An easy, fast, and efficient assay for the quantification of peptide Hepcidin-25 in serum and plasma with LC-MS/MS

BACKGROUND

The peptide hormone hepcidin-25 plays an important role in iron metabolism. Low or high levels of hepcidin-25 are associated with various iron disorders; therefore, hepcidin-25 is an important biomarker. This study describes an easy and fast analytical assay for the quantification of hepcidin-25 with liquid chromatography-tandem mass spectrometry (LC-MS/MS).

METHODS

Sample preparation was performed by protein precipitation with trichloroacetic acid, and injection onto a LC-MS/MS was directly conducted from a LoBind 96-well plate.

RESULTS

The concentration range covered by the quality control samples, ranged from 0.25 nmol/L (12.3% CV) to 11.9 nmol/L (CV < 9%). Matrix effect was limited (mean recovery of 99.9% with a CV of 6.4%). The assay was validated for serum, EDTA and heparin plasma. An international secondary reference material was used for calibration. The reference interval (90% CL) was estimated for hepcidin-25 by analysing serum and plasma samples from 156 healthy subjects with a lower limit: 0.12 (0.07-0.19) and upper limit: 11.2 nmol/L (9.5-13.0).

CONCLUSIONS

We present a fast and easy assay for the quantification of hepcidin-25 in serum and plasma samples. The assay was successfully used for the detection of various forms of hereditary haemolytic anaemias, to characterize the interplay between erythropoiesis and iron levels.

Peptidomics: A Review of Clinical Applications and Methodologies

Improvements in both liquid chromatography (LC) and mass spectrometry (MS) instrumentation have greatly enhanced proteomic and small molecule metabolomic analysis in recent years. Less focus has been on the improved capability to detect and quantify small bioactive peptides, even though the exact sequences of the peptide species produced can have important biological consequences. Endogenous bioactive peptide hormones, for example, are generated by the targeted and regulated cleavage of peptides from their prohormone sequence. This process may include organ specific variants, as proglucagon is converted to glucagon in the pancreas but glucagon-like peptide-1 (GLP-1) in the small intestine, with glucagon raising, whereas GLP-1, as an incretin, lowering blood glucose. Therefore, peptidomics workflows must preserve the structure of the processed peptide products to prevent the misidentification of ambiguous peptide species. The poor in vivo and in vitro stability of peptides in biological matrices is a major factor that needs to be considered when developing methods to study them. The bioinformatic analysis of peptidomics data sets requires the inclusion of specific post-translational modifications, which are critical for the function of many bioactive peptides. This review aims to discuss and contrast the various extraction, analytical, and bioinformatics approaches used for human peptidomics studies in a multitude of matrices.

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.

Evaluation of a commercial liquid-chromatography high-resolution mass-spectrometry method for the determination of hepcidin-25

Introduction

Reliable determination of hepcidin-25, a key regulator of iron metabolism, is important. This study aimed at evaluating the performance of the Hepcidin-25 Liquid Chromatography-Tandem Mass-Spectrometry (LC-MS/MS) Kit (Immundiagnostik AG, Bensheim, Germany) for quantification of the hepcidin-25 protein.

Materials and methods

Precision, accuracy, linearity, and preanalytical requirements of the liquid-chromatography high-resolution mass-spectrometry (LC-HR-MS) method were evaluated. The imprecision and bias acceptance criteria were defined ≤ 15%. We investigated sample stability at room temperature (RT) and after repeated freeze and thaw cycles. Additionally, we assessed serum hepcidin-25 concentrations of 165 healthy adults referred for a medical check-up.

Results

The hepcidin-25 LC-MS/MS assay was linear over the concentration range of 3 – 200 ng/mL. Within- and between-run precision ranged between 1.9 – 8.6% and 5.1 – 12.4%, respectively. The mean bias of the low and high control material was - 2.7% and 2.1%, respectively. At RT, serum samples were stable for 3 h (mean bias + 0.3%). After two and three freeze and thaw cycles, hepcidin-25 concentrations showed a bias of + 8.0 and + 20%, respectively. Of 165 healthy adults, 109 females had a significantly lower median of 8.42 (range: 1.00 – 60.10) ng/mL compared to 56 males with 15.76 (range: 1.50 – 60.50) ng/mL (P = 0.002).

Conclusions

The hepcidin-25 LC-MS/MS kit shows a broad analytical range and meets the imprecision and bias acceptance criteria of ≤ 15%. Serum samples can be stored at RT for 3 h and resist up to two freeze and thaw cycles.