The Association of Serum Prolidase Activity and Erectile Dysfunction

Abstract

Prolidase is a cytosolic exopeptidase that cleaves iminodipeptides with carboxy-terminal proline or hydroxyproline and plays a major role in collagen turnover. Collagen is the essential content in atherosclerotic plaque, playing a key role in the stability/instability and progression of endothelial dysfunction in the pathogenesis of erectile dysfunction (ED). Consequently, in this study we sought to determine serum prolidase activity and markers of oxidative stress, such as lipid hydroperoxide and total free sulfhydryl, in vasculogenic ED. We evaluated 92 patients with vasculogenic ED and 50 control subjects by clinical and laboratory investigations. We measured serum prolidase activity and serum total free sulfhydryl levels spectrophotometrically. Serum lipid hydroperoxide levels were determined with ferrous ion oxidation-xylenol orange method. We assessed the association of serum prolidase activity with the presence and severity of vasculogenic ED and clinical characteristics, as well as laboratory parameters. We also assessed the association of serum prolidase activity with the variables according to the vascular status of patients with vasculogenic ED. The comparison included 92 vasculogenic ED patients grouped into 3 categories according to the vascular status of patients with ED-arterial insufficiency (n = 26), veno-occlusive dysfunction (n = 37), and mixed-type impotence (n = 29)-and 50 controls. Receiver-operator characteristics (ROCs) were analyzed to find a cutoff value with the best sensitivity and lowest false-positive rate. Serum prolidase activity (53.5 +/- 5.5 U/L vs 45.7 +/- 4.9 U/L, respectively; P < .001) and serum lipid hydroperoxide levels were significantly increased in patients with vasculogenic ED compared with controls, whereas serum total free sulfhydryl levels were significantly decreased in patients with vasculogenic ED compared with controls (P < .001). The lowest and highest mean serum prolidase activities were detected in control participants and in patients with arterial insufficiency, respectively (analysis of variance P < .001). The overall findings of this study support the predictive accuracy of the serum prolidase activity in our cohort, with a statistically significant ROC value of 0.78. Findings of this study have shown that serum prolidase activity is significantly associated with the presence and severity of vasculogenic ED, and elevated serum prolidase activity might be an independent predictor of ED.