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

Abstract

The objective of this study was to examine the in vitro hydrolysis of vitamin E esters (α-tocopheryl acetate, α-tocopheryl succinate and α-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 α-tocopherol released by porcine pancreatic juice upon addition to different solutions of α-tocopheryl esters, which were dispersed in bile acid mixed micelles at 37°C, 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 α-tocopheryl acetate. The hydrolysis of α-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 α-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 glycochenodeoxycholate were the most effective activators of CEH among the bile acids tested in this assay. The presence of γ-tocopherol or all- trans-retinyl acetate in the assay showed a non-competitive inhibition of the hydrolysis rate of α-tocopheryl acetate.