The compound is considered as a potential Alzheimer's drug because it prevents the harmful clumping of so-called tau proteins typically associated with this disease, but until now it was unknown why it had this effect.
According to scientists including Markus Zweckstetter and Eckhard Mandelkow, methylene blue inactivates molecular residues that promote the bonding of tau proteins.
The researchers also found indications that the substance acts as a spacer to keep the proteins apart.
These findings could lead to the development of modified forms of methylene blue and new types of treatment.
Methylene blue is a multi-talented substance with a long history. The synthetic compound was first produced in 1876, and since then has served not only as a blue dye, but also as a medical drug - for example to treat malaria and prevent urinary tract infections. It is now also being debated as a potential treatment for Alzheimer's disease.
The study was published in "Angewandte Chemie".