Angiostatin4.5 (AS4.5) is the product of plasmin autoproteolysis and consists of kringles 1 to 4 and f85% of kringle 5. In culture, cancer cell surface globular B-actin mediates plasmin autoproteolysis to AS4.5. We now show that plasminogen binds to prostate cancer cells and that the binding colocalizes with surface B-actin, but AS4.5 does not bind to the cell surface. Plasminogen and plasmin bind to immobilized B-actin similarly, with a K d of f140 nmol/L. The binding is inhibited by E-aminocaproic acid (EACA), indicating the requirement for a lysine-kringle domain interaction. Using a series of peptides derived from B-actin in competitive binding studies, we show that the domain necessary for plasminogen binding is within amino acids 55 to 69 (GDEAQSKRGILTLKY). Substitution of Lys 61 or Lys 68 with arginine results in the loss of the ability of the peptide to block plasminogen binding, indicating that Lys 61 and Lys 68 are essential for plasminogen binding. Other actin peptides, including peptides with lysine, did not inhibit the plasminogen-actin interaction. AS4.5 did not bind actin at concentrations up to 40 Mmol/L. Plasminogen, plasmin, and AS4.5 all contain kringles 1 to 4; however, kringle 5 is truncated in AS4.5. Isolated kringle 5 binds to actin, suggesting intact kringle 5 is necessary for plasminogen and plasmin to bind to cell surface B-actin, and the truncated kringle 5 in AS4.5 results in its release from B-actin. These data may explain the mechanism by which AS4.5 is formed locally on cancer cell surfaces and yet acts on distant sites.

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Carbon-based materials are considered to be promising as implants because of their unique mechanical and biocompatibility properties. This article investigates the use of carbon-based materials as a functional interface for tissue scaffolds and medical implants. Three basic parameters were explored: graphene orientation, crystallinity, and surface interaction. These parameters were measured using optical microscopy, x-ray diffraction, and atomic force microscopy. To explore the effect of the orientation, samples were made with and without a preferred carbon orientation. Conversely, the crystallinity was studied using graphitic and carbonaceous matrices. Finally, the surface interaction study was carried out using oxygen surface functionalized and non-functionalized carbon fibers. Fluorescent, confocal, and environmental scanning microscopy were used to visualize cell response. The cell attachment, proliferation, and elongation were prevalent on the unidirectional carbon preform. Cells tended to orient parallel to the fiber axis (parallel to the 002 graphene plane) and proliferate as a function of higher crystallinity, although the addition of oxygen or other functional groups disrupted the interaction between cells and graphene surface and inhibited the growth. In conclusion, osteoblast (bone-forming cells) attachment and overall growth is a function of crystallite size, graphene orientation, and carbon graphitization.

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The objective of this study was to investigate the use of three fibrous carbon materials (T300, P25, and P120) for bone repair and develop and validate theoretical and computational methods in which bone tissue regeneration and repair could be accurately predicted. T300 was prepared from polyacrylonitrile precursor while P25 and P120 fibers were prepared from pitch, both common fiber precursors. Results showed that osteoblast growth on carbon scaffolds was enhanced with increased crystallinity, surface roughness, and material orientation. For unidirectional scaffolds at 120 h, there was 33% difference in cell growth between T300 and P25 fibers and 64% difference between P25 and P120 fibers. Moreover, for multidirectional fibers at 120 h, there was 35% difference in cell growth between T300 and P25 fibers and 43% difference between P25 and P120 fibers. Results showed that material alignment was integral to promoting cell growth with multidirectional scaffolds having the capacity for greater growth over unidirectional scaffolds. At 120 h there was 24% increase in cell growth between unidirectional alignment and multidirectional alignment on high-crystalline carbon fibers. Ultimately, data indicated that carbon scaffolds exhibited excellent bioactivity and may be tuned to stimulate unique reactions. Additionally, numerical and computational simulations provided evidence that corroborated experimental data with simulations. Results illustrated the capability of cellular automata models for assessing osteoblast cell response to biomaterials.