title: Nickel and binary metal mixture responses in Daphnia magna: molecular fingerprints and (sub)organismal effects.
abstract: The recent development of a custom cDNA microarray platform for one of the standard organisms in aquatic toxicology, Daphnia magna, opened up new ways to mechanistic insights of toxicological responses. In this study, the mRNA expression of several genes and (sub)organismal responses (Cellular Energy Allocation, growth) were assayed after short-term waterborne metal exposure. Microarray analysis of Ni-exposed daphnids revealed several affected functional gene classes, of which the largest ones were involved in different metabolic processes (mainly protein and chitin related processes), cuticula turnover, transport and signal transduction. Furthermore, transcription of genes involved in oxygen transport and heme metabolism (haemoglobin, delta-aminolevilunate synthase) was down-regulated. Applying a Partial Least Squares regression on nickel fingerprints and biochemical (sub)organismal parameters revealed a set of co-varying genes (haemoglobin, RNA terminal phosphate cyclase, a ribosomal protein and an "unknown" gene fragment). An inverse relationship was seen between the mRNA expression levels of different cuticula proteins and available energy reserves. In addition to the nickel exposure, daphnids were exposed to binary mixtures of nickel and cadmium or nickel and lead. Using multivariate analysis techniques, the mixture mRNA expression fingerprints (Ni2+ + Cd2+, Ni2+ + Pb2+) were compared to those of the single metal treatments (Ni2+, Cd2+, Pb2+). It was hypothesized that the molecular fingerprints of the mixtures would be additive combinations of the gene transcription profiles of the individual compounds present in the mixture. However, our results clearly showed additionally affected pathways after mixture treatment (e.g. additional affected genes involved in carbohydrate catabolic processes and proteolysis), indicating interactive molecular responses which are not merely the additive sum of the individual metals. These findings, although indicative of the complex nature of mixture toxicity evaluation, underline the potential of a toxicogenomics approach in gaining more mechanistic information on the effects of single compounds and mixtures.
authors.affiliation: Department of Biology, Laboratory for Ecophysiology, Biochemistry and Toxicology, University of Antwerp (UA), Groenenborgerlaan 171, B-2020 Antwerp, Belgium. tine.vandenbrouck@ua.ac.be
authors.forename: Tine
authors.initials: T
authors.lastname: Vandenbrouck
authors.forename: Anneleen
authors.initials: A
authors.lastname: Soetaert
authors.forename: Karlijn
authors.initials: K
authors.lastname: van der Ven
authors.forename: Ronny
authors.initials: R
authors.lastname: Blust
authors.forename: Wim
authors.initials: W
authors.lastname: De Coen
mesh_terms: D000818:Animals; D003621:Daphnia / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D004734:Energy Metabolism / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects*; D019216:Metals, Heavy / Q000633:toxicity*; D015999:Multivariate Analysis; D009532:Nickel / Q000633:toxicity*; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D019216:Metals, Heavy; D014874:Water Pollutants, Chemical; D009532:Nickel