Development of a multipurpose time-resolved fluorescence immunoassay for rat insulin

A dual-label time-resolved fluorescence immunoassay for the simultaneous determination of carcinoembryonic antigen and squamous cell carcinoma antigen

Among women worldwide, cervical cancer is the second-most common cancer, and cervical smears and DNA detection have low sensitivity or are too expensive. The concentrations of carcinoembryonic antigen (CEA) and squamous cell carcinoma (SCC) in the serum were detected using a sandwich immunoassay. The CEA and SCC in the serum were captured by anti-CEA and anti-SCC antibodies. After combining other anti-CEA- and anti-SCC-labeled antibodies with europium (III) (Eu³⁺ ) and samarium (III) (Sm³⁺ ) chelates, CEA and SCC were detected with time-resolved fluorometry (TRF). The linear correlation coefficients (R² ) of the CEA and SCC standard curves were 0.9997 and 0.9997, respectively. The minimum detection level for CEA was 1.15 ng/mL (the linear dynamic range was 3.24-543.67 ng/mL), and the average recovery was 100.83%. The sensitivity for SCC detection was 0.54 ng/mL (the linear dynamic range was 2.47-96.58 ng/mL), and the average recovery was 101.02%. High R² between the results of commercial assays and this method were obtained (R²  = 0.9983 for CEA, R²   = 0.9878 for SCC). These findings indicated that the dual-label TRFIA invented in this study has high sensitivity, accuracy, and specificity in clinical analysis, which indicates that this method could be used for the early diagnosis and follow-up surveillance of cervical cancer.

Sensitive and specific time-resolved fluorescence immunoassay of rat C-peptide for measuring hormone secretory and storage capacity of β-cells in vivo and in vitro

The limitations of current rat C-peptide assays led us to develop a time-resolved fluorescence immunoassay for measurements in plasma, incubation media, and tissue/cell extracts. The assay uses 2 monoclonal antibodies, binding to different parts of the C-peptide molecule, and allowing, respectively, capture of the peptide and its detection by europium-labeled streptavidin. It is performed on 25-μL samples for a dynamic range from 66pM up to 3900pM C-peptide and displays over 95% recovery of added peptide in the range of 111pM to 2786pM. Its inter- and intra-assay coefficients of variations are, respectively, lower than 7.6% and 4.8%. Cross-reactivities by rat insulin and by human and porcine C-peptide are negligible, and cross-reactivity by mouse C-peptide is 6% ± 2%. The assay has been validated for in vivo and in vitro measurements of C-peptide release and cellular content. Release patterns were similar to those for insulin and occurred in equimolar concentrations for both peptides. The molar C-peptide contents in purified β-cells and isolated islets were similar to the corresponding insulin contents. This was also the case for pancreatic extracts containing protease inhibitors.

Validation of an enzyme-linked immunosorbent assay for C-peptide analysis in Cameroon

AIMS

To validate an ELISA method for C-peptide analysis in Cameroon.

METHODS

We evaluated the linearity, detection limit, functional sensitivity, precision and accuracy, and further investigated for cross-reactivity by proinsulin, and interferences by lipids, bilirubin and hemoglobin. This method was compared with the Roche electrochemiluminescence immunoassay. C-peptide stability was assessed following a series of freeze-thaw cycles, and after storage at room temperature. The C-peptide reference range was determined by analyzing fifty plasma samples of Cameroonians without diabetes.

RESULTS

The ELISA was linear at least up to 7.09 μg/L, and had a detection limit of 0.09 μg/L, and a functional sensitivity of 0.32 μg/L. The inter- and intraassay %CV were 2.9-9.9%, and 5.2-9.4%, respectively. Recoveries were 81-94% in serum, and 93-98% in buffer. Comparison with the ECLIA yielded a good correlation coefficient (R(2)=0.98). There was no cross-reactivity with proinsulin, and no interference with lipids, bilirubin and hemoglobin. C-peptide was stable at room temperature for 24 h and up to 7 freeze-thaw cycles for medium (1-6 μg/L) and high (>6 μg/L) levels (<-15°C and <-70°C). The reference range for C-peptide was 0.38-3.63 μg/L.

CONCLUSIONS

This method is suitable for C-peptide analysis in low-income countries like Cameroon.