If you ever take the time to think about snails, and there is no particular reason as to why you should, but if it happens to be a particularly rainy Friday afternoon you might. As you cogitate, there are probably two main thoughts that come to mind. First, snails are slow, I mean really slow. It would take a snail nine and a half weeks to cover a mile. The other thing about snails is that cooked in white wine and garlic butter they can be pretty tasty. Unless you’re a fan of 1950s sci-fi B movies, the idea of killer snails coming up from the ocean depths is not one you would be familiar with, yet scientists have recently found one sea snail, that is probably the most venomous snail known, and responsible for several human deaths. Intriguingly, this snail may also hold the key to a therapy for around 8 million people in the US, and even more world-wide.
The geographic cone snail spends its time in the tropical waters of the Indian Ocean, where it lives as a carnivore, feeding on small fish, worms and mollusks. Although the snail may move slowly, creeping up on its prey, once it attacks it fires a lightning fast harpoon, tipped with venom to stun, and sometimes kill, its prey before it is devoured. Like many animal venoms, the cone snail venom contains neurotoxins to attack the prey’s nervous system, but it also has one remarkable component, a snaily version of insulin that targets the prey’s sugar levels.
Insulin is that essential hormone that regulates the level of sugar in our blood; sugar this is needed as a fuel source to make our body work properly. Too little insulin, and blood sugar stays dangerously high, causing nerve damage, an inability to repair wounds properly, and ironically a lack of energy since the muscles can’t utilize blood sugar in the absence of insulin. To much insulin, and the blood is rapidly cleared of all sugar, leaving no fuel left for the brain, which quickly shuts down. Cone snails inject their insulin into fish, causing the fish to become lethargic and stunned, and readily eaten. As far as scientists know, the cone snail is the only animal to contain insulin in its venom, but that doesn’t mean snails are the only ones to use insulin to kill.
Colin Bouwer, was Chair of the Department of Psychiatry at Otago Medical School in Dunedin, New Zealand. For several months, Colin had been writing fake prescription for a long list of drugs, including insulin; drugs that would not normally be needed by a psychiatrist. In 2000, Colin was arrested on charges of murdering his wife, a murder that seemed to involve insulin as the murder weapon. Clearly convinced he would never be caught, Colin’s computer was full of emails resulting from communications he had had with international hypoglycaeima (very low blood sugar) experts. Colin had requested information on how easy it was to establish that insulin overdoses were the cause of hypoglycaemia. Following an initial attempt at murder, Colin’s wife had been rushed to hospital with severe hypoglycaemia and hypothermia (quite common in people who have been hypoglycaemic for some time), where she gradually recovered and was sent home. Not to be outwitted, Colin again gave his wife large doses of insulin, sending her into a deep hypoglycaemic coma from which she was never to recover. Colin’s trial lasted just over a month, with the jury returning a guilting verdict in just three and a half hours. Colin Bouwer is currently in prison for a minimum of 15 years.
Because snail insulin is simpler and faster acting that human insulin, drug makers hope that the snail insulin will hold clues to the manufacture of quicker-acting insulin to treat people with diabetes. To be fair, insulin dosing is a tricky business, and faster is not always better when controlling a diabetic person’s blood sugar. Pharmaceutical companies are trying to find better ways to make safer more stable insulin, and there may be things to learnt from nature about making human insulin better. Scientists have ben trying to remove the “hinge” from human insulin for years, but that seems to kill its effectiveness. Maybe making human insulin more snail-like may make the life of millions of patients with diabetes just a little easier.
Dr Neil Bradbury 