Comparative characterization of organ-specific phase I and II biotransformation enzyme kinetics in salmonid S9 sub-cellular fractions and cell lines.

Advancing in vitro systems to address the effects of chemical pollution requires a thorough characterization of their functionalities, such as their repertoire of biotransformation enzymes. Currently, knowledge regarding the presence, activity magnitudes, and inducibility of different biotransformation pathways in vitro is scarce, particularly across organs. We report organ-specific kinetics for phase I and II biotransformation enzymes, under basal and induced conditions, in two in vitro systems using salmonid fish: S9 sub-cellular fractions from brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) were compared with rainbow trout cell lines. Cyp1a and glutathione S-transferase (Gst) activities were the highest in liver S9 fractions and RTL-W1 liver cells, yet systems derived from the intestine, gills, and brain also displayed these biotransformation pathways. Cyp3a-like activity was only measurable in liver and intestinal S9 fractions, but all rainbow trout cell lines, including RTgill-W1 and RTbrain, displayed this type of activity. Furthermore, despite RTgutGC having the highest constitutive Cyp3a-like activity, its inducibility was the highest in RTL-W1 cells. Similarly, both RTL-W1 and RTgutGC cells displayed Cyp2b-like activity, but this was only measurable upon induction. Contrarily, S9 fractions from the liver, intestine and gills displayed constitutive Cyp2b-like activity. While these differences could be related to differential functionality of biological processes at the in vivo level, we provide important evidence of a broad spectrum of in vitro enzymatic activity in salmonid models. As such, both S9 fractions and cell lines represent important alternatives to animal testing for evaluating the biotransformation and bioaccumulation of environmental pollutants.