Postnatal Intermittent Hypoxia and Developmental Programming of Hypertension in Spontaneously Hypertensive Rats

SIRTUINS MODULATORS MITIGATE HYPOXIA-INDUCED CELL DEATH DUE TO CHANGES IN HISTONE 3 ACETYLATION, AND MITOCHONDRIAL FUNCTION, DYNAMICS, AND CONTENT

Hypoxia is a key environmental factor linked to neurodevelopmental complications, primarily through its impact on mitochondrial dysfunction. Given that sirtuins regulate mitochondrial and cellular metabolism, we aimed to investigate whether pharmacological modulation of sirtuins could protect neurons from hypoxia-induced mitochondrial dysfunction and cell death. To explore this, primary cortical neurons from male Wistar rats (control) and Spontaneously Hypertensive Rats (a model for neonatal hypoxia and schizophrenia) were exposed to cobalt chloride (CoCl2) to chemically induce hypoxia. Neurons were also treated with Nicotinamide (50 μM), Resveratrol (0.5 μM), and Sirtinol (5 μM) to modulate sirtuin activity. We first assessed histone deacetylation, cell death, mitochondrial calcium retention capacity, mitochondrial membrane potential, and levels of reactive oxygen species (ROS). In addition, we analysed the expression of genes related to mitochondrial metabolism, dynamics, and biogenesis, as well as high-energy compound levels. Our data indicate that both chemical and neonatal hypoxia caused mitochondrial depolarization, reduced calcium retention, increased ROS levels, and elevated Nfe2l2 expression in primary cortical neurons. Hypoxia also led to increased expression of genes associated with mitochondrial biogenesis and fission, as well as reduced ATP levels and elevated pyruvate and lactate levels. Importantly, treatment with sirtuin modulators enhanced neuron viability, likely by further increasing Nfe2l2 expression and reducing ROS production. These modulators also improved metabolic outcomes, including higher ATP levels, and normalized pyruvate and lactate production, as well as mitochondrial fusion gene expression. Collectively, our findings suggest that sirtuin modulators could mitigate hypoxia-induced damage and may represent a potential therapeutic strategy for managing neurodevelopmental disorders.

Neonatal intermittent hypoxemia events are associated with later systemic hypertension

BACKGROUND

Approximately 5% of very premature infants delivered at less than 30 weeks' gestation have systemic hypertension. In adult human and animal models, intermittent hypoxemia events are associated with systemic hypertension. In neonates, intermittent hypoxemia events are associated with adverse outcomes, but it is unknown if they are a risk factor for hypertension. We hypothesize that early intermittent hypoxemia events in very preterm neonates are associated with systemic hypertension at 34-36 weeks' postmenstrual age.

METHODS

Secondary analysis of a single-center cohort study of 164 infants, <31 weeks' gestational age. Intermittent hypoxemia events were continuously recorded during the first 21 days of age.

RESULTS

There was a significant association between the number of intermittent hypoxemia events (per 100) and systemic hypertension (OR (95% CI) = 1.08 (1.01-1.15)), and both the number of intermittent hypoxemia events (per 100 β (95% CI) = 0.22 (0.10-0.34)) and percent of time with hypoxemia (β (95% CI) = 0.10 (0.01-0.19)) and systolic blood pressure at 34-36 weeks' postmenstrual age.

CONCLUSION

This study demonstrated a higher incidence of early intermittent hypoxemia events in preterm infants with hypertension. Decreasing intermittent hypoxemia during this critical period may reduce incidence of later vascular stress in this population.

IMPACT

Intermittent hypoxemia events are very common in premature infants and increased frequency of intermittent hypoxemia events is associated with morbidity. Intermittent hypoxemia events in adult human as well as adult and neonatal animal models are associated with systemic hypertension. This study demonstrated an association between early intermittent hypoxemia events and systemic hypertension in very preterm neonates, adding to the body of literature of possible morbidities caused by intermittent hypoxemia events. This study addresses the common, though under-recognized, issue of neonatal hypertension, and suggests increased intermittent hypoxemia events may be contributory.

Chronic intermittent hypoxia-induced hypertension: the impact of sex hormones

Obstructive sleep apnea, a common form of sleep-disordered breathing, is characterized by intermittent cessations of breathing that reduce blood oxygen levels and contribute to the development of hypertension. Hypertension is a major complication of obstructive sleep apnea that elevates the risk of end-organ damage. Premenopausal women have a lower prevalence of obstructive sleep apnea and cardiovascular disease than men and postmenopausal women, suggesting that sex hormones play a role in the pathophysiology of sleep apnea-related hypertension. The lack of protection in men and postmenopausal women implicates estrogen and progesterone as protective agents but testosterone as a permissive agent in sleep apnea-induced hypertension. A better understanding of how sex hormones contribute to the pathophysiology of sleep apnea-induced hypertension is important for future research and possible hormone-based interventions. The effect of sex on the pathophysiology of sleep apnea and associated intermittent hypoxia-induced hypertension is of important consideration in the screening, diagnosis, and treatment of the disease and its cardiovascular complications. This review summarizes our current understanding of the impact of sex hormones on blood pressure regulation in sleep apnea with a focus on sex differences.

SIRTUINS MODULATORS COUNTERACT MITOCHONDRIAL DYSFUNCTION IN CELLULAR MODELS OF HYPOXIA: RELEVANCE TO SCHIZOPHRENIA

Schizophrenia (SZ) is a neurodevelopmental-associated disorder strongly related to environmental factors, such as hypoxia. Because there is no cure for SZ or any pharmacological approach that could revert hypoxia-induced cellular damages, we evaluated whether modulators of sirtuins could abrogate hypoxia-induced mitochondrial deregulation as a neuroprotective strategy. Firstly, astrocytes from control (Wistar) and Spontaneously Hypertensive Rats (SHR), a model of both SZ and neonatal hypoxia, were submitted to chemical hypoxia. Then, cells were exposed to different concentrations of Nicotinamide (NAM), Resveratrol (Resv), and Sirtinol (Sir) for 48hrs. Our data indicate that sirtuins modulation reduces cell death increasing the acetylation of histone 3. This outcome is related to the rescue of loss of mitochondrial membrane potential, changes in mitochondrial calcium buffering capacity, decreased O₂^-• levels and increased expression of metabolic regulators (Nrf-1 and Nfe2l2) and mitochondrial content. Such findings are relevant not only for hypoxia-associated conditions, named pre-eclampsia but also for SZ since prenatal hypoxia is a relevant environmental factor related to this burdensome neuropsychiatric disorder.

Perinatal intermittent hypoxia increases early susceptibility to ANG II-induced hypertension in adult male but not in female Sprague-Dawley rats

Prenatal, perinatal, and adulthood exposure to chronic intermittent hypoxia (IH) increases blood pressure in rodents. Males exposed to chronic IH have higher blood pressure versus females. However, it is unknown if this same-sex difference exists with acute perinatal IH. We tested the hypothesis that acute perinatal IH increases baseline blood pressure and enhances sensitivity to angiotensin II (ANG II)-induced hypertension in male Sprague-Dawley rats. Male and female pups were randomized to control (room air) or IH (10 min of ∼10% O2 for 3 times/day) for the first 8 days of life. IH decreased oxygen saturation, as confirmed via a pulse oximeter. Pups were weaned at postnatal day 21. Blood pressure was measured via telemetry beginning at 14 wk of age and analyzed separately into light and dark phases to assess circadian rhythm. Osmotic minipumps to deliver ANG II were implanted at 15 wk of age. Perinatal IH exposure did not alter baseline blood pressure. One week of ANG II treatment increased blood pressure in light and dark periods in males exposed to IH versus control; there was no effect in females. Blood pressure among the groups was comparable following 2 wk of ANG II infusion. Perinatal IH did not change the circadian rhythm. Following ANG II treatment, indexes of renal injury were measured. Perinatal IH did not alter kidney size, structure, nephron number, or creatinine clearance. These data indicate that acute perinatal IH enhances early ANG II-induced hypertension in males, independent of nephron loss or decreases in body weight or kidney function.NEW & NOTEWORTHY The impact of acute intermittent hypoxia (IH) in early life on blood pressure in adulthood is unknown. This study used a new model exposing female and male rat pups to acute IH in the first 8 days of life, without exposing the dam. Although baseline blood pressure was not altered in adulthood, IH increased susceptibility to angiotensin II hypertension only in males, supporting increased susceptibility of males exposed to IH to a second cardiovascular stressor.

Neonatal exposure to hypoxia induces early arterial stiffening via activation of lysyl oxidases

Hypoxia in the neonatal period is associated with early manifestations of adverse cardiovascular health in adulthood including higher risk of hypertension and atherosclerosis. We hypothesize that this occurs due to activation of lysyl oxidases (LOXs) and the remodeling of the large conduit vessels, leading to early arterial stiffening. Newborn C57Bl/6 mice were exposed to hypoxia (FiO2  = 11.5%) from postnatal day 1 (P1) to postnatal day 11 (P11), followed by resumption of normoxia. Controls were maintained in normoxia. Using in vivo (pulse wave velocity; PWV) and ex vivo (tensile testing) arterial stiffness indexes, we determined that mice exposed to neonatal hypoxia had significantly higher arterial stiffness compared with normoxia controls by young adulthood (P60), and it increased further by P120. Echocardiography performed at P60 showed that mice exposed to hypoxia displayed a compensated dilated cardiomyopathy. Western blotting revelated that neonatal hypoxia accelerated age-related increase in LOXL2 protein expression in the aorta and elevated LOXL2 expression in the PA at P11 with a delayed decay toward normoxic controls. In the heart and lung, gene and protein expression of LOX/LOXL2 were upregulated at P11, with a delayed decay when compared to normoxic controls. Neonatal hypoxia results in a significant increase in arterial stiffness in early adulthood due to aberrant LOX/LOXL2 expression. This suggests an acceleration in the mechanical decline of the cardiovascular system, that contributes to increased risk of hypertension in young adults exposed to neonatal hypoxia that may increase susceptibility to further insults.

Effects of swimming training on myocardial protection in rats

Swimming is important for promoting and maintaining health, as it can increase the efficiency of the cardiovascular system and decrease the occurrence of cardiovascular diseases. The objective of the present study was to examine whether swimming training could decrease myocardial injury in rats caused by myocardial ischemia/reperfusion (I/R). Sprague-Dawley rats were randomized into four groups, namely the Sham, coronary artery occlusion, swimming training and ischemic preconditioning (IPC) groups. Myocardial I/R was induced in anesthetized male Sprague-Dawley rats by a 40-min occlusion followed by a 3-h reperfusion of the left anterior descending coronary artery. The rats were sacrificed after surgery and their hearts were examined. The results demonstrated that the number of TUNEL-positive nuclei and degree of caspase-3 activation were both significantly increased in the myocardium following myocardial I/R in rats, indicating increased cardiomyocyte apoptosis. On the other hand, swimming training decreased the serum levels of creatine phosphokinase, lactate dehydrogenase and cardiac troponin I, and was associated with reduced histological damage and myocardial infarct size. Furthermore, swimming training also reduced TNF-α levels, caspase-3 activation and enhanced Bcl-2 activation, which decreased the number of apoptotic cells in the myocardium. The findings of the present study showed that swimming training and IPC could similarly decrease myocardial injury following myocardial I/R, and may therefore be used as exercise training to effectively prevent myocardial injury.

The impact of preterm adversity on cardiorespiratory function

NEW FINDINGS

What is the topic of this review? We review the influence of prematurity on the cardiorespiratory system and examine the common sequel of alterations in oxygen tension, and immune activation in preterm infants. What advances does it highlight? The review highlights neonatal animal models of intermittent hypoxia, hyperoxia and infection that contribute to our understanding of the effect of stress on neurodevelopment and cardiorespiratory homeostasis. We also focus on some of the important physiological pathways that have a modulatory role on the cardiorespiratory system in early life.

ABSTRACT

Preterm birth is one of the leading causes of neonatal mortality. Babies that survive early-life stress associated with immaturity have significant prevailing short- and long-term morbidities. Oxygen dysregulation in the first few days and weeks after birth is a primary concern as the cardiorespiratory system slowly adjusts to extrauterine life. Infants exposed to rapid alterations in oxygen tension, including exposures to hypoxia and hyperoxia, have altered redox balance and active immune signalling, leading to altered stress responses that impinge on neurodevelopment and cardiorespiratory homeostasis. In this review, we explore the clinical challenges posed by preterm birth, followed by an examination of the literature on animal models of oxygen dysregulation and immune activation in the context of early-life stress.

Neonatal Intermittent Hypoxia Induces Lasting Sex-Specific Augmentation of Rat Microglial Cytokine Expression

Sleep disordered breathing (SDB) affects 3-5% of the pediatric population, including neonates who are highly susceptible due to an underdeveloped ventilatory control system, and REM-dominated sleep. Although pediatric SDB is associated with poor cognitive outcomes, very little research has focused on models of pediatric SDB, particularly in neonates. In adults and neonates, intermittent hypoxia (IH), a hallmark of SDB, recapitulates multiple physiological aspects of severe SDB, including neuronal apoptosis, sex-specific cognitive deficits, and neuroinflammation. Microglia, resident CNS immune cells, are important mediators of neurodevelopment and neuroinflammation, but to date, no studies have examined the molecular properties of microglia in the context of neonatal IH. Here, we tested the hypothesis that neonatal IH will enhance microglial inflammation and sex-specifically lead to long-term changes in working memory. To test this hypothesis, we exposed post-natal day (P1) neonates with dams to an established adult model of pathological IH consisting of 2 min cycles of 10.5% O₂ followed by 21% O₂, 8 h/day for 8 days. We then challenged the offspring with bacterial lipopolysaccharide (LPS) at P9 or at 6-8 weeks of age and immunomagnetically isolated microglia for gene expression analyses and RNA-sequencing. We also characterized neonatal CNS myeloid cell populations by flow cytometry analyses. Lastly, we examined working memory performance using a Y-maze in the young adults. Contrary to our hypothesis, we found that neonatal IH acutely augmented basal levels of microglial anti-inflammatory cytokines, attenuated microglial responses to LPS, and sex-specifically altered CNS myeloid populations. We identified multiple sex differences in basal neonatal microglial expression of genes related to chemotaxis, cognition, and aging. Lastly, we found that basal, but not LPS-induced, anti-inflammatory cytokines were augmented sex-specifically in the young adults, and that there was a significant interaction between sex and IH on basal working memory. Our results support the idea that neonates may be able to adapt to IH exposures that are pathological in adults. Further, they suggest that male and female microglial responses to IH are sex-specific, and that these sex differences in basal microglial gene expression may contribute to sexual dimorphisms in vulnerability to IH-induced cognitive disruption.

The impact of chronic intermittent hypoxia on hematopoiesis and the bone marrow microenvironment

Obstructive sleep apnea (OSA) is a highly prevalent sleep-related breathing disorder which is associated with patient morbidity and an elevated risk of developing hypertension and cardiovascular diseases. There is ample evidence for the involvement of bone marrow (BM) cells in the pathophysiology of cardiovascular diseases but a connection between OSA and modulation of the BM microenvironment had not been established. Here, we studied how chronic intermittent hypoxia (CIH) affected hematopoiesis and the BM microenvironment, in a rat model of OSA. We show that CIH followed by normoxia increases the bone marrow hypoxic area, increases the number of multipotent hematopoietic progenitors (CFU assay), promotes erythropoiesis, and increases monocyte counts. In the BM microenvironment of CIH-subjected animals, the number of VE-cadherin-expressing blood vessels, particularly sinusoids, increased, accompanied by increased smooth muscle cell coverage, while vWF-positive vessels decreased. Molecularly, we investigated the expression of endothelial cell-derived genes (angiocrine factors) that could explain the cellular phenotypes. Accordingly, we observed an increase in colony-stimulating factor 1, vascular endothelium growth factor, delta-like 4, and angiopoietin-1 expression. Our data shows that CIH induces vascular remodeling in the BM microenvironment, which modulates hematopoiesis, increasing erythropoiesis, and circulating monocytes. Our study reveals for the first time the effect of CIH in hematopoiesis and suggests that hematopoietic changes may occur in OSA patients.

The Perinatal Origins of Cardiovascular Disease

In recent decades, with advances in neonatal intensive care, extremely premature infants are now surviving into adulthood. Epidemiologic data on the health of these ex-premature infants have begun to reveal a concerning motif-that is, prematurity, in and of itself, seems to be a risk factor for cardiovascular and metabolic disease in later adulthood. The mechanisms underlying this increased risk are unclear, but it is believed that both adverse fetal environment and postnatal exposures for a premature infant likely contribute to the developmental programming of disease by altering the normal trajectory of maturation and aging of multiple organ systems. This article specifically focuses on perinatal factors that may affect risk for cardiovascular disease.

Cardiovascular dysfunction in adult mice following postnatal intermittent hypoxia

BACKGROUND

Ex-premature infants are at higher risk for hypertension and cardiovascular disease as adults, although the mechanisms underlying such increased risks are unknown. We hypothesize that postnatal exposure to intermittent hypoxia (IH) leads to cardiovascular dysfunction in adulthood with alterations of the renin-angiotensin pathway.

METHODS

Neonatal mice were exposed to IH for 4 wk. At the age of 3 mo, various cardiovascular measurements were obtained.

RESULTS

IH-exposed mice exhibited higher systolic blood pressure, impaired baroreflex responses, and decreased heart rate variability. Furthermore, IH-exposed mice manifested evidence of endothelial dysfunction, as shown by reduced reperfusion indices after tail vessel occlusion and impaired vasodilatory responses to acetylcholine. CD31(+) endothelial cells isolated from mesenteric arteries of IH-exposed mice expressed higher levels of angiotensin-converting enzyme and reactive oxygen species; plasma angiotensin-II levels were also significantly higher in these animals. In addition, DNA methylation patterns of the Ace1 and the Agt genes in these cells were congruent with their expression patterns.

CONCLUSION

Our results suggest that exposures to postnatal IH alter the normal development of the renin-angiotensin system and promote the occurrence of cardiovascular dysfunction during adulthood in mice.

The efficacy of antihypertensive drugs in chronic intermittent hypoxia conditions

Sleep apnea/hypopnea disorders include centrally originated diseases and obstructive sleep apnea (OSA). This last condition is renowned as a frequent secondary cause of hypertension (HT). The mechanisms involved in the pathogenesis of HT can be summarized in relation to two main pathways: sympathetic nervous system stimulation mediated mainly by activation of carotid body (CB) chemoreflexes and/or asphyxia, and, by no means the least important, the systemic effects of chronic intermittent hypoxia (CIH). The use of animal models has revealed that CIH is the critical stimulus underlying sympathetic activity and hypertension, and that this effect requires the presence of functional arterial chemoreceptors, which are hyperactive in CIH. These models of CIH mimic the HT observed in humans and allow the study of CIH independently without the mechanical obstruction component. The effect of continuous positive airway pressure (CPAP), the gold standard treatment for OSA patients, to reduce blood pressure seems to be modest and concomitant antihypertensive therapy is still required. We focus this review on the efficacy of pharmacological interventions to revert HT associated with CIH conditions in both animal models and humans. First, we explore the experimental animal models, developed to mimic HT related to CIH, which have been used to investigate the effect of antihypertensive drugs (AHDs). Second, we review what is known about drug efficacy to reverse HT induced by CIH in animals. Moreover, findings in humans with OSA are cited to demonstrate the lack of strong evidence for the establishment of a first-line antihypertensive regimen for these patients. Indeed, specific therapeutic guidelines for the pharmacological treatment of HT in these patients are still lacking. Finally, we discuss the future perspectives concerning the non-pharmacological and pharmacological management of this particular type of HT.

Chemoreceptors, baroreceptors, and autonomic deregulation in children with obstructive sleep apnea

Obstructive sleep apnea (OSA) is highly prevalent sleep disorder of breathing in both adults and children that is fraught with substantial cardiovascular morbidities, the latter being attributable to a complex interplay between intermittent hypoxia (IH), episodic hypercapnia, recurrent large intra-thoracic pressure swings, and sleep disruption. Alterations in autonomic nervous system function could underlie the perturbations in cardiovascular, neurocognitive, immune, endocrine and metabolic functions that affect many of the patients suffering from OSA. Although these issues have received substantial attention in adults, the same has thus far failed to occur in children, creating a quasi misperception that children are protected. Here, we provide a critical overview of the evidence supporting the presence of autonomic nervous system (ANS) perturbations in children with OSA, draw some parallel assessments to known mechanisms in rodents and adult humans, particularly, peripheral and central chemoreceptor and baroreceptor pathways, and suggest future research directions.

Sympathetic and catecholaminergic alterations in sleep apnea with particular emphasis on children

Sleep is involved in the regulation of major organ functions in the human body, and disruption of sleep potentially can elicit organ dysfunction. Obstructive sleep apnea (OSA) is the most prevalent sleep disorder of breathing in adults and children, and its manifestations reflect the interactions between intermittent hypoxia, intermittent hypercapnia, increased intra-thoracic pressure swings, and sleep fragmentation, as elicited by the episodic changes in upper airway resistance during sleep. The sympathetic nervous system is an important modulator of the cardiovascular, immune, endocrine and metabolic systems, and alterations in autonomic activity may lead to metabolic imbalance and organ dysfunction. Here we review how OSA and its constitutive components can lead to perturbation of the autonomic nervous system in general, and to altered regulation of catecholamines, both of which then playing an important role in some of the mechanisms underlying OSA-induced morbidities.

Obstructive sleep apnea syndrome in children

The clinical syndrome of obstructive sleep apnea (OSAS) in children is a distinct, yet somewhat overlapping disorder with the condition that occurs in adults, such that the clinical manifestations, polysomnographic findings, diagnostic criteria and treatment approaches need to be considered in an age-specific manner. Childhood OSAS has now become widely recognized as a frequent disorder and as a major public health problem. Pediatric OSAS, particularly when obesity is concurrently present, is associated with substantial end-organ morbidities and increased healthcare utilization. Although adenotonsillectomy (T&A) remains the first line of treatment, evidence in recent years suggests that the outcomes of this surgical procedure may not be as favorable as expected, such that post-T&A polysomnographic evaluation may be needed, especially in high-risk patient groups. In addition, incorporation of nonsurgical approaches for milder forms of the disorder and for residual OSAS after T&A is now being investigated.

The association of testosterone, sleep, and sexual function in men and women

Testosterone has been the focus of several investigations and review studies in males, but few have addressed its effects on sleep and sexual function, despite evidence of its androgenic effects on circadian activity in both sexes. Studies have been conducted to understand how sleeping increases (and how waking decreases) testosterone levels and how this rhythm can be related to sexual function. This review addresses the inter-relationships among testosterone, sexual function and sleep, including sleep-disordered breathing in both sexes, specifically its effects related to sleep deprivation. In addition, hormonal changes in testosterone that occur in the gonadal and adrenal axis with obstructive sleep apnea and other conditions of chronic sleep deprivation, and which consequently affect sexual life, have also been explored. Nevertheless, hormone-associated sleep disruptions occur across a lifetime, particularly in women. The association between endogenous testosterone and sex, sleep and sleep disturbances is discussed, including the results of clinical trials as well as animal model studies. Evidence of possible pathophysiological mechanisms underlying this relationship is also described. Unraveling the associations of sex steroid hormone concentrations with sleep and sexual function may have clinical implications, as sleep loss reduces testosterone levels in males, and low sex steroid hormone concentrations have been associated with sexual dysfunction.

Hypoxia. 4. Hypoxia and ion channel function

The ability to sense and respond to oxygen deprivation is required for survival; thus, understanding the mechanisms by which changes in oxygen are linked to cell viability and function is of great importance. Ion channels play a critical role in regulating cell function in a wide variety of biological processes, including neuronal transmission, control of ventilation, cardiac contractility, and control of vasomotor tone. Since the 1988 discovery of oxygen-sensitive potassium channels in chemoreceptors, the effect of hypoxia on an assortment of ion channels has been studied in an array of cell types. In this review, we describe the effects of both acute and sustained hypoxia (continuous and intermittent) on mammalian ion channels in several tissues, the mode of action, and their contribution to diverse cellular processes.

Leukotriene B4 receptor-1 mediates intermittent hypoxia-induced atherogenesis

RATIONALE

Obstructive sleep apnea, which is characterized by intermittent hypoxia (IH) during sleep, has emerged as an independent risk factor for cardiovascular disease, including atherosclerosis. Leukotriene B4 (LTB4) production is increased in patients with obstructive sleep apnea and negatively correlates to hypoxic levels during sleep, with continuous positive airway pressure therapy decreasing LTB4 production.

OBJECTIVES

Determine the potential role of LTB4 in IH-induced atherosclerosis in a monocyte cellular model and a murine model.

METHODS

THP-1 cells were exposed to IH for 3, 6, 24, and 48 hours. Macrophage transformation and foam cell formation were assessed after IH exposures. Apolipopotein E (ApoE)(-/-) or BLT1(-/-)/ApoE(-/-) mice were fed an atherogenic diet and exposed to IH (alternating 21% and 5.7% O(2) from 7 am to 7 PM each day) for 10 weeks. Atherosclerotic lesion formation in en face aorta was examined by oil red O staining.

MEASUREMENTS AND MAIN RESULTS

IH increased production of LTB4 and the expression of 5-lipoxygenase and leukotriene A4 hydrolase, the key enzymes for producing LTB4. IH was associated with transformation of monocytes to activated macrophages, as evidenced by increased expression of CD14 and CD68. In addition, IH exposures promoted increased cellular cholesterol accumulation and foam cell formation. The LTB4 receptor 1 (BLT1) antagonist U-75302 markedly attenuated IH-induced changes. Furthermore, IH promoted atherosclerotic lesion formation in ApoE(-/-) mice. IH-induced lesion formation was markedly attenuated in BLT1(-/-)/ApoE(-/-) mice.

CONCLUSIONS

BLT1-dependent pathways underlie IH-induced atherogenesis, and may become a potential novel therapeutic target for obstructive sleep apnea-associated cardiovascular disease.

Differences in left ventricular cardiomyocyte loss induced by chronic intermittent hypoxia between spontaneously hypertensive and Wistar-Kyoto rats

RATIONALE

Chronic intermittent hypoxia (CIH) is thought to induce several cardiovascular effects in patients with obstructive sleep apnoea (OSA). However, the effects of CIH on patients with long-standing hypertension are unknown.

PURPOSE

This prospective study aimed to investigate the influence of combined OSA and hypertension on cardiomyocyte death.

METHODS

Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were exposed to repetitive hypoxia-reoxygenation cycles (30 s of 5% O(2); 45 s of 21% O(2)) or room air for 6 h/day during the light phase (10 a.m.-4 p.m.) for 10, 20, or 30 days, and the levels of necrosis and apoptosis induced in their left ventricular cardiomyocyte were examined.

RESULTS

CIH increased the accumulation of reactive oxygen species, which induced cardiomyocyte necrosis in WKY and SHR (both p < 0.05). Cardiomyocyte oxidative stress levels by CIH were higher in SHR than in WKY (p < 0.05); therefore, cardiomyocyte necrosis was amplified (p < 0.05). Notably, if a superoxide-scavenging agent is injected beforehand, cardiomyocyte necrosis can be effectively inhibited (p < 0.05). When WKY and SHR are exposed to CIH, increases in mitochondria-released cytochrome c and activation of caspase-3 are found in the cytosolic fraction only in WKY.

CONCLUSIONS

CIH causes cardiomyocyte loss in SHR mainly through cardiomyocyte necrosis. In WKY however, CIH simultaneously induces apoptosis and necrosis of cardiomyocytes.

Role of KATP and L-type Ca2+ channel activities in regulation of ovine uterine vascular contractility: effect of pregnancy and chronic hypoxia

OBJECTIVE

Our objective was to determine whether the pregnancy and high altitude long-term hypoxia-mediated changes in uterine artery contractility were regulated by K(ATP) and L-type Ca(2+) channel activities.

STUDY DESIGN

Uterine arteries were isolated from nonpregnant and near-term pregnant ewes that had been maintained at sea level (∼300 m) or exposed to high altitude (3801 m) for 110 days. Isometric tension was measured in a tissue bath.

RESULTS

Pregnancy increased diazoxide, but not verapamil-induced relaxations. Long-term hypoxia attenuated diazoxide-induced relaxations in near-term pregnant uterine arteries, but enhanced verapamil-induced relaxations in nonpregnant uterine arteries. Diazoxide decreased the maximal response (E(max)) of phenylephrine-induced contractions in near-term pregnant uterin arteries but not nonpregnant uterine arteries in normoxic sheep. In contrast, diazoxide had no effect on phenylephrine-induced E(max) in near-term pregnant uterine arteries but decreased it in nonpregnant uterine arteries in long-term hypoxia animals. Verapamil decreased the E(max) and pD(2) (-logEC(50)) of phenylephrine-induced contractions in both nonpregnant uterine arteries and near-term pregnant uterine arteries in normoxic and long-term hypoxia animals, except nonpregnant uterine arteries of normoxic animals in which verapamil showed no effect on the pD(2).

CONCLUSION

The results suggest that pregnancy selectively increases K(ATP), but not L-type Ca(2+) channel activity. Long-term hypoxia decreases the K(ATP) channel activity, which may contribute to the enhanced uterine vascular myogenic tone observed in pregnant sheep at high altitude hypoxia.

Superoxide dismutase mimics: chemistry, pharmacology, and therapeutic potential

Oxidative stress has become widely viewed as an underlying condition in a number of diseases, such as ischemia-reperfusion disorders, central nervous system disorders, cardiovascular conditions, cancer, and diabetes. Thus, natural and synthetic antioxidants have been actively sought. Superoxide dismutase is a first line of defense against oxidative stress under physiological and pathological conditions. Therefore, the development of therapeutics aimed at mimicking superoxide dismutase was a natural maneuver. Metalloporphyrins, as well as Mn cyclic polyamines, Mn salen derivatives and nitroxides were all originally developed as SOD mimics. The same thermodynamic and electrostatic properties that make them potent SOD mimics may allow them to reduce other reactive species such as peroxynitrite, peroxynitrite-derived CO(3)(*-), peroxyl radical, and less efficiently H(2)O(2). By doing so SOD mimics can decrease both primary and secondary oxidative events, the latter arising from the inhibition of cellular transcriptional activity. To better judge the therapeutic potential and the advantage of one over the other type of compound, comparative studies of different classes of drugs in the same cellular and/or animal models are needed. We here provide a comprehensive overview of the chemical properties and some in vivo effects observed with various classes of compounds with a special emphasis on porphyrin-based compounds.

Mechanisms of intermittent hypoxia induced hypertension

Exposing rodents to brief episodes of hypoxia mimics the hypoxemia and the cardiovascular and metabolic effects observed in patients with obstructive sleep apnoea (OSA), a condition that affects between 5% and 20% of the population. Apart from daytime sleepiness, OSA is associated with a high incidence of systemic and pulmonary hypertension, peripheral vascular disease, stroke and sudden cardiac death. The development of animal models to study sleep apnoea has provided convincing evidence that recurrent exposure to intermittent hypoxia (IH) has significant vascular and haemodynamic impact that explain much of the cardiovascular morbidity and mortality observed in patients with sleep apnoea. However, the molecular and cellular mechanisms of how IH causes these changes is unclear and under investigation. This review focuses on the most recent findings addressing these mechanisms. It includes a discussion of the contribution of the nervous system, circulating and vascular factors, inflammatory mediators and transcription factors to IH-induced cardiovascular disease. It also highlights the importance of reactive oxygen species as a primary mediator of the systemic and pulmonary hypertension that develops in response to exposure to IH.

Obstructive sleep apnea and cardiovascular disease: a perspective and future directions

Data from animal and human studies provide a biological plausibility to the notion that obstructive sleep apnea activates pathways that lead to insulin resistance, atherosclerosis and hypertension. Sleep apnea thus activates the same pathways as does obesity. That obstructive sleep apnea is a risk factor for cardiovascular disease is supported by epidemiological association studies. Longitudinal cohort studies also provide evidence that patients with untreated severe sleep apnea have an increased rate of cardiovascular events. But these studies, while highly suggestive, do not provide the evidence needed to convince the skeptic. This would only be obtained by randomized treatment trials with hard cardiovascular endpoints such as cardiac events and deaths. While such studies are in the planning stages, they will be challenging. There are issues about randomizing individuals with severe sleep apnea and excessive sleepiness into no therapy, since they are at known increased risk for car crashes. Thus, lack of therapy puts others on the road at risk as well as the subject with sleep apnea. There is, moreover, the concern that treating obstructive sleep apnea in very obese individuals will have little impact, since any effect of therapy for OSA will be overwhelmed by the effects of obesity itself. Data from randomized treatment trials for cardiovascular endpoints will likely not be available for many years. In the interim, physicians need to consider how to treat such patients. It is proposed that given that CPAP treatment for obstructive sleep apnea is highly effective and essentially totally safe, and that the evidence is suggestive that sleep apnea is a risk factor for cardiovascular disease, then we propose all patients with severe sleep apnea should be treated to reduce cardiovascular risk.

Strategic plan for pediatric respiratory diseases research: an NHLBI working group report

The Division of Lung Diseases of the National Heart, Lung, and Blood Institute (NHLBI) recently held a workshop to identify gaps in our understanding and treatment of childhood lung diseases and to define strategies to enhance translational research in this field. Leading experts with diverse experience in both laboratory and patient-oriented research reviewed selected areas of pediatric lung diseases, including perinatal programming and epigenetic influences; mechanisms of lung injury, repair, and regeneration; pulmonary vascular disease; sleep and control of breathing; and the application of novel translational methods to enhance personalized medicine. This report summarizes the proceedings of this workshop and provides recommendations for emphasis on targeted areas for future investigation. The priority areas identified for research in pediatric pulmonary diseases included: (1) epigenetic and environmental influences on lung development that program pediatric lung diseases; (2) injury, regeneration, and repair in the developing lung; (3) pulmonary vascular disease in children; (4) development and adaptation of ventilatory responses to postnatal life; (5) nonatopic wheezing: aberrant large airway development or injury?; (6) strategies to improve assessment, diagnosis, and treatment of pediatric respiratory diseases; and (7) predictive and personalized medicine for children.

Strategic plan for pediatric respiratory diseases research: an NHLBI working group report

The Division of Lung Diseases of the National Heart, Lung and Blood Institute (NHLBI) recently held a workshop to identify gaps in our understanding and treatment of childhood lung diseases and to define strategies to enhance translational research in this field. Leading experts with diverse experience in both laboratory and patient-oriented research reviewed selected areas of pediatric lung diseases, including perinatal programming and epigenetic influences; mechanisms of lung injury, repair, and regeneration; pulmonary vascular disease (PVD); sleep and control of breathing; and the application of novel translational methods to enhance personalized medicine. This report summarizes the proceedings of this workshop and provides recommendations for emphasis on targeted areas for future investigation. The priority areas identified for research in pediatric pulmonary diseases included: (1) epigenetic and environmental influences on lung development that program pediatric lung diseases, (2) injury, regeneration, and repair in the developing lung, (3) PVD in children, (4) development and adaptation of ventilatory responses to postnatal life, (5) nonatopic wheezing: aberrant large airway development or injury? (6) strategies to improve assessment, diagnosis, and treatment of pediatric respiratory diseases, and (7) predictive and personalized medicine for children.

The multiple challenges of obstructive sleep apnea in children: morbidity and treatment

PURPOSE OF REVIEW

To delineate some of the major morbid phenotypes that have emerged in pediatric obstructive sleep apnea (OSA), address new concepts in our understanding of OSA-associated morbidities, and elaborate on innovative therapeutic schemes that may improve outcomes for this condition. In addition, the conceptual framework whereby a childhood condition such as OSA can be linked to specific adult diseases will be presented.

RECENT FINDINGS

OSA in children is a frequent condition that affects up to 3% of nonobese, otherwise healthy children. In recent years, increased awareness of OSA and changes in obesity rates in children have contributed to significant changes in disease prevalence and clinical presentation, such that distinct morbidity-related phenotypes have become apparent. Furthermore, oxidative stress and systemic inflammatory pathways are mechanistically involved in the pathophysiology of OSA-associated morbidity. Adenotonsillectomy, the treatment of choice for pediatric OSA, may not be as efficacious as previously thought. Alternative nonsurgical therapies have started to emerge and may become an essential component of treatment.

SUMMARY

Pediatric OSA, particularly when obesity is concurrently present, is associated with substantial end-organ morbidities that primarily but not exclusively affect central nervous and cardiovascular systems. These morbidities are pathophysiologically mediated by inflammatory and free radical mediators. Although adenotonsillectomy remains the first line of treatment, more critical assessment of its role is needed, and incorporation of nonsurgical approaches to pediatric OSA seems warranted.