Transcriptomic and proteomic effects of a neonicotinoid insecticide mixture in the marine mussel (Mytilus galloprovincialis, Lam.)

Background: Imidacloprid and Thiacloprid are two neonicotinoid insecticides whose use have been raising exponentially. Both act selectively as agonist of the insect nicotinic-Acetylcholine Receptor (nAChR) and therefore, by definition, they hold the same mode of action. Notwithstanding the growing attention to the ecotoxicological effects of neonicotinoids, there is a lack of information on their toxicodynamics and their mixture effects, in particular, in aquatic organisms. Objectives: The main objectives of this work were: (i) assess sublethal effects of two neonicotinoids-Imidacloprid and Thiacloprid-in the tissues of the marine mussel (Mytilus galloprovincialis Lam.); (ii) identify the molecular dynamics elicited by the two chemicals through gene/protein expression profiling and a functional genomics approach; (iii) assess the effects of a neonicotinoid binary mixture. Methods: Sublethal effects were measured by means of digestive gland lysosomal membrane stability (LMS) and gill acetylcholinesterase (AChE) activity. Gene expression profiles were evaluated in the digestive gland using a 1.7. K cDNA microarray and quantitative-PCR (Q-PCR). Proteome profiling was performed by means of two-dimensional electrophoresis of digestive gland cytosolic proteins. Functional genomics was based on the over-representation of Gene Ontology (GO) terms. Results and discussion: Our results showed that (i) biomarkers responded in the micromolar range; (ii) Imidacloprid and Thiacloprid elicited distinct toxicodynamics as depicted by the different transcriptomic and proteomic profiles and the opposite trend of AChE activity; (iii) at biomarkers level, the joint effects of the two chemicals appeared to fulfill the principle of independence, but this was less evident at molecular level where a novel specific molecular signature took place. Conclusions: These findings imply that different toxicodynamics may occur also as a response of chemicals with the same mode of action. Our results unveil also the incongruousness of the actual concept of pesticide mode of action in the context of ecological risk assessment analysis of chemical mixtures.