Lactoferrin: Bioactive properties and applications

Lactoferrin (Lf) is a protein that is present in the milk of many mammals, as well as in tears, saliva and other secretions, and in white blood cells, suggesting a protective role. Lf is closely related to transferrin, the iron carrier in blood, but binds iron more strongly and retains it to considerably lower pH. Lf possesses multiple bioactive properties that can be understood in terms of its molecular structure. The exceptional iron binding affinity of Lf stems from the nature and location of its iron binding sites, and gives it antioxidant and bacteriostatic properties, by sequestration of free iron. These properties are augmented by a bactericidal domain on the protein surface, and by the liberation of potent antibacterial peptides when Lf is digested with pepsin. A positively charged region on the surface enables Lf to bind anionic molecules such as DNA and heparin. Lf can also bind to many kinds of cells, and although it is unclear whether specific receptors are involved, this leads to regulation of some cytokines and a likely role in inflammation control. Evaluation of the biological role of Lf, and of potential applications, is confused by this multifunctional character. However it is clear that Lf does function in host defence in a variety of ways, and has strong potential for therapeutic applications.