Preeclampsia is a major cause of morbidity and mortality during pregnancy. To date, the pathogenesis of the disease is not fully understood. Recent studies show that preeclampsia is associated with overexpression of hemoglobin genes α2 and γ and accumulation of the protein in the vascular lumen of the placenta. Hypothesizing that cell-free hemoglobin leaks from the placenta into the maternal circulation and contributes to the endothelial damage and symptoms by inducing oxidative stress, we analysed fetal and adult hemoglobin (HbF, HbA), haptoglobin, oxidation markers and the heme scavenger and antioxidant α 1 -microglobulin in plasma, urine and placenta in preeclamptic women (n=28) and normal pregnancies (n=27).The mean plasma concentrations of HbF, HbA, protein carbonyl groups, membrane peroxidation capacity and α 1 -microglobulin were significantly increased in preeclamptic women. The levels of total plasma Hb correlated strongly with the systolic blood pressure.The plasma haptoglobin concentrations of women with preeclampsia were significantly depressed. Increased amounts of α 1 -microglobulin-mRNA and protein were found in placenta from preeclamptic women and the levels of plasma and placenta α 1 -microglobulin correlated to plasma Hb-concentrations. The heme-degrading form t-α 1 -microglobulin was significantly increased in urine in preeclampsia. These results support that hemoglobin-induced oxidative stress is a pathogenic factor in preeclampsia.
Preeclampsia (PE) is a serious pregnancy complication that manifests as hypertension and proteinuria after the 20th gestation week. Previously, fetal hemoglobin (HbF) has been identified as a plausible causative factor. Cell-free Hb and its degradation products are known to cause oxidative stress and tissue damage, typical of the PE placenta. A1M (α1-microglobulin) is an endogenous scavenger of radicals and heme. Here, the usefulness of A1M as a treatment for PE is investigated in the pregnant ewe PE model, in which starvation induces PE symptoms via hemolysis. Eleven ewes, in late pregnancy, were starved for 36 hours and then treated with A1M (n = 5) or placebo (n = 6) injections. After injections, the ewes were re-fed and observed for additional 72 hours. They were monitored for blood pressure, proteinuria, blood cell distribution and clinical and inflammation markers in plasma. Before termination, the utero-placental circulation was analyzed with Doppler velocimetry and the kidney glomerular function was analyzed by Ficoll sieving. At termination, blood, kidney and placenta samples were collected and analyzed for changes in gene expression and tissue structure. The starvation resulted in increased amounts of the hemolysis marker bilirubin in the blood, structural damages to the placenta and kidneys and an increased glomerular sieving coefficient indicating a defect filtration barrier. Treatment with A1M ameliorated these changes without signs of side-effects. In conclusion, A1M displayed positive therapeutic effects in the ewe starvation PE model, and was well tolerated. Therefore, we suggest A1M as a plausible treatment for PE in humans.
Background: Alpha-1-microglobulin (A1M), a small lipocalin protein found in plasma and tissues, has been identified as a heme1 and radical scavenger that may participate in the mitigation of toxicities caused by degradation of hemoglobin. The objective of this work was to investigate heme interactions with A1M in vitro using various analytical techniques and to optimize analytical methodology suitable for rapid evaluation of the ligand binding properties of recombinant A1M versions.Methods: To examine heme binding properties of A1M we utilized UV/Vis absorption spectroscopy, visible circular dichroism (CD), catalase-like activity, migration shift electrophoresis, and surface plasmon resonance (SPR), which was specifically developed for the assessment of His-tagged A1M.Results: The results of this study confirm that A1M is a heme binding protein that can accommodate heme at more than one binding site and/or in coordination with different amino acid residues depending upon heme concentration and ligand-to-protein molar ratio. UV/Vis titration of A1M with heme revealed an unusually large bathochromic shift, up to 38 nm, observed for heme binding to a primary binding site. UV/Vis spectroscopy, visible CD and catalase-like activity suggested that heme is accommodated inside His-tagged (tgA1M) and tagless A1M (ntA1M) in a rather similar fashion although the His-tag is very likely involved into coordination with iron of the heme molecule. SPR data indicated kinetic rate constants and equilibrium binding constants with KD values in a μM range.Conclusions: This study provided experimental evidence of the A1M heme binding properties by aid of different techniques and suggested an analytical methodology for a rapid evaluation of ligand-binding properties of recombinant A1M versions, also suitable for other His-tagged proteins.
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