Electrophysiologic and cellular characteristics of cardiomyocytes after X-ray irradiation

A Human 3D Cardiomyocyte Risk Model to Study the Cardiotoxic Influence of X-rays and Other Noxae in Adults

The heart tissue is a potential target of various noxae contributing to the onset of cardiovascular diseases. However, underlying pathophysiological mechanisms are largely unknown. Human stem cell-derived models are promising, but a major concern is cell immaturity when estimating risks for adults. In this study, 3D aggregates of human embryonic stem cell-derived cardiomyocytes were cultivated for 300 days and characterized regarding degree of maturity, structure, and cell composition. Furthermore, effects of ionizing radiation (X-rays, 0.1–2 Gy) on matured aggregates were investigated, representing one of the noxae that are challenging to assess. Video-based functional analyses were correlated to changes in the proteome after irradiation. Cardiomyocytes reached maximum maturity after 100 days in cultivation, judged by α-actinin lengths, and displayed typical multinucleation and branching. At this time, aggregates contained all major cardiac cell types, proven by the patch-clamp technique. Matured and X-ray-irradiated aggregates revealed a subtle increase in beat rates and a more arrhythmic sequence of cellular depolarisation and repolarisation compared to non-irradiated sham controls. The proteome analysis provides first insights into signaling mechanisms contributing to cardiotoxicity. Here, we propose an in vitro model suitable to screen various noxae to target adult cardiotoxicity by preserving all the benefits of a 3D tissue culture.

Novel in vitro assay to investigate radiation induced changes in the functionality of human embryonic stem cell-derived neurospheres

Ionizing radiation (IR) is increasingly used for diagnostics and therapy of severe brain diseases. However, IR also has adverse effects on the healthy brain tissue, particularly on the neuronal network. This is true for adults but even more pronounced in the developing brain of unborn and pediatric patients. Epidemiological studies on children receiving radiotherapy showed an increased risk for cognitive decline ranging from mild deficits in academic functioning to severe late effects in intellectual ability and language as a consequence of altered neuronal development and connectivity. To provide a comprehensive approach for the analysis of radiation-induced alterations in human neuronal functionality, we developed an in vitro assay by combining microelectrode array (MEA) analyses and human embryonic stem cell (hESC) derived three-dimensional neurospheres (NS). In our proof of principle study, we irradiated hESC with 1 Gy X-rays and let them spontaneously differentiate into neurons within NS. After the onset of neuronal activity, we recorded and analyzed the activity pattern of the developing neuronal networks. The network activity in NS derived from irradiated hESC was significantly reduced, whereas no differences in molecular endpoints such as cell proliferation and transcript or protein expression analyses were found. Thus, the combination of MEA analysis with a 3D model for neuronal functionality revealed radiation sequela that otherwise would not have been detected. We therefore strongly suggest combining traditional biomolecular methods with the new functional assay presented in this work to improve the risk assessment for IR-induced effects on the developing brain.

Radiotherapy-induced heart disease: a review of the literature

Radiotherapy as one of the four pillars of cancer therapy plays a critical role in the multimodal treatment of thoracic cancers. Due to significant improvements in overall cancer survival, radiotherapy-induced heart disease (RIHD) has become an increasingly recognized adverse reaction which contributes to major radiation-associated toxicities including non-malignant death. This is especially relevant for patients suffering from diseases with excellent prognosis such as breast cancer or Hodgkin’s lymphoma, since RIHD may occur decades after radiotherapy. Preclinical studies have enriched our knowledge of many potential mechanisms by which thoracic radiotherapy induces heart injury. Epidemiological findings in humans reveal that irradiation might increase the risk of cardiac disease at even lower doses than previously assumed. Recent preclinical studies have identified non-invasive methods for evaluation of RIHD. Furthermore, potential options preventing or at least attenuating RIHD have been developed. Ongoing research may enrich our limited knowledge about biological mechanisms of RIHD, identify non-invasive early detection biomarkers and investigate potential treatment options that might attenuate or prevent these unwanted side effects. Here, we present a comprehensive review about the published literature regarding clinical manifestation and pathological alterations in RIHD. Biological mechanisms and treatment options are outlined, and challenges in RIHD treatment are summarized.

Gene expression changes in human iPSC-derived cardiomyocytes after X-ray irradiation

Purpose: Radiation-induced heart disease caused by cardiac exposure to ionizing radiation comprises a variety of cardiovascular effects. Research in this field has been hampered by limited availability of clinical samples and appropriate test models. In this study, we wanted to elucidate the molecular mechanisms underlying electrophysiological changes, which we have observed in a previous study. Materials and methods: We employed RNA deep-sequencing of human-induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) 48 h after 5 Gy X-ray irradiation. By comparison to public data from hiPSC-CMs and human myocardium, we verified the expression of cardiac-specific genes in hiPSC-CMs. Results were validated by qRT-PCR. Results: Differentially gene expression analysis identified 39 and 481 significantly up- and down-regulated genes after irradiation, respectively. Besides, a large fraction of genes associated with cell cycle processes, we identified genes implicated in cardiac calcium homeostasis (PDE3B), oxidative stress response (FDXR and SPATA18) and the etiology of cardiomyopathy (SGCD, BBC3 and GDF15). Conclusions: Notably, observed gene expression characteristics specific to hiPSC-CMs might be relevant regarding further investigations of the response to external stressors like radiation. The genes and biological processes highlighted in our study present promising starting points for functional follow-up studies for which hiPSC-CMs could pose an appropriate cell model when cell type specific peculiarities are taken into account.

High LET radiation shows no major cellular and functional effects on primary cardiomyocytes in vitro

It is well known that ionizing radiation causes adverse effects on various mammalian tissues. However, there is little information on the biological effects of heavy ion radiation on the heart. In order to fill this gap, we systematically examined DNA-damage induction and repair, as well as proliferation and apoptosis in avian cardiomyocyte cultures irradiated with heavy ions such as titanium and iron, relevant for manned space-flight, and carbon ions, as used for radiotherapy. Further, and to our knowledge for the first time, we analyzed the effect of heavy ion radiation on the electrophysiology of primary cardiomyocytes derived from chicken embryos using the non-invasive microelectrode array (MEA) technology. As electrophysiological endpoints beat rate and field action potential duration were analyzed. The cultures clearly exhibited the capacity to repair induced DNA damage almost completely within 24 h, even at doses of 7 Gy, and almost completely recovered from radiation-induced changes in proliferative behavior. Interestingly, no significant effects on apoptosis could be detected. Especially the functionality of primary cardiac cells exhibited a surprisingly high robustness against heavy ion radiation, even at doses of up to 7 Gy. In contrast to our previous study with X-rays the beat rate remained more or less unaffected after heavy ion radiation, independently of beam quality. The only change we could observe was an increase of the field action potential duration of up to 30% after titanium irradiation, diminishing within the following three days. This potentially pathological observation may be an indication that heavy ion irradiation at high doses could bear a long-term risk for cardiovascular disease induction.