Sulfonation of 17beta-estradiol and inhibition of sulfotransferase activity by polychlorobiphenylols and celecoxib in channel catfish, Ictalurus punctatus.
The sulfonation of 17beta-estradiol (E2) by human liver and recombinant sulfotransferases is influenced by environmental contaminants such as hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs), which are potent inhibitors, and the therapeutic drug, celecoxib, which affects positional sulfonation of E2. In some locations, the aquatic environment is contaminated by PCBs, OH-PCBs and widely used therapeutic drugs. The objectives of this study were to investigate the sulfonation kinetics of E2 in liver cytosol from channel catfish (Ictalurus punctatus); to examine the effect of OH-PCBs on E2 sulfonation; and to determine if celecoxib altered the position of E2 sulfonation, as it does with human liver cytosol. E2 was converted to both 3- and 17-sulfates by catfish liver cytosol. At E2 concentrations below 1 microM, formation of E2-3-sulfate (E2-3-S) predominated, but substrate inhibition was observed at higher concentrations. Rates of E2-3-S formation at different E2 concentrations were fit to a substrate inhibition model, with K'm and V'max values of 0.40 +/- 0.10 microM and 91.0 +/- 4.7 pmol/min/mg protein, respectively and K(i) of 1.08 +/- 0.09 microM. The formation of E2-17-S fit Michaelis-Menten kinetics over the concentration range 25 nM to 2.5 microM, with K(m) and V(max) values of 1.07 +/- 0.23 microM and 25.7 +/- 4.43 pmol/min/mg protein, respectively. The efficiency (V(max)/K(m)) of formation of E2-3-S was 9.8-fold higher than that of E2-17-S. Several OH-PCBs inhibited E2 3-sulfonation, measured at an E2 concentration of 1 nM. Of those tested, the most potent inhibitor was 4'-OH-CB79, with two chlorine atoms flanking the OH group (IC(50): 94 nM). The inhibition of estrogen sulfonation by OH-PCBs may disrupt the endocrine system and thus contribute to the known toxic effects of these compounds. Celecoxib did not stimulate E2-17-S formation, as is the case with human liver cytosol, but did inhibit the formation of E2-3-S (IC(50): 44 microM) and to a lesser extent, E2-17-S (IC(50): > 160 microM), suggesting the previously found effect of celecoxib on E2-17-S formation may be specific to human SULT2A1.
Wang
Li-Quan
LQ
Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL 32610, USA.
James
Margaret O
MO
D000818:Animals; D000068579:Celecoxib; D003600:Cytosol / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000633:toxicity; D004958:Estradiol / Q000032:analysis / Q000378:metabolism*; D005260:Female; D007059:Ictaluridae / Q000378:metabolism*; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008099:Liver / Q000187:drug effects; D008297:Male; D011078:Polychlorinated Biphenyls / Q000737:chemistry / Q000633:toxicity*; D011720:Pyrazoles / Q000737:chemistry / Q000633:toxicity*; D013449:Sulfonamides / Q000737:chemistry / Q000633:toxicity*; D015238:Sulfotransferases / Q000037:antagonists & inhibitors / Q000187:drug effects*
D004791:Enzyme Inhibitors; D011720:Pyrazoles; D013449:Sulfonamides; D004958:Estradiol; D011078:Polychlorinated Biphenyls; D015238:Sulfotransferases; D000068579:Celecoxib