Sharks contain a compound, squalamine, that fights viruses, scientists… (David Royal / AP )
An extract from sharks seems to fight a broad array of viruses, according to a study published this week in the journal Proceedings of the National Academy of Sciences. The chemical, called squalamine, was discovered in 1993 by Dr. Michael Zasloff, now at Georgetown University Medical Center and the lead investigator of the paper. He’s been studying it ever since, mostly for its immune properties.
Working with a variety of scientists at Georgetown, UCLA and elsewhere, Zasloff and his colleagues tested the ability of squalamine to fight off infections by a variety of viruses including dengue virus, yellow fever and hepatitis A, B and D. Some of the experiments were done in tissue culture cells of various types: human liver cells for the hepatitis viruses, for example, and human blood vessel cells for the dengue virus. In other cases, such as yellow fever and cytomegalovirus, the tests were done in hamsters and mice. Some of the animals recovered from the infections.
Squalamine, which is naturally found in shark liver, seems to do what it does by interfering with the ability of viruses to replicate inside the cells they infect.
This isn’t the first time that the disease-fighting abilities of sharks have gotten attention. You may recall a 1992 book titled, “Sharks Don’t Get Cancer: How Shark Cartilage Could Save Your Life,” and the 1996 sequel, “Sharks Still Don’t Get Cancer.”
Those hyperbolically named books were inspired by several lines of study:
One of them was work in the field known as antiangiogenesis, pioneered by Dr. Judah Folkman of Children’s Hospital Boston. He and his colleagues noted that cartilage inhibits blood vessel formation. (Blood vessels don’t readily grow into cartilage, which is why tears in cartilage don’t heal readily.) Tumors need blood vessels to feed them, and so if you block the formation of blood vessels, you essentially starve the tumors. Could there be something naturally in cartilage (no, not just shark cartilage) that could be tapped for that purpose? Lots of research into antiangiogenic drugs is underway, and some of them (Avastin is one) are on the market.
Another of them was Zasloff’s. He had earlier found that squalamine inhibits the formation of blood vessels.
But as is the case with most “miracle cure” books, facts get contorted and exaggerated. The author of “Sharks Don’t Get Cancer” noted that shark skeletons are made entirely of cartilage.. and thus… and thus… But it turns out that sharks DO get cancer. (The fact that not many shark cancers have been documented might have something to do with the fact that shark cancer is not a high research priority.)
Furthermore, trials testing shark cartilage extract, taken orally, on fighting cancer have had negative results.
And finally, those interested in the welfare of sharks were deeply worried about the possibility that the demand for shark cartilage extract would threaten sharks, already overfished. (Luckily for sharks, squalamine can be synthesized in the lab these days: Zasloff's studies don't involve extracting squalamine from sharks.)
Read all about the evolution of the shark-cancer myth right here.
Though the authors believe squalamine has promise and might yield some new drugs for some tricky-to-fight human viruses, it's still early for the study of squalamine's virus-fighting abilities. Still, it surely won't be long before “Sharks Don’t Get Dengue!” hits the bookstores.