Gastric Inhibitory Polypeptide and Fragments

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Introduction

Gastric inhibitory polypeptide (GIP) is an important metabolic hormone in animals. It has a special molecular structure and plays an important physiological role in animal organisms. GIP is an incretin synthesized and secreted by the enteroendocrine cell-K cells in the upper part of the small intestine of the mammal and is an important member of the gastrointestinal regulatory peptide secretin family. GIP was originally isolated in the pig intestines and inhibits the secretion of gastric acid. The half-life of GIP in plasma is shorter, less than 2 min in mice and 7 and 5 min in normal and type 2 diabetic patients, respectively. The highest concentration in the jejunum and a certain amount of secretion in the duodenum and ileum. Its physiological role is inhibition of gastric acid secretion; inhibition of pepsin secretion; stimulation of insulin release; inhibition of gastric peristalsis and emptying; stimulation of intestinal secretion; stimulation of glucagon secretion.

Mechanism of action

GIP has its special precursor structure. GIP is released when the precursor is hydrolyzed by a protease. The released GIP still cannot directly play its role and must be combined with its receptor to produce biological effects. GIP has a role in promoting insulin secretion. When GIP binds to its receptor, it activates adenylate cyclase (AC), which causes an increase in intracellular cyclic AMP (cAMP). cAMP further activates downstream effector proteins including protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). Activated PKA and Epac cause the downstream KATP channel to shut down, the mitochondrial membrane potential to depolarize, the Ca²⁺ channel to open and influx, and the intracellular Ca²⁺ concentration to increase. Finally, the insulin secreting granules are secreted from the pancreatic β cells.

Application of Gastric Inhibitory Polypeptide and Fragments

GIP is an important incretin found to date, which promotes insulin secretion, increases β cell proliferation, and reduces β cell apoptosis. GIP plays a vital role in the accumulation of fat. At present, a novel agonist of GIPR, D-Ala2GIP (1-30), has a further potential in anti-diabetic treatment. In addition to the regulation of β-cell function by GIP, it can also reduce the activity of LPL in 3T3-L1 cells and reduce body weight, reducing the incidence of obesity caused by GIP.

References

1. Pederson, R. A. , & Mcintosh, C. H. . (2016). Discovery of gastric inhibitory polypeptide and its subsequent fate: personal reflections. Journal of Diabetes Investigation, 7(Suppl Suppl 1), 4-7.
2. Yamane, S. , Harada, N. , & Inagaki, N. . (2016). Mechanisms of fat-induced gastric inhibitory polypeptide/glucose-dependent insulinotropic polypeptide secretion from k cells. Journal of Diabetes Investigation, 7(Suppl Suppl 1), 20-26.