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CHICAGO — Scientists have finally uncovered how one of the world’s most prescribed diabetes medications actually works in the body. The findings solve a decades-old puzzle about metformin, a drug taken by over 200 million people worldwide to control blood sugar levels.
Metformin has been a first-line treatment for Type 2 diabetes for years, helping millions manage their condition at a relatively low cost. However, despite its widespread use, researchers weren’t entirely sure how it accomplished its blood sugar-lowering effects – until now.
A team led by researchers at Northwestern University has demonstrated that metformin works primarily by targeting a specific part of our cells’ energy-producing machinery called mitochondrial complex I. This complex is like a molecular engine that helps power our cells, and metformin essentially acts as a gentle brake on this system.
“This research significantly advances our understanding of metformin’s mechanism of action,” says corresponding author Navdeep Chandel from the Northwestern University Feinberg School of Medicine in a media release. “While millions of people take metformin, understanding its exact mechanism has been a mystery. This study helps explain that metformin lowers blood sugar by interfering with mitochondria in cells.”
To prove this, the scientists employed an innovative approach using genetically modified mice. They introduced a special protein called NDI1, originally found in yeast, into the mice’s cells. This protein essentially acts as a backup generator that can keep working even when metformin is present, allowing researchers to test whether blocking mitochondrial complex I is truly essential for metformin’s effects.
The results published in Science Advances were striking. Normal mice given metformin showed significantly lower blood sugar levels after consuming glucose, as expected. However, mice with the NDI1 backup system were notably less responsive to metformin’s blood sugar-lowering effects, suggesting that inhibiting mitochondrial complex I is indeed crucial for how the drug works.
“The NDI1-expressing mice were not completely resistant to its glucose-lowering effects, suggesting metformin may also target other pathways to some extent, but more research is needed,” Chandel notes.
The researchers tested this both in mice eating regular food and in those fed a high-fat diet to mimic the conditions that often lead to Type 2 diabetes in humans. In both cases, the presence of NDI1 significantly reduced metformin’s effectiveness, though it didn’t completely eliminate it.
This discovery is particularly significant because metformin has shown promise beyond diabetes treatment. Studies have suggested it might help reduce cancer risk, decrease inflammation, and even improve longevity. Understanding exactly how metformin works could help researchers develop more targeted treatments for these conditions and potentially create more effective diabetes medications.
“We think that the diverse effects metformin has on lowering glucose levels, decreasing inflammation and its potential anti-cancer effects could, in part, be explained by inhibiting mitochondrial complex I,” Chandel concludes. “Eventually, others will have to corroborate our idea of mitochondrial complex I inhibition as a unifying mechanism to explain how metformin could improve healthspan in humans.”
The study also helps explain why metformin’s effects can vary among different people and why it works best when taken orally rather than injected. When taken as a pill, the drug primarily affects the intestines and liver – key organs in controlling blood sugar levels – before reaching other parts of the body.
Paper Summary
Methodology
The researchers created special mice that expressed a yeast protein called NDI1 throughout their bodies. This protein can perform similar functions to the cellular target of metformin (mitochondrial complex I) but is resistant to metformin’s effects. They then compared how these mice and normal mice responded to metformin treatment, measuring blood sugar levels after giving them glucose. The mice were tested both on regular diets and after eight weeks on a high-fat diet to simulate obesity-related conditions.
Key Results
The study found that mice with the NDI1 protein showed significantly less response to metformin’s blood sugar-lowering effects compared to normal mice. This was true both for mice on regular diets and those on high-fat diets. However, the NDI1 mice still showed some response to metformin, suggesting there might be additional mechanisms involved in the drug’s effects.
Study Limitations
The researchers noted that their genetically modified mice showed varying levels of NDI1 expression, which could have affected the results. Additionally, since NDI1 cannot perfectly replicate all functions of the natural mitochondrial complex I, some differences in response might be due to these functional variations rather than metformin’s effects.
Discussion & Takeaways
This research provides the first clear evidence that metformin works primarily by inhibiting mitochondrial complex I. This understanding could help develop more targeted treatments for diabetes and other conditions where metformin shows promise. The findings also suggest that metformin might have multiple targets in the body, explaining why it wasn’t completely ineffective in mice with NDI1.
Funding & Disclosures
The study was funded by multiple grants from the National Institutes of Health, the Glenn Foundation for Medical Research, and other organizations. The researchers declared no competing interests, suggesting no potential conflicts of interest that might have influenced their findings or conclusions.
