Intermittent Hypoxia Exposure Research Articles

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Cover Photograph:Upper left: Newt (P. waltl) juveniles and Xenopus froglets were subjected to agarose‐embedded heat‐shock (AeHS) method. GFP expression was induced specifically in the regenerating limbs (see Matsubara et al. 86–93).Upper right: Schematic diagram of the intermittent hypoxia exposure model. Pimonidazole‐positive cells were detected in the pulmonary tissues of Xenopus laevis during repeated dives, indicating tissue hypoxia (see Fujiyama, 94–99).Lower left: The intercalary element of Zhangixalus schlegelii (arrowheads). Such skeletal elements are seen between the terminal and subterminal phalanges of all the digits of arboreal frogs (see Nakanishi, 100–108).Lower right: Tetraspanin9 expressions in Xenopus laevis (above) and X. tropicalis embryo (below) hybridized in the same tube. (see Kuriyama and Tanaka, 109–119).Bottom right corner: A 48 hpf early four‐armed pluteus taken through a confocal microscope. Catecholamine‐positive cells are colored in yellow (see Kalachev and Tankovich, 120–131). image

Sacubitril/valsartan mitigated intermittent hypoxia related intestinal microbiota alteration and aortic injury.

To investigate the influence of sacubitril valsartan sodium (SVS) on chronic intermittent hypoxia (IH) related gut microbiome composition alteration and aortic injury. Experiments were performed using SD rats, which were divided into three groups: control, IH, and SVS group. O2 concentration was decreased to 7-8% at nadir approximately every 3min in IH group (8h per day for 6weeks) or was left unchanged in control group. Rats in SVS group were orally gavaged with SVS at the dosage of 30mg/kg/day (2weeks after chronic IH exposure). At week 6, fecal and aortic samples were harvested for 16s rDNA analysis and histological analysis, respectively. Principal coordinate analysis and non-metric multidimensional scaling analysis indicated that the bacterial community was altered by chronic IH exposure, while SVS treatment restored the intestinal microbial communities. Further analysis showed that IH decreased the relative abundance of Lactobacillus and Prevotella, while rats treated with SVS was enriched with Firmicutes, Bacilli, Prevotellaceae, and Lactobacillus, which was similar to control rats. Immunohistochemical staining showed that SVS prevented the upregulation of transforming growth factor-β1 and tumor necrosis factor-alpha in theaorta. SVS prevented aortic adverse response to IH, possibly through modulating intestinal microbiota.

Chronic Breathlessness in Obstructive Sleep Apnea and the Use of Lymphocyte Parameters to Identify Overlap Syndrome among Patients.

Little is known about the distribution of etiology in obstructive sleep apnea (OSA) combined with chronic breathlessness. A significant portion of patients in this group have so-called "overlap syndrome (OVS)", characterized by chronic obstructive pulmonary disease (COPD). OVS has more complications and a poorer prognosis compared to patients with either OSA or COPD alone, which makes it important to identify OVS early in OSA. The current study was a retrospective cross-sectional analysis of consecutive adult patients who were diagnosed with OSA (n = 1062), of whom 275 were hospitalized due to chronic breathlessness. Respiratory and cardiac diseases accounted for the vast majority of causes, followed by gastrointestinal and renal disorders. The final study population comprised 115 patients with OSA alone (n = 64) and OVS (n = 51), who had chronic breathlessness as the primary complaint, not secondary as one of many other complaints. Lymphocytes, CD4 counts, neutrophil-to-lymphocyte ratio (NLR), and PLR were differently expressed between the OSA-alone group and OVS group. The NLR, lymphocytes, and CD4 counts had a moderate diagnostic value for OVS in OSA patients, with AUCs of 0.708 (95% CI, 0.614-0.802), 0.719 (95% CI, 0.624-0.813), and 0.744 (95% CI, 0.653-0.834), respectively. The NLR had the highest AUC for predicting a 6-month re-admission of OVS, with a cut-off of 3.567 and a moderate prognostic value. The sensitivity and specificity were 0.8 and 0.732, respectively. In the animal model, the spleen hematoxylin- and eosin-stained, electron microscopy images showed germinal-center damage, chromatin activation, and mitochondrial swelling under the overlapping effect of intermittent hypoxia and cigarette smoke exposure. OSA with chronic breathlessness cannot be overstated. A significant proportion of patients with COPD in this group had poor lung function at initial diagnosis. The NLR is a useful biomarker to differentiate OVS among OSA patients combined with chronic breathlessness.

Reduced circulating growth hormone and insulin-like growth factor-1 and delayed growth of premature rats are aggravated by longer daily duration of chronic intermittent hypoxia exposure.

This study mainly aimed to investigate the effect of daily duration of chronic intermittent hypoxia (CIH) exposure on circulating growth hormone (GH)/insulin-like growth factor-1 (IGF-1) concentrations and body weight changes of premature rats. 40 healthy male SD rats aged six weeks were enrolled in this study. These rats were randomly divided into four groups (n = 10 per group), including normal control (NC) group (normal oxygen exposure every day), CIH-1 group (daily CIH exposure for 2 h), CIH-2 group (daily CIH exposure for 4 h), and CIH-3 group (daily CIH exposure for 8 h). The serum GH/IGF-1 concentrations and body weights in all rats were determined after 30 days of normal oxygen or CIH exposure. No significant difference was found with respect to the baseline body weight among the four groups of rats. After establishments of animal models with a duration of 30 days, significant differences were found respect to body weight, body weight changes, and serum GH/IGF-1 concentrations among the four groups of rats with a same trend (all P < 0.05): the highest values were all in NC group rats, followed CIH-1 group, CIH-2 group, and CIH-3 group rats. Among all the rats, the body weight changes correlated significantly with both serum GH and IGF-1 concentrations (both P < 0.05). CIH decreases circulating GH/IGF-1 concentrations and causes growth delay in premature rats. Such effects could be aggravated by increased daily duration of CIH exposures.

Intermittent Hypoxia and Diet-Induced Obesity on the Intestinal Wall Morphology in a Murine Model of Sleep Apnea.

This work analyzes the impact of two conditions, intermittent hypoxia exposure and high-fat diet in rats as models of sleep apnea. We studied the autonomic activity and histological structure of the rat jejunum and whether the overlapping of both conditions, as often observed in patients, induces more deleterious effects on the intestinal barrier. We found alterations in jejunum wall histology, predominantly in HF rats, based on increased crypt depth and submucosal thickness, as well as decreased muscularis propria thickness. These alterations were maintained with the IH and HF overlap. An increase in the number and size of goblet cells in the villi and crypts and the infiltration of eosinophils and lymphocytes in the lamina propria suggest an inflammatory status, confirmed by the increase in plasma CRP levels in all experimental groups. Regarding the CAs analysis, IH, alone or combined with HF, causes a preferential accumulation of NE in the catecholaminergic nerve fibers of the jejunum. In contrast, serotonin increases in all three experimental conditions, with the highest level in the HF group. It remains to be elucidated whether the alterations found in the present work could affect the permeability of the intestinal barrier, promoting sleep apnea-induced morbidities.

Intermittent hypoxia conditioning as a potential prevention and treatment strategy for ischemic stroke: Current evidence and future directions.

Ischemic stroke (IS) is the leading cause of disability and death worldwide. Owing to the aging population and unhealthy lifestyles, the incidence of cerebrovascular disease is high. Vascular risk factors include hypertension, diabetes, dyslipidemia, and obesity. Therefore, in addition to timely and effective reperfusion therapy for IS, it is crucial to actively control these risk factors to reduce the incidence and recurrence rates of IS. Evidence from human and animal studies suggests that moderate intermittent hypoxia (IH) exposure is a promising therapeutic strategy to ameliorate common vascular risk factors and comorbidities. Given the complex pathophysiological mechanisms underlying IS, effective treatment must focus on reducing injury in the acute phase and promoting repair in the recovery phase. Therefore, this review discusses the preclinical perspectives on IH conditioning as a potential treatment for neurovascular injury and highlights IH pre and postconditioning strategies for IS. Hypoxia conditioning reduces brain injury by increasing resistance to acute ischemic and hypoxic stress, exerting neuroprotective effects, and promoting post-injury repair and regeneration. However, whether IH produces beneficial effects depends not only on the hypoxic regimen but also on inter-subject differences. Therefore, we discuss the factors that may influence the effectiveness of IH treatment, including age, sex, comorbidities, and circadian rhythm, which can be used to help identify the optimal intervention population and treatment protocols for more accurate, individualized clinical translation. In conclusion, IH conditioning as a non-invasive, non-pharmacological, systemic, and multi-targeted intervention can not only reduce brain damage after stroke but can also be applied to the prevention and functional recovery of IS, providing brain protection at different stages of the disease. It represents a promising therapeutic strategy. For patients with IS and high-risk groups, IH conditioning is expected to develop as an adjunctive clinical treatment option to reduce the incidence, recurrence, disability, and mortality of IS and to reduce disease burden.

Influence of cardiac function on intermittent hypoxia in rats fed with high-fat diet

A high-fat diet (HFD) accumulates fat in the cardiovascular system, alters the metabolism, and affects cardiac function. Dyslipidemia is associated with the development of sleep apnea syndrome (SAS), which is associated with intermittent hypoxia (IH); however, it is unclear whether SAS affects cardiac function in patients with dyslipidemia. The purpose of this study was to evaluate how IH affects cardiac function in rats fed with a HFD. Male 5-week-old Sprague-Dawley rats of two groups (normal diet (SD) and HFD) were divided into IH-exposed and unexposed groups. Zinc protoporphyrin-9 (ZnPPIX) was administered as a heme oxygenase-1 (HO-1) inhibitor to the SD and IH + HFD groups, and cardiac function and blood viscosity were examined. In the IH + HFD group, echocardiography showed an increased fractional shortening (FS), which peaked on day 4. Western blot analysis revealed an increase in HO-1 after 2 weeks. This peak continued even after the HO-1 inhibitor and ZnPPIX were administered. One cause of increased FS is the stagnation of blood flow due to an increased blood viscosity. To be able to send highly viscous blood to every corner of the body, the heart must contract strongly. Therefore, HO-1 is released by the body as a biological defense reaction. HO-1 has a vasodilatory effect and suppresses hyper constriction. Thus, IH exposure to HFD causes and drives transient hyper constriction, releasing HO-1 as a biological response. This led to dilated blood vessels, after which the FS returned to normal.

Malondialdehyde and carbonyl levels in skeletal muscle tissues after intermittent hypobaric hypoxia exposures

Background: Hypobaric hypoxia is a state of decreased oxygen pressure at high altitudes that can lead to hypoxia and oxidative stress as a result. Skeletal muscle is one of the important organs that can be affected by oxidative stress and cause contractile dysfunction.&#x0D; Objective: This study aimed to evaluate the impact of intermittent hypobaric hypoxia on oxidative stress markers in rat skeletal muscle, by measuring malondialdehyde (MDA) and carbonyl levels.&#x0D; Methods: Twenty-five Wistar rats were allocated into five groups, including one control group and four hypoxic groups (I-IV). The hypoxic groups were exposed to an altitude of 25,000 feet for 5 minutes using hypobaric chamber in once (I), twice (II), three (III), and four (IV) times, with a 7-day interval period between exposures. The control group remained in normobaric conditions throughout the study. MDA levels were measured by thiobarbituric acid (TBA) test, while carbonyl levels were measured using 2,4-dinitrophenylhydrazine (DNPH) reagent.&#x0D; Results: The MDA level was significantly increased in group I compared to the control group (p=0.008). There were decreasing MDA levels in groups II, III, and IV compared to group I. The carbonyl level was significantly higher in group I than the control group (p=0.000), with an even higher level observed in group II. Although the carbonyl levels tended to decrease in groups III and IV, they still remained higher than those of the control group.&#x0D; Conclusion: Exposure to hypobaric hypoxia leads to an increase in MDA and carbonyl levels in the skeletal muscles, indicating an elevation of oxidative stress levels. However, the subsequent intermittent hypobaric hypoxia exposure resulted in a reduction in these levels, implying that skeletal muscles may adapt to hypoxic conditions.

Obstructive sleep apnoea is related to melanoma aggressiveness through paraspeckle protein-1 upregulation.

In patients with obstructive sleep apnoea (OSA), intermittent hypoxia induces overexpression of paraspeckle component (PSPC)1, a master modulator of transforming growth factor (TGF)-β signalling, which promotes cell cancer progression through epithelial-mesenchymal transition (EMT) and acquisition of cancer stem cell (CSC)-like features. However, the persistence of intermittent hypoxia-induced effects on PSPC1, and their consequences in cancer patients are not known. To this effect, circulating PSPC1 levels were compared in patients with cutaneous melanoma with or without OSA, and their relationship with tumour aggressiveness along with the in vitro effects of soluble PSPC1 and intermittent hypoxia on melanoma cell aggressiveness mechanisms were assessed. In 292 cutaneous melanoma patients, sleep studies and serum levels of PSPC1 and TGF-β were evaluated. The effect of PSPC1 on expression of EMT and CSC transcription factors was assessed using melanoma cell lines with patient sera under both normoxia and intermittent hypoxia conditions. PSPC1 levels were higher in patients with moderate-severe OSA compared with mild OSA or non-OSA patients. Serum levels of PSPC1 were associated with several cutaneous melanoma clinical aggressiveness indicators. Both intermittent hypoxia exposures and serum from OSA patients upregulated TGF-β expression and amplified the expression of transcription factors associated with EMT activation and acquisition of CSC characteristics. In cutaneous melanoma patients, OSA severity is associated with higher PSPC1 serum levels, which jointly with intermittent hypoxia would enhance the self-reprogramming capabilities of EMT and CSC feature acquisition of melanoma cells, promoting their intrinsic aggressiveness.

Intermittent hypoxia exposure alleviates 2,4,6-trinitrobenzene sulfonic acid-induced enteritis by enhancing the intestinal barrier and inhibiting endoplasmic reticulum stress in juvenile largemouth bass

Hypoxia has long been considered to be one of the most drastic abiotic stresses in aquatic environments. However, increasing evidence has shown that hypoxia can also prove beneficial for living organisms. The purpose of our study was to investigate the effects of intermittent hypoxia (IH) exposure on growth performance, intestinal flora, intestinal immunity, and anti-inflammation capacity in juvenile largemouth bass. Growth data showed that IH suppressed the growth of juvenile largemouth bass (the mean final weight of the control fish was 20.5 g, but was 14.76 g in the IH-1 h and 12.88 g in the IH-3 h) by regulating the expression of appetite factors. In addition, IH also reconstructed intestinal flora homeostasis, enriched α diversity, and changed composition. It is worth noting that IH mitigated the cumulative mortality rates (33.3% in C, 13.3% in IH-1 h, 20.0% in IH-3 h) and reversed the development of enteritis after 2,4,6-trinitrobenzene sulfonic acid (TNBS) injection. IH exposure significantly inhibited TNBS-induced mucosal injury and increased goblet cells. These results might be due to enhanced antioxidant (CAT, GSH-PX, T-SOD) and immune capacity (ACP, AKP, LZM). We also found that enteritis increased intestinal endoplasmic reticulum stress (ERS) and proinflammatory response. However, these reactions were significantly less in the IH groups. Taken together, the findings of the current study reveal that the IH exposure suppressed growth but also improved stress resistance via inhibition of ERS and the proinflammatory response in largemouth bass.

The effects of intermittent hypoxia on hepatic expression of fatty acid translocase CD36 in lean and diet-induced obese mice

BackgroundBoth obstructive sleep apnea (OSA) and non-alcoholic fatty liver disease (NAFLD) are prevalent within obese individuals. We aimed to investigate the effects of intermittent hypoxia (IH), a clinical feature of OSA, on hepatic expression of fatty acid translocase (CD36) in relation to liver injury in lean and diet-induced obese mice. MethodsFour-week-old male C57BL/6J mice were randomized to standard diet (SD) or high fat (HF) diet groups. At 13-week-old, all mice were exposed to either air or IH (IH30; thirty hypoxic episodes per hour) for four weeks. We assessed liver injury through lipid profile, oxidative and inflammatory stress, histological scoring and hepatic CD36 expression. ResultsIn lean mice, IH elevated serum and hepatic triglyceride and free fatty acid (FFA) levels, in line with upregulation of hepatic CD36 expression and myeloperoxidase (MPO)-positive cells in support of inflammatory infiltrates along with increase in serum malondialdehyde (MDA), C-X-C motif chemokine ligand 1(CXCL-1) and monocyte chemoattractant protein-1 (MCP-1). In diet-induced obese mice, an increase in hepatic alanine transaminase (ALT) activity, serum and hepatic levels of lipid parameters and inflammatory markers, serum MDA level, hepatic expressions of CD36 and α-smooth muscle actin (α-SMA), and MPO-positive cells was observed. IH potentiated hepatic ALT activity, serum CXCL-1 and hepatic interleukin-6 (IL-6), in line with inflammatory infiltrates, but paradoxically, reduced hepatic FFA level and hepatic CD36 expression, compared to obese mice without IH exposure. However, IH further augmented diet-induced liver steatosis and fibrosis as shown by histological scores. ConclusionThis study contributes to support that IH featuring OSA may lead to liver injury via differential regulation of hepatic CD36 expression in lean and diet-induced obese mice.

Initiating daily acute intermittent hypoxia (dAIH) therapy at 1-week after contusion spinal cord injury (SCI) improves lower urinary tract function in rat

Spinal cord injury (SCI) above the level of the lumbosacral spinal cord produces lower urinary tract (LUT) dysfunction, resulting in impairment of urine storage and elimination (voiding). While spontaneous functional recovery occurs due to remodeling of spinal reflex micturition pathways, it is incomplete, indicating that additional strategies to further augment neural plasticity following SCI are essential. To this end, acute intermittent hypoxia (AIH) exposure has been proposed as a therapeutic strategy for improving recovery of respiratory and other somatic motor function following SCI; however, the impact of AIH as a therapeutic intervention to improve LUT dysfunction remains to be determined. Therefore, we examined the effects of daily AIH (dAIH) on both spontaneous micturition patterns and reflex micturition event (rME) behaviors in adult female Sprague-Dawley rats with mid-thoracic moderate contusion SCI. For these experiments, dAIH gas exposures (five alternating 3 min 12% O2 and 21% O2 episodes) were delivered for 7 consecutive days beginning at 1-week after SCI, with awake micturition patterns being evaluated weekly for 2–3 sessions before and for 4 weeks after SCI and rME behaviors elicited by continuous infusion of saline into the bladder being evaluated under urethane anesthesia at 4-weeks after SCI; daily normoxia (dNx; 21% O2 episodes) served as a control. At 1-week post-SCI, both an areflexic phenotype (i.e., no effective voiding events) and a functional voiding phenotype (i.e., infrequent voiding events with large volumes) were observed in spontaneous micturition patterns (as expected), and subsequent dAIH, but not dNx, treatment led to recovery of spontaneous void frequency pattern to pre-SCI levels; both dAIH- and dNx-treated rats exhibited slightly increased void volumes. At 4-weeks post-SCI, rME behaviors showed increased effectiveness in voiding in dAIH-treated (compared to dNx-treated) rats that included an increase in both bladder contraction pressure (delta BP; P = 0.014) and dynamic voiding efficiency (P = 0.018). Based on the voiding and non-voiding bladder contraction behaviors (VC and NVC, respectively) observed in the BP records, bladder dysfunction severity was classified into mild, moderate, and severe phenotypes, and while rats in both treatment groups included each severity phenotype, the primary phenotype observed in dAIH-treated rats was mild and that in dNx-treated rats was moderate (P = 0.044). Taken together, these findings suggest that 7-day dAIH treatment produces beneficial improvements in LUT function that include recovery of micturition pattern, more efficient voiding, and decreased NVCs, and extend support to the use of dAIH therapy to treat SCI-induced LUT dysfunction.

Regulation of Genes Related to Cognition after tDCS in an Intermittent Hypoxic Brain Injury Rat Model.

Background: Hypoxic brain injury is a condition caused by restricted oxygen supply to the brain. Several studies have reported cognitive decline, particularly in spatial memory, after exposure to intermittent hypoxia (IH). However, the effect and mechanism of action of IH exposure on cognition have not been evaluated by analyzing gene expression after transcranial direct current stimulation (tDCS). Hence, the purpose of this study was to investigate the effects of tDCS on gene regulation and cognition in a rat model of IH-induced brain injury. Methods: Twenty-four 10-week-old male Sprague–Dawley rats were divided into two groups: IH exposed rats with no stimulation and IH-exposed rats that received tDCS. All rats were exposed to a hypoxic chamber containing 10% oxygen for twelve hours a day for five days. The stimulation group received tDCS at an intensity of 200 µA over the frontal bregma areas for 30 min each day for a week. As a behavior test, the escape latency on the Morris water maze (MWM) test was measured to assess spatial memory before and after stimulation. After seven days of stimulation, gene microarray analysis was conducted with a KEGG mapper tool. Results: Although there were no significant differences between the groups before and after stimulation, there was a significant effect of time and a significant time × group interaction on escape latency. In the microarray analysis, significant fold changes in 12 genes related to neurogenesis were found in the stimulation group after tDCS (p < 0.05, fold change > 2 times, the average of the normalized read count (RC) > 6 times). The highly upregulated genes in the stimulation group after tDCS were SOS, Raf, PI3K, Rac1, IRAK, and Bax. The highly downregulated genes in the stimulation group after tDCS were CHK, Crk, Rap1, p38, Ras, and NF-kB. Conclusion: In this study, we confirmed that SOS, Raf, PI3K, Rac1, IRAK, and Bax were upregulated and that CHK, Crk, Rap1, p38, Ras, and NF-kB were downregulated in a rat model of IH-induced brain injury after application of tDCS.

Caloric restriction prevents obesity- and intermittent hypoxia-induced cardiac remodeling in leptin-deficient ob/ob mice.

Background: Intermittent hypoxia (IH), a key characteristic of obstructive sleep apnea, is independently associated with cardiometabolic impairment. While endogenous leptin levels may provide cardioprotective effects against hypoxia, leptin resistance is common among obese individuals presenting with obstructive sleep apnea. Methods: Here, we assessed left ventricle (LV) function using M-mode echocardiography in lean wild-type, calorically-restricted ob/ob, and obese ob/ob mice before and after 6 days of IH to determine how obesity and intermittent hypoxia interact to affect cardiac function independent of leptin signaling. Results: Calorically-restricting ob/ob mice for 4 weeks prior to IH exposure prevented weight gain (−2.1 ± 1.4 g) compared to free-fed ob/ob mice (8.7 ± 1.1 g). Free-fed ob/ob mice exhibited increased LV mass (0.713 ± 0.008 g) relative to wild-type mice (0.685 ± 0.004 g) and increased posterior wall thickness (0.089 ± 0.006 cm) relative to calorically-restricted ob/ob mice (0.072 ± 0.004 cm). Following 6 days of IH, free-fed ob/ob mice exhibited increases in cardiac output (44.81 ± 2.97 pre-IH vs. 57.14 ± 3.09 ml/min post-IH), LV diameter (0.400 ± 0.007 pre-IH vs. 0.428 ± 0.009 cm post-IH) and end diastolic volume (0.160 ± 0.007 pre-IH vs. 0.195 ± 0.012 ml post-IH) that were not detected in wild-type or calorically-restricted ob/ob mice. Conclusion: Caloric restriction can prevent obesity-induced LV hypertrophy and protect against acute IH-induced cardiac remodeling independent of leptin signaling. These findings may have clinical implications for obstructive sleep apnea.

Shashen-Maidong Decoction inhibited cancer growth under intermittent hypoxia conditions by suppressing oxidative stress and inflammation

Ethnopharmacological relevanceLung cancer is one of the most common malignant tumours and has become the leading cause of cancer-related deaths worldwide. Abnormal microcirculation during tumour growth leads to intermittent hypoxia (IH), which is responsible for promoting cancer cell proliferation and migration. Patients with advanced lung cancers show deficiency of both Qi and Yin Syndrome (DQYS) in TCM, and studies have confirmed that IH exposure is related to DQYS. Shashen-Maidong Decoction (SMD), has been widely applied clinically targeting DQYS and has a long history for treating lung cancer by nourishing the body's “zheng qi” and resisting “xie qi”. However, whether SMD could be beneficial to lung cancer under IH conditions remains unclear. Aim of the studyThis study aimed to clarify the effects and mechanism of SMD on non-small cell lung cancer (NSCLC) growth under IH conditions. Materials and methodsC57 mice were injected subcutaneously into the right axilla with Lewis lung cancer (LLC) cells and exposed to IH conditions (21%–5% O2, 5 min/cycle, 8 h/day) for 21 days. SMDs were orally treated with different concentrations (2.6, 5.2 or 10.4 g/kg/day) 30 min before IH exposure. Tumour proliferation and migration were assessed by HE and IHC staining, and oxidative stress was assessed by DHE staining and MDA or SOD detection. IL-6, IL-1β and TNF-α levels were assessed by IHC staining, and the IL-6/JAK2/STAT3 signalling pathway was detected by western blotting. ResultsOur results showed that SMD treatment inhibited tumour growth and liver metastasis in LLC-bearing mice exposed to IH, decreased Ki67, CD31, VEGF, and MMP-2, and increased E-cadherin expression in tumourt tissue. SMD reduced ROS production, increased SOD levels and SOD-2 expression, and decreased MDA levels and NOX-2 expression. SMD decreased IL-6, IL-1β and TNF-α levels, reduced IL-6 expression and inhibited JAK2 and STAT3 phosphorylation. Additionally, SMD treatment improved DQYS and liver and kidney function in LLC-bearing mice under IH conditions. ConclusionOur research suggests that SMD treatment can inhibit tumour growth in mice exposed to IH. The antitumour effect of SMD may be related to attenuated oxidative stress and inflammation through inactivation of the IL-6/JAK2/STAT3 signalling pathway under IH conditions.

Tetraplegia is associated with increased hypoxic ventilatory response during nonrapid eye movement sleep

People with cervical spinal cord injury (SCI) are likely to experience chronic intermittent hypoxia while sleeping. The physiological effects of intermittent hypoxia on the respiratory system during spontaneous sleep in individuals with chronic cervical SCI are unknown. We hypothesized that individuals with cervical SCI would demonstrate higher short‐ and long‐term ventilatory responses to acute intermittent hypoxia (AIH) exposure than individuals with thoracic SCI during sleep. Twenty participants (10 with cervical SCI [9 male] and 10 with thoracic SCI [6 male]) underwent an AIH and sham protocol during sleep. During the AIH protocol, each participant experienced 15 episodes of isocapnic hypoxia using mixed gases of 100% nitrogen (N2) and 40% carbon dioxide (CO2) to achieve an oxygen saturation of less than 90%. This was followed by two breaths of 100% oxygen (O2). Measurements were collected before, during, and 40 min after the AIH protocol to obtain ventilatory data. During the sham protocol, participants breathed room air for the same amount of time that elapsed during the AIH protocol and at approximately the same time of night. Hypoxic ventilatory response (HVR) during the AIH protocol was significantly higher in participants with cervical SCI than those with thoracic SCI. There was no significant difference in minute ventilation (V .E.), tidal volume (V .T.), or respiratory frequency (f) during the recovery period after AIH in cervical SCI compared to thoracic SCI groups. Individuals with cervical SCI demonstrated a significant short‐term increase in HVR compared to thoracic SCI. However, there was no evidence of ventilatory long‐term facilitation following AIH in either group.

Metabolic response provides insights into the mechanism of adaption to hypoxia in largemouth bass (Micropterus salmoides) under intermittent hypoxic conditions

In metabolism, molecular oxygen is a necessary substrate. Oxygen imbalances are linked to a variety of circumstances in the organism's homeostasis. Recently, the positive effects of hypoxia treatment in improving exercise ability and hypoxia tolerance have become a research focus. We explored the effects of intermittent hypoxia exposure (IHE, for one hour or three hours per day) on the hypoxia tolerance of largemouth bass in this study. The results showed that (1) IHE significantly reduced the LOEcrit (the critical O2 tension for loss of equilibrium) value of largemouth bass, indicating that its hypoxia tolerance was enhanced. (2) The level of oxidative stress in the liver decreased in the HH3 group (exposed to a hypoxic condition for 3 h per day) compared to HH1 group (exposed to a hypoxic condition for 1 h per day). (3) IHE reduced the content of lactic acid and enhanced the process of gluconeogenesis in the liver. (4) Importantly, lipid mobilization and fatty acid oxidation in the liver of largemouth bass were significantly enhanced during IHE. In short, the results of this study indicate that IHE can improve hypoxia tolerance by regulating the energy metabolism of largemouth bass.

Chronic intermittent hypoxia, a hallmark of obstructive sleep apnea, promotes 4T1 breast cancer development through endothelin-1 receptors

The association between obstructive sleep apnea (OSA) and cancer is still debated and data are scarce regarding the link between OSA and breast cancer progression. Since conclusive epidemiological studies require large sample sizes and sufficient duration of exposure before incident cancer occurrence, basic science studies represent the most promising approach to appropriately address the topic. Here we assessed the impact of intermittent hypoxia (IH), the major hallmark of OSA, on the development of breast cancer and explored the specific involvement of the endothelin signaling pathway. Original in vitro and in vivo models were used where 3D-spheroids or cultures of murine 4T1 breast cancer cells were submitted to IH cycles, and nude NMRI mice, orthotopically implanted with 4T1 cells, were submitted to chronic IH exposure before and after implantation. The role of the endothelin-1 in promoting cancer cell development was investigated using the dual endothelin receptor antagonist, macitentan. In vitro exposure to IH significantly increased 4T1 cell proliferation and migration. Meta-analysis of 4 independent in vivo experiments showed that chronic IH exposure promoted tumor growth, assessed by caliper measurement (overall standardized mean difference: 1.00 [0.45–1.55], p < 0.001), bioluminescence imaging (1.65 [0.59–2.71]; p < 0.01) and tumor weight (0.86 [0.31–1.41], p < 0.01), and enhanced metastatic pulmonary expansion (0.77 [0.12–1.42]; p = 0.01). Both in vitro and in vivo tumor-promoting effects of IH were reversed by macitentan. Overall, these findings demonstrate that chronic intermittent hypoxia exposure promotes breast cancer growth and malignancy and that dual endothelin receptor blockade prevents intermittent hypoxia-induced tumor development.

Mild intermittent hypoxia exposure alters gut microbiota composition in men with overweight and obesity.

Results from high altitude studies in humans and controlled animal experiments suggest that hypoxia exposure induces alterations in gut microbiota composition, which may in turn affect host metabolism. However, well-controlled studies investigating the effects of normobaric hypoxia exposure on gut microbiota composition in humans are lacking. The aim of this study was to explore the impact of mild intermittent hypoxia (MIH) exposure on gut microbiota composition in men with overweight and/or obesity. We performed a randomised, single-blind crossover study, in which participants were exposed to MIH (FiO2: 15%, 3×2 h per day) and normoxia (FiO2: 21%) for seven consecutive days. Following the MIH and normoxia exposure regimens, faecal samples were collected for determination of faecal microbiota composition using 16S rRNA gene-amplicon sequencing in the morning of day 8. Paired faecal samples were available for five individuals. Furthermore, tissue-specific insulin sensitivity was determined using the gold-standard two-step hyperinsulinemic-euglycemic clamp. MIH did not affect microbial alpha and beta-diversity but reduced the relative abundance of Christensenellaceae and Clostridiaceae bacterial families. MIH significantly increased the abundances of obligate anaerobic bacterial genera including Fusicatenibacter, Butyricicoccus and Holdemania, whilst reducing Christensenellaceae R-7 group and Clostridium sensu stricto 1, although these findings were not statistically significant after correction for multiple testing. Furthermore, MIH-induced alterations in abundances of several genera were associated with changes in metabolic parameters such as adipose and peripheral insulin sensitivity, plasma levels of insulin, fatty acids, triacylglycerol and lactate, and substrate oxidation. In conclusion, we demonstrate for the first time that MIH exposure induces modest effects on faecal microbiota composition in humans, shifting several bacterial families and genera towards higher abundances of anaerobic butyrate-producing bacteria. Moreover, MIH-induced effects on faecal microbial composition were associated with parameters related to glucose and lipid homeostasis, supporting a link between MIH-induced alterations in faecal microbiota composition and host metabolism. The study was registered at the Netherlands Trial Register: NL7120/NTR7325.

An Inexpensive Open-Source Chamber for Controlled Hypoxia/Hyperoxia Exposure.

Understanding hypoxia/hyperoxia exposure requires either a high-altitude research facility or a chamber in which gas concentrations are precisely and reproducibly controlled. Hypoxia-induced conditions such as hypoxic-ischemic encephalopathy (HIE), obstructive or central apneas, and ischemic stroke present unique challenges for the development of models with acute or chronic hypoxia exposure. Many murine models exist to study these conditions; however, there are a variety of different hypoxia exposure protocols used across laboratories. Experimental equipment for hypoxia exposure typically includes flow regulators, nitrogen concentrators, and premix oxygen/nitrogen tanks. Commercial hypoxia/hyperoxia chambers with environmental monitoring are incredibly expensive and require proprietary software with subscription fees or highly expensive software licenses. Limitations exist in these systems as most are single animal systems and not designed for extended or intermittent hypoxia exposure. We have developed a simple hypoxia chamber with off-the-shelf components, and controlled by open-source software for continuous data acquisition of oxygen levels and other environmental factors (temperature, humidity, pressure, light, sound, etc.). Our chamber can accommodate up to two mouse cages and one rat cage at any oxygen level needed, when using a nitrogen concentrator or premixed oxygen/nitrogen tank with a flow regulator, but is also scalable. Our system uses a Python-based script to save data in a text file using modules from the sensor vendor. We utilized Python or R scripts for data analysis, and we have provided examples of data analysis scripts and acquired data for extended exposure periods (≤7 days). By using FLOS (Free-Libre and open-source) software and hardware, we have developed a low-cost and customizable system that can be used for a variety of exposure protocols. This hypoxia/hyperoxia exposure chamber allows for reproducible and transparent data acquisition and increased consistency with a high degree of customization for each experimenter’s needs.