Department of Thoracic Surgery, Daping Hospital and Research Institute of Surgery, Third Military Medical University, Chongqing 400042, China.
Int J Pharm. 2010 Jan 15;384(1-2):165-72. doi: 10.1016/j.ijpharm.2009.09.036. Epub 2009 Sep 25.
Uricase-containing lipid vesicles (UOXLVs) were prepared by reverse-phase evaporation method with high efficiency and the characteristics of UOXLVs were described. The average size and zeta potential of UOXLVs obtained by the optimized formulation were 205.47 nm and -37.33 mV, respectively. Uricase was encapsulated in the alkaline aqueous phase of the lipid vesicle and the stability of its tetrameric structure was thus improved and its activity preserved. The storage stability of uricase in lipid vesicles was significantly increased compared to that of free uricase at 4 degrees C in borate buffer of pH 8.5. At 55 degrees C, free uricase was deactivated much more quickly especially at lower concentration predominantly due to enhanced dissociation of uricase into subunits. An intrinsic tryptophan of uricase recovered from the lipid vesicle thermally treated at 55 degrees C revealed that a partially denatured uricase molecule was stabilized through its hydrophobic interaction with lipid vesicle membrane. This interaction was depressed mainly by dissociation of uricase into subunits. At the physiological pH, significant increase of enzyme activity was found for the uricase entrapped in the lipid vesicles (1.8 times that of free uricase) at their respective optimum pH. The shift of optimum pH and increased uricolytic activity suggested the conformation change of the uricase during the entrapment process. The stability to proteolytic digestion was increased obviously by entrapping the uricase in the lipid vesicles. UOXLVs also showed relatively slower loss in activity compared with free uricase when treated with some chemical reagents. Lastly, in vitro study explicitly indicated that the uricase entrapped by UOXLVs possessed higher uricolytic activity than that of native uricase solution.
载尿酸酶脂质体（UOXLVs）通过反相蒸发法高效制备，并对其特性进行了描述。通过优化的配方获得的 UOXLVs 的平均粒径和 zeta 电位分别为 205.47nm 和-37.33mV。尿酸酶被包裹在脂质体的碱性水相中，从而提高了其四聚体结构的稳定性并保持了其活性。与游离尿酸酶相比，尿酸酶在脂质体中的储存稳定性在 4°C 下显著提高，在硼酸盐缓冲液 pH8.5 中。在 55°C 下，游离尿酸酶失活速度明显加快，尤其是在较低浓度下，主要是由于尿酸酶更容易解离成亚基。从在 55°C 热处理的脂质体中回收的尿酸酶的固有色氨酸表明，部分变性的尿酸酶分子通过与脂质体膜的疏水相互作用得到稳定。这种相互作用主要通过尿酸酶解离成亚基而被抑制。在生理 pH 下，与游离尿酸酶相比，包封在脂质体中的尿酸酶（比游离尿酸酶高 1.8 倍）在各自的最适 pH 下，酶活性显著增加。最适 pH 的偏移和尿酸酶活性的增加表明尿酸酶在包封过程中构象发生了变化。将尿酸酶包封在脂质体中可明显提高其对蛋白水解酶的消化稳定性。与游离尿酸酶相比，UOXLVs 处理一些化学试剂时，其活性损失也相对较慢。最后，体外研究明确表明，与天然尿酸酶溶液相比，包封在 UOXLVs 中的尿酸酶具有更高的尿酸酶活性。
