Carrageenan seaweed food additive by Ray Sahelian, M.D.
Agars and carrageenans are 1,3-alpha-1,4-beta-galactans from the cell walls of red algae, substituted by zero (agarose), one (kappa-), two (iota-), or three (lambda-carrageenan) sulfate groups per disaccharidic monomer. Agars, kappa-, and iota-carrageenans auto-associate into crystalline fibers and are well known for their gelling properties, used in a variety of laboratory and industrial applications. These sulfated galactans constitute a crucial carbon source for a number of marine bacteria. These microorganisms secrete glycoside hydrolases specific for these polyanionic, insoluble polysaccharides, agarases and carrageenases. Carrageenan is a chemical commonly found in commercial products, including food and sexual lubricants.
Carrageenan and HPV
Carrageenan appears to be a potent inhibitor of human papilloma viruses HPV virus -- particularly the types that cause cervical cancer and genital warts. In a test tube, carrageenan inhibits the infectious ability of genital HPV with nearly a thousand-fold greater potency than other inhibitors tested. How effective the compound would be in the human body remains to be demonstrated, but the discovery raises the possibility that carrageenan could be used with vaccines, condoms and lubricants as a protection against HPV. The chemical is extracted from marine red algae, or seaweed. The human papilloma virus normally attacks cells by attaching to the proteins on the cell surface and then using chemicals to work its way in. Carrageenan blocks this process by attaching to the virus and preventing its access to cells. The carrageenan discovery was made in the lab of Dr. John Schiller, senior investigator at the National Cancer Institute, who also was a key player in the initial development of the HPV vaccine. Schiller says, "Our results do not prove that carrageenan will work as a practical HPV topical microbicide. The potent inhibition of infection of cells in dishes, coupled with the fact that carrageenan-based products are already in use, are promising. But we will need to do a well-controlled clinical trial before use of any of these products as an HPV inhibitor could be recommended."
Carrageenan is a potent inhibitor of papillomavirus infection.
PLoS Pathog. 2006.
Laboratory of Cellular Oncology, National Cancer Institute, Bethesda, Maryland,
Comparison of a variety of compounds revealed that carrageenan, a type of sulfated polysaccharide extracted from red algae, is an extremely potent infection inhibitor for a broad range of sexually transmitted HPVs. Although carrageenan can inhibit herpes simplex viruses and some strains of HIV in vitro, genital HPVs are about a thousand-fold more susceptible. Carrageenan acts primarily by preventing the binding of HPV virions to cells. This finding is consistent with the fact that it resembles heparan sulfate, an HPV cell-attachment factor. However, carrageenan is three orders of magnitude more potent than heparin, a form of cell-free heparan sulfate that has been regarded as a highly effective model HPV inhibitor. Carrageenan is in widespread commercial use as a thickener in a variety of cosmetic and food products, ranging from sexual lubricants to infant feeding formulas. Some of these products block HPV infectivity in vitro, even when diluted a million-fold.