Impact of lactoferrin on bone regenerative processes and its possible implementation in oral surgery – a systematic review of novel studies with metanalysis and metaregression

Lactoferrin is glycoprotein 80 kDa able to chelate two ferric ions per molecule. It is a component of many externally secreted substances such as saliva, tears, colostrum, milk, gastrointestinal fluids, nasal and bronchial mucosa [1]. Lactoferrin contains 691 amino acid residues assembled into two homologous lobes connected through a peptide. All these structures form a 3-turn α-helix. This glycoprotein is able to retain iron ions in the chelated form to pH values as low as 3.0. Because of its structure, it is a component of the innate immune response and a potent immunomodulator [2, 3]. Its ability to bind free iron ions as well as deactivate reactive oxygen forms prevents the tissues from excessive inflammatory processes and also decreases bacterial growth and the development of biofilm [2, 4].

It was also found to have a direct effect on cell differentiation and growth [5], as well as modulation of the cytokine production processes i.e. the ones with direct impact on bone tissue regeneration and growth [6‐8]. Lactoferrin stimulates the growth and activity of chondrocytes and osteoblasts, while inhibiting osteoclastogenesis, without affecting mature osteoclast activity [9]. Its administration decreases secretion of a number of cytokines such as tumor necrosis factor α (TNFα) and interleukin 1 beta (IL-1β) which promote osteolytic processes in tissues [7, 8], and at the same time stabilize the balance in the Receptor activator of nuclear factor κ B (RANK)/ Receptor activator of nuclear factor κ B Ligand (RANKL)/ osteoprotegrin (OPG) system [9]. Since the discovery of the RANKL / RANK / OPG system in the mid-1990s, there is a much more considerable understanding of osteoclast formation and activation. Osteoblasts and stromal stem cells express the receptor activator of ligand (RANKL), which binds to its receptor, RANK, on the surface of osteoclasts and their precursors which activate them. If the ligand is present, this system increases the differentiation of precursors into multinucleated osteoclasts and the activation of osteoclasts and survival in both physiological and pathological conditions associated with increased bone resorption. When the ligand is no ligand, the differentiation of osteoclast is decreased. Osteoprotegrin (OPG) is secreted by osteoblasts and osteogenic stromal stem cells and protects the skeleton from excessive bone resorption by binding to RANKL and preventing its interaction with RANK [10]. Lactoferrin stabilizes the osteinductive effect of hydroxyapatite crystals by acting on osteoblast and osteoclast cells through the RANK / RANK / OPG system mentioned above [11].

In 2006 it was discovered how lactoferrin acts by directly reinforcing bone healing processes at the cellular level [12]. Lactoferrin has a mitogenic effect on osteoblasts close to the wound, mediating through the low-density lipoprotein receptor-related protein-1 (LRP1) and activating two kinases of osteoblast cells: p42/44 mitogen-activated protein kinase (MAPK) and the PI3-kinase-dependentphosphorylation of Akt [12]. Recently, lactoferrin has become the focus of many studies. This increasing interest may result from a deeper understanding of its function and from its greater availability to scientists and practitioners. This results from the fact that the species of origin and the method of preparation of lactoferrin does not substantially affect the extent of proliferation on osteoblast cells [8], which makes the studies on lactoferrin and its possible implementation in medicine cheaper and more universal.

The aim of the study is to answer the question if lactoferrin is a promising factor for bone regenerative process in oral surgery.

As a stabilizer for the immune response to the inflammatory process lactoferrin has undoubtedly a visible effect on the process of bone formation. Many studies carried out in other parts of the body of experimental animals clearly indicate its positive effect [25, 26]. Recently it has been proved that the process of osteodistraction within rabbit’s fibula occurs more efficiently and has more stable results. Authors suggested that the increased tissue growth relative to the control group is attributed to the tilting balance in the RANK / RANKL / OPG system towards increased osteoprotegrin expression and significant decrease expression of RANK-ligand [11]. The same effect is indicated by the study carried out by Montesi et al. on cells culture [10].

In an organ culture study of intraverbal discs it was found that the addition of lactoferrin causes a number of not only anabolic but also anti-catabolic reactions. Through inhibiting the reaction sequence caused by Il-1 and lipopolisacharid (LPS) lactoferrin reduced the expression of multiple metaproteinaseas and disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) at the mRNA level, thus reducing tissue degeneration in bovine, rabbit and mouse cells in vivo and ex vivo [25]. Additionally, it increases several times the bone morphogenic protein 7 (BMP-7) gene expression relative to the control group. Furthermore, lactoferrin diminishes the presence of nitric oxide, which was associated as a pro-inflammatory factor, which leads to cartilage destruction in knee joints and spine discs [10, 11, 25]. Pelletier JP et al. indicted that the higher level of nitric oxide is directly proportional to a higher level of metalloproteinases (MMPs) [24]. The results of such studies are promising, because the human is one of the most biologically responsive species to bovine lactoferrin [27]. Several authors who also examined the degree of graphite resorption during a long-term follow-up found that the bovine graft (BioOss), used in all the studies, is gradually resorbed and replaced with the host bone with only a slight decrease in the bone volume [28]. Not only slow resorption [29], but also no resorption within six years [30] were reported in the literature. Among the studies reviewed in the review - Görmez et al. [16] found that the addition of lactoferrin during implantation significantly accelerates this process, even with a short (4 weeks) follow-up (− 3.42!). In research conducted by Paknejad et al. [17] the differences are also noticeable, but they are not so staggering. However, there is always the effect of speeding up the graft replacement process. With one exception (Yoshimaki et al.) [15], lactoferrin was administered locally in all evaluated studies. The question should be asked: Where does this tendency come from? During the implantation procedure, topical agents are already used to increase osteoblast proliferation, such as various growth factors, platelet-derived growth factor (PDGF) [31], and accelerate their differentiation such as bone morphogenetic protein-2 [32]. Through its interaction with preosteoblasts lactoferrin provides an acceleration of both processes. Additionally, locally active lactoferrin increases the amount of growth factors, which can be combined with implants or orthopedic scaffolds to act synergistically in order to improve osseointegration and ultimately lead to better clinical results. What is more, systemic administrated lactoferrin is characterized by poor bioavailability in human subjects [33]. Free lactoferrin is a protein simply digested in the digestive system. The form of injection used by Yoshimaki et al. [14] overcame the problem of absorbability in the gastrointestinal tract, but it seems practically impossible to be introduced in a typical daily practice, whereas a local application as a possible alternative treatment is available. The possibility of using lactoferrin as a component of a dressing or collagen membranes during surgery saves the patient from an unpleasant series of injections and is much less time consuming. Nowadays, it should be stated that the therapeutic and utility potential of this glycoprotein should be considered untapped.

Experiments using an animal model suggest that lactoferrin may be a useful factor in the regeneration of bone defect in the head and neck area. However, the purpose of our research was to determine whether it is a promising factor for bone regeneration in oral surgery. Nevertheless, it is not only necessary to continue experimental research, but also to extend it to the clinical studies on patients, due to the limitations of different animal model research and different methodology, to introduce lactoferrin as a standard procedure for the treatment of bone defects, because it is a promising product.