Metabonomic profiling of chronic intermittent hypoxia in a mouse model

Altered Metabolism during the Dark Period in Drosophila Short Sleep Mutants

Sleep is regulated via circadian mechanisms, but effects of sleep disruption on physiological rhythms, in particular metabolic cycling, remain unclear. To examine this question, we probed diurnal metabolic alterations of two Drosophila short sleep mutants, fumin and sleepless. Samples were collected with high temporal sampling (every 2 h) over 24 h under a 12:12 light:dark cycle, and profiling was done using an ion-switching LCMS/MS method. Fewer metabolites with 24 h oscillations were noted with short sleep (50 and 46 in fumin and sleepless, BH. Q < 0.2 by RAIN analysis) compared to a wild-type control (iso31, 63 with BH. Q < 0.2), and peak phases of the sleep mutants were consolidated into two major phase peaks at mid-day and middle of night. Overall, altered nicotinate/nicotinamide, alanine/aspartate/glutamate, acetylcholine, glyoxylate/dicarboxylate, and TCA cycle metabolism were observed in the short sleep mutants, indicative of increased energetic demand and oxidative stress compared to wild type. Both changes in cycling and discriminant models suggest unique alterations in the dark period indicative of constrained metabolic networks. Thus, we conclude that sleep loss alters metabolic function uniquely throughout the day, and further examination of specific mechanisms is warranted.

Assessing the causal association between sleep apnea and the human gut microbiome composition: A two-sample Mendelian randomization study

Background

Studies have linked gut microbiota dysbiosis with sleep apnea; however, no causal relationship was found in human subjects. Finding new targets for the pathophysiology of sleep apnea might be made possible by systematically investigating the causal relationship between the human gut microbiota and sleep apnea.

Methods

A two-sample Mendelian randomization analysis was conducted. The human gut microbiome composition data, spanning five taxonomic levels, were acquired from a genome-wide association study that included 18,340 participants from 24 cohorts. Genome-wide association study data for sleep apnea were obtained from the Sleep Disorder Knowledge Portal for primary analysis and the FinnGen consortium for meta-analysis. Sensitivity analyses were conducted to evaluate heterogeneity and pleiotropy.

Results

Using inverse-variance weighted analysis, eight microbial taxa were initially found to be substantially linked with the apnea-hypopnea index. Only three microbial taxa remained significant associations with sleep apnea when combined with the FinnGen consortium (the class Bacilli: B = 8.21%, 95% CI = 0.93%-15.49%; p = 0.03; the order Lactobacillales: B = 7.55%, 95% CI = 0.25%-4.85%; p = 0.04; the genus RuminococcaceaeUCG009: B = -21.63%, 95% CI = -41.47% to -1.80%; p = 0.03).

Conclusions

Sleep apnea may lead to gut dysbiosis as significant reductions in butyrate-producing bacteria and increases in lactate-producing bacteria. By integrating genomes and metabolism, the evidence that three microbiome species are causally linked to sleep apnea may offer a fresh perspective on the underlying mechanisms of the condition.

Altered Metabolism During the Dark Period in Drosophila Short Sleep Mutants

Sleep is an almost universally required state in biology. Disrupted sleep has been associated with adverse health risks including metabolic perturbations. Sleep is in part regulated via circadian mechanisms, however, metabolic dysfunction at different times of day arising from sleep disruption is unclear. We used targeted liquid chromatography-mass spectrometry to probe metabolic alterations using high-resolution temporal sampling of two Drosophila short sleep mutants, fumin and sleepless, across a circadian day. Discriminant analyses revealed overall distinct metabolic profiles for mutants when compared to a wild type dataset. Altered levels of metabolites involved in nicotinate/nicotinamide, alanine, aspartate, and glutamate, glyoxylate and dicarboxylate metabolism, and the TCA cycle were observed in mutants suggesting increased energetic demands. Furthermore, rhythmicity analyses revealed fewer 24 hr rhythmic metabolites in both mutants. Interestingly, mutants displayed two major peaks in phases while wild type displayed phases that were less concerted. In contrast to 24 hr rhythmic metabolites, an increase in the number of 12 hr rhythmic metabolites was observed in fumin while sleepless displayed a decrease. These results support that decreased sleep alters the overall metabolic profile with short sleep mutants displaying altered metabolite levels associated with a number of pathways in addition to altered neurotransmitter levels.

Causality Investigation between Gut Microbiota, Derived Metabolites, and Obstructive Sleep Apnea: A Bidirectional Mendelian Randomization Study

Various studies have highlighted the important associations between obstructive sleep apnea (OSA) and gut microbiota and related metabolites. Nevertheless, the establishment of causal relationships between these associations remains to be determined. Multiple mendelian randomization (MR) analyses were performed to genetically predict the causative impact of 196 gut microbiota and 83 metabolites on OSA. Two-sample MR was used to assess the potential association, and causality was evaluated using inverse variance weighted (IVW), MR-Egger, and weighted median (WM) methods. Multivariable MR (MVMR) was employed to ascertain the causal independence between gut microbiota and the metabolites linked to OSA. Additionally, Cochran's Q test, the MR Egger intercept test and the MR Steiger test were used for the sensitivity analyses. The analysis of the 196 gut microbiota revealed that genus_Ruminococcaceae (UCG009) (PIVW = 0.010) and genus_Subdoligranulum (PIVW = 0.041) were associated with an increased risk of OSA onset. Conversely, Family_Ruminococcaceae (PIVW = 0.030), genus_Coprococcus2 (PWM = 0.025), genus_Eggerthella (PIVW = 0.011), and genus_Eubacterium (xylanophilum_group) (PIVW = 0.001) were negatively related to the risk of OSA. Among the 83 metabolites evaluated, 3-dehydrocarnitine, epiandrosterone sulfate, and leucine were determined to be potential independent risk factors associated with OSA. Moreover, the reverse MR analysis demonstrated a suggestive association between OSA exposure and six microbiota taxa. This study offers compelling evidence regarding the potential beneficial or detrimental causative impact of the gut microbiota and its associated metabolites on OSA risk, thereby providing new insights into the mechanisms of gut microbiome-mediated OSA development.

Obstructive sleep apnea and metabolic syndrome

Metabolic syndrome (MS) is a heterogeneous condition associated with increased cardiovascular risk. There is growing evidence from experimental, translational, and clinical investigations that has suggested that obstructive sleep apnea (OSA) is associated with prevalent and incident components of MS and MS itself. The biological plausibility is supportive, primarily related to one of the main features of OSA, namely intermittent hypoxia: increased sympathetic activation with hemodynamic repercussions, increased hepatic glucose output, insulin resistance through adipose tissue inflammation, pancreatic β-cell dysfunction, hyperlipidemia through the worsening of fasting lipid profiles, and the reduced clearance of triglyceride-rich lipoproteins. Although there are multiple related pathways, the clinical evidence relies mainly on cross-sectional data preventing any causality assumptions. The overlapping presence of visceral obesity or other confounders such as medications challenges the ability to understand the independent contribution of OSA on MS. In this review, we revisit the evidence on how OSA/intermittent hypoxia could mediate adverse effects of MS parameters independent of adiposity. Particular attention is devoted to discussing recent evidence from interventional studies. This review describes the research gaps, the challenges in the field, perspectives, and the need for additional high-quality data from interventional studies addressing the impact of not only established but promising therapies for OSA/obesity.

Comparative Tandem Mass Tag-Based Quantitative Proteomics Analysis of Liver Against Chronic Hypoxia: Molecular Insights Into Metabolism in Rats

Xu, Jin, Shenhan Gao, Mingyuan Xin, Wenjie Chen, Kaikun Wang, Wenjing Liu, Xinzong Yan, Sinan Peng, and Yanming Ren. Comparative tandem mass tag-based quantitative proteomics analysis of liver against chronic hypoxia: molecular insights into metabolism in rats. High Alt Med Biol. 24:49-58, 2023. Objective: Using a metabolomic approach, we uncovered key regulators in metabolism from tandem mass tag (TMT)-based proteomic analysis in animals chronically exposed to hypoxia. Methods: Sixteen Sprague-Dawley rats (n = 8 per group) were exposed to chronic normoxia or hypoxia (380 mmHg corresponding to a simulated altitude of 5,500 m) for 35 consecutive days. Hypoxia-induced alterations in metabolic pathways were analyzed from TMT-based proteomic analysis, complemented by western blot validation of key regulators. Results: We profiled biochemical parameters and serum lipids, found that serum alanine aminotransferase and blood glucose were not significantly changed due to chronic hypoxia. However, serum triglycerides, total cholesterol, high-density lipoprotein, and low-density lipoprotein (LDL) were significantly affected by chronic hypoxia. And the levels of LDL nearly doubled (p < 0.05) after hypoxia exposure for 35 days. Through Kyoto Encyclopedia of Genes and Genomes classification, we found several metabolic pathways were enriched, including lipid metabolism, cofactor and vitamin metabolism, amino acids metabolism, carbohydrate metabolism, and energy metabolism. To explore the potential functions of proteins in metabolic pathways that become a coordinated shift under chronic hypoxic conditions, Gene Ontology and pathway analysis were carried out on differentially expressed proteins. As the co-expression network shown in Figure, we identified the most significant differentially expressed proteins after chronic hypoxic changes in the livers of rats. Furthermore, we validated the gene expression profiles at the protein level using western blot. Results of western blot were in accordance with our quantitative polymerase chain reaction findings. The levels of fatty acid synthase and aquaporin 1 were significantly downregulated after 35 days and the levels of ATP citrate lyase, 2'-5'-oligoadenylate synthetase 1A, aldehyde dehydrogenase 2, and Ras-related protein Rap-1A were significantly upregulated after 35 days. Conclusions: Although this study cannot completely account for all the molecular mechanisms in rats, we provide a good analysis of protein expression and profiling of rats under chronic hypoxia conditions.

Chronic intermittent hypoxia impaired collagen synthesis in mouse genioglossus via ROS accumulation: A transcriptomic analysis

Obstructive sleep apnea (OSA) is a sleep-related breathing disorder characterized by intermittent and recurrent upper airway collapse during sleep that leads to chronic intermittent hypoxia (CIH). The genioglossus (GG) is the largest dilator muscle, which controls the upper airway and plays an important role in OSA pathology. Elucidating its genetic alterations may help identify potential targets for OSA. However, the genetic aspects of the GG in CIH mice remain unclear. Here, we have conducted an RNA sequencing (RNA-Seq) analysis to assess the differentially expressed genes (DEGs) in the GG between CIH mice and normoxia (NOR) mice. A total of 637 DEGs were identified to be dysregulated in CIH mice compared with control mice. Bioinformatics analysis showed that the DEGs were related to various physiological processes, such as the endogenous stimulus responses, cellular component organization and metabolic processes. Extracellular matrix (ECM)-receptor interaction was the top KEGG pathway in the environmental information processing category with high significance and large fold changes. From the gene weight distributions of collagen (Col)-related biological processes (BPs), we found several significant DEGs, such as Col1a1, Col1a2, Mmp2, Col3a1, Col5a1, Fmod, and Col5a2. A PPI network showed that Col1a1 was linked to ECM-receptor interactions, responses to reactive oxygen species (ROS) and Col-related BPs. It was verified in vivo and in vitro that hypoxia can induce excess ROS and reduce Col expression levels. Moreover, we found NAC can effectively scavenge ROS and restore collagen synthesis. These findings contribute to a better understanding of the mechanisms linking OSA and upper airway muscle injury and may help identify potential therapeutic targets.

The gut microbiome and obstructive sleep apnea syndrome in children

Obstructive sleep apnea syndrome (OSAS) in children has become a major public health problem that affects the physical and mental growth of children. OSAS can result in adverse outcomes during growth and development, inhibiting the normal development of the metabolic, cardiovascular, and immune systems. OSAS is characterized by partial or complete obstruction of the upper airway, and prolonged obstruction that causes intermittent hypoxia and sleep fragmentation in children. The human microbiota is a complex community that is in dynamic equilibrium in the human body. Intermittent hypoxia and sleep fragmentation induced by childhood OSAS alter the composition of the gut microbiome. At the same time, changes in the gut microbiome affect sleep patterns in children through immunomodulatory and metabolic mechanisms, and induce further comorbidities, such as obesity, hypertension, and cardiovascular disease. This article discusses recent progress in research into the mechanisms of OSAS-induced changes in the gut microbiota and its pathophysiology in children.

Chronic exposure to ammonia induces oxidative stress and enhanced glycolysis in lung of piglets

Ammonia is one of the major environmental pollutants in the pig industry that seriously affects the airway health of pigs. In this study, we aimed to investigate the metabolic profiling changes of piglets' lung tissue after the exposure of 0 ppm (CG), 20 ppm (LG) and 50 ppm (HG) ammonia for 30 days. Compared with the control group, the obvious lung lesions were observed in HG, including interstitial thickening, inflammatory cell infiltration and focal hemorrhage. The significantly increased content of malondialdehyde in HG, combined with the significantly decreased mRNA expression of antioxidase and inflammatory-regulators in exposure groups, implied that ammonia exposure induced oxidative stress and diminished the anti-inflammatory response in lung tissues. Metabolomic analyses of lung tissues revealed 15 significantly altered metabolites among the three groups including multiple amino acids, carbohydrates and lipids. The accumulation of succinic acid, linoleic acid and phosphorylethanolamine and consumption of glucose, quinolinic acid and aspartic acid in ammonia exposure groups, indicated that energy supply from glucose aerobic oxidation was suppressed and the glycolysis and lipolysis were activated in lung tissues induced by chronic ammonia exposure.

Effects of Chronic Intermittent Hypoxia and Chronic Sleep Fragmentation on Gut Microbiome, Serum Metabolome, Liver and Adipose Tissue Morphology

Chronic intermittent hypoxia (CIH) and chronic sleep fragmentation (CSF) are two cardinal pathological features of obstructive sleep apnea (OSA). Dietary obesity is a crucial risk intermediator for OSA and metabolic disorders. Gut microbiota affect hepatic and adipose tissue morphology under conditions of CIH or CSF through downstream metabolites. However, the exact relationship is unclear. Herein, chow and high-fat diet (HFD)-fed mice were subjected to CIH or CSF for 10 weeks each and compared to normoxia (NM) or normal sleep (NS) controls. 16S rRNA amplicon sequencing, untargeted liquid chromatography-tandem mass spectrometry, and histological assessment of liver and adipose tissues were used to investigate the correlations between the microbiome, metabolome, and lipid metabolism under CIH or CSF condition. Our results demonstrated that CIH and CSF regulate the abundance of intestinal microbes (such as Akkermansia mucinphila, Clostridium spp., Lactococcus spp., and Bifidobacterium spp.) and functional metabolites, such as tryptophan, free fatty acids, branched amino acids, and bile acids, which influence adipose tissue and hepatic lipid metabolism, and the level of lipid deposition in tissues and peripheral blood. In conclusion, CIH and CSF adversely affect fecal microbiota composition and function, and host metabolism; these findings provide new insight into the independent and synergistic effects of CIH, CSF, and HFD on lipid disorders.

Hypoxia and Hypoxia-Inducible Factor Signaling in Muscular Dystrophies: Cause and Consequences

Muscular dystrophies (MDs) are a group of inherited degenerative muscle disorders characterized by a progressive skeletal muscle wasting. Respiratory impairments and subsequent hypoxemia are encountered in a significant subgroup of patients in almost all MD forms. In response to hypoxic stress, compensatory mechanisms are activated especially through Hypoxia-Inducible Factor 1 α (HIF-1α). In healthy muscle, hypoxia and HIF-1α activation are known to affect oxidative stress balance and metabolism. Recent evidence has also highlighted HIF-1α as a regulator of myogenesis and satellite cell function. However, the impact of HIF-1α pathway modifications in MDs remains to be investigated. Multifactorial pathological mechanisms could lead to HIF-1α activation in patient skeletal muscles. In addition to the genetic defect per se, respiratory failure or blood vessel alterations could modify hypoxia response pathways. Here, we will discuss the current knowledge about the hypoxia response pathway alterations in MDs and address whether such changes could influence MD pathophysiology.

Metabolomics and microbiome profiling as biomarkers in obstructive sleep apnoea: a comprehensive review

Introduction

Obstructive sleep apnoea (OSA) is a common sleep disorder with a high social and economic burden. Thus, early prediction and diagnosis of OSA are important. Changes in metabolism and the microbiome may serve as biomarkers for OSA. Herein, we review the literature on the metabolomic and microbiome changes associated with OSA, and identify the metabolites and microorganisms involved.

Methods

We searched the PUBMED and EMBASE electronic databases using the following terms: “obstructive sleep apnea”, “OSA”, “sleep disordered breathing”, “SDB”, “intermittent hypoxia”, “sleep fragmentation”, and either “metabolomics” or “microbiome”. In total, 273 papers were identified, of which 28 were included in our study.

Results

Changes in the levels of certain metabolites related to fatty acid, carbohydrate and amino acid metabolism were associated with the incidence of OSA. The diversity and abundance of microflora, particularly Firmicutes and Bacteroidetes, were altered in humans and rodents with OSA.

Conclusions

Certain changes in metabolism and the microbiota play an integral role in the pathophysiology of OSA and OSA-induced cardiovascular complications. Metabolomic and microbiome biomarkers shed light on the pathogenesis of OSA, and facilitate early diagnosis and treatment.

Unique alterations in metabolism and the microbiome play an integral role in the pathophysiology of OSA and OSA-induced cardiovascular complicationshttps://bit.ly/3mW2rD5

1H-NMR and LC-MS Based Metabolomics Analysis of Wild and Cultivated Amaranthus spp

Amaranthus crops are important for their use as food and nutritional sources, as well as for their medicinal properties. They are mostly harvested from the wild, and cultivation of Amaranthus species is still rare, and therefore, attempts are being made to commercialize and market this important crop. This research investigated the effect of cultivation and environment on the chemical profile of both cultivated and wild A. cruentus and A. hybridus by multivariate statistical analysis of spectral data deduced by Nuclear Magnetic Resonance (NMR). Furthermore, wild samples of A. cruentus and A. hybridus were subjected to Liquid Chromatography-Mass Spectrometry (LC-MS) for further analysis. Through NMR analysis, it was found that maltose and sucrose increased in both cultivated A. cruentus and A. hybridus. Moreover, the amino acid, proline was present in cultivated A. cruentus in high quantity whereas, proline and leucine were prominent in A. hybridus. Other compounds that were found in both wild and cultivated A. cruentus and A. hybridus are trehalose, trigonelline, lactulose, betaine, valine, alanine, fumarate, formate and kynurenine. LC-MS analysis revealed the presence of rutin, 2-phenylethenamine and amaranthussaponin I in both wild A. cruentus and A. hybridus, while chlorogenic acid was identified only in cultivated A. hybridus. On the contrary, L-tryptophan, kaempferol, phenylalanine and quercetin were detected only in wild A. cruentus. Amaranth is not only rich in macro and micronutrients, but the leaves also contain phytochemicals that vary between species and cultivated plants, and might, therefore, affect the medicinal properties of the material.

Understanding the pathophysiological mechanisms of cardiometabolic complications in obstructive sleep apnoea: towards personalised treatment approaches

In January 2019, a European Respiratory Society research seminar entitled "Targeting the detrimental effects of sleep disturbances and disorders" was held in Dublin, Ireland. It provided the opportunity to critically review the current evidence of pathophysiological responses of sleep disturbances, such as sleep deprivation, sleep fragmentation or circadian misalignment and of abnormalities in physiological gases such as oxygen and carbon dioxide, which occur frequently in respiratory conditions during sleep. A specific emphasis of the seminar was placed on the evaluation of the current state of knowledge of the pathophysiology of cardiovascular and metabolic diseases in obstructive sleep apnoea (OSA). Identification of the detailed mechanisms of these processes is of major importance to the field and this seminar offered an ideal platform to exchange knowledge, and to discuss pitfalls of current models and the design of future collaborative studies. In addition, we debated the limitations of current treatment strategies for cardiometabolic complications in OSA and discussed potentially valuable alternative approaches.

Circadian and Sleep Metabolomics Across Species

Under normal circadian function, metabolic control is temporally coordinated across tissues and behaviors with a 24-h period. However, circadian disruption results in negative consequences for metabolic homeostasis including energy or redox imbalances. Yet, circadian disruption has become increasingly prevalent within today's society due to many factors including sleep loss. Metabolic consequences of both have been revealed by metabolomics analyses of circadian biology and sleep. Specifically, two primary analytical platforms, mass spectrometry and nuclear magnetic resonance spectroscopy, have been used to study molecular clock and sleep influences on overall metabolic rhythmicity. For example, human studies have demonstrated the prevalence of metabolic rhythms in human biology, as well as pan-metabolome consequences of sleep disruption. However, human studies are limited to peripheral metabolic readouts primarily through minimally invasive procedures. For further tissue- and organism-specific investigations, a number of model systems have been studied, based upon the conserved nature of both the molecular clock and sleep across species. Here we summarize human studies as well as key findings from metabolomics studies using mice, Drosophila, and zebrafish. While informative, a limitation in existing literature is a lack of interpretation regarding dynamic synthesis or catabolism within metabolite pools. To this extent, future work incorporating isotope tracers, specific metabolite reporters, and single-cell metabolomics may provide a means of exploring dynamic activity in pathways of interest.

Hypoxia inducible factor-1 promotes liver fibrosis in nonalcoholic fatty liver disease by activating PTEN/p65 signaling pathway

Obesity is a major contributor to the development of steatohepatitis and fibrosis from nonalcoholic fatty liver disease (NAFLD). Hypoxia aggravates progression of NAFLD. In mice on high-fat diet (HFD), hepatic steatosis leads to liver tissue hypoxia, evidenced by accumulation of hypoxia inducible factor-1-alpha (HIF-1α), which is a central regulator of the global response to hypoxia. Hepatocyte cell signaling is an important factor in hepatic fibrogenesis. We here hypothesize that HIF-1α knockout in hepatocyte may protect against liver fibrosis. We first found that HFD led to 80% more hepatic collagen deposition than Hif1a^-/- hep mice, which was confirmed by a-SMA staining of liver tissue. Body weight and liver weight were similar between groups. We then found the increasing HIF1a expression and decreasing PTEN expression in the mice on HFD and in PA-treated HepG2 cells. Finally, we found that HIF1 mediated PTEN/nfkb-p65 pathway plays an important role in the development of NAFLD to liver fibrosis. Collectively, these results identify a novel HIF1a/PTEN/NF-κ Bp65 signaling pathway in NAFLD, which could be targeted for the therapy.

Exosome and Macrophage Crosstalk in Sleep-Disordered Breathing-Induced Metabolic Dysfunction

Obstructive sleep apnea (OSA) is a highly prevalent worldwide public health problem that is characterized by repetitive upper airway collapse leading to intermittent hypoxia, pronounced negative intrathoracic pressures, and recurrent arousals resulting in sleep fragmentation. Obesity is a major risk factor of OSA and both of these two closely intertwined conditions result in increased sympathetic activity, oxidative stress, and chronic low-grade inflammation, which ultimately contribute, among other morbidities, to metabolic dysfunction, as reflected by visceral white adipose tissue (VWAT) insulin resistance (IR). Circulating extracellular vesicles (EVs), including exosomes, are released by most cell types and their cargos vary greatly and reflect underlying changes in cellular homeostasis. Thus, exosomes can provide insights into how cells and systems cope with physiological perturbations by virtue of the identity and abundance of miRNAs, mRNAs, proteins, and lipids that are packaged in the EVs cargo, and are secreted from the cells into bodily fluids under normal as well as diseased states. Accordingly, exosomes represent a novel pathway via which a cohort of biomolecules can travel long distances and result in the modulation of gene expression in selected and targeted recipient cells. For example, exosomes secreted from macrophages play a critical role in innate immunity and also initiate the adaptive immune response within specific metabolic tissues such as VWAT. Under normal conditions, phagocyte-derived exosomes represent a large portion of circulating EVs in blood, and carry a protective signature against IR that is altered when secreting cells are exposed to altered physiological conditions such as those elicited by OSA, leading to emergence of IR within VWAT compartment. Consequently, increased understanding of exosome biogenesis and biology should lead to development of new diagnostic biomarker assays and personalized therapeutic approaches. Here, the evidence on the major biological functions of macrophages and exosomes as pathophysiological effectors of OSA-induced metabolic dysfunction is discussed.