The effect of intermittent hypoxia on bodyweight, serum glucose and cholesterol in obesity mice

Intermittent Hypoxic Training as an Effective Tool for Increasing the Adaptive Potential, Endurance and Working Capacity of the Brain

This review is devoted to the phenomenon of intermittent hypoxic training and is aimed at drawing the attention of researchers to the necessity of studying the mechanisms mediating the positive, particularly neuroprotective, effects of hypoxic training at the molecular level. The review briefly describes the historical aspects of studying the beneficial effects of mild hypoxia, as well as the use of hypoxic training in medicine and sports. The physiological mechanisms of hypoxic adaptation, models of hypoxic training and their effectiveness are summarized, giving examples of their beneficial effects in various organs including the brain. The review emphasizes a high, far from being realized at present, potential of hypoxic training in preventive and clinical medicine especially in the area of neurodegeneration and age-related cognitive decline.

Chronic Intermittent Hypoxia Exposure Alternative to Exercise Alleviates High-Fat-Diet-Induced Obesity and Fatty Liver

Obesity often concurs with nonalcoholic fatty liver disease (NAFLD), both of which are detrimental to human health. Thus far, exercise appears to be an effective treatment approach. However, its effects cannot last long and, moreover, it is difficult to achieve for many obese people. Thus, it is necessary to look into alternative remedies. The present study explored a noninvasive, easy, tolerable physical alternative. In our experiment, C57BL/6 mice were fed with a high-fat diet (HFD) to induce overweight/obesity and were exposed to 10% oxygen for one hour every day. We found that hypoxia exerted protective effects. First, it offset HFD-induced bodyweight gain and insulin resistance. Secondly, hypoxia reversed the HFD-induced enlargement of white and brown adipocytes and fatty liver, and protected liver function. Thirdly, HFD downregulated the expression of genes required for lipolysis and thermogenesis, such as UCP1, ADR3(beta3-adrenergic receptor), CPT1A, ATGL, PPARα, and PGC1α, M2 macrophage markers arginase and CD206 in the liver, and UCP1 and PPARγ in brown fat, while these molecules were upregulated by hypoxia. Furthermore, hypoxia induced the activation of AMPK, an energy sensing enzyme. Fourthly, our results showed that hypoxia increased serum levels of epinephrine. Indeed, the effects of hypoxia on bodyweight, fatty liver, and associated changes in gene expression ever tested were reproduced by injection of epinephrine and prevented by propranolol at varying degrees. Altogether, our data suggest that hypoxia triggers stress responses where epinephrine plays important roles. Therefore, our study sheds light on the hope to use hypoxia to treat the daunting disorders, obesity and NAFLD.

[Into thin air - Altitude training and hypoxic conditioning: From athlete to patient]

INTRODUCTION

Hypoxic exposure should be considered as a continuum, the effects of which depend on the dose and individual response to hypoxia. Hypoxic conditioning (HC) represents an innovative and promising strategy, ranging from improved human performance to therapeutic applications.

STATE OF THE ART

With the aim of improving sports performance, the effectiveness of hypoxic exposure, whether natural or simulated, is difficult to demonstrate because of the large variability of the protocols used. In therapeutics, the benefits of HC are described in many pathological conditions such as obesity or cardiovascular pathologies. If the HC benefits from a strong preclinical rationale, its application to humans remains limited.

PERSPECTIVES

Advances in training and acclimation will require greater personalization and precise periodization of hypoxic exposures. For patients, the harmonization of HC protocols, the identification of biomarkers and the development and subsequent validation of devices allowing a precise control of the hypoxic stimulus are necessary steps for the development of HC.

CONCLUSIONS

From the athlete to the patient, HC represents an innovative and promising field of research, ranging from the improvement of human performance to the prevention and treatment of certain pathologies.

Inhibition of miR-27b Regulates Lipid Metabolism in Skeletal Muscle of Obese Rats During Hypoxic Exercise by Increasing PPARγ Expression

Hypoxic exercise may represent a novel therapeutic strategy to reduce and prevent obesity through the regulation of lipid metabolism. During hypoxic exercise, the targeting of peroxisome proliferator-activated receptor gamma (PPARγ) by miR-27b has been proposed to be one of the mechanisms involved in the modulation of lipid metabolism. We have previously shown that miR-27b can repress PPARγ and lipid metabolism-associated factors, thereby affecting lipid metabolism during hypoxic exercise in a rat model of obesity. In the current study, we aimed to confirm the role of miR-27b in the regulation of lipid metabolism. First, miR-27b expression was either upregulated or downregulated through the injection of adeno-associated virus (AAV) 9 containing a miR-27b expression cassette or miR-27b-3p inhibitor, respectively, into the right gastrocnemius muscle of obese rats. The rats were then subjected to a 4-week program of hypoxic exercise, and a series of parameters related to lipid metabolism were systematically evaluated, including body composition, blood lipid levels, miR-27b RNA levels, and mRNA and protein levels of PPARγ and those of its downstream lipid metabolism-associated factors. No significant differences were found in body composition between rats expressing different levels of miR-27b. However, regarding blood lipids, miR-27b overexpression led to increased concentrations of triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and free fatty acids (FFAs), while inhibition of miR-27b decreased the total cholesterol (TC) level and increased that of high-density lipoprotein cholesterol (HDL-C). At the mRNA level, miR-27b overexpression downregulated the expression of Pparγ, but upregulated that of lipid metabolism-associated factors such as heart-type fatty acid-binding protein (H-FABP), fatty acid transport protein 1 (FATP1), adipose triglyceride lipase (ATGL), and lipoprotein lipase (LPL), whereas miR-27b inhibition elicited the opposite effect; however, inhibition of miR-27b led to elevated cholesterol 7 alpha-hydroxylase (CYP7A1) and fatty acid translocase 36 (CD36) levels. Similarly, at the protein level, miR-27b overexpression promoted a decrease in the concentration of PPARγ, whereas miR-27b inhibition led to an increase in PPARγ levels, as well as those of CYP7A1, CD36, ATGL, and LPL. Overall, our results indicated that hypoxic exercise regulates lipid metabolism via the miR-27b/PPARγ pathway and modulates ATGL and LPL expression through inducing their post-transcriptional modifications.

Effects of Active and Passive Hypoxic Conditioning for 6 Weeks at Different Altitudes on Blood Lipids, Leptin, and Weight in Rats

Du, Xia, Olivier Girard, Rong yun Fan, and Fuhai Ma. Effects of active and passive hypoxic conditioning for 6 weeks at different altitudes on blood lipids, leptin, and weight in rats. High Alt Med Biol. 21:243-248, 2020. Objective: To compare the effects of 6 weeks of passive and active hypoxia exposure at different altitudes on lipid metabolism, leptin, and weight in rats. Materials and Methods: Eighty 9-week-old male Wistar rats were assigned to either non-exercise or exercise groups. Each group was subdivided into four categories (n = 10) based on hypoxic conditions: 0, 2200, 2200 + 3500, and 3500 m. Rats in the exercise group trained on a treadmill at a speed of 20-22 m/min (0° incline) for 90 minutes, 5 days per week for 6 weeks. Serum lipid and leptin levels and weight were measured following the intervention. Results: Total cholesterol (-8.2% ± 3.5%), low-density lipoproteins (-29.8% ± 8.1%), and triglyceride (TG) levels (-17.2% ± 3.8%) were lower, and high-density lipoproteins (+7.4% ± 4.0%) higher, in exercise versus non-exercise groups (all p < 0.001), independent of condition. TG levels were lower at altitude (-13.0% ± 27.3%, -10.9% ± 24.3%, and -9.2% ± 20.9% at 2200, 2200 + 3500, and 3500 m, respectively) compared to 0 m (p < 0.001). Hypoxic exposure decreased leptin with lower values at 2200 + 3500 m and 3500 m compared to 0 m (p < 0.05). Weight was lower in exercise than non-exercise groups (-8.2% ± 21.0%; p < 0.001), and at altitude (-2.7% ± 2.6%, -5.5% ± 3.7%, and -5.7% ± 2.7% at 2200, 2200 + 3500, and 3500 m, respectively) compared to 0 m. Conclusion: Regular aerobic exercise led to more favorable responses for lipid metabolism and weight control than the oxygenation conditions the animals are in.

The Bidirectional Relationship Between Obstructive Sleep Apnea and Metabolic Disease

Obstructive sleep apnea (OSA) is a common sleep disorder, effecting 17% of the total population and 40-70% of the obese population (1, 2). Multiple studies have identified OSA as a critical risk factor for the development of obesity, diabetes, and cardiovascular diseases (3-5). Moreover, emerging evidence indicates that metabolic disorders can exacerbate OSA, creating a bidirectional relationship between OSA and metabolic physiology. In this review, we explore the relationship between glycemic control, insulin, and leptin as both contributing factors and products of OSA. We conclude that while insulin and leptin action may contribute to the development of OSA, further research is required to determine the mechanistic actions and relative contributions independent of body weight. In addition to increasing our understanding of the etiology, further research into the physiological mechanisms underlying OSA can lead to the development of improved treatment options for individuals with OSA.

Exposure and Exercise Training in Hypoxic Conditions as a New Obesity Therapeutic Modality: A Mini Review

Obesity is an important health problem caused by positive energy balance. Generally, low calorie dietary intake combined with regular exercise is the most common modality to lose bodily fat in obese people. Although this is the first modality of choice for obesity treatment, it needs to be applied to obese patients for at least 12 weeks or more and it does not provide consistent results because it is difficult to suppress increased appetite due to exercise. Recently, many researchers have been applying hypoxic conditions for the treatment of obesity, as many studies show that people residing in high altitudes have a lower percentage of body fat and fewer obesity-related illnesses than people living at sea level. Hypoxic therapy treatment, including hypoxic exposure or hypoxic exercise training, is recommended as a way to treat and prevent obesity by suppression of appetite, increasing basal metabolic rate and fat oxidation, and minimizing side effects. Hypoxic therapy inhibits energy intake and appetite-related hormones, and enhances various cardiovascular and metabolic function parameters. These observations indicate that hypoxic therapy is a new treatment modality for inducing fat reduction and promoting metabolic and cardiovascular health, which may be an important and necessary strategy for the treatment of obesity. As such, hypoxic therapy is now used as a general medical practice for obesity treatment in many developed countries. Therefore, hypoxic therapy could be a new, practical, and useful therapeutic modality for obesity and obesity-related comorbidities.

The phosphodiesterase-4 inhibitor roflumilast reverts proteolysis in skeletal muscle cells of patients with COPD cachexia

Peripheral muscle weakness and mass loss are characteristic features in severe chronic obstructive pulmonary disease (COPD). We hypothesized that the phosphodiesterase (PDE)-4 inhibitor roflumilast-induced cAMP may ameliorate proteolysis and metabolism in skeletal muscles of COPD patients with severe muscle wasting. In myogenic precursor cells (isolated from muscle biopsies and cultured up to obtain differentiated myotubes) from 10 severe COPD patients and 10 healthy controls, which were treated with 1 μM roflumilast N-oxide (RNO) for three time cohorts (1, 6, and 24 h), genes of antioxidant defense and oxidative stress marker, myogenesis and muscle metabolism, proteolysis (tyrosine release assay) and ubiquitin-proteasome system markers, autophagy, and myosin isoforms were analyzed using RT-PCR and immunoblotting. In COPD patients at 6 h RNO treatment, myotube tyrosine release, total protein ubiquitination, and tripartite motif-containing protein 32 levels were significantly lower than healthy controls, whereas at 24 h RNO treatment, myotube myosin heavy chain ( MyHC) -I and MyHC-IIx expression levels were upregulated in both patients and controls. In the 6-h RNO cohort, in patients and controls, myotube expression of nuclear factor (erythroid-derived 2)-like 2 ( NRF2) and its downstream antioxidants sirtuin-1, FGF-inducible 14, and insulin-like growth factor-1 was upregulated, whereas that of myocyte-specific enhancer factor 2C, myogenic differentiation, myogenin, myostatin, atrogin-1, and muscle RING-finger protein-1 was downregulated. In myotubes of severe COPD patients with cachexia, roflumilast-induced cAMP signaling exerts beneficial effects by targeting muscle protein breakdown (tyrosine release), along with reduced expression of proteolytic markers of the ubiquitin-proteasome system and that of myostatin. In both patients and controls, roflumilast also favored antioxidant defense through upregulation of the NRF2 pathway and that of the histone deacetylase sirtuin-1, whereas it improved the expression of slow- and fast-twitch myosin isoforms. These findings show that muscle dysfunction and wasting may be targeted by roflumilast-induced cAMP signaling in COPD. These results have potential therapeutic implications, as this PDE-4 inhibitor is currently available for the treatment of systemic inflammation and exacerbations in patients with severe COPD. NEW & NOTEWORTHY In myotubes of cachectic chronic obstructive pulmonary disease (COPD) patients, cAMP signaling exerted beneficial effects by targeting muscle proteolysis and reducing gene expression of proteolytic markers of the ubiquitin-proteasome system and that of myostatin. In myotubes of patients and controls, roflumilast also favored antioxidant defense through upregulation of the nuclear factor (erythroid-derived 2)-like 2 pathway, of sirtuin-1, and of gene expression of slow- and fast-twitch isoforms. These findings have potential clinical implications for the treatment of muscle wasting in patients with COPD and cachexia.

Normobaric hypoxic conditioning to maximize weight loss and ameliorate cardio-metabolic health in obese populations: a systematic review

Normobaric hypoxic conditioning (HC) is defined as exposure to systemic and/or local hypoxia at rest (passive) or combined with exercise training (active). HC has been previously used by healthy and athletic populations to enhance their physical capacity and improve performance in the lead up to competition. Recently, HC has also been applied acutely (single exposure) and chronically (repeated exposure over several weeks) to overweight and obese populations with the intention of managing and potentially increasing cardio-metabolic health and weight loss. At present, it is unclear what the cardio-metabolic health and weight loss responses of obese populations are in response to passive and active HC. Exploration of potential benefits of exposure to both passive and active HC may provide pivotal findings for improving health and well being in these individuals. A systematic literature search for articles published between 2000 and 2017 was carried out. Studies investigating the effects of normobaric HC as a novel therapeutic approach to elicit improvements in the cardio-metabolic health and weight loss of obese populations were included. Studies investigated passive (n = 7; 5 animals, 2 humans), active (n = 4; all humans) and a combination of passive and active (n = 4; 3 animals, 1 human) HC to an inspired oxygen fraction ([Formula: see text]) between 4.8 and 15.0%, ranging between a single session and daily sessions per week, lasting from 5 days up to 8 mo. Passive HC led to reduced insulin concentrations (-37 to -22%) in obese animals and increased energy expenditure (+12 to +16%) in obese humans, whereas active HC lead to reductions in body weight (-4 to -2%) in obese animals and humans, and blood pressure (-8 to -3%) in obese humans compared with a matched workload in normoxic conditions. Inconclusive findings, however, exist in determining the impact of acute and chronic HC on markers such as triglycerides, cholesterol levels, and fitness capacity. Importantly, most of the studies that included animal models involved exposure to severe levels of hypoxia ([Formula: see text] = 5.0%; simulated altitude >10,000 m) that are not suitable for human populations. Overall, normobaric HC demonstrated observable positive findings in relation to insulin and energy expenditure (passive), and body weight and blood pressure (active), which may improve the cardio-metabolic health and body weight management of obese populations. However, further evidence on responses of circulating biomarkers to both passive and active HC in humans is warranted.

Inflammatory Events and Oxidant Production in the Diaphragm, Gastrocnemius, and Blood of Rats Exposed to Chronic Intermittent Hypoxia: Therapeutic Strategies

We hypothesized that inflammatory events and reactive oxygen species (ROS) production may be differentially expressed in respiratory and limb muscles, and blood of a chronic intermittent hypoxia (CIH) experimental model and that antioxidants and TNF-alpha blockade may influence those events. In blood, diaphragm, and gastrocnemius of rats non-invasively exposed to CIH (10% hypoxia, 2 h/day, 14 consecutive days) with/without concomitant treatment with either anti-TNF-alpha antibody (infliximab) or N-acetyl cysteine (NAC), inflammatory cytokines, superoxide anion production, muscle structural abnormalities, and fiber-type composition were assessed. Compared to non-exposed controls, in CIH-exposed rats, body weight gain was reduced, TNF-alpha, IL-1beta, IL-6, and interferon-gamma levels were increased in diaphragm, TNF-alpha, and IL-1 beta plasma levels were greater, systemic and muscle superoxide anion production was higher, diaphragm and gastrocnemius inflammatory cells and internal nuclei were higher, and muscle fiber-type and morphometry remained unmodified. CIH rats treated with infliximab further increased TNF-alpha, IL-1beta, IL-6, and interferon-gamma diaphragm levels, whereas NAC induced a reduction only in TNF-alpha and IL-1beta levels in diaphragm and plasma. Infliximab and NAC elicited a significant decline in superoxide anion production in diaphragm, gastrocnemius, and plasma, while inducing a further increase in inflammatory cells and internal nuclei in both muscles. Proinflammatory cytokines are differentially expressed in respiratory and limb muscles and plasma of CIH-exposed rats, while superoxide anion production increased in both muscle types and blood. Infliximab and NAC exerted different effects. These findings may help understand the biology underlying CIH in skeletal muscles and blood of patients with chronic respiratory diseases. J. Cell. Physiol. 232: 1165-1175, 2017. © 2016 Wiley Periodicals, Inc.

Effects of hypoxic exercise training on microRNA expression and lipid metabolism in obese rat livers

To investigate the effects of hypoxic exercise training on microRNA (miRNA) expression and the role of miRNA expression in regulating lipid metabolism, 20 dietary-induced obese SD rats were divided into a normoxic sedentary group (N, n=10) and a hypoxic exercise training group (H, n=10). After four weeks, measurements were taken of body weight, body length, fat mass, serum lipid concentration, miRNAs differentially expressed in rat liver, and gene and protein expression levels of peroxisome proliferator activated receptor α (PPARα), fatty acid synthetase (FAS), and carnitine palmitoyl transferase 1A (CPT1A) in rat liver. Body weight, Lee's index, fat mass, fat/weight ratio, and serum levels of total cholesterol (TC) and high density lipoprotein cholesterol (HDL-C) were all significantly lower in the H group than in the N group (P<0.01). Six miRNAs expressed significantly differently in the liver (P<0.05). Specifically, expression levels of miR-378b were significantly lower in the H group than in the N group (P<0.05). Compared with the normoxic sedentary group, hypoxic exercise training resulted in a lower ratio of FAS mRNA to CPT1A mRNA (P<0.05), as well as lower CPT1A protein levels (P<0.01), while a higher ratio of FAS to CPT1A protein levels (P<0.01) was observed. In conclusion, hypoxic training may elevate the resistance of high fat diet induced obesity in rats by reducing the expression of miR-378b, and decrease the fatty acid mitochondrial oxidation in obese rat livers by decreasing the protein expression of CPT1A and increasing the protein expression ratio of FAS/CPT1A.

Hypoxic Conditioning as a New Therapeutic Modality

Preconditioning refers to a procedure by which a single noxious stimulus below the threshold of damage is applied to the tissue in order to increase resistance to the same or even different noxious stimuli given above the threshold of damage. Hypoxic preconditioning relies on complex and active defenses that organisms have developed to counter the adverse consequences of oxygen deprivation. The protection it confers against ischemic attack for instance as well as the underlying biological mechanisms have been extensively investigated in animal models. Based on these data, hypoxic conditioning (consisting in recurrent exposure to hypoxia) has been suggested a potential non-pharmacological therapeutic intervention to enhance some physiological functions in individuals in whom acute or chronic pathological events are anticipated or existing. In addition to healthy subjects, some benefits have been reported in patients with cardiovascular and pulmonary diseases as well as in overweight and obese individuals. Hypoxic conditioning consisting in sessions of intermittent exposure to moderate hypoxia repeated over several weeks may induce hematological, vascular, metabolic, and neurological effects. This review addresses the existing evidence regarding the use of hypoxic conditioning as a potential therapeutic modality, and emphasizes on many remaining issues to clarify and future researches to be performed in the field.

Therapeutic potential of intermittent hypoxia: a matter of dose

Intermittent hypoxia (IH) has been the subject of considerable research in recent years, and triggers a bewildering array of both detrimental and beneficial effects in multiple physiological systems. Here, we review the extensive literature concerning IH and its impact on the respiratory, cardiovascular, immune, metabolic, bone, and nervous systems. One major goal is to define relevant IH characteristics leading to safe, protective, and/or therapeutic effects vs. pathogenesis. To understand the impact of IH, it is essential to define critical characteristics of the IH protocol under investigation, including potentially the severity of hypoxia within episodes, the duration of hypoxic episodes, the number of hypoxic episodes per day, the pattern of presentation across time (e.g., within vs. consecutive vs. alternating days), and the cumulative time of exposure. Not surprisingly, severe/chronic IH protocols tend to be pathogenic, whereas any beneficial effects are more likely to arise from modest/acute IH exposures. Features of the IH protocol most highly associated with beneficial vs. pathogenic outcomes include the level of hypoxemia within episodes and the number of episodes per day. Modest hypoxia (9-16% inspired O2) and low cycle numbers (3-15 episodes per day) most often lead to beneficial effects without pathology, whereas severe hypoxia (2-8% inspired O2) and more episodes per day (48-2,400 episodes/day) elicit progressively greater pathology. Accumulating evidence suggests that "low dose" IH (modest hypoxia, few episodes) may be a simple, safe, and effective treatment with considerable therapeutic potential for multiple clinical disorders.

The effect of 'sleep high and train low' on weight loss in overweight Chinese adolescents: study protocol for a randomized controlled trial

Background

Exercise and diet are the cornerstones for the treatment of obesity in obese children and adolescents. However, compensatory changes in appetite and energy expenditure elicited by exercise and dieting make it hard to maintain a reduced weight over the longterm. The anorexic effect of hypoxia can be potentially utilized to counteract this compensatory increase, thereby enhancing the success of weight loss. The purpose of the study is to assess the effectiveness of four week intermittent hypoxia exposure added to a traditional exercise and diet intervention on inducing short- and longterm weight loss in obese adolescents.

Methods/Design

In this randomized parallel group controlled clinical trial, 40 obese adolescents (20 boys and 20 girls, 11 to 15-years-old), will be recruited from a summer weight loss camp at the Shanghai University of Sport, China. Participants will be stratified by gender and randomly assigned to either the control group or the hypoxia group. During the four-week intervention period, both groups will exercise and eat a balanced diet. Additionally, the control group will sleep in normal conditions, while the hypoxia group will sleep in a normobaric hypoxia chamber (sleep high and train low). The primary outcome will be body composition and the main secondary outcomes will be the circulating levels of appetite regulatory gastrointestinal hormones. All the outcome measures will be assessed at baseline, after the four-week intervention, and at two months follow-up.

Discussion

Our study will be the first to evaluate the effectiveness of ‘sleep high and train low’ on short- and longterm weight loss among obese adolescents. A potential mechanism for the appetite regulatory effect of hypoxia will also be explored. The results of the study will provide an evidence-based recommendation for the use of hypoxia in a weight loss intervention among obese children and adolescents. Furthermore, the clarification of mechanisms leading to weight loss in ‘sleep high and train low’ might provide information for the development of new strategies in combating obesity.

Trial registration

This trial was registered on 10 January 2014 at the Chinese Clinical Trial Registry with the registration number: ChiCTR-TRC-14004106.

Intermittent hypoxia impairs glucose homeostasis in C57BL6/J mice: partial improvement with cessation of the exposure

OBJECTIVES

Obstructive sleep apnea is associated with insulin resistance, glucose intolerance, and type 2 diabetes mellitus. Although several studies have suggested that intermittent hypoxia in obstructive sleep apnea may induce abnormalities in glucose homeostasis, it remains to be determined whether these abnormalities improve after discontinuation of the exposure. The objective of this study was to delineate the effects of intermittent hypoxia on glucose homeostasis, beta cell function, and liver glucose metabolism and to investigate whether the impairments improve after the hypoxic exposure is discontinued.

INTERVENTIONS

C57BL6/J mice were exposed to 14 days of intermittent hypoxia, 14 days of intermittent air, or 7 days of intermittent hypoxia followed by 7 days of intermittent air (recovery paradigm). Glucose and insulin tolerance tests were performed to estimate whole-body insulin sensitivity and calculate measures of beta cell function. Oxidative stress in pancreatic tissue and glucose output from isolated hepatocytes were also assessed.

RESULTS

Intermittent hypoxia increased fasting glucose levels and worsened glucose tolerance by 67% and 27%, respectively. Furthermore, intermittent hypoxia exposure was associated with impairments in insulin sensitivity and beta cell function, an increase in liver glycogen, higher hepatocyte glucose output, and an increase in oxidative stress in the pancreas. While fasting glucose levels and hepatic glucose output normalized after discontinuation of the hypoxic exposure, glucose intolerance, insulin resistance, and impairments in beta cell function persisted.

CONCLUSIONS

Intermittent hypoxia induces insulin resistance, impairs beta cell function, enhances hepatocyte glucose output, and increases oxidative stress in the pancreas. Cessation of the hypoxic exposure does not fully reverse the observed changes in glucose metabolism.

Hypoxia, energy balance and obesity: from pathophysiological mechanisms to new treatment strategies

High altitude exposure is often accompanied by weight loss. Postulated mechanisms are a reduction of nutritional energy intake, a reduction of intestinal energy uptake from impaired intestinal function and increased energy expenditure. Beyond the field of altitude, there are good reasons for renewed interest in the relationship between hypoxia and energy balance. The increasing prevalence of obesity and associated comorbidities represent a major health concern. Obesity is frequently associated with sleep disorders leading to intermittent systemic hypoxia with deleterious cardiovascular and metabolic consequences. Hypoxic regions may be present within hypertrophic white adipose tissue leading to chronic systemic inflammation. Among the increasing number of people commuting to altitude for work or leisure, obesity is a risk factor for acute mountain sickness. Paradoxically, exposure to intermittent hypoxia might be considered as a means to lose body mass and to improve metabolic risk factors. Daytime exposure to intermittent hypoxia has been used to treat hypertension in former Soviet Union countries and is now being experimented elsewhere. Such intermittent hypoxic exposure at rest or during exercise may lead to improvement in body composition and health status with improved exercise tolerance, metabolism and systemic arterial pressure. Future research should confirm whether hypoxic training could be a new treatment strategy for weight loss and comorbidities in obese subjects and elucidate the underlying mechanisms and signalling pathways.

Metabolic effects of intermittent hypoxia in mice: steady versus high-frequency applied hypoxia daily during the rest period

Intermittent hypoxia (IH) is a frequent occurrence in sleep and respiratory disorders. Both human and murine studies show that IH may be implicated in metabolic dysfunction. Although the effects of nocturnal low-frequency intermittent hypoxia (IH(L)) have not been extensively examined, it would appear that IH(L) and high-frequency intermittent hypoxia (IH(H)) may elicit distinct metabolic adaptations. To this effect, C57BL/6J mice were randomly assigned to IH(H) (cycles of 90 s 6.4% O(2) and 90 s 21% O(2) during daylight), IH(L) (8% O(2) during daylight hours), or control (CTL) for 5 wk. At the end of exposures, some of the mice were subjected to a glucose tolerance test (GTT; after intraperitoneal injection of 2 mg glucose/g body wt), and others were subjected to an insulin tolerance test (ITT; 0.25 units Humulin/kg body wt), with plasma leptin and insulin levels being measured in fasting conditions. Skeletal muscles were harvested for GLUT4 and proliferator-activated receptor gamma coactivator 1-α (PGC1-α) expression. Both IH(H) and IH(L) displayed reduced body weight increases compared with CTL. CTL mice had higher basal glycemic levels, but GTT kinetics revealed marked differences between IH(L) and IH(H), with IH(L) manifesting the lowest insulin sensitivity compared with either IH(H) or CTL, and such findings were further confirmed by ITT. No differences emerged in PGC1-α expression across the three experimental groups. However, while cytosolic GLUT4 protein expression remained similar in IH(L), IH(H), and CTL, significant decreases in GLUT4 membrane fraction occurred in hypoxia and were most pronounced in IH(L)-exposed mice. Thus IH(H) and IH(L) elicit differential glucose homeostatic responses despite similar cumulative hypoxic profiles.

Usefulness of combining intermittent hypoxia and physical exercise in the treatment of obesity

Obesity is an important public health problem worldwide and is a major risk factor for a number of chronic diseases such as type II diabetes, adverse cardiovascular events and metabolic syndrome-related features. Different treatments have been applied to tackle body fat accumulation and its associated clinical manifestations. Often, relevant weight loss is achieved during the first 6 months under different dietary treatments. From this point, a plateau is reached, and a gradual recovery of the lost weight may occur. Therefore, new research approaches are being investigated to assure weight maintenance. Pioneering investigations have reported that oxygen variations in organic systems may produce changes in body composition. Possible applications of intermittent hypoxia to promote health and in various pathophysiological states have been reported. The hypoxic stimulus in addition to diet and exercise can be an interesting approach to lose weight, by inducing higher basal noradrenalin levels and other metabolic changes whose mechanisms are still unclear. Indeed, hypoxic situations increase the diameter of arterioles, produce peripheral vasodilatation and decrease arterial blood pressure. Furthermore, hypoxic training increases the activity of glycolytic enzymes, enhancing the number of mitochondria and glucose transporter GLUT-4 levels as well as improving insulin sensitivity. Moreover, hypoxia increases blood serotonin and decreases leptin levels while appetite is suppressed. These observations allow consideration of the hypothesis that intermittent hypoxia induces fat loss and may ameliorate cardiovascular health, which might be of interest for the treatment of obesity. This new strategy may be useful and practical for clinical applications in obese patients.

Mice Exposed to Chronic Intermittent Hypoxia Simulate Clinical Features of Deficiency of both Qi and Yin Syndrome in Traditional Chinese Medicine

Deficiency of both Qi and Yin Syndrome (DQYS) is one of the common syndromes in traditional Chinese medicine (TCM), mainly characterized by tiredness, emaciation, anorexia, fidget, palpitation and rapid pulse, and so forth. Currently, there is no available animal model which can reflect the clinical features of this syndrome. In the present paper, we observed the time-course changes of whole behavior, body weight, food intake, locomotive activity and electrocardiogram in mice exposed to chronic intermittent hypoxia for 6 weeks, and measured bleeding time at last according to the clinical features of DQYS and one key pathological factor. The results showed that the mice exposed to intermittent hypoxia for certain time presented lackluster hair, dull looking hair, resistance, attacking, body weight loss, food intake decline, locomotive activity decrease, heart rate quickening and T wave elevating, which were similar to the major clinical features of DQYS. Meanwhile, bleeding time shortening was also found, which was consistent with the clinical fact that DQYS often accompanied with blood stasis. The possible explanation was also outlined according to the available literature. Such findings suggested chronic intermittent hypoxia could induce similar symptoms and signs in mice accorded with the clinical features of DQYS, which provided a suitable animal model for evaluation of drugs for the treatment of this syndrome and further exploration of pathological process or correlation of the syndrome and related diseases.