Does leptin link sleep loss and breathing disturbances with major public diseases?

Leptin and the Blood-Brain Barrier: Curiosities and Controversies

Leptin for over 25 years has been a central theme in the study of appetite, obesity, and starvation. As the major site of leptin production is peripheral, and the site of action of greatest interest is the hypothalamus, how leptin accesses the central nervous system (CNS) and crosses the blood-brain barrier (BBB) has been of great interest. We review here the ongoing research that addresses fundamental questions such as the sites of leptin resistances in obesity and other conditions, the causes of resistances and their relations to one another, the three barrier sites of entry into the CNS, why recent studies using suprapharmacological doses cannot address these questions but give insight into nonsaturable entry of leptin into the CNS, and how that might be useful in using leptin therapeutically. The current status of the controversy of whether the short form of the leptin receptor acts as the BBB leptin transporter and how obesity may transform leptin transport is reviewed. Review of these and other topics summarizes in a new appreciation of what leptin may have actually evolved to do and what physiological role leptin resistance may play. © 2021 American Physiological Society. Compr Physiol 11:1-19, 2021.

Self-reported snoring and metabolic syndrome: the Korean Multi-Rural Communities Cohort Study

PURPOSE

We investigated the association between self-reported snoring and metabolic syndrome (MetS) and its components among a community-dwelling Korean population.

METHODS

A total of 7,038 subjects participated in the Korean Multi-Rural Communities Cohort Study between January 2005 and February 2010 and were included in the analysis. Frequency of snoring was classified into never, rarely (<1 day/week), occasionally (1-3 days/week), and habitually (≥4 days/week).

RESULTS

In the fully adjusted model, compared to non-snorers, the odds ratio (OR) for MetS of snorers was significantly higher in subjects with rare snoring (OR, 1.42; 95% confidence interval (CI), 1.23-1.64), occasional snoring (OR, 1.79; 95% CI, 1.55-2.07), and habitual snoring (OR, 2.03; 95% CI, 1.77-2.33) than those who did not snore. The ORs for abdominal obesity were significantly higher in rare snoring subjects (OR, 1.51; 95% CI, 1.30-1.75), occasional snoring (OR, 1.71; 95% CI, 1.47-1.98), and habitual snoring (OR, 2.07; 95% CI, 1.80-2.38) than in non-snorers after adjusting for covariates.

CONCLUSIONS

Snoring was significantly and linearly associated with MetS, and this association was consistently present in both sexes. Positive and graded associations were observed between snoring frequency and MetS components including high blood pressure, elevated fasting glucose levels, and abdominal obesity, independent of conventional risk factors and other MetS components.

Markers of Sleep-Disordered Breathing and Metabolic Syndrome in a Multiethnic Sample of US Adults: Results from the National Health and Nutrition Examination Survey 2005-2008

Previous studies have documented an association between markers of sleep-disordered breathing (SDB) and metabolic syndrome. However, it is not clear if there are gender or ethnic differences in this association. We examined 6,122 participants aged ≥20 years from the National Health and Nutrition Examination Survey 2005–08. Metabolic syndrome was defined as the presence of ≥3 of the following components: (1) abdominal obesity, (2) elevated blood triglycerides, (3) low HDL cholesterol, (4) high BP, and (5) hyperglycemia. SDB severity was defined based on an additive summary score including sleep duration, snoring, snorting, and daytime sleepiness. We found that short sleep duration, snoring, snorting, daytime sleepiness and the summary SDB score were significantly associated with metabolic syndrome independent of potential confounders. Compared to those without any sleep disturbance, the multivariable odds ratio (OR) (95% confidence interval [CI]) of metabolic syndrome among those with three or more sleep disturbances was 3.92 (2.98–5.16). In subgroup analyses, this association was consistently present among men and women and all race-ethnic groups. In summary, SDB was independently associated with metabolic syndrome in a nationally representative sample of US adults.

Obstructive sleep apnea syndrome in children

The clinical syndrome of obstructive sleep apnea (OSAS) in children is a distinct, yet somewhat overlapping disorder with the condition that occurs in adults, such that the clinical manifestations, polysomnographic findings, diagnostic criteria and treatment approaches need to be considered in an age-specific manner. Childhood OSAS has now become widely recognized as a frequent disorder and as a major public health problem. Pediatric OSAS, particularly when obesity is concurrently present, is associated with substantial end-organ morbidities and increased healthcare utilization. Although adenotonsillectomy (T&A) remains the first line of treatment, evidence in recent years suggests that the outcomes of this surgical procedure may not be as favorable as expected, such that post-T&A polysomnographic evaluation may be needed, especially in high-risk patient groups. In addition, incorporation of nonsurgical approaches for milder forms of the disorder and for residual OSAS after T&A is now being investigated.

Interaction of sleep quality and psychosocial stress on obesity in African Americans: the Cardiovascular Health Epidemiology Study (CHES)

Background

Compared with whites, sleep disturbance and sleep deprivation appear more prevalent in African Americans (AA). Long-term sleep deprivation may increase the risk of obesity through multiple metabolic and endocrine alterations. Previous studies have reported contradictory results on the association between habitual sleep duration and obesity. Accordingly, we aimed to assess whether sleep quality and duration are inversely associated with body mass index (BMI) and obesity and test whether these associations are modified by psychosocial stress, known to influence sleep quality.

Methods

A sample of 1,515 AA residents of metropolitan Atlanta, aged 30-65 years, was recruited by a random-digit-dialing method in 2007-08. The outcome obesity was defined by BMI (kg/m²) continuously and categorically (BMI ≥ 30 versus BMI < 30). Global sleep quality (GSQ) score was computed as the sum of response values for the seven components of the Pittsburgh Sleep Quality Index (PSQI) scale. GSQ score was defined as a continuous variable (range 0-21) and as tertiles. The general perceived stress (GPS), derived from the validated Cohen scale, was categorized into tertiles to test the interaction. Chi-square tests, correlation coefficients and weighted multiple linear and logistic regression were used to assess the associations of GSQ, GPS and obesity.

Results

The mean (standard deviation) age was 47.5 (17.0) years, and 1,096 (72%) were women. GSQ score categorized into tertiles was associated with BMI. Among women, after multivariable adjustment that included age, gender, physical activity, smoking status, education, total family income, financial stress and history of hypertension, hypercholesterolemia, diabetes and myocardial infarction, obesity was associated with sleep quality as assessed by GSQ continuous score, [odds ratio, OR (95% C.I.): 1.08 (1.03 - 1.12)], and with a worse sleep disturbance subcomponent score [OR (95% C.I.): 1.48 (1.16 - 1.89)]. Among all participants, stress modified the association between obesity and sleep quality; there was an increased likelihood of obesity in the medium stress category, OR (95% C.I.): 1.09 (1.02 - 1.17).

Conclusion

Sleep quality was associated with obesity in women. The association of sleep quality with obesity was modified by perceived stress. Our results indicate the need for simultaneous assessment of sleep and stress.

Mouse models of neurological disorders: a view from the blood-brain barrier

The number of disease models that involve an aspect of blood-brain barrier (BBB) dysregulation have increased tremendously. The main factors contributing to this expansion have been an increased number of diseases in which the BBB is known to be involved, an increase in the known functions of the BBB, and an increase in the number of models and tools with which those diverse functions can be studied. In many cases, the BBB may be a target of disease; current thinking would include hypertensive encephalopathy and perhaps stroke in this category. Another category are those diseases in which special attributes of the BBB may predispose to disease; for example, the ability of a pathogen to cross the BBB often depends on the pathogen's ability to invoke transcytotic pathways in the brain endothelial or choroid plexus cell. Of special interest are those diseases in which the BBB may be the primary seat of disease or play a major role in the onset or progression of the disease. An increasing number of diseases are so categorized in which BBB dysfunction or dysregulation plays a major role; this review highlights such roles for the BBB including those proposed for Alzheimer's disease and obesity.

Oxidative stress and metabolic changes after continuous positive airway pressure treatment according to previous metabolic disorders in sleep apnea-hypopnea syndrome patients

Sleep apnea-hypopnea syndrome (SAHS) is characterized by recurrent episodes of hypoxia/reoxygenation, which seems to promote oxidative stress. SAHS patients experience increases in hypertension, obesity, and dyslipidemia, and the oxidative state has been related to the genesis of these disorders. The purpose of this study was to examine the changes in oxidative stress markers and metabolic parameters in S AHS patients after 1 month of treatment with continuous positive airway pressure (CPAP), in relation to their previous metabolic disorders. The study included 78 SAHS patients who required CPAP. The patients were classified according to their disorders, including hypertension, obesity, and dyslipidemia. Measurements were made before and after 1 month of treatment with CPAP. The diastolic blood pressure decreased after treatment in all the patients, significantly so in those who were nondyslipidemic, obese, or hypertensive (the systolic pressure also fell in these latter patients). Plasma oxidative stress biomarkers showed a significant antioxidant capacity and increased activity (P<0.05) after treatment, more so in the nondyslipidemic and hypertensive patients. Furthermore, serum lipid peroxidation levels decreased after CPAP (P<0.01). No change was observed in insulin resistance (IR) after CPAP treatment in any of the different disorders. In conclusion, oxidative stress markers improved significantly after CPAP treatment in SAHS patients, especially in the nondyslipidemic and hypertensive patients. Moreover, the blood pressure decreased after CPAP treatment, particularly in the obese, nondyslipidemic, and hypertensive patients. No significant change in IR was found in any of the SAHS patients after CPAP treatment.

Does leptin play a role in obesity-asthma relationship?

The increase of asthma has paralleled the rising obesity during the past decades. Obesity is characterized by the increase of leptin in the circulation. Leptin is an obesity gene product, and it can stimulate the production of pro-inflammatory mediators, such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-6 and interferon (IFN)-gamma. There is a link between leptin and asthma, especially in children. It remains unclear however, if leptin is in the pathway of obesity-asthma relationship and if it plays a distinctive role in asthma in obese vs. non-obese subjects. Since leptin is in a positive feedback loop with the pro-inflammatory cytokines such as TNF-alpha, there is a possibility that leptin is involved as a regulatory rather than an etiologic mechanism of asthma development. Weight loss is associated with decreased circulating leptin concentration in children. Weight control program may need to be considered in the treatment of asthma in obese children.

Obesity and Obstructive Sleep Apnoea Hypopnoea Syndrome in Singapore Children

Introduction: Obesity affects about 10% to 15% of our school-going population in Singapore and is a risk factor for development of obstructive sleep apnoea hypopnoea syndrome (OSAHS). This article reviews the prevalence, aetiology, pathophysiology, diagnosis, complications and treatment of obese children with OSAHS with particular reference to children in Singapore. Methods: Review of articles or conference papers reporting data with regards to OSAHS in Singapore children. Results: Prevalence of OSAHS was high in obese children in Singapore and was more common in males with no racial predisposition. Hypersomnolence as a presenting symptom was uncommon. Cognitive function, behaviour, attention and processing speed was affected and improved after intervention. Abnormalities of glucose metabolism were also found with the respiratory disturbance index (RDI) as an independent predictor of insulin resistance. Tonsillectomy and or adenoidectomy was efficacious as treatment and risk of complications was low. No significant increase in weight occurred post intervention in those enrolled in concurrent weight management programmes. Conclusions: Prevalence of OSAHS is high in obese Singapore children and many are ‘asymptomatic’. A low threshold for evaluation is necessary for early diagnosis and intervention for prevention of morbidity. Tonsillectomy and/or adenoidectomy is safe and efficacious and remains the first-line treatment in most obese patients. Key words: Complications, Diagnosis, Prevalence, Treatment

Short sleep is a questionable risk factor for obesity and related disorders: statistical versus clinical significance

Habitually insufficient sleep could contribute towards obesity, metabolic syndrome, etc., via sleepiness-related inactivity and excess energy intake; more controversially, through more direct physiological changes. Epidemiological studies in adult/children point to small clinical risk only in very short (around 5h in adults), or long sleepers, developing over many years, involving hundreds of hours of 'too little' or 'too much' sleep. Although acute 4h/day sleep restriction leads to glucose intolerance and incipient metabolic syndrome, this is too little sleep and cannot be sustained beyond a few days. Few obese adults/children are short sleepers, and few short sleeping adults/children are obese or suffer obesity-related disorders. For adults, about 7h uninterrupted daily sleep is 'healthy'. Extending sleep, even with hypnotics, to lose weight, may take years, compared with the rapidity of utilising extra sleep time to exercise and evaluate one's diet. The real health risk of inadequate sleep comes from a sleepiness-related accident.

The cardiovascular toll of stress

Psychological stress elicits measurable changes in sympathetic-parasympathetic balance and the tone of the hypothalamic-pituitary-adrenal axis, which might negatively affect the cardiovascular system both acutely-by precipitating myocardial infarction, left-ventricular dysfunction, or dysrhythmia; and chronically-by accelerating the atherosclerotic process. We provide an overview of the association between stress and cardiovascular morbidity, discuss the mechanisms for this association, and address possible therapeutic implications.

Sleep and the body mass index and overweight status of children and adolescents

Associations between sleep and the body mass index (BMI) and overweight status of children and adolescents were estimated using longitudinal data from a nationally representative sample of 2,281 children aged 3-12 years at baseline. Controlling for baseline BMI, children who slept less, went to bed later, or got up earlier at the time of the first assessment had higher BMIs 5 years later and were more likely to be overweight. Child age moderated the relationship between bedtime and BMI. In addition, the study reports nationally representative data on the sleep habits of American children aged 3-18 years. This study underscores the likely importance of sleep on children's physical health and suggests that sleep is important for understanding childhood weight problems.

Obesity and obstructive sleep apnea in children

The prevalence and severity of obesity in children and adolescent is dramatically increasing worldwide with a corresponding increase in the prevalence of obesity-associated morbidities particularly those involving OSAS and metabolic and cardiovascular sequelae. Obstructive sleep apnea and obesity hypoventilation syndrome are important and serious consequences of obesity, and may in fact mediate components of the association between obesity and metabolic and cardiovascular morbidities, most likely via potentiation of inflammatory cascades. It is anticipated that the increased prevalence of obesity in children and adolescents in our society will be accompanied by a steady increase in the incidence of OSAS. In this review, we will examine our current understanding of sleep-disordered breathing and associated morbidities in obese children, and summarize the range of therapeutic modalities currently available for this high-risk population.

The effects of high fat diets on the blood–brain barrier transport of leptin: Failure or adaptation?

Leptin is a pluripotent regulatory protein secreted by fat and exerts many effects through the CNS. Interpretation of the characteristics by which it crosses the blood-brain barrier (BBB) supports the view that leptin most potently signals the brain at serum levels well below those associated with the current definition of ideal body weight. This fits with the perspective that low serum levels of leptin are a signal to brain that a sufficient store of calories are available for the organism to expend energy for efforts unrelated to acquisition of calories. This would explain why low serum levels of leptin are permissive in many of the non-feeding actions of leptin, such as enhancing CNS-mediated immune function, memory, bone growth, reproduction, breathing, and neurogenesis. Triglycerides inhibit the transport of leptin across the BBB and so could be key in the onset of the peripheral leptin resistance, which is a hallmark of obesity. These results explain the paradox of why obesity should induce resistance to an anorectic: hypertriglyceridemia also occurs with starvation and we postulate that triglyceride-induced resistance to leptin transport across the BBB initially evolved to limit the signal of an anorectic to the brain during starvation.

Pathophysiologic changes of obesity

This article builds on the well-known changes that occur with obesity by drawing from recent advances reported in the literature for an improved understanding of obese patients. The dissemination of information regarding the health risks with being overweight or obese to both the public and the health care community are widespread and effective from a public health perspective. The mechanisms underlying these associated risks must continue to be explored for physicians' knowledge to truly increase, and lead to advances in our understanding of the pathophysiology of obesity.