Incretins are a group of

metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...

s that stimulate a decrease in blood glucose levels. Incretins are released after eating and augment the secretion of

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism ...

released from pancreatic

beta cells Beta cells (β-cells) are a type of cell found in pancreatic islets that synthesize and secrete insulin and amylin. Beta cells make up 50–70% of the cells in human islets. In patients with Type 1 diabetes, beta-cell mass and function are dim ...

of the

islets of Langerhans The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of ...

by a blood-glucose–dependent mechanism. Some incretins (GLP-1) also inhibit

glucagon Glucagon is a peptide hormone, produced by alpha cells of the pancreas. It raises concentration of glucose and fatty acids in the bloodstream, and is considered to be the main catabolic hormone of the body. It is also used as a medication to tre ...

release from the

alpha cell Alpha cells (α cells) are endocrine cells that are found in the Islets of Langerhans in the pancreas. Alpha cells secrete the peptide hormone glucagon in order to increase glucose levels in the blood stream. Discovery Islets of Langerhans were ...

s of the

. In addition, they slow the rate of absorption of nutrients into the blood stream by reducing gastric emptying and may directly reduce food intake. The two main candidate molecules that fulfill criteria for an incretin are the intestinal

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...

s glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP, also known as: glucose-dependent insulinotropic polypeptide). Both GLP-1 and GIP are rapidly inactivated by the enzyme

dipeptidyl peptidase-4 Dipeptidyl peptidase-4 (DPP4), also known as adenosine deaminase complexing protein 2 or CD26 (cluster of differentiation 26) is a protein that, in humans, is encoded by the ''DPP4'' gene. DPP4 is related to FAP, DPP8, and DPP9. The enzyme was ...

(DPP-4). Both GLP-1 and GIP are members of the glucagon peptide superfamily.

Medical uses

Medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...

s based on incretins are used in the treatment of

diabetes mellitus type 2 Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urinati ...

. Several long-lasting GLP-1 analogs having insulinotropic activity have been developed, and several, including

dulaglutide Dulaglutide, sold under the brand name Trulicity among others, is a medication used for the treatment of type 2 diabetes in combination with diet and exercise. It is also approved in the United States for the reduction of major adverse cardiov ...

(Trulicity), exenatide (Byetta), liraglutide (Victoza), semaglutide (Ozempic, Wegovy and Rybelsus) and exenatide extended-release (Bydureon), have been approved for use in the U.S. Another approach is to inhibit

DPP-4 Dipeptidyl peptidase-4 (DPP4), also known as adenosine deaminase complexing protein 2 or CD26 (cluster of differentiation 26) is a protein that, in humans, is encoded by the ''DPP4'' gene. DPP4 is related to FAP, DPP8, and DPP9. The enzyme was ...

, the enzyme that inactivates GLP-1 and GIP. Several DPP-4 inhibitors that can be taken orally as tablets have been developed.

Incretin effect

The incretin effect describes the phenomenon whereby oral glucose intake elicits a higher insulin response compared to intravenously introduced glucose that produces the same levels of serum glucose levels.

History

In 1932,

Belgian Belgian may refer to: * Something of, or related to, Belgium * Belgians, people from Belgium or of Belgian descent * Languages of Belgium, languages spoken in Belgium, such as Dutch, French, and German *Ancient Belgian language, an extinct languag ...

physiologist Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...

Jean La Barre used the word "incretin" for a gut hormone, which stimulates the

endocrine pancreas The pancreatic islets or islets of Langerhans are the regions of the pancreas that contain its endocrine (hormone-producing) cells, discovered in 1869 by German pathological anatomist Paul Langerhans. The pancreatic islets constitute 1–2% of ...

including

release. He also proposed that such incretins could be used as a treatment for diabetes mellitus.

References

{{reflist Peptide hormones Intestinal hormones Gastric hormones

Medical uses

Incretin effect

History

See also

References