Leptin-mediated neural targets in obesity hypoventilation syndrome

Obesity hypoventilation syndrome: Current status and future directions for optimizing care of a complex and diverse condition (a narrative review)

The global obesity pandemic contributes to an increase in the prevalence of obesity hypoventilation syndrome (OHS). OHS is associated with poor prognosis and early mortality. Definitions of OHS and disease severity classifications differ between international guidelines, and consideration of polysomnographic features is often lacking. To address this, the European Respiratory Society has proposed a severity classification approach. It is also important to consider the possibility that patients with OHS might have multiple factors contributing to hypercapnia, including obesity-related changes in the respiratory system, alterations in central respiratory drive, and different sleep-disordered breathing (SDB) abnormalities. There are also multiple health trajectories that occur before an OHS diagnosis. Positive airway pressures such as continuous positive airway pressure or non-invasive ventilation are the mainstay of OHS treatment. The choice of therapy needs to be guided by appropriate SDB phenotyping and daytime hypercapnia severity. Comorbidities are common in patients with OHS and these trigger and increase the risk of acute on chronic respiratory failure. Appropriate management of comorbidities, and weight loss management, are essential (including behavioral interventions, physical activity, pharmacotherapy, and metabolic/bariatric procedures, as appropriate for each individual). Newer pharmacological treatments such as glucagon-like peptide-1 receptor agonists, recombinant human leptin, and orexin receptor antagonists are promising, but have not yet been specifically investigated in OHS populations. Overall, there is a need for a significant redesign in assessment and care to facilitate the evidence-based management of the complex and diverse OHS presentations in clinical practice.

Altered cognitive function in obese patients: relationship to gut flora

Obesity is a risk factor for non-communicable diseases such as cardiovascular disease and diabetes, which are leading causes of death and disability. Today, China has the largest number of overweight and obese people, imposing a heavy burden on China's healthcare system. Obesity adversely affects the central nervous system (CNS), especially cognitive functions such as executive power, working memory, learning, and so on. The gradual increase in adult obesity rates has been accompanied by a increase in childhood obesity rates. In the past two decades, the obesity rate among children under 5 years of age has increased from 32 to 42 million. If childhood obesity is not intervened in the early years, it will continue into adulthood and remain there for life. Among the potential causative factors, early lifestyle may influence the composition of the gut flora in childhood obesity, such as the rate and intake of high-energy foods, low levels of physical activity, may persist into adulthood, thus, early lifestyle interventions may improve the composition of the gut flora in obese children. Adipose Axis plays an important role in the development of obesity. Adipose tissue is characterized by increased expression of nucleoside diphosphate-linked molecule X-type motif 2 (NUDT2), amphiphilic protein AMPH genes, which encode proteins that all play important roles in the CNS. NUDT2 is associated with intellectual disability. Furthermore, amphiphysin (AMPH) is involved in glutamatergic signaling, ganglionic synapse development, and maturation, which is associated with mild cognitive impairment (MCI) and Alzheimer's disease (AD). All of the above studies show that obesity is closely related to cognitive decline in patients. Animal experiments have confirmed that obesity causes changes in cognitive function. For example, high-fat diets rich in long- and medium-chain saturated fatty acids may adversely affect cognitive function in obese mice. This process may be attributed to the Short-Chain Fatty Acid (SCFA)-rich high-fat diet (HFD) activating enterocyte TLR signaling, especially TLR-2 and TLR-4, altering the downstream MyD88-4 signaling, thereby impacting the downstream MyD88-NF-κB signaling cascade and up-regulating the levels of pro-inflammatory factors and lipopolysaccharide (LPS). These changes result in the loss of integrity of the intestinal mucosa and cause an imbalance in the internal environment. Obesity may lead to the disruption of the intestinal flora and damage the intestinal barrier function, causing intestinal flora dysbiosis. In recent years, a growing number of studies have investigated the relationship between obesity and the intestinal flora. For example, high-fat and high-sugar diets have been found to lead to the thinning of the mucus layer of the colon, a decrease in the number of tight junction proteins, and an increase in intestinal permeability in mice. Such changes alter the composition of intestinal microorganisms, allow endotoxins into the blood circulation, and induce neuroinflammation and brain damage. Therefore, obesity affects cognitive function and is even hereditary. This paper reviews the obesity-induced cognitive dysfunction, the underlying mechanisms, the research progress of intestinal flora dysregulation in obese patients, the relationship between intestinal flora and cognitive function changes, and the research progress on intestinal flora dysregulation in obese patients. We want to regulate the internal environment of obese patients from the perspective of intestinal flora, improving the cognitive function of obese patients, and prevent obesity-induced changes in related neurological functions.

The multifunctionality of the brainstem breathing control circuit

Subconscious breathing is generated by a network of brainstem nodes with varying purposes, like pacing breathing or patterning a certain breath phase. Decades of anatomy, pharmacology, and physiology studies have identified and characterized the system's fundamental properties that produce robust breathing, and we now have well-conceived computational models of breathing that are based on the detailed descriptions of neuronal connectivity, biophysical properties, and functions in breathing. In total, we have a considerable understanding of the brainstem breathing control circuit. But, in the last five years, the utilization of molecular and genetic approaches to study the neural subtypes within each node has led to a new era of breathing control circuit research that explains how breathing is integrated with more complex behaviors like speaking and running and how breathing is connected with other physiological systems and our state-of-mind. This review will describe the basic role of the key components of the brainstem breathing control circuit and then will highlight the new transformative discoveries that broaden our understanding of these breathing control brain areas. These new studies serve to illustrate the creativity and exciting future of breathing control research.

Gender Differences in Outcomes of Ambulatory and Hospitalized Patients With Obesity Hypoventilation Syndrome

BACKGROUND

Obesity hypoventilation syndrome (OHS) is associated with high morbidity and mortality. There are few data on whether there are gender differences in outcomes.

RESEARCH QUESTION

Do women with OHS experience worse outcomes in ambulatory and hospitalized settings compared to men?

STUDY DESIGN AND METHODS

Post hoc analyses were performed on two separate OHS cohorts: (1) stable ambulatory patients from the two Pickwick randomized controlled trials; and (2) hospitalized patients with acute-on-chronic hypercapnic respiratory failure from a retrospective international cohort. We first conducted bivariate analyses of baseline characteristics and therapeutics between genders. Variables of interest from these analyses were then grouped into linear mixed effects models, Cox proportional hazards models, or logistic regression models to assess the association of gender on various clinical outcomes.

RESULTS

The ambulatory prospective cohort included 300 patients (64% self-identified as women), and the hospitalized retrospective cohort included 1,162 patients (58% self-identified as women). For both cohorts, women were significantly older and more obese than men. Compared with men, baseline Paco2 was similar in ambulatory patients but higher in hospitalized women. In the ambulatory cohort, in unadjusted analysis, women had increased risk of emergency department visits. However, gender was not associated with the composite outcome of emergency department visit, hospitalization, or all-cause mortality in the fully adjusted model. In the hospitalized cohort, prescription of positive airway pressure was less prevalent in women at discharge. In unadjusted analysis, hospitalized women had a higher mortality at 3, 6, and 12 months following hospital discharge compared with men. However, after adjusting for age, gender was not associated with mortality.

INTERPRETATION

Our findings indicate that although the diagnosis of OHS is established at a more advanced age in women, gender is not independently associated with worse clinical outcomes after adjusting for age. Future studies are needed to examine gender-related health disparities in diagnosis and treatment of OHS.

Increased Leptin Levels in Plasma and Serum in Patients with Metabolic Disorders: A Systematic Review and Meta-Analysis

A large number of studies have reported the relationships between leptin levels and diabetes or obesity. However, the results are still controversial, and no consensus has been reached. Therefore, the purpose of the study was to collect data from various databases to perform a meta-analysis and address the inconsistencies in these studies. A systematic literature search was conducted on PubMed, Web of Science, and EBSCO for relevant available articles. The pooled standard mean difference (SMD) with 95% confidence interval (CI) was used to estimate the association by a meta-analysis. Fifteen reports with 1,388 cases and 3,536 controls were chosen for the meta-analysis. First, an increase in leptin levels in serum (SMD 0.69; 95% CI 0.36-1.02 ng/mL) and plasma (SMD 0.46; 95% CI 0.18-0.74 ng/mL) was observed in individuals with diabetes compared to controls. This increased level was also observed by gender and population. Second, statistical analysis showed that leptin levels in serum were significantly increased in individuals with obesity (SMD 1.03; 95% CI 0.72-1.34 ng/mL). This meta-analysis analyzed leptin in individuals with diabetes or obesity and emphasized the importance of monitoring serum/plasma leptin levels in patients with these diseases. However, more comprehensive studies are necessary in order to draw firm conclusions.

Revisiting the Role of Serotonin in Sleep-Disordered Breathing

Serotonin or 5-hydroxytryptamine (5-HT) is a ubiquitous neuro-modulator-transmitter that acts in the central nervous system, playing a major role in the control of breathing and other physiological functions. The midbrain, pons, and medulla regions contain several serotonergic nuclei with distinct physiological roles, including regulating the hypercapnic ventilatory response, upper airway patency, and sleep-wake states. Obesity is a major risk factor in the development of sleep-disordered breathing (SDB), such as obstructive sleep apnea (OSA), recurrent closure of the upper airway during sleep, and obesity hypoventilation syndrome (OHS), a condition characterized by daytime hypercapnia and hypoventilation during sleep. Approximately 936 million adults have OSA, and 32 million have OHS worldwide. 5-HT acts on 5-HT receptor subtypes that modulate neural control of breathing and upper airway patency. This article reviews the role of 5-HT in SDB and the current advances in 5-HT-targeted treatments for SDB.

Inhibition of SOCS3 signaling in the nucleus tractus solitarii and retrotrapezoid nucleus alleviates hypoventilation in diet-induced obese male mice

The central leptin signaling system has been found to facilitate breathing and is linked to obesity-related hypoventilation. Activation of leptin signaling in the nucleus tractus solitarii (NTS) and retrotrapezoid nucleus (RTN) enhances respiratory drive. In this study, we investigated how medullary leptin signaling contributes to hypoventilation and whether respective deletion of SOCS3 in the NTS and RTN could mitigate hypoventilation in diet-induced obesity (DIO) male mice. Our findings revealed a decrease in the number of CO2-activated NTS neurons and downregulation of acid-sensing ion channels in DIO mice compared to lean control mice. Moreover, NTS leptin signaling was disrupted, as evidenced by the downregulation of phosphorylated STAT3 and the upregulation of SOCS3 in DIO mice. Importantly, deleting SOCS3 in the NTS and RTN significantly improved the diminished hypercapnic ventilatory response in DIO mice. In conclusion, our study suggests that disrupted medullary leptin signaling contributes to obesity-related hypoventilation, and inhibiting the upregulated SOCS3 in the NTS and RTN can alleviate this condition.

On the origins of sleep disordered breathing, cardiorespiratory and metabolic dysfunction: which came first, the chicken or the egg?

Sleep disordered breathing (SDB) is a complex, sex specific and highly heterogeneous group of respiratory disorders. Nevertheless, sleep fragmentation and repeated fluctuations of arterial blood gases for several hours per night are at the core of the problem; together, they impose significant stress to the organism with deleterious consequences on physical and mental health. SDB increases the risk of obesity, diabetes, depression and anxiety disorders; however, the same health issues are risk factors for SDB. So, which came first, the chicken or the egg? What causes the appearance of the first significant apnoeic events during sleep? These are important questions because although moderate to severe SDB affects ∼500 million adults globally, we still have a poor understanding of the origins of the disease, and the main treatments (and animal models) focus on the symptoms rather than the cause. Because obesity, metabolic dysfunction and stress-related neurological disorders generally appear progressively, we discuss how the development of these diseases can lead to specific anatomical and non-anatomical traits of SDB in males and females while considering the impacts of sex steroids. In light of the growing evidence indicating that the carotid bodies are important sensors of key metabolic and endocrine signals associated with stress and dysmetabolism, we propose that these organs play a key role in the process.

Effects of sex, age, and body mass index on serum bicarbonate

Rationale

Obesity hypoventilation syndrome (OHS) is often underdiagnosed, with significant morbidity and mortality. Bicarbonate, as a surrogate of arterial carbon dioxide, has been proposed as a screening tool for OHS. Understanding the predictors of serum bicarbonate could provide insights into risk factors for OHS. We hypothesized that the bicarbonate levels would increase with an increase in body mass index (BMI), since the prevalence of OHS increases with obesity.

Methods

We used the TriNetX Research Network, an electronic health record database with de-identified clinical data from participating healthcare organizations across the United States, to identify 93,320 adults without pulmonary or advanced renal diseases who had serum bicarbonate and BMI measurements within 6 months of each other between 2017 and 2022. We used linear regression analysis to examine the associations between bicarbonate and BMI, age, and their interactions for the entire cohort and stratified by sex. We also applied a non-linear machine learning algorithm (XGBoost) to examine the relative importance of age, BMI, sex, race/ethnicity, and obstructive sleep apnea (OSA) status on bicarbonate.

Results

This cohort population was 56% women and 72% white and 80% non-Hispanic individuals, with an average (SD) age of 49.4 (17.9) years and a BMI of 29.1 (6.1) kg/m2. The mean bicarbonate was 24.8 (2.8) mmol/L, with higher levels in men (mean 25.2 mmol/L) than in women (mean 24.4 mmol/L). We found a small negative association between bicarbonate and BMI, with an expected change of -0.03 mmol/L in bicarbonate for each 1 kg/m2 increase in BMI (p < 0.001), in the entire cohort and both sexes. We found sex differences in the bicarbonate trajectory with age, with women exhibiting lower bicarbonate values than men until age 50, after which the bicarbonate levels were modestly higher. The non-linear machine learning algorithm similarly revealed that age and sex played larger roles in determining bicarbonate levels than the BMI or OSA status.

Conclusion

Contrary to our hypothesis, BMI is not associated with elevated bicarbonate levels, and age modifies the impact of sex on bicarbonate.

Obesity, Bariatric Surgery and Obstructive Sleep Apnea-A Narrative Literature Review

The purpose of this review was to analyze the available literature on the subject of obesity and obstructive sleep apnea. We searched for available articles for the time period from 2013 to 2023. Obesity is listed as one of the most important health issues. Complications of obesity, with obstructive sleep apnea (OSA) listed among them, are common problems in clinical practice. Obesity is a well-recognized risk factor for OSA, but OSA itself may contribute to worsening obesity. Bariatric surgery is a treatment of choice for severely obese patients, especially with present complications, and remains the only causative treatment for patients with OSA. Though improvement in OSA control in patients after bariatric surgery is well-established knowledge, the complete resolution of OSA is achieved in less than half of them. The determination of subpopulations of patients in whom bariatric surgery would be especially advantageous is an important issue of OSA management. Increasing the potential of non-invasive strategies in obesity treatment requires studies that assess the efficacy and safety of combined methods.

Intermittent Hypoxia and Weight Loss: Insights into the Etiology of the Sleep Apnea Phenotype

Sleep apnea (SA) is a major respiratory disorder with increased risk for hypertension and obesity; however, our understanding of the origins of this complex disorder remains limited. Because apneas lead to recurrent drops in O₂ during sleep, intermittent hypoxia (IH) is the main animal model to explore the pathophysiology of SA. Here, we assessed the impacts of IH on metabolic function and related signals. Adult male rats were exposed to 1 week of moderate IH (FiO₂ = 0.10-30 s, ten cycles/hour, 8 h/day). Using whole-body plethysmography, we measured respiratory variability and apnea index during sleep. Blood pressure and heart rate were measured by the tail-cuff method; blood samples were taken for multiplex assay. At rest, IH augmented arterial blood pressure, respiratory instability, but not apnea index. IH induced weight, fat, and fluid loss. IH also reduced food intake and plasma leptin, adrenocorticotropic hormone (ACTH), and testosterone levels but increased inflammatory cytokines. We conclude that IH does not replicate the metabolic clinical features of SA patient, thus raising our awareness of the limitations of the IH model. The fact that the risk for hypertension occurs before the appearance of apneas provides new insights into the progression of the disease.