In Vitro Inhibition of Human UDP-Glucuronosyl-Transferase (UGT) Isoforms by Astaxanthin, β-Cryptoxanthin, Canthaxanthin, Lutein, and Zeaxanthin: Prediction of in Vivo Dietary Supplement-Drug Interactions

Abstract

Despite the widespread use of the five major xanthophylls astaxanthin, β-cryptoxanthin, canthaxanthin, lutein, and zeaxanthin as dietary supplements, there have been no studies regarding their inhibitory effects on hepatic UDP-glucuronosyltransferases (UGTs). Here, we evaluated the inhibitory potential of these xanthophylls on the seven major human hepatic UGTs (UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, UGT2B7 and UGT2B15) in vitro by LC-MS/MS using specific marker reactions in human liver microsomes (except UGT2B15) or recombinant supersomes (UGT2B15). We also predicted potential dietary supplement-drug interactions for β-cryptoxanthin via UGT1A1 inhibition. We demonstrated that astaxanthin and zeaxanthin showed no apparent inhibition, while the remaining xanthophylls showed only weak inhibitory effects on the seven UGTs. β-Cryptoxanthin mildly inhibited UGT1A1, UGT1A3, and UGT1A4, with IC50 values of 18.8 ± 2.07, 28.3 ± 4.40 and 34.9 ± 5.98 μM, respectively. Canthaxanthin weakly inhibited UGT1A1 and UGT1A3, with IC50 values of 38.5 ± 4.65 and 41.2 ± 3.14 μM, respectively; and lutein inhibited UGT1A1 and UGT1A4, with IC50 values of 45.5 ± 4.01 and 28.7 ± 3.79 μM, respectively. Among the tested xanthophyll-UGT pairs, β-cryptoxanthin showed the strongest competitive inhibition of UGT1A1 (Ki, 12.2 ± 0.985 μM). In addition, we predicted the risk of UGT1A1 inhibition in vivo using the reported maximum plasma concentration after oral administration of β-cryptoxanthin in humans. Our data suggests that these xanthophylls are unlikely to cause dietary supplement-drug interactions mediated by inhibition of the hepatic UGTs. These findings provide useful information for the safe clinical use of the tested xanthophylls.

Keywords: in vitro UGTs inhibition; in vitro-in vivo extrapolation; xanthophylls; β-cryptoxanthin.

Figure 1

IC₅₀ curves of β-cryptoxanthin for human UGTs activities including UGT1A1 for β-estradiol-3-glucuronidation (A); UGT1A3 for chenodeoxycholic acid 24-acyl-β-d-glucuronidation (B); UGT1A4 for trifluoperazine-N-glucuronidation (C); UGT1A6 for serotonin-O-glucuronidation (D); UGT1A9 for propofol-O-glucuronidation (E); and UGT2B7 for zidovudine-5′-glucuronidation (F) in human liver microsomes, and UGT2B15 for 4-methylumbelliferyl glucuronidation (G) in recombinant human UGT2B15 supersomes. Data are the mean ± standard deviation of triplicate determinations. The dashed lines represent the best fit to the data using non-linear regression.

Figure 2

Dixon plots of the inhibitory effects of β-cryptoxanthin (A) and nilotinib (B) against UGT1A1-catalyzed β-estradiol-3- glucuronide in human liver microsomes. The concentrations of β-estradiol were determined 5 (●), 10 (○), and 20 (▲) μM, respectively. The v represents formation rate of β-estradiol-3-glucuronidation (nmol/min/mg protein). Data are the mean ± standard deviation of triplicate experiments. The solid lines of β-cryptoxanthin and nilotinib fit well with a competitive mode of inhibition.