Fish cell lines : a screening tool for multiple stress scenarios. Interaction between fatty acid profile and heavy metals in rainbow trout liver (RTL-W1)

In aquatic ecosystems, environmental conditions (e.g. temperature, food quality, water quantity...) are seldom optimal and change overtime. Though these variations may affect organisms' capacity to cope with chemical contamination, they are rarely taken into account in classical ecotoxicological tests and most of the regulation on chemicals is based on single substance test performed under optimal conditions. Nevertheless, different environmental conditions (e.g. food quality) can modify the characteristics of an organism (e.g. nutritional status) and thus can influence both the entrance of chemicals within this organism and its ability to cope with it. In particular, in fish, fatty acid composition can modulate membrane fluidity and thus influence contaminant uptake. Due to their different antioxidant properties, fatty acids are also likely to influence cells' sensibility to oxidative stress induced by contaminants. Fish fatty acid profile is influenced strongly by nutrition and temperature, thus, fish from the same species may present strong differences in their fatty acid profile and may respond differently to contamination. Few studies have been exploring this hypothesis therefore an in vitro approach was set up to better explore the role of a wide range of fatty acids in fish response to contaminants such as metals. Fish hepatocytes from the same cell line (RTL-W1) but with up to 7 different fatty acid profiles were then obtained by enriching the growth medium with 6 different fatty acids of interest. Though these cells were from the same cell line; the modification of their fatty acid profile changed certain of their properties (e.g. membrane fluidity) and modified their response to increasing concentrations of mercury (HgCl2 or CH3HgCl) or cadmium (CdCl2). For instance, cells enriched with the omega-3 fatty acid: alpha-linolenic acid showed a stronger resistance to organic mercury (EC50CH3HgCl = 6.6 µM) than non-enriched cells (EC50CH3HgCl = 2.9 µM) but a similar resistance to cadmium and inorganic mercury. The use of a fish cell line allowed screening the influence of various types of fatty acid profiles on heavy metals' sensitivity of fish. Based on these result, the multiple stress scenarios more likely to present a risk for the environment have been selected for further mechanistic (in vitro) and ecotoxicologic (in vivo) investigation.