Effects of ethanolic extracts from Eschscholtzia californica and Corydalis cavan on dimerization and oxidation of enkephalins

The endogenous pentapeptides, met-enkephalin and leu-enkephalin, similar to their parent structures, β-endorphin or dynorphin, bind to opioid receptors of the nociceptive system thus provoking analgesic responses. Peroxidases and phenolases (tyrosinase, catecholase) were shown to dimerize these pentapeptides thus possibly modulating their activity and/or lifetime. Extracts from plants from the order of the Papaverales contain isoquinoline alkaloids. Since the benzoisoquinolines are known to possess sedative-hypnotic activities, the potential effects of extracts from two species from this plant group, Eschscholtzia californica (Papaveraceae) and Corydalis cava (Fumaraceae), on the peroxidase- and tyrosinase-catalyzed dimerization and/or oxidation of met-enkephalin were investigated. The results of the study show that the peroxidase-catalyzed dimerization via the tyr-residues is especially inhibited by the C. cava extract. The tyrosinase-catalyzed reaction yields five different products A-E, according to their HPLC-retention times. Consisting of the 4:1 (v/v) combination of the extracts from E. californica and C. cava. Phytonoxon® N (abbreviated as PN) stimulates the formation of minor products A, B and E, whereas the formation of the major products C and D is inhibited. Only products C and D exhibit properties similar to the peroxidase-derived dimer. Product A is likely to be identical to DOPA-enkephalin.