Time-of-flight mass spectrometry analysis of the ferroportin-hepcidin binding domain complex for accurate mass confirmation of bioactive hepcidin 25

Surface plasmon resonance based on molecularly imprinted nanoparticles for the picomolar detection of the iron regulating hormone Hepcidin-25

BACKGROUND

Molecularly imprinted polymer (MIP) technique is a powerful mean to produce tailor made synthetic recognition sites. Here precipitation polymerization was exploited to produce a library of MIP nanoparticles (NPs) targeting the N terminus of the hormone Hepcidin-25, whose serum levels correlate with iron dis-metabolisms and doping. Biotinylated MIP NPs were immobilized to NeutrAvidin™ SPR sensor chip. The response of the MIP NP sensor to Hepcidin-25 was studied.

FINDINGS

Morphological analysis showed MIP NPs of 20-50 nm; MIP NP exhibited high affinity and selectivity for the target analyte: low nanomolar Kds for the interaction NP/Hepcidin-25, but none for the NP/non regulative Hepcidin-20. The MIP NP were integrated as recognition element in SPR allowing the detection of Hepcidin-25 in 3 min. Linearity was observed with the logarithm of Hepcidin-25 concentration in the range 7.2-720 pM. LOD was 5 pM. The response for Hepcidin-20 was limited. Hepcidin-25 determination in real serum samples spiked with known analyte concentrations was also attempted.

CONCLUSION

The integration of MIP NP to SPR allowed the determination of Hepcidin-25 at picomolar concentrations in short times outperforming the actual state of art. Optimization is still needed for real sample measurements in view of future clinical applications.

Hepcidin quantification: methods and utility in diagnosis

Hepcidin is a 25-amino acid peptide hormone that is produced and secreted predominantly by hepatocytes, circulates in the bloodstream, and is excreted by the kidneys. Since the discovery of hepcidin and the elucidation of its important role in iron homeostasis, hepcidin has been suggested as a promising diagnostic marker for iron-related disorders. In this regard, a number of analytical methods have been developed in order to assess hepcidin concentration in different biological fluids, particularly serum and urine. In this critical review we have tried to address the issues still pending in accurate determination of this peptide by evaluating the available analytical methodologies. Among them, the use of ELISA strategies (in competitive or sandwich formats) and molecular mass spectrometry (MS) including MALDI and/or LC-MS has been critically compared. The use of elemental mass spectrometry (ICP-MS) has also been included as a possible complementary tool to the previous ones. In addition, this manuscript has revised the existing and potentially emerging clinical applications of hepcidin testing for diagnosis. These include the iron disorders such as iron deficiency anemia (IDA, low hepcidin), anemia of chronic disease (ACD, high hepcidin) and the combined state of ACD and IDA or hemochromatosis. Other applications such as using hepcidin in assessing the response to existing therapies in cancer have also been revised in the manuscript.

Second round robin for plasma hepcidin methods: first steps toward harmonization

Measurements of the iron regulatory hormone hepcidin by various methodologies and laboratories are not harmonized. As a result different numeric results are obtained for the same clinical sample. We investigated whether better agreement between plasma hepcidin methods can be achieved by harmonization. Native plasma pools (n = 11) of a variety of hepcidin concentrations and blank plasma spiked with three different quantities of synthetic hepcidin-25 purchased from two different commercial sources (n = 6), were distributed in duplicate among 21 methods worldwide. We assessed commutability by comparing results from synthetic hepcidin with those from native samples in various method couples by Bland-Altman plots. Methods differed substantially in absolute values and reproducibility. For the majority of methods we found that samples with synthetic hepcidin-25 were noncommutable with the native samples. In an attempt to harmonize by using native hepcidin results, we selected two methods that showed good mutual agreement of native results and calculated consensus values as the medians for the 11 duplicate native samples obtained by these two methods. Finally, we constructed algorithms enabling the laboratories to calculate the hepcidin consensus (HEPCON) value using their own native hepcidin results. We found that the use of these algorithms substantially reduced the between-method CV. Until commutable materials are defined, hepcidin harmonization can be achieved by exploiting specific algorithms, allowing each lab to report their native hepcidin concentrations in HEPCON values. This study represents the first step toward harmonization of plasma hepcidin methods and facilitates aggregation of hepcidin data from different research investigations.

Preanalytical factors and reference intervals for serum hepcidin LC-MS/MS method

BACKGROUND

Hepcidin is a potential biomarker for anemia of chronic diseases and disorders of iron metabolism. Thus, data of preanalytical factors, reference values and method characteristics are critical for clinical use of hepcidin determination.

METHODS

We studied the effects of sample storage, sampling device and a meal on hepcidin levels using a liquid-chromatography tandem mass spectrometric (LC-MS/MS) method for serum hepcidin. Age- and gender-dependent reference values were determined using serum samples from healthy volunteers (n=231). The results were also compared with those obtained by a commercial competitive ELISA for hepcidin.

RESULTS

In serum samples, hepcidin is stable for one day at room temperature, six days at +4°C and at least 42 days at -20°C. Breakfast or type of sampling device does not affect hepcidin concentration. Significantly lower hepcidin concentrations were observed in women ≤50 than >50 years of age or in men (p<0.0001 for both). Reference values for females aged 18-50 years were 0.4-9.2 nmol/L, for those >50 years 0.7-16.8 nmol/L and for males ≥18 years 1.1-15.6 nmol/L. Comparison with a competitive ELISA showed poor correlation.

CONCLUSIONS

Fasting before sampling and type of blood collection were not critical. Samples can be transported to laboratory at room temperature if they arrive within a day. Significantly lower concentrations of serum hepcidin were observed in menstruating than in post-menopausal women and in men.

Hepcidin in human iron disorders: diagnostic implications

BACKGROUND

The peptide hormone hepcidin plays a central role in regulating dietary iron absorption and body iron distribution. Many human diseases are associated with alterations in hepcidin concentrations. The measurement of hepcidin in biological fluids is therefore a promising tool in the diagnosis and management of medical conditions in which iron metabolism is affected.

CONTENT

We describe hepcidin structure, kinetics, function, and regulation. We moreover explore the therapeutic potential for modulating hepcidin expression and the diagnostic potential for hepcidin measurements in clinical practice.

SUMMARY

Cell-culture, animal, and human studies have shown that hepcidin is predominantly synthesized by hepatocytes, where its expression is regulated by body iron status, erythropoietic activity, oxygen tension, and inflammatory cytokines. Hepcidin lowers serum iron concentrations by counteracting the function of ferroportin, a major cellular iron exporter present in the membrane of macrophages, hepatocytes, and the basolateral site of enterocytes. Hepcidin is detected in biologic fluids as a 25 amino acid isoform, hepcidin-25, and 2 smaller forms, i.e., hepcidin-22 and -20; however, only hepcidin-25 has been shown to participate in the regulation of iron metabolism. Reliable assays to measure hepcidin in blood and urine by use of immunochemical and mass spectrometry methods have been developed. Results of proof-of-principle studies have highlighted hepcidin as a promising diagnostic tool and therapeutic target for iron disorders. However, before hepcidin measurements can be used in routine clinical practice, efforts will be required to assess the relevance of hepcidin isoform measurements, to harmonize the different assays, to define clinical decision limits, and to increase assay availability for clinical laboratories.