Osteopontin is an argentophilic protein in the bone matrix and in cells of kidney convoluted tubules

Nucleolar organising regions (NOR) are part of the nucleolus, containing argyrophilic proteins (nucleoclin/C23, nucleophosmin/B23). They are identified by silver staining at low pH. The method also reveals osteocyte canaliculi and cement lines and granules in the cytoplasm of kidney cells in locations that mimic osteopontin distribution. Human bone and kidney sections, benign and lymphomatous pleural effusions were processed for silver staining to identify AgNOR. Sections were processed in parallel for immunohistochemistry with an antibody direct against osteopontin. In pleural effusions, AgNORs were found increased in the nuclei of lymphoma cells. In bone, Ag staining identified AgNOR in cell nuclei, as well as in osteocyte canaliculi, cement and resting lines. In the distal convoluted tubules of the kidney, silver deposits were also observed in cytoplasmic granules on the apical side of the cells. Immunolocalization of osteopontin closely matched with all these locations in bone and kidney. NOR proteins and osteopontin are proteins containing aspartic acid rich repeats that can bind Ag. Staining protocols using silver nitrate at low pH can identify these proteins on histological sections. AgNOR is a useful histochemical method to identify osteopontin in bone sections.

The influence of processes for the purification of human bone allografts on the matrix surface and cytocompatibility

Different industrial processes exist to purify allogenic bone, providing safe and cleaned blocks for bone allografting. However, they often make use of chemical reagents that can be aggressive for the bone matrix. Bone samples were processed with several soaking techniques used in industry: NaHCO3, H2O2, NaOH and H2O2+NaOH combined; the consequences on the bone matrix and cytocompoatibility were evaluated on femoral heads from osteoarthritic patients. Alterations of matrix were searched by histochemistry, atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cytocompatibility was evaluated by coculturing human osteoblast-like cells (SaOS-2) on bone slices. Collagen fibers were dramatically altered at the surface of bone treated with H2O2, NaOH (and their association), but not with NaHCO3. A marked reduction in the number of hydroxyapatite crystals was observed on the trabecular surfaces by TEM and morphological changes were evidenced in SEM and AFM. Argyrophilic proteins of the bone matrix were removed by H2O2 and NaOH (and their association), but not by NaHCO3. As a consequence, attachment, spreading, proliferation and alkaline phosphatase activity of SaOS-2 were reduced by H2O2 and NaOH treatments. Strong oxidizing reagents altered matrix integrity by modifying collagenous and non-collagenous proteins. Whether these changes have clinical consequences on the bone bonding and osseointegration in human necessitate further investigations.

Evaluation of LR white resin for histology of the undecalcified rat tibia

Histology of plastic embedded undecalcified bone represents a challenging problem to the histotechnologist. We outline here an exploration of LR White resin as a suitable medium for histologic study of undecalcified rat tibia. A procedure was developed for light microscopy of rat tibia embedded in LR White and sectioned by sawing-grinding technics. The specimens were fixed in 10% neutral buffered formalin or alcohol-acetic acid-formol, dehydrated in ethanol, defatted in chloroform followed by resin infiltration and heat-curing of embedded blocks. The procedure of dehydration, defatting, infiltration, and polymerization can be completed within 10 days. Cold curing with accelerator provided by the manufacturer did not yield superior results compared to blocks cured with heat. Thick sections were obtained using a diamond wire saw, attached to plexiform slides, then ground and polished. Surface staining with Von Kossa silver reagent or toluidine blue revealed satisfactory morphological preservation of the mineralized bone sections. Artifacts like small bubbles appeared occasionally and could not be avoided despite prolonged infiltration or cold curing of blocks. Our method is relatively simple for base-line histologic study of rat tibia. The method offers advantages such as easy adaptability, reliable stainability, contrast, and resolution of bone architecture and marrow cells. Two other embedding media, Micro-Bed resin and Unicryl, were also tested, but produced inferior results.