Organ Culture of Rat Myocardial Slices: An Alternative in Vitro Tool in Organ-Specific Toxicology

Sarcomeric network analysis of ex vivo cultivated human atrial appendage tissue using super-resolution microscopy

Investigating native human cardiac tissue with preserved 3D macro- and microarchitecture is fundamental for clinical and basic research. Unfortunately, the low accessibility of the human myocardium continues to limit scientific progress. To overcome this issue, utilizing atrial appendages of the human heart may become highly beneficial. Atrial appendages are often removed during open-heart surgery and can be preserved ex vivo as living tissue with varying durability depending on the culture method. In this study, we prepared living thin myocardial slices from left atrial appendages that were cultured using an air-liquid interface system for overall 10 days. Metabolic activity of the cultured slices was assessed using a conventional methyl thiazolyl tetrazolium (MTT) assay. To monitor the structural integrity of cardiomyocytes within the tissue, we implemented our recently described super-resolution microscopy approach that allows both qualitative and quantitative in-depth evaluation of sarcomere network based on parameters such as overall sarcomere content, filament size and orientation. Additionally, expression of mRNAs coding for key structural and functional proteins was analyzed by real-time reverse transcription polymerase chain reaction (qRT-PCR). Our findings demonstrate highly significant disassembly of contractile apparatus represented by degradation of [Formula: see text]-actinin filaments detected after three days in culture, while metabolic activity was constantly rising and remained high for up to seven days. However, gene expression of crucial cardiac markers strongly decreased after the first day in culture indicating an early destructive response to ex vivo conditions. Therefore, we suggest static cultivation of living myocardial slices derived from left atrial appendage and prepared according to our protocol only for short-termed experiments (e.g. medicinal drug testing), while introduction of electro-mechanical stimulation protocols may offer the possibility for long-term integrity of such constructs.

Heart Slices to Model Cardiac Physiology

Translational research in the cardiovascular field is hampered by the unavailability of cardiac models that can recapitulate organ-level physiology of the myocardium. Outside the body, cardiac tissue undergoes rapid dedifferentiation and maladaptation in culture. There is an ever-growing demand for preclinical platforms that allow for accurate, standardized, long-term, and rapid drug testing. Heart slices is an emerging technology that solves many of the problems with conventional myocardial culture systems. Heart slices are thin (<400 µm) slices of heart tissue from the adult ventricle. Several recent studies using heart slices have shown their ability to maintain the adult phenotype for prolonged periods in a multi cell-type environment. Here, we review the current status of cardiac culture systems and highlight the unique advantages offered by heart slices in the light of recent efforts in developing physiologically relevant heart slice culture systems.

A practical guide for investigating cardiac physiology using living myocardial slices

Ex vivo multicellular preparations are essential tools to study tissue physiology. Among them, the recent methodological and technological developments in living myocardial slices (LMS) are attracting increasing interest by the cardiac research field. Despite this, this research model remains poorly perceived and utilized by most research laboratories. Here, we provide a practical guide on how to use LMS to interrogate multiple aspects of cardiac function, structure and biochemistry. We discuss issues that should be considered to conduct successful experiments, including experimental design, sample preparation, data collection and analysis. We describe how laboratory setups can be adapted to accommodate and interrogate this multicellular research model. These adaptations can often be achieved at a reasonable cost with off-the-shelf components and operated reliably using well-established protocols and freely available software, which is essential to broaden the utilization of this method. We will also highlight how current measurements can be improved to further enhance data quality and reliability to ensure inter-laboratory reproducibility. Finally, we summarize the most promising biomedical applications and envision how living myocardial slices can lead to further breakthroughs.

Myocardial slices come to age: an intermediate complexity in vitro cardiac model for translational research

Although past decades have witnessed significant reductions in mortality of heart failure together with advances in our understanding of its cellular, molecular, and whole-heart features, a lot of basic cardiac research still fails to translate into clinical practice. In this review we examine myocardial slices, a novel model in the translational arena. Myocardial slices are living ultra-thin sections of heart tissue. Slices maintain the myocardium's native function (contractility, electrophysiology) and structure (multicellularity, extracellular matrix) and can be prepared from animal and human tissue. The discussion begins with the history and current advances in the model, the different interlaboratory methods of preparation and their potential impact on results. We then contextualize slices' advantages and limitations by comparing it with other cardiac models. Recently, sophisticated methods have enabled slices to be cultured chronically in vitro while preserving the functional and structural phenotype. This is more timely now than ever where chronic physiologically relevant in vitro platforms for assessment of therapeutic strategies are urgently needed. We interrogate the technological developments that have permitted this, their limitations, and future directions. Finally, we look into the general obstacles faced by the translational field, and how implementation of research systems utilizing slices could help in resolving these.

Precision-cut organ slices to investigate target organ injury

Drug-induced organ injury is a multifaceted process, involving numerous cell types and mediators, and remains a significant safety issue in pharmaceutical development and clinical therapy. Organ slices, an in vitro model representing the multicellular, structural and functional features of in vivo tissue, is a promising model for elucidating mechanisms of drug-induced organ injury and for characterising species susceptibilities. Time- and concentration-dependent drug-induced effects on organ slice gene expression, function and morphology are providing insight into the molecular and biochemical pathways leading to organ dysfunction, an altered morphology and the induction of repair pathways. Human organ slice studies are valuable for bridging the extrapolation of animal-derived data and for identifying mechanisms relevant for humans. The liver is the major organ used in organ slice studies; however, the utility of extrahepatic-derived slices, as well as cocultures for investigating multiple organ involvement in tissue injury is increasing. Organ slice investigations can further our understanding of the cell types and cell interactions involved in drug-induced injury and the consequences of drug-induced off-target effects for identifying compound liabilities that will impact safety.

Organ slices for the evaluation of human drug toxicity

Human organ slices, an in vitro model representing the multicellular and functional features of in vivo tissue, is a promising model for characterizing mechanisms of drug-induced organ injury and for identifying biomarkers of organ injury. Target organ injury is a significant clinical issue. In vitro models, which compare human and animal tissue to improve the extrapolation of animal in vivo studies for predicting human outcome, will contribute to improving drug candidate selection and to defining species susceptibilities in drug discovery and development programs. A critical aspect to the performance and outcome of human organ slice studies is the use of high quality tissue, and the use of culture conditions that support optimum organ slice survivability, in order to accurately reproduce mechanisms of organ injury in vitro. The attribute of organ slices possessing various cell types and interactions contributes to the overall biotransformation, inflammatory response and assessment of injury. Regional differences and changes in morphology can be readily evaluated by histology and special stains, similar to tissue obtained from in vivo studies. The liver is the major organ of which slice studies have been performed, however the utility of extra-hepatic derived slices, as well as co-cultures is increasing. Recent application of integrating gene expression, with human organ slice function and morphology demonstrate the increased potential of this model for defining the molecular and biochemical pathways leading to drug-induced tissue changes. By gaining a more detailed understanding of the mechanisms of drug-induced organ injury, and by correlating clinical measurements with drug-induced effects in the in vitro models, the vision of human in vitro models to identify more sensitive and discriminating markers of organ damage is attainable.

Precision-cut tissue slices: applications in pharmacology and toxicology

Almost a decade has passed since the first paper describing the isolation and maintenance of precision-cut liver slices produced using a mechanical tissue slicer was published (1). Although tissue slices of various organs have been employed as an in vitro system for several decades, the lack of reproducibility within the slices and the relatively limited viability of the tissue preparations has prevented a widespread acceptance of the technique. The production of an automated slicer, capable of reproducibly producing relatively thin slices of tissue, as well as the development of a dynamic organ culture system, overcame several of these obstacles. Since that time, significant advances in the methods to produce and culture tissue slices have been made, as well as the application of the technique to several other organs, including kidney, lung and heart. This review will i) summarize the historical use of tissue slices prior to the development of the precision-cut tissue slice system; ii) briefly analyze current methods to produce precision-cut liver, kidney, lung and heart slices; and iii) discuss the applications of this powerful in vitro system to the disciplines of pharmacology and toxicology.

Toxicity of 3-methylindole, 1-nitronaphthalene and paraquat in precision-cut rat lung slices

The toxicity of 3-methylindole, 1-nitronaphthalene and paraquat has been studied in precision-cut rat lung slice cultures. Lung slices were prepared from male Sprague-Dawley rats using an agarose gel instilling technique with a Krumdieck tissue slicer and cultured for 24 h in a dynamic organ culture system. Treatment of rat lung slices with 3-methylindole, 1-nitronaphthalene or paraquat produced concentration dependent decreases in lung slice protein synthesis and potassium content. EC50 values (concentration to produce a 50% inhibition) for protein synthesis were 0.024, 0.27 and 0.57 mM for paraquat, 1-nitronaphthalene and 3-methylindole, respectively. These results demonstrate that precision-cut lung slices are a useful in vitro model system for studying the pulmonary toxicity of xenobiotics. Lung slices offer the potential as a rapid in vitro screen for identifying pulmonary toxicants and to evaluate species differences in response.

Comparison of the metabolism of 7-ethoxycoumarin and coumarin in precision-cut rat liver and lung slices

The metabolism of 7-ethoxycoumarin and [3-(14)C]coumarin was compared in precision-cut rat liver and lung slices. The lung slices were prepared using an agarose gel instilling technique enabling the production of tissue cylinders followed by lung slices employing a Krumdieck tissue slicer. Both 50 microM 7-ethoxycoumarin and 50 microM [3-(14)C]coumarin were metabolized by rat liver and lung slices. 7-Ethoxycoumarin was converted to 7-hydroxycoumarin (7-HC) which was conjugated with both D-glucuronic acid and sulfate. 7-HC sulfate was the major metabolite formed by both liver and lung slices. [3-(14)C]Coumarin was metabolized by rat liver and lung slices to both polar products and to metabolite(s) that bound covalently to tissue slice proteins. The polar products included unidentified metabolites and 3-hydroxylation pathway products, with only very small quantities of 7-HC being formed. These results demonstrate that precision-cut lung slices are a useful model in vitro system for studying the pulmonary metabolism of xenobiotics. Moreover, the precision-cut tissue slice technique may be employed for comparisons of hepatic and extrahepatic xenobiotic metabolism.

Use of precision-cut liver slices for studies of unscheduled DNA synthesis

Precision-cut liver slices were prepared from untreated and Aroclor 1254 (ARO)-treated male Sprague-Dawley rats with a Krumdieck tissue slicer. Liver slices were cultured for 24 hr in medium containing [3H]thymidine and 0-0.1 mM 2-acetylaminofluorene (2-AAF) using a dynamic organ culture system and processed for autoradiographic evaluation of unscheduled DNA synthesis (UDS). Compared with control (i.e. 0 mM 2-AAF) liver slice cultures, 2-AAF produced a concentration-dependent increase in UDS, the effect being more marked in liver slices from ARO-treated than from untreated rats. With liver slices from untreated rats, 2-AAF produced the greatest increase in UDS in centrilobular hepatocytes. 2-AAF-induced UDS in liver slices from ARO-treated rats was most marked in centrilobular hepatocytes but the effect also extended to other areas of the liver lobule. These results demonstrate that precision-cut liver slices may be a valuable alternative in vitro system to hepatocyte cultures for screening chemicals for potential genotoxicity. Unlike hepatocyte cultures, liver slices permit the study of zonal differences in UDS. Moreover, this technique could be applied to other tissues and the study of species differences in response.