The inflammasome and caspase-1 activation: a new mechanism underlying increased inflammatory activity in human visceral adipose tissue

Exploring the Link between Inflammatory Biomarkers and Adipometrics in Healthy Young Adults Aged 20-35 Years

Obesity and aging are associated with an inflammatory state, which represents the common background for a wide range of diseases. This study aims to explore the correlation between hsCRP, IL-1β, IL-6, TNF-α, IFN-γ, and white blood cell count (WBC) and adipometrics (arm, waist, and hip circumferences: AC, WC, HC; total body fat mass: TBFM, visceral fat level: VFL, body mass index: BMI; waist/hip ratio: WHR; waist/height ratio: WHtR) in young and healthy adults aged 20-35 years old. The subjects were divided by BMI into the overweight/obesity (OW/OB) group and normal weight (NW) group, and by hsCRP level into Group 1 (<1 mg/L), Group 2 (≥1-2.99 mg/L), and Group 3 (≥3 mg/L). The concentration of all inflammatory biomarkers was significantly higher in the OW/OB group compared to the NW group, with the exception of IL-1β. Significant positive correlations were found between hsCRP, TNF-α, WBC, and all adipometrics; between IL-6 and WHR, WHtR, BMI, TBFM, and VFL; and between IFN-γ and HC, BMI, and TBFM. IL-1β correlates positively with WHR and VFL. In Groups 1-3, all the differences between the adipometrics showed significant differences. Subclinical inflammation persists in association with being overweight and obese in healthy young adults aged 20-35 years old.

Dihydrotestosterone, and Not Testosterone, Enhances the LPS-Induced Inflammatory Cytokine Gene Expression in Human Adipocytes

BACKGROUND

The development of obesity-related complications lies in the low-grade inflammatory state consequent to adipocyte dysfunction. The direct involvement of sex hormones in adipose tissue inflammation has been previously suggested, but the evidence is scarce. In this study, we evaluated the effects of sex steroids on the in-vitroexpression of inflammatory mediators in human-derived adipocytes before and after lipopolysaccharide (LPS) exposure.

METHODS

Human adipocytes were differentiated from the vascular stromal fraction of adipose tissue samples of subjects undergoing abdominoplasty. We evaluated MCP-1, IL-1β, IL-6, and TNF-α gene expression in the presence of the main sex steroids, testosterone (T), and 17β-estradiol (E). Furthermore, we analyzed the effects of adipocytes exposure to the non-aromatizable androgen dihydrotestosterone (DHT), together with the effects of adipocytes pre-incubation with the aromatase inhibitor anastrozole alone (A), and in combination with T (A/T) before incubation with LPS.

RESULTS

DHT, but not T, significantly enhanced the LPSinduction of MCP-1, IL-1β, IL-6, and TNF-α. Intriguingly, the exposure of adipocytes with A/T dramatically increased the LPS-induced expression of all considered inflammatory cytokines, even more than a hundred-fold.

CONCLUSIONS

DHT and A/T dramatically enhance LPS-induced inflammatory cytokine expression in human-derived adipocytes. These results confirm the involvement of sex hormones in adipose tissue inflammation, suggesting a specific role for non-aromatizable androgens as the amplificatory sex hormones of the inflammatory response.

Fat-to-heart crosstalk in health and disease

According to the latest World Health Organization statistics, cardiovascular disease (CVD) is one of the leading causes of death globally. Due to the rise in the prevalence of major risk factors, such as diabetes mellitus and obesity, the burden of CVD is expected to worsen in the decades to come. Whilst obesity is a major and consistent risk factor for CVD, the underlying pathological molecular communication between peripheral fat depots and the heart remains poorly understood. Adipose tissue (AT) is a major endocrine organ in the human body, with composite cells producing and secreting hormones, cytokines, and non-coding RNAs into the circulation to alter the phenotype of multiple organs, including the heart. Epicardial AT (EAT) is an AT deposit that is in direct contact with the myocardium and can therefore influence cardiac function through both mechanical and molecular means. Moreover, resident and recruited immune cells comprise an important adipose cell type, which can create a pro-inflammatory environment in the context of obesity, potentially contributing to systemic inflammation and cardiomyopathies. New mechanisms of fat-to-heart crosstalk, including those governed by non-coding RNAs and extracellular vesicles, are being investigated to deepen the understanding of this highly common risk factor. In this review, molecular crosstalk between AT and the heart will be discussed, with a focus on endocrine and paracrine signaling, immune cells, inflammatory cytokines, and inter-organ communication through non-coding RNAs.

Cell death and inflammation during obesity: "Know my methods, WAT(son)"

Obesity is a state of low-grade chronic inflammation that causes multiple metabolic diseases. During obesity, signalling via cytokines of the TNF family mediate cell death and inflammation within the adipose tissue, eventually resulting in lipid spill-over, glucotoxicity and insulin resistance. These events ultimately lead to ectopic lipid deposition, glucose intolerance and other metabolic complications with life-threatening consequences. Here we review the literature on how inflammatory responses affect metabolic processes such as energy homeostasis and insulin signalling. This review mainly focuses on the role of cell death in the adipose tissue as a key player in metabolic inflammation.

Artesunate protects pancreatic β-cells from streptozotocin-induced diabetes via inhibition of the NLRP3/caspase-1/GSDMD pathway

BACKGROUND

Reports in recent years have shown that pancreatic β-cell pyroptosis represents a critical mechanism involved with the progressive failure of pancreatic function. Previous research from our laboratory has indicated that artemether can increase the number of cells in pancreatic islets of db/db mice. In this study, we further examined whether artesunate (ART) protects pancreatic β-cells from the damage of streptozotocin (STZ) by inhibiting pyroptosis.

MATERIALS AND METHODS

In vitro, MIN6 cells exposed to 1 mM STZ were treated with ART (0.8 or 1.6 μM). The effects of ART on STZ-treated cells were evaluated through CCK-8 assay, flow cytometry and western blot, and further compared the effects of ART with the NLRP3 inhibitor, Mcc950 upon pyroptosis pathway proteins using western blot. In vivo, Male C57 mice were administered with a single intraperitoneal injection of STZ, and those with confirmed diabetes mellitus were given ART (0.5 or 1.0 mg/ml in drinking water) for 18 days. The effects of ART on STZ-induced diabetes were assessed by the observation of the general situation, glucose tolerance test, hematoxylin-eosin (HE) staining and immunohistochemistry.

RESULTS

In MIN6 cells treated with STZ, we found that ART increased cell viability, decreased the number of late apoptotic cells (including pyroptosis cells) and inhibited the expression of proteins associated with the pyroptosis pathway. In STZ-induced animal model, the administration of ART reduced blood glucose levels, improved the consumption status within this diabetic mouse model and inhibited the expression of proteins include in the pyroptosis pathway in mice pancreats.

CONCLUSIONS

Inhibition of pyroptosis may be a critical mechanism through which artesunate exerts protective effects upon pancreatic β cells.

Macrophage Polarization Mediated by Mitochondrial Dysfunction Induces Adipose Tissue Inflammation in Obesity

Obesity is one of the prominent global health issues, contributing to the growing prevalence of insulin resistance and type 2 diabetes. Chronic inflammation in adipose tissue is considered as a key risk factor for the development of insulin resistance and type 2 diabetes in obese individuals. Macrophages are the most abundant immune cells in adipose tissue and play an important role in adipose tissue inflammation. Mitochondria are critical for regulating macrophage polarization, differentiation, and survival. Changes to mitochondrial metabolism and physiology induced by extracellular signals may underlie the corresponding state of macrophage activation. Macrophage mitochondrial dysfunction is a key mediator of obesity-induced macrophage inflammatory response and subsequent systemic insulin resistance. Mitochondrial dysfunction drives the activation of the NLRP3 inflammasome, which induces the release of IL-1β. IL-1β leads to decreased insulin sensitivity of insulin target cells via paracrine signaling or infiltration into the systemic circulation. In this review, we discuss the new findings on how obesity induces macrophage mitochondrial dysfunction and how mitochondrial dysfunction induces NLRP3 inflammasome activation. We also summarize therapeutic approaches targeting mitochondria for the treatment of diabetes.

Macrophages in obesity are characterised by increased IL-1β response to calcium-sensing receptor signals

Objective

Obesity is complicated by inflammatory activation of the innate immune system. Stimulation of the calcium-sensing receptor (CaSR) by extra-cellular calcium ions ([Ca²⁺]_ex) can trigger NLRP3 inflammasome activation and inflammation. We hypothesised, that this mechanism might contribute to the activation of adipose tissue (AT) in obesity, and investigated [Ca²⁺]_ex-induced, CaSR mediated IL-1β release by macrophages in obesity.

Methods

[Ca²⁺]_ex-induced IL-1β release was investigated in monocyte-derived macrophages (MDM) generated from peripheral blood of patients with obesity and from normal-weight controls. Visceral and subcutaneous AT biosamples were stimulated with [Ca²⁺]_ex, and IL-1β release, as well as expression of NLRP3 inflammasome and cytokine genes, was determined.

Results

Both MDM and AT readily responded with concentration-dependent IL-1β release already at low, near physiological concentrations to addition of [Ca²⁺]_ex, which was more than 80 fold higher than the LPS-induced effect. IL-1β levels induced by [Ca²⁺]_ex were significantly higher not only in MDM from patients with obesity compared to controls, but also in visceral versus subcutaneous AT. This fat-depot difference was also reflected by mRNA expression levels of inflammasome and cytokine genes.

Conclusions

Obesity renders macrophages more susceptible to [Ca²⁺]_ex-induced IL-1β release and pyroptosis. Increased susceptibility was independent of the response to LPS and circulating CRP arguing against mere pro-inflammatory pre-activation of monocytes. Instead, we propose that CaSR mediated signalling is relevant for the deleterious innate immune activation in obesity.

Irisin reduces inflammatory signaling pathways in inflammation-mediated metabolic syndrome

Irisin is an exercise induced myokine first shown to induce the browning of white adipose tissue (WAT) which increases energy expenditure, improves glucose tolerance, and reduces insulin resistance. Among irisin's involvement in lipid homeostasis, osteoblast proliferation, and muscle growth, it also acts as a mediator of many inflammatory pathways throughout the body. This review aims to describe the role of irisin in inflammatory processes and understand how targeting irisin can alter the inflammatory response in metabolic syndrome (MetS). The mechanisms involved in irisin's anti-inflammatory functions include reducing production of pro-inflammatory cytokines while increasing production of anti-inflammatory cytokines, reducing macrophage proliferation, inducing alternatively activated (M2-type) macrophage polarization, inhibiting pathways of increased vascular permeability, and preventing the formation of inflammasomes. While there are some contradictory results, most studies found reduced levels of irisin in MetS and type II diabetes mellitus (T2DM). Irisin treatment of cells exposed to inflammatory stimuli ameliorates the inflammatory response and promotes cellular viability. Numerous methods have been studied to increase plasma irisin levels including dietary, behavioral, and pharmaceutical. Further investigation is necessary to understand how irisin can be targeted for disease modification.

Interleukin-18 in metabolism: From mice physiology to human diseases

Interleukin-18 (IL-18) is a classical member of the IL-1 superfamily of cytokines. As IL-1β, IL-18 precursor is processed by inflammasome/caspase-1 into a mature and biologically active form. IL-18 binds to its specific receptor composed of two chains (IL-18Rα and IL-18Rβ) to trigger a similar intracellular signaling pathway as IL-1, ultimately leading to activation of NF-κB and inflammatory processes. Independently of this IL-1-like signaling, IL-18 also specifically induces IFN-γ production, driving the Th1 immune response. In circulation, IL-18 binds to the IL-18 binding protein (IL-18BP) with high affinity, letting only a small fraction of free IL-18 able to trigger receptor-mediated signaling. In contrast to other IL-1 family members, IL-18 is produced constitutively by different cell types, suggesting implications in normal physiology. If the roles of IL-18 in inflammatory processes and infectious diseases are well described, recent experimental studies in mice have highlighted the action of IL-18 signaling in the control of energy homeostasis, pancreatic islet immunity and liver integrity during nutritional stress. At the same time, clinical observations implicate IL-18 in various metabolic diseases including obesity, type 1 and 2 diabetes and nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH). In the present review, we summarize and discuss both the physiological actions of IL-18 in metabolism and its potential roles in pathophysiological mechanisms leading to the most common human metabolic disorders, such as obesity, diabetes and NAFLD/NASH.

Exenatide improves hepatocyte insulin resistance induced by different regional adipose tissue

Obesity is resulted from energy surplus and is characterized by abnormal adipose tissue accumulation and/or distribution. Adipokines secreted by different regional adipose tissue can induce changes in key proteins of the insulin signaling pathway in hepatocytes and result in impaired hepatic glucose metabolism. This study aimed to investigate whether exenatide affects key proteins of IRS2/PI3K/Akt2 signaling pathway in hepatocytes altered by the different regional fat depots. Six non-obese patients without endocrine diseases were selected as the research subjects. Their subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT)were co-cultured with HepG2 cells in the transwell chamber. In the presence or absence of exenatide, adipokines content in the supernatant of each experimental group was detected by ELISA. In addition, HepG2 cells in each co-culture group with and without insulin were collected, and the expression of key proteins IRS2, p-IRS2(S731), PI3K-p85, Akt2, and p-Akt2(S473) was detected by western blotting (WB). The results showed that the adipokines IL-8, MCP-1, VEGF, and sTNFR2 in the supernatant of HepG2 cells induced by different regional adipose tissue were significantly higher than those in the HepG2 group, and VAT released more adipokines than SAT. Furthermore, these adipokines were significantly inhibited by exenatide. Importantly, the different regional fat depot affects the IRS2/PI3K/Akt2 insulin signaling pathway of hepatocytes. Exenatide can up-regulate the expression of hepatocyte proteins IRS2, PI3K-p85, p-Akt2(S731) inhibited by adipose tissue, and down-regulate the expression of hepatocyte proteins p-IRS2(S731) promoted by adipose tissue. The effect of VAT on the expression of these key proteins in hepatocytes is more significant than that of SAT. But there was no statistical difference in the expression of Akt2 protein among each experimental group, suggesting that exenatide has no influence on the expression of Akt2 protein in hepatocytes. In conclusion, exenatide may improve hepatic insulin resistance (IR) by inhibiting adipokines and regulating the expression of key proteins in the IRS2/PI3K/Akt2 pathway.

Impact of Bariatric Surgery on Adipose Tissue Biology

Bariatric surgery (BS) procedures are actually the most effective intervention to help subjects with severe obesity achieve significant and sustained weight loss. White adipose tissue (WAT) is increasingly recognized as the largest endocrine organ. Unhealthy WAT expansion through adipocyte hypertrophy has pleiotropic effects on adipocyte function and promotes obesity-associated metabolic complications. WAT dysfunction in obesity encompasses an altered adipokine secretome, unresolved inflammation, dysregulated autophagy, inappropriate extracellular matrix remodeling and insufficient angiogenic potential. In the last 10 years, accumulating evidence suggests that BS can improve the WAT function beyond reducing the fat depot sizes. The causal relationships between improved WAT function and the health benefits of BS merits further investigation. This review summarizes the current knowledge on the short-, medium- and long-term outcomes of BS on the WAT composition and function.

Proteins associated with incident metabolic syndrome in population-based cohorts

BACKGROUND

The metabolic syndrome (MetS) identifies persons with clustering of multiple cardiometabolic risk factors. The underlying pathology inducing this clustering is not fully known. We used a targeted proteomics assay to identify associations of circulating proteins with MetS and its components, cross-sectionally and longitudinally.

METHODS

We explored and validated associations of 86 cardiovascular proteins, assessed using a proximity extension assay, with the MetS in two independent cohorts; the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS, n = 996) and Uppsala Longitudinal Study of Adult Men (ULSAM, n = 785). The analyses were adjusted for smoking, exercise habits, education, and energy and alcohol intake.

RESULTS

Nine proteins were associated with all five components of the MetS in PIVUS using FDR < 0.05 in a cross-sectional analysis. Of those nine proteins, only Interleukin-1 receptor antagonist protein (IL-1RA) was associated with all five components of the MetS in ULSAM using p < 0.05. IL-1RA levels were associated with incident MetS (n = 109) in PIVUS during a 5-year follow-up (HR 1.76 for a 1 SD change (95% CI 1.38, 2.24), p = 4.3*10^-6). IL-1RA was however not causally related to MetS in a two-sample Mendelian randomization analysis using published data.

CONCLUSION

Circulating IL-1RA was related to all five components of the MetS in a cross-sectional analysis in two independent samples, as well as to incident MetS in a longitudinal analysis. However, Mendelian randomization analyses did not provide support for a causal role for IL-1RA in the development of MetS.

Pyroptosis: A possible link between obesity-related inflammation and inflammatory diseases

The main manifestation of obesity is persistent low-level inflammation and insulin resistance, which is an important factor inducing or promoting other obesity-related diseases. As a proinflammatory programmed cell death, pyroptosis plays an important role, especially in the activation and regulation of the NLRP3 inflammasome pathway. Pyroptosis is associated with the pathogenesis of many chronic inflammatory diseases and is characterized by the formation of micropores in the plasma membrane and the release of a large number of proinflammatory cytokines. This article mainly introduces the main pathways and key molecules of pyroptosis and focuses on the phenomenon of pyroptosis in obesity. It is suggested that the regulation of pyroptosis-related targets may become a new potential therapy for the prevention and treatment of systemic inflammatory response caused by obesity, and we summarize the potential molecular substances that may be beneficial to obesity-related inflammatory diseases through target pyroptosis.

Pro-inflammatory profile of visceral adipose tissue and oxidative stress in severe obese patients carrying the variant rs4612666 C of NLRP3 gene

BACKGROUND

the activation of NLRP3 inflammasome machinery has a central role in obesity-induced inflammation. Genetic studies well support the involvement of functional variants of NLRP3 and its negative regulator, CARD8, in the pathogenesis of complex diseases with an inflammatory background. We have investigated the influence of NLRP3 (rs4612666; rs10754558) and CARD8 (rs204321) genetic variants in both the inflammatory status of visceral adipose tissue (VAT) from patients with severe obesity and in the systemic oxidative stress before and after sleevegastrectomy (SLG).

METHODS

23 consecutive severe obese patients candidate to SLG were enrolled in the study. Visceral adipose tissue (VAT) biopsies, obtained during SLG, were used to evaluate the expression of NLRP3, IL-1β, IL-6, and MCP-1 by real-time RT-PCR. DNA was extracted from peripheral blood lymphocytes and genotyped by RFLP analysis. Before and 3 months after SLG, all patients underwent the assessment of oxidative stress, biochemical parameters, and body-composition as measured by bioelectrical impedance analysis (BIA).

RESULTS

Increased expression of NLRP3, IL-6, IL-1β, and MCP-1 mRNA was observed in VAT of rs4612666 C variant carriers, in which higher oxidative stress was also detected as compared to non-carrier individuals. In all patients, oxidative stress, biochemical and BIA parameters improved after SLG, regardless of genotype. No significant correlations were found with the other genetic variants.

CONCLUSIONS

Our results suggest that the NLRP3 rs4612666 C variant may promote a worse pro-inflammatory-milieu and higher oxidative stress, thus leading patients to a more severe obesity phenotype. A larger study is needed to confirm this assumption and to investigate the impact of the NLRP3 rs4612666 C variant on severe obesity.

Anti-NLRP3 Inflammasome Natural Compounds: An Update

The nucleotide-binding domain and leucine-rich repeat related (NLR) family, pyrin domain containing 3 (NLRP3) inflammasome is a multimeric protein complex that recognizes various danger or stress signals from pathogens, the host, and the environment, leading to activation of caspase-1 and inducing inflammatory responses. This pro-inflammatory protein complex plays critical roles in pathogenesis of a wide range of diseases including neurodegenerative diseases, autoinflammatory diseases, and metabolic disorders. Therefore, intensive efforts have been devoted to understanding its activation mechanisms and to searching for its specific inhibitors. Approximately forty natural compounds with anti-NLRP3 inflammasome properties have been identified. Here, we provide an update about new natural compounds that have been identified within the last three years to inhibit the NLRP3 inflammasome and offer an overview of the underlying molecular mechanisms of their anti-NLRP3 inflammasome activities.

Lower plasma PCSK9 in normocholesterolemic subjects is associated with upregulated adipose tissue surface-expression of LDLR and CD36 and NLRP3 inflammasome

Background

LDL‐cholesterol lowering variants that upregulate receptor uptake of LDL, such as in PCSK9 and HMGCR, are associated with diabetes via unclear mechanisms. Activation of the NLRP3 inflammasome/interleukin‐1 beta (IL‐1β) pathway promotes white adipose tissue (WAT) dysfunction and type 2 diabetes (T2D) and is regulated by LDL receptors (LDLR and CD36). We hypothesized that: (a) normocholesterolemic subjects with lower plasma PCSK9, identifying those with higher WAT surface‐expression of LDLR and CD36, have higher activation of WAT NLRP3 inflammasome and T2D risk factors, and; (b) LDL upregulate adipocyte NLRP3 inflammasome and inhibit adipocyte function.

Methodology

Post hoc analysis was conducted in 27 overweight/ obese subjects with normal plasma LDL‐C and measures of disposition index (DI during Botnia clamps) and postprandial fat metabolism. WAT was assessed for surface‐expression of LDLR and CD36 (immunohistochemistry), protein expression (immunoblot), IL‐1β secretion (AlphaLISA), and function (³H‐triolein storage).

Results

Compared to subjects with higher than median plasma PCSK9, subjects with lower PCSK9 had higher WAT surface‐expression of LDLR (+81%) and CD36 (+36%), WAT IL‐1β secretion (+284%), plasma IL‐1 receptor‐antagonist (+85%), and postprandial hypertriglyceridemia, and lower WAT pro‐IL‐1β protein (−66%), WAT function (−62%), and DI (−28%), without group‐differences in body composition, energy intake or expenditure. Adjusting for WAT LDLR or CD36 eliminated group‐differences in WAT function, DI, and postprandial hypertriglyceridemia. Native LDL inhibited Simpson‐Golabi Behmel‐syndrome (SGBS) adipocyte differentiation and function and increased inflammation.

Conclusion

Normocholesterolemic subjects with lower plasma PCSK9 and higher WAT surface‐expression of LDLR and CD36 have higher WAT NLRP3 inflammasome activation and T2D risk factors. This may be due to LDL‐induced inhibition of adipocyte function.

Retinol binding protein 4 primes the NLRP3 inflammasome by signaling through Toll-like receptors 2 and 4

Adipose tissue (AT) inflammation contributes to systemic insulin resistance. In obesity and type 2 diabetes (T2D), retinol binding protein 4 (RBP4), the major retinol carrier in serum, is elevated in AT and has proinflammatory effects which are mediated partially through Toll-like receptor 4 (TLR4). We now show that RBP4 primes the NLRP3 inflammasome for interleukin-1β (IL1β) release, in a glucose-dependent manner, through the TLR4/MD2 receptor complex and TLR2. This impairs insulin signaling in adipocytes. IL1β is elevated in perigonadal white AT (PGWAT) of chow-fed RBP4-overexpressing mice and in serum and PGWAT of high-fat diet-fed RBP4-overexpressing mice vs. wild-type mice. Holo- or apo-RBP4 injection in wild-type mice causes insulin resistance and elevates PGWAT inflammatory markers, including IL1β. TLR4 inhibition in RBP4-overexpressing mice reduces PGWAT inflammation, including IL1β levels and improves insulin sensitivity. Thus, the proinflammatory effects of RBP4 require NLRP3-inflammasome priming. These studies may provide approaches to reduce AT inflammation and insulin resistance in obesity and diabetes.

The Influence of Metformin to the Transcriptional Activity of the mTOR and FOX3 Genes in Parapancreatic Adipose Tissue of Streptozotocin-Induced Diabetic Rats

The mammalian target of rapamycin is not only a central regulator of lipid metabolism that controls the processes of adipogenesis and lipolysis but also a regulator of the immunometabolism of immune cells that infiltrate adipose tissue. In turn, the level of progression of diabetes is significantly influenced by the Treg subpopulation, the complexity and heterogeneity of which is confirmed by the detection of numerous tissue-specific Tregs, including the so-called VAT Tregs (visceral adipose tissue CD4+Foxp3+ regulatory T cells). Therefore, the purpose of the study was to determine the mRNA expression levels of mTOR, Foxp3, IL1β, and IL17A genes in rat parapancreatic adipose tissue with experimental streptozotocin-induced diabetes mellitus, with or without metformin administration. The experiments were performed on male Wistar rats with induced diabetes as a result of streptozotocin administration. Molecular genetic studies were performed using real-time reverse transcription-polymerase chain reaction. The development of diabetes caused transcriptional activation of the mammalian target of rapamycin protein kinase gene, as well as increased mRNA expression of the pro-inflammatory cytokines IL1β and IL17A, but did not affect Foxp3 mRNA expression. The intervention with metformin in diabetic rats inhibited the mammalian target of rapamycin mRNA expression and caused an increase in the transcriptional activity of the Foxp3 gene in parapancreatic adipose tissue.

Chronic Adipose Tissue Inflammation Linking Obesity to Insulin Resistance and Type 2 Diabetes

Obesity is one of the major health burdens of the 21st century as it contributes to the growing prevalence of its related comorbidities, including insulin resistance and type 2 diabetes. Growing evidence suggests a critical role for overnutrition in the development of low-grade inflammation. Specifically, chronic inflammation in adipose tissue is considered a crucial risk factor for the development of insulin resistance and type 2 diabetes in obese individuals. The triggers for adipose tissue inflammation are still poorly defined. However, obesity-induced adipose tissue expansion provides a plethora of intrinsic signals (e.g., adipocyte death, hypoxia, and mechanical stress) capable of initiating the inflammatory response. Immune dysregulation in adipose tissue of obese subjects results in a chronic low-grade inflammation characterized by increased infiltration and activation of innate and adaptive immune cells. Macrophages are the most abundant innate immune cells infiltrating and accumulating into adipose tissue of obese individuals; they constitute up to 40% of all adipose tissue cells in obesity. In obesity, adipose tissue macrophages are polarized into pro-inflammatory M1 macrophages and secrete many pro-inflammatory cytokines capable of impairing insulin signaling, therefore promoting the progression of insulin resistance. Besides macrophages, many other immune cells (e.g., dendritic cells, mast cells, neutrophils, B cells, and T cells) reside in adipose tissue during obesity, playing a key role in the development of adipose tissue inflammation and insulin resistance. The association of obesity, adipose tissue inflammation, and metabolic diseases makes inflammatory pathways an appealing target for the treatment of obesity-related metabolic complications. In this review, we summarize the molecular mechanisms responsible for the obesity-induced adipose tissue inflammation and progression toward obesity-associated comorbidities and highlight the current therapeutic strategies.

The 1α,25(OH)2D3 Analogs ZK159222 and ZK191784 Show Anti-Inflammatory Properties in Macrophage-Induced Preadipocytes via Modulating the NF-κB and MAPK Signaling

PURPOSE

Key research findings suggest that attenuating metaflammation in adipose tissue might be a strategic step to prevent the metabolic syndrome and its associated disease outcomes. The anti-inflammatory effects of 1α,25(OH)₂D₃ have been confirmed in our previous studies, but adverse effects induced at high concentrations restrict its potential clinical translation. Two synthetic 1α,25(OH)₂D₃ analogs ZK159222 and ZK191784 have manifested promising tissue-specific immunomodulatory actions, but limited data are available on adipose tissue. Hence, in this study, we investigated whether ZK159222 and ZK191784 act on preadipocytes or macrophages to attenuate metaflammatory responses via modulating inflammatory and metabolic signaling in macrophage-induced preadipocytes.

METHODS

Preadipocyte-specific effects of ZK159222 and ZK191784 on macrophage-induced preadipocytes were tested by pre-incubating and incubating preadipocytes with the analogs and MacCM. Separately, macrophage-specific effects of both analogs on macrophage-induced preadipocytes were tested by incubating preadipocytes with analog-MacCM or MacCM. The effects of 1α,25(OH)₂D₃ were also examined and set as the positive control. Metaflammatory responses were determined as the concentrations and gene expression of major pro-inflammatory cytokines including IL-1β, IL-6, IL-8, MCP-1 and RANTES, measured using ELISA and qPCR. Inflammatory and metabolic signaling including NF-κB and MAPK were probed using Western blotting.

RESULTS

ZK159222 and ZK191784 act on preadipocytes and macrophages to decrease the secretion and gene expression of the major pro-inflammatory cytokines in macrophage-induced preadipocytes. The anti-inflammatory effects were at least as potent as 1α,25(OH)₂D₃, and no preadipocyte apoptosis was induced at high concentrations. In addition, mostly at high concentrations, both analogs moderately decreased the phosphorylation of relA, p44/42 and p38 MAPK in macrophage-induced preadipocytes.

CONCLUSION

ZK159222 and ZK191784 act on macrophages and preadipocytes to attenuate metaflammatory responses in macrophage-induced preadipocytes, by decreasing phosphorylation of relA/NF-κB, p44/42 and p38 MAPK.

Red Raspberry Polyphenols Attenuate High-Fat Diet-Driven Activation of NLRP3 Inflammasome and its Paracrine Suppression of Adipogenesis via Histone Modifications

SCOPE

The authors aim to investigate the mechanisms by which red raspberry (RR) polyphenolic fractions regulate obesity and inflammation with an emphasis on the crosstalk between adipose tissue macrophages (ATM) and adipocyte progenitors.

METHODS AND RESULTS

C57BL/6 male mice are fed either a high-fat (HF) diet or an HF diet supplemented with a RR polyphenolic fraction from whole fruit, pulp, or seed. Supplementation with pulp significantly increases energy expenditure and reduces HF-diet-induced obesity and insulin resistance. The pulp, and to a lesser extent, whole polyphenols, decreases the recruitment of ATM, activation of the nod-like receptor protein 3 (NLRP3) inflammasome, and adipocyte hypertrophy, which is associated with epigenetic modulation of adipogenesis (e.g., H3K27Ac, H3K9Ac). Results from an IL-1β reporter assay in J774 macrophages recapitulate the inhibitory role of RR polyphenols on NLRP3 inflammasome activation. Using conditioned media from macrophages, it is demonstrated that RR polyphenols reverse the IL-1β-mediated epigenetic suppression of H3K27Ac in adipocyte progenitor cells.

CONCLUSIONS

RR polyphenols from pulp and whole fruit serve as an inhibitor for NLRP3 inflammasome activation and an epigenetic modifier to regulate adipogenesis, which confers resistance against diet-induced obesity and metabolic dysfunction.

Visceral obesity is a preoperative risk factor for postoperative ileus after surgery for colorectal cancer: Single-institution retrospective analysis

AIM

Visceral obesity (VO) reportedly has a stronger association with complications after colorectal surgery than does body mass index. Here, we retrospectively assessed VO as a risk factor for postoperative ileus (POI) after colorectal resection in patients with colorectal cancer.

METHODS

This study included 417 consecutive patients with colorectal cancer who underwent elective surgery at our institute from January 2010 to December 2012. Visceral fat area (VFA) was calculated by image analysis software. VO was defined as VFA ≥100 cm2. We assessed 49 factors, including VO, comorbidities, surgical procedure, and postoperative complications. Data were analyzed using a propensity score-matching strategy.

RESULTS

Postoperative ileus occurred in 18 patients (4.3%) from the entire cohort, and in 14 (5.5%) of the 256 matched patients. Multivariate analysis (n = 417 patients) showed that significant risk factors for POI included VO (OR 7.9, 95% confidence interval [CI] 1.9-32.1, P = .004), open surgery (OR 6.4, 95% CI 1.6-26.7, P = .010), and pelvic/intra-abdominal abscess (OR 11.0, 95% CI 1.1-110.2, P = .041). Propensity score matching showed two independent risk factors in the multivariate analysis: VO (OR 6.2, 95% CI 1.3-30.4, P = .025) and open surgery (OR 9.1, 95% CI 2.0-40.5, P = .004).

CONCLUSION

Visceral obesity may be an independent risk factor for POI in patients with colorectal cancer.

Molecular Links between Central Obesity and Breast Cancer

Worldwide, breast cancer (BC) is the most common malignancy in women, in regard to incidence and mortality. In recent years, the negative role of obesity during BC development and progression has been made abundantly clear in several studies. However, the distribution of body fat may be more important to analyze than the overall body weight. In our review of literature, we reported some key findings regarding the role of obesity in BC development, but focused more on central adiposity. Firstly, the adipose microenvironment in obese people bears many similarities with the tumor microenvironment, in respect to associated cellular composition, chronic low-grade inflammation, and high ratio of reactive oxygen species to antioxidants. Secondly, the adipose tissue functions as an endocrine organ, which in obese people produces a high level of tumor-promoting hormones, such as leptin and estrogen, and a low level of the tumor suppressor hormone, adiponectin. As follows, in BC this leads to the activation of oncogenic signaling pathways: NFκB, JAK, STAT3, AKT. Moreover, overall obesity, but especially central obesity, promotes a systemic and local low grade chronic inflammation that further stimulates the increase of tumor-promoting oxidative stress. Lastly, there is a constant exchange of information between BC cells and adipocytes, mediated especially by extracellular vesicles, and which changes the transcription profile of both cell types to an oncogenic one with the help of regulatory non-coding RNAs.

CD8+ T cell/adipocyte inflammatory cross talk and ensuing M1 macrophage polarization are reduced by fish-oil-derived n-3 polyunsaturated fatty acids, in part by a TNF-α-dependent mechanism

Obese visceral adipose tissue (AT) inflammation is driven by adipokine-mediated cross talk between CD8⁺ T cells and adipocytes, a process mitigated by long-chain (LC) n-3 polyunsaturated fatty acids (PUFA) but underlying mechanisms and ensuing effects on macrophage polarization status are unknown. Using an in vitro co-culture model that recapitulates the degree of CD8⁺ T cell infiltration reported in obese AT, 3T3-L1 adipocytes were co-cultured for 24 h with purified splenic CD8⁺ T cells from C57Bl/6 mice consuming either a 10% w/w safflower oil (control, CON) or 7% w/w safflower oil + 3% w/w fish oil (FO) diet for 4 weeks (n=8-10/diet). Co-cultured cells were in direct contact or in a contact-independent condition separated by a Transwell permeable membrane and stimulated with lipopolysaccharide (10 ng/ml) to mimic in vivo obese endotoxin levels. In contact-dependent co-cultures, FO reduced inflammatory (IL-6, TNFα, IFN-γ) and macrophage chemotactic (CCL2, CCL7, CCL3) mRNA expression and/or secreted protein, NF-κB p65 activation, ROS accumulation, NLRP3 inflammasome priming (Nlrp3, Il1β mRNA) and activation (caspase-1 activity) compared to CON (P<.05). The anti-inflammatory action of FO was reproduced by the addition of a TNF-α neutralizing antibody (1 μg/ml) to CON co-cultures (CON/anti-TNF-α), albeit to a lesser degree. Conditioned media from FO and CON/anti-TNF-α co-cultures, in turn, reduced RAW 264.7 macrophage mRNA expression of M1 polarization markers (iNos, Cd11c, Ccr2) and associated inflammatory cytokines (Il6, Tnfα, Il1β) compared to CON. These data suggest that inflammatory CD8⁺ T cell/adipocyte cross talk is partially attributable to TNF-α signaling, which can be mitigated by LC n-3 PUFA.

NLRP3 Inflammasome: A Novel Player in Metabolically Induced Inflammation-Potential Influence on the Myocardium

Metabolic and immune systems are among the most fundamental requirements for survival. Many metabolic and immune response pathways or nutrient- and pathogen-sensing systems are evolutionarily conserved throughout species. As a result, the immune response and metabolic regulation are highly integrated and the proper function of each is dependent on the other. This interaction between metabolic disturbances and the immune system has been most extensively studied in disorders related to obesity such as insulin resistance, type 2 diabetes, and nonalcoholic fatty liver disease. Metabolically induced inflammation seems also to play a role in the development and progression of atherosclerosis including its complications such as myocardial infarction (MI) and post-MI remodeling. There are several lines of evidence suggesting that NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is a sensor of metabolic stress linking metabolic disturbances to inflammation. Here, we will discuss the role of the NLRP3 inflammasome in the pathogenesis of obesity and diabetes, 2 important risk factors for atherosclerosis and MI. We will also discuss the role of NLRP3 inflammasome in the interaction between metabolic disturbances and myocardial inflammation during MI and during metabolically induced myocardial remodeling.

Plant Extracts and Reactive Oxygen Species as Two Counteracting Agents with Anti- and Pro-Obesity Properties

Obesity is a complex disease of great public health significance worldwide: It entails several complications including diabetes mellitus type 2, cardiovascular dysfunction and hypertension, and its prevalence is increasing around the world. The pathogenesis of obesity is closely related to reactive oxygen species. The role of reactive oxygen species as regulatory factors in mitochondrial activity in obese subjects, molecules taking part in inflammation processes linked to excessive size and number of adipocytes, and as agents governing the energy balance in hypothalamus neurons has been examined. Phytotherapy is the traditional form of treating health problems using plant-derived medications. Some plant extracts are known to act as anti-obesity agents and have been screened in in vitro models based on the inhibition of lipid accumulation in 3T3-L1 cells and activity of pancreatic lipase methods and in in vivo high-fat diet-induced obesity rat/mouse models and human models. Plant products may be a good natural alternative for weight management and a source of numerous biologically-active chemicals, including antioxidant polyphenols that can counteract the oxidative stress associated with obesity. This review presents polyphenols as natural complementary therapy, and a good nutritional strategy, for treating obesity without serious side effects.

Tissue Immune Cells Fuel Obesity-Associated Inflammation in Adipose Tissue and Beyond

Obesity-associated inflammation stems from a combination of cell-intrinsic changes of individual immune cell subsets and the dynamic crosstalk amongst a broad array of immune cells. Although much of the focus of immune cell contributions to metabolic disease has focused on adipose tissue-associated cells, these potent sources of inflammation inhabit other metabolic regulatory tissues, including liver and gut, and recirculate to promote systemic inflammation and thus obesity comorbidities. Tissue-associated immune cells, especially T cell subpopulations, have become a hotspot of inquiry based on their contributions to obesity, type 2 diabetes, non-alcoholic fatty liver diseases and certain types of cancers. The cell-cell interactions that take place under the stress of obesity are mediated by intracellular contact and cytokine production, and constitute a complicated network that drives the phenotypic alterations of immune cells and perpetuates a feed-forward loop of metabolic decline. Herein we discuss immune cell functions in various tissues and obesity-associated cancers from the viewpoint of inflammation. We also emphasize recent advances in the understanding of crosstalk amongst immune cell subsets under obese conditions, and suggest future directions for focused investigations with clinical relevance.

'Beauty and the beast' in infection: How immune-endocrine interactions regulate systemic metabolism in the context of infection

The immune and endocrine systems ensure two vital functions in the body. The immune system protects us from lethal pathogens, whereas the endocrine system ensures proper metabolic function of peripheral organs by regulating systemic homeostasis. These two systems were long thought to operate independently. The immune system uses cytokines and immune receptors, whereas the endocrine system uses hormones to regulate metabolism. However, recent findings show that the immune and endocrine systems closely interact, especially regarding regulation of glucose metabolism. In response to pathogen encounter, cytokines modify responsiveness of peripheral organs to endocrine signals, resulting in altered levels of blood hormones such as insulin, which promotes the ability of the body to fight infection. Here we provide an overview of recent literature describing various mechanisms, which the immune system utilizes to modify endocrine regulation of systemic metabolism. Moreover, we will describe how these immune-endocrine interactions derail in the context of obesity. From a clinical perspective we will elaborate how infection and obesity aggravate the development of metabolic diseases such as diabetes mellitus type 2 in humans. In summary, this review provides a comprehensive overview of immune-induced changes in systemic metabolism following infection, with a focus on regulation of glucose metabolism.

Role of Pyroptosis in Cardiovascular Diseases and its Therapeutic Implications

Pyroptotic cell death or pyroptosis is characterized by caspase-1-dependent formation of plasma membrane pores, leading to the release of pro-inflammatory cytokines and cell lysis. Pyroptosis tightly controls the inflammatory responses and coordinates antimicrobial host defenses by releasing pro-inflammatory cellular contents, such as interleukin (IL)-1β and IL-18, and consequently expands or sustains inflammation. It is recognized as an important innate immune effector mechanism against intracellular pathogens. The induction of pyroptosis is closely associated with the activation of the NOD-like receptor 3 (NLRP3) inflammasome which has been linked to key cardiovascular risk factors including hyperlipidemia, diabetes, hypertension, obesity, and hyperhomocysteinemia. Emerging evidence has indicated pyroptosis as an important trigger and endogenous regulator of cardiovascular inflammation. Thus, pyroptosis may play an important role in the pathogenesis of cardiovascular diseases. Design of therapeutic strategies targeting the activation of NLRP3 inflammasome and pyroptosis holds promise for the treatment of cardiovascular diseases.

Momordica charantia (bitter melon) modulates adipose tissue inflammasome gene expression and adipose-gut inflammatory cross talk in high-fat diet (HFD)-fed mice

Systemic and tissue-specific inflammation has a profound influence on regulation of metabolism, and therefore, strategies to reduce inflammation are of special interest in prevention and treatment of obesity and type 2 diabetes (T2D). Antiobesity and antidiabetic properties of Momordica charantia (bitter melon, BM) have been linked to its protective effects on inflammation and gut microbial dysbiosis. We investigated the mechanisms by which freeze-dried BM juice reduces adipose inflammation in mice fed a 60% high-fat diet (HFD) for 16 weeks. Although earlier studies indicated that BM inhibited recruitment of macrophages (Mφ) infiltration in adipose tissue of rodents and reduced NF-kB and IL-1β secretions, the mechanisms remain unknown. We demonstrate that freeze-dried BM juice inhibits recruitment of Mφ into adipose tissue and its polarization to inflammatory phenotype possibly due to reduction of sphingokinase 1 (SPK1) mRNA in HFD-fed mice. Furthermore, reduction of IL-1β secretion by freeze-dried BM juice in the adipose tissue of HFD-fed mice is correlated to alleviation of NLRP3 inflammasome components and their downstream signaling targets. We confirm previous observations that BM inhibited inflammation of colon and gut microbial dysbiosis in HFD-fed mice, which in part may be associated with the observed anti-inflammatory effects in adipose tissue if HFD-fed mice. Overall, functional foods such as BM may offer potential dietary interventions that may impact sterile inflammatory diseases such as obesity and T2D.

1α,25(OH)2D3 attenuates IL-6 and IL-1β-mediated inflammatory responses in macrophage conditioned medium-stimulated human white preadipocytes by modulating p44/42 MAPK and NF-κB signaling pathways

BACKGROUND

Metabolic syndrome is characterized by macrophage infiltration and inflammatory responses-metaflammation in adipose tissue. IL-6 and IL-1β could mediate the inflammatory responses in macrophage stimulated-preadipocytes by modulating MAPK and NF-κB pathways. To test this hypothesis we used antibodies to block IL-6 and IL-1β action in macrophage conditioned medium (MacCM)-stimulated human white preadipocytes. Moreover, as interventions that prevent this could potentially be used to treat or prevent metabolic syndrome, and 1α,25(OH)₂D₃ has previously been reported to exert an anti-inflammatory action on macrophage-stimulated adipocytes, in this study we also investigated whether 1α,25(OH)₂D₃ could attenuate inflammatory responses in MacCM-stimulated preadipocytes, and explored the potential anti-inflammatory mechanisms.

METHODS

Human white preadipocytes were cultured with 25% MacCM for 24 h to elicit inflammatory responses. This was confirmed by measuring the concentrations and mRNA levels of major pro-inflammatory factors [IL-1β, IL-6, IL-8, monocyte chemoattractant protein (MCP)-1 and regulated on activation, normal T cell expressed and secreted (RANTES)] by ELISA and qPCR, respectively. IL-6 and IL-1β actions were blocked using IL-6 antibody (300 ng/ml) and IL-1β antibody (15 μg/ml), respectively. Potential anti-inflammatory effects of 1α,25(OH)₂D₃ were investigated by pre-treatment and treatment of 1α,25(OH)₂D₃ (0.01 to 10 nM) for 48 h in MacCM-stimulated preadipocytes. In parallel, western blotting was used to determine inflammatory signaling molecules including relA of the NF-κB pathway and p44/42 MAPK modified during these processes.

RESULTS

MacCM enhanced the secretion and gene expression of IL-1β, IL-6, IL-8, MCP-1 and RANTES by increasing the phosphorylation levels of relA and p44/42 MAPK in preadipocytes, whereas blocking IL-6 and IL-1β action inhibited the inflammatory responses by decreasing p44/42 MAPK and relA phosphorylation, respectively. Furthermore, 10 nM of 1α,25(OH)₂D₃ generally inhibited the IL-6 and IL-1β-mediated inflammatory responses, and reduced both p44/42 MAPK and relA phosphorylation in MacCM-stimulated preadipocytes.

CONCLUSIONS

1α,25(OH)₂D₃ attenuates IL-6 and IL-1β-mediated inflammatory responses, probably by inhibiting p44/42 MAPK and relA phosphorylation in MacCM-stimulated human white preadipocytes.

Interleukin-18 and the NLR family pyrin domain containing-3 inflammasome in adipose tissue are strongly associated with glucometabolic variables in a cohort of middle-aged men

BACKGROUND

Previous studies have indicated an association between interleukin-18 and glucose. Interleukin-18 becomes active when cleaved by caspase-1, activated by the NLR family pyrin domain containing-3 inflammasome.

AIM

To investigate associations between glucometabolic variables and serum levels of interleukin-18 and genetic expression of interleukin-18, caspase-1 and NLR family pyrin domain containing-3 in adipose tissue and circulating leukocytes, and whether these mediators are related to the amount of abdominal adipose tissue .

MATERIALS AND METHODS

Fasting blood samples and subcutaneous adipose tissue were collected in a cohort of 103 middle-aged men. Serum levels of interleukin-18 were determined by enzyme-linked immunosorbent assay, gene expression by real-time polymerase chain reaction and insulin sensitivity by glucose clamp. The distribution of abdominal adipose tissue, separated into superficial- and deep subcutaneous, and visceral adipose tissue, was assessed by computed tomography scan.

RESULTS

Glucometabolic variables correlated significantly to serum levels of interleukin-18, and to the expression of interleukin-18 and NLR family pyrin domain containing-3 in subcutaneous adipose tissue ( p < 0.05). Significant correlations were further observed between the amount of fat in the different compartments of abdominal adipose tissue and both serum levels of interleukin-18 and genetic expression of interleukin-18 and NLR family pyrin domain containing-3 in adipose tissue.

CONCLUSION

The results implicate that the glucometabolic state is of importance for the inflammasome-related inflammation expressed both circulatory and genetically in subcutaneous adipose tissue, the latter highly reflected in the amount of abdominal adipose tissue.

The role of obesity and adipose tissue dysfunction in gestational diabetes mellitus

Gestational diabetes mellitus is defined as diabetes diagnosed in the second or third trimester of pregnancy in patients with no history of diabetes prior to gestation. It is the most common complication of pregnancy. The underlying pathophysiology shares some common features with type 2 diabetes mellitus (T2DM) combining relatively insufficient insulin secretion with increased peripheral insulin resistance. While a certain degree of insulin resistance is the physiological characteristics of the second half of pregnancy, it is significantly more pronounced in patients with gestational diabetes. Adipose tissue dysfunction and subclinical inflammation in obesity are well-described causes of increased insulin resistance in non-pregnant subjects and are often observed in individuals with T2DM. Emerging evidence of altered adipokine expression and local inflammation in adipose tissue in patients with gestational diabetes suggests an important involvement of adipose tissue in its etiopathogenesis. This review aims to summarize current knowledge of adipose tissue dysfunction and its role in the development of gestational diabetes. We specifically focus on the significance of alterations of adipokines and immunocompetent cells number and phenotype in fat. Detailed understanding of the role of adipose tissue in gestational diabetes may provide new insights into its pathophysiology and open new possibilities of its prevention and treatment.

Inflammation in the subcutaneous adipose tissue does not attenuate endothelial function in subjects with diabetes mellitus and subjects with dyslipidaemia and hypertension: A cross-sectional study

BACKGROUND

Obesity is associated with low-grade inflammation that may be related to vascular disease. We hypothesized that inflammation in the subcutaneous adipose tissue is associated with impaired endothelium-dependent vasodilatation.

METHODS

We assessed endothelial function by measuring forearm vascular response to acetylcholine and determined inflammation in subcutaneous fat biopsies in 2 groups of subjects; 15 patients with type 2 diabetes mellitus (T2DM) and 19 subjects with dyslipidaemia combined with hypertension (DcH). The adipose tissue inflammation score was based on adipocyte size, influx of macrophages and presence of crown-like structures. We compared the vascular response to acetylcholine between subjects with and without adipose tissue inflammation.

RESULTS

Patients with diabetes had clearly decreased vasodilatation compared to patients with DcH. In total, 23 of the 34 fulfilled the criteria of subcutaneous adipose tissue inflammation. However, there was no difference in vascular response to acetylcholine between the group with and without inflammation (changes in FBF from baseline 3.9 ± 0.8, 7.8 ± 1.0 and 13.6 ± 1.0 mL/dL/min compared to 4.3 ± 1.0, 7.9 ± 2.1 and 12.2 ± 2.4 mL/dL/min in response to acetylcholine 0.5, 2.0 and 8.0 μg/dL/min), nor was there a relationship between systemic hs-CRP levels and endothelial function.

CONCLUSIONS

We confirm that subjects with T2DM have impaired endothelial function compared to age- and BMI-matched subjects with DcH. However, endothelial function did not differ between participants with or without inflammation in the subcutaneous adipose tissue. These results suggest that fat tissue inflammation, at least in the subcutaneous compartment, does not affect vascular function.

Obesity Exacerbates the Cytokine Storm Elicited by Francisella tularensis Infection of Females and Is Associated with Increased Mortality

Infection with Francisella tularensis, the causative agent of the human disease tularemia, results in the overproduction of inflammatory cytokines, termed the cytokine storm. Excess metabolic byproducts of obesity accumulate in obese individuals and activate the same inflammatory signaling pathways as F. tularensis infection. In addition, elevated levels of leptin in obese individuals also increase inflammation. Since leptin is produced by adipocytes, we hypothesized that increased fat of obese females may make them more susceptible to F. tularensis infection compared with lean individuals. Lean and obese female mice were infected with F. tularensis and the immunopathology and susceptibility monitored. Plasma and tissue cytokines were analyzed by multiplex ELISA and real-time RT-PCR, respectively. Obese mice were more sensitive to infection, developing a more intense cytokine storm, which was associated with increased death of obese mice compared with lean mice. This enhanced inflammatory response correlated with in vitro bacteria-infected macrophage cultures where addition of leptin led to increased production of inflammatory cytokines. We conclude that increased basal leptin expression in obese individuals causes a persistent low-level inflammatory response making them more susceptible to F. tularensis infection and heightening the generation of the immunopathological cytokine storm.

Calcium-sensing receptor activates the NLRP3 inflammasome in LS14 preadipocytes mediated by ERK1/2 signaling

The study of the mechanisms that trigger inflammation in adipose tissue is key to understanding and preventing the cardiometabolic consequences of obesity. We have proposed a model where activation of the G protein-coupled calcium sensing receptor (CaSR) leads to inflammation and dysfunction in adipose cells. Upon activation, CaSR can mediate the expression and secretion of proinflammatory factors in human preadipocytes, adipocytes, and adipose tissue explants. One possible pathway involved in CaSR-induced inflammation is the activation of the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome, that promotes maturation and secretion of interleukin (IL)-1β. The present work aimed to study whether CaSR mediates the activation of NLRP3 inflammasome in the human adipose cell model LS14. We assessed NLRP3 inflammasome priming and assembly after cinacalcet-induced CaSR activation and evaluated if this activation is mediated by downstream ERK1/2 signaling in LS14 preadipocytes. Exposure to 2 μM cinacalcet elevated mRNA expression of NLRP3, CASP-1, and IL-1β, as well as an increase in pro-IL-1β protein. In addition, CaSR activation triggered NLRP3 inflammasome assembly, as evidenced by a 25% increase in caspase-1 activity and 63% IL-1β secretion. CaSR silencing (siRNA) abolished the effect. Upstream ERK pathway inhibition decreased cinacalcet-dependent activation of NLRP3 inflammasome. We propose CaSR-dependent NLRP3 inflammasome activation in preadipocytes through ERK signaling as a novel mechanism for the development of adipose dysfunction, that may favor the cardiovascular and metabolic consequences of obesity. To the best of our knowledge, this is the first report linking the inflammatory effect of CaSR to NLRP3 inflammasome induction in adipose cells.

Parallels in Immunometabolic Adipose Tissue Dysfunction with Ageing and Obesity

Ageing, like obesity, is often associated with alterations in metabolic and inflammatory processes resulting in morbidity from diseases characterised by poor metabolic control, insulin insensitivity, and inflammation. Ageing populations also exhibit a decline in immune competence referred to as immunosenescence, which contributes to, or might be driven by chronic, low-grade inflammation termed "inflammageing". In recent years, animal and human studies have started to uncover a role for immune cells within the stromal fraction of adipose tissue in driving the health complications that come with obesity, but relatively little work has been conducted in the context of immunometabolic adipose function in ageing. It is now clear that aberrant immune function within adipose tissue in obesity-including an accumulation of pro-inflammatory immune cell populations-plays a major role in the development of systemic chronic, low-grade inflammation, and limiting the function of adipocytes leading to an impaired fat handling capacity. As a consequence, these changes increase the chance of multiorgan dysfunction and disease onset. Considering the important role of the immune system in obesity-associated metabolic and inflammatory diseases, it is critically important to further understand the interplay between immunological processes and adipose tissue function, establishing whether this interaction contributes to age-associated immunometabolic dysfunction and inflammation. Therefore, the aim of this article is to summarise how the interaction between adipose tissue and the immune system changes with ageing, likely contributing to the age-associated increase in inflammatory activity and loss of metabolic control. To understand the potential mechanisms involved, parallels will be drawn to the current knowledge derived from investigations in obesity. We also highlight gaps in research and propose potential future directions based on the current evidence.

Low expression of IL-18 and IL-18 receptor in human skeletal muscle is associated with systemic and intramuscular lipid metabolism-Role of HIV lipodystrophy

Introduction

Interleukin (IL)-18 is involved in regulation of lipid and glucose metabolism. Mice lacking whole-body IL-18 signalling are prone to develop weight gain and insulin resistance, a phenotype which is associated with impaired fat oxidation and ectopic skeletal muscle lipid deposition. IL-18 mRNA is expressed in human skeletal muscle but a role for IL-18 in muscle has not been identified. Patients with HIV-infection and lipodystrophy (LD) are characterized by lipid and glucose disturbances and increased levels of circulating IL-18. We hypothesized that skeletal muscle IL-18 and IL-18 receptor (R) expression would be altered in patients with HIV-lipodystrophy.

Design and methods

Twenty-three HIV-infected patients with LD and 15 age-matched healthy controls were included in a cross-sectional study. Biopsies from the vastus lateralis muscle were obtained and IL-18 and IL-18R mRNA expression were measured by real-time PCR and sphingolipids (ceramides, sphingosine, sphingosine-1-Phosphate, sphinganine) were measured by HPLC. Insulin resistance was assessed by HOMA and the insulin response during an OGTT.

Results

Patients with HIV-LD had a 60% and 54% lower level of muscular IL-18 and IL-18R mRNA expression, respectively, compared to age-matched healthy controls. Patients with HIV-LD had a trend towards increased levels of ceramide (18.3±4.7 versus 14.8±3.0,p = 0.06) and sphingosine (0.41±0.13 versus 0.32±0.07, and lower level of sphinganine (p = 0.06). Low levels of muscle IL-18 mRNA correlated to high levels of ceramides (r = -0.31, p = 0.038) and sphingosine-1P (r = -0.29, p = 0.046) in skeletal muscle, whereas such a correlation was not found in healthy controls. Low expression of IL-18 mRNA in skeletal muscle correlated to elevated concentration of circulating triglycerides (R_p = -0.73, p<0.0001). Neither muscle expression of IL-18 mRNA or ceramide correlated to parameters of insulin resistance.

Conclusion

IL-18 (mRNA) in skeletal muscle appears to be involved in the regulation of intramuscular lipid metabolism and hypertriglyceridemia.

Alterations in systemic levels of Th1, Th2, and Th17 cytokines in overweight adolescents and obese mice

BACKGROUND

Obesity represents a major problem for patients and health care systems in most industrialized countries. A chronic inflammatory state in obese individuals leads to disease conditions associated with activation of cellular immune mechanisms. Here, we sought to investigate the role of Th1-, Th2-, and Th17-related cytokines in overweight adolescents and mice on a high-fat diet.

METHODS

Plasma samples were obtained from 79 male adolescents aged 13-17 years. Thirty-seven of them had a body mass index (BMI) above the 90th age-specific percentile. Th1, Th2, and Th17 cytokines were measured using Bio-Plex multiplex technology (Bio-Rad, Hercules, USA). In an experimental approach, mice were fed with high-fat (HFD) or normal chow for 15 weeks.

RESULTS

Interleukin (IL)-17 concentrations were significantly decreased in overweight adolescents compared to lean controls [99.8 ± 7.3 pg/mL standard error of the mean (SEM) vs 146.6 ± 11.5 pg/mL SEM P = .001]. Levels of IL-17 correlated significantly with anthropometrical parameters of obesity. A concordant response was found in mice consuming a HFD for 15 weeks compared to controls (861 ± 165 pg/mL SEM vs 1575 ± 187 pg/ml SEM, P = .0183). However, a biphasic response was evident for most Th1, Th2, and Th17 cytokines as levels initially increased within the first 5 weeks on HFD and showed a decline afterwards.

CONCLUSIONS

In contrast to previous studies showing elevated levels of IL-17 in obese adults, we found a decreasing trend in overweight adolescents. This difference could possibly be related to the fact that disease conditions associated with obesity such as hypertension, vascular pathologies, diabetes, and a triggering of the Th1/Th17 axis were not yet present in overweight teenagers.

Integrated Immunomodulatory Mechanisms through which Long-Chain n-3 Polyunsaturated Fatty Acids Attenuate Obese Adipose Tissue Dysfunction

Obesity is a global health concern with rising prevalence that increases the risk of developing other chronic diseases. A causal link connecting overnutrition, the development of obesity and obesity-associated co-morbidities is visceral adipose tissue (AT) dysfunction, characterized by changes in the cellularity of various immune cell populations, altered production of inflammatory adipokines that sustain a chronic state of low-grade inflammation and, ultimately, dysregulated AT metabolic function. Therefore, dietary intervention strategies aimed to halt the progression of obese AT dysfunction through any of the aforementioned processes represent an important active area of research. In this connection, fish oil-derived dietary long-chain n-3 polyunsaturated fatty acids (PUFA) in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been demonstrated to attenuate obese AT dysfunction through multiple mechanisms, ultimately affecting AT immune cellularity and function, adipokine production, and metabolic signaling pathways, all of which will be discussed herein.

Current role of the NLRP3 inflammasome on obesity and insulin resistance: A systematic review

NLRP3 inflammasome activation seems to be a culprit behind the chronic inflammation characteristic of obesity and insulin resistance (IR). Nutrient excess generates danger-associated molecules that activate NLRP3 inflammasome-caspase 1, leading to maturation of IL-1β and IL-18, which are proinflammatory cytokines released by immune cells infiltrating the adipose tissue (AT) from obese subjects. Although several studies have reported an association of the NLRP3 inflammasome with obesity and/or IR; contradictory results were also reported by other studies. Therefore, we conducted a systematic review to summarize results of studies that evaluated the association of the NLRP3 with obesity and IR. Nineteen studies were included in the review. These studies focused on NLRP3 expression/polymorphism analyses in AT. Overall, human studies indicate that obesity and IR are associated with increased NLRP3 expression in AT. Studies in obese mice corroborate this association. Moreover, high fat diet (HFD) increases Nlrp3 expression in murine AT while calorie-restricted diet decreases its expression. Hence, Nlrp3 blockade in mice protects against HFD-induced obesity and IR. NLRP3 rs10754558 polymorphism is associated with risk for T2DM in Chinese Han populations. In conclusion, available studies strongly points for an association between NLRP3 inflammasome and obesity/IR.

Lymphocytes and macrophages in adipose tissue in obesity: markers or makers of subclinical inflammation?

Obesity is accompanied by the development of chronic low-grade inflammation in adipose tissue. The presence of chronic inflammatory response along with metabolically harmful factors released by adipose tissue into the circulation is associated with several metabolic complications of obesity such as type 2 diabetes mellitus or accelerated atherosclerosis. The present review is focused on macrophages and lymphocytes and their possible role in low-grade inflammation in fat. Both macrophages and lymphocytes respond to obesity-induced adipocyte hypertrophy by their migration into adipose tissue. After activation and differentiation, they contribute to the development of local inflammatory response and modulation of endocrine function of adipose tissue. Despite intensive research, the exact role of lymphocytes and macrophages within adipose tissue is only partially clarified and various data obtained by different approaches bring ambiguous information with respect to their polarization and cytokine production. Compared to immunocompetent cells, the role of adipocytes in the obesity-related adipose tissue inflammation is often underestimated despite their abundant production of factors with immunomodulatory actions such as cytokines or adipokines such as leptin, adiponektin, and others. In summary, conflicting evidence together with only partial correlation of in vitro findings with true in vivo situation due to great heterogeneity and molecular complexity of tissue environment calls for intensive research in this rapidly evolving and important area.

Inability to replete white adipose tissue during recovery phase of sepsis is associated with increased autophagy, apoptosis, and proteasome activity

Adipose tissue is an important energy depot and endocrine organ, and the degree of adiposity impacts the host response to infection. However, little is known regarding the mechanisms by which white adipose tissue (WAT) is lost acutely and then restored after the resolution of sepsis. Therefore, the signaling pathways governing protein synthesis, autophagy, apoptosis, and the ubiquitin-proteasome were investigated to identify potential mechanisms mediating the acute (24 h) loss of WAT after cecal ligation and puncture as well as the failure to replenish WAT during recovery (day 10). While whole body fat mass was decreased equally in pair-fed control and septic mice at 5 days after cecal ligation and puncture, fat mass remained 35% lower in septic mice at day 10 During sepsis-recovery, protein synthesis in epididymal WAT was increased compared with control values, and this increase was associated with an elevation in eukaryotic translation initiation factor (eIF)2Bε but no change in mammalian target of rapamycin complex 1 activity (eIF4E-binding protein-1 or S6 kinase 1 phosphorylation). Protein breakdown was increased during sepsis-recovery, as evidenced by the elevation in ubiquitin-proteasome activity. Moreover, indexes of autophagy (light chain 3B-II, autophagy-related protein 5/12, and beclin) were increased during sepsis-recovery and associated with increased AMP-activated kinase-dependent Ser⁵⁵⁵-phosphorylated Unc-51-like autophagy activating kinase-1. Apoptosis was increased, as suggested by the increased cleavage of caspase-3 and poly(ADP-ribose) polymerase. These changes were associated with increased inflammasome activity (increased NLR family, pyrin domain containing 3; TMS1; and caspase-1 cleavage) and the endoplasmic reticulum stress response (increased eIF2α and activating transcription factor-4) and browning (uncoupling protein-1) in epididymal WAT. Our data suggest that WAT stores remain depleted during recovery from sepsis due to sustained inflammation and elevations in protein and cellular degradation, despite the increase in protein synthesis.