The importance of plasma arginine level and its downstream metabolites in diagnosing prostate cancer

There is still no certain threshold value of prostate-specific antigen (PSA) for prostate cancer diagnosis. We aimed to investigate the predictive value of arginine and its metabolites for diagnosing prostate cancer in patients with PSA 4-10 ng/ml and evaluate their usefulness as prognostic tumor markers.

Seventy-eight patients with a mean age of 64.50 ± 5.49 years were included in our prospective observational study between November 2016 and March 2017. They were divided into two equal groups according to the pathologic results of prostate biopsy (benign vs. malignant). Plasma arginine and ornithine levels were analyzed before biopsy by liquid chromatography-tandem mass spectrometry. ELISA was used for analyzing urinary diacetylspermine.

In PSA-adjusted analysis, the malignant group had lower plasma arginine levels (p = 0.021) and arginine to ornithine ratio (AOR) (p = 0.010), but higher plasma ornithine levels (p = 0.012) and urinary diacetylspermine levels (p < 0.001) as compared with the benign group. While arginine (r = - 0.628, p < 0.001) and AOR (r = - 0.714, p < 0.001) were negatively correlated with D'Amico clinical classification (p < 0.001), ornithine (r = 0.659, p < 0.001) and diacetylspermine (r = 0.710, p < 0.001) were found to be positively correlated (p < 0.001). In multivariate analysis, ornithine [OR 3.264, 95% CI (1.045-10.196), p = 0.042] and diacetylspermine [OR 6.982, 95% CI (2.403-20.290), p < 0.001] were found to be more significant in detection of prostate cancer.

Plasma arginine, ornithine, AOR and urinary diacetylspermine levels may be used as molecular markers to predict prostate biopsy outcomes in patients with PSA 4-10 ng/ml. But according to our results, the use of ornithine and diacethylspermine prior to biopsy seems to be the most cost-effective diagnostic strategy.