Y1 and Y5 Receptors Are Both Required for the Regulation of Food Intake and Energy Homeostasis in Mice

Neuropeptide Y (NPY) acting in the hypothalamus is one of the most powerful orexigenic agents known. Of the five known Y receptors, hypothalamic Y1 and Y5 have been most strongly implicated in mediating hyperphagic effects. However, knockout of individual Y1 or Y5 receptors induces late-onset obesity – and Y5 receptor knockout also induces hyperphagia, possibly due to redundancy in functions of these genes. Here we show that food intake in mice requires the combined actions of both Y1 and Y5 receptors. Germline Y1Y5 ablation in Y1Y5−/− mice results in hypophagia, an effect that is at least partially mediated by the hypothalamus, since mice with adult-onset Y1Y5 receptor dual ablation targeted to the paraventricular nucleus (PVN) of the hypothalamus (Y1Y5Hyp/Hyp) also exhibit reduced spontaneous or fasting-induced food intake when fed a high fat diet. Interestingly, despite hypophagia, mice with germline or hypothalamus-specific Y1Y5 deficiency exhibited increased body weight and/or increased adiposity, possibly due to compensatory responses to gene deletion, such as the decreased energy expenditure observed in male Y1Y5−/− animals relative to wildtype values. While Y1 and Y5 receptors expressed in other hypothalamic areas besides the PVN – such as the dorsomedial nucleus and the ventromedial hypothalamus – cannot be excluded from having a role in the regulation of food intake, these studies demonstrate the pivotal, combined role of both Y1 and Y5 receptors in the mediation of food intake

Chronic neuropeptide Y infusion into the lateral ventricle induces sustained feeding and obesity in mice lacking either Npy1r or Npy5r expression

Neuropeptide Y (NPY) is a powerful orexigenic neurotransmitter. The NPY Y1 and Y5 receptors have been implicated in mediating the appetite-stimulating activity of NPY. To further investigate the importance of these two receptors in NPY-induced hyperphagia after chronic central administration, we used mice lacking either Npy1r or Npy5r expression. NPY infusion into the lateral ventricle of wild-type mice stimulated food intake and induced obesity over a 7-d period. Fat pad weight as well as plasma insulin, leptin, and corticosterone levels were strongly increased in NPY-treated mice. In addition, NPY infusion resulted in a significant decrease in hypothalamic NPY and proopiomelanocortin expression. Interestingly, the lack of either Npy1r or Npy5r expression in knockout mice did not affect such feeding response to chronic NPY infusion. Moreover, the obesity syndrome that developed in these animals was similar to that in wild-type animals. Taken together, these data strongly suggest biological redundancies between Y1 and Y5 receptor signaling in the NPY-mediated control of food intake

Chronic blockade of the melanocortin 4 receptor subtype leads to obesity independently of neuropeptide Y action, with no adverse effects on the gonadotropic and somatotropic axes

Neuropeptide Y (NPY) is a powerful orexigenic factor, and alphaMSH is a melanocortin (MC) peptide that induces satiety by activating the MC4 receptor subtype. Genetic models with disruption of MC4 receptor signaling are associated with obesity. In the present study, a 7-day intracerebroventricular infusion to male rats of either the MC receptor antagonist SHU9119 or porcine NPY (10 nmol/day) was shown to strongly stimulate food and water intake and to markedly increase fat pad mass. Very high plasma leptin levels were found in NPY-treated rats (27.1 +/- 1.8 ng/ml compared with 9.9 +/- 0.9 ng/ml in SHU9119-treated animals and 2.1 +/- 0.2 ng/ml in controls). As expected, NPY infusion induced hypogonadism, characterized by an impressive decrease in seminal vesicle and prostate weights. No such effects were seen with the SHU9119 infusion. Similarly, whereas the somatotropic axis of NPY-treated rats was fully inhibited, this axis was normally activated in the obese SHU9119-treated rats. Chronic infusion of SHU9119 strikingly reduced hypothalamic gene expression for NPY (65.2 +/- 3.6% of controls), whereas gene expression for POMC was increased (170 +/- 19%). NPY infusion decreased hypothalamic gene expression for both POMC and NPY (70 +/- 9% and 75.4 +/- 9.5%, respectively). In summary, blockade of the MC4 receptor subtype by SHU9119 was able to generate an obesity syndrome with no apparent side-effects on the reproductive and somatotropic axes. In this situation, it is unlikely that hyperphagia was driven by increased NPY release, because hypothalamic NPY gene expression was markedly reduced, suggesting that hyperphagia mainly resulted from loss of the satiety signal driven by MC peptides. NPY infusion produced hypogonadism and hyposomatotropism in the face of markedly elevated plasma leptin levels and an important reduction in hypothalamic POMC synthesis. In this situation NPY probably acted both by exacerbating food intake through Y receptors and by reducing the satiety signal driven by MC peptides

Preparation and biological evaluation of cyclopentadienyl-based 99mTc-complexes [(Cp-R)99mTc(CO)3] mimicking benzamides for malignant melanoma targeting

The biological evaluation of half-sandwich (99m)Tc-complexes that surrogate iodobenzamide with a high affinity for melanin tumor tissue is described. We have synthesized via retro Diels-Alder reaction two models of (99m)Tc complexes which possess the piano stool [Cp(99m)Tc(CO)(3)] motif instead of a phenyl ring as in the original iodobenzamide (123)I-N-(N-benzylpiperidin-4-yl)-2-iodobenzamide (2-IBP) and N-(2-diethylaminoethyl)-4-iodobenzamide (BZA). Diels-Alder products 2a-b (HCp-CONHR)(2) (2a, R=2-diethylaminoethyl; 2b, R=benzylpiperidin-4-yl) were prepared and reacted with fac-[(99m)Tc(H(2)O)(3)(CO)(3))](+) 1 in water to produce the corresponding (99m)Tc complexes [(2a)(99m)Tc(CO)(3))] 4a and [(2b)(99m)Tc(CO)(3))] 4b. The structures of the (99m)Tc complexes on the no-carrier-added level have been confirmed by chromatographic comparison with the corresponding rhenium complexes 3a and 3b, macroscopically characterized by IR, NMR, ESI-MS and X-ray crystallography for 3a [triclinic, P-1, a=7.3518(1) A, b=8.0309(2) A, c=17.5536(3) A, alpha=99.1260(5) degrees, beta=90.4215(14) degree , gamma=117.0187(11) degrees]. The radioconjugate 4b showed good in vitro stability. In murine melanoma B16F1 cells, significant cellular uptake (43.9% of the total applied activity) was attained after 4 h at 37 degrees C with about 50% of the cell-associated radioactivity being internalized in the cells (22% of the applied activity). Furthermore, in melanoma-bearing C57BL6 mice, tumor uptake values of 3.39+/-0.50 %ID g(-1) and 3.21+/-0.26 %ID g(-1) at 1 and 4 h postinjection, respectively, were observed indicating a good retention of 4b in the tumor. Copyright 2010 Elsevier Inc. All rights reserved

Chronic blockade of the melanocortin 4 receptor subtype leads to obesity independently of neuropeptide Y action, with no adverse effects on the gonadotropic and somatotropic axes

Neuropeptide Y (NPY) is a powerful orexigenic factor, and alphaMSH is a melanocortin (MC) peptide that induces satiety by activating the MC4 receptor subtype. Genetic models with disruption of MC4 receptor signaling are associated with obesity. In the present study, a 7-day intracerebroventricular infusion to male rats of either the MC receptor antagonist SHU9119 or porcine NPY (10 nmol/day) was shown to strongly stimulate food and water intake and to markedly increase fat pad mass. Very high plasma leptin levels were found in NPY-treated rats (27.1 +/- 1.8 ng/ml compared with 9.9 +/- 0.9 ng/ml in SHU9119-treated animals and 2.1 +/- 0.2 ng/ml in controls). As expected, NPY infusion induced hypogonadism, characterized by an impressive decrease in seminal vesicle and prostate weights. No such effects were seen with the SHU9119 infusion. Similarly, whereas the somatotropic axis of NPY-treated rats was fully inhibited, this axis was normally activated in the obese SHU9119-treated rats. Chronic infusion of SHU9119 strikingly reduced hypothalamic gene expression for NPY (65.2 +/- 3.6% of controls), whereas gene expression for POMC was increased (170 +/- 19%). NPY infusion decreased hypothalamic gene expression for both POMC and NPY (70 +/- 9% and 75.4 +/- 9.5%, respectively). In summary, blockade of the MC4 receptor subtype by SHU9119 was able to generate an obesity syndrome with no apparent side-effects on the reproductive and somatotropic axes. In this situation, it is unlikely that hyperphagia was driven by increased NPY release, because hypothalamic NPY gene expression was markedly reduced, suggesting that hyperphagia mainly resulted from loss of the satiety signal driven by MC peptides. NPY infusion produced hypogonadism and hyposomatotropism in the face of markedly elevated plasma leptin levels and an important reduction in hypothalamic POMC synthesis. In this situation NPY probably acted both by exacerbating food intake through Y receptors and by reducing the satiety signal driven by MC peptides

Evidence that the inhibition of luteinizing hormone secretion exerted by central administration of neuropeptide Y (NPY) in the rat is predominantly mediated by the NPY-Y5 receptor subtype

A number of studies have indicated that neuropeptide Y (NPY) is a central regulator of the gonadotropic axis, and the Y1 receptor was initially suggested to be implicated. As at least five different NPY receptor subtypes have now been characterized, the aim of the present study was to reinvestigate the pharmacological profile of the receptor(s) mediating the inhibitory action of NPY on LH secretion by using a panel of NPY analogs with different selectivity toward the five NPY receptor subtypes. When given intracerebroventricularly (icv) to castrated rats, a bolus injection of native NPY (0.7-2.3 nmol) dose-dependently decreased plasma LH. Peptide YY (PYY; 2.3 nmol) was as potent as NPY, suggesting that the Y3 receptor is not implicated. Confirming previous data, the mixed Y1, Y4, and Y5 agonist [Leu31,Pro34]NPY (0.7-2.3 nmol) inhibited LH release with potency and efficacy equal to those of NPY. Neither the selective Y2 agonist C2-NPY (2.3 nmol) nor the selective Y4 agonist rat pancreatic polypeptide affected plasma LH, excluding Y2 and Y4 subtypes for the action of NPY on LH secretion. The mixed Y4-Y5 agonist human pancreatic polypeptide (0.7-7 nmol) as well as the mixed Y2-Y5 agonist PYY3-36 (0.7-7 nmol) that displayed very low affinity for the Y1 receptor, thus practically representing selective Y5 agonists in this system, decreased plasma LH with potency and efficacy similar to those of NPY, indicating that the Y5 receptor is mainly involved in this inhibitory action of NPY on LH secretion. [D-Trp32]NPY, a selective, but weak, Y5 agonist, also inhibited plasma LH at a dose of 7 nmol. Furthermore, the inhibitory action of NPY (0.7 nmol) on LH secretion could be fully prevented, in a dose-dependent manner (6-100 microg, icv), by a nonpeptidic Y5 receptor antagonist. This antagonist (60 microg, icv) also inhibited the stimulatory action of NPY (0.7 nmol) on food intake. The selectivity of PYY3-36, human PP, [D-Trp32]NPY, and the Y5 antagonist for the Y5 receptor subtype was further confirmed by their ability to inhibit the specific [125I][Leu31,Pro34]PYY binding to rat brain membrane homogenates in the presence of the Y1 receptor antagonist BIBP3226, a binding assay system that was described as being highly specific for Y5-like receptors. With the exception of [D-Trp32]NPY, all analogs able to inhibit LH secretion were also able to stimulate food intake. Taken together, these results indicate that the Y5 receptor is involved in the negative control by NPY of the gonadotropic axis