Aminoguanidine, an inducible nitric oxide synthase inhibitor, plus N-acetylcysteine treatment reduce the lipopolysaccharide-augmented hepatotoxicity in rats with cirrhosis

Melatonin ameliorates experimental hepatic fibrosis induced by carbon tetrachloride in rats

AIM: To investigate the protective effects of melatonin on carbon tetrachloride (CCl₄)-induced hepatic fibrosis in experimental rats.

METHODS: All rats were randomly divided into normal control group, model control group treated with CCl₄ for 12 wk, CCl₄ + NAC group treated with CCl₄ + NAC (100 mg/kg, i.p.) for 12 wk, CCl₄ + MEL-1 group treated with CCl₄ + melatonin (2.5 mg/kg) for 12 wk, CCl₄ + MEL-2 group treated with CCl₄ + melatonin (5.0 mg/kg) for 12 wk, and CCl₄ + MEL-3 group treated with CCl₄ + melatonin (10 mg/kg). Rats in the treatment groups were injected subcutaneously with sterile CCl₄ (3 mL/kg, body weight) in a ratio of 2:3 with olive oil twice a week. Rats in normal control group received hypodermic injection of olive oil at the same dose and frequency as those in treatment groups. At the end of experiment, rats in each group were anesthetized and sacrificed. Hematoxylin and eosin (HE) staining and Van Gieson staining were used to examine changes in liver pathology. Serum activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and protein concentration were measured with routine laboratory methods using an autoanalyzer. Hydroxyproline (HYP) content in liver and malondialdehyde (MDA) and glutathione peroxidase (GPx) levels in liver homogenates were assayed by spectrophotometry. Serum hyaluronic acid (HA), laminin (LN), and procollagen III N-terminal peptide (PIIINP) were determined by radioimmunoassay.

RESULTS: Pathologic grading showed that the fibrogenesis was much less severe in CCl₄ + MEL3 group than in model control group (u = 2.172, P < 0.05), indicating that melatonin (10 mg/kg) can significantly ameliorate CCl₄-induced hepatic fibrotic changes. The serum levels of ALT and AST were markedly lower in CCl₄ + MEL treatment groups (5, 10 mg/kg) than in model control group (ALT: 286.23 ± 121.91 U/L vs 201.15 ± 101.16 U/L and 178.67 ± 103.14 U/L, P = 0.028, P = 0.007; AST: 431.00 ± 166.35 U/L vs 321.23 ± 162.48 U/L and 292.42 ± 126.23 U/L, P = 0.043, P = 0.013). Similarly, the serum laminin (LN) and hyaluronic acid (HA) levels and hydroxyproline (HYP) contents in liver were significantly lower in CCl₄ + MEL-3 group (10 mg/kg) than in model control group (LN: 45.89 ± 11.71 &mgr;g/L vs 55.26 ± 12.30 &mgr;g/L, P = 0.012; HA: 135.71 ± 76.03 &mgr;g/L vs 201.10 ± 68.46 &mgr;g/L, P = 0.020; HYP: 0.42 ± 0.08 mg/g tissue vs 0.51 ± 0.07 mg/g tissue, P = 0.012). Moreover, treatment with melatonin (5, 10 mg/kg) significantly reduced the MDA content and increased the GPx activity in liver homogenates compared with model control group (MDA: 7.89 ± 1.49 noml/mg prot vs 6.29 ± 1.42 noml/mg prot and 6.25 ± 2.27 noml/mg prot, respectively, P = 0.015, P = 0.015; GPx: 49.13 ± 8.72 U/mg prot vs 57.38 ± 7.65 U/mg prot and 61.39 ± 13.15 U/mg prot, respectively, P = 0.035, P = 0.003).

CONCLUSION: Melatonin can ameliorate CCl₄ -induced hepatic fibrosis in rats. The protective effect of melatonin on hepatic fibrosis may be related to its antioxidant activities.

The effects of N-acetylcysteine on bile duct ligation-induced liver fibrosis in rats

Stellate cells are activated by free radicals, and synthesize collagen. N-acetylcysteine (NAC) is a precursor of reduced glutathione and a potent scavenger of hydroxyl radicals and has potential antifibrotic effects. We aimed to test the effects of NAC on bile duct ligation (BDL) induced liver damage in rats. Forty-seven Wistar rats were divided into 5 groups: group 1, BDL+NAC (n=10); group 2, BDL (n=10); group 3, sham+NAC (n=10); group 4, sham (n=10); and group 5, control group (n=10). NAC (50 micromol/kg per day) or saline of single doses were administered intraperitoneally for 28 days. Serum biochemical and liver oxidative stress parameters were studied. Liver collagen level was determined by the method of Lopez de Leon and Rojkind. Liver slides were stained by hematoxylin and eosin and Masson trichrome\Gomory reticulum staining. Aspartate aminotransferase (AST) and alkaline phosphatase levels in the BDL+NAC group were lower than the BDL group and were higher than the control groups (all P< .001). Malondialdehyde, luminal, and glutathione levels in group 1 were lower than the BDL group (P= .01, P= .002, and P< .001) and higher than the control groups (all P< .001). NAC had no effect on alanine aminotransferase (ALT), gammaglutamyl transferase, bilirubin, albumin, or lucigenin levels. Liver collagen levels were higher in the BDL groups (P< .001); however, NAC had no effect on the collagen levels. The BDL groups showed stage 3 fibrosis; all the control groups were normal. NAC improved some biochemical parameters (AST, alkaline phosphatase) and oxidative stress parameters (malondialdehyde, luminol, glutathione) in the BDL model. NAC was found to be effective on cholestasis-induced hepatotoxicity. However, NAC was inefficient as an antifibrotic agent within a 1-month period of administration in the BDL model.

Nitrotyrosine formation and heme oxygenase-1 expression in endotoxemic cirrhotic rats

BACKGROUND

Endotoxemia increases hepatic toxicity and mortality in cirrhosis. Because the mechanism of augmented hepatotoxicity in endotoxemic cirrhotic rats is still unclear, we wanted to investigate whether oxidative and nitrosative stress play a causative role in lipopolysaccharide (LPS)-treated cirrhotic rats.

METHODS

Liver cirrhosis was produced by the administration of thioacetamide (0.3 g/L of tap water) for a period of 3 months in rats. At the end of this period, cirrhotic rats were sacrificed 6 h after LPS injection (5 mg/kg, intraperitoneally). Serum transaminase activities, plasma total nitrite and nitrotyrosine (NT) levels as well as hepatic lipid peroxides, NT formation and heme oxygenase 1 (HO-1) expression were determined.

RESULTS

LPS administration to cirrhotic rats caused further increases in serum transaminase activities, and plasma total nitrite and NT levels as well as hepatic lipid peroxide levels as compared to cirrhotic rats. Hepatic NT formation and HO-1 expression were also found to be increased in LPS-injected cirrhotic rats.

CONCLUSIONS

Our results indicate that increased oxidative and nitrosative stress may have a synergistic effect in LPS-augmented hepatotoxicity in cirrhotic rats.

Single injection of naked plasmid encoding alpha-melanocyte-stimulating hormone protects against thioacetamide-induced acute liver failure in mice

Oxidative stress has been implicated in the propagation of acute liver injury. The aim of our study was to investigate whether gene transfer of alpha-melanocyte-stimulating hormone (alpha-MSH), a potent anti-inflammatory peptide, could prevent fulminant hepatic failure in mice. Acute liver damage was induced by intraperitoneal administration of thioacetamide. Hydrodynamics-based gene transfection with alpha-MSH expression plasmid via rapid tail vein injection was initiated 1 day prior to intoxication. The mortality in the alpha-MSH-treated mice was significantly lower compared to the vehicle group 3 days after injury. Liver histology significantly improved and TUNEL-positive hepatocytes decreased in the treated mice. The degradation of IkappaBalpha, endogenous inhibitor of nuclear factor kappaB, and upregulation of inducible nitric oxide synthase and tumor necrosis factor-alpha mRNA levels were prevented in the alpha-MSH-treated group, indicating decreased oxidative stress and inflammation. These results suggest alpha-MSH gene therapy might protect against acute hepatic necroinflammatory damage with further potential applications.

The effect of N-acetylcysteine (NAC) on liver and renal tissue inducible nitric oxide synthase (iNOS) and tissue lipid peroxidation in obstructive jaundice stimulated by lipopolysaccharide (LPS)

Morbidity and mortality rates are very high in obstructive jaundice when it is associated with sepsis and multiple organ failure. Nitric oxide (NO) formation and increased expression of inducible nitric oxide synthase (iNOS) also take place in obstructive jaundice (OJ). N-Acetylcysteine (NAC) has a beneficial effect by demonstrating anti-inflammatory activity such as inhibits cytokine expression/release, inhibiting the adhesion molecule expression and inhibiting nuclear factor kappa B (NFkappaB). The aim of this study was to investigate the effects of NAC on liver and renal tissue iNOS, and liver tissue lipid peroxidation in lipopolysaccharide (LPS) induced obstructive jaundice. We randomized 48 rats into six groups. Group A: Sham group; group B: OJ group; group C: OJ+NAC; group D: OJ+LPS (Escherichia coli LPS serotype L-2630, 100mg, Sigma) group E: OJ+NAC+LPS; group F: OJ+LPS+NAC. NAC was started subcutaneously 100mg/kg. LPS was injected intraperitoneally and then at the tenth day we sacrificed the rats. Liver malondialdehyde (MDA) increased and liver ATPase decreased in groups B-D when compared to group A. After the administration of NAC (groups C-E), liver MDA levels decreased, tissue ATPase levels increased as compared to other groups. The liver and renal tissue iNOS expression was increased in groups B, D, and F. After the administration of NAC (groups C-E) the liver and renal tissue iNOS expression were decreased. Our results indicated that NAC prevented the deleterious effects of LPS in OJ by reducing iNOS expression via lipid peroxidation in liver and renal tissue; if it was administrated before LPS. But NAC failed to prevent the iNOS expression and lipid peroxidation if there was established endotoxemia in OJ.

Protective effect of MDL28170 against thioacetamide-induced acute liver failure in mice

Liver injury is known to often progress even after the hepatotoxicant is dissipated. The hydrolytic enzyme calpain, which is released from dying hepatocytes, destroys the surrounding cells and results in progression of injury. Therefore, control of calpain activation may be a suitable therapeutic intervention in cases of fulminant hepatic failure. This study evaluated the effects of a potent cell-permeable calpain inhibitor, MDL28170, and its mechanisms of action on thioacetamide (TAA)-induced hepatotoxicity in mice. We found that MDL28170 significantly decreased mortality and change in serum transaminase after TAA administration. The necroinflammatory response in the liver was also suppressed. Furthermore, a significant suppression of hepatocyte apoptosis could be found by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay. The upregulation of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha), both of which are known to mediate the propagation of inflammation, was abolished. MDL2810 also effectively blocked hepatic stellate cell activation, which is assumed to be the early step in liver fibrosis. These results demonstrated that MDL28170 attenuated TAA-induced acute liver failure by inhibiting hepatocyte apoptosis, abrogating iNOS and TNF-alpha mRNA upregulation and blocking hepatic stellate cell activation.

NO plays a role in LPS-induced decreases in circulating IGF-I and IGFBP-3 and their gene expression in the liver

In this study, we administered aminoguanidine, a relatively selective inducible nitric oxide synthase (iNOS) inhibitor, to study the role of nitric oxide (NO) in LPS-induced decrease in IGF-I and IGFBP-3. Adult male Wistar rats were injected intraperitoneally with LPS (100 microg/kg), aminoguanidine (100 mg/kg), LPS plus aminoguanidine, or saline. Rats were injected at 1730 and 0830 the next day and killed 4 h after the last injection. LPS administration induced an increase in serum concentrations of nitrite/nitrate (P < 0.01) and a decrease in serum concentrations of growth hormone (GH; P < 0.05) and IGF-I (P < 0.01) as well as in liver IGF-I mRNA levels (P < 0.05). The LPS-induced decrease in serum concentrations of IGF-I and liver IGF-I gene expression seems to be secondary to iNOS activation, since aminoguanidine administration prevented the effect of LPS on circulating IGF-I and its gene expression in the liver. In contrast, LPS-induced decrease in serum GH was not prevented by aminoguanidine administration. LPS injection decreased IGFBP-3 circulating levels (P < 0.05) and its hepatic gene expression (P < 0.01), but endotoxin did not modify the serum IGFBP-3 proteolysis rate. Aminoguanidine administration blocked the inhibitory effect of LPS on both IGFBP-3 serum levels and its hepatic mRNA levels. When aminoguanidine was administered alone, IGFBP-3 serum levels were increased (P < 0.05), whereas its hepatic mRNA levels were decreased. This contrast can be explained by the decrease (P < 0.05) in serum proteolysis of this binding protein caused by aminoguanidine. These data suggest that iNOS plays an important role in LPS-induced decrease in circulating IGF-I and IGFBP-3 by reducing IGF-I and IGFBP-3 gene expression in the liver.