Drosera tokaiensis extract containing multiple phenolic compounds inhibits the formation of advanced glycation end-products

The accumulation of advanced glycation end-products (AGEs) correlates with aging and accompanies the onset of age-related diseases, such as diabetes and arteriosclerosis. Therefore, a daily intake of natural compounds that inhibit the production of AGEs may be beneficial in preventing these diseases. In this study, we evaluated the inhibitory effects of 14 natural crude extracts, including those of Drosera species, which possess anti-inflammatory activity, on the formation of AGEs, such as N-omega-(carboxymethyl)arginine (CMA) and N-epsilon-(carboxymethyl)lysine (CML). Crude extracts of Drosera inhibited the formation of CMA and CML by incubation on gelatin with ribose more effectively than with other extracts, so active compounds that prevent AGE formation were purified from Drosera tokaiensis, which is endemic to Japan. Several compounds were purified from D. tokaiensis extracts using HPLC and identified by NMR analysis. These compounds included ellagic acid, 3,3'-di-O-methylellagic acid 4'-glucoside, myricitrine, and quercimelin. Furthermore, all compounds showed a significantly higher inhibitory effect on CMA and CML formations than aminoguanidine. Specifically, ellagic acid and myricitrine had the highest inhibitory effects of the compounds tested. However, not all compounds showed inhibition of CMA formation in a mixture of gelatin and glyoxal (GO). These results suggest that the compounds in D. tokaiensis inhibit CMA and CML formations via the antioxidative activity of phenolic compounds, rather than GO trapping action. This study provides the first evidence that D. tokaiensis inhibits CMA and CML formations and that phenolic compounds such as ellagic acid and myricitrine play an important role as active components of D. tokaiensis extracts.