A groundbreaking study has revealed a new dimension to how metformin, a decades-old diabetes drug, works. While it’s long been known that metformin primarily reduces glucose production in the liver or affects the gut, researchers from Baylor College of Medicine and collaborators found that it also acts directly in the brain. The team discovered that the drug suppresses a protein called Rap1 in a specific brain region, the ventromedial hypothalamus (VMH). By doing so, metformin activates certain neurons (specifically SF1 neurons) that help lower blood sugar — and it does so even at very low, brain-targeted doses. To confirm this, scientists used genetically engineered mice that lacked Rap1 in their VMH. When given low doses of metformin, their blood sugar levels did not improve. In contrast, other diabetes treatments such as insulin and GLP-1 agonists remained effective, suggesting a specific role for Rap1 in metformin’s action. Additionally, when researchers injected extremely small amounts of metformin directly into the brains of diabetic mice, the treatment significantly reduced blood sugar levels. This discovery changes how we think about metformin: it’s not just working in the liver or the gut, it’s also acting in the brain. The findings open the door to developing more precise and effective diabetes treatments that directly target this brain pathway.
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