Alarin stimulates food intake and gonadotrophin release in male rats

Comparison of cord blood alarin levels of full-term infants according to birth weight

OBJECTIVES

To compare the cord blood alarin levels of infants in different birth weight groups with those of infants born to mothers diagnosed with gestational diabetes mellitus (GDM) who were not subgrouped according to birth weight.

METHODS

This prospective study was conducted between September 2023 and January 2024. Healthy term babies whose families agreed to participate in the study were divided into four groups according to their birth weight (small for gestational age (SGA), appropriate for gestational age (AGA) and large for gestational age (LGA)) and whether their mothers had GDM.

RESULTS

There was a significant difference between the cord blood alarin levels of the AGA and SGA groups (p=0.014). There was also a significant difference between the cord blood alarin levels of the AGA and GDM groups (p=0.012). However, the cord blood alarin levels of the LGA group (whose mothers did not have GDM) were similar to those of the AGA group (p=0.394).

CONCLUSIONS

We found evidence that alarin levels in umbilical cord blood are associated with low birth weight and GDM.

Neuroanatomical characterization of the G protein-coupled receptor activity evoked by galanin-related ligands

Galanin neuropeptide is distributed throughout the mammalian nervous system modulating a plethora of diverse physiological functions, including nociception, cognition and neuroendocrine regulation. The regulation of the galaninergic system is an interesting approach for the treatment of different diseases associated to those systems. Nevertheless, the pharmacological selectivity and activities of some galanin receptor (GalR) ligands are still in discussion and seem to depend on the dose, the receptor subtype and the second messengers to which they are coupled at different brain areas. The activity of different GalR ligands on G_i/o proteins, was evaluated by the guanosine 5'-(γ-[³⁵S]thio)triphosphate ([³⁵S]GTPγS) autoradiography in vitro assay applied to rat brain tissue slices in the presence of galanin, M15, M35, M40, gal(2-11) or galnon. The enhancement of the [³⁵S]GTPγS binding induced by the chimerical peptides M15, M35 and M40 was similar to that produced by Gal in those brain areas showing the highest stimulations, such as dorsal part of the olfactory nucleus and ventral subiculum. In contrast to these peptides, using gal(2-11) no effect was measured on G_i/o protein coupling in areas of the rat brain with high GalR₁ density such as posterior hypothalamic nucleus and amygdala, indicating low selectivity for GalR₁ receptors. The effects evoked by the non-peptide ligand, galnon, were different from those induced by galanin, behaving as agonist or antagonist depending on the brain area, but the stimulations were always blocked by M35. Thus, the activity of most used GalR ligands on G_i/o protein mediated signalling is complex and depends on the brain area. More selective and potent GalR ligands are necessary to develop new treatments aimed to modulate the galaninergic system.

Androgenetic Alopecia and Metabolic Syndrome: Is Alarin a Missing Link?

BACKGROUND

The field of research into the probable link between androgenetic alopecia (AGA) and metabolic syndrome (MetS) is rapidly expanding. The exact underlying pathogenesis yet to be identified. Alarin, a galanin neuropeptide, found to be elevated in patients with metabolic syndrome and may represent a potential link between AGA and MetS.

OBJECTIVE

The aim of this study was to assess serum levels of alarin in patients with AGA and investigate its possible correlation, if any, with criteria of MetS in those patients.

METHODS

The study included 50 male patients with AGA and 30 healthy controls. Weight, height, waist circumference, and body mass index (BMI) were all measured. Systolic and diastolic blood pressure readings were recorded. Serum level of lipids, fasting blood glucose (FBG) and alarin were also assessed.

RESULTS

Anthropometric measures, serum lipids, FBG, and serum alarin were much higher in patients with AGA compared to controls (p<0.05). Forty-one patients with AGA (82%) met the criteria for diagnosis of MetS. Serum level of alarin was significantly higher in those patients and correlated positively with severity and duration of AGA.

CONCLUSION

Serum level of alarin might represent a potential link between AGA and MetS, opening the door for better understanding of the pathogenesis of both conditions and the possible association between them.

Alarin: A new predictive marker in infertile women with polycystic ovary syndrome: A case-control study

AIM

There is scant evidence concerning the relationship of alarin concentrations for polycystic ovary syndrome (PCOS) status in the existing literature. Therefore, we aimed to reveal the relationship about predictive value of serum alarin concentrations for PCOS risk in infertile women.

METHODS

This prospective case-control study included a total of 151 infertile women who met eligibility criteria of the study. Infertile women diagnosed with PCOS formed the study group (n = 80). Women with diagnoses of unexplained infertility constituted the control group (n = 71). The biochemical analyses of serum concentrations of lipid profiles, estradiol (E2), follicle-stimulating hormone (FSH), luteinizing hormone (LH), anti-Mullerian hormone (AMH) and alarin were performed.

RESULTS

There were no differences for the study parameters, including age, body mass index, fasting glucose, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, total triglyceride, E2, and FSH levels in either group. Serum LH, AMH, alarin concentrations, and antral follicle counts had higher values in the PCOS group compared with the controls. Correlation analysis revealed that serum alarin levels were significantly positively correlated with LH and AMH levels, only in the PCOS group. Multivariate binary logistic regression analysis demonstrated that infertile women with high alarin concentrations were significantly more likely to develop PCOS (OR = 1.77, 95% CI = 0.095-0.332, p < 0.001).

CONCLUSION

Higher serum concentrations of alarin and a positive correlation with serum LH levels were found in infertile women with PCOS. This evidence supported that high alarin concentrations might play a role in the development of PCOS.

The evolving roles of alarin in physiological and disease conditions, and its future potential clinical implications

Alarin is a member of the galanin family of neuropeptides that is widely expressed in the central nervous system and peripheral tissues in humans and rodents. It was initially isolated fifteen years ago in ganglionic cells of human neuroblastoma. Subsequently, it was demonstrated to be broadly distributed in the blood vessels, skin, eyes, peripheral and central nervous systems, thymus, gastrointestinal tract, and endocrine organs of different species. Alarin is a 25 amino acid neuropeptide derived from the alternative splicing of the GALP gene, missing exon 3. It is found to be involved in several physiological functions that include feeding behavior, energy homeostasis, glucose homeostasis, body temperature, and reproduction. It has also vasoactive, anti-inflammatory, anti-edema, and antimicrobial activities. However, the physiological effects of alarin have not been fully elucidated and the receptors that mediate these effects are not currently known. Unearthing the novel biological effects of alarin and its unidentified receptors will therefore be a task in future biomedical research. In addition, alarin is involved in various disease conditions, such as metabolic syndrome, obesity, insulin resistance, type 2 diabetes, diabetic retinopathy, hypertension, cardiac fibrosis, polycystic ovarian syndrome, and depression. Thus, alarin may serve as a promising tool for future pharmacological treatment and diagnosis. But further research is awaited to confirm whether alarin has a protective or pathological role in these diseases. This article provides a comprehensive review on the evolving implications of alarin in a variety of physiological and disease conditions, and its future perspectives.

Serum Tenascin-C and Alarin Levels Are Associated with Cardiovascular Diseases in Type 2 Diabetes Mellitus

BACKGROUND

Tenascin-C (TNC), an extracellular matrix glycoprotein, is elevated in inflammatory and cardiovascular pathologies, whereas alarin, a novel orexigenic peptide, participates in insulin resistance and glycometabolism. The roles of these molecules in individuals with cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM), clinical conditions associating with metabolic disorders, and chronic inflammation, remain controversial. Our study aimed at determining the potential role of TNC and alarin in CVD adult patients with T2DM.

METHODS

This was a cross-sectional study. Basic and clinical information for 250 patients with T2DM were analyzed. Based on their cardiovascular disease status, participants were assigned into the CVD and non-CVD groups. Serum TNC and alarin levels were assessed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Serum TNC and alarin concentrations in the CVD group were significantly higher than those of the non-CVD group. Moreover, serum TNC levels were positively correlated with age, waist circumference, and waist-hip ratio; however, they were negatively correlated with TC, LDL-C, and eGFR levels. Alarin levels were positively correlated with BMI, waist circumference, and hip circumference. In logistic regression models, TNC and alarin were also established to be independent determinants for CVD in T2DM patients and their increases were associated with CVD severity. Receiver operating characteristic (ROC) curve analysis showed that the area under curve (AUC) values for TNC and alarin were 0.68 and 0.67, respectively. TNC and alarin were good predictors of CVD occurrence. When the cutoff value for TNC was 134.05 pg/mL, its sensitivity was 69.47% while its specificity was 61.29%. When the cutoff value for alarin was 142.69 pg/mL, sensitivity and specificity were 38.95% and 90.97%, respectively.

CONCLUSION

Elevated TNC and alarin levels are independently associated with the occurrence and severity of CVD in T2DM individuals. Therefore, these two biomarkers are potential diagnostic and prognostic indicators for CVD in diabetics.

Regulatory effects and potential therapeutic implications of alarin in depression, and arguments on its receptor

Alarin is a pleiotropic peptide involved in a multitude of putative biological activities, notably, it has a regulatory effect on depression-like behaviors. Although further elucidating research is needed, animal-based cumulative evidence has shown the antidepressant-like effects of alarin. In light of its regulatory role in depression, alarin could be used as a promising antidepressant in future treatment for depression. Nevertheless, the available information is still insufficient and the therapeutic relevance of alarin in depression is still of concern. Moreover, a plethora of studies have reported that the actions of alarin, including antidepressant activities, are mediated by a separate yet unidentified receptor, highlighting the need for more extensive research. This review focuses on the current understanding of the regulatory effects and future therapeutic relevance of alarin on depression, and the arguments on its receptors.

The circulating alarin level was elevated in infertile women with poor ovarian reserve

OBJECTIVE

We aimed to reveal the association of serum alarin level with POR status of the infertile women in the present study.

METHODS

The eligibility criteria for this prospective cross-sectional study included a total of 92 infertile women attending the Hitit University Hospital, and all participant women were categorized into two main groups of ovarian reserve: (i) Poor ovarian reserve (POR) group (n = 40) based on ESHRE consensus and (ii) Control group (NOR) (n = 52).

RESULTS

The mean adjusted-ages and BMI values of the NOR and POR groups were statistically comparable (p = .057 and p = .600, respectively). The mean E2, FSH, and LH levels were elevated in the POR group (p < .001, for all). The mean AFC and AMH concentration were significantly reduced in the POR group (p < .001, for both). In addition, there was a significant increase in the serum alarin level in the POR group (p < .001). Pearson's analysis revealed that the mean BMI value of the POR group had a weak and negative correlation (r = 0.318, p = .046). Also, there was no correlation between serum alarin with E2 and FSH levels in both study groups. A weak and positive correlation was found between serum alarin and LH concentration only in the POR group (r = 0.318, p = .045). The mean AMH and AFC values were not significantly correlated with serum alarin levels.

CONCLUSION

The circulating alarin level was significantly elevated in infertile women with POR patterns. In addition, the alarin level was significantly correlated with the serum LH concentration in the POR pattern.

Alarin alleviated cardiac fibrosis via attenuating oxidative stress in heart failure rats

The present study was to explore whether alarin could alleviate heart failure (HF) and attenuate cardia fibrosis via inhibiting oxidative stress. The fibrosis of cardiac fibroblasts (CFs) was induced by angiotensin (Ang) II. HF models were induced by ligation of the left anterior descending artery to cause ischemia myocardial infarction (MI) in Sprague–Dawley rats. Alarin (1.0 nM/kg/d) was administrated by intraperitoneal injection for 28 days. The decreases of left ventricular (LV) ejection fraction (EF), fractional shortening (FS), the maximum of the first differentiation of LV pressure (LV ± dp/dt_max) and LV systolic pressure (LVSP), and the increases of LV volume in systole (LVVS), LV volume in diastole (LVVD), LV end-systolic diameter (LVESD) and LV end-diastolic diameter (LVEDD) in MI rats were improved by alarin treatment. The increases in the expression levels of collagen I, collagen III, and transforming growth factor (TGF)-β were inhibited by alarin treatment in CFs and in the hearts of MI rats. The levels of NADPH oxidase (Nox) activity, superoxide anions and malondialdehyde (MDA) levels were increased, and the level of superoxide dismutase (SOD) activity was reduced in Ang II-treated CFs, which were reversed by alarin. Nox1 overexpression reversed the effects of alarin on attenuating the increases of collagen I, collagen III and TGF-β expression levels induced by Ang II in CFs. These results indicated that alarin improved HF and cardiac fibrosis via inhibiting oxidative stress in HF rats. Nox1 played important roles in the regulation of alarin effects on attenuating CFs fibrosis induced by Ang II.

Plasma Alarin Level and Its Influencing Factors in Obese Newly Diagnosed Type 2 Diabetes Patients

OBJECTIVE

To investigate the plasma alarin level in newly diagnosed obese type 2 diabetes mellitus (T2DM) and its correlation with glucose and lipid metabolism and insulin resistance.

METHODS

From October 2018 to June 2020, 239 newly diagnosed T2DM patients were collected. According to obesity, patients were divided into T2DM obese group (n=135) and T2DM non-obese group (n =104). Gender, age, body mass index (BMI), blood lipids, blood glucose, glycosylated hemoglobin A1c (HbA1c), fasting insulin (FINS), plasma alarin concentration, homeostasis model assessment for insulin resistance (HOMA-IR), homeostasis model assessment for β-cell function (HOMA-β) and other clinical data were collected and analyzed.

RESULTS

BMI, triacylglycerol (TG), total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C), fasting blood glucose (FPG), HbA1c, FINS, plasma alarin levels and HOMA-IR in the control group, T2DM non-obese group and T2DM obese group increased sequentially, and high-density lipoprotein-cholesterol (HDL-L) and HOMA-β decreased sequentially (P<0.05). Correlation analysis results showed that plasma alarin levels in T2DM patients were positively correlated with waistline, BMI, TC, LDL-C, FPG, HbA1c, FINS and HOMA-IR (P<0.05), and negatively correlated with HDL-C and HOMA-β (P <0.05), and the correlation coefficient of T2DM obese group was significantly higher than that of T2DM non-obese group (P<0.05). Multiple linear stepwise regression analysis showed that BMI, FPG, HbA1c, HOMA-β, and HOMA-IR were independent factors related to plasma alarin levels in T2DM non-obese and T2DM obese patients, and the correlation coefficient of the T2DM obese group was significantly higher than that of the T2DM non-obese group (P <0.05).

CONCLUSION

Plasma alarin levels increase in newly diagnosed T2DM and obese T2DM patients, which are affected by TC, BMI, FPG, HbA1c, HOMA-β and HOMA-IR, and may be involved in development of T2DM.

Epigenetic upregulation of galanin-like peptide mediates deoxynivalenol induced-growth inhibition in pituitary cells

Deoxynivalenol (DON) is an unavoidable contaminant in human food, animal feeds, and agricultural products. Growth retardation in children caused by extensive DON pollution has become a global problem that cannot be ignored. Previous studies have shown that DON causes stunting in children through intestinal dysfunction, insulin-like growth factor-1 (IGF-1) axis disorder and peptide YY (PYY). Galanin-like peptide (GALP) is an important growth regulator, but its role in DON-induced growth retardation is unclear. In this study, we report the important role of GALP during DON-induced growth inhibition in the rat pituitary tumour cell line GH3. DON was found to increase the expression of GALP through hypomethylationin the promoter region of the GALP gene and upregulate the expression of proinflammatory factors, while downregulate the expression of growth hormone (GH). Furthermore, GALP overexpression promoted proinflammatory cytokines, including TNF-α, IL-1β, IL-11 and IL-6, and further reduced cell viability and cell proliferation, while the inhibitory effect of GALP was the opposite. The expression of GALP and insulin like growth factor binding protein acid labile subunit (IGFALS) showed the opposite trend, which was the potential reason for the regulation of cell proliferation by GALP. In addition, GALP has anti-apoptotic effects, which could not eliminate the inflammatory damage of cells, thus aggravating cell growth inhibition. The present findings provide new mechanistic insights into the toxicity of DON-induced growth retardation and suggest a therapeutic potential of GALP in DON-related diseases.

Superoxide anions modulate the effects of alarin in the paraventricular nucleus on sympathetic activity and blood pressure in spontaneously hypertensive rats

Neuropeptides are involved in the regulation of the sympathetic activity and blood pressure in the paraventricular nucleus of the hypothalamus (PVN). The present study was designed to determine how alarin modulates the renal sympathetic nerve activity (RSNA), arterial blood pressure and mean arterial pressure (MAP) in the PVN, and whether superoxide anions regulate the effects of alarin in the PVN of spontaneously hypertensive rats (SHRs). Acute experiment was carried out with male Wistar-Kyoto rats (WKY) and SHRs under anesthesia. RSNA, systolic blood pressure (SBP), diastolic blood pressure (DBP), and MAP were measured. Alarin microinjection into the PVN increased RSNA (7.8 ± 1.8 vs. 14.8 ± 2.3%), SBP (5.9 ± 1.4 vs. 12.1 ± 1.6 mmHg), DBP (5.1 ± 0.8 vs. 10.0 ± 1.1 mmHg), and MAP (5.4 ± 1.2 vs. 10.7 ± 1.3 mmHg) in WKY rats and SHRs,. Alarin antagonist ala6-25 Cys decreased RSNA, SBP, DBP, and MAP in SHRs, and inhibited the effects of alarin. The alarin level was increased in the PVN of SHR compared to WKY rats. (29.7 ± 4.9 vs. 14.6 ± 2.4 pg/mg protein). PVN microinjection of superoxide anion scavengers tempol and tiron, or NAD(P)H oxidase inhibitor apocynin, decreased RSNA, SBP, DBP, and MAP in SHRs, and inhibited the effects of alarin, but the superoxide dismutase inhibitor diethyldithiocarbamic acid potentiated the effects of alarin. Superoxide anions and NAD(P)H oxidase activity levels in the PVN were increased by alarin, but decreased by alarin antagonist ala6-25 Cys. The alarin-induced increases in superoxide anions and NAD(P)H oxidase activity levels were abolished by pre-treatment with ala6-25 Cys. The results suggest that alarin in the PVN increases sympathetic outflow and blood pressure. The enhanced activity of endogenous alarin in the PVN contributes to sympathetic activation in hypertension, and the superoxide anion is involved in these alarin-mediated processes in the PVN.

Circulating alarin concentrations are high in patients with type 2 diabetes and increased by glucagon-like peptide-1 receptor agonist treatment: An Consort-compliant study

CONTEXT

Alarin has been reported to be relative to food intake and an increase in body weight. However, to date, no report has demonstrated the relationship between circulating alarin and diabetes in humans.

OBJECTIVE

The objective of this study is to gain insight into the possible role of alarin in humans.

DESIGN AND METHODS

164 patients with newly diagnosed type 2 diabetes mellitus (nT2DM), 112 IGT and 134 healthy subjects were recruited for this study. In an interventional study, 29 nT2DM patients were treated by a weekly GLP-1RA for 6 months. Plasma alarin concentrations were measured by ELISA.

RESULTS

Circulating alarin concentrations were significantly higher in both IGT and nT2DM subjects than in healthy individuals (0.40 ± 0.14 and 0.54 ± 0.24 vs 0.37 ± 0.10 μg/L, P < .05 or P < .01), whereas in T2DM patients, circulating alarin levels were higher than in IGT subjects. Circulating alarin positively correlated with FBG, HbA1c, HOMA-IR, AUCglucose and TNFα (P < .05 or P < .01). Multivariate logistic regression revealed that circulating alarin levels were correlated with IGT and T2DM. GLP-1RA treatment for 6 months increased circulating alarin levels in T2DM patients (from 0.34 ± 0.10 for baseline, to 0.39 ± 0.14 for 12 weeks, and finally to 0.38 ± 0.15 μg/L for 24 weeks; vs. pre-treatment P < .05).

CONCLUSIONS

These data suggest that alarin might be involved in the pathogenesis of T2DM in humans.

CLINICAL TRIAL REGISTRATION NUMBER

ChiCTR-OCS-13003185 (18/03/2013 ).

Alarin in different human intestinal epithelial cell types

Alarin (AL), a new member of the galanin family, has been localized in various CNS regions, mainly in rodents. Among other effects, it modulates food intake. Therefore, we analyzed the immunohistochemical distribution pattern of AL in human intestinal epithelia. Cryosections of 12 human bowel samples were immunohistochemically double-stained for AL and α-defensin 5 (αD; first set). Two further sets of sections were quadruple-stained either (second set) for AL, chromogranin (CG), synaptophysin (SY), and somatostatin (SO) or (third set) for AL, CG, Peptide Y (PY), and 5-hydroxytryptamine (5-HT). Slides were digitized and quantitative analysis of co-localization rates was undertaken. Small bowel: most of AL-positive cells (56%) were αD-positive Paneth cells located within the base of the crypts (first set). In the second set, about 27% of AL-labeled cells were co-reactive for SY and CG, likely representing entero-endocrine cells. In the third set, the largest subpopulation of AL-positive cells was not co-reactive for other markers applied (89%); most of them were likely Paneth cells. Large bowel: co-localization of AL with αD was not detected (first set). In the second set, AL was frequently co-localized with the other three markers applied (68%). In the third set, AL was frequently co-localized with 5-HT and CG (31%) as well as with PY and 5-HT (22%). Due to its presence in various enteroendocrine as well as Paneth cells, AL may be involved in different physiological and pathological processes.

Acute central effects of alarin on the regulation on energy homeostasis

Hypothalamic neuropeptides influence the main components of energy balance: metabolic rate, food intake, body weight as well as body temperature, by exerting either an overall anabolic or catabolic effect. The contribution of alarin, the most recently discovered member of the galanin peptide family to the regulation of energy metabolism has been suggested. Our aim was to analyze the complex thermoregulatory and food intake-related effects of alarin in rats. Adult male Wistar rats received different doses of alarin (0.3; 1; 3 and 15μg corresponding approximately to 0.1, 0.33, 1, and 5 nmol, respectively) intracerebroventricularly. Regarding thermoregulatory analysis, oxygen consumption (indicating metabolic rate), core temperature and heat loss (assessed by tail skin temperature) were recorded in an Oxymax indirect calorimeter system complemented with thermocouples and Benchtop thermometer. In order to investigate potential prostaglandin-mediated mechanisms of the hyperthermic effect of alarin, effects of intraperitoneally applied non-selective (indomethacin, 2mg/kg) or selective cyclooxygenase inhibitor (COX-2 inhibitor meloxicam, 1; 2mg/kg) were tested. Effects of alarin on daytime and nighttime spontaneous food intake, as well as, 24-h fasting-induced re-feeding were recorded in an automated FeedScale system. Alarin increased oxygen consumption with simultaneous suppression of heat loss leading to a slow coordinated rise in core temperature. Both applied COX-inhibitors suppressed this action. Alarin failed to induce daytime food intake, but suppressed spontaneous nighttime and also fasting-induced re-feeding food intake. Alarin appears to elicit a slow anorexigenic and prostaglandin-mediated, fever-like hyperthermic response in rats. Such a combination would characterize a catabolic mediator. The potential involvement of alarin in sickness behavior may be assumed.

The galanin and galanin receptor subtypes, its regulatory role in the biological and pathological functions

The multitalented neuropeptide galanin was first discovered 30 years ago but initially no biologic activity was found. Further research studies discovered the presence of galanin in the brain and some peripheral tissues, and galanin was identified as a modulator of neurotransmission in the central and peripheral nervous system. Over the last decade there were performed very intensive studies of the neuronal actions and also of nonneuronal actions of galanin. Other galanin family peptides have been described, namely galanin, galanin-like peptide, galanin-message associated peptide and alarin. The effect of these peptides is mediated through three galanin receptors subtypes, GalR1, GalR2 and GalR3 belonging to G protein coupled receptors, and signaling via multiple transduction pathways, including inhibition of cyclic AMP/protein kinase A (GalR1, GalR3) and stimulation of phospholipase C (GalR2). This also explains why one specific molecule of galanin can be responsible for different roles in different tissues. The present review summarizes the information currently available on the relationship between the galaninergic system and known pathological states. The research of novel galanin receptor specific agonists and antagonists is also very promising for its future role in pharmacological treatment. The galaninergic system is important target for current and future biomedical research.

Cytokines and glucocorticoid receptors are associated with the antidepressant-like effect of alarin

Little is known about the physiological or pharmacological properties of alarin, a new neuropeptide belonging to the galanin family. We previously showed that alarin has an antidepressant-like effect and is associated with a decrease in the hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis that is observed in patients with depression using unpredictable chronic mild stress (UCMS) mouse model of depression. However, the mechanisms underlying these effects have not been uncovered. Inflammatory cytokines are reportedly associated with depression. Animal studies and cytokine immune therapy in humans suggest that pro-inflammatory cytokines induce depressive symptomatology and potently activate the HPA axis, whereas anti-inflammatory cytokines may decrease activation. Thus, we first determined the levels of inflammatory cytokines in the blood and brain to evaluate whether the antidepressant-like effect of alarin in UCMS-treated mice is related to its regulation of these inflammatory cytokines. Pro-inflammatory cytokines disrupt the function and/or expression of glucocorticoid receptors (GRs), which mediate the negative feedback of glucocorticoids on the HPA axis to keep it from being overactivated. We next explored the expression level of GRs in the brains of mice subjected to UCMS and to the administration of alarin. We found that intracerebroventricular administration of alarin significantly ameliorated depression-like behaviors in the UCMS-treated mice. Alarin restored the UCMS-induced an increase in the levels of the pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor α and a decrease in the anti-inflammatory cytokine IL-10 level in the blood, prefrontal cortex, hippocampus and hypothalamus. Alarin also reversed the UCMS-induced down-regulation of GR expression in these brain regions. Thus, the antidepressant-like effects of alarin may be mediated by restoring altered pro-inflammatory and anti-inflammatory cytokine levels and GR expression to decrease HPA axis hyperactivity. Our findings provide additional knowledge to interpret the pathophysiology of depression.

Intracerebroventricular Injection of Alarin Increased Glucose Uptake in Skeletal Muscle of Diabetic Rats

In order to investigate the central effect of alarin on glucose uptake, we administered alarin and/ or its inhibitor, ala6-25Cys into the cerebral ventricles of the type 2 diabetic rats. Then the relative parameters about glucose uptake in skeletal muscles were measured. We found that central treatment with alarin significantly increased the food intake, body weight and glucose infusion rates in hyperinsulinemic euglycemic clamp tests of the animals. Besides, the treatment also enhanced 2-deoxy-[3H]-D-glucose uptake, vesicle-associated membrane protein 2 contents, glucose transporter 4 protein and mRNA expression, as well as pAktThr308, pAktSer473 and total Akt levels in muscle cells, but reduced plasma glucose and insulin levels of the rats. All of the alarin-inducing events may be antagonised by central injection of ala6-25Cys. These results suggest that central administration of alarin stimulates glucose uptake mediated by activation of Akt signal pathway in type 2 diabetic animals.

The regulative effect of galanin family members on link of energy metabolism and reproduction

It is essential for the species survival that an efficient coordination between energy storage and reproduction through endocrine regulation. The neuropeptide galanin, one of the endocrine hormones, can potently coordinate energy metabolism and the activities of hypothalamic-pituitary-gonadal reproductive axis to adjust synthesis and release of metabolic and reproductive hormones in animals and humans. However, few papers have summarized the regulative effect of the galanin family members on the link of energy storage and reproduction as yet. To address this issue, this review attempts to summarize the current information available about the regulative effect of galanin, galanin-like peptide and alarin on the metabolic and reproductive events, with special emphasis on the interactions between galanin and hypothalamic gonadotropin-releasing hormone, pituitary luteinizing hormone and ovarian hormones. This research line will further deepen our understanding of the physiological roles of the galanin family in regulating the link of energy metabolism and reproduction.

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.

A paradoxical role for alarin in the nervous control of energy homeostasis and thermoregulation: orexigenic but hypermetabolic

Alarin is a lately discovered member of the galanin family of peptides. Although it has orexigenic effects in the brain, alarin induces thermoregulatory responses, which promote an increase of core temperature in rats. With some delay intracerebroventricular injections of alarin causes a 15% rise in metabolic rate at an ambient temperature of 25°C and a pronounced fall in tail skin temperature, i.e. peripheral vasoconstriction, at 28°C.

Galanin and galanin-like peptide modulate vasopressin and oxytocin release in vitro: the role of galanin receptors

Galanin (Gal) and galanin-like peptide (GALP) may be involved in the mechanisms of the hypothalamo-neurohypophysial system. The aim of the present in vitro study was to compare the influence of Gal and GALP on vasopressin (AVP) and oxytocin (OT) release from isolated rat neurohypophysis (NH) or hypothalamo-neurohypophysial explants (Hth-NH). The effect of Gal/GALP on AVP/OT secretion was also studied in the presence of galantide, the non-selective galanin receptors antagonist. Gal at concentrations of 10(-10 )M and 10(-8 )M distinctly inhibited basal and K(+)-stimulated AVP release from the NH and Hth-NH explants, whereas Gal exerted a similar action on OT release only during basal incubation. Gal added to the incubation medium in the presence of galantide did not exert any action on the secretion of either neurohormone from NH and Hth-NH explants. GALP (10(-10 )M and 10(-9 )M) induced intensified basal AVP release from the NH and Hth-NH complex as well as the release of potassium-evoked AVP from the Hth-NH. The same effect of GALP has been observed in the presence of galantide. GALP added to basal incubation medium was the reason for stimulated OT release from the NH as well as from the Hth-NH explants. However, under potassium-stimulated conditions, OT release from the NH and Hth-NH complexes has been observed to be distinctly impaired. Galantide did not block this inhibitory effect of GALP on OT secretion. It may be concluded that: (i) Gal as well as GALP modulate AVP and OT release at every level of the hypothalamo-neurohypophysial system; (ii) Gal acts in the rat central nervous system as the inhibitory neuromodulator for AVP and OT release via its galanin receptors; (iii) the stimulatory effect of GALP on AVP and OT release is likely to be mediated via an unidentified specific GALP receptor(s).

Central alarin ameliorated insulin resistance of adipocytes in type 2 diabetic rats

Alarin, a regulatory peptide, belongs to the galanin family and plays the same regulatory roles as galanin in orexigenic activity and energy metabolism. Our previous studies had found that galanin might facilitate insulin sensitivity via activation of its central receptors. To date, little is known about whether central alarin may exert similar effects on insulin sensitivity. In order to investigate this, alarin and its specific antagonist, alarin 6-25Cys, were administered into the cerebral ventricles of type 2 diabetic rats (T2DR) to evaluate the changes in insulin resistance. The results indicated that central treatment with alarin significantly increased the body weight of animals, the 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose uptake, the plasma adiponectin levels, the glucose infusion rates in hyperinsulinemic-euglycemic clamp tests, the vesicle-associated membrane protein 2 as well as glucose transporter 4 (GLUT4 (SLC2A4)) protein and mRNA levels, and the ratios of GLUT4 contents in plasma membranes to total cell membranes in adipocytes, but reduced blood glucose and plasma retinol-binding protein 4 levels. These effects of alarin may be inhibited by pretreatment with alarin 6-25Cys. The above-mentioned results suggest that the central alarin projective system may facilitate insulin sensitivity and glucose uptake via the increase in GLUT4 content and GLUT4 translocation from intracellular pools to plasma membranes in T2DR.

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.

Alarin-induced antidepressant-like effects and their relationship with hypothalamus-pituitary-adrenal axis activity and brain derived neurotrophic factor levels in mice

Alarin is a newly identified member of the galanin family of peptides. Galanin has been shown to exert regulatory effects on depression. Similar to galanin in distribution, alarin is also expressed in the medial amygdala and hypothalamus, i.e., regions interrelated with depression. However, it remains a puzzle whether alarin is involved in depression. Accordingly, we established the depression-like mouse model using behavioral tests to ascertain the possible involvement of alarin, with fluoxetine as a positive control. With the positive antidepressant-like effects of alarin, we further examined its relationship to HPA axis activity and brain-derived neurotrophic factor (BDNF) levels in different brain areas in a chronic unpredictable mild stress (CUMS) paradigm. In the acute studies, alarin produced a dose-related reduction in the immobility duration in tail suspension test (TST) in mice. In the open-field test, intracerebroventricular (i.c.v.) injection of alarin (1.0 nmol) did not impair locomotion or motor coordination in the treated mice. In the CUMS paradigm, alarin administration (1.0 nmol, i.c.v.) significantly improved murine behaviors (FST and locomotor activity), which was associated with a decrease in corticotropin-releasing hormone (CRH) mRNA levels in the hypothalamus, as well as a decline in serum levels of CRH, adrenocorticotropic hormone (ACTH) and corticosterone (CORT), all of which are key hormones of the HPA axis. Furthermore, alarin upregulated BDNF mRNA levels in the prefrontal cortex and hippocampus. These findings suggest that alarin may potentiate the development of new antidepressants, which would be further secured with the identification of its receptor(s).

Evolution of a potential hormone antagonist following gene splicing during primate evolution

Alternative splicing of genes generates novel mRNAs, leading to the evolution of new functional proteins. Cholecystokinin (CCK) induces the release of pancreatic enzymes and the contraction of the gallbladder to promote the digestion of fat and proteins. CCK activates two G-protein-coupled receptors, CCKA and CCKB. Here, we showed that a CCKsv (splicing variant), originated de novo during Catarrhini evolution by including a portion of intronic sequence of the CCK gene, encodes novel C-terminal peptide sequence followed by a new poly-adenylation signal. CCKsv is expressed in many human tissues and likely a secreted peptide retaining the original signal peptide and the N-terminal proteolytic processing signal, together with novel C-terminal sequences. Although CCKsv cannot activate CCK receptors, it partially inhibits the CRE- or SRF-driven reporter activities stimulated by wide type CCK-8 mediated by both CCK receptors. Co-treatment with CCKsv also partially antagonizes Ewing tumor cell growth stimulated by CCK-8. Our study provides an example of new peptide hormone antagonist evolution in primates.

Alarin but not its alternative-splicing form, GALP (Galanin-like peptide) has antimicrobial activity

Alarin is an alternative-splicing form of GALP (galanin-like peptide). It shares only 5 conserved amino acids at the N-terminal region with GALP which is involved in a diverse range of normal brain functions. This study seeks to investigate whether alarin has additional functions due to its differences from GALP. Here, we have shown using a radial diffusion assay that alarin but not GALP inhibited the growth of Escherichia coli (strain ML-35). The conserved N-terminal region, however, remained essential for the antimicrobial activity of alarin as truncated peptides showed reduced killing effect. Moreover, alarin inhibited the growth of E. coli in a similar potency as human cathelicidin LL-37, a well-studied antimicrobial peptide. Electron microscopy further showed that alarin induced bacterial membrane blebbing but unlike LL-37, it did not cause hemolysis of erythrocytes. In addition, alarin is only active against the gram-negative bacteria, E. coli but not the gram-positive bacteria, Staphylococcus aureus. Thus, these data suggest that alarin has potentials as an antimicrobial and should be considered for the development in human therapeutics.

Alarin 6-25Cys antagonizes alarin-specific effects on food intake and luteinizing hormone secretion

Previous data from our labs and from others have demonstrated that intracerebroventricular (ICV) injection of alarin has orexigenic activity and significantly increases plasma luteinizing hormone (LH) secretion in a gonadotropin-releasing hormone (GnRH) dependent manner. The purpose of the current experiments was to determine if the amino acids at the amino-terminal end of the alarin peptide are critical for alarin's effects on reproductive and feeding systems. First, we injected male mice ICV with full-length alarin (Ala1-25) or peptide fragments missing residues at the amino-terminal end (Ala3-25 or Ala6-25 Cys). Neither peptide fragment alone, significantly increased food intake in male mice compared to controls. Second, ICV injection of Ala1-25, but not Ala3-25, significantly (p < 0.01) increased GnRH-mediated LH secretion. Surprisingly, Ala6-25 Cys significantly (p < 0.05) inhibited plasma LH secretion and inhibited Ala1-25 actions. In conclusion, elimination of the first five amino acids of alarin not only abolishes the biological activity of alarin, but becomes an antagonist to alarin-specific effects. Furthermore, Ala6-25 Cys seems to act as a specific antagonist to putative alarin receptors and therefore may be an important tool in identifying alarin-specific receptors.

Galanin peptide family as a modulating target for contribution to metabolic syndrome

Metabolic syndrome (MetS) is defined as abdominal central obesity, atherogenic dyslipidemia, insulin resistance, glucose intolerance and hypertension. The rapid increasing prevalence of MetS and the consequent diseases, such as type 2 diabetes mellitus and cardiovascular disorder, are becoming a global epidemic health problem. Despite considerable research into the etiology of this complex disease, the precise mechanism underlying MetS and the association of this complex disease with the development of type 2 diabetes mellitus and increased cardiovascular disease remains elusive. Therefore, researchers continue to actively search for new MetS treatments. Recent animal studies have indicated that the galanin peptide family of peptides may increase food intake, glucose intolerance, fat preference and the risk for obesity and dyslipidemia while decreasing insulin resistance and blood pressure, which diminishes the probability of type 2 diabetes mellitus and hypertension. To date, however, few papers have summarized the role of the galanin peptide family in modulating MetS. Through a summary of available papers and our recent studies, this study reviews the updated evidences of the effect that the galanin peptide family has on the clustering of MetS components, including obesity, dyslipidemia, insulin resistance and hypertension. This line of research will further deepen our understanding of the relationship between the galanin peptide family and the mechanisms underlying MetS, which will help develop new therapeutic strategies for this complex disease.

Galanin and its receptors: a novel strategy for appetite control and obesity therapy

The rapid increase in the prevalence of overweight and obesity is becoming an important health problem. Overweight and obesity may cause several metabolic complications, including type 2 diabetes mellitus, hyperlipidemia, high cholesterol, coronary artery disease as well as hypertension. Prevention and treatment of obesity will benefit the treatment of these related diseases. Current strategies for treatment of obesity are not adequately effective and are frequently companied with many side effects. Thus, new ways to treat obesity are urgently needed. Galanin is undoubtedly involved in the regulation of food intake and body weight. The aim of this review is to provide up-to-date knowledge concerning the roles of central and peripheral galanin as well as its receptors in the regulation of metabolism, obesity and appetite. We also highlight the mechanisms of galanin and its receptors in experimental obesity, trying to establish a novel anti-obesity strategy.

Effects of alarin on food intake, body weight and luteinizing hormone secretion in male mice

Alarin is a member of the galanin family of neuropeptides that includes galanin and galanin-like peptide (GALP). Alarin is an alternate transcript of the GALP gene and is expressed in the brain and periphery. Recently, it was shown in male rats that alarin is an orexigenic peptide that also regulates reproductive hormone secretion. We hypothesized that alarin would also have similar central effects on feeding and luteinizing hormone (LH) secretion in mice as observed in rats. To test this hypothesis, we treated male mice with alarin intracerebroventricularly (i.c.v.) and measured its effects on food intake, body weight, body temperature, LH secretion, and Fos induction. We observed that i.c.v. injection of 1.0 nmol alarin significantly increased immediate food intake (p<0.01) from 30 to 120 min post-injection and relative body weight (p<0.05) after 24 h. Alarin had no effect on body temperature compared to controls. Alarin increased LH levels in male mice, an effect that was dependent on gonadotropin-Releasing-Hormone (GnRH) signaling. Furthermore, alarin-stimulated Fos immunoreactivity was observed in diencephalic nuclei, including the hypothalamic dorsomedial nucleus and the bed nucleus of the stria terminalis. Our studies demonstrated that alarin, like other members of the galanin peptide family, is a neuromediator of food intake and reproductive hormone secretion in male mice.

Hypothalamic neuropeptides and the regulation of appetite

Neuropeptides released by hypothalamic neurons play a major role in the regulation of feeding, acting both within the hypothalamus, and at other appetite regulating centres throughout the brain. Where classical neurotransmitters signal only within synapses, neuropeptides diffuse over greater distances affecting both nearby and distant neurons expressing the relevant receptors, which are often extrasynaptic. As well as triggering a behavioural output, neuropeptides also act as neuromodulators: altering the response of neurons to both neurotransmitters and circulating signals of nutrient status. The mechanisms of action of hypothalamic neuropeptides with established roles in feeding, including melanin-concentrating hormone (MCH), the orexins, α-melanocyte stimulating hormone (α-MSH), agouti-gene related protein (AgRP), neuropeptide Y, and oxytocin, are reviewed in this article, with emphasis laid on both their effects on appetite regulating centres throughout the brain, and on examining the evidence for their physiological roles. In addition, evidence for the involvement of several putative appetite regulating hypothalamic neuropeptides is assessed including, ghrelin, cocaine and amphetamine-regulated transcript (CART), neuropeptide W and the galanin-like peptides. This article is part of a Special Issue entitled 'Central control of Food Intake'.

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 role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.

Distribution of alarin immunoreactivity in the mouse brain

Alarin is a 25 amino acid peptide that belongs to the galanin peptide family. It is derived from the galanin-like peptide gene by a splice variant, which excludes exon 3. Alarin was first identified in gangliocytes of neuroblastic tumors and later shown to have a vasoactive function in the skin. Recently, alarin was demonstrated to stimulate food intake as well as the hypothalamic–pituitary–gonadal axis in rodents, suggesting that it might be a neuromodulatory peptide in the brain. However, the individual neurons in the central nervous system that express alarin have not been identified. Here, we determined the distribution of alarin-like immunoreactivity (alarin-LI) in the adult murine brain. The specificity of the antibody against alarin was demonstrated by the absence of labeling after pre-absorption of the antiserum with synthetic alarin peptide and in transgenic mouse brains lacking neurons expressing the GALP gene. Alarin-LI was observed in different areas of the murine brain. A high intensity of alarin-LI was detected in the accessory olfactory bulb, the medial preoptic area, the amygdala, different nuclei of the hypothalamus such as the arcuate nucleus and the ventromedial hypothalamic nucleus, the trigeminal complex, the locus coeruleus, the ventral chochlear nucleus, the facial nucleus, and the epithelial layer of the plexus choroideus. The distinct expression pattern of alarin in the adult mouse brain suggests potential functions in reproduction and metabolism.

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.

Beyond Leptin: Emerging Candidates for the Integration of Metabolic and Reproductive Function during Negative Energy Balance

Reproductive status is tightly coupled to metabolic state in females, and ovarian cycling in mammals is halted when energy output exceeds energy input, a metabolic condition known as negative energy balance. This inhibition of reproductive function during negative energy balance occurs due to suppression of gonadotropin-releasing hormone (GnRH) release in the hypothalamus. The GnRH secretagogue kisspeptin is also inhibited during negative energy balance, indicating that inhibition of reproductive neuroendocrine circuits may occur upstream of GnRH itself. Understanding the metabolic signals responsible for the inhibition of reproductive pathways has been a compelling research focus for many years. A predominant theory in the field is that the status of energy balance is conveyed to reproductive neuroendocrine circuits via the adipocyte hormone leptin. Leptin is stimulatory for GnRH release and lower levels of leptin during negative energy balance are believed to result in decreased stimulatory drive for GnRH cells. However, recent evidence found that restoring leptin to physiological levels did not restore GnRH function in three different models of negative energy balance. This suggests that although leptin may be an important permissive signal for reproductive function as indicated by many years of research, factors other than leptin must critically contribute to negative energy balance-induced reproductive inhibition. This review will focus on emerging candidates for the integration of metabolic status and reproductive function during negative energy balance.