Anthraquinones from the roots of Knoxia valerianoides inhibit the formation of advanced glycation end products and rat lens aldose reductase in vitro

Eight known compounds, lucidin (1), lucidin-omega-methyl ether (2), rubiadin (3), damnacanthol (4), 1,3,6-trihydroxy-2-methoxymethylanthraquinone (5), 3,6-dihydroxy-2-hydroxymethyl-9,10-anthraquinone (6), 1,3,6-trihydroxy-2-hydroxymethyl-9,10-anthraquinone 3-O-beta-primeveroside (7), and vanillic acid (8), were isolated from EtOAc- and n-BuOH-soluble fractions of the roots of Knoxia valerianoides. The structures of 1-8 were identified by analysis of spectroscopic data as well as by comparison with published values. All the isolates were subjected to in vitro bioassays to evaluate advanced glycation end products (AGEs) formation and rat lens Aldose Reductase (RLAR) inhibitory activity. Compound 5 showed the most potent inhibitory activity (IC(50) = 52.72 microM) against AGEs formation. Compounds 1, 2, and 8 also showed potent inhibitory activity on AGEs formation with IC(50) values of 79.28, 62.79, and 93.93 microM, respectively, compared with positive control, aminoguanidine (IC(50) = 962 microM). While, compounds 1 and 5-7 showed strong inhibitory activity against RLAR with IC(50) values of 3.35, 3.04, 6.39, and 2.05 microM, respectively.