Silencing of Hypoglossal Motoneurons Leads to Sleep Disordered Breathing in Lean Mice

Bioluminescence-optogenetics-mediated gene therapy in a sleep-disordered breathing mouse model

Obstructive sleep apnea (OSA) incurs a huge individual, societal, and economic burden. Specific and selective targeting of hypoglossal motor neurons could be an effective means to treat OSA. Bioluminescent-optogenetics (BL-OG) is a novel genetic regulatory approach in which luminopsins, fusion proteins of light-generating luciferase and light-sensing ion channels, increase neuronal excitability when exposed to a suitable substrate. Here we develop and validate the feasibility of BL-OG for sleep-disordered breathing (SDB). Upon confirming that diet-induced obese mice represent an excellent SDB model, we employed a method of targeting the hypoglossal nucleus (12 N) by peripherally injecting retrogradely transported rAAV2/Retro. With AAV transduction, the eLMO3 protein is expressed in hypoglossal motor neurons (HMN); administration of CTZ results in production of bioluminescence that in turn activates the tethered channelrhodopsin, leading to an increase in the firing of HMN and a 2.7 ± 0.8-fold increase in phasic activity of the genioglossus muscle, a 7.6 ± 1.8-fold increase in tonic activity, and improvements in hypoventilation and apnea index without impacting sleep structure. This is therefore the first study to leverage the rAAV2/Retro vector to execute the BL-OG approach in SDB, which amplified genioglossus muscle discharge activity and increased airflow in mice after activation. This study marks the pioneering utilization of BL-OG in SDB research.

Chemogenetic stimulation of phrenic motor output and diaphragm activity

Impaired diaphragm activation contributes to morbidity and mortality in many neurodegenerative diseases and neurologic injuries. We conducted experiments to determine if expression of an excitatory DREADD (designer receptors exclusively activation by designer drugs) in the mid-cervical spinal cord would enable respiratory-related activation of phrenic motoneurons to increase diaphragm activation. Wild type (C57/bl6) and ChAT-Cre mice received bilateral intraspinal (C4) injections of an adeno-associated virus (AAV) encoding the hM3D(Gq) excitatory DREADD. In wild type mice, this produced non-specific DREADD expression throughout the mid-cervical ventral horn. In ChAT-Cre mice, a Cre-dependent viral construct was used to drive DREADD expression in C4 ventral horn motoneurons, targeting the phrenic motoneuron pool. Diaphragm EMG was recorded during spontaneous breathing at 6-8 weeks post-AAV delivery. The selective DREADD ligand JHU37160 (J60) caused a bilateral, sustained (>1 hr) increase in inspiratory EMG bursting in both groups; the relative increase was greater in ChAT-Cre mice. Additional experiments in a ChAT-Cre rat model were conducted to determine if spinal DREADD activation could increase inspiratory tidal volume (VT) during spontaneous breathing without anesthesia. Three to four months after intraspinal (C4) injection of AAV driving Cre-dependent hM3D(Gq) expression, intravenous J60 resulted in a sustained (>30 min) increase in VT assessed using whole-body plethysmography. Subsequently, direct nerve recordings confirmed that J60 evoked a >50% increase in inspiratory phrenic output. The data show that mid-cervical spinal DREADD expression targeting the phrenic motoneuron pool enables ligand-induced, sustained increases in the neural drive to the diaphragm. Further development of this technology may enable application to clinical conditions associated with impaired diaphragm activation and hypoventilation.

Direct optogenetic activation of upper airway muscles in an acute model of upper airway hypotonia mimicking sleep onset

STUDY OBJECTIVES

Obstructive sleep apnea (OSA), where the upper airway collapses repeatedly during sleep due to inadequate dilator muscle tone, is challenging to treat as current therapies are poorly tolerated or have variable and unpredictable efficacy. We propose a novel, optogenetics-based therapy, that stimulates upper airway dilator muscle contractions in response to light. To determine the feasibility of a novel optogenetics-based OSA therapy, we developed a rodent model of human sleep-related upper airway muscle atonia. Using this model, we evaluated intralingual delivery of candidate optogenetic constructs, notably a muscle-targeted approach that will likely have a favorable safety profile.

METHODS

rAAV serotype 9 viral vectors expressing a channelrhodopsin-2 variant, driven by a muscle-specific or nonspecific promoter were injected into rat tongues to compare strength and specificity of opsin expression. Light-evoked electromyographic responses were recorded in an acute, rodent model of OSA. Airway dilation was captured with ultrasound.

RESULTS

The muscle-specific promoter produced sufficient opsin expression for light stimulation to restore and/or enhance electromyographic signals (linear mixed model, F = 140.0, p < 0.001) and induce visible tongue contraction and airway dilation. The muscle-specific promoter induced stronger (RM-ANOVA, F(1,8) = 10.0, p = 0.013) and more specific opsin expression than the nonspecific promoter in an otherwise equivalent construct. Viral DNA and RNA were robust in the tongue, but low or absent in all other tissues.

CONCLUSIONS

Significant functional responses to direct optogenetic muscle activation were achieved following muscle-specific promoter-driven rAAV-mediated transduction, providing proof-of-concept for an optogenetic therapy for patients with inadequate dilator muscle activity during sleep.

Targets for obstructive sleep apnea pharmacotherapy: principles, approaches, and emerging strategies

INTRODUCTION

Obstructive sleep apnea (OSA) is a common and serious breathing disorder. Several pathophysiological factors predispose individuals to OSA. These factors are quantifiable, and modifiable pharmacologically.

AREAS COVERED

Four key pharmacotherapeutic targets are identified and mapped to the major determinants of OSA pathophysiology. PubMed and Clinicaltrials.gov were searched through April 2023.

EXPERT OPINION

Target #1: Pharyngeal Motor Effectors. Increasing pharyngeal muscle activity and responsivity with noradrenergic-antimuscarinic combination is central to recent breakthrough OSA pharmacotherapy. Assumptions, knowledge gaps, future directions, and other targets are identified. #2: Upper Airway Sensory Afferents. There is translational potential of sensitizing and amplifying reflex pharyngeal dilator muscle responses to negative airway pressure via intranasal delivery of new potassium channel blockers. Rationales, advantages, findings, and potential strategies to enhance effectiveness are identified. #3: Chemosensory Afferents and Ventilatory Control. Strategies to manipulate ventilatory control system sensitivity by carbonic anhydrase inhibitors are supported in theory and initial studies. Intranasal delivery of agents to stimulate central respiratory activity are also introduced. #4: Sleep-Wake Mechanisms. Arousability is the fourth therapeutic target rationalized. Evolving automated tools to measure key pathophysiological factors predisposing to OSA will accelerate pharmacotherapy. Although not currently ready for general clinical settings, the identified targets are of future promise.

Multilevel Airway Obstruction Phenotypes in Adult OSA

Objective

To describe multilevel phenotypes of airway obstruction identified on drug-induced sleep endoscopy (DISE) in adults.

Study Design

Retrospective chart review.

Setting

Tertiary care center.

Methods

Video recordings of DISE on adult patients were retrospectively scored. A cross-correlation matrix was created to detect significant correlations between DISE findings at anatomical subsites. Three multilevel phenotypes resulted from the matrix: complete collapse at the tongue base with complete collapse at the epiglottis (T2-E2), complete circumferential obstruction at the velum with complete lateral pharyngeal wall collapse at the oropharynx (V2C-O2LPW), and incomplete collapse at the velum with complete collapse due to tonsillar hypertrophy (V0/1-O2T). The mean difference (MD) and 95% confidence interval (CI) were calculated for demographic and polysomnogram metrics of each phenotype compared to all other subjects.

Results

Phenotype 1 (T2-E2) (n = 88) had older ages (MD 5.784 years, CI [1.992, 9.576]), lower body mass index (BMI) (MD -1.666 kg/m², CI [02.570, -0.762]), and smaller neck circumferences (MD -0.448 in., CI [-9.14, -0.009]) than the other phenotypes. Phenotype 2 (V2C-O2LPW) (n = 25) had higher BMIs (MD 2.813 kg/m², CI [1.362, 4.263]), higher neck circumference (MD 0.714 in., CI [0.004, 1.424]), and higher apnea-hypopnea index (MD 8.252, CI [0.463, 16.041]). Phenotype 3 (V0/1-O2T) (n = 20) had younger ages (MD -17.697, CI [-25.215, -11.179]).

Conclusion

Three distinct multilevel phenotypes of obstruction were identified on DISE, suggesting different anatomic subsites collapse in a nonrandom pattern. The phenotypes appear to represent distinct patient groups and their identification may have implications in terms of pathophysiology and treatment modalities.

Effects of clozapine-N-oxide and compound 21 on sleep in laboratory mice

Designer receptors exclusively activated by designer drugs (DREADDs) are chemogenetic tools for remote control of targeted cell populations using chemical actuators that bind to modified receptors. Despite the popularity of DREADDs in neuroscience and sleep research, potential effects of the DREADD actuator clozapine-N-oxide (CNO) on sleep have never been systematically tested. Here, we show that intraperitoneal injections of commonly used CNO doses (1, 5, and 10 mg/kg) alter sleep in wild-type male laboratory mice. Using electroencephalography (EEG) and electromyography (EMG) to analyse sleep, we found a dose-dependent suppression of rapid eye movement (REM) sleep, changes in EEG spectral power during non-REM (NREM) sleep, and altered sleep architecture in a pattern previously reported for clozapine. Effects of CNO on sleep could arise from back-metabolism to clozapine or binding to endogenous neurotransmitter receptors. Interestingly, we found that the novel DREADD actuator, compound 21 (C21, 3 mg/kg), similarly modulates sleep despite a lack of back-metabolism to clozapine. Our results demonstrate that both CNO and C21 can modulate sleep of mice not expressing DREADD receptors. This implies that back-metabolism to clozapine is not the sole mechanism underlying side effects of chemogenetic actuators. Therefore, any chemogenetic experiment should include a DREADD-free control group injected with the same CNO, C21, or newly developed actuator. We suggest that electrophysiological sleep assessment could serve as a sensitive tool to test the biological inertness of novel chemogenetic actuators.

Gasotransmitter modulation of hypoglossal motoneuron activity

Obstructive sleep apnea (OSA) is characterized by sporadic collapse of the upper airway leading to periodic disruptions in breathing. Upper airway patency is governed by genioglossal nerve activity that originates from the hypoglossal motor nucleus. Mice with targeted deletion of the gene Hmox2, encoding the carbon monoxide (CO) producing enzyme, heme oxygenase-2 (HO-2), exhibit OSA, yet the contribution of central HO-2 dysregulation to the phenomenon is unknown. Using the rhythmic brainstem slice preparation that contains the preBötzinger complex (preBötC) and the hypoglossal nucleus, we tested the hypothesis that central HO-2 dysregulation weakens hypoglossal motoneuron output. Disrupting HO-2 activity increased the occurrence of subnetwork activity from the preBötC, which was associated with an increased irregularity of rhythmogenesis. These phenomena were also associated with the intermittent inability of the preBötC rhythm to drive output from the hypoglossal nucleus (i.e. transmission failures), and a reduction in the input-output relationship between the preBötC and the motor nucleus. HO-2 dysregulation reduced excitatory synaptic currents and intrinsic excitability in inspiratory hypoglossal neurons. Inhibiting activity of the CO-regulated H2S producing enzyme, cystathionine-γ-lyase (CSE), reduced transmission failures in HO-2 null brainstem slices, which also normalized excitatory synaptic currents and intrinsic excitability of hypoglossal motoneurons. These findings demonstrate a hitherto uncharacterized modulation of hypoglossal activity through mutual interaction of HO-2/CO and CSE/H2S, and support the potential importance of centrally derived gasotransmitter activity in regulating upper airway control.

Association between residential greenness and obstructive sleep apnoea among adults in Southern China

BACKGROUND

No previous study has explored the association of residential greenness with obstructive sleep apnoea (OSA) indexes.

OBJECTIVE

To investigate the association of exposure to residential greenness with OSA indexes in adults in Guangdong Province, Southern China.

METHODS

From January 1, 2005 to December 31, 2015, a total of 3925 participants were recruited from the Sleep Center of Guangdong Provincial People's Hospital. Apnea-hypopnea index (AHI) and oxygen desaturation index (ODI) were measured by polysomnography or home sleep test (HST). Participants' daytime sleepiness scores were evaluated using The Epworth Sleeping Scale (ESS). The normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) were used to assess residential greenness levels. Generalized linear regression models were used to assess the associations of residential greenness with OSA indexes after adjusting for multiple covariates.

RESULTS

The mean (standard deviation) age of the participants was 63.3 (14.4) years. In adjusted models, an interquartile range (IQR) increase in 3-year average NDVI was significantly associated with 9.8 % (95 % confidence interval [95 % CI]: 17.5 %, 2.1 %); 14.5 % (95 % CI: 24.5 %, 4.4 %) and 6.9 % (95 % CI: 13.7 %, 0.0 %) decreases in AHI, ODI and ESS scores, respectively. Furthermore, an IQR increase in 3-year average EVI was significantly associated with 7.8 % (95 % CI: 13.7 %, 1.9 %); 10.8 % (95 % CI: 18.3 %, 3.2 %) and 7.2 % (95 % CI: 12.5 %, 2.0 %) declines in AHI, ODI and ESS scores, respectively. Significant associations were only observed among males, adults aged ≥65 years old, and in the warm season.

CONCLUSIONS

Our study indicates that higher residential greenness was significantly associated with lower OSA indexes in adult population in South China, especially in males, in the elderly, and in the warm season.

Chemogenetic activation of hypoglossal motoneurons in a mouse model of Pompe disease

Pompe disease is a lysosomal storage disease resulting from absence or deficiency of acid α-glucosidase (GAA). Tongue-related disorders including dysarthria, dysphagia, and obstructive sleep apnea are common in Pompe disease. Our purpose was to determine if designer receptors exclusively activated by designer drugs (DREADDs) could be used to stimulate tongue motor output in a mouse model of Pompe disease. An adeno-associated virus serotype 9 (AAV9) encoding an excitatory DREADD (AAV9-hSyn-hM3D(Gq)-mCherry, 2.44 × 1010 vg) was administered to the posterior tongue of 5-7-wk-old Gaa null (Gaa-/-) mice. Lingual EMG responses to intraperitoneal injection of saline or a DREADD ligand (JHU37160-dihydrochloride, J60) were assessed 12 wk later during spontaneous breathing. Saline injection produced no consistent changes in lingual EMG. Following the DREADD ligand, there were statistically significant (P < 0.05) increases in both tonic and phasic inspiratory EMG activity recorded from the posterior tongue. Brainstem histology confirmed mCherry expression in hypoglossal (XII) motoneurons in all mice, thus verifying retrograde movement of the AAV9 vector. Morphologically, Gaa-/- XII motoneurons showed histological characteristics that are typical of Pompe disease, including an enlarged soma and vacuolization. We conclude that lingual delivery of AAV9 can be used to drive functional expression of DREADD in XII motoneurons in a mouse model of Pompe disease.NEW & NOTEWORTHY In a mouse model of Pompe disease, lingual injection of adeno-associated virus (AAV) serotype 9 encoding DREADD was histologically verified to produce transgene expression in hypoglossal motoneurons. Subsequent intraperitoneal delivery of a DREADD ligand stimulated tonic and phase tongue motor output.In a mouse model of Pompe disease, lingual injection of adeno-associated virus (AAV) serotype 9 encoding DREADD was histologically verified to produce transgene expression in hypoglossal motoneurons. Subsequent intravenous delivery of a DREADD ligand stimulated tonic and phase tongue motor output.

Association of traffic air pollution with severity of obstructive sleep apnea in urban areas of Northern Taiwan: A cross-sectional study

BACKGROUND

Although recent studies have indicated an association between obstructive sleep apnea (OSA) and air pollution, they have reported inconsistent results. Moreover, few studies investigated the effects of short-term air pollution exposure.

OBJECTIVE

To estimate the health effects of short- and long-term exposure to traffic air pollution on mild OSA in Taipei.

METHODS

We collected participants' data from Taipei Sleep Center and air pollution data from Taiwan Environmental Protection Administration. A spatiotemporal model was used to estimate the individual exposure level. Generalized linear models were used to assess the percent change of overall apnea-hypopnea index (AHI), AHI in rapid eye movement period (AHI-REM), AHI in non-REM (AHI-NREM), and oxygen desaturation index (ODI) associated with an interquartile (IQR) increase in personal pollution exposure. A generalized logistic model was used to estimate the ORs of different severities of OSA compared with the reference group.

RESULTS

In the patients with AHI of <15, both short- and long-term exposure to NO₂ were significantly associated with AHI and ODI increases: an IQR increase in 2-year mean NO₂ increased 7.3% of AHI and 8.4% of ODI; these values were the highest among all exposure windows. The effects of NO₂ on AHI increase were stronger in the men and younger patients. Moreover, the association between AHI and NO₂ in the patients with AHI of <15 was mediated by the REM stage. NO₂ exposure was associated with an increased risk of mild OSA that reached up to 24.8% per IQR increase in NO₂ averaged over 2 years. PM_2.5 exerted no effects on AHI, but an IQR increase in 1-year and 2-year mean PM_2.5 was associated with 6.8% and 8.8% increases in ODI, respectively.

CONCLUSIONS

Both short- and long-term exposure to traffic air pollution were associated with the risk of mild OSA, which was modified by REM stage.

Management of Obstructive Sleep Apnea in Patients With Heart Failure

Sleep apnea is traditionally classified as obstructive sleep apnea (OSA), which occurs when the upper airway collapses due to the relaxation of oropharyngeal musculature, and central sleep apnea occurs when the brainstem cannot stimulate breathing. Most sleep apnea in patients with heart failure (HF) results from coexisting OSA and central sleep apnea (CSA), or complex sleep apnea syndrome. OSA and CSA are common in HF and can be involved in its progression by exposure to the heart to intermittent hypoxia, increased preload and afterload, activating sympathetic, and decreased vascular endothelial function. A majority of treatments have been investigated in patients with CSA and HF; however, less or short-term randomized trials demonstrated whether treating OSA in patients with HF could improve morbidity and mortality. OSA could directly influence the patient's recovery. This review will focus on past and present studies on the various therapies for OSA in patients with HF and summarize CSA treatment options for reasons of reference and completeness. More specifically, the treatment covered include surgical and non-surgical treatments and reported the positive and negative consequences for these treatment options, highlighting possible implications for clinical practice and future research directions.

Targeting Parasympathetic Activity to Improve Autonomic Tone and Clinical Outcomes

In this review we will briefly summarize the evidence that autonomic imbalance, more specifically reduced parasympathetic activity to the heart, generates and/or maintains many cardiorespiratory diseases and will discuss mechanisms and sites, from myocytes to the brain, that are potential translational targets for restoring parasympathetic activity and improving cardiorespiratory health.

Gene delivery to the hypoglossal motor system: preclinical studies and translational potential

Dysfunction and/or reduced activity in the tongue muscles contributes to conditions such as dysphagia, dysarthria, and sleep disordered breathing. Current treatments are often inadequate, and the tongue is a readily accessible target for therapeutic gene delivery. In this regard, gene therapy specifically targeting the tongue motor system offers two general strategies for treating lingual disorders. First, correcting tongue myofiber and/or hypoglossal (XII) motoneuron pathology in genetic neuromuscular disorders may be readily achieved by intralingual delivery of viral vectors. The retrograde movement of viral vectors such as adeno-associated virus (AAV) enables targeted distribution to XII motoneurons via intralingual viral delivery. Second, conditions with impaired or reduced tongue muscle activation can potentially be treated using viral-driven chemo- or optogenetic approaches to activate or inhibit XII motoneurons and/or tongue myofibers. Further considerations that are highly relevant to lingual gene therapy include (1) the diversity of the motoneurons which control the tongue, (2) the patterns of XII nerve branching, and (3) the complexity of tongue muscle anatomy and biomechanics. Preclinical studies show considerable promise for lingual directed gene therapy in neuromuscular disease, but the potential of such approaches is largely untapped.

Designer Receptors Exclusively Activated by Designer Drugs Approach to Treatment of Sleep-disordered Breathing

Rationale: Obstructive sleep apnea is recurrent upper airway obstruction caused by a loss of upper airway muscle tone during sleep. The main goal of our study was to determine if designer receptors exclusively activated by designer drugs (DREADD) could be used to activate the genioglossus muscle as a potential novel treatment strategy for sleep apnea. We have previously shown that the prototypical DREADD ligand clozapine-N-oxide increased pharyngeal diameter in mice expressing DREADD in the hypoglossal nucleus. However, the need for direct brainstem viral injections and clozapine-N-oxide toxicity diminished translational potential of this approach, and breathing during sleep was not examined.Objectives: Here, we took advantage of our model of sleep-disordered breathing in diet-induced obese mice, retrograde properties of the adeno-associated virus serotype 9 (AAV9) viral vector, and the novel DREADD ligand J60.Methods: We administered AAV9-hSyn-hM3(Gq)-mCherry or control AAV9 into the genioglossus muscle of diet-induced obese mice and examined the effect of J60 on genioglossus activity, pharyngeal patency, and breathing during sleep.Measurements and Main Results: Compared with control, J60 increased genioglossus tonic activity by greater than sixfold and tongue uptake of 2-deoxy-2-[¹⁸F]fluoro-d-glucose by 1.5-fold. J60 increased pharyngeal patency and relieved upper airway obstruction during non-REM sleep.Conclusions: We conclude that following intralingual administration of AAV9-DREADD, J60 can activate the genioglossus muscle and improve pharyngeal patency and breathing during sleep.

Intranasal Leptin Prevents Opioid-induced Sleep-disordered Breathing in Obese Mice

Respiratory depression is the main cause of morbidity and mortality associated with opioids. Obesity increases opioid-related mortality, which is mostly related to comorbid obstructive sleep apnea. Naloxone, a μ-opioid receptor blocker, is an effective antidote, but it reverses analgesia. Like humans with obesity, mice with diet-induced obesity hypoventilate during sleep and develop obstructive sleep apnea, which can be treated with intranasal leptin. We hypothesized that intranasal leptin reverses opioid-induced sleep-disordered breathing in obese mice without decreasing analgesia. To test this hypothesis, mice with diet-induced obesity were treated with morphine at 10 mg/kg subcutaneously and with leptin or placebo intranasally. Sleep and breathing were recorded by barometric plethysmography, and pain sensitivity was measured by the tail-flick test. Excitatory postsynaptic currents were recorded in vitro from hypoglossal motor neurons after the application of the μ-opioid receptor agonist [D-Ala², N-MePhe⁴, Gly-ol]-enkephalin and leptin. Morphine dramatically increased the frequency of apneas and greatly increased the severity of hypoventilation and obstructive sleep apnea. Leptin decreased the frequency of apneas, improved obstructive sleep apnea, and completely reversed hypoventilation, whereas morphine analgesia was enhanced. Our in vitro studies demonstrated that [D-Ala², N-MePhe⁴, Gly-ol]-enkephalin reduced the frequency of excitatory postsynaptic currents in hypoglossal motoneurons and that application of leptin restored excitatory synaptic neurotransmission. Our findings suggest that intranasal leptin may prevent opioid respiratory depression during sleep in patients with obesity receiving opioids without reducing analgesia.

Disrupted Coordination of Hypoglossal Motor Control in a Mouse Model of Pediatric Dysphagia in DiGeorge/22q11.2 Deletion Syndrome

We asked whether the physiological and morphologic properties of hypoglossal motor neurons (CNXII MNs) that innervate protruder or retractor tongue muscles are disrupted in neonatal LgDel mice that carry a heterozygous deletion parallel to that associated with DiGeorge/22q11.2 deletion syndrome (22q11.2DS). Disrupted coordination of tongue movement in LgDel mouse pups may contribute to suckling, feeding, and swallowing (S/F/S) disruptions that parallel pediatric dysphagia in infants and toddlers with 22q11.2DS. Using an in vitro rhythmically active medullary slice preparation, we found spontaneous firing as well as IPSC frequency differed significantly in neonatal LgDel versus wild-type (WT) protruder and retractor CNXII MNs that were identified by retrograde tracing from their target muscles. In response to respiration-related activity, initiation and decay of transiently increased firing in WT protruder MNs is delayed in LgDel, accompanied by altered excitatory/inhibitory (E/I) balance. In addition, LgDel retractor MNs have a transient increase in firing with diminished IPSC frequency that is not seen in WT. There were no significant differences in cell body volume of either XII class in WT and LgDel Sholl analysis showed the total numbers of dendritic intersections (at 50- and 90-μm radii from the cell soma) were significantly greater for LgDel versus WT retractor MNs. Thus, the physiological, synaptic and cellular properties of distinct classes of CNXII MNs that coordinate tongue movement in neonatal WT mice are altered in LgDel Such changes could contribute to sub-optimal coordination of S/F/S that underlies pediatric dysphagia in 22q11.2DS.

Intranasal oxytocin increases respiratory rate and reduces obstructive event duration and oxygen desaturation in obstructive sleep apnea patients: a randomized double blinded placebo controlled study

BACKGROUND

Activation of the oxytocin network has shown benefits in animal models of Obstructive Sleep Apnea (OSA) as well as other cardiorespiratory diseases. We sought to determine if nocturnal intranasal oxytocin administration could have beneficial effects in reducing the duration and/or frequency of obstructive events in obstructive sleep apnea subjects.

METHODS

Two sequential standard "in-lab" polysomnogram (PSG) sleep studies were performed in patients diagnosed with OSA that were randomly assigned to initially receive either placebo or oxytocin (40 i.u.) administered intranasally in this double blinded randomized placebo controlled study. Changes in cardiorespiratory events during sleep, including apnea and hypopnea durations and frequency, risk of event-associated bradycardias, arterial oxygen desaturation and respiratory rate were assessed in 2 h epochs following sleep onset. Oxytocin significantly decreased the duration of obstructive events, as well as the oxygen desaturations and incidence of bradycardia that were associated with these events. Notably, oxytocin increased respiratory rate during non-obstructive periods. There were no significant changes in sleep architecture and no adverse effects were reported.

CONCLUSIONS

Oxytocin administration can benefit OSA subjects by reducing the duration and adverse consequences of obstructive events. Oxytocin could also be beneficial in situations involving respiratory depression as oxytocin increased respiratory rate. Additional studies are needed to further understand the mechanisms by which oxytocin promotes these changes in cardiorespiratory function. The long-term efficacy and optimal dose of intranasal oxytocin treatment should also be determined in OSA subjects. ClinicalTrials.gov NCT03148899.

The Role of Animal Models in Developing Pharmacotherapy for Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a highly prevalent disease characterized by recurrent closure of the upper airway during sleep. It has a complex pathophysiology involving four main phenotypes. An abnormal upper airway anatomy is the key factor that predisposes to sleep-related collapse of the pharynx, but it may not be sufficient for OSA development. Non-anatomical traits, including (1) a compromised neuromuscular response of the upper airway to obstruction, (2) an unstable respiratory control (high loop gain), and (3) a low arousal threshold, predict the development of OSA in association with anatomical abnormalities. Current therapies for OSA, such as continuous positive airway pressure (CPAP) and oral appliances, have poor adherence or variable efficacy among patients. The search for novel therapeutic approaches for OSA, including pharmacological agents, has been pursued over the past years. New insights into OSA pharmacotherapy have been provided by preclinical studies, which highlight the importance of appropriate use of animal models of OSA, their applicability, and limitations. In the present review, we discuss potential pharmacological targets for OSA discovered using animal models.

Off-Target Effects of Clozapine-N-Oxide on the Chemosensory Reflex Are Masked by High Stress Levels

Respiratory chemosensory circuits are implicated in several physiological and behavioral disorders ranging from sudden infant death syndrome to panic disorder. Thus, a comprehensive map of the chemosensory network would be of significant value. To delineate chemosensory neuronal populations, we have utilized pharmacogenetic Designer Receptors Exclusively Activated by Designer Drugs (DREADD) perturbations for acute neuronal perturbations in respiratory circuit mapping. Recent studies show that the biologically inert DREADD ligand clozapine-N-oxide (CNO) is back-metabolized into the bioactive compound clozapine in rodents, emphasizing the need for CNO-only DREADD-free controls, which have been carried out in several studies. However, we show that high CNO doses used in several chemosensory circuit mapping studies nonetheless affect the chemosensory ventilatory reflexes in control mice, which is unmasked by extensive habituation. Here, unhabituated control animals showed no differences in respiratory parameters after CNO administration, whereas habituated animals receiving the commonly used dose of 10 mg/kg of CNO show a deficit in the hypercapnic (high CO₂) chemosensory reflex, which is not present in 1 mg/kg CNO treated or saline control groups. Our findings indicate that even in appropriately controlled studies, additional masked CNO off-target effects may exist and underscore the importance of using minimal doses of activating ligand in combination with high levels of habituation.