Hydrolysis of tocopheryl and retinyl esters by porcine carboxyl ester hydrolase is affected by their carboxylate moiety and bile acids

The objective of this study was to examine the in vitro hydrolysis of vitamin E esters (alpha -tocopheryl acetate, alpha -tocopheryl succinate and alpha -tocopheryl nicotinate) by pancreatic carboxyl ester hydrolase (CEH) at the concurrent presence of different bile acids at different concentrations. The assay was performed by measuring the amount of alpha -tocopherol released by porcine pancreatic juice upon addition to different solutions of alpha -tocopheryl esters, which were dispersed in bile acid mixed micelles at 37 degreesC, pH 7.4. The CEH activity was 10 U in the final assay, and the optimal concentration of cholate in this in vitro-system was determined to 30 mM for the hydrolysis of alpha -tocopheryl acetate. The hydrolysis of alpha -tocopheryl esters required presence of pancreatic juice and bile acids, and the results showed furthermore that the ability of pancreatic CEH towards hydrolysis of different alpha -tocopheryl esters increased with increasing lipophility, irrespective of the type or concentration of bile acid present in the assay. Likewise, retinyl palmitate was hydrolyzed at a faster rate than retinyl acetate. The structure of the bile acid influenced the rate of hydrolysis. Thus, cholate followed by glycodeoxy- and glycochenode-oxycholate were the most effective activators of CEH among the bile acids tested in this assay. The presence of gamma -tocopherol or all-trans-retinyl acetate in the assay showed a non-competitive inhibition of the hydrolysis rate of alpha -tocopheryl acetate. (C) 2001 Elsevier Science inc. Ail rights reserved.