Glycation of the Complement Regulatory Protein CD59 Is a Novel Biomarker for Glucose Handling in Humans

Context: Human CD59, an inhibitor of the membrane attack complex of complement, is inactivated by glycation. Glycation inactivation of CD59 enhances complement-mediated injury in target organs of diabetes complications. Objective: We hypothesized that circulating soluble glycated CD59 (GCD59) represents a novel biomarker of blood glucose handling and aimed to conduct human study protocols to test this hypothesis. Design, Setting, Participants, and Outcome Measures: Using a newly developed ELISA, we measured circulating soluble GCD59 in samples from 3 separate human studies evaluating acute and chronic glucose handling and glucose responses to insulin therapy. Study 1 (normal vs diabetic subjects) evaluated the cross-sectional association between GCD59 and glycated hemoglobin (HbA1c) in 400 subjects with and without type 2 diabetes. Study 2 (oral glucose tolerance test [OGTT] in nondiabetics) evaluated whether fasting GCD59 independently predicted the 2-hour glucose response to an OGTT in 109 subjects without a diagnosis of diabetes. Study 3 (intensified insulin treatment) evaluated the effect of intensification of glycemic control with insulin on GCD59 in 21 poorly controlled individuals with diabetes. Results: In study 1 (normal vs diabetic subjects), GCD59 was independently and positively associated with HbA1c in individuals with and without diabetes (beta = 1.1, P < .0001 and beta = 1.1, P < .001, respectively). In study 2 (OGTT in nondiabetics), a single GCD59 measurement independently predicted the results of the 2-hour OGTT (beta = 19.8, P < .05) after multivariate modeling. In study 3 (intensified insulin treatment), intensification of glucose control with insulin resulted in a concomitant and parallel reduction of average weekly glucose and GCD59 within 2 weeks. Conclusions: We observed robust relationships between a single measurement of blood levels of GCD59 and both acute (2-hour OGTT) and chronic (HbA1c) measures of glucose handling. Lowering of GCD59 levels closely reflected lowering of average weekly glucose within 2 weeks. The role of GCD59 in the diagnosis, management, and vascular risk stratification in diabetes warrants further investigation.