Magnetic resonance imaging determination of tissue sodium across the CKD spectrum-associations and implications for health.

Background: Increased tissue sodium (Na+) concentration is associated with adverse clinical outcomes in people with chronic kidney disease (CKD) including hypertension, inflammation and increased cardiovascular disease (CVD). 23-Sodium magnetic resonance imaging (23Na-MRI) can non-invasively quantify tissue Na+ concentration. However, in the CKD population, few studies have evaluated relationships between 23Na-MRI-derived tissue Na+ concentrations and measures of Na+ metabolism, surrogate markers of CVD and other CKD-related health complications. Methods: We conducted a cross-sectional cohort study, involving 51 participants with CKD (28 with non-dialysis CKD, 23 on dialysis), to explore relationships between 23Na-MRI-derived tissue Na+ concentrations (including skin, bone, muscle and whole leg-tissue), measures of Na+ metabolism and CKD-related health outcomes. Multivariable regression and correlation analyses were used to assess associations. Results: Skin and whole leg-tissue Na+ concentrations were positively associated with surrogate cardiovascular markers of troponin I and brain natriuretic peptide (P < .05). Bone and whole leg-tissue Na+ concentrations were negatively associated with bone mineral density. Higher muscle Na+ concentration was associated with lower levels of physical well-being. Tissue Na+ concentration was positively correlated with extracellular fluid volume as measured by proton (1H) MRI (P ≤ .001) and body composition monitor (P < .05). Conclusion: Whole leg-tissue Na+ in addition to skin Na+ concentration may be a useful clinical marker of body Na+ with related health outcomes. Tissue Na+ may play a role in CVD, bone health and quality of life in people with CKD, representing a potential therapeutic target to improve clinical outcomes.