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

The immune competent abdominal adipose tissue, either stored viscerally [visceral adipose tissue (VAT)] or sc [sc adipose tissue (SAT)], has been identified as a source of IL-1ß and IL-18. To become active, the proforms of these cytokines require processing by caspase-1, which itself is mediated by the inflammasome. In this descriptive study, we investigate the expression of inflammasome components and caspase-1 in human fat and determine whether caspase-1 activity contributes to the enhanced inflammatory status of VAT. Paired SAT and VAT biopsies from 10 overweight subjects (body mass index, 25-28 kg/m(2)) were used to study the cellular composition and the intrinsic inflammatory capacity of both adipose tissue depots. The percentage of CD8(+) T cells within the lymphocyte fraction was significantly higher in VAT compared with SAT (41.6 vs. 30.4%; P < 0.05). Adipose tissue cultures showed a higher release of IL-1ß (10-fold; P < 0.05), IL-18 (3-fold; P < 0.05), and IL-6 and IL-8 (3-fold, P < 0.05; and 4-fold, P < 0.05, respectively) from VAT compared with SAT that was significantly reduced by inhibiting caspase-1 activity. In addition, caspase-1 activity was 3-fold (P < 0.05) higher in VAT compared with SAT, together with an increase in the protein levels of the inflammasome members apoptosis-associated speck-like protein containing a C-terminal caspase-recruitment domain (2-fold; P < 0.05) and nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (2-fold; nonsignificant). Finally, caspase-1 activity levels were positively correlated with the percentage of CD8(+) T cells present in adipose tissue. Our results show that caspase-1 and nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 inflammasome members are abundantly present in human VAT. The increased intrinsic caspase-1 activity in VAT represents a novel and specific inflammatory pathway that may determine the proinflammatory character of this specific depot.

Treatment with Anakinra improves disposition index but not insulin sensitivity in nondiabetic subjects with the metabolic syndrome: a randomized, double-blind, placebo-controlled study.

CONTEXT: Obesity induces low-grade inflammation that may promote the development of insulin resistance. IL-1 is one of the key inflammatory factors. OBJECTIVE: The objective of the study was to demonstrate improvement of insulin sensitivity by blocking IL-1. DESIGN: This was a randomized, double-blind, crossover study. SETTING: The study was based on ambulatory care. PARTICIPANTS: Participants included nondiabetic, obese subjects with the metabolic syndrome. INTERVENTION: Intervention included 150 mg anakinra sc once daily or matching placebo for 4 wk. MAIN OUTCOME MEASURE: Insulin sensitivity as measured by euglycemic hyperinsulinemic clamp. RESULTS: A total of 13 of 19 subjects completed the study. Although anakinra treatment resulted in a significantly lower level of inflammation illustrated by a reduction in circulating C-reactive protein concentrations and leukocyte numbers, insulin sensitivity was not significantly different after anakinra treatment (2.8 × 10(-2) ± 0.5 × 10(-2)) compared with placebo treatment (2.4 × 10(-2) ± 0.3 × 10(-2) µmol/kg(-1) · min(-1) · pmol(-1), P = 0.15). Adipose tissue examination, performed to analyze local effects of IL-1 receptor antagonist, showed an increased influx of macrophages after treatment with anakinra most likely due to an injection site reaction caused by the vehicle (0.28 ± 0.05 vs. 0.11 ± 0.01 macrophages per adipocyte, P = 0.005). The differences in individual subject insulin sensitivity after anakinra as compared with placebo between subjects were negatively correlated with macrophage infiltration into the adipose tissue (r(2) = 0.46, P = 0.01). The disposition index increased significantly after anakinra treatment (P = 0.04), reflecting an improvement in ß-cell function. CONCLUSIONS: Our results suggest that anakinra does not improve insulin sensitivity in obese, insulin-resistant, nondiabetic subjects.

Hyperglycemia activates caspase-1 and TXNIP-mediated IL-1beta transcription in human adipose tissue.

OBJECTIVE: Obesity is characterized by elevated levels of proinflammatory cytokines, including interleukin (IL)-1ß, that contribute to the development of insulin resistance. In this study, we set out to investigate whether hyperglycemia drives IL-1ß production and caspase-1 activation in murine and human adipose tissue, thus inducing insulin resistance. RESEARCH DESIGN AND METHODS: ob/ob animals were used as a model to study obesity and hyperglycemia. Human adipose tissue fragments or adipocytes were cultured in medium containing normal or high glucose levels. Additionally, the role of thioredoxin interacting protein (TXNIP) in glucose-induced IL-1ß production was assessed. RESULTS: TXNIP and caspase-1 protein levels were more abundantly expressed in adipose tissue of hyperglycemic ob/ob animals as compared with wild-type mice. In human adipose tissue, high glucose resulted in a 10-fold upregulation of TXNIP gene expression levels (P < 0.01) and a 10% elevation of caspase-1 activity (P < 0.05), together with induction of IL-1ß transcription (twofold, P < 0.01) and a significant increase in IL-1ß secretion. TXNIP suppression in human adipocytes, either by a small interfering RNA approach or a peroxisome proliferator-activated receptor-γ agonist, counteracted the effects of high glucose on bioactive IL-1 production (P < 0.01) mainly through a decrease in transcription levels paralleled by reduced intracellular pro-IL-1ß levels. CONCLUSIONS: High glucose activates caspase-1 in human and murine adipose tissue. Glucose-induced activation of TXNIP mediates IL-1ß mRNA expression levels and intracellular pro-IL-1ß accumulation in adipose tissue. The concerted actions lead to enhanced secretion of IL-1ß in adipose tissue that may contribute to the development of insulin resistance.

The inflammasome-mediated caspase-1 activation controls adipocyte differentiation and insulin sensitivity.

Obesity-induced inflammation originating from expanding adipose tissue interferes with insulin sensitivity. Important metabolic effects have been recently attributed to IL-1ß and IL-18, two members of the IL-1 family of cytokines. Processing of IL-1ß and IL-18 requires cleavage by caspase-1, a cysteine protease regulated by a protein complex called the inflammasome. We demonstrate that the inflammasome/caspase-1 governs adipocyte differentiation and insulin sensitivity. Caspase-1 is upregulated during adipocyte differentiation and directs adipocytes toward a more insulin-resistant phenotype. Treatment of differentiating adipocytes with recombinant IL-1ß and IL-18, or blocking their effects by inhibitors, reveals that the effects of caspase-1 on adipocyte differentiation are largely conveyed by IL-1ß. Caspase-1 and IL-1ß activity in adipose tissue is increased both in diet-induced and genetically induced obese animal models. Conversely, mice deficient in caspase-1 are more insulin sensitive as compared to wild-type animals. In addition, differentiation of preadipocytes isolated from caspase-1(-/-) or NLRP3(-/-) mice resulted in more metabolically active fat cells. In vivo, treatment of obese mice with a caspase-1 inhibitor significantly increases their insulin sensitivity. Indirect calorimetry analysis revealed higher fat oxidation rates in caspase-1(-/-) animals. In conclusion, the inflammasome is an important regulator of adipocyte function and insulin sensitivity, and caspase-1 inhibition may represent a novel therapeutic target in clinical conditions associated with obesity and insulin resistance.

The effect of the interleukin-1 cytokine family members IL-1F6 and IL-1F8 on adipocyte differentiation.

Obesity is characterized by chronic low-grade inflammation originating from expanding adipose tissue. In the present study, we examined the adipogenic expression levels of IL-1F6 and IL-1F8, both members of the IL-1 family of cytokines, and their effects on adipose tissue gene expression. Although IL-1F6 is primarily present in adipose tissue resident macrophages and induced by inflammation, IL-1F8 is absent. IL-1F6, but not IL-1F8, reduces adipocyte differentiation, as shown by a significant decrease in PPARγ gene expression. Finally, both IL-1F6 and IL-1F8 are able to induce inflammatory gene expression in mature adipocytes. In conclusion, we demonstrate for the first time that IL-1F6 is present in adipose tissue and that IL-1F6 and IL-1F8 are involved in the regulation of adipose tissue gene expression. Importantly, IL-1F6 inhibits PPARγ expression which may lead to reduced adipocyte differentiation suggesting metabolic effects of this cytokine.

Pioglitazone treatment enlarges subcutaneous adipocytes in insulin-resistant patients.

CONTEXT: Obesity-related insulin resistance is associated with an increase in adipocyte size. In rodent models, treatment with the insulin-sensitizers thiazolidinediones (TZDs) leads to the appearance of small, insulin-sensitive adipocytes. Whether such TZD-dependent morphological changes occur in adipose tissue of insulin-resistant patients is unclear. OBJECTIVE: The objective of the study was to study the effects of treatment with the TZD pioglitazone on sc adipose tissue morphology and function in insulin-resistant subjects. DESIGN: This was a placebo-controlled, randomized crossover study. SETTING: The study was conducted at a university medical center. PATIENTS: Twelve adult patients with congenital adrenal hyperplasia (CAH) characterized by insulin resistance were included in this study. INTERVENTION: After a 4-wk run-in phase, patients were treated with pioglitazone (45 mg/d) followed by placebo, each for 16 wk or vice versa. MAIN OUTCOME MEASURES: After both placebo and pioglitazone treatment, insulin sensitivity was determined by hyperinsulinemic euglycemic clamp and abdominal sc adipose tissue was obtained to measure adipocyte cell surface and expression of genes involved in glucose uptake and inflammation. RESULTS: Pioglitazone treatment significantly improved the insulin sensitivity index (placebo: 0.35 +/- 0.16 micromol/kg . min per milliunit per liter; pioglitazone 0.53 +/- 0.16 micromol/kg . min per milliunit per liter, P < 0.001) and increased mRNA expression levels of adiponectin and glucose transporter-4 in adipose tissue. The increase in insulin sensitivity was accompanied by a significant enlargement of the sc adipocyte cell surface (placebo: 2323 +/- 725 microm(2); pioglitazone 2821 +/- 885 microm(2), P = 0.03). CONCLUSIONS: In the human situation, treatment of insulin-resistant subjects with pioglitazone improves insulin sensitivity, whereas at the same time, sc adipocyte cell surface increases.

Adiponectin multimer distribution in patients with familial combined hyperlipidemia.

Adiponectin is secreted from adipocytes in different multimers, of which the high molecular weight (HMW) form is supposed to mediate favorable metabolic and anti-atherogenic effects. We determined adiponectin multimers in 29 female and 22 male patients with familial combined hyperlipidemia (FCH) and 51 age-, gender-, and BMI-matched controls in relation to cardiovascular disease (CVD). We observed a clear sexual dimorphism of total adiponectin and its multimers. Female, but not male, FCH patients had significant lower total adiponectin and both HMW and low molecular weight (LMW) adiponectin than controls. The adiponectin sensitivity index (ASI), reflected by HMW/total adiponectin, and the LMW/HMW adiponectin ratio did not differ significantly between FCH females and control females. However, FCH females with CVD exhibited significantly lower ASI (34.2+/-10.1% vs 46.0+/-7.1%) and higher LMW/HMW ratio (1.5+/-0.8 vs 0.7+/-0.3) compared to FCH females without CVD, reflecting a more atherogenic adiponectin multimer distribution.

Early postnatal lethality and cardiovascular defects in CXCR7-deficient mice.

CXCR7 is a G-protein coupled receptor that was recently deorphanized and shown to have SDF1 and I-TAC as high affinity ligands. Here we describe the characterization of CXCR7-deficient mice that were generated to further investigate the function of this receptor in vivo. Expression analysis using a LacZ reporter knockin revealed that postnatally Cxcr7 was specifically expressed in cardiomyocytes, vascular endothelial cells of the lung and heart, the cerebral cortex and in osteocytes of the bone. Adult tissues revealed high expression in cardiomyocytes and osteocytes. The observation that 70% of the Cxcr7-/- mice died in the first week after birth coincides with expression of Cxcr7 in vascular endothelial cells and in cardiomyocytes. An important role of CXCR7 in the cardiovascular system was further supported by the observation that hearts of the Cxcr7-/- mice were enlarged, showed myocardial degeneration and fibrosis of postnatal origin, and hyperplasia of embryonic origin. Despite high expression in osteocytes no apparent bone phenotype was observed, neither in combination with ovariectomy nor orchidectomy. Thus as CXCR7 does not seem to play an important role in bone our data indicate an important function of CXCR7 in the cardiovascular system during multiple steps of development.