Artemether-lumefantrine to treat malaria in pregnancy is associated with reduced placental haemozoin deposition compared to quinine in a randomized controlled trial

Abstract

Background: Data on efficacy of artemisinin-based combination therapy (ACT) to treat Plasmodium falciparum during pregnancy in sub-Saharan Africa is scarce. A recent open label, randomized controlled trial in Mbarara, Uganda demonstrated that artemether-lumefantrine (AL) is not inferior to quinine to treat uncomplicated malaria in pregnancy. Haemozoin can persist in the placenta following clearance of parasites, however there is no data whether ACT can influence the amount of haemozoin or the dynamics of haemozoin clearance.

Methods: Women attending antenatal clinics with weekly screening and positive blood smears by microscopy were eligible to participate in the trial and were followed to delivery. Placental haemozoin deposition and inflammation were assessed by histology. To determine whether AL was associated with increased haemozoin clearance, population haemozoin clearance curves were calculated based on the longitudinal data.

Results: Of 152 women enrolled in each arm, there were 97 and 98 placental biopsies obtained in the AL and quinine arms, respectively. AL was associated with decreased rates of moderate to high grade haemozoin deposition (13.3% versus 25.8%), which remained significant after correcting for gravidity, time of infection, re-infection, and parasitaemia. The amount of haemozoin proportionately decreased with the duration of time between treatment and delivery and this decline was greater in the AL arm. Haemozoin was not detected in one third of biopsies and the prevalence of inflammation was low, reflecting the efficacy of antenatal care with early detection and prompt treatment of malaria.

Conclusions: Placental haemozoin deposition was decreased in the AL arm demonstrating a relationship between pharmacological properties of drug to treat antenatal malaria and placental pathology at delivery. Histology may be considered an informative outcome for clinical trials to evaluate malaria control in pregnancy.

Registry: http://clinicaltrials.gov/ct2/show/NCT00495508.

Figure 1

Key features of placental malaria. Haematoxylin and eosin stained placental sections from the Mbarara trial are shown at 600X. A) Normal placental histology. B) Parasitized erythrocytes sequester in the intervillous space. C) Monocyte-macrophages accumulate and phagocytose parasitized erythrocytes and haemozoin. D) Monocyte macrophages become enmeshed in fibrin and degenerate. E) Residual haemozoin persists in fibrin following successful treatment.

Figure 2

Quantification of haemozoin deposition. Giemsa stained sections are shown at 200X. A) A selected field from the placenta of a woman with infection at 162days prior to delivery demonstrating a focus of haemozoin (inset, 600X), which was quantified as 2% of HPF. B) A representative field from the placenta of a woman with infection at 77days prior to delivery demonstrating heavy haemozoin deposition quantified as 35% of HPF. Arrowheads: haemozoin deposits. HPF: 600X high power fields.

Figure 3

Trial profile. The blue box contains the original CONSORT trial flow chart, adapted from [9]. Placental histology was performed as a secondary analysis. AL- Artemether-lumefantrine.

Figure 4

Population haemozoin clearance curves. Estimated curves derived from A) women in the trial (y=4.44ln(x)+9.71; R²=0.237), B) stratified by treatment arm, and C) treatment arm and gravidity. Excluding 22 women who experienced re-infection. HPF= high power fields.

Figure 5

Proposed model of increased ACT efficacy during pregnancy. AL is active on early ring stages with a greater parasite reduction ratio, limiting parasite sequestration. Quinine is only active on mature parasites, which are sequestered in the placenta. Parasite sequestration leads to mononuclear cell infiltration and risk of poor pregnancy outcome. Haemozoin-laden macrophages become enmeshed in fibrin resulting in haemozoin deposition that persists until delivery. If women receive no or ineffective treatment, sequestered parasites, inflammation and haemozoin deposits persist until delivery.