Lactoferrin is an iron-binding glycoprotein of the transferrin family that is expressed in most biologic fluids, such as the breast milk, particularly the colostrums, tears, sweat, saliva and other exocrine secretions of
As a major component of mammals' innate immune system, lactoferrin has been shown to have numerous functions such as below.
By binding to the envelope of the Hepatitis C virus (HCV), lactoferrin prevents infiltration of HCV to the target cells, and suppresses viral replication.
2. "Antibacterial effect”
By chelating iron, lactoferrin suppresses the proliferation of iron requiring bacteria.
3. ”Anti-inflammatory effect”
By strongly binding to endotoxin (LPS), lactoferrin inhibits the binding of LPS to macrophages and suppresses the production of inflammatory cytokines such as TNF-&alphs; and IL-6.
4. ”Immunoregulatory effect”
Lactoferrin stimulates cytotoxic activity of natural killer cells (NK cells).
5. ”Antitumor effect”
Lactofferin induces the apoptosis of tumor cells, or prevent the propagation of tumors by inhibiting angiogenesis.
Focusing on anti-inflammatory effects, the lactoferrin in various biologic fluids are considered as markers of inflammation. It has been reported that fecal lactoferrin is useful as a sensitive and specific marker in identifying intestinal inflammation such as Crohn’s disease and chronic inflammatory bowel disease (IBD). Combination of several markers, such as S100A8/A9 complex, defensin, elastase, MPO and I-FABP may be useful for classifying IBD.
In addition, bovine milk prior to high temperature pasteurization (raw milk) contains large quantities of lactoferrin, and oral intake of lactoferrin has
been reported to cause several effects that maintain and promote health:
1. Proliferation of Lactobacillus biffidus
2. Improvement of anemia
3. Reduction of visceral fat
4. Prevention of arteriosclerosis by inhibiting the uptake of denatured LDL
Because of these effects, taking lactoferrin by milk products and supplements attracts public interest.
Thioredoxin-interacting protein (TXNIP), the endogenous inhibitor of thioredoxin also known as vitamin D3 up-regulated protein-1 or thioredoxin-binding protein-2, inhibits thioredoxin antioxidative function by binding to its active-site thiols.
It was also demonstrated that TXNIP plays a crucial role for caspase-1 activation caused by high glucose treatment in murine cells by direct interaction with the NLRP3-inflammasome. TXNIP-dependent inflammasome activation appears to be specific for NLRP3, as TXNIP deficiency did not affect the activity of other inflammasomes, e.g., NLRC4 and AIM2. TXNIP levels are elevated in subjects with type 2 diabetes mellitus, and its expression is induced by glucose-6-phosphate through an intracellular transcriptional complex of MondoA and Max-like protein X. TXNIP is induced by various types of cellular stress, including oxidative stress, UV irradiation, heat shock and apoptotic signaling, and is often suppressed in various human tumors. Overexpression of TXNIP inhibits proliferation via cell-cycle arrest and promotes apoptosis.
14-3-3 proteins are a family of conserved regulatory molecules expressed in all eukaryotic cells. There are seven genes, β, γ, ε, σ, ζ, τ and η, that encode 14-3-3s in most mammals. The family dynamically regulates the activity of target proteins in
various signaling pathways that control diverse physiological and pathological processes.
Either an abnormal state of 14-3-3 protein expression or dysregulation of 14-3-3/target protein interactions contributes to the development of many human diseases.
Clinical investigations have demonstrated a correlation between up-regulated 14-3-3 protein levels and poor survival of cancer patients. Several studies have also suggested that 14-3-3 isoforms are differentially regulated in cancer and neurological syndromes. Especially, elevated amounts of the gamma isoform (14-3-3 Gamma) are found in the cerebrospinal fluid (CSF) of Creutzfeldt-Jakob disease (CJD) patients and could be as a specific marker of the disease as well as tau protein level.
The UCHL1, also called PARK5 or neuronal-specific protein gene product 9.5, is a carboxyl-terminal ubiquitin hydrolase regulating ubiquitin dependent signaling pathways, recently suggested as a tumor suppressor. UCHL1 is expressed predominantly in neurons, representing 1 to 2% of total soluble brain protein, as well as in testis and ovary. In vivo, UCHL1 has been shown to be involved in the regulation of the ubiquitin pool, apoptosis, learning and memory, and its absence in mice because of spontaneous intragenic deletions yields phenotypes with neurological defects.
Mutations in UCHL1 have been discovered in a German family with Parkinson's disease (PD), which caused a partial loss of the catalytic activity of this thiol protease. This mutation has been linked to an increased risk of developing an autosomal-dominant form of PD. Based on the abundance in the CNS, UCHL1 has been proposed as a candidate biomarker for brain injury and ischemic strokes. It was demonstrated that UCHL1 was released from injured neurons and flow into the cerebrospinal fluid and eventually into circulating blood.
DJ-1 (PARK7/CAP1/RS) was originally cloned as a putative oncogene capable of transforming NIH-3T3
cells in cooperation with H-ras, a protein expressed in sperm, and a regulator of RNA-protein interactions. DJ-1 has also been isolated as a gene associated with autosomal early-onset Parkinson's disease (PD). Several lines of evidence suggest that DJ-1 plays a role in the oxidative stress response. In cultured mammalian ce11s, DJ-1 quenches reactive oxygen species and is converted into a variant with a more acidic isoelectric point. Therefore, DJ-1 protects against reactive oxygen species-induced cell death, and its suppression with small interfering RNA (siRNA) sensitizes cells to such insults. Mutations in DJ-1 that are associated with familial Parkinson's disease have been shown to decrease the anti-oxidative stress function.
In addition, DJ-1 concentration is reported to be elevated within 3 hours after cerebral infarction, suggesting the possibility that DJ-1 could be a promising biomarker for early stage of cerebral infarction. Moreover, breast cancer patients have elevated levels of circulating DJ-1 and anti-DJ-1 autoantibodies compared to healthy and non-breast cancer patients.
ISG15 (Interferon (IFN)-Stimulated Gene 15) is a ubiquitin-like protein containing two ubiquitin homology domains and becomes conjugated to a variety of proteins when cells are treated with type I interferon or lipopolysaccharide. Therefore this modification (so called, ISGylation) appears to be involved in type I interferon signal transduction. Unlike ubiquitylation, ISGylation does not drive protein degradation (regulated by K48-linked ubiquitin).
ISG15 can also be found extracellularly in an unconjugated form (free form). Human lymphocytes and monocytes were reported to release free ISG15 following treatment with IFN-β. More than 50 % of the total ISG15 could be detected in the culture medium after 24 hours following IFN stimulation. In addition, ISG15 is highly elevated and extensively conjugated to cellular proteins in many tumors and tumor cell lines. The increased levels of ISG15 in tumor cells were found to be associated with decreased levels of polyubiquitinated proteins.
Fibulin-1 is the first described member of a seven-gene family of extracellular matrix (ECM) proteins
that have a common structural signature consisting of a series of repeated EGF-like domains followed by
a fibulin-type module at its carboxyl terminus. Fibulin-1 is a secreted glycoprotein that is an
intercellular component of a wide range of connective tissues. In blood vessel walls, fibulin-1 is a
component of elastic lamina and ECM fibers that surround smooth muscle cells and underlie the
endothelium. Although its actual function remains to be elucidated, fibulin-1 has been suggested to be
involved in cell adhesion, migration, proliferation, and malignant transformation through binding to
many ECM proteins, including laminin, fibrinogen, fibronectin, nidogen-1, endostatin, β-amyloid
precursor protein and proteoglycans, aggrecan, versican, receptors and growth factors. In
addition, fibulin-1 has been found to bind to the plasma protein fibrinogen and to incorporate into fibrin
clots formed in vitro and in vivo. Targeted inactivation of fibulin-1 gene in mice caused dilation and
ruptures in the endothelial lining of small blood vessels, indicating that fibulin-1 was important in
the stabilization of blood vessel walls.
Fibulin-1 is one of a few ECM proteins normally found in blood in high concentrations. It was reported that plasma fibulin-1 concentrations increased in T2DM patients with prevalent cardiovascular disease destined for vascular surgery as well as in asthmatics.
C-Reactive protein (CRP) is a pentameric acute phase reactant that is synthesized by the liver. Its production is controlled primarily by interleukin-6. The serum CRP concentration may increase by up to 1000-fold with infection, ischemia, trauma, surgery, and other acute inflammatory events. Thus CRP can be used as an extremely sensitive systemic marker of inflammation.
A growing number of studies suggest that CRP is an independent risk factor for atherosclerotic vascular disease. Plasma CRP concentrations in the highest quartile are associated, depending on the subject group, with 1.5- to 7-fold increases in relative risk of symptomatic atherosclerosis. The baseline plasma concentration of C-reactive protein predicts the risk of future myocardial infarction and stroke and is associated with a poor prognosis in unstable angina. Plasma CRP levels are also strongly associated with obesity and obesity-related diseases, including insulin resistance, diabetes mellitus, and hyperlipidemia. Although a recent report indicated that the plasma CRP level decreased during weight reduction, the precise interaction of CRP with obesity has not been fully elucidated.
Clusterin, also called apolipoprotein J, sulfated glycoprotein-2, and testosterone-repressed prostate message-2, is a highly conserved secreted heterodimeric glycoprotein constitutively expressed by diverse epithelial cells. Clusterin has been implicated in diverse physiological processes, including lipid transportation, complement inhibition, tissue remodeling, membrane recycling, clearance of cellular debris, regulation of apoptosis, membrane protection, and promotion of cell-cell interactions. Clusterin is induced in injured organs in various disease states, such as Alzheimer's disease, atherosclerosis, myocardial infarction, and multiple forms of acute and chronic renal disease. Clusterin has been shown to associate with both normal in vitro aging, namely replicative senescence, as well as with stress induced premature senescence. In vivo, the protein is up-regulated in many severe physiological disturbances that relate to advanced aging, including accumulation in the artery wall during the development of atherosclerosis. In cancer, clusterin up-regulation has been described in renal cell carcinoma, breast carcinoma, ovarian cancer, anaplastic large cell lymphomas, desmoplastic melanoma , transitional cell carcinoma of the bladder, pancreatic cancer, and serous carcinoma and hepatocellular carcinoma. However, a number of tumor processes where clusterin is downregulated have also been described such as esophageal squamous cell carcinoma, testicular germ cell tumors and prostate cancer. The structure of clusterin has not provided much insight into function. Mammalian clusterins are approximately 80-kDa heterodimers consisting of two 40-kDa chains joined by a unique five-disulfide-bond motif. The protein has limited homology to other proteins and lacks clear functional motifs. It does contain three putative amphipathic α-helical regions, which could allow it to interact with lipids and hydrophobic regions of other proteins.
Progranulin (PGRN) also called granulin/epithelin, proepithelin, prostate cancer cell-derived growth
factor, acrogranin, or paragranulin, is a 593aa cysteine-rich protein that is typically secreted in a highly
glycosylated 88kDa form. PGRN is a growth factor involved in the regulation of multiple
processes including cell proliferation, tumorigenesis, wound healing, development and inflammation.
PGRN is widely expressed in epithelia, bone marrow, immune cells, solid organs, and the nervous
system both during development and in adulthood.
In 2006, mutations in PGRN were discovered to be a cause of frontotemporal lobar degeneration (FTLD) with ubiquitinated TDP-43-positive inclusions. More than 70 mutations in PGRN, almost all of which result in null alleles, have been identified in FTLD patients. A few causative missense mutations also result in reduced levels of PGRN.
PGRN can be found in adipose tissue, epithelial tissue, gastrointestinal tract, reproductive organs, and so forth. Previous studies have demonstrated that increased gene expression of PGRN stimulates cancer cell division, invasion, and against anoikis, promoting tumor formation.
It has been shown that PGRN could restrain rheumatoid arthritis by binding directly to tumor necrosis factor receptors (TNFR) and play an anti-inflammatory role in the processes. In addition, it was reported that circulating PGRN levels are elevated in patients with type 2 diabetes. Moreover, increased plasma PGRN levels are associated with impaired glucose tolerance rather than impaired fasting glucose. Although type 2 diabetes is often accompanied by obesity, the respective role of elevation of circulating PGRN levels in obesity and type 2 diabetes remains to be elucidated.
Lacritin is a 12.3 kDa tear glycoprotein that is apically released from human lacrimal acinar cells during reflex tearing and can be detected in mixed reflex and basal human tears. Lacritin is produced by corneal, conjunctival, meibomian as one of the most eye-restricted genes. However it has been detected in a subpopulation of ductal cells in salivary glands, thyroid and mammary glands. Lacritin modulates lacrimal acinar cell secretion, promotes ductal cell proliferation, and stimulates signaling through tyrosine phosphorylation and release of calcium. Since a decrease of tear lacritin was reported in patients with blepharitis and in contact lens–related dry eye, lacritin might play an important role in maintaining tear fluid and the ocular surface. In fact, ocular instillation of recombinant human lacritin stimulated basal tear flow in rabbits. Lacritin also promotes basal tear secretion by cultured rat and monkey lacrimal acinar cells and stimulates human corneal epithelial cell growth. Thus, lacritin appears to be a multifunctional eye-specific factor with a potential role in tear secretion and corneal epithelial renewal.