Chronic intermittent hypoxia aggravates intrahepatic endothelial dysfunction in cirrhotic rats

The role of adipose tissue and subsequent liver tissue hypoxia in obesity and early stage metabolic dysfunction associated steatotic liver disease

BACKGROUND

Obesity is linked to several health complication, including Metabolic Dysfunction Associated Steatotic Liver Disease (MASLD). Adipose tissue hypoxia has been suggested as an important player in the pathophysiological mechanism leading to chronic inflammation in obesity, and in the progression of MASLD. The study aims to investigate the effect of progressive obesity on adipose and liver tissue hypoxia.

METHODS

Male 8-week-old C57BL/6J mice were fed a high-fat high-fructose diet (HFHFD) or control diet (CD) for 4, 8, 12, 16 and 20 weeks. Serum ALT, AST and lipid levels were determined, and glucose and insulin tolerance testing was performed. Liver, gonadal and subcutaneous adipose tissue was assessed histologically. In vivo tissue pO2 measurements were performed in gonadal adipose tissue and liver under anesthesia. A PCR array for hypoxia responsive genes was performed in liver and adipose tissue. The main findings in the liver were validated in another diet-induced MASLD mice model, the choline-deficient L-amino acid defined high-fat diet (CDAHFD).

RESULTS

HFHFD feeding induced a progressive obesity, dyslipidaemia, insulin resistance and MASLD. In vivo pO2 was decreased in gonadal adipose tissue after 8 weeks of HFHFD compared to CD, and decreased further until 20 weeks. Liver pO2 was only significantly decreased after 16 and 20 weeks of HFHFD. Gene expression and histology confirmed the presence of hypoxia in liver and adipose tissue. Hypoxia could not be confirmed in mice fed a CDAHFD.

CONCLUSION

Diet-induced obesity in mice is associated with hypoxia in liver and adipose tissue. Adipose tissue hypoxia develops early in obesity, while liver hypoxia occurs later in the obesity development but still within the early stages of MASLD. Liver hypoxia could not be directly confirmed in a non-obese liver-only MASLD mice model, indicating that obesity-related processes such as adipose tissue hypoxia are important in the pathophysiology of obesity and MASLD.

Ginsenoside Rg1 ameliorates chronic intermittent hypoxia-induced vascular endothelial dysfunction by suppressing the formation of mitochondrial reactive oxygen species through the calpain-1 pathway

Background

As the major pathophysiological feature of obstructive sleep apnea (OSA), chronic intermittent hypoxia (CIH) is vital for the occurrence of cardiovascular complications. The activation of calpain-1 mediates the production of endothelial reactive oxygen species (ROS) and impairs nitric oxide (NO) bioavailability, resulting in vascular endothelial dysfunction (VED). Ginsenoside Rg1 is thought to against endothelial cell dysfunction, but the potential mechanism of CIH-induced VED remains unclear.

Methods

C57BL/6 mice and human coronary artery endothelial cells (HCAECs) were exposed to CIH following knockout or overexpression of calpain-1. The effect of ginsenoside Rg1 on VED, oxidative stress, mitochondrial dysfunction, and the expression levels of calpain-1, PP2A and p-eNOS were detected both in vivo and in vitro.

Results

CIH promoted VED, oxidative stress and mitochondrial dysfunction accompanied by enhanced levels of calpain-1 and PP2A and reduced levels of p-eNOS in mice and cellular levels. Ginsenoside Rg1, calpain-1 knockout, OKA, NAC and TEMPOL treatment protected against CIH-induced VED, oxidative stress and mitochondrial dysfunction, which is likely concomitant with the downregulated protein expression of calpain-1 and PP2A and the upregulation of p-eNOS in mice and cellular levels. Calpain-1 overexpression increased the expression of PP2A, reduced the level of p-eNOS, and accelerated the occurrence and development of VED, oxidative stress and mitochondrial dysfunction in HCAECs exposed to CIH. Moreover, scavengers of O₂ ^{• -}, H₂O₂, complex Ⅰ or mitoK_ATP abolished CIH-induced impairment in endothelial-dependent relaxation.

Conclusion

Ginsenoside Rg1 may alleviate CIH-induced vascular endothelial dysfunction by suppressing the formation of mitochondrial reactive oxygen species through the calpain-1 pathway.

Chronic intermittent hypoxia promotes early intrahepatic endothelial impairment in rats with nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a progressive disease that ranges from simple steatosis to cirrhosis. Obstructive sleep apnea syndrome (OSAS) and chronic intermittent hypoxia (CIH) are implicated in the pathogenesis of NAFLD. However, the overlapping consequences of CIH on liver sinusoidal endothelial function over time in NAFLD are largely unknown. We explored endothelial dysfunction in a rat model of NAFLD with a high-fat diet exposed to CIH [12 h/day, every 30 s to fractional concentration of oxygen ([Formula: see text] 8%-10%]. The livers were isolated and perfused, and the endothelial function was determined by testing the vasodilation of the liver circulation to increased concentrations of acetylcholine and von Willebrand factor (vWF) and intercellular adhesion molecule 1 (ICAM-1) expression. Phosphorylated endothelial nitric oxide synthase (p-eNOS), cGMP, and oxidative stress were assessed to determine nitric oxide bioavailability. Inflammation and fibrosis were evaluated by transaminases, myeloperoxidase activity, hydroxyproline, and histological evaluation. Hypoxia-inducible factors (HIFs) were studied as a marker of hypoxia and after a second insult with acetaminophen. CIH exposure provoked typical systemic features of OSAS and provoked a decreased response in vasodilation to acetylcholine. This was associated with increased oxidative stress and reduced p-eNOS and cGMP. The microcirculation impairment due to CIH preceded significant hepatic inflammation and fibrotic changes, despite the presence of HIF expression. In conclusion, CIH exacerbates endothelial dysfunction in NAFLD rats associated with increased oxidative stress and reduced nitric oxide bioavailability. This occurs before inflammation and fibrosis establish. Our results suggest that with CIH endothelial dysfunction should be considered an early target.NEW & NOTEWORTHY We believe the findings are of relevance because we demonstrate that chronic intermittent hypoxia further augments impaired hepatic endothelial dysfunction in nonalcoholic fatty liver disease rats. Because obstructive sleep apnea syndrome is associated with systemic endothelial dysfunction in cardiovascular disorders, and chronic intermittent hypoxia is an independent and reversible risk factor for hypertension and coronary artery disease, we hypothesized that this entity may be of potential relevance in the pathophysiology of nonalcoholic fatty liver disease.

The potential role of vascular alterations and subsequent impaired liver blood flow and hepatic hypoxia in the pathophysiology of non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) covers a spectrum of disease ranging from steatosis to steatohepatitis (NASH) and fibrosis, but the underlying pathophysiological mechanisms remain largely unknown. As there is currently no approved pharmacological therapy and the prevalence of NAFLD keeps increasing, understanding of its pathophysiology is crucial. We hypothesise that vascular alterations in early NAFLD play a role in the progression of the disease by inducing an increased intrahepatic vascular resistance and consequently relative hypoxia in the liver. Evidence of the detrimental effects of hypoxia in NAFLD has already been observed in liver surgery, where the outcomes of steatotic livers after ischaemia-reperfusion are worse than in healthy livers, and in obstructive sleep apnoea, which is an independent risk factor of NAFLD. Moreover, early histological damage in NAFLD is situated in the pericentral zone, which is also the first zone to be affected by a decreased oxygen tension because of the unique hepatic vacsular anatomy that causes the pericentral oxygen tension to be the lowest. Angiogenesis is also a characteristic of NAFLD, driven by hypoxia-induced mechanisms, as demonstrated in both animal models and in humans with NAFLD. Relative hypoxia is most probably induced by impaired blood flow to the liver, caused by increased intrahepatic vascular resistance. An increased intrahepatic vascular resistance early in the development of disease has been convincingly demonstrated in several animal models of NAFLD, whereas an increased portal pressure, a consequence of increased intrahepatic vascular resistance, has been proven in patients with NAFLD. Animal studies demonstrated a decreased intrahepatic effect of vasodilators and an increased reactivity to vasoconstrictors that results in an increased intrahepatic vascular resistance, thus the presence of a functional component. Pharmacological products that target vasoregulation can hence improve the intrahepatic vascular resistance and this might prevent or reverse progression of NAFLD, representing an important therapeutic option to study. Some of the drugs currently under evaluation in clinical trials for NASH have interesting properties related to the hepatic vasculature. Some other interesting drugs have been tested in animal models but further study in patients with NAFLD is warranted. In summary, in this paper we summarise the evidence that leads to the hypothesis that an increased intrahepatic vascular resistance and subsequent parenchymal hypoxia in early NAFLD is an important pathophysiological driving mechanism for the progression of the disease.

Fasudil improves endothelial dysfunction in rats exposed to chronic intermittent hypoxia through RhoA/ROCK/NFATc3 pathway

Endothelial dysfunction is one of the main pathological changes in Obstructive sleep apnoea (OSA). The Rho kinase (ROCK) pathway is associated with endothelial dysfunction. However, the interaction between ROCK and nuclear factor of activated T cells isoform c3 (NFATc3) in the development of this pathological response under chronic intermittent hypoxia (CIH) is unclear. To simulate the OSA model, we established a moderate CIH rat model by administering the fraction of inspired O2 (FiO2) from 21% to 9%, 20 times/h, 8 h/day for 3 weeks. Fasudil (ROCK inhibitor, 8 mg/kg/d, i.p.) was administrated in the rats exposed to CIH for 3 weeks. Our results demonstrated that CIH caused significantly endothelial dysfunction, accompanying with increased ET-1 level, decreased eNOS expression and NO production, which reduced ACh-induced vascular relaxation responses. Moreover, RhoA/ROCK-2/NFATc3 expressions were up-regulated. Fasudil significantly improved CIH induced endothelial dysfunction. Data suggested that the ROCK activation is necessary for endothelial dysfunction during CIH.

Detection and analysis of apoptosis- and autophagy-related miRNAs of mouse vascular endothelial cells in chronic intermittent hypoxia model

Endothelial dysfunction is the main pathogenic mechanism of cardiovascular complications induced by obstructive sleep apnea/hyponea syndrome (OSAHS). Chronic intermittent hypoxia (CIH) is the primary factor of OSAHS-associated endothelial dysfunction. The hypoxia inducible factor (HIF) pathway regulates the expression of downstream target genes and mediates cell apoptosis caused by CIH-induced endothelial injury. miRNAs play extensive and important negative regulatory roles in this process at the post-transcriptional level. However, the regulatory mechanism of miRNAs in CIH tissue models remains unclear. The present study established a mouse aortic endothelial cell model of CIH in an attempt to screen out specific miRNAs by using miRNA chip analysis. It was found that 14 miRNAs were differentially expressed. Of them, 6 were significantly different and verified by quantitative real-time PCR (Q-PCR), of which four were up-regulated and two were down-regulated markedly. To gain an unbiased global perspective on subsequent regulation by altered miRNAs, we established signaling networks by GO to predict the target genes of the 6 miRNAs. It was found that the 6 identified miRNAs were apoptosis- or autophagy-related target genes. Down-regulation of miR-193 inhibits CIH induced endothelial injury and apoptosis- or autophagy-related protein expression. In conclusion, our results showed that CIH could induce differential expression of miRNAs, and alteration in the miRNA expression pattern was associated with the expression of apoptosis- or autophagy-related genes.

Uncoupling of Vascular Nitric Oxide Synthase Caused by Intermittent Hypoxia

Objective. Obstructive sleep apnea (OSA), characterized by chronic intermittent hypoxia (CIH), is often present in diabetic (DB) patients. Both conditions are associated with endothelial dysfunction and cardiovascular disease. We hypothesized that diabetic endothelial dysfunction is further compromised by CIH. Methods. Adult male diabetic (BKS.Cg-Dock7^m +/+ Lepr^db/J) (db/db) mice (10 weeks old) and their heterozygote littermates were subjected to CIH or intermittent air (IA) for 8 weeks. Mice were separated into 4 groups: IA (intermittent air nondiabetic), IH (intermittent hypoxia nondiabetic), IADB (intermittent air diabetic), and IHDB (intermittent hypoxia diabetic) groups. Endothelium-dependent and endothelium-independent relaxation and modulation by basal nitric oxide (NO) were analyzed using wire myograph. Plasma 8-isoprostane, interleukin-6 (IL-6), and asymmetric dimethylarginine (ADMA) were measured using ELISA. Uncoupling of eNOS was measured using dihydroethidium (DHE) staining. Results. Endothelium-dependent vasodilation and basal NO production were significantly impaired in the IH and IADB group compared to IA group but was more pronounced in IHDB group. Levels of 8-isoprostane, IL-6, ADMA, and eNOS uncoupling were ≈2-fold higher in IH and IADB groups and were further increased in the IHDB group. Conclusion. Endothelial dysfunction is more pronounced in diabetic mice subjected to CIH compared to diabetic or CIH mice alone. Oxidative stress, ADMA, and eNOS uncoupling were exacerbated by CIH in diabetic mice.

Adiponectin protects the rats liver against chronic intermittent hypoxia induced injury through AMP-activated protein kinase pathway

This study was performed to assess the effect of chronic intermittent hypoxia (CIH) on the liver, the associated mechanisms and the potential therapeutic roles of adiponectin (Ad). Sixty rats were randomly assigned to four groups: the normal control (NC), NC and Ad supplement (NC + Ad), CIH, and CIH and Ad supplement (CIH + Ad) groups. The rats in the CIH and CIH + Ad groups were exposed to a hypoxic environment for 4 months. Rats in the NC + Ad and CIH + Ad groups were also treated with an intravenous injection of Ad (10 ug), twice a week. The plasma levels of hepatic enzymes, serum triglyceride, liver triglyceride, fasting blood glucose and hepatic cell apoptosis in hepatic tissue, were higher in the CIH group than in the NC and NC + Ad groups. However, the Ad supplementation in the CIH + Ad group rescued the hepatic tissue insult by activating the AMP-activated protein kinase (AMPK) pathway. In conclusion, Ad could protect against CIH-induced hepatic injury partly through the AMPK pathway.

WITHDRAWN: Detection and analysis of apoptosis- and autophagy-related miRNAs of vascular endothelial cells in a mouse chronic intermittent hypoxia model

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Contribution of Cyclooxygenase End Products and Oxidative Stress to Intrahepatic Endothelial Dysfunction in Early Non-Alcoholic Fatty Liver Disease

Introduction

Metabolic syndrome induces endothelial dysfunction, a surrogate marker of cardiovascular disease. In parallel, metabolic syndrome is frequently associated with non-alcoholic fatty liver disease (NAFLD), which may progress to cirrhosis. The aim of the present study was to evaluate intrahepatic endothelial dysfunction related to cyclooxygenase end products and oxidative stress as possible mechanisms involved in the pathophysiology of NAFLD.

Materials and Methods

Sprague-Dawley rats were fed standard diet (control-diet, CD) or high-fat-diet (HFD) for 6 weeks. Metabolic syndrome was assessed by recording arterial pressure, lipids, glycemia and rat body weight. Splanchnic hemodynamics were measured, and endothelial dysfunction was evaluated using concentration-effect curves to acetylcholine. Response was assessed with either vehicle, L-N^G-Nitroarginine (L-NNA), indomethacin, tempol, or a thromboxane receptor antagonist, SQ 29548. We quantified inflammation, fibrosis, oxidative stress, nitric oxide (NO) bioavailability and thromboxane B₂ levels.

Results

HFD rats exhibited metabolic syndrome together with the presence of NAFLD. Compared to control-diet livers, HFD livers showed increased hepatic vascular resistance unrelated to inflammation or fibrosis, but with decreased NO activity and increased oxidative stress. Endothelial dysfunction was observed in HFD livers compared with CD rats and improved after cyclooxygenase inhibition or tempol pre-incubation. However, pre-incubation with SQ 29548 did not modify acetylcholine response.

Conclusions

Our study provides evidence that endothelial dysfunction at an early stage of NAFLD is associated with reduced NO bioavailability together with increased cyclooxygenase end products and oxidative stress, which suggests that both pathways are involved in the pathophysiology and may be worth exploring as therapeutic targets to prevent progression of the disease.

Adiponectin protects the kidney against chronic intermittent hypoxia-induced injury through inhibiting endoplasmic reticulum stress

PURPOSE

The current study was carried out to assess the effects of chronic intermittent hypoxia (CIH) on the kidney, the intervention roles of adiponectin (Ad), and the associated mechanisms.

METHODS

Sixty Wistar rats were randomly divided into four groups: the normal control (NC), normal control plus Ad supplement (NC + Ad), CIH, and CIH plus Ad supplement (CIH + Ad) groups. The rats in both CIH and CIH + Ad groups were submitted to a CIH environment for 4 months, while the rats in NC and NC + Ad groups were housed with the normal air for 4 months. In addition, the rats in NC + Ad and CIH + Ad groups were treated with an intravenous injection of Ad at a dosage of 10 μg per injection, twice a week, for four successive months.

RESULTS

The production level of reactive oxygen species (ROS) and the protein levels of endoplasmic reticulum (ER) stress, as well as the cell apoptosis level in kidney, were all higher in the CIH group than in the NC and NC + Ad groups (all p < 0.05). However, the ROS production, the protein of ER stress, and cell apoptosis levels in kidney were all lower in the CIH + Ad group than those in the CIH group (all p < 0.05).

CONCLUSION

Ad could protect against CIH-induced renal cell apoptosis through inhibiting ROS-related ER stress.

The Crosstalk between Hypoxia and Innate Immunity in the Development of Obesity-Related Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) has become a major health issue in western countries in parallel with the dramatic increase in the prevalence of obesity and all obesity related conditions, including respiratory diseases as obstructive sleep apnea-hypopnea syndrome (OSAHS). Interestingly, the severity of the liver damage in obesity-related NAFLD has been associated with the concomitant presence of OSAHS. In the presence of obesity, the proinflammatory state in these patients together with intermittent episodes of hypoxia, characteristic of OSAHS pathogenesis, may lead to an enhanced inflammatory response mediated by a positive feedback loop mechanism that implicates HIF-1 and NFκB. Thus, the severity of liver involvement in obese NAFLD patients with a concomitant diagnosis of OSAHS could be explained. In this review, we focus on the molecular mechanisms underlying the hepatic response to chronic intermittent hypoxia and its interaction with innate immunity in obesity-related NAFLD.

Evaluation of circulating markers of hepatic apoptosis and inflammation in obese children with and without obstructive sleep apnea

OBJECTIVE

Hepatocyte apoptosis and macrophage activation contribute to the disease progression of nonalcoholic fatty liver disease (NAFLD). Obstructive sleep apnea (OSA) in obese children is associated with the severity of NAFLD. The aim of this study was to evaluate plasma levels of soluble Fas (sFas), soluble Fas ligand (sFasL), cytokeratin 18 (CK18) (markers of apoptosis), and soluble CD163 (sCD163) (marker of macrophage activation) in obese children with and without OSA.

METHODS

Consecutive obese children who were evaluated for OSA were recruited. The diagnosis of OSA was made using overnight polysomnography (PSG). Fasting blood samples were used to determine plasma CK18, sFas, sFasL, and sCD163 levels using specific sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

Fifty-eight subjects were included in the analysis with a mean age of 8.9 ± 3.2 years and a mean body mass index (BMI) z-score of 2.4 ± 0.49. Circulating sFas and sFasL levels were significantly lower in subjects with mild and severe OSA compared with those without OSA (p < 0.005 for both). In addition, sCD163 levels increased with an increasing severity of OSA (no OSA = 1.6 ± 0.25 mg/L, mild OSA = 2.3 ± 0.45, and severe OSA = 3.0 ± 0.52; p < 0.001), and they correlated with the apnea-hypopnea index (AHI) [rho (95% confidence interval, CI) of 0.71 (0.41, 1.00), p-value <0.001]. In six patients with severe OSA from whom samples were taken before and after tonsillectomy, the sCD163 level decreased significantly after treatment, and there was a trend toward an increase in sFasL.

CONCLUSION

Markers of apoptosis and macrophage activation are altered in obese children with OSA, indicating increased apoptotic and inflammatory pressures.

A switch in the source of ATP production and a loss in capacity to perform glycolysis are hallmarks of hepatocyte failure in advance liver disease

BACKGROUND & AIMS

The cause of hepatic failure in the terminal stages of chronic injury is unknown. Cellular metabolic adaptations in response to the microenvironment have been implicated in cellular breakdown.

METHODS

To address the role of energy metabolism in this process we studied mitochondrial number, respiration, and functional reserve, as well as cellular adenosine-5'-triphosphate (ATP) production, glycolytic flux, and expression of glycolysis related genes in isolated hepatocytes from early and terminal stages of cirrhosis using a model that produces hepatic failure from irreversible cirrhosis in rats. To study the clinical relevance of energy metabolism in terminal stages of chronic liver failure, we analyzed glycolysis and energy metabolism related gene expression in liver tissue from patients at different stages of chronic liver failure according to Child-Pugh classification. Additionally, to determine whether the expression of these genes in early-stage cirrhosis (Child-Pugh Class A) is related to patient outcome, we performed network analysis of publicly available microarray data obtained from biopsies of 216 patients with hepatitis C-related Child-Pugh A cirrhosis who were prospectively followed up for a median of 10years.

RESULTS

In the early phase of cirrhosis, mitochondrial function and ATP generation are maintained by increasing energy production from glycolytic flux as production from oxidative phosphorylation falls. At the terminal stage of hepatic injury, mitochondria respiration and ATP production are significantly compromised, as the hepatocytes are unable to sustain the increased demand for high levels of ATP generation from glycolysis. This impairment corresponds to a decrease in glucose-6-phosphatase catalytic subunit and phosphoglucomutase 1. Similar decreased gene expression was observed in liver tissue from patients at different stages of chronic liver injury. Further, unbiased network analysis of microarray data revealed that expression of these genes was down regulated in the group of patients with poor outcome.

CONCLUSIONS

An adaptive metabolic shift, from generating energy predominantly from oxidative phosphorylation to glycolysis, allows maintenance of energy homeostasis during early stages of liver injury, but leads to hepatocyte dysfunction during terminal stages of chronic liver disease because hepatocytes are unable to sustain high levels of energy production from glycolysis.

Mg supplementation protects against ritonavir-mediated endothelial oxidative stress and hepatic eNOS downregulation

Ritonavir (RTV), a prototypical protease inhibitor currently used as a key component of anti-HIV therapy, is known for its endothelial and hepatic toxicity. The effects of RTV and magnesium supplementation on cultured bovine endothelial cell (EC) and rat hepatic endothelial nitric oxide synthase (eNOS) status were investigated. RTV dose-dependently (5-30 µM) decreased EC viability after 48 h; high Mg (2mM) significantly attenuated the lost viability. ECs incubated with 15 µM RTV for 6 to 24h resulted in two- to fourfold elevation of oxidized glutathione and a 25% loss of total glutathione. At 24h, EC superoxide production due to RTV was detected by dihydroethidium staining and increased 41% when quantified by flow cytometry; altered glutathione status and superoxide levels were both substantially reversed by 2mM Mg. RTV reduced eNOS mRNA (-25% at 24 h) and led to decreased eNOS dimer/monomer ratios; nitric oxide-derived products decreased 40%; both changes were attenuated by Mg supplementation. In male Lewis-Brown Norway rats, RTV administration (75 mg/kg/day, 5 weeks) resulted in an 85% increase in plasma 8-isoprostane and a 23% decrease in hepatic eNOS mRNA; concomitantly, eNOS protein decreased 75%, whereas plasma nitrite level was reduced 48%. Dietary Mg supplementation (sixfold higher than control) prevented the eNOS mRNA decrease along with lowering 8-isoprostane and restored the eNOS protein and plasma nitrite levels comparable to controls. In conclusion, Mg attenuates RTV-mediated EC oxidative eNOS dysfunction and downregulation of hepatic eNOS expression; we suggest that Mg can serve as a beneficial adjunct therapeutic against RTV-mediated eNOS toxicity.

Hyperoxia accelerates progression of hepatic fibrosis by up-regulation of transforming growth factor-β expression

AIM: To investigate the effect of hypoxia or hyperoxia on the progression of hepatic fibrosis and to examine the role of transforming growth factor-β (TGF-β) in the livers of rats exposed to hypoxic or hyperoxic conditions.

METHODS: Male Sprague-Dawley rats were injected intraperitoneally with thioacetamide to induce hepatic fibrosis and were randomly divided into a hypoxia group, a hyperoxia group and an untreated control group. Ten rats in the hypoxia group were exposed to an altitude of 20000 ft for 1 h/d during 7 wk. Ten rats in the hyperoxia group were exposed to a water depth of 20 m with 100% oxygen supply for 1 h/d during 7 wk. We evaluated the degree of hepatic fibrosis using Masson trichrome stain and examined the expression level of hepatic TGF-β mRNA using quantitative real-time reverse transcriptase-polymerase chain reaction analysis.

RESULTS: Eight of 10 rats exposed to hypoxia showed diffuse and confluent fibrosis with the formation of structurally abnormal parenchymal nodules involving the entire liver, consistent with hepatic cirrhosis. Nine of 10 rats exposed to hyperoxia also demonstrated obvious histological findings of hepatic cirrhosis identical to those in hypoxic rat livers. In contrast, 8 of 10 untreated rats had periportal or septal fibrosis only. The frequency of hepatic cirrhosis in hypoxic rats (P = 0.009) and hyperoxic rats (P = 0.003) was significantly higher than that in untreated rats. In addition, hepatic TGF-β mRNA levels in hyperoxic rats were significantly higher than those in untreated rats. The mean value of the normalized TGF-β mRNA/β-actin expression ratio in the hyperoxic rats was 1.9-fold higher than that in the untreated rats (P = 0.027).

CONCLUSION: We demonstrated that both hypoxia and hyperoxia accelerated the progression of hepatic fibrosis in rats. Significant up-regulation of hepatic TGF-β in hyperoxic rats suggests that TGF-β is involved in the acceleration of hepatic fibrosis under hyperoxic conditions.

Conduit artery structure and function in lowlanders and native highlanders: relationships with oxidative stress and role of sympathoexcitation

Research detailing the normal vascular adaptions to high altitude is minimal and often confounded by pathology (e.g., chronic mountain sickness) and methodological issues. We examined vascular function and structure in: (1) healthy lowlanders during acute hypoxia and prolonged (∼2 weeks) exposure to high altitude, and (2) high-altitude natives at 5050 m (highlanders). In 12 healthy lowlanders (aged 32 ± 7 years) and 12 highlanders (Sherpa; 33 ± 14 years) we assessed brachial endothelium-dependent flow-mediated dilatation (FMD), endothelium-independent dilatation (via glyceryl trinitrate; GTN), common carotid intima-media thickness (CIMT) and diameter (ultrasound), and arterial stiffness via pulse wave velocity (PWV; applanation tonometry). Cephalic venous biomarkers of free radical-mediated lipid peroxidation (lipid hydroperoxides, LOOH), nitrite (NO2-) and lipid soluble antioxidants were also obtained at rest. In lowlanders, measurements were performed at sea level (334 m) and between days 3-4 (acute high altitude) and 12-14 (chronic high altitude) following arrival to 5050 m. Highlanders were assessed once at 5050 m. Compared with sea level, acute high altitude reduced lowlanders' FMD (7.9 ± 0.4 vs. 6.8 ± 0.4%; P = 0.004) and GTN-induced dilatation (16.6 ± 0.9 vs. 14.5 ± 0.8%; P = 0.006), and raised central PWV (6.0 ± 0.2 vs. 6.6 ± 0.3 m s(-1); P = 0.001). These changes persisted at days 12-14, and after allometrically scaling FMD to adjust for altered baseline diameter. Compared to lowlanders at sea level and high altitude, highlanders had a lower carotid wall:lumen ratio (∼19%, P ≤ 0.04), attributable to a narrower CIMT and wider lumen. Although both LOOH and NO2- increased with high altitude in lowlanders, only LOOH correlated with the reduction in GTN-induced dilatation evident during acute (n = 11, r = -0.53) and chronic (n = 7, r = -0.69; P ≤ 0.01) exposure to 5050 m. In a follow-up, placebo-controlled experiment (n = 11 healthy lowlanders) conducted in a normobaric hypoxic chamber (inspired O2 fraction (F IO 2) = 0.11; 6 h), a sustained reduction in FMD was evident within 1 h of hypoxic exposure when compared to normoxic baseline (5.7 ± 1.6 vs. 8.0 ±1.3%; P < 0.01); this decline in FMD was largely reversed following α1-adrenoreceptor blockade. In conclusion, high-altitude exposure in lowlanders caused persistent impairment in vascular function, which was mediated partially via oxidative stress and sympathoexcitation. Although a lifetime of high-altitude exposure neither intensifies nor attenuates the impairments seen with short-term exposure, chronic high-altitude exposure appears to be associated with arterial remodelling.