Abstract
Background
Fe sucrose (FeS) administration induces a state of renal preconditioning, protecting against selected forms of AKI. Recent evidence suggests that recombinant hepcidin also mitigates acute renal damage. Hence, the goals of this study were as follows: i) Determine whether a new proprietary FeS formulation (“RBT-3”), can acutely activate the hepcidin (HAMP1) gene in humans, raising plasma and renal hepcidin concentrations; ii) assess whether the kidney participates in this posited RBT-3-hepcidin generation response; iii) test whether RBT-3 can mitigate a clinically relevant AKI model (experimental cisplatin toxicity); and iv) explore whether mechanisms in addition to hepcidin generation are operative in RBT-3’s cytoprotective effects.
Methods
Healthy human volunteers (n, 9) and subjects with stage 3-4 CKD (n, 9) received 120, 240, or 360 mg of RBT-3 (IV over 2 hrs). Plasma and urine samples were collected and assayed for hepcidin levels (0-72 hrs post RBT-3 injection). In complementary mouse experiments, RBT-3 effects on hepatic vs. renal hepcidin (HAMP1) mRNA and protein levels were compared. RBT-3’s impact on the mouse Nrf2 pathway, and on experimental cisplatin nephrotoxicity, were assessed. Direct effects of exogenous hepcidin on in vivo and in vitro (HK-2 cells) cisplatin toxicity were also tested.
Results
RBT-3 induced rapid, dose dependent, and comparable plasma hepcidin increases in both HVs and CKD subjects (∼15x baseline within 24 hrs). Human kidney hepcidin exposure was confirmed by 4 fold urinary hepcidin increases. RBT-3 up-regulated mouse hepcidin mRNA, but much more so in kidney (>25x) vs. liver (∼2x). RBT-3 also activated kidney Nrf2 (increased Nrf2 nuclear binding; increased Nrf2-responsive gene mRNAs: HO-1, SrXN1, GCLC, NQO1). RBT-3 preconditioning (18 hr time lapse) markedly attenuated experimental cisplatin nephrotoxicity (∼50% BUN/creatinine decrements), in part, by reducing renal cisplatin uptake by 40%. Exogenous hepcidin (without RBT-3) treatment conferred protection against mild in vivo (but not in vitro) cisplatin toxicity.
Conclusions
RBT-3 acutely and dramatically up-regulates cytoprotective hepcidin production, increasing renal hepcidin levels. However, additional cytoprotective mechanisms are activated by RBT-3 (e.g., Nrf2 activation; reduced cisplatin uptake). Thus, RBT-3-induced preconditioning likely confers renal resistance to cisplatin via an interplay of multiple cytoprotective activities.