Cees J. Tack

Inflammasome is a central player in the induction of obesity and insulin resistance

Inflammation plays a key role in the pathogenesis of obesity. Chronic overfeeding leads to macrophage infiltration in the adipose tissue, resulting in proinflammatory cytokine production. Both microbial and endogenous danger signals trigger assembly of the intracellular innate immune sensor Nlrp3, resulting in caspase-1 activation and production of proinflammatory cytokines IL-1β and IL-18. Here, we showed that mice deficient in Nlrp3, apoptosis-associated speck-like protein, and caspase-1 were resistant to the development of high-fat diet-induced obesity, which correlated with protection from obesity-induced insulin resistance. Furthermore, hepatic triglyceride content, adipocyte size, and macrophage infiltration in adipose tissue were all reduced in mice deficient in inflammasome components. Monocyte chemoattractant protein (MCP)-1 is a key molecule that mediates macrophage infiltration. Indeed, defective inflammasome activation was associated with reduced MCP-1 production in adipose tissue. Furthermore, plasma leptin and resistin that affect energy use and insulin sensitivity were also changed by inflammasome-deficiency. Detailed metabolic and molecular phenotyping demonstrated that the inflammasome controls energy expenditure and adipogenic gene expression during chronic overfeeding. These findings reveal a critical function of the inflammasome in obesity and insulin resistance, and suggest inhibition of the inflammasome as a potential therapeutic strategy.

Deficiency of interleukin-18 in mice leads to hyperphagia, obesity and insulin resistance

Here we report the presence of hyperphagia, obesity and insulin resistance in knockout mice deficient in IL-18 or IL-18 receptor, and in mice transgenic for expression of IL-18 binding protein. Obesity of Il18−/− mice resulted from accumulation of fat tissue based on increased food intake. Il18−/− mice also had hyperinsulinemia, consistent with insulin resistance and hyperglycemia. Insulin resistance was secondary to obesity induced by increased food intake and occurred at the liver level as well as at the muscle and fat-tissue level. The molecular mechanisms responsible for the hepatic insulin resistance in the Il18−/− mice involved an enhanced expression of genes associated with gluconeogenesis in the liver of Il18−/− mice, resulting from defective phosphorylation of STAT3. Recombinant IL-18 (rIL-18) administered intracerebrally inhibited food intake. In addition, rIL-18 reversed hyperglycemia in Il18−/− mice through activation of STAT3 phosphorylation. These findings indicate a new role of IL-18 in the homeostasis of energy intake and insulin sensitivity.

The Inflammasome Puts Obesity in the Danger Zone

Obesity-induced inflammation is an important contributor to the induction of insulin resistance. Recently, the cytokine interleukin-1β (IL-1β) has emerged as a prominent instigator of the proinflammatory response in obesity. Several studies over the last year have subsequently deciphered the molecular mechanisms responsible for IL-1β activation in adipose tissue, liver, and macrophages and demonstrated a central role of the processing enzyme caspase-1 and of the protein complex leading to its activation called the inflammasome. These data suggest that activation of the inflammasome represents a crucial step in the road from obesity to insulin resistance and type 2 diabetes.

Troglitazone Decreases the Proportion of Small, Dense LDL and Increases the Resistance of LDL to Oxidation in Obese Subjects

OBJECTIVE Insulin resistance is associated with a predominance of small, atherogenic LDL particles that are more prone to oxidative modification. Treatment with the insulin-sensitizer troglitazone may improve LDL composition and resistance to oxidation. RESEARCH DESIGN AND METHODS In a randomized double-blind crossover design, 15 obese subjects were treated with either 400 mg troglitazone daily or placebo for 8 weeks. Insulin sensitivity (clamp), (apo)lipoproteins, LDL subclass pattern, plasma TBARS, and ex vivo LDL oxidation were determined. RESULTS Troglitazone treatment improved insulin sensitivity. LDL cholesterol increased from 2.58 ± 0.18 to 2.77 ± 0.20 mmol/1 (P = 0.03) because of an increase in large (buoyant) LDL1 (from 0.45 ± 0.04 to 0.62 ± 0.09 mmol/1, P = 0.008). Because small (dense) LDL3 decreased, LDL1:LDL3 ratio increased (P = 0.02). Plasma TBARS concentration declined significantly, and the lag time of ex vivo LDL oxidation showed a small but significant increase. CONCLUSIONS In obese subjects, treatment with troglitazone improves insulin sensitivity, increases the ratio of large buoyant to small dense LDL, and appears to enhance the resistance of the LDL particle to oxidation. These qualitative changes in lipoproteins may have a beneficial effect on cardiovascular risk profile and compensate for a small increase in LDL cholesterol.

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 β-cell function. CONCLUSIONS Our results suggest that anakinra does not improve insulin sensitivity in obese, insulin-resistant, nondiabetic subjects.

Prevalence of comorbid depression is high in out-patients with Type 1 or Type 2 diabetes mellitus. Results from three out-patient clinics in the Netherlands.

Diabet. Med. 27, 217–224 (2010)

Hyperglycemia Activates Caspase-1 and TXNIP-Mediated IL-1β Transcription in Human Adipose Tissue

OBJECTIVE Obesity is characterized by elevated levels of proinflammatory cytokines, including interleukin (IL)-1β, that contribute to the development of insulin resistance. In this study, we set out to investigate whether hyperglycemia drives IL-1β 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-1β 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-1β transcription (twofold, P < 0.01) and a significant increase in IL-1β 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-1β levels. CONCLUSIONS High glucose activates caspase-1 in human and murine adipose tissue. Glucose-induced activation of TXNIP mediates IL-1β mRNA expression levels and intracellular pro-IL-1β accumulation in adipose tissue. The concerted actions lead to enhanced secretion of IL-1β in adipose tissue that may contribute to the development of insulin resistance.

Autophagy activity is up-regulated in adipose tissue of obese individuals and modulates proinflammatory cytokine expression

Autophagy, an evolutionary conserved process aimed at recycling damaged organelles and protein aggregates in the cell, also modulates proinflammatory cytokine production in peripheral blood mononuclear cells. Because adipose tissue inflammation accompanied by elevated levels of proinflammatory cytokines is characteristic for the development of obesity, we hypothesized that modulation of autophagy alters adipose tissue inflammatory gene expression and secretion. We tested our hypothesis using ex vivo and in vivo studies of human and mouse adipose tissue. Levels of the autophagy marker LC3 were elevated in sc adipose tissue of obese vs. lean human subjects and positively correlated to both systemic insulin resistance and morphological characteristics of adipose tissue inflammation. Similarly, autophagic activity levels were increased in adipose tissue of obese and insulin resistant animals as compared with lean mice. Inhibition of autophagy by 3-methylalanine in human and mouse adipose tissue explants led to a significant increase in IL-1β, IL-6, and IL-8 mRNA expression and protein secretion. Noticeably, the enhancement in IL-1β, IL-6, and keratinocyte-derived chemoattractant (KC) by inhibition of autophagy was more robust in the presence of obesity. Similar results were obtained by blocking autophagy using small interfering RNA targeted to ATG7 in human Simpson-Golabi-Behmel syndrome adipocytes. Our results demonstrate that autophagy activity is up-regulated in the adipose tissue of obese individuals and inhibition of autophagy enhances proinflammatory gene expression both in adipocytes and adipose tissue explants. Autophagy may function to dampen inflammatory gene expression and thereby limit excessive inflammation in adipose tissue during obesity.

Inflammation links excess fat to insulin resistance: the role of the interleukin-1 family.

A growing body of evidence suggests that cytokines of the interleukin‐1 (IL‐1) family, particularly IL‐1β but also IL‐1Ra and IL‐18, are involved in obesity‐associated inflammation. IL‐1β is produced via cleavage of pro‐IL‐1β by caspase‐1, which in turn is activated by a multiprotein complex called the inflammasome. The components of the NLRP3 inflammasome are involved in sensing obesity‐associated danger signals, both in mice and in human (obese) subjects, with caspase‐1 seemingly the most crucial regulator. Autophagy is upregulated in obesity and may function as a mechanism to control IL‐1β gene expression in adipose tissue to mitigate chronic inflammation. All these mechanisms are operative in human adipose tissue and appear to be more pronounced in human visceral compared to subcutaneous tissue. In animal studies, blocking caspase‐1 activity results in decreased weight gain, decreased inflammation, and improved insulin sensitivity. Human intervention studies with IL‐1Ra (anakinra) have reported beneficial effects in patients with diabetes, yet without significant changes in insulin sensitivity. Clearly, the IL‐1 family of cytokines, especially IL‐1β, plays an important role in obesity‐associated inflammation and insulin resistance and may represent a therapeutic target to reverse the detrimental metabolic consequences of obesity.

A new-generation ultra-long-acting basal insulin with a bolus boost compared with insulin glargine in insulin-naive people with type 2 diabetes: a randomized, controlled trial

OBJECTIVE Insulin degludec/insulin aspart (IDegAsp) is a soluble coformulation of the novel basal analog insulin degludec (IDeg: 70%) and insulin aspart (IAsp: 30%). We compared the safety and efficacy of IDegAsp, an alternative formulation (AF) (55% IDeg and 45% IAsp), and insulin glargine (IGlar) in insulin-naïve subjects with type 2 diabetes inadequately controlled with oral antidiabetic drugs. RESEARCH DESIGN AND METHODS In this 16-week, open-label trial, subjects (mean age 59.1 years, A1C 8.5%, BMI 30.3 kg/m2) were randomized to once-daily IDegAsp (n = 59), AF (n = 59), or IGlar (n = 60), all in combination with metformin. Insulin was administered before the evening meal and dose-titrated to a fasting plasma glucose (FPG) target of 4.0–6.0 mmol/L. RESULTS After 16 weeks, mean A1C decreased in all groups to comparable levels (IDegAsp: 7.0%; AF: 7.2%; IGlar: 7.1%). A similar proportion of subjects achieved A1C <7.0% without confirmed hypoglycemia in the last 4 weeks of treatment (IDegAsp: 51%; AF: 47%; IGlar: 50%). Mean 2-h postdinner plasma glucose increase was lower for IDegAsp (0.13 mmol/L) and AF (0.24 mmol/L) than IGlar (1.63 mmol/L), whereas mean FPG was similar (IDegAsp: 6.8 mmol/L; AF: 7.4 mmol/L; IGlar: 7.0 mmol/L). Hypoglycemia rates were lower for IDegAsp and IGlar than AF (1.2, 0.7, and 2.4 events/patient year). Nocturnal hypoglycemic events occurred rarely for IDegAsp (1 event) and IGlar (3 events) compared with AF (27 events). CONCLUSIONS In this proof-of-concept trial, once-daily IDegAsp was safe, well tolerated, and provided comparable overall glycemic control to IGlar at similar low rates of hypoglycemia, but better postdinner plasma glucose control.