INDUCTION OF VANADIUM ACCUMULATION AND NUCLEAR SEQUESTRATION CAUSING CELL SUICIDE IN HUMAN CHANG LIVER-CELLS

Very little is known about the modulation of vanadium accumulation in cells, although this ultratrace element has long been seen as an essen tial nutrient in lower life forms, but not necessarily in humans where factors modulating cellular uptake of vanadium seem unclear. Using nu clear microscopy, which is capable of the direct evaluation of free an d bound (total) elemental concentrations of single cells we show here that an NH4Cl acidification prepulse causes distinctive accumulation o f vanadium (free and bound) in human Chang liver cells, concentrating particularly in the nucleus. Vanadium loaded with acidification but le aked away with realkalinization, suggests proton-dependent loading. Va nadyl(4), the oxidative state of intracellular vanadium ions, is known to be a potent source of hydroxyl free radicals (OH.). The high oxida tive state of nuclei after induction of vanadyl(4) loading was shown b y the redox indicator methylene blue, suggesting direct oxidative dama ge to nuclear DNA. Flow cytometric evaluation of cell cycle phase-spec ific DNA composition showed degradation of both 2N and 4N DNA phases i n G(1), S and G(2)/M cell cycle profiles to a solitary 1N DNA peak, in a dose-dependent manner, effective from micromolar vanadyl(4) levels. This trend was reproduced with microccocal nuclease digestion in a ti me response, supporting the notion of DNA fragmentation effects. Sever al other approaches confirmed fragmentation occurring in virtually all cells after 4 mM V(4) loading. Ultrastructural profiles showed variou s stages of autophagic autodigestion and well defined plasma membrane outlines, consistent with programmed cell death but not with necrotic cell death. Direct intranuclear oxidative damage seemed associated wit h the induction of mass suicide in these human Chang liver cells follo wing vanadium loading and nuclear sequestration.