Binding of Human Serum Proteins to Titanium Dioxide Particles In Vitro

Binding of Human Serum Proteins to Titanium 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 (TiO2) particles of different polymorphs and sizes. Methods: TiO2 particles were mixed with diluted human serum, purified human serum albumin (HSA) or purified human serum gamma-globulin (HGG) solutions. After incubation at 37 degrees 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 TiO2, whereas the albumin/globulin ratio was elevated by the particles. Incubation with TiO2 also lowered the immunoglobulin, pre-albumin, beta2-microglobulin, ceruloplasmin and retinol-binding protein levels, but not ferritin levels, in the supernatant. After sodium dodecyl sulfate-polyacrylamide 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 TiO2. Purified HGG and HSA were also bound to TiO2, 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 TiO2 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)