Study On Light-triggered Nitric Oxide Release Platform Based On Upconversion Nanoparticles For The Treatment Of Osteoporosis

Osteoporosis is one of the most common diseases affecting the metabolic function of bone tissue,leading to bone loss and the reduction of mechanical strength,which in turn increases the risk of fractures.Osteoporosis seriously reduces the quality of patient’s life,especially when fracture occurs,placing a great burden on families and communities.At present,with the aging of the population,the prevalence of osteoporosis is also increasing year by year.Hormone replacement therapy（HRT）was one of the most important methods to prevent osteoporosis.Although it has achieved certain efficacy,long-term use of estrogen will increase the risk of malignant lesions of reproductive organs.Furthermore,traditional anabolic drugs and anti-absorption drugs can prevent osteoporosis to a certain extent,but the cost and side effects of these drugs are also burdensome.Currently,researchers have tried to shift their focus on nanomaterials with fewer side effects than synthetic drugs.Nitric oxide（NO）is an endogenous free radical involved in a variety of biological processes including bone remodeling,which can reverse osteoporosis to a certain extent.However,NO is an endogenous gas with a transitory half-life（about 5 seconds）and short diffusion radius（40-200μm）,which limit its application in vivo.Releasing NO in bone tissue in a controlled manner with an appropriate way will be of great significance for the treatment of osteoporosis.Light-controlled release is an ideal way to achieve this goal.However,light-controlled release of NO usually requires direct excitation of NO donor by UV/blue light,but the tissue penetration depth of UV/blue light is often strictly limited,which limits its application in vivo.How to achieve effective and controlled release of NO in bone tissue in response to light is the prerequisite to ensure that NO could reverse osteoporosis.In this study,the bone targeting NO release gas therapy nanoplatform（UCPA）was prepared,based on near-infrared（NIR）light excitation and upconversion nanoparticles（UCNPs）,which could deliver and stimulate NO donor（BNN）to release NO in situ in bone tissue,and ultimately reverse osteoporosis.The main research contents of this work are as follows:（1）Theβphase UCNPs were synthesized using the thermal decomposition method（including core,core-shell and core-shell-shell structures）.Then,according to the St（?）ber method and the selective surface modification,the UCNPs were then coated with a layer of mesoporous silica modified by selective external surface aminoization.The drug delivery of NO donor was then realized.Next,the bisphosphonate of alendronate was decorated on mesoporous silica surface to endow the nanocarrier bone targeting property.Finally,the characterization and physicochemical properties of this nanoplatform were investigated.The results showed thatβphase UCNPs had good luminescence properties（UV/blue light）,which could effectively stimulate NO release from NO donor（BNN）and achieve NO release in osteoblasts（mouse osteoblastic cell line,MC3T3-E1）.In addition,the alendronate modificated nanocomposite showed good bone targeting ability in vitro and in vivo,providing a solid foundation for the in-situ release of NO in bone tissue,indicating that the nanocarrier is a potential biomaterial for the treatment of osteoporosis.（2）The biosafety of biomaterials is the guarantee for realizing their application in vivo.The common excitation wavelength of UCNPs is 980 nm near infrared（NIR）light,but the light source is overlaped with the strongest absorption band of water,and the human tissues are rich with water.Under the irradiation of 980 nm NIR light,it is easy to cause severe tissue heating and the penetration depth is also shallow,so it is not suitable for its application in vivo.However,the 808 nm NIR light is far from the strongest absorption band of water,which is a safer light source.In order to avoid potential tissue damage caused by heating effect,Nd³⁺was doped in the intermediate shell during the synthesis of core-shell-shell UCNPs,so that UCNPs could be excited by 808 nm NIR light.Subsequently,we further verified the favorable biosafety of 808nm NIR light.Meanwhile,the biosafety of UCPA-BNN was also verified in vitro by cell experiments.Moreover,under 808 nm NIR light irradiation,NO released from UCPA-BNN showed the potential to promote osteogenesis in vitro,which provided a basis for reversing osteoporosis in vivo.（3）Although UCPA had good bone targeting ability and light conversion ability under NIR light excitation（NIR light→UV/blue light）,which could further stimulate NO donor（BNN）to release NO for osteogenesis effectively,its biosafety and ability to reverse osteoporosis in vivo were not clear.Therefore,we further applied it in osteoporosis mice induced by ovariectomy.During several months of observation,we found that compared with the Sham group,the weight of ovariectomized mice increased relatively quickly,with no difference between every ovariectomized group.In addition,the hematoxylin-eosin（H&E）staining of the major organs was normal,indicating the success of modeling and the in vivo biosafety of the material.After treatment,Micro-CT（Micro-computed tomography）was carried out to analyze the corresponding bone tissues,and it was found that under 808 nm NIR light,UCPA-BNN had the favorable curative effect in reversing osteoporosis,compared with the pure ovariectomized group and UCPA-BNN group without irradiation.These results suggested that NO release was the key factor in promoting osteogenesis and reversing osteoporosis.