Structural and Biochemical Characterization of Compounds Inhibiting Mycobacterium tuberculosis Pantothenate Kinase

Mycobacterium tuberculosis, the bacterial causative agent of tuberculosis, currently affects millions of people. The emergence of drug-resistant strains makes development of new antibiotics targeting the bacterium a global health priority. Pantothenate kinase, a key enzyme in the universal biosynthesis of the essential cofactor CoA, was targeted in this study to find new tuberculosis drugs. The biochemical characterizations of two new classes of compounds that inhibit pantothenate kinase from M. tuberculosis are described, along with crystal structures of their enzyme-inhibitor complexes. These represent the first crystal structures of this enzyme with engineered inhibitors. Both classes of compounds bind in the active site of the enzyme, overlapping with the binding sites of the natural substrate and product, pantothenate and phosphopantothenate, respectively. One class of compounds also interferes with binding of the cofactor ATP. The complexes were crystallized in two crystal forms, one of which is in a new space group for this enzyme and diffracts to the highest resolution reported for any pantothenate kinase structure. These two crystal forms allowed, for the first time, modeling of the cofactor-binding loop in both open and closed conformations. The structures also show a binding mode of ATP different from that previously reported for the M. tuberculosis enzyme but similar to that in the pantothenate kinases of other organisms.     

Optimization of prednisolone-loaded long-circulating liposomes via application of Quality by Design (QbD) approach

Quality by design principles (QbD) were used to assist the formulation of prednisolone-loaded long-circulating liposomes (LCL-PLP) in order to gain a more comprehensive understanding of the preparation process. This approach enables us to improve the final product quality in terms of liposomal drug concentration, encapsulation efficiency and size, and to minimize preparation variability. A 19-run D-optimal experimental design was used to study the impact of the highest risk factors on PLP liposomal concentration (Y₁- μg/ml), encapsulation efficiency (Y₂-%) and size (Y₃-nm). Out of six investigated factors, four of them were identified as critical parameters affecting the studied responses. PLP molar concentration and the molar ratio of DPPC to MPEG-2000-DSPE had a positive impact on both Y₁ and Y₂, while the rotation speed at the formation of the lipid film had a negative impact. Y₃ was highly influenced by prednisolone molar concentration and extrusion temperature. The accuracy and robustness of the model was further on confirmed. The developed model was used to optimize the formulation of LCL-PLP for efficient accumulation of the drug to tumor tissue. The cytotoxicity of the optimized LCL-PLP on C26 murine colon carcinoma cells was assessed. LCL-PLP exerted significant anti-angiogenic and anti-inflammatory effects on M2 macrophages, affecting indirectly the C26 colon carcinoma cell proliferation and development.     

Comparing methods for metabolic network analysis and an application to metabolic engineering

Bioinformatics tools have facilitated the reconstruction and analysis of cellular metabolism of various organisms based on information encoded in their genomes. Characterization of cellular metabolism is useful to understand the phenotypic capabilities of these organisms. It has been done quantitatively through the analysis of pathway operations. There are several in silico approaches for analyzing metabolic networks, including structural and stoichiometric analysis, metabolic flux analysis, metabolic control analysis, and several kinetic modeling based analyses. They can serve as a virtual laboratory to give insights into basic principles of cellular functions. This article summarizes the progress and advances in software and algorithm development for metabolic network analysis, along with their applications relevant to cellular physiology, and metabolic engineering with an emphasis on microbial strain optimization. Moreover, it provides a detailed comparative analysis of existing approaches under different categories.     

苦丁茶防晒组分萃取工艺的可视化分析

对采用超声辅助法萃取苦丁茶防晒组分进行了较为系统的研究。选择萃取时间、萃取剂体积分数、萃取温度、样品细度4个主要影响因素,运用多因素多水平可视化设计法安排实验。以防晒光区的紫外吸收面积值作为防晒组分萃取含量的实验评定指标。用自主提出的多因素多水平实验结果可视化分析方法对多维空间实验数据进行分析。得出当ρ(苦丁茶)=0.20 g/L时,最佳工艺范围为萃取时间30～60 min、萃取剂体积分数φ(C2H5OH)为50%～70%、萃取温度50～65℃、萃取样品细度140～160目。     

Ethical Research Issues: Going Beyond the Declaration of Helsinki

La Vaque and Rossiter made a strong, supported argument that it is unethical to use a no treatment control group in a research study if a known, effective treatment is available. Their argument is based on the supposition that the Declaration of Helsinki is the ethical world standard for research with humans. Their argument appears to be straightforward, but is not simple to apply. The issues are very complex, include issues not discussed in their argument, and can lead to a different conclusion as pointed out in this paper. The World Medical Association developed the Declaration of Helsinki as one of their official policies. The Declaration of Helsinki, however, is not accepted as the world ethical standard, as demonstrated by its lack of adoption by many professional associations or even by the United States Federal Government. Perhaps it is not mentioned because its ethical provisions are aspirational rather than mandatory as implied by La Vaque and Rossiter. Researchers and clinicians should also be aware of other ethical issues not directly discussed in the La Vaque and Rossiter paper. The Belmont Report is the basis for the ethical protection of human research subjects for at least 17 federal agencies and does not mention the Declaration of Helsinki. The Belmont Report mentions several ethical principles that form the basis for informed consent, risk/benefit assessment, confidentiality of data, subject selection, Institutional Review Boards, and other protections needed when doing research with human subjects. At least 2 of these core principles have direct implications to the discussion related to the use of placebo controls. The ethical principle of fidelity is also important in guiding research activities with human subjects. Researchers should be familiar with the La Vaque and Rossiter argument, the Belmont Report, and the federal policies developed to implement the provisions of that report, for example, Regulation 45 CFR 46.