Release of biotin from biotinylated proteins occurs enzymatically and nonenzymatically in human plasma

Optimizing interpretation of survival studies of fresh and aged transfused biotin-labeled RBCs

BACKGROUND

Ex vivo labeling with 51 chromium represents the standard method to determine red blood cell (RBC) survival after transfusion. Limitations and safety concerns spurred the development of alternative methods, including biotinylated red blood cells (BioRBC).

STUDY DESIGN AND METHODS

Autologous units of whole blood were divided equally into two bags and stored under standard blood bank conditions at 2 to 6°C (N = 4 healthy adult volunteers). One bag was biotinylated (15 μg/ml) on storage days 5 to 7 (fresh) and the other was biotinylated (3 μg/ml) on days 35 to 42 (aged). The proportion of circulating BioRBC was measured serially, and cell-surface biotin was quantified with reference to molecules of equivalent soluble fluorochrome. Clearance kinetics were modeled by RBC age distribution at infusion (Gaussian vs. uniform) and decay over time (constant vs. exponential).

RESULTS

Data were consistent with biphasic exponential clearance of cells of uniform age. Our best estimate of BioRBC clearance (half-life [T1/2 ]) was 49.7 ± 1.2 days initially, followed by more rapid clearance 82 days after transfusion (T1/2  = 15.6 ± 0.6 days). As BioRBC aged in vivo, molecules of equivalent soluble fluorochrome declined with a T1/2 of 122 ± 9 days, suggesting gradual biotin cleavage. There were no significant differences between the clearance of fresh and aged BioRBC.

CONCLUSION

Similar clearance kinetics of fresh and aged BioRBC may be due to the extensive washing required during biotinylation. Survival kinetics consistent with cells with uniform rather than Gaussian or other non-uniform age distributions suggest that washing, and potentially RBC culling, may extend the storage life of RBC products.

Microbiological Sensing Technologies: A Review

Microorganisms have a significant influence on human activities and health, and consequently, there is high demand to develop automated, sensitive, and rapid methods for their detection. These methods might be applicable for clinical, industrial, and environmental applications. Although different techniques have been suggested and employed for the detection of microorganisms, and the majority of these methods are not cost effective and suffer from low sensitivity and low specificity, especially in mixed samples. This paper presents a comprehensive review of microbiological techniques and associated challenges for bioengineering researchers with an engineering background. Also, this paper reports on recent technological advances and their future prospects for a variety of microbiological applications.

Measurement of posttransfusion red cell survival with the biotin label

The goal of this review is to summarize and critically assess information concerning the biotin method to label red blood cells (RBC) for use in studies of RBC and transfusion biology-information that will prove useful to a broad audience of clinicians and scientists. A review of RBC biology, with emphasis on RBC senescence and in vivo survival, is included, followed by an analysis of the advantages and disadvantages of biotin-labeled RBC (BioRBC) for measuring circulating RBC volume, posttransfusion RBC recovery, RBC life span, and RBC age-dependent properties. The advantages of BioRBC over (51)Cr RBC labeling, the current reference method, are discussed. Because the biotin method is straightforward and robust, including the ability to follow the entire life spans of multiple RBC populations concurrently in the same subject, BioRBC offers distinct advantages for studying RBC biology and physiology, particularly RBC survival. The method for biotin labeling, validation of the method, and application of BioRBCs to studies of sickle cell disease, diabetes, and anemia of prematurity are reviewed. Studies documenting the safe use of BioRBC are reviewed; unanswered questions requiring future studies, remaining concerns, and regulatory barriers to broader application of BioRBC including adoption as a new reference method are also presented.

N-biotinyl-S-(1,2-dichlorovinyl)-L-cysteine sulfoxide as a potential model for S-(1,2-dichlorovinyl)-L-cysteine sulfoxide: characterization of stability and reactivity with glutathione and kidney proteins in vitro

S-(1,2-Dichlorovinyl)-L-cysteine sulfoxide (DCVCS) is a reactive and potent nephrotoxic metabolite of the human trichloroethylene metabolite S-(1,2-dichlorovinyl)-L-cysteine (DCVC). Because DCVCS covalent binding to kidney proteins likely plays a role in its nephrotoxicity, in this study biotin-tagged DCVCS, N-biotinyl-DCVCS (NB-DCVCS), was synthesized, and its stability in buffer alone and in the presence of rat blood or plasma was characterized in vitro. In addition, reactivity toward GSH and covalent binding to selected model enzymes and isolated kidney proteins were characterized. The half-lives of NB-DCVCS (39.6 min) and the DCVCS (diastereomer 1, 14.4 min; diastereomer 2, 6 min) in the presence of GSH were comparable. Incubating the model enzymes glutathione reductase and malate dehydrogenase with 10 μM NB-DCVCS for 3 h at 37 °C followed by immunoblotting using antibiotin antibodies demonstrated that glutathione reductase and malate dehydrogenase were extensively modified by NB-DCVCS. When rat kidney cytosol (6 μg/μL) was incubated with NB-DCVCS (312.5 nM to 5 μM) for 3 h at 37 °C followed by immunoblotting, a concentration-dependent increase in signal with multiple proteins with different molecular weights was observed, suggesting that NB-DCVCS binds to multiple kidney proteins with different selectivity. Incubating rat kidney cytosol with DCVCS (10-100 μM) prior to the addition of NB-DCVCS (2.5 μM) reduced the immunoblotting signal, suggesting that NB-DCVCS and DCVCS compete for the same binding sites. A comparison of the stability of NB-DCVCS and DCVCS in rat blood and plasma was determined in vitro, and NB-DCVCS exhibited higher stability than DCVCS in both media. Collectively, these results suggest that NB-DCVCS shows sufficient stability, reactivity, and selectivity to warrant further investigations into its possible use as a tool for future characterization of the role of covalent modification of renal proteins by DCVCS in nephrotoxicity.

Protein biotinylation

Since its discovery in the first half of the twentieth century, the high-affinity, noncovalent interaction between biotin (vitamin H) and the avian protein avidin (and its bacterial homologs) has been exploited for many diverse biotechnology applications. This unit provides several basic protocols for labeling various protein reactive groups with biotin. These protocols can be applied not only to labeling in vitro or in tissue culture, but also to in vivo labeling of whole laboratory animals or to ex vivo labeling of surgically resected organs.

An immunoassay method for quantitative detection of proteins using single antibodies

A new immunoassay method called specific analyte labeling and recapture assay (SALRA) to quantitatively measure protein abundance was developed, and the assay conditions were optimized. The key features of this method include labeling the antigen bound to the capture antibody, eluting the labeled antigen, and recapturing it by the same capture antibody on the detection plate. The reporter molecules on the labeled antigen provide a convenient and reliable means for signal detection. We demonstrated that the dose-response curve of SALRA was comparable to that of sandwich enzyme-linked immunosorbent assay (ELISA) and better than that of the antigen direct labeling method. In addition, multiple proteins can be measured simultaneously by SALRA. Using the SALRA method, the detection limit for most of the cytokines tested was approximately 0.01ng/ml. Further SALRA tests on interleukin 6 (IL-6) showed the linear dose-response was 3.3 to 0.01ng/ml, the accuracy of the test was 71 to 91%, the intraassay variation was 3.6 to 7.4%, and the interassay variation was 3.8 to 10.0%. The applications of SALRA include quantitatively measuring proteins for which there are no ELISA tools available and providing a new platform for protein microarrays.

Biotin-protein bond: instability and structural modification to provide stability for in vivo applications

Biotinylation of proteins is a powerful tool for investigating biological phenomenon, both in vitro and in vivo. Biotinylating reagents that form covalent bonds with several types of amino acid residues are commercially available. However, most, if not all, of these commercially available biotinylating agents produce biotin-protein bonds that are susceptible to cleavage in human plasma. Here, we describe the use of immunoglobulin G as a model protein for evaluation of biotin-protein bond stability and for the investigation of the mechanism of biotin release. We also describe the synthesis of a biotin-protein bond that is stable in human plasma and a method for evaluation of that stability.

Synthesis of a biotin-derived alkyne for pd-catalyzed coupling reactions

[reaction: see text] An efficient synthesis of a terminal alkyne derived from d-biotin was developed to provide an alternative for carboxyl-based biotinylation. This approach was illustrated by the preparation of alkyne- and alkene-linked phenylalanine derivatives using palladium-catalyzed Sonogashira and Oh methodology. (Strept)avidin binding was observed using soluble and immobilized receptors. These results demonstrate the applicability of carbon-linked biotin derivatives for use in affinity-based purification and bioanalytical applications.

A biotin–protein bond with stability in plasma

A nonradioactive label for peptide hormones would be useful for pharmacokinetic studies in infants, children, and pregnant women. Because the binding affinity between biotin and avidin is large (Ka=10(15) M(-1)), biotin could also serve as a covalent label for subsequent detection using a variety of avidin conjugates. However, biotin labels produced by most commercially available biotinylating reagents are rapidly cleaved from protein in plasma. We sought to synthesize a stable biotin label for protein. With the use of immunoglobulin G (IgG) as a model protein, biotin was conjugated through a cysteine residue; a carboxylate group was positioned alpha to the biotinamide bond. Stability of the bond in the presence of plasma and buffer control was assessed by release of biotin. Released biotin was separated from biotinylated IgG by ultrafiltration and was quantitated by an avidin-binding assay. In plasma, less than 0.6% of bound biotin was released. This release rate is not significantly different from buffer and is less than 7% of the release rate for IgG biotinylated by N-hydroxysuccinimide-LC-biotin. We conclude that this biotin-protein bond is stable in plasma. We speculate that many uses of avidin-biotin technology could be improved by using this method for protein labeling.

Voltammetric Homogeneous Binding Assay of Biotin without a Separation Step Using Iminobiotin Labeled with an Electroactive Compound

Avidin, which is one type of glycoprotein, has a strong affinity with biotin (Ka = 10(15) M(-1)). Iminobiotin also forms a complex with avidin (Ka = 10(8) M(-1) at pH 9.5). The avidin-iminobiotin complex changes to the avidin-biotin complex in the presence of biotin because of the difference of the binding constant to avidin. In this study, the interaction between avidin and iminobiotin labeled with an electroactive compound was investigated by voltammetry. After avidin and the labeled iminobiotin (LI) were incubated in 0.1 M phosphate buffer (pH 7.0), the peak currents of LI were measured in various concentrations of biotin. The peak currents increased with increasing the concentration of biotin. Thus, this observation indicates the formation of avidin-biotin complex. On the other hand, the formation of avidin-iminobiotin complex depended on the pH of the solution. LI combines with the avidin at pH 5.6-8.9 and dissociates at pH 4.6.