Ghrelin Exerts Analgesic Effects through Modulation of IL-10 and TGF-β Levels in a Rat Model of Inflammatory Pain

Ghrelin Induces the Production of Hypothalamic NPY Through the AMPK-mTOR Pathway to Alleviate Cancer-induced Bone Pain

BACKGROUND/AIM

Cancer-induced bone pain (CIBP) is one of the most common symptoms of bone metastasis of tumor cells. The hypothalamus may play a pivotal role in the regulation of CIBP. However, little is known about the exact mechanisms.

MATERIALS AND METHODS

First, we established a CIBP model to explore the relationship among hypothalamic ghrelin, NPY and CIBP. Then, we exogenously administered NPY and NPY receptor antagonists to investigate whether hypothalamic NPY exerted an antinociceptive effect through binding to NPY receptors. Finally, we exogenously administered ghrelin to investigate whether ghrelin alleviated CIBP by inducing the production of hypothalamic NPY through the AMPK-mTOR pathway. Body weight, food intake and behavioral indicators of CIBP were measured every 3 days. Hypothalamic ghrelin, NPY and the AMPK-mTOR pathway were also measured.

RESULTS

The expression of hypothalamic ghrelin and NPY was simultaneously decreased in cancer-bearing rats, which was accompanied by CIBP. Intracerebroventricular (i.c.v.) administration of NPY significantly alleviated CIBP in the short term. The antinociceptive effect of NPY was reversed with the i.c.v. administration of the Y1R and Y2R antagonists. The administration of ghrelin activated the AMPK-mTOR pathway and induced hypothalamic NPY production to alleviate CIBP. This effect of ghrelin on NPY and antinociception was reversed with the administration of a GHS-R1α antagonist.

CONCLUSION

Ghrelin could induce the production of hypothalamic NPY through the AMPK-mTOR pathway to alleviate CIBP, which can provide a novel therapeutic mechanism for CIBP.

Orexin and MCH neurons: regulators of sleep and metabolism

Sleep-wake and fasting-feeding are tightly coupled behavioral states that require coordination between several brain regions. The mammalian lateral hypothalamus (LH) is a functionally and anatomically complex brain region harboring heterogeneous cell populations that regulate sleep, feeding, and energy metabolism. Significant attempts were made to understand the cellular and circuit bases of LH actions. Rapid advancements in genetic and electrophysiological manipulation help to understand the role of discrete LH cell populations. The opposing action of LH orexin/hypocretin and melanin-concentrating hormone (MCH) neurons on metabolic sensing and sleep-wake regulation make them the candidate to explore in detail. This review surveys the molecular, genetic, and neuronal components of orexin and MCH signaling in the regulation of sleep and metabolism.

Transcriptional profiles of TGF-β superfamily members in the lumbar DRGs and the effects of activins A and C on inflammatory pain in rats

Signaling by the transforming growth factor (TGF)-β superfamily is necessary for proper neural development and is involved in pain processing under both physiological and pathological conditions. Sensory neurons that reside in the dorsal root ganglia (DRGs) initially begin to perceive noxious signaling from their innervating peripheral target tissues and further convey pain signaling to the central nervous system. However, the transcriptional profile of the TGF-β superfamily members in DRGs during chronic inflammatory pain remains elusive. We developed a custom microarray to screen for transcriptional changes in members of the TGF-β superfamily in lumbar DRGs of rats with chronic inflammatory pain and found that the transcription of the TGF-β superfamily members tends to be downregulated. Among them, signaling of the activin/inhibin and bone morphogenetic protein/growth and differentiation factor (BMP/GDF) families dramatically decreased. In addition, peripherally pre-local administration of activins A and C worsened formalin-induced acute inflammatory pain, whereas activin C, but not activin A, improved formalin-induced persistent inflammatory pain by inhibiting the activation of astrocytes. This is the first report of the TGF-β superfamily transcriptional profiles in lumbar DRGs under chronic inflammatory pain conditions, in which transcriptional changes in cytokines or pathway components were found to contribute to, or be involved in, inflammatory pain processing. Our data will provide more targets for pain research.

An unexpected connection: A narrative review of the associations between Gut Microbiome and Musculoskeletal Pain

PURPOSE

Multiple diverse factors contribute to musculoskeletal pain, a major cause of physical dysfunction and health-related costs worldwide. Rapidly growing evidence demonstrates that the gut microbiome has overarching influences on human health and the body's homeostasis and resilience to internal and external perturbations. This broad role of the gut microbiome is potentially relevant and connected to musculoskeletal pain, though the literature on the topic is limited. Thus, the literature on the topic of musculoskeletal pain and gut microbiome was explored.

METHODS

This narrative review explores the vast array of reported metabolites associated with inflammation and immune-metabolic response, which are known contributors to musculoskeletal pain. Moreover, it covers known modifiable (e.g., diet, lifestyle choices, exposure to prescription drugs, pollutants, and chemicals) and non-modifiable factors (e.g., gut architecture, genetics, age, birth history, and early feeding patterns) that are known to contribute to changes to the gut microbiome. Particular attention is devoted to modifiable factors, as the ultimate goal of researching this topic is to implement gut microbiome health interventions into clinical practice.

RESULTS

Overall, numerous associations exist in the literature that could converge on the gut microbiome's pivotal role in musculoskeletal health. Particularly, a variety of metabolites that are either directly produced or indirectly modulated by the gut microbiome have been highlighted.

CONCLUSION

The review highlights noticeable connections between the gut and musculoskeletal health, thus warranting future research to focus on the gut microbiome's role in musculoskeletal conditions.

The neurobiology of pain and facial movements in rodents: Clinical applications and current research

One of the most controversial aspects of the use of animals in science is the production of pain. Pain is a central ethical concern. The activation of neural pathways involved in the pain response has physiological, endocrine, and behavioral consequences, that can affect both the health and welfare of the animals, as well as the validity of research. The strategy to prevent these consequences requires understanding of the nociception process, pain itself, and how assessment can be performed using validated, non-invasive methods. The study of facial expressions related to pain has undergone considerable study with the finding that certain movements of the facial muscles (called facial action units) are associated with the presence and intensity of pain. This review, focused on rodents, discusses the neurobiology of facial expressions, clinical applications, and current research designed to better understand pain and the nociceptive pathway as a strategy for implementing refinement in biomedical research.

Advances in the Development of Nonpeptide Small Molecules Targeting Ghrelin Receptor

Ghrelin is an octanoylated peptide acting by the activation of the growth hormone secretagogue receptor, namely, GHS-R1a. The involvement of ghrelin in several physiological processes, including stimulation of food intake, gastric emptying, body energy balance, glucose homeostasis, reduction of insulin secretion, and lipogenesis validates the considerable interest in GHS-R1a as a promising target for the treatment of numerous disorders. Over the years, several GHS-R1a ligands have been identified and some of them have been extensively studied in clinical trials. The recently resolved structures of GHS-R1a bound to ghrelin or potent ligands have provided useful information for the design of new GHS-R1a drugs. This perspective is focused on the development of recent nonpeptide small molecules acting as GHS-R1a agonists, antagonists, and inverse agonists, bearing classical or new molecular scaffolds, as well as on radiolabeled GHS-R1a ligands developed for imaging. Moreover, the pharmacological effects of the most studied ligands have been discussed.

Combined spinal-epidural anesthesia with acupoint injection for labor anesthesia reduces IL-1β/IL-10 ratio in maternal peripheral blood, umbilical cord blood and improves the labor outcomes: A prospective randomized controlled trial

BACKGROUND

This study aimed to investigate the effects of combined spinal-epidural anesthesia (CSEA) with acupoint injection (AI) on the maternal-fetal expression of interleukin-1β (IL-1β), interleukin-10 (IL-10), analgesia effect, and labor outcomes.

METHODS

A total of 360 healthy primiparas were randomized into the CSEA+AI group, the CSEA group, the AI group, and the control group (n = 90, each group) according to the labor analgesia methods.

RESULTS

Compared to the CSEA group, the CSEA+AI group had significantly lower visual analog scale (VAS) scores, adverse events, dose of ropivacaine/sufentanil, and shorter labor durations. The IL-1β/IL-10 ratio in maternal peripheral blood and umbilical cord blood was reduced in the CSEA+AI group compared with the CSEA group.

CONCLUSION

The combination of CSEA and AI can reduce the ratio of IL-1β/ IL-10 in maternal peripheral blood and umbilical cord blood, which can effectively relieve labor pain.

Potential role of ghrelin on the micturition reflex in rats

Introduction

The aim of this study was to investigate the effects of intravenous ghrelin administration on the micturition reflex in rats.

Material and methods

Continuous cystometrograms were performed with female Sparague-Dawley rats under urethane anesthesia. Stable micturition cycles were established, and ghrelin was then administered intravenously to evaluate changes in bladder activity. In this experiment investigating the role of opioid systems, ghrelin was administered intravenously at the time of first observed bladder contraction after intravenous administration of naloxone methiodide, an opioid receptor antagonist.

Results

Intravenous administration of ghrelin increased intercontraction interval that was dose-dependent. These inhibitory effects returned to pre-controls level within 80 minutes of administration. Similarly, intravenous administration of ghrelin increased threshold pressure in a dose-dependent fashion. These inhibitory effects of ghrelin were antagonized by intravenous naloxone methiodide administration.

Conclusions

These results show that ghrelin inhibits the micturition reflex through an opioid-dependent mechanism in rats under urethane anesthesia.

Electroacupuncture Relieves Pain and Attenuates Inflammation Progression Through Inducing IL-10 Production in CFA-Induced Mice

The therapeutic effect of electroacupuncture (EA) on inflammatory pain has been well recognized clinically, but the mechanism is unclear. Interleukin-10 (IL-10), which is produced by regulatory T (Treg) cell, is a key anti-inflammatory cytokine for relieving inflammatory pain. Therefore, the aim of this study is to investigate whether EA could inhibit CFA-induced pain and attenuate inflammation progression by regulating the activation of immunocyte and inducing the expression of IL-10. In this study, mice were treated with EA (2/100 Hz, 2 mA) for five consecutive days after 1 day of CFA injection. The behavioral tests were measured and analyzed after the daily EA treatment; then, hind paw, spinal cord, and spleen tissues were prepared for assessment. The results showed that EA treatment significantly increased the mechanical threshold and thermal latency after CFA injection and boosted the expression of IL-10 in paw and spinal cord tissues. EA treatment promoted Treg cells; suppressed macrophage and neutrophils cells; reduced the expression of IL-1β, NLRP3, and TNF-α; and ultimately relieved inflammatory pain. The findings suggested that the analgesic and anti-inflammatory effect of EA treatment could be partially associated with suppression of pro-inflammatory cytokines mediated by induction of IL-10.

Role of the CXCR4/ALK5/Smad3 Signaling Pathway in Cancer-Induced Bone Pain

Purpose

The chemokine receptor, CXCR4, and the transforming growth factor-beta receptor, ALK5, both contribute to various processes associated with the sensation of pain. However, the relationship between CXCR4 and ALK5 and the possible mechanisms promoted by ALK5 in the development of pain have not been evaluated.

Materials and Methods

Tumor cell implantation (TCI) technology was used to generate a model of cancer-induced bone pain (CIBP) in rats; intrathecal (i.t.) injections of small interfering (si) RNAs targeting CXCR4 and the ALK5-specific inhibitor, RepSox, were performed. Behavioral outcomes, Western blotting, and immunofluorescence techniques were used to evaluate the expression of the aforementioned specific target proteins in the CIBP model.

Results

The results revealed that i.t. administration of siRNAs targeting CXCR4 resulted in significant reductions in both mechanical and thermal hyperalgesia in rats with CIBP and likewise significantly reduced the expression of ALK5 in the spinal cord. Similarly, i.t. administration of RepSox also resulted in significant reductions in mechanical and thermal hyperalgesia in rats with CIBP together with diminished levels of spinal p-Smad3.

Conclusion

Taken together, our results suggest that CXCR4 expression in the spinal cord may be a critical mediator of CIBP via its capacity to activate ALK5 and downstream signaling pathways.

Attenuation of Visceral and Somatic Nociception by Ghrelin Mimetics

Purpose

The anti-nociceptive properties of ghrelin have been demonstrated in alleviating inflammatory and neuropathic pain. Whether a ghrelin receptor-mediated mechanism attenuates visceral and somatic pain in the absence of active inflammation remains to be explored. Here, we investigate the efficacy of peripherally restricted (ipamorelin) and a globally active (HM01) selective ghrelin receptor agonist in an experimental model of non-inflammatory visceral hypersensitivity and somatic mechanical allodynia.

Materials and Methods

Visceral hypersensitivity was induced by dilute acetic acid (0.6%) infusion in the colon of rats in the absence of colonic epithelial inflammation. Ghrelin mimetics HM01 and ipamorelin were administered orally or intravenously, respectively. The ghrelin receptor antagonist H0900 was administered orally. Colonic sensitivity was assessed via a visceromotor behavioral response (VMR) quantified as the number of abdominal contractions in response to graded isobaric pressures (0-60 mmHg) of colorectal distension (CRD). Somatic mechanical allodynia was quantified by the number of ipsilateral paw withdrawals in response to a calibrated von Frey filament.

Results

Compared to vehicle controls, ghrelin mimetics HM01 and ipamorelin significantly attenuated colonic hypersensitivity and somatic allodynia. The anti-nociceptive effects of the ghrelin mimetics were blocked after administration of the ghrelin receptor antagonist H0900.

Conclusion

We have shown that ghrelin receptor-mediated mechanisms are involved in visceral and somatic hypersensitivity in the absence of active colonic inflammation. Furthermore, visceral and somatic hypersensitivity could be attenuated by a peripherally restricted ghrelin mimetic. These results highlight a potential novel approach for treating acute visceral and somatic pain by ghrelin mimetics.

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.

Physiological Effect of Ghrelin on Body Systems

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

Effects of phenanthrene on oxidative stress and inflammation in lung and liver of female rats

Phenanthrene (Phe) female rat model was established to explore the effects of Phe on oxidative stress and inflammation. The rats were randomly divided into three groups including control (C), low (L), and high (H) group. Phe was supplied to L and H groups at the dosage of 180 mg/kg and 900 mg/kg orally at first day, and with the dose 90 mg/kg and 450 mg/kg by intraperitoneal injection at the last 2 days. The C group was enriched with the same volume of corn oil. The blood, lung, and liver tissues were collected. The superoxide dismutase (SOD), malonaldehyde (MDA), and 8-hydroxy-2-deoxyguanosine (8-OHdG) were detected to evaluate oxidative stress. The protein and mRNA expressions of interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), and interleukin 10 (IL-10) were detected to evaluate inflammation. Further, the forkhead box transcription factor 3 (Foxp3) was analyzed to hint the injury mechanism of inflammation. The results showed SOD and MDA in lung and liver, and serum 8-OHdG elevated significantly in H groups (P < .05). Meanwhile, there were significant increases in the protein and mRNA expression of TNF-α and IL-6 in lung and liver of H groups (P < .05). In addition, the protein and mRNA expressions of TGF-β and Foxp3 were all decreased significantly in both lung and liver of H groups (P < .05). Results demonstrated that an obvious change of Phe exposure could induce oxidative stress and inflammation in female rats. This is a first pilot study to explore the association between Phe exposure and oxidative stress and inflammation using a female rat model.

Effects of ghrelin on pGSK-3β and β-catenin expression when protects against neuropathic pain behavior in rats challenged with chronic constriction injury

Ghrelin has been shown to alleviate neuropathic pain by inhibiting the release of proinflammatory cytokines. The purpose of this study was to investigate the role of GSK-3β/β-catenin signaling in mediating the effect of ghrelin on neuropathic pain and to understand the associated mechanisms. Chronic constriction injury (CCI) of the sciatic nerve was used to establish a rat model of neuropathic pain. Hyperalgesia and allodynia were evaluated by observing the mechanical withdrawal threshold and the thermal withdrawal latency. Wnt3a and β-catenin protein expression and GSK-3β phosphorylation were detected by western blotting analysis. The levels of tumor necrosis factor-α and IL-1β were determined using an enzyme-linked immunosorbent assay. In addition, we used immunohistochemical analysis to determine the levels of GSK-3β phosphorylation in the dorsal horn of the spinal cord. Intrathecal delivery of ghrelin effectively ameliorated CCI-induced mechanical allodynia and thermal hyperalgesia at 7 and 14 days and reduced the levels of tumor necrosis factor-α. Ghrelin inhibited CCI-induced GSK-3β activation and β-catenin overexpression in the spinal dorsal horn. Moreover, intrathecal injection of ghrelin suppressed the activation of GSK-3β in the spinal dorsal horn of CCI rats, as assessed by immunohistochemical analysis. Our data indicated that ghrelin could markedly alleviate neuropathic pain by inhibiting the expression of β-catenin, via the suppression of GSK-3β activation, in the spinal cord of CCI rats.

Mesenchymal stem cell therapy assisted by nanotechnology: a possible combinational treatment for brain tumor and central nerve regeneration

Mesenchymal stem cells (MSCs) intrinsically possess unique features that not only help in their migration towards the tumor-rich environment but they also secrete versatile types of secretomes to induce nerve regeneration and analgesic effects at inflammatory sites. As a matter of course, engineering MSCs to enhance their intrinsic abilities is growing in interest in the oncology and regenerative field. However, the concern of possible tumorigenesis of genetically modified MSCs prompted the development of non-viral transfected MSCs armed with nanotechnology for more effective cancer and regenerative treatment. Despite the fact that a large number of successful studies have expanded our current knowledge in tumor-specific targeting, targeting damaged brain site remains enigmatic due to the presence of a blood–brain barrier (BBB). A BBB is a barrier that separates blood from brain, but MSCs with intrinsic features of transmigration across the BBB can efficiently deliver desired drugs to target sites. Importantly, MSCs, when mediated by nanoparticles, can further enhance tumor tropism and can regenerate the damaged neurons in the central nervous system through the promotion of axon growth. This review highlights the homing and nerve regenerative abilities of MSCs in order to provide a better understanding of potential cell therapeutic applications of non-genetically engineered MSCs with the aid of nanotechnology.

Effects of Intracerebroventricular and Intra-Arcuate Nucleus Injection of Ghrelin on Pain Behavioral Responses and Met-Enkephalin and β-Endorphin Concentrations in the Periaqueductal Gray Area in Rats

Ghrelin is an endogenous ligand for orphan growth hormone secretagogue receptors. Ghrelin receptors have been found in central nervous system (CNS) areas responsible for pain modulation and transmission. This study investigated the effects of intracerebroventricular (ICV) and intra-arcuate nucleus (ARC) injection of ghrelin on pain behavioral responses and levels of β-endorphin (β-EP) and met-enkephalin (MENK) in the periaqueductal gray area (PAG) during the formalin test in rats. Thirty-five male rats were studied in five groups. Ghrelin was injected into the left lateral ventricle (ICV, 5 µL) or into the ARC (1 µL). After 15 min, formalin (2.5%) was subcutaneously injected into the left hind paw. Behavioral nociceptive scores were recorded for 60 min. MENK and β-EP were collected by microdialysis in the PAG and determined by high-performance liquid chromatography (HPLC). ICV and ARC injection of ghrelin significantly reduced pain in all phases of the formalin test (p < 0.001). Dialysate concentrations of MENK and β-EP in the PAG increased in all the phases (p < 0.01). In conclusion, the present study shows that the ARC nucleus and the endogenous opioid system are involved in ghrelin-induced pain modulation.

Attenuated levels of ghrelin in synovial fluid is related to the disease severity of ankle post-traumatic osteoarthritis

Post-traumatic osteoarthritis (PTOA) of ankle joints results in pain and reduced joint function. Ghrelin, a 28-amino-acid polypeptide, has been previously identified as the first cognate natural ligand that binds to the growth hormone secretagogue receptor. In the present study, ghrelin has been validated to exert cartilage-protective and anti-inflammatory effects. The current study was aimed at investigating the potential role of the levels of serum and synovial fluid (SF) ghrelin on the severity of disease in patients suffering from ankle PTOA. Ninety-seven patients with ankle osteoarthritis who received an arthroscopical examination and debridement or replacement of the ankle joint were included in the study cohort. Meanwhile, 95 healthy individuals (whose age and sex were matched) who received periodic body checkups were enrolled as healthy controls. Enzyme-linked immunosorbent assay (ELISA) was used to analyze the ghrelin levels in serum and SF. SF was also probed for cartilage degradation enzyme matrix metalloproteinases-3 (MMP-3) and tumor necrosis factor alpha (TNF-α), which is a known pro-inflammatory cytokine. The clinical evaluation was carried out using the American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot rating scale and visual analogue scale (VAS). The radiographic severity was evaluated using the modified Kellgren-Lawrence (K-L) grading system. We scored for the modified Mankin's score to depict histopathological changes due to cartilage lesions. The diagnostic relevance of the ghrelin concentrations in the prediction of the radiographic grading (in comparison with MMP-3 and TNF-α) was evaluated by calculating the area under the curve of the receiver operating characteristic (ROC) curve. The serum abundance of ghrelin was not significantly altered between ankle PTOA patients and healthy controls. SF ghrelin was negatively correlated with radiographic progression determined by modified ankle K-L grades. In addition SF ghrelin concentrations were negatively related to VAS scores, and positively associated with AOFAS ankle-hindfoot rating. Moreover, SF ghrelin was inversely proportional to the expressions of MMP-3 and TNF-α. ROC analysis curve demonstrated that ghrelin serves as a favorable marker for the diagnosis of radiographic severity by modified ankle K-L grade. The ghrelin concentration in SF is negatively proportional to disease progression in patients suffering from ankle PTOA. Local administration of ghrelin may function as a decent adjuvant therapy to delay the progress of ankle PTOA. © 2019 BioFactors, 45(3):463-470, 2019.

A Systematic Review of Growth Hormone in Pain Medicine: From Rodents to Humans

Objective

Growth hormone (GH) and GH-related signaling molecules play an important role in nociception and development of chronic pain. This review aims to examine the potential molecular mechanisms through which GH-related signaling modulates sensory hypersensitivity in rodents, the clinical pharmacology of GH, and the clinical evidence of GH treatment for several common pain syndromes.

Methods

A search was conducted using the PUBMED/MEDLINE database, Scopus, and the Cochrane library for all reports published in English on GH in pain management from inception through May 2018. A critical review was performed on the mechanisms of GH-related signaling and the pharmacology of GH. The levels of clinical evidence and implications for recommendations of all of the included studies were graded.

Results

The search yielded 379 articles, of which 201 articles were deemed irrelevant by reading the titles. There were 53 reports deemed relevant after reading abstracts. All of these 53 articles were retrieved for the analysis and discussion.

Conclusions

Dysfunction of the GH/insulin-like growth factor 1 (IGF-1)/ghrelin axis was linked to hyperalgesia and several common clinical pain syndromes. Low levels of GH and IGF-1 were linked to pain hypersensitivity, whereas ghrelin appeared to provide analgesic effects. Pretreatment of GH reversed mechanical and thermal hypersensitivity in an animal model of inflammatory pain. Clinical trials support GH treatment in a subgroup of patients with fibromyalgia syndrome (level of evidence: 1B+) or chronic lower back pain syndrome (level of evidence: 2C+).

Ghrelin attenuated hyperalgesia induced by chronic nitroglycerin: CGRP and TRPV1 as targets for migraine management

Background

According to the neurovascular theory of migraine, activation of the trigeminovascular system contributes to the development of migraine. This study examined the effects of chronic intraperitoneal ghrelin (150 µg/kg) treatment on the development of chronic migraine induced by intermittent injection of nitroglycerin 10 mg/kg.

Methods

Baseline and post-drug (2 h following nitroglycerin injection) mechanical and thermal sensitivity were assessed by von Frey hair and tail immersion tests, respectively on days 1, 3, 5, 7, 9 and 11. Moreover, we investigated the effect of ghrelin treatment on nitroglycerin-induced aversive behavior by using a two-chamber conditioned place aversion paradigm. At the end of behavioral testing, on day 11, animals were sacrificed and plasma concentration of calcitonin gene-related peptide was measured using a rat-specific enzyme-linked immunosorbent assay kit. Also, real time polymerase chain reaction was used to quantify mRNA expression of calcitonin gene-related peptide and transient receptor potential vanilloid 1 in the trigeminal ganglion.

Results

Our results indicated that nitroglycerin activated the trigeminovascular system, which was reflected by mechanical and thermal hypersensitivity and elevation of mRNA expression of calcitonin gene-related peptide and transient receptor potential vanilloid-1, as migraine markers, and plasma calcitonin gene-related peptide levels. Moreover, chronic nitroglycerin injection induced conditioned place aversion and body weight loss. Nevertheless, ghrelin modulated nitroglycerin-triggered changes in transient receptor potential vanilloid-1 and calcitonin gene-related peptide expression, and mitigated nitroglycerin-induced hyperalgesia.

Conclusion

These results provide the first convincing evidence that ghrelin has a modulating effect on central sensitization induced by chronic intermittent nitroglycerin, and its antinociceptive effect may be related to a reduction of these factors in the trigeminal ganglion.

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 Impact of Ghrelin in Metabolic Diseases: An Immune Perspective

Obesity and insulin resistance have reached epidemic proportions. Obesogenic conditions are associated with increased risk for the development of other comorbidities and obesity-related diseases. In metabolic disorders, there is chronic low-grade inflammation induced by the activation of immune cells, especially in metabolic relevant organs such as white adipose tissue (WAT). These immune cells are regulated by environmental and systemic cues. Ghrelin is a peptide secreted mainly by X/A-like gastric cells and acts through the growth hormone secretagogue receptor (GHS-R). This receptor is broadly expressed in the central nervous system (CNS) and in several cell types, including immune cells. Studies show that ghrelin induces an orexigenic state, and there is increasing evidence implicating an immunoregulatory role for ghrelin. Ghrelin mainly acts on the innate and adaptive immune systems to suppress inflammation and induce an anti-inflammatory profile. In this review, we discuss the immunoregulatory roles of ghrelin, the mechanisms by which ghrelin acts and potential pharmacological applications for ghrelin in the treatment of obesity-associated inflammatory diseases, such as type 2 diabetes (T2D).