- Email: [email protected]
Reductions of vascular endothelial growth factor and placental growth factor concentrations in severe preeclampsia
Reductions of vascular endothelial growth factor and placental growth factor concentrations in severe preeclampsia Jeffrey C. Livingston, MD, Robert Chin, MD, PhD, Bassam Haddad, MD, Elizabeth T. McKinney, MD, Robert Ahokas, PhD, and Baha M. Sibai, MD Memphis, Tennessee, and Cincinnati, Ohio OBJECTIVE: The aim of this study was to determine whether plasma concentrations of vascular endothelial growth factor and placental growth factor are altered in women with severe preeclampsia. STUDY DESIGN: We performed a case-control study to compare plasma concentrations of vascular endothelial growth factor and placental growth factor between women with severe preeclampsia and normotensive women admitted for delivery. Twenty-one women with severe preeclampsia were matched for gestational age and ethnicity with 21 normotensive women. Vascular endothelial growth factor and placental growth factor concentrations were measured with a specific antigen-capture enzyme-linked immunosorbent assay. RESULTS: Women with severe preeclampsia demonstrated significantly lower plasma concentrations of both vascular endothelial growth factor (6.36 ± 3.96 pg/mL vs 18.65 ± 5.98 pg/mL; P < .0001) and placental growth factor (138 ± 119 pg/mL vs 531 ± 340 pg/mL; P < .0001) than did women with normotensive pregnancy. Logistic regression analysis showed an independent association between plasma vascular endothelial growth factor concentration and plasma placental growth factor concentration and preeclampsia. CONCLUSION: Patients with severe preeclampsia had decreased maternal serum concentrations of both vascular endothelial growth factor and placental growth factor. (Am J Obstet Gynecol 2000;183:1554-7.)
Key words: Placental growth factor, preeclampsia, pregnancy, vascular endothelial growth factor
Although the exact pathophysiologic characteristics of preeclampsia remain unknown, vascular changes resulting in vasospasm and increased permeability are clinical hallmarks of the disease process. Preeclampsia may reflect a microvasculopathy that is initiated or exacerbated by factors produced within the placenta.1 Placental growth factor (PLGF) and vascular endothelial growth factor (VEGF) are two related protein members of the endothelial growth factor family with potent angiogenic and mitogenic activities that result in enhanced permeability of vascular endothelium. VEGF is a dimeric glycoprotein that is produced and secreted in vivo by a wide variety of cells. Several groups have investigated its role in preeclampsia, with conflicting results.2-5 The production of PLGF, unlike that of VEGF, is limited to placental tissue and endothelial cells.6, 7 There are limited data describing PLGF concentrations in women with preeclampsia. Two retrospective case-control studies found decreased plasma concentrations of PLGF in From the Department of Obstetrics and Gynecology, University of Tennessee, Memphis, and the Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine. Received for publication December 1, 1999; revised February 29, 2000; accepted April 18 2000. Reprint requests: Jeffrey C. Livingston, MD, Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Tennessee, Memphis, 853 Jefferson Ave, Room E102, Memphis, TN 38163. Copyright © 2000 by Mosby, Inc. 0002-9378/2000 $12.00 + 0 6/1/108022 doi:10.1067/mob.2000.108022
1554
women with preeclampsia relative to women with normotensive pregnancy.8, 9 Conflicting reports in the literature indicate that PLGF may or may not share the stimulatory effect of VEGF on endothelial cells, because PLGF and VEGF bind some but not all, VEGF receptors.10 Growth factors generally work locally; however, dysfunctional cytotropic invasion may result in altered maternal plasma concentrations. An alteration in plasma concentrations may have an effect on maternal endothelial cells. In this study we investigated whether circulating concentrations of VEGF and PLGF are altered in women with severe preeclampsia. Material and methods The study subjects included a group of 21 women with severe preeclampsia (severe hypertension defined by systolic blood pressure >160 mm Hg or diastolic blood pressure >110 mm Hg on at least 2 occasions >6 hours apart accompanied by proteinuria; n = 12), HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome (n = 5), or eclampsia (n = 4) and a control group of 21 women with normotensive pregnancies who were matched for gestational age (control: range, 28-41 weeks’ gestation; preeclampsia: range, 27-40 weeks’ gestation) and race. Exclusionary criteria included maternal chronic hypertension, multifetal gestation, known preexisting microvascular disease, diabetes mellitus, and fetal growth restriction. Fetal growth restriction was defined as a birth weight at <10% according to population growth
Livingston et al 1555
Volume 183, Number 6 Am J Obstet Gynecol
Table I. Clinical parameters and growth factor plasma levels in study groups
Gestational age (wk, mean ± SD) Systolic blood pressure (mm Hg, mean ± SD) Diastolic blood pressure (mm Hg, mean ± SD) Proteinuria (g/24 h, mean ± SD) Maternal weight (lb, mean) Birth weight (g, mean ± SD) Placental weight (g, mean ± SD) PLGF (pg/mL) Mean ± SD Median and range VEGF (pg/mL) Mean ± SD Median and range
Preeclampsia (n = 21)
Control (n = 21)
Statistical significance
35.6 ± 3.1 174 ± 21 113 ± 4 6.6 ± 4.6 195.7 2352 ± 746 472 ± 174
37.1 ± 3 135 ± 14 81 ± 11 — 166.7 3038 ± 869 656 ± 247
NS P < .0001 P < .0001 — NS P < .001 P < .01
531 ± 339 564 (16-1233)
P < .0001 P < .0001
18.65 ± 5.98 18.7 (6.4-27.7)
P < .0001 P < .0001
138 ± 119 110 (5.7-581) 6.36 ± 3.96* 6.0 (6.0-21.7)*
NS, Not significant. *VEGF concentrations were below detection threshold in 15 of 21 patients. A value of 6.0 pg/mL was used for data analysis in these cases.
curves.11 These exclusionary conditions alter placental mass and therefore could be possible confounders. No patients reported tobacco or illicit drug use. HELLP syndrome was diagnosed by the following criteria: platelet count <100,000 cells/mm3, serum aminotransferase activity ≥72 IU/L, and total bilirubin concentration <1.2 md/dL or lactate dehydrogenase concentration ≥600 IU/L. Blood samples were collected within 24 hours before delivery into standard ethylenediaminetetraacetic acid– containing collection tubes and then centrifuged at room temperature at 5000 rpm for 5 minutes. Plasma aliquots were stored at –70°C until assay. Concentrations of VEGF and PLGF present in maternal plasma were measured by specific antigen-capture enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, Minn) as previously described elsewhere.8 A standard curve was generated for each sample plate, and sample concentrations of VEGF and PLGF were calculated with SoftMax 4-parameter logistic curve fit software (Molecular Devices Corporation, Sunnyvale, Calif). The minimum detectable concentration of VEGF with this assay is 6.0 pg/mL. No significant cross-reactivity or interference with factors related to VEGF (including PLGF) has been noted with this assay. There is, however, approximately a 20% cross-reactivity with the VEGF-PLGF heterodimer across the range of the VEGF assay. The minimum detectable concentration of PLGF by this assay is 5 pg/mL. Again, neither significant cross-reactivity nor interference has been noted with related growth factors. The VEGF-PLGF heterodimer has as much as 5% cross-reactivity in this PLGF assay. Data were calculated with a value of 6.0 pg/mL when the concentration of VEGF was below the detection threshold. Continuous variables were compared with the MannWhitney rank sum test. The Student t test was used when the results were normally distributed. When appropriate regression analysis was performed to analyze the relation-
ship between continuous variables. Model-defined logistic regression analysis (with independent variables for preeclampsia, VEGF concentration, PLGF concentration, and placental weight) was performed to discover relationships between one or more of these independent variables. Data are expressed as mean ± SD. P < .05 was considered to be statistically significant. The institutional review board at the University of Tennessee, Memphis, approved this study. Calculations were performed with StatView 5.0 (SAS Institute, Inc, Cary, NC) statistical software. Results Compared with normotensive women, the women with severe preeclampsia had significantly higher blood pressure, but there were no differences between groups with respect to maternal age, parity, gestational age at delivery, maternal weight, or ethnicity (15/21 African Americans in both groups). Table I compares the clinical findings and the VEGF and PLGF concentrations between the 2 groups. In addition, concentrations of VEGF were below the detection threshold in 15 of 21 patients with preeclampsia (Fig 1). All patients with HELLP syndrome and eclampsia had nondetectable concentrations of VEGF. No control patients had concentrations below the detection threshold. PLGF concentrations were detectable in all samples (Fig 2). Significant linear correlations were found between plasma VEGF concentration and placental weight (r = 0.5; P < .01), plasma PLGF concentration and placental weight (r = 0.55; P < .001), and plasma PLGF and plasma VEGF concentrations (r = 0.72; P < .0001). Logistic regression analysis was performed to evaluate the relationships between preeclampsia and VEGF or PLGF concentration after we controlled for placental weight. Both VEGF and PLGF concentrations were statistically independent variables associated with the development of preeclampsia (P < .01 and P = .02, respectively).
1556 Livingston et al
Fig 1. VEGF concentrations in control women (open circles) and women with severe preeclampsia (open squares). Concentrations below detection threshold are represented at 6.0 pg/mL.
Comment Growth factors are critical during the initial cytotrophoblastic invasion that occurs during early pregnancy.12, 13 Our study demonstrated decreased concentrations of these growth factors in patients with severe preeclampsia. Decreased concentrations of VEGF could be partially attributable to the smaller placental size commonly seen in pregnancies complicated by preeclampsia. Logistic regression analysis, however, demonstrated a relationship between VEGF concentration and preeclampsia independent of placental weight. Altered concentrations of this angiogenic substance may represent decreased and dysfunctional trophoblastic proliferation commonly seen in pregnancies complicated by preeclampsia. VEGF, formerly known as vascular permeability factor, is thought to lead to increased endothelial cell permeability, which is a pathologic abnormality in women with preeclampsia. Our findings demonstrate that women with a definite increase in endothelial permeability (those with HELLP syndrome and eclampsia) indeed had nondetectable concentrations of VEGF. The finding of an association of decreased VEGF concentrations with a disease of increased endothelial cell leakage is perplexing, and we cannot explain it. There are several reasons that our data differ from those of other investigators. The assay that we used measured free rather than total VEGF concentration.14 Other investigators have not specified which assay was used.4 In addition, our assay analyzed only the common 165 isoforms. We cannot comment on other isoform concentrations or how these isoforms may interfere with other assays. Our findings are in agreement with those of Lyall et al5 and Reuvekamp et al,9 who used an identical assay technique. We also found that PLGF serum concentrations were significantly reduced among women with severe preeclampsia, a finding that is in agreement with the reports of Torry et al8 and Reuvekamp et al.9 The decrease of this
December 2000 Am J Obstet Gynecol
Fig 2. PLGF concentrations in control women (open circles) and women with severe preeclampsia (open squares).
angiogenic growth factor may also be involved with the placental microvasculopathy of preeclampsia. In our study plasma concentrations of PLGF were also strongly correlated with VEGF concentrations. There are multiple explanations for the reduced concentrations of endothelial growth factors in women with pregnancy complicated by preeclampsia. First, decreased growth factor concentrations may result in inadequate trophoblastic proliferation into the maternal spiral arteries earlier in pregnancy. Lower concentrations may be maintained throughout a pregnancy complicated by preeclampsia. Renal loss, capillary leakage, downward regulation, and increased metabolism are other possible explanations. It is certainly equally possible that reduced concentrations of growth factors result from inadequate placental production, as with the abnormal placental function commonly seen in preeclampsia. Moreover, there are several limitations to our study. First, a number of our control patients were delivered as a result of preterm labor. No information is currently available regarding concentrations of these growth factors in preterm labor; therefore we cannot comment on this possible confounder. Second, the pathophysiologic changes in preeclampsia occur during early pregnancy. We measured growth factors in the maternal circulation at a late gestational age. No conclusions can be made regarding lower concentrations of these growth factors at the beginning of the microvasculopathy of placentation in pregnancies complicated by preeclampsia. Third, VEGF-binding proteins, heterodimer formation between PLGF and VEGF, and VEGF isoform production may have interfered with our assay results. Although we used standard sample collection, storage, and processing techniques, sample manipulation may have affected our data. We did not control for medication administration, blood product transfusion, or the effects of labor. Any of these factors may be a confounder.
Livingston et al 1557
Volume 183, Number 6 Am J Obstet Gynecol
Further studies are needed to determine the serum concentrations of VEGF and PLGF in pregnant women before the development of preeclampsia. This would require a longitudinal, nested, case-control study. The interrelationship between VEGF and PLGF and the role of PLGF-VEGF heterodimers in preeclampsia also warrant further investigation.
7.
8.
9.
REFERENCES
1. Sibai BM. Hypertension in pregnancy. Obstet Gynecol Clin North Am 1992;19:615-32. 2. Sharkey AM, Cooper JC, Bamforth JR, McLaren J, Clark DE, Charnock-Jones DS, et al. Maternal plasma concentrations of vascular endothelial growth factor in normotensive pregnancies and in pregnancies complicated by preeclampsia. Eur J Clin Invest 1996;26:1182-5. 3. Baker PN, Krasnow J, Roberts JM, Yeo KT. Elevated plasma concentrations of vascular endothelial growth factor in patients with preeclampsia. Obstet Gynecol 1995;86:815-21. 4. Kupferminc MJ, Daniel Y, Englender T, Baram A, Many A, Jaffa AJ, et al. Vascular endothelial growth factor is increased in patients with preeclampsia. Am J Reprod Immunol 1997;38:302-6. 5. Lyall F, Greer IA, Boswell F, Fleming R. Suppression of plasma vascular endothelial growth factor immunoreactivity in normal pregnancy and in preeclampsia. Br J Obstet Gynaecol 1997;104: 223-8. 6. Maglione D, Guerriero V, Viglietto G, Delli-Bovi P, Persico MG. Isolation of a human placenta cDNA coding for a protein
10.
11.
12.
13.
14.
related to the vascular permeability factor. Proc Natl Acad Sci U S A 1991;88:9267-71. Hauser S, Weich HA. A heparin-binding form of placental growth factor (PLGF-2) is expressed in human vein endothelial cells and in the placenta. Growth Factors 1993;9:259-68. Torry DS, Wang HS, Wang TH, Caudle MR, Torry RJ. Preeclampsia is associated with reduced serum levels of placenta growth factor. Am J Obstet Gynecol 1998;179:1539-44. Reuvekamp A, Velsing-Aarts FV, Poulina IE, Capello JJ, Duits AJ. Selective deficit of angiogenic growth factors characterized pregnancies complicated by pre-eclampsia. Br J Obstet Gynaecol 1999;106:1019-22. DiSalvo J, Bayne ML, Conn G, Kwok PW, Trivedi PG, Sodermann DD, et al. Purification and characterization of a naturally occurring vascular endothelial growth factor–placenta growth factor heterodimer. Biol Chem 1995;31:7717-23. Genbacev O, Zhou Y, Ludwig JW, Fisher SJ. Regulation of human placental development by oxygen tension. Science 1997;92: 1669-72. Vuorela P, Hatva E, Lymboussaki A, Kaipainen A, Joukov V, Persico MG, et al. Expression of vascular endothelial growth factor and placental growth factor in human placenta. Biol Reprod 1997;56:489-94. Anthony FW, Evans PW, Wheeler T, Wood PJ. Variation in detection of VEGF in maternal serum by immunoassay and the possible influence of binding proteins. Ann Clin Biochem 1997; 34:276-80. Lubchenco LO, Hansman C, Boyd E. Intrauterine growth in length and head circumference as estimated from live births at gestational ages from 26 to 42 weeks. Pediatrics 1966; 37:403-8.
Key words: Placental growth factor, preeclampsia, pregnancy, vascular endothelial growth factor
Although the exact pathophysiologic characteristics of preeclampsia remain unknown, vascular changes resulting in vasospasm and increased permeability are clinical hallmarks of the disease process. Preeclampsia may reflect a microvasculopathy that is initiated or exacerbated by factors produced within the placenta.1 Placental growth factor (PLGF) and vascular endothelial growth factor (VEGF) are two related protein members of the endothelial growth factor family with potent angiogenic and mitogenic activities that result in enhanced permeability of vascular endothelium. VEGF is a dimeric glycoprotein that is produced and secreted in vivo by a wide variety of cells. Several groups have investigated its role in preeclampsia, with conflicting results.2-5 The production of PLGF, unlike that of VEGF, is limited to placental tissue and endothelial cells.6, 7 There are limited data describing PLGF concentrations in women with preeclampsia. Two retrospective case-control studies found decreased plasma concentrations of PLGF in From the Department of Obstetrics and Gynecology, University of Tennessee, Memphis, and the Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine. Received for publication December 1, 1999; revised February 29, 2000; accepted April 18 2000. Reprint requests: Jeffrey C. Livingston, MD, Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Tennessee, Memphis, 853 Jefferson Ave, Room E102, Memphis, TN 38163. Copyright © 2000 by Mosby, Inc. 0002-9378/2000 $12.00 + 0 6/1/108022 doi:10.1067/mob.2000.108022
1554
women with preeclampsia relative to women with normotensive pregnancy.8, 9 Conflicting reports in the literature indicate that PLGF may or may not share the stimulatory effect of VEGF on endothelial cells, because PLGF and VEGF bind some but not all, VEGF receptors.10 Growth factors generally work locally; however, dysfunctional cytotropic invasion may result in altered maternal plasma concentrations. An alteration in plasma concentrations may have an effect on maternal endothelial cells. In this study we investigated whether circulating concentrations of VEGF and PLGF are altered in women with severe preeclampsia. Material and methods The study subjects included a group of 21 women with severe preeclampsia (severe hypertension defined by systolic blood pressure >160 mm Hg or diastolic blood pressure >110 mm Hg on at least 2 occasions >6 hours apart accompanied by proteinuria; n = 12), HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome (n = 5), or eclampsia (n = 4) and a control group of 21 women with normotensive pregnancies who were matched for gestational age (control: range, 28-41 weeks’ gestation; preeclampsia: range, 27-40 weeks’ gestation) and race. Exclusionary criteria included maternal chronic hypertension, multifetal gestation, known preexisting microvascular disease, diabetes mellitus, and fetal growth restriction. Fetal growth restriction was defined as a birth weight at <10% according to population growth
Livingston et al 1555
Volume 183, Number 6 Am J Obstet Gynecol
Table I. Clinical parameters and growth factor plasma levels in study groups
Gestational age (wk, mean ± SD) Systolic blood pressure (mm Hg, mean ± SD) Diastolic blood pressure (mm Hg, mean ± SD) Proteinuria (g/24 h, mean ± SD) Maternal weight (lb, mean) Birth weight (g, mean ± SD) Placental weight (g, mean ± SD) PLGF (pg/mL) Mean ± SD Median and range VEGF (pg/mL) Mean ± SD Median and range
Preeclampsia (n = 21)
Control (n = 21)
Statistical significance
35.6 ± 3.1 174 ± 21 113 ± 4 6.6 ± 4.6 195.7 2352 ± 746 472 ± 174
37.1 ± 3 135 ± 14 81 ± 11 — 166.7 3038 ± 869 656 ± 247
NS P < .0001 P < .0001 — NS P < .001 P < .01
531 ± 339 564 (16-1233)
P < .0001 P < .0001
18.65 ± 5.98 18.7 (6.4-27.7)
P < .0001 P < .0001
138 ± 119 110 (5.7-581) 6.36 ± 3.96* 6.0 (6.0-21.7)*
NS, Not significant. *VEGF concentrations were below detection threshold in 15 of 21 patients. A value of 6.0 pg/mL was used for data analysis in these cases.
curves.11 These exclusionary conditions alter placental mass and therefore could be possible confounders. No patients reported tobacco or illicit drug use. HELLP syndrome was diagnosed by the following criteria: platelet count <100,000 cells/mm3, serum aminotransferase activity ≥72 IU/L, and total bilirubin concentration <1.2 md/dL or lactate dehydrogenase concentration ≥600 IU/L. Blood samples were collected within 24 hours before delivery into standard ethylenediaminetetraacetic acid– containing collection tubes and then centrifuged at room temperature at 5000 rpm for 5 minutes. Plasma aliquots were stored at –70°C until assay. Concentrations of VEGF and PLGF present in maternal plasma were measured by specific antigen-capture enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, Minn) as previously described elsewhere.8 A standard curve was generated for each sample plate, and sample concentrations of VEGF and PLGF were calculated with SoftMax 4-parameter logistic curve fit software (Molecular Devices Corporation, Sunnyvale, Calif). The minimum detectable concentration of VEGF with this assay is 6.0 pg/mL. No significant cross-reactivity or interference with factors related to VEGF (including PLGF) has been noted with this assay. There is, however, approximately a 20% cross-reactivity with the VEGF-PLGF heterodimer across the range of the VEGF assay. The minimum detectable concentration of PLGF by this assay is 5 pg/mL. Again, neither significant cross-reactivity nor interference has been noted with related growth factors. The VEGF-PLGF heterodimer has as much as 5% cross-reactivity in this PLGF assay. Data were calculated with a value of 6.0 pg/mL when the concentration of VEGF was below the detection threshold. Continuous variables were compared with the MannWhitney rank sum test. The Student t test was used when the results were normally distributed. When appropriate regression analysis was performed to analyze the relation-
ship between continuous variables. Model-defined logistic regression analysis (with independent variables for preeclampsia, VEGF concentration, PLGF concentration, and placental weight) was performed to discover relationships between one or more of these independent variables. Data are expressed as mean ± SD. P < .05 was considered to be statistically significant. The institutional review board at the University of Tennessee, Memphis, approved this study. Calculations were performed with StatView 5.0 (SAS Institute, Inc, Cary, NC) statistical software. Results Compared with normotensive women, the women with severe preeclampsia had significantly higher blood pressure, but there were no differences between groups with respect to maternal age, parity, gestational age at delivery, maternal weight, or ethnicity (15/21 African Americans in both groups). Table I compares the clinical findings and the VEGF and PLGF concentrations between the 2 groups. In addition, concentrations of VEGF were below the detection threshold in 15 of 21 patients with preeclampsia (Fig 1). All patients with HELLP syndrome and eclampsia had nondetectable concentrations of VEGF. No control patients had concentrations below the detection threshold. PLGF concentrations were detectable in all samples (Fig 2). Significant linear correlations were found between plasma VEGF concentration and placental weight (r = 0.5; P < .01), plasma PLGF concentration and placental weight (r = 0.55; P < .001), and plasma PLGF and plasma VEGF concentrations (r = 0.72; P < .0001). Logistic regression analysis was performed to evaluate the relationships between preeclampsia and VEGF or PLGF concentration after we controlled for placental weight. Both VEGF and PLGF concentrations were statistically independent variables associated with the development of preeclampsia (P < .01 and P = .02, respectively).
1556 Livingston et al
Fig 1. VEGF concentrations in control women (open circles) and women with severe preeclampsia (open squares). Concentrations below detection threshold are represented at 6.0 pg/mL.
Comment Growth factors are critical during the initial cytotrophoblastic invasion that occurs during early pregnancy.12, 13 Our study demonstrated decreased concentrations of these growth factors in patients with severe preeclampsia. Decreased concentrations of VEGF could be partially attributable to the smaller placental size commonly seen in pregnancies complicated by preeclampsia. Logistic regression analysis, however, demonstrated a relationship between VEGF concentration and preeclampsia independent of placental weight. Altered concentrations of this angiogenic substance may represent decreased and dysfunctional trophoblastic proliferation commonly seen in pregnancies complicated by preeclampsia. VEGF, formerly known as vascular permeability factor, is thought to lead to increased endothelial cell permeability, which is a pathologic abnormality in women with preeclampsia. Our findings demonstrate that women with a definite increase in endothelial permeability (those with HELLP syndrome and eclampsia) indeed had nondetectable concentrations of VEGF. The finding of an association of decreased VEGF concentrations with a disease of increased endothelial cell leakage is perplexing, and we cannot explain it. There are several reasons that our data differ from those of other investigators. The assay that we used measured free rather than total VEGF concentration.14 Other investigators have not specified which assay was used.4 In addition, our assay analyzed only the common 165 isoforms. We cannot comment on other isoform concentrations or how these isoforms may interfere with other assays. Our findings are in agreement with those of Lyall et al5 and Reuvekamp et al,9 who used an identical assay technique. We also found that PLGF serum concentrations were significantly reduced among women with severe preeclampsia, a finding that is in agreement with the reports of Torry et al8 and Reuvekamp et al.9 The decrease of this
December 2000 Am J Obstet Gynecol
Fig 2. PLGF concentrations in control women (open circles) and women with severe preeclampsia (open squares).
angiogenic growth factor may also be involved with the placental microvasculopathy of preeclampsia. In our study plasma concentrations of PLGF were also strongly correlated with VEGF concentrations. There are multiple explanations for the reduced concentrations of endothelial growth factors in women with pregnancy complicated by preeclampsia. First, decreased growth factor concentrations may result in inadequate trophoblastic proliferation into the maternal spiral arteries earlier in pregnancy. Lower concentrations may be maintained throughout a pregnancy complicated by preeclampsia. Renal loss, capillary leakage, downward regulation, and increased metabolism are other possible explanations. It is certainly equally possible that reduced concentrations of growth factors result from inadequate placental production, as with the abnormal placental function commonly seen in preeclampsia. Moreover, there are several limitations to our study. First, a number of our control patients were delivered as a result of preterm labor. No information is currently available regarding concentrations of these growth factors in preterm labor; therefore we cannot comment on this possible confounder. Second, the pathophysiologic changes in preeclampsia occur during early pregnancy. We measured growth factors in the maternal circulation at a late gestational age. No conclusions can be made regarding lower concentrations of these growth factors at the beginning of the microvasculopathy of placentation in pregnancies complicated by preeclampsia. Third, VEGF-binding proteins, heterodimer formation between PLGF and VEGF, and VEGF isoform production may have interfered with our assay results. Although we used standard sample collection, storage, and processing techniques, sample manipulation may have affected our data. We did not control for medication administration, blood product transfusion, or the effects of labor. Any of these factors may be a confounder.
Livingston et al 1557
Volume 183, Number 6 Am J Obstet Gynecol
Further studies are needed to determine the serum concentrations of VEGF and PLGF in pregnant women before the development of preeclampsia. This would require a longitudinal, nested, case-control study. The interrelationship between VEGF and PLGF and the role of PLGF-VEGF heterodimers in preeclampsia also warrant further investigation.
7.
8.
9.
REFERENCES
1. Sibai BM. Hypertension in pregnancy. Obstet Gynecol Clin North Am 1992;19:615-32. 2. Sharkey AM, Cooper JC, Bamforth JR, McLaren J, Clark DE, Charnock-Jones DS, et al. Maternal plasma concentrations of vascular endothelial growth factor in normotensive pregnancies and in pregnancies complicated by preeclampsia. Eur J Clin Invest 1996;26:1182-5. 3. Baker PN, Krasnow J, Roberts JM, Yeo KT. Elevated plasma concentrations of vascular endothelial growth factor in patients with preeclampsia. Obstet Gynecol 1995;86:815-21. 4. Kupferminc MJ, Daniel Y, Englender T, Baram A, Many A, Jaffa AJ, et al. Vascular endothelial growth factor is increased in patients with preeclampsia. Am J Reprod Immunol 1997;38:302-6. 5. Lyall F, Greer IA, Boswell F, Fleming R. Suppression of plasma vascular endothelial growth factor immunoreactivity in normal pregnancy and in preeclampsia. Br J Obstet Gynaecol 1997;104: 223-8. 6. Maglione D, Guerriero V, Viglietto G, Delli-Bovi P, Persico MG. Isolation of a human placenta cDNA coding for a protein
10.
11.
12.
13.
14.
related to the vascular permeability factor. Proc Natl Acad Sci U S A 1991;88:9267-71. Hauser S, Weich HA. A heparin-binding form of placental growth factor (PLGF-2) is expressed in human vein endothelial cells and in the placenta. Growth Factors 1993;9:259-68. Torry DS, Wang HS, Wang TH, Caudle MR, Torry RJ. Preeclampsia is associated with reduced serum levels of placenta growth factor. Am J Obstet Gynecol 1998;179:1539-44. Reuvekamp A, Velsing-Aarts FV, Poulina IE, Capello JJ, Duits AJ. Selective deficit of angiogenic growth factors characterized pregnancies complicated by pre-eclampsia. Br J Obstet Gynaecol 1999;106:1019-22. DiSalvo J, Bayne ML, Conn G, Kwok PW, Trivedi PG, Sodermann DD, et al. Purification and characterization of a naturally occurring vascular endothelial growth factor–placenta growth factor heterodimer. Biol Chem 1995;31:7717-23. Genbacev O, Zhou Y, Ludwig JW, Fisher SJ. Regulation of human placental development by oxygen tension. Science 1997;92: 1669-72. Vuorela P, Hatva E, Lymboussaki A, Kaipainen A, Joukov V, Persico MG, et al. Expression of vascular endothelial growth factor and placental growth factor in human placenta. Biol Reprod 1997;56:489-94. Anthony FW, Evans PW, Wheeler T, Wood PJ. Variation in detection of VEGF in maternal serum by immunoassay and the possible influence of binding proteins. Ann Clin Biochem 1997; 34:276-80. Lubchenco LO, Hansman C, Boyd E. Intrauterine growth in length and head circumference as estimated from live births at gestational ages from 26 to 42 weeks. Pediatrics 1966; 37:403-8.