Activity of the glycosylating enzyme, core 2 GlcNAc (beta 1,6) transferase, is higher in polymorphonuclear leukocytes from diabetic patients comparedwith age-matched control subjects - Relevance to capillary occlusion in diabetic retinopathy

The exact mechanism for capillary occlusion in diabetic retinopathy is stil l unclear, but increased leukocyte-endothelial cell adhesion has been impli cated. We examined the possibility that posttranslational modification of s urface O-glycans by increased activity of core 2 transferase (UDP-Glc:Gal b eta 1-3GalNAc alpha R beta-N-acetylglucoaminyltransferase) is responsible f or increased adhesion of leukocytes to vascular endothelium in diabetes. Th e mean activity of core 2 transferase in polymorphonuclear leukocytes isola ted from type 1 and type 2 diabetic patients was higher compared with age m atched control subjects (1,638 +/- 91 [n = 42] vs. 249 +/- 35 pmol h(-1) mg (-1) protein [n = 24], P = 0.00013; 1,459 +/- 194 [n = 58] vs. 334 +/- 86 [ n = 11], P = 0.01). As a group, diabetic patients with retinopathy had sign ificantly higher mean activity of core 2 transferase compared with individu als with no retinopathy, There was a significant association between enzyme activity and severity of retinopathy in type 1 and type 2 diabetic patient s, There was a strong correlation between activity of core 2 transferase an d extent of leukocyte adhesion to cultured retinal capillary endothelial ce lls for diabetic patients but not for age-matched control subjects. Results from transfection experiments using human myelocytic cell line (U937) demo nstrated a direct relationship between increased activity of core 2 transfe rase and increased binding to cultured endothelial cells. There was no rela tionship between activity of core 2 transferase and HbA(1e) (P = 0.8314), s erum advanced glycation end product levels (P = 0.4159), age of the patient (P = 0.7896), and duration of diabetes (P = 0.3307), On the basis that bra nched O-glycans formed by the action of core 2 transferase participate in l eukocyte adhesion, the present data suggest the involvement of this enzyme in increased leukocyte-;endothelial cell adhesion and the pathogenesis of c apillary occlusion in diabetic retinopathy.