Lactoferrin (LF), also known aslactotransferrin (LTF), is a multifunctionalprotein of thetransferrin family. Lactoferrin is aglobularglycoprotein with a molecular mass of about 80kDa that is widely represented in various secretory fluids, such asmilk,saliva,tears, andnasal secretions. Lactoferrin is also present in secondary granules ofPMNs and is secreted by someacinar cells. Lactoferrin can be purified from milk or producedrecombinantly. Humancolostrum ("first milk") has the highest concentration, followed by human milk, then cow milk (150 mg/L).[5]
Lactoferrin is one of the components of theimmune system of the body; it has antimicrobial activity (bacteriocide,fungicide) and is part of the innate defense, mainly at mucoses.[5] It is constantly produced and released into saliva, tears, as well as seminal and vaginal fluid.[6] Lactoferrin providesantibacterial activity to human infants.[7][8] Lactoferrin interacts withDNA andRNA,polysaccharides andheparin, and shows some of its biological functions in complexes with theseligands.
Lactoferrin supplements reduce the risk of respiratory tract infections, based on a recent meta-analysis of randomized controlled trials.[9] As with any supplements sold online, quality may be an issue because nutritional supplement production quality controls are not subject to the same strict regulatory process as medicines.[10]
Occurrence of iron-containing red protein in bovine milk was reported as early as in 1939;[11] however, the protein could not be properly characterized because it could not be extracted with sufficient purity. Its first detailed studies were reported around 1960. They documented the molecular weight,isoelectric point, optical absorption spectra and presence of two iron atoms per protein molecule.[12][13] The protein was extracted from milk, contained iron and was structurally and chemically similar toserumtransferrin. Therefore, it was named lactoferrin in 1961, though the name lactotransferrin was used in some earlier publications, and later studies demonstrated that the protein is not restricted to milk. The antibacterial action of lactoferrin was also documented in 1961, and was associated with its ability to bind iron.[14]
At least 60 gene sequences of lactoferrin have been characterized in 11 species of mammals.[15] In most species,stop codon is TAA, and TGA inMus musculus. Deletions, insertions and mutations of stop codons affect the coding part and its length varies between 2,055 and 2,190nucleotide pairs. Gene polymorphism between species is much more diverse than the intraspecific polymorphism of lactoferrin. There are differences in amino acid sequences: 8 inHomo sapiens, 6 inMus musculus, 6 inCapra hircus, 10 inBos taurus and 20 inSus scrofa. This variation may indicate functional differences between different types of lactoferrin.[15]
In humans, lactoferrin geneLTF is located on the thirdchromosome in thelocus 3q21-q23. Inoxen, the coding sequence consists of 17exons and has a length of about 34,500nucleotide pairs. Exons of the lactoferrin gene in oxen have a similar size to the exons of other genes of thetransferrin family, whereas the sizes of introns differ within the family. Similarity in the size of exons and their distribution in the domains of the protein molecule indicates that the evolutionary development of lactoferrin gene occurred by duplication.[16] Study of polymorphism of genes that encode lactoferrin helps selecting livestock breeds that are resistant tomastitis.[17]
Lactoferrin is one of the transferrin proteins that transferiron to the cells and control the level of free iron in the blood and external secretions. It is present in the milk of humans and other mammals,[13] in theblood plasma andneutrophils and is one of the major proteins of virtually all exocrine secretions of mammals, such assaliva,bile,tears andpancreas.[18] Concentration of lactoferrin in the milk varies from 7 g/L in thecolostrum to 1 g/L in mature milk.[citation needed][clarification needed]
X-ray diffraction reveals that lactoferrin is based on onepolypeptide chain that contains about 700 amino acids and forms two homologous globulardomains named N-and C-lobes. N-lobe corresponds to amino acid residues 1-333 and C-lobe to 345-692, and the ends of those domains are connected by a short α-helix.[19][20] Each lobe consists of two subdomains, N1, N2 and C1, C2, and contains one iron binding site and oneglycosylation site. The degree of glycosylation of the protein may be different and therefore the molecular weight of lactoferrin varies between 76 and 80 kDa. The stability of lactoferrin has been associated with the high glycosylation degree.[21]
Lactoferrin belongs to the basic proteins, itsisoelectric point is 8.7. It exists in two forms: iron-rich hololactoferrin and iron-free apolactoferrin. Their tertiary structures are different; apolactoferrin is characterized by "open" conformation of the N-lobe and the "closed" conformation of the C-lobe, and both lobes are closed in the hololactoferrin.[22]
Each lactoferrin molecule can reversibly bind two ions of iron,zinc,copper or other metals.[23] The binding sites are localized in each of the two protein globules. There, each ion is bonded with six ligands: four from the polypeptide chain (twotyrosine residues, onehistidine residue and oneaspartic acid residue) and two fromcarbonate orbicarbonate ions.
Lactoferrin forms a reddish complex with iron; its affinity for iron is 300 times higher than that oftransferrin.[24] The affinity increases in weakly acidic medium. This facilitates the transfer of iron from transferrin to lactoferrin duringinflammations, when the pH of tissues decreases due to accumulation oflactic and other acids.[25] The saturated iron concentration in lactoferrin inhuman milk is estimated as 10 to 30% (100% corresponds to all lactoferrin molecules containing 2 iron atoms). It is demonstrated that lactoferrin is involved not only in the transport of iron, zinc and copper, but also in the regulation of their intake.[26] Presence of loose ions of zinc and copper does not affect the iron binding ability of lactoferrin, and might even increase it.
Both in blood plasma and in secretory fluids lactoferrin can exist in different polymeric forms ranging frommonomers totetramers. Lactoferrin tends to polymerize bothin vitro andin vivo, especially at high concentrations.[25] Several authors found that the dominant form of lactoferrin in physiological conditions is a tetramer, with the monomer:tetramer ratio of 1:4 at the protein concentrations of 10−5 M.[27][28][29]
It is suggested that theoligomer state of lactoferrin is determined by its concentration and thatpolymerization of lactoferrin is strongly affected by the presence of Ca2+ ions. In particular, monomers were dominant at concentrations below 10−10−10−11 M in the presence of Ca2+, but they converted into tetramers at lactoferrin concentrations above 10−9−10−10 M.[27][30]Titer of lactoferrin in the blood corresponds to this particular "transition concentration" and thus lactoferrin in the blood should be presented both as a monomer and tetramer. Many functional properties of lactoferrin depend on its oligomeric state. In particular, monomeric, but not tetrameric lactoferrin can strongly bind to DNA.
Lactoferrin belongs to theinnate immune system. Apart from its main biological function, namely binding and transport of iron ions, lactoferrin also has antibacterial, antiviral,antiparasitic, catalytic, anti-cancer, and anti-allergic functions and properties.[31]
Lactoferrin hydrolyzesRNA and exhibits the properties ofpyrimidine-specific secretoryribonucleases[citation needed]. In particular, by destroying the RNA genome, milk RNase inhibits reverse transcription ofretroviruses that causebreast cancer in mice.[32]Parsi women in WestIndia have the milk RNase level markedly lower than in other groups, and theirbreast cancer rate is three times higher than average.[33] Thus,ribonucleases of milk, and lactoferrin in particular, might play an important role inpathogenesis.
Thelactoferrin receptor plays an important role in theinternalization of lactoferrin; it also facilitates absorption of iron ions by lactoferrin. It was shown thatgene expression increases with age in theduodenum and decreases in thejejunum.[34]The moonlighting glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been demonstrated to function as a receptor for lactoferrin.[35]
Ribonuclease-enriched lactoferrin has been used to examine how lactoferrin affects bone. Lactoferrin has shown to have positive effects on bone turnover. It has aided in decreasing bone resorption and increasing bone formation. This was indicated by a decrease in the levels of two bone resorption markers (deoxypyridinoline andN-telopeptide) and an increase in the levels two bone formation markers (osteocalcin andalkaline phosphatase).[36] It has reducedosteoclast formation, which signifies a decrease in pro-inflammatory responses and an increase in anti-inflammatory responses[37] which indicates a reduction in bone resorption as well.
One of the important properties of lactoferrin is its ability to bind with nucleic acids. The fraction of protein extracted from milk, contains 3.3% RNA,[27]but, the protein preferably binds to double-stranded DNA rather than single-stranded DNA. The ability of lactoferrin to bind DNA is used for its isolation and purification usingaffinity chromatography with columns containing immobilized DNA-containingsorbents, such asagarose with the immobilized single-stranded DNA.[38]
Lactoferrin (larger protein) and asiderophore ofE. coli (smaller protein) are shown. Lactoferrin is a protein found in the immune system, and is a common defense against bacterial infections. Lactoferrin restricts access to host iron by binding to iron with a higher affinity than bacterial proteins.[39]
Lactoferrin's primary role is to sequester free iron, and in doing so remove essential substrate required for bacterial growth.[40] Antibacterial action of lactoferrin is also explained by the presence of specificreceptors on the cell surface of microorganisms. Lactoferrin binds to lipopolysaccharide of bacterial walls, and the oxidized iron part of the lactoferrin oxidizes bacteria via formation ofperoxides. This affects the membrane permeability and results in the cell breakdown (lysis).[40]
Although lactoferrin also has other antibacterial mechanisms not related to iron, such as stimulation of phagocytosis,[41] the interaction with the outer bacterial membrane described above is the most dominant and most studied.[42] Lactoferrin not only disrupts the membrane, but even penetrates into the cell. Its binding to the bacteria wall is associated with the specificpeptidelactoferricin, which is located at the N-lobe of lactoferrin and is produced byin vitro cleavage of lactoferrin with another protein,trypsin.[43][44] A mechanism of the antimicrobial action of lactoferrin has been reported as lactoferrin targets H+-ATPase and interferes with proton translocation in the cell membrane, resulting in a lethal effectin vitro.[45]
Lactoferrin prevents the attachment ofH. pylori in the stomach, which in turn, aids in reducing digestive system disorders. Bovine lactoferrin has more activity againstH. pylori than human lactoferrin.[46]
The most studied mechanism of antiviral activity of lactoferrin is its diversion of virus particles from the target cells. Many viruses tend to bind to thelipoproteins of the cell membranes and then penetrate into the cell.[54] Lactoferrin binds to the same lipoproteins thereby repelling the virus particles. Iron-free apolactoferrin is more efficient in this function than hololactoferrin; and lactoferricin, which is responsible for antimicrobial properties of lactoferrin, shows almost no antiviral activity.[47]
Beside interacting with the cell membrane, lactoferrin also directly binds to viral particles, such as thehepatitis viruses.[54] This mechanism is also confirmed by the antiviral activity of lactoferrin against rotaviruses,[44] which act on different cell types.
Lactoferrin and lactoferricin inhibitin vitro growth ofTrichophyton mentagrophytes, which are responsible for several skin diseases such asringworm.[62] Lactoferrin also acts against theCandida albicans – adiploidfungus (a form ofyeast) that causesopportunistic oral andgenital infections in humans.[63][64]Fluconazole has long been used againstCandida albicans, which resulted in emergence ofstrains resistant to this drug. However, a combination of lactoferrin with fluconazole can act against fluconazole-resistant strains ofCandida albicans as well as other types ofCandida:C. glabrata, C. krusei, C. parapsilosis andC. tropicalis.[63] Antifungal activity is observed for sequential incubation ofCandida with lactoferrin and then with fluconazole, but not vice versa. The antifungal activity of lactoferricin exceeds that of lactoferrin. In particular, synthetic peptide 1–11 lactoferricin shows much greater activity againstCandida albicans than native lactoferricin.[63]
Administration of lactoferrin through drinking water to mice with weakened immune systems and symptoms ofaphthous ulcer reduced the number ofCandida albicans strains in the mouth and the size of the damaged areas in the tongue.[65] Oral administration of lactoferrin to animals also reduced the number of pathogenic organisms in the tissues close to thegastrointestinal tract.Candida albicans could also be completely eradicated with a mixture containing lactoferrin,lysozyme anditraconazole in HIV-positive patients who were resistant to other antifungal drugs.[66] Such antifungal action when other drugs deem inefficient is characteristic of lactoferrin and is especially valuable for HIV-infected patients.[67] Contrary to the antiviral and antibacterial actions of lactoferrin, very little is known about the mechanism of its antifungal action. Lactoferrin seems to bind theplasma membrane ofC. albicans inducing an apoptotic-like process.[64][68]
Theanticancer activity ofbovine lactoferrin (bLF) has been demonstrated in experimental lung, bladder, tongue, colon, and liver carcinogeneses on rats, possibly by suppression of phase I enzymes, such as cytochrome P450 1A2 (CYP1A2).[69] Also, in another experiment done onhamsters, bovine lactoferrin decreased the incidence oforal cancer by 50%.[70] Currently, bLF is used as an ingredient inyogurt,chewing gums,infant formulas, andcosmetics.[70]
The human lung and saliva contain a wide range of antimicrobial compound including lactoperoxidase system, producinghypothiocyanite and lactoferrin, with hypothiocyanite missing incystic fibrosis patients.[71] Lactoferrin, a component of innate immunity, prevents bacterialbiofilm development.[72][73] The loss of microbicidal activity and increased formation of biofilm due to decreased lactoferrin activity is observed in patients with cystic fibrosis.[74] In cystic fibrosis, antibiotic susceptibility may be modified by lactoferrin.[75] These findings demonstrate the important role of lactoferrin in human host defense and especially in lung.[76] Lactoferrin with hypothiocyanite has been grantedorphan drug status by theEMEA[77] and theFDA.[78]
Low quality evidence suggests that oral lactoferrin supplementation with or without the addition of a probiotic may decrease late onset of sepsis andnecrotizing enterocolitis (stage II or III) in preterm infants with no adverse effects.[79]
Lactoferrin levels in tear fluid have been shown to decrease in dry eye diseases such asSjögren's syndrome.[80] A rapid, portable test utilizing microfluidic technology has been developed to enable measurement of lactoferrin levels in human tear fluid at the point-of-care with the aim of improving diagnosis of Sjögren's syndrome and other forms of dry eye disease.[81]
Bovine lactoferrin can be isolated from raw milk, colostrum, orwhey using methods such as salt extraction, chromatography, and membrane filtration. Lactoferrin from a variety of species, including humans, can also be produced using transgenic organisms as arecombinant protein.[82]
^abKang JF, Li XL, Zhou RY, Li LH, Feng FJ, Guo XL (June 2008). "Bioinformatics analysis of lactoferrin gene for several species".Biochemical Genetics.46 (5–6):312–22.doi:10.1007/s10528-008-9147-9.PMID18228129.S2CID952135.
^Seyfert HM, Tuckoricz A, Interthal H, Koczan D, Hobom G (June 1994). "Structure of the bovine lactoferrin-encoding gene and its promoter".Gene.143 (2):265–9.doi:10.1016/0378-1119(94)90108-2.PMID8206385.
^O'Halloran F, Bahar B, Buckley F, O'Sullivan O, Sweeney T, Giblin L (January 2009). "Characterisation of single nucleotide polymorphisms identified in the bovine lactoferrin gene sequences across a range of dairy cow breeds".Biochimie.91 (1):68–75.doi:10.1016/j.biochi.2008.05.011.PMID18554515.
^Birgens HS (April 1985). "Lactoferrin in plasma measured by an ELISA technique: evidence that plasma lactoferrin is an indicator of neutrophil turnover and bone marrow activity in acute leukaemia".Scandinavian Journal of Haematology.34 (4):326–31.doi:10.1111/j.1600-0609.1985.tb00757.x.PMID3858982.
^Jameson GB, Anderson BF, Norris GE, Thomas DH, Baker EN (November 1998). "Structure of human apolactoferrin at 2.0 A resolution. Refinement and analysis of ligand-induced conformational change".Acta Crystallographica Section D.54 (Pt 6 Pt 2):1319–35.Bibcode:1998AcCrD..54.1319J.doi:10.1107/S0907444998004417.PMID10089508.
^Levay PF, Viljoen M (1995). "Lactoferrin: a general review".Haematologica.80 (3):252–67.PMID7672721.
^Mazurier J, Spik G (May 1980). "Comparative study of the iron-binding properties of human transferrins. I. Complete and sequential iron saturation and desaturation of the lactotransferrin".Biochimica et Biophysica Acta.629 (2):399–408.doi:10.1016/0304-4165(80)90112-9.PMID6770907.
^abBroc JH, De Sousa M (1989).Iron in immunity, cancer, and inflammation. New York: Wiley.ISBN978-0-471-92150-9.
^Shongwe MS, Smith CA, Ainscough EW, Baker HM, Brodie AM, Baker EN (May 1992). "Anion binding by human lactoferrin: results from crystallographic and physicochemical studies".Biochemistry.31 (18):4451–8.doi:10.1021/bi00133a010.PMID1581301.
^abcBennett RM, Davis J (January 1982). "Lactoferrin interacts with deoxyribonucleic acid: a preferential reactivity with double-stranded DNA and dissociation of DNA-anti-DNA complexes".The Journal of Laboratory and Clinical Medicine.99 (1):127–38.PMID6274982.
^Mantel C, Miyazawa K, Broxmeyer HE (1994). "Physical Characteristics and Polymerization During Iron Saturation of Lactoferrin, A Myelopoietic Regulatory Molecule with Suppressor Activity".Lactoferrin Structure and Function. Advances in, Experimental Medicine and Biology. Vol. 357. pp. 121–32.doi:10.1007/978-1-4615-2548-6_12.ISBN978-0-306-44734-1.PMID7762423.
^Das MR, Padhy LC, Koshy R, Sirsat SM, Rich MA (August 1976). "Human milk samples from different ethnic groups contain RNase that inhibits, and plasma membrane that stimulates, reverse transcription".Nature.262 (5571):802–5.Bibcode:1976Natur.262..802D.doi:10.1038/262802a0.PMID60710.S2CID4216981.
^Rawat P, Kumar S, Sheokand N, Raje CI, Raje M (June 2012). "The multifunctional glycolytic protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a novel macrophage lactoferrin receptor".Biochemistry and Cell Biology.90 (3):329–38.doi:10.1139/o11-058.PMID22292499.
^Bharadwaj S, Naidu AG, Betageri GV, Prasadarao NV, Naidu AS (September 2009). "Milk ribonuclease-enriched lactoferrin induces positive effects on bone turnover markers in postmenopausal women".Osteoporosis International.20 (9):1603–11.doi:10.1007/s00198-009-0839-8.PMID19172341.S2CID10711802.
^Bharadwaj S, Naidu TA, Betageri GV, Prasadarao NV, Naidu AS (November 2010). "Inflammatory responses improve with milk ribonuclease-enriched lactoferrin supplementation in postmenopausal women".Inflammation Research.59 (11):971–8.doi:10.1007/s00011-010-0211-7.PMID20473630.S2CID3180066.
^Kuwata H, Yip TT, Yip CL, Tomita M, Hutchens TW (April 1998). "Bactericidal domain of lactoferrin: detection, quantitation, and characterization of lactoferricin in serum by SELDI affinity mass spectrometry".Biochemical and Biophysical Research Communications.245 (3):764–73.doi:10.1006/bbrc.1998.8466.PMID9588189.
^Fujihara T, Hayashi K (1995). "Lactoferrin inhibits herpes simplex virus type-1 (HSV-1) infection to mouse cornea".Archives of Virology.140 (8):1469–1472.doi:10.1007/BF01322673.PMID7661698.S2CID4396295.
^abGiansanti F, Rossi P, Massucci MT, Botti D, Antonini G, Valenti P, et al. (2002). "Antiviral activity of ovotransferrin discloses an evolutionary strategy for the defensive activities of lactoferrin".Biochemistry and Cell Biology.80 (1):125–130.doi:10.1139/o01-208.PMID11908636.
^Harmsen MC, Swart PJ, de Béthune MP, Pauwels R, De Clercq E, The TH, et al. (August 1995). "Antiviral effects of plasma and milk proteins: lactoferrin shows potent activity against both human immunodeficiency virus and human cytomegalovirus replication in vitro".The Journal of Infectious Diseases.172 (2):380–388.doi:10.1093/infdis/172.2.380.PMID7622881.
^abPuddu P, Borghi P, Gessani S, Valenti P, Belardelli F, Seganti L (September 1998). "Antiviral effect of bovine lactoferrin saturated with metal ions on early steps of human immunodeficiency virus type 1 infection".The International Journal of Biochemistry & Cell Biology.30 (9):1055–1062.doi:10.1016/S1357-2725(98)00066-1.hdl:11573/83805.PMID9785469.
^Tsuda H, Sekine K, Fujita K, Ligo M (2002). "Cancer prevention by bovine lactoferrin and underlying mechanisms--a review of experimental and clinical studies".Biochemistry and Cell Biology.80 (1):131–6.doi:10.1139/o01-239.PMID11908637.
^abChandra Mohan KV, Kumaraguruparan R, Prathiba D, Nagini S (September 2006). "Modulation of xenobiotic-metabolizing enzymes and redox status during chemoprevention of hamster buccal carcinogenesis by bovine lactoferrin".Nutrition.22 (9):940–6.doi:10.1016/j.nut.2006.05.017.PMID16928475.
^Ohashi Y, Ishida R, Kojima T, Goto E, Matsumoto Y, Watanabe K, et al. (August 2003). "Abnormal protein profiles in tears with dry eye syndrome".American Journal of Ophthalmology.136 (2):291–9.doi:10.1016/S0002-9394(03)00203-4.PMID12888052.
^Karns K, Herr AE (November 2011). "Human tear protein analysis enabled by an alkaline microfluidic homogeneous immunoassay".Analytical Chemistry.83 (21):8115–22.doi:10.1021/ac202061v.PMID21910436.
1cb6: STRUCTURE OF HUMAN APOLACTOFERRIN AT 2.0 A RESOLUTION.
1dsn: D60S N-TERMINAL LOBE HUMAN LACTOFERRIN
1eh3: R210K N-TERMINAL LOBE HUMAN LACTOFERRIN
1fck: STRUCTURE OF DICERIC HUMAN LACTOFERRIN
1h43: R210E N-TERMINAL LOBE HUMAN LACTOFERRIN
1h44: R210L N-TERMINAL LOBE HUMAN LACTOFERRIN
1h45: R210G N-TERMINAL LOBE HUMAN LACTOFERRIN
1hse: H253M N TERMINAL LOBE OF HUMAN LACTOFERRIN
1l5t: Crystal Structure of a Domain-Opened Mutant (R121D) of the Human Lactoferrin N-lobe Refined From a Merohedrally-Twinned Crystal Form.
1lcf: CRYSTAL STRUCTURE OF COPPER-AND OXALATE-SUBSTITUTED HUMAN LACTOFERRIN AT 2.0 ANGSTROMS RESOLUTION
1lct: STRUCTURE OF THE RECOMBINANT N-TERMINAL LOBE OF HUMAN LACTOFERRIN AT 2.0 ANGSTROMS RESOLUTION
1lfg: MOLECULAR REPLACEMENT SOLUTION OF THE STRUCTURE OF APOLACTOFERRIN, A PROTEIN DISPLAYING LARGE-SCALE CONFORMATIONAL CHANGE
1lfh: MOLECULAR REPLACEMENT SOLUTION OF THE STRUCTURE OF APOLACTOFERRIN, A PROTEIN DISPLAYING LARGE-SCALE CONFORMATIONAL CHANGE
1lfi: METAL SUBSTITUTION IN TRANSFERRINS: THE CRYSTAL STRUCTURE OF HUMAN COPPER-LACTOFERRIN AT 2.1 ANGSTROMS RESOLUTION
1lgb: INTERACTION OF A LEGUME LECTIN WITH THE N2 FRAGMENT OF HUMAN LACTOTRANSFERRIN OR WITH THE ISOLATED BIANTENNARY GLYCOPEPTIDE: ROLE OF THE FUCOSE MOIETY
1n76: CRYSTAL STRUCTURE OF HUMAN SEMINAL LACTOFERRIN AT 3.4 A RESOLUTION
1sqy: Structure of human diferric lactoferrin at 2.5A resolution using crystals grown at pH 6.5
1vfd: HUMAN LACTOFERRIN, N-TERMINAL LOBE MUTANT WITH ARG 121 REPLACED BY GLU (R121E)
1vfe: HUMAN LACTOFERRIN, N-TERMINAL LOBE MUTANT WITH ARG 121 REPLACED BY SER (R121S)
1z6v: Human lactoferricin
1z6w: Human Lactoferricin
2bjj: STRUCTURE OF RECOMBINANT HUMAN LACTOFERRIN PRODUCED IN THE MILK OF TRANSGENIC COWS
