N-glycosylation of disease-specific haptoglobin for the early screening of diabetic retinopathy

Purpose: Diabetic retinopathy (DR), as one of the microvascular complications of diabetes, is a leading cause of acquired vision loss. Most DR cases are detected in the advanced stage through fundoscopy, making molecular biomarkers urgently needed for early diagnosis of DR. Experimental design: Serum disease-specific haptoglobin-beta (Hp-beta) chains of 100 patients with type 2 diabetes mellitus (T2DM) and 156 T2DM patients with non-proliferative diabetic retinopathy (NPDR) were separated using polyacrylamide gel electrophoresis. After in-gel digestion and enrichment, the intact N-glycopeptides were detected by mass spectrometry. Results: Fucosylation of Hp-beta was significantly increased and sialylation of Hp-beta was significantly decreased in background DR (BDR, an early-stage DR) patients compared with non-diabetic retinopathy patients (p < 0.05) and yielded area under curves (AUCs) of 0.801 and 0.829 in training and validation groups, respectively, which had an advantage over glycated hemoglobin A1c (AUC >= 0.691). Moreover, a significant increase in sialylated Hp-beta was found in severe NPDR patients compared with BDR patients and yielded an AUC of 0.828 to distinguish severe NPDR from BDR. Conclusion: Changes in Hp-beta glycosylation are closely related to DR, and may be used for early diagnosis and screening of DR.