Evaluation of Aldose Reductase, Protein Glycation, and Antioxidant Inhibitory Activities of Bioactive Flavonoids in L. and Their Structure-Activity Relationship.

The inhibitory activities of L. 70% methanol extract were evaluated by isolating and testing 10 of its compounds on rat lens aldose reductase (RLAR), advanced glycation end products (AGEs), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging. Among these compounds, apigenin-7---D-glucoside, luteolin-7---D-glucoside, apigenin-7---D-glucuronide, luteolin-7---D-glucuronide, 3,5--di-caffeoylquinic acid, apigenin, and luteolin showed potent inhibition, and their IC values in RLAR were 4.25, 1.12, 1.16, 0.85, 0.72, 1.72, and 1.42 M, respectively. Furthermore, these compounds suppressed sorbitol accumulation in rat lens under high-glucose conditions, demonstrating their potential to prevent sorbitol accumulation ex vivo. Notably, luteolin-7---D-glucuronide and luteolin showed antioxidative as well as AGE-inhibitory activities (IC values of these compounds in AGEs were 3.39 and 6.01 M). These results suggest that the extract and its constituents may be promising agents for use in the prevention or treatment of diabetic complications.