Interaction between combustion-generated organic nanoparticles and biological systems: in vitro study of cell toxicity and apoptosis in human keratinocytes.

The purpose of this work was to evaluate the effect of flame-generated nucleation mode particles with an organic carbon structure on growth and apoptosis in immortalized human keratinocytes. In this study, cells were stimulated with nanoparticles collected from flames that produce only nucleation mode particles operating with a fuel:air mixture typical of low-emission combustion systems. Cytotoxicity as a function of particle concentration was monitored by fluorescence-activated cell sorting (FACS) analysis, and apoptosis was observed by FACS using DNA fragmentation and hypodiploidism and confirmed by annexin assay. A dose-dependent reduction in cell viability by apoptosis in incubation periods of 48 and 72 hours was observed with a statistically significant increase in apoptosis over controls for a dose larger than 7 μg/mL (1.4 μg/cm²). The results presented here may be relevant for understanding the association between exposure to traffic-generated particulate pollution and enhanced skin aging reported in epidemiology studies.