Pharmacological treatment of sleep apnea: Current situation and future strategies

New pharmacologic agents for obstructive sleep apnoea: what do we know and what can we expect?

PURPOSE OF REVIEW

This review provides a condensed description of pharmacological remedies explored in patients with obstructive sleep apnoea (OSA) as well as projections of what we might expect in terms of clinical performance of these drugs.

RECENT FINDINGS

Conventional drug therapies explored in OSA have generally produced disappointing results and there is a shortage of pharmacological treatment alternatives in this disorder. Recent insights into pathophysiological mechanisms potentially involved in OSA suggest that the condition may be divided into distinct subgroups based on clusters or defined by means of unique functional endotypic criteria. In fact, positive outcomes in clinical trials have now resulted in several drug candidates that show a convincing reduction of sleep disordered breathing in both short and intermediate term. Such drugs may be particularly useful in certain variants of OSA but not in others. These insights have also raised the ambition to create personalized therapies in OSA. Another recent development is the insight that OSA-linked conditions such as obesity, daytime somnolence and various forms of cardiovascular/metabolic disease may provide drug-based targets. For instance, pharmacological obesity therapy may provide not only positive metabolic effects but may also be a way to eliminate the anatomic component in obese OSA patients.

SUMMARY

Recent insights into the pathophysiology of OSA have opened possibilities to develop personalized therapy. Drugs addressing fundamental aspects of the sleep and breathing disorder provide a particularly promising avenue for development of novel forms of treatment in OSA.

Turning Over a New Leaf-Pharmacologic Therapy in Obstructive Sleep Apnea

Despite extensive research, there is currently no approved drug for obstructive sleep apnea (OSA) treatment. OSA is a heterogeneous condition that involves multiple dominating pathophysiological traits. Drug development in this field needs to address both pathophysiological mechanisms and associated comorbid conditions in order to meet requirements for long-term therapy in OSA. Several drug candidates have been proposed and ongoing phase II trials that target various forms of sleep-disordered breathing have been initiated. The field is moving toward tailored therapeutic approaches in patients with OSA.

Managing comorbid cardiovascular disease and sleep apnea with pharmacotherapy

INTRODUCTION

Highly prevalent sleep disordered breathing (SDB) has been recognized as an independent cardiovascular disease (CVD) risk factor. Although these two entities often coexist, there is a shortage of sufficiently-powered studies testing the interplay between the course of sleep apnea and CVD pharmacotherapy. The mutual relationship between treated/untreated obstructive sleep apnea (OSA) with ongoing cardiovascular pharmacotherapies is an evident gap in clinical expertise.

AREAS COVERED

In this article, the authors review the available evidence and outline future research directions concerning the reciprocal relationship between the pharmacological treatment of CVD and SDB. Several attempts have been made to identify the most efficacious hypotensive agents for patients with both OSA and hypertension. Various cardiovascular drugs are also evaluated in terms of their influence on sleep apnea severity.

EXPERT OPINION

The question of whether OSA should be included in cardiovascular pharmacotherapy individualization algorithms is a matter of debate and more evidence is needed. Cautious intensification of diuretics with the use of aldosterone receptor antagonists deserves attention when both high blood pressure and sleep apnea coexist.

Drug effects on ventilatory control and upper airway physiology related to sleep apnea

Understanding the inter-relationship between pharmacological agents, ventilatory control, upper airway physiology and their consequent effects on sleep-disordered breathing may provide new directions for targeted drug therapy. Where available, this review focuses on human studies that contain both drug effects on sleep-disordered breathing and measures of ventilatory control or upper airway physiology. Many of the existing studies are limited in sample size or comprehensive methodology. At times, the presence of paradoxical findings highlights the complexity of drug therapy for OSA. The existing studies also highlight the importance of considering inter-individual pharmacokinetics and underlying causes of sleep apnea in interpreting drug effects on sleep-disordered breathing. Practical ways to assess an individual's ventilatory control and how it interacts with upper airway physiology is required for future targeted pharmacotherapy in sleep apnea.

Sensitization of upper airway mechanoreceptors as a new pharmacologic principle to treat obstructive sleep apnea: investigations with AVE0118 in anesthetized pigs

STUDY OBJECTIVES

Drug treatment for obstructive sleep apnea (OSA) is desirable because at least 30% of patients do not tolerate continuous positive airway pressure (CPAP) treatment. The negative pressure reflex (NPR) involving superficially located mechanoreceptors in the upper airway (UA) is an important mechanism for UA patency inhibitable by topical UA anesthesia (lidocaine). The NPR may serve as a target for pharmacological intervention for a topical treatment of OSA. The objective was to determine the effect of pharmacological augmentation of the NPR on UA collapsibility.

DESIGN

We developed a model of UA collapsibility in which application of negative pressures caused UA collapses in spontaneously breathing α-chloralose-urethane anesthetized pigs as indicated by characteristic tracheal pressure and air flow changes.

SETTING

N/A.

PATIENTS OR PARTICIPANTS

N/A.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

The potassium channel blocker AVE0118 administered topically to the UA in doses of 1, 3, and 10 mg per nostril sensitized the NPR, shifting the mechanoreceptor response threshold for the genioglossus muscle to more positive pressures (P < 0.001; n = 6 per group) and dose-dependently inhibited UA collapsibility. Ten mg of AVE0118 prevented UA collapses against negative pressures of -150 mbar (P < 0.01) for > 4 h in all pigs, while in control pigs the UA collapsed at -50 mbar or less negative pressures. The effect of AVE0118 was abolished by UA lidocaine anesthesia. Acute intravenous administration of naloxone or acetazolamide was ineffective; paroxetine and mirtazepine were weakly effective and fluoxetine was moderately effective in line with reported clinical efficacy.

CONCLUSION

Topical administration of AVE0118 to the UA is a promising pharmacologic approach for the treatment of OSA.

Upper airway dilator muscle weakness following intermittent and sustained hypoxia in the rat: effects of a superoxide scavenger

Obstructive sleep apnoea syndrome (OSAS) is a common disorder associated with upper airway muscle dysfunction. Agents that improve respiratory muscle performance may have considerable therapeutic value. We examined the effects of acute exposure to sustained and intermittent hypoxia on rat pharyngeal dilator muscle function. Additionally, we sought to test the efficacy of antioxidant treatment in ameliorating or preventing hypoxia-related muscle dysfunction. Isometric contractile and endurance properties of isolated rat sternohyoid muscle bundles were examined at 35 °C in vitro. Muscle bundles were exposed to one of four gas treatments: hyperoxia (control), sustained hypoxia (SH), intermittent hypoxia (IH) or hypoxia/re-oxygenation (HR), in the absence or presence of the superoxide scavenger--Tempol (10 mM). Stress-frequency relationship was determined in response to electrical stimulation (10-100 Hz in increments of 10-20 Hz, train duration: 300 ms). Muscle performance was also assessed during repetitive muscle stimulation (40 Hz, 300 ms every 2 s for 2.5 min). Compared to control, IH and HR treatments significantly decreased sternohyoid muscle force. The negative inotropic effect of the two gas protocols was similar, but both were of lesser magnitude than the effects of SH. SH, but not IH and HR, increased muscle fatigue. Tempol significantly increased sensitivity to stimulation in all muscle preparations and caused a leftward shift in the stress-frequency relationship of IH and SH treated muscles. Tempol did not ameliorate sternohyoid muscle fatigue during SH. We conclude that Tempol increases upper airway muscle sensitivity to stimulation but only modestly ameliorates respiratory muscle weakness during intermittent and sustained hypoxic conditions in vitro. Respiratory muscle fatigue during sustained hypoxia appears unrelated to oxidative stress.

Obstructive sleep apnea syndrome

Obstructive sleep apnea (OSA) syndrome is a common but often unrecognized disorder caused by pharyngeal collapse during sleep and characterized by frequent awakenings, disrupted sleep and consequent excessive daytime sleepiness. With the increasing epidemic of obesity, the most important risk factor for OSA, prevalence of the disease will increase over the coming years thus representing an important public-health problem. In fact, it is now recognized that there is an association between OSA and hypertension, metabolic syndrome, diabetes, heart failure, coronary artery disease, arrhythmias, stroke, pulmonary hypertension, neurocognitive and mood disorders. Diagnosis is based on the combined evaluation of clinical manifestations and objective sleep study findings. Cardinal symptoms include snoring, sleepiness and significant reports of sleep apnea episodes. Polysomnography represents the gold standard to confirm the clinical suspicion of OSA syndrome, to assess its severity and to guide therapeutic choices. Behavioral, medical and surgical options are available for the treatment. Continuous positive airway pressure (CPAP) represents the treatment of choice in most patients. CPAP has been demonstrated to be effective in reducing symptoms, cardiovascular morbidity and mortality and neurocognitive sequelae, but it is often poorly tolerated. The results of clinical studies do not support surgery and pharmacological therapy as first-line treatment, but these approaches might be useful in selected patients. A better understanding of mechanisms underlying the disease could improve therapeutic strategies and reduce the social impact of OSA syndrome.

Structural and functional properties of an upper airway dilator muscle in aged obese male rats

BACKGROUND

Age, obesity and male sex are risk factors for the development of obstructive sleep apnoea syndrome.

OBJECTIVE

We examined structural and functional properties of the sternohyoid muscle in young lean and aged obese male rats. We hypothesized that the aged muscle would be vulnerable to oxidative stress (hypoxia).

METHODS

Isometric contractile and endurance properties of the sternohyoid muscle were assessed in vitro with or without the superoxide scavenger Tempol (10 mM). Muscle fibre size and density were determined by myosin heavy chain immunofluorescence. Succinate dehydrogenase (SDH) and glycerol-3- phosphate dehydrogenase (GPDH) enzyme activities were determined.

RESULTS

Fibre hypertrophy, increased fast twitch (type 2X) fibre density, decreased SDH activity and increased GPDH activity, together with increased force and fatigue, were observed in aged obese muscles compared to young lean muscles. Tempol treatment increased strength and sensitivity to stimulation. Hypoxic depression of force was ameliorated by antioxidant treatment with equivalent effects in young lean and aged obese muscle.

CONCLUSIONS

We conclude that the rat sternohyoid exhibits indefinite growth and is protected from oxidative stress as the animal ages.

Tempol ameliorates pharyngeal dilator muscle dysfunction in a rodent model of chronic intermittent hypoxia

Respiratory muscle dysfunction is implicated in the pathophysiology of obstructive sleep apnea syndrome (OSAS), an oxidative stress disorder prevalent in men. Pharmacotherapy for OSAS is an attractive option, and antioxidant treatments may prove beneficial. We examined the effects of chronic intermittent hypoxia (CIH) on breathing and pharyngeal dilator muscle structure and function in male and female rats. Additionally, we tested the efficacy of antioxidant treatment in preventing (chronic administration) or reversing (acute administration) CIH-induced effects in male rats. Adult male and female Wistar rats were exposed to alternating cycles of normoxia and hypoxia (90 s each; Fi(O(2)) = 5% O(2) at nadir; Sa(O(2)) ∼ 80%) or sham treatment for 8 h/d for 9 days. Tempol (1 mM, superoxide dismutase mimetic) was administered to subgroups of sham- and CIH-treated animals. Breathing was assessed by whole-body plethysmography. Sternohyoid muscle contractile and endurance properties were examined in vitro. Muscle fiber type and cross-sectional area and the activity of key metabolic enzymes were determined. CIH decreased sternohyoid muscle force in male rats only. This was not attributable to fiber transitions or alterations in oxidative or glycolytic enzyme activity. Muscle weakness after CIH was prevented by chronic Tempol supplementation and was reversed by acute antioxidant treatment in vitro. CIH increased normoxic ventilation in male rats only. Sex differences exist in the effects of CIH on the respiratory system, which may contribute to the higher prevalence of OSAS in male subjects. Antioxidant treatment may be beneficial as an adjunct OSAS therapy.

Advances in treatment of obstructive sleep apnea syndrome

The treatments for obstructive sleep apnea (OSA) described in this paper represent the latest information and data. Nasal continuous positive airway pressure, initially described in 1981, remains the cornerstone of therapy. Advances in mask interfaces, the use of humidification, the downloading of usage information, the development of pressure delivery modifications, and reductions in the size and noise of the machines have improved the devices over the past decade. Nevertheless, the basic premise of positive pressure delivery to splint the airway remains the primary driver of efficacy. Surgery for OSA, other than tracheostomy, has also been used for about the same period (uvulopalatopharyngoplasty was also initially described in 1981), but its efficacy has probably improved only marginally. The advances in surgical techniques have come through improved patient selection, minimally invasive techniques, and the performance of outcome studies. Surgery clearly remains a second-line or third-line therapy for moderate to severe OSA. Dental appliances were also introduced over two decades ago and clearly have become more mainstream in our treatment approach to OSA. Dental appliances are now considered a reasonable first-line therapy for mild OSA and perhaps even for some patients with moderate OSA. Custom-made appliances are clearly superior to those that cannot be adjusted, and in the hands of an experienced dentist or similarly trained expert, they are moderately successful for most patients. Among the newer therapies, transnasal insufflation and nasal expiratory resistance clearly have promise, again for patients with mild to moderate OSA. Further study may determine who will benefit from such modalities. No medications have been shown to have clinically significant efficacy, and drug treatment remains adjunctive.

Obstructive sleep apnea syndrome: from phenotype to genetic basis

Obstructive sleep apnea syndrome (OSAS) is a complex chronic clinical syndrome, characterized by snoring, periodic apnea, hypoxemia during sleep, and daytime hypersomnolence. It affects 4-5% of the general population. Racial studies and chromosomal mapping, familial studies and twin studies have provided evidence for the possible link between the OSAS and genetic factors and also most of the risk factors involved in the pathogenesis of OSAS are largely genetically determined. A percentage of 35-40% of its variance can be attributed to genetic factors. It is likely that genetic factors associated with craniofacial structure, body fat distribution and neural control of the upper airway muscles interact to produce the OSAS phenotype. Although the role of specific genes that influence the development of OSAS has not yet been identified, current researches, especially in animal model, suggest that several genetic systems may be important. In this chapter, we will first define the OSAS phenotype, the pathogenesis and the risk factors involved in the OSAS that may be inherited, then, we will review the current progress in the genetics of OSAS and suggest a few future perspectives in the development of therapeutic agents for this complex disease entity.

Eszopiclone increases the respiratory arousal threshold and lowers the apnoea/hypopnoea index in obstructive sleep apnoea patients with a low arousal threshold

Recent insights into sleep apnoea pathogenesis reveal that a low respiratory arousal threshold (awaken easily) is important for many patients. As most patients experience stable breathing periods mediated by upper-airway dilator muscle activation via accumulation of respiratory stimuli, premature awakening may prevent respiratory stimuli build up as well as the resulting stabilization of sleep and breathing. The aim of the present physiological study was to determine the effects of a non-benzodiazepine sedative, eszopiclone, on the arousal threshold and the AHI (apnoea/hypopnoea index) in obstructive sleep apnoea patients. We hypothesized that eszopiclone would increase the arousal threshold and lower the AHI in patients with a low arousal threshold (0 to -15 cm H(2)O). Following a baseline overnight polysomnogram with an epiglottic pressure catheter to quantify the arousal threshold, 17 obstructive sleep apnoea patients, without major hypoxaemia [nadir SaO(2) (arterial blood oxygen saturation) >70%], returned on two additional nights and received 3 mg of eszopiclone or placebo immediately prior to each study. Compared with placebo, eszopiclone significantly increased the arousal threshold [-14.0 (-19.9 to -10.9) compared with -18.0 (-22.2 to -15.1) cm H(2)O; P<0.01], and sleep duration, improved sleep quality and lowered the AHI without respiratory event prolongation or worsening hypoxaemia. Among the eight patients identified as having a low arousal threshold, reductions in the AHI occurred invariably and were most pronounced (25±6 compared with 14±4 events/h of sleep; P<0.01). In conclusion, eszopiclone increases the arousal threshold and lowers the AHI in obstructive sleep apnoea patients that do not have marked overnight hypoxaemia. The greatest reductions in the AHI occurred in those with a low arousal threshold. The results of this single night physiological study suggest that certain sedatives may be of therapeutic benefit for a definable subgroup of patients. However, additional treatment strategies are probably required to achieve elimination of apnoea.

A new animal model of obstructive sleep apnea responding to continuous positive airway pressure

STUDY OBJECTIVES

An improved animal model of obstructive sleep apnea (OSA) is needed for the development of effective pharmacotherapies. In humans, flexion of the neck and a supine position, two main pathogenic factors during human sleep, are associated with substantially greater OSA severity. We postulated that these two factors might generate OSA in animals.

DESIGN

We developed a restraining device for conditioning to investigate the effect of the combination of 2 body positions-prone (P) or supine (S)-and 2 head positions-with the neck flexed at right angles to the body (90°) or in extension in line with the body (180°)-during sleep in 6 cats. Polysomnography was performed twice on each cat in each of the 4 sleeping positions-P180, S180, P90, or S90. The effect of continuous positive airway pressure (CPAP) treatment was then investigated in 2 cats under the most pathogenic condition.

SETTING

NA.

PATIENTS OR PARTICIPANTS

NA.

INTERVENTIONS

NA.

MEASUREMENTS AND RESULTS

Positions P180 and, S90 resulted, respectively, in the lowest and highest apnea-hypopnea index (AHI) (3 ± 1 vs 25 ± 2, P < 0.001), while P90 (18 ± 3, P<0.001) and S180 (13 ± 5, P<0.01) gave intermediate values. In position S90, an increase in slow wave sleep stage 1 (28% ± 3% vs 22% ± 3%, P<0.05) and a decrease in REM sleep (10% ± 2% vs 18% ± 2%, P<0.001) were also observed. CPAP resulted in a reduction in the AHI (8 ± 1 vs 27 ± 3, P<0.01), with the added benefit of sleep consolidation.

CONCLUSION

By mimicking human pathogenic sleep conditions, we have developed a new reversible animal model of OSA.

Effects of phytoestrogen genistein on genioglossus function and oestrogen receptors expression in ovariectomized rats

OBJECTIVE

This study was designed to investigate the effects of genistein on genioglossal muscle function and the expression of oestrogen receptors (ERs) in the ovariectomized rats.

DESIGN

Fifty female Sprague-Dawley rats were randomly divided into 5 groups: the control group (SHAM), the ovariectomized group (OVX), the ovariectomized rats receiving low genistein dosage (OVX+L), the moderate genistein dosage group (OVX+M) and the high genistein dosage group (OVX+H). Oestradiol level was detected by radioimmunity. The isometric twitch tension (P(t)) and tetanic tension (P(0)) of the GG muscle were measured in response to electrical field stimulation. The expression of ERs on the mRNA and protein levels was measured by real-time PCR and western blot respectively.

RESULTS

Ovariectomy decreased muscle fatigue resistance and the expression of different ERs significantly. Genistein treatment resulted in a dose-dependent protective effect on muscle fatigability and a parallel dose-responsive increase in the expression of oestrogen receptors mRNA and protein levels in genioglossus, with larger effects on oestrogen receptor beta vs. alpha. In contrast to the improvements in fatigability, there was no treatment effect on isometric twitch or tetanic tensions.

CONCLUSION

The results indicated that genistein increased muscle fatigue resistance in addition to effects on receptors, and the up-regulation of receptors expression may be a possible mechanism by which genistein improved fatigue.