Plasma vascular endothelial growth factor in acute mountain sickness

The role of hypoxia related hormones responses in acute mountain sickness susceptibility individuals unaccustomed to high altitude

Acute mountain sickness (AMS) is caused by rapid ascent to altitude (>2500 m) and remains a poorly understood pathophysiological condition. Accordingly, we investigated the relationship between acute exposure to high altitude and hypoxia related biochemical proteins. 21 healthy subjects (Female (8) and male (13), Age: 36.7±8.5, BMI: 23.2±3.1) volunteers participated in this project and fasting blood samples were taken before (sea level) and after 1 and 24-h exposure to high altitude (3,550 m). Blood oxygen saturation (SpO2), AMS status (Lake Louise Score) and serum HIF-1, Endothelin-1, VEGF and Orexin-A were measured (via ELISA) at 1, 6 and 24 h after exposure to high altitude. Pre-ascent measurement of hypoxia related proteins (Orexin-A, HIF-1, VEGF and Endothelin-1) where all significantly (<0.05) higher in the AMS-resistant individuals (No-AMS) when compared to AMS susceptible individuals (AMS+). Upon ascent to high altitude, 11 out of 21 volunteers had AMS (10.1±0.6 in AMS+ vs. 0.9±0.6 in No-AMS, P<0.05) and presented with lower resting SpO2 levels (77.7±0.4 vs. 83.5±0.3 respectively, p<0.05). Orexin-A, HIF-1, VEGF and Endothelin-1, significantly increased 24 hrs after exposure to high altitude in both AMS+ and No-AMS. The response of Orexin-A was similar between two groups, also, HIF-1 elevation 24 hrs after exposure to altitude was more in AMS+ (13% vs. 19%), but the increase of VEGF and Endothelin-1, 1 and 24 hrs after exposure to altitude in No-AMS was double that of AMS+. Hypoxia related proteins include Orexin-A, HIF-1, VEGF and Endothelin-1 may play a pathophysiological role in those who are susceptible to AMS.

Serum vascular endothelial growth factor is a potential biomarker for acute mountain sickness

Background: Acute mountain sickness (AMS) is the most common disease caused by hypobaric hypoxia (HH) in high-altitude (HA) associated with high mortality when progressing to high-altitude pulmonary edema (HAPE) and/or high-altitude cerebral edema (HACE). There is evidence for a role of pro- and anti-inflammatory cytokines in development of AMS, but biological pathways and molecular mechanisms underlying AMS remain elusive. We aimed to measure changes in blood cytokine levels and their possible association with the development of AMS.

Method: 15 healthy mountaineers were included into this prospective clinical trial. All participants underwent baseline normoxic testing with venous EDTA blood sampling at the Bangor University in United Kingdom (69 m). The participants started from Beni at an altitude of 869 m and trekked same routes in four groups the Dhaulagiri circuit in the Nepali Himalaya. Trekking a 14-day route, the mountaineers reached the final HA of 5,050 m at the Hidden Valley Base Camp (HVBC). Venous EDTA blood sampling was performed after active ascent to HA the following morning after arrival at 5,050 m (HVBC). A panel of 21 cytokines, chemokines and growth factors were assessed using Luminex system (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p40, IL-1ra, sIL-2Rα, IFN-γ, TNF-α, MCP-1, MIP-1α, MIP-1β, IP-10, G-CSF, GM-CSF, EGF, FGF-2, VEGF, and TGF-β1).

Results: There was a significant main effect for the gradual ascent from sea-level (SL) to HA on nearly all cytokines. Serum levels for TNF-α, sIL-2Rα, G-CSF, VEGF, EGF, TGF-β1, IL-8, MCP-1, MIP-1β, and IP-10 were significantly increased at HA compared to SL, whereas levels for IFN-γ and MIP-1α were significantly decreased. Serum VEGF was higher in AMS susceptible versus AMS resistant subjects (p &lt; 0.027, main effect of AMS) and increased after ascent to HA in both AMS groups (p &lt; 0.011, main effect of HA). Serum VEGF increased more from SL values in the AMS susceptible group than in the AMS resistant group (p &lt; 0.049, interaction effect).

Conclusion: Cytokine concentrations are significantly altered in HA. Within short interval after ascent, cytokine concentrations in HH normalize to values at SL. VEGF is significantly increased in mountaineers suffering from AMS, indicating its potential role as a biomarker for AMS.

Temporal changes in biomarkers in individuals with and without acute mountain sickness following rapid ascent

BACKGROUND

Field studies have reported conflicting results regarding changes in biomarkers at high altitude. This study measured temporal changes in biomarkers and compared the differences between individuals with and without acute mountain sickness (AMS).

MATERIALS AND METHODS

This study included 34 nonacclimatized healthy participants. Ten-milliliters of blood were collected at four time points: 3 days before ascent (T0), on two successive nights at 3150 m (T1 and T2), and 2 days after descent (T3). Participants were transported by bus from 555 m to 3150 m within 3 hours. AMS was diagnosed using the self-reported Lake Louise Scoring (LLS) questionnaire.

RESULTS

Compared with T0, significant increases in E-selectin and decreases in vascular endothelial growth factor (VEGF) levels were observed at high altitude. Significantly increased C-reactive protein (CRP), monocyte chemoattractant protein-1 (MCP-1), and S100 calcium-binding protein B (S100B) levels were observed at T2, and significantly decreased vascular cell adhesion molecule-1 (VCAM-1) levels were observed at T3. Eighteen (53%) participants developed AMS. Changes in E-selectin, CRP, MCP-1, and S100B levels were independent of AMS. Relative to individuals without AMS, those with AMS had significantly higher atrial natriuretic peptide (ANP) and VCAM-1 levels and lower plasminogen activator inhibitor-1 (PAI-1) levels at T1 and higher brain natriuretic peptide and lower VEGF and PAI-1 levels at T3. LLSs were positively correlated with ANP and VCAM-1 levels and negatively correlated with PAI-1 levels measured at T1.

CONCLUSIONS

After acute ascent, individuals with and without AMS exhibited different trends in biomarkers associated with endothelial cell activation and natriuretic peptides.

Acute Mountain Sickness Following Incremental Trekking to High Altitude: Correlation With Plasma Vascular Endothelial Growth Factor Levels and the Possible Effects of Dexamethasone and Acclimatization Following Re-exposure

Purpose: The recognition and treatment of high-altitude illness (HAI) is increasingly important in global emergency medicine. High altitude related hypobaric hypoxia can lead to acute mountain sickness (AMS), which may relate to increased expression of vascular endothelial growth factor (VEGF), and subsequent blood-brain barrier (BBB) compromise. This study aimed to establish the relationship between AMS and changes in plasma VEGF levels during a high-altitude ascent. VEGF level changes with dexamethasone, a commonly used AMS medication, may provide additional insight into AMS.

Methods: Twelve healthy volunteers ascended Mt Fuji (3,700 m) and blood samples were obtained at distinct altitudes for VEGF analysis. Oxygen saturation (SPO2) measurements were also documented at the same time-point. Six out of the 12 study participants were prescribed dexamethasone for a second ascent performed 48 h later, and blood was again collected to establish VEGF levels.

Results: Four key VEGF observations could be made based on the data collected: (i) the baseline VEGF levels between the two ascents trended upwards; (ii) those deemed to have AMS in the first ascent had increased VEGF levels (23.8–30.3 pg/ml), which decreased otherwise (23.8–30.3 pg/ml); (iii) first ascent AMS participants had higher VEGF level variability for the second ascent, and similar to those not treated with dexamethasone; and (iv) for the second ascent dexamethasone participants had similar VEGF levels to non-AMS first ascent participants, and the variability was lower than for first ascent AMS and non-dexamethasone participants. SPO2 changes were unremarkable, other than reducing by around 5% irrespective of whether measurement was taken for the first or second ascent.

Conclusion: First ascent findings suggest a hallmark of AMS could be elevated VEGF levels. The lack of an exercise-induced VEGF level change strengthened the notion that elevated plasma VEGF was brain-derived, and related to AMS.

Primer for Mainstreaming Mind-Body Techniques for Extreme Climates-Insights and Future Directions

Background: The deprivation of oxygen reaching the tissues (also termed as hypoxia) affects the normal functioning of the body. This results in development of many diseases like ischemia, glaucoma, MCI (Mild Cognitive Impairment), pulmonary and cerebral edema, stress and depression. There are no effective drugs that can treat such diseases. Despite such failure, alternative interventions such as mind-body techniques (MBTs) have not been adequately investigated. Methods: The first part of this review has been focused on philosophical aspects of various MBTs besides evolving an ayurgenomic perspective. The potential of MBTs as a preventive non-pharmacological intervention in the treatment of various general and hypoxic pathologies has been further described in this section. In the second part, molecular, physiological, and neuroprotective roles of MBTs in normal and hypoxic/ischemic conditions has been discussed. Results: In this respect, the importance of and in vivo studies has also been discussed. Conclusions: Although several studies have investigated the role of protective strategies in coping with the hypoxic environment, the efficacy of MBTs at the molecular level has been ignored.

Roles of the hypoximir microRNA-424/322 in acute hypoxia and hypoxia-induced pulmonary vascular leakage

Acute mountain sickness (AMS) occurs in up to 25% of unacclimatized persons who ascend to 3000 m and can result in high-altitude pulmonary edema (HAPE). MicroRNAs (miRs) can regulate gene expression at the post-transcriptional level. Hypoxia selectively disrupts endothelial tight junction complexes through a hypoxia-inducible factor-1α (HIF-1α)-dependent mechanism. Though increased HIF-1α expression is associated with adaptation and protection from AMS development in the early stage of hypoxia, a downstream effector of HIF-1α, VEGF, can induce overzealous endothelial barrier dysfunction, increase vascular permeability, and ultimately result in HAPE and high-altitude cerebral edema. We hypothesized that the fine-tuning of downstream effectors by miRs is paramount for the preservation of endothelial barrier integrity and the prevention of vascular leakage. We found that several miRs were up-regulated in healthy volunteers who were subjected to a 3100-m height. By reviewing the literature and using online bioinformatics prediction software, we specifically selected miR-424 for further investigation because it can modulate both HIF-1α and VEGF. Hypoxia-induced miR-424 overexpression is HIF-1α dependent, and miR-424 stabilized HIF-1α, decreased VEGF expression, and promoted vascular endothelial cadherin phosphorylation. In addition, hypoxia resulted in endothelial barrier dysfunction with increased permeability; miR-424 thus attenuated hypoxia-induced endothelial cell senescence and apoptosis. miR-322 knockout mice were susceptible to hypoxia-induced pulmonary vascular leakage. miR-322 mimics improved hypoxia-induced pulmonary vascular leakage in vivo. We conclude that several miRs were up-regulated in healthy adult volunteers subjected to hypobaric hypoxemia. miR-424/322 could modulate the HIF-1α-VEGF axis and prevent hypoxia-induced pulmonary vascular leakage under hypoxic conditions.-Tsai, S.-H., Huang, P.-H., Tsai, H.-Y., Hsu, Y.-J., Chen, Y.-W., Wang, J.-C., Chen, Y.-H., Lin, S.-J. Roles of the hypoximir microRNA-424/322 in acute hypoxia and hypoxia-induced pulmonary vascular leakage.

The plasma level changes of VEGF and soluble VEGF receptor-1 are associated with high-altitude pulmonary edema

Hypoxia-induced plasma levels of VEGF and sFlt-1 are responsible for increased vascular permeability occurred in both brain and pulmonary edema. Currently, it remains unclear the exact roles of VEGF and sFlt-1 in High Altitude Pulmonary Edema (HAPE) pathogenesis. In this study, plasma levels of VEGF and sFlt-1 from 10 HAPE and 10 non-HAPE subjects were measured and compared. The results showed that plasma levels of both VEGF and sFlt-1 in HAPE patients were significantly increased as compared to the non-HAPE group. Interestingly, increased plasma levels of these two protein factors were markedly reduced after treatments. As compared to VEGF, sFlt-1 was much more affected by hypoxia and treatments, suggesting this factor was a key factor contributed to HAPE pathogenesis. Importantly, the ratio of sFlt-1 and VEGF in group of either non-HAPE or HAPE after recovery was significantly lower than the ratio in HAPE patients prior to treatments. Our findings suggested that sFlt-1 was a key factor that involved in HAPE pathogenesis and the sFlt-1/VEGF ratio could be used as a sensitive diagnostic marker for HAPE. J. Med. Invest. 65:64-68, February, 2018.

Vascular Endothelial Function Assessed by Postischemic Diastolic Blood Pressure Is Associated with Acclimatization and Acute Mountain Sickness

BACKGROUND

This study assessed whether the brachial diastolic blood pressure (DBP) decline induced by 5-minute arm ischemia is associated with acclimatization and acute mountain sickness (AMS).

METHODS

Forty-two age- and body mass index-matched young male residents at sea level (<400 m) or moderate altitude (1000-2000 m above sea level) were enrolled. All subjects had never been to 3200 m before. Brachial BP was measured at a station at 1380 m altitude before and 1, 5, and 10 minutes after right arm ischemia. AMS score was evaluated after 3-day training at a high altitude of 3200 m.

RESULTS

In moderate altitude versus sea-level residents: (1) systolic BP curves for both arms overlapped well; (2) mean right arm DBP decline post right arm ischemia was larger, while left arm, which was not subjected to ischemia, did not show DBP decline in either group; and (3) AMS scores were significantly lower (3.19 ± 2.16 vs. 5.52 ± 4.58, p = 0.043) in those residing at moderate altitude compared to those from low altitude. There was a low negative correlation between AMS score and right arm area between curves-DBP (r = -0.320, p = 0.039).

CONCLUSION

Moderate altitude relative to sea-level residents had a larger mean postischemic DBP decline in weak but significant association with lower mean AMS score at 3200 m. These data suggest that differences in vascular endothelial function related to altitude of residence persist during travel to high altitude and might contribute to AMS risk.

Regulatory SNPs and transcriptional factor binding sites in ADRBK1, AKT3, ATF3, DIO2, TBXA2R and VEGFA

Abstract Regulatory single nucleotide polymorphisms (rSNPs) which change the transcriptional factor binding sites (TFBS) for transcriptional factors (TFs) to bind DNA were reviewed for the ADRBK1 (GRK2), AKT3, ATF3, DIO2, TBXA2R and VEGFA genes. Changes in the TFBS where TFs attach to regulate these genes may result in human sickness and disease. The highlights of this previous work were reviewed for these genes.

Plasma leptin and vascular endothelial growth factor (VEGF) in normal subjects at high altitude (5050 m)

CONTEXT

High altitude (HA) is a model of severe hypoxia exposure in humans. We hypothesized that nocturnal hypoxemia or acute maximal exercise at HA might affect plasma leptin and VEGF levels.

OBJECTIVES

Plasma leptin, VEGF and other metabolic variables were studied after nocturnal pulse oximetry and after maximal exercise in healthy lowlanders on the 3rd-4th day of stay in Lobuche (5050 m, HA) and after return to sea level (SL).

RESULTS

Leptin was similar at SL or HA in both pre- and post-exercise conditions. Pre-exercise VEGF at HA was lower, and cortisol was higher, than at SL, suggesting that nocturnal intermittent hypoxia associated with periodic breathing at HA might affect these variables.

CONCLUSIONS

Leptin levels appear unaffected at HA, whereas nocturnal hypoxic stress may affect plasma VEGF. Future HA studies should investigate the possible role of nocturnal intermittent hypoxemia on metabolism.

Upregulation of cytoprotective defense mechanisms and hypoxia-responsive proteins imparts tolerance to acute hypobaric hypoxia

Exposure to high altitude is a well-known environmental stress with physiological and metabolic consequences, with the major stressor being hypobaric hypoxia. The disruption in cellular homeostasis elicits several acute and chronic adaptations designed to diminish the stress imposed by the hypoxic insult. Highly conserved cellular machinery protects the myocardium from damage under reduced oxygen tension. In the present study, adult Sprague-Dawley rats were exposed to an altitude of 9754 m in a decompression chamber and screened on the basis of the time taken for onset of gasping. The animals were grouped as susceptible (<10 min), normal (10-25 min), and tolerant (>25 min). Histologically, susceptible animals showed increased myocardial inflammation and infiltration and greater CK-MB activity. These animals showed a three-fold increase in reactive oxygen species levels and subsequent oxidative damage to proteins and lipids as compared to control unexposed group. In tolerant animals, the damage was minimal. The resistance to damage in these animals was possibly due to enhanced myocardial antioxidant enzymes, catalase and superoxide dismutase. A significantly higher expression of HIF-1α and its responsive genes, including EPO, HO-1, and GLUT1, was seen in tolerant animals, although VEGF expression was enhanced in the susceptible group. Cytoprotective chaperones, HSP70 and HSP90, were elevated in the tolerant animals. The differential expression of these hypoxia-responsive molecules may thus act as potential biochemical markers for screening and identifying individuals susceptible to environmental stress.

VEGFA SNPs and transcriptional factor binding sites associated with high altitude sickness in Han and Tibetan Chinese at the Qinghai-Tibetan Plateau

Mountain sickness (MS) occurs among humans visiting or inhabiting high altitude environments. We conducted genetic analyses of seven single nucleotide polymorphisms (SNPs) in the promoter region of VEGFA gene for lowland (Han) and highland (Tibetan) Chinese. The seven SNPs were evaluated in Han and Tibetan patients with acute (A) and chronic (C) MS. We compared 64 patients with AMS with 64 Han unaffected with MS, as well as 48 CMS patients with 32 unaffected Tibetans. The SNPs studied are rs699947, rs34357231, rs79469752, rs13207351, rs28357093, rs1570360, and rs2010963 which are found in the promoter ranging from -2,578 to -634 bp from the transcriptional start site (TSS), respectively. Direct sequencing was used to identify individual genotypes for these SNPs. Arterial oxygen saturation of hemoglobin (SaO2) was found to be significantly associated with the rs699947, rs34357231, rs13207351, and rs1570360 SNPs in Han patients with AMS, while the rs2010963 SNP was found to approach significance in the AMS study group, but found to be significantly associated in the normal Tibetan study group. The Han and Tibetan control groups were found to diverge significantly for the rs28357093 and rs2010963 SNPs, as measured by genetic distances of 0.073 and 0.054, respectively. All the SNPs are found in transcriptional factor binding sites (TFBS), and their possible role in gene regulation was evaluated with regard to MS. MS was found to be significantly associated with these SNPs compared with their Han and Tibetan control groups, indicating that these nucleotide substitutions result in TFBS changes which apparently have a physiological effect on the development of high altitude sickness.

Associations between Vascular Endothelial Growth Factor Gene Polymorphisms and Susceptibility to Acute Mountain Sickness

Objective:

This study investigated associations between polymorphisms in the vascular endothelial growth factor (VEGF) gene and susceptibility to acute mountain sickness.

Methods:

Two hundred Han Chinese soldiers who developed acute mountain sickness after rapidly ascending to an altitude of < 3600 m and 200 control soldiers (who did not develop the condition) were enrolled in the study. Twelve single nucleotide polymorphisms (SNPs) of the VEGF gene were genotyped in all the study participants. Plasma VEGF concentrations were measured by enzyme-linked immunosorbent assay in 40 subjects with acute mountain sickness and 40 controls before and after exposure to high altitude.

Results:

The frequencies of the rs3025039 genotype and allele were significantly different between the groups. Two SNPs, rs3025039 (which involves a C→T allele variation at position 936 in the 3′ untranslated region) and rs3025030 (which involves a G→C allele variation in the intronic sequence), were associated with a decreased risk of acute mountain sickness.

Conclusion:

The SNPs rs3025039 and rs3025030 of the VEGF gene may be associated with a decreased risk of acute mountain sickness development.

Altitude illness: update on prevention and treatment

Altitude illness is a broad category of disease encompassing acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE) that can affect persons who travel to altitude without adequate acclimatization. Initial symptoms of AMS and the more serious HACE or HAPE can be subtle, and it is important that the practitioner be able to recognize and differentiate between these diagnoses because they can progress rapidly and be fatal if untreated. There are well-established criteria and many proven therapies both for prophylaxis and treatment of altitude illness; however, despite intense research efforts, the specific mechanisms of these complex diseases remain elusive. Adequate acclimatization via controlled ascent remains the most important factor in preventing altitude illness, although prophylactic pharmacotherapy also may be useful. Rapid descent remains the most important treatment factor, although treatment at altitude with various therapies is possible for mild cases with adequate resources.

AKT3, ANGPTL4, eNOS3, and VEGFA associations with high altitude sickness in Han and Tibetan Chinese at the Qinghai-Tibetan Plateau

Mountain sickness (MS) occurs among humans visiting or inhabiting high altitude environments. We conducted genetic analyses of the AKT3, ANGPTL4, eNOS3 and VEGFA genes in lowland (Han) and highland (Tibetan) Chinese. Ten single nucleotide polymorphisms (SNPs) were evaluated in Han and Tibetan patients with acute (A) and chronic (C) MS. We compared 74 patients with AMS to 79 Han unaffected with MS, as well as 48 CMS patients to 31 unaffected Tibetans. The ten SNPs studied are AKT3 (rs4590656, rs2291409), ANGPTL4 (rs1044250), eNOS3 (rs1007311, rs1799983) and VEGFA (rs79469752, rs13207351, rs28357093, rs1570360, rs3025039). Direct sequencing was used to identify individual genotypes for these SNPs. Hemoglobin (Hb), hematocrit (Hct), and red blood cell count (RBC) were found to be significantly associated with the AKT3 SNP (rs4590656), Hb was found to be associated with the eNOS3 SNP (rs1007311), and RBC was found to be significantly associated with the VEGFA SNP (rs1570360) in Tibetan patients with CMS. CMS patients were found to diverge significantly for both eNOS3 SNPs as measured by genetic distance (0.042, 0.047) and for the VEGFA SNP (rs28357093) with a genetic distance of 0.078 compared to their Tibetan control group. Heart rate (HR) was found to be significantly associated with the eNOS3 SNP (rs1799983) and arterial oxygen saturation of hemoglobin (SaO2) was found to be significantly associated with the VEGFA SNPs (rs13207351, rs1570360) in Han patients with AMS. The Han and Tibetan control groups were found to diverge significantly for the ANGPTL4 SNP and VEGFA SNP (rs28357093), as measured by genetic distances of 0.049 and 0.073, respectively. Seven of the SNPs from non-coding regions are found in the transcriptional factor response elements and their possible role in gene regulation was evaluated with regard to MS. AMS and CMS were found to be significantly associated with the four genes compared to their Han and Tibetan control groups, respectively, indicating that these nucleotide alterations have a physiological effect for the development of high altitude sickness.

No correlation between plasma levels of vascular endothelial growth factor or its soluble receptor and acute mountain sickness

Increased plasma levels of vascular endothelial growth factor (VEGF) due to lower levels of its soluble receptor (sFlt-1) had been suggested to cause vasogenic brain edema and thereby to cause the symptoms of acute mountain sickness (AMS). We tested this hypothesis after active ascent to high altitude. Plasma was collected from 31 subjects at low altitude (100 m) before (LA1) and after (LA2) 4 weeks of aerobic exercise training in normobaric hypoxia or normoxia, and one night after ascent to high altitude (4559 m). Training modalities (hypoxia or normoxia) did not influence VEGF- and sFlt-1-levels. Therefore, data of both training groups were analyzed together. After one night at 4559 m, 18 subjects had AMS (AMS+), 13 had no AMS (AMS-). In AMS+ and AMS-, VEGF was 110 ± 75 (SD) pg/ml vs. 104 ± 82 (p = 0.74) at LA1, 63 ± 40 vs. 73 ± 50 (p = 0.54) at LA2, and 88 ± 62 vs. 104 ± 81 (p = 0.54) at 4559 m, respectively. Corresponding values for sFlt-1 in AMS+ and AMS- were 81 pg/ml ± 13.1 vs. 82 ± 17 (p = 0.97), 79 ± 11 vs. 80 ± 16 (p = 0.92) and 139 ± 28 vs. 135 ± 31 (p = 0.70), respectively. Absolute values or changes of VEGF were not correlated and those of sFlt-1 slightly correlated with AMS scores. These data provide no evidence for a role of plasma VEGF and sFlt-1 in the pathophysiology of AMS. They do, however, not exclude paracrine effects of VEGF in the brain.

Hypoxia: adapting to high altitude by mutating EPAS-1, the gene encoding HIF-2α

Living at high altitude is demanding and thus drives adaptational mechanisms. The Tibetan population has had a longer evolutionary period to adapt to high altitude than other mountain populations such as Andeans. As a result, some Tibetans living at high altitudes do not show markedly elevated red blood cell production as compared to South American high altitude natives such as Quechuas or Aymaras, thereby avoiding high blood viscosity creating cardiovascular risk. Unexpectedly, the responsible mutation(s) reducing red blood cell production do not involve either the gene encoding the blood hormone erythropoietin (Epo), or the corresponding regulatory sequences flanking the Epo gene. Similarly, functional mutations in the hypoxia-inducible transcription factor 1α (HIF-1α) gene that represents the oxygen-dependent subunit of the HIF-1 heterodimer, the latter being the main regulator of over 100 hypoxia-inducible genes, have not been described so far. It was not until very recently that three independent groups showed that the gene encoding HIF-2α, EPAS-1 (Wenger et al. 1997), represents a key gene mutated in Tibetan populations adapted to living at high altitudes (Beall et al. 2010 , Yi et al. 2010 , Simonson et al. 2010). Hypoxia-inducible transcription factors were first identified by the description of HIF-1 (Semenza et al. 1991 , 1992), which was subsequently found to enhance transcription of multiple genes that encode proteins necessary for rescuing from hypoxic exposure, including erythropoietic, angiogenic and glycolytic proteins. Then HIF-2 was identified (Ema et al. 1997 ; Flamme et al. 1997 ; Hogenesch et al. 1997 ; and Tian et al. 1997) and although it is highly similar to HIF-1 and has the potential to bind (Camenisch et al. 2001) and mediate (Mole et al. 2009) many of the same genes as HIF-1, its biological actions in response to hypoxia are distinct from those of HIF-1 (reviewed by Loboda et al. 2010). By now, several of these HIF-2 mediated processes have been implicated in the human response to high altitude exposure including erythropoiesis (Kapitsinou et al. 2010), iron homeostasis (Peyssonnaux et al. 2008), metabolism (Shohet et al. 2007; Tormos et al. 2010; Biswas et al. 2010 ; Rankin et al. 2009) and vascular permeability (Chen et al. 2009; Tanaka et al. 2005), among others. Clearly, mutation of EPAS-1 has the potential to bring far more advantage when adapting to high altitude than solely mutating the Epo gene.

Vascular endothelial growth factor and acute mountain sickness

Study Objective:

Despite causing significant morbidity throughout the mountainous regions of the world, the pathophysiology of acute mountain sickness (AMS) remains poorly understood. This study aims to improve the understanding of altitude illness by determining if vascular endothelial growth factor (VEGF) plays a role in the development of AMS. The purpose of this study was to determine if elevated plasma VEGF correlates with increased symptoms of AMS at high altitude.

Patients and Methods:

This is a prospective study of a cohort of healthy climbers on Denali (Mount McKinley) in Alaska at 14, 200 feet. Baseline demographics, medications, rates of ascent, and AMS scores were recorded. Pulse oximetry measurements and venous blood samples were obtained. Comparisons were made between mountaineers with and without AMS.

Results:

Seventy-two climbers were approached for participation in the study; 21 (29%) refused. Of the 51 climbers participating in the study, 14 subjects (27.5%) had symptoms of AMS and 37 subjects (72.5%) were free of symptoms of AMS. Plasma VEGF levels were 79.14 pg/dl (SD: 121.44) and 57.57pg/dl (SD: 102.71) in the AMS and non-AMS groups, respectively. These results were nonsignificant. Similarly, comparison of sex, age, rate of ascent, pulse oximetry values, or history of altitude illness did not reveal significant differences between the AMS and non-AMS groups.

Conclusion:

This study does not provide evidence in support of the theory that plasma VEGF correlates with symptoms of AMS.

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.

Ophthalmodynamometry for ICP prediction and pilot test on Mt. Everest

BACKGROUND

A recent development in non-invasive techniques to predict intracranial pressure (ICP) termed venous ophthalmodynamometry (vODM) has made measurements in absolute units possible. However, there has been little progress to show utility in the clinic or field. One important application would be to predict changes in actual ICP during adaptive responses to physiologic stress such as hypoxia. A causal relationship between raised intracranial pressure and acute mountain sickness (AMS) is suspected. Several MRI studies report that modest physiologic increases in cerebral volume, from swelling, normally accompany subacute ascent to simulated high altitudes.

OBJECTIVES

1) Validate and calibrate an advanced, portable vODM instrument on intensive patients with raised intracranial pressure and 2) make pilot, non-invasive ICP estimations of normal subjects at increasing altitudes.

METHODS

The vODM was calibrated against actual ICP in 12 neurosurgical patients, most affected with acute hydrocephalus and monitored using ventriculostomy/pressure transducers. The operator was blinded to the transducer read-out. A clinical field test was then conducted on a variable data set of 42 volunteer trekkers and climbers scaling Mt. Everest, Nepal. Mean ICPs were estimated at several altitudes on the ascent both across and within subjects.

RESULTS

Portable vODM measurements increased directly and linearly with ICP resulting in good predictability (r = 0.85). We also found that estimated ICP increases normally with altitude (10 ± 3 mm Hg; sea level to 20 ± 2 mm Hg; 6553 m) and that AMS symptoms did not correlate with raised ICP.

CONCLUSION

vODM technology has potential to reliably estimate absolute ICP and is portable. Physiologic increases in ICP and mild-mod AMS are separate responses to high altitude, possibly reflecting swelling and vasoactive instability, respectively.

Effects of acute hypoxia tests on blood markers in high-level endurance athletes

The aim of this study was to determine the response of blood markers to acute hypoxia in high-level endurance athletes before training based on "living high-training low" model. Thirty endurance athletes performed a hypoxic cycling test and spent 3 h at rest in a simulated altitude of 3,000 m. At the end of the hypoxic cycling test, the quantity of the natural antisense transcript of HIF-1alpha mRNA (aHIF) transcript increased significantly (+37%, P = 0.024). After 3-h exposure, at a simulated altitude of 3,000 m, the amount of HIF-1alpha mRNA increased significantly (+57%, P = 0.012). Moreover, a large inter-subject range was observed in response to the hypoxic cycling test and to the prolonged hypoxic exposure: -133%/+79% and -82%/+653% for HIF-1alpha mRNA, 69%/+324% and -76%/+229% for aHIF. This study shows a large inter-variability of blood markers in elite athletes in response to acute hypoxic exposure corroborating previous observations made in other populations.

Polymorphisms of human vascular endothelial growth factor gene in high-altitude pulmonary oedema susceptible subjects

BACKGROUND AND OBJECTIVE

Based on the reported biological properties and function of vascular endothelial growth factor (VEGF) in hypoxic conditions, many investigations have studied the hypothesis that VEGF has an important role in the pathogenesis of high altitude sicknesses, including high-altitude pulmonary oedema (HAPE). Unfortunately, the results are inconsistent. Therefore, the association of VEGF gene single nucleotide polymorphisms (SNP) with being susceptible to HAPE was investigated.

METHODS

The study included 53 HAPE-susceptible subjects (HAPE-s) and 69 HAPE-resistant mountaineer controls (HAPE-r). Subjects were Japanese and the two groups were comparable in terms of age and gender. The SNP of the VEGF gene, namely C-2578A, G-1154A and T-460C in the promoter, G + 405C in the 5'-untranslated region and C936T in the 3'-untranslated region, were examined by allele discrimination experiments. In addition, arterial oxygen tension (PaO(2)) and pulmonary haemodynamic data were available for 21 of the HAPE-s subjects.

RESULTS

There were no statistically significant differences in the allele frequencies, genotype distributions or haplotype frequencies of VEGF SNP between the HAPE-s and HAPE-r groups. Furthermore, neither PaO(2) nor pulmonary haemodynamic parameters were associated with the VEGF SNP in the 21 HAPE-s subjects.

CONCLUSIONS

This genetic study did not provide evidence that functional SNP of the VEGF gene are associated with susceptibility to HAPE in a Japanese population.

Relationship between oxidative stress and HIF-1 alpha mRNA during sustained hypoxia in humans

The aim of this study was to investigate the relations among reactive oxygen species (ROS), hypoxia inducible factor (HIF-1 alpha) gene expression, HIF-1 alpha target gene erythropoietin (EPO), and vascular endothelium growth factor (VEGF) in humans. Five healthy men (32+/-7 years, mean+/-SD) were exposed to 12 h of sustained poikilocapnic hypoxia (P(ET)O(2)=60 mmHg). DNA oxidation (8-hydroxy-2'-deoxyguanosine, 8-OHdG), advanced oxidation protein products (AOPP), EPO, and VEGF were measured in plasma and HIF-1 alpha mRNA was assessed in leukocytes before and after 1, 2, 4, 6, 8, 10, and 12 h of exposure to hypoxia. HIF-1 alpha mRNA amount increased during the first two hours of hypoxic exposure and then returned to baseline levels. The findings reveal an up-regulation of HIF-1 alpha (+68%), VEGF (+46%), and EPO (+74%). AOPP increased continuously from 4 h (+69%) to 12 h (+216%) of hypoxic exposure while 8-OHdG increased after 6 h (+78%) and remained elevated until 12 h. During the "acute" increase phase of HIF-1 alpha (between 0 and 2 h), 8-OHdG was positively correlated with HIF-1 alpha (r=0.55). These findings suggest that hypoxia induces oxidative stress via an overgeneration of reactive oxygen species (ROS). Finally, this study in humans corroborates the previous in vitro findings demonstrating that ROS is involved in HIF-1 alpha transcription.

T allele for VEGF-460 gene polymorphism at 5'-untranslated region is associated with higher susceptibility of leiomyoma

Vascular endothelial growth factor (VEGF) is a regulator of angiogenesis and a mediator of sex steroid-induced cell growth and differentiation. We aimed to investigate if VEGF gene 5'-UTR -460 polymorphism could be used as markers of susceptibility in leiomyoma. Women were divided into two groups: (1) leiomyoma (n = 159); (2) nonleiomyoma groups (n = 131). VEGF gene -460 polymorphism were detected by polymerase chain reaction and BstUI restriction enzyme analysis. Genotypes and allelic frequencies between both groups were compared. We noted that the proportions of different VEGF polymorphisms in both groups were significantly different. Proportions of cuttable (C) homozygote/heterozygote/uncuttable (T) homozygote for VEGF in both groups were: (1) 0/32/68% and (2) 0/63/37%. Higher percentage of T homozygote and T allele presented in the leiomyoma population. Proportions of C/T alleles in both groups were: (1) 16/84% and (2) 32/68%. We concluded that T homozygotes and T allele of VEGF gene -460 polymorphism are associated with higher risk of leiomyoma development. Heterozygotes and C allele are related with lower risk of leiomyoma formation. VEGF gene polymorphism likely contributes to the pathogenesis of leiomyoma.

Cerebrovascular responses to altitude

The regulation of cerebral blood flow (CBF) is a complex process that is altered significantly with altitude exposure. Acute exposure produces a marked increase in CBF, in proportion to the severity of the hypoxia and mitigated by hyperventilation-induced hypocapnia when CO(2) is uncontrolled. A number of mediators contribute to the hypoxia-induced cerebral vasodilation, including adenosine, potassium channels, substance P, prostaglandins, and NO. Upon acclimatization to altitude, CBF returns towards normal sea-level values in subsequent days and weeks, mediated by a progressive increase in PO2, first through hyperventilation followed by erythropoiesis. With long-term altitude exposure, a number of mechanisms play a role in regulating CBF, including acid-base balance, hematological modifications, and angiogenesis. Finally, several cerebrovascular disorders are associated with altitude exposure. Existing gaps in our knowledge of CBF and altitude, and areas of future investigation include effects of longer exposures, intermittent hypoxia, and gender differences in the CBF responses to altitude.

[Guidelines based on decision support software. Quality management in neurological outpatient schizophrenia treatment]

The positive effect of greater adherence to evidence-based guidelines on possibilities of optimizing diagnosis and therapy has been shown various times. Electronic systems for interactive support and systematization of physicians' decision-making represent a relatively new method for implementing guidelines. Introducing the "schizophrenia module", newly developed decision support software is presented combining electronic data processing-based, quality-oriented documentation and interactive decision support in the outpatient treatment for schizophrenic disorders. Structure, functionality, and options of use are presented. Besides classic measures of quality management (benchmarking), electronic decision support systems can contribute to improve process quality and outcome in the treatment of mental diseases.

Change in plasma vascular endothelial growth factor during onset and recovery from acute mountain sickness

There is an increasing body of evidence suggesting that altered vascular permeability may be an important component of the pathogenesis of acute mountain sickness (AMS). Vascular endothelial growth factor (VEGF) is a potent permeability factor subject to hypoxic regulation but its role in the pathogenesis of AMS is yet to be defined. We examined the relationship between plasma VEGF and AMS on ascent to high altitude and subsequent acclimatisation. Thirty-eight healthy lowlanders (median age 21, range 18-31) flew to La Paz, Bolivia (3650 m) on the Apex 2 research expedition. After 4-5 days acclimatisation, they ascended by vehicle over 90 min to the Chacaltaya laboratory (5200 m). We measured plasma VEGF in venous blood at sea level and at 6 h and 3 and 7 days at 5200 m. AMS was scored using the Lake Louise consensus system. Using serial measurement of plasma VEGF at 5200 m, following partial acclimatisation at 3650 m, we demonstrated a highly significant change in VEGF levels (P<0.0005) with a rise in VEGF in approximately 80% of subjects by day 7 at 5200 m. We found no evidence of an association between AMS and change in VEGF levels on ascent to either 3650 or 5200 m. We provide novel data of change in plasma VEGF levels during acclimatisation to high altitude, but our results do not support the hypothesis that circulating unbound VEGF is an important component of the pathogenesis of AMS.

Acute hypoxia decreases plasma VEGF concentration in healthy humans

Vascular endothelial growth factor (VEGF) is known to be upregulated by hypoxia in vitro. However, in vivo data about VEGF regulation in chronic hypoxic diseases are conflicting. We investigated the effects of hypoxia on plasma VEGF concentration in healthy subjects. To control known confounders, such as insulin, glucose concentrations, or exercise, hypoxic effects on VEGF were studied during experimentally clamping glucose concentrations at rest. In a double-blind crossover study design, we induced hypoxia for 30 min by decreasing oxygen saturation to 75% (vs. normoxic control) in 14 healthy men. Plasma VEGF concentration was determined at baseline, immediately after hypoxia had ended, and after a further 150 min. Levels of its soluble (s)Flt-1 receptor were assessed at baseline and at the end of the clamp. In parallel, catecholamine and cortisol levels were monitored. To investigate potential effects of glucose administration on the release of VEGF, we performed a third session, reducing glucose infusion for 30 min while serum insulin was held stable thereby inducing hypoglycemia. Hypoxia decreased VEGF levels compared with the normoxic control (P<0.05). VEGF concentrations increased during hypoglycemia (P<0.02) but were comparable to the normoglycemic control at the end of the clamp (P>0.80). sFlt-1 receptor concentration remained unchanged during hypoxia and hypoglycemia compared with control (both P>0.4). Epinephrine concentration (P<0.01) increased upon hypoxia, whereas norepinephrine and cortisol did not change. Contrary to in vitro studies, in healthy humans hypoxia decreases plasma VEGF concentration, suggesting that systemic VEGF concentration may be differently regulated than the expression on cellular basis.

An evolutionary model for identifying genetic adaptation to high altitude

Coordinated maternal/fetal responses to pregnancy are required to ensure continuous O2 delivery to the developing organism. Mammals employ distinctive reproductive strategies that afford their young an improved chance of survival through the completion or the reproductive period. Thus, mortality prior to the end of the reproductive period is concentrated in the earliest phases of the lifecycle. At high altitude, fetal growth restriction reduces birth weight and likely compromises survival during the early postnatal period. Population variation in the frequency of the altitude-associated increase in intrauterine growth restriction (IUGR) demonstrates that multigenerational Tibetan and Andean high-altitude populations are protected compared with shorter duration, European or Han (Chinese) residents. This experiment of nature permits testing the hypothesis that genetic factors (a) influence susceptibility to altitude-associated IUGR, (b) act on maternal vascular adjustments to pregnancy determining uteroplacental blood flow, and (c) involve genes which regulate and/or are regulated by hypoxia-inducible factors (HIFs). Serial, studies during pregnancy as well as postpartum in Andean and European residents of high (3600 m) and low (300 m) altitude will permit evaluation of whether uteroplacental O2 delivery is lower in the European than Andean women and, if so, the physiological factors responsible. Comparisons of HIF-targeted vasoactive substances and SNPs in or near HIF-regulatory or targeted genes will permit determination of whether these regions are distinctive in the Andean population. Studies coupling genetic and genomic approaches with more traditional physiological measures may be productively employed for determining the genetic mechanisms influencing physiological adaptation to high altitude.

Epidemiology, Risk Factors, and Genetics of High-Altitude–Related Pulmonary Disease

High-altitude-related pulmonary disease is a spectrum of acute and chronic illnesses with a well-described epidemiology. The risk for these illnesses is related to well-known environmental risk factors and lesser-known but important genetic factors. Prevention of acute high-altitude illness is possible in most visitors from lower elevations. Chronic high-altitude illnesses have an important worldwide impact.

Pathogenesis of high altitude pulmonary edema: does alveolar epithelial lining fluid vascular endothelial growth factor exacerbate capillary leak?

Vascular endothelial growth factor (VEGF) is a potent mediator of capillary leak if it gains access to its receptors on the capillary endothelium. We have observed that there are high levels of VEGF compartmentalized in the alveolar epithelial lining fluid of normal humans at levels 500-fold greater than plasma. The potential for high altitude to result in compromise of alveolar epithelial tight junctions and experimental animal studies in which pulmonary edema is induced when VEGF is overexpressed in the alveolar epithelium, suggest a mechanism. We hypothesize that when the epithelial barrier is compromised at high altitude the normally high level of VEGF in the alveolar epithelial fluid has access to the pulmonary endothelium, where it acutely alters permeability, markedly exacerbating the high permeability pulmonary edema that characterizes high altitude pulmonary edema. If correct, this paradigm opens the possibility of testing available anti-VEGF therapies to treat this potentially fatal disorder.

Greater free plasma VEGF and lower soluble VEGF receptor-1 in acute mountain sickness

Vascular endothelial growth factor (VEGF) is a hypoxia-induced protein that produces vascular permeability, and limited evidence suggests a possible role for VEGF in the pathophysiology of acute mountain sickness (AMS) and/or high-altitude cerebral edema (HACE). Previous studies demonstrated that plasma VEGF alone does not correlate with AMS; however, soluble VEGF receptor (sFlt-1), not accounted for in previous studies, can bind VEGF in the circulation, reducing VEGF activity. In the present study, we hypothesized that free VEGF is greater and sFlt-1 less in subjects with AMS compared with well individuals at high altitude. Subjects were exposed to 4,300 m for 19–20 h (baseline 1,600 m). The incidence of AMS was determined by using a modified Lake Louise symptom score and the Environmental Symptoms Questionnaire for cerebral effects. Plasma was collected at low altitude and after 24 h at high altitude, or at time of illness, and then analyzed by ELISA for VEGF and for soluble VEGF receptor, sFlt-1. AMS subjects had lower sFlt-1 at both low and high altitude compared with well subjects and a significant rise in free plasma VEGF on ascent to altitude compared with well subjects. We conclude that increased free plasma VEGF on ascent to altitude is associated with AMS and may play a role in pathophysiology of AMS.

Circulating plasma levels of vascular endothelial growth factor in patients with sleep disordered breathing

INTRODUCTION

Cellular vascular endothelial growth factor (VEGF) expression is increased in response to regional hypoxia, however, contradictory results were reported on the effects of systemic hypoxemia on circulating VEGF levels. This study investigated plasma concentrations of VEGF in patients with a variable degree of overnight hypoxemia due to sleep disordered breathing (SDB).

METHODS

VEGF levels were assessed by ELISA in non-activated (VEGFbl) and thrombin stimulated platelet rich plasma (VEGFprp) of 45 patients with SDB: Group 1 patients with obstructive sleep apnea and an apnea-hypopnea index (AHI) > 15/h; Group 2 subjects with an AHI < 5/h; Group 3 patients on CPAP treatment for sleep apnea.

RESULTS

39 patients were included in the final analysis. Patients in Group 1 had a higher %time of sleep with SaO2 <90% and a significantly lower mean and minimum overnight oxygen saturation than subjects in Group 2 and patients in Group 3 (P<0.05). Despite significant differences in overnight oxygenation, VEGFbl and VEGFprp concentrations were not significantly different between the three study groups. However, plasma levels of VEGFbl were significantly higher (P = 0.02) in SDB patients with arterial hypertension (n = 19; VEGFbl: 14.0+/-3.3 pg/ml) than in those without arterial hypertension (n = 20; VEGFbl: 10.9+/-5.2 pg/ml). There were no relationships between VEGF levels and polysomnographic oxygenation parameters. In univariate analysis we observed significant relationships for VEGFbl with BMI (C: 0.393; P<0.05) and serum fibrinogen (C: 0.399; P<0.05).

CONCLUSIONS

Circulating plasma VEGF levels in patients with sleep disordered breathing may be unrelated to night time hypoxemia (257 Words).

High-altitude illness

High-altitude illness is the collective term for acute mountain sickness (AMS), high-altitude cerebral oedema (HACE), and high-altitude pulmonary oedema (HAPE). The pathophysiology of these syndromes is not completely understood, although studies have substantially contributed to the current understanding of several areas. These areas include the role and potential mechanisms of brain swelling in AMS and HACE, mechanisms accounting for exaggerated pulmonary hypertension in HAPE, and the role of inflammation and alveolar-fluid clearance in HAPE. Only limited information is available about the genetic basis of high-altitude illness, and no clear associations between gene polymorphisms and susceptibility have been discovered. Gradual ascent will always be the best strategy for preventing high-altitude illness, although chemoprophylaxis may be useful in some situations. Despite investigation of other agents, acetazolamide remains the preferred drug for preventing AMS. The next few years are likely to see many advances in the understanding of the causes and management of high-altitude illness.

Vascular endothelial growth factor in patients with high-altitude pulmonary edema

To examine the role of VEGF in the pathogenesis of high-altitude pulmonary edema (HAPE), we measured the concentrations of VEGF in venous serum and bronchoalveolar lavage fluid in patients with HAPE and in healthy volunteers. The VEGF in venous serum of the patients was normal at admission and significantly increased at recovery. Similarly, the VEGF in bronchoalveolar lavage fluid of the patients was increased at recovery compared with admission, but values at both admission and recovery were significantly lower than those of the controls. The present finding suggests that VEGF probably is destroyed in the lung of HAPE, and it appears less likely to have a critical part in the pathogenesis of HAPE but has rather an important role in the repair process for the impaired cell layer.

Hypoxia and High Altitude

Increased erythropoietin plasma levels and the consequent augmented production of red blood cells is the best known systemic adaptation to reduced oxygen partial pressure (pO2). Intensive research during the last years revealed that the molecular mechanism behind the regulation of erythropoietin is ubiquitous and has far more implications than first thought. Erythropoietin regulation results from the activation of the hypoxia-inducible factor-1 (HIF-1) pathway under hypoxic conditions. HIF-1 is a heterodimer consisting of an oxygen sensitive--HIF-1--and an oxygen-independent subunit--HIF-1beta (also known as the aryl hydrocarbon receptor nuclear translocator--ARNT). In addition to erythropoietin, more than 30 genes are now known to be up-regulated by HIF-1. Recently, the critical involvement of HIF-1alpha post-translational modifications in the cellular oxygen sensing mechanism was discovered. In this review we will focus on the regulation of the HIF-1 pathway and the cellular oxygen sensor and discuss their implications in high altitude hypoxia.

Plasma vascular endothelial growth factor in sleep apnea syndrome: effects of nasal continuous positive air pressure treatment

Sleep apnea syndrome is associated with recurrent episodic hypoxia during sleep, which has been implicated in the development of cardiovascular morbidity. Hypoxia is the major stimulus of vascular endothelial growth factor (VEGF), which is a potent angiogenic cytokine. In the present article we describe the results of three experiments in which plasma concentrations of VEGF were measured in patients with sleep apnea. In Experiment 1, apnea-hypopnea index was found to be a significant independent predictor of morning VEGF concentrations in 85 male subjects investigated in the sleep laboratory, of whom 47 had an apnea-hypopnea index greater than 20. In Experiment 2, VEGF concentrations measured hourly during the sleep period were found to be significantly higher in a group of five sleep apnea patients compared with six age-similar snorers and six normal young adults (129.1 +/- 43.4 versus 74.6 +/- 11.5 and 32.5 +/- 12.8 pg/ml, respectively [p < 0.007]). In Experiment 3, VEGF concentrations were compared in patients with sleep apnea before and 1 year after nasal continuous positive airway pressure treatment. A significant decrease in VEGF concentrations was found only in patients in whom nocturnal hypoxia improved after treatment (57.1 +/- 62.5 versus 39.6 +/- 46.9 pg/ml, p < 0.01). There was no comparable improvement in patients who did not accept treatment (53.9 +/- 23.6 versus 54.0 +/- 21.5 pg/ml, ns). These results raise the possibility that VEGF may contribute to the long-term adaptation of sleep apnea syndrome to recurrent nocturnal hypoxia.

Pitfalls in the Measurement of Circulating Vascular Endothelial Growth Factor

Background: Vascular endothelial growth factor (VEGF) is a protein with antiapoptotic, mitogenic, and permeability-increasing activities specific for vascular endothelium. VEGF mRNA, which has five isoforms, is produced by nonmalignant cells in response to hypoxia and inflammation and by tumor cells in constitutively high concentrations. Because VEGF plays a crucial role in physiological and pathophysiological angiogenesis, measurements of circulating VEGF are of diagnostic and prognostic value, e.g., in cardiovascular failures, inflammatory diseases, and malignancies. However, there are major quantitative differences in the published results. This review attempts to identify reasons for these disparities.

Approach: The literature was reviewed through a Medline search covering 1995 to 2000. A selection of exemplary references had to be made for this perspective overview.

Content: Data are included from studies on healthy humans, gynecological patients, and persons suffering from inflammatory or malignant diseases. The results indicate that competitive immunoassays detect the total amount of circulating VEGF, which enables observations regarding the increase in VEGF in pregnancy and preeclampsia to be made. In these cases, capture immunoassays utilizing neutralizing antibodies are insufficient because of an accompanying increase in VEGF-binding soluble receptors (sFlt-1). Measurements of circulating free VEGF are useful for study of malignant diseases, which are associated with both genetically and hypoxia-induced overproduction of VEGF. The VEGF isoform specificity of the antibodies is also critical because both VEGF121 and VEGF165 are secreted. It is important to consider that platelets and leukocytes release VEGF during blood clotting.

Conclusions: Future efforts should concentrate on the balance between free VEGF, total VEGF, and sFlt-1. Plasma, rather than serum, should be used for analysis.