Effect of Chronic Alcohol Exposure on Physiological and Molecular Aspects of Pancreatic Acinar Cells Ascorbic Acid Transport

Abstract

Vitamin C (ascorbic acid, AA) is required for normal cellular metabolism including that of pancreatic acinar cells (PAC). The vitamin is a potent antioxidant and acts as a cofactor for several important enzymes, while low intracellular level of AA leads to oxidative stress. PAC obtain the vitamin from their surroundings via transport across their cell membrane. A negative effect of chronic alcohol exposure on uptake of AA that is important for reducing cellular oxidative stress may contribute to the known deleterious effects of alcohol on the pancreas. Recent studies have shown that such alcohol exposure affects PAC uptake of other micronutrients, however its effect on PAC AA uptake is not clear. We address this issue in the present study using mouse‐derived pancreatic acinar 266‐6 cells (in vitro exposure; 50 mM ethanol for 96hrs) and mice fed alcohol chronically and controls were pair‐fed the same diet without alcohol (in vivo exposure; 25%, v/v for 4 weeks). We first determined the relative expression of the two known AA transporters in mouse and human PAC, the sodium‐dependent vitamin C transporter‐1 and ‐2 (SVCT‐1 and SVCT‐2; products of the SLC23A1 and SLC23A2 genes, respectively) and found SVCT‐2 to be the predominant transporter in PAC. Chronic exposure of 266‐6 cells to alcohol significantly inhibited AA uptake, and this inhibition was associated with a marked reduction in SVCT‐2 expression at the protein, mRNA, and heterogenous nuclear RNA (hnRNA) levels. Also, chronic alcohol feeding of mice led to a significant reduction in the level of expression of SVCT‐2 protein, mRNA and hnRNA in PAC. These findings suggest the possible involvement of transcriptional mechanism(s) in mediating the chronic alcohol effect and this observation was supported by the significant epigenetic changes (histone modifications) affecting the Slc23a2 promoter (a decrease in euchromatin H3K4me3 and an increase in heterochromatin H3K27me3) that we found in the alcohol exposed 266‐6 cells compared to controls. No significant changes in the methylation status of the predicted CpG island within the Slc23a2 promoter was found. Collectively, these findings show that chronic alcohol exposure inhibits AA uptake by PAC and that the effect is in part mediated at the level of transcription of the Slc23a2 gene and involves epigenetic mechanism(s).Support or Funding InformationSupported by grants from the DVA and the NIH (AA18071, DK56061, and DK58057).