Search PubMed⌕ Search

Biomedical subjects

D Knaack

Publications and source records attributed to D Knaack.

10 recordsLinked to original sources
PubMed1999

alpha-BSM: a biomimetic bone substitute and drug delivery vehicle.

alpha-BSM is a biomimetic endothermically setting apatitic calcium phosphate bone substitute material. Its injectability and ability to harden at body temperature in the presence of physiologic saline, and other buffering agents, makes it an attractive clinical bone substitute and delivery vehicle for therapeutic agents in orthopaedic and dental applications. In osseous tissue, alpha-BSM alone remodels into bone and promotes bone healing. alpha-BSM treatment has been shown in several animal models to be effective in promoting healing of surgically created critical size defects and restoring bone biomechanical strength to values equal to or greater than values achieved with autograft controls. In vitro studies with alpha-BSM containing gentamicin show that antibiotics can be incorporated stably into alpha-BSM and that the release kinetics can be controlled with the appropriate formulation and preparative procedures. Growth factors and enzymes also are compatible with the alpha-BSM setting reaction. The incorporation of recombinant human bone morphogenetic protein-2 with alpha-BSM was shown to be effective in stimulating bone formation and accelerating restoration of the differentiated phenotype in an osteotomy model. Clinical trial investigators in Europe currently are using alpha-BSM implantations for treatment of fractures and other indications.

Animals↗
PubMed1998

Resorbable calcium phosphate bone substitute.

The in vitro and in vivo properties of a novel, fully resorbable, apatitic calcium phosphate bone substitute (ABS) are described. The ABS was prepared from calcium phosphate precursors that were hydrated to form an injectable paste that hardens endothermically at 37 degrees C to form a poorly crystalline apatitic calcium phosphate (PCA). The PCA reaction product is stable in vivo as determined by FTIR and XRD analysis of rabbit intramuscular implants of ABS retrieved 4, 7, and 14 days postimplantation. Bone formation and resorption characteristics of the ABS material were characterized in a canine femoral slot defect model. Femoral slot defects in dogs were filled with either autologous bone implants or the ABS material. Sections of femoral bone defect site from animals sacrificed at 3, 4, 12, 26, and 52 weeks demonstrated that new bone formation proceeded similarly in both autograft and ABS filled slots. Defects receiving either material were filled with trabecular bone in the first 3 to 4 weeks after implantation; lamellar or cortical bone formation was well established by week 12. New bone formation in ABS filled defects followed a time course comparable to autologous bone graft filled defects. Histomorphometric evaluation of ABS resorption and new bone formation indicated that the ABS material was greater than 99% resorbed within 26 weeks; residual ABS occupied 0.36+/-0.36% (SEM, n = 4) of the original defect area at 26 weeks. Quantitatively and qualitatively, the autograft and ABS were associated with similar new bone growth and defect filling characteristics.

Animals↗
PubMed1994

Clonal insulinoma cell line that stably maintains correct glucose responsiveness.

A number of pancreatic beta-tumor cell (beta TC) lines have been derived from insulinomas arising in transgenic mice expressing the SV40 T antigen gene under control of the insulin promoter. Some of these lines secrete insulin in response to physiological glucose concentrations. However, this phenotype is unstable. After propagation in culture, these nonclonal lines become responsive to subphysiological glucose levels and/or manifest reduced insulin release. Here we report the use of soft-agar cloning to isolate single-cell clones from a beta TC line, which give rise to sublines that maintain correct glucose responsiveness and high insulin production and secretion for > 55 passages (over a year) in culture. One of these clonal lines, denoted beta TC6-F7, was characterized in detail. beta TC6-F7 cells expressed high glucokinase and low hexokinase activity, similarly to normal islets. In addition, they expressed mRNA for the GLUT2 glucose transporter isotype and no detectable GLUT1 mRNA, as is characteristic of normal beta-cells. These results demonstrate that transformed beta-cells can maintain a highly differentiated phenotype during prolonged propagation in culture, which has implications for the development of continuous beta-cell lines for transplantation therapy of diabetes.

Animals↗
PubMed1992

[RoTrac capillary pore membranes for laboratory filtration. I. Degermination filtration].

RoTrac capillary pore membranes (CPM) are produced by means of the nuclear track technology. Thus a defined and in wide ranges independent adjunction of the different membrane parameters (diameter, density, shape and inclination of pores) is possible. The wanted uniform separation diameter of the membrane can exactly be chosen according to the size of the microorganisms to be rejected. By dead end filtration experiments with E. coli and Serratia marcescens the suitability of RoTrac-CPM in bacteria removal filtration was proven. Blocking was very strong for membranes with pore diameters in size range of the microorganisms (approximately 0.45 micron). Though the filtrate had immense reduced bacteria counts (from 10(7)-10(8) to 10-100 bacteria/ml), it was generally not sterile. For membranes with a pore diameter of 0.2 micron and smaller blocking was essentially lesser. Here filtrate was always sterile. Flux (and thus the filterable volume) corresponds to values of competitive membranes. Compared with those the proven possibility of simple cleaning is an advantage, because rejection and blocking of symmetrical CPM occur directly on the membrane surface. This is promising for use of CPM in cross flow filtration.

Disinfection↗
PubMed1992

[RoTrac capillary pore membranes for laboratory filtration. II. Bacteria-free filtration].

Because of their special characteristics Capillary pore membranes (CPM) are now applied in several branches of separation techniques and analytics. Besides applications in particle analytics and microfiltration of different media capillary pore membranes can be used in microorganism separation. It was shown that RoTrac CPM can be used for bacteria free (or so called sterile) filtration. Acceptable fluxes were reached in separation of Pseudomonas diminuta (test species ATCC 19146). Membranes with pore diameters of 0.2 micron and smaller always assure a bacteria free filtrate even for a very high bacteria count of about 10(7)-10(8) bacteria/ml. In filtration of Mycoplasma arginini no sterile filtrate was obtained for a pore diameter of 0.08 micron and a high bacteria count of 3 * 10(7) bacteria/ml. The bacteria rejection by a factor of 10(5) was however remarkable. Only for 0.05 and 0.08 micron with reduced bacteria load the filtrate was bacteria free.

Colony Count, Microbial↗
PubMed1989

Acetylcholine receptor alpha-subunit mRNA is increased by ascorbic acid in cloned L5 muscle cells: Northern blot analysis and in situ hybridization.

Ascorbic acid is the major factor in brain extract responsible for increasing the average acetylcholine receptor (AChR) site density on the cloned muscle cell line L5. In the present study, we show that this effect of ascorbic acid requires mRNA synthesis, and that the mRNA level for the AChR alpha-subunit is increased to about the same level as are the surface receptors. We have found no increase in the mRNA levels of the beta-, gamma-, and delta-subunits, or in the mRNAs of other muscle-specific proteins, such as that of light chain myosin 2, alpha-actin, and creatine kinase. By in situ hybridization, we further show that the increase in alpha-mRNA in response to ascorbic acid is exclusively in myotubes and is located near clusters of nuclei. mRNA levels for the alpha-subunit in mononucleated cells are very low and do not significantly increase in response to ascorbic acid. The mononucleated cells are thus excluded as a possible source for the increase in alpha-subunit mRNA detected by Northern blot analysis. Our results indicate that there is a very specific action of ascorbic acid on the regulation of AChR alpha-mRNA in the L5 muscle cells, and that the expression of surface receptors in these cells is limited by the amount of AChR alpha-subunit mRNA.

Animals↗
PubMed1986

Selective effects of ascorbic acid on acetylcholine receptor number and distribution.

Ascorbic acid in soluble extracts of neural tissue can account for the increase in surface acetylcholine receptors (AChR's) seen on L5 myogenic cells treated with crude brain extract (Knaack, D., and T. R. Podleski, 1985, Proc. Natl. Acad. Sci. USA., 82:575-579). The present study further elucidates the nature of the response of L5 cells to ascorbic acid. Light autoradiography showed that ascorbic acid treatment affects both the number and distribution of surface AChR's. Ascorbic acid, like crude brain extracts, caused a three- to fourfold increase in average AChR site density. However, the number of AChR clusters induced by ascorbic acid was only one-fifth that observed with crude brain extract. The rate constant for degradation of AChR in ascorbic acid-treated cells of 0.037 +/- 0.006 h-1 (t1/2 = 19 h) was not significantly different from that in untreated controls of 0.050 +/- 0.001 h-1 (t1/2 = 14 h). The increase in AChR site density is primarily due to a 2.8-fold increase in the average rate of AChR incorporation. Ascorbic acid also stimulates thymidine incorporation and increases the total number of nuclei per culture. However, cellular proliferation is not responsible for the increase in AChR's since 10 microM cytosine arabinofuranoside blocks the mitogenic effect without affecting the AChR increase. The specificity of ascorbic acid on AChR expression was established by showing that (a) ascorbic acid produced only a slight increase in total protein, which can be accounted for by the mitogenic effect, and (b) the normal increase seen in creatine kinase activity during muscle differentiation was not altered by the addition of ascorbic acid. We conclude that the action of ascorbic acid on AChR number cannot be explained by changes in cell growth, survival, differentiation, or protein synthesis. Therefore, in addition to a minor stimulation of AChR clustering, ascorbic acid specifically affects some aspect of the AChR biosynthetic pathway.

Animals↗
PubMed1985

Ascorbic acid mediates acetylcholine receptor increase induced by brain extract on myogenic cells.

Extracts of fetal calf brain cause a 3- to 5-fold increase in acetylcholine receptors (AcChoR) on cultured myogenic L5 cells. Purification of the substance causing the major portion of this receptor increase has been completed. Ultraviolet spectral characteristics, nuclear magnetic resonance, mass spectra, and AcChoR induction by the active factor are the same as those of commercially available ascorbic acid. The biological activity of ascorbic acid is not mimicked by reducing agents with or without sulfhydryl groups. Compounds related to ascorbic acid were tested for their ability to induce AcChoR increases on L5 cells. D-Isoascorbic acid is the only substance with identical biological activity to ascorbic acid. Dehydroascorbic acid and ascorbic acid 2-O-sulfate also induce AcChoR increases but with lower specific activity. These data show that ascorbic acid can play a role in regulating AcChoR expression in myogenic tissue, and the presence of ascorbic acid in the purified fraction from fetal calf brain accounts for its ability to increase AcChoR in L5 cells.

Animals↗