Background: In patients with iron deficiency anemia, ferric carboxymaltose (FCM) and ferric derisomaltose (FDI) allow high-dose iron repletion. While FCM is reported to induce hypophosphatemia, the frequency of hypophosphatemia after an equivalent dosage of FDI had not been assessed prospectively. Methods: In the prospective, single-center, double-blind HOMe aFers study, 26 women with iron deficiency anemia (hemoglobin < 12 g/dL plus either plasma ferritin ≤ 100 ng/mL or a plasma ferritin ≤ 300 ng/mL and transferrin saturation (TSAT) ≤ 30%) were randomized to a single intravenous infusion of 20 mg/kg body weight (up to a maximum of 1000 mg) FCM or FDI. The primary endpoint was the incidence of hypophosphatemia (plasma phosphorus levels < 2.0 mg/dL at day 1, day 7 ± 2, and/or day 35 ± 2 after the infusion). In order to investigate potential skeletal and cardiovascular implications, we assessed changes in other components of mineral and bone metabolism, left ventricular function, and arrhythmias. Results: Hypophosphatemia occurred more frequently in women treated with FCM (9 out of 12 [75%]) than in those treated with FDI (1 out of 13 [8%]; p = 0.001). Within 24 h after iron supplementation, women in the FCM group had significant higher plasma intact FGF23 (p < 0.001) and lower plasma 1.25-dihydroxyvitamin D (p < 0.001). As an indicator of urinary phosphorus losses, urinary fractional phosphorus excretion was higher in the FCM group (p = 0.021 at day 7 ± 2 after iron supplementation). We did not observe differences in skeletal and cardiovascular markers, potentially because of the limited number of participants. Conclusions: While both FCM and FDI provide efficient iron repletion in participants with iron deficiency anemia, FCM induced hypophosphatemia more often than FDI. Trial registration: Clinical Trials.gov NCT02905539. Registered on 8 September 2016. 2015-004808-36 (EudraCT Number) U1111-1176-4563 (WHO Universal Trial Number) DRKS00010766 (Deutsches Register Klinischer Studien)

Background: Various epidemiological studies linked high fibroblast growth factor 23 (FGF23) levels with cardiovascular events in chronic kidney disease (CKD). It remains enigmatic whether high FGF23 exerts adverse cardiovascular effects, or whether it reflects detrimental effects of residual confounders. Earlier studies adjusted for CKD-mineral bone disease (CKD-MBD) regulators of FGF23 rather than for recently discovered non-CKD-MBD regulators, among which iron deficiency and heart failure are of particular importance. Moreover, they used c-terminal FGF23 (cFGF23) assays rather than more specific intact FGF23 (iFGF23) assays. Methods: The CARE FOR HOMe study analyzed plasma ferritin, iFGF23, cFGF23 and N-terminal proBNP (NT-proBNP) along with conventional risk factors, among 575 CKD G2-G4 patients to determine the interaction between FGF23, its non-CKD-MBD regulators, and incident cardiovascular events in CKD patients. The participants were followed up for 5.1 ± 2.1 years for the occurrence of atherosclerotic events and hospitalization for acute decompensated heart failure. Results: cFGF23 correlated strongly with high iFGF23 (r = 0.607), fairly with high NT-proBNP (r = 0.453) and weakly with low ferritin (r = –0.207); correlation coefficients of iFGF23 with NT-proBNP and ferritin were numerically lower. In Kaplan-Meier analyses, both endpoints were predicted by cFGF23 and iFGF23. In Cox regression models, cFGF23 remained an outcome predictor after adjustment for conventional risk factors and ferritin. This prediction was largely eliminated when further adjusting for NT-proBNP. iFGF23 was less consistently associated with adverse outcome in partly adjusted models, and failed to predict outcome in fully adjusted models. Conclusion: In summary, iron deficiency and heart failure affect plasma FGF23. As adjustment for NT-proBNP virtually eliminates the association between plasma FGF23 and predefined outcome, we speculate that high FGF23, rather than exerting detrimental cardiovascular effects, mirrors prevalent heart disease.

Since the introduction of sacubitril/valsartan in clinical cardiology, neprilysin has become a major target for heart failure treatment. Plasma neprilysin concentration has been discussed as a novel biomarker that predicts cardiac events. Natriuretic peptides may inhibit plasma neprilysin. As they accumulate in chronic kidney disease (CKD), we hypothesized that high plasma neprilysin loses its predictive role in CKD patients. We measured plasma levels of neprilysin concentration, neprilysin activity and brain natriuretic peptide (BNP) in 542 CKD G2–G4 patients within the CARE FOR HOMe study. Patients were followed for predefined endpoints of hospitalization for acute decompensated heart failure and incident atherosclerotic cardiovascular events. During 5.1 ± 2.1 years, 63 patients had acute decompensated heart failure and 125 patients had incident atherosclerotic cardiovascular events. In both Kaplan–Meier and multivariate Cox regression analyses, high plasma BNP and low, rather than elevated, neprilysin activity predicted future hospitalization for acute decompensated heart failure; neprilysin concentration was not predictive. Furthermore, only BNP was an independent predictor of incident atherosclerotic cardiovascular events. In line with experimental studies, high natriuretic peptides may inhibit neprilysin activity in CKD. Therefore, high neprilysin activity and concentrations are not predictors of adverse cardiovascular outcome in CKD patients. Thus neprilysin inhibitors should be implemented with caution in patients with advanced CKD.

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