Serum Xylosyltransferase Activity in Diabetic Patients as a Possible Marker of Reduced Proteoglycan Biosynthesis

OBJECTIVE—Proteoglycan metabolism is altered in diabetic patients. The xylosyltransferases (XTs) are the initial and rate-limiting enzymes in the biosynthesis of the glycosaminoglycan chains in proteoglycans. Here, we analyzed whether the changed proteoglycan metabolism leads to altered serum XT levels in diabetic patients. RESEARCH DESIGN AND METHODS—Serum XT activity was determined in 100 diabetic patients and 100 blood donors using a novel high-performance liquid chromatography electrospray ionization tandem mass spectrometry assay. RESULTS—Serum XT activities in male and female diabetic patients were significantly decreased compared with those in the corresponding normoglycemic control subjects (mean ± SD: male patients, 19.3 ± 4.44 mU/l; male nondiabetic control subjects, 26.6 ± 2.79 mU/l; female patients, 18.9 ± 3.14 mU/l; female nondiabetic control subjects, 21.8 ± 3.74 mU/l; P < 0.0001). No significant differences were detected between patients with type 1 and type 2 diabetes. CONCLUSIONS—Our data show decreased XT activity in patients with diabetes, a disease that is accompanied by an altered proteoglycan biosynthesis.