Molecular form and concentration of serum α ₂-macroglobulin in diabetes

Abstract

α ₂-Macroglobulin is a highly abundant serum protein involved in the development of atherosclerosis and cardiac hypertrophy. However, its circulating molecular form and exact concentrations in human health/diseases are not known. Blue native-polyacrylamide gel electrophoresis of human serum was used to confirm the native conformation of α ₂-macroglobulin. We created an enzyme-linked immunosorbent assay suitable for quantifying its circulating molecular form and undertook a cross-sectional study to measure its serum levels in 248 patients with diabetes mellitus and 59 healthy volunteers. The predominant circulating molecular form of α ₂-macroglobulin was the tetramer, whereas its dimer was detectable in patients with high serum levels of α ₂-macroglobulin. The serum α ₂-macroglobulin concentration was not associated with glycated hemoglobin or any other glycemic variable as evaluated from 48-h continuous glucose monitoring, but showed close correlation with left ventricular posterior wall thickness, carotid artery intima-media thickness, urinary albumin:creatinine ratio (ACR) and brachial–ankle pulse wave velocity (baPWV). Multivariate analysis revealed only the ACR and baPWV to be independent variables influencing serum levels of α ₂-macroglobulin. Thus, an increased ACR and baPWV are associated with higher serum concentrations of α ₂-macroglobulin, and the latter may contribute to the mechanism by which albuminuria increases the risk of developing cardiovascular diseases.