Circadian and Sleep Metabolomics Across Species

Decoding the nexus: branched-chain amino acids and their connection with sleep, circadian rhythms, and cardiometabolic health

The sleep-wake cycle stands as an integrative process essential for sustaining optimal brain function and, either directly or indirectly, overall body health, encompassing metabolic and cardiovascular well-being. Given the heightened metabolic activity of the brain, there exists a considerable demand for nutrients in comparison to other organs. Among these, the branched-chain amino acids, comprising leucine, isoleucine, and valine, display distinctive significance, from their contribution to protein structure to their involvement in overall metabolism, especially in cerebral processes. Among the first amino acids that are released into circulation post-food intake, branched-chain amino acids assume a pivotal role in the regulation of protein synthesis, modulating insulin secretion and the amino acid sensing pathway of target of rapamycin. Branched-chain amino acids are key players in influencing the brain's uptake of monoamine precursors, competing for a shared transporter. Beyond their involvement in protein synthesis, these amino acids contribute to the metabolic cycles of γ-aminobutyric acid and glutamate, as well as energy metabolism. Notably, they impact GABAergic neurons and the excitation/inhibition balance. The rhythmicity of branched-chain amino acids in plasma concentrations, observed over a 24-hour cycle and conserved in rodent models, is under circadian clock control. The mechanisms underlying those rhythms and the physiological consequences of their disruption are not fully understood. Disturbed sleep, obesity, diabetes, and cardiovascular diseases can elevate branched-chain amino acid concentrations or modify their oscillatory dynamics. The mechanisms driving these effects are currently the focal point of ongoing research efforts, since normalizing branched-chain amino acid levels has the ability to alleviate the severity of these pathologies. In this context, the Drosophila model, though underutilized, holds promise in shedding new light on these mechanisms. Initial findings indicate its potential to introduce novel concepts, particularly in elucidating the intricate connections between the circadian clock, sleep/wake, and metabolism. Consequently, the use and transport of branched-chain amino acids emerge as critical components and orchestrators in the web of interactions across multiple organs throughout the sleep/wake cycle. They could represent one of the so far elusive mechanisms connecting sleep patterns to metabolic and cardiovascular health, paving the way for potential therapeutic interventions.

A carnitine transporter at the blood-brain barrier modulates sleep via glial lipid metabolism in Drosophila

To regulate brain function, peripheral compounds must traverse the blood-brain barrier (BBB), an interface between the brain and the circulatory system. To determine whether specific transport mechanisms are relevant for sleep, we conducted a BBB-specific inducible RNAi knockdown (iKD) screen for genes affecting sleep in Drosophila. We observed reduced sleep with knockdown of solute carrier CG6126, a carnitine transporter, as determined by isotope flux. Our findings suggest that CG6126 regulation of sleep is through the role of the carnitine shuttle in regulating fatty acid metabolism as lipid droplets accumulate in the brains of CG6126 BBB iKD flies. Knocking down mitochondrial carnitine transferases in non-BBB glial cells mimicked the reduced sleep of the CG6126 BBB iKD flies, while bypassing the necessity of carnitine transport with dietary medium-chain fatty acids or palmitoylcarnitine rescued sleep. We propose that carnitine transport via CG6126 promotes brain fatty acid metabolism necessary for maintaining sleep.

Balancing brain metabolic states during sickness and recovery sleep

Sickness sleep and rebound following sleep deprivation share humoral signals including the rise of cytokines, in particular interleukins. Nevertheless, they represent unique physiological states with unique brain firing patterns and involvement of specific circuitry. Here, we performed untargeted metabolomics of mouse cortex and hippocampus to uncover changes with sickness and rebound sleep as compared with normal daily sleep. We found that the three settings are biochemically unique with larger differences in the cortex than in the hippocampus. Both sickness and rebound sleep shared an increase in tryptophan. Surprisingly, these two sleep conditions showed opposite modulation of the methionine-homocysteine cycle and differences in terms of the energetic signature, with sickness impinging on glycolysis intermediates whilst rebound increased the triphosphorylated form of nucleotides. These findings indicate that rebound following sleep deprivation stimulates an energy rich setting in the brain that is devoid during sickness sleep.

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.

Glucose Challenge Uncovers Temporal Fungibility of Metabolic Homeostasis over a day:night cycle

Rhythmicity is a cornerstone of behavioral and biological processes, especially metabolism, yet the mechanisms behind metabolite cycling remain elusive. This study uncovers a robust oscillation in key metabolite pathways downstream of glucose in humans. A purpose-built 13C6-glucose isotope tracing platform was used to sample Drosophila every 4h and probe these pathways, revealing a striking peak in biosynthesis shortly after lights-on in wild-type flies. A hyperactive mutant (fumin) demonstrates increased Krebs cycle labelling and dawn-specific glycolysis labelling. Surprisingly, neither underlying feeding rhythms nor the presence of food availability explain the rhythmicity of glucose processing across genotypes, suggesting a robust internal mechanism for metabolic control of glucose processing. These results align with clinical data highlighting detrimental effects of mistimed energy intake. Our approach offers a unique insight into the dynamic range of daily metabolic processing and provides a mechanistic foundation for exploring circadian metabolic homeostasis in disease contexts.

Human serum proteomics reveals a molecular signature after one night of sleep deprivation

Study Objectives

Sleep deprivation is highly prevalent and caused by conditions such as night shift work or illnesses like obstructive sleep apnea. Compromised sleep affects cardiovascular-, immune-, and neuronal systems. Recently, we published human serum proteome changes after a simulated night shift. This pilot proteomic study aimed to further explore changes in human blood serum after 6 hours of sleep deprivation at night.

Methods

Human blood serum samples from eight self-declared healthy females were analyzed using Orbitrap Eclipse mass spectrometry (MS-MS) and high-pressure liquid chromatography. We used a within-participant design, in which the samples were taken after 6 hours of sleep at night and after 6 hours of sleep deprivation the following night. Systems biological databases and bioinformatic software were used to analyze the data and comparative analysis were done with other published sleep-related proteomic datasets.

Results

Out of 494 proteins, 66 were found to be differentially expressed proteins (DEPs) after 6 hours of sleep deprivation. Functional enrichment analysis revealed the associations of these DEPs with several biological functions related to the altered regulation of cellular processes such as platelet degranulation and blood coagulation, as well as associations with different curated gene sets.

Conclusions

This study presents serum proteomic changes after 6 hours of sleep deprivation, supports previous findings showing that short sleep deprivation affects several biological processes, and reveals a molecular signature of proteins related to pathological conditions such as altered coagulation and platelet function, impaired lipid and immune function, and cell proliferation. Data are available via ProteomeXchange with identifier PXD045729. This paper is part of the Genetic and other molecular underpinnings of sleep, sleep disorders, and circadian rhythms including translational approaches Collection.

The interplay between sleep and ecophysiology, behaviour and responses to environmental change in fish

Evidence of behavioural sleep has been observed in every animal species studied to date, but current knowledge of the behaviour, neurophysiology and ecophysiology associated with sleep is concentrated on mammals and birds. Fish are a hugely diverse group that can offer novel insights into a variety of sleep-related behaviours across environments, but the ecophysiological relevance of sleep in fish has been largely overlooked. Here, we systematically reviewed the literature to assess the current breadth of knowledge on fish sleep, and surveyed the diverse physiological effects and behaviours associated with sleep. We also discuss possible ways in which unstudied external factors may alter sleep behaviours. For example, predation risk may alter sleep patterns, as has been shown in mammalian, avian and reptilian species. Other environmental factors - such as water temperature and oxygen availability - have the potential to alter sleep patterns in fish differently than for terrestrial endotherms. Understanding the ecological influences on sleep in fish is vital, as sleep deprivation has the potential to affect waking behaviour and fitness owing to cognitive and physiological impairments, possibly affecting ecological phenomena and sensitivity to environmental stressors in ways that have not been considered.

Metastatic effects of perfluorooctanoic acid (PFOA) on Drosophila melanogaster with metabolic reprogramming and dysrhythmia in a multigenerational exposure scenario

Perfluorooctanoic acid (PFOA) exposure correlated with various cancers and their mortality. Its persistence in the environment made its long-term multigenerational influences of significant concerns. However, it remained unanswered whether its multigenerational exposure could influence metastasis which contributes ~90 % to cancer mortality. In the present study, long-term effects of PFOA were measured in Drosophila melanogaster over 3 consecutive generations. In the morning-eclosed (AM) adult flies, PFOA significantly promoted tumor invasion rates and distances which increased over generations. Regarding metabolic reprogramming, PFOA disturbed the expressions of Glut1 and Pdk1, activities and contents of FASN1 (fatty acid synthase), ACC (acetyl-CoA carboxylase) and SREBP1 (sterol regulatory element binding protein). Regarding antioxidant responses, PFOA exposure generated provoked oxidative stress via H2O2 and stimulated antioxidants including glutathione (GSH), catalase (CAT), melatonin, serotonin and cortisol, with downregulations on PI3K/AKT pathways and upregulations on MAPK ones. The biochemical and molecular effects altered over generations. In the afternoon-eclosed (PM) adult flies, the metastasis of PFOA was more deteriorated than in AM adults. The significant influences of dysrhythmia were also observed in the multigenerational effects of PFOA on the metabolism reprogramming and antioxidant responses. The effects on rhythm-regulating gene expressions and protein levels explained the dysrhythmia and also indicated close interactions among metabolism reprogramming, antioxidant responses and rhythm regulation. ENVIRONMENTAL IMPLICATION: Numerous emerging per- and polyfluoroalkyl substances (PFASs) are being detected. Meanwhile, the toxicities of the emerging PFASs still depend on the progress of legacy PFASs for the continuity of scientific studies. As one legacy PFAS, perfluorooctanoic acid (PFOA) exposure correlated with various cancers and their mortality. Its persistence in the environment made its long-term multigenerational influences of significant concerns. However, it remained unanswered whether its multigenerational exposure could influence metastasis which contributes ~90 % to cancer mortality. The present study performed PFOA exposure for 3 consecutive generations. Results showed that the metastasis by PFOA increased over generations, and it was further deteriorated by dysrhythmia. Further analysis demonstrated the interactive involvement of metabolism reprogramming, antioxidant responses and rhythm regulation. The findings of the present study would highlight considerate points for studying the toxicities of emerging PFASs.

Time-of-day-dependent variation of the human liver transcriptome and metabolome is disrupted in MASLD

Background & Aims

Liver homeostasis is ensured in part by time-of-day-dependent processes, many of them being paced by the molecular circadian clock. Liver functions are compromised in metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH), and clock disruption increases susceptibility to MASLD progression in rodent models. We therefore investigated whether the time-of-day-dependent transcriptome and metabolome are significantly altered in human steatotic and MASH livers.

Methods

Liver biopsies, collected within an 8 h-window from a carefully phenotyped cohort of 290 patients and histologically diagnosed to be either normal, steatotic or MASH hepatic tissues, were analyzed by RNA sequencing and unbiased metabolomic approaches. Time-of-day-dependent gene expression patterns and metabolomes were identified and compared between histologically normal, steatotic and MASH livers.

Results

Herein, we provide a first-of-its-kind report of a daytime-resolved human liver transcriptome-metabolome and associated alterations in MASLD. Transcriptomic analysis showed a robustness of core molecular clock components in steatotic and MASH livers. It also revealed stage-specific, time-of-day-dependent alterations of hundreds of transcripts involved in cell-to-cell communication, intracellular signaling and metabolism. Similarly, rhythmic amino acid and lipid metabolomes were affected in pathological livers. Both TNFα and PPARγ signaling were predicted as important contributors to altered rhythmicity.

Conclusion

MASLD progression to MASH perturbs time-of-day-dependent processes in human livers, while the differential expression of core molecular clock components is maintained.

Impact and implications

This work characterizes the rhythmic patterns of the transcriptome and metabolome in the human liver. Using a cohort of well-phenotyped patients (n = 290) for whom the time-of-day at biopsy collection was known, we show that time-of-day variations observed in histologically normal livers are gradually perturbed in liver steatosis and metabolic dysfunction-associated steatohepatitis. Importantly, these observations, albeit obtained across a restricted time window, provide further support for preclinical studies demonstrating alterations of rhythmic patterns in diseased livers. On a practical note, this study indicates the importance of considering time-of-day as a critical biological variable which may significantly affect data interpretation in animal and human studies of liver diseases.

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.

The neurobehavioral impacts of typical antibiotics toward zebrafish larvae

Due to the widely usage in livestock, aquaculture and clinics, antibiotic residues are existed in aqueous environments and their potential toxicity to aquatic organisms is concerning. Here, we used zebrafish as the model to investigate the neurotoxicity and involved mechanism of seven antibiotics that were frequently detected in surface waters. The results revealed that the short-term exposure to clarithromycin (CLA), chlortetracycline (CTC) and roxithromycin (ROX) induced behavioral effects, with effective concentration of 1 μg/L (CTC and ROX) and 100 μg/L (CLA, CTC and ROX) respectively. A significant decrease in the travel distance and velocity as well as an increase in turn angle was measured. TUNEL assay identified increased cell apoptosis in brain sections of larvae exposed to three neurotoxic antibiotics, which raised the possibility that the behavioral symptoms were associated with neural damage. Transcriptome sequencing showed that the three antibiotics could affect the nervous system of zebrafish including the alteration of synaptogenesis and neurotransmission. Additionally, ROX and CTC affected pathways involved in mitochondrial stress response and endocrine system in zebrafish larvae. Besides, BDNF, ASCL1, and CREBBP are potential upstream regulatory factors that mediated these impacts. These findings indicated that exposure of CTC, ROX and CLA may cause abnormal behavior toward zebrafish larvae under environmental relevant concentration and revealed the potential role of neural cell apoptosis and synaptogenesis signaling in mediating this effect.

Pallidin function in Drosophila surface glia regulates sleep and is dependent on amino acid availability

The Pallidin protein is a central subunit of a multimeric complex called biogenesis of lysosome-related organelles complex 1 (BLOC1) that regulates specific endosomal functions and has been linked to schizophrenia. We show here that downregulation of Pallidin and other members of BLOC1 in the surface glia, the Drosophila equivalent of the blood-brain barrier, reduces and delays nighttime sleep in a circadian-clock-dependent manner. In agreement with BLOC1 involvement in amino acid transport, downregulation of the large neutral amino acid transporter 1 (LAT1)-like transporters JhI-21 and mnd, as well as of TOR (target of rapamycin) amino acid signaling, phenocopy Pallidin knockdown. Furthermore, supplementing food with leucine normalizes the sleep/wake phenotypes of Pallidin downregulation, and we identify a role for Pallidin in the subcellular trafficking of JhI-21. Finally, we provide evidence that Pallidin in surface glia is required for GABAergic neuronal activity. These data identify a BLOC1 function linking essential amino acid availability and GABAergic sleep/wake regulation.

Day-night fluctuations in choroid plexus transcriptomics and cerebrospinal fluid metabolomics

The cerebrospinal fluid (CSF) provides mechanical protection for the brain and serves as a brain dispersion route for nutrients, hormones, and metabolic waste. The CSF secretion rate is elevated in the dark phase in both humans and rats, which could support the CSF flow along the paravascular spaces that may be implicated in waste clearance. The similar diurnal CSF dynamics pattern observed in the day-active human and the nocturnal rat suggests a circadian regulation of this physiological variable, rather than sleep itself. To obtain a catalog of potential molecular drivers that could provide the day-night-associated modulation of the CSF secretion rate, we determined the diurnal fluctuation in the rat choroid plexus transcriptomic profile with RNA-seq and in the CSF metabolomics with ultraperformance liquid chromatography combined with mass spectrometry. We detected significant fluctuation of 19 CSF metabolites and differential expression of 2,778 choroid plexus genes between the light and the dark phase, the latter of which encompassed circadian rhythm-related genes and several choroid plexus transport mechanisms. The fluctuating components were organized with joint pathway analysis, of which several pathways demonstrated diurnal regulation. Our results illustrate substantial transcriptional and metabolic light-dark phase-mediated changes taking place in the rat choroid plexus and its encircling CSF. The combined data provide directions toward future identification of the molecular pathways governing the fluctuation of this physiological process and could potentially be harnessed to modulate the CSF dynamics in pathology.

FABP7: a glial integrator of sleep, circadian rhythms, plasticity, and metabolic function

Sleep and circadian rhythms are observed broadly throughout animal phyla and influence neural plasticity and cognitive function. However, the few phylogenetically conserved cellular and molecular pathways that are implicated in these processes are largely focused on neuronal cells. Research on these topics has traditionally segregated sleep homeostatic behavior from circadian rest-activity rhythms. Here we posit an alternative perspective, whereby mechanisms underlying the integration of sleep and circadian rhythms that affect behavioral state, plasticity, and cognition reside within glial cells. The brain-type fatty acid binding protein, FABP7, is part of a larger family of lipid chaperone proteins that regulate the subcellular trafficking of fatty acids for a wide range of cellular functions, including gene expression, growth, survival, inflammation, and metabolism. FABP7 is enriched in glial cells of the central nervous system and has been shown to be a clock-controlled gene implicated in sleep/wake regulation and cognitive processing. FABP7 is known to affect gene transcription, cellular outgrowth, and its subcellular localization in the fine perisynaptic astrocytic processes (PAPs) varies based on time-of-day. Future studies determining the effects of FABP7 on behavioral state- and circadian-dependent plasticity and cognitive processes, in addition to functional consequences on cellular and molecular mechanisms related to neural-glial interactions, lipid storage, and blood brain barrier integrity will be important for our knowledge of basic sleep function. Given the comorbidity of sleep disturbance with neurological disorders, these studies will also be important for our understanding of the etiology and pathophysiology of how these diseases affect or are affected by sleep.

Chronic sleep loss sensitizes Drosophila melanogaster to nitrogen stress

Chronic sleep loss profoundly impacts metabolic health and shortens lifespan, but studies of the mechanisms involved have focused largely on acute sleep deprivation.1,2 To identify metabolic consequences of chronically reduced sleep, we conducted unbiased metabolomics on heads of three adult Drosophila short-sleeping mutants with very different mechanisms of sleep loss: fumin (fmn), redeye (rye), and sleepless (sss).3,4,5,6,7 Common features included elevated ornithine and polyamines, with lipid, acyl-carnitine, and TCA cycle changes suggesting mitochondrial dysfunction. Studies of excretion demonstrate inefficient nitrogen elimination in adult sleep mutants, likely contributing to their polyamine accumulation. Increasing levels of polyamines, particularly putrescine, promote sleep in control flies but poison sleep mutants. This parallels the broadly enhanced toxicity of high dietary nitrogen load from protein in chronically sleep-restricted Drosophila, including both sleep mutants and flies with hyper-activated wake-promoting neurons. Together, our results implicate nitrogen stress as a novel mechanism linking chronic sleep loss to adverse health outcomes-and perhaps for linking food and sleep homeostasis at the cellular level in healthy organisms.

Insights into the circadian rhythm alterations of the novel PFOS substitutes F-53B and OBS on adult zebrafish

As alternatives to perfluorooctane sulfonate (PFOS), 6:2 Cl-PFESA (F-53B) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) are frequently detected in aquatic environments, but little is known about their neurotoxicity, especially in terms of circadian rhythms. In this study, adult zebrafish were chronically exposed to 1 μM PFOS, F-53B and OBS for 21 days taking circadian rhythm-dopamine (DA) regulatory network as an entry point to comparatively investigate their neurotoxicity and underlying mechanisms. The results showed that PFOS may affect the response to heat rather than circadian rhythms by reducing DA secretion due to disruption of calcium signaling pathway transduction caused by midbrain swelling. In contrast, F-53B and OBS altered the circadian rhythms of adult zebrafish, but their mechanisms of action were different. Specifically, F-53B might alter circadian rhythms by interfering with amino acid neurotransmitter metabolism and disrupting blood-brain barrier (BBB) formation, whereas OBS mainly inhibited canonical Wnt signaling transduction by reducing cilia formation in ependymal cells and induced midbrain ventriculomegaly, finally triggering imbalance in DA secretion and circadian rhythm changes. Our study highlights the need to focus on the environmental exposure risks of PFOS alternatives and the sequential and interactive mechanisms of their multiple toxicities.

Do macrophages follow the beat of circadian rhythm in TIME (Tumor Immune Microenvironment)?

Advances in cancer research have made clear the critical role of the immune response in clearing tumors. This breakthrough in scientific understanding was heralded by the success of immune checkpoint blockade (ICB) therapies such as anti-programmed cell death protein 1 (PD-1)/ programmed death-ligand 1 (PD-L1) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), as well as the success of chimeric antigen receptor (CAR) T cells in treating liquid tumors. Thus, much effort has been made to further understand the role of the immune response in tumor progression, and how we may target it to treat cancer. Macrophages are a component of the tumor immune microenvironment (TIME) that can promote tumor growth both indirectly, by suppressing T cell responses necessary for tumor killing, as well as directly, through deposition of extracellular matrix and promotion of angiogenesis. Thus, understanding regulation of macrophages within the tumor microenvironment (TME) is key to targeting them for immunotherapy. However, circadian rhythms (24-hour cycles) are a fundamental aspect of macrophage biology that have yet to be investigated for their role in macrophage-mediated suppression of the anti-tumor immune response Circadian rhythms regulate macrophage-mediated immune responses through time-of-day-dependent regulation of macrophage function. A better understanding of the circadian biology of macrophages in the context of the TME may allow us to exploit synergy between existing and upcoming treatments and circadian regulation of immunity.

Sleep duration, plasma metabolites, and obesity and diabetes: a metabolome-wide association study in US women

Short and long sleep duration are associated with adverse metabolic outcomes, such as obesity and diabetes. We evaluated cross-sectional differences in metabolite levels between women with self-reported habitual short (<7 h), medium (7-8 h), and long (≥9 h) sleep duration to delineate potential underlying biological mechanisms. In total, 210 metabolites were measured via liquid chromatography-mass spectrometry in 9207 women from the Nurses' Health Study (NHS; N = 5027), the NHSII (N = 2368), and the Women's Health Initiative (WHI; N = 2287). Twenty metabolites were consistently (i.e. praw < .05 in ≥2 cohorts) and/or strongly (pFDR < .05 in at least one cohort) associated with short sleep duration after multi-variable adjustment. Specifically, levels of two lysophosphatidylethanolamines, four lysophosphatidylcholines, hydroxyproline and phenylacetylglutamine were higher compared to medium sleep duration, while levels of one diacylglycerol and eleven triacylglycerols (TAGs; all with ≥3 double bonds) were lower. Moreover, enrichment analysis assessing associations of metabolites with short sleep based on biological categories demonstrated significantly increased acylcarnitine levels for short sleep. A metabolite score for short sleep duration based on 12 LASSO-regression selected metabolites was not significantly associated with prevalent and incident obesity and diabetes. Associations of single metabolites with long sleep duration were less robust. However, enrichment analysis demonstrated significant enrichment scores for four lipid classes, all of which (most markedly TAGs) were of opposite sign than the scores for short sleep. Habitual short sleep exhibits a signature on the human plasma metabolome which is different from medium and long sleep. However, we could not detect a direct link of this signature with obesity and diabetes risk.

Effect of the Citrus Flavone Nobiletin on Circadian Rhythms and Metabolic Syndrome

The importance of the circadian clock in maintaining human health is now widely acknowledged. Dysregulated and dampened clocks may be a common cause of age-related diseases and metabolic syndrome Thus, circadian clocks should be considered as therapeutic targets to mitigate disease symptoms. This review highlights a number of dietary compounds that positively affect the maintenance of the circadian clock. Notably the polymethoxyflavone nobiletin has shown some encouraging results in pre-clinical experiments. Although many more experiments are needed to fully elucidate its exact mechanism of action, it is a promising candidate with potential as a chronotherapeutic agent.

Disruptions of circadian rhythms, sleep, and stress responses in zebrafish: New infrared-based activity monitoring assays for toxicity assessment

Behavioural disruptions are sensitive indicators of alterations to normal animal physiology and can be used for toxicity assessment. The small vertebrate zebrafish is a leading model organism for toxicological studies. The ability to continuously monitor the toxicity of drugs, pollutants, or environmental changes over several days in zebrafish can have high practical application. Although video-recordings can be used to monitor short-term zebrafish behaviour, it is challenging to videorecord prolonged experiments (e.g. circadian behaviour over several days) because of the darkness periods (nights) and the heavy data storage and image processing requirements. Alternatively, infrared-based activity monitors, widely used in invertebrate models such as drosophila, generate simple and low-storage data and could optimize large-scale prolonged behavioural experiments in zebrafish, thus favouring the implementation of high-throughput testing strategies. Here, we validate the use of a Locomotor Activity Monitor (LAM) to study the behaviour of zebrafish larvae, and we characterize the behavioural phenotypes induced by abnormal light conditions and by the Parkinsonian toxin MPP⁺. When zebrafish were deprived from daily light-cycle synchronization, the LAM detected various circadian disruptions, such as increased activity period, phase shifts, and decreased inter-daily stability. Zebrafish exposed to MPP⁺ (10, 100, 500 μM) showed a concentration-dependent decrease in activity, sleep disruptions, impaired habituation to repetitive startles (visual-motor responses), and a slower recovery to normal activity after the startle-associated stress. These phenotypes evidence the feasibility of using infrared-based LAM to assess multi-parameter behavioural disruptions in zebrafish. The procedures in this study have wide applicability and may yield standard methods for toxicity testing.

Melatonin protects against body weight gain induced by sleep deprivation in mice

Sleep deprivation is an epidemic phenomenon in modern society. Lack of sleep has been shown to result in metabolic and endocrine disorders that predispose to obesity and other chronic metabolic diseases. Melatonin is a sleep-related neurohormone and affected by the circadian rhythm and light/dark cycles. Melatonin has recently been used to ameliorate diet-induced or night light-induced energy metabolic imbalance. However, the effect of melatonin on sleep deprivation-induced obesity has been poorly characterized. This study focuses on the protective effects of melatonin on lipid metabolism and body weight homeostasis in sleep-deprived mice. Mice subjected to sleep deprivation had significantly decreased plasma melatonin content and increased food intake and body weight gain compared to that of control. Meanwhile, the transcription factor PPARγ protein in liver increased, but there were no significant changes in hepatic circadian proteins BMAL1 and REV-ERBα after 10 consecutive days of sleep deprivation. Moreover, melatonin supplementation increased liver AMPKα/PPARα signaling pathway activity, which leads to lipid catabolism and reduced fat accumulation. These findings suggested that melatonin may be a potential agent for protecting against sleep deprivation-induced obesity.

Mild-to-Moderate Traumatic Brain Injury: A Review with Focus on the Visual System

Traumatic Brain Injury (TBI) is a major global public health problem. Neurological damage from TBI may be mild, moderate, or severe and occurs both immediately at the time of impact (primary injury) and continues to evolve afterwards (secondary injury). In mild (m)TBI, common symptoms are headaches, dizziness and fatigue. Visual impairment is especially prevalent. Insomnia, attentional deficits and memory problems often occur. Neuroimaging methods for the management of TBI include computed tomography and magnetic resonance imaging. The location and the extent of injuries determine the motor and/or sensory deficits that result. Parietal lobe damage can lead to deficits in sensorimotor function, memory, and attention span. The processing of visual information may be disrupted, with consequences such as poor hand-eye coordination and balance. TBI may cause lesions in the occipital or parietal lobe that leave the TBI patient with incomplete homonymous hemianopia. Overall, TBI can interfere with everyday life by compromising the ability to work, sleep, drive, read, communicate and perform numerous activities previously taken for granted. Treatment and rehabilitation options available to TBI sufferers are inadequate and there is a pressing need for new ways to help these patients to optimize their functioning and maintain productivity and participation in life activities, family and community.

Harnessing Metabolomics to Advance Epilepsy Research

Metabolomics is the laboratory analysis and scientific study of the metabolome—that is, the entire collection of small molecule chemicals in an organism. The metabolome represents the functional state of an organism and provides a multifaceted readout of the aggregate activity of endogenous (cellular) and exogenous (environmental) processes. In this review, we discuss how the integrative and dynamic properties of the metabolome create unique opportunities to study complex pathologies that evolve and oscillate over time, like epilepsy. We explain how the scientific progress and clinical applications of metabolomics remain hampered by biological and technical challenges, and we propose best practices to overcome these challenges so that metabolomics can be used in a rigorous and effective manner to further epilepsy research.

Untargeted and Targeted Circadian Metabolomics Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) and Flow Injection-Electrospray Ionization-Tandem Mass Spectrometry (FIA-ESI-MS/MS)

A diverse array of 24-h oscillating hormones and metabolites direct and reflect circadian clock function. Circadian metabolomics uses advanced high-throughput analytical chemistry techniques to comprehensively profile these small molecules (<1.5 kDa) across 24 h in cells, media, body fluids, breath, tissues, and subcellular compartments. The goals of circadian metabolomics experiments are often multifaceted. These include identifying and tracking rhythmic metabolic inputs and outputs of central and peripheral circadian clocks, quantifying endogenous free-running period, monitoring relative phase alignment between clocks, and mapping pathophysiological consequences of clock disruption or misalignment. Depending on the particular experimental question, samples are collected under free-running or entrained conditions. Here we describe both untargeted and targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) and flow injection-electrospray ionization-tandem mass spectrometry (FIA-ESI-MS/MS) based assays we have used for circadian metabolomics studies. We discuss tissue homogenization, chemical derivatization, measurement, and tips for data processing, normalization, scaling, how to handle outliers, and imputation of missing values.

Regional Brain Analysis of Modified Amino Acids and Dipeptides during the Sleep/Wake Cycle

Sleep is a state in which important restorative and anabolic processes occur. Understanding changes of these metabolic processes during the circadian rhythm in the brain is crucial to elucidate neurophysiological mechanisms important for sleep function. Investigation of amino acid modifications and dipeptides has recently emerged as a valuable approach in the metabolic profiling of the central nervous system. Nonetheless, very little is known about the effects of sleep on the brain levels of amino acid analogues. In the present study, we examined brain regional sleep-induced alterations selective for modified amino acids and dipeptides using Ultra-high performance liquid chromatography-MS/MS (UHPLC-MS/MS) based metabolomics. Our approach enabled the detection and identification of numerous amino acid-containing metabolites in the cortex, the hippocampus, the midbrain, and the cerebellum. In particular, analogues of the aromatic amino acids phenylalanine, tyrosine and tryptophan were significantly altered during sleep in the investigated brain regions. Cortical levels of medium and long chain N-acyl glycines were higher during sleep. Regional specific changes were also detected, especially related to tyrosine analogues in the hippocampus and the cerebellum. Our findings demonstrate a strong correlation between circadian rhythms and amino acid metabolism specific for different brain regions that provide previously unknown insights in brain metabolism.

Multi-Modal Regulation of Circadian Physiology by Interactive Features of Biological Clocks

The circadian clock is a fundamental biological timing mechanism that generates nearly 24 h rhythms of physiology and behaviors, including sleep/wake cycles, hormone secretion, and metabolism. Evolutionarily, the endogenous clock is thought to confer living organisms, including humans, with survival benefits by adapting internal rhythms to the day and night cycles of the local environment. Mirroring the evolutionary fitness bestowed by the circadian clock, daily mismatches between the internal body clock and environmental cycles, such as irregular work (e.g., night shift work) and life schedules (e.g., jet lag, mistimed eating), have been recognized to increase the risk of cardiac, metabolic, and neurological diseases. Moreover, increasing numbers of studies with cellular and animal models have detected the presence of functional circadian oscillators at multiple levels, ranging from individual neurons and fibroblasts to brain and peripheral organs. These oscillators are tightly coupled to timely modulate cellular and bodily responses to physiological and metabolic cues. In this review, we will discuss the roles of central and peripheral clocks in physiology and diseases, highlighting the dynamic regulatory interactions between circadian timing systems and multiple metabolic factors.

Differential regulation of oxidative stress, microbiota-derived, and energy metabolites in the mouse brain during sleep

Sleep has evolved as a universal core function to allow for restorative biological processes. Detailed knowledge of metabolic changes necessary for the sleep state in the brain is missing. Herein, we have performed an in-depth metabolic analysis of four mouse brain regions and uncovered region-specific circadian variations. Metabolites linked to oxidative stress were altered during sleep including acylcarnitines, hydroxylated fatty acids, phenolic compounds, and thiol-containing metabolites. These findings provide molecular evidence of a significant metabolic shift of the brain energy metabolism. Specific alterations were observed for brain metabolites that have previously not been associated with a circadian function including the microbiome-derived metabolite ergothioneine that suggests a regulatory function. The pseudopeptide β-citryl-glutamate has been linked to brain development and we have now discovered a previously unknown regioisomer. These metabolites altered by the circadian rhythm represent the foundation for hypothesis-driven studies of the underlying metabolic processes and their function.

Circadian Rhythms, Disease and Chronotherapy

Circadian clocks are biological timing mechanisms that generate 24-h rhythms of physiology and behavior, exemplified by cycles of sleep/wake, hormone release, and metabolism. The adaptive value of clocks is evident when internal body clocks and daily environmental cycles are mismatched, such as in the case of shift work and jet lag or even mistimed eating, all of which are associated with physiological disruption and disease. Studies with animal and human models have also unraveled an important role of functional circadian clocks in modulating cellular and organismal responses to physiological cues (ex., food intake, exercise), pathological insults (e.g. virus and parasite infections), and medical interventions (e.g. medication). With growing knowledge of the molecular and cellular mechanisms underlying circadian physiology and pathophysiology, it is becoming possible to target circadian rhythms for disease prevention and treatment. In this review, we discuss recent advances in circadian research and the potential for therapeutic applications that take patient circadian rhythms into account in treating disease.

Metabolomic Signature of Patients With Narcolepsy

BACKGROUND AND OBJECTIVE

Narcolepsy type 1 (NT1) is an orphan brain disorder caused by the irreversible destruction of orexin neurons. Metabolic disturbances are common in patients with NT1 who have a body mass index (BMI) 10-20% higher than the general population, with one third being obese (BMI>30 kg/m²). Besides the destruction of orexin neurons in NT1, the metabolic alterations in obese and non-obese patients with narcolepsy type 1 remain unknown. The aim of the study was to identify possible differences in plasma metabolic profiles between patients with NT1 and controls as a function of their BMI status.

METHODS

We used a targeted liquid chromatography-mass spectrometry metabolomics approach to measure 141 circulating, low molecular weight metabolites in drug-free fasted plasma samples from 117 NT1 patients (including 41 obese subjects) compared with 116 BMI-matched controls (including 57 obese subjects).

RESULTS

Common metabolites driving the difference between NT1 and controls, irrespective of BMI, were identified, namely sarcosine, glutamate, nonaylcarnitine (C9), 5 long chain lysophosphatidylcholine acyls, one sphingolipid, 12 phosphatidylcholine diacyls and 11 phosphatidylcholine acyl-akyls, all showing increased concentrations in NT1. Metabolite concentrations significantly affected by NT1 (n = 42) and BMI category (n = 40) showed little overlap (n = 5). Quantitative enrichment analysis revealed common metabolic pathways that were implicated in the NT1/control differences, in both normal BMI and obese comparisons, namely glycine and serine, arachidonic acid, and tryptophan metabolisms. The metabolites driving these differences were glutamate, sarcosine and ornithine (glycine and serine metabolism), glutamate and PC aa C34:4 (arachidonic acid metabolism) and glutamate, serotonin and tryptophan (tryptophan metabolism). Linear metabolite-endophenotype regression analyses highlight that as part of the NT1 metabolic phenotype, most of the relationships between the sleep parameters (i.e. slow wave sleep duration, sleep latency and periodic leg movement) and metabolite concentrations seen in the controls were lost.

DISCUSSION

These results represented the most comprehensive metabolic profiling of patients with NT1 as a function of BMI and propose some metabolic diagnostic biomarkers for NT1, namely glutamate, sarcosine, serotonin, tryptophan, nonaylcarnitine and some phosphatidylcholines. The metabolic pathways identified offer, if confirmed, possible targets for treatment of obesity in NT1.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that a distinct metabolic profile can differentiate patients with Narcolepsy Type 1 from patients without the disorder.

Features of age-related response to sleep deprivation: in vivo experimental studies

Insomnia is currently considered one of the potential triggers of accelerated aging. The frequency of registered sleep-wake cycle complaints increases with age and correlates with the quality of life of elderly people. Nevertheless, whether insomnia is actually an age-associated process or whether it acts as an independent stress-factor that activates pathological processes, remains controversial. In this study, we analyzed the effects of long-term sleep deprivation modeling on the locomotor and orienting-exploratory activity, spatial learning abilities and working memory of C57BL/6 female mice of different ages. We also evaluated the modeled stress influence on morphological changes in brain tissue, the functional activity of the mitochondrial apparatus of nerve cells, and the level of DNA methylation and mRNA expression levels of the transcription factor HIF-1α (Hif1) and age-associated molecular marker PLIN2. Our findings point to the age-related adaptive capacity of female mice to the long-term sleep deprivation influence. For young (1.5 months) mice, the modeled sleep deprivation acts as a stress factor leading to weight loss against the background of increased food intake, the activation of animals' locomotor and exploratory activity, their mnestic functions, and molecular and cellular adaptive processes ensuring animal resistance both to stress and risk of accelerated aging development. Sleep deprivation in adult (7-9 months) mice is accompanied by an increase in body weight against the background of active food intake, increased locomotor and exploratory activity, gross disturbances in mnestic functions, and decreased adaptive capacity of brain cells, that potentially increasing the risk of pathological reactions and neurodegenerative processes.

Chronotherapy

The objective of chronotherapy is to optimize medical treatments taking into account the body's circadian rhythms. Chronotherapy is referred to and practiced in two different ways: (1) to alter the sleep-wake rhythms of patients to improve the sequels of several pathologies; (2) to take into account the circadian rhythms of patients to improve therapeutics. Even minor dysfunction of the biological clock can greatly affect sleep/wake physiology causing excessive diurnal somnolence, increase in sleep onset latency, phase delays or advances in sleep onset, frequent night awakenings, reduced sleep efficiency, delayed and shortened rapid eye movement sleep, or increased periodic leg movements. Chronotherapy aims to restore the proper circadian pattern of the sleep-wake cycle, through adequate sleep hygiene, timed light exposure, and the use of chronobiotic medications, such as melatonin, that affect the output phase of circadian rhythms, thus controlling the clock. Concerning the second use of chronotherapy, therapeutic outcomes as diverse as the survival after open-heart surgery or the efficacy and tolerance to chemotherapy vary according to the time of day. However, humans are heterogeneous concerning the timing of their internal clocks. Not only different chronotypes exist but also the endogenous human circadian period (τ) is not a stable trait as it depends on many internal and external factors. If any scheduled therapeutic intervention is going to be optimized, a tool is needed for simple diagnostic and objectively measurement of an individual's internal time at any given time. Methodologic advances like the use of single-sample gene expression and metabolomics are discussed.

Cross-species physiological interactions of endocrine disrupting chemicals with the circadian clock

Endocrine disrupting chemicals (EDCs) are endocrine-active chemical pollutants that disrupt reproductive, neuroendocrine, cardiovascular and metabolic health across species. The circadian clock is a transcriptional oscillator responsible for entraining 24-hour rhythms of physiology, behavior and metabolism. Extensive bidirectional cross talk exists between circadian and endocrine systems and circadian rhythmicity is present at all levels of endocrine control, from synthesis and release of hormones, to sensitivity of target tissues to hormone action. In mammals, a range of hormones directly alter clock gene expression and circadian physiology via nuclear receptor (NR) binding and subsequent genomic action, modulating physiological processes such as nutrient and energy metabolism, stress response, reproductive physiology and circadian behavioral rhythms. The potential for EDCs to perturb circadian clocks or circadian-driven physiology is not well characterized. For this reason, we explore evidence for parallel endocrine and circadian disruption following EDC exposure across species. In the reviewed studies, EDCs dysregulated core clock and circadian rhythm network gene expression in brain and peripheral organs, and altered circadian reproductive, behavioral and metabolic rhythms. Circadian impacts occurred in parallel to endocrine and metabolic alterations such as impaired fertility and dysregulated metabolic and energetic homeostasis. Further research is warranted to understand the nature of interaction between circadian and endocrine systems in mediating physiological effects of EDC exposure at environmental levels.

Metabolomics in Sleep, Insomnia and Sleep Apnea

Sleep-wake disorders are highly prevalent disorders, which can lead to negative effects on cognitive, emotional and interpersonal functioning, and can cause maladaptive metabolic changes. Recent studies support the notion that metabolic processes correlate with sleep. The study of metabolite biomarkers (metabolomics) in a large-scale manner offers unique opportunities to provide insights into the pathology of diseases by revealing alterations in metabolic pathways. This review aims to summarize the status of metabolomic analyses-based knowledge on sleep disorders and to present knowledge in understanding the metabolic role of sleep in psychiatric disorders. Overall, findings suggest that sleep-wake disorders lead to pronounced alterations in specific metabolic pathways, which might contribute to the association of sleep disorders with other psychiatric disorders and medical conditions. These alterations are mainly related to changes in the metabolism of branched-chain amino acids, as well as glucose and lipid metabolism. In insomnia, alterations in branched-chain amino acid and glucose metabolism were shown among studies. In obstructive sleep apnea, biomarkers related to lipid metabolism seem to be of special importance. Future studies are needed to examine severity, subtypes and treatment of sleep-wake disorders in the context of metabolite levels.