Interleukin-1 mediates the anorexic and febrile actions of galanin-like Peptide

Transcriptomic (DNA Microarray) and Metabolome (LC-TOF-MS) Analyses of the Liver in High-Fat Diet Mice after Intranasal Administration of GALP (Galanin-like Peptide)

The aim of this research was to test the efficacy and potential clinical application of intranasal administration of galanin-like peptide (GALP) as an anti-obesity treatment under the hypothesis that GALP prevents obesity in mice fed a high-fat diet (HFD). Focusing on the mechanism of regulation of lipid metabolism in peripheral tissues via the autonomic nervous system, we confirmed that, compared with a control (saline), intranasally administered GALP prevented further body weight gain in diet-induced obesity (DIO) mice with continued access to an HFD. Using an omics-based approach, we identified several genes and metabolites in the liver tissue of DIO mice that were altered by the administration of intranasal GALP. We used whole-genome DNA microarray and metabolomics analyses to determine the anti-obesity effects of intranasal GALP in DIO mice fed an HFD. Transcriptomic profiling revealed the upregulation of flavin-containing dimethylaniline monooxygenase 3 (Fmo3), metallothionein 1 and 2 (Mt1 and Mt2, respectively), and the Aldh1a3, Defa3, and Defa20 genes. Analysis using the DAVID tool showed that intranasal GALP enhanced gene expression related to fatty acid elongation and unsaturated fatty acid synthesis and downregulated gene expression related to lipid and cholesterol synthesis, fat absorption, bile uptake, and excretion. Metabolite analysis revealed increased levels of coenzyme Q10 and oleoylethanolamide in the liver tissue, increased levels of deoxycholic acid (DCA) and taurocholic acid (TCA) in the bile acids, increased levels of taurochenodeoxycholic acid (TCDCA), and decreased levels of ursodeoxycholic acid (UDCA). In conclusion, intranasal GALP administration alleviated weight gain in obese mice fed an HFD via mechanisms involving antioxidant, anti-inflammatory, and fatty acid metabolism effects and genetic alterations. The gene expression data are publicly available at NCBI GSE243376.

The effects of Bisphenol A (BPA) on sympathetic nerve fibers in the uterine wall of the domestic pig

Bisphenol A (BPA), used in the production of plastic, shows multidirectional negative effects on the living organism. BPA may affect the reproductive and nervous systems; however, its influence on the nerves supplying the uterus has not been studied. During the present study, the impact of BPA on the sympathetic nerves in the uterus was investigated using a double immunofluorescence technique. The results have shown that even low doses of BPA may change the neurochemical characterization of uterine sympathetic nerves, and the severity of these changes depends on the part of the uterus and the dose of the toxic substance. Probably the changes observed during the present study resulted from the neurotoxic and/or pro-inflammatory activity of BPA, but the exact mechanism for the observed fluctuation still remains unknown. The fluctuations of the neurochemical characterization of the uterine intramural nerves may be the first subclinical signs of harmful exposure to BPA.

Anti-obesity effect of intranasal administration of galanin-like peptide (GALP) in obese mice

Galanin-like peptide (GALP) has an anti-obesity effect in rats and mice. It has been reported that the uptake of GALP by the brain is higher after intranasal administration than with intravenous injection. This study therefore aimed to clarify the effect of intranasal administration of GALP on the feeding behavior of lean and obese mice. Autoradiography revealed the presence of (125)I-GALP in the olfactory bulb and the brain microcirculation. The body weights of ob/ob mice gradually increased during vehicle treatment, but remained unchanged in response to repeated intranasal administration of GALP, with both ob/ob and diet-induced obese mice displaying significantly decreased food intake, water intake and locomotor activity when treated with GALP. These results suggest that intranasal administration is an effective route whereby GALP can exert its effect as an anti-obesity drug.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Thermoregulatory effect of alarin, a new member of the galanin peptide family

In the background of obesity, among other factors, regulatory alterations in energy balance affecting peptide systems may also be assumed. Regulation of energy balance does not only involve maintenance of body weight but also that of metabolic rate and core temperature. The contribution of alarin, a new member of the potentially orexigenic galanin peptide family, to the regulation of energy metabolism has been recently suggested. Our aim was to analyze the thermoregulatory effects of alarin in rats.

 

Adult male Wistar rats received full-length alarin (alarin 1–25), its truncated form (alarin 6–25Cys) or scrambled alarin in various doses intracerebroventricularly at different ambient temperatures. Oxygen consumption, heat loss (assessed by tail skin temperature) and core temperature of rats were recorded in an indirect calorimeter system.

Upon alarin injection at 25 °C, an increase in oxygen consumption and continuous tail skin vasoconstriction induced a slow rise in core temperature that reached 0.5 °C by 120 and 1.0 °C by 180 min. At cooler or slightly warmer temperatures similar responses were seen. Neither the truncated nor the scrambled alarin elicited any significant thermoregulatory response, however, the truncated form antagonized the hyperthermic actions of the full-length peptide.

Alarin appears to elicit a slow hypermetabolic, hyperthermic response in rats. Such a thermoregulatory response would characterize a catabolic (anorexic and hypermetabolic) mediator. Further investigations are needed to clarify the complex role of alarin in energy homeostasis.

Interactive effect of galanin-like peptide (GALP) and spontaneous exercise on energy metabolism

Galanin-like peptide (GALP) is a neuropeptide involved in energy metabolism. The interactive effect of GALP and exercise on energy metabolism has not been investigated. The aim of this study was to determine if energy metabolism in spontaneously exercising mice could be promoted by intracerebroventricular (ICV) GALP administration. Changes in respiratory exchange ratio in response to GALP ICV administration indicated that lipids were primarily consumed followed by a continuous consumption of glucose throughout the dark period in non-exercising mice. In mice permitted to spontaneously exercise on a running-wheel, GALP ICV administration increased the consumed oxygen volume and heat production level from 5 to 11h after administration. These effects occurred independently from the total running distance. The interaction between GALP ICV administration and spontaneous exercise decreased body weight within 24h (F(1,16)=5.772, p<0.05), with no significant interaction observed regarding food and water intake or total distance. Energy metabolism-related enzymes were assessed in liver and skeletal muscle samples, with a significant interaction on mRNA expression between GALP ICV administration and spontaneous exercise observed in phosphoenolpyruvate carboxykinase (F(1,16)=18.602, p<0.001) that regulates gluconeogenesis and glucose transporter-4 (F(1,16)=21.092, p<0.001). GALP significantly decreased the mRNA expression of sterol regulatory element-binding protein-1c (p<0.05) that regulates fatty acid synthesis regardless of spontaneous exercise with no changes to acetyl-CoA carboxylase a and fatty acid synthetase. These results indicate the GALP ICV administration can further promote energy metabolism when administered to spontaneously exercising mice.

Galanin-like peptide (GALP) facilitates thermogenesis via synthesis of prostaglandin E2 by astrocytes in the periventricular zone of the third ventricle

Administration of galanin-like peptide (GALP) leads to a decrease in both total food intake and body weight 24 h after injection, compared to controls. Moreover, GALP induces an increase in core body temperature. To elucidate the mechanism by which GALP exerts its effect on energy homeostasis, urethane-anesthetized rats were intracerebroventricularly injected with GALP or saline, after which oxygen consumption, heart rate, and body temperature were monitored for 4 h. In some cases, animals were also pretreated with the cyclooxygenase (COX) inhibitor, diclofenac, via intracerebroventricular (i.c.v.) or intravenous (i.v.) injection. c-Fos expression in the brain was also examined after injection of GALP, and the levels of COX and prostaglandin E(2) synthetase (PGES) mRNA in primary cultured astrocytes treated with GALP were analyzed by using qPCR. The i.c.v. injection of GALP caused biphasic thermogenesis, an effect which could be blocked by pretreatment with centrally (i.c.v.), but not peripherally (i.v.) administered diclofenac. c-Fos immunoreactivity was observed in astrocytes in the periventricular zone of the third ventricle. GALP treatment also increased COX-2 and cytosolic PGES, but not COX-1, microsomal PGES-1, or microsomal PGES-2 mRNA levels in cultured astrocytes. We, therefore, suggest that GALP elicits thermogenesis via a prostaglandin E(2)-mediated pathway in astrocytes of the central nervous system.

Galanin receptors and ligands

The neuropeptide galanin was first discovered 30 years ago. Today, the galanin family consists of galanin, galanin-like peptide (GALP), galanin-message associated peptide (GMAP), and alarin and this family has been shown to be involved in a wide variety of biological and pathological functions. The effect is mediated through three GPCR subtypes, GalR1-3. The limited number of specific ligands to the galanin receptor subtypes has hindered the understanding of the individual effects of each receptor subtype. This review aims to summarize the current data of the importance of the galanin receptor subtypes and receptor subtype specific agonists and antagonists and their involvement in different biological and pathological functions.

The galanin peptide family in inflammation

The immune system defends the organism against invading pathogens. In recent decades it became evident that elimination of such pathogens, termination of inflammation, and restoration of host homeostasis all depend on bidirectional crosstalk between the immune system and the neuroendocrine system. This crosstalk is mediated by a complex network of interacting molecules that modulates inflammation and cell growth. Among these mediators are neuropeptides released from neuronal and non-neuronal components of the central and peripheral nervous systems, endocrine tissues, and cells of the immune system. Neuropeptide circuitry controls tissue inflammation and maintenance, and an imbalance of pro- and anti-inflammatory neuropeptides results in loss of host homeostasis and triggers inflammatory diseases. The galanin peptide family is undoubtedly involved in the regulation of inflammatory processes, and the aim of this review is to provide up-to-date knowledge from the literature concerning the regulation of galanin and its receptors in the nervous system and peripheral tissues in experimental models of inflammation. We also highlight the effects of galanin and other members of the galanin peptide family on experimentally induced inflammation and discuss these data in light of an anti-inflammatory role for this family of peptides.

Galanin-like peptide and the regulation of feeding behavior and energy metabolism

The hypothalamic neuropeptides modulate physiological activity via G protein-coupled receptors (GPCRs). Galanin-like peptide (GALP) is a 60 amino acid neuropeptide that was originally isolated from porcine hypothalamus using a binding assay for galanin receptors, which belong to the GPCR family. GALP is mainly produced in neurons in the hypothalamic arcuate nucleus. GALP-containing neurons form neuronal networks with several other types of peptide-containing neurons and then regulate feeding behavior and energy metabolism. In rats, the central injection of GALP produces a dichotomous action that involves transient hyperphasia followed by hypophasia and a reduction in body weight, whereas, in mice, it has only one action that reduces both food intake and body weight. In the present minireview, we discuss current evidence regarding the function of GALP, particularly in relation to feeding and energy metabolism. We also examine the effects of GALP activity on food intake, body weight and locomotor activity after intranasal infusion, a clinically viable mode of delivery. We conclude that GALP may be of therapeutic value for obesity and life-style-related diseases in the near future.

Galanin-like peptide (GALP) is a hypothalamic regulator of energy homeostasis and reproduction

Galanin-like peptide (GALP) was discovered in 1999 in the porcine hypothalamus and was found to be a 60 amino acid neuropeptide. GALP shares sequence homology to galanin (1-13) in position 9-21 and can bind to, as well as activate, the three galanin receptor subtypes (GalR1-3). GALP-expressing cells are limited, and are mainly found in the arcuate nucleus of the hypothalamus (ARC) and the posterior pituitary. GALP-positive neurons in the ARC project to several brain regions where they appear to make contact with multiple neuromodulators. These neuromodulators are involved in the regulation of energy homeostasis and reproduction, anatomical evidence that suggests a role for GALP in these physiological functions. In support of this idea, GALP gene expression is regulated by several factors that reflect metabolic state including the metabolic hormones leptin and insulin, thyroid hormones, and blood glucose. Considerable evidence now exists to support the hypothesis that GALP has a role in the regulation of energy homeostasis and reproduction; and, that GALP's role may be independent of the known galanin receptors. In this review, we (1) provide an overview of the distribution of GALP, and discuss the potential relationship between GALP and other neuromodulators of energy homeostasis and reproduction, (2) discuss the metabolic factors that regulate GALP expression, (3) review the evidence for the role of GALP in energy homeostasis and reproduction, (4) discuss the potential downstream mediators and mechanisms underlying GALP's effects, and (5) discuss the possibility that GALP may mediate its effects via an as yet unidentified GALP-specific receptor.

Galanin-like peptide: a key player in the homeostatic regulation of feeding and energy metabolism?

The hypothalamus has a critical role in the regulation of feeding behavior, energy metabolism and reproduction. Galanin-like peptide (GALP), a novel 60 amino-acid peptide with a nonamidated C-terminus, was first discovered in porcine hypothalamus. GALP is mainly produced in the hypothalamic arcuate nucleus and is involved in the regulation of feeding behavior and energy metabolism, with GALP-containing neurons forming networks with several feeding-regulating peptide-containing neurons. The effects of GALP on food intake and body weight are complex. In rats, the central effect of GALP is to first stimulate and then reduce food intake, whereas in mice, GALP has an anorectic function. Furthermore, GALP regulates plasma luteinizing hormone levels through activation of gonadotropin-releasing hormone-producing neurons, suggesting that it is also involved in the reproductive system. This review summarizes the research on these topics and discusses current evidence regarding the function of GALP, particularly in relation to feeding and energy metabolism. We also discuss the effects of GALP activity on food intake, body weight and locomotor activity after intranasal infusion, a clinically viable mode of delivery.