Mobilisation of lipophilic pollutants from adipose tissue during periods of lipolysis by in vitro and in vivo approaches

Since several decades, a specific attention has been focused on a class of molecules called persistent organic pollutants (POPs). All of them present a lipophilic character, they resist to degradation and they can be transported far away from the production sites, contaminating biota until remote locations. Highly toxic for humans and wildlife, they biomagnify through the food chain. The adipose tissue is the main reservoir of POPs. However, it can become a source of POPs through their release into the circulation during periods of negative energy balance. To date, little is known regarding the factors that govern the mobilisation of POPs from adipose tissue. The present study aimed at investigating the toxicokinetics of POPs during periods of adipose tissue lipolysis through in vivo and in vitro approaches. The selected in vivo model was the weaned northern elephant seal (NES) pup. Concentrations of POPs increased within blubber over the NES fast, despite a mobilisation into the circulation. The rise was more pronounced in the inner blubber layer compared to the outer blubber layer, which suggests a more efficient release of lipids than POPs, especially from the inner layer. The POP release mainly depended on their degree of lipophilicity. The retention of the more lipophilic POPs and the discharge of the less lipophilic POPs were highlighted. This selective mobilisation might be linked to the one of fatty acids (FAs), which was also in favour of the less lipophilic FAs, leading to an enrichment of adipocytes with more lipophilic FAs at late fast. Concurrently to the in vivo study, we set up an efficient in vitro lipolytic model of primary cell cultures of differentiated rat adipocytes by using isoproterenol, a well-known catecholamine, and a regular renewal of the lipolytic culture medium. We used this model to follow the mobilisation of three POPs (PCB-28, -118 and -153), which differed by their lipophilicity and bulk. The results showed that PCB-153, the more lipophilic and bulky POP, was preferentially retained within adipocytes, confirming the in vivo data. This work brings additional information regarding the parameters that govern the dynamics of POPs released from the adipose tissue and points out the complementarity of the in vivo and in vitro models in such research.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201