ABSTRACT
It is well established that, in multicellular systems, conventional cryopreservation results in damaging ice formation, both in the cells and in the surrounding extracellular matrix. As an alternative to conventional cryopreservation, we performed a feasibility study using vitrification (ice-free cryopreservation) to cryopreserve tissue-engineered blood vessels. Fresh, frozen, and vitrified tissue-engineered blood vessels were compared using histological methods, cellular viability, and mechanical properties. Cryosubstitution methods were used to determine the location of ice in conventionally cryopreserved engineered vessels. Ice formation was negligible (0.0 +/- 0.0% of vessel area) in the vitrified specimens, and extensive (68.3 +/- 4.5% of vessel area) in the extracellular matrix of frozen specimens. The metabolic assay and TUNEL staining results indicated that vitrified tissue had similar viability to fresh controls. The contractility results for vitrified samples were >82.7% of fresh controls and, in marked contrast, the results for frozen samples were only 10.7% of fresh controls (p < 0.001). Passive mechanical testing revealed enhanced tissue strength after both freezing and vitrification. Vitrification is a feasible storage method for tissue-engineered blood vessel constructs, and their successful storage brings these constructs one step closer to clinical utility.
Subject(s)
Biocompatible Materials/chemistry , Cryopreservation/methods , Muscle, Smooth, Vascular/cytology , Animals , Apoptosis , Biomechanical Phenomena , Carotid Arteries/cytology , Carotid Arteries/physiology , Carotid Arteries/ultrastructure , Cell Adhesion , Cell Culture Techniques , Cell Survival , Cells, Cultured , Culture Media/chemistry , Endothelin-1/pharmacology , Endothelium, Vascular/cytology , Endothelium, Vascular/physiology , Endothelium, Vascular/ultrastructure , Feasibility Studies , Freezing , Glucose/metabolism , Muscle Contraction/drug effects , Muscle, Smooth, Vascular/physiology , Muscle, Smooth, Vascular/ultrastructure , Organ Preservation Solutions , Papaverine/pharmacology , Permeability , Polyglycolic Acid/chemistry , Swine , Time Factors , Tissue Engineering/methodsABSTRACT
OBJECTIVES: Fifty percent of human aortocoronary saphenous vein grafts are occluded after 10 years. Intimal hyperplasia is an initial step in graft occlusion and consists of vascular smooth muscle cell proliferation. Phosphatidylinositol 3-kinase and its downstream regulator, the inositol 3-phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10), are important regulators of vascular smooth muscle cell proliferation, migration, and cell death. This study tests whether overexpression of PTEN in aortocoronary saphenous vein grafts can reduce intimal hyperplasia. METHODS: Adult dogs underwent aortocoronary bypass grafting to the left anterior descending artery by using the autologous saphenous vein. Saphenous vein grafts were treated with phosphate-buffered saline (n = 9), empty adenovirus (n = 8), or adenovirus encoding for PTEN (n = 8). Arteriography at 30 and 90 days assessed saphenous vein graft patency. A subset received saphenous vein grafts treated with a marker transgene (beta-galactosidase, n = 3), empty adenovirus (n = 4), or adenovirus encoding for PTEN (n = 4) and were killed on postoperative day 3 to confirm expression. Vascular smooth muscle cells were isolated from canine saphenous vein infected with adenovirus encoding for PTEN, and immunoblotting and proliferation assays were performed. RESULTS: Saphenous vein graft transgene expression was confirmed by means of immunohistochemistry, immunoblotting, and polymerase chain reaction. Arteriograms revealed all saphenous vein grafts to be patent. Saphenous vein grafts treated with adenovirus encoding for PTEN demonstrated reduced intimal area compared with those treated with empty adenovirus and phosphate-buffered saline (1.39 +/- 0.11 vs 2.35 +/- 0.3 and 2.57 +/- 0.4 mm 2 , P < .05), and the intima/media ratio was lower in saphenous vein grafts treated with adenovirus encoding for PTEN (0.50 +/- 0.05 vs 1.43 +/- 0.18 and 1.11 +/- 0.14, P < .005). PTEN overexpression in vascular smooth muscle cells inhibited platelet-derived growth factor-induced phosphorylation of Akt, a downstream effector of phosphatidylinositol 3-kinase. PTEN-treated vascular smooth muscle cells demonstrated decreased basal, platelet-derived growth factor-stimulated, and serum-stimulated proliferation. CONCLUSION: This study demonstrates that PTEN overexpression in aortocoronary saphenous vein grafts reduces intimal hyperplasia. The mechanism of this antiproliferative effect in vascular smooth muscle cells is likely due to inhibition of phosphatidylinositol 3-kinase signaling through Akt, with resultant decreases in vascular smooth muscle cell growth and survival. Therefore modulation of the phosphatidylinositol 3-kinase pathway through PTEN overexpression might represent a novel therapy to prevent saphenous vein graft intimal hyperplasia after coronary artery bypass grafting.
Subject(s)
Coronary Artery Bypass , Graft Occlusion, Vascular/etiology , Phosphatidylinositol 3-Kinases/physiology , Saphenous Vein/pathology , Saphenous Vein/transplantation , Tunica Intima/pathology , Animals , Cell Division , Dogs , Hyperplasia , Muscle, Smooth, Vascular/pathology , Signal TransductionABSTRACT
Polyglycolic acid (PGA) is commonly used as a scaffold for tissue engineering. Recent studies utilized PGA as a scaffold for vascular tissue engineering using bovine and porcine smooth muscle cells (SMCs). In engineered vessels, the SMCs displayed high rates of mitosis and dedifferentiation in areas where PGA fragments were present. We hypothesized that PGA breakdown products, sequestered within a SMC vessel at the conclusion of culture, led to increased proliferation and dedifferentiation of vascular SMCs. To test this hypothesis, the current study assessed possible means by which PGA breakdown products could lead to changes in SMC phenotype. SMCs grown in high concentrations of PGA breakdown products showed, by Western blotting, decreased expression of calponin, a marker for SMC differentiation. The same was true for SMCs grown in glycolic acid (GA), which also showed decreased expression of proliferating cell nuclear antigen (PCNA), a marker for SMC proliferation. In contrast, cells grown in varying amounts of NaCl or HCl showed little change in differentiation. We conclude that, independent of acidity or osmolality, plausible products of PGA degradation appear to induce dedifferentiation of porcine SMCs in vitro. Because of dedifferentiation and decreased mitosis, commercially available PGA may not represent an optimal scaffold for vascular tissue engineering.
Subject(s)
Cell Differentiation/drug effects , Myocytes, Smooth Muscle/drug effects , Polyglycolic Acid/pharmacology , Animals , Aorta, Abdominal/drug effects , Blotting, Western , Cell Count , Cell Division/drug effects , Swine/metabolismABSTRACT
Techniques have been developed to culture bovine or porcine vascular cells on polyglycolic acid (PGA) scaffolds to form engineered vessels. Previously, it was shown that smooth muscle cells (SMCs) that were in close proximity to PGA remnants after 8 weeks of culture had lower expression of SMC markers of differentiation and were more mitotic compared with SMCs that were distant from polymer residuals. Modifications of PGA were explored as a means to minimize residual polymer fragments after culture. To hasten degradation, polymer was treated with heat, NaOH, or gamma-irradiation. Differential scanning calorimetry, mass and tensile strength degradation, and inherent viscosity were used to assess polymer characteristics. When polymer was maintained in aqueous conditions, tensile strength of treated PGA degraded to zero within 3 weeks for each treatment. Engineered vessel constructs cultured on NaOH and gamma-treated polymer displayed smooth muscle alpha-actin throughout the vessel wall. Scaffold treatment impacted graft morphology, cellular differentiation, and mechanical integrity.
