Insights into human carboxylesterase 2 stability and activity in vivo and in vitro

Dissertation to obtain a Master Degree in Biotechnology

Due to its role in ester containing xenobiotics metabolization, such as the activation of pro-drugs, carboxylesterase 2 (CES2) has become an attractive enzyme, with potential applications in the field of chemotherapy. Still, it hasn’t been as thoroughly characterized as the other main human carboxylesterase, the carboxylesterase 1 (CES1), having no described structure yet. The original hypothesis being tested in this work was the possibility of enzyme-enzyme interaction that had been suggested from previous work in the host laboratory. The initial task of this project was therefore to further assess CES2 stability and to test possible enzyme-enzyme interaction with CES1, by characterizing enzyme hydrolytic kinetics in different assay conditions and evaluating the behaviour of enzyme mixtures. Different CES2 activity rates were observed when tested in different reaction conditions suggesting a stabilizing/destabilizing effect on the enzyme, but evidence of in vitro interactions was not confirmed. Considering the dependence of conclusions on test methods as well as the extreme care measures that have to be taken for avoiding enzyme degradation during the preparation of cell extracts, a second goal was envisaged for this project. This consisted in the development of a new method capable of determining CES activity in conditions closer to those that are found physiologically. A new spectrofluorometric method able to assess carboxylesterase activity in intact living cells, using loperamide as a specific CES2 inhibitor and Bis(4-nitrophenyl) phosphate as a total carboxylesterase inhibitor was therefore developed and applied to Caco-2, HT-29. Hep G2 and HEK-293T cell lines. The method proved itself capable of detecting CES total activity in living cells, as well as to differentiate between CES2 and other CES activities. Differences were shown between this and the traditional methods using cell extracts, suggesting that the latter may not be the best option when trying to predict in vivo CES behavior.

Fundação para a Ciência e Tecnologia - (PTDC/EBB-BIO/111530/2009, PEst-OE/EQB/LA0004/2011)