Pregnancy Hypertension: An International Journal of Women’s Cardiovascular Health 1 (2011) 17–21

Contents lists available at ScienceDirect

Pregnancy Hypertension: An InternationalJournal of Women’s Cardiovascular Health

journal homepage: www.elsevier .com/locate /preghy

Review

Preeclampsia and the anti-angiogenic state

Isha Agarwal a, S. Ananth Karumanchi a,b,⇑a Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United Statesb Howard Hughes Medical Institute, Boston, MA, United States

a r t i c l e i n f o a b s t r a c t

Article history:Available online 5 November 2010

Keywords:AngiogenesisHypertensionGlomerular endotheliosisVEGFEndoglin

2210-7789/$ - see front matter � International Socdoi:10.1016/j.preghy.2010.10.007

⇑ Corresponding author. Address: Center for VaIsrael Deaconess Medical Center, 330 Brookline AvMA 02215, United States. Tel.: +1 617 667 1018; fa

E-mail address: sananth@bidmc.harvard.edu (S.A

Preeclampsia is a major cause of maternal and fetal morbidity and mortality worldwide,however, its etiology remains unclear. Abnormal placental angiogenesis during pregnancyresulting from high levels of anti-angiogenic factors, soluble Flt1 (sFlt1) and soluble endog-lin (sEng) has been implicated in preeclampsia pathogenesis. Accumulating evidence alsopoints to a role for these anti-angiogenic proteins as serum biomarkers for the clinical diag-nosis and prediction of preeclampsia. Uncovering the mechanisms of altered angiogenicfactors in preeclampsia may also provide insights into novel preventive and therapeuticoptions.� International Society for the Study of Hypertension in Pregnancy. Published by Elsevier

B.V. All rights reserved.

1. Introduction tors in preeclampsia are still being proposed. This review

Preeclampsia, a pregnancy-related disorder character-ized by hypertension and proteinuria after 20 weeks of ges-tation, affects 5% of pregnancies and is a major cause ofmaternal and fetal mortality [1]. Delivery of the placentahas been shown to resolve the acute clinical symptoms ofpreeclampsia, suggesting that the placenta plays a centralrole in preeclampsia pathogenesis [2]. During normal preg-nancy, the placenta undergoes dramatic vascularization toenable circulation between the fetus and the mother. Pla-cental vascularization involves vasculogenesis, angiogene-sis, and pseudovasculogenesis or maternal spiral arteryremodeling. These processes require a delicate balance ofpro-angiogenic and anti-angiogenic factors. In preeclamp-tic pregnancies, several anti-angiogenic factors, such as sol-uble Flt1 (sFlt1) and soluble endoglin (sEng), are producedby the placenta in higher than normal quantities [3]. Theimbalance of pro-angiogenic and anti-angiogenic factorsin preeclampsia is thought to trigger abnormal placentalvascularization and disease onset. Underlying geneticexplanations for the overproduction of anti-angiogenic fac-

iety for the Study of Hypert

scular Biology, Bethe., RN 370D, Boston,x: +1 617 667 2913.. Karumanchi).

will focus on normal vascular development in the placenta,the angiogenic imbalance that occurs during preeclampsia,and the role of genetics in preeclamptic pregnancies.

2. Placental vascular development

The development of the placental vascular networkinvolves vasculogenesis, angiogenesis, and pseudovasculo-genesis or maternal spiral artery remodeling. Vasculogene-sis, the differentiation of endothelial precursors intoendothelial cells lining the vascular system, begins in thefirst few weeks of a normal pregnancy. During vasculogen-esis, a subpopulation of mesenchymal precursor cellstransforms into hemiangioblastic endothelial precursors[4]. Differentiation of these cells results in the generationof new blood vessels in the placenta [4].

Vasculogenesis is followed by angiogenesis, the forma-tion of new capillaries from preexisting ones [5]. Startingat day 21 of pregnancy, soluble angiogenic factors, ex-pressed in the trophoblasts of the placenta, maternal de-cidua, and macrophages mediate capillary formation inthe chorionic villi of the placenta [5]. The capillary bedsof the villi expand continuously until week 26 of gestation.From week 26 until term, villous vascular growth isprimarily limited to non-branching angiogenesis due to

ension in Pregnancy. Published by Elsevier B.V. All rights reserved.

18 I. Agarwal, S.A. Karumanchi / Pregnancy Hypertension: An International Journal of Women’s Cardiovascular Health 1 (2011) 17–21

the formation of mature intermediate villi that containpoorly branched capillary loops [4]. Among the angiogenicfactors expressed by the placenta during this phase, VEGFand PlGF play a central role. The vascular endothelialgrowth factor family includes VEGF-A, VEGF-B, VEGF-C,and VEGF-D [6]. VEGF-A, an endothelial specific mitogen,is expressed in three different isoforms (121, 165, and189) [7]. VEGF-A induces placental vascular developmentthrough its interactions with high affinity receptor tyrosinekinases Flt1 and KDR on placental endothelial cells [8].VEGF has been shown to be involved in the regulation ofendothelial cell stability, ependymal cell function, andperiventricular permeability [9]. Inactivation of VEGF re-sults in embryonic lethality and significant defects in pla-cental vasculature [10]. In addition to VEGF, placentalgrowth factor is another key pro-angiogenic factor pro-duced by the placenta. PlGF is also expressed as several dif-ferent isoforms (PlGF-1, PlGF-2, PlGF-3, and PlGF-4) [11].Expression of PlGF is primarily in the syncitiotrophoblastlayer of the placenta, which is in direct contact with mater-nal circulation [12]. Placental growth factor binds to Flt1but not to KDR [13]. Though PlGF expression inducesangiogenic activity, PlGF knockout mice do not exhibit pla-cental or embryonic angiogenic defects [14].

As gestation progresses, placental cytotrophoblasts par-ticipate in pseudovasculogenesis or maternal spiral arteryremodeling. During pseudovasculogenesis, cytotropho-blasts leave the trophoblast basement membrane andmigrate to and invade the uterine spiral arteries and decid-ual arterioles. At this stage, cytotrophoblasts undergo anepithelial-to-endothelial phenotypic transformation [15].Invasive cytotrophoblasts downregulate the expression ofepithelial cell adhesion molecules, such as E-cadherinand a6b4, and begin expressing endothelial cell-specificadhesion molecules such as vascular endothelial-cadherinand aVb3 [16]. Replacement of the endothelial layer ofuterine spiral arteries decreases resistance in these bloodvessels and thereby increases blood flow to the placenta.This process is critical to provide nutrients and oxygen tothe developing placenta and fetus [17]. Maternal spiral ar-tery remodeling is also thought to be regulated by angio-genic factors Tie-1 and Tie-2 [18]. More work is neededto uncover the mechanisms underlying the progressionfrom vasculogenesis to angiogenesis to pseudovasculogen-esis in normal placentation and the reasons for maternaltolerance of cytotrophoblast invasion.

3. Abnormal angiogenesis in preeclampsia

In preeclamptic patients, high circulating levels of anti-angiogenic factors produced by the placenta contribute tomaternal endothelial dysfunction and the clinical syn-drome of preeclampsia. Placental expression and circulat-ing levels of soluble Flt1 (sFlt1) and soluble endoglin(sEng) are markedly increased in preeclamptic patients[18,3,19,20]. Elevation of these factors precedes the onsetof clinical symptoms of preeclampsia and is correlatedwith disease severity [18,19,21,22]. Both sFlt1 and sEngare truncated variants of cell surface receptors for angio-genic factors.

Soluble Flt1 is a truncated splice variant of VEGFreceptor Flt1 lacking the transmembrane and cytoplas-mic domains [23]. Soluble Flt1 is made in higher thannormal quantities by the placenta beginning approxi-mately 5 weeks prior to onset of preeclampsia [19]. Itis believed to compromise angiogenesis by binding tocirculating VEGF and PlGF and inhibiting their mitogenicand homoestatic actions on endothelial cells [23,24].Pregnant rats administered exogenous sFlt1 via adenovi-ral vector develop characteristic symptoms of preeclamp-sia including hypertension, proteinuria, and glomerularendotheliosis [3]. In non-pregnant mice, antibodiesagainst VEGF have been shown to induce glomerularendothelial damage and proteinuria [25]. Furthermore,in vitro studies have shown that exogenous antibodiesagainst sFlt1 can reverse the anti-angiogenic state in hu-man preeclamptic plasma [24]. Soluble Flt1 levels arealso thought to contribute to the increased risk of pre-eclampsia in molar pregnancies [26,27] and twin preg-nancies [28]. The use of vascular endothelial growthfactor inhibitors in cancer patients for the treatment ofcancer-related angiogenesis has been associated withhypertension, proteinuria, glomerular endothelial dam-age, elevated circulating liver enzymes, cerebral edema,and reversible posterior leukoencephalopathy – featuresresembling those found in human preeclampsia andeclampsia [29–31]. These studies point to the central roleof sFlt1 and impaired VEGF signaling in the developmentof preeclampsia.

Recently, several variants of sFlt1 have been discovered,including sFlt1–14, which is expressed only in primates[32]. Soluble Flt1–14 expression is increased dramaticallyin patients with preeclampsia [32,33]. It is produced pri-marily by abnormal clusters of degenerative syncitiotroph-oblasts, known as syncitial knots [32]. Soluble Flt1–14 isthe predominant VEGF inhibiting protein produced bythe placenta and is capable of neutralizing VEGF activityin distant organs implicated in preeclampsia, such as thekidney [32]. It has been proposed that sFlt1–14 may haveevolved in humans to protect organs from adverse VEGFsignaling. Several pathways have been proposed to regu-late sFlt1 production, including placental hypoxia, geneticabnormalities, oxidative stress, inflammation, and defi-cient catechol-O-methyl transferase, however no consen-sus has been reached [14].

Although sFlt1 plays an important role in preeclamp-sia pathogenesis, it is unlikely that sFlt1 levels alonegovern disease onset. Soluble endoglin (sEng), a trun-cated form of endoglin (CD105), is upregulated in pre-eclampsia and acts in concert with sFlt1 to causeendothelial dysfunction [34]. Similar to sFlt1, circulatingsEng levels are elevated weeks before preeclampsia on-set [18]. Endoglin is a cell surface receptor that bindsto and antagonizes TGF-b [9]. Animals treated with bothsFlt1 and sEng display severe signs of preeclampsiaincluding HELLP syndrome, hemolysis and thrombocyto-penia [34]. The effects of sEng can be mediated byinterference with nitric-oxide mediated vasodilation,suggesting that NO production is downstream of sEng[35,36] (see Fig. 1).

Fig. 1. sFlt1 and sEng cause endothelial dysfunction by antagonizing VEGF and TGF-b1 signaling. There is mounting evidence that VEGF and TGF-b1 arerequired to maintain endothelial health in several tissues including the kidney and perhaps the placenta. During normal pregnancy, vascular homeostasis ismaintained by physiological levels of VEGF and TGF-b1 signaling in the vasculature. In preeclampsia, excess placental secretion of sFlt1 and sEng (twoendogenous circulating anti-angiogenic proteins) inhibits VEGF and TGF-b1 signaling, respectively, in the vasculature. This results in endothelial celldysfunction, including decreased prostacyclin, nitric oxide production and release of procoagulant proteins. Figure reproduced with permission from Ref.[58].

I. Agarwal, S.A. Karumanchi / Pregnancy Hypertension: An International Journal of Women’s Cardiovascular Health 1 (2011) 17–21 19

4. Role of genetics in preeclampsia

Although the risk factors for preeclampsia are both ge-netic and environmental, the presence of preeclampsia infirst degree relatives increases a woman’s risk of pre-eclampsia by 2- to 4-fold [37,38]. Genetic factors may playan important role in the angiogenic imbalance found in pa-tients with preeclampsia. Recently, several polymorphismsin sFlt1 and VEGF have been associated with severity of pre-eclampsia [39,40]. Patients with the VEGF 936 C/T genotypehave been shown to have significantly lower VEGF plasmalevels than subjects carrying the VEGF 936 C/C genotype[41]. Another group has found that women carrying theG-allele of the VEGF 405 G/C polymorphism have a de-creased risk for developing severe preeclampsia [42] andwomen carrying the A allele of the VEGF 2578 C/A polymor-phism face an accelerated disease progression [43].Although circulating PlGF, sFlt1, and sEng levels have beenshown to be important markers of preeclampsia, no causalmutations in these genes associated with preeclampsiahave been identified so far [44]. However, women with tri-somy 13 fetuses have a higher incidence of preeclampsia[45], suggesting that gene dosage or copy number variationmay contribute to the development of preeclampsia. Nota-bly, the Flt1 gene is located on chromosome 13.

There is some evidence to suggest that in addition tomaternal genotype, paternal (or fetal) genotype may alsocontribute to risk of preeclampsia. The risk of fathering apreeclamptic pregnancy is increased among males whofathered a preeclamptic pregnancy with a different partner[46]. Also, men who are born from a pregnancy compli-cated by preeclampsia are at a higher risk of fathering apreeclamptic pregnancy [47]. To explain the contributionof paternal (fetal) genes in preeclampsia, several groupshave proposed the genetic conflict hypothesis. Accordingto the genetic conflict hypothesis, fetal genes contributedby the father are selected to increase uteroplacental bloodflow and deliver nutrients to the fetus while maternalgenes are selected to limit blood flow to the fetus [48].An abnormality in the interaction between the fetus and

the mother during pregnancy may contribute to the devel-opment of preeclampsia. One theory is that maternalimmune cells in the decidua interact with specific tropho-blast cells from the fetal placenta to mediate, and in somecases limit, fetal trophoblast invasion of the decidua [49].This interaction takes place between the killer immuno-globulin receptor on the maternal immune cell and theHLA receptor on the fetal trophoblast. Mothers carryingan inhibitory KIR (AA genotype) have been reported to beat an increased risk for preeclampsia when the fetus hada HLA-C2 allotype, a combination that is associated withimpaired trophoblast invasion [50]. Other groups havesuggested that paternal imprinting at the STOX1 gene lo-cus may contribute to preeclampsia [51].

The Genetics of Preeclampsia Collaborative (GOPEC)study currently ongoing in Great Britain may shed lighton genetic factors predisposing women to preeclampsiaonce its results are made public [2]. This study and othersare using unbiased approaches such as genome wideassociation studies, whole genome exon capture andsequencing approaches to identify causal genetic changesin preeclampsia.

5. Clinical significance

As the role of angiogenic imbalance in preeclampsia be-comes more clear, new avenues for diagnosis, predication,and therapy may become available. Automated immunoas-says for sFlt1 and PlGF have been recently developed forin vitro diagnostic testing of preeclampsia [52,53]. ThePlGF/sEng ratio has been shown to have an excellent pre-dictive performance for the prediction of early-onset pre-eclampsia, with very high likelihood ratios for a positivetest result and very low likelihood ratios for a negative testresult [54]. In preeclamptic patients, changes in the mater-nal plasma sEng and PlGF levels may also be predictive for asmall for gestational age (SGA) neonate [55]. Therapeuticstrategies addressing the angiogenic imbalance in pre-eclampsia have also been suggested. In a rat model, treat-

20 I. Agarwal, S.A. Karumanchi / Pregnancy Hypertension: An International Journal of Women’s Cardiovascular Health 1 (2011) 17–21

ment with VEGF-121 has been shown to improve glomeru-lar filtration rate and endothelial function and reduce highblood pressure associated with placental ischemia [56] andsFlt1 overexpression [57]. In the future, therapeutic strate-gies addressing the angiogenic imbalance found in pre-eclampsia may significantly reduce maternal and neonatalmortality associated with this disease.

6. Conclusion

Substantial evidence now supports the role of sFlt1 andother soluble anti-angiogenic proteins in preeclampsia.Several important questions remain to be explored,however. Do polymorphisms, copy number variations, orepigenetic changes affect the balance of angiogenic andanti-angiogenic factors produced by the placenta inpreeclampsia? Are paternal (or fetal) genes relevant tomaternal preeclampsia – if so, which genes are involved?More work is also needed to further define the regulationof placenta vascular development and expression of theseangiogenic factors in normal and diseased pregnancies. Aswe continue studying preeclampsia and the pathwaysinvolved in this disease, hopefully it will become possibleto create diagnostic tools that can detect preeclampsia be-fore the onset of clinical symptoms and develop therapiesthat change the course of the disease. Such interventionscould significantly affect maternal and neonatal morbidityand mortality, worldwide.

Disclosure

S.A.K. reports having served as a consultant to Abbott,Beckman Coulter, Roche, and Johnson & Johnson and hav-ing been named co-inventor on multiple provisional pat-ents filed by Beth Israel Deaconess Medical Center for theuse of angiogenesis-related proteins for the diagnosis andtreatment of preeclampsia. These patents have been non-exclusively licensed to several companies.

Acknowledgements

S.A.K. is an investigator of the Howard Hughes MedicalInstitute. S.A.K. is supported by a Clinical Scientist Awardfrom the Burroughs Wellcome Fund and an EstablishedInvestigator grant from the American Heart Association.

References

[1] Villar J, Abalos E, Nardin JM, Merialdi M, Carroli G. Strategies toprevent and treat preeclampsia: evidence from randomizedcontrolled trials. Semin Nephrol 2004;24(6):607–15.

[2] Wang A, Rana S, Karumanchi SA. Preeclampsia: the role ofangiogenic factors in its pathogenesis. Physiology (Bethesda)2009;24:147–58.

[3] Maynard SE, Min JY, Merchan J, Lim KH, Li J, Mondal S, et al. Excessplacental soluble fms-like tyrosine kinase 1 (sFlt1) may contribute toendothelial dysfunction, hypertension, and proteinuria inpreeclampsia. J Clin Invest 2003;111(5):649–58.

[4] Bdolah Y, Sukhatme VP, Karumanchi SA. Angiogenic imbalance in thepathophysiology of preeclampsia: newer insights. Semin Nephrol2004;24(6):548–56.

[5] Zygmunt M, Herr F, Munstedt K, Lang U, Liang OD. Angiogenesis andvasculogenesis in pregnancy. Eur J Obstet Gynecol Reprod Biol2003;110(Suppl. 1):S10–8.

[6] Ferrara N, Gerber HP. The role of vascular endothelial growth factorin angiogenesis. Acta Haematol 2001;106(4):148–56.

[7] Tsatsaris V, Goffin F, Munaut C, Brichant JF, Pignon MR, Noel A, et al.Overexpression of the soluble vascular endothelial growth factorreceptor in preeclamptic patients: pathophysiological consequences.J Clin Endocrinol Metab 2003;88(11):5555–63.

[8] Shibuya M. Structure and function of VEGF/VEGF-receptor systeminvolved in angiogenesis. Cell Struct Funct 2001;26(1):25–35.

[9] Maharaj AS, Walshe TE, Saint-Geniez M, Venkatesha S, MaldonadoAE, Himes NC, et al. VEGF and TGF-beta are required for themaintenance of the choroid plexus and ependyma. J Exp Med2008;205(2):491–501.

[10] Ferrara N, Davis-Smyth T. The biology of vascular endothelial growthfactor. Endocr Rev 1997;18(1):4–25.

[11] Torry DS, Mukherjea D, Arroyo J, Torry RJ. Expression and function ofplacenta growth factor: implications for abnormal placentation. JSoc Gynecol Invest 2003;10(4):178–88.

[12] Kuroda M, Oka T, Oka Y, Yamochi T, Ohtsubo K, Mori S, et al.Colocalization of vascular endothelial growth factor (vascularpermeability factor) and insulin in pancreatic islet cells. J ClinEndocrinol Metab 1995;80(11):3196–200.

[13] Carmeliet P, Moons L, Luttun A, Vincenti V, Compernolle V, De Mol M,et al. Synergism between vascular endothelial growth factor andplacental growth factor contributes to angiogenesis and plasmaextravasation in pathological conditions. Nat Med 2001;7(5): 575–83.

[14] Steinberg G, Khankin EV, Karumanchi SA. Angiogenic factors andpreeclampsia. Thromb Res 2009;123(Suppl. 2):S93–9.

[15] Zhou Y, Fisher SJ, Janatpour M, Genbacev O, Dejana E, Wheelock M,et al. Human cytotrophoblasts adopt a vascular phenotype as theydifferentiate. A strategy for successful endovascular invasion? J ClinInvest 1997;99(9):2139–51.

[16] Zhou Y, Damsky CH, Fisher SJ. Preeclampsia is associated with failureof human cytotrophoblasts to mimic a vascular adhesion phenotype.One cause of defective endovascular invasion in this syndrome? JClin Invest 1997;99(9):2152–64.

[17] Maynard S, Epstein FH, Karumanchi SA. Preeclampsia andangiogenic imbalance. Annu Rev Med 2008;59:61–78.

[18] Levine RJ, Lam C, Qian C, Yu KF, Maynard SE, Sachs BP, et al. Solubleendoglin and other circulating antiangiogenic factors inpreeclampsia. N Engl J Med 2006;355(10):992–1005.

[19] Levine RJ, Maynard SE, Qian C, Lim KH, England LJ, Yu KF, et al.Circulating angiogenic factors and the risk of preeclampsia. N Engl JMed 2004;350(7):672–83.

[20] Venkatesha S, Toporsian M, Lam C, Hanai J, Mammoto T, Kim YM,et al. Soluble endoglin contributes to the pathogenesis ofpreeclampsia. Nat Med 2006;12(6):642–9.

[21] Hertig A, Berkane N, Lefevre G, Toumi K, Marti HP, Capeau J, et al.Maternal serum sFlt1 concentration is an early and reliablepredictive marker of preeclampsia. Clin Chem 2004;50(9):1702–3.

[22] Chaiworapongsa T, Romero R, Kim YM, Kim GJ, Kim MR, Espinoza J,et al. Plasma soluble vascular endothelial growth factor receptor-1concentration is elevated prior to the clinical diagnosis of pre-eclampsia. J Matern Fetal Neonatal Med 2005;17(1):3–18.

[23] Kendall RL, Thomas KA. Inhibition of vascular endothelial cellgrowth factor activity by an endogenously encoded solublereceptor. Proc Natl Acad Sci USA 1993;90(22):10705–9.

[24] Ahmad S, Ahmed A. Elevated placental soluble vascular endothelialgrowth factor receptor-1 inhibits angiogenesis in preeclampsia. CircRes 2004;95(9):884–91.

[25] Sugimoto H, Hamano Y, Charytan D, Cosgrove D, Kieran M, SudhakarA, et al. Neutralization of circulating vascular endothelial growthfactor (VEGF) by anti-VEGF antibodies and soluble VEGF receptor 1(sFlt-1) induces proteinuria. J Biol Chem 2003;278(15):12605–8.

[26] Kanter D, Lindheimer MD, Wang E, Borromeo RG, Bousfield E,Karumanchi SA, et al. Angiogenic dysfunction in molar pregnancy.Am J Obstet Gynecol 2010;202(2):184.e1–5.

[27] Koga K, Osuga Y, Tajima T, Hirota Y, Igarashi T, Fujii T, et al. Elevatedserum soluble fms-like tyrosine kinase 1 (sFlt1) level in women withhydatidiform mole. Fertil Steril 2009.

[28] Bdolah Y, Lam C, Rajakumar A, Shivalingappa V, Mutter W, Sachs BP,et al. Twin pregnancy and the risk of preeclampsia: bigger placentaor relative ischemia? Am J Obstet Gynecol 2008;198(4):428.e1–6.

[29] Eremina V, Jefferson JA, Kowalewska J, Hochster H, Haas M,Weisstuch J, et al. VEGF inhibition and renal thromboticmicroangiopathy. N Engl J Med 2008;358(11):1129–36.

[30] Patel TV, Morgan JA, Demetri GD, George S, Maki RG, Quigley M,et al. A preeclampsia-like syndrome characterized by reversiblehypertension and proteinuria induced by the multitargeted kinaseinhibitors sunitinib and sorafenib. J Natl Cancer Inst 2008;100(4):282–4.

I. Agarwal, S.A. Karumanchi / Pregnancy Hypertension: An International Journal of Women’s Cardiovascular Health 1 (2011) 17–21 21

[31] Kamba T, McDonald DM. Mechanisms of adverse effects of anti-VEGF therapy for cancer. Br J Cancer 2007;96(12):1788–95.

[32] Sela S, Itin A, Natanson-Yaron S, Greenfield C, Goldman-Wohl D,Yagel S, et al. A novel human-specific soluble vascular endothelialgrowth factor receptor 1: cell-type-specific splicing and implicationsto vascular endothelial growth factor homeostasis and preeclampsia.Circ Res 2008;102(12):1566–74.

[33] Thomas CP, Andrews JI, Raikwar NS, Kelley EA, Herse F, Dechend R,et al. A recently evolved novel trophoblast-enriched secreted form offms-like tyrosine kinase-1 variant is up-regulated in hypoxia andpreeclampsia. J Clin Endocrinol Metab 2009;94(7):2524–30.

[34] Venkatesha S, Toporsian M, Lam C, Hanai JI, Mammoto T, Kim YM,et al. Soluble endoglin contributes to the pathogenesis ofpreeclampsia. Nat Med 2006;12(6):642–9.

[35] Podjarny E, Losonczy G, Baylis C. Animal models of preeclampsia.Semin Nephrol 2004;24(6):596–606.

[36] Sandrim VC, Palei AC, Metzger IF, Gomes VA, Cavalli RC, Tanus-Santos JE. Nitric oxide formation is inversely related to serum levelsof antiangiogenic factors soluble fms-like tyrosine kinase-1 andsoluble endogline in preeclampsia. Hypertension 2008;52(2):402–7.

[37] Carr DB, Epplein M, Johnson CO, Easterling TR, Critchlow CW. Asister’s risk: family history as a predictor of preeclampsia. Am JObstet Gynecol 2005;193(3 Pt. 2):965–72.

[38] Carr DB, Newton KM, Utzschneider KM, Tong J, Gerchman F, Kahn SE,et al. Preeclampsia and risk of developing subsequent diabetes.Hypertens Pregnancy 2009;28(4):435–47.

[39] Srinivas SK, Morrison AC, Andrela CM, Elovitz MA. Allelic variationsin angiogenic pathway genes are associated with preeclampsia. Am JObstet Gynecol 2010.

[40] Papazoglou D, Galazios G, Koukourakis MI, Panagopoulos I,Kontomanolis EN, Papatheodorou K, et al. Vascular endothelialgrowth factor gene polymorphisms and pre-eclampsia. Mol HumReprod 2004;10(5):321–4.

[41] Ranheim T, Staff AC, Henriksen T. VEGF mRNA is unaltered indecidual and placental tissues in preeclampsia at delivery. ActaObstet Gynecol Scand 2001;80(2):93–8.

[42] Banyasz I, Szabo S, Bokodi G, Vannay A, Vasarhelyi B, Szabo A, et al.Genetic polymorphisms of vascular endothelial growth factor insevere pre-eclampsia. Mol Hum Reprod 2006;12(4):233–6.

[43] Widmer M, Villar J, Benigni A, Conde-Agudelo A, Karumanchi SA,Lindheimer M. Mapping the theories of preeclampsia and the role ofangiogenic factors: a systematic review. Obstet Gynecol2007;109(1):168–80.

[44] Mutze S, Rudnik-Schoneborn S, Zerres K, Rath W. Genes and thepreeclampsia syndrome. J Perinat Med 2008;36(1):38–58.

[45] Tuohy JF, James DK. Pre-eclampsia and trisomy 13. Br J ObstetGynaecol 1992;99(11):891–4.

[46] Lie RT, Rasmussen S, Brunborg H, Gjessing HK, Lie-Nielsen E, IrgensLM. Fetal and maternal contributions to risk of pre-eclampsia:population based study. BMJ 1998;316(7141):1343–7.

[47] Esplin MS, Fausett MB, Fraser A, Kerber R, Mineau G, Carrillo J, et al.Paternal and maternal components of the predisposition topreeclampsia. N Engl J Med 2001;344(12):867–72.

[48] Haig D. Genetic conflicts of pregnancy and childhood. In: Stearns SC,editor. Evolution in health and in disease. Oxford: Oxford UniversityPress; 1999. p. 77–90.

[49] Roberts JM, Gammill HS. Preeclampsia: recent insights.Hypertension 2005;46(6):1243–9.

[50] Hiby SE, Walker JJ, O’Shaughnessy KM, Redman CW, Carrington M,Trowsdale J, et al. Combinations of maternal KIR and fetal HLA-Cgenes influence the risk of preeclampsia and reproductive success. JExp Med 2004;200(8):957–65.

[51] van Dijk M, Mulders J, Poutsma A, Konst AA, Lachmeijer AM, DekkerGA, et al. Maternal segregation of the Dutch preeclampsia locus at10q22 with a new member of the winged helix gene family. NatGenet 2005;37(5):514–9.

[52] Ohkuchi A, Hirashima C, Suzuki H, Takahashi K, Yoshida M,Matsubara S, et al. Evaluation of a new and automatedelectrochemiluminescence immunoassay for plasma sFlt-1 andPlGF levels in women with preeclampsia. Hypertens Res 2010.

[53] Sunderji S, Gaziano E, Wothe D, Rogers LC, Sibai B, Karumanchi SA,et al. Automated assays for sVEGF R1 and PlGF as an aid in thediagnosis of preterm preeclampsia: a prospective clinical study. Am JObstet Gynecol 2010;202(1):40.e1–7.

[54] Kusanovic JP, Romero R, Chaiworapongsa T, Erez O, Mittal P,Vaisbuch E, et al. A prospective cohort study of the value ofmaternal plasma concentrations of angiogenic and anti-angiogenicfactors in early pregnancy and midtrimester in the identification ofpatients destined to develop preeclampsia. J Matern Fetal NeonatalMed 2009;22(11):1021–38.

[55] Romero R, Nien JK, Espinoza J, Todem D, Fu W, Chung H, et al. Alongitudinal study of angiogenic (placental growth factor) and anti-angiogenic (soluble endoglin and soluble vascular endothelialgrowth factor receptor-1) factors in normal pregnancy andpatients destined to develop preeclampsia and deliver a small forgestational age neonate. J Matern Fetal Neonatal Med 2008;21(1):9–23.

[56] Gilbert JS, Verzwyvelt J, Colson D, Arany M, Karumanchi SA, GrangerJP. Recombinant vascular endothelial growth factor 121 infusionlowers blood pressure and improves renal function in rats withplacentalischemia-induced hypertension. Hypertension 2010;55(2):380–5.

[57] Li Z, Zhang Y, Ying Ma J, Kapoun AM, Shao Q, Kerr I, et al.Recombinant vascular endothelial growth factor 121 attenuateshypertension and improves kidney damage in a rat model ofpreeclampsia. Hypertension 2007;50(4):686–92.

[58] Karumanchi SA, Epstein FH. Placental ischemia and soluble fms-liketyrosine kinase 1: cause or consequence of preeclampsia? Kidney Int2007;71(10):959–61.