STUDY OF THE STABILITY OF A PARAMAGNETIC LABEL LINKED TO MESOPOROUS SILICA SURFACE IN CONTACT WITH RAT MESOTHELIAL CELLS IN CULTURE

Stable radicals detectable by electron paramagnetic resonance (EPR) ma y be of use in the investigation of early events in cell-particle toxi city. Pipridine-N-oxyl derivatives (nitroxides), covalently linked to the surface of a high surface area silica (used as model solid for the technique), served as probes in the investigation of the effects of i ncubation of silica particles with mesothelial cells. A mesoporous sil ica (MCM-41), prepared by precipitation from a micellar solution, was the most appropriate silica-based particle for this purpose, as its ch annels allow direct contact with small molecules but not with macromol ecules. The cytotoxicity of this amorphous silica is very low, allowin g relatively high particle loading in the cell cultures. Both the high surface area of the sample and the large amount of inorganic material extracted from the cell culture provide enough material to run reason ably intense EPR spectra. Computer-aided analysis of the EPR spectra o f silica-bound nitroxides provided information on the sensitivity of t he labeled silica monitoring different environments, e.g., to follow t he path of particles in a mammalian cell culture. Upon contact of the particles with mesothelial cells, the mean distance among the labels a t the silica surface decreased as a consequence of the release of oxid izing and/or radical moieties from the cells.