Screening potential ligands of endothelin receptor A from Choerospondias axillaris and evaluation of their drug-like properties by affinity chromatographic methods

Abstract

Tibetan medicine is traditionally prescribed as crude extracts or mixtures owing to the theoretical basis with cross fertilization from other medical systems like Ayurveda and traditional Chinese medicine. This is challenged to elucidate the action mechanism and material foundation of Tibetan medicine due to lacking a method to confirm the bioactive compounds determining the therapy. This work created a new strategy for screening and evaluating the bioactive compounds against cardiovascular ailments from Choerospondias axillaris. It involved the immobilization of endothelin receptor A (ETAR) by a one-step covalent assay, the screening and identification of the bioactive compounds by ETAR column combined with tandem mass spectrometry, and the evaluation of their drug-like properties by calculating the efficiency indexes using the data collected by frontal analysis and adsorption energy distribution. The immobilized ETAR remained good stability in three weeks in terms of specificity and repeatability. Catechin, pinocembrin, and hyperoside were identified as potential ETAR ligands from Choerospondias axillaris with two types of binding sites on the immobilized receptor. Their association constants on the high and low affinity binding sites were (2.53 ± 0.11) × 105 and (9.94 ± 0.02) × 103 M−1 for catechin, (1.01 ± 0.12) × 106 and (7.40 ± 0.03) × 104 for hyperoside, and (2.05 ± 0.04) × 105 and (2.47 ± 0.09)× 104 M−1 for pinocembrin, respectively. Owing to the highest association constant, hyperoside presented a surface efficiency index of 7.95, and binding efficiency index of 20.7, and the ligand­lipophilicity efficiency of 1.38. These indicated that the three compounds were the main ingredients for the therapy of Choerospondias axillaris, and had potential to become lead compounds for anti-cardiovascular drugs based on drug-ETAR interaction. The immobilized receptor-based strategy is possible to become an alternative for screening and assessing bioactive compounds from Tibetan medicine.