title: Toxicity mechanisms identification via gene set enrichment analysis of time-series toxicogenomics data: impact of time and concentration.
abstract: The advance in high-throughput "toxicogenomics" technologies, which allows for concurrent monitoring of cellular responses globally upon exposure to chemical toxicants, presents promises for next-generation toxicity assessment. It is recognized that cellular responses to toxicants have a highly dynamic nature, and exhibit both temporal complexity and dose-response shifts. Most current gene enrichment or pathway analysis lack the recognition of the inherent correlation within time series data, and may potentially miss important pathways or yield biased and inconsistent results that ignore dynamic patterns and time-sensitivity. In this study, we investigated the application of two score metrics for GSEA (gene set enrichment analysis) to rank the genes that consider the temporal gene expression profile. One applies a novel time series CPCA (common principal components analysis) to generate scores for genes based on their contributions to the common temporal variation among treatments for a given chemical at different concentrations. Another one employs an integrated altered gene expression quantifier-TELI (transcriptional effect level index) that integrates altered gene expression magnitude over the exposure time. By comparing the GSEA results using two different ranking metrics for examining the dynamic responses of reporter cells treated with various dose levels of three model toxicants, mitomycin C, hydrogen peroxide, and lead nitrate, the analysis identified and revealed different toxicity mechanisms of these chemicals that exhibit chemical-specific, as well as time-aware and dose-sensitive nature. The ability, advantages, and disadvantages of varying ranking metrics were discussed. These findings support the notion that toxicity bioassays should account for the cells' complex dynamic responses, thereby implying that both data acquisition and data analysis should look beyond simple traditional end point responses.
authors.affiliation: †Department of Civil and Environmental Engineering, Northeastern University, Boston, Massachusetts 02115, United States.
authors.forename: Ce
authors.initials: C
authors.lastname: Gao
authors.affiliation: ‡Department of Biology, University of Massachusetts, Boston, Massachusetts 02125, United States.
authors.forename: David
authors.initials: D
authors.lastname: Weisman
authors.affiliation: †Department of Civil and Environmental Engineering, Northeastern University, Boston, Massachusetts 02115, United States.
authors.forename: Jiaqi
authors.initials: J
authors.lastname: Lan
authors.affiliation: †Department of Civil and Environmental Engineering, Northeastern University, Boston, Massachusetts 02115, United States.
authors.forename: Na
authors.initials: N
authors.lastname: Gou
authors.affiliation: †Department of Civil and Environmental Engineering, Northeastern University, Boston, Massachusetts 02115, United States.
authors.forename: April Z
authors.initials: AZ
authors.lastname: Gu
mesh_terms: D000891:Anti-Infective Agents, Local / Q000633:toxicity; D000903:Antibiotics, Antineoplastic / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000633:toxicity*; D048168:Escherichia coli K12 / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D015386:Hazardous Substances / Q000633:toxicity; D006861:Hydrogen Peroxide / Q000633:toxicity; D007854:Lead / Q000633:toxicity; D046228:Microarray Analysis; D016685:Mitomycin / Q000633:toxicity; D009566:Nitrates / Q000633:toxicity; D025341:Principal Component Analysis; D043922:Toxicogenetics / Q000379:methods*; D059467:Transcriptome
chemical_list: D000891:Anti-Infective Agents, Local; D000903:Antibiotics, Antineoplastic; D004785:Environmental Pollutants; D015386:Hazardous Substances; D009566:Nitrates; D007854:Lead; D016685:Mitomycin; C017461:lead nitrate; D006861:Hydrogen Peroxide