High-phosphate induced vascular calcification is reduced by iron citrate through inhibition of extracellular matrix osteo-chondrogenic shift in VSMCs

Background: High serumphosphate (Pi) levels strongly associate with cardiovascularmorbidity andmortality in chronic kidney disease (CKD) patients with vascular calcification playing a major role in the pathogenesis of related cardiovascular disease. High-Pi challenged vascular smooth muscle cells (VSMCs) undergo similosteoblastic transformation and actively deposit calcium-phosphate crystals. Iron-based Pi-binders are used to treat hyperphosphatemia in CKD patients. Methods: In this study, we investigated the direct effect of iron citrate on extracellularmatrix (ECM) modification induced by high-Pi, following either prophylactic or therapeutic approach. Results: Iron prophylactically prevents and therapeutically blocks high-Pi induced calcification. Masson's staining highlights the changes of muscular ECM that after high-Pi stimulation becomes fibrotic and which modifications are prevented or partially reverted by iron. Interestingly, iron preserves glycogen granules and either prevents or partially reverts the formation of non- glycogen granules induced by high-Pi. In parallel, iron addition is able to either prevent or block the high-Pi induced acid mucin deposition. Iron inhibited calcification also by preventing exosome osteo-chondrogenic shift by reducing phosphate load ( 0,61 +/- 0.04vs0,45 +/- 0.05, PivsPi + Fe, p < 0,05, nmol Pi/mg protein) and inducing miRNA 30c (0.62 +/- 0.05vs3.07 +/- 0.62; PivsPi + Fe, p < 0.01, relative expression). Studying aortic rings, we found that iron significantly either prevents or reverts the high- Pi induced collagen deposition and the elastin decrease, preserving elastin structure (0.7 +/- 0.1 vs 1.2 +/- 0.1; Pi vs Pi+ Fe, p < 0.05, elastin mRNA relative expression). Conclusions: Iron directly either prevents or partially reverts the high- Pi induced osteo-chondrocytic shift of ECM. The protection of muscular nature of VSMC ECM may be one of the mechanisms elucidating the anti-calcific effect of iron. (C) 2019 Elsevier B.V. All rights reserved.