Lipopolysaccharide activates an innate immune system response in human adipose tissue in obesity and type 2 diabetes

Abstract

examined the innate immune pathway in AbdSc AT from lean, obese, and T2DM subjects, and 4) examined the association of circulating LPS in T2DM subjects. The findings showed that LPS increased TLR-2 protein expression twofold (P Ͻ 0.05). Treatment of AbdSc adipocytes with LPS caused a significant increase in TNF-␣ and IL-6 secretion (IL-6, Control: 2.7 Ϯ 0.5 vs. LPS: 4.8 Ϯ 0.3 ng/ml; P Ͻ 0.001; TNF-␣, Control: 1.0 Ϯ 0.83 vs. LPS: 32.8 Ϯ 6.23 pg/ml; P Ͻ 0.001). NF-B inhibitor reduced IL-6 in AbdSc adipocytes (Control: 2.7 Ϯ 0.5 vs. NF-B inhibitor: 2.1 Ϯ 0.4 ng/ml; P Ͻ 0.001). AbdSc AT protein expression for TLR-2, MyD88, TRAF6, and NF-B was increased in T2DM patients (P Ͻ 0.05), and TLR-2, TRAF-6, and NF-B were increased in LPStreated adipocytes (P Ͻ 0.05). Circulating LPS was 76% higher in T2DM subjects compared with matched controls. LPS correlated with insulin in controls (r ϭ 0.678, P Ͻ 0.0001). Rosiglitazone (RSG) significantly reduced both fasting serum insulin levels (reduced by 51%, P ϭ 0.0395) and serum LPS (reduced by 35%, P ϭ 0.0139) in a subgroup of previously untreated T2DM patients. In summary, our results suggest that T2DM is associated with increased endotoxemia, with AT able to initiate an innate immune response. Thus, increased adiposity may increase proinflammatory cytokines and therefore contribute to the pathogenic risk of T2DM.toll-like receptors; adipocytes; nuclear factor-B; inflammation; insulin OBESITY IS KNOWN TO REPRESENT one of the single most important risk factors for the increased risk of type 2 diabetes mellitus (T2DM) and cardiovascular disease. In addition, an increase in central (visceral) adiposity confers higher metabolic risk. This increased metabolic risk is associated with subclinical inflammation, with several studies demonstrating increased levels of proinflammatory adipocytokines, such as IL-6 and TNF-␣ (32, 33), in patients with obesity and T2DM. Activation of proinflammatory adipocytokines in adipose tissue (AT) is coordinated through NF-B, a key transcription factor in the inflammatory cascade (2,10, 11,18,21,22,33,35,37,38). Adipocytes also secrete adiponectin (29,30,36,41,42), which has been shown to possess anti-inflammatory properties through its action on NF-B and is inversely correlated with obesity and diabetes (29,30,36,41,42). Evidence for the role of NF-B in AT has been shown in studies overexpressing the NF-B activator IKK␤ in mice, which resulted in increased inflammatory cytokine production and the onset of diabetes (7). In contrast, hepatocyte IKK␤ knockout (KO) mice demonstrated a decrease in circulating proinflammatory cytokines (3). This indicates that IKK␤ KO mice do not develop hepatic insulin resistance and glucose intolerance compared with their high-fat diet-fed counterparts. Further studies also illustrate that an inflammatory reaction, induced by the bacterial endotoxin lipopolysaccharide (LPS), is markedly attenuated in the IKK␤ KO mice (3

Oligomeric Cocoa Procyanidins Possess Enhanced Bioactivity Compared to Monomeric and Polymeric Cocoa Procyanidins for Preventing the Development of Obesity, Insulin Resistance, and Impaired Glucose Tolerance during High-Fat Feeding

“…Low-grade inflammation in skeletal muscle has been shown to impair insulin signaling and induce metabolic derangements in skeletal muscle 77,129 . A key mediator of this inflammatory state is endotoxin (LPS), the major glycolipid component of the outer membrane of gram-negative commensal bacteria in the gut.…”

The influence of probiotic supplementation on gut permeability in patients with metabolic syndrome: an open label, randomized pilot study

“…In obesity, patients with type 2 diabetes LBP and endotoxin levels have been shown to be elevated. 25 In animal models lowgrade 'metabolic' endotoxemia has been described as a key factor in weight gain, insulin resistance and low-grade inflammation. 26 However, in our study we could not detect endotoxin in peripheral blood of any of the patients with MetS although we used an optimized endotoxin test.…”

The inflammatory receptor CD40 is expressed on human adipocytes: contribution to crosstalk between lymphocytes and adipocytes

“…CD40 can bind five of the six TRAF family members (TRAF1, −2, −3, −5, −6) depending on cell type or function [37]. Interestingly, TRAF6 is expressed in human adipocytes [38] and may participate to CD40 signalling in adipocytes.…”