CELLULAR NEUROTOXICITY OF TRIVALENT MANGANESE BOUND TO TRANSFERRIN ORPYROPHOSPHATE STUDIED IN HUMAN NEUROBLASTOMA (SH-SY5Y) CELL-CULTURES

Previous studies have shown that cellular uptake of manganese is relat ed to its binding to transferrin. However, it is not known how transfe rrin binding influences manganese toxicity. Therefore, the cytotoxic a ctivity of manganese bound as manganic ion to either transferrin or py rophosphate was investigated in the cloned human neuroblastoma cell li ne SH-SY5Y. The toxicity of the two compounds was studied as changes i n cell growth and survival by lipid and protein determinations. There was a significant difference in the toxicity between the two complexes after 72 hr of exposure. The toxicity of the manganic-pyrophosphate ( MnPPi) complex differed from that of the manganic-transferrin (MnTf) c omplex by a factor of 2(IC50: 26 +/- 2.6 and 65 +/- 2.4 mu M, respecti vely). After 3 days of exposure to MnPPi and MnTf, the mitochondrial i ntegrity was monitored by the mitochondrial dehydrogenase activity. Th e two manganese complexes reduced the enzyme activity to the same exte nt. Measurements of membrane integrity, using (3)[H]-2-deoxy-D-glucose as a probe, showed an increase in the membrane permeability of cells exposed to MnPPi for 60 min. Exposure to MnTf did not result in any si gnificant change in membrane permeability. These findings suggest that transferrin not only mediates manganese transport into the neurone, b ut also protects the cell from damage caused by the manganic ion. The increase in cell membrane permeability after MnPPi exposure indicates that this complex may enter the cell. Furthermore, the results show th at inhibited mitochondrial function is part of the mechanism of mangan ese neurotoxicity.