Thyrotropin-Releasing Hormone and Food Intake in Mammals: An Update.

Thyrotropin-releasing hormone (TRH; pGlu-His-Pro-NH2) is an intercellular signal produced mainly by neurons. Among the multiple pharmacological effects of TRH, that on food intake is not well understood. We review studies demonstrating that peripheral injection of TRH generally produces a transient anorexic effect, discuss the pathways that might initiate this effect, and explain its short half-life. In addition, central administration of TRH can produce anorexic or orexigenic effects, depending on the site of injection, that are likely due to interaction with TRH receptor 1. Anorexic effects are most notable when TRH is injected into the hypothalamus and the nucleus accumbens, while the orexigenic effect has only been detected by injection into the brain stem. Functional evidence points to TRH neurons that are prime candidate vectors for TRH action on food intake. These include the caudal raphe nuclei projecting to the dorsal motor nucleus of the vagus, and possibly TRH neurons from the tuberal lateral hypothalamus projecting to the tuberomammillary nuclei. For other TRH neurons, the anatomical or physiological context and impact of TRH in each synaptic domain are still poorly understood. The manipulation of TRH expression in well-defined neuron types will facilitate the discovery of its role in food intake control in each anatomical scene.

Bufadienolides preferentially inhibit aminopeptidase N among mammalian metallo-aminopeptidases; relationship with effects on human melanoma MeWo cells.

Bufadienolides are steroids that inhibit Na+/K+-ATPase; recent evidence shows that bufalin inhibits the activity of porcine aminopeptidase N (pAPN). We evaluated the selectivity of some bufadienolides on metallo-aminopeptidases. Among the enzymes of the M1 and M17 families, pAPN and porcine aminopeptidase A (pAPA) were the only targets of some bufadienolides. ѱ-bufarenogin, telocinobufagin, marinobufagin, bufalin, cinobufagin, and bufogenin inhibited the activity of pAPN in a dose-dependent manner in the range of 10-7-10-6 M. The inhibition mechanism was classical reversible noncompetitive for telocinobufagin, bufalin and cinobufagin. Bufogenin had the lowest Ki value and a non-competitive behavior. pAPA activity was inhibited by ѱ-bufarenogin, cinobufagin, and bufogenin, with a classical competitive type of inhibition. The models of enzyme-inhibitor complexes agreed with the non-competitive type of inhibition of pAPN by telocinobufagin, bufalin, cinobufagin, and bufogenin. Since APN is a target in cancer therapy, we tested the effect of bufadienolides on the MeWo APN+ human melanoma cell line; they induced cell death, but we obtained scant evidence that inhibition of APN contributed to their effect. Thus, APN is a selective target of some bufadienolides, and we suggest that inhibition of APN activity by bufadienolides is not a major contributor to their antiproliferative properties in MeWo cells.

Sex-dependent and -independent regulation of thyrotropin-releasing hormone expression in the hypothalamic dorsomedial nucleus by negative energy balance, exercise, and chronic stress.

The dorsomedial nucleus of the hypothalamus (DMH) is part of the brain circuits that modulate organism responses to the circadian cycle, energy balance, and psychological stress. A large group of thyrotropin-releasing hormone (Trh) neurons is localized in the DMH; they comprise about one third of the DMH neurons that project to the lateral hypothalamus area (LH). We tested their response to various paradigms. In male Wistar rats, food restriction during adulthood, or chronic variable stress (CVS) during adolescence down-regulated adult DMH Trh mRNA levels compared to those in sedentary animals fed ad libitum; two weeks of voluntary wheel running during adulthood enhanced DMH Trh mRNA levels compared to pair-fed rats. Except for their magnitude, female responses to exercise were like those in male rats; in contrast, in female rats CVS did not change DMH Trh mRNA levels. A very strong negative correlation between DMH Trh mRNA levels and serum corticosterone concentration in rats of either sex was lost in CVS rats. CVS canceled the response to food restriction, but not that to exercise in either sex. TRH receptor 1 (Trhr) cells were numerous along the rostro-caudal extent of the medial LH. In either sex, fasting during adulthood reduced DMH Trh mRNA levels, and increased LH Trhr mRNA levels, suggesting fasting may inhibit the activity of TRHDMH->LH neurons. Thus, in Wistar rats DMH Trh mRNA levels are regulated by negative energy balance, exercise and chronic variable stress through sex-dependent and -independent pathways.

Origin of thyrotropin-releasing hormone neurons that innervate the tuberomammillary nuclei.

Hypophysiotropic thyrotropin-releasing hormone (TRH) neurons function as metabolic sensors that regulate the thyroid axis and energy homeostasis. Less is known about the role of other hypothalamic TRH neurons. As central administration of TRH decreases food intake and increases histamine in the tuberomammillary nuclei (TMN), and TMN histamine neurons are densely innervated by TRH fibers from an unknown origin, we mapped the location of TRH neurons that project to the TMN. The retrograde tracer, cholera toxin B subunit (CTB), was injected into the TMN E1-E2, E4-E5 subdivisions of adult Sprague-Dawley male rats. TMN projecting neurons were observed in the septum, preoptic area, bed nucleus of the stria terminalis (BNST), perifornical area, anterior paraventricular nucleus, peduncular and tuberal lateral hypothalamus (TuLH), suprachiasmatic nucleus and medial amygdala. However, CTB/pro-TRH178-199 double-labeled cells were only found in the TuLH. The specificity of the retrograde tract-tracing result was confirmed by administering the anterograde tracer, Phaseolus vulgaris leuco-agglutinin (PHAL) into the TuLH. Double-labeled PHAL-pro-TRH boutons were identified in all subdivisions of the TMN. TMN neurons double-labeled for histidine decarboxylase (Hdc)/PHAL, Hdc/Trh receptor (Trhr), and Hdc/Trh. Further confirmation of a TuLH-TRH neuronal projection to the TMN was established in a transgenic mouse that expresses Cre recombinase in TRH-producing cells following microinjection of a Cre recombinase-dependent AAV that expresses mCherry into the TuLH. We conclude that, in rodents, the TRH innervation of TMN originates in part from TRH neurons in the TuLH, and that this TRH population may contribute to regulate energy homeostasis through histamine Trhr-positive neurons of the TMN.

Discovery of tight-binding competitive inhibitors of dipeptidyl peptidase IV.

Dipeptidyl peptidase IV (DPP-IV, EC 3.4.14.5) is an abundant serine aminopeptidase that preferentially cleaves N-terminal Xaa-Pro or Xaa-Ala dipeptides from oligopeptides. Inhibitors of DPP-IV activity are used for treating type 2 diabetes mellitus and other diseases. DPP-IV is also involved in tumor progression. We identified four new non-peptide tight-binding competitive inhibitors of porcine DPP-IV by virtual screening and enzymatic assays. Molecular docking simulations supported the competitive behavior, and the selectivity of one of the compounds in the DPP-IV family. Since three of these inhibitors are also aminopeptidase N (APN) inhibitors, we tested their impact on APN+/DPP-IV+ and DPP-IV+ human tumor cells' viability. Using kinetic assays, we determined that HL-60 tumor cells express both APN and DPP-IV activities and that MDA-MB-231 tumor cells express DPP-IV activity. The inhibitors had a slight inhibitory effect on human HEK-293 cell viability but reduced the viability of APN+/DPP-IV+ and DPP-IV+ human tumor cells more potently. Remarkably, the intraperitoneal injection of these compounds inhibited DPP-IV activity in rat brain, liver, and pancreas. In silico studies suggested inhibitors binding to serum albumin contribute to blood-brain barrier crossing. The spectrum of action of some of these compounds may be useful for niche applications.

Sex Dimorphic Responses of the Hypothalamus-Pituitary-Thyroid Axis to Energy Demands and Stress.

The hypothalamus-pituitary-thyroid-axis (HPT) is one of the main neuroendocrine axes that control energy expenditure. The activity of hypophysiotropic thyrotropin releasing hormone (TRH) neurons is modulated by nutritional status, energy demands and stress, all of which are sex dependent. Sex dimorphism has been associated with sex steroids whose concentration vary along the life-span, but also to sex chromosomes that define not only sexual characteristics but the expression of relevant genes. In this review we describe sex differences in basal HPT axis activity and in its response to stress and to metabolic challenges in experimental animals at different stages of development, as well as some of the limited information available on humans. Literature review was accomplished by searching in Pubmed under the following words: "sex dimorphic" or "sex differences" or "female" or "women" and "thyrotropin" or "thyroid hormones" or "deiodinases" and "energy homeostasis" or "stress". The most representative articles were discussed, and to reduce the number of references, selected reviews were cited.

Sex Dimorphic Changes in Trh Gene Methylation and Thyroid-Axis Response to Energy Demands in Maternally Separated Rats.

The hypothalamus-pituitary-thyroid (HPT) axis regulates energy balance through the pleiotropic action of thyroid hormones. HPT basal activity and stimulation by cold or voluntary exercise are repressed by previous chronic stress in adults. Maternal separation (MS) modifies HPT basal activity; we thus studied the response of the axis to energy demands and analyzed possible epigenetic changes on Trh promoter. Nonhandled (NH) or MS male Wistar rats were cold exposed 1 h at adulthood; Trh expression in the hypothalamic paraventricular nucleus (PVN) and serum thyrotropin (TSH) concentration were increased only in NH rats. Two weeks of voluntary exercise decreased fat mass and increased Trh expression, and thyroid hormones concentration changed proportionally to running distance in NH male rats and MS male rats. Although NH females ran more than MS and much more than males, exercise decreased body weight and fat mass only in NH rats with no change on any parameter of the HPT axis but increased Pomc expression in arcuate-nucleus of NH and Npy in MS females. Overall, the methylation pattern of PVN Trh gene promoter was similar in NH males and females; MS modified methylation of specific CpG sites, a thyroid hormone receptor (THR)-binding site present after the initiation site was hypomethylated in MS males; in MS females, the THR binding site of the proximal promoter (site 4) and 2 sites in the first intron were hypermethylated. Our studies showed that, in a sex-dimorphic manner, MS blunted the responses of HPT axis to energy demands in adult animals and caused methylation changes on Trh promoter that could alter T3 feedback.

Bacitracin is a non-competitive inhibitor of porcine M1 family neutral and glutamyl aminopeptidases.

Membrane alanyl and glutamyl aminopeptidases (APN and APA, respectively) are established targets for the development of biomedical tools in human pathologies. APN overexpression correlates with the progression of tumours, including melanoma. Bacitracin, widely used as a topical antibiotic, inhibits subtilisin-like serine peptidases and disulphide isomerases. In the present contribution, we demonstrate that bacitracin is a non-competitive α = 1 and α < 1 inhibitor of porcine kidney APN and APA, respectively, with Ki values in the micromolar range. To test a potential application of this result, we assayed the effect of bacitracin on murine melanoma MB16F10 cell line viability. We demonstrated the cell line expresses an APN-like activity inhibited by bacitracin and bestatin. Additionally, we identified a cytotoxic effect of bacitracin. Further experiments are required to understand in depth the mechanisms of action of bacitracin on melanoma cells. They will clarify the therapeutic potential of bacitracin for melanoma treatment.

Evolution of thyrotropin-releasing factor extracellular communication units.

Thyroid hormones (THs) are ancient signaling molecules that contribute to the regulation of metabolism, energy homeostasis and growth. In vertebrates, the hypothalamus-pituitary-thyroid (HPT) axis links the corresponding organs through hormonal signals, including thyrotropin releasing factor (TRF), and thyroid stimulating hormone (TSH) that ultimately activates the synthesis and secretion of THs from the thyroid gland. Although this axis is conserved among most vertebrates, the identity of the hypothalamic TRF that positively regulates TSH synthesis and secretion varies. We review the evolution of the hypothalamic factors that induce TSH secretion, including thyrotropin-releasing hormone (TRH), corticotrophin-releasing hormone (CRH), urotensin-1-3, and sauvagine, and non-mammalian glucagon-like peptide in metazoans. Each of these peptides is part of an extracellular communication unit likely composed of at least 3 elements: the peptide, G-protein coupled receptor and bioavailability regulator, set up on the central neuroendocrine articulation. The bioavailability regulators include a TRH-specific ecto-peptidase, pyroglutamyl peptidase II, and a CRH-binding protein, that together with peptide secretion/transport rate and transduction coupling and efficiency at receptor level shape TRF signal intensity and duration. These vertebrate TRF communication units were coopted from bilaterian ancestors. The bona fide elements appeared early in chordates, and are either used alternatively, in parallel, or sequentially, in different vertebrate classes to control centrally the activity of the HPT axis. Available data also suggest coincidence between apparition of ligand and bioavailability regulator.

Bestatin and bacitracin inhibit porcine kidney cortex dipeptidyl peptidase IV activity and reduce human melanoma MeWo cell viability.

Bestatin and bacitracin are inhibitors of metallo aminopeptidases and bacterial proteases. However, their effects on other human peptidases, like dipeptidyl peptidase IV (DPP-IV, EC 3.4.14.5) are not established. Inhibitors of DPP-IV activity are used for treating type 2 diabetes mellitus, cancers and immune system diseases. Bacitracin and bestatin inhibited porcine membrane-bound DPP-IV (pDPP-IV) activity. Mechanisms were different, i.e. non-competitive with α > 1 (α = 3.9) and Ki value of 75 µM for bestatin, and competitive with Ki value of 630 µM for bacitracin. The binding mode in the tertiary complex enzyme:substrate:bestatin suggested the structural basis of the inhibitory effect and that bestatin is potentially selective for DPP-IV, ineffective vs. S9 family members dipeptidyl peptidase 8/9 and fibroblast activation protein. In the human melanoma MeWo cell line, bestatin and bacitracin inhibited aminopeptidase N (APN) and DPP-IV activities, reduced cell viability and increased DNA fragmentation, suggesting induction of apoptosis. Since bacitracin and bestatin are already marketed drugs, studying in depth the molecular mechanisms underlying their effects on melanoma cells is warranted. Additionally, bestatin emerges as a new lead compound for the development of DPP-IV inhibitors, and a promising dual APN/DPP-IV inhibitor for the treatment of pathologies in which both enzymes are upregulated.

Biochemical evidences for M1-, M17- and M18-like aminopeptidases in marine invertebrates from Cuban coastline.

Metallo-aminopeptidases (mAPs) control many physiological processes. They are classified in different families according to structural similarities. Neutral mAPs catalyze the cleavage of neutral amino acids from the N-terminus of proteins or peptide substrates; they need one or two metallic cofactors in their active site. Information about marine invertebrate's neutral mAPs properties is scarce; available data are mainly derived from genomics and cDNA studies. The goal of this work was to characterize the biochemical properties of the neutral APs activities in eight Cuban marine invertebrate species from the Phyla Mollusca, Porifera, Echinodermata, and Cnidaria. Determination of substrate specificity, optimal pH and effects of inhibitors (1,10-phenanthroline, amastatin, and bestatin) and cobalt on activity led to the identification of distinct neutral AP-like activities, whose biochemical behaviors were similar to those of the M1 and M17 families of mAPs. Additionally, M18-like glutamyl AP activities were detected. Thus, marine invertebrates express biochemical activities likely belonging to various families of metallo-aminopeptidases.

The Thyrotropin-Releasing Hormone-Degrading Ectoenzyme, a Therapeutic Target?

Thyrotropin releasing hormone (TRH: Glp-His-Pro-NH2) is a peptide mainly produced by brain neurons. In mammals, hypophysiotropic TRH neurons of the paraventricular nucleus of the hypothalamus integrate metabolic information and drive the secretion of thyrotropin from the anterior pituitary, and thus the activity of the thyroid axis. Other hypothalamic or extrahypothalamic TRH neurons have less understood functions although pharmacological studies have shown that TRH has multiple central effects, such as promoting arousal, anorexia and anxiolysis, as well as controlling gastric, cardiac and respiratory autonomic functions. Two G-protein-coupled TRH receptors (TRH-R1 and TRH-R2) transduce TRH effects in some mammals although humans lack TRH-R2. TRH effects are of short duration, in part because the peptide is hydrolyzed in blood and extracellular space by a M1 family metallopeptidase, the TRH-degrading ectoenzyme (TRH-DE), also called pyroglutamyl peptidase II. TRH-DE is enriched in various brain regions but is also expressed in peripheral tissues including the anterior pituitary and the liver, which secretes a soluble form into blood. Among the M1 metallopeptidases, TRH-DE is the only member with a very narrow specificity; its best characterized biological substrate is TRH, making it a target for the specific manipulation of TRH activity. Two other substrates of TRH-DE, Glp-Phe-Pro-NH2 and Glp-Tyr-Pro-NH2, are also present in many tissues. Analogs of TRH resistant to hydrolysis by TRH-DE have prolonged central efficiency. Structure-activity studies allowed the identification of residues critical for activity and specificity. Research with specific inhibitors has confirmed that TRH-DE controls TRH actions. TRH-DE expression by ß2-tanycytes of the median eminence of the hypothalamus allows the control of TRH flux into the hypothalamus-pituitary portal vessels and may regulate serum thyrotropin secretion. In this review we describe the critical evidences that suggest that modification of TRH-DE activity in tanycytes, and/or in other brain regions, may generate beneficial consequences in some central and metabolic disorders and identify potential drawbacks and missing information needed to test these hypotheses.

A Glial-Neuronal Circuit in the Median Eminence Regulates Thyrotropin-Releasing Hormone-Release via the Endocannabinoid System.

Based on the type-I cannabinoid receptor (CB1) content of hypophysiotropic axons and the involvement of tanycytes in the regulation of the hypothalamic-pituitary-thyroid (HPT) axis, we hypothesized that endocannabinoids are involved in the tanycyte-induced regulation of TRH release in the median eminence (ME). We demonstrated that CB1-immunoreactive TRH axons were associated to DAGLα-immunoreactive tanycyte processes in the external zone of ME and showed that endocannabinoids tonically inhibit the TRH release in this tissue. We showed that glutamate depolarizes the tanycytes, increases their intracellular Ca2+ level and the 2-AG level of the ME via AMPA and kainite receptors and glutamate transport. Using optogenetics, we demonstrated that glutamate released from TRH neurons influences the tanycytes in the ME. In summary, tanycytes regulate TRH secretion in the ME via endocannabinoid release, whereas TRH axons regulate tanycytes by glutamate, suggesting the existence of a reciprocal microcircuit between tanycytes and TRH terminals that controls TRH release.

Sexually dimorphic dynamics of thyroid axis activity during fasting in rats.

Starvation induces tertiary hypothyroidism in adult rodents. Response of the hypothalamus-pituitary-thyroid (HPT) axis to starvation is stronger in adult males than in females. To improve the description of this sexual dimorphism, we analyzed the dynamics of HPT axis response to fasting at multiple levels. In adult rats of the same cohort, 24 and 48 h of starvation inhibited paraventricular nucleus Trh expression and serum concentrations of TSH and T4 earlier in males than in females, with lower intensity in females than in males. In adult females fasted for 36-72 h, serum TSH concentration decreased after 36 h, when the activity of thyrotropin-releasing hormone (TRH)-degrading ectoenzyme was increased in the median eminence. The kinetics of these events were distinct from those previously observed in male rats. We suggest that the sex difference in TSH secretion kinetics is driven not only at the level of paraventricular nucleus TRH neurons, but also by differences in post-secretory catabolism of TRH, with enhancement of TRH-degrading activity more sustained in male than female animals.

Tanycytes and the Control of Thyrotropin-Releasing Hormone Flux Into Portal Capillaries.

Central and peripheral mechanisms that modulate energy intake, partition and expenditure determine energy homeostasis. Thyroid hormones (TH) regulate energy expenditure through the control of basal metabolic rate and thermogenesis; they also modulate food intake. TH concentrations are regulated by the hypothalamus-pituitary-thyroid (HPT) axis, and by transport and metabolism in blood and target tissues. In mammals, hypophysiotropic thyrotropin-releasing hormone (TRH) neurons of the paraventricular nucleus of the hypothalamus integrate energy-related information. They project to the external zone of the median eminence (ME), a brain circumventricular organ rich in neuron terminal varicosities and buttons, tanycytes, other glial cells and capillaries. These capillary vessels form a portal system that links the base of the hypothalamus with the anterior pituitary. Tanycytes of the medio-basal hypothalamus express a repertoire of proteins involved in transport, sensing, and metabolism of TH; among them is type 2 deiodinase, a source of 3,3',5-triiodo-L-thyronine necessary for negative feedback on TRH neurons. Tanycytes subtypes are distinguished by position and phenotype. The end-feet of ß2-tanycytes intermingle with TRH varicosities and terminals in the external layer of the ME and terminate close to the ME capillaries. Besides type 2 deiodinase, ß2-tanycytes express the TRH-degrading ectoenzyme (TRH-DE); this enzyme likely controls the amount of TRH entering portal vessels. TRH-DE is rapidly upregulated by TH, contributing to TH negative feedback on HPT axis. Alterations in energy balance also regulate the expression and activity of TRH-DE in the ME, making ß2-tanycytes a hub for energy-related regulation of HPT axis activity. ß2-tanycytes also express TRH-R1, which mediates positive effects of TRH on TRH-DE activity and the size of ß2-tanycyte end-feet contacts with the basal lamina adjacent to ME capillaries. These end-feet associations with ME capillaries, and TRH-DE activity, appear to coordinately control HPT axis activity. Thus, down-stream of neuronal control of TRH release by action potentials arrival in the external layer of the median eminence, imbricated intercellular processes may coordinate the flux of TRH into the portal capillaries. In conclusion, ß2-tanycytes appear as a critical cellular element for the somatic and post-secretory control of TRH flux into portal vessels, and HPT axis regulation in mammals.

Voluntary Exercise-Induced Activation of Thyroid Axis and Reduction of White Fat Depots Is Attenuated by Chronic Stress in a Sex Dimorphic Pattern in Adult Rats.

The activity of the hypothalamus-pituitary-thyroid (HPT) axis is inhibited by energy deficit, by acute or chronic stress, but activated by cold exposure or exercise. Because stress curtails acute cold induced activation of HPT, we evaluated the effect of chronic stress on HPT axis response to voluntary exercise, a persistent energy-demanding situation. Adult male and female Wistar rats were exposed to restraint stress, 30 min/day for 2 weeks, or to isolation (Iso) [post-natal day [PND] 30-63]. Exercise was performed (7 p.m.-7 a.m.) in a running wheel, sedentary controls stayed in individual cages (Sed); at 7 a.m. they were housed with their cage mate or individually (Iso); food intake by the exercised group was measured day and night to pair-fed Sed. At sacrifice, hormones, mRNA levels and tissue weights were quantified. Control or restrained adult rats had access to running wheel daily for 2 weeks. Compared to C, exercise decreased white adipose tissue (WAT) mass in females and males, increased hypothalamic paraventricular nucleus (PVN)-Trh expression in males proportionally to exercise performed, and increased TSH and T4 serum concentration in females. These changes were not detected in restrained groups. Starting at PND 63 control (2/cage) and isolated (1/cage) rats either exercised on 10 alternated nights or were sedentary. In control male animals, compared to Sed rats, exercise did not decrease WAT mass, nor changed HPT axis activity, but increased Pomc and deiodinase 2 (Dio2) expression in mediobasal hypothalamus (MBH), adrenergic receptor ß3 and uncoupling protein-1 in brown adipose tissue. In control female animals, exercise decreased WAT mass, increased Pomc, Dio2, and Trhde expression in MBH, and TSH serum concentration. Iso females had lower TSH and T4 serum concentration, Dio2 and Trhde expression in MBH than controls. The stress response was higher in isolated males than females, but in males it did not alter the effects of exercise, in contrast to isolated females that had a blunted response to exercise compared to controls. In conclusion, chronic stress interferes with metabolic effects produced by exercise, such as loss of WAT mass, coincident with dampening of HPT activity.

Sex Dimorphic Responses of the Hypothalamus-Pituitary-Thyroid Axis to Maternal Separation and Palatable Diet.

Neonatal stress contributes to the development of obesity and has long-lasting effects on elements of the hypothalamus-pituitary-thyroid (HPT) axis. Given the importance of thyroid hormones in metabolic regulation, we studied the effects of maternal separation and a high-fat/high-carbohydrate diet (HFC), offered from puberty or adulthood, on HPT axis activity of adult male and female Wistar rats. Pups were non-handled (NH) or maternally separated (MS) 3 h/day at postnatal days (Pd) 2-21. In a first experiment, at Pd60, rats had access to chow or an HFC diet (cookies, peanuts, chow) for 1 month. Male and female NH and MS rats that consumed the HFC diet increased their caloric intake, body weight, and serum insulin levels; fat weight increased in all groups except in MS males, and serum leptin concentration increased only in females. Mediobasal hypothalamus (MBH) Pomc expression increased in NH-HFC females and Npy decreased in NH-HFC males. MS males showed insulinemia and hypercortisolemia that was attenuated by the HFC diet. The HPT axis activity response to an HFC diet was sex-specific; expression of MBH thyrotropin-releasing hormone-degrading ectoenzyme (Trhde) increased in NH and MS males; serum TSH concentration decreased in NH males, and T4 increased in NH females. In a second experiment, rats were fed chow or an HFC diet from Pd30 or 60 until Pd160 and exposed to 1 h restraint before sacrifice. Regardless of neonatal stress, age of diet exposition, or sex, the HFC diet increased body and fat weight and serum leptin concentration; it induced insulinemia in males, but in females only in Pd30 rats. The HFC diet's capacity to curtail the hypothalamus-pituitary-adrenal axis response to restraint was impaired in MS males. In restrained rats, expression of Trh in the paraventricular nucleus of the hypothalamus, Dio2 and Trhde in MBH, and serum thyroid hormone concentration were altered differently depending on sex, age of diet exposition, and neonatal stress. In conclusion, metabolic alterations associated to an HFC-diet-induced obesity are affected by sex or time of exposition, while various parameters of the HPT axis activity are additionally altered by MS, pointing to the complex interplay that these developmental influences exert on HPT axis activity in adult rats.

Discovery of novel non-competitive inhibitors of mammalian neutral M1 aminopeptidase (APN).

Neutral metallo-aminopeptidase (APN) catalyzes the cleavage of neutral and basic amino acids from the N-terminus of protein or peptide substrates. APN expression is dysregulated in inflammatory diseases as well as in several types of cancer. Therefore, inhibitors of APN may be effective against cancer and inflammation. By virtual screening and enzymatic assays, we identified three non-competitive inhibitors (α > 1) of the porcine and human APN with Ki values in the µM range. These non-peptidic compounds lack the classical zinc-binding groups (ZBG) present in most of the APN inhibitors. Molecular docking simulations suggested the novel inhibitors suppress APN activity by an alternative mechanism to Zn coordination: they interacted with residues comprising the S1 and S5' subsites of APN. Of note, these compounds also inhibited the porcine aminopeptidase A (pAPA) using a competitive inhibition mode. This indicated differences in the binding mode of these compounds with APN and APA. Based on sequence and structural analyses, we predicted the significance of targeting human APN residues: Ala-351, Arg-442, Ala-474, Phe-896 and Asn-900 for improving the selectivity of the identified compounds. Remarkably, the intraperitoneal injection of compounds BTB07018 and JFD00064 inhibited APN activity in rat brain, liver and kidney indicating good bio-distribution of these inhibitors in vivo. These data reinforce the idea of designing novel APN inhibitors based on lead compounds without ZBG.

The Kv1.3 channel blocker Vm24 enhances muscle glucose transporter 4 mobilization but does not reduce body-weight gain in diet-induced obese male rats.

AIMS: Voltage-gated potassium channels 1.3 (Kv1.3) can be targeted to reduce diet-induced obesity and insulin resistance in mice. Since species-specific differences in Kv1.3 expression and pharmacology have been observed, we tested the effect of Vm24, a high-affinity specific blocker of Kv1.3 channels from Vaejovis mexicanus smithi, on body weight (BW), glucose tolerance and insulin resistance in diet-induced obese rats. MATERIALS AND METHODS: Young adult male Wistar rats were switched to a high-fat/high-fructose (HFF) diet. Eighteen days later animals were divided in two groups: vehicle and Vm24 group. Subcutaneous injections were applied every other day until sacrifice 2months later. An additional cohort was maintained on standard chow. KEY FINDINGS: The HFF diet promoted obesity. Treatment with Vm24 did not alter various metabolic parameters such as food intake, BW gain, visceral white adipose tissue mass, adipocyte diameter, serum glucose, leptin and thyroid hormone concentrations, brown adipose tissue mass or uncoupling protein-1 expression, and insulin tolerance. Vm24 did reduce basal and glucose-stimulated serum insulin concentrations, serum C-peptide concentration, increased QUICKI, and tended to lower HOMA-IR. Vm24 treatment did not change the activation of insulin receptor substrate-1, but enhanced protein-kinase B activation and membrane glucose-transporter 4 (GLUT4) protein levels in skeletal muscle. SIGNIFICANCE: In conclusion, in male rats, long-term blockade of Kv1.3 channels with Vm24 does not reduce weight gain and visceral adiposity induced by HFF diet; instead, it reduces serum insulin concentration, and enhances GLUT4 mobilization in skeletal muscle.

A screen for modulators reveals that orexin-A rapidly stimulates thyrotropin releasing hormone expression and release in hypothalamic cell culture.

In the paraventricular nucleus of the mammalian hypothalamus, hypophysiotropic thyrotropin releasing hormone (TRH) neurons integrate metabolic information and control the activity of the thyroid axis. Additional populations of TRH neurons reside in various hypothalamic areas, with poorly defined connections and functions, albeit there is evidence that some may be related to energy balance. To establish extracellular modulators of TRH hypothalamic neurons activity, we performed a screen of neurotransmitters effects in hypothalamic cultures. Cell culture conditions were chosen to facilitate the full differentiation of the TRH neurons; these conditions had permitted the characterization of the effects of known modulators of hypophysiotropic TRH neurons. The major end-point of the screen was Trh mRNA levels, since they are generally rapidly (0.5-3h) modified by synaptic inputs onto TRH neurons; in some experiments, TRH cell content or release was also analyzed. Various modulators, including histamine, serotonin, ß-endorphin, met-enkephalin, and melanin concentrating hormone, had no effect. Glutamate, as well as ionotropic agonists (kainate and N-Methyl-d-aspartic acid), increased Trh mRNA levels. Baclofen, a GABAB receptor agonist, and dopamine enhanced Trh mRNA levels. An endocannabinoid receptor 1 inverse agonist promoted TRH release. Somatostatin increased Trh mRNA levels and TRH cell content. Orexin-A rapidly increased Trh mRNA levels, TRH cell content and release, while orexin-B decreased Trh mRNA levels. These data reveal unaccounted regulators, which exert potent effects on hypothalamic TRH neurons in vitro.