22
| 1 | 2012
Klinisk Biokemi i Norden
Copeptin: A new peptide in clinical measurement
Ola Hammarsten
1
and Jens P. Goetze
2
1
Department of Clinical Biochemistry, Sahlgrenska University Hospital, Göteborg, and
2
Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen.
Plasma measurement of the peptide hormone vaso-
pressin (AVP) has proven difficult in routine labora-
tories. Vasopressin is a nonapeptide produced in the
hypothalamus and released to circulation from the
pituitary gland (figure 1). In circulation, vasopres-
sin regulates several biological functions including
peripheral vasoconstriction (via V
1
receptors) and
renal water retention (via V
2
receptors). Vasopressin
is also a potent stimulator of endothelial von Wil-
lebrand release. For clinical use as a plasma marker,
vasopressin measurement has been hampered by its
marked instability in vitro, strong binding to throm-
bocytes and small peptide size preventing measure-
ment by sandwich immunoassays. Plasma vasopres-
sin measurement has consequently been used mainly
for research purposes and is not on the standard
analytical repertoire in most hospital laboratories.
Human vasopressin is derived from provasopressin,
which is a 145 amino acid residue precursor. Besides
vasopressin, the precursor structure contains two
other peptide fragments: Neurophysin II and copeptin
(
figure 2). Copeptin is the C-terminal part of prova-
sopressin and constitutes 39 amino acids. Copeptin is
covalently modified and stored in the posterior region
of the pituitary gland as a glycopeptide (1). Copeptin
and vasopressin are co-secreted to the circulation
upon relevant stimulus and copeptin thus represents
a surrogate marker of vasopressin release (2). A well-
established analogy in routine measurement is the
C-peptide, which is derived from proinsulin and
used as a surrogate marker of endogenous insulin
production.
Copeptin plasma measurement is a relatively new
entity, which is reflected in the few research papers
published so far (September 2011: n = 153 via Pub-
Med). Basically, most papers are based on measure-
ment in plasma samples from already collected clinical
studies. Biochemical and physiological data are still
needed on molecular forms in plasma and the eli-
mination phase. Nevertheless, the published data are
encouraging in especially cardiovascular disease, and
the present mini-review aims at summarizing the most
interesting applications in human medicine.
Figur 1
:
Copeptin production, axonal transportation and
pituitary secretion (modified with permission from Nils
Morgenthaler)
