In Vitro Enzyme Inhibition Experiment

Negligible inhibition of UGT1A1 by mitragynine

Negligible Inhibition was detected.  Cutoff used —

IC50 > 10 μM are low potential inhibitors.
1 μM < IC50 < 10 μM are moderate potential inhibitors. 
IC50 < 1 μM are high potential inhibitors.



4-methylumbelliferone glucuronide

  • UGT1A1 40782950

Recombinant expression system Baculovirus-insect cells
Cytochrome B5 Not available


The IC50 values were all greater than the highest concentrations used (IC50 > 100 μM) since inhibition at more than 50% did not occur at the highest concentration.

Concentration of precipitant and % inhibition of UGT1A1 (some values estimated from figure 4)
0.01 μM: -4 ± 0%
0.1 μM: 8 ± 6%
1 μM: 15 ± 4% (p < 0.05)
10 μM:19 ± 0% (p < 0.05)
100 μM: See above data

Sample Compound measured Value Measurement Study sequence Additional information N replicates

Experimental Conditions

The amount of protein, the incubation time and the concentration of 4-MU used in the measurement of 4-MU glucuronidation were described in the method by Uchaipichat et al.

Microsomes expressing recombinant human UGT1A1 and UGT2B7 were obtained from BD Biosciences (Woburn, MA, United States);incubations (total volume 250 μL) contained phosphate buffer (100 mM) (pH 7.4), MgCl 2 (5 mM), cell lysate (83.3 μg/mL for UGT1A1 or 62.5 μg/mL for UGT2B7), UDPGA (5 mM), and 4-MU (substrate) (100 μM for UGT1A1 assay or 350 μM for UGT2B7 assay).

Tested concentrations of precipitant only up to 100 μM due to limited solubility

Control=no inhibitor

200 μg/incubation

Commercially available

250 μL

120 min



Not available

Not available

100 μM

0.01-100 μM