ABSTRACT
Useofliposomesasaneffectivedrug-deliverysystemrequiresthedevelopmentofvesicles withphysicalcharacteristicsappropriatetothedrugitselfandthetherapeuticfunctionitis toperform.1Inmanyapplications,theliposomalcarrierwouldprovemosteffectiveifit wereablebothtoremainforlongperiodsoftimeinthecirculationandtoretainentrapped drugsquantitativelysothatinteractionwithtargetcellswithinthevascularsystemmayoccur effectively.Alternatively,controlledreleaseofdrugscouldbeachievedwithacarrierthat leakssolutesinthepresenceofblood(butnototherwise)inapredictablemannermanipulated bysynthesizingthecarrierfromappropriatematerials.Previousworkfromthisandother laboratorieshasshownthatcontrolofsurvivaltimeof,andsoluteretentionby,circulating liposomes(foragivenamountofinjectedlipid)isinfluencedbysize,Zsurfacecharge,3 .4 andlipidcomposition.57Thelatteralsoinfluencesdrugretentionbyliposomesinthepresence ofbloodinvitroandinvivo. 4 . 17Intermsofcontrolofbothsurvivaltimeandsoluteretention, smallunilamellarliposomes(SUV)composedofneutrallipidshaveprovedmosteffective foranumberofentrappedmaterials. 4 -8 •10-14
HerewedescribethepreparationofSUVfromawiderangeofneutralphospholipids withoutorwithvariousamountsofcholesterol(Chol),inthepresenceofcarboxyfluorescein (CF).CFisawater-solublefluorescentdye,especiallysuitedforstudiesofliposomalstability asdeterminedbythepermeabilityofthecarriertothismarker:whenentrappedinfully quenchedform,onlyfreedyethathasleakedoutintoadilutesystemcanbemeasured. Henceadistinctionmaybemadebetweenfreeandentrappedmarker.Forawiderdiscussion ontheapplicationofCFinliposomeresearch,seeChapter13byWeinsteinandcolleagues. SUV,preparedbyprobesonicationwhichallowsformationofunilamellarvesiclesofdefined smallaveragesizeinareasonablyreproduciblemanner,wereusedtoassessandoptimize liposomalstabilityinthepresenceofbloodorplasmainvitroandinthecirculatingblood andclearancefromthecirculationoninjectionintoanimals.TechniquesdescribedforSUV alsoapplyforothertypesofliposomes.
