Obesity is becoming an epidemic in the United States and worldwide and increases risk for many diseases, particularly insulin resistance, type 2 diabetes mellitus, and cardiovascular disease. The mechanisms linking obesity with these diseases remain incompletely understood. Over the past 2 to 3 decades, it has been recognized that in obesity, inflammation, with increased accumulation and inflammatory polarization of immune cells, takes place in various tissues, including adipose tissue, skeletal muscle, liver, gut, pancreatic islet, and brain and may contribute to obesity-linked metabolic dysfunctions, leading to insulin resistance and type 2 diabetes mellitus. Therapies targeting inflammation have shed light on certain obesity-linked diseases, including type 2 diabetes mellitus and atherosclerotic cardiovascular disease, but remain to be tested further and confirmed in clinical trials. This review focuses on inflammation in adipose tissue and its potential role in insulin resistance associated with obesity.

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.

Background—: We evaluated whether cardiac troponin T (cTnT) measured with a new highly sensitive assay was associated with incident coronary heart disease (CHD), mortality, and hospitalization for heart failure (HF) in a general population of participants in the Atherosclerosis Risk in Communities (ARIC) Study. Methods and Results—: Associations between increasing cTnT levels and CHD, mortality, and HF hospitalization were evaluated with Cox proportional hazards models adjusted for traditional CHD risk factors, kidney function, high-sensitivity C-reactive protein, and N-terminal pro–B-type natriuretic peptide in 9698 participants aged 54 to 74 years who at baseline were free from CHD and stroke (and HF in the HF analysis). Measurable cTnT levels (≥0.003 μg/L) were detected in 66.5% of individuals. In fully adjusted models, compared with participants with undetectable levels, those with cTnT levels in the highest category (≥0.014 μg/L; 7.4% of the ARIC population) had significantly increased risk for CHD (hazard ratio=2.29; 95% confidence interval, 1.81 to 2.89), fatal CHD (hazard ratio=7.59; 95% confidence interval, 3.78 to 15.25), total mortality (hazard ratio=3.96; 95% confidence interval, 3.21 to 4.88), and HF (hazard ratio=5.95; 95% confidence interval, 4.47 to 7.92). Even minimally elevated cTnT (≥0.003 μg/L) was associated with increased risk for mortality and HF ( P <0.05). Adding cTnT to traditional risk factors improved risk prediction parameters; the improvements were similar to those with N-terminal pro–B-type natriuretic peptide and better than those with the addition of high-sensitivity C-reactive protein. Conclusions—: cTnT detectable with a highly sensitive assay was associated with incident CHD, mortality, and HF in individuals from a general population without known CHD/stroke.

Background— Obesity is associated with chronic inflammation, which includes increased macrophage accumulation in adipose tissue (AT) and upregulation of chemokines and cytokines. T cells also play important roles in chronic inflammatory diseases such as atherosclerosis but have not been well studied in obesity. Methods and Results— Flow cytometric analysis showed higher numbers of T cells and macrophages in AT of diet-induced obese insulin-resistant male mice than in lean mice and obese females ( P <0.05). RNase protection assay, ELISA, and flow cytometry indicated gender-dependent upregulation of mRNA and protein levels of regulated on activation, normal T cell expressed and secreted (RANTES) and its receptor CCR5 in AT of obese mice. Adipocytes, stromal/vascular cells from mouse AT, and human and murine adipocytes expressed RANTES. RANTES mRNA levels were negatively correlated with adiponectin in mouse AT. Adiponectin-deficient mice fed high-fat diet showed higher RANTES mRNA levels in AT than wild-type mice. Activated T cells coincubated with preadipocytes in vitro significantly suppressed preadipocyte-to-adipocyte differentiation. Obese humans with metabolic syndrome had higher mRNA levels of RANTES and CCR5 in subcutaneous AT than lean humans. RANTES and CCR5 mRNA levels were significantly higher in visceral than subcutaneous AT of morbidly obese humans. RANTES mRNA levels were positively correlated with CD3 and CD11b in human visceral AT. Conclusions— Obesity is associated with increased accumulation of T cells and macrophages in AT, which may play important roles in obesity-related disease by influencing preadipocyte/adipocyte functions. RANTES is an adipokine that is upregulated in AT by obesity in both mice and humans.

Background— Despite the established efficacy of statins, many patients do not achieve recommended LDL cholesterol (LDL-C) goals. Contributing factors may be inadequate dosing, increased risk for adverse effects with high-dose monotherapy, and increased potential for intolerance and adverse effects with combinations of available agents. Methods and Results— In a double-blind study, 628 patients with baseline LDL-C 145 to 250 mg/dL and triglycerides ≤350 mg/dL were randomly assigned to receive 1 of the following for 12 weeks: ezetimibe (10 mg/d); atorvastatin (10, 20, 40, or 80 mg/d); ezetimibe (10 mg) plus atorvastatin (10, 20, 40, or 80 mg/d); or placebo. The primary efficacy end point was percentage reduction in LDL-C for pooled ezetimibe plus atorvastatin versus pooled atorvastatin treatment groups. Ezetimibe plus atorvastatin significantly improved LDL-C, HDL cholesterol (HDL-C), triglycerides, total cholesterol:HDL-C, and high-sensitivity C-reactive protein (hs-CRP) compared with atorvastatin alone ( P <0.01). Coadministration of ezetimibe provided a significant additional 12% LDL-C reduction, 3% HDL-C increase, 8% triglyceride reduction, and 10% hs-CRP reduction versus atorvastatin alone. Ezetimibe plus atorvastatin provided LDL-C reductions of 50% to 60%, triglyceride reductions of 30% to 40%, and HDL-C increases of 5% to 9%, depending on atorvastatin dose. LDL-C reductions with ezetimibe plus 10 mg atorvastatin (50%) and 80 mg atorvastatin alone (51%) were similar. Conclusions— Ezetimibe plus atorvastatin was well tolerated, with a safety profile similar to atorvastatin alone and to placebo. When coadministered with atorvastatin, ezetimibe provided significant incremental reductions in LDL-C and triglycerides and increases in HDL-C. Coadministration of ezetimibe and atorvastatin offers a well-tolerated and highly efficacious new treatment option for patients with hypercholesterolemia.

Background— Measuring C-reactive protein (CRP) has been recommended to identify patients at high risk for coronary heart disease (CHD) with low LDL cholesterol (LDL-C). Lipoprotein-associated phospholipase A ₂ (Lp-PLA ₂ ) is a proinflammatory enzyme associated primarily with LDL. Methods and Results— In a prospective, case cohort study in 12 819 apparently healthy middle-aged men and women in the Atherosclerosis Risk in Communities study, the relation between Lp-PLA ₂ , CRP, traditional risk factors, and risk for CHD events over a period of ≈6 years was examined in a proportional hazards model, stratified by LDL-C. Lp-PLA ₂ and CRP levels were higher in the 608 cases than the 740 noncases. Both Lp-PLA ₂ and CRP were associated with incident CHD after adjustment for age, sex, and race with a hazard ratio of 1.78 for the highest tertile of Lp-PLA ₂ and 2.53 for the highest category of CRP versus the lowest categories. Lp-PLA ₂ correlated positively with LDL-C ( r =0.36) and negatively with HDL-C ( r =−0.33) but not with CRP ( r =−0.05). In a model adjusted for traditional risk factors including LDL-C, the association of Lp-PLA ₂ with CHD was attenuated and not statistically significant. For individuals with LDL-C below the median (130 mg/dL), Lp-PLA ₂ and CRP were both significantly and independently associated with CHD in fully adjusted models. For individuals with LDL-C <130 mg/dL, those with both Lp-PLA ₂ and CRP levels in the highest tertile were at the greatest risk for a CHD event. Conclusions— Lp-PLA ₂ and CRP may be complementary in identifying individuals at high CHD risk who have low LDL-C.