How does the treatment based on “lizard spit” work?
The treatment based on lizard spit is exenatide (Byetta®), which is a synthetic version of a compound found in the saliva of a specific type of poisonous lizard that inhabits the southwestern United States and parts of Central America. The compound from the saliva is unrelated to the venom and is not poisonous. This compound (exendin-4) is a reptilian version of a compound that is released upon eating from cells lining the human intestine (glucagon-like peptide-1 or GLP- 1). GLP-1 has several actions that favorably regulate glucose levels in the body. It travels in the bloodstream to the pancreas and increases the release of insulin, thereby lowering blood glucose. It also reduces the release of the hormone glucagon. This is useful because glucagon tends to raise blood glucose through an action on the liver. The remarkable feature of these actions of GLP-1 is that they only occur when the blood sugar is elevated above fasting levels. Thus, GLP-1 does not cause hypoglycemia. GLP-1 decreases the rate of emptying of the stomach, slowing delivery of calories to the intestine and making their absorption more gradual. This also serves to keep blood glucose levels lower. GLP-1 acts on the brain to increase the feeling of fullness after eating (known as satiety) and to reduce hunger, which helps to limit food intake. Unfortunately, however, human GLP-1 is very rapidly broken down and inactivated by the body after release into the bloodstream, most being removed within a few minutes. This is where exenatide comes in. This derivative of the reptilian compound is resistant to the human mechanism for breaking it down and lasts in the bloodstream for several hours. This makes it approximately ten times as powerful as natural human GLP-1. For these reasons, exenatide, which must be taken by twice-daily injection, is effective at lowering blood sugar in people with diabetes and, in more than eight out of ten people who take it, it leads to weight loss, in part due to its appetitesuppressant properties. More than four out of ten people who start exenatide treatment will experience nausea and about one out of seven will experience at least one episode of vomiting. This often passes after a few uses, but some patients cannot tolerate this medication. To minimize this problem, it is given in a lower dose initially and the dosage is increased after the first month. It comes in prefilled pens containing one month's treatment.