Rubimetide,humanin, and MMK1 exert anxiolytic-like activities via the formyl peptide receptor 2 in mice followed by the successive activation of DP1, A2A,and GABAA receptors

Rubimetide (Met-Arg-Trp), which had been isolated as an antihypertensive peptide from an enzymatic digest of spinach ribulose-bisphosphate carboxylase/oxygenase (Rubisco), showed anxiolytic-like activity prostaglandin (PG) D₂-dependent manner in the elevated plus-maze test after administration at a dose of 0.1 mg/kg (ip.) or 1 mg/kg (p.o.) in male mice of ddY strain. In this study, we found that rubimetide has weak affinities for the FPR1 and FPR2, subtypes of formyl peptide receptor (FPR). The anxiolytic-like activity of rubimetide (0.1 mg/kg, ip.) was blocked by WRW4, an antagonist of FPR2, but not by Boc-FLFLF, an antagonist of FPR1, suggesting that the anxiolytic-like activity was mediated by the FPR2. Humanin, an endogenous agonist peptide of the FPR2, exerted an anxiolytic-like activity after intracerebroventricular (icv) administration, which was also blocked by WRW4. MMK1, a synthetic agonist peptide of the FPR2, also exerted anxiolytic-like activity. Thus, FPR2 proved to mediate anxiolytic-like effect as the first example of central effect exerted by FPR agonists. As well as the anxiolytic-like activity of rubimetide, that of MMK1 was blocked by BW A868C, an antagonist of the DP₁-receptor. Furthermore, anxiolytic-like activity of rubimetide was blocked by SCH58251 and bicuculline, antagonists for adenosine A_2A and GABA_A receptors, respectively. From these results, it is concluded that the anxiolytic-like activities of rubimetide and typical agonist peptides of the FPR2 were mediated successively by the PGD₂-DP₁ receptor, adenosine-A_2A receptor, and GABA-GABA_A receptor systems downstream of the FPR2.