Engineering an antiplatelet adhesion layer on an electrospun scaffold using porcine endothelial progenitor cells

Efficient and safe correction of hemophilia A by lentiviral vector-transduced BOECs in an implantable device

Hemophilia A (HA) is a rare bleeding disorder caused by deficiency/dysfunction of the FVIII protein. As current therapies based on frequent FVIII infusions are not a definitive cure, long-term expression of FVIII in endothelial cells through lentiviral vector (LV)-mediated gene transfer holds the promise of a one-time treatment. Thus, here we sought to determine whether LV-corrected blood outgrowth endothelial cells (BOECs) implanted through a prevascularized medical device (Cell Pouch) would rescue the bleeding phenotype of HA mice. To this end, BOECs from HA patients and healthy donors were isolated, expanded, and transduced with an LV carrying FVIII driven by an endothelial-specific promoter employing GMP-like procedures. FVIII-corrected HA BOECs were either directly transplanted into the peritoneal cavity or injected into a Cell Pouch implanted subcutaneously in NSG-HA mice. In both cases, FVIII secretion was sufficient to improve the mouse bleeding phenotype. Indeed, FVIII-corrected HA BOECs reached a relatively short-term clinically relevant engraftment being detected up to 16 weeks after transplantation, and their genomic integration profile did not show enrichment for oncogenes, confirming the process safety. Overall, this is the first preclinical study showing the safety and feasibility of transplantation of GMP-like produced LV-corrected BOECs within an implantable device for the long-term treatment of HA.

Engineering blood outgrowth endothelial cells to optimize endothelial nitric oxide synthase and extracellular matrix production for coating of blood contacting surfaces

Coverage of blood contacting surfaces by a functional endothelial layer is likely required to induce and maintain homeostasis. Blood outgrowth endothelial cells (BOECs), cultured from human peripheral blood monocytes, are readily available and functional autologous endothelial source that may represent a reasonable alternative to vascular derived cells. Endothelial nitric oxide synthase (eNOS) produces NO, an important factor that regulates homeostasis at the blood-contacting surface. We found that BOECs express markedly lower levels of eNOS protein (34% ± 13%, Western blot) and mRNA (29% ± 17%, qRT-PCR), as well as exhibiting reduced activity (49% ± 18%, Nitrite analysis) when compared to human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells. HUVECs grown on fibronectin, type I collagen, or laminin -coated surfaces exhibited significant reduction of eNOS mRNA and protein expression. However, no decrease in eNOS levels was observed in BOECs. Interestingly BOECs expressed significantly higher Collagen (Col) I compared to HUVECs, and blocking Col I synthesis significantly enhanced eNOS expression in BOECs. Inhibition of β1 integrin, focal adhesion kinase (FAK), or actin polymerization increased eNOS in both BOECs and HUVECs suggesting involvement of a signaling pathway culminating in stabilization of the cytoskeleton. Finally, we demonstrated that a Rho-associated protein kinases (ROCK) inhibitor, as a disruptor of actin stabilization, enhanced both eNOS expression and bioactivity. Taken together, our findings demonstrate that cell-ECM interactions are fundamental to the regulation of eNOS in BOECs and suggest that disruption of key intracellular pathways (such as ROCK) may be necessary to enhance functional activity of an endothelialized surface. STATEMENT OF SIGNIFICANCE: Development of biocompatible blood-contacting biomaterial surfaces has not been possible to date, leading many investigators to believe that a complete autologous endothelial layer will be necessary. Blood outgrowth endothelial cells (BOECs), cultured from human peripheral blood monocytes, are readily available and functional autologous endothelial source. Endothelial nitric oxide synthase (eNOS) produces NO, an important factor that regulates homeostasis at the blood-contacting surface. In this study, we show that eNOS displays limited expression in cultured BOECs. We further demonstrate that a strong negative regulation of eNOS is mediated by collagen substrates and that treatment with ROCK inhibitor could enhance both eNOS expression and activity in BOECs and help to rapidly establish a functional autologous endothelial layer on cardiovascular biomaterials.

Electrospun tecophilic/gelatin nanofibers with potential for small diameter blood vessel tissue engineering

Tissue engineering techniques particularly using electrospun scaffolds have been intensively used in recent years for the development of small diameter vascular grafts. However, the development of a completely successful scaffold that fulfills multiple requirements to guarantee complete vascular regeneration remains challenging. In this study, a hydrophilic and compliant polyurethane namely Tecophilic (TP) blended with gelatin (gel) at a weight ratio of 70:30 (TP(70)/gel(30)) was electrospun to fabricate a tubular composite scaffold with biomechanical properties closely simulating those of native blood vessels. Hydrophilic properties of the composite scaffold induced non-thrombogenicity while the incorporation of gelatin molecules within the scaffold greatly improved the capacity of the scaffold to serve as an adhesive substrate for vascular smooth muscle cells (SMCs), in comparison to pure TP. Preservation of the contractile phenotype of SMCs seeded on electrospun TP(70)/gel(30) was yet another promising feature of this scaffold. The nanostructured TP(70)/gel(30) demonstrated potential feasibility toward functioning as a vascular graft.

Cells and stimuli in small-caliber blood vessel tissue engineering

The absence of successful solutions in treatments of small-caliber vessel diseases led to the Vascular Tissue Engineering approach to develop functional nonimmunogenic tissue engineered blood vessels. In this context, the choice of cells to be seeded and the microenvironment conditioning are pivotal. Biochemical and biomechanical stimuli seem to activate physiological regulatory pathways that induce the production of molecules and proteins stimulating stem cell differentiation toward vascular lineage and reproducing natural cross-talks among vascular cells to improve the maturation of tissue engineered blood vessels. Thus, this review focuses on (1) available cell sources, and (2) biochemical and biomechanical stimuli, with the final aim to obtain the long-term stability of the endothelium and mechanical properties suitable for withstanding physiological load.

Extract of fetal membrane would inhibit thrombosis and hemolysis

The innermost layer of fetal membranes is amnion which has anti-adhesive, anti-inflammation and viscoelastic properties, as well as low immunogenicity. Amniotic membrane has been employed in variety of clinical fields as a natural biomaterial. Amniotic epithelial cells possess stem cell characteristics and capability to differentiate into endothelial cells. The basement membrane of amnion is an extracellular matrix enriched scaffold to support adhesion of endothelial cells. The matrix of amniotic membrane contains two kinds of glycosaminoglycans including perlecan (a heparan sulfate proteoglycan) and hyaluronic acid which both inhibit blood coagulation. Moreover, the other ingredients of amniotic membrane such as pigment-epithelium derived factor (PEDF), IL-10, MMP-9 inhibit platelet aggregation. Based on some biochemical and biomechanical evidences, we hypothesized in this paper that amniotic membrane could prevent thrombosis and hemolysis; therefore, has the capability to be applied in blood contacting devices and implants.

Generation and grafting of tissue-engineered vessels in a mouse model

The construction of vascular conduits is a fundamental strategy for surgical repair of damaged and injured vessels resulting from cardiovascular diseases. The current protocol presents an efficient and reproducible strategy in which functional tissue engineered vessel grafts can be generated using partially induced pluripotent stem cell (PiPSC) from human fibroblasts. We designed a decellularized vessel scaffold bioreactor, which closely mimics the matrix protein structure and blood flow that exists within a native vessel, for seeding of PiPSC-endothelial cells or smooth muscle cells prior to grafting into mice. This approach was demonstrated to be advantageous because immune-deficient mice engrafted with the PiPSC-derived grafts presented with markedly increased survival rate 3 weeks after surgery. This protocol represents a valuable tool for regenerative medicine, tissue engineering and potentially patient-specific cell-therapy in the near future.

Tri-layered elastomeric scaffolds for engineering heart valve leaflets

Tissue engineered heart valves (TEHVs) that can grow and remodel have the potential to serve as permanent replacements of the current non-viable prosthetic valves particularly for pediatric patients. A major challenge in designing functional TEHVs is to mimic both structural and anisotropic mechanical characteristics of the native valve leaflets. To establish a more biomimetic model of TEHV, we fabricated tri-layered scaffolds by combining electrospinning and microfabrication techniques. These constructs were fabricated by assembling microfabricated poly(glycerol sebacate) (PGS) and fibrous PGS/poly(caprolactone) (PCL) electrospun sheets to develop elastic scaffolds with tunable anisotropic mechanical properties similar to the mechanical characteristics of the native heart valves. The engineered scaffolds supported the growth of valvular interstitial cells (VICs) and mesenchymal stem cells (MSCs) within the 3D structure and promoted the deposition of heart valve extracellular matrix (ECM). MSCs were also organized and aligned along the anisotropic axes of the engineered tri-layered scaffolds. In addition, the fabricated constructs opened and closed properly in an ex vivo model of porcine heart valve leaflet tissue replacement. The engineered tri-layered scaffolds have the potential for successful translation towards TEHV replacements.

The therapeutic effect of monocyte chemoattractant protein-1 delivered by an electrospun scaffold for hyperglycemia and nephrotic disorders

Here, we investigated in diabetic mice the therapeutic effect of monocyte chemoattractant protein-1 (MCP-1), locally delivered by an electrospun scaffold, on transplanted islets. This therapeutic scheme is expected to exert a synergistic effect to ameliorate hyperglycemia and its associated nephrotic disorders. The cumulative amount of MCP-1 released from the scaffold in vitro within a 3-week window was 267.77±32.18 ng, without a compromise in bioactivity. After 8 weeks following the transplantation, the islet population stimulated by MCP-1 was 35.14%±7.23% larger than the non-stimulated islet population. Moreover, MCP-1 increased concentrations of blood insulin and C-peptide 2 by 49.83%±5.29% and 43.49%±9.21%, respectively. Consequently, the blood glucose concentration in the MCP-1 group was significantly lower than that in the control group at week 2 post-surgery. MCP-1 also enhanced the tolerance of sudden oral glucose challenge. The rapid decrease of blood creatinine, urine creatinine, and blood urea nitrogen suggested that the recovery of renal functions compromised by hyperglycemia could also be attributed to MCP-1. Our study shed new light on a synergistic strategy to alleviate hyperglycemia and nephrotic disorders in diabetic patients.

A synergistic therapeutic scheme for hyperglycemia and nephrotic disorders in diabetes

We previously demonstrated that the utilization of an electrospun scaffold could boost functional outputs of transplanted islets. In this study, we aim to develop a drug-eluting scaffold with a payload of pioglitazone to simultaneously rein in hyperglycemia and recoup lost renal functions in diabetic mice that underwent islet transplantation. The in vivo proliferation of islets was measured by a non-invasive bio-imaging technology whereas the blood insulin, blood glucose and renal proteins were assayed. The local stimulation of transplanted islets by pioglitazone saw an accelerated in vivo proliferation without apoptosis caused by the drug-eluting scaffold. In addition, pioglitazone contributed to an increased secretion of insulin and C-peptide 2, giving rise to an accelerated rein-in of hyperglycemia and enhanced tolerance of sudden oral glucose challenge. Moreover, the accelerated decrease of blood creatinine, urine creatinine and blood urea nitrogen suggested that pioglitazone contributed to the recovery of renal functions compromised by diabetes. Our bioengineering strategy effectively ameliorated hyperglycemia and associated nephrotic disorders, and shed a new light on an engineering approach to combat diabetes.

Endothelial outgrowth cells: function and performance in vascular grafts

The clinical need for vascular grafts continues to grow. Tissue engineering strategies have been employed to develop vascular grafts for patients lacking sufficient autologous vessels for grafting. Restoring a functional endothelium on the graft lumen has been shown to greatly improve the long-term patency of small-diameter grafts. However, obtaining an autologous source of endothelial cells for in vitro endothelialization is invasive and often not a viable option. Endothelial outgrowth cells (EOCs), derived from circulating progenitor cells in peripheral blood, provide an alternative cell source for engineering an autologous endothelium. This review aims at highlighting the role of EOCs in the regulation of processes that are central to vascular graft performance. To characterize EOC performance in vascular grafts, this review identifies the characteristics of EOCs, defines functional performance criteria for EOCs in vascular grafts, and summarizes the existing work in developing vascular grafts with EOCs.

Drug-eluting scaffold to deliver chemotherapeutic medication for management of pancreatic cancer after surgery

Traditional post-surgical chemotherapy for pancreatic cancer is notorious for its devastating side effects due to the high dosage required. On the other hand, legitimate concerns have been raised about nanoparticle-mediated drug delivery because of its potential cytotoxicity. Therefore, we explored the local delivery of a reduced dosage of FOLFIRINOX, a four-drug regimen comprising oxaliplatin, leucovorin, irinotecan, and fluorouracil, for pancreatic cancer using a biocompatible drug-eluting scaffold as a novel chemotherapy strategy after palliative surgery. In vitro assays showed that FOLFIRINOX in the scaffold caused massive apoptosis and thereby a decrease in the viability of pancreatic cancer cells, confirming the chemotherapeutic capability of the drug-eluting scaffold. In vivo studies in an orthotopic murine xenograft model demonstrated that the FOLFIRINOX in the scaffold had antitumorigenic and antimetastatic effects comparable with those achieved by intraperitoneal injection, despite the dose released by the scaffold being roughly two thirds lower. A mechanistic study attributed our results to the excellent ability of the FOLFIRINOX in the scaffold to destroy the CD133⁺CXCR4⁺ cell population responsible for pancreatic tumorigenesis and metastasis. This clinically oriented study gives rise to a promising alternative strategy for postsurgical management of pancreatic cancer, featuring a local chemotherapeutic effect with considerable attenuation of side effects.

A tissue-engineered gastric cancer model for mechanistic study of anti-tumor drugs

The use of the traditional xenograft subcutaneous tumor model has been contested because of its limitations, such as a slow tumorigenesis, inconsistent chemotherapeutic results, etc. In light of these challenges, we aim to revamp the traditional model by employing an electrospun scaffold composed of polydioxanone, gelatin and elastin to boost the tumorigenesis. The scaffold featured a highly porous microstructure and successfully supported the growth of tumor cells in vitro without provoking apoptosis. In vivo studies showed that in the scaffold model the tumor volume increased by 43.27% and the weight by 75.58%, respectively, within a 12-week period. In addition, the scaffold model saw an increase of CD24(+) and CD44(+) cells in the tumor mass by 42% and 313%, respectively. The scaffolding materials did not lead to phenotypic changes during the tumorigenesis. Thereafter, in the scaffold model, we found that the chemotherapeutic regimen of docetaxel, cisplatin and fluorouracil unleashed a stronger capability than the regimen comprising cisplatin and fluorouracil to deplete the CD44(+) subpopulation. This discovery sheds mechanistic lights on the role of docetaxel for its future chemotherapeutic applications. This revamped model affords cancer scientists a convenient and reliable platform to mechanistically investigate the chemotherapeutic drugs on gastric cancer stem cells.

A tissue-engineered subcutaneous pancreatic cancer model for antitumor drug evaluation

The traditional xenograft subcutaneous pancreatic cancer model is notorious for its low incidence of tumor formation, inconsistent results for the chemotherapeutic effects of drug molecules of interest, and a poor predictive capability for the clinical efficacy of novel drugs. These drawbacks are attributed to a variety of factors, including inoculation of heterogeneous tumor cells from patients with different pathological histories, and use of poorly defined Matrigel^®. In this study, we aimed to tissue-engineer a pancreatic cancer model that could readily cultivate a pancreatic tumor derived from highly homogenous CD24⁺CD44⁺ pancreatic cancer stem cells delivered by a well defined electrospun scaffold of poly(glycolide-co-trimethylene carbonate) and gelatin. The scaffold supported in vitro tumorigenesis from CD24⁺CD44⁺ cancer stem cells for up to 7 days without inducing apoptosis. Moreover, CD24⁺CD44⁺ cancer stem cells delivered by the scaffold grew into a native-like mature pancreatic tumor within 8 weeks in vivo and exhibited accelerated tumorigenesis as well as a higher incidence of tumor formation than the traditional model. In the scaffold model, we discovered that oxaliplatin-gemcitabine (OXA-GEM), a chemotherapeutic regimen, induced tumor regression whereas gemcitabine alone only capped tumor growth. The mechanistic study attributed the superior antitumorigenic performance of OXA-GEM to its ability to induce apoptosis of CD24⁺CD44⁺ cancer stem cells. Compared with the traditional model, the scaffold model demonstrated a higher incidence of tumor formation and accelerated tumor growth. Use of a tiny population of highly homogenous CD24⁺CD44⁺ cancer stem cells delivered by a well defined scaffold greatly reduces the variability associated with the traditional model, which uses a heterogeneous tumor cell population and poorly defined Matrigel. The scaffold model is a robust platform for investigating the antitumorigenesis mechanism of novel chemotherapeutic drugs with a special focus on cancer stem cells.

The therapeutic role of monocyte chemoattractant protein-1 in a renal tissue engineering strategy for diabetic patients

In this study we aim to boost the functional output of the intra-kidney islet transplantation for diabetic patients using a tissue engineered polymeric scaffold. This highly porous electrospun scaffold featured randomly distributed fibers composed of polycaprolactone (PCL) and poliglecaprone (PGC). It successfully sustained murine islets in vitro for up to 4 weeks without detected cytotoxicity. The in vivo study showed that the islet population proliferated by 89% within 12 weeks when they were delivered by the scaffold but only 18% if freely injected. Correspondingly, the islet population delivered by the scaffold unleashed a greater capability to produce insulin that in turn further drove down the blood glucose within 12 weeks after the surgery. Islets delivered by the scaffold most effectively prevented diabetic deterioration of kidney as evidenced by the lack of a kidney or glomerular enlargement and physiological levels of creatinine, urea nitrogen and albumin through week 12 after the surgery. Unlike traditional wisdom in diabetic research, the mechanistic study suggested that monocytes chemoattractant protein-1 (MCP-1) was responsible for the improved preservation of renal functions. This study revealed a therapeutic role of MCP-1 in rescuing kidneys in diabetic patients, which can be integrated into a tissue engineered scaffold to simultaneously preserved renal functions and islet transplantation efficacy. Also, this study affords a simple yet effective solution to improve the clinical output of islet transplantation.