Soymorphins, Novel μ Opioid Peptides Derived from Soy β-Conglycinin β-Subunit, Have Anxiolytic Activities

Abstract

Based on the amino acid sequence YPFV found in the soy -conglycinin -subunit, which is common to an opioid peptide human -casomorphin-4, peptides YPF-VV, YPFVVN, and YPFVVNA were synthesized according to their primary structure. On guinea pig ileum (GPI) assay, they showed opioid activity (IC 50 = 6.0, 9.2 and 13 M respectively) more potent than humancasomorphins, and were named soymorphins-5, -6, and -7, respectively. Their opioid activities on mouse vas deferens (MVD) assay were less potent than on GPI assay, suggesting that they are selective for the opioid receptor. Human -casomorphin-4 and soymorphin-5 were released from the soy 7S fraction (-conglycinin) by the action of gastrointestinal proteases. Soymorphins-5, -6, and -7 had anxiolytic activities after oral administration at doses of 10-30 mg/kg in the elevated plus-maze test in mice.Key words: opioid peptide; opioid receptor; anxiolytic effect; soy protein; -conglycinin -subunitOpioid is a chemical substance that has morphine-like action. An opioid peptide, bovine -casomorphin-7 (YPFPGPI), isolated from casein peptone, was the first example of bioactive peptides released from food proteins.1) We have reported that human -casomorphin-4 (YPFV) and related peptides derived from human -casein also have opioid activities, though they are less potent than their bovine counterparts.2) Of three soyconglycinin subunits (, 0 , and ), 3) the -subunit has the human -casomorphin-4 sequence (YPFV). Longer peptides, YPFVV, YPFVVN, and YPFVVNA, were synthesized according to the primary structure of theconglycinin -subunit by the Fmoc strategy, and their opioid activities were tested by guinea pig ileum (GPI) and mouse vas deferens (MVD) assay, as previously described.4) All experiments were approved by the Kyoto University Ethics Committee for Animal Research Use.The peptides were found to have opioid activities on GPI assay. Figure 1 indicates the typical suppressive effect of YPFVV on electrically stimulated contractions on GPI assay. YPFVVN and YPFVVNA also dosedependently inhibited ileum contractions (data not shown). These results suggest that YPFVV, YPFVVN, and YPFVVNA have opioid activities; they were named soymorphins-5, -6, and -7 respectively. The opioid activities of synthetic peptides derived from the soyconglycinin -subunit are summarized in Table 1. The IC 50 values of soymorphins-5, -6, and -7 on GPI assay were 6.0, 9.2, and 13 mM respectively, and their opioid activities were more potent than those of humancasomorphin-4, -5, and -6 (IC 50 = 20, 14, and 25 mM, respectively). There are three types of opioid receptors: , , and . 5,6) The opioid activities of soymorphins were larger on GPI assay than those on MVD assay, suggesting that these peptides are selective for theopioid receptor. The affinities for the -opioid receptor were 17, 39, and 47 mM respectively, and the rank order of their affinities for the receptor was consistent with that of the opioid activities on GPI assay. Taking all this 1 µM 3 µM 10 µM 1 min Guinea Pig Ileum (GPI) Assay. Ileum-...

Orally administered soymorphins, soy-derived opioid peptides, suppress feeding and intestinal transit via gut μ1-receptor coupled to 5-HT1A, D2, and GABABsystems

“…role in suppression of food intake and gut motility by soymorphins. We previously demonstrated that soymorphin-5, -6, and -7 inhibits smooth muscle contraction induced by electric stimulation (IC 50 ϭ 6.0, 9.2, and 13 M, respectively) in the guinea pig ileum (GPI) assay (30). The rank order of their affinities for the -receptor (IC 50 ϭ 17, 39, and 47 M, respectively) was consistent with that of the opioid activities on the GPI assay.…”

“…A number of opioid peptides have been identified from enzymatic digest of food proteins (6,13,30,42,43,45). ␤-Casomorphin, a -opioid peptide derived from bovine ␤-casein, has more potent opioid activity than that of soymorphin in a guinea pig ileum-contraction assay; however, ␤-casomorphin-5 did not suppress food intake and gut motility after oral administration under our experimental conditions.…”

“…For example, -opioid agonists, including morphine or endomorphin-1 or -2, stimulate food intake after central administration in rodents (2,20); however, we found that soymorphins, -opioid agonist peptides derived from ␤-conglycinin ␤-subunit (soymorphins-5, -6, and -7: Tyr-Pro-Phe-Val-Val, Tyr-Pro-Phe-Val-Val-Asn, and Tyr-ProPhe-Val-Val-Asn-Ala, respectively) (30), suppressed food intake after oral administration at a lower dose than that of our previously reported anorexigenic peptides derived from food proteins in mice (14,24). Since anorexigenic peptides sometimes suppress gastrointestinal motility (24), we then investigated whether soymorphins suppressed gastrointestinal motility.…”

Central PGE2exhibits anxiolytic-like activity via EP1and EP4receptors in a manner dependent on serotonin 5-HT1A, dopamine D1and GABAAreceptors

“…Soymorphin-5 and rubiscolin-6, which are l and d opioid peptides derived from soy b-conglycinin and spinach Rubisco, respectively, have anxiolytic-like activities after oral administration [18,19]. Rubiscolin-6 exhibits anxiolytic activity by activating r 1 receptor, downstream of d opioid receptor [19]; however, PGE 2 -induced anxiolytic-like activity was not blocked by antagonists for l and d opioid receptors, naloxone and naltrindole and BMY14802, respectively (data not shown), suggesting that PGE 2 shows anxiolytic-like activity independently of these opioid systems.…”

“…Anxiolytic-like behavior was measured using the elevated plusmaze (EPM) test, which was performed as described previously [12,[18][19][20][21]. Four arms (25 cm long  5 cm wide) were placed 50 cm above the ground.…”