Chronic alcohol administration stimulates nitric oxide formation in the rat liver with or without pretreatment by lipopolysaccharide

Antioxidant and immunomodulatory effect of AKSS16-LIV01 – a multi herbal formulation against ethanol induced liver dysfunction in mice

Background

Liver complication arises commonly due to high alcohol consumption rate. Majority of the people residing in both developed and under developed countries consuming alcohol face various liver complications such as liver fibrosis, fatty liver, liver cirrhosis and even hepatocellular carcinoma. Invention of safe and symptomatic medication to overcome this situation is a new challenge worldwide. The main objective of the study is to deliver a safe and symptomatic medication to reduce the ethanol induced liver dysfunction.

Methods

In this study we have developed a multi herbal formulation (AKSS-16-LIV01) which minimised liver damage against various toxicants. Swiss albino mice were divided into seven groups where ethanol induced damage was observed for weeks followed by sanative response observation by our herbal formulation. The groups are normal control group, ethanol treated group (50% v/v), AKSS16-LIV01 low dose (75 mg/kg/day) pre-treated group, AKSS16-LIV01 middle dose (150 mg/kg/day) pre-treated group, AKSS16-LIV01 high dose (300 mg/kg/day) pre-treated group, Sylimarin pre-treated group (100 mg/kg/day) and only AKSS16-LIV01 (300 mg/kg/day) treated group.

Results

The results potrayed significant elevation of various biochemical parameters, lipid profile parameters, lipid peroxidation, nitric oxide (NO) concentration, nitric oxide synthase level and pro inflammatory cytokines level i.e. tumor necrosis factor (TNF-α) and transforming growth factor (TGF-β1) in the ethanol induced mice. On the other hand serum total protein, total albumin, albumin globulin ratio and level of tissue antioxidant enzymes activity (SOD, CAT, GSH and GPx) were significantly reduced by ethanol. Dose depended therapeutic application of the formulation (AKSS16-LIV01) significantly suppressed all the relevant above parameters and protected the liver from ethanol induced fibrogenesis. Apart from this gross morphology of the liver, H&E liver histology and massontrichrome&serius red examination of the liver section strongly supported the hepatoprotive effect of the formulation as compared with standard drug Sylimarin. Result of the study implies that developed multi herbal formulation (AKSS16-LIV01) at a dose of 300 mg/kg/day gave the best optimum response to reduce the ethanol intoxication.

Conclusion

Result clearly depict that AKSS16-LIV01 may be a safe and nontoxic medication which protect the liver against ethanol induced oxidative injury and maintained pro inflammatory cytokines level in the future.

Graphical Abstract

Lipid peroxidation derived reactive aldehydes in alcoholic liver disease

Lipid peroxidation is a known consequence of oxidative stress and is thought to play a key role in numerous disease pathologies, including alcoholic liver disease (ALD). The overaccumulation of lipid peroxidation products during chronic alcohol consumption results in pathogenic lesions on protein, DNA, and lipids throughout the cell. Molecular adducts due to secondary end products of lipid peroxidation impact a host of biochemical processes, including inflammation, antioxidant defense, and metabolism. The aggregate burden of lipid peroxidation which occurs due to chronic alcohol metabolism, including downstream signaling events, contributes to the development and progression of ALD. In this current opinion we highlight recent studies and approaches relating cellular mechanisms of lipid peroxidation to the pathogenesis of alcoholic liver disease.

Effect of acute endotoxin tolerance on NO production by isolated hepatic parenchymal and nonparenchymal cells and alveolar macrophages in rats

The changes in NO production induced by endotoxin (LPS) tolerance are controversial. The aim of this study was to explore modulation of NO production by LPS tolerance in different liver cell types and alveolar macrophages. Such cells were studied in three groups of male Sprague Dawley rats: non-tolerant rats (sal-LPS) received saline or no treatment 48 h before a 3 mg/kg LPS injection, tolerant rats received low dose LPS (0.5 mg/kg) 48 h before a second injection of saline (LPS-sal) or LPS 3 mg/kg (LPS-LPS). All injections were delivered i.v. Animals were studied 1 and 6 h after the second injection. NO production (assessed by nitrite release) by hepatocytes, Kupffer cells, endothelial cells and alveolar macrophages was simultaneously determined after 20 h of culture in the presence or in the absence of LPS, interferon-y (IFN) or both. Basal NO production by hepatocytes of tolerant and nontolerant LPS injected rats was high 1 h after the second injection, and was dramatically reduced 6 h after the second injection. Hepatocytes of tolerized LPSinjected (LPS-LPS) rats were significantly less sensitive to in vitro stimulation by LPS and IFN at 1 h than hepatocytes of tolerized saline-injected rats and this difference disappeared by 6 h. In Kupffer cells of tolerant rats 6 h after the second LPS injection, basal NO generation was significantly less than in nontolerant rats. In both cell types of tolerant LPS-LPS rats, in vitro stimulated NO production was moderately upregulated at 1 h and then highly upregulated at 6 h, whereas in nontolerant (sal-LPS) animals, stimulated NO production was only slightly upregulated or not at all. Sensitivity to LPS and IFN stimulation of Kupper cells of LPS-LPS rats was not different from Kupffer cells of LPS-sal rats at 1 h, but became significantly higher at 6 h relative to both LPS-sal and sal-LPS animals. In endothelial cells of tolerant saline-injected (LPS-sal) rats, basal NO production was significantly less than in the sal-LPS group both at 1 and 6 h after the second injection. In endothelial cells of tolerant LPS-LPS animals, a significant upregulation of stimulated NO production higher than in the other groups was observed only at 1 h. No difference was evident in basal or stimulated NO production by alveolar macrophages of the different treatment groups, except for a significant increase in basal NO production in tolerant rats (LPS-LPS) at 6 h relative to 1 h after the second LPS injection.

Functional roles of protein nitration in acute and chronic liver diseases

Nitric oxide, when combined with superoxide, produces peroxynitrite, which is known to be an important mediator for a number of diseases including various liver diseases. Peroxynitrite can modify tyrosine residue(s) of many proteins resulting in protein nitration, which may alter structure and function of each target protein. Various proteomics and immunological methods including mass spectrometry combined with both high pressure liquid chromatography and 2D PAGE have been employed to identify and characterize nitrated proteins from pathological tissue samples to determine their roles. However, these methods contain a few technical problems such as low efficiencies with the detection of a limited number of nitrated proteins and labor intensiveness. Therefore, a systematic approach to efficiently identify nitrated proteins and characterize their functional roles is likely to shed new insights into understanding of the mechanisms of hepatic disease pathophysiology and subsequent development of new therapeutics. The aims of this review are to briefly describe the mechanisms of hepatic diseases. In addition, we specifically describe a systematic approach to efficiently identify nitrated proteins to study their causal roles or functional consequences in promoting acute and chronic liver diseases including alcoholic and nonalcoholic fatty liver diseases. We finally discuss translational research applications by analyzing nitrated proteins in evaluating the efficacies of potentially beneficial agents to prevent or treat various diseases in the liver and other tissues.

Alcohol abuse and the injured host: dysregulation of counterregulatory mechanisms review

Traumatic injury ranks as the number one cause of death for the younger than 44 years age group and fifth leading cause of death overall (www.nationaltraumainstitute.org/home/trauma_statistics.html). Although improved resuscitation of trauma patients has dramatically reduced immediate mortality from hemorrhagic shock, long-term morbidity and mortality continue to be unacceptably high during the postresuscitation period particularly as a result of impaired host immune responses to subsequent challenges such as surgery or infection. Acute alcohol intoxication (AAI) is a significant risk factor for traumatic injury, with intoxicating blood alcohol levels present in more than 40% of injured patients. Severity of trauma, hemorrhagic shock, and injury is higher in intoxicated individuals than that of sober victims, resulting in higher mortality rates in this patient population. Necessary invasive procedures (surgery, anesthesia) and subsequent challenges (infection) that intoxicated trauma victims are frequently subjected to are additional stresses to an already compromised inflammatory and neuroendocrine milieu and further contribute to their morbidity and mortality. Thus, dissecting the dynamic imbalance produced by AAI during trauma is of critical relevance for a significant proportion of injured victims. This review outlines how AAI at the time of hemorrhagic shock not only prevents adequate responses to fluid resuscitation but also impairs the ability of the host to overcome a secondary infection. Moreover, it discusses the neuroendocrine mechanisms underlying alcohol-induced hemodynamic dysregulation and its relevance to host defense restoration of homeostasis after injury.

Nitric oxide and oral cancer: a review

Nitric oxide (NO), a short-lived, endogenously produced gas, plays key role in various physiological as well as pathological processes. NO-inducing cell signaling events within the cell producing it and the diffusibility of it in other cells have led to the discovery of various physiological functions of NO including vasodilation, respiration, cell migration, immune response and apoptosis. On the other hand, excessive and unregulated NO synthesis has been implicated in many pathophysiological conditions including cancer. Research on NO, during the past few years is one of the growing areas in cancer biology. The high incidence of oral cancer and precancer has been linked with habits of tobacco chewing and smoking and NO has been said as the "messenger of death" in tobacco related diseases. NO seems to play a part in various stages of carcinogenesis from initiation to progression. However, there is considerable controversy and confusion in understanding its role in cancer biology. It is said to have both, tumoricidal as well as tumor promoting effects and these depend on its timing, location and concentration. Further, NO has also been shown to have antitumor, chemopreventive and therapeutic abilities. Here is an overview in which efforts are made to understand the role of this molecule in oral carcinogenesis.

Catechin suppresses an array of signalling molecules and modulates alcohol-induced endotoxin mediated liver injury in a rat model

Induction of nuclear factor kappa B (NF-κB)-mediated gene expression has been implicated in the pathogenesis of alcoholic liver disease through enhanced production of reactive oxygen species and pro-inflammatory mediators. The present study was carried out to investigate the role of catechin as a chain breaking inhibitor against experimental alcoholic liver injury. Rats were administered 35% v/v ethanol orally at a dose of 10 g/Kg/day for two weeks, followed by 14 g/Kg/day for 10 weeks. Catechin (50 mg/Kg) was co-supplemented after 4 weeks of alcohol treatment till the end of the dosing period. Following chronic alcohol exposure, rats developed endotoxemia and severe pathological changes in the liver such as pronounced fatty change, vacuolar degeneration and inflammation. These changes were accompanied by activation of NF-κB and induction of inflammatory and cytotoxic mediators leading to increased level of tumor necrosis factor-alpha, enhanced formation of malondialdehyde in the liver followed by drastic alterations in the hepatic antioxidant defense systems. Additionally, nitrite levels and lactate dehydrogenase activities were also significantly elevated on chronic alcohol consumption. Alcohol exposure also increased the number of micronucleated cells indicating that alcohol abuse may again be associated with the nuclear changes. Supplementation with catechin ameliorated the alcohol-induced liver injury by downregulating the endotoxin-mediated activation of initial signalling molecule NF-κB and further going downstream the signalling cascade including tumor necrosis factor-alpha, nitric oxide and reactive oxygen species and by enhancing the antioxidant profile. These observations correlated well with the histological findings. Moreover, a remarkable decrease in the percentage of micronucleated cells was observed with catechin supplementation indicating an apparent protection against alcohol-induced toxicity. These findings suggest that catechin may alleviate experimental alcoholic liver disease by suppressing induction of NF-κB, a key component of signalling pathway, thus forming a pharmacological basis for designing novel therapeutic agents against alcohol induced endotoxin-mediated liver injury.

Protective Effect of Emblica officinalis Against Alcohol-Induced Hepatic Injury by Ameliorating Oxidative Stress in Rats

The effect of Emblica officinalis fruit extract (EFE) against alcohol-induced hepatic damage in rats was investigated in the present study. In vitro studies showed that EFE possesses antioxidant as well nitric oxide (NO) scavenging activity. In vivo administration of alcohol (5 g/kg b.wt/day) for 60 days resulted increased liver lipid peroxidation, protein carbonyls, nitrite plus nitrate levels. Alcohol administration also significantly lowers the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase and reduced glutathione as compared with control rats. Administration of EFE (250 mg/kg body weight) to alcoholic rats significantly brought the plasma enzymes towards near normal level and also significantly reduced the levels of lipid peroxidation, protein carbonyls and restored the enzymic and non-enzymatic antioxidants level. This observation was supplemented by histopathological examination in liver. Our data indicate that the tannoid, flavonoid and NO scavenging compounds present in EFE may offer protection against free radical mediated oxidative stress in rat hepatocytes of animals with alcohol-induced liver injury.

[The role of oxidative stress in alcoholic liver injury]

INTRODUCTION

Oxidative stress plays an important role in pathogenesis of alcoholic liver injury. The main source of free oxygen species is cytochrome P450-dependent monooxygenase, which can be induced by ethanol. ROLE OF CYTOCHROME P4502E1 IN ETHANOL-INDUCED OXIDATIVE STRESS: Reactive oxygen species produced by this enzyme are more important in intracellular oxidative damage compared to species derived from activated phagocytes. Free radicals lead to lipid peroxidation, enzymatic inactivation and protein oxidation. ROLE OF MITOCHONDRIA IN ALCOHOL-INDUCED OXIDATIVE STRESS. Production of mitochondrial reactive oxygen species is increased, and glutathione content is decreased in chronically ethanol-fed animals. Oxidative stress in mitochondria leads to mitochondrial DNA damage and has a dual effect on apoptosis. ROLE OF KUPFFER CELLS IN ALCOHOL-INDUCED LIVER INJURY: Chronic ethanol consumption is associated with increased release of endotoxin from gut lumen into portal circulation. Endotoxin activates Kupffer cells, which then release proinflammatory cytokines and oxidants. ROLE OF NEUTROPHILS IN ALCOHOL-INDUCED LIVER INJURY: Alcoholic liver injury leads to the accumulation of neutrophils, which release reactive oxygen species and lysosomal enzymes and contribute to hepatocyte damage and necrosis. ROLE OF NITRIC OXIDE IN ALCOHOL-INDUCED OXIDATIVE STRESS: High amounts of nitric oxide contribute to the oxidative damage, mainly by generating peroxynitrites. ROLE OF ANTIOXIDANTS IN ETHANOL-INDUCED OXIDATIVE STRESS: Chronic ethanol consumption is associated with reduced liver glutathione and alpha-tocopherol level and with reduced superoxide dismutase, catalase and glutathione peroxidase activity.

CONCLUSION

Oxidative stress in alcoholic liver disease is a consequence of increased production of oxidants and decreased antioxidant defense in the liver.

Role of oxidative stress in alcohol-induced liver injury

Reactive oxygen species (ROS) are highly reactive molecules that are naturally generated in small amounts during the body's metabolic reactions and can react with and damage complex cellular molecules such as lipids, proteins, or DNA. Acute and chronic ethanol treatments increase the production of ROS, lower cellular antioxidant levels, and enhance oxidative stress in many tissues, especially the liver. Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol produces liver injury. Many pathways play a key role in how ethanol induces oxidative stress. This review summarizes some of the leading pathways and discusses the evidence for their contribution to alcohol-induced liver injury. Special emphasis is placed on CYP2E1, which is induced by alcohol and is reactive in metabolizing and activating many hepatotoxins, including ethanol, to reactive products, and in generating ROS.

Role of nitric oxide and nuclear factor-kappaB in the CYP2E1 potentiation of tumor necrosis factor alpha hepatotoxicity in mice

Induction of CYP2E1 by pyrazole (PY) potentiated the hepatotoxicity induced by TNFalpha in mice. We evaluated the role of nitrosative and oxidative stress and the NF-kappaB activation pathway in this liver injury. The iNOS inhibitor N-(3-aminomethyl)benzylacetamindine (1400W) or the antioxidant N-acetyl-l-cysteine (NAC) prevented this liver injury. TNFalpha plus PY treatment triggered radical stress in the liver with increased lipid peroxidation and decreased glutathione and caused mitochondrial damage as reflected by elevated membrane swelling and cytochrome c release. The radical stress and mitochondrial damage were prevented by 1400W and NAC. TNFalpha plus PY treatment elevated 3-nitrotyrosine adduct formation and induced NOS2 in the liver; 1400W and NAC blocked these changes. A lower extent of liver injury and oxidative stress was found in NOS2(-/-) mice treated with TNFalpha plus PY compared with wild-type controls. Neither 1400W nor NAC modified CYP2E1 activity or protein. Activation of JNK and p38MAPK was weaker in TNFalpha plus PY-treated NOS2(-/-) mice and 1400W and NAC blocked the activation of JNK and p38MAPK in wild-type mice. IKKalpha/beta protein levels were decreased by TNFalpha plus PY treatment, whereas IkappaBalpha and IkappaBbeta protein levels were elevated compared with saline, PY, or TNFalpha alone. NF-kappaB DNA binding activity was increased by TNFalpha alone but lowered by TNFalpha plus PY. All these changes were blocked by 1400W and NAC. NF-kappaB activation products such as Bcl-2, Bcl-X(L), cFLIP(S), cFLIP(L), and Mn-SOD were reduced by TNFalpha plus PY and restored by 1400W or NAC. We conclude that TNFalpha plus CYP2E1 induces oxidative/nitrosative stress, which plays a role in the activation of JNK or p38MAPK and mitochondrial damage. These effects combine with the blunting of the NF-kappaB activation pathways and the synthesis of protective factors to cause liver injury.

Ethanol acutely stimulates islet blood flow, amplifies insulin secretion, and induces hypoglycemia via nitric oxide and vagally mediated mechanisms

Hypoglycemia induced by alcohol ingestion is a well-known problem in diabetic patients. However, the mechanisms underlying this phenomenon have largely remained elusive. Because insulin secretion in vivo can be rapidly tuned by changes in pancreatic microcirculation, we evaluated the influence of acute alcohol administration on pancreatic islet blood flow (IBF), and dynamic changes in insulin secretion and glycemia in the rat. Ethanol (10%) or saline was iv injected as a bolus into Wistar rats, yielding serum ethanol concentrations of approximately 8 mmol/liter. Measurements of pancreatic blood flow (PBF) were performed by a microsphere technique in combination with a freeze-thawing technique after 10-min injection. Ethanol preferentially and significantly increased pancreatic IBF approximately 4-fold, whereas not influencing whole PBF. The alcohol also augmented late-phase insulin secretion and induced late hypoglycemia upon ip glucose tolerance tests. The nitric oxide synthase inhibitor N-w-nitro-L-arginine methyl ester and atropine prevented the increased pancreatic IBF, enhanced insulin secretion, and hypoglycemia evoked by ethanol. Thus, our findings demonstrate that ethanol acutely exerts substantial influences on pancreatic microcirculation by evoking a massive redistribution of PBF from the exocrine into the endocrine part via mechanisms mediated by nitric oxide and vagal stimuli, augmenting late-phase insulin secretion, and thereby evoking hypoglycemia. This effect may in part underlie the well-known hypoglycemic properties of alcohol in diabetic patients or in alcoholics with hepatic failure.

Nitric oxide donors prevent while the nitric oxide synthase inhibitor l-NAME increases arachidonic acid plus CYP2E1-dependent toxicity

Polyunsaturated fatty acids such as arachidonic acid (AA) play an important role in alcohol-induced liver injury. AA promotes toxicity in rat hepatocytes with high levels of cytochrome P4502E1 and in HepG2 E47 cells which express CYP2E1. Nitric oxide (NO) participates in the regulation of various cell activities as well as in cytotoxic events. NO may act as a protectant against cytotoxic stress or may enhance cytotoxicity when produced at elevated concentrations. The goal of the current study was to evaluate the effect of endogenously or exogenously produced NO on AA toxicity in liver cells with high expression of CYP2E1 and assess possible mechanisms for its actions. Pyrazole-induced rat hepatocytes or HepG2 cells expressing CYP2E1 were treated with AA in the presence or absence of an inhibitor of nitric oxide synthase L-N(G)-Nitroarginine Methylester (L-NAME) or the NO donors S-nitroso-N-acetylpenicillamine (SNAP), and (Z)-1-[-(2-aminoethyl)-N-(2-aminoethyl)]diazen-1-ium-1,2-diolate (DETA-NONO). AA decreased cell viability from 100% to 48+/-6% after treatment for 48 h. In the presence of L-NAME, viability was further lowered to 23+/-5%, while, SNAP or DETA-NONO increased viability to 66+/-8 or 71+/-6%. The L-NAME potentiated toxicity was primarily necrotic in nature. L-NAME did not affect CYP2E1 activity or CYP2E1 content. SNAP significantly lowered CYP2E1 activity but not protein. AA treatment increased lipid peroxidation and lowered GSH levels. L-NAME potentiated while SNAP prevented these changes. Thus, L-NAME increased, while NO donors decreased AA-induced oxidative stress. Antioxidants prevented the L-NAME potentiation of AA toxicity. Damage to mitochondria by AA was shown by a decline in the mitochondrial membrane potential (MMP). L-NAME potentiated this decline in MMP in association with its increase in AA-induced oxidative stress and toxicity. NO donors decreased this decline in MMP in association with their decrease in AA-induced oxidative stress and toxicity. These results indicate that NO can be hepatoprotective against CYP2E1-dependent toxicity, preventing AA-induced oxidative stress.

Alcohol and oxidative liver injury

Acute and chronic ethanol treatment has been shown to increase the production of reactive oxygen species, lower cellular antioxidant levels, and enhance oxidative stress in many tissues, especially the liver. Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol produces liver injury. Many pathways play a key role in how ethanol induces oxidative stress. This review summarizes some of the leading pathways and discusses the evidence for their contribution to alcohol-induced liver injury. Many of the seminal reports in this topic have been published in Hepatology , and it is fitting to review this research area for the 25th Anniversary Issue of the Journal.

Potential effects of L-NAME on alcohol-induced oxidative stress

AIM: Nitric oxide (NO) is a highly reactive oxidant synthesized from L-arginine by nitric oxide synthase (NOS). NO may cause injury through the generation of potent radicals. Nw- nitro-L-arginine methyl ester (L-NAME) is a non-selective inhibitor of NOS. We aimed to evaluate whether L-NAME treatment had protective effects against oxidative stress in rats intragastrically fed with ethanol during a 4 wk-period.

METHODS: Thirty-six male Wistar rats were divided into 3 equal groups: group 1 (control group-isocaloric dextrose was given), group 2 (6 g/kg·d ethanol-induced group) and group 3 (both ethanol 6 g/kg·d and L-NAME 500 mg/L in drinking water-given group). Animals were sacrificed at the end of 4 wk-experimental period, and intracardiac blood and liver tissues were obtained. Biochemical measurements were performed both in plasma and in homogenized liver tissues. Alanine amino transferase (ALT), aspartate amino transferase (AST), malondialdehyde (MDA), NO, superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) levels were measured by spectrophotometry.

RESULTS: ALT and AST in group 2 (62 U/L and 128 U/L, respectively) were higher than those in group 1 (24 U/L and 38 U/L) and group 3 (37 U/L and 81 U/L) (P<0.001 for both). Plasma and tissue levels of MDA in group 2 (4.66 μmol/L and 0.55 nmol/mg protein) were higher than in group 1 (2.65 μmol/L and 0.34 nmol/mg protein) and group 3 (3.43 μmol/L and 0.36 nmol/mg protein) (P<0.001 for both). Plasma and liver tissue levels of NO in group 2 (54.67 μmol/L and 586.50 nmol/mg protein) were higher than in group 1 (34.67 μmol/L and 435.33 nmol/mg protein) and group 3 (27.50 μmol/L and 412.75 nmol/mg protein ) (P<0.001 for both). Plasma and liver tissue SOD activities in group 2 (15.25 U/mL and 5.38 U/ mg protein, respectively) were lower than in group 1 (20.00 U/mL and 8.13 U/ mg protein) and group 3 (19.00 U/mL and 6.93 U/ mg protein) (P<0.001 for both). Plasma and liver tissue CAT activities in group 2 (145 U/mL and 37 U/ mg protein, respectively) were lower than in group 1 (176 U/mL and 73 U/mg protein) and group 3 (167 U/mL and 61 U/mg protein) (P<0.001 for both). Meanwhile, erythrocytes and liver tissue levels of GSH in group 2 (4.12 mg/g Hb and 5.38 nmol/mg protein, respectively) were lower than in group 1 (5.52 mg/g Hb and 4.49 nmol/mg protein) and group 3 (5.64 mg/g Hb and 4.18 nmol/mg protein) (P<0.001 for both).

CONCLUSION: Our findings show that L-NAME may produce a restorative effect on ethanol-induced liver damage via decreasing oxidative stress and increasing antioxidant status.

The role of iNOS in alcohol-dependent hepatotoxicity and mitochondrial dysfunction in mice

Nitric oxide (NO) is now known to control both mitochondrial respiration and organelle biogenesis. Under conditions of ethanol-dependent hepatic dysfunction, steatosis is increased, and this is associated with increased expression of inducible nitric oxide synthase (iNOS). We have previously shown that after chronic exposure to ethanol, the sensitivity of mitochondrial respiration to inhibition by NO is enhanced, and we have proposed that this contributes to ethanol-dependent hypoxia. This study examines the role of iNOS in controlling the NO-dependent modification of mitochondrial function. Mitochondria were isolated from the livers of both wild-type (WT) and iNOS knockout (iNOS-/-) mice that were fed an isocaloric ethanol-containing diet for a period of 5 weeks. All animals that consumed ethanol showed some evidence of fatty liver; however, this was to a lesser extent in the iNOS-/- mice compared to controls. At this early stage in ethanol-dependent hepatic dysfunction, infiltration of inflammatory cells and the formation of nitrated proteins was also decreased in response to ethanol feeding in the iNOS-/- animals. Mitochondria isolated from wild-type ethanol-fed mice showed a significant decrease in respiratory control ratio and an increased sensitivity to NO-dependent inhibition of respiration relative to their pair-fed controls. In contrast, liver mitochondria isolated from iNOS-/- mice fed ethanol showed no change in the sensitivity to NO-dependent inhibition of respiration. In conclusion, the hepatic response to chronic alcohol-dependent cytotoxicity involves a change in mitochondrial function dependent on the induction of iNOS.

Inducible nitric oxide synthase is required in alcohol-induced liver injury: studies with knockout mice

BACKGROUND & AIMS

Oxidative stress contributes to early alcohol-induced liver injury, and superoxide (O(2)*-) production from NADPH oxidase plays a key role. However, the production of the free radical nitric oxide (NO*) by inducible nitric oxide synthase (iNOS) could also be involved.

METHODS

To test this hypothesis, iNOS knockout (B6.129P2-Nos2 (tm1 Lau)) and wild-type mice were fed high-fat control or ethanol-containing diets for 4 weeks.

RESULTS

Mean body weight gains were not significantly different between treatment groups, and average urine ethanol concentrations were similar in wild-type and iNOS knockout mice. After 4 weeks, serum alanine aminotransferase (ALT) levels were increased significantly about 4-fold over control values (29 +/- IU/L) by enteral ethanol (113 +/- 20) in wild-type mice; this effect of ethanol was significantly blunted in iNOS knockout mice (50 +/- 9). Similar protective effects against liver damage were observed if wild-type mice were treated with the iNOS inhibitor N -(3-aminomethyl)benzyl-acetamindine (1400W). Enteral ethanol also caused severe fatty accumulation, mild inflammation, and necrosis in the liver in wild-type mice but had no effect in iNOS knockout mice. The accumulation of 4-hydroxynonenal (lipid peroxidation) and 3-nitrotyrosine (reactive nitrogen species formation) protein adducts caused by alcohol was completely blocked in iNOS knockout mice.

CONCLUSIONS

These data strongly support the hypothesis that iNOS is required for the pathogenesis of early alcohol-induced hepatitis by production of nitric oxide-derived pro-oxidants (e.g., peroxynitrite).

Prevention of ethanol-induced liver injury in rats by an agonist of peroxisome proliferator-activated receptor-gamma, pioglitazone

Agonists of peroxisome proliferator-activated receptor (PPAR)-gamma have been shown to reduce tumor necrosis factor-alpha (TNF-alpha)-induced insulin resistance. On the other hand, sensitization of Kupffer cells to lipopolysaccharide (LPS) and their production of TNF-alpha are critical for progression of alcoholic liver injury. This study was intended to determine whether pioglitazone, a PPAR-gamma agonist, could prevent alcohol-induced liver injury. Rats were given ethanol (5 g/kg b.wt.) and pioglitazone (500 microg/kg) once every 24 h intragastrically. Ethanol for 8 weeks caused pronounced steatosis, necrosis, and inflammation in the liver. These pathological parameters were diminished greatly by pioglitazone. Kupffer cells were sensitized to LPS after ethanol for 4 weeks as evidenced by aggravation of liver pathology induced by LPS (5 mg/kg) and enhancement of LPS (100 ng/ml)-induced intracellular Ca2+ concentration elevation in Kupffer cells. The parameters were diminished by treatment with pioglitazone. LPS-induced TNF-alpha production by Kupffer cells from the 4-week ethanol group was 3 to 4 times higher than control. This increase was blunted by 70% with pioglitazone. Gut permeability was 10-fold higher in the 4-week ethanol group, and pioglitazone treatment did not change the value. Inclusion of TNF-alpha in culture media of Kupffer cells enhanced CD14 expression, LPS-induced intracellular Ca2+ concentration response, and production of TNF-alpha. These results indicate that pioglitazone prevents alcoholic liver injury through abrogation of Kupffer cell sensitization to LPS.

Chronic alcohol consumption increases the sensitivity of rat liver mitochondrial respiration to inhibition by nitric oxide

Chronic alcohol consumption is a well-known risk factor for hepatic injury, and mitochondrial damage plays a significant role in this process. Nitric oxide (NO) is an important modulator of mitochondrial function and is known to inhibit mitochondrial respiration. However, the impact of chronic alcohol consumption on NO-dependent control of liver mitochondrial function is unknown. This study examines the effect of alcohol exposure on liver mitochondria in a rat model and explores the interaction of NO and mitochondrial respiration in this context. Mitochondria were isolated from the liver of both control and ethanol-fed rats after 5 to 6 weeks of alcohol consumption. Mitochondria isolated from ethanol-treated rats showed a significant decrease in state 3 respiration and respiratory control ratio that was accompanied by an increased sensitivity to NO-dependent inhibition of respiration. In conclusion, we show that chronic alcohol consumption leads to increased sensitivity to the inhibition of respiration by NO. We propose that this results in a greater vulnerability to hypoxia and the development of alcohol-induced hepatotoxicity.

A review of the role of reactive oxygen and nitrogen species in alcohol-induced mitochondrial dysfunction

Our understanding of the mechanisms involved in the development of alcohol-induced liver disease has increased substantially in recent years. Specifically, reactive oxygen and nitrogen species have been identified as key components in initiating and possibly sustaining the pathogenic pathways responsible for the progression from alcohol-induced fatty liver to alcoholic hepatitis and cirrhosis. Ethanol has been demonstrated to increase the production of reactive oxygen and nitrogen species and decrease several antioxidant mechanisms in liver. However, the relative contribution of the proposed sites of ethanol-induced reactive species production within the liver is still not clear. It has been proposed that chronic ethanol-elicited alterations in mitochondria structure and function might result in increased production of reactive species at the level of the mitochondrion in liver from ethanol consumers. This in turn might result in oxidative modification and inactivation of mitochondrial macromolecules, thereby contributing further to mitochondrial dysfunction and a loss in hepatic energy conservation. Moreover, ethanol-related increases in reactive species may shift the balance between pro- and anti-apoptotic factors such that there is activation of the mitochondrial permeability transition, which would lead to increased cell death in the liver after chronic alcohol consumption. This article will examine the critical role of these reactive species in ethanol-induced liver injury with specific emphasis on how chronic ethanol-associated alterations to mitochondria influence the production of reactive oxygen and nitrogen species and how their production may disrupt hepatic energy conservation in the chronic alcohol abuser.

Thalidomide prevents alcoholic liver injury in rats through suppression of Kupffer cell sensitization and TNF-alpha production

BACKGROUND & AIMS

Sensitization of Kupffer cells (KCs) to lipopolysaccharide (LPS) and overproduction of tumor necrosis factor (TNF) alpha are critical for progression of alcoholic liver injury. Thalidomide has been shown to suppress TNF-alpha production from macrophages. Accordingly, the purpose of this study was to determine whether thalidomide could prevent alcohol-induced liver injury.

METHODS

Rats were given ethanol (5 g/kg body wt) and thalidomide (5 mg/kg) once every 24 hours intragastrically. To assess the sensitization of Kupffer cells, LPS (5 mg/kg intravenously) was administered and liver histology was evaluated 24 hours later. KCs were isolated after 4 weeks of ethanol treatment and intracellular Ca2+ ([Ca2+]i) was measured using fura-2, whereas TNF-alpha was evaluated by reverse-transcription polymerase chain reaction and enzyme-linked immunosorbent assay. CD14 was determined by Western and fluorescence staining.

RESULTS

Treatment with ethanol for 8 weeks caused marked steatosis, necrosis, and inflammation in the liver. These pathologic parameters were diminished markedly by treatment with thalidomide. In the 4-week ethanol group, the LPS-induced liver damage was aggravated and KCs were sensitized to LPS. Coadministration of thalidomide with ethanol prevented the KC sensitization completely. Furthermore, thalidomide abolished the LPS-induced increase in CD14 expression and [Ca2+]i elevation in KCs. Gut permeability was increased about 10-fold after 4 weeks of ethanol exposure, which was not affected by thalidomide. Moreover, thalidomide reduced the LPS-induced TNF-alpha production by KCs by decreasing TNF-alpha messenger RNA.

CONCLUSIONS

These results collectively indicate that thalidomide prevents alcoholic liver injury through suppression of TNF-alpha production and abolishment of KC sensitization.

Mediation by nitric oxide of the stimulatory effects of ethanol on blood flow

The contribution of nitric oxide (NO) to the hemodynamic effects associated with alcohol oxidation was assessed in rats given either ethanol or water by gastric tube, with and without pre-treatment with either the NO synthase inhibitor N(omega)-monomethyl-L-arginine (L-NMMA; 15 mg/Kg i.p.) or the alcohol dehydrogenase inhibitor 4-methylpyrazole (4-MP; 82 mg/Kg i.p.). Alcohol increased plasma NO (measured with chemiluminescence) by 63%. This was prevented by either L-NMMA or 4-MP. Cardiac output and regional blood flows were determined with 57Cobalt-labeled microspheres. Alcohol markedly enhanced portal blood flow (130 +/- 6 ml/min/Kg vs. 62 +/- 4, in controls; p < 0.01) with no changes in the hepatic, splenic or pancreatic arterial blood flows, indicating that the vasodilatation is mainly mesenteric. In addition, it quadrupled the coronary blood flow, doubled the renal flow and increased cardiac output by 38%, with no significant changes in pulmonary, cerebral or testicular flows. All the stimulatory effects of ethanol on flow, as well as the rise in NO levels, were prevented by L-NMMA, incriminating NO as the mediator of the hemodynamic effects of ethanol oxidation, acting probably via acetate and adenosine.

Long-term alcohol exposure changes sensitivity of rat Kupffer cells to lipopolysaccharide

BACKGROUND

Chronic ethanol treatment enhances Kupffer cell sensitivity to lipopolysaccharide (LPS). In this model, CD14 in Kupffer cells was increased significantly 4 weeks after ethanol. Moreover, it was shown that prostaglandin E2 produced by activated Kupffer cells participated in the mechanism of ethanol-induced fatty liver. This study was designed to elucidate the temporal effect of chronic ethanol exposure on Kupffer cell sensitization to LPS.

METHODS

Rats were given ethanol every 24 hr intragastrically for up to 12 weeks, and Kupffer cells were isolated 24 hr after the final ethanol administration and cultured in RPMI 1640 with 10% fetal bovine serum. After addition of LPS to Kupffer cells, intracellular calcium ([Ca2+]i) was measured.

RESULTS

CD14 in Kupffer cells was increased approximately 2-fold, and then it decreased and returned to control levels. The LPS-induced increases in [Ca2+]i and tumor necrosis factor-alpha by Kupffer cells were also increased approximately 3-fold over control values, but they also returned to control levels. Triglyceride content increased with the duration of chronic ethanol treatment. At 8 weeks, prostaglandin E2 produced by Kupffer cells increased approximately 3-fold over control values and triglycerides by approximately 4-fold before gradually decreasing to basal levels. After 12 weeks of ethanol exposure, LPS-induced increases in [Ca2+]i and tumor necrosis factor-alpha production were only approximately 50% as high as peak levels at 4 weeks. Liver triglyceride content at 12 weeks was reduced significantly compared with values at 8 weeks.

CONCLUSIONS

Kupffer cells at the early stage of chronic ethanol exposure exhibited sensitization to LPS, but this sensitivity was blunted later. This correlated with triglyceride accumulation in the liver. These data indicate that long-term alcohol exposure changes the sensitivity of rat Kupffer cells to LPS but that the magnitude of the effect is time dependent.

Nitric oxide from the inducible nitric oxide synthase (iNOS) increases the expression of cytochrome P450 2E1 in iNOS-null hepatocytes in the absence of inflammatory stimuli

Nitric oxide (NO) can modulate numerous genes through several pathways, yet some genes may be modulated only in the presence of the inflammatory stimuli that upregulate the inducible nitric oxide synthase (iNOS) rather than by NO alone. Furthermore, the role of prior expression of iNOS in the modulation of genes by NO is unknown. We addressed these issues in hepatocytes harvested from iNOS-null (iNOS(-/-)) mice exposed to NO by treatment with NO donors or by infection with an adenovirus-expressing human iNOS (Ad-iNOS), rather than by stimulation with inflammatory cytokines. Differential display and gene array analyses performed on mRNA derived from iNOS(-/-) hepatocytes demonstrated that infection with Ad-iNOS, but not infection with a control adenovirus expressing the beta-galactosidase gene (Ad-LacZ), induced a gene fragment identical to cytochrome P450 2E1 (CYP2E1). Northern analysis performed with this fragment demonstrated that treatment of iNOS(-/-) hepatocytes with Ad-iNOS or with the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP), but not control treatment or infection with Ad-LacZ, resulted in increased expression of CYP2E1. Inhibition of soluble guanylyl cyclase partially blocked the induction of CYP2E1 mRNA by Ad-iNOS. Rat hepatocytes treated with SNAP also exhibited increased expression of CYP2E1 mRNA. Preliminary studies, however, suggest that the induction of CYP2E1 in the rat hepatocytes treated with cytokines was not reduced in the presence of a NOS inhibitor. Our results suggest that CYP2E1 can be induced solely by NO derived from iNOS, at least partly in a cyclic GMP-dependent manner and independently of inflammatory stimuli or of prior exposure to NO.

Ethanol and oxidative mechanisms in the brain

There is strong evidence showing that chronic and excessive ethanol consumption may enhance oxidative damage to neurons and result in cell death. Although not yet well understood, ethanol may enhance ROS production in brain through a number of pathways including increased generation of hydroxyethyl radicals, induction of CYP2E1, alteration of the cytokine signaling pathways for induction of iNOS and sPLA(2), and production of prostanoids through the PLA(2)/COX pathways. Since many neurodegenerative diseases are also associated with oxidative and inflammatory mechanisms in the brain, it would be important to find out whether chronic and excessive ethanol consumption may exacerbate the progression of these diseases. There is evidence that the polyphenolic antioxidants, especially those extracted from grape skin and seed, may protect the brain from neuronal damage due to chronic ethanol administration. Among the polyphenols from grapes, resveratrol seems to have unique antioxidant properties. The possible use of this compound as a therapeutic agent to ameliorate neurodegenerative processes should be further explored.

Ethanol inhibits cytokine-induced iNOS and sPLA2 in immortalized astrocytes: evidence for posttranscriptional site of ethanol action

Chronic and excessive ethanol consumption is known to alter neuron and glial cell functions in the central nervous system (CNS). Astrocytes comprise the major cell type in the brain. These immune active cells are capable of responding to proinflammatory cytokines and endotoxins, which stimulate transcriptional pathways leading to induction of genes, including the inducible nitric oxide synthase (iNOS) and secretory phospholipase A2 (sPLA2). In this study, we investigate the effects of ethanol on cytokine-induced iNOS and sPLA2 in immortalized astrocytes (DITNC). When DITNC cells were exposed to ethanol (0-200 mM) for 4 h prior to subsequent stimulation with cytokines for 16 h, NO production decreased with increasing ethanol concentrations starting from 50 mM. At ethanol concentrations higher than 100 mM, ethanol also inhibited cytokine-induced sPLA2 release into the culture medium. The inhibitory effect of ethanol on NO production corresponds well with the decrease in iNOS protein and NOS enzyme activity, but not with iNOS and sPLA2 mRNA nor binding of NF-kappaB to DNA. The inhibition of cytokine-induced NO production by ethanol was also dependent on the time of ethanol exposure to the cells, but addition of acetaldehyde up to 200 microM did not elicit any changes. Taken together, these results provide evidence for a posttranscriptional mode of ethanol action on the cytokine induction pathway for NO production in astrocytes.

Role of Kupffer cells and gut-derived endotoxins in alcoholic liver injury

The hepatotoxic effects of alcohol have been described in detail, but factors responsible for its hepatotoxicity have only partially been characterized. For example, it is known that chronic ethanol ingestion increases hepatotoxicity and produces fatty liver, hepatitis and cirrhosis. However, acute ethanol consumption reduces endotoxin hepatotoxicity. It now appears that Kupffer cells participate in several aspects of these phenomena. Previously, most studies on the effects of alcohol on liver function have focused chiefly on the hepatocyte. Recently, attention has been directed towards the effect of ethanol ingestion on Kupffer cell function, which is stimulated by gut-derived endotoxins (lipopolysaccharides) via mechanisms dependent on increased gut permeability and the possible relationship between Kupffer cells and alcohol-induced liver injury. Here we will review new evidence for the proposal that Kupffer cells and endotoxins play a pivotal role in hepatotoxicity following alcohol exposure, based on studies using the continuous intragastric enteral feeding model developed by Tsukamoto and French and an acute model developed by us.

Estriol sensitizes rat Kupffer cells via gut-derived endotoxin

The relationship between gender and alcohol-induced liver disease is complex; however, endotoxin is most likely involved. Recently, it was reported that estriol activated Kupffer cells by upregulation of the endotoxin receptor CD14. Therefore, the purpose of this work was to study how estriol sensitizes Kupffer cells. Rats were given estriol (20 mg/kg ip), and Kupffer cells were isolated 24 h later. After addition of lipopolysaccharide (LPS), intracellular Ca2+ concentration was measured using a microspectrofluorometer with the fluorescent indicator fura 2, and tumor necrosis factor-alpha was measured by ELISA. CD14 was evaluated by Western analysis. One-half of the rats given estriol intraperitoneally 24 h before an injection of a sublethal dose of LPS (5 mg/kg) died within 24 h, whereas none of the control rats died. Mortality was prevented totally by sterilization of the gut with antibiotics. A similar pattern was obtained with liver histology and serum transaminases. Translocation of horseradish peroxidase was increased about threefold in gut segments by treatment with estriol. This increase was not altered by treatment with nonabsorbable antibiotics. On the other hand, endotoxin levels were increased to 60-70 pg/ml in plasma of rats treated with estriol. As expected, this increase was prevented (<20 pg/ml) by antibiotics. In isolated Kupffer cells, LPS-induced increases in intracellular Ca2+ concentration, tumor necrosis factor-alpha production, and CD14 were increased, as previously reported. All these phenomena were blocked by antibiotics. Therefore, it is concluded that estriol treatment in vivo sensitizes Kupffer cells to LPS via mechanisms dependent on increases in CD14. This is most likely due to elevated portal blood endotoxin caused by increased gut permeability.

Ethanol metabolism is not required for inhibition of LPS-stimulated transcription of inducible nitric oxide synthase

We examined the effect of inhibition of ethanol metabolism on ethanol-mediated suppression of Escherichia coli endotoxin (LPS-induced upregulation of transcription and release of inducible nitric oxide synthase (iNOS) and tumor necrosis factor alpha (TNFalpha) from rat alveolar macrophages (AM) in vivo. Ethanol (3.45 and 5.5 g/kg/IP) and t-butanol (3.7 g/kg, IP), given 30 min before intratracheal administration of LPS (1.0 mg/kg), inhibited the upregulation of iNOS mRNA and protein, determined by competitor equalized RT-PCR and Western immunoblot, respectively, but not TNFalpha mRNA in AM obtained 2 h after LPS administration by bronchoalveolar lavage (BAL). However, ethanol and t-butanol inhibited LPS-stimulated nitrate and nitrite (RNI) and TNFalpha protein in BAL fluid. Pretreatment of rats with 4-methylpyrazole (100 mg/kg, IP) 2 h before, or disulfiram 30 min before, administration of ethanol (3.45 g/kg, IP) failed to attenuate the inhibitory effect on iNOS mRNA or protein. t-Butyl hydroperoxide (100 mg/kg, IP) given to rats 30 min before administration of LPS enhanced LPS-mediated upregulation of iNOS mRNA and TNFalpha protein in AM and BAL fluid. The inhibitory effect of ethanol on iNOS mRNA was not mediated by an interaction with elevated levels of circulating corticosterone because pretreatment of rats with RU-38486 (100 mg/kg, IM), which inhibited prednisolone (50 mg/kg, IM), induced suppression of LPS-stimulated iNOS mRNA, and failed to attenuate ethanol-mediated inhibition of LPS-stimulated iNOS mRNA in AM. We conclude that metabolism of ethanol to acetaldehyde via alcohol dehydrogenase is not required for ethanol-mediated suppression of LPS-induced iNOS transcription and TNFalpha synthesis/release in AM. Moreover, an interaction of ethanol or acetaldehyde with circulating corticosterone is not involved in ethanol-mediated attenuation of LPS-stimulated iNOS mRNA or protein or TNFalpha protein in the lung. Speculatively, because oxidation of t-butanol to t-butylhydroperoxide results in activation, rather than inhibition, of iNOS and TNF-alpha, the reported ethanol-mediated enhancement of iNOS mRNA may result from the action of the hydroxyethyl radical.

Regulation of IGF binding protein-1 in hep G2 cells by cytokines and reactive oxygen species

The liver is a major site of synthesis for insulin-like growth factor binding protein (IGFBP)-1. Because IGFBP-1 inhibits many anabolic actions of IGF-I, increases in IGFBP-1 may be partly responsible for the decrease in lean body mass observed in catabolic/inflammatory conditions. This study aimed to determine in Hep G2 cells 1) the sensitivity of IGFBP-1 synthesis to treatment with interleukin (IL)-1, tumor necrosis factor-alpha (TNF-alpha), and IL-6, 2) the ability of reactive oxygen species (ROS) to enhance IGFBP-1 production, and 3) the role of ROS in mediating cytokine-induced increases in IGFBP-1. Hep G2 cells responded to IL-1beta, TNF-alpha, and IL-6 with maximal 8- to 10-fold increases in IGFBP-1 production. Although the maximal responsiveness of cells treated with TNF-alpha and IL-6 was 20-30% less than that with IL-1beta, cells demonstrated a similar sensitivity to all cytokines (half-maximal responsive dose of approximately 10 ng/ml). A low concentration (3 ng/ml) of all three cytokines had an additive effect on IGFBP-1 production. Cytokines also increased IGFBP-1 mRNA. The half-life of IGFBP-1 mRNA was approximately 4 h and not altered by IL-1beta. Incubation with ROS, including H2O2 and nitric oxide (NO) donors, resulted in a relatively smaller increase in IGFBP-1. However, preincubating Hep G2 cells with various free radical scavengers and NO synthase and eicosanoid inhibitors failed to prevent or attenuate cytokine-induced increases in IGFBP-1. Finally, preincubating cells with pyrrolidinedithiocarbamate (PDTC) but not SN50 (inhibitors of nuclear factor-kappaB activation and nuclear translocation, respectively) attenuated increases in IGFBP-1 induced by IL-1. These results indicate that 1) proinflammatory cytokines directly enhance IGFBP-1 synthesis by stimulating transcription without altering mRNA stability, 2) addition of exogenous ROS also stimulates IGFBP-1 production but to a smaller extent than cytokines, and 3) the cytokine-induced increase in IGFBP-1 production is not mediated by endogenous production of ROS or eicosanoids but appears to at least partially involve a PDTC-sensitive pathway.

Effects of exogenous superoxide anion and nitric oxide on the scavenging function and electron microscopic appearance of the sinusoidal endothelium in the isolated, perfused rat liver

BACKGROUND/AIMS

Functional and morphological alterations of the hepatic sinusoidal endothelial cell occur in several models of experimental liver injury and in clinical settings. The causes of these alterations are multiple. The aim of this study was to test the hypothesis that the early functional impairment and morphological alterations of the sinusoidal endothelial cell and hepatic sinusoid associated with liver injury are mediated by free radical species, such as superoxide anion and nitric oxide.

METHODS

Isolated rat livers were perfused by recirculation with hemoglobin-free, Krebs-Henseleit bicarbonate buffer and presented with a source of superoxide anion (xanthine oxidase+hypoxanthine) or nitric oxide (S-nitroso-N-acetyl penicillamine). Hyaluronan uptake (an index of sinusoidal endothelial cell scavenging function), thiobarbituric acid-reactive substances content of the tissue (a marker of lipid peroxidation), reduced and oxidized glutathione (a marker of the thiol system oxidation/reduction state), lactate dehydrogenase and alanine aminotransferase activities (markers of cytolysis), as well as scanning and transmission electron microscopic appearance of the sinusoid were evaluated.

RESULTS

At the high concentrations used, both free radical generating systems suppressed hyaluronan uptake, increased malondialdehyde content of the tissue, enhanced the release of both liver enzymes, decreased the total glutathione content of the liver, and altered the ratio of reduced/oxidized glutathione. Both free radical species induced dose-dependent morphological alterations of the sinusoid, consisting of the appearance of large gaps replacing the sieve-plated fenestration.

CONCLUSIONS

The free radical species-induced functional impairment and morphological alterations of the liver sinusoid, presented in this study, closely resemble the early in vivo changes associated with liver injury under a variety of conditions, such as preservation and reperfusion, or administration of hepatotoxicants such as D-galactosamine, Gram-negative bacterial lipopolysaccharides, acetaminophen, alcohol and others. Therefore, we suggest that early liver sinusoid injury, observed under these conditions, can be attributed to the action of free radicals, such as superoxide anion and nitric oxide.

Alcohol causes both tolerance and sensitization of rat Kupffer cells via mechanisms dependent on endotoxin

BACKGROUND & AIMS

Ethanol causes both tolerance and sensitization of Kupffer cells. This study was designed to evaluate temporal effects of ethanol in an attempt to understand this paradox.

METHODS

Rats were given ethanol (4 g/kg body wt) intragastrically, and Kupffer cells were isolated 0-48 hours later. After addition of lipopolysaccharide (LPS), intracellular calcium concentration ([Ca2+]i) was measured using a microspectrofluorometer with the fluorescent indicator fura-2, and tumor necrosis factor alpha (TNF-alpha) was measured by enzyme-linked immunosorbent assay. CD14 was evaluated by Western and Northern analysis.

RESULTS

Two hours after ethanol administration, the LPS-induced increase in [Ca2+]i and TNF-alpha release by Kupffer cells was diminished by 50%, and these parameters were reciprocally enhanced twofold at 24 hours. Sterilization of the gut with antibiotics blocked all effects of ethanol on [Ca2+]i and TNF-alpha release completely. Twenty-four hours after ethanol, CD14 in Kupffer cells was elevated about fivefold.

CONCLUSIONS

Kupffer cells isolated from rats early after ethanol exhibited tolerance to LPS, whereas sensitization was observed later. It is likely that both of these phenomena are caused by gut-derived endotoxin and that sensitization in Kupffer cells is caused by increases in CD14.

Alcohol intoxication and withdrawal: the role of nitric oxide

Nitric oxide is an important messenger in the central nervous system and several types of evidence suggest that it mediates various alcohol effects. Treatment with a nitric oxide synthase inhibitor enhances the acute central depressant or anesthetic effect of alcohol and decreases some stimulatory effects of alcohol withdrawal after chronic alcohol treatment. Conversely, treatment with a nitric oxide donor inhibits the anesthetic effect of alcohol, blocks the effect of the nitric oxide synthase inhibitor on alcohol anesthesia, and enhances the severity of some alcohol withdrawal signs. These results indicate that changes in nitric oxide synthesis mediate some aspects of alcohol intoxication and withdrawal and that nitric oxide systems represent an important therapeutic target for the development of agents to treat alcoholism and alcohol intoxication.

The effect of ethanol and its metabolites upon methionine synthase activity in vitro

The association of alcoholism with macrocytic anaemia has lead to investigation of the role of cobalamin-dependent methionine synthase in mediating alcohol toxicity. Several studies have found that long-term ingestion of large quantities of ethanol causes inhibition of liver methionine synthase activity in vivo: however, ethanol has not been found to inhibit the enzyme directly. The effect of ethanol and its breakdown products, acetate and acetaldehyde, on highly purified rat liver methionine synthase was tested in vitro. Enzyme activity was not inhibited by ethanol or acetate. Acetaldehyde was found to inhibit methionine synthase activity, with an apparent IC50 of 2 mM. The reported inhibition by acetaldehyde was found to become irreversible over time. Acetaldehyde-induced inhibition of liver methionine synthase activity is thus proposed as the most likely explanation of the reported in vivo effect of ethanol upon methionine synthase.

Role of nitric oxide in acetaminophen-induced hepatotoxicity in the rat

Acetaminophen is a mild analgesic and antipyretic agent known to cause centrilobular hepatic necrosis at toxic doses. Although this may be due to a direct interaction of reactive acetaminophen metabolites with hepatocyte proteins, recent studies have suggested that cytotoxic mediators produced by parenchymal and nonparenchymal cells also contribute to the pathophysiological process. Nitric oxide is a highly reactive oxidant produced in the liver in response to inflammatory mediators. In the present studies we evaluated the role of nitric oxide in the pathophysiology of acetaminophen-induced liver injury. Treatment of male Long Evans Hooded rats with acetaminophen (1 g/kg) resulted in damage to centrilobular regions of the liver and increases in serum transaminase levels, which were evident within 6 hours of treatment of the animals and reached a maximum at 24 hours. This was correlated with expression of inducible nitric oxide synthase (iNOS) protein in these regions. Hepatocytes isolated from both control and acetaminophen-treated rats were found to readily synthesize nitric oxide in response to inflammatory stimuli. Cells isolated from acetaminophen-treated rats produced more nitric oxide than cells from control animals. Production of nitric oxide by cells from both control and acetaminophen-treated rats was blocked by aminoguanidine, a relatively specific inhibitor of iNOS. Arginine uptake and metabolism studies revealed that the inhibitory effects of aminoguanidine were due predominantly to inhibition of iNOS enzyme activity. Pretreatment of rats with aminoguanidine was found to prevent acetaminophen-induced hepatic necrosis and increases in serum transaminase levels. This was associated with reduced nitric oxide production by hepatocytes. Inhibition of toxicity was not due to alterations in acetaminophen metabolism since aminoguanidine had no effect on hepatocyte cytochrome P4502E1 protein expression or N-acetyl-p-benzoquinone-imine formation. Taken together, these data demonstrate that nitric oxide is an important mediator of acetaminophen-induced hepatotoxicity.

Regulation of endometrial blood flow in ovariectomized rats: assessment of the role of nitric oxide

The purpose of this study was to evaluate the role of nitric oxide (NO) in the maintenance of basal endometrial blood flow of ovariectomized rats and in the increase of endometrial blood flow after administration of estradiol 17beta (E2beta). Endometrial blood flow was repeatedly measured with the H2 gas clearance technique in ovariectomized rats. N(omega)-nitro-L-arginine methyl ester (L-NAME) dose dependently reduced basal endometrial blood flow and increased mean arterial blood pressure and endometrial vascular resistance. E2beta (1 microg/kg i.v.) increased endometrial blood flow and reduced endometrial vascular resistance, which peaked by 2 h after the injection. The vasoconstrictive activity of L-NAME (an inhibitor for NO synthesis) was compared with that of phenylephrine (PE, an alpha-receptor agonist acting through an NO-independent mechanism). Doses of L-NAME (1 and 3 mg/kg i.v.) were matched with those of PE (3.2 and 6.4 mg x kg(-1) x h(-1) i.v.), as they induced an approximately equivalent percent increase in basal endometrial vascular resistance. The percent increases of endometrial vascular resistance in E2beta-treated animals by the two agents in matched doses were also of a similar magnitude. When animals were first treated with L-NAME or PE, E2beta lost the ability to reduce endometrial vascular resistance. Enzyme activity and gene expression of NO synthase in the rat uterine tissue were also examined after E2beta treatment, and no significant changes were observed. These data raise doubts about the role of NO in the regulation of endometrial blood flow after acute administration of E2beta and suggest that other mechanisms may be involved.

Endogenous nitric oxide in exhaled air from patients with liver cirrhosis

BACKGROUND

The aim of this study was to investigate the potential effects of liver insufficiency on nitric oxide concentrations in exhaled air.

METHODS

Nitric oxide concentrations in the exhaled air from 13 patients with liver cirrhosis and 11 healthy control subjects was examined by the single-breath technique.

RESULTS

There was a clear correlation between Child-Pugh score and NO in exhaled air (peak after 15 sec of breathholding, R = 0.623, P = 0.023). Similarly, there were significant correlations in peak NO concentrations and alkaline phosphatase, bilirubin, aspartate and alanine aminotransferase, and albumin. The most severely ill patient in our study had the highest NO concentrations in her exhaled air. On recovery from her liver illness the concentration of NO in her exhaled air decreased. There was no correlation between circulating levels of the endogenous NO synthase inhibitors asymmetric and symmetric N(G), N(G)-dimethyl-arginine and exhaled NO concentrations.

CONCLUSIONS

The present data show a correlation between endogenous NO formation in the respiratory system and liver dysfunction. This might contribute to the understanding of the pathophysiology in pulmonary vasodilatation in liver disease.

Interaction of phosducin-like protein with G protein betagamma subunits

Phosducin-like protein (PhLP), a widely expressed ethanol-responsive gene (Miles, M. F., Barhite, S., Sganga, M., and Elliott, M. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 10831-10835), is a homologue of phosducin, a known major regulator of Gbetagamma signaling in retina and pineal gland. However, although phosducin has a well characterized role in retinal phototransduction, function of the PhLP remains unclear. In this study we examine the ability of PhLP to bind Gbetagamma dimer in vitro and in vivo. Using PhLP glutathione S-transferase fusion proteins, we show that PhLP directly binds Gbetagamma in vitro. Studies with a series of truncated PhLP fusion proteins indicate independent binding of Gbetagamma to both the amino- and C-terminal halves of PhLP. Protein-protein interactions between Gbetagamma and PhLP are inhibited by the alpha subunit of Go and Gi3, suggesting that PhLP can bind only free Gbetagamma. Finally, we show that PhLP complexes, at least partially, with Gbetagamma in vivo. Following overexpression of epitope-tagged PhLP together with Gbeta1gamma2 proteins in COS-7 cells, a PhLP-Gbetagamma complex is co-immunoprecipitated by monoclonal antibody directed against the epitope tag. Similarly, polyclonal anti-PhLP antibody co-precipitates endogenous PhLP and Gbetagamma proteins from NG108-15 cell lysates. These data are consistent with the hypothesis that PhLP is a widely expressed modulator of Gbetagamma function. Furthermore, because alternate forms of the PhLP transcript are expressed, there may be functional implications for the existence of two Gbetagamma-binding domains on PhLP.