Higher blood flow and circulating NO products offset high-altitude hypoxia among Tibetans

GCH1 plays a role in the high-altitude adaptation of Tibetans

Tibetans are well adapted to high-altitude hypoxia. Previous genome-wide scans have reported many candidate genes for this adaptation, but only a few have been studied. Here we report on a hypoxia gene ( GCH1, GTP-cyclohydrolase I), involved in maintaining nitric oxide synthetase (NOS) function and normal blood pressure, that harbors many potentially adaptive variants in Tibetans. We resequenced an 80.8 kb fragment covering the entire gene region of GCH1 in 50 unrelated Tibetans. Combined with previously published data, we demonstrated many GCH1 variants showing deep divergence between highlander Tibetans and lowlander Han Chinese. Neutrality tests confirmed a signal of positive Darwinian selection on GCH1 in Tibetans. Moreover, association analysis indicated that the Tibetan version of GCH1 was significantly associated with multiple physiological traits in Tibetans, including blood nitric oxide concentration, blood oxygen saturation, and hemoglobin concentration. Taken together, we propose that GCH1 plays a role in the genetic adaptation of Tibetans to high altitude hypoxia.

Dietary nitrate supplementation in cardiovascular health: an ergogenic aid or exercise therapeutic?

Oral consumption of inorganic nitrate, which is abundant in green leafy vegetables and roots, has been shown to increase circulating plasma nitrite concentration, which can be converted to nitric oxide in low oxygen conditions. The associated beneficial physiological effects include a reduction in blood pressure, modification of platelet aggregation, and increases in limb blood flow. There have been numerous studies of nitrate supplementation in healthy recreational and competitive athletes; however, the ergogenic benefits are currently unclear due to a variety of factors including small sample sizes, different dosing regimens, variable nitrate conversion rates, the heterogeneity of participants’ initial fitness levels, and the types of exercise tests used. In clinical populations, the study results seem more promising, particularly in patients with cardiovascular diseases who typically present with disruptions in the ability to transport oxygen from the atmosphere to working tissues and reduced exercise tolerance. Many of these disease-related, physiological maladaptations, including endothelial dysfunction, increased reactive oxygen species, reduced tissue perfusion, and muscle mitochondrial dysfunction, have been previously identified as potential targets for nitric oxide restorative effects. This review is the first of its kind to outline the current evidence for inorganic nitrate supplementation as a therapeutic intervention to restore exercise tolerance and improve quality of life in patients with cardiovascular diseases. We summarize the factors that appear to limit or maximize its effectiveness and present a case for why it may be more effective in patients with cardiovascular disease than as ergogenic aid in healthy populations.

Effects of beetroot juice supplementation on intermittent high-intensity exercise efforts

Beetroot juice contains high levels of inorganic nitrate (NO3-) and its intake has proved effective at increasing blood nitric oxide (NO) concentrations. Given the effects of NO in promoting vasodilation and blood flow with beneficial impacts on muscle contraction, several studies have detected an ergogenic effect of beetroot juice supplementation on exercise efforts with high oxidative energy metabolism demands. However, only a scarce yet growing number of investigations have sought to assess the effects of this supplement on performance at high-intensity exercise. Here we review the few studies that have addressed this issue. The databases Dialnet, Elsevier, Medline, Pubmed and Web of Science were searched for articles in English, Portuguese and Spanish published from 2010 to March 31 to 2017 using the keywords: beet or beetroot or nitrate or nitrite and supplement or supplementation or nutrition or "sport nutrition" and exercise or sport or "physical activity" or effort or athlete. Nine articles fulfilling the inclusion criteria were identified. Results indicate that beetroot juice given as a single dose or over a few days may improve performance at intermittent, high-intensity efforts with short rest periods. The improvements observed were attributed to faster phosphocreatine resynthesis which could delay its depletion during repetitive exercise efforts. In addition, beetroot juice supplementation could improve muscle power output via a mechanism involving a faster muscle shortening velocity. The findings of some studies also suggested improved indicators of muscular fatigue, though the mechanism involved in this effect remains unclear.

Human Genetic Adaptation to High Altitudes: Current Status and Future Prospects

The question of whether human populations have adapted genetically to high altitude has been of interest since studies began there in the early 1900s. Initially there was debate as to whether genetic adaptation to high altitude has taken place based, in part, on disciplinary orientation and the sources of evidence being considered. Studies centered on short-term responses, termed acclimatization, and the developmental changes occurring across lifetimes. A paradigm shift occurred with the advent of single nucleotide polymorphism (SNP) technologies and statistical methods for detecting evidence of natural selection, resulting in an exponential rise in the number of publications reporting genetic adaptation. Reviewed here are the various kinds of evidence by which adaptation to high altitude has been assessed and which have led to widespread acceptance of the idea that genetic adaptation to high altitude has occurred. While methodological and other challenges remain for determining the specific gene or genes involved and the physiological mechanisms by which they are exerting their effects, considerable progress has been realized as shown by recent studies in Tibetans, Andeans and Ethiopians. Further advances are anticipated with the advent of new statistical methods, whole-genome sequencing and other molecular techniques for finer-scale genetic mapping, and greater intradisciplinary and interdisciplinary collaboration to identify the functional consequences of the genes or gene regions implicated and the time scales involved.

Effects of Beetroot Juice Supplementation on a 30-s High-Intensity Inertial Cycle Ergometer Test

Background: Beetroot juice (BJ) is rich in inorganic nitrates and has proved effective at increasing blood nitric oxide (NO) levels. When used as a supplement BJ has shown an ergogenic effect on cardiorespiratory resistance exercise modalities, yet few studies have examined its impact on high intensity efforts. Objective: To assess the effects of BJ intake on anaerobic performance in a Wingate test. Methods: Fifteen trained men (age 21.46 ± 1.72 years, height 1.78 ± 0.07 cm and weight 76.90 ± 8.67 kg) undertook a 30-s maximum intensity test on an inertial cycle ergometer after drinking 70 mL of BJ (5.6 mmol NO₃^-) or placebo. Results: Despite no impacts of BJ on the mean power recorded during the test, improvements were produced in peak power (6%) (p = 0.034), average power 0-15 s (6.7%) (p = 0.048) and final blood lactate levels (82.6%) (p < 0.001), and there was a trend towards a shorter time taken to attain peak power (-8.4%) (p = 0.055). Conclusions: Supplementation with BJ has an ergonomic effect on maximum power output and on average power during the first 15 s of a 30-s maximum intensity inertial cycle ergometer test.

Effects of dietary nitrate on respiratory physiology at high altitude - Results from the Xtreme Alps study

Nitric oxide (NO) production plays a central role in conferring tolerance to hypoxia. Tibetan highlanders, successful high-altitude dwellers for millennia, have higher circulating nitrate and exhaled NO (ENO) levels than native lowlanders. Since nitrate itself can reduce the oxygen cost of exercise in normoxia it may confer additional benefits at high altitude. Xtreme Alps was a double-blinded randomised placebo-controlled trial to investigate how dietary nitrate supplementation affects physiological responses to hypoxia in 28 healthy adult volunteers resident at 4559 m for 1 week; 14 receiving a beetroot-based high-nitrate supplement and 14 receiving a low-nitrate 'placebo' of matching appearance/taste. ENO, vital signs and acute mountain sickness (AMS) severity were recorded at sea level (SL) and daily at altitude. Moreover, standard spirometric values were recorded, and saliva and exhaled breath condensate (EBC) collected. There was no significant difference in resting cardiorespiratory variables, peripheral oxygen saturation or AMS score with nitrate supplementation at SL or altitude. Median ENO levels increased from 1.5/3.0  mPa at SL, to 3.5/7.4 mPa after 5 days at altitude (D5) in the low and high-nitrate groups, respectively (p = 0.02). EBC nitrite also rose significantly with dietary nitrate (p = 0.004), 1.7-5.1  μM at SL and 1.6-6.3 μM at D5, and this rise appeared to be associated with increased levels of ENO. However, no significant changes occurred to levels of EBC nitrate or nitrosation products (RXNO). Median salivary nitrite/nitrate concentrations increased from 56.5/786 μM to 333/5,194  μM  with nitrate supplementation at SL, and changed to 85.6/641 μM and 341/4,553 μM on D5. Salivary RXNO rose markedly with treatment at SL from 0.55 μM to 5.70 μM. At D5 placebo salivary RXNO had increased to 1.90 μM whilst treatment RXNO decreased to 3.26 μM. There was no association with changes in any observation variables or AMS score. In conclusion, dietary nitrate supplementation is well tolerated at altitude and significantly increases pulmonary NO availability and both salivary and EBC NO metabolite concentrations. Surprisingly, this is not associated with changes in hemodynamics, oxygen saturation or AMS development.

Anthropometric and hematological tests to diagnose nutritional deficiencies in schoolchildren of indigenous communities living in the Andean region of Ecuador

ABSTRACT Objective To carry out the anthropometric and biometric-hematological assessments in schoolchildren of the Andean region of Ecuador, in order to improve the diagnosis of nutritional deficiencies. Methods The study has been carried out in the San Juan School (Chimborazo, Ecuador), located at 3,240m of altitude, to 36 children of 5 and 6 years old. Anthropometric analyses (weight, height and body mass index), and hematocrit and hemoglobin concentrations were measured. The hemoglobin measurement was evaluated considering the normal value and the one adapted to the altitude of the area. Results The schoolchildren showed high prevalence of stunting (44%). The values of hematocrit (.=0.001) and hemoglobin (.=0.003) were higher in girls. It should be highlighted that using the normal value of hemoglobin, anemia was not detected. However almost a fifth of the schoolchildren studied were diagnosed with anemia when we applied the correction factors adapted to the altitude. Conclusion The use of correction factors adapted to the altitude is considered essential to do the hematology test in populations that live in high altitude in order to avoid a false diagnosis. Moreover, it is necessary to establish the environmental factors related to the stunted growth of this population of the Andean region.

Plasma Nitrate and Incidence of Cardiovascular Disease and All-Cause Mortality in the Community: The Framingham Offspring Study

BACKGROUND

Nitrate is a dietary component as well as an endogenously formed metabolite and source of the signaling molecule nitric oxide. Harmful as well as beneficial effects of nitrate have been advocated. Data regarding the prognostic relevance of plasma nitrate are limited. The aim of this study was to evaluate the prospective association of plasma nitrate with cardiovascular disease (CVD) and all-cause mortality.

METHODS AND RESULTS

We assayed plasma nitrate in 2855 Framingham Offspring Study participants (mean age 59 years, 54% women) by gas chromatography-mass spectrometry and evaluated its association with all-cause mortality and incident CVD. On follow-up (median 17.3 years), 775 participants died and 522 developed new-onset CVD (of 2546 participants free of CVD at baseline). In multivariable models adjusting for standard risk factors, plasma nitrate was associated with an increased risk of death in participants (hazard ratio per unit increase in log-nitrate 1.21; 95% confidence interval, 1.04-1.40 [P=0.015]). The strength of the association was attenuated by additional adjustment for estimated glomerular filtration rate (hazard ratio, 1.16; 95% confidence interval, 1.00-1.35 [P=0.057]). In contrast, no evidence was found for an association of plasma nitrate with incident CVD (multivariable-adjusted hazard ratio per unit increase log-nitrate 1.08; 95% confidence interval, 0.89-1.31 [P=0.42]).

CONCLUSIONS

In our prospective community-based investigation, a higher plasma nitrate concentration was associated with all-cause mortality but not with incident CVD. The association of nitrate with mortality may at least in part be attributable to its association with renal function.

Natural Selection on Genes Related to Cardiovascular Health in High-Altitude Adapted Andeans

The increase in red blood cell mass (polycythemia) due to the reduced oxygen availability (hypoxia) of residence at high altitude or other conditions is generally thought to be beneficial in terms of increasing tissue oxygen supply. However, the extreme polycythemia and accompanying increased mortality due to heart failure in chronic mountain sickness most likely reduces fitness. Tibetan highlanders have adapted to high altitude, possibly in part via the selection of genetic variants associated with reduced polycythemic response to hypoxia. In contrast, high-altitude-adapted Quechua- and Aymara-speaking inhabitants of the Andean Altiplano are not protected from high-altitude polycythemia in the same way, yet they exhibit other adaptive features for which the genetic underpinnings remain obscure. Here, we used whole-genome sequencing to scan high-altitude Andeans for signals of selection. The genes showing the strongest evidence of selection-including BRINP3, NOS2, and TBX5-are associated with cardiovascular development and function but are not in the response-to-hypoxia pathway. Using association mapping, we demonstrated that the haplotypes under selection are associated with phenotypic variations related to cardiovascular health. We hypothesize that selection in response to hypoxia in Andeans could have vascular effects and could serve to mitigate the deleterious effects of polycythemia rather than reduce polycythemia itself.

Transfusion Decision Making in Pediatric Critical Illness

Transfusion decision making (TDM) in the critically ill requires consideration of: (1) anemia tolerance, which is linked to active pathology and to physiologic reserve, (2) differences in donor RBC physiology from that of native RBCs, and (3) relative risk from anemia-attributable oxygen delivery failure vs hazards of transfusion, itself. Current approaches to TDM (e.g. hemoglobin thresholds) do not: (1) differentiate between patients with similar anemia, but dissimilar pathology/physiology, and (2) guide transfusion timing and amount to efficacy-based goals (other than resolution of hemoglobin thresholds). Here, we explore approaches to TDM that address the above gaps.

Comparative Response of Brain to Chronic Hypoxia and Hyperoxia

Two antithetic terms, hypoxia and hyperoxia, i.e., insufficient and excess oxygen availability with respect to needs, are thought to trigger opposite responses in cells and tissues. This review aims at summarizing the molecular and cellular mechanisms underlying hypoxia and hyperoxia in brain and cerebral tissue, a context that may prove to be useful for characterizing not only several clinically relevant aspects, but also aspects related to the evolution of oxygen transport and use by the tissues. While the response to acute hypoxia/hyperoxia presumably recruits only a minor portion of the potentially involved cell machinery, focusing into chronic conditions, instead, enables to take into consideration a wider range of potential responses to oxygen-linked stress, spanning from metabolic to genic. We will examine how various brain subsystems, including energetic metabolism, oxygen sensing, recruitment of pro-survival pathways as protein kinase B (Akt), mitogen-activated protein kinases (MAPK), neurotrophins (BDNF), erythropoietin (Epo) and its receptors (EpoR), neuroglobin (Ngb), nitric oxide (NO), carbon monoxide (CO), deal with chronic hypoxia and hyperoxia to end-up with the final outcomes, oxidative stress and brain damage. A more complex than expected pattern results, which emphasizes the delicate balance between the severity of the stress imposed by hypoxia and hyperoxia and the recruitment of molecular and cellular defense patterns. While for certain functions the expectation that hypoxia and hyperoxia should cause opposite responses is actually met, for others it is not, and both emerge as dangerous treatments.

Anti-obesity and anti-diabetic effects of nitrate and nitrite

Prevalence of obesity is increasing worldwide and type 2 diabetes to date is the most devastating complication of obesity. Decreased nitric oxide bioavailability is a feature of obesity and diabetes that links these two pathologies. Nitric oxide is synthesized both by nitric oxide synthase enzymes from l-arginine and nitric oxide synthase-independent from nitrate/nitrite. Nitric oxide production from nitrate/nitrite could potentially be used for nutrition-based therapy in obesity and diabetes. Nitric oxide deficiency also contributes to pathogeneses of cardiovascular disease and hypertension, which are associated with obesity and diabetes. This review summarizes pathways for nitric oxide production and focuses on the anti-diabetic and anti-obesity effects of the nitrate-nitrite-nitric oxide pathway. In addition to increasing nitric oxide production, nitrate and nitrite reduce oxidative stress, increase adipose tissue browning, have favorable effects on nitric oxide synthase expression, and increase insulin secretion, all effects that are potentially promising for management of obesity and diabetes. Based on current data, it could be suggested that amplifying the nitrate-nitrite-nitric oxide pathway is a diet-based strategy for increasing nitric oxide bioavailability and the management of these two interlinked conditions. Adding nitrate/nitrite to drugs that are currently used for managing diabetes (e.g. metformin) and possibly anti-obesity drugs may also enhance their efficacy.

Down-Regulation of EPAS1 Transcription and Genetic Adaptation of Tibetans to High-Altitude Hypoxia

Tibetans are well adapted to the hypoxic environments at high altitude, yet the molecular mechanism of this adaptation remains elusive. We reported comprehensive genetic and functional analyses of EPAS1, a gene encoding hypoxia inducible factor 2α (HIF-2α) with the strongest signal of selection in previous genome-wide scans of Tibetans. We showed that the Tibetan-enriched EPAS1 variants down-regulate expression in human umbilical endothelial cells and placentas. Heterozygous EPAS1 knockout mice display blunted physiological responses to chronic hypoxia, mirroring the situation in Tibetans. Furthermore, we found that the Tibetan version of EPAS1 is not only associated with the relatively low hemoglobin level as a polycythemia protectant, but also is associated with a low pulmonary vasoconstriction response in Tibetans. We propose that the down-regulation of EPAS1 contributes to the molecular basis of Tibetans’ adaption to high-altitude hypoxia.

Why Are High-Altitude Natives So Strong at Altitude? Maximal Oxygen Transport to the Muscle Cell in Altitude Natives

In hypoxia aerobic exercise performance of high-altitude natives is suggested to be superior to that of lowlanders; i.e., for a given altitude natives are reported to have higher maximal oxygen uptake (VO2max). The likely basis for this is a higher pulmonary diffusion capacity, which in turn ensures higher arterial O2 saturation (SaO2) and therefore also potentially a higher delivery of O2 to the exercising muscles. This review focuses on O2 transport in high-altitude Aymara. We have quantified femoral artery O2 delivery, arterial O2 extraction and calculated leg VO2 in Aymara, and compared their values with that of acclimatizing Danish lowlanders. All subjects were studied at 4100 m. At maximal exercise SaO2 dropped tremendously in the lowlanders, but did not change in the Aymara. Therefore arterial O2 content was also higher in the Aymara. At maximal exercise however, fractional O2 extraction was lower in the Aymara, and the a-vO2 difference was similar in both populations. The lower extraction levels in the Aymara were associated with lower muscle O2 conductance (a measure of muscle diffusion capacity). At any given submaximal exercise intensity, leg VO2 was always of similar magnitude in both groups, but at maximal exercise the lowlanders had higher leg blood flow, and hence also higher maximum leg VO2. With the induction of acute normoxia fractional arterial O2 extraction fell in the highlanders, but remained unchanged in the lowlanders. Hence high-altitude natives seem to be more diffusion limited at the muscle level as compared to lowlanders. In conclusion Aymara preserve very high SaO2 during hypoxic exercise (likely due to a higher lung diffusion capacity), but the effect on VO2max is reduced by a lower ability to extract O2 at the muscle level.

Metabolic basis to Sherpa altitude adaptation

The Himalayan Sherpas, a human population of Tibetan descent, are highly adapted to life in the hypobaric hypoxia of high altitude. Mechanisms involving enhanced tissue oxygen delivery in comparison to Lowlander populations have been postulated to play a role in such adaptation. Whether differences in tissue oxygen utilization (i.e., metabolic adaptation) underpin this adaptation is not known, however. We sought to address this issue, applying parallel molecular, biochemical, physiological, and genetic approaches to the study of Sherpas and native Lowlanders, studied before and during exposure to hypobaric hypoxia on a gradual ascent to Mount Everest Base Camp (5,300 m). Compared with Lowlanders, Sherpas demonstrated a lower capacity for fatty acid oxidation in skeletal muscle biopsies, along with enhanced efficiency of oxygen utilization, improved muscle energetics, and protection against oxidative stress. This adaptation appeared to be related, in part, to a putatively advantageous allele for the peroxisome proliferator-activated receptor A (PPARA) gene, which was enriched in the Sherpas compared with the Lowlanders. Our findings suggest that metabolic adaptations underpin human evolution to life at high altitude, and could have an impact upon our understanding of human diseases in which hypoxia is a feature.

Polygenic study of endurance-associated genetic markers ACE I/D, ACTN3 Arg(R)577Ter(X), CKMM A/G NcoI and eNOS Glu(G)298Asp(T) in male Gorkha soldiers

Background

Gorkhas, a sub-mountainous population of the Himalayan region, are known for strength and bravery. In the present study when “Gorkha” is used without brackets, we are mentioning Gorkhas of Tibeto-Burman origin. Physical capability, strength and endurance are important components of fitness associated with genetic traits. The aim of this study was to examine the endurance potential of male Gorkha soldiers, based on endurance-related genetic markers ACE I/D, ACTN3 Arg (R)577Ter(X), CKMM A/G NcoI and eNOS Glu(G)298Asp(T).

Methods

Genotypic and allelic frequencies were determined in 374 male Gorkha soldiers (Tibeto-Burman). These frequencies were compared with frequencies obtained from Gorkha (Indo-Aryan), high-altitude natives (Tibeto-Burman) and Indian lowlanders (Indo-Aryan). “Total genotype score” (TGS) was calculated from accumulated combination of polymorphisms with maximum value “100” for theoretically “optimal” polygenic score. Probability of occurrence of “optimal” endurance profile was also determined.

Results

ACE II genotypic frequency was highest in Tamangs followed by Gurungs, Rais, Limbus and Magars. No statistical difference in genotypic and allelic frequency of ACTN3 Arg(R)577Ter(X) was noted within the groups. Rais showed the highest CKMM A allele frequency (0.908) compared to other Gorkha (Tibeto-Burman) groups. Limbus and Tamangs showed the highest eNOS G allele frequency (0.938 and 0.915, respectively) compared to that of other groups. Probability of male Gorkha soldiers possessing a theoretically optimal polygenic endurance profile for four candidate polymorphisms was ~3.35% (1 in 30). Four percent of the population of male Gorkha soldiers (15 in 374) exhibited an optimal TGS 100, and 16% exhibited TGS 87 for endurance compared to male Indian soldiers belonging to the lowland (Indo-Aryan) and Gorkha (Indo-Aryan) populations suggesting an overall more “favourable” polygenic profile in the male Gorkha soldier (Tibeto-Burman) population.

Conclusions

This study presents evidence of higher frequency of endurance-associated genes in the Gorkhas implying thereby that such genetically endowed individuals from the population may be selected and trained for achieving excellence in endurance-related elite sports activities.

Electronic supplementary material

The online version of this article (doi:10.1186/s40798-017-0085-0) contains supplementary material, which is available to authorized users.

Thin Air Resulting in High Pressure: Mountain Sickness and Hypoxia-Induced Pulmonary Hypertension

With rising altitude the partial pressure of oxygen falls. This phenomenon leads to hypobaric hypoxia at high altitude. Since more than 140 million people permanently live at heights above 2500 m and more than 35 million travel to these heights each year, understanding the mechanisms resulting in acute or chronic maladaptation of the human body to these circumstances is crucial. This review summarizes current knowledge of the body's acute response to these circumstances, possible complications and their treatment, and health care issues resulting from long-term exposure to high altitude. It furthermore describes the characteristic mechanisms of adaptation to life in hypobaric hypoxia expressed by the three major ethnic groups permanently dwelling at high altitude. We additionally summarize current knowledge regarding possible treatment options for hypoxia-induced pulmonary hypertension by reviewing in vitro, rodent, and human studies in this area of research.

Sleep quality among elderly high-altitude dwellers in Ladakh

It has been already known that people who temporarily stay at high altitude may develop insomnia as a symptom of acute mountain sickness. However, much less is known about people living at high altitude. The aim of this study was to determine the effect of high altitude environment on sleep quality for the elderly who have been living at high altitude for their whole lives. A cross-sectional study was conducted in Domkhar valley at altitudes of 2800-4200m, Ladakh. Sleep quality was assessed using Insomnia Severity Index (ISI). Measurement items include body mass index, blood pressure, blood sugar, hemoglobin, timed Up and Go test, oxygen saturation during wakefulness, respiratory function test, Oxford Knee Score (OKS), and Geriatric Depression Scale (GDS), and so on. The participants were Ladakhi older adults aged 60 years or over (n=112) in Domkhar valley. The participation rate was 65.1% (male: female=47:65, mean age: 71.3 years and 67.9 years, respectively). The prevalence of the high score of ISI (8 or more) was 15.2% (17 out of 112). Altitude of residence was significantly correlated with ISI. Stepwise multiple regression analysis showed that OKS and altitude of residence were significantly related with ISI.

A Signature of Circulating microRNAs Predicts the Susceptibility of Acute Mountain Sickness

Background: Acute mountain sickness (AMS) is a common disabling condition in individuals experiencing high altitudes, which may progress to life-threatening high altitude cerebral edema. Today, no established biomarkers are available for prediction the susceptibility of AMS. MicroRNAs emerge as promising sensitive and specific biomarkers for a variety of diseases. Thus, we sought to identify circulating microRNAs suitable for prediction the susceptible of AMS before exposure to high altitude.

Methods: We enrolled 109 healthy man adults and collected blood samples before their exposure to high altitude. Then we took them to an elevation of 3648 m for 5 days. Circulating microRNAs expression was measured by microarray and quantitative reverse-transcription polymerase chain reaction (qRT-PCR). AMS was defined as Lake Louise score ≥3 and headache using Lake Louise Acute Mountain Sickness Scoring System.

Results: A total of 31 microRNAs were differentially expressed between AMS and Non-AMS groups, 15 up-regulated and 16 down-regulated. Up-regulation of miR-369-3p, miR-449b-3p, miR-136-3p, and miR-4791 in patients with AMS compared with Non-AMS individuals were quantitatively confirmed using qRT-PCR (all, P < 0.001). With multiple logistic regression analysis, a unique signature encompassing miR-369-3p, miR-449b-3p, and miR-136-3p discriminate AMS from Non-AMS (area under the curve 0.986, 95%CI 0.970–1.000, P < 0.001, LR+: 14.21, LR–: 0.08). This signature yielded a 92.68% sensitivity and a 93.48% specificity for AMS vs. Non-AMS.

Conclusion: The study here, for the first time, describes a signature of three circulating microRNAs as a robust biomarker to predict the susceptibility of AMS before exposure to high altitude.

Sublingual microcirculatory blood flow and vessel density in Sherpas at high altitude

Anecdotal reports suggest that Sherpa highlanders demonstrate extraordinary tolerance to hypoxia at high altitude, despite exhibiting lower arterial oxygen content than acclimatized lowlanders. This study tested the hypothesis that Sherpas exposed to hypobaric hypoxia on ascent to 5,300 m develop increased microcirculatory blood flow as a means of maintaining tissue oxygen delivery. Incident dark-field imaging was used to obtain images of the sublingual microcirculation from 64 Sherpas and 69 lowlanders. Serial measurements were obtained from participants undertaking an ascent from baseline testing (35 m or 1,300 m) to Everest base camp (5,300 m) and following subsequent descent in Kathmandu (1,300 m). Microcirculatory flow index and heterogeneity index were used to provide indexes of microcirculatory flow, while capillary density was assessed using small vessel density. Sherpas demonstrated significantly greater microcirculatory blood flow at Everest base camp, but not at baseline testing or on return in Kathmandu, than lowlanders. Additionally, blood flow exhibited greater homogeneity at 5,300 and 1,300 m (descent) in Sherpas than lowlanders. Sublingual small vessel density was not different between the two cohorts at baseline testing or at 1,300 m; however, at 5,300 m, capillary density was up to 30% greater in Sherpas. These data suggest that Sherpas can maintain a significantly greater microcirculatory flow per unit time and flow per unit volume of tissue at high altitude than lowlanders. These findings support the notion that peripheral vascular factors at the microcirculatory level may be important in the process of adaptation to hypoxia.NEW & NOTEWORTHY Sherpa highlanders demonstrate extraordinary tolerance to hypoxia at high altitude, yet the physiological mechanisms underlying this tolerance remain unknown. In our prospective study, conducted on healthy volunteers ascending to Everest base camp (5,300 m), we demonstrated that Sherpas have a higher sublingual microcirculatory blood flow and greater capillary density at high altitude than lowlanders. These findings support the notion that the peripheral microcirculation plays a key role in the process of long-term adaptation to hypoxia.

Effects of Beetroot Juice Supplementation on Cardiorespiratory Endurance in Athletes. A Systematic Review

Athletes use nutritional supplementation to enhance the effects of training and achieve improvements in their athletic performance. Beetroot juice increases levels of nitric oxide (NO), which serves multiple functions related to increased blood flow, gas exchange, mitochondrial biogenesis and efficiency, and strengthening of muscle contraction. These biomarker improvements indicate that supplementation with beetroot juice could have ergogenic effects on cardiorespiratory endurance that would benefit athletic performance. The aim of this literature review was to determine the effects of beetroot juice supplementation and the combination of beetroot juice with other supplements on cardiorespiratory endurance in athletes. A keyword search of DialNet, MedLine, PubMed, Scopus and Web of Science databases covered publications from 2010 to 2016. After excluding reviews/meta-analyses, animal studies, inaccessible full-text, and studies that did not supplement with beetroot juice and adequately assess cardiorespiratory endurance, 23 articles were selected for analysis. The available results suggest that supplementation with beetroot juice can improve cardiorespiratory endurance in athletes by increasing efficiency, which improves performance at various distances, increases time to exhaustion at submaximal intensities, and may improve the cardiorespiratory performance at anaerobic threshold intensities and maximum oxygen uptake (VO_2max). Although the literature shows contradictory data, the findings of other studies lead us to hypothesize that supplementing with beetroot juice could mitigate the ergolytic effects of hypoxia on cardiorespiratory endurance in athletes. It cannot be stated that the combination of beetroot juice with other supplements has a positive or negative effect on cardiorespiratory endurance, but it is possible that the effects of supplementation with beetroot juice can be undermined by interaction with other supplements such as caffeine.

Alternative hematological and vascular adaptive responses to high-altitude hypoxia in East African highlanders

Elevation of hemoglobin concentration, a common adaptive response to high-altitude hypoxia, occurs among Oromo but is dampened among Amhara highlanders of East Africa. We hypothesized that Amhara highlanders offset their smaller hemoglobin response with a vascular response. We tested this by comparing Amhara and Oromo highlanders at 3,700 and 4,000 m to their lowland counterparts at 1,200 and 1,700 m. To evaluate vascular responses, we assessed urinary levels of nitrate (NO₃^-) as a readout of production of the vasodilator nitric oxide and its downstream signal transducer cyclic guanosine monophosphate (cGMP), along with diastolic blood pressure as an indicator of vasomotor tone. To evaluate hematological responses, we measured hemoglobin and percent oxygen saturation of hemoglobin. Amhara highlanders, but not Oromo, had higher NO₃^- and cGMP compared with their lowland counterparts. NO₃^- directly correlated with cGMP (Amhara R² = 0.25, P < 0.0001; Oromo R² = 0.30, P < 0.0001). Consistent with higher levels of NO₃^- and cGMP, diastolic blood pressure was lower in Amhara highlanders. Both highland samples had apparent left shift in oxyhemoglobin saturation characteristics and maintained total oxyhemoglobin content similar to their lowland counterparts. However, deoxyhemoglobin levels were significantly higher, much more so among Oromo than Amhara. In conclusion, the Amhara balance minimally elevated hemoglobin with vasodilatory response to environmental hypoxia, whereas Oromo rely mainly on elevated hemoglobin response. These results point to different combinations of adaptive responses in genetically similar East African highlanders.

Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

Walking economy at simulated high altitude in human healthy young male lowlanders

We measured oxygen consumption during walking per unit distance (C_w) values for 12 human healthy young males at six speeds from 0.667 to 1.639 m s⁻¹ (four min per stage) on a level gradient under normobaric normoxia, moderate hypoxia (15% O₂), and severe hypoxia (11% O₂). Muscle deoxygenation (HHb) was measured at the vastus lateralis muscle using near-infrared spectroscopy. Economical speed which can minimize the C_w in each individual was calculated from a U-shaped relationship. We found a significantly slower economical speed (ES) under severe hypoxia [1.237 (0.056) m s⁻¹; mean (s.d.)] compared to normoxia [1.334 (0.070) m s⁻¹] and moderate hypoxia [1.314 (0.070) m s⁻¹, P<0.05 respectively] with no differences between normoxia and moderate hypoxia (P>0.05). HHb gradually increased with increasing speed under severe hypoxia, while it did not increase under normoxia and moderate hypoxia. Changes in HHb between standing baseline and the final minute at faster gait speeds were significantly related to individual ES (r=0.393 at 1.250 m s⁻¹, r=0.376 at 1.444 m s⁻¹, and r=0.409 at 1.639 m s⁻¹, P<0.05, respectively). These results suggested that acute severe hypoxia slowed ES by ∼8%, but moderate hypoxia left ES unchanged.

Summary: Acute severe hypoxia slowed the economical speed (ES) which can minimize energy cost of walking. Muscle O₂ extraction may be one of the determining factors of an individual's ES.

Anti-hypoxia Activity of the Novel NO Donor Acetyl Ferulic Isosorbide Mononitrate in Acute High-Altitude Hypoxia Mice

Nitric oxide (NO) may act as either a pro-oxidant or an antioxidant in biological systems. Previous work has found inhalation of NO improved survival in a high altitude rat model. NO donor isosorbide mononitrate derivants might have a protective effect against hypoxia. We synthesized a series of isosorbide mononitrate derivant compounds to test their anti-hypoxia activities. Normobaric hypoxia and hypobaric hypoxia models were used to study the protective role of NO donor in mice. The results showed isosorbide mononitrate derivants had protective effects in hypoxia mice. Among those compounds, acetyl ferulic isosorbide mononitrate (AFIM) was the most effective. It prolonged the survival time during the normobaric hypoxia test. It decreased malondialdehyde (MDA) and H2O2 in hypobaric hypoxia mice. The antioxidase activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) remained in normal ranges in the AFIM group. As a sign of mitochondrial dysfunction, the activities of ATPase were down regulated in mice under hypobaric hypoxia conditions. AFIM also protected ATPase activities. The protective effects of AFIM might come from a sustained NO supply and the release of acetyl ferulic acid with anti-oxidant activity.

Genome-wide analysis reveals adaptation to high altitudes in Tibetan sheep

Tibetan sheep have lived on the Tibetan Plateau for thousands of years; however, the process and consequences of adaptation to this extreme environment have not been elucidated for important livestock such as sheep. Here, seven sheep breeds, representing both highland and lowland breeds from different areas of China, were genotyped for a genome-wide collection of single-nucleotide polymorphisms (SNPs). The FST and XP-EHH approaches were used to identify regions harbouring local positive selection between these highland and lowland breeds, and 236 genes were identified. We detected selection events spanning genes involved in angiogenesis, energy production and erythropoiesis. In particular, several candidate genes were associated with high-altitude hypoxia, including EPAS1, CRYAA, LONP1, NF1, DPP4, SOD1, PPARG and SOCS2. EPAS1 plays a crucial role in hypoxia adaption; therefore, we investigated the exon sequences of EPAS1 and identified 12 mutations. Analysis of the relationship between blood-related phenotypes and EPAS1 genotypes in additional highland sheep revealed that a homozygous mutation at a relatively conserved site in the EPAS1 3' untranslated region was associated with increased mean corpuscular haemoglobin concentration and mean corpuscular volume. Taken together, our results provide evidence of the genetic diversity of highland sheep and indicate potential high-altitude hypoxia adaptation mechanisms, including the role of EPAS1 in adaptation.

Assessment of the Physiological Adaptations to Chronic Hypoxemia in Eisenmenger Syndrome

OBJECTIVE

Eisenmenger syndrome is characterized by severe and lifelong hypoxemia and pulmonary hypertension. Despite this, patients do surprisingly well and report a reasonable quality of life. The aim of this study was to investigate whether these patients undergo adaptation of their skeletal and cardiac muscle energy metabolism which would help explain this paradox.

DESIGN AND SETTING

Ten patients with Eisenmenger syndrome and eight age- and sex-matched healthy volunteers underwent symptom-limited treadmill cardiopulmonary exercise testing, transthoracic echocardiography and (31) P magnetic resonance spectroscopy of cardiac and skeletal muscle. Five subjects from each group also underwent near infrared spectroscopy to assess muscle oxygenation.

RESULTS

Despite having a significantly lower peak VO2 , patients with Eisenmenger syndrome have a similar skeletal muscle phosphocreatine (PCr) recovery, a measure of oxidative capacity, when compared to healthy controls (34.9 s ± 2.9 s vs. 35.2 s ± 1.7 s, P = .9). Furthermore their intracellular pH falls to similar levels during exercise suggesting they are not reliant on early anaerobic metabolism (0.3 ± 0.06 vs. 0.28 ± 0.04, P = .7). While their right ventricular systolic function remained good, the Eisenmenger group had a lower cardiac PCr/ATP ratio compared to the control group (1.55 ± 0.10 vs. 2.17 ± 0.15, P < .05).

CONCLUSIONS

These results show that adult patients with Eisenmenger syndrome have undergone beneficial physiological adaptations of both skeletal and cardiac muscle. This may, in part, explain their surprisingly good survival despite a lifetime of severe hypoxemia and adverse cardiopulmonary hemodynamics.

Exhaled nitric oxide is associated with postnatal adaptation to hypoxia in Tibetan and non-Tibetan newborn infants

AIM

This Chinese study assessed partial pressure of exhaled nitric oxide (PeNO) in healthy Tibetan and non-Tibetan newborn infants born at a very high altitude.

METHODS

Full-term Tibetan and non-Tibetan neonates born in Lhasa, 3658 metres above sea level, were compared to non-Tibetan neonates born in Kunming (1891 m) and Huai'an (16 m). The chemiluminiscence technique was used to measure the fraction of exhaled nitric oxide during spontaneous tidal breathing and this was then converted to partial pressure of exhaled nitric oxide (PeNO).

RESULTS

In their first week, Tibetan and non-Tibetan neonates born in Lhasa had persistently higher PeNO levels than non-Tibetan neonates born in Kunming and Huai'an, which was further verified by partial pressure of inspired oxygen adjustment. However, the non-Tibetans born in Lhasa required short-term oxygen therapy to improve their early postnatal oxygenation. The temporal changes of PeNO and cardio-respiratory function measurements demonstrated that Tibetan and non-Tibetan newborns in Lhasa initially needed to adapt to attain homoeostasis in oxygenation and gas exchange.

CONCLUSION

Tibetan and non-Tibetan newborn infants living at the same high altitude demonstrated comparable PeNO levels during postnatal adaptation to hypobaric hypoxia, which warrants further investigation of the mechanism of endogenous nitric oxide and hypoxic tolerance.

Point-of-care devices for physiological measurements in field conditions. A smorgasbord of instruments and validation procedures

Point-of-care (POC) devices provide quick diagnostic results that increase the efficiency of patient care. Many POC devices are currently available to measure metabolites, blood gases, hormones, disease biomarkers or pathogens in samples as diverse as blood, urine, feces or exhaled breath. This diversity is potentially very useful for the comparative physiologist in field studies if proper validation studies are carried out to justify the accuracy of the devices in non-human species under different conditions. Our review presents an account of physiological parameters that can be monitored with POC devices and surveys the literature for suitable quantitative and statistical procedures for comparing POC measurements with reference "gold standard" procedures. We provide a set of quantitative tools and report on different correlation coefficients (Lin's Concordance Correlation Coefficient or the more widespread Pearson correlation coefficient), describe the graphical assessment of variation using Bland-Altman plots and discuss the difference between Model I and Model II regression procedures. We also report on three validation datasets for lactate, glucose and hemoglobin measurements in birds using the newly proposed procedures. We conclude the review with a haphazard account of future developments in the field, emphasizing the interest in lab-on-a-chip devices to carry out more complex experimental measurements than the ones currently available in POC devices.

Altitude Adaptation: A Glimpse Through Various Lenses

Simonson, Tatum S. Altitude adaptation: A glimpse through various lenses. High Alt Med Biol 16:125-137, 2015.--Recent availability of genome-wide data from highland populations has enabled the identification of adaptive genomic signals. Some of the genomic signals reported thus far among Tibetan, Andean, and Ethiopian are the same, while others appear unique to each population. These genomic findings parallel observations conveyed by decades of physiological research: different continental populations, resident at high altitude for hundreds of generations, exhibit a distinct composite of traits at altitude. The most commonly reported signatures of selection emanate from genomic segments containing hypoxia-inducible factor (HIF) pathway genes. Corroborative evidence for adaptive significance stems from associations between putatively adaptive gene copies and sea-level ranges of hemoglobin concentration in Tibetan and Amhara Ethiopians, birth weights and metabolic factors in Andeans and Tibetans, maternal uterine artery diameter in Andeans, and protection from chronic mountain sickness in Andean males at altitude. While limited reports provide mechanistic insights thus far, efforts to identify and link precise genetic variants to molecular, physiological, and developmental functions are underway, and progress on the genomics front continues to provide unprecedented movement towards these goals. This combination of multiple perspectives is necessary to maximize our understanding of orchestrated biological and evolutionary processes in native highland populations, which will advance our understanding of both adaptive and non-adaptive responses to hypoxia.

Effect of dietary nitrate supplementation on metabolic rate during rest and exercise in human: A systematic review and a meta-analysis

BACKGROUND

Recent randomized controlled trials have suggested that dietary nitrate (NO3(-)), found in beetroot and other vegetables, and inorganic NO3(-) salts decrease metabolic rate under resting and exercise conditions.

OBJECTIVE

Our aim was therefore to determine from a systematic review and meta-analysis whether dietary NO3(-) supplementation significantly reduces metabolic rate, expressed as oxygen uptake (VO2), under resting and exercise conditions in healthy humans and those with cardiorespiratory diseases.

DESIGN

A systematic article search was performed on electronic databases (PubMed, Scopus and Web of Science) from February to March 2015. The inclusion criteria included 1) randomized controlled trials; 2) studies reporting the effect of NO3(-) on VO2 under resting and/or exercise conditions; 3) comparison between dietary NO3(-) supplementation and placebo. Random-effects models were used to calculate the pooled effect size.

RESULTS

Twenty nine randomized placebo-controlled trials were included in the systematic review, and 26 of which were included in the meta-analysis. Dietary NO3(-) supplementation significantly decreases VO2 during submaximal intensity exercise [-0.26 (95% IC: -0.38, -0.15), p < 0.01], but not in the sub-analysis of subjects with chronic diseases [-0.09 (95% IC: -0.50, 0.32), p = 0.67]. When data were separately analyzed by submaximal intensity domains, NO3(-) supplementation reduces VO2 during moderate [-0.29 (95% IC: -0.48,-0.10), p < 0.01] and heavy [-0.33 (95% IC: -0.54,-0.12), p < 0.01] intensity exercise. When the studies with the largest effects were excluded from the meta-analysis, there is a trend for a VO2 decrease under resting condition in dietary NO3(-) supplementation [-0.28 (95% IC: -0.62, 0.05), p = 0.10].

CONCLUSION

Dietary NO3(-) supplementation decreases VO2 during exercise performed in the moderate and heavy intensity domains in healthy subjects. The present meta-analysis did not show any significant effect of dietary NO3(-) supplementation on metabolic rate in subjects with chronic diseases, despite enhanced exercise tolerance.

Novel Insights into Cardiovascular Regulation in Patients with Chronic Mountain Sickness

Studies of high-altitude populations, and in particular of maladapted subgroups, may provide important insight into underlying mechanisms involved in the pathogenesis of hypoxemia-related disease in general. Chronic mountain sickness (CMS) is a major public health problem in mountainous regions of the world affecting many millions of high-altitude dwellers. It is characterized by exaggerated chronic hypoxemia, erythrocytosis, and mild pulmonary hypertension. In later stages these patients often present with right heart failure and are predisposed to systemic cardiovascular disease, but the underlying mechanisms are poorly understood. Here, we present recent new data providing insight into underlying mechanisms that may cause these complications.

Extreme, expedition, and wilderness medicine

Extreme, expedition, and wilderness medicine are modern and rapidly evolving specialties that address the spirit of adventure and exploration. The relevance of and interest in these specialties are changing rapidly to match the underlying activities, which include global exploration, adventure travel, and military deployments. Extreme, expedition, and wilderness medicine share themes of providing best available medical care in the outdoors, especially in austere or remote settings. Early clinical and logistics decision making can often have important effects on subsequent outcomes. There are lessons to be learned from out-of-hospital care, military medicine, humanitarian medicine, and disaster medicine that can inform in-hospital medicine, and vice-versa. The future of extreme, expedition, and wilderness medicine will be defined by both recipients and practitioners, and empirical observations will be transformed by evidence-based practice.

The cytoprotective effect of nitrite is based on the formation of dinitrosyl iron complexes

Nitrite protects various organs from ischemia-reperfusion injury by ameliorating mitochondrial dysfunction. Here we provide evidence that this protection is due to the inhibition of iron-mediated oxidative reactions caused by the release of iron ions upon hypoxia. We show in a model of isolated rat liver mitochondria that upon hypoxia, mitochondria reduce nitrite to nitric oxide (NO) in amounts sufficient to inactivate redox-active iron ions by formation of inactive dinitrosyl iron complexes (DNIC). The scavenging of iron ions in turn prevents the oxidative modification of the outer mitochondrial membrane and the release of cytochrome c during reoxygenation. This action of nitrite protects mitochondrial function. The formation of DNIC with nitrite-derived NO could also be confirmed in an ischemia-reperfusion model in liver tissue. Our data suggest that the formation of DNIC is a key mechanism of nitrite-mediated cytoprotection.

Acute high-altitude illness: a clinically orientated review

Acute high-altitude illness is an encompassing term for the range of pathology that the unacclimatised individual can develop at increased altitude. This includes acute mountain sickness, high-altitude cerebral oedema and high-altitude pulmonary oedema. These conditions represent an increasing clinical problem as more individuals are exposed to the hypobaric hypoxic environment of high altitude for both work and leisure. In this review of acute high-altitude illness, the epidemiology, risk factors and pathophysiology are explored, before their prevention and treatment are discussed. Appropriate ascent rate remains the most effective acute high-altitude illness prevention, with pharmacological prophylaxis indicated in selected individuals. Descent is the definitive treatment for acute high-altitude illness, with the adjuncts of oxygen and specific drug therapies.

Hypoxia tolerance, nitric oxide, and nitrite: lessons from extreme animals

Among vertebrates able to tolerate periods of oxygen deprivation, the painted and red-eared slider turtles (Chrysemys picta and Trachemys scripta) and the crucian carp (Carassius carassius) are the most extreme and can survive even months of total lack of oxygen during winter. The key to hypoxia survival resides in concerted physiological responses, including strong metabolic depression, protection against oxidative damage and-in air-breathing animals-redistribution of blood flow. Each of these responses is known to be tightly regulated by nitric oxide (NO) and during hypoxia by its metabolite nitrite. The aim of this review is to highlight recent work illustrating the widespread roles of NO and nitrite in the tolerance to extreme oxygen deprivation, in particular in the red-eared slider turtle and crucian carp, but also in diving marine mammals. The emerging picture underscores the importance of NO and nitrite signaling in the adaptive response to hypoxia in vertebrate animals.

Wilderness medicine at high altitude: recent developments in the field

Travel to high altitude is increasingly popular. With this comes an increased incidence of high-altitude illness and therefore an increased need to improve our strategies to prevent and accurately diagnose these. In this review, we provide a summary of recent advances of relevance to practitioners who may be advising travelers to altitude. Although the Lake Louise Score is now widely used as a diagnostic tool for acute mountain sickness (AMS), increasing evidence questions the validity of doing so, and of considering AMS as a single condition. Biomarkers, such as brain natriuretic peptide, are likely correlating with pulmonary artery systolic pressure, thus potential markers of the development of altitude illness. Established drug treatments include acetazolamide, nifedipine, and dexamethasone. Drugs with a potential to reduce the risk of developing AMS include nitrate supplements, propagators of nitric oxide, and supplemental iron. The role of exercise in the development of altitude illness remains hotly debated, and it appears that the intensity of exercise is more important than the exercise itself. Finally, despite copious studies demonstrating the value of preacclimatization in reducing the risk of altitude illness and improving performance, an optimal protocol to preacclimatize an individual remains elusive.

Polymorphism profiling of nine high altitude relevant candidate gene loci in acclimatized sojourners and adapted natives

Background

Sea level sojourners, on ascent to high altitude, undergo acclimatization through integrated physiological processes for defending the body against oxygen deprivation while the high altitude natives (resident population) are adapted to the prevailing hypobaric hypoxic condition through natural selection. Separating the acclimatization processes from adaptive changes and identifying genetic markers in lowlanders that may be beneficial for offsetting the high altitude hypoxic stress, although challenging, is worth investigating. We genotyped nine candidate gene polymorphisms, suggested to be relevant in high altitude environment, in sea level acclimatized sojourners and adapted natives for understanding differences/commonality between the acclimatized and the adapted cohorts at the genetic level.

Results

Statistically similar genotypic and allelic frequencies were observed between the sea level sojourners (acclimatized) and the high altitude natives (adapted) in six loci viz., EDN1 (endothelin 1) -3A/-4A VNTR, ADRB2 (beta-2 adrenergic receptor, surface) Arg16Gly (rs1042713:A > G), ADRB3 (beta-3 adrenergic receptor) Trp64Arg (rs4994:T > C), eNOS (nitric oxide synthase, endothelial) Glu298Asp (rs1799983:T > G), TH (tyrosine hydroxylase) Val81Met (rs6356:G > A) and VEGF (vascular endothelial growth factor) 963C > T (rs3025039:C > T) while SCNN1B (amiloride-sensitive sodium channel, subunit beta) Thr594Met (rs1799979:C > T) was monomorphic. Genotypic and allelic frequencies in EDN1 9465G > A (rs2071942:G > A) and ADRB2 Gln27Glu (rs1042714:G > C) were significantly different between the acclimatized sojourners and the high altitude natives with higher frequency of GG and GA genotypes of EDN1 rs2071942 and CC genotype of ADRB2 rs1042714 being observed in Ladakh natives. Mutated A allele (AA genotype) of rs2071942 and carriers of G allele (GG + GC genotypes) of rs1042714 were less favorable during acclimatization under recessive and dominant genetic models of inheritance respectively indicating thereby that GG genotype and G allele of EDN1 rs2071942 and CC genotype of ADRB2 rs1042714 conferred acclimatization benefit.

Conclusion

Sea level acclimatized individuals shared similarity with the adapted natives in certain high altitude relevant genetically based trait variation suggesting advantageous consequence as well as commonality in gene regulatory pathways in which these gene products function both during process of acclimatization and adaptation in high altitude environment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0268-y) contains supplementary material, which is available to authorized users.

Serum nitric oxide metabolites are associated with the risk of hypertriglyceridemic-waist phenotype in women: Tehran Lipid and Glucose Study

BACKGROUND AND AIM

There are some controversial issues regarding the association of nitric oxide and obesity-related states. This study was conducted to investigate whether serum nitric oxide metabolites (NOx) could predict the occurrence of visceral lipid accumulation, defined as hypertriglyceridemic-waist (HTW) phenotype.

METHODS

We used a prospective approach for this study conducted on participants of the Tehran Lipid and Glucose Study, 2243 adult men and women were followed for a median of 6.3 years. Serum NOx concentrations were measured at baseline (2006-2008), and demographics, anthropometrics and biochemical variables were evaluated at baseline and again after a 3-year (2009-2011) and a 6-year follow-up (2012-2014). The occurrence of HTW phenotype, defined as waist circumference ≥90 cm in men and ≥85 cm in women, along with serum triglyceride levels ≥177 mg/dL, were assessed across serum NOx tertiles.

RESULTS

Mean age of participants was 41.5 ± 14.5 years at baseline and 39.4% were male. The cumulative incidence of HTW phenotype was 37.6% (33.2% in men, 40.5% in women). There was no significant association between serum NOx and the occurrence of HTW phenotype in men. After adjustment of confounding variables, risk of HTW phenotype in women, in the highest compared to the lowest tertile of serum NOx (≥30.9 vs. <19.9 μmol/L), increased by 39% (OR = 1.39, 95% CI = 1.05-1.93, P for trend = 0.053).

CONCLUSION

Serum NOx level was an independent predictor of HTW phenotype in women.

Oxidized Low Density Lipoprotein Among the Elderly in Qinghai-Tibet Plateau

OBJECTIVE

Several environmental factors including hypoxia have been reported to contribute to oxidative stress in individuals living in the highlands. However, little is known about the role of oxidized low-density lipoprotein (ox-LDL) among community-dwelling elderly in the Qinghai-Tibet plateau.

METHODS

The study population comprised 168 community-dwelling elderly subjects aged 60 years or older (male to female ratio, 70:98; mean age, 65.8 years) living in Haiyan County, located 3000 to 3200 m above sea level, 30 km northwest of Xining, Qinghai. The subjects were volunteers who joined a Comprehensive Geriatric Assessment. Plasma ox-LDL was measured in 168 community-dwelling elderly subjects aged 60 years or older (23 Tibetans and 145 Hans) with a monoclonal antibody-based enzyme-linked immunosorbent assay.

RESULTS

Mean ox-LDL level was higher among Tibetan elderly than Han elderly (Tibetan, 79.0 ± 29.6 U/L; Han, 62.8 ± 23.5 U/L; P = .003). Tibetan ethnicity was significantly associated with ox-LDL levels after adjusting for LDL cholesterol levels. In addition, high ox-LDL levels (≥70 U/L) were significantly associated with a homeostasis model assessment insulin resistance index of at least 1.6 (odds ratio [OR], 2.82; 95% confidence interval [95% CI], 1.11 to 7.15; P = .029) and ankle brachial pressure index of less than 1.0 (OR, 4.85; 95% CI, 1.14 to 10.00; P = .028), after adjusting for age, sex, and ethnicity.

CONCLUSIONS

Our findings support the hypothesis that ox-LDL levels are higher among Tibetan elderly highlanders compared with those among Han elderly. As ox-LDL levels can affect insulin resistance and arteriosclerosis, further research is needed to determine how oxidative stress influences the health situation among elderly individuals at high altitudes.