Chronic alcohol feeding potentiates hormone‐induced calcium signalling in hepatocytes

Abstract

Chronic alcohol consumption causes a spectrum of liver diseases, but the pathogenic mechanisms driving the onset and progression of disease are not clearly defined. We show that chronic alcohol feeding sensitizes rat hepatocytes to Ca -mobilizing hormones resulting in a leftward shift in the concentration-response relationship and the transition from oscillatory to more sustained and prolonged Ca increases. Our data demonstrate that alcohol-dependent adaptation in the Ca signalling pathway occurs at the level of hormone-induced inositol 1,4,5 trisphosphate (IP ) production and does not involve changes in the sensitivity of the IP receptor or size of internal Ca stores. We suggest that prolonged and aberrant hormone-evoked Ca increases may stimulate the production of mitochondrial reactive oxygen species and contribute to alcohol-induced hepatocyte injury. ABSTRACT: 'Adaptive' responses of the liver to chronic alcohol consumption may underlie the development of cell and tissue injury. Alcohol administration can perturb multiple signalling pathways including phosphoinositide-dependent cytosolic calcium ([Ca ] ) increases, which can adversely affect mitochondrial Ca levels, reactive oxygen species production and energy metabolism. Our data indicate that chronic alcohol feeding induces a leftward shift in the dose-response for Ca -mobilizing hormones resulting in more sustained and prolonged [Ca ] increases in both cultured hepatocytes and hepatocytes within the intact perfused liver. Ca increases were initiated at lower hormone concentrations, and intercellular calcium wave propagation rates were faster in alcoholics compared to controls. Acute alcohol treatment (25 mm) completely inhibited hormone-induced calcium increases in control livers, but not after chronic alcohol-feeding, suggesting desensitization to the inhibitory actions of ethanol. Hormone-induced inositol 1,4,5 trisphosphate (IP ) accumulation and phospholipase C (PLC) activity were significantly potentiated in hepatocytes from alcohol-fed rats compared to controls. Removal of extracellular calcium, or chelation of intracellular calcium did not normalize the differences in hormone-stimulated PLC activity, indicating calcium-dependent PLCs are not upregulated by alcohol. We propose that the liver 'adapts' to chronic alcohol exposure by increasing hormone-dependent IP formation, leading to aberrant calcium increases, which may contribute to hepatocyte injury.

Causality Analysis and Cell Network Modeling of Spatial Calcium Signaling Patterns in Liver Lobules

“…For example, Fluo-8 AM and Rhod4 have been utilized for cytosolic calcium reporting in hepatocytes with small differences in Kd values and photostability (Lock et al, 2015 ). We have been using Fluo-8 AM with good success in previous studies (Bartlett et al, 2017 ) and therefore utilized this reporter for obtaining the dynamic data analyzed in the present study.…”

“…All animal procedures used in this study were handled in accordance with mandated standards of humane care and were approved by the Thomas Jefferson University Institutional Animal Care and Use Committee. Confocal imaging of intact perfused livers was performed as previously described (Robb-Gaspers and Thomas, 1995 ; Bartlett et al, 2017 ). Briefly, livers from 8–12 weeks old male C57 BL/6 mice were perfused via the hepatic portal vein with a HEPES-buffered balance salt solution (121 mM NaCl, 25 mM HEPES, 5 mM NaHCO3, 4.7 mM KCl, 1.2 mM KH 2 PO 4 , 1.2 mM MgSO 4 , 1.3 mM CaCl 2 , 5.5 mM glucose, 0.5 mM glutamine, 3 mM lactate, 0.3 mM pyruvate, 0.2 mM bromosulfophthalein (BSP), 0.1% BSA, pH 7.4) equilibrated with 100% O 2 at 30°C.…”

Alcohol and calcium make a potent cocktail

“…The study by Bartlett and colleagues in this issue of The Journal of Physiology may provide important insights into this question (Bartlett et al . ). They observed that chronic alcohol feeding increased the sensitivity of hepatocytes to Ca 2+ agonist hormones.…”

Changes in the microstructure of compact and trabecular bone tissues of mice subchronically exposed to alcohol

“…daily for 3 months). Also, chronic alcohol abuse caused changes in calcium regulating hormones, mineral homeostasis, mechanical loading [ 10 ] and led to an accumulation of reactive oxygen species (ROS) [ 11 ]. Furthermore, NADPH oxidase expression was upregulated in osteoblasts of rats infused intragastrically with ethanol-containing liquid diets (12 g ethanol kg −1 daily for 4 weeks) [ 12 ].…”