Polymethylmethacrylate-based bone cement modified with hydroxyapatite.

A commercial acrylic bone cement was modified by the incorporation of different weight fractions of polycrystalline hydroxyapatite (HA), and the modified formulation was investigated. The influence of the filler proportion on the flow characteristics and the mechanical behavior of the resultant composite was evaluated. The residual monomer present in the cured materials was measured by gas chromatography. The comparison of the residual monomer present in the cements with and without reinforcement demonstrated that the degree of polymerization was not affected by the addition of HA. Porosity morphology was analyzed by optical and scanning electron microscopy. Image examination revealed that the porosity and the pore size of the hardened cement increased with an increasing amount of particulate filler. Flexural, compressive, and fracture properties of the cement with varying amounts of HA reinforcement were measured. It was found that up to 15 wt% HA could be added for increases in flexural modulus and fracture toughness. HA acts as a rigid filler that enhances fracture resistance and flexural modulus. Our results show that the workability of the modified formulation limited the incorporation of the ceramic filler to a maximum value of 15 wt%.     

Nanocomposites of hydroxyapatite with aspartic acid and glutamic acid and their interaction with osteoblast-like cells

The direct synthesis of hydroxyapatite (HA)-aspartic acid (ASP) and HA-glutamic acid (GLU) nanocrystals was carried out in presence of different amounts of the amino acids in solution. ASP and GLU incorporation into HA crystals reduces the coherent length of the perfect crystalline domains along the long dimension (002) and, even more, along the cross section (310) of the apatite crystals, suggesting a specific interaction of the amino acids with the HA structure. FTIR analysis indicates that the carboxylic groups of the acidic amino acids interact with the calcium ions of HA. The relative amount of ASP incorporation into HA nanocrystals is greater than that of GLU, suggesting a greater affinity of ASP for HA. Osteoblast-like, MG63, cells cultured on the composite nanocrystals display good proliferation and increased values of ALP activity, collagen type I, TGF-betaI and osteocalcin production, indicating that the presence of the acidic amino acids enhances osteoblast activation and extra-cellular matrix mineralization processes.     

Interaction of blood components with cathelicidins and their modified versions

Cationic antimicrobial peptides (cAMPs) serve as effective components of the innate host defense against microbial infections. cAMPs often show broad-spectrum antimicrobial activity, but narrow-band activity is also observed. Despite their great potential, the polycationic nature of cAMPs could cause serious side effects once in the bloodstream which may limit their applications. However, there is very limited knowledge available on AMPs interaction with blood components in spite of the fact that the most likely route of administration to treat systemic microbial infections for these peptides is intravenous, where they immediately come in contact with all blood components. In order to evaluate the therapeutic potential of cAMPs as new alternative to antibiotics, we investigated the impact of cathelicidin related cAMPs on red blood cell lysis, aggregation, platelet activation, blood coagulation, and complement activation. The influence of cAMPs on blood depends on hydrophobicity and number of charges in the peptides. The hemolytic activity of cathelicidin (bactenecin) variants was much less than that of indolicidin due to their lower hydrophobicity. Except indolicidin, none of the peptides induce platelet activation. Some of bactenecin variants (R3, Sub3 and W3) with higher charge inhibited the blood coagulation. The cAMPs did not activate or inhibit complement at the concentrations studied, expect for the peptide (Sub3). Our data shows that it is important to investigate cAMP-based drug candidates regarding their interaction with blood components early on in the development process. We anticipate that this new knowledge on blood interaction of antimicrobial peptides will help to design peptides with a better therapeutic window and with less side effects.     

Interaction of Sr-doped hydroxyapatite nanocrystals with osteoclast and osteoblast-like cells

This article reports the effect of strontium incorporation into hydroxyapatite nanocrystals on bone cells response. Hydroxyapatite nanocrystals were synthesized at strontium contents of 0, 1, 3, 7 atom %. Strontium incorporation for calcium is confirmed by the linear increase of the unit cell parameters of hydroxyapatite, in agreement with the different ionic radii of the two ions. Moreover, strontium substitution slightly affects hydroxyapatite structural order and the shape of the nanocrystals. Osteoblast-like MG63 cells cultured on the nanocrystals display good proliferation and increased values of the differentiation parameters. In particular, when cultured on samples with Sr concentration in the range 3-7 atom %, osteoblasts display increased values of ALP activity, collagen type I, and osteocalcin production. Moreover, the osteoclast number on all the Sr-doped samples is significantly smaller than on hydroxyapatite, and it decreases on increasing strontium content. The data indicate that strontium stimulates osteoblast activity and exerts its inhibitory effect on osteoclast proliferation even when incorporated into hydroxyapatite.     

A sensitive automated procedure for the determination of glucuronic acid.

A newly automated method for the detection of uronic acids, particularly glucuronic acid is described. Data showing the limitations of this method are also presented. The advantages of the method are: (1) greatly increased sensitivity compared to the carbazole methods and increased range; (2) lowered interference from other sugars, proteins and salts; (3) variability to allow small sample volumes and/or continuous flow; (4) a more stable color reagent solution.     

Interaction of isolated Lp(a) lipoprotein with calcium ions and glycosaminoglycans in vitro.

The interaction between the lipoprotein carrying the Lp(a) antigen, i.e. the Lp(a) lipoprotein, and agarose gels substituted with glycosaminoglycans, as well as the precipitation of the Lp(a) lipoprotein by Ca++ were studied. Comparisons between Lp(a) lipoprotein and other serum lipoproteins were conducted. Very low density lipoprotein (VLDL) and low density lipoprotein (LDL) were bound to the tested glycosaminoglycans at low ionic strength of sodium chloride, but no binding was found with the Lp(a) lipoprotein. However, Ca++ as a divalent buffer cation gave a precipitating Ca++-Lp(a) lipoprotein complex even at a physiological Ca++ concentration. VLDL and LDL were not precipitated under these conditions. These findings may be of interest in relation to the previously reported higher frequency of the phenotype Lp(a+) in subjects with coronary heart disease.     

Interaction of a plasma-sprayed hydroxyapatite coating in contact with human osteoblasts and culture medium.

The loss of calcium from plasma-sprayed calcium phosphate ceramics (CPCs) on bioinert metal substrate (Ti-6Al-4V) immersed in cell culture medium with or without human osteoblast culture was measured. The ceramics were a CPC and a duplex system composed of a CPC layer on an alumina coating. The dissolution of calcium compounds was monitored by measuring the calcium leaked from the coatings into the culture medium in 15 days. Calcium was measured by flame photometry. The surfaces of the ceramics exposed to the culture medium and in contact with osteoblasts were analysed by X-ray diffraction (XRD). The dissolution process occurred in the first 6 days of contact, but the calcium released into the culture medium was only a small fraction of the calcium content of the coatings. The presence or absence of osteoblasts on the surface of the ceramics did not make significant difference for the calcium release. The XRD spectra of the ceramics before and after immersion and in contact with cells did not show a significant change in the compounds of the coatings.     

The role of sulphation of glycosaminoglycans in their structural and functional characteristics.

The CD spectra in the far ultraviolet and the CD and ORD spectra of methylene blue-complexes (MB-complex) of glycosaminoglycans (GAG) with different sulphate contents were studied in comparison with their effect on the in vitro formation of collagen fibres. The following polyanions were investigated: Chondroitin sulphate-A with different sulphate contents, oversulphated chondroitin sulphate, heparin and dextran sulphate and their desulphated derivatives. It was observed that the MB-complex of polysaccharides with the same backbone structure, but with different sulphate contents might show ORD and CD spectra of exciton type, but of inverse sign. This phenomenon was interpreted on the basis of different types of aggregation of dye molecules bound to the polysaccharides. The biological effect of GAG changed also with the sulphate content. This suggests that it is the extent of sulphation rather than the glycosidic structure of GAG which determines their chiroptical and functional properties.     

Dissolution rates of carbonated hydroxyapatite in hydrochloric acid.

Osteoclasts have been shown to dissolve efficiently and effectively the mineral phase of bone by locally controlling the environment surrounding the cell. Although this mineral phase has been identified and well characterized as carbonated hydroxyapatite, there is little understanding of the factors that affect the dissolution properties of this mineral phase. Mimicking the mechanism by which osteoclasts dissolve the mineral phase of bone may provide insight into methods for the decalcification of atherosclerotic mineral deposits in the vascular system. Accordingly, a detailed characterization of the effects of various chemical and mechanical parameters on the dissolution of carbonated hydroxyapatite mineral was investigated in this study. Increases in the mineral dissolution rate (2-10 times) were associated with increases in dissolving solution [H+], osmolality, temperature, and flow rate. Mineral dissolution rate increases (5-8 times) were associated with greater surface area of the mineral and mechanical agitation of the dissolving solution.     

一种具有骨诱导活性的羟基磷灰石结晶的制备与研究

目的将骨形成蛋白2（BMP2）活性多肽与Ⅰ型胶原复合煅烧牛松质骨以制备出具有骨诱导活性的矿化羟基磷灰石结晶,并进一步探讨其生物学性能,为组织工程化人工骨提供实验基础。方法将BMP2活性多肽与Ⅰ型胶原复合煅烧牛松质骨作为实验组,以Ⅰ型胶原复合煅烧牛松质骨作为对照组。通过环境扫描电镜和能谱法以及x射线衍射实验观察能否生成羟基磷灰石结晶,同时对2组材料进行体外细胞培养,计算2组材料细胞黏附率,初步评价BMP2活性多肽引导Ⅰ型胶原复合煅烧牛松质骨表面矿化生成羟基磷灰石结晶的作用与能力。结果环境扫描电镜下可见实验组煅烧骨表面有矿化羟基磷灰石结晶生成,而对照组没有：能谱法对实验组矿化骨部分进行钙磷元素检测,质量比分别为16．23％、7．76％．原子百分数分别为6．34％、3．88％,X射线衍射检测证实矿化物的成分为磷灰石。大鼠骨髓基质干细胞分别与2组材料体外复合培养24h,实验组细胞黏附率明显高于对照组（a〈0．05）。结论BMP2活性多肽能引导Ⅰ型胶原复合煅烧骨表面矿化生成羟基磷灰石结晶,可以改善煅烧骨的骨诱导活性,提高细胞黏附性能,与煅烧骨复合后是一种理想的骨组织支架复合材料。     

Interaction of isolated Lp(a) lipoprotein with calcium ions and glycosaminoglycans in vitro

The interaction between the lipoprotein carrying the Lp(a) antigen, i.e. the Lp(a) lipoprotein, and agarose gels substituted with glycosaminoglycans, as well as the precipitation of the Lp(a) lipoprotein by Ca⁺⁺ were studied. Comparisons between Lp(a) lipoprotein and other serum lipoproteins were conducted.
Very low density lipoprotein (VLDL) and low density lipoprotein (LDL) were bound to the tested glycosaminoglycans at a low ionic strength of sodium chloride, but no binding was found with the Lp(a) lipoprotein. However, Ca⁺⁺ as a divalent buffer cation gave a precipitating Ca⁺⁺-Lp(a) lipoprotein complex even at a physiological Ca⁺⁺ concentration. VLDL and LDL were not precipitated under these conditions. These findings may be of interest in relation to the previously reported higher frequency of the phenotype Lp(a+) in subjects with coronary heart disease.     

Simulation of vascular surfaces: differential saturation with glycosaminoglycans and their quantitative analysis

Surface layers of sulphated glycosaminoglycan can be quantified by X-ray microanalysis using the local mass-fraction of the element sulphur. As a calibration standard radiolabelled chondroitin sulphate has been attached covalently to a nylon surface at various densities to the point where the molecules are packed as close as the radius of gyration permits.     

Interaction between the structural glycoprotein of connective tissue and proteoglycans and glycosaminoglycans

Structural glycoprotein (SGP) of connective tissue isolated from bovine heart valves and nasal septal cartilage forms water-soluble complexes with protein-chondroitin-4-sulfate and with various fractions of heparin. SGP does not form these complexes with hyaluronic acid. It is postulated that this phenomenon plays an important role in the formation of collagen and elastic fibers.Institute of Rheumatism, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR S. S. Debov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 12, pp. 1430–1432, December, 1976.     

Initial responses of human osteoblasts to sol-gel modified titanium with hydroxyapatite and titania composition

Sol-gel thin films of hydroxyapatite (HA) and titania (TiO(2)) have received a great deal of attention in the area of bioactive surface modification of titanium (Ti) implants. Sol-gel coatings were developed on Ti substrates of pure HA and TiO(2) and two composite forms, HA+10% TiO(2) and HA+20% TiO(2), and the biological properties of the coatings were evaluated. All the coating layers exhibited thin and homogeneous structures and phase-pure compositions (either HA or TiO(2)). Primary human osteoblast cells showed good attachment, spreading and proliferation on all the sol-gel coated surfaces, with enhanced cell numbers on all the coated surfaces relative to uncoated Ti control at day 1, as observed by MTT assay and scanning electron microscopy. Cell attachment rates were also enhanced on the pure HA coating relative to control Ti. The pure HA and HA+10% TiO(2) composite coating furthermore enhanced proliferation of osteoblasts at 4 days. Moreover, the gene expression level of several osteogenic markers including bone sialoprotein and osteopontin, as measured by RT-PCR at 24h, was shown to vary according to coating composition. These findings suggest that human primary bone cells show marked and rapid early functional changes in response to HA and TiO(2) sol-gel coatings on Ti.     

Interaction of recombinant and natural soluble CD5 forms with an alternative cell surface ligand.

CD5, a member of the scavenger receptor cysteine-rich (SRCR) receptor family, plays a role in the thymocyte maturation, T cell activation and T cell-antigen-presenting cell interactions. To date only CD5 ligands (CD5L) compatible with a T-B co-stimulatory role have been described (CD72, gp40-80 and IgV(H) framework region) so the existence of alternative CD5L involved in other aspects of T cell biology warrants further exploration. Here we characterize the cell binding properties of a recombinant soluble human CD5 extracellular domain glycoprotein (rsCD5). In contrast to previously characterized ligands, this molecule binds to a broadly distributed cell surface receptor expressed on monocytes, lymphocytes and various cell lines of lymphoid, myelomonocytic and epithelial origin. The cell binding of rsCD5 is divalent cation independent and inhibited by high molar concentrations of certain monosaccharides. Both human CD5 Ig fusion proteins and a natural soluble CD5 form (present in human serum and resulting from proteolytic cleavage following lymphocyte activation) reproduce the cell binding pattern of rsCD5 and block its binding in a competitive form. The involvement of the most N-terminal CD5 SRCR domains (D1 and D2) in binding is deduced from competition cell binding assays with CD5 Ig fusion proteins. These results imply a novel CD5/CD5L interaction model recalling some aspects of the interaction of CD6 with activated leukocyte cell adhesion molecule (ALCAM).     

Circadian rhythms and the urinary excretion of acid glycosaminoglycans in normal human adults.

Urine from normal human adults (11 males, 4 females) was collected for 24 hours in four-hour samples, commencing at 08.00 hours. The urine volume, and concentrations of chondroitin sulfate, heparan sulfate, cetylpyridinium turbidity, and creatinine were measured on every sample. Concentrations and total output of glycosaminoglycans were significantly higher in male urine than in female urine. Chondroitin sulfate total output/four hours showed a significant negative correlation with creatinine concentration in males, but not in females. A testicular hyaluronidase is implicated. No such correlation was observed for heparan sulfate. Glycosaminoglycans are filtered into the urine. Plasma clearances are very low. Heparan sulfate is excreted with a circadian rhythm, as is glycosaminoglycan assayed by cetyl pyridinium turbidity. Peak excretions are at 06.00 and 10.00 hours respectively. Chondroitin sulfate excretion is not rhythmic in the male, perhaps because hyaluronidase activity in the urine complicates the assay. A rhythm may be present in the female.