Excess placental soluble fms-like tyrosine kinase 1 (sFlt1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia

Genetic dissection of tumor angiogenesis: are PlGF and VEGFR-1 novel anti-cancer targets?

Many proliferative diseases, most typically cancer, are driven by uncontrolled blood vessel growth. Genetic studies have been very helpful in unraveling the cellular and molecular players in pathological blood vessel formation and have provided opportunities to reduce tumor growth and metastasis. The fact that tumor vessels and normal blood vessels have distinct properties may help in designing more specific--and therefore safer--anti-angiogenic strategies. Such strategies may interfere with angiogenesis at the cellular or molecular level. Possible molecular targets include angiogenic growth factors and their receptors, proteinases, coagulation factors, junctional/adhesion molecules and extracellular matrix (ECM) components. Some anti-angiogenic drugs, i.e., vascular endothelial growth factor (VEGF) antibodies and VEGF receptor-2 (VEGFR-2) inhibitors, have progressed into clinical cancer trials. While the results of these trials support the potential of anti-angiogenic therapy to treat cancer, they also demonstrate the need for more effective and safer alternatives. Targeting placental growth factor (PlGF) or VEGFR-1 may constitute such an alternative since animal studies have proven their pleiotropic working mechanism and attractive safety profile. Together, these insights may bring anti-angiogenic drugs closer from bench to bedside.

Leukocyte adhesion molecules and reactive oxygen species in preeclampsia

OBJECTIVE

The aim of our study was to compare the expression of leukocyte adhesion molecules, intracellular reactive oxygen species, and vasoactive substances in preeclampsia and matched normotensive pregnancies and to explore differences between pregnancy and the nonpregnant state regarding these parameters.

METHODS

Flow cytometry was used to analyze the monocyte and granulocyte expression of adhesion molecules from 20 matched pairs of preeclampsia/normotensive pregnancies and 12 nonpregnant subjects. Basal levels of CD11b, CD11c, CD62L, and CD14 were measured. In addition, expression of human lymphocyte antigen-DR, CD4, CD8, and CD4/CD8 ratio were assessed. Basal reactive oxygen species levels, as well as reactivity upon in vitro stimulation with phorbol 12-myristate 13-acetate, were measured in monocytes and granulocytes with the probes dihydroethidium, dichlorofluorescein-diacetate, and dihydrorhodamine-123. Further, the plasma levels of endothelin-1, the nitric oxide metabolites nitrite/nitrate, and total antioxidant status were analyzed.

RESULTS

Monocytes expressed significantly higher levels of CD11b and CD14 in preeclamptic patients compared with normotensive pregnant subjects, whereas CD11c was elevated on both monocytes and granulocytes in pregnancy compared with the nonpregnant state. Both monocytes and granulocytes displayed higher basal, as well as phorbol 12-myristate 13-acetate-stimulated, amounts of reactive oxygen species in the preeclampsia group compared with the normotensive group. We also found the endothelin-1 and antioxidant levels significantly elevated in preeclampsia patients compared with normotensive subjects, whereas no differences were seen between the groups regarding nitrite/nitrate levels.

CONCLUSION

These results show that the maternal blood leukocytes are activated in preeclampsia and support the view that oxidative stress is a contributing factor in the pathophysiology of preeclampsia.

Evidence supporting a role for blockade of the vascular endothelial growth factor system in the pathophysiology of preeclampsia. Young Investigator Award

OBJECTIVE

Soluble vascular endothelial growth factor receptor 1 (sVEGFR-1), which antagonizes VEGF functions, has been implicated in the pathophysiology of preeclampsia. The purpose of this study was to determine whether preeclampsia is associated with a change in the plasma concentration of sVEGFR-1, and, if so, whether such a change is correlated with the severity of the disease.

METHODS

A cross-sectional study was conducted to determine the concentrations of sVEGFR-1 in plasma obtained from normal pregnant women (n=61) and patients with preeclampsia (n=61). Plasma concentrations of sVEGFR-1 were determined by enzyme-linked immunoassay.

RESULTS

Preeclampsia had a higher median plasma concentration of sVEGFR-1 than normal pregnancy (P <.001). The median plasma concentration of sVEGFR-1 was higher in early-onset (< or =34 weeks) than late-onset (>34 weeks) preeclampsia (P=.005), and higher in severe than in mild preeclampsia (P=.002). In normal pregnancy, there was a correlation between plasma concentration of sVEGFR-1 and gestational age (r=0.5; P <.001). In contrast, there was a negative correlation between plasma concentration of sVEGFR-1 and gestational age at the onset of preeclampsia (r=-0.5; P <.001).

CONCLUSION

Preeclampsia is associated with an increased plasma sVEGFR-1 concentration. The elevation of sVEGFR-1 concentration is correlated with the severity of the disease. These observations suggest the participation of VEGF and its soluble receptor in the pathophysiology of preeclampsia.

Avancées dans la physiopathologie de la pré-éclampsie : place de la réponse inflammatoire

Inflammatory response is a major component in physiopathology of preeclampsia and intra-uterine growth retardation. Endothelium is a main connection between placental ischemia and clinical manifestations during vascular pregnancy complications. In this review recent findings concerning inflammatory response and its links with endothelium are reported. Studies concerning isolated intra-uterine growth retardation confirm the hypothesis of a similar pathophysiology with an activation confined to utero-placental bed or at a lower level. Current information on oxidative stress, atherosclerosis, and apoptosis in vascular pregnancy complications are available in this review. These concepts offer innovative possibilities of treatment.

A Naturally Occurring Soluble Form of Vascular Endothelial Growth Factor Receptor 2 Detected in Mouse and Human Plasma

Angiogenesis and vasculogenesis are regulated in large part by several different growth factors and their associated receptor tyrosine kinases (RTKs). Foremost among these is the vascular endothelial growth factor (VEGF) family including VEGF receptor (VEGFR)-2 and -1. VEGFR ligand binding and biological activity are regulated at many levels, one of which is by a soluble, circulating form of VEGFR-1 (sVEGFR-1). This sVEGFR-1 can act as a competitive inhibitor of its ligand, serve as a possible biomarker, and play important roles in cancer and other diseases such as preeclampsia. Recombinant forms of sVEGFR-2 have been shown to have antiangiogenic activity, but a naturally occurring sVEGFR-2 has not been described previously. Here, we report such an entity. Having a molecular weight of ∼160 kDa, sVEGFR-2 can be detected in mouse and human plasma with several different monoclonal and polyclonal anti-VEGFR-2 antibodies using both ELISA and immunoprecipitation techniques. In vitro studies have determined that the sVEGFR-2 fragment can be found in the conditioned media of mouse and human endothelial cells, thus suggesting that it may be secreted, similar to sVEGFR-1, or proteolytically cleaved from the cell. Potential biological activity of this protein was inferred from experiments in which mouse sVEGFR-2 could bind to VEGF-coated plates. Similar to sVEGFR-1 and other soluble circulating RTKs, sVEGFR-2 may have regulatory consequences with respect to VEGF-mediated angiogenesis as well as potential to serve as a quantitative biomarker of angiogenesis and antiangiogenic drug activity, particularly for drugs that target VEGF or VEGFR-2.

Clinical management of thrombophilia-related placental vascular complications

Pregnancy is a hypercoagulable state with an increased thrombotic risk throughout gestation and the postpartum period. Women with thrombophilia may have a further increased risk of placental vascular complications, including pregnancy loss, preeclampsia, intrauterine growth restriction, and placental abruption. Preliminary data suggest that maternal antithrombotic prophylaxis may result in improved gestational outcome. Randomized trials are under way and hopefully will optimize maternal and neonatal outcome.

CD40-induced transcriptional activation of vascular endothelial growth factor involves a 68-bp region of the promoter containing a CpG island

Vascular endothelial growth factor (VEGF) is produced by several cell types in the kidney, and its expression is tightly regulated for the maintenance of normal renal physiology. Increases or decreases in its expression are associated with proteinuria and renal disease. Recently, we found that the expression of VEGF is markedly induced following interactions between CD40 ligand (CD40L) and CD40. Here, endothelial cells (EC) or Jurkat T cell lines were transiently transfected with luciferase reporter constructs under the control of the human VEGF promoter and were treated with human soluble CD40L (sCD40L). We identified a CD40-responsive 68-bp region (bp -50 to +18) of the promoter and 43 bp within this region (bp -25 to +18) that have 97% homology to a sequence of CpG dinucleotides. A computerized search revealed that the CpG region has putative binding domains for the transcriptional repressor protein methyl CpG binding protein-2 (MeCP2). In EMSA, we found that the 43-bp methylated sequence formed four complex(es) with nuclear extracts from untreated EC and reduced binding of at least one complex when nuclear lysates from sCD40L-activated EC (30 min) were used. Supershift analysis using anti-MeCP2 demonstrated that most of the complex(es) in both untreated and sCD40L-activated EC involved interactions between the 43-bp DNA and MeCP2. In addition, we found that other CpG binding proteins may also interact with this region of the promoter. Taken together, this is the first demonstration that CpG binding transcriptional repressor proteins including MeCP2 may be of importance in VEGF biology.

Endothelium as an organ system

The endothelium is a highly dynamic cell layer that is involved in a multitude of physiologic functions, including the control of vasomotor tone, the trafficking of cells and nutrients, the maintenance of blood fluidity, and the growth of new blood vessels. Over the past several decades, advances in basic research of the endothelium have far outstripped those in the clinic. One explanation for this growing bench-to-bedside chasm relates to the inflexible and largely outdated nature of the present-day medical infrastructure. The constraints of medical subspecialization have created a conceptual blind spot, namely, the inability to appreciate the endothelium for what it is: a cell layer that is teeming with life, every bit as active as any other organ in the body. The overall goal of this review is to bring the endothelium "to life" and to argue that future breakthroughs in biomedicine are contingent on acceptance of the endothelium as a bona fide organ system.

Maternal vascular underperfusion: nosology and reproducibility of placental reaction patterns

Placental examination can be a useful tool for specifying the etiology, prognosis, and recurrence risk of pregnancy disorders. The purpose of this study was to test the reliability of a predetermined set of placental reaction patterns seen with maternal vascular underperfusion in the hope that this might provide a useful diagnostic framework for practicing pathologists. Study cases (14 with clinical and pathologic evidence of maternal underperfusion plus 6 controls) were evaluated for the presence or absence of 11 lesions by eight perinatal pathologists. After analysis of initial results, diagnostic criteria were refined and a second, overlapping set of cases was reviewed. The collective sensitivity, specificity, and efficiency of individual assessments for the 11 lesions relative to the group consensus ranged from 74-93% (22/33 > 90%). Reproducibility was measured by unweighted kappa-values and interpreted as follows: < 0.2 poor, 0.2-0.6 fair/moderate, > 0.6 substantial. Kappa values for lesions affecting villi and the intervillous space were increased syncytial knots (any -0.42, severe -0.50), villous agglutination (0.42), increased intervillous fibrin (0.25), and distal villous hypoplasia (0.57). Individual estimates of percent involvement for syncytial knots, intervillous fibrin, and distal villous hypoplasia were correlated with placental and fetal weight for gestational age. Extent of increased intervillous fibrin showed the strongest correlation with both placental weight ( R = -0.64) and fetal weight ( R = -0.45). Kappa values for lesions affecting maternal vessels and the implantation site were acute atherosis (0.50), mural hypertrophy of membrane arterioles (0.43), muscularized basal plate arteries (0.48), increased placental site giant cells (0.54), and immature intermediate trophoblast (0.36). Correlation of maternal vessel and implantation site lesions with the clinical diagnosis of preeclampsia showed that excessive placental site giant cells and immature intermediate trophoblast were more sensitive and efficient predictors, whereas atherosis and muscularized basal plate arteries were more specific. Kappa value for a thin umbilical cord, a possible indicator of fetal volume depletion, was 0.61. Reproducibility for a global impression of maternal vascular underperfusion, taking into account all of the above lesions, was moderate (kappa 0.54) and improved after inclusion of additional pathologic and clinical data (kappa 0.68). Adoption of this clearly defined, clinically relevant, and pathologically reproducible terminology could enhance clinicopathologic correlation and provide a more objective framework for future clinical research.

A podocentric view of nephrology

PURPOSE OF REVIEW

The glomerular visceral epithelial cell plays a central role in ultrafiltration of the blood and in a wide variety of inherited and acquired diseases of the kidney. The discovery of nephrin and other slit diaphragm proteins has led to an explosion of knowledge in the biology of this cell type. The most significant recent discoveries are reviewed in this paper.

RECENT FINDINGS

Together with the glomerular endothelial cells and intervening glomerular basement membrane, the podocyte constitutes a major portion of the glomerular filtration barrier that separates blood from the urinary space. A number of proteins have been identified that are localized to the slit diaphragms that separate podocyte foot processes. Although it has been suggested that the slit diaphragm represents the ultimate filtration barrier, additional roles for this structure as a signaling centre and in endocytosis have been identified. Mutations in genes that reside in the slit pore or interact with the actin cytoskeleton have been linked to a variety of inherited diseases of the podocyte. Additional mutations in these genes have been linked to sporadic forms of nephrotic syndrome and proposed as modifiers of renal risk. The generation of podocyte-specific transgenic models and genomic tools for the murine podocyte provide important resources for the glomerular biologist.

SUMMARY

Over the past year, studies using human genetics, conditional gene targeting and cell biological approaches have led to a rapid increase in our understanding of podocyte and glomerular biology, which should lead to the development of novel therapies for individuals with glomerular disease.

Differential expression of vascular endothelial growth factor (VEGF), endocrine gland derived-VEGF, and VEGF receptors in human placentas from normal and preeclamptic pregnancies

Vascular endothelial growth factor (VEGF) is a potent regulator of placental vascular function. Endothelial dysfunction is a key factor associated with preeclampsia. In this study, we examined expression of VEGF, endocrine gland-derived VEGF (EG-VEGF), VEGF receptors 1 and 2 (VEGFR-1 and VEGFR-2), and neuropilin-1 and -2 (NP-1 and NP-2) in human placentas from women with normal and preeclamptic (PE) pregnancies using quantitative or semiquantitative PCR. We found that total VEGF mRNA expression was increased 2.8-fold (P < 0.05), along with increases in mRNA expression of VEGF121, 165, and 189 (P < 0.05; 1.7-, 1.9-, and 1.8-fold, respectively) in PE vs. normal placentas. Expression of VEGFR-1 mRNA, but not EG-VEGF and the other three VEGF receptors studied, was elevated (P < 0.05) 2.7-fold in PE vs. normal placentas. Protein expression of VEGF and its four receptors was determined using Western blot analysis. For VEGF, two major isoforms (VEGF165 and 189) were detected. For VEGFR-1, VEGFR-2, NP-1, and NP-2, one major band was observed at 180, 235, 130, and 130 kDa, respectively. All of these bands were corresponding to their positive controls. Of these five proteins studied, only VEGFR-1 levels were increased (P < 0.05; 1.7-fold) in PE placentas. The expression of VEGF and the four VEGF receptors was confirmed using immunohistochemistry. They were primarily present in syncytiotrophoblasts and endothelial cells of villous capillaries and large vessels. Thus, together with previous reports that VEGFR-1 mediates trophoblast function and inhibits VEGF-induced angiogenesis and endothelium-dependent vasodilation, these data suggest that the increased VEGFR-1 expression may alter VEGF- mediated function on trophoblast and endothelial cells in PE placentas.

Vascular factors altered in glucose-treated mesangial cells and diabetic glomeruli. Changes in vascular factors impair endothelial cell growth and matrix

We studied the effect of a high glucose (HG) environment on the vascular factors that are secreted by mesangial cells, and regulate endothelial growth and mesangial matrix deposition. To this effect, we measured the vascular factors in the glomeruli of streptozotocin-induced diabetic kidneys and in mesangial cells exposed to a HG concentration. We then transferred the media of mesangial cells previously exposed to high glucose to cultured endothelial cells to study the effects on endothelial growth, matrix formation, and in vitro capillary proliferation. In 1-week diabetic kidneys, glomerular vascular endothelial growth factor (VEGF) and angiopoietin-1 were inhibited by 38 and 57%, respectively, but angiopoietin-2 was increased by 318%. We found similar results in mesangial cells exposed to HG. There was a decrease of VEGF (50% by enzyme immunoassay, 27% by mRNA), decrease of angiopoietin-1 (65% by mRNA), and a much greater increase of angiopoietin-2 (280% by immunoassay, 523% by mRNA). Compared to controls, the media of mesangial cells previously exposed to HG impaired endothelial cell growth by 61%, increased extracellular matrix by 100%, and decreased capillary formation by 90%. We conclude that high ambient glucose alters the secretion of vascular factors elaborated by mesangial cells, resulting in an expansion of the endothelial cell matrix and disruption of capillary structure.

The pathogenesis of fibrosis and renal disease in scleroderma: Recent insights from glomerulosclerosis

Acute and chronic renal diseases remain common complications of systemic sclerosis. Although treatment for acute scleroderma renal crisis may arrest the rapid progression of renal disease, many patients develop persistent renal dysfunction. Based on recent insights gained from progressive renal diseases of diverse etiologies, novel approaches to understanding the pathobiology of scleroderma renal disease may be applicable. Key factors involved in progression of renal disease include accumulation of extracellular matrix in the glomerular and tubulointerstitial compartments, epithelial to mesenchymal transformation, and vascular changes. The relevant factors mediating these events include the renin-angiotensin system, the profibrotic growth factors, transforming growth factor-beta and connective tissue growth factor, and reactive oxygen species. Much of the molecular details of the role of these factors have been revealed and promise to alter the practice of therapy of progressive renal disease.

Determinants of Placental Vascularity

PROBLEM

Vascular growth during implantation and placentation is critical for successful gestation and it is thought that vascular insufficiencies during placentation contribute to a number of obstetrical complications. However, relatively little is known regarding the regulation of angiogenesis in the placenta.

METHOD OF STUDY

We review literature concerning the potential significance of inadequate placental vascularity as a contributor to the obstetrical complications of spontaneous abortion, fetal growth restriction and preeclampsia. Gene expression assays were used to compare fluctuations of placenta growth factor (PlGF) and PlGF receptor expression in normal and preeclamptic trophoblast in vitro.

RESULTS

Studies have shown that common obstetrical complications manifest altered placental vascularity. Both intrinsic defects (gene knockouts) and extrinsic factors (O(2) tension, cytokines, etc) may be responsible for the defects. Some of these factors have been shown to influence trophoblast vascular endothelial growth factor (VEGF)/PlGF expression suggesting this particular family of angiogenic proteins play an important role in placental angiogenesis.

CONCLUSION

Placental vascularization reflects a complex interaction of regulatory factors. Understanding the regulation of vascular growth in the placenta will provide much needed insight into placenta-related vascular insufficiencies.

Insulin resistance and alterations in angiogenesis: additive insults that may lead to preeclampsia

Altered angiogenesis and insulin resistance, which are intimately related at a molecular level, characterize preeclampsia. To test if an epidemiological interaction exists between these two alterations, we performed a nested case-control study of 28 women who developed preeclampsia and 57 contemporaneous controls. Serum samples at 12 weeks of gestation were measured for sex hormone binding globulin (SHBG; low levels correlate with insulin resistance) and placental growth factor (PlGF; a proangiogenic molecule). Compared with controls, women who developed preeclampsia had lower serum levels of SHBG (208+/-116 versus 256+/-101 nmol/L, P=0.05) and PlGF (16+/-14 versus 67+/-150 pg/mL, P<0.001), and in multivariable analysis, women with serum levels of PlGF < or =20 pg/mL had an increased risk of developing preeclampsia (odds ratio [OR] 7.6, 95% CI 1.4 to 38.4). Stratified by levels of serum SHBG (< or =175 versus >175 mg/dL), women with low levels of SHBG and PlGF had a 25.5-fold increased risk of developing preeclampsia (P=0.10), compared with 1.8 (P=0.38) among women with high levels of SHBG and low levels of PlGF. Formal testing for interaction (PlGFxSHBG) was significant (P=0.02). In a model with 3 (n-1) interaction terms (high PlGF and high SHBG, reference), the risk for developing preeclampsia was as follows: low PlGF and low SHBG, OR 15.1, 95% CI 1.7 to 134.9; high PlGF and low SHBG, OR 4.1, 95% CI 0.45 to 38.2; low PlGF and high SHBG, OR 8.7, 95% CI 1.2 to 60.3. Altered angiogenesis and insulin resistance are additive insults that lead to preeclampsia.

Two-stage elevation of cell-free fetal DNA in maternal sera before onset of preeclampsia

OBJECTIVE

The purpose was to determine whether preeclampsia (PE) is caused by microfragments of syncytial trophoblast shed into the maternal circulation that stimulate an exaggerated inflammatory response.

STUDY DESIGN

A nested case control study was performed within the Calcium for Preeclampsia Prevention trial cohort of healthy nulliparous women. Each preeclampsia case was matched to 1 normotensive control. One hundred twenty pairs were randomly chosen for analysis of serum cell-free fetal DNA (cffDNA), a marker of placental debris, and C-reactive protein (CRP), a marker of inflammation, in all 658 specimens obtained before labor.

RESULTS

At 29 to 41 weeks of gestation, cffDNA concentrations were significantly higher after preeclampsia than before (219 vs 112 genome equivalents [GE]/mL, P<.001). Before preeclampsia, cffDNA in cases exceeded controls at 17 to 28 weeks (36 vs 16 GE/mL, P<.001), but at 29 to 41 weeks, only within 3 weeks before preeclampsia (176 vs 75 GE/mL, P<.001). CRP serum concentrations were neither associated with cffDNA nor elevated before preeclampsia.

CONCLUSION

Preeclampsia is accompanied by a 2-stage elevation of fetal DNA, but not by elevation of CRP. Elevated cffDNA at 17 to 28 weeks may be due to placental necrosis and apoptosis. Subsequent elevations may reflect impaired DNA elimination. The 2-stage elevation suggests the possibility of measurement of fetal DNA both to screen for preeclampsia and to indicate impending clinical disease.

Circulating angiogenic factors and the risk of preeclampsia

BACKGROUND

The cause of preeclampsia remains unclear. Limited data suggest that excess circulating soluble fms-like tyrosine kinase 1 (sFlt-1), which binds placental growth factor (PlGF) and vascular endothelial growth factor (VEGF), may have a pathogenic role.

METHODS

We performed a nested case-control study within the Calcium for Preeclampsia Prevention trial, which involved healthy nulliparous women. Each woman with preeclampsia was matched to one normotensive control. A total of 120 pairs of women were randomly chosen. Serum concentrations of angiogenic factors (total sFlt-1, free PlGF, and free VEGF) were measured throughout pregnancy; there were a total of 655 serum specimens. The data were analyzed cross-sectionally within intervals of gestational age and according to the time before the onset of preeclampsia.

RESULTS

During the last two months of pregnancy in the normotensive controls, the level of sFlt-1 increased and the level of PlGF decreased. These changes occurred earlier and were more pronounced in the women in whom preeclampsia later developed. The sFlt-1 level increased beginning approximately five weeks before the onset of preeclampsia. At the onset of clinical disease, the mean serum level in the women with preeclampsia was 4382 pg per milliliter, as compared with 1643 pg per milliliter in controls with fetuses of similar gestational age (P<0.001). The PlGF levels were significantly lower in the women who later had preeclampsia than in the controls beginning at 13 to 16 weeks of gestation (mean, 90 pg per milliliter vs. 142 pg per milliliter, P=0.01), with the greatest difference occurring during the weeks before the onset of preeclampsia, coincident with the increase in the sFlt-1 level. Alterations in the levels of sFlt-1 and free PlGF were greater in women with an earlier onset of preeclampsia and in women in whom preeclampsia was associated with a small-for-gestational-age infant.

CONCLUSIONS

Increased levels of sFlt-1 and reduced levels of PlGF predict the subsequent development of preeclampsia.

Uric acid, endothelial dysfunction and pre-eclampsia

BACKGROUND

Pre-eclampsia is strongly associated with hyperuricemia, and in some studies the increase in serum uric acid has been found to correlate with both maternal and fetal morbidity. The hyperuricemia is believed to result primarily from the decreased renal excretion that occurs as a consequence of the pre-eclampsia, and as such is widely viewed as a marker for pre-eclampsia as opposed to having a role in the pathogenesis.

HYPOTHESIS

We present the hypothesis that hyperuricemia may also have a contributory role in the development of hypertension and renal disease in these patients, and we review recent experimental data that would support this hypothesis.

RECOMMENDATION

We suggest that studies addressing the role of uric acid in pre-eclampsia may provide new insights into both the pathogenesis and treatment of this condition.

Confocal laser scanning microscope study of cytokeratin immunofluorescence differences between villous and extravillous trophoblast: Cytokeratin downregulation in pre-eclampsia

Pre-eclampsia is a disease characterized by failures in interstitial implantation. One product of the implantation process is the basal plate; a structure whose complexity makes it hard to fully appreciate the pathological changes in significant diseases of pregnancy. This article describes our use of CLSM immunofluorescence to examine the cytokeratin composition of the cells of trophoblastic origin in the term placental basal plate. Large differences in the content of the structural polymeric protein were compared using analysis of digital images. We show that greater pancytokeratin immunofluorescence is observed in extravillous cytotrophoblast cells as compared with villous trophoblast. There is a >30-fold difference in the mean area percent of the most intensely immunofluorescent pixels in the tissue containing these cells. This is a very high, statistically significant difference as defined by the Wilcoxon Signed Ranks Test Asym. Sig. (two-tailed): P < 0.001. The most invasive population of cells of the trophoblast lineage (the extravillous trophoblast) exhibits a significant reduction in cytokeratin immunofluorescence when comparisons of healthy and pre-eclamptic pregnancies are made. This ratio was 2.4:1. It was tested using the Mann-Whitney U-test. From healthy to pre-eclamptic the reduction was from mean rank 83.42((healthy)) to 51.13((pre-eclamptic)). The difference was very highly statistically significant (n = 53 + 75 = 128; U = 984.500; Z = -4.852; P < 0.001). There was also less cytokeratin-related immunofluorescence in villous trophoblast when healthy villi were compared with pre-eclamptic villi. The observed alterations in trophoblastic cytoskeletal components are expected to damage the anchorage and motility of cells. The extravillous trophoblast is known to be necessary for implantation. This leads to a cellular hypothesis of the failure of implantation resulting in reduced depth of uterine invasion and failure to adapt the spiral arterioles for low-pressure perfusion of the intervillus space, two well-known features of pre-eclampsia. The reduction in cytokeratin-related immunofluorescence in the villus trophoblast seen on comparing healthy term placentae with those from pre-eclamptics implies that the trophoblast is a weaker epithelial layer in the hypertensive pregnancy. This could account for the rise in deported trophoblast associated with pre-eclampsia. Deported trophoblast has been invoked as the systemic messenger that leads to generalized maternal hypertension seen in this condition.

Increased endothelial uptake of paclitaxel as a potential mechanism for its antiangiogenic effects: Potentiation by Cox-2 inhibition

Paclitaxel has antiangiogenic properties, but the mechanisms for the enhanced sensitivity of endothelial cells (ECs) to this drug are not established. The aims of our study were to compare the distribution of paclitaxel into ECs with other cell types, to assess the effects of low doses of paclitaxel on Cox-2 expression and to determine the combined effects of paclitaxel and Cox-2 inhibitors on angiogenesis in vitro and in patients with cancer. Upon exposure to low (5 nM) concentrations of [3H]-paclitaxel, uptake of radioactivity was more than 5 times higher in ECs than other cell types. Exposing human umbilical vein ECs to low nanomolar (1-50 nM) concentrations of paclitaxel enhanced Cox-2 expression more than 2-fold, as measured by ELISA. Combined treatment with paclitaxel and the Cox-2 inhibitor NS-398 resulted in increased antiendothelial effects as compared to each agent alone. To assess the biologic effects of the combined treatment in vivo, 4 cancer patients were treated with a prolonged intravenous infusion of paclitaxel (10 mg/m2/day) and the Cox-2 inhibitor celecoxib (400 mg p.o. BID), and plasma angiogenic activity and drug levels were measured. The treatment was well tolerated, providing steady-state concentrations of paclitaxel in plasma near 10 nM and potent plasma antiendothelial effects were observed. These findings suggest that antiangiogenic effects of paclitaxel may be due its preferential accumulation in ECs. Low dose paclitaxel in combination with a Cox-2 inhibitor is an attractive antiangiogenic and antitumor strategy that deserves further evaluation in clinical trials.

Trophoblast expression of fms-like tyrosine kinase 1 is not required for the establishment of the maternal-fetal interface in the mouse placenta

Fms-like tyrosine kinase 1 (Flt1)/vascular endothelial growth factor (VEGF) receptor 1, a receptor for VEGF-A and placental growth factor, is expressed in the spongiotrophoblast layer that segregates the maternal and fetal vasculature in the mouse placenta. A soluble form of Flt1 (sFlt1) produced in the mouse and human placenta can also be detected in the maternal blood. Levels of maternal sFlt1 are elevated in preeclampsia, suggesting that placental sFlt1 plays roles in regulating the maternal vasculature during pregnancy. However, it remains to be determined whether placental Flt1/sFlt1 serves as a regulator of VEGF-A activity in the placenta per se. Here, we investigated the placental development in Flt1-deficient mice. Flt1 is expressed in a subpopulation of ectoplacental cone cells and later marks the spongiotrophoblast cells, peri/endovascular trophoblast cells, and trophoblast glycogen cells. The labyrinth of Flt1lacZ/lacZ placentae lacked the fetal capillary network because of a defect in allantoic mesoderm invasion. To address whether the absence of Flt1 in the trophoblast alone affects placental development, we investigated chimeric placentae comprised of Flt1lacZ/lacZ trophoblast and Flt1+/+ mesoderm, generated by tetraploid aggregation. Fetal growth was supported normally, and no defect in the formation of placental circulation into the maternal spiral artery or invasion of peri/endovascular trophoblast was detected. These findings indicate that trophoblast-derived Flt1/sFlt1 is dispensable for the initial establishment of the maternal-fetal interface in the mouse placenta. Targeting maternal sFlt1 levels for treatment of preeclampsia may thus be possible without affecting the proper formation of the placenta.

VEGF-receptor signal transduction

The vascular endothelial growth factor (VEGF) family of ligands and receptors has been the focus of attention in vascular biology for more than a decade. There is now a consensus that the VEGFs are crucial for vascular development and neovascularization in physiological and pathological processes in both embryo and adult. This has facilitated a rapid transition to their use in clinical applications, for example, administration of VEGF ligands to enhance vascularization of ischaemic tissues and, conversely, inhibitors of VEGF-receptor function in anti-angiogenic therapy. More recent data indicate essential roles for the VEGFs in haematopoietic cell function and in lymphangiogenesis.

Overexpression of the soluble vascular endothelial growth factor receptor in preeclamptic patients: pathophysiological consequences

Several growth factors such as vascular endothelial growth factor (VEGF)-A and placental growth factor (PlGF) are involved in the placental vascular development. We investigated whether dysregulation in the VEGF family may explain the defective uteroplacental vascularization characterizing preeclampsia. We compared pregnancies complicated by early onset severe preeclampsia or intrauterine growth retardation to normal pregnancies. Maternal plasma, placentas, and placental bed biopsies were collected. The mRNA levels of VEGF-A, PlGF, and their receptors were quantified in placentas and placental beds. Levels of VEGF-A, PlGF, and soluble VEGF receptor (VEGFR) were assessed in maternal plasma. In compromised pregnancies, elevated levels of VEGF-A and VEGFR-1 mRNAs may reflect the hypoxic status of the placenta. On contrast, the membrane-bound VEGFR-1 was decreased in the placental bed of preeclamptic patients. Preeclampsia was associated with low levels of circulating PlGF and increased levels of total VEGF-A and soluble VEGFR-1. Free VEGF-A was undetectable in maternal blood. Immunohistochemical studies revealed that VEGF-A and PlGF were localized in trophoblastic cells. Altogether, our results suggest two different pathophysiological mechanisms associated with preeclampsia. The first one is related to an overproduction of competitive soluble VEGFR-1 that may lead to suppression of VEGF-A and PlGF effects. The second one is the down-regulation of its membrane bound form (VEGFR-1) in the placental bed, which may result in the defective uteroplacental development.

Increased Oxidative Stress in Pre-eclamptic Placenta is Associated with Altered Proteasome Activity and Protein Patterns

Analysis of the amount of oxidatively damaged proteins in placenta proteins from normal pregnancies and pre-eclampsia revealed a relative increase of about 30 per cent of damaged proteins in pre-eclamptic placenta. Previous work has demonstrated that these cell- and tissue-damaging oxidatively stressed proteins are metabolized particularly by the 20S proteasome. Evaluation of the proteasomal activity revealed a significantly reduced proteasome function in pre-eclamptic placenta by about 30 per cent, suggesting that the accumulation of oxidatively damaged proteins in pre-eclampsia is associated with reduced proteasomal activity. To investigate these effects at molecular levels, separation of placental proteins by two-dimensional SDS-PAGE and subsequent anti-proteasome Western blot revealed several sets of approximately 20 kDa and 30 kDa protein subunits in normal placenta which appear at low or undetectable expression levels in pre-eclamptic placenta. Control Western blots against the placenta protein 14 (PP14) demonstrated equal loading and no significant differences in the PP14 protein patterns. These data suggested that alteration of the multifactorial proteasomal protein complex in pre-eclamptic placenta is accompanied by reduced metabolization of oxidatively damaged proteins. Consequently, the accumulation of these damaged proteins in the placenta may be associated with metabolic interference and thus contribute to certain developments of pre-eclampsia. Silver staining of the two-dimensional SDS-PAGE revealed a variety of acidic proteins in the range of 20 kDa and 45 kDa, respectively, which are differentially expressed in normal and pre-eclamptic placenta and thus provide further analytic potential for metabolic interference.

Relation between insulin kinetics and insulin sensitivity in pregnancy

BACKGROUND

Different time-concentration profiles of plasma insulin following insulin modification of a frequently sampled intravenous glucose-tolerance-test (FSIVGTT) were observed in a study investigating maternal metabolism and fetal macrosomia. We aimed to investigate whether these differences were related to the volume of distribution of insulin, insulin clearance, or both.

DESIGN

Forty-four women were studied between 33 and 35 weeks' gestation using an insulin-modified FSIVGTT. Specific insulin was assayed with an enzyme-linked immunosorbent assay. Insulin sensitivity was calculated using the minimal model and the homeostasis model assessment (HOMA). The volume of distribution and clearance of insulin were calculated from measurements between 2 and 155 min after insulin modification using a one-compartment model.

RESULTS

In accordance with the method for deriving the volume of distribution, there was a significant negative correlation between the increment in insulin concentration and the volume of distribution (rho=-0.92, P<0.0001). The insulin increment was also related negatively to the clearance of insulin (rho=-0.88, P<0.0001). There was a significant correlation between the volume of distribution and both the insulin sensitivity index (rho=0.56, P<0.0001) and HOMA-%S (rho=0.30, P=0.048), and between the clearance of insulin and both the insulin sensitivity index (rho=0.83, P<0.0001)) and HOMA-%S (rho=0.34, P=0.025).

CONCLUSION

The different time-concentration profiles of plasma insulin resulted from differences in the volume of distribution and clearance of insulin. There was a correlation between insulin kinetics and the insulin sensitivity index. Further research is required to investigate possible mechanisms by which insulin kinetics may be related to insulin sensitivity.

The genetics of pre-eclampsia: a feto-placental or maternal problem?

Pre-eclampsia is a potentially life-threatening disease of women during pregnancy leading to hypertension and proteinuria. It affects 1 in 15 pregnancies but, despite intense research efforts, the cause of the disease remains mysterious. Because pre-eclampsia only occurs during pregnancy and its symptoms resolve after delivery, factors from the placenta are thought to be involved. The role of the placenta could be production of 'abnormal' factors that initiate widespread inflammation and vaso-constriction. Alternatively, because the placenta normally contributes to maternal cardiovascular adaptations of pregnancy, it may be that normal placental functions fail in pre-eclampsia or that susceptibilities in the mother to hypertensive, vascular and/or renal disease prevent the appropriate normal responses to them. The potential contributions of both maternal and fetal genes to the onset of the disease have complicated the genetic analysis of the disease in humans. Recent studies have identified strains of transgenic and mutant mice that develop the hallmark features of pre-eclampsia-like disease - gestational hypertension, proteinuria and kidney lesions (glomerulosclerosis). Comparison of three different mouse models suggests that pre-eclampsia can be initiated by at least three independent mechanisms: pre-existing borderline maternal hypertension that is exacerbated by pregnancy (BPH/5 strain of mice), elevated levels of the vasoconstrictor angiotensin II in the maternal circulation by placental over-production of renin (renin/angiotensinogen transgenic mice), and placental pathology (p57Kip2 mutant mice). These findings imply that the pathogenesis of pre-eclampsia cannot be explained by a single mechanism. Therefore, segregation of the human disease into different subtypes may be a key first step in identifying genetic risk factors.

Preventing pathological regression of blood vessels

Oxygen administration to premature infants suppresses retinal VEGF expression and results in the catastrophic vessel loss associated with retinopathy of prematurity. A study investigating the development of the retinal vasculature in mice (see related article on pages 50–57) demonstrates that specific activation of VEGF receptor-1 by placental growth factor-1 protects against oxygen-induced vessel loss without stimulating vascular proliferation and neovascularization.

The biology of VEGF and its receptors

Vascular endothelial growth factor (VEGF) is a key regulator of physiological angiogenesis during embryogenesis, skeletal growth and reproductive functions. VEGF has also been implicated in pathological angiogenesis associated with tumors, intraocular neovascular disorders and other conditions. The biological effects of VEGF are mediated by two receptor tyrosine kinases (RTKs), VEGFR-1 and VEGFR-2, which differ considerably in signaling properties. Non-signaling co-receptors also modulate VEGF RTK signaling. Currently, several VEGF inhibitors are undergoing clinical testing in several malignancies. VEGF inhibition is also being tested as a strategy for the prevention of angiogenesis, vascular leakage and visual loss in age-related macular degeneration.

Angiogenesis in health and disease

Blood vessels constitute the first organ in the embryo and form the largest network in our body but, sadly, are also often deadly. When dysregulated, the formation of new blood vessels contributes to numerous malignant, ischemic, inflammatory, infectious and immune disorders. Molecular insights into these processes are being generated at a rapidly increasing pace, offering new therapeutic opportunities that are currently being evaluated.