No abstract

The relationship of uric acid with macrophages has not been fully elucidated. We investigated the effect of uric acid on the proinflammatory ability of human macrophages and then examined the possible molecular mechanism involved. Primary human monocytes were differentiated into macrophages for subsequent exposure to 0, 0.23, 0.45, or 0.9 mmol/L uric acid for 12 h, in the presence or absence of 1 mmol/L probenecid. Flow cytometry was used to measure proinflammatory marker production and phagocytic activity that was quantified as a percentage of GFP-labeled Escherichia coli positive macrophages. qPCR was used to measure the macrophage expression of the urate anion transporter 1 (URAT1). As compared to control cells, the production of tumor necrosis factor-alpha (TNF-alpha), toll-like receptor 4 (TLR4), and cluster of differentiation (CD) 11c was significantly increased by uric acid. In contrast, macrophages expressing CD206, CX3C-motif chemokine receptor 1 (CX3CR1), and C-C chemokine receptor type 2 (CCR2) were significantly reduced. Uric acid progressively increased macrophage phagocytic activity and downregulated URAT1 expression. Probenecid-a non-specific blocker of URAT1-dependent uric acid transport-inhibited both proinflammatory cytokine production and phagocytic activity in macrophages that were exposed to uric acid. These results suggest that uric acid has direct proinflammatory effects on macrophages possibly via URAT1.

Experimental evidence in mice suggests a role for interleukin- (IL-) 13 in insulin resistance and low-grade systemic inflammation. However, IL-13 serum levels have not been assessed in subjects with insulin resistance, and associations of IL-13 with parameters of low-grade systemic inflammation are still unknown. Our main goal was to examine the systemic levels of IL-13 in patients with insulin resistance, while also studying the relationship of IL-13 with anthropometric, metabolic, and low-grade systemic inflammatory markers. Ninety-two participants were included in the study and divided into insulin-resistant patients and noninsulin-resistant controls. Blood levels of IL-13, glucose, insulin, triglycerides, cholesterol, tumor necrosis factor-alpha (TNF-α), IL-10, proinflammatory (Mon-CD11c+CD206−), and anti-inflammatory (Mon-CD11c−CD206+) monocytes, as well as anthropometric parameters, were measured in all volunteers. Insulin-resistant patients showed 2.5-fold higher serum levels of IL-13 than controls (P < 0.0001) and significantly increased values of TNF-α and Mon-CD11c+CD206−, with concomitant reductions in IL-10 and Mon-CD11c−CD206+. Increased IL-13 was extraordinarily well associated with hyperglycemia (r = 0.7362) and hypertriglyceridemia (r = 0.7632) but unexpectedly exhibited no significant correlations with TNF-α (r = 0.2907), IL-10 (r = −0.3882), Mon-CD11c+CD206− (r = 0.2745) or Mon-CD11c−CD206+ (r = −0.3237). This study demonstrates that IL-13 serum levels are elevated in patients with insulin resistance without showing correlation with parameters of low-grade systemic inflammation.

Insulin resistance is the inability to respond to insulin and is considered a key pathophysiological factor in the development of type 2 diabetes. Tumor necrosis factor-alpha (TNF-alpha) can directly contribute to insulin resistance by disrupting the insulin signalling pathway via protein-tyrosine phosphatase 1B (PTP1B) activation, especially in adipocytes. Infliximab (Remicade ) is a TNF-alpha-neutralizing antibody that has not been fully studied in insulin resistance. We investigated the effect of infliximab on TNF-alpha-induced insulin resistance in 3T3L1 adipocytes in vitro, and examined the possible molecular mechanisms involved. Once differentiated, adipocytes were cultured with 5 mmol L 2-deoxy-D-glucose- H and stimulated twice with 2 μmol L insulin, in the presence or absence of 5 ng/mL TNF-alpha and/or 10 ng/mL infliximab. Glucose uptake was measured every 20 minutes for 2 hour, and phosphorylated forms of insulin receptor (IR), insulin receptor substrate-2 (IRS-2), protein kinase B (AKT) and PTP1B were determined by Western blotting. TNF-alpha-treated adipocytes showed a significant 64% decrease in insulin-stimulated glucose uptake as compared with control cells, whereas infliximab reversed TNF-alpha actions by significantly improving glucose incorporation. Although IR phosphorylation remained unaltered, TNF-alpha was able to increase PTP1B activation and decrease phosphorylation of IRS-2 and AKT. Notably, infliximab restored phosphorylation of IRS-2 and AKT by attenuating PTP1B activation. This work demonstrates for the first time that infliximab ameliorates TNF-alpha-induced insulin resistance in 3T3L1 adipocytes in vitro by restoring the insulin signalling pathway via PTP1B inhibition. Further clinical research is needed to determine the potential benefit of using infliximab for treating insulin resistance in patients.