Drug-induced mitochondrial dysfunction in cardiac and skeletal muscle injury

Challenging the status quo: a framework for mechanistic and human-relevant cardiovascular safety screening

Traditional approaches to preclinical drug safety assessment have generally protected human patients from unintended adverse effects. However, these assessments typically occur too late to make changes in the formulation or in phase 1 and beyond, are highly dependent on animal studies and have the potential to lead to the termination of useful drugs due to liabilities in animals that are not applicable in patients. Collectively, these elements come at great detriment to both patients and the drug development sector. This phenomenon is particularly problematic in the area of cardiovascular safety assessment where preclinical attrition is high. We believe that a more efficient and translational approach can be defined. A multi-tiered assessment that leverages our understanding of human cardiovascular biology, applies human cell-based in vitro characterizations of cardiovascular responses to insult, and incorporates computational models of pharmacokinetic relationships would enable earlier and more translational identification of human-relevant liabilities. While this will take time to develop, the ultimate goal would be to implement such assays both in the lead selection phase as well as through regulatory phases.

Successful energy shift from glycolysis to mitochondrial oxidative phosphorylation in freshly isolated hepatocytes from humanized mice liver

Mitochondrial toxicity is a factor of drug-induced liver injury. Previously, we reported an in vitro rat hepatocyte assay where mitochondrial toxicity was more sensitively evaluated, using sugar resource substitution and increased oxygen supply. Although this method could be applicable to human cell-based assay, cryopreserved human hepatocyte (CHH) has some disadvantages/uncertainty, including unstable same donor supply and potential organelle damage due to cryopreservation. Herein, we compared the mitochondrial functions of freshly-isolated hepatocytes from humanized chimeric mice liver (PXB-cells) and three CHH lots to determine the better cell source for mitochondrial toxicity assay. Two CHH lots declined after replacing glucose with galactose. To confirm the shift in energy production from glycolysis to oxidative phosphorylation, lactate and oxygen consumption rate (indicators of glycolytic activity and mitochondrial oxidative phosphorylation, respectively) were measured. In PXB-cells, lactate amount decreased, while oxygen consumption in 100 min increased. These effects were less evident in CHH. The cytotoxicity of the select respiratory chain inhibitors was enhanced in PXB-cells upon sugar replacement, but no change occurred with negative control drugs (bicalutamide and metformin). Altogether, PXB-cells was less vulnerable to sugar resource substitution than CHH. The substitution activated mitochondrial function and enhanced cytotoxicity of respiratory chain inhibitors in PXB-cells.

Assessment of mitochondrial dysfunction-related, drug-induced hepatotoxicity in primary rat hepatocytes

Evidence that mitochondrial dysfunction plays a central role in drug-induced liver injury is rapidly accumulating. In contrast to physiological conditions, in which almost all adenosine triphosphate (ATP) in hepatocytes is generated in mitochondria via aerobic respiration, the high glucose content and limited oxygen supply of conventional culture systems force primary hepatocytes to generate most ATP via cytosolic glycolysis. Thus, such anaerobically poised cells are resistant to xenobiotics that impair mitochondrial function, and are not suitable to identify drugs with mitochondrial liabilities. In this study, primary rat hepatocytes were cultured in galactose-based medium, instead of the conventional glucose-based medium, and in hyperoxia to improve the reliance of energy generation on aerobic respiration. Activation of mitochondria was verified by diminished cellular lactate release and increased oxygen consumption. These conditions improved sensitivity to the mitochondrial complex I inhibitor rotenone. Since oxidative stress is also a general cause of mitochondrial impairment, cells were exposed to test compounds in the presence of transferrin to increase the generation of reactive oxygen species via increased uptake of iron. Finally, 14 compounds with reported mitochondrial liabilities were tested to validate this new drug-induced mitochondrial toxicity assay. Overall, the culture of primary rat hepatocytes in galactose, hyperoxia and transferrin is a useful model for the identification of mitochondrial dysfunction-related drug-induced hepatotoxicity.

Role of endoplasmic reticulum stress in drug-induced toxicity

Drug‐induced toxicity is a key issue for public health because some side effects can be severe and life‐threatening. These adverse effects can also be a major concern for the pharmaceutical companies since significant toxicity can lead to the interruption of clinical trials, or the withdrawal of the incriminated drugs from the market. Recent studies suggested that endoplasmic reticulum (ER) stress could be an important event involved in drug liability, in addition to other key mechanisms such as mitochondrial dysfunction and oxidative stress. Indeed, drug‐induced ER stress could lead to several deleterious effects within cells and tissues including accumulation of lipids, cell death, cytolysis, and inflammation. After recalling important information regarding drug‐induced adverse reactions and ER stress in diverse pathophysiological situations, this review summarizes the main data pertaining to drug‐induced ER stress and its potential involvement in different adverse effects. Drugs presented in this review are for instance acetaminophen (APAP), arsenic trioxide and other anticancer drugs, diclofenac, and different antiretroviral compounds. We also included data on tunicamycin (an antibiotic not used in human medicine because of its toxicity) and thapsigargin (a toxic compound of the Mediterranean plant Thapsia garganica) since both molecules are commonly used as prototypical toxins to induce ER stress in cellular and animal models.

Hypoxia and free radicals: role in tumor progression and the use of engineering-based platforms to address these relationships

Hypoxia is a feature of all solid tumors, contributing to tumor progression and therapy resistance. Through stabilization of the hypoxia-inducible factor 1 alpha (HIF-1α), hypoxia activates the transcription of a number of genes that sustain tumor progression. Since the seminal discovery of HIF-1α as a hypoxia-responsive master regulator of numerous genes and transcription factors, several groups have reported a novel mechanism whereby hypoxia mediates stabilization of HIF-1α. This process occurs as a result of hypoxia-generated reactive oxygen species (ROS), which, in turn, stabilize the expression of HIF-1α. As a result, a number of genes regulating tumor growth are expressed, fueling ongoing tumor progression. In this review, we outline a role for hypoxia in generating ROS and additionally define the mechanisms contributing to ROS-induced stabilization of HIF-1α.We further explore how ROS-induced HIF-1α stabilization contributes to tumor growth, angiogenesis, metastasis, and therapy response. We discuss a future outlook, describing novel therapeutic approaches for attenuating ROS production while considering how these strategies should be carefully selected when combining with chemotherapeutic agents. As engineering-based approaches have been more frequently utilized to address biological questions, we discuss opportunities whereby engineering techniques may be employed to better understand the physical and biochemical factors controlling ROS expression. It is anticipated that an improved understanding of the mechanisms responsible for the hypoxia/ROS/HIF-1α axis in tumor progression will yield the development of better targeted therapies.

Sodium ferulate protects against daunorubicin-induced cardiotoxicity by inhibition of mitochondrial apoptosis in juvenile rats

Daunorubicin (DNR) is a widely used chemotherapeutic agent; however, its clinical use is limited because of its cardiotoxicity. This study was aimed to investigate the protective effect of sodium ferulate (SF), an effective component from traditional Chinese herbs, against DNR-induced cardiotoxicity in juvenile rats. DNR was administered intraperitoneally to rats at the dosage of 2.5 mg·kg(-1)·wk(-1) for 5 consecutive weeks (cumulative dose of 12.5 mg/kg) or in combination with intraperitoneal injection of SF at 50 mg·kg(-1)·d(-1) over a period of 30 days. The animals were killed 6 days after the last injection of DNR. SF significantly ameliorated the DNR-induced cardiac dysfunction, structural damage of the myocardium, and release of lactate dehydrogenase and creatine kinase. Treatment with SF also reversed DNR-induced oxidative stress as evidenced by a decrease in malondialdehyde levels with a concomitant increase in myocardical superoxide dismutase activities. Furthermore, SF afforded significant cardioprotection against DNR-induced apoptosis in vivo and effectively suppressed the complex mitochondrion-dependent apoptotic signaling triggered by DNR. This study indicates that SF may improve cardiac function by inhibition of oxidative stress and apoptosis, thus providing a beneficial effect on the prevention of DNR-induced cardiotoxicity.

Ferritin heavy chain as main mediator of preventive effect of metformin against mitochondrial damage induced by doxorubicin in cardiomyocytes

The efficacy of doxorubicin (DOX) as an antitumor agent is greatly limited by the induction of cardiomyopathy, which results from mitochondrial dysfunction and iron-catalyzed oxidative stress in the cardiomyocyte. Metformin (MET) has been seen to have a protective effect against the oxidative stress induced by DOX in cardiomyocytes through its modulation of ferritin heavy chain (FHC), the main iron-storage protein. This study aimed to assess the involvement of FHC as a pivotal molecule in the mitochondrial protection offered by MET against DOX cardiotoxicity. The addition of DOX to adult mouse cardiomyocytes (HL-1 cell line) increased the cytosolic and mitochondrial free iron pools in a time-dependent manner. Simultaneously, DOX inhibited complex I activity and ATP generation and induced the loss of mitochondrial membrane potential. The mitochondrial dysfunction induced by DOX was associated with the release of cytochrome c to the cytosol, the activation of caspase 3, and DNA fragmentation. The loss of iron homeostasis, mitochondrial dysfunction, and apoptosis induced by DOX were prevented by treatment with MET 24h before the addition of DOX. The involvement of FHC and NF-κB was determined through siRNA-mediated knockdown. Interestingly, the presilencing of FHC or NF-κB with specific siRNAs blocked the protective effect induced by MET against DOX cardiotoxicity. These findings were confirmed in isolated primary neonatal rat cardiomyocytes. In conclusion, these results deepen our knowledge of the protective action of MET against DOX-induced cardiotoxicity and suggest that therapeutic strategies based on FHC modulation could protect cardiomyocytes from the mitochondrial damage induced by DOX by restoring iron homeostasis.

In vitro salicylate does not further impair aging-induced brain mitochondrial dysfunction

Aging and drug-induced side effects may contribute to the deterioration of mitochondrial bioenergetics in the brain. One hypothesis is that the combination of both deleterious stimuli accelerates the process of mitochondrial degradation, leading to progressive bioenergetic disruption. The hypothesis was tested by analyzing the isolated and combined effect of aging and salicylate, a vastly used anti-inflammatory drug, on isolated brain fractions in rats. Male Wistar rats were divided according to age in two groups: adult (n=8, 19 weeks of age) and aged (n=8, 106 weeks of age). In vitro endpoints of brain mitochondrial function including oxygen consumption and transmembrane electric potential (ΔΨ) were evaluated in the absence and in the presence of salicylate (0.5mM). Brain mitochondrial susceptibility to calcium-induced permeability transition pore (MPTP) was also assessed. Mitochondrial oxidative stress was determined by measuring aconitase and manganese-superoxide dismutase (SOD) activity, and content in sulfhydryl groups (SH) and malondialdehyde (MDA). Mitochondrial content in apoptotic-related proteins Bax, Bcl-2 and cyclophilin D was determined by Western Blotting. Under basal, untreated, conditions, aging affected brain mitochondrial state 3 respiration, maximal ΔΨ developed, ADP phosphorylation lag phase and calcium-induced MPTP. Interestingly, MDA decreased and Mn-SOD activity increased in the aged group. Brain mitochondrial Bcl-2 content decreased and Bax/Bcl-2 ratio increased in aged group. Salicylate incubation for 20min increased lipid peroxidation in the aged group only and stimulated respiration during state 2, accompanied by decreased ΔΨ, although both effects were independent of the animal age. We confirmed that both aging and salicylate per se impaired brain mitochondrial bioenergetics, although the combination of both does not seem to worsen the mitochondrial end-points studied.

Fatty Acid Oxidation and Cardiovascular Risk during Menopause: A Mitochondrial Connection?

Menopause is a consequence of the normal aging process in women. This fact implies that the physiological and biochemical alterations resulting from menopause often blur with those from the aging process. It is thought that menopause in women presents a higher risk for cardiovascular disease although the precise mechanism is still under discussion. The postmenopause lipid profile is clearly altered, which can present a risk factor for cardiovascular disease. Due to the role of mitochondria in fatty acid oxidation, alterations of the lipid profile in the menopausal women will also influence mitochondrial fatty acid oxidation fluxes in several organs. In this paper, we propose that alterations of mitochondrial bioenergetics in the heart, consequence from normal aging and/or from the menopausal process, result in decreased fatty acid oxidation and accumulation of fatty acid intermediates in the cardiomyocyte cytosol, resulting in lipotoxicity and increasing the cardiovascular risk in the menopausal women.

Regulation and protection of mitochondrial physiology by sirtuins

The link between sirtuin activity and mitochondrial biology has recently emerged as an important field. This conserved family of NAD(+)-dependent deacetylase proteins has been described to be particularly involved in metabolism and longevity. Recent studies on protein acetylation have uncovered a high number of acetylated mitochondrial proteins indicating that acetylation/deacetylation processes may be important not only for the regulation of mitochondrial homeostasis but also for metabolic dysfunction in the context of various diseases such as metabolic syndrome/diabetes and cancer. The functional involvement of sirtuins as sensors of the redox/nutritional state of mitochondria and their role in mitochondrial protection against stress are hereby described, suggesting that pharmacological manipulation of sirtuins is a viable strategy against several pathologies.

Exercise as a beneficial adjunct therapy during Doxorubicin treatment--role of mitochondria in cardioprotection

One of the mostly used chemotherapeutic drugs is the highly effective anthracycline Doxorubicin. However, its clinical use is limited by the dose-related and cumulative cardiotoxicity and consequent dysfunction. It has been proposed that the etiology of this toxicity is related to mitochondrial dysfunction. The present review aimed to analyze the promising results regarding the effect of several types of physical exercise in cardiac tolerance of animals treated with acute and sub-chronic doses of Doxorubicin (DOX), highlighting the importance of cardiac mitochondrial-related mechanisms in the process. Physical exercise positively modulates some important cardiac defense systems to antagonize the toxic effects caused by DOX treatment, including antioxidant capacity, the overexpression of heat shock proteins and other anti-apoptotic proteins. An important role in this protective phenotype afforded by exercise should be attributed to mitochondrial plasticity, as related adaptations could be translated into improved cardiac function in the setting of the DOX cardiomyopathy.

Lipophilic caffeic and ferulic acid derivatives presenting cytotoxicity against human breast cancer cells

In the present work, lipophilic caffeic and ferulic acid derivatives were synthesized, and their cytotoxicity on cultured breast cancer cells was compared. A total of six compounds were initially evaluated: caffeic acid (CA), hexyl caffeate (HC), caffeoylhexylamide (HCA), ferulic acid (FA), hexyl ferulate (HF), and feruloylhexylamide (HFA). Cell proliferation, cell cycle progression, and apoptotic signaling were investigated in three human breast cancer cell lines, including estrogen-sensitive (MCF-7) and insensitive (MDA-MB-231 and HS578T). Furthermore, direct mitochondrial effects of parent and modified compounds were investigated by using isolated liver mitochondria. The results indicated that although the parent compounds presented no cytotoxicity, the new compounds inhibited cell proliferation and induced cell cycle alterations and cell death, with a predominant effect on MCF-7 cells. Interestingly, cell cycle data indicates that effects on nontumor BJ fibroblasts were predominantly cytostatic and not cytotoxic. The parent compounds and derivatives also promoted direct alterations on hepatic mitochondrial bioenergetics, although the most unexpected and never before reported one was that FA induces the mitochondrial permeability transition. The results show that the new caffeic and ferulic acid lipophilic derivatives show increased cytotoxicity toward human breast cancer cell lines, although the magnitude and type of effects appear to be dependent on the cell type. Mitochondrial data had no direct correspondence with effects on intact cells suggesting that this organelle may not be a critical component of the cellular effects observed. The data provide a rational approach to the design of effective cytotoxic lipophilic hydroxycinnamic derivatives that in the future could be profitably applied for chemopreventive and/or chemotherapeutic purposes.

Acute exercise protects against calcium-induced cardiac mitochondrial permeability transition pore opening in doxorubicin-treated rats

The use of DOX (doxorubicin), an antibiotic used in oncological treatments, is limited by a dose-related cardiotoxicity against which acute exercise is protective. However, the mitochondrial-related mechanisms of this protection remain unknown. Therefore the present study aimed to determine the effects of an acute endurance exercise bout performed 24 h before DOX treatment on heart and liver mitochondrial function. A total of 20 adult male Wistar rats were divided into groups as follows: non-exercised with saline (NE + SAL), non-exercised DOX-treated (NE + DOX), exercised with saline (EX + SAL) and exercised DOX-treated (EX + DOX). The animals performed a 60 min exercise bout on a treadmill or remained sedentary 24 h before receiving either a DOX bolus (20 mg/kg of body weight) or saline. Heart and liver mitochondrial function [oxygen consumption, membrane potential (DeltaPsi) and cyclosporin-A-sensitive calcium-induced MPTP (mitochondrial permeability transition pore) opening] were evaluated. The activities of the respiratory complex, Mn-SOD (superoxide dismutase), caspases 3 and 9, as well as the levels of ANT (adenine nucleotide translocase), VDAC (voltage-dependent anion channel), CypD (cyclophilin D), Bax and Bcl-2, were measured. Acute exercise prevented the decreased cardiac mitochondrial function (state 3, phosphorylative lagphase; maximal DeltaPsi generated both with complex I- and II-linked substrates and calcium-induced MPTP opening) induced by DOX treatment. Exercise also prevented the DOX-induced decreased activity of cardiac mitochondrial chain complexes I and V, and increased caspase 3 and 9 activities. DOX administration and exercise caused increased cardiac mitochondrial SOD activity. Exercise ameliorated liver mitochondrial complex activities. No alterations were observed in the measured MPTP and apoptosis-related proteins in heart and liver mitochondria. The results demonstrate that acute exercise protects against cardiac mitochondrial dysfunction, preserving mitochondrial phosphorylation capacity and attenuating DOX-induced decreased tolerance to MPTP opening.

Can Drug Safety be Predicted and Animal Experiments Reduced by Using Isolated Mitochondrial Fractions?

Mitochondrial toxicity has resulted in the withdrawal of several drugs from the market. One particular example is nefazodone, an anti-depressant withdrawn in the USA due to hepatoxicity caused by drug-induced mitochondrial dysfunction. Drug development and safety testing can involve the use of large numbers of laboratory animals, which, without a decisive pre-screening for mitochondrial toxicity, are often unable to pre-empt higher mortality rates in some patient groups. The use of isolated mitochondria as a screening tool for drug safety can decrease the number of laboratory animals used in pre-clinical studies, thus improving animal welfare and healthcare outcomes and costs. Novel techniques involving high-throughput methods can be used to investigate whether a molecule is a mitochondrial toxicant. Moreover, these screens are mechanistically-based, since the effects of the drug on oxidative phosphorylation, calcium homeostasis and mitochondrial genetics can be assessed. This review is intended to demonstrate that isolated mitochondrial fractions are suitable for predicting drug and general chemical safety in toxicological screenings, thus contributing to the refinement and reduction of animal use in laboratory research.