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

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.

Trans fat intake during pregnancy or lactation increases anxiety-like behavior and alters proinflammatory cytokines and glucocorticoid receptor levels in the hippocampus of adult offspring

Changes in dietary habits, including the increased consumption of processed foods, rich in trans fatty acids (TFA), have profound effects on offspring health in later life. Thus, this study aimed to assess the influence of maternal trans fat intake during pregnancy or lactation on anxiety behavior, as well as markers of inflammation, oxidative stress, and expression of glucocorticoid receptors (GR) of adult male offspring. Female Wistar rats were supplemented daily with soybean oil/fish oil (SO/FO) or hydrogenated vegetable fat (HVF) by oral gavage (3.0 g/kg body weight) during pregnancy or lactation. After weaning, male offspring received only standard diet. On the postnatal day 60, anxiety-like symptoms were assessed, the plasma was collected for the quantification of cytokines levels and the hippocampus removed for biochemical and molecular analysis. Our findings have evidenced that offspring from HVF-supplemented dams during pregnancy or lactation showed significantly greater levels of anxiety behavior. HVF supplementation increased plasma levels of proinflammatory cytokines and these levels were higher in the lactation period. In contrast, HVF supplementation decreased plasma levels of IL-10 in relation to SO/FO in both periods. Biochemical evaluations showed higher reactive species generation, protein carbonyl levels and catalase activity in offspring from HVF-supplemented dams during lactation. In addition, offspring from HVF-supplemented dams showed decreased GR expression in both supplemented periods. Together, these data indicate that consumption of TFA in different periods of development may increase anxiety-like behavior at least in part via alterations in proinflammatory and anti-inflammatory cytokine levels and GR expression in limbic brain regions.

Predisposition of Neonatal Maternal Separation to Visceral Hypersensitivity via Downregulation of Small-Conductance Calcium-Activated Potassium Channel Subtype 2 (SK2) in Mice

Background

Visceral hypersensitivity is a common occurrence of gastrointestinal diseases such as irritable bowel syndrome (IBS), wherein early-life stress (ELS) may have a high predisposition to the development of visceral hypersensitivity in adulthood, with the specific underlying mechanism still elusive. Herein, we assessed the potential effect of small-conductance calcium-activated potassium channel subtype 2 (SK2) in the spinal dorsal horn (DH) on the pathogenesis of visceral hypersensitivity induced by maternal separation (MS) in mice.

Methods

Neonatal mice were subjected to the MS paradigm, an established ELS model. In adulthood, the visceral pain threshold and the abdominal withdrawal reflex (AWR) were measured with an inflatable balloon. The elevated plus maze, open field test, sucrose preference test, and forced swim test were employed to evaluate the anxiety- and depression-like behaviors. The expression levels of SK2 in the spinal DH were determined by immunofluorescence and western blotting. The mRNA of SK2 and membrane palmitoylated protein 2 (MPP2) were determined by quantitative real-time polymerase chain reaction (qRT-PCR). Electrophysiology was applied to evaluate the neuronal firing rates and SK2 channel-mediated afterhyperpolarization current (I _AHP). The interaction between MPP2 and SK2 was validated by coimmunoprecipitation.

Results

In contrast to the naïve mice, ethological findings in MS mice revealed lowered visceral pain threshold, more evident anxiety- and depression-like behaviors, and downregulated expression of membrane SK2 protein and MPP2 protein. Moreover, electrophysiological results indicated increased neuronal firing rates and decreased I _AHP in the spinal DH neurons. Nonetheless, intrathecal injection of the SK2 channel activator 1-ethyl-2-benzimidazolinone (1-EBIO) in MS mice could reverse the electrophysiological alterations and elevate the visceral pain threshold. In the naïve mice, administration of the SK2 channel blocker apamin abated I _AHP and elevated spontaneous neuronal firing rates in the spinal DH neurons, reducing the visceral pain threshold. Finally, disruption of the MPP2 expression by small interfering RNA (siRNA) could amplify visceral hypersensitivity in naïve mice.

Conclusions

ELS-induced visceral pain and visceral hypersensitivity are associated with the underfunction of SK2 channels in the spinal DH.

The type of stress matters: repeated injection and permanent social isolation stress in male mice have a differential effect on anxiety- and depressive-like behaviours, and associated biological alterations

Chronic stress can alter the immune system, adult hippocampal neurogenesis and induce anxiety- and depressive-like behaviour in rodents. However, previous studies have not discriminated between the effect(s) of different types of stress on these behavioural and biological outcomes. We investigated the effect(s) of repeated injection vs. permanent social isolation on behaviour, stress responsivity, immune system functioning and hippocampal neurogenesis, in young adult male mice, and found that the type of stress exposure does indeed matter. Exposure to 6 weeks of repeated injection resulted in an anxiety-like phenotype, decreased systemic inflammation (i.e., reduced plasma levels of TNFα and IL4), increased corticosterone reactivity, increased microglial activation and decreased neuronal differentiation in the dentate gyrus (DG). In contrast, exposure to 6 weeks of permanent social isolation resulted in a depressive-like phenotype, increased plasma levels of TNFα, decreased plasma levels of IL10 and VEGF, decreased corticosterone reactivity, decreased microglial cell density and increased cell density for radial glia, s100β-positive cells and mature neuroblasts-all in the DG. Interestingly, combining the two distinct stress paradigms did not have an additive effect on behavioural and biological outcomes, but resulted in yet a different phenotype, characterized by increased anxiety-like behaviour, decreased plasma levels of IL1β, IL4 and VEGF, and decreased hippocampal neuronal differentiation, without altered neuroinflammation or corticosterone reactivity. These findings demonstrate that different forms of chronic stress can differentially alter both behavioural and biological outcomes in young adult male mice, and that combining multiple stressors may not necessarily cause more severe pathological outcomes.

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 ).

Inhibition of activated astrocyte ameliorates lipopolysaccharide- induced depressive-like behaviors

BACKGROUND

Numerous studies indicate that inflammation plays important roles in the development of depression. Astrocytes are crucial regulators of immune response in the central nervous system, and strongly activated by pro-inflammatory cytokines. We hypothesized that inhibition of activated astrocytes contributed to ameliorate depressive-like symptoms.

METHODS

This study evaluated the antidepressant-like effect of inhibition of activated astrocytes, by a well-established astrocyte inactivator fluorocitrate (FC), on a lipopolysaccharide (LPS)-induced model of depression. Forced swim test (FST), tail suspension test (TST) and sucrose preference test were used to assess depressive-like behaviors. The expression of fibrillary acidic protein (GFAP), brain-derived neurotrophic factor (BDNF) and neuroinflammation were determined in the hippocampus and cortex.

RESULTS

The results demonstrated that LPS increased immobility time in the TST and FST, reduced sucrose preference as well. LPS also enhanced the expression of IL-1β, TNF-α, iNOS and GFAP, accompanying with decreased expression of BDNF in the hippocampus and cortex. Inhibition of activated astrocytes by FC significantly prevented LPS- induced alteration in the FST, TST and sucrose preference test. Moreover, in the hippocampus and cortex, inhibition of activated astrocytes by FC significantly attenuated increases of neuroinflammation and GFAP whereas reversed decrease of BDNF in LPS- challenged depression.

CONCLUSIONS

Taken together, the results suggest that inhibition of activated astrocytes ameliorates LPS-induced depressive-like behavior, providing the first evidence that inhibition of activated astrocytes might represent a novel therapeutic target for depression.

Prefrontal cortical trkB, glucocorticoids, and their interactions in stress and developmental contexts

The tropomyosin/tyrosine receptor kinase B (trkB) and glucocorticoid receptor (GR) regulate neuron structure and function and the hormonal stress response. Meanwhile, disruption of trkB and GR activity (e.g., by chronic stress) can perturb neuronal morphology in cortico-limbic regions implicated in stressor-related illnesses like depression. Further, several of the short- and long-term neurobehavioral consequences of stress depend on the developmental timing and context of stressor exposure. We review how the levels and activities of trkB and GR in the prefrontal cortex (PFC) change during development, interact, are modulated by stress, and are implicated in depression. We review evidence that trkB- and GR-mediated signaling events impact the density and morphology of dendritic spines, the primary sites of excitatory synapses in the brain, highlighting effects in adolescents when possible. Finally, we review the role of neurotrophin and glucocorticoid systems in stress-related metaplasticity. We argue that better understanding the long-term effects of developmental stressors on PFC trkB, GR, and related factors may yield insights into risk for chronic, remitting depression and related neuropsychiatric illnesses.

Current Status of Animal Models of Posttraumatic Stress Disorder: Behavioral and Biological Phenotypes, and Future Challenges in Improving Translation

Increasing predictability of animal models of posttraumatic stress disorder (PTSD) has required active collaboration between clinical and preclinical scientists. Modeling PTSD is challenging, as it is a heterogeneous disorder with ≥20 symptoms. Clinical research increasingly utilizes objective biological measures (e.g., imaging, peripheral biomarkers) or nonverbal behaviors and/or physiological responses to complement verbally reported symptoms. This shift toward more-objectively measurable phenotypes enables refinement of current animal models of PTSD, and it supports the incorporation of homologous measures across species. We reviewed >600 articles to examine the ability of current rodent models to probe biological phenotypes of PTSD (e.g., sleep disturbances, hippocampal and fear-circuit dysfunction, inflammation, glucocorticoid receptor hypersensitivity) in addition to behavioral phenotypes. Most models reliably produced enduring generalized anxiety-like or depression-like behaviors, as well as hyperactive fear circuits, glucocorticoid receptor hypersensitivity, and response to long-term selective serotonin reuptake inhibitors. Although a few paradigms probed fear conditioning/extinction or utilized peripheral immune, sleep, and noninvasive imaging measures, we argue that these should be incorporated more to enhance translation. Data on female subjects, on subjects at different ages across the life span, or on temporal trajectories of phenotypes after stress that can inform model validity and treatment study design are needed. Overall, preclinical (and clinical) PTSD researchers are increasingly incorporating homologous biological measures to assess markers of risk, response, and treatment outcome. This shift is exciting, as we and many others hope it not only will support translation of drug efficacy from animal models to clinical trials but also will potentially improve predictability of stage II for stage III clinical trials.

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.

Chronic venlafaxine treatment fails to alter the levels of galanin system transcripts in normal rats

It is widely accepted that efficacy and speed of current antidepressants' therapeutic effect are far from optimal. Thus, there is a need for the development of antidepressants with new mechanisms of action. The neuropeptide galanin and its receptors (GalR1, GalR2 and GalR3) are among the promising targets. However, it is not clear whether or not the galanin system is involved in the antidepressant effect exerted by the currently much used inhibitors of the reuptake of serotonin and/or noradrenaline. To answer this question we administered the selective serotonin and noradrenaline reuptake inhibitor (SNRI) venlafaxine (40mg/kg/day via osmotic minipumps) to normal rats and examined the levels of the transcripts for galanin and GalR1-3 after a 3-week venlafaxine treatment in the dorsal raphe, hippocampus and frontal cortex. These areas are known to be involved in the effects of antidepressants and in depression itself. Venlafaxine failed to alter the expression of any of the galanin system genes in these areas. Our results show that one of the most efficient, currently used SNRIs does not alter transcript levels of galanin or its three receptors in normal rats. These findings suggest that the pro- and antidepressive-like effects of galanin reported in animal experiments may employ a novel mechanism(s).