Calcitriol counteracts endothelial cell pro-inflammatory processes in a chronic kidney disease-like environment

In advanced chronic kidney disease (CKD), hypocalcemia, high levels of advanced glycation end products (AGEs), and parathyroid hormone (PTH) coexist and are considered to play a role in the development of chronic vasculopathies. The aim of the present study was to evaluate the impact of a CKD-like environment on cultured endothelial cell (EC) functions and to assess the impact of calcitriol on the expression of parameters such as endothelial nitric oxide synthase (eNOS), receptor of AGEs (RAGE), interleukin 6 (IL-6) and nuclear factor kappa B (NFκB). Human umbilical vein cord endothelial cells (HUVEC) were grown in medium containing low Ca2+ concentration stimulated with AGE-HSA and PTH and treated with calcitriol for additional incubation. mRNA expression was established by reverse transcriptase-PCR, protein expression by Western blot analysis, IL-6 secretion by ELISA, NOS activity by conversion of [14C]arginine to [14C]citrulline and DNA-binding activity of NFκB-p65 assayed colorimetrically in nuclear extracts. The CKD-like environment characterized by the association of low Ca2+ and high levels of AGEs and PTH, depressed eNOS system activity and enhanced RAGE and IL-6 expression/secretion. DNA-binding activity of nuclear NFκB-p65 was increased and the expression of IκBα decreased. Addition of calcitriol normalized the expression, secretion and activity of eNOS, RAGE and IL-6. The enhanced NFκB activity was also counteracted probably due to the increased IκBα expression. The effect of CKD-like environment on EC may partly explain the increased vasculopathies in CKD patients, in contrast to calcitriol, which suggests a vascular protective action.

Research highlights▶ CKD-like environment (low Ca2+, high AGEs and PTH) affected endothelial function. ▶ CKD-like environment depressed eNOS and enhanced pro-inflammatory parameters. ▶ These changes may be explained by activation of the intracellular NFκB pathway. ▶ Calcitriol blunts these effects through NFκB pathway.