MACROMOLECULAR AGGREGATION STATES IN RELATION TO MINERALIZATION: THE COLLAGEN-HYDROXYAPATITE SYSTEM AS STUDIED IN VITRO

Unusual collagen aggregates induced in rat incisor dentin after vinblastine administration

Young male Wistar rats weighing 100 g were injected intravenously with 0.2 mg of vinblastine sulfate (VBL). At 24, 27, and 36 hours and 2, 4, and 6 days after introduction of the drug, the rats were fixed by means of perfusion and the upper incisors were removed for electron microscopy. Many secretion granules had accumulated in the young odontoblasts 24 hours after VBL administration. Newly formed predentin located between odontoblasts contained small amounts of an unusual collagen aggregate characterized by a fine, symmetrically striated structure, and paired, dense bands, which were present at both ends. After 27 hours, following the disappearance of the secretion granules in the odontoblasts, unusual collagen aggregates had increased in amount. Two days after administration, the predentin layer, which was close to the odontoblasts, was composed largely of unusual collagen aggregates. During dentinogenesis, the layer of unusual collagen aggregates gradually shifted into the dentin, where, 4 days after VBL administration, it was, to a large degree, located. Mineralization of the unusual collagen aggregates began with the deposition of fine, filamentous crystals that later grew into needle-shaped crystals 40 A thick. These findings suggest that unusual collagen aggregates are produced as a result of the secreting function of odontoblasts and are mineralized, as are normal collagen fibrils in dentin.

Recent studies of the mineral phase in bone and its possible linkage to the organic matrix by protein-bound phosphate bonds

The most widely accepted hypothesis to account for maturational changes in the X-ray diffraction characteristics of bone mineral has been the 'amorphous calcium phosphate theory', which postulates that an initial amorphous calcium phosphate solid phase is deposited that gradually converts to poorly crystalline hydroxyapatite. Our studies of bone mineral of different ages by X-ray radial distribution function analysis and 31P n.m.r. have conclusively demonstrated that a solid phase of amorphous calcium phosphate does not exist in bone in any significant amount. 31P n.m.r. studies have detected the presence of acid phosphate groups in a brushite-like configuration. Phosphoproteins containing O-phosphoserine and O-phosphothreonine have been isolated from bone matrix and characterized. Tissue and cell culture have established that they are synthesized in bone, most likely by the osteoblasts. Physiochemical and pathophysiological studies support the thesis that the mineral and organic phases of bone and other vertebrate mineralized tissues are linked by the phosphomonester bonds of O-phosphoserine and O-phosphothreonine, which are constituents of both the structural organic matrix and the inorganic calcium phosphate crystals.

Biochemical characterization of guanidinium chloride-soluble dentine collagen from lathyritic-rat incisors

alpha- and beta-Chains were isolated by sequential ion-exchange and gel-filtration chromatography of guanidinium chloride-soluble dentine collagen obtained from Tris/NaCl-extracted EDTA-demineralized lathyritic-rat incisors. The alpha-chains were identified as alpha 1 I and alpha 2 by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and amino acid analysis of the intact chains and their CNBr peptides. The dentine alpha-chains exhibited higher lysine hydroxylation and phosphate content, but lower hydroxylysine glycosylation, than alpha-chains from skin. Increased lysine hydroxylation was observed in the helical sequences. The alpha 1 I/alpha 2 ratio was approx. 3:1, and was presumably due to the presence of (alpha 1 I)3 molecules along with (alpha 1 I)2 alpha 2 molecules as shown recently for neutral-salt-soluble dentine collagen [Wohllebe & Carmichael (1978) Eur. J. Biochem. 92, 183--188]. In the borohydride-reduced beta 11- and beta 12-chains from guanidinium chloride-soluble dentine collagen, the reduced cross-links hydroxylysinohydroxynorleucine and hydroxylysinonorleucine were present. A higher proportion of hydroxylysinonorleucine in the reduced beta 12-chain probably reflects differences in extent of hydroxylation of specific lysine residues of the alpha 1 I- and alpha 2-chains.

Precipitation of calcium phosphates under conditions of double diffusion in collagen and gels of gelatin and agar

One-dimensional double diffusion was applied to determine critical concentrations at which the precipitation of calcium phosphates occurs in reconstituted connective tissue collagen and agar gels at 37 degrees C and in gelatin gels at 25 degrees C. Experiments were performed in the presence of unbuffered 0.15 mol dm-3 NaCl, or 0.15 mol dm-3 NaCl-veronal adjusted to pH 7.4. It was found that critical concentrations of precipitation of both precipitating components, CaCl2 and phosphate buffer (pH 7.4), were equimolar and independent of the ratios of initial concentrations of the components. Critical concentrations of precipitation were not affected by the concentrations and kinds of gels used. The first-formed precipitates showed amorphous structure by X-ray diffraction analyses. Infrared (IR) spectra of the precipitates indicated CaHPO4 . H2O to be their predominant species. The molar Ca/P ratio obtained by chemical analyses was 1.08. This precipitate transformed in time into octacalcium phosphate. In all experiments, two very thin membranes of precipitate were formed in the gel column at the onset of precipitation simultaneously on both sides of the actual disc of precipitate. IR spectra and chemical analyses showed that both membranes were identical to the actual precipitation discs.

Localization of collagenase in human middle ear cholesteatoma

The process of connective tissue breakdown in chronic otitis media is described in the context of recent advances in our understanding of collagen degradation and bone resorption. The significance of the initial step in collagen breakdown, brought about by the action of a specific collagen dissolving enzyme is emphasized in terms of recent studies in other chronic inflammatory diseases characterized by connective tissue breakdown. Bone resorption, a characteristic feature of chronic otitis media, requires the breakdown of collagen, which comprises over 90 percent of bone protein. Evidence in support of collagenase in bone resorption from adjacent tissue (in this case, inflammatory connective tissue) would require identification of the enzyme in cells involved in the inflammatory process adjacent to the resorbing bone. Collagenase was found localized in frozen sections of canal wall skin, middle ear granulation and in cholesteatoma by a specific binding of the enzyme with an antiserum produced against purified human skin collagenase. The antigen antibody complex was labelled with fluorescein. Collagenase appeared in the subepithelial connective tissue of cholesteatoma, granulation tissue from the middle ear and the dermis of canal skin; but was not seen in the keratin layer, epithelium or the epidermal appendages. The enzyme appeared within certain fibroblasts, macrophages and endothelial cells of capillary buds. Collagenase enhanced by chronic inflammation attacks the intact collagen molecule, making it susceptible to further digestion by other proteases that are also products of inflammation. This process brings about resorption of connective tissue and bone.

An ultrastructural study of the articular cartilage in calcium pyrophosphate dihydrate (CPPD) crystal deposition disease (chondrocalcinosis articularis)

An ultrastructural study of articular cartilage from five patients with calcium pyrophosphate dihydrate (CPPD) crystal deposition disease was performed. The CPPD crystals, identified by micro X-ray diffraction, were usually found in clusters, located in intercellular areas of the intermediate cartilage layer. The matrix surrounding the clusters either showed a normal morphology or a homogeneous appearance, within which faint cross striations but no distinctly fibrillar outlines could be identified. Another change in the matrix, characterized by an increased electron density and longitudinally fragmented collagen fibres, was also seen. This latter change was generally seen without concomitant CPPD crystal deposition. No specific relationship between the crystals and the collagen fibres or the granular background material of the matrix was encountered.

Formation of mineralized scar tissue induced by implants containing collagen-calcium phosphate gel

The ability of a collagen-calcium phosphate gel to induce physiologic closure of subcutaneous polyethylene tube implants was tested. The openings of several tubes that had been filled with the gel were occluded by scars of mineralized connective tissue. Differentiation of cells into palisading fibroblasts and elaboration of a linear collagen matrix at the tissue-gel interface was seen.

Nucleation of monosodium urate crystals

(1) Calcium greatly increased crystallization of monosodium urate in otherwise pure water, by enhancing both nucleation and growth. (2) Acid accelerated urate nucleation, both by its direct action and indirectly by increasing the free calcium in physiological fluids. (3) Synovial fluid from one gouty patient accelerated urate nucleation, while that from one rheumatoid patient inhibited nucleation. (4) X-rays, collagen, ethyl alcohol, cupric ion, and potassium ion all had negligible influence on urate nucleation. (5) Mechanical shock greatly increased urate nucleation.

Urolithiasis induced with DL-3,a-dimethyltyrosine methylester HCl. I. A scanning electron microscopic investigation

Scanning electron microscopic investigations on rats subjected to DL-3,a-dimethyltyrosine methylester HCl treatment, indicated that the drug in reference induces renal lesions substantiated by proximal tubular epithelial cell regression and eventual exfoliation, coupled by formation of 3,a-dimethyltyrosine calculi both in the upper and lower segments of the urinary tract. The development of calculi was found to be preceded by a moderate to massive precipitation of a fibrin-like substance intermixed with blood cells, and with an occasionally concomitant deposition of exfoliated cells of epithelial origin, to be succeeded by precipitation of crystals.

Bone growth in organ culture modified by an electric field

Unidirectional pulsating electric fields caused changes in the patterns of growth in rat calvaria grown in organ culture. Morphologic pattern variations were studied by radioautographic techniques. The changes occurred at the negatively charged bone surface. In a strong field, the growth pattern became disoriented.

The ultrastructural interface of bone crystals and organic matrix in woven and lamellar endochondral bone

Endochondral bone consists of three calcified regions: calcified cartilage, woven bone, and lamellar bone. Woven or immature bone begins when osteoblastic extrusions or buds calcify; from initial calcification loci, bone crystals grow radially to form spheroidal bone nodules. Nodules eventually coalesce into bone seams. Lamellar bone develops as a sequel to the calcification of cartilage or woven bone. Hydroxyapatite grows into lamellar bone and then is oriented parallel to collagen. Except for the stage of cartilage calcification, intramembranous and endochondral osteogenesis are similar.

Carbonic Anhydrase and the Precipitation of Apatite

On theoretical grounds it is unlikely that the catalytic action of the enzyme carbonic anhydrase would be required for the precipitation of apatite in vitro. The presence of carbonic anhydrase in either active or inactivate form did not initiate precipitation in a metastable calcifying solution. It is unlikely that carbonate (or bicarbonate) ions are essential for the precipitation of apatite in vitro or in vivo.

Electronmicroscopy of Dental Calculus

Electron microscopy of ultrathin osmium-fixed sections of dental calculus, cut with a diamond knife without prior decalcification, revealed densely mineralized areas entrapping many degenerating microorganisms, within which were deposited similarly electron-dense crystals. Two principal forms of crystals were found, the predominant type being of the same order of magnitude and shape as those found in bone, and showing the typical characteristics of apatite in selected area electron diffraction patterns.