Delivery of HFE mRNA by lipid nanoparticles corrects iron parameters and BMP responsiveness in murine hereditary hemochromatosis

Abstract Introduction: Disease-causing mutations in HFE lead to inappropriately low levels of the hepatic iron regulatory hormone hepcidin, resulting in increased dietary iron absorption, release of iron from splenic macrophages and pathologic hepatic iron accumulation. Current management of hereditary hemochromatosis, phlebotomy, unloads liver iron but does not relieve all symptoms and is not universally tolerated. We hypothesize that restoring hepatic HFE using lipid nanoparticle delivery of HFE mRNA, will increase hepcidin expression and treat iron overload. Methods: Hfe-/-mice were treated with lipid nanoparticles encapsulating human HFE mRNA (HFE-LNP), or carrier, by tail vein injection. Mice were analyzed after a single dose at 2- and 7-days post-dose, and after a repeated dosing regimen where mice received one dose every three days for up to 18 days. Results: Compared to vehicle, HFE-LNP treated Hfe-/- mice demonstrated restored hepatic HFE expression, increased Hamp1 expression (- delta Cq of 4.9 +/- 0.62 for vehicle vs 6.3 +/- 0.63 for HFE-LNP; p < 0.05 ) without a significant change in Bmp6 , and decreased transferrin saturation at 2 days post dose (75.7 +/- 3.3% for vehicle v 48.1 +/- 13 for HFE-LNP ; p < .001). The ratio of Hamp1 relative to Bmp6 returned to wild-type levels in HFE-LNP treated mice. At 7 days post dose, liver iron concentrations were decreased (3243+/- 160 ug/g dry weight for vehicle vs 2565 +/- 482 for HFE-LNP; p < 0.05). By this time, liver hepcidin expression had returned to pre-treatment baseline, and serum iron and transferrin saturation had begun to return as well. Repeated dosing resulted in a sustained decrease in serum iron (312 +/- 36 ug/dL for vehicle vs 267 +/- 21 for HFE-LNP; p < 0.01), transferrin saturation (74.3 +/- 4.5 % for vehicle vs 56.2 +/- 7.9 for HFE-LNP; p < 0.001) and liver iron concentration (2328 +/- 486 ug/g dry weight for vehicle vs 1710 +/- 396 for HFE-LNP; p < 0.01) at day 18. Repeated dosing resulted in transient effects on liver Hamp1, with a significant increase only observed 2 days after the first dose. Hepatic Bmp6 expression was lower in HFE-LNP treated mice compared to vehicle at days 9 (p <0.01) and 18 (p < 0.05), likely related to the suppressive effects of the lowered serum and hepatic iron. Conclusions: HFE-LNP treatment acutely restores hepatic HFE expression and increases hepcidin expression, effectively normalizing Bmp responsiveness. Repeated dosing results in a sustained correction of iron parameters. We speculate that lipid nanoparticle delivery of HFE mRNA has the potential to attenuate liver iron loading and decrease the need for therapeutic phlebotomy in hemochromatosis patients.