In Vitro Activities of Kissorphin, a Novel Hexapeptide KiSS-1 Derivative, in Neuronal Cells

The primary products of the metastasis-suppressor KiSS-1 gene are the kisspeptin (KP) peptides that stimulate gonadotrophin-releasing-hormone (GnRH) release via GPR-54 receptor activation. Recent studies have suggested that the KP-10 peptide also activates neuropeptide FF (NPFF) receptors. The aim of the current study was to determine the activities of the KiSS-1 derivative kissorphin (KSO), which contains the first six amino acids of the KP-10 peptide, is C-terminally amidated, and shares amino acid similarities with the biologically active NPFF 3–8 sequence. The KSO peptide inhibited forskolin-stimulated cyclic adenosine monophosphate (cAMP) production in ND7/23 neuroblastoma cells via an action that could be inhibited by the NPFF receptor antagonist RF9. Release of GnRH by LA-N-1 neuroblastoma cells was not altered by the KSO peptide. In ND7/23 neuroblastoma cells, the KSO peptide was able to reduce forskolin neuroprotection against H2O2 toxicity. The KSO peptide was also able to prevent prostaglandin E2-induced apoptosis in rat cortical neurons. The NPFF receptor antagonist RF9 could inhibit these actions of the KSO peptide in oxidative stress and apoptosis models. In conclusion, the kissorphin peptide, comprising the amino acid sequence Tyr-Asn-Trp-Asn-Ser-Phe-NH2, has NPFF-like biological activity without showing any GnRH releasing activity and inhibits forskolin-activated cAMP release. 1. Introduction Recent studies have shown that kisspeptin (KP) peptides can activate the two neuropeptide FF (NPFF) receptors, NPFFR1 (GPR-147) and NPFFR2 (GPR-74) [1–3]. These actions of KP peptides can be blocked by NPFF receptor antagonists including RF9 [4]. The NPFF peptide is a ligand for both these receptors [5–7], and the biologically active NPFF 3–8 form [8] shows amino acid sequence similarities to KP peptides (Table 1). Table 1: Comparison of kisspeptin, kissorphin, and NPFF sequences. The KP peptides themselves play a central role in the hypothalamic-pituitary-gonadal (HPG)-axis by acting on gonadotrophin-releasing hormone (GnRH) neurons to activate GnRH release [9]. The KP peptides are encoded by the metastasis-suppressor KiSS-1 gene and are ligands for the GPR-54 receptor [1, 10–12]. A range of KP peptides are found in vitro and in vivo with the largest 54 amino acid form corresponding to residues 68–121 of the KiSS-1 encoded pre-pro-KP [10]. Shorter derivatives of KP comprising the C-terminal 14, 13, and 10 amino acids have also been found in tissues and corresponding to residues 108–121, 109–121, and 112–121 of the KiSS-1 encoded pre-pro-KP [10,