Potential markers of preeclampsia--a review

Preeclampsia is a leading cause of maternal and fetal/neonatal mortality and morbidity worldwide. The early identification of patients with an increased risk for preeclampsia is therefore one of the most important goals in obstetrics. The availability of highly sensitive and specific physiologic and biochemical markers would allow not only the detection of patients at risk but also permit a close surveillance, an exact diagnosis, timely intervention (e.g. lung maturation), as well as simplified recruitment for future studies looking at therapeutic medications and additional prospective markers. Today, several markers may offer the potential to be used, most likely in a combinatory analysis, as predictors or diagnostic tools. We present here the current knowledge on the biology of preeclampsia and review several biochemical markers which may be used to monitor preeclampsia in a future, that, we hope, is not to distant from today.

Is preeclampsia an autoimmune disease?

Preeclampsia is a life-threatening hypertensive disease of pregnancy. The condition is characterized by the presence of autoantibodies that activate the major angiotensin receptor, AT(1). Research conducted during the past decade has shown that these autoantibodies activate AT(1) receptors on a variety of cell types and provoke biological responses that are relevant to the pathophysiology of preeclampsia. The introduction of these autoantibodies into pregnant mice results in hypertension, proteinuria and a variety of other features of preeclampsia including small fetuses and placentas. These findings demonstrate the pathophysiological role of these autoantibodies in preeclampsia. The biological properties of these autoantibodies can be blocked by a 7-amino acid peptide that corresponds to a specific sequence associated with the second extracellular loop of the AT(1) receptor. The fact that autoantibodies from different individuals are directed to a common epitope provides obvious diagnostic and therapeutic opportunities. Research reviewed here raises the intriguing possibility that preeclampsia may be a pregnancy-induced autoimmune condition characterized by the presence of disease-causing angiotensin receptor activating autoantibodies.

Autoimmune mediated G-protein receptor activation in cardiovascular and renal pathologies

Antibodies directed against G-protein coupled receptors (GPCR) can act as allosteric receptor agonists or antagonists. Prototypic disease for agonistic antibody action is a Graves disease of the thyroid gland where antibodies that stimulate G-protein coupled thyroid-stimulating hormone receptor (TSHR) were first described 50 years ago. Myasthenia gravis is the prototype for antagonistic autoimmune actions, where antibodies directed against the nicotinic acetylcholine receptor (AChR) cause blockade of neuromuscular junctions. Antibodies and B-cells are increasingly recognised as major modulators of various cardiovascular and renal pathologies. We aim to critically review the notion that antibodies targeting other GPCRs may amplify or cause various cardiovascular and renal pathologies and summarise the current state of research, as well as perspectives in diagnostic and therapeutic strategies. In terms of targets we will focus on the alpha-adrenergic receptor (alpha(1)AR), the beta-adrenergic receptor (beta(1)AR), and the angiotensin II type 1 receptor (AT(1)R).

Estradiol increases angiotensin II type 1 receptor in hearts of ovariectomized rats

We tested the hypothesis that 17beta-estradiol (E(2)) has dual effects on the heart, increasing levels of proteins thought to have beneficial cardiovascular effects (e.g. endothelial nitric oxide (NO) synthase (eNOS)) as well as those thought to have detrimental cardiovascular effects (e.g. type 1 angiotensin II (AngII) receptor (AT(1)R)). Ovariectomized Wistar rats consuming a high-sodium diet received one of four treatments (n=7 per group): group 1, placebo pellets; group 2, E(2) (0 x 5 mg/pellet, 21-day release); group 3, NOS inhibitor, N(omega)-nitro-L-arginine-methyl-ester (L-NAME; 40 mg/kg per day for 14 days) plus Ang II (0 x 225 mg/kg per day on days 11-14); group 4, E(2) plus L-NAME/Ang II. E(2) increased cardiac levels of estrogen receptors ESR1 and ESR2, an ESR-associated membrane protein caveolin-3, eNOS, and phosphorylated (p)eNOS, thus, exerting potentially beneficial cardiovascular effects on NO. However, E(2) also increased cardiac levels of proteins associated with cardiovascular injury and inflammation including, AT(1)R, protein kinase C delta (PRKCD), phosphorylated PRKC, and phosphorylated extracellular signal regulated kinase (pMAPK)3/1, plasminogen activator inhibitor-1 (PAI-1), osteopontin and ED-1, a monocyte/macrophage-specific protein. E(2) treatment led to similar protein changes in the hearts of L-NAME/Ang II-treated rats except that the increase in peNOS was prevented, and L-NAME/Ang II and E(2) had additive effects in increasing cardiac PRKCD and PAI-1. Thus, the highest levels of cardiac PAI-1 and PRKCD occurred in L-NAME/Ang II-treated rats receiving E(2). In summary, E(2) treatment increased cardiac expression of AT(1)R as well as the expression of pro-inflammatory and prothrombotic factors.

Autoantibodies to the angiotensin type I receptor in response to placental ischemia and tumor necrosis factor alpha in pregnant rats

Circulating factors, such as agonistic autoantibodies to the angiotensin II type 1 (AT1) receptor (AT1-AAs), and inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), are suggested to be important links between placental ischemia and hypertension in preeclamptic women. The purpose of this study was to determine the role of placental ischemia and TNF-alpha in stimulating the AT1-AA and the importance of AT1 receptor activation in mediating hypertension during reductions in uterine perfusion pressure (RUPP) and chronic TNF-alpha excess in pregnant rats. Increased mean arterial pressure in RUPP pregnant rats (122+/-1 mm Hg RUPP versus 101+/-1 mm Hg normal pregnant [NP]; P<0.001) was associated with increased circulating TNF-alpha (RUPP 48+/-13 pg/mL versus N 8+/-1 pg/mL; P<0.05) and AT1-AA (RUPP 15.3+/-1.6 U versus NP 0.6+/-0.3 U; P<0.001). Moreover, TNF-alpha-induced hypertension (97+/-2 to 112+/-2 mm Hg; P<0.05) in pregnant rats was associated with AT1-AA production (TNF-alpha rats 9.2+/-2.3 U versus NP rats 1.0+/-0.8 U; P<0.05). To determine the importance of AT1 receptor activation in mediating hypertension in RUPP- and TNF-alpha-treated rats, we administered an AT1 receptor antagonist to RUPP-, TNF-alpha-treated, and NP rats. Blood pressure responses were attenuated in RUPP rats (Delta 32 mm Hg versus Delta 20 mm Hg, NP; P<0.001), as well as in TNF-alpha-treated rats (Delta 10 mm Hg versus Delta 5 mm Hg, NP; P<0.05). Collectively, these data indicate that placental ischemia and TNF-alpha are important stimuli of AT1-AA, and activation of the AT1 receptor appears to, in part, mediate hypertension produced by RUPP and TNF-alpha in pregnant rats.

Changes in angiotensin II type 1 receptor signalling pathways evoked by a monoclonal antibody raised to the N-terminus

The extracellular N-terminus of G-protein-coupled receptors may be involved in signalling events. We examined this in the angiotensin II type 1 receptor (AT1-R) using monoclonal antibody 6313/G2, raised against a conserved sequence in the N-terminal domain, and found it evokes inhibitory and stimulatory responses. In rat aortic smooth muscle cell (RASMC) primary cultures, 6313/G2 (2.5 microg/ml) inhibited both basal and angiotensin II (Ang II; 10(-7) mol/l)-stimulated [H(3)]thymidine incorporation. Exposure to 6313/G2 gave sustained increases in phosphorylated protein kinase Calpha (PKCalpha) but gave a decrease in phosphorylated p44/42 extracellular signal-regulated kinases (ERK1/2) sustained from 10 min to 48 h compared with untreated control RASMC. In contrast, Ang II had no effect on PKCalpha, and, though it is acutely stimulatory (up to 5 min), it had no sustained effect on ERK1/2 either. Using Fura-2 and microfluorimetry, 6313/G2 added alone induced a transient increase in intracellular calcium ([Ca2+](i)), with a characteristic response curve different from that of Ang II itself. The antibody was without effect on an Ang II-stimulated activator protein-1 reporter system, though it reduced unstimulated reporter activity. Such discriminatory effects on intracellular signalling suggest that the AT1-R N-terminus itself might be a target for therapeutic intervention in chronic vascular disease.

Anti-cancer actions of a recombinant antibody (R6313/G2) against the angiotensin II AT1 receptor

Although several tumour types express both AT1 and AT2 angiotensin II receptors, and angiotensin II stimulates cell proliferation, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are not effective anti-cancer agents. Development of a biologically active monoclonal antibody (6313/G2) against the AT1 receptor prompted the testing of a recombinant short-chain variable fragment form (R6313/G2) against breast cancer cells in vitro and in vivo. Cell lines MCF-7, MDA-MB-231 and T47D all expressed both receptor subtypes. In vitro, R6313/G2 suppressed cell proliferation in the presence of 100 nM angiotensin II, with IC50s of 30 nM, 153 nM and 2.8 microM for the three cell types respectively; in contrast, the AT1 receptor blocker losartan was effective only in T47D cells, at 25 microM. Studies on MCF-7 and T47D cells showed R6313/G2 also opposed the angiotensin II-induced inhibition of caspase-3/7 activity. In vivo, hollow fibres containing the cell lines were implanted in nu/nu balb-c mice at two sites, s.c. and i.p. Treatments of R6313/G2 at 2.5 nmol/kg and 25 nmol/kg twice per day for 7 days dose dependently reduced cell numbers for all three cell lines, but here MCF-7 cells responded most sensitively and MDA-MB-231 cells least. Although T47D cells were refractory at the s.c. site, growth was inhibited at the i.p. location, and otherwise results were similar at the two sites. In xenografts, MCF-7 cell tumours were dose dependently reduced by R6313/G2, and 13 and 27 nmol/kg R6313/G2 twice/day gave means of 74 and 76% tumour regression after 7 days. The data suggest that the anti-cancer action of R6313/G2 is considerably more effective than AT1 antagonists.

The renin-angiotensin system and therapeutic vaccines for hypertension

With increased understanding of the pharmacology of the renin-angiotensin system (RAS), many researchers have explored immunological approaches to inhibit components of the RAS for the treatment of hypertension. Active and passive immunizations of the various components of the RAS have been performed, utilizing renin, angiotensin I, angiotensin II and angiotensin II receptor type 1 vaccines. This review discusses the RAS as a target for the development of a hypertension vaccine, and evaluates the safety and efficacy of these vaccines.

The mechanism of signal transduction during vascular smooth muscle cell proliferation induced by autoantibodies against angiotensin AT1 receptor from hypertension

BACKGROUND

Autoantibodies against angiotensin AT1 receptor have been discovered in patients with preeclampsia or malignant hypertension. Some studies have demonstrated that the autoantibodies are involved in the immunopathogenesis of hypertension and have an agonist effect similar to angiotensin II.

METHODS

Autoantibodies against AT1 receptor were purified from sera of patients with primary hypertension by affinity chromatography. Proliferation of cultured rat vascular smooth muscle cells was detected by bromodeoxyuridine incorporation and activation of signalling molecules detected by Western blotting and electrophoretic mobility shift assay.

RESULTS

The AT1-RAb caused a significant proliferation similar to the Ang II during first 24 hours. The levels of nuclear factor-kappaB (NF-kappaB), phosphorylated JAK2, phosphorylated STAT1 (pSTAT1) and phosphorylated STAT3 (pSTAT3) molecules were increased in response to the autoantibodies. In contrast, the activations of NF-kappaB and JAK-STAT were blocked by losartan, pyrrolidinedithiocarbamate (a specific inhibitor of NF-kappaB) and AG490 (a specific inhibitor of the JAK2 tyrosine kinase). The expressions of NF-kappaB, pSTAT1 and pSTAT3 reached peak levels at different times. Moreover, the relative densities of electrophoretic bands showed that activation of pSTAT3 was more significant than STAT1 induced by AT1-RAb.

CONCLUSIONS

These results suggest that the autoantibodies against AT1 receptor have an agonist effect similar to Ang II in proliferation of VSMCs and the NF-kappaB and JAK-STAT proteins play essential roles. The effect is different from Ang II in that STAT3 is the main downstream activating molecule in JAK-STAT signalling pathway.

[Increased autoantibody production against AT(1)-receptors and alpha(1)-adrenergic receptors in hypertensive patients]

OBJECTIVE

To observe autoantibodies production against AT(1)-receptors and alpha(1)-adrenergic receptors and association to risk factors, such as sex, age, family history, course of hypertension and other cardiovascular diseases in hypertensive patients.

METHODS

A total of 690 patients with essential hypertension admitted to our hospital were selected and autoantibodies against AT(1)-receptors and alpha(1)-adrenergic receptors were detected by ELISA. Multiple logistic regression analysis was performed based on obtained data.

RESULTS

Positive rates for antibody against AT(1)-receptors and alpha(1)-adrenergic receptors were 47.1% (325/690) and 36.4% (251/690) respectively in this group of patients. Duration of hypertension history was significantly longer in the antibody against AT(1)-receptors and alpha(1)-adrenergic receptors positive groups [(9.3 +/- 11.0) year, (9.9 +/- 11.1) year] compared to the negative groups [(7.3 +/- 9.3) year, (7.2 +/- 9.5) year, all P < 0.01]. The ratio of family history with hypertension was also significantly higher in antibody positive groups than negative ones (47.69% vs 39.18%, P < 0.01). Regression analysis demonstrated that 5 risk factors were related to positive production of autoantibody against AT(1)-receptors including female gender, age, family history, duration of hypertension history and diabetes. However, just age, family history, duration of hypertension history were main factors responsible to the production of autoantibody against alpha(1)-adrenergic receptors (all P < 0.05).

CONCLUSION

The environmental and genetic factors contributed to the autoantibody production in patients with essential hypertension.

Emerging Concepts of Regulation of Angiotensin II Receptors

Angiotensin (Ang) II exerts its important physiological functions through 2 distinct receptor subtypes, type 1 (AT 1 ) and type 2 (AT 2 ) receptors. Recently, new evidence has accumulated showing the existence of several novel receptor interacting proteins and various angiotensin II receptor activation mechanisms beyond the classical actions of receptors for Ang II. These associated proteins could contribute not only to Ang II receptors’ functions, but also to influencing pathophysiological states. Receptor dimerization of Ang II receptors such as homodimer, heterodimer, and complex formation with other G protein-coupled receptors has also been focused on as a new mechanism of their activation or inactivation. Moreover, ligand-independent receptor activation systems such as mechanical stretch for the AT 1 receptor have also been revealed. These emerging concepts of regulation of Ang II receptors and a new insight into future drug discovery are discussed in this review.

[Association between positive autoantibodies against AT1-receptor and cardiac remodeling in patients with hypertension]

OBJECTIVE

To observe the association between positive autoantibodies against AT(1)-receptor and cardiac remodeling in primary hypertensive patients.

METHODS

Echocardiography was performed and serum autoantibodies against AT(1)-receptor were detected by enzyme linked immunosorbent assay (ELISA) in 592 patients with primary hypertension. The differences on blood pressure level, course of hypertension, vasoactive substance and echocardiography parameters between the positive group and negative group were compared. Factors related to left ventricular enlargement were analyzed by multiple logistic regressions.

RESULTS

The positive percentage of autoantibodies against AT(1)-receptor was 38.0% (225/592). End-diastolic right atrial and left ventricular diameters in positive group were significantly larger than that in negative group (P = 0.049 and P = 0.044, respectively). Regression analysis demonstrated that positive autoantibodies against AT(1)-receptor, male gender, diastolic blood pressure and course of hypertension were related to left ventricular enlargement (all P < 0.05).

CONCLUSION

The autoantibodies against AT(1)-receptor is associated with left ventricular and right atrial enlargement in hypertensive patients.

Angiotensin receptors, autoimmunity, and preeclampsia

Preeclampsia is a pregnancy-induced hypertensive disorder that causes substantial maternal and fetal morbidity and mortality. Despite being a leading cause of maternal death and a major contributor to maternal and perinatal morbidity, the mechanisms responsible for the pathogenesis of preeclampsia are poorly understood. Recent studies indicate that women with preeclampsia have autoantibodies that activate the angiotensin receptor, AT1, and that autoantibody-mediated receptor activation contributes to pathophysiology associated with preeclampsia. The research reviewed here raises the intriguing possibility that preeclampsia may be a pregnancy-induced autoimmune disease.

Agonist autoantibodies against the angiotensin AT1 receptor in renal and hypertensive disorders

Previous studies demonstrated the significance of an agonistic angiotensin II receptor AT1 autoantibody (AT1-AA) in preeclampsia. Because of its ability to release calcium in vascular smooth muscle cells, stimulate reactive oxygen species, and initiate proinflammatory processes, this antibody was thought to be important in the etiology and pathogenesis of preeclampsia. Recent investigations, however, have broadened and refined the pathobiological relevance of this antibody and refuted its role as the primary cause for preeclampsia. Because AT1-AA has been linked to an impaired uteroplacental perfusion and has been detected in patients with renal allograft rejection, its occurrence and function seem to be wider and more complex. This review summarizes current knowledge about the generation, function, and clinical importance of AT1-AA.

Value of posttransplant antibody tests in the evaluation of patients with renal graft dysfunction

Posttransplant HLA antibodies correlate with C4d positive rejection and decreased graft survival. However, the diagnostic value of various antibody tests in the management of patients presenting with graft dysfunction is uncertain. Whether all or some patients should be tested, how often, what antibodies to test for and how to interpret results in presensitized or transfused patients, are issues still unresolved. We tested for HLA and non-HLA antibodies by flow cytometry assays in 103 consecutive patients with graft dysfunction. The results show that: (1) C4d positive rejection was diagnosed in 75% of patients who developed posttransplant HLA antibodies, but only in 2% in antibody negative patients. (2) The correlation existed for donor specific IgG antibodies but not for IgM or nondonor specific IgG antibodies. (3) Weak antibody reactivity required confirmation by alternative testing as there were false positive results. (4) Posttransplant transfusions did not induce de novo HLA antibodies. (5) Negative antibody results were unlikely to turn positive after several months of follow-up. (6) Antibodies to the angiotensin II type 1 receptor, HLA-DP and MICA did not correlate with C4d+ rejection. We conclude that testing for posttransplant HLA antibodies is critical in narrowing the diagnostic alternatives in patients with graft dysfunction.

The role of angiotensin II type 1 receptor-activating antibodies in renal allograft vascular rejection

Acute rejection with vascular involvement remains a challenging problem in renal allotransplantation. Fibrinoid necrosis of the arteries with secondary thrombotic occlusions is C4d negative in 50% of cases and has the worst prognosis among all allograft vascular lesions. Nonhuman leukocyte antigen (HLA) non-complement-fixing antibodies reacting to artery-specific antigens have been speculated to be responsible for causing severe vascular injury. We recently reported the presence of agonistic antibodies against the angiotensin II type 1 receptor (AT(1)R-AA) in 16 recipients of renal allografts who had severe vascular rejection and malignant hypertension but who did not have anti-HLA antibodies. AT(1)R-AA stimulate AT(1)R and induce mediators of inflammation and thrombosis. Removal of AT(1)R-AA by plasmapheresis in combination with pharmacologic AT(1)R blockade leads to improved renal function and graft survival in AT(1)R-AA-positive patients. We have shown that the analysis of the subtle diagnostic and mechanistic differences may help to identify patients at particular risk and improve outcome of rejections with vascular pathology.

Autoantibodies against G-protein-coupled receptors modulate heart mast cells

Mast cells are believed to be involved in myocardial tissue remodelling under pathophysiological conditions. We examined the effects of autoantibodies against G-protein-coupled receptors in sera of patients with heart diseases on myocardial mast cells in the cultured neonatal Sprague-Dawley rat heart cells. Cells collected at day 3 and 10 of the culture were preincubated with autoantibodies against alpha1-adrenoceptor and angiotensin II AT1-receptor, agonist phenylephrine and angiotensin II, and control IgG. The pretreated cultured cells were stained for selected mast cell markers tryptase, chymase and TNF-alpha. The cultured cells were also processed for observation with electron microscopy. The autoantibodies-treatment of the 3-day cultured cells caused both increased intensity of immunofluorescence (p < 0.05) and their enlarged diameters of the mast cells when compared to age-matched ones. In contrast, the fluorescence of preincubated 10-day-old mast cells was decreased compared with controls (p < 0.01). In control samples, the fluorescence of 10-day-old mast cells was significantly higher than that of 3-day-old ones (p < 0.001). Results of electron microscopy examination demonstrated there was an increased granulation of treated 3-day-old mast cells, while a degranulation of mast cells at day 10 of application. The results suggest the modulation effect of the autoantibodies against G-protein-coupled receptors on mast cells, indicating a potential functional link between the autoantibodies against G-protein-coupled receptors and the mast cells in progression of heart disease.

Agonistic Angiotensin II Type 1 Receptor Autoantibodies in Postpartum Women With a History of Preeclampsia

Activating angiotensin II type 1 autoantibodies (AT1-AAs) develop in women with preeclampsia and may contribute to the disorder. Insulin resistance and serum concentrations of the antiangiogenic soluble fms-like tyrosine kinase 1 (sFlt-1) are also increased in women with preeclampsia compared with normal pregnancy. sFlt-1 and insulin resistance decrease substantially after delivery; however, significant group differences persist postpartum. Women who have had preeclampsia are at increased cardiovascular risk later in life. We measured AT1-AAs in groups of women with previous preeclampsia (n=29) and previous normal pregnancies (n=35) 18+/-9 months after the first completed pregnancy. These women had had sFlt-1, insulin resistance homeostasis model assessment score, and related cardiovascular risk factors measured. Activating antibodies were detected by the chronotropic response of cultured neonatal rat cardiomyocytes coupled with receptor-specific antagonists (losartan and prazosin). AT1-AAs were detected in 17.2% of women with previous preeclampsia versus 2.9% of women with previous uncomplicated pregnancies (P<0.05). In contrast, there was no difference in the prevalence of autoantibodies against the alpha1-adrenoceptor (10% of previous preeclamptic versus 14% of previous normal pregnant). Women with activating autoantibodies had significantly increased sFlt-1, reduced free vascular endothelial growth factor, and higher insulin resistance homeostasis model assessment values compared with autoantibody-negative women. These data suggest that, as with sFlt-1 and insulin resistance, the AT1-AA does not regress completely after delivery and, secondarily, that correlations exist among these variables. The impact of AT1-AA after preeclampsia, especially in the context of cardiovascular risk, remains to be determined.

Dysregulation of the circulating and tissue-based renin-angiotensin system in preeclampsia

The renin-angiotensin system (RAS) participates in preeclampsia; however, the relative contributions from the circulating RAS and the tissue-based, uteroplacental RAS are unknown. We hypothesized that the tissue-based uteroplacental RAS is dysregulated in preeclampsia. We performed microarray and gene expression studies and confirmed the findings on the protein level by immunohistochemistry in ureteroplacental units from 10 preeclamptic women and 10 women with uneventful pregnancies. All of the women were delivered by cesarean section. We also analyzed plasma renin activity and circulating agonistic angiotensin II type 1 (AT1) receptor autoantibodies. In preeclampsia, we found that the angiotensin II AT1 receptor gene was 5-fold upregulated in decidua (maternal origin). We also found AT1 autoantibodies in preeclamptic women and in their offspring by neonatal cardiomyocyte bioassay compared with women with normal pregnancies and their infants (mother: 17.5+/-2.2 versus 0.05+/-0.4; fetus: 14.5+/-1.8 versus 0.5+/-0.5 Deltabpm). Gene expressions for renin (35.0-fold), angiotensin-converting enzyme (2.9-fold), and angiotensinogen (8.9-fold) were higher in decidua than placenta (fetal origin) in both control and preeclamptic women, whereas the AT1 receptor was expressed 10-fold higher in placenta than in decidua in both groups. Our findings elucidate the ureteroplacental unit RAS in preeclamptic and normal pregnancies. We found that, in preeclampsia, the AT1 receptor expression is particularly high in decidua, combined with pregnancy-specific tissue RAS involving decidual angiotensin II production and AT1 autoantibodies. We also showed that AT1 autoantibodies cross the ureteroplacental barrier. These components could participate in the pathophysiology of preeclampsia.

[Endothelin 1 and angiotensin II in preeeclampsia]

INTRODUCTION

It is generally thought that development of hypertension in preeclampsia (PE) is due to generalized endothelial dysfunction and/or results from an imbalance in the production and/or action of vasoactive factors, resulting in higher cytosolic Ca2+ concentration which in turn leads to vasoconstriction and decreased blood pressure perfusion in organs, including the fetoplacental unit. Among vasoactive factors involved in blood pressure regulation, endothelin 1 (ET-1) and angiotensin II (Ang II) regulate cytosolic Ca2+ concentrations and therefore are considered in this review. PE is associated with higher circulating and placental ET-1 levels, observation that explains, at least in part, vasoconstriction and oxidative stress. Higher and lower Ang II sensitivity seen in PE and normal pregnancy, respectively, could not be explained by changes in renin-angiotensin system components, including Ang II receptors (AT1). During normal pregnancy, AT1 receptors are found as monomers and are inactivated by reactive oxygen species (ROS) leading to lower Ang II sensitivity. In contrast, PE is associated with increased AT1/bradykinin receptors (B2) heterodimers which are resistant to inactivation by ROS, maintaining increased AT1-receptor stimulated signaling in PE. In addition, AT-1 agonistic antibodies (AT1-AA) obtained from PE women increases intracellular Ca2+, NADPH oxidase components and ROS, effects not observed with normal pregnancy AT1-AA.

CONCLUSION

High ET-1 levels, the presence of AT1/B2 receptor heterodimers and increased AT1-AA are involved, at least in part, in the hypertensive and oxidative stress states in PE.

Is parvovirus B19 the cause for autoimmunity against the angiotensin II type receptor?

Initial studies have demonstrated the significance of the agonistic angiotensin II receptor AT1 autoantibody (AT1-AA) in preeclampsia, although it is unclear what factors induce its generation. Since the epitope recognized by AT1-AA shares high homology with parvovirus B19 (PVB19) capsid proteins, we have investigated the relationship between the presence of AT1-AA in maternal circulation and PVB19 sero-prevalence in normal and abnormal pregnancy. We determined the parvovirus IgG sero-prevalence in normal pregnancies in the second trimester and those with abnormal uterine perfusion that are at risk for preeclampsia. Secondly, pregnancies at delivery with preeclampsia or intrauterine growth restriction were included. All women with normal perfusion were AT1-AA-negative and 80% were parvovirus-IgG-positive. Sixty-three percent of pregnancies with abnormal uterine perfusion were AT1-AA-positive and 71% IgG-positive. Fifty-two percent of the IgG-positive pregnancies in this subgroup were also AT1-AA-positive, and 9 of the 10 parvovirus IgG-negative women were AT1-AA-positive. In the third trimester, 87% of pregnancies with manifest disease were AT1-AA-positive and 58% IgG-positive. While 79% of the PVB19 IgG-positive pregnancies were also AT1-AA-positive, all parvovirus IgG-negative women were AT1-AA-positive. In all groups, AT1-AA activity did not differ between parvovirus IgG-negative and positive women. We find parvovirus IgG-positive pregnant women in all subgroups without relation to AT1-AA presence. This favors AT1-AA generation to be independent of epitope mimicry between parvovirus B19 capsid proteins and the AT1 receptor.