Acute Ethanol Causes Hepatic Mitochondrial Depolarization in Mice: Role of Ethanol Metabolism

Abstract

Background/AimsAn increase of ethanol metabolism and hepatic mitochondrial respiration occurs in vivo after a single binge of alcohol. Here, our aim was to determine how ethanol intake affects hepatic mitochondrial polarization status in vivo in relation to ethanol metabolism and steatosis.MethodsHepatic mitochondrial polarization, permeability transition (MPT), and reduce pyridine nucleotides, and steatosis in mice were monitored by intravital confocal/multiphoton microscopy of the fluorescence of rhodamine 123 (Rh123), calcein, NAD(P)H, and BODIPY493/503, respectively, after gavage with ethanol (1–6 g/kg).ResultsMitochondria depolarized in an all-or-nothing fashion in individual hepatocytes as early as 1 h after alcohol. Depolarization was dose- and time-dependent, peaked after 6 to 12 h and maximally affected 94% of hepatocytes. This mitochondrial depolarization was not due to onset of the MPT. After 24 h, mitochondria of most hepatocytes recovered normal polarization and were indistinguishable from untreated after 7 days. Cell death monitored by propidium iodide staining, histology and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was low throughout. After alcohol, mitochondrial NAD(P)H autofluorescence increased and decreased, respectively, in hepatocytes with polarized and depolarized mitochondria. Ethanol also caused steatosis mainly in hepatocytes with depolarized mitochondria. Depolarization was linked to ethanol metabolism, since deficiency of alcohol dehydrogenase and cytochrome-P450 2E1 (CYP2E1), the major ethanol-metabolizing enzymes, decreased mitochondrial depolarization by ∼70% and ∼20%, respectively. Activation of aldehyde dehydrogenase decreased depolarization, whereas inhibition of aldehyde dehydrogenase enhanced depolarization. Activation of aldehyde dehydrogenase also markedly decreased steatosis.ConclusionsAcute ethanol causes reversible hepatic mitochondrial depolarization in vivo that may contribute to steatosis and increased mitochondrial respiration. Onset of this mitochondrial depolarization is linked, at least in part, to metabolism of ethanol to acetaldehyde.

MitoNEET Deficiency Alleviates Experimental Alcoholic Steatohepatitis in Mice by Stimulating Endocrine Adiponectin-Fgf15 Axis

“…Liver is the most important organ for expression and secretion of Saa1 during the acute-phase response. However, during the non-acute phase, adipose tissue is the main source of Saa1 in obese subjects (55,56). Unlike in liver, adipose Saa1 gene expression was not elevated in the ethanol-fed mNTKO mice.…”

“…Considerable evidence indicates that hepatic ethanol metabolism is associated with alterations in hepatic mitochondria function, and consequently, promotes liver injury (29,30). For instance, hepatic ethanol metabolism is required for mitochondrial depolarization in mouse liver (56). The role of mNT in mediating effects of hepatic ethanol metabolism on mitochondrial function is currently under investigation in our laboratory.…”

Highlight report: mitochondrial depolarization by ethanol

“…Recently, a study has been published by the group of John Lemasters, showing that high acute doses of ethanol in mice cause a widespread but reversible depolarization of mitochondria (Zhong et al 2014). In their study, Zhong and colleagues used a two-photon imaging with vital dyes to visualize mitochondrial potential.…”

“…This technique allows generating videos of the living organ with a spatial resolution of approximately 200 nm. Living mice received injections of Rhodamine 123, a cationic fluorophore that is taken up by polarized mitochondria and by its green fluorescence indicates mitochondrial activity (Zhong et al 2014). Loss of green fluorescence signal indicates mitochondrial depolarization.…”

“…As a consequence, a transient mitochondrial depolarization of almost all hepatocytes was observed. More than 24 h were required until mitochondria returned to the control situation (Zhong et al 2014). Mitochondrial depolarization depends on ethanol metabolism, since deficiency of CYP2E1 as well as alcohol dehydrogenase antagonized the effect (Zhong et al 2014).…”