Inhibition of Adhesion of Plasmodium falciparum -Infected Erythrocytes by Structurally Defined Hyaluronic Acid Dodecasaccharides

Abstract

We recently reported that Plasmodium falciparum-infected erythrocytes (IRBCs) can adhere to hyaluronic acid (HA), which appears to be a receptor, in addition to chondroitin sulfate A (CSA), for parasite sequestration in the placenta. Further investigations of the nature and specificity of this interaction indicate that HA oligosaccharide fragments competitively inhibit parasite adhesion to immobilized purified HA in a sizedependent manner, with dodecasaccharides being the minimum size for maximum inhibition. Rigorously purified and structurally defined HA dodecasaccharides, free of contamination by CSA or other glycosaminoglycans, effectively inhibited IRBC adhesion to HA but not CSA, providing compelling evidence of a specific interaction between IRBCs and HA.A characteristic of infection with the malaria parasite Plasmodium falciparum is the ability of parasite-infected erythrocytes (IRBCs) to adhere to host endothelial cells and accumulate in various organs. During pregnancy, the accumulation of IRBCs in the placenta is a key feature of infection and is associated with adverse outcomes and excess perinatal and maternal mortality (6,18). Studies in Africa suggest that sequestration of IRBCs in the placenta is mediated in part by adhesion of parasites to the glycosaminoglycan (GAG) chondroitin sulfate A (CSA) present on syncytiotrophoblasts lining the placental blood spaces (2, 11).We have recently reported that hyaluronic acid (HA) can also support the adhesion of IRBCs in vitro and appears to be an additional receptor for parasite sequestration in the placenta (4). HA is nonsulfated and is the simplest member of the GAG family composed of repeating disaccharide units, -4GlcA␤1-3GlcNAc␤1-, in a linear chain that varies in size from 2,000 to 25,000 disaccharide units. It has been identified on syncytiotrophoblasts (17, 28), and we found that most parasite isolates from infected placentas bound to immobilized HA, whereas isolates from the peripheral blood bound to a lesser extent (4). HA is also present on the surfaces of microvascular endothelial cells (19), raising the possibility that it acts as a receptor for parasite sequestration in other organs.To further investigate the nature and specificity of the interaction of HA with IRBCs, we generated oligosaccharide fragments, including high-performance liquid chromatography (HPLC)-purified and structurally defined dodecasaccharides, and examined their abilities to competitively inhibit parasite adhesion to immobilized HA. Some HA preparations can be contaminated with other GAGs, such as CSs, and it was therefore important to exclude the possibility that the adhesion observed could be explained by such contaminants. MATERIALS AND METHODSPartial depolymerization of HA. HA (from bovine vitreous humor; Sigma) (HA-BVH) was partially depolymerized by controlled digestion with either testicular hyaluronidase (EC 3.2.1.35; from bovine testes; Sigma) or hyaluronate lyase (EC 4.2.2.1; from Streptomyces hyalurolyticus; Sigma). Testicular hyaluronidase digestion was carried...

Chondroitin Sulfate Proteoglycan but Not Hyaluronic Acid Is the Receptor for the Adherence of Plasmodium falciparum-Infected Erythrocytes in Human Placenta, and Infected Red Blood Cell Adherence Up-Regulates the Receptor Expression

“…Previously, the binding of IRBCs to bvhHA was considered indicative of HA binding specificity. [27][28][29][30] Our conclusion that HA is not a receptor for P. falciparum IRBC is consistent with the recent observation by Fried and colleagues 38 that IRBCs in the blood samples from 46 infected placentas could bind only to C4S but not to HA. Of note, although Fried and colleagues 38 found that IRBCs from 2 of 46 placentas showed significant binding to HA-BSA conjugate, the binding was inhibited by C4S but not by HA.…”

“…It has been previously reported that the laboratory parasite strain named CS2, when selected for C4S binding, can adhere to both HA and C4S, exhibiting dual-receptor binding specificity. 28 However, in our study, CS2-CSA IRBCs could bind only to the placental CSPG but not to the HA-BSA conjugate ( Figure 2A). As in the case of the placental parasite isolates, the binding of CS2-CSA IRBCs to the placental CSPG was inhibited by soluble C4S but not by HA or C6S ( Figure 2B and data not shown).…”

“…In previous studies that reported IRBC binding to HA, bvhHA was used for the analysis of IRBC binding. [27][28][29][30] Therefore, we also assessed the coating of bvhHA to plastic plates. As shown in Figure 1A, a low but significant amount of HA was coated onto the plastic surface; the immobilization of HA when coated with bvhHA is likely through HABPs present in samples that are adsorbed onto the plastic surface.…”

“…[27][28][29][30] However, the presence of HA in human placenta at locations where IRBCs are known to adhere has not been demonstrated, and thus, it remains unclear whether HA is a receptor for placental IRBC adherence or not. If HA is indeed an additional receptor in the placenta for IRBC adherence, then this phenomenon has profound implications for the rational design of vaccine for women of child-bearing age, because a vaccine that specifically blocks the adherence of IRBC to C4S would not be sufficient to control placental infections.…”

Inhibition of Chondroitin-4-Sulfate-Specific Adhesion of Plasmodium falciparum -Infected Erythrocytes by Sulfated Polysaccharides

“…This is particularly evident for pregnancy-associated malaria, where the glycosaminoglycan chondroitin-4-sulfate (chondroitin sulfate A [CSA]) appears to be the major host receptor in the placenta (18). Another glycosaminoglycan, hyaluronic acid, has also been implicated as a placental receptor (6,12).…”