The cytokine GDF15 signals through a population of brainstem cholecystokinin neurons to mediate anorectic signalling.

The cytokine, GDF15, is produced in pathological states which cause cellular stress, including cancer. When over expressed, it causes dramatic weight reduction, suggesting a role in disease-related anorexia. Here, we demonstrate that the GDF15 receptor, GFRAL, is located in a subset of cholecystokinin neurons which span the area postrema and the nucleus of the tractus solitarius of the mouse. GDF15 activates GFRALAP/NTS neurons and supports conditioned taste and place aversions, while the anorexia it causes can be blocked by a monoclonal antibody directed at GFRAL or by disrupting CCK neuronal signalling. The cancer-therapeutic drug, cisplatin, induces the release of GDF15 and activates GFRALAP/NTS neurons, as well as causing significant reductions in food intake and body weight in mice. These metabolic effects of cisplatin are abolished by pre-treatment with the GFRAL monoclonal antibody. Our results suggest that GFRAL neutralising antibodies or antagonists may provide a co-treatment opportunity for patients undergoing chemotherapy.

Dual Exosite-binding Inhibitors of Insulin-degrading Enzyme Challenge Its Role as the Primary Mediator of Insulin Clearance in Vivo.

Insulin-degrading enzyme (IDE, insulysin) is the best characterized catabolic enzyme implicated in proteolysis of insulin. Recently, a peptide inhibitor of IDE has been shown to affect levels of insulin, amylin, and glucagon in vivo. However, IDE(-/-) mice display variable phenotypes relating to fasting plasma insulin levels, glucose tolerance, and insulin sensitivity depending on the cohort and age of animals. Here, we interrogated the importance of IDE-mediated catabolism on insulin clearance in vivo. Using a structure-based design, we linked two newly identified ligands binding at unique IDE exosites together to construct a potent series of novel inhibitors. These compounds do not interact with the catalytic zinc of the protease. Because one of these inhibitors (NTE-1) was determined to have pharmacokinetic properties sufficient to sustain plasma levels >50 times its IDE IC50 value, studies in rodents were conducted. In oral glucose tolerance tests with diet-induced obese mice, NTE-1 treatment improved the glucose excursion. Yet in insulin tolerance tests and euglycemic clamp experiments, NTE-1 did not enhance insulin action or increase plasma insulin levels. Importantly, IDE inhibition with NTE-1 did result in elevated plasma amylin levels, suggesting the in vivo role of IDE action on amylin may be more significant than an effect on insulin. Furthermore, using the inhibitors described in this report, we demonstrate that in HEK cells IDE has little impact on insulin clearance. In total, evidence from our studies supports a minimal role for IDE in insulin metabolism in vivo and suggests IDE may be more important in helping regulate amylin clearance.

LLY-2707, a novel nonsteroidal glucocorticoid antagonist that reduces atypical antipsychotic-associated weight gain in rats.

Weight gain and diabetes have been reported during treatment with atypical antipsychotic drugs (AAPDs). Patients treated with the glucocorticoid receptor antagonist (GRA) and the progesterone receptor antagonist (PRA) mifepristone [estra-4,9-dien-3-one, 11-[4-(dimethylamino)phenyl]-17-hydroxy-17-(1-propynyl)-(11ß,17ß)-(9CI)] experienced significant reduction in the weight gain observed when patients were treated with olanzapine or risperidone. To understand the pharmacology responsible for this finding, we discovered LLY-2707 [N-(5-(tert-butyl)-3-(2-fluoro-5-methylpyridin-4-yl)-2-methyl-1H-indol-7-yl)methanesulfonamide], a novel and selective GRA, and evaluated its utility in preclinical models of AAPD-associated weight gain and diabetes. In vitro, LLY-2707 was a highly selective and potent GRA. GR occupancy in vivo was assessed using ex vivo binding where LLY-2707 inhibited [(3)H]dexamethasone binding to the liver. Modest but statistically significant decreases in brain ex vivo binding were observed with high doses of CORT-108297 [(R)-4α-(ethoxymethyl)-1-(4-fluorophenyl)-6-((4-(trifluoromethyl)phenyl)sulfonyl)-4,4a,5,6,7,8-hexahydro-1H-pyrazolo[3,4-g]isoquinoline] and LLY-2707, but mifepristone inhibited at all doses. Central activity of the GRAs was confirmed by their ability to suppress amphetamine-induced increases in locomotor activity. The increases in the body weight of female rats treated with olanzapine (2 mg/kg PO) over 14 days were reduced in a dose-dependent manner by coadministration of LLY-2707. Similar decreases, although less robust, in body weight were seen with mifepristone and CORT-108297. In addition, sGRAs prevented the glucose excursion after intragastric olanzapine infusions consistent with a direct effect on the hyperglycemia observed during treatment with AAPDs. At doses effectively preventing weight gain, LLY-2707 did not substantially interfere with the dopamine D2 receptor occupancy by olanzapine. Therefore, GRA coadministration may provide a novel treatment modality to prevent the weight gain and diabetes observed during treatment with AAPDs.

Activation of mesolimbic dopamine neurons during novel and daily limited access to palatable food is blocked by the opioid antagonist LY255582.

An analog of the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine series (LY255582) exhibits high in vitro binding affinity and antagonist potency for the mu-, delta-, and kappa-opioid receptors. In vivo, LY255582 exhibits potent effects in reducing food intake and body weight in several rodent models of obesity. In the present study, we evaluated the effects of LY255582 to prevent the consumption of a highly palatable (HP) diet (a high-fat/high-carbohydrate diet) both when the food was novel and following daily limited access to the HP diet. Additionally, we examined the effects of consumption of the HP diet and of LY255582 treatment on mesolimbic dopamine (DA) signaling by in vivo microdialysis. Consumption of the HP diet increased extracellular DA levels within the nucleus accumbens (NAc) shell. Increased DA in the NAc shell was not related to the quantity of the HP diet consumed, and the DA response did not habituate following daily scheduled access to the HP diet. Interestingly, treatment with LY255582 inhibited consumption of the HP diet and the HP diet-associated increase in NAc shell DA levels. Moreover, the increased HP diet consumption observed following daily limited access to the HP diet was completely prevented by LY255582 treatment. LY255582 may be a useful tool in understanding the neural mechanisms involved in the reinforcement mechanisms regulating food intake.

The relationship of in vivo central CB1 receptor occupancy to changes in cortical monoamine release and feeding elicited by CB1 receptor antagonists in rats.

RATIONALE: Cannabinoid type 1 (CB(1)) receptor antagonists are reportedly effective in reducing food intake both preclinically and clinically. This may be due in part to their effects on monoamine release in the brain. The level of central CB(1) receptor occupancy underlying these neurobiological effects is unclear. OBJECTIVES: We explored the relationship between in vivo CB(1) receptor occupancy in the frontal cortex and changes in both monoamine release in the medial prefrontal cortex (mPFC) and feeding behavior in rats in response to two orally administered CB(1) receptor antagonists presently in clinical trials, SR141716A (rimonabant) and SLV319. METHODS: CB(1) receptor occupancy was measured using [(3)H] SR141716A, and these occupancies were related to potencies to mediate increases in dopamine (DA) and norepinephrine (NE) release measured with microdialysis and decreases in consumption of a highly palatable diet (HP). RESULTS: High receptor occupancy levels (>65%) were required to detect increases in monoamine release that were achieved with 3 and 10 mg/kg of SR141716A and 10 mg/kg of SLV319 for DA and 10 mg/kg of SR141716A for NE. Decreases in HP consumption were seen at occupancies higher than 65% for SR141716A that were achieved with 3 and 10 mg/kg. In contrast, decreases in HP consumption were seen at relatively low CB(1) receptor occupancies (11%) for SLV319. CONCLUSIONS: The occupancy method described here is an effective tool for interrelating central CB(1) receptor occupancy with neurobiological actions of CB(1) receptor antagonists and for furthering our understanding of the role of CB(1) receptors in central nervous system physiology and pathology.

Central H3R activation by thioperamide does not affect energy balance.

The central histamine 3 receptor (H3R) is a presynaptic autoreceptor that regulates neuronal release and synthesis of histamine, and is thought to play a key role in controlling numerous central nervous system (CNS)-mediated parameters, including energy homeostasis. Thioperamide, the prototypical selective H3R antagonist, was used to examine the role that H3R plays in regulating energy balance in vivo. Thioperamide was administered either intraperitoneally or orally to rats and the pharmacokinetic parameters were examined along with central H3R binding and histaminergic system activation. Food intake and metabolic parameters of either route of thioperamide administration were likewise examined. In a dose-dependent manner, both the intraperitoneal and oral route of administration resulted in similar ex vivo binding curves and tele-methylhistamine dose-response curves despite the route of administration. However, only intraperitoneal administration of 30 mg/kg thioperamide resulted in a significant decrease in 24-h food intake (60% lower than control) and respiratory quotient (RQ), while the oral route of delivery did not. Moreover, the decrease in RQ with the 30 mg/kg ip administration also decreased energy expenditure (EE) thus resulting in an unchanged energy balance. The decrease in food intake and EE was coupled with a conditioned taste aversion with the 30-mg/kg ip administration. These data indicate that the activation of the central H3R system by thioperamide does not play a direct role in decreasing food intake or altering energy homeostasis.

Non-catalytic role of carbonic anhydrase in rat intestinal absorption.

Carbonic anhydrase (CA) inhibition reduces NaCl absorption in rat distal ileum, a pH-sensitive, low CA activity tissue, and in distal colon, a CO(2)-sensitive, high CA activity tissue. We hypothesized that CA plays a non-catalytic role in NaCl absorption in these segments. Unidirectional fluxes of Na(+) and Cl(-), and total HCO(3)(-) generation (estimated as the sum of radiolabeled HCO(3)(-) and CO(2) produced from glucose) were measured in Ussing chambers in nominally CO(2), HCO(3)(-)-free HEPES Ringer. Measurements were made in the presence and absence of 0.1 mM methazolamide, a membrane-permeant CA inhibitor. Ringer pH reduction from 7.6 to 7.1 stimulated ileal but not colonic Na(+) and Cl(-) absorption. In the ileum, methazolamide reduced J(ms)(Na) and J(ms)(Cl) and caused net Cl(-) secretion at pH 7.6, and prevented the stimulatory effect of lowering pH. In the colon, methazolamide reduced Na(+) and Cl(-) absorption at pH 7.6. Total HCO(3)(-) generation was minimal in HEPES at pH 7.6 and 7.1 in both segments, was minimally affected by methazolamide, and did not account for the changes in Cl(-) absorption caused by pH or methazolamide. We conclude that CA plays a role in ileal and colonic NaCl absorption independent of its catalytic function.

Acid-base effects on intestinal Na(+) absorption and vesicular trafficking.

We examined for vesicular trafficking of the Na(+)/H(+) exchanger (NHE) in pH-stimulated ileal and CO(2)-stimulated colonic Na(+) absorption. Subapical vesicles in rat distal ileum were quantified by transmission electron microscopy at x27,500 magnification. Internalization of ileal apical membranes labeled with FITC-phytohemagglutinin was assessed using confocal microscopy, and pH-stimulated ileal Na(+) absorption was measured after exposure to wortmannin. Apical membrane protein biotinylation of ileal and colonic segments and Western blots of recovered proteins were performed. In ileal epithelial cells incubated in HCO/Ringer or HEPES/Ringer solution, the number of subapical vesicles, the relative quantity of apical membrane NHE isoforms 2 and 3 (NHE2 and NHE3, respectively), and apical membrane fluorescence under the confocal microscope were not affected by pH values between 7.1 and 7.6. Wortmannin did not inhibit pH-stimulated ileal Na(+) absorption. In colonic epithelial apical membranes, NHE3 protein content was greater at a PCO(2) value of 70 than 21 mmHg, was internalized when PCO(2) was reduced, and was exocytosed when PCO(2) was increased. We conclude that vesicle trafficking plays no part in pH-stimulated ileal Na(+) absorption but is important in CO(2)-stimulated colonic Na(+) absorption.