Abstract
In this study, a chemiluminescence immunoassay (CLIA) for human serum 25-hydroxyvitamin D (25(OH)D) was established by a competition model. In serum, more than 99% of total circulating 25(OH)D binds to protein and less than 1% of 25(OH)D is in free form (Jassil et al., 2017). Before measuring concentration of 25(OH)D in serum, a releasing procedure should be conducted. A new reagent is used to release binding 25(OH)D to free form. Streptavidin (SA) was labeled to magnetic beads by a 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) method. Biotinylated VD was used as a competitor of 25(OH)D in samples. Anti-VD antibody (aby) was labeled to horseradish peroxidase (HRP) by EDC to react with 25(OH)D and biotinylated-VD molecules. The pretreated samples or standards were added into the reaction tube with biotin-VD and anti-VD aby-HRP, free 25(OH)D in the sample competes with biotinylated VD for binding to anti-VD aby-HRP, an SA-labeled magnetic particle is added to isolate the signal-generating complex, and the signal is inversely proportional to the 25(OH)D concentration in the sample. The method established shows good thermostability and performance. The limitation of detection (LoD) is 1.43 ng/mL. The intra-assay coefficient of variation (CV) is 3.66%–6.56%, the interassay CV is 4.19%–7.01%, and the recovery rate is 93.22%–107.99%. Cross-reactivity (CR) was remarkably low with vitamin D2, vitamin D3, 1, 25-dihydroxyvitamin D3, and 1, 25-dihydroxyvitamin D2. At the same time, the cross-reaction values with 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 were 97% and 100%, respectively. The developed method shows good correlation with the total VD product from Roche and DiaSorin. 1096 clinical patient samples were measured with developed reagent kit in this study. 7 types of disease were involved, and the concentration of 25(OH)D is less than 30 ng/mL in 94.98% of patients.
Highlights
Vitamin D (VD), known as sunshine vitamin, plays an important role in bone metabolism [1,2,3]
Dynabeads MyOne carboxylic TM acid beads, EZLink Sulfo-NHS-LC-Biotinylation Kit, succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC), and 4′-hydroxyazobenzene-2-carboxylic acid (HABA) solution are obtained from ermo Fisher; perfluorohexanoate(PFHxA), methanol, EDC, and NHS are purchased from Sigma; an AKTA purifier is purchased from GE healthcare; biotinylated vitamin D (BVD) is obtained from DIASource; horseradish peroxidase (HRP) is purchased from BBI solutions; streptavidin is purchased from NeuroPeptide from China; a microscope is purchased from Olympus; an automicroplate chemiluminescent analyzer is supplied by Baiming Biotechnology from China; and an automagnetic beads chemiluminescent analyzer is supplied by Zecheng Biotechnology from China
According to the previous literature studies, there are many quantification methods for 25(OH)D, such as antibodybased isoluminol derivate direct competitive two-step chemiluminescent system used by DiaSorin; antibody-based acridinium ester competitive assay used by IDS plc, Abbott, and Siemens; 25-OH-vitamin D binding protein based electrochemiluminescence competitive assay used by Roche; and LC-MS/MS-based nonimmunological direct detection method used by PerkinElmer
Summary
Vitamin D (VD), known as sunshine vitamin, plays an important role in bone metabolism [1,2,3]. Erefore, detection of vitamin D concentration is a quite vital requirement of clinical diagnostics. ® D, and the ADVIA Centaur Vitamin D Total, and none of these immunoassays gave results equivalent to the liquid chromatography-tandem mass spectrometry (LC-MS/MS) method [16]. Journal of Analytical Methods in Chemistry spectrometry was developed for 25(OH)D detection [17], but this method is quite expensive and requires special training for the operator. CLIA is a simple, sensitive, and cheap method for the high-throughput quantification of analyses in samples. A direct competitive immunoassay was established on the CLIA platform
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