HEPARIN IN HUMAN PLACENTAL DEVELOPMENT AND THE PREVENTION OF PLACENTAL COMPLICATIONS OF PREGNANCY

Overview of low molecular weight heparin for preventative treatment of adverse obstetric outcomes related to abnormal placentation

Different proportions of cases of preterm and severe preeclampsia, placental abruption, fetal growth restriction, and fetal death share a common causal pathway of abnormal placental implantation. Documentation of an association between the risk of such adverse pregnancy outcomes (APOs) and inherited thrombophilias prompted initial studies to evaluate the benefit of anticoagulants for the prevention of recurrences both in patients with and without inherited thrombophilias. Prenatal administration of low molecular weight heparin (LMWH) has been evaluated in case control, cohort and randomized clinical trials. The evidence suggests a benefit of LMWH in the reduction of recurrences of APOs, with a number needed to treat of 6 (95% confidence interval: 4-10) to prevent one case of recurrent APOs. Such benefit is independent of the presence of inherited thrombophilias or the administration of low dose aspirin. Further studies are needed to establish the optimal duration for the prophylaxis, to better delineate the mechanism of action of LMWH and to explore the role, if any, of maternal serum markers and uterine artery Doppler findings in the modulation of the LMWH prophylaxis.

Low-molecular-weight heparin added to aspirin in the prevention of recurrent early-onset pre-eclampsia in women with inheritable thrombophilia: the FRUIT-RCT

BACKGROUND

Early-onset hypertensive disorders (HD) of pregnancy and small-for-gestational age infants (SGA) are associated with placental vascular thrombosis, these often recur and are also associated with inheritable thrombophilia. Aspirin reduces the recurrence risk.

OBJECTIVES

Adding low-molecular-weight heparin (LMWH) to aspirin at < 12 weeks gestation reduces the recurrence of HD in women with previous early-onset HD (pre-eclampsia, hemolysis, elevated liver enzymes and low platelets [HELLP] syndrome and eclampsia) and/or SGA, in the context of inheritable thrombophilia without antiphospholipid antibodies.

PATIENTS/METHODS

In a multicenter randomized control trial (RCT), 139 women included were< 12 weeks gestation.

INCLUSION CRITERIA

previous delivery< 34 weeks gestation with HD and/or SGA; inheritable thrombophilia (protein C deficiency, protein S deficiency, activated protein C resistance, factor V Leiden heterozygosity and prothrombin gene G20210A mutation heterozygosity); and no antiphospholipid antibodies detected.

INTERVENTION

either daily LMWH (dalteparin, 5000 IU weight-adjusted dosage) with aspirin 80 mg or aspirin 80 mg alone.

MAIN OUTCOME MEASURES

PRIMARY OUTCOMES

recurrent HD onset (i) < 34 weeks gestation and (ii) irrespective of gestational age.

SECONDARY OUTCOMES

recurrent SGA, preterm birth, maternal/neonatal hospitalization, spontaneous abortion and individual HD. Analysis by intention-to-treat.

RESULTS

Low-molecular-weight heparin with aspirin reduced recurrent HD onset < 34 weeks gestation (risk difference [RD] 8.7%: confidence interval [CI] of RD 1.9–15.5%; P = 0.012; number needed to treat [NNT] 12). Recurrent HD irrespective of gestational age was not different between the arms. No women withdrew as a result of adverse effects.

TRIAL REGISTRATION

http://www.isrctn.org) (isrctn87325378).

CONCLUSIONS

Adding LMWH to aspirin at < 12 weeks gestation reduces recurrent HD onset < 34 weeks gestation in women with inheritable thrombophilia and prior delivery for HD/SGA <34 weeks. However, close monitoring of the mother and fetus remains important throughout pregnancy.

Heparin promotes soluble VEGF receptor expression in human placental villi to impair endothelial VEGF signaling

BACKGROUND

Severe preeclampsia is characterized by hypertension, renal injury and placental dysfunction. Prothrombotic disorders are discovered in 10-20% of women with preeclampsia, providing the rationale for prescribing low-molecular-weight heparin (LMWH) in future pregnancies. Heparin has diverse molecular actions and appears to reduce the recurrence risk of preeclampsia in women without prothrombotic disorders. The placenta-derived anti-angiogenic splice-variant protein soluble vascular endothelial growth factor (VEGF) receptor-1 (sFLT1) is strongly implicated in the pathogenesis of the underlying endothelial dysfunction. As the placental syncytiotrophoblast is the principal source of sFLT1, we tested the hypothesis that heparin suppresses placental sFLT1 secretion.

METHODS AND RESULTS

First trimester placental villi exposed to LMWH (0.25-25 IU mL(-1)) in an in vitro explant model significantly increased the expression and release of sFLT1 by the syncytiotrophoblast into culture media, reducing phosphorylation of FLT1 and KDR receptors in cultured human umbilical vein endothelial cells. This response was significantly diminished in placental villi from healthy term pregnancies. Placental villi from severely preeclamptic pregnancies had a higher baseline sFLT1 release, compared with first trimester placental villi and did not respond to LMWH treatment. LMWH promoted villous cytotrophoblast proliferation (BrdU incorporation) and impaired syncytial fusion-differentiation, causing syncytiotrophoblast apoptosis (by caspase 3&7 activity and TUNEL staining) and necrosis (ADP/ATP ratio).

CONCLUSION

 LMWH promotes sFLT1 synthesis and release from first trimester placental villi in a manner similar to that of severely preeclamptic placental villi, which antagonizes VEGF signaling in endothelial cells. These effects in part are mediated by an interaction between heparin and the cytotrophoblasts that regenerates the overlying syncytiotrophoblast responsible for sFLT1 secretion into the maternal blood.

Unfractionated heparin for second trimester placental insufficiency: a pilot randomized trial

OBJECTIVE

To conduct a pilot randomized controlled trial of unfractionated heparin (UFH) in women considered at high risk of placental insufficiency in the second trimester.

METHODS

Women with either false-positive first trimester (pregnancy-associated placental protein-A [PAPP-A] < 0.35 MoM) or second trimester (alpha-fetoprotein [AFP] > 2.0 MoM, inhibin > 3.0 MoM, human chorionic gonadotropin > 4.0 MoM) serum screening tests or medical/obstetric risk factors were screened for placental insufficiency by sonographic evaluation of the placenta and uterine artery Doppler between 18 and 22 weeks. Thrombophilia screen-negative women with two or three abnormal test categories were randomized by 23+6 weeks to self-administration of subcutaneous unfractionated heparin (UFH) 7500 IU twice daily until birth or 34 weeks, or to standard care. Maternal anxiety and other maternal-infant outcomes were determined.

RESULTS

Thirty-two out of 41 eligible women consented, with 16 women randomized to UFH and 16 to standard care. There was no statistically significant difference identified between the two treatment groups (standard care vs. UFH) for the following: maternal anxiety score (mean [standard deviation]), 14.2 [± 1.6] vs. 14.0 [± 1.8]; birth weight (median [range]), 1795 [470-3295]g vs. 1860 [730-3050]g; perinatal death, 3 vs. 0; severe preeclampsia, 2 vs. 6; placental weight < 10th percentile, 7 vs. 4; or placental infarction, 4 vs. 3.

CONCLUSION

Our study design identified women at high risk of adverse maternal-infant outcomes attributable to placental insufficiency. Women with evidence of placental insufficiency were willing to undergo randomization and self-administration of UFH without increased maternal anxiety.

Glial cell missing-1 mediates over-expression of tissue inhibitor of metalloproteinase-4 in severe pre-eclamptic placental villi

BACKGROUND

Severe pre-eclampsia (sPE) causes significant maternal morbidity and intrauterine growth restriction as a result of severe placental dysfunction. Defects in the formation of both extra-villous and villous trophoblast are characteristic of this disease. The outer syncytiotrophoblast layer covering the placental villi develops syncytial knots and focal necrosis while reduced invasion of the extra-villous trophoblast results in a reduced maternal blood supply and ischemia of the placental villi. The transcription factor glial cell missing-1 (GCM1) regulates formation of both types of trophoblast. GCM1 expression is reduced in placental villi of women with sPE but the functional downstream consequences of reduced GCM1 expression are unknown.

METHODS AND RESULTS

In floating first trimester villous explants we demonstrated increased mRNA (2.5-fold, n = 12) and protein level (9.8-fold) of tissue inhibitor of metalloproteinase-4 (TIMP4) following repression of GCM1 (70 ± 7%) by small interfering-RNA, using RT-PCR and western blot, respectively. Similar increases in TIMP4 mRNA (4.2-fold, n = 7, P< 0.001 versus control) and protein levels were found following gene silencing of GCM1 in BeWo cells (<90% knock down of protein). TIMP4 protein was increased in placenta from women with sPE (3.5 ± 0.4 pg/µg, n = 8), compared with preterm (1.7 ± 0.17 pg/µg, n = 9) and term controls (1.6 ± 0.16 pg/µg, n = 9; P< 0.01; quantified by enzyme-linked immunosorbent assay and visualized using immunohistochemistry) with reduced GCM1 expression, mostly in the pathologic syncytial knots.

CONCLUSIONS

TIMP4 is a downstream target of GCM1 that may link the consequences of reduced GCM-1-directed trophoblast differentiation to histologic and functional components of disordered placentation in sPE.