Effects of Chronic Ghrelin Treatment on Hypoxia-Induced Brain Oxidative Stress and Inflammation in a Rat Normobaric Chronic Hypoxia Model

The neuroimmune pathway of high-altitude adaptation: influence of erythrocytes on attention networks through inflammation and the autonomic nervous system

Introduction

Many studies have shown that the functional adaptation of immigrants to high-altitude is closely related to oxygen transport, inflammatory response and autonomic nervous system. However, it remains unclear how human attention changes in response to hypoxia-induced neurophysiological activity during high-altitude exposure.

Methods

In the present study, we analyzed the relationship between hypoxic-induced neurophysiological responses and attention networks in 116 immigrants (3,680 m) using an attention network test to simultaneously record electroencephalogram and electrocardiogram in combination with specific routine blood markers.

Results

Our analysis revealed that red blood cells exert an indirect influence on the three attention networks, mediated through inflammatory processes and heart rate variability.

Discussion

The present study provides experimental evidence for the role of a neuroimmune pathway in determining human attention performance at high- altitude. Our findings have implications for understanding the complex interactions between physiological and neurocognitive processes in immigrants adapting to hypoxic environments.

Protective effect and mechanism of Polygonatum kingianum against hypoxia-induced injury

Background

Hypoxia is an essential cause of fatigue and aging, and is associated with the occurrence and development of many diseases. Polygonatum kingianum (PK) is a deficiency-nourishing Chinese herbal medicine utilized as both medicine and food, and it has long been used to ameliorate human conditions associated with fatigue and aging over 2000 years in China. PK is an important genuine-medicinal-materials cultivated in Yunnan, China, and is used by the Bai, Wa, and Zhuang nationalities as a traditional medicine for enhancing immunity, anti-fatigue, and anti-aging, while the preventive effect of PK on hypoxia-induced injury and the underlying mechanism are indefinite.

Aim of the study

The present study aimed to evaluate the anti-hypoxia efficacy and understand the corresponding mechanism of PK water extract.

Materials and methods

The main active ingredients and targets of PK were predicted using network pharmacology, and the anti-hypoxia activities of Gracillin and Liquiritigenin were verified by in vitro experiments. The pharmacodynamic experiments were conducted to evaluate the major signal pathways of PK for detecting anti-hypoxia activity.

Results

Fifty active ingredients and 371 potential targets were screened by network pharmacology, then, we confirmed that Gracillin and Liquiritigenin were the main active components of PK to exert anti-hypoxia effect in vitro. The pharmacodynamic experiments revealed that PK enhanced the extension rate of the survival time (ERST) and regulated the targets-related biochemical parameters of rats under hypoxia, showing significant anti-hypoxia effects on rats.

Conclusion

The network pharmacology results suggested that PK exerts its anti-hypoxia effect through a multi-component and multi-target manner. Simultaneously, we also observed that Gracillin (saponins) and Liquiritigenin (flavonoids) are the main active components of PK to play a role in anti-hypoxia. The anti-hypoxia effect of PK could be associated with scavenging excess free radicals, maintaining the activities of antioxidant enzymes, and inhibiting oxidative stress due to lipid peroxidation. These findings provide insight into the Polygonatum kingianum as promising medicines or healthcare products for preventing and treating hypoxia.

Characterization of EPO H131S as a key mutation site in the hypoxia-adaptive evolution of Gymnocypris dobula

Erythropoietin (EPO) is a glycoprotein hormone involved in proerythropoiesis, antioxidation, and antiapoptosis. It also contributes to cellular immune function in high-altitude species, such as the schizothoracine fish Gymnocypris dobula. Six mutation sites previously identified in EPO from G. dobula (GD-EPO) were injected into zebrafish embryos, and their effects were compared with EPO from the low-altitude schizothoracine Schizothorax prenanti. The key mutation site in GD-EPO was identified as H131S. Under hypoxic conditions, the levels of superoxide dismutase and malondialdehyde were decreased, whereas that of nitric oxide was increased in zebrafish injected with GD-EPO compared with those injected with S. prenanti-EPO (SP-EPO). The results suggest that EPO in high-altitude schizothoracine species is both antioxidative and antiapoptotic, driven by the H131S mutation site. Thus, this enhanced the ability of this species to adapt to the high-altitude hypoxic environment. These results provide a basis for investigating further the hypoxia adaptation mechanisms of teleosts.

Anti-apoptosis effects of codonolactone on cerebral ischemia-reperfusion injury

Codonolactone is the main biologically active ingredient in Atractylodes lancea. Studies have shown various functions of codonolactone, while its protective effect against neurotoxicity caused by ischemic stroke is unclear. This study investigated the roles of codonolactone in inflammation, oxidative stress and apoptosis after cerebral ischemia-reperfusion (I/R) injury. Rats with codonolactone treatment, I/R treatment and the sham operation group were used in this study. After reperfusion for 24 hours, nerve damage was detected by nerve staining, and the neurological deficits of the rats were analyzed. The contents of superoxide dismutase (SOD), malondialdehyde (MDA), interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in rat brain tissues were also determined. Western blot analysis was performed to determine the expression levels of Akt/Nrf2 pathway-associated proteins. Compared with the I/R group, the cerebral blood flow, infarct volume, brain water content, coronary blood flow and neurological deficits in the codonolactone treatment group, especially with the 80 mg/kg dosage, were significantly reduced. Codonolactone could significantly reduce the expression levels of caspase-3 and Bax, and significantly increase the expression levels of Bcl-2 after I/R. In addition, codonolactone could significantly reduce MDA content and the expression levels of TNF-α and IL-1β in ischemic brain tissues. It also significantly increased SOD activity, the expression levels of heme oxygenase-1 (HO-1) and the phosphorylation of Akt and Nrf2. Codonolactone ameliorated the cerebral I/R injury by improving anti-oxidant, anti-inflammatory activities and reducing apoptosis. Besides, the Akt/Nrf2 pathway was involved in the pharmacological action of the codonolactone.

Ghrelin attenuates depressive-like behavior, heart failure, and neuroinflammation in postmyocardial infarction rat model

Depression after myocardial infarction (MI) and chronic heart failure (CHF) is a common condition that is resistant to anti-depressive drugs. Ghrelin (a peptide hormone) shows dual protective effects on heart and brain. Whether ghrelin treatment attenuated depression after MI was investigated. Coronary artery occlusion was performed to induce MI and subsequent CHF in rats. Ghrelin (100 μg/kg in 0.5 ml of saline) or vehicle (0.5 ml of saline) was injected subcutaneously twice a day for 4 weeks. At week 5, all the animals underwent behavioral assessments including sucrose preference test (SPT), elevated plus maze test (EPM), and open field test (OFT). After cardiac function analysis, brain tissues were processed to determine inflammatory cytokines and microglial activations in hippocampus. Results showed that ghrelin substantially improved cardiac dysfunction, infarction size, and cardiac remodeling and modulated the release of inflammatory cytokines and the increase of Iba-1 positive microglia and glial fibrillary acidic protein-positive astrocytes in the CA1 area of hippocampus. Behavioral tests revealed that this treatment remarkably increased sucrose preference and mobile times and numbers. These findings provided evidence that peripheral ghrelin administration inhibits depression-like behavior and neuroinflammation and thus could be a new approach for the treatment of CHF-associated depression.

Regulatory effects of ghrelin on endoplasmic reticulum stress, oxidative stress, and autophagy: Therapeutic potential

Ghrelin is a regulatory peptide that is the endogenous ligand of the growth hormone secretagogue 1a (GHS-R1a) which belongs to the G protein-coupled receptor family. Ghrelin and GHS-R1a are widely expressed in the central and peripheral tissues and play therapeutic potential roles in the cytoprotection of many internal organs. Endoplasmic reticulum stress (ERS), oxidative stress, and autophagy dysfunction, which are involved in various diseases. In recent years, accumulating evidence has suggested that ghrelin exerts protective effects by regulating ERS, oxidative stress, and autophagy in diverse diseases. This review article summarizes information about the roles of the ghrelin system on ERS, oxidative stress, and autophagy in multiple diseases. It is suggested that ghrelin positively affects the treatment of diseases and may be considered as a therapeutic drug in many illnesses.

Memantine ameliorates cognitive impairment induced by exposure to chronic hypoxia environment at high altitude by inhibiting excitotoxicity

AIMS

Memantine is a non-competitive antagonist of glutamatergic NMDA receptor that is mainly used in the treatment of Alzheimer's disease. The excitatory toxicity mediated by glutamate via glutamatergic receptor signals is considered to be one of the mechanisms mediating neuronal injury and cognitive impairment after exposure to a hypoxic environment at a high altitude. Therefore, in this study, we hypothesized that inhibiting glutamate signaling using memantine could alleviate neuronal injury and cognitive impairment in rats exposed to chronic hypoxia.

MAIN METHODS

we made animal models in the natural environment of the Qinghai-Tibet Plateau at an altitude of 4300 m, and used animal behavior, morphology, molecular biology and other methods to evaluate the impact of chronic hypoxia exposure on cognitive function and the neuroprotective effect of Memantine.

KEY FINDINGS

Our results showed that the expression of NMDA receptors increased, while the expression of AMPA receptors decreased, after 4 weeks of chronic hypoxia exposure. Concomitantly, apoptotic neuronal cell death in the hippocampus and frontal cortex was significantly increased, along with levels of oxidative stress, whereas innate ability to inhibit free radicals decreased. Moreover, after 8 weeks of hypoxia exposure, learning, memory, and space exploration abilities were significantly decreased. Notably, after treatment with memantine, apoptotic neuronal cell death, oxidative stress, and free radical levels decreased, and the cognitive function of the animals improved.

SIGNIFICANCE

Present study shows that chronic hypoxia can produce the excitatory toxicity leading to neural injury and cognitive impairment that can be suppressed with memantine treatment by inhibiting excitatory toxicity.

Modulatory effects of ghrelin on sperm quality alterations induced by a fructose-enriched diet

The objectives of this study were: 1) to evaluate the effects of a fructose enriched diet (FED) on rat sperm quality, epididymal function (i.e. oxidative stress and alpha-glucosidase expression) and testosterone concentrations; 2) to determine if the administration of ghrelin (Ghrl), reverses the effects induced by FED. After validating the protocol as an inductor of metabolic syndrome like-symptoms, adult male rats were assigned to one of the following treatments for 8 weeks: FED = 10% fructose enriched in water (v/v); FED + Ghrl = fructose enriched diet plus Ghrl (6 nmol/animal/day, s.c.) from week 6-8; or C = water without fructose (n = 5-10 animals/group). FED significantly decreased sperm concentration and motile sperm count/ml vs C (FED: 19.0 ± 1.6 × 10⁶sperm/ml and 834.6 ± 137.0, respectively vs C: 25.8 ± 2.8 × 10⁶ and 1300.4 ± 202.4, respectively; p < 0.05); ghrelin injection reversed this negative effect (23.5 ± 1.6 × 10⁶sperm/ml and 1381.7 ± 71.3 respectively). FED resulted in hypogonadism, but Ghrl could not normalize testosterone concentrations (C: 1.4 ± 0.1 ng/ml vs FED: 0.8 ± 0.2 ng/ml and FED + Ghrl: 0.6 ± 0.2 ng/ml; p < 0.05). Ghrelin did not reverse metabolic abnormalities secondary to FED. FED did not alter epididymal expression of antioxidants enzymes (superoxido-dismutase, catalase and glutathione peroxidases -Gpx-). Nevertheless, FED + Ghrl significantly increased the expression of Gpx3 (FED + Ghrl: 3.47 ± 0.48 vs FED: 0.69 ± 0.28 and C: 1.00 ± 0.14; p < 0.05). The expression of neutral alpha-glucosidase, which is a marker of epididymal function, did not differ between treatments. In conclusion, the administration of Ghrl modulated the negative effects of FED on sperm quality, possibly by an epididymal increase in Gpx3 expression. However, Ghrl could not neither normalize the metabolism of FED animals, nor reverse hypogonadism.

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.

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).