New Study Reveals Brain Pathway in Metformin's Glucose-Lowering Effect

A new study from Baylor College of Medicine, published in Science Advances, reveals that Metformin may lower blood sugar through an unexpected brain-based mechanism, challenging long-held assumptions about how the drug works.

For more than six decades, metformin has been the first-line therapy for Type 2 Diabetes, mainly believed to act by reducing glucose production in the liver and influencing gut metabolism. However, researchers led by Makoto Fukuda investigated whether the brain—known to regulate whole-body energy balance—also contributes to its effects.

The team focused on Rap1, a molecule found in the Ventromedial Hypothalamus, which plays a critical role in glucose regulation. Using genetically engineered mice lacking Rap1 in this region, researchers found that low-dose metformin no longer reduced blood glucose levels.

In contrast, other treatments such as insulin and GLP-1 receptor agonists remained effective, highlighting the specific importance of Rap1 in metformin’s action.

To further confirm the brain’s role, scientists delivered extremely small amounts of metformin directly into the brain. Even at doses thousands of times lower than oral administration, the drug significantly lowered blood sugar.

The study also identified SF1 neurons as key mediators. Metformin increased their electrical activity—but only when Rap1 was present—demonstrating that this signaling pathway is essential.

These findings show that the brain is highly sensitive to metformin, requiring much lower concentrations than the liver or gut.

This discovery opens the door to developing more precise, brain-targeted therapies for diabetes. It may also help explain metformin’s broader benefits, including potential effects on brain aging, though further research is needed.

REFERENCE: Hsiao-Yun Lin, Weisheng Lu, Yanlin He, Yukiko Fu, Kentaro Kaneko, Peimeng Huang, Ana B. De la Puente-Gomez, Chunmei Wang, Yongjie Yang, Feng Li, Yong Xu, Makoto Fukuda. Low-dose metformin requires brain Rap1 for its antidiabetic action. Science Advances, 2025; 11 (31) DOI: 10.1126/sciadv.adu3700