Is hypoxia involved in the mechanism of alcohol-induced liver injury?

Risk and Prognosis of Acute Liver Injury Among Hospitalized Patients with Hemodynamic Instability: A Nationwide Analysis

Risk and Prognosis of Acute Liver Injury Among Hospitalized Patients with Hemodynamic Instability: A Nationwide Analysis Introduction and aim. Critically ill patients in states of circulatory failure are at risk of acute liver injury, from mild elevations in aminotransferases to substantial rises consistent with hypoxic hepatitis or "shock liver". The present study aims to quantify the national prevalence of acute liver injury in patients with hemodynamic instability, identify risk factors for its development, and determine predictors of mortality.

MATERIAL AND METHODS

The 2009-2010 Nationwide Inpatient Sample was interrogated using ICD-9-CM codes for hospital admissions involving states of hemodynamic lability. Multivariable logistic regression was used to evaluate the risks of acute liver injury and death in patients with baseline liver disease, congestive heart failure, malnutrition, and HIV.

RESULTS

Of the 2,865,446 patients identified in shock, 4.60% were found to have acute liver injury. A significantly greater proportion of patients with underlying liver disease experienced acute liver injury (22.03%) and death (28.47%) as compared to those without liver disease (3.18% and 18.82%, respectively). The odds of developing acute liver injury were increased in all baseline liver diseases studied, including all-cause cirrhosis, hepatitis B, hepatitis C, alcoholic liver disease, and non-alcoholic fatty liver disease, as well as in congestive heart failure and malnutrition. All-cause cirrhosis and alcoholic liver disease, however, conferred the greatest risk. Similar trends were seen with mortality. HIV was not a predictor for acute liver injury.

CONCLUSION

Liver injury is a major concern among patients with protracted circulatory instability, especially those suffering from underlying liver disease, heart failure, or malnutrition.

Design of optimized hypoxia-activated prodrugs using pharmacokinetic/pharmacodynamic modeling

Hypoxia contributes to resistance of tumors to some cytotoxic drugs and to radiotherapy, but can in principle be exploited with hypoxia-activated prodrugs (HAP). HAP in clinical development fall into two broad groups. Class I HAP (like the benzotriazine N-oxides tirapazamine and SN30000), are activated under relatively mild hypoxia. In contrast, Class II HAP (such as the nitro compounds PR-104A or TH-302) are maximally activated only under extreme hypoxia, but their active metabolites (effectors) diffuse to cells at intermediate O2 and thus also eliminate moderately hypoxic cells. Here, we use a spatially resolved pharmacokinetic/pharmacodynamic (SR-PK/PD) model to compare these two strategies and to identify the features required in an optimal Class II HAP. The model uses a Green's function approach to calculate spatial and longitudinal gradients of O2, prodrug, and effector concentrations, and resulting killing in a digitized 3D tumor microregion to estimate activity as monotherapy and in combination with radiotherapy. An analogous model for a normal tissue with mild hypoxia and short intervessel distances (based on a cremaster muscle microvessel network) was used to estimate tumor selectivity of cell killing. This showed that Class II HAP offer advantages over Class I including higher tumor selectivity and greater freedom to vary prodrug diffusibility and rate of metabolic activation. The model suggests that the largest gains in class II HAP antitumor activity could be realized by optimizing effector stability and prodrug activation rates. We also use the model to show that diffusion of effector into blood vessels is unlikely to materially increase systemic exposure for realistic tumor burdens and effector clearances. However, we show that the tumor selectivity achievable by hypoxia-dependent prodrug activation alone is limited if dose-limiting normal tissues are even mildly hypoxic.

Cytochrome P450 2E1 potentiates ethanol induction of hypoxia and HIF-1α in vivo

Ethanol induces hypoxia and elevates HIF-1α in the liver. CYP2E1 plays a role in the mechanisms by which ethanol generates oxidative stress, fatty liver, and liver injury. This study evaluated whether CYP2E1 contributes to ethanol-induced hypoxia and activation of HIF-1α in vivo and whether HIF-1α protects against or promotes CYP2E1-dependent toxicity in vitro. Wild-type (WT), CYP2E1-knock-in (KI), and CYP2E1 knockout (KO) mice were fed ethanol chronically; pair-fed controls received isocaloric dextrose. Ethanol produced liver injury in the KI mice to a much greater extent than in the WT and KO mice. Protein levels of HIF-1α and downstream targets of HIF-1α activation were elevated in the ethanol-fed KI mice compared to the WT and KO mice. Levels of HIF prolyl hydroxylase 2, which promotes HIF-1α degradation, were decreased in the ethanol-fed KI mice in association with the increases in HIF-1α. Hypoxia occurred in the ethanol-fed CYP2E1 KI mice as shown by an increased area of staining using the hypoxia-specific marker pimonidazole. Hypoxia was lower in the ethanol-fed WT mice and lowest in the ethanol-fed KO mice and all the dextrose-fed mice. In situ double staining showed that pimonidazole and CYP2E1 were colocalized to the same area of injury in the hepatic centrilobule. Increased protein levels of HIF-1α were also found after acute ethanol treatment of KI mice. Treatment of HepG2 E47 cells, which express CYP2E1, with ethanol plus arachidonic acid (AA) or ethanol plus buthionine sulfoximine (BSO), which depletes glutathione, caused loss of cell viability to a greater extent than in HepG2 C34 cells, which do not express CYP2E1. These treatments elevated protein levels of HIF-1α to a greater extent in E47 cells than in C34 cells. 2-Methoxyestradiol, an inhibitor of HIF-1α, blunted the toxic effects of ethanol plus AA and ethanol plus BSO in the E47 cells in association with inhibition of HIF-1α. The HIF-1α inhibitor also blocked the elevated oxidative stress produced by ethanol/AA or ethanol/BSO in the E47 cells. These results suggest that CYP2E1 plays a role in ethanol-induced hypoxia, oxidative stress, and activation of HIF-1α and that HIF-1α contributes to CYP2E1-dependent ethanol-induced toxicity. Blocking HIF-1α activation and actions may have therapeutic implications for protection against ethanol/CYP2E1-induced oxidative stress, steatosis, and liver injury.

Antioxidant and hepatoprotective effect of Garcinia indica fruit rind in ethanol-induced hepatic damage in rodents

The protective effects of aqueous extracts of the fruit rind of Garcinia indica (GIE) on ethanol-induced hepatotoxicity and the probable mechanisms involved in this protection were investigated in rats. Liver damage was induced in rats by administering ethanol (5 g/kg, 20% w/v p.o.) once daily for 21 days. GIE at 400 mg/kg and 800 mg/kg and the reference drug silymarin (200 mg/kg) were administered orally for 28 days to ethanol treated rats, this treatment beginning 7 days prior to the commencement of ethanol administration. Levels of marker enzymes (aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP)), triglyceride (sTG), albumin (Alb) and total protein (TP) were evaluated in serum. Antioxidant parameters (reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR)), hepatic triglycerides (hTG) and the lipid peroxidation marker malondialdehyde (MDA) were determined in liver. GIE and silymarin elicited significant hepatoprotective activity by attenuating the ethanol–elevated levels of AST, ALT, ALP, sTG, hTG and MDA and restored the ethanol-depleted levels of GSH, SOD, CAT, GPx, GR, Alb and TP. GIE 800 mg/kg demonstrated greater hepatoprotection than GIE 400 mg/kg. The present findings indicate that hepatoprotective effects of GIE in ethanol-induced oxidative damage may be due to an augmentation of the endogenous antioxidants and inhibition of lipid peroxidation in liver.

Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy response

Hypoxia and free radicals, such as reactive oxygen and nitrogen species, can alter the function and/or activity of the transcription factor hypoxia-inducible factor 1 (HIF1). Interplay between free radicals, hypoxia and HIF1 activity is complex and can influence the earliest stages of tumour development. The hypoxic environment of tumours is heterogeneous, both spatially and temporally, and can change in response to cytotoxic therapy. Free radicals created by hypoxia, hypoxia-reoxygenation cycling and immune cell infiltration after cytotoxic therapy strongly influence HIF1 activity. HIF1 can then promote endothelial and tumour cell survival. As discussed here, a constant theme emerges: inhibition of HIF1 activity will have therapeutic benefit.

Mouse glucose transporter 9 splice variants are expressed in adult liver and kidney and are up-regulated in diabetes

A novel glucose transporter (GLUT), mouse GLUT9 (mGLUT9), was recently cloned from mouse 7-d embryonic cDNA. Several splice variants of mGLUT9 were described, two of which were cloned (mGLUT9a and mGLUT9a Delta 209-316). This study describes the cloning and characterization of another splice variant, mGLUT9b. Cloned from adult liver, mGLUT9b is identical to mGLUT9a except at the amino terminus. Based on analysis of the genomic structure, the different amino termini result from alternative transcriptional/translational start sites. Expression and localization of these two mGLUT9 splice variants were examined in control and diabetic adult mouse tissues and in cell lines. RT-PCR analysis demonstrated expression of mGLUT9a in several tissues whereas mGLUT9b was observed primarily in liver and kidney. Using a mGLUT9-specific antibody, Western blot analysis of total membrane fractions from liver and kidney detected a single, wide band, migrating at approximately 55 kDa. This band shifted to a lower molecular mass when deglycosylated with peptide-N-glycosidase F. Both forms were present in liver and kidney. Immunohistochemical localization demonstrated basolateral distribution of mGLUT9 in liver hepatocytes and the expression of mGLUT9 in specific tubules in the outer cortex of the kidney. To investigate the alternative amino termini, mGLUT9a and mGLUT9b were overexpressed in kidney epithelium cell lines. Subcellular fractions localized both forms to the plasma membrane. Immunofluorescent staining of polarized Madin Darby canine kidney cells overexpressing mGLUT9 depicted a basolateral distribution for both splice variants. Finally, mGLUT9 protein expression was significantly increased in the kidney and liver from streptozotocin-induced diabetic mice compared with nondiabetic animals.

Antioxidants and fetal protection against ethanol teratogenicity. I. Review of the experimental data and implications to humans

Ethanol is the most common human teratogen, and heavy drinking during pregnancy can result in serious adverse outcomes to the fetus. The cellular mechanisms by which ethanol induces damage in utero are not well understood, while induction of oxidative stress is believed to be one putative mechanism. Our objective is to review the data of antioxidant effects in experimental models of fetal alcohol syndrome. Prior to the description of the available experimental data, we will briefly review the mechanisms leading to ethanol-induced oxidative stress. Ethanol-induced oxidative damage to the fetus could be attenuated by a variety of antioxidants as was documented in whole animal and tissue culture studies. Experiments, retrieved from the literature search, are described and criticized. Although experimental data are still limited, the application of a treatment strategy that includes antioxidants is justified since antioxidant treatment in human pregnancy for pre-eclampsia was demonstrated to be safe and effective. The available experimental evidence and the safety of vitamins C and E in pregnancy suggest that experimental use of antioxidants in alcohol-consuming mothers should be seriously considered to reduce fetal alcohol damage.

Chronic ethanol exposure potentiates lipopolysaccharide liver injury despite inhibiting Jun N-terminal kinase and caspase 3 activation

Although ethanol is known to sensitize hepatocytes to tumor necrosis factor (TNF) lethality, the mechanisms involved remain controversial. Recently, others have shown that adding TNFalpha to cultures of ethanol-pretreated hepatocytes provokes the mitochondrial permeability transition, cytochrome c release, procaspase 3 activation, and apoptosis. Although this demonstrates that ethanol can sensitize hepatocytes to TNF-mediated apoptosis, the hepatic inflammation and ballooning hepatocyte degeneration that typify alcohol-induced liver injury suggest that other mechanisms might predominate in vivo. To evaluate this possibility, acute responses to lipopolysaccharide (LPS), a potent inducer of TNFalpha, were compared in mice that had been fed either an ethanol-containing or control diet for 5 weeks. Despite enhanced induction of cytokines such as interleukin (IL)-10, IL-15, and IL-6 that protect hepatocytes from apoptosis, ethanol-fed mice exhibited a 4-5-fold increase in serum alanine aminotransferase after LPS, confirming increased liver injury. Six h post-LPS histology also differed notably in the two groups, with control livers demonstrating only scattered apoptotic hepatocytes, whereas ethanol-exposed livers had large foci of ballooned hepatocytes, inflammation, and scattered hemorrhage. No caspase 3 activity was noted during the initial 6 h after LPS in ethanol-fed mice, but this tripled by 1.5 h after LPS in controls. Procaspase 8 cleavage and activity of the apoptosis-associated kinase, Jun N-terminal kinase, were also greater in controls. In contrast, ethanol exposure did not inhibit activation of cytoprotective mitogen-activated protein kinases and AKT or attenuate induction of the anti-apoptotic factors NF-kappaB and inducible nitric oxide synthase. Consistent with these responses, neither cytochrome c release, an early apoptotic response, nor hepatic oligonucleosomal DNA fragmentation, the ultimate consequence of apoptosis, was increased by ethanol. Thus, ethanol exacerbates TNF-related hepatotoxicity in vivo without enhancing caspase 3-dependent apoptosis.

Metabolic, idiosyncratic toxicity of drugs: overview of the hepatic toxicity induced by the anxiolytic, panadiplon

Preclinical drug safety evaluation studies, typically conducted in two or more animal species, reveal and define dose-dependent toxicities and undesirable effects related to pharmacological mechanism of action. Idiosyncratic toxic responses are often not detected during this phase in development due to their relative rarity in incidence and differences in species sensitivity. This paper reviews and discusses the metabolic idiosyncratic toxicity and species differences observed for the experimental non-benzodiazepine anxiolytic, panadiplon. This compound produced evidence of hepatic toxicity in Phase 1 clinical trial volunteers that was not predicted by rat, dog or monkey preclinical studies. However, subsequent studies in Dutch-belted rabbits revealed a hepatic toxic syndrome consistent with a Reye's Syndrome-like idiosyncratic response. Investigations into the mechanism of toxicity using rabbits and cultured hepatocytes from several species, including human, provided a sketch of the complex pathway required to produce hepatic injury. This pathway includes drug metabolism to a carboxylic acid metabolite (cyclopropane carboxylic acid), inhibition of mitochondrial fatty acid beta-oxidation, and effects on intermediary metabolism including depletion of glycogen and disruption of glucose homeostasis. We also provide evidence suggesting that the carboxylic acid metabolite decreases the availability of liver CoA and carnitine secondary to the formation of unusual acyl derivatives. Hepatic toxicity could be ameliorated by administration of carnitine, and to a lesser extent by pantothenate. These hepatocellular pathway defects, though not directly resulting in cell death, rendered hepatocytes sensitive to secondary stress, which subsequently produced apoptosis and hepatocellular necrosis. Not all rabbits showed evidence of hepatic toxicity, suggesting that individual or species differences in any step along this pathway may account for idiosyncratic responses. These differences may be roughly applied to other metabolic idiosyncratic hepatotoxic responses and include variations in drug metabolism, effects on mitochondrial function, nutritional status, and health or underlying disease.

Mitochondrial adaptations to obesity-related oxidant stress

It is not known why viable hepatocytes in fatty livers are vulnerable to necrosis, but associated mitochondrial alterations suggest that reactive oxygen species (ROS) production may be increased. Although the mechanisms for ROS-mediated lethality are not well understood, increased mitochondrial ROS generation often precedes cell death, and hence, might promote hepatocyte necrosis. The aim of this study is to determine if liver mitochondria from obese mice with fatty hepatocytes actually produce increased ROS. Secondary objectives are to identify potential mechanisms for ROS increases and to evaluate whether ROS increase uncoupling protein (UCP)-2, a mitochondrial protein that promotes ATP depletion and necrosis. Compared to mitochondria from normal livers, fatty liver mitochondria have a 50% reduction in cytochrome c content and produce superoxide anion at a greater rate. They also contain 25% more GSH and demonstrate 70% greater manganese superoxide dismutase activity and a 35% reduction in glutathione peroxidase activity. Mitochondrial generation of H(2)O(2) is increased by 200% and the activities of enzymes that detoxify H(2)O(2) in other cellular compartments are abnormal. Cytosolic glutathione peroxidase and catalase activities are 42 and 153% of control values, respectively. These changes in the production and detoxification of mitochondrial ROS are associated with a 300% increase in the mitochondrial content of UCP-2, although the content of beta-1 ATP synthase, a constitutive mitochondrial membrane protein, is unaffected. Supporting the possibility that mitochondrial ROS induce UCP-2 in fatty hepatocytes, a mitochondrial redox cycling agent that increases mitochondrial ROS production upregulates UCP-2 mRNAs in primary cultures of normal rat hepatocytes by 300%. Thus, ROS production is increased in fatty liver mitochondria. This may result from chronic apoptotic stress and provoke adaptations, including increases in UCP-2, that potentiate necrosis.

Mechanisms of hepatic microcirculatory disturbances induced by acute ethanol administration in rats, with special reference to alterations of sinusoidal endothelial fenestrae

Elucidation of the hepatic hemodynamics in acute ethanol administration is an issue of clinical importance for better understanding of alcoholic liver diseases. The purpose of this study is to clarify the mechanism of hepatic microcirculatory disturbances after acute ethanol administration, especially regarding the effects of ethanol on alterations of sinusoidal endothelial fenestrae (SEF) and the involvement of endothelin-1 (ET-1) in the mechanism of portal hypertension induced by ethanol. Ethanol was administrated into the portal vein via the mesenteric vein branch of rats as a continuous infusion (4 and 8 mg/min of ethanol) for 60 min. Hepatic tissue blood flow measured with a laser Doppler blood flowmeter was found to be remarkably decreased with time, whereas portal pressure began to increase at 10 min and showed a significant increase by approximately 1.5 cm H2O at 60 min. Ethanol concentrations in blood at 60 min after 4 and 8 mg/min of ethanol infusion were 0.75 mg/ml and 1.77 mg/ml, respectively. At this point, scanning electron microscopy revealed significant decreases in number and diameter of SEF both in zone 1 and zone 3, with the increase in ethanol level. These findings suggested that decreases in number and diameter of SEF, whether primary or secondary, may lead to the impairment of the transport of plasma substances from sinusoids to hepatocytes in acute ethanol administration. Furthermore, the pretreatment of BQ-123 inhibited a decrease in hepatic tissue blood flow and an increase in portal pressure caused by ethanol, indicating that ET-1 may be involved in the mechanism of hepatic circulatory disturbances in acute ethanol administration.

Potentiation of hypoxic injury in cultured rabbit hepatocytes by the quinoxalinone anxiolytic, panadiplon

The quinoxalinone anxiolytic, panadiplon, produces hepatic metabolic inhibition (mitochondrial impairment), microvesicular steatosis and centrilobular necrosis in rabbits. Metabolic inhibition occurs in cultured hepatocytes without cytotoxicity, suggesting that hepatic injury is influenced by additional factors. The present experiments were conducted to determine if metabolic inhibition by panadiplon predisposed hepatocytes to hypoxic injury. Injury (cell death) was evaluated by lactate dehydrogenase (LDH) release from cells; ATP and glycogen levels were also evaluated. Under hypoxic conditions, control cultures showed a 6.5-fold increase in LDH release compared to normoxic controls, with a coincident 80% decrease in ATP and 50% decrease in glycogen levels. Under normoxic conditions 10 microgram/ml panadiplon treatment for 48 h reduced ATP and glycogen levels by 40% but did not cause an increase in LDH leakage. Cells treated with panadiplon, then exposed to hypoxia conditions, showed a significant level of injury compared to normoxic control cultures, and a further reduction in ATP. No additional decrease in glycogen ws observed. In an attempt to prevent panadiplon-mediated injury, glycolytic substrates (dihydroxyacetone or pyruvate) were included during normoxic and hypoxic incubations. Both cotreatments reduced the level of LDH leakage produced by panadiplon during hypoxia. Cotreatment did not generally increase ATP or glycogen levels (compared to panadiplon treatment groups) during hypoxia, though individual experiments showed a slight increase in ATP levels. During normoxia both cotreatments with panadiplon resulted in significantly higher glycogen levels than in panadiplon cultures alone. These results suggest that cellular glycogen and subsequently ATP levels are reduced during panadiplon exposure, metabolically predisposing hepatocytes to hypoxic injury.

Maternal risk factors in fetal alcohol syndrome: provocative and permissive influences

We present an hypothesis integrating epidemiological, clinical case, and basic biomedical research to explain why only relatively few women who drink alcohol during pregnancy give birth to children with alcohol-related birth defects (ARBDs), in particular, Fetal Alcohol Syndrome (FAS). We argue that specific sociobehavioral risk factors, e.g., low socioeconomic status, are permissive for FAS in that they provide the context for increased vulnerability. We illustrate how these permissive factors are related to biological factors, e.g., decreased antioxidant status, which in conjunction with alcohol, provoke FAS/ARBDs in vulnerable fetuses. We propose an integrative heuristic model hypothesizing that these permissive and provocative factors increase the likelihood of FAS/ARBDs because they potentiate two related mechanisms of alcohol-induced teratogenesis, specifically, maternal/fetal hypoxia and free radical formation.

Effect of propylthiouracil treatment on NADPH-cytochrome P450 reductase levels, oxygen consumption and hydroxyl radical formation in liver microsomes from rats fed ethanol or acetone chronically

The antithyroid drug propylthiouracil (PTU) has been shown previously to reduce hepatic oxygen utilization and to protect the liver from ethanol-induced injury. The present study examined the effect of PTU on hepatic microsomal oxygen consumption and on the activities of NADPH-cytochrome P450 reductase (CYP-reductase) and cytochrome P4502E1 (CYP2E1) in rats receiving ethanol or acetone chronically. Liver microsomes from rats treated with ethanol for 29 days displayed increases in (i) O2 consumption (70%), (ii) hydroxyl radical (.OH) production (49%) and (iii) ethanol oxidation (50%). Microsomal CYP2E1 levels were increased markedly by chronic ethanol administration, while CYP-reductase was affected marginally, but not significantly (P = 0.06). Chronic treatment with acetone for 14 days, produced similar effects, except that .OH production was not enhanced. Administration of PTU (25 mg/kg/day) to ethanol- or acetone-fed rats, for 10 and 14 days, respectively, led to a marked reduction in the levels and activity of CYP-reductase, and to a decrease in the rates of microsomal O2 consumption, .OH production and ethanol oxidation, but did not lower the levels of CYP2E1 or the metabolism of the CYP2E1 substrate N,N-nitrosodimethylamine. These data suggest that the ability of PTU to protect the liver from ethanol-induced injury may be due to a reduction in the levels of CYP-reductase, thereby minimizing the enhancement of microsomal oxygen consumption and free radical generation associated with ethanol-induced CYP2E1 activity.

Chronic ethanol treatment induces H2O2 production selectively in pericentral regions of the liver lobule

Chronic treatment with ethanol damages pericentral regions of the liver selectively, and reactive oxygen species such as H2O2 may be involved in the mechanism of hepatotoxicity. To test this idea, the effect of chronic treatment with ethanol on rates of H2O2 production was measured in tissue cylinders isolated from periportal and pericentral regions of livers from ethanol-treated rats. Rates of hydrogen peroxide production, assessed from the oxidation of methanol to formaldehyde by catalase-H2O2, were similar in tissue cylinders isolated from periportal regions in control and ethanol-treated rats. In contrast, rates of H2O2 production were over 4-fold higher in tissue isolated from pericentral regions of livers from ethanol-treated than control animals (1.7 +/- 0.5 vs. 0.4 +/- 0.3 nmol/min/mg protein, respectively). Rates of H2O2-generating acyl CoA oxidase activity were equivalent in tissue cylinders from periportal regions of livers from both groups (approximately 2 nmol/min/mg protein), but were over 2-fold higher in tissue cylinders from pericentral regions of livers from ethanol-treated rats than from controls. In contrast, catalase activity was increased nearly 2-fold in homogenates from both periportal and pericentral regions by ethanol treatment while glutathione peroxidase activity was decreased significantly in both regions. These data demonstrate that ethanol increases H2O2 generation in pericentral regions of the liver lobule in part by elevating rates of peroxisomal beta-oxidation of acyl CoA compounds and are consistent with the hypothesis that local increases in H2O2 production may be involved in the mechanism of ethanol-induced hepatotoxicity.

Ethanol-induced vasoconstriction causes focal hepatocellular injury in the isolated perfused rat liver

The role of microcirculation in the pathogenesis of alcoholic liver injury was investigated in isolated perfused livers from fed rats. Infusion of ethanol into the portal vein at concentrations ranging from 25 to 200 mmol/L increased portal pressure, which is an indicator of hepatic vasoconstriction, in a concentration-dependent fashion. Portal pressure started to rise immediately on initiation of ethanol load and remained at higher than basal levels throughout the period of ethanol infusion. Release of lactate dehydrogenase, an indicator of cell injury, into the effluent perfusate began to increase after 20 to 30 min of ethanol infusion and continued to increase until the end of the experiment (60 min after the initiation of ethanol infusion). The lactate dehydrogenase level in the effluent perfusate at 60 min was dependent on the ethanol concentration (0 mmol/L, 8 +/- 3 IU/L; 25 mmol/L, 22 +/- 3 IU/L; 50 mmol/L, 51 +/- 11 IU/L; 100 mmol/L, 60 +/- 7 IU/L; 200 mmol/L, 120 +/- 7 IU/L). Simultaneous infusion of sodium nitroprusside (100 mumol/L), a known vasodilator, inhibited significantly the ethanol-induced increases in portal pressure and lactate dehydrogenase release by abolishing hepatic vasoconstriction. In histological examinations focal hepatocellular necrosis, evidenced by trypan blue staining of cell nuclei, was detected predominantly in midzonal and pericentral areas of the liver lobule after 60 min of ethanol infusion. Change in portal pressure during 60 min of ethanol infusion correlated significantly with levels of lactate dehydrogenase after ethanol infusion (r = 0.82; p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen dependence of oxidative stress. Rate of NADPH supply for maintaining the GSH pool during hypoxia

NADPH supply for oxidized glutathione (GSSG) reduction was studied in hepatocytes under different steady-state O2 concentrations with controlled infusions of diamide, a thiol oxidant. When bis-chloro-nitrosourea (BCNU) was used to inhibit GSSG reductase, the rate of GSH depletion approximated the rate of diamide infusion, showing that diamide reacted preferentially with GSH under these experimental conditions. Under aerobic conditions without BCNU treatment, the GSH and NADPH pools were largely unaffected and little diamide accumulation or protein thiol oxidation occurred with diamide infusion rates up to 5.3 nmol/10(6) cells per min. However, at greater infusion rates, GSH and NADPH decreased, diamide and GSSG concentrations increased, and protein thiols were oxidized. This critical infusion rate was easily discernible and provided a convenient means to assess the capacity of cells to reduce GSSG as a function of O2 concentration. As the O2 concentration was decreased below 15 microM, the critical infusion rate decreased from the aerobic value of 5.3 to less than 2 nmol/10(6) cells per min in anoxic cells; half-maximal change occurred at 5 microM O2. Although cells could not maintain normal thiol and NADPH pools at infusion rates above the critical value, analysis of the rates of thiol depletion showed that the maximal NADPH supply rate for GSSG reduction under aerobic conditions was 7-8 nmol/10(6) cells per min and was affected by hypoxia to the same degree as the critical value. Thus, hypoxia and anoxia impair the capability of cells to supply NADPH for the reduction of thiol oxidants. This could be an important factor in the sensitivity of hypoxic and ischemic tissues to oxidative injury.

Impaired oxygen utilization. A new mechanism for the hepatotoxicity of ethanol in sub-human primates

The role of oxygenation in the pathogenesis of alcoholic liver injury was investigated in six baboons fed alcohol chronically and in six pair-fed controls. All animals fed alcohol developed fatty liver with, in addition, fibrosis in three. No evidence for hypoxia was found, both in the basal state and after ethanol at moderate (30 mM) or high (55 mM) levels, as shown by unchanged or even increased hepatic venous partial pressure of O2 and O2 saturation of hemoglobin in the tissue. In controls, ethanol administration resulted in enhanced O2 consumption (offset by a commitant increase in splanchnic blood flow), whereas in alcohol fed animals, there was no increase. At the moderate ethanol dose, the flow-independent O2 extraction, measured by reflectance spectroscopy on the liver surface, tended to increase in control animals only, whereas a significant decrease was observed after the high ethanol dose in the alcohol-treated baboons. This was associated with a marked shift in the mitochondrial redox level in the alcohol-fed (but not in control) baboons, with striking rises in splanchnic output of glutamic dehydrogenase and acetaldehyde, reflecting mitochondrial injury. Increased acetaldehyde, in turn, may aggravate the mitochondrial damage and exacerbate defective O2 utilization. Thus impaired O2 consumption rather than lack of O2 supply characterizes liver injury produced by high ethanol levels in baboons fed alcohol chronically.

Treatment of alcoholic liver disease

With advances in our understanding of the pathophysiology of alcoholic liver disease, pharmacological treatments of some of the basic disease processes are now in sight. The most notable development has been the introduction of propylthiouracil for the treatment of alcoholic hepatitis. In a recent trial the mortality rate of patients treated with this drug was 62% lower than that of a control group. Its beneficial effects may stem not from its anti-thyroid properties but rather from other actions such as free radical scavenging. Corticosteroids now appear to have no place in the treatment of alcoholic liver disease. Anabolic steroids, however, show promise, though longer term trials are required before this can be confirmed. Colchicine, too, has been reported to improve survival in patients with established cirrhosis. More experience is required with this and other anti-inflammatory and anti-fibrogenic drugs. beta Adrenergic blocking drugs, such as propranolol, reduce portal venous pressure. In a trial among patients with alcoholic cirrhosis who had oesophageal varices, 39% of those receiving propranolol had not experienced a haemorrhage by 2 years compared with 74% in the control group. The mortality rates at this time were 28% and 49% respectively. Results of treatment once the first haemorrhage has occurred are less impressive. Treatment of the alcohol withdrawal syndrome in patients with liver disease is often problematic. The dose of any sedative should be reduced to 25-50% of the usual dose and sedatives should be avoided in patients who are encephalopathic. Once the patient has recovered from the acute illness, abstinence from alcohol remains the single most important factor that determines long term survival.

Long-term treatment of alcoholic liver disease with propylthiouracil

Propylthiouracil has been shown experimentally to protect against alcohol-induced hepatocellular necrosis in hypoxic conditions. An earlier, short-term study of patients with alcoholism and liver disease indicated clinical improvement with propylthiouracil, but the effect on mortality could not be assessed. In the present study, we investigated the effect of propylthiouracil on mortality in patients with alcoholic liver disease in a long-term, double-blind, randomized clinical trial involving 310 compliant patients who received propylthiouracil (n = 157) or placebo (n = 153) for a maximum of two years. There were no differences between the two groups in demographic and clinical characteristics and biopsy-confirmed diagnoses at randomization, or in daily urinary alcohol levels during the study. The cumulative dropout rate over two years was not significantly different (propylthiouracil group, 0.68; placebo group, 0.60). The group receiving propylthiouracil (300 mg per day) had a cumulative mortality rate half that in the group receiving placebo (0.13 vs. 0.25 [P less than 0.05] in the total sample, and 0.25 vs. 0.55 [P less than 0.03] in a subgroup of severely ill patients [propylthiouracil group, n = 56; placebo group, n = 41]). Proportional-hazards stepwise regression analyses indicated that only propylthiouracil treatment, prothrombin time, hemoglobin levels, and mean daily urinary alcohol levels significantly affected mortality. The hazards ratio for the complete group indicated that mortality in the propylthiouracil group was 0.38 (95 percent confidence interval, 0.20 to 0.83) that of the placebo group. Protection by propylthiouracil was not observed in patients with high morning urinary alcohol levels. No clinically important side effects of propylthiouracil were observed at the dose used. We conclude that the administration of propylthiouracil can reduce mortality due to alcoholic liver disease.

Role of alcohol dehydrogenase in the swift increase in alcohol metabolism (SIAM). Studies with deer mice deficient in alcohol dehydrogenase

Previous studies have shown that rates of ethanol metabolism increase markedly 2-4 hr after the administration of ethanol in rats and in four inbred strains of mice. This phenomenon, called the swift increase in alcohol metabolism (SIAM), also exists in humans. To determine whether alcohol dehydrogenase (ADH) is necessary for the SIAM response, we compared ethanol metabolism in two strains of the deer mouse, Peromyscus maniculatus. One strain lacks alcohol dehydrogenase (ADH-negative), whereas the other strain has normal ADH levels (ADH-positive). Rates of ethanol elimination were determined after a single intraperitoneal injection of ethanol at different doses (0.5 to 3.0 g/kg) and also after both strains were exposed to various levels of ethanol vapor for 4 hr. The ADH-positive strain exhibited up to a 72% increase in the rate of ethanol elimination after exposure to ethanol vapor compared to the ethanol-injected controls. In contrast, treatment with ethanol vapor did not alter rates of ethanol elimination in the ADH-negative strain. These data demonstrate clearly that ADH is required for SIAM in the deer mouse. In addition, in both the ADH-positive and the ADH-negative strain, rates of ethanol elimination increased in both the ethanol-injected and vapor-treated groups 2- to 3-fold as the dose of ethanol was increased from 100 to 500 mg/100 ml. Thus, it is concluded that this "concentration effect" of ethanol on rates of ethanol metabolism does not involve ADH in the . deer mouse.

Sublobular compartmentation of pharmacologic events (SCOPE): metabolic fluxes in periportal and pericentral regions of the liver lobule

New techniques have been developed employing microlight guides and miniature O2 electrodes which permit metabolic events to be studied noninvasively in periportal and pericentral zones of the liver lobule. These events include O2 uptake, fat and carbohydrate metabolism, monooxygenation and glucuronidation. The lobular distribution of maximal enzyme activities measured by immunohistochemical or microchemical techniques does not always correlate with metabolic flux rates as measured in periportal and pericentral regions with the new noninvasive methods. The region of the liver lobule exhibiting highest metabolic flux rates can be shifted to another region of the lobule by changing the direction of flow from anterograde to retrograde. These data are consistent with the hypothesis that many metabolic pathways (e.g., oxygen, carbohydrate and fat metabolism which are under dynamic short-term regulation) operate below maximal velocity in intact hepatocytes.