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Incretins

Posted on May 17, 2018 | No Comments on Incretins

Diabetes Mellitus remains a growing problem worldwide and the scientific community continues to search for ways to prevent, slow down the progression, control and treat this complex hormonal/metabolic disease. In order to understand this, a basic overview of hormones and their effects in the body (Science of Endocrinology) needs to be elaborated—so let us start with some definitions in “Endocrinology 101”.

Hormones are composed of chains of molecules that are secreted by different glands in our body—such as the pancreas, the thyroid, the ovaries, pituitary, adrenals, etc. The hormones travel in the blood to act on different “gates” or receptors located in other parts of the body to cause changes in our cells’ function or development in order to sustain our survival. Problems in the secretion, action and effects of hormones can lead to devastating problems that affect our lives—and one very good example of a classic, truly “endocrine” disease is Diabetes Mellitus (DM).

We already know that problems with the secretion and action of the hormone insulin that comes from our pancreas lead to diabetes mellitus—a disease where the sugar or glucose remains high in the blood instead of entering inside the cells of the body to be used up as energy source. But the body’s ways to regulate how we handle our food to sustain life is not that simplistic. When we were in grade school, we were taught that food is digested by acids and other chemicals or enzymes that are in our stomachs and intestines. But aside from breaking down the food we eat, our small intestines read to the presence of food by secreting their own hormones that come from the glands that line the walls of the gut. These hormones go to the pancreas to make it increase the secretion of insulin in response to eating so that the glucose entering the blood stream from the breakdown of food can effectively enter the cells. Not only do these gut hormones stimulate the release of insulin; they also reduce the secretion of the hormone glucagon which has the opposite effect of insulin because it increases the level of glucose in the blood instead of decreasing it. These gut hormones that increase the secretion of insulin are called the incretins. Medicines for diabetes that have been developed based on the principle of gut hormones are termed “incretin-based” therapies.

Let Us Meet The Incretins
There are two principal gut hormones or incretins secreted by the small intestinal glands—glucagon¬like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). They do not remain in the bloodstream for a long time because they are easily degraded in the blood by the enzyme dipeptidyl peptidase IV (DPP IV). So if we were to give GLP-1 and GIP to diabetic patients to control their blood sugar throughout the day, these hormones would need to be infused into the bloodstream continuously like an intravenous fluid in order for them to be effective. Another important point to remember is that incretin-based therapies are designed for patients who still have enough functioning pancreas that can secrete insulin—this means they do not work in type 1 DM wherein insulin remains the only effective treatment.

Incretin Mimetics
One way to avoid the fast degradation is to create a molecule that will mimic the action of the incretin when it attaches to the receptor; but at the same time, be different enough so that it is not recognized and degraded by the human enzyme DPP IV. This is how the drug EXENATIDE was developed. It comes from the saliva of the big lizard—the Gila Monster—and it ads on the receptors of GLP-1 leading to decreased blood sugar level. It also promotes feeling of fullness thereby reducing food intake leading to weight loss. Just like insulin, it needs to be injected. Side effects include nausea, vomiting, diarrhea and a significant dent on the budgetbecause it is more expensive than the other therapies for diabetes. It can be given together with other tablets for diabetes your doctor prescribes for you. Exenatide has become increasingly popular among overweight and obese diabetics because it can cause weight loss.

DPP-IV Inhibitors
Another way to use the incretins in the treatment of diabetes is to give a drug that will block the “janitor” enzyme DPP-IV so that the GLP-1 and GIP will not be de-activated and can stay longer in the body to stimulate the pancreas to secrete more insulin in timing with the meals. This is how the two other drugs—SITAGLIPTIN and VILDAGLIPTIN—work. They are in tablet form and can be given once or twice a day. The side effects include nausea, diarrhea, runny nose, rashes and headache. These drugs can be given in combination with other diabetic tablets or as single agents in some cases. Just like with most drugs, it is always best to consult your doctor about these agents and trust that they are updated enough to know what is safe and effective for you.

As our technology improves, more and more body functions and hormone effects are being discovered in the exciting field of endocrinology. This little bit of “Endocrine 101” gives you an idea of how elaborate the principles of hormone action can be; and there are a lot of researches being done in order to improve how we manage endocrine diseases like diabetes mellitus.

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