Determination of native lactoferrin in milk by HPLC on HiTrapTM Heparin HP column

Self-Responsive Fluorescence Aptasensor for Lactoferrin Determination in Dairy Products

In this study, a self-responsive fluorescence aptasensor was established for the determination of lactoferrin (Lf) in dairy products. Herein, the aptamer itself functions as both a recognition element that specifically binds to Lf and a fluorescent signal reporter in conjunction with fluorescent moiety. In the presence of Lf, the aptamer preferentially binds to Lf due to its specific and high-affinity recognition by folding into a self-assembled and three-dimensional spatial structure. Meanwhile, its reduced spatial distance in the aptamer-Lf complex induces a FRET phenomenon based on the quenching of 6-FAM by amino acids in the Lf protein, resulting in a turn-off of the fluorescence of the system. As a result, the Lf concentration can be determined straightforwardly corresponding to the change in the self-responsive fluorescence signal. Under the optimized conditions, good linearities (R2 > 0.99) were achieved in an Lf concentration range of 2~10 μg/mL for both standard solutions and the spiked matrix, as well as with the desirable detection limits of 0.68 μg/mL and 0.46 μg/mL, respectively. Moreover, the fluorescence aptasensor exhibited reliable recoveries (89.5-104.3%) in terms of detecting Lf in three commercial samples, which is comparable to the accuracy of the HPCE method. The fluorescence aptasensor offers a user-friendly, cost-efficient, and promising sensor platform for point-of-need detection.

The Multifaceted Roles of Bovine Lactoferrin: Molecular Structure, Isolation Methods, Analytical Characteristics, and Biological Properties

Bovine lactoferrin (bLF) is widely known as an iron-binding glycoprotein from the transferrin family. The bLF molecule exhibits a broad spectrum of biological activity, including iron delivery, antimicrobial, antiviral, immunomodulatory, antioxidant, antitumor, and prebiotic functions, thereby making it one of the most valuable representatives for biomedical applications. Remarkably, LF functionality might completely differ in dependence on the iron saturation state and glycosylation patterns. Recently, a violently growing demand for bLF production has been observed, mostly for infant formulas, dietary supplements, and functional food formulations. Unfortunately, one of the reasons that inhibit the development of the bLF market and widespread protein implementation is related to its negligible amount in both major sources─colostrum and mature milk. This study provides a comprehensive overview of the significance of bLF research by delineating the key structural characteristics of the protein and elucidating their impact on its physicochemical and biological properties. Progress in the development of optimal isolation techniques for bLF is critically assessed, alongside the challenges that arise during its production. Furthermore, this paper presents a curated list of the most relevant instrumental techniques for the characterization of bLF. Lastly, it discusses the prospective applications and future directions for bLF-based formulations, highlighting their potential in various fields.

Contractile Hairpin DNA-Mediated Dual-Mode Strategy for Simultaneous Quantification of Lactoferrin and Iron Ion by Surface-Enhanced Raman Scattering and Fluorescence Analysis

DNA-mediated self-assembly technology with good sensitivity and affinity ability has been rapidly developed in the field of probe sensing. The efficient and accurate quantification of lactoferrin (Lac) and iron ions (Fe³⁺) in human serum and milk samples by the probe sensing method can provide useful clues for human health and early diagnosis of anemia. In this paper, contractile hairpin DNA-mediated dual-mode probes of Fe₃O₄/Ag-ZIF8/graphitic quantum dot (Fe₃O₄/Ag-ZIF8/GQD) NPs were prepared to realize the simultaneous quantification of Lac by surface-enhanced Raman scattering (SERS) and Fe³⁺ by fluorescence (FL). In the presence of targets, these dual-mode probes would be triggered by the recognition of aptamer and release GQDs to produce FL response. Meanwhile, the complementary DNA began to shrink and form a new hairpin structure on the surface of Fe₃O₄/Ag, which produced hot spots and generated a good SERS response. Thus, the proposed dual-mode analytical strategy possessed excellent selectivity, sensitivity, and accuracy due to the dual-mode switchable signals from "off" to "on" in SERS mode and from "on" to "off" in FL mode. Under the optimized conditions, a good linear range was obtained in the range of 0.5-100.0 μg/L for Lac and 0.01-5.0 μmol/L for Fe³⁺ and with detection limits of 0.14 μg/L and 3.8 nmol/L, respectively. Finally, the contractile hairpin DNA-mediated SERS-FL dual-mode probes were successfully applied in the simultaneous quantification of iron ion and Lac in human serum and milk samples.

N, S-Doped Carbon Dots Prepared by Peanut Protein Isolates and Cysteamine as Highly Sensitive Fluorescent Sensors for Fe2+, Fe3+ and Lactoferrin

Lactoferrin (LF) is an iron-binding glycoprotein with various biological activities that has been extensively used in food and medical applications. Several methods for detecting LF have been reported, but they still face challenges in terms of sensitivity and simplicity of detection. To achieve an accurate and efficient detection of LF, we developed a method for the determination of LF in lactoferrin supplements using carbon dots (CDs) fluorescent probes. The N, S-doped PPI carbon dots (N, S-PPI-CDs) were prepared using a protein (peanut protein isolate) and cysteamine as precursors. The prepared N, S-PPI-CDs exhibited intense blue fluorescence and good biocompatibility, while the fluorescence intensity of the N, S-PPI-CDs showed a good linear relationship with Fe²⁺/Fe³⁺ concentration (0-2 μM). The N, S-PPI-CDs exhibited a high potential ability to rapidly detect Fe²⁺/Fe³⁺ within 30 s, with a limit of detection (LoD) of 0.21 μM/0.17 μM. Due to the reversible binding of LF to Fe, the N, S-PPI-CDs showed a high sensitivity and selectivity for LF, with a limit of detection (LoD) of 1.92 μg/mL. In addition, LF was quantified in real sample LF supplements and showed a fluctuation in recovery of less than 2.48%, further demonstrating the effectiveness of the fluorescent N, S-PPI-CDs sensor.

Fluorescence Polarization Immunoassay of Human Lactoferrin in Milk Using Small Single-Domain Antibodies

Due to its unique structure and properties, human breast milk lactoferrin (hLF) has many nutritional and health-promoting functions in infants, including protection against inflammation and bacterial infections. The lack of LF in breastmilk or formula can result in the weakening of the infant's immune system. Noncompetitive polarization fluorescence immunoassay (FPIA) is a promising method for hLF quantification in milk and dairy products, which does not require the separation of the bound and free protein and allows to avoid time-consuming sample preparation. The use of fluorescently labeled single-domain camelid antibodies (nanobodies) for protein recognition in FPIA makes it possible to quantify relatively large antigens, in particular, hLF. In this work, we used previously obtained fluorescein isothiocyanate (FITC)-conjugated anti-hLF5 and anti-hLF16 nanobodies, which selectively recognized two different human lactoferrin epitopes, but did not bind to goat lactoferrin. The kinetics of hLF interaction with the FITC-labeled nanobodies was studied. The dissociation constant (K_D) for the anti-LF5 and antiLF16 nanobodies was 3.2 ± 0.3 and 4.9 ± 0.4 nM, respectively, indicating the high-affinity binding of these nanobodies to hLF. We developed the FPIA protocol and determined the concentration of FITC-labeled anti-hLF5 and anti-hLF16 nanobodies that provided the optimal fluorescence signal and stable fluorescence polarization value. We also studied the dependence of fluorescence polarization on the hLF concentration in the noncompetitive FPIA with FITC-anti-hLF5 nanobody. The detection limit for hLF was 2.1 ± 0.2 µg/ml and the linear range for determining the hLF concentration was 3-10 µg/ml. FPIA is commonly used to assay low-molecular-weight substances; however, the use of fluorescently labeled nanobodies allows quantification of high-molecular-weight proteins. Here, we demonstrated that FPIA with fluorescently labeled nanobodies can be used for hLF quantification in milk.

Lactoferrin Alleviates Lipopolysaccharide-Induced Infantile Intestinal Immune Barrier Damage by Regulating an ELAVL1-Related Signaling Pathway

As the most important intestinal mucosal barrier of the main body, the innate immune barrier in intestinal tract plays especially pivotal roles in the overall health conditions of infants and young children; therefore, how to strengthen the innate immune barrier is pivotal. A variety of bioactivities of lactoferrin (LF) has been widely proved, including alleviating enteritis and inhibiting colon cancer; however, the effects of LF on intestinal immune barrier in infants and young children are still unclear, and the specific mechanism on how LF inhibits infantile enteritis by regulating immune signaling pathways is unrevealed. In the present study, we firstly performed pharmacokinetic analyses of LF in mice intestinal tissues, stomach tissues and blood, through different administration methods, to confirm the metabolic method of LF in mammals. Then we constructed in Vitro and in Vivo infantile intestinal immune barrier damage models utilizing lipopolysaccharide (LPS), and evaluated the effects of LF in alleviating LPS-induced intestinal immune barrier damage. Next, the related immune molecular mechanism on how LF exerted protective effects was investigated, through RNA-seq analyses of the mouse primary intestinal epithelial cells, and the specific genes were analyzed and screened out. Finally, the genes and their related immune pathway were validated in mRNA and protein levels; the portions of special immune cells (CD4⁺ T cells and CD8⁺ T cells) were also detected to further support our experimental results. Pharmacokinetic analyses demonstrated that the integrity of LF could reach mice stomach and intestine after oral gavage within 12 h, and the proper administration of LF should be the oral route. LF was proven to down-regulate the expression levels of inflammatory cytokines in both the primary intestinal epithelial cells and mice blood, especially LF without iron (Apo-LF), indicating LF alleviated infantile intestinal immune barrier damage induced by LPS. And through RNA-seq analyses of the mouse primary intestinal epithelial cells treated with LPS and LF, embryonic lethal abnormal vision Drosophila 1 (ELAVL1) was selected as one of the key genes, then the ELAVL1/PI3K/NF-κB pathway regulated by LF was verified to participate in the protection of infantile intestinal immune barrier damage in our study. Additionally, the ratio of blood CD4⁺/CD8⁺ T cells was significantly higher in the LF-treated mice than in the control mice, indicating that LF distinctly reinforced the overall immunity of infantile mice, further validating the strengthening bioactivity of LF on infantile intestinal immune barrier. In summary, LF was proven to alleviate LPS-induced intestinal immune barrier damage in young mice through regulating ELAVL1-related immune signaling pathways, which would expand current knowledge of the functions of bioactive proteins in foods within different research layers, as well as benefit preclinical and clinical researches in a long run.

Self-assembly and label-free fluorescent aptasensor based on deoxyribonucleic acid intercalated dyes for detecting lactoferrin in milk powder

Lactoferrin (Lf), an iron-binding glycoprotein, regulates the immune system. It has broad-spectrum antimicrobial activity and is critical for child physical growth and development. As a common additive in the dairy industry, it is crucial to quantify LF content. This study established a self-assembly and universal fluorescence aptasensor for detecting LF in milk powder based on structure-selective dyes of PicoGreen intercalated in the label-free aptamer. Herein, the aptamer functions as both a specific recognition element against targets and a fluorescent signal reporter integrated with structure-selective dyes. First, the aptamer folds into a three-dimensional spatial structure based on complementary base pairings and intermolecular weak non-covalent interactions. Then, the dye is intercalated into the minor groove structures of the aptamer and triggers its potential fluorescent property. When the target exists, the aptamer binds to it preferentially, and its space structure unfolds. This causes the freeing of the subsequent dye and decreases the corresponding fluorescence. Hence, the reflected fluorescence signals could directly determine the target concentrations. Under the optimum conditions, a good linear relationship (R2, 0.980) was obtained in the Lf range from 20 to 500 nM with a detection limit of 3 nM (2.4 mg/kg) and good specificity, as well as a reliable recovery of 95.8–105.1% in milk powder. In addition, the universality was also confirmed with a good performance by quickly changing the aptamers against other targets (chlorpyrifos, acetamiprid, bovine thyroglobulin, and human transferrin) or utilizing another fluorescence dye. Therefore, this self-assembly aptasensor provides a universal and concise strategy for effective detection.

Analysis of Bovine Lactoferrin in Infant Formula and Adult Nutritional Products by Optical Biosensor Immunoassay: First Action 2021.07

Background

Bovine lactoferrin is increasingly being used as an ingredient in infant formula manufacture to enhance nutritional efficacy through the provision of immunoprotective, growth, and antimicrobial factors to the neonate.

Objective

To evaluate the analytical performance of an optical biosensor immunoassay for compliance with the method performance requirements described in SMPR 2020.005.

Method

Following dilution of the sample in buffer, an automated, label-free, real-time optical biosensor immunoassay was used in a direct assay format to quantitate bovine lactoferrin by its interaction with an immobilized anti-lactoferrin antibody. Quantitation was accomplished by the external standard technique with interpolation from a 4-parameter calibration regression.

Results

The analytical range (0–200 mg/hg), method detection limit (0.8 mg/hg), recovery (96.1–109.2%), and repeatability (1.0–5.3%) complied with the requirements given in the lactoferrin SMPR. The method was shown to be specific for native, intact lactoferrin; thermally denatured lactoferrin generated no measurable binding response.

Conclusion

The method described is suitable for the quantification of intact, undenatured lactoferrin in milk products, infant formulas (bovine milk protein-based, soy protein-based, and amino acid-based), and adult nutritionals and has been demonstrated to meet the performance requirements defined in SMPR 2020.005.

Highlights

A single-laboratory validation (SLV) of an automated biosensor immunoassay for the determination of intact, undenatured lactoferrin is described.

Carboxyl-Rich Carbon Dots as Highly Selective and Sensitive Fluorescent Sensor for Detection of Fe3+ in Water and Lactoferrin

As lactoferrin (LF) plays an essential role in physiological processes, the detection of LF has attracted increasing attention in the field of disease diagnosis. However, most current methods require expensive equipment, laborious pretreatment, and long processing time. In this work, carboxyl-rich carbon dots (COOH-CDs) were facilely prepared through a one-step, low-cost hydrothermal process with tartaric acid as the precursor. The COOH-CDs had abundant carboxyl on the surface and showed strong blue emission. Moreover, COOH-CDs were used as a fluorescent sensor toward Fe3+ and showed high selectivity for Fe3+ with the limit of detection (LoD) of 3.18 nM. Density functional theory (DFT) calculations were performed to reveal the mechanism of excellent performance for Fe3+ detection. Meanwhile, COOH-CDs showed no obvious effect on lactobacillus plantarum growth, which means that COOH-CDs have good biocompatibility. Due to the nontoxicity and excellent detection performance for Fe3+, COOH-CDs were employed as a fluorescent sensor toward LF and showed satisfying performance with an LoD of 0.776 µg/mL, which was better than those of the other methods.

An Efficient Heparin Affinity Column Purification Method Coupled with Ultraperformance Liquid Chromatography for the Quantification of Native Lactoferrin in Breast Milk

Lactoferrin (LF) is a bioactive multifunctional protein and found in the highest amounts in human milk. Several methods can be used to quantify LF. However, quantification of native LF has garnered relatively little interest to date. This study aimed to develop a novel efficient two-step method for quantifying native LF in breast milk. During the analysis, LF was first extracted with phosphate buffer (pH 5.0), purified using a heparin affinity column. Subsequently, LF was detected using ultraperformance liquid chromatography (UPLC) at a wavelength of 201 nm. A linear calibration curve was obtained in the range of 5–200 mg/L. The limit of detection and limit of quantitation were 1 mg/L and 5 mg/L, respectively, indicating that the validated method could be employed to quantify LF in breast milk. Compared with previous HPLC methods, this method demonstrated several remarkable advantages, including simple operation, low-cost detection, and high accuracy. Hence, the results demonstrate an efficient method that can be employed commercially to purify and analyze LF in human milk samples.

An aptamer affinity column for purification and enrichment of lactoferrin in milk

As an active glycoprotein with high nutritional value, lactoferrin is widely used in food and medical treatment. Therefore, it is very important to establish an accurate and efficient detection method for lactoferrin. At present, the detection of lactoferrin in milk faces many challenges, such as low separation degree and poor parallelism. To address this issue, we developed an aptamer affinity column (AAC) for purification and enrichment of lactoferrin in milk. The column was prepared by covalent conjugation of an amino-modified aptamer with NHS-activated Sepharose. The washing buffer type (0.01 mol/L phosphate buffer) and volume (10 mL) and the sodium chlorideconcentration (1 mol/L) in the elution buffer were optimized for the AAC method. The performance of the AAC was then evaluated in terms of the column capacity, specificity, stability, and reusability. The column capacity was 500 ± 13.7 μg and the column could be reused up to ten times with a large loss in performance. The AAC method combined with high-performance liquid chromatography gave excellent linearity over a wide range, good sensitivity with a limit of detection of 3 μg/mL, and acceptable recoveries for different concentrations of lactoferrin spiked in real raw milk samples from cattle. Finally, the AAC was successfully applied to analyze lactoferrin in milk. This method could be applied to routine analysis of samples for lactoferrin in testing laboratories and dairy factories.

A ratiometric electrochemiluminescence resonance energy transfer platform based on novel dye BODIPY derivatives for sensitive detection of lactoferrin

A ratiometric electrochemiluminescence resonance energy transfer (ECL-RET) platform depended on novel dye BODIPY derivatives was proposed for rapid detection of lactoferrin. This ECL-RET platform is composed of aptamer decorated BODIPY composites and C₆₀@BSA, in which BODIPY derivative is the ECL probe and can generate significant resonance energy transfer with K₂S₂O₈. BODIPY derivative and K₂S₂O₈ are used as built-in reference signal and calibration signal respectively to eliminate background signal and abnormal change signal by double signal self-calibration process. At the same time, C₆₀, as the accelerator of K₂S₂O₈, can effectively increase the ECL signal and further transfer as much energy as possible to BODIPY derivative. Under optimal conditions, the constructed ECL-RET platform exhibited sensitive detection of lactoferrin in the wide linear range of 10^-4- 850 ng/mL with a LOD of 42 fg/mL. Meanwhile, the proposed ECL-RET aptasensor demonstrated superior stability, specificity and reproducibility, displaying favorable application value in practical diagnosis of this method.