Plasmatic Concentrations of ADMA and Homocystein in Llama (Lama glama) and Regulation of Arginase Type II: An Animal Resistent to the Development of Pulmonary Hypertension Induced by Hypoxia

Adipose-derived stem cells ameliorate radiation-induced lung injury by activating the DDAH1/ADMA/eNOS signaling pathway

Background

Ionizing radiation-induced lung injury is caused by the initial inflammatory reaction and leads to advanced fibrosis of lung tissue. Adipose-derived stem cells (ASCs) are a type of mesenchymal stem cell that can differentiate into various functional cell types with broad application prospects in the treatment of tissue damage. The purpose of this study was to explore the protective effect of ASCs against radiation-induced lung injury and to provide a novel basis for prevention and treatment of radiation-induced lung injury.

Materials and methods

Fifty mice were randomly divided into a control group (Ctrl), radiation exposure group (IR), radiation exposure plus ASC treatment group (IR + ASC), radiation exposure plus L-257 group (IR + L-257), and radiation exposure plus ASC treatment and L-257 group (IR + ASC + L-257). Mice in IR, IR + ASC, and IR + ASC + L-257 groups were exposed to a single whole-body dose of 5 Gy X-rays (160 kV/25 mA, 1.25 Gy/min). Within 2 h after irradiation, mice in IR + ASC and IR + ASC + L-257 groups were injected with 5 × 106 ASCs via the tail vein. Mice in IR + L-257 and IR + ASC + L-257 groups were intraperitoneally injected with 30 mg/kg L-257 in 0.5 mL saline.

Results

The mice in the IR group exhibited lung hemorrhage, edema, pulmonary fibrosis, and inflammatory cell infiltration, increased release of proinflammatory cytokines, elevation of oxidative stress and apoptosis, and inhibition of the dimethylarginine dimethylamino hydratase 1 (DDAH1)/ADMA/eNOS signaling pathway. ASC treatment alleviated radiation-induced oxidative stress, apoptosis, and inflammation, and restored the DDAH1/ADMA/eNOS signaling pathway. However, L-257 pretreatment offset the protective effect of ASCs against lung inflammation, oxidative stress, and apoptosis.

Conclusions

These data suggest that ASCs ameliorate radiation-induced lung injury, and the mechanism may be mediated through the DDAH1/ADMA/eNOS signaling pathway.

Untargeted Metabolomics Analysis Using UHPLC-Q-TOF/MS Reveals Metabolic Changes Associated with Hypertension in Children

The mechanism of hypertension in children remains elusive. The objective of this study was to analyze plasma metabolomics characteristics to explore the potential mechanism of hypertension in children. Serum samples from 29 control children, 38 children with normal body mass index and simple hypertension (NBp), 8 children overweight with simple hypertension (OBp), 37 children with normal body mass index and H-type hypertension (NH) and 19 children overweight with H-type hypertension (OH) were analyzed by non-targeted metabolomics. A total of 1235 differential metabolites were identified between children with hypertension and normal controls, of which 193 metabolites including various lipids were significantly expressed. Compared with the control group, 3-dehydroepiandrosterone sulfate, oleic acid and linoleic acid were up-regulated, and gamma-muricholic acid was down-regulated in the NBp group; 3-dehydroepiandrosterone sulfate, 4-acetamidobutanoate and 1-hexadecanoyl-2-octadecadienoyl-sn-glyero-3-phosphocholine were up-regulated in the OBp group, whereas adenosine and 1-myristoyl-sn-glyero-3-phosphocholine were down-regulated; in the NH group, 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine, phenol and 3-methoxytyramine were up-regulated, while pentadecanoic acid was down-regulated; in the OH group, NG,NG-dimethyl-L-arginine, 1-palmitoyl-sn-glycero-3-phosphocholine and monoethyl phthalate were up-regulated, while phloretin and glycine were down-regulated. The results showed that the children with hypertension had obvious disorders of lipid metabolism (especially in the overweight hypertension group), which led to the occurrence of hypertension. Additionally, the concentration of NO production-related NG, NG-dimethyl-L-arginine, was significantly increased, which may play an important role in H-type hypertension in children.

Association of Genes of the NO Pathway with Altitude Disease and Hypoxic Pulmonary Hypertension

Chronic intermittent hypoxia leads to high-altitude pulmonary hypertension, which is associated with high asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis. Therefore, we aimed to understand the relation of single nucleotide polymorphisms in this pathway to high-altitude pulmonary hypertension (HAPH). We genotyped 69 healthy male Chileans subjected to chronic intermittent hypoxia. Acclimatization to altitude was determined using the Lake Louise Score and the presence of acute mountain sickness. Echocardiography was performed after six months in 24 individuals to estimate pulmonary arterial pressure. The minor allele of dimethylarginine dimethylaminohydrolase (DDAH)1 rs233112 was associated with high-baseline plasma ADMA concentration, while individuals homozygous for the major allele of DDAH2 rs805304 had a significantly greater increase in ADMA during chronic intermittent hypoxia. The major allele of alanine glyoxylate aminotransferase-2 (AGXT2) rs37369 was associated with a greater reduction of plasma symmetric dimethylarginine (SDMA). Several genes were associated with high-altitude pulmonary hypertension, and the nitric oxide synthase (NOS)3 and DDAH2 genes were related to acute mountain sickness. In conclusion, DDAH1 determines baseline plasma ADMA, while DDAH2 modulates ADMA increase in hypoxia. AGXT2 may be up-regulated in hypoxia. Genomic variation in the dimethylarginine pathway affects the development of HAPH and altitude acclimatization.

Hydrogen Sulfide Metabolism and Pulmonary Hypertension

Pulmonary hypertension (PH) is a severe and multifactorial disease characterized by a progressive elevation of pulmonary arterial resistance and pressure due to remodeling, inflammation, oxidative stress, and vasoreactive alterations of pulmonary arteries (PAs). Currently, the etiology of these pathological features is not clearly understood and, therefore, no curative treatment is available. Since the 1990s, hydrogen sulfide (H₂S) has been described as the third gasotransmitter with plethoric regulatory functions in cardiovascular tissues, especially in pulmonary circulation. Alteration in H₂S biogenesis has been associated with the hallmarks of PH. H₂S is also involved in pulmonary vascular cell homeostasis via the regulation of hypoxia response and mitochondrial bioenergetics, which are critical phenomena affected during the development of PH. In addition, H₂S modulates ATP-sensitive K⁺ channel (K_ATP) activity, and is associated with PA relaxation. In vitro or in vivo H₂S supplementation exerts antioxidative and anti-inflammatory properties, and reduces PA remodeling. Altogether, current findings suggest that H₂S promotes protective effects against PH, and could be a relevant target for a new therapeutic strategy, using attractive H₂S-releasing molecules. Thus, the present review discusses the involvement and dysregulation of H₂S metabolism in pulmonary circulation pathophysiology.

Activation of arginase II by asymmetric dimethylarginine and homocysteine in hypertensive rats induced by hypoxia: a new model of nitric oxide synthesis regulation in hypertensive processes?

In recent years, the increase in blood pressure at high altitudes has become an interesting topic among high-altitude researchers. In our animal studies using Wistar rats, we observed the existence of two rat populations that exhibit differential physiological responses during hypoxic exposure. These rats were classified as hypoxia-induced hypertensive rats and nonhypertensive rats. A decrease in nitric oxide levels was reported in different hypertension models associated with increased concentrations of asymmetric dimethylarginine (ADMA) and homocysteine, and we recently described an increase in arginase type II expression under hypoxia. ADMA and homocysteine decrease nitric oxide (NO) bioavailability; however, whether ADMA and homocysteine have a regulatory effect on arginase activity and therefore regulate another NO synthesis pathway is unknown. Therefore, the aim of this study was to measure basal ADMA and homocysteine levels in hypoxia-induced hypertensive rats and evaluate their effect on arginase II activity. Our results indicate that hypoxia-induced hypertensive rats presented lower nitric oxide concentrations than nonhypertensive rats, associated with higher concentrations of homocysteine and ADMA. Hypoxia-induced hypertensive rats also presented lower dimethylarginine dimethylaminohydrolase-2 and cystathionine β-synthase levels, which could explain the high ADMA and homocysteine levels. In addition, we observed that both homocysteine and ADMA had a significant effect on arginase II activation in the hypertensive rats. Therefore, we suggest that ADMA and homocysteine have dual regulatory effects on NO synthesis. The former has an inhibitory effect on eNOS, and the latter has a secondary activating effect on arginase II. We propose that arginase II is activated by AMDA and homocysteine in hypoxia-induced hypertensive rats.

Perinatal cardiopulmonary adaptation to the thin air of the Alto Andino by a native Altiplano dweller, the llama

Most mammals have a poor tolerance to hypoxia, and prolonged O₂ restriction can lead to organ injury, particularly during fetal and early postnatal life. Nevertheless, the llama (Lama Glama) has evolved efficient mechanisms to adapt to acute and chronic perinatal hypoxia. One striking adaptation is the marked peripheral vasoconstriction measured in the llama fetus in response to acute hypoxia, which allows efficient redistribution of cardiac output toward the fetal heart and adrenal glands. This strong peripheral vasoconstrictor tone is triggered by a carotid body reflex and critically depends on α-adrenergic signaling. A second adaptation is the ability of the llama fetus to protect its brain against hypoxic damage. During hypoxia, in the llama fetus there is no significant increase in brain blood flow. Instead, there is a fall in brain O₂ consumption and temperature, together with a decrease of Na⁺-K⁺-ATPase activity and Na⁺ channels expression, protecting against seizures and neuronal death. Finally, the newborn llama does not develop pulmonary hypertension in response to chronic hypoxia. In addition to maintaining basal pulmonary arterial pressure at normal levels the pulmonary arterial pressor response to acute hypoxia is lower in highland than in lowland llamas. The protection against hypoxic pulmonary arterial hypertension and pulmonary contractile hyperreactivity is partly due to increased hemoxygenase-carbon monoxide signaling and decreased Ca²⁺ sensitization in the newborn llama pulmonary vasculature. These three striking physiological adaptations of the llama allow this species to live and thrive under the chronic influence of the hypobaric hypoxia of life at high altitude.

Metabolism of asymmetric dimethylarginine in hypoxia: from bench to bedside

Acute hypoxia and chronic hypoxia induce pulmonary vasoconstriction. While hypoxic pulmonary vasoconstriction is a physiological response if parts of the lung are affected, global exposure to hypoxic conditions may lead to clinical conditions like high-altitude pulmonary hypertension. Nitric oxide is the major vasodilator released from the vascular endothelium. Nitric oxide-dependent vasodilation is impaired in hypoxic conditions. Inhibition of nitric oxide synthesis is the most rapid and easily reversible molecular mechanism to regulate nitric oxide-dependent vascular function in response to physiological and pathophysiological stimuli. Asymmetric dimethylarginine is an endogenous, competitive inhibitor of nitric oxide synthase and a risk marker for major cardiovascular events and mortality. Elevated asymmetric dimethylarginine has been observed in animal models of hypoxia as well as in human cohorts under chronic and chronic intermittent hypoxia at high altitude. In lowlanders, asymmetric dimethylarginine is high in patients with pulmonary hypertension. We have recently shown that high asymmetric dimethylarginine at sea level is a predictor for high-altitude pulmonary hypertension. Asymmetric dimethylarginine is a highly regulated molecule, both by its biosynthesis and metabolism. Methylation of L-arginine by protein arginine methyltransferases was shown to be increased in hypoxia. Furthermore, the metabolism of asymmetric dimethylarginine by dimethylarginine dimethylaminohydrolases (DDAH1 and DDAH2) is decreased in animal models of hypoxia. Whether these changes are caused by transcriptional or posttranslational modifications remains to be elucidated. Current data suggest a major role of asymmetric dimethylarginine in regulating pulmonary arterial nitric oxide production in hypoxia. Further studies are needed to decipher the molecular mechanisms regulating asymmetric dimethylarginine in hypoxia and to understand their clinical significance.

Elevated serum circ_0068481 levels as a potential diagnostic and prognostic indicator in idiopathic pulmonary arterial hypertension

Circular RNAs have continuous, stable, and covalently closed circular structures and are not easily degraded by nucleases, thus they are ideal serum biomarkers for detecting diseases. However, research is still lacking on circular RNAs as diagnostic and prognostic markers for idiopathic pulmonary arterial hypertension. This study investigated the potential role of serum circ_0068481 levels in idiopathic pulmonary arterial hypertension diagnosis and prognosis. This prospective cohort study enrolled 82 patients with idiopathic pulmonary arterial hypertension between January 2016 and July 2018 at Guangdong Provincial People's Hospital. Serum circ_0068481 levels were measured using quantitative reverse transcription-polymerase chain reaction. Baseline data, including clinical background, hemodynamic variables, and biochemical variables, were collected. Receiver operating characteristic curves were used to investigate diagnostic effect, the Kaplan-Meier method was used to estimate survival rates, and univariate analysis of prognostic factors was performed with a Cox proportional hazard model. We found that serum circ_0068481 expression levels were significantly higher in patients with idiopathic pulmonary arterial hypertension and had higher sensitivity and specificity for predicting idiopathic pulmonary arterial hypertension. Additionally, we found that circ_0068481 expression correlated significantly with heart function, 6-min walk distance, serum N-terminal pro-B-type natriuretic peptide, serum H2S, the 6th World Symposium on Pulmonary Hypertension risk stratification, right heart failure, and patient death. Moreover, serum circ_0068481 levels were elevated in patients with idiopathic pulmonary arterial hypertension and right heart failure and were able to predict right heart failure. Serum circ_0068481 levels were also elevated in patients who died with idiopathic pulmonary arterial hypertension and were able to predict poorer clinical outcomes. Circ_0068481 is a novel and noninvasive biomarker for diagnosing idiopathic pulmonary arterial hypertension and predicting poor clinical outcome in patients with idiopathic pulmonary arterial hypertension.