John Kingdom

Research Synopsis

1. Placental imaging and pathology of FGR

My early publications arising from my MD thesis focused on dysregulation of feto-placental vasomotor tone in IUGR, but then led on to an interest in the microvasculature; my most significant early publication was the demonstration of the major capillary defects in placental villi in the most extreme forms of FGR which led on to an international workshop on the placental basis of fetal hypoxia for which I was awarded the International Placenta Association Castellucci Prize in 1997.

My interest in placental pathology of FGR has been sustained in Toronto due to our clinical resources and to a long-standing productive relationship (27 publications) with a series of Section Head perinatal pathologists (Dr.s S. Keating, Eric Morgen & A. Parks).

• Krebs C, Macara LM, Leiser R, Bowman AW, Greer IA, Kingdom JC. Intrauterine growth restriction with absent end-diastolic flow velocity in the umbilical artery is associated with maldevelopment of the placental terminal villous tree.. Am J Obstet Gynecol. 1996 Dec;175(6):1534-42.
• Kingdom JC, Kaufmann P. Placenta. Oxygen and placental villous development: origins of fetal hypoxia. 1997 Nov;18(8):613-21; discussion 623-6
• Proctor LK, Toal M, Keating S, Chitayat D, Okun N, Windrim RC, Smith GC, Kingdom JC. Placental size and the prediction of severe early-onset intrauterine growth restriction in women with low pregnancy-associated plasma protein-A. Ultrasound Obstet Gynecol. 2009 Sep;34(3):274-82. 
• Porat S, Fitzgerald B, Wright E, Keating S, Kingdom JC. Placental hyperinflation and the risk of adverse perinatal outcome. Ultrasound Obstet Gynecol. 2013 Sep;42(3):315-21. 

2. Non-anticoagulant actions of heparin

Heparin, in particular low-molecular weight heparin (LMWH) appears to prevent recurrences of the most severe forms of placental dysfunction.

Following delivery the placentas are commonly infarcted, therefore there is a widely-held view amongst MFMs and OBs that heparin is a “placental anticoagulant”. I believe this to be wrong. We have shown that multifocal infarction associates strongly with disorders of the development of placental villi, rather than with any demonstrable maternal thrombophilia.

Next, I led a novel design pilot randomized control trial of heparin in this context, recruiting women based on multiply-abnormal tests of placental function and subjecting their placentas to pathologic analysis. Most placentas were abnormal, but no differences in infarction rates were seen between the 2 trial arms.

In-vitro, I mentored a resident and my then post-doc, to demonstrate that heparin and especially LMWH, was able to reverse the strongly anti-angiogenic properties of media conditioned by 1st trimester placental villi, for which the resident (now on faculty at UofT), won the American College of OBGYN Resident Research prize. In tandem, we were able to show that heparin and LMWH both achieve these pro-angiogenic responses despite elevating 3-4-fold circulating levels of the VEGF decoy protein sflt-1, based on which we have coined the term the “heparin-sflt-1 paradox” of pre-eclampsia. These observations drive my current CIHR grants. 

• Franco C, Walker M, Robertson J, Fitzgerald B, Keating S, McLeod A, Kingdom JC. Placental infarction and thrombophilia. Obstet Gynecol. 2011 Apr;117(4):929-34. 
• D'Souza R, Keating S2, Walker M1, Drewlo S1, Kingdom J. Unfractionated heparin and placental pathology in high-risk pregnancies: secondary analysis of a pilot randomized controlled trial. Placenta. 2014 Oct;35(10):816-23. 
• Sobel ML, Kingdom J, Drewlo S. Angiogenic response of placental villi to heparin. Obstet Gynecol. 2011 Jun;117(6):1375-83. 
• Drewlo S, Levytska K, Sobel M, Baczyk D, Lye SJ, Kingdom JC. Heparin promotes soluble VEGF receptor expression in human placental villi to impair endothelial VEGF signaling. J Thromb Haemost. 2011 Dec;9(12):2486-97
• McLaughlin K, Snelgrove JW, Audette MC, Syed A, Hobson SR, Windrim RC, Melamed N, Carmona S, Kingdom JC. PlGF (Placental Growth Factor) Testing in Clinical Practice: Evidence from a Canadian Tertiary Maternity Referral Center. Hypertension. 2021 Jun;77(6):2057-2065. 
• McLaughlin K, Hobson SR, Ravi Chandran A, Agrawal A, Windrim RC, Parks WT, Bowman AW, Sovio U, Smith GC, Kingdom JC. Circulating Maternal Placenta Growth Factor Responses to Low Molecular Weight Heparin in Pregnant Patients at Risk of Placental Dysfunction: A Pilot Study. Am J Obstet Gynecol. 2021 Aug 27:S0002-9378(21)00961-3. 

3. Molecular Placental Pathology of Pre-eclampsia and FGR

My National grant funding for the period 2003-2012 was focused on the molecular control of syncytiotrophoblast formation and shedding, and its disruption in diseased states.

My major contribution in this period was the development of the ‘floating villous explant model”, as opposed to netwell explants, such that the in-vivo system whereby villi are bathed in blood, is recapitulated. We were able to demonstrate that the human homolog (GCM1) of the murine trophoblast transcription factor glial cell missing-1 (Gcm-1) had an analgous function. Earlier, our work exploring the role of fibroblast growth factor-4 (FGF4) in this system uncovered the bi-potential behavior of villous cytotrophopblasts, since when the outer syncytiotrophoblast layer is cleaved off enzymatically, the exposure to FGF4 redirects the exposed cytotrophoblasts to proliferate along the extra-villous pathway.

More recently, we have demonstrated the upstream regulation of GCM1 by DREAM and have now gone on to show that the post-transcriptional regulatory process of hyperSUMOylation is present in severe pre-eclamptic placentas and may be induced by hypoxia-reperfusion injury and pro-inflammatory cytokines - 2015 Society for Reproductive Investigation abstract. We are currently studying how this post-transcriptional phenomenon may explain shifts in secretion from placental villi of pro-angiogenic to anti-angiogenic molecules that contribute to the maternal vasculopathy of severe pre-eclampsia. 

• Baczyk D, Drewlo S, Proctor L, Dunk C, Lye S, Kingdom J. Glial cell missing-1 transcription factor is required for the differentiation of the human trophoblast. Cell Death Differ. 2009 May;16(5):719-27. 
• Baczyk D, Dunk C, Huppertz B, Maxwell C, Reister F, Giannoulias D, Kingdom JC. Bi-potential behaviour of cytotrophoblasts in first trimester chorionic villi. Placenta. 2006 Apr-May;27(4-5):367-74. 
• Baczyk D, Kibschull M, Mellstrom B, Levytska K, Rivas M, Drewlo S, Lye SJ, Naranjo JR, Kingdom JC.
• DREAM mediated regulation of GCM1 in the human placental trophoblast. PLoS One. 2013;8(1):e51837. 
• Baczyk D, Drewlo S, Kingdom JC. Emerging role of SUMOylation in placental pathology. Placenta. 2013 Jul;34(7):606-12. 
• Armistead B, Kadam L, Siegwald E, McCarthy FP, Kingdom JC, Kohan-Ghadr HR, Drewlo S.Induction of the PPARγ (Peroxisome Proliferator-Activated Receptor γ)-GCM1 (Glial Cell Missing 1) Syncytialization Axis Reduces sFLT1 (Soluble fms-Like Tyrosine Kinase 1) in the Preeclamptic Placenta. Hypertension. 2021 Jul;78(1):230-240.

4. Screening and Intervention to Prevent Placental Complications of Pregnancy 

We developed the concept of screening for “placental health” by incorporating placental morphologic assessment into an algorithm comprising uterine artery Doppler and maternal blood tests, initially in high-risk women. Subsequently we launched this as a screening program, to conduct a pilot randomized control trial of unfractionated heparin in screen-positive women to test the hypothesis that heparin would improve clinical outcomes via a non-anticoagulant mechanism.

We extended this work by performing non-invasive hemodynamic studies in screen-positive women, to show an asymptomatic phenotype (low cardiac output, high systemic vascular resistance, elevated circulating uric acid and sflt-1) that precedes overt preeclampsia by up to 4 weeks. We subsequently conducted the “placental health study” in 976 healthy nulliparous women, incorporating a structured clinical assessment, biomarkers, uterine artery Doppler and placental morphology, to predict chronic placental vascular disease.

• Toal M, Chan C, Fallah S, Alkazaleh F, Chaddha V, Windrim RC, Kingdom JC. Usefulness of a placental profile in high-risk pregnancies. Am J Obstet Gynecol. 2007 Apr;196(4):363.e1-7.
• Franco C, Walker M, Robertson J, Fitzgerald B, Keating S, McLeod A, Kingdom JC. Placental infarction and thrombophilia. Obstet Gynecol. 2011 Apr;117(4):929-34. 
• Doherty A, Carvalho JC, Drewlo S, El-Khuffash A, Downey K, Dodds M, Kingdom J. Altered hemodynamics and hyperuricemia accompany an elevated sFlt-1/PlGF ratio before the onset of early severe preeclampsia. J Obstet Gynaecol Can. 2014 Aug;36(8):692-700.
• Wright E, Audette MC, Ye X, Keating S, Hoffman B, Lye SJ, Shah PS, Kingdom JC. Maternal vascular malperfusion and adverse perinatal outcomes in low risk nulliparous women. Obstet Gynecol. 2017 Nov;130(5):1112-1120.
• McLaughlin K, Snelgrove JW, Audette MC, Syed A, Hobson SR, Windrim RC, Melamed N, Carmona S, Kingdom JC. PlGF (Placental Growth Factor) Testing in Clinical Practice: Evidence from a Canadian Tertiary Maternity Referral Center. Hypertension. 2021 Jun;77(6):2057-2065. 
• McLaughlin K, Snelgrove JW, Sienas LE, Easterling TR, Kingdom JC, Albright CM. Phenotype-Directed Management of Hypertension in Pregnancy. J Am Heart Assoc. 2022 Apr 5;11(7):e023694