Lycopene isomerisation and storage in an in vitro model of murine hepatic stellate cells

Background Lycopene is a carotenoid whose biological activities and protective effect on prostate and breast cancer have been described, but little is known on its extraintestinal metabolism and storage. While most alimentary lycopene is in all-trans configuration, in animal and human tissues approximately half of the lycopene is in cis isoforms. Aim of study Our object was to monitor the capacity of storage, isomerisation, and intracellular localization of all-trans and cis lycopene in hepatic stellate cells, which are the major sites of metabolism and storage of retinoids and carotenoids in the body. Methods We used the GRX cell line representative of murine hepatic stellate cells, incubated with 1-30 mu M lycopene in culture medium. Analysis was done by high-performance liquid chromatography. Results Lycopene was able to induce expression of the lipocyte phenotype and it was internalized into GRX cells. Its cellular release only occurred in presence of albumin with a rapid initial decrease of intracellular lycopene. A corresponding increase in the culture medium was observed at 24 h. All-trans, 13-cis and 9-cis lycopene isoforms were identified in all the cell compartments. The membrane fraction contained the major part of lycopene, followed by the cytoplasmic fraction, lipid droplets and nuclei. The ratio between all-trans and cis isomers was approximately 2/1 in the majority parts of cell compartments. Conclusions This study identified a novel hepatic cell type able to store and isomerise lycopene. Liver can contribute to the serum and tissue equilibrium of cis/trans isomers of lycopene, and to participate in storage of lycopene under high extracellular concentration such as observed after the alimentary input.