Evaluation of the Dehydration-Rehydration Method for Production of Contrast-Carrying Liposomes

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Abstract
We measured the amounts of three types of radiographic contrst media (RCM) that could be entrapped in liposomes prepared by the dehydration-rehydration vesicle (DRV) technique. To make DRVs, one initially makes water-containing, small unilamellar vesicles, adds contrast media and lyophilizes the mixture. Upon rehydration, the DRVs re-form, passively entrapping RCM. Diatrizoate, iohexol and iotrolan proved to be entrappable in similar amounts (diatrizoate was best), but all of these amounts were less than for other small molecules, such as carboxyfluorescein (P < 0.05). Entrapment was directly proportional to lipid concentration (r = 0.76; P < 0.002), and inversely related to iodine concentration (r = - 0.86; P < 0.002). Under ideal conditions with neutral lipids, 19.45 .+-. 9.9% of diatrizoate was entrapped, corresponding to 1.05 .+-. 0.50 g I per g lipid. These values are close to those achievable for large unilamellar vesicles. Use of an automated mixing device (the Microfluidizer) in place of sonication, facilitated production of large liposome batches and improved entrapment (P < 0.05). Computed tomography (CT) scans of rats showed 30 and 218HU of liver and spleen enhancement, respectively, per g I/kg injected DRVs. These studies showed this method (possibly augmented by the Microfluidizer) allows efficient production of contrast-carrying liposomes.