Ethanol alters the metabolic response of isolated perfused rat liver to a phagocytic stimulus

Laboratory models available to study alcohol-induced organ damage and immune variations: choosing the appropriate model

The morbidity and mortality resulting from alcohol-related diseases globally impose a substantive cost to society. To minimize the financial burden on society and improve the quality of life for individuals suffering from the ill effects of alcohol abuse, substantial research in the alcohol field is focused on understanding the mechanisms by which alcohol-related diseases develop and progress. Since ethical concerns and inherent difficulties limit the amount of alcohol abuse research that can be performed in humans, most studies are performed in laboratory animals. This article summarizes the various laboratory models of alcohol abuse that are currently available and are used to study the mechanisms by which alcohol abuse induces organ damage and immune defects. The strengths and weaknesses of each of the models are discussed. Integrated into the review are the presentations that were made in the symposium "Methods of Ethanol Application in Alcohol Model-How Long is Long Enough" at the joint 2008 Research Society on Alcoholism (RSA) and International Society for Biomedical Research on Alcoholism (ISBRA) meeting, Washington, DC, emphasizing the importance not only of selecting the most appropriate laboratory alcohol model to address the specific goals of a project but also of ensuring that the findings can be extrapolated to alcohol-induced diseases in humans.

Role of free radicals in failure of fatty liver grafts caused by ethanol

Alcohol is associated with accidental deaths and suicides leading to organ donation, and hepatic steatosis is an important risk factor for initial poor function and failure of human liver grafts. Mechanisms of fatty graft failure are not fully understood, but increased oxidative stress may be a major factor. To characterize the role of free radical stress and the efficacy of antioxidant treatments in fatty liver graft injury, donors for orthotopic rat liver transplantation were treated chronically (3 or more weeks) and acutely (single dose) with ethanol. After transplantation, necrosis and alanine aminotransferase release were threefold to fourfold higher in recipients of fatty grafts from donors treated with ethanol either acutely or chronically compared with findings for recipients of grafts from untreated donors. Moreover, graft survival decreased from nearly 100% to less than 20%. Free radical adducts, as measured by electron spin resonance spectroscopy, were detected in the blood and bile of rats receiving fatty grafts caused by ethanol. Markers of lipid peroxidation also increased after transplantation. Destruction of Kupffer cells with gadolinium chloride decreased free radical production and improved graft survival. Leukocyte adhesion increased beginning early after implantation, and adherent white blood cells obtained from transplanted fatty livers produced the same free radical species as were detected in blood. Therefore, Kupffer cells and adherent white blood cells are important sources of free radicals. Free radicals not only damage fatty grafts directly but also lead to enhanced inflammation and disturbed microcirculation. Delivery of superoxide dismutase-1 and superoxide dismutase-2 genes, free radical-scavenging polyphenols, and antioxidant-containing Carolina Rinse solution reduced injury and improved survival of fatty grafts caused by ethanol. Taken together, these findings indicate that free radicals increase in fatty grafts after transplantation and play an important role in injury of fatty grafts obtained from ethanol-exposed donors. Treatment of fatty donor livers with antioxidants and free radical scavengers may thus be an effective clinical therapy to prevent failure of fatty grafts.

Vascular function in alcohol-treated pregnant and nonpregnant mice

The effect of alcohol on maternal vascular adaptations to pregnancy is unknown. This study was designed to determine the effect of alcohol consumption on nitric oxide-mediated vascular function in mice during pregnancy. Female pregnant or nonpregnant C57BL/6J mice were fed a control diet or a liquid diet of 25% ethanol-derived calories for 13 days (from gestational days 6-18). Phenylephrine vasoconstriction was blunted in pregnancy compared with the nonpregnant state due to enhanced nitric oxide modulation, which was impaired by ethanol exposure. Although the EC50 and maximal responses to methacholine were not different in nonpregnant vs. pregnant mice, the nitric oxide component to methacholine-induced vasorelaxation was greater in the pregnant mice. Interestingly, alcohol affected only the pregnant animals in their response to methacholine. These data indicate that alcohol reduced the nitric oxide modulation of vascular response, which was more pronounced during pregnancy. These studies provide novel information regarding the effects of alcohol on the maternal vascular system during pregnancy and thereby contribute to further understanding of the adverse effects associated with prenatal alcohol exposure.

Ethanol metabolism by macrophages: possible role in organ damage

Macrophages and hepatocytes oxidize ethanol to acetate in vitro at comparable rates but by different biochemical pathways. Ethanol metabolism by macrophages is largely ADH-independent and mainly based on cytochrome P450 and on the extracellular release of superoxide anion radicals. There is also evidence that during ethanol metabolism, macrophages release more acetaldehyde extracellularly than hepatocytes; the high concentrations of acetaldehyde around macrophages may damage surrounding tissue cells. Some of this acetaldehyde forms unstable cytotoxic complexes with serum albumin and with erythrocytes. The superoxide anion radicals released by macrophages may not only oxidize ethanol to acetaldehyde but also react with and damage cells in their immediate vicinity. After exposure to ethanol, macrophage-depleted rodents show markedly reduced levels of cytotoxic acetaldehyde-albumin complexes in the blood and reduced levels of hydroxyethyl radicals in the bile compared to control animals, indicating that the generation of such potentially pathogenic molecules is, to a large extent, dependent on macrophage activity. Macrophage-depleted animals also show less early liver damage than control animals. The reduction in ethanol-induced liver damage in macrophage-depleted mice and rats may be due to a reduction or elimination of the generation of various Kupffer-cell-derived hepatotoxic substances, including acetaldehyde and reactive oxygen radicals, in such animals. These data suggest that ethanol metabolism by tissue macrophages may play an important role in mediating ethanol-related tissue damage.

II. Alcoholic liver injury involves activation of Kupffer cells by endotoxin

It is well known that females show a greater susceptibility to alcohol-induced liver injury than males. Additionally, females who consume alcohol regularly and have been obese for 10 years or more are at greater risk for both hepatitis and cirrhosis. Female rats on an enteral alcohol protocol exhibit injury more quickly than males, with widespread fatty changes over a larger portion of the liver lobule. Levels of plasma endotoxin, intercellular adhesion molecule-1, free radical adducts, infiltrating neutrophils, and nuclear factor-kappaB are increased about twofold more in livers from female than male rats after enteral alcohol treatment. Estrogen treatment in vivo increases the sensitivity of Kupffer cells to endotoxin. Evidence has been presented that Kupffer cells are pivotal in the development of alcohol-induced liver injury. Destruction of Kupffer cells with gadolinium chloride (GdCl3) or reduction of bacterial endotoxin by sterilization of the gut with antibiotics blocks early inflammation due to alcohol. Similar results have been obtained with anti-tumor necrosis factor-alpha antibody. These findings led to the hypothesis that alcohol-induced liver injury involves increases in circulating endotoxin, leading to activation of Kupffer cells, which causes a hypoxia-reoxygenation injury. This idea has been tested using pimonidazole, a nitroimidazole marker, to quantitate hypoxia in downstream pericentral regions of the liver lobule. After chronic enteral alcohol, pimonidazole binding increases twofold. Enteral alcohol also increases free radicals detected with electron spin resonance. Importantly, hepatic hypoxia and radical production detected in bile are decreased by destruction of Kupffer cells with GdCl3. These data are consistent with the hypothesis that Kupffer cells participate in important gender differences in liver injury caused by alcohol.

Stimulation of oxygen uptake by prostaglandin E2 is oxygen dependent in perfused rat liver

The aim of this study was to determine if the effect of prostaglandin E2 (PGE2) on hepatic oxygen uptake was affected by oxygen tension. Livers from fed female Sprague-Dawley rats were perfused at normal or high flow rates (4 or 8 ml . g-1 . min-1) to vary local oxygen tension within the liver lobule. During perfusion at normal flow rates, PGE2 (5 microM) infusion increased oxygen uptake by about 50 micromol . g-1 . h-1; however, when livers were perfused at high flow rates, the increase was nearly twice as large. Simultaneously, glucose output was increased rapidly by about 50%, whereas glycolysis was decreased about 60%. When flow rate was held constant, increases in oxygen uptake due to PGE2 were proportional to oxygen delivery. Infusion of PGE2 into livers perfused at normal flow rates increased state 3 rates of oxygen uptake of subsequently isolated mitochondria by about 25%; however, rates were increased 50-75% in mitochondria isolated from livers perfused at high flow rates. Thus it is concluded that PGE2 stimulates oxygen uptake via mechanisms regulated by oxygen tension in perfused rat liver. High flow rates also increased basal rates of oxygen uptake: this increase was prevented by inactivation of Kupffer cells with GdCl3. In addition, conditioned medium from Kupffer cells incubated at high oxygen tension (75% oxygen) stimulated oxygen uptake of isolated parenchymal cells by >30% and elevated PGE2 production about twofold compared with Kupffer cells exposed to normal air-saturated buffer (21% oxygen). These effects were blocked completely by both indomethacin and nisoldipine. These data support the hypothesis that oxygen stimulates Kupffer cells to release mediators such as PGE2 which elevate oxygen consumption in parenchymal cells, possibly by mechanisms involving cyclooxygenase and calcium channels.

The role of gut-derived bacterial toxins and free radicals in alcohol-induced liver injury

Previous research from this laboratory using a continuous enteral ethanol (EtOH) administration model demonstrated that Kupffer cells are pivotal in the development of EtOH-induced liver injury. When Kupffer cells were destroyed using gadolinium chloride (GdCl₃ ) or the gut was sterilized with polymyxin B and neomycin, early inflammation due to EtOH was blocked. Anti-tumour necrosis factor (TNF)-α antibody markedly decreased EtOH-induced liver injury and increased TNF-mRNA. These findings led to the hypothesis that EtOH-induced liver injury involves increases in circulating endotoxin leading to activation of Kupffer cells. Pimonidazole, a nitro-imidazole marker, was used to detect hypoxia in downstream pericentral regions of the lobule. Following one large dose of EtOH or chronic enteral EtOH for 1 month, pimonidazole binding was increased significantly in pericentral regions of the liver lobule, which was diminished with GdCl₃ . Enteral EtOH increased free radical generation detected with electron spin resonance (ESR). These radical species had coupling constants matching α-hydroxyethyl radical and were shown conclusively to arise from EtOH based on a doubling of the ESR lines when ¹³ C-EtOH was given. α-Hydroxyethyl radical production was also blocked by the destruction of Kupffer cells with GdCl₃ . It is known that females develop more severe EtOH-induced liver injury more rapidly and with less EtOH than males. Female rats on the enteral protocol exhibited more rapid injury and more widespread fatty changes over a larger portion of the liver lobule than males. Plasma endotoxin, ICAM-1, free radical adducts, infiltrating neutrophils and transcription factor NFκB were approximately two-fold greater in livers from females than males after 4 weeks of enteral EtOH treatment. Furthermore, oestrogen treatment increased the sensitivity of Kupffer cells to endotoxin. These data are consistent with the hypothesis that Kupffer cells participate in important gender differences in liver injury caused by ethanol.

Role of free radicals in primary nonfunction of marginal fatty grafts from rats treated acutely with ethanol

Acute treatment with one large dose of ethanol, which mimics binge drinking, causes marginal fatty liver and decreases survival significantly after liver transplantation in rats, yet mechanisms remain unclear. Therefore, we evaluated the possible role of free radicals in primary nonfunction caused by acute ethanol. Female donor rats were administered ethanol (5 g/kg orally) 20 hr before explantation, and grafts were stored in UW cold storage solution for 24-42 hr before implantation. Free radicals were trapped with alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone after transplantation, and adducts were detected using electron spin resonance spectrometry. Ethanol increased a carbon-centered radical adduct in bile approximately 2-fold and elevated serum lipid hydroperoxides approximately 4-fold. Ethanol also increased transaminase release 3.7-fold and decreased bile production by 55%. Catechin, a free radical scavenger, minimized the increase in free radicals, blunted transaminase release, and elevated bile production significantly, indicating that free radical production plays an important role in ethanol-induced fatty graft injury. GdCl3 (20 mg/kg intravenously), a selective Kupffer cell toxicant, largely blocked the increases in free radical and lipid hydroperoxide production caused by ethanol. In addition, ethanol nearly doubled white blood cell adhesion after transplantation, leading to increased superoxide production in fatty grafts. GdCl3 largely blocked leukocyte adhesion as well as superoxide production. Allopurinol, an inhibitor of xanthine oxidase, also diminished free radical production, blunted transaminase release, and improved bile production in fatty grafts significantly. Taken together, we conclude that free radical formation increases in ethanol-induced fatty grafts due mainly to activation of Kupffer cells and increased adhesion of white blood cells. Antioxidants can effectively block free radical formation and minimize injury to marginal fatty grafts caused by binge drinking.

Transient liver accumulation of Tc-99m phytate in hepatocellular carcinoma after percutaneous ethanol injection

PURPOSE

We report that colloid liver scanning gave early evidence of the return to normal of Kupffer cell functions after ethanol injections into the liver.

PATIENT AND METHODS

A 71-year-old man with hepatocellular carcinoma received percutaneous ethanol injections twice of 15 mL of ethanol, 1 week apart.

RESULTS

Abdominal CT after the second injection showed an irregularly shaped low-density area in the left side of the tumor, extending outside the tumor. Liver imaging with To-99m phytate 10 days later showed increased activity at the corresponding site. Thirty days after the second injection, liver imaging did not show high activity.

CONCLUSIONS

Ethanol that leaked into the normal part of the liver probably temporarily activated Kupffer cell function.

Hepatic sinusoidal endothelial cell in alcoholemia and endotoxemia

The experimental data reviewed in this study tend to indicate that the hepatic sinusoidal endothelial cell (SEC) is, chronologically, the first hepatic cell that undergoes pathologic changes in alcoholemia. Due to its strategic position in the liver sinusoid, SEC dysfunction and structural alterations have far-reaching repercussions for the whole liver. The authors gather experimental evidence suggesting that alcohol-induced SEC alterations are mostly due to Kupffer cell activation induced by alcohol rather than to a direct action of alcohol on SEC. Once activated, the Kupffer cell secretes a spectrum of mediators that affect both function and structure of SEC. Kupffer cell activation is regarded as a result of both direct and indirect actions of alcohol on the cell. The indirect action of alcohol is ascribed to alcohol-induced elevated plasma levels of Gram-negative bacterial lipopolysaccharide (LPS), a strong activator of Kupffer cell. However, a comparison of alcohol and LPS effects on SEC functions and structure reveals that these two agents may have, under many circumstances, different actions on the SEC, at least in laboratory animals. However, this issue continues to be a matter of debate. Also the review presents justification for the necessity to extend research on mechanisms underlying alcoholic liver disease to the effects of alcohol on the SEC. Finally, several future research directions are suggested in this review to better understand the mechanisms underlying alcohol-induced liver dysfunction.

Phagocytic function and metabolite production in thioacetamide-induced liver cirrhosis: a comparative study in perfused livers and cultured Kupffer cells

BACKGROUND/AIMS

The aim of the study presented here was to evaluate the basal and stimulated phagocytic activities and the metabolite production of isolated perfused livers, and also the phagocytic capacity of cultured Kupffer cells from rats with macronodular cirrhosis.

METHODS

Rats were made cirrhotic by oral administration of thioacetamide. The phagocytic activity was assessed by the rate of removal of colloidal carbon. The Kupffer cells were prepared by a pronase/collagenase digestion method followed by elutriation.

RESULTS

The phagocytic activity and production of glucose, lactate and pyruvate were reduced in cirrhotic livers when calculated per g liver. Due to hyperplastic-regenerative processes the mass of the cirrhotic livers was markedly augmented so that the colloidal carbon uptake calculated per cirrhotic liver was not significantly different from the controls. Colloidal carbon-induced glucose release increased more markedly in the controls than in cirrhotic livers. Isoproterenol considerably stimulated phagocytosis and glucose production in controls, whereas the response was clearly reduced in cirrhotic livers when calculated either per g liver or per total liver weight. The cyclic AMP analogue elicited a marked glycogenolytic response in the controls, whereas there was only a slight increase in glucose production in cirrhotic livers. Phagocytosis of cirrhotic livers was only moderately stimulated by opsonized zymosan when compared with the controls. Freshly isolated Kupffer cells exhibited a reduced phagocytic activity. Stimulation by zymosan was observed only in cell suspensions of the controls. In contrast, Kupffer cells from cirrhotic livers did not differ from controls with respect to basal or zymosan-stimulated phagocytic activity after 48-h cultivation.

CONCLUSION

The stimulated phagocytic function was disturbed in perfused macronodular-cirrhotic livers as compared to controls. In contrast, 48-h cultured Kupffer cells from cirrhotic livers exhibited the same basal and stimulated phagocytic capacity as controls. The glucose release from perfused livers, initiated by stimulation of Kupffer cells or hepatocytes, was significantly reduced in cirrhotic livers. Therefore, we postulate an impaired intra- and/or intercellular signalling in macronodular-cirrhotic livers.

Role of Kupffer cells in failure of fatty livers following liver transplantation and alcoholic liver injury

Kupffer cells have been implicated in mechanisms of pathophysiology following liver transplantation. Recently, postoperative injury in ethanol-induced fatty liver has been evaluated because fatty livers often fail following transplantation. The low-flow, reflow liver perfusion model was used to study the role of Kupffer cells (KC) in reperfusion injury to fatty livers from rats fed a diet containing ethanol for 4-5 weeks. Treatment with GdCl3, which selectively destroys KC, decreased cell death significantly. Thus, destruction of KC minimized hepatic reperfusion injury, most likely by inhibiting free radical formation and improving microcirculation. Since it was demonstrated recently that destruction of KC prevented the hypermetabolic state observed with acute alcohol exposure, their involvement in events leading to alcohol-induced liver disease was investigated. In rats exposed to ethanol continuously via intragastric feeding for up to 4 weeks, GdCl3 treatment prevented elevation of aspartate aminotransferase (AST) and dramatically reduced the average hepatic pathological score. These results indicate that KC participate in the early phases of alcohol-induced liver injury. Endotoxaemia occurs in alcoholics and activates KC; therefore, we evaluated the effect of minimizing bacterial endotoxin by intestinal sterilization with the antibiotics polymyxin B and neomycin. Antibiotics diminished plasma endotoxin levels significantly and prevented ethanol-induced increases in AST values. These results indicate that endotoxin is involved in the mechanism of ethanol-induced liver injury. A six-line radical spectrum was detected with electron paramagnetic resonance spectroscopy in bile from alcohol-treated rats which was blocked by GdCl3. The free radical adducts had hyperfine coupling constants characteristic of lipid-derived free radical products. In conclusion, these studies demonstrate that KC are involved in reperfusion injury to ethanol-induced fatty livers and hepatic injury due to long-term treatment with ethanol.

Expression of tumor necrosis factor-alpha and interleukin-6 cell-surface receptors of the alveolar macrophage in alcohol-treated rats

The hypothesis was tested that alcohol may modulate alveolar macrophage cytokine receptors, thus interfering in lung immune defense mechanisms. Male rats were treated with alcohol either acutely (7 hr continuous intravenous alcohol infusion at a rate of 30 mg/100 g body weight/hr after a priming dose of 175 mg/100 g body weight) or chronically (feeding an alcohol-containing liquid diet for 12-14 weeks). Three hr before killing, the rats received an intravenous injection of Gram-negative bacterial lipopolysaccharide (LPS; Escherichia coli, O26:B6, 100 micrograms/100 g body weight). After anesthesia with sodium pentobarbital, the trachea was cannulated, and the lungs excised and lavaged to obtain alveolar macrophages. The recovered cells were used to measure the binding of recombinant human [125I]tumor necrosis factor-alpha (TNF-alpha) and [125I]interleukin-6 (IL-6). Kd and Bmax were determined at 4 degrees C, thus reflecting only the cell-surface binding sites and their affinity. Two binding sites were detected for both cytokines: high-affinity (Kd1 in the range of 20-110 pM), low-capacity (Bmax1 in the range of 1-13 fmol/10(6) cells), and low-affinity (Kd2 in the range of 0.6-1.3 nM), high-capacity (Bmax2 in the range of 34-100 fmol/10(6) cells). Acute alcohol treatment significantly decreased Bmax1 (39%) and Bmax2 (79%) for TNF-alpha, whereas chronic alcohol feeding abrogated the Bmax1 (Bmax1 = 0), without affecting Bmax2. In the acute group, LPS had an effect similar to that of alcohol. Alcohol administration did not modify the LPS effects. The following changes were monitored for IL-6 binding. Acute alcohol treatment markedly reduced (86%) Bmax2.(ABSTRACT TRUNCATED AT 250 WORDS)

Inactivation of Kupffer cells prevents early alcohol-induced liver injury

It is well recognized that consumption of alcohol leads to liver disease in a dose-dependent manner; however, the exact mechanisms remain unclear. Hypoxia subsequent to a hypermetabolic state may be involved; therefore, when it was observed recently that inactivation of Kupffer cells prevented stimulation of hepatic oxygen uptake by alcohol, the idea that Kupffer cells participate in early events that ultimately lead to alcohol-induced liver disease became a real possibility. The purpose of this study was to test that hypothesis. Male Wistar rats were exposed to ethanol continuously by means of intragastric feeding for up to 4 weeks using the model developed by Tsukamoto and French. In this model, ethanol causes fatty liver, necrosis and inflammation--changes characteristic of alcohol-induced liver disease in human beings. Kupffer cells were inactivated by twice weekly treatment with gadolinium chloride (GdCl3), a selective Kupffer cell toxicant. AST levels were elevated to 192 +/- 13 and 244 +/- 56 IU/L in rats exposed to ethanol for 2 and 4 wk, respectively (control value, 88 +/- 7). This injury was prevented almost completely by GdCl3 treatment. Fatty changes, inflammation and necrosis were also all reduced dramatically by GdCl3 treatment. The average hepatic pathological score of rats treated with ethanol for 4 wk was 4.3 +/- 0.6, which was reduced significantly in ethanol- and GdCl3-treated rats to 1.8 +/- 0.5 (p < 0.05). Rates of ethanol elimination were elevated 2- to 3-fold in rats exposed to ethanol for 2 to 4 wk. This elevation was blocked by GdCl3 treatment.(ABSTRACT TRUNCATED AT 250 WORDS)