Poisons of the Day - Part Ia

News Flash! Napoleon probably did not die of arsenic poisoning. I would like to say that I’m surprised by this, but I can’t since I had never heard of the “Napoleon was poisoned by arsenic” theory in the first place. Apparently, arsenic had previously been found in a sample of Napoleon’s hair, and when combined with reports of his severe stomach pain (a symptom of arsenic poisoning), it had been speculated that Napoleon was either poisoned by the British during his captivity or had been exposed to poisonous arsenic fumes generated by mold infested wallpaper containing an arsenic-based dye. But a team of Italian scientists has now cast considerable doubt on this theory. By collecting samples of Napoleon’s hair at various stages of his life, along with hair from his son and first wife, they were able to show that all three of them had had elevated levels of arsenic in their bodies long before Napoleon’s imprisonment.

What made the story interesting was that the levels of arsenic in Napoleon’s hair were 100 times greater than expected today. Apparently, back in the day, consuming small amounts of arsenic was a highly regarded practice. It was supposed to make the body more vigorous, it was believed to be a sexual stimulant, and its tendency to produce bright, rosy cheeks was much in demand by the women of the time. (The rosy cheeks were a result of blood vessel damage in the skin.) The knowledge that arsenic was a poison, and that it caused severe stomach pain, was apparently not much of a deterrent. (To make things worse, facial powders were often loaded with white lead, Pb3(CO3)2(OH)2, in order to make the face more pale -- a sign of nobility.)

Now the reason I mention this story relates to the “Poisons of the Day” post from last week in which I mentioned that much of arsenic’s toxicity arises from its tendency to replace phosphorus in the body. My question was: How could people continue to survive the continuous ingestion of arsenic if it’s slowly replacing the body’s phosphorus? In fact, anecdotal reports suggest that it is possible to build up some immunity to arsenic by regularly ingesting it -- although some experts reject that possibility. Now, I know that you can build up an immunity to the poison "iocane" (warning: Princess Bride reference ;) ), but how would that work with arsenic? One theory involves metallothioneins, which are proteins produced by the body that seem to bond to ions of dangerous elements like arsenic and cadmium and help minimize their effects. Constant exposure to arsenic might increase the levels of metallothioneins produced by the body. I don’t think anyone knows the answer just yet.

By the way, I found a few references to a second mechanism by which arsenic can be toxic. It tends to bind to the sulfhydryl (thiol) groups (-SH) in proteins, which as you can imagine, really screws up the operation of these proteins.