Marc Parrish

Hypertension in Response to Autoantibodies to the Angiotensin II Type I Receptor (AT1-AA) in Pregnant Rats: Role of Endothelin-1

Agonistic autoantibodies to the angiotensin II type I receptor (AT1-AA) and endothelin -1 (ET-1) are suggested to be important links between placental ischemia and hypertension during preeclampsia. Activation of the angiotensin II type 1 receptor (AT1R) increases endothelial cell production of ET-1; however, the importance of ET-1 in response to AT1-AA–mediated AT1 R activation during preeclampsia is unknown. Furthermore, the role of AT1-AA–mediated increases in blood pressure during pregnancy remains unclear. The objective of this study was to test the hypothesis that AT1-AA, increased to levels observed in preeclamptic women and placental ischemic rats, increases mean arterial pressure (MAP) by activation of the ET-1 system. Chronic infusion of purified rat AT1-AA into normal pregnant (NP) rats for 7 days increased AT1-AA from 0.68±0.5 to 10.88±1.1 chronotropic units (P<0.001). The increased AT1-AA increased MAP from 99±1 to 119±2 mm Hg (P<0.001). The hypertension was associated with significant increases in renal cortices (11-fold) and placental (4-fold) ET-1. To determine whether ET-1 mediates AT1-AA–induced hypertension, pregnant rats infused with AT1-AA and NP rats were treated with an ETA receptor antagonist. MAP was 100±1 mm Hg in AT1-AA+ETA antagonist-treated rats versus 98±2 mm Hg in ETA antagonist-treated rats. Collectively, these data support the hypothesis that one potential pathway whereby AT1-AAs increase blood pressure during pregnancy is by an ET-1–dependent mechanism.

The effect of immune factors, tumor necrosis factor-alpha, and agonistic autoantibodies to the angiotensin II type I receptor on soluble fms-like tyrosine-1 and soluble endoglin production in response to hypertension during pregnancy.

BACKGROUND Preeclampsia is considered a disease of immunological origin associated with abnormalities in inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), and activated lymphocytes secreting autoantibodies to the angiotensin II receptor (AT1-AA). Recent studies have also demonstrated that an imbalance of angiogenic factors, soluble fms-like tyrosine kinase (sFlt-1), and sEndoglin, exists in preeclampsia; however, the mechanisms that initiate their overproduction are unclear. METHODS To determine the role of immune regulation of these factors, circulating and placental sFlt-1 and/or sEndoglin was examined from pregnant rats chronically treated with TNF-alpha or AT1-AA. On day 19 of gestation blood pressure was analyzed and serum and tissues were collected. Placental villous explants were excised and cultured on matrigel coated inserts for 24 h and sFlt-1 and sEndoglin was measured from media. RESULTS In response to TNF-alpha-induced hypertension, sFlt-1 increased from 180 +/- 5 to 2,907 +/- 412 pg/ml. sFlt-1 was also increased from cultured placental explants of TNF-alpha induced hypertensive pregnant rats (n = 12) (2,544 +/- 1,132 pg/ml) vs. explants from normal pregnant (NP) rats (n = 12) (2,189 +/- 586 pg/ml) where as sEng was undetectable. Circulating sFlt-1 increased from 245 +/- 38 to 3,920 +/- 798 pg/ml in response to AT1-AA induced hypertension. sFlt-1 levels were higher (3,400 +/- 350 vs. 2,480 +/- 900 pg/ml) in placental explants from AT1-AA infused rats (n = 12) than NP rats (n = 7). In addition, sEndoglin increased from 30 +/- 2.7 to 44 +/- 3.3 pg/ml (P < 0.047) in AT1-AA infused rats but was undetectable in the media of the placental explants. CONCLUSIONS These data suggest that immune factors may serve as an important stimulus for both sFlt-1 and sEndoglin production in response to placental ischemia.

Hypertension in Response to AT1-AA: Role of Reactive Oxygen Species in Pregnancy-Induced Hypertension

BACKGROUND Agonistic autoantibodies to the angiotensin II type I receptor (AT1-AA) and reactive oxygen species (ROS) are implicated in the pathophysiology of preeclampsia. The objective of this study was to determine the role of AT1-AA to stimulate placental oxidative stress in vivo and role ROS in mediating hypertension in response to AT1-AA during pregnancy. METHODS To achieve these goals, blood pressure (mean arterial pressure (MAP)) and ROS were analyzed in AT1-AA-induced hypertensive pregnant rats in the presence and absence of a superoxide dismutase mimetic, tempol. Rat AT1-AA (1:50) and tempol (30 mg/kg/day) were administered to pregnant rats beginning on day 12 of gestation. On day 19, MAP was analyzed and tissues collected for ROS analysis via lucigenin chemiluminescence. RESULTS MAP increased from 101 ± 2 normal pregnant (NP) rats to 116 ± 2 mm Hg in chronic AT1-AA infused rats (P = 0.002). Placental basal and NADPH oxidase stimulated ROS was 29 ± 6 and 92 ± 10 relative light units (RLUs) in NP rats. These levels increased to 159 ± 29 (P < 0.0001) and 287 ± 60 RLUs (P < 0.006) in AT1-AA infused rats. MAP in AT1-AA + tempol rats was 109 ± 2 mm Hg, no difference than tempol-treated controls (109 ± 3 mm Hg). Administration of tempol decreased basal and NADPH-stimulated placental ROS in AT1-AA-treated rats (121 ± 13; 262 ± 21 RLUs). Basal and NADPH-stimulated ROS in tempol-treated controls were 69 ± 24; 141 ± 33 RLUs. CONCLUSION This study indicates that AT1-AAs contribute to placental oxidative stress; one mechanism whereby the AT1-AA mediates hypertension during pregnancy.

Control of soluble fms-like tyrosine-1 (sFlt-1) production response to placental ischemia/hypoxia: role of tumor necrosis factor-α

Although abnormal soluble fms-like tyrosine kinase-1 (sFlt-1) production is thought to be an important factor in the pathogenesis of preeclampsia (PE), the mechanisms that regulate the production of sFlt-1 during PE are unclear. While our laboratory has shown tumor necrosis factor-α (TNF-α) and sFlt-1 to be elevated in pregnant rats in response to placental ischemia, the importance of TNF-α in the regulation of sFlt-1 production is unknown. Therefore, the purpose of this study was to determine the role of TNF-α in mediating the increase in sFlt-1 in response to placental ischemia or hypoxia. Reductions in uterine perfusion pressure in pregnant rats significantly increased plasma levels of sFlt-1 and tended to increase TNF-α, an effect markedly attenuated by pretreatment with a TNF-α inhibitor etanercept (0.4 mg/kg). To further assess chronic interactions between TNF-α and sFlt-1, we examined a chronic effect of TNF-α infusion (50 ng/day) into normal pregnant rats to increase plasma sFlt-1 levels, as well as the effects of acute hypoxia on placental sFlt-1 production in the absence and presence of TNF-α blockade. Placental explants exposed to hypoxic conditions had enhanced TNF-α levels versus normoxic conditions, as well as increased sFlt-1 production. Pretreatment of placental explants with etanercept (15 μM) significantly reduced TNF-α levels in response to hypoxia but did not attenuate sFlt-1 production. These data suggest that while TNF-α may not play an important role in stimulating sFlt-1 production in response to acute hypoxia, a more chronic hypoxia, or placental ischemia may be an important stimulus for enhanced sFlt-l production.

Standardized Mississippi Protocol Treatment of 190 Patients with HELLP Syndrome: Slowing Disease Progression and Preventing New Major Maternal Morbidity

Objective. To evaluate the effectiveness of the Mississippi Protocol (MP) to treat HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome. Methods. Uniform early initiation of MP (corticosteroids, magnesium sulfate, systolic blood pressure control) was studied prospectively in patients admitted with severe preeclampsia/class 1 or class 2 HELLP syndrome. Results. One hundred and ninety patients between 2000 and 2007 received MP without suffering maternal death, stroke, or liver rupture. Only 39 of 163 patients (24%) not class 1 when MP began progressed to class 1 disease; only 18.2% of class 1 and 2.4% of class 2 subsequently developed major maternal morbidity. Conclusion. Early initiation of MP inhibits HELLP syndrome disease progression and severity.

Angiotensin II type 1 autoantibody induced hypertension during pregnancy is associated with renal endothelial dysfunction.

BACKGROUND Previous investigations suggested that agonistic autoantibodies to the angiotensin II type I receptor (AT1-AA) might mediate a hypertensive response through dysregulation of the endothelin-1 system. AT1-AA induced hypertension was attenuated by the AT1 receptor and/or endothelin-1 type A receptor antagonists. OBJECTIVES This study was undertaken to determine if AT1-AA induced hypertension was associated with renal endothelial dysfunction. METHODS We compared the vascular reactivity of renal interlobar arteries from normal pregnant control rats and AT1-AA long-term infused pregnant rats in the presence and absence of endothelin type A (ET(A)) receptor antagonism. Renal endothelial function was tested using isolated renal interlobar arteries in a pressure myograph, which were exposed to acetylcholine or sodium nitroprusside. RESULTS Vasodilatory responses to the endothelial-dependent agonist acetylcholine were impaired in AT1-AA rats (74 [10]%) compared with normal pregnant controls (95 [5]%, P < 0.05). In the presence of ET(A) receptor antagonism, no differences were observed between controls or the AT1-AA treated group with regard to endothelial-dependent (acetylcholine) relaxation. CONCLUSION AT1-AA induced hypertension during pregnancy was associated with disparate renal endothelial responses to acetylcholine. The difference in renal vascular responses between AT1-AA and normal pregnant rats was abolished by ET(A) receptor blockade.

Agonistic autoantibodies to the angiotensin II type I receptor cause pathophysiologic characteristics of preeclampsia.

BACKGROUND Preeclampsia (PE), new-onset hypertension with proteinuria during pregnancy, is associated with increased reactive oxygen species, the vasoactive peptide endothelin-1 (ET-1), T and B lymphocytes, soluble antiangiogenic factors sFlt-1 and sEndoglin (sFlt-1 and sEng), and agonistic autoantibodies to the angiotensin II type I receptor (AT1-AA). OBJECTIVES One important area of investigation for our laboratory was to determine what role AT1-AA plays in the pathophysiology associated with PE. METHODS To achieve this goal, we examined the effect of AT1-AA suppression on hypertension in response to placental ischemia as well as the effect of AT1-AA on increased blood pressure, ET-1, reactive oxygen species, and sFlt-1 in normal pregnant rats (NP). RESULTS We demonstrated reductions in uterine perfusion pressure (RUPP) to be a stimulus for AT1-AA during pregnancy. We utilized the technique of B-cell depletion to suppress circulating AT1-AA in RUPP rats and found that AT1-AA suppression in RUPP rats was associated with lower blood pressure and ET-1 activation. To determine a role for AT1-AA to mediate hypertension during pregnancy, we infused purified rat AT1-AA (1:50) into NP rats, and analyzed blood pressure and soluble factors. We consistently found that AT1-AA infused rats had significantly increased AT1-AA and blood pressure above NP rats. This hypertension was associated with significantly increased ET-1 in renal cortices (11-fold) and placenta (4-fold), and there was an approximately 2- to 3-fold increase in placental oxidative stress. Furthermore, antiangiogenic factors sFlt-1 and sEng were significantly increased in the AT1-AA induced hypertensive group compared with the NP controls. CONCLUSIONS Collectively, these data indicated an important role for AT1-AA stimulated in response to placental ischemia that caused hypertension during pregnancy.

Effects of 17-Hydroxyprogesterone on Tumor Necrosis Factor-α-Induced Hypertension During Pregnancy

BACKGROUND Inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) may be an important link between placental ischemia and hypertension in preeclampsia. We examined the effect of 17-hydroxyprogesterone caproate (17-OHP) on TNF-alpha-stimulated endothelin (ET) production and hypertension during pregnancy. METHODS TNF-alpha-stimulated ET was examined from endothelial cells cultured in the presence and absence of progesterone. Blood pressure and tissue ET-1 were measured in the following groups of pregnant rats: controls, 17-OHP (3.32 mg/kg), TNF-alpha treated (50 ng/day), TNF-alpha treated+17-OHP. RESULTS Progesterone abolished TNF-alpha-stimulated ET-1 from endothelial cells. TNF-alpha-induced hypertension was associated with significant increases in renal and placental ET-1. Administration of 17-OHP attenuated TNF-alpha-induced hypertension and decreased renal ET-1. CONCLUSION Progesterone directly abolished TNF-alpha-stimulated ET-1 and attenuated TNF-alpha-induced hypertension, possibly via suppression of the renal ET-1 system. These data suggest that treatment with progesterone of hypertension associated with elevated cytokines during pregnancy may be worthy of further consideration.

Hyperuricemia facilitates the prediction of maternal and perinatal adverse outcome in patients with severe/superimposed preeclampsia.

Objective. Hyperuricemia has received much attention and debate recently with regard to its utility as a marker for preeclampsia and as a predictor of adverse maternal–fetal outcome. This investigation was undertaken in patients with severe/superimposed preeclampsia to determine whether the maternal uric acid (UA) level at initial hospital admission is a useful predictor of subsequent adverse maternal and/or perinatal outcomes. Methods. Retrospective analysis of all patients diagnosed with severe preeclampsia, superimposed preeclampsia or HELLP syndrome during 2005 at the University of Mississippi Medical Center (UMMC). Clinical and laboratory data were collected, entered and stored electronically in a password protected, secure system. Results. Adverse maternal outcomes occurred in 15.3% of 258 patients in the cohort. Mean UA concentration in the absence of adverse maternal outcomes was 342.6 ± 77.3 compared to 396.1 ± 117.2 μmol/l in pregnancies with complications (p < 0.001). The positive likelihood ratio (LR) for adverse maternal outcome was 5.3 with UA ≥ 76.3 μmol/l and creatinine ≥1.0 mg/dl. LRs rose in association with other abnormal preeclampsia serum markers. Adverse perinatal outcomes occurred in 45.2% of births. The LRs for adverse perinatal outcomes remained unchanged around 1.0. Mean UA was 363.4 ± 91.0 compared to 339.0 ± 80.9 μmol/l in pregnancies without adverse outcomes (p = 0.021). Conclusions. Maternal hyperuricemia is a better predictor of maternal than perinatal risk and adverse outcome.

HELLP Syndrome with and without Eclampsia

We assessed pregnancy outcomes for patients with HELLP syndrome (hemolysis; elevated liver enzymes; low platelet count) with and without concurrent eclampsia. We performed a retrospective investigation of data spanning three decades of patients with class 1 or 2 HELLP syndrome with concurrent eclampsia (HELLP + E) and patients with HELLP syndrome without eclampsia. Data were analyzed by appropriate tests for continuous or categorical outcomes with differences considered significant if P < 0.05. During 1981 to 1996 and 2000 to 2006, there were 693 patients with class 1 or 2 HELLP syndrome; altogether, 70 patients had HELLP + E. The only demographic difference was greater nulliparity in HELLP + E patients. Otherwise, inconsistent and clinically insignificant differences were observed between groups. Despite the relatively large size of the study groups, we were unable to detect a significant worsening of maternal or perinatal outcome in HELLP + E patients compared with HELLP patients. In our experience, eclampsia does not appear to contribute a significant adverse impact upon the course or outcome of HELLP syndrome pregnancies.