Sustained Release Of Melatonin From Poly(Lactic-co-Glycolic Acid)(PLGA) Microspheres To Induce Osteogenesis Of HMSCs In Vitro

Melatonin has been proven to promote bone formation and prevent bonedegradation via receptor-dependent or receptor-independent actions. The aim of thisstudy is to encapsulate melatonin into Poly(lactic-co-glycolic acid)(PLGA)microspheres (PLGA-MEL-MS) and create a melatonin sustained release system,then to evaluate its effect on the osteogenesis of human mesenchymal stem cells(hMSCs) in vitro. PLGA-MEL-MS were prepared by single emulsion-solventevaporation technique. Scanning electron microscopy demonstrated theincorporation of melatonin did not disturb the conventional generation of PLGAmicrospheres in size and morphology. In vitro drug release assay showed thatPLGA-MEL-MS exhibited a biphasic drug release pattern: a low initial burst releaseeffect with approximately40%drug release at the first3days, and a relatively tardyand continuous release with about85%drug release over the25days. Cellproliferation assay demonstrated that PLGA-MEL-MS had no apparent effect onproliferation of human MSCs. In osteogenesis assay, PLGA-MEL-MS obviously enhanced alkaline phosphatase (ALP) mRNA expression and increased ALP activitycompared to that in control group. Meanwhile, several markers of osteoblastdifferentiation were also significantly up-regulated, including runx2, osteopontin,and ostocalcin. Furthermore, quantificational alizarin red-based assay demonstratedthat PLGA-MEL-MS significantly enhanced calcium deposit of hMSCs compared tocontrol group. Therefore, this simple melatonin sustained release system cancontrol released melatonin to generate a microenvironment with relative stableconcentration of melatonin for a period of time to support osteogenic differentiationof hMSCs in vitro, suggesting that this system may be used as bone growthstimulator in bone healing in vivo.