Circulating IL-18 concentration is associated with insulin sensitivity and glucose tolerance through increased fat-free mass

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.

Age- and Gender-Related Serum Level of Interleukin 18 in Iranian Fars Ethnic Group with Metabolic Syndrome

Background: The purpose of the present study was to investigate the age- and gender-related serum level of interleukin 18 (IL18) in male and female Iranian Fars ethnic group with metabolic syndrome components. Methods: The study included 226 native Iranian Fars ethnic groups. One hundred sixteen females and 110 men were selected. There were 60 females and 50 males with metabolic syndrome and 56 females and 60 males without metabolic syndrome. The serum fasting blood glucose (FBS), lipid profiles, and IL18 were measured. The National Cholesterol Education Program Adult treatment Panel III criteria were used to determine metabolic syndrome components. Results: There were significant differences between the males and females [except high-density lipoprotein (HDL)] with and without metabolic syndrome for the mean body mass index, FBS, HDL-cholesterol, waist circumference (WC), triglyceride (TG), and IL18 levels in all age groups. Serum IL18 was the highest in males and females in age groups 61-70 and 41-50 years with metabolic syndrome, respectively. Serum IL18 levels significantly correlated with TG and waist WC in males (and also correlated with HDL) and females with the metabolic syndrome. There were significant correlations between IL18 and TG and WC in males (and also correlated with HDL) in ages 61-70 years and females in ages 41-50 years with the metabolic syndrome. Conclusions: The increased IL18 level in both gender and different ages may have an important role in the alteration of some metabolic syndrome components. These alterations may be made to happen in different related metabolic diseases. IL18 seems to be a useful biomarker for the management of metabolic syndrome components and the risk factors of cardiovascular disease.

Higher levels of IL-18 in patients with prediabetes compared to obese normoglycaemic controls

Background: Overweight and obesity are linked to low-grade chronic inflammation that can impair normal insulin function and induce insulin resistance. The aim of this study was to compare IL-18 levels between patients with prediabetes and obese normoglycaemic controls.Patients and methods: In this study, we included 131 patients with mean age 54.9 ± 9.1 years, divided into two groups - group 1 with obesity without glycaemic disturbances (n = 66) and group 2 with prediabetes (n = 65). IL-18 was measured using enzyme-linked immunosorbent assay (ELISA) method.Results: Patients with prediabetes had significantly higher levels of IL-18 compared to obese controls (304.0 ± 220.4 vs. 233.6 ± 103.6 pg/l, p=.029). When patients with prediabetes were divided into IFG only, IGT only and IFG + IGT the highest levels of IL-18 were found in IGT only patients.Conclusions: Patients with prediabetes have higher levels of IL18 compared to obese normoglycemic controls.

IL-18 and infections: Is there a role for targeted therapies?

Interleukin (IL)-18 is a pro-inflammatory cytokine belonging to the IL-1 family, first identified for its interferon-γ-inducing properties. IL-18 regulates both T helper (Th) 1 and Th2 responses. It acts synergistically with IL-12 in the Th1 paradigm, whereas with IL-2 and without IL-12 it can induce Th2 cytokine production from cluster of differentation (CD)4⁺ T cells, natural killer (NK cells, NKT cells, as well as from Th1 cells. IL-18 also plays a role in the hemophagocytic lymphohistiocytosis, a life-threatening condition characterized by a cytokine storm that can be secondary to infections. IL-18-mediated inflammation was largely studied in animal models of bacterial, viral, parasitic, and fungal infections. These studies highlight the contribution of either IL-18 overproduction by the host or overresponsiveness of the host to IL-18 causing an exaggerated inflammatory burden and leading to tissue injury. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the coronavirus disease 2019 (COVID-19). The damage in the later phase of the disease appears to be driven by a cytokine storm, including interleukin IL-1 family members and secondary cytokines like IL-6. IL-18 may participate in this hyperinflammation, as it was previously found to be able to cause injury in the lung tissue of infected animals. IL-18 blockade has become an appealing therapeutic target and has been tested in some IL-18-mediated rheumatic diseases and infantile-onset macrophage activation syndrome. Given its role in regulating the immune response to infections, IL-18 blockade might represent a therapeutic option for COVID-19, although further studies are warranted to investigate more in detail the exact role of IL-18 in SARS-CoV-2 infection.

Hydrogen sulfide modulates high glucose-induced NLRP3 inflammasome activation in 3T3-L1 adipocytes

Activation of the NACHT leucine rich repeat and pyd domains-containing 3 (NLRP3) inflammasome plays an important role in the initiation of inflammation in adipose tissue in diabetic patients. However, the mechanisms underlying this are not fully understood. Hydrogen sulfide (H₂S) has been shown to have anti-inflammatory properties in various cell types. The present study aimed to investigate the effect of H₂S on high glucose (HG)-induced NLRP3 inflammasome activation in adipocytes. Adipocytes were differentiated from 3T3-L1 cells and treated with low glucose (LG), HG, H₂S donor sodium hydrosulfide (NaHS) or N-acetyl-tyrosyl-valyl- alanyl-aspartyl chloromethyl ketone, an inhibitor of the cysteine protease caspase-1. The expression levels of NLRP3, apoptosis-associated speck-like protein containing A CARD (ASC) and caspase-1, and the release of interleukin (IL)-1β and IL-18 were measured. The results of the present study indicated that HG increased the expression levels of NLRP3, ASC and cleaved caspase-1, and the release of IL-1β and IL-18 in adipocytes. Caspase-1 inhibition abolished HG-induced production of IL-1β and IL-18 in adipocytes. Furthermore, NaHS inhibited the expression of NLRP3, ASC and cleaved caspase-1, and the production of IL-1β and IL-18 in adipocytes treated with HG. In conclusion, HG may increase and exogenous H₂S may inhibit HG-induced NLRP3 inflammasome activation in adipocytes.

Interleukin-18 and testosterone levels in men with metabolic syndrome

OBJECTIVE

Interleukin 18 (IL-18) is an adipokine associated with obesity. Data about the relationship of IL-18 to the metabolic syndrome (MS) are still scarce. Low testosterone (T) levels are common in men with MS, but we did not find data about the levels of IL-18 in men with low T. The aim of this study was to determine the levels of IL-18 in men with MS with or without low T.

PATIENTS AND METHODS

A total of 251 men were included in the study. Of them 218 had MS (IDF 2005) and they were divided according to their morning total testosterone (TT) level (cutoff 10.4 nmol/l) into two groups: MS-low T (N = 84) and MS-normal T (N = 134). The control group consisted of 33 men without MS and low T. IL-18 was determined in serum using enzyme-linked immunosorbent assay. A small group of eight men with MS and low T levels received testosterone therapy for three months and physical and laboratory parameters were monitored at the end of that period.

RESULTS

MS men were at mean age (±SD) = 53.77 ± 9.59 years; body mass index (BMI) = 34.0 ± 6.3 kg/m²; and TT = 12.59 ± 5.66 nmol/l. The control group was at age = 52.12 ± 5.2 years (NS); BMI = 25.6 ± 2.4 kg/m² (p < .001); and TT = 17.8 ± 5.68 nmol/l (p < .001), respectively. The levels of IL-18 were higher in the MS group - 345 pg/ml compared to the control one - 264 pg/ml (p < .01). There was no significant difference between MS-low T (330.6 pg/ml) and MS-normal T (350.2 pg/ml) subgroups. The MS-normal T differed more significantly from the control group (p < .001). Significant correlation of testosterone with IL-18 levels was not found. IL-18 correlated with parameters of obesity, lipids, fasting blood sugar (p < .05) and the number of criteria for MS (p < .001). Three months on T treatment showed improvement in obesity parameters and only in one patient IL-18 had clear reduction while the rest showed no change.

CONCLUSIONS

In this study, higher IL-18 levels were found in the presence of MS compared to healthy men, but they did not differ between men having MS with or without LOH.

Interleukin-18 serum level is elevated in type 2 diabetes and latent autoimmune diabetes

BACKGROUND

Interleukin-18 (IL-18) is an inflammatory cytokine found to be elevated in obesity, metabolic syndrome and type 2 diabetes (T2D) as a part of the chronic low-grade inflammatory process in these states. The aim of the study was to evaluate the interleukin level in patients with latent autoimmune diabetes of the adults (LADA) in comparison to that in T2D subjects.

MATERIALS AND METHODS

IL-18 was analyzed through enzyme-linked immunosorbent assay in 76 participants with T2D and 24 with LADA and 14 control subjects. Evaluation was also carried out in body mass index (BMI)- and glycemic control-matched diabetic patients.

RESULTS

The serum concentration of IL-18 was higher in patients with T2D (389.04 ± 203.44 pg/mL) and LADA (327.04 ± 144.48 pg/mL) than that in control subjects (219.88 ± 91.03 pg/mL), P < 0.05. However, it was not significantly different between both diabetic groups (P = 0.255) despite higher IL-6 (4.78 ± 5.84 vs 1.79 ± 0.96 pg/mL, P < 0.001) and hs-CRP (2.60 ± 1.70 vs 1.29 ± 1.20 mg/L, P = 0.002) level in T2D patients. The results were persistent in BMI-matched subjects with diabetes (IL-18 = 403.48 ± 226.32 vs 329.30 ± 146.30 pg/mL, respectively for T2D and LADA, P = 0.391). The correlations in T2D group concerning HDL cholesterol (r = -0.377, P = 0.001), postprandial glucose (r = 0.244, P = 0.043), IL-6 (r = 0.398, P < 0.001) and hs-CRP (r = 0.427, P = 0.001) were not confirmed in LADA and control subjects.

CONCLUSION

The IL-18 serum level was higher in T2D and LADA than that in control subjects, but did not differ between both diabetic groups, even when they were BMI matched. Correlations with lipid, glycemic and inflammatory parameters were present in T2D only.

Increased adipose tissue expression of IL-18R and its ligand IL-18 associates with inflammation and insulin resistance in obesity

INTRODUCTION

The proinflammatory cytokine IL-18 is involved in the pathogenesis of metabolic syndrome. While the changes in IL-18 are known, IL-18R expression and relationship with IL-18 and other inflammatory markers in the adipose tissue in obesity/type-2 diabetes (T2D) remain unclear.

METHODS

We, therefore, determined the adipose tissue expression of IL-18R and IL-18 mRNA/protein in lean, overweight, and obese individuals with and without T2D, 15 each, using qRT-PCR, immunohistochemistry, and confocal microscopy. Data (mean ± SEM) were analyzed using unpaired t-test and Pearson's correlation (r); all P values ≤0.05 were considered statistically significant.

RESULTS

We found the upregulated gene/protein expression of IL-18R and IL-18 in non-diabetic obese/overweight as compared with lean individuals (P < 0.05). BMI correlated positively (P < 0.05) with the adipose tissue expression of IL-18R (mRNA: r = 0.90 protein: r = 0.84) and IL-18 (mRNA: r = 0.84 protein: r = 0.80). Similarly, in T2D individuals, gene and protein expression of IL-18R/IL-18 was significantly higher in obese as compared with overweight/lean individuals. The BMI was associated with the changes in both IL-18R (mRNA: r = 0.55 protein: r = 0.50) and IL-18 (mRNA: r = 0.53 protein: r = 0.57) expression. IL-18R/IL-18 gene expression in the adipose tissue was positively associated (P < 0.05) with local gene expression of other inflammatory markers including CD11c, CD86, CD68, CD163, TNF-α, and CCL5. Homeostatic model assessment of insulin resistance (HOMA-IR) was higher in diabetic/non-diabetic obese and it correlated with BMI (P < 0.05). IL-18R and IL-18 mRNA/protein expression in obesity was associated with HOMA-IR only in non-diabetics.

CONCLUSIONS

The adipose tissue IL-18R/IL-18 expression is enhanced in obesity which associates with proinflammatory gene signature and insulin resistance in these individuals.

Adiponectin and pro-inflammatory cytokines are modulated in Vietnamese patients with type 2 diabetes mellitus

AIMS/INTRODUCTION

Adipose tissue-derived hormones are associated with metabolic disorders including type 2 diabetes mellitus. The present study investigated the levels of adiponectin and pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin-1 beta (IL-1β) and IL-10 in Vietnamese patients with type 2 diabetes mellitus, and their correlations with clinical parameters of overweight and type 2 diabetes mellitus.

MATERIALS AND METHODS

Based on body mass index, 73 patients with type 2 diabetes mellitus were categorized either as overweight or non-overweight. As healthy controls, 57 overweight and non-overweight individuals without type 2 diabetes mellitus were included. The adiponectin, TNF-α, IL-1β and IL-10 levels were measured in the sera samples in all study participants by enzyme-linked immunosorbent assay and were correlated with clinical parameters.

RESULTS

The adiponectin levels were lower in patients with type 2 diabetes mellitus (2.5 ± 1.5 μg/mL) compared with controls (16 ± 18.6 μg/mL; P < 0.0001), and were decreased in overweight individuals compared with those who were not overweight. The TNF-α and IL-1β levels were increased, whereas the IL-10 levels were decreased in patients with type 2 diabetes mellitus and in overweight controls compared with non-overweight controls (P < 0.0001). The adiponectin levels were correlated with the TNF-α, IL-1β, IL-10 levels, and the clinical parameters of overweight and type 2 diabetes mellitus. The quantitative insulin sensitivity check index and homeostasis model assessment insulin resistance indexes were correlated with the relative ratios of adiponectin/TNF-α, adiponectin/IL-1β, adiponectin/IL-10, TNF-α/IL-10 and IL-1β/IL-10.

CONCLUSIONS

Adiponectin and pro-inflammatory cytokines are associated with type 2 diabetes mellitus, and might serve as a prognostic marker and a therapeutic intervention for overweight-related type 2 diabetes mellitus.

A Study to Investigate the Efficacy and Safety of an Anti-Interleukin-18 Monoclonal Antibody in the Treatment of Type 2 Diabetes Mellitus

Objective

Evidence suggests that chronic subclinical inflammation plays an important role in the pathogenesis of type 2 diabetes (T2DM). Circulating levels of interleukin (IL)-18 appear to be associated with a number of micro- and macrovascular comorbidities of obesity and T2DM. This study was designed to investigate whether inhibition of IL-18 had any therapeutic benefit in the treatment of T2DM. Preliminary efficacy, safety and tolerability, pharmacokinetics, and pharmacodynamics of the anti-IL-18 monoclonal antibody, GSK1070806, were assessed.

Research Design and Methods

This was a multicentre, randomized, single-blind (sponsor-unblinded), placebo-controlled, parallel-group, phase IIa trial. Obese patients of either sex, aged 18–70 years, with poorly controlled T2DM on metformin monotherapy were recruited. Patients received two doses, of placebo (n = 12), GSK1070806 0.25 mg/kg (n = 13) or GSK1070806 5 mg/kg (n = 12). The primary end-point was the change from baseline in fasting plasma glucose and weighted mean glucose area under the curve (AUC)(0–4 hours) postmixed meal test on Days 29, 57, and 85.

Results

Thirty-seven patients were randomized to one of the three treatment arms. There were no statistically significant effects of GSK1070806 doses on fasting plasma glucose levels, or weighted mean glucose AUC(0–4 hours) compared with placebo.

Conclusions

GSK1070806 was well tolerated, and inhibition of IL-18 did not lead to any improvements in glucose control. However, because of study limitations, smaller, potentially clinically meaningful effects of IL-18 inhibition cannot be excluded.

Trial Registration

ClinicalTrials.gov NCT01648153

Potential role of interleukin-18 in patients with rheumatoid arthritis-associated carotid intima-media thickness but not insulin resistance

OBJECTIVE

Plasma interleukin-18 (IL-18) has been reported to be associated with homeostasis model assessment of insulin resistance (HOMA-IR). It also has been described as one of the factors that, in addition to insulin resistance, may also contribute to atherosclerosis. Parameters of systemic inflammation are also significantly associated with circulating IL-18. Our objective was to investigate whether IL-18 is associated with insulin resistance and atherosclerosis in patients with rheumatoid arthritis (RA) in which accelerated atherogenesis develops.

MATERIAL AND METHODS

Fifty-one female RA patients and 30 female controls were enrolled in the study; 31 of them were without disease-modifying antirheumatic drug (DMARD) treatment and had a relatively short disease duration. Disease activity was assessed by Disease Activity Score (DAS) 28 index. HOMA-IR method was used to detect insulin resistance. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), fasting plasma glucose (FPG), insulin, tumor necrosis factor alpha (TNF-α), and IL-18 levels were evaluated. Also, carotid intima-media thickness (cIMT) was measured.

RESULTS

There were no differences between patients and the control group according to age, sex, and body mass index. ESR, CRP, insulin, FPG, HOMA-IR, TNF-α, IL-18 levels, and cIMT measurements were significantly high in the patient group. HOMA-IR and cIMT measurements were similar and high in both the DMARD and non-DMARD patient groups. HOMA-IR correlated with TNF-α (r=0.308, p=0.028), but no correlation was found between IL-18 and HOMA-IR. However, IL-18 was correlated positively with cIMT (r= 0.318, p=0.028) and negatively with BMI (r=-0.360, p=0.01).

CONCLUSION

IL-18 is associated with atherosclerosis in RA patients. However, no significant relation was found with insulin resistance. IL-18 may be a marker for early evaluation of atherosclerosis in RA patients.

Obesity development in caspase-1-deficient mice

Caspase-1 is a member of the intracellular cysteine protease family that mediates inflammation through the activation of the cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18). As mice lacking IL-18 become obese and insulin resistant, and both IL-18 and IL-1β have a role in overall energy balance, we sought to determine whether caspase-1 deficiency also causes obesity. Male and female caspase-1-deficient (caspase-1-/-) and control (wild-type (WT)) mice were fed either a high-fat (HF, 45% of kcal) or a low-fat (LF, 10% of kcal) synthetic diet starting at 6 weeks of age. Caspase-1-/- mice maintained lower but detectable levels of IL-18 compared with WT mice. Plasma IL-1β levels were below the detection limit for both KO and WT mice. Male caspase-1-/- mice gained extra fat mass by 16 weeks on the HF diet, but not until 40 weeks on the LF diet. Female capase-1-/- mice gained more fat by 28 weeks but only on the HF diet. These data indicate that caspase-1-/- mice develop obesity with an age and sex-dependent differences, and only male mice display obesity on LF diet. Overall, this study suggests that the lower level of IL-18 in caspase-1-/- mice might be causing obesity development similarly to IL-18-deficient mice.

Left ventricular function impairment in patients with normal-weight obesity: contribution of abdominal fat deposition, profibrotic state, reduced insulin sensitivity, and proinflammatory activation

BACKGROUND

Obesity predisposes to left ventricular (LV) dysfunction and heart failure; however, the risk of these complications has not been assessed in patients with a normal body mass index (BMI) but increased body fat content (normal-weight obesity, NWO). We hypothesized that LV performance in NWO may be impaired and sought to investigate potential contributors to cardiac functional abnormalities.

METHODS AND RESULTS

One hundred sixty-eight subjects (age, 38±7 years) with BMI <25kg/m(2) and no history of any disease affecting the myocardium were classified on the basis of body fat content into 2 groups: with NWO and without NWO. Echocardiographic indices of LV systolic and diastolic function, including myocardial velocities and deformation, serological fibrosis markers, indicators of proinflammatory activation, and metabolic control, were evaluated. Subjects with NWO demonstrated impaired LV systolic and diastolic function, increased fibrosis intensity (assessed by procollagen type I carboxy-terminal propeptide [PICP]), impaired insulin sensitivity, and increased proinflammatory activation as compared with individuals with normal body fat. The independent correlates of LV systolic and diastolic function variables were as follows: for strain, IL-18 (β=-0.17, P<0.006), C-reactive protein (β=-0.20, P<0.002) and abdominal fat deposit (β=-0.20, P<0.003); for tissue S velocity, PICP (β=-0.21, P<0.002) and abdominal fat deposit (β=-0.43, P<0.0001); for tissue E velocity, abdominal fat deposit (β=-0.30, P<0.0001), PICP (β=-0.31, P<0.0001) and homeostasis model assessment of insulin resistance index (HOMA IR; β=-0.20, P<0.002); and for E/e'-PICP, IL-18 (both β=0.18, P<0.01) and HOMA IR (β=0.16, P<0.04).

CONCLUSIONS

In patients with NWO, subclinical disturbances of LV function are independently associated with the extent of abdominal fat deposit, profibrotic state (as reflected by circulating PICP), reduced insulin sensitivity, and proinflammatory activation.

Lean body mass, interleukin 18, and metabolic syndrome in apparently healthy Chinese

OBJECTIVE

We aimed to investigate how lean body mass is related to circulating Interleukin 18 (IL-18) and its association with metabolic syndrome (MetS) among apparently healthy Chinese.

METHODS

A population-based sample of 1059 Chinese men and women aged 35-54 years was used to measure plasma IL-18, glucose, insulin, lipid profile, inflammatory markers and high-molecular-weight (HMW)-adiponectin. Fat mass index (FMI) and lean mass index (LMI) were measured by dual-energy X-ray absorptiometry. MetS was defined by the updated National Cholesterol Education Program Adult Treatment Panel III criteria for Asian-Americans.

RESULTS

Circulating IL-18 was positively correlated with LMI after adjustment for FMI (correlation coefficient = 0.11, P<0.001). The association with the MetS (odds ratio 3.43, 95% confidence interval 2.01-5.85) was substantially higher in the highest than the lowest quartile of IL-18 after multiple adjustments including body mass index. In the stratified multivariable regression analyses, the positive association between IL-18 and MetS was independent of tertiles of FMI, inflammatory markers and HMW-adiponectin, but significantly interacted with tertile of LMI (P for interaction = 0.010).

CONCLUSION

Elevated plasma IL-18 was associated with higher MetS prevalence in apparently healthy Chinese, independent of traditional risk factors, FMI, inflammatory markers and HMW-adiponectin. More studies are needed to clarify the role of lean mass in IL-18 secretion and its associated cardio-metabolic disorders.

The role of interleukin-18 in the metabolic syndrome

The metabolic syndrome is thought to be associated with a chronic low-grade inflammation, and a growing body of evidence suggests that interleukin-18 (IL-18) might be closely related to the metabolic syndrome and its consequences. Circulating levels of IL-18 have been reported to be elevated in subjects with the metabolic syndrome, to be closely associated with the components of the syndrome, to predict cardiovascular events and mortality in populations with the metabolic syndrome and to precede the development of type 2 diabetes. IL-18 is found in the unstable atherosclerotic plaque, in adipose tissue and in muscle tissue, and is subject to several regulatory steps including cleavage by caspase-1, inactivation by IL-18 binding protein and the influence of other cytokines in modulating its interaction with the IL-18 receptor. The purpose of this review is to outline the role of IL-18 in the metabolic syndrome, with particular emphasis on cardiovascular risk and the potential effect of life style interventions.

Circulating IL-18 and the risk of type 2 diabetes in women

AIMS/HYPOTHESIS

The pathophysiology of type 2 diabetes involves pro-inflammatory pathways. We tested the hypothesis that IL-18 predicts future diabetes cases.

METHODS

We used a nested case-control design based in the Nurses' Health Study. Baseline blood samples were collected between 1989 and 1990. Questionnaires to assess body weight, lifestyle (physical activity, diet, smoking) and diabetes diagnosis were sent out and assessed biennially (follow-up until 2002). Cases (n = 1,012) were defined as women developing type 2 diabetes at least 1 year after blood sampling. Control women (n = 1,081) were matched to cases by age, date of blood draw, fasting status and race. We calculated the RR (95% CI) of type 2 diabetes in quintiles of IL-18 using conditional logistic regression with the first quintile as referent; adjustments included matching factors, diabetes risk factors, BMI, adipokine levels (adiponectin, resistin) and inflammatory proteins (C-reactive protein, tumour necrosis factor receptor 2 (TNFalpha-R2) and IL-6).

RESULTS

Higher IL-18 levels were associated with increased risk of developing diabetes, even after adjustment for matching factors and multiple diabetes risk factors: being in the highest quintile of IL-18 was associated with a RR of 1.75 (1.41-2.18) for diabetes relative to the first quintile (p < 0.0001 for trend). Significant trends in association were still observed after adjustment for BMI (RR 1.44 [1.15-1.80], p < 0.0001 for trend) and adiponectin levels (RR 1.28 [1.02-1.60], p = 0.006 for trend). Further adjustment for inflammatory markers in a sub-sample did not significantly change the results.

CONCLUSIONS/INTERPRETATION

Elevated IL-18 levels are associated with higher risk of diabetes. This association is independent of usual risk factors, including BMI and adipokine levels.

Salicylates increase insulin secretion in healthy obese subjects

CONTEXT

Conflicting results on the effects of salicylates on glucose tolerance in subjects with normal glucose tolerance or type 2 diabetes have been reported.

OBJECTIVE

The objective of the study was to investigate the effects of a salicylate derivative (triflusal) on insulin sensitivity and insulin secretion.

DESIGN, SETTING, AND PARTICIPANTS

This was a double-blind, randomized, crossover study with three treatment periods corresponding to two dose levels of triflusal and placebo in healthy obese subjects.

MAIN OUTCOME MEASURES

Insulin sensitivity and insulin secretion, evaluated through frequently sampled iv glucose tolerance test that was performed after each treatment period, were measured. Insulin secretion was also evaluated in vitro in mice and human islets of Langerhans.

RESULTS

The administration of triflusal led to decreased fasting serum glucose concentration in the study subjects. Insulin sensitivity did not significantly change after each treatment period. Insulin secretion, however, significantly increased in a dose-dependent fashion after each triflusal treatment period. The administration of 800 mum of the main triflusal metabolite to whole mice islets of Langerhans led to a sustained increase in intracellular calcium concentration level. This was followed by a significantly increase in insulin secretion. In human islets, 200 mum of 2-hydroxy-4-trifluoromethylbenzoic acid was sufficient to increase insulin release.

CONCLUSIONS

The administration of a salicylate compound led to lowering of serum glucose concentration. We suggest that this effect was mediated through increased insulin secretion induced by salicylate directly on the beta-cell.

Effect of weight loss induced by gastric bypass on proinflammatory interleukin-18, soluble tumour necrosis factor-alpha receptors, C-reactive protein and adiponectin in morbidly obese patients

OBJECTIVE

Interleukin-18 (IL-18) is a potent proinflammatory cytokine whose role in human obesity has recently been suggested. The aim of our study was to analyse in morbidly obese patients undergoing gastric bypass, the relationship of IL-18 with insulin resistance and with proinflammatory cytokines (tumour necrosis factor-alpha receptors, sTNFR), C-reactive protein (CRP) and with adiponectin.

DESIGN

Observational and prospective study.

PATIENTS

Sixty-five morbidly obese patients, aged 45 +/- 8.9 years, were studied before and 12 months after gastric bypass.

MEASUREMENTS

We analysed plasma concentrations of IL-18, sTNFR, CRP and adiponectin.

RESULTS

Plasma concentrations of sTNFR2, IL-18 and CRP were decreased and adiponectin significantly increased after bypass surgery. In the multiple regression analysis, preoperative values of IL-18 remained significantly associated with preoperative triglycerides (beta = 0.47, P = 0.005) and TNFR2 (beta = 0.47, P = 0.004). R(2) for the model = 0.38. Postoperative IL-18 concentrations in the multiple regression analysis were significantly associated with postoperative homeostasis model assessment of insulin resistance (HOMA-IR) (beta = 0.092, P = 0.019) and triglycerides (beta = 0.40, P = 0.036). R(2) for the model = 0.46. IL-18 did not correlate with body mass index, fat mass, fat-free mass or body fat. No relationship was either found between adiponectin and IL-18, TNFR1 and -2 and CRP.

CONCLUSIONS

Massive weight loss induced by gastric bypass reduces IL-18, TNFR2 and CRP. IL-18 might be a marker of the chronic inflammatory process underlying insulin resistance but its lack of association with anthropometric and body composition parameters does not support a major secretion by human adipocytes. IL-18 and sTNFR1 and -2 do not play a main role in the inhibition of the secretion of adiponectin.

Interleukin-18, the Metabolic Syndrome, and Subclinical Atherosclerosis

OBJECTIVE

Although IL-18 promotes atherogenesis in animal studies and predicts cardiovascular risk in humans, it is unknown whether elevated IL-18 levels are associated with coronary atherosclerosis in the general population.

METHODS AND RESULTS

IL-18 plasma levels were determined by ELISA in 2231 subjects from the Dallas Heart Study. In univariable analysis, IL-18 levels associated with traditional cardiovascular risk factors and particularly with components of the metabolic syndrome (MS, P<0.01 for trend across the number of MS components); IL-18 also associated with coronary artery calcium (CAC) scores measured by electron beam computed tomography and aortic plaque measured by MRI (P<0.01 for each). In multivariable analyses, IL-18 remained associated with multiple components of the MS but not with CAC or aortic plaque.

CONCLUSIONS

In a large population-based sample, elevated IL-18 plasma levels associated with risk factors for atherosclerosis and with the metabolic syndrome. The association between IL-18 and atherosclerosis diminished after accounting for traditional cardiovascular risk factors. These data suggest that IL-18 does not add independently to detection of atherosclerotic burden in asymptomatic individuals.

Increased serum interleukin-18 concentration is associated with hypoadiponectinemia in obesity, independently of insulin resistance

OBJECTIVE

Interleukin-18 (IL-18) is a cytokine with proinflammatory and proatherogenic properties, which might be associated with the development of insulin resistance. In contrast, adiponectin, a protein secreted by adipose tissue, might exert insulin-sensitizing and antiatherogenic effects. The aim of the present study was to analyze the association between serum IL-18 and adiponectin in lean and obese subjects, in relation to insulin resistance.

DESIGN

Cross-sectional study.

SUBJECTS

One hundred and thirty individuals, 62 lean (body mass index (BMI)<25 kg/m(2), 30 men and 32 women) and 68 with overweight or obesity (BMI>25 kg/m(2), 24 men and 44 women), with normal glucose tolerance and without concomitant diseases.

MEASUREMENTS

Oral glucose tolerance test, euglycemic hyperinsulinemic clamp, serum concentrations of IL-18, IL-6, soluble tumor necrosis factor-alpha receptors and adiponectin.

RESULTS

Obese subjects had lower insulin sensitivity (M value, P=0.00029) and serum adiponectin (P=0.01) and higher levels of serum IL-18 (P=0.00055). Circulating IL-18 was negatively related to adiponectin (r=-0.31, P=0.00027) and insulin sensitivity (r=-0.33, P=0.00012). Subgroup analysis revealed that these associations were present in the obese (adiponectin, r=-0.38, P=0.0014; M, r=-0.29, P=0.016), but not in lean individuals (r=-0.17, P=0.18 and r=-0.20, P=0.12, respectively). Association of IL-18 with adiponectin remained significant after adjustment for other estimated parameters, including insulin sensitivity. Also, relationship between IL-18 and insulin sensitivity was independent of other estimated parameters.

CONCLUSION

Serum IL-18 is inversely related to serum adiponectin, independently of insulin resistance. The relationships of IL-18 with adiponectin and insulin sensitivity are influenced by the presence of overweight/obesity.

Genetic predispositions to low-grade inflammation and type 2 diabetes

Insulin resistance and cardiovascular disease share common pathophysiological mechanisms, as the chronic activation of the innate immune system. This system constitutes the first line of body's defense and is constituted by different barriers (e.g., epithelia, adipose tissue) and different blood and tissue components (e.g., macrophages, neutrophils). This system generates the acute-phase response in which different acute-phase proteins and cytokines are produced in response to different aggressions as infections and traumatisms. The aim of this response is to eradicate these agents, to repair the harmed tissues, and, through increased insulin resistance, to optimize the energetic substrates, which will be drained to vital tissues and organs (i.e., brain and the immune system). Evolutionary pressures have led to survival of the fittest individuals, those with the genetics that allows the best defense against infection and periods of famine. Evidence is reported according to which gene polymorphisms in the molecules regulating the inflammatory cascade are associated with body composition, insulin action, and characteristics of the metabolic syndrome. The evolutive advantages of increased inflammatory responses, hypersecretion of proinflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, and IL-18], or decreased anti-inflammatory molecules (adiponectin, certain TNF-alpha isoforms, soluble CD14, etc.), would lead in westernized countries to chronic inflammation conditions, such as obesity and type 2 diabetes, resulting in cardiovascular disease.