eNOS allelic variants at the same locus associate with HAPE and adaptation

The Telomere-Telomerase System Is Detrimental to Health at High-Altitude

The hypobaric-hypoxia environment at high-altitude (HA, >2500 m) may influence DNA damage due to the production of reactive molecular species and high UV radiation. The telomere system, vital to chromosomal integrity and cellular viability, is prone to oxidative damages contributing to the severity of high-altitude disorders such as high-altitude pulmonary edema (HAPE). However, at the same time, it is suggested to sustain physical performance. This case-control study, comprising 210 HAPE-free (HAPE-f) sojourners, 183 HAPE-patients (HAPE-p) and 200 healthy highland natives (HLs) residing at ~3500 m, investigated telomere length, telomerase activity, and oxidative stress biomarkers. Fluidigm SNP genotyping screened 65 single nucleotide polymorphisms (SNPs) in 11 telomere-maintaining genes. Significance was attained at p ≤ 0.05 after adjusting for confounders and correction for multiple comparisons. Shorter telomere length, decreased telomerase activity and increased oxidative stress were observed in HAPE patients; contrarily, longer telomere length and elevated telomerase activity were observed in healthy HA natives compared to HAPE-f. Four SNPs and three haplotypes are associated with HAPE, whereas eight SNPs and nine haplotypes are associated with HA adaptation. Various gene-gene interactions and correlations between/among clinical parameters and biomarkers suggested the presence of a complex interplay underlining HAPE and HA adaptation physiology. A distinctive contribution of the telomere-telomerase system contributing to HA physiology is evident in this study. A normal telomere system may be advantageous in endurance training.

Molecular Mechanisms of High-Altitude Acclimatization

High-altitude illnesses (HAIs) result from acute exposure to high altitude/hypoxia. Numerous molecular mechanisms affect appropriate acclimatization to hypobaric and/or normobaric hypoxia and curtail the development of HAIs. The understanding of these mechanisms is essential to optimize hypoxic acclimatization for efficient prophylaxis and treatment of HAIs. This review aims to link outcomes of molecular mechanisms to either adverse effects of acute high-altitude/hypoxia exposure or the developing tolerance with acclimatization. After summarizing systemic physiological responses to acute high-altitude exposure, the associated acclimatization, and the epidemiology and pathophysiology of various HAIs, the article focuses on molecular adjustments and maladjustments during acute exposure and acclimatization to high altitude/hypoxia. Pivotal modifying mechanisms include molecular responses orchestrated by transcription factors, most notably hypoxia inducible factors, and reciprocal effects on mitochondrial functions and REDOX homeostasis. In addition, discussed are genetic factors and the resultant proteomic profiles determining these hypoxia-modifying mechanisms culminating in successful high-altitude acclimatization. Lastly, the article discusses practical considerations related to the molecular aspects of acclimatization and altitude training strategies.

The deleterious impact of a non-synonymous SNP on protein structure and function is apparent in hypertension

Essential hypertension (EH) is a significant health issue around the globe. The indifferent therapy regimen suggests varied physiological functions due to the lifestyle and genetic presentations of an individual. The endothelial nitric oxide synthase (NOS3) gene is a crucial vascular system marker in EH that contributes significantly to the phenotype. Hence, the present study aimed to employ the candidate gene approach and investigate the association between NOS3 single nucleotide polymorphism (SNP) E298D (G894T/rs1799983) by applying several in silico tools and validation through human samples screening. We corroborated computational findings through a case-control study comprising 294 controls and 299 patients; the 894T allele emerged significantly as the risk allele (odds ratio=2.07; P=6.38E-05). The in silico analyses highlighted the significance of E298D on the native structure and function of NOS3. The dynamics simulation study revealed that the variant type 298D caused structural destabilization of the protein to alter its function. Plasma nitrite levels were reduced in patients (P=0.0002), and the same correlated with the 894T allele. Furthermore, correlations were apparent between clinical, genotype, and routine biochemical parameters. To conclude, the study demonstrated a perceptible association between the SNP E298D and NOS3 protein structure stability that appears to have a bearing on the enzyme's function with a deleterious role in EH.

Vascular homeostasis at high-altitude: role of genetic variants and transcription factors

High-altitude pulmonary edema occurs most frequently in non-acclimatized low landers on exposure to altitude ≥2500 m. High-altitude pulmonary edema is a complex condition that involves perturbation of signaling pathways in vasoconstrictors, vasodilators, anti-diuretics, and vascular growth factors. Genetic variations are instrumental in regulating these pathways and evidence is accumulating for a role of epigenetic modification in hypoxic responses. This review focuses on the crosstalk between high-altitude pulmonary edema-associated genetic variants and transcription factors, comparing high-altitude adapted and high-altitude pulmonary edema-afflicted subjects. This approach might ultimately yield biomarker information both to understand and to design therapies for high-altitude adaptation.

Structural and functional alterations of nitric oxide synthase 3 due to missense variants associate with high-altitude pulmonary edema through dynamic study

The human endothelial nitric oxide synthase (NOS3) is 28 Kbp at 7q36.1 and encodes protein comprising of 1280 amino acids. Being a major source of nitric oxide, the enzyme is crucial to the vascular homeostasis and thereby to be an important pharmaceutical target. We hence have been investigating this molecule in a high-altitude disorder namely, high-altitude pulmonary edema (HAPE). We performed a genome-wide association study (GWAS) in a case-control design of sojourners that included healthy controls and HAPE patients (n = 200) each. Four NOS3 missense SNPs i.e. rs1799983 (E298D), rs3918232 (V827M), rs3918201 (R885M) and rs3918234 (Q982L), were associated significantly with HAPE (P-value < 0.05). Furthermore, extensive in silico analyses were performed to predict the detrimental effect of the four variant types and their three most relevant co-factors namely, heme, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) that are accountable for amendment of protein stability leading to structural de-construction. Subsequently, we validated the findings in a larger sample size of the two study groups. HAPE patients had a higher frequency of the four variants and significantly decreased levels of circulating nitric oxide (NO) (P-value < 0.001). The in silico and human subjects findings complement each other. This study explored the impact of HAPE-associated NOS3 variants with its protein structure stability and holds promise to be current and future drug targets.Communicated by Ramaswamy H. Sarma.

A case-control study of the genetic polymorphism of IL6 and HAPE risk in a Chinese Han population

AIMS

The role of inflammatory cytokines in High-altitude pulmonary edema (HAPE) remains unclear. The purpose of this study was to evaluate the role of IL4 and IL6 gene polymorphism in the development of HAPE in Chinese people.

METHODS

In the present study, we screened ten polymorphisms of IL4 and IL6 gene in 265 HAPE and 303 healthy volunteers. Genotypes were determined using the Sequenom MassARRAY method. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by unconditional logistic regression.

RESULTS

Two single-nucleotide polymorphisms (SNPs) in the IL6 gene were significantly associated with HAPE. Rs1800796 and rs1524107 (G vs C, OR = 1.31, 95%CI = 1.01-1.69, P = .041 and T vs C, OR = 1.35, 95%CI = 1.05-1.74, P = .020, respectively). However, there did not found any association for IL4 gene.

CONCLUSION

Inflammatory cytokines may play a role in the progress of HAPE. These polymorphisms could be genetic markers for predicting the susceptibility to HAPE.

Evidence for and Against Genetic Predispositions to Acute and Chronic Altitude Illnesses

MacInnis, Martin J., and Michael S. Koehle. Evidence for and against genetic predispositions to acute and chronic altitude illnesses. High Alt Med Biol. 17:281-293, 2016.-Humans exhibit marked variation in their responses to hypoxia, with susceptibility to acute and chronic altitude illnesses being a prominent and medically important example. Many have hypothesized that genetic differences are the cause of these variable responses to hypoxia; however, until recently, these hypotheses were based primarily on small (and sometimes anecdotal) reports pertaining to apparent differences in altitude illness susceptibility between populations, the notion that a history of altitude illness is indicative of subsequent risk, the heritability of hypoxia-related traits, and candidate gene association studies. In the past 5 years, the use of genomic techniques has helped bolster the claim that susceptibility to some altitude illnesses is likely the result of genetic variation. For each of the major altitude illnesses, we summarize and evaluate the evidence stemming from three important characteristics of a genetic trait: (1) individual susceptibility and repeatability across assessments, (2) biogeographical differences and familial aggregation, and (3) association(s) with genetic variants. Evidence to support a genetic basis for susceptibilities to acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) is limited, owing partially to the subjective and unclear phenotype of AMS and the rarity and severity of HACE. In contrast, recent genomic studies have identified genes that influence susceptibility to high-altitude pulmonary edema, chronic mountain sickness, and high-altitude pulmonary hypertension. The collection of more individual, familial, and biogeographical susceptibility data should improve our understanding of the extent to which genetic variation contributes to altitude illness susceptibility, and genomic and molecular investigations have the potential to elucidate the mechanisms that underpin altitude illness susceptibility.

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.

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.

Lungs at high-altitude: genomic insights into hypoxic responses

Hypobaric hypoxia at high altitude (HA) results in reduced blood arterial oxygen saturation, perfusion of organs with hypoxemic blood, and direct hypoxia of lung tissues. The pulmonary complications in the cells of the pulmonary arterioles due to hypobaric hypoxia are the basis of the pathophysiological mechanisms of high-altitude pulmonary edema (HAPE). Some populations that have dwelled at HA for thousands of years have evolutionarily adapted to this environmental stress; unadapted populations may react with excessive physiological responses that impair health. Individual variations in response to hypoxia and the mechanisms of HA adaptation provide insight into physiological responses. Adaptive and maladaptive responses include alterations in pathways such as oxygen sensing, hypoxia signaling, K+- and Ca2+-gated channels, redox balance, and the renin-angiotensin-aldosterone system. Physiological imbalances are linked with genetic susceptibilities, and nonhomeostatic responses in gene regulation that occur by small RNAs, histone modification, and DNA methylation predispose susceptible humans to these HA illnesses. Elucidation of the interaction of these factors will lead to a more comprehensive understanding of HA adaptations and maladaptations and will lead to new therapeutics for HA disorders related to hypoxic lungs.

Genetic differences and aberrant methylation in the apelin system predict the risk of high-altitude pulmonary edema

Hypoxia-inducible factor stimulates the expression of apelin, a potent vasodilator, in response to reduced blood arterial oxygen saturation. However, aberrations in the apelin system impair pulmonary vascular function, potentially resulting in the development of high-altitude (HA)-related disorders. This study aimed to elucidate the genetic and epigenetic regulation of apelin, apelin receptor (APLNR), and endothelial nitric oxide synthase (NOS3) in HA adaptation and HA pulmonary edema (HAPE). A genome-wide association study and sequencing identified variants of apelin, APLNR, and NOS3 that were validated in a larger sample size of HAPE-patients (HAPE-p), HAPE-free controls (HAPE-f), and healthy highland natives (HLs). Apelin-13 and nitrite levels and apelin and NOS3 expression were down-regulated in HAPE-p (P < 0.001). Among the several studied polymorphisms, apelin rs3761581, rs2235312, and rs3115757; APLNR rs11544374 and rs2282623; and NOS3 4b/4a, rs1799983, and rs7830 were associated with HAPE (P < 0.03). The risk allele rs3761581G was associated with a 58.6% reduction in gene expression (P = 0.017), and the risk alleles rs3761581G and rs2235312T were associated with low levels of apelin-13 and nitrite (P < 0.05). The latter two levels decreased further when both of these risk alleles were present in the patients (P < 0.05). Methylation of the apelin CpG island was significantly higher in HAPE-p at 11.92% than in HAPE-f and HLs at ≤ 7.1% (P < 0.05). Moreover, the methylation effect was 9% stronger in the 5' UTR and was associated with decreased apelin expression and apelin-13 levels. The rs3761581 and rs2235312 polymorphisms and methylation of the CpG island influence the expression of apelin in HAPE.

High-altitude pulmonary edema

High-altitude pulmonary edema (HAPE), a not uncommon form of acute altitude illness, can occur within days of ascent above 2500 to 3000 m. Although life-threatening, it is avoidable by slow ascent to permit acclimatization or with drug prophylaxis. The critical pathophysiology is an excessive rise in pulmonary vascular resistance or hypoxic pulmonary vasoconstriction (HPV) leading to increased microvascular pressures. The resultant hydrostatic stress causes dynamic changes in the permeability of the alveolar capillary barrier and mechanical injurious damage leading to leakage of large proteins and erythrocytes into the alveolar space in the absence of inflammation. Bronchoalveolar lavage and hemodynamic pressure measurements in humans confirm that elevated capillary pressure induces a high-permeability noninflammatory lung edema. Reduced nitric oxide availability and increased endothelin in hypoxia are the major determinants of excessive HPV in HAPE-susceptible individuals. Other hypoxia-dependent differences in ventilatory control, sympathetic nervous system activation, endothelial function, and alveolar epithelial active fluid reabsorption likely contribute additionally to HAPE susceptibility. Recent studies strongly suggest nonuniform regional hypoxic arteriolar vasoconstriction as an explanation for how HPV occurring predominantly at the arteriolar level causes leakage. In areas of high blood flow due to lesser HPV, edema develops due to pressures that exceed the dynamic and structural capacity of the alveolar capillary barrier to maintain normal fluid balance. This article will review the pathophysiology of the vasculature, alveolar epithelium, innervation, immune response, and genetics of the lung at high altitude, as well as therapeutic and prophylactic strategies to reduce the morbidity and mortality of HAPE.

Polymorphisms of angiotensin converting enzyme and nitric oxide synthase 3 genes as risk factors of high-altitude pulmonary edema: a case-control study and meta-analysis

High-altitude pulmonary edema (HAPE) is a non-cardiogenic type of pulmonary edema developing altitudes > 2,500 m. Angiotensin converting enzyme (ACE) and nitric oxide synthase 3 (NOS3) play important roles in regulating pulmonary vascular tone. To assess associations between genetic variants in the ACE and NOS3 genes and HAPE risk, 27 HAPE patients and 108 matched controls were genotyped and analyzed. The indicated HAPE association of the NOS3 G894T (Glu298Asp) single nucleotide polymorphism (SNP), which may change NO production, was further evaluated by a meta-analysis of six studies involving 399 HAPE patients and 495 controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were determined with fixed-effects models. Stratification analyses of ethnicity and geographic location were performed. Significant associations were observed for the dominant model in two ACE tag SNPs influencing serum ACE concentrations (rs8066114 polymorphism: GG+CG vs. CC; rs4461142 polymorphism: TT+CT vs. CC). Furthermore, Single-locus analysis indicated significantly different distributions of G allele frequency between the cases (29.63%) and controls (17.13%) for the ACE rs8066114 polymorphism. The case-control distributions of genotype frequencies and T allele frequency of NOS3 G894T (Glu298Asp) polymorphism were significantly higher in the cases than controls, and the NOS3 G894T (Glu298Asp) SNP showed elevated HAPE risk under the dominant model (TT+GT vs. GG). Meta-analysis showed overall association of NOS3 G894T SNP with HAPE risk under the allele contrast and dominant genetic models, which remained significant for Asians. In conclusion, ACE rs8066114 and rs4461142 and NOS3 rs1799983 (G894T) polymorphisms may be associated with increased HAPE risk in Asians.

Interactions among vascular-tone modulators contribute to high altitude pulmonary edema and augmented vasoreactivity in highlanders

BACKGROUND

The interactions among various biomarkers remained unexplored under the stressful environment of high-altitude. Present study evaluated interactions among biomarkers to study susceptibility for high altitude pulmonary edema (HAPE) in HAPE-patients (HAPE-p) and adaptation in highland natives (HLs); both in comparison to HAPE-free sojourners (HAPE-f).

METHODOLOGY/PRINCIPAL FINDINGS

All the subjects were recruited at 3500 m. We measured clinical parameters, biochemical levels in plasma and gene expression using RNA from blood; analyzed various correlations between and among the clinical parameters, especially arterial oxygen saturation (SaO(2)) and mean arterial pressure (MAP) and biochemical parameters like, asymmetric dimethylarginine (ADMA), serotonin (5-HT), 8-iso-prostaglandin F2α (8-isoPGF2α), endothelin-1 (ET-1), plasma renin activity (PRA), plasma aldosterone concentration (PAC), superoxide dismutase (SOD) and nitric oxide (NO) in HAPE-p, HAPE-f and HLs. ADMA, 5-HT, 8-isoPGF2α, ET-1 levels, and PAC were significantly higher (p<0.0001, each), whereas SOD activity and NO level were significantly lower in HAPE-p than HAPE-f (p ≤ 0.001). Furthermore, ADMA, 5-HT, 8-isoPGF2α, NO levels and PAC were significantly higher (p<0.0001), whereas ET-1 level significantly (p<0.0001) and SOD activity non-significantly (p>0.05) lower in HLs than HAPE-f. The expression of respective genes differed in the three groups. In the correlations, SaO(2) inversely correlated with ADMA, 5-HT and 8-isoPGF2α and positively with SOD in HAPE-p (p≤0.009). MAP correlated positively with 5-HT and 8-isoPGF2α in HAPE-p and HLs (p ≤ 0.004). A strong positive correlation was observed between ADMA and 5-HT, 5-HT and 8-isoPGF2α (p≤0.001), whereas inverse correlation of SOD with ET-1 in HAPE-p and HLs (p ≤ 0.004), with 5-HT and 8-isoPGF2α in HAPE-p (p = 0.01) and with 5-HT in HLs (p = 0.05).

CONCLUSIONS/SIGNIFICANCE

The interactions among these markers confer enhanced vascular activity in HLs and HAPE in sojourners.

Nitric oxide in adaptation to altitude

This review summarizes published information on the levels of nitric oxide gas (NO) in the lungs and NO-derived liquid-phase molecules in the acclimatization of visitors newly arrived at altitudes of 2500 m or more and adaptation of populations whose ancestors arrived thousands of years ago. Studies of acutely exposed visitors to high altitude focus on the first 24-48 h with just a few extending to days or weeks. Among healthy visitors, NO levels in the lung, plasma, and/or red blood cells fell within 2h, but then returned toward baseline or slightly higher by 48 h and increased above baseline by 5 days. Among visitors ill with high-altitude pulmonary edema at the time of the study or in the past, NO levels were lower than those of their healthy counterparts. As for highland populations, Tibetans had NO levels in the lung, plasma, and red blood cells that were at least double and in some cases orders of magnitude greater than other populations regardless of altitude. Red blood cell-associated nitrogen oxides were more than 200 times higher. Other highland populations had generally higher levels although not to the degree shown by Tibetans. Overall, responses of those acclimatized and those presumed to be adapted are in the same direction, although the Tibetans have much larger responses. Missing are long-term data on lowlanders at altitude showing how similar they become to the Tibetan phenotype. Also missing are data on Tibetans at low altitude to see the extent to which their phenotype is a response to the immediate environment or expressed constitutively. The mechanisms causing the visitors' and the Tibetans' high levels of NO and NO-derived molecules at altitude remain unknown. Limited data suggest processes including hypoxic upregulation of NO synthase gene expression, hemoglobin-NO reactions, and genetic variation. Gains in understanding will require integrating appropriate methods and measurement techniques with indicators of adaptive function under hypoxic stress.

Evidence for a genetic basis for altitude illness: 2010 update

Altitude illness refers to a group of environmentally mediated pathophysiologies. Many people will suffer acute mountain sickness shortly after rapidly ascending to a moderately hypoxic environment, and an unfortunate few will develop potentially fatal conditions such as high altitude pulmonary edema or high altitude cerebral edema. Some individuals seem to be predisposed to developing altitude illness, suggesting an innate contribution to susceptibility. The implication that there are altitude-sensitive and altitude-tolerant individuals has stimulated much research into the contribution of a genetic background to the efficacy of altitude acclimatization. Although the effect of altitude attained and rate of ascent on the etiology of altitude illness is well known, there are only tantalizing, but rapidly accumulating, clues to the genes that may be involved. In 2006, we reviewed what was then known about the genetics of altitude illness. This article updates that review and attempts to tabulate all the available genetic data pertaining to these conditions. To date, 58 genes have been investigated for a role in altitude illness. Of these, 17 have shown some association with the susceptibility to, or the severity of, these conditions, although in many cases the effect size is small or variable. Caution is recommended when evaluating the genes for which no association was detected, because a number of the investigations reviewed in this article were insufficiently powered to detect small effects. No study has demonstrated a clear-cut altitude illness gene, but the accumulating data are consistent with a polygenic condition with a strong environmental component. The genes that have shown an association affect a variety of biological pathways, suggesting that either multiple systems are involved in altitude pathophysiology or that gene-gene interactions play a role. Although numerous studies have been performed to investigate specific genes, few have looked for evidence of heritability or familial transmission, or for epidemiological patterns that would be consistent with genetically influenced conditions. Future trends, such as genome-wide association studies and epigenetic analysis, should lead to enhanced understanding of the complex interactions within the genome and between the genome and hypoxic environments that contribute to an individual's capacity to acclimatize rapidly and effectively to altitude.

Endothelial nitric oxide synthase gene polymorphisms associated with susceptibility to high altitude pulmonary edema in Chinese railway construction workers at Qinghai-Tibet over 4 500 meters above sea level

OBJECTIVE

To examine whether the polymorphisms of endothelial nitric oxide synthase (eNOS) gene are associated with the susceptibility to high altitude pulmonary edema (HAPE) in Chinese railway construction workers at Qinghai-Tibet where the altitude is over 4 500 m above sea level.

METHODS

A case-control study was conducted including 149 HAPE patients in the construction workers and 160 healthy controls randomly recruited from their co-workers, matching the patients in ethnicity, age, sex, lifestyle, and working conditions. Three polymorphisms of eNOS gene, T-786C in promoter, 894G/T in exon 7, and 27bp variable number tandem repeat (VNTR) in intron 4, were genotyped using polymerase chain reaction (PCR) and confirmed with DNA sequencing.

RESULTS

The frequencies of 894T allele and heterozygous G/T of the 894G/T variant were significantly higher in HAPE patients group than in the control group (P=0.0028 and P=0.0047, respectively). However, the frequencies of the T-786C in promoter and the 27bp VNTR in intron 4 were not significantly different between the two groups. Haplotypic analysis revealed that the frequencies of two haplotypes (H3,T-T-b, b indicates 5 repeats of 27 bp VNTR; H6, C-G-a, a indicates 4 repeats of 27 bp VNTR) were significantly higher in HAPE patients (both Pü0.0001). On the contrary, the frequencies of H1 (T-G-b) and H2 (T-G-a) were lower in HAPE patients than in healthy controls (both Pü0.001).

CONCLUSIONS

Two haplotypes (T-T-b and C-G-a) may be strongly associated with susceptibility to HAPE. Compared with the individual alleles of eNOS gene, the interaction of multiple genetic markers within a haplotype may be a major determinant for the susceptibility to HAPE.

Polymorphisms of renin-angiotensin system genes as a risk factor for high-altitude pulmonary oedema

The genes of the renin—angiotensin system (RAS) play an important role in the regulation of pulmonary vascular tone. Although studies on individual genes polymorphisms have reported association with high-altitude pulmonary oedema (HAPE), studies on multiple genes or epistasis are lacking. We therefore investigated the association of the RAS polymorphisms with HAPE. In a case-control design, we screened 163 HAPE-resistant/controls (HAPE-r) and 160 HAPEpatients (HAPE-p) of Indian origin for eight polymorphisms of four RAS genes, ACE, AGT, AGTR1 and AGTR2. Significant difference in genotype and allele frequencies of the ACE I/D and AGT M235T polymorphisms was observed between HAPE-p and HAPE-r ( p < 0.05). In three-locus haplotype analysis of AGT the haplotype GTM was significantly higher in HAPE-p (29%) and haplotype GTT in HAPE-r (27%) after Bonferroni correction ( p < 0.006). The differences were insignificant for polymorphisms from AGTR1 and AGTR2. The MDR (multifactor dimensional reduction) approach for gene—gene interaction depicted individual polymorphism M235T as the best disease predicting model (cross validation consistency, CVC = 10/10). We found a significant association of D allele of ACE and M allele of AGT with HAPE. The findings are supported at the haplotypic level as well as through nested genetic interaction between the RAS gene polymorphisms using the MDR approach.

High-Altitude Pulmonary Edema

High-altitude pulmonary edema (HAPE) is an uncommon form of pulmonary edema that occurs in healthy individuals within a few days of arrival at altitudes above 2,500–3,000 m. The crucial pathophysiology is an excessive hypoxia-mediated rise in pulmonary vascular resistance (PVR) or hypoxic pulmonary vasoconstriction (HPV) leading to increased microvascular hydrostatic pressures despite normal left atrial pressure. The resultant hydrostatic stress can cause both dynamic changes in the permeability of the alveolar capillary barrier and mechanical damage leading to leakage of large proteins and erythrocytes into the alveolar space in the absence of inflammation. Bronchoalveolar lavage (BAL) and pulmonary artery (PA) and microvascular pressure measurements in humans confirm that high capillary pressure induces a high-permeability non-inflammatory-type lung edema; a concept termed “capillary stress failure.” Measurements of endothelin and nitric oxide (NO) in exhaled air, NO metabolites in BAL fluid, and NO-dependent endothelial function in the systemic circulation all point to reduced NO availability and increased endothelin in hypoxia as a major cause of the excessive hypoxic PA pressure rise in HAPE-susceptible individuals. Other hypoxia-dependent differences in ventilatory control, sympathetic nervous system activation, endothelial function, and alveolar epithelial sodium and water reabsorption likely contribute additionally to the phenotype of HAPE susceptibility. Recent studies using magnetic resonance imaging in humans strongly suggest nonuniform regional hypoxic arteriolar vasoconstriction as an explanation for how HPV occurring predominantly at the arteriolar level can cause leakage. This compelling but not yet fully proven mechanism predicts that in areas of high blood flow due to lesser vasoconstriction edema will develop owing to pressures that exceed the structural and dynamic capacity of the alveolar capillary barrier to maintain normal alveolar fluid balance. Numerous strategies aimed at lowering HPV and possibly enhancing active alveolar fluid reabsorption are effective in preventing and treating HAPE. Much has been learned about HAPE in the past four decades such that what was once a mysterious alpine malady is now a well-characterized and preventable lung disease. This chapter will relate the history, pathophysiology, and treatment of HAPE, using it not only to illuminate the condition, but also for the broader lessons it offers in understanding pulmonary vascular regulation and lung fluid balance.

EGLN1 involvement in high-altitude adaptation revealed through genetic analysis of extreme constitution types defined in Ayurveda

It is being realized that identification of subgroups within normal controls corresponding to contrasting disease susceptibility is likely to lead to more effective predictive marker discovery. We have previously used the Ayurvedic concept of Prakriti, which relates to phenotypic differences in normal individuals, including response to external environment as well as susceptibility to diseases, to explore molecular differences between three contrasting Prakriti types: Vata, Pitta, and Kapha. EGLN1 was one among 251 differentially expressed genes between the Prakriti types. In the present study, we report a link between high-altitude adaptation and common variations rs479200 (C/T) and rs480902 (T/C) in the EGLN1 gene. Furthermore, the TT genotype of rs479200, which was more frequent in Kapha types and correlated with higher expression of EGLN1, was associated with patients suffering from high-altitude pulmonary edema, whereas it was present at a significantly lower frequency in Pitta and nearly absent in natives of high altitude. Analysis of Human Genome Diversity Panel-Centre d'Etude du Polymorphisme Humain (HGDP-CEPH) and Indian Genome Variation Consortium panels showed that disparate genetic lineages at high altitudes share the same ancestral allele (T) of rs480902 that is overrepresented in Pitta and positively correlated with altitude globally (P < 0.001), including in India. Thus, EGLN1 polymorphisms are associated with high-altitude adaptation, and a genotype rare in highlanders but overrepresented in a subgroup of normal lowlanders discernable by Ayurveda may confer increased risk for high-altitude pulmonary edema.

High-altitude disorders: pulmonary hypertension: pulmonary vascular disease: the global perspective

Globally, it is estimated that > 140 million people live at a high altitude (HA), defined as > 2,500 m (8,200 ft), and that countless others sojourn to the mountains for work, travel, and sport. The distribution of exposure to HA is worldwide, including 35 million in the Andes and > 80 million in Asia, including China and central Asia. HA stress primarily is due to the hypoxia of low atmospheric pressure, but dry air, intense solar radiation, extreme cold, and exercise contribute to acute and chronic disorders. The acute disorders are acute mountain sickness (also known as soroche), HA cerebral edema, and HA pulmonary edema (HAPE). Of these, HAPE is highly correlated with acute pulmonary hypertension. The first chronic syndrome described in HA dwellers in Peru was chronic mountain sickness (Monge disease), which has a large component of relative hypoventilation and secondary erythrocytosis. The prevalence of chronic mountain sickness in HA dwellers ranges from 1.2% in native Tibetans to 5.6% in Chinese Han; 6% to 8% in male residents of La Paz, Bolivia; and 15.6% in the Andes. Subacute mountain sickness is an exaggerated pulmonary hypertensive response to HA hypoxia occurring over months, most often in infants and very young children. Chronic pulmonary hypertension with heart failure but without hypoventilation is seen in Asia. Not only does HA pulmonary hypertension exact health consequences for the millions affected, but also the mechanisms of disease relate to pulmonary hypertension associated with multiple other disorders. Genetic understanding of these disorders is in its infancy.

Pulmonary-artery pressure and exhaled nitric oxide in Bolivian and Caucasian high altitude dwellers

There is evidence that high altitude populations may be better protected from hypoxic pulmonary hypertension than low altitude natives, but the underlying mechanism is incompletely understood. In Tibetans, increased pulmonary respiratory NO synthesis attenuates hypoxic pulmonary hypertension. It has been speculated that this mechanism may represent a generalized high altitude adaptation pattern, but direct evidence for this speculation is lacking. We therefore measured systolic pulmonary-artery pressure (Doppler chocardiography) and exhaled nitric oxide (NO) in 34 healthy, middle-aged Bolivian high altitude natives and in 34 age- and sex-matched, well-acclimatized Caucasian low altitude natives living at high altitude (3600 m). The mean+/-SD systolic right ventricular to right atrial pressure gradient (24.3+/-5.9 vs. 24.7+/-4.9 mmHg) and exhaled NO (19.2+/-7.2 vs. 22.5+/-9.5 ppb) were similar in Bolivians and Caucasians. There was no relationship between pulmonary-artery pressure and respiratory NO in the two groups. These findings provide no evidence that Bolivian high altitude natives are better protected from hypoxic pulmonary hypertension than Caucasian low altitude natives and suggest that attenuation of pulmonary hypertension by increased respiratory NO synthesis may not represent a universal adaptation pattern in highaltitude populations.

The genetic aspects of pre-eclampsia: achievements and limitations

Pre-eclampsia, a life-threatening disease during pregnancy, is a leading cause of global maternal mortality. Although there is substantial evidence of a genetic background, the complexity of the processes involved and nature of the maternal-fetal phenomenon do not make the search for the causative genes easy. Recent retrospective studies on the subject suggest the heritable allelic variations, particularly the utero-placental renin-angiotensin system with defective placental vascular development, could become the cornerstone for the genetics of pre-eclampsia and hence might well be associated with such defective development. Moreover, the role of immune mechanisms (immune maladaptation) deserves not to be ignored. Large-scale studies entailing genomewide scanning, sib-pair linkage analysis, and family-based association studies with appropriate power to detect genes with a lower relative risk are necessary to understand the puzzle of the disease. Moreover, recently, the importance of epigenetic features and the effect of imprinted genes related to trophoblast growth as well as fetal development on hypertension in pregnancy have been highlighted. All these possibilities are intuitively attractive and are supported by some circumstantial evidence. Although the consistent tenor of a series of papers instill some confidence, we need meticulously designed larger-scale investigations including large numbers of affected women and their babies to provide the analytic stringency essential to study the polygenic multifactorial basis of pre-eclampsia.

Pathogenesis of pulmonary edema: learning from high-altitude pulmonary edema

Pulmonary edema is a problem of major clinical importance resulting from a persistent imbalance between forces that drive water into the airspace of the lung and the biological mechanisms for its removal. Here, we will review the fundamental mechanisms implicated in the regulation of alveolar fluid homeostasis. We will then describe the perturbations of pulmonary fluid homeostasis implicated in the pathogenesis of pulmonary edema in conditions associated with increased pulmonary capillary pressure, namely cardiogenic pulmonary edema and high-altitude pulmonary edema (HAPE), with particular emphasis on the latter that has provided important new insight into underlying mechanisms of pulmonary edema. We will provide evidence that impaired pulmonary endothelial and epithelial nitric oxide synthesis and/or bioavailability may represent a central underlying defect predisposing to exaggerated hypoxic pulmonary vasoconstriction, and, in turn, capillary stress failure and alveolar fluid flooding. We will then demonstrate that exaggerated pulmonary hypertension, while possibly a prerequisite, may not always be sufficient to cause HAPE, and how defective alveolar fluid clearance may represent a second important pathogenic mechanism. Finally, we will outline, how this new insight gained from studies in HAPE, may be translated into the management of pulmonary edema and hypoxemia related disease states in general.

Evidence for a genetic basis for altitude-related illness

Altitude-related illnesses are a family of interrelated pulmonary, cerebral, hematological, and cardiovascular medical conditions associated with the diminished oxygen availability at moderate to high altitudes. The acute forms of these debilitating and potentially fatal conditions, which include acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE), often develop in incompletely acclimatized lowlanders shortly after ascent, whereas, the chronic conditions, such as chronic mountain sickness (CMS) and high altitude pulmonary hypertension (HAPH), usually afflict native or long-term highlanders and may reflect a loss of adaptation. Anecdotal reports of particularly susceptible people or families are frequently cited as evidence that certain individuals have an innate susceptibility (or resistance) to developing these conditions and, in recent decades, there have been a number of studies designed to characterize the physiology of individuals predisposed to these conditions, as well as to identify the specific genetic variants that contribute to this predisposition. This paper reviews the epidemiological evidence for a genetic component to the various forms of altitude-related illness, such as innate susceptibility, familial clustering, and patterns of population susceptibility, as well as the molecular evidence for specific genetic risk factors. While the evidence supports some role for genetic background in the etiology of altitude-related illness, limitations in individual studies and a general lack of corroborating research limit the conclusions that can be drawn about the extent of this contribution and the specific genes or pathways involved. The paper closes with suggestions for future work that could support and expand on previous studies, as well as provide new insights.

Heterozygotes of NOS3 Polymorphisms Contribute to Reduced Nitrogen Oxides in High-Altitude Pulmonary Edema

STUDY OBJECTIVES

High-altitude pulmonary edema (HAPE), which develops on exertion under hypoxic conditions, aggravates due to endothelial dysfunction. Repeat events of the disorder suggests of genetic susceptibility. Endothelial nitric oxide synthase gene (NOS3), a regulator of vasodilation, has emerged as a strong candidate marker. In the present study, we investigated G894T, 27-base-pair 4b/4a (variable number of tandem repeat), -922A/G, and -786T/C polymorphisms of NOS3, individually or in combination, for an association with HAPE.

DESIGN

A cross-sectional case control study.

SETTINGS

Blood samples of HAPE-resistant lowlanders (HAPE-r) were obtained at sea level, and blood samples of patients with HAPE (HAPE-p) were obtained at Sonam Norboo Memorial Hospital, Leh, at 3,500 m.

PARTICIPANTS

The study groups consisted of 60 HAPE-r inducted two to three times to altitudes > 3,600 m; and 72 HAPE-p, who had HAPE on their first visit to high altitude.

RESULTS

Nitrogen oxides (NOx) at 77.9 +/- 28.6 micromol/L were significantly elevated in HAPE-r as compared to 42.39 +/- 12.93 micromol/L in HAPE-p (p < 0.0001). Genotype distribution of G894T and 4b/4a polymorphisms was significantly different in the two groups (p = 0.001 and 0.009, respectively). Haplotype analysis revealed -922A/G and -786T/C polymorphisms in complete linkage disequilibrium. The wild-type haplotypes G-b (G894T, 4b/4a), G-A (G894T, -922A/G), and G-b-A (G894T, 4b/4a, -922A/G) were significantly overrepresented in HAPE-r (p < 0.0001, p = 0.03, and p = 0.02, respectively). The heterozygote genotype combination GTba as compared to wild-type combination GGbb was significantly higher in HAPE-p (chi2 = 18.62, p = 0.00009; odds ratio, 7.20; 95% confidence interval, 2.82 to 18.38). The combination of four heterozygotes GTbaAGTC was overrepresented in HAPE-p (p = 0.04), whereas the wild-type genotype combination GGbbAATT was overrepresented in HAPE-r (p = 0.002). Furthermore, the GGbb combination correlated with significantly elevated NOx as compared to remaining combinations as a whole in both HAPE-r and HAPE-p (p = 0.01 and 0.004, respectively).

CONCLUSIONS

Reduced NOx and combination of heterozygotes associate with the susceptibility to HAPE. The study impels another step toward application of NOx as a diagnostic marker for HAPE. The NOS3 GTba and GTbaAGTC genotype combinations may find application as genetic markers for predicting the risk for HAPE.

Predominance of interaction among wild-type alleles of CYP11B2 in Himalayan natives associates with high-altitude adaptation

Sojourners visiting high-altitude (HA) (>2500 m) are susceptible to HA disorders; on the contrary, HA natives are well adapted to the extreme hypoxic environment. High aldosterone levels are believed to be involved in HA disorders, we, therefore, envisaged role of CYP11B2 gene variants in HA adaptation and therefore investigated the -344T/C, intron-2 conversion (Iw/Ic), K173R, and A5160C polymorphisms. In addition, polymorphisms in AGT, AT1R, ATP1A1, ADRB2, and GSTP1 genes were also investigated. The study comprised of 662 subjects, comprising of 426 Himalayan highlanders (HLs) and 236 lowlanders (LLs). The -344T/C and K173R polymorphisms were found to be in complete linkage disequilibrium. The wild-type allele -344T and combination of wild-type homozygous genotypes between -344T/C, Iw/Ic, and A5160C polymorphisms, containing all the six wild-type alleles were over-represented in the HLs (p < 0.0001, and p = 0.008, respectively). The wild-type haplotypes -344T-Iw, -344T-5160A, and -344T-Iw-5160A also showed over-representation in the HLs (p < 0.0001). Furthermore, greater the number of wild-type alleles, lower was the ARR (p < 0.05). The genotype distribution in remaining genes did not differ. To conclude, the over-representation of wild-type -344T allele, genotype combinations and haplotypes of CYP11B2, and their correlation with lower aldosterone levels associate with HA adaptation in the HLs. Such an allelic presentation in sojourners may help them cope with adverse HA environment.

Endothelin-1 gene variants and levels associate with adaptation to hypobaric hypoxia in high-altitude natives

High-altitude natives are adapted to hypobaric hypoxia, suggestive of genetic basis of adaptation. Since endothelin-1 (ET-1) is of prime importance in high-altitude disorders in sojourners, we envisaged the role of allelic variants of ET-1 in high-altitude adaptation. Four ET-1 polymorphisms, viz., (CT)(n)-(CA)(n) repeat, -3A/-4A, G2288T, and Lys198Asn, were investigated in 426 highlanders (HLs) and 236 lowlanders (LLs). The plasma ET-1 levels, SBP and BMI were significantly lower in the HLs than those in LLs (p<0.0001). The Longer-repeats (31-45), G allele, Longer-repeats/GG, and Longer-repeats/Lys198Lys combinations were overrepresented in the HLs (p<0.0001, p=0.03, p<0.0001, and p<0.0001, respectively). The Longer-repeats, -3A/-3A, GG and Lys198Lys genotypes associated with significantly lower ET-1 levels in the HLs (p<0.0001, p=0.001, p<0.0001, and p<0.0001, respectively). Combinations of Longer-repeats with -3A/-3A, GG, and Lys198Lys genotypes, and -3A/-3A/Lys198Lys combination revealed association with lower ET-1 levels in the HLs (p<0.001). The study reports over-representation of Longer-repeats, G allele, and wild-type genotype combinations in high-altitude natives. Interaction between these alleles and association with lower ET-1 levels strengthen their association with high-altitude adaptation. Presence of such alleles in sojourners may help in acclimatization.

Pulmonary hypertension in high-altitude dwellers: novel mechanisms, unsuspected predisposing factors

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 states in general. Over the past decade, studies involving short-term hypoxic exposure have greatly advanced our knowledge regarding underlying mechanisms and predisposing events of hypoxic pulmonary hypertension. Studies in high altitude pulmonary edema (HAPE)-prone subjects, a condition characterized by exaggerated hypoxic pulmonary hypertension, have provided evidence for the central role of pulmonary vascular endothelial and respiratory epithelial nitric oxide (NO) for pulmonary artery pressure homeostasis. More recently, it has been shown that pathological events during the perinatal period (possibly by impairing pulmonary NO synthesis), predispose to exaggerated hypoxic pulmonary hypertension later in life. In an attempt to translate some of this new knowledge to the understanding of underlying mechanisms and predisposing events of chronic hypoxic pulmonary hypertension, we have recently initiated a series of studies among high-risk subpopulations (experiments of nature) of high-altitude dwellers. These studies have allowed to identify novel risk factors and underlying mechanisms that may predispose to sustained hypoxic pulmonary hypertension. The aim of this article is to briefly review this new data, and demonstrate that insufficient NO synthesis/bioavailability, possibly related in part to augmented oxidative stress, may represent an important underlying mechanism predisposing to pulmonary hypertension in high-altitude dwellers.

Effect of aging on blood pressure in Leh, Ladakh, a high-altitude (3524 m) community, by comparison with a Japanese town

The effect of aging on blood pressure (BP) and heart rate (HR) was investigated in a cross-sectional study in the high-altitude community of Leh, Ladakh (altitude: 3524 m) and a Japanese community in U town, Hokkaido (altitude: 25 m). BP and HR were obtained in a sitting position from 332 subjects 13-81 years of age in Ladakh, and from 216 Japanese citizens, 24-79 years of age. Measurements were taken after a 2-min rest, using a semi-automated BP device (UA-767 PC, A and D Co. LTD, Tokyo). High-altitude people showed higher diastolic BP and HR values than lowland people (83.2 vs. 76.9 mmHg and 78.6 vs. 69.2 bpm, P < 0.001), but no difference in systolic BP. Highland people also showed a steeper BP increase with age than the lowland people (systolic BP: 0.7476 vs. 0.3179 mmHg/year, P < 0.0005; diastolic BP: 0.3196 vs. 0.0750 mmHg/year, P < 0.001). This chronoecologic investigation in Ladakh examined the circulation as a physiological system at high-altitude. Our data indicate the need for a more comprehensive cardiovascular assessment for a better diagnosis and a more fruitful treatment. Longitudinal observations of effects of socio-ecologic factors on the cardiovascular system should help prevent strokes and other cardiovascular events, especially at high altitude.

The Indian Genome Variation database (IGVdb): a project overview. Hum Genet. 2005;118:1-11. [PMID: 16133172 DOI: 10.1007/s00439-005-0009-9]

Indian population, comprising of more than a billion people, consists of 4693 communities with several thousands of endogamous groups, 325 functioning languages and 25 scripts. To address the questions related to ethnic diversity, migrations, founder populations, predisposition to complex disorders or pharmacogenomics, one needs to understand the diversity and relatedness at the genetic level in such a diverse population. In this backdrop, six constituent laboratories of the Council of Scientific and Industrial Research (CSIR), with funding from the Government of India, initiated a network program on predictive medicine using repeats and single nucleotide polymorphisms. The Indian Genome Variation (IGV) consortium aims to provide data on validated SNPs and repeats, both novel and reported, along with gene duplications, in over a thousand genes, in 15,000 individuals drawn from Indian subpopulations. These genes have been selected on the basis of their relevance as functional and positional candidates in many common diseases including genes relevant to pharmacogenomics. This is the first large-scale comprehensive study of the structure of the Indian population with wide-reaching implications. A comprehensive platform for Indian Genome Variation (IGV) data management, analysis and creation of IGVdb portal has also been developed. The samples are being collected following ethical guidelines of Indian Council of Medical Research (ICMR) and Department of Biotechnology (DBT), India. This paper reveals the structure of the IGV project highlighting its various aspects like genesis, objectives, strategies for selection of genes, identification of the Indian subpopulations, collection of samples and discovery and validation of genetic markers, data analysis and monitoring as well as the project's data release policy.