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Role of mitochondrial dysfunction in cardiac glycoside toxicity.

ABSTRACT: Cardiac glycosides, which inhibit the plasma membrane Na(+) pump, are one of the four categories of drug recommended for routine use to treat heart failure, yet their therapeutic window is limited by toxic effects. Elevated cytoplasmic Na(+) ([Na(+)](i)) compromises mitochondrial energetics and redox balance by blunting mitochondrial Ca(2+) ([Ca(2+)](m)) accumulation, and this impairment can be prevented by enhancing [Ca(2+)](m). Here, we investigate whether this effect underlies the toxicity and arrhythmogenic effects of cardiac glycosides and if these effects can be prevented by suppressing mitochondrial Ca(2+) efflux, via inhibition of the mitochondrial Na(+)/Ca(2+) exchanger (mNCE). In isolated cardiomyocytes, ouabain elevated [Na(+)](i) in a dose-dependent way, blunted [Ca(2+)](m) accumulation, decreased the NADH/NAD+redox potential, and increased reactive oxygen species (ROS). Concomitant treatment with the mNCE inhibitor CGP-37157 ameliorated these effects. CGP-37157 also attenuated ouabain-induced cellular Ca(2+) overload and prevented delayed afterdepolarizations (DADs). In isolated perfused hearts, ouabain's positive effects on contractility and respiration were markedly potentiated by CGP-37157, as were those mediated by ?-adrenergic stimulation. Furthermore, CGP-37157 inhibited the arrhythmogenic effects of ouabain in both isolated perfused hearts and in vivo. The findings reveal the mechanism behind cardiac glycoside toxicity and show that improving mitochondrial Ca(2+) retention by mNCE inhibition can mitigate these effects, particularly with respect to the suppression of Ca(2+)-triggered arrhythmias, while enhancing positive inotropic actions. These results suggest a novel strategy for the treatment of heart failure.

SUBMITTER: Liu T

PROVIDER: S-EPMC2949492 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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Role of mitochondrial dysfunction in cardiac glycoside toxicity.

Liu Ting T Brown David A DA O'Rourke Brian B

Journal of molecular and cellular cardiology 20100708 5

Cardiac glycosides, which inhibit the plasma membrane Na(+) pump, are one of the four categories of drug recommended for routine use to treat heart failure, yet their therapeutic window is limited by toxic effects. Elevated cytoplasmic Na(+) ([Na(+)](i)) compromises mitochondrial energetics and redox balance by blunting mitochondrial Ca(2+) ([Ca(2+)](m)) accumulation, and this impairment can be prevented by enhancing [Ca(2+)](m). Here, we investigate whether this effect underlies the toxicity an ...[more]

PMID: 20620145

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Project description:AimsIn cardiomyocytes, there is microRNA (miR) in the mitochondria that originates from the nuclear genome and matures in the cytoplasm before translocating into the mitochondria. Overexpression of one such miR, miR-181c, can lead to heart failure by stimulating reactive oxygen species (ROS) production and increasing mitochondrial calcium level ([Ca2+]m). Mitochondrial calcium uptake 1 protein (MICU1), a regulatory protein in the mitochondrial calcium uniporter complex, plays an important role in regulating [Ca2+]m. Obesity results in miR-181c overexpression and a decrease in MICU1. We hypothesize that lowering miR-181c would protect against obesity-induced cardiac dysfunction.Methods and resultsWe used an in vivo mouse model of high-fat diet (HFD) for 18 weeks and induced high lipid load in H9c2 cells with oleate-conjugated bovine serum albumin in vitro. We tested the cardioprotective role of lowering miR-181c by using miR-181c/d-/- mice (in vivo) and AntagomiR against miR-181c (in vitro). HFD significantly upregulated heart levels of miR-181c and led to cardiac hypertrophy in wild-type mice, but not in miR-181c/d-/- mice. HFD also increased ROS production and pyruvate dehydrogenase activity (a surrogate for [Ca2+]m), but the increases were alleviated in miR-181c/d-/- mice. Moreover, miR-181c/d-/- mice fed a HFD had higher levels of MICU1 than did wild-type mice fed a HFD, attenuating the rise in [Ca2+]m. Overexpression of miR-181c in neonatal ventricular cardiomyocytes (NMVM) caused increased ROS production, which oxidized transcription factor Sp1 and led to a loss of Sp1, thereby slowing MICU1 transcription. Hence, miR-181c increases [Ca2+]m through Sp1 oxidation and downregulation of MICU1, suggesting that the cardioprotective effect of miR-181c/d-/- results from inhibition of Sp1 oxidation.ConclusionThis study has identified a unique nuclear-mitochondrial communication mechanism in the heart orchestrated by miR-181c. Obesity-induced overexpression of miR-181c increases [Ca2+]m via downregulation of MICU1 and leads to cardiac injury. A strategy to inhibit miR-181c in cardiomyocytes can preserve cardiac function during obesity by improving mitochondrial function. Altering miR-181c expression may provide a pharmacologic approach to improve cardiomyopathy in individuals with obesity/type 2 diabetes.

Project description:Purpose:RNA-Seq analysis was performed on mouse hearts with or without hispidulin treatment 4 weeks after arotic banding or sham surgery to determining the effect of hispidulin on pressure overload induced cardiac hypertrophy. Methods: the mRNA profiles of mouse hearts underwent sham or arotic banding surgery with treatment of hispidulin or DMSO were generated by RNA-seq analysis in triplicate. The expression level of gene was calculated by RSEM(v.1.2.12). Differential expression analysis was performed using the DESeq2(V 1.4.5). Results: RNA isolation, library construction, and sequencing were performed on a BGISEQ-500 (Beijing Genomic Institution, www.genomics.org.cn, BGI). For the gene expression analysis, the fold changes were also estimated according to the fragments per kilobase of exon per million fragments mapped (FPKM) in each sample. The significance of different gene expression was defined by the following filter criteria: false discovery rate (FDR) ≤0.001 and log2-ratio 1. After comparing of DMSO+AB group and hispidulin+AB group, we found that 113 genes were significantly differentially expressed. Gene ontology and cluster analysis indicated that alternated genes were enriched in fatty acid oxidation, glucose metabolism, TCA cycle, oxidative phosphorylation, hypertrophic cardiomyopathy, ECM organism, oxidative stress and unfolded protein binding. This result indicated that hispidulin improved mitochondrial function. Conclusions: Our study represents the first detailed analysis of heart transcriptomes, with biologic replicates, generated by RNA-seq technology. The optimized data analysis workflows reported here should provide a framework for comparative investigations of expression profiles. Our results show that NGS offers a comprehensive and more accurate quantitative and qualitative evaluation of mRNA content within a cell or tissue. We conclude that RNA-seq based transcriptome characterization would expedite genetic network analyses and permit the dissection of complex biologic functions.

Project description:Hypertrophic cardiomyopathy (HCM) is a complex disease partly explained by the effects of individual gene variants on sarcomeric protein biomechanics. At the cellular level, HCM mutations most commonly enhance force production, leading to higher energy demands. Despite significant advances in elucidating sarcomeric structure-function relationships, there is still much to be learned about the mechanisms that link altered cardiac energetics to HCM phenotypes. In this work, we test the hypothesis that changes in cardiac energetics represent a common pathophysiologic pathway in HCM. We performed a comprehensive multi-omics profile of the molecular (transcripts, metabolites, and complex lipids), ultrastructural, and functional components of HCM energetics using myocardial samples from 27 HCM patients and 13 normal controls (donor hearts). Integrated omics analysis revealed alterations in a wide array of biochemical pathways with major dysregulation in fatty acid metabolism, reduction of acylcarnitines, and accumulation of free fatty acids. HCM hearts showed evidence of global energetic decompensation manifested by a decrease in high energy phosphate metabolites (ATP, ADP, and phosphocreatine) and a reduction in mitochondrial genes involved in the creatine kinase and ATP synthesis. Accompanying these metabolic derangements, quantitative electron microscopy showed an increased fraction of severely damaged mitochondria with reduced cristae density, coinciding with reduced citrate synthase (CS) activity and mitochondrial oxidative respiration. These mitochondrial abnormalities were associated with elevated reactive oxygen species (ROS) and reduced antioxidant defenses. However, despite significant mitochondrial injury, HCM hearts failed to upregulate mitophagic clearance. Overall, our findings suggest that perturbed metabolic signaling and mitochondrial dysfunction are common pathogenic mechanisms in patients with HCM. These results highlight potential new drug targets for attenuation of the clinical disease through improving metabolic function and reducing mitochondrial injury.

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Role of mitochondrial dysfunction in cardiac glycoside toxicity.

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Role of mitochondrial dysfunction in cardiac glycoside toxicity.

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