The anticancer agent Adriamycin (ADR) has long been recognized to induce a dose-limiting cardiotoxicity. Numerous studies have attempted to characterize and elucidate the mechanism(s) behind its cardiotoxic effect. Despite a wealth of data covering a wide-range of effects mediated by the drug, the definitive mechanism remains a matter of debate. However, there is consensus that this toxicity is related to the induction of reactive oxygen species (ROS). Induction of ROS in the heart by ADR occurs via redox cycling of the drug at complex I of the electron transport chain. Many studies support the theory that mitochondria are a primary target of ADR-induced oxidative stress, both acutely and long-term. This review focuses on the effects of ADR redox cycling on the mitochondrion, which support the hypothesis that these organelles are indeed a major factor in ADR cardiotoxicity. This review has been constructed with particular emphasis on studies utilizing cardiac models with clinically relevant doses or concentrations of ADR in the hope of advancing our understanding of the mechanisms of ADR toxicity. This compilation of current data may reveal valuable insights for the development of therapeutic strategies better tailored to minimizing the dose-limiting effect of ADR.

No abstract

Specific therapies must be supported by an optimal understanding of changes in mitochondrial redox state and how it influences other cellular compartments; this field has begun to surface as a therapeutic target for the diabetic heart. We propose an approach based on an alternate mitochondrial electron transport that normalizes the mitochondrial redox state and improves cardiac function in diabetes. Antioxid. Redox Signal. 00, 000-000.

We identified the specific defective sites in the electron transport chain responsible for the decreased mitochondrial oxidative phosphorylation in the diabetic heart. Mitochondrial protein lysine acetylation is the common consequence of both increased fatty acid oxidation and mitochondrial Complex I defect, and may be responsible for the metabolic inflexibility of the diabetic heart.

Increased generation of reactive oxygen species (ROS) is implicated in "glucose toxicity" in diabetes. However, little is known about the action of glucose on the expression of transcription factors in hepatocytes, especially those involved in mitochondrial DNA (mtDNA) replication and transcription. Since mitochondrial functional capacity is dynamically regulated, we hypothesized that stressful conditions of hyperglycemia induce adaptations in the transcriptional control of cellular energy metabolism, including inhibition of mitochondrial biogenesis and oxidative metabolism. Cell viability, mitochondrial respiration, ROS generation and oxidized proteins were determined in HepG2 cells cultured in the presence of either 5.5 mM (control) or 30 mM glucose (high glucose) for 48 h, 96 h and 7 days. Additionally, mtDNA abundance, plasminogen activator inhibitor-1 (PAI-1), mitochondrial transcription factor A (TFAM) and nuclear respiratory factor-1 (NRF-1) transcripts were evaluated by real time PCR. High glucose induced a progressive increase in ROS generation and accumulation of oxidized proteins, with no changes in cell viability. Increased expression of PAI-1 was observed as early as 96 h of exposure to high glucose. After 7 days in hyperglycemia, HepG2 cells exhibited inhibited uncoupled respiration and decreased MitoTracker Red fluorescence associated with a 25% decrease in mtDNA and 16% decrease in TFAM transcripts. These results indicate that glucose may regulate mtDNA copy number by modulating the transcriptional activity of TFAM in response to hyperglycemia-induced ROS production. The decrease of mtDNA content and inhibition of mitochondrial function may be pathogenic hallmarks in the altered metabolic status associated with diabetes.

Biological systems that produce or are exposed to nitric oxide (NO ⅐ ) exhibit changes in the rate of oxygen free radical production. Considering that mitochondria are the main intracellular source of oxygen radicals, and based on the recently documented production of NO ⅐ by intact mitochondria, we investigated whether NO ⅐ , produced by the mitochondrial nitric-oxide synthase, could affect the generation of oxygen radicals. Toward this end, changes in H 2 O 2 production by rat liver mitochondria were monitored at different rates of endogenous NO ⅐ production. The observed changes in H 2 O 2 production indicated that NO ⅐ affected the rate of oxygen radical production by modulating the rate of O 2 consumption at the cytochrome oxidase level. This mechanism was supported by these three experimental proofs: 1) the reciprocal correlation between H 2 O 2 production and respiratory rates under different conditions of NO ⅐ production; 2) the pattern of oxidized/reduced carriers in the presence of NO ⅐ , which pointed to cytochrome oxidase as the crossover point; and 3) the reversibility of these effects, evidenced in the presence of oxymyoglobin, which excluded a significant role for other NO ⅐ -derived species such as peroxynitrite. Other sources of H 2 O 2 investigated, such as the aerobic formation of nitrosoglutathione and the GSH-mediated decay of nitrosoglutathione, were found quantitatively negligible compared with the total rate of H 2 O 2 production.Biological systems of diverse complexity, when exposed to NO ⅐ 1 or stimulated to produce NO ⅐ , usually present changes in the rate of oxygen free radical production (Ref. 1 and references therein). Decreases in the rate of oxygen free radical production are often attributed to the diffusion-controlled reaction between O 2 . and NO ⅐ , which yields peroxynitrite. Increases in reactive oxygen species (ROS) production are usually associated with the damage and/or inactivation of mitochondrial components by peroxynitrite or peroxynitrite-like species.Considering that under physiological conditions mitochondria constitute the main intracellular source of oxygen free radicals (2, 3) and that these organelles can produce NO ⅐ (4 -8), it becomes of interest to examine whether the production of mitochondrial ROS is affected by endogenous NO ⅐ . The accurate documentation of the rates of production of nitrogen and oxygen radicals is an essential step to understanding the role of these interactions in different, more complex pathophysiological situations and underlines the relevance of studying the mechanisms behind these processes in relatively simpler models. Furthermore, transient changes in ROS production have become an area of intense research given the growing interest in the role of ROS as mediators of signal transduction pathways, organ preconditioning (9), and apoptotic processes (10).In this study, we examined the rates of O 2 free radical production by intact mitochondria under various conditions of endogenous NO ⅐ production; different mechanisms underlying th...

Doxorubicin (DOX, Adriamycin) is a potent antineoplastic agent used to treat a number of cancers. Despite its utility, DOX causes a cumulative, irreversible cardiomyopathy that may become apparent shortly after treatment or years subsequent to therapy. Numerous studies have been conducted to elucidate the basis of DOX cardiotoxicity, but the precise mechanism responsible remains elusive. This investigation was designed to assess global gene expression using microarrays in order to identify the full spectrum of potential molecular targets of DOX cardiotoxicity to further delineate the underlying pathological mechanism(s) responsible for this dose-limiting cardiomyopathy. Male, Sprague-Dawley rats received 6 weekly injections of 2 mg/kg (s.c.) DOX followed by a 5 week drug-free period prior to analysis of cardiac tissue transcripts. Ontological evaluation in terms of subcellular targets identified gene products involved in mitochondrial processes are significantly suppressed, consistent with the well-established persistent mitochondrial dysfunction. Further classification of genes into biochemical networks revealed several pathways modulated by DOX, including glycolysis and fatty acid metabolism, supporting the notion that mitochondria are key targets in DOX toxicity. In conclusion, this comprehensive transcript profile provides important insights into critical targets and molecular adaptations that characterize the persistent cardiomyopathy associated with long-term exposure to DOX.

This article is available online at http://www.jlr.org Acyl-CoAs are a class of important molecules that play essential roles in many physiological processes ( 1 ), such as fatty acid oxidation, lipid synthesis/remodeling, ketone body synthesis, xenobiotic metabolism, and signaling pathways. Classically, acyl-CoAs such as free CoA, acetyl-CoA, and malonyl-CoA are recognized as regulators of metabolic fl ux. The ratio of acetyl-CoA versus free CoA tightly regulates glycolysis and fatty acid oxidation. Malonyl-CoA attenuates fatty acid oxidation by inhibiting acyl-CoA transport into the mitochondrion for oxidation and is utilized in fatty acid synthesis when its concentration is elevated ( 2 ). Many proteins and genes are dynamically regulated by deacylation and acylation via various acyl-CoAs, such as acetyl-CoA, succinyl-CoA, palmitoyl-CoA, etc. ( 3 ). However, acyl-CoAs present in the cell are diverse and may involve molecules beyond fatty acids and their oxidized derivatives. The metabolism of xenobiotics can also lead to the formation of acyl-CoAs, as demonstrated in our previous work on the metabolism of 4-hydroxy acids from C 4 to C 11 in perfused rat liver. The identifi cation of these novel acyl-CoAs extends our understanding of the new catabolic pathways involved in the disposal of 4-hydroxy acids including drugs of abuse and lipid peroxidation products ( 4-8 ).Acyl-CoAs are exclusive to the intracellular metabolites, and the profi le of these biomolecules is indicative of the local metabolic status. Each organ has its specifi c physiological roles with different energetic demands, and therefore, would be expected to exhibit a unique acyl-CoA profi le. The heart preferentially utilizes fatty acids to meet the ATP demand of mechanical contraction. Glucose and/or ketone bodies serve as the primary substrate of the brain for energy