Albumin adsorption to contact lens materials A review.docx

Albumin adsorption to contact lens materials A review.docx

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AlbuminadsorptiontocontactlensmaterialsAreview

Albuminadsorptiontocontactlensmaterials:

Areview

DoerteLuensmann

a,

andLyndonJonesa

aCentreforContactLensResearch,SchoolofOptometry,UniversityofWaterloo,200,UniversityAvenueWest,Waterloo,Ontario,N2L3G1,Canada

Availableonline7July2008.

Abstract

Duringcontactlenswear,tearfilmcomponentssuchaslipids,mucinsandproteinstendtodepositonandwithinthelensmaterialandmaycausediscomfort,reducedvisionandinflammatoryreactions.Thetearfilmproteinthathasattractedmostinterestwhenstudyingcontactlensdepositionisthesmall（14 kDa）,positivelychargedproteinlysozyme.Albumin,whichisamuchlargerprotein（66 kDa）withanoverallnetnegativechargeisalsoofinterest,andshowsverydifferentadsorptionpatternstolysozyme.

Theconcentrationofalbumininthetearfilmisrelativelylowcomparedtotheconcentrationinbloodserum,butthisvalueincreasesmarkedlyundervariousconditions,includingwhentheeyeisclosed,duringcontactlenswearandinvariousdryeyestates.

Gaininganunderstandingofthemannerinwhichalbumindepositsonbiomaterialsisofimportanceforcontactlenswear,aswellasforothermedicalapplicationswhereHEMA-basedmaterialsareusedforimplants,artificialbloodvesselsordrugdeliverydevices.

Thisreviewpapersummarizestheimpactofindividualmaterialcompositions,watercontent,hydrophobicityandelectrostaticattractionontheadsorptionbehavioroftheproteinalbumin.

Keywords:

Serumalbumin;Contactlensmaterials;Proteindeposition

ArticleOutline

1.Albumininthepreoculartearfilm

2.Albuminadhesiontovarioussubstrates

3.Albuminadsorptionatbiomaterialinterfaces

4.Albuminadsorptiononcontactlensmaterials

5.Watercontent

6.Hydrophobicity

7.Charge

8.Poresizeandsurfaceroughness

9.Temperatureandionicstrength

10.Conclusion

References

Contactlensdepositionwithsubstancesfromthehumantearfilmhasbeenextensivelystudied[1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28],[29]and[30].Themajorityofpublishedstudieshavereportedontheinvivoorinvitrodepositionofeither“totalprotein”[23],[31]and[32]or,morespecifically,lysozyme[11],[33]and[34].However,lysozymeonlyaccountsforaproportionoftheproteinsinthetears,withothermajortearfilmproteinssuchaslactoferrin,albuminandlipocalinbeingalsopresentinhighquantities[35],[36],[37],[38],[39],[40],[41],[42]and[43].To-date,littlehasbeenpublishedontheinteractionbetweencontactlensesandalbuminandthepurposeofthisreviewarticleistodescribethefactorsthatinfluencethedegreetowhichthisproteininteractswithvariousmaterialsusedforcontactlenses.

Albuminissynthesizedintheliverandhasanestimatedlifetimeof27days[44]and[45].Itisthemostabundantproteininhumanserumandisalsothemostprominentsolubleproteininthebodyofallvertebrates[44].Hippocrates（circa460–370BC）wasprobablythefirstscientisttomentionsomedistinctivepropertiesofalbumininthehumanbody.SerumalbuminkeepstheosmoticbloodpressureandbloodpHvalueconstantandtransportsvariousmolecules,includinghormones,fattyacidsanddrugs[46].Inahumanbodyweighing70 kg,41%ofthetotalextravascularalbuminisfoundintheskin（100 g）and40%inthemuscles（96 g）,withsmallamountsbeingdetectedintheliver,gutandsubcutaneousregion[47].Intheserum（intravascular）,anaveragealbuminconcentrationof45.1–49.9 ± 2.6 mg/mlhasbeenreported[46],whichapproximatesto118 gforatypical70 kgbodyweight[44].

Overthelast60yearsinformationconcerningthestructureofhumanserumalbumin（HSA）hascontinuallybeenupdatedandrefined.In1956TanfordandBuzzell[45]andLoebandScheraga[48]describedthehydratedproteinasacompactspheroidparticle,whereas12yearslaterSquireetal.[49]reportedacigar-shapedmodelof140 Å × 40 Å.Thiswastheacceptedtextbookmodeluntil1990,whenCarterandHepresentedthefirsthigh-resolutioncrystallographicdataforHSA[50].Usingthismethodataresolutionof4 Åtheyfoundathree-dimensionalheart-shapedstructureforHSAinacrystallizedformat,whichwasconfirmed10yearslaterforbovineserumalbumin（BSA）inahydratedstate[51]（Fig.1）.

Fig.1. Overalldimensionoftheheart-shapedstructureforalbumin,asdescribedbyCarterandHe[50].

Full-sizeimage（43K）

Fig.1. Overalldimensionoftheheart-shapedstructureforalbumin,asdescribedbyCarterandHe[50].

ViewWithinArticle

Theshapeandphysicochemicalpropertiesofalbuminfromhumanandbovineserumareverysimilar（Table1）.Thesecondarystructureofalbuminconsistsofthreeverysimilardomains（I,II,III）arrangedinnineloopswith17disulfidebridgestostabilizethenativeform.Eachdomainhastwosubdomains（AandB）,withsubdomainAbeingcomposedofsixα-helixchainsandsubdomainBoffourα-helixchains.Thehelicesrangeinsizefrom5to31aminoacidsinlength[44],[52]and[53].DuetothesimilarityofHSAandBSA,andtherelativeavailabilityandlowercostofBSA,manyinvitrostudieshaveusedBSAasasurrogateforHSA[54],[55]and[56].

Table1.

ComparisoninstructurebetweenHSAandBSA[44]

Molecularweight（Da）

Isoionicpoint

Numberoffattyacids

Human（HSA）

66,438

5.16

585

Bovine（BSA）

66,411

5.15

583

Full-sizetable

ViewWithinArticle

1.Albumininthepreoculartearfilm

Farmorethan100differentproteinshavebeenidentifiedinthehumantearfilm[40]and[57].Specifictearproteinssuchaslysozyme,lactoferrinandlipocalinaresynthesizedbythelacrimalgland;howeveralbuminisaserumproteinandbecomesmixedwiththetearfilmbyleakagefromtheconjunctivalcapillaries.TheconcentrationofHSAinthetearfilmhasbeeninvestigatedbyanumberofresearchers,usingavarietyofdifferentanalyticaltechniques.In1993,BrightandTighereviewedninetearfilmstudiesandfoundavastrangeofpublishedconcentrations,between0.0103 mg/mland390 mg/ml[58].

Tearsmaybecollectedusing“stimulatedmethods”,suchasthoseinvolvingan“eye-flushing”techniqueorbystimulatinga“sneeze”,ascomparedwithan“unstimulatedmethod”,wheretearsarecollectedviaacapillarytubewhichdoesnottouchtheocularsurface[59],[60],[61]and[62].Generally,higherHSAconcentrationsarefoundduringsleep[37],[38]and[41],inunstimulatedtears[37],[59]and[61]andinpatientswithsymptomsofdryeye[63],[66]and[67]orwhenwearingcontactlenses[38]and[64].Table2summarizestypicalreportedalbuminlevelsinthepreoculartearfilmundervariousconditions.

Table2.

Albuminconcentrationinthetearfilm（mg/ml）

Nonstimulatedtears

0.042 ± 0.012[59]

0.023 ± 0.015[61]

0.06 ± 0.02[37]

Stimulatedtears

0.012 ± 0.004[59]

0.008 ± 0.001[65]

0.02 ± 0.01[37]

Duringsleep

0.20（0.15–0.58）[38]

1.1 ± 0.76[37]

1.0 ± 0.5[41]

Dryeyes

Increase17%[66]

3.7（0.2–22.6）[63]

4.74 ± 0.72[67]

Wearingcontactlenses

0.059 ± 0.054[64]（healthyeye）

0.079 ± 0.060[64]（presenceofbacteriaonCL）

0.54（0.33–1.24）[38]（wearingOrtho-KCLovernight）

Full-sizetable

ViewWithinArticle

Lundhandcoworkersfitted50eyeswithcontactlensesandinvestigatedIgGandHSAconcentrationsinthetearfilm.Theconcentrationofbothserumproteinsincreasedin20eyes,indicatingahigherpermeabilityoftheblood–tearbarrier[68].TheimpactofetafilconAlenseswornonanextendedwearscheduleonproteinlevelsinthetearfilmwasinvestigatedbyCarnyetal.[69].Lactoferrin,lysozymeandHSAlevelsincollectedtearsweremeasuredon10neophytesbeforelenswearingandafteraperiodof6months.TherewasatrendforincreasingHSAconcentrationinthetearfilmoverthe6monthsofextendedwear,butthisincreasewasnotstatisticallysignificant.Inanorthokeratologystudy,Choyetal.[38]foundincreasingamountsofHSA,whileothertearfilmproteins（lysozyme,lactoferrinandlipocalin）remainedinanunchangedconcentration.TheratiobetweenHSAandlactoferrinhasalsobeenreportedasanindicatorfordiagnosingprimarySjogren'sSyndrome（SS）[70].Bjerrummeasuredtheproteinconcentrationinpatientswithconnectivetissuediseases,SSandcontrolsandconcludedthatanalbumin:

lactoferrinratioabove2:

1iscommonlyfoundinpatientsdiagnosedwithSS.Thesefindingsareofpotentialsignificance,sincehigherproteinconcentrationsinthetearfilmalsoappeartoleadtoincreaseddepositionlevelsoncontactlenses[15],[71],[72]and[73].

2.Albuminadhesiontovarioussubstrates

Theprocessofproteinadsorptionfromanaqueoussolutionontoasolidsurfaceistypicallydescribedinthreesteps.Firstly,transportationoftheproteinfromthesolutiontowardsthesolidsurfaceoccurs.Thisisfollowedbyattachmentoftheproteintothesurface,andfinallytheproteinstructureundergoesaconformationalchangeafteradsorption[74].CarterandHoinvestigatedthephysicochemicalpropertiesofHSAanddescribeditasaflexibleproteinthateasilychangesitsmolecularstructure[75].FluorescentX-raytechniquesrevealedthattheBSAmoleculesflattenedwhenboundonagoldsubstrateandtheheart-shapedprotein,withaninitialsidelengthof3 × 80 Å,increasedtoasidelengthof127 Å,withasimultaneousreductionindepthfrom30 Åto11.6 Å,withthisshortaxisbeingperpendiculartothesolidsurface[44]and[76].TheamountofHSAthatformsamonomolecularlayeronmostsurface