Abstract
The bile salt-dependent cholesteryl ester hydrolase (CEH; EC 3.1.1.13) has been proposed to promote the intestinal absorption of both the free and esterified (FC, CE) forms of dietary cholesterol. For example, it was recently reported that in the human intestinal cell line CaCo2, addition of bovine CEH to the medium increased the uptake and intracellular esterification of micellar FC supplied at subphysiological concentrations [Lopez-Candales et al. (1993) Biochemistry 32, 12085-12089]. To test the ability of CEH to promote micellar cholesterol uptake in a CaCo2 system under more physiological conditions, an in vitro model was developed. Cells stably expressing rat CEH were created by DNA transfection (Tr cells), and the uptake of micellar FC and its intracellular esterification were measured using isotopic methods in Tr and control cells. Experimental parameters that were varied included micellar composition (monoolein or egg PC; FC, CE, or both), the final concentration of micellar cholesterol (1 nM to 50 microM), the origin of CEH (endogenously synthesized vs exogenously added), and the species source of enzyme (rat, pig, man). The uptake of cholesterol that was derived from micellar CE was significantly increased 5-10-fold (p < 0.001) in Tr vs control cells as a result of the hydrolysis of the CE by the CEH and subsequent uptake of the liberated free cholesterol. In contrast, the uptake of micellar FC was not increased by the presence of CEH, whether it was endogenous or exogenous. In addition, based on TLC analysis of extracted cellular lipids, there was no evidence that CEH promoted the esterification of the FC that was taken up.(ABSTRACT TRUNCATED AT 250 WORDS)
Published Version
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