Intestinal redox status of major intracellular thiols in a rat model of chronic alcohol consumption

Organic Solute Transporter α-β Protects Ileal Enterocytes From Bile Acid-Induced Injury

BACKGROUND & AIMS

Ileal bile acid absorption is mediated by uptake via the apical sodium-dependent bile acid transporter (ASBT), and export via the basolateral heteromeric organic solute transporter α-β (OSTα-OSTβ). In this study, we investigated the cytotoxic effects of enterocyte bile acid stasis in Ostα-/- mice, including the temporal relationship between intestinal injury and initiation of the enterohepatic circulation of bile acids.

METHODS

Ileal tissue morphometry, histology, markers of cell proliferation, gene, and protein expression were analyzed in male and female wild-type and Ostα-/- mice at postnatal days 5, 10, 15, 20, and 30. Ostα-/-Asbt-/- mice were generated and analyzed. Bile acid activation of intestinal Nrf2-activated pathways was investigated in Drosophila.

RESULTS

As early as day 5, Ostα-/- mice showed significantly increased ileal weight per length, decreased villus height, and increased epithelial cell proliferation. This correlated with premature expression of the Asbt and induction of bile acid-activated farnesoid X receptor target genes in neonatal Ostα-/- mice. Expression of reduced nicotinamide adenine dinucleotide phosphate oxidase-1 and Nrf2-anti-oxidant responsive genes were increased significantly in neonatal Ostα-/- mice at these postnatal time points. Bile acids also activated Nrf2 in Drosophila enterocytes and enterocyte-specific knockdown of Nrf2 increased sensitivity of flies to bile acid-induced toxicity. Inactivation of the Asbt prevented the changes in ileal morphology and induction of anti-oxidant response genes in Ostα-/- mice.

CONCLUSIONS

Early in postnatal development, loss of Ostα leads to bile acid accumulation, oxidative stress, and a restitution response in ileum. In addition to its essential role in maintaining bile acid homeostasis, Ostα-Ostβ functions to protect the ileal epithelium against bile acid-induced injury. NCBI Gene Expression Omnibus: GSE99579.

Alcoholic Cardiomyopathy: Multigenic Changes Underlie Cardiovascular Dysfunction

Alcoholism is the third leading cause of preventable death in the United States. Aside from promoting cardiomyopathies, chronic alcohol consumption is associated with an increased risk of dementia, the development of liver or pancreas failure, and cancers of the oral cavity and pharynx. Although a J-shaped curve for all cause mortality has been identified for average alcohol consumption, irregular heavy drinking also carries significantly greater risks for cardiovascular disease. Alcohol induced cardiovascular disease has a complex multigenic etiology. There is significant variation in the initial presentation of alcoholic cardiomyopathy with diastolic dysfunction possibly being the first indication. Ethanol exposure generates toxic metabolites, primarily acetaldehyde and ROS, which activate several cell signaling systems to alter cell function across many levels. Sudden cardiac death is a known occurrence of alcoholism that may be linked to an arrhythmogenic effect of alcohol. Microscopic and molecular examination of diseased hearts has demonstrated abnormal alterations to various cellular components, including the mitochondria and myofibrils. These studies have shown not only the direct impact on myocardial contractility but also disrupted metabolism that determines the long-term survival of the myocardium. Significant variations in the response to chronic alcohol consumption may be related to unique genotypes that modify the metabolic response to ethanol. Future studies to further characterize the role of different genotypes will help indentify those genotypes are more susceptible to chronic alcohol consumption.

Adaptive unfolded protein response attenuates alcohol-induced pancreatic damage

BACKGROUND & AIMS

Endoplasmic reticulum (ER) stress responses (collectively known the unfolded protein response [UPR]) have important roles in several human disorders, but their contribution to alcoholic pancreatitis is not known. We investigated the role of X-box binding protein 1 (XBP1), a UPR regulator, in prevention of alcohol-induced ER stress in the exocrine pancreas.

METHODS

Wild-type and Xbp1(+/-) mice were fed control or ethanol diets for 4 weeks. Pancreatic tissue samples were then examined by light and electron microscopy to determine pancreatic alterations; UPR regulators were analyzed biochemically.

RESULTS

In wild-type mice, ethanol activated a UPR, increasing pancreatic levels of XBP1 and XBP1 targets such as protein disulfide isomerase (PDI). In these mice, pancreatic damage was minor. In ethanol-fed Xbp1(+/-) mice, XBP1 and PDI levels were significantly lower than in ethanol-fed wild-type mice. The combination of XBP1 deficiency and ethanol feeding reduced expression of regulators of ER function and the up-regulation of proapoptotic signals. Moreover, ethanol feeding induced oxidation of PDI, which might compromise PDI-mediated disulfide bond formation during ER protein folding. In ethanol-fed Xbp1(+/-) mice, ER stress was associated with disorganized and dilated ER, loss of zymogen granules, accumulation of autophagic vacuoles, and increased acinar cell death.

CONCLUSIONS

Long-term ethanol feeding causes oxidative ER stress, which activates a UPR and increases XBP1 levels and activity. A defective UPR due to XBP1 deficiency results in ER dysfunction and acinar cell pathology.

Inactivation of hepatocyte nuclear factor-4{alpha} mediates alcohol-induced downregulation of intestinal tight junction proteins

Chronic alcohol exposure has been shown to increase the gut permeability in the distal intestine, in part, through induction of zinc deficiency. The present study evaluated the molecular mechanisms whereby zinc deficiency mediates alcohol-induced intestinal barrier dysfunction. Examination of zinc finger transcription factors in the gastrointestinal tract of mice revealed a prominent distribution of hepatocyte nuclear factor-4alpha (HNF-4alpha). HNF-4alpha exclusively localizes in the epithelial nuclei and exhibited an increased abundance in mRNA and protein levels in the distal intestine. Chronic alcohol exposure to mice repressed the HNF-4alpha gene expression in the ileum and reduced the protein level and DNA binding activity of HNF-4alpha in all of the intestinal segments with the most remarkable changes in the ileum. Chronic alcohol exposure also decreased the mRNA levels of tight junction proteins, particularly in the ileum. Caco-2 cell culture studies were conducted to determine the role of HNF-4alpha in regulation of the epithelial tight junction and barrier function. Knockdown of HNF-4alpha in Caco-2 cells decreased the mRNA and protein levels of tight junction proteins in association with disruption of the epithelial barrier. Alcohol treatment inactivated HNF-4alpha, which was prevented by N-acetyl-cysteine or zinc. The link between zinc and HNF-4alpha function was confirmed by zinc deprivation, which inhibited HNF-4alpha DNA binding activity. These results indicate that inactivation of HNF-4alpha due to oxidative stress and zinc deficiency is likely a novel mechanism contributing to the deleterious effects of alcohol on the tight junctions and the intestinal barrier function.