Cardiovascular effects of intravenous administered 26RFa, a novel RFamide peptide ligand for GPR103, in anaesthetised rats

New Peptides as Potential Players in the Crosstalk Between the Brain and Obesity, Metabolic and Cardiovascular Diseases

According to the World Health Organization report published in 2016, 650 million people worldwide suffer from obesity, almost three times more than in 1975. Obesity is defined as excessive fat accumulation which may impair health with non-communicable diseases such as diabetes, cardiovascular diseases (hypertension, coronary artery disease, stroke), and some cancers. Despite medical advances, cardiovascular complications are still the leading causes of death arising from obesity. Excessive fat accumulation is caused by the imbalance between energy intake and expenditure. The pathogenesis of this process is complex and not fully understood, but current research is focused on the role of the complex crosstalk between the central nervous system (CNS), neuroendocrine and immune system including the autonomic nervous system, adipose tissue, digestive and cardiovascular systems. Additionally, special attention has been paid to newly discovered substances: neuropeptide 26RFa, preptin, and adropin. It was shown that the above peptides are synthesized both in numerous structures of the CNS and in many peripheral organs and tissues, such as the heart, adipose tissue, and the gastrointestinal tract. Recently, particular attention has been paid to the role of the presented peptides in the pathogenesis of obesity, metabolic and cardiovascular system diseases. This review summarizes the role of newly investigated peptides in the crosstalk between brain and peripheral organs in the pathogenesis of obesity, metabolic, and cardiovascular diseases.

The Arg-Phe-amide peptide 26RFa/glutamine RF-amide peptide and its receptor: IUPHAR Review 24

The RFamide neuropeptide 26RFa was first isolated from the brain of the European green frog on the basis of cross-reactivity with antibodies raised against bovine neuropeptide FF (NPFF). 26RFa and its N-terminally extended form glutamine RF-amide peptide (QRFP) have been identified as cognate ligands of the former orphan receptor GPR103, now renamed glutamine RF-amide peptide receptor (QRFP receptor). The 26RFa/QRFP precursor has been characterized in various mammalian and non-mammalian species. In the brain of mammals, including humans, 26RFa/QRFP mRNA is almost exclusively expressed in hypothalamic nuclei. The 26RFa/QRFP transcript is also present in various organs especially in endocrine glands. While humans express only one QRFP receptor, two isoforms are present in rodents. The QRFP receptor genes are widely expressed in the CNS and in peripheral tissues, notably in bone, heart, kidney, pancreas and testis. Structure-activity relationship studies have led to the identification of low MW peptidergic agonists and antagonists of QRFP receptor. Concurrently, several selective non-peptidic antagonists have been designed from high-throughput screening hit optimization. Consistent with the widespread distribution of QRFP receptor mRNA and 26RFa binding sites, 26RFa/QRFP exerts a large range of biological activities, notably in the control of energy homeostasis, bone formation and nociception that are mediated by QRFP receptor or NPFF2. The present report reviews the current knowledge concerning the 26RFa/QRFP-QRFP receptor system and discusses the potential use of selective QRFP receptor ligands for therapeutic applications.

Anxiolytic effect of the GPR103 receptor agonist peptide P550 (homolog of neuropeptide 26RFa) in mice. Involvement of neurotransmitters

The GPR103 receptor is a G protein-coupled receptor, which plays a role in several physiological functions. However, the role of the GPR103 receptor in anxiety has not been clarified. The first aim of our study was to elucidate the involvement of the GPR103 receptor in anxious behavior. Mice were treated with peptide P550, which is the mouse homolog of neuropeptide 26RFa and has similar activity for the GPR103 receptor as neuropeptide 26RFa. The anxious behavior was investigated using an elevated plus-maze paradigm. The second aim of our study was to investigate the underlying neurotransmissions. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a γ-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a nonselective β-adrenergic receptor antagonist, propranolol. Our results demonstrated that peptide P550 reduces anxious behavior in elevated plus maze test in mice. Our study shows also that GABAA-ergic, α- and β-adrenergic transmissions are all involved in this action, whereas 5-HT1 and 5-HT2 serotonergic, muscarinic cholinergic and D2, D3, D4 dopaminergic mechanisms may not be implicated.

Pyroglutamylated RF-amide peptide (QRFP) gene is regulated by metabolic endotoxemia

Pyroglutamylated RF-amide peptide (QRFP) is involved in the regulation of food intake, thermogenesis, adipogenesis, and lipolysis. The expression of QRFP in adipose tissue is reduced in diet-induced obesity, a mouse model in which plasma concentrations of endotoxins are slightly elevated. The present study investigated the role of metabolic endotoxemia (ME) on QRFP gene regulation. Our results uncovered the expression of QRFP in murine macrophages and cell lines. This expression has been found to be decreased in mice with ME. Low doses of lipopolysaccharide (LPS) transiently down-regulated QRFP by 59% in RAW264.7 macrophages but not in 3T3-L1 adipocytes. The effect of LPS on QRFP expression in macrophages was dependent on the inhibitor of kB kinase and TIR-domain-containing adapter-inducing interferon (IFN)-β (TRIF) but not myeloid differentiation primary response gene 88. IFN-β was induced by ME in macrophages. IFN-β sustainably reduced QRFP expression in macrophages (64%) and adipocytes (49%). IFN-γ down-regulated QRFP (74%) in macrophages only. Both IFNs inhibited QRFP secretion from macrophages. LPS-stimulated macrophage-conditioned medium reduced QRFP expression in adipocytes, an effect blocked by IFN-β neutralizing antibody. The effect of IFN-β on QRFP expression was dependent on phosphoinositide 3-kinase, p38 MAPK, and histone deacetylases. The effect of IFN-γ was dependent on MAPK/ERK kinase 1/2 and histone deacetylases. Macrophage-conditioned medium containing increased amounts of QRFP preserved adipogenesis in adipocytes. In conclusion, LPS induces IFN-β release from macrophages, which reduces QRFP expression in both macrophages and adipocytes in an autocrine/paracrine-dependent manner, suggesting QRFP as a potential biomarker in ME.

Rational design of a low molecular weight, stable, potent, and long-lasting GPR103 aza-β3-pseudopeptide agonist

26RFa, a novel RFamide neuropeptide, is the endogenous ligand of the former orphan receptor GPR103. Intracerebroventricular injection of 26RFa and its C-terminal heptapeptide, 26RFa((20-26)), stimulates food intake in rodents. To develop potent, stable ligands of GPR103 with low molecular weight, we have designed a series of aza-β(3)-containing 26RFa((20-26)) analogues for their propensity to establish intramolecular hydrogen bonds, and we have evaluated their ability to increase [Ca(2+)](i) in GPR103-transfected cells. We have identified a compound, [Cmpi(21),aza-β(3)-Hht(23)]26RFa((21-26)), which was 8-fold more potent than 26RFa((20-26)) in mobilizing [Ca(2+)](i). This pseudopeptide was more stable in serum than 26RFa((20-26)) and exerted a longer lasting orexigenic effect in mice. This study constitutes an important step toward the development of 26RFa analogues that could prove useful for the treatment of feeding disorders.

The RFamide neuropeptide 26RFa and its role in the control of neuroendocrine functions

Identification of novel neuropeptides and their cognate G protein-coupled receptors is essential for a better understanding of neuroendocrine regulations. The RFamide peptides represent a family of regulatory peptides that all possess the Arg-Phe-NH2 motif at their C-terminus. In mammals, seven RFamide peptides encoded by five distinct genes have been characterized. The present review focuses on 26RFa (or QRFP) which is the latest member identified in this family. 26RFa is present in all vertebrate phyla and its C-terminal domain (KGGFXFRF-NH2), which is responsible for its biological activity, has been fully conserved during evolution. 26RFa is the cognate ligand of the orphan G protein-coupled receptor GPR103 that is also present from fish to human. In all vertebrate species studied so far, 26RFa-expressing neurons show a discrete localization in the hypothalamus, suggesting important neuroendocrine activities for this RFamide peptide. Indeed, 26RFa plays a crucial role in the control of feeding behavior in mammals, birds and fish. In addition, 26RFa up-regulates the gonadotropic axis in mammals and fish. Finally, evidence that the 26RFa/GPR103 system regulates steroidogenesis, bone formation, nociceptive transmission and arterial blood pressure has also been reported. Thus, 26RFa appears to act as a key neuropeptide in vertebrates controlling vital neuroendocrine functions. The pathophysiological implication of the 26RFa/GPR103 system in human is totally unknown and some fields of investigation are proposed.

RFamide Peptides: Structure, Function, Mechanisms and Pharmaceutical Potential

Different neuropeptides, all containing a common carboxy-terminal RFamide sequence, have been characterized as ligands of the RFamide peptide receptor family. Currently, five subgroups have been characterized with respect to their N-terminal sequence and hence cover a wide pattern of biological functions, like important neuroendocrine, behavioral, sensory and automatic functions. The RFamide peptide receptor family represents a multiligand/multireceptor system, as many ligands are recognized by several GPCR subtypes within one family. Multireceptor systems are often susceptible to cross-reactions, as their numerous ligands are frequently closely related. In this review we focus on recent results in the field of structure-activity studies as well as mutational exploration of crucial positions within this GPCR system. The review summarizes the reported peptide analogs and recently developed small molecule ligands (agonists and antagonists) to highlight the current understanding of the pharmacophoric elements, required for affinity and activity at the receptor family. Furthermore, we address the biological functions of the ligands and give an overview on their involvement in physiological processes. We provide insights in the knowledge for the design of highly selective ligands for single receptor subtypes to minimize cross-talk and to eliminate effects from interactions within the GPCR system. This will support the drug development of members of the RFamide family.

Anti-allodynic effects of intrathecally and intracerebroventricularly administered 26RFa, an intrinsic agonist for GRP103, in the rat partial sciatic nerve ligation model

26RFa and QRFP are endogenous ligands of GPR103. 26RFa binding sites are widely distributed in the brain and the spinal cord where they are involved in processing pain. In the present study, the effects of intrathecal and intracerebroventricular applications of 26RFa on the level of mechanical allodynia induced by partial sciatic nerve ligation were examined in rats. The level of mechanical allodynia was measured using von Frey filaments. Intrathecal and intracerebroventricular injection of 26RFa attenuated the level of mechanical allodynia. 26RFa has been reported to activate not only GPR103 but also neuropeptide FF2 receptor and the effect of intrathecally and intracerebroventricularly administered 26RFa was not antagonized by BIBP3226, an antagonist of neuropeptide FF receptor. Immunohistochemical examination revealed that QRFP-like immunoreactivity (QRFP-LI) was expressed mainly in the small to medium sized neurons in the L5 dorsal root ganglion (DRG) and that partial sciatic nerve injury increased the percentage of QRFP-LI positive neurons. 7 days after the nerve injury, QRFP-LI positive neurons in the L5 DRG ipsilateral to the partial sciatic nerve injury were larger than those in the L5 DRG ipsilateral to the sham operation. These data suggest that (1) exogenously applied 26RFa modulates nociceptive transmission at the spinal and the supraspinal brain in the neuropathic pain model, (2) the mechanism 26RFa uses to produce an anti-allodynic effect may be mediated by the activation of GPR103, and (3) partial sciatic nerve ligation affects the expression of QRFP-LI in the dorsal root ganglion.

QRFP in female rats: effects on high fat food intake and hypothalamic gene expression across the estrous cycle

Pyroglutamylated arginine-phenylalanineamide peptide (QRFP) is a neuropeptide involved in feeding behavior. Central administration of QRFP selectively increases the intake of a high fat diet in male rats. QRFP administration also stimulates the hypothalamic-pituitary-gonadal axis via gonadotrophin-releasing hormone in male and female rats. Prepro-QRFP mRNA is expressed in localized regions of the mediobasal hypothalamus which are abundant in neurotransmitters, neuropeptides and receptor systems important for food intake regulation and reproductive behaviors. The current experiments were conducted to investigate the effects of centrally administered QRFP-26 on the intake of a high fat diet (HFD, 60%kcal from fat) in female rats and to investigate alterations in hypothalamic prepro-QRFP and its receptors, GPR130a and GPR103b, mRNA levels over the estrous cycle. In Experiment 1, female rats were administered QRFP-26 (intracerebroventricular; 0.3nmol, 0.5nmol, 1.0nmol) in rats consuming either a HFD or a low fat diet. All doses of QRFP-26 selectively increased the intake of the HFD in female rats. These data suggest that QRFP-26 regulates the intake of energy dense foods in female rats, which is similar to previous findings in male rats. In Experiment 2, hypothalamic levels of prepro-QRFP mRNA and its receptors were assessed during diestrus, proestrus, or estrus. The level of prepro-QRFP mRNA in the ventromedial/arcuate nucleus (VMH/ARC) of the hypothalamus was increased during proestrus, which suggests that endogenous estrogen levels regulate QRFP expression in the VMH/ARC. These data suggest that QRFP may play a role in coordinating feeding behaviors with reproductive function when energy demand is increased.

Human RFamide-related peptide-1 diminishes cellular and integrated cardiac contractile performance

Peptides influence cardiac dysfunction; however, peptidergic modulation of contractile performance remains relatively uncharacterized. We identified a novel human peptide that modulates mammalian contractile performance. Members of the FMRFamide-related peptide (FaRP) family contain a C-terminal RFamide but structurally variant N-terminal extension. We report human RFamide-related peptide-1 (hRFRP-1) and rat RFRP-1 rapidly and reversibly decreased shortening and relaxation in isolated mammalian cardiac myocytes in a dose dependent manner. The mammalian FaRP, 26RFa, structurally related to RFRP-1 by only an RFamide did not influence myocyte contractile function. The protein kinase C (PKC) inhibitor bisindolylmaleimide-1 blocked hRFRP-1 activity. Pretreatment with pertussis toxin (PTX) did not diminish hRFRP-1 influence on contractile function. In addition, intravenous injection of hRFRP-1 in mice decreased heart rate, stroke volume, ejection fraction, and cardiac output. Collectively these findings are consistent with the conclusion RFRP-1 is an endogenous signaling molecule that activates PKC and acts through a PTX-insensitive pathway to modulate cardiac contractile function. Taken together these negative chronotropic, inotropic, and lusitropic effects of hRFRP-1 are significant; they suggest direct acute cellular and organ-level responses in mammalian heart. This is the first known study to identify a mammalian FaRP with cardio-depressant effects, opening a new area of research on peptidergic modulation of contractile performance. The high degree of RFRP structure conservation from amphibians to mammals, and similarity to invertebrate cardioinhibitory peptides suggests RFRP-1 is involved in important physiological functions. Elucidation of mechanisms involved in hRFRP-1 synthesis, release, and signaling may aid the development of strategies to prevent or attenuate cardiac dysfunction.

Pressor and tachycardic responses to intrathecal administration of neuropeptide FF in anesthetized rats

Neuropeptide FF (NPFF) belongs to a neuropeptide family including two precursors (pro-NPFF(A) and pro-NPFF(B)) and two receptors (NPFF(1) and NPFF(2)). NPFF and NPFF receptor mRNAs have been reported to be highly expressed and localized in the rat and human spinal cord. In the present study, the i.t. action of NPFF system on blood pressure and heart rate were examined using NPFF and two related agonists, NPVF and dNPA, which exhibit highest selectivities for NPFF(1) and NPFF(2) receptors, respectively. In urethane-anesthetized rats, NPFF and related peptides (5-40 nmol, i.t.) produced significant pressor and tachycardic responses at the spinal cord level. These effects were dose-dependent and similar with respect to time-course for the three peptides. Furthermore, i.t. injection of RF9 (20 nmol), a selective NPFF antagonist, significantly antagonized the cardiovascular responses to 20 nmol NPFF and related peptides (i.t.). Moreover, pretreatment of the rats with alpha-adrenoceptor antagonist phentolamine (1mg/kg, i.v.) significantly reduced the pressor effects of NPFF. Nevertheless, pretreatment with muscarinic receptor and adrenoceptor antagonists (i.v.) could block the tachycardic effects induced by NPFF. Collectively, our results suggested that i.t. administration of NPFF and related peptides increased MAP and HR which were possibly mediated by the activation of both NPFF(1) and NPFF(2) receptors in the rat spinal cord. In addition, our results showed that the muscarinic receptor and adrenoceptor participated in the tachycardic response to i.t. NPFF, while alpha-adrenoceptor played an important role in the regulation of pressor effect of NPFF.