Protein-Bound Plasma Nε-(Carboxymethyl)lysine Is Inversely Associated with Central Obesity and Inflammation and Significantly Explain a Part of the Central Obesity-Related Increase in Inflammation: The Hoorn and CODAM Studies
Adipose tissue inflammation contributes to the development of complications, such as insulin resistance and type 2 diabetes mellitus. We previously reported that plasma levels of N ε -(carboxymethyl)lysine (CML) were decreased in obese subjects resulting from CML accumulation in adipose tissue and that this CML accumulation plays an important role in adipose tissue inflammation. The objective of this study is to investigate associations between obesity (body mass index, waist circumference, and trunk fat mass), plasma CML (as an inversely correlated marker of CML accumulation in adipose tissue), and low-grade inflammation (LGI) in a large sample of individuals whose weight status ranged from normal to morbid obesity. Approach and Results-We studied 1270 individuals of the Cohort on Diabetes and Atherosclerosis Maastricht Study and Hoorn Study, in whom protein-bound CML levels were measured by UPLC-Tandem MS (ultra performance liquid chromatography-tandem mass spectrometry), and 6 inflammatory markers were measured with multiarrays. These inflammatory markers were compiled into an LGI score. Multiple linear regression, adjusted for covariates, showed that (1) waist circumference was inversely associated with protein-bound CML plasma levels (standardized regression coefficient [β]=-0.357 [95% confidence interval:-0.414;-0.301] ); (2) protein-bound CML was inversely associated with LGI score (β=-0.073 [-0.130;-0.015]); and (3) the association between waist circumference and LGI (β=0.262 [0.203;0.321] ) was attenuated after adjustment for protein-bound CML plasma levels and other potential mediators (to β=0.202 [0.138;0.266]), with CML explaining the greatest portion of the attenuation (≈12%). Further analysis with dual-energy X-ray absorptiometry measures of body composition confirmed a strong inverse association of fat mass preferentially accumulated in the trunk with protein-bound CML plasma levels, significantly explaining ≈21% of the trunk fat-LGI association. Conclusions-Obesity, in particular central obesity, is characterized by greater levels of LGI but by lower levels of circulating CML; the latter significantly explaining a portion of the positive association between central obesity and inflammation.