Human stem cells shape the future of cardiac regeneration research

Functional properties of human embryonic stem cell-derived cardiomyocytes: intracellular Ca2+ handling and the role of sarcoplasmic reticulum in the contraction

Since cardiac transplantation is limited by the small availability of donor organs, regeneration of the diseased myocardium by cell transplantation is an attractive therapeutic modality. To determine the compatibility of human embryonic stem cell-derived cardiomyocytes (hESC-CMs) (7 to 55 days old) with the myocardium, we investigated their functional properties regarding intracellular Ca2+ handling and the role of the sarcoplasmic reticulum in the contraction. The functional properties of hESC-CMs were investigated by recording simultaneously [Ca2+]i transients and contractions. Additionally, we performed Western blot analysis of the Ca2+-handling proteins SERCA2, calsequestrin, phospholamban, and Na+/Ca2+ exchanger (NCX). Our major findings are, first, that hESC-CMs displayed temporally related [Ca2+]i transients and contractions, negative force-frequency relations, and lack of post-rest potentiation. Second, ryanodine, thapsigargin, and caffeine did not affect the [Ca2+]i transient and contraction, indicating that at this developmental stage, contraction depends on transsarcolemmal Ca2+ influx rather than on sarcoplasmic reticulum Ca2+ release. Third, in agreement with the notion that a voltage-dependent Ca2+ current is present in hESC-CMs and contributes to the mechanical function, verapamil completely blocked contraction. Fourth, whereas hESC-CMs expressed SERCA2 and NCX at levels comparable to those of the adult porcine myocardium, calsequestrin and phospholamban were not expressed. Our study shows for the first time that functional properties related to intracellular Ca2+ handling of hESC-CMs differ markedly from the adult myocardium, probably due to immature sarcoplasmic reticulum capacity.

Top of the charts: download versus citations in the International Journal of Cardiology

The medical literature is growing at an alarming rate. Research assessment exercises, research quality frameworks, league tables and the like have attempted to quantify the volume, quality and impact of research. Yet the established measures (such as citation rates) are being challenged by the sheer number of journals, variability in the "gold standard" of peer-review and the emergence of open-source or web-based journals. In the last few years, we have seen a growth in downloads to individual journal articles that now easily exceeds formal journal subscriptions. We have recorded the 10 top cited articles over a 12-month period and compared them to the 10 most popular articles being downloaded over the same time period. The citation-based listing included basic and applied, observational and interventional original research reports. For downloaded articles, which have shown a dramatic increase for the International Journal of Cardiology from 48,000 in 2002 to 120,000 in 2003 to 200,000 in 2004, the most popular articles over the same period are very different and are dominated by up-to-date reviews of either cutting-edge topics (such as the potential of stem cells) or of the management of rare or unusual conditions. There is no overlap between the two lists despite covering exactly the same 12-month period and using measures of peer esteem. Perhaps the time has come to look at the usage of articles rather than, or in addition to, their referencing.

Radiolabeled Cell Distribution After Intramyocardial, Intracoronary, and Interstitial Retrograde Coronary Venous Delivery

Background— Several clinical studies are evaluating the therapeutic potential of delivery of various progenitor cells for treatment of injured hearts. However, the actual fate of delivered cells has not been thoroughly assessed for any cell type. We evaluated the short-term fate of peripheral blood mononuclear cells (PBMNCs) after intramyocardial (IM), intracoronary (IC), and interstitial retrograde coronary venous (IRV) delivery in an ischemic swine model.

Methods and Results— Myocardial ischemia was created by 45 minutes of balloon occlusion of the left anterior descending coronary artery. Six days later, 10 7 111 indium-oxine–labeled human PBMNCs were delivered by IC (n=5), IM (n=6), or IRV (n=5) injection. The distribution of injected cells was assessed by γ-emission counting of harvested organs. For each delivery method, a significant fraction of delivered cells exited the heart into the pulmonary circulation, with 26±3% (IM), 47±1% (IC), and 43±3% (IRV) of cells found localized in the lungs. Within the myocardium, significantly more cells were retained after IM injection (11±3%) compared with IC (2.6±0.3%) ( P <0.05) delivery. IRV delivery efficiency (3.2±1%) trended lower than IM infusion for PBMNCs, but this difference did not reach significance. The IM technique displayed the greatest variability in delivery efficiency by comparison with the other techniques.

Conclusions— The majority of delivered cells is not retained in the heart for each delivery modality. The clinical implications of these findings are potentially significant, because cells with proangiogenic or other therapeutic effects could conceivably have effects in other organs to which they are not primarily targeted but to which they are distributed. Also, we found that although IM injection was more efficient, it was less consistent in the delivery of PBMNCs compared with IC and IRV techniques.

Ethical sourcing of human embryonic stem cells — rational solutions?

At the heart of the extensive ethical and regulatory debates that have surrounded human embryonic stem cells is the human pre-implantation embryo. Advances in the understanding of cellular reprogramming, both by cell nuclear replacement and by potential new protocols, should lead to methods that circumvent the use of a practicably viable embryo.