Complement activation is critical for placental ischemia-induced hypertension in the rat

Abstract

Preeclampsia is a major obstetric problem defined by new-onset hypertension and proteinuria associated with compromised placental perfusion. Although activation of the complement system is increased in preeclampsia compared to normal pregnancy, it remains unclear whether excess complement activation is a cause or consequence of placental ischemia. Therefore, we hypothesized that complement activation is critical for placental ischemia-induced hypertension. We employed the reduced utero-placental perfusion pressure (RUPP) model of placental ischemia in the rat to induce hypertension in the third trimester and evaluated the effect of inhibiting complement activation with a soluble recombinant form of an endogenous complement regulator, human complement receptor 1 (sCR1; CDX-1135). On day 14 of a 21-day gestation, rats received either RUPP or Sham surgery and 15 mg/kg/day sCR1 or saline intravenously on days 14–18. Circulating complement component 3 decreased and complement activation product C3a increased in RUPP vs Sham (p<0.05), indicating complement activation had occurred. Mean arterial pressure (MAP) measured on day 19 increased in RUPP vs Sham rats (109.8±2.8 mmHg vs 93.6±1.6 mmHg). Treatment with sCR1 significantly reduced elevated MAP in RUPP rats (98.4±3.6 mmHg, p<0.05) and reduced C3a production. Vascular endothelial growth factor (VEGF) decreased in RUPP compared to Sham rats, and the decrease in VEGF was not affected by sCR1 treatment. Thus, these studies have identified a mechanistic link between complement activation and the pregnancy complication of hypertension apart from free plasma VEGF and have identified complement inhibition as a potential treatment strategy for placental ischemia-induced hypertension in preeclampsia.

Differential Effects of Complement Activation Products C3a and C5a on Cardiovascular Function in Hypertensive Pregnant Rats

“…Antagonist treatment of Sham animals did not significantly alter circulating free plasma VEGF or fetal weight compared with Sham Veh animals. As previously reported, no increase in soluble fms-like tyrosine kinase-1 (soluble VEGF receptor 1), as measured by the commercially available mouse kit from R&D Systems, was detected in EDTA plasma collected on GD 19 from RUPP versus Sham animals in our experiments (Lillegard et al, 2013b). In addition, a significant increase in protein in urine was also not detected between RUPP and Sham animals in these studies, consistent with previous reports regarding the inconsistency of this measure in the RUPP model (Granger et al, 2006).…”

“…Using the reduced uterine perfusion pressure (RUPP) rat model of placental ischemia-induced hypertension and soluble complement receptor 1 as an inhibitor of complement activation, our studies were the first to describe a link between complement system activation and the hypertension resulting from thirdtrimester placental ischemia in pregnancy (Lillegard et al, 2013b). We also demonstrated that angiogenic imbalance as well as impaired endothelial-dependent relaxation in isolated blood vessels occur in this model (Gilbert et al, 2010).…”

“…The RUPP procedure was performed on gestational day (GD) 14 to achieve chronic placental ischemia and hypertension in pregnant rats on GD 19 (see Supplemental Methods for details) (Lillegard et al, 2013b). All animal experiments were approved by the University of Minnesota Institutional Animal Care and Use Committee and conformed to the National Institutes of Health Guide for Care and Use of Laboratory Animals.…”

“…Mean arterial pressure (MAP) and heart rate were measured via intra-arterial catheter in unanesthetized, restrained animals on GD 19, and serum, plasma, and fetal and placental tissue were harvested as described previously (Lillegard et al, 2013b). Circulating white blood cells (WBCs) in EDTA blood were counted by standard methods in a hemacytometer.…”

“…C3a serum concentration was measured by Western immunoblot as described previously (Lillegard et al, 2013b) and is expressed as C3a units per microliter relative to the signal intensity of 1 ml of standard pool of yeast-activated rat serum. Total complement hemolytic activity was measured as previously described and expressed as inverse dilution of serum causing 50% hemolysis of sensitized sheep erythrocytes (CH 50 ) (Lillegard et al, 2013b). The ability of C3aRA or C5aRA to inhibit complement activation in vitro was also assessed by incubation of antagonist or Veh with a pool of nonpregnant rat serum prior to determination of CH 50 .…”