Serum Apolipoprotein A-Ⅰ Depletion Is Causative To Silica Nanoparticle-induced Cardiovascular Damage

Silica nanoparticles are one of the most widely used nanomaterials and have important applications in industry and life.In addition,the pollution of particulate matter in the environment and exposure to occupational diseases also increase the potential harm of silica nanoparticles.Current studies have shown that there is a certain correlation between particulate matter exposure and cardiovascular disease.However,the underlying mechanism remains to be explored.PartⅠ:In order to explore the impact of silica nanoparticles（SiNPs）on the cardiovascular system,we established a model of respiratory exposure of SiNPs in mouse and explored its damage to the mouse cardiovascular system.In this model,intranasal instillation of silica nanoparticles（SiNPs）was proceeded on male Apo E^-/-C57BL/6 mice.Three months later,the heart,liver,spleen,lung,kidney and mice aorta were collected,tissue sections were prepared and used for corresponding pathological staining examinations.The results showed that the aorta of mice exposed to SiNPs exhibit more severe damage,accompanied by significant lipid deposition.At the same time,the lungs of SiNPs-exposed mice have extremely significant fibrotic lesions,and the liver and kidneys also have varying degrees of damage.In addition,the presence of respiratory-exposed SiNPs was directly observed in mice blood.The above experimental results show that long-term respiratory exposure of SiNPs can induce significant cardiovascular damage in mice,and SiNPs have been shown to enter the blood circulation through respiratory exposure,thereby providing potential evidence for SiNPs-induced cardiovascular damage.PartⅡ:In order to explore the interaction of SiNPs with the body in the lungs and blood circulation,we introduced the concept of protein corona to investigate the interaction between SiNPs and biomolecules in various biological fluids.Respiratory exposed SiNPs first reach the lungs,contact with the pulmonary surfactant（PS）in the alveoli,and then pass through the air-blood barrier into the blood circulation and come into contact with blood components.Therefore,in order to explore how the pre-contact of SiNPs with PS in the alveoli will affect their fate in the blood circulation,we simulated and prepared the complexes formed by SiNPs in the alveoli（SiNPs-PS）and SiNPs formed in the blood in vitro.SiNPs-MP represents the product of SiNPs directly interacting with the blood,and SiNPs-PS-MP represents the product of SiNPs interacting with the blood after passing through air-blood barrier.In order to deeply explore the components of the protein corona formed by SiNPs and SiNPs-PS in the blood circulation,we used proteomics to quantify the components of the protein corona.The results showed that pre-inbucation with PS could significantly increase the adsorption of apolipoprotein A-Ⅰ（Apo A-Ⅰ）in plasma.The main lipid component of PS,dipalmitoyl phosphatidylcholine（DPPC）can be adsorbed on the surface of SiNPs,increase the hydrophobicity of the surface of SiNPs,thereby facilitate the adsorption of Apo A-Ⅰ in the blood.In addition,the adsorption of Apo A-Ⅰ by SiNPs will cause a certain change in the secondary structure of Apo A-Ⅰ protein.Therefore,the pre-incubation of PS in the alveoli will increase the hydrophobicity of the SiNPs surface,thereby enriching the Apo A-Ⅰ adsorption in the blood,resulting in a significant increase in the proportion of Apo A-Ⅰ in the protein corona.Different components of the protein corona may affect the fate of nanomaterials in the body.PartⅢ:In order to explore the effects of SiNPs on its toxicity after the formation of protein corona,we studied the biological effects of SiNPs adsorption of Apo A-Ⅰ from the perspectives of cellular uptake,cytotoxicity,and inflammatory damage.The results show that the formation of protein corona（SiNPs-MP）can reduce the uptake of SiNPs by macrophages,and the enriched adsorption of Apo A-Ⅰ（SiNPs-PS-MP）further reduces the cellular uptake level.Protein corona coating can reduce the cytotoxicity of SiNPs,and the enrichment and adsorption of Apo A-Ⅰ further reduces the cytotoxicity of SiNPs.In addition,transcriptomics results show that SiNPs can significantly induce upregulations of atherosclerosis-related inflammatory factors（including interleukins and chemokines）,while the formation of protein corona and the enriched adsorption of Apo A-Ⅰ significantly alleviated this toxic effect.RT-q PCR verified the results of transcriptomics.Consequently,adsorption of Apo A-Ⅰ significantly reduced the uptake level of SiNPs by macrophages,and the cytotoxicity as well as inflammation induced by SiNPs were also significantly reduced.PartⅣ:In order to explore the biological effects of SiNPs on the body caused by the enriched adsorption of Apo A-Ⅰ,we investigated the effect of long-term respiratory exposure of SiNPs on the concentration of Apo A-Ⅰ in the mice blood.Through blood circulation testing,it was found that SiNPs and SiNPs-PS can be quickly cleared in blood circulation.Enzyme-linked immunosorbent assay（ELISA）was applied to evaluate the effects of SiNPs,SiNPs-PS and SiNPs-PS-MP exposure on Apo A-Ⅰ concentration in the blood.The results showed that SiNPs can reduce the concentration of Apo A-Ⅰ in the blood to a certain extent,and SiNPs-PS can further reduce the concentration of Apo A-Ⅰ in the blood because it can enrich and adsorb Apo A-Ⅰ.Long-term respiratory exposure of SiNPs can also significantly induce Apo A-Ⅰ depletion in serum,increase the serum inflammation levels（lactate dehydrogenase,LDH）,and lipid accumulation in the aortic wall;while additional supplementation of Apo A-Ⅰ mimetic peptides significantly alleviated the above symptoms.In addition,Apo A-Ⅰ concentration of silicosis patients was found to be notably lower than that of healthy people,and even significantly lower than that of patients with coronary heart disease,indicating the decrease in serum Apo A-Ⅰ in silicosis patients may be the potential reason to induce cardiovascular damage.