Impact of cholesterol lowering treatment on plasma kynurenine and tryptophan concentrations in chronic kidney disease: Relationship with oxidative stress improvement

• CKD patients show increased plasma levels of inflammation and oxidative markers.
• We found that treatment with simvastatin/ezetimibe improve oxidative stress in CKD.
• We describe as oxidative stress improvement are related to the decrease of Kyn plasma levels.
• Inflammation improvement may be mediated by OS reduction due to the restoring of normal Tau levels.

Background and aimTryptophan (Trp) degradation via indoleamine (2,3)-dioxygenase (IDO), with consequent increased in kynurenine (Kyn) concentrations, has been proposed as marker of immune system activation. Oxidative stress (OS) might contribute to the pro-inflammatory state in chronic kidney disease (CKD) through the activation of NF-kB, with consequent activation and recruitment of immune cells.Methods and resultsSerum concentrations of Trp and Kyn, oxidative stress indices malondialdehyde (MDA) and allantoin/uric acid (All/UA) ratio and anti-oxidant amino acid taurine were measured in 30 CKD patients randomized to 40 mg/day simvastatin (group 1), ezetimibe/simvastatin 10/20 mg/day (group 2) or ezetimibe/simvastatin 10/40 mg/day (group 3) and treated for 12 months. Baseline Kyn and Kyn/Trp ratio were higher in CKD patients vs. healthy controls (1.67 ± 0.62 μmol/L vs 1.25 ± 0.40 μmol/L, p < 0.01 and 0.036 ± 0.016 vs 0.023 ± 0.010, p < 0.001 respectively). Both Kyn and Kyn/Trp ratio significantly decreased after cholesterol lowering treatment, to values comparable with healthy controls after one year treatment (1.67 ± 0.62 μmol/L vs 1.31 ± 0.51 μmol/L, p < 0.0001 and 0.036 ± 0.016 vs 0.028 ± 0.012 p < 0.0001, respectively). This was paralleled by a significant decrease in MDA (218 ± 143 nmol/L vs 176 ± 123 nmol/L, p < 0.01) and All/UA ratio (1.47 ± 0.72 vs 1.19 ± 0.51, p < 0.01) in CKD patients.ConclusionsAmelioration of both oxidative and inflammation status after cholesterol lowering treatment in CKD might be mediated by restoration of antioxidant taurine concentrations during therapy (from 51.1 ± 13.3 μmol/L at baseline to 63.1 ± 16.4 μmol/L, p < 0.001 by ANOVA), suggesting that improvement of both oxidative and inflammation status in CKD patients could be explained, at least partly, by the cholesterol lowering effects.