Inhibition of nitric oxide production increases dimethylnitrosamine-induced liver injury in rats

Bovine milk-derived α-lactalbumin prevents hepatic fibrosis induced by dimethylnitrosamine via nitric oxide pathway in rats

The present study was designed to evaluate the hepatoprotective potential of α-lactalbumin (αLA) against dimethylnitrosamine (DMN)-induced toxic insults in the rat liver. The liver damage was induced in rats by the repeated administration of DMN (10 mg/kg, i.p.) on three consecutive days per week for three weeks. The rats were maintained on either a standard AIN-93 M or αLA-enriched diet starting one week before the DMN injection until the termination of the experiment. The DMN treatment produced a progressive increase in the plasma markers (aspartate aminotransferase, alanine aminotransferase, total bililbin, hyarulonic acid, and matrix metalloproteinase-2) in 28 days after the first DMN injection. Dietary treatment with αLA significantly reduced the DMN-induced damage toward normalcy. N^Ｇ-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor, significantly attenuated the hepatoprotective effect of αLA. These findings show that αLA has a marked suppressive effect on hepetic fibrosis through a nitric oxide-mediated mechanism.

Morphological and immunobiochemical analysis of the liver in L-arginine induced experimental chronic pancreatitis

BACKGROUND

Clinical evidence indicates that hepatic abnormalities in patients with chronic pancreatitis are not uncommon. Here we aimed to study the possible association between liver and pancreatic damage in a recently described experimental mouse model of CP.

METHODS

The severity of the damage to pancreas, liver and other organs was assessed by biochemical markers and histopathology. The methods applied included Hematoxylin Eosin staining, electron microscope examination, biochemical measurements, RT-PCR, ELISA, and the correlations among some of the parameters contributing to these changes were statistically analyzed.

RESULTS

The hepatic aberrations were mainly represented by mild infiltration of inflammatory cells in portal triad and congestion of central vein of liver, and the main features of drug-induced hepatotoxicity could not be observed. Severe fibrosis of pancreatic tissue was noticed in experimental group, and the existence of multiple organ injuries was also seen under the microscope. Hepatic pathologic scores were positively correlated with those from the corresponding pancreatic specimens (r = 0.72, P < 0.01). TGF-β1 protein levels significantly elevated both in the test pancreas and liver (P < 0.05) and these values were positively correlated (r = 0.86, P < 0.01). The level of interleukin-1β was increased in the serum and tissue of the liver. In addition, cardiac troponin (Tn-I) level not only significantly increased in myocardial homogenates (P < 0.05) but also was positively correlated with the corresponding pathologic score of the liver (r = 0.88, P < 0.01).

CONCLUSION

The liver aberrations might be associated with L-arginine induced chronic pancreatitis.

Acute liver injury induced by low dose dimethylnitrosamine alters mediators of hepatic vascular flow

Alterations in liver vascular tone play an important role in chronic liver disease. The hepatic stellate cell (HSC) and mediators such as nitric oxide (NO) and hydrogen sulfide (H₂S) have been implicated in regulation of vascular tone and intra-hepatic pressure. Though these have been studied in chronic liver damage, changes in response to acute liver injury induced by hepatotoxins such as dimethyl nitrosamine are not well understood. Liver injury was induced in mice by a single intra-peritoneal injection of dimethylnitrosamine (DMN), following which animals were sacrificed at 24, 48 and 72 h. Changes in vascular mediators such as NO and H₂S as well as stellate cell activation was then examined. It was found that a single low dose of DMN in mice is sufficient to induce activation of hepatic stellate cells within 24 h, accompanied by oxidative stress, compromised metabolism of H₂S and decreased levels of the von Willebrand factor (vWF) cleaving protease; a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), which functions in intravascular thrombosis. A suppression of hepatic NO levels is also initiated at this time point, which progresses further and is sustained up to 72 h, at which point the HSC activation is still present. Compromised levels of ADAMTS13 and H₂S metabolism however, begin to recover by 48 h and are almost similar to control by 72 h. In conclusion, these data suggest that even moderate acute insults in the liver can have far reaching consequences on a number of mediators of vascular flow in the liver.

The effects of L-arginine on liver damage in experimental acute cholestasis an immunohistochemical study

Obstructive jaundice damages critical functions in the liver. Nitric oxide modulation would influence liver damage induced by biliary obstruction, and little is known about it Acute cholestasis was induced by bile duct ligation (BDL) in two groups of male Sprague-Dawley rats. L-Arginine or serum physiologic was administered to treatment and control group. Histopathological and immunohistochemical iNOS expression was investigated in hepatic tissue. Plasma enzyme activities were increased in acute cholestasis, and that L-arginine treatment partially but significantly prevented the elevation of these markers of liver damage (P <  .05). Also histopathology scoring showed that the liver injury was prevented and immunohistochemical iNOS activity was increased significantly in L-arginine group (P <  .05). This study shows that, after 7 days of biliary obstruction, liver damage is well established and exogenous L-arginine treatment partially but significantly prevented the liver injury in acute cholestasis.

Early iNOS impairment and late eNOS enhancement during reperfusion following 2.49 MHz continuous ultrasound exposure after ischemia

OBJECTIVE

Ischemia reperfusion (IR) injury, occurring during heart attacks, hemorrhagic shock, and bypass and transplant surgeries, impairs microcirculatory function and nitric oxide (NO) synthesis. We report the regulation of endothelial and inducible NO synthase (eNOS and iNOS) proteins as a consequence of the application of continuous mode diagnostic frequency ultrasound application following IR injury.

METHODS

Animals were assigned to one of five groups for microcirculatory assessment or Western blot analysis (WB) as follows: (1) IR+iNOS inhibition (1400W); and (2) IR+1400W+ultrasound for microcirculatory assessment, (3) Control; (4) IR; and (5) IR+ultrasound for WB. Functional capillary density and microvascular diameter, flow velocity, and flow were monitored for microcirculatory assessment. Skin tissue samples were harvested for WB. 2.49MHz continuous ultrasound was used for application.

RESULTS

Both the inhibition of iNOS alone and iNOS inhibition with ultrasound irradiation positively influenced the microcirculation of observed animals relative to baseline values. Ultrasound exposure resulted in a significant production of eNOS protein in skin tissue harvested 24h into reperfusion (p<0.01). iNOS levels from the same tissue of ultrasound exposed animals were found to be significantly decreased 0.5h into reperfusion (p<0.05).

CONCLUSION

Protection from lasting IR injury effects in the microcirculation, with continuous mode diagnostic frequency ultrasound, results from augmented eNOS protein levels during late reperfusion. Ultrasound inhibited iNOS protein production during early reperfusion may also confer protection from IR injury.

Melatonin inhibits nuclear factor kappa B activation and oxidative stress and protects against thioacetamide induced liver damage in rats

BACKGROUND/AIMS

Free radical-mediated oxidative stress has been implicated in the pathogenesis of acute liver injury. The aim of our study was to investigate whether melatonin, a potent free radical scavenger could prevent fulminant hepatic failure in rats.

METHODS

Liver damage was induced by two consecutive injections of thioacetamide (TAA, 300 mg/kg/i.p.) at 24 h intervals. Treatment with melatonin (3 mg/kg/daily, i.p) was initiated 24 h prior to TAA.

RESULTS

Twenty-four h after the second TAA injection, serum liver enzymes and blood ammonia were lower in rats treated with TAA+melatonin compared to TAA (P<0.001). Liver histology was significantly improved and the mortality in the melatonin-treated rats was decreased (P<0.001). The increased nuclear binding of nuclear factor kappa B in the livers of the TAA-treated rats, was inhibited by melatonin. The hepatic levels of thiobarbituric acid reactive substances, protein carbonyls and inducible nitric oxide synthase were lower in the TAA+melatonin-treated group (P<0.01), indicating decreased oxidative stress and inflammation.

CONCLUSIONS

In a rat model of TAA-induced fulminant hepatic failure, melatonin improves survival and reduces liver damage and oxidative stress. The results suggest a causative role of oxidative stress in TAA-induced hepatic damage and suggest that melatonin may be utilized to reduce liver injury associated with oxidative stress.

Induction of platelet formation from megakaryocytoid cells by nitric oxide

Although the growth factors that regulate megakaryocytopoiesis are well known, the molecular determinants of platelet formation from mature megakaryocytes remain poorly understood. Morphological changes in megakaryocytes associated with platelet formation and removal of senescent megakaryocytes are suggestive of an apoptotic process. Previously, we have established that nitric oxide (NO) can induce apoptosis in megakaryocytoid cell lines. To determine whether there is an association between NO-induced apoptosis and platelet production, we exposed Meg-01 cells to S-nitrosoglutathione (GSNO) with or without thrombopoeitin (TPO) pretreatment and used flow cytometry and electron microscopy to assess platelet-sized particle formation. Meg-01 cells treated with TPO alone produced few platelet-sized particles (<3% of total counts), whereas treatment with GSNO alone produced a significant percentage of platelet-sized particles (22 +/- 4% of total counts); when combined with TPO pretreatment, however, GSNO led to a marked increase in platelet-sized particle production (48 +/- 3% of total counts). Electron microscopy confirmed that Meg-01 cells treated with TPO and GSNO yielded platelet-sized particles with morphological features specific for platelet forms. The platelet-sized particle population appears to be functional, because addition of calcium, fibrinogen, and thrombin receptor-activating peptide led to aggregation. These results demonstrate that NO facilitates platelet production, thereby establishing the essential role of NO in megakaryocyte development and thrombopoiesis.

Involvement of reactive oxygen species and nitric oxide radicals in activation and proliferation of rat hepatic stellate cells

BACKGROUND/AIMS

Reactive oxygen species (ROS) induce HSCs activation, proliferation and collagen gene expression in vitro. Nitric oxide (NO) represents a reactive molecule that reacts with ROS, yielding peroxynitrite. We thus verified the effect of NO on ROS-induced HSCs proliferation in vitro and correlated iNOS expression and ROS formation to HSCs activation in the early phase of liver injury leading to hepatic fibrosis in vivo.

METHODS/RESULTS

HSCs were incubated with iron ascorbate (FeAsc) in vitro, which induced ROS production, ERK1/2 phosphorylation and increased cell proliferation. This effect was significantly reduced by the presence of the NO donor S-nitroso-N-acetylpenicillamine. Liver injury was induced in vivo in rats by dimethylnitrosamine administration. HSCs activation started 6 h after DMN administration and peaked at 1 week. ROS generation and neutrophil infiltration were evident for at least 48 h after DMN treatment, showing an identical distribution pattern. Only a few inflammatory cells expressed iNOS 6 h after DMN administration.

CONCLUSIONS

we have shown that NO acts as a ROS scavenger in vitro, thus inhibiting HSCs proliferation. ROS production by infiltrating neutrophils occurs in the early phase of liver fibrosis and can represent a stimulus to HSCs activation in vivo. The reduced iNOS expression may account for the low NO levels and the inability to prevent the ROS-induced HSC activation in vivo.

Galactosamine decreases nitric oxide formation in cultured rat hepatocytes: lack of involvement in cytotoxicity

Galactosamine hepatotoxicity in vivo has long been associated with rapid and extensive depletion of hepatic uridine nucleotides. Depletion of uridine nucleotides is considered to be causal in the toxicity, as evidenced by the protective effect of uridine administration. However, the exact mechanism of galactosamine-induced hepatic necrosis is still unclear. We have previously shown that the addition of galactosamine to rat primary hepatocyte cultures dramatically decreases production of nitric oxide, as measured in the 24 hour culture medium. The present study investigates whether decreased nitric oxide production contributes to the toxicity of galactosamine in primary hepatocyte cultures. Similar concentration-response curves were observed for the decrease in nitric oxide production and galactosamine cytotoxicity, raising the possibility that there is a similar mechanism for these effects. Suppression of NO synthesis was a direct effect of galactosamine, rather than an indirect effect due to loss of cells from the cultures. Both cytotoxicity and the decrease in nitric oxide production were attenuated by coaddition of 3 mM uridine. However, galactosamine cytotoxicity was not enhanced by prior inhibition of hepatocellular NO synthesis nor was it attenuated by maintenance of culture NO levels with molsidomine or diethylamine NONOate. These data do not support a role for decreased hepatocyte nitric oxide production in galactosamine hepatocyte toxicity.

Galactosamine decreases nitric oxide formation in cultured rat hepatocytes: mechanism of suppression

We have shown that nitric oxide production is dramatically decreased in rat primary hepatocyte cultures exposed to galactosamine. Cotreatment of the cells with uridine, which is known to prevent cytotoxicity, was found to also attenuate NO loss. In the present study, two possible mechanisms for the decreased nitric oxide production were examined. First, we examined the possibility that galactosamine could interfere with the uptake of extracellular arginine by the cultured hepatocytes. Cellular uptake of arginine was determined after addition of 14C-arginine at the time of hepatocyte attachment. Uptake of arginine was rapid in control cultures, and both the rate and level of uptake were unchanged by the addition of a cytotoxic concentration of galactosamine (4 mM). In addition, increased concentrations of arginine in the cell culture medium did not ameliorate the galactosamine-induced decrease in production of nitric oxide. Second, we determined whether the synthesis of inducible nitric oxide synthase in the hepatocyte cultures was inhibited by addition of galactosamine. Hepatocyte levels of inducible nitric oxide synthase were determined immunochemically at various times after the addition of galactosamine (4 mM). In control cultures, inducible nitric oxide synthase was detectable at 7 and 24 hours after attachment. In contrast, no nitric oxide synthase protein was detectable at any time in the galactosamine-treated cultures. Furthermore, addition of galactosamine after inducible nitric oxide synthase had already been synthesized (6.5 h after attachment) did not result in suppression of nitric oxide production in the hepatocyte cultures. The present studies suggest that galactosamine suppresses nitric oxide production in hepatocyte cultures by inhibiting synthesis of inducible nitric oxide synthase, rather than by interference in cellular uptake of arginine.

The hydroxyl radical scavengers dimethylsulfoxide and dimethylthiourea protect rats against thioacetamide-induced fulminant hepatic failure

BACKGROUND/AIMS

Reactive oxygen species, proinflammatory cytokines, glutathione depletion and nitric oxide have all been implicated in the pathogenesis of fulminant hepatic failure. The aim of the present study was to examine the respective roles of these factors in the pathogenesis of thioacetamide-induced fulminant hepatic failure in rats.

METHODS

Fulminant hepatic failure was induced by 3 consecutive intraperitoneal injections of thioacetamide (400 mg/kg) at 24-h intervals. Rats were pretreated with one of the following agents: the free radical scavengers dimethylsulfoxide (4 g/kg every 6 h) or dimethylthiourea (200 mg/kg every 12 h), the glutathione donor, N-acetylcysteine (130 or 200 mg/kg every 6 h), or the anti-tumor necrosis factor-alpha agents pentoxifylline (100 and 200 mg/kg) and soluble tumor necrosis factor receptor (100 or 1000 microg/rat). The nitric oxide synthase inhibitor N-mono-methyl arginine ester (L-NAME, 0.1 mg/ml) was administered in the drinking water, starting 7 days prior to thioacetamide administration.

RESULTS

Serum levels of liver enzymes, blood ammonia and prothrombin time and the stage of hepatic encephalopathy were significantly improved in rats treated with dimethylsulfoxide or dimethylthiourea compared to the other treatment groups (p<0.001). Liver histology and the survival rate in these rats were not adversely affected by thioacetamide administration (p<0.001), while in all the other treatment groups those parameters were similar to control rats with fulminant hepatic failure. Furthermore, dimethylsulfoxide ameliorated liver damage and improved survival even when its administration was initiated 8 and 16 h after the first thioacetamide injection. The hepatic concentration of methanesulfinic acid, which is produced after direct interaction of dimethylsulfoxide with hydroxyl radicals, was increased five-fold in rats treated with thioacetamide+dimethylsulfoxide (p<0.001), suggesting a role for hydroxyl radical scavenging in the protection from fulminant hepatic failure in this model. In the group of thioacetamide-treated rats that were pretreated with L-NAME, liver enzymes, blood ammonia levels and the mortality rate were higher than in the control group, treated with thioacetamide only.

CONCLUSIONS

In thioacetamide-induced fulminant hepatic failure, the hydroxyl radical scavengers dimethylsulfoxide and dimethylthiourea prevent liver injury. Neither N-acetylcysteine nor antagonists of tumor necrosis factor-alpha are protective in this rat model. Inhibition of nitric oxide formation aggravates liver damage and reduces the survival of rats with thioacetamide-induced liver damage.

Liver damage induced by acute cholestasis in the rat is ameliorated partially by L-arginine

The aim of this paper was to determine if NO modulation would influence liver damage induced by 3 day-biliary obstruction. L-Arginine (500 mg kg-1, p.o. twice a day) or L-NAME (100 mg kg-1, p.o. twice a day) or both were administered to male Wistar rats subjected to bile duct ligation (BDL). In the liver, BDL doubled lipid peroxidation and depleted glycogen (P < 0.05), L-arginine completely prevented the former and partially the latter. Alkaline phosphatase, alanine aminotransferase and gamma-glutamyl transpeptidase serum enzyme activities increased (P < 0.05) by BDL, again L-arginine treatment partially, but significantly, prevented the elevation in these three markers of liver damage. Although L-NAME treatment failed to induce a change in any marker of liver injury studied herein, it abolished the beneficial effects of L-arginine, suggesting that these effects are probably mediated by NO synthesis stimulation.

Nitric oxide protection of rat liver from lipid peroxidation, collagen accumulation, and liver damage induced by carbon tetrachloride

The aim of this work was to determine if the inhibition or stimulation of NO synthesis modulates liver damage induced by the chronic administration of CCl4. CCl4 was administered three times a week for 8 weeks to male Wistar rats treated simultaneously with N omega-nitro-L-arginine methyl ester (L-NAME, 100 mg/kg, p.o., twice a day), aminoguanidine (AG, 4 g/L in the drinking water), or L-arginine (500 mg/kg, p.o., twice a day); appropriate controls were performed. Serum NO2- + NO3- increased in the groups treated with CCl4 and/or L-arginine, but the effect was prevented by either L-NAME or AG. In the liver, lipid peroxidation and collagen content increased, while glycogen content decreased in the CCl4-treated group (P < 0.05); L-NAME and AG accentuated these effects. Serum enzyme activities of alanine aminotransferase (ALT), alkaline phosphatase, and gamma-glutamyl transpeptidase (gamma-GTP) and bilirubin content increased about 2-, 3-, 2-, and 6-fold, respectively, after CCl4 intoxication (P < 0.05); L-NAME or AG cotreatment further increased the enzyme activities (P < 0.05). L-Arginine treatment protected the liver partially from the elevation of collagen, bilirubins, and alkaline phosphatase and from glycogen depletion induced by CCl4 intoxication (P < 0.05), but showed no significant effect on ALT, gamma-GTP, or lipid peroxidation. These results suggest that NO protects the liver against oxidative injury, because NO inhibition by L-NAME or AG increased lipid peroxidation and the other markers of liver injury studied herein.