A selective mobilization of PCB congeners from adipocytes during the lipolysis

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) that are widely spread in the marine and terrestrial biota and biomagnify throughout food chains. They tend to accumulate in lipid-rich tissues due to their highly lipophilic properties. Although the lipid tissue is considered as an internal site of storage for PCBs, these molecules might be mobilized from the adipocytes into the bloodstream during a period of negative energy balance. This release may be problematic because it enables POPs to reach some target tissues and exert potential harmful health effects in humans and animals. Several in vivo studies have already followed the dynamics of PCBs released from adipose tissue during lipolysis. However, the mechanisms involved in this mobilization have been poorly studied. The complexity of the in vivo situation, which is characterized by a large range of POPs, does not allow understanding precisely the behaviour of individual congeners. At the moment, there is a lack of simple in vitro model available for the characterization of the dynamics of release of PCB congeners, differing by the number and position of chlorine atoms. In this study, we compared the kinetics of release of 3 congeners (PCB-28, -118 and -153) from in vitro differentiated rat adipocytes. The present experiment allowed assessing the impact of (i) the number and position of chlorine atoms of PCBs on their release from adipocytes and (ii) the presence of other PCB congeners on the mobilization rate of such molecules. Adipocytes previously contaminated with the 3 PCB congeners alone or in cocktail, underwent a lipolytic treatment with isoproterenol during 12 hours. The PCB assessment was achieved every 3 hours in cells and medium. The release of targeted PCB congeners from adipocytes was efficient during the lipolysis, with an accumulation in lipolytic medium. Interestingly, PCB-153, a hexa-CB with 2 chlorine atoms in ortho-position, was mobilized slower than PCB-28, a tri-CB, and PCB-118, a penta-CB, which are both characterized by 1 chlorine atom in ortho-position. These first results demonstrate the impact of the physico-chemical properties of POPs on their dynamics of mobilization from adipocytes. Moreover, the mobilization of PCB congeners was not influenced by the presence of other congeners within adipocytes in these experimental conditions