A High Throughput Mass Spectrometric Immunoassay for Parathyroid Hormone Microheterogeneity in Renal Failure Populations: Identification of PTH1-84, C-PTH Variants, and C-PTH C-terminally Truncated Variants
Wed 11:30 AM - Track 2: Targeted Proteomics
Paul Oran
Arizona State University
Paul E. Oran, Chad R. Borges, and Randall W. Nelson

Arizona State University
Parathyroid hormone (PTH) has remained an elusive protein despite decades of research aimed at uncovering structural variants that exist within individuals. An emerging paradigm regarding PTH has begun to reconcile the complexity surrounding PTH microheterogeneity by acknowledging PTH to bind to two separate receptors. The PTH/PTHrP type I receptor exerts the classical biological effects of PTH by binding to the intact n-terminal domain of PTH (PTH1-84 accounts for as little as 5% total circulating PTH). The second receptor is a C-PTH receptor that binds C-PTH fragments which correspondingly binds to the intact c-terminal domain (e.g. PTH34-84). These receptors exert opposing biological effects in regulating Ca2+ concentration [1]. Paramount to next-generation PTH assays is the ability to unambiguously distinctly identify and monitor these two types of biologically active forms of PTH while in the presence of additional forms inactivated through multiple n- and c-truncations.

Here we describe a high throughput, multiplexed mass spectrometric immunoassay (MSIA) that in a single analysis detects PTH1-84, C-PTH variants (e.g. PTH34-84), and previously unreported c-terminally truncated variants (e.g. 38-77) using MALDITOF-MS. In application, the assay was successful in stratifying renal failure from matched healthy controls (with ROCAUC > 0.90 for individual variants and in multiplexed mode). Accordingly, from a single PTH MSIA spectrum it may be possible to observe an individual’s unique calcium metabolism and bone turnover profile. Furthermore, this assay intrinsically presents the opportunity to identify additional variant forms of PTH that may come to light from the analysis of more differentiated disease states such as hyperparathyroidism.

Future large scale population studies devoted towards more comprehensive screenings of PTH variants specific for disease will have important clinical utility in the understanding and diagnosis of endocrine and bone diseases.
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