Effects of BIBP3226 and BIBP3435 on cytosolic calcium in neuropeptide Y Y1 receptor-transfected Chinese hamster ovary cells and wild type CHO-K1 cells

Complex FFA1 receptor (in)dependent modulation of calcium signaling by free fatty acids

The expression of free fatty acid 1 receptors (FFA1R), activated by long chain fatty acids in human pancreatic β-cells and enhancing glucose-stimulated insulin secretion are an attractive target to treat type 2 diabetes. Yet several clinical studies with synthetic FFA1R agonists had to be discontinued due to cytotoxicity and/or so-called "liver concerns". It is not clear whether these obstructions are FFA1R dependent. In this context we used CHO-AEQ cells expressing the bioluminescent calcium-sensitive protein aequorin to investigate calcium signaling elicited by FFA1 receptor ligands α-linolenic acid (ALA), oleic acid (OLA) and myristic acid (MYA). This study revealed complex modulation of intracellular calcium signaling by these fatty acids. First these compounds elicited a typical transient increase of intracellular calcium via binding to FFA1 receptors. Secondly slightly higher concentrations of ALA substantially reduced ATP mediated calcium responses in CHO-AEQ cells and Angiotensin II responses in CHO-AEQ cells expressing human AT₁ receptors. This effect was less pronounced with MYA and OLA and was not linked to FFA1 receptor activation nor to acute cytotoxicity as a result of plasma membrane perturbation. Yet it can be hypothesized that, in line with previous studies, unsaturated long chain fatty acids such as ALA and OLA are capable of inactivating the G-proteins involved in purinergic and Angiotensin AT₁ receptor calcium signaling. Alternatively the ability of fatty acids to deplete intracellular calcium stores might underly the observed cross-inhibition of these receptor responses in the same cells.

Effects of direct QRFP-26 administration into the medial hypothalamic area on food intake in rats

The RFamide peptide family comprises a number of biologically active peptides sharing RF motif at their C-terminal end. These peptides are involved in the control of multiple physiological functions including regulation of metabolism and feeding behavior. QRFP-43 as well as its 26-aminoacid residue QRFP-26 are able to cause orexigenic effect when administered to the rodents' cerebral ventricles. QRFPs have been suggested as the endogenous ligands of the previously orphan GPR103 receptors. GPR103 receptors share amino acid identity with other receptors of neuropeptides involved in feeding (NPY, NPFF, galanin). QRFP-26 expressing neurons and binding sites are densely present in the rat medial hypothalamus (MHA), an area directly responsible for the regulation of feeding. QRFP-26 was delivered to the target area by direct intrahypothalamic microinjection, and the consumption of liquid food was measured over a 60 min period. Both doses (100 and 200 ng) significantly increased food intake. Non-specific receptor antagonist BIBP3226 eliminated the orexigenic effect caused by QRFP-26 administration. Effective doses of QRFP-26 did not modify general locomotor activity and behavioral patterns examined in the open-field test. This study is the first reporting feeding modulating effects following direct intrahypothalamic QRFP-26 administration.

Neuropeptide Y inhibits capsaicin-sensitive nociceptors via a Y1-receptor-mediated mechanism

Neuropeptide Y (NPY) is expressed in certain primary afferent fibers, is up-regulated in response to tissue injury and is capable of inhibiting nociceptive behavior at the spinal level. However, the spinal mechanism(s) for NPY-evoked antinociception is unknown. In this study, we evaluated the hypothesis that agonists at the NPY Y1 receptor subtype (Y1-R) inhibit exocytosis from the capsaicin-sensitive class of nociceptors. Using in vitro superfusion of rat dorsal spinal cord slices, pre-treatment with the Y1-R agonist [Leu(31)Pro(34)]NPY significantly inhibited capsaicin-evoked release of immunoreactive calcitonin gene-related peptide with an EC(50) value of 10.6 nM. This inhibitory effect was concentration dependent, significantly attenuated by pre-treatment with the Y1 receptor antagonist BIBP3226 and reproduced by synthetic NPY. Examination of adult rat dorsal root ganglia using double immunofluorescent labeling revealed frequent co-localization of Y1 receptor immunoreactivity in vanilloid receptor type 1-immunoreactive neurons, indicating that Y1 agonists may directly modulate the capsaicin-sensitive class of nociceptors. Collectively, these results indicate that NPY is capable of inhibiting capsaicin-sensitive neurons via a Y1 receptor mechanism, suggesting the mechanisms for spinal NPY-induced antinociception is due, at least in part, to inhibition of central terminals of capsaicin-sensitive nociceptors.

Recent developments in our understanding of the physiological role of PP-fold peptide receptor subtypes

The three peptides pancreatic polypeptide (PP), peptide YY (PYY), and neuropeptide Y (NPY) share a similar structure known as the PP-fold. There are four known human G-protein coupled receptors for the PP-fold peptides, namely Y1, Y2, Y4, and Y5, each of them being able to bind at least two of the three endogenous ligands. All three peptides are found in the circulation acting as hormones. Although NPY is only released from neurons, PYY and PP are primarily found in endocrine cells in the gut, where they exert such effects as inhibition of gall bladder secretion, gut motility, and pancreatic secretion. However, when PYY is administered in an experimental setting to animals, cloned receptors, or tissue preparations, it can mimic the effects of NPY in essentially all studies, making it difficult to study the effects of PP-fold peptides and to delineate what receptor and peptide accounts for a particular effect. Initial studies with transgenic animals confirmed the well-established action of NPY on metabolism, food-intake, vascular systems, memory, mood, neuronal excitability, and reproduction. More recently, using transgenic techniques and novel antagonists for the Y1, Y2, and Y5 receptors, NPY has been found to be a key player in the regulation of ethanol consumption and neuronal development.