Targeted LC-MS/MS profiling of PTH fragments establishes a quantitative framework for clinical investigation

Objective: This research project aims to develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying parathyroid hormone (PTH) fragments and to use this approach to investigate their potential role in skeletal hyporesponsiveness to PTH in patients with chronic kidney disease (CKD).
Methods: We developed an LC-MS/MS method to quantify four of the eight currently identified PTH fragments (PTH (38-77), PTH (38-84), PTH (37-84), and PTH (34-84)). A proof-of-concept study was then conducted by quantifying these four fragments in pooled serum samples from patients stratified according to estimated glomerular filtration rate (eGFR: <15, 15-30, 30-45, and 45-60 mL/min/1.73 m2).
Results: As reported in the literature, serum concentrations of C-terminal PTH fragments increased as eGFR decreased. However, substantial interindividual variability was observed among patients with similar eGFR values. For example, the highest concentration of PTH (34-84) was up to 13-fold higher than the lowest observed concentration, whereas the concentration of PTH (1–84) in the same patient was only threefold higher at maximum. These findings suggest that PTH fragments concentrations depend not only on eGFR but may also reflect varying degrees of skeletal resistance to PTH. This observation indicates that PTH (1- 84) alone lacks sufficient precision for reliable monitoring, as no correlation was observed between PTH fragments and PTH (1–84).
Conclusion: In conclusion, thanks to our LC–MS/MS method, we were able to observe large variability in PTH peptides concentrations in CKD patients across different eGFR levels. This research project paves the way for elucidating the mechanisms underlying skeletal resistance to PTH, which may ultimately lead to more effective patient care, help prevent fractures that are often fatal, and significantly reduce associated healthcare costs.