Binding of Human Serum Proteins toTitanium Dioxide Particles In Vitro: Mazen S.K. Zaqout, et al. Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Japan-Objectives: To determine the capacity of human serum proteins to bind to titanium dioxide (TiO 2 ) particles of different polymorphs and sizes. Methods: TiO 2 particles were mixed with diluted human serum, purified human serum albumin (HSA) or purified human serum gamma-globulin (HGG) solutions. After incubation at 37°C for 1 h, the particles were sedimented by centrifugation, and proteins in the supernatant, as well as those bound to the particles, were analyzed. Results: The total protein concentration in the supernatant was lowered by TiO 2 , whereas the albumin/globulin ratio was elevated by the particles. Incubation with TiO 2 also lowered the immunoglobulin, pre-albumin, beta2-microglobulin, ceruloplasmin and retinol-binding protein levels, but not ferritin levels, in the supernatant. After sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE), proteins in the supernatant, especially HGG, were observed to decrease, while those released from the particles (after adding 1% SDS and heating) increased, depending on the dose of TiO 2 . Purified HGG and HSA were also bound to TiO 2 , although the former appeared to have a higher affinity. All the proteins tested showed the highest binding potency to the amorphous particles (<50 nm) and the lowest to the rutile particles (<5,000 nm), while binding to anatase particles was intermediate. The affinity to the larger anatase was higher than that to smaller anatase particles in most cases. Conclusions: Human serum proteins, including the two major components, HSA and HGG, are bound by TiO 2 particles. The polymorph of the particles seems to be important for determining the binding capacity of the particles and it may affect distribution of the particles in the body. (J Occup Health 2011; 53: 75-83)
These findings, although based on a purified form of LDH, suggest that TiO₂ NPs bind to LDH, and consequently, TiO₂ NP-induced toxicity could be underestimated by the LDH activity assay.
: Research over recent years have shown that titanium dioxide (TiO 2 ) nanoparticles (NPs) induce inf lammation in various lung, kidney, liver and brain cells. Although the mechanism of inf lammation is unclear, existing literature suggests the underlying role of oxidative stress. On the other hand, it has also been shown that nuclear factor-kappa B (NF-κB) is activated in response to pro-inf lammatory cytokines. In this study we investigated the involvement of NF-κB in TiO 2 -induced inf lammation in human lung adenocarcinomic epithelial cells (A549 cells). After 24h of treatment, IL-8 protein release from A549 cells, induced by 10, 50 and 250 μg/ml of P25 TiO 2 NPs, were statistically significantly raised, compared to that of the control. This finding corroborates existing literature in that TiO 2 NPs induce a dose-dependent increase in the release of IL-8 protein when exposed to A549 cells. However, the binding of NF-κB DNA was not affected after 6 h of incubation with P25. Therefore, NF-κB DNA binding is not the likely transcription pathway that leads to TiO 2 -induced inflammation.
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