Daidzein is the in vivo active compound of Puerariae Lobatae Radix water extract for muscarinic receptor-3 inhibition against overactive bladder

Background: In the previous study, Puerariae Lobatae Radix (named Gegen in Chinese) water extract attenuated M3 receptor agonist carbachol-induced detrusor contraction after 3-week oral administration in a hypertension-associated OAB (overactive bladder) model. This research aimed to investigate the active ingredients from Gegen water extract against OAB. Methods: Bioassay-guided fractionation was performed by using preparative HPLC for fast isolation of fractions followed by screening their ex vivo activity through carbachol-induced bladder strip contraction assay. Chemicals in each active fraction were analyzed by HPLC-UV. Urine metabolites were quantified by LC-MS/MS after sub-acute administration. Thermal shift assay with the recombinant human M3 receptor protein was performed, and molecular docking analysis was used for molecular modelling of M3 receptor inhibition. Results: Bioassay-guided fractionation results for isolating M3 receptor inhibitors indicated that four compounds were identified as active ingredients of Gegen water extract, and their inhibition potency on carbachol-induced detrusor contraction was ranked in descending order according to their inhibition concentrations as follows: genistein > daidzein > biochanin A >> puerarin. Daidzein in urine reached an ex vivo effective concentration to inhibit detrusor contraction, but others did not. Daidzein concentration-dependently increased the melt temperature (Tm) of recombinant human M3 receptor protein with a positive binding (delta Tm = 2.12 ? at 100 mu g/ml). Molecular docking analysis showed that daidzein can potently bind to the ligand binding pocket of the M3 receptor via hydrogen bonding. Conclusion: Puerarin and its derivatives were pro-drugs, and daidzein was their in vivo active form via M3 receptor inhibition for treating OAB.

Automated summary

This study found that daidzein in Puerariae Lobatae Radix extract can treat OAB by inhibiting the M3 receptor, while the other compounds in the extract do not have this activity. Daidzein can bind to the M3 receptor via hydrogen bonding and increase its melting temperature.