Cholecystokinin (CCK) Peptides and Mimics
Cholecystokinin (CCK) (or Pancreozymin) coordinates gastrointestinal activity and controls meal size by modulating digestion, glucose levels, neurotransmitters, and memory. Recent studies suggest that CCK also exhibits neuroprotective effects in Alzheimer’s disease (AD) and Parkinson’s disease (PD).
CCK, also called Pancreozymin, is a peptide hormone found in the small intestine and is part of the classical gut hormone triad with gastrin and secretin. CCK stimulates fat and protein digestion in the gastrointestinal system and signals fullness to the brain. CCK is secreted into the blood after a meal and plays a critical role in digestion, absorption, intestinal motility, satiety signaling, and the inhibition of gastric acid secretion.
Duodenal enteroendocrine I-cells (I-cells) synthesize CCK in the mucosal epithelium of the small intestine and secrete it into the duodenum, the first segment of the small intestine, where it triggers the release of digestive enzymes and bile from the pancreas and gallbladder. It also suppresses appetite and has a major role in inducing drug tolerance to opioids like morphine and heroin and is partly implicated in experiences of pain hypersensitivity during opioid withdrawal.
CCK was discovered in 1928 because it induces gallbladder contraction. CCK is a neuropeptide that belongs to a family of hormones defined by amino acid length, for example, CCK58 and CCK33. Prepro-CCK, a 115-amino-acid peptide, is first cleaved to pro-CCK, which in turn yields CCK58, the major processed form of CCK that assumes a helix-turn-helix configuration. CCK binds to CCK receptors on the cell membrane that, when activated, increase phosphatidylinositol turnover, resulting in the release of intracellular calcium. The released calcium increases enzyme secretion, either directly or through activation of protein kinase C.
The reported processing pattern starts with the Cholecystokinin preproprotein (1-115), which contains the signal peptide (1-20). The gastrin/cholecystokinin family protein contains the sequence from amino acid 3-115. Amino acid residues 23-52 are disordered in 3D. Residue S31 is O-linked glycosylated with chondroitin sulfate. Consecutive proteolytic processing produces cholecytokinin-58 (AA 46-103), cholecystokinin-39 (AA 65-103), cholecystokinin-33 (AA 71-103), Cholecystokinin-25 (AA 79-103), Cholecystokinin-18 (AA 86-103), Cholecystokinin-12 (AA 92-108), Cholecystokinin-8 (AA 96-103), Cholecystokinin-7 (AA 97-103) and Cholecystokinin-5 (99-103).
Cholecystokinin preproprotein processing pattern
Pellegrini & Mierke (1999) solved the structure of the molecular complex of cholecystokinin-8 and N-terminus of the cholecystokinin A receptor by NMR spectroscopy. Dinge et al. (2022) studied several cholecystokinin receptor complexes using cryo-electron microscopy.
| 1D6G: COMPLEX OF CHOLECYSTOKININ-8 AND N-TERMINUS OF THE CHOLECYSTOKININ A RECEPTOR (in cyan). |
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| CCK-8: DYMGWMDFX Tyrosine is shown as a spheric model (at the right). | 
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| 7XOU: Structural insights into human brain gut peptide cholecystokinin receptors. Structure solved by electron microscopy at a resolution of 3.20 Å. |
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| Structural model of the complex between the sulfated neuro-peptide CCK-8 and the cholescystokinin receptor type A. | Zoom in to the binding pocket of sulfated CCK-8. CCK-8 is shown as a stick model (left) and as a surfcase model (right) to illustrate the receptor’s binding mode. |
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In the gallbladder, CCK induces gallbladder contraction and bile release into the intestine and stimulates pancreatic acinar cells to release water and ions, secreting a juice rich in pancreatic digestive enzymes. CCK is known to induce growth of the exocrine pancreas and to stimulate insulin secretion.
In the brain, CCK is the most abundant neuropeptide and induces panic attacks, which a central cholecystokinin receptor antagonist can antagonize. ProCCK is expressed in certain neuroendocrine tumors and sarcomas, and the secretion of CCK is impaired in celiac disease and bulimia nervosa.
CCK induces satiety by acting on the central nervous system and the vagus nerve to signal brain receptors that the body is full, reducing appetite during meals.
In the pancreas: CCK triggers pancreatic acinar cells to release digestive enzymes, such as lipase, protease, and amylase, into the duodenum. CCK slows or delays gastric emptying so that the small intestine has adequate time to process and absorb nutrients.
The biochemistry of cholecystokinin is quite complex since the target cells for CCK peptides also express receptors for many other bioactive peptide systems. For example, different peptide systems interact and crosstalk along intracellular signal‐transduction pathways. Examples are the mutual potentiation of CCK peptides with secretin in their stimulation of exocrine pancreatic enzyme and bicarbonate secretion; the CCK/gastrin potentiation of GLP‐1 in stimulation of pancreatic beta‐cell growth; the interaction of CCK with GLP‐1 and PYY in signaling to the brain via afferent vagal fibers to regulate food intake; and the balance between sulfated and nonsulfated CCK peptides from CCKomas, a very rare neuroendocrine tumor of the pancreas, in the inhibition or stimulation of gastric acid secretion.
Cholecystokinin (CCK) mimics, pharmacologically known as CCK receptor agonists, are natural or synthetic compounds that bind to and activate CCK receptors, reproducing the hormone's biological effects in the body.
Because native CCK degrades rapidly in the bloodstream, with a half-life of just a few minutes, synthetic mimics are designed to be more stable for clinical and research applications.
| Peptide Agonists and Analogs | Structure |
| Sincalide (Kinevac) A synthetic 8-amino-acid peptide (CCK-8) that acts as a potent CCK1 receptor agonist. Administered intravenously to stimulate gallbladder contraction during diagnostic imaging, for example, in cholescintigraphy / HIDA scans, or to induce pancreatic enzyme secretion during diagnostic procedures. DY(SO3H)MGWMDF-NH2 | 
1143.27 g·mol−1 |
| Ceruletide (Caerulein): A decapeptide originally isolated from the skin of an Australian frog (Litoria caerulea) that chemically resembles CCK-8. Used in diagnostic radiology to stimulate bowel motility and widely used in animal research models to induce experimental pancreatitis. (Pyr)QDXTGWMDF | 
1352.41 g·mol−1
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| CCK Mimics | Structure |
| CCK Mimics are designed to enhance the binding affinity of native CCK rather than activating the receptor directly. |
| Gski181771 X Investigational small drug under investigation in clinical trial NCT00600743 to study the effect of a CCK-1R Agonist on Food Intake in Humans for the treatment of obesity due to their ability to trigger satiety without requiring intravenous administration. The drug is designed to enhance the binding affinity of native CCK rather than activating the receptor directly. | 
605.6 g/mol |
| Devazepide (L-364,718, MK-329) is an CCKA receptor antagonist. It increases appetite and accelerates gastric emptying, suggested as a potential treatment for a variety of common gastrointestinal problems including dyspepsia, gastroparesis and gastric reflux. It is also widely used in scientific research into the CCKA receptor. | 
408.5 g/mol |
Receptors Targeted by CCK Mimics
| Receptor | Primary Locations | Main Effects when Activated by a Mimic |
| CCK1 (CCKA) | Gallbladder, pancreas, stomach, vagal nerve fibers. | Gallbladder contraction, pancreatic enzyme secretion, delayed gastric emptying, satiety signal. |
| CCK2 (CCKB) | Brain (CNS), parietal cells in the stomach. | Regulation of anxiety/mood, cognitive modulation, and stimulation of gastric acid secretion. |
Therapeutic Potential & Challenges
Since CCK1 activation suppresses appetite, CCK mimics were heavily researched as anti-obesity drugs. However, single-agent CCK agonists showed limited long-term weight loss in clinical trials because the body quickly develops tolerance (tachyphylaxis) to the satiety signal. Modern research explores combining CCK mimics with other gut peptide analogs, such as GLP-1 receptor agonists, for example, semaglutide, to achieve a synergistic effect on satiety and blood glucose regulation.
References
Cholecystokinin
Ding Y, Zhang H, Liao YY, Chen LN, Ji SY, Qin J, Mao C, Shen DD, Lin L, Wang H, Zhang Y, Li XM. Structural insights into human brain-gut peptide cholecystokinin receptors. Cell Discov. 2022 Jun 7;8(1):55. [PMC]
Eberlein GA, Eysselein VE, Davis MT, Lee TD, Shively JE, Grandt D, Niebel W, Williams R, Moessner J, Zeeh J, et al. Patterns of prohormone processing. Order revealed by a new procholecystokinin-derived peptide. J Biol Chem. 1992 Jan 25;267(3):1517-21. [jbc]
Genecard-CCK
Moran TH, Kinzig KP. Gastrointestinal satiety signals II. Cholecystokinin. Am J Physiol Gastrointest Liver Physiol. 2004 Feb;286(2):G183-8. [PubMed]
Noborn,F., Nilsson,J., Sihlbom,C., Nikpour,M., Kjellen,L. and Larson,G.; Mapping the Human Chondroitin Sulfate Glycoproteome Reveals an Unexpected Correlation Between Glycan Sulfation and Attachment Site Characteristics. Mol Cell Proteomics 22 (8), 100617 (2023). [PMC]
Pellegrini M, Mierke DF. Molecular complex of cholecystokinin-8 and N-terminus of the cholecystokinin A receptor by NMR spectroscopy. Biochemistry. 1999 Nov 9;38(45):14775-83. [acs]
Rehfeld JF, Bundgaard JR, Hannibal J, Zhu X, Norrbom C, Steiner DF, Friis-Hansen L. The cell-specific pattern of cholecystokinin peptides in endocrine cells versus neurons is governed by the expression of prohormone convertases 1/3, 2, and 5/6. Endocrinology. 2008 Apr;149(4):1600-8. [PMC]
Rehfeld JF. Cholecystokinin: Clinical aspects of the new biology. J Intern Med. 2025 Sep;298(3):251-267. [PMC]
Reich N, Hölscher C. Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease. Front Neuroendocrinol. 2024 Apr;73: 101122. [Sciencedirect]
Sykaras AG, Demenis C, Case RM, McLaughlin JT, Smith CP. Duodenal enteroendocrine I-cells contain mRNA transcripts encoding key endocannabinoid and fatty acid receptors. PLoS One. 2012;7(8):e42373. [PMC]
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