Chronic ethanol ingestion potentiates TNF-alpha-mediated oxidative stress and apoptosis in rat type II cells

Mitochondrial Glutathione and Chemically Induced Stress Including Ethanol

The mechanisms of alcohol toxicity as related to mitochondrial dysfunction and the glutathione-dependent protective systems are reviewed. The pathophysiology of ethanol-induced liver damage is defined in terms of an early phase and a late phase. CYP2E1 dependent toxicity appears closely related to oxidative stress injury with possible roles of peroxynitrite, TNFalpha, protein adducts, and enhanced protein expression. Modulation of mitochondrial glutathione affects mitochondrial function and cell survival with superoxide and hydrogen peroxide generation being crucial to mitochondrial membrane permeability transition and apoptosis.

Transforming Growth Factor β1Expression and Activation Is Increased in the Alcoholic Rat Lung

Alcohol abuse increases the incidence of acute respiratory distress syndrome more than threefold in patients with septic shock. We have shown that chronic ethanol ingestion in a rat model impairs alveolar epithelial barrier function and enhances lung injury during sepsis. We speculated that transforming growth factor beta(1) (TGFbeta(1)), a pluripotent cytokine implicated in models of epithelial barrier disruption and lung injury, could mediate alveolar epithelial injury in the alcoholic lung. We report that chronic ethanol ingestion (6 weeks) in rats increased both TGFbeta(1) mRNA and protein tissue expression (p < 0.05), but alone did not induce the release of TGFbeta(1) into the alveolar space. However, during endotoxemia, ethanol-fed rats released fivefold more TGFbeta(1) protein (by ELISA, p < 0.05) into the alveolar space than control-fed rats. Furthermore, lung lavage fluid from endotoxemic, ethanol-fed rats had more biologically active TGFbeta(1) protein than control-fed rats (p < 0.05), as reflected by anti-TGFbeta(1) antibody-inhibitable induction of permeability in rat alveolar epithelial monolayers in vitro. We conclude that chronic ethanol ingestion increases lung expression of TGFbeta(1,) which, during endotoxemia, is released and activated in the alveolar space in which it can disrupt the normally tight epithelial barrier. We speculate that this mechanism could contribute to the increased risk of acute respiratory distress syndrome in alcoholic patients.

Chronic ethanol ingestion and the risk of acute lung injury: a role for glutathione availability?

Although pulmonary function is not altered, a history of alcohol abuse is an independent outcome variable in the development of acute respiratory distress syndrome. In the absence of cirrhosis, alcohol abuse decreased glutathione, the key antioxidant lining the alveolar space, by 80% and is associated with alveolar barrier leak. Neither the glutathione pool nor barrier leak was corrected by abstinence for 1 week. This aberrant glutathione homeostasis may contribute to enhanced alveolar permeability, thereby increasing susceptibility to the development of acute respiratory distress syndrome. In a rat model, chronic ingestion of ethanol decreased pulmonary glutathione concentration, increased alveolar barrier permeability, and increased the risk of acute lung injury. In alveolar type II cells, chronic ingestion of ethanol altered cellular functions such as decreased surfactant processing, decreased barrier integrity, and increased sensitivity to cytotoxin-induced apoptosis in vitro and in vivo. In alveolar macrophages, chronic ingestion of ethanol decreased phagocytosis of microorganisms and decreased cell viability, events that would increase the risk of pneumonia. A central role for glutathione availability was demonstrated by the normalization of cellular function and viability of type II cells and macrophages as well as decreased sensitivity to endotoxemia-induced acute lung injury when glutathione precursors were added to the ethanol diet. These results support the suggestion that chronic ingestion of ethanol increased the risk of acute lung injury not through ethanol per se but through the chronic oxidative stress that resulted from ethanol-induced glutathione depletion. Because chronic oxidative stress alters cellular functions and viability, the lung becomes more susceptible when a second hit such as sepsis occurs.

Enhanced pulmonary and systemic response to endotoxin in transgenic sickle mice

Some suggest that sickle cell disease (SCD) is associated with a "proinflammatory state" that predisposes patients to acute chest syndrome in the setting of triggering factors. Conflicting data emerged when inflammation markers in SCD were compared with healthy individuals. Therefore, we examined transgenic sickle and control mice at baseline and with endotoxin (LPS) intraperitoneal injection to determine whether a proinflammatory state truly exists. At baseline, sickle mice had elevated levels of circulating leukocytes and soluble vascular cell adhesion molecule 1 (sVCAM-1). No other differences were observed at baseline or in response to saline. However, LPS challenge was associated with significant increases in mortality (p<0.05), airway tone (p<0.03), serum and bronchoalveolar lavage levels of cytokines tumor necrosis factor-alpha (p<0.03), interleukin-1beta (p<0.02), and sVCAM-1 (p<0.01) in sickle mice compared with control subjects. Furthermore, 4 hours after LPS, microarray analysis identified 413 genes differentially expressed in the sickle mice (n=5) compared with only 7 in the control subjects (n=5). No difference in lung parenchyma was observed by light microscopy. This enhanced response to LPS suggests that the sickle red blood cell confers a subclinical "proinflammatory state." This enhanced response to inflammatory insult, particularly by adhesion molecules such as sVCAM-1, could play a role in the increased susceptibility to pulmonary dysfunction that has been observed clinically in SCD.

Pneumocystis pneumonia increases the susceptibility of mice to sublethal hyperoxia

Patients with Pneumocystis pneumonia often develop respiratory failure after entry into medical care, and one mechanism for this deterioration may be increased alveolar epithelial cell injury. In vitro, we previously demonstrated that Pneumocystis is not cytotoxic for alveolar epithelial cells. In vivo, however, infection with Pneumocystis could increase susceptibility to injury by stressors that, alone, would be sublethal. We examined transient exposure to hyperoxia as a prototypical stress that does cause mortality in normal mice. Mice were depleted of CD4+ T cells and inoculated intratracheally with Pneumocystis. Control mice were depleted of CD4+ T cells but did not receive Pneumocystis. After 4 weeks, mice were maintained in normoxia, were exposed to hyperoxia for 4 days, or were exposed to hyperoxia for 4 days followed by return to normoxia. CD4-depleted mice with Pneumocystis pneumonia demonstrated significant mortality after transient exposure to hyperoxia, while all uninfected control mice survived this stress. We determined that organism burdens were not different. However, infected mice exposed to hyperoxia and then returned to normoxia demonstrated significant increases in inflammatory cell accumulation and lung cell apoptosis. We conclude that Pneumocystis pneumonia leads to increased mortality following a normally sublethal hyperoxic insult, accompanied by alveolar epithelial cell injury and increased pulmonary inflammation.

Granulocyte/macrophage colony-stimulating factor treatment improves alveolar epithelial barrier function in alcoholic rat lung

Chronic alcohol abuse increases the risk of developing acute lung injury approximately threefold in septic patients, and ethanol ingestion for 6 wk in rats impairs alveolar epithelial barrier function both in vitro and in vivo. Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a trophic factor for the alveolar epithelium, and a recent phase II clinical study suggests that GM-CSF therapy decreases sepsis-mediated lung injury. Therefore, we hypothesized that GM-CSF treatment could improve ethanol-mediated defects in the alveolar epithelium during acute stresses such as endotoxemia. In this study, we determined that recombinant rat GM-CSF improved lung liquid clearance (as reflected by lung tissue wet:dry ratios) in ethanol-fed rats anesthetized and then challenged with 2 ml of saline via a tracheostomy tube. Furthermore, GM-CSF treatment improved lung liquid clearance and decreased epithelial protein leak in both control-fed and ethanol-fed rats after 6 h of endotoxemia induced by Salmonella typhimurium lipopolysaccharide given intraperitoneally, but with the greater net effect seen in the ethanol-fed rats. Our previous studies indicate that chronic ethanol ingestion decreases lung liquid clearance by increasing intercellular permeability. Consistent with this, GM-CSF treatment in vitro decreased permeability of alveolar epithelial monolayers derived from both control-fed and ethanol-fed rats. As in the endotoxemia model in vivo, the effect of GM-CSF was most dramatic in the ethanol group. Together, these results indicate that GM-CSF treatment has previously unrecognized effects in promoting alveolar epithelial barrier integrity and that these salutary effects may be particularly relevant in the setting of chronic alcohol abuse.

Chronic ethanol ingestion increases expression of the angiotensin II type 2 (AT2) receptor and enhances tumor necrosis factor-alpha- and angiotensin II-induced cytotoxicity via AT2 signaling in rat alveolar epithelial cells

BACKGROUND

Alcohol abuse increases the risk of acute lung injury in critically ill patients. We have shown that alveolar epithelial cell (AEC) apoptosis in response to inflammatory mediators, including tumor necrosis factor-alpha (TNF-alpha), parallels endotoxin-mediated acute lung injury in ethanol-fed rats. Although angiotensin II mediates TNF-alpha-induced apoptosis of AECs in vitro, its role in ethanol-mediated susceptibility to AEC apoptosis is unknown.

METHODS

Adult male rats were fed the Lieber-DeCarli diet for 6 weeks. AECs were isolated, and TNF-alpha- and angiotensin II-induced cytotoxicity (by terminal transferase-mediated dUTP nick end labeling staining) was determined with or without the addition of the angiotensin-converting enzyme inhibitor (lisinopril) or a selective blocker of the angiotensin II type 1 receptor (AT(1)) or type 2 receptor (AT(2)). Finally, the relative expression of the AT(1) and AT(2) receptors in AECs was determined by Western blot analysis.

RESULTS

TNF-alpha-induced cytotoxicity, but not angiotensin II-induced cytotoxicity, was prevented by lisinopril, indicating that de novo angiotensin II synthesis is required for TNF-alpha-induced apoptosis in these cells. Both TNF-alpha- and angiotensin II-induced cytotoxicity in AECs from control-fed and ethanol-fed rats were inhibited by the selective AT(2) blocker, PD123319, but not by the selective AT(1) blocker, losartan. In parallel, ethanol ingestion doubled AT(2) expression in AECs (by Western blot) but had no significant effect on AT(1) receptor expression.

CONCLUSIONS

Chronic ethanol ingestion increases AT(2) expression in the alveolar epithelium and enhances TNF-alpha- and angiotensin II-induced cytotoxicity, both of which act via AT(2). Together, these findings suggest that selective AT(2) receptor inhibition could limit the development of acute lung injury in alcoholic patients.

Chronic alcohol abuse, acute respiratory distress syndrome, and multiple organ dysfunction

OBJECTIVE

To review the effects of chronic alcohol abuse on the incidence, severity, and pathogenesis of acute respiratory distress syndrome (ARDS) and multiple organ dysfunction.

DATA SOURCES

A summary of published medical literature from MEDLINE search files and other reviews published concerning chronic alcohol abuse and critical illness.

DATA SUMMARY

A history of chronic alcohol abuse is associated with an increased incidence and severity of ARDS in critically ill patients. In two separate epidemiologic studies, involving 571 intensive care patients, chronic alcohol abuse was a significant comorbid variable that increased the incidence of ARDS by nearly three-fold and was associated with more severe nonpulmonary organ dysfunction. In addition, nearly 50% of all ARDS patients had a significant history of chronic alcohol abuse, making the association between chronic alcohol abuse and ARDS a common scenario in the intensive care unit. By using animal models of chronic ethanol ingestion, researchers have identified alcohol-mediated alterations in epithelial and endothelial cell function, surfactant synthesis and secretion, alveolar-capillary barrier function, and lung matrix content and composition. More importantly, similar changes have been reported in humans with a history of chronic alcohol abuse. Individuals with a history of chronic alcohol abuse have decreased concentrations of glutathione in the epithelial lining fluid of the lung, which do not significantly increase after 1 wk of abstinence from alcohol. The total protein concentration in the epithelial lining fluid also is increased in these individuals with a history of chronic alcohol abuse compared with healthy controls, suggesting alterations in alveolar-capillary barrier function.

CONCLUSIONS

Chronic alcohol abuse is associated with an increased incidence of ARDS and the severity of multiple organ dysfunction. This research has implications in understanding the diagnosis of, and prognosis for, critically ill patients who are at risk of developing ARDS. It also may lead to the development of novel therapies for those patients at greatest risk of acute lung injury as a consequence of chronic alcohol abuse.

Oxidative stress in viral and alcoholic hepatitis

Liver damage ranges from acute hepatitis to hepatocellular carcinoma, through apoptosis, necrosis, inflammation, immune response, fibrosis, ischemia, altered gene expression and regeneration, all processes that involve hepatocyte, Kupffer, stellate, and endothelial cells. Reactive oxygen and nitrogen species (ROS, RNS) play a crucial role in the induction and in the progression of liver disease, independently from its etiology. They are involved in the transcription and activation of a large series of cytokines and growth factors that, in turn, can contribute to further production of ROS and RNS. The main sources of free radicals are represented by hepatocyte mitochondria and cytochrome p450 enzymes, by endotoxin-activated macrophages (Kupffer cells), and by neutrophils. The consequent alteration of cellular redox state is potentiated by the correlated decrease of antioxidant and energetic reserves. Indices of free radical-mediated damage, such as the increase of malondialdehyde, 4-hydroxynonenal, protein-adducts, peroxynitrite, nitrotyrosine, etc., and/or decrease of glutathione, vitamin E, vitamin C, selenium, etc., have been documented in patients with viral or alcoholic liver disease. These markers may contribute to the monitoring the degree of liver damage, the response to antiviral therapies and to the design of new therapeutic strategies. In fact, increasing attention is now paid to a possible "redox gene therapy." By enhancing the antioxidant ability of hepatocytes, through transgene vectors, one could counteract oxidative/nitrosative stress and, in this way, contribute to blocking the progression of liver disease.

Chronic ethanol ingestion increases susceptibility to acute lung injury: role of oxidative stress and tissue remodeling

Clinical studies have demonstrated that chronic alcohol abuse is an independent outcome variable in acute lung injury. The Emory Center for the Study of Acute Lung Injury is determining the mechanisms by which ethanol increases susceptibility to acute lung injury. We developed a rat model of chronic ethanol ingestion and demonstrated that ethanol predisposes rats to edematous lung injury elicited by endotoxemia or sepsis. Chronic ethanol ingestion in rats led to decreased levels of glutathione, an important antioxidant in the lung, and this defect was associated with alterations in epithelial cell permeability, decreased alveolar liquid clearance, decreased cell viability, and decreased surfactant production. Chronic ethanol ingestion also led to the activation of lung tissue remodeling as demonstrated by the increased expression of profibrotic growth factors, matrix components, and metalloproteases. In cultured fibroblasts, the induction of the matrix glycoprotein fibronectin by ethanol was mediated via nicotinic acetylcholine receptor-dependent signal transduction. We speculate that these alterations render the host susceptible to acute lung injury by diminishing the protective mechanisms of the lung and promoting exaggerated inflammatory and tissue repair responses elicited against injurious agents.