Saw an article that I found particularly interesting in my perusal of Science this week…”Sugary Achilles’ Heel Raises Hope For Broad-Acting Antiviral Drugs” by Robert F. Service (Science 4 September 2009 325: 1200 [DOI: 10.1126/science.325_1200a]).
I had always wondered how the immune systems of plants and simple creatures worked. Sure, our immune system is adaptive and has all those macrophages and T-cells and B-cells, but would a plant or a lobster do the same thing? Turns out they don’t. I can’t say I really understand how these work, but from what I can tell many organisms have passive immune systems that simply emit toxins and broad-spectrum antiviral compounds to protect themselves when they come under attack by bugs. Innate social behavior is also part of the immune response of certain simple animals; sick ones may instinctively isolate themselves from the group, for example, to prevent the further spread of disease.
Apparently, researchers at the US National Cancer Institute have discovered that red algae emit a compound called griffithsin (GRFT). GRFT targets mannose sugars commonly attached to viral protein particles that are also not commonly attached to human proteins. The article dives a little bit into the mechanism for the specificity, but what I found most interesting were the results of early studies:
For nearly all HIV strains, it takes less than 0.23 billionths of a mole, or nanomoles, of GRFT to inhibit half the viruses in vitro—a standard measure of drug effectiveness known as the compound’s IC50, in which the lower the number the more potent the compound. For SARS, GRFT’s IC50 is about 50 nanomoles, and for Ebola it is 380 nanomoles. That makes all three mannose binders some of the most powerful antivirals around.
In mice infected with SARS, 70% of the animals that received no antivirals died. By contrast, among those that received an intranasal dose of 5 milligrams per kilogram per day of GRFT for 4 days, 100% lived. With mice exposed to Ebola, one of nature’s most lethal viruses, all of the 10 control animals that didn’t receive GRFT died within 12 days. In the five groups of 10 animals that each received different injected doses of GRFT, up to 90% survived. Even when they were injected with the antiviral 2 days after being exposed to Ebola, 30% still lived.
That’s pretty remarkable. It’s also effective against H1N1. Of course, it’s only a matter of time before viruses manage to adapt, but until then this could cure a lot of very sick people. Hurray for red algae!
