When the fat tissue was given serotonin (a chemical the body uses in mood and digestion), it made over twice as many harmful molecules — but adding methylene blue cut that increase in half, showing the enzyme MAO-A is involved.

When the fat tissue was given serotonin (a chemical that MAO-A breaks down), it made more harmful molecules—but adding methylene blue stopped some of that increase.

When fat tissue around the heart and blood vessels was soaked in a blue dye called methylene blue for a day in the lab, it made less of a harmful enzyme and produced fewer damaging chemicals, which might help explain how the dye could protect cells.

When fat tissue around the heart and blood vessels from heart failure patients was soaked in a small amount of methylene blue for a day, the levels of a specific enzyme (MAO-A) that makes harmful molecules went down.