Hormone-Producing Intestinal Cells Could Be Tapped As A Weight-Loss Remedy
By Deborah Borfitz
March 7, 2022 | An organoid model is being used to flush out what’s behind production of a rare subset of cells in the human intestine and the hormones they manufacture, including four that seem to have the most effect on decreasing appetite, according to Daniel Zeve, M.D., Ph.D., attending physician in the division of endocrinology at Boston Children’s Hospital and instructor of pediatrics at Harvard Medical School. The most immediate use of the platform will be to screen a library of marketed drugs to see if any might help improve weight loss by boosting levels of those chemical messengers.
The hormones of interest—glucose-dependent insulinotropic polypeptide (GIP, from K cells), glucagon-like peptide-1 (GLP-1, from L cells), peptide YY (PYY, from L cells), and cholecystokinin (CCK, from I cells)—would likewise have therapeutic potential in treating type 2 diabetes, Zeve says. But the available medicines for weight loss are fewer in number and “most of them are not that great.”
GIP, GLP-1, PYY, and CCK are a subset of the roughly 15 different hormones produced by enteroendocrine cells (EE) cells, accounting for a scant 1% of all cells in the gut but responsible for critical metabolic functions such as insulin secretion as well as appetite regulation, says Zeve. EE cells send out signals to the rest of the body about how to react when food is or isn’t ingested.
EE cells help control intestinal function, including the speed of digestion. But of particular interest to Zeve and his colleague David Breault, M.D., Ph.D. (associate chief of the division of endocrinology at Boston Children’s and founder and director of its Gastrointestinal Organoid Core) is the hormone-secreting role of EE cells telling the brain it’s time to start or stop eating and the pancreas when insulin is needed because a meal has just been consumed.
Along with metformin, one of the first-line drugs for treating type 2 diabetes is liraglutide, a GLP-1 receptor agonist that at higher doses can also help improve weight loss, says Zeve. The treatment potential of other EE-secreted hormones is only starting to be looked at, if they’ve been investigated at all, he adds.
The organoid platform, recently described in an article appearing in Nature Communications (DOI: 10.1038/s41467-021-27901-5), has been used to identify drugs that could expand the number of EE cells and get them to make more of the needed hormones, or both. Three chemicals were identified that in different combinations drive the formation of EE cells and production of six different hormones (the four above plus somatostatin and serotonin).
“Our method is unique in that we are starting with intestinal stem cells and manipulating those without a specific [genetic] target in mind,” Zeve says, while generating five to 10 times the amount of EE cells normally produced in vivo. “We’re just adding small molecules and that is causing the differentiation to occur.”
That makes the platform ideal for screening drugs, he notes. Typically, labs will use a genetic manipulation model to overexpress neurogenin3 and create organoids that are perhaps 20% enteroendocrine cells, a “sledgehammer” approach ill-suited to downstream experiments.
Tales From the Crypts
The organoid models being used here are three-dimensional (3D) mini-organs that replicate the biology of the duodenum and rectum. The organoids are grown from intestinal stem cells extracted from human biopsy samples in a cell culture dish. The tissue is available from intestinal biopsies of patients at Boston Children’s, housed in a biorepository, and from adult gastrointestinal patients at Massachusetts General Hospital.
Stem cells are all stored in intestinal “crypts”—the valleys between intestinal villi where mature cells are made and “all the action happens”—which naturally assume a U shape but once cultured in a gel matrix (Matrigel), close and form a hollow sphere, Zeve explains. Using a novel technique, those balls of stem cells can then be differentiated into hormone-producing EE cells, or any other cell type, on which various small molecules might be tested.
If left to grow over time, the cultured organoids can get big enough to see with the naked eye, Zeve adds. “If you differentiate them, sometimes they’ll stop growing or get a little bit smaller and every once in a while, … they like to twist and take different shapes.”
Organoids described in the literature can vary widely, sometimes joining together and other times growing tiny buds and breaking in two, he says. “Ours are mostly spheres, or some sort of derivation of that.”
Eventually, predicts Zeve, organoids could be replacing animals models more universally. In addition to the intestine, researchers have to date produced 3D cultures resembling the brain, kidney, lung, stomach, and liver as vehicles for drug screening.
One potential next step for the researchers is to identify the transcription factors that are involved in turning stem cells into enteroendocrine cells and prompting them to produce hormones so they can be specifically targeted, Zeve says. He and Breault have also filed a U.S. patent application on the organoid platform and are currently working on modifying it to accommodate high-throughput drug screening using a standard 96- or 384-well plate system.
The pair most immediately intend to use the organoid model to look at a compound library maintained by the U.S. Food and Drug Administration, containing roughly 800 marketed drugs, to see if any of them help improve weight loss based on the activity of the four main hormones (GIP, GLP-1, PYY, and CCK) for obesity and type 2 diabetes, he adds. The search could then be expanded to other, larger and less explored compound libraries and possibly even natural product repositories.
EE-produced hormones are dysregulated in many diseases, so it might make sense at some point to try boosting their production across the board, says Zeve. “This most likely mimics what happens in the body after a meal and may prevent side effects that could occur with the over-production of just one hormone.”
Preliminary data suggests there might be a “slight difference” in the way adult and pediatric cells differentiate, he says. In unpublished data, adult cell lines differentiated only slightly better than pediatric ones, suggesting if a drug works in one population it should also work in the other at the appropriate dosing level.
Further down the road, Zeve says, he and Breault hope to discover an oral drug enabling people with type 1 diabetes to make insulin or enable people with obesity to lose weight by getting them to produce hormones to help regulate appetite and food intake. Drugs that mimic GLP-1 activity have been approved for weight loss and are frequently prescribed for type 2 diabetes but have a long list of unpleasant side effects.
The duodenum and insulin-producing pancreas develop together in the embryo and their EE cells share a lot of the same transcription factors required for differentiation, says Zeve. “Maybe we can nudge those along a little to make insulin.”
Substantial progress has already been made on this front by Semma Therapeutics, founded by Douglas Melton, Ph.D., and acquired by Vertex Pharmaceuticals in 2019, he notes. Vertex currently has a curative, cell-based treatment for type 1 diabetes in phase 1 trials.