Biomechanical Comparison of Glutaraldehyde-Crosslinked Gelatin Fibrinogen Electrospun Scaffolds to Porcine Coronary Arteries.

Cardiovascular disease (CVD) is the leading cause of death for Americans. As coronary artery bypass graft surgery (CABG) remains a mainstay of therapy for CVD and native vein grafts are limited by issues of supply and lifespan, an effective readily available tissue-engineered vascular graft (TEVG) for use in CABG would provide drastic improvements in patient care. Biomechanical mismatch between vascular grafts and native vasculature has been shown to be the major cause of graft failure, and therefore, there is need for compliance-matched biocompatible TEVGs for clinical implantation. The current study investigates the biaxial mechanical characterization of acellular electrospun glutaraldehyde (GLUT) vapor-crosslinked gelatin/fibrinogen cylindrical constructs, using a custom-made microbiaxial optomechanical device (MOD). Constructs crosslinked for 2, 8, and 24 hrs are compared to mechanically characterized porcine left anterior descending coronary (LADC) artery. The mechanical response data were used for constitutive modeling using a modified Fung strain energy equation. The results showed that constructs crosslinked for 2 and 8 hrs exhibited circumferential and axial tangential moduli (ATM) similar to that of the LADC. Furthermore, the 8-hrs experimental group was the only one to compliance-match the LADC, with compliance values of 0.0006±0.00018 mm Hg-1 and 0.00071±0.00027 mm Hg-1, respectively. The results of this study show the feasibility of meeting mechanical specifications expected of native arteries through manipulating GLUT vapor crosslinking time. The comprehensive mechanical characterization of cylindrical biopolymer constructs in this study is an important first step to successfully develop a biopolymer compliance-matched TEVG.

Flow cytometric analysis of deoxyribonucleic acid ploidy and proliferation in choroid plexus tumors.

The deoxyribonucleic acid (DNA) content of 10 choroid plexus tumors, including 4 malignant tumors and 3 normal choroid plexus controls, was analyzed by flow cytometry to determine whether a ploidy or proliferation rate is a better predictor of tumor behavior than histological features. Nine of 10 neoplasms had both diploid and aneuploid modal populations. One neoplasm and all three control cases had only a diploid peak. Among the tumors, the DNA indices of the aneuploid peaks ranged from 1.1 to 2.2. The percentage of aneuploid cells ranged from 7 to 99, and no distinction was made between benign and malignant. Proliferation rates were estimated from the combined S-phase fractions (SPF). The mean SPF of the control group was 0.7% +/- 0.15% SD. The mean SPF of the benign tumors (1.1 +/- 0.82% SD) was significantly different from the malignant group (7.0 +/- 1.25% SD; range, 5.3 to 8.6%) P = 0.0095. Low SPF fractions always correlated with favorable outcome. Higher proliferation rates were generally associated with an aggressive course. Evaluation of proliferation rates may help predict the behavior of choroid plexus tumors, particularly when histological features are equivocal. Measurement of DNA ploidy does not appear to have a role in the evaluation of choroid plexus tumors.

In vitro colony-forming cells in the marrow of leukemic and preleukemic mice.

In vitro colony-forming cells (CFUc) were evaluated in preleukemic and leukemic AK mice. Increased concentrations of CFUc were found in normal appearing marrow of superinfected animals 2-3 wk prior to the onset of lymphoma. CFUc were present in marrows of mice with virus-accelerated, spontaneous, and transplanted lymphoma. CFUc concentration was often increased in mice with advanced disease and marrow replacement by lymphoblasts. When calculated on the basis of CFUc per normal marrow cells, this increase was marked. The colonies developed only in the presence of added colony-stimulating activity (CSA) and had the morphologic features of colonies from normal marrow. Leukemic cells did not form colonies. Lymphoma cells, from virus accelerated, spontaneous and transplanted lymphoma, did not produce CSA in feeder layers or conditioned medium. Leukemic and nonleukemic AK bone were found to produce similar small amounts of CSA. These studies showed that the preleukemic state as well as marrow replacement by lymphoblasts resulted in increased marrow CFUc's. No evidence for increased local production of CSA by lymphoblasts or the marrow microenvironment was found to account for this.

Proliferation and motility responses of primary and recurrent gliomas related to changes in epidermal growth factor receptor expression.

Astrocytic neoplasms show a high incidence of elevated or mutated epidermal growth factor receptor (EGFR) expression. Although proliferative effects from EGFR activation are well described, the role that changes in this receptor play in glioma growth and migration remain poorly addressed. This report characterizes changes in the levels of EGFR expression in three glial tumors at initial presentation (resection) and at the time of recurrence. By quantitative flow cytometry the mean level of EGFR expression increased, decreased, or remained the same in different recurrent astrocytomas relative to their primary tumor cells. Immunocytochemistry for EGFR on monolayer cells corroborated the level of expression in the recurrent tumors relative to their matched primary specimen. Immunoprecipitation indicated that 170 kd EGFR was expressed in each of the tumors, and showed normal down regulation following treatment with EGF. Proliferation response to EGF was seen in only 1/6 instances, but was concentration-dependent when observed. Stimulated migration of the cells was frequently seen and was also concentration-dependent on EGF; the magnitude of response was related to the relative level of 170 kd EGFR expression in the cells. EGFR immunostaining of tissue sections from the tumors confirmed the levels of EGFR expressed in primary and recurrent astrocytomas as was seen in the cultured cells. These results indicate that the relative levels of EGFR in early passage cell cultures from glioma specimens concurs with the measured tissue levels of expression. Human glioma cells are more responsive to migration induction than proliferation induction by EGF.

Dichotomy of astrocytoma migration and proliferation.

Astrocytomas often show high rates of local invasion that lead to local recurrence of the disease. Histologically, the most highly invasive astrocytoma cells are detected in isolation rather than as nests of tumor. Our study attempted to determine whether the migratory response to extracellular substrates influences the proliferative behavior of these highly invasive cells. The preferential and specific migratory response of human astrocytoma cells to extracellular matrix proteins was assessed by a microliter scale migration assay. Growth curve studies on protein ligands permissive (merosin) for cell migration indicated that the lag phase was protracted compared with cells seeded on non-permissive proteins (vitronectin). Once a certain cell density was reached, logarithmic proliferation was indistinguishable on the different proteins. The proliferation index of populations of cells migrating on merosin and vitronectin was measured by both BrdU incorporation and MIB-1 immunocytochemistry labeling. Cells seeded on vitronectin showed higher proliferation throughout the population than cells seeded on merosin. On merosin, the more migratory cells at the periphery were less proliferative than non-migratory cells in the central region of that population. The integrin-associated signal transduction protein, p125FAK, was heavily localized in the membrane of non-migrating cells and largely absent in migrating astrocytoma cells. We conclude that temporally, proliferation and migration are mutually exclusive behaviors. Cell density or non-permissive substrates that inhibit cell motility favor a more proliferative phenotype. Conversely, active migration suppresses cell proliferation.