Establishing GPCR Targets of hMAO Active Anthraquinones from Cassia obtusifolia Linn Seeds Using In Silico and In Vitro Methods

[Image: see text] The present study examines the effect of human monoamine oxidase active anthraquinones emodin, alaternin (=7-hydroxyemodin), aloe-emodin, and questin from Cassia obtusifolia Linn seeds in modulating human dopamine (hD(1)R, hD(3)R, and hD(4)R), serotonin (h5-HT(1A)R), and vasopressin (hV(1A)R) receptors that were predicted as prime targets from proteocheminformatics modeling via in vitro cell-based functional assays, and explores the possible mechanisms of action via in silico modeling. Emodin and alaternin showed a concentration-dependent agonist effect on hD(3)R with EC(50) values of 21.85 ± 2.66 and 56.85 ± 4.59 μM, respectively. On hV(1A)R, emodin and alaternin showed an antagonist effect with IC(50) values of 10.25 ± 1.97 and 11.51 ± 1.08 μM, respectively. Interestingly, questin and aloe-emodin did not have any observable effect on hV(1A)R. Only alaternin was effective in antagonizing h5-HT(1A)R (IC(50): 84.23 ± 4.12 μM). In silico studies revealed that a hydroxyl group at C1, C3, and C8 and a methyl group at C6 of anthraquinone structure are essential for hD(3)R agonist and hV(1A)R antagonist effects, as well as for the H-bond interaction of 1-OH group with Ser192 at a proximity of 2.0 Å. Thus, based on in silico and in vitro results, hV(1A)R, hD(3)R, and h5-HT(1A)R appear to be prime targets of the tested anthraquinones.