• NegativecontrolforstudieswithPhorbol12,13-Didecanoate,formerlyourCat.No.P-1925,forexample,seeTrewyn,R.W.andGatz,H.B."Alteredgrowthpropertiesofnormalhumancellsinducedbyphorbol12,13-didecanoate."InVitro.20:409-15(1984).
• PleaserequestTechnicalNote#13foradditionalinformation.
• 4α-PDDActivationofTRPV4ChannelsLongthoughttobeabiologicallyinactiveorextremelyweakphorbolesteranalog(i.e.,anED50>25µMforbindingtoproteinkinaseC),4α-PDDhasnowbeenshowntobeareasonablypotentactivatoroftwoTRPV4channels,namelyhumanVRL-2andmurineTRP12channels[Watanabe,H.,etal."ActivationofTRPV4channels(hVRL-2/mTRP12)byphorbolderivatives."J.Biol.Chem.277:13569-13577(2002)].TheED50of4α-PDDforactivationoftheTRP12channelwas~400nM,andforincreasinginternalcalciumlevelsin1321N1astrocytomacellsexpressinghumanVRL-2,theED50of4α-PDDwas~185nM.Thisworkextendsearlierresultsshowingnon-phorbol-ester-likeeffectsof4α-PDD[Reeve,H.,etal."EnhancementofCa2+channelcurrentsinhumanneuroblastoma(SH-SY5Y)cellsbyphorbolesterswithandwithoutactivationofproteinkinaseC."PflugersArch.Eur.J.Physiol.429:729-737(1995)]and4α-phorbol12,13-dibutyrate(4-PDBu)[Doerner,D.,etal."ProteinkinaseC-dependentand-independenteffectsofphorbolestersonhippocampalcalciumchannelcurrent."J.Neurosci.10:1699-1706(1990)]oncalciumcurrents.Because4α-PDDhasfew,ifany,recognizedBIOLOGicaleffectsatsub-micromolarconcentrationsotherthantheseeffectsonTRPV4channels,Watanabeetal.certainlyseemjustifiedinstatingthat"4α-PDDcanbeusedasarobustandreliabletooltostudyseveralfeaturesofTRPVchannelsandtoprobefunctionaleffectsoftheactivationofthischannelininvivosystems".Thatsaid,itisalsoimportanttonotethatabsoluteselectivityof4α-PDDforactivatingTRPV4channelshasnotbeendemonstrated.Though4α-PDDhasbeenshownovertheyearstohavelittleornoeffectinafairlywiderangeofbiologicalassays,4α-PDDmightprovetohaveother,as-yet-unidentifiedactivitiesifsubjectedtomoreextensivetestingagainstvarioustargets.[Asanaside,wepointoutthatreference#25intheWatanabearticle,citedinsupportoftheinactivityof4α-PDDonPKC,appearsnottocontainanymentionatallof4α-PDDorother4α-phorbolesters.Fortheconvenienceofthosewhoarepreparingmanuscriptsdealingwith4α-phorbolesters,oneormoreappropriatereferencessupportingthelowactivityofthesecompoundsonPKCwillbeaddedtothisLCLabsproductdescriptionshortly.][Also,seebelowforanimportantnoteaboutnomenclature.Technically,4α-PDDisnotaphorbolester,itisa4α-phorbolester—asmallbutimportantdistinction—andmustalwaysbespecifiedassuchtoavoidconfusionwiththedramaticallydifferentpropertiesofthephorbolesters.]Surprisingly(inviewofhistoricalstructure-activitydata),PMA(phorbol12-myristate13-acetate),theclassicalnanomolar-potencyPKCactivator,was10-to50-foldweakerthan4α-PDDforactivationoftheTRPV4channels.IfbothPMAand4α-PDDweretargetingaPKC-relatedprotein,viaamechanismfundamentallysimilartothatofclassicalPKCactivationbyphorbolesters,PMAwouldbeexpectedtobemanyordersofmagnitudemorepotentthan4α-PDD.Watanabeetal.testedawiderangeofPMAand4α-PDDconcentrations,andthereappearstobenodoubtthattherelativepotenciesexpectedforPMAand4α-PDDforclassicalPKC-relatedeffectsarestrikinglyreversedfortheTRPV4channelactivationphenomenon.FurThermore,insomeassaysPMAwasmerelya"partialagoNIST",showingonly50-65%oftheresponseelicitedby4α-PDD.ThePMA/4α-PDDpotencyinversioninturnstronglysuggeststhat4α-PDDmustbeactingviaamechanismdistinctfromtheclassicalinteractionofaphorbol12,13-diesterwithaphorbolester/diacylglycerol-typereceptortarget,suchasthosefoundonthePKCfamilyofproteins.Giventhelonghistoryand,untilnow,largelysettledpictureofthebiologicalpropertiesofphorboland4α-phorbolesters,thisquestionofmechanismisofhighinterest,andtheanswer(s)mightturnouttohaveawideimpactonseveralareasofpharmacology.LCLaboratoriesalsooffersother4α-phorboldiestersofvaryinghydrophobicity;thesepresumablycanbeusedforstructure-activitystudiesoftheTRPV4activationeffect.Specifically,weoffer4α-PMA(Cat.No.P-8880)and4α-phorbol12,13-dibutyrate(4α-PDBu;formerlyourCat.No.P-4678),bothofwhich(especially4α-PDBu)arelesshydrophobicthan4α-PDD.Theseanalogsof4α-PDDhaveconsiderablepotentialutility.Thehighhydrophobicity(highlipidpartitioncoefficient)of4α-PDDmakesitquitesolubleincellularmembranecompartments,anditisreliablypresumedtobeverydifficulttowashthiscompoundoutofmembranepreparationsorcellcultures.4α-PMAand4α-PDBumayprovetobelesspotentthan4α-PDD,butiftheyretainsufficientpotencyvis-a-vis4α-PDD,theymightbepreferableasresearchtoolsbecauseoftheirenhancedpotentialtoequilibrateamongaqueousandlipidcellularcompartmentsandtobewashedoutofexperimentalpreparations.Inthepast,inadditionto4α-PMAand4α-PDBu,wehavealsomadesomeother4α-phorboldiesters,suchas4α-phorbol12,13-diacetate,acompoundofverylowhydrophobicity.Theseother4α-phorbolderivativesarenotcurrentlylistedasLCLabsproductsbutareavailablebyspecialrequest.Wearealsopleasedtoofferallofour4α-phorbolproductsinbulkquantitiesatsubstantialdiscounts.
• ChemicalStructures.Theprimarystructuraldifferencebetween4α-PDDandthehighlypotentphorbolester-typePKCactivatorsistheconfigurationatC4.Inthehighlyactivephorbolesterfamily,thehydroxygroupatC4isintheβconfiguration,i.e.,risingupoutofthetwo-dimensionalstructureasviewedonpaperoracomputermonitor.The4-α-phorbolesterssuchas4α-PDD,4α-PMAand4α-PDBuhavethe4-OHgrouporienteddownbelowthepaperorcomputerscreen"stwo-dimensionalplane.
• Nomenclature.Unless"4α"isspecified,all"phorbol"compoundsareautomaticallydefined,byoperationofstandardchemicalnomenclatureconventions,ashavingthe4β-configuration,aspartofthemeaningoftheword"phorbol."Thisismuchliketheword"cholesterol",whichautomaticallymeansthatitshydroxygroupatcarbon3isintheβconfiguration;thereisnoneedtospecify"3β-cholesterol",whereasacholesterolderivativewitha3αhydroxygroupwouldrequirea"3α-cholesterol"specification.Toavoidconfusioninthisfield,itisusefultonotethat,technically,4α-PDDisnota"phorbolester",itisa"4α-phorbolester",andthestructuraldifferences,thoughminoroverall,arequitesignificantbiologically.Giventheextremedifferencesintheirbiologicalproperties,bothonPKCandTRPV4channel-basedphenomena,effortstomaintaindistinctivenamesformembersofthesetwobiologicallyquitedistinctclassesofcompoundsappeartobewelljustified.
• Soldforlaboratoryormanufacturingpurposesonly;notforhuman,medical,veterinary,food,orhouseholduse.

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