More than a million people die each year from malaria, which is caused by the parasite Plasmodium falciparum. The parasite has developed resistance to many antimalarial drugs and has begun to show resistance to artemisinin – today’s most important antimalarial drug. The stakes are high because half of the world’s population is at risk for the disease.
Multifunctionality is a common characteristic of natural chemical compounds. Often, each of the functions is utilized by the organism producing the compound, such as beetles’ chitin-based covering that provides, among other functions, hard shielding, waterproofing, and coloring.
In the case of the Fijian red seaweed, an organic compound called bromophycolide A serves as an antifungal agent. This same compound also disrupts the metabolism of the malarial parasite, Plasmodium falciparum. While that’s a non-issue for the seaweed itself, it’s good news to red-blooded humans because the malarial parasite feasts on our oxygen-carrying hemoglobin. As the parasite masticates hemoglobin, free heme molecules are released. To protect themselves from the toxicity of free heme, the parasite transforms it into nontoxic hemozoin. It’s this transformation that bromophycolide A disrupts, leaving the parasite vulnerable to the toxic crumbs left at its dining table.
Electron micrograph of crystals of hemozoin isolated from the malaria parasite Plasmodium falciparum. Magnified 68,490 times. Photo by David Sullivan.
Chemists have examined the chemical architecture of bromophycolide A to determine which functional groups decorating the molecule play key roles in the antimalarial process. It appears that carbon atoms at positions 15 and 18 (see structure diagram) play key roles, the former designed with functional groups that do not facilitate hydrogen bonding with free heme and carbon 18 designed to promote it. Such results will provide insight for potential future designs of bromophycolide-inspired antimalarial compounds. It is not clear at this time if the antifungal activity of bromophycolide uses a similar mechanism.
Structure of bromophycolide A.
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“The human malaria parasite remains a burden in developing nations. It is responsible for up to one million deaths a year, a number that could rise due to increasing multi-drug resistance to all antimalarial drugs currently available.” (Cervantes et al. 2012: 1)
“A group of chemical compounds used by a species of tropical seaweed to ward off fungus attacks may have promising antimalarial properties for humans. The compounds are part of a unique chemical signaling system that seaweeds use to battle enemies – and that may provide a wealth of potential new pharmaceutical compounds.” (Toon 2011: 1)
“We observed a distinct phenotype of cell cycle arrest and lack of hemozoin formation when cultures were incubated with extracts from which bromophycolide A was purified and thus pure bromophycolide A as well. These observations indicated that bromophycolide A’s potential mode of action may prevent hemozoin formation. Further investigation using a fluorescent coumarin tagged bromophycolide A for sub-cellular localization and molecular target identification studies validated that heme crystallization was disrupted by the natural product bromophycolide A.” (Cervantes et al. 2012: 8)