The effect of immobilized RGD peptide in alginate scaffolds on cardiac tissue engineering.

Cardiac tissue engineering aims to regenerate damaged myocardial tissues by applying heart patches created in vitro. The present study was undertaken to explore the possible role of matrix-attached RGD peptide in the engineering of cardiac tissue within macroporous scaffolds. Neonatal rat cardiac cells were seeded into RGD-immobilized or unmodified alginate scaffolds. The immobilized RGD peptide promoted cell adherence to the matrix, prevented cell apoptosis and accelerated cardiac tissue regeneration. Within 6 days, the cardiomyocytes reorganized their myofibrils and reconstructed myofibers composed of multiple cardiomyocytes in a typical myofiber bundle. The nonmyocyte cell population, mainly cardiofibroblasts, benefited greatly from adhering to the RGD-alginate matrix and consequently supported the cardiomyocytes. They often surrounded bundles of cardiac myofibers in a manner similar to that of native cardiac tissue. The benefits of culturing the cardiac cells in RGD-immobilized alginate scaffolds were further substantiated by Western blotting, revealing that the relative expression levels of α-actinin, N-cadherin and connexin-43 were better maintained in cells cultured within these scaffolds. Collectively, the immobilization of RGD peptide into macroporous alginate scaffolds proved to be a key parameter in cardiac tissue engineering, contributing to the formation of functional cardiac muscle tissue and to a better preservation of the regenerated tissue in culture.

The effect of immobilized RGD peptide in macroporous alginate scaffolds on TGFbeta1-induced chondrogenesis of human mesenchymal stem cells.

Human bone marrow-derived mesenchymal stem cells (hMSCs) are promising cell candidates for cartilage regeneration. Building the appropriate microenvironment for cell differentiation in response to exogenous stimuli is a critical step towards the clinical utilization of hMSCs. In this study, the effects of RGD peptide immobilization onto macro-porous alginate scaffolds on TGF-beta1-induced hMSC chondrogenesis were evaluated. The results revealed different cell morphology, viability and proliferation extent in the RGD-immobilized vs. un-modified scaffolds. The TGF-beta1-induced activation of both Smad-dependent (SMAD2) and Smad-independent (ERK1/2) signaling pathways was stronger and persisted for over 3 weeks in the RGD-immobilized scaffolds, indicating greater accessibility of the cells to the inducer. By contrast, in the un-modified alginate scaffolds, the cells aggregated into compacted clusters resulting in lesser effects of TGF-beta1. The efficient and prolonged exposure to the chondrogenic inducer in the RGD-modified scaffolds ensured the appropriate progression of MSC differentiation from the initial phase of cell condensation until the appearance of committed chondrocytes, at 3 weeks of cultivation. Taken together, our results highlight the fundamental importance of the microenvironment design of the scaffold as well as the presentation of the inductive cue for inducing efficient stem-cell controlled differentiation.

Intracoronary injection of in situ forming alginate hydrogel reverses left ventricular remodeling after myocardial infarction in Swine.

OBJECTIVES: This study sought to determine whether alginate biomaterial can be delivered effectively into the infarcted myocardium by intracoronary injection to prevent left ventricular (LV) remodeling early after myocardial infarction (MI). BACKGROUND: Although injectable biomaterials can improve infarct healing and repair, the feasibility and effectiveness of intracoronary injection have not been studied. METHODS: We prepared a calcium cross-linked alginate solution that undergoes liquid to gel phase transition after deposition in infarcted myocardium. Anterior MI was induced in swine by transient balloon occlusion of left anterior descending coronary artery. At 4 days after MI, either alginate solution (2 or 4 ml) or saline was injected selectively into the infarct-related coronary artery. An additional group (n = 19) was treated with incremental volumes of biomaterial (1, 2, and 4 ml) or 2 ml saline and underwent serial echocardiography studies. RESULTS: Examination of hearts harvested after injection showed that the alginate crossed the infarcted leaky vessels and was deposited as hydrogel in the infarcted tissue. At 60 days, control swine experienced an increase in left ventricular (LV) diastolic area by 44%, LV systolic area by 45%, and LV mass by 35%. In contrast, intracoronary injection of alginate (2 and 4 ml) prevented and even reversed LV enlargement (p < 0.01). Post-mortem analysis showed that the biomaterial (2 ml) increased scar thickness by 53% compared with control (2.9 +/- 0.1 mm vs. 1.9 +/- 0.3 mm; p < 0.01) and was replaced by myofibroblasts and collagen. CONCLUSIONS: Intracoronary injection of alginate biomaterial is feasible, safe, and effective. Our findings suggest a new percutaneous intervention to improve infarct repair and prevent adverse remodeling after reperfused MI.

The effects of peptide-based modification of alginate on left ventricular remodeling and function after myocardial infarction.

Adverse cardiac remodeling and dysfunction after myocardial infarction (MI) is associated with (BioLineRx, BL-1040 myocardial implant) excessive damage to the extracellular matrix. Biomaterials, such as the in situ-forming alginate hydrogel, provide temporary support and attenuate these processes. Here, we tested the effects of decorating alginate biomaterial with cell adhesion peptides, containing the sequences RGD and YIGSR, or a non-specific peptide (RGE), in terms of therapeutic outcome soon after MI. The biomaterial (i.e., both unmodified and peptide-modified alginate) solutions retained the ability to flow after cross-linking with calcium ions, and could be injected into 7-day infarcts, where they underwent phase transition into hydrogels. Serial echocardiography studies performed before and 60 days after treatment showed that alginate modification with the peptides reduced the therapeutical effects of the hydrogel, as revealed by the extent of scar thickness, left ventricle dilatation and function. Histology and immunohistochemistry revealed no significant differences in blood vessel density, scar thickness, myofibroblast or macrophage infiltration or cell proliferation between the experimental groups BioLineRx BL-1040 myocardial implant. Our studies thus reveal that the chemical and physical traits of the biomaterial can affect its therapeutical efficacy in attenuating left ventricle remodeling and function, post-MI.

Signal transducer and activator of transcription 3-A key molecular switch for human mesenchymal stem cell proliferation.

Human bone marrow mesenchymal stem cells are multipotent cells with enormous potential for cellular therapies. Identifying those mediators that induce human bone marrow mesenchymal stem cell proliferation and elucidating the signaling networks involved will encourage clinical efforts exploiting such cells. Here, we demonstrate that platelet-derived growth factor-BB and basic fibroblast growth factor induce human bone marrow mesenchymal stem cell proliferation. Platelet-derived growth factor-BB induced human bone marrow mesenchymal stem cell proliferation via complete activation of the Janus-activated kinase-signal transducers and activators of transcription cascade, inducing signal transducer and activator of transcription 3 tyrosine and serine phosphorylation as well as Janus-activated kinase 2 tyrosine phosphorylation. Janus-activated kinase 2 was required for signal transducer and activator of transcription 3 tyrosine phosphorylation, whereas the extracellular signal-regulated kinase 1/2 mediated signal transducer and activator of transcription 3 serine phosphorylation in response to platelet-derived growth factor-BB. Furthermore, platelet-derived growth factor-BB was shown to promote nuclear translocation of signal transducer and activator of transcription 3. By contrast, basic fibroblast growth factor-stimulated human bone marrow mesenchymal stem cell proliferation was mediated via the extracellular signal-regulated kinase 1/2 pathway without involvement of the Janus-activated kinase-signal transducers and activators of transcription cascade. Importantly, platelet-derived growth factor-BB and basic fibroblast growth factor induced human bone marrow mesenchymal stem cell proliferation without affecting their osteogenic differentiation potential. Together, our study highlights the role of several growth factors in human bone marrow mesenchymal stem cell proliferation and the signaling pathways involved in the process. This information is crucial for achieving a better control over the human bone marrow mesenchymal stem cell expansion process.