Cytokines in bronchoalveolar lavage fluid in patients with high altitude pulmonary oedema at moderate altitude in Japan

Genetic and immune changes in Tibetan high-altitude populations contribute to biological adaptation to hypoxia

BACKGROUND

Tibetans have lived at very high altitudes for thousands of years, and have a distinctive suite of physiological traits that enable them to tolerate environmental hypoxia. Expanding awareness and knowledge of the differences in hematology, hypoxia-associated genes, immune system of people living at different altitudes and from different ethnic groups may provide evidence for the prevention of mountain sickness.

METHOD

Ninety-five Han people at mid-altitude, ninety-five Tibetan people at high-altitude and ninety-eight Han people at high-altitude were recruited. Red blood cell parameters, immune cells, the contents of cytokines, hypoxia-associated gene single nucleotide polymorphisms (SNPs) were measured.

RESULTS

The values of Hematocrit (HCT), Mean cell volume (MCV) and Mean cell hemoglobin (MCH) in red blood cell, immune cell CD19⁺ B cell number, the levels of cytokines Erb-B2 receptor tyrosine kinase 3 (ErbB3) and Tumor necrosis factor receptor II (TNF-RII) and the levels of hypoxia-associated factors Hypoxia inducible factor-1α (HIF-1α), Hypoxia inducible factor-2α (HIF-2α) and HIF prolyl 4-hydroxylase 2 (PHD2) were decreased, while the frequencies of SNPs in twenty-six Endothelial PAS domain protein 1 (EPAS1) and Egl-9 family hypoxia inducible factor 1 (EGLN1) were increased in Tibetan people at high-altitude compared with that of Han peoples at high-altitude. Furthermore, compared with mid-altitude individuals, high-altitude individuals showed lower blood cell parameters including Hemoglobin concentration (HGB), HCT, MCV and MCH, higher Mean cell hemoglobin concentration (MCHC), lower immune cells including CD19⁺ B cells, CD4⁺ T cells and CD4/CD8 ratio, higher immune cells containing CD8⁺ T cells and CD16/56NK cells, decreased Growth regulated oncogene alpha (GROa), Macrophage inflammatory protein 1 beta (MIP-1b), Interleukin-8 (IL-8), and increased Thrombomodulin, downregulated hypoxia-associated factors including HIF1α, HIF2α and PHD2, and higher frequency of EGLN1 rs2275279.

CONCLUSIONS

These results indicated that biological adaption to hypoxia at high altitude might have been mediated by changes in immune cells, cytokines, and hypoxia-associated genes during the evolutionary history of Tibetan populations. Furthermore, different responses to high altitude were observed in different ethnic groups, which may provide a useful knowledge to improve the protection of high-altitude populations from mountain sickness.

Hypoxia and Inflammation: Insights From High-Altitude Physiology

The key regulators of the transcriptional response to hypoxia and inflammation (hypoxia inducible factor, HIF, and nuclear factor-kappa B, NF-κB, respectively) are evolutionarily conserved and share significant crosstalk. Tissues often experience hypoxia and inflammation concurrently at the site of infection or injury due to fluid retention and immune cell recruitment that ultimately reduces the rate of oxygen delivery to tissues. Inflammation can induce activity of HIF-pathway genes, and hypoxia may modulate inflammatory signaling. While it is clear that these molecular pathways function in concert, the physiological consequences of hypoxia-induced inflammation and how hypoxia modulates inflammatory signaling and immune function are not well established. In this review, we summarize known mechanisms of HIF and NF-κB crosstalk and highlight the physiological consequences that can arise from maladaptive hypoxia-induced inflammation. Finally, we discuss what can be learned about adaptive regulation of inflammation under chronic hypoxia by examining adaptive and maladaptive inflammatory phenotypes observed in human populations at high altitude. We aim to provide insight into the time domains of hypoxia-induced inflammation and highlight the importance of hypoxia-induced inflammatory sensitization in immune function, pathologies, and environmental adaptation.

Chinese medicinal plants for the potential management of high-altitude pulmonary oedema and pulmonary hypertension

CONTEXT

Despite the abundance of knowledge regarding high-altitude pulmonary edoema (HAPE) and high-altitude pulmonary hypertension (HAPH), their prevalence continues to be on the rise. Thus, there is an urgent need for newer safe, effective, and relatively economic drug candidates. China is particularly known for the use of medicinal plants.

OBJECTIVE

This review summarizes the medicinal plants used for HAPE and HAPH in the past 30 years, as well as some potential plants.

METHODS

Publications on HAPE and HAPH from 1990 to 2020 were identified using Web of Science, PubMed, SCOPUS, Springer Link, Google Scholar databases, Chinese Clinical Trial Registry and CNKI with the following keywords: 'medicinal plants,' 'hypoxia,' 'high altitude pulmonary edema,' 'high altitude pulmonary hypertension,' 'pathophysiology,' 'mechanisms,' 'prevention,' 'treatment,' 'human,' 'clinical,' 'safety,' and 'pharmacokinetics.'

RESULTS

We found 26 species (from 20 families) out of 5000 plants which are used for HAPE and HAPH prevention or treatment. Rhodiola rosea Linn. (Crassulaceae) is the most widely utilized. The most involved family is Lamiaceae, which contains 5 species.

DISCUSSION AND CONCLUSIONS

We mainly reviewed the medicinal plants and mechanisms for the treatment of HAPE and HAPH, and we also assessed related toxicology experiments, pharmacokinetics and bioavailability. Potential medicinal plants were also identified. Further research is needed to determine the pharmacological effects and active ingredients of these potential medicinal plants.

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 effects of a graded increase in chronic hypoxia exposure duration on healthy rats at high-altitude

To investigate the effects of chronic hypoxia exposure at high altitude on the formation of pulmonary edema in rats, we randomized rats into normoxic control groups and hypoxic 24, 48, and 72-hour exposure groups. In the hypoxic exposure group, the arterial blood gas, wet-dry weight ratio (W/D), lung tissue permeability index (LPI), bronchoalveolar lavage fluid (BALF) and plasma levels of the inflammatory factors were measured after continuous, chronic hypoxic exposure for a corresponding time, and the pathological changes in the lung tissue and the expression of tight junction-associated protein occludin were observed. We found that the contents of arterial blood gas, W/D, LPI, BALF and plasma IL-6, TNF-α, and IL-10 in the hypoxic exposure group were significantly different from the contents of arterial blood gas in the normoxic control group. H&E staining showed tissue effusion, a marked thickening of the pulmonary septum, interstitial inflammatory cells, and erythrocytic infiltration. Compared with the normoxic control group, the pulmonary edema score was significantly increased in the hypoxic 48-hour group. Toluidine blue staining showed that the mast cell count and degranulation rate were significantly increased in the hypoxic 48-hour and 72-hour groups, but massone staining showed no significant pulmonary interstitial fibrosis in the 4 groups. Occludin expression was significantly higher in the normoxic control group than it was in the hypoxic exposure group. These results indicated that different chronic hypoxic exposure durations at the plateau all caused high-altitude pulmonary edema in rats, but there was no significant difference in some indicators among the groups.

Positive association between moderate altitude and chronic lower respiratory disease mortality in United States counties

For patients with chronic lower respiratory disease, hypobaric hypoxia at a high altitude is considered a risk factor for mortality. However, the effects of residing at moderately high altitudes remain unclear. We investigated the association between moderate altitude and chronic lower respiratory disease mortality. In particular, we examined the lower 48 United States counties for age-adjusted chronic lower respiratory disease mortality rates, altitude, and socioeconomic factors, including tobacco use, per capita income, population density, sex ratio, unemployment, poverty, and education between 1979 and 1998. The socioeconomic factors were incorporated into the correlation analysis as potential covariates. Considerable positive (R = 0.235; P <0.001) and partial (R = 0.260; P <0.001) correlations were observed between altitude and chronic lower respiratory disease mortality rate. In the subgroup with high COPD prevalence subgroup, even stronger positive (R = 0.346; P <0.001) and partial (R = 0.423, P <0.001) correlations were observed. Multivariate regression analysis of all available socioeconomic factors revealed that additional knowledge on altitude improved the adjusted R2 values from 0.128 to 0.186 for all counties and from 0.301 to 0.421 for counties with high COPD prevalence. We concluded that in the lower 48 United States counties, even a moderate altitude may pose considerable risks in patients with chronic lower respiratory disease.

The MAPK-activator protein-1 signaling regulates changes in lung tissue of rat exposed to hypobaric hypoxia

This study reports the role of MAPKs (JNK, ERK, and p38), and activator protein-1 (AP-1) transcription factor in the hypobaric hypoxia induced change in lung tissue. Healthy male Sprague-Dawley rats were exposed to hypobaric hypoxia for 6, 12, 24, 48, 72, and 120 hr. Hypoxia resulted in significant increase in reactive oxygen species (ROS), vascular endothelial growth factor (VEGF) and decreased nitric oxide (NO), these act as signaling molecules for activation of MAPK and also contribute in development of vascular leakage (an indicator of pulmonary edema) as confirmed by histological studies. Our results confirmed JNK activation as an immediate early response (peaked at 6-48 hr), activation of ERKs (peaked at 24-72 hr) and p38 (peaked at 72-120 hr) as a secondary response to hypoxia. The MAPK pathway up regulated its downstream targets phospho c-Jun (peaked at 6-120 hr), JunB (peaked at 24-120 hr) however, decreased c-Fos, and JunD levels. DNA binding activity also confirmed activation of AP-1 transcription factor in lung tissue under hypobaric hypoxia. Further, we analyzed the proliferative and inflammatory genes regulated by different subunits of AP-1 to explore its role in vascular leakage. Increased expression of cyclin D1 (peaked at 12-72 hr) and p16 level (peaked at 48-120 hr) were correlated to the activation of c-jun, c-Fos and JunB. Administration of NFκB inhibitor caffeic acid phenethyl ester (CAPE) and SP600125 (JNK inhibitor) had no effect on increased levels of Interferon-γ (IFN-γ), Interleukin-1 (IL-1), and Tumor Necrosis Factor-α (TNF-α) thereby confirming the involvement of AP-1 as well as NFκB in inflammation. Expression of c-jun, c-Fos were correlated with activation of proliferative genes and JunB, Fra-1 with pro-inflammatory cytokines. In conclusion immediate response to hypobaric hypoxia induced c-Jun:c-Fos subunits of AP-1; responsible for proliferation that might cause inhomogeneous vasoconstriction leading to vascular leakage and inflammation at increased duration of hypobaric hypoxia exposure.

A journey between high altitude hypoxia and critical patient hypoxia: What can it teach us about compression and the management of critical disease?

High altitude sickness (hypobaric hypoxia) is a form of cellular hypoxia similar to that suffered by critically ill patients. The study of mountaineers exposed to extreme hypoxia offers the advantage of involving a relatively homogeneous and healthy population compared to those typically found in Intensive Care Units (ICUs), which are heterogeneous and generally less healthy. Knowledge of altitude physiology and pathology allows us to understanding how hypoxia affects critical patients. Comparable changes in mitochondrial biogenesis between both groups may reflect similar adaptive responses and suggest therapeutic interventions based on the protection or stimulation of such mitochondrial biogenesis. Predominance of the homozygous insertion (II) allele of the angiotensin-converting enzyme gene is present in both individuals who perform successful ascensions without oxygen above 8000 m and in critical patients who overcome certain disease conditions.

Significance of the changes occurring in the levels of interleukins, SOD and MDA in rat pulmonary tissue following exposure to different altitudes and exposure times

The aim of the present study was to investigate the changes occurring in the levels of interleukin, superoxide dismutase (SOD) and malondialdehyde (MDA) in rat lung tissue at different altitudes and times, and to determine the significance of such changes. A total of 88 Wistar rats were randomly divided into 3 groups as follows: the control group [low altitude (LA), 1,500 m; n=8], the moderate altitude group (MA group, 2,260 m; n=40) and the high altitude group (HA group, 5,000 m; n=40). The moderate and high altitude groups were subdivided into the 1, 3, 7, 15 and 30 day groups (MA1, 3, 7, 15, 30 and HA1, 3, 7, 15, 30; n=8). The levels of interleukins (IL-6, IL-8 and IL-10) in the rat lung tissue were determined by ELISA. The WST-1 Cell Proliferation Assay kit and total bile acids assay were used to determine the activity levels of SOD and the content of MDA, respectively. Compared to the control group, the levels of IL-6/IL-8/IL-10 were higher in the MA1 group; however, no significant differences were observed between the other MA subgroups. In addition, no significant differences were detected in SOD activity and the MDA content in the MA subgroups. The levels of IL-6/IL-8 in all the HA subgroups were higher compared to those of the control group, and with the passing of time, the levels of IL-6/IL-8 decreased, but were still higher than those of the control group. However, the level of IL-10 decreased with the passing of time, and was lower in all the HA subgroups compared to the control group. With the passing of time, SOD activity decreased, and the MDA content gradually increased. On the whole, the findings of this study indicate that hypoxia due to high altitude induces lung inflammation and oxidative damage, which subsequently causes severe damage to lung tissue.

Hypoxia-Induced Inflammatory Chemokines in Subjects with a History of High-Altitude Pulmonary Edema

High altitude hypoxia is known to induce an inflammatory response in immune cells. Hypoxia induced inflammatory chemokines may contribute to the development of high altitude pulmonary edema (HAPE) by causing damage to the lung endothelial cells and thereby capillary leakage. In the present study, we were interested to know whether chronic inflammation may contribute to HAPE susceptibility. We examined the serum levels of macrophage inflammatory protein-1α (MIP-1α), monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 in group (1) HAPE Susceptible subjects (n = 20) who had past history of HAPE and group (2) Control (n = 18) consist of subjects who had stayed at high altitude for 2 years without any history of HAPE. The data obtained confirmed that circulating MCP-1, MIP-1α were significantly upregulated in HAPE-S individuals as compared to the controls suggestive of chronic inflammation. However, it is not certain whether chronic inflammation is cause or consequence of previous episode of HAPE. The moderate systemic increase of these inflammatory markers may reflect considerable local inflammation. The existence of enhanced level of inflammatory chemokines found in this study support the hypothesis that subjects with past history of HAPE have higher baseline chronic inflammation which may contribute to HAPE susceptibility.

Differential plasma proteome analysis in patients with high-altitude pulmonary edema at the acute and recovery phases

This study aimed to investigate the differential expression of plasma proteins in patients suffering from high-altitude pulmonary edema (HAPE) at different phases. A complete proteomic analysis was performed using two-dimensional gel electrophoresis followed by mass spectrometry in three patients with HAPE at the acute stage and recovery phase. Comparisons between the expression patterns of the patients with HAPE at the two different phases led to the identification of eight protein spots with a >1.5-fold difference in expression between the acute and recovery phases. These differentially expressed proteins were apolipoproteins, serum amyloid P component, complement components and others. Apolipoprotein A-I (Apo A-I), serum amyloid P component and fibrinogen were overexpressed in the patients with HAPE in the acute stage compared with their expression levels in the recovery phase. However, Apo A-IV and antithrombin-III were overexpressed in the patients with HAPE in the recovery phase compared with their expression levels in the acute stage. The results indicate that the differential plasma proteome in patients with HAPE may be associated with the occurrence of HAPE, and the expression changes of Apo A-I and A-IV may offer further understanding of HAPE to aid its prognosis, diagnosis and treatment.

Genome wide expression analysis suggests perturbation of vascular homeostasis during high altitude pulmonary edema

Background

High altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic edema which occurs in unacclimatized but otherwise normal individuals within two to four days after rapid ascent to altitude beyond 3000 m. The precise pathoetiology and inciting mechanisms regulating HAPE remain unclear.

Methodology/Principle findings

We performed global gene expression profiling in individuals with established HAPE compared to acclimatized individuals. Our data suggests concurrent modulation of multiple pathways which regulate vascular homeostasis and consequently lung fluid dynamics. These pathways included those which regulate vasoconstriction through smooth muscle contraction, cellular actin cytoskeleton rearrangements and endothelial permeability/dysfunction. Some notable genes within these pathways included MYLK; rho family members ARGEF11, ARHGAP24; cell adhesion molecules such as CLDN6, CLDN23, PXN and VCAM1 besides other signaling intermediates. Further, several important regulators of systemic/pulmonary hypertension including ADRA1D, ECE1, and EDNRA were upregulated in HAPE. We also observed significant upregulation of genes involved in paracrine signaling through chemokines and lymphocyte activation pathways during HAPE represented by transcripts of TNF, JAK2, MAP2K2, MAP2K7, MAPK10, PLCB1, ARAF, SOS1, PAK3 and RELA amongst others. Perturbation of such pathways can potentially skew vascular homeostatic equilibrium towards altered vascular permeability. Additionally, differential regulation of hypoxia-sensing, hypoxia-response and OXPHOS pathway genes in individuals with HAPE were also observed.

Conclusions/Significance

Our data reveals specific components of the complex molecular circuitry underlying HAPE. We show concurrent perturbation of multiple pathways regulating vascular homeostasis and suggest multi-genic nature of regulation of 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.

EGLN1 variants influence expression and SaO2 levels to associate with high-altitude pulmonary oedema and adaptation

EGLN1 [encoding HIF (hypoxia-inducible factor)-prolyl hydroxylase 2] plays a pivotal role in the HIF pathway and has emerged as one of the most intriguing genes with respect to physiology at HA (high altitude). EGLN1, being an actual oxygen sensor, appears to have a potential role in the functional adaptation to the hypobaric hypoxic environment. In the present study, we screened 30 polymorphisms of EGLN1, evaluated its gene expression and performed association analyses. In addition, the role of allelic variants in altering TF (transcription factor)-binding sites and consequently the replacement of TFs at these loci was also investigated. The study was performed in 250 HAPE-p [HAPE (HA pulmonary oedema)-patients], 210 HAPE-f (HAPE-free controls) and 430 HLs (healthy Ladakhi highland natives). The genotypes of seven polymorphisms, rs1538664, rs479200, rs2486729, rs2790879, rs480902, rs2486736 and rs973252, differed significantly between HAPE-p and HAPE-f (P<0.008). The genotypes AA, TT, AA, GG, CC, AA and GG of rs1538664, rs479200, rs2486729, rs2790879, rs480902, rs2486736 and rs973252, prevalent in HAPE-p, were identified as risk genotypes and their counterpart homozygotes, prevalent in HLs, were identified as protective. EGLN1 expression was up-regulated 4.56-fold in HAPE-p (P=0.0084). The risk genotypes, their haplotypes and interacting genotypes were associated with up-regulated EGLN1 expression (P<0.05). Similarly, regression analysis showed that the risk alleles and susceptible haplotypes were associated with decreased SaO2 (arterial oxygen saturation) levels in the three groups. The significant inverse correlation of SaO2 levels with PASP (pulmonary artery systolic pressure) and EGLN1 expression and the association of these polymorphisms with SaO2 levels and EGLN1 expression contributed to uncovering the molecular mechanism underlying hypobaric hypoxic adaptation and maladaptation.

Lung oxidative damage by hypoxia

One of the most important functions of lungs is to maintain an adequate oxygenation in the organism. This organ can be affected by hypoxia facing both physiological and pathological situations. Exposure to this condition favors the increase of reactive oxygen species from mitochondria, as from NADPH oxidase, xanthine oxidase/reductase, and nitric oxide synthase enzymes, as well as establishing an inflammatory process. In lungs, hypoxia also modifies the levels of antioxidant substances causing pulmonary oxidative damage. Imbalance of redox state in lungs induced by hypoxia has been suggested as a participant in the changes observed in lung function in the hypoxic context, such as hypoxic vasoconstriction and pulmonary edema, in addition to vascular remodeling and chronic pulmonary hypertension. In this work, experimental evidence that shows the implied mechanisms in pulmonary redox state by hypoxia is reviewed. Herein, studies of cultures of different lung cells and complete isolated lung and tests conducted in vivo in the different forms of hypoxia, conducted in both animal models and humans, are described.

Nifedipine inhibits hypoxia induced transvascular leakage through down regulation of NFkB

We have studied the prophylactic administration of nifedipine and its molecular mechanism involved in reducing the transvascular leakage and inflammation in rats under hypoxia. Rats exposed to an altitude of 7620m for 6h resulted into significant increase in transvascular leakage, oxidative stress with increased NFkB expression in lungs followed by significant increase in pro inflammatory cytokines (IL-1, TNF-α) with up regulation of cell adhesion molecules (ICAM-I, VCAM-I, E-selectin, and P-selectin) in the lungs over control. Prophylactic administration of nifedipine significantly reduced the transvascular leakage, oxidative stress, inhibited the up regulation of NFkB in lungs of rats compared to control. In addition, nifedipine significantly suppressed the levels of proinflammatory cytokines and cell adhesion molecules and stabilized the HIF1-α accumulation in the lungs of rats compared to control. These results indicate that, nifedipine has an inhibitory effect on initial leaking and showed reduction in progression of inflammation through down regulation of NFkB activity in lungs of rats under hypoxia.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

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.

Role of Oxidative Stress and NFkB in Hypoxia-Induced Pulmonary Edema

Hypoxia is well known to increase the free radical generation in the body, leading to oxidative stress. In the present study, we have determined whether the increased oxidative stress further upregulates the nuclear transcription factor (NFkB) in the development of pulmonary edema. The rats were exposed to hypobaric hypoxia at 7620 m (280 mm Hg) for different durations, that is, 3 hrs, 6 hrs, 12 hrs, and 24 hrs at 25 ± 1°C. The results revealed that exposure of animals to hypobaric hypoxia led to a significant increase in vascular leakage, with time up to 6 hrs (256.38 ± 61 rfu/g) as compared with control (143.63 ± 60.1 rfu/g). There was a significant increase in reactive oxygen species, lipid peroxidation, and superoxide dismutase levels, with a concurrent decrease in lung glutathione peroxidase activity. There was 13-fold increase in the expression of NFkB level in nuclear fraction of lung homogenates of hypoxic animals over control rats. The DNA binding activity of NFkB was found to be increased significantly ( P < 0.001) in the lungs of rats exposed to hypoxia as compared with control. Further, we observed a significant increase in proinflammatory cytokines such as IL-1, IL-6, and TNF-α with concomitant upregulation of cell adhesion molecules such as ICAM-I, VCAM-I, and P-selectin in the lung of rats exposed to hypoxia as compared with control. Interestingly, pretreatment of animals with curcumin (NFkB blocker) attenuated hypoxia-induced vascular leakage in lungs with concomitant reduction of NFkB levels. The present study therefore reveals the possible involvement of NFkB in the development of pulmonary edema.

Tumor necrosis factor and stroke: role of the blood-brain barrier

The progression and outcome of stroke is affected by the intricate relationship between the blood-brain barrier (BBB) and tumor necrosis factor alpha (TNFalpha). TNFalpha crosses the intact BBB by a receptor-mediated transport system that is upregulated by CNS trauma and inflammation. In this review, we discuss intracellular trafficking and transcytosis of TNFalpha, regulation of TNFalpha transport after stroke, and the effects of TNFalpha on stroke preconditioning. TNFalpha can activate cytoprotective pathways by pretreatment or persistent exposure to low doses. This explains the paradoxical observation that transport of this proinflammatory cytokine improves the survival and function of hypoxic cells and of mice with stroke. The dual effects of TNFalpha may be related to differential regulation of TNFalpha trafficking downstream to TNFR1 and TNFR2 receptors. As we better understand how peripheral TNFalpha affects its own transport and modulates neuroregeneration, we may be in a better position to pharmacologically manipulate its regulatory transport system to treat stroke.

High-altitude physiology and pathophysiology: implications and relevance for intensive care medicine

Cellular hypoxia is a fundamental mechanism of injury in the critically ill. The study of human responses to hypoxia occurring as a consequence of hypobaria defines the fields of high-altitude medicine and physiology. A new paradigm suggests that the physiological and pathophysiological responses to extreme environmental challenges (for example, hypobaric hypoxia, hyper-baria, microgravity, cold, heat) may be similar to responses seen in critical illness. The present review explores the idea that human responses to the hypoxia of high altitude may be used as a means of exploring elements of the pathophysiology of critical illness.

Capillary pressure-induced lung injury: fact or fiction?

Lung capillary pressure in healthy humans at rest ranges between 6 and 10 mmHg. At maximal effort or in pathophysiological conditions such as left sided heart disease or massive pulmonary vasoconstriction, for example in high-altitude pulmonary disease, capillary pressure may be markedly elevated. Increased capillary pressure directly affects transendothelial fluid dynamics and thus results in the formation of hydrostatic lung edema. Excessive pressure increases may cause capillary stress failure. Recent studies, however, suggest that the microvascular response to lung capillary hypertension is more complex. Pressure, strain and shear stress cause dysfunction of the capillary endothelium characterized by an imbalanced release of vasoactive mediators. Endothelial dysfunction evokes a multicellular response with features of vasoconstriction, inflammation, and vascular leakage, thrombosis, and remodeling. These active cellular reactions contribute to the pathophysiological process and may be specifically targeted by new therapeutic strategies.

High altitude cerebral and pulmonary edema

Altitude illness, which comprises of acute mountain sickness (AMS) and its life threatening complications, high altitude cerebral edema (HACE) and high altitude pulmonary edema (HAPE) is now a well recognized disease process. AMS and HACE are generally thought to be a continuum. Some historical facts about the illness, its new intriguing pathophysiological processes, and clinical picture are discussed here. Although the review deals with both HACE and HAPE, HAPE is covered in greater detail due to the recent important findings related to its pathophysiology and prevention mechanisms. Relevant clinical correlation, the differential diagnosis of altitude sickness for a more sophisticated approach to the disease phenomenon, the possibility of dehydration being a risk factor for altitude sickness, the hypothetical role of angiogenesis in cerebral edema, and the emphasis on some vulnerable groups at high altitude are some of the other newer material discussed in this review. A clear-cut treatment and basic prevention guidelines are included in two panels, and finally the limited literature on the role of genetic factors on susceptibility to altitude sickness is briefly discussed.

Hypoxia, leukocytes, and the pulmonary circulation

Data are rapidly accumulating in support of the idea that circulating monocytes and/or mononuclear fibrocytes are recruited to the pulmonary circulation of chronically hypoxic animals and that these cells play an important role in the pulmonary hypertensive process. Hypoxic induction of monocyte chemoattractant protein-1, stromal cell-derived factor-1, vascular endothelial growth factor-A, endothelin-1, and tumor growth factor-beta(1) in pulmonary vessel wall cells, either directly or indirectly via signals from hypoxic lung epithelial cells, may be a critical first step in the recruitment of circulating leukocytes to the pulmonary circulation. In addition, hypoxic stress appears to induce release of increased numbers of monocytic progenitor cells from the bone marrow, and these cells may have upregulated expression of receptors for the chemokines produced by the lung circulation, which thus facilitates their specific recruitment to the pulmonary site. Once present, macrophages/fibrocytes may exert paracrine effects on resident pulmonary vessel wall cells stimulating proliferation, phenotypic modulation, and migration of resident fibroblasts and smooth muscle cells. They may also contribute directly to the remodeling process through increased production of collagen and/or differentiation into myofibroblasts. In addition, they could play a critical role in initiating and/or supporting neovascularization of the pulmonary artery vasa vasorum. The expanded vasa network may then act as a conduit for further delivery of circulating mononuclear cells to the pulmonary arterial wall, creating a feedforward loop of pathological remodeling. Future studies will need to determine the mechanisms that selectively induce leukocyte/fibrocyte recruitment to the lung circulation under hypoxic conditions, their direct role in the remodeling process via production of extracellular matrix and/or differentiation into myofibroblasts, their impact on the phenotype of resident smooth muscle cells and adventitial fibroblasts, and their role in the neovascularization observed in hypoxic pulmonary hypertension.

Pressure-induced leukocyte margination in lung postcapillary venules

Although pressure elevation in lung postcapillary venules increases endothelial P-selectin expression, the extent to which P-selectin causes lung leukocyte margination remains controversial. To address this issue, we optically viewed postcapillary venules of the isolated blood-perfused rat lung by real-time fluorescence imaging. To determine leukocyte margination in single postcapillary venules, we quantified the fluorescence of leukocytes labeled in situ with rhodamine 6G (R6G). Although baseline fluorescence was sparse, a 10-min pressure elevation by 10 cmH(2)O markedly increased R6G fluorescence. Both stopping blood flow during pressure elevation and eliminating leukocytes from the perfusion blocked the fluorescence increase, affirming that these fluorescence responses were attributable to pressure-induced leukocyte margination. A P-selectin-blocking MAb and the L- and P-selectin blocker fucoidin each inhibited the fluorescence increase, indicating that P-selectin was critical for inducing margination. Time-dependent imaging of blood-borne fluorescent beads revealed reduction of plasma velocity during pressure elevation. After pressure returned to baseline, a similar reduction of plasma velocity, established by manually decreasing the perfusion rate, prolonged margination. Our findings show that in lung postcapillary venules, the decrease in plasma velocity critically determines pressure-induced leukocyte margination.

Physiological aspects of high-altitude pulmonary edema

High-altitude pulmonary edema (HAPE) develops in rapidly ascending nonacclimatized healthy individuals at altitudes above 3,000 m. An excessive rise in pulmonary artery pressure (PAP) preceding edema formation is the crucial pathophysiological factor because drugs that lower PAP prevent HAPE. Measurements of nitric oxide (NO) in exhaled air, of nitrites and nitrates in bronchoalveolar lavage (BAL) fluid, and forearm NO-dependent endothelial function all point to a reduced NO availability in hypoxia as a major cause of the excessive hypoxic PAP rise in HAPE-susceptible individuals. Studies using right heart catheterization or BAL in incipient HAPE have demonstrated that edema is caused by an increased microvascular hydrostatic pressure in the presence of normal left atrial pressure, resulting in leakage of large-molecular-weight proteins and erythrocytes across the alveolarcapillary barrier in the absence of any evidence of inflammation. These studies confirm in humans that high capillary pressure induces a high-permeability-type lung edema in the absence of inflammation, a concept first introduced under the term “stress failure.” Recent studies using microspheres in swine and magnetic resonance imaging in humans strongly support the concept and primacy of nonuniform hypoxic arteriolar vasoconstriction to explain how hypoxic pulmonary vasoconstriction occurring predominantly at the arteriolar level can cause leakage. This compelling but as yet unproven mechanism predicts that edema occurs in areas of high blood flow due to lesser vasoconstriction. The combination of high flow at higher pressure results in pressures, which exceed the structural and dynamic capacity of the alveolar capillary barrier to maintain normal alveolar fluid balance.

Direct ANP inhibition of hypoxia-induced inflammatory pathways in pulmonary microvascular and macrovascular endothelial monolayers

Atrial natriuretic peptide (ANP) has been shown to reduce hypoxia-induced pulmonary vascular leak in vivo, but no explanation of a mechanism has been offered other than its vasodilatory and natriuretic actions. Recently, data have shown that ANP can protect endothelial barrier functions in TNF-alpha-stimulated human umbilical vein endothelial cells. Therefore, we hypothesized that ANP actions would inhibit pulmonary vascular leak by inhibition of TNF-alpha secretion and F-actin formation. Bovine pulmonary microvascular (MVEC) and macrovascular endothelial cell (LEC) monolayers were stimulated with hypoxia, TNF-alpha, or bacterial endotoxin (LPS) in the presence or absence of ANP, and albumin flux, NF-kappa B activation, TNF-alpha secretion, p38 mitogen-activated protein kinase (MAPK), and F-actin (stress fiber) formation were assessed. In Transwell cultures, ANP reduced hypoxia-induced permeability in MVEC and TNF-alpha-induced permeability in MVEC and LEC. ANP inhibited hypoxia and LPS increased NF-kappa B activation and TNF-alpha synthesis in MVEC and LEC. Hypoxia decreased activation of p38 MAPK in MVEC but increased activation of p38 MAPK and stress fiber formation in LEC; TNF-alpha had the opposite effect. ANP inhibited an activation of p38 MAPK in MVEC or LEC. These data indicate that in endothelial cell monolayers, hypoxia activates a signal cascade analogous to that initiated by inflammatory agents, and ANP has a direct cytoprotective effect on the pulmonary endothelium other than its vasodilatory and natriuretic properties. Furthermore, our data show that MVEC and LEC respond differently to hypoxia, TNF-alpha-stimulation, and ANP treatment.

High altitude hypoxia: an intricate interplay of oxygen responsive macroevents and micromolecules

Physiological responses to high altitude hypoxia are complex and involve a range of mechanisms some of which occur within minutes of oxygen deprivation while others reset a cascade of biosynthetic and physiological programs within the cellular milieu. The O2 sensitive events occur at various organisational levels in the body: at the level of organism through an increase in alveolar ventilation involving interaction of chemoreceptors, the respiratory control centers in the medulla and the respiratory muscles and the lung/chest wall systems; at tissue level through the pulmonary vascular smooth muscle constriction and coronary and cerebral vessel vasodilation leading to optimized blood flow to tissues; at cellular level through release of neurotransmitters by the glomus cells of the carotid body, secretion of erythropoietin hormone by kidney and liver cells and release of vascular growth factors by parenchymal cells in many tissues; at molecular level there is expression/activation of an array of genes redirecting the metabolic and other cellular mechanisms to achieve enhanced cell survival under hypoxic environment. Transactivation of various oxygen responsive genes is regulated by the activation of various transcriptional factors which results in expression of genes in a highly coordinated manner. There is thus an intricate cascading interplay of biochemical pathways in response to hypoxia, which causes changes at the physiological and molecular levels. Added to this interplay is the possibility of genetic polymorphism and protein changes to adapt to environmental influences, which may allow a variability in the activity of the pathway. Our understanding of these interactions is growing and one may be close to the precise combination of genetic factors and protein factors that underlie the mechanism of what goes on under high altitude hypoxic stress and who will cope at high altitude.

Interleukin-6 response to exercise during acute and chronic hypoxia

Prolonged exercise is associated with increased plasma levels of the cytokine interleukin-6 (IL-6). Both circulating catecholamine levels and exercise intensity have been related to the exercise-derived IL-6. During hypoxia and acclimatization, changes in sympathetic activity is seen, and also a given workload becomes more intense in hypoxia. Therefore, hypoxia offers a unique opportunity to study the effect of catecholamines and intensity on exercise-derived IL-6. In the present study, eight Danish sea-level residents performed 60 min of cycle ergometer exercise at sea level (SL) (154 W, 45% maximal O(2) consumption, VO(2)max), in acute (AH) and chronic hypoxia (CH), at the same absolute ((abs)) (AH(abs)=154 W, 54% VO(2)max; CH(abs)=154 W, 59% VO(2)max) and same relative ((rel)) (AH(rel)=130 W, 46% VO(2)max; CH(rel)=120 W, 44% VO(2)max) workload. We hypothesized that the IL-6 response to exercise at the same absolute workload would be augmented during hypoxia compared with sea level, and that these changes would not correlate with changes in catecholamines. In AH(abs) (2.35 pg.ml(-1)) and CH(abs) (3.34 pg.ml(-1)) the IL-6 response to exercise was augmented ( p<0.05) compared with that at sea level (0.78.ml(-1)). In addition, after 60 min of bicycling at sea level, AH(rel) (1.02 pg.ml(-1)) and CH(rel) (1.31 pg.ml(-1)) resulted in similar IL-6 responses. The augmented IL-6 response during AH(abs) and CH(abs) did not match changes in circulating catecholamine levels when comparing all trials. We conclude that the plasma IL-6 concentration during exercise in hypoxia is intensity dependent, and that factors other than catecholamine levels are more important for its regulation.

Pulmonary edema and pleural effusion in norepinephrine-stimulated rats--hemodynamic or inflammatory effect?

Stimulation with norepinephrine (NE) leads to pulmonary edema and pleural effusion in rats. These pulmonary fluid shifts may result from pulmonary congestion due to the hemodynamic effects of NE and/or inflammation with an increase in vascular permeability. The contribution of these two factors were investigated in the present study. Female Sprague-Dawley rats received continuous i.v. NE infusion (0.1 mg/kg/h) over time intervals between 90 min and 72 h. After heart catheterization, pleural fluid (PF) and lung tissue were obtained. In some of the animals, a bronchoalveolar lavage (BAL) was performed. Pulmonary edema and inflammation were shown histologically. We determined the expression of interleukin (IL)-6 as one of the most potent acute-phase protein mediators in serum, PF and BAL supernatant fluid (BALF) using ELISA as well as in the lung tissue using Western blotting. Total protein concentration in BALF and PF served as indicators of increased capillary permeability. Pulmonary edema and pleural effusion appeared coincidentally with an increase in total peripheral resistance (TPR) after 6 h of NE infusion. PF reached a maximum between 8 and 16 h (2.2 +/- 0.3 ml, controls < 0.5 ml) and disappeared within 48 h. Activation of IL-6 in the fluids was observed after 8 h of NE stimulation. In the lung tissue it started after 12 h and reached 330% of the control value after 48 h. Pulmonary inflammation was documented histologically. It was accompanied by increased protein concentration in BALF after 24 h of NE treatment. Hemodynamic effects of NE are the main causative factors in the initial phase of the pulmonary fluid shifts. Additionally, NE leads to an activation of cytokines such as IL-6 and to inflammation and to an increase in capillary permeability. However, inflammation and increased capillary permeability occurred later than pulmonary edema and pleural effusion. Hence, we conclude that they are secondary factors which may contribute to maintain the fluid shifts over a longer period of time.

Changes in functional and histological distributions of nitric oxide synthase caused by chronic hypoxia in rat small pulmonary arteries

1. Chronic hypoxia (CH) increases lung tissue expression of all types of nitric oxide synthase (NOS) in the rat. However, it remains unknown whether CH-induced changes in functional and histological NOS distributions are correlated in rat small pulmonary arteries. 2. We measured the effects of NOS inhibitors on the internal diameters (ID) of muscular (MPA) and elastic (EPA) pulmonary arteries (100-700 micro m ID) using an X-ray television system on anaesthetized rats. We also conducted NOS immunohistochemical localization on the same vessels. 3. Nonselective NOS inhibitors induced ID reductions in almost all MPA of CH rats (mean reduction, 36+/-3%), as compared to approximately 60% of control rat MPA (mean, 10+/-2%). The inhibitors reduced the ID of almost all EPA with similar mean values (approximately 26%) in both CH and control rats. On the other hand, inducible NOS (iNOS)-selective inhibitors caused ID reductions in approximately 60% of CH rat MPA (mean, 15+/-3%), but did so in only approximately 20% of control rat MPA (mean, 2+/-2%). This inhibition caused only a small reduction (mean, approximately 4%) in both CH and control rat EPA. A neuronal NOS-selective inhibitor had no effect. 4. The percentage of endothelial NOS (eNOS)-positive vessels was approximately 96% in both MPA and EPA from CH rats, whereas it was 51 and 91% in control MPA and EPA, respectively. The percentage for iNOS was approximately 60% in both MPA and EPA from CH rats, but was only approximately 8% in both arteries from control rats. 5. The data indicate that in CH rats, both functional and histological upregulation of eNOS extensively occurs within MPA. iNOS protein increases sporadically among parallel-arranged branches in both MPA and EPA, but its vasodilatory effect is predominantly observed in MPA. Such NOS upregulation may serve to attenuate hypoxic vasoconstriction, which occurs primarily in MPA and inhibit the progress of pulmonary hypertension.

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.

Exercise and hypoxia: effects on leukocytes and interleukin-6-shared mechanisms?

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It has been suggested that exercise can be employed as a model of temporary immunosuppression, which occurs during physical stress, such as hypoxia. Acute exercise and acute hypoxia mediate in principle identical effects on circulating lymphocyte and neutrophil numbers. Thus, during exercise and hypoxia, lymphocytes are recruited to the blood. After the stress, the number of lymphocytes declines after the stress, whereas the neutrophil number continues to increase. When exercise is performed during hypoxia, the exercise-induced immune changes are pronounced. There is some evidence that the exercise- and hypoxia-induced changes in leukocyte subpopulations are mediated by neuroendocrinological factors such as catecholamines, growth hormone, and cortisol. In contrast, although exercise, as well as hypoxia, is associated with increased plasma levels of IL-6, the mechanisms are not likely to be the same. Thus, during exercise, contracting skeletal muscles are the main source of IL-6 production, whereas the source of IL-6 during hypoxia has not been demonstrated. The increased level of adrenaline contributes to the enormous increase in plasma IL-6 only to a minor degree during strenuous exercise. However, the only modest increase in IL-6 during hypoxia may be linked to hormonal changes, whereas the prolonged increase in IL-6 during chronic hypoxia is likely to be multifactorial.

Update: High altitude pulmonary edema

Recent high altitude studies with pulmonary artery (PA) catheterization and broncho-alveolar lavage (BAL) in early high altitude pulmonary edema(HAPE) have increased our understanding of the pathogenetic sequence in HAPE. High preceding PA and pulmonary capillary pressures lead to a non-inflammatory leak of the alveolar-capillary barrier with egress of red cells, plasma proteins and fluid into the alveolar space. The mechanisms accounting for an increased capillary pressure remain speculative. The concept that hypoxic pulmonary vasoconstriction (HPV) is uneven so that regions with less vasoconstriction are over-perfused and become edematous remains compelling but unproved. Also uncertain is the role and extent of pulmonary venoconstriction. With disruption of the normal alveolar-capillary barrier, some individuals may later develop a secondary inflammatory reaction. A high incidence of preceding or concurrent respiratory infection in children with HAPE has been used to support a causative role of inflammation in HAPE. However, alternatively even mild HPV may simply lower the threshold at which inflammation-mediated increases in alveolar capillary permeability cause significant fluid flux into the lung. Other major questions to be addressed in future research are: 1.) What is the mechanism of exaggerated hypoxic pulmonary vasoconstriction? Is there a link to primary pulmonary hypertension? Several observations suggest that susceptibility to HAPE is associated with endothelial dysfunction in pulmonary vessels. This has not yet been studied adequately. 2.) What is the nature of the leak? Is there structural damage, i. e. stress failure, or does stretch cause opening of pores? 3.) What is the pathophysiologic significance of a decreased sodium and water clearance across alveolar epithelial cells in hypoxia? 4.) What is the role of exercise? Do HAPE-susceptible individuals develop pulmonary edema when exposed to hypoxia without exercise? Answers to these questions will increase our understanding of the pathophysiology of HAPE and also better focus research on the genetic basis of susceptibility to HAPE.

Pressure-induced endothelial Ca(2+) oscillations in lung capillaries

Endothelial second messenger responses may contribute to the pathology of high vascular pressure but remain poorly understood because of the lack of direct in situ quantification. In lung venular capillaries, we determined endothelial cytosolic Ca(2+) concentration [Ca(2+)](i) by the fura 2 ratioing method. Pressure elevation increased mean endothelial [Ca(2+)](i) by Ca(2+) influx through gadolinium-inhibitable channels and amplified [Ca(2+)](i) oscillations by Ca(2+) release from intracellular stores. Endothelial [Ca(2+)](i) transients were induced by pressure elevations of as little as 5 cmH(2)O and increased linearly with higher pressures. Heptanol inhibition of [Ca(2+)](i) oscillations in a subset of endothelial cells indicated that oscillations originated from pacemaker endothelial cells and were propagated to adjacent nonpacemaker cells by gap junctional communication. Our findings indicate the presence of a sensitive, active endothelial response to pressure challenge in lung venular capillaries that may be relevant in the pathogenesis of pressure-induced lung microvascular injury.

Atrial natriuretic peptide blockade exacerbates high altitude pulmonary edema in endotoxin-primed rats

High altitude pulmonary edema (HAPE) is associated with increases in pulmonary arterial and hydrostatic pressures and an increase in pulmonary vascular permeability. There is evidence to suggest that inflammatory mediators may cause some forms of HAPE, and Salmonella enteritidis endotoxin (ETX) is known to activate neutrophils and inflammatory mediators, such as TNF-alpha and IL1-beta. Since HAPE has been produced in rats primed with ETX, we hypothesized that ANP release and action may ameliorate HAPE and that ANP blockade may exacerbate HAPE in ETX-primed rats exposed to high altitude (HA). Plasma ANP, right atrial ANP mRNA, and indexes of lung injury were measured in rats primed with endotoxin (ETX) (0.1 mg/kg BW, i.p.) and exposed to simulated HA (4267 m; P(B) = 440 mmHg) for either 12 or 24 h. Catheters were chronically inserted into the right carotid artery, pulmonary artery, and jugular vein for assessment of hemodynamic parameters in response to ETX and/or HA. In addition, some rats were injected with an antibody against ANP (alphaANP) prior to normoxic (NX) or HA exposure. Pulmonary arterial pressure increased in the alphaANP group (50 +/- 20%; p < or = 0.05) and in the HA + alphaANP (51 +/- 15%; p < or = 0.05) group at 12 h compared to NX sham rats injected with normal rabbit serum. In addition, systemic arterial pressure was significantly lower in the HA + ETX rats compared to HA + ETX + alphaANP rats (p < or = 0.001). Plasma ANP levels were significantly higher at 12 and 24 h in ETX, HA, and HA + ETX groups (p <or = 0.05) compared to NX controls. There was an inverse relationship (p <or = 0.001) between plasma ANP levels and lung wet to dry (W/D) weight when data from NX, ETX, HA, and HA + ETX groups were pooled. The HA + alphaANP rats had significantly higher lung W/D ratios (p < 0.001) compared to sham rats. These results support the hypothesis that ANP, at physiological levels, modulates the development of pulmonary edema in HA-exposed ETX-primed rats.

Acute hypoxia and hypoxic exercise induce DNA strand breaks and oxidative DNA damage in humans

The present study investigated the effect of a single bout of exhaustive exercise on the generation of DNA strand breaks and oxidative DNA damage under normal conditions and at high-altitude hypoxia (4559 meters for 3 days). Twelve healthy subjects performed a maximal bicycle exercise test; lymphocytes were isolated for analysis of DNA strand breaks and oxidatively altered nucleotides, detected by endonuclease III and formamidipyridine glycosylase (FPG) enzymes. Urine was collected for 24 h periods for analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a marker of oxidative DNA damage. Urinary excretion of 8-oxodG increased during the first day in altitude hypoxia, and there were more endonuclease III-sensitive sites on day 3 at high altitude. The subjects had more DNA strand breaks in altitude hypoxia than at sea level. The level of DNA strand breaks further increased immediately after exercise in altitude hypoxia. Exercise-induced generation of DNA strand breaks was not seen at sea level. In both environments, the level of FPG and endonuclease III-sensitive sites remained unchanged immediately after exercise. DNA strand breaks and oxidative DNA damage are probably produced by reactive oxygen species, generated by leakage of the mitochondrial respiration or during a hypoxia-induced inflammation. Furthermore, the presence of DNA strand breaks may play an important role in maintaining hypoxia-induced inflammation processes. Hypoxia seems to deplete the antioxidant system of its capacity to withstand oxidative stress produced by exhaustive exercise.

Urinary leukotriene E(4) levels are not increased prior to high-altitude pulmonary edema

STUDY OBJECTIVE

To examine whether increased urinary cysteinyl-leukotriene E(4) (LTE(4)) excretion, which has been found to be elevated in patients presenting with high-altitude pulmonary edema (HAPE), precedes edema formation.

DESIGN

Prospective studies in a total of 12 subjects with susceptibility to HAPE.

SETTING

In a chamber study, seven subjects susceptible to HAPE and five nonsusceptible control subjects were exposed for 24 h to an altitude of 450 m (control day), and exposed for 20 h to 4,000 m after slow decompression over 4 h. In a field study, prospective measurements at low and high altitude were performed in five subjects developing HAPE at 4,559 m.

PARTICIPANTS

Mountaineers with a radiographically documented history of HAPE and control subjects who did not develop HAPE with identical high-altitude exposure.

INTERVENTIONS

24-h urine collections.

MEASUREMENTS AND RESULTS

In the hypobaric chamber, none of the subjects developed HAPE. The 24-h urinary LTE(4) did not differ between HAPE susceptible and control subjects, nor between hypoxia and normoxic control day. In the field study, urinary LTE(4) was not increased in subjects with HAPE compared to values obtained prior to HAPE at high altitude and during 2 control days at low altitude.

CONCLUSIONS

These data do not provide evidence that cysteinyl-leukotriene-mediated inflammatory response is associated with HAPE susceptibility or the development of HAPE within the context of our studies.

High altitude increases circulating interleukin-6, interleukin-1 receptor antagonist and C-reactive protein

Hypoxic pulmonary vasoconstriction is associated with but may not be sufficient for the development of high-altitude pulmonary oedema (HAPO). Hypoxia is known to induce an inflammatory response in immune cells and endothelial cells. It has been speculated that hypoxia-induced inflammatory cytokines at high altitude may contribute to the development of HAPO by causing capillary leakage in the lung. We were interested if such an inflammatory response, possibly involved in a later development of HAPO, is detectable at high altitude in individuals without HAPO. We examined the plasma levels of interleukin 6 (IL-6), interleukin 1 receptor antagonist (IL-1ra) and C-reactive protein (CRP) in two independent studies: study A, Jungfraujoch, Switzerland, three overnight stays at 3458 m, n=12; study B: Capanna Regina Margherita, Italy, 3 overnight stays at 3647 m and one overnight stay at 4559 m, n=10. In both studies, probands showed symptoms of acute mountain sickness but no signs of HAPO. At the Jungfraujoch, IL-6 increased from 0.1+/-0.03 pg/ml to 2. 0+/-0.5 pg/ml (day 2, P=0.03), IL-1ra from 101+/-21 to 284+/-73 pg/ml (day 2, P=0.01), and CRP from 1.0+/-0.4 to 5.8+/-1.5 micrograms/ml (day 4, P=0.01). At the Capanna Margherita, IL-6 increased from 0. 5+/-0.2 pg/ml to 2.0+/-0.8 pg/ml (P=0.02), IL-1ra from 118+/-25 to 213+/-28 pg/ml (P=0.02), and CRP from 0.4+/-0.03 to 3.5+/-1.1 micrograms/ml (P=0.03). IL-8 was below the detection limit of the ELISA (<25 pg/ml) in both studies. The increase of IL-6 and IL-1ra in response to high altitude was delayed and preceded the increase of CRP. We conclude that: (1) circulating IL-6, IL-1ra and CRP are upregulated in response to hypobaric hypoxic conditions at high altitude, and (2) the moderate systemic increase of these inflammatory markers may reflect considerable local inflammation. The existence and the kinetics of high altitude-induced cytokines found in this study support the hypothesis that inflammation is involved in the development of HAPO.

Pressure is proinflammatory in lung venular capillaries

Endothelial responses may contribute importantly to the pathology of high vascular pressure. In lung venular capillaries, we determined endothelial [Ca(2+)](i) by the fura-2 ratioing method and fusion pore formation by quantifying the fluorescence of FM1-43. Pressure elevation increased endothelial [Ca(2+)](i). Concomitantly evoked exocytotic events were evident in a novel spatial-temporal pattern of fusion pore formation. Fusion pores formed predominantly at vascular branch points and colocalized with the expression of P-selectin. Blockade of mechanogated Ca(2+) channels inhibited these responses, identifying entry of external Ca(2+) as the critical triggering mechanism. These endothelial responses point to a proinflammatory effect of high vascular pressure that may be relevant in the pathogenesis of pressure-induced lung disease.

High altitude pulmonary edema

High altitude pulmonary edema. Med. Sci. Sports Exerc., Vol. 31, No. 1 (Suppl.), pp. S23-S27, 1999. Altitude, speed and mode of ascent, and, above all, individual susceptibility are the most important determinants for the occurrence of high altitude pulmonary edema (HAPE). This illness usually occurs only 2-5 d after acute exposure to altitudes above 2500-3000 m. Chest radiographs and CT scans show a patchy predominantly peripheral distribution of edema. Wedge pressure is normal at rest, and there is an excessive rise of pulmonary artery pressure (PAP) that precedes edema formation and appears to be a crucial pathophysiologic factor for HAPE. Additional factors such as an inflammatory response and/or a decreased fluid clearance from the lung may, however, be necessary for the development of this noncardiogenic pulmonary edema. Bronchoalveolar lavage in patients with mostly advanced HAPE shows evidence of inflammatory response with increased permeability. There are, however, no prospective data to decide whether the inflammatory response is a primary cause of HAPE or a consequence of edema formation. Supplemental oxygen is the primary treatment in areas with medical facilities whereas the treatment of choice in remote mountain areas is immediate descent. When this is impossible and supplemental oxygen is not available, treatment with nifedipine is recommended until descent is possible. Even susceptible individuals can avoid HAPE when they ascend slowly with an average gain of altitude not exceeding 300-350 m.d-1 above an altitude of 2500 m.

Association of high-altitude pulmonary edema with the major histocompatibility complex

BACKGROUND

A constitutional susceptibility has been suggested in the development of high-altitude pulmonary edema (HAPE) because HAPE generally affects healthy young people, some of whom suffer recurrent episodes. We examined whether immunogenetic susceptibility is present in HAPE-susceptible subjects.

METHODS AND RESULTS

The frequencies of human leukocyte antigen (HLA) alleles in 28 male and 2 female subjects with a history of HAPE were compared with those in 100 healthy volunteers. We assayed the HLA-A, -B, -C, -DR, and -DQ antigens serologically. The pulmonary hemodynamics on admission to the hospital and the ventilatory response to hypoxia and hypercapnia were retrospectively examined in 10 of the HAPE-susceptible subjects. HLA-DR6 was positive in 14 (46.7%) of the subjects with HAPE but only 16.0% of the control subjects (P=.0005), and HLA-DQ4 was positive in 12 (40.0%) of the subjects with HAPE but only 10.0% of the control subjects (P=.0001). HLA-DR6 or HLA-DQ4 was positive in 8 (100%) of the subjects with recurrent HAPE. The pulmonary arterial pressure on admission of the HLA-DR6-positive subjects with HAPE was significantly higher than that of the HLA-DR6-negative subjects with HAPE.

CONCLUSIONS

There were significant associations of HAPE with HLA-DR6 and HLA-DQ4 and of pulmonary hypertension with HLA-DR6. An immunogenetic susceptibility, which is associated with HLA class II alleles located within the major histocompatibility complex, may underlie the development of HAPE, at least in some of its forms.