Glucose homeostasis during short-term and prolonged exposure to high altitudes

Activity of Lipoprotein-Associated Enzymes in Indigenous Children Living at Different Altitudes

BACKGROUND

High altitude is associated with hypobaric hypoxia, and metabolic modifications. In particular, alterations to lipoprotein-associated enzymes have been reported under hypoxia.

OBJECTIVE

To determine the association between paraoxonase 1 (PON-1) and Cholesteryl-ester transfer protein (CETP) activities and altitude in two groups of Argentinean Indigenous schoolchildren living at different altitudes.

METHODS

A cross-sectional study compared 151 schoolchildren from San Antonio de los Cobres (SAC), 3,750 m, with 175 schoolchildren from Chicoana (CH), 1,400 m. Anthropometric data, lipids, apolipoprotein (apo) A-I, apo B, plus PON-1 and CETP activities were determined.

RESULTS

The prevalence of overweight/obesity was significantly lower in SAC than in CH. Z- BMI (0.3 vs 0.7), Apo A-I/Apo B (1.67 vs. 1.85) and PON-1 (170 vs. 243 nmol/mL.min) were significantly lower in SAC than in CH, respectively. Total cholesterol (156 vs 144 mg/dL), triglycerides (TG) (119 vs. 94 mg/dL), apo A-I (133 vs. 128 mg/dL), apo B (84 vs. 73 mg/dL), hematocrit (48 vs. 41%), transferrin (295 vs. 260 mg/dL) and CETP (181 vs. 150%/mL.h) were significantly higher in SAC than in CH. There was a significant univariate association between altitude and transferrin (r0.38), hematocrit (r0.75), TG (r0.24), apo B (r0.29), PON-1 (r-0.40), and CETP (r0.37). Multiple linear regression analyses showed that altitude was significantly associated with children's TG (β = 0.28, R² = 0.14), HDL-C (β = ‒0.27; R² = 0.23), apo B (β = 0.32; R² = 0.14), CETP (β = 0.38; R² = 0.15) and PON-1 (β = ‒0.36; R² = 0.16), adjusted for age, gender and BMI.

CONCLUSION

SAC children presented a more atherogenic lipid profile, plus lower PON1 and higher CETP activities, than CH children.

Adverse effects of BMPR2 suppression in macrophages in animal models of pulmonary hypertension

Inflammatory cells contribute to irreversible damage in pulmonary arterial hypertension (PAH). We hypothesized that in PAH, dysfunctional BMPR2 signaling in macrophages contributes to pulmonary vascular injury and phenotypic changes via proinflammatory cytokine production. Studies were conducted in: (1) Rosa26-rtTA2 3 X TetO7-Bmpr2delx4 FVB/N mice (mutant Bmpr2 is universally expressed, BMPR2delx4 mice) given a weekly intra-tracheal liposomal clodronate injections for four weeks; and (2) LysM-Cre X floxed BMPR2 X floxed eGFP monocyte lineage-specific BMPR2 knockout (KO) mouse model (Bmpr2 gene expression knockdown in monocytic lineage cells) (BMPR2KO) following three weeks of sugen/hypoxia treatment. In the BMPR2delx4 mice, increased right ventricular systolic pressure (RVSP; P  < 0.05) was normalized by clodronate, and in monocyte lineage-specific BMPR2KO mice sugen hypoxia treatment increased (P  < 0.05) RVSP compared to control littermates, suggesting that suppressed BMPR2 in macrophages modulate RVSP in animal models of PH. In addition, in these mouse models, muscularized pulmonary vessels were increased (P  < 0.05) and surrounded by an increased number of macrophages. Elimination of macrophages in BMPR2delx4 mice reduced the number of muscularized pulmonary vessels and macrophages surrounding these vessels. Further, in monocyte lineage-specific BMPR2KO mice, there was significant increase in proinflammatory cytokines, including C-X-C Motif Chemokine Ligand 12 (CXCL12), complement component 5 a (C5a), Interleukin-16 (IL-16), and secretory ICAM. C5a positive inflammatory cells present in and around the pulmonary vessels in the PAH lung could potentially be involved in pulmonary vessel remodeling. In summary, our data indicate that, in BMPR2-related PAH, macrophages with dysfunctional BMPR2 influence pulmonary vascular remodeling and phenotypic outcomes via proinflammatory cytokine production.

Human physiological and metabolic responses to an attempted winter crossing of Antarctica: the effects of prolonged hypobaric hypoxia

An insufficient supply of oxygen to the tissues (hypoxia), as is experienced upon high‐altitude exposure, elicits physiological acclimatization mechanisms alongside metabolic remodeling. Details of the integrative adaptive processes in response to chronic hypobaric hypoxic exposure remain to be sufficiently investigated. In this small applied field study, subjects (n = 5, male, age 28–54 years) undertook a 40 week Antarctica expedition in the winter months, which included 24 weeks residing above 2500 m. Measurements taken pre‐ and postexpedition revealed alterations to glucose and fatty acid resonances within the serum metabolic profile, a 7.8 (±3.6)% increase in respiratory exchange ratio measured during incremental exercise (area under curve, P > 0.01, mean ± SD) and a 2.1(±0.8) % decrease in fat tissue (P < 0.05) postexpedition. This was accompanied by an 11.6 (±1.9) % increase (P > 0.001) in VO₂ max corrected to % lean mass postexpedition. In addition, spine bone mineral density and lung function measures were identified as novel parameters of interest. This study provides, an in‐depth characterization of the responses to chronic hypobaric hypoxic exposure in one of the most hostile environments on Earth.

Human Genetic Adaptation to High Altitude: Evidence from the Andes

Whether Andean populations are genetically adapted to high altitudes has long been of interest. Initial studies focused on physiological changes in the O₂ transport system that occur with acclimatization in newcomers and their comparison with those of long-resident Andeans. These as well as more recent studies indicate that Andeans have somewhat larger lung volumes, narrower alveolar to arterial O₂ gradients, slightly less hypoxic pulmonary vasoconstrictor response, greater uterine artery blood flow during pregnancy, and increased cardiac O₂ utilization, which overall suggests greater efficiency of O₂ transfer and utilization. More recent single nucleotide polymorphism and whole-genome sequencing studies indicate that multiple gene regions have undergone recent positive selection in Andeans. These include genes involved in the regulation of vascular control, metabolic hemostasis, and erythropoiesis. However, fundamental questions remain regarding the functional links between these adaptive genomic signals and the unique physiological attributes of highland Andeans. Well-designed physiological and genome association studies are needed to address such questions. It will be especially important to incorporate the role of epigenetic processes (i.e.; non-sequence-based features of the genome) that are vital for transcriptional responses to hypoxia and are potentially heritable across generations. In short, further exploration of the interaction among genetic, epigenetic, and environmental factors in shaping patterns of adaptation to high altitude promises to improve the understanding of the mechanisms underlying human adaptive potential and clarify its implications for human health.

Liver mitochondrial respiratory plasticity and oxygen uptake evoked by cobalt chloride in rats with low and high resistance to extreme hypobaric hypoxia

High-altitude intolerance and consequently high-altitude sickness, is difficult to predict. Liver is an essential organ in glucose and lipid metabolism, and may play key role in the adaptation to high altitude. In response to extreme high altitude, mitochondrial respiration exhibits changes in substrate metabolism, mitochondrial electron transport chain activity, and respiratory coupling. We determined the cobalt chloride (CoCl₂) effects on liver mitochondrial plasticity and oxygen uptake in rats with low resistance (LR) and high resistance (HR) to extreme hypobaric hypoxia. The polarographic method proposed by Chance and Williams was used as a simple and effective tool to trace mitochondrial functionality and oxygen consumption. HR rats had more efficient processes of NADH- and FAD-generated mitochondrial oxidation. CoCl₂ promoted more efficient NADH-generated and diminished less efficient FAD-generated mitochondrial respiratory reactions in HR rats. CoCl₂ diminished both aerobic and anaerobic processes in LR rats. Glutamate and pyruvate substrates of NADH-generated mitochondrial pathways were highly affected by CoCl₂. Red blood cells acted as cobalt depots in HR and LR rats. We have unveiled several mechanisms leading to differentiated mitochondrial respiratory responses to hypobaric hypoxia in LR and HR rats. Our study strongly supports the existence of adaptive liver mitochondrial plasticity to extreme hypoxia.

The Effects of High Altitude on Glucose Homeostasis, Metabolic Control, and Other Diabetes-Related Parameters: From Animal Studies to Real Life

Exposure to high altitude activates several complex and adaptive mechanisms aiming to protect human homeostasis from extreme environmental conditions, such as hypoxia and low temperatures. Short-term exposure is followed by transient hyperglycemia, mainly triggered by the activation of the sympathetic system, whereas long-term exposure results in lower plasma glucose concentrations, mediated by improved insulin sensitivity and augmented peripheral glucose disposal. An inverse relationship between altitude, diabetes, and obesity has been well documented. This is the result of genetic and physiological adaptations principally to hypoxia that favorably affect glucose metabolism; however, the contribution of financial, dietary, and other life-style parameters may also be important. According to existing evidence, people with diabetes are capable of undertaking demanding physical challenges even at extreme altitudes. Still, a number of issues should be taken into account, including the increased physical activity leading to changes in insulin demands and resistance, the performance of measurement systems under extreme weather conditions and the potential deterioration of metabolic control during climbing expeditions. The aim of this review is to present available evidence in the field in a comprehensive way, beginning from the physiology of glucose homeostasis adaptation mechanisms to high altitudes and ending to what real life experience has taught us.

Gestational Diabetes Prevalence at Moderate and High Altitude

BACKGROUND

High-altitude (HA) pregnancies have been associated with decreased glucose levels and increased insulin sensitivity versus sea level. Our objective was to determine if the prevalence of gestational diabetes mellitus (GDM) and the impact of demographic characteristics on GDM diagnosis differed at moderate altitude (MA) versus HA.

METHODS

Using a retrospective cohort design, we compared women living at HA (>8250 ft) and MA (4000-7000 ft) during pregnancy. Exclusion criteria were as follows: multiple gestation, preexisting diabetes, unavailable GDM results, or relocation from a different altitude during pregnancy. GDM diagnosis was determined using Carpenter and Coustan criteria. Data were compared by t-test (continuous variables) or chi-squared tests (categorical variables). Univariate, multivariate, and stepwise regression models were used to assess the impact of various factors on GDM prevalence.

RESULTS

There was no difference in GDM prevalence between altitudes in these populations; the relationship between altitude and GDM was nonsignificant in all regression analyses. At MA, maternal age, Hispanic ethnicity, body mass index (BMI), and gestational age (GA) at testing increased GDM incidence in univariate analyses. At HA, maternal age, Hispanic ethnicity, and multiparity increased GDM incidence in univariate analyses.

CONCLUSION

While GDM prevalence did not differ between MA and HA, the impact of maternal demographic characteristics on GDM risk varied by altitude group. Higher BMI and greater GA at testing increased the incidence of GDM at MA, but not at HA. Multiparity had an effect at HA, but not MA. These differences may represent subtle differences in glucose metabolism at HA.

Life Under Hypoxia Lowers Blood Glucose Independently of Effects on Appetite and Body Weight in Mice

Blood glucose and the prevalence of diabetes are lower in mountain than lowland dwellers, which could among other factors be due to reduced oxygen availability. To investigate metabolic adaptations to life under hypoxia, male mice on high fat diet (HFD) were continuously maintained at 10% O2. At variance to preceding studies, the protocol was designed to dissect direct metabolic effects from such mediated indirectly via hypoxia-induced reductions in appetite and weight gain. This was achieved by two separate control groups on normal air, one with free access to HFD, and one fed restrictedly in order to obtain a weight curve matching that of hypoxia-exposed mice. Comparable body weight in restrictedly fed and hypoxic mice was achieved by similar reductions in calorie intake (-22%) and was associated with parallel effects on body composition as well as on circulating insulin, leptin, FGF-21, and adiponectin. Whereas the effects of hypoxia on the above parameters could thus be attributed entirely to blunted weight gain, hypoxia improved glucose homeostasis in part independently of body weight (fasted blood glucose, mmol/l: freely fed control, 10.2 ± 0.7; weight-matched control, 8.0 ± 0.3; hypoxia, 6.8 ± 0.2; p < 0.007 each; AUC in the glucose tolerance test, mol/l*min: freely fed control, 2.54 ± 0.15; weight-matched control, 1.86 ± 0.08; hypoxia, 1.67 ± 0.05; p < 0.05 each). Although counterintuitive to lowering of glycemia, insulin sensitivity appeared to be impaired in animals adapted to hypoxia: In the insulin tolerance test, hypoxia-treated mice started off with lower glycaemia than their weight-matched controls (initial blood glucose, mmol/l: freely fed control, 11.5 ± 0.7; weight-matched control, 9.4 ± 0.3; hypoxia, 8.1 ± 0.2; p < 0.02 each), but showed a weaker response to insulin (final blood glucose, mmol/l: freely fed control, 7.0 ± 0.3; weight-matched control, 4.5 ± 0.2; hypoxia, 5.5 ± 0.3; p < 0.01 each). Furthermore, hypoxia weight-independently reduced hepatic steatosis as normalized to total body fat, suggesting a shift in the relative distribution of triglycerides from liver to fat (mg/g liver triglycerides per g total fat mass: freely fed control, 10.3 ± 0.6; weight-matched control, 5.6 ± 0.3; hypoxia, 4.0 ± 0.2; p < 0.0004 each). The results show that exposure of HFD-fed mice to continuous hypoxia leads to a unique metabolic phenotype characterized by improved glucose homeostasis along with evidence for impaired rather than enhanced insulin sensitivity.

Long-Term Chronic Intermittent Hypobaric Hypoxia Induces Glucose Transporter (GLUT4) Translocation Through AMP-Activated Protein Kinase (AMPK) in the Soleus Muscle in Lean Rats

Background: In chronic hypoxia (CH) and short-term chronic intermittent hypoxia (CIH) exposure, glycemia and insulin levels decrease and insulin sensitivity increases, which can be explained by changes in glucose transport at skeletal muscles involving GLUT1, GLUT4, Akt, and AMPK, as well as GLUT4 translocation to cell membranes. However, during long-term CIH, there is no information regarding whether these changes occur similarly or differently than in other types of hypoxia exposure. This study evaluated the levels of AMPK and Akt and the location of GLUT4 in the soleus muscles of lean rats exposed to long-term CIH, CH, and normoxia (NX) and compared the findings.

Methods: Thirty male adult rats were randomly assigned to three groups: a NX (760 Torr) group (n = 10), a CIH group (2 days hypoxia/2 days NX; n = 10) and a CH group (n = 10). Rats were exposed to hypoxia for 30 days in a hypobaric chamber set at 428 Torr (4,600 m). Feeding (10 g daily) and fasting times were accurately controlled. Measurements included food intake (every 4 days), weight, hematocrit, hemoglobin, glycemia, serum insulin (by ELISA), and insulin sensitivity at days 0 and 30. GLUT1, GLUT4, AMPK levels and Akt activation in rat soleus muscles were determined by western blot. GLUT4 translocation was measured with confocal microscopy at day 30.

Results: (1) Weight loss and increases in hematocrit and hemoglobin were found in both hypoxic groups (p < 0.05). (2) A moderate decrease in glycemia and plasma insulin was found. (3) Insulin sensitivity was greater in the CIH group (p < 0.05). (4) There were no changes in GLUT1, GLUT4 levels or in Akt activation. (5) The level of activated AMPK was increased only in the CIH group (p < 0.05). (6) Increased GLUT4 translocation to the plasma membrane of soleus muscle cells was observed in the CIH group (p < 0.05).

Conclusion: In lean rats experiencing long-term CIH, glycemia and insulin levels decrease and insulin sensitivity increases. Interestingly, there is no increase of GLUT1 or GLUT4 levels or in Akt activation. Therefore, cellular regulation of glucose seems to primarily involve GLUT4 translocation to the cell membrane in response to hypoxia-mediated AMPK activation.

Appetite Suppression and Altered Food Preferences Coincide with Changes in Appetite-Mediating Hormones During Energy Deficit at High Altitude, But Are Not Affected by Protein Intake

Karl, J. Philip, Renee E. Cole, Claire E. Berryman, Graham Finlayson, Patrick N. Radcliffe, Matthew T. Kominsky, Nancy E. Murphy, John W. Carbone, Jennifer C. Rood, Andrew J. Young, and Stefan M. Pasiakos. Appetite suppression and altered food preferences coincide with changes in appetite-mediating hormones during energy deficit at high altitude, but are not affected by protein intake. High Alt Med Biol. 19:156-169, 2018.-Anorexia and unintentional body weight loss are common during high altitude (HA) sojourn, but underlying mechanisms are not fully characterized, and the impact of dietary macronutrient composition on appetite regulation at HA is unknown. This study aimed to determine the effects of a hypocaloric higher protein diet on perceived appetite and food preferences during HA sojourn and to examine longitudinal changes in perceived appetite, appetite mediating hormones, and food preferences during acclimatization and weight loss at HA. Following a 21-day level (SL) period, 17 unacclimatized males ascended to and resided at HA (4300 m) for 22 days. At HA, participants were randomized to consume measured standard-protein (1.0 g protein/kg/d) or higher protein (2.0 g/kg/d) hypocaloric diets (45% carbohydrate, 30% energy restriction) and engaged in prescribed physical activity to induce an estimated 40% energy deficit. Appetite, food preferences, and appetite-mediating hormones were measured at SL and at the beginning and end of HA. Diet composition had no effect on any outcome. Relative to SL, appetite was lower during acute HA (days 0 and 1), but not different after acclimatization and weight loss (HA day 18), and food preferences indicated an increased preference for sweet- and low-protein foods during acute HA, but for high-fat foods after acclimatization and weight loss. Insulin, leptin, and cholecystokinin concentrations were elevated during acute HA, but not after acclimatization and weight loss, whereas acylated ghrelin concentrations were suppressed throughout HA. Findings suggest that appetite suppression and altered food preferences coincide with changes in appetite-mediating hormones during energy deficit at HA. Although dietary protein intake did not impact appetite, the possible incongruence with food preferences at HA warrants consideration when developing nutritional strategies for HA sojourn.

Excessive Erythrocytosis and Cardiovascular Risk in Andean Highlanders

Corante, Noemí, Cecilia Anza-Ramírez, Rómulo Figueroa-Mujíca, José Luis Macarlupú, Gustavo Vizcardo-Galindo, Grzegorz Bilo, Gianfranco Parati, Jorge L. Gamboa, Fabiola León-Velarde, and Francisco C. Villafuerte. Excessive erythrocytosis and cardiovascular risk in Andean highlanders. High Alt Med Biol. 19:221–231, 2018.—Cardiovascular diseases are the main cause of death worldwide. Life under high-altitude (HA) hypoxic conditions is believed to provide highlanders with a natural protection against cardiovascular and metabolic diseases compared with sea-level inhabitants. However, some HA dwellers become intolerant to chronic hypoxia and develop a progressive incapacitating syndrome known as chronic mountain sickness (CMS), characterized by excessive erythrocytosis (EE; Hb ≥21 g/dL in men, Hb ≥19 g/dL in women). Evidence from HA studies suggests that, in addition to CMS typical signs and symptoms, these highlanders may also suffer from metabolic and cardiovascular disorders. Thus, we hypothesize that this syndrome is also associated to the loss of the cardiometabolic protection observed in healthy highlanders (HH), and therefore to a higher cardiovascular risk (CVR). The aim of the present work was to evaluate the association between EE and CVR calculated using the Framingham General CVR Score and between EE and CVR factors in male highlanders. This cross-sectional study included 342 males from Cerro de Pasco, Peru at 4340 m (HH = 209, CMS = 133). Associations were assessed by multiple logistic regressions adjusted for potential confounders (BMI, pulse oxygen saturation and age). The adjusted models show that the odds of high CVR (>20%) in highlanders with EE was 3.63 times the odds in HH (CI 95%:1.22–10.78; p = 0.020), and that EE is associated to hypertension, elevated fasting serum glucose, insulin resistance, and elevated fasting serum triglycerides. Our results suggest that individuals who suffer from EE are at increased risk of developing cardiovascular events compared with their healthy counterparts.

High Altitude and Cancer Mortality

Thiersch, Markus, and Erik R. Swenson. High altitude and cancer mortality. High Alt Med Biol 19:116-123, 2018.-Humans living at high altitude (HA) are exposed to chronic (hypobaric) hypoxia. Despite the permanent stress of hypoxic exposure, humans populating HA areas have reduced cancer mortality over a broad spectrum of cancer types. In fact, the majority of the physiological adaptive processes at HA occurring in response to hypoxia might be the driving force for reduced cancer mortality at HA. In this review, we summarize epidemiological and animal studies that compare cancer incidence and cancer mortality between HA and low altitude or between hypoxia and normoxia, respectively. We discuss the potential role of oxygen-independent and oxygen-dependent mechanisms that might contribute to reduced cancer mortality at HA. Reactive oxygen species and their detoxification as well as the hypoxia-inducible factors are especially promising targets and may be related to why cancer mortality is reduced at HA. In addition, we briefly discuss two aspects with a proven impact on tumorigenesis, namely the immune system and tumor surveillance as well as HA-induced metabolic changes. Further animal and clinical studies are clearly needed to explain why cancer mortality is reduced at HA and to decide whether HA or hypoxia-based therapeutic approaches could be implemented for cancer treatment. However, exposure to HA activates multiple adaptive mechanisms (oxygen independent and oxygen dependent) sharing common pathways as well as activating counteracting pathways, which complicate the identification of specific HA-induced mechanisms of tumor suppression.

Risk of Type 2 Diabetes Mellitus Development in the Native Population of Low- and High-Altitude Regions of Kyrgyzstan: Finnish Diabetes Risc Score Questionnaire Results

Moldobaeva, Marina S., Anastasiya V. Vinogradova, and Marina K. Esenamanova. Risk of type 2 diabetes mellitus development in the native population of low- and high-altitude regions of Kyrgyzstan: Finnish Diabetes Risc Score questionnaire results. High Alt Med Biol. 18:428-435, 2017.

OBJECTIVE

The number of patients with diabetes is steadily growing, but likely only half of all cases are ever identified. The Kyrgyz, native inhabitants of Central Asia, live in the mountainous area and have a particular lifestyle and nutrition. However, the risk of type 2 diabetes mellitus (T2DM) in our population is not well defined. Therefore, we aimed at determining the risk of T2DM development in the Kyrgyz population residing in low- and high-altitude (HAlt) regions by using the Finnish Diabetes Risc Score (FINDRISC) questionnaire.

METHODS

We included in the study 3190 randomly selected participants, including 1780 low-altitude (LAlt) residents (Chu region, 500-1200 m) and 1410 HAlt residents (Naryn region, 2000-4500 m), among whom there were 1207 men and 1983 women. Assessment of T2DM development was conducted by using the FINDRISC questionnaire and risk stratification was performed by region of residency, gender, and age.

RESULTS

An irregular intake of vegetables and fruits, increased waist circumference (WC), and increased body mass index (BMI) were identified as leading risk factors of T2DM development in native residents of Chu and Naryn regions of Kyrgyzstan. The 10-year risk stratification of T2DM development revealed the absence of a very high-risk group; high-risk status was more frequently identified among residents of the LAlt Chu district (4.7% of women and 2.1% of men), as compared with the HAlt population (1.9% of women and 1% of men) (p = 0.0018 for women and p = 0.09 for men).

CONCLUSIONS

In the Kyrgyz population, a 10-year high risk of T2DM development is greater among residents of LAlts as compared with HAlts, irrespective of gender. No very high-risk group was detected in residents of low or HAlts. The leading composites of FINDRISC score are increased WC and BMI, possibly due to irregular intake of vegetables and fruits that are dependent on the altitude of residence and age.

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.

Managing diabetes at high altitude: personal experience with support from a Multidisciplinary Physical Activity and Diabetes Clinic

OBJECTIVE

Physical activity is important for well-being but can be challenging for people with diabetes. Data informing support of specialist activities such as climbing and high-altitude trekking are limited. A 42-year-old man with type 1 diabetes (duration 30 years) attended a Multidisciplinary Physical Activity and Diabetes Clinic planning to climb Mont Blanc during the summer and trek to Everest Base Camp in the autumn. His aims were to complete these adventures without his diabetes impacting on their success.

METHODS

We report the information provided that enabled him to safely facilitate his objectives, in particular, the requirement for frequent checking of blood glucose levels, the effects of altitude on insulin dose requirements, and recognition that acute mountain sickness may mimic the symptoms of hypoglycaemia and vice versa. Real-time continuous glucose monitoring was made available for his treks.

RESULTS

The effects of high altitude on blood glucose results and glycaemic variability while treated on multiple daily injections of insulin are reported. In addition, we present a first-person account of his experience and lessons learnt from managing diabetes at high altitude.

CONCLUSIONS

A dedicated Multidisciplinary Physical Activity and Diabetes Clinic delivering individualised, evidence-based, patient-focused advice on the effects of altitude on blood glucose levels, and provision of real-time continuous glucose monitoring enabled uneventful completion of a trek to Everest Base Camp in a person with type 1 diabetes.

Measuring high-altitude adaptation

High altitudes (>8,000 ft or 2,500 m) provide an experiment of nature for measuring adaptation and the physiological processes involved. Studies conducted over the past ~25 years in Andeans, Tibetans, and, less often, Ethiopians show varied but distinct O₂ transport traits from those of acclimatized newcomers, providing indirect evidence for genetic adaptation to high altitude. Short-term (acclimatization, developmental) and long-term (genetic) responses to high altitude exhibit a temporal gradient such that, although all influence O₂ content, the latter also improve O₂ delivery and metabolism. Much has been learned concerning the underlying physiological processes, but additional studies are needed on the regulation of blood flow and O₂ utilization. Direct evidence of genetic adaptation comes from single-nucleotide polymorphism (SNP)-based genome scans and whole genome sequencing studies that have identified gene regions acted upon by natural selection. Efforts have begun to understand the connections between the two with Andean studies on the genetic factors raising uterine blood flow, fetal growth, and susceptibility to Chronic Mountain Sickness and Tibetan studies on genes serving to lower hemoglobin and pulmonary arterial pressure. Critical for future studies will be the selection of phenotypes with demonstrable effects on reproductive success, the calculation of actual fitness costs, and greater inclusion of women among the subjects being studied. The well-characterized nature of the O₂ transport system, the presence of multiple long-resident populations, and relevance for understanding hypoxic disorders in all persons underscore the importance of understanding how evolutionary adaptation to high altitude has occurred.NEW & NOTEWORTHY Variation in O₂ transport characteristics among Andean, Tibetan, and, when available, Ethiopian high-altitude residents supports the existence of genetic adaptations that improve the distribution of blood flow to vital organs and the efficiency of O₂ utilization. Genome scans and whole genome sequencing studies implicate a broad range of gene regions. Future studies are needed using phenotypes of clear relevance for reproductive success for determining the mechanisms by which naturally selected genes are acting.

Non-shivering thermogenesis as a mechanism to facilitate sustainable weight loss

Currently, there is a significant percentage of the population who are or will be classified as obese, necessitating novel strategies to facilitate sustainable weight loss. Reductions in basal metabolic rate occur in the face of weight loss and pose formidable barriers to individuals attempting to sustain meaningful weight reductions. Here, we discuss the mechanisms by which non-shivering thermogenesis may provide insight into metabolic pathways that can become druggable targets to facilitate sustainable weight loss. Specifically, we highlight the fact that non-shivering thermogenesis results in activation and expansion of brown and beige adipose tissues as well as activates pathways in skeletal muscle which increase metabolic flux and activity of muscle fibres through futile calcium cycling across the endoplasmic reticulum all facilitating an increase in metabolism. Finally, we highlight the fact there are sexual dimorphisms with respect to these metabolic processes in keeping with the National Institutes of Health mandate of treating sex as a biologic variable.

Enhanced hepatic insulin signaling in the livers of high altitude native rats under basal conditions and in the livers of low altitude native rats under insulin stimulation: a mechanistic study

This study was designed to investigate the role of the liver in lowering fasting blood glucose levels (FBG) in rats native to high (HA) and low altitude (LA) areas. As compared with LA natives, besides the improved insulin and glucose tolerance, HA native rats had lower FBG, at least mediated by inhibition of hepatic gluconeogenesis and activation of glycogen synthesis. An effect that is mediated by the enhancement of hepatic insulin signaling mediated by the decreased phosphorylation of TSC induced inhibition of mTOR function. Such effect was independent of activation of AMPK nor stabilization of HIF1α, but most probably due to oxidative stress induced REDD1 expression. However, under insulin stimulation, and in spite of the less activated mTOR function in HA native rats, LA native rats had higher glycogen content and reduced levels of gluconeogenic enzymes with a more enhanced insulin signaling, mainly due to higher levels of p-IRS1 (tyr612).

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.

The prevalence of obesity and metabolic syndrome in Tibetan immigrants living in high altitude areas in Ladakh, India

OBJECTIVE

To examine the prevalence of obesity and related cardiovascular disease risk factors among Tibetan immigrants living in high altitude areas.

RESEARCH METHODS & PROCEDURES

A total of 149 Tibetan immigrants aged 20 years and over were recruited in 2016 in Ladakh, India. Anthropometric indices and biochemical factors were measured. Using the provided Asia-Pacific criteria from the World Health Organization, overweight and obese status were determined. Metabolic syndrome (MetS) was defined according to the American Heart Association.

RESULTS

In general, men were older, taller, and had a greater amount of fasting glucose, and uric acid when compared to women. The prevalence of overweight, general obesity, and central obesity was 23.4, 42.6, and 42.6% in men and 7.8, 64.7, and 69.6% in women, respectively. The prevalence of MetS was 10.6% in men and 33.3% in women, respectively. In older subjects, the prevalence of obesity and MetS was found to be greater. In both genders, the prevalence of hypertension, central obesity, and MetS was significantly different among these body mass index (BMI) groups. Compared to the non-central obesity group, the central obesity group has higher weight, BMI, body fat, hip circumference, systolic and diastolic BP, and prevalence of hypertension. No relationship was found between the prevalence of diabetes and fasting glucose and BMI groups or central obesity groups in both genders.

CONCLUSIONS

Among this group of Tibetan immigrants living in high altitude areas, women have a higher prevalence of obesity and MetS than men. No relationship was found between diabetes and obesity.

Reduced cancer mortality at high altitude: The role of glucose, lipids, iron and physical activity

Residency at high altitude (HA) demands adaptation to challenging environmental conditions with hypobaric hypoxia being the most important one. Epidemiological and experimental data suggest that chronic exposure to HA reduces cancer mortality and lowers prevalence of metabolic disorders like diabetes and obesity implying that adaption to HA modifies a broad spectrum of physiological, metabolic and cellular programs with a generally beneficial outcome for humans. However, the complexity of multiple, potentially tumor-suppressive pathways at HA impedes the understanding of mechanisms leading to reduced cancer mortality. Many adaptive processes at HA are tightly interconnected and thus it cannot be ruled out that the entirety or at least some of the HA-related alterations act in concert to reduce cancer mortality. In this review we discuss tumor formation as a concept of competition between healthy and cancer cells with improved fitness - and therefore higher competitiveness - of healthy cells at high altitude. We discuss HA-related changes in glucose, lipid and iron metabolism that may have an impact on tumorigenesis. Additionally, we discuss two parameters with a strong impact on tumorigenesis, namely drug metabolism and physical activity, to underpin their potential contribution to HA-dependent reduced cancer mortality. Future studies are needed to unravel why cancer mortality is reduced at HA and how this knowledge might be used to prevent and to treat cancer patients.

Acceptability, Safety, and Efficacy of Oral Administration of Extracts of Black or Red Maca (Lepidium meyenii) in Adult Human Subjects: A Randomized, Double-Blind, Placebo-Controlled Study

The plant maca, grown at 4000 m altitude in the Peruvian Central Andes, contains hypocotyls that have been used as food and in traditional medicine for centuries. The aim of this research was to provide results on some health effects of oral administration of spray-dried extracts of black or red maca (Lepidium meyenii) in adult human subjects living at low (LA) and high altitude (HA). A total of 175 participants were given 3 g of either placebo, black, or red maca extract daily for 12 weeks. Primary outcomes were changes in sexual desire, mood, energy, health-related quality of life score (HRQL), and chronic mountain sickness (CMS) score, or in glycaemia, blood pressure, and hemoglobin levels. Secondary outcomes were acceptability and safety, assessed using the Likert test and side effect self-recording, respectively, and the effect of altitude. At low altitude, 32, 30, and 32 participants started the study receiving placebo, red maca, or black maca, respectively. At high altitudes, 33, 35, and 31 participants started the study receiving placebo, red maca, and black maca, respectively. Consumption of spray-dried extracts of red and black maca resulted in improvement in mood, energy, and health status, and reduced CMS score. Fatty acids and macamides were higher in spray-dried extracts of black maca than in red maca. GABA predominated in spray-dried extracts of red maca. Effects on mood, energy, and CMS score were better with red maca. Black maca and, in smaller proportions, red maca reduced hemoglobin levels only in highlanders with abnormally high hemoglobin levels; neither variety of maca reduced hemoglobin levels in lowlanders. Black maca reduced blood glucose levels. Both varieties produced similar responses in mood, and HRQL score. Maca extracts consumed at LA or HA had good acceptability and did not show serious adverse effects. In conclusion, maca extract consumption relative to the placebo improved quality of life parameters. Differences in the level of improvement between red and black maca are probably due to differences in the composition of these two plant varieties. Both maca extracts were well tolerated and safe.

Synergistic Inhibitory Effects of Hypoxia and Iron Deficiency on Hepatic Glucose Response in Mouse Liver

Hypoxia and iron both regulate metabolism through multiple mechanisms, including hypoxia-inducible transcription factors. The hypoxic effects on glucose disposal and glycolysis are well established, but less is known about the effects of hypoxia and iron deficiency on hepatic gluconeogenesis. We therefore assessed their effects on hepatic glucose production in mice. Weanling C57BL/6 male mice were fed an iron-deficient (4 ppm) or iron-adequate (35 ppm) diet for 14 weeks and were continued in normoxia or exposed to hypoxia (8% O2) for the last 4 weeks of that period. Hypoxic mice became hypoglycemic and displayed impaired hepatic glucose production after a pyruvate challenge, an effect accentuated by an iron-deficient diet. Stabilization of hypoxia-inducible factors under hypoxia resulted in most glucose being converted into lactate and not oxidized. Hepatic pyruvate concentrations were lower in hypoxic mice. The decreased hepatic pyruvate levels were not caused by increased utilization but rather were contributed to by decreased metabolism from gluconeogenic amino acids. Pyruvate carboxylase, which catalyzes the first step of gluconeogenesis, was also downregulated by hypoxia with iron deficiency. Hypoxia, and more so hypoxia with iron deficiency, results in hypoglycemia due to decreased levels of hepatic pyruvate and decreased pyruvate utilization for gluconeogenesis. These data highlight the role of iron levels as an important determinant of glucose metabolism in hypoxia.

Inverse association between altitude and obesity: A prevalence study among andean and low-altitude adult individuals of Peru

OBJECTIVE

To determine the association between altitude and obesity in a nationally representative sample of the Peruvian adult population.

METHODS

This is a cross-sectional analysis of publicly available data from the Food and Nutrition National Center (CENAN, Peru), period 2009-2010. The Prevalence ratio of obesity and abdominal obesity was determined as a measure of association. Obesity and abdominal obesity were diagnosed based on direct anthropometric measurements.

RESULTS

The final data set consisted of 31,549 individuals ≥20 years old. The prevalence ratio of obesity was as follows: 1.00 between 0 and 499 m (reference category), 1.00 (95% confidence interval 0.87-1.16) between 500-1,499 m, 0.74 (0.63-0.86) between 1,500-2,999 m, and 0.54 (0.45-0.64) at ≥3,000 m, adjusting for age, sex, self-reported physical activity, out-migration rate, urbanization, poverty, education, and geographical latitude and longitude. In the same order, the adjusted prevalence ratio of abdominal obesity was 1.00, 1.01 (0.94-1.07), 0.93 (0.87-0.99), and 0.89 (0.82-0.95), respectively. We found an interaction between altitude and sex and between altitude and age (P < 0.001, for both interactions) on the association with obesity and abdominal obesity.

CONCLUSIONS

Among Peruvian adult individuals, we found an inverse association between altitude and obesity, adjusting for multiple covariates. This adjusted association varied by sex and age.

Cardiometabolic risk factors in native populations living at high altitudes

BACKGROUND

It is generally accepted that metabolic changes that take place in individuals exposed to high elevation are because of ambient hypoxia, which occurs as a consequence of a low total atmospheric pressure. The discovery of hypoxia inducible factor 1 (HIF1), a transcription factor, has been a breakthrough in the understanding of adaption to high altitudes.

OBJECTIVE

The purpose of the present review was to discuss specific epidemiological aspects of cardiovascular disease (CVD) risk factors and their mechanisms in vulnerable, understudied populations living at high altitudes.

RESULTS

Obesity prevalence has been inversely associated with elevation. HIF1 has been related to plasma leptin--a hormone secreted by adipose tissue that produces negative feedback on appetite--and inversely associated with obesity. Diverse factors, such as genetics, chronic hypoxia, diet and lifestyle behaviours, could have an influence on the high dyslipidaemia rates of high-altitude natives. Hypoxia could mediate the effects of altitude on human physiology, including lipid metabolism. Genetic studies suggest that dyslipidaemia could be related to the HIF1. Hypoxia inhibits oxidative phosphorylation and stimulates the oxygen signalling pathway through the HIF1. Low fasting glycaemia in individuals at high altitudes has been shown. An increased GLUT4 protein content in skeletal muscle in response to hypoxia has been reported and could be associated with lower glucose levels. Given the high prevalence of dyslipidaemia and the low prevalence of obesity and diabetes in these impoverished high-altitude communities, changes in lifestyle including decreased physical activity and the consumption of a more westernised diet would likely increase the prevalence of CVD related mortality.

CONCLUSIONS

Control over major CVD risk factors, when identified early, could be the key to reducing morbidity and mortality in patients with limited access to medical services such as Native populations.

The Circulatory and Metabolic Responses to Hypoxia in Humans - With Special Reference to Adipose Tissue Physiology and Obesity

Adipose tissue metabolism and circulation play an important role in human health. It is well-known that adipose tissue mass is increased in response to excess caloric intake leading to obesity and further to local hypoxia and inflammatory signaling. Acute exercise increases blood supply to adipose tissue and mobilization of fat stores for energy. However, acute exercise during systemic hypoxia reduces subcutaneous blood flow in healthy young subjects, but the response in overweight or obese subjects remains to be investigated. Emerging evidence also indicates that exercise training during hypoxic exposure may provide additive benefits with respect to many traditional cardiovascular risk factors as compared to exercise performed in normoxia, but unfavorable effects of hypoxia have also been documented. These topics will be covered in this brief review dealing with hypoxia and adipose tissue physiology.

A Molecular and Whole Body Insight of the Mechanisms Surrounding Glucose Disposal and Insulin Resistance with Hypoxic Treatment in Skeletal Muscle

Although the mechanisms are largely unidentified, the chronic or intermittent hypoxic patterns occurring with respiratory diseases, such as chronic pulmonary disease or obstructive sleep apnea (OSA) and obesity, are commonly associated with glucose intolerance. Indeed, hypoxia has been widely implicated in the development of insulin resistance either via the direct action on insulin receptor substrate (IRS) and protein kinase B (PKB/Akt) or indirectly through adipose tissue expansion and systemic inflammation. Yet hypoxia is also known to encourage glucose transport using insulin-dependent mechanisms, largely reliant on the metabolic master switch, 5' AMP-activated protein kinase (AMPK). In addition, hypoxic exposure has been shown to improve glucose control in type 2 diabetics. The literature surrounding hypoxia-induced changes to glycemic control appears to be confusing and conflicting. How is it that the same stress can seemingly cause insulin resistance while increasing glucose uptake? There is little doubt that acute hypoxia increases glucose metabolism in skeletal muscle and does so using the same pathway as muscle contraction. The purpose of this review paper is to provide an insight into the mechanisms underpinning the observed effects and to open up discussions around the conflicting data surrounding hypoxia and glucose control.