Differential effects of complement activation products c3a and c5a on cardiovascular function in hypertensive pregnant rats

Abstract

Early-onset pre-eclampsia is characterized by decreased placental perfusion, new-onset hypertension, angiogenic imbalance, and endothelial dysfunction associated with excessive activation of the innate immune complement system. Although our previous studies demonstrated that inhibition of complement activation attenuates placental ischemia-induced hypertension using the rat reduced uterine perfusion pressure (RUPP) model, the important product(s) of complement activation has yet to be identified. We hypothesized that antagonism of receptors for complement activation products C3a and C5a would improve vascular function and attenuate RUPP hypertension. On gestational day (GD) 14, rats underwent sham surgery or vascular clip placement on ovarian arteries and abdominal aorta (RUPP). Rats were treated once daily with the C5a receptor antagonist (C5aRA), PMX51 (acetyl-F-[Orn-P-(D-Cha)-WR]), the C3a receptor antagonist (C3aRA), SB290157 (N(2)-[(2,2-diphenylethoxy)acetyl]-l-arginine), or vehicle from GD 14-18. Both the C3aRA and C5aRA attenuated placental ischemia-induced hypertension without affecting the decreased fetal weight or decreased concentration of free circulating vascular endothelial growth factor (VEGF) also present in this model. The C5aRA, but not the C3aRA, attenuated placental ischemia-induced increase in heart rate and impaired endothelial-dependent relaxation. The C3aRA abrogated the acute pressor response to C3a peptide injection, but it also unexpectedly attenuated the placental ischemia-induced increase in C3a, suggesting nonreceptor-mediated effects. Overall, these results indicate that both C3a and C5a are important products of complement activation that mediate the hypertension regardless of the reduction in free plasma VEGF. The mechanism by which C3a contributes to placental ischemia-induced hypertension appears to be distinct from that of C5a, and management of pregnancy-induced hypertension is likely to require a broad anti-inflammatory approach.

Fig. 1.

Major pathways of complement activation leading to generation of anaphylatoxins C3a and C5a.

Fig. 2.

C3a and C5a receptor antagonists differentially attenuate placental ischemia–induced hypertension and heart rate. Sham or RUPP animals were treated with Veh, C3aRA, or C5aRA from GD 14–18. Values represent mean ± S.E. of MAP or heart rate measured on GD 19. (A) Increase in MAP in the RUPP Veh group (n = 23) was significantly inhibited by the C3aRA (n = 12) or C5aRA (n = 11). MAP did not differ between Sham animals treated with Veh (n = 19), C3aRA (n = 6), or C5aRA (n = 5). (B) Increased heart rate in RUPP Veh (n = 23) versus Sham Veh (n = 19) animals was significantly inhibited by the C5aRA (n = 11; P < 0.05) but not the C3aRA (n = 12; P = 0.11). Heart rate did not differ between Sham animals treated with Veh, C3aRA (n = 6), or C5aRA (n = 5). *P < 0.05 for indicated comparisons.

Fig. 3.

C3a and C5a receptor antagonists do not reverse decreased free plasma VEGF or average fetal weight following placental ischemia. Sham or RUPP animals were treated with Veh, C3aRA, or C5aRA from GD 14–18. Values represent geometric mean ± S.E. of VEGF in GD 19 plasma or fetal weight measured at GD 19. (A) Decrease in VEGF in the RUPP Veh group (n = 23) was not affected by the C3aRA (n = 12) or C5aRA (n = 11). Free plasma VEGF at GD 19 did not differ between Sham animals treated with Veh (n = 19), C3aRA (n = 6), or C5aRA (n = 5). (B) Decrease in fetal weight in the RUPP Veh group (n = 22) was not affected by the C3aRA (n = 11) or C5aRA (n = 10). Fetal weight did not differ between Sham animals treated with Veh (n = 19), C3aRA (n = 6), or C5aRA (n = 5). *P < 0.05 for indicated comparisons.

Fig. 4.

The C3aRA, but not the C5aRA, attenuates increased serum C3a following placental ischemia. Sham or RUPP animals were treated with Veh, C3aRA, or C5aRA from GD 14–18. The increase in C3a in RUPP Veh animals (n = 23) was significantly inhibited by the C3aRA (n = 12) but not the C5aRA (n = 11). Compared with Sham Veh animals (n = 19), the C3a concentration was significantly decreased by the C3aRA (n = 6) but not the C5aRA (n = 5). Values represent mean ± S.E. of serum C3a measured on GD 19. *P < 0.05 for indicated comparisons.

Fig. 5.

The C3aRA prevents increased MAP induced by C3a peptide in pregnant (GD 19) and nonpregnant females. C3a peptide increased MAP in GD 19 animals or nonpregnant females. The C3aRA did not increase MAP but inhibited the C3a peptide–induced increase in MAP. Values represent mean ± S.E. of percent increase in MAP in 4–8 animals per treatment group. *P < 0.05 versus C3a peptide injection alone.

Fig. 6.

The C5aRA, but not the C3aRA, attenuates numbers of circulating neutrophils. Sham or RUPP animals were treated with Veh, C3aRA, or C5aRA from GD 14–18. A significant decrease in circulating neutrophils occurred with C5aRA treatment. Values represent mean ± S.E. of circulating neutrophils measured on GD 19. **P < 0.05 for C5aRA effect by analysis of variance.

Fig. 7.

The C5aRA, but not the C3aRA, prevents placental ischemia–induced endothelial dysfunction. Sham or RUPP animals were treated with Veh, C3aRA, or C5aRA from GD 14–18. Mesenteric arteries were isolated on GD 19 and precontracted with the thromboxane mimetic U46619, and relaxation to Ach (endothelial-dependent vasodilation) was assessed. Relaxation to Ach was reduced in RUPP Veh (n = 14) compared with Sham Veh (n = 10) animals. The C5aRA (n = 9), but not the C3aRA (n = 6), prevented the RUPP-induced change in Ach vasodilation. Values represent mean ± S.E. of fractional relaxation in precontracted arteries. *P < 0.05, RUPP versus Sham; ^#P < 0.05, RUPP Veh versus RUPP C3aRA or RUPP C5aRA. No difference was detected between the Sham Veh and Sham C5aRA groups.