Digital Movie Analysis for Quantification of Beating Frequencies, Chronotropic Effects, and Beating Areas in Cardiomyocyte Cultures

Advances in Multidimensional Cardiac Biosensing Technologies: From Electrophysiology to Mechanical Motion and Contractile Force

Cardiovascular disease is currently a leading killer to human, while drug-induced cardiotoxicity remains the main cause of the withdrawal and attrition of drugs. Taking clinical correlation and throughput into account, cardiomyocyte is perfect as in vitro cardiac model for heart disease modeling, drug discovery, and cardiotoxicity assessment by accurately measuring the physiological multiparameters of cardiomyocytes. Remarkably, cardiomyocytes present both electrophysiological and biomechanical characteristics due to the unique excitation-contraction coupling, which plays a significant role in studying the cardiomyocytes. This review mainly focuses on the recent advances of biosensing technologies for the 2D and 3D cardiac models with three special properties: electrophysiology, mechanical motion, and contractile force. These high-performance multidimensional cardiac models are popular and effective to rebuild and mimic the heart in vitro. To help understand the high-quality and accurate physiologies, related detection techniques are highly demanded, from microtechnology to nanotechnology, from extracellular to intracellular recording, from multiple cells to single cell, and from planar to 3D models. Furthermore, the characteristics, advantages, limitations, and applications of these cardiac biosensing technologies, as well as the future development prospects should contribute to the systematization and expansion of knowledge.

Spatiotemporal Characterizations of Spontaneously Beating Cardiomyocytes with Adaptive Reference Digital Image Correlation

We developed an Adaptive Reference-Digital Image Correlation (AR-DIC) method that enables unbiased and accurate mechanics measurements of moving biological tissue samples. We applied the AR-DIC analysis to a spontaneously beating cardiomyocyte (CM) tissue, and could provide correct quantifications of tissue displacement and strain for the beating CMs utilizing physiologically-relevant, sarcomere displacement length-based contraction criteria. The data were further synthesized into novel spatiotemporal parameters of CM contraction to account for the CM beating homogeneity, synchronicity, and propagation as holistic measures of functional myocardial tissue development. Our AR-DIC analyses may thus provide advanced non-invasive characterization tools for assessing the development of spontaneously contracting CMs, suggesting an applicability in myocardial regenerative medicine.

Sinoatrial Beat to Beat Variability Assessed by Contraction Strength in Addition to the Interbeat Interval

Beat to beat variability of cardiac tissue or isolated cells is frequently investigated by determining time intervals from electrode measurements in order to compute scale dependent or scale independent parameters. In this study, we utilize high-speed video camera recordings to investigate the variability of intervals as well as mechanical contraction strengths and relative contraction strengths with nonlinear analyses. Additionally, the video setup allowed us simultaneous electrode registrations of extracellular potentials. Sinoatrial node tissue under control and acetylcholine treated conditions was used to perform variability analyses by computing sample entropies and Higuchi dimensions. Beat to beat interval variabilities measured by the two recording techniques correlated very well, and therefore, validated the video analyses for this purpose. Acetylcholine treatment induced a reduction of beating rate and contraction strength, but the impact on interval variability was negligible. Nevertheless, the variability analyses of contraction strengths revealed significant differences in sample entropies and Higuchi dimensions between control and acetylcholine treated tissue. Therefore, the proposed high-speed video camera technique might represent a non-invasive tool that allows long-lasting recordings for detecting variations in beating behavior over a large range of scales.

The acceleration of cardiomyogenesis in embryonic stem cells in vitro by serum depletion does not increase the number of developed cardiomyocytes

The differentiation of pluripotent embryonic stem (ES) cells into various lineages in vitro represents an important tool for studying the mechanisms underlying mammalian embryogenesis. It is a key technique in studies evaluating the molecular mechanisms of cardiomyogenesis and heart development and also in embryotoxicology. Herein, modest modifications of the basic protocol for ES cell differentiation into cardiomyocytes were evaluated in order to increase the yield and differentiation status of developed cardiomyocytes. Primarily, the data show that ES cell cultivation in the form of non-adherent embryoid bodies (EBs) for 5 days compared to 8 days significantly improved cardiomyogenic differentiation. This is illustrated by the appearance of beating foci in the adherent EBs layer at earlier phases of differentiation from day 10 up to day 16 and by the significantly higher expression of genes characteristic of cardiomyogenic differentiation (sarcomeric alpha actinin, myosin heavy chain alpha and beta, myosin light chain 2 and 7, and transcriptional factor Nkx2.5) in EBs cultivated under non-adherent conditions for 5 days. The ratio of cardiomyocytes per other cells was also potentiated in EBs cultivated in non-adherent conditions for only 5 days followed by cultivation in adherent serum-free culture conditions. Nevertheless, the alteration in the percentage of beating foci among these two tested cultivation conditions vanished at later phases and also did not affect the total number of cardiomyocytes determined as myosin heavy chain positive cells at the end of the differentiation process on day 20. Thus, although these modifications of the conditions of ES cells differentiation may intensify cardiomyocyte differentiation, the final count of cardiomyocytes might not change. Thus, serum depletion was identified as a key factor that intensified cardiomyogenesis. Further, the treatment of EBs with N-acetylcysteine, a reactive oxygen species scavenger, did not affect the observed increase in cardiomyogenesis under serum depleted conditions. Interestingly, a mild induction of the ventricular-like phenotype of cardiomyocytes was observed in 5-day-old EBs compared to 8-day-old EBs. Overall, these findings bring crucial information on the mechanisms of ES cells differentiation into cardiomyocytes and on the establishment of efficient protocols for the cardiomyogenic differentiation of ES cells. Further, the importance of determining the absolute number of formed cardiomyocyte-like cells per seeded pluripotent cells in contrast to the simple quantification of the ratios of cells is highlighted.

Simple non-invasive analysis of embryonic stem cell-derived cardiomyocytes beating in vitro

The analysis of digital video output enables the non-invasive screening of various active biological processes. For the monitoring and computing of the beating parameters of cardiomyocytes in vitro, CB Analyser (cardiomyocyte beating analyser) software was developed. This software is based on image analysis of the video recording of beating cardiomyocytes. CB Analyser was tested using cardiomyocytes derived from mouse embryonic stem cells at different stages of cardiomyogenesis. We observed that during differentiation (from day 18), the beat peak width decreased, which corresponded to the increased speed of an individual pulse. However, the beating frequency did not change. Further, the effects of epinephrine modulating mature cardiomyocyte functions were tested to validate the CB Analyser analysis. In conclusion, data show that CB Analyser is a useful tool for evaluating the functions of both developing and mature cardiomyocytes under various conditions in vitro.

An optical multi-sensing system for detection of cardiovascular toxicity

A mini-microscope-based system for multisite detection of cardiovascular toxicity was developed. The mini-microscope consisted of an image sensor and lens module extracted from an inexpensive webcam. The flipped lens module enabled cells to be magnified and monitored during testing. The portability and compactness of this system enables short-term and potential long-term experimentation inside a conventional incubator. The toxicity test results demonstrated that the normalized beating rates of cardiac muscle cells selected from multiple regions increased over time when treated with 100 nM isoprenaline. The presented system could be a promising cost-effective cell-based testing tool for discovering and screening drugs.

Video Evaluation of the Kinematics and Dynamics of the Beating Cardiac Syncytium: An Alternative to the Langendorff Method

Many important observations and discoveries in heart physiology have been made possible using the isolated heart method of Langendorff. Nevertheless, the Langendorff method has some limitations and disadvantages such as the vulnerability of the excised heart to contusions and injuries, the probability of preconditioning during instrumentation, the possibility of inducing tissue edema, and high oxidative stress, leading to the deterioration of the contractile function. To avoid these drawbacks associated with the use of a whole heart, we alternatively used beating mouse cardiac syncytia cultured in vitro in order to assess possible ergotropic, chronotropic, and inotropic effects of drugs. To achieve this aim, we developed a method based on image processing analysis to evaluate the kinematics and the dynamics of the drug-stimulated beating syncytia starting from the video recording of their contraction movement. In this manner, in comparison with the physiological no-drug condition, we observed progressive positive ergotropic, positive chronotropic, and positive inotropic effects of 10 μM isoproterenol (β-adrenergic agonist) and early positive ergotropic, negative chronotropic, and positive inotropic effects of 10 μM phenylephrine (α-adrenergic agonist), followed by a late phase with negative ergotropic, positive chronotropic, and negative inotropic trends.

Our method permitted a systematic study of in vitro beating syncytia, producing results consistent with previous works. Consequently, it could be used in in vitro studies of beating cardiac patches, as an alternative to Langendorff's heart in biochemical and pharmacological studies, and especially when the Langendorff technique is inapplicable (e.g., in studies about human cardiac syncytium in physiological and pathological conditions, patient-tailored therapeutics, and syncytium models derived from induced pluripotent/embryonic stem cells with genetic mutations).

Furthermore, the method could be helpful in heart tissue engineering and bioartificial heart research to “engineer the heart piece by piece.” In particular, the proposed method could be useful in the identification of a suitable cell source, in the development and testing of “smart” biomaterials, and in the design and use of novel bioreactors and microperfusion systems.

A cell-based biosensor for real-time detection of cardiotoxicity using lensfree imaging

A portable and cost-effective real-time cardiotoxicity biosensor was developed using a CMOS imaging module extracted from a commercially available webcam. The detection system consists of a CMOS imaging module, a white LED and a pinhole. Real-time image processing was conducted by comparing reference and live frame images. To evaluate the engineered system, the effects of two different drugs, isoprenaline and doxorubicin, on the beating rate and beat-to-beat variations of ESC-derived cardiomyocytes were measured. The detection system was used to conclude that the beat-to-beat variability increased under treatment with both isoprenaline and doxorubicin. However, the beating rates increased upon the addition of isoprenaline but decreased for cultures supplemented with doxorubicin. Moreover, the response time for both the beating rates and the beat-to-beat variability of ESC-derived cardiomyocytes under treatment of isoprenaline was shorter than for doxorubicin, although the amount of isoprenaline used in the measurement was three orders of magnitude lower than that of doxorubicin. Given its ability to perform real-time cell monitoring in a simple and inexpensive manner, the proposed system may be useful for a range of cell-based biosensing applications.

Non-invasive characterization of mouse embryonic stem cell derived cardiomyocytes based on the intensity variation in digital beating video

The interest in cardiomyocytes derived from differentiation of embryonic stem (ES) cells or induced pluripotent stem (iPS) cells is increasing due to their potential for regenerative therapeutics and as a pharmaceutical model of drug screening. Characterization of ES or iPS derived cardiomyocytes is challenging and inevitable for the intended usage of such cells. In this paper we have outlined a novel, non-invasive method for evaluating in vitro beating properties of cardiomyocytes. The method is based on the analysis of time dependent variation in the total pixel intensities in derivative images obtained from the consecutive systolic and diastolic frames from the light microscopic video recordings of beating tissue. Fast Fourier transform (FFT) yielded the frequency domains for these images. The signal to noise ratio for the analysis met the Rose criterion. We have successfully applied our method for monitoring mouse ES cell (mESC) derived cardiac muscle cells to determine the initiation of beating, organization and maturation of beating tissue, calculating the beating rhythms in terms of beating interval or frequency and the strength of beating. We have shown the successful application of our image analysis method in direct monitoring of the responses of differentiated cardiomyocytes towards caffeine hydrate, p-hydroxyphenylacetamide and calcium chloride dehydrate - respectively as positive, neutral and negative inotropic agents. This non-invasive method of characterization will be useful in studying the response of these cells to various external stimulations, such as differentiation promoting agents or treatments, as well as in preliminary drug screening in a quick and inexpensive manner without needing much expertise.