Glycated Human Serum Albumin Isolated from Poorly Controlled Diabetic Patients Impairs Cholesterol Efflux from Macrophages: An Investigation by Mass Spectrometry

Advanced glycation end-products impair ABCA-1-mediated cholesterol efflux by eliciting inflammation, the generation of reactive oxygen species and endoplasmatic reticulum (ER) stress. The glycation level of human serum albumin (HSA) from type 1 and type 2 diabetic patients was determined by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and related to possible impairment of ER function and cellular cholesterol efflux. Comparison of the MALDI spectra from healthy and diabetic subjects allowed us to determine an increased HSA mean mass of 1297 Da for type 1 and 890 Da for type 2. These values reflect a mean condensation of at least 8 glucose units and 5 glucose units, respectively. Mouse peritoneal macrophages were treated with HSA from control, type 1 and type 2 diabetic subjects in order to measure the expression of Grp78, Grp94, protein disulfide isomerase (PDI), calreticulin (CRT), and ABCA-1. ¹⁴C-cholesterol overloaded-J774 macrophages were treated with HSA from control and diabetic subjects and further incubated with apo A-1 to determine the cholesterol efflux. Combined analyses comprising HSA from type 1 and type 2 diabetic patients were performed in cellular functional assays. In macrophages, PDI expression increased 89% and CRT 3.4 times in comparison to HSA from the control subjects. ABCA-1 protein level and apo A-I-mediated cholesterol efflux were, respectively, 50% and 60% reduced in macrophages exposed to HSA from type 1 and type 2 diabetic patients when compared to that exposed to HSA from control subjects. We provide evidence that the level of glycation that occurs in albumin in vivo damages the ER function related to the impairment in macrophage reverse cholesterol transport, and so contributes to atherosclerosis in diabetes.