Cysteine 467 of the ASCT2 Amino Acid Transporter Is a Molecular Determinant of the Antiport Mechanism

The plasma membrane transporter ASCT2 is a well-known Na⁺-dependent obligatory antiporter of neutral amino acids. The crucial role of the residue C467 in the recognition and binding of the ASCT2 substrate glutamine, has been highlighted by structure/function relationship studies. The reconstitution in proteoliposomes of the human ASCT2 produced in P. pastoris is here employed to unveil another role of the C467 residue in the transport reaction. Indeed, the site-directed mutant C467A displayed a novel property of the transporter, i.e., the ability of mediating a low but measurable unidirectional transport of [³H]-glutamine. This reaction conforms to the main features of the ASCT2-mediated transport, namely the Na⁺-dependence, the pH dependence, the stimulation by cholesterol included in the proteoliposome membrane, and the specific inhibition by other common substrates of the reconstituted human ASCT2. Interestingly, the WT protein cannot catalyze the unidirectional transport of [³H]-glutamine, demonstrating an unspecific phenomenon. This difference is in favor of a structural conformational change between a WT and C467A mutant that triggers the appearance of the unidirectional flux; this feature has been investigated by comparing the available 3D structures in two different conformations, and two homology models built on the basis of hEAAT1 and GLT_Ph.     

共递送姜黄素和EGCG脂质体的构建及其对神经炎症的作用

为克服姜黄素和表没食子儿茶素没食子酸酯(EGCG)两种生物活性成分在稳定性和代谢动力学方面的局限性,进一步发挥其协同抗氧化和抗炎作用,采用薄膜超声法构建共递送姜黄素和EGCG的脂质体。以粒径、PDI和电位为评价指标,分析磷脂与胆固醇质量比、磷脂与吐温80质量比、水合时间及超声时间对脂质体的影响,并通过静电吸附作用对脂质体进行乳铁蛋白和透明质酸修饰。使用脂多糖构建BV2小胶质细胞炎症模型,探讨乳铁蛋白和透明质酸修饰的共递送姜黄素和EGCG的脂质体对神经炎症的改善作用。在磷脂与胆固醇质量比为10∶1,磷脂和吐温80质量比为10∶3,水合时间40min,以及超声时间15min时,成功制备了呈均匀球形、平均粒径为(131.53±0.258)nm的共递送姜黄素和EGCG的脂质体,在乳铁蛋白体积为0.3mL,透明质酸体积为0.5mL时对脂质体进行修饰。实验结果显示,乳铁蛋白和透明质酸修饰的共递送姜黄素和EGCG的脂质体显著提高了姜黄素和EGCG的稳定性和抗氧化特性,抑制了脂多糖诱导的细胞形态的改变,恢复线粒体功能障碍,降低细胞内活性氧的产生,改善了脂多糖诱导的BV2小胶质细胞的炎症作用。研究结果旨在为进一步开发具有神经保护作用的功能食品提供新的思路。     

Controlled Liposome Delivery from Chitosan-Based Thermosensitive Hydrogel for Regenerative Medicine

This work describes the development of an injectable nanocomposite system based on a chitosan thermosensitive hydrogel combined with liposomes for regenerative medicine applications. Liposomes with good physicochemical properties are prepared and embedded within the chitosan network. The resulting nanocomposite hydrogel is able to provide a controlled release of the content from liposomes, which are able to interact with cells and be internalized. The cellular uptake is enhanced by the presence of a chitosan coating, and cells incubated with liposomes embedded within thermosensitive hydrogels displayed a higher cell uptake compared to cells incubated with liposomes alone. Furthermore, the gelation temperature of the system resulted to be equal to 32.6 °C; thus, the system can be easily injected in the target site to form a hydrogel at physiological temperature. Given the peculiar performance of the selected systems, the resulting thermosensitive hydrogels are a versatile platform and display potential applications as controlled delivery systems of liposomes for tissue regeneration.     

脂质体载药系统经皮给药的研究进展

脂质体是一类具有特殊性质的磷脂，近几年已开始被广泛用作多种药物的载体。药物经皮给药系统是药剂学中的一新兴的领域，通过脂质体包埋技术制备的各种经皮给药系统同样在我国的制药和化妆品行业得到广泛应用。通过对脂质体的组成及一般特性、脂质体载药系统经皮给药的药剂学促透机制和最新的基础实验和应用研究进展的综合分析后显示，脂质体包裹技术在国内相关领域中的应用将具广阔的前景。     

Antioxidant activity of green teas in different lipid systems

Different commercial green teas from Japan, China, and India, were compared in different lipid systems. Green teas were active antioxidants in bulk corn oil oxidized at 50°C but were prooxidant in the corresponding oil-in-water emulsions. Green teas also were active antioxidants in soybean lecithin liposomes oxidized at 37°C in the presence of cupric acetate as catalyst. At 50°C, however, three of the samples of green tea were active antioxidants in the absence of copper catalyst, and two samples showed prooxidant activity in the presence of copper catalyst. The marked variation in activity among green tea samples may be due partly to differences in their relative partition between phases in different lipid systems. The improved antioxidant activity observed for green teas in lecithin liposomes compared to corn oil emulsions can be explained by the greater affinity of the polar tea catechin gallates for the polar surface of the lecithin bilayers, thus affording better protection against oxidation. Liposomes may thus be appropriate lipid models to evaluate antioxidants for foods containing phospholipids.     

聚乙烯醇包覆的果酸脂质体的制备及性质研究

用聚乙烯醇(PVA)包覆脂质体来提高脂质体的稳定性。先用反相蒸发法制备果酸脂质体，然后将PVA溶液与果酸脂质体混合即可制得PVA包覆的脂质体。电镜照片与粒径证明PVA在脂质体外形成了一层膜。相比较于未包覆的脂质体，PVA包覆的脂质体的包封率和粒径都有所增加，泄漏率降低，其包封率随果酸质量浓度的增加而增加，泄漏率随时间和果酸／脂质体质量比的增加而增加，但低于未包覆的脂质体。通过测定粒径和泄漏率的变化说明包覆PVA的脂质体要比未包覆的稳定。     

薄膜蒸发-冷冻干燥法制备乳糖酶脂质体

以蛋黄卵磷脂和胆固醇为膜材,采用薄膜蒸发-冷冻干燥法制备乳糖酶脂质体。以包埋率为指标,通过单因素试验研究制备工艺,并研究其形态、粒径分布和红外光谱性质。最佳工艺参数为:蛋黄卵磷脂与胆固醇摩尔比为2︰1,乳糖酶的添加量为150 U,海藻糖与脂质质量比为4︰1,磷酸盐缓冲液pH6.8,包埋率可达到28%以上;乳糖酶脂质体在电镜下呈球状或近似球状的小囊泡;平均粒径为463.18±5.09 nm;红外光谱分析表明海藻糖可与脂质体磷脂C=O基团形成氢键。     

DHA脂质体的制备及其性质研究

以大豆卵磷脂、胆固醇为膜材,采用薄膜蒸发、逆相蒸发和薄膜蒸发-冷冻干燥三种方法制备了DHA脂质体,研究不同方法制备的DHA脂质体的可行性与稳定性。通过对DHA脂质体的包埋率、粒径、ζ-电位和DSC曲线进行研究,得出薄膜蒸发-冷冻干燥法制备的DHA脂质体包埋率可达到53.33%;粒径小,平均粒径在1～2μm之间;DSC曲线表明有良好的结合性。因此,采用薄膜蒸发-冷冻干燥法制备DHA脂质体具有可行性。     

Altered plasma and brain disposition of isopropylidene shikimic acid liposome in rats and the brain protection in cerebral ischemia–reperfusion

Context: Cerebral ischemia–reperfusion (I/R) injury is a secondary injury caused by oxidative stresses and inflammatory responses after recovery from cerebral ischemia. Brain protective drugs were used to reduce the injury. In order to improve the distribution in brain and enhance the brain-protective efficacy, some pharmaceutical technologies were used to achieve brain targeting delivery.

Objective: To investigate the physiological disposition of ISA liposome, and provide references for the further study about high-efficacy brain-protective preparations for I/R injury.

Materials and methods: Comparative studies were carried out. The pharmacodynamics in t-MCAO model rats were studied first, and then the pharmacokinetics and brain distribution of the two preparations were determined.

Results: At the same dose, the efficacy of ISA liposome was better (P < 0.05). The efficacy was dose dependent, with significant difference of 20?mg/kg (P < 0.01) and indistinctive difference of 10?mg/kg (P = 0.22), compared with vehicle-treated rats. The parameters, T_1/2β, MRT and AUC were different significantly between the two preparations. The enhancement of brain distribution for ISA in the liposome was obvious, with the maximum concentration 7.18 μg/g, while close to zero for the solution group.

Discussion and conclusion: ISA liposome could increase the distribution in brain and enhance the efficacy significantly. The results revealed that the liposomal DDS was potential as a novel strategy for the treatment of cerebral I/R injury. In addition, further targeted modification, such as PEG-modified liposomes, which possess a long circulating property in the bloodstream, would further improve the targeting delivery to the brain and lead to more significant efficacy.     

聚乙烯醇脂质体的制备及性能研究

以大豆卵磷脂为包封材料,用反相蒸发法制备脂质体,同时用不同浓度的聚乙烯醇(PVA)进行包覆。实验结果表明,PVA在脂质体外形成了一层膜,而且包覆量随其浓度的增加而增加。相比较于未包覆的脂质体,PVA包覆的脂质体具有较高的包封率和较小的泄露率。当ρ(PVA)=3g/L时,脂质体的包封率最高为58%,当ρ(PVA)=4g/L时,脂质体的泄漏最慢。