Characterization of lipoprotein secreted by cultured eel hepatocytes and its comparison with serum lipoproteins

The lipoprotein secreted by cultured eel hepatocytes was fractionated by density gradient ultracentrifugation and compared with eel serum lipoproteins. Eel hepatocytes were cultured for 7 to 10 days as a monolayer in Williams' medium E containing 5% fetal bovine serum and 0.16 microM insulin on a dish precoated with fibronectin of horse serum. The only lipoprotein secreted by eel hepatocytes was a very-low-density lipoprotein like one which consisted of 69% triglyceride, 15% phospholipid, 4% cholesterol, and 12% protein. On the other hand, very-low-density lipoprotein and high density lipoprotein were found in eel serum, in which high density lipoprotein was a main lipoprotein. The secreted lipoprotein contained apo B and apo A as the main protein components. Furthermore, the lipoprotein contained proapo A-I in addition to apo A-I, which was proved by comparing the amino acid composition of both proteins. In our discussion, we noted that the lipoprotein secreted by eel hepatocytes was a good material for the study of high-density lipoprotein formation.