Inhibition of Human Sulfotransferase 2A1-Catalyzed Sulfonation of Lithocholic Acid, Glycolithocholic Acid, and Taurolithocholic Acid by Selective Estrogen Receptor Modulators and Various Analogs and Metabolites

Abstract

Lithocholic acid (LCA) is a bile acid associated with adverse effects, including cholestasis, and it exists in vivo mainly as conjugates known as glyco-LCA (GLCA) and tauro-LCA (TLCA). Tamoxifen has been linked to the development of cholestasis, and it inhibits sulfotransferase 2A1 (SULT2A1)-catalyzed dehydroepiandrosterone (DHEA) sulfonation. The present study was done to characterize the sulfonation of LCA, GLCA, and TLCA and to investigate whether triphenylethylene (clomifene, tamoxifen, toremifene, ospemifene, droloxifene), benzothiophene (raloxifene, arzoxifene), tetrahydronaphthalene (lasofoxifene, nafoxidine), indole (bazedoxifene), and benzopyran (acolbifene) classes of selective estrogen receptor modulator (SERM) inhibit LCA, GLCA, and TLCA sulfonation. Human recombinant SULT2A1, but not SULT2B1b or SULT1E1, catalyzed LCA, GLCA, and TLCA sulfonation, whereas each of these enzymes catalyzed DHEA sulfonation. LCA, GLCA, and TLCA sulfonation is catalyzed by human liver cytosol, and SULT2A1 followed the substrate inhibition model with comparable apparent K m values (#1 mM). Each of the SERMs inhibited LCA, GLCA, and TLCA sulfonation with varying potency and mode of enzyme inhibition. The potency and extent of inhibition of LCA sulfonation were attenuated or increased by structural modifications to toremifene, bazedoxifene, and lasofoxifene. The inhibitory effect of raloxifene, bazedoxifene, and acolbifene on LCA sulfonation was also observed in HepG2 human hepatocellular carcinoma cells. Overall, among the SERMs investigated, bazedoxifene and raloxifene were the most effective inhibitors of LCA, GLCA, and TLCA sulfonation. These findings provide insight into the structural features of specific SERMs that contribute to their inhibition of SULT2A1-catalyzed LCA sulfonation. Inhibition of LCA, GLCA, and TLCA detoxification by a SERM may provide a biochemical basis for adverse effects associated with a SERM.

In-Depth Characterization of EpiIntestinal Microtissue as a Model for Intestinal Drug Absorption and Metabolism in Human

“…However, raloxifene was identified as a substrate for various SULTs and the sulfation of raloxifene occurs during incubation with cytosols from human liver and intestine [40,41] and in Caco-2 cells [42]. Moreover, raloxifene is reported to be a potent competitive inhibitor of sulfotransferase 2A1 (SULT2A1) with a K i value very similar to its K m value for SULT2A1 [41,43]. The sulfation of raloxifene we observed in EpiIntestinal microtissues was in line with the reported in vitro data in the literature and was obviously not due to a biased expression of SULTs in this model.…”

Assessing causal associations of bile acids with obesity indicators: A Mendelian randomization study

“…[40] LCA is one of the most toxic BAs, most of which exists in the form of GLCA. [41,42] GLCA is the product of glycine coupling to LCA, in which the carboxylate group of LCA combines with glycine to form bile salts, [41,43,44] which are allowed to dissolve lipids in the small intestine, increasing the lipid surface area to be more easily absorbed, and thus lipid reduction affects obesity. [43][44][45][46][47][48] Following oral administration of GLCA to rats, a swift reduction in phospholipid and cholesterol secretion was observed, reaching 25% and 50% of their initial levels, respectively, as reported by Kuipers et al [49] The transportation of bile phospholipids to the canalicular membrane occurs via a calcium-dependent microtubulemediated vesicle pathway.…”

The Effect of Lithocholic Acid on the Gut-Liver Axis

“…The total BA pool is about 1,300–3,650 mg, while the physiological concentration of LCA is about 50–150 mg ( Sarathy et al, 2017 ). In the enterohepatic circulation, LCA is mainly detected in the portal vein as conjugates, such as glyco-LCA (GLCA) and tauro-LCA (TLCA) ( Bansal and Lau, 2019 ), the free form of LCA can reach 0.5 μM in the peripheral circulation ( Steiner et al, 2011 ). During the enterohepatic circulation, the high-affinity intestinal bile acid transporter (IBAT) actively transports conjugated and unconjugated BAs from the intestinal lumen to the ileocytes, where they are bound to ileal bile acid-binding protein (IBABP), exported across the basement membrane to the portal circulation, and eventually back to the liver ( Dawson and Karpen, 2015 ; Ridlon et al, 2016b ).…”

“…LCA can be sulfated in Caco-2 cells, this sulfation appeared to be an important mechanism for blocking LCA-induced malignant epithelial phenotype, as LCA alone induces a tumor-invasive phenotype in Caco-2 cell, whereas its sulfate counterpart LCA-S does not ( Halvorsen et al, 2000 ). Once the sulfation is impaired, excessive accumulation of LCA may lead to associated adverse effects (e.g., cholestasis) ( Bansal and Lau, 2019 ).…”