Serum prolidase activity as a marker of osteoporosis in type 2 diabetes mellitus.

OBJECTIVES: Prolidase is a specific imidodipeptidase involved in collagen degradation. The increase in the enzyme activity is believed to be correlated with the increased intensity of collagen degradation This study aimed to evaluate serum prolidase activity and urinary deoxypyridinoline cross links in type 2 diabetic subjects with and without osteoporosis assessed by bone mineral density. DESIGN AND METHODS: Seventy-five patients (54 F/21 M) with type 2 DM and 43 age and gender matched healthy subjects (30 F/13 M) were recruited for this study. Serum prolidase activity was assessed with colorimetric determination. Urinary deoxypyridinoline (Dpy) was determined with electrochemiluminesence immunoassay.
RESULTS: Serum prolidase activity was significantly lower in patients with type 2 DM than in the healthy controls (mean +/- SEM; 43.3 +/- 1.4 U/L and 53.3 +/- 2.2 U/L respectively, p: 0.000). Non osteoporotic diabetic patients had lower serum prolidase activity (median: 25th-75th percentiles; 39.5: 30.3-50.5 U/L) than osteoporotic diabetic patients (50.0: 41.8-56.3 U/L, p: 0.030) and healthy controls (52.0: 43.0-58.0 U/L, p: 0.004). Urinary Dpy excretion was not different between osteoporotic and nonosteoporotic diabetic patients. However it was lower in both diabetic groups than the healthy controls. We did not observe a statistically significant difference between the serum prolidase activity of dislipidemic/normolipidemic, hypertensive/normotensive, obese/nonobese, insulin/OAD treated, poorly/well-controlled patients and patients with/without diabetic nephropathy and retinopathy (p > 0.05).
CONCLUSION: This study shows a significant decrease in serum prolidase activity in patients affected with type 2 DM, which may be interpreted as evidence of decreased bone resorption. Our data also suggest that serum prolidase activity may be a better marker of osteoporosis in diabetic state than Dpy.