Surface reduction of amorphous NiS particles potentiates their phagocytosis and subsequent induction of morphological transformation in Syrian hamster embryo cells.

The incidence of morphological transformation following exposure of Syrian hamster embryo (SHE) cells to crystalline alphaNiS particles was considerably greater than that following a similar exposure to amorphous NiS particles. These differences in potency were attributable to the selective phagocytosis of crystalline alphaNiS particles into cells, since untreated amorphous NiS particles were not readily taken up. Chemical reduction of the amorphous NiS particles' surface with LiAlH4 resulted in an increase both in their phagocytic uptake by Chinese hamster ovary (CHO) cells and in their ability to induce transformation in SHE cells. The phagocytosis and transforming activity of crystalline alphaNiS particles was also enhanced by LiAlH4 reduction. These results are consistent with previous observations showing that untreated crystalline NiS particles have a negative surface charge while amorphous NiS particles possess positively charged surfaces. These findings support the general hypothesis that the transforming activity of particulate metal compounds is proportional to their phagocytic uptake. Specifically, these observations show that the entry of metal sulfide particles into cells is related to their surface properties and, in particular, to the degree of negative charge on the surface microenvironment.