S1: Percellome Project on Sick-Building-Syndrome level inhalation
Percellome Project on Sick-Building-Syndrome level inhalation for the prediction of neurobehavioral toxicity
Biological Safety Research Center, National Institute of Health Sciences, Japan
Section Chief, Division of Cellular & Molecular Toxicology
Toxicity of volatile organic compounds (VOCs) in indoor air, such as formaldehyde (FA), xylene (Xy) and p-dichlorobenzene (pDB), at the levels of Sick House/Building Syndrome (SHS) is difficult to assess by the ordinary inhalation animal studies; histopathological endpoints are negative for toxicity at such concentration levels. Here we applied our Percellome Toxicogenomics Project that has been launched to develop a comprehensive gene network for the mechanism-based predictive toxicology using time- and dose-dependent transcriptomic responses induced by a chemical in mice. This Project was initiated to reinforce and eventually replace the “safety factor (uncertainty factor)” widely used for the extrapolation of experimental animal data to humans. For this purpose, a normalization method designated as “Percellome” is developed (BMC Genomics 7:64, 2006) to generate mRNA expression values in “copy numbers per one cell” from microarrays and Q-PCR. Over 140 chemicals have already been tested in this Project for single oral exposure. Here, we report that the Percellome analysis is capable of predicting functional insults by short-term inhalation at SHS-level concentration.
FA, Xy and pDB at concentrations 0.08, 0.20 and 0.04 ppm, respectively, close to the “Indicative indoor exposure value of SHS (MHLW, Japan)”, were applied to the C57BL/6J mice 22hr/day x 7 days inhalation protocol (4 concentrations x 4 time points, triplicate). Lung, liver and hippocampus were analyzed. At this concentration, FA had no significant effect on lung and liver. Xy showed oxidative stress and glutathione responses in lung and liver. pDB induced oxidative stress and glutathione responses only in the lung. In contrast to the slight transcriptomic changes in lungs and livers, a remarkable finding common to the three chemicals were the strong suppression of gene expression related to neuronal activity in hippocampus, i.e. the immediate early genes (IEGs) including Arc, Dusp1 and Fos. Review of the lung and liver gene profile pointed out a candidate cytokine upstream of IEGs. Our finding may be considered as a first substantial data that would explain the indefinite or unidentified complaint in SHS patients. The analysis of emotional & cognitive behavior induced by these indoor VOCs will be presented.