89immunoassays unable to discriminate between full-length CgA and fragments, vary
within the 0.5–2 nM range, depending on the different antibodies and reagents used
(Helle et al. 2007 ). Increased levels of circulating CgA have been detected in
patients with carcinoids or with other neuroendocrine tumors (O’Connor and
Bernstein 1984 ; O’Connor and Deftos 1986 ). Elevated serum levels have been
detected also in subpopulations of patients with breast, prostate or non-small cell
lung cancer, or in patients with renal failure, hypertension, atrophic gastritis, sepsis
and other inflammatory diseases (Helle et al. 2007 ; Taupenot et al. 2003 ; O’Connor
and Bernstein 1984 ; Ligumsky et al. 2001 ; Waldum and Brenna 2000 ; O’Connor
et al. 2000 ; Syversen et al. 2004 ; Borch et al. 1997 ; Zhang et al. 2009 ; Di Comite
et al. 2009b; Castoldi et al. 2010 ). Circulating CgA is markedly increased also in
patients with heart failure, depending on the severity of the disease, or with rheuma-
toid arthritis (Pieroni et al. 2007 ; Di Comite et al. 2009a; Ceconi et al. 2002 ). In
patients with heart failure and rheumatoid arthritis CgA correlates with soluble
tumor necrosis factor receptors (sTNF-Rs), which are sensitive markers of inflam-
mation (Corti et al. 2000 ). Furthermore, increased levels of serum CgA have been
detected in subjects treated with proton pump inhibitors, a class of drugs commonly
used to treat acid-peptic disorders (Giusti et al. 2004 ; Sanduleanu et al. 1999 ).
Thus, several pathological conditions are characterized by variable and abnormal
plasma levels of CgA, for a variety of reasons. This implies that endothelial cells,
either close to CgA-secreting cells or distant, are exposed to variable levels of this
protein.
Hematological studies performed with a series of enzyme-linked immunosor-
bent assays (ELISA) capable of discriminating between intact and cleaved mole-
cules showed that various CgA-derived polypeptides are present in the blood of
healthy subjects, consisting of full-length CgA (about 0.1 nM) and a larger propor-
tion of fragments lacking part of, or the entire, C-terminal region (Crippa et al.
2013 ). In addition, normal plasma contains a considerable amount of vasostatin-1
(about 0.3–0.4 nM) (Crippa et al. 2013 ). Other fragments, not detected by these
assays, might be also present. For example, catestatin has been reported to be pres-
ent in the blood of normal subjects at concentrations ranging from 0.03 nM (Ji et al.
2012 ) to 0.33 nM (Meng et al. 2013 ). The discrepancies between these values might
be related to the use of different antibodies that detect catestatin as well as uncleaved
precursors with different efficiency.
Although many reports describe the levels of circulating CgA in different patho-
logical conditions, it is important to remark that most studies have been performed
with immunoassays unable to discriminate between full-length CgA and fragments.
Thus, only few studies have addressed the circulating levels of CgA fragments in
pathological conditions. One of these studies has shown that VS-I plasma levels are
increased in critically ill patients and that VS-I concentrations >0.44 nM (i.e. >1.4-
fold higher than normal values), are associated with poor outcome (Schneider et al.
2012 ). Other investigators showed a reduction of CgA processing in patients with
diabetic retinopathy (Fournier et al. 2011 ). Studies on the catestatin region, per-
formed with an anti-catestatin antibody capable of cross-reacting with free peptide
and full-length CgA, showed a reduction of immunoreactivity in patients with
Chromogranin A in Endothelial Homeostasis and Angiogenesis