Anthracycline anticancer drugs (e.g., doxorubicin or daunorubicin) can induce chronic cardiotoxicity and heart failure (HF), both of which are believed to be based on oxidative injury and mitochondrial damage. In this study, molecular and functional changes induced by chronic anthracycline treatment with progression into HF in post-treatment follow-up were analyzed with special emphasis on nuclear factor erythroid 2-related factor 2 (Nrf2) and peroxisome proliferator-activated receptor-␥ coactivator-1␣ (PGC1␣) pathways. Chronic cardiotoxicity was induced in rabbits with daunorubicin (3 mg/kg, weekly for 10 weeks), and the animals were followed for another 10 weeks. Echocardiography revealed a significant drop in left ventricular (LV) systolic function during the treatment with marked progression to LV dilation and congestive HF in the follow-up. Although daunorubicin-induced LV lipoperoxidation was found, it was only loosely associated with cardiac performance. Furthermore, although LV oxidized glutathione content was increased, the oxidized-to-reduced glutathione ratio itself remained unchanged. Neither Nrf2, the master regulator of antioxidant response, nor the majority of its target genes showed up-regulation in the study. However, down-regulation of manganese superoxide dismutase and NAD(P)H dehydrogenase [quinone] 1 were observed together with heme oxygenase 1 up-regulation. Although marked perturbations in mitochondrial functions were found, no induction of PGC1␣-controlled mitochondrial biogenesis pathway was revealed. Instead, especially in the post-treatment period, an impaired regulation of this pathway was observed along with down-regulation of the expression of mitochondrial genes. These results imply that global oxidative stress need not be a factor responsible for the development of anthracycline-induced HF, whereas suppression of mitochondrial biogenesis might be involved.

The effect of repeated i.v. administration (once weekly, 12 administrations) of a new antineoplastic agent, Oracin (6-[2-(2-hydroxyethyl)aminoethyl]-5, 11-dioxo-5,6-dihydro-11 H-indeno [1,2-c]-isochinoline hydrochloride, 10 mg/kg) and daunorubicin (3 mg/kg) were investigated in rabbits in vivo. The criterion of occurrence of cardiotoxicity was compared with a control group of animals. Noninvasive polygraphic records were used to evaluate the function of the heart. The morphological changes of the heart were evaluated after the death of animals. There were no significant changes found in the ratio of the pre-ejection period/left ventricular ejection time (PEP: LVET ratio) after administration of Oracin (values between 0.3080 and 0.3310) or in the control group (values between 0.3425 and 0.3885). The administration of daunorubicin induced a significant, progressive increase in the PEP: LVET ratio (0.3775-0.9473), which was significantly different both from the Oracin-treated and the control group of animals. Histological examination of the hearts from the control group revealed normal structure of the myocardium including minute changes (dispersed cardiomyocytes with intensively eosinophilic cytoplasm, and several single cells with degenerated myofibrils) similar to the normal changes in muscle tissue. A very similar scenario was found in the Oracin group with the exception of one case where a slightly higher number of degenerated and necrotic cells was occurring. Administration of daunorubicin resulted in severe dispersed damage of the myocardium (myocytolysis with subsequent interstitial fibrosis), the changes being markedly different from those of the Oracin treatment and the control group. On the basis of our results it is possible to conclude that the administration of Oracin (10 mg/kg i.v.) did not induce signs of cardiotoxicity in rabbits in vivo.

Cardiotoxicity represents the main drawback of clinical usefulness of anthracycline antineoplastic drugs. In this study, a content of selected elements (Ca, Mg, K, Se, Fe) in the post-mortem removed samples of the myocardial tissue was studied in three groups of rabbits: 1) control group (i.v. saline; n = 10); 2) daunorubicin-receiving animals (DAU; 3 mg/kg, i.v; n = 11); 3) animals receiving cardioprotective iron-chelating agent dexrazoxane (DEX; 60 mg/kg, i.p.; n = 5) prior to DAU. Drugs were administered once weekly for 10 weeks. 5-7 days after the last administration, cardiac left ventricular contractility (dP/dtmax) was significantly decreased in DAU-treated animals (745 +/- 69 versus 1245 +/- 86 kPa/s in the control group; P < 0.05), while in the DEX + DAU group it was insignificantly increased (1411 +/- 77 kPa/s). Of the myocardial elements' content studied, a significant increase in total Ca against control (16.2 +/- 2.4 versus 10.6 +/- 0.9 microg/g of dry tissue; P < 0.05) was determined in the DAU-group, which was accompanied with significant decreases in Mg and K. In the heart tissue of DEX-pretreated animals, no significant changes of elements' content were found as compared to controls, while the Ca content was in these animals significantly lower than in the DAU group (9.1 +/- 0.4 versus 16.2 +/- 2.4 microg/g; P < 0.05). Hence, in this study we show that systolic heart failure induced by chronic DAU administration is primarily accompanied by persistent calcium overload of cardiac tissue and the protective action of DEX is associated with the restoration of normal myocardial Ca content.

Salicylaldehyde Isonicotinoyl Hydrazone (SIH) – a Pyridoxal Isonicotinoyl Hydrazone (PIH) analogue – is an effective iron chelator with antioxidant and antimalarial effects, as documented in numerous in vitro studies. However, no toxicological data obtained from in vivo studies have been made available yet. In this study, the potential toxic effects of repeated administration of SIH (50 mg/kg, once weekly, 10 weeks, i.p.), partially dissolved in a 10 % Cremophor solution, on various biochemical, haematological, and cardiovascular parameters and on morphology of selected tissues were investigated in rabbits. The obtained values were compared with data from the control (saline, 1 ml/kg, i.v.) and the Cremophor (10 % Cremophor solution, 2 ml/kg, i.p.) groups. In this study, SIH did not induced marked signs of toxicity: No premature deaths occurred, the body weight increase was comparable with the control and Cremophor groups. Only few and mild changes in some biochemical and haematological parameters could be determined, most of them were noticed also in the control or Cremophor groups. The morphological changes in the kidney were mild and did not manifest in the biochemical examination. The cardiac function was also not affected markedly – the values of left ventricular ejection fraction and systolic time interval did not differ from the values of control group. Only an increased left ventricular contractility (dP/dtmax) was noticed in the SIH group at the end of the experiment as compared to the controls (13354±1191 vs. 9339±647 mmHg/s, resp.). These results seem to be promising from the standpoint of possible clinical use of SIH.

Anthracycline cardiotoxicity represents a serious risk of anticancer chemotherapy. The aim of the present pilot study was to compare the potential of both the left ventricular (LV) filling pattern evaluation and cardiac troponin T (cTnT) plasma levels determination for the early detection of daunorubicin-induced cardiotoxicity in rabbits. The echocardiographic measurements of transmitral LV inflow as well as cTnT determinations were performed weekly for 10 weeks in daunorubicin (3 mg/kg weekly) and control groups (n=5, each). Surprisingly, no significant changes in LV-filling pattern were observed through the study, most likely due to the xylazine-containing anesthesia, necessary for appropriate resolving of the E and A waves. In contrast to the echographic measurement, the dP/dt(min) index obtained invasively at the end of the study revealed a significant impairment in LV relaxation, which was further supported by observed disturbances in myocardial collagen content and calcium homeostasis. However, at the same time cTnT plasma levels were progressively rising in the daunorubicin-treated animals from the fifth week (0.024+/-0.008 microg/l) until the end of the experiment (0.186+/-0.055 microg/l). Therefore, in contrast to complicated non-invasive evaluation of diastolic function, cTnT is shown to be an early and sensitive marker of anthracycline-induced cardiotoxicity in the rabbit model.