Peripheral and central localization of the nesfatin-1 receptor using autoradiography in rats.

Nesfatin-1 was recently identified and introduced as food intake-regulatory hormone. Soon thereafter, mounting evidence indicated a much broader role for nesfatin-1 with an involvement in the regulation of food intake, gastrointestinal motility, glucose homeostasis, blood pressure and stress. Despite the growing knowledge on the physiological regulation and functions of nesfatin-1, the receptor mediating these effects remains to be characterized. Therefore, the aim of this study was to investigate the peripheral and central localization of the nesfatin-1 receptor by autoradiography. Male Sprague-Dawley rats were used and peripheral as well as brain tissue was processed for (125)I-nesfatin-1 autoradiography. In peripheral tissues, an autoradiographic signal was observed in the gastric mucosa of corpus and antrum, in duodenum, jejunum and ileum, while no signal was detected in the colon. Preabsorption of (125)I-nesfatin-1 with non-labeled nesfatin-1 greatly diminished the autoradiographic signal in the stomach indicating specificity (-32%, p < 0.001). A displacement assay showed an effective concentration by which 50% of (125)I-nesfatin-1 bound to the receptor (EC50) in the gastric corpus of 80 pM. Moreover, autoradiography was observed in endocrine tissues including the pituitary, pancreas, adrenal gland, testis and visceral adipose tissue. In addition, also heart, skeletal muscle, lung, liver and kidney showed autoradiographic signals. In the brain, strong (125)I-nesfatin-1 autoradiography was detected in the cortex, paraventricular nucleus of the hypothalamus, area postrema, dorsal motor nucleus of the vagus nerve and cerebellum. Based on the distribution of nesfatin-1 autoradiography, nesfatin-1 is a pleiotropic hormone that is involved in the regulation of several homeostatic functions.

A RAPID Method for Blood Processing to Increase the Yield of Plasma Peptide Levels in Human Blood.

Research in the field of food intake regulation is gaining importance. This often includes the measurement of peptides regulating food intake. For the correct determination of a peptide's concentration, it should be stable during blood processing. However, this is not the case for several peptides which are quickly degraded by endogenous peptidases. Recently, we developed a blood processing method employing Reduced temperatures, Acidification, Protease inhibition, Isotopic exogenous controls and Dilution (RAPID) for the use in rats. Here, we have established this technique for the use in humans and investigated recovery, molecular form and circulating concentration of food intake regulatory hormones. The RAPID method significantly improved the recovery for (125)I-labeled somatostatin-28 (+39%), glucagon-like peptide-1 (+35%), acyl ghrelin and glucagon (+32%), insulin and kisspeptin (+29%), nesfatin-1 (+28%), leptin (+21%) and peptide YY3-36 (+19%) compared to standard processing (EDTA blood on ice, p <0.001). High performance liquid chromatography showed the elution of endogenous acyl ghrelin at the expected position after RAPID processing, while after standard processing 62% of acyl ghrelin were degraded resulting in an earlier peak likely representing desacyl ghrelin. After RAPID processing the acyl/desacyl ghrelin ratio in blood of normal weight subjects was 1:3 compared to 1:23 following standard processing (p = 0.03). Also endogenous kisspeptin levels were higher after RAPID compared to standard processing (+99%, p = 0.02). The RAPID blood processing method can be used in humans, yields higher peptide levels and allows for assessment of the correct molecular form.

Nesfatin-130-59 Injected Intracerebroventricularly Differentially Affects Food Intake Microstructure in Rats Under Normal Weight and Diet-Induced Obese Conditions.

Nesfatin-1 is well-established to induce an anorexigenic effect. Recently, nesfatin-130-59, was identified as active core of full length nesfatin-11-82 in mice, while its role in rats remains unclear. Therefore, we investigated the effects of nesfatin-130-59 injected intracerebroventricularly (icv) on the food intake microstructure in rats. To assess whether the effect was also mediated peripherally we injected nesfatin-130-59 intraperitoneally (ip). Since obesity affects the signaling of various food intake-regulatory peptides we investigated the effects of nesfatin-130-59 under conditions of diet-induced obesity (DIO). Male Sprague-Dawley rats fed ad libitum with standard diet were icv cannulated and injected with vehicle (5 µl ddH2O) or nesfatin-130-59 at 0.37, 1.1, and 3.3 µg (0.1, 0.3, 0.9 nmol/rat) and the food intake microstructure assessed using a food intake monitoring system. Next, naïve rats were injected ip with vehicle (300 µl saline) or nesfatin-130-59 (8.1, 24.3, 72.9 nmol/kg). Lastly, rats were fed a high fat diet for 10 weeks and those developing DIO were icv cannulated. Nesfatin-1 (0.9 nmol/rat) or vehicle (5 µl ddH2O) was injected icv and the food intake microstructure assessed. In rats fed standard diet, nesfatin-130-59 caused a dose-dependent reduction of dark phase food intake reaching significance at 0.9 nmol/rat in the period of 4-8 h post injection (-29%) with the strongest reduction during the fifth hour (-75%), an effect detectable for 24 h (-12%, p < 0.05 vs. vehicle). The anorexigenic effect of nesfatin-130-59 was due to a reduction in meal size (-44%, p < 0.05), while meal frequency was not altered compared to vehicle. In contrast to icv injection, nesfatin-130-59 injected ip in up to 30-fold higher doses did not alter food intake. In DIO rats fed high fat diet, nesfatin-130-59 injected icv reduced food intake in the third hour post injection (-71%), an effect due to a reduced meal frequency (-27%, p < 0.05), while meal size was not altered. Taken together, nesfatin-130-59 is the active core of nesfatin-11-82 and acts centrally to reduce food intake in rats. The anorexigenic effect depends on the metabolic condition with increased satiation (reduction in meal size) under normal weight conditions, while in DIO rats satiety (reduction in meal frequency) is induced.

The dopamine antagonist flupentixol does not alter ghrelin-induced food intake in rats.

It has been shown that dopamine antagonists suppress the ghrelin-induced increased motivation to work for food. The aim of this study was to investigate the influence of the dopamine antagonist flupentixol on ghrelin-induced food intake. Ad libitum fed male Sprague-Dawley (SD) rats were injected intraperitoneally (ip) with vehicle plus vehicle, vehicle plus ghrelin (13 µg/kg), 0.25mg/kg or 0.5mg/kg flupentixol plus ghrelin, or 0.25mg/kg or 0.5 mg/kg flupentixol plus vehicle. In a second experiment, intracerebroventricularly (icv) cannulated rats received an ip injection of vehicle (0.15M NaCl) or flupentixol (0.25mg/kg) and 20 min later an icv injection of vehicle or ghrelin (1 µg/rat). Both experiments were performed twice: first, rats were offered only standard chow, while in the second experiment they could choose between standard chow and a palatable/preferred chow. Cumulative light phase food intake was assessed for 7h. Ip as well as icv injected ghrelin reliably increased intake of standard chow. Flupentixol did not affect ghrelin-induced intake of standard chow. Ip injected ghrelin failed to increase the intake of palatable chow, whereas icv injected ghrelin did. This effect was not blocked by ip flupentixol. In summary, ip administered ghrelin did not increase the intake of chow the rats preferred; whereas icv injected ghrelin further stimulated the intake of preferred chow suggesting a direct central mediation of this effect. Our results show that the dopamine antagonist flupentixol does not influence ghrelin-induced feeding in our choice paradigm.

Obese patients have higher circulating protein levels of dipeptidyl peptidase IV.

Dipeptidyl peptidase IV (DPPIV) is a protease with broad distribution involved in various homeostatic processes such as immune defense, psychoneuroendocrine functions and nutrition. While DPPIV protein levels were investigated in patients with hyporectic disorders, less is known under conditions of obesity. Therefore, we investigated DPPIV across a broad range of body mass index (BMI). Blood samples from hospitalized patients with normal weight (BMI 18.5-25 kg/m(2)), anorexia nervosa (BMI <17.5 kg/m(2)) and obesity (BMI 30-40, 40-50 and >50 kg/m(2), n = 15/group) were tested cross-sectionally and DPPIV concentration and total enzyme activity and the DPPIV targets, pancreatic polypeptide (PP) and glucagon-like peptide (GLP-1) were measured. DPPIV protein expression was detected in human plasma indicated by a strong band at the expected size of 110 kDa and another major band at 50 kDa, likely representing a fragment comprised of two heavy chains. Obese patients had higher DPPIV protein levels compared to normal weight and anorexics (+50%, p<0.05) resulting in a positive correlation with BMI (r = 0.34, p = 0.004). DPPIV serum activity was similar in all groups (p>0.05), while the concentration/activity ratio was higher in obese patients (p<0.05). Plasma PP levels were highest in anorexic patients (∼ 2-fold increase compared to other groups, p<0.05), whereas GLP-1 did not differ among groups (p<0.05). Taken together, circulating DPPIV protein levels depend on body weight with increased levels in obese resulting in an increased concentration/activity ratio. Since DPPIV deactivates food intake-inhibitory hormones like PP, an increased DPPIV concentration/activity ratio might contribute to reduced food intake-inhibitory signaling under conditions of obesity.

The ghrelin activating enzyme ghrelin-O-acyltransferase (GOAT) is present in human plasma and expressed dependent on body mass index.

Ghrelin is the only known peripherally produced and centrally acting peptide hormone stimulating food intake. The acylation of ghrelin is essential for binding to its receptor. Recently, the ghrelin activating enzyme ghrelin-O-acyltransferase (GOAT) was identified in mice, rats and humans. In addition to gastric mucosal expression, GOAT was also detected in the circulation of rodents and its expression was dependent on metabolic status. We investigated whether GOAT is also present in human plasma and whether expression levels are affected under different conditions of body weight. Normal weight, anorexic and obese subjects with body mass index (BMI) 30-40, 40-50 and >50 were recruited (n=9/group). In overnight fasted subjects GOAT protein expression was assessed by Western blot and ghrelin measured by ELISA. GOAT protein was detectable in human plasma. Anorexic patients showed reduced GOAT protein levels (-42%, p<0.01) whereas obese patients with BMI>50 had increased concentrations (+34%) compared to normal weight controls. Ghrelin levels were higher in anorexic patients compared to all other groups (+62-78%, p<0.001). Plasma GOAT protein expression showed a positive correlation with BMI (r=0.71, p<0.001) and a negative correlation with ghrelin (r=-0.60, p<0.001). Summarized, GOAT is also present in human plasma and GOAT protein levels depend on the metabolic environment with decreased levels in anorexic and increased levels in morbidly obese patients. These data may indicate that GOAT counteracts the adaptive changes of ghrelin observed under these conditions and ultimately contributes to the development or maintenance of anorexia and obesity as it is the only enzyme acylating ghrelin.