Interleukin-6 contributes to early fasting-induced free fatty acid mobilization in mice

Gut microbiome remodeling and metabolomic profile improves in response to protein pacing with intermittent fasting versus continuous caloric restriction

The gut microbiome (GM) modulates body weight/composition and gastrointestinal functioning; therefore, approaches targeting resident gut microbes have attracted considerable interest. Intermittent fasting (IF) and protein pacing (P) regimens are effective in facilitating weight loss (WL) and enhancing body composition. However, the interrelationships between IF- and P-induced WL and the GM are unknown. The current randomized controlled study describes distinct fecal microbial and plasma metabolomic signatures between combined IF-P (n = 21) versus a heart-healthy, calorie-restricted (CR, n = 20) diet matched for overall energy intake in free-living human participants (women = 27; men = 14) with overweight/obesity for 8 weeks. Gut symptomatology improves and abundance of Christensenellaceae microbes and circulating cytokines and amino acid metabolites favoring fat oxidation increase with IF-P (p < 0.05), whereas metabolites associated with a longevity-related metabolic pathway increase with CR (p < 0.05). Differences indicate GM and metabolomic factors play a role in WL maintenance and body composition. This novel work provides insight into the GM and metabolomic profile of participants following an IF-P or CR diet and highlights important differences in microbial assembly associated with WL and body composition responsiveness. These data may inform future GM-focused precision nutrition recommendations using larger sample sizes of longer duration. Trial registration, March 6, 2020 (ClinicalTrials.gov as NCT04327141), based on a previous randomized intervention trial.

Interleukin-6 promotes visceral adipose tissue accumulation during aging via inhibiting fat lipolysis

BACKGROUND

Age-related visceral obesity could contribute to the development of cardiometabolic complications. The pathogenesis of visceral fat mass accumulation during the aging process remains complex and largely unknown. Interleukin-6 (IL-6) has emerged as one of the prominent inflammaging markers which are elevated in circulation during aging. However, the precise role of IL-6 in regulating age-related visceral adipose tissue accumulation remains uncertain.

RESULTS

A cross-sectional study including 77 older adults (≥65 years of age) was initially conducted. There was a significant positive association between serum IL-6 levels and visceral fat mass. We subsequently validated a modest but significant elevation in serum IL-6 levels in aged mice. Furthermore, we demonstrated that compared to wildtype control, IL-6 deficiency (IL-6 KO) significantly attenuated the accumulation of visceral adipose tissue during aging. Further metabolic characterization suggested that IL-6 deficiency resulted in improved lipid metabolism parameters and energy expenditure in aged mice. Moreover, histological examinations of adipose depots revealed that the absence of IL-6 ameliorated adipocyte hypertrophy in visceral adipose tissue of aged mice. Mechanically, the ablation of IL-6 could promote the PKA-mediated lipolysis and consequently mitigate lipid accumulation in adipose tissue in aged mice.

CONCLUSION

Our findings identify a detrimental role of IL-6 during the aging process by promoting visceral adipose tissue accumulation through inhibition of lipolysis. Therefore, strategies aimed at preventing or reducing IL-6 levels may potentially ameliorate age-related obesity and improve metabolism during aging.

Neuroprotective Effects of Intermittent Fasting in the Aging Brain

BACKGROUND

A major risk factor for neurodegenerative disorders is old age. Nutritional interventions that delay aging, such as calorie restriction (CR) and intermittent fasting (IF), as well as pharmaceuticals that affect the pathways linking nutrition and aging processes, have been developed in recent decades and have been shown to alleviate the effects of aging on the brain.

SUMMARY

CR is accomplished by alternating periods of ad libitum feeding and fasting. In animal models, IF has been shown to increase lifespan and slow the progression and severity of age-related pathologies such as cardiovascular and neurodegenerative diseases and cancer. According to recent research, dietary changes can help older people with dementia retain brain function. However, the mechanisms underlying the neuroprotective effect of IF on the aging brain and related questions in this area of study (i.e., the potential of IF to treat neurodegenerative disorders) remain to be examined.

KEY MESSAGES

This review addresses the hypothesis that IF may have translational potential in protecting the aged brain while summarizing the research supporting the putative neuroprotective mechanisms of IF in animal models. Additionally, given the emerging understanding of the connection between aging and dementia, our investigations may offer a fresh perspective on the use of dietary interventions for enhancing brain function and preventing dementia in elderly individuals. Finally, the absence of guidelines regarding the application of IF in patients hampers its broad utilization in clinical practice, and further studies are needed to improve our knowledge of the long-term effects of IF on dementia before it can be widely prescribed. In conclusion, IF may be an ancillary intervention for preserving memory and cognition in elderly individuals.

Acute exercise modulates the inflammatory response in adipose tissue in both lean and obese mice

OBJECTIVES

Acute physical exercise acts as a metabolic stressor, promoting activation of the immune system, and this response could be relevant in the adipose tissue remodeling process. In addition, some cytokines have important functions in lipolysis. Because chronic exercise improves obesity-related metabolic and inflammatory dysfunction, herein we investigated the effect of acute exercise on the inflammatory responses in the adipose tissues of lean and obese mice.

METHODS

Lean mice were fed a standard chow diet, whereas obese mice were fed a high-refined carbohydrate diet for 8 wk. Both groups were subjected to 60 min of moderate-intensity exercise.

RESULTS

In the epididymal adipose tissue of lean mice, exercise enhanced interleukin (IL)-6 and tumor necrosis factor-α levels, which correlated positively with increased serum free fatty acid concentrations. In vivo confocal imaging of epididymal adipose tissue vessels revealed higher recruitment of neutrophils after exercise. Also, the number of leukocytes expressing CD11b+F480- was elevated 6 h after exercise. Similarly, the chemokine (C-X-C motif) ligand 1 level increased at 6 h and remained high until 24 h after exercise. Myeloperoxidase activity was increased at 6, 12, and 24 h after exercise. Surprisingly, however, no changes were observed in epididymal adipose tissue from obese mice, considering proinflammatory cytokines (IL-6 and tumor necrosis factor-α). On the other hand, IL-13, IL-4, and IL-10 levels were higher in obese mice after exercise.

CONCLUSIONS

These data suggest that acute exercise promotes an inflammatory response in the adipose tissue of lean mice that is observed as part of its role in adipose tissue remodeling. In contrast, acute exercise promotes an antiinflammatory response in adipose tissue from obese mice, likely as an important tool for restoring homeostasis.

Association of plasma cytokines and antidepressant response following mild-intensity whole-body hyperthermia in major depressive disorder

Whole-body hyperthermia (WBH) shows promise for the treatment of major depressive disorder (MDD). Because MDD is associated with increased inflammation, and anti-inflammatory agents show some promise as antidepressants, the current study sought to identify the acute and longer-term immune effects of WBH in participants with MDD and to explore whether these effects associate with the procedure's antidepressant properties. Thirty participants who met DSM-IV-TR criteria for MDD were randomized to receive a single session of WBH (n = 16) or sham treatment (n = 14). Hamilton Depression Rating Scale (HDRS) scores were assessed at baseline and 1, 2, 4, and 6 weeks post-treatment (WBH vs. sham), and plasma cytokine concentrations were assessed at baseline, immediately post-treatment, and 1 and 4 weeks post-treatment. As previously reported, WBH produced a rapid and sustained antidepressant effect. When compared to sham, WBH increased plasma interleukin (IL)-6 immediately post-treatment (time by treatment: χ²_{(3, N=108)} = 47.33, p < 0.001), while having no effect on other cytokines acutely and no impact on IL-6, or any other cytokine, at 1 or 4 weeks post treatment. In the study sample as a whole, increased IL-6 post-treatment was associated with reduced HDRS depression scores over the 6 weeks of follow-up (F_{(1, 102.3)} = 6.74, p = 0.01). These results suggest a hitherto unrecognized relationship between hyperthermia, the immune system, and depression, and may point to WBH as a novel modality for exploring behavioral effects of IL-6 when the cytokine is activated in isolation from the inflammatory mediators with which it frequently travels.

The impact of fasting on adipose tissue metabolism

Fasting and starvation were common occurrences during human evolution and accordingly have been an important environmental factor shaping human energy metabolism. Humans can tolerate fasting reasonably well through adaptative and well-orchestrated time-dependent changes in energy metabolism. Key features of the adaptive response to fasting are the breakdown of liver glycogen and muscle protein to produce glucose for the brain, as well as the gradual depletion of the fat stores, resulting in the release of glycerol and fatty acids into the bloodstream and the production of ketone bodies in the liver. In this paper, an overview is presented of our current understanding of the effects of fasting on adipose tissue metabolism. Fasting leads to reduced uptake of circulating triacylglycerols by adipocytes through inhibition of the activity of the rate-limiting enzyme lipoprotein lipase. In addition, fasting stimulates the degradation of stored triacylglycerols by activating the key enzyme adipose triglyceride lipase. The mechanisms underlying these events are discussed, with a special interest in insights gained from studies on humans. Furthermore, an overview is presented of the effects of fasting on other metabolic pathways in the adipose tissue, including fatty acid synthesis, glucose uptake, glyceroneogenesis, autophagy, and the endocrine function of adipose tissue.

The Role of Crosstalk between Adipose Cells and Myocytes in the Pathogenesis of Sarcopenic Obesity in the Elderly

As a result of aging, body composition changes, with a decline in muscle mass and an increase in adipose tissue (AT), which reallocates from subcutaneous to visceral depots and stores ectopically in the liver, heart and muscles. Furthermore, with aging, muscle and AT, both of which have recognized endocrine activity, become dysfunctional and contribute, in the case of positive energy balance, to the development of sarcopenic obesity (SO). SO is defined as the co-existence of excess adiposity and low muscle mass and function, and its prevalence increases with age. SO is strongly associated with greater morbidity and mortality. The pathogenesis of SO is complex and multifactorial. This review focuses mainly on the role of crosstalk between age-related dysfunctional adipose and muscle cells as one of the mechanisms leading to SO. A better understanding of this mechanisms may be useful for development of prevention strategies and treatments aimed at reducing the occurrence of SO.

Adipose tissue macrophages in remote modulation of hepatic glucose production

Hepatic glucose production (HGP) is fine-regulated via glycogenolysis or gluconeogenesis to maintain physiological concentration of blood glucose during fasting-feeding cycle. Aberrant HGP leads to hyperglycemia in obesity-associated diabetes. Adipose tissue cooperates with the liver to regulate glycolipid metabolism. During these processes, adipose tissue macrophages (ATMs) change their profiles with various physio-pathological settings, producing diverse effects on HGP. Here, we briefly review the distinct phenotypes of ATMs under different nutrition states including feeding, fasting or overnutrition, and detail their effects on HGP. We discuss several pathways by which ATMs regulate hepatic gluconeogenesis or glycogenolysis, leading to favorable or unfavorable metabolic consequences. Furthermore, we summarize emerging therapeutic targets to correct metabolic disorders in morbid obesity or diabetes based on ATM-HGP axis. This review puts forward the importance and flexibility of ATMs in regulating HGP, proposing ATM-based HGP modulation as a potential therapeutic approach for obesity-associated metabolic dysfunction.

Remodeling of Macrophages in White Adipose Tissue under the Conditions of Obesity as well as Lipolysis

Adipose tissue macrophages (ATM) are a major source of low-grade inflammation in obesity, and yet reasons driving ATM accumulation in white adipose tissue (WAT) are not fully understood. Emerging evidence suggested that ATM underwent extensive remodeling in obesity. In addition to abundance, ATM in obesity were lipid-laden and metabolically reprogrammed, which in turn was tightly related to their functional alterations and persistence in obesity. Herein, we aimed to discuss that activation of lipid sensing signaling associated with metabolic reprogramming in ATM was indispensible for their migration, retention, or proliferation in obesity. Likewise, lipolysis also induced similar but transient ATM remodeling. Therefore, we assumed that obesity might share overlapping mechanisms with lipolysis in remodeling ATM. Formation of crown-like structures (CLS) in WAT was presumably a common event initiating ATM remodeling, with a spectrum of lipid metabolites released from adipocytes being potential signaling molecules. Moreover, adipose interlerkin-6 (IL-6) exhibited homologous alterations by obesity and lipolysis. Thus, we postulated a positive feedback loop between ATM and adipocytes via IL-6 signaling backing ATM persistence by comparison of ATM remodeling under obesity and lipolysis. An elucidation of ATM persistence could help to provide novel therapeutic targets for obesity-associated inflammation.

A Pilot Study of Associations Between Visceral Fat, IL-6, and Urinary F2-Isoprostanes in Older Adults Exposed to a Diet Intervention

BACKGROUND

Short-term markers of successful visceral adipose tissue (VAT) loss are needed. Urinary F2-isoprostanes might serve as a marker for intensified lipid metabolism, whereas circulating IL-6 might stimulate fat oxidation and enhance mobilization of VAT.

OBJECTIVES

This pilot study was designed to explore the hypotheses that 1) reduction in VAT is associated with increase in IL-6, and 2) that increases in urinary F2-isoprostanes are associated with increases in IL-6 and reduction in VAT.

METHODS

Eighteen participants (aged 60-75 y, BMI 30-40 kg/m2) were randomly assigned to either a very-low-carbohydrate diet (VLCD; <10:25:>65% energy from carbohydrate:protein:fat) or a low-fat diet (LFD; 55:25:20%) for 8 wk. Changes in fat distribution were assessed by MRI. Four urinary F2-isoprostane isomers were quantified in 24-h urine collection using LC-MS/MS analyses. Changes in 4 F2-isoprostane isomers were summarized using factor analysis (Δ-F2-isoprostane factor). Statistical significance was set at P < 0.1.

RESULTS

Within the VLCD group, change in VAT was inversely associated with change in IL-6 (r = -0.778, P = 0.069) and Δ-F2-isoprostane factor (r = -0.690, P = 0.086), demonstrating that participants who maintained higher concentrations of F2-isoprostane factor across the intervention showed greater decreases in VAT. A positive relation between Δ-F2-isoprostane factor and change in IL-6 was observed (r = 0.642, P = 0.062). In the LFD group, no significant associations between changes in VAT, F2-isoprostane factor, or IL-6 were observed.

CONCLUSIONS

Results from this exploratory study in older adults with obesity suggest that, in the context of a VLCD, IL-6 could be involved in VAT mobilization, and urinary F2-isoprostanes could reflect intensified oxidation of mobilized fatty acids.Trial registration: This study is registered at clinicaltrials.gov as NCT02760641.

Immuno-metabolic interfaces in cardiac disease and failure

The interplay between the cardiovascular system, metabolism, and inflammation plays a central role in the pathophysiology of a wide spectrum of cardiovascular diseases, including heart failure. Here, we provide an overview of the fundamental aspects of the interrelation between inflammation and metabolism, ranging from the role of metabolism in immune cell function to the processes how inflammation modulates systemic and cardiac metabolism. Furthermore, we discuss how disruption of this immuno-metabolic interface is involved in the development and progression of cardiovascular disease, with a special focus on heart failure. Finally, we present new technologies and therapeutic approaches that have recently emerged and hold promise for the future of cardiovascular medicine.

The IL-6 antagonist tocilizumab is associated with worse depression and related symptoms in the medically ill

Because medical illness is associated with increased inflammation and an increased risk for treatment-resistant major depressive disorder, anti-cytokine therapy may represent a novel, and especially efficacious, treatment for depression. We hypothesized that blockade of the interleukin (IL)-6 signaling pathway with tocilizumab would decrease depression and related symptomatology in a longitudinal cohort of allogeneic hematopoietic stem cell transplantation (HCT) patients, a medically ill population with a significant inflammation and psychopathology. Patients undergoing allogeneic HCT received either a single dose of tocilizumab one day prior to HCT (n = 25), or HCT alone (n = 62). The primary outcome included depressive symptoms at 28 days post HCT; anxiety, fatigue, sleep, and pain were assessed at pretreatment baseline and days +28, +100, and +180 post HCT as secondary outcomes. Multivariate regression demonstrated that preemptive treatment with tocilizumab was associated with significantly higher depression scores at D28 vs. the comparison group (β = 5.74; 95% CI 0.75, 10.73; P = 0.03). Even after adjustment for baseline depressive symptoms, propensity score, and presence of acute graft-versus-host disease (grades II-IV) and other baseline covariates, the tocilizumab-exposed group continued to have significantly higher depression scores compared to the nonexposed group at D28 (β = 4.73; 95% CI 0.64, 8.81; P = 0.02). Despite evidence that IL-6 antagonism would be beneficial, blockade of the IL-6 receptor with tocilizumab among medically ill patients resulted in significantly more-not less-depressive symptoms.

Hydrothermotherapy in prevention and treatment of mild to moderate cases of COVID-19

COVID-19 is a new contagious disease caused by a new coronavirus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is a disease that has reached every continent in the world; it has overloaded the medical system worldwide and it has been declared a pandemic by the World Health Organization. Currently there is no definite treatment for COVID-19. We realize that host immunity is a critical factor in the outcome of coronavirus 2 infection. Here, however, we review the pathophysiology of the disease with a focus on searching for what we can do to combat this new disease. From this, we find that coronavirus is sensitive to heat. We have thus focused on this area of vulnerability of the virus. The emphasis of this hypothesis is on the action of body heat-internal (fever) and external (heat treatment)-in activating the immune system and its antiviral activities, and specifically related to the coronavirus. We hypothesize from this review that heat treatments has the potential to prevent COVID-19 and to decrease the severity of mild and moderate cases of Coronavirus. We propose heat treatments for this uncontrolled worldwide coronavirus pandemic while studies are being done to test the effectiveness of heat treatments in the prevention and treatment of COVID-19.

Cardiotrophin-1 contributes to metabolic adaptations through the regulation of lipid metabolism and to the fasting-induced fatty acid mobilization

It is becoming clear that several human pathologies are caused by altered metabolic adaptations. During liver development, there are physiological changes, from the predominant utilization of glucose (fetal life) to the use of lipids (postnatal life). Fasting is another physiological stress that elicits well-known metabolic adjustments. We have reported the metabolic properties of cardiotrophin-1 (CT-1), a member of the interleukin-6 family of cytokines. Here, we aimed at analyzing the role of CT-1 in response to these metabolic changes. We used different in vivo models. Furthermore, a differential study was carried out with wild-type and CT-1 null mice in fed (ad libitum) and food-restricted conditions. We demonstrated that Ct-1 is a metabolic gene induced in the liver via PPARα in response to lipids in mice (neonates- and food-restricted adults). We found that Ct-1 mRNA expression in white adipose tissue directly involved PPARα and PPARγ. Finally, the physiological role of CT-1 in fasting is confirmed by the impaired food restriction-induced adipose tissue lipid mobilization in CT-1 null mice. Our findings support a previously unrecognized physiological role of CT-1 in metabolic adaptations, through the regulation of lipid metabolism and contributes to fasting-induced free fatty acid mobilization.

Extramyocellular interleukin-6 influences skeletal muscle mitochondrial physiology through canonical JAK/STAT signaling pathways

Interleukin-6 (IL-6) is a pleiotropic cytokine that has been shown to be produced acutely by skeletal muscle in response to exercise, yet chronically elevated with obesity and aging. The mechanisms by which IL-6 influences skeletal muscle mitochondria acutely and chronically are unclear. To better understand the influence of extramyocellular IL-6 on skeletal muscle mitochondrial physiology, we treated differentiated myotubes with exogenous IL-6 to evaluate the dose- and duration-dependent effects of IL-6 on salient aspects of mitochondrial biology and the role of canonical IL-6 signaling in muscle cells. Acute exposure of myotubes to IL-6 increased the mitochondrial reactive oxygen species (mtROS) production and oxygen consumption rates (JO₂ ) in a manner that was dependent on activation of the JAK/STAT pathway. Furthermore, STAT3 activation by IL-6 was partly attenuated by MitoQ, a mitochondrial-targeted antioxidant, suggesting that mtROS potentiates STAT3 signaling in skeletal muscle in response to IL-6 exposure. In concert with effects on mitochondrial physiology, acute IL-6 exposure induced several mitochondrial adaptations, consistent with the stress-induced mitochondrial hyperfusion. Exposure of myotubes to chronically elevated IL-6 further increased mtROS with eventual loss of respiratory capacity. These data provide new evidence supporting the interplay between cytokine signaling and mitochondrial physiology in skeletal muscle.

The controversial role of IL-6 in adipose tissue on obesity-induced dysregulation of glucose metabolism

Interleukin (IL)-6 is a pleotropic cytokine with various physiological and pathophysiological functions in different cells and tissues. In cells residing within white adipose tissue, several, and sometimes conflicting, IL-6 actions have been described in the development of obesity-associated derangements of glucose metabolism. Herein, we aim to summarize opposing findings and discuss recent evidence that IL-6 signaling in adipose tissue is regulated in a depot and cell-specific manner.

Pro- and anti-inflammatory properties of interleukin (IL6) in vitro: relevance for major depression and for human hippocampal neurogenesis

BACKGROUND

Although the pro-inflammatory cytokine, interleukin (IL)6, has been generally regarded as "depressogenic", recent research has started to question this assumption, in light of the fact that this cytokine can also have anti-inflammatory properties. This bimodal action seems to be dependent on its concentration levels, and on the concomitant presence of other pro-inflammatory cytokines.

METHODS

We exposed a human hippocampal progenitor cell line HPC0A07/03C to cytokine levels described in depressed patients (IL6 5pg/ml with IL1β 10pg/ml or Macrophage Migration Inhibitory Factor (MIF) 300pg/ml), in healthy subjects (IL6 with IL1β, 1pg/ml or MIF 10pg/ml), as well as to the potentially anti-inflammatory, much higher concentrations of IL6 (50000pg/ml).

RESULTS

Treatment with high concentrations of IL6 with IL1β or MIF (resembling depressed patients) decreases neurogenesis when compared with low concentrations of the same cytokines (healthy subjects), and that this is mediated via production of, respectively, IL8 and IL1β in cell supernatant. Instead, treatment with the very high, anti-inflammatory concentration of IL6 (50000pg/ml) together with high IL1β or MIF prevents the decrease in neurogenesis and reduces both IL8 and IL1β. When the high concentrations of both IL1β and MIF were used in co-treatment, as a model of treatment resistant depression, we also demonstrate a reduction in neurogenesis, and that this is mediated via a decrease in IL4; moreover, co-treatment with high IL1β and MIF and the very high concentration of IL6 prevents the reduction in neurogenesis, and increases IL4.

CONCLUSIONS

Our results demonstrate that IL6 can exert both pro- and anti-inflammatory (potentially antidepressant) properties, depending on its concentrations and combinations with other inflammatory cytokines.

Intermittent fasting, adipokines, insulin sensitivity, and hypothalamic neuropeptides in a dietary overload with high-fat or high-fructose diet in mice

The intermittent fasting (IF) might have benefits on metabolism and food intake. Twelve-week old C57BL/6 J mice were fed a control diet (C, 10% kcal fat), a high-fat diet (HF, 50% kcal fat) or a high-fructose diet (HFru, 50% kcal fructose) for 8 weeks, then half of the animals in each group underwent IF (24 h fed, 24 h fasting) for an additional 4 weeks. Although food intake on the fed day remained the same for all groups, all fasting groups showed a reduction in body mass compared to their counterparts. IF reduced total cholesterol, triacylglycerol, fasting glucose, fasting insulin resistance index, and plasma leptin, but increased plasma adiponectin. IF reduced Leptin gene expression in the HF-IF group, but increased proinflammatory markers in the hypothalamus, also in the C-IF group. Both groups HFru-IF and C-IF, showed alterations in the leptin signaling pathway (Leptin, OBRb, and SOCS3), mainly in the HFru-IF group, suggesting leptin resistance. NPY and POMC neuropeptides labeled the neurons of the hypothalamus by immunofluorescence, corroborating qualitatively other quantitative findings of the study. In conclusion, current results are convincing in demonstrating the IF effect on central regulation of food intake control, as shown by NPY and POMC neuropeptide expressions, resulting in a lower weight gain. Besides, IF improves glycemia, lipid metabolism, and consequently insulin and leptin resistance. However, there is increased expression of inflammatory markers in mouse hypothalamus challenged by the HF and HFru diets, which in the long term may induce adverse effects.

Impact of adipokines and myokines on fat browning

Since the discovery of leptin in 1994, the adipose tissue (AT) is not just considered a passive fat storage organ but also an extremely active secretory and endocrine organ that secretes a large variety of hormones, called adipokines, involved in energy metabolism. Adipokines may not only contribute to AT dysfunction and obesity, but also in fat browning, a process that induces a phenotypic switch from energy-storing white adipocytes to thermogenic brown fat-like cells. The fat browning process and, consequently, thermogenesis can also be stimulated by physical exercise. Contracting skeletal muscle is a metabolically active tissue that participates in several endocrine functions through the production of bioactive factors, collectively termed myokines, proposed as the mediators of physical activity-induced health benefits. Myokines affect muscle mass, have profound effects on glucose and lipid metabolism, and promote browning and thermogenesis of white AT in an endocrine and/or paracrine manner. The present review focuses on the role of different myokines and adipokines in the regulation of fat browning, as well as in the potential cross-talk between AT and skeletal muscle, in order to control body weight, energy expenditure and thermogenesis.

Intermittent fasting improves metabolic flexibility in short-term high-fat diet-fed mice

Four days of high-fat diet (HFD) feeding are sufficient to induce glucose intolerance and hepatic steatosis in mice. While prolonged HFD-induced metabolic complications are partly mediated by increased food intake during the light (inactive) phase, such a link has not yet been established in short-term HFD-fed mice. Herein, we hypothesized that a short bout of HFD desynchronizes feeding behavior, thereby contributing to glucose intolerance and hepatic steatosis. To this end, 12-wk-old C57BL/6J littermates were fed a HFD for 4 days either ad libitum or intermittently. Intermittent-fed mice were fasted for 8 h during their inactive phase. Initiation of HFD led to an immediate increase in food intake already during the first light phase. Moreover, glucose tolerance was significantly impaired in ad libitum- but not in intermittent HFD-fed mice, indicating that desynchronized feeding behavior contributes to short-term HFD-induced glucose intolerance. Of note, overall food intake was similar between the groups, as was body weight. However, intermittent HFD-fed mice revealed higher fat depot weights. Phosphorylation of hormone sensitivity lipase and free fatty acid release from isolated adipocytes were significantly elevated, suggesting increased lipolysis in intermittent HFD-fed mice. Moreover, hepatic mRNA expression of lipogenetic enzymes and liver triglyceride levels were significantly increased in intermittent HFD-fed mice. Importantly, food deprivation decreased respiratory exchange ratio promptly in intermittent- but not in ad libitum HFD-fed mice. In conclusion, retaining a normal feeding pattern prevented HFD-induced impairment of metabolic flexibility in short-term HFD-fed mice.

Beyond adiponectin and leptin: adipose tissue-derived mediators of inter-organ communication

The breakthrough discoveries of leptin and adiponectin more than two decades ago led to a widespread recognition of adipose tissue as an endocrine organ. Many more adipose tissue-secreted signaling mediators (adipokines) have been identified since then, and much has been learned about how adipose tissue communicates with other organs of the body to maintain systemic homeostasis. Beyond proteins, additional factors, such as lipids, metabolites, noncoding RNAs, and extracellular vesicles (EVs), released by adipose tissue participate in this process. Here, we review the diverse signaling mediators and mechanisms adipose tissue utilizes to relay information to other organs. We discuss recently identified adipokines (proteins, lipids, and metabolites) and briefly outline the contributions of noncoding RNAs and EVs to the ever-increasing complexities of adipose tissue inter-organ communication. We conclude by reflecting on central aspects of adipokine biology, namely, the contribution of distinct adipose tissue depots and cell types to adipokine secretion, the phenomenon of adipokine resistance, and the capacity of adipose tissue to act both as a source and sink of signaling mediators.

Immunometabolic cross-talk in the inflamed heart

Inflammatory processes underlie many diseases associated with injury of the heart muscle, including conditions without an obvious inflammatory pathogenic component such as hypertensive and diabetic cardiomyopathy. Persistence of cardiac inflammation can cause irreversible structural and functional deficits. Some are induced by direct damage of the heart muscle by cellular and soluble mediators but also by metabolic adaptations sustained by the inflammatory microenvironment. It is well established that both cardiomyocytes and immune cells undergo metabolic reprogramming in the site of inflammation, which allow them to deal with decreased availability of nutrients and oxygen. However, like in cancer, competition for nutrients and increased production of signalling metabolites such as lactate initiate a metabolic cross-talk between immune cells and cardiomyocytes which, we propose, might tip the balance between resolution of the inflammation versus adverse cardiac remodeling. Here we review our current understanding of the metabolic reprogramming of both heart tissue and immune cells during inflammation, and we discuss potential key mechanisms by which these metabolic responses intersect and influence each other and ultimately define the prognosis of the inflammatory process in the heart.

Effect of skeletal muscle phenotype and gender on fasting-induced myokine expression in mice

Skeletal muscle secretes myokines, which are involved in metabolism and muscle function regulation. The role of fasting on myokine expression in skeletal muscle is largely unknown. In this study, we used gastrocnemius skeletal muscle RNA sequencing data from fasting male mice in the Gene Expression Omnibus (GEO) database. Adopted male and female C57BL/6J mice that fasted for 24 h were included to examine the effect of fasting on myokine expression in slow-twitch soleus and fast-twitch tiabialis anterior (TA) skeletal muscle. We found that fasting significantly affected many myokines in muscle. Fasting reduced Fndc5 and Igf1 gene expression in soleus and TA muscles in both male and female mice without muscle phenotype or gender differences, but Il6, Mstn and Erfe expression was influenced by fasting with fibre type- and gender-dependent effects. Fasting also induced muscle atrophy marker genes Murf1 and Fbxo32 and reduced myogenesis factor Mef2 expression without muscle fibre or gender differences. We further found that the expression of transcription factors Pgc1α, Pparα, Pparγ and Pparδ had muscle fibre type-dependent effects, and the expression of Pgc1α and Pparα had gender-dependent effects. The sophisticated expression pattern of myokines would partially explain the complicated cross-talk between skeletal muscle and other organs in different genders and muscles phenotypes, and it is worth further investigation.

Walnuts change lipoprotein composition suppressing TNFα-stimulated cytokine production by diabetic adipocyte

Walnut consumption can provide both vascular and metabolic health benefits, and walnut-induced changes in lipoprotein particle chemical payloads may be responsible for these health benefits. To explore this possibility with a focus on metabolic health, this study investigated the impact of walnut consumption on lipoprotein lipid composition and changes in LDL anti-inflammatory properties, as reported by inflamed adipocyte. Hypercholesterolemic, postmenopausal females were treated with 40 g/day (i.e., 1.6 servings/day; n=15) of walnuts for 4 weeks. Fatty acids and their oxygenated metabolites, i.e., oxylipins, were quantified in isolated lipoproteins. Human primary adipocytes were exposed to LDL and TNFα-stimulated adipokine production was measured. Walnut treatment elevated α-linolenic acid and its epoxides in all lipoproteins and depleted mid-chain alcohols in VLDL and LDL, but not HDL. Walnuts also reduced TNFα-induced diabetic adipocyte production of IL-6 (-48%, P=.0006) and IL-8 (-30%, P=.01), changes inversely correlated with levels of α-linolenic acid-derived epoxides but not α-linolenic acid itself. In conclusion, modest walnut consumption can alter lipoprotein lipid profiles and enhance their ability to inhibit TNFα-dependent pro-inflammatory responses in human diabetic primary adipocytes. Moreover, this study suggests the oxylipins, rather than the parent fatty acids, mediate LDL action of adipocytes.

Endocrine Crosstalk Between Skeletal Muscle and the Brain

Skeletal muscle is an essential regulator of energy homeostasis and a potent coordinator of exercise-induced adaptations in other organs including the liver, fat or the brain. Skeletal muscle-initiated crosstalk with other tissues is accomplished though the secretion of myokines, protein hormones which can exert autocrine, paracrine and long-distance endocrine effects. In addition, the enhanced release or uptake of metabolites from and into contracting muscle cells, respectively, likewise can act as a powerful mediator of tissue interactions, in particular in regard to the central nervous system. The present review will discuss the current stage of knowledge regarding how exercise and the muscle secretome improve a broad range of brain functions related to vascularization, neuroplasticity, memory, sleep and mood. Even though the molecular and cellular mechanisms underlying the communication between muscle and brain is still poorly understood, physical activity represents one of the most effective strategies to reduce the prevalence and incidence of depression, cognitive, metabolic or degenerative neuronal disorders, and thus warrants further study.

Impact of skeletal muscle IL-6 on regulation of liver and adipose tissue metabolism during fasting

The liver and adipose tissue are important tissues in whole-body metabolic regulation during fasting. Interleukin 6 (IL-6) is a cytokine shown to be secreted from contracting muscle in humans and suggested to signal to the liver and adipose tissue. Furthermore, skeletal muscle IL-6 has been proposed to play a role during fasting. Therefore the aim of the present study was to investigate the role of skeletal muscle IL-6 in the regulation of substrate production in the liver and adipose tissue during fasting. Male skeletal muscle-specific IL-6 knockout (IL-6 MKO) mice and littermate floxed (control) mice fasted for 6 or 18 h (6 h fasting or 18 h fasting) with corresponding fed control groups (6 h fed or 18 h fed) and liver and adipose tissue were quickly obtained. Plasma β-hydroxybutyrate increased and hepatic glucose, lactate and glycogen decreased with fasting. In addition, fasting increased phosphoenolpyruvate carboxykinase protein and phosphorylation of pyruvate dehydrogenase (PDH) in the liver as well as hormone-sensitive lipase (HSL)^Ser660 and HSL^Ser563 phosphorylation, PDH phosphorylation, adipose triglyceride lipase phosphorylation and perilipin phosphorylation and protein content in adipose tissue without any effect of lack of skeletal muscle IL-6. In conclusion, fasting induced regulation of enzymes in adipose tissue lipolysis and glyceroneogenesis as well as regulation of hepatic gluconeogenic capacity and hepatic substrate utilization in mice. However, skeletal muscle IL-6 was not required for these fasting-induced effects, but had minor effects on markers of lipolysis and glyceroneogenesis in adipose tissue as well as markers of hepatic gluconeogenesis in the fed state.

Interleukin-6 as a "metabolic hormone"

Interleukin 6 (IL-6) is a cytokine that is involved in divers immune responses and implicated in a number of diseases. However, this cytokine has other non-immune functions. Within this review, we highlight selected effects on metabolic pathways, which are mediated, controlled or modified by the IL-6. Importantly, putting spotlight on such concepts could allow us to classify IL-6 among the metabolic hormones and further study it to both deepen our knowledge on disorders involving metabolic or energy imbalances such as obesity and develop novel therapeutic strategies. Furthermore, potential explanations related to IL-6 roles in both physiology and pathology as well as relevant implications and applications on both research and therapeutic fields are also pointed as consequences of the involvement of IL-6 in the energy and metabolic homeostasis via its "endocrine" roles.

Intermittent metabolic switching, neuroplasticity and brain health

During evolution, individuals whose brains and bodies functioned well in a fasted state were successful in acquiring food, enabling their survival and reproduction. With fasting and extended exercise, liver glycogen stores are depleted and ketones are produced from adipose-cell-derived fatty acids. This metabolic switch in cellular fuel source is accompanied by cellular and molecular adaptations of neural networks in the brain that enhance their functionality and bolster their resistance to stress, injury and disease. Here, we consider how intermittent metabolic switching, repeating cycles of a metabolic challenge that induces ketosis (fasting and/or exercise) followed by a recovery period (eating, resting and sleeping), may optimize brain function and resilience throughout the lifespan, with a focus on the neuronal circuits involved in cognition and mood. Such metabolic switching impacts multiple signalling pathways that promote neuroplasticity and resistance of the brain to injury and disease.

Exercise Protects Against Olanzapine-Induced Hyperglycemia in Male C57BL/6J Mice

Olanzapine is a widely prescribed antipsychotic drug. While effective in reducing psychoses, treatment with olanzapine causes rapid increases in blood glucose. We wanted to determine if a single bout of exercise, immediately prior to treatment, would attenuate the olanzapine-induced rise in blood glucose and if this occurred in an IL-6 dependent manner. We found that exhaustive, but not moderate exercise, immediately prior to treatment, prevented olanzapine-induced hyperglycemia and this occurred in parallel with increases in serum IL-6. To determine if IL-6 was involved in the mechanisms through which exhaustive exercise protected against olanzapine-induced hyperglycemia several additional experiments were completed. Treatment with IL-6 (3 ng/g bw, IP) alone did not protect against olanzapine-induced increases in blood glucose. The protective effects of exhaustive exercise against olanzapine-induced increases in blood glucose were intact in whole body IL-6 knockout mice. Similarly, treating mice with an IL-6 neutralizing antibody prior to exhaustive exercise did not negate the protective effect of exercise against olanzapine-induced hyperglycemia. Our findings provide evidence that a single bout of exhaustive exercise protects against acute olanzapine-induced hyperglycemia and that IL-6 is neither sufficient, nor required for exercise to protect against increases in blood glucose with olanzapine treatment.

Skeletal muscle IL-6 regulates muscle substrate utilization and adipose tissue metabolism during recovery from an acute bout of exercise

An acute bout of exercise imposes a major challenge on whole-body metabolism and metabolic adjustments are needed in multiple tissues during recovery to reestablish metabolic homeostasis. It is currently unresolved how this regulation is orchestrated between tissues. This study was undertaken to clarify the role of skeletal muscle derived interleukin 6 (IL-6) in the coordination of the metabolic responses during recovery from acute exercise. Skeletal muscle specific IL-6 knockout (IL-6 MKO) and littermate Control mice were rested or ran on a treadmill for 2h. Plasma, skeletal muscle, liver and adipose tissue were obtained after 6 and 10h of recovery. Non-exercised IL-6 MKO mice had higher plasma lactate and lower plasma non-esterified fatty acids than Controls. The activity of pyruvate dehydrogenase in the active form was, in skeletal muscle, higher in IL-6 MKO mice than Controls in non-exercised mice and 6h after exercise. IL-6 MKO mice had lower glucose transporter 4 protein content in inguinal adipose tissue (WAT) than Control in non-exercised mice and 10h after treadmill running. Epididymal WAT hormone sensitive lipase phosphorylation and inguinal WAT mitogen activated kinase P38 phosphorylation were higher in IL-6 MKO than Control mice 6h after exercise. These findings indicate that skeletal muscle IL-6 may play an important role in the regulation of substrate utilization in skeletal muscle, basal and exercise-induced adaptations in adipose tissue glucose uptake and lipolysis during recovery from exercise. Together this indicates that skeletal muscle IL-6 contributes to reestablishing metabolic homeostasis during recovery from exercise by regulating WAT and skeletal muscle metabolism.

PGC-1α and fasting-induced PDH regulation in mouse skeletal muscle

The purpose of the present study was to examine whether lack of skeletal muscle peroxisome proliferator‐activated receptor gamma coactivator 1 alpha (PGC‐1α) affects the switch in substrate utilization from a fed to fasted state and the fasting‐induced pyruvate dehydrogenase (PDH) regulation in skeletal muscle. Skeletal muscle‐specific PGC‐1α knockout (MKO) mice and floxed littermate controls were fed or fasted for 24 h. Fasting reduced PDHa activity, increased phosphorylation of all four known sites on PDH‐E1α and increased pyruvate dehydrogenase kinase (PDK4) and sirtuin 3 (SIRT3) protein levels, but did not alter total acetylation of PDH‐E1α. Lack of muscle PGC‐1α did not affect the switch from glucose to fat oxidation in the transition from the fed to fasted state, but was associated with lower and higher respiratory exchange ratio (RER) in the fed and fasted state, respectively. PGC‐1α MKO mice had lower skeletal muscle PDH‐E1α, PDK1, 2, 4, and pyruvate dehydrogenase phosphatase (PDP1) protein content than controls, but this did not prevent the fasting‐induced increase in PDH‐E1α phosphorylation in PGC‐1α MKO mice. However, lack of skeletal muscle PGC‐1α reduced SIRT3 protein content, increased total lysine PDH‐E1α acetylation in the fed state, and prevented a fasting‐induced increase in SIRT3 protein. In conclusion, skeletal muscle PGC‐1α is required for fasting‐induced upregulation of skeletal muscle SIRT3 and maintaining high fat oxidation in the fasted state, but is dispensable for preserving the capability to switch substrate during the transition from the fed to the fasted state and for fasting‐induced PDH regulation in skeletal muscle.

Impact of fasting followed by short-term exposure to interleukin-6 on cytochrome P450 mRNA in mice

The gene expression of the cytochrome P450 (CYP) enzyme family is regulated by numerous factors. Fasting has been shown to induce increased hepatic CYP mRNA in both humans and animals. However, the coordinated regulation of CYP, CYP-regulating transcription factors, and transcriptional co-factors in the liver linking energy metabolism to detoxification has never been investigated. Interleukin-6 (IL-6) has been suggested to be released during fasting and has been shown to regulate CYP expression. The present study investigated the hepatic mRNA content of selected CYP, AhR, CAR, PXR and PPARα in mice fasted for 18h and subsequently exposed to IL-6. Furthermore, the impact of fasting on PGC-1α, HNF-4α, SIRT1 and SIRT3 mRNA was examined. Fasting induced a marked increase in Cyp2b10, Cyp2e1 and Cyp4a10 mRNA, while CYP1a1, Cyp1a2, Cyp2a4 and Cyp3a11 mRNA levels remained unchanged. In accordance, the mRNA levels of CAR and PPARα were also increased with fasting. The PGC-1α, SIRT1 and SIRT3 mRNA levels were also increased after fasting, while the HNF-4α mRNA levels remained unchanged. In mice subjected to IL-6 injection, the fasting-induced PXR, PPARα and PGC-1α mRNA responses were lower than after saline injection. In conclusion, fasting was demonstrated to be a strong inducer of hepatic CYP mRNA as well as selected transcription factors controlling the expression of the investigated CYP. Moreover, the mRNA levels of transcriptional co-factors acting as energy sensors and co-factors for CYP regulation was also increased in the liver, suggesting crosstalk at the molecular level between regulation of energy metabolism and detoxification.

Muscle interleukin-6 and fasting-induced PDH regulation in mouse skeletal muscle

Fasting prompts a metabolic shift in substrate utilization from carbohydrate to predominant fat oxidation in skeletal muscle, and pyruvate dehydrogenase (PDH) is seen as a controlling link between the competitive oxidation of carbohydrate and fat during metabolic challenges like fasting. Interleukin (IL)-6 has been proposed to be released from muscle with concomitant effects on both glucose and fat utilization. The aim was to test the hypothesis that muscle IL-6 has a regulatory impact on fasting-induced suppression of skeletal muscle PDH. Skeletal muscle-specific IL-6 knockout (IL-6 MKO) mice and floxed littermate controls (control) were either fed or fasted for 6 or 18 h. Lack of muscle IL-6 elevated the respiratory exchange ratio in the fed and early fasting state, but not with prolonged fasting. Activity of PDH in the active form (PDHa) was higher in fed and fasted IL-6 MKO than in control mice at 18 h, but not at 6 h, whereas lack of muscle IL-6 did not prevent downregulation of PDHa activity in skeletal muscle or changes in plasma and muscle substrate levels in response to 18 h of fasting. Phosphorylation of three of four sites on PDH-E1α increased with 18 h of fasting, but was lower in IL-6 MKO mice than in control. In addition, both PDK4 mRNA and protein increased with 6 and 18 h of fasting in both genotypes, but PDK4 protein was lower in IL-6 MKO than in control. In conclusion, skeletal muscle IL-6 seems to regulate whole body substrate utilization in the fed, but not fasted, state and influence skeletal muscle PDHa activity in a circadian manner. However, skeletal muscle IL-6 is not required for maintaining metabolic flexibility in response to fasting.

The Obesity-Impulsivity Axis: Potential Metabolic Interventions in Chronic Psychiatric Patients

Pathological impulsivity is encountered in a broad range of psychiatric conditions and is thought to be a risk factor for aggression directed against oneself or others. Recently, a strong association was found between impulsivity and obesity which may explain the high prevalence of metabolic disorders in individuals with mental illness even in the absence of exposure to psychotropic drugs. As the overlapping neurobiology of impulsivity and obesity is being unraveled, the question asked louder and louder is whether they should be treated concomitantly. The treatment of obesity and metabolic dysregulations in chronic psychiatric patients is currently underutilized and often initiated late, making correction more difficult to achieve. Addressing obesity and metabolic dysfunction in a preventive manner may not only lower morbidity and mortality but also the excessive impulsivity, decreasing the risk for aggression. In this review, we take a look beyond psychopharmacological interventions and discuss dietary and physical therapy approaches.

CD301b(+) Mononuclear Phagocytes Maintain Positive Energy Balance through Secretion of Resistin-like Molecule Alpha

Mononuclear phagocytes (MNPs) are a highly heterogeneous group of cells that play important roles in maintaining the body's homeostasis. Here, we found CD301b (also known as MGL2), a lectin commonly used as a marker for alternatively activated macrophages, was selectively expressed by a subset of CD11b(+)CD11c(+)MHCII(+) MNPs in multiple organs including adipose tissues. Depleting CD301b(+) MNPs in vivo led to a significant weight loss with increased insulin sensitivity and a marked reduction in serum Resistin-like molecule (RELM) α, a multifunctional cytokine produced by MNPs. Reconstituting RELMα in CD301b(+) MNP-depleted animals restored body weight and normoglycemia. Thus, CD301b(+) MNPs play crucial roles in maintaining glucose metabolism and net energy balance.

Mesenteric Fat Lipolysis Mediates Obesity-Associated Hepatic Steatosis and Insulin Resistance

Hepatic steatosis and insulin resistance are among the most prevalent metabolic disorders and are tightly associated with obesity and type 2 diabetes. However, the underlying mechanisms linking obesity to hepatic lipid accumulation and insulin resistance are incompletely understood. Glycoprotein 130 (gp130) is the common signal transducer of all interleukin 6 (IL-6) cytokines. We provide evidence that gp130-mediated adipose tissue lipolysis promotes hepatic steatosis and insulin resistance. In obese mice, adipocyte-specific gp130 deletion reduced basal lipolysis and enhanced insulin's ability to suppress lipolysis from mesenteric but not epididymal adipocytes. Consistently, free fatty acid levels were reduced in portal but not in systemic circulation of obese knockout mice. Of note, adipocyte-specific gp130 knockout mice were protected from high-fat diet-induced hepatic steatosis as well as from insulin resistance. In humans, omental but not subcutaneous IL-6 mRNA expression correlated positively with liver lipid accumulation (r = 0.31, P < 0.05) and negatively with hyperinsulinemic-euglycemic clamp glucose infusion rate (r = -0.28, P < 0.05). The results show that IL-6 cytokine-induced lipolysis may be restricted to mesenteric white adipose tissue and that it contributes to hepatic insulin resistance and steatosis. Therefore, blocking IL-6 cytokine signaling in (mesenteric) adipocytes may be a novel approach to blunting detrimental fat-liver crosstalk in obesity.

Skeletal muscle as an endocrine organ: PGC-1α, myokines and exercise

An active lifestyle is crucial to maintain health into old age; inversely, sedentariness has been linked to an elevated risk for many chronic diseases. The discovery of myokines, hormones produced by skeletal muscle tissue, suggests the possibility that these might be molecular mediators of the whole body effects of exercise originating from contracting muscle fibers. Even though less is known about the sedentary state, the lack of contraction-induced myokines or the production of a distinct set of hormones in the inactive muscle could likewise contribute to pathological consequences in this context. In this review, we try to summarize the most recent developments in the study of muscle as an endocrine organ and speculate about the potential impact on our understanding of exercise and sedentary physiology, respectively. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Lipolytic and thermogenic depletion of adipose tissue in cancer cachexia

Although muscle wasting is the obvious manifestation of cancer cachexia that impacts on patient quality of life, the loss of lipid reserves and metabolic imbalance in adipose tissue also contribute to the devastating impact of cachexia. Depletion of fat depots in cancer patients is more pronounced than loss of muscle and often precedes, or even occurs in the absence of, reduced lean body mass. Rapid mobilisation of triglycerides stored within adipocytes to supply the body with fatty acids in periods of high-energy demand is normally mediated through a well-defined process of lipolysis involving the lipases ATGL, HSL and MGL. Studies into how these lipases contribute to fat loss in cancer cachexia have revealed the prominent role for ATGL in initiating lipolysis during adipose tissue atrophy, together with links between tumour-derived factors and the signalling pathways that control lipid flux within fat cells. The recent findings of increased thermogenesis in brown fat during cancer cachexia indicate that metabolically active adipose tissue contributes to the imbalance in energy homeostasis involved in catabolic wasting. Such energetically futile use of fatty acids liberated from adipose tissue to generate heat represents a maladaptive response in conjunction with anorexia experienced by cancer patients. As IL-6 release by tumours provokes lipolysis and activates the thermogenic programme in brown fat, this review explores the overlap in dysregulated metabolic processes due to inflammatory mediators in cancer cachexia and other disease states characterised by elevated cytokines such as obesity and diabetes.

Differential regulation of metabolic parameters by energy deficit and hunger

AIMS

Hypocaloric diet decreases both energy expenditure (EE) and respiratory exchange rate (RER), affecting the efficacy of dieting inversely. Energy deficit and hunger may be modulated separately both in human and animal studies by drug treatment or food restriction. Thus it is important to separate the effects of energy deficit and hunger on EE and RER.

METHODS

Three parallel and analogous experiments were performed using three pharmacologically distinct anorectic drugs: rimonabant, sibutramine and tramadol. Metabolic parameters of vehicle- and drug-treated and pair-fed diet-induced obese mice from the three experiments underwent common statistical analysis to identify effects independent of the mechanisms of action. Diet-induced obesity (DIO) test of tramadol was also performed to examine its anti-obesity efficacy.

RESULTS

RER was decreased similarly by drug treatments and paired feeding throughout the experiment irrespective of the cause of reduced food intake. Contrarily, during the passive phase, EE was decreased more by paired feeding than by both vehicle and drug treatment irrespective of the drug used. In the active phase, EE was influenced by the pharmacological mechanisms of action. Tramadol decreased body weight in the DIO test.

CONCLUSIONS

Our results suggest that RER is mainly affected by the actual state of energy balance; conversely, EE is rather influenced by hunger. Therefore, pharmacological medications that decrease hunger may enhance the efficacy of a hypocaloric diet by maintaining metabolic rate. Furthermore, our results yield the proposal that effects of anorectic drugs on EE and RER should be determined compared to vehicle and pair-fed groups, respectively, in animal models.

Human skeletal myotubes display a cell-autonomous circadian clock implicated in basal myokine secretion

OBJECTIVE

Circadian clocks are functional in all light-sensitive organisms, allowing an adaptation to the external world in anticipation of daily environmental changes. In view of the potential role of the skeletal muscle clock in the regulation of glucose metabolism, we aimed to characterize circadian rhythms in primary human skeletal myotubes and investigate their roles in myokine secretion.

METHODS

We established a system for long-term bioluminescence recording in differentiated human myotubes, employing lentivector gene delivery of the Bmal1-luciferase and Per2-luciferase core clock reporters. Furthermore, we disrupted the circadian clock in skeletal muscle cells by transfecting siRNA targeting CLOCK. Next, we assessed the basal secretion of a large panel of myokines in a circadian manner in the presence or absence of a functional clock.

RESULTS

Bioluminescence reporter assays revealed that human skeletal myotubes, synchronized in vitro, exhibit a self-sustained circadian rhythm, which was further confirmed by endogenous core clock transcript expression. Moreover, we demonstrate that the basal secretion of IL-6, IL-8 and MCP-1 by synchronized skeletal myotubes has a circadian profile. Importantly, the secretion of IL-6 and several additional myokines was strongly downregulated upon siClock-mediated clock disruption.

CONCLUSIONS

Our study provides for the first time evidence that primary human skeletal myotubes possess a high-amplitude cell-autonomous circadian clock, which could be attenuated. Furthermore, this oscillator plays an important role in the regulation of basal myokine secretion by skeletal myotubes.

Evidence for fatty acids mediating CL 316,243-induced reductions in blood glucose in mice

CL 316,243, a β3-adrenergic agonist, was developed as an antiobesity and diabetes drug and causes rapid decreases in blood glucose levels in mice. The mechanisms mediating this effect have not been fully elucidated; thus, the purpose of the current study was to examine the role of fatty acids and interleukin-6, reputed mediators of insulin secretion, in this process. To address this question, we used physiological and pharmacological approaches in combination with knockout mouse models. CL 316,243 treatment in male C57BL6 mice increased plasma fatty acids, glycerol, interleukin-6, and insulin and reduced blood glucose concentrations 2 h following injections. The ability of CL 316,243 to increase insulin and fatty acids and reduce glucose was preserved in interleukin-6-deficient mice. CL 316,243-induced drops in blood glucose occurred in parallel with increases in circulating fatty acids but prior to increases in plasma interleukin-6. CL 316,243-mediated increases in plasma insulin levels and reductions in blood glucose were attenuated when mice were pretreated with the lipase inhibitor nicotinic acid or in whole body adipose tissue triglyceride lipase knockout mice. Collectively, our findings demonstrate an important role for fatty acids in mediating the effects of CL 316,243 in mice. Not only do our results provide new insight into the mechanisms of action of CL 316,243, but they also hint at an unappreciated aspect of adipose tissue -pancreas cross-talk.

IL-6 strikes a balance in metabolic inflammation

Interleukin-6 (IL-6) is a pleiotropic cytokine that exerts either proinflammatory or anti-inflammatory effects and is implicated in diverse settings, including obesity, exercise, arthritis, and colitis. A new study shows that modulation of macrophage activation by IL-6 maintains glucose homeostasis in diet-induced obesity while limiting inflammation in endotoxemia (Mauer et al., 2014).