Multiple molecular forms of human lactoferrin. Identification of a class of lactoferrins that possess ribonuclease activity and lack iron-binding capacity

A review of the safety evidence on recombinant human lactoferrin for use as a food ingredient

Published studies on the glycosylation, absorption, distribution, metabolism, excretion, and safety outcomes of orally ingested recombinant human lactoferrin (rhLF) were reviewed in the context of unanswered safety questions, including alloimmunization, allergenicity, and immunotoxicity potential of rhLF during repeated exposure. The primary objective was to summarize current safety data of rhLF produced in transgenic host expression systems. Overall, results from animal and human studies showed that rhLF was well tolerated and safe. Animal data showed no significant toxicity-related outcomes among any safety or tolerability endpoints. The no observed adverse effect levels (NOAEL) were at the highest level tested in both iron-desaturated and -saturated forms of rhLF. Although one study reported outcomes of rhLF on immune parameters, no animal studies directly assessed immunogenicity or immunotoxicity from a safety perspective. Data from human studies were primarily reported as adverse events (AE). They showed no or fewer rhLF-related AE compared to control and no evidence of toxicity, dose-limiting toxicities, or changes in iron status in various subpopulations. However, no human studies evaluated the immunomodulatory potential of rhLF as a measure of safety. Following this review, a roadmap outlining preclinical and clinical studies with relevant safety endpoints was developed to address the unanswered safety questions.

To Boost or to Reset: The Role of Lactoferrin in Energy Metabolism

Many pathological conditions, including obesity, diabetes, hypertension, heart disease, and cancer, are associated with abnormal metabolic states. The progressive loss of metabolic control is commonly characterized by insulin resistance, atherogenic dyslipidemia, inflammation, central obesity, and hypertension, a cluster of metabolic dysregulations usually referred to as the "metabolic syndrome". Recently, nutraceuticals have gained attention for the generalized perception that natural substances may be synonymous with health and balance, thus becoming favorable candidates for the adjuvant treatment of metabolic dysregulations. Among nutraceutical proteins, lactoferrin (Lf), an iron-binding glycoprotein of the innate immune system, has been widely recognized for its multifaceted activities and high tolerance. As this review shows, Lf can exert a dual role in human metabolism, either boosting or resetting it under physiological and pathological conditions, respectively. Lf consumption is safe and is associated with several benefits for human health, including the promotion of oral and gastrointestinal homeostasis, control of glucose and lipid metabolism, reduction of systemic inflammation, and regulation of iron absorption and balance. Overall, Lf can be recommended as a promising natural, completely non-toxic adjuvant for application as a long-term prophylaxis in the therapy for metabolic disorders, such as insulin resistance/type II diabetes and the metabolic syndrome.

Overview on Adjunct Ingredients Used in Hydroxyapatite-Based Oral Care Products

Hydroxyapatite, Ca₅(PO₄)₃(OH), is a biomimetic active ingredient, which is used in commercial oral care products such as toothpastes and mouthwashes worldwide. Clinical studies (in vivo) as well as in situ and in vitro studies have shown the preventive effects of hydroxyapatite in various field of oral care. In some products, hydroxyapatite is combined with other active ingredients, to achieve an additional antibacterial effect or to promote gum health. This review analyzes the efficacy of six selected natural and nature-inspired ingredients that are commonly used together with hydroxyapatite. These additional actives are either antibacterial (lactoferrin, xylitol, and zinc) or promote gum health (allantoin, bisabolol, and hyaluronic acid). A systematic literature search was performed, and all studies found on each ingredient were analyzed. In summary, all analyzed ingredients mentioned in this review are well described in scientific studies on their beneficial effect for oral health and can be used to expand the preventive effect of hydroxyapatite in oral care products.

Lactoferrin: from the structure to the functional orchestration of iron homeostasis

Iron is by far the most widespread and essential transition metal, possessing crucial biological functions for living systems. Despite chemical advantages, iron biology has forced organisms to face with some issues: ferric iron insolubility and ferrous-driven formation of toxic radicals. For these reasons, acquisition and transport of iron constitutes a formidable challenge for cells and organisms, which need to maintain adequate iron concentrations within a narrow range, allowing biological processes without triggering toxic effects. Higher organisms have evolved extracellular carrier proteins to acquire, transport and manage iron. In recent years, a renewed interest in iron biology has highlighted the role of iron-proteins dysregulation in the onset and/or exacerbation of different pathological conditions. However, to date, no resolutive therapy for iron disorders has been found. In this review, we outline the efficacy of Lactoferrin, a member of the transferrin family mainly secreted by exocrine glands and neutrophils, as a new emerging orchestrator of iron metabolism and homeostasis, able to counteract iron disorders associated to different pathologies, including iron deficiency and anemia of inflammation in blood, Parkinson and Alzheimer diseases in the brain and cystic fibrosis in the lung.

An overview on in vitro and in vivo antiviral activity of lactoferrin: its efficacy against SARS-CoV-2 infection

Beyond the absolute and indisputable relevance and efficacy of anti-SARS-CoV-2 vaccines, the rapid transmission, the severity of infection, the absence of the protection on immunocompromised patients, the propagation of variants, the onset of infection and/or disease in vaccinated subjects and the lack of availability of worldwide vaccination require additional antiviral treatments. Since 1987, lactoferrin (Lf) is well-known to possess an antiviral activity related to its physico-chemical properties and to its ability to bind to both heparan sulfate proteoglycans (HSPGs) of host cells and/or surface components of viral particles. In the present review, we summarize in vitro and in vivo studies concerning the efficacy of Lf against DNA, RNA, enveloped and non-enveloped viruses. Recent studies have revealed that the in vitro antiviral activity of Lf is also extendable to SARS-CoV-2. In vivo, Lf oral administration in early stage of SARS-CoV-2 infection counteracts COVID-19 pathogenesis. In particular, the effect of Lf on SARS-CoV-2 entry, inflammatory homeostasis, iron dysregulation, iron-proteins synthesis, reactive oxygen formation, oxidative stress, gut-lung axis regulation as well as on RNA negativization, and coagulation/fibrinolysis balance will be critically reviewed. Moreover, the molecular mechanisms underneath, including the Lf binding to HSPGs and spike glycoprotein, will be disclosed and discussed. Taken together, present data not only support the application of the oral administration of Lf alone in asymptomatic COVID-19 patients or as adjuvant of standard of care practice in symptomatic ones but also constitute the basis for enriching the limited literature on Lf effectiveness for COVID-19 treatment.

Lactoferrin as a Human Genome “Guardian”—An Overall Point of View

Structural abnormalities causing DNA modifications of the ethene and propanoadducts can lead to mutations and permanent damage to human genetic material. Such changes may cause premature aging and cell degeneration and death as well as severe impairment of tissue and organ function. This may lead to the development of various diseases, including cancer. In response to a damage, cells have developed defense mechanisms aimed at preventing disease and repairing damaged genetic material or diverting it into apoptosis. All of the mechanisms described above are part of the repertoire of action of Lactoferrin—an endogenous protein that contains iron in its structure, which gives it numerous antibacterial, antiviral, antifungal and anticancer properties. The aim of the article is to synthetically present the new and innovative role of lactoferrin in the protection of human genetic material against internal and external damage, described by the modulation mechanisms of the cell cycle at all its levels and the mechanisms of its repair.

A review on lactoferrin as a proton pump inhibitor

Lactoferrin (Lf) is a versatile natural milk-derived protein that exhibits multiple interesting biological activities. Since it is safe for human administration and currently manufactured using low cost and well-established large-scale processes, the Lf scientific community has been devoted at dissecting its mechanisms of action towards its more rational and efficient use for various applications. Emerging literature has identified proton pumping ATPases as molecular targets of Lf in different cellular models linked to distinct activities of this natural protein. Information on this subject has not been systematically analysed before, hence herein we review the current state of art on the effect of Lf on proton pumping ATPases. Though structurally different, we propose that Lf holds a proton pump inhibitor (PPI)-like activity based on the functional resemblance with the classical inhibitors of the stomach H⁺/K⁺-ATPase. The downstream events and outcomes of the PPI-like activity of Lf, as well as its impact for the development of improved Lf applications are also discussed.

Kidney protective potential of lactoferrin: pharmacological insights and therapeutic advances

Kidney disease is becoming a global public health issue. Acute kidney injury (AKI) and chronic kidney disease (CKD) have serious adverse health outcomes. However, there is no effective therapy to treat these diseases. Lactoferrin (LF), a multi-functional glycoprotein, is protective against various pathophysiological conditions in various disease models. LF shows protective effects against AKI and CKD. LF reduces markers related to inflammation, oxidative stress, apoptosis, and kidney fibrosis, and induces autophagy and mitochondrial biogenesis in the kidney. Although there are no clinical trials of LF to treat kidney disease, several clinical trials and studies on LF-based drug development are ongoing. In this review, we discussed the possible kidney protective mechanisms of LF, as well as the pharmacological and therapeutic advances. The evidence suggests that LF may become a potent pharmacological agent to treat kidney diseases.

A Review on Lactoferrin and Central Nervous System Diseases

Central nervous system (CNS) diseases are currently one of the major health issues around the world. Most CNS disorders are characterized by high oxidative stress levels and intense inflammatory responses in affected tissues. Lactoferrin (Lf), a multifunctional iron-binding glycoprotein, plays a significant role in anti-inflammatory, antibacterial, antiviral, reactive oxygen species (ROS) modulator, antitumor immunity, and anti-apoptotic processes. Previous studies have shown that Lf is abnormally expressed in a variety of neurological diseases, especially neurodegenerative diseases. Recently, the promotion of neurodevelopment and neuroprotection by Lf has attracted widespread attention, and Lf could be exploited both as an active therapeutic agent and drug nanocarrier. However, our understanding of the roles of Lf proteins in the initiation or progression of CNS diseases is limited, especially the roles of Lf in regulating neurogenesis. This review highlights recent advances in the understanding of the major pharmacological effects of Lf in CNS diseases, including neurodegenerative diseases, cerebrovascular disease, developmental delays in children, and brain tumors.

Protein adsorption to poly(tetrafluoroethylene) membranes modified with grafted poly(acrylic acid) chains

Protein adsorption to biomaterial surfaces is important for the function of such materials with anchorage-dependent cell adhesion requiring the presence of adsorbed proteins. The current study evaluated five solid surfaces with poly(acrylic acid) (PAA) grafted from the surface of a poly(tetrafluoroethylene) membrane with respect to the adsorption of serum albumin (SA), lactoferrin (Lf), and lysozyme (Lys) from a phosphate buffer and NaCl solution or water for specific combinations. With the use of x-ray photoelectron spectroscopy, the relative amounts and protein layer thickness were evaluated. SA adsorption was governed by ionic repulsive forces and hydrophobic interactions as evidenced from an increase in the protein adsorption at lower pH (6.5 compared to 7.4) and a correlation with surface coverage when water (pH 6.5) was used as the medium. The adsorption of Lf and Lys followed similar trends for all samples. In general, ionic attractive forces dominated and a strong correlation of increasing protein adsorption with the PAA chain length was evident. This study concluded that all surfaces appear suitable for use in biomaterial applications where tissue ingrowth is desired and that the enhanced protein adsorption in a medium with high ionic strength (e.g., biological fluid) correlates with the PAA chain length rather than the surface coverage.

The Biology of Lactoferrin, an Iron-Binding Protein That Can Help Defend Against Viruses and Bacteria

Lactoferrin is a nutrient classically found in mammalian milk. It binds iron and is transferred via a variety of receptors into and between cells, serum, bile, and cerebrospinal fluid. It has important immunological properties, and is both antibacterial and antiviral. In particular, there is evidence that it can bind to at least some of the receptors used by coronaviruses and thereby block their entry. Of importance are Heparan Sulfate Proteoglycans (HSPGs) and the host receptor angiotensin-converting enzyme 2 (ACE2), as based on other activities lactoferrin might prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from attaching to the host cells. Lactoferrin (and more specifically enteric-coated LF because of increased bioavailability) may consequently be of preventive and therapeutic value during the present COVID-19 pandemic.

Lactoferrin's Anti-Cancer Properties: Safety, Selectivity, and Wide Range of Action

Despite recent advances in cancer therapy, current treatments, including radiotherapy, chemotherapy, and immunotherapy, although beneficial, present attendant side effects and long-term sequelae, usually more or less affecting quality of life of the patients. Indeed, except for most of the immunotherapeutic agents, the complete lack of selectivity between normal and cancer cells for radio- and chemotherapy can make them potential antagonists of the host anti-cancer self-defense over time. Recently, the use of nutraceuticals as natural compounds corroborating anti-cancer standard therapy is emerging as a promising tool for their relative abundance, bioavailability, safety, low-cost effectiveness, and immuno-compatibility with the host. In this review, we outlined the anti-cancer properties of Lactoferrin (Lf), an iron-binding glycoprotein of the innate immune defense. Lf shows high bioavailability after oral administration, high selectivity toward cancer cells, and a wide range of molecular targets controlling tumor proliferation, survival, migration, invasion, and metastasization. Of note, Lf is able to promote or inhibit cell proliferation and migration depending on whether it acts upon normal or cancerous cells, respectively. Importantly, Lf administration is highly tolerated and does not present significant adverse effects. Moreover, Lf can prevent development or inhibit cancer growth by boosting adaptive immune response. Finally, Lf was recently found to be an ideal carrier for chemotherapeutics, even for the treatment of brain tumors due to its ability to cross the blood-brain barrier, thus globally appearing as a promising tool for cancer prevention and treatment, especially in combination therapies.

Cow Milk Lactoferrin Possesses Several Catalytic Activities

Lactoferrin (LF) is a Fe³⁺-binding glycoprotein, that was first recognized in milk and then in other epithelial secretions and barrier body fluids to which many different functions have been attributed to LF including protection from iron-induced lipid peroxidation, immunomodulation, cell growth regulation, DNA and RNA binding, as well as transcriptional activation, еtс. The polyfunctional physiological role of LF is still unclear, but it has been suggested to be responsible for primary defense against microbial and viral infections. It was shown previously that human milk LF possesses several enzymatic activities: DNase, RNase, ATPase, phosphatase, and amylase. Analysis of human, cow, horse, buffalo and camel LF showed a highly conserved three-dimensional (3D) structure including only detail differences in the species. Recently, it was shown that similar to human cow LF possesses DNase and RNase activities. Using different methods here we have shown for the first time that LFs from the milk of seven cows of different breeds possess high peroxidase, protease, amylase, protease, and phosphatase activities. Protease activity of cow LFs was activated by Mg²⁺ and Ca²⁺ ions. In contrast to human LFs, ATPase activity was revealed only in three of seven cow LF preparations. The discovery that LF possesses these activities may contribute to understanding the multiple physiological functions of this extremely polyfunctional protein including its protective role against microbial and viral infections.

Pulmonary immunity to viruses

Mucosal surfaces, such as the respiratory epithelium, are directly exposed to the external environment and therefore, are highly susceptible to viral infection. As a result, the respiratory tract has evolved a variety of innate and adaptive immune defenses in order to prevent viral infection or promote the rapid destruction of infected cells and facilitate the clearance of the infecting virus. Successful adaptive immune responses often lead to a functional state of immune memory, in which memory lymphocytes and circulating antibodies entirely prevent or lessen the severity of subsequent infections with the same virus. This is also the goal of vaccination, although it is difficult to vaccinate in a way that mimics respiratory infection. Consequently, some vaccines lead to robust systemic immune responses, but relatively poor mucosal immune responses that protect the respiratory tract. In addition, adaptive immunity is not without its drawbacks, as overly robust inflammatory responses may lead to lung damage and impair gas exchange or exacerbate other conditions, such as asthma or chronic obstructive pulmonary disease (COPD). Thus, immune responses to respiratory viral infections must be strong enough to eliminate infection, but also have mechanisms to limit damage and promote tissue repair in order to maintain pulmonary homeostasis. Here, we will discuss the components of the adaptive immune system that defend the host against respiratory viral infections.

Studying Lactoferrin N-Glycosylation

Lactoferrin is a multifunctional glycoprotein found in the milk of most mammals. In addition to its well-known role of binding iron, lactoferrin carries many important biological functions, including the promotion of cell proliferation and differentiation, and as an anti-bacterial, anti-viral, and anti-parasitic protein. These functions differ among lactoferrin homologs in mammals. Although considerable attention has been given to the many functions of lactoferrin, its primary nutritional contribution is presumed to be related to its iron-binding characteristics, whereas the role of glycosylation has been neglected. Given the critical role of glycan binding in many biological processes, the glycan moieties in lactoferrin are likely to contribute significantly to the biological roles of lactoferrin. Despite the high amino acid sequence homology in different lactoferrins (up to 99%), each exhibits a unique glycosylation pattern that may be responsible for heterogeneity of the biological properties of lactoferrins. An important task for the production of biotherapeutics and medical foods containing bioactive glycoproteins is the assessment of the contributions of individual glycans to the observed bioactivities. This review examines how the study of lactoferrin glycosylation patterns can increase our understanding of lactoferrin functionality.

Lactoferrin, a Pleiotropic Protein in Health and Disease

SIGNIFICANCE

Lactoferrin (Lf) is a nonheme iron-binding glycoprotein strongly expressed in human and bovine milk and it plays many functions during infancy such as iron homeostasis and defense against microorganisms. In humans, Lf is mainly expressed in mucosal epithelial and immune cells. Growing evidence suggests multiple physiological roles for Lf after weaning.

RECENT ADVANCES

The aim of this review is to highlight the recent advances concerning multifunctional Lf activities.

CRITICAL ISSUES

First, we will provide an overview of the mechanisms related to Lf intrinsic synthesis or intestinal absorption as well as its interaction with a wide spectrum of mammalian receptors and distribution in organs and cell types. Second, we will discuss the large variety of its physiological functions such as iron homeostasis, transportation, immune regulation, oxidative stress, inflammation, and apoptosis while specifying the mechanisms of action. Third, we will focus on its recent physiopathology implication in metabolic disorders, including obesity, type 2 diabetes, and cardiovascular diseases. Additional efforts are necessary before suggesting the potential use of Lf as a diagnostic marker or as a therapeutic tool.

FUTURE DIRECTIONS

The main sources of Lf in human cardiometabolic disorders should be clarified to identify new perspectives for future research and develop new strategies using Lf in therapeutics. Antioxid. Redox Signal. 24, 813-836.

Anticancer effects of lactoferrin: underlying mechanisms and future trends in cancer therapy

Lactoferrin has been widely studied over the last 70 years, and its role in diverse biological functions is now well known and generally accepted by the scientific community. Usually, alterations of the lactoferrin gene in cells are associated with an increased incidence of cancer. Several studies suggest that exogenous treatment with lactoferrin and its derivatives can efficiently inhibit the growth of tumors and reduce susceptibility to cancer. None of these studies, however, reported a consistent outcome with regard to the mechanisms underlying the anticancer effects of lactoferrin. In this review, the association of lactoferrin with cancer is thoroughly discussed, from lactoferrin gene expression to the potential use of lactoferrin in cancer therapy. Lactoferrin cytotoxicity against several cancers is reported to occur in distinct ways under different conditions, namely by cell membrane disruption, apoptosis induction, cell cycle arrest, and cell immunoreaction. Based on these mechanisms, new strategies to improve the anticancer effects of the lactoferrin protein and/or its derivatives are proposed. The potential for lactoferrin in the field of cancer research (including as a chemotherapeutic agent in cancer therapy) is also discussed.

Bovine lactoferrin induces cell cycle arrest and inhibits mTOR signaling in breast cancer cells

Lactoferrin (LF) is predominantly found in mammalian secretions with recognized anticancer potential, although the mechanisms involved in such activity are still unclear. Here, the stability, internalization, and cytotoxicity of bovine LF (bLF) and its variants were tested against a panel of breast cancer cells. bLF was found to be very stable under incubation with cells and also able to internalize them, although most of the protein remained in the culture medium. Furthermore, bLF (up to 30 μM) inhibited the growth of breast cancer cells (T-47D, MDA-MB-231, Hs578T, and MCF-7) in a higher extent than in the normal counterpart cell line (MCF-10-2A), thus suggesting its selectivity. Regarding its variants, only the iron-saturated protein showed a higher activity compared with the commercial bLF. bLF growth inhibitory activity was associated with the induction of cell cycle arrest, but not with apoptosis. Moreover, exposure to bLF increased the cells phospho-AMPKα levels and decreased both phospho threonine mammalian target of rapamycin (mTOR) and total mTOR levels, indicating a novel mechanism of action through its ability to induce nutrient/energy-related stress. This study disclosed important findings to better understand the mechanisms underlying the bLF effects on breast cancer cell lines, which could be valuable for novel advances in the cancer research field.

The intracellular inhibition of HCV replication represents a novel mechanism of action by the innate immune Lactoferrin protein

Hepatitis C virus (HCV) is a major public-health problem with 130-170 million individuals chronically infected worldwide. In order to halt the epidemic, therapy against HCV will need to be both effective and widely available. Studies focusing on safe and affordable natural product active against HCV have revealed the antiviral activity of the human Lactoferrin (hLF) protein which binds and neutralizes the circulating virion. In the current study, investigation of hLF activity on the HCV subgenomic replicon system, which is independent from viral entry and shedding, revealed a distinct antireplicative activity of hLF against HCV. Hepatocellular uptake of hLF was confirmed and correlated with qualitative HCV staining reduction. Quantitative dose-response inhibition assays confirmed an hLF-mediated and dose-dependent HCV replication reduction reaching up to 60%. The in cellulo anti-HCV activity of hLF was additive to both Ribavirin and Interferon-α-2b. Further investigation of hLF activity against the essential viral proteins involved in HCV genome replication revealed an inhibitory activity against the HCV ATPase/Helicase NS3 protein but not against the HCV RNA-dependent RNA polymerase (NS5B protein). NS3 inhibition was mediated by a direct and specific interaction between hLF and an allosteric binding site on NS3. Taken together, our findings reveal a new antiviral mechanism of action by which hLF inhibits intracellular HCV replication.

Recognition of specific and nonspecific DNA by human lactoferrin

The general principles of recognition of nucleic acids by proteins are among the most exciting problems of molecular biology. Human lactoferrin (LF) is a remarkable protein possessing many independent biological functions, including interaction with DNA. In human milk, LF is a major DNase featuring two DNA-binding sites with different affinities for DNA. The mechanism of DNA recognition by LF was studied here for the first time. Electrophoretic mobility shift assay and fluorescence measurements were used to probe for interactions of the high-affinity DNA-binding site of LF with a series of model-specific and nonspecific DNA ligands, and the structural determinants of DNA recognition by LF were characterized quantitatively. The minimal ligands for this binding site were orthophosphate (K(i)  = 5 mM), deoxyribose 5'-phosphate (K(i)  = 3 mM), and different dNMPs (K(i)  = 0.56-1.6 mM). LF interacted additionally with 9-12 nucleotides or nucleotide pairs of single- and double-stranded ribo- and deoxyribooligonucleotides of different lengths and sequences, mainly through weak additive contacts with internucleoside phosphate groups. Such nonspecific interactions of LF with noncognate single- and double-stranded d(pN)(10) provided ~6 to ~7.5 orders of magnitude of the enzyme affinity for any DNA. This corresponds to the Gibbs free energy of binding (ΔG(0)) of -8.5 to -10.0 kcal/mol. Formation of specific contacts between the LF and its cognate DNA results in an increase of the DNA affinity for the enzyme by approximately 1 order of magnitude (K(d)  = 10 nM; ΔG(0)  ≈ -11.1 kcal/mol). A general function for the LF affinity for nonspecific d(pN)(n) of different sequences and lengths was obtained, giving the K(d) values comparable with the experimentally measured ones. A thermodynamic model was constructed to describe the interactions of LF with DNA.

Lactoferrin and necrotizing enterocolitis

Lactoferrin (LF) is a multifunctional protein and a member of the transferrin family. LF and lysozyme in breast milk kill bacteria. In the stomach, pepsin digests and releases a potent peptide antibiotic called lactoferricin from native LF. The antimicrobial characteristics of LF may facilitate a healthy intestinal microbiome. LF is the major whey in human milk; its highest concentration is in colostrum. This fact highlights early feeding of colostrum and also fresh mature milk as a way to prevent necrotizing enterocolitis.

Molecular biology of lactoferrin and its role in modulating immunity and viral pathogenesis

Lactoferrin (Lf), also known as lactotransferrin, is a globular glycoprotein belonging to the transferrin family that is widely expressed in several fluids such as milk, tears, gastric fluid and saliva. Apart from its ability to bind and regulate iron levels in body secretions, Lf possesses antimicrobial activity and is specifically a component of the innate immune system. The antibacterial activity of Lf occurs by depriving the environment of iron essential for bacterial growth. In the case of antiviral activity, Lf may act as a competitor for the cell membrane receptors commonly used by viruses to enter cells. This review summarizes the roles of Lf under normal physiology, with a special emphasis on viruses. The authors also discuss in great detail the interactions between Lf and Kaposi’s sarcoma-associated herpesvirus, as well as possible future directions of research that may progress toward designing modern-day therapeutics to counter viral infections.

Lactoferrin a multiple bioactive protein: an overview

BACKGROUND

Lactoferrin (Lf) is an 80kDa iron-binding glycoprotein of the transferrin family. It is abundant in milk and in most biological fluids and is a cell-secreted molecule that bridges innate and adaptive immune function in mammals. Its protective effects range from anticancer, anti-inflammatory and immune modulator activities to antimicrobial activities against a large number of microorganisms. This wide range of activities is made possible by mechanisms of action involving not only the capacity of Lf to bind iron but also interactions of Lf with molecular and cellular components of both hosts and pathogens.

SCOPE OF REVIEW

This review summarizes the activities of Lf, its regulation and potential applications.

MAJOR CONCLUSIONS

The extensive uses of Lf in the treatment of various infectious diseases in animals and humans has been the driving force in Lf research however, a lot of work is required to obtain a better understanding of its activity.

GENERAL SIGNIFICANCE

The large potential applications of Lf have led scientists to develop this nutraceutical protein for use in feed, food and pharmaceutical applications. This article is part of a Special Issue entitled Molecular Mechanisms of Iron Transport and Disorders.

Lactoferrin in human tumours: immunohistochemical investigations during more than 25 years

Lactoferrin (LF) is an iron-binding glycoprotein of the transferrin family, today known to have multifunctional physiological activities. In humans, under normal conditions, LF has been found in blood, mucosal secretions, gastrointestinal fluids, urine and mostly in milk and colostrum. The first pioneering immunohistochemical report about LF distribution in human tissues dated in 1978; successively, many studies have been performed to analyze the LF immunohistochemical pattern in different normal and neoplastic tissues. In this review, we present data from literature concerning the evidence of LF in tumors together with those by us obtained during more than 25 years; the immunohistochemical applications to human neoplastic tissues have been done to investigate the LF pathogenetic role as well as its activity in cancer. After a systematic analysis of LF immunoreactivity in different human districts, a possible explanation for its presence and function has been modulated for each site or tissue, according to experimental evidences obtained either by in vivo as well as by in vitro studies.

miR-214 regulates lactoferrin expression and pro-apoptotic function in mammary epithelial cells

Lactoferrin (Lf) is an abundantly expressed protein in human milk. Lactoferrin exhibits several important biological functions, and its expression is regulated by multiple environmental factors. Cellular endogenous factors, however, have not been extensively studied with regard to lactoferrin gene expression. In this study, we showed that lactoferrin gene expression and function are directly targeted by miR-214 in HC11 and MCF7 cells. In the lactoferrin mRNA 3 prime untranslated region (UTR) of human, mouse, rat, pig, bovine, camel, and goat species, there is a conserved region that perfectly matches the seed region of miR-214. Transfection of miR-214 mimic in HEK293 cells dose-dependently inhibited the activity of pGL3-control vector containing lactoferrin mRNA 3 prime UTR downstream of the luciferase gene. In HC11 cells, miR-214 overexpression inhibited the induction of lactoferrin expression by beta -estradiol (E2) and dexamethasone-prolactin-insulin (DPI). Furthermore, in MCF7 cells, overexpression of miR-214 markedly decreased lactoferrin expression (P lt 0.05), and inhibition of endogenous miR-214 expression increased lactoferrin expression and cellular apoptotic activities (P lt 0.05). In summary, our data showed that miR-214 is directly involved in lactoferrin expression and lactoferrin mediated cancer susceptibility (proapoptotic activities) in mammary epithelial cells.

Deposition of lactoferrin in fibrillar-type senile plaques in the brains of transgenic mouse models of Alzheimer's disease

We and others have previously reported that lactoferrin (LF), which acts as both an iron-binding protein and an inflammatory modulator, is strongly up-regulated in the brains of patients with Alzheimer's disease (AD). We have also studied the expression and localization of LF mRNA in the brain cortices of patients with AD. In this study, we investigated immunohistochemically the localization of LF in the brains of APP-transgenic mice, representing a model of AD. No LF immunoreactivity was detected in the brains of the wild-type mice. In the transgenic AD mice, LF deposition was detected in the brains. Double-immunofluorescence staining with antibodies directed against the amyloid-beta peptide (Abeta) and LF localized the LF depositions to amyloid deposits (senile plaques) and regions of amyloid angiopathy. Senile plaque formation precedes LF deposition in AD. In the transgenic mice aged <18 months, most of senile plaques were negative for LF. LF deposits appeared weakly at about 18 months of age in these mice. Both the intensity and number of LF-positive depositions in the transgenic mice increased with age. Double-staining for LF and thioflavin-S revealed that LF accumulated in thioflavin-S-positive, fibrillar-type senile plaques. The up-regulation of LF in the brains of both AD patients and the transgenic mouse model of AD provides evidence of an important role for LF in AD-affected brain tissues.

DNA, oligosaccharides, and mononucleotides stimulate oligomerization of human lactoferrin

Using small-angle X-ray scattering (SAXS), light scattering (LS), and soft laser ablation we have shown that lactoferrin (LF) in solution at neutral pH is oligomerized in the absence of salt or at physiological salt concentrations. The level of oligomerization depends on the concentration of LF, KCl or NaCl, and on the duration of the protein storage in solution. At the concentrations comparable with those in human milk (1-6 mg/ml), the average radius of gyration (R(g)) values of LF can attain 400-480 A, while fresh solution of previously lyophylized LF demonstrate a lower average R(g) (50-100 A), and R(g) value characterizing the LF monomer formed at 1 M NaCl is 26.7 A. The addition of oligonucleotides, oligosaccharides, or mononucleotides to LF in the presence or in the absence of KCl with different level of initial oligomerization accelerates the oligomerization rate and increases the R(g) values up to approximately 600-700 A, which correspond to associates containing ten or more protein molecules. During gel filtration on Sepharose 4B, high-degree LF oligomers dissociate nearly completely forming different degraded complexes, but in some cases it is possible to reveal small amount of a decamer. A possible role for oligomerization of LF, a highly polyfunctional protein, for its different biological activities is discussed.

Lactoferrin and cancer disease prevention

Lactoferrin (LF) is an iron-binding glycoprotein that is composed of the transferrin family and is predominantly found in the products of the exocrine glands located in the gateways of the digestive, respiratory, and reproductive systems, suggesting a role in the non-specific defence against invading pathogens. Additionally, several physiological roles have been attributed to LF, namely regulation of iron homeostasis, host defence against infection and inflammation, regulation of cellular growth, and differentiation and protection against cancer development and metastasis. These findings have suggested LF's great potential therapeutic use in cancer disease prevention and/or treatment, namely as a chemopreventive agent. This review looks at the recent advances in understanding the mechanisms underlying the multifunctional roles of LF and future perspectives on its potential therapeutic applications.

Polymorphisms within the lactoferrin gene promoter in various cattle breeds

Lactoferrin (Lf) is an iron-binding protein and belongs to the serum transferrin family. It has broad spectrum antimicrobial action, and it is found in exocrine secretions including milk. The sequence of the bovine lactoferrin gene promoter was analyzed in five different cattle breeds (Holstein Friesian, New Zealand Holstein, Montebéliard, Normande, and Norwegian Red) to determine the extent of polymorphic variation, which exists in this region both within and across cattle breeds. Fifteen different single nucleotide polymorphisms (SNPs) were identified throughout this region. Numerous polymorphisms were found throughout the Holstein Friesian, New Zealand Holstein, Montebéliard, and Normande populations. The most frequently encountered polymorphism found in all breeds was at position -28, which is immediately proximal to the TATA box of the promoter. The most variable base position was -131, which included three types of heterozygotes including a single base deletion in one allele, and three homozygote variants. This polymorphism occurs in a putative transcription factor binding site, for the nuclear factor of activated T cells (NF-ATc). A unique polymorphism was identified in one Normande animal, and three polymorphisms were found in one Montebéliard animal. In general, Norwegian Red cattle displayed fewer SNPs than other breeds. Most nucleotide changes in these animals were within the 190 base pairs of the transcription start point, with the exception of an insertion seen in three animals at position -478. In conclusion, SNPs were found in abundance throughout this regulatory region. Whether or not these polymorphisms have an effect on the regulation of the bovine lactoferrin gene is yet to be elucidated. However, the identification of lactoferrin promoter variants may serve as a marker for healthier animals, thereby accelerating the improvement of animals through breeding.

Antibacterial peptides and proteins with multiple cellular targets

Native antimicrobial peptides and proteins represent bridges between innate and adaptive immunity in mammals. On the one hand they possess direct bacterial killing properties, partly by disintegrating bacterial membranes, and some also by inhibiting functions of intracellular biopolymers. On the other, native antimicrobial peptides and proteins upregulate the host defense as chemoattractants or by various additional immunostimulatory effects. Structure-activity relationship studies indicate that residues responsible for the activities on bacterial membranes or for the secondary functions do not perfectly overlap. In reality, in spite of the relatively short size (18-20 amino acid residues) of some of these molecules, the functional domains can frequently be separated, with the cell-penetrating fragments located at the C-termini and the protein binding domains found upstream. As a cumulative effect, multifunctional and target-specific (agonist or antagonist) antimicrobial peptides and proteins interfere with more than one bacterial function at low concentrations, eliminating toxicity concerns of the earlier generations of antibacterial peptides observed in the clinical setting.

Safety determination for the use of bovine milk-derived lactoferrin as a component of an antimicrobial beef carcass spray

Bovine milk-derived lactoferrin (BMDL), an iron-binding glycoprotein, is known to be an effective natural antimicrobial. It is used as a spray, applied electrostatically, to raw beef carcasses to detach bacteria adhering to the surface in order to reduce microbial contamination. The use of BMDL as a component (at not more than 2% by weight) of an antimicrobial spray was determined Generally Recognized As Safe (GRAS) (GRN 67) for three proposed uses (i.e., beef carcasses, subprimals, and finished cuts), provided that the ingredient statement of food products that contain milk-derived lactoferrin identifies the source of the protein. The use of BMDL spray on only beef carcasses (not subprimals or finished cuts) at a level not to exceed 0.20 ml of formulation per kg of beef was determined safe without the requirement of labeling of food products so treated. The two key components of the assessment are: (1) a determination that exogenous lactoferrin exposure (resulting from its application to beef carcasses) is in the range of existing background exposures of lactoferrin as a result of lactoferrin found naturally in beef, and (2) a determination that this potentially small incremental increase in lactoferrin is safe (i.e., there is no reasonable expectation that BMDL will become an allergen under the conditions of its intended use).

Multiple enzymic activities of human milk lactoferrin

Lactoferrin (LF) is a Fe3+-binding glycoprotein, first recognized in milk and then in other human epithelial secretions and barrier fluids. Many different functions have been attributed to LF, including protection from iron-induced lipid peroxidation, immunomodulation and cell growth regulation, DNA binding, and transcriptional activation. Its physiological role is still unclear, but it has been suggested to be responsible for primary defense against microbial and viral infection. We present evidence that different subfractions of purified human milk LF possess five different enzyme activities: DNase, RNase, ATPase, phosphatase, and malto-oligosaccharide hydrolysis. LF is the predominant source of these activities in human milk. Some of its catalytically active subfractions are cytotoxic and induce apoptosis. The discovery that LF possesses these activities may help to elucidate its many physiological functions, including its protective role against microbial and viral infection.

Lactoferrin down-regulates the LPS-induced cytokine production in monocytic cells via NF-kappa B

Lactoferrin, a glycoprotein present in milk, mucosal secretions and neutrophils contributes to host defense. We have previously shown that orally given milk lactoferrin (LF) mediates anti-infectious and anti-inflammatory activities in vivo. Moreover, we have shown that LF could inhibit the LPS-induced IL-6 secretion in a human monocytic cell line, THP-1. This observation was expanded in the present study investigating the capacity of LF to inhibit cytokine mRNA expression and the involvement of nuclear transcription factor kappa B (NF-kappa B). Cells (THP-1 and Mono Mac 6 monocytic cell lines) were stimulated with Escherichia coli LPS (5-10 ng/10(6) cells) and LF was added (50-500 microg/10(6) cells) 30 min before, or after the LPS addition. By a semiquantitative RT-PCR lower levels of TNF-alpha, IL-1 beta, IL-6, and IL-8 mRNA expression were detected at the peak of the expression in THP-1 cells treated with LF. The reduction in the cytokine expression was followed by a similar reduction in the secreted cytokines as analyzed by ELISA. LF down-regulated also the IL-10 secretion (detected only in LPS-stimulated Mono Mac 6 cells). A similar level of inhibition of these cytokines was detected regardless of the time at which LF was added to the cells in relation to LPS. In addition, LF was internalized into cells and detected in the nucleoli as determined by immunostaining and immunofluorescence. Moreover, by electrophoretic mobility shift assay (EMSA) analysis LF decreased the LPS-induced binding of NF-kappa B to the TNF-alpha promoter. The results show that LF down-regulates the LPS-induced cytokine production in monocytic cells. The inhibitory mechanism is suggested to involve the interference of LF with NF-kappa B activation.

The physiology of lactoferrin

This paper reviews our current knowledge of the structure and function of the iron-binding protein lactoferrin. In particular, it attempts to relate the various proposed physiological functions of lactoferrin to its most characteristic biochemical properties, i.e. its ability to bind iron and its highly basic nature. The extent to which various physiological functions can be considered as definitely established is critically reviewed, and suggestions for future research are proposed.

Lactoferrin gene expression and regulation: an overview

Lactoferrin is highly conserved among human, mouse, bovine, and porcine species. The numbers of amino acids encoded by 15 of the 17 exons in these species are identical, and in 12 locations, they have identical codon interruptions at the intron-exon splice junctions. However, lactoferrin expression is both ubiquitous and species, tissue, and cell-type specific. It is differentially regulated through multiple signaling pathways such as steroid hormone, growth factor, and kinase cascade pathways. Comparing the lactoferrin gene promoters from different species, common and different characteristics are observed. The human, mouse, bovine, porcine, and bubaline (African antelope) promoters all contain a noncanonical TATA box with an adjacent Sp1 site. Both human and mouse have multiple steroid hormone response elements, while none are found in the other species studied, suggesting that the lactoferrin gene is differentially regulated among different species by steroid hormones. Several transcription factors have been identified that are crucial for the expression of the lactoferrin gene during differentiation of the myeloid cells and in estrogen and epidermal growth factor regulation. This article provides an overview on lactoferrin expression and regulation in different species.