Phosphatidylcholine Hydrolysis Is Required for Pancreatic Cholesterol Esterase- and Phospholipase A2-facilitated Cholesterol Uptake into Intestinal Caco-2 Cells

Abstract

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 A 2 . Anti-phospholipase A 2 antibodies abolished virtually all of the phospholipase A 2 and cholesterol transport activity of solubilized Viokase. We demonstrate that both phospholipase A 2 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 A 2 , uptake of cholesterol from micelles containing phosphatidylcholine is not as efficient as uptake from micelles containing phospholipase A 2 -hydrolytic products. These results indicate that phospholipase A 2 may mediate cholesterol absorption by altering the physical-chemical state of cholesterol within the intestine.

Hydrolysis of Micellar Phosphatidylcholine Accelerates Cholesterol Absorption in Rats and Caco-2 Cells

“…19) They pointed out a possibility that PC hydrolysis might be compensated by another digestive enzyme in phospholipase A 2 knockout mice. Our observations together with previous studies 9,20,21) suggest that cholesterol esterase is the first candidate for an alternative enzyme of phospholipase A 2 in phospholipase A 2 knockout mice. Since cholesterol is absorbed without phospholipase A 2 or cholesterol esterase 9) (Fig.…”

“…20) In addition, acceleration of cholesterol incorporation was also observed when micellar PC was replaced with its hydrolysis products, LysoPC and fatty acid. Homan and Hamelehle have reported a similar observation.…”

Apolipoprotein E regulates dietary cholesterol absorption and biliary cholesterol excretion: Studies in C57BL/6 apolipoprotein E knockout mice

“…In addition, Hauser (18,19) has shown that specific proteins derived from enterocyte brush border membranes promote the uptake of cholesterol by vesicles and more recently that SR-BI might be involved in this process. Also implicated in the regulation of dietary cholesterol absorption are pancreatic enzymes, CEL, and phospholipase A2 (20,21), the enterocyte ACAT that esterifies dietary cholesterol (22), apoA-IV (23,24), and different bile acid species that are the result of the classical and alternative bile acid biosynthetic pathways (25,26). The actual in vivo role for many of these processes is under active evaluation in a number of laboratories.…”

Carboxyl ester lipase

“…In these studies, absorption of micellar cholesterol by Caco-2 cells was inhibited by incorporation of phospholipid in the micelles (50,97). The Ikeda study also showed that CEL facilitated cholesterol absorption in bile and pancreatic juice-diverted rats when the substrate was presented in a phospholipid-rich vesicle (97).…”

“…Thus, it is difficult to know if CEL or these other enzymes plays the primary role in each digestive process or if CEL provides only supplemental or compensatory lipolytic capacity in the digestive tract. Mackay et al have suggested that CEL works with phospholipase A 2 in promoting optimal intestinal cholesterol absorption from vesicular substrates (50). However, demonstrating the physiological significance of CEL in the absorption of any of these lipid nutrients is a difficult task.…”