Takahiro Tsuruki

Soymetide, an immunostimulating peptide derived from soybean β-conglycinin, is an fMLP agonist

A tridecapeptide (MITLAIPVNKPGR) that stimulates phagocytosis of human neutrophils was isolated from a trypsin digest of soybean proteins. This peptide is derived from the soybean β‐conglycinin α′ subunit and was named soymetide‐13. The N‐terminal methionine residue of soymetide‐13 is essential for its activity, and removal of C‐terminal residues revealed that soymetide‐4 (MITL) is the minimal structure required for phagocytosis stimulation. Although they are not formylated at their N‐termini, soymetides have a weak affinity for the N‐formyl‐methionyl‐leucyl‐phenylalanine (fMLP) receptor and their phagocytosis‐stimulating activity is inhibited by the fMLP antagonist Boc‐MLP. Interestingly, soymetide‐4 promotes tumor necrosis factor α production at a higher level than soymetide‐13 following oral administration in mice.

Creation of soybean β-conglycinin β with strong phagocytosis-stimulating activity

β-Conglycinin is composed of three kinds of subunit: α, α′ and β. A phagocytosis-stimulating peptide sequence (MITLAIPVNKPGR), soymetide, exists in the α′ subunit of β-conglycinin. Met at N terminus of the soymetide is essential for the activity. When Thr at the third residue from N terminus of the soymetide is replaced by Phe or Trp, the phagocytosis-stimulating activity greatly increases (Thr<Phe<Trp). The β subunit does not exhibit the phagocytosis-stimulating activity because the residues corresponding to the first and third residues in the soymetide are Ile and Lys, respectively. In this study, we introduced the phagocytosis-stimulating peptide sequence (Ile→Met, Lys→Thr, Phe, or Trp) into the β subunit after confirmation of the effects of residue replacements by molecular modeling, suggesting that the introduced mutations might not prevent the correct folding. The studies of circular dichroism (CD), gel filtration and differential scanning calorimetry (DSC) of the mutants (I122M/K124T, I122M/K124F, I122M/K124W) expressed in E. coli demonstrated that they folded and self-assembled similarly to the wild type. This was confirmed by X-ray analysis of I122M/K124W crystal where the biggest residue tryptophane was introduced. The three mutants exhibited phagocytosis activities after digestion by trypsin, and the order was the wild type<I122M/K124T<I122M/K124F<I122M/K124W as expected.

Design of soymetide-4 derivatives to potentiate the anti-alopecia effect.

Previously, we found that soymetide-4 (MITL), an N-formyl-methionyl-leucyl-phenylalanine (fMLP) agonist peptide derived from soybean β-conglycinin α′ subunit, stimulated phagocytosis of human polymorphonuclear leukocytes, and inhibited alopecia induced by etoposide, an anticancer drug, in neonatal rats after oral administration. We found that the fMLP receptor affinity and phagocytosis-stimulating activity of soymetide-4 was potentiated by replacement of Thr3 with hydrophobic residues. Among the derivatives synthesized, [Trp]3-soymetide-4 (MIWL) was the most potent, stronger by 180 and 130 times than soymetide-4 in receptor affinity and phagocytosis-stimulating activity, respectively. The anti-alopecia effect of [Trp]3-soymetide-4 was about 3 times larger than that of soymetide-4 after oral administration.

Mechanism of the Protective Effect of Intraperitoneally Administered Agonists for Formyl Peptide Receptors against Chemotherapy-Induced Alopecia

Previously, we found that an intraperitoneally administered chemotactic peptide, N-formyl-Met-Leu-Phe (fMLP), and MMK-1, a selective agonist of formyl peptide receptor-like 1 (FPRL1) receptor, the low affinity subtype of the fMLP receptor, prevented the alopecia in neonatal rats induced by the anticancer agent etoposide. The anti-alopecia effect of fMLP was not inhibited at all by Boc-FLFLF, a selective antagonist of formylpeptide receptor (FPR), which is the high affinity subtype of the fMLP receptor, but it was partly inhibited by Trp-Arg-Trp-Trp-Trp-Trp-NH2 (WRW4), an antagonist of FPRL1 receptor. On the other hand, the anti-alopecia effect of MMK-1 was completely abolished by WRW4. The anti-alopecia effects of fMLP and MMK-1 were also inhibited by Lys-D-Pro-Thr (K(D)PT) and pyrrolidine dithiocarbamate, which are inhibitors of interleukin-1 (IL-1) and nuclear factor-κB (NF-κB) respectively. Hence, we suggest that the anti-alopecia mechanisms of intraperitoneally administered fMLP and MMK-1 include activation of NF-κB via IL-1 release downstream of the FPRL1 receptor homolog in rats.

Orally administered FPRL1 receptor agonist peptide MMK-1 inhibits etoposide-induced alopecia by a mechanism different from intraperitoneally administered MMK-1.

Oral administration for 6 days of 100 mg/kg MMK-1, an agonist peptide selective for the FPRL1 receptor, suppressed alopecia induced by the anticancer drug etoposide in neonatal rats. The anti-alopecia effect of orally administered MMK-1 was not inhibited by pyrilamine or cimetidine, antagonists for histamine H1 and H2 receptors, respectively, which blocked the anti-alopecia effect of intraperitoneally administered MMK-1 at a dose of 10 mg/kg for 4 days. However, the anti-alopecia effect of orally administered MMK-1 was inhibited by indomethacin, an inhibitor of cyclooxygenase (COX), or AH-23848B, an antagonist of the EP4 receptor for prostaglandin (PG) E2, suggesting involvement of PGE2 release and the EP4 receptor in the oral MMK-1 anti-alopecia mechanism. The anti-alopecia effect of orally administered MMK-1 was also blocked by an inhibitor of nuclear factor-kappaB (NF-kappaB), pyrrolidine dithiocarbamate, suggesting that the oral anti-alopecia effect of MMK-1 may be mediated by activation of NF-kappaB. These results suggest that MMK-1 bound to FPRL1 receptor might suppress etoposide-induced apoptosis of hair follicle cells and alopecia by way of PGE2 release and NF-kappaB activation.

Anti-Alopecia Effect of Gly-Leu-Phe, an Immunostimulating Peptide Derived from α-Lactalbumin

Gly-Leu-Phe (GLF), an immunostimulating peptide derived from α-lactalbumin, prevented alopecia induced by an anticancer agent etoposide in a neonatal rat model after intraperitoneal injection at a dose of 100 mg/kg for 4 d or oral administration at a dose of 300 mg/kg for 6 d. By microscopic analysis of skin sections, GLF proved to inhibit etoposide-induced loss of hair, thickening of the epidermis, and thinning of the adipocyte layer. The anti-alopecia effect of GLF was inhibited by pyrilamine, a histamine H1 receptor antagonist, suggesting that the anti-alopecia effect is mediated by histamine release.