Ghrelin: a link between ageing, metabolism and neurodegenerative disorders

The Aggravating Role of Failing Neuropeptide Networks in the Development of Sporadic Alzheimer's Disease

Alzheimer's disease imposes an increasing burden on aging Western societies. The disorder most frequently appears in its sporadic form, which can be caused by environmental and polygenic factors or monogenic conditions of incomplete penetrance. According to the authors, in the majority of cases, Alzheimer's disease represents an aggravated form of the natural aging of the central nervous system. It can be characterized by the decreased elimination of amyloid β1-42 and the concomitant accumulation of degradation-resistant amyloid plaques. In the present paper, the dysfunction of neuropeptide regulators, which contributes to the pathophysiologic acceleration of senile dementia, is reviewed. However, in the present review, exclusively those neuropeptides or neuropeptide families are scrutinized, and the authors' investigations into their physiologic and pathophysiologic activities have made significant contributions to the literature. Therefore, the pathophysiologic role of orexins, neuromedins, RFamides, corticotrope-releasing hormone family, growth hormone-releasing hormone, gonadotropin-releasing hormone, ghrelin, apelin, and natriuretic peptides are discussed in detail. Finally, the therapeutic potential of neuropeptide antagonists and agonists in the inhibition of disease progression is discussed here.

Activation of bitter taste receptors (TAS2R) protects against rotenone-induced neurotoxicity: Could ghrelin have a role?

AIMS

Bitter taste receptors (TAS2Rs) and their downstream signaling pathways are expressed not only in the oral tissues but also in extraoral tissues. Emerging data has demonstrated the beneficial effect of ghrelin in neurodegenerative diseases. Gaining more insight into the interaction between TAS2Rs and gut hormones may expand their therapeutic applications. Herein, we aimed to assess the possible effect of TAS2R activation by denatonium benzoate (DB) in modulating functional and neurobiochemical alterations in a model of Parkinson's disease (PD).

MAIN METHODS

PD model was induced by daily injection of rotenone (2 mg/kg). Rats received DB (5 mg/kg), atenolol (10 mg/kg), or both concomitantly with rotenone, daily for 28 days. Evaluation of the motor abnormalities and histological examination of brain tissues were conducted. In addition, striatal dopamine contents, immunohistochemical expression of tyrosine hydroxylase, plasma ghrelin level, and biochemical analysis of markers of inflammation and oxidative stress were assessed.

KEY FINDINGS

Treatment with DB increased serum levels of ghrelin and striatal dopamine contents with consequent amelioration of oxidative stress and attenuation of inflammatory cytokines. Moreover, DB treatment significantly ameliorated motor disturbance and histological abnormalities compared to untreated rats. Atenolol inhibited ghrelin release and abolished the positive effect of DB suggesting the involvement of ghrelin on such effects.

SIGNIFICANCE

The current study suggests that TAS2Rs agonists are promising candidates for ameliorating rotenone-induced PD pathology in rats, an action that could be linked to the enhancement of ghrelin release with consequent antioxidant and anti-inflammatory activities.

Ghrelin for Neuroprotection in Post-Cardiac Arrest Coma: A Randomized Clinical Trial

Importance

Out-of-hospital cardiac arrest survival rates have markedly risen in the last decades, but neurological outcome only improved marginally. Despite research on more than 20 neuroprotective strategies involving patients in comas after cardiac arrest, none have demonstrated unequivocal evidence of efficacy; however, treatment with acyl-ghrelin has shown improved functional and histological brain recovery in experimental models of cardiac arrest and was safe in a wide variety of human study populations.

Objective

To determine safety and potential efficacy of intravenous acyl-ghrelin to improve neurological outcome in patients in a coma after cardiac arrest.

Design, Setting, and Participants

A phase 2, double-blind, placebo-controlled, multicenter, randomized clinical trial, Ghrelin Treatment of Comatose Patients After Cardiac Arrest: A Clinical Trial to Promote Cerebral Recovery (GRECO), was conducted between January 18, 2019, and October 17, 2022. Adult patients 18 years or older who were in a comatose state after cardiac arrest were assessed for eligibility; patients were from 3 intensive care units in the Netherlands. Expected death within 48 hours or unfeasibility of treatment initiation within 12 hours were exclusion criteria.

Interventions

Patients were randomized to receive intravenous acyl-ghrelin, 600 μg (intervention group), or placebo (control group) within 12 hours after cardiac arrest, continued for 7 days, twice daily, in addition to standard care.

Main Outcomes and Measures

Primary outcome was the score on the Cerebral Performance Categories (CPC) scale at 6 months. Safety outcomes included any serious adverse events. Secondary outcomes were mortality and neuron-specific enolase (NSE) levels on days 1 and 3.

Results

A total of 783 adult patients in a coma after cardiac arrest were assessed for eligibility, and 160 patients (median [IQR] age, 68 [57-75] years; 120 male [75%]) were enrolled. A total of 81 patients (51%) were assigned to the intervention group, and 79 (49%) were assigned to the control group. The common odds ratio (OR) for any CPC improvement in the intervention group was 1.78 (95% CI, 0.98-3.22; P = .06). This was consistent over all CPC categories. Mean (SD) NSE levels on day 1 after cardiac arrest were significantly lower in the intervention group (34 [6] μg/L vs 56 [13] μg/L; P = .04) and on day 3 (28 [6] μg/L vs 52 [14] μg/L; P = .08). Serious adverse events were comparable in incidence and type between the groups. Mortality was 37% (30 of 81) in the intervention group vs 51% (40 of 79) in the control group (absolute risk reduction, 14%; 95% CI, -2% to 29%; P = .08).

Conclusions and Relevance

In patients in a coma after cardiac arrest, intravenous treatment with acyl-ghrelin was safe and potentially effective to improve neurological outcome. Phase 3 trials are needed for conclusive evidence.

Trial Registration

Clinicaltrialsregister.eu: EUCTR2018-000005-23-NL.

The interaction between insulin resistance and Alzheimer's disease: a review article

Insulin serves multiple functions as a growth-promoting hormone in peripheral tissues. It manages glucose metabolism by promoting glucose uptake into cells and curbing the production of glucose in the liver. Beyond this, insulin fosters cell growth, drives differentiation, aids protein synthesis, and deters degradative processes like glycolysis, lipolysis, and proteolysis. Receptors for insulin and insulin-like growth factor-1 are widely expressed in the central nervous system. Their widespread presence in the brain underscores the varied and critical functions of insulin signaling there. Insulin aids in bolstering cognition, promoting neuron extension, adjusting the release and absorption of catecholamines, and controlling the expression and positioning of gamma-aminobutyric acid (GABA). Importantly, insulin can effortlessly traverse the blood-brain barrier. Furthermore, insulin resistance (IR)-induced alterations in insulin signaling might hasten brain aging, impacting its plasticity and potentially leading to neurodegeneration. Two primary pathways are responsible for insulin signal transmission: the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway, which oversees metabolic responses, and the mitogen-activated protein kinase (MAPK) pathway, which guides cell growth, survival, and gene transcription. This review aimed to explore the potential shared metabolic traits between Alzheimer's disease (AD) and IR disorders. It delves into the relationship between AD and IR disorders, their overlapping genetic markers, and shared metabolic indicators. Additionally, it addresses existing therapeutic interventions targeting these intersecting pathways.

Understanding the Gut-Brain Axis and Its Therapeutic Implications for Neurodegenerative Disorders

The gut-brain axis (GBA) is a complex bidirectional communication network connecting the gut and brain. It involves neural, immune, and endocrine communication pathways between the gastrointestinal (GI) tract and the central nervous system (CNS). Perturbations of the GBA have been reported in many neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), among others, suggesting a possible role in disease pathogenesis. The gut microbiota is a pivotal component of the GBA, and alterations in its composition, known as gut dysbiosis, have been associated with GBA dysfunction and neurodegeneration. The gut microbiota might influence the homeostasis of the CNS by modulating the immune system and, more directly, regulating the production of molecules and metabolites that influence the nervous and endocrine systems, making it a potential therapeutic target. Preclinical trials manipulating microbial composition through dietary intervention, probiotic and prebiotic supplementation, and fecal microbial transplantation (FMT) have provided promising outcomes. However, its clear mechanism is not well understood, and the results are not always consistent. Here, we provide an overview of the major components and communication pathways of the GBA, as well as therapeutic approaches targeting the GBA to ameliorate NDDs.

Endogenous Ghrelin Levels and Perception of Hunger: A Systematic Review and Meta-Analysis

BACKGROUND

Ghrelin is an orexigenic hormone primarily released by the stomach and has 2 isoforms: acylated ghrelin (AG) and de-acylated ghrelin (DAG), that appear to have different functions in humans.

OBJECTIVES

To perform a systematic review and meta-analysis of the association between plasma concentrations of total ghrelin (TG), AG, and DAG and perceptions of hunger in healthy adults.

METHODS

The following criteria were used for inclusion: 1) sample contained adults ≥18 y of age, 2) body mass index [BMI kg/m2] was ≥18.5, 3) ghrelin was sampled through blood, 4) subjective hunger was measured on a validated scale, 5) study reported a Pearson product correlation of ghrelin or had relevant figure(s) for data extraction, 6) participants were healthy with no overt disease, 7) protocols contained no physical activity or weight loss medication that suppressed appetite, 8) interventions were conducted without environmental manipulations. Moderators assessed were age, BMI, percentage of body fat (%BF), macronutrient content of test meals, energy intake (kcals), sex, and ghrelin isoform (AG, DAG, or TG).

RESULTS

The analysis included 47 studies (110 trials, n = 1799, age: 31.4 ± 12.0 y, BMI: 26.0 ± 4.75 kg/m2) and measured AG (n = 47 trials), DAG (n = 12 trials), and TG (n = 51 trials). The overall model indicated that ghrelin concentrations and perceptions of hunger were moderately correlated (r = 0.43, P < 0.001), and ghrelin isoform significantly moderated this relationship (AG: r = 0.60, P < 0.001; TG: r = 0.215, P = 0.01; DAG: r = 0.53, P = 0.695). Other significant moderators included age (b = -0.02, P = 0.01), BMI (b = -0.03, P = 0.05), %BF (b = -0.03, P = 0.05), energy intake (b = 0.0003, P = 0.04), and percentage of carbohydrates of test meals (b = 0.008, P = 0.05).

CONCLUSIONS

Ghrelin is associated with perceptions of hunger in humans, and this relationship is strengthened when AG is isolated; thus, AG may have a large impact on hunger signals in various populations. Future research should attempt to understand the role of DAG in hunger sensations.

Insulin resistance in Alzheimer's disease: The genetics and metabolomics links

Alzheimer's disease (AD) is a neurodegenerative disease with significant socioeconomic burden worldwide. Although genetics and environmental factors play a role, AD is highly associated with insulin resistance (IR) disorders such as metabolic syndrome (MS), obesity, and type two diabetes mellitus (T2DM). These findings highlight a shared pathogenesis. The use of metabolomics as a downstream systems' biology (omics) approach can help to identify these shared metabolic traits and assist in the early identification of at-risk groups and potentially guide therapy. Targeting the shared AD-IR metabolic trait with lifestyle interventions and pharmacological treatments may offer promising AD therapeutic approach. In this narrative review, we reviewed the literature on the AD-IR pathogenic link, the shared genetics and metabolomics biomarkers between AD and IR disorders, as well as the lifestyle interventions and pharmacological treatments which target this pathogenic link.

Dietary restriction in senolysis and prevention and treatment of disease

Aging represents a key risk factor for a plethora of diseases. Targeting detrimental processes which occur during aging, especially before onset of age-related disease, could provide drastic improvements in healthspan. There is increasing evidence that dietary restriction (DR), including caloric restriction, fasting, or fasting-mimicking diets, extend both lifespan and healthspan. This has sparked interest in the use of dietary regimens as a non-pharmacological means to slow aging and prevent disease. Here, we review the current evidence on the molecular mechanisms underlying DR-induced health improvements, including removal of senescent cells, metabolic reprogramming, and epigenetic rejuvenation.

The Interplay between Ghrelin and Microglia in Neuroinflammation: Implications for Obesity and Neurodegenerative Diseases

Numerous studies have shown that microglia are capable of producing a wide range of chemokines to promote inflammatory processes within the central nervous system (CNS). These cells share many phenotypical and functional characteristics with macrophages, suggesting that microglia participate in innate immune responses in the brain. Neuroinflammation induces neurometabolic alterations and increases in energy consumption. Microglia may constitute an important therapeutic target in neuroinflammation. Recent research has attempted to clarify the role of Ghre signaling in microglia on the regulation of energy balance, obesity, neuroinflammation and the occurrence of neurodegenerative diseases. These studies strongly suggest that Ghre modulates microglia activity and thus affects the pathophysiology of neurodegenerative diseases. This review aims to summarize what is known from the current literature on the way in which Ghre modulates microglial activity during neuroinflammation and their impact on neurometabolic alterations in neurodegenerative diseases. Understanding the role of Ghre in microglial activation/inhibition regulation could provide promising strategies for downregulating neuroinflammation and consequently for diminishing negative neurological outcomes.

Gastric Mobility and Gastrointestinal Hormones in Older Patients with Sarcopenia

Sarcopenia has serious clinical consequences and poses a major threat to older people. Gastrointestinal environmental factors are believed to be the main cause. The aim of this study was to describe the relationship between sarcopenia and gastric mobility and to investigate the relationship between sarcopenia and the concentration of gastrointestinal hormones in older patients. Patients aged ≥ 75 years were recruited for this prospective study from August 2018 to February 2019 at the emergency department. The enrolled patients were tested for sarcopenia. Gastric emptying scintigraphy was conducted, and laboratory tests for cholecystokinin(CCK), glucagon-like peptide-1 (GLP-1), peptide YY (PYY), nesfatin, and ghrelin were performed during the fasting period. We enrolled 52 patients with mean age of 86.9 years, including 17 (32.7%) patients in the non-sarcopenia group, 17 (32.7%) patients in the pre-sarcopenia group, and 18 (34.6%) in the sarcopenia group. The mean gastric emptying half-time had no significant difference among three groups. The sarcopenia group had significantly higher fasting plasma concentrations of CCK, GLP-1, and PYY. We concluded that the older people with sarcopenia had significantly higher plasma concentrations of CCK, GLP-1, and PYY. In the elderly population, anorexigenic gastrointestinal hormones might have more important relationships with sarcopenia than orexigenic gastrointestinal hormones.

Diverse and Complementary Effects of Ghrelin and Obestatin

Ghrelin and obestatin are two “sibling proteins” encoded by the same preproghrelin gene but possess an array of diverse and complex functions. While there are ample literature documenting ghrelin’s functions, the roles of obestatin are less clear and controversial. Ghrelin and obestatin have been perceived to be antagonistic initially; however, recent studies challenge this dogma. While they have opposing effects in some systems, they function synergistically in other systems, with many functions remaining debatable. In this review, we discuss their functional relationship under three “C” categories, namely complex, complementary, and contradictory. Their functions in food intake, weight regulation, hydration, gastrointestinal motility, inflammation, and insulin secretion are complex. Their functions in pancreatic beta cells, cardiovascular, muscle, neuroprotection, cancer, and digestive system are complementary. Their functions in white adipose tissue, thermogenesis, and sleep regulation are contradictory. Overall, this review accumulates the multifaceted functions of ghrelin and obestatin under both physiological and pathological conditions, with the intent of contributing to a better understanding of these two important gut hormones.

Pharmacological Management of Apathy in Dementia

Apathy is a highly prevalent symptom of dementia. Despite its association with faster cognitive and functional decline, decreased quality of life and increased mortality, no therapies are currently approved to treat apathy. The objective of this review was to summarize the drugs that have been studied for apathy treatment in patients with dementia (specifically Alzheimer's disease [AD], Huntington's disease [HD] and Parkinson's disease [PD] dementia; dementia with Lewy bodies [DLB]; vascular dementia [VaD]; and frontotemporal dementia [FTD]) based on their putative mechanisms of action. A search for relevant studies was performed using ClinicalTrials.gov and PubMed. Eligible studies were randomized controlled trials that were available in English and included at least one drug intervention and an apathy measure scale. A total of 52 studies that included patients with AD (n = 33 studies), PD (n = 5), HD (n = 1), DLB (n = 1), FTD (n = 3), VaD (n = 1), VaD and AD (n = 4), VaD and mixed dementia (n = 1), and AD, VaD and mixed dementia (n = 3) were eligible for inclusion. These studies showed that methylphenidate, olanzapine, cholinesterase inhibitors, choline alphoscerate, citalopram, memantine, and mibampator are the only beneficial drugs in AD-related apathy. For PD-related apathy, only methylphenidate, rotigotine and rivastigmine showed benefits. Regarding FTD- and DLB-related apathy, initial studies with agomelatine and rivastigmine showed benefits, respectively. As for HD- and only-VaD-related apathy, no drugs demonstrated benefits. With regards to mixed populations, memantine, galantamine and gingko biloba showed effects on apathy in the AD plus VaD populations and nimodipine in the VaD plus mixed dementia populations. Of the drugs with positive results, some are already prescribed to patients with dementia to target other symptoms, some have characteristics-such as medical contraindications (e.g., cardiovascular) and adverse effects (e.g., gastrointestinal disturbances)-that limit their clinical use and some require further study. Future studies should investigate apathy as a primary outcome, making use of appropriate sample sizes and study durations to ensure durability of results. There should also be a consensus on using scales with high test/retest and interrater reliabilities to limit the inconsistencies between clinical trials. In conclusion, there are currently no US FDA-approved drugs that target apathy in dementia, so there is an ongoing need for the development of such drugs.

Ghrelin mediated regulation of neurosynaptic transmitters in depressive disorders

Ghrelin is a peptide released by the endocrine cells of the stomach and the neurons in the arcuate nucleus of the hypothalamus. It modulates both peripheral and central functions. Although ghrelin has emerged as a potent stimulator of growth hormone release and as an orexigenic neuropeptide, the wealth of literature suggests its involvement in the pathophysiology of affective disorders including depression. Ghrelin exhibits a dual role through the advancement and reduction of depressive behavior with nervousness in the experimental animals. It modulates depression-related signals by forming neuronal networks with various neuropeptides and classical neurotransmitter systems. The present review emphasizes the integration and signaling of ghrelin with other neuromodulatory systems concerning depressive disorders. The role of ghrelin in the regulation of neurosynaptic transmission and depressive illnesses implies that the ghrelin system modulation can yield promising antidepressive therapies.

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Ghrelin is the orexigenic type of neuropeptide.

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It binds with the growth hormone secretagogue receptor (GHSR).

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GHSR is ubiquitously present in the various brain regions.

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Ghrelin is involved in the regulation of depression-related behavior.

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The review focuses on the neurotransmission and signaling of ghrelin in neuropsychiatric and depressive disorders.

Circulating levels of ghrelin, galanin, and orexin-A orexigenic neuropeptides in obstructive sleep apnea syndrome

PURPOSE

The orexigenic peptides, ghrelin, galanin, and orexin-A, have an important role in food intake and energy homeostasis and regulate the higher brain functions including the sleep-wake state. Although the interactions of these neuropeptides affect neuroendocrine systems resulting in obesity, a major risk factor for obstructive sleep apnea syndrome (OSAS), the mechanism has not been fully elucidated. The objective of this study was to evaluate the association of serum ghrelin, galanin, and orexin-A levels with OSAS.

METHODS

In this cross-sectional study, patients who underwent one-night polysomnography and conformed to the inclusion criteria were asked to participate. A blood sample was obtained from all participants on the morning of the sleep test to evaluate the serum levels of ghrelin, galanin, and orexin-A using the enzyme-linked immunosorbent assay (ELISA) method. Demographic characteristics, polysomnography data, and serum levels of the participants were recorded and analyzed. Comparison between the OSAS groups was performed by independent sample t-test, Mann-Whitney U test, and Kruskal-Wallis test with post hoc K-W test using SPSS 20.0.

RESULTS

Of 272 patients, those in the OSAS group (n=210) were older than patients in the non-OSAS group (n=62), p < 0.003, and had increased BMI, p < 0.006. Patients with, serum ghrelin, galanin, and orexin-A levels were significantly elevated in patients with OSAS (635.9 pg/mL vs. 420.7 pg/mL, 91.0 pg/mL vs. 60.0 pg/mL, 600.3 pg/mL vs. 485.6 pg/mL, respectively) and found to be higher in patients with severe OSAS than mild and moderate cases (p < 0.01). In multinomial logistic regression to predict the OSAS severity, levels of serum ghrelin (OR = 1.016 [1.010-1.021]; p < 0.001), galanin (OR = 1.050 [1.020-1.081]; p < 0.001), and orexin-A (OR = 1.021 [1.012-1.030]; p < 0.001) were significantly associated only with a moderate level of OSAS.

CONCLUSION

The orexigenic neuropeptides were found to be an independent determinant of the presence of OSAS and correlate with the severity of OSAS. Increased levels of ghrelin, galanin, and orexin-A were associated with the presence of moderate OSAS.

Neuroprotective and Preventative Effects of Molecular Hydrogen

One of the beneficial effects of molecular hydrogen (H₂, hydrogen gas) is neuroprotection and prevention of neurological disorders. It is important and useful if taking H₂ every day can prevent or ameliorate the progression of neurodegenerative disorders, such as Parkinson's disease or Alzheimer's disease, both lacking specific therapeutic drugs. There are several mechanisms of how H₂ protects neuronal damage. Anti-oxidative, anti-inflammatory, and the regulation of the endocrine system via stomach-brain connection seem to play an important role. At the cellular and tissue level, H₂ appears to prevent the production of reactive oxygen species (ROS), and not only hydroxy radical (•OH) but also superoxide. In Parkinson's disease model mice, chronic intake of H₂ causes the release of ghrelin from the stomach. In Alzheimer's disease model mice, sex-different neuroprotection is observed by chronic intake of H₂. In female mice, declines of estrogen and estrogen receptor-β (ERβ) are prevented by H₂, upregulating brain-derived neurotrophic factor (BDNF) and its receptor, tyrosine kinase receptor B (TrkB). The question of how drinking H₂ upregulates the release of ghrelin or attenuates the decline of estrogen remains to be investigated and the mechanism of how H₂ modulates endocrine systems and the fundamental question of what or where is the target of H₂ needs to be elucidated for a better understanding of the effects of H₂.

Ghrelin-Mediated Regeneration and Plasticity After Nervous System Injury

The nervous system is highly vulnerable to different factors which may cause injury followed by an acute or chronic neurodegeneration. Injury involves a loss of extracellular matrix integrity, neuronal circuitry disintegration, and impairment of synaptic activity and plasticity. Application of pleiotropic molecules initiating extracellular matrix reorganization and stimulating neuronal plasticity could prevent propagation of the degeneration into the tissue surrounding the injury. To find an omnipotent therapeutic molecule, however, seems to be a fairly ambitious task, given the complex demands of the regenerating nervous system that need to be fulfilled. Among the vast number of candidates examined so far, the neuropeptide and hormone ghrelin holds within a very promising therapeutic potential with its ability to cross the blood-brain barrier, to balance metabolic processes, and to stimulate neurorepair and neuroactivity. Compared with its well-established systemic effects in treatment of metabolism-related disorders, the therapeutic potential of ghrelin on neuroregeneration upon injury has received lesser appreciation though. Here, we discuss emerging concepts of ghrelin as an omnipotent player unleashing developmentally related molecular cues and morphogenic cascades, which could attenuate and/or counteract acute and chronic neurodegeneration.

Acylated Ghrelin Administration Inhibits Sleeve Gastrectomy-Induced Hippocampal Oxidative Stress, Apoptosis and Tau-Hyperphosphorylation by Activating the PI3K/Akt Pathway

This study investigated the impact of exogenous replacement therapy with acylated ghrelin (AG) post sleeve gastrectomy (SG) on the memory function in rats. In addition, we investigated the possible underlying mechanisms, including the effects on markers of oxidative stress, tau phosphorylation, and apoptosis. Adult male Wistar rats were divided into four groups (N = 18/group) as follows: sham (control), SG, SG+AG (100 μM), and SG+AG+LY294002 (0.25 μg/100 g). We continued all treatments daily for four weeks post-surgery. SG impaired the spatial, retention, and recognition memories as tested by the Morris water maze test, passive avoidance test, and novel object recognition test, respectively. Also, it enhanced the levels of reactive oxygen species and lipid peroxides, reduced glutathione and protein levels of Bcl-2, and increased the levels of Bax and cleaved caspase-3 in the hippocampus. In addition, SG reduced the hippocampal levels of acetylcholine and brain-derived neurotrophic factor. Concomitantly, it inhibited the hippocampal activity of Akt and increased the activity of glycogen synthase kinase 3β and tau protein phosphorylation. Exogenous administration of acylated ghrelin to rats that had undergone SG prevented memory deficits. Also, it prevented the alteration in the above-mentioned biochemical parameters, an effect that was abolished by co-administration of LY294002 (phosphoinositide 3-kinase inhibitor). In conclusion, AG replacement therapy after SG in rats protects them against memory deficits and hippocampal damage by suppressing tau protein phosphorylation, mediated by activating PI3K/Aktinduced inhibition of glycogen synthase kinase 3β.

Acylated Ghrelin as a Multi-Targeted Therapy for Alzheimer's and Parkinson's Disease

Much thought has been given to the impact of Amyloid Beta, Tau and Alpha-Synuclein in the development of Alzheimer's disease (AD) and Parkinson's disease (PD), yet the clinical failures of the recent decades indicate that there are further pathological mechanisms at work. Indeed, besides amyloids, AD and PD are characterized by the culminative interplay of oxidative stress, mitochondrial dysfunction and hyperfission, defective autophagy and mitophagy, systemic inflammation, BBB and vascular damage, demyelination, cerebral insulin resistance, the loss of dopamine production in PD, impaired neurogenesis and, of course, widespread axonal, synaptic and neuronal degeneration that leads to cognitive and motor impediments. Interestingly, the acylated form of the hormone ghrelin has shown the potential to ameliorate the latter pathologic changes, although some studies indicate a few complications that need to be considered in the long-term administration of the hormone. As such, this review will illustrate the wide-ranging neuroprotective properties of acylated ghrelin and critically evaluate the hormone's therapeutic benefits for the treatment of AD and PD.

Dysregulation of Insulin-Linked Metabolic Pathways in Alzheimer's Disease: Co-Factor Role of Apolipoprotein E ɛ4

BACKGROUND

Brain insulin resistance and deficiency are well-recognized abnormalities in Alzheimer's disease (AD) and likely mediators of impaired energy metabolism. Since apolipoprotein E (APOE) is a major risk factor for late-onset AD, it was of interest to examine its potential contribution to altered insulin-linked signaling networks in the brain.

OBJECTIVE

The main goal was to evaluate the independent and interactive contributions of AD severity and APOE ɛ4 dose on brain expression of insulin-related polypeptides and inflammatory mediators of metabolic dysfunction.

METHODS

Postmortem fresh frozen frontal lobe tissue from banked cases with known APOE genotypes and different AD Braak stages were used to measure insulin network polypeptide immunoreactivity with a commercial multiplex enzyme-linked immunosorbent assay (ELISA).

RESULTS

Significant AD Braak stage and APOE genotype-related abnormalities in insulin, C-peptide, gastric inhibitory polypeptide (GIP), glucaton-like peptide-1 (GLP-1), leptin, ghrelin, glucagon, resistin, and plasminogen activator inhibitor-1 (PAI-1) were detected. The main factors inhibiting polypeptide expression and promoting neuro-inflammatory responses included AD Braak stage and APOE ɛ4/ɛ4 rather than ɛ3/ɛ4.

CONCLUSION

This study demonstrates an expanded role for impaired expression of insulin-related network polypeptides as well as neuroinflammatory mediators of brain insulin resistance in AD pathogenesis and progression. In addition, the findings show that APOE has independent and additive effects on these aberrations in brain polypeptide expression, but the impact is decidedly greater for APOE ɛ4/ɛ4 than ɛ3/ɛ4.

The Good, the Bad and the Unknown Aspects of Ghrelin in Stress Coping and Stress-Related Psychiatric Disorders

Ghrelin is a peptide hormone released by specialized X/A cells in the stomach and activated by acylation. Following its secretion, it binds to ghrelin receptors in the periphery to regulate energy balance, but it also acts on the central nervous system where it induces a potent orexigenic effect. Several types of stressors have been shown to stimulate ghrelin release in rodents, including nutritional stressors like food deprivation, but also physical and psychological stressors such as foot shocks, social defeat, forced immobilization or chronic unpredictable mild stress. The mechanism through which these stressors drive ghrelin release from the stomach lining remains unknown and, to date, the resulting consequences of ghrelin release for stress coping remain poorly understood. Indeed, ghrelin has been proposed to act as a stress hormone that reduces fear, anxiety- and depression-like behaviors in rodents but some studies suggest that ghrelin may - in contrast - promote such behaviors. In this review, we aim to provide a comprehensive overview of the literature on the role of the ghrelin system in stress coping. We discuss whether ghrelin release is more than a byproduct of disrupted energy homeostasis following stress exposure. Furthermore, we explore the notion that ghrelin receptor signaling in the brain may have effects independent of circulating ghrelin and in what way this might influence stress coping in rodents. Finally, we examine how the ghrelin system could be utilized as a therapeutic avenue in stress-related psychiatric disorders (with a focus on anxiety- and trauma-related disorders), for example to develop novel biomarkers for a better diagnosis or new interventions to tackle relapse or treatment resistance in patients.

Microbiota modulation as preventative and therapeutic approach in Alzheimer's disease

The gut microbiota coevolves with its host, and numerous factors like diet, lifestyle, drug intake and geographical location continuously modify its composition, deeply influencing host health. Recent studies demonstrated that gut dysbiosis can alter normal brain function through the so-called gut-brain axis, a bidirectional communication network between the central nervous system and the gastrointestinal tract, thus playing a key role in the pathogenesis of neurodegenerative disorders, such as Alzheimer's disease (AD). In this perspective, in the constant search for novel treatments in AD, the rational modulation of gut microbiota composition could represent a promising approach to prevent or delay AD onset or to counteract its progression. Preclinical and human studies on microbiota modulation through oral bacteriotherapy and faecal transplantation showed anti-inflammatory and antioxidant effects, upregulation of plasma concentration of neuroprotective hormones, restoration of impaired proteolytic pathways, amelioration of energy homeostasis with consequent decrease of AD molecular hallmarks and improvement of behavioural and cognitive performances. In this review, we dissect the role of gut microbiota in AD and highlight recent advances in the development of new multitarget strategies for microbiota modulation to be used as possible preventative and therapeutic approaches in AD.

Correlation of lower 2 h C-peptide and elevated evening cortisol with high levels of depression in type 2 diabetes mellitus

BACKGROUND

A number of studies have explored the association between depression and ghrelin, leptin, and cortisol; further, postprandial C-peptide levels have a therapeutic effect on type 2 diabetes mellitus (T2DM). However, the relationship between C-peptide and depression in patients with diabetes, remains unclear. The aim of this study was to explore the association between depression and ghrelin, leptin, cortisol, and C-peptide in patients with diabetes.

METHODS

We enrolled 50 adults without T2DM, 77 non-depressed adults with T2DM (free of Axis-I psychiatric disorders as assessed using the Mental Illness Needs Index (MINI), Patient Health Questionnaire (PHQ-9 score ≤ 4)) and 59 patients with T2DM and depression (PHQ-9 ≥ 7 and positive by the Structured Clinical Interview for DSM-5). The age range of the participants was 45-59 years of age. We compared the above three groups and explored the association between ghrelin, leptin, cortisol, C-peptide, and depression in patients with diabetes. A post-hoc power-analysis was finished.

RESULTS

Compared with the non-depression T2DM group, the depression T2DM group had significantly higher blood glucose fluctuations. Further, compared with the non-depression T2DM and non-diabetic groups, the depression T2DM group had significantly lower levels of post-meal 2-h C-peptide and elevated evening cortisol (p < 0.01). Regression analysis revealed a significant negative correlation between depression severity and 2-h postprandial C-peptide in patients with diabetes (p < 0.01) and a significant positive correlation with midnight cortisol levels (p < 0.01). A post hoc power analysis showed that we had an adequate sample size and met the minimum requirement to attain 80% power. A post hoc power calculation also demonstrated that this study basically achieved power of 80% at 5% alpha level.

CONCLUSIONS

Our findings indicate a correlation of low fasting levels of 2-h C-peptide as well as higher midnight cortisol levels with higher depression severity in middle-aged patients with T2DM.

Selective neuronal vulnerability in Alzheimer's disease

Alzheimer's disease (AD) is defined by a deficiency in specific behavioural and/or cognitive domains, pointing to selective vulnerabilities of specific neurons from different brain regions. These vulnerabilities can be compared across neuron subgroups to identify the most vulnerable neuronal types, regions, and time points for further investigation. Thus, the relevant organizational frameworks for brain subgroups will hold great values for a clear understanding of the progression in AD. Presently, the neuronal vulnerability has yet urgently required to be elucidated as not yet been clearly defined. It is suggested that cell-autonomous and non-cell-autonomous mechanisms can affect the neuronal vulnerability to stressors, and in turn modulates AD progression. This review examines cell-autonomous and non-cell-autonomous mechanisms that contribute to the neuronal vulnerability. Collectively, the cell-autonomous mechanisms seem to be the primary drivers responsible for initiating specific stressor-related neuronal vulnerability with pathological changes in certain brain areas, which then utilize non-cell-autonomous mechanisms and result in subsequent progression of AD. In summary, this article has provided a new perspective on the preventative and therapeutic options for AD.

Physiological Effect of Ghrelin on Body Systems

Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.

Ghrelin in Alzheimer's disease: Pathologic roles and therapeutic implications

Ghrelin, which has many important physiological roles, such as stimulating food intake, regulating energy homeostasis, and releasing insulin, has recently been studied for its roles in a diverse range of neurological disorders. Despite the several functions of ghrelin in the central nervous system, whether it works as a therapeutic agent for neurological dysfunction has been unclear. Altered levels and various roles of ghrelin have been reported in Alzheimer's disease (AD), which is characterized by the accumulation of misfolded proteins resulting in synaptic loss and cognitive decline. Interestingly, treatment with ghrelin or with the agonist of ghrelin receptor showed attenuation in several cases of AD-related pathology. These findings suggest the potential therapeutic implications of ghrelin in the pathogenesis of AD. In the present review, we summarized the roles of ghrelin in AD pathogenesis, amyloid beta (Aβ) homeostasis, tau hyperphosphorylation, neuroinflammation, mitochondrial deficit, synaptic dysfunction and cognitive impairment. The findings from this review suggest that ghrelin has a novel therapeutic potential for AD treatment. Thus, rigorously designed studies are needed to establish an effective AD-modifying strategy.

Ghrelin-mediated improvements in the metabolic phenotype in the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is a heritable neurodegenerative disorder, characterised by metabolic disturbances, along with cognitive and psychiatric impairments. Targeting metabolic HD dysfunction via the maintenance of body weight and fat mass and restoration of peripheral energy metabolism can improve the progression of neurological symptoms. In this respect, we focused on the therapeutic potential of the orexigenic peptide hormone ghrelin, which plays an important role in promoting a positive energy balance. In the present study, we found a significant disruption of circadian metabolic regulation in a R6/2 mouse HD model in the late stage of disease. Daily circadian rhythms of activity, energy expenditure, respiratory exchange ratio and feeding were strongly attenuated in R6/2 mice. During the rest phase, R6/2 mice had a higher total activity, elevated energy expenditure and excessive water consumption compared to control mice. We also found that, in the late stage of disease, R6/2 mice had ghrelin axis deficiency as a result of low circulating ghrelin levels, in addition to down-regulation of the ghrelin receptor and several key signalling molecules in the hypothalamus, as well as a reduced responsiveness to exogenous peripheral ghrelin. We demonstrated that, in pre-symptomatic mice, responsiveness to ghrelin is preserved. Chronic ghrelin treatment efficiently increased lean body mass and decreased the energy expenditure and fat utilisation of R6/2 mice in the early stage of disease. In addition, ghrelin treatment was also effective in the normalisation of drinking behaviour and the rest activity of these mice. Ghrelin treatment could provide a novel therapeutic possibility for delaying disease progression; however, deficiency in ghrelin receptor expression could limit its therapeutic potential in the late stage of disease.

Association between use of internet and the cognitive function in older adults, populational longitudinal study EpiFloripa Idoso

OBJECTIVE

To estimate the association between the internet and the gain or loss cognite along of four years in older adults.

METHODS

Longitudinal study, a population-based, with older adults residents in a capital of southern Brazil (≥ 60 years) surveyed in 2009-10 (baseline) and in 2013-14 (follow-up). The outcome was assessed by clinically significant gain or loss of four or more points in the score of the Mini Mental State Examination between the two interviews. The use of internet was measured longitudinally (maintained or not internet usage, stop use of internet, started using the internet, retained the use of internet). Odds Ratios (OR) were estimated adjusted for sex, age, household income, education level and cognitive screening at baseline.

RESULTS

Respondents were 1.705 older adults in 2009-10 and 1.197 in 2013-14. There was a significant association between keep using internet and cognitive performance, with greater chance of cognitive gain (OR= 3.3; 95%CI 1.1 - 9.8) and lower cognitive impairment (OR = 0.39; 95%CI 0.17 - 0.88) for older adults who kept using the internet.

CONCLUSION

Older adults who continue using the internet were more likely to gain significant cognitive and lower cognitive loss. Topromote the internet use in older adults can help a strategy for cognitive stimulation in older adults.

Neuropeptides Exert Neuroprotective Effects in Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by cognitive deficits and neuronal loss. Deposition of beta-amyloid peptide (Aβ) causes neurotoxicity through the formation of plaques in brains of Alzheimer's disease. Numerous studies have indicated that the neuropeptides including ghrelin, neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), neuropeptide Y, substance P and orexin are closely related to the pathophysiology of Alzheimer's disease. The levels of neuropeptides and their receptors change in Alzheimer's disease. These neuropeptides exert neuroprotective roles mainly through preventing Aβ accumulation, increasing neuronal glucose transport, increasing the production of neurotrophins, inhibiting endoplasmic reticulum stress and autophagy, modulating potassium channel activity and hippocampal long-term potentiation. Therefore, the neuropeptides may function as potential drug targets in the prevention and cure of Alzheimer's disease.

Neuroendocrinology of Adipose Tissue and Gut-Brain Axis

Food intake and energy expenditure are closely regulated by several mechanisms which involve peripheral organs and nervous system, in order to maintain energy homeostasis.Short-term and long-term signals express the size and composition of ingested nutrients and the amount of body fat, respectively. Ingested nutrients trigger mechanical forces and gastrointestinal peptide secretion which provide signals to the brain through neuronal and endocrine pathways. Pancreatic hormones also play a role in energy balance exerting a short-acting control regulating the start, end, and composition of a meal. In addition, insulin and leptin derived from adipose tissue are involved in long-acting adiposity signals and regulate body weigh as well as the amount of energy stored as fat over time.This chapter focuses on the gastrointestinal-, pancreatic-, and adipose tissue-derived signals which are integrated in selective orexigenic and anorexigenic brain areas that, in turn, regulate food intake, energy expenditure, and peripheral metabolism.

Ghrelin Causes a Decline in GABA Release by Reducing Fatty Acid Oxidation in Cortex

Lipid metabolism, specifically fatty acid oxidation (FAO) mediated by carnitine palmitoyltransferase (CPT) 1A, has been described to be an important actor of ghrelin action in hypothalamus. However, it is not known whether CPT1A and FAO mediate the effect of ghrelin on the cortex. Here, we show that ghrelin produces a differential effect on CPT1 activity and γ-aminobutyric acid (GABA) metabolism in the hypothalamus and cortex of mice. In the hypothalamus, ghrelin enhances CPT1A activity while GABA transaminase (GABAT) activity, a key enzyme in GABA shunt metabolism, is unaltered. However, in cortex CPT1A activity and GABAT activity are reduced after ghrelin treatment. Furthermore, in primary cortical neurons, ghrelin reduces GABA release through a CPT1A reduction. By using CPT1A floxed mice, we have observed that genetic ablation of CPT1A recapitulates the effect of ghrelin on GABA release in cortical neurons, inducing reductions in mitochondrial oxygen consumption, cell content of citrate and α-ketoglutarate, and GABA shunt enzyme activity. Taken together, these observations indicate that ghrelin-induced changes in CPT1A activity modulate mitochondrial function, yielding changes in GABA metabolism. This evidence suggests that the action of ghrelin on GABA release is region specific within the brain, providing a basis for differential effects of ghrelin in the central nervous system.

The association of short-term memory and cognitive impairment with ghrelin, leptin, and cortisol levels in non-diabetic and diabetic elderly individuals

AIMS

This study assessed short-term memory and biochemical indicators with the levels of ghrelin, leptin, and cortisol between cognitive impairment and normal older adults with or without diabetes.

METHODS

We enrolled 286 older adults (aged 65-85 years) with or without diabetes from the local community. Short-term memory was assessed using pictures of common objects; cognitive functioning was assessed using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). The physiological indexes assessed were plasma levels of fasting ghrelin and leptin, ghrelin level at 2_h after breakfast, 24-h urinary cortisol value, body mass index, and plasma cortisol levels at 8:00 a.m., 4:00 p.m., and 12:00 p.m.

RESULTS

In both non-diabetic and diabetic subjects, short-term memory was significantly lower in the impaired cognition group (5.99 ± 2.90 in non-diabetic subjects and 4.71 ± 2.14 in diabetic subjects) than in the normal cognition group (8.14 ± 2.23 in non-diabetic subjects and 7.82 ± 3.37 in diabetic subjects). Baseline ghrelin level was significantly lower in the impaired cognition group (9.07 ± 1.13 ng/mL in non-diabetic subjects and 7.76 ± 1.34 ng/mL in diabetic subjects) than in the normal cognition group (10.94 ± 1.53 ng/mL in non-diabetic subjects and 9.93 ± 1.76 ng/mL in diabetic subjects); plasma cortisol levels at 8:00 a.m., 4:00 p.m., and 12:00 p.m. were significantly higher in the impaired cognition group than in the normal cognition group, while no significant difference was observed in plasma levels of fasting leptin between different groups.

CONCLUSIONS

Fasting plasma ghrelin and cortisol levels may be markers of cognitive decline and memory loss. It is possible that adjusting their levels may have a therapeutic effect, and this should be investigated in future studies.

Ischemic stroke and select adipose-derived and sex hormones: a review

Ischemic stroke is the fifth leading cause of death in the USA and is the leading cause of serious, long-term disability worldwide. The principle sex hormones (estrogen, progesterone, and testosterone), both endogenous and exogenous, have profound effects on various stroke outcomes and have become the focus of a number of studies evaluating risk factors and treatment options for ischemic stroke. In addition, the expression of other hormones that may influence stroke outcome, including select adipose-derived hormones (adiponectin, leptin, and ghrelin), can be regulated by sex hormones and are also the focus of several ischemic stroke studies. This review aims to summarize some of the preclinical and clinical studies investigating the principle sex hormones, as well as select adipose-derived hormones, as risk factors or potential treatments for ischemic stroke. In addition, the potential for relaxin, a lesser studied sex hormone, as a novel treatment option for ischemic stroke is explored.

Metabolic Biomarkers of Ageing in C57BL/6J Wild-Type and Flavin-Containing Monooxygenase 5 (FMO5)-Knockout Mice

It was recently demonstrated in mice that knockout of the flavin-containing monooxygenase 5 gene, Fmo5, slows metabolic ageing via pleiotropic effects. We have now used an NMR-based metabonomics approach to study the effects of ageing directly on the metabolic profiles of urine and plasma from male, wild-type C57BL/6J and Fmo5^-/- (FMO5 KO) mice back-crossed onto the C57BL/6J background. The aim of this study was to identify metabolic signatures that are associated with ageing in both these mouse lines and to characterize the age-related differences in the metabolite profiles between the FMO5 KO mice and their wild-type counterparts at equivalent time points. We identified a range of age-related biomarkers in both urine and plasma. Some metabolites, including urinary 6-hydroxy-6-methylheptan-3-one (6H6MH3O), a mouse sex pheromone, showed similar patterns of changes with age, regardless of genetic background. Others, however, were altered only in the FMO5 KO, or only in the wild-type mice, indicating the impact of genetic modifications on mouse ageing. Elevated concentrations of urinary taurine represent a distinctive, ageing-related change observed only in wild-type mice.

SLAB51 Probiotic Formulation Activates SIRT1 Pathway Promoting Antioxidant and Neuroprotective Effects in an AD Mouse Model

The gut-brain axis is a bidirectional communication network functionally linking the gut and the central nervous system (CNS). Based on this, the rational manipulation of intestinal microbiota represents a novel attractive therapeutic strategy for the treatment of CNS-associated disorders. In this study, we explored the properties of a probiotic formulation (namely SLAB51) in counteracting brain oxidative damages associated with Alzheimer's disease (AD). Specifically, transgenic AD mice (3xTg-AD) were treated with SLAB51 and the effects on protein oxidation, neuronal antioxidant defence and repair systems were monitored, with the particular focus on the role of SIRT1-related pathways. We demonstrated that SLAB51 markedly reduced oxidative stress in AD mice brain by activating SIRT1-dependent mechanisms, thus representing a promising therapeutic adjuvant in AD treatment.

Caloric restriction stimulates autophagy in rat cortical neurons through neuropeptide Y and ghrelin receptors activation

Caloric restriction is an anti-aging intervention known to extend lifespan in several experimental models, at least in part, by stimulating autophagy. Caloric restriction increases neuropeptide Y (NPY) in the hypothalamus and plasma ghrelin, a peripheral gut hormone that acts in hypothalamus to modulate energy homeostasis. NPY and ghrelin have been shown to be neuroprotective in different brain areas and to induce several physiological modifications similar to those induced by caloric restriction. However, the effect of NPY and ghrelin in autophagy in cortical neurons is currently not known. Using a cell culture of rat cortical neurons we investigate the involvement of NPY and ghrelin in caloric restriction-induced autophagy. We observed that a caloric restriction mimetic cell culture medium stimulates autophagy in rat cortical neurons and NPY or ghrelin receptor antagonists blocked this effect. On the other hand, exogenous NPY or ghrelin stimulate autophagy in rat cortical neurons. Moreover, NPY mediates the stimulatory effect of ghrelin on autophagy in rat cortical neurons. Since autophagy impairment occurs in aging and age-related neurodegenerative diseases, NPY and ghrelin synergistic effect on autophagy stimulation may suggest a new strategy to delay aging process.

Interactions between metabolic, reward and cognitive processes in appetite control: Implications for novel weight management therapies

Traditional models of appetite control have emphasised the role of parallel homeostatic and hedonic systems, but more recently the distinction between independent homeostatic and hedonic systems has been abandoned in favour of a framework that emphasises the cross talk between the neurochemical substrates of the two systems. In addition, evidence has emerged more recently, that higher level cognitive functions such as learning, memory and attention play an important role in everyday appetite control and that homeostatic signals also play a role in cognition. Here, we review this evidence and present a comprehensive model of the control of appetite that integrates cognitive, homeostatic and reward mechanisms. We discuss the implications of this model for understanding the factors that may contribute to disordered patterns of eating and suggest opportunities for developing more effective treatment approaches for eating disorders and weight management.

Ghrelin rescues skeletal muscle catabolic profile in the R6/2 mouse model of Huntington's disease

Accumulating evidence suggests altered energy metabolism as a key feature in Huntington’s disease (HD) pathology. Hyper-catabolism, including weight loss and muscle atrophy, is seen in HD patients and HD mouse models. Metabolic hormones are key players, not only in energy metabolism, but also in neurodegenerative processes. Ghrelin, a gut peptide-hormone, plays an important role in regulating energy metabolism, stimulating appetite, and affects brain function and increases neuronal survival. The R6/2 mouse model of HD has previously been shown to exhibit progressive weight loss, dysregulated glucose metabolism, skeletal muscle atrophy and altered body composition. In this study, we targeted energy metabolism in R6/2 mice using ghrelin administration, with the primary aim to delay weight loss and reduce muscle atrophy. We also evaluated glucose metabolism and behaviour. We here demonstrate that ghrelin administration (subcutaneous 150 μg/kg daily injections) for 4 weeks, reversed the catabolic gene expression profile (increased expression of Caspase 8, Traf-5 and Creb1) seen in R6/2 mouse skeletal muscle. Skeletal muscle morphology was also improved with ghrelin, and importantly, ghrelin administration normalized behavioural deficits in R6/2 mice. Taken together, our findings encourage further studies targeting metabolism in HD.

Association of plasma ghrelin levels and ghrelin rs4684677 polymorphism with mild cognitive impairment in type 2 diabetic patients

BACKGROUND AND AIMS

People with insulin resistance and type 2 diabetes mellitus (T2DM) are at increased risks of cognitive impairment. We aimed to investigate the association of plasma ghrelin levels and ghrelin rs4684677 polymorphism with mild cognitive impairment (MCI) in T2DM patients.

RESULTS

In addition to elevated glycosylated hemoglobin (HbA1c), fasting blood glucose (FBG) and homeostasis model assessment of insulin resistance (HOMA-IR), T2DM patients with MCI had decreased plasma ghrelin levels compared with their healthy-cognition subjects (all p < 0.05). Further logistic regression analysis showed that ghrelin level was one of independent factors for MCI in T2DM patients (p < 0.05). Moreover, partial correlation analysis demonstrated that ghrelin levels were positively associated with the scores of Montreal Cognitive Assessment (r = 0.196, p = 0.041) and Auditory Verbal Learning Test-delayed recall (r = 0.197, p = 0.040) after adjustment for HbA1c, FBG and HOMA-IR, wherein the latter represented episodic memory functions. No significant differences were found for the distributions of genotype and allele of ghrelin rs4684677 polymorphism between MCI and control group.

MATERIALS AND METHODS

A total of 218 T2DM patients, with 112 patients who satisfied the MCI diagnostic criteria and 106 who exhibited healthy cognition, were enrolled in this study. Demographic characteristics, clinical variables and cognitive performances were extensively assessed. Plasma ghrelin levels and ghrelin rs4684677 polymorphism were also determined.

CONCLUSIONS

Our results suggest that decreased ghrelin levels are associated with MCI, especially with episodic memory dysfunction in T2DM populations.

Suppression of adiponectin receptor 1 promotes memory dysfunction and Alzheimer's disease-like pathologies

Recent studies on neurodegeneration have focused on dysfunction of CNS energy metabolism as well as proteinopathies. Adiponectin (ADPN), an adipocyte-derived hormone, plays a major role in the regulation of insulin sensitivity and glucose homeostasis in peripheral organs via adiponectin receptors. In spite of accumulating evidence that adiponectin has neuroprotective properties, the underlying role of adiponectin receptors has not been illuminated. Here, using gene therapy-mediated suppression with shRNA, we found that adiponectin receptor 1 (AdipoR1) suppression induces neurodegeneration as well as metabolic dysfunction. AdipoR1 knockdown mice exhibited increased body weight and abnormal plasma chemistry and also showed spatial learning and memory impairment in behavioural studies. Moreover, AdipoR1 suppression resulted in neurodegenerative phenotypes, diminished expression of the neuronal marker NeuN, and increased expression and activity of caspase 3. Furthermore, AD-like pathologies including insulin signalling dysfunction, abnormal protein aggregation and neuroinflammatory responses were highly exhibited in AdipoR1 knockdown groups, consistent with brain pathologies in ADPN knockout mice. Together, these results suggest that ADPN-AdipoR1 signalling has the potential to alleviate neurodegenerative diseases such as Alzheimer’s diseases.

Identification and Characterization of a New Series of Ghrelin O-Acyl Transferase Inhibitors

Ghrelin O-acyl transferase (GOAT; MBOAT4) catalyzes O-acylation at serine-3 of des-acyl ghrelin. Acyl ghrelin is secreted by stomach X/A-like cells and plays a role in appetite and metabolism. Therefore, GOAT has been expected to be a novel antiobesity target because it is responsible for acyl ghrelin production. Here, we report homogeneous time-resolved fluorescence (HTRF) and enzyme-linked immunosorbent assay (ELISA) methods utilizing human GOAT-expressing microsomes as a novel high-throughput assay system for the discovery of hit compounds and optimization of lead compounds. Hit compounds exemplified by compound A (2-[(2,4-dichlorobenzyl)sulfanyl]-1,3-benzoxazole-5-carboxylic acid) were identified by high-throughput screening using the HTRF assay and confirmed to have GOAT inhibitory activity using the ELISA. Based on the hit compound information, the novel lead compound (compound B, (4-chloro-6-{[2-methyl-6-(trifluoromethyl)pyridin-3-yl]methoxy}-1-benzothiophen-3-yl)acetic acid) was synthesized and exhibited potent GOAT inhibition with oral bioavailability. Both the hit compound and lead compound showed octanoyl-CoA competitive inhibitory activity. Moreover, these two compounds decreased acyl ghrelin production in the stomach of mice after their oral administration. These novel findings demonstrate that GOAT is a druggable target, and its inhibitors are promising antiobesity drugs.

Central insulin modulates food valuation via mesolimbic pathways

Central insulin is thought to act at the neural interface between metabolic and hedonic drives to eat. Here, using pharmacological fMRI, we show that intranasal insulin (INI) changes the value of food cues through modulation of mesolimbic pathways. Overnight fasted participants rated the palatability of food pictures and attractiveness of non-food items (control) after receiving INI or placebo. We report that INI reduces ratings of food palatability and value signals in mesolimbic regions in individuals with normal insulin sensitivity. Connectivity analyses reveal insulinergic inhibition of forward projections from the ventral tegmentum to the nucleus accumbens. Importantly, the strength of this modulation predicts decrease of palatability ratings, directly linking neural findings to behaviour. In insulin-resistant participants however, we observe reduced food values and aberrant central insulin action. These data demonstrate how central insulin modulates the cross-talk between homeostatic and non-homeostatic feeding systems, suggesting that dysfunctions of these neural interactions may promote metabolic disorders.

The influence of insulin on food preference and the corresponding underlying neural circuits are unknown in humans. Here, the authors show that increasing insulin changes food preference by modulating mesolimbic neural circuits, and that this pattern is changed in insulin-resistant individuals.

Assessments of plasma ghrelin levels in the early stages of parkinson's disease

BACKGROUND

Gastrointestinal symptoms are early events in Parkinson's disease (PD). The gastrointestinal hormone ghrelin was neuroprotective in the nigrostriatal dopamine system. The objective of this study was to assess ghrelin levels in the early stages of PD.

METHODS

Plasma was collected in the fasting state in 291 PD patients in stages 1-3 and 303 age- and sex-matched healthy controls. Additional samples were taken in the glucose response test to assess nutrition-related ghrelin levels in 20 PD patients and 20 healthy controls. The enzyme-linked immunosorbent assay was used to measure total and active plasma ghrelin levels.

RESULTS

We reported that total and active plasma ghrelin levels were decreased in PD, although there was no difference across progressive PD stages. Postprandial ghrelin suppression and preprandial peak responses were both attenuated in PD.

CONCLUSIONS

Plasma ghrelin levels were decreased in PD; however, this event might be irrelevant to PD progression. Ghrelin responses to meals were also impaired in PD. © 2017 International Parkinson and Movement Disorder Society.

Ghrelin ameliorates nerve growth factor Dysmetabolism and inflammation in STZ-induced diabetic rats

Diabetic encephalopathy is characterized by cognitive impairment and neuroinflammation, deficient neurotrophic support, and neuronal and synaptic loss. Ghrelin, a 28 amino acid peptide, is associated with neuromodulation and cognitive improvement, which has been considered as a potential protective agent for several neurodegenerative diseases. Here we sought to investigate the role of ghrelin in preventing diabetic-related neuropathology. We found that ghrelin attenuated astrocytic activation and reduced levels of interleukin-6 and tumor necrosis factor-α in streptozotocin-induced diabetic rats. In addition, ghrelin inhibited p38 mitogen-associated protein kinase activation. The upregulation of nerve growth factor (NGF) precursor and matrix metalloproteinase (MMP)-9 and downregulation of mature NGF and MMP-7 in the diabetic brain were reversed by ghrelin. Treatment with ghrelin elevated synaptophysin expression and synaptic density in diabetic rats. Taken together, our results demonstrate that ghrelin ameliorates diabetes-related neurodegeneration by preventing NGF dysmetabolism and synaptic degeneration through regulating MMP levels as well as inhibiting neuroinflammation.

Microbiota modulation counteracts Alzheimer's disease progression influencing neuronal proteolysis and gut hormones plasma levels

Gut microbiota has a proven role in regulating multiple neuro-chemical pathways through the highly interconnected gut-brain axis. Oral bacteriotherapy thus has potential in the treatment of central nervous system-related pathologies, such as Alzheimer’s disease (AD). Current AD treatments aim to prevent onset, delay progression and ameliorate symptoms. In this work, 3xTg-AD mice in the early stage of AD were treated with SLAB51 probiotic formulation, thereby affecting the composition of gut microbiota and its metabolites. This influenced plasma concentration of inflammatory cytokines and key metabolic hormones considered therapeutic targets in neurodegeneration. Treated mice showed partial restoration of two impaired neuronal proteolytic pathways (the ubiquitin proteasome system and autophagy). Their cognitive decline was decreased compared with controls, due to a reduction in brain damage and reduced accumulation of amyloid beta aggregates. Collectively, our results clearly prove that modulation of the microbiota induces positive effects on neuronal pathways that are able to slow down the progression of Alzheimer’s disease.

Future Treatment of Constipation-associated Disorders: Role of Relamorelin and Other Ghrelin Receptor Agonists

There is an unmet need for effective pharmacological therapies for constipation, a symptom that significantly deteriorates patients’ quality of life and impacts health care. Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor and has been shown to exert prokinetic effects on gastrointestinal (GI) motility via the vagus and pelvic nerves. The pharmacological potential of ghrelin is hampered by its short half-life. Ghrelin receptor (GRLN-R) agonists with enhanced pharmacokinetics were thus developed. Centrally penetrant GRLN-R agonists stimulate defecation and improve impaired lower GI transit in animals and humans. This review summarizes the current knowledge on relamorelin, a potent ghrelin mimetic, and other GRLN-R analogs which are in preclinical or clinical stages of development for the management of disorders with underlying GI hypomotility, like constipation.