The role of lactoferrin in cancer prevention

摘要

Lactoferrin is a 80 kDa glycoprotein found in many body fluids that are at risk of microbial invasion, such as tears, saliva, seminal plasma, and milk. Human (hLF) and bovine (bLF) lactoferrin have 69 percent identical amino acids; their threedimensional structure is even more highly conserved (BAKER et al., 2002), which explains the similar effects of hLF and bLF seen in many experimental models. Cow's milk contains 0.02-0.2 mg/mL lactoferrin, that due to its basic character (the theoretical pi of the polypeptide without sugar moieties is 8.7) can be purified by cation exchange chromatography. Lactoferrin consists of two lobes connected by a helix domain. Both lobes can bind one molecule of iron. Only 15-20 percent of iron binding sites in native bovine milk lactoferrin are occupied; thus, lactoferrin is able to sequester iron from the environment, thereby preventing microorganisms to utilize this essential micronutrient. Titration studies have shown that iron sequestration by lactoferrin results in inhibition of bacterial growth, the "stasis" effect. Recent data indicate that inhibition of biofilm forma-tion by lactoferrin also depends on its iron chelating activity (SINGH et al., 2002). In addition to the stasis effect, lactoferrin is able to kill a variety of microorganisms by other mechanisms, and inhibits the attachment of cellular and viral pathogens to host tissue (NAIDU and ARNOLD, 1997; BROCK, 2002). This makes lactoferrin a vital component of the innate immune system, the first line of defence against microorganisms.