Circulating mononuclear cells in the obese are in a proinflammatory state

Association of systemic concentrations of macrophage migration inhibitory factor with impaired glucose tolerance and type 2 diabetes: results from the Cooperative Health Research in the Region of Augsburg, Survey 4 (KORA S4)

OBJECTIVE

Macrophage migration inhibitory factor (MIF) is a central cytokine in innate immunity. MIF expression can be regulated by glucose and insulin, but data on the association with type 2 diabetes are sparse. The aim of this study was to test whether MIF is associated with impaired glucose tolerance (IGT) and type 2 diabetes and whether these associations are independent of metabolic and immunological risk factors and to compare the associations of MIF and IGT/type 2 diabetes with those of C-reactive protein (CRP) and interleukin-6 (IL-6) with IGT/type 2 diabetes.

RESEARCH DESIGN AND METHODS

The Cooperative Health Research in the Region of Augsburg/Kooperative Gesundheitsforschung im Raum Augsburg, Survey 4 (KORA S4) is a population-based survey performed in Southern Germany (1999-2001). Of 1,653 participants aged 55-74 years, 236 patients with type 2 diabetes, 242 subjects with IGT, and 244 normoglycemic control subjects matched for age and sex were included in this cross-sectional study. Serum concentrations of MIF were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum MIF concentrations are highly increased in individuals with IGT and type 2 diabetes. The associations of MIF with IGT and type 2 diabetes were independent of classical risk factors and of CRP and IL-6 and were much stronger before and after multivariate adjustment than the associations of CRP and IL-6 with IGT and type 2 diabetes.

CONCLUSIONS

Our data suggest that elevations of systemic MIF concentrations precede the onset of type 2 diabetes. This finding may be relevant because MIF has been reported to contribute to the development of type 2 diabetes-related diseases such as atherosclerosis and cancer.

Metformin inhibits proinflammatory responses and nuclear factor-kappaB in human vascular wall cells

OBJECTIVE

Metformin may benefit the macrovascular complications of diabetes independently of its conventional hypoglycemic effects. Accumulating evidence suggests that inflammatory processes participate in type 2 diabetes and its atherothrombotic manifestations. Therefore, this study examined the potential action of metformin as an inhibitor of pro-inflammatory responses in human vascular smooth muscle cells (SMCs), macrophages (Mphis), and endothelial cells (ECs).

METHODS AND RESULTS

Metformin dose-dependently inhibited IL-1beta-induced release of the pro-inflammatory cytokines IL-6 and IL-8 in ECs, SMCs, and Mphis. Investigation of potential signaling pathways demonstrated that metformin diminished IL-1beta-induced activation and nuclear translocation of nuclear factor-kappa B (NF-kappaB) in SMCs. Furthermore, metformin suppressed IL-1beta-induced activation of the pro-inflammatory phosphokinases Akt, p38, and Erk, but did not affect PI3 kinase (PI3K) activity. To address the significance of the anti-inflammatory effects of a therapeutically relevant plasma concentration of metformin (20 micromol/L), we conducted experiments in ECs treated with high glucose. Pretreatment with metformin also decreased phosphorylation of Akt and protein kinase C (PKC) in ECs under these conditions.

CONCLUSIONS

These data suggest that metformin can exert a direct vascular anti-inflammatory effect by inhibiting NF-kappaB through blockade of the PI3K-Akt pathway. The novel anti-inflammatory actions of metformin may explain in part the apparent clinical reduction by metformin of cardiovascular events not fully attributable to its hypoglycemic action.

Obesity is an independent contributor to functional capacity and inflammation in systemic lupus erythematosus

OBJECTIVE

Obesity induces a proinflammatory state and is a major cause of morbidity in the general population. However, little is known about the effects of obesity in patients with chronic inflammatory illnesses such as systemic lupus erythematosus (SLE).

METHODS

One hundred consecutive patients with SLE were studied to determine the relationship between body mass index (BMI) and functional capacity, measures of fatigue, quality of life, and the inflammation markers C-reactive protein (CRP), the erythrocyte sedimentation rate, and interleukin-6 (IL-6). The association between BMI and patient characteristics was determined, and multiple logistic regression models were used to adjust for age, sex, disease activity, and disease-related damage.

RESULTS

Thirty-three patients had a normal BMI (< 25 kg/m(2)), 28 were overweight (25-29.9 kg/m(2)), and 39 were obese (> or =30 kg/m(2)). Obese patients had worse functional capacity, more fatigue, and higher concentrations of inflammation markers. The mean +/- SD modified Health Assessment Questionnaire (M-HAQ) score was 0.6 +/- 0.4 in obese patients compared with 0.3 +/- 0.4 and 0.2 +/- 0.3 in overweight patients and those with a normal BMI, respectively (P = 0.001). The mean +/- SD concentrations of CRP in obese patients (10.0 +/- 8.6 mg/liter) were higher than those in patients who were overweight (4.7 +/- 5.4 mg/liter) or had a normal BMI (6.2 +/- 9.9 mg/liter) (P < 0.001). Similarly, concentrations of IL-6 were higher in obese patients (P = 0.003). After adjusting for age, sex, disease activity, and damage indices, the associations between BMI and CRP (P < 0.001), M-HAQ scores (P = 0.005), and IL-6 concentrations (P = 0.01) remained significant.

CONCLUSION

Obesity is independently associated with impaired functional capacity and inflammation markers in patients with lupus. Thus, weight loss may improve functional capacity and decrease cardiovascular risk factors.

Adipose tissue metabolism and CD11b expression on monocytes in obese hypertensives

At a given degree of adiposity, metabolic and cardiovascular risk varies markedly between individuals. Animal studies suggest that differentially expressed systemic activation of monocytes contributes to the obesity-associated risk variability. We tested the hypothesis that systemic monocyte activation is associated with changes in adipose tissue and skeletal muscle metabolism. In 17 obese hypertensive patients, we assessed CD11b expression on circulating monocytes, gene expression in adipose tissue biopsies, and obtained blood samples and adipose tissue and skeletal muscle microdialysis samples in the fasted state and during a glucose load. Patients were stratified into groups with higher and lower CD11b expression on monocytes. Expression of the macrophage marker CD68 was increased markedly in adipose tissue of subjects with higher CD11b expression. Although no differences in systemic insulin sensitivity were found between both groups, patients with higher peripheral CD11b expression showed a markedly augmented increase in dialysate glucose in adipose tissue during oral glucose tolerance testing and increased adipose tissue lipolysis as well. Our data demonstrate that human monocyte activation is associated with tissue-specific changes in glucose and lipid metabolism. These findings may be explained in part by monocyte/macrophage infiltration of adipose tissue, which appears to interfere with insulin responsiveness.

Three measures of tumor necrosis factor alpha activity and insulin resistance in nonobese Japanese type 2 diabetic patients

The aim of the present study was to investigate the relationship between insulin resistance and tumor necrosis factor alpha (TNF-alpha) as well as soluble TNF receptors (sTNF-R), body mass index (BMI), leptin, adiponectin, and serum lipid profile including triglycerides in nonobese Japanese patients with type 2 diabetes. A total of 88 nonobese Japanese type 2 diabetic patients were studied. The duration of diabetes was 11.0 +/- 0.8 years. In conjunction with BMI, glycosylated hemoglobin (HbA1c), fasting concentrations of plasma glucose, serum lipids (triglycerides, high-density lipoprotein cholesterol, and total cholesterol), serum leptin, serum adiponectin, serum TNF-alpha, and soluble TNF receptors (sTNF-R1 and sTNF-R2) were also measured. Insulin resistance was estimated by the insulin resistance index of homeostasis model assessment. Insulin resistance was positively correlated with BMI, triglycerides, leptin, and total cholesterol and negatively correlated with adiponectin and high-density lipoprotein cholesterol. In contrast, insulin resistance was not associated with TNF-alpha, nor sTNF-R (sTNF-R1 and sTNF-R2) in our diabetic patients. There was no significant relationship between the 3 measures of TNF-alpha system (TNF-alpha, sTNF-R1, and sTNF-R2) and BMI, serum triglycerides, leptin, or adiponectin in these patients. From these results, it can be concluded that peripheral levels of TNF-alpha system activity are not a major factor responsible for insulin resistance in nonobese Japanese type 2 diabetic patients.

Activation of peripheral blood CD14+ monocytes occurs in diabetes

Blood levels of inflammatory markers associated with endothelial dysfunction and atherosclerosis are increased in diabetic patients; the highest levels occur in poorly controlled diabetes. We investigated the activation state of peripheral blood monocytes in diabetes with respect to scavenger receptor (CD36) expression and monocyte chemoattractant protein-1, intracellular adhesion molecule-1, vascular cell adhesion molecule-1, and peroxisome proliferator-activated receptors mRNA expression. CD14(+) monocytes were isolated from peripheral blood of type 1 and type 2 diabetic patients with good (HbA(1c) <7.0%) or poor (>9.4%) glycemic control and a group of nondiabetic subjects. Monocytes from diabetic subjects displayed increased CD36 cell surface expression (P < 0.0005) and increased uptake of oxidized LDL (P < 0.05). Monocyte chemoattractant protein-1 gene expression was increased in monocytes from both groups of diabetic subjects (P < 0.05). Both CD68 and peroxisome proliferator-activated receptor-gamma gene expression were increased in the poorly controlled diabetic group (P < 0.05 for each), whose monocytes also displayed increased attachment to endothelial monolayers (P < 0.0005 vs. nondiabetic control subjects). In poorly controlled diabetes, CD14(+) monocytes are functionally activated and show some of the differentiation markers associated with macrophages. These monocytes also demonstrate an increased ability for attachment to normal endothelial cells, one of the early stages in atherogenesis.

Defining the proinflammatory phenotype using high sensitive C-reactive protein levels as the biomarker

CONTEXT

Inflammation is pivotal in atherosclerosis. The prototypic marker of inflammation is C-reactive protein (CRP). Numerous studies have confirmed that high CRP levels in normal volunteers predict cardiovascular events.

OBJECTIVE

The objective of this study was to define proximal and associated abnormalities of the proinflammatory phenotype using CRP levels as the biomarker.

DESIGN AND SUBJECTS

Two groups of normal, healthy subjects, selected by stringent criteria from an initial cohort of 252, were studied over the period of 12 months. Group 1 included subjects with consistently low CRP (<0.004 microM or <0.5 mg/liter; low CRP group; n = 15). Group 2 included subjects with consistently high CRP (>2.0 or >0.016 microM to <10 mg/liter or <0.085 microM; high CRP group; n = 13).

MAIN OUTCOME MEASURES

Fasting blood (50 ml) was obtained, and the following parameters were assayed: high sensitivity CRP, fibrinogen, lipid profile, insulin, whole blood cytokines after stimulation with lipopolysaccharide (LPS; 100 ng/ml for 24 h), soluble cell adhesion molecules, plasminogen activator inhibitor-1, CD40, CD40 ligand, leptin, adiponectin, monocyte chemoattractant protein-1, IL-8, matrix metalloproteinase-3 (MMP-3), and MMP-9. Genomic DNA was obtained from peripheral blood leukocytes, and the TNF-alpha -308 genotype was determined.

RESULTS

The median CRP levels were 0.0018 microM (0.21 mg/liter) and 0.031 microM (3.7 mg/liter) for the low and high groups, respectively. High CRP subjects were older and had significantly higher body mass indexes, triglycerides, insulin, homeostasis model assessment, and leptin levels compared with low CRP subjects. The markers of inflammation, plasminogen activator inhibitor-1, MMP-9, fibrinogen, and vascular cell adhesion molecule-1 levels were significantly higher in the high compared with the low CRP group. LPS-stimulated levels of whole blood IL-1beta, IL-6, and TNF were significantly higher, and IL-4 levels were significantly lower in the high CRP group. After age- and body mass index-adjusted analysis of covariance, only plasma MMP-9 levels and LPS-stimulated whole blood IL-1beta and TNF levels were significantly higher in the high CRP group. The frequency of the rare A allele at TNF-alpha -308 was equivalent in high and low CRP groups.

CONCLUSIONS

A phenotype characterized by increased plasma inflammatory mediators as well as increased LPS-stimulated whole blood TNF-alpha and IL-1beta levels is associated with high plasma CRP levels. This systemic inflammatory phenotype may contribute to vascular inflammation or may reflect inflammation in vessels or at other sites.

Role of macrophage tissue infiltration in metabolic diseases

PURPOSE OF REVIEW

White adipose tissue is necessary for optimal energy homeostasis and the excessive development of fat mass is clearly associated with the metabolic syndrome. The fact that adipocytes secrete a number of specific factors or 'adipokines' has forced a reassessment of the involvement of adipose tissue in a wide range of physiological and pathophysiological processes. Obesity has recently been described as a 'low-grade' inflammatory condition, a state proposed to represent a common determinator in the genesis of obesity-associated pathologies, i.e. diabetes and atherosclerosis.

RECENT FINDINGS

Recent reports of an increase in the number of macrophages that infiltrate the fat mass in obese individuals led to the suggestion that adipose tissue itself is a source and site of inflammation.

SUMMARY

This review summarizes recent data on the characterization of the macrophage population in fat tissue. Their origin, fate and activation will be considered. The potential involvement of adipose tissue macrophages in the development of insulin resistance and vascular pathologies, as well as in the control of adipose tissue growth and metabolism, will be examined.

Monocyte chemoattractant protein-1 release is higher in visceral than subcutaneous human adipose tissue (AT): implication of macrophages resident in the AT

Human adipose tissue (AT) produces several adipokines including monocyte chemoattractant protein (MCP)-1, involved in the pathogenesis of atherosclerosis.

OBJECTIVE

Human AT cultures, isolated adipocytes, and stromal-vascular cells were used to investigate the relationship among AT-resident macrophages, MCP-1, and adiposity and the regulation of MCP-1.

RESULTS

mRNA levels of specific macrophage markers (CD68 and CD14) are correlated with adiposity in sc AT and visceral AT (P < 0.05). MCP-1 production is higher in stromal-vascular cells vs. adipocytes (P < 0.01) and correlates with macrophage markers in both AT compartments (P < 0.05). MCP-1 release is higher in obese subjects (P < 0.05) and in VAT (P < 0.01), but after adjusting for AT-resident macrophages, the differences disappear. MCP-1 is stimulated by IL-1beta, TNF-alpha, IL-8, IL-4, and IL-6 + IL-6-soluble receptor and is decreased by dexamethasone, IL-10, metformin, and thiazolidinediones.

DISCUSSION

MCP-1 is correlated with specific macrophage markers, adiposity, and AT localization, but the relationship seems to be related to the number of AT-resident macrophages. Despite this, MCP-1 may be involved in obesity-related health complications, and the decrease of MCP-1 by metformin and thiazolidinediones suggests that these antidiabetic compounds have antiinflammatory properties improving the low-grade inflammatory state observed in obesity.

The calcium-dependent protease calpain causes endothelial dysfunction in type 2 diabetes

Cardiovascular complications are the leading cause of morbidity and mortality in diabetic patients. Endothelial dysfunction with impaired endothelial nitric oxide (NO) synthase (eNOS) activity is a widely accepted cause of diabetic vasculopathy. The mechanisms of endothelial dysfunction in diabetes remain elusive, thus limiting effective therapeutic interventions. We report novel evidence demonstrating that the calcium-dependent protease calpain causes endothelial dysfunction and vascular inflammation in the microcirculation of the ZDF (Zucker diabetic fatty) rat, a genetic rat model of type 2 diabetes. We found evidence of increased calpain activity and leukocyte trafficking in the microcirculation of ZDF rats. Inhibition of calpain activity significantly attenuated leukocyte-endothelium interactions in the vasculature of ZDF rats. Expression of cell adhesion molecules in the vascular endothelium of ZDF rats was consistently increased, and it was suppressed by calpain inhibition. In vivo measurement of endothelial NO availability demonstrated a 60% decrease in NO levels in the microcirculation of diabetic rats, which was also prevented by calpain inhibition. Immunoprecipitation studies revealed calpain-dependent loss of association between eNOS and the regulatory protein heat shock protein 90. Collectively, these data provide evidence for a novel mechanism of endothelial dysfunction and vascular inflammation in diabetes. Calpains may represent a new molecular target for the prevention and treatment of diabetic vascular complications.

FFAs: do they play a role in vascular disease in the insulin resistance syndrome?

The insulin resistance syndrome, otherwise known as the metabolic syndrome, describes a cluster of cardiovascular and metabolic abnormalities, which are strongly associated with overweight and obesity. The importance of the syndrome is due to its increased rates of cardiovascular morbidity and mortality. Insulin resistance is also characterized by elevated free fatty acid (FFA) levels. In otherwise healthy human subjects, elevation of FFA impairs endothelial function. This appears to be largely the result of blunting of nitric oxide-dependent tone, most likely at the level of the endothelial isoform of nitric oxide synthase (eNOS). Some of the potential mediatory mechanisms include oxidative stress, proinflammatory cytokines, C-reactive protein, or endogenous inhibitors of eNOS. Regardless of the mechanism(s) that mediates the effects of increased FFA on the vasculature, impaired vascular function is likely to account, at least in part, for the increase in cardiovascular mortality in subjects with the insulin resistance syndrome.