Cytotoxic and transforming effects of silica particles with different surface properties in Syrian hamster embryo (SHE) cells

Several crystalline and amorphous silica dusts (two quartz of natural origi n, one cristobalite of natural and two of biogenic origin, three amorphous diatomite earths and one pyrogenic amorphous silica) were studied in the SH E cell transformation assay, in order to compare their cytotoxic and transf orming potencies and examine the role of the structure and of the state of the surface on these effects. Some samples were modified by grinding, etchi ng and heating with the aim of establishing relationships between single su rface properties and biological responses. The results showed that some qua rtz and cristobalite dusts (crystalline) as well as the diatomaceous earths (amorphous), but not the pyrogenic amorphous silica, were cytotoxic and in duced morphological transformation of SHE cells in a concentration-dependen t manner. The ranking in cytotoxicity was different from that in transformi ng potency, suggesting two separate molecular mechanisms for the two effect s. The cytotoxic and transforming potencies were different from one dust to another. even among the same structural silicas, The type of crystalline s tructure (quartz vs cristobalite) and the crystalline vs biogenic amorphous form did not correlate with cytotoxic or transforming potency of silica du sts, Comparison of cellular effects induced by original and surface modifie d samples revealed that several surface functionalities modulate cytotoxic and transforming potencies. The cytotoxic effects appeared to be related to the distribution and abundance of silanol groups and to the presence of tr ace amounts of iron on the silica surface, Silica particles with fractured surfaces and/or iron-active sites, able to generate reactive oxygen species , induced SHE cell transformation. The results show that the activity of si lica at the cellular level is sensitive to the composition and structure of surface functionalities and confirm that the biological response to silica is a surface originated phenomenon. (C) 2000 Elsevier Science Ltd. All rig hts reserved.