Graphite particles induce ROS formation in cell free systems and human cells

It is commonly accepted that the toxicity of carbonaceous particulate matter (PM) is due to the production of reactive oxygen species (ROS) which induce biological damages in the exposed cells. It is also known that PM produced during the combustion processes consists of a carbonaceous core “dressed” with other organic and/or inorganic materials. In spite of this knowledge, the role of these materials in the production of ROS is not yet clear. This work aims at understanding whether “naked” carbonaceous particles are capable to form ROS either in cell-free or in-cell systems. The problem has been treated based on the data collected on pure graphite samples of different size obtained by ball–milling pure graphite for various time lengths. The experimental approach considered Raman, ESR (spin trapping), cell viability and fluorescence spectroscopy measurements. These techniques allowed to carry out measurements both in cell and cell-free systems and the results consistently indicate that also pure naked carbonaceous particles can catalyze the electron transfer that produces superoxide ions. The process depends on the particle size and enlightens the role of the edges of the graphitic platelets. Evidence has been collected that even “naked” graphitic nanoparticles are capable to produce ROS and decrease the cell viability thus representing a potential danger to human health.