Huang Shao-Ling, McPherson David D, Macdonald Robert C
Department of Internal Medicine, Division of Cardiology, University of Texas Medical Science Center at Houston, Houston, TX, USA.
Ultrasound Med Biol. 2008 Aug;34(8):1272-80. doi: 10.1016/j.ultrasmedbio.2008.01.005. Epub 2008 Apr 14.
We describe a novel method for the facile production of gas-containing liposomes with simultaneous drug encapsulation. Liposomes of phospholipid and cholesterol were prepared by conventional procedures of hydrating the lipid film, sonicating, freezing and thawing. A single but critical modification of this procedure generates liposomes that contain gas (air, perfluorocarbon, argon); after sonication, the lipid is placed under pressure with the gas of interest. After equilibration, the sample is frozen. The pressure is then reduced to atmospheric and the suspension thawed. This procedure leads to entrapment of air in amounts up to 10% by volume in lipid dispersions at moderate (10 mg/mL) concentrations of lipids. The amount of gas encapsulated increases with gas pressure and lipid concentration. Using 0.32 mol/L mannitol to provide an aqueous phase with physiological osmolarity, 1, 3, 6 or 9 atm of pressure was applied to 4 mg of lipid. This led to encapsulation of 10, 15, 20 and 30 microl of gas in a total of 400 microl of liposome dispersion (10 mg lipids/mL), respectively. The mechanism for gas encapsulation presumably depends on the fact that air (predominantly nitrogen and oxygen), like most solutes, dissolves poorly in ice and is excluded from the ice that forms during freezing. The excluded air then comes out of solution as air pockets that are stabilized in some form by a lipid coating. The presence of air in these preparations sensitizes them to ultrasound (1MHz, 8 W/cm2,10 s) such that up to half of their aqueous contents (which could be a water soluble drug) can be released by short (10 s) applications of ultrasound. Both diagnostic and therapeutic applications of the method are conceivable.
我们描述了一种简便的方法来制备同时包载药物的含气脂质体。通过水合脂质膜、超声处理、冷冻和解冻的常规程序制备磷脂和胆固醇脂质体。对该程序进行一个关键的单一修改即可生成含气（空气、全氟化碳、氩气）的脂质体；超声处理后，将脂质置于感兴趣的气体压力下。平衡后，将样品冷冻。然后将压力降至大气压并解冻悬浮液。该程序导致在脂质浓度适中（10 mg/mL）的脂质分散体中截留体积分数高达10%的空气。包封的气体量随气体压力和脂质浓度的增加而增加。使用0.32 mol/L甘露醇提供具有生理渗透压的水相，对4 mg脂质施加1、3、6或9个大气压的压力。这分别导致在总共400 μL脂质体分散体（10 mg脂质/mL）中包封10、15、20和30 μL气体。气体包封的机制可能取决于这样一个事实，即空气（主要是氮气和氧气）与大多数溶质一样，在冰中溶解性很差，并在冷冻过程中形成的冰中被排除。被排除的空气然后以气泡形式从溶液中逸出，并通过脂质涂层以某种形式稳定下来。这些制剂中空气的存在使它们对超声（1MHz，8 W/cm2，10 s）敏感，以至于通过短时间（10 s）的超声处理可以释放高达一半的水相内容物（可以是水溶性药物）。该方法的诊断和治疗应用都是可以想象的。
