Location and dynamics of astaxanthin in the membrane

Astaxanthin (ASX) is a natural xanthophyll carotenoid recognized for its strong antioxidant bioactive function, and it has been used in the prevention of heart disease, inflammation, neurological disorders, scavenger of environmental produced free radicals and as an anti-aging and anti-cancer biomolecule. ASX is a long lipophilic molecule with two terminal relatively polar rings connected by a long hydrophobic chain. This work describes the dynamics, orientation, location and interactions of ASX in a complex biomembrane. In water, ASX form high-order aggregates where the molecules are joined together by the hydrophobic chain. Depending on the number of ASX molecules, the aggregates can have different structures and the polar groups positioned superficially contacting the solvent. ASX molecules are not able to insert themselves into the membrane, forming high-order aggregates quickly. In the membrane, ASX molecules do not aggregate, remaining all time in the monomeric state. ASX is capable of reaching both membrane surfaces, one at a time. The ASX molecules form an approximate angle of 20º with respect to the membrane perpendicular and it is inserted between the phospholipid hydrocarbon chains, increasing slightly the membrane fluidity. ASX is readily miscible with membrane phospholipids and its location within the membrane is suited for its potent antioxidant activity. Furthermore, since ASX has two polar groups at both ends, the molecule can function in a wide range of depths. ASX is therefore perfectly suited for its antioxidant task in the membrane.