Growth hormone releasing hormone (GHRH) signaling modulates intermittent hypoxia-induced oxidative stress and cognitive deficits in mouse

Role of Oxidative Stress in the Occurrence and Development of Cognitive Dysfunction in Patients with Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) causes recurrent apnea and intermittent hypoxia at night, leading to several complications such as cognitive dysfunction. However, the molecular mechanisms underlying cognitive dysfunction in OSAS are unclear, and oxidative stress mediated by intermittent hypoxia is an important mechanism. In addition, the improvement of cognitive dysfunction in patients with OSAS varies by different treatment regimens; among them, continuous positive airway pressure therapy (CPAP) is mostly recognized for improving cognitive dysfunction. In this review, we discuss the potential mechanisms of oxidative stress in OSAS, the common factors of affecting oxidative stress and the Links between oxidative stress and inflammation in OSAS, focusing on the potential links between oxidative stress and cognitive dysfunction in OSAS and the potential therapies for neurocognitive dysfunction in patients with OSAS mediated by oxidative stress. Therefore, further analysis on the relationship between oxidative stress and cognitive dysfunction in patients with OSAS will help to clarify the etiology and discover new treatment options, which will be of great significance for early clinical intervention.

Recovery Mimicking "Ideal" CPAP Adherence Does Not Improve Wakefulness or Cognition in Chronic Murine Models of OSA: Effect of Wake-Promoting Agents

INTRODUCTION

Obstructive sleep apnea (OSA) is a chronic condition characterized by intermittent hypoxia (IH) and sleep fragmentation (SF). OSA can induce excessive daytime sleepiness (EDS) and is associated with impaired cognition and anxiety. Solriamfetol (SOL) and modafinil (MOD) are widely used wake-promoting agents in OSA patients with EDS.

METHODS

Male C57Bl/6J mice were exposed to SF along with sleep controls (SC) or to IH and room air (RA) controls during the light (inactive) phase for 4 and 16 weeks, respectively. Both IH and SF exposures were then discontinued to mimic "ideal" continuous positive airway pressure (CPAP) adherence. All groups were then randomly assigned to receive once daily intraperitoneal injections of SOL, MOD, or vehicle (VEH) for 6 days. Sleep/wake activity was assessed along with tests of explicit memory, anxiety and depression were performed before and after treatments.

RESULTS

IH and SF exposures increased sleep percentage in the dark phase and reduced wake bouts lengths (i.e., EDS), and induced cognitive deficits and impulsivity in mice. Both SOL and MOD treatments effectively mitigated EDS when combined with recovery, while recovery alone did not improve EDS over the 6-day period. Furthermore, improvements explicit memory emerged only after SOL.

CONCLUSION

Chronic IH and SF induce EDS in young adult mice that is not ameliorated by recovery except when combined with either SOL or MOD. SOL, but not MOD, significantly improves IH-induced cognitive deficits. Thus, SOL emerges as a viable adjuvant medication for residual EDS in OSA along with its positive impact on cognition.

Comparison of hyperoxia or normoxia resolution of intermittent hypoxia and intermittent hyperoxia episodes on liver histopathology, IGF-1, IGFBP-3, and GHBP in neonatal rats

OBJECTIVE

Extremely low gestational age neonates requiring oxygen therapy for chronic lung disease experience repeated fluctuations in arterial oxygen saturation, or intermittent hypoxia (IH), during the first few weeks of life. These events are associated with a high risk for reduced growth, hypertension, and insulin resistance in later life. This study tested the hypothesis that IH, or intermittent hyperoxia have similar negative effects on the liver; somatic growth; and liver insulin-like growth factor (IGF)-I, IGF binding protein (BP)-3, and growth hormone binding protein (GHBP), regardless of resolution in normoxia or hyperoxia between episodes.

DESIGN

Newborn rats on the first day of life (P0) were exposed to two IH paradigms: 1) hyperoxia (50% O2) with brief hypoxia (12% O2); or 2) normoxia (21% O2) with hypoxia (12% O2); intermittent hypoxia (50% O2/21% O2); hyperoxia only (50% O2); or room air (RA, 21% O2). Pups were euthanized on P14 or placed in RA until P21. Controls remained in RA from P0-P21. Growth, liver histopathology, apoptosis, IGFI, IGFBP-3, and GHBP were assessed.

RESULTS

Pathological findings of the liver hepatocytes, including cellular swelling, steatosis, apoptosis, necrosis and focal sinusoid congestion were seen in the IH and intermittent hyperoxia groups, and were particularly severe in the 21-12% O2 group during exposure (P14) with no significant improvements during recovery/reoxygenation (P21). These effects were associated with induction of HIF1α, and reductions in liver IGFI, IGFBP-3, and GHBP.

CONCLUSIONS

Exposure to IH or intermittent hyperoxia during the first few weeks of life regardless of resolution in RA or hyperoxia is detrimental to the immature liver. These findings may suggest that interventions to prevent frequent fluctuations in oxygen saturation during early neonatal life remain a high priority.

Summary of drug therapy to treat cognitive impairment-induced obstructive sleep apnea

Obstructive sleep apnea (OSA) is a severe sleep disorder associated with intermittent hypoxia and sleep fragmentation. Cognitive impairment is a signifi- cant and common OSA complication often described in such patients. The most commonly utilized methods in clinical OSA treatment are oral appliances and continuous positive airway pressure (CPAP). However, the current therapeutic methods for improving cognitive function could not achieve the expected efficacy in same patients. Therefore, further understanding the molecular mechanism behind cognitive dysfunction in OSA disease will provide new treatment methods and targets. This review briefly summarized the clinical manifestations of cognitive impairment in OSA disease. Moreover, the pathophysiological molecular mechanism of OSA was outlined. Our study concluded that both SF and IH could induce cognitive impairment by multiple signaling pathways, such as oxidative stress activation, inflammation, and apoptosis. However, there is a lack of effective drug therapy for cognitive impairment in OSA. Finally, the therapeutic potential of some novel compounds and herbal medicine was evaluated on attenuating cognitive impairment based on certain preclinical studies.

Solriamfetol enhances wakefulness and improves cognition and anxiety in a murine model of OSA

BACKGROUND

Obstructive sleep apnea (OSA) is a chronic condition characterized by intermittent hypoxia (IH). Excessive daytime sleepiness (EDS) is a common consequence of OSA and is associated with cognitive deficits and anxiety. Modafinil (MOD) and Solriamfetol (SOL) are potent wake-promoting agents clinically used to improve wakefulness in OSA patients with EDS.

METHODS

Male C57Bl/6J mice were exposed to either IH or room air (RA) controls during the light phase for 16 weeks. Both groups were then randomly assigned to receive once-daily intraperitoneal injections of SOL (200 mg/kg), MOD (200 mg/kg) or vehicle (VEH) for 9 days while continuing IH exposures. Sleep/wake activity was assessed during the dark (active) phase. Novel object recognition (NOR), elevated-plus maze test (EPMT), and forced swim test (FST) were performed before and after drug treatment.

RESULTS

IH exposure increased dark phase sleep percentage and reduced wake bouts lengths and induced cognitive deficits and anxiogenic effects. Both SOL and MOD treatments decreased sleep propensity under IH conditions, but only SOL promoted improvements in NOR performance (explicit memory) and reduced anxiety-like behaviors.

CONCLUSION

Chronic IH, a hallmark feature of OSA, induces EDS in young adult mice that is ameliorated by both SOL and MOD. SOL, but not MOD, significantly improves IH-induced cognitive deficits and promotes anxiolytic effects. Thus, SOL could potentially benefit OSA patients beyond EDS management.

Explicit memory, anxiety and depressive like behavior in mice exposed to chronic intermittent hypoxia, sleep fragmentation, or both during the daylight period

Obstructive sleep apnea (OSA) is a chronic and highly prevalent condition characterized by chronic intermittent hypoxia (IH) and sleep fragmentation (SF), and can lead to a vast array of end-organ morbidities, particularly affecting cardiovascular, metabolic and neurobehavioral functioning. OSA can induce cognitive and behavioral and mood deficits.

Male C57Bl/6J 8-week-old mice were housed in custom-designed cages with a silent motorized mechanical sweeper traversing the cage floor at 2-min intervals (SF) during daylight for four weeks. Sleep control (SC) consisted of keeping sweeper immobile. IH consisted of cycling FiO₂ 21% 90 seconds-6.3% 90s or room air (RA; FiO₂ 21%) for sixteen weeks and combined SF-IH was conducted for nine weeks. Open field novel object recognition (NOR) testing, elevated-plus maze test (EPMT), and forced swimming test (FST) were performed.

SF induced cognitive NOR performance impairments in mice along with reduced anxiety behaviors while IH induced deficits in NOR performance, but increased anxiety behaviors. SF-IH induced impaired performance in NOR test of similar magnitude to IH or SF alone. Combined SF-IH exposures did not affect anxiety behaviors.

Thus, both SF an IH altered cognitive function while imposing opposite effects on anxiety behaviors. SF-IH did not magnify the detrimental effects of isolated SF or IH and canceled out the effects on anxiety. Based on these findings, the underlying pathophysiologic processes underlying IH and SF adverse effects on cognitive function appear to differ, while those affecting anxiety counteract each other.

The effect of central growth hormone action on hypoxia ventilatory response in conscious mice

Growth hormone (GH)-responsive neurons regulate several homeostatic behaviors including metabolism, energy balance, arousal, and stress response. Therefore, it is possible that GH-responsive neurons play a role in other responses such as CO2/H+-dependent breathing behaviors. Here, we investigated whether central GH receptor (GHR) modulates respiratory activity in conscious unrestrained mice. First, we detected clusters of GH-responsive neurons in the tyrosine hydroxylase-expressing cells in the rostroventrolateral medulla (C1 region) and within the locus coeruleus (LC). No significant expression was detected in phox2b-expressing cells in the retrotrapezoid nucleus. Whole body plethysmography revealed a reduction in the tachypneic response to hypoxia (FiO2 = 0.08) without changing baseline breathing and the hypercapnic ventilatory response. Contrary to the physiological findings, we did not find significant differences in the number of fos-activated cells in the nucleus of the solitary tract (NTS), C1, LC and paraventricular nucleus of the hypothalamus (PVH). Our finding suggests a possible secondary role of central GH action in the tachypneic response to hypoxia in conscious mice.

Reduced circulating growth hormone and insulin-like growth factor-1 and delayed growth of premature rats are aggravated by longer daily duration of chronic intermittent hypoxia exposure

OBJECTIVE

This study mainly aimed to investigate the effect of daily duration of chronic intermittent hypoxia (CIH) exposure on circulating growth hormone (GH)/insulin-like growth factor-1 (IGF-1) concentrations and body weight changes of premature rats.

METHODS

40 healthy male SD rats aged six weeks were enrolled in this study. These rats were randomly divided into four groups (n = 10 per group), including normal control (NC) group (normal oxygen exposure every day), CIH-1 group (daily CIH exposure for 2 h), CIH-2 group (daily CIH exposure for 4 h), and CIH-3 group (daily CIH exposure for 8 h). The serum GH/IGF-1 concentrations and body weights in all rats were determined after 30 days of normal oxygen or CIH exposure.

RESULTS

No significant difference was found with respect to the baseline body weight among the four groups of rats. After establishments of animal models with a duration of 30 days, significant differences were found respect to body weight, body weight changes, and serum GH/IGF-1 concentrations among the four groups of rats with a same trend (all P < 0.05): the highest values were all in NC group rats, followed CIH-1 group, CIH-2 group, and CIH-3 group rats. Among all the rats, the body weight changes correlated significantly with both serum GH and IGF-1 concentrations (both P < 0.05).

CONCLUSION

CIH decreases circulating GH/IGF-1 concentrations and causes growth delay in premature rats. Such effects could be aggravated by increased daily duration of CIH exposures.

Mechanisms Underlying the Protective Effect of the Peroxiredoxin-6 Are Mediated via the Protection of Astrocytes during Ischemia/Reoxygenation

Ischemia-like conditions reflect almost the entire spectrum of events that occur during cerebral ischemia, including the induction of oxidative stress, Ca²⁺ overload, glutamate excitotoxicity, and activation of necrosis and apoptosis in brain cells. Mechanisms for the protective effects of the antioxidant enzyme peroxiredoxin-6 (Prx-6) on hippocampal cells during oxygen-glucose deprivation/reoxygenation (OGD/R) were investigated. Using the methods of fluorescence microscopy, inhibitory analysis, vitality tests and PCR, it was shown that 24-h incubation of mixed hippocampal cell cultures with Prx-6 does not affect the generation of a reversible phase of a OGD-induced rise in Ca²⁺ ions in cytosol ([Ca²⁺]_i), but inhibits a global increase in [Ca²⁺]_i in astrocytes completely and in neurons by 70%. In addition, after 40 min of OGD, cell necrosis is suppressed, especially in the astrocyte population. This effect is associated with the complex action of Prx-6 on neuroglial networks. As an antioxidant, Prx-6 has a more pronounced and astrocyte-directed effect, compared to the exogenous antioxidant vitamin E (Vit E). Prx-6 inhibits ROS production in mitochondria by increasing the antioxidant capacity of cells and altering the expression of genes encoding redox status proteins. Due to the close bond between [Ca²⁺]_i and intracellular ROS, this effect of Prx-6 is one of its protective mechanisms. Moreover, Prx-6 effectively suppresses not only necrosis, but also apoptosis during OGD and reoxygenation. Incubation with Prx-6 leads to activation of the basic expression of genes encoding protective kinases—PI3K, CaMKII, PKC, anti-apoptotic proteins—Stat3 and Bcl-2, while inhibiting the expression of signaling kinases and factors involved in apoptosis activation—Ikk, Src, NF-κb, Caspase-3, p53, Fas, etc. This effect on the basic expression of the genome leads to the cell preconditions, which is expressed in the inhibition of caspase-3 during OGD/reoxygenation. A significant effect of Prx-6 is directed on suppression of the level of pro-inflammatory cytokine IL-1β and factor TNFα, as well as genes encoding NMDA- and kainate receptor subunits, which was established for the first time for this antioxidant enzyme. The protective effect of Prx-6 is due to its antioxidant properties, since mutant Prx-6 (mutPrx-6, Prx6-C47S) leads to polar opposite effects, contributing to oxidative stress, activation of apoptosis and cell death through receptor action on TLR4.

Depletion of SENP1-mediated PPARγ SUMOylation exaggerates intermittent hypoxia-induced cognitive decline by aggravating microglia-mediated neuroinflammation

Intermittent hypoxia (IH)-associated cognition decline is related to the neuroinflammation of microglia. SUMOylation is a post-translational modification related to multiple human diseases, which can be reversed by SENP1. Studies showed that SENP1 and PPARγ play essential roles in restricting inflammation by blocking NF-κB activation. However, the mechanism remains unclear. Herein, we investigated the precise mechanism underlying SENP1 and PPARγ in cognitive decline after IH insult. Biochemical analysis results revealed that IH triggered the inflammatory response and neuronal apoptosis, increased the SUMOylation of PPARγ, and decreased the level of PPARγ compared to that in the normoxia group. After SENP1 downregulation, the inflammatory response, neuronal apoptosis and the SUMOylation of PPARγ were enhanced, and the level of PPARγ was further decreased in vitro and in vivo. However, the application of PPARγ agonist, GW1929, abolished the enhancement of inflammation and neuronal apoptosis in vitro. The Morris Water Maze results showed that both IH groups mice exhibited longer latency and shorter dwell-time in the goal quadrant than normoxia groups. Notably, SENP1 downregulation aggravated these alterations. Overall, these results showed that SENP1 played an essential role in IH-associated cognitive dysfunction. SENP1 depletion aggravated neuroinflammation and neuronal apoptosis via promoting the SUMOylation of PPARγ, reducing the level of PPARγ, thus exaggerating IH-induced cognitive decline.

Gestational sleep apnea perturbations induce metabolic disorders by divergent epigenomic regulation

Aim: Late-gestational sleep fragmentation (LG-SF) and intermittent hypoxia (LG-IH), two hallmarks of obstructive sleep apnea, lead to metabolic dysfunction in the offspring. We investigated specific biological processes that are epigenetically regulated by LG-SF and LG-IH. Materials & methods: We analyzed DNA methylation profiles in offspring visceral white adipose tissues by MeDIP-chip followed by pathway analysis. Results: We detected 1187 differentially methylated loci (p < 0.01) between LG-SF and LG-IH. Epigenetically regulated genes in LG-SF offspring were associated with lipid and glucose metabolism, whereas those in LG-IH were related to inflammatory signaling and cell proliferation. Conclusion: While LG-SF and LG-IH will result in equivalent phenotypic alterations in offspring, each paradigm appears to operate through epigenetic regulation of different biological processes.

Intermittent Hypoxia Activates N-Methyl-D-Aspartate Receptors to Induce Anxiety Behaviors in a Mouse Model of Sleep-Associated Apnea

Sleep apnea disrupts physiologic homeostasis and causes neuronal dysfunction. In addition to signs of mental disorders and cognitive dysfunction, patients with sleep apnea have a higher anxiety rate. Here, we examined the mechanisms underlying this critical health issue. We used a mouse model with sleep-associated chronic intermittent hypoxia (IH) to verify the effects of sleep apnea on neuronal dysfunction. To evaluate how IH alters neuronal function to yield anxiety-like behavior and cognitive dysfunction, we examined synaptic plasticity and neuronal inflammation in related brain areas, including the medial prefrontal cortex (mPFC), striatum, and hippocampus. Mice subjected to chronic IH for 10 days exhibited significant anxiety-like behaviors in the elevated plus maze test. IH mice spent less travel time in open arms and more travel time in enclosed arms compared to control mice. However, cognitive impairment was minimal in IH mice. Increased glutamate N-methyl-D-aspartate (NMDA) receptor subunits 2B (GluN2B) and phosphorylated-ERK1/2 were seen in the mPFC, striatum, and hippocampus of IH mice, but no significant microglial and astrocyte activation was found in these brain areas. Chronic IH in mice induced compensatory increases in GluN2B to disturb neuronal synaptic plasticity, without neuronal inflammation. The altered synaptic plasticity subsequently led to anxiety-like behavior in mice. Treatment with the NMDA receptor antagonist dextromethorphan attenuated chronic IH-induced anxiety-like behavior and GluN2B expression. Our findings provide mechanistic evidence of how IH may provoke anxiety and support for the importance of early intervention to alleviate anxiety-associated complications in patients with chronic sleep apnea.

Integration of quantitative proteomics and metabolomics reveals tissue hypoxia mechanisms in an ischemic-hypoxic rat model

Tissues hypoxia caused by hemorrhage is a common complication in many clinical diseases. However, its pathological mechanism remains largely unknown. To partly address this issue, an ischemic-hypoxic rat model was established and the plasma proteomic and metabolic profiles were quantified and analyzed using TMT-based quantitative proteomics and metabolomics. The analysis revealed a total of 177 differentially expressed proteins and 32 metabolites that were uniquely altered in the hypoxic rat plasma, compared to the control. Bioinformatics analysis showed that these altered proteins and metabolites were involved in a wide range of biological processes. Twelve of the 177 differentially expressed proteins were involved in PI3K-Akt signaling, a pathway that has been reported to be strongly associated with tissue hypoxia. Other signaling pathways such as complement and coagulation cascades, GnRH signaling, relaxin signaling, protein processing in endoplasmic reticulum, as well as AGE-RAGE signaling were markedly altered in the ischemic-hypoxic response, implying their potential roles in tissue hypoxia. A joint analysis of proteome and metabolome showed that the significantly altered metabolites such as guanine, tryptamine, dopamine, hexadecenoic, l-methionine, and fumarate may have participated in the pathogenesis of tissue hypoxia. Further, we found that changes in the levels of metabolites matched the changes in protein abundance within the same pathway. Overall, this study presents an overview of the molecular networks in ischemic-hypoxic pathology and offers biochemical basis for further study on the mechanism of tissue hypoxia. SIGNIFICANCE: We employed an integrated metabonomic-proteomic method to systematically analyze the profiles of metabolites and proteins in an ischemic-hypoxic rat model. Bioinformatics and enrichment analysis showed that the differentially expressed proteins were mainly involved in complement and coagulation cascades, PI3K-Akt signaling, GnRH signaling, relaxin signaling, protein processing in endoplasmic reticulum, and AGE-RAGE signaling. Moreover, a panel of 12 candidate proteins involved in PI3K-Akt signaling (i.e., Vtn, Hsp90b1, Ywhae, Tnc, Ywhaz, Thbs4, Lamc1, Col1a1, Il2rg, Egfr, Newgene 621,351, and Tfrc) may serve as the potential biomarkers to predict tissue hypoxia.

Antinflammatory, antioxidant, and behavioral effects induced by administration of growth hormone-releasing hormone analogs in mice

Growth hormone-releasing hormone (GHRH) antagonist MIA-690 and GHRH agonist MR-409, previously synthesized and developed by us have demonstrated potent antitumor effects. However, little is known about the effects of these analogs on brain functions. We investigated the potential antinflammatory and antioxidant effects of GHRH antagonist MIA-690 and GHRH agonist MR-409, on isolated mouse prefrontal cortex specimens treated with lipopolysaccharide (LPS). Additionally, we studied their effects on emotional behavior after chronic in vivo treatment. Ex vivo, MIA-690 and MR-409 inhibited LPS-induced inflammatory and pro-oxidative markers. In vivo, both MIA-690 and MR-409 induced anxiolytic and antidepressant-like effects, increased norepinephrine and serotonin levels and decreased nuclear factor-kB, tumor necrosis factor-α and interleukin-6 gene expression in prefrontal cortex. Increased nuclear factor erythroid 2–related factor 2 expression was also found in mice treated with MIA-690 and MR-409. MIA-690 showed higher efficacy in inhibiting all tested inflammatory and oxidative markers. In addition, MR-409 induced a down regulation of the gene and protein expression of pituitary-type GHRH-receptor in prefrontal cortex of mice after 4 weeks of treatment at 5 µg/day. In conclusion, our results demonstrate anxiolytic and antidepressant-like effects of GHRH analogs that could involve modulatory effects on monoaminergic signaling, inflammatory and oxidative status.

Sleep and the GH/IGF-1 axis: Consequences and countermeasures of sleep loss/disorders

This article presents an up-to-date review of the state-of-the-art knowledge regarding the effect of sleep on the anabolic growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis. This axis is involved in learning and memory and neuroprotection at the central level, and in the crosstalk between sleep and the immune system, with respect to its anti-inflammatory properties. We also aim to provide insight into the consequences of sleep loss on cognitive capacities in healthy individuals and patients with obstructive sleep apnea (OSA), regarding the mechanistic association with the GH/IGF-1 axis. Finally, this review examines the inflammatory/endocrine pathways that are affected by sleep loss, and which may consequently interact with the GH/IGF-1 axis. The deleterious effects of sleep loss include fatigue, and can cause several adverse age-dependent health outcomes. It is therefore important to improve our understanding of the fundamental physiology underlying these effects in order to better apply non-pharmacological countermeasures (e.g., sleep strategies, exercise training, continuous positive airway pressure therapy) as well as pharmacological solutions, so as to limit the deleterious consequences of sleep loss/disorders.

Effects of somatotropic axis on cognitive dysfunction of obstructive sleep apnea

PURPOSE

Obstructive sleep apnea (OSA) is associated with a variety of neuroendocrine disorders and may lead to many complications, including cognitive dysfunction. The aim of this study was to assess the change of somatotropic axis and to detect the relation between somatotropic axis hormone and cognitive dysfunction.

METHODS

Sixty-six patients with OSA and 16 healthy controls were enrolled in this cross-sectional study. Cognitive function assessment using the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) and polysomnography were performed on all individuals. Blood samples were taken the next morning following the polysomnography and the level of serum growth hormone-releasing hormone (GHRH) and growth hormone (GH) were analyzed by enzyme-linked immunosorbent assay.

RESULTS

Compared with the control group, OSA patients showed significantly lower serum GH level (p < 0.05), whereas no statistical significance of GHRH level was found. In addition, lower MMSE and MoCA scores were found only in the severe OSA patients when compared with the controls. Furthermore, in severe OSA patients with cognitive dysfunction (MMSE score < 27 and MoCA score < 26), serum GHRH and GH levels were significantly lower than those without cognitive dysfunction. Logistic analysis revealed that cognitive dysfunction in severe OSA patients was associated with micro-arousal index and the level of serum GHRH and GH.

CONCLUSION

Decreased serum GH and GHRH levels were found among severe OSA patients with cognitive dysfunction who were overweight, which might promote the occurrence of cognitive dysfunction.

Taxifolin protects neurons against ischemic injury in vitro via the activation of antioxidant systems and signal transduction pathways of GABAergic neurons

Cerebral blood flow disturbances lead to the massive death of brain cells. The death of >80% of cells is observed in hippocampal cell cultures after 40 min of oxygen and glucose deprivation (ischemia-like conditions, OGD). However, there are some populations of GABAergic neurons which are characterized by increased vulnerability to oxygen-glucose deprivation conditions. Using fluorescent microscopy, immunocytochemical assay, vitality tests and PCR-analysis, we have shown that population of GABAergic neurons are characterized by a different (faster) Ca²⁺ dynamics in response to OGD and increased basal ROS production under OGD conditions. A plant flavonoid taxifolin inhibited an excessive ROS production and an irreversible cytosolic Ca²⁺ concentration increase in GABAergic neurons, preventing the death of these neurons and further excitation of a neuronal network; neuroprotective effect of taxifolin increased after incubation of 24 h and correlated with increased expression of antiapoptocic and antioxidant genes Stat3 Nrf-2 Bcl-2, Bcl-xL, Ikk2, and genes coding for AMPA and kainate receptor subunits; in addition, taxifolin decreased expression of prooxidant enzyme NOS and proinflammatory cytokine IL-1β.

Intermittent hypoxia suppression of growth hormone and insulin-like growth factor-I in the neonatal rat liver

OBJECTIVES

Extremely low gestational age neonates with chronic lung disease requiring oxygen therapy frequently experience fluctuations in arterial oxygen saturation or intermittent hypoxia (IH). These infants are at risk for multi-organ developmental delay, reduced growth, and short stature. The growth hormone (GH)/insulin-like growth factor-I (IGF-1) system, an important hormonal regulator of lipid and carbohydrate metabolism, promotes neonatal growth and development. We tested the hypothesis that increasing episodes of IH delay neonatal growth by influencing the GH/IGF-I axis.

DESIGN

Newborn rats were exposed to 2, 4, 6, 8, 10, or 12 hypoxic episodes (12% O₂) during hyperoxia (50% O₂) from P0-P7, P0-P14 (IH), or allowed to recover from P7-P21 or P14-P21 (IHR) in room air (RA). RA littermates at P7, P14, and P21 served as RA controls; and groups exposed to hyperoxia only (50% O₂) served as zero IH controls. Histopathology of the liver; hepatic levels of GH, GHBP, IGF-I, IGFBP-3, and leptin; and immunoreactivities of GH, GHR, IGF-I and IGF-IR were determined.

RESULTS

Pathological findings of the liver, including cellular swelling, steatosis, necrosis and focal sinusoid congestion were seen in IH, and were particularly severe in the P7 animals. Hepatic GH levels were significantly suppressed in the IH groups exposed to 6-12 hypoxic episodes per day and were not normalized during IHR. Deficits in the GH levels were associated with reduced body length and increase body weight during IHR suggesting increased adiposity and catchup fat. Catchup fat was also associated with elevations in GHBP, IGF-I, leptin.

CONCLUSIONS

IH significantly impairs hepatic GH/IGF-1 signaling during the first few weeks of life, which is likely responsible for hepatic GH resistance, increased body fat, and hepatic steatosis. These hormonal perturbations may contribute to long-term organ and body growth impairment, and metabolic dysfunction in preterm infants experiencing frequent IH and/or apneic episodes.

Interactions between GHRH and GABAARs in the brains of patients with epilepsy and in animal models of epilepsy

Growth hormone releasing hormone (GHRH) has recently been shown to increase the level of γ-aminobutyric acid (GABA) and activate GABA receptors (GABARs) in the cerebral cortex. GABA is an inhibitory neurotransmitter that can inhibit seizures. Does GHRH enhance the inhibitory effect of GABA to prevent epilepsy by increasing the GABA level and activating GABARs? In this study, patients with epilepsy and C57/BL6 mice with epilepsy induced by kainic acid (KA) or pentylenetetrazol (PTZ) served as the research subjects. Western blots were used to observe the differences in GHRH expression between the normal group and the epilepsy group, immunofluorescence was performed to explore the localization of GHRH in the brain, and coimmunoprecipitation was used to observe the interaction between GHRH and GABARs. GHRH expression was significantly increased in both patients with temporal lobe epilepsy (TLE) and in two mouse models induced by KA or PTZ compared with that in the normal groups (P < 0.05 or P < 0.01). GHRH was expressed in neurons in both humans and mice. Additionally, GHRH co-localized with presynaptic and postsynaptic sites of inhibitory neurons. Coimmunoprecipitation confirmed that GHRH interacted with GABAAα1 and GABAAβ2 + 3. GHRH may play an important role in inhibiting seizures by activating GABAARs.

Temporal trajectories of novel object recognition performance in mice exposed to intermittent hypoxia

Intermittent hypoxia is one of the major perturbations of sleep-disordered breathing and has been causally implicated in neurocognitive deficits. However, the reversibility of such deficits is unclear.

Male C57BL/6J mice were exposed to either intermittent hypoxia or room air for 3–240 days, and then half were randomly selected and allowed to recover in normoxic conditions for the same duration of the previous exposure. A novel object recognition (NOR) test was performed.

NOR performance was stable over time in room air. Intermittent hypoxia induced significant reductions in recognition index that progressed over the first 45 days and stabilised thereafter. Normoxic recovery of recognition index was essentially complete and indistinguishable from room air in mice exposed to shorter intermittent hypoxia times (<90 days). However, significant residual deficits emerged after normoxic recovery following prolonged intermittent hypoxia exposures (p<0.01). In addition, gradual attenuation of the magnitude of recovery in recognition index occurred with increasingly longer intermittent hypoxia exposures (MANOVA p<0.0001).

Intermittent hypoxia during the resting period reduces NOR performance in a time-dependent fashion. Reversal of NOR performance deficits is unlikely after prolonged intermittent hypoxia duration. These findings suggest that early recognition of sleep apnoea and effective treatment are critical for restoration of the adverse cognitive effects of the disease.

Monoamine oxidase A upregulated by chronic intermittent hypoxia activates indoleamine 2,3-dioxygenase and neurodegeneration

Co-morbid depression is prevalent in patients with obstructive sleep apnea. Here we report that monoamine oxidase A (MAO-A) plays pathogenic roles in the comorbidity. We found that chronic intermittent hypoxia significantly increased the MAO-A expression in the rat hippocampus and markedly decreased the dendritic length and spine density in the pyramidal neurons with less pre- and post-synaptic proteins. The MAO-A upregulation resulted in increased 5-hydroxyindoleacetic acid/serotonin ratio, oxidative stress, leading to NF-κB activation, inflammation and apoptosis. Also, the expression of cytokine-responsive indoleamine 2,3-dioxygenase-1 (IDO-1) was significantly augmented in hypoxia, resulting in increased kynurenine/tryptophan ratio and lowered serotonin level in the hippocampus. Moreover, depressive-like behaviors were observed in the hypoxic rat. Administration of M30, a brain-selective MAO-A inhibitor with iron-chelating properties, prior to hypoxic treatment prevented the aberrant changes in the hippocampus and depressive behavior. In human SH-SY5Y cells expressing MAO-A but not MAO-B, hypoxia significantly increased the MAO-A expression, which was blocked by M30 or clorgyline. Collectively, the MAO-A upregulation induced by chronic intermittent hypoxia plays significant pathogenic role in oxidative stress, inflammation and IDO-1 activation resulting in serotonin depletion and neurodegeneration.

Role of Oxidative Stress in the Neurocognitive Dysfunction of Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is characterized by chronic nocturnal intermittent hypoxia and sleep fragmentations. Neurocognitive dysfunction, a significant and extraordinary complication of OSAS, influences patients' career, family, and social life and reduces quality of life to some extent. Previous researches revealed that repetitive hypoxia and reoxygenation caused mitochondria and endoplasmic reticulum dysfunction, overactivated NADPH oxidase, xanthine oxidase, and uncoupling nitric oxide synthase, induced an imbalance between prooxidants and antioxidants, and then got rise to a series of oxidative stress (OS) responses, such as protein oxidation, lipid peroxidation, and DNA oxidation along with inflammatory reaction. OS in brain could trigger neuron injury especially in the hippocampus and cerebral cortex regions. Those two regions are fairly susceptible to hypoxia and oxidative stress production which could consequently result in cognitive dysfunction. Apart from continuous positive airway pressure (CPAP), antioxidant may be a promising therapeutic method to improve partially reversible neurocognitive function. Understanding the role that OS played in the cognitive deficits is crucial for future research and therapeutic strategy development. In this paper, recent important literature concerning the relationship between oxidative stress and cognitive impairment in OSAS will be summarized and the results can provide a rewarding overview for future breakthrough in this field.

Chronic intermittent hypoxia and obstructive sleep apnea: an experimental and clinical approach

Obstructive sleep apnea (OSA) is a prevalent sleep disorder considered as an independent risk factor for cardiovascular consequences, such as systemic arterial hypertension, ischemic heart disease, cardiac arrhythmias, metabolic disorders, and cognitive dysfunction. The pathogenesis of OSA-related consequence is assumed to be chronic intermittent hypoxia (IH) inducing alterations at the molecular level, oxidative stress, persistent systemic inflammation, oxygen sensor activation, and increase of sympathetic activity. Overall, these mechanisms have an effect on vessel permeability and are considered to be important factors for explaining vascular, metabolic, and cognitive OSA-related consequences. The present review attempts to examine together the research paradigms and clinical studies on the effect of acute and chronic IH and the potential link with OSA. We firstly describe the literature data on the mechanisms activated by acute and chronic IH at the experimental level, which are very helpful and beneficial to explaining OSA consequences. Then, we describe in detail the effect of IH in patients with OSA that we can consider "the human model" of chronic IH. In this way, we can better understand the specific pathophysiological mechanisms proposed to explain the consequences of IH in OSA.

Tumor circulating DNA profiling in xenografted mice exposed to intermittent hypoxia

Intermittent hypoxia (IH) a hallmark characteristic of obstructive sleep apnea (OSA), is proposed as a major determinant of processes involving tumor growth, invasion and metastasis. To examine whether circulating DNA (cirDNA) in blood plasma reflects changes in tumor cells under IH conditions, we used a xenografted murine model. Mice engrafted with TC1 epithelial lung cancer cells and controls were exposed to IH or room air (RA) conditions. Plasma cirDNA amounts were significantly increased in mice exposed to IH (p<0.05). Significant associations between plasma cirDNA concentrations and tumor size, weight and invasiveness also emerged (p<0.05). Using a methylation microarray-based approach, we identified 2,094 regions showing significant differential cirDNA modifications. Systems biology analyses revealed an association with molecular pathways deregulated in cancer progression and with distal and TSS-associated transcription factor binding sites. We detected clusters of highly variable regions in chromosomes 7, 13, 14 and X, which may highlight hotspots for DNA deletions. Single locus displayed high intragroup variation, suggesting cellular heterogeneity within the tissue may be associated to cirDNA release. Thus, exposures to IH increase the shedding of cirDNA into circulation, which carries epigenetic modifications that may characterize cell populations within the tumor that preferentially release their DNA upon IH exposure.

GRK5 deficiency leads to susceptibility to intermittent hypoxia-induced cognitive impairment

Obstructive sleep apnea (OSA) leads to cognitive impairment in about 25% patients, though it remains elusive what makes one more susceptible than the other to be cognitively impaired. G protein-coupled receptor kinase-5 (GRK5) deficiency is recently found to render subjects more susceptible to cognitive impairment triggered by over-expression of Swedish mutant ß-amyloid precursor protein. This study is to determine whether GRK5 deficiency also renders subjects more susceptible to the OSA-triggered cognitive impairment. Both wild type (WT) and GRK5 knockout (KO) mice were placed in conditions absence and presence of intermittent hypoxia (IH) with 8%/21% O2 90-s cycle for 8h a day for a month, and then followed by behavioral assessments with battery of tasks. We found that the selected IH condition only induced marginally abnormal behavior (slightly elevated anxiety with most others unchanged) in the WT mice but it caused significantly more behavioral deficits in the KO mice, ranging from elevated anxiety, impaired balancing coordination, and impaired short-term spatial memory. These results suggest that GRK5 deficiency indeed makes the mice more susceptible to wide range of behavioral impairments, including cognitive impairments.

Increased incidence of intermittent hypoxemia in the Ts65Dn mouse model of Down syndrome

In addition to nervous system, cardiovascular and respiratory systems are primarily affected in Down syndrome (DS). The Ts65Dn mouse model is widely used to recapitulate cognitive dysfunction in DS. While these mice consistently show failure in learning and memory along with functional and structural abnormalities in the hippocampal region, the underlying mechanisms behind cognitive dysfunction remain to be fully elucidated. Convergent evidence implicates chronic episodes of hypoxemia in cognitive dysfunction in people with DS. Using an infra-red detection system to assess oxygen saturation in free-moving mice, we assessed arterial blood oxygenation in both adolescent and adult Ts65Dn mice and found a significant increase in the incidence of hypoxemia in both groups. Notably, the severity of hypoxemia increased during the dark cycle, suggesting a link between hypoxemia and increased motor activity. Postmortem analysis showed significant increase in the expression of mitochondrial Cox4i2, the terminal enzyme of the mitochondrial respiratory chain and oxygen response element. Altogether these data suggest early and chronic occurrence of hypoxemia in the Ts65Dn mouse model of DS, which can contribute to cognitive dysfunction in these mice.

Efficacy of Acute Intermittent Hypoxia on Physical Function and Health Status in Humans with Spinal Cord Injury: A Brief Review

Spinal cord injury (SCI) results in a loss of motor and sensory function and is consequent with reductions in locomotion, leading to a relatively sedentary lifestyle which predisposes individuals to premature morbidity and mortality. Many exercise modalities have been employed to improve physical function and health status in SCI, yet they are typically expensive, require many trained clinicians to implement, and are thus relegated to specialized rehabilitation centers. These characteristics of traditional exercise-based rehabilitation in SCI make their application relatively impractical considering the time-intensive nature of these regimens and patients' poor access to exercise. A promising approach to improve physical function in persons with SCI is exposure to acute intermittent hypoxia (IH) in the form of a small amount of sessions of brief, repeated exposures to low oxygen gas mixtures interspersed with normoxic breathing. This review summarizes the clinical application of IH in humans with SCI, describes recommended dosing and potential side effects of IH, and reviews existing data concerning the efficacy of relatively brief exposures of IH to modify health and physical function. Potential mechanisms explaining the effects of IH are also discussed. Collectively, IH appears to be a safe, time-efficient, and robust approach to enhance physical function in chronic, incomplete SCI.

IGF-1: a potential biomarker for efficacy of sleep improvement with automatic airway pressure therapy for obstructive sleep apnea?

BACKGROUND

Positive airway pressure (PAP) reverses obstructive sleep apnea (OSA)-related hypoxia and restores slow wave sleep (SWS). Insulin-like growth factor 1 (IGF-1) is a neuropeptide that facilitates the repair of neurons from hypoxia and improves sleep regulation. IGF-1 concentrations are lower in OSA, and likely increase following PAP treatment; however, this relationship has not yet been determined in a younger cohort of OSA patients.

METHODS

This was a prospective, observational pilot study of 58 young men, who were diagnosed with OSA and provided PAP as an intervention. Adherence to PAP treatment over 3 months was objectively measured, as well as changes in the apnea-hypopnea index (AHI). Serum concentrations of IGF-1and C-reactive protein (CRP) were measured and correlated with PAP adherence.

RESULTS

IGF-1 concentrations at baseline were similar between PAP adherent 55.5 ± 34.4 ng/ml and PAP nonadherent participants 61.2 ± 27.1 ng/ml (p = 0.4), with the overall mean IGF-1 concentration of 59.0 ± 29.9 ng/ml. At follow-up, adherent participants had concentrations of IGF-1 that were significantly higher 128 ± 59.5 ng/ml compared to nonadherent participants 86.0 ± 47.4 ng/ml (p < 0.01). Increases in IGF-1 concentrations were significantly associated with reductions in AHI (Spearman's rho = -0.409, p = 0.015). Conversely, CRP concentrations did not differ between baseline and follow-up measurements in either group.

CONCLUSIONS

Adherence to PAP treatment leads to significant increases in IGF-1 concentrations in young men with OSA. While an objective measure of adherence exists, PAP usage does not allow for measure of sleep improvement. IGF-1 may serve as a potential biomarker for the efficacy of PAP therapy on improved sleep.

Developmental programming: the role of growth hormone

Developmental programming of the fetus has consequences for physiologic responses in the offspring as an adult and, more recently, is implicated in the expression of altered phenotypes of future generations. Some phenotypes, such as fertility, bone strength, and adiposity are highly relevant to food animal production and in utero factors that impinge on those traits are vital to understand. A key systemic regulatory hormone is growth hormone (GH), which has a developmental role in virtually all tissues and organs. This review catalogs the impact of GH on tissue programming and how perturbations early in development influence GH function.

Cognitive dysfunction in type 2 diabetes patients accompanied with obstructive sleep apnea syndrome

OBJECTIVE

To investigate cognitive dysfunction of type 2 diabetes patients accompanied with obstructive sleep apnea syndrome (OSAS), and to analyze its relevant characteristics.

METHODS

Total 115 type 2 diabetes patients were divided into OSAS group (O group, n=83) and non-OSAS group (N group, n=32); Physical examination patients (C1 group, n=64) and OSAS patients without diabetes (C2 group, n=47) served as the control group. Apnea-hypopnea index (AHI), nocturnal lowest saturation of pulse oxygen (LSPO2) and simple mental state examination scale (MMSE) were evaluated.

RESULTS

Among diabetes patients, patients with OSAS have lower glycated hemoglobin, platelet count, thrombocytocrit, MMSE score and lowest mean arterial oxygen than non-OSAS patients; cognitive dysfunction state and glycemic control of patients are related to their diabetic duration, and then along with increase of diabetic duration, glycemic control becomes poor, so that cognitive dysfunction becomes more and more obvious.

CONCLUSION

Along with increased diabetic duration in type 2 diabetes accompanied with OSAS, glycemic control becomes poor, so that cognitive dysfunction more easily occurs. Meanwhile, coagulation function of blood system in OSAS patients with diabetes is impacted to some extent.

The polymorphic and contradictory aspects of intermittent hypoxia

Intermittent hypoxia (IH) has been extensively studied during the last decade, primarily as a surrogate model of sleep apnea. However, IH is a much more pervasive phenomenon in human disease, is viewed as a potential therapeutic approach, and has also been used in other disciplines, such as in competitive sports. In this context, adverse outcomes involving cardiovascular, cognitive, metabolic, and cancer problems have emerged in obstructive sleep apnea-based studies, whereas beneficial effects of IH have also been identified. Those a priori contradictory findings may not be as contradictory as initially thought. Indeed, the opposite outcomes triggered by IH can be explained by the specific characteristics of the large diversity of IH patterns applied in each study. The balance between benefits and injury appears to primarily depend on the ability of the organism to respond and activate adaptive mechanisms to IH. In this context, the adaptive or maladaptive responses can be generally predicted by the frequency, severity, and duration of IH. However, the presence of underlying conditions such as hypertension or obesity, as well as age, sex, or genotypic variance, may be important factors tilting the balance between an appropriate homeostatic response and decompensation. Here, the two possible facets of IH as derived from human and experimental animal settings will be reviewed.

Ghrelin-Derived Peptides: A Link between Appetite/Reward, GH Axis, and Psychiatric Disorders?

Psychiatric disorders are often associated with metabolic and hormonal alterations, including obesity, diabetes, metabolic syndrome as well as modifications in several biological rhythms including appetite, stress, sleep-wake cycles, and secretion of their corresponding endocrine regulators. Among the gastrointestinal hormones that regulate appetite and adapt the metabolism in response to nutritional, hedonic, and emotional dysfunctions, at the interface between endocrine, metabolic, and psychiatric disorders, ghrelin plays a unique role as the only one increasing appetite. The secretion of ghrelin is altered in several psychiatric disorders (anorexia, schizophrenia) as well as in metabolic disorders (obesity) and in animal models in response to emotional triggers (psychological stress …) but the relationship between these modifications and the physiopathology of psychiatric disorders remains unclear. Recently, a large literature showed that this key metabolic/endocrine regulator is involved in stress and reward-oriented behaviors and regulates anxiety and mood. In addition, preproghrelin is a complex prohormone but the roles of the other ghrelin-derived peptides, thought to act as functional ghrelin antagonists, are largely unknown. Altered ghrelin secretion and/or signaling in psychiatric diseases are thought to participate in altered appetite, hedonic response and reward. Whether this can contribute to the mechanism responsible for the development of the disease or can help to minimize some symptoms associated with these psychiatric disorders is discussed in the present review. We will thus describe (1) the biological actions of ghrelin and ghrelin-derived peptides on food and drugs reward, anxiety and depression, and the physiological consequences of ghrelin invalidation on these parameters, (2) how ghrelin and ghrelin-derived peptides are regulated in animal models of psychiatric diseases and in human psychiatric disorders in relation with the GH axis.