Volume 272, Number 20,
Issue of May 16, 1997
pp. 13380-13389
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Phosphatidylcholine Hydrolysis Is Required for Pancreatic
Cholesterol Esterase- and Phospholipase A2-facilitated
Cholesterol Uptake into Intestinal Caco-2 Cells
(Received for publication, December 4, 1996, and in revised form, February 6, 1997)
Katrina
Mackay
,
Jacqueline R.
Starr
§
,
Richard M.
Lawn
§
and
Jeff L.
Ellsworth
§
From the
Falk Cardiovascular Research Center,
Stanford University, Stanford, California 94305 and § CV
Therapeutics, Palo Alto, California 94304
Pancreatic secretion is required for efficient
cholesterol absorption by the intestine, but the factors responsible
for this effect have not been clearly defined. To identify factors
involved and to investigate their role in cholesterol uptake, we
studied the effect of Viokase®, a porcine pancreatic
extract, on cholesterol uptake into human intestinal Caco-2 cells.
Viokase is capable of facilitating cholesterol uptake into these cells
such that the level of uptake is 5-fold higher in the presence of
solubilized Viokase. This stimulation is time-dependent and
is dependent on the presence of bile salt. However, bile
salt-stimulated pancreatic cholesterol esterase, which has been
proposed to mediate cholesterol uptake, is not fully responsible. The
major cholesterol transport activity was purified and identified as
pancreatic phospholipase A2. Anti-phospholipase A2 antibodies abolished virtually all of the phospholipase
A2 and cholesterol transport activity of solubilized
Viokase. We demonstrate that both phospholipase A2 and
cholesterol esterase increase cholesterol uptake by hydrolyzing the
phosphatidylcholine that is used to prepare the cholesterol-containing
micelles. In the absence of cholesterol esterase or phospholipase
A2, uptake of cholesterol from micelles containing
phosphatidylcholine is not as efficient as uptake from micelles
containing phospholipase A2-hydrolytic products. These
results indicate that phospholipase A2 may mediate
cholesterol absorption by altering the physical-chemical state of
cholesterol within the intestine.