羟基磷灰石人工骨体外降解实验

目的：探讨在体外条件下羟基磷灰石人工骨（HAB）材料的降解规律。方法：将材料放入磷酸盐缓冲液和蒸馏水中，观察在不同时间点其表面形态、重量、pH值、机械强度的变化。结果：羟基磷灰石人工骨材料在磷酸盐缓冲液中4周时开始降解，8周当前重量丧失速度较快，8周后速度减缓；4－12周压缩强度降低幅度较大；pH值先降后升，28周时接近中性。结论：羟基磷灰石人工骨材料具有一定的可降解性，材料降解引起材料压缩强度和pH值的显著变化。     

(iii) Wear in highly crosslinked polyethylenes

Because of its improved wear-resistance, crosslinked polyethylene is now regarded as a desirable technology for hip articulations. In the present review, we focus specifically on applications of crosslinked polyethylene in the hip. We begin with an overview of the basic science concepts and terminology surrounding crosslinked polyethylene and the two main thermal processing techniques, which involve either annealing or remelting the polymer after irradiative crosslinking. The second part of the review is a critical assessment of the peer-reviewed literature on the subject of femoral head penetration and wear in crosslinked polyethylenes measured in clinical studies.     

Analysis of cationic liposomes by reversed-phase HPLC with evaporative light-scattering detection

Cationic lipid-mediated drug delivery of small pharmaceutical molecules and biological molecules, such as proteins and DNA, has gained increasing popularity for many in vitro and in vivo applications. For this purpose, 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) is one of the most widely used and efficient cationic lipids. In this work, a simple and rapid reversed-phase HPLC method was developed for the simultaneous determination of cationic lipid DOTAP and neutral co-lipids cholesterol and phosphatidylcholine (DPPC or DSPC) as well as their degradation products in liposome-based drug formulations. Due to the poor UV absorbance of the lipids and their degradation products, an evaporative light-scattering detector (ELSD) was used to monitor the separation. The HPLC separation was achieved using a Phenomenex Luna C18 column at 50 °C by a linear gradient elution with methanol–water mobile phase at a flow rate of 2.0 mL/min. 0.1% (v/v) trifluoroacetic acid (TFA) was added into the mobile phase to enhance the retaining of the cationic lipid DOTAP. This newly developed method enabled direct analysis of liposomes without solvent lipid extraction, and was validated to be linear, precise, accurate, specific and sensitive. The limit of detection (LOD) and limit of quantitation (LOQ) were determined to be 0.15 and 0.30 μg, respectively, for all the four lipids. The method has been successfully employed in a wide range of lipid-based formulation screening, process development and stability testing. Studies of liposome samples under accelerated thermal conditions revealed that the hydrolysis of DOTAP, DPPC and DSPC followed pseudo-first-order kinetics.     

Mechanical and Biological Properties of a Biodegradable Mg‐Zn‐Ca Porous Alloy

Objectives

As promising alternative to current metallic biomaterials, the porous Mg scaffold with a 3‐D open‐pore framework has drawn much attention in recent years due to its suitable biodegradation, biocompatibility, and mechanical properties for human bones. This experiment's aim is to study the mechanical properties, biosafety, and osteogenesis of porous Mg‐Zn alloy.

Methods

A porous Mg‐2Zn‐0.3Ca (wt%) alloy was successfully prepared by infiltration casting, and the size of NaCl particles was detected by a laser particle size analyzer. The microstructure of the Mg‐2Zn‐0.3Ca alloy was characterized by the stereoscopic microscope and Sirion Field emission scanning electron microscope. X‐ray computerized tomography scanning (x‐CT) was used to create the 3‐D image. The degradation rate was measured using the mass loss method and the pH values were determined together. The engineering stress–strain curve, compressive modulus, and yield strength were tested next. The bone marrow stromal cells (BMSC) were cultured in vitro. The CCK‐8 method was used to detect the proliferation of the BMSC. Alkaline phosphatase (ALP) and alizarin red staining were used to reflect the differentiation effects. After co‐culturing, cell growth on the material's surface was observed by scanning electron microscope (SEM). The cell adhesion was tested by confocal microscopy.

Results

The obtained results showed that by using near‐spherical NaCl filling particles, the porous Mg alloy formed complete open‐cell foam with a very uniform size of pores in the range of 500–600 μm. Benefitting from the small size and uniform distribution of pores, the present porous alloy exhibited a very high porosity, up to 80%, and compressive yield strength up to 6.5 MPa. The degradation test showed that both the pH and the mass loss rate had similar change tendency, with a rapid rise in the early stage for 1–2 day's immersion and subsequently remaining smooth after 3 days. In vitro cytocompatibility trials demonstrated that in comparison with Ti, the porous alloy accelerated proliferation in 1, 3, 5, and 7 days (P < 0.001), and the osteogenic differentiation test showed that the ALP activity in the experimental group was significantly higher (P = 0.017) and has more osteogenesis nodules. Cell adhesion testing showed good osteoconductivity by more BMSC adhesion around the holes. The confocal microscopy results showed that cells in porous Mg‐based alloy had better cytoskeletal morphology and were larger in number than in titanium.

Conclusions

These results indicated that this porous Mg‐based alloy fabricated by infiltration casting shows great mechanical properties and biocompatibilities, and it has potential as an ideal bone tissue engineering scaffold material for bone regeneration.

     

Mitigating base-catalysed degradation of periodate-oxidized capsular polysaccharides: Conjugation by reductive amination in acidic media

Reductive amination coupling an aldehyde-containing polysaccharide, generated by periodate oxidation, with the amino groups in protein has been widely used in the synthesis of glycoconjugate vaccines. The conjugation is often achieved under slightly basic conditions via a Schiff’s base intermediate followed by its reduction with sodium cyanoborohydride. We observed that oxidized capsular polysaccharides such as Streptococcus pneumoniae type 6B (Pn-6B) and Haemophilus influenzae type a (HiA) underwent significant degradation during the conjugation in slightly basic media leading to sub-optimal glycoconjugates. Further study on oxidized Pn-3, Pn-6A, Pn-6C, Pn-2 polysaccharides and dextran provided evidence that the degradation is a result of base-catalysed β-elimination. In contrast to HiA, Pn-2, Pn-3, Pn-6B polysaccharides and dextran, oxidized Pn-6A and Pn-6C polysaccharides were stable under basic conditions due to lack of the leaving group at the β-position of the aldehyde. By performing conjugation of oxidized polysaccharides to bovine serum albumin (BSA) in phosphate buffer at pH 6.0, 6.8, 7.2 and 8.0, we concluded that the reductive amination proceeds best in slightly acidic media, particularly with those β-elimination susceptible polysaccharides.     

LC, LC-MS/TOF and MS(n) studies for the identification and characterization of degradation products of nelfinavir mesylate

The objective of the present investigation was to separate, identify and characterize the major degradation products (DPs) of nelfinavir mesylate generated under hydrolytic, oxidative, photolytic and thermal stress conditions as advised in International Conference on Harmonization (ICH) guideline Q1A(R2). The drug was found to degrade under acidic, basic, oxidative and photolytic stress, while it was stable in neutral and thermal stress conditions. A total of three degradation products were formed, which were separated on a C-18 column employing a gradient HPLC method. A complete mass fragmentation pathway of the drug was first established with the help of multi-stage (MS(n)) and MS/TOF accurate mass studies. Then stressed samples were subjected to LC-MS/TOF studies, which provided their fragmentation pattern and accurate masses. The mass spectral data were employed to characterize the DPs and assign structures to them. The total information was also used to establish the degradation pathway of the drug. The degradation products were identified as 3-hydroxy-N-((2R,3R)-3-hydroxy-1-(phenylthio)butan-2-yl)-2-methylbenzamide and (3S,4aS,8aS)-N-tert-butyl-2-((2R,3R)-2-hydroxy-3-(3-hydroxy-2-methylbenzamido)-4-(phenylsulfinyl)butyl)decahydroisoquinoline-3-carboxamide.     

周期蛋白D1降解调控的研究进展

细胞周期蛋白D1是细胞周期进程的重要调节因子,并且可以作为一个转录辅助调节因子发挥作用。细胞周期蛋白D1的过度表达参与癌症的发生和发展。解除细胞周期蛋白D1降解的调控将导致癌症中细胞周期蛋白D1水平升高。一些关于细胞周期蛋白D1稳定性的调控机制近来被研究发现。抑制细胞周期蛋白D1的表达对于癌症的预防与治疗有一定作用。     

Role of environmental fluctuations and microbial diversity in degradation of hydrocarbons in contaminated sludge

Little is known about microbial communities involved in hydrocarbon degradation, whether it be their structural and functional diversity or their response to environmental constraints such as oxygen fluctuation. Here, current knowledge of the impact of diversity and redox oscillations upon ecosystem processes is reviewed. In addition, we present the main conclusions of our studies in this field. Oxic/anoxic oscillations had a strong impact upon bacterial community structures, influencing their ability to degrade hydrocarbons and their capacity to reduce hydrocarbon toxicity. Furthermore, a decrease in functional diversity has a strong impact on pollutant degradation.