Mannosereceptortargetingbymannosylatedliposomeshasbeendemonstratedforavarietyofmannosylatedlipidconjugatesinavarietyofliposomemorphologiesandcompositionsinseveraldifferent invitro and invivo models.Averylargenumberofpublicationsisaboutusingahydrophobicderivativeofmannose(4-aminophenylalpha-D-mannopyranoside)ratherthanusingamannosylatedlipidinClodronateliposomes.Thisismainlyduetothehighcostandcomplexityofsynthesizingandconjugatingmannosetolipid.4-aminophenylalpha-D-mannopyranosideiscommerciallyavailableandfarlessexpensivethansynthesizingmannoseconjugatedlipid.
Whymannose?Mannoseisoneofthecarbohydratecomponentsofmanybacterialandviralcellsurfaces;therefore,theever-efficient,highlyredundantimmunesystemhasevolvedmultiplemechanismsforidentifyingpathogensbasedonmannoserecognition.Theanimalandplantkingdomslikewiseutilizecarbohydraterecognitionsignalingmechanismsincludingmannoseresidues.Manypublicationsevaluateothercarbohydratesastargetingmechanismsforvariouscelltypes,howevermannosetargetingtophagocytesappearstobeoneofthemorespecificmechanismsidentifiedtodate.Mammaliancellsurfaceidentificationmoleculesbasedonmannosebinding,suchastheICAMfamilyofleukocyteadhesionmolecules,targettheSIGNfamilyofmannosereceptorstoaccomplishself-recognition invivo.
Awell-knownandcitedstudybyUmezawa&Eto [1]demonstratesthatliposomescontainingaminophenylmannosideweremostefficientlyincorporatedintothemousebrainacrossthebloodbrainbarrier.TherADIolabeledliposomesbearingaminophenyl-alpha-D-mannopyranosideweremaximallyincorporatedintothemousebrainafter48hours,whereasinthespleenandliver,theseradioactivitiesweremaximumafter12hours.Thestudiesalsoshowedthatliposomesweremostincorporatedwasglialcellsratherthanneuronalcell.Thesubcellularfractionationstudyindicatesthatmannoselabeledliposomesareincorporatedintolysosomesrichfractionbothinliverandbrain.
Therearefivemannosylatedfluorescentcontrolliposomeproducts(m-Fluoroliposome®)form-Clodrosome®(mannosylatedclodronateliposomes).Allfivemannosylatedfluorescentliposomesincorporatealipophilicdyeinsidetheirmembranes.Theyareinsolubleinwater;however,theirfluorescenceiseasilydetectedwhenincorporatedintomembranes.DiI,DiO,DiD,DiRandDiAcoverawiderangeofexcitationandemissionwavelengthsfrom300sto900s.DiIandDiOhavefluorescenceexcitationandemissionmaximaseparatedbyabout65nm,facilitatingtwo-colorlabeling.TheemissionspectrumofDiAisverybroad,allowingittobedetectedasgreen,orange,orevenredfluorescencedependingontheopticalfilterused.DiI,DiO,DiDandDiRbelongtothedialkylcarbocyaninesfamilyofcompounds.Thespectralpropertiesofthedialkylcarbocyaninesarelargelyindependentofthelengthsofthealkylchainsbutareinsteaddeterminedbytheheteroatomsintheterminalringsystemsandthelengthoftheconnectingbridge.Theyhaveextremelyhighextinctioncoefficients,moderatefluorescencequantumyields,andshortexcitedstatelifetimesinlipidenvironments(~1ns).Thefluorescencespectrumofeachdyeisshownbelow.
Youcanchoosethem-Fluoroliposome®basedonthetypeofthefluorescentequipmentandfiltersthatyouuseinyourlab.Mannosylatedclodronateliposomescannotbemadefluorescentsimplyduetothepotentialforinaccurateand/oruninterpretabledatabeinggeneratedbylabelledm-Clodrosome®.Formoreinformation,pleaserefertothetechnicalnotesection.
