Diabetes: Risks of strict glycaemic control in diabetic nephropathy

ATP-binding cassette A1 deficiency causes cardiolipin-driven mitochondrial dysfunction in podocytes

Fibroblasts from patients with Tangier disease carrying ATP-binding cassette A1 (ABCA1) loss-of-function mutations are characterized by cardiolipin accumulation, a mitochondrial-specific phospholipid. Suppression of ABCA1 expression occurs in glomeruli from patients with diabetic kidney disease (DKD) and in human podocytes exposed to DKD sera collected prior to the development of DKD. We demonstrated that siRNA ABCA1 knockdown in podocytes led to reduced oxygen consumption capabilities associated with alterations in the oxidative phosphorylation (OXPHOS) complexes and with cardiolipin accumulation. Podocyte-specific deletion of Abca1 (Abca1fl/fl) rendered mice susceptible to DKD, and pharmacological induction of ABCA1 improved established DKD. This was not mediated by free cholesterol, as genetic deletion of sterol-o-acyltransferase-1 (SOAT1) in Abca1fl/fl mice was sufficient to cause free cholesterol accumulation but did not cause glomerular injury. Instead, cardiolipin mediates ABCA1-dependent susceptibility to podocyte injury, as inhibition of cardiolipin peroxidation with elamipretide improved DKD in vivo and prevented ABCA1-dependent podocyte injury in vitro and in vivo. Collectively, we describe a pathway definitively linking ABCA1 deficiency to cardiolipin-driven mitochondrial dysfunction. We demonstrated that this pathway is relevant to DKD and that ABCA1 inducers or inhibitors of cardiolipin peroxidation may each represent therapeutic strategies for the treatment of established DKD.

Phosphate Binding Therapy to Lower Serum Fibroblast-Growth-Factor-23 Concentrations in Chronic Kidney Disease: Rationale and Study Design of the Sevelamer on FGF23 Trial (SoFT)

BACKGROUND

Increased levels of phosphate and fibroblast growth factor-23 (FGF23) are strong predictors of cardiovascular morbidity and mortality in patients with chronic kidney disease (CKD). Preliminary data suggest that interventions lowering gastro-intestinal phosphate uptake lowers serum FGF23 concentrations and improves cardiovascular risk and subsequently survival. However, data are lacking about the magnitude of effects, the effect in different stages of CKD and whether there is a dose-effect relationship.

METHODS

Therefore, the Sevelamer on FGF23 Trial (SoFT) is designed as an open-label, single-arm, clinical pilot study aiming to demonstrate the feasibility of a phosphate-restricted diet in combination with the phosphate binder sevelamer to induce an effective, predictable and sustained decrease in FGF23 level in patients with an estimated glomerular filtration rate (eGFR) of 15-90 or >90 ml/min/1.73 m2 with proteinuria >1.0 g in 24 h urine collection, despite optimally dosed RAAS blockade, without inducing hypophosphatemia using a forced uptitration treatment regimen aimed at restricting phosphate uptake.