The Effect And Mechanism Of Near Infrared Light Induced Black TiO₂ Nanoprobes On Foam Cells

Atherosclerosis（AS）is one of major diseases that seriously threatens people’s life and health.It is of great clinical value and scientific significance to develop novel nanotechnology-based AS treatment.Macrophages and macrophages-derived foam cells are the key processes in the development of AS,therefore make these cells become promising therapeutic target.In this thesis,we synthesized black titanium dioxide（bTiO₂）nanoprobes with functions of near infrared light（NIR）-activated photothermal-photodynamic therapy,study the regulations and mechanisms of lipid metabolism in macrophage derived foam cells which are treated by 808nm of NIR laser triggered bTiO₂ nanoprobes,and preliminary research the inhibitory effect on foam cells formated from macrophages,which will come up with a new strategy for treating AS.The main results are summarized as follows:（1）Preparetion and characterizations of black TiO₂ based nanoprobes.Sodium borohydride was used to reduce white TiO₂ nanoparticles to black TiO₂ nanoparticles.Hyaluronic acid（HA）was coated on the surface of black TiO₂ nanoparticles to enhance the ability to target macrophages.Furthermore,to ehance the photodynamic performance,photosensitizer porphyrin was attached to the surface of black TiO₂-HA nanoprobes by electrostatic absorption to form TiO₂-HA-porphyrin nanoprobes.The results showed that the average size of black TiO₂-HA-porphyrin nanoprobes was 211 nm,the zeta potential was-32.2 m V,and the loading rate of porphyrin was 9.3%.Black TiO₂-HA nanoprobes exhibited efficient photothermal conversion and high level of singlet oxygen productions under the excitation of 808 nm near-infrared light,which indicated the nanoprobes possessing photothermal-photodynamic synergistic therapeutic effects.（2）Regulation of lipid metabolism in foam cells and inhibition of macrophage foam induced by 808nm NIR-excited nanoprobes.The results showed that the cell viabilities of foam cells were close to 90% after incubated with 75μg/mL bTiO₂-HA-porphyrin nanoprobes,indicating that the nanoprobes we synthesized were highly biocompatible,and effectively reduced the cytotoxicity of porphyrin.In addition,the phagocytosis of bTiO₂-HA-porphyrin nanoprobes by foam cells and macrophages were significantly increased after HA modification,showing the targeting effect of bTiO₂-HA-porphyrin nanoprobes.After 808 nm NIR irradiated at 1.5 W/cm² for 10 minutes,the cell viabilities of foam cells were higher than 90% without significant apoptosis or necrosis,it might contribute to the increased protein level of heat shock protein 27（HSP27）after photothermal effect,which performed protective effects and thereby inhibited cell apoptosis.The study of cholesterol metabolism showed that,on the one hand,the 808 nm NIR laser triggered phototherapy of bTiO₂-HA-porphyrin nanoprobes performed a potential anti-AS effect by inhibiting the synthesis of cholesteryl ester（CE）,promoting CE hydrolysis,increasing the free cholesterol（FC）and therefore reducing the accumulation of lipid in foam cells.The further studies showed that bTiO₂-HA-porphyrin nanoprobes could regulate lipid metabolism in foam cells by increasing the gene expression of ATP binding cassette transporter A1（ABCA1）that can promote cholesterol efflux,as well as decreasing the protein expression of cholesterol regulatory element binding proteins 2（SREBP2）and low-density lipoprotein receptor（LDLR）,which can reduce intracellular lipid accumulation.On the other hand,for macrophages,808 nm NIR laser irradiated bTiO₂-HA-porphyrin nanoprobes reduced intracellular TC level by decreasing the cellular uptake of oxidized low-density lipoprotein（ox-LDL）,promoting intracellular CE hydrolysis and increasing FC efflux,thereby inhibiting the process of foam cells formation.