Phytosterol ester substrate specificity of pancreatic cholesterol esterase

Abstract

Consuming phytosterols and their esters results in decreased LDL cholesterol, an atherosclerotic risk factor. To more completely characterize how phytosterols impart their effects, the present study aimed to determine if pancreatic cholesterol esterase (PCE; EC 3.1.1.13), the enzyme primarily responsible for cholesterol ester hydrolysis in the duodenum, is capable of hydrolyzing various phytosterol esters, and to compare their rates of hydrolysis in vitro. We found that 1) PCE hydrolyzes palmitate, oleate, and stearate esters of cholesterol, stigmasterol, stigmastanol, and sitosterol; 2) specificity was dependent on both the sterol and the fatty acid moieties in the following order of rates of hydrolysis: cholesterol > (sitosterol = stigmastanol) > stigmasterol, oleate > (palmitate = stearate); 3) addition of free phytosterols did not change hydrolytic activity of PCE, while addition of palmitate, oleate, or stearate increased hydrolytic activity. Thus, PCE may play an important but discriminatory role in vivo in the liberation of free phytosterols to compete with cholesterol for micellar solubilization and absorption.Grant Funding SourceUSDA‐NRI competitive grant no. 2007‐35200‐18298