Circulating Levels and Dietary Intake of the Advanced Glycation End-product Marker Carboxymethyl Lysine in Chronic Kidney Disease Patients on Conservative Predialysis Therapy: A Pilot Study

Abstract

Advanced glycation end-products (AGEs) are proposed to influence inflammatory pathways and cardiovascular risk in chronic kidney disease (CKD). Dietary AGEs are believed to sustain circulating levels and toxicity in this condition. We investigated this aspect in a cross-sectional pilot study measuring levels of the AGE marker carboxymethyl lysine (CML) and fluorescent AGEs in the blood of pre-dialysis patients with CKD and hemodialysis (HD) patients (n = 10 each), and in a group of matched healthy controls (Ctr). Plasma CML was measured by immuno-dot blot and fluorescent AGEs were determined by high-performance liquid chromatography (HPLC) analysis measuring the fluorescence of the cross-link pentosidine. The dietary intake of CML was assessed by dietary recall to trace total AGE intake in patients with CKD and the Ctr group. All the subjects included in the study were assessed for dietary intake while maintaining their usual diet. Main exclusion criteria for patients with CKD and HD were severe protein-caloric malnutrition and inflammation (measured by high sensitivity C-reactive protein and interleukin-6 levels). Plasma CML, as well as free and protein-bound fluorescent AGEs, significantly increased in CKD and even more in HD patients than that of the Ctr group. In patients with CKD, the average dietary intake of CML was less than half than that of the Ctr group (6 vs. 13 MU/day) and the lowered protein intake adopted spontaneously by these patients appear to explain this finding. The results show that the intake of CML does not affect circulating levels of this as well as of other AGEs, in well nourished predialysis CKD patients.