Miki Nonaka

Experimental models of inherited cardiomyopathy and its therapeutics

Cardiomyopathy is a disease of myocardium categorized into three major forms, hypertrophic (HCM), dilated (DCM) and restrictive cardiomyopathy (RCM), which has recently been demonstrated to be a monogenic disease due to mutations in various proteins expressed in cardiomyocytes. Mutations in HCM and RCM typically increase the myofilament sensitivity to cytoplasmic Ca(2+), leading to systolic hyperfunction and diastolic dysfunction. In contrast, mutations in DCM typically decrease the myofilament sensitivity to cytoplasmic Ca(2+) and/or force generation/transmission, leading to systolic dysfunction. Creation of genetically-manipulated transgenic and knock-in animals expressing mutant proteins exogenously and endogenously, respectively, in their hearts provides valuable animal models to discover the molecular and cellular mechanisms for pathogenesis and promising therapeutic strategy in vivo. Recently, cardiomyocytes have been differentiated from patients induced pluripotent stem cells as a model of inherited cardiomyopathies in vitro. In this review, we provide overview of experimental models of cardiomyopathies with a focus on revealed molecular and cellular pathogenic mechanisms and potential therapeutics.

Stage‐dependent benefits and risks of pimobendan in mice with genetic dilated cardiomyopathy and progressive heart failure

The Ca2+ sensitizer pimobendan is a unique inotropic agent that improves cardiac contractility with less of an increase in oxygen consumption and potentially fewer adverse effects on myocardial remodelling and arrhythmia, compared with traditional inotropes. However, clinical trials report contradictory effects of pimobendan in patients with heart failure (HF). We provide mechanistic experimental evidence of the efficacy of pimobendan using a novel mouse model of progressive HF.

Cardiotonic actions of quercetin and its metabolite tamarixetin through a digitalis-like enhancement of Ca 2+ transients

The plant-derived flavonoid, quercetin (QCT), has many biological actions, including cardioprotective actions, resulting from its antioxidant and anti-inflammatory effects. In this study, effects of QCT and its metabolites on the contraction and Ca2+ transients (CaT) of mouse single cardiomyocytes were simultaneously measured and compared with those of isoproterenol and digoxin. Furthermore, cardiac function and plasma concentrations were analyzed after bolus intravenous administration of QCT in mice. QCT and its metabolite, tamarixetin, as well as isoproterenol and digoxin, enhanced the contraction and CaT of cardiomyocytes. The inotropic action of isoproterenol was accompanied by an increase in the velocities of sarcomere shortening and relengthening and CaT decay through activation of cAMP-dependent protein kinase; however, no such lusitropic effects accompanied the inotropic action of QCT, tamarixetin or digoxin. Intravenous administration of QCT to mice resulted in a sustained increase in cardiac systolic function; QCT was rapidly metabolized to tamarixetin and its plasma concentration was maintained at high levels over a similar time frame as the enhancement of cardiac systolic function. These results suggest that QCT exerts a cardiotonic action in vivo at least, in part, through digitalis-like enhancement of CaT by itself and its metabolite tamarixetin.

Therapeutic potential of ghrelin and des-acyl ghrelin against chemotherapy-induced cardiotoxicity

Cancer was considered an incurable disease for many years; however, with the development of anticancer drugs and state-of-the art technologies, it has become curable. Cardiovascular diseases in patients with cancer or induced by cancer chemotherapy have recently become a great concern. Certain anticancer drugs and molecular targeted therapies cause cardiotoxicity, which limit the widespread implementation of cancer treatment and decrease the quality of life in cancer patients significantly. The anthracycline doxorubicin (DOX) causes cardiotoxicity. The cellular mechanism underlying DOX-induced cardiotoxicity include free-radical damage to cardiac myocytes, leading to mitochondrial injury and subsequent death of myocytes. Recently, circulating orexigenic hormones, ghrelin and des-acyl ghrelin, have been reported to inhibit DOX-induced cardiotoxicity. However, little is known about the molecular mechanisms underlying their preventive effects. In the present study, we show the possible mechanisms underlying the effects of ghrelin and des-acyl ghrelin against DOX-induced cardiotoxicity through in vitro and in vivo researches.

Leukemia inhibitory factor via the Toll-like receptor 5 signaling pathway involves aggravation of cachexia induced by human gastric cancer-derived 85As2 cells in rats

Cancer cachexia is highly prevalent in gastric cancer patients and characterized by decreased food consumption and body weight. We previously created a rat model of cancer cachexia using MKN45cl85 and 85As2 cells derived from human gastric cancer. The 85As2 cells induced cachexia more potently compared to MKN45cl85 cells. To clarify the mechanism underlying the difference in the cachexia-inducing ability of these cells, we conducted DNA microarray analysis, focusing on cell proliferation and the production of leukemia inhibitory factor (LIF), a cachexia-inducing factor. The plasma human LIF levels of 85As2-induced cachexic rats increased as symptoms worsened, whereas the plasma levels of MKNcl85 were low. 85As2 cells displayed more genetic changes compared to MKN45cl85 cells, which were related to Toll-like receptor (TLR) 4/5 signaling. Stimulation of both cells with TLR4 (lipopolysaccharide) or TLR5 (flagellin) agonists did not affect proliferation. However, in 82As2 cells, LIF production was significantly increased by stimulation with TLR5, which was suppressed by an inhibitor of interleukin-1 receptor-associated kinase-1/4, which are important factors in the TLR5 signaling pathway. The increase in LIF production resulting from activation of the TLR5 signaling pathway may contribute to the cachexia-inducing ability of 85As2 cells.

Modulation of synaptic inputs in magnocellular neurones in a rat model of cancer cachexia

In cancer cachexia, abnormal metabolism and neuroendocrine dysfunction cause anorexia, tissue damage and atrophy, which can in turn alter body fluid balance. Arginine vasopressin, which regulates fluid homeostasis, is secreted by magnocellular neurosecretory cells (MNCs) of the hypothalamic supraoptic nucleus. Arginine vasopressin secretion by MNCs is regulated by both excitatory and inhibitory synaptic activity, alterations in plasma osmolarity and various peptides, including angiotensin II. In the present study, we used whole‐cell patch‐clamp recordings of brain slices to determine whether hyperosmotic stimulation and/or angiotensin II potentiate excitatory synaptic input in a rat model of cancer cachexia, similar to their effects in normal (control) rats. Hyperosmotic (15 and 60 mmol L‐1 mannitol) stimulation and angiotensin II (0.1 μmol L‐1) increased the frequency, but not the amplitude, of miniature excitatory postsynaptic currents in normal rats; in model rats, both effects were significantly attenuated. These results suggest that cancer cachexia alters supraoptic MNC sensitivity to osmotic and angiotensin II stimulation.

Multifunctional Actions of Ninjinyoeito, a Japanese Kampo Medicine: Accumulated Scientific Evidence Based on Experiments With Cells and Animal Models, and Clinical Studies

Herbal medicines are currently employed for the treatment of several types of diseases, and also employed for the improvement of Quality of Life (QOL) of patients over the world, in particular, in Asian countries. In Japan, a Japanese herbal medicine namely kampo medicine has been prescribed for the improvement of QOL of patients. Ninjinyoeito (NYT), composed of 12 herbal plants, is one of kampo medicines and used for helping recovery of diseases and improving several symptoms that suffer patients such as anemia, anorexia and fatigue. Recent scientific research approaches to kampo medicines with cells and animal models enable to prove that NYT has multiple functions for improvement of symptoms. Also, clinical studies using NYT support such actions to be widely used for the improvement of symptoms that reduce the QOL of patients.

Usefulness for the combination of G protein- and β-arrestin-biased ligands of μ-opioid receptors: Prevention of antinociceptive tolerance

Background µ-Opioid receptor internalization is considered to be critically linked to antinociceptive tolerance. Although µ-opioid receptor agonists have been administered simultaneously with other drugs to control pain, little information is available regarding opioid–opioid interactions. Therefore, the present study was designed to further investigate the utility of a new G protein-biased ligand for µ-opioid receptors, TRV130, which has an antinociceptive effect without β-arrestin-dependent µ-opioid receptor internalization, and its combination with fentanyl using µ-opioid receptor-expressing cells and mice. Results In the present study, we confirmed that fentanyl produced a profound increase in β-arrestin-2 recruitment accompanied by µ-opioid receptor internalization, whereas TRV130 did not induce either the recruitment of β-arrestin-2 or µ-opioid receptor internalization in µ-opioid receptor-expressing cells. Under these conditions, β-arrestin-2 recruitment accompanied by µ-opioid receptor internalization induced by fentanyl was abolished by TRV130, whereas TRV130 did not alter the reduction of cyclic adenosine monophosphate formation by fentanyl in µ-opioid receptor-expressing cells. In a behavioral assay, TRV130 exerted an antinociceptive effect in a hot-plate test in mice. In a combination test, the antinociceptive effect of TRV130 was synergistically increased by fentanyl. Fentanyl induced antihyperalgesia and development of its tolerance under a neuropathic pain-like state following sciatic nerve ligation. However, treatment of mice with an antinociceptive dose of TRV130 did not induce the rapid development of tolerance to its antihyperalgesic effect under a neuropathic pain-like state. Furthermore, the rapid development of tolerance to the antihyperalgesic effect induced by fentanyl plus TRV130 in mice with sciatic nerve ligation was not observed, unlike in the case of fentanyl alone. Conclusions These findings provide evidence that activation of the G protein-biased pathway through µ-opioid receptors can alter signaling in the β-arrestin-2 pathway linked to the stimulation of µ-opioid receptors. Furthermore, the combination of G protein-biased and β-arrestin-biased ligands of µ-opioid receptors exerts an ideal antinociceptive effect without the rapid development of antinociceptive tolerance.