Albumin downregulates Klotho in tubular cells.

Background: Kidney tubular cells are the main sources of Klotho, a protein with phosphaturic action. Genetic Klotho deficiency causes premature cardiovascular aging in mice. Human chronic kidney disease (CKD) is characterized by acquired Klotho deficiency. Despite the lack of uremic toxin accumulation, Category G1 CKD [(normal glomerular filtration rate (GFR)] is already associated with decreased Klotho and with premature cardiovascular aging. Methods: We have explored whether albuminuria, a criterion to diagnose CKD when GFR is normal, may directly decrease Klotho expression in human CKD, preclinical models and cultured tubular cells. Results: In a CKD cohort, albuminuria correlated with serum phosphate after adjustment for GFR, age and sex. In this regard, urinary Klotho was decreased in patients with pathological albuminuria but preserved GFR. Proteinuria induced in rats by puromycin aminonucleoside and in mice by albumin overload was associated with interstitial inflammation and reduced total kidney Klotho messenger ribonucleic acid (mRNA) expression. Western blot disclosed reduced kidney Klotho protein in proteinuric rats and mice and immunohistochemistry localized the reduced kidney Klotho expression to tubular cells in proteinuric animals. In cultured murine and human tubular cells, albumin directly decreased Klotho mRNA and protein expression. This was inhibited by trichostatin A, an inhibitor of histone deacetylases, but unlike cytokine-induced Klotho downregulation, not by inhibitors of nuclear factor kappa-light-chain-enhancer of activated B cells. Conclusions: In conclusion, albumin directly decreases Klotho expression in cultured tubular cells. This may explain, or at least contribute to, the decrease in Klotho and promote fibroblast growth factor 23 resistance in early CKD categories, as observed in preclinical and clinical proteinuric kidney disease.

Next-generation phosphate binders: focus on iron-based binders.

Phosphate excess is associated with increased mortality in patients with chronic kidney disease (CKD) and has recently been linked to accelerated aging. Oral phosphate binders are prescribed to patients with CKD to prevent absorption of dietary phosphate. Currently available binders have been associated with impaired outcomes (calcium-based binders) or are expensive (non-calcium-based binders). Iron-based phosphate binders represent a new class of phosphate binders. Four iron-based phosphate binders have undergone testing in clinical trials. The development of fermagate and SBR759 is currently on hold due to suboptimal and adverse effect profiles in at least some clinical trials. Ferric citrate and sucroferric oxyhydroxide (PA21) are at different stages of application for regulatory approval after being found safe and efficacious in decreasing serum phosphate. Iron from ferric citrate is more readily absorbed than that from sucroferric oxyhydroxide. Sucroferric oxyhydroxide was launched in the USA in 2014 for the treatment of hyperphosphatemia in adult dialysis patients. Ferric citrate may be more suited for chronic treatment of hyperphosphatemia in CKD patients requiring iron supplements but its use may have to be limited in time because of potential for iron overload in patients not needing iron or not receiving erythropoiesis-stimulating agents. In contrast, sucroferric oxyhydroxide may be more suited for hyperphosphatemic CKD patients not requiring iron supplements.