Molecular Mechanism Of Cell Membrane Damage By Rare Earth Oxide Nanoparticles

The increasing use of rare earth oxides(REOs)nanoparticles makes them inevitably released into the environment and potentially harmful to human beings.REOs entering the human beings can damage biological membrane and induce a series of adverse biological effects,including inflammatory and fibrotic effects.Biological membrane damage by REOs is a molecular initiating event in the pathway for adverse outcomes,but the underlying molecular mechanisms remain controversial.To elucidate the molecular mechanism of biological membrane damage by REOs,this study analyzed the effects of two typical REOs,Gd2O3 and CeO2,on red blood cell membrane.Combined with visualization by electron microscopy and vesicle,the key events of cell membrane damage by REOs were revealed,and the underlying molecular mechanism of key events was further elucidated through theoretical calculation.The rate of hemolysis of erythrocytes by REOs was measured to provide direct evidence of cell membrane damage.Hemolysis test showed that Gd2O3 exhibited higher hemolysis than CeO2,and significantly damaged the morphology of cell membrane.Visualization of the cell membrane interface by electron microscopy and analysis of the adsorption and dephosphorylation of phospholipids by REOs using liquid chromatography-tandem mass spectrometry(LC-MS/MS)revealed two key events that damaged cell membrane:firstly,Gd2O3 with positive surface charge was more likely to accumulate on the negatively charged membrane surface;secondly,due to its strong affinity for phosphate,the aggregated Gd2O3 could strip phosphate from the phospholipid head,resulting in biotransformation at the nanobiological interface,accompanied by dephosphorylation of 3.3%phospholipid at 10 mg/L,and ultimately induce cell membrane damage.In addition,two key events of cell membrane damage were further confirmed by verifying that the passivation effect of phosphate could alleviate the cell membrane damage by REOs.To reveal the mechanism of dephosphorylation,density functional theory(DFT)was used to reveal the reaction path and mechanism of phosphate stripping from phospholipid head group by REOs.The energy step diagram of the dissociation of the phospholipid head on the REOs surface showed that the dissociation energy barrier of the P-O bond on the Gd2O3(222)and CeO2(111)surface was much lower than that of the C-O bond.Notably,Gd2O3(222)surface compared with CeO2(111)surface was easier to induce phospholipid head to dissociate P-O bond.This result indicated that Gd2O3(222)dephosphorylated the phospholipid head by dissociating P-O bond to capture phosphate in phospholipid molecules and induced cell membrane damage.Based on DFT calculation,the adsorption behavior of phosphate on REOs surface was further simulated,and it was found that the adsorption energy of phosphate on Gd2O3(222)surface(-3.79 eV)was higher than that on CeO2(111)surface(-1.61 eV).Combined with molecular orbital theory and density of state analysis,the molecular orbital energy level diagram of REOs adsorbed phosphate was constructed.It was found that the d orbital of Gd atom,which was higher than Fermi level,was hybridized with the p orbital of phosphate oxygen atom,splitting the anti-bonding orbital,which was higher than Fermi level,and stabilized the adsorption system.The d-band center,a descriptor to characterize adsorbate-metal interactions,was introduced to quantitatively describe the energy level structure of the d-orbital of rare earth atoms to evaluate the adsorption energy of REOs for phosphate.Based on this,this study proposed a new mechanism for controlling the d-band center of rare earth atoms based on crystal planes.Finally,the d-band center and zeta potential of REOs were used as descriptors to quantitatively analyze the potential of REOs to damage cell membranes(R2=0.87).In this study,the key events and molecular mechanism of cell membrane damage by REOs were revealed,and a new mechanism for regulating the interaction between REOs and cell membranes based on d-band center was proposed.The results provided a theoretical basis for regulating the biological effects of REOs and the safe design for nanomaterials.