Lactoferrin

Lactoferrin (formerly known as lactotransferrin) is a glycoprotein, and a member of a transferrin family, thus belonging to those proteins capable of binding and transferring Fe3+ ions (Metz-Boutique et al., 1984).It is produced by various mammals and is found in milk, nasal secretions, saliva and tears, and it is in great abundance in human colostrum. It has intrigued scientists for decades.

Lactoferrin was first isolated by Sorensen and Sorensen from bovine milk in 1939. In 1960 it was concurrently determined to be the main iron binding protein in human milk by three independent laboratories (Groves, 1960; Johanson, 1960; Montreuil et al., 1960).
Subsequent research identified lactoferrin in secretions from exocrine glands and in specific granules of neutrophils. Neutrophils after degranulation were obser ved to be the main source of lactoferrin in blood plasma (Iyer and Lonnerdal, 1993).
Due to the increase in its concentration during most inflammatory reactions and some viral in fections, several authors classify lactoferrin as an acute-phase protein (Kanyshkova et al., 2001). Its concentration increases in all biological fluids, but the highest levels have been detected in the nidus of inflammation (Birgens, 1985).
Thus, lactoferrin has a wide variety of biological functions, many of which do not appear to be connected with its iron binding ability (Brock, 2002).​

Lactoferrin is a glycoprotein with a molecular weight of about 80 kDa, which shows high affinity for iron. The molecular structure and amino acid sequence of human lactoferrin were discovered in 1984. Lactoferrin was then classified as a member of the transferrin family, due to its 60% sequence identity with serum transferrin (Metz-Boutique et al., 1984).
Three different isoforms of lactoferrin have been isolated. Lactoferrin-α is the iron binding form, but has no ribonuclease activity. On the other hand lactoferrin-β and lactoferrin-γ demonstrate ribonuclease activity but they are not able to bind iron (Furmanski et al., 1989).
Lactoferrin is comprised of a single polypeptide chain containing 703 amino acids folded into two globular lobes. These lobes, also called C-(carboxy) and N-(amino) terminal regions, are connected with a α-helix. Each lobe consists of two domains known as C1, C2, N1, and N2. The domains create one iron binding site on each lobe. Lactoferrin molecules contain (according to the species and protein) varying numbers of sites for potential glycosylation, mostly on the surface of the molecule. The most common sacharide is mannose; around 3% are hexoses, and 1% hexosamines. The degree of glycosylation varies and determines the rate of resistance to proteases or to very low pH.

Human lactoferrin (hLF) is a valuable protein for pharmaceutical products and functional foods, and worldwide demand for this protein has steadily increased. However, large-scale recombinant human lactoferrin (rhLF) production using current animal bioreactor techniques is limited by the low expression of foreign proteins, the use of antibiotic resistance genes and the down-regulation of endogenous milk proteins. 

Lactoferrin expression can first be detected in two- and four-cell embryos during embryonic development, then throughout the blastocyst stage up to implantation. Lactoferrin cannot be detected from the time of implantation until halfway through gestation. Later, it is found in neutrophils and epithelial cells of forming reproductive and digestive systems (Ward et al., 1999).
The predominant cell types involved in lactoferrin synthesis are of the myeloid series and secretory epithelia (Baynes and Bezwoda, 1994). In adults, higher levels of lactoferrin are present in milk and colostrum (Masson and Heremans, 1971; Brock, 1980). It is also found in most mucosal secretions such as uterine fluid, vaginal secretion, seminal fluid, saliva, bile, pancreatic juice, small intestine secretions, nasal secretion, and tears (Masson et al., 1966; Baker, 1994; Levay and Viljoen, 1995; Lonnerdal and Iyer, 1995; Kikuchi et al., 2003; Baker and Baker, 2005).
The production of lactoferrin by human kidneys was described by Abrink et al. (2000). Lactoferrin is expressed and secreted throughout the collecting tubules, and in the distal part of the tubules it may be reabsorbed. These results show that the kidney produces lactoferrin in a highly ordered manner and that only a minor fraction of this protein is secreted into the urine. Therefore, lactoferrin is thought to have important functions in both the immune defense of the urinary tract and in general iron metabolism.

Lactoferrin improves the composition of the intestinal microflora and reduces allergy symptoms. It can have beneficial effects on skin problems (acne, skin inflammation, psoriasis). It helps people with lactose intolerance to cope with digestive problems after eating it. Lactoferrin has antibacterial, antiviral, antifungal and antiparasitic effects.
lactoferrin can improve the condition of the bones in postmenopausal women who are at the time vulnerable to their weakness. In pregnant women is a powerful support in the fight against anemia caused by iron deficiency, and also supports the development of the fetus. A positive effect of lactoferrin on the treatment of the effects of obesity was also observed.
lactoferrin strengthens the immune system, especially in children. Her support for intestinal bacterial flora causes us to move away from us the spectrum of problems and inflammations in this part of our body. Finally, lactoferrin regulates the concentration of iron in the blood.

The regulation of lactoferrin synthesis depends on the type of cells producing this protein. The amount of lactoferrin synthesized in the mammary gland is controlled by prolactin (Green and Pastewka, 1978), whereas its production in reproductive tissues is determined by estrogens (Pentecost and Teng, 1987; Walmer et al., 1992; Teng et al., 2002). The synthesis of lactoferrin in endometrium is influenced by not only estrogens but also epidermal growth factor (Nelson et al., 1991). Exocrine glands produce and secrete lactoferrin in a continuous manner. In neutrophils, lactoferrin is synthesized during their differentiation (when promyelocytes develop into myelocytes) and is afterwards stored in specific granules. Mature neutrophils cease to produce lactoferrin (Masson et al., 1969).
Lactoferrin levels might vary with gender and age although the results from different studies are inconsistent (Bennett and Mohla, 1976; Bezwoda et al., 1985; Antonsen et al., 1993).
Lactoferrin plasma levels change from the very beginning of pregnancy. There is a progressive rise in its concentration up to the 29th week, after which it settles at a constant level that is higher than the average (Sykes et al., 1982). There are several factors which may cause this increase: leukocytosis associated with pregnancy, the selective increase of lactoferrin in neutrophil granules (Oberg et al., 1983), or other organs like endometrium, decidua, and mammary glands may all contribute (Levay and Viljoen, 1995).

There are two ways in which lactoferrin can be eliminated from the organism: either through re-ceptor-mediated endocytosis of phagocytic cells (macrophages, monocytes, and other cells belonging to the reticuloendothelial system) with subsequent iron transfer to ferritin or through direct uptake by the liver. Endoc ytosis performed by Kupffer cells, liver endothelial cells, and hepatocytes contributes to lactoferrin removal (Levay and Viljoen, 1995). Kidneys seem to be involved in the removal of lactoferrin from the circulation since lactoferrin and its fragments, mainly of maternal origin, have been found in the urine of breast-fed infants (Hutchens et al., 1991).

As mentioned, lactoferrin was discovered first in bovine and later in human milk. Most research has be en carried out in the human field, followed by work on bovine milk.In other animal species , information regarding lactoferrin levels is very scarce. Different methods have been used to either detect or even measure lactoferrin. The relationships between lactoferrin concentrations and gender, age or inflammatory processes have been examined with contradictory results. Lactoferrin concentrations in adult human blood were reported to be in the range of 0.02-1.52 μg/ml depending on the method used. Human lactoferrin venous plasma, colostrum and milk concentrations were determined to be 0.12 μg/ml, 3.1-6.7 mg/ml, and 1.0-3.2 mg/ml, respectively (Levay and Viljoen, 1995).
A quite wide range of lactoferrin concentrations has been determined in healthy bovine milk.The values vary from 1.15μg/ml (Hagiwara et al., 2003), to 485.63 μg/ml in milk from healthy animals . Lactoferrin was shown to be significantly associated with the stage of lactation (r = 0.557) and daily milk production (r = –0.472) (Cheng et al., 2008). Its concentration increased many times (even to 100 mg/ml) during mammar y gland involution (Welty et al., 1976).
Lactoferrin levels in mare colostrum, in the serum of newborns, and in three day old foals were also measured. The obtained results were 21.7 μg/ml, 0.249 μg/ml, and 0.445 μg/ml, respectively (Barton et al., 2006). The mean milk lactoferrin concentration was reported to be 0.229 ± 0.135 mg/ml in the camel (Konuspayeva et al., 2007).
Previously, it had been thought that canine milk did not contain any lactoferrin (Masson and Heremans, 1971). However, in 2007, Berlov et al. succeeded in detecting lactoferrin in canine milk. The concentration was lower (40 μg/ml) than in human milk. Coincidently Sinkora et al. (2007) were able to detect lactoferrin in canine, swine and bovine neutrophils using flow cytometry and commercially available rabbit anti-human polyclonal antisera.
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Lactoferrin, a granule-associated glycoprotein, is a cationic protein with a high proportion of arginine and lysine at the N-terminal region, with two glycosylation and several iron-binding sites. Lactoferrin is highly antibacterial against both gram-positive and gram-negative bacteria at concentrations ranging from 3 to 50 μg/ml. It is believed that these lethal effects are due to a direct interaction of lactoferrin with the cell surface and subsequent disruption of normal permeability functions of the membrane, a so-called dissipation of proton motive force action (23). Similarly, expression of an antimicrobial tachyplesin gene from Asian horseshoe crabs led to antibacterial activity against Erwinia spp. in transgenic potato (24).

Lactoferrin was used to grow Streptococcus mutans in an iron-limiting medium. It was used to test if lactoferrin impedes epithelial cell adhesion in vitro.

Lactoferrin was used in the fractionation of lactoperoxidase and lactoferrin from bovine whey using a cation exchange membrane. It was used in the determination of lactoferrin and immunoglobulin G in animal milks by new immunosensors.

Lactoferrin is an iron binding protein. It is structurally similar to transferrin, the plasma iron transport protein; but lactoferrin has a much higher affinity for iron (250 fold). It is very abundant in colostrum and small amounts can also be found in tears, saliva, mucous secretions and in the secondary granules of neutrophils. It is made by mucosal epithelium and neutrophils and is released by these cells in response to inflammatory stimuli. Bacterial growth is inhibited by its ability to sequester iron and also permeabilize bacterial cell walls by binding to lipopolysaccharides through its N-terminus. Lactoferrin can inhibit viral infection by binding tightly to the viral envelope protein. This prevents cell-virus fusion by blocking the binding domain. Lactoferrin appears to activate host defense systems in part by stimulating the release of interleukin-8, a neutrophil activator. It may also be involved in antibody and interleukin synthesis, lymphocyte proliferation and complement activation.

Lactoferrin is an iron binding protein. It is structurally similar to transferrin, the plasma iron transport protein; but lactoferrin has a much higher affinity for iron (250 fold). It is very abundant in colostrum and small amounts can also be found in tears, saliva, mucous secretions and in the secondary granules of neutrophils. It is made by mucosal epithelium and neutrophils and is released by these cells in response to inflammatory stimuli. Bacterial growth is inhibited by its ability to sequester iron and also permeabilize bacterial cell walls by binding to lipopolysaccharides through its N-terminus. Lactoferrin can inhibit viral infection by binding tightly to the viral envelope protein. This prevents cell-virus fusion by blocking the binding domain. Lactoferrin appears to activate host defense systems in part by stimulating the release of interleukin-8, a neutrophil activator. It may also be involved in antibody and interleukin synthesis, lymphocyte proliferation and complement activation.