Optimizing hepcidin measurement with a proficiency test framework and standardization improvement.

Objectives: Hepcidin measurement advances insights in pathophysiology, diagnosis, and treatment of iron disorders, but requires analytically sound and standardized measurement procedures (MPs). Recent development of a two-level secondary reference material (sRM) for hepcidin assays allows worldwide standardization. However, no proficiency testing (PT) schemes to ensure external quality assurance (EQA) exist and the absence of a high calibrator in the sRM set precludes optimal standardization. Methods: We developed a pilot PT together with the Dutch EQA organization Stichting Kwaliteitsbewaking Medische Laboratoriumdiagnostiek (SKML) that included 16 international hepcidin MPs. The design included 12 human serum samples that allowed us to evaluate accuracy, linearity, precision and standardization potential. We manufactured, value-assigned, and validated a high-level calibrator in a similar manner to the existing low- and middle-level sRM. Results: The pilot PT confirmed logistical feasibility of an annual scheme. Most MPs demonstrated linearity (R2>0.99) and precision (duplicate CV>12.2%), although the need for EQA was shown by large variability in accuracy. The high-level calibrator proved effective, reducing the inter-assay CV from 42.0% (unstandardized) to 14.0%, compared to 17.6% with the two-leveled set. The calibrator passed international homogeneity criteria and was assigned a value of 9.07±0.24 nmol/L. Conclusions: We established a framework for future PT to enable laboratory accreditation, which is essential to ensure quality of hepcidin measurement and its use in patient care. Additionally, we showed optimized standardization is possible by extending the current sRM with a third high calibrator, although international implementation of the sRM is a prerequisite for its success.

Provisional standardization of hepcidin assays: creating a traceability chain with a primary reference material, candidate reference method and a commutable secondary reference material.

Background Hepcidin concentrations measured by various methods differ considerably, complicating interpretation. Here, a previously identified plasma-based candidate secondary reference material (csRM) was modified into a serum-based two-leveled sRM. We validated its functionality to increase the equivalence between methods for international standardization. Methods We applied technical procedures developed by the International Consortium for Harmonization of Clinical Laboratory Results. The sRM, consisting of lyophilized serum with cryolyoprotectant, appeared commutable among nine different measurement procedures using 16 native human serum samples in a first round robin (RR1). Harmonization potential of the sRM was simulated in RR1 and evaluated in practice in RR2 among 11 measurement procedures using three native human plasma samples. Comprehensive purity analysis of a candidate primary RM (cpRM) was performed by state of the art procedures. The sRM was value assigned with an isotope dilution mass spectrometry-based candidate reference method calibrated using the certified pRM. Results The inter-assay CV without harmonization was 42.1% and 52.8% in RR1 and RR2, respectively. In RR1, simulation of harmonization with sRM resulted in an inter-assay CV of 11.0%, whereas in RR2 calibration with the material resulted in an inter-assay CV of 19.1%. Both the sRM and pRM passed international homogeneity criteria and showed long-term stability. We assigned values to the low (0.95±0.11 nmol/L) and middle concentration (3.75±0.17 nmol/L) calibrators of the sRM. Conclusions Standardization of hepcidin is possible with our sRM, which value is assigned by a pRM. We propose the implementation of this material as an international calibrator for hepcidin.

Toward Worldwide Hepcidin Assay Harmonization: Identification of a Commutable Secondary Reference Material.

BACKGROUND: Absolute plasma hepcidin concentrations measured by various procedures differ substantially, complicating interpretation of results and rendering reference intervals method dependent. We investigated the degree of equivalence achievable by harmonization and the identification of a commutable secondary reference material to accomplish this goal. METHODS: We applied technical procedures to achieve harmonization developed by the Consortium for Harmonization of Clinical Laboratory Results. Eleven plasma hepcidin measurement procedures (5 mass spectrometry based and 6 immunochemical based) quantified native individual plasma samples (n = 32) and native plasma pools (n = 8) to assess analytical performance and current and achievable equivalence. In addition, 8 types of candidate reference materials (3 concentrations each, n = 24) were assessed for their suitability, most notably in terms of commutability, to serve as secondary reference material. RESULTS: Absolute hepcidin values and reproducibility (intrameasurement procedure CVs 2.9%-8.7%) differed substantially between measurement procedures, but all were linear and correlated well. The current equivalence (intermeasurement procedure CV 28.6%) between the methods was mainly attributable to differences in calibration and could thus be improved by harmonization with a common calibrator. Linear regression analysis and standardized residuals showed that a candidate reference material consisting of native lyophilized plasma with cryolyoprotectant was commutable for all measurement procedures. Mathematically simulated harmonization with this calibrator resulted in a maximum achievable equivalence of 7.7%. CONCLUSIONS: The secondary reference material identified in this study has the potential to substantially improve equivalence between hepcidin measurement procedures and contributes to the establishment of a traceability chain that will ultimately allow standardization of hepcidin measurement results.

Serum hepcidin measured with an improved ELISA correlates with parameters of iron metabolism in patients with myelodysplastic syndrome.

Patients with myelodysplastic syndromes (MDS) often show elevated serum ferritin levels at diagnosis, probably caused by increased intestinal iron uptake attributable to ineffective erythropoiesis. Many patients also develop transfusional iron overload. Hepcidin, a pivotal regulator of iron homeostasis, controls iron uptake in the duodenum as well as iron release from macrophages and is potentially involved in iron distribution to different organs. We measured serum hepcidin, together with other laboratory parameters related to iron metabolism and hematopoiesis (ferritin, transferrin, transferrin saturation, soluble transferrin receptor, erythropoietin, and hemoglobin), and C-reactive protein as marker of inflammation, in 89 MDS patients. Hepcidin levels were measured with two different competitive ELISAs: (a) EIA-4705 as described by Schwarz et al. (J Gastroenterol 46:648-656; 2011) and (b) Hepcidin 25 bioactive ELISA (EIA-5258), which was develop by DRG Diagnostics, Marburg, in 2012. Median hepcidin levels with EIA-5258 were as follows: entire cohort 17.5 ng/ml (n = 89), RA/RARS 5.9 ng/ml (n = 5), RCMD 17.8 ng/ml (n = 38), RS-RCMD 8.7 ng/ml (n = 7), RAEB I/II 29.1 ng/ml (n = 22), CMML I/II 16.9 ng/ml (n = 10), and MDS with del(5q) 26.3 ng/ml (n = 7). Hepcidin levels of the RA/RARS patients were significantly lower than in the other groups except RS-RCMD. RS-RCMD had significantly lower levels than RAEB and 5q- patients. There was a positive correlation between hepcidin levels and serum ferritin and transferrin saturation, and a negative correlation between hepcidin and hemoglobin and transferrin. Malcovati et al. (Blood 112:2676a, 2008), Santini et al. (PLoS One 6:e23109, 2011), and Ambaglio et al. (Haematologica 98:420-423, 2013), using mass spectrometry, reported similar results. We further assessed transfusional status and could show that patients who had been transfused have significantly higher hepcidin levels (median 33.3 versus 8.8 ng/ml (p < 0.001)). A dichotomized hepcidin level correlated with worse survival. EIA-4705 as described by Schwarz showed no correlation with markers of iron metabolism. Measurement of serum hepcidin with an improved ELISA yield results that correlate with other parameters of iron metabolism as well as survival and transfusion needs.

Analytical comparison of ELISA and mass spectrometry for quantification of serum hepcidin in critically ill patients.

Aim: To compare methods of quantifying serum hepcidin (based on MS and ELISA) and their ability to diagnose true iron deficiency anemia in critically ill patients. Materials & methods: Serum hepcidin was measured in 119 critically ill patients included in the HEPCIDANE clinical trial, using either an ultra-sensitive ELISA kit (from DRG) or two different MS methods. Results: The results show a good correlation between the different methods studied. The Bland-Altman analysis and the Kappa test for clinical groups show a good or very good agreement between the different tests. Conclusion: ELISA or MS show a satisfactory commutability to quantify serum hepcidin. This is of great importance for the determination of therapeutic strategies in iron deficiency.

Evaluation of an ELISA for p16INK4a as a screening test for cervical cancer.

BACKGROUND: The low sensitivity of cytology and low specificity of human papillomavirus testing prompts searching for more accurate cervical cancer screening strategies. Our goal was to evaluate an ELISA-based test for p16(INK4a). METHODS: 1,781 women undergoing routine screening provided cervical specimens for p16(INK4a) ELISA (original and enhanced versions of a prototype), liquid-based cytology, and Hybrid Capture II (hc2) testing. All women with a positive result and a random sample of those with negative results on all tests were referred for histologic diagnosis. Cervical intraepithelial neoplasia grade >or=3 (>or=CIN3) was the main outcome. The original analysis included all >or=CIN3 outcomes (n = 28). The a posteriori analysis was used to represent clinically relevant results with >or=CIN3 as outcomes only when detected after a positive screening test (n = 27). RESULTS: Participants had a median age of 23 years. The prevalence of high-risk human papillomavirus DNA was 30.6%. In a posteriori analyses, the sensitivity and specificity for p16(INK4a) ELISA (>or=8 pg/mL cut-point), cytology, and hc2 were 50.9%, 58.1%, and 100.0%, respectively, and 90.4%, 89.3%, and 69.2%, respectively. Referral to colposcopy of women with positive results for hc2 and p16(INK4a) (enhanced ELISA, >or=6 pg/mL cut-point) had a sensitivity of 91.8% (95% confidence interval, 79.1-100.0%) and specificity of 86.0% (95% confidence interval, 82.0-89.0%). Results of the original analyses had similar specificity but substantially lower sensitivity due to the strong influence of the single CIN3 case with completely negative screening results. CONCLUSIONS: An enhanced version of this prototypic p16(INK4a) ELISA showed promise in screening, particularly when combined with hc2.

Evaluation of a new p16(INK4A) ELISA test and a high-risk HPV DNA test for cervical cancer screening: results from proof-of-concept study.

p16(INK4a), a cell cycle regulation protein, accumulates in abnormal epithelial cells infected with high-risk human papilloma virus (HPV). In immunostaining studies, p16(INK4a) has shown potential as a marker of high grade cervical intraepithelial neoplasia (CIN) and invasive cervical cancer. To evaluate its potential use in cervical cancer screening, we conducted a feasibility study to compare the performance of a new enzyme linked immunosorbant assay (ELISA) for p16(INK4a) (mtm laboratories, Heidelberg, Germany) to that of the Hybrid Capture 2 (hc2) test for high-risk HPV DNA for the detection of CIN3. Three hundred and nineteen women were referred from Western Washington Planned Parenthood clinics for colposcopy examination and cervical biopsy because of abnormal Pap test results. Cervical samples were obtained from study participants for p16(INK4a) ELISA, liquid-based cytology and hc2. The order (first and second) for obtaining samples for cervical cytology and p16(INK4a) ELISA changed with every other subject. Concentrations of p16(INK4a) protein were higher when the sample was taken before the cytology. The sensitivity of p16(INK4a) ELISA (concentration > or = 8 units/ml) taken as first sample was 90.0% for CIN3, and the sensitivity of HC2 taken as a second sample was 85%. In the same group, the specificity of p16(INK4a) ELISA (46.9%) was slightly better than hc2 (35.4%) Results from this proof-of-concept study suggest that p16(INK4a) ELISA has a similar sensitivity and slightly better specificity for CIN3 compared to hc2. These findings support proceeding with a larger study with samples from a population of women presenting for routine cytology screening.

Identification of high-grade cervical dysplasia by the detection of p16INK4a in cell lysates obtained from cervical samples.

BACKGROUND: Current cervical cancer screening approaches are based on cytology supplemented by human papillomavirus (HPV) testing in some settings. Whereas cytology is laborious and depends on the cytologists' experience, HPV testing has limited specificity when it is used to detect high-grade lesions. A dichotomous test to identify high-grade lesions with greater specificity may be a useful tool for cervical cancer screening. p16(INK4a) is a cell-cycle regulator that has demonstrated strong overexpression in cervical precancer cells and cervical cancer induced by the deregulated expression of HPV oncogenes. METHODS: The authors used a sandwich enzyme-linked immunosorbent assay (ELISA) to quantify the amount of solubilized p16(INK4a) protein in lysates that were prepared from cervical samples to detect high-grade cervical lesions. In total, 187 specimens that were obtained after sampling for conventional cytology in women who attended a cervical colposcopy clinic were analyzed. Seventy-six women underwent a biopsy, and 45 of those women showed histologically confirmed, high-grade cervical intraepithelial neoplasia. RESULTS: For 76 women with biopsy-proven diagnoses, receiver operating characteristic (ROC) analysis of different cutoff values showed an area under the ROC curve of 0.89 for the detection of high-grade cervical dysplasia. At a cutoff value of 8 U/mL, the sensitivity of the p16(INK4a) ELISA for detecting high-grade dysplastic cervical lesions was 96%. CONCLUSIONS: The data obtained in this study suggested that ELISA-based quantification of solubilized p16(INK4a) protein may have high sensitivity for detecting cervical precancer. Further population-based studies will be necessary to analyze the specificity and predictive values of p16(INK4a) protein quantification in cervical samples.

Induction by beta-bungarotoxin of apoptosis in cultured hippocampal neurons is mediated by Ca(2+)-dependent formation of reactive oxygen species.

The component of the venom of the Taiwanese banded krait Bungarus multicinctus, beta-bungarotoxin (beta-BuTx), acts as an extremely potent inducer of neuronal apoptosis when applied to rat hippocampal cultures. While induction of cell death is dependent on toxin binding to voltage-activated K+ channels and subsequent internalization, the pro-apoptotic signals triggered by picomolar concentrations of beta-BuTx are not understood. Following toxin binding, a dramatic increase in intracellular Ca2+ became detectable after 30 min, and in reactive oxygen species (ROS) after 3-4 h. Conversely, Ca2+ chelators, radical quenchers and antioxidants efficiently antagonized beta-BuTx induced apoptosis. As shown for the antioxidant 2,3-dihydroxybenzoic acid, analysis by matrix assisted laser desorbtion-time of flight (MALDI-TOF) mass spectrometry excluded the protective effects to be due to reductive cleavage of the toxic beta-BuTx dimer. Inhibitors of the intracellular antioxidant defence system enhanced neuronal susceptibility to beta-BuTx, supporting the essential role of ROS in beta-BuTx-initiated apoptosis. Cell damage was accompanied by an accumulation of markers of oxidative cell stress, phospholipid hydroxyperoxides and the lipid peroxidation product, malonyl dialdehyde. These observations indicate that beta-BuTx-induced cell death resulted from an intracellular signalling cascade involving subsequent stages of a dramatic rise in free Ca2+, the accumulation of ROS, membrane lipid peroxidation and, finally, apoptosis.

Formation of molecular complexes by N-methyl-D-aspartate receptor subunit NR2B and ryanodine receptor 2 in neonatal rat myocard.

The N-methyl-d-aspartate (NMDA) receptor is a glutamate gated cation channel prevalent in the postsynaptic membranes of central nervous system neurons. The neurotransmitter receptor complex is thought to represent a tetramer where variable NR2 or NR3 polypeptides form heteromeric assemblies with an obligatory NR1 subunit. Recently, we showed that cardiac myocytes from perinatal rats transiently express the NMDA receptor subunit NR2B, the function of which in heart is unknown. To characterize the cardiac NR2B protein, we determined its subcellular distribution and specific molecular interaction partners. By immunostaining of rat heart tissue slices and acutely dissociated cardiac myocytes, the NR2B antigen was localized at the sarcomeric Z-bands. Using immunoprecipitation of detergent-solubilized NR2B protein and subsequent analysis employing matrix-assisted laser desorption/ionization time of flight mass spectrometry, ryanodine receptor 2 was identified as a molecular interaction partner of the cardiac NR2B polypeptide. Differences in antibody recognition indicate that the cardiac NR2B polypeptide carries a structurally altered C terminus as compared with the NR2B variant prevalent in central nervous system. Based on its localization and protein interaction, the function of cardiac NR2B protein may relate to mechanosensitivity or play a role in the regulation of the contractile apparatus of neonatal heart.