Background: The human plasma constituent hemopexin (Hx), following incubation with renal tissue, is able to induce glomerular alterations in vitro that are similar to those seen in minimal change disease (MCD). Whether this acute phase reactant is also able to induce proteinuria and minimal change-like alterations in vivo is questioned.
Methods: In the first set of experiments, Hx (4.0 mg in 5.0 mL saline) or equal amounts of control fraction, that is, heat-inactivated Hx (HI-Hx), were infused into conscious rats (N = 6) that had been surgically equipped with a cannula inserted into the suprarenal artery (SRA), enabling direct contact of the infusate and the renal microvasculature. Each animal received HI-Hx at day 1 for 15 minutes (flow rate 20.0 mL/h), subsequently followed by saline for seven hours (Flow rate 5.0 mL/h), after which the cannula was disconnected. At day 2, identical infusions in the same rat were carried out, using native Hx. Urine samples collected every 30 minutes during the experiments were monitored for protein content using standard methods. In the second set of experiments, unilateral perfusion was done ex vivo in anesthetized rats with Hx (N = 5) or HI-Hx (N = 3; 1.5 mg/mL; 4.0 mL during 6 min). After reconnection of the circulation, urine samples of both kidneys were collected every 30 minutes during five hours via ureter cannulation. Urinary protein (expressed as the difference in excretion between perfused and nonperfused kidney) was calculated in mg/24 h. In additional experiments, rats were sacrificed two hours after perfusion of Hx or heat-inactivated (control) Hx (first set of experiments) or after five hours (second set of experiments), and kidneys were processed for immunohistochemical and ultrastructural examination.
Results: The results of experiment 1 show a significant increase of proteinuria after Hx infusion versus HI-Hx (means +/- SD, 41.91 +/- 16.01 mg/24 h vs. control, 21.22 +/- 5.69 mg/24 h; P </= 0.03). Histochemical and electron microscopical examination of kidney tissue fragments taken at the time of proteinuria showed diminished expression of glomerular ecto-ATPase and enhanced effacement of epithelial foot processes at the ultrastructural level. In the second set of experiments, the results show significant urinary protein excretion peaking one hour after perfusion (6.63 +/- 7.06 mg/24 h), exclusively in Hx-perfused animals (analysis of variance, P < or = 0.001).
Conclusion: It is concluded that Hx is able to induce proteinuria associated with MCD-like alterations in rat kidney in vivo.