Shockwave as biological therapeutic tool

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InternationalJournalofSurgery

journalhomepage: www.journal-surgery.net

Review

Shockwaveasbiologicaltherapeutictool:Frommechanical stimulationtorecoveryandhealing,throughmechanotransduction

highlights

SWrepresentsarevolutionaryformofmechanotherapy(acusticstimulation).

Unlikeurologicallithotripsy(mechanicalmodel),onlivingtissues,SWexertananti-inflammatoryactionandpro-angiogenicandregenerativeeffectsas well(biologicalmodel).

Mechanotrasductionpathwayssustaintheirclinicalandexperimentalresults.

WepresentasummaryofcurrentknowledgeofSWmechanismsofaction,accordingtomainrecentdata(mechanobiology).

BettercomprehensionofSWmechanobiologycouldledtonewtherapeuticalperspectives.

articleinfo

Articlehistory:

Received21July2015

Receivedinrevisedform

28September2015

Accepted9November2015

Availableonline28November2015

Keywords:

Shockwaves

Mechanotransduction

Tissueregeneration

Tissue

Remodeling

Inflammation

Macrophages

abstract

ExtracorporealShockWaveTherapy(ESWT)isaformof “mechanotherapy”,that,fromitsoriginalapplicationsasurologicallithotripsy,gainedthe fieldofmusculo-skeletaldiseasesasOrthotripsy(mainly tendinopatiesandboneregenerativedisorders)andRegenerativeMedicineaswell.

ThemechanismsofactionofShockWaves(SW),whenappliedinnon-urologicalindications,arenot relatedtothedirectmechanicaleffect,buttothedifferentpathwaysofbiologicalreactions,thatderive fromthatacousticstimulations,through “mechano-transduction”.So,the “mechanicalmodel” ofurologicallithotripsyhasbeensubstitutedbya “biologicalmodel”,alsosupportedbycurrentknowledgein “mechanobiology”,theemergingmultidisciplinary fieldofsciencethatinvestigateshowphysicalforces andchangesincell/tissuemechanicscaninfluencethetissuedevelopment,physiologyanddiseases.

Althoughsomedetailsarestillunderstudy,itisknownthatSWareabletoreliefpain,aswellto positivelyregulateinflammation(probablyasimmunomodulator),toinduceneoangiogenesisandstem cellsactivities,thusimprovingtissueregenerationandhealing.

ESWTcanbenowadaysconsideredaneffective,safe,versatile,repeatable,noninvasivetherapyforthe treatmentofmanymusculo-skeletaldiseases,andforsomepathologicalconditionswhereregenerative effectsaredesirable,especiallywhensomeothernoninvasive/conservativetherapieshavefailed. Moreover,basedonthecurrentknowledgeinSWmechanobiology,itseemspossibletoforeseenew interestingandpromisingapplicationsinthe fieldsofRegenerativeMedicine,tissueengineeringandcell therapies.

© 2015IJSPublishingGroupLimited.PublishedbyElsevierLtd.Allrightsreserved.

1.Introduction

ShockWaves(SW)wereoriginallyintroducedinmedicineas ExtracorporealShockWavesLithotripsy(ESWL)intheearly1980s forkidneystonestreatmentandtheseclinicalapplications

* Correspondingauthor.

E-mailaddress: info@cristinadagostino.it (M.C.d'Agostino).

widespreadedallovertheworlduntiltoday.Afteritsoriginal introductioninmedicineas urologicallithotripsy,thistechnology indeedhasbeenincreasinglyappliedalsotoabroadrangeof musculoskeletaldiseases,uptopresentday,whenitrepresentsan interestingtherapeutictoolinthe fieldofRegenerativeMedicine

Nowadaysinfact,ExtracorporealShockWaveTherapy(ESWT)is currentlyappliedtoawiderangeofpathologiesofdifferentorigins

http://dx.doi.org/10.1016/j.ijsu.2015.11.030 1743-9191/© 2015IJSPublishingGroupLimited.PublishedbyElsevierLtd.Allrightsreserved.

M.C.d'Agostino a, *,K.Craig b,E.Tibalt a,S.Respizzi a a ESWTCenter,RehabilitationDepartment,HumanitasResearchHospital,Rozzano,Milan,Italy b KompassHealthAssociates,Auckland,NewZealand

andlocalization,bothinorthopedicsandrehabilitativemedicine (tendonpathologies,bonehealingdisturbances,vascularbone diseases) [1 3,5 8],dermatology/vulnology(woundhealingdisturbances,ulcers,painfulscars) [9 12] andneurology(spastichypertoniaandrelatedsyndromes) [13 15].Morerecently,the positiveeffectsofESWTonsofttissuesandthelocalvasculature alloweditsapplication,inclinicalpractice,alsoforsomeandrologic disturbances(induratiopenisplastic anderectyledisfunctions) [16 18].Regenerativeandtrophiceffectshavealsobeendemonstratedforischemicheartdiseases,although,atpresent,SW applicationinthis fieldhasstilltobeconsideredasanexperimental one [19]

Ingeneral,ESWT,invirtueofitsnoninvasiveapproach,absence ofmainsideeffects,repeatability,goodtolerabilityandcompliance bythepatients(ifproperlyapplied,onthebasisofacorrectdiagnosis),seemstooffernewtherapeuticalperspectivesin Orthopadic andRegenerativeMedicine [1 3].Inparticular,itmayrepresenta veryusefultool,especiallywhenallothernoninvasivetreatments wereineffectiveorsurgeryfailed,especiallyinthe fieldoforthopedicsandrehabilitation [20],betterifinsynergisticactionwith someothertherapeuticaloptions(as,forexample,rehabilitation programs) [21]

2.Shockwavesasmechanotherapy:from fisicsto mechanobiologyandmechanotransduction

SWare “mechanical” waves,whoseshapeischaracterizedbyan initialpositiveveryrapidphase,ofhighamplitude,followed,after veryfewmicroseconds,byasuddenphaseofmildnegativepressure,afterwardsreturningtotheambient(basic)values.Medical SWaregenerated,througha fluidmedium(water),bya source (electrohydraulic,piezoelectricorelectromagnetictypegenerator). Theyaresonicpulsescharacterizedby:highpeakpressure,upto 100mpa(500bar)orevenmore,rapidriseinpressure(<10ns), shortduration(<10 ms)andabroadrangeoffrequency [22,23] (Fig.1).

Independentlyofthetypeofgenerator(source)mountedinthe lithotripter,SWareproducedasconsequenceofarapidincreasein pressure(likea “micro-explosion”)intothewater,andsoonerthey are “focused” onthe target (thatistheanatomicalareatobe treated).Focusingispossibleforaparaboliclens,whichconcentratesthefrontofSW,assoonastheyareproducedfromthesource. These focused ExtracorporealSW(fesw)arewelldefinedintheir characteristics,thatdifferentiatethemfromthe radialwaves [23,24].RadialWavesaremechanicalstimulations(acousticwaves) aswell,butdifferfromfswaccordingtotheirshape,andact

througha ballistic mechanism.Technically,intheapplicator(a barrelhandpiece),ametallicbulletisacceleratedatveryhighspeed bycompressedair(pneumaticsource)orbyanelectromagnetic mechanism.Duetothehighkineticenergyproduced,itimpacts againstthetipoftheapplicatoritself,whichisdirectlyappliedon thebodysurface:asaconsequence,thekineticenergy,forfeited duringrunning,isdirectlytransferredtotheskinontheareaof treatment.DifferentlythanSW,this pressurewaves propagateinto thebodyasasphericalorball-shapedwaves,thatisinaradial fashion,thatgivesthemthedescriptivetermof “radialwaves”.They arenotfocusedinthedeeperlayers,and,atsomeextent,jointhe moresuperficiallayersintheareaoftreatment.Fromthephysical pointofview,bothfswandradialwavesaremechanicalwaves,but differrelativelytotheshapeofthewaveitself;nevertheless,they share,as mechanotherapies,someusefulclinicalapplicationsin somesofttissuedisorders [23 25]

Theimportanceofmechanicalstimulionlivingbeings,aswell astheinfluencethatbiomechanicaldeformationscanexerton cellularbiologyandphysiology,inhealthanddiseases,havebeen recentlyseenareneviewedinterestinscientificliterature,especiallywiththepurposeofpossibletherapeuticalapplications [4,26,27]

Mechanicalstimulation usuallybringstomindtheobsolete conceptof “physicaltherapies”,especiallyinthe fieldsoforthopedicsandrehabilitation:foralongtime,studiesandresearchesfor exploringtheapplicationsof “physical” stimulationshavebeen generallylimitedtodescribeandquantifythe finalgeneraloutcomesofthesetherapies,withoutanalyzingindetailsthepathways ofactions,atbiologicallevel,thatthese “physicalmeans” may produceonthetreatedtissuesandcells [4]

Onlyinmorerecentyears,duetothedevelopingofthenew branchofsciencenamed Mechanobiology,researchersbeganto analyzeindetailstheeffectsofthephysicalstimulusand,mostof all,tocorrelatetheinteractionsofphysicalenergieswiththe varioustissuesandcellelements [28,29]

Itcanbeconsidereda fieldofscienceatthe “cross-road” betweenbiologyandengineeringofmechanics,whosemaingoalisto describe mechanotransduction,thatisallthemolecularmechanisms,bywhichcellscansensemechanicalstimulationsandadapt theirbehaviortomechanicalsignals [30,31]

“Mechanotransduction” isa biologicalpathway towhichmany celltypesaresensible:aftersensingandprocessingthemechanical informationsfromtheextracellularenvironment,thesebiomechanicalforcesareconvertedinbiochemicalresponses,thus influencingsomefundamentalcellfunctionsasmigration,proliferation,differentiation,andapoptosis [31]

Originallystudiedin “adhesionbiology”,where integrins have beendescribedtoconveyforcetransmissionbetweentheextracellularmatrixandtheintracellularactincytoskeleton,ithasbeen describedthatthephenomenonof mechanosensing iscorrelated withthelaterallyrearrangementofproteinswithinthemembrane, thusinducingsomechangesintheirtridimensionalstructureand modifyingtheiractivity,accordingtothedifferentandchanging biomechanicalconditions [32].

Manycellsstructureshavebeendescribedtocontributeto mechanotransduction:stretch-activatedionchannels,caveolae, integrins,cadherins,growthfactorreceptors,myosinmotors, cytoskeletal filaments,nuclei,extracellularmatrix,intercellular “gapjunctions” , “hemichannels” amongmembraneproteins, “primarycilia” amongcellorganelles(capableofperceiving possiblemechanical,physicalorother “perturbations”), “transient receptorpotentialchannels” intracellularmechanical-signalling“pathways” andnumerousothermolecularstructuresand signalingmolecules.Moreover,endogenouscell-generatedtraction forcessignificantlycontributetotheseresponsesbymodulating

Fig.1. Typical “biphasic” formofthetherapeuticalextracorporealshockwaves.(from: OdgenJA,Toth-KischkatA,SchulteissR.PrinciplesofShockWaveTherapy.Clinical OrthopedicandRelatedResearch,2001;387:8 17).

tensionalprestresswithincells,tissues,andorgansthatgovern theirmechanicalstability,aswellasmechanicalsignaltransmissionfromthemacroscaletothenanoscale [30,31].

Iforiginallythemechanotransductionphenomenonwas extensivelyinvestigatedinendothelialcellbiologyuponshear stressstimulation,morerecentevidencesindicateitsimportant rolealsoinfunctionandphysiologyofmanyothercelltypes, including fibroblasts,bonecells,andmesenchymalstemcells [32 34];evenmacrophagesandsomeothercellsoftheimmune system,seemtobeendowedwithsomemechanosensingproperties [35]

Nowadays,althoughitisstillnotcompletelypossibletoapply Mechanobiologyfordiagnosis,treatment,healthmaintenanceand upgradingofvariousbiologicalsystems,andiswellknownthat HumanMechanobiologyisstilla fieldoftheoreticalspeculation andresearch,nevertheless,wecanalreadyapplysomemechanical stimulations,betterknownas Mechanotherapies, thatcanbesuccessfullyusedinclinicalpracticeformanydisordersofboneand softtissuesaswell.Accordingtoarevisiteddefinitionoftheterm, onthebasisofthecurrentknowledgeinmechanobiology, Mechanotherapies havebeendefinedas “alltherapeuticinterventionsthat reduceandreverseinjurytodamagedtissues,orpromotethehomeostasisofhealthytissuesbymechanicalmeansatthemolecular, cellular,ortissuelevel”;inotherwords,theyincludeall “active mechano interventions,thataimtoconvertpotentiallydestructivemechanicaleffectsintoconstructiveinfluencesandtarget normalmechano adaptationtopromoterecovery” [4]

Inthe fieldofMechanotherapies,aspecificplaceisreservedto ExtracorporealShockWavesTherapy(ESWT):itsmanifoldbiologicalmechanismsofaction(basedonmechanotransduction) havebeenpartiallyunderstoodanddescribedoverrecentyears, althoughstillremainingpartlyunderscientificinvestigation [4].

3.Whichbiologicaleffectsfromshockwavesas mechanotherapy?

Asalreadyintroduced,nowadaysitisscientificallyrecognized thatSW,onlivingstructures,althoughactingaspurephysicalenergy,donotevokeamechanicaldisruptiveresult,butreallyinduce somebiologicaleffectsontissuesandcells,whosefunctionsand metabolismcanbepositivelyregulatedandstimulated;inother words,themechanicalstimuluscouldbeonlya “trigger”,butnot properlythedirectresponsibleoftheultimateeffectsofstimulationitself.Thisphenomenaissupportedbysome “mechanotransductionpathways”,whichimplytheactivationofaseriesof cellularevents(largelyunknownuntilnow),responsibleforthe positiveeffectsofESWToncellmetabolismandcellcycle,which ultimatelyaccountfortheductilityofthetherapy [1 3,36].

Regardingthe fieldof SWmechanobiology,itisimportantto underlinethat invitro cellexperimentsmayshowsomedifferent results,accordingtothetypeandenergylevelstimulationapplied, fromapositive,regenerativeandtrophiceffect,toadangerousand disruptiveoneaswell.Cellexperimentscanbeconsideredvery usefulforunderstandingbasicpathwaysofreaction,aswellasfor postulatingthemechanismsofinteractionatthetissuelevel,but cannotbeusedtodefineclinicalprotocolsandgeneralindications. Atthecellularlevel,inanycase,itwasdemonstratedthatSWcan induce asshearstresses-adeformationofsomecytoskeletal proteins(actinandtubulin,butnotvimentin),butthisisonlya transienteffect,ascellswereabletoreorganizetheiroriginal cytoskeletalnetworkwithin3h,withapatternsimilartothe control [37]

Inthe fieldofmechanotrasductionandpossibletherapeutical mechano-interventions,definitely,SW,as mechanotherapy,can playanimportantroleinpositivelyinfluencingsomecellsfunctions

andlocalhomeostasis,thusconditioningthetissue self-healing capabilities.Evidencesfrombasicscienceandclinicaltrials,infact, seemtoindicatethatultimatelythiseffectinvolvestheSWactionof inducingproliferation,migrationanddifferentiationofstemcells, whichsignificantlycontributetotissuehealingandregeneration. Besidesstemcellsandbonemarrow stromalcells,manyother cellsrevealedthemselvesastargetsformechanotransductionafter SWexposure,includingtenocytes,bonecellsandtheirprecursors, endothelialcells, fibroblastsandsomeotherones [1 3,38 45].

SWrepresentafundamentaltherapeutictoolfortendinopathies,irrespectiveofthepresenceornotofcalcifications,with successratesreportedintheliteratureupto91%(forrotatorcuff “tendinitis”,trocanteritis,Achillestendinitis,plantarfasciitisand jumper'sknee) [1 3,24].ManyclinicaldataindicatethatSWcanbe effectiveinresolvingtendonpathologies,especiallyasaneffective interventiontobeconsideredwhenothernonoperativetreatments havefailed,althoughthespecificmechanismsofactionremain partlyunknown [1 3,20,46]

Indeed,betweenthedifferentcelltypes,tenocytes,wellknown sincealongtimetobeverysensibletomechanicalstimulations, havebeenextensivelystudiedregardingSWMechanobiology.

Inanimalexperiments,ithasbeenobserved,forexample,that anoptimalSWtreatmentpromotedhealingof “collagenaseAchillestendinitis”,byinducingTGF-beta1andIGF-I.Histological observationsdemonstratedthatESWTresolvededema,swelling, andinflammatorycellinfiltrationininjuredtendons.Lesionsite underwentintensivetenocyteproliferationandprogressivetendon tissueregeneration.Tenocytes,atthehypertrophiedcellulartissue andnewlydevelopedtendontissue,expressedstrongproliferating cellnuclearantigen(PCNA)afterESWtreatment,coincidingwith intensiveTGF-beta1andIGF-Iexpression,rightasintheearlystage oftendonhealing.So,ithasbeenhypothesizedthatphysicalSW stimulationcouldincreasethemitogenicresponsesoftendons [47] Moreover,itwasdescribedthatSWcanexertadirectactionon tendoncells,asbelowsummarized,thusimplyingalsoapossible futureinvolvementintendonhealingandregenerativetherapies:

1.Reducedexpressionofseveralmetalloproteinasesandinterleukins(MMPsandILs) [48];

2.Positiveregulationofcellvitalityandproliferation,besides expressionoftypicaltendonmarkersandanti-inflammatory citokines [49 51];

3.Stimulustoproliferationandcollagensynthesis, firstlymediatedbyearlyup-regulationofPCNAandTGF-beta1gene expression,endogenousNOreleaseandsynthesisandTGFbeta1proteinandthencollagensynthesis [47];

4.Enhancingof invitro functionalactivitiesofrupturedtendonderivedtenocytes(proliferationandmigration),whichcould probablycontributetotendonhealing invivo [52];

5.Increasedexpressionoflubrycin [53]

Regardingthistopic,veryrecentlysomeAuthorsstudiedwith microdialysis,inhumans,thebiochemicalresponsesoftendons afterSWstimulation,andhypothesizedthatthismechanical stimulusmightaidtendonremodelingintendinopathies,bypromotingtheinflammatoryandcatabolicprocesses,thatareassociatedwithremovalof “pathological” matrixconstituents,thus suggestingapotentialargumentforfuturestudies [54]

Anotherimportantclinical field,whereSWplayaprimaryrole as mechanotherapy isrepresentedbybonehealingdisordersand bonevasculardiseases.Nowadays,manyclinicalandexperimental dataseemtoconfirmSWasanimportanttherapeutictoolfor enhancingosteoregenerativeprocessesinpseudoarthrosisand bonehealingdelays,asavalidalternativetosurgeryinmanycases [1,3,5,55],besidesthepossibilitytopositivelyinterpherewith

alteredlocalboneturnover(asforexampleinbonemarrowedema syndromes) [8] ortoimprovelocalosseoustrophism(asinosteonecrosisandrelateddisorders) [6,7].

Boneisperhapsthetissuewheremechanobiologicalpathways arewellexpressedintheirdifferentforms:bothduetoitsparticularmechanosensitivity,anditscomplexstructureandphysiology aswell.Cellexperimentsseemtodemonstrateinfact,thattheeffectsofSWinthistissuecanactatdifferentlevels:notonlydirectly onbonyandperiostealcellsandtheirprecursors,butalsointhe complex cross talk betweenosteoblastsandosteoclasts,involving osseousvasculatureaswell [43,56]

Moreindetails,atthebonelevel,therehavebeendescribed afterSWexposure:

-directstimulationofosteoblastsandperiostealcells [57 61];

-osteogenicdifferentiationofmesenchymalstemcellsthrough superoxide mediatedsignaltransduction,followedbyactivationoftyrosinekinase mediatedextracellularsignal-regulated kinase(ERK)andcorebindingfactorA1 [62];

-acceleratedmigrationofosteoblasts [63];

-earlyexpressionofangiogenesis-relatedgrowthfactors, includingendothelialnitricoxidesynthase(eNOS),vascular endothelialgrowthfactor(VEGF)andproliferatingcellnuclear antigen,thusproducingnewvesselin-growthwithimproved bloodsupply,increasingcellproliferation,acceleratingtissue regenerationandhealing [55,56,64 66];

-stimulationofperiosteumtowardorthotopicboneregeneration [42];

-reductionofosteoclastsactivity,throughinhibitionofproosteoclastogenicfactors [43]

Moreover,assomeothermechanotherapiesappliedinclinical practice,mainactionofESWTseemstofocusoninducingtissue regenerationand,accordingly,experimentalandclinicalresults indicatethatitsclinicalefficacyistightlyrelatedtoitsabilityto induceneovascularizationandmatrixremodeling “invivo” [1,3,10,19,38,39,67 72].

Fromthemechanobiologicpointofview,ithasbeendescribed, forexample,thatthisneoangiogeniccapacity,couldberelated,as firststep,totheinhibitionofendothelialcellsapoptosisand adhesion,occurringintheveryearlyphaseafterSWstimulation (first3h),asinitialresponsetothemechanicalstimulus.Morein details,ithasbeenhypothesizedthatsomeaspectsoftheearly generesponseofendothelialcellstoSW,asmechanotherapy,are similartothoseinducedbythelaminarshearstress flow,mainly characterizedbyananti-apoptoticeffect.Inotherwords,at3h afterSWexposure,stilllackingneoangiogenicactivity(usually appearingnoearlierthan12h),neverthelessitseemspossibleto detectsome “preparatory” signals,suchasdownregulationofthe genesinvolvedincellcycleandadhesion,probablycorrelatedtoan upcomingdetachmentofendothelialjunction [40].Although invitro data,theyseemtoconfirminanycasethat,fromageneral pointofview,forapplyingmechanicalinterventionsinviewofa therapeuticalpurposeitisusefultounderstandmanydetailsatthe molecular,cellularandtissuelevel [4,28,73]

Asalreadymentioned,increasingevidencesintheliterature describethatmechanotransductionevents,afterSWstimulation, arenotonlydose-dependentbutalsocanvaryindifferentcelltypes andstemcellsatdifferentstagesofdifferentiation.Moreover,each celltypeseemstoberesponsivetoSW,butprobablywithdifferent optimalpatternsandrangesofmechanicalstimulation,thus developingdifferentbiologicalanswers,including,forexample, upregulationofTGF-alfa-1expressionandNOproduction,aswell assuppressionofNF-kappa-Bactivityandpro-inflammatorycytokinesproduction [4,38,39,74,75].

Furthermore,accordingtothemorerecentknowledgeinSW mechanobiology,thereisincreasingevidenceofSWasmechanotherapyactingas “immunomodulator” inwoundhealingandtissue regeneration,mainlythroughananti-inflammatorystrategy [75 78];veryinterestingly,someAuthorsdescribedthatSWmay modulateinflammationviatheToll-LikeReceptor3(TLR3) pathway,throughthereleaseofcytosolicRNA [79]

Thesebasicsciencedatamaybesomerevolutionary findings, asonlyinrecentyearsithasbeendemonstratedtheimportant roleandinvolvementoftheinnateimmunitysysteminthe complexseriesofinterplayedcellularandbiochemicalevents,that leadtotissueregeneration,healingandremodeling.Averycritical pointintissuehealingandregenerationisrepresentedbythe delicatephase,whereacuteinflammation(asforexampleina woundsoonaftertrauma)canshifttowarditsphysiologicalresolutionorchronicization(pathologicalconditions).Itiswell known,nowadays,thatmacrophagesplayanimportantrolein controllingmanyphasesofthe “healing” process,bothinthe initialinflammatoryphase(asM1or “classically” activatedmacrophages),andintheresolvingstage(asM2or “alternativeactivated” one),byregulatingthisdelicatetransition.Theycan perceiveinfactsomeendogenousaswellasexogenous “danger signals” (asafterlocaltraumaorinthepresenceofpathogens)and respondwithaproinflammatoryactivityas firstresponse as M1-,togenerateanti-inflammatoryandpro-resolvingmediators, whilerecruitingandstimulatingstemcellsaswellintheirM2 mode.Inotherwords,macrophagescanbeconsideredhighly plasticcells,that,intheirdifferentstagesofactivation,duringthe courseoftheinflammatoryprocess,canintegratesignalsfromthe microenvironmentandcoordinatetheevolutionofthelocalinflammatoryresponse(chronicization versus resolution),according tothemediatorsthatdominates [80 82].Surprisingly,notonly macrophageshadalreadybeendemonstratedtoberesponsiveto mechanicalstimuli,butalso,averyrecent invitro studyshows that,afterexposuretolowenergySW,itispossibletodampenthe inductionofthepro-inflammatoryprofilecharacterizingM1 macrophages,whilepromotingtheacquisitionofanantiinflammatoryprofile(M2),insynergywiththemacrophage alternativeactivation.Thesepreliminarydataseemtosuggestthis couldbeapossibleanotherkey pointofregulationinSW mechanobiology,bothrelatedtotissueregenerationandremodelingaswell [83].

Ontheotherhand,someexperimentalmodelalreadydescribed thatESWTapplication,basedonintramuscularsiliconeinjection, reducedformationofthedense fibrouscapsuleand,whenapplied asmultipleSWsessions,coulddegradethe fibrousenvelope, relatedtoasynergisticalterationsinpro-andanti-fibroticproteins (TGF-beta1andmatrixmetalloproteinase2,respectively),thus suggestingthatSWcouldreducecapsuleformationandmay induce fibrotictissueremodeling/resorption [84]

Fromthisoneandsimilarexperimentalandclinicaldata,it seemspossibletoconcludethatESWTwouldenhancenotsimply “healing” processes,butproperly “regenerative” events,where fibroustissuecanbereducedattheorigin,orevenremodeledina secondphase(asinscars,forexample).Theseimportantmechanobiological findingsmayhavemultiple,interestingandpromising applicationsinclinicalpractice, firstofallincardiology,where restorationoftissueintegrity,insteadof fibroustissue,isvitalfor heartperformance [79,85].

AnotherimportantissueinSWmechanobiologyisthepossibilityofpositivelyinterferingwiththe nervoussystem andsome neurophysiologicalprocessesatdifferentlevels.Itiswellknown sincemanyyears,thepossibleanalgesiceffect,inducedbySW application.If,ononehand,itcouldbepartiallyexplainedwiththe resolutionof “inflammation” andallrelateddiseases,nevertheless

someclinicalandincreasingevidencesintheliteratureseemto suggestanimportantroleofESWTalsoinmodulatingsome “neurological” activities,althoughthemechanismsofactionhave tobeclarifiedindetails [86].Itiswellknownforexample,thatSW exposurecanmodifythepresenceand/orfunctionofsmallunmyelinatednerve fibersandsomeneurotransmitters(asfor exampleSubstancePandCalcitoninGeneRelatedPeptide) [87,88]

Ontheotherhand,ifitiswellrecognizeditspotentialin reducinghypertoniainspasticsyndromes,although,inanycase,it islessclearhowSWcanmodifythesepathologicmuscleactivities, althoughsomehypothesishavebeenpostulated [89,90]

Moreover,ifsomestudiesrecentlybegantodemonstratethe possibilityofaregenerativeeffectalsoonnervesandspinal structures [91,92],alreadyin2008,WessO.hadpublishedan article,hypothesizinghowSW(asmechanicalstimulation)could reorganizepathologicmemorytraces,thusgivingcausetoareal andpermanentpainrelief(throughacentraleffect),thusopening thedoorsfornewtreatmentapproachestochronicpainandseveral otherdisordersofthenervoussystem [93].Onlymorerecently, Lohse-BuschH.etall.publishedthe firststudyoffocusedtranscranialESWT(TESWT),showingthepossibilitytostimulatevigilanceinpatientswithunresponsivewakefulnesssyndrome, althoughtheexactneurophysiologicalmechanismremaintobe verifiedbyfurtherstudies [94]

Definitely,althoughmorerecentlyintroducedandwiththe necessityoffurtherstudiesconfirmingpreliminaryresults,SW,as mechanotherapy,seemtoforeshadownewinterestingtherapeuticalimplicationsalsointhe fieldofsomeneurological diseases.

4.Conclusions

Inclinicalpractice,asSWstimulationcanpositivelyinfluence theinterplayedchainofbiologicalreactionsthat,through controlledinflammationleadtissueregenerationand “reset” local metabolism,newhorizonsandinsightsseemtobeopening,inview ofcounteractingmanyacquiredpathologicalconditions(especially post traumaticsequelaewithmuscleandskinlesionsandheart failureaswell),forwhich fibrosisisthemainissue.FurtherinvestigationsexploringSWapplicationinaveryearlyphasesof healing,inordertoreducetheamountof fibroustissueduring recovering,couldfurtherunderlinetheimportanceanddignityof thisirreplaceablemechanotherapyinthe fieldofRegenerative Medicine.

Alreadyin1997,Hauptwrote: “ ..inpatientsinwhomconservativetreatmenthasfailed,surgeryusedtobetheonlychoice,but itssuccessratebarelyexceedsthatofshockwavetherapyand surgerycanstillbedoneifshockwavetherapyfails.Extracorporeal shockwaveswillhaveanimpactonorthopedicscomparabletoits effectinurology.Scientificevaluations,professionalcertifications, qualityassuranceandreimbursementissuespresentgreatchallenges..” [20].OnthebasisofallscientificdataaboutSWandaccordingtoitsmechanobiology,itseemslikehoodthatthose propheticwordsofHauptinthat “pioneeringera” becamerealistic, goingbeyondexpectations,evenimplyingforSWnewpromising perspectivesindifferent fieldsofRegenerativeMedicine,Tissue EngineeringandCellsTherapyinthenearfuture [83,95]

Ethicalapproval

Ethicalapprovalnotrequested.

Funding

Therewasnofundingofthisresearch.

Authorcontribution

M.Cristinad’AgostinoandKennethCraigconceivedtheideaof thearticle,studiedthescientificarticlesandwrotethepaper. ElisabettaTibaltparticipatedinwritingthepaperandin reviewingscientificliteratures.

M.Cristinad’Agostino,KennethCraigandStefanoRespizzi revisedthe finalversionandgavethe finalapprovaloftheversion tobesubmitted.

Conflictsofinterest

Allauthorsdeclare,thattheyhavenoconflictofinterest.

Guarantor

Dr.M.C.d’Agostino.

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