Abstract 1565: Nϵ-(carboxymethyl)lysine Trapping in Adipose Tissue: Implications for Obesity-associated Changes in Adipokine Expression
Introduction: Dysregulated production of adipokines is associated with obesity-related complications, but factors that lead to such a dysregulated production remain largely unknown. We assessed the hypothesis that the accumulation of the advanced lipoxidation endproduct Nϵ-(Carboxymethyl)lysine (CML) in adipose tissue contributes to the altered expression of adipocytokines in obesity.
Methods: CML in adipose tissue was determined by immunohistochemistry. Plasma levels of protein-bound CML were measured by UPLC-MSMS in controls (n=77), patients with familial combined hyperlipidemia (n=42, FCHL) and obese patients (n=44). Blood clearance of fluorescently labeled CML-albumin was studied in Db/Db mice and trapping was assessed by two-photon microscopy. The effect of CML was studied in human preadipocytes and changes in expression of interleukin-6 (IL-6), plasminogen activator inhibitor-1 (PAI-1) and the receptor for AGE (RAGE) were analyzed by real time PCR.
Results and conclusions: We showed the presence of CML in adipocytes, macrophages and endothelial cells in adipose tissue. CML immunostaining was higher in visceral adipose tissue (VAT) than in subcutaneous adipose tissue (SAT) (1.5±0.2 and 1.3±0.2, respectively, P<0.001). However, plasma CML levels were lower in obese (1.3±0.2μM, P<0.001) and FCHL patients (1.3±0.3μM, P<0.001) compared with controls (1.9±0.5μM). In accordance, weight reduction of obese patients by gastric restrictive surgery led to an increase of plasma CML levels (P=0.01). CML plasma levels were negatively correlated with BMI (r=−0.475, P<0.001) and the amount of VAT (r=−0.548, P<0.001), but not with SAT (r=−0.148, P=0.238). Experiments in Db/Db mice showed higher plasma clearance of injected CML-albumin than unmodified albumin, with trapping of CML-albumin in adipose tissue. Incubation of human preadipocytes with CML-albumin during 72h increased the gene expression of IL-6, PAI-1 and RAGE by 2.4-, 1.8- and 4.9-fold, respectively, which was inhibited by anti-RAGE and by sRAGE. In conclusion, the accumulation of CML in VAT of obese patients and the increased pro-inflammatory gene expression by CML-albumin indicate that the trapping of CML has biological effects regarding the dysregulation of adipokines.