Magnetic Particle Characterization and Quantification of Endocytosis Mechanisms of Cultured Mammalian Cells by Magnetic Cytometry

Abstract

Magnetic characterization and quantification of individual magnetic particles and magnetically labeled cells of the sample is of much importance to assess the sample quality and better application in the fields of drug delivery, cell purification, endocytosis, cell separation, biomedical, pharmaceutical and cell therapeutics. A particle tracking velocimeter is utilized to measure magnetophoretic mobility, size, sedimentation rate, intensity and other morphological parameters of magnetic particles and magnetically labeled cells by magnetic cytometry. Magnetic cytometry by particle tracking velocimetry records the motion of labeled cells in an isodynamic magnetic field thereby estimating the key parameter, magnetophoretic mobility of labeled cells. The calibration capability of the instrument has been extended in order to estimate the actual particle size and thereby estimate the intrinsic magnetic properties of several commercial beads on a particle-by-particle basis. Different methods have been explored to estimate the magnetophoretic mobility of individual nanoparticles using the instrument. The chain velocity method is used to extrapolate mobility of the nanoparticles, which is in agreement with the theory. The receptor-independent uptake by cultured mammalian cells of magnetic nanoparticles with different surface coatings was studied to reveal the role of nanoparticle endocytosis mechanisms by using specific mechanism-based inhibitors, genistein and chlorpromazine hydrochloride. The cellular survival rate/ viability, toxicity and inhibition rate of the mechanism-based inhibitors, genistein and chlorpromazine hydrochloride is quantified by magnetophoretic mobility measurement of thousands of magnetically labeled CHO-K1 cells. Caveolae mediated and clathrin dependent endocytosis mechanisms were dominant for aminated starch and dextran-sulfate coated beads. Magnetic cytometry analysis reveals that the magnetic nanoparticle surface charge, composition and inhibitor toxicity strongly affect the cellular uptake. The particle-cell system can be optimized using velocimetry by the estimation of intrinsic magnetic properties on a particle-by-particle basis and the determination of roles of different endocytosis mechanisms.