Direct effects of alcohol on hepatic fibrinolytic balance: implications for alcoholic liver disease

BACKGROUND/AIMS

The pathogenesis of alcoholic liver disease (ALD) remains uncertain. Fibrin production and degradation are altered in experimental liver injury. We have recently identified increased expression of a number of genes (annexin A2 (ANXA2), p11, tPA and PAI-1) that implicate fibrinolysis in ALD progression. Aim of our study was to study the direct effect of alcohol on fibrinolysis and plasmin activity in hepatic cell lines and in vivo.

METHODS

Expression of pro- and anti-fibrinolytic genes was determined in liver biopsies from patients with progressive ALD and in HepG2, Huh7 and LX-2 cells exposed to alcohol. The functional effects on fibrinolysis and plasmin activities were determined. C57BL6 female mice were given a single dose of alcohol and serum and liver triglyceride content and serum plasmin activity determined.

RESULTS

Alcohol induced a significant up-regulation of ANXA2, PLG, PAI-1 and p11 in human ALD, cell lines and in mice exposed to alcohol. Up-regulation of ANXA2 and p11 was inhibited by the alcohol dehydrogenase inhibitor 4-methylpyrazole. Fibrinolysis and plasmin were increased in HepG2 and LX-2 cells by 10mM alcohol and was inhibited by ANXA2 blocking antibody. Plasmin also increased in mice given a moderate dose of alcohol. By contrast, there was striking up-regulation of PAI-1 in mice given a high dose of alcohol with associated decrease in plasmin.

CONCLUSIONS

Alcohol directly alters hepatic expression of pro- and anti-fibrinolytic genes in a dose dependent manner with low dose promoting fibrinolysis and high dose inhibiting fibrinolysis. After a large dose of alcohol in vivo, the dominant effect was up-regulation of hepatic PAI-1 with suppression of plasmin. The effect of alcohol on fibrinolysis and plasmin is mediated in part by ANXA2. Alcohol directly influences hepatic pathways of fibrinolysis that may contribute to ALD.

Mechanism by which Alcohol and Wine Polyphenols Affect Coronary Heart Disease Risk

The reduction in coronary heart disease (CHD) from moderate alcohol intake may be mediated, in part, by increased fibrinolysis; endothelial cell (EC)-mediated fibrinolysis should decrease acute atherothrombotic consequences (eg, plaque rupture) of myocardial infarction (MI). We have shown that alcohol and individual polyphenols modulate EC fibrinolytic protein (t-PA, u-PA, PAI-1, u-PAR and Annexin-II) expression at the cellular, molecular, and gene levels to sustain increased fibrinolytic activity. Herein we describe the sequence of molecular events by which EC t-PA expression is increased through common activation of p38 MAPK signaling. Up-regulation of t-PA gene transcription, through specific alcohol and polyphenol transcription factor binding sites in the t-PA promoter, results in increased in vitro fibrinolysis and in vivo clot lytic activity (using real-time fluorescence [Fl] imaging of Cy5.5-labeled fibrin clot lysis in a mouse model). Fl-labeled fibrin clots injected into untreated C56Bl/6 wild-type control mice are lysed in approximately 2 hours and clot lytic rates significantly increased in mice treated with either alcohol, catechins, or quercetin (4-6 weeks). Fl-labeled clot lysis in ApoE knock-out mice (atherosclerosis model) showed impaired in vivo clot lysis that was "normalized" to wild-type control levels by treatment with alcohol, catechin, or quercetin for 6 to 8 weeks.

Induction of the expression of cardioprotective proteins after mild-to-moderate consumption of alcohol

A growing body of evidence supports the notion that mild-to-moderate alcohol consumption is associated with a reduced incidence of mortality and morbidity from coronary heart disease. While the cardioprotective effects of wine have been attributed to the polyphenolic antioxidants present in the wines, the mechanism(s) of cardioprotection afforded by alcohol consumption remain speculative. The present study demonstrates an induction of the expression of several cardioprotective proteins in the rat hearts after 3 weeks of low dose of alcohol consumption. These cardioprotective proteins include heat shock protein 70 (HSP 70), heme oxygenase 1 (HO-1) and manganese superoxide dismutase (MnSOD). Alcohol consumption also improved post-ischemic ventricular function and reduced myocardial infarct size and cardiomyocyte apoptosis. The results of the present study suggest a role of these cardioprotective proteins in alcohol-mediated cardioprotection.

Ethanol-Induced Activation of Myosin Light Chain Kinase Leads to Dysfunction of Tight Junctions and Blood-Brain Barrier Compromise

BACKGROUND

Brain endothelial cells form the blood-brain barrier (BBB) that regulates solute and macromolecule flux in and out of the brain, leukocyte migration, and maintains the homeostasis of the central nervous system. BBB dysfunction is associated with disruption of tight junctions (TJ) in the brain endothelium. We propose that alcohol abuse may impair BBB permeability through TJ modification.

METHODS

Primary cultured bovine brain microvascular endothelial cells (BBMEC) were treated with 50 mM ethanol (EtOH), and monolayer tightness was assessed by measurement of transendothelial electrical resistance (TEER). Changes in TEER were correlated with alterations in TJ protein distribution [occludin, zonula occludens-1 (ZO-1), claudin-5] using immunofluorescence (IF). Expression of myosin light chain (MLC) kinase (MLCK), ZO-1, claudin-5, and phosphorylated MLC, occludin and claudin-5 were determined by immunoprecipitation and Western blot. EtOH-induced changes in monocyte migration across in vitro BBB constructs were also examined.

RESULTS

EtOH induced a decrease in TEER of BBMEC monolayers that was reversed by EtOH withdrawal. Treatment of BBMEC with EtOH or its metabolite, acetaldehyde, prior to monocyte application resulted in a 2-fold increase in monocyte migration across the BBB. IF demonstrated decrease in claudin-5 staining, occludin translocation from cell borders to cytoplasm and gap formation in EtOH-treated BBMEC monolayer. These changes paralleled significant increase in phosphorylation of MLC, occludin and claudin-5. EtOH-treated BBMEC showed reduction of total occludin and claudin-5 without changes in ZO-1 or MLC. TEER decrease, changes in occludin/claudin staining, increase in MLC, occludin and claudin-5 phosphorylation and enhanced monocyte migration across the BBB were all reversed by inhibition of MLCK. Inhibition of EtOH metabolism in BBMEC also reversed these events.

CONCLUSION

These results suggest that EtOH activates MLCK leading to phosphorylation of MLC, occludin and claudin-5. Cytoskeletal alterations (MLC) and TJ changes (occludin and claudin-5 phosphorylation) result in BBB impairment (decrease in TEER). TJ compromise is associated with increased monocyte migration across the BBB.

Gene expression profiling of alcoholic liver disease in the baboon (Papio hamadryas) and human liver

The molecular pathogenesis of alcoholic liver disease (ALD) is not well understood. Gene expression profiling has the potential to identify new pathways and altered molecules in ALD. Gene expression profiles of ALD in a baboon model and humans were compared using DNA arrays. Reverse transcriptase-polymerase chain reaction and immunohistochemistry were used for downstream analysis of array results. cDNA array analysis revealed differential expression of several novel genes and pathways in addition to genes known to be involved in ALD pathogenesis. Overall gene expression profiles were similar in both species, with a majority of genes involved with fibrogenesis and xenobiotic metabolism, as well as inflammation, oxidant stress, and cell signaling. Genes associated with stellate cell activation (collagens, matrix metalloproteinases, tissue inhibitors of matrix metalloproteinase) were up-regulated in humans. Decreased expression of several metallothioneins was unexpected. Fourteen molecules related to the annexin family were up-regulated, including annexin A1 and A2. Immunofluorescence revealed a marked overexpression of annexin A2 in proliferating bile duct cells, hepatocyte cell surface, and selective co-localization with CD14-positive cells in human ALD. The gene expression profile of ALD is dominated by alcohol metabolism and inflammation and differs from other liver diseases. Annexins may play a role in the progression of fibrosis in ALD.

Effects of alcohol on the heart

Some evidence suggests that light to moderate alcohol consumption protects against cardiovascular diseases. However, this cardioprotective effect of alcohol consumption in adults is absent at the population level. Approximately 20 to 30% of patients admitted to a hospital are alcohol abusers. In medical practice, it is essential that patients' levels of consumption are known because of the many adverse effects that might result in the course of routine care. Ethanol damage to the heart is evident if alcohol consumption exceeds 90 to 100 g/d. Heavy ethanol consumption leads to increased risk for sudden cardiac death and cardiac arrhythmias. In patients with coronary heart disease, alcohol use was associated with increased mortality. An early response to drinking was an increased ventricular wall thickness to diameter ratio, possibly proceeding with continuous drinking to alcoholic cardiomyopathy, which had a worse outcome compared with idiopathic dilative cardiomyopathy if drinking was not stopped or at least reduced (< 60 g/d). In the ICU, patients with chronic alcoholism have more cardiac complications postoperatively. These complications probably are caused by biventricular dysfunction, particularly with the occurrence of severe infections or septic shock, events that are three to four times more frequent among chronic alcoholics than occasional drinkers or nondrinkers. To prevent further complications from drinking and for long-term management of drinking, patients with alcohol abuse and heart failure should be treated in brief intervention and follow-up programs. Prognosis is good even in patients with New York Heart Association class IV heart failure caused by cardiomyopathy if complete abstinence is accomplished. Noncompliance to smoking and alcohol restrictions, which are amenable to change, dramatically increases the risk for hospital readmissions among patients with heart failure.