Anthraquinones from the seeds of Cassia tora with inhibitory activity on protein glycation and aldose reductase

Nine anthraquinones, aurantio-obtusin (1), chryso-obtusin (2), obtusin (3), chryso-obtusin-2-O-beta-D-glucoside (4), physcion (5), emodin (6), chrysophanol (7), obtusifolin (8), and obtusifolin-2-O-beta-D-glucoside (9), isolated from an EtOAc-soluble extract of the seeds of Cassia tora, were subjected to in vitro bioassays to evaluate their inhibitory activity against advanced glycation end products (AGEs) formation and rat lens aldose reductase (RLAR). Among the isolates, compounds 6 and 8 exhibited a significant inhibitory activity on AGEs formation with observed IC50 values of 118 and 28.9 mu M, respectively, in an AGEs-bovine serum albumin (BSA) assay by specific fluorescence. Furthermore, compounds 6 and 8 inhibited AGEs-BSA formation more effectively than aminoguanidine, an AGEs inhibitor, by indirect AGEs-ELISA. N-epsilon-Carboxymethyllysine (CML)-BSA formation was also inhibited by compounds 6 and 8. Whereas compounds 1, 4, and 6 showed a significant inhibitory activity on RLAR with IC50 values of 13.6, 8.8, and 15.9 mu M, respectively.