ROLE OF LYSOPHOSPHATIDYLCHOLINE AND APOLIPOPROTEIN-A1 IN THE CHOLESTEROL-REMOVING CAPACITY OF LIPOPROTEIN-DEFICIENT SERUM IN TISSUE-CULTURE

Lipoprotein-deficient serum (d > 1.21 or 1.25 g/ml fraction) is commonly used to deplete cellular cholesterol from cultured cells and presently we have studied some of the potential promoters of this process. Although serum albumin is the main protein component of the fraction, its cholesterol-removing capacity was quite limited, even in the presence of lysophosphatidylcholine, which is the major phospholipid of the d > 1.25 g/ml infranatant of serum. On the other hand, apolipoprotein A1, especially when complexed with lysophosphatidylcholine promoted considerable release of cellular cholesterol. The cholesterol-removing capacity of lysophosphatidylcholine alone was related to the fatty acid chain length and was low when the fatty acid chain length was below C-14. The release of cellular cholesterol is not related to shedding of surface glycoproteins and depends on the presence of suitable acceptors in the medium. Such acceptors were presently found in an ultra-filtrate of serum prepared by membrane filtration. It is proposed that in human serum there are low molecular weight protein-phospholipid complexes (less than 100 000), which can cross the capillary endothelial barrier, in preference to lipoproteins, and promote cholesterol removal from peripheral cells. © 1979.