Urinary TBARS as a Non-Invasive Proxy of Plasma Lipid Peroxidation in Essential Hypertension: A Translational Study...

Lipid peroxidation is a relevant oxidative-inflammatory mechanism in essential hypertension and cardiovascular disease. Plasma thiobarbituric acid reactive substances (TBARS), commonly reported as malondialdehyde-equivalent values, provide an operational index of lipid peroxidation-related aldehydic reactivity, but blood-based assessment is limited by venipuncture and preanalytical handling requirements. Urine is an attractive non-invasive matrix for redox biomarker development, although whether urinary TBARS reflect plasma lipid peroxidation in hypertensive patients remains insufficiently characterized. This study aimed to evaluate whether matrix-specific normalization-total cholesterol for plasma TBARS and creatinine for urinary TBARS-reveals a measurable intra-individual relationship between these matrices in essential hypertension.

In this paired observational study, plasma and urine samples were obtained from 39 treated patients with essential hypertension under standardized fasting conditions. TBARS were quantified using a colorimetric thiobarbituric acid reaction assay. Plasma TBARS were normalized to total cholesterol and expressed as TBARSp, while urinary TBARS were normalized to creatinine and expressed as TBARSu. Associations were assessed using Spearman's rank correlation, exploratory receiver operating characteristic (ROC) analyses based on internally derived plasma TBARS percentile thresholds, and Bayesian bootstrap inference.

Cholesterol-normalized plasma TBARS and creatinine-normalized urinary TBARS showed a moderate-to-strong positive monotonic association (Spearman's ρ = 0.717, p < 0.001). Bayesian bootstrap analysis supported this relationship, with a 95% credible interval of 0.57-0.83 and a Bayes factor > 300 for ρ ≥ 0.5. Urinary TBARS showed exploratory within-cohort discriminatory capacity for identifying elevated plasma TBARS using internally derived thresholds, with an AUC of 0.892 for the median-based classification.

Creatinine-normalized urinary TBARS showed a moderate-to-strong association with cholesterol-normalized plasma TBARS in treated essential hypertension. These findings provide hypothesis-generating paired-sample evidence that urinary TBARS may serve as a low-burden, non-invasive proxy of plasma lipid peroxidation-related redox alterations. Further validation in larger and clinically diverse cohorts, ideally including more specific lipid peroxidation markers and renal-function-aware analyses, is required to define their translational and clinical utility.