Expression of cortisol metabolism-related genes shows circadian rhythmic patterns in human adipose tissue

Recent Advances in Adipose Tissue Dysfunction and Its Role in the Pathogenesis of Non-Alcoholic Fatty Liver Disease

Obesity is a serious ongoing health problem that significantly increases the incidence of nonalcoholic fatty liver disease (NAFLD). During obesity, adipose tissue dysfunction is obvious and characterized by increased fat deposition (adiposity) and chronic low-grade inflammation. The latter has been implicated to critically promote the development and progression of NAFLD, whose advanced form non-alcoholic steatohepatitis (NASH) is considered one of the most common causes of terminal liver diseases. This review summarizes the current knowledge on obesity-related adipose dysfunction and its roles in the pathogenesis of hepatic steatosis and inflammation, as well as liver fibrosis. A better understanding of the crosstalk between adipose tissue and liver under obesity is essential for the development of new and improved preventive and/or therapeutic approaches for managing NAFLD.

The association of energy and macronutrient intake at dinner vs breakfast with the incidence of type 2 diabetes mellitus in a cohort study: The China Health and Nutrition Survey, 1997-2011

BACKGROUND

This study aims to investigate the association of energy and macronutrient intake at dinner vs breakfast with the incidence of type 2 diabetes mellitus (T2DM).

METHODS

A total of 11 153 adults, including 811 with T2DM, completed a questionnaire about energy and macronutrient intake in the China Health and Nutrition Survey (1997-2011). The differences (Δ) in energy and macronutrient intake between dinner and breakfast (Δ = dinner - breakfast) were categorized into quintiles. Cox proportional hazards regression models were performed to explore the association between Δ and the risk of T2DM and to investigate the change of the risk when 5% total energy or energy provided by macronutrients at dinner was substituted with total energy or energy provided by macronutrients at breakfast by isocaloric substitution models.

RESULTS

After adjustment for potential confounders, compared with participants in the lowest quintile, participants in the highest quintile were more likely to develop T2DM (hazard ratio [HR]_Δenergy 1.46, 95% CI 1.13-1.87; HR_Δfat 1.85, 95% CI 1.43-2.41; HR_Δprotein 1.37, 95% CI 1.06-1.78). Isocalorically replacing 5% energy at dinner with energy at breakfast was associated with a 7% lower T2DM risk. Replacing 5% energy provided by fat at dinner with energy provided by carbohydrate, protein, and fat at breakfast was associated with a 9%, 5%, and 7% lower T2DM risk, respectively. Replacing 5% energy provided by protein at dinner with energy provided by carbohydrate or protein at breakfast was associated with a 5% lower T2DM risk.

CONCLUSIONS

Higher intake of energy, protein, and fat at dinner than at breakfast increased the risk of T2DM.

Improved Urinary Cortisol Metabolome in Addison Disease: A Prospective Trial of Dual-Release Hydrocortisone

CONTEXT

Oral once-daily dual-release hydrocortisone (DR-HC) replacement therapy has demonstrated an improved metabolic profile compared to conventional 3-times-daily (TID-HC) therapy among patients with primary adrenal insufficiency. This effect might be related to a more physiological cortisol profile, but also to a modified pattern of cortisol metabolism.

OBJECTIVE

This work aimed to study cortisol metabolism during DR-HC and TID-HC.

DESIGN

A randomized, 12-week, crossover study was conducted.

INTERVENTION AND PARTICIPANTS

DC-HC and same daily dose of TID-HC were administered to patients with primary adrenal insufficiency (n = 50) vs healthy individuals (n = 124) as controls.

MAIN OUTCOME MEASURES

Urinary corticosteroid metabolites were measured by gas chromatography/mass spectrometry at 24-hour urinary collections.

RESULTS

Total cortisol metabolites decreased during DR-HC compared to TID-HC (P < .001) and reached control values (P = .089). During DR-HC, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) activity measured by tetrahydrocortisol + 5α-tetrahydrocortisol/tetrahydrocortisone ratio was reduced compared to TID-HC (P < .05), but remained increased vs controls (P < .001). 11β-HSD2 activity measured by urinary free cortisone/free cortisol ratio was decreased with TID-HC vs controls (P < .01) but normalized with DR-HC (P = .358). 5α- and 5β-reduced metabolites were decreased with DR-HC compared to TID-HC. Tetrahydrocortisol/5α-tetrahydrocortisol ratio was increased during both treatments, suggesting increased 5β-reductase activity.

CONCLUSIONS

The urinary cortisol metabolome shows striking abnormalities in patients receiving conventional TID-HC replacement therapy, with increased 11β-HSD1 activity that may account for the unfavorable metabolic phenotype in primary adrenal insufficiency. Its change toward normalization with DR-HC may mediate beneficial metabolic effects. The urinary cortisol metabolome may serve as a tool to assess optimal cortisol replacement therapy.

Endogenous Glucocorticoid Metabolism in Bone: Friend or Foe

The role of tissue specific metabolism of endogenous glucocorticoids (GCs) in the pathogenesis of human disease has been a field of intense interest over the last 20 years, fuelling clinical trials of metabolism inhibitors in the treatment of an array of metabolic diseases. Localised pre-receptor metabolism of endogenous and therapeutic GCs by the 11β-hydroxysteroid dehydrogenase (11β-HSD) enzymes (which interconvert endogenous GCs between their inactive and active forms) are increasingly recognised as being critical in mediating both their positive and negative actions on bone homeostasis. In this review we explore the roles of endogenous and therapeutic GC metabolism by the 11β-HSD enzymes in the context of bone metabolism and bone cell function, and consider future strategies aimed at modulating this system in order to manage and treat various bone diseases.

Moderate Weight Loss Modifies Leptin and Ghrelin Synthesis Rhythms but Not the Subjective Sensations of Appetite in Obesity Patients

Obesity is characterized by a resistance to appetite-regulating hormones, leading to a misalignment between the physiological signals and the perceived hunger/satiety signal. A disruption of the synthesis rhythm may explain this situation. The aim of this study was to evaluate the effect of dietary-induced weight loss on the daily rhythms of leptin and ghrelin and its influence on the daily variability of the appetite sensations of patients with obesity. Twenty subjects with obesity underwent a hypocaloric dietary intervention for 12 weeks. Plasma leptin and ghrelin were analyzed at baseline and at the end of the intervention and in 13 normal-weight controls. Appetite ratings were analyzed. Weight loss decreased leptin synthesis (pauc < 0.001) but not the rhythm characteristics, except the mean variability value (pmesor = 0.020). By contrast, the mean ghrelin level increased after weight loss. The rhythm characteristics were also modified until a rhythm similar to the normal-weight subjects was reached. The amount of variability of leptin and ghrelin was correlated with the effectiveness of the dietary intervention (p < 0.020 and p < 0.001, respectively). Losing weight partially restores the daily rhythms of leptin and modifies the ghrelin rhythms, but appetite sensations are barely modified, thus confirming that these hormones cannot exercise their physiological function properly.

Timing of eating in adults across the weight spectrum: Metabolic factors and potential circadian mechanisms

Timing of eating is recognized as a significant contributor to body weight regulation. Disruption of sleep-wake cycles from a predominantly diurnal (daytime) to a delayed (evening) lifestyle leads to altered circadian rhythms and metabolic dysfunction. This article reviews current evidence for timed and delayed eating in individuals of normal weight and those with overweight or obesity: although some findings indicate a benefit of eating earlier in the daytime on weight and/or metabolic outcomes, results have not been uniformly consistent, and more rigorous and longer-duration studies are needed. We also review potential circadian mechanisms underlying the metabolic- and weight-related changes resulting from timed and delayed eating. Further identification of such mechanisms using deep phenotyping is required to determine targets for medical interventions for obesity and for prevention of metabolic syndrome and diabetes, and to inform clinical guidelines regarding eating schedules for management of weight and metabolic disease.

Menopause status is associated with circadian- and sleep-related alterations

OBJECTIVE

The aim of the study was to investigate whether postmenopausal women show differences in circadian-related variables and sleep characteristics compared with premenopausal women, and to analyze potential associations between these circadian-related variables and abdominal fat distribution or metabolic syndrome (MetS) components.

METHODS

A total of 177 women were studied (127 premenopausal, 50 postmenopausal). Sixty percent of the total population was overweight/obese, with no significant differences between premenopausal (60%) and postmenopausal women (62%) (P = 0.865). Wrist temperature (WT) and rest-activity cycles were measured during 8 consecutive days, and sleep and food diaries collected. MetS characteristics and daily patterns of saliva cortisol were analyzed. Sleep characteristics were assessed with domiciliary polysomnography.

RESULTS

Postmenopausal women showed a less robust rhythm in WT with lower amplitude (°C) (0.8 ± 0.4 vs 0.9 ± 0.5) (P < 0.05) and lower mean temperature values at the midpoint of sleep than premenopausal women. Postmenopausal women were also more morning-type than premenopausal women, showing a phase advance of approximately 1 hour in WT and rest-activity rhythms, and more morning-type habits (earlier sleep onset/offset and breakfast intake) (P < 0.05). Postmenopausal women showed higher levels of activity in the morning and lower in the evening compared with premenopausal women (P < 0.05). Daily variability in cortisol was significantly reduced in postmenopausal women compared with premenopausal women (P < 0.05). Postmenopausal women had increased frequency of sleep-related breathing abnormalities (P < 0.0001). In the women studied, abdominal fat and MetS were associated with an increase in circadian alterations (high fragmentation and low amplitude of the rhythm) (P < 0.05).

CONCLUSIONS

Postmenopausal women exhibit loss of circadian robustness and an increase in sleep abnormalities compared with premenopausal women.

The Functional and Clinical Significance of the 24-Hour Rhythm of Circulating Glucocorticoids

Adrenal glucocorticoids are major modulators of multiple functions, including energy metabolism, stress responses, immunity, and cognition. The endogenous secretion of glucocorticoids is normally characterized by a prominent and robust circadian (around 24 hours) oscillation, with a daily peak around the time of the habitual sleep-wake transition and minimal levels in the evening and early part of the night. It has long been recognized that this 24-hour rhythm partly reflects the activity of a master circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus. In the past decade, secondary circadian clocks based on the same molecular machinery as the central master pacemaker were found in other brain areas as well as in most peripheral tissues, including the adrenal glands. Evidence is rapidly accumulating to indicate that misalignment between central and peripheral clocks has a host of adverse effects. The robust rhythm in circulating glucocorticoid levels has been recognized as a major internal synchronizer of the circadian system. The present review examines the scientific foundation of these novel advances and their implications for health and disease prevention and treatment.

Steroid biosynthesis in adipose tissue

Tissue-specific expression of steroidogenic enzymes allows the modulation of active steroid levels in a local manner. Thus, the measurement of local steroid concentrations, rather than the circulating levels, has been recognized as a more accurate indicator of the steroid action within a specific tissue. Adipose tissue, one of the largest endocrine tissues in the human body, has been established as an important site for steroid storage and metabolism. Locally produced steroids, through the enzymatic conversion from steroid precursors delivered to adipose tissue, have been proven to either functionally regulate adipose tissue metabolism, or quantitatively contribute to the whole body's steroid levels. Most recently, it has been suggested that adipose tissue may contain the steroidogenic machinery necessary for the initiation of steroid biosynthesis de novo from cholesterol. This review summarizes the evidence indicating the presence of the entire steroidogenic apparatus in adipose tissue and discusses the potential roles of local steroid products in modulating adipose tissue activity and other metabolic parameters.

Updated survey of the steroid-converting enzymes in human adipose tissues

Over the past decade, adipose tissues have been increasingly known for their endocrine properties, that is, their ability to secrete a number of adipocytokines that may exert local and/or systemic effects. In addition, adipose tissues have long been recognized as significant sites for steroid hormone transformation and action. We hereby provide an updated survey of the many steroid-converting enzymes that may be detected in human adipose tissues, their activities and potential roles. In addition to the now well-established role of aromatase and 11β-hydroxysteroid dehydrogenase (HSD) type 1, many enzymes have been reported in adipocyte cell lines, isolated mature cells and/or preadipocytes. These include 11β-HSD type 2, 17β-HSDs, 3β-HSD, 5α-reductases, sulfatases and glucuronosyltransferases. Some of these enzymes are postulated to bear relevance for adipose tissue physiology and perhaps for the pathophysiology of obesity. This elaborate set of steroid-converting enzymes in the cell types of adipose tissue deserves further scientific attention. Our work on 20α-HSD (AKR1C1), 3α-HSD type 3 (AKR1C2) and 17β-HSD type 5 (AKR1C3) allowed us to clarify the relevance of these enzymes for some aspects of adipose tissue function. For example, down-regulation of AKR1C2 expression in preadipocytes seems to potentiate the inhibitory action of dihydrotestosterone on adipogenesis in this model. Many additional studies are warranted to assess the impact of intra-adipose steroid hormone conversions on adipose tissue functions and chronic conditions such as obesity, diabetes and cancer.

Diurnal rhythms of plasma GLP-1 levels in normal and overweight/obese subjects: lack of effect of weight loss

Food intake is regulated by not only neurohormonal, but also social, educational, and even cultural factors. Within the former, there is a complex interaction between orexigenic (ghrelin) and anorexigenic (glucagon-like peptide-1 (GLP-1)) factors in order to adjust the food intake to caloric expenditure; however, the number of subjects that are unable to properly balance appetite and body weight is increasing continuously. A loss of circadian or diurnal coordination of any of these factors may be implied in this situation. Special attention has retrieved GLP-1 due to its usefulness as a therapeutic agent against obesity and related alterations. Thus, the objective of the present study was to compare GLP-1 diurnal synthesis between normal weight and overweight/obese subjects, and to evaluate whether weight loss can restore the synthesis rhythms of GLP-1. Three groups of 25 subjects were divided attending to their body mass index (BMI) in normal weight, overweight, or obese subjects. Diurnal (5 points) GLP-1 levels were analyzed. Secondly, an intervention (behavioral-dietary treatment) study was conducted to analyze the effect of weight loss on plasma GLP-1 concentrations. Our results showed that baseline GLP-1 level was significantly lower in normal weight subjects (p = 0.003); furthermore, our cosinor analysis revealed a higher amplitude (p = 0.040) and daily GLP-1 variation (47%) in these subjects. In fact, our ANOVA data showed a lack of rhythmicity in overweight/obese patients. Weight loss was not able to restore a diurnal rhythm of plasma GLP-1 levels. In summary, the present work shows a disruption of diurnal GLP-1 levels in overweight/obese subjects, which worsen as body fat progresses. The attenuation of the GLP-1 synthesis rhythms may be important to understand the impairment of food intake regulation in overweight/obese subjects.

Ruano E, C. Figueroa AL, Aranda G, Momblan D, Carmona F, Gomis R, Vidal J, Hanzu FA. Altered clock gene expression in obese visceral adipose tissue is associated with metabolic syndrome

Clock gene expression was associated with different components of metabolic syndrome (MS) in human adipose tissue. However, no study has been done to compare the expression of clock genes in visceral adipose tissue (VAT) from lean and obese subjects and its clinical implications. Therefore, we studied in lean and obese women the endogenous 24 h expression of clock genes in isolated adipocytes and its association with MS components. VAT was obtained from lean (BMI 21-25 kg/m2; n = 21) and morbidly obese women (BMI >40 kg/m2; n = 28). The 24 h pattern of clock genes was analyzed every 6 hours using RT-PCR. Correlation of clinical data was studied by Spearman analysis. The 24 h pattern of clock genes showed that obesity alters the expression of CLOCK, BMAL1, PER1, CRY2 and REV-ERB ALPHA in adipocytes with changes found in CRY2 and REV-ERB ALPHA throughout the 24 h period. The same results were confirmed in VAT and stromal cells (SC) showing an upregulation of CRY2 and REV-ERB ALPHA from obese women. A positive correlation was observed for REV-ERB ALPHA gene expression with BMI and waist circumference in the obese population. Expression of ROR ALPHA was correlated with HDL levels and CLOCK with LDL. Obese subjects with MS exhibited positive correlation in the PER2 gene with LDL cholesterol, whereas REV-ERB ALPHA was correlated with waist circumference. We identified CRY2 and REV-ERB ALPHA as the clock genes upregulated in obesity during the 24 h period and that REV-ERB ALPHA is an important gene associated with MS.

Study of the association between 3111T/C polymorphism of the CLOCK gene and the presence of overweight in schoolchildren

OBJECTIVES

To evaluate the association between 3111T/C polymorphism of the CLOCK gene and the presence of obesity and sleep duration in children aged 6-13 years. In adults, this genetic variant has been associated with duration of sleep, ghrelin levels, weight, and eating habits. Although short sleep duration has been linked to obesity in children, no study has aimed to identify the possible molecular mechanisms of this association to date.

METHODS

Weight, height, and circumferences were transformed into Z-scores for age and gender. Genotyping was performed using TaqMan methodology. A questionnaire regarding hours of sleep was provided to parents. The appropriate statistical tests were performed.

RESULTS

This study evaluated 370 children (45% males, 55% females, mean age 8.5 ± 1.5 years). The prevalence of overweight was 18%. The duration of sleep was, on average, 9.7hours, and was inversely related to age (p<0.001). Genotype distribution was: 4% CC, 31% CT, and 65% TT. There was a trend toward higher prevalence of overweight in children who slept less than nine hours (23%) when compared to those who slept more than ten hours (16%, p=0.06). Genotype was not significantly correlated to any of the assessed outcomes.

CONCLUSIONS

The CLOCK 3111T/C polymorphism was not significantly associated with overweight or sleep duration in children in this city.

Salivary estradiol and testosterone in Filipino men: Diurnal patterns and relationships with adiposity

OBJECTIVES

We used detailed saliva sampling procedures to test for diurnal changes in men's salivary estradiol (E2) and testosterone (T) and assessed whether greater adiposity predicted higher E2 and T.

METHODS

We drew on a subsample of young adults enrolled in a long-running birth cohort study in Metro Cebu, Philippines. Subjects provided saliva samples at four time points during the day (waking, waking +40 min, early evening, and bedtime), which were assayed for E2 and T. Using these detailed hormonal data, we calculated E2 (n = 29) and T (n = 44) area-under-the-curve values, which provide insights on hormonal production over the study period.

RESULTS

While T declined immediately after waking and reached a nadir in the early evening, E2 did not show significant diurnal change (P ≥ 0.1) but was positively correlated to T at multiple time points (P ≤ 0.05). Subjects with higher adiposity (BMI, waist circumference, skinfolds) had elevated E2 secretion throughout the day (P ≤ 0.01), but adiposity was not related to salivary T.

CONCLUSIONS

Consistent with past research, our results indicate that adipose tissue is a significant site of E2 production in males but differ from a limited number of prior studies of young men in that we did not find lower T with increasing adiposity. Given E2's role in male hypothalamic-pituitary-gonadal function and complex interfaces with the immune system, these results have important implications for models of male life history as rates of overweight and obesity rise in populations around the world.

PPARs Integrate the Mammalian Clock and Energy Metabolism

Peroxisome proliferator-activated receptors (PPARs) are a group of nuclear receptors that function as transcription factors regulating the expression of numerous target genes. PPARs play an essential role in various physiological and pathological processes, especially in energy metabolism. It has long been known that metabolism and circadian clocks are tightly intertwined. However, the mechanism of how they influence each other is not fully understood. Recently, all three PPAR isoforms were found to be rhythmically expressed in given mouse tissues. Among them, PPARα and PPARγ are direct regulators of core clock components, Bmal1 and Rev-erbα, and, conversely, PPARα is also a direct Bmal1 target gene. More importantly, recent studies using knockout mice revealed that all PPARs exert given functions in a circadian manner. These findings demonstrated a novel role of PPARs as regulators in correlating circadian rhythm and metabolism. In this review, we summarize advances in our understanding of PPARs in circadian regulation.

Changes in adipose glucocorticoid metabolism before and after bariatric surgery assessed by direct hormone measurements

OBJECTIVES

Increased intra-adipose cortisol is thought to promote obesity, but few human studies have investigated intra-adipose glucocorticoid hormones and none have demonstrated prospective changes with fat loss.

DESIGN AND METHODS

Subcutaneous adipose tissue (SAT) was obtained from obese subjects before and 1-year after surgery-induced fat loss, and from nonobese controls. In a second similar cohort of obese subjects, adipocytes and stromal-vascular fraction were isolated. Intra-adipose cortisol and cortisone levels were analyzed by liquid chromatography mass spectrometry and HSD11B1/HSD11B2 mRNA by qPCR.

RESULTS

SAT cortisol/cortisone ratio before fat loss, median 4.8 (interquartile range, 4.1-5.7), was higher than after fat loss, 1.9 (1.0-2.7) (P = 0.001), and compared to nonobese controls, 3.2 (2.4-3.9) (P = 0.005). Cortisone before fat loss, 2.3 (1.2-2.9) nmol/kg, was lower than after fat loss, 5.8 (3.0-10.2) nmol/kg (P = 0.042), and compared to controls, 5.1 (3.8-6.7) nmol/kg (P = 0.013). HSD11B1 was predominantly expressed in mature adipocytes, whereas HSD11B2 was expressed at a higher level in stromal-vascular fraction.

CONCLUSIONS

The intra-adipose glucocorticoid metabolism was markedly altered in the extremely obese state with increased cortisol levels relative to cortisone, whereas fat loss restored this balance approximating nonobese subjects. Changes were more pronounced for cortisone than cortisol, suggesting an adaptive response to insufficient intra-adipose cortisol levels in obesity.

Diurnal variation in vascular and metabolic function in diet-induced obesity: divergence of insulin resistance and loss of clock rhythm

Circadian rhythms are integral to the normal functioning of numerous physiological processes. Evidence from human and mouse studies suggests that loss of rhythm occurs in obesity and cardiovascular disease and may be a neglected contributor to pathophysiology. Obesity has been shown to impair the circadian clock mechanism in liver and adipose tissue but its effect on cardiovascular tissues is unknown. We investigated the effect of diet-induced obesity in C57BL6J mice upon rhythmic transcription of clock genes and diurnal variation in vascular and metabolic systems. In obesity, clock gene function and physiological rhythms were preserved in the vasculature but clock gene transcription in metabolic tissues and rhythms of glucose tolerance and insulin sensitivity were blunted. The most pronounced attenuation of clock rhythm occurred in adipose tissue, where there was also impairment of clock-controlled master metabolic genes and both AMPK mRNA and protein. Across tissues, clock gene disruption was associated with local inflammation but diverged from impairment of insulin signaling. We conclude that vascular tissues are less sensitive to pathological disruption of diurnal rhythms during obesity than metabolic tissues and suggest that cellular disruption of clock gene rhythmicity may occur by mechanisms shared with inflammation but distinct from those leading to insulin resistance.

Glucocorticoids affect 24 h clock genes expression in human adipose tissue explant cultures

AIMS

to examine firstly whether CLOCK exhibits a circadian expression in human visceral (V) and subcutaneous (S) adipose tissue (AT) in vitro as compared with BMAL1 and PER2, and secondly to investigate the possible effect of the glucocorticoid analogue dexamethasone (DEX) on positive and negative clock genes expression.

SUBJECTS AND METHODS

VAT and SAT biopsies were obtained from morbid obese women (body mass index ≥ 40 kg/m(2)) (n = 6). In order to investigate rhythmic expression pattern of clock genes and the effect of DEX on CLOCK, PER2 and BMAL1 expression, control AT (without DEX) and AT explants treated with DEX (2 hours) were cultured during 24 h and gene expression was analyzed at the following times: 10:00 h, 14:00 h, 18:00 h, 22:00 h, 02:00 h and 06:00 h, using qRT-PCR.

RESULTS

CLOCK, BMAL1 and PER2 expression exhibited circadian patterns in both VAT and SAT explants that were adjusted to a typical 24 h sinusoidal curve. PER2 expression (negative element) was in antiphase with respect to CLOCK and in phase with BMAL1 expression (both positive elements) in the SAT (situation not present in VAT). A marked effect of DEX exposure on both positive and negative clock genes expression patterns was observed. Indeed, DEX treatment modified the rhythmicity pattern towards altered patterns with a period lower than 24 hours in all genes and in both tissues.

CONCLUSIONS

24 h patterns in CLOCK and BMAL1 (positive clock elements) and PER2 (negative element) mRNA levels were observed in human adipose explants. These patterns were altered by dexamethasone exposure.

Site-specific circadian expression of leptin and its receptor in human adipose tissue

INTRODUCTION

Circadian variability of circulating leptin levels has been well established over the last decade. However, the circadian behavior of leptin in human adipose tissue remains unknown. This also applies to the soluble leptin receptor.

OBJECTIVE

We investigated the ex vivo circadian behavior of leptin and its receptor expression in human adipose tissue (AT).

SUBJECTS AND METHODS

Visceral and subcutaneous abdominal AT biopsies (n = 6) were obtained from morbid obese women (BMI ≥ 40 kg/m²). Anthropometric variables and fasting plasma glucose, leptin, lipids and lipoprotein concentrations were determined. In order to investigate rhythmic expression pattern of leptin and its receptor, AT explants were cultured during 24-h and gene expression was analyzed at the following times: 08:00, 14:00, 20:00, 02:00 h, using quantitative real-time PCR.

RESULTS

Leptin expression showed an oscillatory pattern that was consistent with circadian rhythm in cultured AT. Similar patterns were noted for the leptin receptor. Leptin showed its achrophase (maximum expression) during the night, which might be associated to a lower degree of fat accumulation and higher mobilization. When comparing both fat depots, visceral AT anticipated its expression towards afternoon and evening hours. Interestingly, leptin plasma values were associated with decreased amplitude of LEP rhythm. This association was lost when adjusting for waist circumference.

CONCLUSION

Circadian rhythmicity has been demonstrated in leptin and its receptor in human AT cultures in a site-specific manner. This new knowledge paves the way for a better understanding of the autocrine/paracrine role of leptin in human AT.

Adipose circadian rhythms: translating cellular and animal studies to human physiology

Emerging links between circadian rhythms and metabolism promise much for the understanding of metabolic physiology and pathophysiology, in which white adipose tissue (WAT) plays a prominent role. Many WAT endocrine molecules, termed adipokines, display rhythmic plasma concentration. Moreover, similar to most other tissues, WAT exhibits widespread 24-h variation in gene expression, with approximately 20% of the murine adipose transcriptome estimated to undergo daily variation. A major limitation to human chronobiology research is the availability of physiologically defined peripheral tissues. To date most analyses of in vivo human peripheral clocks has been limited to blood leucocytes. However, subcutaneous adipose tissue represents a novel opportunity to study peripheral molecular rhythms that are of clearly defined metabolic relevance. This review summarises basic concepts of circadian and metabolic physiology before then comparing alternative protocols used to analyse the rhythmic properties of human adipose tissue.

Changes in gene expression profile in human subcutaneous adipose tissue during significant weight loss

OBJECTIVE

To analyze the expression of peroxisome proliferator-activated receptor-γ1 and 2 (PPARγ1 and 2), 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), and leptin in adipose tissue (AT) of obese women during weight loss following Roux-en-Y gastric bypass (RYGB) and to compare these levels with those obtained in AT of nonobese subjects.

METHODS

Gene expression was determined by real-time RT-PCR prior to surgery and at 3, 6, and 12 months after RYGB.

RESULTS

All obese patients lost weight, reaching a mean BMI of 29.3 ± 1.0 kg/m(2) at 1 year after surgery (-33.9 ± 1.5% of their initial body weight). In obese subjects leptin and 11βHSD1 were over-expressed, whereas PPARγ1 was expressed at lower levels compared to controls. After surgery, leptin and 11βHSD1 gene expression decreased, whereas PPARγ1 expression increased. At 12 months after RYGB, these 3 genes had reached levels similar to the controls. In contrast, PPARγ2 gene expression was not different between groups and types of tissue and remained unchanged during weight loss. We found a positive correlation between BMI and levels of gene expression of leptin and 11βHSD1.

CONCLUSION

Gene expression of leptin, PPARγ1, and 11βHSD1 in AT is modified in human obesity. This default is completely corrected by RYGB.

[Chronobiological aspects of obesity and metabolic syndrome]

Circadian rhythms (approximately 24h) are widely characterized at molecular level and their generation is acknowledged to originate from oscillations in expression of several clock genes and from regulation of their protein products. While general entrainment of organisms to environmental light-dark cycles is mainly achieved through the master clock of the suprachiasmatic nucleus in mammals, this molecular clockwork is functional in several organs and tissues. Some studies have suggested that disruption of the circadian system (chronodisruption (CD)) may be causal for manifestations of the metabolic syndrome. This review summarizes (1) how molecular clocks coordinate metabolism and their specific role in the adipocyte; (2) the genetic aspects of and scientific evidence for obesity as a chronobiological illness; and (3) CD and its causes and pathological consequences. Finally, ideas about use of chronobiology for the treatment of obesity are discussed.

An approximation to the temporal order in endogenous circadian rhythms of genes implicated in human adipose tissue metabolism

Although it is well established that human adipose tissue (AT) shows circadian rhythmicity, published studies have been discussed as if tissues or systems showed only one or few circadian rhythms at a time. To provide an overall view of the internal temporal order of circadian rhythms in human AT including genes implicated in metabolic processes such as energy intake and expenditure, insulin resistance, adipocyte differentiation, dyslipidemia, and body fat distribution. Visceral and subcutaneous abdominal AT biopsies (n=6) were obtained from morbid obese women (BMI≥40 kg/m(2) ). To investigate rhythmic expression pattern, AT explants were cultured during 24-h and gene expression was analyzed at the following times: 08:00, 14:00, 20:00, 02:00 h using quantitative real-time PCR. Clock genes, glucocorticoid metabolism-related genes, leptin, adiponectin and their receptors were studied. Significant differences were found both in achrophases and relative-amplitude among genes (P<0.05). Amplitude of most genes rhythms was high (>30%). When interpreting the phase map of gene expression in both depots, data indicated that circadian rhythmicity of the genes studied followed a predictable physiological pattern, particularly for subcutaneous AT. Interesting are the relationships between adiponectin, leptin, and glucocorticoid metabolism-related genes circadian profiles. Their metabolic significance is discussed. Visceral AT behaved in a different way than subcutaneous for most of the genes studied. For every gene, protein mRNA levels fluctuated during the day in synchrony with its receptors. We have provided an overall view of the internal temporal order of circadian rhythms in human adipose tissue.

Expression of genes related to glucocorticoid action in human subcutaneous and omental adipose tissue

Adipose tissue glucocorticoid action relies on local enzymatic interconversion and glucocorticoid receptor (GR) availability. 11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1), 2 (11β-HSD2) and hexose-6-phosphate dehydrogenase (H6PDH) are likely involved in glucocorticoid activation/inactivation within adipose tissue. We examined adipose tissue mRNA expression of genes related to glucocorticoid action and their association with total and visceral adiposity. Messenger RNA was measured in paired subcutaneous and omental fat samples obtained from 56 women (age: 47.3 ± 4.8 years, BMI: 27.1 ± 5.2 kg/m(2)) undergoing gynaecological surgery. Expression levels of 11β-HSD2, H6PDH and GRα were higher in omental adipose tissue while 11β-HSD1 expression was similar between fat compartments. Subcutaneous and omental 11β-HSD1 mRNA abundances were positively associated with total and visceral adiposity whereas omental H6PDH mRNA abundance was negatively associated with these measures. Only omental 11β-HSD1 mRNA expression remained significantly associated with visceral adipose tissue area following statistical adjustment for fat mass, age and menopausal status. Omental 11β-HSD1 mRNA expression explained 19.1% of the variance in visceral adipose tissue area. Omental fat tissue 11β-HSD-1 protein and cortisol levels were higher in visceral obese women, supporting findings obtained with 11β-HSD-1 mRNA. These results suggest that among the transcripts examined only omental 11β-HSD1 is independently associated with visceral obesity in women.

Chronobiological aspects of nutrition, metabolic syndrome and obesity

The present review starts from the classical physiological and nutritional studies related with food intake control, digestion, transport and absorption of nutrients. It continues with studies related with the metabolism of adipose tissue, and finish with modern experiments in genetics and molecular biology - all from a fresh, chronobiological point of view. Obesity will be explained as a fault in the circadian system, as pathology associated with "chronodisruption". The main gaps in chronobiological research related to obesity will be also identified and chronobiological-based therapies will be proposed in order to allow the resetting of the circadian rhythm among obese subjects.

The chronobiology, etiology and pathophysiology of obesity

The effect of CD on human health is an emerging issue. Many records link CD with diseases such as cancer, cardiovascular, cognitive impairment and obesity, all of them conducive to premature aging. The amount of sleep has declined by 1.5 h over the past century, accompanied by an important increase in obesity. Shift work, sleep deprivation and exposure to bright light at night increase the prevalence of adiposity. Animal models have shown that mice with Clock gene disruption are prone to developing obesity and MetS. This review summarizes the latest developments with regard to chronobiology and obesity, considering (1) how molecular clocks coordinate metabolism and the specific role of the adipocyte; (2) CD and its causes and pathological consequences; (3) the epidemiological evidence of obesity as a chronobiological illness; and (4) theories of circadian disruption and obesity. Energy intake and expenditure, relevance of sleep, fat intake from a circadian perspective and psychological and genetic aspects of obesity are examined. Finally, ideas about the use of chronobiology in the treatment of obesity are discussed. Such knowledge has the potential to become a valuable tool in the understanding of the relationship between the chronobiology, etiology and pathophysiology of obesity.

Circadian rhythms and metabolic syndrome: from experimental genetics to human disease

The incidence of the metabolic syndrome represents a spectrum of disorders that continue to increase across the industrialized world. Both genetic and environmental factors contribute to metabolic syndrome and recent evidence has emerged to suggest that alterations in circadian systems and sleep participate in the pathogenesis of the disease. In this review, we highlight studies at the intersection of clinical medicine and experimental genetics that pinpoint how perturbations of the internal clock system, and sleep, constitute risk factors for disorders including obesity, diabetes mellitus, cardiovascular disease, thrombosis and even inflammation. An exciting aspect of the field has been the integration of behavioral and physiological approaches, and the emerging insight into both neural and peripheral tissues in disease pathogenesis. Consideration of the cell and molecular links between disorders of circadian rhythms and sleep with metabolic syndrome has begun to open new opportunities for mechanism-based therapeutics.

CLOCK gene is implicated in weight reduction in obese patients participating in a dietary programme based on the Mediterranean diet

INTRODUCTION

The success of obesity therapy is dependent on the genetic background of the patient. Circadian Locomotor Output Cycles Kaput (CLOCK), one of the transcription factors from the positive limb of the molecular clock, is involved in metabolic alterations.

OBJECTIVE

To investigate whether five candidate polymorphisms from CLOCK were associated with anthropometric, metabolic measures and weight loss in response to a behavioural weight reduction programme based on the Mediterranean diet.

METHODS

Five hundred overweight/obese subjects, aged 20-65 years, who attended outpatient clinics specializing in obesity, were studied. Anthropometric, biochemical and dietary intake variables were analysed. Effectiveness of the programme and weight loss progression during 28 weeks of treatment was assessed.

RESULTS

Four of five CLOCK SNPs selected were significantly associated with obesity variables (P<0.05). The genetic variation in the rs1801260 CLOCK was associated with obesity at baseline and also affected weight loss. Patients with the variant allele (G) lost significantly less weight i(P=0.008) compared with wild type. Repeated measures analysis showed that weight loss over time was significantly different between rs1801260 CLOCK variations (P=0.038). Carriers of the G allele displayed greater difficulty in losing weight than non-carriers. In this particular polymorphism, the frequency of short-time sleepers (< or =6 h per day) was greater in minor allele carriers than in non-carriers (59% vs 41%; P<0.05). CLOCK polymorphisms were also associated with significant differences in total plasma cholesterol at the completion of dietary treatment (P<0.05).

CONCLUSIONS

We have replicated previous studies showing a relationship between CLOCK gene polymorphisms and obesity. CLOCK rs1801260 SNP may predict the outcome of body weight reduction strategies based on low-energy diets.

Circadian expression of adiponectin and its receptors in human adipose tissue

Adiponectin is one of the most clinically relevant cytokines associated with obesity. However, circadian rhythmicity of adiponectin in human adipose tissue (AT) has not been analyzed. To assess whether the mRNA levels of adiponectin and its receptors (ADIPOR1 and ADIPOR2) might show daily circadian rhythms in visceral and sc fat explants obtained from morbid obese women, visceral and sc abdominal AT biopsies (n = 6) were obtained from morbidly obese women (body mass index >or=40 kg/m(2)). Anthropometric variables were measured and fasting plasma glucose, lipid, and lipoprotein concentrations were analyzed. To investigate rhythmic expression pattern, AT explants were cultured during 24 h, and gene expression was analyzed at the following times: 0800, 1400, 2000, and 0200 h, using quantitative real-time PCR. All genes investigated showed a circadian rhythmicity and oscillated accurately and independently of the suprachiasmatic nucleus in both AT explants (P < 0.05). Adiponectin gene expression fluctuated in the same phase as its receptors. Correlation analyses between the genetic circadian oscillation and components of the metabolic syndrome revealed that adiposity and abdominal obesity correlated with a decrease in adiponectin and adiponectin receptors ADIPOR1 and ADIPOR2 amplitude (P < 0.05). Visceral fat showed a trend toward a phase delay and dampening of the mRNA amplitude of adiponectin as compared with sc fat. The mRNA expression of adiponectin and its receptors showed 24-h rhythmicity in human AT from morbidly obese patients.

Circadian rhythm of clock genes in human adipose explants

To analyze in severely obese women the circadian expression of the clock genes hPer2, hBmal1, and hCry1 in explants from subcutaneous (SAT) and visceral (VAT) adipose tissue (AT), in order to elucidate whether this circadian clockwork can oscillate accurately and independently of the suprachiasmatic nucleus (SCN) and if glucocorticoid metabolism-related genes such as glucocorticoid receptor (hGr) and 11beta-hydroxysteroid dehydrogenase 1 (h11 beta Hsd1) and the transcription factor peroxisome proliferator activated receptor gamma (hPPAR gamma) are part of the clock controlled genes. AT biopsies were obtained from morbid obese patients (BMI > or =40 kg/m(2)) (n = 7). Anthropometric variables were measured and fasting plasma lipids and lipoprotein concentrations were analyzed. In order to carry out rhythmic expression analysis, AT explants were cultured during 24 h and gene expression was performed at the following times (T): 0, 6, 12, and 18 h, with quantitative real-time PCR. Clock genes oscillated accurately and independently of the SCN in AT explants. Their intrinsic oscillatory mechanism regulated the timing of other genes such as hPPAR gamma and glucocorticoid-related genes. Circadian patterns differed between VAT and SAT. Correlation analyses between the genetic circadian oscillation and components of the metabolic syndrome (MetS) revealed that subjects with a higher sagittal diameter showed an increased circadian variability in hPer2 expression (r = 0.91; P = 0.031) and hBmal1 (r = 0.90; P = 0.040). Data demonstrate the presence of peripheral circadian oscillators in human AT independently of the central circadian control mechanism. This knowledge paves the way for a better understanding of the circadian contribution to medical conditions such as obesity and MetS.

Expression profile of mRNAs encoding core circadian regulatory proteins in human subcutaneous adipose tissue: correlation with age and body mass index

Objective

Circadian mechanisms underlie the physiology of mammals as an adaptation to the earth’s rotation on its axis. Highly conserved core circadian regulatory proteins (CCRP) maintain an oscillatory expression profile in the central and peripheral tissues. The CCRP include both a positive and negative arm as well as downstream transcriptional regulators. Recent studies in murine models have determined that the mRNAs encoding the CCRP are present in multiple adipose tissue depots and exhibit a robust oscillatory expression profile. The current study set out to examine the expression of CCRP mRNAs in human subcutaneous adipose tissues.

Design

Retrospective analysis of total RNA isolated from subcutaneous adipose tissue.

Subjects

150 healthy female and male lean (BMI < 25), overweight (BMI between 25 and 29.99) or obese (BMI >30) subjects of varied ethnic backgrounds undergoing elective liposuction or surgical procedures.

Results

The expression of the CCRP mRNAs displayed a significant correlation between each other and mRNAs representative of adipogenic biomarkers. Hierarchical cluster analyses of mRNAs isolated from the cohort of female Caucasian subjects (n = 116) identified three major clusters based on expression of downstream CCRP mRNAs. The mRNAs encoding D site of albumin promoter binding protein (DBP), E4 promoter binding protein 4 (E4BP4), PPARγ Co-Activator 1β (PGC-1β), and Rev-erb α were negatively correlated with BMI in a lean cluster (n = 66), positively correlated with BMI in a younger overweight/obese cluster (n = 19), and not significantly correlated with BMI in an older, overweight/obese cluster (n = 31).

Conclusions

These data confirm and extend findings that link the CCRP and circadian mechanisms to the risk of obesity.

Fat circadian biology

While adipose tissue has long been recognized for its major role in metabolism, it is now appreciated as an endocrine organ. A growing body of literature has emerged that identifies circadian mechanisms as a critical regulator of adipose tissue differentiation, metabolism, and adipokine secretory function in both health and disease. This concise review focuses on recent data from murine and human models that highlights the interplay between the core circadian regulatory proteins and adipose tissue in the context of energy, fat, and glucose metabolism. It will be important to integrate circadian mechanisms and networks into future descriptions of adipose tissue physiology.