis, compared with iNOS-deficient mice, as evident by Sirius red staining and higher expression levels of profibrotic genes. Enhanced liver fibrosis in the presence of iNOS was associated with hypoxia-inducible factor-1α stabilization, matrix metalloproteinase-9 expression, and enhanced hepatic DNA damage. The profibrotic role of iNOS was also demonstrated in vivo using a selective inhibitor of iNOS as well as in vitro in a rat liver stellate cell line (HSC-T6). In conclusion, these findings suggest that iNOS is an important mediator in HCD-induced liver fibrosis.

Adiponectin attenuates liver fibrosis by inducing nitric oxide production of hepatic stellate cells

Adiponectin protects against liver fibrosis, but the mechanisms have not been fully elucidated. Here, we showed that adiponectin upregulated inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) and protein expression in hepatic non-parenchymal cells, particularly in hepatic stellate cells (HSCs), and increased nitric oxide (NO2-/NO3-) concentration in HSC-conditioned medium. Adiponectin attenuated HSC proliferation and migration but promoted apoptosis in a NO-dependent manner. More advanced liver fibrosis with decreased iNOS/NO levels was observed in adiponectin knockout mice comparing to wide-type mice when administered with CCI4 while NO donor supplementation rescued the phenotype. Further experiments demonstrated that adiponectin-induced iNOS/NO system activation is mediated through adipoR2-AMPK-JNK/Erk1/2-NF-κB signaling. These data suggest that adiponectin inhibits HSC function, further limiting the development of liver fibrosis at least in part through adiponectin-induced NO release. Therefore, adiponectin-mediated NO signaling may be a novel target for the treatment of liver fibrosis.

KEY MESSAGES

• Adiponectin activates HSC iNOS/NO and SEC eNOS/NO systems. • Adiponectin inhibits HSC proliferation and migration but promotes its apoptosis. • Adiponectin inhibits CCL4-induced liver fibrosis by modulation of liver iNOS/NO. • Adiponectin stimulates HSC iNOS/NO via adipoR2-AMPK-JNK/ErK1/2-NF-κB pathway.

The use of nanoparticles to deliver nitric oxide to hepatic stellate cells for treating liver fibrosis and portal hypertension

Polymeric nanoparticles are designed to transport and deliver nitric oxide (NO) into hepatic stellate cells (HSCs) for the potential treatment of both liver fibrosis and portal hypertension. The nanoparticles, incorporating NO donor molecules (S-nitrosoglutathione compound), are designed for liver delivery, minimizing systemic delivery of NO. The nanoparticles are decorated with vitamin A to specifically target HSCs. We demonstrate, using in vitro and in vivo experiments, that the targeted nanoparticles are taken up specifically by rat primary HSCs and the human HSC cell line accumulating in the liver. When nanoparticles, coated with vitamin A, release NO in liver cells, we find inhibition of collagen I and α-smooth muscle actin (α-SMA), fibrogenic genes associated with activated HSCs expression in primary rat liver and human activated HSCs without any obvious cytotoxic effects. Finally, NO-releasing nanoparticles targeted with vitamin A not only attenuate endothelin-1 (ET-1) which elicites HSC contraction but also acutely alleviates haemodynamic disorders in bile duct-ligated-induced portal hypertension evidenced by decreasing portal pressure (≈20%) and unchanging mean arterial pressure. This study clearly shows, for the first time, the potential for HSC targeted nanoparticle delivery of NO as a treatment for liver diseases with proven efficacy for alleviating both liver fibrosis and portal hypertension.

Pituitary tumor transforming gene as a novel regulatory factor of liver fibrosis

AIMS

Pituitary tumor-transforming gene (PTTG) is involved in multiple cellular pathways. We studied the development of liver fibrosis induced by thioacetamide (TAA) in knockout (PTTG-/-) and wildtype (PTTG+/+) mice.

MAIN METHODS

Liver fibrosis in PTTG+/+ and PTTG-/- mice was induced by escalating dose TAA treatment (50-400mg/kg, i.p.) for 12 weeks and assessed by histochemistry, immunohistochemistry, liver hydroxyproline, serum fibrosis markers and fibrosis-related mRNA expression by real-time PCR determination.

KEY FINDINGS

Both PTTG+/+ and PTTG-/- mice treated with TAA developed signs of fibrosis and inflammatory cell infiltration. However, histological signs of bridging fibrosis and connective tissue square morphometry were significantly attenuated in mice lacking PTTG. α-SMA immunohistochemistry revealed that hepatic stellate cell activation was markedly reduced in PTTG-/- mice compared to wildtype controls. Hepatic hydroxyproline levels were significantly lower in fibrotic PTTG-/- group. The serum TNFα and hepatic TNFα mRNA expression were significantly lower in fibrotic PTTG-/- animals, as well as hepatic TGFβ and VEGF mRNA levels compared to TAA-treated wildtype controls. Serum hyaluronate and TGFβ levels were markedly elevated in fibrotic mice of both genotypes, but were not altered by the absence of PTTG.

SIGNIFICANCE

TAA-induced fibrosis development is significantly ameliorated in PTTG-/- mice. These animals demonstrated diminished stellate cell activation, suppressed circulating serum markers of inflammation, fibrogenesis and angiogenesis. The presented findings suggest that PTTG is functionally required for hepatic fibrosis progression in an animal model of chronic liver injury. PTTG can be considered as a new important target for prevention and treatment of liver fibrosis/cirrhosis.

Protective Effects of Norursodeoxycholic Acid Versus Ursodeoxycholic Acid on Thioacetamide-induced Rat Liver Fibrosis

BACKGROUND/OBJECTIVES

Effects of norursodeoxycholic acid (norUDCA) and ursodeoxycholic acid (UDCA) on liver fibrosis progression and liver fibrosis reversal in thioacetamide (TAA)-treated rats were studied.

METHODS

Advanced liver fibrosis was induced by TAA treatment (200 mg/kg, i.p.) for 12 weeks. In the second experiment resolution of liver fibrosis was assessed after 8 weeks of TAA withdrawal. During 8 last weeks of each trial, fibrotic rats were daily administered with UDCA (80 mg/kg) and norUDCA (equimolar to 80 mg/kg of UDCA) by oral gavage. Liver fibrosis was assessed by Sirius red staining, liver hydroxyproline and serum fibrosis markers determination.

RESULTS

The TAA treatment resulted in advanced fibrosis and increase in liver hydroxyproline content and serum fibrosis markers. These signs of fibrosis were less pronounced in rats after TAA withdrawal. Treatment with of norUDCA significantly decreased the total and relative liver hydroxyproline contents in rats with fibrosis reversal, whereas UDCA did not change these parameters. Both compounds decreased serum TGFβ and type IV collagen contents, whereas other serum markers did not differ from the placebo group. In the fibrosis progression model the square of connective tissue was decreased by norUDCA. Serum type IV collagen and procollagen III-NT contents in these experiments were lowered by both UDCA and norUDCA, whereas rest of serum fibrosis markers were diminished only by norUDCA.

CONCLUSIONS

Both norUDCA and UDCA showed therapeutic and prophylactic antifibrotic effect in rats with TAA-induced liver fibrosis. For most of tested parameters norUDCA was more effective than UDCA, especially in the experiment with liver fibrosis regression.

Therapeutic effect of collagenase Ⅱ against rat liver cirrhosis

AIM: To explore the therapeutic effect of an adenovirus-HBV chimeric vector expressing collagenase Ⅱ against cirrhosis in a rat model.

METHODS: Rat liver cirrhosis was induced with 0.03% thioacetamide in drinking water for 16 wk. Ad-CH-tMMP8 and Ad-C-MMP8 were constructed using an adenovirus shuttle plasmid and a HBV chimeric vector expressing truncated and full-length collagenase Ⅱ gene. Ad-CH-RFP2 expressing red fluorescent protein was used as a negative control. Liver cirrhosis rats were injected with the three plasmids through the tail vein.

RESULTS: Compared with the model group and negative control group, fibrosis was dramatically attenuated four weeks after the infection. HE staining and picric acid-Sirius red staining showed that hepatocyte steatosis, necrosis and inflammation were significantly milder in the treatment group, along with hepatocyte proliferation, recovery of hepatic lobule structure, and diminished content of HYP (28.97 µg/g ± 2.36 µg/g vs 17.04 µg/g ± 0.61 µg/g, 17.62 µg/g ± 1.30 µg/g, P < 0.05), whereas the fibrosis in Ad-CH-RFP2-treated rats persisted.

CONCLUSION: Adenovirus-HBV chimeric vector expressing collagenase Ⅱ effectively reduces the degree of liver fibrosis in rats.

Effect of ghrelin on chronic liver injury and fibrogenesis in male rats: possible role of nitric oxide

Recent studies have revealed that ghrelin may be an antioxidant and anti-inflammatory agent in many organs, however its role in chronic liver injury (CLI) remains unclear. The role of nitric oxide (NO) in CLI is controversial as evidence suggests that NO is either a primary mediator of liver cell injury or exhibits a protective effect against injurious stimuli. Recent evidence demonstrated that the therapeutic potential for ghrelin was through eNOS activation and increase in NO production. However, its role on NO production in the liver has not been previously investigated. The aim of this study was to investigate the role of ghrelin in treatment of CLI, and whether this action is mediated through NO. Forty male rats were divided into four groups: Group I: Control; Group II: chronic liver injury (CLI); Group III: CLI+Ghrelin; and Group IV: CLI+Ghrelin+l-NAME. Liver enzymes and tumor necrosis factor alpha (TNF-α), were measured to assess hepatocellular injury. Liver tissue collagen content, malondialdehyde (MDA), gene expression of Bax, Bcl-2, and eNOS were assessed to determine the mechanism of ghrelin action. Results showed that ghrelin decreased serum liver enzymes and TNF-α levels. Ghrelin also reduced liver tissue collagen, MDA, and Bax gene expression, and increased Bcl-2 and eNOS gene expression. The effects on TNF-α, collagen, MDA, Bax, and eNOS were partially reversed in Group IV, suggesting that ghrelin's action could be through modulation of NO levels. Therefore, ghrelin's hepatoprotective effect is partially mediated by NO release.

Downregulation of connective tissue growth factor by LPS/IFN-γ-induced nitric oxide is reversed by aristolochic acid treatment in glomerular mesangial cells via STAT-1α and NF-κB signaling

Aristolochic acid (AA) is a common cause of Chinese herb nephropathy. The mechanisms involved in the pathogenesis of AA nephropathy (AAN) are intricate. One well-documented effect of AA in the kidney is its pro-fibrotic activity. Nitric oxide (NO), a messenger gas generated from l-arginine, is the product of nitric oxide synthase (NOS). NO is involved in renal hemodynamics and exerts cytoprotective effects against renal injury. In the present study, the role of NO in AAN was investigated in MES-13 cells, a glomerular mesangial cell line. NO endogenously generated by the induction of inducible nitric oxide synthase (iNOS) with lipopolysaccharide (LPS)/interferon-γ (IFN-γ) significantly downregulated connective tissue growth factor (CTGF) protein expression in MES-13 cells. AA significantly suppressed LPS/IFN-γ-induced NO production and reversed CTGF expression that was downregulated by LPS/IFN-γ. AA decreased iNOS gene and protein expressions in a concentration-dependent manner. AA caused declines in LPS/IFN-γ-induced signal transducer and activator of transcription-1α (STAT-1α) phosphorylation and interferon response factor-1 (IRF-1) mRNA expression. Furthermore, AA attenuated IκB phosphorylation and reduced NF-κB translocation to the nuclear fraction. Taken together, our data indicate that AA reversed the CTGF expression inhibited by LPS/IFN-γ treatment via suppression of NO and iNOS expressions in MES-13 cells through inhibition of the JAK/STAT-1α and NF-κB signaling pathways. NO potentially exerts antifibrotic activity by down regulation of CTGF in MES-13 cells and inhibition of the iNOS gene by AA might partially account for the fibrotic effects of AA in nephropathy.

Interaction of the nitric oxide signaling system with the sphingomyelin cycle and peroxidation on transmission of toxic signal of tumor necrosis factor-α in ischemia-reperfusion

This review discusses the functional role of nitric oxide in ischemia-reperfusion injury and mechanisms of signal transduction of apoptosis, which accompanies ischemic damage to organs and tissues. On induction of apoptosis an interaction is observed of the nitric oxide signaling system with the sphingomyelin cycle, which is a source of a proapoptotic agent ceramide. Evidence is presented of an interaction of the sphingomyelin cycle enzymes and ceramide with nitric oxide and enzymes synthesizing nitric oxide. The role of a proinflammatory cytokine TNF-α in apoptosis and ischemia-reperfusion and mechanisms of its cytotoxic action, which involve nitric oxide, the sphingomyelin cycle, and lipid peroxidation are discussed. A comprehensive study of these signaling systems provides insight into the molecular mechanism of apoptosis during ischemia and allows us to consider new approaches for treatment of diseases associated with the activation of apoptosis.

S-Nitroso-N-acetylcysteine induces de-differentiation of activated hepatic stellate cells and promotes antifibrotic effects in vitro

Nitric oxide (NO) has been shown to act as a potent antifibrogenic agent by decreasing myofibroblast differentiation. S-Nitroso-N-acetylcysteine (SNAC), a NO donor, attenuates liver fibrosis in rats, but the cellular and molecular mechanisms on liver myofibroblast-like phenotype still remain unknown. Here, we investigate the antifibrotic effects of SNAC on hepatic stellate cells, the major fibrogenic cell type in the liver. A murine GRX cell line was incubated with SNAC (100μM) or vehicle (control group) for 72h. Cell viability was measured by MTT colorimetric assay and the conversion of myofibroblast into quiescent fat-storing cell phenotype was evaluated by Oil-Red-O staining. TGFβ-1, TIMP-1, and MMP-13 levels were measure in the supernatant by ELISA. Profibrogenic- and fibrolytic-related gene expression was quantified using real-time qPCR. SNAC induced phenotype conversion of myofibroblast-like phenotype into quiescent cells. SNAC decreased gene and protein expression of TGFβ-1 and MMP-2 compared to control groups. Besides, SNAC down-regulated profibrogenic molecules and up-regulated MMP-13 gene expression, which plays a key role in the degradation of interstitial collagen in liver fibrosis. In conclusion, these findings demonstrate that SNAC efficiently can modulate the activation and functionality of murine hepatic stellate cells and could be considered as an antifibrotic treatment to human liver fibrosis.

Evaluation of nitrite/nitrate levels in relation to oxidative stress parameters in liver cirrhosis

BACKGROUND AND OBJECTIVE

Nitric oxide and reactive oxygen species have been implicated in several pathophysiological events leading to fibrosis and cirrhosis. The aim of the present study was to investigate the possible contribution of peroxynitrite (formed by the interaction of nitric oxide and superoxide anion) in the pathophysiology of cirrhosis.

METHODS

Twenty-six cirrhotic patients classified as Child-Pugh A, and seven as Child-Pugh B, were included in the study, and nine healthy volunteers served as controls. Levels of nitrite/nitrate (NOx), thiobarbituric acid-reactive substances (TBARS), nitrotyrosine (peroxynitrite marker), superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) were measured in blood samples.

RESULTS

NOx, TBARS, CAT, SOD and GSH levels were higher in cirrhosis patients than in the controls (NOx: 0.17 ± 0.02, 0.95 ± 0.12, 1.3 ± 0.1; TBARS: 2.0 ± 0.05, 4.6 ± 0.3, 5 ± 0.3; CAT: 1.8 ± 0.1, 4 ± 0.3, 4.5 ± 0.4; SOD: 1.8 ± 0.2, 4.8 ± 0.5, 7 ± 0.4; and GSH: 1.3 ± 0.05, 3.6 ± 0.3, 4.5 ± 0.6 in controls, and Child-Pugh A and B patients, respectively). However, there were no differences in nitrotyrosine levels across these groups (controls: 11.4 ± 0.4; Child-Pugh A: 11.1 ± 0.4; Child-Pugh B: 11.9 ± 1.6). NOx levels showed significant and strongly positive correlations with TBARS, SOD, CAT and GSH levels. In contrast, no correlations were found between either NOx or TBARS and nitrotyrosine levels.

CONCLUSION

Nitric oxide and reactive oxygen species, but not peroxynitrite, are overproduced in patients with cirrhosis in spite of evidence of an increase in antioxidant defenses. This suggests that therapeutic measures aimed at attenuating oxidative stress as well as increasing antioxidant defenses may well benefit patients with cirrhosis.

The role of nitric oxide during healing of trauma to the skeletal muscle

INTRODUCTION

The role of NO in muscle injury is not clear.

METHODS

We examined the involvement of the NO system in the development of muscle damage in an experimental model of crush injury. The animals were divided into four groups: (1) control (CO), (2) sham trauma, (3) trauma, (4) trauma + L -NAME, in two experimental phases, 24 h and 7 days after injury.

RESULTS

Twenty-four hours post-trauma, the crushed muscle was characterized by an intense inflammatory reaction. These changes were accompanied by increased oxidative damage, increased cytokine mRNA transcription, NF-κB binding ability and TGF-β growth factor expression in the gastrocnemius muscle. Treatment with L: -NAME markedly decreased these histological and molecular abnormalities at 24 h. However, at 7 days post-trauma, increased collagen formation was observed in the L: -NAME group.

DISCUSSION

These findings indicate that NO is involved in the balance between fibrosis and healing with regeneration.

Involvement of MMP-9 in peribiliary fibrosis and cholangiocarcinogenesis via Rac1-dependent DNA damage in a hamster model

Peribiliary fibrosis caused by chronic infection with Opisthorchis viverrini (OV) is a risk factor of cholangiocarcinoma (CCA) in northeastern Thailand. Matrix metalloproteinases (MMPs) are enzymes capable of degrading and remodeling the extracellular matrix in the process of fibrosis and carcinogenesis. We examined MMPs expression and their role in fibrogenesis and cholangiocarcinogenesis in hamsters treated with OV and N-nitrosodimethylamine (NDMA). We assessed the time profiles of MMPs, inducible nitric oxide synthase (iNOS), Rac1, α-smooth muscle actin (α-SMA) and DNA lesions (8-nitroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine, 8-oxodG) in relation to fibrosis and CCA development. Histopathology revealed OV and NDMA synergistically induced peribiliary fibrosis time-dependently, and CCA occurred at 3 months, whereas OV or NDMA alone induced less fibrosis. Hydroxyproline levels in the liver and plasma were positively associated with the expression of collagen I and α-SMA. MMP-9 expression was significantly increased and correlated with the accumulation of myofibroblast, fibrosis levels and cholangiocarcinogenesis. MMP-9 activity was correlated with iNOS, and immunocolocalization was observed in inflammed tissues, early and invasive CCA. OV and NDMA synergistically induced MMP-9 expression in association to Rac1. In addition, Rac1 was colocalized with iNOS, and 8-nitroguanine, in inflammed tissues and CCA. Formation of 8-nitroguanine and 8-oxodG increased with tumor progression. The results suggest that MMP-9 expression is associated with the accumulation of peribiliary fibrosis in conjunction to the induction of iNOS and Rac1 that may potentiate DNA damage and cholangiocarcinogenesis.

Effect of carnosine against thioacetamide-induced liver cirrhosis in rat

Carnosine (beta-alanyl-L-histidine) is a dipeptide with antioxidant properties. Oxidative stress has been proposed to be involved in thioacetamide (TAA)-induced liver cirrhosis in rats, that is similar to human disease. In this study we aimed to investigate the role of carnosine on the development of TAA-induced cirrhosis. 200mg TAA/kg body weight has been given i.p. twice a week for three months to female wistar rats. Another group received same dose of TAA in the same pattern plus 2g carnosine/L of drinking water for three months. TAA administration resulted in hepatic fibrosis, significant increases in plasma transaminase activities as well as hepatic hydroxyproline and lipid peroxide levels, while liver glutathione (GSH) and superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) protein expressions and activities decreased. Carnosine was found to behave as an antioxidant reducing malondialdehyde (MDA) and diene conjugate (DC) levels although it was not effective on increased transaminase activities and decreased antioxidants. It also did not affect the histopathological changes observed in TAA group. Thus our findings indicate that carnosine appears to attenuate peroxidation as an antioxidant itself but does not seem to prevent the development of TAA-induced cirrhotic process.

Nitric oxide suppresses transforming growth factor-beta1-induced epithelial-to-mesenchymal transition and apoptosis in mouse hepatocytes

Nitric oxide (NO) is a multifunctional regulator that is implicated in various physiological and pathological processes. Here we report that administration of NO donor S-nitroso-N-acetylpenicillamine (SNAP) inhibited transforming growth factor-beta1 (TGF-beta1)-induced epithelial-to-mesenchymal transition (EMT) and apoptosis in mouse hepatocytes. Overexpression of inducible NO synthase (iNOS) by transfection of the iNOS-expressing vector, which increased NO production, also inhibited the TGF-beta1-induced EMT and apoptosis in these cells. Treatment of cells with proinflammatory mediators, including tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and interferon (IFN)-gamma, which increased the endogenous NO production, produced the same inhibitory effect. Furthermore, exogenous NO donor SNAP treatment caused a decrease in the intracellular adenosine triphosphate (ATP) levels. Consistently, depletion of intracellular ATP by mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) inhibited the TGF-beta1-induced EMT and apoptosis, suggesting that an NO-induced decrease of ATP involved in the NO-mediated inhibition of TGF-beta1-induced EMT and apoptosis. NO and FCCP also inhibited TGF-beta1-induced STAT3 activation, suggesting that signal transducer and activator of transcription 3 inactivation is involved in the NO-induced effects on TGF-beta1-induced EMT and apoptosis.

CONCLUSION

Our study indicates that NO plays an important role in the inhibition of TGF-beta1-induced EMT and apoptosis in mouse hepatocytes through the downregulation of intracellular ATP levels. The data provide an insight into the in vivo mechanisms on the function of NO during the processes of both EMT and apoptosis.

The involvement of nitric oxide in maneb- and paraquat-induced oxidative stress in rat polymorphonuclear leukocytes

Oxidative stress plays a crucial role in the manifestations of maneb (MB) and paraquat (PQ)-induced toxicity including MB+PQ-induced Parkinson's disease (PD). Polymorphonuclear leukocytes (PMNs) actively participate in the oxidative stress-mediated inflammation and organ toxicity. The present study was undertaken to investigate the MB- and/or PQ-induced alterations in the indices of oxidative stress in rat PMNs. Animals were treated with or without MB and/or PQ in an exposure time dependent manner. In some sets of experiments, the animals were pre-treated with NOS inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine (AG) along with respective controls. A significant increase in myeloperoxidase (MPO), superoxide dismutase (SOD), nitric oxide, iNOS expression and lipid peroxidation (LPO) was observed in PMNs of MB- and/or PQ-treated animals, while catalase and glutathione S-transferase (GST) activities were attenuated. L-NAME and AG significantly reduced the augmented nitrite content, iNOS expression and MPO activity to control level in MB and PQ exposed animals. Although the augmented LPO was also reduced significantly in L-NAME and AG treated rat PMNs, the level was still higher as compared with controls. Alterations induced in SOD and GST activities were not affected by NOS inhibitors. The results thus suggest that MB and/or PQ induce iNOS-mediated nitric oxide production, which in turn increases MPO activity and lipid peroxidation, thereby oxidative stress.