Disproportionate transport of excess circulating heme to kidney induces AKI in sickle mice. (A) Plasma concentration of A1M is elevated in sickle transgenic (SS) mice compared with control (AA) mice (n = 8-12). Ratio of molar concentration of A1M and hemopexin (A1M/Hx) in plasma from SS and AA mice (n = 8-12). (B-L) Transgenic sickle (SS) and littermate control (AA) mice were infused with hemin (20 μmol/kg body weight [BW]). (B) Total heme content in kidney and liver tissue 2 days following infusion of hemin (H) or vehicle (V) in sickle transgenic mice (SS) and control (AA) mice (n = 6). Heme was scavenged preferentially to the kidneys in SS mice, and to the liver in AA mice. (C) Paired analysis of plasma Cr in AA and SS mice (n = 6) at baseline (BL) and 2 days (D2) following infusion of exogenous hemin. (D) Ratio of albumin and Cr in spot urine (uACR) collected from the same cohort of mice as in panel C. (E) ELISA of urine samples from AA and SS mice, showing an ∼3.6-fold increase in urinary KIM-1 in SS mice following hemin infusion (n = 8-12). (F-G) Relative fluorescence showing real-time clearance of infused FITC-sinstrin from circulation in (F) AA mice and (G) SS mice prior to and 2 days following hemin infusion. Delayed clearance of FITC-sinistrin in hemin-infused SS mice indicates reduced renal function. (H) GFR representing kidney function in AA and SS mice at baseline and following hemin infusion (n = 4-7). (I) Representative images of cortex and medulla from hematoxylin-and-eosin–stained renal sections of AA and SS mice challenged with vehicle or hemin showing cortical tubular vacuolation and atrophy with severe medullary peritubular capillary congestion in heme-infused SS mice kidney (original magnification ×400). (J) Semiquantitative histological kidney injury score in AA and SS mice in panel I. (K) Represented renal histology following TUNEL staining (blue stain indicates fragmented DNA content) showing tubular cell death/apoptosis in SS mice kidney tubules (original magnification ×400). (L) Semiquantitative apoptotic index showing percentage of TUNEL⁺ tubules in panelK. (M) Control (HxWT) mice and mice lacking hemopexin expression (HxKO) were transplanted with bone marrow from SS mice to create sickle mice with (HxWT^SS) or without (HxKO^SS) hemopexin in nonhematopoietic tissues. Level of plasma hemopexin (Hx; left y-axis) and plasma A1M (right y-axis) in HxWT, HxKO, HxWT^SS, and HxKO^SS mice showing that 2 heme scavengers are inversely related (n = 3-5). (N) Paired analysis of GFR at baseline and following hemin (20 μmol/kg BW) challenge (H) in indicated group of mice (n = 3-5) showing that absence of plasma hemopexin severely impairs renal function in SS mice leading to AKI. (O) SS mice were treated with hemopexin (1 mg per mouse) or A1M (0.25 mg per mouse) or vehicle immediately prior to hemin (20 μmol/kg BW) infusion. Calculated GFR at baseline and 2 days following hemin infusion in SS mice treated with vehicle, hemopexin, or A1M showing protection from AKI development in hemopexin-treated mice. *P < .05, **P < .01, ***P < .001.