High Altitude Renal Syndrome (HARS)

Preexisting Hyperuricemia Before High-Altitude Ascent is Associated with a Slower Recovery of Estimated Glomerular Filtration Rate Following Descent

Zhao, Linggong, Yujie Huang, and Xiaoling Tan. Preexisting hyperuricemia before high-altitude ascent is associated with a slower recovery of estimated glomerular filtration rate following descent. High Alt Med Biol. 00:00-00, 2024. Objectives: Hypoxia at high altitudes results in elevated uric acid (UA) and reduced estimated glomerular filtration rate (eGFR). However, the impact of a prolonged high-altitude sojourn on UA levels and renal function in patients with preexisting hyperuricemia warrants further exploration. The study was to investigate the eGFR and related factors in patients with preexisting hyperuricemia following exposure to high altitude. Methods: The study included 345 participants, who worked at a high altitude for 1 year. Anthropometric and laboratory indices were collected before ascent (i.e., baseline), as well as 20 and 80 days after descent. The participants were categorized into individuals with hyperuricemia (HUA) or normal uric acid (NUA) group based on the presence or absence of hyperuricemia at baseline. Results: No difference in baseline eGFR was observed between the two groups before ascend or on day 20 after descent (p > 0.05). However, on day 80, eGFR of the HUA group was lower compared with the NUA group (p < 0.05). Correlations existed between post-descent eGFR levels and variables, including sampling time, UA levels, total and direct bilirubin, and baseline grouping. Conclusions: After high-altitude exposure, the recovery of eGFR was delayed in participants with preexisting hyperuricemia. Preexisting hyperuricemia and high-altitude hypoxia jointly contribute to renal impairment.

Alveolar hypoxia induces organ-specific inflammasome-related inflammation in male mouse lungs

Inflammation through activation of caspase-1, seems to play a role in pulmonary hypertension induced by alveolar hypoxia. Whether alveolar hypoxia induces caspase-1-mediated inflammation and influx of leukocytes in other organs than the lungs, is not known. Our aim was to explore sites of caspase-1-related inflammation in alveolar hypoxia. Wild type (WT) mice were exposed to environmental hypoxia or room-air, and organs were analyzed. Right heart catheterization was performed after 14 days of alveolar hypoxia in WT mice and mice transplanted with WT or caspase-1-/- bone marrow. Hypoxia induced leukocyte accumulation and increased caspase-1 protein in the lungs, not in other organs. WT mice transplanted with WT or caspase-1-/- bone marrow showed no difference in pulmonary leukocyte accumulation or development of pulmonary hypertension after alveolar hypoxia. Caspase-1 and IL-18 were detected in bronchial epithelium in WT mice, and hypoxia induced IL-18 secretion from bronchial epithelial cells. IL-18 stimulation generated IL-6 mRNA in monocytes. Phosphorylated STAT3 was increased in hypoxic lungs, not in other organs. Alveolar hypoxia induces caspase-1 activation and leukocyte accumulation specific to the lungs, not in other organs. Caspase-1 activation and IL-18 secretion from bronchial epithelial cells might initiate hypoxia-induced inflammation, leading to pulmonary hypertension.

A Case of High-Altitude Renal Syndrome

Wang, Si-Yang, Jun Liang, and Jing-Hong Zhao. A Case of High-Altitude Renal Syndrome. High Alt Med Biol. 00:000-000, 2024.-Epidemiological studies have confirmed that high-altitude exposure increases the risk of proteinuria. The concept of high-altitude renal syndrome (HARS) was proposed in 2011. HARS is a group of clinical syndromes consisting of high-altitude polycythemia, hyperuricemia, systemic hypertension, and microalbuminuria. At present, no standardized and unified treatment methods of HARS have been proposed. We report a case of HARS without other organ involvement in a young man exposed to high altitude. Decreasing the red blood cell count and hemodynamic changes as soon as possible may be of great importance for reducing proteinuria. In addition, angiotensin receptor blockers are effective in the treatment of HARS.

Exploring the impact of high-altitude de-acclimatization on renal function: The roles of oxidative and endoplasmic reticulum stress in rat models

BACKGROUND

High-altitude de-acclimatization (HADA) significantly impacts physiological functions when individuals acclimatize to high altitudes return to lower altitudes. This study investigates HADA's effects on renal function and structure in rats, focusing on oxidative and endoplasmic reticulum stress as potential mechanisms of renal injury.

OBJECTIVE

To elucidate the pathophysiological mechanisms of renal damage in HADA and evaluate the efficacy of antioxidants Vitamin C (Vit C) and tauroursodeoxycholic acid (TUDCA) in mitigating these effects.

METHODS

88 male Sprague-Dawley rats were randomly divided into a control group, a high-altitude (HA) group, a high-altitude de-acclimatization (HADA) group, and a treatment group. The control group was housed in a sea level environment (500 m), while the HA, HADA, and treatment groups were placed in a simulated high-altitude chamber (5000 m) for 90 days. After this period, the HA group completed the modeling phase; the HADA group was further subdivided into four subgroups, each continuing to be housed in a sea level environment for 3, 7, 14, and 30 days, respectively. The treatment group was split into the Vit C group, the TUDCA group, and two placebo groups, receiving medication for 3 consecutive days, once daily upon return to the sea level. The Vit C group received 100 mg/kg Vit C solution via intravenous injection, the TUDCA group received 250 mg/kg TUDCA solution via intraperitoneal injection, and the placebo groups received an equivalent volume of saline similarly. Serum, urine, and kidney tissues were collected immediately after the modeling phase. Renal function and oxidative stress levels were assessed using biochemical and ELISA methods. Renal histopathology was observed with H&E, Masson's trichrome, PAS, and PASM staining. Transmission electron microscopy was used to examine the ultrastructure of glomeruli and filtration barrier. TUNEL staining assessed cortical apoptosis in the kidneys. Metabolomics was employed for differential metabolite screening and pathway enrichment analysis.

RESULTS

Compared to the control and HA groups, the HADA 3-day group (HADA-3D) exhibited elevated renal function indicators, significant pathological damage, observable ultrastructural alterations including endoplasmic reticulum expansion and apoptosis. TUNEL-positive cells significantly increased, indicating heightened oxidative stress levels. Various differential metabolites were enriched in pathways related to oxidative and endoplasmic reticulum stress. Early intervention with Vit C and TUDCA markedly alleviated renal injury in HADA rats, significantly reducing the number of apoptotic cells, mitigating endoplasmic reticulum stress, and substantially lowering oxidative stress levels.

CONCLUSION

This study elucidates the pivotal roles of oxidative and endoplasmic reticulum stress in the early-stage renal injury in rats undergoing HADA. Early intervention with the Vit C and TUDCA significantly mitigates renal damage caused by HADA. These findings provide insights into the pathophysiological mechanisms of HADA and suggest potential therapeutic strategies for its future management.

Erythrocytosis and CKD: A Review

Erythrocytosis or polycythemia is defined as an increase in red blood cell concentration above the age- and sex-specific normal levels. Unlike anemia, which is very common in patients with chronic kidney disease (CKD), erythrocytosis is less frequent but requires specific understanding by health care professionals in order to provide the best care. Erythrocytosis, especially when undiagnosed and untreated, can lead to serious thrombotic events and higher mortality. Classic causes of erythrocytosis associated with CKD include cystic kidney diseases, kidney or other erythropoietin-secreting neoplasms, high-altitude renal syndrome, overdosage of erythropoietin-stimulating agents, androgen therapy, heavy smoking, chronic lung disease, obstructive sleep apnea, IgA nephropathy, post-kidney transplant erythrocytosis, renal artery stenosis, and congenital etiologies. After ruling out the common acquired causes of erythrocytosis and/or in the presence of suggestive parameters, primary erythrocytosis or polycythemia vera (PV) should be considered, and patients should be screened for JAK2V617F somatic mutation. The newest entity inducing erythrocytosis is linked to the use of sodium/glucose cotransporter 2 (SGLT2) inhibitors that hypothetically activate hypoxia-inducible factor 2α (HIF-2α) and in some cases unmask PV. This Review focuses on the pathogenesis, renal manifestations and management of PV, the pathophysiology of erythrocytosis induced by SGLT2 inhibitors and the relevance of timely JAK2 mutation screening in these patients.

Antibiotic intervention exacerbated oxidative stress and inflammatory responses in SD rats under hypobaric hypoxia exposure

The gut microbiota plays a crucial role in maintaining host nutrition, metabolism, and immune homeostasis, particularly in extreme environmental conditions. However, the regulatory mechanisms of the gut microbiota in animal organisms hypobaric hypoxia exposure require further study. We conducted a research by comparing SD rats treated with an antibiotic (ABX) cocktail and untreated SD rats that were housed in a low-pressure oxygen chamber (simulating low pressure and hypoxic environment at 6000 m altitude) for 30 days. After the experiment, blood, feces, and lung tissues from SD rats were collected for analysis of blood, 16S rRNA amplicon sequencing, and non-targeted metabolomics. The results demonstrated that the antibiotic cocktail-treated SD rats exhibited elevated counts of neutrophil (Neu) and monocyte (Mon) cells, an enrichment of sulfate-reducing bacteria (SBC), reduced levels of glutathione, and accumulated phospholipid compounds. Notably, the accumulation of phospholipid compounds, particularly lysophosphatidic acid (LPA), lipopolysaccharide (LPS), and lysophosphatidylcholine (LPC), along with the aforementioned changes, contributed to heightened oxidative stress and inflammation in the organism. In addition, we explored the resistance mechanisms of SD rats in low-oxygen and low-pressure environments and found that increasing the quantity of the Prevotellaceae and related beneficial bacteria (especially Lactobacillus) could reduce oxidative stress and inflammation. These findings offer valuable insights into enhancing the adaptability of low-altitude animals under hypobaric hypoxia exposure.

Untargeted metabolomics analysis on kidney tissues from mice reveals potential hypoxia biomarkers

Chronic hypoxia may have a huge impact on the cardiovascular and renal systems. Advancements in microscopy, metabolomics, and bioinformatics provide opportunities to identify new biomarkers. In this study, we aimed at elucidating the metabolic alterations in kidney tissues induced by chronic hypoxia using untargeted metabolomic analyses. Reverse phase ultrahigh performance liquid chromatography-mass spectroscopy/mass spectroscopy (RP-UPLC-MS/MS) and hydrophilic interaction liquid chromatography (HILIC)-UPLC-MS/MS methods with positive and negative ion mode electrospray ionization were used for metabolic profiling. The metabolomic profiling revealed an increase in metabolites related to carnitine synthesis and purine metabolism. Additionally, there was a notable increase in bilirubin. Heme, N-acetyl-L-aspartic acid, thyroxine, and 3-beta-Hydroxy-5-cholestenoate were found to be significantly downregulated. 3-beta-Hydroxy-5-cholestenoate was downregulated more significantly in male than female kidneys. Trichome Staining also showed remarkable kidney fibrosis in mice subjected to chronic hypoxia. Our study offers potential intracellular metabolite signatures for hypoxic kidneys.

The benefits of early continuous renal replacement therapy in critically ill patients with acute kidney injury at high-altitude areas: a retrospective multi-center cohort study

Severe hypoxia would aggravate the acute kidney injury (AKI) in high-altitude areas and continuous renal replacement therapy (CRRT) has been used to treat critically ill patients with AKI. However, the characteristics and outcomes of CRRT in critically ill patients at AKI in high altitudes and the optimal timing of CRRT initiation remain unclear. 1124 patients were diagnosed with AKI and treated with CRRT in the ICU, comprising a high-altitude group (n = 648) and low-altitude group (n = 476). Compared with the low-altitude group, patients with AKI at high altitude showed longer CRRT (4.8 vs. 3.7, P = 0.036) and more rapid progression of AKI stages (P < 0.01), but without any significant minor or major bleeding episodes (P > 0.05). Referring to the analysis of survival and kidney recovery curves, a higher mortality but a lower possibility of renal recovery was observed in the high-altitude group (P < 0.001). However, in the high-altitude group, the survival rate of early CRRT initiation was significantly higher than that of delayed CRRT initiation (P < 0.001). The findings showed poorer clinical outcomes in patients undergoing CRRT for AKI at high altitudes. CRRT at high altitudes was unlikely to increase the adverse events. Moreover, early CRRT initiation might reduce the mortality and promote renal recovery in high-altitude patients.

Hypobaric Hypoxia Aggravates Renal Injury by Inducing the Formation of Neutrophil Extracellular Traps through the NF-κB Signaling Pathway

OBJECTIVE

The hypersensitivity of the kidney makes it susceptible to hypoxia injury. The involvement of neutrophil extracellular traps (NETs) in renal injury resulting from hypobaric hypoxia (HH) has not been reported. In this study, we aimed to investigate the expression of NETs in renal injury induced by HH and the possible underlying mechanism.

METHODS

A total of 24 SD male rats were divided into three groups (n=8 each): normal control group, hypoxia group and hypoxia+pyrrolidine dithiocarbamate (PDTC) group. Rats in hypoxia group and hypoxia+PDTC group were placed in animal chambers with HH which was caused by simulating the altitude at 7000 meters (oxygen partial pressure about 6.9 kPa) for 7 days. PDTC was administered at a dose of 100 mg/kg intraperitoneally once daily for 7 days. Pathological changes of the rat renal tissues were observed under a light microscope; the levels of serum creatinine (SCr), blood urea nitrogen (BUN), cell-free DNA (cf-DNA) and reactive oxygen species (ROS) were measured; the expression levels of myeloperoxidase (MPO), citrullinated histone H3 (cit-H3), B-cell lymphoma 2 (Bcl-2), Bax, nuclear factor kappa B (NF-κB) p65 and phospho-NF-κB p65 (p-NF-κB p65) in rat renal tissues were detected by qRT-qPCR and Western blotting; the localization of NF-κB p65 expression in rat renal tissues was observed by immunofluorescence staining and the expression changes of NETs in rat renal tissues were detected by multiplex fluorescence immunohistochemical staining.

RESULTS

After hypoxia, the expression of NF-κB protein in renal tissues was significantly increased, the levels of SCr, BUN, cf-DNA and ROS in serum were significantly increased, the formation of NETs in renal tissues was significantly increased, and a large number of tubular dilatation and lymphocyte infiltration were observed in renal tissues. When PDTC was used to inhibit NF-κB activation, NETs formation in renal tissue was significantly decreased, the expression level of Bcl-2 in renal tissues was significantly increased, the expression level of Bax was significantly decreased, and renal injury was significantly alleviated.

CONCLUSION

HH induces the formation of NETs through the NF-κB signaling pathway, and it promotes apoptosis and aggravates renal injury by decreasing Bcl-2 and increasing Bax expression.

Prevalence of High-Altitude Polycythemia and Hyperuricemia and Risk Factors for Hyperuricemia in High-Altitude Immigrants

Song Zhen, Anxin Zhang, Jie Luo, Guanghai Xiong, Haibo Peng, Rang Zhou, Yuanfeng Li, Hongqiang Xu, Zhen Li, Wei Zhao, and Haoxiang Zhang. Prevalence of high-altitude polycythemia and hyperuricemia and risk factors for hyperuricemia in high-altitude immigrants. High Alt Med Biol. 24:132-138, 2023. Background: Few studies have investigated the epidemiology of chronic mountain sickness (CMS) in high-altitude immigrants. This study evaluated the prevalence of polycythemia and hyperuricemia (HUA) and risk factors for HUA in high-altitude immigrants. Methods: A cross-sectional study was conducted with 7,070 immigrants 15-45 years of age living on the Tibetan Plateau between January and December 2021. Information from routine physical examinations was obtained from each participant. Binary logistic regression analysis was performed to determine the correlation of several risk factors for HUA. Results: The prevalence of high-altitude polycythemia (HAPC) and HUA was 25.8% (28.7% in males and 9.4% in females) and 54.2% (59.9% in males and 22.5% in females), respectively. The highest prevalence of HAPC in males and females was observed in participants 26-30 and 21-25 years of age, respectively. The highest prevalence of HUA in both males and females was observed in participants 26-30 years of age. Binary logistic regression analysis showed that age, sex, and hemoglobin (Hb) concentration were risk factors for HUA, among which age was a negative factor and male sex and Hb concentration were positive factors. Conclusions: Immigrants are more susceptible to HAPC and HUA. The high prevalence of CMS of immigrants may be associated with Hb concentration, age, and sex.

Prevalence and Risk Factors of Ovine and Caprine Fasciolosis in the Last 20 Years in China: A Systematic Review and Meta-Analysis

Fasciolosis is a significant zoonotic and common parasitic disease for animals and humans, creating public health concerns worldwide. This study retrieved articles related to the occurrence of Fasciola hepatica and Fasciola gigantica in sheep and goats in China by searching five databases: PubMed, ScienceDirect, the Chinese National Knowledge Infrastructure (CNKI), Wanfang Data, and the VIP Chinese Journal Database. A total of 60 valid articles were captured. The pooled prevalence of ovine and caprine fasciolosis was 26.00%. It was also found to be higher in the subgroups of Northwest China and Shaanxi Province, as well as in areas with a high altitude, rainfall of ≥800 mm, and temperature ranging between 10 °C and 20 °C. Analysis of the type of season and sampling years showed significant (p < 0.05) difference. In other subgroups, sheep (34.74%), hosts aged over 2 years (32.26%), females (48.33%) and free-range animals (26.83%) showed a higher disease prevalence. These results indicated that ovine and caprine fasciolosis was widely distributed, especially in Northwest China. The sampling years and the type of season are risk factors for the prevalence of ovine and caprine fasciolosis. Therefore, strategies for ovine and caprine fasciolosis control should be developed based on these epidemic risk factors, which will reduce the prevalence of fasciolosis in China.

K. Sagi S. Hypobaric hypoxia induced renal injury in rats: Prophylactic amelioration by quercetin supplementation

The present study aims at assessing the effect of hypobaric hypoxia induced renal damage and associated renal functions in male SD rats. Further, this study was extended to explore the protective efficacy of quercetin in ameliorating the functional impairment in kidneys of rats under hypobaric hypoxia. Rats were exposed to 7620m (25000 ft.) at 25°C ±2 in a simulated hypobaric hypoxia chamber for different time durations (0h,1h, 3h, 6h, 12h, 24h and 48h) in order to optimize the time at which maximum renal damage would occur. The rats were exposed to hypoxia for 12h duration was considered as the optimum time, due to significant increase in oxidative stress (ROS, MDA) and renal metabolites (creatinine, BUN and uric acid) with remarkable reduction (p<0.001) in antioxidants (GSH) in plasma, as compared to other tested durations. Moreover, these findings were in support with the histopathology analysis of renal tissues. For optimum quercetin dose selection, the rats were administered with different doses of quercetin (25mg, 50mg, 100mg and 200mg/Kg BW) for 12h at 7620 m, 25°C ±2, 1h prior to hypoxia exposure. Quercetin 50mg/kg BW was considered as the optimum dose at which significant (p<0.001) reduction in oxidative stress levels followed by reduction in creatinine and BUN levels were obtained in plasma of the rats compared to hypoxia control rats. Quercetin prophylaxis (50mg/kg BW) stabilized the HIF-1α protein expression followed by reduced VEGF protein expression along with reduced levels of LDH (p<0.001) in the kidneys of rats compared to hypoxia control. Histopathological observations further substantiated these findings in reducing the renal tissue injury. The study findings revealed that, quercetin prophylaxis abrogates the possibility of hypobaric hypoxia induced renal injury by reducing the oxidative stress in rats.

Two a posteriori dietary patterns are associated with risks of hyperuricemia among adults in less-developed multiethnic regions in Southwest China

Diet is a major determinant of hyperuricemia, but little is known about the association between diet and hyperuricemia in less-developed multiethnic regions (LMERs). This study aimed to assess the hypothesis that dietary patterns (including 2 a-priori and 3 a posteriori dietary patterns) are associated with hyperuricemia in LMERs. The 2 a priori dietary patterns were the Dietary Approaches to Stop Hypertension (DASH) and the alternative Mediterranean diet (aMED). We derived 3 a posteriori dietary patterns from the China Multi-Ethnic Cohort study by principal component factor analysis. Given that those dietary patterns had high geographic discrimination, they were named the Sichuan Basin (economically developed industrial region), Yunnan-Guizhou Plateau (agricultural region), and Qinghai-Tibet Plateau (nomadic region) dietary pattern, respectively. We performed a logistic regression model to investigate associations between dietary patterns and hyperuricemia with potential confounders identified by the directed acyclic graph. Comparing the highest with the lowest quintiles, the Sichuan Basin dietary pattern was positively associated with hyperuricemia, whereas the Yunnan-Guizhou Plateau dietary pattern showed an inverse association with hyperuricemia. For the Qinghai-Tibet Plateau dietary pattern, DASH, or aMED, our results did not show a significant association with hyperuricemia. The results were robust among stratified analyses and different analyzing strategies. The dietary patterns showed great diversity in Southwest China. Both DASH and aMED, which many studies widely recommended, did not show expected beneficial effects on preventing hyperuricemia. However, the plant-based protein dietary pattern in the Yunnan-Guizhou Plateau showed a beneficial association with the risk of hyperuricemia, which can provide insights for dietary guidance in LMERs.

High-altitude Hypoxia Influences the Activities of the Drug-Metabolizing Enzyme CYP3A1 and the Pharmacokinetics of Four Cardiovascular System Drugs

(1) Background: High-altitude hypoxia has been shown to affect the pharmacokinetic properties of drugs. Although there is a high incidence of cardiovascular disease among individuals living in high-altitude areas, studies on the effect of high-altitude hypoxia on the pharmacokinetic properties of cardiovascular drugs are limited. (2) Methods: The aim of this study was to evaluate the pharmacokinetics of nifedipine, bosentan, simvastatin, sildenafil, and their respective main metabolites, dehydronifedipine, hydroxybosentan, simvastatin hydroxy acid, and N-desmethyl sildenafil, in rats exposed to high-altitude hypoxia. Additionally, the protein and mRNA expression of cytochrome P450 3A1 (CYP3A1), a drug-metabolizing enzyme, were examined. (3) Results: There were significant changes in the pharmacokinetic properties of the drugs in rats exposed to high-altitude hypoxia, as evidenced by an increase in the area under the curve (AUC) and the half-life (t_1/2z) and a decrease in total plasma clearance (CL_z/F). However, most of these changes were reversed when the rats returned to a normoxic environment. Additionally, there was a significant decrease in CYP3A1 expression in rats exposed to high-altitude hypoxia at both the protein and mRNA levels. (4) Conclusions: High-altitude hypoxia suppressed the metabolism of the drugs, indicating that the pharmacokinetics of the drugs should be re-examined, and the optimal dose should be reassessed in patients living in high-altitude areas.

Effects of high altitude on renal physiology and kidney diseases

The hypobaric and hypoxic conditions of high-altitude areas exert adverse effects on the respiratory, circulatory and nervous systems. The kidneys have an abundant blood supply (20%–25% of cardiac output) and high blood flow; thus, they are susceptible to the effects of hypoxia. However, the effects of acute and chronic exposure to high altitudes on renal physiology and pathology are not fully understood. Moreover, few studies have investigated the impact of high-altitude exposure on patients with chronic kidney disease or acute kidney injury. In this review, we summarized changes in renal physiology and renal pathology due to high-altitude exposure as well as the impact of high-altitude exposure on existing kidney diseases, with the aim of informing the prevention and treatment of kidney diseases at high altitudes.

Where do you live and what do you do? Two questions that might impact your kidney health

In many cases the social determinants of health need to be assessed through their interaction with environmental factors. This review looks at the impact of physical location and occupation of individuals on their kidney health. It examines the effect of living at high altitude on kidney function and the relationship between extreme cold or hot temperatures and the incidence of kidney injury. It reviews as well the many occupations that have been linked to kidney disease in high-income and low-and-middle-income countries. As a conclusion, this overview proposes preventive recommendations that could be individualized based on weather, altitude, socio-economic level of the country and occupation of the individual.

Role of Arginase-II in Podocyte Injury under Hypoxic Conditions

Hypoxia plays a crucial role in acute and chronic renal injury, which is attributable to renal tubular and glomerular cell damage. Some studies provide evidence that hypoxia-dependent upregulation of the mitochondrial enzyme arginase type-II (Arg-II) in tubular cells promotes renal tubular injury. It is, however, not known whether Arg-II is also expressed in glomerular cells, particularly podocytes under hypoxic conditions, contributing to hypoxia-induced podocyte injury. The effects of hypoxia on human podocyte cells (AB8/13) in cultures and on isolated kidneys from wild-type (wt) and arg-ii gene-deficient (arg-ii−/−) mice ex vivo, as well as on mice of the two genotypes in vivo, were investigated, respectively. We found that the Arg-II levels were enhanced in cultured podocytes in a time-dependent manner over 48 h, which was dependent on the stabilization of hypoxia-inducible factor 1α (HIF1α). Moreover, a hypoxia-induced derangement of cellular actin cytoskeletal fibers, a decrease in podocin, and an increase in mitochondrial ROS (mtROS) generation—as measured by MitoSOX—were inhibited by adenoviral-mediated arg-ii gene silencing. These effects of hypoxia on podocyte injury were mimicked by the HIFα stabilizing drug DMOG, which inhibits prolyl hydroxylases (PHD), the enzymes involved in HIFα degradation. The silencing of arg-ii prevented the detrimental effects of DMOG on podocytes. Furthermore, the inhibition of mtROS generation by rotenone—the inhibitor of respiration chain complex-I—recapitulated the protective effects of arg-ii silencing on podocytes under hypoxic conditions. Moreover, the ex vivo experiments with isolated kidney tissues and the in vivo experiments with mice exposed to hypoxic conditions showed increased Arg-II levels in podocytes and decreased podocyte markers regarding synaptopodin in wt mice but not in arg-ii−/− mice. While age-associated albuminuria was reduced in the arg-ii−/− mice, the hypoxia-induced increase in albuminuria was, however, not significantly affected in the arg-ii−/−. Our study demonstrates that Arg-II in podocytes promotes cell injury. Arg-ii ablation seems insufficient to protect mice in vivo against a hypoxia-induced increase in albuminuria, but it does reduce albuminuria in aging.

The clinical and pathological characteristics of IgA nephropathy patients in Tibet

Background

There are few studies on immunoglobulin A nephropathy (IgAN) at high altitude. This study aimed to analyze the clinical and pathological characteristics of IgAN between Tibet and Beijing, which provided a basis for improving diagnosis and treatment in Tibet.

Method

The clinical and pathological data of 80 patients from the People’s Hospital of Tibet Autonomous Region (Tibetan group) and 991 patients from Peking University First Hospital (Beijing group) with IgAN proven by renal biopsy were compared retrospectively between January 2016 and July 2020. The kidney biopsy tissue was sent to the Department of Nephrology, Peking University First Hospital for pathological evaluation.

Results

The proteinuria (2.9 [2.0, 4.9] vs. 1.1 [0.5, 2.4] g/day, P < 0.001) in the Tibetan group was significantly higher than that in the Beijing group. The serum albumin (30.4 ± 7.7 vs. 38.2 ± 5.5 g/L, P < 0.001) was significantly lower in the Tibetan group. The eGFR (77.7 ± 37.8 vs. 62.1 ± 33.6 ml/min/1.73 m², P = 0.001) was higher in the Tibetan group. The percentage of patients with nephrotic syndrome in the Tibetan group was significantly higher than that in the Beijing group (33.8% vs. 4.7%, P < 0.001).

Conclusion

There are differences in the clinical and pathological characteristics of IgAN between plateau and plain regions.

Prevalence of hypertension and its relationship with altitude in highland areas: a systematic review and meta-analysis

This systematic review and meta-analysis synthesized the pooled prevalence of hypertension at high altitudes and explored its correlation with altitude using studies published in Chinese and English from database inception to February 2021. A systematic literature search was conducted among bibliographic databases (PubMed, Embase, and Web of Science) and three Chinese databases (CNKI, VIP, and Wanfang data) to identify eligible studies. A random-effects model was used to calculate the overall pooled prevalence of hypertension. The I² statistic was used to assess heterogeneity across studies. Random-effects meta-regression was conducted to investigate covariates that may have influenced between-study heterogeneity. The pooled prevalence of hypertension among the general population in high-altitude areas was 33.0% (95% CI: 29.0-38.0%), with high between-study heterogeneity (I² = 99.4%, P < 0.01). Subgroup analyses showed the pooled prevalence of hypertension in Tibetan individuals was significantly higher than that in non-Tibetan individuals living in the Himalayas and Pamir Mountains (41% vs. 18%). A trend toward an increase in the prevalence of hypertension was found with every 100-m increase in elevation (coefficient: 0.012, 95% CI: -0.001 to 0.025, P = 0.069) only in Tibetan individuals. In addition, in these individuals, we found an increase in mean diastolic BP with each 100-m increase in altitude (coefficient: 0.763, 95% CI: 0.122-1.403, P = 0.025). Our meta-analysis suggests that the pooled prevalence of hypertension among the general population in high-altitude areas is 33.0%. Subjects of Tibetan ethnicity were more prone to developing hypertension at high altitudes. However, a very weak relationship between altitude and the prevalence of hypertension was found only in Tibetan individuals.

Clotting factor genes are associated with preeclampsia in high-altitude pregnant women in the Peruvian Andes

Preeclampsia is a multi-organ complication of pregnancy characterized by sudden hypertension and proteinuria that is among the leading causes of preterm delivery and maternal morbidity and mortality worldwide. The heterogeneity of preeclampsia poses a challenge for understanding its etiology and molecular basis. Intriguingly, risk for the condition increases in high-altitude regions such as the Peruvian Andes. To investigate the genetic basis of preeclampsia in a population living at high altitude, we characterized genome-wide variation in a cohort of preeclamptic and healthy Andean families (n = 883) from Puno, Peru, a city located above 3,800 meters of altitude. Our study collected genomic DNA and medical records from case-control trios and duos in local hospital settings. We generated genotype data for 439,314 SNPs, determined global ancestry patterns, and mapped associations between genetic variants and preeclampsia phenotypes. A transmission disequilibrium test (TDT) revealed variants near genes of biological importance for placental and blood vessel function. The top candidate region was found on chromosome 13 of the fetal genome and contains clotting factor genes PROZ, F7, and F10. These findings provide supporting evidence that common genetic variants within coagulation genes play an important role in preeclampsia. A selection scan revealed a potential adaptive signal around the ADAM12 locus on chromosome 10, implicated in pregnancy disorders. Our discovery of an association in a functional pathway relevant to pregnancy physiology in an understudied population of Native American origin demonstrates the increased power of family-based study design and underscores the importance of conducting genetic research in diverse populations.

Clinicopathological characteristics of high-altitude polycythemia-related kidney disease in Tibetan inhabitants

High-altitude polycythemia (HAPC) is a clinical syndrome that occurs in native inhabitants or long-term residents living at altitude. The kidney is one of the most affected organs. However, the clinical and kidney histopathological profiles of HAPC-related kidney disease have rarely been reported. Here, we report kidney biopsy-based clinicopathological study on this disease. HAPC was defined as excessive erythrocytosis [females, hemoglobin 190 g/L or more; males, 210 g/L or more] in patients living above an altitude of 2500 m for more than ten years. A total of 416 Tibetan patients underwent kidney biopsy between January 1, 2016, and November 31, 2020. Of these patients 17 met the diagnostic criteria for HAPC-related kidney disease. Clinically, these patients had a median urinary protein level of 2.5 g/24-hour (range 1.81-6.85). Twelve patients had hyperuricemia, nine had hypertension, and three had kidney insufficiency. On histopathology, glomerular hypertrophy, glomerular basement membrane thickening, podocyte foot process effacement, segmental glomerulosclerosis and global glomerulosclerosis were the main features. Extraglomerular arterial/arteriolar lesions were common, presenting as intimal fibrosis, hyalinosis and endothelial cell swelling/subintimal edema. Expansion of the arterial/arteriolar medial wall area characterized by smooth muscle cell proliferation was clearly observed, potentially indicating vascular remodeling. Hypoxia-inducible factor 2α was expressed in the kidney tissues of these patients. Thus, the pathological changes of HAPC-related kidney disease encompassed both glomerular and extraglomerular vascular lesions, suggesting a key role of both chronic hypoxia itself and secondary hemodynamic changes in the pathogenesis of this disease.

Treatment of Focal and Segmental Glomerulosclerosis Secondary to High Altitude Polycythemia with Acetazolamide

Vizcarra-Vizcarra, Cristhian A., Eduardo Chávez-Velázquez, Carmen Asato-Higa, and Abdías Hurtado-Aréstegui. Treatment of focal and segmental glomerulosclerosis secondary to high altitude polycythemia with acetazolamide. High Alt Med Biol 00:000-000, 2022.-Focal segmental glomerulosclerosis (FSGS) is a morphological pattern, caused by glomerular injury and is the leading cause of nephrotic syndrome in adults. We present the case of a 59-year-old female patient, resident of a high-altitude city (3,824 m), who had polycythemia and nephrotic syndrome. A renal biopsy was performed, and the findings were compatible with FSGS. The patient received phlebotomy 500 ml three times, which reduced, partially, the hemoglobin concentration. However, she had refractory proteinuria, despite the use of enalapril and spironolactone. We observed that proteinuria worsened with the increase in hemoglobin levels. So, she was treated with acetazolamide 250 mg bid for 4 months, which reduced proteinuria and hemoglobin. During the coronavirus disease 2019 (COVID-19) pandemic, the patient did not take acetazolamide and again, she had an increase in hemoglobin and proteinuria levels. We conclude that acetazolamide may be an effective treatment in FSGS due to high altitude polycythemia.

Glomerular Biomechanical Stress and Lipid Mediators during Cellular Changes Leading to Chronic Kidney Disease

Hyperfiltration is an important underlying cause of glomerular dysfunction associated with several systemic and intrinsic glomerular conditions leading to chronic kidney disease (CKD). These include obesity, diabetes, hypertension, focal segmental glomerulosclerosis (FSGS), congenital abnormalities and reduced renal mass (low nephron number). Hyperfiltration-associated biomechanical forces directly impact the cell membrane, generating tensile and fluid flow shear stresses in multiple segments of the nephron. Ongoing research suggests these biomechanical forces as the initial mediators of hyperfiltration-induced deterioration of podocyte structure and function leading to their detachment and irreplaceable loss from the glomerular filtration barrier. Membrane lipid-derived polyunsaturated fatty acids (PUFA) and their metabolites are potent transducers of biomechanical stress from the cell surface to intracellular compartments. Omega-6 and ω-3 long-chain PUFA from membrane phospholipids generate many versatile and autacoid oxylipins that modulate pro-inflammatory as well as anti-inflammatory autocrine and paracrine signaling. We advance the idea that lipid signaling molecules, related enzymes, metabolites and receptors are not just mediators of cellular stress but also potential targets for developing novel interventions. With the growing emphasis on lifestyle changes for wellness, dietary fatty acids are potential adjunct-therapeutics to minimize/treat hyperfiltration-induced progressive glomerular damage and CKD.

Residential elevation and its effects on hypertension incidence among older adults living at low altitudes: a prospective cohort study

Background

Research on the relationship between residential altitude and hypertension incidence has been inconclusive. Evidence at low altitudes (i.e., <1,500 m) is scarce, let alone in older adults, a population segment with the highest hypertension prevalence. Thus, the objective of this study is to determine whether hypertension risk may be affected by altitude in older adults living at low altitudes.

Methods

This prospective cohort study collected data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS). We selected 6,548 older adults (≥65 years) without hypertension at baseline (2008) and assessed events by the follow-up surveys done in 2011, 2014, and 2018 waves. The mean altitude of 613 residential units (county or district) in which the participants resided was extracted from the Digital Elevation Model (DEM) of the National Aeronautics and Space Administration (NASA) and was accurate to within 30 m. The Cox regression model with penalized splines examined the linear or nonlinear link between altitude and hypertension. A random-effects Cox regression model was used to explore the linear association between altitude and hypertension.

Results

The overall rate of incident hypertension was 8.6 per 100-person years. The median altitude was 130.0 m (interquartile range [IQR] = 315.5 m). We observed that the exposure–response association between altitude and hypertension incidence was not linear. The shape of the exposure–response curve showed that three change points existed. Hypertension risk increased from the lowest to the first change point (247.1 m) and slightly fluctuated until the last change point (633.9 m). The risk decreased above the last change point. According to the categories stratified by the change points, altitude was only significantly associated with hypertension risk (hazard ratio [HR] = 1.003; 95% confidence interval [CI] = 1.002–1.005) under the first change point (247.1 m) after adjusting for related covariates.

Conclusion

Our study found that the association between altitude and hypertension risk might not be linear. We hope the further study can be conducted to confirm the generality of our findings.

Supplementary information

The online version contains supplementary material available at https://doi.org/10.1265/ehpm.22-00001.

Urinary Metabolites as Predictors of Acute Mountain Sickness Severity

Individuals sojourning at high altitude (≥2,500m) often develop acute mountain sickness (AMS). However, substantial unexplained inter-individual variability in AMS severity exists. Untargeted metabolomics assays are increasingly used to identify novel biomarkers of susceptibility to illness, and to elucidate biological pathways linking environmental exposures to health outcomes. This study used untargeted nuclear magnetic resonance (NMR)-based metabolomics to identify urine metabolites associated with AMS severity during high altitude sojourn. Following a 21-day stay at sea level (SL; 55m), 17 healthy males were transported to high altitude (HA; 4,300m) for a 22-day sojourn. AMS symptoms measured twice daily during the first 5days at HA were used to dichotomize participants according to AMS severity: moderate/severe AMS (AMS; n=11) or no/mild AMS (NoAMS; n=6). Urine samples collected on SL day 12 and HA days 1 and 18 were analyzed using proton NMR tools and the data were subjected to multivariate analyses. The SL urinary metabolite profiles were significantly different (p≤0.05) between AMS vs. NoAMS individuals prior to high altitude exposure. Differentially expressed metabolites included elevated levels of creatine and acetylcarnitine, and decreased levels of hypoxanthine and taurine in the AMS vs. NoAMS group. In addition, the levels of two amino acid derivatives (4-hydroxyphenylpyruvate and N-methylhistidine) and two unidentified metabolites (doublet peaks at 3.33ppm and a singlet at 8.20ppm) were significantly different between groups at SL. By HA day 18, the differences in urinary metabolites between AMS and NoAMS participants had largely resolved. Pathway analysis of these differentially expressed metabolites indicated that they directly or indirectly play a role in energy metabolism. These observations suggest that alterations in energy metabolism before high altitude exposure may contribute to AMS susceptibility at altitude. If validated in larger cohorts, these markers could inform development of a non-invasive assay to screen individuals for AMS susceptibility prior to high altitude sojourn.

Global REACH 2018: Volume regulation in high-altitude Andeans with and without chronic mountain sickness

The high-altitude maladaptation syndrome known as chronic mountain sickness (CMS) is characterized by polycythemia and is associated with proteinuria despite unaltered glomerular filtration rate. However, it remains unclear if indigenous highlanders with CMS have altered volume regulatory hormones. We assessed N-terminal pro-B-type natriuretic peptide (NT pro-BNP), plasma aldosterone concentration, plasma renin activity, kidney function (urinary microalbumin, glomerular filtration rate), blood volume, and estimated pulmonary artery systolic pressure (ePASP), in Andean males without (n=14; age=39±11) and with (n=10; age=40±12) CMS at 4330 meters (Cerro de Pasco, Peru). Plasma renin activity (non-CMS: 15.8±7.9 vs. CMS: 8.7±5.4 ng/ml; p=0.025) and plasma aldosterone concentration (non-CMS: 77.5±35.5 vs. CMS: 54.2±28.9 pg/ml; p=0.018) were lower in highlanders with CMS compared to non-CMS, while NT pro-BNP was not different between groups (non-CMS: 1394.9±214.3 vs. CMS: 1451.1±327.8 pg/ml; p=0.15). Highlanders had similar total blood volume (non-CMS: 90±15 vs. CMS: 103±18 ml • kg^-1; p=0.071), but Andeans with CMS had greater total red blood cell volume (non-CMS: 46±10 vs. CMS 66±14 ml • kg^-1; p<0.01) and smaller plasma volume (non-CMS 43±7 vs. CMS 35±5 ml • kg^-1; p=0.03) compared to non-CMS. There were no differences in ePASP between groups (non-CMS 32±9 vs. CMS 31±8 mmHg; p=0.6). A negative correlation was found between plasma renin activity and glomerular filtration rate in both groups (group: r=-0.66; p<0.01; non-CMS: r=-0.60; p=0.022; CMS: r=-0.63; p=0.049). A smaller plasma volume in Andeans with CMS may indicate an additional CMS maladaptation to high-altitude, causing potentially greater polycythemia and clinical symptoms.

Prevalence of and risk factors for high-altitude hyperuricaemia in Bai individuals: a cross-sectional study

OBJECTIVE

Hyperuricaemia is common in Bai individuals; however, its prevalence remains unclear. This work aimed to investigate high-altitude hyperuricaemia prevalence and risk factors in Bai individuals.

METHODS

All eligible participants of Bai ethnicity (aged ≥18 years and undergoing routine medical examination at the People's Hospital of Jianchuan County between January and December 2019) were consecutively enrolled. Demographic and laboratory data were collected to investigate hyperuricaemia prevalence and associated risk factors.

RESULTS

A total of 1393 participants were assessed, comprising 345 (24.8%) with hyperuricaemia showing a male predominance (287/865 [33.2%] males versus 58/528 [11.0%] females). Hyperuricaemia prevalence was significantly higher in participants aged ≥50 years (100/332 [30.1%]) versus those aged 30-40 years (59/308 [19.2%]), and in overweight/obese individuals compared with those showing an underweight or normal body mass index (BMI; 267/885 [30.2%] versus 78/508 [15.4%]). Finally, haemoglobin concentrations and serum uric acid levels were positively correlated.

CONCLUSION

Besides traditional risk factors, including age, sex and BMI, polycythaemia due to prolonged exposure to high altitude may also cause hyperuricaemia in Bai individuals residing in Yunnan Province.

Incidence and Risk Factors of Hyperuricemia among 2.5 Million Chinese Adults during the Years 2017-2018

Objective: To assess the incidence and risk factors of hyperuricemia among Chinese adults in 2017-2018. Methods: A total of 2,015,847 adults (mean age 41.2 ± 12.7, 53.1% men) with serum uric acid concentrations assayed on at least two separate days in routine health examinations during 2017-2018 were analyzed. Hyperuricemia was defined as fasting serum urate concentration >420 μmol/L in men and >360 μmol/L in women. The overall and sex-specific incidence rate were stratified according to age, urban population size, geographical region, annual average temperature and certain diseases. Logistic regression analyses were performed to explore risk factors associated with hyperuricemia. Results: 225,240 adults were newly diagnosed with hyperuricemia. The age- and sex-standardized incidence rate per 100 person-years was 11.1 (95%CI: 11.0-11.1) (15.2 for men and 6.80 for women). The risk of hyperuricemia was positively associated with younger age, being male, larger urban population size, higher annual temperature, higher body mass index, lower estimate glomerular filtration rate, hypertension, dyslipidemia and fat liver. Conclusions: The incidence of hyperuricemia was substantial and exhibited a rising trend among younger adults, especially among men. Socioeconomic and geographic variation in incidence were observed. The risk of hyperuricemia was associated with estimate glomerular filtration rate, fat liver and metabolic factors.

Chronic hypoxia exacerbates diabetic glomerulosclerosis through mesangiolysis and podocyte injury in db/db mice

BACKGROUND

Chronic hypoxia may play a pivotal role in the development of diabetic nephropathy (DN). However, the precise mechanisms underlying progressive hypoxia-induced glomerular injury remain unclear.

METHODS

We housed db/db mice in a hypoxia chamber (12% O2) for up to 16 weeks beginning at 8 weeks of age. Various urine, serum and kidney abnormalities and glomerular messenger RNA (mRNA) expression were compared with those in age-matched db/db mice housed under normoxia.

RESULTS

Levels of urinary albumin and podocalyxin (PCX) were significantly higher in hypoxic mice early during hypoxia. Ultracentrifugation of urine samples revealed that podocytes in the hypoxic mice shed PCX-positive microparticles into the urine. After 16 weeks of hypoxia, the mice also had higher hematocrits with lower serum glucose and various degrees of mesangiolytic glomerulosclerosis with microaneurysms and the infrequent occurrence of nodular lesions. Immunohistologically, hypoxic mice showed significantly decreased endothelial cell densities early during hypoxia and decreased podocyte densities later. In both hypoxic and normoxic mice, glomerular macrophage and transforming growth factor-β1 (TGF-β1) staining significantly increased with aging, without changes in vascular endothelial growth factor or endothelial nitric oxide synthase (eNOS). Glomerular mRNA expression of monocyte chemoattractant protein-1, eNOS and TGF-β1 was significantly enhanced in the hypoxic mice.

CONCLUSIONS

These results indicate that chronic hypoxia induces advanced glomerulosclerosis with accelerated albuminuria triggered by mesangiolysis and podocyte injury in a murine model of DN.

Associations Between High-Altitude Residence and End-Stage Kidney Disease in Chinese Patients with Type 2 Diabetes

Zhao, Lijun, Xi Wang, Tingli Wang, Wenxin Fan, Honghong Ren, Rui Zhang, Yutong Zou, Huan Xu, Jie Zhang, Yunhong Wu, and Fang Liu. Associations between high-altitude residence and end-stage kidney disease in Chinese patients with type 2 diabetes. High Alt Med Biol. 21:396-405, 2020. Background: This study investigated whether living at high altitude was associated with progression to end-stage kidney disease (ESKD) in Chinese patients with diabetic nephropathy (DN). Materials and Methods: This retrospective study included 369 patients with type 2 diabetes mellitus (T2DM) and biopsy-confirmed DN. Cox proportional hazards models were used to estimate hazard ratios (HRs) for the influence of living at high altitude on ESKD. Results: Patients living at ≥2,000 m above sea level were more likely to be Tibetan, and they had higher mean body mass indexes, glycosylated hemoglobin, hemoglobin concentrations, and baseline estimated glomerular filtration rates than those living at lower altitudes. During a median follow-up period of 20 months, 141 (38%) patients progressed to ESKD. In multivariable Cox analysis adjusted for age, sex, ethnicity, and clinical and pathological parameters, living at high altitude was independently associated with progression to ESKD in Chinese DN patients [HR 2.83, 95% confidence interval (CI) 1.05-7.58]. Compared with Han Chinese, Tibetans were at a lower risk of progression to ESKD (HR 0.15, 95% CI 0.04-0.59). Conclusions: Living at high altitude was independently associated with renal outcome in Han Chinese patients with T2DM and DN, but not native Tibetans.

Prioritizing natural-selection signals from the deep-sequencing genomic data suggests multi-variant adaptation in Tibetan highlanders

Human genetic adaptation to high altitudes (>2500 m) has been extensively studied over the last few years, but few functional adaptive genetic variants have been identified, largely owing to the lack of deep-genome sequencing data available to previous studies. Here, we build a list of putative adaptive variants, including 63 missense, 7 loss-of-function, 1,298 evolutionarily conserved variants and 509 expression quantitative traits loci. Notably, the top signal of selection is located in TMEM247, a transmembrane protein-coding gene. The Tibetan version of TMEM247 harbors one high-frequency (76.3%) missense variant, rs116983452 (c.248C > T; p.Ala83Val), with the T allele derived from archaic ancestry and carried by >94% of Tibetans but absent or in low frequencies (<3%) in non-Tibetan populations. The rs116983452-T is strongly and positively correlated with altitude and significantly associated with reduced hemoglobin concentration (p = 5.78 × 10-5), red blood cell count (p = 5.72 × 10-7) and hematocrit (p = 2.57 × 10-6). In particular, TMEM247-rs116983452 shows greater effect size and better predicts the phenotypic outcome than any EPAS1 variants in association with adaptive traits in Tibetans. Modeling the interaction between TMEM247-rs116983452 and EPAS1 variants indicates weak but statistically significant epistatic effects. Our results support that multiple variants may jointly deliver the fitness of the Tibetans on the plateau, where a complex model is needed to elucidate the adaptive evolution mechanism.

Elevated FGF23 and disordered renal mineral handling with reduced bone mineralization in chronically erythropoietin over-expressing transgenic mice

Fibroblast Growth Factor 23 (FGF23) is a phosphaturic factor causing increased renal phosphate excretion as well as suppression of 1,25 (OH)₂-vitamin D_3. Highly elevated FGF23 can promote development of rickets and osteomalacia. We and others previously reported that acute application of erythropoietin (EPO) stimulates FGF23 production. Considering that EPO is clinically used as chronic treatment against anemia, we used here the Tg6 mouse model that constitutively overexpresses human EPO in an oxygen-independent manner, to examine the consequences of long-term EPO therapy on mineral and bone metabolism. Six to eight weeks old female Tg6 mice showed elevated intact and C-terminal fragment of FGF23 but normal plasma levels of PTH, calcitriol, calcium and phosphate. Renal function showed moderate alterations with higher urea and creatinine clearance and mild albuminuria. Renal phosphate excretion was normal whereas mild hypercalciuria was found. Renal expression of the key proteins TRPV5 and calbindin D28k involved in active calcium reabsorption was reduced in Tg6 mice. Plasma levels of the bone turnover marker osteocalcin were comparable between groups. However, urinary excretion of deoxypyridinoline (DPD) was lower in Tg6 mice. MicroCT analysis showed reduced total, cortical, and trabecular bone mineral density in femora from Tg6 mice. Our data reveal that chronic elevation of EPO is associated with high FGF23 levels and disturbed mineral homeostasis resulting in reduced bone mineral density. These observations imply the need to study the impact of therapeutically applied EPO on bone mineralization in patients, especially those suffering from chronic kidney disease.

Urbanization and Altitude Are Associated with Low Kidney Function in Peru

Background: Kidney health needs to be studied in low- and middle-income countries with populations living at high altitude and undergoing urbanization. We studied whether greater level of urbanization was associated with worse kidney function and higher hemoglobin was associated with worse kidney function at high altitude.

Methods: Cross-sectional analysis of population-based studies in Peru including five sites at different altitude above the sea level and urbanization level (in decreasing order of urbanization): Lima (sea level), Arequipa (2335 m), urban Puno (3825 m), Tumbes (sea level), and rural Puno (3825 m). The exposures were urbanization and altitude as per study site, and hemoglobin (g/dL). The outcome was the estimated glomerular filtration rate (eGFR).

Results: Four thousand two hundred eight people were studied: mean age was 57.4 years (standard deviation: 12.4) and 51.9% were women. In comparison to rural Puno, eGFR was similar in Lima; in comparison to rural Puno, Arequipa, urban Puno, and Tumbes had worse eGFR, for example, in Arequipa, β = −8.07 (95% confidence interval [CI]: −10.90 to −5.24). Intermediate (β = −8.60; 95% CI: −10.55 to −6.66) and high (β = −11.21; 95% CI: −14.19 to −8.24) altitude were negatively correlated with eGFR when only urban places were analyzed. At high altitude, there was a trend for a negative association between hemoglobin and eGFR: β = −1.09 (95% CI: −2.22 to 0.04).

Conclusions: Apparently, higher altitude and level of urbanization, except for one highly urbanized site, were associated with worse kidney function. Our findings suggest that some of the adverse impact of high altitude on kidney function has been balanced by the lower risk conferred by rural environments.

Prevalence and risk factors associated with hyperuricemia among working population at high altitudes: a cross-sectional study in Western China

Chronic exposure to high altitude may lead to hyperuricemia. We investigated the prevalence of hyperuricemia and its risk factors among employees in high-altitude areas. A cross-sectional survey with cluster sampling was performed at 23 worksites on the Qinghai-Tibet Plateau. Subjects were evaluated by using questionnaires, anthropometric and laboratory measurements, and abdominal ultrasound. A multilevel logistic regression model and restricted cubic spline were used to explore the associated factors of hyperuricemia. Of the 4198 employees included in the study, the age-standardized prevalence of hyperuricemia was 28.1% (95% confidence interval (CI) 26.7-29.5), with 31.9% (95%CI 30.2-33.6) in men and 17.9% (95%CI 15.7-20.1) in women. Hypertension, hyperlipidemia, and a meat-food pattern were positively associated with hyperuricemia in both sexes, while diabetes, shift work, body mass index, non-alcoholic fatty liver disease, and low intake of fruits and vegetables were significantly associated with hyperuricemia only in men. Furthermore, a nonlinear dose-response association between the number of cardiovascular risk factors (CRFs) and hyperuricemia was observed. Compared with those having 0 CRFs, the full-adjusted odds ratios (ORs) and 95%CIs for 1, 2, and ≥ 3 CRFs were 1.76 (95%CI 1.25-2.47), 2.54 (95%CI 1.81-3.55), and 3.05 (95%CI 2.16-4.31) in men, respectively, and 2.13 (95%CI 1.43-3.17), 2.78 (95%CI 1.71-4.53), and 3.13 (95%CI 1.50-6.55) in women, respectively. Hyperuricemia is common in employees at high-altitude areas. However, working at higher altitudes does not mean necessarily higher risk of hyperuricemia, as dietary factors and clustered CRFs are more significant. Thus, workplace-based lifestyle modifications should be promoted.

The Process of Acclimation to Chronic Hypoxia Leads to Submandibular Gland and Periodontal Alterations: An Insight on the Role of Inflammatory Mediators

The exposition to hypoxia is a stressful stimulus, and the organism develops acclimation mechanisms to ensure homeostasis, but if this fails, it leads to the development of pathological processes. Considering the large number of people under hypoxic conditions, it is of utmost importance to study the mechanisms implicated in hypoxic acclimation in oral tissues and the possible alteration of some important inflammatory markers that regulate salivary and periodontal function. It is the aim of the present study to analyze submandibular (SMG) and periodontal status of animals chronically exposed to continuous (CCH) or intermittent (CIH) hypoxia in order to elucidate the underlying molecular mechanisms that may lead to hypoxic acclimation. Adult Wistar rats were exposed to CCH or CIH simulating 4200 meters of altitude during 90 days. Salivary secretion was decreased in animals exposed to hypoxia, being lower in CIH, together with increased prostaglandin E₂ (PGE₂) content, TBARS concentration, and the presence of apoptotic nuclei and irregular secretion granules in SMG. AQP-5 mRNA levels decreased in both hypoxic groups. Only the CCH group showed higher HIF-1α staining, while CIH alone exhibited interradicular bone loss and increased concentration of the bone resorption marker CTX-I. In summary, animals exposed to CIH show a worse salivary secretion rate, which related with higher levels of PGE₂, suggesting a negative role of this inflammatory mediator during hypoxia acclimation. We link the weak immunorreactivity of HIF-1α in CIH with improper hypoxia acclimation, which is necessary to sustaining SMG physiology under this environmental condition. The alveolar bone loss observed in CIH rats could be due mainly to a direct effect of PGE₂, as suggested by its higher content in gingival tissue, but also to the indirect effect of hyposalivation. This study may eventually contribute to finding therapeutics to treat the decreased salivary flow, improving in that way oral health.

Effect of Oral Vitamin C Supplementation on High-Altitude Hyperuricemia in Young Men Initially Migrating to High Altitude: A Pilot Study

OBJECTIVE

Clinical studies have shown that oral vitamin C supplementation can reduce serum uric acid levels in multiple populations and may also improve acute mountain sickness. However, it is unclear whether this protocol can improve high-altitude hyperuricemia. Therefore, we aimed to evaluate the role of vitamin C supplementation on high-altitude hyperuricemia.

METHODS

A preliminary prospective control study was performed in 2015. Young male army recruits (n = 66), who had recently arrived on the Tibetan Plateau for the first time, were recruited for study I. Subjects were assigned to either the vitamin C group, who took an oral daily dose of 500 mg vitamin C for 1 month, or the blank control group, who had no intervention. The levels of serum uric acid, serum creatinine, and blood urea nitrogen were monitored at baseline and at the end of 1 month. In a second study II in 2016 (n = 120), the effect of 500 mg/d vitamin C on high-altitude hyperuricemia was compared with 75 IU/d of vitamin E.

RESULTS

In study I, the level of serum uric acid at 1 month was significantly higher than at baseline (436.1 ± 79.3 μmol/L vs. 358.0 ± 79.8 μmol/L, p < 0.001) and the prevalence of hyperuricemia was also significantly higher (63.6% [95% confidence interval, CI: 52.0%-75.2%] vs. 19.7% [95% CI: 10.1%-29.3%], p < 0.001). Both the level of serum uric acid (411.5 ± 74.2 μmol/L vs. 460.8 ± 54.8 μmol/L, p = 0.003) and the prevalence of hyperuricemia (48.5% [95% CI: 31.4%-65.6%] vs. 78.8% [95% CI: 64.9%-92.7%], p = 0.020) were significantly lower in the vitamin C group than in the blank control group. In study II, the levels of serum uric acid and the frequency of hyperuricemia also increased over 1 month and were similar in the vitamin C and the vitamin E groups at both baseline and 1 month (p > 0.05). The change in serum uric acid was positively correlated with both the changes in serum creatinine (r = 0.599, p < 0.001) and blood urea nitrogen (r = 0.207, p = 0.005).

CONCLUSIONS

These findings indicate that healthy young men develop an increase in serum uric acid within a month of moving from low to high altitude. Oral vitamin C supplementation can safely reduce this increase at a low cost.

Clinicopathological features of pediatric renal biopsies in the plateau regions of China

Objective

This study aimed to analyze the clinicopathological features of pediatric renal biopsies from plateau regions of China.

Methods

Clinicopathological features of pediatric renal biopsies were compared between plateau and non-plateau regions in patients who were admitted to West China Second University Hospital, Sichuan University between April 2001 and March 2017. Patients were children younger than 18 years.

Results

The proportion of primary glomerular disease in the plateau group was lower than that in the non-plateau group (45.56% vs 62.09%, respectively). In the plateau group, IgA nephropathy (IgAN) was the major primary glomerulonephritis (GN) pathology. IgAN accounted for 36.54% and 21.63% of GN cases with nephrotic syndrome and hematuria, respectively. Henoch-Schönlein purpura nephritis was the most common secondary GN in both groups. The proportion of hepatitis B virus-associated GN was higher and that of lupus nephritis was lower in the plateau group than in the non-plateau group.

Conclusions

There are differences in renal pathological types between children in plateau regions and those in non-plateau regions. Among children in plateau regions, IgAN and Henoch-Schönlein purpura nephritis were the most common kidney diseases.

Hypobaric hypoxia induced renal damage is mediated by altering redox pathway

Systemic hypobaric hypoxia is reported to cause renal damage; nevertheless the exact pathophysiological mechanisms are not completely understood. Therefore, the present study aims to explore renal pathophysiology by using proteomics approach under hypobaric hypoxia. Six to eight week old male Sprague Dawley rats were exposed to hypobaric hypoxia equivalent to altitude of 7628 metres (pO₂-282mmhg) at 28°C and 55% humidity in decompression chamber for different time intervals; 1, 3, and7 days. Various physiological, proteomic and bioinformatic studies were carried out to examine the effect of chronic hypobaric hypoxia on kidney. Our data demonstrated mild to moderate degenerative tubular changes, altered renal function, injury biomarkers and systolic blood pressure with increase in duration of hypobaric hypoxia exposure. Renal proteomic analysis showed 38 differential expressed spots, out of which 25 spots were down regulated and 13 were up regulated in 7 dayhypobarichypoxic exposure group of rats as compared to normoxia control. Identified proteins were involved in specific molecular changes pertinent to endogenous redox pathways, cellular integrity and energy metabolism. The study provides an empirical evidence of renal homeostasis under hypobaric hypoxia by investigating both physiological and proteomics changes. The identification of explicit key proteins provides a valuable clue about redox signalling mediated renal damage under hypobaric hypoxia.

Prevalence and risk factors associated with chronic kidney disease in adults living in 3 different altitude regions in the Tibetan Plateau

BACKGROUND

Living at high altitude may have undesirable effects on the kidney. We explored the chronic kidney disease (CKD) prevalence and risk factors among the residents living at different altitude in Tibetan Plateau.

METHODS

A cross-sectional study was carried out in 2014 to 2016 in Linzhi (2900 m altitude), Lhasa (3650 m) and Anduo (4700 m). Information on the cardiovascular risk factors was collected and blood and urine samples were measured.

RESULTS

The data of 1707 subjects aged ≥35 y were analyzed. The age-standardized prevalence of CKD in Linzhi, Lhasa and Anduo was 27.7% (95% CI: 22.1-33.3%), 18.3% (12.7-24.0%) and 30.4% (23.5-37.3%) in men and 37.7% (31.8-43.6%), 29.5% (24.6-34.4%) and 36.7% (29.0-44.4%) in women, respectively. Multivariable logistic regression showed that age, female gender, systolic blood pressure, fasting serum glucose, with primary school education or lower were associated with higher risk of CKD and living in Lhasa was associated with lower risk of CKD.

CONCLUSION

A higher prevalence of CKD was found in the residents living in the Tibetan Plateau. However, for the highlanders living at higher altitude does not mean higher risk. The CKD risk factors found in this study are similar to those in other studies.

Acute high-altitude exposure shortens survival after uncontrolled hemorrhagic shock in rats

BACKGROUND

Uncontrolled hemorrhage (UH) remains the most common cause of death on the battlefield. This study examined the pathophysiological characteristics of UH in rats acutely exposed to high altitude.

MATERIAL AND METHODS

Rats raised at sea level were randomly divided into two groups. Rats in the high-altitude group were exposed to hypobaric hypoxia in a hypobaric chamber (simulating 4000 m above sea level) for 2 d and then were performed a hemorrhagic shock protocol in the hypobaric chamber. Rats that underwent the same hemorrhage procedure at sea level were used as control. Anesthetized rats were bled to maintain their mean arterial pressure at 45 mmHg for 1 h. The distal quarter of the tail was amputated to allow free blood loss. After 1 h, the tail cut was ligated to induce hemostasis. mean arterial pressure, acid-base balance, blood loss, and survival were recorded. Rats were killed, and tissues were obtained for histological analysis.

RESULTS

Rats in the high-altitude group suffered less uncontrolled blood loss, more severe acidosis (lower pH and base excess), and inferior tissue oxygen supply (lower oxygen saturation and higher arterial lactate concentration) during the hemorrhage periods compared with the control group. Survival rates were significantly lower in the high-altitude group than those in the control group (P < 0.05), which was consistent with the results of pathological tissue injury.

CONCLUSIONS

In this rat model of hemorrhagic shock, acute high-altitude exposure resulted in decreased UH but more serious hemorrhagic shock injuries than that at sea level.

Risk score for first-screening of prevalent undiagnosed chronic kidney disease in Peru: the CRONICAS-CKD risk score

BACKGROUND

Chronic Kidney Disease (CKD) represents a great burden for the patient and the health system, particularly if diagnosed at late stages. Consequently, tools to identify patients at high risk of having CKD are needed, particularly in limited-resources settings where laboratory facilities are scarce. This study aimed to develop a risk score for prevalent undiagnosed CKD using data from four settings in Peru: a complete risk score including all associated risk factors and another excluding laboratory-based variables.

METHODS

Cross-sectional study. We used two population-based studies: one for developing and internal validation (CRONICAS), and another (PREVENCION) for external validation. Risk factors included clinical- and laboratory-based variables, among others: sex, age, hypertension and obesity; and lipid profile, anemia and glucose metabolism. The outcome was undiagnosed CKD: eGFR < 60 ml/min/1.73m². We tested the performance of the risk scores using the area under the receiver operating characteristic (ROC) curve, sensitivity, specificity, positive/negative predictive values and positive/negative likelihood ratios.

RESULTS

Participants in both studies averaged 57.7 years old, and over 50% were females. Age, hypertension and anemia were strongly associated with undiagnosed CKD. In the external validation, at a cut-off point of 2, the complete and laboratory-free risk scores performed similarly well with a ROC area of 76.2% and 76.0%, respectively (P = 0.784). The best assessment parameter of these risk scores was their negative predictive value: 99.1% and 99.0% for the complete and laboratory-free, respectively.

CONCLUSIONS

The developed risk scores showed a moderate performance as a screening test. People with a score of ≥ 2 points should undergo further testing to rule out CKD. Using the laboratory-free risk score is a practical approach in developing countries where laboratories are not readily available and undiagnosed CKD has significant morbidity and mortality.

Higher prevalence of unrecognized kidney disease at high altitude

BACKGROUND

High altitude renal syndrome has been described in populations with excessive erythrocytosis. We evaluated whether high altitude (HA) dwellers might be at increased risk for kidney disease.

METHODS

We performed a cross-sectional study to investigate differences in prevalence of kidney function and metabolic syndrome in healthy subjects living at HA vs. sea level (SL) without any known history of hypertension, diabetes or chronic kidney disease.

RESULTS

We examined 293 subjects, aged 40 to 60 years: 125 SL (154 m) and 168 HA (3640 m) dwellers. HA dwellers had higher serum creatinine, lower estimated glomerular function rate (eGFR) (69.5 ± 15.2 vs. 102.1 ± 17.8 ml/min/1.73 m², p < 0.0001), more proteinuria and higher hemoglobin concentrations compared to SL subjects. HA subjects had a lower prevalence of metabolic syndrome. Hemoglobin concentrations correlated inversely with eGFR in female (p = 0.001) and male (p = 0.03) HA dwellers. Using logistic regression analysis to compare subjects with eGFR < 90 vs. > 90 ml/min/1.73 m², a lower eGFR was associated with female gender (odds ratio adjusted: 5.65 [95% confidence interval: 2.43-13.13]; p = 0.001), high altitude (14.78 [6.46-33.79]; p = 0.001), hemoglobin (1.68 [1.16-2.43]; p = 0.001) and uric acid (1.93 [1.36-2.72]; p = 0.001).

CONCLUSIONS

Dwellers at high altitude who are considered healthy have worse kidney function, a higher prevalence of proteinuria and a lower prevalence of metabolic syndrome compared to people living at SL.

Chronic Hypobaric Hypoxia Modulates Primary Cilia Differently in Adult and Fetal Ovine Kidneys

Hypoxic environments at high altitude have significant effects on kidney injury. Following injury, renal primary cilia display length alterations. Primary cilia are mechanosensory organelles that regulate tubular architecture. The effect of hypoxia on cilia length is still controversial in cultured cells, and no corresponding in vivo study exists. Using fetal and adult sheep, we here study the effect of chronic hypobaric hypoxia on the renal injury, intracellular calcium signaling and the relationship between cilia length and cilia function. Our results show that although long-term hypoxia induces renal fibrosis in both fetal and adult kidneys, fetal kidneys are more susceptible to hypoxia-induced renal injury. Unlike hypoxic adult kidneys, hypoxic fetal kidneys are characterized by interstitial edema, tubular disparition and atrophy. We also noted that there is an increase in the cilia length as well as an increase in the cilia function in the hypoxic fetal proximal and distal collecting epithelia. Hypoxia, however, has no significant effect on primary cilia in the adult kidneys. Increased cilia length is also associated with greater flow-induced intracellular calcium signaling in renal epithelial cells from hypoxic fetuses. Our studies suggest that while hypoxia causes renal fibrosis in both adult and fetal kidneys, hypoxia-induced alteration in cilia length and function are specific to more severe renal injuries in fetal hypoxic kidneys.

Prevalence and risk factors associated with hypertension and prehypertension in a working population at high altitude in China: a cross-sectional study

Background

Little information is available on the epidemiology of hypertension and prehypertension at high altitude in China, the aim of this study was to determine the prevalence of hypertension, prehypertension and their risk factors among Chinese working population at high altitude regions.

Methods

A cross-sectional survey was performed in an occupational sample of 4198 employees aged 20–59 years on Qinghai-Tibet Plateau between May to July 2013. Information from a self-administered questionnaire, physical examinations and laboratory measurements were obtained from each participant. Multivariable analysis was performed to determine the association of various risk factors with hypertension and prehypertension.

Results

The total crude prevalence of hypertension and prehypertension was 28.1 and 41.5%, respectively; the overall standardized prevalence of hypertension and prehypertension was 26.7 and 41.3%, respectively. Multivariate logistic regression showed that age, sex, ethnicity, job position, overweight or obesity, frequent drinking, family history of hypertension, diabetes and hyperuricemia were risk factors for hypertension, and age, sex, education, job position, overweight or obesity, current smoking and family history of hypertension were risk factors for prehypertension. Among the hypertensives, 36.5% were aware of their condition, 19.4% were being treated and 6.2% had their blood pressure (BP) controlled; among the treated hypertensives, 31.9% had their BP under control.

Conclusions

There is a high prevalence of hypertension and prehypertension in the working population at high altitude in China, but with very low awareness, treatment and control rates. Workplace-based BP screening and intervention programs that aim to modify risk factors such as high BMI, tobacco use, alcohol consumption and inappropriate use of antihypertensive medicine are urgently needed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12199-017-0634-7) contains supplementary material, which is available to authorized users.

The impact of hypoxia on nephrogenesis

PURPOSE OF REVIEW

Kidney development depends on outgrowth of the ureteric bud into the metanephric mesenchyme. The number of ureteric bud branching events determines the final number of nephrons, which correlates inversely with the risk for development of chronic kidney disease and arterial hypertension during lifetime. The purpose of this review is to highlight the influence of oxygen on nephrogenesis and to describe cellular mechanisms by which hypoxia can impair nephron formation.

RECENT FINDINGS

Although kidney development normally takes place under hypoxic conditions, nephrogenesis is impaired when oxygen availability falls below the usual range. Hypoxia-inducible factors (HIF) play an important role in linking low oxygen concentrations to the biology of nephron formation, but their effect appears to be cell type dependent. In ureteric bud cells, HIF stimulates tubulogenesis, whereas HIF stabilization in cells of the metanephric mesenchyme results in secretion of growth factors, including vascular endothelial growth factor A, which in aggregate inhibit ureteric bud branching. The balance between pro and antibranching effects may be altered in various ways, but the inhibitory effect usually seems to predominate under reduced oxygen concentrations, explaining how intrauterine hypoxia can lead to low nephron numbers.

SUMMARY

Oxygen availability has a complex influence on nephrogenesis. Oxygen concentrations outside an optimal low range may affect nephron endowment. Associations between placental insufficiency and increased risk for chronic kidney disease and arterial hypertension during later life may to a large extent be due to direct effects of reduced oxygen supply to the metanephric mesenchyme and mediated through the HIF pathway.