【作者】 徐巍；

【导师】 凌沛学；

【作者基本信息】 山东大学 ， 微生物与生化药学， 2014， 博士

【摘要】 氧气的供给往往是发酵过程中影响产物产率的一个限制因素,因此充足的氧供成为发酵稳定、产量提高和降低成本的关键。传统的供氧方法如增加通气量等存在着高耗能和对设备条件的要求苛刻等问题。20世纪70年代末透明颤菌(Vitreoscilla)中血红蛋白(Vitreoscilla Hemoglobin, VHb)的发现,促使血红蛋白基因工程走上舞台并对抗生素工业和其他药物发酵工业的发展起了巨大推动作用。将透明颤菌血红蛋白基因(Vitreoscilla Hemoglobin gene, vgb)通过基因工程的手段转入宿主细胞,构建工程菌,可以大大提高发酵菌株对氧的利用率,从而提高产量,节约成本。纳米技术是指利用单个原子、分子制造物质的科学技术,研究结构尺寸在0.1至100nm范围内材料的性质和应用。纳米药物是指运用纳米技术和纳米载体制备的一类药物新制剂。这其中,纳米胶束作为一种多功能纳米技术在难溶性药物的递送研究中获得了巨大的关注,其载药能力强、稳定性高、制备工艺简单、载体多样性、体内可降解、跨膜能力强及对抗肠道上皮p-糖蛋白等特点,被认为是未来提高难溶性药物口服生物利用度的主要研究方向。本研究通过对啦基因工程菌的构建、新型纳米载体材料的合成、纳米胶束的制备及体内外药学性质的考察等研究,为他克莫司原料和新剂型的开发研究及未来应用奠定基础。课题主要研究方法与结果如下。1Vgb基因工程菌的构建及vgb基因对他克莫司产量影响的研究首先,通过传统的紫外诱变技术初步提高筑波链霉菌(Streptomyces tsukubaensis)发酵产他克莫司的产量。紫外诱变条件为：孢子浓度为107～108CFU/mL,15W紫外灯管距离20cm照射100s,致死率可达90%以上。在此条件下,以白色念球菌为指示菌进行双层平板抑菌实验,并经HPLC最终测定他克莫司的量,获得两株正突变菌株,他克莫司产量最大提高量为27.7%。其次利用基因工程技术进一步提高他克莫司产量。PCR扩增vgb基因,构建含vgb基因的重组质粒,采用大肠杆菌-链霉菌属间接合转移的方式将重组质粒整合入链霉菌基因组中,获得重组vgb基因工程菌。经CO-差光谱分析法检测到重组菌株中表达的有活性的VHb,证实重组vgb基因筑波链霉菌的成功构建。与原始菌相比,插入vgb基因的重组菌株在控氧条件下发酵他克莫司产量提高了两倍。最后,对发酵培养基和发酵条件进行了优化。确定的发酵培养基为：葡萄糖25g/L,糊精80g/L,甘油10g/L,豆饼粉10g/L,大豆蛋白胨10g/L。通过对种龄与接种量的优化,确定了筑波链霉菌工程茵在种子培养基中生长20h,以2%的接种量接种发酵培养基为最佳条件。经过优化后的他克莫司产量最高可达127.78～130.31mg/L。这些结果为提高工业菌中他克莫司及其他抗生素产量提供了一个有效的策略。2他克莫司甲氧基聚乙二醇-聚乳酸纳米胶束的制备、表征及体外释放行为研究以辛酸亚锡为催化剂,由丙交酯和单甲氧基聚乙二醇通过开环聚合反应合成了不同嵌段比的两亲性二嵌段聚合物甲氧基聚乙二醇-聚乳酸(MPEG-PLA),经过筛选,嵌段比为1：1的甲氧基聚乙二醇-聚乳酸(MPEG5000-PLA5000)共聚物装载他克莫司所形成的纳米胶束效果最佳。选择乳液溶剂去除法制备纳米胶束,并采用均匀设计-效应面法优化处方及工艺,确定最优处方为：4.5%的MPEG-PLA的四氢呋喃溶液作为有机相,他克莫司的投药量为5mg,油/水比例1：20。优化后制得纳米胶束呈球形外观,符合核-壳结构的特征。平均粒径为90.5nm,分散均匀(PDI=0.100±0.023),载药量达到9.5%,包封率98.8%。体外释放结果显示,他克莫司纳米胶束具有明显的缓释特性,对体外释放数据进行数学模型拟合,符合Higuchi方程,其相关系数最大为0.9992。体外安全性实验显示,当MPEG5000-PLA5000载体材料浓度为1000μg/mL时,HEK293细胞存活率达到70%以上,说明该载体材料安全性较好,不会对机体产生毒性。3他克莫司甲氧基聚乙二醇-聚乳酸纳米胶束大鼠体内药动学及肝移植大鼠体内药效学研究以上市他克莫司胶囊为对照,研究了他克莫司纳米胶束大鼠体内的药动学规律,建立肝移植大鼠模型,并进行了肝移植大鼠药效学研究。他克莫司纳米胶束大鼠体内的药动学结果显示,与口服他克莫司胶囊相比,他克莫司纳米胶束给药后吸收速度更快,Tmax由3h提前至1h,半衰期和平均滞留时间均延长,分别由13.698h和23.593h延长至16.573h和24.044h,生物利用度明显提升,药-时曲线下面积由508.251ng/mL-h提高至886.703ng/mL-h。本研究实现了纳米胶束增强吸收、提高生物利用度和缓释的作用。肝移植大鼠体内药效学研究结果显示,他克莫司纳米胶束组能更好地延长肝移植大鼠的生存期。移植后大鼠给予他克莫司纳米胶束后谷丙转氨酶和总胆红素水平明显低于对照组；肝脏病理图片结果表明,他克莫司纳米胶束能够更好地对抗排斥反应所造成的肝损伤,起到肝脏保护作用。综上所述,本研究构建的vgb基因筑波链霉菌工程菌能够显著改善发酵过程中因溶氧低造成的他克莫司产量低的问题,为提高他克莫司产量提供了新的思路。所制备的他克莫司纳米胶束具有制备工艺简单、粒径分布均匀、载药量高、稳定性好、吸收迅速、释药缓慢、生物利用度高、生物相容性好等特点,为提高难溶性药物口服生物利用度提供了一种新思路、新工具和和新手段。更多还原

【Abstract】 The supply of oxygen is a limiting factor in the production of fermentation products. Adequate oxygen supply is the key of stabilizing the fermentation, increasing the output and decreasing the cost. Traditional oxygen supply methods, such as increasing ventilation, demand high energy-consuming and expensive equipment. In the late1970s, the finding of Vitreoscilla hemoglobin (VHb) promoted the development of industrial fermentation of antibiotics and other drugs. The transfer of Vitreoscilla hemoglobin gene (vgb) into the host cell by means of genetic engineering can greatly improve the utilization of oxygen, and thereby enhancing the yield and saving the cost.Nanotechnology is the technology using individual atom or molecule to prepare materials with the structural dimensions in the range of0.1to100nanometers and study the quality and application of the materials. Nanomedicine is a new class of drug formulations prepared by nanotechnology and nano-carrier, among of which, nano-micelle has drawn great concern in the delivery of insoluble drugs. Micelles have the characteristics of high drug loading, high stability, simple preparation process, diversity carrier, degradation in vivo, strong transmembrane ability and antagonizing epithelial intestinal p-glycoprotein, etc. It is considered to be the main research direction of improving the oral bioavailability of poorly soluble drugs in the future.In this study, we have constructed one kind of genetically engineered tacrolimus producing bacteria with vgb, synthesized a novel nano-carrier material, prepared nano-micelles and studied it’s pharmacological properties. All of these results layed a foundation for the development of materials and new formulations, as well as the future applications of tacrolimus. The main research methods and results are as follows.1Construction of genetically engineered bacteria with vgb and the influence of vgb on the yield of tacrolimusFirstly, the production of tacrolimus by Streptomyces tsukubaensis was improved by conventional UV mutagenesis techniques. The UV mutagenesis conditions are: spore concentration of107～108CFU/mL, UV irradiation using a15W UV lamp for100s in a distance of20cm, and the lethality over90%. Canidia albicans was used as the indicator in double-layer plate bacterial inhibition test and HPLC was used to determine the yield of tacrolimus. We obtained two positive mutation strains, one of which could increase the yield of tacrolimus by27.7%. Then, the vgb gene was integrated into the genome of the tacrolimus-producing strains to further improve the yield of tacrolimus. The vgb gene, encoding VHb, was integrated into the chromosome of Streptomyces tsukubaensis to alleviate oxygen limitation and enhance the yield of tacrolimus. The VHb-specific spectrum was observed for the recombinant strain by CO-difference spectrum analysis. Compared to the original, the yield of tacrolimus produced by the strain bearing vgb increased2.0-fold under oxygen-limited condition. Last, the fermentation medium and conditions were optimized. The optimal fermentation medium consisted of glucose25g/L, dextrin80g/L, soybean meal10g/L, soya peptone10g/L, and glycerol10g/L. Based on the optimal fermentation medium, the seed age and inoculation amount were optimized as: seed age of20h and inoculation amount of2%. Under this conditions, the production of tacrolimus could reach to127.78-130.31mg/L. These results provide an effective strategy for improving the yield of tacrolimus and other antibiotics production.2Preparation, characterization and in vitro release study of MPEG-PLA/FK506micellesThe MPEG-PLA copolymers with different block ratios were synthesized via a ring opening polymerization of D, L-lactide (LA) initiated by MPEG using stannous octoate as the catalyst. After screening, the copolymer MPEG5000-PLA5000with the block ratio of1:1was found to be the best one which could form better micelles than other coploymers after loading tacrolimus. Tacrolimus was encapsulated into MPEG-PLA block copolymer using a double emulsion-solvent evaporation technique. The formula and process were optimized with homogeneous design-response surface methodology. The best formula is4.5%MPEG-PLA tetrahydrofuran solution as the organic phase,5mg of tacrolimus, and oil/water ratio of1:20. The micelles were spherical appearance, in line with core-shell structure. The micelles were monodisperse (PDI=0.100±0.023) with a mean particle size of90.5±.5nm, drug loading of9.5%and encapsulation efficiency of98.8%. Compared with FK506capsule, in vitro release profile showed that FK506/MPEG-PLA nanoparticles exhibited sustained release in the Higuchi equation, mathematical model, with the correlation coefficient up to0.9992. In vitro experiments showed that HEK293cell viability was over70%with MPEG5000-PLA5000’s concentration of1000μg/mL, indicating that the carrier material was safe and no toxic to the body.3Pharmacokinetics study in mouse and pharmacodynamic study in liver transplantation rat of MPEG-PLA/FK506micellesUsing FK506capsules as the control, we studied the pharmacokinetics of MPEG-PLA/FK506micelles in rats, established rat liver transplantation model, and carried out the pharmacodynamic study. Compared with oral FK506capsules, MPEG-PLA/FK506micelles showed faster absorption and better bioavailability. The Tmax shifted from3h to1h. The half-life was prolonged from13.698h to16.573h, the mean residence time were prolonged from23.593h to24.044h, and the AUC increased from508.251ng/mL-h to886.703ng/mL·h. All of these results proved the action of enhanced absorption, improved bioavailability and sustained release of micelles. MPEG-PLA/FK506micelles could prolong the survival time of liver transplantation rats. Compared with control, rats administered with MPEG-PLA/FK506micelles had a lower aminotransferase and bilirubin level. The liver pathology results showed that MPEG-PLA/FK506micelles were better able to fight against liver damage caused by rejection reaction and play a better liver protective effect. In summary, the constructed genetically engineered Streptomyces tsukubaensis with vgb can significantly improve low dissolved oxygen in the fermentation process, and provides a new way for improving the yield of FK506. The MPEG-PLA/FK506have the characteristics of simple preparation process, uniform particle size distribution, high drug loading, stableness, rapid absorption, sustained release, high bioavailability and good biocompatibility. So, it provides a new strategy and new method for enhancing the oral bioavailability of poorly soluble drugs.更多还原