Improving ultrasound reflectivity and stability of echogenic liposomal dispersions for use as targeted ultrasound contrast agents.

Targeted echogenic liposome dispersions for ultrasonic enhancement of vasoactive and pathological components of endothelium and atherosclerosis have recently been developed. The component lipids required for acoustic and targeting properties include phosphatidylcholine, phosphatidylethanolamine phosphatidylglycerol (PG), and cholesterol (CH), initially in a 60:8:2:30 mol % ratio. Component lipids, lyophilization, sugars, and freezing conditions were varied to optimize acoustic ultrasound reflectivity and acoustic stability. Echogenic liposome dispersions were made by using the dehydration-rehydration process. The lipid concentrations were varied (CH in the range 1 to 40 mol % and PG from 1 to 16 mol %). Variations in type and concentration of sugars were examined. The effect of freezing conditions and re-lyophilization was examined. Ultrasound reflectivity was assessed by using a 20-MHz intravascular ultrasound catheter and computer-assisted videodensitometry. Ultrasound reflectivity was optimized at a CH concentration of 10 mol %; PG concentration variation had essentially no effect on initial values of echogenicity. Optimal acoustic stability was observed with concentrations of 10-15 mol % CH and with a PG concentration greater than 4 mol %. Preparations made with 0.2 M mannitol were more ultrasound reflective than those made with lactose, trehalose, and sucrose. Re-lyophilization and freezing temperatures below -20 degrees C increased ultrasound reflectivity. We optimized the ultrasound properties of echogenic liposomal dispersions, the conditions of which provide some insight into the underlying lipid structures responsible. The preparations developed are now more stable and acoustically reflective than our previous preparations. This advances the development of echogenic lipid dispersions as targeted ultrasound contrast agents for use in general ultrasound as well as cardiovascular imaging.

[1]  R. Macdonald,et al.  Relationship between turbidity of lipid vesicle suspensions and particle size. , 2001, Analytical biochemistry.

[2]  H. Kikuchi,et al.  Gene delivery using liposome technology. , 1999, Journal of controlled release : official journal of the Controlled Release Society.

[3]  K. Taylor,et al.  Factors affecting the size distribution of liposomes produced by freeze-thaw extrusion. , 1999, International journal of pharmaceutics.

[4]  J Szebeni,et al.  Hemodynamic changes induced by liposomes and liposome-encapsulated hemoglobin in pigs: a model for pseudoallergic cardiopulmonary reactions to liposomes. Role of complement and inhibition by soluble CR1 and anti-C5a antibody. , 1999, Circulation.

[5]  U. Sleytr,et al.  Stabilizing effect of an S-layer on liposomes towards thermal or mechanical stress. , 1999, Biochimica et biophysica acta.

[6]  D. McPherson,et al.  In vivo targeting of acoustically reflective liposomes for intravascular and transvascular ultrasonic enhancement. , 1999, Journal of the American College of Cardiology.

[7]  S. Risbud,et al.  Effect of sugars on headgroup mobility in freeze-dried dipalmitoylphosphatidylcholine bilayers: solid-state 31P NMR and FTIR studies. , 1998, Biophysical journal.

[8]  M. Taskinen,et al.  Aggregation of dimyristoylphosphatidylglycerol liposomes by human plasma low density lipoprotein. , 1998, Biochimica et biophysica acta.

[9]  T. Hianik,et al.  Cholesterol-induced variations in the volume and enthalpy fluctuations of lipid bilayers. , 1998, Biophysical journal.

[10]  David D Spragg,et al.  Immunotargeting of liposomes to activated vascular endothelial cells: a strategy for site-selective delivery in the cardiovascular system. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[11]  D. McPherson,et al.  In vitro targeting of antibody-conjugated echogenic liposomes for site-specific ultrasonic image enhancement. , 1997, Journal of pharmaceutical sciences.

[12]  J. Kuszak,et al.  Development of inherently echogenic liposomes as an ultrasonic contrast agent. , 1996, Journal of pharmaceutical sciences.

[13]  D. Crommelin,et al.  Adhesion molecules: a new target for immunoliposome‐mediated drug delivery , 1995, FEBS letters.

[14]  K. Morris,et al.  Dielectric characterization of thermodynamic first order events in model frozen systems intended for lyophilization. , 1995, PDA journal of pharmaceutical science and technology.

[15]  R. Waugh,et al.  Bending rigidity of SOPC membranes containing cholesterol. , 1993, Biophysical journal.

[16]  D. Goldstein,et al.  Advances in drug delivery and targeting , 1991, Current opinion in oncology.

[17]  P. Kinnunen,et al.  Cation-induced aggregation of acidic phospholipid vesicles: the role of fatty acid unsaturation and cholesterol. , 1991, Chemistry and physics of lipids.

[18]  R. Macdonald.  Surface chemistry of phospholipid vesicles relevant to their aggregation and fusion. , 1990, Hepatology.

[19]  R. K. Zee-Cheng,et al.  Delivery of anticancer drugs. , 1989, Methods and findings in experimental and clinical pharmacology.

[20]  E. Evans,et al.  Thermomechanical and transition properties of dimyristoylphosphatidylcholine/cholesterol bilayers. , 1988, Biochemistry.

[21]  T. Yotsuyanagi,et al.  Effect of cholesterol on liposome stability to ultrasonic disintegration and sodium cholate solubilization. , 1987, Chemical & pharmaceutical bulletin.

[22]  J. Carpenter,et al.  Stabilization of dry phospholipid bilayers and proteins by sugars. , 1987, The Biochemical journal.

[23]  B. Roelofsen,et al.  Effect of membrane cholesterol on dimyristoylphosphatidylcholine-induced vesiculation of human red blood cells. , 1986, Biochimica et biophysica acta.

[24]  J. Crowe,et al.  Interactions of phospholipid monolayers with carbohydrates. , 1984, Biochimica et biophysica acta.

[25]  L. Guidoni,et al.  Targeting of liposomes: monoclonal antibodies coupled to phospholipid vesicles provide selective transfer of trapped reagents into cultured cells. , 1984, Tumour biology : the journal of the International Society for Oncodevelopmental Biology and Medicine.

[26]  S. Georghiou,et al.  Phase transitions and cholesterol effects in phospholipid liposomes. A new method employing the enhancement of the O-O vibronic transition of pyrene. , 1981, Biochimica et biophysica acta.

[27]  M. Chaudhury,et al.  Correlation between membrane expansion and temperature-induced membrane fusion. , 1981, Biochimica et biophysica acta.

[28]  L. Leserman,et al.  Monoclonal antibody covalently coupled to liposomes: specific targeting to cells. , 1981, Journal of supramolecular structure and cellular biochemistry.

[29]  S. Nojima,et al.  Transfer of cholesterol between liposomal membranes. , 1979, Biochimica et biophysica acta.

[30]  G. Gregoriadis,et al.  Homing of liposomes to target cells. , 1975, Biochemical and biophysical research communications.