Semisynthesis and properties of a fluorescent phosphatidyl-inositol analogue containing a cis-parinaroyl moiety

A method for the preparation of a fluorescent phosphatidylinositol analogue, 1-acl,-2-prinaroyl-sn-glycero-3-phospho-sn-1-myo-inositol has been developed. This method makes use of yeast phosphatidylinositol as the starting material and includes the following steps: (1) acetylation of the free hydroxyl groups of the inositol moeity; (2) removal of the fatty acid from the sn-2-position of the glycerol moiety by phospholipase A₂; (3) reacylation with parimaroyl anhydride; (4) removal of the protecting acetyl groups by alkaline solvolysis. The identity of the product was established by thin-layer chromatography (TLC), UV absorption spectroscopy, enzymatic degradation and by a transfer assay using the phosphatidylinositol transfer protein from bovine brain.Some properties of the fluorescent phosphatidylinositol analogue are reported.     

Structural and functional characterization of the N-terminal acetyltransferase Naa50

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Ds excision from extrachromosomal geminivirus vector DNA is coupled to vector DNA replication in maize

Analysis of transposition products generated after Activator (Ac) excision from the P locus in maize suggest that Ac excises either during or after replication of the P locus. The frequency of excision of the non-autonomous Ac derivative, Dissociation ( Ds ), from extrachromosomal replicating and nonreplicating vector DNAs in transfected black mexican sweet maize protoplasts was compared to assess directly a role of extrachromosomal vector DNA replication in Ds excision. Replicating (rep⁺) and non-replicating (rep⁻) vector DNAs comprised a Ds element that harbored a geminivirus, wheat dwarf virus (WDV), origin of replication and WDV genes required for viral DNA replication (rep⁺) or mutant, inactive derivatives of these genes (rep⁻). Excision of Ds was detected only in those cell nuclei co-transfected with the replicating Ds -vector DNA and a transposase expression vector. Quantitative reconstruction experiments showed that Ds excised at least 3 × 10⁵-fold more frequently from replicating vector DNA as compared with nonreplicating vector DNA. Therefore, these results provide direct evidence for a coupling of Ds excision from extrachromosomal vector DNA to vector DNA replication in maize.     

Action of phospholipases on the phosphatidylcholine exchange protein from beef liver.

The phospholipases A2, C and D have been used to investigate the localization of phosphatidylcholine in the phosphatidylcholine exchange protein from beef liver. The rate of enzymatic hydrolysis of the protein-bound phosphatidylcholine was found to be very low. Addition of deoxycholate, isobutanol or dioxane to the native protein, under conditions where delipidation did not occur, greatly enhanced the hydrolytic action of the phospholipases. From these results it is concluded that phosphatidylcholine may be buried in the protein molecule.     

Stretched polyethylene (UHMWPE)--a new substance modification for minimizing wear in artificial knee joint replacement]

Polyethylene wear is a major cause of aseptic loosening of knee endoprostheses. With the aim of minimizing this mechanical wear, we stretch-modified the structure of polyethylene. From plates of UHMWPE, stretched PE samples were produced under defined conditions, and subsequently submitted to friction tests in a fluid environment (cycles 5 x 10(5), frequency 1.5 Hz, load 500 N, contact stress 10 MPa). After load testing, the stretched samples revealed a 70% reduced wear rate in comparison with non-stretched samples. Microscopic examination (light microscopy, scanning electron microscopy) showed abrasive scratches in all test samples, but only in the non-stretched specimens were signs of pitting found. Translating these results to unidirectional tractive rolling on the tibial plateau in the knee joint suggests that a significant reduction in polyethylene wear can be expected. However, further experimental investigations need to be carried out to confirm this highly promising possibility.     

A new coating method for cemented femur shaft implants--biocompatibility, stability during sterlization and adhesive strength]

The main cause of aseptic loosening of cemented stems in total hip arthroplasty is the hydrolytic degradation of the metal-cement interface. In order to prevent this debonding a new multilayer method of coating the implant surface involving the use of a silica-/silane technique to create a durable adhesive bond between metal stem and bone cement has been developed. The biocompatibility of all the elements of the multilayer system was confirmed using a human osteoblast cell culture test. For sterilization purposes, gamma irradiation with a 25 kGy effective dose proved to be the method of choice. The proven biocompatibility and successful sterilization of the coated implants are the main prerequisites for in-vivo usage. On the technical side, the bonding effectiveness of the multilayer coating system was demonstrated by the tensile test, which revealed a significant improvement in the adhesive strength of the cement-metal bond under prolonged moist conditions similar to those met with in the human body.     

Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique]

Aseptic loosening of tibial components due to degradation of the interface between bone cement and metallic tibial shaft component is still a persistent problem, particularly for surface-cemented tibial components. The surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by SiOx-PVD layering to avoid crack formation. A biomechanical model for a vibration fatigue test was done to prove that crack formation can be significantly reduced in the case of coated surfaces. It was found that coated tibial components showed a highly significant reduction of cement cracking near the metal/bone cement interface (p < 0.01) and a significant reduction of gap formation in the metal-to-bone cement interface (p < 0.05). Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis metal/bone cement interface. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the metal/bone cement/bone interfaces. With surface coating of the tibial component it should become possible that surface-cemented TKAs reveal similar loosening rates as TKAs both surface- and stem-cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in the case of revision and stress shielding for a better bone health.