Development of a primary reference material of natural C-reactive protein: verification of its natural pentameric structure and certification by two isotope dilution mass spectrometry

Absolute quantification methods for Prostate-Specific antigen by Isotope-Dilution mass spectrometry

Prostate-specific antigen (PSA) is a diagnostic marker for prostate cancer; however, because it is a macromolecular glycoprotein with complex and diverse isoforms, it is difficult to standardize clinical PSA detection results. To overcome this limitation, herein, naturally extracted PSA was characterized as free PSA (fPSA), and the PSA solution was successfully quantified by amino acid analysis coupled with isotope-dilution mass spectrometry (AAA-IDMS) and enzymatic hydrolysis-IDMS; the results could be traced to the International System of Units (SI) through absolutely quantified amino acids and peptides. After protein hydrolysis or digestion condition optimization, amino acids and signature peptides were detected by liquid chromatography-mass spectrometry with the multiple reaction monitoring mode. The mass concentrations of PSA obtained through AAA-IDMS and enzymatic hydrolysis-IDMS were (75.3 ± 1.5) µg/g (k = 2) and (74.7 ± 1.7) µg/g (k = 2), respectively. The PSA weighted average mass concentration was (75.0 ± 1.6) µg/g (k = 2). The consistency assessment between the two methods was successfully validated, ensuring absolute quantitative accuracy. This study lays the foundation for the development of high-order reference materials for the clinical detection of PSA, which can improve the accuracy, reliability, and consistency of clinical PSA test results.

Development of an Ephedrine In-House Matrix Reference Material and Its Application to Doping Analysis

Biomatrix-based reference materials (RMs) improve the quality of laboratory test results by better representing actual samples. However, a matrix RM of ephedrine (EP) for threshold substances that require accurate analysis results has not yet been developed. Therefore, this study aimed to develop an in-house matrix RM for EP and subsequently apply it to analytical procedures. During the development of the in-house matrix EP RM, the system underwent homogeneity and stability studies. Additionally, it was subjected to interlaboratory comparison study in 11 laboratories, including 10 World Anti-Doping Agency (WADA)-accredited laboratories and our laboratory. Stability testing revealed no significant changes in the RM characteristics. For homogeneity, 10 random batches out of 200 were analyzed to confirm the uniformity within and between bottles. These results, combined with data from 11 laboratories, ensured retroactive validation. The traceability value of the in-house matrix EP RM was assigned as 9.83 ± 0.57 μg/mL (k = 2) by interlaboratory comparison studies and traceable uncertain evaluation. The feasibility of this method as a single calibration standard was confirmed in two laboratories. This substance is reliable and consistent for quality control during EP quantification, ensuring accurate and trustworthy outcomes. Consequently, this study establishes a framework and guidelines for producing in-house matrix RMs and serves as a reference for generating similar matrix RMs in other contexts.

Development of cancer biomarker heat shock protein 90α certified reference material using two different isotope dilution mass spectrometry techniques

Heat shock protein 90α (HSP90α) has been regarded as an important indicator for judging tumor metastasis and prognosis due to its significant upregulation in various tumors. Therefore, the accurate quantification of HSP90α is of great significance for clinical diagnosis and therapy of cancers. However, the lack of HSP90α certified reference material (CRM) leads to the accuracy and consistency of quantification methods not being effectively evaluated. Besides, quantitative results without traceability make comparisons between different studies difficult. In this study, an HSP90α solution CRM was developed from the recombinant protein raw material. The recombinant protein is a dimer, and the purity of the CRM candidate reached 96.71%. Both amino acid analysis-isotope dilution mass spectrometry (AAA-IDMS) and unique peptide analysis-isotope dilution mass spectrometry (UPA-IDMS) were performed to measure the content of HSP90α in the solution CRM candidate, and the certified value was assessed to be 66.2 ± 8.8 µg/g. Good homogeneity of the CRM was identified, and the stability examination suggested that the CRM was stable for at least 4 months at - 80 °C and for 7 days at 4 °C. With traceability to SI unit (kg), this CRM has potential to help establish a metrological traceability chain for quantification of HSP90α, which will make the quantification results standardized and comparable regardless of the quantitative methods.

Traceable value of immunoglobulin G against receptor-binding domain of SARS-CoV-2 confirmation and application to point-of-care testing system development

A highly purified and bioactive immunoglobulin G monoclonal antibody against receptor-binding domain of SARS-CoV-2 (RBD-IgG-MAb) has been accurately quantified by amino acid determination using isotope dilution liquid chromatography-mass spectrometry. Absolute quantification of RBD-IgG-MAb was achieved by averaging 4 amino acid certified reference materials, which allows the quantitative value (66.1 ± 5.8 μg/L) to be traced to SI unit (mol). Afterwards, the RBD-IgG-MAb was employed as control and calibration compound for the development of a point-of-care testing (POCT) system based on colloidal gold lateral flow immunoassay, which aimed to rapidly and accurately detect the level of protective RBD-IgG after vaccination. Under the detection parameters, a sigmoidal curve has been plotted between signal intensity and the logarithmic concentration for quantitative detection with the limit of detection of about 0.39 μg/mL. The relative standard deviations of intra-assay and inter-assay were lower than 2.3% and 14%, and the recoveries ranged from 87 to 100%, respectively. Fingertip blood samples from 37 volunteers after vaccination were analyzed by the POCT system; results showed that levels of RBD-IgG in 33 out of 37 samples ranged from 0.45 to 2.46 μg/mL with the average level of 0.91 μg/mL. The developed POCT system has been successfully established with the quantity-traceability RBD-IgG-MAb as control and calibration compound, and the scientific contribution of this work can be promoted to other areas.

Production and Characterization of a SARS-CoV-2 Nucleocapsid Protein Reference Material

Rapid antigen tests have become a widely used COVID-19 diagnostic tool with demand accelerating in response to the highly contagious SARS-CoV-2 Omicron variant. Hundreds of such test kits are approved for use worldwide, predominantly reporting on the presence of the viral nucleocapsid (N) protein, yet the comparability among manufacturers remains unclear and the need for reference standards is recognized. To address this lack of standardization, the National Research Council Canada has developed a SARS-CoV-2 nucleocapsid protein reference material solution, NCAP-1. Reference value determination for N protein content was realized by amino acid analysis (AAA) via double isotope dilution liquid chromatography-tandem mass spectrometry (LC-ID-MS/MS) following acid hydrolysis of the protein, in conjunction with UV spectrophotometry based on tryptophan and tyrosine absorbance at 280 nm. The homogeneity of the material was established through spectrophotometric absorbance readings at 280 nm. The molar concentration of the N protein in NCAP-1 was 10.0 ± 1.9 μmol L-1 (k = 2, 95% confidence interval). Reference mass concentration and mass fraction values were subsequently calculated using the protein molecular weight and density of the NCAP-1 solution. Changes to protein higher-order structure, probed by size-exclusion liquid chromatography (LC-SEC) with UV detection, were used to evaluate transportation and storage stabilities. LC-SEC revealed nearly 90% of the N protein in the material is present as a mixture of hexamers and tetramers. The remaining low molecular weight species (<30 kDa) were interrogated by top-down mass spectrometry and determined to be autolysis products homologous to those previously documented for N protein of the original SARS-CoV [Biochem. Biophys. Res. Commun.2008t, 377, 429-433].

Epitope mapping of antibodies in C-reactive protein assay kits by hydrogen-deuterium exchange mass spectrometry explains differential results across kits

C-Reactive protein (CRP) is an important marker for in vitro diagnosis (IVD) of inflammation. However, CRP immunoturbidimetric kits from different manufacturers exhibit inconsistency in evaluation, making clinical diagnosis challenging. The use of immunological methods in diagnosis means that the differences in epitopes across kits may directly lead to inconsistent results. Therefore, to provide consistent results, it is essential to perform epitope mapping of different kits. The composition of antibodies in a single kit is typically complex, with a combination of polyclonal antibodies or monoclonal antibodies. Here, we show an epitope screening strategy for complex antibodies in a kit based on hydrogen-deuterium exchange mass spectrometry (HDX-MS). We applied this workflow to successfully map the epitopes for three kits from three different manufacturers and compared their quantitative results. We obtained different quantitative results using kits from different manufacturers upon epitope mapping, confirming the correlation between the quantitative results and the epitopes. Thus, we have established a workflow based on HDX-MS to screen epitopes in IVD kits. This work helps determine the quantitative accuracy of a kit based on structural information, can guide the design and production of IVD reagents, and further improves the accuracy of IVD.

Quantification of SARS-CoV-2 spike and nucleocapsid proteins using isotope dilution tandem mass spectrometry

The emergence and subsequent global outbreak of the novel coronavirus SARS-CoV-2 prompted our laboratory to launch efforts to develop methods for SARS-CoV-2 antigen detection and quantification. We present an isotope dilution mass spectrometry method (IDMS) for rapid and accurate quantification of the primary antigens, spike and nucleocapsid proteins. This IDMS method utilizes liquid chromatography-tandem mass spectrometry (LC-MS/MS) to analyze sample tryptic digests for detection and quantification of selected conserved peptides of SARS-CoV-2 spike and nucleocapsid proteins. The IDMS method has the necessary attributes to be successfully utilized for accurate quantification in SARS-CoV-2 protein-based vaccines and as targets of rapid diagnostic tests. Absolute quantification was achieved by quantifying and averaging 5 peptides for spike protein (3 peptides in the S1 subunit and 2 peptides in the S2 subunit) and 4 peptides for nucleocapsid protein. The overall relative standard deviation of the method was 3.67% for spike protein and 5.11% for nucleocapsid protein. IDMS offers speed (5 h total analysis time), sensitivity (LOQ; 10 fmol/µL) and precision for quantification of SARS-CoV-2 spike and nucleocapsid proteins.

Predictive Value of C-Reactive Protein for Early Postoperative Complications in Children After Hypospadias Surgery

Background: This study explored the predictive value of postoperative C-reactive protein in children with hypospadias for postoperative complications and the risk factors. Methods: The clinical and follow-up data of 106 children with hypospadias who were treated with operations at Kunming Children's Hospital in 2020 were, respectively, analyzed. According to the occurrence of postoperative complications, the patients were divided into two groups: 25 patients with postoperative complications were the complications group, and 81 without postoperative complications were the control group. The baseline data, clinical characteristics, laboratory test indexes, and outcome of the two groups were collected. Receiver operating characteristic (ROC) was used to calculate the optimal cutoff value of C-reaction protein (CRP). Logistic regression was used to analyze the risk factors of hypospadias after surgery. A probability value (P) < 0.05 was considered statistically significant. Results: According to the result of the ROC curve, the optimal cutoff value of CRP was 11.7 mg/L. Logistic regression showed that the length of urethral defect, the urethral material, the operative produce, and the postoperative CRP level were related to the occurrence of postoperative complications of patients with DCC. The length of the urethral defect and the CRP level were the independent risk factors of the prognosis of hypospadias patients. The CRP level was related to the occurrence of postoperative complications and fistula. Conclusions: Postoperative CRP level can be used as a reliable marker for predicting the prognosis of hypospadias patients.