Heart regeneration after myocardial infarction using synthetic biomaterials

Conductive Hydrogen Sulfide-Releasing Hydrogel Encapsulating ADSCs for Myocardial Infarction Treatment

Hydrogen sulfide (H₂S) exhibits extensive protective actions in cardiovascular systems, such as anti-inflammatory and stimulating angiogenesis, but its therapeutic potential is severely discounted by the short half-life and the poorly controlled releasing behavior. Herein, we developed a macromolecular H₂S prodrug by grafting 2-aminopyridine-5-thiocarboxamide (a small-molecule H₂S donor) on partially oxidized alginate (ALG-CHO) to mimic the slow and continuous release of endogenous H₂S. In addition, tetraaniline (a conductive oligomer) and adipose-derived stem cells (ADSCs) were introduced to form a stem cell-loaded conductive H₂S-releasing hydrogel through the Schiff base reaction between ALG-CHO and gelatin. The hydrogel exhibited adhesive property to ensure a stable anchoring to the wet and beating hearts. After myocardial injection, longer ADSCs retention period and elevated sulfide concentration in rat myocardium were demonstrated, accompanied by upregulation of cardiac-related mRNA (Cx43, α-SMA, and cTnT) and angiogenic factors (VEGFA and Ang-1) and downregulation of inflammatory factors (tumor necrosis factor-α). Echocardiography and histological analysis strongly demonstrated an increase in the ejection fraction value and smaller infarction size, suggesting a remarkable improvement of the cardiac functions of Sprague-Dawley rats. The ADSC-loaded conductive hydrogen sulfide-releasing hydrogel dramatically promoted the therapeutic effects, offering a promising therapeutic strategy for treating myocardial infarction.

Rebuilding Postinfarcted Cardiac Functions by Injecting TIIA@PDA Nanoparticle-Cross-linked ROS-Sensitive Hydrogels

Drug-loaded injectable hydrogels have been proven to possess huge potential for applications in tissue engineering. However, increasing the drug loading capacity and regulating the release system to adapt to the microenvironment after myocardial infarction face a huge challenge. In this research, an ROS-sensitive injectable hydrogel strengthened by self-nanodrugs was constructed. A hyperbranched ROS-sensitive macromer (HB-PBAE) with multiacrylate end groups was synthesized through dynamic controlled Michael addition. Meanwhile, a simple protocol based on dopamine polymerization was employed to generate a polydopamine (PDA) layer deposited on the tanshinone IIA (TIIA) nanoparticles (NPs) formed from spontaneous hydrophobic self-assembly. The HB-PBAE reacted with thiolate-modified hyaluronic acid (HA-SH) to form an in situ hydrogel, where TIIA@PDA NPs can be conveniently entrapped through the chemical cross-link between thiolate and quinone groups on PDA, which doubles the modulus of hydrogels. The in vivo degradation behavior of the hydrogels was characterized by MRI, exhibiting a much slower degradation behavior that is markedly different from that of in vitro. Importantly, a significant improvement of cardiac functions was achieved after hydrogel injection in terms of increased ejection fraction and decreased infarction size, accompanied by inhibition of the expression of inflammation factors, such as IL-1β, IL-6, and TNF-α.

In Situ Gelling Scaffolds Loaded with Platelet Growth Factors to Improve Cardiomyocyte Survival after Ischemia

Myocardial infarction is caused by prolonged ischemia and it is one of the main cause that leads to heart failures. The aim of the present work was the development of in situ gelling systems, based on poloxamer 407 (P407) or sodium alginate (Alg), loaded with platelet lysate (PL) to enhance cardiomyocyte survival after ischemia. Chondroitin sulfate (CS), a negatively charged glycosaminoglycan able to interact with different positively charged bioactive molecules, such as growth factors, was also investigated with both the systems. The gelation properties of both systems (viscosity, viscoelasticity, consistency by means of penetrometry, and injectability) were characterized in a physiological environment. In vitro evaluation of biocompatibility using fetal cardiac cells (cardiomyocytes and cardiac fibroblasts) demonstrated that the PL loaded alginate/chondroitin sulfate system retained the highest number of viable cells with equal distribution of the populations of cardiomyocytes and fibroblasts. Furthermore, the ability of the systems to improve cardiomyocyte survival after ischemia was also assessed. PL allowed for the highest degree of survival of cardiomyocytes after oxidative damage (simulating ischemic conditions due to MI) and both the Alg + CS PL and, to a greater extent, the PL alone demonstrated a considerable increase in survival of cardiomyocytes. In conclusion, an in situ gelling alginate-chondroitin sulfate system, loaded with platelet lysate, was able to improve the survival of cardiomyocytes after oxidative damage resulting in a promising system to improve cardiac cell viability after ischemia.

Therapeutic approaches for cardiac regeneration and repair

Ischaemic heart disease is a leading cause of death worldwide. Injury to the heart is followed by loss of the damaged cardiomyocytes, which are replaced with fibrotic scar tissue. Depletion of cardiomyocytes results in decreased cardiac contraction, which leads to pathological cardiac dilatation, additional cardiomyocyte loss, and mechanical dysfunction, culminating in heart failure. This sequential reaction is defined as cardiac remodelling. Many therapies have focused on preventing the progressive process of cardiac remodelling to heart failure. However, after patients have developed end-stage heart failure, intervention is limited to heart transplantation. One of the main reasons for the dramatic injurious effect of cardiomyocyte loss is that the adult human heart has minimal regenerative capacity. In the past 2 decades, several strategies to repair the injured heart and improve heart function have been pursued, including cellular and noncellular therapies. In this Review, we discuss current therapeutic approaches for cardiac repair and regeneration, describing outcomes, limitations, and future prospects of preclinical and clinical trials of heart regeneration. Substantial progress has been made towards understanding the cellular and molecular mechanisms regulating heart regeneration, offering the potential to control cardiac remodelling and redirect the adult heart to a regenerative state.

Electrospinning: An enabling nanotechnology platform for drug delivery and regenerative medicine

Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.

Current Trends in Biomaterial Utilization for Cardiopulmonary System Regeneration

The cardiopulmonary system is made up of the heart and the lungs, with the core function of one complementing the other. The unimpeded and optimal cycling of blood between these two systems is pivotal to the overall function of the entire human body. Although the function of the cardiopulmonary system appears uncomplicated, the tissues that make up this system are undoubtedly complex. Hence, damage to this system is undesirable as its capacity to self-regenerate is quite limited. The surge in the incidence and prevalence of cardiopulmonary diseases has reached a critical state for a top-notch response as it currently tops the mortality table. Several therapies currently being utilized can only sustain chronically ailing patients for a short period while they are awaiting a possible transplant, which is also not devoid of complications. Regenerative therapeutic techniques now appear to be a potential approach to solve this conundrum posed by these poorly self-regenerating tissues. Stem cell therapy alone appears not to be sufficient to provide the desired tissue regeneration and hence the drive for biomaterials that can support its transplantation and translation, providing not only physical support to seeded cells but also chemical and physiological cues to the cells to facilitate tissue regeneration. The cardiac and pulmonary systems, although literarily seen as just being functionally and spatially cooperative, as shown by their diverse and dissimilar adult cellular and tissue composition has been proven to share some common embryological codevelopment. However, necessitating their consideration for separate review is the immense adult architectural difference in these systems. This review also looks at details on new biological and synthetic biomaterials, tissue engineering, nanotechnology, and organ decellularization for cardiopulmonary regenerative therapies.

New strategies for improving stem cell therapy in ischemic heart disease

Stem cell therapy is a promising approach to the treatment of ischemic heart disease via replenishing cell loss after myocardial infarction. Both preclinical studies and clinical trials have indicated that cardiac function improved consistently, but very modestly after cell-based therapy. This mainly attributed to low cell survival rate, engraftment and functional integration, which became the major challenges to regenerative medicine. In recent years, several new cell types have been developed to regenerate cardiomyocytes and novel delivery approaches helped to increase local cell retention. New strategies, such as cell pretreatment, gene-based therapy, tissue engineering, extracellular vesicles application and immunologic regulation, have surged and brought about improved cell survival and functional integration leading to better therapeutic effects after cell transplantation. In this review, we summarize these new strategies targeting at challenges of cardiac regenerative medicine and discuss recent evidences that may hint their effectiveness in the future clinical settings.

An Injectable Oxygen Release System to Augment Cell Survival and Promote Cardiac Repair Following Myocardial Infarction

Oxygen deficiency after myocardial infarction (MI) leads to massive cardiac cell death. Protection of cardiac cells and promotion of cardiac repair are key therapeutic goals. These goals may be achieved by re-introducing oxygen into the infarcted area. Yet current systemic oxygen delivery approaches cannot efficiently diffuse oxygen into the infarcted area that has extremely low blood flow. In this work, we developed a new oxygen delivery system that can be delivered specifically to the infarcted tissue, and continuously release oxygen to protect the cardiac cells. The system was based on a thermosensitive, injectable and fast gelation hydrogel, and oxygen releasing microspheres. The fast gelation hydrogel was used to increase microsphere retention in the heart tissue. The system was able to continuously release oxygen for 4 weeks. The released oxygen significantly increased survival of cardiac cells under the hypoxic condition (1% O₂) mimicking that of the infarcted hearts. It also reduced myofibroblast formation under hypoxic condition (1% O₂). After implanting into infarcted hearts for 4 weeks, the released oxygen significantly augmented cell survival, decreased macrophage density, reduced collagen deposition and myofibroblast density, and stimulated tissue angiogenesis, leading to a significant increase in cardiac function.

An injectable conductive hydrogel encapsulating plasmid DNA-eNOs and ADSCs for treating myocardial infarction

Myocardial infarction (MI) leads to the mass death of cardiomyocytes accompanying with the unfavorable alternation of microenvironment, a fibrosis scar deprived of electrical communications, and the lack of blood supply in the infarcted myocardium. The three factors are inextricably intertwined and thus result in a conservative MI therapy efficacy in clinic. A holistic approach pertinently targeted to these three key points would be favorable to rebuild the heart functions. Here, an injectable conductive hydrogel was constructed via in situ Michael addition reaction between multi-armed conductive crosslinker tetraaniline-polyethylene glycol diacrylate (TA-PEG) and thiolated hyaluronic acid (HA-SH). The resultant soft conductive hydrogel with equivalent myocardial conductivity and anti-fatigue performance was loaded with plasmid DNA encoding eNOs (endothelial nitric oxide synthase) nanocomplexes and adipose derived stem cells (ADSCs) for treating MI. The TA-PEG/HA-SH/ADSCs/Gene hydrogel-based holistic system was injected into the infarcted myocardium of SD rats. We demonstrated an increased expression of eNOs in myocardial tissue the heightening of nitrite concentration, accompanied with upregulation of proangiogenic growth factors and myocardium related mRNA. The results of electrocardiography, cardiogram, and histological analysis convincingly revealed a distinct increase of ejection fraction (EF), shortened QRS interval, smaller infarction size, less fibrosis area, and higher vessel density, indicating a significant improvement of heart functions. This conception of combination approach by a conductive injectable hydrogel loaded with stem cells and gene-encoding eNOs nanoparticles will become a robust therapeutic strategy for the treatment of MI.

Autophagy protects cardiomyocytes from the myocardial ischaemia-reperfusion injury through the clearance of CLP36

Cardiovascular disease (CVD) is the leading cause of the death worldwide. An increasing number of studies have found that autophagy is involved in the progression or prevention of CVD. However, the precise mechanism of autophagy in CVD, especially the myocardial ischaemia-reperfusion injury (MI/R injury), is unclear and controversial. Here, we show that the cardiomyocyte-specific disruption of autophagy by conditional knockout of Atg7 leads to severe contractile dysfunction, myofibrillar disarray and vacuolar cardiomyocytes. A negative cytoskeleton organization regulator, CLP36, was found to be accumulated in Atg7-deficient cardiomyocytes. The cardiomyocyte-specific knockout of Atg7 aggravates the MI/R injury with cardiac hypertrophy, contractile dysfunction, myofibrillar disarray and severe cardiac fibrosis, most probably due to CLP36 accumulation in cardiomyocytes. Altogether, this work reveals autophagy may protect cardiomyocytes from the MI/R injury through the clearance of CLP36, and these findings define a novel relationship between autophagy and the regulation of stress fibre in heart.

Stem cells cardiac patch from decellularized umbilical artery improved heart function after myocardium infarction

The construction of the high biocompatible biomaterials pretreated with MSC offers a promising strategy to improve the effects of stem cell therapy for the myocardial infarction (MI). However, assembling vascularized three-dimensional (3-D) myocardial tissues remains an enormous challenge. In this study, we optimized the decellularization protocol with the umbilical artery to construct microporous 3-D scaffold which is suitable for the stem cells (SC) proliferation. The SD rats underwent proximal left coronary ligation and a 5-mm diameter microporous SC patch was implanted directly on the infarct area (SC patch group). The LV contractile function, regional myocardial wall compliance, and tissue histology were assessed 4 weeks after patch implantation. The MSC patch integrated to the local heart tissue and the neo-vessels have been observed in the MSC patch. The vessels in the MSC patch were positive for the CD31 (marker for the mature endothelial cells). The left ventricle wall was thicker in the MSC patch group than the control group (p<0.05 vs. empty patch group). And the LVEF has been improved in the MSC patch group than empty patch group (59±6.7% vs. 31±4.5%, p<0.05).

CONCLUSIONS

Our results showed that the implantation of the MSC patch improved cardiac contractile function in heart infarction rat model. The construction of artificial tissue from the decellularized umbilical artery and the MSC may open a promising perspective for the tissue therapy for MI.

Spatiotemporal delivery of nanoformulated liraglutide for cardiac regeneration after myocardial infarction

The local, intramyocardial injection of proteins into the infarcted heart is an attractive option to initiate cardiac regeneration after myocardial infarction (MI). Liraglutide, which was developed as a treatment for type 2 diabetes, has been implicated as one of the most promising protein candidates in cardiac regeneration. A significant challenge to the therapeutic use of this protein is its short half-life in vivo. In this study, we evaluated the therapeutic effects and long-term retention of liraglutide loaded in poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticles (NP-liraglutide) on experimental MI. PLGA-PEG nanoparticles (NPs) have been shown to efficiently load liraglutide and release bioactive liraglutide in a sustained manner. For in vitro test, the released liraglutide retained bioactivity, as measured by its ability to activate liraglutide signaling pathways. Next, we compared the effects of an intramyocardial injection of saline, empty NPs, free liraglutide and NP-liraglutide in a rat model of MI. NPs were detected in the myocardium for up to 4 weeks. More importantly, an intramyocardial injection of NP-liraglutide was sufficient to improve cardiac function (P<0.05), attenuate the infarct size (P<0.05), preserve wall thickness (P<0.05), promote angiogenesis (P<0.05) and prevent cardiomyocyte apoptosis (P<0.05) at 4 weeks after injection without affecting glucose levels. The local, controlled, intramyocardial delivery of NP-liraglutide represents an effective and promising strategy for the treatment of MI.

Multimodal Hydrogel-Based Platform To Deliver and Monitor Cardiac Progenitor/Stem Cell Engraftment

Retention and survival of transplanted cells are major limitations to the efficacy of regenerative medicine, with short-term paracrine signals being the principal mechanism underlying current cell therapies for heart repair. Consequently, even improvements in short-term durability may have a potential impact on cardiac cell grafting. We have developed a multimodal hydrogel-based platform comprised of a poly(ethylene glycol) network cross-linked with bioactive peptides functionalized with Gd(III) in order to monitor the localization and retention of the hydrogel in vivo by magnetic resonance imaging. In this study, we have tailored the material for cardiac applications through the inclusion of a heparin-binding peptide (HBP) sequence in the cross-linker design and formulated the gel to display mechanical properties resembling those of cardiac tissue. Luciferase-expressing cardiac stem cells (CSC-Luc2) encapsulated within these gels maintained their metabolic activity for up to 14 days in vitro. Encapsulation in the HBP hydrogels improved CSC-Luc2 retention in the mouse myocardium and hind limbs at 3 days by 6.5- and 12- fold, respectively. Thus, this novel heparin-binding based, Gd(III)-tagged hydrogel and CSC-Luc2 platform system demonstrates a tailored, in vivo detectable theranostic cell delivery system that can be implemented to monitor and assess the transplanted material and cell retention.

Fibroblast Growth Factor-1 Released from a Heparin Coacervate Improves Cardiac Function in a Mouse Myocardial Infarction Model

Emerging evidence supports the beneficial effect of fibroblast growth factor-1 (FGF1) on heart diseases, but its application has been hindered by the short half-life and limited bioactivity of the free protein. We designed an injectable coacervate to facilitate robust growth factor delivery, which would both protect and increase the bioactivity of growth factors. In this study, a model for acute myocardial infarction was established in mice, and the cardioprotective effect of the FGF1 coacervate was investigated. Echocardiographic results showed that the FGF1 coacervate inhibited ventricular dilation and preserved cardiac contractibility more than the free FGF1 and the saline control within the 6-week duration of the experiments. Histological examination revealed that the FGF1 coacervate reduced inflammation and fibrosis post-MI, significantly increased the proliferation of endothelial and mural cells, and resulted in stable arterioles and capillaries. Furthermore, the FGF1 coacervate improved the proliferation of cardiac stem cells 6 weeks post-MI. However, free FGF1, dosed identically, did not show significant difference from saline treatment. Thus, one injection of FGF1 coacervate was sufficient to attenuate the injury caused by MI, and the results were significantly better than those obtained from an equal dose of free FGF1.

Intramyocardial Injection of Recombinant Adeno-Associated Viral Vector Coexpressing PR39/Adrenomedullin Enhances Angiogenesis and Reduces Apoptosis in a Rat Myocardial Infarction Model

Cotransfer of angiogenic and antiapoptotic genes could be the basis of new gene therapy strategies for myocardial infarction. In this study, rAAV-PR39-ADM, coexpressing antimicrobial peptide (PR39) and adrenomedullin (ADM), was designed with the mediation of recombinant adeno-associated virus. In vitro, CRL-1730 cells were divided into four groups, namely, the sham group, the AAV-null group, the NS (normal saline) group, and the PR39-ADM group. Immunocytochemistry analysis, CCK-8 assays, Matrigel assays, and apoptotic analysis were performed; in vivo, myocardial infarction model was established through ligation of the left coronary artery on rats, and treatment groups corresponded to those used in vitro. Myocardial injury, cardiac performance, and the extent of myocardial apoptosis were assessed. Results suggested that rAAV-PR39-ADM administration after myocardial infarction improved cell viability and cardiac function, attenuated apoptosis and myocardial injury, and promoted angiogenesis. Subsequently, levels of 6×His, HIF-1α, VEGF, p-Akt, Akt, ADM, Bcl-2, and Bax were measured by western blot. rAAV-PR39-ADM increased p-Akt, HIF-1α, and VEGF levels and induced higher Bcl-2 expression and lower Bax expression. In conclusion, our results demonstrate that rAAV-PR39-ADM mitigates myocardial injury by promoting angiogenesis and reducing apoptosis. This study suggests a potential novel gene therapy-based method that could be used clinically for myocardial infarction.

Novel Platform of Cardiomyocyte Culture and Coculture via Fibroblast-Derived Matrix-Coupled Aligned Electrospun Nanofiber

For cardiac tissue engineering, much attention has been given to the artificial cardiac microenvironment in which anisotropic design of scaffold and extracellular matrix (ECM) are the major cues. Here we propose poly(l-lactide-co-caprolactone) and fibroblast-derived ECM (PLCL/FDM), a hybrid scaffold that combines aligned electrospun PLCL fibers and FDM. Fibroblasts were grown on the PLCL fibers for 5-7 days and subsequently decellularized to produce PLCL/FDM. Various analyses confirmed aligned, FDM-deposited PLCL fibers. Compared to fibronectin (FN)-coated electrospun PLCL fibers (control), H9c2 cardiomyoblast differentiation was significantly effective, and neonatal rat cardiomyocyte (CM) phenotype and maturation was improved on PLCL/FDM. Moreover, a coculture platform was created using multilayer PLCL/FDM in which two different cells make indirect or direct cell-cell contacts. Such coculture platforms demonstrate their feasibility in terms of higher cell viability, efficiency of target cell harvest (>95% in noncontact; 85% in contact mode), and molecular diffusion through the PLCL/FDM layer. Coculture of primary CMs and fibroblasts exhibited much better CM phenotype and improvement of CM maturity upon either direct or indirect interactions, compared to the conventional coculture systems (transwell insert and tissue culture plate (TCP)). Taken together, our platform should be very useful and have significant contributions in investigating some scientific or practical issues of crosstalks between multiple cell types.

Cytokine-loaded PLGA and PEG-PLGA microparticles showed similar heart regeneration in a rat myocardial infarction model

Neuregulin (NRG1) and fibroblast growth factor (FGF1) are well known growth factors implicated in cardiomyocyte proliferation and survival, as well as in angiogenesis, the development of adult heart and the maintenance of cardiac function. NRG1 and FGF1 have become promising therapeutic agents to treat myocardial infarction (MI) disorder. Unfortunately, clinical trials performed so far reported negative efficacy results, because growth factors are rapidly degraded and eliminated from the biological tissues once administered. In order to increase their bioavailability and favour their therapeutic effects, they have been combined with poly(lactic-co-glycolic acid) and polyethylene glycol microparticles (PLGA MPs and PEG-PLGA MPs). Here we compare both types of microparticles loaded with NRG1 or FGF1 in terms of efficacy in a rat MI model. Our results showed that intramyocardial injection of NRG1 or FGF1-loaded PLGA and PEG-PLGA MPs brought about similar improvements in the ejection fraction, angiogenesis and arteriogenesis after administration into the infarcted hearts. PEG coating did not add any effect regarding MP efficacy. Both PLGA and PEG-PLGA MPs were equally phagocyted in the heart. To our knowledge, this is the first study analysing the opsonisation process in heart tissue. The results allow us to conclude that the opsonisation process is different in heart tissue compared to blood.

How Biomaterials Can Influence Various Cell Types in the Repair and Regeneration of the Heart after Myocardial Infarction

The healthy heart comprises many different cell types that work together to preserve optimal function. However, in a diseased heart the function of one or more cell types is compromised which can lead to many adverse events, one of which is myocardial infarction (MI). Immediately after MI, the cardiac environment is characterized by excessive cardiomyocyte death and inflammatory signals leading to the recruitment of macrophages to clear the debris. Proliferating fibroblasts then invade, and a collagenous scar is formed to prevent rupture. Better functional restoration of the heart is not achieved due to the limited regenerative capacity of cardiac tissue. To address this, biomaterial therapy is being investigated as an approach to improve regeneration in the infarcted heart, as they can possess the potential to control cell function in the infarct environment and limit the adverse compensatory changes that occur post-MI. Over the past decade, there has been considerable research into the development of biomaterials for cardiac regeneration post-MI; and various effects have been observed on different cell types depending on the biomaterial that is applied. Biomaterial treatment has been shown to enhance survival, improve function, promote proliferation, and guide the mobilization and recruitment of different cells in the post-MI heart. This review will provide a summary on the biomaterials developed to enhance cardiac regeneration and remodeling post-MI with a focus on how they control macrophages, cardiomyocytes, fibroblasts, and endothelial cells. A better understanding of how a biomaterial interacts with the different cell types in the heart may lead to the development of a more optimized biomaterial therapy for cardiac regeneration.

Cardiac Chemical Exchange Saturation Transfer MR Imaging Tracking of Cell Survival or Rejection in Mouse Models of Cell Therapy

Purpose To examine whether cardiac chemical exchange saturation transfer (CEST) imaging can be serially and noninvasively used to probe cell survival or rejection after intramyocardial implantation in mice. Materials and Methods Experiments were compliant with the National Institutes of Health Guidelines on the Use of Laboratory Animals and approved by the Institutional Animal Care and Use Committee. One million C2C12 cells labeled with either europium (Eu) 10-(2-hydroxypropyl)-1,4,7-tetraazacyclododecane-1,4,7-triacetic acid (HP-DO3A) or saline via the hypotonic swelling technique were implanted into the anterior-lateral left ventricular wall in C57BL/6J (allogeneic model, n = 17) and C3H (syngeneic model, n = 13) mice. Imaging (frequency offsets of ±15 parts per million) was performed 1, 10, and 20 days after implantation, with the asymmetrical magnetization transfer ratio (MTR_asym) calculated from image pairs. Histologic examination was performed at the conclusion of imaging. Changes in MTR_asym over time and between mice were assessed by using two-way repeated-measures analysis of variance. Results MTR_asym was significantly higher in C3H and C57BL/6J mice in grafts of Eu-HP-DO3A-labeled cells (40.2% ± 5.0 vs 37.8% ± 7.0, respectively) compared with surrounding tissue (-0.67% ± 1.7 vs -1.8% ± 5.3, respectively; P < .001) and saline-labeled grafts (-0.4% ± 6.0 vs -1.2% ± 3.6, respectively; P < .001) at day 1. In C3H mice, MTR_asym remained increased (31.3% ± 9.2 on day 10, 28.7% ± 5.2 on day 20; P < .001 vs septum) in areas of in Eu-HP-DO3A-labeled cell grafts. In C57BL/6J mice, corresponding MTR_asym values (11.3% ± 8.1 on day 10, 5.1% ± 9.4 on day 20; P < .001 vs day 1) were similar to surrounding myocardium by day 20 (P = .409). Histologic findings confirmed cell rejection in C57BL/6J mice. Estimation of graft area was similar with cardiac CEST imaging and histologic examination (R² = 0.89). Conclusion Cardiac CEST imaging can be used to image cell survival and rejection in preclinical models of cell therapy. ^© RSNA, 2016 Online supplemental material is available for this article.

RNA therapeutics - The potential treatment for myocardial infarction

RNA therapeutics mainly control gene expression at the transcript level. In contrast to conventional gene therapy which solely increases production of a protein, delivered RNAs can enhance, reduce or abolish synthesis of a particular protein, which control its relevant activities in a more diverse fashion. Thus, they hold promise to treat many human diseases including myocardial infarction (MI). MI is a serious health burden that causes substantial morbidity and mortality. An unmet clinical need for treating MI is the recovery of cardiac function, which requires regeneration of the functional tissues including the vasculature, nerves, and myocardium. Several classes of RNA therapeutics have been investigated in preclinical MI models, and the results have demonstrated their benefits and encourage their future development. In this review, we summarize the common RNA therapeutic approaches and highlight their application in MI therapy.

In vitro and in vivo assessment of heart-homing porous silicon nanoparticles

Chronic heart failure, predominantly developed after myocardial infarction, is a leading cause of high mortality worldwide. As existing therapies have still limited success, natural and/or synthetic nanomaterials are emerging alternatives for the therapy of heart diseases. Therefore, we aimed to functionalize undecylenic acid thermally hydrocarbonized porous silicon nanoparticles (NPs) with different targeting peptides to improve the NP's accumulation in different cardiac cells (primary cardiomyocytes, non-myocytes, and H9c2 cardiomyoblasts), additionally to investigate the behavior of the heart-targeted NPs in vivo. The toxicity profiles of the NPs evaluated in the three heart-type cells showed low toxicity at concentrations up to 50 μg/mL. Qualitative and quantitative cellular uptake revealed a significant increase in the accumulation of atrial natriuretic peptide (ANP)-modified NPs in primary cardiomyocytes, non-myocytes and H9c2 cells, and in hypoxic primary cardiomyocytes and non-myocytes. Competitive uptake studies in primary cardiomyocytes showed the internalization of ANP-modified NPs takes place via the guanylate cyclase-A receptor. When a myocardial infarction rat model was induced by isoprenaline and the peptide-modified [(111)In]NPs administered intravenously, the targeting peptides, particularly peptide 2, improved the NPs' accumulation in the heart up to 3.0-fold, at 10 min. This study highlights the potential of these peptide-modified nanosystems for future applications in heart diseases.

Stem cells and injectable hydrogels: Synergistic therapeutics in myocardial repair

One of the major problems in the treatment of cardiovascular diseases is the inability of myocardium to self-regenerate. Current therapies are unable to restore the heart's function after myocardial infarction. Myocardial tissue engineering is potentially a key approach to regenerate damaged heart muscle. Myocardial patches are applied surgically, whereas injectable hydrogels provide effective minimally invasive approaches to recover functional myocardium. These hydrogels are easily administered and can be either cell free or loaded with bioactive agents and/or cardiac stem cells, which may apply paracrine effects. The aim of this review is to investigate the advantages and disadvantages of injectable stem cell-laden hydrogels and highlight their potential applications for myocardium repair.

Towards comprehensive cardiac repair and regeneration after myocardial infarction: Aspects to consider and proteins to deliver

Ischemic heart disease is a leading cause of death worldwide. After the onset of myocardial infarction, many pathological changes take place and progress the disease towards heart failure. Pathologies such as ischemia, inflammation, cardiomyocyte death, ventricular remodeling and dilation, and interstitial fibrosis, develop and involve the signaling of many proteins. Proteins can play important roles in limiting or countering pathological changes after infarction. However, they typically have short half-lives in vivo in their free form and can benefit from the advantages offered by controlled release systems to overcome their challenges. The controlled delivery of an optimal combination of proteins per their physiologic spatiotemporal cues to the infarcted myocardium holds great potential to repair and regenerate the heart. The effectiveness of therapeutic interventions depends on the elucidation of the molecular mechanisms of the cargo proteins and the spatiotemporal control of their release. It is likely that multiple proteins will provide a more comprehensive and functional recovery of the heart in a controlled release strategy.

Harnessing the secretome of cardiac stem cells as therapy for ischemic heart disease

Adult stem cells continue to promise opportunities to repair damaged cardiac tissue. However, precisely how adult stem cells accomplish cardiac repair, especially after ischemic damage, remains controversial. It has been postulated that the clinical benefit of adult stem cells for cardiovascular disease results from the release of cytokines and growth factors by the transplanted cells. Studies in animal models of myocardial infarction have reported that such paracrine factors released from transplanted adult stem cells contribute to improved cardiac function by several processes. These include promoting neovascularization of damaged tissue, reducing inflammation, reducing fibrosis and scar formation, as well as protecting cardiomyocytes from apoptosis. In addition, these factors might also stimulate endogenous repair by activating cardiac stem cells. Interestingly, stem cells discovered to be resident in the heart appear to be functionally superior to extra-cardiac adult stem cells when transplanted for cardiac repair and regeneration. In this review, we discuss the therapeutic potential of cardiac stem cells and how the proteins secreted from these cells might be harnessed to promote repair and regeneration of damaged cardiac tissue. We also highlight how recent controversies about the efficacy of adult stem cells in clinical trials of ischemic heart disease have not dampened enthusiasm for the application of cardiac stem cells and their paracrine factors for cardiac repair: the latter have proved superior to the mesenchymal stem cells used in most clinical trials in the past, some of which appear to have been conducted with sub-optimal rigor.

Facile Synthesis of Reductively Degradable Biopolymers Using Cystamine Diisocyanate as a Coupling Agent

Reductively degradable biopolymers have emerged as a unique class of smart biomedical materials. Here, a functional coupling agent, cystamine diisocyanate (CDI), was designed to offer a facile access to reductively degradable biopolymers via polycondensation with various diols. CDI was readily obtained with a decent yield of 46% by reacting cystamine dihydrochloride with triphosgene. The polycondensation of oligo(ethylene glycol) diol (Mn = 0.4 or 1.5 kg/mol) or oligo(ε-caprolactone) diol (Mn = 0.53 kg/mol) with CDI in N,N-dimethylformamide at 60 °C using dibutyltin dilaurate as a catalyst afforded reductively degradable poly(ethylene glycol) (SSPEG, Mn = 6.2-76.8 kg/mol) or poly(ε-caprolactone) (SSPCL, Mn = 6.8-16.3 kg/mol), in which molecular weights were well controlled by diol/CDI molar ratios. Moreover, PEG-SSPCL-PEG triblock copolymers could be readily prepared by reacting dihydroxyl-terminated SSPCL with PEG-isocyanate derivative. PEG-SSPCL-PEG with an Mn of 5.0-16.3-5.0 kg/mol formed small-sized micelles with an average diameter of about 85 nm in PB buffer. The in vitro release studies using doxorubicin (DOX) as a model drug showed that, in sharp contrast to reduction-insensitive PEG-PCL(HDI)-PEG controls, drug release from PEG-SSPCL-PEG micelles was fast and nearly complete in 24 h under a reductive condition containing 10 mM glutathione. The confocal microscopy experiments in drug-resistant MCF-7 cells (MCF-7/ADR) displayed efficient cytoplasmic DOX release from PEG-SSPCL-PEG micelles. MTT assays revealed that DOX-loaded PEG-SSPCL-PEG micelles were much more potent against MCF-7/ADR cells than reduction-insensitive PEG-PCL(HDI)-PEG controls (IC50: 6.3 vs 55.4 μg/mL). It should further be noted that blank PEG-SSPCL-PEG micelles were noncytotoxic up to a tested concentration of 1 mg/mL. Hence, cystamine diisocyanate appears to be an innovative coupling agent that facilitates versatile synthesis of biocompatible and reductively degradable biopolymers.

Integration of mesenchymal stem cells with nanobiomaterials for the repair of myocardial infarction

The integration of nanobiomaterials with stem cells represents a promising strategy for the treatment of myocardial infarction. While stem cells and nanobiomaterials each demonstrated partial success in cardiac repair individually, the therapeutic efficacy of the clinical settings for each of these has been low. Hence, a combination of nanobiomaterials with stem cells is vigorously studied to create synergistic effects for treating myocardial infarction. To date, various types of nanomaterials have been incorporated with stem cells to control cell fate, modulate the therapeutic behavior of stem cells, and make them more suitable for cardiac repair. Here, we review the current stem cell therapies for cardiac repair and describe the combinatorial approaches of using nanobiomaterials and stem cells to improve therapeutic efficacy for the treatment of myocardial infarction.

The mesmiRizing complexity of microRNAs for striated muscle tissue engineering

microRNAs (miRs) are small non-protein-coding RNAs, able to post-transcriptionally regulate many genes and exert pleiotropic effects. Alteration of miR levels in tissues and in the circulation has been associated with various pathological and regenerative conditions. In this regard, tissue engineering of cardiac and skeletal muscles is a fascinating context for harnessing the complexity of miR-based circuitries and signals. In this review, we will focus on miR-driven regulation of cardiac and skeletal myogenic routes in homeostatic and challenging states. Furthermore, we will survey the intriguing perspective of exosomal and circulating miRs as novel paracrine players, potentially useful for current and future approaches of regenerative medicine for the striated muscles.

Translational aspects of cardiac cell therapy

Cell therapy has been intensely studied for over a decade as a potential treatment for ischaemic heart disease. While initial trials using skeletal myoblasts, bone marrow cells and peripheral blood stem cells showed promise in improving cardiac function, benefits were found to be short-lived likely related to limited survival and engraftment of the delivered cells. The discovery of putative cardiac ‘progenitor’ cells as well as the creation of induced pluripotent stem cells has led to the delivery of cells potentially capable of electromechanical integration into existing tissue. An alternative strategy involving either direct reprogramming of endogenous cardiac fibroblasts or stimulation of resident cardiomyocytes to regenerate new myocytes can potentially overcome the limitations of exogenous cell delivery. Complimentary approaches utilizing combination cell therapy and bioengineering techniques may be necessary to provide the proper milieu for clinically significant regeneration. Clinical trials employing bone marrow cells, mesenchymal stem cells and cardiac progenitor cells have demonstrated safety of catheter based cell delivery, with suggestion of limited improvement in ventricular function and reduction in infarct size. Ongoing trials are investigating potential benefits to outcome such as morbidity and mortality. These and future trials will clarify the optimal cell types and delivery conditions for therapeutic effect.

Biocompatible and bioreducible micelles fabricated from novel α-amino acid-based poly(disulfide urethane)s: design, synthesis and triggered doxorubicin release

Novel α-amino acid-based poly(disulfide urethane)s have been developed for the construction of smart triblock copolymer micelles that show good biocompatibility, fast reductive degradation, and triggered intracellular drug release behavior.