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The Biological Potency Of Carbonaceous Nanoparticles Is Associated With The State Of Oxidation Of Surface Carbon Atoms
Citation:
SILBAJORIS, R. A., W. P. Linak, A. Kota, S. Steinmetz, P. A. BROMBERG, AND J. M. SAMET. The Biological Potency Of Carbonaceous Nanoparticles Is Associated With The State Of Oxidation Of Surface Carbon Atoms. Presented at American Thoracic Society (ATS) Annual Meeting, San Fancisco, CA, May 18 - 23, 2012.
Impact/Purpose:
Taken together, these results show that the biological potency of DD is associated with the surface content of specific oxygen-containing functional groups. These findings further suggest that the state of oxidation of surface carbon atoms in carbonaceous cores is a determinant ofthe biological potency of PM.
Description:
Epidemiological studies have shown that exposure to ambient particulate matter (PM) is associated with excess morbidity and mortality. An important component of PM consists of inorganic and organic compounds adsorbed onto a carbonaceous particle core. Toxicological studies indicate that the particle core itself is responsible for a significant fraction ofthe toxicity of PM inhalation. As particle size is reduced the surface/mass ratio increases and the toxicological effects of nanoparticles become dependent on surface properties. Detonational nanodiamonds (DD) are industrially important synthetic nanomaterials that can also be viewed as a model for studying the effect of carbonaceous particle surfaces. Human airway epithelial cells (HAEC) are a primary target of respired particles and a major source of inflammatory mediators such as the chemokine IL-8. We previously reported that non-cytotoxic exposure to DD caused a marked increase in IL-8 mRNA expression in HAEC and that its bioactivity was not driven by surface contamination with a volatile organic compound or endotoxin. We also showed that heating DD in air at 400°C resulted in ~5O% loss of potency in inducing IL-8 expression in HAEC. To identify surface chemical determinants of the toxicity associated with the DD carbonaceous surfaces, we compared the biological potency of DD activity heated at 425°C in room air or anoxic conditions. There was no difference between the IL-8-inducing potency of DD heated at 425°C in an atmosphere containing air or 100% N2 , indicating that the presence of O2 is not necessary for the deactivation reaction to occur. To identify functional groups that may be responsible for the toxicity of DD, we used Fourier Transform Infrared Spectroscopy (FTIR) to compare the surface functional groups of heated DD to the unheated starting material. FTIR spectra showed that heating DD in room air resulted in an overall increase in the content of surface carboxyl and hydroxy groups, consistent with a shift in the ratio of Sp²/Sp³ hybridization of surface carbon atoms. Taken together, these results show that the biological potency of DD is associated with the surface content of specific oxygen-containing functional groups. These findings further suggest that the state of oxidation of surface carbon atoms in carbonaceous cores is a determinant of the biological potency of PM. THIS ABSTRACT OF A PROPOSED PRESENTATION DOES NOT NECESSARILY REFLECT EPA POLICY.