The Involvement of Acetaldehyde in Ethanol-Induced Cell Cycle Impairment.

BACKGROUND: Hepatocytes metabolize the vast majority of ingested ethanol. This metabolic activity results in hepatic toxicity and impairs the ability of hepatocytes to replicate. Previous work by our group has shown that ethanol metabolism results in a G2/M cell cycle arrest. The intent of these studies was to discern the roles of acetaldehyde and reactive oxygen, two of the major by-products of ethanol metabolism, in the G2/M cell cycle arrest. METHODS: To investigate the role of ethanol metabolites in the cell cycle arrest, VA-13 and VL-17A cells were used. These are recombinant Hep G2 cells that express alcohol dehydrogenase or alcohol dehydrogenase and cytochrome P450 2E1, respectively. Cells were cultured with or without ethanol, lacking or containing the antioxidants N-acetylcysteine (NAC) or trolox, for three days. Cellular accumulation was monitored by the DNA content of the cultures. The accumulation of the cyclin-dependent kinase, Cdc2 in the inactive phosphorylated form (p-Cdc2) and the cyclin-dependent kinase inhibitor p21 were determined by immunoblot analysis. RESULTS: Cultures maintained in the presence of ethanol demonstrated a G2/M cell cycle arrest that was associated with a reduction in DNA content and increased levels of p-Cdc2 and p21, compared with cells cultured in its absence. Inclusion of antioxidants in the ethanol containing media was unable to rescue the cells from the cell cycle arrest or these ethanol metabolism-mediated effects. Additionally, culturing the cells in the presence of acetaldehyde alone resulted in increased levels of p-Cdc2 and p21. CONCLUSIONS: Acetaldehyde produced during ethanol oxidation has a major role in the ethanol metabolism-mediated G2/M cell cycle arrest, and the concurrent accumulation of p21 and p-Cdc2. Although reactive oxygen species are thought to have a significant role in ethanol-induced hepatocellular damage, they may have a less important role in the inability of hepatocytes to replace dead or damaged cells.

Alcoholic pancreatitis: New insights into the pathogenesis and treatment.

Acute pancreatitis is a necro-inflammatory disease of the exocrine pancreas that is characterized by inappropriate activation of zymogens, infiltration of the pancreas by inflammatory cells, and destruction of the pancreatic exocrine cells. Acute pancreatitis can progress to a severe life-threatening disease. Currently there is no pharmacotherapy to prevent or treat acute pancreatitis. One of the more common factors associated with acute pancreatitis is alcohol abuse. Although commonly associated with pancreatitis alcohol alone is unable to cause pancreatitis. Instead, it appears that alcohol and its metabolic by-products predispose the pancreas to damage from agents that normally do not cause pancreatitis, or to more severe disease from agents that normally cause mild pancreatic damage. Over the last 10 to 20 years, a tremendous amount of work has defined a number of alcohol-mediated biochemical changes in pancreatic cells. Among these changes are: Sustained levels of intracellular calcium, activation of the mitochondrial permeability transition pore, endoplasmic reticulum stress, impairment in autophagy, alteration in the activity of transcriptional activators, and colocalization of lysosomal and pancreatic digestive enzymes. Elucidation of these changes has led to a deeper understanding of the mechanisms by which ethanol predisposes acinar cells to damage. This greater understanding has revealed a number of promising targets for therapeutic intervention. It is hoped that further investigation of these targets will lead to the development of pharmacotherapy that is effective in treating and preventing the progression of acute pancreatitis.

Molecular mechanisms of alcohol associated pancreatitis.

Alcohol abuse is commonly associated with the development of both acute and chronic pancreatitis. Despite this close association, the fact that only a small percentage of human beings who abuse alcohol develop pancreatitis indicates that alcohol abuse alone is not sufficient to initiate clinical pancreatitis. This contention is further supported by the fact that administration of ethanol to experimental animals does not cause pancreatitis. Because of these findings, it is widely believed that ethanol sensitizes the pancreas to injury and additional factors trigger the development of overt pancreatitis. How ethanol sensitizes the pancreas to pancreatitis is not entirely known. Numerous studies have demonstrated that ethanol and its metabolites have a number of deleterious effects on acinar cells. Important acinar cells properties that are affected by ethanol include: calcium signaling, secretion of zymogens, autophagy, cellular regeneration, the unfolded protein response, and mitochondrial membrane integrity. In addition to the actions of ethanol on acinar cells, it is apparent that ethanol also affects pancreatic stellate cells. Pancreatic stellate cells have a critical role in normal tissue repair and the pathologic fibrotic response. Given that ethanol and its metabolites affect so many pancreatic functions, and that all of these effects occur simultaneously, it is likely that none of these effects is "THE" effect. Instead, it is most likely that the cumulative effect of ethanol on the pancreas predisposes the organ to pancreatitis. The focus of this article is to highlight some of the important mechanisms by which ethanol alters pancreatic functions and may predispose the pancreas to disease.

Ethanol administration impairs pancreatic repair after injury.

OBJECTIVES: Alcohol abuse is one of the most common factors associated with acute and chronic pancreatitis. Although it is evident that alcohol abuse can have an important role in the development of pancreatitis, it does not seem that alcohol abuse alone is responsible for this disease. We investigated the involvement of ethanol in the impairment of pancreatic repair after induction of pancreatitis. METHODS: A biologically relevant mouse model of alcoholic pancreatitis, combining long-term ethanol consumption and coxsackievirus infection, was used to investigate the effects of ethanol on pancreatic regeneration. Tissues were harvested and analyzed by reverse transcription-polymerase chain reaction and immunoblot. RESULTS: These studies demonstrate that long-term ethanol consumption impairs the structural repair of the exocrine pancreas. This is accompanied by a delay in the restitution of lipase expression. In addition, impaired expression of the critical pancreatic transcription factors, PDX1 and PTF1, and the mediator of Notch signaling, HES1, was observed. CONCLUSIONS: Long-term ethanol consumption impairs the structural repair and functional restitution of the pancreas after severe injury. These impairments may, in part, be explained by the impaired expression of factors important in the development and maintenance of the exocrine pancreas. Impaired pancreatic regeneration may have a role in the pathogenesis of alcoholic pancreatitis.

Ethanol metabolism activates cell cycle checkpoint kinase, Chk2.

Chronic ethanol abuse results in hepatocyte injury and impairs hepatocyte replication. We have previously shown that ethanol metabolism results in cell cycle arrest at the G2/M transition, which is partially mediated by inhibitory phosphorylation of the cyclin-dependent kinase, Cdc2. To further delineate the mechanisms by which ethanol metabolism mediates this G2/M arrest, we investigated the involvement of upstream regulators of Cdc2 activity. Cdc2 is activated by the phosphatase Cdc25C. The activity of Cdc25C can, in turn, be regulated by the checkpoint kinase, Chk2, which is regulated by the kinase ataxia telangiectasia mutated (ATM). To investigate the involvement of the regulators of Cdc2 activity, VA-13 cells, which are Hep G2 cells modified to efficiently express alcohol dehydrogenase, were cultured in the presence or absence of 25 mM ethanol. Immunoblots were performed to determine the effects of ethanol metabolism on the activation of Cdc25C, Chk2, and ATM. Ethanol metabolism increased the active forms of ATM and Chk2, as well as the phosphorylated form of Cdc25C. Additionally, inhibition of ATM resulted in approximately 50% of the cells being rescued from the G2/M cell cycle arrest and ameliorated the inhibitory phosphorylation of Cdc2. Our findings demonstrated that ethanol metabolism activates ATM. ATM can activate the checkpoint kinase Chk2, resulting in phosphorylation of Cdc25C and ultimately in the accumulation of inactive Cdc2. This may, in part, explain the ethanol metabolism-mediated impairment in hepatocyte replication, which may be important in the initiation and progression of alcoholic liver injury.