Doxorubicin affects the cardiac muscarinic system in the rat

Acetylcholine receptor agonists provide cardioprotection in doxorubicin-induced cardiotoxicity via modulating muscarinic M2 and α7 nicotinic receptor expression

The balance between cardiac sympathetic and parasympathetic activities has been intricately linked to mitochondrial function, cellular oxidative status, and immunomodulation in healthy and diseased myocardium. Cardiac autonomic neuropathy, along with the associated mitochondrial and cellular dysfunction, is an important pathophysiological feature of doxorubicin-induced cardiotoxicity (DIC). We tested the hypothesis that autonomic modulation by activation of acetylcholine receptors (AChR) effectively attenuates DIC. Rats were divided into control (0.9% sodium chloride solution) and doxorubicin groups (DOX, 3 mg/kg/d, 6 doses). Rats in the DOX group were equally subdivided into 4 interventional groups and treated for 30 days: vehicle, α7 nicotinic receptor agonist (PNU: PNU-282987, 3 mg/kg/d), muscarinic receptor agonist (BET: bethanechol, 12 mg/kg/d), and combined α7nAChR and mAChR agonists group (COM). Cardiac biochemical and functional analyses were done. The results show that AChR agonists protected the heart against DIC via improving mitochondrial and cardiac function, which was accompanied by reducing mitochondrial oxidative damage, apoptosis, and inflammation. Strikingly, PNU and BET exerted cardioprotection through different molecular pathways. PNU-mediated α7nAChR activation promoted mitochondrial fusion via upregulation of Mfn1-2 and attenuated DOX-induced autophagy. Contrarily, activation of mAChR by BET attenuated mitochondrial fission and mitophagy. The in vitro experiments confirmed the cytoprotective effects of AChR activation in DOX-treated H9c2 cells without compromising the anticancer effect of DOX in cancer cells. In conclusion, α7nAChR and mAChR agonists exerted cardioprotection against DIC via rebalancing autonomic function, improving mitochondrial function, reducing oxidative stress, and decreased cardiomyocyte apoptosis and inflammation, leading to improved cardiac function.

Breast cancer: Muscarinic receptors as new targets for tumor therapy

The development of breast cancer is a complex process that involves the participation of different factors. Several authors have demonstrated the overexpression of muscarinic acetylcholine receptors (mAChRs) in different tumor tissues and their role in the modulation of tumor biology, positioning them as therapeutic targets in cancer. The conventional treatment for breast cancer involves surgery, radiotherapy, and/or chemotherapy. The latter presents disadvantages such as limited specificity, the appearance of resistance to treatment and other side effects. To prevent these side effects, several schedules of drug administration, like metronomic therapy, have been developed. Metronomic therapy is a type of chemotherapy in which one or more drugs are administered at low concentrations repetitively. Recently, two chemotherapeutic agents usually used to treat breast cancer have been considered able to activate mAChRs. The combination of low concentrations of these chemotherapeutic agents with muscarinic agonists could be a useful option to be applied in breast cancer treatment, since this combination not only reduces tumor cell survival without affecting normal cells, but also decreases pathological neo-angiogenesis, the expression of drug extrusion proteins and the cancer stem cell fraction. In this review, we focus on the previous evidences that have positioned mAChRs as relevant therapeutic targets in breast cancer and analyze the effects of administering muscarinic agonists in combination with conventional chemotherapeutic agents in a metronomic schedule.

Detrimental effects of chemotherapy on human coronary microvascular function

Chemotherapy (CT) is a necessary treatment to prevent the growth and survival of cancer cells. However, CT has a well-established adverse impact on the cardiovascular (CV) system, even years after cessation of treatment. The effects of CT drugs on tumor vasculature have been the focus of much research, but little evidence exists showing the effects on the host microcirculation. Microvascular (MV) dysfunction is an early indicator of numerous CV disease phenotypes, including heart failure. The goal of this study was to evaluate the direct effect of doxorubicin (Dox) on human coronary MV function. To study the effect of CT on the cardiac MV function, flow-mediated dilation (FMD), pharmacologically-induced endothelial dependent dilation to acetylcholine (ACh), and smooth muscle-dependent dilation to papaverine were investigated. Vessels were freshly isolated from atrial appendages of adult patients undergoing cardiopulmonary bypass surgery or from cardiac tissue of pediatric patients, collected at the time of surgery to repair congenital heart defects. Isolated vessels were incubated in endothelial culture medium containing vehicle or Dox (100 nm, 15-20 h) and used to measure dilator function by video microscopy. Ex vivo treatment of adult human coronary microvessels with Dox significantly impaired flow-mediated dilation (FMD). Conversely, in pediatric coronary microvessels, Dox-induced impairment of FMD was significantly reduced in comparison with adult subjects. In both adult and pediatric coronary microvessels, ACh-induced constriction was reversed into dilation in the presence of Dox. Smooth muscle-dependent dilation remained unchanged in all groups tested. In vessels from adult subjects, acute treatment with Dox in clinically relevant doses caused significant impairment of coronary arteriolar function, whereas vessels from pediatric subjects showed only marginal impairment to the same stressor. This interesting finding might explain the delayed onset of future adverse CV events in children compared with adults after anthracycline therapy.NEW & NOTEWORTHY We have characterized, for the first time, human microvascular responses to acute ex vivo exposure to doxorubicin in coronary vessels from patients without cancer. Our data show an augmented impairment of endothelial function in vessels from adult subjects compared with pediatric samples.

Accelerated structure-based design of chemically diverse allosteric modulators of a muscarinic G protein-coupled receptor

Design of ligands that provide receptor selectivity has emerged as a new paradigm for drug discovery of G protein-coupled receptors, and may, for certain families of receptors, only be achieved via identification of chemically diverse allosteric modulators. Here, the extracellular vestibule of the M2 muscarinic acetylcholine receptor (mAChR) is targeted for structure-based design of allosteric modulators. Accelerated molecular dynamics (aMD) simulations were performed to construct structural ensembles that account for the receptor flexibility. Compounds obtained from the National Cancer Institute (NCI) were docked to the receptor ensembles. Retrospective docking of known ligands showed that combining aMD simulations with Glide induced fit docking (IFD) provided much-improved enrichment factors, compared with the Glide virtual screening workflow. Glide IFD was thus applied in receptor ensemble docking, and 38 top-ranked NCI compounds were selected for experimental testing. In [(3)H]N-methylscopolamine radioligand dissociation assays, approximately half of the 38 lead compounds altered the radioligand dissociation rate, a hallmark of allosteric behavior. In further competition binding experiments, we identified 12 compounds with affinity of ≤30 μM. With final functional experiments on six selected compounds, we confirmed four of them as new negative allosteric modulators (NAMs) and one as positive allosteric modulator of agonist-mediated response at the M2 mAChR. Two of the NAMs showed subtype selectivity without significant effect at the M1 and M3 mAChRs. This study demonstrates an unprecedented successful structure-based approach to identify chemically diverse and selective GPCR allosteric modulators with outstanding potential for further structure-activity relationship studies.

Strain echocardiography combined with pharmacological stress test for early detection of anthracycline induced cardiomyopathy

INTRODUCTION

Advances in echocardiography, including 2-D speckle tracking to quantitate myocardial strain and strain rate, have improved myocardial functional and mechanical evaluation and may provide a more sensitive assessment of cardiac functional and mechanical changes. Additionally, evaluating myocardial performance induced by a pharmacologic stress test (dobutamine infusion) may further improve the evaluation of potential changes in cardiac function. This study evaluates the use of 2-D speckle tracking strain echocardiography (2DSE) combined with a dobutamine stress test to detect doxorubicin induced cardiomyopathy in the rat.

METHODS

Rats were dosed once per week with 2 mg/kg doxorubicin for 6 weeks. Echocardiography was performed weekly at rest and during dobutamine infusion (20 mcg/kg/min IV).

RESULTS

Throughout the study there were no differences between control and doxorubicin treated groups at rest for radial strain, circumferential strain, fractional shortening (FS), or heart rate (HR). During dobutamine infusion, radial strain, circumferential strain, FS, and HR similarly increased significantly in both the control and doxorubicin treated groups at weeks 0, 1, and 2. At week 3 there was a significant attenuation of the increase in radial strain in the doxorubicin treated group, and at weeks 4 and 6 there was significant attenuation in radial strain and circumferential strain. No significant differences were detected in FS or HR between the two groups at any time points. Histology of the left ventricle at week 7 showed mild changes (mild cardiomyocyte vacuolation with minimal inflammation and no fibrosis) in the doxorubicin treated animals as compared to the control animals, which were consistent with mild doxorubicin induced injury.

DISCUSSION

These data suggest that 2 D speckle tracking strain echocardiography combined with dobutamine stress test can detect early changes in myocardial function and may be useful tools in early detection of drug-induced cardiac dysfunction.

Cardiovascular and survival effects of sympatho-inhibitors in adriamycin-induced cardiomyopathy in rats

Adriamycin (ADR) is a widely used drug for the treatments of cancers. This study evaluates the effects of moxonidine and metoprolol on cardiac hemodynamics and survival in ADR-induced left ventricular dysfunction (total dose of 20 mg/kg in a 4-week regimen). Rats were treated with the centrally acting I(1)R agonist sympatho-inhibitor, moxonidine, or with the non-selective beta-adrenergic antagonist, metoprolol, during 1 month or until death. Treatments began 1 week after the onset of the ADR administration. Low doses (0.5 and 1 mg/kg/day) of moxonidine and metoprolol (10 mg/kg/day) improved cardiovascular function. High doses of moxonidine (3 mg/kg/day) and metoprolol (150 mg/kg/day) were cardiodepressive. Moxonidine and metoprolol both failed to improve survival. These data indicate that a treatment with these sympatho-inhibitors can reduce the left ventricular dysfunction induced by ADR. Moreover, these cardioprotective effects where obtained even when ADR was used at a dose regimen usually employed for its antineoplastic effects in rodents. Nevertheless, in this particular cardiomyopathy, we did not find any association between improvements of functional parameters and survival whatever the drug and the dose used. This problem points out the difficulty to prevent, at least with sympatho-inhibitory drugs alone, the mortality linked to the chronic cardiotoxicity of ADR.

Effects of Anticancer Chemotherapeutic Drugs on the Acetylcholine Receptor-Operated Potassium Current in Guinea Pig Atrial Myocytes

The effects of 7 anticancer chemotherapeutic drugs on the muscarinic acetylcholine receptor-operated potassium current (I(K.ACh)) in guinea pig atrial myocytes were investigated using the whole cell patch clamp technique. Doxorubicin, pirarubicin, and mitoxantrone inhibited the carbachol-induced I(K.ACh) in a concentration-dependent manner in atrial cells at a holding potential of -40 mV. IC50 values of doxorubicin, pirarubicin, and mitoxantrone for the carbachol-induced I(K.ACh) were 7.7 microM, 3.7 microM, and 9.1 microM, respectively. Pirarubicin inhibited the adenosine-induced and the GTPgammaS-induced I(K.ACh) in a concentration-dependent manner (IC50=6.0 and 5.1 microM, respectively). Doxorubicin and mitoxantrone up to 100 microM did not have an influence on the adenosine-induced I(K.ACh). Doxorubicin did not affect the GTPgammaS-induced I(K.ACh). Mitoxantrone 100 microM inhibited the current only by 25%. For concentrations up to 100 microM, anticancer drugs that have chemical structures entirely different from that of doxorubicin, i.e., 5-fluorouracil, 6-mercaptopurine, cyclophosphamide, and actinomycin D, did not have an influence on the carbachol-induced I(K.ACh). Doxorubicin and chemically related compounds possess anticholinergic effects mediated via an inhibitory action on I(K.ACh) by different underlying molecular mechanisms. Doxorubicin and mitoxantrone may inhibit I(K.ACh) by the blockade of muscarinic receptors, whereas pirarubicin may inhibit the current not only via blocking the muscarinic receptors but also by depressing the functions of the K+ channel itself and/or GTP-binding proteins.

Changes in Myocardial .BETA.1-Adrenergic Receptor and Stimulatory G-Protein Gene Expression after Chronic Treatment with Doxorubicin in Rat

The gene expression of beta(1)-adrenergic receptor (beta(1)AR) and stimulatory G-protein Gsalpha in ventricle after chronic treatment with doxorubicin (DOX) in rat was investigated. The rats were treated with DOX in a dose of 2.5 mg/kg once a week for 5 weeks, the cumulative dose being 12.5 mg/kg. Two weeks after the last injection, the positive inotropic effect of isoproterenol was noticeably decreased in left atrial muscle preparations isolated from DOX-treated rats. Northern blot hybridization showed that the mRNA transcripts of beta(1)AR and Gsalpha, important signal transduction elements for regulating heart rate and contractility, were significantly decreased in the ventricle of DOX-treated rats. Thus, chronic treatment with DOX decreases the gene expression levels of myocardial beta(1)AR and Gsalpha.

Impaired Gene Expression of .BETA.1-Adrenergic Receptor, but Not Stimulatory G-Protein Gs.ALPHA., in Rat Ventricular Myocardium Treated with Isoproterenol

We investigated the gene expression of beta(1)-adrenergic receptor (beta(1)AR) and stimulatory G-protein Gsalpha, important signal transduction elements for regulating heart rate and contractility, in ventricle after chronic treatment with isoproterenol (ISO) in rat. Rats were treated with ISO (4 mg/kg, intraperitoneal) twice a day for 4 d. Ventricle weight of the heart and ventricle weight/body weight ratio were increased by 23% and 25% compared with control, respectively. Positive inotropic responses to ISO in left atrial muscle preparations isolated from ISO-treated rats were markedly decreased. Northern blot hybridization showed that the mRNA transcript of beta(1)AR was significantly decreased in ventricle of ISO-treated rats, whereas Gsalpha mRNA level was unchanged. Present results demonstrate that the gene expression of myocardial beta(1)AR, but not Gsalpha, was decreased in rat myocardium of ISO-induced cardiac hypertrophy, and suggesting that decrease in the gene expression of beta(1)AR may be one of the mechanisms responsible for the diminished cardiac function.