Intermittent Hypobaric Hypoxia Research Articles

P6480Asymmetric dimethylarginine (ADMA) predicts altitude-associated hypoxic pulmonary arterial hypertension

Abstract Prolonged exposure to altitude-associated chronic hypoxia (CH) may cause high altitude pulmonary hypertension (HAPH). Chronic intermittent hypobaric hypoxia (CIH) occurs in individuals who commute between sea level and high altitude. CIH is associated with repetitive acute hypoxic acclimatization and conveys the long-term risk of HAPH. As nitric oxide (NO) is an important regulator of systemic and pulmonary vascular tone and asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthesis that increases in hypoxia, we aimed to investigate whether ADMA predicts the incidence of HAPH among Chilean frontiers personnel exposed to six months of CIH. We performed a prospective study of 123 healthy male subjects who were subjected to CIH (5 days at appr. 3,550 m, followed by 2 days at sea level) for six months. ADMA, SDMA, L-arginine, arterial oxygen saturation, systemic arterial blood pressure, and haematocrit were measured at baseline and at months 1, 4, and 6 at high altitude. Acclimatization to high altitude was determined using the Lake Louise Score and the presence of acute mountain sickness (AMS). Echocardiography was performed after six months of CIH in a subgroup of 43 individuals with either good (n=23) or poor (n=20) aclimatization to altitude, respectively. Logistic regression was used to assess the association of biomarkers with HAPH. 100 study participants aged 18.3±1.3 years with complete data sets were included in the final analysis. Arterial oxygen saturation decreased upon the first ascent to altitude and plateaued at about 90% during the further course of the study. Haematocrit increased to about 47% after one month and remained stable thereafter. ADMA continuously increased and SDMA decreased during the study course, whilst L-arginine levels showed no distinct pattern. The incidence of AMS and the Lake Louise Score were high after the first ascent (53 and 3.1±2.4, respectively) and at one month of CIH (47 and 3.0±2.6, respectively), but decreased to 20 and 1.4±2.0 at month 6, respectively (both p<0.001 for trend). In echocardiography, 18 participants (42%) showed a mean pulmonary arterial pressure (mPAP) greater than 25 mm Hg (mean ± SD, 30.4±3.9 mm Hg), out of which 9 (21%) were classified as HAPH (mPAP ≥30 mm Hg; mean ± SD, 33.9±2.2 mm Hg). Baseline ADMA, but not SDMA, was significantly associated with mPAP at month 6 in univariate logistic regression analysis (R = 0.413; p=0.007). In ROC analysis, a cut-off for baseline ADMA of 0.665 μmol/l was determined as the optimal cut-off level to predict HAPH (mPAP >30 mm Hg) with a sensitivity of 100% and a specificity of 63.6%. ADMA concentration increases during long-term CIH. It is an independent predictive biomarker for the incidence of HAPH. SDMA concentration decreases during CIH and shows no association with HAPH. Our data support a role of impaired NO-mediated pulmonary vasodilation in the pathogenesis of high altitude pulmonary hypertension. Acknowledgement/Funding CONICYT/FONDEF/FONIS Sa 09I20007; FIC Tarapaca BIP 30477541-0; BMBF grant 01DN17046 (DECIPHER); Georg & Jürgen Rickertsen Foundation, Hamburg

Effect of chronic intermittent hypobaric hypoxia on heart rate variability in conscious rats

To examine the effect of chronic intermittent hypobaric hypoxia (CIHH) on heart rate variability (HRV), male adult Sprague Dawley rats were exposed to hypoxia (oxygen 11.1%) in a hypobaric chamber for 42days, 6hours each day, simulating an altitude of 5000m. The body weight and blood pressure of rats were recorded once a week, electrocardiograms were analyzed continuously using biotelemetry, before, during and after CIHH treatment each day, and HRV was evaluated using spectrum analysis. No significant difference of body weight and blood pressure was found between CIHH and control rats. After 4weeks of CIHH treatment, total power (TP) and very low-frequency component (VLF) were lower in CIHH rats than in control rats under hypobaric hypoxia condition. During CIHH treatment, low frequency (LF) was higher in 1 week and lower in 5-6weeks in CIHH rats than control rats under hypobaric hypoxia, but not normoxic conditions. The high-frequency component (HF) was not changed during CIHH treatment, so LF/HF increased initially, and then recovered under the hypobaric hypoxia condition following 3weeks of CIHH treatment. In addition, the HR was increased in CIHH rats after 4weeks of CIHH treatment compared with control rats. Furthermore, HRV was altered significantly in control rats, but not in CIHH rats exposed to acute normobaric hypoxia. These data suggest that CIHH treatment modulates cardiac autonomic activity adaptively and inhibits the acute normobaric hypoxia-induced changes in HRV.

Aerobic Capacity, Lactate Concentration, and Work Assessment During Maximum Exercise at Sea Level and High Altitude in Miners Exposed to Chronic Intermittent Hypobaric Hypoxia (3,800 m).

We previously showed that arterial oxygen content during maximum exercise remains constant at high altitude (HA) in miners exposed to chronic intermittent hypobaric hypoxia (CIHH). Nevertheless, information about VO2, lactate concentration [Lac], and work efficiency are absent in this CIHH miner population. Our aim was to determine aerobic capacity, [Lac], and work efficiency at sea level (SL) and HA during maximum exercise in miners acclimatized to CIHH at 3,800 m. Eight volunteer miners acclimatized to CIHH at HA (> 4 years) performed an exercise test at SL and HA. The test was performed on the 4th day at HA or SL and consisted of three phases: Rest (5 min); Exercise test, where the load was increased by 50 W every 3 min until exhaustion; and a Recovery period of 30 min. During the procedure VO2, transcutaneous arterial saturation (SpO2, %), and HR (bpm) were assessed at each step by a pulse oximeter and venous blood samples were taken to measure [Lac] and hemoglobin concentration. No differences in VO2 and [Lac] in SL vs. HA were observed in this CIHH miner population. By contrast, a higher HR and lower SpO2 were observed at SL compared with HA. During maximum exercise, a reduction in VO2 and [Lac] was observed without differences in intensity (W) and HR. A decrease in [Lac] was observed at maximum effort (250 W) and recovery at HA vs. SL. These findings are related to an increased work efficiency assessment such as gross and net efficiency. This study is the first to show that miners exposed to CIHH maintain their work capacity (intensity) with a fall in oxygen consumption and a decrease in plasmatic lactate concentration at maximal effort at HA. These findings indicate that work efficiency at HA is enhanced.

Cardioprotection of post-ischemic moderate ROS against ischemia/reperfusion via STAT3-induced the inhibition of MCU opening.

Enhanced reactive oxygen species (ROS) at the beginning of reperfusion activated signal transducer and activator of transcription 3 (STAT3) in intermittent hypobaric hypoxia (IHH)-afforded cardioprotection against ischemia/reperfusion (I/R). However, its mechanism remains largely unknown. This study aimed to investigate the role and the downstream of STAT3 in exogenous enhanced post-ischemic ROS-induced cardioprotection using the model of moderate hydrogen peroxide postconditioning (H2O2PoC) mimicking endogenous ROS in IHH. Moderate H2O2PoC not only improved the post-ischemic myocardial contractile recovery and reduced the infarct size in isolated rat I/R hearts, but also alleviated mitochondrial calcium overload and ameliorated Ca2+ transients, cell contraction, and mitochondrial membrane potential in rat I/R cardiomyocytes. However, the cardioprotective effects of moderate H2O2PoC were abrogated by Janus kinase 2 (JAK2)/STAT3 inhibitor AG490 in rat hearts as well as adenovirus-delivered short hairpin RNA specific for STAT3 and the opener of mitochondrial calcium uniporter (MCU) spermine in rat cardiomyocytes. Notably, the moderate H2O2PoC-afforded cardioprotection abrogated by spermine could be rescued by STAT3 over-expression with adenovirus in rat I/R cardiomyocytes. Besides, moderate H2O2PoC enhanced mitochondrial STAT3 expression during I/R. A co-localization/interaction of STAT3 or phospho-STAT3ser727 and MCU was observed in rat cardiomyocytes with moderate H2O2PoC at 5 and 30min of reperfusion but not in rat I/R cardiomyocytes. Further, STAT3 interacted with the N-terminal domain (NTD) of MCU in rat cardiomyocytes with moderate H2O2PoC. These findings indicated that post-ischemic moderate ROS activate STAT3 against cardiac I/R by inhibiting MCU opening via its interaction with the NTD of MCU to alleviate mitochondrial calcium overload.

Abstract 311: Signal Transducer and Activator of Transcription 3 Inhibits the Opening of Mitochondrial Calcium Uniporter Against Cardiac Ischemia/reperfusion in Hydrogen Peroxide Postconditioning

Reactive oxygen species (ROS) generated during early reperfusion activated signal transducer and activator of transcription 3 (STAT3) contribute to intermittent hypobaric hypoxia (IHH)-afforded cardioprotection against ischemia/reperfusion (I/R)-induced mitochondrial calcium overload, but its mechanisms are not fully understood. This study investigated whether ROS signaling activated STAT3 is involved in moderate hydrogen peroxide postconditioning (H 2 O 2 PoC) mimicked IHH against cardiac I/R injury and the possible downstream target of STAT3 in mitochondria that mediates H 2 O 2 PoC-afforded cardioprotection. Moderate H 2 O 2 PoC not only improved the post-ischemic recovery of myocardial contractile performance and reduce the infarct size in isolated rat I/R hearts, but also alleviated cytosolic Ca 2+ and mitochondrial Ca 2+ overload and improved Ca 2+ transients and cell contraction in rat I/R cardiomyocytes. However, the cardioprotective effects of moderate H 2 O 2 PoC was abrogated by janus kinase 2 (JAK2)/STAT3 inhibitor AG490 in rat hearts as well as adenovirus-delivered shRNAs specific for STAT3 and the opener of mitochondrial calcium uniporter (MCU) spermine, respectively, in rat adult cardiomyoctes with simulated I/R. Besides, the moderate H 2 O 2 PoC-afforded cardioprotection abrogated by spermine could be rescued by STAT3 overexpression in rat cardiomyoctes with simulated I/R. Moreover, H 2 O 2 PoC enhanced the expression of serine 727 phosphorylation of STAT3 and STAT3 in mitochondria of rat cardiomyoctes with simulated I/R. Furthermore, immunofluorescence and co-immunoprecipitation assay revealed a co-localization/interaction of STAT3 and MCU in rat cardiomyoctes with moderate H 2 O 2 PoC at reperfusion 5 min and reperfusion 30 min but not in I/R cells. Co-immunoprecipitation further confirmed that STAT3 interacted with the N-terminal domain (NTD) of MCU in rat cardiomyoctes with moderate H 2 O 2 PoC. These findings indicate that STAT3 mediates the cardioprotection of moderate H 2 O 2 PoC against I/R injury by alleviating mitochondrial calcium overload through inhibiting MCU opening via the interaction with the NTD of MCU. Our finds provide new insight into the mechanisms of STAT3 in the cardioprotection.

Determining the Operating Costs of a Medical Surveillance Program for Copper Miners Exposed to High Altitude–Induced Chronic Intermittent Hypoxia in Chile Using a Combination of Microcosting and Time-Driven Activity-Based Costing

BackgroundCopper mining installations in Chile use a large number of workers who do their jobs at high altitudes, exposing them to the conditions of chronic intermittent hypobaric hypoxia. The Chilean Safety Association implements the surveillance program. ObjectiveThis organization, under the sponsorship of the Chilean Superintendency of Social Security, was interested in determining the costs involved in this program to support its decision-making processes and to improve its performance. MethodsDirect operating costs of the Hypoxia Medical Surveillance Program were determined through on-site surveys applied to the organization’s local agencies in charge. The microcosting method was used, quantifying personnel costs, consumables, and equipment and overhead costs. Time-driven activity-based costing was partially adapted for the allocation of personnel and equipment costs. Costs concerning activities, groups of activities and items, and average cost per exposed worker were determined. ResultsThe annual costs of the program were $127 299.58. The highest costs corresponded to the assessment activities, which were $89 192.13, representing 60.06% of the total. The labor factor costs were $77 568.50, which represents 60.93% of the total. The average cost per worker in the program is $21.17. ConclusionsThe partial adaptation of the time-driven activity-based costing method in combination with the microcosting method provides a suitable solution to determine the total costs of running a healthcare program of this kind. The information generated by this study will aid in the decision-making and management processes of the Hypoxia Medical Surveillance Program.

Myocardial interstitial matrix as novel target for succinic acid treatment strategies during experimental hypobaric hypoxia

Objective — Quantitative morphological studies of myocardial cellular elements. Aim of research is to study myocardial interstitial matrix with and without succinic acid treatment in the rats exposed to intermittent hypobaric hypoxia. Material and Methods — The study was conducted on 26 adult males of Wistar rats weighing 220-310 g, divided into 3 groups. The first control group consisted of 6 intact animals. The second group included 10 rats which were exposed to hypobaric hypoxia without medication for 30 days. Third group was composed of 10 rats, which were medicated by succinic acid solution which was injected intraperitoneally once a day at the rate of 0.5 ml/100 g of animal body weight 15 minutes before hypoxic exposure for 30 days. Results — In the second group almost the entire stroma was consisting of the thickened collagen fibers and proliferating cells of the connective tissue. Their total number increased relatively to the control by 31% initiating the processes of collagenases. An increase in the number of myofibroblasts which was observed in the hypoxic rat heart in the second group followed by high MPP-9 expression. Hypoxic effects in the third group were not significantly different from control according to the observed changes in the stroma. In rats of the third group the capillary diameter exceeded the indicator of the second group, but was significantly lower than the control indicator. Accordingly, compared with the series without correction, the cross-sectional area of the capillaries was increased – 28.44±0.14 μm2 against 24.53±0.20 μm2. The total cross-sectional area of the capillaries is 0.77±0.10 x103 μm2. The relative surface area of the vascular area was lower than the control by 21.8%. Conclusion ― Fibrosis in the myocardium inevitably leads to increased myocardial stiffness, resulting in systolic and diastolic dysfunction, neurohormonal activation and, ultimately, heart failure caused by hypobaric hypoxia. Reduced oxygen delivery by microvascular damage, increased perivascular fibrosis may contribute to contractile failure. Succinic acid combined with inosine acts as a high-energy phosphate reserve, to maintain adenosine triphosphate at levels sufficient to support contractile function.

Chronic intermittent hypobaric hypoxia attenuates skeletal muscle ischemia-reperfusion injury in mice

AimThe aim of this study was to investigate the protective effect of chronic intermittent hypobaric hypoxia (CIHH) against skeletal muscle ischemia-reperfusion (IR) injury and to determine the underlying mechanism. Main methodsC57BL/6 mice were randomly divided into 3 groups: skeletal muscle IR injury group (IR), CIHH pretreatment following IR group (IR + CIHH), and sham operation group (Sham). The skeletal muscle IR injury model was induced by the unilateral application of a tourniquet on a hind limb for 3 h and then releasing it for 24 h. CIHH pretreatment simulating a 5000-m altitude was applied 6 h per day for 28 days. The functional and morphological performance of IR-injured gastrocnemius muscle was evaluated using contraction force, H&E staining, and transmission electron microscopy. IR injury-induced CD68+ macrophage infiltration was assessed by immunofluorescence. TNFα levels in serum and muscle were measured by ELISA and western blotting, respectively. Apoptosis was examined by TUNEL staining and Cleaved Caspase-3 protein expression. Key findingsAcute IR injury resulted in reduced contraction tension, morphological destruction, macrophage infiltration, increased TNFα levels, and apoptosis in gastrocnemius muscle. CIHH pretreatment significantly ameliorated contraction function and morphological performance in IR-injured skeletal muscle. In addition, CIHH pretreatment resulted in marked decreases in CD68+ macrophage infiltration, TNFα levels, and apoptosis. SignificanceThese data demonstrated that CIHH has a protective effect against acute IR injury in skeletal muscle via inhibition of inflammation and apoptosis.

Low altitude simulation without hypoxia improves left ventricular function after myocardial infarction by reducing ventricular afterload.

Humans have a lower risk of death from myocardial infarction (MI) living at low elevations (<2500 m), which are not high enough to induce hypoxia. Both chronic hypoxia pre-MI, achieved by altitude simulation >5000 m, and intermittent hypobaric hypoxia post-MI can reduce MI size in rodents, and it is believed that hypoxia is the key stimulus. To explore mechanisms beyond hypoxia we studied whether altitude simulation <2500 m would also be associated with reduced infarct size. We performed left-anterior descending artery ligation on C57BL6 mice. Control mice (n = 12) recovered at 754 mmHg (atmospheric pressure, control), and treatment group mice (n = 13) were placed in a hypobaric chamber to recover 3-hours daily at 714 mmHg for 1 week. Echocardiographic evaluation of left ventricular function was performed on Day 0, Day 1 and Day 8. Intermittent hypobaric treatment was associated with a 14.2±5.3% improvement in ejection fraction for treatment group mice (p<0.01 vs. Day 1), with no change observed in control mice. Cardiac output, stroke volume, and infarct size were also improved in treated mice, but no changes were observed in HIF-1 activation or neovascularization. Next, we studied the acute hemodynamic effects of low altitude stimulation in intact mice breathing 100% oxygen using left ventricular catheterization and recording of pressure-volume loops. Acute reductions in barometric pressure from 754 mmHg to 714 mmHg and 674 mmHg were associated with reduced systemic vascular resistance, increased stroke volume and cardiac output, and no change in blood pressure or heart rate. Ex-vivo vascular function was studied using murine mesenteric artery segments. Acute reductions in barometric pressure were associated with greater vascular distensibility. We conclude that intermittent hypobaric treatment using simulated altitudes <2500 m reduces infarct size and increases ventricular function post-MI, and that these changes are related to altered arterial function and not hypoxia-associated neovascularization.

Asymmetric Dimethylarginine at Sea Level Is a Predictive Marker of Hypoxic Pulmonary Arterial Hypertension at High Altitude.

Background: Prolonged exposure to altitude-associated chronic hypoxia (CH) may cause high-altitude pulmonary hypertension (HAPH). Chronic intermittent hypobaric hypoxia (CIH) occurs in individuals who commute between sea level and high altitude. CIH is associated with repetitive acute hypoxic acclimatization and conveys the long-term risk of HAPH. As nitric oxide (NO) regulates pulmonary vascular tone and asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthesis, we investigated whether ADMA concentration at sea level predicts HAPH among Chilean frontiers personnel exposed to 6 months of CIH. Methods: In this prospective study, 123 healthy army draftees were subjected to CIH (5 days at 3,550 m, 2 days at sea level) for 6 months. In 100 study participants with complete data, ADMA, symmetric dimethylarginine (SDMA), L-arginine, arterial oxygen saturation (SaO2), systemic blood pressure, and hematocrit were assessed at months 0 (sea level), 1, 4, and 6. Acclimatization to altitude was determined using the Lake Louise Score (LLS) and the presence of acute mountain sickness (AMS). Echocardiography was performed after 6 months of CIH in 43 individuals with either good (n = 23) or poor (n = 20) acclimatization. Results: SaO2 acutely decreased at altitude and plateaued at 90% thereafter. ADMA increased and SDMA decreased during the study course. The incidence of AMS and the LLS was high after the first ascent (53 and 3.1 ± 2.4) and at 1 month of CIH (47 and 3.0 ± 2.6), but decreased to 20 and 1.4 ± 2.0 at month 6 (both p < 0.001). Eighteen participants (42%) showed a mean pulmonary arterial pressure (mPAP) >25 mm Hg, out of which 9 (21%) were classified as HAPH (mPAP ≥ 30 mm Hg). ADMA at sea level was significantly associated with mPAP at high altitude in month 6 (R = 0.413; p = 0.007). In ROC analysis, a cutoff for baseline ADMA of 0.665 μmol/L was determined to predict HAPH (mPAP > 30 mm Hg) with a sensitivity of 100% and a specificity of 63.6%. Conclusions: ADMA concentration increases during CIH. ADMA at sea level is an independent predictive biomarker of HAPH. SDMA concentration decreases during CIH and shows no association with HAPH. Our data support a role of impaired NO-mediated pulmonary vasodilation in the pathogenesis of HAPH.

Expression profile of circular RNAs in myocardial ischemia/reperfusion with and without intermittent hypobaric hypoxia preconditioning.

Expression profile of circular RNAs in myocardial ischemia/reperfusion with and without intermittent hypobaric hypoxia preconditioning.

Hypobaric hypoxia regulates iron metabolism in rats.

Intermittent hypobaric hypoxia can produce a protective effect on both the nervous system and non-nervous system tissues. Intermittent hypobaric hypoxia preconditioning has been shown to protect rats from cardiac ischemia-reperfusion injury by decreasing cardiac iron levels and reactive oxygen species (ROS) production, thereby decreasing oxidative stress to achieve protection. However, the specific mechanism underlying the protective effect of hypobaric hypoxia is unclear. To shed light on this phenomenon, we subjected Sprague-Dawley rats to hypobaric hypoxic preconditioning (8 hours/day). The treatment was continued for 4 weeks. We then measured the iron content in the heart, liver, spleen, and kidney. The iron levels in all of the assessed tissues decreased significantly after hypobaric hypoxia treatment, corroborating previous results that hypobaric hypoxia may produce its protective effect by decreasing ROS production by limiting the levels of catalytic iron in the tissue. We next assessed the expression levels of several proteins involved in iron metabolism (transferrin receptor, L-ferritin, and ferroportin1 [FPN1]). The increased transferrin receptor and decreased L-ferritin levels after hypobaric hypoxia were indicative of a low-iron phenotype, while FPN1 levels remained unchanged. We also examined hepcidin, transmembrane serine proteases 6 (TMPRSS6), erythroferrone (ERFE), and erythropoietin (EPO) levels, all of which play a role in the regulation of systemic iron metabolism. The expression of hepcidin decreased significantly after hypobaric hypoxia treatment, whereas the expression of TMPRSS6 and ERFE and EPO increased sharply. Finally, we measured serum iron and total iron binding capacity in the serum, as well as red blood cell count, mean corpuscular volume, hematocrit, red blood cell distribution width SD, and red blood cell distribution width CV. As expected, all of these values increased after the hypobaric hypoxia treatment. Taken together, our results show that hypobaric hypoxia can stimulate erythropoiesis, which systemically draws iron away from nonhematopoietic tissue through decreased hepcidin levels.

Anti-arrhythmic Cardiac Phenotype Elicited by Chronic Intermittent Hypoxia Is Associated With Alterations in Connexin-43 Expression, Phosphorylation, and Distribution.

Remodeling of the cellular distribution of gap junctions formed mainly by connexin-43 (Cx43) can be related to the increased incidence of cardiac arrhythmias. It has been shown that adaptation to chronic intermittent hypobaric hypoxia (IHH) attenuates the incidence and severity of ischemic and reperfusion ventricular arrhythmias and increases the proportion of anti-arrhythmic n-3 polyunsaturated fatty acids (n−3 PUFA) in heart phospholipids. Wistar rats were exposed to simulated IHH (7,000 m, 8-h/day, 35 exposures) and compared with normoxic controls (N). Cx43 expression, phosphorylation, localization and n−3 PUFA proportion were analyzed in left ventricular myocardium. Compared to N, IHH led to higher expression of total Cx43, its variant phosphorylated at Ser368 [p-Cx43(Ser368)], which maintains “end to end” communication, as well as p-Cx43(Ser364/365), which facilitates conductivity. By contrast, expression of non-phosphorylated Cx43 and p-Cx43(Ser278/289), attenuating intercellular communication, was lower in IHH than in N. IHH also resulted in increased expression of protein kinase A and protein kinase G while casein kinase 1 did not change compared to N. In IHH group, which exhibited reduced incidence of ischemic ventricular arrhythmias, Cx43 and p-Cx43(Ser368) were more abundant at “end to end” gap junctions than in N group and this difference was preserved after acute regional ischemia (10 min). We further confirmed higher n-3 PUFA proportion in heart phospholipids after adaptation to IHH, which was even further increased by ischemia. Our results suggest that adaptation to IHH alters expression, phosphorylation and distribution of Cx43 as well as cardioprotective n-3PUFA proportion suggesting that the anti-arrhythmic phenotype elicited by IHH can be at least partly related to the stabilization of the “end to end” conductivity between cardiomyocytes during brief ischemia.

Chronic Intermittent Hypobaric Hypoxia Ameliorates Renal Vascular Hypertension Through Up-regulating NOS in Nucleus Tractus Solitarii.

Chronic intermittent hypobaric hypoxia (CIHH) is known to have an anti-hypertensive effect, which might be related to modulation of the baroreflex in rats with renal vascular hypertension (RVH). In this study, RVH was induced by the 2-kidney-1-clip method (2K1C) in adult male Sprague-Dawley rats. The rats were then treated with hypobaric hypoxia simulating 5000m altitude for 6h/day for 28days. The arterial blood pressure (ABP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were measured before and after microinjection of L-arginine into the nucleus tractus solitarii (NTS) in anesthetized rats. Evoked excitatory postsynaptic currents (eEPSCs) and spontaneous EPSCs (sEPSCs) were recorded in anterogradely-labeled NTS neurons receiving baroreceptor afferents. We measured the protein expression of neuronal nitric oxide synthase (nNOS) and endothelial NOS (eNOS) in the NTS. The results showed that the ABP in RVH rats was significantly lower after CIHH treatment. The inhibition of ABP, HR, and RSNA induced by L-arginine was less in RVH rats than in sham rats, and greater in the CIHH-treated RVH rats than the untreated RVH rats. The eEPSC amplitude in NTS neurons receiving baroreceptor afferents was lower in the RVH rats than in the sham rats and recovered after CIHH. The protein expression of nNOS and eNOS in the NTS was lower in the RVH rats than in the sham rats and this decrease was reversed by CIHH. In short, CIHH treatment decreases ABP in RVH rats via up-regulating NOS expression in the NTS.

Effects of high-intensity interval training while using a breathing-restrictive mask compared to intermittent hypobaric hypoxia

Background: Previous studies of the Elevation Training Mask (ETM) describe comparisons between groups using the ETM and controls for effects on aerobic performance. However, comparisons have not been made to intermittent hypoxic training (IHT). Further, how the ETM impacts exercise economy is unknown. Therefore, we sought to determine the effects of training with the ETM compared to IHT on aerobic performance and cycling economy. Methods: Thirty participants were randomized into an ETM, IHT, or control group (n = 10 each). Pre- and post-testing occurred using a ramp VO2max test on a cycle ergometer allowing submaximal power output (PO) measures of economy. Economy was measured using POs of 100, 125, and 150W. High-intensity cycling interval training (HIIT) occurred 2x/week for 30 min/session for six weeks. Sessions were 20 min of HIIT (30s at 100% peak power output (PPO) of pre VO2max, 90s active recovery at 25W, 10 bouts) with a 5-minute warm-up and cool-down. Repeated measures ANOVA was used for statistical analyses. RESULTS: All participants improved VO2max, PPO, and PO at ventilatory threshold 2 pre- to post-training (p < 0.05). Interactions between groups showed that the RER for the IHT group increased at 100W and 125W, and decreased at RERmax pre- to post-training while the ETM group showed the opposite response (p < 0.05). Conclusion: The ETM and IHT groups performed similarly to the control at maximal and submaximal effort following six weeks of training. The IHT group, but not the ETM group, experienced an increased glycolytic energy shift during submaximal exercise.

The effect of intermittent hypobaric hypoxia on oxidative stress status and antioxidant enzymes activity in rat brain

Background: High altitude can cause hypobaric hypoxia (HH), resulted from the lower barometric pressure and hence partial pressure of oxygen. Hypoxia can lead to a lot of deleterious molecular and cellular changes, such as generation of free radicals or reactive oxygen species (ROS). Increasing of ROS can cause oxidative stress if the antioxidant enzyme does not increase simultaneously. Oxidative damage in brain has toxic effect on cognitive functions.&#x0D; Objective: In this study, we investigate effect of acute intermittent HH on oxidative stress and antioxidant enzyme activity in rat brain.&#x0D; Method: Wistar rats divided into 5 groups, consisting control group and four experimental groups which treated to HH. Rats were exposed to simulated HH equivalent to 35.000 feet in hypobaric chamber for 1 minute, repeated once a week.&#x0D; Results: Level of malondialdehyde and carbonyl in rat brain under acute HH increased at HH exposure (group I) compare to control group. These levels decreased afterward at intermittent HH exposure (group II-IV). Specific activity of superoxide dismutase (SOD) shows increasing level at intermittent HH exposure, especially group IV was increasing of SOD level significantly. The increasing pattern of specific activity of catalase was inversely from SOD pattern, but it still has higher activity in intermittent HH compare to control group.&#x0D; Conclusion: Brain tissue seems to be able to perform an adequate adaptive response to hypobaric hypoxia after the training, shown by its significantly decreased MDA and carbonyl level and also increased specific activity of SOD and catalase.

Vitamin E Reduces Hypobaric Hypoxia-Induced Immune Responses in Male Rats.

In hypobaric hypoxia (HH) at high altitude, the immune responses are changed probably due to oxidative stress-induced production of free radicals and nonradicals. Vitamin E is an antioxidant and protects the cells from oxidative damage. The present study was carried out to study the antioxidant role of vitamin E on the immune changes induced by oxidative stress in HH at high altitude. Select immune responses (phagocytic activity of white blood cell [WBC], cytotoxic activity of splenic mononuclear cells [MNCs], and delayed type of hypersensitivity [DTH]) and hematological changes (total count and differential count [DC] of WBC) were measured in male rats exposed to intermittent HH (at 5486.4 m in a simulated chamber for 8 hours/d for 6 consecutive days) and in normobaric condition with and without p.o. administration of vitamin E in three different doses (20, 40, and 60 mg/kg body weight). The increase of phagocytic activity of blood WBC, and reduction of cytotoxic activity of splenic MNC and DTH response were observed in rats exposed to HH. After the administration of vitamin E at different doses, the immune changes were blocked in a dose-dependent manner. Exposure to HH also led to the elevation of serum corticosterone (CORT), which was arrested after administration of vitamin E. The results indicate that the immune changes in HH at high altitude are probably mediated by the production of free radicals and nonradicals, and vitamin E can block these immune changes by its reactive oxygen species quenching effects.

The role of the hypoxia-Nrp-1 axis in the activation of M2-like tumor-associated macrophages in the tumor microenvironment of cervical cancer.

To explore the mechanisms through which hypoxic tumor microenvironment (TME) modulates the transition of tumor-associated macrophages (TAMs). The migration ability of RAW264.7 macrophages was determined by transwell assay. Flow cytometric, western blot and immunofluorescence analyses of CD206 further validated the M2 polarization of macrophages. Immunofluorescence, western blot and qRT-PCR were performed to detect the expression of neuropilin-1 (Nrp-1) and carbonic anhydrase IX (CAIX). An intermittent hypobaric hypoxia (IH) animal model was established to evaluate the role of hypoxia in activating M2-like TAMs in vivo. We also used immunohistochemistry to analyze the association between CAIX, CD163+ macrophages and Nrp-1 in a series of 72 human cervical cancer specimens. We found that the hypoxic cervical TME educated the recruited macrophages to transform into the M2 phenotype. Nrp-1 expression was significantly increased in hypoxia-primed cervical cancer cells. Blocking Nrp-1 expression prevented hypoxic cells from recruiting and polarizing macrophages towards the M2 phenotype. Hypoxia exposure significantly increased the expression of Nrp-1 as well as the infiltration of macrophages in vivo. Consistently, immunochemical staining in serial tissue sections of cervical cancer revealed upregulated levels of Nrp-1 in CAIX-positive hypoxic regions along with a concurrent significant elevation of M2 macrophages. Nrp-1 and M2-like TAMs were related to the malignant properties of cervical cancer, such as the FIGO stage and lymph node metastasis. Nrp-1 plays critical roles in hypoxic TME-induced activation and pro-tumoral effects of TAMs in cervical cancer. Interfering with Nrp-1 may be a potential therapeutic strategy in treating cervical cancer.

Chronic Intermittent Hypobaric Hypoxia Attenuates Irradiation Induced Hippocampus Damage in Mice

To observe the manifestations of radiation induced hippocampus damage and the potential injury mechanisms in mice. To examine the protective effects with chronic intermittent hypobaric hypoxia (CIHH) on radiation induced hippocampus damage. A total of 48 male adult C57/BL mice were randomly divided into four groups as control group (group A), CIHH group (group B), irradiation group (group C) and CIHH plus irradiation group (group D). Whole brain irradiation was delivered to them with a single fraction of 10.0Gy. Before radiation, mice in Group B and Group D were treated with CIHH for 28 consecutive days. Thirty days later, the Mirros water maze test was used to evaluate the memory and cognitive function of the mice. Morphological alterations of hippocampal CA1 area were examined by Nissl staining. The expression level of mTOR, Beclin-1, LC3II/I as well as GRP78 and CHOP were quantitatively analyzed by Western blot. The expression of doublecortin (DCX) in the subgranular zone (SGZ) of dentate gyrus (DG) in hippocampus was detected by immunofluorescence to evaluate the neurogenesis. The time of escape latency was increased in group C when compared with group A, whereas it was decreased when compared to group D. The exploration time in the first quadrant within one minute of the mice in group C was significantly reduced than that in group A, the times of cross the platform within one minute was also decreased. The exploration time and the times of cross the platform within one minute were 14.12 ±0.82 S and 2.08 ±0.26 in group D, and were 7.42 ±0.73S and 0.83 ±0.24 times in group C. After irradiation was performed, pathological changes as swelling, nuclear deviation, disorder of cell structure, degeneration and necrosis in neuronal cells of CA1 in hippocampus could be observed by Nissl staining, whereas the damages in hippocampus were ameliorated in group D. In comprison with group A, The levels of GRP78, CHOP, Beclin-1 and LC3II/Iin hippocampus were significantly increased, but the expression of mTOR protein was decreased in group C. When compared with group D, the levels of GRP78, CHOP and mTOR were increased (P < 0.01 for both), and the expression of Beclin-1 and LC3II/Iwere reduced (P < 0.05 for both) in group C. Compared with group A, the expression of DCX in CA1 region of the hippocampus was significantly decreased than that in group C. After pretreatment with CIHH, the expression of it in group D was much higher than that in group C. Irradiation could cause histopathological damage in hippocampus in mice. The potential mechanisms of radiation induced hippocampus damage might be attributed to ER stress and neurogenesis reduction. Simultaneously, irradiation could activate autophagy in hippocampus, which might play a protective role by reducing the damage of ER stress. Pretreated with CIHH could attenuates irradiation induced hippocampus injury by inducting of autophagy as well as increasing the neurogenesis in CA1 region in mice.

Protective effects of quercetin from oxidative/nitrosative stress under intermittent hypobaric hypoxia exposure in the rat’s heart

Exposure to high altitude in hypobaric hypoxia (HH) is considered to be a physiological oxidative/nitrosative stress. Quercetin (Que) is an effective antioxidant and free radical scavenger against oxidative/nitrosative stress. The aim of this study was to investigate the cardioprotective effects of Que in animals exposed to intermittent HH (IHH) and therefore exposed to oxidative/nitrosative stress. Wistar albino male rats were exposed to short-term (2 days) or long-term (4 weeks; 5 days/week) IHH in a hypobaric chamber (5,500m, 8h/day, 380mmHg, 12% O2, and 88% N2). Half of the animals received natural antioxidant Que (body weight: 30mg/kg) daily before each IHH exposure and the remaining rats received vehicle (carboxymethylcellulose solution). Control rats were kept under normobaric normoxia (Nx) and treated in a corresponding manner. One day after the last exposure to IHH, we measured the cardiac hypoxia-induced oxidative/nitrosative stress biomarkers: the malondialdehyde (MDA) level and protein carbonyl (PC) content, the activity of some antioxidant enzymes [superoxide dismutase (SOD) and catalase (CAT)], the nitrite plus nitrate (NOx) production, and the inducible nitric oxide synthase (iNOS) protein expression. Heart tissue MDA and PC levels, NOx level, and iNOS expression of IHH-exposed rats had increased, and SOD and CAT activities had decreased compared with those of the Nx-exposed rats (control groups). MDA, CP, NOx, and iNOS levels had decreased in Que-treated IHH-exposed rats compared with IHH-exposed rats (control groups). However, Que administration increased SOD and CAT activities of the heart tissue in the IHH-exposed rats. HH exposure increases oxidative/nitrosative stress in heart tissue and Que is an effective cardioprotective agent, which further supports the oxidative cardiac dysfunction induced by hypoxia.