Cellular Uptake of Ti⁴⁺ by Human Cell Lines, and Presence in Mitochondria

Objectives: 1. To determine of Ti(IV)-hTF uptake into human cell lines using ICP
2. To examine mitochondria within these cells for uptake of Ti(IV) using ICP
3. To determine the effects of Ti(IV) on cell viability in the presence of transferrin
Methods: 1. Human cell line culture (HL60 and NB4)
2. Synthesis of Ti⁴⁺-transferrin (Ti(IV)-Tf) complex
3. Exposure of cell lines to Ti(IV)-Tf (0.5 - 400μM) for 24 hours
4. ICP analysis of whole cell and mitochondrial fraction
5. Cell viability using XTT
Results: Intracellular Ti(IV) was detected at a medium concentration of 0.54 µM Ti, the lowest level tested. As Ti concentration of the medium increased, a significant increase in intracellular Ti was not seen. At higher Ti concentrations a significant decrease in uptake ratio was seen. In medium containing 5~15 µM Ti, between 16%~30% (HL60) and 12%~17% (NB4) of total cellular Ti was found in mitochondria. At concentrations under ~0.6 mM (HL60) or 0.4 mM (NB4) Ti-citrate. Over 50% of cells were still viable, whilst viability dropped to 0.4 mM (HL60) and 50 µM (NB4) Ti₂-hTF was used.
Conclusions: These studies suggest that cellular uptake of Ti(IV) occurs at micromolar sublethal concentrations. While Ti(IV) alone impacts cell viability, the presence of transferrin lowers cell viability. A difference in the TC50 between cell lines suggests differences in the metabolic effects at given Ti(IV) concentrations. Ti(IV) has been detected in mitochondria in cells exposed to micromolar levels at which the cells are viable.