Site specific PEGylation of β-lactoglobulin at glutamine residues and its influence on conformation and antigenicity

The Effect of PEGylation on Drugs' Pharmacokinetic Parameters; from Absorption to Excretion

Until the drugs enter humans life, they may face problems in transportation, drug delivery, and metabolism. These problems can cause reducing drug's therapeutic effect and even increase its side effects. Together, these cases can reduce the patient's compliance with the treatment and complicate the treatment process. Much work has been done to solve or at least reduce these problems. For example, using different forms of a single drug molecule (like Citalopram and Escitalopram); slight changes in the drug's molecule like Meperidine and α-Prodine, and using carriers (like Tigerase®). PEGylation is a recently presented method that can use for many targets. Poly Ethylene Glycol or PEG is a polymer that can attach to drugs by using different methods and resulting sustained release, controlled metabolism, targeted delivery, and other cases. Although they will not necessarily lead to an increase in the effect of the drug, they will lead to the improvement of the treatment process in certain ways. In this article, the team of authors has tried to collect and carefully review the best cases based on the PEGylation of drugs that can help the readers of this article.

Purification and characterization of a glycoprotein from Sipunculus nudus and its immune-enhancing activity to RAW 264.7 macrophages

Sipunculus nudus, an edible marine invertebrate, has long been used as traditional Chinese medicine in folk remedies. In order to assess the immunoregulatory activity of glycoproteins in Sipunculus nudus and conduct a structure-activity relationship, a glycoprotein (SGP1) with molecular mass of 9.26 kDa was purified from Sipunculus nudus, and its chemical structure as well as immune-enhancing activity was investigated in this study. Structure analysis revealed that SGP1, a protein-dominate glycoprotein with O-glycosidic bonds, contained 92.8 % protein and 3.1 % saccharide. GC-MS result indicated that the saccharide moieties of SGP1 basically consisted of lyxose (Lyx), xylose (Xyl) as well as glucose (Glu) at a molar proportion of 0.87:4.16:1.36. The fourier transform infrared specoscopy (FT-IR) result proved that SGP1 have a typical characteristic of glycoprotein. Besides, circular dichroism (CD) result showed that SGP1 contained 4.1 % α-helix, 42.5 % β-sheet, 21.4 % β-turn, and 32.0 % random coil, indicating it's mainly a β-sheet glycoprotein. The amino acid sequence of SGP1 shared a similarity to the Myohemerythrin (sp|Q5K473|HEMTM) with protein sequence coverage of 28.3 %. Moreover, the activity evaluation results showed that SGP1 exhibited significant immune-enhancing activity to the RAW 264.7 macrophages by promoting macrophages proliferation, enhancing phagocytic capacity, and simultaneously stimulating the secretions of nitric oxide (NO), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) via NF-κB pathways. In this study, SGP1 as a novel glycoprotein had an obvious immune-enhancing activity to macrophages, and thus could be applied in the functional foods as a potential immunopotentiator for the hypoimmune population.

Characteristics and Functional Properties of Maillard Reaction Products from α-Lactalbumin and Polydextrose

The characteristics and the functions of Maillard reaction products (MRPs) produced by polydextrose (PD), a new type of prebiotic, and α-lactalbumin (α-LA) were valued. PD and α-LA were incubated at 60 °C and 79% relative humidity for up to 72 h to prepare MRPs. The results showed that the absorbance and fluorescence intensity of heated α-LA-PD increased, and the amount of free amino groups reduced as the reaction progressed, which confirmed the formation of different stages of MRPs. Electrophoresis revealed an increase in molecular mass and the degree of covalent cross-linking. The secondary structure of MRPs experienced no significant changes with the measurement of circular dichroism (CD), while the tertiary structure gradually unfolded, exposing hydrophobic groups. Furthermore, a significant increase was detected in the radical-scavenging activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the ferric reducing/antioxidant power (FRAP) of MRPs. The findings offer a foundation for understanding the structural and functional features of MRPs in formula milk powder.

Improved pH stability, heat stability, and functionality of phycocyanin after PEGylation

Phycocyanin (PC), a spirulina-derived protein-chromophore complex, suffers from poor techno-functional properties and is highly susceptible to aggregation and color changes upon heating and pH fluctuations. We tackled these issues by modifying PC via PEGylation. Electrophoresis and Fourier transform infrared spectroscopy proved successful conjugation of methoxy PEG (mPEG) chains on PC after PEGylation. Circular dichroism indicated highly ordered folding states adopted by PEGylated PC, which we attributed to the mPEG chains on the protein surface that sterically stabilized the protein structure. Consequently, the mPEG-PC conjugates exhibited high blue color intensity and improved thermodynamic stability. Further, benefit from an electrostatic shielding effect of mPEG chains, surface charges of PEGylated PC were neutralized over pH 2-9 and the blue hue of PC was stabilized against pH variations. Additionally, the flexible and hydrophilic mPEG polymers on the PC surface promoted protein-protein and protein-water interactions. PEGylated PC thus gained increased protein solubility, techno-functionality (emulsifying, foaming, and gelling performance), and antioxidant activities, when compared to unmodified PC. Heat-induced gels formed by mPEG-PC conjugates exhibited increased stiffness, higher water retention, and weak gel-type rheological properties. After PEGylation, the improved functional properties, bioactivity, and color stability against heat and pH fluctuations will facilitate food and pharmaceutical applications of PC.

Impact of the PEG length and PEGylation site on the structural, thermodynamic, thermal, and proteolytic stability of mono-PEGylated alpha-1 antitrypsin

Conjugation to polyethylene glycol (PEG) is a widely used approach to improve the therapeutic value of proteins essentially by prolonging their body residence time. PEGylation may however induce changes in the structure and/or the stability of proteins and thus on their function(s). The effects of PEGylation on the thermodynamic stability can either be positive (stabilization), negative (destabilization), or neutral (no effect). Moreover, various factors such as the PEG length and PEGylation site can influence the consequences of PEGylation on the structure and stability of proteins. In this study, the effects of PEGylation on the structure, stability, and polymerization of alpha1-antitrypsin (AAT) were investigated, using PEGs with different lengths, different structures (linear or 2-armed) and different linking chemistries (via amine or thiol) at two distinct positions of the sequence. The results show that whatever the size, position, and structure of PEG chains, PEGylation (a) does not induce significant changes in AAT structure (either at the secondary or tertiary level); (b) does not alter the stability of the native protein upon both chemical- and heat-induced denaturation; and (c) does not prevent AAT to fully refold and recover its activity following chemical denaturation. However, the propensity of AAT to aggregate upon heat treatment was significantly decreased by PEGylation, although PEGylation did not prevent the irreversible inactivation of the enzyme. Moreover, conjugation to PEG, especially 2-armed 40 kDa PEG, greatly improved the proteolytic resistance of AAT. PEGylation of AAT could be a promising strategy to prolong its half-life after infusion in AAT-deficient patients and thereby decrease the frequency of infusions.

Characterization and functional properties of Maillard reaction products of β-lactoglobulin and polydextrose

The Maillard reaction products (MRPs) between polydextrose (PDX), a popular polysaccharide in formula powder, and β-lactoglobulin (β-LG), a major whey protein, were studied in aggregation degree, structure, hydrophobic, antigenic and antioxidant activity changes of β-LG. Incubation of PDX and β-LG (60 ℃, 79% relative humidity) for up to 72 h yielded MRPs with increases in furosine, UV absorbance, fluorescence intensity and loss of free amino groups. High molecular weight β-LG-PDX MRPs were observed by SDS-PAGE. Circular dichroism spectroscopy revealed negligible change in β-LG secondary structure. Changes in the tertiary structure of β-LG were detected by tryptophan fluorescence spectroscopy consistent with an increase in surface hydrophobicity of heated β-LG-PDX. Antigenicity reduction of β-LG in β-LG-PDX reached its peak when heated for 24 h. After heating for 72 h, DPPH radical-scavenging activity of β-LG-PDX increased by 7.4-fold, and the ferric reducing antioxidant power reached 61.1 µmol ascorbic acid/g protein.

Experimental and computational studies on the mechanism of the β-lactoglobulin-derived peptide inhibiting the antigenicity of β-lactoglobulin

In this study, through a combined simulated enzymolysis-molecular docking-molecular simulation-activity determination-action mechanism strategy, we screened a β-LG-derived peptide (VAGTWYSL) to inhibit the antigenicity of β-LG and explored its mechanism of action. Our results indicate that the inhibitory effect of the peptide on the antigenicity of β-LG is affected by different experimental conditions, including pH, reaction time and concentration. Three factors may contribute to the reduced allergenicity of β-LG. First, there must be sufficient forces between the peptide and β-LG, as a result, hydrophobic forces and hydrogen bonds are the main forces to maintain the structural stability of the complex. Second, the binding of the peptide changes the secondary structure of β-LG, especially with an increase in α-helices and a decrease in β-turns. Third, the peptide binds to the hydrophobic region of β-LG, involving the antigenic epitope region Val41-Lys60, which may reduce the antigenicity.

Towards toxin PEGylation: The example of rCollinein-1, a snake venom thrombin-like enzyme, as a PEGylated biopharmaceutical prototype

PEGylation was firstly described around 50 years ago and has been used for more than 30 years as a strategy to improve the drugability of biopharmaceuticals. However, it remains poorly employed in toxinology, even though it may be a promising strategy to empower these compounds in therapeutics. This work reports the PEGylation of rCollinein-1, a recombinant snake venom serine protease (SVSP), able to degrade fibrinogen and inhibit the hEAG1 potassium channel. We compared the functional, structural, and immunogenic properties of the non-PEGylated (rCollinein-1) and PEGylated (PEG-rCollinein-1) forms. PEG-rCollinein-1 shares similar kinetic parameters with rCollinein-1, maintaining its capability of degrading fibrinogen, but with reduced activity on hEAG1 channel. CD analysis revealed the maintenance of protein conformation after PEGylation, and thermal shift assays demonstrated similar thermostability. Both forms of the enzyme showed to be non-toxic to peripheral blood mononuclear cells (PBMC). In silico epitope prediction indicated three putative immunogenic peptides. However, immune response on mice showed PEG-rCollinein-1 was devoid of immunogenicity. PEGylation directed rCollinein-1 activity towards hemostasis control, broadening its possibilities to be employed as a defibrinogenant agent.

A new site-specific monoPEGylated β-lactoglobulin at the N-terminal: Effect of different molecular weights of mPEG on its conformation and antigenicity

A new method was investigated to decline the antigenicity of β-Lactoglobulin (β-LG) by site specifically conjugating β-LG at the N-terminus with 5 kDa and 10 kDa monomethoxy polyethylene glycol propyl aldehyde (mPEG-ALD). The optimal reaction conditions were molar ratio of 1:10 (β-LG:mPEG-ALD), reaction time for 16 h, and pH 5.0, and the content of mono-PEGylated β-LG was 51.3%. The results showed that mono-PEGylated β-LG with molecular mass of 23.2 kDa and 28.5 kDa. The peptide fragments of mPEG_5kDa-ALD-β-LG produced the same sequence pattern of β-LG except for the absence of one peptides f(1-14), indicating that α-amino group at the N-terminal was selectively modified. Furthermore, the conformation of modified β-LG underwent into slight change. The antigenicity of mPEG_5kDa-ALD-β-LG and mPEG_10kDa-ALD-β-LG decreased from 144.4 μg/mL to 66.7 and 39.0 μg/mL respectively. It was speculated that the steric hindrance effect of PEG was the main reason for the decline of antigenicity of β-LG.

Beta-lactoglobulin-nutrition allergen and nanotransporter of different nature ligands therapy with therapeutic action

β-lactoglobulin is one of the nutrition allergens present in the milk of many mammals, with the exception of human. This protein belongs to the family of lipocalins, consisting of nine antiparallel β-strands (β-A to β-I) and one α-helix. This structure allows it to serve as a nanotransporter of various nature ligands in a pH dependent manner, which allows us to confidently consider it as a reliable carrier of drugs directly into the intestine, bypassing the destructive acidic environment of the stomach. Based on the latest data, this review describes the currently known methods of reducing the allergenicity of beta-lactoglobulin, as well as the mechanisms and methods of forming complexes of this protein with ligands, which emphasizes its importance and versatility and explains the growing interest in studying its properties in recent decades, and also opens up prospects for its practical application in medicine and pharmaceuticals.