Toward Innovative Hemocompatible Surfaces: Crystallographic Plane Impact on Platelet Activation.

The anticoagulation treatment of cardiovascular patients, which is mandatory after implantation of heart valves or stents, has significantly adverse effects on life quality. This treatment can be reduced or even circumvented by developing novel antithrombogenic surfaces of blood-contacting implants. Thus, we aim to discover materials exhibiting outstanding hemocompatibility compared to other available synthetic materials. We present promising surficial characteristics of single crystalline alumina in terms of platelet activation inhibition. In order to elucidate the relation between its crystallographic properties including the plane orientation and blood cell behavior, we examined endothelialization, cytocompatibility, and platelet activation at the blood-alumina interfaces in a controlled experimental setup. We observed that the cell response is highly sensitive to the plane orientation and differs significantly for (0001) and (11-20) planes of Al2O3. Our results reveal for the first time the dependence of platelet activation on crystallographic orientation, which is assumed to be a critical condition controlling the thrombogenicity. Additionally, we used an endothelial cell monolayer as an internal control since endothelial cells have an impact on vessel integrity and implant acceptance. We successfully demonstrate that Al2O3(11-20) exhibits enhanced hemocompatibility in contrast to Al2O3(0001) and is comparable to the physiological endothelial monolayer in vitro.

Ultrastructural analysis of vascular calcifications in uremia.

Accelerated intimal and medial calcification and sclerosis accompany the increased cardiovascular mortality of dialysis patients, but the pathomechanisms initiating microcalcifications of the media are largely unknown. In this study, we systematically investigated the ultrastructural properties of medial calcifications from patients with uremia. We collected iliac artery segments from 30 dialysis patients before kidney transplantation and studied them by radiography, microcomputed tomography, light microscopy, and transmission electron microscopy including electron energy loss spectrometry, energy dispersive spectroscopy, and electron diffraction. In addition, we performed synchrotron x-ray analyses and immunogold labeling to detect inhibitors of calcification. Von Kossa staining revealed calcification of 53% of the arteries. The diameter of these microcalcifications ranged from 20 to 500 nm, with a core-shell structure consisting of up to three layers (subshells). Many of the calcifications consisted of 2- to 10-nm nanocrystals and showed a hydroxyapatite and whitlockite crystalline structure and mineral phase. Immunogold labeling of calcification foci revealed the calcification inhibitors fetuin-A, osteopontin, and matrix gla protein. These observations suggest that uremic microcalcifications originate from nanocrystals, are chemically diverse, and intimately associate with proteinaceous inhibitors of calcification. Furthermore, considering the core-shell structure of the calcifications, apoptotic bodies or matrix vesicles may serve as a calcification nidus.

Analysis of calcifications in patients with coral reef aorta.

BACKGROUND: Coral reef aorta is a rare vascular disease with intraluminal calcifications of the dorsal part of the visceral aorta. The pathogenesis of this disease with its topographic and morphologic characteristics is unknown. The aim of our study was to investigate calcification inhibitors and the ultrastructure of calcifications in patients with coral reef aorta. METHODS: Ten patients with coral reef aorta were examined. Calcified specimens were investigated by immunohistochemical techniques for the expression of the calcification inhibitors matrix gla protein (MGP) and fetuin-A. Vessel walls were also assessed by electron microscopic techniques including electron energy-lost spectroscopy, electron dispersive spectroscopy, and electron diffraction. Sera of patients were analyzed for fetuin-A, uncarboxylated MGP (ucMGP), and osteoprotegerin. RESULTS: As assessed by immunohistochemistry, most MGP was detected in the vicinity of calcified regions. Serum levels of the calcification inhibitors ucMGP, fetuin-A, and osteoprotegerin were 370+/-107 nmol/L, 0.57+/-0.03 g/L, and 5.64+/-0.79 pmol/L, respectively. Ultrastructural analysis of calcified specimens showed a core-shell structure with multiple calcification nuclei. Calcifications displayed a fine-crystalline character, and elemental analysis revealed hydroxyl apatite as the chemical compound. CONCLUSION: The coral reef aorta represents an extreme exophytic growth of vascular calcification with multiple nuclei which resemble typical media calcification. Positive vascular immunostaining and low serum levels of both fetuin-A and ucMGP suggest a pathophysiologic role of these calcification inhibitors in the development of coral reef aorta.

Hierarchical role of fetuin-A and acidic serum proteins in the formation and stabilization of calcium phosphate particles.

The serum protein fetuin-A is a potent systemic inhibitor of soft tissue calcification. Fetuin-A is highly effective in the formation and stabilization of protein-mineral colloids, referred to as calciprotein particles (CPPs). These particles ripen in vitro in a two-step process, indicated by a morphological conversion from spheres to larger prolate ellipsoids. Using a combined light scattering and electron microscopic imaging approach we determined that the second-stage particles resulted from a highly anisotropic outgrowth of the first-stage particles. Electron microscopy of ascites fluid from a patient with calcifying peritonitis revealed particles reminiscent of secondary CPPs. Thus, CPPs form in the body and undergo the two-step ripening at least in pathological conditions. Unlike in vitro generated CPPs, ascites-derived CPPs contained little fetuin-A but large amounts of albumin. This prompted us to study the role of fetuin-A combined with other serum proteins in CPP formation. Fetuin-A was indispensable for primary CPP formation. Albumin and acidic proteins in general greatly enhanced the fetuin-A triggered formation of secondary CPPs and, thus, substituted substantial amounts of fetuin-A without loss of inhibition of calcium phosphate precipitation. Thus, direct mineral deposition from solute in the body is unlikely even at low fetuin-A serum levels as long as sufficient bulk acidic protein is available. Collectively fetuin-A and other acidic bulk plasma proteins may be considered as mineral chaperones mediating the stabilization, safe transport, and clearance in the body of calcium and phosphate as colloidal complexes, thus, preventing ectopic calcification.