History Treatment of myocardial infarction with mesenchymal stem cells (MSCs) has proven beneficial effects in both animal and clinical studies. of amorphous 50?nm SiO2-NPs on viability and function of human bone marrow-derived MSCs (hMSCs); 2) to Arzoxifene HCl optimize a protocol of harmless hMSCs labelling and test its feasibility in a beating heart model. Results Optimal cell labelling is usually obtained after 16?h exposure of hMSCs to fluorescent 50?nm SiO2-NPs (50?μg mL?1); interestingly lysosomal activation consequent to NPs storage is not associated to oxidative stress. During prolonged culture hMSCs Arzoxifene HCl do not undergo cyto- or genotoxicity preserve their proliferative potential and their stemness/differentiation properties. Finally the bright fluorescence emitted by internalized SiO2-NPs allows both obvious visualization of hMSCs in normal and infarcted rat hearts and ultrastructural analysis of cell engraftment inside Arzoxifene HCl myocardial tissue. Conclusions Overall 50 SiO2-NPs display elevated compatibility with hMSCs in terms of lack IgG2b Isotype Control antibody (PE) of cyto- and genotoxicity Arzoxifene HCl and maintenance of important features of these cells. The exhibited biosafety combined with proper cell labelling and visualization in histological sections make these SiO2-NPs optimal candidates for the purpose of stem cell tracking inside heart tissue. Electronic supplementary material The online version of this article (doi:10.1186/s12951-015-0141-1) contains supplementary material which is available to authorized users. evaluation of the biosafety of 50?nm SiO2-NPs on hMSCs hMSCs exposed for 16?h-50?nm SiO2-NPs 50?μg·mL?1 display good labeling enclose SiO2-NPs inside lysosomes and are not subjected to oxidative stressPrevious works from our laboratory documented that 50?nm SiO2-NPs at the dose of 20?μg·mL?1 were taken by hMSCs via active endocytosis stored inside late endosomes and lysosomes and maintained elevated photostability at the acidic pH typical of these organelles [23 24 However for the final purpose of visualizing labelled cells inside rat hearts increased dose and incubation time need to be tested due to the small magnification necessary to appreciate the cells inside the whole tissue. Indeed in the present study confocal analysis after 16?h exposure of hMSCs to the dose of 50?μg·mL?1 (here referred as t0) produced appropriate and bright fluorescent staining (Fig.?1a arrowheads). Correspondingly circulation cytometry analysis (Fig.?1b) revealed that this mean variety of labelled cells was 95.78?±?1.27?% indicating that 50?nm SiO2-NPs on the dosage of 50?μg·mL?1are optimum contrast agents for hMSCs. Furthermore regardless of the different dosage and incubation period confocal evaluation of SiO2-NPs-exposed hMSCs labelled with Lysotracker Green verified these NPs had been kept inside lysosomes (Fig.?1d) according using the results obtained inside our previously research . Fig.?1 16 exposure of hMSCs to 50?nm SiO2-NPs 50?μg·mL?1: cell labelling intracellular localization and ROS creation. a Staining of hMSCs with SiO2-NPs (viewers) as well as for representation of consequential pieces (viewers). hMSCs labelling with SiO2-NPs and evaluation of ROS production hMSCs treated onto glass coverslips were washed twice with PBS and fixed for 15?min room heat (r.t.) with chilly 4?% paraformaldehyde (PAF) in PBS (pH 7.3). After nuclear counterstaining with Hoechst-33342 5?μg mL?1 for 15?min r.t coverslips were mounted onto glass slides with Mowiol (Calbiochem USA) and conserved at 4?°C. The labelling rate at t0 was quantified by circulation cytometry: both UT and SiO2-NPs -treated cells were harvested collected with a CyAN ADP circulation cytometer (at least 30 0 events per sample) and analysed with Summit 4.3 software (Beckman Coulter USA). Autofluorescence of UT cells was previously subtracted from your analysis data were presented in a histogram of quantity of events (Counts) vs. FL-2 Log (FL-2) and labelled cells were quantified as percentage of the total population. To mark late endosomes and lysosomes cells treated onto glass-bottomed dishes (MatTeck USA) were incubated 15?min at 37° C with the fluorescent dye LysoTracker Green 2?μmol L?1 (Life Technologies Italy) in complete DMEM washed with sterile PBS and analysed with confocal microscopy. For each time.