Placenta
Volume 30, Supplement , Pages 55-65, March 2009

Gabor Than Award Lecture 2008: Pre-eclampsia – From Placental Oxidative Stress to Maternal Endothelial Dysfunction

  • T. Cindrova-Davies

      Affiliations

    • Corresponding Author InformationCorresponding author. Tel.: +44 01223 333 816; fax: +44 01223 333 840.

Centre for Trophoblast Research, Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK

Accepted 17 November 2008. published online 05 January 2009.

Article Outline

Abstract 

Pre-eclampsia is the most important complication of human pregnancy worldwide and a major contributor to maternal and fetal morbidity and mortality. Strong evidence exists that generation of placental oxidative stress, secondary to deficient spiral artery remodelling, is a key intermediary event, triggering the secretion of a mixture of placental factors that culminate in an enhanced maternal inflammatory response. Reactive oxygen species (ROS) have been recognised as secondary messengers in intracellular signalling cascades. Experiments studying placental ischaemia-reperfusion in vitro or in vivo during labour provide strong evidence suggesting that oxidative stress and ROS production can activate downstream stress-signalling pathways, p38 and SAPK/JNK MAPK, and the pro-inflammatory NF-κB signalling pathway, culminating in the release of inflammatory mediators, apoptotic debris, anti-angiogenic factors and other mediators, which then stimulate a maternal inflammatory reaction that manifests in endothelial dysfunction and the symptoms of pre-eclampsia. Addition of anti-oxidants or blocking the stress or inflammatory pathways in vitro attenuates these effects and opens possibilities for therapeutic intervention.

Keywords: Oxidative stress, Signalling pathways, Pre-eclampsia, Inflammation, Endothelial dysfunction

 

Back to Article Outline

1. Introduction 

Pre-eclampsia is an unpredictable and potentially dangerous complication of the second half of pregnancy, labour or early puerperium, characterised by the onset of hypertension (>140/90mmHg) and proteinuria after 20weeks of gestation in previously normotensive, non-proteinuric women [1], [2], [3]. The condition affects about 5% of pregnancies in the USA and Europe and is a leading cause of maternal morbidity and mortality worldwide. The pathophysiology of the disease remains elusive. Strong evidence exists that generation of placental oxidative stress is a key intermediary event in the pathology of pre-eclampsia [1], [4], [5]. The stress is thought to induce the placenta to release a mixture of factors, including inflammatory cytokines, anti-angiogenic factors and apoptotic debris, which culminates in an enhanced maternal inflammatory response and endothelial dysfunction [6], [7]. The aim of this paper is to review the role of placental stress and reactive oxygen species (ROS) in downstream signalling processes and how these events can precipitate the pathophysiology of pre-eclampsia.

Back to Article Outline

2. Reactive oxygen species and oxidative stress 

Eukaryotic cells utilise oxygen in order to produce ATP as an energy source. However, aerobic respiration is associated with the generation of reactive oxygen species (ROS). ROS and reactive nitrogen species (RNS) include both free radical species bearing unpaired electrons and their non-radical intermediates. ROS and RNS are generated by cytosolic processes, and are principally derived from mitochondria, where the superoxide anion is generated by electron leakage from complex I and III of the electron transport chain. Microsomes and peroxisomes also generate ROS, principally H2O2. In immune cells, ROS play a fundamental role in the mammalian immune response by facilitating the killing of invading microorganisms [8]. The most relevant radicals in biological regulation are superoxide and nitric oxide (NO). The superoxide anion (O2−) is formed by the univalent reduction of triplet-state molecular oxygen (3O2). This process is regulated enzymatically by NAD(P)H oxidases and xanthine oxidase or non-enzymatically by redox-reactive compounds (e.g. semi-ubiquinone compound) [9]. O2− is detoxified by manganese (if in mitochondria) or copper/zinc (if in cytosol) superoxide dismutase enzyme (MnSOD or Cu/ZnSOD). SOD converts superoxide into hydrogen peroxide (H2O2), which can subsequently be converted into water by the enzymes catalase or glutathione peroxidase. Alternatively, H2O2 can be converted to the highly reactive hydroxyl radical (OH) in the presence of reduced transition metals via the Fe2+-dependent Fenton reaction [9]. OH ions are the most reactive of all ROS, to the extent that their reactions are diffusion limited and there is no known scavenger (Fig. 1).

  • View full-size image.
  • Fig. 1 

    An overview of redox generation and clearance. The superoxide anion (O2−) is formed by the univalent reduction of triplet-state molecular oxygen (3O2). This process is regulated enzymatically by NAD(P)H oxidases and xanthine oxidase or non-enzymatically by redox-reactive compounds (e.g. semi-ubiquinone compound). O2− is detoxified by manganese (if in mitochondria) or copper/zinc (if in cytosol) superoxide dismutase enzyme (MnSOD or Cu/ZnSOD). SOD converts superoxide into hydrogen peroxide (H2O2), which can subsequently be converted into water by the enzymes catalase or glutathione peroxidase. Alternatively, H2O2 can be converted into the highly reactive hydroxyl radical (OH) in the presence of reduced transition metals via the Fe2+-dependent Fenton reaction. GSH – glutathione; GSSG – glutathione disulphide.

Eukaryotic organisms have evolved many defence mechanisms to cope with the constant generation of potentially damaging oxygen radicals. These include anti-oxidants, e.g. glutathione, vitamins C and E, and β-carotene, which act as free radical scavengers. The anti-oxidant enzymes such as SOD, catalase and glutathione peroxidase (GPx) catalyse the reduction of the reactive oxygen intermediates. These defences are not perfect and when the balance between oxidants and anti-oxidants is disturbed and oxidation prevails, a cell or organism is considered to be in a state of oxidative stress [9], [10].

Back to Article Outline

3. Oxidative stress in pregnancy 

Oxidative stress is regarded as a key element in the pathogenesis of pre-eclampsia, although its precise role has not been fully elucidated [1], [4], [5]. ROS production seems increased in pre-eclamptic placentae, as evidenced by increased peroxynitrite formation [11]. Peroxynitrite could arise from local NO production coupled with increased xanthine oxidase generation of O2− and decreased SOD. NO and O2− can be produced by a variety of cells by inflammatory stimuli or post-ischaemic reoxygenation. Additionally, the concentration of ascorbic acid is decreased in the maternal circulation in pre-eclamptic women, which could be indicative of reduced anti-oxidant potential. Increased ROS and potentially decreased anti-oxidant capacity will propagate lipid peroxidation leading to leukocyte activation, platelet adhesion, and vasoconstriction [4].

The cause of the oxidative stress is not certain, but strong evidence suggests that deficient conversion of the uterine spiral arteries and subsequent impaired perfusion of the placenta provides the initiating insult [12]. In normal pregnancy, spiral arteries undergo substantial remodelling during early pregnancy. Extravillous cytotrophoblast cells penetrate into the myometrium and convert muscular spiral arteries into flaccid tubes with no muscularis or elastic lamina, capable of supplying the hugely expanded blood flow of the third trimester placenta. In pre-eclamptic pregnancies, the remodelling is minimal and modification only occurs in the decidual segments of the spiral arteries and most of the vessels retain their vasoreactivity [12]. Maternal blood thus enters the intervillous space at a higher pressure and a faster rate, in a pulsatile jet-like manner, exposing placental villi to fluctuating oxygen concentrations [13], [14]. These effects could contribute to the ischaemia-reperfusion (I/R) type injury of the placenta [15]. Ischaemia-reperfusion injury is caused by high concentrations of free radicals that are generated when molecular oxygen is reintroduced into ischaemic tissue.

Placental OS could lead to maternal endothelial cell activation through release of toxic products or activation of signalling pathways and secretion of soluble factors. For example, pre-eclampsia is consistently associated with hyperglyceridaemia, insulin resistance [16], oxidative stress [4] and chronic inflammation [17], [18]. Increased placental oxidative stress in pre-eclampsia promotes formation of lipid peroxides, which alter cell membranes by increasing incorporation of cholesterol, oxidised free fatty acids and low density lipoprotein [19]. Increased lipid peroxide formation by pre-eclamptic placentae is associated with increased production of thromboxane A2, a potent vasoconstrictor, which can mediate maternal endothelial dysfunction. In conjunction with these effects, GPx may be deficient in placental tissue from pre-eclamptic women. Chemical inhibition of placental GPx induces increased production of lipid hydroperoxides and an increase in the placental thromboxane A2 to prostaglandin I2 ratio. The altered prostaglandin ratio could precipitate vasospasm and increased placental ischaemia, cell damage and lipid peroxidation [19].

Back to Article Outline

4. ROS signalling pathways 

ROS have been recognised as secondary messengers in intracellular signalling cascades. ROS can regulate cellular processes by several mechanisms, including transcriptional regulation, direct oxidative modification, regulation of redox-sensitive interacting proteins, and modification of enzyme function and protein turn-over [10] (see Table 1). A brief overview of stress, inflammatory and pro-survival pathways activated by ROS is summarised below and in Fig. 2.

Table 1. Mechanisms of intracellular signalling regulated by ROS [10].
Intracellular signallingMechanism of action
Transcriptional regulationSeveral transcription factors, including NF-κB, HIF-1α, AP-1 and p53, contain redox-sensitive cysteine residues at their DNA-binding sites [20]
Direct oxidative modificationNewly synthesised proteins can be directly modified and their function altered by oxidation of amino acids (e.g. Cys, Tyr, Met) [21], [22]
Regulation of redox-sensitive interacting proteinsCertain proteins can by stabilised by contact with others (e.g. ASK-1-TRX, JNK-GST, p53-JNK) [23]
Regulation of redox-sensitive modifying enzymesPost-translational modification of proteins, especially by phosphorylation, can either activate or inhibit protein function. Phosphorylation status is determined by the balance of kinases (phosphorylate) and phosphatases (dephosphorylate). Phosphatases can be oxidatively dephosphorylated, promoting phosphorylation of proteins [24], [25]
Regulation of protein turn-overThe ubiquitin-proteosome system facilitates the degradation of most proteins. Oxidative stress can inactivate ubiquitin-activating enzyme E1 and proteosome 26S and 20S [26]
  • View full-size image.
  • Fig. 2 

    An overview of redox-regulated protein kinase signalling in the route to apoptosis. Cells are equipped with various intracellular signal transduction systems, including protein kinases that facilitate transmission of physiological ROS-mediated signals. TNF-α induces ROS production via mitochondria. ASK1 is an upstream regulator of the stress-activated MAPK cascades and has been shown to play a critical role in apoptosis. TRX is a key protein that can act as a negative (ASK1) or, in combination with Ref, as a positive regulator. p38 and SAPK MAPKs promote apoptosis through activation of caspase-3. AKT, a key target of PI3-K, inactivates pro-apoptotic proteins (GSK-3) and activates transcription factors, which target anti-apoptotic proteins. Under oxidative stress, this pathway is activated by oxidative inactivation of phosphatases (e.g. PTEN), allowing constitutive activation of tyrosine kinase receptor and PI3-K. AKT acts in concert with ERK, SAPK and p38 to signal the intracellular apoptotic machinery for a full execution of apoptosis. Expression or product activity of some specific transcription factor genes are regulated in response to oxidative stress, which in turn determines the transcription level of genes that control proliferation, differentiation and cell death. Positive (e.g. MAPK-mediated) and negative (e.g. anti-oxidant response) regulatory circuits determine the final levels of ROS.

4.1. Mitogen activated protein kinases 

Mitogen activated protein kinases (MAPK) constitute pathways that convey signals from the cell surface to the nucleus via a cascade of phosphorylation events. They get activated through phosphorylation. The MAPK family consist of extracellular regulated kinases (ERK1/2), stress activated protein kinase/Jun N-terminal kinase (SAPK/JNK), p38 kinase, ERK3/4, and the big mitogen-activated protein kinase 1 (BMK1/ERK5) pathways [27]. In general, ROS-induced ERK1/2 activation promotes cell survival and proliferation, whereas SAPK/JNK and p38 pathways mostly induce apoptosis [28]. SAPK/JNK and p38 pathways are major transducers that signal cell death or survival in response to oxidative stress. Both of these stress pathways can be activated by apoptosis-regulating signal kinase 1 (ASK1), which is preferentially activated in response to various types of stress, such as oxidative stress, and plays pivotal roles in a variety of cellular responses. Under non-stress conditions, ASK1 is inhibited by the reduced form of thioredoxin (Trx) or glutaredoxin (Grx). Increased oxidative stress or TNF-α cause oxidation of Trx or Grx and release ASK1, which can then form a multimeric complex with active kinase activity. The activation of ASK1 subsequently activates SAPK/JNK and p38 MAPK, resulting in cell death [29]. In placental villous explants, in vitro hypoxia–reoxygenation (H/R) was reported to activate p38 and SAPK/JNK MAPK stress pathways. This activation was associated with induction of apoptosis and inflammation, and both processes could be blocked by inhibitors of the p38 pathway [30]. Similarly, in vivo labour induced phosphorylation of the p38 pathway but not that of SAPK/JNK (Fig. 3A). Our recent data indicate that H/R and also H2O2 treatment of placental villi in vitro can induce the activation of the up-stream stress kinase ASK1, which is known to activate both SAPK/JNK and p38 MAPK pathways (Fig. 3B). This activation could be blocked by anti-oxidant vitamins, suggesting the involvement of oxidative stress in ASK1 regulation (Fig. 3B). Similarly, increased activity of SAPK/JNK and p38 MAPK was reported in heart failure secondary to ischaemic heart disease [31] and in an ex vivo study I/R of the myocardium activated p38 MAPK and TNF-α secretion, which could be blocked by a p38 inhibitor [32].

  • View full-size image.
  • Fig. 3 

    Stress pathways regulated by labour in vivo and hypoxia–reoxygenation and H2O2 in vitro. (A) Lysates from placentae delivered by caesarean section (CS) or vaginally with labour (L) were immunoblotted and analyzed with anti-cleaved caspase-3, anti-cleaved caspase-9 and anti-cleaved PARP antibodies. All blots were re-probed with anti-β-actin to normalise gel loading and normalised results (±SE) are plotted, expressing caesarean controls as 100%. (B) Protein lysates from placentae cultured under H/R or H2O2 (1mM) in the presence or absence of vitamins C and E (V) for 7h (n=6) were analysed for ASK1. Different letters indicate groups that are significantly different using the PLSD test with P<0.05.

4.2. PI3-kinase/AKT pathway 

PI3-kinase(PI3K)/AKT pathways play an important role in cell survival, growth, proliferation and motility. PI3K signalling can be activated by moderate levels of ROS, but sustained oxidative stress inhibits this pathway and promotes apoptosis [33]. AKT has been shown to phosphorylate and inactivate the BclXL/Bcl2-associated death promoter (BAD) via a PI3K-dependent PDK-activation mechanism. Phosphorylation of BAD prevents the association between BAD and Bcl-2 and Bcl-xl by promoting the binding of BAD to 14-3-3 protein [34] and prevents it from triggering mitochondrial-induced caspase activation, the terminal effectors of the apoptotic machinery. AKT detaches from the inner surface of the plasma membrane, where it is initially activated and relocalises to the nucleus within 30min of activation by growth factors. In addition, AKT phosphorylates glycogen synthase kinase (GSK-3) on a serine residue (Ser21 and Ser9 for α and β isoforms, respectively), which inactivates its catalytic activity. This in turn promotes cell survival as GSK-3αβ is a potent inducer of apoptosis. AKT also phosphorylates and inhibits ASK1 activity, which prevents stress-induced apoptosis [35]. AKT is additionally involved in regulation of the translation machinery through the control of mTOR activity (via two distinct mechanisms). The critical role of AKT in placental and fetal growth was elucidated by Yung et al. who reported reduced AKT and mTOR protein activity and activation of GSK-3 in IUGR placentae. This reduction in AKT signaling was associated with protein synthesis down-regulation and increased endoplasmic reticulum (ER) stress [36].

4.3. Inflammation and NF-κB pathway 

ROS are important mediators of inflammation. ROS activate nuclear factor-κB (NF-κB) and activating protein-1 (AP-1) signal transduction pathways, which promote transcription of genes involved in cell growth, immunity, inflammation, apoptosis and the stress response. NF-κB is a hetero- or homo-dimer consisting of five subunits of the Rel family of polypeptides – NF-κB1 (p50/p105), NF-κB2 (p52/p100), RelA (p65), c-Rel and RelB. NF-κB mainly exists in the form of the heterodimer p65/p50. Prior to activation, most NF-κB molecules are retained in the cytoplasm bound to one of the IκB (inhibitor of NF-κB) proteins [37]. Upon stimulation, e.g. by inflammatory cytokines or ROS, the IKK (IκB kinase) complex is activated, which phosphorylates NF-κB-bound IκB and targets it for ubiquitination, allowing release of NF-κB and its translocation to the nucleus where it binds to κB-regulatory elements and co-ordinates transcription activation of over 200 genes [37]. These genes can be categorised into four functional groups: inflammatory and immunoregulatory genes, cell cycle regulating genes, anti-apoptotic genes and genes that encode negative regulators of NF-κB. NF-κB activation can thus induce the transcription of a large number of genes implicated in vascular inflammation, including adhesion molecules, cytokines and chemokines, and chronic activation of NF-κB is believed to predispose arteries to atherosclerosis [38]. Oxidative stress-induced NF-κB activation was shown to increase monocyte adhesion to endothelial cells of aged arteries via induction of adhesion molecules [39].

Back to Article Outline

5. The link between NF-κB activation and ER stress 

ER stress has recently been identified as a major regulator of cell homeostasis through its involvement in post-translational protein processing and folding, and its capacity to activate the unfolded protein response (UPR) [40], [41], [42]. ER stress can promote oxidative stress through generation and accumulation of ROS. A link has been identified between increased oxidative stress, ER stress and inflammation. An increase in ER stress results in the activation of NF-κB, which can be blocked by both calcium chelators and anti-oxidants, suggesting NF-κB activation could be a result of the oxidative stress arising from excessive protein folding and/or ER-stress mediated Ca2+ leakage [43]. ER stress activates UPR signalling pathways, which are initiated by three ER-localised protein sensors: IRE1α (inositol-requiring 1α), PERK (double-stranded RNA-dependent protein kinase (PKR)-like ER kinase) and ATF6 (activating transcription factor 6). NF-κB activation in response to ER stress can be promoted through two pathways. Firstly, PERK-eIF2α-mediated attenuation of translation increases the ratio of NF-κB to IκB due to the shorter half-life of the latter, allowing free NF-κB to translocate to the nucleus. Secondly, autophosphorylation of IRE1α enables its binding to the adaptor protein TNF-α-receptor-associated-factor 2 (TRAF2), leading to phosphorylation of IκB and nuclear translocation of NF-κB. The formation of the IRE1α-TRAF2 complex can also activate SAPK/JNK, which induces the expression of inflammatory genes by phosphorylating the AP1 transcription factor [43].

A recent animal study provided encouraging evidence suggesting that restoring ER function might be therapeutic. Oral treatment with small ER stress chemical chaperones in a mouse model of type 2 diabetes resulted in normalisation of hyperglycaemia, restoration of systemic insulin sensitivity, resolution of fatty liver disease, and enhancement of insulin action in various tissues [44]. ER stress has been implicated in the pathophysiology of pre-eclampsia and IUGR [36], and similarities exist between pre-eclampsia and metabolic syndrome, including dyslipidaemia, inflammation, insulin resistance, oxidative stress and ER stress. The ER chaperones used in the study (PBA, TUDCA) have excellent in vivo safety profiles and their use has been approved in clinical trials for the treatment of urea-cycle disorders, thalassemia and cystic fibrosis [44]. They could potentially be applied for the treatment of pre-eclampsia.

Back to Article Outline

6. Inflammation, NF-κB and the peripheral syndrome 

Excessive inflammatory response has been proposed by Redman et al. to be the driving force that contributes to endothelial cell dysfunction and clinical syndrome of pre-eclampsia [18]. A robust leukocyte inflammatory response was shown to be a feature of all pregnancies, and it was further enhanced in pre-eclamptic pregnancies. Differences in the leukocyte inflammatory response between normal pregnancy and non-pregnancy were more pronounced than those between normal pregnancy and pre-eclampsia [17]. There are several pregnancy-associated stimuli that could account for such an increase in inflammation. These include cellular particles, cytoplasmic proteins, soluble fetal DNA, placental lipid peroxidation products, TNF-α and other cytokines, sFlt-1 and sEng, which are shed from the syncytiotrophoblast surface into maternal blood [1], [4].

Pre-eclampsia is associated with marked activation of leukocytes [17]. The potential consequences of leukocyte activation include release of pro-inflammatory cytokines, increase in leukocyte adherence to the vascular endothelium and consequent vascular dysfunction [45]. Despite an earlier report which suggested NF-κB activity was suppressed in pre-eclampsia [46], several more recent studies demonstrated increased NF-κB activation in pre-eclampsia [45], [47]. Luppi et al. reported that, compared to normal pregnancy, pre-eclamptic women showed activation of L-selectin on neutrophils, monocytes and T cells, and these changes were associated with increase in nuclear translocation of NF-κB and increased levels of IL-6 [45]. Shah et al. demonstrated activation of NF-κB and expression of COX-2 in systemic vasculature of women with pre-eclampsia, associated with neutrophil infiltration [47]. These findings are supported by in vitro studies. Treatment of HUVEC with pre-eclamptic plasma increased NF-κB activation and ICAM-1 expression. The effect could be inhibited by vitamin E and N-acetyl-cysteine [48]. Similarly, H/R or H2O2 treatment of placental explants induced NF-κB activation, associated with increased COX-2 expression, TNF-α and IL-1β secretion. Addition of vitamins C and E blocked NF-κB activation and the other inflammatory effects [30]. The suppression of NF-κB activation by vitamins is a result of their anti-oxidant activity, as well as direct vitamin C-driven inhibition of the NF-κB pathway [30]. We recently verified the beneficial effects of NF-κB inhibition on placental explants in vitro with the use of sulfasalazine, an inhibitor of NF-κB activation (Fig. 4). In addition to inhibiting NF-κB activation (Fig. 4A), sulfasalazine treatment led to a significant reduction of apoptosis (cleaved caspase-3 (CC-3)), COX-2 and soluble VEGF-R1 (sFlt-1) expression (Fig. 4B). This is an interesting finding since sFlt-1, a naturally occurring VEGF-A and PlGF antagonist, has been implicated in the pathogenesis of pre-eclampsia [49], [50]. Sulfasalazine has been used to treat patients with chronic inflammatory bowel disease and current evidence does not suggest any adverse effect of this drug in pregnancy, in terms of major malformations, fetal mortality or morbidity [51].

  • View full-size image.
  • Fig. 4 

    The effect of sulfasalazine on H/R-induced expression of NF-κB, COX-2, sFlt-1 and cleaved caspase-3. Protein lysates from placentae cultured under H/R in the presence or absence of 0.5mM sulfasalazine (+0.5SS) or 2.5mM sulfasalazine (+2.5SS) for 7h (A) or 16h (B) were analysed for NF-κB pathway activation (A) or COX-2, sFlt-1 and cleaved caspase-3 (CC-3) protein expression (B). Different letters indicate groups that are significantly different using the PLSD test with P<0.05.

Back to Article Outline

7. Pre-eclampsia and anti-oxidant interventions 

The regulatory role of ROS in the I/R-type injury in pre-eclampsia and cardiovascular disease, together with encouraging in vitro and ex vivo data introduced the paradigm that anti-oxidant vitamins might play an important role in the treatment of the ischaemic disease pathology. However, many large randomised trials failed to confirm a role for vitamin E supplementation in cardiovascular prevention [52], despite encouraging in vitro data and cohort trials. The most recent trial additionally showed that not only does long-term vitamin E supplementation fail to prevent cancer or major cardiovascular complications, it may increase the risk for heart failure [53]. Similarly, recent clinical trials aimed to treat women at risk of pre-eclampsia with vitamins C and E [54], [55] failed to reduce the incidence of the disease and in some instances, the administration of vitamins C and E even had an adverse effect on the pregnancy outcome. There are several explanations for these disappointing results. It is possible that vitamins were administered too late in pregnancy and their administration could not reverse the disease pathology already established. A recent study showed that women who report periconceptional vitamin use have lower rates of severe preterm births and extreme SGA, which seems to suggest that vitamin use might be effective during conception and early pregnancy [56]. There is also evidence that a healthy Mediterranean diet lowers the incidence of pre-term birth [57] and coronary heart disease [58]. The composition of artificial vitamins versus natural vitamins might therefore also affect the outcome.

Back to Article Outline

8. Apoptosis and pre-eclampsia 

ROS can mediate signalling pathways that turn on the cell death machinery. In general, at the lowest death-promoting ROS level apoptosis or type 1 cell death will occur; at intermediate levels ROS cause autophagy, or type 2 cell death; and at the highest concentration ROS will precipitate necrotic cell death. Classically, two major pathways of apoptotic cell death are recognised – the death receptor pathway and Ca2+ influx, which activates the mitochondrial pathway. Caspase enzymes are the main instigators in both scenarios. Caspase-8 is up-regulated by activated death receptors, activating effector caspase-3. Ca2+ influx leads to the release of cytochrome c from disrupted mitochondria, activating caspase-9 (caspase-9 and cytochrome c form apoptosome) and subsequently the effector caspase-3. Mitochondria or NADPH-generated ROS can induce mitochondrial-dependent cell death via activation of MAPK pathways and the pro-apoptotic Bcl-2 family proteins, Bax and Bak [59]. ROS can also activate cell death receptors and induce the extrinsic apoptotic pathway. TNF-α receptor can initiate two death pathways – via direct activation of caspases through adaptor proteins, or a distinct pathway involving the production of ROS and activation of the NF-κB pathway and SAPK/JNK MAPK pathway [60].

Pre-eclamptic placentae have been reported to have an increased rate of trophoblast apoptosis [61], and increased secretion of other circulating markers of syncytial debris, including cytokeratin [62], fetal DNA [63] and syncytiotrophoblast microfragments (STBM) [64]. Hypoxia–reoxygenation proved a potent stimulus for apoptotic changes and oxidative stress within the syncytiotrophoblast [30], [65], [66]. The distribution of these markers was identical to that reported in pre-eclamptic placentae [11]. In contrast, hypoxia alone has little effect [66]. I/R-type injury also occurs in vivo during labour and it is associated with similar changes, including increased oxidative stress, induction of inflammatory and angiogenic regulators and increased incidence of apoptosis in the human placenta [67]. Additionally, we showed that this H/R-induced increase in syncytiotrophoblast apoptosis (and also necrosis) was the source of cell-free fetal DNA, and the release of cell-free DNA and apoptosis could be significantly reduced by the addition of anti-oxidant vitamins C and E [65]. It thus seems feasible that placental oxidative stress in pre-eclampsia promotes increased apoptosis and shedding of syncytiotrophoblast and related cellular debris. This in turn can activate maternal inflammatory response and endothelial dysfunction. Evidence exists that STBMs can directly damage endothelial cells but also stimulate systemic inflammatory reaction. Microparticles in general are known to contain many proteins and lipids from the membranes and cytoplasm of the cells of origin, even mRNA and infectious particles. In vitro studies showed that STBMs prepared from normal placentae interacted with endothelial cells and caused secondary activation of neutrophils, and STBMs stimulated production of inflammatory cytokines when cultured with monocytes from healthy non-pregnant women [68].

Back to Article Outline

9. Anti-angiogenic factors 

A growing body of evidence suggests that soluble fms-like tyrosine kinase-1 (sFlt-1), a naturally occurring circulating antagonist of VEGF-A and PlGF, is one of the secreted factors involved in the pathogenesis of pre-eclampsia, as indicated by an increased expression of sFlt-1 in maternal serum [49] and placenta [50] of pre-eclamptic patients. Soluble Flt-1 is formed by alternative splicing of the pre-mRNA encoding VEGF-R1 (Flt-1). It lacks the cytoplasmic and transmembrane domain. sFlt-1 can thus bind circulating VEGF-A and PlGF, preventing their interactions with endogenous receptors. The expression of VEGF and sFlt-1 can be regulated by the hypoxia-inducible factor-1 (HIF-1). HIF-1 is a key component of a widely operative transcriptional response activated by hypoxia, Co ions and Fe chelation. HIF-1α stability is increased by hypoxia, but it can also be up-regulated under non-hypoxic conditions by inflammatory cytokines or microtubule-depolymerising agents involving the NF-κB pathway [69], [70], [71].

Administration of sFlt-1 can block VEGF-A and PlGF-induced microvascular relaxation of rat renal arterioles in vitro [50]. The levels of circulating sFlt-1 increase and PlGF decrease during the last 2months of pregnancy in normotensive women. However, these changes are significantly more pronounced in women who later develop pre-eclampsia and occur on average about 5weeks before the onset of pre-eclampsia [49]. Additionally, treatment of pregnant rats with an adenovirus encoding sFlt-1 can induce hypertension, proteinuria, and glomerular endotheliosis, the classic lesion of pre-eclampsia [50]. These observations suggest that excess circulating sFlt-1 contributes to the pathogenesis of pre-eclampsia. We recently showed that labour increases sFlt-1 mRNA and tissue protein level, in parallel to increased placental VEGF-A but not PlGF (both mRNA and protein). HIF-1α expression was increased in labour samples, which suggests its involvement in the regulation of sFlt-1 and VEGF-A in labour [67]. Similarly, H/R stimulation promotes increase of sFlt, HIF-1α and VEGF protein levels in placental explants in vitro (Fig. 5A). These effects can be blocked by anti-oxidant vitamin administration, by blocking of the p38 MAPK, and as shown previously, sFlt-1 can also be blocked by NF-κB inhibitor sulfasalazine (Fig. 4B), suggesting the involvement of oxidative stress, NF-κB and p38 signalling in sFlt-1 and HIF-1α regulation.

  • View full-size image.
  • Fig. 5 

    The effect of in vitro H/R on activation of sFlt, ADMA and on eNOS. Protein lysates from placentae cultured under H/R in the presence or absence of vitamins C and E (V) or PD169316 (p38i) for 7h were analysed with: (A) anti-sFlt, anti-HIF-1α, anti-VEGF; or (B) anti-P-eNOS (B), and anti-eNOS. (C) Secretion of ADMA into supernatants was measured by ELISA and normalised against wet tissue weight. (D) Immunostaining for endothelin-1 (green) and HNE (red) localised both markers principally to the syncytiotrophoblast. Different letters indicate groups that are significantly different using the PLSD test with P<0.05.

Soluble TGF-β co-receptor, endoglin (sEng), is elevated in the sera of pre-eclamptic women and correlates with disease severity. sEng induces vascular permeability and hypertension in vivo. These effects can be amplified by addition of sFlt-1 (even presenting as HELLP syndrome), suggesting that these two placenta-derived factors could act in concert to induce severe pre-eclampsia [72]. sEng acts by inhibition of TGF-β signaling in the vasculature, which includes effects on activation of eNOS and vasodilatation.

Back to Article Outline

10. Endothelial dysfunction 

Endothelial dysfunction in pre-eclampsia is manifested by increased expression of markers of endothelial activation in pre-eclamptic patients, including VCAM, endothelin, von Willebrand Factor, and thrombomodulin [3]. Endothelium plays a crucial role in regulating vascular tone. NO released by endothelial cells is a major endogenous vasodilator molecule, counter-balancing the vasoconstriction produced by the sympathetic nervous system and the renin-angiotensin system. Endothelial NO exerts many vasoprotective and anti-atherosclerotic properties, including protection from thrombosis, reduction of adhesion molecule expression and leukocyte adhesion. l-arginine is used as a substrate in NO synthesis. The endothelium can also produce methylated amino acids such as asymmetric dimethylarginine (ADMA), an endogenous competitive inhibitor of nitric oxide synthase. Circulating levels of ADMA are elevated in patients with cardiovascular risk factors and renal failure and are associated with the presence of endothelial dysfunction [73]. Raised concentrations of ADMA are also found in women with high resistance placental circulation at risk of pre-eclampsia, IUGR, or both. Raised ADMA is thus a potential contributory factor for pre-eclampsia, and is associated with endothelial dysfunction in some women [74]. We measured ADMA secretion by H/R-treated placental explants and found a small but significant increase in placental secretion of ADMA (Fig. 5C). In addition to the increase in ADMA, H/R treatment increased nitrotyrosine formation (marker of peroxynitrite formation) [30], but it had no significant effect on the protein levels of P-eNOS or eNOS (Fig. 5B). Conflicting results have been reported with regard to eNOS in pre-eclamptic placentae, ranging from down-regulated [75], unchanged [76], or increased mRNA expression [77]. Increased ADMA and peroxynitrite formation would be indicative of reduced NO bioavailability in H/R-treated explants. Increased concentrations of ADMA might attenuate the physiological vasodilatation of pregnancy and contribute to the development of pre-eclampsia. Not all women with increased ADMA develop pre-eclampsia. Its occurrence might be dependent on genetic polymorphisms of eNOS [78].

One of the proteins secreted by endothelial cells is endothelin (ET), which is a potent vasoconstrictor and pressor agent involved in the regulation of blood pressure. There are four isoforms of ET of which ET-1 is the best studied [79]. Receptors for ET-1 are expressed not only in smooth muscle cells but also in adipocytes and a number of other tissues. ET-1 causes an initial transient fall in blood pressure, followed by a persistent increase in peripheral resistance and blood pressure. ET-1 levels in first trimester plasma samples from women who went on to develop pre-eclampsia were significantly higher than in those who did not [80]. Additionally, long-term infusion of ET-1 into sheep replicated the symptoms of pre-eclampsia i.e. hypertension, proteinuria, and decreased uteroplacental blood flow [81]. We demonstrated an increased immunodetection of ET-1 in H/R-treated placental explants. This immunostaining co-localised with the expression of hydroxynonenal (HNE), a marker of lipid peroxidation, which was also increased in H/R samples compared to controls (Fig. 5D).

Back to Article Outline

11. Conclusion 

Pre-eclampsia is a complex multifactorial disease, where many factors, including genetic predisposition, immunological interactions, maternal endothelial function and environmental factors, interact and culminate in the disease manifestation. Placental oxidative stress, a result of deficient spiral artery remodelling, plays an important role in the pathophysiology of pre-eclampsia. Experiments studying placental ischaemia-reperfusion in vitro or in vivo during labour provide strong evidence that placental oxidative stress and ROS production can potentiate downstream stress and inflammatory signalling pathways, culminating in the release of inflammatory mediators, apoptotic debris, anti-angiogenic factors and other mediators, which then stimulate the maternal inflammatory reaction that manifests in endothelial dysfunction and the symptoms of pre-eclampsia (Fig. 6). Activation of stress-signalling pathways, p38, SAPK/JNK, and of the pro-inflammatory NF-κB pathway seems to play an important role in mediating the effects of placental ischaemia-reperfusion and oxidative stress.

  • View full-size image.
  • Fig. 6 

    A proposed overview summarising how placental-derived factors mediate the symptoms of pre-eclampsia. Deficient conversion of spiral arteries leads to fluctuations in O2 concentration and triggers ischaemia-reperfusion type injury of the placenta and consequent oxidative stress and ER stress. ROS activate various stress pathways, including pro-apoptotic p38 and SAPK/JNK MAPK pathways and inflammatory NF-κB pathway. These pathways promote increased shedding of microparticles, anti-angionenic factors and inflammatory cytokines, which lead to development of the peripheral maternal symptoms.

Back to Article Outline

12. Conflict of interest 

The authors do not have any potential or actual personal, political, or financial interest in the material, information, or techniques described in this paper.

Back to Article Outline

Acknowledgements 

I would like to acknowledge the support of the Wellcome Trust (069027/Z/02/Z) and the guidance and mentoring of Professor Graham J. Burton and Dr D. Stephen Charnock-Jones.

Back to Article Outline

References 

  1. Redman CWG, Sargent IL. Placental debris, oxidative stress and pre-eclampsia. Placenta. 2000;21:597–602
  2. Roberts JM, Lain KY. Recent insights into the pathogenesis of pre-eclampsia. Placenta. 2002;23:359–372
  3. Mutter WP, Karumanchi SA. Molecular mechanisms of preeclampsia. Microvasc Res. 2008;75:1–8
  4. Hubel CA. Oxidative stress in the pathogenesis of preeclampsia. Proc Soc Exp Biol Med. 1999;222:222–235
  5. Burton GJ, Jauniaux E. Placental oxidative stress: from miscarriage to preeclampsia. J Soc Gynecol Investig. 2004;11:342–352
  6. Roberts JM. Endothelial dysfunction in preeclampsia. Semin Reprod Endocrinol. 1998;16:5–15
  7. Redman CW, Sargent IL. Latest advances in understanding preeclampsia. Science. 2005;308:1592–1594
  8. Nathan C, Shiloh MU. Reactive oxygen and nitrogen intermediates in the relationship between mammalian hosts and microbial pathogens. Proc Natl Acad Sci U S A. 2000;97:8841–8848
  9. Droge W. Free radicals in the physiological control of cell function. Physiol Rev. 2002;82:47–95
  10. Trachootham D, Lu W, Ogasawara MA, Nilsa RD, Huang P. Redox regulation of cell survival. Antioxid Redox Signal. 2008;10:1343–1374
  11. Myatt L, Rosenfield RB, Eis AL, Brockman DE, Greer I, Lyall F. Nitrotyrosine residues in placenta. Evidence of peroxynitrite formation and action. Hypertension. 1996;28:488–493
  12. Brosens JJ, Pijnenborg R, Brosens IA. The myometrial junctional zone spiral arteries in normal and abnormal pregnancies: a review of the literature. Am J Obstet Gynecol. 2002;187:1416–1423
  13. Jauniaux E, Ramsay B, Campbell S. Ultrasonographic investigation of placental morphologic characteristics and size during the second trimester of pregnancy. Am J Obstet Gynecol. 1994;170:130–137
  14. Jauniaux E, Jurkovic D, Campbell S. Current topic: in vivo investigation of the placental circulations by Doppler echography. Placenta. 1995;16:323–331
  15. Burton GJ. Hung T-H. Hypoxia–reoxygenation; a potential source of placental oxidative stress in normal pregnancy and preeclampsia. Fetal Maternal Med Rev. 2003;14:97–117
  16. Kaaja R, Tikkanen MJ, Viinikka L, Ylikorkala O. Serum lipoproteins, insulin, and urinary prostanoid metabolites in normal and hypertensive pregnant women. Obstet Gynecol. 1995;85:353–356
  17. Sacks GP, Studena K, Sargent K, Redman CW. Normal pregnancy and preeclampsia both produce inflammatory changes in peripheral blood leukocytes akin to those of sepsis. Am J Obstet Gynecol. 1998;179:80–86
  18. Redman CW, Sacks GP, Sargent IL. Preeclampsia: an excessive maternal inflammatory response to pregnancy. Am J Obstet Gynecol. 1999;180:499–506
  19. Hubel CA, Roberts JM, Taylor RN, Musci TJ, Rogers GM, McLaughlin MK. Lipid peroxidation in pregnancy: new perspectives on preeclampsia. Am J Obstet Gynecol. 1989;161:1025–1034
  20. Haddad JJ. Antioxidant and prooxidant mechanisms in the regulation of redox(y)-sensitive transcription factors. Cell Signal. 2002;14:879–897
  21. Bourdon E, Blache D. The importance of proteins in defense against oxidation. Antioxid Redox Signal. 2001;3:293–311
  22. England K, Cotter TG. Direct oxidative modifications of signalling proteins in mammalian cells and their effects on apoptosis. Redox Rep. 2005;10:237–245
  23. Cross JV, Templeton DJ. Regulation of signal transduction through protein cysteine oxidation. Antioxid Redox Signal. 2006;8:1819–1827
  24. Chiarugi P. PTPs versus PTKs: the redox side of the coin. Free Radic Res. 2005;39:353–364
  25. Cho SH, Lee CH, Ahn Y, Kim H, Kim H, Ahn CY, et al. Redox regulation of PTEN and protein tyrosine phosphatases in H(2)O(2) mediated cell signaling. FEBS Lett. 2004;560:7–13
  26. Reinstein E, Ciechanover A. Narrative review: protein degradation and human diseases: the ubiquitin connection. Ann Intern Med. 2006;145:676–684
  27. Kyriakis JM, Avruch J. Mammalian mitogen-activated protein kinase signal transduction pathways activated by stress and inflammation. Physiol Rev. 2001;81:807–869
  28. Matsuzawa A, Ichijo H. Stress-responsive protein kinases in redox-regulated apoptosis signaling. Antioxid Redox Signal. 2005;7:472–481
  29. Liu H, Nishitoh H, Ichijo H, Kyriakis JM. Activation of apoptosis signal-regulating kinase 1 (ASK1) by tumor necrosis factor receptor-associated factor 2 requires prior dissociation of the ASK1 inhibitor thioredoxin. Mol Cell Biol. 2000;20:2198–2208
  30. Cindrova-Davies T, Spasic-Boskovic O, Jauniaux E, Charnock-Jones DS, Burton GJ. NF-κB, p38 and stress activated protein kinase mitogen-activated protein kinase signaling pathways regulate proinflammatory cytokines and apoptosis in human placental explants in response to oxidative stress. Am J Path. 2007;170:1511–1520
  31. Cook SA, Sugden PH, Clerk A. Activation of c-Jun N-terminal kinases and p38-mitogen-activated protein kinases in human heart failure secondary to ischaemic heart disease. J Mol Cell Cardiol. 1999;31:1429–1434
  32. Cain BS, Meldrum DR, Meng X, Dinarello CA, Shames BD, Banerjee A, et al. p38 MAPK inhibition decreases TNF-alpha production and enhances postischemic human myocardial function. J Surg Res. 1999;83:7–12
  33. Leslie NR. The redox regulation of PI 3-kinase-dependent signaling. Antioxid Redox Signal. 2006;8:1765–1774
  34. Zha J, Harada H, Yang E, Jockel J, Korsmeyer SJ. Serine phosphorylation of death agonist BAD in response to survival factor results in binding to 14-3-3 not BCL-X(L). Cell. 1996;87:619–628
  35. Lawlor MA, Alessi DR. PKB/Akt: a key mediator of cell proliferation, survival and insulin responses?. J Cell Sci. 2001;114:2903–2910
  36. Yung HW, Calabrese S, Hynx D, Hemmings BA, Cetin I, Charnock-Jones DS, et al. Evidence of placental translation inhibition and endoplasmic reticulum stress in the etiology of human intrauterine growth restriction. Am J Pathol. 2008;173:451–462
  37. Karin M. Nuclear factor-kappaB in cancer development and progression. Nature. 2006;441:431–436
  38. Hajra L, Evans AI, Chen M, Hyduk SJ, Collins T, Cybulsky MI. The NF-kappa B signal transduction pathway in aortic endothelial cells is primed for activation in regions predisposed to atherosclerotic lesion formation. Proc Natl Acad Sci U S A. 2000;97:9052–9057
  39. Ungvari Z, Orosz Z, Labinskyy N, Rivera A, Xiangmin Z, Smith K, et al. Increased mitochondrial H2O2 production promotes endothelial NF-kappaB activation in aged rat arteries. Am J Physiol Heart Circ Physiol. 2007;293:H37–H47
  40. Xu C, Bailly-Maitre B, Reed JC. Endoplasmic reticulum stress: cell life and death decisions. J Clin Invest. 2005;115:2656–2664
  41. Cullinan SB, Diehl JA. Coordination of ER and oxidative stress signaling: the PERK/Nrf2 signaling pathway. Int J Biochem Cell Biol. 2006;38:317–332
  42. Yoshida H. ER stress and diseases. FEBS J. 2007;274:630–658
  43. Zhang K, Kaufman RJ. From endoplasmic-reticulum stress to the inflammatory response. Nature. 2008;454:455–462
  44. Ozcan U, Yilmaz E, Ozcan L, Furuhashi M, Vaillancourt E, Smith RO, et al. Chemical chaperones reduce ER stress and restore glucose homeostasis in a mouse model of type 2 diabetes. Science. 2006;313:1137–1140
  45. Luppi P, Tse H, Lain KY, Markovic N, Piganelli JD, DeLoia JA. Preeclampsia activates circulating immune cells with engagement of the NF-kappaB pathway. Am J Reprod Immunol. 2006;56:135–144
  46. McCracken SA, Drury CL, Lee HS, Morris JM. Pregnancy is associated with suppression of the nuclear factor kappaB/IkappaB activation pathway in peripheral blood mononuclear cells. J Reprod Immunol. 2003;58:27–47
  47. Shah TJ, Walsh SW. Activation of NF-kappaB and expression of COX-2 in association with neutrophil infiltration in systemic vascular tissue of women with preeclampsia. Am J Obstet Gynecol. 2007;196(48):e1–e8
  48. Takacs P, Kauma SW, Sholley MM, Walsh SW, Dinsmoor MJ, Green K. Increased circulating lipid peroxides in severe preeclampsia activate NF-kappaB and upregulate ICAM-1 in vascular endothelial cells. FASEB J. 2001;15:279–281
  49. Levine RJ, Maynard SE, Qian C, Lim KH, England LJ, Yu KF, et al. Circulating angiogenic factors and the risk of preeclampsia. N Engl J Med. 2004;350:672–683
  50. Maynard SE, Min JY, Merchan J, Lim KH, Li J, Mondal S, et al. Excess placental soluble fms-like tyrosine kinase 1 (sFlt1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia. J Clin Invest. 2003;111:649–658
  51. Brar H, Einarson A. Effects and treatment of inflammatory bowel disease during pregnancy. Can Fam Physician. 2008;54:981–983
  52. Vivekananthan DP, Penn MS, Sapp SK, Hsu A, Topol EJ. Use of antioxidant vitamins for the prevention of cardiovascular disease: meta-analysis of randomised trials. Lancet. 2003;361:2017–2023
  53. Lonn E, Bosch J, Yusuf S, Sheridan P, Pogue J, Arnold JM, et al. Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial. JAMA. 2005;293:1338–1347
  54. Poston L, Briley AL, Seed PT, Kelly FJ, Shennan AH. Vitamin C and vitamin E in pregnant women at risk for pre-eclampsia (VIP trial): randomised placebo-controlled trial. Lancet. 2006;367:1145–1154
  55. Rumbold AR, Crowther CA, Haslam RR, Dekker GA, Robinson JS. Vitamins C and E and the risks of preeclampsia and perinatal complications. N Engl J Med. 2006;354:1796–1806
  56. Catov JM, Bodnar LM, Ness RB, Markovic N, Roberts JM. Association of periconceptional multivitamin use and risk of preterm or small-for-gestational-age births. Am J Epidemiol. 2007;166:296–303
  57. Haugen M, Meltzer HM, Brantsaeter AL, Mikkelsen T, Osterdal ML, Alexander J, et al. Mediterranean-type diet and risk of preterm birth among women in the Norwegian Mother and Child Cohort Study (MoBa): a prospective cohort study. Acta Obstet Gynecol Scand. 2008;87:319–324
  58. Aravanis C, Corcondilas A, Dontas AS, Lekos D, Keys A. Coronary heart disease in seven countries. IX. The Greek islands of Crete and Corfu. Circulation. 1970;41:I88–I100
  59. Ueda S, Masutani H, Nakamura H, Tanaka T, Ueno M, Yodoi J. Redox control of cell death. Antioxid Redox Signal. 2002;4:405–414
  60. Shen HM, Pervaiz S. TNF receptor superfamily-induced cell death: redox-dependent execution. FASEB J. 2006;20:1589–1598
  61. Leung DN, Smith SC, To KF, Sahota DS, Baker PN. Increased placental apoptosis in pregnancies complicated by preeclampsia. Am J Obstet Gynecol. 2001;184:1249–1250
  62. Schrocksnadel H, Daxenbichler G, Artner E, Steckel-Berger G, Dapunt O. Tumor markers in hypertensive disorders of pregnancy. Gynecol Obstet Invest. 1993;35:204–208
  63. Lo YM, Leung TN, Tein MS, Sargent IL, Zhang J, Lau TK, et al. Quantitative abnormalities of fetal DNA in maternal serum in preeclampsia. Clin Chem. 1999;45:184–188
  64. Knight M, Redman CW, Linton EA, Sargent IL. Shedding of syncytiotrophoblast microvilli into the maternal circulation in pre-eclamptic pregnancies. Br J Obstet Gynaecol. 1998;105:632–640
  65. Tjoa M-L, Cindrova-Davies T, Spasic-Boskovic O, Bianchi DW, Burton GJ. Trophoblastic oxidative stress and the release of cell-free feto-placental DNA. Am J Path. 2006;169:400–404
  66. Hung TH, Skepper JN, Charnock-Jones DS, Burton GJ. Hypoxia–reoxygenation: a potent inducer of apoptotic changes in the human placenta and possible etiological factor in preeclampsia. Circ Res. 2002;90:1274–1281
  67. Cindrova-Davies T, Yung HW, Johns J, Spasic-Boskovic O, Korolchuk S, Jauniaux E, et al. Oxidative stress, gene expression, and protein changes induced in the human placenta during labor. Am J Pathol. 2007;171:1168–1179
  68. Germain SJ, Sacks GP, Sooranna SR, Sargent IL, Redman CW. Systemic inflammatory priming in normal pregnancy and preeclampsia: the role of circulating syncytiotrophoblast microparticles. J Immunol. 2007;178:5949–5956
  69. Jung Y-J, Isaacs JS, Lee S, Trepel J, Neckers L. IL-1β mediated up-regulation of HIF-1α via an NFκB/COX-2 pathway identifies HIF-1 as a critical link between inflammation and oncogenesis. FASEB J. 2003;17:2115–2117
  70. Jung Y-J, Isaacs JS, Lee S, Trepel J, Liu ZG, Neckers L. Hypoxia-inducible factor induction by tumour necrosis factor in normoxic cells requires receptor-interacting protein-dependent nuclear factor kappaB activation. Biochem J. 2003;370:1011–1017
  71. Jung Y-J, Isaacs JS, Lee S, Trepel J, Neckers L. Microtubule disruption utilizes an NFkappa B-dependent pathway to stabilize HIF-1alpha protein. J Biol Chem. 2003;278:7445–7452
  72. Venkatesha S, Toporsian M, Lam C, Hanai J, Mammoto T, Kim YM, et al. Soluble endoglin contributes to the pathogenesis of preeclampsia. Nat Med. 2006;12:642–649
  73. Schnabel R, Blankenberg S, Lubos E, Lackner KJ, Rupprecht HJ, Espinola-Klein C, et al. Asymmetric dimethylarginine and the risk of cardiovascular events and death in patients with coronary artery disease: results from the AtheroGene Study. Circ Res. 2005;97:e53–e59
  74. Savvidou MD, Hingorani AD, Tsikas D, Frolich JC, Vallance P, Nicolaides KH. Endothelial dysfunction and raised plasma concentrations of asymmetric dimethylarginine in pregnant women who subsequently develop pre-eclampsia. Lancet. 2003;361:1511–1517
  75. Kim YJ, Park HS, Lee HY, Ha EH, Suh SH, Oh SK, et al. Reduced l-arginine level and decreased placental eNOS activity in preeclampsia. Placenta. 2006;27:438–444
  76. Orange SJ, Painter D, Horvath J, Yu B, Trent R, Hennessy A. Placental endothelial nitric oxide synthase localization and expression in normal human pregnancy and pre-eclampsia. Clin Exp Pharmacol Physiol. 2003;30:376–381
  77. Napolitano M, Miceli F, Calce A, Vacca A, Gulino A, Apa R, et al. Expression and relationship between endothelin-1 messenger ribonucleic acid (mRNA) and inducible/endothelial nitric oxide synthase mRNA isoforms from normal and preeclamptic placentas. J Clin Endocrinol Metab. 2000;85:2318–2323
  78. Yoshimura T, Yoshimura M, Tabata A, Shimasaki Y, Nakayama M, Miyamoto Y, et al. Association of the missense Glu298Asp variant of the endothelial nitric oxide synthase gene with severe preeclampsia. J Soc Gynecol Investig. 2000;7:238–241
  79. Sokolovsky M. Endothelin receptor subtypes and their role in transmembrane signaling mechanisms. Pharmacol Ther. 1995;68:435–471
  80. Nova A, Sibai BM, Barton JR, Mercer BM, Mitchell MD. Maternal plasma level of endothelin is increased in preeclampsia. Am J Obstet Gynecol. 1991;165:724–727
  81. Greenberg SG, Baker RS, Yang D, Clark KE. Effects of continuous infusion of endothelin-1 in pregnant sheep. Hypertension. 1997;30:1585–1590

PII: S0143-4004(08)00388-3

doi:10.1016/j.placenta.2008.11.020

Placenta
Volume 30, Supplement , Pages 55-65, March 2009

Article Tools

* Image Usage & Resolution