Lipolysisplaysacentralroleintheregulationofenergybalance.Lipolysisistheprocessinwhichtriglycerides(TG)arehydrolyzedintoglycerolandfreefattyacids.Thisprocessreleasesfreefattyacids(FFA)intothebloodstreamwheretheymaybeeitherre-esterifiedbytheADIpocyteortraveltoothertissuesandexertothereffectsthroughoutthebody.Elevatedadipocytelipolysishasbeenobservedinobeseanddiabeticindividuals(Arner1996).Excessivefreefattyacidproductionisbelievedtocontributetoinsulinresistanceinskeletalmusclethatisobservedinobesity.Hormonesensitivelipaseistherate-limitingenzymecatalyzingtriglyceridebreakdown.Perilipins,oneofthePAT(perilipins,adipophilin,TIP47proteins)familyoflipid-associatedproteins,areimplicatedinadipocytelipolysisbymediatingtheinteractionofHSLwiththetriacylglycerolmolecule(Brasaemleetal.2004;reviewedin,Tanseyetal.2004.)Thepresenceoftheseproteinscorrespondstolipolyticstimulationinculturedadipocytes(Braemleetal.2004).

Thesympatheticnervoussystemalsoplaysakeyroleintheregulationoflipidmobilization.Themainlipolyticpathwayinvolvesbeta-agoNISTs(β-agonists),whichactivateβ-adrenergicreceptorsviatheintracellularGsproteinsinadipocytes.Thisleadstotheactivationofadenylatecyclase(AC),whichthenincreasescyclicAMP(cAMP)levels.ElevatedcAMPactsasasecondmessengertoactivatehormonesensitivelipase(HSL).HSL,therate-limitingenzymeregulatingadipocytelipolysis,thencatalyzesthehydrolysisoftriglyceridesandresultsinthereleaseofglycerolandFFA(increasedlipolysis).Phosphodiesterases(PDE)areenzymesthathydrolyzecAMPto5"-AMP(5primeadenosinemonophosphate).Thisactionresultsinadecreaseinlipolysis.PDEinhibitorsincreaseintracellularcAMPlevels.3-isobutyl-1-methylxanthine(IBMX),anon-specificinhibitorofcAMPphosphodiesterases(PDE),isusedasthepositivecontrolifyourtestcompoundsaresUSPectedPDEinhibitors.Isoproterenol,anon-specificβ-adrenergicagonistisusedasthepositivecontrolifyourtestcompoundsaffectlipolysisviaβ-adrenergicreceptors(Robidouxetal.2004).

Ourlipolysisassaykitsprovidethetooltostudychemicalcompoundsthatmayinfluencelipolysisinculturedhumanor3T3-L1adipocytes.Kitsareavailablewithandwithoutaplateofcells.Kitscanmeasuretheglyceroland/orfreefattyacidsreleasedinlipolysis.

Overviewofadipocytelipolysis