Hypocretin/orexin modulates body weight and the metabolism of glucose and insulin

Orexins mitigate obesity-associated dysfunctions in mice

OBJECTIVE

Obesity is a chronic disease that affects more than 400 million adults with severe comorbidities. The search for new treatments to reduce its negative consequences is necessary. Orexins are hypothalamic neuropeptides involved in various physiological processes related to obesity. The aim of this study was to investigate the consequences of chronic orexin-A treatment in mouse models.

METHODS

Female wild-type C57BL/6 mice that were obesity-prone or obesity-resistant and mice that were deficient for orexin receptors were fed with a high-fat diet. Glucose tolerance, indirect calorimetry, expression of brain neuropeptides and receptors, microglial activation, and microbiota were determined to evaluate the role of orexins on metabolic flexibility.

RESULTS

Orexin-A reduces weight gain in obesity-prone mice. This reduction is associated with a decrease in body fat, food intake, steatosis, and insulin resistance, as well as alterations of intestinal microbiota composition. A decreased expression of orexin receptors and neuropeptides involved in food intake was also observed in the hypothalamus.

CONCLUSIONS

Our data support the notion that orexin receptor signaling is involved in different aspects of energy metabolism and can mitigate several dysfunctions associated with obesity, suggesting that orexin receptors can represent new targets for obesity treatment.

Artificial Light at Night and Type 2 Diabetes Mellitus

The widespread and pervasive use of artificial light at night (ALAN) in our modern 24-hour society has emerged as a substantial disruptor of natural circadian rhythms, potentially leading to a rise in unhealthy lifestyle-related behaviors (e.g., poor sleep; shift work). This phenomenon has been associated with an increased risk of type 2 diabetes mellitus (T2DM), which is a pressing global public health concern. However, to date, reviews summarizing associations between ALAN and T2DM have primarily focused on the limited characteristics of exposure (e.g., intensity) to ALAN. This literature review extends beyond prior reviews by consolidating recent studies from 2000 to 2024 regarding associations between both indoor and outdoor ALAN exposure and the incidence or prevalence of T2DM. We also described potential biological mechanisms through which ALAN modulates glucose metabolism. Furthermore, we outlined knowledge gaps and investigated how various ALAN characteristics beyond only light intensity (including light type, timing, duration, wavelength, and individual sensitivity) influence T2DM risk. Recognizing the detrimental impact of ALAN on sleep health and the behavioral correlates of physical activity and dietary patterns, we additionally summarized studies investigating the potential mediating role of each component in the relationship between ALAN and glucose metabolism. Lastly, we proposed implications of chronotherapies and chrononutrition for diabetes management in the context of ALAN exposure.

Adropin: A crucial regulator of cardiovascular health and metabolic balance

Adropin, a peptide discovered in 2008, has gained recognition as a key regulator of cardiovascular health and metabolic balance. Initially identified for its roles in energy balance, lipid metabolism, and glucose regulation, adropin has also been found to improve cardiovascular health by enhancing endothelial function, modulating lipid profiles, and reducing oxidative stress. These protective mechanisms suggest that adropin may be able to help prevent conditions such as atherosclerosis, hypertension, and other cardiovascular diseases. Research has established connections between adropin and cardiovascular risk factors, such as obesity, insulin resistance, and dyslipidemia, positioning it as a valuable biomarker for evaluating cardiovascular disease risk. New studies highlight adropin's diagnostic and prognostic significance, showing that higher levels are linked to better cardiovascular outcomes, while lower levels are associated with a higher risk of cardiovascular diseases. This review aims to summarize current knowledge on adropin, emphasizing its significance as a promising focus in the intersection of cardiovascular health and metabolic health. By summarizing the latest research findings, this review aims to offer insights into the potential applications of adropin in both clinical practice and research, leading to a deeper understanding of its role in maintaining cardiovascular and metabolic health.

Clinical safety and narcolepsy-like symptoms of dual orexin receptor antagonists in patients with insomnia: a systematic review and meta-analysis

STUDY OBJECTIVES

Dual orexin receptor antagonists (DORAs) are emerging treatments for insomnia. This meta-analysis study aimed to assess the safety of FDA-approved DORAs (suvorexant, lemborexant, and daridorexant), focusing on narcolepsy-like symptoms associated with these drugs.

METHODS

Five prominent databases were searched to identify randomized controlled trials (RCTs) on this topic. Primary safety outcomes included treatment-emergent adverse events (TEAEs), treatment-related TEAEs, TEAEs leading to discontinuation, and serious TEAEs. Excessive daytime sleepiness (EDS), sleep paralysis, and hallucinations were categorized as adverse events (AEs)-related narcolepsy-like symptoms.

RESULTS

Eleven RCTs with 7703 patients were included. DORAs were associated with a higher risk of TEAEs (risk ratio [RR], 1.09; 95% confidence interval [CI], 1.03 to 1.15) and treatment-related TEAEs (RR, 1.69; 95% CI: 1.49 to 1.92) when compared to placebo. The DORA group exhibited a significantly higher risk of EDS (RR, 2.15; 95% CI: 1.02 to 4.52) and sleep paralysis (RR, 3.40; 95% CI: 1.18 to 9.80) compared to the placebo group.

CONCLUSION

This meta-analysis achieved a comparative evaluation of the clinical safety and tolerability of FDA-approved DORAs for primary insomnia, specifically focusing on AEs-related narcolepsy-like symptoms. This study contributes to understanding the safety profile of FDA-approved DORAs for treating insomnia.

Rethinking the Role of Orexin in the Regulation of REM Sleep and Appetite

Orexin plays a significant role in the modulation of REM sleep, as well as in the regulation of appetite and feeding. This review explores, first, the current evidence on the role of orexin in the modulation of sleep and wakefulness and highlights that orexin should be considered essentially as a neurotransmitter inhibiting REM sleep and, to a much lesser extent, a wake promoting agent. Subsequently, the relationship between orexin, REM sleep, and appetite regulation is examined in detail, shedding light on their interconnected nature in both physiological conditions and diseases (such as narcolepsy, sleep-related eating disorder, idiopathic hypersomnia, and night eating syndrome). Understanding the intricate relationship between orexin, REM sleep, and appetite regulation is vital for unraveling the complex mechanisms underlying sleep-wake patterns and metabolic control. Further research in this field is encouraged in order to pave the way for novel therapeutic approaches to sleep disorders and metabolic conditions associated with orexin dysregulation.

In Type 2 Diabetes Mellitus, normalization of hemoglobin A1c accompanies reduced sensitivity to pressure at the sternum

Background

The autonomic nervous system (ANS) maintains glucose homeostasis. While higher than normal glucose levels stimulate the ANS toward reduction, previous findings suggest an association between sensitivity to, or pain from, pressure at the chest bone (pressure or pain sensitivity, PPS) and activity of the ANS. A recent randomized controlled trial (RCT) of type 2 diabetes (T2DM) suggested that addition of an experimental, non-pharmacological intervention more effectively than conventional treatment lowered the levels of both PPS and HbA1c.

Materials and analyses

We tested the null hypothesis that conventional treatment (n = 60) would reveal no association between baseline HbA1c and normalization of HbA1c in 6 months, related to change of PPS. We compared the changes of HbA1c in PPS reverters who experienced a minimum reduction of 15 units of PPS and in PPS non-reverters who experienced no reduction. Depending on the result, we tested the association in a second group of participants with addition of the experimental program (n = 52).

Results

In the conventional group, PPS reverters experienced normalization of HbA1c that corrected the basal increase, thus disproving the null hypothesis. With the addition of the experimental program, PPS reverters experienced similar reduction. The reduction of HbA1c among reverters averaged 0.62 mmol/mol per mmol/mol increase of baseline HbA1c (P < 0.0001 compared to non-reverters). For baseline HbA1c ≥ 64 mmol/mol, reverters averaged 22% reduction of HbA1c (P < 0.01).

Conclusion

In consecutive analyses of two different populations of individuals with T2DM, we demonstrated that the higher the baseline HbA1c, the greater the reduction of HbA1c but only in individuals with a concomitant reduction of sensitivity to PPS, suggesting a homeostatic effect of the autonomic nervous system on glucose metabolism. As such, ANS function, measured as PPS, is an objective measure of HbA1c homeostasis. This observation may be of great clinical importance.

Orexin/Hypocretin System Dysfunction in ESSENCE (Early Symptomatic Syndromes Eliciting Neurodevelopmental Clinical Examinations)

Early Symptomatic Syndromes Eliciting Neurodevelopmental Clinical Examinations (ESSENCE) is an umbrella term covering a wide range of neurodevelopmental difficulties and disorders. Thus, ESSENCE includes attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and other neurodevelopmental disorders (NDDs) and difficulties, with a variety of symptoms in cognitive, motor, sensory, social, arousal, regulatory, emotional, and behavioral developmental domains, frequently co-occurring and likely having partly common neurobiological substrates. The ESSENCE concept is a clinical paradigm that promotes organizing NDDs in everyday clinical practice according to their coexistence, symptom dimensions overlapping, and treatment possibilities. Despite increased knowledge regarding NDDs, the neurobiological mechanisms that underlie them and other ESSENCE-related problems, are not well understood. With its wide range of neural circuits and interactions with numerous neurotransmitters, the orexin/hypocretin system (Orx-S) is possibly associated with a variety of neurocognitive, psychobiological, neuroendocrine, and physiological functions and behaviors. Dysfunction of Orx-S has been implicated in various psychiatric and neurological disorders. This article provides an overview of Orx-S dysfunctions' possible involvement in the development, presentation, and maintenance of ESSENCE. We provide a focused review of current research evidence linking orexin neuropeptides with specific clinical NDDs symptoms, mostly in ADHD and ASD, within the Research Domain Criteria (RDoC) framework. We propose that Orx-S dysfunction might have an important role in some of these neurodevelopmental symptom domains, such as arousal, wakefulness, sleep, motor and sensory processing, mood and emotional regulation, fear processing, reward, feeding, attention, executive functions, and sociability. Our perspective is presented from a clinical point of view. Further, more thorough systematic reviews are needed as well as planning of extensive new research into the Orx-S's role in ESSENCE, especially considering RDoC elements.

Orexin/hypocretin system dysfunction in patients with Takotsubo syndrome: A novel pathophysiological explanation

Takotsubo syndrome (TTS) is an acute heart failure syndrome. Emotional or physical stressors are believed to precipitate TTS, while the pathophysiological mechanism is not yet completely understood. During the coronavirus disease (COVID-19) pandemic, an increased incidence of TTS has been reported in some countries; however, the precise pathophysiological mechanism for developing TTS with acute COVID-19 infection is unknown. Nevertheless, observing the symptoms of COVID-19 might lead to new perspectives in understanding TTS pathophysiology, as some of the symptoms of the COVID-19 infection could be assessed in the context of an orexin/hypocretin-system dysfunction. Orexin/hypocretin is a cardiorespiratory neuromodulator that acts on two orexin receptors widely distributed in the brain and peripheral tissues. In COVID-19 patients, autoantibodies against one of these orexin receptors have been reported. Orexin-system dysfunction affects a variety of systems in an organism. Here, we review the influence of orexin-system dysfunction on the cardiovascular system to propose its connection with TTS. We propose that orexin-system dysfunction is a potential novel explanation for the pathophysiology of TTS due to direct or indirect dynamics of orexin signaling, which could influence cardiac contractility. This is in line with the conceptualization of TTS as a cardiovascular syndrome rather than merely a cardiac abnormality or cardiomyopathy. To the best of our knowledge, this is the first publication to present a plausible connection between TTS and orexin-system dysfunction. We hope that this novel hypothesis will inspire comprehensive studies regarding orexin's role in TTS pathophysiology. Furthermore, confirmation of this plausible pathophysiological mechanism could contribute to the development of orexin-based therapeutics in the treatment and prevention of TTS.

Adropin’s Role in Energy Homeostasis and Metabolic Disorders

Adropin is a novel 76-amino acid-peptide that is expressed in different tissues and cells including the liver, pancreas, heart and vascular tissues, kidney, milk, serum, plasma and many parts of the brain. Adropin, encoded by the Enho gene, plays a crucial role in energy homeostasis. The literature review indicates that adropin alleviates the degree of insulin resistance by reducing endogenous hepatic glucose production. Adropin improves glucose metabolism by enhancing glucose utilization in mice, including the sensitization of insulin signaling pathways such as Akt phosphorylation and the activation of the glucose transporter 4 receptor. Several studies have also demonstrated that adropin improves cardiac function, cardiac efficiency and coronary blood flow in mice. Adropin can also reduce the levels of serum triglycerides, total cholesterol and low-density lipoprotein cholesterol. In contrast, it increases the level of high-density lipoprotein cholesterol, often referred to as the beneficial cholesterol. Adropin inhibits inflammation by reducing the tissue level of pro-inflammatory cytokines such as tumor necrosis factor alpha and interleukin-6. The protective effect of adropin on the vascular endothelium is through an increase in the expression of endothelial nitric oxide synthase. This article provides an overview of the existing literature about the role of adropin in different pathological conditions.

Orexin-A Reverse Bone Mass Loss Induced by Chronic Intermittent Hypoxia Through OX1R-Nrf2/HIF-1α Pathway

Background

Recent studies suggest that there is a potential connection between obstructive sleep apnea (OSA) and osteoporosis through dysregulation of bone metabolism. Orexin-A, a neuroprotective peptide secreted by the hypothalamus, is at a lower level in the plasma of OSA patients, which regulates appetite, energy expenditure and sleep-wake states. However, the protective effect of orexin-A on bone metabolism in OSA is unclear.

Purpose

To investigate whether the activation of OX1R by orexin-A can reverse bone mass loss induced by chronic intermittent hypoxia (CIH).

Methods

Mice were randomly divided into the normoxia group and CIH group. Within the CIH or normoxia groups, treatment groups were given a subcutaneous injection of either orexin-A or saline vehicle once every day for 4 weeks and then femurs were removed for micro-CT scans. Histology and immunohistochemical staining were performed to observe and calculate the changes in femurs as a result of hypoxia. Cell immunofluorescence and immunohistochemical staining were used to detect the expression of orexin receptors in MC3T3-E1 cells or in bones. CCK-8 assay, ALP assay kit and alizarin red staining were used to detect the viability, alkaline phosphatase (ALP) activity, and capacity of mineralization, respectively. The effect of orexin-A on osteogenic differentiation of MC3T3-E1 cells was evaluated using qRT-PCR, Western blot and cell staining.

Results

CIH led to a decrease in the amount and density of trabecular bone, downregulated OCN expression while increasing osteoclast numbers in femurs and inhibited the expression of RUNX2, OSX, OPN and Nrf2 in MC3T3-E1 cells. Orexin-A treatment alleviated these CIH-induced effects by combining to OX1R. The level of HIF-1α was elevated both in CIH and orexin-A treatment groups.

Conclusion

CIH environment inhibits osteogenesis and orexin-A can reverse bone mass loss induced by CIH through OX1R-Nrf2/HIF-1α pathway.

IKKβ signaling mediates metabolic changes in the hypothalamus of a Huntington disease mouse model

Huntington disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin (HTT) gene. Metabolic changes are associated with HD progression, but underlying mechanisms are not fully known. As the IKKβ/NF-κB pathway is an essential regulator of metabolism, we investigated the involvement of IKKβ, the upstream activator of NF-κB in hypothalamus-specific HD metabolic changes. We expressed amyloidogenic N-terminal fragments of mutant HTT (mHTT) in the hypothalamus of mice with brain-specific ablation of IKKβ (Nestin/IKKβ^lox/lox) and control mice (IKKβ^lox/lox). We assessed effects on body weight, metabolic hormones, and hypothalamic neuropathology. Hypothalamic expression of mHTT led to an obese phenotype only in female mice. CNS-specific inactivation of IKKβ prohibited weight gain in females, which was independent of neuroprotection and microglial activation. Our study suggests that mHTT in the hypothalamus causes metabolic imbalance in a sex-specific fashion, and central inhibition of the IKKβ pathway attenuates the obese phenotype.

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Mutant huntingtin in the hypothalamus causes sex-specific metabolic imbalance

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CNS-specific inactivation of the IKKβ pathway prevents the obese phenotype

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IKKβ inactivation leads to an increased number of mutant huntingtin inclusions

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IKKβ inactivation does not prevent orexin or A13 TH neuron loss

Human adipose tissue is a putative direct target of daytime orexin with favorable metabolic effects: A cross-sectional study

OBJECTIVE

Orexin/hypocretin (Ox) and its receptors (OxR), a neuroendocrine system centrally regulating sleep/wakefulness, were implicated in the regulation of peripheral metabolism. It was hypothesized that human adipose tissue constitutes a direct target of the OxA/OxR system that associates with distinct metabolic profile(s).

METHODS

Serum Ox levels and abdominal subcutaneous and visceral adipose tissue expression of Ox/HCRT, OxR1/HCRTR1, and OxR2/HCRTR2 were measured in n = 81 patients.

RESULTS

Higher morning circulating Ox levels were associated with improved lipid profile and insulin sensitivity, independently of BMI (β = -0.363, p = 0.018 for BMI-adjusted homeostatic model of insulin resistance). Adipose HCRT mRNA was detectable in <20% of patients. Visceral HCRT expressers were mostly (80%) males and, compared with nonexpressers, had lower total and LDL cholesterol. HCRTR1 was readily detectable, and HCRTR2 was undetectable. HCRTR1 mRNA and OxR1 protein expression were higher in subcutaneous than visceral adipose tissue, and among nonobese patients, patients with obesity, and patients with obesity and T2DM were 3.4 (1.0), 0.7 (0.1), 0.6 (0.1) (AU) (p < 0.001) and 1.0 (0.2), 0.5 (0.1), 0.4 (0.1) (AU) (p = NS), respectively. Higher visceral HCRTR1 expression was associated with lower fasting insulin and homeostatic model of insulin resistance, also after adjusting for BMI. In human adipocytes, HCRTR1 expression did not exhibit significant oscillation.

CONCLUSIONS

Human adipose tissue is a putative direct target of the OxA-OxR1 system, with higher morning input being associated with improved metabolic profile.

Cardiovascular and Metabolic Responses to Carbon Dioxide Euthanasia in Conscious and Anesthetized Rats

Euthanasia is a necessary component in research and must be conducted humanely. Currently, regulated CO₂ exposure in conscious rats is acceptable, but data are divided on whether CO₂ alone is more distressing than anesthesia prior to CO₂. To evaluate distress in rats, we compared physiologic responses to CO₂ euthanasia with and without isoflurane preanesthesia. Male Sprague-Dawley rats were implanted with telemetry devices to measure mean arterial pressure (MAP), heart rate (HR), and blood glucose. Animals recovered for 2 wk and were then exposed to either 5% isoflurane (n = 6) or 100% CO₂ (n = 7; calculated 30% chamber volume/min displacement) in their home cages to induce loss of consciousness. Euthanasia was then completed with CO₂ in both groups. MAP and HR increased when the gas delivery lids were placed on the home cages of both groups. Both MAP and HR gradually decreased with isoflurane exposure. MAP increased and HR decreased with CO₂ exposure. Glucose levels remained stable throughout the procedure, except for a small drop in conscious animals initially exposed to 100% CO₂. These data suggest that both gases affect the measured parameters in a similar manner, and that environmental factors, such as gas delivery lid placement, also change these measurements.

Can the effects of the mitochondrial DNA mutations found in Leber’s hereditary optic neuropathy be protective against the development of cluster headache in smokers?

Is it possible that some mitochondrial DNA (mtDNA) mutations enhance the risk of developing a headache disorder while other mutations actually confer a protective effect? Mitochondrial disorders have been linked to migraine but very rarely to cluster headache (CH). The true pathogenesis of CH is unknown but a linkage to cigarette smoking is irrefutable. Leber’s hereditary optic neuropathy is a syndrome of bilateral vision loss that typically manifests in a patient’s 20s and 30s, is male predominant, and its sufferers are heavy smokers and heavy drinkers. Tobacco exposure is so linked to the condition that only smokers appear to develop vision loss while nonsmokers remain unaffected carriers of their mutations. In essence, the Leber’s hereditary optic neuropathy population is the CH population but at present there have been no reported cases of CH in this mitochondrial subgroup. Thus, could the effects of the mtDNA mutations found in Leber’s hereditary optic neuropathy, which involve complex I of the electron transport chain, actually confer a protective effect against the development of CH? This article will delve into this theory.