Inhibitory effect of herbal medicines and their trapping abilities against methylglyoxal-derived advanced glycation end-products

Background: Methylglyoxal (MG) is one of the most reactive glycating agents, which result the formation of advanced glycation end-products (AGEs) that have been implicated in the progression of age-related diseases. Inhibition of MG-induced AGE formation is the imperative approach for alleviating diabetic complications. The objective of this study was to investigate the MG-trapping abilities of herbal medicines and their inhibitory activities on the formation of MG-derived AGEs. Methods: The aqueous extract of herbal medicines was measured for the content of total phenolic compounds and the antioxidant activity by Folin-Ciocalteu assay and the 1,1-diphenyl 2-picrylhydrazyl (DPPH) radical scavenging activity, respectively. The extracts were investigated the MG-trapping ability by high performance liquid chromatography (HPLC). The extracts were incubated with BSA and MG at 37 degrees C for 1 day. The formation of MG-derived AGEs was measured. Results: Total phenolic compounds of eleven herbal medicines showed marked variations, ranging from 12.16 to 272.36 mg gallic acid equivalents/g extract. All extracts (1 mg/mL) markedly exhibited the DPPH radical scavenging activity (0.31-73.52 %) and the MG-trapping abilities (13.97-58.97 %). In addition, they also inhibited the formation of MG-derived AGEs by 4.01-79.98 %. The results demonstrated that Rhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus were the potent inhibitors against the formation of MG-derived AGEs. The positive correlations between the contents of phenolics and % MG trapping (r = 0.912, p < 0.01) and % inhibition of MG-derived AGEs (r = 0.716, p < 0.01) were observed in the study. Furthermore, there was a moderate positive correlation between % MG trapping and % inhibition of MG-derived AGEs (r = 0.584, p < 0.01). Conclusions: Rhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus could reduce the formation of MG-derived AGEs through their MG-trapping abilities. These findings are relevant for focusing on potential herbal medicines to prevent or ameliorate AGE-mediated diabetic complications.