Metformin has been used for more than 60 years to treat type 2 diabetes, but we still do not fully know how it works. New research from Baylor College of Medicine shows that the drug also talks to the brain.
Rap1 Protein in the Hypothalamus
Scientists looked at a tiny protein named Rap1 that lives in a part of the brain called the ventromedial hypothalamus (VMH). They found that metformin can lower blood sugar only when it blocks Rap1 in this spot.
To test this, researchers made mice that do not have Rap1 in the VMH. The mice ate a high‑fat diet to become diabetic. When they received a low dose of metformin, their sugar levels stayed high. Other medicines like insulin still worked, showing that the effect was specific to metformin and Rap1.
Direct Brain Injection
The team also gave tiny amounts of metformin straight into the brains of diabetic mice. Even at doses that are thousands of times smaller than a normal pill, blood sugar dropped dramatically.
"We saw that a special group of neurons called SF1 cells became active when metformin reached the brain," said lead researcher Dr. Fukuda. "These cells help the drug do its job."
Neurons Need Rap1 to Respond
When researchers measured the electrical signals of the SF1 neurons, they discovered that metformin boosted activity only if Rap1 was present. Mice lacking Rap1 showed no change, proving that Rap1 is required for the brain’s response.
"This changes our view of metformin," Dr. Fukuda added. "It does not just act in the liver or gut; the brain reacts to very low amounts of the drug."
What This Means for Diabetes and the Brain
Most diabetes drugs target the body, not the brain. This study suggests that future medicines could aim directly at the brain pathway involving Rap1. Metformin is also known to protect the brain as we age, so researchers will explore whether the same Rap1 signal explains those benefits.
Funding for the work came from the National Institutes of Health, the American Heart Association, the American Diabetes Association, and several private foundations.