As well as being used as a spice to add flavour and colour to a variety of dishes, turmeric has long been valued in parts of Asia for its medicinal properties. Although turmeric has been used for centuries as an antiseptic and has been claimed to be effective in a wide range of conditions including autoimmune diseases, heart disease, Alzheimer’s disease and cancer, it is only recently that scientists have begun to explore its properties in detail.
Curcumin, a molecule with a broad spectrum of antioxidant and anti-inflammatory properties, has been identified as the main active ingredient of turmeric and scientists at the University of Michigan have now described how curcumin acts in the body. Instead of interacting directly with numerous unrelated membrane proteins, the team found that curcumin regulates the action of membrane proteins indirectly by changing the physical properties of the bilayer.
Writing in the Journal of the American Chemical Society, the researchers describe in detail how curcumin inserts deep into the membrane in a transbilayer orientation, anchored by hydrogen bonds to the phosphate groups of lipids. The insertion into the membrane is similar to that seen with cholesterol and, like cholesterol, curcumin induces segmental ordering in the membrane. Using a combination of solid-state NMR and differential scanning calorimetry experiments, the team showed that curcumin has a strong effect on membrane structure even at low concentrations. The team plan to use similar experiments to explore the action of other drugs, such as capsaicin, which also interact with membranes.