Processing-independent analysis of peptide hormones and prohormones in plasma.

Peptide hormones are post-translationally matured before they reach a structure in which they can fulfill their biological functions. The prohormone processing may encompass a variety of endoproteolytic cleavages, N- and C-terminal trimmings, and amino acid derivatizations. The same prohormone can be variably processed in different cell types and, in addition, diseased cells often change the processing of a given precursor. The translational process is often either increased or decreased in diseased cells, which renders the ensuing modifications of the prohormone incomplete. Consequently, a variable mixture of precursors and processing-intermediates accumulates in plasma. In order to exploit disturbed posttranslational processing for diagnostic use and at the same time provide an accurate measure of the translational product, a simple analytical principle named "processing-independent analysis" (PIA) was designed. PIA-methods quantitate the total mRNA product irrespective of the degree of processing. PIA-methods have now been developed for a number of prohormones and proteins, and their diagnostic potential appears promising in diagnosis of cardiovascular disease and in several malignancies.