ROS Scavenging Mn₃O₄ Nanozymes For In Vivo Anti-inflammation

Reactive oxygen species(ROS)are by-products of biological aerobic metabolism,which are often highly oxidative and play important roles in cell signaling and maintenance of homeostasis.ROS can lead to oxidative stress,which is associated with a series of diseases,such as aging,diabetes,cardiovascular diseases,inflammation,neurological diseases(Parkinson’s disease and Alzheimer’s disease),and cancer.There are a number of ROS scavenging natural enzymes such as superoxide dismutase(SOD),catalase(CAT)and peroxidase(POD).Among them,SOD can catalyze the disproportionation of superoxide radicals.According to different active centers,natural SOD can be divided into three categories:MnSOD,CuZnSOD,and FeNiSOD.Among them,MnSOD has many advantages,such as long life span,low molecular weight and anti-radiation effects.Besides,pathological studies have shown that MnSOD is advantageous over CuZnSOD and FeNiSOD in the treatment of acute diseases.However,these natural enzymes,including MnSOD,are not stable.They are easily denatured under high temperature and extreme pH conditions and difficult to prepare and store.Therefore,researchers have been trying to find natural enzyme mimics to overcome the shortcomings of natural enzymes,especially mimetic enzymes that can eliminate ROS.With the development of nanoscience,some nanomaterials with natural enzyme activity(termed as nanozymes)have attracted wide attentions.Researchers have prepared a variety of Mn-based artificial enzymes such as Mn porphyrins to mimic natural SOD.However,there are very few reports of Mn-based nanomaterials for mimicking natural SOD to eliminate ROS.The thesis focuses on Mn-based nanomaterials,and studies Mn3O4 nanozymes for the treatment of inflammation in vivo by eliminating ROS.(1)We synthesized Mn3O4 nanoparticles by a hydrothermal method and characterized their size,crystal form,and surface chemistry properties by TEM,XRD,XPS and other characterization methods.It is proved that we have synthesized Mn3O4 nanoparticles with uniform morphology and all the measured diffraction peaks matched well to the standard pattern of hausmannite Mn3O4.In vitro,we demonstrated that Mn3O4 nanozymes had good elimination effects on common reactive oxygen radicals,such as superoxide dismutase(·O2-),hydrogen peroxide(H2O2),and hydroxyl radical(·OH).Mn3O4 nanozymes also had better elimination ability than commonly used CeO2 nanozymes.In terms of stability,Mn3O4 nanozymes were superior to natural SOD and CAT.Subsequently,we established a mouse ear inflammation model.After injecting Mn3O4 nanozymes in situ,it was confirmed by living animals imaging and H&E tissue section staining that the ear inflammation in mice had been alleviated to some extent.Both in vitro and in vivo experiments have shown that Mn3O4 nanozymes had ROS scavenging capability and achieved the treatment of inflammation by reducing ROS levels.(2)In order to improve the long-term stability of Mn3O4 nanozymes in vivo,we used an oil phase strategy to synthesize oleylamine-encapsulated Mn3O4 nanozymes.Then we used amphiphilic phospholipid polymer DSPE-PEG-COOH to achieve oil-to-water modification and eventually we synthesized Mn3O4@OLA@DSPE-PEG-COOH(termed as DPO-Mn3O4)nanozymes with good water solubility and uniform size.The in vitro results showed that the DPO-Mn3O4 nanozymes retained the capability of eliminating ROS.Based on the results of in vitro experiments,we established inflammatory bowel disease in mice and injected DPO-Mn3O4 nanozymes by the method of enema.By observing the length and degree of swelling of the mice edema,we further verified that Mn3O4 nanozymes can alleviate living inflammation through the elimination of ROS.