Inhibitory Effect Of Metformin On Osteolysis And Vascular Calcification Via AMPK Pathway

Total joint arthroplasty is a widely successful procedure that reduces pain,restores mobility, and enables arthritis patients to return to varied activities ofdaily living. The treatment of end-stage osteoarthritis by way of total jointarthroplasty has overtime led to a struggle to mitigate the effects of asepticloosening secondary to periprosthetic osteolysis. There is a wealth of evidence toindicate that the implant-derived wear debris induced osteolysis remain aprincipal cause of implant failure. The osteolytic process is believed to start withthe activation of macrophages and foreign-body giant cells and with phagocytosisof particulate wear debris. This appears to induce the release of proinfammatorycytokines and mediators that provoke the diferentiation of phagocyte precursorsinto osteoclasts, which, in turn, results in periprosthetic osteolysis and implantloosening. Therefore, the key point for prevention and/or treatment forperi-prosthetic osteolysis and aseptic loosening consists in inhibiting theproduction of inflammatory factors and activation of osteoclast that induced byactivation of macrophages. In addition, most of the patients receiving total joint replacement are the elderly, who often suffer from osteoporosis and diabetes,which states is closely related to some cardiovascular diseases such asatherosclerosis and vascular calcification. More surprisingly, someanti-osteoporotic drugs(such as estrogen, bisphosphonates and OPG) also havebeneficial effect on vascular calcification, which suggest that the coincidence ofvascular calcifcation with low bone activity and osteoporosis could bebiologically linked.AMPK is a serine/threonine protein kinase that plays a key role in metabolichomeostasis in all eukaryotic cell types. There is a wealth of evidence to indicatethat as an AMPK agonist, metformin have bone-protective property. This drugnot only could enhance the differentiation and mineralization of osteoblastic cells,but also could negative regulate the RANKL in the differentiation of osteoclasts.Morever, AMPK could promote macrophage polarization to an anti-inflammatoryfunctional phenotype. In addition, recent fndings showed that the activation ofAMPK is favorable for prevention of vascular calcification. The purpose of thisstudy is to investigate the in vitro effects of metformin on macrophage-derivedcytokines production stimulated by UHMWPE particle, and the in vivo effects ofmetformin on UHMWPE particle induced osteolysis, and whether metformincould attenuate polyethylene particle-induced mouse calvarial osteolysis,associated with a reduction in severity of inflammation and osteoclast number,and the in vitro effects of metformin on β-glycerophosphate-induced vascularcalcification and the involved mechanism.The in vitro cell culture results showed metformin could significangtlyinhibit UHMWPE particles induced proinflammatory cytokines(TNF-α and IL-6)production and promote anti-inflammatory cytokines(IL-10) release, and thiseffect is AMPK-dependent. Using metformin（100mg/kg/d）treated UHMWPE particles induced mouse calvarial osteolysis model showed that metformin notonly reduce proinflammatory cytokines production, osteoclasts formation and thearea of osteolysis, but also enhance anti-inflammatory cytokines release, and thiseffect is closely related to the effect of metformin on the expression ofmacrophage function phenotype associated protein via AMPK activation. The invitro β-glycerophosphate-induced vascular calcification results showedmetformin significantly suppressed β-Glycerophosphate-induced Ca depositionand ALP activity in dose dependent manner, and metformin might exert itsinhibitory effects on vascular calcification throughAMPK-eNOS-NO pathway.This study showed metformin could inhibit UHMWPE particles inducedproinflammatory cytokines production, osteoclastogenesis and osteolysis viaAMPK pathway and also have an inhibitory effect onβ-glycerophosphate-induced vascular calcification. Therefore, we have reason tobelieve that in the near future, metformin, or some other more tissue-specifichigh-selective AMPK aonist as a therapeutic target will have a broader prospectsin the treatment of bone and cardiovascular metabolic disorders related diseases.