title: Metformin as a prevention and treatment for preeclampsia: effects on soluble fms-like tyrosine kinase 1 and soluble endoglin secretion and endothelial dysfunction.
abstract: BACKGROUND
  Preeclampsia is associated with placental ischemia/hypoxia and secretion of soluble fms-like tyrosine kinase 1 and soluble endoglin into the maternal circulation. This causes widespread endothelial dysfunction that manifests clinically as hypertension and multisystem organ injury. Recently, small molecule inhibitors of hypoxic inducible factor 1α have been found to reduce soluble fms-like tyrosine kinase 1 and soluble endoglin secretion. However, their safety profile in pregnancy is unknown. Metformin is safe in pregnancy and is also reported to inhibit hypoxic inducible factor 1α by reducing mitochondrial electron transport chain activity.
  
  
  OBJECTIVE
  The purposes of this study were to determine (1) the effects of metformin on placental soluble fms-like tyrosine kinase 1 and soluble endoglin secretion, (2) to investigate whether the effects of metformin on soluble fms-like tyrosine kinase 1 and soluble endoglin secretion are regulated through the mitochondrial electron transport chain, and (3) to examine its effects on endothelial dysfunction, maternal blood vessel vasodilation, and angiogenesis.
  
  
  METHODS
  We performed functional (in vitro and ex vivo) experiments using primary human tissues to examine the effects of metformin on soluble fms-like tyrosine kinase 1 and soluble endoglin secretion from placenta, endothelial cells, and placental villous explants. We used succinate, mitochondrial complex II substrate, to examine whether the effects of metformin on soluble fms-like tyrosine kinase 1 and soluble endoglin secretion were mediated through the mitochondria. We also isolated mitochondria from preterm preeclamptic placentas and gestationally matched control subjects and measured mitochondrial electron transport chain activity using kinetic spectrophotometric assays. Endothelial cells or whole maternal vessels were incubated with metformin to determine whether it rescued endothelial dysfunction induced by either tumor necrosis factor-α (to endothelial cells) or placenta villous explant-conditioned media (to whole vessels). Finally, we examined the effects of metformin on angiogenesis on maternal omental vessel explants.
  
  
  RESULTS
  Metformin reduced soluble fms-like tyrosine kinase 1 and soluble endoglin secretion from primary endothelial cells, villous cytotrophoblast cells, and preterm preeclamptic placental villous explants. The reduction in soluble fms-like tyrosine kinase 1 and soluble endoglin secretion was rescued by coadministration of succinate, which suggests that the effects of metformin on soluble fms-like tyrosine kinase 1 and soluble endoglin were likely to be regulated at the level of the mitochondria. In addition, the mitochondrial electron transport chain inhibitors rotenone and antimycin reduced soluble fms-like tyrosine kinase 1 secretion, which further suggests that soluble fms-like tyrosine kinase 1 secretion is regulated through the mitochondria. Mitochondrial electron transport chain activity in preterm preeclamptic placentas was increased compared with gestation-matched control subjects. Metformin improved features of endothelial dysfunction relevant to preeclampsia. It reduced endothelial cell messenger RNA expression of vascular cell adhesion molecule 1 that was induced by tumor necrosis factor-α (vascular cell adhesion molecule 1 is an inflammatory adhesion molecule up-regulated with endothelial dysfunction and is increased in preeclampsia). Placental conditioned media impaired bradykinin-induced vasodilation; this effect was reversed by metformin. Metformin also improved whole blood vessel angiogenesis impaired by fms-like tyrosine kinase 1.
  
  
  CONCLUSIONS
  Metformin reduced soluble fms-like tyrosine kinase 1 and soluble endoglin secretion from primary human tissues, possibly by inhibiting the mitochondrial electron transport chain. The activity of the mitochondrial electron transport chain was increased in preterm preeclamptic placenta. Metformin reduced endothelial dysfunction, enhanced vasodilation in omental arteries, and induced angiogenesis. Metformin has potential to prevent or treat preeclampsia.
authors.affiliation: Translational Obstetrics Group, Department of Obstetrics and Gynaecology, University of Melbourne, Mercy Hospital for Women, Heidelberg, Victoria, Australia.
authors.forename: Fiona C
authors.initials: FC
authors.lastname: Brownfoot
authors.affiliation: Translational Obstetrics Group, Department of Obstetrics and Gynaecology, University of Melbourne, Mercy Hospital for Women, Heidelberg, Victoria, Australia.
authors.forename: Roxanne
authors.initials: R
authors.lastname: Hastie
authors.affiliation: Translational Obstetrics Group, Department of Obstetrics and Gynaecology, University of Melbourne, Mercy Hospital for Women, Heidelberg, Victoria, Australia.
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Hannan
authors.affiliation: Translational Obstetrics Group, Department of Obstetrics and Gynaecology, University of Melbourne, Mercy Hospital for Women, Heidelberg, Victoria, Australia.
authors.forename: Ping
authors.initials: P
authors.lastname: Cannon
authors.affiliation: Translational Obstetrics Group, Department of Obstetrics and Gynaecology, University of Melbourne, Mercy Hospital for Women, Heidelberg, Victoria, Australia.
authors.forename: Laura
authors.initials: L
authors.lastname: Tuohey
authors.affiliation: Biosciences, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Parry
authors.affiliation: Biosciences, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Sevvandi
authors.initials: S
authors.lastname: Senadheera
authors.affiliation: Department of Obstetrics and Gynecology, Laboratory of Reproductive Biology, Faculty of Medicine, Universidad de Los Andes, Santiago, Chile.
authors.forename: Sebastian E
authors.initials: SE
authors.lastname: Illanes
authors.affiliation: Translational Obstetrics Group, Department of Obstetrics and Gynaecology, University of Melbourne, Mercy Hospital for Women, Heidelberg, Victoria, Australia.
authors.forename: Tu'uhevaha J
authors.initials: TJ
authors.lastname: Kaitu'u-Lino
authors.affiliation: Translational Obstetrics Group, Department of Obstetrics and Gynaecology, University of Melbourne, Mercy Hospital for Women, Heidelberg, Victoria, Australia. Electronic address: s.tong@unimelb.edu.au.
authors.forename: Stephen
authors.initials: S
authors.lastname: Tong
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D002317:Cardiovascular Agents / Q000494:pharmacology / Q000627:therapeutic use*; D045222:Electron Transport Chain Complex Proteins / Q000378:metabolism; D000071063:Endoglin; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008687:Metformin / Q000494:pharmacology / Q000627:therapeutic use*; D010920:Placenta / Q000187:drug effects / Q000378:metabolism; D011225:Pre-Eclampsia / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology / Q000517:prevention & control*; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000378:metabolism*; D016896:Treatment Outcome; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000378:metabolism*; D014664:Vasodilation / Q000187:drug effects
chemical_list: D015703:Antigens, CD; D015415:Biomarkers; D002317:Cardiovascular Agents; C064206:ENG protein, human; D045222:Electron Transport Chain Complex Proteins; D000071063:Endoglin; D011956:Receptors, Cell Surface; D008687:Metformin; C501162:FLT1 protein, human; D040281:Vascular Endothelial Growth Factor Receptor-1
keywords: electron transport chain; metformin; preeclampsia; soluble endoglin; soluble fms-like tyrosine kinase 1