Search

Endogenous peptides – naturally secreted by the body – are of significant interest in the clinical field due to their utility as diagnostic tools. The idea is that some diseases alter the secretion or metabolism of certain peptides, leading to changes in concentrations found in the blood. If these concentrations are measurable, it becomes possible to diagnose a patient based on values deviating from those found in a healthy population. Three main challenges mark the development of these assays. Endogenous peptides circulate at extremely low concentrations, are rapidly metabolized into smaller fragments, and undergo chemical and physical degradations that alter their concentration. Thus, it requires highly sensitive and specific methods coupled with pre-analytical management ensuring peptide stability from collection to extraction to obtain reliable results. Recently, Neuropeptide Y (NPY) has emerged as a potential biomarker for prostate cancer and pheochromocytoma. Moreover, angiotensins (ANGs) are peptides at the core of the blood pressure regulation system, making them highly relevant in managing hypertension. The goal of this thesis was to develop methods for the quantification of NPY and its fragments (NPYs), as well as angiotensins, and apply these assays to healthy populations to establish reference values. Subsequently, they were applied to populations suspected of prostate cancer, pheochromocytomas, or hypertension-related conditions to evaluate the diagnostic potential of these peptides. This thesis demonstrates that NPYs are not superior to metanephrines, the current gold standard, for pheochromocytoma diagnosis, but they may be valuable when metanephrine assays are not feasible. NPYs also do not enhance prostate cancer diagnosis, but their use in a population with specific PSA values, the current gold standard, has shown improved diagnostic specificity. Finally, our method for angiotensin assays is the first to thoroughly investigate the impact of pre-ana

Neuropeptide Y (NPY1-36) is a vasoconstrictor peptide co-secreted with catecholamines by sympathetic nerves, the adrenal medulla, and neoplasms such as pheochromocytomas and paragangliomas (PPGLs). It is produced by the intracellular cleavage of proNPY and metabolized into multiple fragments with distinct biological activities. NPY immunoassays for PPGL have a diagnostic sensitivity ranging from 33 to 100%, depending on the antibody used. We have validated a multiplex micro-UHPLC-MS/MS assay for the specific and sensitive quantification of proNPY, NPY1-39, NPY1-37, NPY1-36, NPY2-36, NPY3-36, NPY1-35, NPY3-35, and the C-flanking peptide of NPY (CPON) (collectively termed NPYs), and determined the NPYs reference intervals and concentrations in 32 PPGL patients before, during, and after surgery. Depending on the peptide measured, NPYs were above the upper reference limit (URL) in 20% to 67% of patients, whereas plasma free metanephrine and normetanephrine, the gold standard for PPGL, were above the URL in 40% and 87% of patients, respectively. Age, sex, tachycardia, and tumor localization were not correlated with NPYs. Plasma free metanephrines performed better than NPYs in the detection of PPGL, but NPYs may be a substitute for an early diagnosis of PPGL for patients that suffer from severe kidney impairment or receiving treatments that interfere with catecholamine reuptake.