Ghrelin is neuroprotective in Parkinson's disease: molecular mechanisms of metabolic neuroprotection

Ghrelin/GHSR System in Depressive Disorder: Pathologic Roles and Therapeutic Implications

Depression is the most common chronic mental illness and is characterized by low mood, insomnia, and affective disorders. However, its pathologic mechanisms remain unclear. Numerous studies have suggested that the ghrelin/GHSR system may be involved in the pathophysiologic process of depression. Ghrelin plays a dual role in experimental animals, increasing depressed behavior and decreasing anxiety. By combining several neuropeptides and traditional neurotransmitter systems to construct neural networks, this hormone modifies signals connected to depression. The present review focuses on the role of ghrelin in neuritogenesis, astrocyte protection, inflammatory factor production, and endocrine disruption in depression. Furthermore, ghrelin/GHSR can activate multiple signaling pathways, including cAMP/CREB/BDNF, PI3K/Akt, Jak2/STAT3, and p38-MAPK, to produce antidepressant effects, given which it is expected to become a potential therapeutic target for the treatment of depression.

Function and Mechanism of Abscisic Acid on Microglia-Induced Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD), as a neurologically implemented disease with complex etiological factors, has a complex and variable pathogenesis. Accompanying further research, neuroinflammation has been found to be one of the possible factors in its pathogenesis. Microglia, as intrinsic immune cells in the brain, play an important role in maintaining microenvironmental homeostasis in the brain. However, over-activation of neurotoxic microglia in PD promotes neuroinflammation, which further increases dopaminergic (DA) neuronal damage and exacerbates the disease process. Therefore, targeting and regulating the functional state of microglia is expected to be a potential avenue for PD treatment. In addition, plant extracts have shown great potential in the treatment of neurodegenerative disorders due to their abundant resources, mild effects, and the presence of multiple active ingredients. However, it is worth noting that some natural products have certain toxic side effects, so it is necessary to pay attention to distinguish medicinal ingredients and usage and dosage when using to avoid aggravating the progression of diseases. In this review, the roles of microglia with different functional states in PD and the related pathways inducing microglia to transform into neuroprotective states are described. At the same time, it is discussed that abscisic acid (ABA) may regulate the polarization of microglia by targeting them, promote their transformation into neuroprotective state, reduce the neuroinflammatory response in PD, and provide a new idea for the treatment of PD and the selection of drugs.

GUCY2C signaling limits dopaminergic neuron vulnerability to toxic insults

Mitochondrial dysfunction and reactive oxygen species (ROS) accumulation within the substantia nigra pars compacta (SNpc) are central drivers of dopaminergic (DA) neuron death in Parkinson's disease (PD). Guanylyl cyclases and their second messenger cyclic (c)GMP support mitochondrial function, protecting against ROS and promoting cell survival in several tissues. However, the role of the guanylyl cyclase-cGMP axis in defining the vulnerability of DA neurons in the SNpc in PD remains unclear, in part due to the challenge of manipulating cGMP levels selectively in midbrain DA neurons. In that context, guanylyl cyclase C (GUCY2C), a receptor primarily expressed by intestinal epithelial cells, was discovered recently in midbrain DA neurons. Here, we demonstrate that GUCY2C promotes mitochondrial function, reducing oxidative stress and protecting DA neurons from degeneration in the 1-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine (MPTP) mouse model. GUCY2C is overexpressed in the SNpc in PD patients and in mice treated with MPTP, possibly reflecting a protective response to oxidative stress. Moreover, cGMP signaling protects against oxidative stress, mitochondrial impairment, and cell death in cultured DA neurons. These observations reveal a previously unexpected role for the GUCY2C-cGMP signaling axis in controlling mitochondrial dysfunction and toxicity in SNpc DA neurons, highlighting the therapeutic potential of targeting DA neuron GUCY2C to prevent neurodegeneration in PD.

Association Between Body Mass Index Changes and All-Cause Mortality in Parkinson's Disease

Background

Whether body weight changes are associated with Parkinson's disease (PD) mortality remains uncertain.

Objective

To investigate the association between changes in body mass index (BMI) and all-cause mortality in patients with PD.

Methods

This nationwide cohort study enrolled 20,703 individuals with new-onset PD (ICD-10 code: G20 and a rare intractable disease registration code: V124) who underwent health screening program by the Korean National Health Insurance Service within two years from pre- and post-PD diagnosis. We identified nine BMI change groups based on three BMI status: underweight (BMI < 18.5 kg/m2), normal or overweight (18.5 kg/m2≤BMI < 25 kg/m2), and obese (BMI≥25 kg/m2).

Results

Of 20,703 individuals, 3,789 (18.0%) died during the follow-up period. Excessive weight loss to underweight in the obese group (hazard ratio [HR] = 3.36, 95% CI:1.60-7.08), weight loss in the normal to overweight group (HR = 2.04, 95% CI:1.75-2.39), sustained underweight status (HR = 2.05, 95% CI:1.67-2.52), and weight gain from underweight to normal or overweight (HR = 1.52, 95% CI:1.15-2.02) were associated with increased mortality. Sustained obese status (HR = 0.80, 95% CI:0.74-0.87) and weight gain in the normal to overweight group (HR = 0.82, 95% CI:0.71-0.95) were associated with reduced mortality.

Conclusions

We found that BMI change at diagnosis was associated with mortality in patients with PD. Specifically, being underweight either before or after diagnosis as well as experiencing weight loss, were associated with increased mortality. These findings provide valuable insights for weight management planning in PD, highlighting the importance of individualized approach that consider pre-diagnosis BMI.

GUCY2C signaling limits dopaminergic neuron vulnerability to toxic insults

Mitochondrial dysfunction and reactive oxygen species (ROS) accumulation within the substantia nigra pars compacta (SNpc) are central drivers of dopaminergic (DA) neuron death in Parkinson's disease (PD). Guanylyl cyclases, and their second messengers cyclic (c)GMP, support mitochondrial function, protecting against ROS and promoting cell survival in a number of tissues. However, the role of the guanylyl cyclase-cGMP axis in defining the vulnerability of DA neurons in the SNpc in PD remains unclear, in part due to the challenge of manipulating cGMP levels selectively in midbrain DA neurons. In that context, guanylyl cyclase C (GUCY2C), a receptor primarily expressed by intestinal epithelial cells, was discovered recently in midbrain DA neurons. Here, we demonstrate that GUCY2C promotes mitochondrial function, reducing oxidative stress and protecting DA neurons from degeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of neurodegeneration. GUCY2C is overexpressed in the SNpc in PD patients and in mice treated with MPTP, possibly reflecting a protective response to oxidative stress. Moreover, cGMP signaling protects against oxidative stress, mitochondrial impairment, and cell death in cultured DA neurons. These observations reveal a previously unexpected role for the GUCY2C-cGMP signaling axis in controlling mitochondrial dysfunction and toxicity in nigral DA neurons, highlighting the therapeutic potential of targeting DA neuron GUCY2C to prevent neurodegeneration in PD.

Targeting neuroendocrine abnormalities in Parkinson's disease with exercise

Parkinson's Disease (PD) is a prevalent and complex age-related neurodegenerative condition for which there are no disease-modifying treatments currently available. The pathophysiological process underlying PD remains incompletely understood but increasing evidence points to multiple system dysfunction. Interestingly, the past decade has produced evidence that exercise not only reduces signs and symptoms of PD but is also potentially neuroprotective. Characterizing the mechanistic pathways that are triggered by exercise and lead to positive outcomes will improve understanding of how to counter disease progression and symptomatology. In this review, we highlight how exercise regulates the neuroendocrine system, whose primary role is to respond to stress, maintain homeostasis and improve resilience to aging. We focus on a group of hormones - cortisol, melatonin, insulin, klotho, and vitamin D - that have been shown to associate with various non-motor symptoms of PD, such as mood, cognition, and sleep/circadian rhythm disorder. These hormones may represent important biomarkers to track in clinical trials evaluating effects of exercise in PD with the aim of providing evidence that patients can exert some behavioral-induced control over their disease.

Defective mitophagy and the etiopathogenesis of Alzheimer's disease

Accumulation of impaired mitochondria and energy metabolism disorders are non-negligible features of both aging and age-related neurodegeneration, including Alzheimer’s disease (AD). A growing number of studies suggest that mitophagy disorders play an important role in AD occurrence and development. The interaction between mitophagy deficits and Aβ or Tau pathology may form a vicious cycle and cause neuronal damage and death. Elucidating the molecular mechanism of mitophagy and its role in AD may provide insights into the etiology and mechanisms of AD. Defective mitophagy is a potential target for AD prevention and treatment.

Demystifying the Neuroprotective Role of Neuropeptides in Parkinson's Disease: A Newfangled and Eloquent Therapeutic Perspective

Parkinson's disease (PD) refers to one of the eminently grievous, preponderant, tortuous nerve-cell-devastating ailments that markedly impacts the dopaminergic (DArgic) nerve cells of the midbrain region, namely the substantia nigra pars compacta (SN-PC). Even though the exact etiopathology of the ailment is yet indefinite, the existing corroborations have suggested that aging, genetic predisposition, and environmental toxins tremendously influence the PD advancement. Additionally, pathophysiological mechanisms entailed in PD advancement encompass the clumping of α-synuclein inside the lewy bodies (LBs) and lewy neurites, oxidative stress, apoptosis, neuronal-inflammation, and abnormalities in the operation of mitochondria, autophagy lysosomal pathway (ALP), and ubiquitin-proteasome system (UPS). The ongoing therapeutic approaches can merely mitigate the PD-associated manifestations, but until now, no therapeutic candidate has been depicted to fully arrest the disease advancement. Neuropeptides (NPs) are little, protein-comprehending additional messenger substances that are typically produced and liberated by nerve cells within the entire nervous system. Numerous NPs, for instance, substance P (SP), ghrelin, neuropeptide Y (NPY), neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), nesfatin-1, and somatostatin, have been displayed to exhibit consequential neuroprotection in both in vivo and in vitro PD models via suppressing apoptosis, cytotoxicity, oxidative stress, inflammation, autophagy, neuronal toxicity, microglia stimulation, attenuating disease-associated manifestations, and stimulating chondriosomal bioenergetics. The current scrutiny is an effort to illuminate the neuroprotective action of NPs in various PD-experiencing models. The authors carried out a methodical inspection of the published work procured through reputable online portals like PubMed, MEDLINE, EMBASE, and Frontier, by employing specific keywords in the subject of our article. Additionally, the manuscript concentrates on representing the pathways concerned in bringing neuroprotective action of NPs in PD. In sum, NPs exert substantial neuroprotection through regulating paramount pathways indulged in PD advancement, and consequently, might be a newfangled and eloquent perspective in PD therapy.

Ghrelin attenuates methylmercury-induced oxidative stress in neuronal cells

Methylmercury (MeHg) is a global pollutant, which can cause damage to the central nervous system at both high-acute and chronic-low exposures, especially in vulnerable populations, such as children and pregnant women. Nowadays, acute-high poisoning is rare. However, chronic exposure to low MeHg concentrations via fish consumption remains a health concern. Current therapeutic strategies for MeHg poisoning are based on the use of chelators. However, these therapies have limited efficacy. Ghrelin is a gut hormone with an important role in regulating physiologic processes. It has been reported that ghrelin plays a protective role against the toxicity of several xenobiotics. Here, we explored the role of ghrelin as a putative protector against MeHg-induced oxidative stress. Our data show that ghrelin was able to ameliorate MeHg-induced reactive oxygen species (ROS) production in primary neuronal hypothalamic and hippocampal cultures. An analogous effect was observed in mouse hypothalamic neuronal GT 1-7 cells. Using this model, our novel findings show that antioxidant protection of ghrelin against MeHg is mediated by glutathione upregulation and induction of the NRF2/NQO1 pathway.

Are We What We Eat? Impact of Diet on the Gut-Brain Axis in Parkinson's Disease

Parkinson’s disease is characterized by motor and non-motor symptoms, such as defects in the gut function, which may occur before the motor symptoms. To date, there are therapies that can improve these symptoms, but there is no cure to avoid the development or exacerbation of this disorder. Dysbiosis of gut microbiota could have a crucial role in the gut–brain axis, which is a bidirectional communication between the central nervous system and the enteric nervous system. Diet can affect the microbiota composition, impacting gut–brain axis functionality. Gut microbiome restoration through probiotics, prebiotics, synbiotics or other dietary means could have the potential to slow PD progression. In this review, we will discuss the influence of diet on the bidirectional communication between gut and brain, thus supporting the hypothesis that this disorder could begin in the gut. We also focus on how food-based therapies might then have an influence on PD and could ameliorate non-motor as well as motor symptoms.

The Interactions between Adipose Tissue Secretions and Parkinson's disease; The Role of Leptin

Leptin is a hormone that regulates appetite by acting on receptors in the hypothalamus, where it modifies food intake to maintain equilibrium with the body energy resources. Leptin and its receptors are widely distributed in the central nervous system, suggesting that they may give neuronal survival signals. The potential of leptin to decrease/increase neuronal damage and neuronal plasticity in Parkinson's diseases (PD) is the subject of this review, which outlines our current knowledge of how leptin acts in the brain. Although leptin-mediated neuroprotective signaling results in neuronal death prevention, it can affect neuroinflammatory cascades and also neuronal plasticity which contribute to PD pathology. Other neuroprotective molecules, such as insulin and erythropoietin, share leptin-related signaling cascades, and therefore constitute a component of the neurotrophic effects mediated by endogenous hormones. With the evidence that leptin dysregulation causes increased neuronal vulnerability to damage in PD, using leptin as a target for therapeutic modification is an appealing and realistic option.

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.

Mitochondrial dysfunction and apoptosis are attenuated through activation of AMPK/GSK-3β/PP2A pathway in Parkinson's disease

Parkinson's disease (PD) is a common neurological disorder worldwide, characterized by loss of dopaminergic neurons and decrease of dopamine content. Mitochondria plays an important role in the development of PD. Adenosine 5'-monophosphate-activated protein kinase (AMPK), glycogen synthase kinase 3 (GSK-3β) and protein phosphatase 2A (PP2A) are all key proteins that regulate mitochondrial metabolism and apoptosis, and they are involved in a variety of neurodegenerative diseases. Here, we aimed to explore the involvement of mitochondrial dysfunction and apoptosis in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine hydrochloride (MPTP)-induced PD mice and MPP+ iodide-induced PC12 cells. MPTP-induced mice were subjected to behavioral testing to assess PD-like behaviors. Various molecular biological techniques including ELISA, Western blot, TUNEL assay, flow cytometry, and the important instruments Seahorse XF24 Extracellular and high performance liquid chromatography (HPLC), were used to identify the underlying molecular events of mitochondria. Treatment with the AMPK activator GSK621 dramatically ameliorated PD by increasing the levels of dopamine and rescuing the loss of dopaminergic neurons, which is dependent on the mitochondrial pathway. Moreover, regulation of AMPK/GSK-3β/PP2A pathway-related proteins by GSK621 was partially inhibited the development of PD, suggesting a negative feedback loop exists between AMPK action and mitochondrial dysfunction-mediated apoptosis. Our data preliminarily indicated that mitochondrial dysfunction and apoptosis in the pathogenesis of PD might be mediated by AMPK/GSK-3β/PP2A pathway action, which might be a promising new option for future therapy of PD.

Association between body weight variability and incidence of Parkinson disease: A nationwide, population-based cohort study

BACKGROUND AND PURPOSE

Although body weight variability has been associated with mortality, cardiovascular disease, and dementia, the relationship between body weight variability and Parkinson disease (PD) has rarely been studied. We aimed to investigate the longitudinal association between body weight variability and PD incidence.

METHODS

A nationwide population-based, cohort study was conducted using the database from the Health Insurance Review and Assessment Service of the whole Korean population. We analyzed 2,815,135 participants (≥40 years old, mean age = 51.7 ± 8.6 years, 66.8% men) without a previous PD diagnosis. We determined individual body weight variability from baseline weight and follow-up visits. We used Cox proportional hazards regression models.

RESULTS

The highest quartile group was associated with increased PD incidence compared with the lowest quartile group after adjustment for confounding factors (hazard ratio [HR] = 1.18, 95% confidence interval [CI] = 1.08-1.29). In contrast, baseline body mass index, baseline waist circumference, and waist circumference variability were not associated with increased PD incidence. In the body weight loss group, individuals within the quartile of the highest variation in body weight showed a higher HR of PD risk than those within other quartiles (HR = 1.41, 95% CI = 1.18-1.68).

CONCLUSIONS

Body weight variability, especially weight loss, was associated with higher PD incidence. This finding has important implications for clinicians and supports the need for preventative measures and surveillance for PD in individuals with fluctuating body weight.

Ghrelin protects against rotenone-induced cytotoxicity: Involvement of mitophagy and the AMPK/SIRT1/PGC1α pathway

Parkinson's disease (PD) is the second most common neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra and the deposition of Lewy bodies. Mitochondrial dysfunction, oxidative stress, and autophagy dysfunction are involved in the pathogenesis of PD. Ghrelin is a brain-gut peptide that has been reported that protected against 1-methyl-4-phenyl-1,2,3,6- tetrahydropyran (MPTP)/MPP⁺-induced toxic effects. In the present work, human neuroblastoma SH-SY5Y cells were exposed to rotenone as a PD model to explore the underlying mechanism of ghrelin. We found that ghrelin inhibited rotenone-induced cytotoxicity, mitochondrial dysfunction, and apoptosis by improving cell viability, increasing the ratio of red/green of JC-1, inhibiting the production of reactive oxidative species (ROS), and regulating Bcl-2, Bax, Cytochrome c, caspase-9, and caspase-3 expression. Besides, ghrelin promoted mitophagy accompanied by up-regulating microtubule-associated protein 1 Light Chain 3B-II/I(LC3B-II/I) and Beclin1 but decreasing the expression of p62. Moreover, ghrelin promoted PINK1/Parkin mitochondrial translocation. Additionally, we investigated that ghrelin activated the AMPK/SIRT1/PGC1α pathway and pharmacological inhibition of AMPK and SIRT1 abolished the cytoprotection of ghrelin, decreased the level of mitophagy, and PINK1/Parkin mitochondrial translocation. Taken together, our findings suggested that mitophagy and AMPK/SIRT1/PGC1α pathways were related to the cytoprotection of ghrelin. These findings provided novel insights into the underlying mechanisms of ghrelin, further mechanistic studies on preclinical and clinical levels are required to be conducted with ghrelin to avail and foresee it as a potential agent in the treatment and management of PD.

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.

The Emerging Role of Neuropeptides in Parkinson's Disease

Parkinson’s disease (PD), the second most common age-related neurodegenerative disease, results from the loss of dopamine neurons in the substantia nigra. This disease is characterized by cardinal non-motor and motor symptoms. Several studies have demonstrated that neuropeptides, such as ghrelin, neuropeptide Y, pituitary adenylate cyclase-activating polypeptide, substance P, and neurotensin, are related to the onset of PD. This review mainly describes the changes in these neuropeptides and their receptors in the substantia nigra-striatum system as well as the other PD-related brain regions. Based on several in vitro and in vivo studies, most neuropeptides play a significant neuroprotective role in PD by preventing caspase-3 activation, decreasing mitochondrial-related oxidative stress, increasing mitochondrial biogenesis, inhibiting microglial activation, and anti-autophagic activity. Thus, neuropeptides may provide a new strategy for PD therapy.

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.

Teaghrelin Protects SH-SY5Y Cells against MPP+-Induced Neurotoxicity through Activation of AMPK/SIRT1/PGC-1α and ERK1/2 Pathways

The prevalence and incidence of Parkinson’s disease (PD), an age-related neurodegenerative disease, are higher among elderly people. Independent of etiology, dysfunction and loss of dopaminergic neurons are common pathophysiological changes in PD patients with impaired motor and non-motor function. Currently, preventive or therapeutic treatment for combating PD is limited. The ghrelin axis and ghrelin receptor have been implicated in the preservation of dopaminergic neurons and have potential implications in PD treatment. Teaghrelin, a compound originating from Chin-Shin Oolong tea, exhibits ghrelin agonist activity. In this study, the neuroprotective potential of teaghrelin against PD was explored in a cell model in which human neuroblastoma SH-SY5Y cells were treated with the mitochondrial toxin 1-methyl-4-phenylpyridinium (MPP⁺). Upon MPP⁺ exposure, SH-SY5Y cells exhibited decreased mitochondrial complex I activity and apoptotic cell death. Teaghrelin activated AMP-activated protein kinase (AMPK)/sirtuin 1(SIRT1)/peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1α (PGC-1α) and extracellular signal–regulated kinases 1 and 2 (ERK1/2) pathways to antagonize MPP⁺-induced cell death. Herein, we propose that teaghrelin is a potential candidate for the therapeutic treatment of PD.

Developmental stage-dependent relationships between ghrelin levels and hippocampal white matter connections in low-weight anorexia nervosa and atypical anorexia nervosa

INTRODUCTION

Disruptions in homeostatic and hedonic food motivation are proposed to underlie anorexia nervosa (AN) and atypical AN, restrictive eating disorders which commonly onset in puberty. Ghrelin, a neuroprotective hormone that drives hedonic eating is increased in AN and is expressed in the hippocampus. White matter (WM) undergoes significant change during puberty in regions involved in food motivation, particularly WM tracts connected with the hippocampus. The association between ghrelin and WM region of interest (ROI) with hippocampal connections in restrictive eating disorders, particularly in adolescence during key neurodevelopmental growth, is unknown.

METHODS

We evaluated fasting plasma ghrelin and WM microstructure (measured by free-water corrected fractional anisotropy (FA-t)) in WM ROIs with hippocampal connections - the fornix and the hippocampal portion of the cingulum - in 56 adolescent females (age range: 11.9 - 22.1 y; mean: 19.0 y) with low-weight eating disorders including AN and atypical AN (N = 36) and healthy controls (N = 20).

RESULTS

FA-t in the fornix or hippocampal portion of the fornix did not differ between groups. Ghrelin was higher in AN/atypical AN vs. HC and was positively correlated with puberty stage in the AN/atypical AN group, but not the HC group. The correlation between ghrelin and FA-t in the fornix was significantly different in females with AN/atypical AN compared to controls. In AN/atypical AN, pubertal stage moderated the relation between fasting plasma ghrelin and FA-t in the fornix: higher fasting ghrelin was associated with lower FA-t in the fornix in late-post-puberty, but was not associated with FA-t in the early to mid stages of puberty.

CONCLUSIONS

In post-pubertal females with low-weight AN/atypical AN, higher levels of ghrelin are associated with lower FA-t in the fornix. This relationship is not evident in the early to mid stages of puberty in AN/atypical AN or in HC, and may reflect a lack of possible neuroprotective effects of ghrelin in late-post puberty only. Understanding the effects of ghrelin on WM microstructure longitudinally and following recovery from AN/Atypical AN and how this differs across pubertal stages will be an important next step. These findings could ultimately inform treatment staging and aid in diagnosis and detection of AN/atypical AN.

Effects of exogenous ghrelin administration and ghrelin receptor blockade, in combination with alcohol, on peripheral inflammatory markers in heavy-drinking individuals: Results from two human laboratory studies

The ghrelin system has been garnering interest for its role in different neuropsychiatric disorders, including alcohol use disorder (AUD). Accordingly, targeting the ghrelin system is under investigation as a potential novel therapeutic approach. While alcohol provokes the immune system and inflammatory responses, ghrelin has potent immunomodulatory and anti-inflammatory properties. The present study aimed to shed light on the "crosstalk" between ghrelin and inflammation by examining the effects of exogenous ghrelin administration and ghrelin receptor blockade on peripheral inflammatory markers in the context of two human laboratory studies with alcohol administration. Non-treatment-seeking, heavy-drinking individuals with alcohol dependence, the majority of whom were African American males, were enrolled. In the first randomized, crossover, double-blind, placebo-controlled human laboratory study, participants underwent two experimental paradigms - an intravenous alcohol self-administration (IV-ASA) and an intravenous alcohol clamp (IV-AC) - each consisting of two counterbalanced sessions (ghrelin, placebo). A loading dose of intravenous ghrelin (3 mcg/kg) or placebo, followed by a continuous ghrelin (16.9 ng/kg/min) or placebo infusion was administered. In the second dose-escalating, single-blind, placebo-controlled human laboratory phase 1b study, participants were dosed with an oral ghrelin receptor blocker (PF-5190457) and underwent an oral alcohol challenge. Repeated blood samples were collected, and plasma concentrations of the following inflammatory markers were measured: C-reactive protein (CRP), interleukin (IL)-6, IL-10, IL-18, and tumor necrosis factor alpha (TNF-α). During the IV-ASA experiment, significant drug × time interaction effects were observed for IL-6 (F_3,36 = 3.345, p = 0.030) and IL-10 (F_3,53.2 = 4.638, p = 0.006), indicating that ghrelin, compared to placebo, significantly reduced blood concentrations of the proinflammatory cytokine IL-6, while increasing blood concentrations of the anti-inflammatory cytokine IL-10. No significant drug × time interaction effects were observed during the IV-AC experiment, possibly because of its much shorter duration and/or smaller sample. Treatment with PF-5190457, compared to placebo, had no significant effect on the inflammatory markers investigated. In conclusion, a supraphysiologic pharmacological challenge with exogenous ghrelin in heavy-drinking individuals produced anti-inflammatory effects in the context of intravenous alcohol administration. On the contrary, ghrelin receptor blockade did not lead to any change in the inflammatory markers included in this study. Mechanistic studies are required to better understand the interaction between ghrelin, alcohol, and inflammatory processes.

Ghrelin promotes midbrain neural stem cells differentiation to dopaminergic neurons through Wnt/β-catenin pathway

Ghrelin plays a neuroprotective role in the process of dopaminergic (DAergic) neurons degeneration in Parkinson's disease (PD). However, it still largely unknown whether ghrelin could affect the midbrain neural stem cells (mbNSCs) from which DAergic neurons are originated. In the present study, we observed that ghrelin enhanced mbNSCs proliferation, and promoted neuronal differentiation especially DAergic neuron differentiation both in vitro and ex vivo. The messenger RNA levels of Wnt1, Wnt3a, and glial cell line-derived neurotrophic factor were increased in response to the ghrelin treatment. Results showed that Wnt/β-catenin pathway was relevant to this DAergic neuron differentiation induced by ghrelin. Our finding gave a new evidence that ghrelin may enable clinical therapies for PD by its neurogenesis role.

The Complex Signaling Pathways of the Ghrelin Receptor

The ghrelin receptor (GhrR) is known for its strong orexigenic effects in pharmacological doses and has long been considered as a promising target for the treatment of obesity. Several antagonists have been developed to decrease the orexigenic signaling, but none of these have been approved for the treatment of obesity because of adverse effects and lack of efficacy. Heterodimerization and biased signaling are important concepts for G-protein coupled receptor (GPCR) signaling, and the influence of these aspects on the GhrR may be important for feeding behavior and obesity. GhrR has been described to heterodimerize with other GPCRs, such as the dopamine receptors 1 and 2, leading to a modulation of the signaling properties of both dimerization partners. Another complicating factor of GhrR-mediated signaling is its ability to activate several different signaling pathways on ligand stimulation. Importantly, some ligands have shown to be "biased" or "functionally selective," implying that the ligand favors a particular signaling pathway. These unique signaling properties could have a sizeable impact on the physiological functions of the GhrR system. Importantly, heterodimerization may explain why the GhrR is expressed in areas of the brain that are difficult for peptide ligands to access. One possibility is that the purpose of GhrR expression is to modulate the function of other receptors in addition to merely being independently activated. We suggest that a deeper understanding of the signaling properties of the GhrR will facilitate future drug discovery in the areas of obesity and weight management.

Diet in Parkinson's Disease: Critical Role for the Microbiome

Background: Parkinson's disease (PD) is the most common movement disorder affecting up to 1% of the population above the age of 60 and 4–5% of those above the age of 85. Little progress has been made on efforts to prevent disease development or halt disease progression. Diet has emerged as a potential factor that may prevent the development or slow the progression of PD. In this review, we discuss evidence for a role for the intestinal microbiome in PD and how diet-associated changes in the microbiome may be a viable approach to prevent or modify disease progression.

Methods: We reviewed studies demonstrating that dietary components/foods were related to risk for PD. We reviewed evidence for the dysregulated intestinal microbiome in PD patients including abnormal shifts in the intestinal microbiota composition (i.e., dysbiosis) characterized by a loss of short chain fatty acid (SCFA) bacteria and increased lipopolysaccharide (LPS) bacteria. We also examined several candidate mechanisms by which the microbiota can influence PD including the NLRP3 inflammasome, insulin resistance, mitochondrial function, vagal nerve signaling.

Results: The PD-associated microbiome is associated with decreased production of SCFA and increased LPS and it is believed that these changes may contribute to the development or exacerbation of PD. Diet robustly impacts the intestinal microbiome and the Western diet is associated with increased risk for PD whereas the Mediterranean diet (including high intake of dietary fiber) decreases PD risk. Mechanistically this may be the consequence of changes in the relative abundance of SCFA-producing or LPS-containing bacteria in the intestinal microbiome with effects on intestinal barrier function, endotoxemia (i.e., systemic LPS), NLRP3 inflammasome activation, insulin resistance, and mitochondrial dysfunction, and the production of factors such as glucagon like peptide 1 (GLP-1) and brain derived neurotrophic factor (BDNF) as well as intestinal gluconeogenesis.

Conclusions: This review summarizes a model of microbiota-gut-brain-axis regulation of neuroinflammation in PD including several new mechanisms. We conclude with the need for clinical trials in PD patients to test this model for beneficial effects of Mediterranean based high fiber diets.

Body mass index, diabetes, and the risk of Parkinson's disease

BACKGROUND

There are conflicting findings in the literature regarding the association of body mass index and incidence of PD.

OBJECTIVES

This study aimed to investigate the association of body mass index with the risk of PD incidence while considering diabetes mellitus as a major confounding factor.

METHODS

We examined 6,800,601 individuals (aged ≥40 years) who were free of PD using the database of the Korean National Health Insurance Service. Cox proportional hazard regression was used to assess adjusted hazard ratios for PD with adjustment for potential confounders. Stratified analyses by diabetes status were also performed.

RESULTS

A total of 33,443 individuals were diagnosed with PD during the follow-up period (7.3 years). An increased risk of PD incidence was observed in the underweight group versus the normal group (adjusted hazard ratio: 1.28; 95% confidence interval: 1.21-1.36), whereas a decreased risk of PD incidence was observed (adjusted hazard ratio: 0.88; 95% confidence interval: 0.88-0.93) in the obese group and (adjusted hazard ratio: 0.77; 95% confidence interval: 0.72-0.82) in the severely obese group. This association consistently persisted after stratification by diabetes mellitus status, with the steepest downward slope for PD risk present with increasing body mass index in patients with severe diabetes mellitus (i.e., long duration or complication).

CONCLUSIONS

Being underweight and diabetes mellitus were associated with an increased risk of PD incidence, and effect of being underweight was more prominent in those with diabetes mellitus, with a dose-response relationship existing according to diabetes mellitus status. Further research is warranted to understand the clinical implications of the significant interaction between being underweight and diabetes mellitus status in the development of PD. © 2020 International Parkinson and Movement Disorder Society.

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.

Neuroprotective Effects of Brain-Gut Peptides: A Potential Therapy for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease and is typically associated with progressive motor and non-motor dysfunctions. Currently, dopamine replacement therapy is mainly used to relieve the motor symptoms, while its long-term application can lead to various complications and does not cure the disease. Numerous studies have demonstrated that many brain-gut peptides have neuroprotective effects in vivo and in vitro, and may be a promising treatment for PD. In recent years, some progress has been made in studies on the neuroprotective effects of some newly-discovered brain-gut peptides, such as glucagon-like peptide 1, pituitary adenylate cyclase activating polypeptide, nesfatin-1, and ghrelin. However, there is still no systematic review on the neuroprotective effects common to these peptides. Thus, here we review the neuroprotective effects and the associated mechanisms of these four peptides, as well as other brain-gut peptides related to PD, in the hope of providing new ideas for the treatment of PD and related clinical research.

Multiple Beneficial Effects of Ghrelin Agonist, HM01 on Homeostasis Alterations in 6-Hydroxydopamine Model of Parkinson's Disease in Male Rats

Background and objective: Developing therapy for non-motor symptoms of Parkinson’s disease (PD) is important for improving patients’ quality of life. Previously, we reported that the ghrelin receptor agonist, HM01 normalized the decreased 4-h fecal output and levodopa-inhibited gastric emptying in 6-OHDA rats, and activated selective areas in brain and spinal cord. In this study, we evaluated whether chronic HM01 treatment influences motor functions and/or has beneficial effects on non-motor symptoms including alterations of body weight and composition, defecation, feeding and water intake in 6-OHDA rats.

Methods: Male rats were microinjected unilaterally into the medial forebrain bundle with either vehicle or 6-OHDA. Three weeks later, we assessed basal body weight, and 24-h fecal output (pellets, weight, dry weight and water content), water intake and food intake (ingested and spillage). Then, HM01 (3 mg/kg) or vehicle was given per gavage daily for 10–12 days and the same parameters were re-assessed daily. Motor behavior (stepping and rotations tests), body composition were monitored before and after the HM01 treatment.

Results: 6-OHDA rats showed motor deficits in rotation test induced by apomorphine and stepping test. They also displayed a significant reduction in body weight, water consumption, fecal weight and water content and an increase in food spillage compared to vehicle microinjected rats. Daily oral treatment of HM01 did not modify motor alterations compared to vehicle but significantly increased the body weight, fat mass, and 24-h fecal weight, fecal water content, food and water intake in 6-OHDA rats, while HM01 had no significant effect in vehicle microinjected rats. Fecal weight and water content were both correlated with water intake, but not with food intake. Fat mass, but not body weight, was correlated with food intake. HM01 effects were significant after 24 h and remained similar during the treatment.

Conclusions: Chronic treatment with ghrelin agonist, HM01 improved several non-motor symptoms in the rat PD model induced by 6-OHDA lesion including the decrease in body weight, water consumption, fecal weight and water content, and increased food intake while not improving the motor deficits. These findings provide pre-clinical evidence of potential benefits of ghrelin agonists to alleviate non-motor symptoms in PD patients.

Dopamine neuronal protection in the mouse Substantia nigra by GHSR is independent of electric activity

Objective

Dopamine neurons in the Substantia nigra (SN) play crucial roles in control of voluntary movement. Extensive degeneration of this neuronal population is the cause of Parkinson's disease (PD). Many factors have been linked to SN DA neuronal survival, including neuronal pacemaker activity (responsible for maintaining basal firing and DA tone) and mitochondrial function. Dln-101, a naturally occurring splice variant of the human ghrelin gene, targets the ghrelin receptor (GHSR) present in the SN DA cells. Ghrelin activation of GHSR has been shown to protect SN DA neurons against 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine (MPTP) treatment. We decided to compare the actions of Dln-101 with ghrelin and identify the mechanisms associated with neuronal survival.

Methods

Histologial, biochemical, and behavioral parameters were used to evaluate neuroprotection. Inflammation and redox balance of SN DA cells were evaluated using histologial and real-time PCR analysis. Designer Receptors Exclusively Activated by Designer Drugs (DREADD) technology was used to modulate SN DA neuron electrical activity and associated survival. Mitochondrial dynamics in SN DA cells was evaluated using electron microscopy data.

Results

Here, we report that the human isoform displays an equivalent neuroprotective factor. However, while exogenous administration of mouse ghrelin electrically activates SN DA neurons increasing dopamine output, as well as locomotion, the human isoform significantly suppressed dopamine output, with an associated decrease in animal motor behavior. Investigating the mechanisms by which GHSR mediates neuroprotection, we found that dopamine cell-selective control of electrical activity is neither sufficient nor necessary to promote SN DA neuron survival, including that associated with GHSR activation. We found that Dln101 pre-treatment diminished MPTP-induced mitochondrial aberrations in SN DA neurons and that the effect of Dln101 to protect dopamine cells was dependent on mitofusin 2, a protein involved in the process of mitochondrial fusion and tethering of the mitochondria to the endoplasmic reticulum.

Conclusions

Taken together, these observations unmasked a complex role of GHSR in dopamine neuronal protection independent on electric activity of these cells and revealed a crucial role for mitochondrial dynamics in some aspects of this process.

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Dln101 is a human splice-variant of the ghrelin gene with different expression pattern.

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Ghrelin and Dln101 display equivalent levels of neuroprotection of SN DA cells.

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Modulation of electrical activity of SN DA cells is not relevant for neuroprotection.

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Mitochondrial fusion protein 2 (MFN 2) blocks DLN101-induced mitochondrial fusion in SN DA neurons and prevents DLN101-induced neuroprotection.

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.

Effects of paeoniflorin on neurobehavior, oxidative stress, brain insulin signaling, and synaptic alterations in intracerebroventricular streptozotocin-induced cognitive impairment in mice

Paeoniflorin (PF) is a natural monoterpene glycoside in Paeonia lactiflora pall with anti-diabetic, antioxidant, anti-inflammatory, and neuro-protective properties. This study was designed to investigate the neuroprotective effects of PF against cognitive deficits induced by intracerebroventricular (ICV) injection of streptozotocin (STZ) in mice. STZ was injected twice intracerebroventrically (3 mg/kg ICV) on alternate days (day 1 and day 3) in mice. Daily treatment with PF (10 mg/kg per day, intraperitoneally) starting from the first dose of STZ for 21 days showed an improvement in ICV-STZ induced cognitive deficits as assessed by novel object recognition and Morris water maze (MWM) test. PF significantly attenuated STZ induced mitochondrial dysfunction manifested by dramatically elevated cytochrome c oxidase activity and ATP synthesis, and restoration of the mitochondrial membrane potential (MMP), and oxidative stress in hippocampus and in the cortex compared to control. Moreover, PF treatment also markedly increased synaptic density in the CA1 region of the hippocampus compared to control. Furthermore, PF ameliorated defective insulin signaling by up-regulating p-PI3K and p-Akt protein expression while downregulating p-IRS-1 protein expression. Taken together, the outcomes of the current study suggest the therapeutic potential of PF in the cognitive deficits induced by ICV-STZ.

Evaluating the Levels of Nesfatin-1 and Ghrelin Hormones in Patients with Moderate and Severe Major Depressive Disorders

OBJECTIVE

The goal of this study was to evaluate the importance of nesfatin-1, acylated and des-acylated ghrelin, which are known as energy regulatory hormones, in patients with moderate and severe major depression disorders (MDD).

METHODS

Thirty patients with a moderate degree of MDD and, 30 with a severe degree of MDD were used as participants in this study. Thirty subjects without depression were enrolled as a control group. The Hamilton Depression Rating Scale was used to classify the patients with MDD. Blood samples were taken after overnight fasting. The plasma nesfatin-1, acylated ghrelin and des-acylated ghrelin levels were measured using a commercially available enzyme-linked immunosorbent assay kit.

RESULTS

The nesfatin-1, the acylated ghrelin and the des-acylated ghrelin levels were found to be significantly higher in severe MDD (3.92±0.4 ng/mL; 88.56±4.1 pg/mL; 962.76±67 pg/mL) as compared to moderate MDD (2.91±0.5 ng/mL; 77.63±4.19 pg/mL; 631.16±35 pg/mL), or the control (1.01±0.3 ng/mL; 58.60±9.00 pg/mL; 543.13±62 pg/mL), respectively.

CONCLUSION

Although nesfatin-1 and ghrelin are known as adversely affecting the hormones involving the regulation of appetite and food intake, they all increase in depressive patients and are even associated with the severity of the disease. In clinical medicine, the evaluation of the role of nesfatin-1 and ghrelin in endocrine and neu-roendocrine regulation of major metabolic functions is an important key mechanism in solving numerous diseases associated with endocrine and neuroendocrine disturbance. Increased levels of nesfatin-1 and ghrelin may also be important criteria in describing the prognoses of the patients and the effectiveness of the treatments.

Weight Loss and Malnutrition in Patients with Parkinson's Disease: Current Knowledge and Future Prospects

Parkinson's Disease (PD) is currently considered a systemic neurodegenerative disease manifested with not only motor but also non-motor symptoms. In particular, weight loss and malnutrition, a set of frequently neglected non-motor symptoms, are indeed negatively associated with the life quality of PD patients. Moreover, comorbidity of weight loss and malnutrition may impact disease progression, giving rise to dyskinesia, cognitive decline and orthostatic hypotension, and even resulting in disability and mortality. Nevertheless, the underlying mechanism of weight loss and malnutrition in PD remains obscure and possibly involving multitudinous, exogenous or endogenous, factors. What is more, there still does not exist any weight loss and malnutrition appraision standards and management strategies. Given this, here in this review, we elaborate the weight loss and malnutrition study status in PD and summarize potential determinants and mechanisms as well. In conclusion, we present current knowledge and future prospects of weight loss and malnutrition in the context of PD, aiming to appeal clinicians and researchers to pay a closer attention to this phenomena and enable better management and therapeutic strategies in future clinical practice.

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.

Involvement of PPARγ in the Anticonvulsant Activity of EP-80317, a Ghrelin Receptor Antagonist

Ghrelin, des-acyl ghrelin and other related peptides possess anticonvulsant activities. Although ghrelin and cognate peptides were shown to physiologically regulate only the ghrelin receptor, some of them were pharmacologically proved to activate the peroxisome proliferator-activated receptor gamma (PPARγ) through stimulation of the scavenger receptor CD36 in macrophages. In our study, we challenged the hypothesis that PPARγ could be involved in the anticonvulsant effects of EP-80317, a ghrelin receptor antagonist. For this purpose, we used the PPARγ antagonist GW9662 to evaluate the modulation of EP-80317 anticonvulsant properties in two different models. Firstly, the anticonvulsant effects of EP-80317 were studied in rats treated with pilocarpine to induce status epilepticus (SE). Secondly, the anticonvulsant activity of EP-80317 was ascertained in the repeated 6-Hz corneal stimulation model in mice. Behavioral and video electrocorticographic (ECoG) analyses were performed in both models. We also characterized levels of immunoreactivity for PPARγ in the hippocampus of 6-Hz corneally stimulated mice. EP-80317 predictably antagonized seizures in both models. Pretreatment with GW9662 counteracted almost all EP-80317 effects both in mice and rats. Only the effects of EP-80317 on power spectra of ECoGs recorded during repeated 6-Hz corneal stimulation were practically unaffected by GW9662 administration. Moreover, GW9662 alone produced a decrease in the latency of tonic-clonic seizures and accelerated the onset of SE in rats. Finally, in the hippocampus of mice treated with EP-80317 we found increased levels of PPARγ immunoreactivity. Overall, these results support the hypothesis that PPARγ is able to modulate seizures and mediates the anticonvulsant effects of EP-80317.

Favorable Impact on Stress-Related Behaviors by Modulating Plasma Butyrylcholinesterase

In the last decade, it has become clear that the neuropeptide “ghrelin” and its principal receptor have a large impact on anxiety and stress. Our recent studies have uncovered a link between plasma butyrylcholinesterase (BChE) and ghrelin. BChE actually turns out to be the key regulator of this peptide. This article reviews our recent work on manipulating ghrelin levels in mouse blood and brain by long term elevation of BChE, leading to sustained decrease of ghrelin. That effect in turn was found to reduce stress-induced aggression in group caged mice. Positive consequences were fewer bite wounds and longer survival times. No adverse effects were observed. Further exploration may pave the way for BChE-based treatment of anxiety in humans.

Acyl ghrelin improves cognition, synaptic plasticity deficits and neuroinflammation following amyloid β (Aβ1-40) administration in mice

Ghrelin is a metabolic hormone that has neuroprotective actions in a number of neurological conditions, including Parkinson's disease (PD), stroke and traumatic brain injury. Acyl ghrelin treatment in vivo and in vitro also shows protective capacity in Alzheimer's disease (AD). In the present study, we used ghrelin knockout (KO) and their wild-type littermates to test whether or not endogenous ghrelin is protective in a mouse model of AD, in which human amyloid β peptide 1-40 (Aβ_1-40 ) was injected into the lateral ventricles i.c.v. Recognition memory, using the novel object recognition task, was significantly impaired in ghrelin KO mice and after i.c.v. Aβ_1-40 treatment. These deficits could be prevented by acyl ghrelin injections for 7 days. Spatial orientation, as assessed by the Y-maze task, was also significantly impaired in ghrelin KO mice and after i.c.v. Aβ_1-40 treatment. These deficits could be prevented by acyl ghrelin injections for 7 days. Ghrelin KO mice had deficits in olfactory discrimination; however, neither i.c.v. Aβ_1-40 treatment, nor acyl ghrelin injections affected olfactory discrimination. We used stereology to show that ghrelin KO and Aβ_1-40 increased the total number of glial fibrillary acidic protein expressing astrocytes and ionised calcium-binding adapter expressing microglial in the rostral hippocampus. Finally, Aβ_1-40 blocked long-term potentiation induced by high-frequency stimulation and this effect could be acutely blocked with co-administration of acyl ghrelin. Collectively, our studies demonstrate that ghrelin deletion affects memory performance and also that acyl ghrelin treatment may delay the onset of early events of AD. This supports the idea that acyl ghrelin treatment may be therapeutically beneficial with respect to restricting disease progression in AD.

Caloric Restriction Protects against Lactacystin-Induced Degeneration of Dopamine Neurons Independent of the Ghrelin Receptor

Parkinson’s disease (PD) is a neurodegenerative disorder, characterized by a loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc). Caloric restriction (CR) has been shown to exert ghrelin-dependent neuroprotective effects in the 1-methyl-4-phenyl-1,2,3,6-tetrathydropyridine (MPTP)-based animal model for PD. We here investigated whether CR is neuroprotective in the lactacystin (LAC) mouse model for PD, in which proteasome disruption leads to the destruction of the DA neurons of the SNc, and whether this effect is mediated via the ghrelin receptor. Adult male ghrelin receptor wildtype (WT) and knockout (KO) mice were maintained on an ad libitum (AL) diet or on a 30% CR regimen. After 3 weeks, LAC was injected unilaterally into the SNc, and the degree of DA neuron degeneration was evaluated 1 week later. In AL mice, LAC injection significanty reduced the number of DA neurons and striatal DA concentrations. CR protected against DA neuron degeneration following LAC injection. However, no differences were observed between ghrelin receptor WT and KO mice. These results indicate that CR can protect the nigral DA neurons from toxicity related to proteasome disruption; however, the ghrelin receptor is not involved in this effect.

Neuroendocrine abnormalities in Parkinson's disease

Neuroendocrine abnormalities are common in Parkinson's disease (PD) and include disruption of melatonin secretion, disturbances of glucose, insulin resistance and bone metabolism, and body weight changes. They have been associated with multiple non-motor symptoms in PD and have important clinical consequences, including therapeutics. Some of the underlying mechanisms have been implicated in the pathogenesis of PD and represent promising targets for the development of disease biomarkers and neuroprotective therapies. In this systems-based review, we describe clinically relevant neuroendocrine abnormalities in Parkinson's disease to highlight their role in overall phenotype. We discuss pathophysiological mechanisms, clinical implications, and pharmacological and non-pharmacological interventions based on the current evidence. We also review recent advances in the field, focusing on the potential targets for development of neuroprotective drugs in Parkinson's disease and suggest future areas for research.

From Belly to Brain: Targeting the Ghrelin Receptor in Appetite and Food Intake Regulation

Ghrelin is the only known peripherally-derived orexigenic hormone, increasing appetite and subsequent food intake. The ghrelinergic system has therefore received considerable attention as a therapeutic target to reduce appetite in obesity as well as to stimulate food intake in conditions of anorexia, malnutrition and cachexia. As the therapeutic potential of targeting this hormone becomes clearer, it is apparent that its pleiotropic actions span both the central nervous system and peripheral organs. Despite a wealth of research, a therapeutic compound specifically targeting the ghrelin system for appetite modulation remains elusive although some promising effects on metabolic function are emerging. This is due to many factors, ranging from the complexity of the ghrelin receptor (Growth Hormone Secretagogue Receptor, GHSR-1a) internalisation and heterodimerization, to biased ligand interactions and compensatory neuroendocrine outputs. Not least is the ubiquitous expression of the GHSR-1a, which makes it impossible to modulate centrally-mediated appetite regulation without encroaching on the various peripheral functions attributable to ghrelin. It is becoming clear that ghrelin’s central signalling is critical for its effects on appetite, body weight regulation and incentive salience of food. Improving the ability of ghrelin ligands to penetrate the blood brain barrier would enhance central delivery to GHSR-1a expressing brain regions, particularly within the mesolimbic reward circuitry.

The neurological effects of ghrelin in brain diseases: Beyond metabolic functions

Ghrelin, a peptide released by the stomach that plays a major role in regulating energy metabolism, has recently been shown to have effects on neurobiological behaviors. Ghrelin enhances neuronal survival by reducing apoptosis, alleviating inflammation and oxidative stress, and accordingly improving mitochondrial function. Ghrelin also stimulates the proliferation, differentiation and migration of neural stem/progenitor cells (NS/PCs). Additionally, the ghrelin is benefit for the recovery of memory, mood and cognitive dysfunction after stroke or traumatic brain injury. Because of its neuroprotective and neurogenic roles, ghrelin may be used as a therapeutic agent in the brain to combat neurodegenerative disease. In this review, we highlight the pre-clinical evidence and the proposed mechanisms underlying the role of ghrelin in physiological and pathological brain function.

Role of metabolism in neurodegenerative disorders

Along with the increase in life expectancy over the last century, the prevalence of age-related disorders, such as neurodegenerative diseases continues to rise. This is the case of Alzheimer's, Parkinson's, Huntington's diseases and Multiple sclerosis, which are chronic disorders characterized by neuronal loss in motor, sensory or cognitive systems. Accumulating evidence has suggested the presence of a strong correlation between metabolic changes and neurodegeneration. Indeed epidemiologic studies have shown strong associations between obesity, metabolic dysfunction, and neurodegeneration, while animal models have provided insights into the complex relationships between these conditions. In this context, hormones such as leptin, ghrelin, insulin and IGF-1 seem to play a key role in the regulation of neuronal damage, toxic insults and several other neurodegenerative processes. This review aims to presenting the most recent evidence supporting the crosstalk linking energy metabolism and neurodegeneration, and will focus on metabolic manipulation as a possible therapeutic tool in the prevention and treatment of neurodegenerative diseases.

Metformin Prevents Nigrostriatal Dopamine Degeneration Independent of AMPK Activation in Dopamine Neurons

Metformin is a widely prescribed drug used to treat type-2 diabetes, although recent studies show it has wide ranging effects to treat other diseases. Animal and retrospective human studies indicate that Metformin treatment is neuroprotective in Parkinson's Disease (PD), although the neuroprotective mechanism is unknown, numerous studies suggest the beneficial effects on glucose homeostasis may be through AMPK activation. In this study we tested whether or not AMPK activation in dopamine neurons was required for the neuroprotective effects of Metformin in PD. We generated transgenic mice in which AMPK activity in dopamine neurons was ablated by removing AMPK beta 1 and beta 2 subunits from dopamine transporter expressing neurons. These AMPK WT and KO mice were then chronically exposed to Metformin in the drinking water then exposed to MPTP, the mouse model of PD. Chronic Metformin treatment significantly attenuated the MPTP-induced loss of Tyrosine Hydroxylase (TH) neuronal number and volume and TH protein concentration in the nigrostriatal pathway. Additionally, Metformin treatment prevented the MPTP-induced elevation of the DOPAC:DA ratio regardless of genotype. Metformin also prevented MPTP induced gliosis in the Substantia Nigra. These neuroprotective actions were independent of genotype and occurred in both AMPK WT and AMPK KO mice. Overall, our studies suggest that Metformin's neuroprotective effects are not due to AMPK activation in dopaminergic neurons and that more research is required to determine how metformin acts to restrict the development of PD.

Ghrelin modulates encoding-related brain function without enhancing memory formation in humans

Ghrelin regulates energy homeostasis in various species and enhances memory in rodent models. In humans, the role of ghrelin in cognitive processes has yet to be characterized. Here we show in a double-blind randomized crossover design that acute administration of ghrelin alters encoding-related brain activity, however does not enhance memory formation in humans. Twenty-one healthy young male participants had to memorize food- and non-food-related words presented on a background of a virtual navigational route while undergoing fMRI recordings. After acute ghrelin administration, we observed decreased post-encoding resting state fMRI connectivity between the caudate nucleus and the insula, amygdala, and orbitofrontal cortex. In addition, brain activity related to subsequent memory performance was modulated by ghrelin. On the next day, however, no differences were found in free word recall or cued location-word association recall between conditions; and ghrelin's effects on brain activity or functional connectivity were unrelated to memory performance. Further, ghrelin had no effect on a cognitive test battery comprising tests for working memory, fluid reasoning, creativity, mental speed, and attention. In conclusion, in contrast to studies with animal models, we did not find any evidence for the potential of ghrelin acting as a short-term cognitive enhancer in humans.

Linking mitochondrial dysfunction, metabolic syndrome and stress signaling in Neurodegeneration

Mounting evidence suggests a link between metabolic syndrome (MetS) such as diabetes, obesity, non-alcoholic fatty liver disease in the progression of Alzheimer's disease (AD), Parkinson's disease (PD) and other neurodegenerative diseases (NDDs). For instance, accumulated Aβ oligomer is enhancing neuronal Ca²⁺ release and neural NO where increased NO level in the brain through post translational modification is modulating the level of insulin production. It has been further confirmed that irrespective of origin; brain insulin resistance triggers a cascade of the neurodegeneration phenomenon which can be aggravated by free reactive oxygen species burden, ER stress, metabolic dysfunction, neuorinflammation, reduced cell survival and altered lipid metabolism. Moreover, several studies confirmed that MetS and diabetic sharing common mechanisms in the progression of AD and NDDs where mitochondrial dynamics playing a critical role. Any mutation in mitochondrial DNA, exposure of environmental toxin, high-calorie intake, homeostasis imbalance, glucolipotoxicity is causative factors for mitochondrial dysfunction. These cumulative pleiotropic burdens in mitochondria leads to insulin resistance, increased ROS production; enhanced stress-related enzymes that is directly linked MetS and diabetes in neurodegeneration. Since, the linkup mechanism between mitochondrial dysfunction and disease phenomenon of both MetS and NDDs is quite intriguing, therefore, it is pertinent for the researchers to identify and implement the therapeutic interventions for targeting MetS and NDDs. Herein, we elucidated the pertinent role of MetS induced mitochondrial dysfunction in neurons and their consequences in NDDs. Further, therapeutic potential of well-known biomolecules and chaperones to target altered mitochondria has been comprehensively documented. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Medium-chain TAG improve energy metabolism and mitochondrial biogenesis in the liver of intra-uterine growth-retarded and normal-birth-weight weanling piglets

We previously reported that medium-chain TAG (MCT) could alleviate hepatic oxidative damage in weanling piglets with intra-uterine growth retardation (IUGR). There is a relationship between oxidative status and energy metabolism, a process involved in substrate availability and glucose flux. Therefore, the aim of this study was to investigate the effects of IUGR and MCT on hepatic energy metabolism and mitochondrial function in weanling piglets. Twenty-four IUGR piglets and twenty-four normal-birth-weight (NBW) piglets were fed a diet of either soyabean oil (SO) or MCT from 21 d of postnatal age to 49 d of postnatal age. Then, the piglets' biochemical parameters and gene expressions related to energy metabolism and mitochondrial function were determined (n 4). Compared with NBW, IUGR decreased the ATP contents and succinate oxidation rates in the liver of piglets, and reduced hepatic mitochondrial citrate synthase (CS) activity (P<0·05). IUGR piglets exhibited reductions in hepatic mitochondrial DNA (mtDNA) contents and gene expressions related to mitochondrial biogenesis compared with NBW piglets (P<0·05). The MCT diet increased plasma ghrelin concentration and hepatic CS and succinate dehydrogenase activities, but decreased hepatic pyruvate kinase activity compared with the SO diet (P<0·05). The MCT-fed piglets showed improved mtDNA contents and PPARγ coactivator-1α expression in the liver (P<0·05). The MCT diet alleviated decreased mRNA abundance of the hepatic PPARα induced by IUGR (P<0·05). It can therefore be postulated that MCT may have beneficial effects in improving energy metabolism and mitochondrial function in weanling piglets.