MicroRNA-34a-5p as a promising early circulating preclinical biomarker of doxorubicin-induced chronic cardiotoxicity.

Cardiotoxicity is a serious adverse effect of an anticancer drug, doxorubicin (DOX), which can occur within a year or decades after completion of therapy. The present study was designed to address a knowledge gap concerning a lack of circulating biomarkers capable of predicting the risk of cardiotoxicity induced by DOX. Profiling of 2083 microRNAs (miRNAs) in mouse plasma revealed 81 differentially expressed miRNAs 1 week after 6, 9, 12, 18, or 24 mg/kg total cumulative DOX doses (early-onset model) or saline (SAL). Among these, the expression of seven miRNAs was altered prior to the onset of myocardial injury at 12 mg/kg and higher cumulative doses. The expression of only miR-34a-5p was significantly (false discovery rate [FDR] < 0.1) elevated at all total cumulative doses compared with concurrent SAL-treated controls and showed a statistically significant dose-related response. The trend in plasma miR-34a-5p expression levels during DOX exposures also correlated with a significant dose-related increase in cardiac expression of miR-34a-5p in these mice. Administration of a cardioprotective drug, dexrazoxane, to mice before DOX treatment, significantly mitigated miR-34a-5p expression in both plasma and heart in conjunction with attenuation of cardiac pathology. This association between plasma and heart may suggest miR-34a-5p as a potential early circulating marker of early-onset DOX cardiotoxicity. In addition, higher expression of miR-34a-5p (FDR < 0.1) in plasma and heart compared with SAL-treated controls 24 weeks after 24 mg/kg total cumulative DOX dose, when cardiac function was altered in our recently established delayed-onset cardiotoxicity model, indicated its potential as an early biomarker of delayed-onset cardiotoxicity.

Candidate early predictive plasma protein markers of doxorubicin-induced chronic cardiotoxicity in B6C3F1 mice.

Cardiotoxicity is a serious adverse effect of doxorubicin (DOX) treatment in cancer patients. Currently, there is a lack of sensitive biomarkers to predict the risk of DOX-induced cardiotoxicity. Using SOMAmer-based proteomic technology, 1129 proteins were profiled to identify potential early biomarkers of cardiotoxicity in plasma from male B6C3F1 mice given a weekly intravenous dose of 3 mg/kg DOX or saline (SAL) for 2, 3, 4, 6, or 8 weeks (6, 9, 12, 18, or 24 mg/kg cumulative DOX doses, respectively). Also, a group of mice received the cardio-protectant, dexrazoxane (DXZ; 60 mg/kg; intraperitoneal) 30 min before a weekly DOX or SAL dose. Proteomic analysis in plasma collected a week after the last dose showed a significant ≥1.2-fold change in level of 18 proteins in DOX-treated mice compared to SAL-treated counterparts during 8-week exposure. Of these, neurogenic locus notch homolog protein 1 (NOTCH1), von Willebrand factor (vWF), mitochondrial glutamate carrier 2, Wnt inhibitory factor 1, legumain, and mannan-binding lectin serine protease 1 were increased in plasma at 6 mg/kg cumulative DOX dose, prior to the release of myocardial injury marker, cardiac troponin I at 12 mg/kg and higher cumulative doses. These six proteins also remained significantly elevated following myocardial injury or pathology at 24 mg/kg. Pretreatment of mice with DXZ significantly attenuated DOX-induced elevated levels of only NOTCH1 and vWF with mitigation of cardiotoxicity. This suggests NOTCH1 and vWF as candidate early biomarkers of DOX cardiotoxicity, which may help in addressing a clinically important question of identifying cancer patients at risk for cardiotoxicity.

Sex-related differential susceptibility to doxorubicin-induced cardiotoxicity in B6C3F1 mice.

Sex is a risk factor for development of cardiotoxicity, induced by the anti-cancer drug, doxorubicin (DOX), in humans. To explore potential mechanisms underlying differential susceptibility to DOX between sexes, 8-week old male and female B6C3F1 mice were dosed with 3mg/kg body weight DOX or an equivalent volume of saline via tail vein once a week for 6, 7, 8, and 9 consecutive weeks, resulting in 18, 21, 24, and 27mg/kg cumulative DOX doses, respectively. At necropsy, one week after each consecutive final dose, the extent of myocardial injury was greater in male mice compared to females as indicated by higher plasma concentrations of cardiac troponin T at all cumulative DOX doses with statistically significant differences between sexes at the 21 and 24mg/kg cumulative doses. A greater susceptibility to DOX in male mice was further confirmed by the presence of cytoplasmic vacuolization in cardiomyocytes, with left atrium being more vulnerable to DOX cardiotoxicity. The number of TUNEL-positive cardiomyocytes was mostly higher in DOX-treated male mice compared to female counterparts, showing a statistically significant sex-related difference only in left atrium at 21mg/kg cumulative dose. DOX-treated male mice also had an increased number of γ-H2A.X-positive (measure of DNA double-strand breaks) cardiomyocytes compared to female counterparts with a significant sex effect in the ventricle at 27mg/kg cumulative dose and right atrium at 21 and 27mg/kg cumulative doses. This newly established mouse model provides a means to identify biomarkers and access potential mechanisms underlying sex-related differences in DOX-induced cardiotoxicity.

Early transcriptional changes in cardiac mitochondria during chronic doxorubicin exposure and mitigation by dexrazoxane in mice.

Identification of early biomarkers of cardiotoxicity could help initiate means to ameliorate the cardiotoxic actions of clinically useful drugs such as doxorubicin (DOX). Since DOX has been shown to target mitochondria, transcriptional levels of mitochondria-related genes were evaluated to identify early candidate biomarkers in hearts of male B6C3F1 mice given a weekly intravenous dose of 3mg/kg DOX or saline (SAL) for 2, 3, 4, 6, or 8 weeks (6, 9, 12, 18, or 24 mg/kg cumulative DOX doses, respectively). Also, a group of mice was pretreated (intraperitoneally) with the cardio-protectant, dexrazoxane (DXZ; 60 mg/kg) 30 min before each weekly dose of DOX or SAL. At necropsy a week after the last dose, increased plasma concentrations of cardiac troponin T (cTnT) were detected at 18 and 24 mg/kg cumulative DOX doses, whereas myocardial alterations were observed only at the 24 mg/kg dose. Of 1019 genes interrogated, 185, 109, 140, 184, and 451 genes were differentially expressed at 6, 9, 12, 18, and 24 mg/kg cumulative DOX doses, respectively, compared to concurrent SAL-treated controls. Of these, expression of 61 genes associated with energy metabolism and apoptosis was significantly altered before and after occurrence of myocardial injury, suggesting these as early genomics markers of cardiotoxicity. Much of these DOX-induced transcriptional changes were attenuated by pretreatment of mice with DXZ. Also, DXZ treatment significantly reduced plasma cTnT concentration and completely ameliorated cardiac alterations induced by 24 mg/kg cumulative DOX. This information on early transcriptional changes during DOX treatment may be useful in designing cardioprotective strategies targeting mitochondria.

Early biomarkers of doxorubicin-induced heart injury in a mouse model.

Cardiac troponins, which are used as myocardial injury markers, are released in plasma only after tissue damage has occurred. Therefore, there is a need for identification of biomarkers of earlier events in cardiac injury to limit the extent of damage. To accomplish this, expression profiling of 1179 unique microRNAs (miRNAs) was performed in a chronic cardiotoxicity mouse model developed in our laboratory. Male B6C3F1 mice were injected intravenously with 3mg/kg doxorubicin (DOX; an anti-cancer drug), or saline once a week for 2, 3, 4, 6, and 8weeks, resulting in cumulative DOX doses of 6, 9, 12, 18, and 24mg/kg, respectively. Mice were euthanized a week after the last dose. Cardiac injury was evidenced in mice exposed to 18mg/kg and higher cumulative DOX dose whereas examination of hearts by light microscopy revealed cardiac lesions at 24mg/kg DOX. Also, 24 miRNAs were differentially expressed in mouse hearts, with the expression of 1, 1, 2, 8, and 21 miRNAs altered at 6, 9, 12, 18, and 24mg/kg DOX, respectively. A pro-apoptotic miR-34a was the only miRNA that was up-regulated at all cumulative DOX doses and showed a significant dose-related response. Up-regulation of miR-34a at 6mg/kg DOX may suggest apoptosis as an early molecular change in the hearts of DOX-treated mice. At 12mg/kg DOX, up-regulation of miR-34a was associated with down-regulation of hypertrophy-related miR-150; changes observed before cardiac injury. These findings may lead to the development of biomarkers of earlier events in DOX-induced cardiotoxicity that occur before the release of cardiac troponins.

The influence of age on serum concentrations of cardiac troponin I: results in rats, monkeys, and commercial sera.

Cardiac troponins serve as serum biomarkers of myocardial injury. The current study examined the influence of age on serum concentrations of cardiac troponin I (cTnI). An ultrasensitive immunoassay was used to monitor cTnI concentrations in Sprague-Dawley (SD) rats and Erythrocebus patas monkeys of different ages. The mean cTnI concentrations were highest in 10-day-old rats compared to 25-, 40-, and 80-day-old SD rats. Cardiomyocyte remodeling was apparent in hearts from 10-day-old SD rats as evident by hypercellularity, irregularly shaped nuclei, and moderate numbers of myocytes undergoing mitosis and apoptosis. The mean concentration of cTnI in 5 newborn monkeys was considerably higher than that of three 1-year-old monkeys. Evidence of cardiomyocyte remodeling was also observed in these newborn hearts (loss of myofibrils and cytoplasmic vacuolation). Commercial animal serum samples were also analyzed. The concentrations of cTnI detected in fetal equine and porcine serum were considerably higher than that found in adult equine and porcine serum samples Likewise, fetal bovine serum had higher cTnI concentrations (>2,400 pg/ml) than did adult caprine and laprine samples (2.5-2.7 pg/ml). The present study found age-related differences in cTnI concentrations, with higher levels occurring at younger ages. This effect was consistent across several animal species.

Sex-related differences in mast cell activity and doxorubicin toxicity: a study in spontaneously hypertensive rats.

Clinically, girls appear to be more sensitive than boys to the cardiotoxic effects of doxorubicin, whereas the opposite may be true for adults. To identify and characterize potential sex-related differences, adult male and female spontaneously hypertensive rats (SHR; some ovariectomized [OVX]) received 1 mg/kg of doxorubicin or saline iv weekly for 9, 10, or 12 weeks. Weight gain was slower in treated males. Serum concentrations of cholesterol and triglycerides increased and those of albumin decreased in both sexes, but changes were more pronounced in treated males. Treated males had significantly more severe cardiomyopathy scores and higher serum levels of cTnT than females. The increased cardiotoxicity was accompanied by higher numbers of cardiac mast cells (MCs) and percentage of cardiac MCs undergoing degranulation. Doxorubicin-treated OVX animals had significantly increased numbers of cardiac MCs, more severe myocardial lesions, and elevated serum concentrations of cTnT compared to doxorubicin-treated normal female SHR. The severity of cardiac lesions in the OVX female was similar to that observed in doxorubicin-treated males. This study demonstrated the presence of sex-related differences in the cardiotoxic effects elicited by doxorubicin and identified variations in the level of cardiac MC activity as a factor which could possibly contribute to the male-female dissimilarity.

Development of doxorubicin-induced chronic cardiotoxicity in the B6C3F1 mouse model.

Serum levels of cardiac troponins serve as biomarkers of myocardial injury. However, troponins are released into the serum only after damage to cardiac tissue has occurred. Here, we report development of a mouse model of doxorubicin (DOX)-induced chronic cardiotoxicity to aid in the identification of predictive biomarkers of early events of cardiac tissue injury. Male B6C3F(1) mice were administered intravenous DOX at 3mg/kg body weight, or an equivalent volume of saline, once a week for 4, 6, 8, 10, 12, and 14weeks, resulting in cumulative DOX doses of 12, 18, 24, 30, 36, and 42mg/kg, respectively. Mice were sacrificed a week following the last dose. A significant reduction in body weight gain was observed in mice following exposure to a weekly DOX dose for 1week and longer compared to saline-treated controls. DOX treatment also resulted in declines in red blood cell count, hemoglobin level, and hematocrit compared to saline-treated controls after the 2nd weekly dose until the 8th and 9th doses, followed by a modest recovery. All DOX-treated mice had significant elevations in cardiac troponin T concentrations in plasma compared to saline-treated controls, indicating cardiac tissue injury. Also, a dose-related increase in the severity of cardiac lesions was seen in mice exposed to 24mg/kg DOX and higher cumulative doses. Mice treated with cumulative DOX doses of 30mg/kg and higher showed a significant decline in heart rate, suggesting drug-induced cardiac dysfunction. Altogether, these findings demonstrate the development of DOX-induced chronic cardiotoxicity in B6C3F(1) mice.

A multifaceted evaluation of imatinib-induced cardiotoxicity in the rat.

Cardiotoxicity was an unanticipated side effect elicited by the clinical use of imatinib (Imb). This toxicity has been examined in only a limited number of experimental studies. The present study sought, by a variety of approaches, to identify important characteristics of Imb-induced cardiac alterations. Male spontaneously hypertensive rats (SHRs) received oral doses of 10, 30, or 50 mg/kg Imb or water daily for 10 d. Cardiac lesions, detected at all doses, were characterized by cytoplasmic vacuolization and myofibrillar loss. In a second experiment, cardiac lesions were found in Sprague Dawley (SD) and SHR rats given 50 or 100 mg/kg Imb for 14 d. Mean cardiac lesion scores and serum levels of cardiac troponin I were higher in SHRs than in SD rats. Imb induced myocyte death by necrosis, autophagy, and apoptosis. Dose-related increases in cardiac expression were observed for several genes associated with endoplasmic reticulum stress response, protein folding, and vascular development and remodeling. Imb caused alterations in isolated myocytes (myofibrillar loss, highly disrupted and disorganized sarcomeric α-actinin, apoptosis, and increased lactate dehydrogenase release) at low concentrations (5 mM). The authors conclude that Imb exerts cardiotoxic effects that are manifest through a complex pattern of cellular alterations, the severity of which can be influenced by arterial blood pressure.

Early alterations in heart gene expression profiles associated with doxorubicin cardiotoxicity in rats.

PURPOSE: The antineoplastic anthracycline doxorubicin can induce a dose-dependent cardiomyopathy that limits the total cumulative dose prescribed to cancer patients. In both preclinical and clinical studies, pretreatment with dexrazoxane, an intracellular iron chelator, partially protects against anthracycline-induced cardiomyopathy. To identify potential additional cardioprotective treatment strategies, we investigated early doxorubicin-induced changes in cardiac gene expression. METHODS: Spontaneously hypertensive male rats (n = 47) received weekly intravenous injections of doxorubicin (3 mg/kg) or saline 30 min after pretreatment with dexrazoxane (50 mg/kg) or saline by intraperitoneal injection. Cardiac samples were analyzed 24 h after the first (n = 20), second (n = 13), or third (n = 14) intravenous injection on days 1, 8, or 15 of the study, respectively. RESULTS: Rats receiving three doses of doxorubicin had minimal myocardial alterations that were attenuated by dexrazoxane. Cardiac expression levels of genes associated with the Nrf2-mediated stress response were increased after a single dose of doxorubicin, but not affected by cardioprotectant pretreatment. In contrast, an early repressive effect of doxorubicin on transcript levels of genes associated with mitochondrial function was attenuated by dexrazoxane pretreatment. Dexrazoxane had little effect on gene expression by itself. CONCLUSIONS: Genomic analysis provided further evidence that mitochondria are the primary target of doxorubicin-induced oxidative damage that leads to cardiomyopathy and the primary site of cardioprotective action by dexrazoxane. Additional strategies that prevent the formation of oxygen radicals by doxorubicin in mitochondria may provide increased cardioprotection.

Histopathology of vascular injury in Sprague-Dawley rats treated with phosphodiesterase IV inhibitor SCH 351591 or SCH 534385.

Histopathological and immunohistochemical studies were conducted to characterize vascular injuries in rats treated with phosphodiesterase (PDE) IV inhibitors SCH 351591 or SCH 534385. Sprague-Dawley rats were administered PDE IV inhibitors by gavage at a range of doses and times. The two PDE IV inhibitors induced comparable levels of vascular injury, primarily in the mesentery and to a lesser extent in the pancreas, kidney, liver, small intestine, and stomach. Mesenteric vascular changes occurred as early as one hour, progressively developed over twenty-four to forty-eight hours, peaked at seventy-two hours, and gradually subsided from seven to nine days. The typical morphology of the vascular toxicity consisted of hemorrhage and necrosis of arterioles and arteries, microvascular injury, fibrin deposition, and perivascular inflammation of a variety of blood vessels. The incidence and severity of mesenteric vascular injury increased in a time- and dose-dependent manner in SCH 351591- or SCH 534385-treated rats. Mesenteric vascular injury was frequently associated with activation of mast cells (MC), endothelial cells (EC), and macrophages (MØ). Immunohistochemical studies showed increases in CD63 immunoreactivity of mesenteric MC and in nitrotyrosine immunoreactivity of mesenteric EC and MØ. The present study also provides a morphological and cellular basis for evaluating candidate biomarkers of drug-induced vascular injury.

Biomarkers in peripheral blood associated with vascular injury in Sprague-Dawley rats treated with the phosphodiesterase IV inhibitors SCH 351591 or SCH 534385.

Drug-associated vascular injury can be caused by phosphodiesterase (PDE) IV inhibitors and drugs from several other classes. The pathogenesis is poorly understood, but it appears to include vascular and innate immunological components. This research was undertaken to identify changes in peripheral blood associated with vascular injury caused by PDE IV inhibitors. We evaluated twelve proteins, serum nitrite, and leukocyte populations in peripheral blood of rats treated with experimental PDE IV inhibitors. We found that these compounds produced histological microvascular injury in a dose- and time-dependent manner. Measurement of these serum proteins showed changes in eight of the twelve examined. Changes were seen in the levels of: tissue inhibitor of metalloproteinase-1, alpha1-acid glycoprotein, GRO/CINC-1, vascular endothelial growth factor, C-reactive protein, haptoglobin, thrombomodulin, and interleukin-6. No changes were seen in levels of tumor necrosis factor-alpha, hepatocyte growth factor, nerve growth factor, and granulocyte-monocyte colony stimulating factor. Serum levels of nitrite were also increased. Circulating granulocyte numbers were increased, and lymphocyte numbers were decreased. The changes in these parameters showed both a dose- and time-dependent association with histopathologic changes. These biomarkers could provide an additional tool for the nonclinical and clinical evaluation of investigational compounds.

Anthracycline cardiotoxicity: from bench to bedside.

Anthracyclines remain among the most widely prescribed and effective anticancer agents. Unfortunately, life-threatening cardiotoxicity continues to compromise their usefulness. Despite more than four decades of investigation, the pathogenic mechanisms responsible for anthracycline cardiotoxicity have not been completely elucidated. In addition, new drugs and combination therapies often exacerbate the toxicity. The First International Workshop on Anthracycline Cardiotoxicity, held in fall 2006, in Como, Italy, focused on the state-of-the-art knowledge and discussed the research needed to address the cardiotoxicity of these drugs. Here, we incorporate these discussions into the framework of a broader review of preclinical and clinical issues.

Isoproterenol-induced cardiotoxicity in sprague-dawley rats: correlation of reversible and irreversible myocardial injury with release of cardiac troponin T and roles of iNOS in myocardial injury.

The present study was undertaken to characterize myocardial lesions in the rat induced by low doses of isoproterenol (Iso) and to correlate lesion severity with release of cardiac troponin T (cTnT) and changes in myocyte iNOS expression. Two types of cardiac injury patterns were observed. A Type I response, noted 3 or 6 hours postdosing with 8, 16, 32, or 64 mug/kg Iso, included potential reversible myocardial alterations associated with slight increases in serum cTnT (< 0.3 ng/mL) and a slight reduction in myocyte cTnT immunoreactivity. The second type of response noted 3, 6, 12, 24 or 48 hours postdosing with 125, 250, or 500 mug/kg Iso consisted of irreversible myocyte alterations, together with significant increases in serum cTnT (3-14 ng/mL) and a marked reduction of cTnT immunoreactivity. By 48 hours the hearts of rats dosed with 125-500 mug/kg Iso had developed interstitial fibrosis, and serum cTnT had declined to near control levels (0.06-0.18 ng/mL). Increases in iNOS immunoreactivity correlated with the lesion severity. These findings suggest that low doses of Iso exert complex effects on the myocardium and that the generation of NO through increased expression of iNOS could be an important factor in the pathogenesis of myocyte injury.

Age-related differences in susceptibility to toxic effects of valproic acid in rats.

A multi-age rat model was evaluated as a means to identify a potential age-related difference in liver injury following exposure to valproic acid (VPA), a known pediatric hepatotoxic agent. Different age groups of Sprague-Dawley (SD) rats (10-, 25-, 40-, 80-day-old) were administered VPA at doses of 160, 320, 500 or 650 mg kg(-1) (i.p.) for 4 days. Animals from all age groups developed toxicity after treatment with VPA; however, the patterns of toxicity were dissimilar within each age group. The high dose of VPA caused significant lethality in 10- and 25-day-old rats. All doses of VPA caused decrease in the platelet counts (10-, 25-day-old rats) and the rate of growth (40-day-old rats) and increases in the urine creatine concentration (high dose, 80-day-old rats). VPA induced hepatic and splenic alterations in all age groups. The most severe lesions were found mostly in 10- and 80-day-old rats. Significant changes in blood urea nitrogen, alanine aminotransferase and alkaline phosphatase were observed in 10-day-old pups after treatment with low doses of VPA. The highest VPA dose caused significant decreases in the levels of serum total protein (40- and 80-day-old rats). Principal component analysis of spectra derived from terminal urine samples of all age groups showed that each age group clusters separately. In conclusion, this study showed that the vulnerability profile of each age group was different indicating that a multi-age pediatric animal model is appropriate to assess more completely age-dependent changes in drug toxicity.

The utility of a rodent model in detecting pediatric drug-induced nephrotoxicity.

A multi-age rat model was used to identify potential age-related differences in renal injury following exposure to gentamicin (GM). In this study, 10-, 25-, 40-, and 80-day-old Sprague-Dawley rats were dosed with GM at 0, 50, or 100 mg kg(-1) body weight per day (mkd) sc for 6 or 14 days. Urine samples were collected up to 72 h after initial dosing. The maximum tolerated dose was lower in 10-day-old rats than for other ages (none survived 11 days of treatment). Eighty-day-old rats given the highest dose showed a diminished rate of growth and an increase in serum creatinine, blood urea nitrogen (BUN), urinary kidney injury molecule-1 (Kim-1), and renal pathology. Ten- and 40-day-old rats given 100 mkd of GM for 6- or 14 days also had increased levels of serum BUN and Cr and renal pathology, whereas only mild renal alterations were found in 25-day-old rats. After 6 days of treatment with 100 mkd GM, significant increases in Havcr-1 (Kim-1) gene expression were detected only in 10- and 80-day-old rats. In urine samples, nuclear magnetic resonance and ultra performance liquid chromatography/mass spectrometry analysis detected changes related to GM efficacy (e.g., hippurate) and increases in metabolites related to antioxidant activity, which was greatest in the 80-day-old rats. The magnitude of the genomic, metabonomic, and serum chemistry changes appeared to correlate with the degree of nephropathy. These findings indicate that an experimental animal model that includes several developmental stages can detect age-related differences in drug-induced organ toxicities and may be a useful predictor of pediatric drug safety in preclinical studies.

Dexrazoxane: how it works in cardiac and tumor cells. Is it a prodrug or is it a drug?

Dexrazoxane is highly effective in reducing anthracycline-induced cardiotoxicity and extravasation injury and is used clinically for these indications. Dexrazoxane has two biological activities: it is a prodrug that is hydrolyzed to an iron chelating EDTA-type structure and it is also a strong inhibitor of topoisomerase II. Doxorubicin is able to be reductively activated to produce damaging reactive oxygen species. Iron-dependent cellular damage is thought to be responsible for its cardiotoxicity. The available experimental evidence supports the conclusion that dexrazoxane reduces doxorubicin cardiotoxicity by binding free iron and preventing site-specific oxidative stress on cardiac tissue. However, it cannot be ruled out that dexrazoxane may also be protective through its ability to inhibit topoisomerase II.