Maternal EDN1 G5665T polymorphism influences circulating endothelin-1 levels and plays a role in determination of preeclampsia phenotype.

OBJECTIVE: Preeclampsia, a pregnancy-specific syndrome characterized by hypertension and proteinuria, has a familial tendency and is an important cause of maternal and neonatal mortality. Abnormal endothelin-1 synthesis and/or release can explain abnormalities seen in preeclampsia. We prospectively evaluated whether endothelin-1 levels are increased in preeclampsia, to verify if placenta is the source, and any association between the maternal EDN1 G5665T single-nucleotide polymorphism and circulating endothelin-1 levels and preeclampsia manifestation.
METHODS: A total of 120 with preeclampsia and 118 normotensive primigravid patients with singleton pregnancy were enrolled. Preeclampsia was defined as new onset of elevated blood pressure greater than 140/90 mmHg and at least 2+ proteinuria on two occasions at least 4 h apart after 20 weeks of gestation in previously normotensive pregnant women. Patients were excluded if they had hypertension before 20 weeks of gestation, diabetes, asthma, heart disease, kidney disease, hematological disorder, autoimmune disease, urinary tract infection, current or past history of smoking, twin pregnancy, molar pregnancy or eclampsia. Genotyping was done using a PCR-RFLP-based method. Placenta samples were collected from 20 preeclampsia and 24 normotensive pregnancies. Reverse transcriptase PCR was done for preproendothelin and beta-actin mRNA. Placental endothelin-1 staining was assessed by immunohistochemistry in villous and extravillous trophoblasts and endothelium. Plasma endothelin-1 levels were measured using ELISA.
RESULTS: The preeclampsia group showed higher circulating endothelin-1 levels (1.45 +/- 0.55 vs. 0.91 +/- 0.42 pg/ml; P < 0.0001), reduced frequency of GG genotype (34 vs. 49%; P = 0.025) and increased T allele frequency (0.43 vs. 0.28; P = 0.04). A significant association was noted between endothelin-1 levels and blood pressure in the entire cohort and in the group with preeclampsia (P < 0.001). Circulating endothelin-1 levels were higher in those bearing even one copy of the T variant (1.08 +/- 0.48 vs. 1.31 +/- 0.59 pg/ml; P = 0.004). Placental endothelin-1/beta-actin mRNA ratio was significantly reduced (0.91 +/- 0.77 vs. 3.20 +/- 1.68; P < 0.001) and endothelin-1 staining was lower (P < 0.001) in placental endothelium in preeclampsia.
CONCLUSION: Maternal endothelin-1 is elevated and correlates with the severity of blood pressure elevation in preeclampsia. The endothelin-1 is likely released from the maternal endothelium. Presence of T allele at 5665 position in maternal EDN1 gene is associated with higher endothelin-1 levels. Placental endothelin-1 synthesis is reduced in preeclampsia. The combination of elevated maternal and reduced placental endothelin-1 may be an adaptive response to reduced uteroplacental flow in preeclampsia.