Potent protein glycation inhibition of plantagoside in Plantago major seeds

Abstract

Plantagoside (5,7,4',5'-tetrahydroxyflavanone-3'-O-glucoside) and its aglycone (5,7,3',4',5'-pentahydroxyflavanone), isolated from a 50% ethanol extract of Plantago major seeds (Plantaginaceae), were established to be potent inhibitors of the Maillard reaction. These compounds also inhibited the formation of advanced glycation end products in proteins in physiological conditions and inhibited protein cross-linking glycation. These results indicate that P. major seeds have potential therapeutic applications in the prevention of diabetic complications.

Figure 1

The structures of the flavonoids that inhibited glycation. 1: Plantagoside (R = glucose), 2: 5,7,3′,4′,5′-pentahydroxyflavanone (R = H), 3: 5,7-dihydroxy-3′,4′,5′-trimethoxyflavone (R¹ = R² = CH₃), 4: 5,7,3′,4′,5′-pentahydroxyflavone (R¹ = R² = H), 5: 5,7,4′,5′-tetrahydroxyflavone-3′-O-glucoside (R¹ = glucose, R² = H), 6: myricetin, and 7: dihydromyricetin.

Figure 2

Inhibition of cross-ink formation by plantagoside (1). This assay was performed at pH 7.4 in phosphate buffer, which contained 20 mM ribose, 5 mg/mL lysozyme, 100 mM of aminoguanidine or NaCNBH₃, or the indicated concentration of plantagoside dissolved in dimethylsulfoxide, for 1 week at 37°C. Each sample was then subjected to 17.5% SDS-PAGE and stained with Coomassie Brilliant Blue. DMSO: dimethylsulfoxide containing no inhibitor; AG: aminoguanidine.

Figure 3

Differences in AGE formation inhibitory activity with different types of amino acids as the substrate. The inhibitory activities were determined at concentrations of 25 μM plantagoside and 10 mM aminoguanidine using N-α-acetyllysine or N-α-acetylarginine as the substrate for glycation. The inhibitory activity was examined by measuring the increase in the fluorescence intensity because of the formation of AGEs. Each value represents the mean ± standard error of three experiments.