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Accumulation of macrophages and T cells within crown-like structures (CLS) in subcutaneous adipose tissue predicts disease severity in obesity-related insulin resistance (OIR). Although rodent data suggest the B cell is an important feature of these lesions, B cells have not been described within the human CLS. In order to identify B cells in the human subcutaneous CLS (sCLS) in obese subjects and determine whether the presence of B cells predict insulin resistance, we examined archived samples of subcutaneous and omental fat from 32 obese men and women and related findings to clinical parameters. Using immunohistochemistry, we identified B (CD19(+)) and T cells (CD3 (+)) within the sCLS and perivascular space. The presence and density of B cells (B cells per high-power field (pHPF), T cells pHPF, and B cell:T cell (B:T) ratio) were compared with measures of insulin resistance (homeostasis model assessment (HOMA)) and other variables. In 16 of 32 subjects (50%) CD19(+) B cells were localized within sCLS and were relatively more numerous than T cells. HOMA was not different between subjects with CD19(+) vs. CD19(-) sCLS (5.5 vs. 5.3, P = 0.88). After controlling for diabetes and glycemia (hemoglobin A(1c) (HbA(1c))), the B:T ratio correlated with current metformin treatment (r = 0.89, P = 0.001). These results indicate that in human OIR, B cells are an integral component of organized inflammation in subcutaneous fat, and defining their role will lead to a better understanding of OIR pathogenesis and potentially impact treatment.

Objective: The purpose of this study was to characterize the relationship between adipose tissue phenotype and depot-specific microvascular function in fat., Methods and Results: In 30 obese subjects (age 42±11 years, body mass index 46±11 kg/m(2)) undergoing bariatric surgery, we intraoperatively collected visceral and subcutaneous adipose tissue and characterized depot-specific adipose phenotypes. We assessed vasomotor function of the adipose microvasculature using videomicroscopy of small arterioles (75-250 μm) isolated from different fat compartments. Endothelium-dependent, acetylcholine-mediated vasodilation was severely impaired in visceral arterioles, compared to the subcutaneous depot (P<0.001 by ANOVA). Nonendothelium dependent responses to papaverine and nitroprusside were similar. Endothelial nitric oxide synthase inhibition with N(ω)-nitro-l-arginine methyl ester reduced subcutaneous vasodilation but had no effect on severely blunted visceral arteriolar responses. Visceral fat exhibited greater expression of proinflammatory, oxidative stress-related, hypoxia-induced, and proangiogenic genes; increased activated macrophage populations; and had a higher capacity for cytokine production ex vivo., Conclusions: Our findings provide clinical evidence that the visceral microenvironment may be intrinsically toxic to arterial health providing a potential mechanism by which visceral adiposity burden is linked to atherosclerotic vascular disease. Our findings also support the evolving concept that both adipose tissue quality and quantity may play significant roles in shaping cardiovascular phenotypes in human obesity.

Objectives: The purpose of this study was to determine whether obese individuals with reduced adipose tissue inflammation exhibit a more favorable cardiovascular risk profile., Background: Obesity is associated with a low-grade state of chronic inflammation that might be causally related to cardiometabolic disease., Methods: With immunohistochemistry, we categorized obese individuals dichotomously as having inflamed fat (n = 78) or noninflamed fat (n = 31) on the basis of the presence (+) or absence (-) of macrophage crown-like structures (CLS) in subcutaneous abdominal fat biopsy samples. We compared their metabolic, vascular, and adipose tissue characteristics with lean subjects (n = 17)., Results: Inflamed CLS+ obese individuals displayed higher plasma insulin, homeostasis model assessment, triglycerides, glucose, blood pressure, high-sensitivity C-reactive protein, low-density lipoprotein cholesterol, lower high-density lipoprotein cholesterol, and brachial artery flow-mediated dilation compared with lean subjects (p < 0.05). Adipose messenger ribonucleic acid expression of inflammatory genes including CD68, leptin, matrix metalloproteinase-9, CD163, and CD8A were significantly greater and vascular endothelial growth factor was lower in the CLS+ group (p < 0.05). In contrast, obese subjects with noninflamed fat exhibited a mixed clinical phenotype with lower insulin resistance, reduced proatherogenic gene expression, and preserved vascular function as in lean subjects. In multiple linear regression adjusting for age and sex, CLS status (beta = -0.28, p = 0.008) and waist circumference (beta = -0.25, p = 0.03) were independent predictors of flow-mediated dilation., Conclusions: These findings lend support to the novel concept that factors in addition to absolute weight burden, such as qualitative features of adipose tissue, might be important determinants of cardiovascular disease. Therapeutic modulation of the adipose phenotype might represent a target for treatment in obesity., (Copyright © 2011 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Inflammation and infiltration of immune cells in white adipose tissue have been implicated in the development of obesity-associated insulin resistance. Likewise, dysregulation of the fuel-sensing enzyme AMP-activated protein kinase (AMPK) has been proposed as a pathogenetic factor for these abnormalities based on both its links to insulin action and its anti-inflammatory effects. In this study, we examined the relationships between AMPK activity, the expression of multiple inflammatory markers in visceral (mesenteric and omental) and abdominal subcutaneous adipose tissue, and whole-body insulin sensitivity in morbidly obese patients (BMI 48±1.9 kg/m(2)) undergoing gastric bypass surgery. AMPK activity was assessed by Western-blots (P-AMPK/T-AMPK) and mRNA levels of various markers of inflammation by qRT-PCR. Patients were stratified as insulin sensitive obese or insulin-resistant obese according to their HOMA-IR values. The results indicate that AMPK activity is lower in visceral than in subcutaneous abdominal adipose tissue of these patients and that this is associated with an increased expression of multiple inflammatory genes. They also revealed that AMPK activity is lower in adipose tissue of obese patients who are insulin resistant (HOMA-IR>2.3) than in BMI-matched insulin sensitive subjects. Furthermore, this difference was evident in all three fat depots. In conclusion, the data suggest that there are close links between reduced AMPK activity and inflammation in white adipose tissue, and whole-body insulin resistance in obese humans. Whether adipose tissue AMPK dysregulation is a causal factor for the development of the inflammation and insulin resistance remains to be determined., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Objective: Experimental studies suggest that adipose inflammation is etiologically linked to obesity-induced systemic disease. Our goal was to characterize the state of inflammation in human fat in relation to vascular function and metabolic parameters in obese individuals., Methods and Results: We collected subcutaneous abdominal fat in 77 obese subjects (BMI >or=30 kg/m(2)) and quantified adipose macrophage population using targeted immunohistochemistry. Brachial artery vasodilator function was examined using high-resolution vascular ultrasound. In 50 subjects, an inflamed adipose phenotype characterized by tissue macrophage accumulation in crown-like structures was associated with systemic hyperinsulinemia and insulin resistance (HOMA-IR 5.5+/-4.5 versus 2.6+/-1.9, P=0.002) and impaired endothelium-dependent flow-mediated vasodilation (8.5+/-4.4% versus 10.8+/-3.8%, P<0.05), as compared to subjects with quiescent noninflamed adipose architecture (n=27). Macrophage retention in fat was linked to upregulated tissue CD68 and tumor necrosis factor (TNF)-alpha mRNA expression in addition to increased plasma hs-CRP., Conclusions: In a cohort of obese subjects, we demonstrate that proinflammatory changes in adipose tissue are associated with systemic arterial dysfunction and insulin resistance. These findings suggest that adipose inflammation may be linked to vascular injury and increased cardiovascular risk in obese subjects.