Albumin Stimulates the Activity of the Human UDP-Glucuronosyltransferases 1 A 7 , 1 A 8 , 1 A 10 , 2 A 1 and 2 B 15 , but the Effects are Enzyme and Substrate Dependent

Human UDP-glucuronosyltransferases (UGTs) are important enzymes in metabolic elimination of endoand xenobiotics. It was recently shown that addition of fatty acid free bovine serum albumin (BSA) significantly enhances in vitro activities of UGTs, a limiting factor in in vitro–in vivo extrapolation. Nevertheless, since only few human UGT enzymes were tested for this phenomenon, we have now performed detailed enzyme kinetic analysis on the BSA effects in six previously untested UGTs, using 2–4 suitable substrates for each enzyme. We also examined some of the previously tested UGTs, but using additional substrates and a lower BSA concentration, only 0.1%. The latter concentration allows the use of important but more lipophilic substrates, such as estradiol and 17-epiestradiol. In five newly tested UGTs, 1A7, 1A8, 1A10, 2A1, and 2B15, the addition of BSA enhanced, to a different degree, the in vitro activity by either decreasing reaction’s Km, increasing its Vmax, or both. In contrast, the activities of UGT2B17, another previously untested enzyme, were almost unaffected. The results of the assays with the previously tested UGTs, 1A1, 1A6, 2B4, and 2B7, were similar to the published BSA only as far as the BSA effects on the reactions’ Km are concerned. In the cases of Vmax values, however, our results differ significantly from the previously published ones, at least with some of the substrates. Hence, the magnitude of the BSA effects appears to be substrate dependent, especially with respect to Vmax increases. Additionally, the BSA effects may be UGT subfamily dependent since Km decreases were observed in members of subfamilies 1A, 2A and 2B, whereas large Vmax increases were only found in several UGT1A members. The results shed new light on the complexity of the BSA effects on the activity and enzyme kinetics of the human UGTs. Citation: Manevski N, Troberg J, Svaluto-Moreolo P, Dziedzic K, Yli-Kauhaluoma J, et al. (2013) Albumin Stimulates the Activity of the Human UDPGlucuronosyltransferases 1A7, 1A8, 1A10, 2A1 and 2B15, but the Effects Are Enzyme and Substrate Dependent. PLoS ONE 8(1): e54767. doi:10.1371/ journal.pone. 0054767 Editor: Fernando Rodrigues-Lima, University Paris Diderot-Paris 7, France Received October 10, 2012; Accepted December 14, 2012; Published January 23, 2013 Copyright: 2013 Manevski et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was supported by the Sigrid Juselius Foundation, the Graduate School in Pharmaceutical Research, the Academy of Finland (project numbers 120975 and 1260010), the University of Helsinki Research Foundation grant for young researchers, and the European Erasmus programme. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: Moshe.Finel@helsinki.fi ¤ Current address: Department of Cell Biology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Poland. These authors contributed equally to this work.