Insulin, a pancreatic hormone, is a specific antidiabetic agent, especially for type I diabetes. Human insulin is a double-chain protein with molecular mass around 6000 that contains 51 amino acids (chain A—21 amino acids, chain B—30 amino acids), which are bound together by disulfide bridges.
NH2S-S nh2 nh2
II I II
NH2NH2 S-S S-S
Pig insulin differs from human insulin only in that it has a different amino acid at position 30, and bovine insulin has different amino acids at positions 8,10, and 30. Insulin was discovered in 1921. It was isolated from pancreatic tissue of mammals [1-9]. Currently, human and some animal insulins (pigs and large oxen) can be synthesized [10-12], and there "are methods for" making it by genetic engineering [13-16]. Rather than relying on insulin extracted from animal sources, genetic technology has permitted the production of large quantities of essentially human insulin by bacterial cells.
In the body, insulin is synthesized by /¡-cells of Langerhans islets in the pancreas. The rate of formation changes depending on the type of food consumed, gastrointestinal hormones, and neuronal control. Insulin circulating in the body has a biological half-life of about 5 min. It is quickly broken down by enzymes and is removed from the blood by the liver or kidneys.
The mechanism of the hypoglycemic action of insulin is not completely understood. However, it has been proposed that insulin acts by binding with specific receptors on the surface of the insulin-sensitive tissues such as skeletal muscle, cardiac muscle, fatty tissue, and leukocytes. Insulin lowers the sugar content in the blood by turning glucose into glycogen. Using insulin in diabetes mellitus leads to lower levels of sugar in the blood, and a build up of glycogen in tissues. Lowering glucose in the blood stops glycosuria, thus lowering elevated diuresis and thirst, normalizing carbohydrate, protein, and fat volume, and reducing diabetic comas. Insulin is effective in insulin-requiring diabetes mellitus. Because insulin is degraded by digestive enzymes, the method of introduction is rarely parenteral. Usually it is hypodermic, and less often intravenous or intramuscular. There are prolonged-action insulin drugs, which are slowly absorbed from the introduction site. Insulin drugs lower the level of blood glucose. Insulin is used in insulin-dependent and non-insulin diabetes mellitus.
For patients with type II diabetes, in which endogenic secretion of insulin functions to some degree, a number of very effective hypoglycemic drugs are prescribed. Six of the most widely used drugs today are subdivided into two groups. First generation drugs—derivatives of sulfonylurea were the most popular in the early 1980s, and include tolbutamide, acetohexamide, tolazamide, and chlorpropamide. Second generation drugs—derivatives of guanidine, such as glyburide and glipizide, entered medical practice after 1984. All of these drugs have very similar chemical structures and mechanism of action, and they differ in the structure of their side chains, and accordingly, activity and pharmacokinetic characteristics.
It is believed that the sulfonylamide action consists of elevated insulin secretion. It is also presumed that the hypoglycemic effect of these drugs is also associated with the suppression of release of glucagon, a hormone produced by a-cells of Langerhans islets in pancreas, and which is a polypeptide made up of 29 amino acid residues. The effect of glucagon on carbohydrate volume is evident by hyperglycemia, which is associated with increased glycogenogenesis (synthesis of glucose from non-carbohydrate precursors) in the liver. An important ability of all of the examined drugs is the possibility of peroral introduction. Many of the medicinal drugs used in various diseases are antagonists of oral hypoglycemic drugs (corticosteroids, thyroid hormones, thiazide diuretics, furosemide, and oral contraceptives). At the same time phenyllanta-zone, clofibrate, dicumarol and salicyclates are potentiating the action of hypoglycemic drugs.
Tolbutamide: Tolbutamide, 1-butyl-3-p-toluenesulfonylurea (26.2.2), is made in a single step reaction by interaction of p-toluenesulfonylamide (in the form of sodium salt) with butyliso-cyanate [17-20].
Was this article helpful?