Chronic effects of ethanol on cultured myocardial cells: ultrastructural and morphometric studies

Cardiac Toxicity From Ethanol Exposure in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Alcohol use prior to and during pregnancy remains a significant societal problem and can lead to developmental fetal abnormalities including compromised myocardia function and increased risk for heart disease later in life. Alcohol-induced cardiac toxicity has traditionally been studied in animal-based models. These models have limitations due to physiological differences from human cardiomyocytes (CMs) and are also not suitable for high-throughput screening. We hypothesized that human-induced pluripotent stem cell-derived CMs (hiPSC-CMs) could serve as a useful tool to study alcohol-induced cardiac defects and/or toxicity. In this study, hiPSC-CMs were treated with ethanol at doses corresponding to the clinically relevant levels of alcohol intoxication. hiPSC-CMs exposed to ethanol showed a dose-dependent increase in cellular damage and decrease in cell viability, corresponding to increased production of reactive oxygen species. Furthermore, ethanol exposure also generated dose-dependent increased irregular Ca2+ transients and contractility in hiPSC-CMs. RNA-seq analysis showed significant alteration in genes belonging to the potassium voltage-gated channel family or solute carrier family, partially explaining the irregular Ca2+ transients and contractility in ethanol-treated hiPSC-CMs. RNA-seq also showed significant upregulation in the expression of genes associated with collagen and extracellular matrix modeling, and downregulation of genes involved in cardiovascular system development and actin filament-based process. These results suggest that hiPSC-CMs can be a novel and physiologically relevant system for the study of alcohol-induced cardiac toxicity.

Ethanol Dose- and Time-dependently Increases α and β Subunits of Mitochondrial ATP Synthase of Cultured Neonatal Rat Cardiomyocytes

Mitochondria are target subcellular organelles of ethanol. In this study, the effects of ethanol on protein composition was examined with 2-dimensional electrophoresis of protein extracts from cultured neonatal rat cardiomyocytes exposed to 100 mM ethanol for 24 hours. A putative β subunit of mitochondrial ATP synthase was increased, which was confirmed by Western blot. The cellular protein abundances in the α and β subunits of ATP synthase increased in dose (0, 10, 50, and 100 mM) - and time (0.5 hour and 24 hours) -dependent manners. The DNA microarray analysis of total RNA extract demonstrated that gene expression of the corresponding messenger RNAs of these subunit proteins did not significantly alter due to 24-hour ethanol exposure. Therefore, protein expression of these nuclear-encoded mitochondrial proteins may be regulated at the translational, rather than the transcriptional, level. Alternatively, degradation of these subunit proteins might be decreased. Additionally, cellular ATP content of cardiomyocytes scarcely decreased following 24-hour exposure to any examined concentrations of ethanol. Previous studies, together with this study, have demonstrated that protein abundance of the α subunit or β subunit or both subunits of ATP synthase after ethanol exposure or dysfunctional conditions might differ according to tissue: significant increases in heart but decreases in liver and brain. Thus, it is suggested that the abundance of subunit proteins of mitochondrial ATP synthase in the ethanol-exposed heart, being different from that in the liver and brain, should increase dose-dependently through either translational upregulation or decreased degradation or both to maintain ATP production, as the heart requires much more energy than other tissues for continuing sustained contractions.

Long term liver specific glucokinase gene defect induced diabetic cardiomyopathy by up regulating NADPH oxidase and down regulating insulin receptor and p-AMPK

Background

The liver-specific glucokinase knockout (gck^w/–) mouse experiences long-term hyperglycemia and insulin resistance. This study was designed to evaluate the functional and structural changes in the myocardium of 60 week-old gck^w/– mice, and to investigate the effect of rosiglitazone on the myocardium in this model.

Methods

60 week-old gck^w/– mice were randomly divided into 3 groups: gck^w/–, gck^w/– mice treated with insulin (1 U/kg) and gck^w/– mice treated with rosiglitazone (18 mg/kg). Insulin or rosiglitazone treatment was for 4 weeks. Gck^w/w litermates were used as controls. Echocardiography, electrocardiogram, biochemical, histopathological, ultrastructural, real time PCR and Western blot studies were performed to examine for structural and functional changes.

Results

Long-term liver-specific gck knockout in mice elicits hyperglycaemia and insulin resistance. Compared to age matched gck^w/w mice, 60 week-old gck^w/– mice showed decreased LV internal dimension, increased posterior wall thickness, lengthened PR and QRS intervals, up-regulated MLC2 protein expression, decreased SOD activity, increased MDA levels and up-regulated Cyba mRNA. Morphological studies revealed that there was an increase in the amount of PAS and Masson positively stained material, as did the number and proportion of the cell occupied by mitochondria in the gck^w/– mice. Western blot analysis revealed that the levels of the insulin receptor, Akt, phosphorylated AMPK beta and phosphorylated ACC were reduced in gck^w/– mice. These effects were partly attenuated or ablated by treatment with rosiglitazone.

Conclusions

Our results indicate that changes in the myocardium occur in the liver-specific glucokinase knockout mouse and suggest that reduced glucokinase expression in the liver may induce diabetic cardiomyopathy by up regulating NADPH oxidase and down regulating insulin receptor and p-AMPK protein levels. Rosiglitazone treatment may protect against diabetic cardiomyopathy by altering the levels of a set of proteins involved in cardiac damage.

Ethanol hyperpolarizes mitochondrial membrane potential and increases mitochondrial fraction in cultured mouse myocardial cells

Cultured mouse heart-derived myocardial and non-muscle cells were exposed to ethanol, stained with cell-permeant fluorescent vital probes, JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide) and oxidation-sensitive dihydrorhodamine 123, and analyzed by flow cytometry to elucidate ethanol-induced time-wise alterations in the mitochondrial membrane potential (DeltaPsim) and the production of reactive oxygen species (ROS). Ethanol (50 and 200 mM) not only hyperpolarized DeltaPsim of both types of cells but also dose-dependently increased ROS production at 24 h, although a 200-mM dose reduced the production until 3 h. These cell pathophysiological reactions suggest the depression of mitochondrial ATPase and mitochondrial respiratory chain. However, differences between these cells appeared after a 24-h exposure to 200 mM ethanol: the increase in ROS production was approximately twice as large for myocardial cells as for non-muscle cells; and the side-scatter parameter of light scattering significantly increased for myocardial cells, but not for non-muscle cells. All these myocyte-specific alterations indicate an increase in the mitochondrial fraction in a cell. This reaction might be a countermeasure against ethanol-induced dysfunction of mitochondrial respiration that is needed to meet the energy requirements of spontaneous myocardial contractions.