Plasma levels of apolipoprotein A1 in malaria-exposed primigravidae are associated with severe anemia

Abstract

Background: Plasmodium falciparum placental malaria (PM) contributes to 10,000 maternal deaths due to severe anemia (SA) each year in Africa, primarily among primigravid women who are most susceptible. Increased levels of proinflammatory cytokines like TNF-alpha are associated with maternal anemia in first time mothers but not in other women. Here we aimed to identify additional changes in the plasma proteome associated with pregnancy malaria that may contribute to the development of malaria-related maternal anemia.

Principal findings: A semi-quantitative mass spectrometry approach was used to compare the relative abundance of plasma proteins in anemic versus non-anemic women with PM. Levels of 24 proteins differed significantly between anemic and non-anemic primigravidae, including several lipid metabolism proteins and molecular transport proteins involved in the acute phase response signaling network. These differences were not observed in multigravid women who enjoy specific immunity that protect them from PM. In a confirmatory study of a larger cohort of primigravid women, levels of the lipid metabolism protein Apolipoprotein (Apo)-AI were significantly lower in PM+ women with SA.

Conclusions: Apo-AI levels are significantly lower in severely anemic primigravidae with PM, and ApoA1 levels positively correlate with hemoglobin levels in primigravid but not multigravid women. Apo-AI is known to have anti-inflammatory effects, and thus Apo-AI reductions may contribute to the inflammatory processes that result in SA.

Figure 1. Network of differentially expressed plasma proteins of primigravid women with SA vesus primigravid women without SA.

24 proteins were eligible for network analysis by Ingenuity Pathways Analysis. The top-scoring network, illustrated here, included 18 focus proteins. Green and red symbols represent proteins that were down- and up-regulated during SA respectively. Gray symbols represent proteins identified in the study for which the difference in expression level did not achieve statistical significance. Direct and indirect interactions are represented by the solid and broken lines respectively.

Figure 2. Comparison of peripheral plasma levels of Apo-A1 between malaria-infected and uninfected women with and without severe anemia.

(A) Apo-AI levels in severely anemic (open boxes) and non-anemic (gray boxes) women stratified by gravidity and malaria infection status. Number of samples tested (severely anemic, non-anemic) and the significance of differences between anemic and non-anemic women (p value analyzed by Mann-Whitney U test): primigravid, PM+ (17, 58; p = 0.016); primigravid, PM- (27, 48; p = 0.015); multigravid, PM+ (7, 26; p = 0.11); multigravid, PM- (54, 58; p = 0.6). (B) Apo-AI levels in severely anemic (open boxes) and non-anemic (gray boxes) primigravid women stratified by 3 stages of infection: active infection (PM+), past infection, and no infection (PM-). Number of samples tested (severely anemic, non-anemic) and the significance of differences between anemic and non-anemic primigravid women (p value analyzed by Mann-Whitney U test): PM+ (17, 58; p = 0.016); past infection (11, 17; p = 0.18); PM- (16, 31; p = 0.06). The box plots include the median (middle line), interquartile ranges (box), and 10-90^th percentiles (whiskers).

Figure 3. Comparison of peripheral plasma levels of Apo-B between malaria-infected primigravid and multigravid women.

Apo-B in malaria-infected (open boxes) and uninfected (gray boxes) women stratified by gravidity. Numbers of samples tested (infected, uninfected) and the significance of the differences between malaria-infected and uninfected women (P value analyzed by Mann-Whitney U test): primigravid (75, 75; p = 0.0008; multigravid (33, 112; p = <.0001). The box plots include the median (middle line), interquartile ranges (box), and 10–90^th percentiles (whiskers).