Terzic, André

K+ channel openers have been recently recognized for their ability to protect mitochondria from anoxic injury. Yet the mechanism responsible for mitochondrial preservation under oxidative stress is not fully understood. Here, mitochondria were isolated from rat hearts and subjected to 20-min anoxia, followed by reoxygenation. At reoxygenation, increased generation of reactive oxygen species (ROS) was associated with reduced ADP-stimulated oxygen consumption, blunted ATP production, and disrupted mitochondrial structural integrity coupled with cytochrome c release. The prototype K+ channel opener diazoxide markedly reduced mitochondrial ROS production at reoxygenation with a half-maximal effect of 29 μM. Diazoxide also preserved oxidative phosphorylation and mitochondrial membrane integrity, as indicated by electron microscopy and reduced cytochrome c release. The protective effect of diazoxide was reproduced by the structurally distinct K+ channel opener nicorandil and antagonized by 5-hydroxydecanoic acid, a short-chain fatty acid derivative and presumed blocker of mitochondrial ATP-sensitive K+ channels. Opener-mediated mitochondrial protection was simulated by the free radical scavenger system composed of superoxide dismutase and catalase. However, the effect of openers on ROS production was maintained in nominally K+-free medium in the presence or absence of the K+ ionophore valinomycin and was mimicked by malonate, a modulator of the mitochondrial redox state. This suggests the existence of a K+ conductance-independent pathway for mitochondrial protection targeted by K+ channel openers. Thus the cardioprotecive mechanism of K+ channel openers includes direct attenuation of mitochondrial oxidant stress at reoxygenation.

The failing ventricular myocardium is characterized by reduction of high-energy phosphates and reduced activity of the phosphotransfer enzymes creatine kinase (CK) and adenylate kinase (AK), which are responsible for transfer of high-energy phosphoryls from sites of production to sites of utilization, thereby compromising excitation-contraction coupling. In humans with chronic atrial fibrillation (AF) unassociated with congestive heart failure (CHF), impairment of atrial myofibrillar energetics linked to oxidative modification of myofibrillar CK has been observed. However, the bioenergetic status of the failing atrial myocardium and its potential contribution to atrial electrical instability in CHF have not been determined. Dogs with ( n = 6) and without ( n = 6) rapid pacing-induced CHF underwent echocardiography (conscious) and electrophysiological (under anesthesia) studies. CHF dogs had more pronounced mitral regurgitation, higher atrial pressure, larger atrial area, and increased atrial fibrosis. An enhanced propensity to sustain AF was observed in CHF, despite significant increases in atrial effective refractory period and wavelength. Profound deficits in atrial bioenergetics were present with reduced activities of the phosphotransfer enzymes CK and AK, depletion of high-energy phosphates (ATP and creatine phosphate), and reduction of cellular energetic potential (ATP-to-ADP and creatine phosphate-to-Cr ratios). AF duration correlated with left atrial area ( r = 0.73, P = 0.01) and inversely with atrial ATP concentration ( r = −0.75, P = 0.005), CK activity ( r = −0.57, P = 0.054), and AK activity ( r = −0.64, P = 0.02). Atrial levels of malondialdehyde, a marker of oxidative stress, were significantly increased in CHF. Myocardial bioenergetic deficits are a conserved feature of dysfunctional atrial and ventricular myocardium in CHF and may constitute a component of the substrate for AF in CHF.

It has been nearly ten years since we joined the editorial organization of Clinical Pharmacology & Therapeutics (CPT), as part of the American Society for Clinical Pharmacology and Therapeutics (ASCPT) family. During that tenure, the primary mandate has been the growth of CPT, recognized as one of the key voices of the discipline and the Society. Set goals were realized in concert with a strong editorial team, a diverse editorial board, a dedicated editorial staff, and outstanding authors, leveraging a leading publishing infrastructure and responding to the needs of a global readership, expanding membership, and the discipline as a whole. The impending decade anniversary, and the transition to a new publisher, offers a natural juncture to reflect on progress, and chart plans for the future of the Journal.

Abstract Congenital heart diseases (CHDs) requiring surgical palliation mandate new treatment strategies to optimize long-term outcomes. Despite the mounting evidence of cardiac regeneration, there are no long-term safety studies of autologous cell-based transplantation in the pediatric setting. We aimed to establish a porcine pipeline to evaluate the feasibility and long-term safety of autologous umbilical cord blood mononuclear cells (UCB-MNCs) transplanted into the right ventricle (RV) of juvenile porcine hearts. Piglets were born by caesarean section to enable UCB collection. Upon meeting release criteria, 12 animals were randomized in a double-blinded fashion prior to surgical delivery of test article (n = 6) or placebo (n = 6). The UCB-MNC (3 × 106 cells per kilogram) or control (dimethyl sulfoxide, 10%) products were injected intramyocardially into the RV under direct visualization. The cohorts were monitored for 3 months after product delivery with assessments of cardiac performance, rhythm, and serial cardiac biochemical markers, followed by terminal necropsy. No mortalities were associated with intramyocardial delivery of UCB-MNCs or placebo. Two animals from the placebo group developed local skin infection after surgery that responded to antibiotic treatment. Electrophysiological assessments revealed no arrhythmias in either group throughout the 3-month study. Two animals in the cell-therapy group had transient, subclinical dysrhythmia in the perioperative period, likely because of an exaggerated response to anesthesia. Overall, this study demonstrated that autologous UCB-MNCs can be safely collected and surgically delivered in a pediatric setting. The safety profile establishes the foundation for cell-based therapy directed at the RV of juvenile hearts and aims to accelerate cell-based therapies toward clinical trials for CHD.

AbstractTissue engineering aims at recapitulating permissive conditions that enable cells to collaborate and form functional tissues. Applications range from human tissue modeling for diagnostic purposes to therapeutic solutions in regenerative medicine and surgery. Across this spectrum, human stem cells are the active ingredient, expandable virtually indefinitely and with the propensity to generate new tissue. Engaging lineage-specific differentiation requires a precise concerto of key spatial and temporal factors, such as soluble molecules and growth factors, but also physical and mechanical stimuli. These stimuli compete to modulate distinct developmental signaling pathways and ultimately affect the differentiation efficiency. The heart is a chemo-mechano-electrical biological system that behaves as both a sensor and an actuator. It can transduce electrical inputs to generate mechanical contraction and electrical wave propagation. Such a complex organ arises from multipart developmental events that interact with one another to self-regulate. Here, we overview the main events of heart development and the role of mechanical forces in modifying the microenvironment of the progenitor cells. We analyze the cascades regulating cardiac gene activation to illustrate how mechanotransduction is already involved in the most popular protocols for stem cell differentiation (SCD) into cardiomyocytes. We then review how forces are transmitted to embryonic stem cells by cell-substrate or cell-cell communications, and how biomaterials can be designed to mimic these interactions and help reproduce key features of the developmental milieu. Putting this back in a clinical perspective, many challenges needs to be overcome before biomaterials-based SCD protocols can be scaled up and marketed. Stem Cells 2015;33:1021–1035

Decoding stem cell metabolism has implicated a tight linkage between energy metabolism and cell fate regulation, a dynamic interplay vital in the execution of developmental and differentiation programs. The inherent plasticity in energy metabolism enables prioritisation of metabolic pathways in support of stage-specific demands. Beyond traditional support of energetic needs, intermediate metabolism may also dictate cell fate choices through regulation of cellular signalling and epigenetic regulation of gene expression. The notion of a ‘metabolism-centric’ control of stem cell differentiation has been informed by developmental embryogenesis based upon an on-demand paradigm paramount in defining diverse developmental behaviours, from a post-fertilisation nascent zygote to complex organogenesis leading to adequate tissue formation and maturation. Monitored through natural or bioengineered stem cell surrogates, nutrient-responsive metabolites are identified as mediators of cross-talk between metabolic flux, cell signalling and epigenetic regulation charting, collectively, whether a cell will self-renew to maintain progenitor pools, lineage specify to ensure tissue (re)generation or remain quiescent to curb stress damage. Thus, bioenergetics are increasingly recognised as integral in governing stemness and associated organogenic decisions, paving the way for metabolism-defined targets in control of embryology, stem cell biology and tissue regeneration.

Background—Nuclear reprogramming inculcates pluripotent capacity by which de novo tissue differentiation is enabled. Yet, introduction of ectopic reprogramming factors may desynchronize natural developmental schedules. This study aims to evaluate the effect of imposed transgene load on the cardiogenic competency of induced pluripotent stem (iPS) cells.Methods and Results—Targeted inclusion and exclusion of reprogramming transgenes (c-MYC,KLF4,OCT4, andSOX2) was achieved using a drug-inducible and removable cassette according to the piggyBac transposon/transposase system. Pulsed transgene overexpression, before iPS cell differentiation, hindered cardiogenic outcomes. Delayed in counterparts with maintained integrated transgenes, transgene removal enabled proficient differentiation of iPS cells into functional cardiac tissue. Transgene-free iPS cells generated reproducible beating activity with robust expression of cardiac α-actinin, connexin 43, myosin light chain 2a, α/β-myosin heavy chain, and troponin I. Although operational excitation–contraction coupling was demonstrable in the presence or absence of transgenes, factor-free derivatives exhibited an expedited maturing phenotype with canonical responsiveness to adrenergic stimulation.Conclusions—A disproportionate stemness load, caused by integrated transgenes, affects the cardiogenic competency of iPS cells. Offload of transgenes in engineered iPS cells ensures integrity of cardiac developmental programs, underscoring the value of nonintegrative nuclear reprogramming for derivation of competent cardiogenic regenerative biologics.

The advent of induced pluripotent stem cell (iPSC) technology creates new opportunities for transplant-based therapeutic strategies. The potential for clinical translation is currently hindered by the risk of dysregulated cell growth. Pluripotent stem cells reprogrammed by three-factor (Sox2, Klf, and Oct4) and four-factor (Sox2, Klf, Oct4, and c-Myc) strategies result in the capacity for teratogenic growth from residual pluripotent progeny upon in vivo transplantation. However, these pluripotent stem cells also have a stage-specific hypersensitivity to DNA-damaging agents that may allow separation of lineage-specific therapeutic subpopulation of cells. We aimed to demonstrate the selective effect of DNA topoisomerase II inhibitor, etoposide, in eliminating pluripotent cells in the early cardiac progenitor population thus decreasing the effect of teratoma formation. Immunodeficient murine hearts were infarcted and received implantation of a therapeutic dose of cardiac progenitors derived from partially differentiated iPSCs. Etoposide-treated cell implantation reduced mass formation in the intracardiac and extracardiac chest cavity compared with the same dose of iPSC-derived cardiac progenitors in the control untreated group. In vivo bioluminescence imaging confirmed the localization and engraftment of transplanted cells in the myocardium postinjection in both groups. Comparatively, the equivalent cell population without etoposide treatment demonstrated a greater incidence and size of teratoma formation. Hence, pretreatment with genotoxic etoposide significantly lowered the threat of teratogenicity by purging the contaminating pluripotent cells, establishing an adjunctive therapy to further harness the clinical value of iPSC-derived cardiac regeneration.