Endothelial function assessed by peripheral arterial tonometry is not related with FGF23 serum levels in pre-dialysis CKD patients A função endotelial avaliada pela tonometria arterial periférica não se correlaciona com os níveis séricos de FGF-23 em doentes renais crónicos pré-diálise

 ABSTRACT Cardiovascular (CV) diseases are the leading causes of morbidity and mortality in patients with chronic kidney disease (CKD) that encompass the mildest degrees of renal impairment. High levels of phosphate and fibroblast growth factor 23 (FGF-23) are associated with increased CV events in this population. However, differences in clinical and pathological manifestations have suggested that distinct mechanisms may underlie cardiovascular events associated with high phosphate and FGF-23 serum levels. In animal studies endothelial dysfunction (ED) has recently been associated with increased levels of phosphorus, but not with the increase of FGF-23 serum levels. In this study, we aimed to assess endothelial function and the relationship with phosphate and FGF23 serum levels in a pre-dialysis CKD population. We examined 43 CKD patients in stages 1 to 5, followed-up in our outpatient clinic. Blood pressure, renal function, proteinuria, phosphate serum levels and Charlson Index were evaluated in the studied population. The FGF-23 levels were assessed by ELISA. Endothelial function was assessed by peripheral arterial tonometry (Endo-Pat 2000) where lower reactive hyperaemia index (RHI) values correspond to greater ED. Estimated GFR (eGFR) negatively correlated either with both serum phosphate (r = -0.42; p < 0.0004), and circulating FGF-23 levels (r = -0.42; p < 0.05); RHI positively correlated with eGFR (r = 0.35; p < 0.03) and negatively correlated with age (r = -0.59; p < 0.0001), proteinuria (r = -0.50; p < 0.03), serum phosphate (r = -0.34; p < 0.04) and Charlson index (r = -0.56; p < 0.0003). However, no significant relationship was observed between RHI and FGF23 serum levels (r = -0.11, n.s.) in the studied population. Our results suggest that peripheral arterial tonometry, a non-invasive method for evaluation of the endothelial function, can be a practical tool that adds clinically useful information to improve risk stratification in CKD pre- dialysis patients. Our results also agree with the view that phosphate and FGF-23 serum levels might contribute to increased cardiovascular risk in CKD through distinct mechanisms.