Tirzepatide is a synthetic analogue of gastric inhibitory polypeptide (GIP) that was developed for its ability to stimulate insulin release and thus address both type 2 diabetes and non-alcoholic fatty liver disease. Made up of 39 amino acids, the relatively large Tirzepatide stimulates the release of insulin from the pancreas by binding to both GIP and GLP-1 (glucagon-like peptide-1) receptors. Taken over longer periods of time, Tirzepatide increases adiponectin levels by as much as 26% as well. Research shows that Tirzepatide reduces feelings of hunger, lowers insulin levels, and increases insulin sensitivity. Taken together, these effects cause significant weight loss of 11 kg (25 lbs), improve glucose tolerance, decrease fat (adipose) tissue, and reduce cardiovascular risk.
Amino Acid Sequence: YE-Aib-GTFTSDYSI-Aib-LDKIAQ (C20 fatty acid) AFVQWLIAGGPSSGAPPPS
Note: Aib is a non-coded (non-proteinogenic) amino acid – H2H-C(CH3)2–COOH
Molecular Formula: C225H348N48O68
Molecular Weight: 4813.527 g/mol
PubChem CID: 156588324
CAS Number: 2023788-19-2
Synonyms: P1206, LY3298176
Simply put, Tirzepatide increases the release of insulin from the pancreas resulting in improved glucose control. Research shows that, in individuals with Type 2 diabetes, Tirzepatide decreases hemoglobin A1c (HbA1c) levels by 2.4% after six months. The peptide also appears to aid in weight loss, showing a dose-dependent relationship and helping individuals lose as much as 11 kg (25 lbs) over six months.
It isn’t just that Tirzepatide increases insulin release though. Research suggests that the peptide actually improves the function of pancreatic beta cells, the cells that make and release insulin. Studies suggest that Tirzepatide may actually make beta cells more effective at processing insulin, which leads not just to increases in insulin levels in the bloodstream, but decreased stress on the beta cells themselves. This may, in turn, help to slow the progressive nature of type 2 diabetes.
Research shows that Tirzepatide doesn’t just increase insulin levels at random though. It appears to do so only in response to increased blood glucose levels. During fasting, Tirzepatide actually decreases insulin levels and thus helps to increase insulin sensitivity over time. It also decreases fasting levels of glucagon, which are thought to exacerbate hyperglycemia by interfering with hepatic glucose metabolism. Overall, these changes are a big part of the reason Tirzepatide has a profound effect on glucose and, ultimately, HbA1c levels.
Tirzepatide is a dual agonist of the gastric inhibitory polypeptide receptor and the glucagon-like peptide-1 receptor. Action at these receptors appears to have synergistic effects that make Tirzepatide more effective than strict GLP-1 agonists that are already approved for the treatment of type 2 diabetes. The affinity of Tirzepatide for the GIP receptor is greater than its affinity for the GLP-1 receptor.
Gastric inhibitory polypeptide, which is also referred to as the glucose-dependent insulinotropic polypeptide, is synthesized naturally in the small intestine. This polypeptide binds to the GIP receptor to inhibit gastric acid secretion and gastrin release while stimulating insulin release. The latter is the primary function of GIP-R and is the primary reason that insulin levels increase following a meal.
Glucagon-like peptide-1 receptors are found on beta cells as well as in neurons in the brain. Like GIP-R, stimulation of GLP-1R stimulates the release of insulin. Natural agonists include glucagon and GLP1, but it has also been shown to bind nearly a dozen synthetic agonists including dulaglutide, lithium, and oxyntomodulin. Activation of GLP-1R increases both insulin synthesis and insulin release, factors that have made it a desirable target in drug development. In the brain, GLP-1R stimulation lowers appetite.
Interestingly, stimulation of GLP-1R appears to increase beta cell density in the pancreas. GLP-1R stimulation increases expression of the anti-apoptotic bcl-2 gene while reducing expression of pro-apoptotic bax and caspase-3 genes. This leads to enhanced beta cell survival and, ultimately, to increased levels of insulin.
The combination of GIPR and GLP-1R activity is what gives Tirzepatide an edge over strict GLP-1R agonists. Research shows that Tirzepatide acts identically to GIP at the GIPR, but favors cAMP production over β-arrestin recruitment when acting at the GLP-1R. These details may seem esoteric to some extent, but this difference in activity from endogenous GLP-1 appears to cause GLP-1R activation without increasing physiological internalization of the receptor. The net result is enhanced GLP-1R activity with Tarazepide compared to both endogenous GLP-1 as well as other synthetic GLP-1R agonists. These slight alterations mean that Tirzepatide drastically enhances insulin secretion, promotes feelings of satiety, and reduces inflammation in adipose tissue. These combined effects make it a highly efficacious anti-diabetes peptide.
Finally, Tirzepatide appears to alter adiponectin levels, raising overall levels of the fat-burning peptide. Increased levels of adiponectin reduce fat cell differentiation and increase energy expenditure by making mitochondria more inefficient. A low level of this peptide hormone has been implicated in diseases such as type 2 diabetes, atherosclerosis, and non-alcoholic fatty liver disease. It is worth noting that elevated adiponectin levels elevate insulin sensitivity, so it would appear that Tirzepatide modulates insulin sensitivity via several mechanisms.