BSA-MnO₂ Nanoprobes For Timely Permeability Imaging Of Blood Brain Barrier And Prediction Of Hemorrhage Transformation In Acute Ischemic Stroke

ObjectiveHemorrhage transformation（HT）is a frequent but maybe fatal complication following the acute ischemic stroke due to the severe damage of blood brain barrier（BBB）.CT examination is sensitive to hemorrhage occurrence in brain,however this method may only indicate certain outcome and cannot predict the risk of hemorrhage.Quantitative BBB permeability imaging is a promising method to predict the HT in stroke patients for a favorable prognosis.Furthermore,the leaky BBB in the infarct area provides a natural opportunity for drug delivery to the brain,thus the accurate evaluation of the BBB permeability could also guide the drug delivery.However,the clinical gadolinium chelates-based magnetic resonance（MR）imaging of stroke suffer from the relatively lower sensitivity and potential side effects of nephrogenic systemic fibrosis and intracranial gadolinium deposition.Herein,this study aims to develop a biocompatible MR nanoprobes for timely permeability imaging of BBB and prediction of HT in acute ischemic stroke.MethodsProtein-templated manganese dioxide nanoprobes（BSA-MnO₂）were firstly synthesized using bovine serum albumin and potassium permanganate through a simple one-step redox reaction.Then a series of physiochemical characterizations,stability and MR imaging ability of BSA-MnO₂ nanoprobes were performed.Subsequently,the real-time imaging ability of BSA-MnO₂ nanoprobes and Gd-DTPA on BBB permeability after acute ischemic stroke was investigated in a rat model of middle cerebral artery occlusion（MCAO）.The predictive value of different imaging patterns displayed by BSA-MnO₂ enhanced MRI on post-stroke HT was further quantitatively analyzed by the receiver operating curve（ROC）and Logistic binary regression.Meanwhile,the matching degree between the contrast-enhanced MRI in vivo and Evans blue-based ex vivo staining for BBB integrity was evaluated.Finally,the biocompatibility of BSA-MnO₂ nanoprobes was systematically evaluated by in vitro cytotoxicity test,in vivo blood biochemical analysis,organ metabolism,neurobehavioral assessment,and histological and pathological analysis.ResultsThe BSA-MnO₂ nanoprobes owned the characteristics of simple and green synthesis method,good water solubility,high stability,and high T₁ relaxation rate.A series of in vivo and in vitro evaluation experiments demonstrated the good biocompatibility of BSA-MnO₂ nanoprobes.The BSA-MnO₂ nanoprobes enhanced MRI could timely visualize the BBB permeability change in MCAO rat model.Moreover,the imaging parameters（increased peak intensity,extended imaging duration,and expanded imaging region）indicated by BSA-MnO₂ nanoprobes enhanced MRI all showed good predictive value for HT.According to the analysis of ROC,the sensitivity of HT prediction were 90%,based on the extended imaging duration alone.While the sensitivity and specificity using the combined predictive model with three patterns were 85%and 80%,respectively.The range and intensity of BSA-MnO₂leaky areas in vivo matched well with the extravasation areas of Evans blue ex vivo in the MCAO rats no matter with or without HT.ConclusionThe BSA-MnO₂ nanoprobes synthesized by the biomimetic method showed excellent MR imaging capability and biocompatibility.The BSA-MnO₂ nanoprobes not only enabled the timely visualization of damaged BBB,but also showed a good prediction of HT in the acute ischemic stroke through the typical imaging characteristics of increased peak intensity,extended imaging duration,and expanded imaging region,highlighting the significance for the clinical treatment of stroke patients.Furthermore,the BSA-MnO₂ nanoprobes guided BBB hyper-permeability imaging can also be generalized to the theranostics of other BBB damage-related neurological disorders（Alzheimer’s disease,traumatic brain injury,and demyelinating disease）.Therefore,the BSA-MnO₂ nanoprobes held immense potential to be promising candidates for substituting the Evans blue staining of the damaged BBB ex vivo and clinical Gd chelate-based contrast agents for MR imaging of stroke in vivo,benefiting the fundamental research and clinical theranostics of stroke patients,respectively.