Measurement of PDE5 concentration in human serum: proof-of-concept and validation of methodology in control and prostate cancer patients.

Purpose: We aimed to investigate if the type 5 phosphodiesterase (PDE5), an enzyme with cardinal biological functions in sexual and cardiovascular health, can be detected and quantited in human serum.

Methods: Blood samples were collected from control male and female subjects. PDE5 levels were measured by a specific ELISA kit. ROC curves weighted for age and serum levels of PSA (male subjects), or age (female subjects) were used to identify the predictive ability in the detection of PCa. Sensitivity, specificity, PPV and NPV values were determined for cut-off value determined during ROC curve analysis.

Results: 41 control male subjects, 18 control female subjects, and 55 consecutive subjects, of which 25 were affected by benign prostatic hypertrophy (BPH) and 30 with histologically confirmed prostate cancer (PCa), were studied. PDE5 serum levels were detectable in all subjects (range: 5 to 65 ng/ml). Analysis by MANCOVA identified a significant difference in serum PDE5 between control subjects or hyperplasia patients and PCa patients. Marginal means of serum PDE5 concentrations showed a significant difference (p < 0.001). The ROC curve demonstrated that PDE5 serum levels can predict men with or without PCa, with 0.806 AUC value (p < 0.0001). Using a 12.705 ng/ml PDE5 serum cut-off yielded sensitivity, specificity, PPV, and NPV of 83.3%, 77.27%, 62.5%, and 91.1% in detecting men with histologically proven PCa, respectively.

Conclusions: We demonstrated, for the first time, that PDE5 levels can be detected in human sera and that PCa patients have significantly higher PDE5 concentration compared to BPH patients or male and female controls. While serum PDE5 level measurement may open new research avenues, the clinical relevance of PDE5 levels in PCa patients deserves further investigation.