SULT1A3-Mediated Regiospecific 7-O-Sulfation of Flavonoids in Caco-2 Cells Can Be Explained by the Relevant Molecular Docking Studies

Abstract

Flavonoids are the polyphenolic compounds with various claimed health benefits, but the extensive metabolism by uridine-5'-diphospho-glucuronosyltransferases (UGTs) and sulfotransferases (SULTs) in liver and intestine led to poor oral bioavailabilities. The effects of structural changes on the sulfonation of flavonoids have not been systemically determined, although relevant effects of structural changes on the glucuronidation of flavonoids had. We performed the regiospecific sulfonation of sixteen flavonoids from five different subclasses of flavonoids, which are represented by apigenin (flavone), genistein (isoflavone), naringenin (flavanone), kaempherol (flavonol), and phloretin (chalcone). Additional studies were performed using 4 mono-hydroxyl flavonoids with –OH group at 3, 4’, 5 or 7 position, followed by 5 di-hydroxyl-flavonoids, and 2 tri-hydroxyl flavonoids by using expressed human SULT1A3 and Caco-2 cell lysates. We found that these compounds were exclusively sulfated at the 7-OH position by SULT1A3 and primarily sulfated at 7-OH position in Caco-2 cell lysates with minor amounts of 4’-O-sulfates formed as well. Sulfonation rates measured using SULT1A3 and Caco-2 cell lysates were highly correlated at substrate concentrations of 2.5 and 10 µM. Molecular docking studies provided structural explanations as to why sulfonation only occurred at the 7-OH position of flavones, flavonols and flavanones. In conclusion, molecular docking studies explain why SULT1A3 exclusively mediates sulfonation at the 7-OH position of flavones/flavonols, and correlation studies indicate that SULT1A3 is the main isoform responsible for flavonoid sulfonation in the Caco-2 cells.

In Silico Prediction of Human Sulfotransferase 1E1 Activity Guided by Pharmacophores from Molecular Dynamics Simulations

“…Second, the docking results were also investigated based on three-dimensional pharmacophore features such as hydrogen bonds, hydrophobic contacts, or aromatic areas. To the best of our knowledge, this approach has rarely been applied to SULT docking studies because primarily hydrogen bonds have been considered to evaluate docked ligand conformations (26,(67)(68)(69). Due to the nature of the active site of SULT1E1 (a barrel-like structure lined with lipophilic and/or aromatic amino acids), the consideration of hydrophobic areas and aromatic contacts bears advantages as shown by the predictive power of the presented in silico model for ligands of SULT1E1.…”

Flavonoid interactions during digestion, absorption, distribution and metabolism: a sequential structure–activity/property relationship-based approach in the study of bioavailability and bioactivity

“…This pathway is important in the understanding of flavonoid bioavailability since sulfated flavonoids have been reported to be effluxed back into the intestinal lumen and thus are not well absorbed (Barrington et al, 2009). Among its many isoforms, the mammalian SULT1A3 has been reported to be the most important isoforms for the metabolism of phenolic compounds, such as flavonoids (Meng et al, 2012;Wu et al, 2011a). Literature regarding the structure-sulfation relationship on a wide range of flavonoids remains scarce.…”

Multidrug Resistance-Associated Protein 4 (MRP4/ABCC4) Controls Efflux Transport of Hesperetin Sulfates in Sulfotransferase 1A3–Overexpressing Human Embryonic Kidney 293 Cells

“…Sulfonation activities were measured following our published procedures (Meng et al, 2012). In brief, SULT293 cell lysate or expressed SULT1A3 enzyme at a final concentration of 0.1 mg protein/ml was added to 100 mM 39-phosphoadenosine-59-phosphosulfate and chrysin/apigenin (at varying concentrations) in a total reaction volume of 200 ml.…”