Identification of an Adrenomedullin precursor fragment in plasma of sepsis patients

Abstract

Adrenomedullin and PAMP are potent vasodilatory peptides derived from a common larger precursor peptide. Elevation of circulating levels of both peptides has been described for diseases involving dysfunction of the cardiovascular system. However, the reliable quantification has been hampered by their short half-life times and – as known for Adrenomedullin – the existence of a binding protein. Here we report the identification of another peptide derived from the Adrenomedullin precursor, termed proADM 45–92, which is present in large concentrations in plasma of septic shock patients. This peptide is produced in stoichiometric amounts to Adrenomedullin and PAMP, but – contrary to them – is apparently non-functional and stable. Thus, proADM 45–92 represents a suitable diagnostic target which could be used to assess the concentrations of Adrenomedullin gene products released into the bloodstream.

Introduction

Adrenomedullin (ADM) is a 52 aminoacids comprising peptide with multiple functions, the most prominent being its strong vasodilatory acitivity [2], [6]. ADM is derived from a larger precursor (preproADM, 185 aminoacids) by posttranslational processing, presumably following a scheme which is generally known for the maturation of various biologically active peptides (Fig. 1) [7]. Besides ADM, another biologically active peptide termed PAMP (proadrenomedullin N-terminal 20 peptide) is generated from preproADM. Similar to ADM, albeit by a different mechanism, PAMP has a strong hypotensive effect [2].

From the processing scheme of preproADM two other peptides can be predicted to be produced, that is the region located between PAMP and ADM, and the region flanking ADM at its C-terminus (Fig. 1). These peptides, termed proADM 45–92 and proADM 153–185 (also known as Adrenotensin), have not been described in the blood circulation so far, but have been synthesized chemically and assessed for their potential function in vitro: while Adrenotensin was found to be vasoconstrictive, no effect of proADM 45–92 was observed [3].

Quantification of ADM gene products would be helpful in the diagnosis, monitoring and prognosis of various cardiovascular diseases and sepsis, for which elevated plasma concentrations of ADM have been described [8], [13]. However, the reliable measurement of ADM is hampered by the existence of a binding protein [12], a short half-life time and extreme physical properties [9]. From their described biological functions it can be inferred, that the accurate quantification of PAMP and Adrenotensin might not be readily achievable as well.

No information exists so far on the fate of endogenous proADM 45–92, whether or not it is subject to further processing steps, whether or not it is rapidly cleared, whether or not it is present in the blood circulation. If present, it could be a highly interesting diagnostic target reflecting the actually released levels of the ADM gene products. Thus, we set out to determine its presence in plasma of septic shock patients.