Protein glycation inhibitors from the fruiting body of Phellinus linteus

To characterize active principles for prevention and treatment of diabetic complications, the isolation of protein glycation inhibitors from the fruiting body of Phellinus linteus was conducted in vitro using the model systems of hemoglobin-delta-gluconolactone (early stage), bovine serum albumin-methylglyoxal (middle stage), and N-alpha-acetyl-glycyl-lysine methyl ester-D-ribose (last stage) assays. Nine compounds were isolated from the active ethylacetate fraction of the fruiting body and identified as protocatechuic acid (1), protocatechualdehyde (2), caffeic acid (3), ellagic acid (4), hispidin (5), davallialactone (6), hypholomine B (7), interfungins A (8), and inoscavin A (9) by spectroscopic analyses. At the early stage of protein glycation, compounds 6, 8, and 9 exhibited inhibitory activity on hemoglobin A,, formation. For the middle stage, compounds 2, 6, and 9 showed a significant inhibitory effect on methylglyoxal-medicated protein modification and their IC50 values were 144.28, 213.15, and 158.66 mu M, respectively. At the last stage of glycation, compound 8 was found to be a potent inhibitor of the cross-linking of proteins, which was more effective than that of aminoguanidine, a well-known inhibitor for advanced glycation end products. Consequently, compound 8 showed the most potent inhibitory effects at each stage of protein glycation. This mechanism may help to provide a protective effect against hyperglycemia-mediated protein damage.