New predictive and diagnostic biomarkers for preeclampsia

University dissertation from Department of Obstetrics and Gynecology, Lund University

Abstract: Abstract
Preeclampsia is a serious pregnancy complication that affects 3-8% of all pregnancies leading to maternal- and fetal morbidity and mortality. The etiology is still not known in detail. Previous findings have shown an up regulation of the genes coding for fetal hemoglobin (HbF) in preeclamptic placentas. The cell-free HbF protein was shown to be accumulating in the vascular lumen, to induce oxidative stress, which damages the blood-placenta-barrier, causing a leak into the maternal blood circulation. Unbound cell-free HbF is highly reactive and toxic and therefore normally being scavenged by haptoglobin, hemopexin (Hpx) and α1-microglobulin (A1M). In the maternal circulation cell-free HbF causes general endothelial- and organ damage.

This thesis describes the role of placentally derived HbF in the etiology of preeclampsia and how it can be used as a biomarker for PE. The five articles also describe the role of hemoglobin- and heme scavenging proteins in prediction and diagnosis of preeclampsia and HbF as a causal factor for renal injury in preeclampsia.

The results in paper I and II show that the maternal HbF plasma concentration is increased as early as the first trimester in women who subsequently develop preeclampsia. Furthermore increased circulating concentrations of A1M and decreased levels of hemopexin were found. The results indicate that HbF, A1M and Hpx can be used as predictive biomarkers as early as the first trimester with 60% prediction rate at 5% false positive rate.

The results in paper III and IV indicate that the constant increased level of HbF strain the scavenging proteins and gradually deplete them. The HbF plasma levels were four fold increased in patients diagnosed with PE compared to controls. Furthermore, the A1M levels were increased and the levels of Hpx, Hpx enzymatic activity and Haptoglobin were significantly lower in patients with preeclampsia.
In both paper III and IV HbF, heme and scavenging proteins were evaluated as biomarkers that support the diagnosis of PE. The results showed that the combination of these biomarkers could detect up to 84% of the PE patients at a false positive rate of 10% in term pregnancy. It was further concluded that HbF and hemoglobin- and heme scavengers potentially can be used to support the diagnosis of PE. In addition, both HO-1 and Hpx activity correlated with the maternal blood pressure and hence the severity of PE.
It is known that excessive amounts of cell-free Hb lead to endotheliosis and kidney injuries. In paper IV it was shown that there was increased urinary concentrations of podocyte specific extracellular vesicles (EVs) in women diagnosed with PE. The excessive circulating concentrations of HbF in women with PE was correlated to the concentration of urinary podocyte specific EVs and proteinuria. It was concluded that increased circulating concentrations of HbF in combination with low scavenging capacity might cause significant damage to the renal podocytes.

In conclusion the thesis present free HbF and its’ scavenging proteins as new important players in the PE etiology. Furthermore, it was shown that HbF and the heme scavenging proteins could be used as predictive- and diagnostic biomarkers for PE as early as the first trimester of pregnancy.