Urine Test for Misfolded Proteins May Diagnose Preeclampsia

Larry Hand

July 18, 2014

The urine and placentas of women who develop preeclampsia (PE) contain aggregates of misfolded proteins, researchers report in an article published online July 16 in Science Translational Medicine. The new findings suggest that PE, a common complication of pregnancy, shares pathophysiological features with other diseases, such as Alzheimer's, that are characterized by protein misfolding.

Although PE occurs in 5% to 10% of all pregnancies worldwide, its etiology is largely unknown. Most cases are characterized by new-onset hypertension and proteinuria after 20 weeks of gestation, but early signs can be "inconspicuous," and reliable diagnostics are needed.

In the current study, Irina A. Buhimschi, MD, from the Center for Perinatal Research, Research Institute at Nationwide Children's Hospital, Ohio State University College of Medicine, Columbus, and the Department of Obstetrics, Gynecology and Reproductive Sciences, Yale University School of Medicine, New Haven, Connecticut, and colleagues analyzed urine samples of 80 pregnant women with known outcomes using mass spectrometry proteomic profiling and Congo red (CR) spotting. (CR is known to bind to misfolded proteins, including amyloid-beta aggregates in Alzheimer's disease.)

Half the women had severe PE requiring medically indicated delivery; the other 40 were healthy control patients who had normal gestation and delivery. The researchers found that a cutoff value of a 15% measure of redness after the test had 100% sensitivity (95% confidence interval [CI], 92% - 100%) and 100% specificity (95% CI, 92% to 100%) to distinguish severe PE cases from controls.

To validate those findings, the researchers repeated their analysis on urine samples from an additional group of 563 unselected pregnant women who had known pregnancy outcomes. In this group, the same measure of redness had a sensitivity of 85.9% (95% CI, 81.1% - 89.9%), a specificity of 85.0% (95% CI, 80.4% - 88.8%), a positive likelihood ratio of 5.7 (95% CI, 4.4 - 7.5), and a negative likelihood ratio of 0.17 (95% CI, 0.1 - 0.2).

The evidence "strengthens the argument that in PE, urine CR dye binds to proteins that are unfolded, are misfolded, and/or have amyloid-like characteristics," the researchers write.

Among the validation cohort, the researchers tested samples from 56 women at several points in their pregnancy. Of those women, 9 developed severe PE that required medically indicated delivery. Seven (78%) of those women had CR levels above 15% at study entry, which was at least 10 weeks before clinical diagnosis.

When the investigators studied placental tissue from women who developed PE, they found that protein aggregates were more abundant than in tissue from women who did not develop PE. Moreover, enzymes involved in protein processing abnormalities in Alzheimer's and other protein-misfolding diseases were also present in the placental tissue.

Immediate Clinical Relevance

Their CR dot (CRD) test has immediate clinical relevance because it can perform better at predicting the need for induced delivery than current dipstick methods of assessing proteinuria, the researchers write. They do not suggest that the CRD test replace the gold standard 24-hour urine protein collection.

"However, both currently used laboratory methods for estimation of proteinuria are unable to provide important qualitative information on misfolded proteins, which, on the basis of our findings, may be a process more closely related to the pathophysiology of PE compared to total proteinuria," they write.

A limitation of the findings may be that the predictive values from the validation cohort are specific to women at an academic referral hospital and may not be generalizable to all healthcare settings.

Ongoing Trials

"We have developed a very simple diagnostic that we hope will make a difference in what is now done to diagnose [PE] and to predict which woman will need to be delivered and which woman will not," Dr. Buhimschi told Medscape Medical News. "We have ongoing clinical trials for that."

Research into other diseases such as Alzheimer's that are characterized by protein misfolding has yielded knowledge, she said. "Applying some of that knowledge from other diseases to [PE] may actually move forward what has been stagnant for many years. We think our findings will unify things that have been observed with [PE] but...have not been explained under the same umbrella."

Earlier Diagnosis

Because the test can identify these proteins in early gestation before symptoms develop, it may eventually help to prevent PE development, she said. "In some women, we may think about intervening early with strategies that perhaps be borrowed from other fields. Just making the connection between [PE] and protein misfolding is very important because we can look at the problem from a different perspective."

James M. Roberts, MD, professor of obstetrics, gynecology, and epidemiology at Magee-Women's Institute & Foundation in Pittsburgh, Pennsylvania, and a member of the Preeclampsia Foundation's medical advisory board, told Medscape Medical News, "From a diagnostic perspective, they've identified a new set of markers that are found in women with [PE], and what we know right now is that they seem to match pretty well with whether women have more serious disease."

Dr. Roberts said the test has the potential to have a greater effect in developing countries, where, as the researchers point out, traditional dipstick tests are not always available.

"They've identified these proteins that are present in a number of different diseases and, at the moment, we're not 100% sure why they happen," he added. "Another thing we don't know yet is whether they actually contribute [to the disease or are just present]. I think we have a whole new area to think about while we're thinking about the disease."

This research was supported by Round 5 Grand Challenges Explorations, Albert McKern Scholar Award for Perinatal Research through Yale University, and the National Institutes of Health. Dr. Buhimschi and a coauthor are inventors or coinventors on patent applications on the use of protein misfolding features in PE for diagnostic and treatment purposes. The other authors and Dr. Roberts have disclosed no relevant financial relationships.

Sci Translat Med. Published online July 16, 2014. Abstract

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