Maternal malaria induces a procoagulant and antifibrinolytic state that is embryotoxic but responsive to anticoagulant therapy

Abstract

Low birth weight and fetal loss are commonly attributed to malaria in endemic areas, but the cellular and molecular mechanisms that underlie these poor birth outcomes are incompletely understood. Increasing evidence suggests that dysregulated hemostasis is important in malaria pathogenesis, but its role in placental malaria (PM), characterized by intervillous sequestration of Plasmodium falciparum, proinflammatory responses, and excessive fibrin deposition is not known. To address this question, markers of coagulation and fibrinolysis were assessed in placentae from malaria-exposed primigravid women. PM was associated with significantly elevated placental monocyte and proinflammatory marker levels, enhanced perivillous fibrin deposition, and increased markers of activated coagulation and suppressed fibrinolysis in placental plasma. Submicroscopic PM was not proinflammatory but tended to be procoagulant and antifibrinolytic. Birth weight trended downward in association with placental parasitemia and high fibrin score. To directly assess the importance of coagulation in malaria-induced compromise of pregnancy, Plasmodium chabaudi AS-infected pregnant C57BL/6 mice were treated with the anticoagulant, low molecular weight heparin. Treatment rescued pregnancy at midgestation, with substantially decreased rates of active abortion and reduced placental and embryonic hemorrhage and necrosis relative to untreated animals. Together, the results suggest that dysregulated hemostasis may represent a novel therapeutic target in malaria-compromised pregnancies.

Figure 1. PM is associated with inflammatory responses, increased markers of coagulation, and suppressed fibrinolysis.

(A) Monocyte levels detected in IVB by flow cytometry. (B–H) TNF, IL-6, IL-10, sICAM-1, sCD163, D-dimers and PAI-1 detected in IVB by ELISA. Samples in all panels were stratified by presence or absence of microscopically evident placental parasitemia. Bars represent the median.

Figure 2. Submicroscopic PM does not induce inflammatory immune responses, but does dysregulate hemostasis.

(A) Monocyte levels in IVB as detected by flow cytometry. (B) TNF levels in IVB. (C) D-dimer levels in IVB. (D) PAI-1 levels in IVB. (E) TAT complex levels in IVB. TNF and coagulation/fibrinolysis markers were measured by ELISA. Statistical results in panels C, D and E represent analysis of submicroscopic (PM^sub) and microscopic (PM+) groups combined versus PM− samples. Bars represent the median.

Figure 3. Chronic PM and high placental fibrin deposition are associated with dysregulated hemostasis and reduced birth weight.

(A) D-dimer levels measured by ELISA in IVB in PCR-confirmed PM− placentae with no leukocytes bearing Hz on a Giemsa-stained IVB thick smear (Hz⁰) and in PM^sub/PM+ women with Hz in <5% (Hz^low) or ≥5% of IVB leukocytes (Hz^high). PM+ samples with no Hz in leukocytes (n = 6) were excluded from the analysis. (B, C) PAI-1 and D-dimer levels measured in IVB by ELISA in PCR-confirmed PM− placentae and in PM^sub/PM+ placentae with fibrin score≤3.4 (Fibrin^low) or >3.4 (Fibrin^high), cut-offs defined by the mean fibrin score in PM− cases. (D) Birthweights (mean ± SEM) stratified by fibrin score and infection status in PCR-confirmed PM− and PM^sub/PM+ cases. Bars represent the median in panels A–C.

Figure 4. Fibrin deposition is enhanced in conceptuses from IP mice.

Total protein from pooled IP and UP conceptuses probed with fibrin antibodies on western blot with control β-actin antibody as a loading control (as described in methods).

Figure 5. Coagulation factor gene expression is elevated in IP mice and malaria-exposed murine trophoblasts.

(A) RNA was isolated from conceptuses removed from ED 10 UP (n = 5) and IP (n = 6) mice. Primers specific for the genes indicated were utilized to measure cDNA expression levels in IP relative to UP mice. Data are normalized against murine 18S RNA. Data are expressed as the ratio of fold increase in IP mice to that of UP mice ± SEM. (B) SM9-1 trophoblasts were stimulated with P. chabaudi AS-iRBCs and RNA isolated over the time course indicated. QRT-PCR was conducted as in panel A. Data are expressed as the ratio of fold increase relative to time matched SM9-1 trophoblasts stimulated with uninfected RBC ± SEM and are representative of four separate experiments.

Figure 6. LMWH and enoxaparin therapy improve midgestational body weight.

(A–C) Percent parasitemia, hematocrit and change in body weight of UP (n = 19), IP (n = 14), IP LMWH-treated (n = 11), and IP enoxaparin-treated (n = 5) mice are shown. Clinical metrics were measured on ED 0 and from ED 6 to 12. Data represent mean ± SEM. *P<0.0033; **P<0.0001.

Figure 7. LMWH treatment improves midgestational embryo survival in IP mice.

(A) Viable embryos per mouse among UP (n = 18), IP (n = 15), IP LMWH-treated (n = 11), and IP enoxaparin-treated mice (n = 5) on ED 12. Bars represent the mean. (B) Mean (± SEM) viable embryos as a proportion of total embryos within each group as described in panel A. *P<0.0001, **P = 0.0008, ***P = 0.0270. (C) Gross pathological view of UP uterus. (D) Gross pathological view of IP uterus, showing active embryonic expulsion (arrow), diminished vascularization (black blunt arrow), and intrauterine hemorrhage (white blunt arrow). (E) Gross pathological view of LMWH-treated IP uterus with one resorption (arrow). (F, I) Hematoxylin and eosin (H&E)-stained thin section of a UP conceptus. (G, J) H&E-stained thin section of an IP conceptus; arrow indicates fibrin deposition. (H, K) H&E-stained thin section of an IP LMWH-treated conceptus. Enlargements (panels I, J and K) delineate the three principle regions of the murine placenta, decidua (d), junctional zone (j), labyrinth (l), and also identify the embryo (e). Gross macroscopic pictures were taken with a Kodak Easyshare DX7630 digital camera at 6 MP. Micrographs were captured on an Olympus BX41TF light microscope using an Olympus D70 digital camera. Panels F, G, and H depict magnification with a 2× objective and panels I, J, and K with a 4× objective. Images were resized, cropped as appropriate, and in some cases brightened using GNU Image Manipulation Program v2.6.