Accurate non-ceruloplasmin bound copper: a new biomarker for the assessment and monitoring of Wilson disease patients using HPLC coupled to ICP-MS/MS.

Objectives: Assessment of Wilson disease is complicated, with neither ceruloplasmin, nor serum or urine copper, being reliable. Two new indices, accurate non-ceruloplasmin copper (ANCC) and relative ANCC were developed and applied to a cohort of 71 patients, as part of a Wilson Disease Registry Study.

Methods: Elemental copper-protein speciation was developed for holo-ceruloplasmin quantitation using strong anion exchange chromatography coupled to triple quadrupole inductively coupled plasma mass spectrometry. The serum proteins were separated using gradient elution and measured at m/z 63 (⁶³Cu⁺) and 48 (³²S¹⁶O⁺) using oxygen reaction mode and Cu-EDTA as calibration standard. The ANCC was calculated by subtraction of the ceruloplasmin bound copper from the total serum copper and the RelANCC was the percentage of total copper present as the ANCC.

Results: The accuracy of the holo-ceruloplasmin measurement was established using two certified reference materials, giving a mean recovery of 94.2 %. Regression analysis between the sum of the copper containing species and total copper concentration in the patient samples was acceptable (slope=0.964, intercept=0, r=0.987) and a difference plot, gave a mean difference for copper of 0.38 μmol/L. Intra-day precision for holo-ceruloplasmin at serum copper concentrations of 0.48 and 3.20 μmol/L were 5.2 and 5.6 % CV and the intermediate precision at concentrations of 0.80 and 5.99 μmol/L were 6.4 and 6.4 % CV, respectively. The limit of detection (LOD) and lower limit of quantification (LLOQ) for holo-ceruloplasmin were 0.08 and 0.27 μmol/L as copper, respectively.

Conclusions: ANCC and Relative ANCC are important new diagnostic and monitoring biomarker indices for Wilson disease (WD).