Changes of hepatic microtubules and secretory proteins in human alcoholic liver disease

Targeting the cytoskeleton as a therapeutic approach to substance use disorders

Substance use disorders (SUD) are chronic relapsing disorders governed by continually shifting cycles of positive drug reward experiences and drug withdrawal-induced negative experiences. A large body of research points to plasticity within systems regulating emotional, motivational, and cognitive processes as drivers of continued compulsive pursuit and consumption of substances despite negative consequences. This plasticity is observed at all levels of analysis from molecules to networks, providing multiple avenues for intervention in SUD. The cytoskeleton and its regulatory proteins within neurons and glia are fundamental to the structural and functional integrity of brain processes and are potentially the major drivers of the morphological and behavioral plasticity associated with substance use. In this review, we discuss preclinical studies that provide support for targeting the brain cytoskeleton as a therapeutic approach to SUD. We focus on the interplay between actin cytoskeleton dynamics and exposure to cocaine, methamphetamine, alcohol, opioids, and nicotine and highlight preclinical studies pointing to a wide range of potential therapeutic targets, such as nonmuscle myosin II, Rac1, cofilin, prosapip 1, and drebrin. These studies broaden our understanding of substance-induced plasticity driving behaviors associated with SUD and provide new research directions for the development of SUD therapeutics.

Alcohol-associated capillarization of sinusoids: A critique since the discovery by Schaffner and Popper in 1963

This article reviews the literature on capillarization of hepatic sinusoids since its discovery in 1963. Liver sinusoidal endothelial cells are uniquely fenestrated and lack an underlying basement membrane. In chronic liver disease, the sinusoids capillarize and transform into systemic capillaries, a process termed capillarization of sinusoids. The histopathology is marked by defenestration, basement membrane formation, and space of Disse fibrogenesis. Capillarized sinusoids compromise the bidirectional exchange of materials between sinusoids and hepatocytes, leading to hepatocellular dysfunction. Sinusoidal capillarization was first described in active cirrhosis of alcoholics in 1963. Since then, it has been found in early and progressive stages of alcoholic hepatic fibrosis before the onset of cirrhosis. The sinusoidal structure is not altered in alcoholic steatosis without fibrosis. Defenestration impairs the ability of the endothelium to filter chylomicron remnants from sinusoids into the Disse's space, contributing to alcohol-induced postprandial hyperlipidemia and possibly atherosclerosis. Ethanol also modulates the fenestration dynamics in animals. In baboons, chronic alcohol consumption diminishes endothelial porosity in concomitance with hepatic fibrogenesis and in rats defenestrates the endothelium in the absence of fibrosis, and sometimes capillarizes the sinusoids. Acute ethanol ingestion enlarges fenestrations in rats and contracts fenestrations in rabbits. In sinusoidal endothelial cell culture, ethanol elicits fenestration dilation, which is likely related to its interaction with fenestration-associated cytoskeleton. Ethanol potentiates sinusoidal injury caused by cocaine, acetaminophen or lipopolysaccharide in mice and rats. Understanding ethanol's mechanisms on pathogenesis of sinusoidal capillarization and fenestration dynamics will lead to development of methods to prevent risks for atherosclerosis in alcoholism.

Increased hepatocellular protein carbonylation in human end-stage alcoholic cirrhosis

OBJECTIVE

Oxidative stress is a significant contributing factor in the pathogenesis of alcoholic liver disease (ALD). In the murine models of chronic alcohol consumption, induction of oxidative stress results in increased peroxidation of polyunsaturated fatty acids to form highly reactive electrophilic α/β unsaturated aldehydes that post-translationally modify proteins altering activity. Data are presented here suggesting that oxidative stress and the resulting carbonylation of hepatic proteins is an ongoing process involved in alcohol-induced cirrhosis.

METHODS

Using age-matched pooled hepatic tissue obtained from healthy humans and patients with end stage cirrhotic ALD, overall carbonylation was assessed by immunohistochemistry and LC-MS/MS of streptavidin purified hepatic whole cell extracts treated with biotin hydrazide. Identified carbonylated proteins were further evaluated using bioinformatics analyses.

RESULTS

Using immunohistochemistry and Western blotting, protein carbonylation was increased in end stage ALD occurring primarily in hepatocytes. Mass spectrometric analysis revealed a total of 1224 carbonylated proteins in normal hepatic and end-stage alcoholic cirrhosis tissue. Of these, 411 were unique to cirrhotic ALD, 261 unique to normal hepatic tissue and 552 common to both groups. Bioinformatic pathway analysis of hepatic carbonylated proteins revealed a propensity of long term EtOH consumption to increase post-translational carbonylation of proteins involved in glutathione homeostatic, glycolytic and cytoskeletal pathways. Western analysis revealed increased expression of GSTA4 and GSTπ in human ALD. Using LC-MS/MS analysis, a nonenaldehyde post-translational modification was identified on Lysine 235 of the cytoskeletal protein vimentin in whole cell extracts prepared from human end stage ALD hepatic tissue.

CONCLUSIONS

These studies are the first to use LC-MS/MS analysis of carbonylated proteins in human ALD and begin exploring possible mechanistic links with end-stage alcoholic cirrhosis and oxidative stress.

Emerging roles of actin cytoskeleton regulating enzymes in drug addiction: actin or reactin'?

Neurons rely on their cytoskeleton to give them shape and stability, and on cytoskeletal dynamics for growth and synaptic plasticity. Because drug addiction is increasingly seen as the inappropriate learning of strongly reinforcing stimuli, the role of the cytoskeleton in shaping drug memories has been of increasing interest in recent years. Does the cytoskeleton have an active role in shaping these memories, and to what extent do alterations in the cytoskeleton reflect the acute actions of drug exposure, or homeostatic reactions to the chronic exposure to drugs of abuse? Here we will review recent advances in understanding the role of the cytoskeleton in the development of drug addiction, with a focus on actin filaments, as they have been studied in greater detail.

Hepatocellular ballooning in nonalcoholic steatohepatitis: the pathologist's perspective

Nonalcoholic fatty liver disease (NAFLD) is an important complication of the metabolic syndrome. The increasing prevalence of the metabolic syndrome is paralleled by an increasing prevalence of NAFLD, which has become one of the most common chronic liver diseases. NAFLD comprises a morphological spectrum ranging from nonalcoholic fatty liver (NAFL), characterized by accumulation of fat in hepatocytes, to nonalcoholic steatohepatitis (NASH). The key histological features of NASH accepted by most pathologists include steatosis, hepatocellular ballooning and lobular inflammation, whereas, like in other chronic liver diseases, the presence of fibrosis is not considered a requirement for the diagnosis. The diagnosis of NASH and the distinction from NAFL carries important prognostic and therapeutic implications because NASH, in contrast to NAFL, is associated with an increased risk of progression to cirrhosis and hepatocellular carcinoma. Hepatocellular ballooning is a key feature required for the diagnosis of NASH and a component of currently used histological grading and staging systems of NAFLD. However, it represents an ill-defined form of liver cell injury associated with cell swelling and rounding of the cytoplasm, the detection of which is prone to intra- as well as inter-observer variation. Some of the factors that may contribute to ballooning are the rearrangement of the intermediate filament cytoskeleton, accumulation of small-droplet fat in the cytoplasm and dilation of the endoplasmic reticulum. The rearrangement of the intermediate filament cytoskeleton can be demonstrated by the loss of keratin 8/18 immunostaining of the cytoplasm, and may thus be evaluated in the future as a marker for the more objective detection of hepatocellular ballooning in NASH.

Ballooned hepatocytes in steatohepatitis: the value of keratin immunohistochemistry for diagnosis

BACKGROUND/AIMS

Hepatocyte "ballooning" is an often used but ill defined term in liver pathology to designate a special form of liver cell degeneration associated with cell swelling and enlargement found particularly in steatohepatitis. Alterations of the intermediate filament cytoskeleton of the hepatocyte may contribute to the pathogenesis of this microscopic change. Ballooning degeneration is considered a hallmark of steatohepatitis, but enlarged hepatocytes may also be observed in a variety of other acute and chronic liver diseases.

METHODS

The intermediate filament cytoskeleton was investigated using keratin 8 and 18 immunohistochemistry in liver diseases associated with enlarged or ballooned hepatocytes.

RESULTS

Keratin 8/18 immunostaining was drastically reduced or lost in the cytoplasm of ballooned hepatocytes in alcoholic and non-alcoholic steatohepatitis, chronic cholestatic conditions, ischemia/reperfusion injury and in ballooned hepatocytes in chronic hepatitis C cases with concurrent steatohepatitis. In contrast, substantial decrease or loss of keratin 8/18 immunostaining was not noted in cases of acute hepatitis, giant cell hepatitis, chronic hepatitis B, or autoimmune hepatitis.

CONCLUSIONS

Loss of keratin 8/18 immunostaining can serve as an objective marker of a specific type of ballooning degeneration of hepatocytes. Oxidative stress may be a common denominator in the pathogenesis of keratin filament alterations in these conditions.

Biochemical markers for alcohol consumption

A variety of laboratory tests are available to assist in the diagnosis of alcohol consumption and related disorders. The levels of intake at which laboratory results become abnormal vary from person to person. Laboratory tests are particularly useful in settings where cooperativeness is suspected or when a history is not available. Several biochemical and hematological tests, such as γ-glutamyltransferase (GGT) activity, aspartate aminotransferase (AST) activity, high-density lipoprotein cholesterol (HDL-C) content of serum, and erythrocyte mean corpuscular volume (MCV) are established markers of alcohol intake. Their validity as markers is based largely on correlations with recent intake at a single time point and on decreases in elevated values when heavy drinkers abstain from alcohol. These readily available laboratory tests provide important prognostic information and should be integral part of the assessment of persons with hazardous alcohol consumption. There are several other markers with considerable potential for more accurate reflection of recent alcohol intake. These include carbohydrate deficient transferrin, β-hexosaminidase, acetaldehyde adducts and the urinary ratio of serotonin metabolites, 5-hydroxytryptophol and 5-hydroxyindoleacetic acid. These markers provide hope for more sensitive and specific aids to diagnosis and improved monitoring for intake.

The cytoskeleton of digestive epithelia in health and disease

The mammalian cell cytoskeleton consists of a diverse group of fibrillar elements that play a pivotal role in mediating a number of digestive and nondigestive cell functions, including secretion, absorption, motility, mechanical integrity, and mitosis. The cytoskeleton of higher-eukaryotic cells consists of three highly abundant major protein families: microfilaments (MF), microtubules (MT), and intermediate filaments (IF), as well as a growing number of associated proteins. Within digestive epithelia, the prototype members of these three protein families are actins, tubulins, and keratins, respectively. This review highlights the important structural, regulatory, functional, and unique features of the three major cytoskeletal protein groups in digestive epithelia. The emerging exciting biological aspects of these protein groups are their involvement in cell signaling via direct or indirect interaction with a growing list of associated proteins (MF, MT, IF), the identification of several disease-causing mutations (IF, MF), the functional role that they play in protection from environmental stresses (IF), and their functional integration via several linker proteins that bridge two or potentially all three of these groups together. The use of agents that target specific cytoskeletal elements as therapeutic modalities for digestive diseases offers potential unique areas of intervention that remain to be fully explored.

In vitro evaluation of dose-effects of ethanol on human osteoblastic cells

Chronic alcoholism represents a high risk for fractures and osteopenia. Previous histomorphometric studies reported a decreased bone formation, but it has never been established whether ethanol has a direct toxic effect on osteoblasts. This present in vitro study was performed on human osteoblast cells derived from bone explants after collagenase digestion. The direct effect of ethanol was determined after 4 days of exposure to various doses, ranging from 0.01 to 5 g/l on the alkaline phosphatase (AP) activity, osteocalcin secretion and [3H]thymidine incorporation. The influence of the duration of exposure to 0.8 g/l ethanol was also determined. A significant and dose-dependent decrease in the cell proliferation was observed. AP activity was significantly decreased by high doses of ethanol (2-5 g/l). A biphasic effect of ethanol was noted on osteocalcin secretion according to the dose: it decreased at doses lower than 0.8 g/l and increased at the highest concentrations. At the dose of 0.8 g/l, whatever the duration of exposure, the decrease of the proliferation was of the same magnitude and no significant change in AP activity was observed. Significant ethanol-induced effects on osteocalcin secretion were observed only after 4 and 8 days of exposure. These data demonstrate that ethanol may have a direct toxic effect on osteoblast activity and proliferation. This could be one of the mechanisms of alcohol-induced osteopenia which has a multifactorial pathophysiology.

Changes in liver and spleen volumes in alcoholic liver disease

Liver and spleen volumes were determined using computed tomography in 57 subjects with alcoholic liver disease and 76 subjects with nonalcoholic liver disease, in order to clarify the clinical characteristics and pathogenetic mechanisms of portal hypertension in alcoholic liver disease. The liver volumes in alcoholic liver disease were significantly larger than those in nonalcoholic liver disease, except in cases of decompensated liver cirrhosis. The increase in liver volume in alcoholic liver disease showed a significant correlation with the degree of hepatocytic ballooning. Overlapping of values for liver volume between alcoholic and nonalcoholic liver disease was quite small, suggesting that determination of liver volumes could be helpful for making etiological diagnoses in chronic liver disease. Spleen volumes were increased in the advanced cases of both alcoholic and nonalcoholic liver disease. The correlations between liver and spleen volumes were quite different between alcoholic and nonalcoholic liver disease. In nonalcoholic liver disease, a negative correlation was obtained, while, on the other hand, it was significantly positive in alcoholic liver disease. This appears to suggest that the pathogenetic mechanism of portal hypertension may differ between the diseases. After abstinence from alcohol, the decrease in liver and spleen volumes showed a statistically significant correlation, suggesting that ballooning of the hepatocytes may play a role in the augmentation of portal hypertension in alcoholic liver disease.

Effects of malotilate on alcoholic liver injury in rats

Malotilate (diisopropyl 1,3-dithio-2-yldenemalonate), a hepatotrophic drug, was administered to rats with alcohol-pyrazole hepatitis, which is considered to be a suitable experimental model for alcoholic liver injury, in order to elucidate the effects of malotilate on alcoholic liver injury. The number of ballooned hepatocytes and necrotic hepatocytes were smaller in the alcohol-pyrazole hepatitis rats treated with malotilate for 12 weeks (Al-Py Mal group) than for those without malotilate treatment (Al-Py group). Immunohistochemically, the retention of transferrin, one of the secretory proteins from the liver, in the ballooned hepatocytes was inhibited by malotilate. Biochemically, transferrin content in the Golgi fraction of the hepatocytes was significantly lower in the Al-Py Mal group than in the Al-Py group. Hepatic acetaldehyde levels in the Al-Py Mal group were significantly lower than those in the Al-Py group, even though ethanol metabolic rates were not different between the two groups. These results indicated that malotilate prevented the development of hepatocytic injury in alcohol-pyrazole hepatitis by decreasing hepatic acetaldehyde levels and preventing the retention of transferrin in the hepatocytes.

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC Working Paper No. 15/2. Metabolism and metabolic effects of ethanol, including interaction with drugs, carcinogens and nutrition

Different pathways of alcohol metabolism, the alcohol dehydrogenase pathway, the microsomal ethanol-oxidizing system and the catalase pathway are discussed. Alcohol consumption leads to accelerated ethanol metabolism by different mechanisms including an increased microsomal function. Microsomal induction leads to interactions of ethanol with drugs, hepatotoxic agents, steroids, vitamins and to an increased activation of mutagens/carcinogens. A number of ethanol-related complications may be explained by the production of its first metabolite, acetaldehyde, such as alterations of mitochondria, increased lipid peroxidation and microtubular alterations with its adverse effects on various cellular activities, including disturbances of cell division. Nutritional factors in alcoholics such as malnutrition are discussed especially with respect to its possible relation to cancer.

Stimulatory effects of ethanol on amino acid transport by rat fetal hepatocytes

Previous studies have indicated that acute, and especially chronic, maternal ethanol consumption can depress placental uptake of various amino acids. Since the fetal cell itself represents a second barrier to nutrients, one which may be altered by ethanol exposure, the effects of ethanol on amino acid net uptake by rat fetal hepatocytes was addressed. The present study determined that ethanol stimulated amino acid net uptake by fetal hepatocytes grown in monolayer culture. Fetal liver cells were grown in custom Williams' E medium (without L-arginine and with L-ornithine) and exposed to epidermal growth factor (0, 1, 2 or 5 ng per ml) and ethanol (1.7 +/- 0.1 or 3.9 +/- 0.2 mg per ml). Addition of ethanol (3.9 mg per ml) to the culture medium completely blocked measurable cell replication during a 48-hr exposure period. Fetal hepatocytes exposed to ethanol accrued both protein and water in a parallel fashion, both in excess of that by control cells. Ethanol (1.7 and 3.9 mg per ml) for 48 hr stimulated alpha-aminoisobutyric acid net uptake by fetal hepatocytes (p less than 0.05). Efflux was not affected (p greater than 0.05). The onset of this significant stimulation of net uptake was progressive and required in excess of 6 hr of contact with ethanol. This ethanol stimulation of alpha-aminoisobutyric acid net uptake persisted for at least 24 hr following ethanol withdrawal. The component(s) of alpha-aminoisobutyric acid net uptake stimulated by ethanol was independent of extracellular Na+.(ABSTRACT TRUNCATED AT 250 WORDS)

Long term alcohol consumption induces microtubular changes in the adult rat cerebellar cortex

The effects of prolonged alcohol consumption on the microtubules of Purkinje cell dendrites and granule cell axons were studied in adult rats fed alcohol for 1, 3, 6, 12 and 18 months and compared with respective age-matched controls. A significant consequential decrease in the number of dendritic microtubules in alcohol-fed rats was found when compared with the respective controls. Conversely, an increase in the number of these organelles was found in both ascending and parallel portion of the axons in the experimental animals. The possibility of a relationship between microtubular changes and previously reported cerebellar cortex alcohol-induced structural alterations is advanced.

Comparison between ballooned hepatocytes occurring in human alcoholic and nonalcoholic liver diseases

To establish clearly what the pathogenetic differences are in the hepatocytic ballooning between human alcoholic and nonalcoholic liver diseases, hepatic microtubules were examined by morphometric and biochemical methods, and staining of transferrin was carried out on liver sections immunohistochemically. Microheterogeneity of serum transferrin was also detected by immunofixation after isoelectric focusing. Hepatic microtubules were significantly decreased in alcoholic liver disease, and transferrin was clearly stained in the ballooned hepatocytes of alcoholic liver disease but not in nonalcoholic liver disease. The degree to which transferrin was stained was related to hepatic microtubular contents and also related to the appearance of the microheterogeneity of serum transferrin in alcoholic liver disease. These findings indicate that ballooning of hepatocytes in alcoholic liver disease, but not in nonalcoholic liver disease, is caused by the accumulation of exportable proteins due to impairment of microtubular polymerization. This accumulation might be related to the inhibition of glycosylation and secretion of glycoproteins by the impairment of microtubular functions. From these results, it was determined that staining of transferrin in the liver may be useful for differentiation of the etiology of liver diseases.

Biochemical markers of chronic alcoholism

Usefulness of several biochemical markers for the monitoring of chronic alcoholism were studied. Among generally used markers, only gamma-GTP showed a significant difference between alcoholic and non-alcoholic liver diseases. Serum glutamate dehydrogenase (GDH) activity was significantly high in alcoholic liver disease. When the ratios of GDH to ornithine carbamyl transferase (OCT) were calculated, differences between alcoholic and non-alcoholic liver diseases became clearer without overlapping of any value. Serum desialo-transferrin was found in about 60% of the alcoholics, and disappeared by abstinence. Microheterogeneity of serum protein was also found in other glycoproteins. Serum prealbumin level was significantly high in alcoholics without severe liver disease. Acetaldehyde dehydrogenase (ALDH) activity of erythrocytes was significantly low in alcoholics, and gradually increased after abstinence. These results indicate that microheterogeneity of glycoproteins, serum prealbumin level and erythrocyte ALDH activity are good markers of alcohol abuse, and serum GDH/OCT ratio is the most sensitive marker of alcoholic liver injury. Serum gamma-GTP activity is a good marker of both conditions.

Comparison of ballooned hepatocytes in alcoholic and non-alcoholic liver injury in rats

Ballooned hepatocytes are commonly observed in alcoholic and sometimes in non-alcoholic liver diseases. To clarify whether pathogenesis of this change is different in alcoholic and non-alcoholic liver diseases, changes of the livers in rats fed alcohol with pyrazole for 12 weeks were compared with those of CCl4 treated rats. Both groups of rats showed marked ballooning of the hepatocytes in the centrolobular area. Immunohistochemically, the ballooned hepatocytes in alcohol-pyrazole treated rats reacted strongly with transferrin and albumin staining. However, staining reaction of the ballooned hepatocytes in the CCl4 treated rats was slight. In alcohol-pyrazole treated rats, hepatic microtubules were significantly decreased. Retention of transferrin and albumin were found only in the ballooned hepatocytes of alcohol-pyrazole treated rats. However, in the CCl4 treated rats, neither microtubular alteration nor retention of the exportable proteins was observed. These findings indicate that the pathogenesis of ballooning of hepatocytes is different in alcoholic and non-alcoholic liver injuries. In alcoholic liver injury, microtubular alteration may lead to retention of protein and ballooning of hepatocytes by interfering with the hepatic secretion of proteins.