Serum neopterin and kynurenine as predictive and prognostic biomarkers in prostate cancer: the role of dietary inflammatory index and biomarker interactions

Background It has been shown that neopterin levels in various body fluids can help predict the diagnosis of different malignancies. Although many studies have investigated the roles of serum neopterin concentrations, tryptophan metabolism, and the dietary inflammation index (DII) in various cancers, the connection between these factors and prostate cancer (PC) remains uncertain. The aim of this study was to investigate the predictive and prognostic roles of serum neopterin, and kynurenine levels, along with the kynurenine-to-tryptophan ratio (KTR) and DII in prostate cancer. Methods This study was conducted with 57 newly diagnosed prostate cancer patients, 55 benign prostate hyperplasia patients, and 56 healthy male individuals in the control group, all aged 40 years and older. Participants had specific anthropometric measurements taken, and three-day food records were kept. DII was calculated based on data for thirty-four available nutrients by using food records. Serum levels of neopterin, kynurenine, tryptophan, tumor necrosis factor alpha (TNF-alpha), and interferon-gamma (IFN-gamma) were measured using an enzyme-linked immunosorbent assay (ELISA) method. Results Serum neopterin (11.79 +/- 6.09), kynurenine (1655.48 +/- 1122.04), TNF-alpha (221.59 +/- 232.06) and IFN-gamma (137.68 +/- 107.11) levels were higher in the malignant group than in both the control (2.72 +/- 0.76, 352.40 +/- 69.33, 223.94 +/- 226.67, and 23.03 +/- 7.28, respectively) and benign groups (3.17 +/- 0.74, 377.94 +/- 109.05, 179.61 +/- 224.36, and 25.63 +/- 7.50, respectively) (p < 0.05). Another result of our study is that in the malignant group, serum neopterin levels exhibited significant positive correlations with serum kynurenine (r = 0.80, p < 0.0001), IFN-gamma (r = 0.86, p < 0.0001) and TNF-alpha levels (r = -0.27, p = 0.0453) and DII (r = 0.30, p = 0.0229), while they exhibited weak correlations with serum PSA, and other diet parameters. Additionally, kynurenine was the only parameter showing significant differences in mean values concerning surgical margins (p < 0.05). Conclusions The findings of this study support the hypothesis that serum neopterin and specific tryptophan catabolites (e.g., kynurenine), could serve as predictive and prognostic biomarkers for prostate cancer diagnosis. However, our results do not support the hypothesis that DII and certain dietary factors play a direct role in the development or diagnosis of prostate cancer.