Novel semi-synthetic carbohydrates as potential therapeutics for severe malaria

Severe malaria is a disease that kills millions every year, especially in developing nations, resulting in widespread suffering and economic damage. Severe malaria is caused by both the aggregation of red blood cells infected by the parasite into rosettes and via cytoadherence, the attachment of red blood cells to the cells of the host, lining the blood vessels. Rosette formation and cytoadherence both prevent proper transport of oxygen by the red blood cells around the capilaries of the brain and causes blockages, damaging the brain, and this is often fatal. This project will identify the simplest fragments, from a novel semi-synthetic library of negatively charged carbohydrates, that are able to disrupt rosetting and cytoadherence while minimising/eliminating any potential side-effects. This will provide information concerning the minimum structures required, allowing cheap, chemical synthesis of the molecules to be undertaken. This project will ultimatley lead to the development of new pharmaceutical agents, which are urgently needed, as resistance emerges to the drugs being administered currently.

Malaria, caused by Plasmodium species, affects one third of the world?s population with over 300 million infections resulting in 2 million deaths annually. Severe malaria, caused by P. falciparum, is the most serious complication of the disease resulting in widespread suffering and economic damage, especially in developing nations. Severe malaria severity correlates with the extent of venule occlusion (by rosetting, auto-aglutination and cytoadherance) resulting in hypoxia and coma. Cell-cell adhesions are facilitated by interactions between parasite expressed proteins and host carbohydrates (hyaluronic acid, chondroitin sulfate, heparan sulfate) and proteins (CD-36, E-selectin, PECAM-1, ICAM-1, VCAM-1 and thrombospondin) while the rosetting process is mediated principally by the parasite expressed protein, P. falciparum erythrocyte membrane protein-1 (PfEMP-1) through attachment to host cell-surface carbohydrates. It has been shown that both naturally occuring and chemically modified carbohydrates are capable of disrupting malaria rosettes and/or cytoadherance, but the structural details of these interactions, and the carbohydrates themselves, remain poorly defined. This project will create an arsenal of semi-synthetic, structurally diverse polysaccharides which will faciitate the generation of a series of size-defined, structurally diverse oligosaccharides from which the simplest structures (i.e. smallest and least charged) capable of inhibiting rosetting and cytoadherence will be selected, purified and their detailed structures defined by a combination of recently developed sequencing techniques (e.g. ES-MS and NMR). As a precaution, successful inhibitors will also be screened for potential side-effects, including the formation of immunogenic platelet factor-IV complexes and activities with the blood clotting cascade (anti-factor Xa, antithrombin and factor II) activities, which can be highly attenuated (down to 0.5 %) with simple chemical modifications. The structural information will not only provide detailed data concerning the nature of the interacting species, leading to improved mechanistic understanding, but will also provide the structurally simplest targets for future chemical synthesis, the first step to producing new pharmaceutical agents.