Intermittent hypoxia-induced cognitive deficits are mediated by NADPH oxidase activity in a murine model of sleep apnea

BACKGROUND

In rodents, exposure to intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), is associated with neurobehavioral impairments, increased apoptosis in the hippocampus and cortex, as well as increased oxidant stress and inflammation. Excessive NADPH oxidase activity may play a role in IH-induced CNS dysfunction.

METHODS AND FINDINGS

The effect of IH during light period on two forms of spatial learning in the water maze and well as markers of oxidative stress was assessed in mice lacking NADPH oxidase activity (gp91phox(_/Y)) and wild-type littermates. On a standard place training task, gp91phox(_/Y) displayed normal learning, and were protected from the spatial learning deficits observed in wild-type littermates exposed to IH. Moreover, anxiety levels were increased in wild-type mice exposed to IH as compared to room air (RA) controls, while no changes emerged in gp91phox(_/Y) mice. Additionally, wild-type mice, but not gp91phox(_/Y) mice had significantly elevated levels of NADPH oxidase expression and activity, as well as MDA and 8-OHDG in cortical and hippocampal lysates following IH exposures.

CONCLUSIONS

The oxidative stress responses and neurobehavioral impairments induced by IH during sleep are mediated, at least in part, by excessive NADPH oxidase activity, and thus pharmacological agents targeting NADPH oxidase may provide a therapeutic strategy in sleep-disordered breathing.

Sleep disorders in succinic semialdehyde dehydrogenase deficiency: a family report

BACKGROUND

Succinic semialdehyde dehydrogenase deficiency (SSADH) is a rare neurometabolic disorder involving the degradation of gamma-aminobutyric acid. Clinically, SSADH deficiency causes progressive or static encephalopathy with late infantile to early childhood onset. It is known that sleep disorders are a common clinical finding in these patients. However, very few studies have investigated sleep disorders with polysomnographies.

AIM OF THE STUDY

To analyze sleep disorders breathing, sleep architecture and paroxysmal EEG activity through polysomnographic recordings of two siblings suffering from SSADH deficiency

METHOD

Each patient underwent laboratory diurnal and overnight video-polysomnographic recordings in a room specially dedicated to mothers and their children.

RESULTS

The background EEG activity during quiet wakefulness consisted in abnormal, diffuse, low-voltage, disorganized slow theta waves. In both patients there was a general disorganisation of the sleep architecture with an increase of light sleep and a decrease of REM sleep. In patient 1, during sleep, there were 36 hypopneas, 13 central apneas and one obstructive apnea with a variable duration of 7-30s. The apnea/hypopnea index (AHI) was 7/h and oxygen saturation dropped to 80% during the respiratory events. In patient 2, the respiratory events consisted in 8 central apneas and 23 hypopneas of 6-20s; no obstructive apneas or hypopneas were observed. The oxygen saturation dropped to 90% during the apneas and the AHI was 5/h.

CONCLUSION

Sleep-disordered breathing (SDB) is a common finding in patients with SSADH deficiency and polysomnography recording is a useful tool for its diagnosis.

[Elevated transaminases - what to do if everything was done?]

Transaminases, gamma-GT and alcalic phosphatase are classically termed as liver enzymes, however they can be found in almost every organ. Elevated levels of the transaminases ALAT (alanin-aminotransferase) and ASAT (aspartat-aminotransferase) are signs of disturbed permeability of the cells, in which these enzymes can be found. In contrast to ALAT, which is mainly liver-specific, the ASAT is found in other organs as well, e.g. heart and skeletal muscle. At a mild elevation of these enzymes a reevaluation is recommended, however if an elevation persists and is suspicious for a liver disease, a specific work up is necessary. In this manuscript, we discuss often overlooked problems and provide a diagnostic algorithm for the workup of elevated liver enzymes.

Sleep apneas are increased in mice lacking monoamine oxidase A

STUDY OBJECTIVES

Alterations in the serotonin (5-HT) system have been suggested as a mechanism of sleep apnea in humans and rodents. The objective is to evaluate the contribution of 5-HT to this disorder.

DESIGN

We studied sleep and breathing (whole-body plethysmography) in mutant mice that lack monoamine oxidase A (MAOA) and have increased concentrations of monoamines, including 5-HT.

MEASUREMENTS AND RESULTS

Compared to wild-type mice, the mutants showed similar amounts of slow wave sleep (SWS) and rapid eye movement sleep (REMS), but exhibited a 3-fold increase in SWS and REMS apnea indices. Acute administration of the MAOA inhibitor clorgyline decreased REMS amounts and increased the apnea index in wild-type but not mutant mice. Parachlorophenylalanine, a 5-HT synthesis inhibitor, reduced whole brain concentrations of 5-HT in both strains, and induced a decrease in apnea index in mutant but not wild-type mice.

CONCLUSION

Our results show that MAOA deficiency is associated with increased sleep apnea in mice and suggest that an acute or chronic excess of 5-HT contributes to this phenotype.

Apnea in a child after oral codeine: a genetic variant - an ultra-rapid metabolizer

We present a case of a 29 months old previously healthy child who experienced apnea resulting in brain injury following a dose of acetaminophen and codeine 2 days after an uneventful anesthetic for tonsillectomy. A genetic polymorphism leading to ultra-rapid metabolism of codeine into morphine resulted in narcosis and apnea. This paper discusses the use of codeine for pain relief, obstructive sleep apnea, the alteration of the CYP2D6 gene and the resulting effect on drug metabolism.

Impaired spatial working memory and altered choline acetyltransferase (CHAT) immunoreactivity and nicotinic receptor binding in rats exposed to intermittent hypoxia during sleep

Exposure to intermittent hypoxia (IH), such as occurs in sleep-disordered breathing (SDB), is associated with cognitive impairment, neurodegeneration, oxidative stress, and inflammatory responses within rodent brain regions such as the basal forebrain. In this region, damage to cholinergic neurons correlates with working memory deficits in a number of neurodegenerative disorders, suggesting that degeneration of cholinergic systems may also contribute to the working memory impairments observed after IH exposures. We therefore examined basal forebrain choline acetyltransferase (CHAT) immunohistochemistry, nicotinic receptor binding in the prefrontal cortex (PFC), and working memory, in male rats tested on a delayed matching to place (DMP) task in the water maze following exposure to either room air (RA) or intermittent hypoxia (IH; alternating 90s epochs of 21% and 10% O(2) during sleep). IH-treated animals displayed impaired working memory with respect to controls, along with significant reductions in CHAT-stained neurons in the medial septal nucleus, in both the vertical and horizontal limbs of the diagonal band, and the substantia inominata after 14 days of IH exposure. In addition, increases in nicotinic binding and receptor affinity in the PFC were observed after 14 days of IH exposure. Thus, a loss of cholinergic neuronal phenotype in the basal forebrain may contribute to the cognitive impairments associated with CIH exposure. However, compensatory mechanisms may also be activated in other brain regions, and may provide potential therapeutic targets for the cognitive impairments associated with SDB.

Increased Levels and Activity of Matrix Metalloproteinase-9 in Obstructive Sleep Apnea Syndrome

Matrix metalloproteinases (MMPs) are involved in the pathogenesis of cardiovascular diseases. We examined serum levels of MMP-9 and its inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1), activity of MMP-9, and the effect of nasal continuous positive airway pressure (nCPAP) in patients with obstructive sleep apnea syndrome (OSAS). After polysomnography, venous blood was collected at 5:00 A.M. from 44 patients with OSAS and 18 control subjects who were obese, and serum levels of MMP-9, TIMP-1, and enzymatic activity of MMP-9 were measured. In addition, the effects of 1 month of treatment with nCPAP were studied in patients with moderate to severe OSAS. Although serum levels of MMP-9 (p < 0.03) and MMP-9 activity (p < 0.01) were higher in patients with OSAS than in control subjects who were obese, TIMP-1 levels did not differ significantly. In patients with OSAS, the severity of OSAS was the primary factor influencing levels (p < 0.01) and activity (p < 0.01) of MMP-9. nCPAP significantly decreased serum levels (p < 0.01) and activity (p < 0.001) of MMP-9 but did not affect TIMP-1 levels. Therefore, OSAS may increase risks of cardiovascular morbidity, and nCPAP might be useful for decreasing these risks.

Intermittent hypoxia induces time-dependent changes in the protein kinase B signaling pathway in the hippocampal CA1 region of the rat

Intermittent hypoxia (IH) during sleep induces temporally defined increases in apoptosis within vulnerable brain regions such as the hippocampal CA1 region in rats. Protein kinase B (AKT) has emerged as major signal transduction protein underlying inhibition of apoptosis and consequent increases in cell survival. Sprague Dawley adult male rats were exposed during sleep to IH or to normoxia (RA) for periods ranging from 0 to 30 days, and expression of total and phosphorylated AKT, of forkhead family members FKHR and FKHRL1, and of glycogen synthase kinase 3beta (GSK3beta) was assessed. Decreases in phosphorylation occurred as early as 1 h IH exposure, reached a nadir at 6 h-3 days, and then progressively returned to baseline levels at 14-30 days. Phosphorylated AKT and GSK3beta were intensely expressed and highly colocalized within neuronal cells (Neu-N positive) in the CA1 region. Thus, IH induces time-dependent biphasic changes in AKT survival pathways within the CA1 region that are temporally correlated with the initial increases and subsequent decreases in neuronal apoptosis.

Cyclooxygenase 2 and intermittent hypoxia-induced spatial deficits in the rat

Intermittent hypoxia (IH) during sleep, a critical feature of sleep apnea, induces significant neurobehavioral deficits in the rat. Cyclooxygenase (COX)-2 is induced during stressful conditions such as cerebral ischemia and could play an important role in IH-induced learning deficits. We therefore examined COX-1 and COX-2 genes and COX-2 protein expression and activity (prostaglandin E2 [PGE2] tissue concentration) in cortical regions of rat brain after exposure to either IH (10% O2 alternating with 21% O2 every 90 seconds) or sustained hypoxia (10% O2). In addition, the effect of selective COX-2 inhibition with NS-398 on IH-induced neurobehavioral deficits was assessed. IH was associated with increased COX-2 protein and gene expression from Day 1 to Day 14 of exposure. No changes were found in COX-1 gene expression after exposure to hypoxia. IH-induced COX-2 upregulation was associated with increased PGE2 tissue levels, neuronal apoptosis, and neurobehavioral deficits. Administration of NS-398 abolished IH-induced apoptosis and PGE2 increases without modifying COX-2 mRNA expression. Furthermore, NS-398 treatment attenuated IH-induced deficits in the acquisition and retention of a spatial task in the water maze. We conclude that IH induces upregulation and activation of COX-2 in rat cortex and that COX-2 may play a role in IH-mediated neurobehavioral deficits.

Angiotensin converting enzyme in patients with sleep apnoea syndrome: plasma activity and gene polymorphisms

The prevalence of several cardiovascular diseases is increased with obstructive sleep apnoea syndrome (OSAS), due to, as yet, unclear reasons. Angiotensin converting enzyme (ACE) abnormalities have been implicated in the pathogenesis of various cardiovascular diseases. In this study, plasma ACE activity and the distribution of an insertion (I)/deletion (D) polymorphism of the ACE gene were determined in OSAS patients and in healthy controls. A total of 63 patients with OSAS (mean+/-SEM 54.5+/-2.5 apnoea/hypopnoeas.h(-1)) and 32 healthy subjects were studied. To avoid potential confounding factors, patients treated with ACE inhibitors or continuous positive airway pressure were excluded, as well as controls in whom a blood sample was not obtained early in the morning. ACE activity was determined spectrophotometrically in 46 OSAS patients and 25 controls. The I/D ACE polymorphism was determined by polymerase chain reaction in 44 patients and 32 controls. ACE activity was higher in OSAS patients (53.9+/-2.5 IU.L(-1)) than in healthy controls (42.4+/-3.1 IU.L(-1), p<0.01). This was independent of the presence of arterial hypertension. The frequency distribution of the DD, II and ID genotypes in OSAS patients (30%, 16%, 54%, respectively) was not significantly different from that seen in healthy subjects (31%, 28%, 41%, respectively, p=0.356). These results indicate that ACE plasma activity is increased in untreated OSAS patients. This increased activity may contribute to the pathogenesis of the cardiovascular disease in these patients.

Decrease in immunoreactive neutral endopeptidase in uvula epithelium of patients with obstructive sleep apnea

The purpose of this study was to determine whether neutral endopeptidase (NEP; EC3.4.24.11) is decreased in the uvula epithelium of patients with obstructive sleep apnea (OSA). Tissues were obtained by uvulopharyngopalatoplasty in seven patients with moderate OSA and by autopsy in five individuals not known to have OSA. Using antisera to human NEP and immunoperoxidase staining, we found that NEP was localized in uvula epithelial cells of both patients with OSA and controls. However, there was a significant decrease in the number of epithelial cells staining for NEP in patients with OSA relative to controls (67 +/- 10 cells versus 261 +/- 33 cells, in 5 randomly selected high-power microscopic fields, respectively; mean +/- SEM; p < .05). The intensity of staining for NEP was similar in both groups. We conclude that immunoreactive NEP is significantly decreased in the uvula epithelium of patients with OSA.

Congenital central hypoventilation syndrome: mutation analysis of the receptor tyrosine kinase RET

Congenital central hypoventilation syndrome (CCHS) usually occurs as an isolated phenotype. However, 16% of the index cases are also affected with Hirschsprung disease (HSCR). Complex segregation analysis suggests that CCHS is familial and has the same inheritance pattern with or without HSCR. We postulate that alteration of normal function of the receptor tyrosine kinase, RET, may contribute to CCHS based on RET's expression pattern and the identification of RET mutations in HSCR patients. To further explore the nature of the inheritance of CCHS, we have undertaken two main routes of investigation: cytogenetic analysis and mutation detection. Cytogenetic analysis of metaphase chromosomes showed normal karyotypes in 13 of the 14 evaluated index cases; one index case carried a familial pericentric inversion on chromosome 2. Mutation analysis showed no sequence changes unique to index cases, as compared to control individuals, and as studied by single strand conformational polymorphism (SSCP) analysis of the coding region of RET. We conclude that point mutations in the RET coding region cannot account for a substantial fraction of CCHS in this patient population, and that other candidate genes involved in neural crest cell differentiation and development must be considered.

Central hypoventilation syndrome in pyruvate dehydrogenase complex deficiency

The presentation and treatment of a central hypoventilation syndrome in a boy with pyruvate dehydrogenase complex (PDHC) deficiency are reported. Dephosphorylated PDHC was assayed in disrupted fibroblasts after pretreatment with dichloroacetate, a pyruvate dehydrogenase kinase inhibitor. Maximal specific activity of activated patient PDHC was 10% to 30% of control values. Patient PDHC activity was not increased by alterations in concentrations of pyruvate or cofactors (thiamine pyrophosphate [TPP], coenzyme A [CoA], oxidized form of nicotinamide adenine dinucleotide [NAD+]). Clinically, normalization of plasma lactate by a high-lipid diet did not prevent slowly progressive neurologic decline. The patient manifested intermittent ataxia, episodic profound weakness, moderate psychomotor retardation, ophthalmoplegia, and retinal pigment epithelial changes. A true central hypoventilation syndrome was documented on the basis of rigorous radiologic, electrophysiologic, and pulmonary function criteria. Theophylline, progesterone, and ritalin neither altered ventilatory response to CO2 nor permitted weaning from the ventilator. In contrast, peripheral chemoreceptor stimulants (intravenous doxapram; oral almitrine) effected an acute doubling of minute ventilation with appropriate decreases in PaCO2. However, a positive response to long-term therapy with almitrine could not be unequivocally shown. It was concluded that measurement of disrupted fibroblast PDHC following dichloroacetate activation constitutes an accurate assay for PDHC deficiency. PDHC deficiency must be considered in the differential diagnosis of the central hypoventilation syndrome; this appears to be the first report of such an association. Finally, a therapeutic trial of a peripheral chemoreceptor agonist is warranted in the management of central hypoventilation syndrome.