Evaluation of a rat model of preeclampsia for HELLP syndrome characteristics

Reduced uterine perfusion pressure as a model for preeclampsia and fetal growth restriction in murine: a systematic review and meta-analysis

The reduced uterine perfusion pressure (RUPP) model is frequently used to study preeclampsia and fetal growth restriction. An improved understanding of influential factors might improve reproducibility and reduce animal use considering the variability in RUPP phenotype. We performed a systematic review and meta-analysis by searching Medline and Embase (until 28 March, 2023) for RUPP studies in murine. Primary outcomes included maternal blood pressure (BP) or proteinuria, fetal weight or crown-rump length, fetal reabsorptions, or antiangiogenic factors. We aimed to identify influential factors by meta-regression analysis. We included 155 studies. Our meta-analysis showed that the RUPP procedure results in significantly higher BP (MD = 24.1 mmHg; [22.6; 25.7]; n = 148), proteinuria (SMD = 2.3; [0.9; 3.8]; n = 28), fetal reabsorptions (MD = 50.4%; [45.5; 55.2]; n = 42), circulating soluble FMS-like tyrosine kinase-1 (sFlt-1) (SMD = 2.6; [1.7; 3.4]; n = 34), and lower fetal weight (MD = -0.4 g; [-0.47; -0.34]; n = 113. The heterogeneity (variability between studies) in primary outcomes appeared ≥90%. Our meta-regression identified influential factors in the method and time point of BP measurement, randomization in fetal weight, and type of control group in sFlt-1. The RUPP is a robust model considering the evident differences in maternal and fetal outcomes. The high heterogeneity reflects the observed variability in phenotype. Because of underreporting, we observed reporting bias and a high risk of bias. We recommend standardizing study design by optimal time point and method chosen for readout measures to limit the variability. This contributes to improved reproducibility and thereby eventually improves the translational value of the RUPP model.

The BPH/5 Mouse Model of Superimposed Preeclampsia Is Not a Model of HELLP Syndrome

Preeclampsia (PE) is a multisystemic disease of pregnancy affecting 2-8% of women worldwide. PE-induced liver disease is a rare but important complication of pregnancy. The pathogenesis of liver dysfunction in PE is poorly understood, but is correlated with dysregulated angiogenic, inflammatory, and hypoxic events in the early phase of placental development. Because BPH/5 mice develop the maternal and fetal hallmarks of PE during pregnancy, we hypothesized that they may also share the clinicopathologic findings of the human PE-associated hemolysis elevated liver transaminases low platelets (HELLP) syndrome. Using this model, we determined that microangiopathic hemolysis, thrombocytopenia, and elevated liver enzymes do not occur in mid to late gestation. Pregnant BPH/5 mice do not develop histologic evidence of hepatic inflammation, but they do have increased microsteatosis scores at preconception and in mid to late gestation that progress to macrosteatosis in a subset of mice in late gestation. The transcriptional upregulation of TNF-α, CXCL-10, and TLR-2 occurs in mid gestation prior to the onset of macrosteatosis. The BPH/5 female mouse is not a model of HELLP syndrome, but may be a model of fatty liver disease associated with pregnancy.

Hypoxia-induced small extracellular vesicle proteins regulate proinflammatory cytokines and systemic blood pressure in pregnant rats

Small extracellular vesicles (sEVs) released from the extravillous trophoblast (EVT) are known to regulate uterine spiral artery remodeling during early pregnancy. The bioactivity and release of these sEVs differ under differing oxygen tensions and in aberrant pregnancy conditions. Whether the placental cell-derived sEVs released from the hypoxic placenta contribute to the pathophysiology of preeclampsia is not known. We hypothesize that, in response to low oxygen tension, the EVT packages a specific set of proteins in sEVs and that these released sEVs interact with endothelial cells to induce inflammation and increase maternal systemic blood pressure. Using a quantitative MS/MS approach, we identified 507 differentially abundant proteins within sEVs isolated from HTR-8/SVneo cells (a commonly used EVT model) cultured at 1% (hypoxia) compared with 8% (normoxia) oxygen. Among these differentially abundant proteins, 206 were up-regulated and 301 were down-regulated (P < 0.05), and they were mainly implicated in inflammation-related pathways. In vitro incubation of hypoxic sEVs with endothelial cells, significantly increased (P < 0.05) the release of GM-CSF, IL-6, IL-8, and VEGF, when compared with control (i.e. cells without sEVs) and normoxic sEVs. In vivo injection of hypoxic sEVs into pregnant rats significantly increased (P < 0.05) mean arterial pressure with increases in systolic and diastolic blood pressures. We propose that oxygen tension regulates the release and bioactivity of sEVs from EVT and that these sEVs regulate inflammation and maternal systemic blood pressure. This novel oxygen-responsive, sEVs signaling pathway, therefore, may contribute to the physiopathology of preeclampsia.

Innate and Adaptive Immune Responses in HELLP Syndrome

Innate and adaptive immune involvement in hemolysis, elevated liver enzymes and low platelet (HELLP) syndrome is an understudied field, although it is of high clinical importance. This syndrome implies a risk of serious morbidity and mortality to both the mother and the fetus during pregnancy. It was proposed that HELLP syndrome occurs in a circulatory inflammatory milieu, that might in turn participate in a complex interplay between the secreted inflammatory immunomodulators and immune cell surface receptors. Meanwhile, reported immune cell attenuation during HELLP may consequently lead to a prolonged immunoactivation and tissue damage. In this regard, learning more about the immune components of this syndrome should widen the understanding of the HELLP pathophysiology and eventually enable development of novel immune-based therapeutics. This review aims to summarize and discuss the recent and previous findings of the innate and adaptive immune responses during HELLP in order to update the current knowledge of the immune involvement in HELLP pathogenesis.

Hypertension, Anxiety, and Blood-Brain Barrier Permeability Are Increased in Postpartum Severe Preeclampsia/Hemolysis, Elevated Liver Enzymes, and Low Platelet Count Syndrome Rats

Hypertension and inflammation during pregnancy are suggested to contribute to the development of postpartum depression and anxiety. Using a rat model of severe preeclampsia and hemolysis, elevated liver enzymes, and low platelet count syndrome, which displays both hypertension and inflammation during pregnancy, we evaluated whether rats were prone to develop depression or anxiety in the postpartum period. On gestational day 12, miniosmotic pumps infusing sFlt-1 (soluble fms-like tyrosine kinase-1) and sEng (soluble endoglin) were placed into rats, a subset of these rats was infused with 2 mg/kg of Orencia (abatacept) the following day to determine whether immune suppression via T-cell depletion prevented any changes in maternal depression or anxiety-like behavior. All rats, including normal pregnant (NP) controls, delivered between gestational days 21 and 22. Postpartum severe preeclamptic rats buried significantly more marbles compared with NP rats ( P=0.002) and Orencia-treated rats ( P=0.05). Severe preeclamptic rats spent significantly more time in closed arms of the elevated plus maze compared with NP rats ( P=0.009) and Orencia-treated rats ( P=0.05). Severe preeclamptic rats were hypertensive compared with NP ( P=0.03) and Orencia-treated rats ( P=0.01). Finally, severe preeclamptic rats had increased blood-brain barrier permeability compared with NP rats ( P=0.03), which was reversed in Orencia-treated rats ( P=0.008). These results suggest that severe preeclampsia/hemolysis, elevated liver enzymes, and low platelet count syndrome during pregnancy contributes to an increase in anxiety-like behavior, blood-brain barrier permeability, and hypertension in the postpartum. The current results suggest that T-cell suppression during pregnancy can also help prevent chronic hypertension and increased anxiety in the postpartum period.

Blockade of CD40 ligand for intercellular communication reduces hypertension, placental oxidative stress, and AT1-AA in response to adoptive transfer of CD4+ T lymphocytes from RUPP rats

Preeclampsia (PE) is associated with altered immune activation during pregnancy. We have previously shown that adoptive transfer of CD4(+) T cells from the reduced uterine perfusion pressure (RUPP) rat model of PE increases blood pressure, oxidative stress (ROS), and inflammation in normal pregnant recipient rats. The objective of this study was to determine if blockade of communication via the CD40-CD40 ligand (CD40L) interaction between placental ischemia-induced CD4(+) T cells with endogenous normal pregnant (NP) cells would improve pathophysiology that was previously observed in NP recipient rats of RUPP CD4(+) T cells. Splenic CD4(+) T lymphocytes were magnetically separated, incubated with 2.5 μg/ml anti-CD40 ligand (αCD40L) overnight, and transferred into NP rats on day 12 of gestation (NP+RUPP CD4(+) T+anti-CD40L). On day 19 of gestation, blood pressure (MAP), blood, and tissues were collected. MAP was 99 ± 2 in NP (n = 13), 116 ± 4 in NP+RUPP CD4(+) T cells (n = 7; P < 0.01); MAP only increased to 104 ± 2 in NP+RUPP CD4(+) T cells+CD40L (n = 24) (P < 0.05 vs. NP+RUPP CD4(+) T cells). Mechanisms of hypertension in response to RUPP CD4(+) T cells include endothelin-1 (ET-1), ROS, and angiotensin II type I receptor (AT1-AA) were analyzed. Inhibition of CD40L binding reduced placental ET-1 to 2.3-fold above NP rats and normalized placental ROS from 318.6 ± 89 in NP+RUPP CD4(+) T cells (P < 0.05) to 118.7 ± 24 in NP+RUPP CD4(+) T+anti-CD40L (P < 0.05). AT1-AA was also normalized with inhibition of CD40L. These data suggest that placental ischemia-induced T-cell communication via the CD40L is one important mechanism leading to much of the pathophysiology of PE.

Hypertension, inflammation and T lymphocytes are increased in a rat model of HELLP syndrome

OBJECTIVE

An animal model of hemolysis, elevated liver enzymes, low platelet count (HELLP) was used to determine if T lymphocytes accompany hypertension and increased inflammatory cytokines.

METHODS

sFlt-1 (4.7 µg/kg/day) and sEndoglin (7 µg/kg/day) were infused into normal pregnant rats (HELLP rats) for 8 days.

RESULTS

HELLP was associated with increased mean arterial pressure (p = 0.0001), hemolysis (p = 0.044), elevated liver enzymes (p = 0.027), and reduced platelets (p = 0.035). HELLP rats had increased plasma levels of TNFα (p = 0.039), IL-6 (p = 0.038) and IL-17 (p = 0.04). CD4(+) and CD8(+) T lymphocytes were increased.

CONCLUSION

These data support the hypothesis that T cells are associated with hypertension and inflammation.

A combined supplementation of omega-3 fatty acids and micronutrients (folic acid, vitamin B12) reduces oxidative stress markers in a rat model of pregnancy induced hypertension

Objectives

Our earlier studies have highlighted that an altered one carbon metabolism (vitamin B₁₂, folic acid, and docosahexaenoic acid) is associated with preeclampsia. Preeclampsia is also known to be associated with oxidative stress and inflammation. The current study examines whether maternal folic acid, vitamin B₁₂ and omega-3 fatty acid supplementation given either individually or in combination can ameliorate the oxidative stress markers in a rat model of pregnancy induced hypertension (PIH).

Materials and Methods

Pregnant Wistar rats were assigned to control and five treatment groups: PIH; PIH + vitamin B₁₂; PIH + folic acid; PIH + Omega-3 fatty acids and PIH + combined micronutrient supplementation (vitamin B₁₂ + folic acid + omega-3 fatty acids). L-Nitroarginine methylester (L-NAME; 50 mg/kg body weight/day) was used to induce hypertension during pregnancy. Blood Pressure (BP) was recorded during pregnancy and dams were dissected at d20 of gestation.

Results

Animals from the PIH group demonstrated higher (p<0.01 for both) systolic and diastolic BP; lower (p<0.01) pup weight; higher dam plasma homocysteine (p<0.05) and dam and offspring malondialdehyde (MDA) (p<0.01), lower (p<0.05) placental and offspring liver DHA and higher (p<0.01) tumor necrosis factor–alpha (TNF–ά) levels as compared to control. Individual micronutrient supplementation did not offer much benefit. In contrast, combined supplementation lowered systolic BP, homocysteine, MDA and placental TNF-ά levels in dams and liver MDA and protein carbonyl in the offspring as compared to PIH group.

Conclusion

Key constituents of one carbon cycle (folic acid, vitamin B₁₂ and DHA) may play a role in reducing oxidative stress and inflammation in preeclampsia.

Inhibition of PPARγ during rat pregnancy causes intrauterine growth restriction and attenuation of uterine vasodilation

Decreased peroxisome proliferator-activated receptor gamma (PPARγ) activity is thought to have a major role in preeclampsia through abnormal placental development. However, the role of PPARγ in adaptation of the uteroplacental vasculature that may lead to placental hypoperfusion and fetal growth restriction during pregnancy is not known. Here, pregnant Sprague-Dawley rats (n = 11/group) were treated during the second half of pregnancy with the PPARγ inhibitor GW9662 (10 mg/kg/day in food) or vehicle. Pregnancy outcome and PPARγ mRNA, vasodilation and structural remodeling were determined in maternal uterine and mesenteric arteries. PPARγ was expressed in uterine vascular tissue of both non-pregnant and pregnant rats with ~2-fold greater expression in radial vs. main uterine arteries. PPARγ mRNA levels were significantly higher in uterine compared to mesenteric arteries. GW9662 treatment during pregnancy did not affect maternal physiology (body weight, glucose, blood pressure), mesenteric artery vasodilation or structural remodeling of uterine and mesenteric vessels. Inhibition of PPARγ for the last 10 days of gestation caused decreased fetal weights on both day 20 and 21 of gestation that was associated with impaired vasodilation of radial uterine arteries in response to acetylcholine and sodium nitroprusside. These results define an essential role of PPARγ in the control of uteroplacental vasodilatory function during pregnancy, an important determinant of blood flow to the placenta and fetus. Strategies that target PPARγ activation in the uterine circulation could have important therapeutic potential in treatment of pregnancies complicated by hypertension, diabetes or preeclampsia.

A model of preeclampsia in rats: the reduced uterine perfusion pressure (RUPP) model

Preeclampsia is defined as new-onset hypertension with proteinuria after 20 wk gestation and is hypothesized to be due to shallow trophoblast invasion in the spiral arteries thus resulting in progressive placental ischemia as the fetus grows. Many animal models have been developed that mimic changes in maternal circulation or immune function associated with preeclampsia. The model of reduced uterine perfusion pressure in pregnant rats closely mimics the hypertension, immune system abnormalities, systemic and renal vasoconstriction, and oxidative stress in the mother, and intrauterine growth restriction found in the offspring. The model has been successfully used in many species; however, rat and primate are the most consistent in comparison of characteristics with human preeclampsia. The model suffers, however, from lack of the ability to study the mechanisms responsible for abnormal placentation that ultimately leads to placental ischemia. Despite this limitation, the model is excellent for studying the consequences of reduced uterine blood flow as it mimics many of the salient features of preeclampsia during the last weeks of gestation in humans. This review discusses these features.

Recombinant vascular endothelial growth factor 121 attenuates autoantibody-induced features of pre-eclampsia in pregnant mice

BACKGROUND

Pre-eclampsia (PE) is a serious hypertensive disorder of pregnancy characterized by excessive production of a soluble form of the vascular endothelial growth factor (VEGF) receptor-1, termed soluble fms-like tyrosine kinase-1 (sFlt-1). This placental-derived factor is believed to be a key contributor to the clinical features of PE. Women with PE are also characterized by the presence of autoantibodies, termed angiotensin type 1 receptor activating autoantibody (AT(1)-AA), that activate the major angiotensin receptor, AT(1). These autoantibodies cause clinical features of PE and elevated sFlt-1 when injected into pregnant mice. The research reported here used this autoantibody-injection model of PE to assess the therapeutic potential of recombinant VEGF(121), a relatively stable form of the natural ligand.

METHODS

Immunoglobulin G (IgG) from women with PE was injected into pregnant mice with or without continuous infusion of recombinant VEGF(121). Injected mice were monitored for symptoms of PE.

RESULTS

As a result of infusion of recombinant VEGF(121) autoantibody-induced hypertension (systolic blood pressure) was reduced from 159 ± 5 to 124 ± 5 mm Hg, proteinuria from 111 ± 16 to 40 ± 5 mg protein/mg creatinine and blood urea nitrogen levels from 31 ± 1 mg/dl to 18 ± 2 mg/dl, P < 0.05. Histological analysis revealed that autoantibody-induced glomerular damage including the narrowing of Bowman's space and occlusion of capillary loop spaces was largely prevented by VEGF(121) infusion. Finally, impaired placental angiogenesis resulting from AT(1)-AA injection was significantly improved by VEGF(121) infusion.

CONCLUSIONS

The infusion of recombinant VEGF(121) significantly attenuated autoantibody-induced features of PE.

Morphologic Changes of the Uteroplacental Unit in Preeclampsia-Like Syndrome in Rats

OBJECTIVE

Chronic administration of the nitric oxide synthase inhibitor NG-nitro-L-arginine methylester (L-NAME) induces a preeclampsia-like syndrome in rats. This animal study aims to determine whether L-NAME-induced preeclampsia-like syndrome is also associated with morphologic changes in the uteroplacental unit.

METHODS

Mating was induced in 20 adult Sprague-Dawley rats. On day 14, five pregnant rats were randomly assigned to receive L-NAME, whereas six served as controls. Weight, continuous blood pressure, urine volume, urine protein content, litter size, number of resorption sites, placental weight, and weight of pups were documented. Uteroplacental tissue of three L-NAME and three control animals were processed for microscopy using corrosion cast technique.

RESULTS

The L-NAME-treated animals had a significantly smaller litter size (p=.033) and a significantly higher number of resorption sites (p=.021) when compared to controls. In L-NAME-treated rats midlength inner-diameter of maternal arterial channels (p<.001) and cross-sectional area (p<.001) were significantly smaller than were those in controls.

CONCLUSIONS

Chronic administration of L-NAME to pregnant rats is associated with significant morphologic changes of the uteroplacental vasculature. The L-NAME-induced pathologic alterations resulted in decreased litter size and increased number of resorption sites that may be contributed to diminished uteroplacental perfusion.

Soluble Fms-like tyrosine kinase 1 and endothelial dysfunction in the pathogenesis of preeclampsia

Preeclampsia, a pregnancy-specific syndrome of hypertension and proteinuria, is characterized by defective placental vasculogenesis and widespread maternal endothelial dysfunction. Although the manifestations of preeclampsia are primarily maternal, the burden of morbidity and mortality is often on the neonate, since the only effective treatment-delivery of the fetus and placenta-often results in iatrogenic prematurity. In this review, we summarize recent advances in our understanding of the pathophysiology of preeclampsia, including normal and aberrant placental vascular development and evidence for endothelial dysfunction. We describe recent evidence that supports a novel mechanism in which a maladaptive shift in placental production of angiogenic factors such as soluble fms-like tyrosine kinase 1 (a circulating antiangiogenic protein) may play an important role in the pathogenesis of preeclampsia.

Placental dysfunction in Suramin-treated rats – a new model for pre-eclampsia

Impaired placentation and oxidative stress are proposed to play major roles in the pathogenesis of placental dysfunction and pre-eclampsia. This study was carried out to evaluate if inhibited angiogenesis by Suramin injections in early pregnancy may cause a condition resembling pre-eclampsia in rats. Rats of two different Sprague-Dawley strains, U and H, were given intraperitoneal injections of Suramin or saline in early pregnancy. The outcome of pregnancy was evaluated on gestational day 20. Suramin injections caused increased blood pressure and decreased renal blood flow in the U rats. In both rat strains Suramin decreased the placental blood flow and caused fetal growth retardation. In both strains the placental concentration of the isoprostane 8-epi-PGF2alpha was increased, indicating oxidative stress. The serum concentration of Endothelin-1 was increased in the U rats. The U strain had a lower basal placental blood flow, and the effects of Suramin were more pronounced in this strain. We conclude, that Suramin injections to pregnant rats cause a state of placental insufficiency, which partly resembles human pre-eclampsia. The induction of this condition is at least partly mediated by oxidative stress, and is subject to varied genetic susceptibility.