| In Vitro Inhibition of Human Hepatic and cDNA-expressed Sulfotransferase Activity with 3-Hydroxybenzo[a]pyrene by Polychlorobiphenylols Li-Quan Wang,1 Hans-Joachim Lehmler,2 Larry W.
Robertson,2 Charles N. Falany,3 and Margaret O. James1 1Department of Medicinal Chemistry, University of Florida, Gainesville,
Florida, USA; 2Department of Occupational and Environmental Health,
College of Public Health, University of Iowa, Iowa City, Iowa, USA; 3Department
of Pharmacology and Toxicology, University of Alabama, Birmingham, Alabama,
USA Abstract
Sulfonation is a major phase II biotransformation reaction. In this study, we found that several polychlorobiphenylols (OH-PCBs) inhibited the sulfonation of 3-hydroxybenzo[a]pyrene (3-OH-BaP) by human liver cytosol and some cDNA-expressed sulfotransferases. At concentrations > 0.15 µM, 3-OH-BaP inhibited its own sulfonation in cytosol fractions that were genotyped for SULT1A1 variants, as well as with expressed SULT1A1*1, SULT1A1*2, and SULT1E1, but not with SULT1A3 or SULT1B1. The inhibition fit a two-substrate kinetic model. We examined the effects of OH-PCBs on the sulfonation of 0.1 or 1.0 µM 3-OH-BaP, noninhibitory and inhibitory substrate concentrations, respectively. At the lower 3-OH-BaP concentration, OH-PCBs with a 3-chloro-4-hydroxy substitution pattern were more potent inhibitors of cytosolic sulfotransferase activity [with concentrations that produced 50% inhibition (IC50) between 0.33 and 1.1 µM] than were OH-PCBs with a 3,5-dichloro-4-hydroxy substitution pattern, which had IC50 values from 1.3 to 6.7 µM. We found similar results with expressed SULT1A1*1 and SULT1A1*2. The OH-PCBs were considerably less potent inhibitors when assay tubes contained 1.0 µM 3-OH-BaP. The inhibition mechanism was noncompetitive, and our results suggested that the OH-PCBs competed with 3-OH-BaP at an inhibitory site on the enzyme. The OH-PCBs tested inhibited sulfonation of 3-OH-BaP by SULT1E1, but the order of inhibitory potency was different than for SULT1A1. SULT1E1 inhibitory potency correlated with the dihedral angle of the OH-PCBs. The OH-PCBs tested were generally poor inhibitors of SULT1A3- and SULT1B1-dependent activity with 3-OH-BaP. These findings demonstrate an interaction between potentially toxic hydroxylated metabolites of PCBs and polycyclic aromatic hydrocarbons, which could result in reduced clearance by sulfonation. Key words: 3-hydroxy-benzo[a]pyrene, human liver cytosol, inhibition of sulfonation, polychlorobiphenylols, SULT1A1*1, SULT1A1*2, SULT1E1. Environ Health Perspect 113:680-687 (2005) . doi:10.1289/ehp.7837 available via http://dx.doi.org/ [Online 24 February 2005]
Address correspondence to M.O. James, Department of Medicinal Chemistry, Room P6-20B, 1600 SW Archer Rd., University of Florida, Gainesville, FL 32610-0485 USA. Telephone: (352) 846-1952. Fax: (352) 846-1972. E-mail: mojames@ufl.edu We thank F.P. Guengerich for providing samples of human liver and W. Farmerie for providing access to instruments for polymerase chain reaction amplification. This study was supported by grants P42 ES07375 and P42 ES07380 from the National Institute of Environmental Health Sciences, National Institutes of Health (NIH) , and grant GM38954 from the National Institute of General Medical Sciences, NIH. This article reflects the authors’ views and not any official views of NIH. The authors declare they have no competing financial interests. Received 8 December 2004 ; accepted 24 February 2005. The full version of this article is available for free in HTML or PDF formats. |
