Clinical Significance of Serum Albumin and Implications of FcRn Inhibitor Treatment in IgG-Mediated Autoimmune Disorders.

Serum albumin (SA), the most abundant soluble protein in the body, maintains plasma oncotic pressure and regulates the distribution of vascular fluid and has a range of other important functions. The goals of this review are to expand clinical knowledge regarding the functions of SA, elucidate effects of dysregulated SA concentration, and discuss the clinical relevance of hypoalbuminemia resulting from various diseases. We discuss potential repercussions of SA dysregulation on cholesterol levels, liver function, and other processes that rely on its homeostasis, as decreased SA concentration has been shown to be associated with increased risk for cardiovascular disease, hyperlipidemia, and mortality.

Engineered Polymer-Transferrin Conjugates as Self-Assembling Targeted Drug Delivery Systems.

Polymer-protein conjugates can be engineered to self-assemble into discrete and well-defined drug delivery systems, which combine the advantages of receptor targeting and controlled drug release. We designed specific conjugates of the iron-binding and transport protein, transferrin (Tf), to combine the advantages of this serum-stable protein as a targeting agent for cancer cells with self-assembling polymers to act as carriers of cytotoxic drugs. Tf variants were expressed with cysteine residues at sites spanning different regions of the protein surface, and the polymer conjugates grown from these variants were compared with polymer conjugates grown from nonselectively derivatized sites on native Tf.

Albumin and its application in drug delivery.

Introduction: Rapid clearance of drugs from the body results in short therapeutic half-life and is an integral property of many protein and peptide-based drugs. To maintain the desired therapeutic effect patients are required to administer higher doses more frequently, which is inconvenient and risks undesirable side effects. Drug delivery technologies aim to minimise the number of administrations and dose-related toxicity while maximising therapeutic efficacy.

Dissection of the neonatal Fc receptor (FcRn)-albumin interface using mutagenesis and anti-FcRn albumin-blocking antibodies.

Albumin is the most abundant protein in blood and plays a pivotal role as a multitransporter of a wide range of molecules such as fatty acids, metabolites, hormones, and toxins. In addition, it binds a variety of drugs. Its role as distributor is supported by its extraordinary serum half-life of 3 weeks.

Extending serum half-life of albumin by engineering neonatal Fc receptor (FcRn) binding.

A major challenge for the therapeutic use of many peptides and proteins is their short circulatory half-life. Albumin has an extended serum half-life of 3 weeks because of its size and FcRn-mediated recycling that prevents intracellular degradation, properties shared with IgG antibodies. Engineering the strictly pH-dependent IgG-FcRn interaction is known to extend IgG half-life.

Single-chain variable fragment albumin fusions bind the neonatal Fc receptor (FcRn) in a species-dependent manner: implications for in vivo half-life evaluation of albumin fusion therapeutics.

Albumin has a serum half-life of 3 weeks in humans. This has been utilized to extend the serum persistence of biopharmaceuticals that are fused to albumin. In light of the fact that the neonatal Fc receptor (FcRn) is a key regulator of albumin homeostasis, it is crucial to address how fusion of therapeutics to albumin impacts binding to FcRn.

Albumin as a versatile platform for drug half-life extension.

Background: Albumin is the most abundant plasma protein, is highly soluble, very stable and has an extraordinarily long circulatory half-life as a direct result of its size and interaction with the FcRn mediated recycling pathway. In contrast, many therapeutic molecules are smaller than the renal filtration threshold and are rapidly lost from the circulation thereby limiting their therapeutic potential. Albumin can be used in a variety of ways to increase the circulatory half-life of such molecules.

A molecular mechanism for modulating plasma Zn speciation by fatty acids.

Albumin transports both fatty acids and zinc in plasma. Competitive binding studied by isothermal titration calorimetry revealed that physiologically relevant levels of fatty acids modulate the Zn-binding capacity of albumin, with far-reaching implications for biological zinc speciation. The molecular mechanism for this effect is likely due to a large conformational change elicited by fatty acid binding to a high-affinity interdomain site that disrupts at least one Zn site.

Structure-based mutagenesis reveals the albumin-binding site of the neonatal Fc receptor.

Albumin is the most abundant protein in blood where it has a pivotal role as a transporter of fatty acids and drugs. Like IgG, albumin has long serum half-life, protected from degradation by pH-dependent recycling mediated by interaction with the neonatal Fc receptor, FcRn. Although the FcRn interaction with IgG is well characterized at the atomic level, its interaction with albumin is not.

High-level production of animal-free recombinant transferrin from Saccharomyces cerevisiae.

Background: Animal-free recombinant proteins provide a safe and effective alternative to tissue or serum-derived products for both therapeutic and biomanufacturing applications. While recombinant insulin and albumin already exist to replace their human counterparts in cell culture media, until recently there has been no equivalent for serum transferrin.

Results: The first microbial system for the high-level secretion of a recombinant transferrin (rTf) has been developed from Saccharomyces cerevisiae strains originally engineered for the commercial production of recombinant human albumin (Novozymes' Recombumin® USP-NF) and albumin fusion proteins (Novozymes' albufuse®).

The production, characterisation and enhanced pharmacokinetics of scFv-albumin fusions expressed in Saccharomyces cerevisiae.

An expression system is described for the production of monomeric scFvs and scFv antibody fragments genetically fused to human albumin (at either the N- or C-terminus or both). Based upon strains of Saccharomyces cerevisiae originally developed for the production of a recombinant human albumin (Recombumin) this system has delivered high levels of secreted product into the supernatant of shake flask and high cell density fed-batch fermentations. Specific binding to the corresponding ligand was demonstrated for each of the scFvs and scFv-albumin fusions and pharmacokinetic studies showed that the fusion products had greatly extended circulatory half-lives.

Structures of native human thymidine phosphorylase and in complex with 5-iodouracil.

Thymidine phosphorylase (TP) first identified as platelet derived endothelial cell growth factor (PD-ECGF) plays a key role in nucleoside metabolism. Human TP (hTP) is implicated in angiogenesis and is overexpressed in several solid tumors. Here, we report the crystal structures of recombinant hTP and its complex with a substrate 5-iodouracil (5IUR) at 3.

Structure, properties, and engineering of the major zinc binding site on human albumin.

Most blood plasma zinc is bound to albumin, but the structure of the binding site has not been determined. Zn K-edge extended x-ray absorption fine structure spectroscopy and modeling studies show that the major Zn(2+) site on albumin is a 5-coordinate site with average Zn-O/N distances of 1.98 A and a weak sixth O/N bond of 2.

Role of Tyr84 in controlling the reactivity of Cys34 of human albumin.

Cys34 in domain I of the three-domain serum protein albumin is the binding site for a wide variety of biologically and clinically important small molecules, provides antioxidant activity, and constitutes the largest portion of free thiol in blood. Analysis of X-ray structures of albumin reveals that the loop containing Tyr84 occurs in multiple conformations. In structures where the loop is well defined, there appears to be an H-bond between the OH of Tyr84 and the sulfur of Cys34.

Interdomain zinc site on human albumin.

Albumin is the major transport protein in blood for Zn(2+), a metal ion required for physiological processes and recruited by various drugs and toxins. However, the Zn(2+)-binding site(s) on albumin is ill-defined. We have analyzed the 18 x-ray crystal structures of human albumin in the PDB and identified a potential five-coordinate Zn site at the interface of domains I and II consisting of N ligands from His-67 and His-247 and O ligands from Asn-99, Asp-249, and H(2)O, which are the same amino acid ligands as those in the zinc enzymes calcineurin, endonucleotidase, and purple acid phosphatase.