Consistency of Spleen and Symptom Reduction Regardless of Cytopenia in Patients With Myelofibrosis Treated With Pacritinib.

BACKGROUND: Pacritinib is a JAK2/IRAK1/ACVR1 inhibitor that is approved in the United States for the treatment of patients with myelofibrosis who have a platelet count < 50 × 109/L. Phase 3 clinical studies of pacritinib included patients across a wide range of baseline platelet and hemoglobin levels. PATIENTS AND METHODS: In order to assess the impact of baseline blood counts on pacritinib efficacy, an analysis of efficacy outcomes by baseline platelet and hemoglobin levels was performed using data pooled from 2 Phase 3 studies of pacritinib in patients with MF (PERSIST-1 and PERSIST-2). RESULTS: Of 276 patients evaluable for spleen response, spleen volume reduction occurred consistently across platelet subgroups (< 100 × 109/L or ≥ 100 × 109/L) and hemoglobin subgroups (< 8 g/dL, ≥ 8 to < 10 g/dL, or > 10 g/dL), with no diminution in treatment effect in patients with severe thrombocytopenia or anemia. Among 159 patients evaluable for symptoms response, improvement in total symptom score (TTS) was similar across platelet subgroups. A ≥ 50% improvement of TSS occurred more frequently in patients with baseline hemoglobin < 8 g/dL compared with those with baseline hemoglobin ≥ 8 to < 10 g/dL or > 10 g/dL. Patients with baseline hemoglobin < 8 g/dL also experienced improved hemoglobin sustained over 24 weeks, whereas subgroups with less severe anemia had stable hemoglobin levels over time. Symptom improvement as assessed using the Patient Global Impression of Change instrument was generally consistent across platelet and hemoglobin subgroups. CONCLUSION: Pacritinib demonstrates consistent efficacy in patients with MF regardless of baseline platelet and hemoglobin counts.

Oxygen Plasma Substrate and Specific Nanopattern Promote Early Differentiation of HepaRG Progenitors.

Fully differentiated HepaRG™ cells are the hepatic cell line of choice for in vitro study in toxicology and drug trials. They are derived from a hepatoblast-like progenitor (HepaRG-P) that differentiates into a coculture of hepatocyte-like and cholangiocyte-like cells. This process that requires 2 weeks of proliferation followed by 2 weeks of differentiation using dimethyl sulfoxide (DMSO) can be time consuming and costly. Identifying a method to accelerate HepaRG-Ps toward a mature lineage would save both time and money. The ability to do this in the absence of DMSO would remove the possibility of confounding toxicology results caused by DMSO induction of CYP pathways. It has been shown that tissue culture substrates play an important role in the development and maturity of a cell line, and this is particularly important for progenitor cells, which retain some form of plasticity. Oxygen plasma treatment is used extensively to modify cell culture substrates. There is also evidence that patterned rather than planar surfaces have a positive effect on proliferation and differentiation. In this study, we compared the effect of standard tissue culture plastic (TCP), oxygen plasma coated (OPC), and nanopatterned substrates (NPS) on early differentiation and function of HepaRG-P cells. Since NPS were OPC we initially compared the effect of TCP and OPC to enable comparison between all three culture surfaces using OPC as control to asses if patterning further enhanced early differentiation and functionality. The results show that HepaRG-P's grown on OPC substrate exhibited earlier differentiation, proliferation, and function compared with TCP. Culturing HepaRG-P's on OPC with the addition of NPS did not confer any additional advantage. In conclusion, OPC surface appeared to enhance hepatic differentiation and functionality and could replace traditional methods of differentiating HepaRG-P cells into fully differentiated and functional HepaRGs earlier than standard methods. Impact statement We show significantly earlier differentiation and function of HepaRG progenitor cells when grown in dimethyl sulfoxide-free medium on oxygen plasma substrates versus standard tissue culture plastic. Further investigation showed that nanopatterning of oxygen plasma substrates did not confer any additional advantage over smooth oxygen plasma, although one pattern (DSQ120) showed comparable early differentiation and function.

Chlorpromazine toxicity is associated with disruption of cell membrane integrity and initiation of a pro-inflammatory response in the HepaRG hepatic cell line.

Chlorpromazine (CPZ) is a neuroleptic drug and prototype compound used to study intrahepatic cholestasis. The exact mechanisms of CPZ induced cholestasis remain unclear. Rat hepatocytes, or a sandwich culture of rat and human hepatocytes, have been the most commonly used models for studying CPZ toxicity in vitro. However, to better predict outcomes in pre-clinical trials where cholestasis may be an unwanted consequence, a human in vitro model, based on human HepaRG cells, capable of real-time, non-invasive and label free monitoring, alongside molecular investigations would be beneficial. To address this we used the human hepatic HepaRG cell line, and established concentrations of CPZ ranging from sub-toxic, 25 µM and 50 µM, to toxic 100 µM and compared them with untreated control. To assess the effect of this range of CPZ concentrations we employed electrical cell-substrate impedance sensing (ECIS) to measure viability and cell membrane interactions alongside traditional viability assays, immunocytostaining and qRT-PCR to assess genes of interest within adaptive and inflammatory pathways. Using these methods, we show a concentration dependant response to CPZ involving pro-inflammatory pathway, loss of tight junctions and membrane integrity, and an adaptive response mediated by Cytochrome P450 (CYP) enzyme activation and up-regulation of membrane phospholipid and xenobiotic transporters. In conclusion, structural changes within the membrane caused by sub-toxic and toxic concentrations of CPZ negatively impact the function of the cellular membrane. Damage to efflux transport proteins caused by CPZ induce cholestasis alongside downstream inflammation, which activates compensatory responses for cell survival. LAY SUMMARY: Chlorpromazine is a drug used to treat patients with schizophrenia, which has a known association with liver damage. Here we show that it causes inflammation and alters the cell membranes in liver and bile duct cells similar to what is seen within a human population. The initiation of the inflammatory response and changes to cellular structure may provide insight into the damage and disease process and inform medical treatment.

HepaRG-Progenitor Cell Derived Hepatocytes Cultured in Bioartificial Livers Are Protected from Healthy- and Acute Liver Failure-Plasma Induced Toxicity.

BACKGROUND/AIMS: For applicability of cell-based therapies aimed at the treatment of liver failure, such as bioartificial livers (BALs) and hepatocyte transplantation, it is essential that the applied hepatocytes tolerate exposure to the patient plasma. However, plasma from both healthy donors and acute liver failure (ALF) patients is detrimental to hepatocytes and hepatic cell lines, such as HepaRG. We aimed to elucidate the underlying mechanisms of plasma-induced toxicity against HepaRG cells in order to ultimately develop methods to reduce this toxicity and render HepaRG-BAL treatment more effective. METHODS: Differentiated HepaRG cells cultured in monolayers and laboratory-scale BALs were exposed to culture medium, healthy human plasma, healthy porcine plasma and ALF porcine plasma. Healthy human plasma was fractionated based on size- and polarity, albumin depleted and heat treated to characterize the toxic fraction. The cells were assessed for viability by total protein content and trypan blue staining. Their hepatic differentiation was assessed on transcript level through qRT-PCR and microarray analysis, and on functional level for Cytochrome P450 3A4 activity and ammonia elimination. Mitochondrial damage was assessed by JC-1 staining and mitochondrial gene transcription. RESULTS: Sixteen hours of healthy human plasma exposure did not affect viability, however, hepatic gene-transcript levels decreased dramatically and dose-dependently within four hours of exposure. These changes were associated with early NF-kB signaling and a shift from mitochondrial energy metabolism towards glycolysis. Healthy human plasma-toxicity was associated with the dose-dependent presence of heat-resistant, albumin-bound and (partly) hydrophobic toxic compound(s). HepaRG cells cultured in BALs were partially protected from plasma-toxicity, which was mainly attributable to medium perfusion and/or 3D configuration applied during BAL culturing. The detrimental human plasma effects were reversible in BAL-cultured cells. Porcine ALF-plasma elicited mitotoxicity additional to the basal detrimental effect of porcine healthy plasma, which were only partially reversible. CONCLUSION: A specific fraction of human plasma reduces hepatic differentiation of HepaRG cultures, in association with early NF-κB activation. In addition, ALF-plasma elicits mitotoxic effects. These findings allow for a targeted approach in preventing plasma-induced cell damage.

Scaling-up of a HepaRG progenitor cell based bioartificial liver: optimization for clinical application and transport.

A new generation of bioartificial livers, based on differentiated proliferative hepatocyte sources, has been developed. Several practicable and regulatory demands have to be addressed before these can be clinically evaluated. We identified three main hurdles: (1) expansion and preservation of the biocomponent, (2) development of scaled-up culture conditions and (3) transport of the device to the bedside. In this study we address these three issues for the HepaRG-progenitor cell line-loaded AMC-Bioartificial Liver. (1) HepaRG cells were expanded in large quantities and then cryopreserved or loaded directly into bioreactors. After 3 weeks of culture, key hepatic functions (ammonia/lactate elimination, apolipoprotein A1 synthesis and cytochrome P450 3A4 activity) did not differ significantly between the two groups. (2) Bioartificial livers were scaled up from 9 ml to 540 ml priming volume, with preservation of normalized hepatic functionality. Quantification of amino acid consumption revealed rapid depletion of several amino acids. (3) Whole-device cryopreservation and cooled preservation induced significant loss of hepatic functionality, whereas simulated transport from culture-facility to the bedside in a clinical-grade transport unit with controlled temperature maintenance, medium perfusion and gas supply did not affect functionality. In addition, we assessed tumorigenicity of HepaRG cells in immune-incompetent mice and found no tumor formation of HepaRG cells (n = 12), while HeLa cells induced formation of carcinomas in eight out of 12 mice in 140 days.

Low-dose acetaminophen induces early disruption of cell-cell tight junctions in human hepatic cells and mouse liver.

Dysfunction of cell-cell tight junction (TJ) adhesions is a major feature in the pathogenesis of various diseases. Liver TJs preserve cellular polarity by delimiting functional bile-canalicular structures, forming the blood-biliary barrier. In acetaminophen-hepatotoxicity, the mechanism by which tissue cohesion and polarity are affected remains unclear. Here, we demonstrate that acetaminophen, even at low-dose, disrupts the integrity of TJ and cell-matrix adhesions, with indicators of cellular stress with liver injury in the human hepatic HepaRG cell line, and primary hepatocytes. In mouse liver, at human-equivalence (therapeutic) doses, dose-dependent loss of intercellular hepatic TJ-associated ZO-1 protein expression was evident with progressive clinical signs of liver injury. Temporal, dose-dependent and specific disruption of the TJ-associated ZO-1 and cytoskeletal-F-actin proteins, correlated with modulation of hepatic ultrastructure. Real-time impedance biosensing verified in vitro early, dose-dependent quantitative decreases in TJ and cell-substrate adhesions. Whereas treatment with NAPQI, the reactive metabolite of acetaminophen, or the PKCα-activator and TJ-disruptor phorbol-12-myristate-13-acetate, similarly reduced TJ integrity, which may implicate oxidative stress and the PKC pathway in TJ destabilization. These findings are relevant to the clinical presentation of acetaminophen-hepatotoxicity and may inform future mechanistic studies to identify specific molecular targets and pathways that may be altered in acetaminophen-induced hepatic depolarization.

Human Hepatic HepaRG Cells Maintain an Organotypic Phenotype with High Intrinsic CYP450 Activity/Metabolism and Significantly Outperform Standard HepG2/C3A Cells for Pharmaceutical and Therapeutic Applications.

Conventional in vitro human hepatic models for drug testing are based on the use of standard cell lines derived from hepatomas or primary human hepatocytes (PHHs). Limited availability, interdonor functional variability and early phenotypic alterations in PHHs restrict their use, whilst standard cell lines such as HepG2 lack a substantial and variable set of liver-specific functions such as CYP450 activity. Alternatives include the HepG2-derivative C3A cells selected as a more differentiated and metabolically active hepatic phenotype. Human HepaRG cells are an alternative organotypic co-culture model of hepatocytes and cholangiocytes reported to maintain in vivo-like liver-specific functions, including intact Phase I-III drug metabolism. In this study, we compared C3A and human HepaRG cells using phenotypic profiling, CYP450 activity and drug metabolism parameters to assess their value as hepatic models for pre-clinical drug testing or therapeutics. Compared with C3As, HepaRG co-cultures exhibit a more organotypic phenotype, including evidence of hepatic polarity with the strong expression of CYP3A4, the major isoform involved in the metabolism of over 60% of marketed drugs. Significantly greater CYP450 activity and expression of CYP1A2, CYP2E1 and CYP3A4 genes in HepaRG cells (comparable with that of human liver tissue) was demonstrated. Moreover, HepaRG cells also preferentially expressed the hepatic integrin α5 ß1 - an important modulator of cell behaviour including growth and survival, differentiation and polarity. Drug metabolite profiling of phenacetin (CYP1A2) and testosterone (CYP3A4) using LC-MS/MS and HPLC, respectively, revealed that HepaRGs had more intact (Phase I-II) metabolism profile. Thus, HepaRG cells significantly outperform C3A cells for the potential pharmaceutical and therapeutic applications.

Proteomic profiling of cellular steatosis with concomitant oxidative stress in vitro.

BACKGROUND: Nutrient excess underpins the development of nonalcoholic fatty liver disease (NAFLD). The ensuing metabolic derangement is characterised by increased cellular respiration, oxidative stress and mitochondrial impairment. We have previously recapitulated these events in an in vitro cellular steatosis model. Here, we examined the distinct patterns of protein expression involved using a proteomics approach. METHODS: Human hepatoblastoma C3A cells were treated with a combination of energy substrates; lactate (L), pyruvate (P), octanoate (O) and ammonia (N). Proteins extracts were trypsinized and analyzed on a capillary HPLC OrbitrapXL mass spectrometer. Proteins were quantified using a label-free intensity based approach. Functional enrichment analysis was performed using ToppCluster via Gene Ontology (GO) database. RESULTS: Of the 1327 proteins identified, 104 were differentially expressed between LPON and untreated cells (defined as: ≥2 peptides; fold change ≥1.5; p-value <0.05). Seventy of these were upregulated with LPON. Functional enrichment analysis revealed enhanced protein biosynthesis accompanied by downregulation of histones H2A type 1-A, H1.2, H1.5 and H1.0I in LPON cells. Lipid binding annotations were also enriched as well as proteins involved in cholesterol synthesis, uptake and efflux. Increased expression of aldo-keto reductase family 1, member C1 and C3 suggests enhanced sterol metabolism and increased ROS-mediated lipid peroxidation. CONCLUSIONS: The surge of energy substrates diverts free fatty acid metabolism towards pathways that can mitigate lipotoxicity. The histones depletion may represent an adaptation to increased protein synthesis. However, this can also expose DNA to oxidative stress thus should be explored further in the context of NAFLD progression.

Acetaminophen cytotoxicity is ameliorated in a human liver organotypic co-culture model.

Organotypic liver culture models for hepatotoxicity studies that mimic in vivo hepatic functionality could help facilitate improved strategies for early safety risk assessment during drug development. Interspecies differences in drug sensitivity and mechanistic profiles, low predictive capacity, and limitations of conventional monocultures of human hepatocytes, with high attrition rates remain major challenges. Herein, we show stable, cell-type specific phenotype/cellular polarity with differentiated functionality in human hepatocyte-like C3A cells (enhanced CYP3A4 activity/albumin synthesis) when in co-culture with human vascular endothelial cells (HUVECs), thus demonstrating biocompatibility and relevance for evaluating drug metabolism and toxicity. In agreement with in vivo studies, acetaminophen (APAP) toxicity was most profound in HUVEC mono-cultures; whilst in C3A:HUVEC co-culture, cells were less susceptible to the toxic effects of APAP, including parameters of oxidative stress and ATP depletion, altered redox homeostasis, and impaired respiration. This resistance to APAP is also observed in a primary human hepatocyte (PHH) based co-culture model, suggesting bidirectional communication/stabilization between different cell types. This simple and easy-to-implement human co-culture model may represent a sustainable and physiologically-relevant alternative cell system to PHHs, complementary to animal testing, for initial hepatotoxicity screening or mechanistic studies of candidate compounds differentially targeting hepatocytes and endothelial cells.

Dynamic Support Culture of Murine Skeletal Muscle-Derived Stem Cells Improves Their Cardiogenic Potential In Vitro.

Ischemic heart disease is the main cause of death in western countries and its burden is increasing worldwide. It typically involves irreversible degeneration and loss of myocardial tissue leading to poor prognosis and fatal outcome. Autologous cells with the potential to regenerate damaged heart tissue would be an ideal source for cell therapeutic approaches. Here, we compared different methods of conditional culture for increasing the yield and cardiogenic potential of murine skeletal muscle-derived stem cells. A subpopulation of nonadherent cells was isolated from skeletal muscle by preplating and applying cell culture conditions differing in support of cluster formation. In contrast to static culture conditions, dynamic culture with or without previous hanging drop preculture led to significantly increased cluster diameters and the expression of cardiac specific markers on the protein and mRNA level. Whole-cell patch-clamp studies revealed similarities to pacemaker action potentials and responsiveness to cardiac specific pharmacological stimuli. This data indicates that skeletal muscle-derived stem cells are capable of adopting enhanced cardiac muscle cell-like properties by applying specific culture conditions. Choosing this route for the establishment of a sustainable, autologous source of cells for cardiac therapies holds the potential of being clinically more acceptable than transgenic manipulation of cells.

Fibrinogen production is enhanced in an in-vitro model of non-alcoholic fatty liver disease: an isolated risk factor for cardiovascular events?

BACKGROUND: Cardiovascular disease (CVD) remains the major cause of excess mortality in patients with non-alcoholic fatty liver disease (NAFLD). The aim of this study was to investigate the individual contribution of NAFLD to CVD risk factors in the absence of pathogenic influences from other comorbidities often found in NAFLD patients, by using an established in-vitro model of hepatic steatosis. METHODS: Histopathological events in non-alcoholic fatty liver disease were recapitulated by focused metabolic nutrient overload of hepatoblastoma C3A cells, using oleate-treated-cells and untreated controls for comparison. Microarray and proteomic data from cell culture experiments were integrated into a custom-built systems biology database and proteogenomics analysis performed. Candidate genes with significant dysregulation and concomitant changes in protein abundance were identified and STRING association and enrichment analysis performed to identify putative pathogenic pathways. RESULTS: The search strategy yielded 3 candidate genes that were specifically and significantly up-regulated in nutrient-overloaded cells compared to untreated controls: fibrinogen alpha chain (2.2 fold), fibrinogen beta chain (2.3 fold) and fibrinogen gamma chain (2.1 fold) (all rank products pfp <0.05). Fibrinogen alpha and gamma chain also demonstrated significant concomitant increases in protein abundance (3.8-fold and 2.0-fold, respectively, p <0.05). CONCLUSIONS: In-vitro modelling of NAFLD and reactive oxygen species formation in nutrient overloaded C3A cells, in the absence of pathogenic influences from other comorbidities, suggests that NAFLD is an isolated determinant of CVD. Nutrient overload-induced up-regulation of all three fibrinogen component subunits of the coagulation cascade provides a possible mechanism to explain the excess CVD mortality observed in NAFLD patients.

Preconditioning of skeletal myoblast-based engineered tissue constructs enables functional coupling to myocardium in vivo.

OBJECTIVE: Skeletal myoblasts fuse to form functional syncytial myotubes as an integral part of the skeletal muscle. During this differentiation process, expression of proteins for mechanical and electrical integration is seized, which is a major drawback for the application of skeletal myoblasts in cardiac regenerative cell therapy, because global heart function depends on intercellular communication. METHODS: Mechanically preconditioned engineered tissue constructs containing neonatal mouse skeletal myoblasts were transplanted epicardially. A Y-chromosomal specific polymerase chain reaction (PCR) was undertaken up to 10 weeks after transplantation to confirm the presence of grafted cells. Histologic and electrophysiologic analyses were carried out 1 week after transplantation. RESULTS: Cells within the grafted construct expressed connexin 43 at the interface to the host myocardium, indicating electrical coupling, confirmed by sharp electrode recordings. Analyses of the maximum stimulation frequency (5.65 ± 0.37 Hz), conduction velocity (0.087 ± 0.011 m/s) and sensitivity for pharmacologic conduction block (0.736 ± 0.080 mM 1-heptanol) revealed effective electrophysiologic coupling between graft and host cells, although significantly less robust than in native myocardial tissue (maximum stimulation frequency, 11.616 ± 0.238 Hz, P < .001; conduction velocity, 0.300 ± 0.057 m/s, P < .01; conduction block, 1.983 ± 0.077 mM 1-heptanol, P < .001). CONCLUSIONS: Although untreated skeletal myoblasts cannot couple to cardiomyocytes, we confirm that mechanical preconditioning enables transplanted skeletal myoblasts to functionally interact with cardiomyocytes in vivo and, thus, reinvigorate the concept of skeletal myoblast-based cardiac cell therapy.

Profiling the impact of medium formulation on morphology and functionality of primary hepatocytes in vitro.

The characterization of fully-defined in vitro hepatic culture systems requires testing of functional and morphological variables to obtain the optimal trophic support, particularly for cell therapeutics including bioartificial liver systems (BALs). Using serum-free fully-defined culture medium formulations, we measured synthetic, detoxification and metabolic variables of primary porcine hepatocytes (PPHs)--integrated these datasets using a defined scoring system and correlated this hepatocyte biological activity index (HBAI) with morphological parameters. Hepatic-specific functions exceeded those of both primary human hepatocytes (PHHs) and HepaRG cells, whilst retaining biotransformation potential and in vivo-like ultrastructural morphology, suggesting PPHs as a potential surrogate for PHHs in various biotech applications. The HBAI permits assessment of global functional capacity allowing the rational choice of optimal trophic support for a defined operational task (including BALs, hepatocellular transplantation, and cytochrome P450 (CYP450) drug metabolism studies), mitigates risk associated with sub-optimal culture systems, and reduces time and cost of research and therapeutic applications.

Noninvasive in vivo tracking of mesenchymal stem cells and evaluation of cell therapeutic effects in a murine model using a clinical 3.0 T MRI.

Cardiac cell therapy with mesenchymal stem cells (MSCs) represents a promising treatment approach for end-stage heart failure. However, little is known about the underlying mechanisms and the fate of the transplanted cells. The objective of the presented work is to determine the feasibility of magnetic resonance imaging (MRI) and in vivo monitoring after transplantation into infarcted mouse hearts using a clinical 3.0 T MRI device. The labeling procedure of bone marrow-derived MSCs with micron-sized paramagnetic iron oxide particles (MPIOs) did not affect the viability of the cells and their cell type-defining properties when compared to unlabeled cells. Using a clinical 3.0 T MRI scanner equipped with a dedicated small animal solenoid coil, 10(5) labeled MSCs could be detected and localized in the mouse hearts for up to 4 weeks after intramyocardial transplantation. Weekly ECG-gated scans using T1-weighted sequences were performed, and left ventricular function was assessed. Histological analysis of hearts confirmed the survival of labeled MSCs in the target area up to 4 weeks after transplantation. In conclusion, in vivo tracking of labeled MSCs using a clinical 3.0 T MRI scanner is feasible. In combination with assessment of heart function, this technology allows the monitoring of the therapeutic efficacy of regenerative therapies in a small animal model.

Mechanical preconditioning enables electrophysiologic coupling of skeletal myoblast cells to myocardium.

OBJECTIVE: The effect of mechanical preconditioning on skeletal myoblasts in engineered tissue constructs was investigated to resolve issues associated with conduction block between skeletal myoblast cells and cardiomyocytes. METHODS: Murine skeletal myoblasts were used to generate engineered tissue constructs with or without application of mechanical strain. After in vitro myotube formation, engineered tissue constructs were co-cultured for 6 days with viable embryonic heart slices. With the use of sharp electrodes, electrical coupling between engineered tissue constructs and embryonic heart slices was assessed in the presence or absence of pharmacologic agents. RESULTS: The isolation and expansion procedure for skeletal myoblasts resulted in high yields of homogeneously desmin-positive (97.1% ± 0.1%) cells. Mechanical strain was exerted on myotubes within engineered tissue constructs during gelation of the matrix, generating preconditioned engineered tissue constructs. Electrical coupling between preconditioned engineered tissue constructs and embryonic heart slices was observed; however, no coupling was apparent when engineered tissue constructs were not subjected to mechanical strain. Coupling of cells from engineered tissue constructs to cells in embryonic heart slices showed slower conduction velocities than myocardial cells with the embryonic heart slices (preconditioned engineered tissue constructs vs embryonic heart slices: 0.04 ± 0.02 ms vs 0.10 ± 0.05 ms, P = .011), lower maximum stimulation frequencies (preconditioned engineered tissue constructs vs embryonic heart slices: 4.82 ± 1.42 Hz vs 10.58 ± 1.56 Hz; P = .0009), and higher sensitivities to the gap junction inhibitor (preconditioned engineered tissue constructs vs embryonic heart slices: 0.22 ± 0.07 mmol/L vs 0.93 ± 0.15 mmol/L; P = .0004). CONCLUSIONS: We have generated skeletal myoblast-based transplantable grafts that electrically couple to myocardium.

Enhanced gap junction expression in myoblast-containing engineered tissue.

Transplantation of skeletal myoblasts (SMs) has been investigated as a potential cardiac cell therapy approach. SM are available autologously, predetermined for muscular differentiation and resistant to ischemia. Major hurdles for their clinical application are limitations in purity and yield during cell isolation as well as the absence of gap junction expression after differentiation into myotubes. Furthermore, transplanted SMs do not functionally or electrically integrate with the host myocardium. Here, we describe an efficient method for isolating homogeneous SM populations from neonatal mice and demonstrate persistent gap junction expression in an engineered tissue. This method resulted in a yield of 1.4 × 10(8) high-purity SMs (>99% desmin positive) after 10 days in culture from 162.12 ± 11.85 mg muscle tissue. Serum starvation conditions efficiently induced differentiation into spontaneously contracting myotubes that coincided with loss of gap junction expression. For mechanical conditioning, cells were integrated into engineered tissue constructs. SMs within tissue constructs exhibited long term survival, ordered alignment, and a preserved ability to differentiate into contractile myotubes. When the tissue constructs were subjected to passive longitudinal tensile stress, the expression of gap junction and cell adherence proteins was maintained or increased throughout differentiation. Our studies demonstrate that mechanical loading of SMs may provide for improved electromechanical integration within the myocardium, which could lead to more therapeutic opportunities.