The role of ghrelin in neuroprotection after ischemic brain injury

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.

Mechanistic insights on impact of Adenosine monophosphate-activated protein kinase (AMPK) mediated signalling pathways on cerebral ischemic injury

Cerebral ischemia is the primary cause of morbidity and mortality worldwide due to the perturbations in the blood supply to the brain. The brain triggers a cascade of complex metabolic and cellular defects in response to ischemic stress. However, due to the disease heterogeneity and complexity, ischemic injury's metabolic and cellular pathologies remain elusive, and the link between various pathological mechanisms is difficult to determine. Efforts to develop effective treatments for these disorders have yielded limited efficacy, with no proper cure available to date. Recent clinical and experimental research indicates that several neuronal diseases commonly coexist with metabolic dysfunction, which may aggravate neurological symptoms. As a result, it stands to a reason that metabolic hormones could be a potential therapeutic target for major NDDs. Moreover, fasting signals also influence the circadian clock, as AMPK phosphorylates and promotes the degradation of the photo-sensing receptor (cryptochrome). Here, the interplay of AMPK signaling between metabolic regulation and neuronal death and its role for pathogenesis and therapeutics has been studied. We have also highlighted a significant signaling pathway, i.e., the adenosine monophosphate-activated protein kinase (AMPK) involved in the relationship between the metabolism and ischemia, which could be used as a target for future studies therapeutics, and review some of the clinical progress in this area.

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.

Brain Damage and Patterns of Neurovascular Disorder after Ionizing Irradiation. Complications in Radiotherapy and Radiation Combined Injury

Exposure to ionizing radiation, mechanical trauma, toxic chemicals or infections, or combinations thereof (i.e., combined injury) can induce organic injury to brain tissues, the structural disarrangement of interactive networks of neurovascular and glial cells, as well as on arrays of the paracrine and systemic destruction. This leads to subsequent decline in cognitive capacity and decompensation of mental health. There is an ongoing need for improvement in mitigating and treating radiation- or combined injury-induced brain injury. Cranial irradiation per se can cause a multifactorial encephalopathy that occurs in a radiation dose- and time-dependent manner due to differences in radiosensitivity among the various constituents of brain parenchyma and vasculature. Of particular concern are the radiosensitivity and inflammation susceptibility of: 1. the neurogenic and oligodendrogenic niches in the subependymal and hippocampal domains; and 2. the microvascular endothelium. Thus, cranial or total-body irradiation can cause a plethora of biochemical and cellular disorders in brain tissues, including: 1. decline in neurogenesis and oligodendrogenesis; 2. impairment of the blood-brain barrier; and 3. ablation of vascular capillary. These changes, along with cerebrovascular inflammation, underlie different stages of encephalopathy, from the early protracted stage to the late delayed stage. It is evident that ionizing radiation combined with other traumatic insults such as penetrating wound, burn, blast, systemic infection and chemotherapy, among others, can exacerbate the radiation sequelae (and vice versa) with increasing severity of neurogenic and microvascular patterns of radiation brain damage.

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.

Potentiality of ghrelin as antioxidant and protective agent

Background

Oxidative stress is the result of cellular troubles related to aerobic metabolism. Furthermore, this stress is always associated with biological responses evoked by physical, chemical, environmental, and psychological factors. Several studies have developed many approaches of antioxidant defense to diminish the severity of many diseases. Ghrelin was originally identified from the rat stomach, and it is a potent growth hormone-releasing peptide that has pleiotropic functions.

Methods

A systematic review was conducted within PubMed, ScienceDirect, MEDLINE, and Scopus databases using keywords such as ghrelin, antioxidant, oxidative stress, and systemic oxidative stress sensor.

Results

In the last decade, many studies show that ghrelin exhibits protection effects against oxidative stress derived probably from its antioxidant effects. Pieces of evidence demonstrate that systemic oxidative stress increase ghrelin levels in the plasma. The expression of ghrelin and its receptor in ghrelin peripheral tissues and extensively in the central nervous system suggests that this endogenous peptide plays an important role as a systemic oxidative stress sensor

Conclusion

The current evidence confirms that ghrelin and its derived peptides (Desacyl-ghrelin, obestatin) act as a protective antioxidant agent. Therefore, stressor modality, duration, and intensity are the parameters of oxidative stress that must be taken into consideration to determine the role of ghrelin, Desacyl-ghrelin, and obestatin in the regulation of cell death pathways.

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.

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.

Neuroprotective effects of food restriction in a rat model of traumatic brain injury - the role of glucocorticoid signaling

OBJECTIVE

Traumatic brain injury (TBI) is one of the most common causes of neurological damage in young and middle aged people. Food restriction (FR) has been shown to act neuroprotectively in animal models of stroke and TBI. Indeed, our previous studies showed that FR attenuates inflammation, through suppression of microglial activation and TNF-α production, suppresses caspase-3-induced neuronal cell death and enhances neuroplasticity in the rat model of TBI. Glucocorticoids (GCs) play a central role in mediating both molecular and behavioral responses to food restriction. However, the exact mechanisms of FR neuroprotection in TBI are still unclear. The goal of the present study was to examine whether FR exerts its beneficial effects by altering the glucocorticoid receptor (GR) signaling alone and/or together with other protective factors.

METHODS

To this end, we examined the effects of FR (50% of regular daily food intake for 3 months prior to TBI) on the protein levels of total GR, GR phosphoisoform Ser232 (p-GR) and its transcriptional activity, as well as 11β-HSD1, NFκB (p65) and HSP70 as factors related to the GR signaling.

RESULTS

Our results demonstrate that FR applied prior to TBI significantly changes p-GR levels, and it's transcriptional activity during the recovery period after TBI. Moreover, as a pretreatment, FR modulates other protective factors in response to TBI, such as 11β-HSD1, NF-κB (p65) and HSP70 that act in parallel with GR in it's anti-inflammatory and neuroprotective effects in the rat model of brain injury.

CONCLUSION

Our results suggest that prophylactic FR represents a potent non-invasive approach capable of changing GR signalling, together with other factors related to the GR signaling in the model of TBI.

Ghrelin attenuates secondary brain injury following intracerebral hemorrhage by inhibiting NLRP3 inflammasome activation and promoting Nrf2/ARE signaling pathway in mice

Ghrelin, a brain-gut peptide, has been proven to exert neuroprotection in different kinds of neurological diseases; however, its role and the potential molecular mechanisms in secondary brain injury (SBI) after intracerebral hemorrhage (ICH) are still unknown. In this study, we investigate whether treatment with ghrelin may attenuate SBI in a murine ICH model, and if so, whether the neuroprotective effects are due to the inhibition of nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasome activation and promotion of nuclear factor-E2-related factor 2 (Nrf2)/antioxidative response element (ARE) signaling pathway. Stereotactically intrastriatal infusion of autologous blood was performed to mimic ICH. Ghrelin was given intraperitoneally immediately following ICH and again 1 h later. Results showed that ghrelin attenuated neurobehavioral deficits, brain edema, hematoma volume, and perihematomal cell death post-ICH. Ghrelin inhibited the NLRP3 inflammasome activation and subsequently suppressed the neuroinflammatory response as evidenced by reduced microglia activation, neutrophil infiltration, and pro-inflammatory mediators release after ICH. Additionally, ghrelin alleviated ICH-induced oxidative stress according to the chemiluminescence of luminol and lucigenin, malondialdehyde (MDA) content, and total superoxide dismutase (SOD) activity assays. These changes were accompanied by upregulation of Nrf2 expression, Nrf2 nuclear accumulation, and enhanced Nrf2 DNA binding activity, as well as by increased expressions of Nrf2 downstream target antioxidative genes, including NAD(P)H quinine oxidoreductase-1 (NQO1), glutathione cysteine ligase regulatory subunit (GCLC), and glutathione cysteine ligase modulatory subunit (GCLM). Together, our data suggested that ghrelin protected against ICH-induced SBI by inhibiting NLRP3 inflammasome activation and promoting Nrf2/ARE signaling pathway.

Hippocampal electrophysiological responses and changes in oxidative stress marker and serum lipid profile to pharmacological and non-pharmacological treatments of high-fat-fructose diet induced metabolic syndrome

The aim of our study was to evaluate the possibility of influencing the risk factors of metabolic syndrome (MetS) and metabolic cognitive syndrome. As a model of MetS, we used high-fat-fructose diet (HFFD) fed hypertriacylglycerolemic (HTG) rats. Control group included HTG rats fed with HFFD during 8 weeks (HFFD8). Furthermore, we tested the effect of pharmacological and non-pharmacological therapies. Non-pharmacological therapy, which we chose, was a change in diet from HFFD (5 weeks) to standard one (3 weeks) and thus caloric restriction (HFFD5+3). The drug we used was rosmarinic acid (RA; 100mg/kg), which we administered to rats after 5 weeks of HFFD once a day for consecutive 3 weeks with current change in diet to standard one (HFFD5+3+RA) or during lasting last 3 weeks of HFFD (HFFD8+RA). After 8 weeks of experiment, lipid peroxidation markers, lipid profile of blood serum, and neuronal transmission and synaptic plasticity (long-term potentiation [LTP]) in hippocampal sections were evaluated in vitro. We observed a significant effect of dietary change in lipid profile (decreased total cholesterol and low-density lipoprotein cholesterol [LDL-cholesterol] and increased high-density lipoprotein cholesterol [HDL-cholesterol]). The combination of pharmacological and non-pharmacological treatments caused a decrease in total cholesterol, LDL-cholesterol, and lipid peroxidation in blood serum. Change in HFFD to standard diet without treatment resulted in slight improvement in neuronal transmission in the hippocampus and caloric restriction alone also had positive effect on LTP maintenance. Our results suggest that combination of pharmacological and non-pharmacological approaches had better impact on the biochemical parameters of MetS in blood serum, but weak impact on neuronal functions in the hippocampus, where the expected positive effect was achieved only by caloric restriction.

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.

Temporospatial effects of acyl-ghrelin on activation of astrocytes after ischaemic brain injury

The protective mechanisms of astrocyte signalling are based on the release of neurotrophic factors and the clearing of toxic substances in the early stages of cerebral ischaemia. However, astrocytes are also responsible for the detrimental effects that occur during the later stages of ischaemia, in which glial scars are formed, thereby impeding neural recovery. Acyl-ghrelin has been found to be neuroprotective after stroke, although the influence of acyl-ghrelin on astrocytes after ischaemic injury is yet to be clarified. In the present study, we used permanent middle cerebral arterial occlusion to establish a brain ischaemia model in vivo, as well as oxygen and glucose deprivation (OGD) to mimic ischaemic insults in vitro. We found that acyl-ghrelin injection significantly increased the number of activated astrocytes in the peri-infarct area at day 3 after brain ischaemia and decreased the number of activated astrocytes after day 9. Moreover, the expression of fibroblast growth factor 2 (FGF2) in the ischaemic hemisphere increased markedly after day 3, and i.c.v. injection of SU5402, an inhibitor of FGF2 signalling, abolished the suppression effects of acyl-ghrelin on astrocyte activation in the peri-infarct region during the later stages of ischaemia. The results from in vitro studies also showed the dual effect of acyl-ghrelin on astrocyte viability. Acyl-ghrelin increased the viability of uninjured astrocytes in an indirect way by stimulating the secretion from OGD-injured astrocytes. It also inhibited the astrocyte viability in the presence of FGF2 in a dose-dependent manner. Furthermore, the expression of acyl-ghrelin receptors on astrocytes was increased after acyl-ghrelin and FGF2 co-treatment. In conclusion, acyl-ghrelin promoted astrocyte activation in the early stages of ischaemia but suppressed the activation in later stages of ischaemic injury. These later effects were likely to be triggered by the increased expression of endogenous FGF2 after brain ischaemia.

A novel therapy, using Ghrelin with pegylated G-CSF, inhibits brain hemorrhage from ionizing radiation or combined radiation injury

Medical treatment becomes challenging when complicated injuries arise from secondary reactive metabolic and inflammatory products induced by initial acute ionizing radiation injury (RI) or when combined with subsequent trauma insult(s) (CI). With such detrimental effects on many organs, CI exacerbates the severity of primary injuries and decreases survival. Previously, in a novel study, we reported that ghrelin therapy significantly improved survival after CI. This study aimed to investigate whether brain hemorrhage induced by RI and CI could be inhibited by ghrelin therapy with pegylated G-CSF (i.e., Neulasta®, an FDA-approved drug). B6D2F1 female mice were exposed to 9.5 Gy 60Co-γ-radiation followed by 15% total-skin surface wound. Several endpoints were measured at several days. Brain hemorrhage and platelet depletion were observed in RI and CI mice. Brain hemorrhage severity was significantly higher in CI mice than in RI mice. Ghrelin therapy with pegylated G-CSF reduced the severity in brains of both RI and CI mice. RI and CI did not alter PARP and NF-κB but did significantly reduce PGC-1α and ghrelin receptors; the therapy, however, was able to partially recover ghrelin receptors. RI and CI significantly increased IL-6, KC, Eotaxin, G-CSF, MIP-2, MCP-1, MIP-1α, but significantly decreased IL-2, IL-9, IL-10, MIG, IFN-γ, and PDGF-bb; the therapy inhibited these changes. RI and CI significantly reduced platelet numbers, cellular ATP levels, NRF1/2, and AKT phosphorylation. The therapy significantly mitigated these CI-induced changes and reduced p53-mdm2 mediated caspase-3 activation. Our data are the first to support the view that Ghrelin therapy with pegylated G-CSF is potentially a novel therapy for treating brain hemorrhage after RI and CI.

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.

Biochemical properties and biological actions of obestatin and its relevence in type 2 diabetes

Obestatin was initially discovered in rat stomach extract, and although it is principally produced in the gastric mucosa, it can be found throughout the gastrointestinal tract. This 23-amino acid C-terminally amidated peptide is derived from preproghrelin and has been ascribed a wide range of metabolic effects relevant to type 2 diabetes. Obestatin reportedly inhibits gastrointestinal motility, reduces food intake and lowers body weight and improves lipid metabolism. Furthermore, it appears to exert actions on the pancreatic β-cell, most notably increasing β-cell mass and upregulating genes associated with insulin production and β-cell regeneration, with relevance to type 2 diabetes. It is becoming evident that obestatin also exerts pleiotropic effects on the cardiovascular system, possibly modulating blood pressure, endothelial function and triggering cardioprotective mechanisms, which may be important in determining cardiovascular outcomes in type 2 diabetes. Furthermore, it seems that like other gut peptides obestatin has neuroprotective properties. This review examines the biochemical properties of the obestatin peptide (its structure, sequence, stability and distribution) and the candidate receptors through which it may act. It provides a balanced examination of the reported pancreatic and extrapancreatic actions of obestatin and evaluates its potential relevance with respect to diabetes therapy, together with discussion of direct evidence linking alterations in obestatin signalling with obesity/diabetes and other diseases.

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.

Ghrelin Therapy Decreases Incidents of Intracranial Hemorrhage in Mice after Whole-Body Ionizing Irradiation Combined with Burn Trauma

Nuclear industrial accidents and the detonation of nuclear devices cause a variety of damaging factors which, when their impacts are combined, produce complicated injuries challenging for medical treatment. Thus, trauma following acute ionizing irradiation (IR) can deteriorate the IR-induced secondary reactive metabolic and inflammatory impacts to dose-limiting tissues, such as bone marrow/lymphatic, gastrointestinal tissues, and vascular endothelial tissues, exacerbating the severity of the primary injury and decreasing survival from the exposure. Previously we first reported that ghrelin therapy effectively improved survival by mitigating leukocytopenia, thrombocytopenia, and bone-marrow injury resulting from radiation combined with burn trauma. This study was aimed at investigating whether radiation combined with burn trauma induced the cerebro-vascular impairment and intracranial hemorrhage that could be reversed by ghrelin therapy. When B6D2F1 female mice were exposed to 9.5 Gy Cobalt-60 γ-radiation followed by 15% total skin surface burn, cerebro-vascular impairment and intracranial hemorrhage as well as platelet depletion were observed. Ghrelin treatment after irradiation combined with burn trauma significantly decreased platelet depletion and brain hemorrhage. The results suggest that ghrelin treatment is an effective therapy for ionizing radiation combined with burn trauma.

Involvement of Astrocytes in Mediating the Central Effects of Ghrelin

Although astrocytes are the most abundant cells in the mammalian brain, much remains to be learned about their molecular and functional features. Astrocytes express receptors for numerous hormones and metabolic factors, including the appetite-promoting hormone ghrelin. The metabolic effects of ghrelin are largely opposite to those of leptin, as it stimulates food intake and decreases energy expenditure. Ghrelin is also involved in glucose-sensing and glucose homeostasis. The widespread expression of the ghrelin receptor in the central nervous system suggests that this hormone is not only involved in metabolism, but also in other essential functions in the brain. In fact, ghrelin has been shown to promote cell survival and neuroprotection, with some studies exploring the use of ghrelin as a therapeutic agent against metabolic and neurodegenerative diseases. In this review, we highlight the possible role of glial cells as mediators of ghrelin's actions within the brain.

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.

Ghrelin Attenuates Intestinal Barrier Dysfunction Following Intracerebral Hemorrhage in Mice

Intestinal barrier dysfunction remains a critical problem in patients with intracerebral hemorrhage (ICH) and is associated with poor prognosis. Ghrelin, a brain-gut peptide, has been shown to exert protection in animal models of gastrointestinal injury. However, the effect of ghrelin on intestinal barrier dysfunction post-ICH and its possible underlying mechanisms are still unknown. This study was designed to investigate whether ghrelin administration attenuates intestinal barrier dysfunction in experimental ICH using an intrastriatal autologous blood infusion mouse model. Our data showed that treatment with ghrelin markedly attenuated intestinal mucosal injury at both histomorphometric and ultrastructural levels post-ICH. Ghrelin reduced ICH-induced intestinal permeability according to fluorescein isothiocyanate conjugated-dextran (FITC-D) and Evans blue extravasation assays. Concomitantly, the intestinal tight junction-related protein markers, Zonula occludens-1 (ZO-1) and claudin-5 were upregulated by ghrelin post-ICH. Additionally, ghrelin reduced intestinal intercellular adhesion molecule-1 (ICAM-1) expression at the mRNA and protein levels following ICH. Furthermore, ghrelin suppressed the translocation of intestinal endotoxin post-ICH. These changes were accompanied by improved survival rates and an attenuation of body weight loss post-ICH. In conclusion, our results suggest that ghrelin reduced intestinal barrier dysfunction, thereby reducing mortality and weight loss, indicating that ghrelin is a potential therapeutic agent in ICH-induced intestinal barrier dysfunction therapy.

Age-related obesity and type 2 diabetes dysregulate neuronal associated genes and proteins in humans

Despite numerous developed drugs based on glucose metabolism interventions for treatment of age-related diseases such as diabetes neuropathies (DNs), DNs are still increasing in patients with type 1 or type 2 diabetes (T1D, T2D). We aimed to identify novel candidates in adipose tissue (AT) and pancreas with T2D for targeting to develop new drugs for DNs therapy.

AT-T2D displayed 15 (e.g. SYT4 up-regulated and VGF down-regulated) and pancreas-T2D showed 10 (e.g. BAG3 up-regulated, VAV3 and APOA1 down-regulated) highly differentially expressed genes with neuronal functions as compared to control tissues. ELISA was blindly performed to measure proteins of 5 most differentially expressed genes in 41 human subjects. SYT4 protein was upregulated, VAV3 and APOA1 were down-regulated, and BAG3 remained unchanged in 1- Obese and 2- Obese-T2D without insulin, VGF protein was higher in these two groups as well as in group 3- Obese-T2D receiving insulin than 4-lean subjects. Interaction networks analysis of these 5 genes showed several metabolic pathways (e.g. lipid metabolism and insulin signaling).

Pancreas is a novel site for APOA1 synthesis. VGF is synthesized in AT and could be considered as good diagnostic, and even prognostic, marker for age-induced diseases obesity and T2D. This study provides new targets for rational drugs development for the therapy of age-related DNs.

Ghrelin and Neurodegenerative Disorders-a Review

Ghrelin, the endogenous ligand of the growth hormone secretagogue receptor 1a (GHS-R1a), is a gut-derived, orexigenic peptide hormone that primarily regulates growth hormone secretion, food intake, and energy homeostasis. With the wide expression of GHS-R1a in extra-hypothalamic regions, the physiological role of ghrelin is more extensive than solely its involvement in metabolic function. Ghrelin has been shown to be involved in numerous higher brain functions, such as memory, reward, mood, and sleep. Some of these functions are disrupted in neurodegenerative disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). This link between ghrelin and these neurodegenerative diseases is supported by numerous studies. This review aims to provide a comprehensive overview of the most recent evidence of the novel neuromodulatory role of ghrelin in PD, AD, and HD. Moreover, the changes in circulating and/or central ghrelin levels that are associated with disease progression are also postulated to be a biomarker for clinical diagnosis and therapy.

Assessment of serum and urine ghrelin levels in patients with acute stroke

INTRODUCTION

Ghrelin is a novel brain-gut peptide hormone consisted of 28 amino-acid. In the plasma, it exists in two major molecular forms, acylated and des-acyled ghrelin, filtered in glomeruli or secreted by nephrons. Primary biological effects of hormones are regulating appetite, foods intake and energy metabolism. We investigated the changing and relationships between serum and urine ghrelin levels in acute stroke patients to provide more information whether diagnostic parameter.

METHODS

Thirty acute stroke patients and thirty consecutive volunteers included in study prospectively. To analyze serum and urine ghrelin levels, at the time of diagnose, all of participant blood and fresh urine (1 ml serum, 2 ml urine respectively) samples were obtained. Serum ghrelin levels analyzed ELISA technique, and urine ghrelin levels studied by validation technique. To compare quantitative data student's t test, and for qualitative data chi-square and Fisher's Exact Chi-square test was used. P<0.05 was considered statistically significant.

RESULTS

Urine acyl ghrelin levels found statistically significant between patient and control groups (P=0.001), but there were no statistically significant differences between both groups (P>0.05) in serum acyl gherelin, des-acyl ghrelin and urine des-acyle ghrelin levels.

CONCLUSIONS

The results indicate that urine acyl ghrelin levels may be considered as a diagnostic parameter in acute ischemic stroke patients. Further studies delineating the mechanism of these observed results are warranted.

Ghrelin-related peptides exert protective effects in the cerebral circulation of male mice through a nonclassical ghrelin receptor(s)

The ghrelin-related peptides, acylated ghrelin, des-acylated ghrelin, and obestatin, are novel gastrointestinal hormones. We firstly investigated whether the ghrelin gene, ghrelin O-acyltransferase, and the ghrelin receptor (GH secretagogue receptor 1a [GHSR1a]) are expressed in mouse cerebral arteries. Secondly, we assessed the cerebrovascular actions of ghrelin-related peptides by examining their effects on vasodilator nitric oxide (NO) and superoxide production. Using RT-PCR, we found the ghrelin gene and ghrelin O-acyltransferase to be expressed at negligible levels in cerebral arteries from male wild-type mice. mRNA expression of GHSR1a was also found to be low in cerebral arteries, and GHSR protein was undetectable in GHSR-enhanced green fluorescent protein mice. We next found that exogenous acylated ghrelin had no effect on the tone of perfused cerebral arteries or superoxide production. By contrast, exogenous des-acylated ghrelin or obestatin elicited powerful vasodilator responses (EC50 < 10 pmol/L) that were abolished by the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester. Furthermore, exogenous des-acylated ghrelin suppressed superoxide production in cerebral arteries. Consistent with our GHSR expression data, vasodilator effects of des-acylated ghrelin or obestatin were sustained in the presence of YIL-781 (GHSR1a antagonist) and in arteries from Ghsr-deficient mice. Using ghrelin-deficient (Ghrl(-/-)) mice, we also found that endogenous production of ghrelin-related peptides regulates NO bioactivity and superoxide levels in the cerebral circulation. Specifically, we show that NO bioactivity was markedly reduced in Ghrl(-/-) vs wild-type mice, and superoxide levels were elevated. These findings reveal protective actions of exogenous and endogenous ghrelin-related peptides in the cerebral circulation and show the existence of a novel ghrelin receptor(s) in the cerebral endothelium.