Abstract

INTRODUCTION: Oxidative stress is an adverse long-term ongoing phenomenon in renal transplant recipients (RTR) and vitamin E has important antioxidant properties that substantially counterbalance it. However, plasma vitamin E affinity with circulating lipids challenges its levels interpretation. We aimed to test the hypothesis that plasma vitamin E standardization by total lipids may introduce error from double correction for variance shared by total cholesterol and triglycerides, whereas erythrocytes vitamin E measurement may offer a non-fasting lipids-influenced alternative to estimate vitamin E status and accurately correlate it with clinical and laboratory parameters. METHODS: Cross-sectional analyses in an extensively phenotyped cohort of RTR, recruited in 2017 in a university setting. We compared linear regression-derived coefficients, calculated using non-standardized and total lipids-standardized atocopherol, measured in both plasma and erythrocytes, in relation to baseline characteristics. RESULTS: We included 113 RTR (mean age 55614 years-old, eGFR 51617 mL/min/1.73 m2). Plasma and erythrocytes a-tocopherol levels (33.167.6 and 6.361.5 mmol/L, respectively) were significantly associated (std. b=0.23; P=0.02). Total lipids explained a considerable part (i.e., 65%) of the variation of plasma a-tocopherol, whereas a limited part (i.e., <1%) of the variation of erythrocytes a-tocopherol levels. Otherwise strongly positive correlations of lipids domain parameters with plasma a-tocopherol became inverse, rather than absent, after correction by total cholesterol plus triglycerides, indicating potential overadjustment. Finally, we consistently found positive associations between erythrocytes a-tocopherol and other antioxidants domain parameters such as vitamin C (std. b=0.26; P=0.02) and HDL cholesterol (std. b=0.24; P=0.02). CONCLUSIONS: Variance shared by total cholesterol and fasting triglycerides may introduce error from double correction of plasma vitamin E and bias interpretation of its association with lipids and antioxidants domain parameters, which could be overcome by using non-standardized vitamin E levels measured in erythrocytes membranes.