Adrenomedullin plasma concentrations in patients
with retinitis pigmentosa
E.M. Vingoloa, S. Lupoa, D. Domanicoa, D. Cotestab, L. Petramalab, R. Grengaa, C. Letiziab,*
aDepartment of Ophthalmology, University of Rome ‘‘La Sapienza’’, Rome, Italy
bDepartment of Clinical Sciences, University of Rome ‘‘La Sapienza’’, Policlinico Umberto I, 00161 Rome, Italy
Received 18 November 2004; received in revised form 9 April 2005; accepted 15 April 2005
Available online 3 June 2005
Purpose: To evaluate the relationship between retinitis pigmentosa (RP) and plasma adrenomedullin (ADM) levels.
Methods: Blood samples were obtained from a group of 40 consecutive patients with RP matched with 35 healthy subjects (HS) as
control. We carried out a complete ophtalmological examination. The study group included 26 patients with RP and 14 patients with
syndromic RP. Plasma ADM levels were determined in duplicate with a specific radioimmunoassay method.
Results: In the HS plasma ADM levels were 13.7 T 6.1 pg/mL. The mean of plasma ADM concentrations in all patients with RP (23.4 T
10.7 pg/mL) was significantly (P < 0.0001) higher than that of HS. Moreover, in the syndromic RP patients, plasma ADM levels (28.6 T
14.35 pg/mL) were higher than those of HS and RP patients (P < 0.0017).
Conclusion: The increase of plasma ADM levels in RP patients may be a response to photoreceptor damage.
D 2005 The Canadian Society of Clinical Chemists. All rights reserved.
Keywords: Adrenomedullin; Retinitis pigmentosa; Syndromic retinitis pigmentosa
Adrenomedullin (ADM) is a novel peptide first isolated
from human pheochromocytoma . ADM has been
detected in plasma [2,3] and other biological fluids [3,4]
from healthy humans and may behave as a circulating
hormone. In plasma, ADM is specifically bound to
adrenomedullin-binding-protein-1 (AMBP-1), identified as
complement factor H . Cytokines, such as tumor necrosis
factor-a, and interleukin-1, lipopolysaccarides, circulating
hormones, such as corticosteroids, thyroid hormones,
angiotensin II, norepinephrine, endothelin-1 and bradykinin,
and physical stress and stretch may stimulate ADM
synthesis and secretion . Studies have revealed that
ADM is widely distributed in various organs and tissues
including the cardiovascular system (myocardium, vascular
endothelium, vascular smooth muscle), lung, kidney, and
endocrine system . ADM is expressed in the outer layer
of the retina, in particular in retinal pigment cells. ADM
dilates retinal arteries, decreases intraocular pressure, and
relaxes the sphincter smooth muscle cells. ADM concen-
tration in vitreous fluid is markedly increased in patients
with proliferative vitreoretinopathy, the most common
complication of retinal detachment originating from pro-
liferation of retinal pigment cells .
Retinal pigment epithelial (RPE) cells are located
between the neural retina and choroids of the eye and form
one component of the blood retinal barrier. RPE cells play
an essential role in the function and survival of photo-
receptors, including phagocytosis of the shed outer seg-
ments of rods and cones and synthesis and transportation of
many substances, such as vitamin A metabolites .
Retinitis pigmentosa (RP) is a primary, chronic, and here-
ditary chorioretinal degeneration characterized by photop-
sia, progressive visual loss with scotoma, and impairment of
dark adaptation . Although molecular biology and
0009-9120/$ - see front matter D 2005 The Canadian Society of Clinical Chemists. All rights reserved.
* Corresponding author. Fax: +39 6 49970524.
E-mail address: firstname.lastname@example.org (C. Letizia).
Clinical Biochemistry 38 (2005) 735 – 738
molecular genetics have identified many causative genes,
the molecular pathophysiology of RP is not fully under-
stood, and no effective treatments have been found yet. The
aim of our study was to investigate the behavior of plasma
ADM concentration in patients with RP and determine the
correlation between ADM and the intensity of retinal
Material and methods
A total of 40 consecutive patients with a diagnosis of
RP (18 F, 22 M, BMI 24.5 T 1.9 kg/m2, mean age 40 T 13
years) with normal renal function and no other medical
problems were enrolled. Several examinations were carried
out on the patients, such as indirect ophthalmoscopic,
manual visual field, electroretinogram (ERG), and visual-
evoked potential (PEV). The diagnosis of RP and all its
variants were made through a careful and experienced
interpretation of all the instrumental examinations. In our
study group, we found 26 patients with RP and 14 patients
with syndromic RP (8 patients affected by Usher’s
syndrome (US), 5 patients with a Cone Rod dystrophy,
and 1 with Laurence–Moon–Bardet–Biedl Syndrome
mean age 40 T 8 years) matched for age, gender, and BMI
were used as the control group. This study was approved by
a local ethic committee, and all subjects were kept in the
supine position for at least 60 min. 10 mL of venous blood
samples was collected from the antecubital vein between 8
and 9 a.m. after overnight fasting. 5 mL of blood was
collected in polystyrene tubes containing EDTA (1 mg/mL)
and aprotinin (500 KIU/mL). Blood samples were then
centrifuged at 3000 ?g at 0-C for 15 min. The plasma was
immediately stored in glass tubes at ?70-C until assayed.
Adrenomedullin (ADM) measurement
Plasma ADM concentration was measured after extrac-
tion and purification of samples in all subjects collected in
the morning after a supine rest of 30 min and stored at
?80-C until analyzed. Briefly, 2 mL of samples was applied
to conditioned Sep-pak C18 centridges (Millipore Corp.,
Waters Chromotography, Milford, MA, USA), and the
column was sequentially washed with 5 mL of isotonic
saline, 5 mL of 0.1% trifluoracetic acid, and 5 mL of 30%
acetonitrile in 0.1% trifluoracetic acid. The adsorbed
material was eluted with 4 mL of 50% acetonitrile, and
the eluted material was lyophilized. After lyophilization,
samples were dissolved in 50 mM phosphate buffer (pH 7.4),
and ADM was measured in plasma by RIA using a
commercial kit (Phoenix Pharmaceuticals Inc., Mountain
View, CA,USA) with rabbit polyclonal antibody raised
against human 1–52, as reported [11,12]. Each measure-
ment was performed in duplicate, and the averages were
reported. The antibody crossreacts 100% with human ADM,
and no crossreactivity was reported with rat ADM, amylin,
CGRP, endothelin-1, and a-atrial natriuretic peptide. The
two intra- and inter-assay coefficients of variance were 5.1%
and 12%, respectively. Recovery of synthetic human ADM
1–52 was 84.5%. The sensitivity of the assay was 2 pg/mL.
All results are expressed as mean T standard deviation
(SD). The statistical calculation was performed using
‘‘Primer’’ Software (Primer of Biostatistics, S.A. Glanz,
Fig. 1. (a) The scattered adrenomedullin (ADM) plasma values in patients with retinitis pigmentosa (RP), syndromic retinitis pigmentosa (syndromic RP), and
healthy subjects (HS). (b) Mean (TSD) plasma adrenomedullin (ADM) levels in patients with RP, syndromic RP, and HS.
E.M. Vingolo et al. / Clinical Biochemistry 38 (2005) 735–738
McGraw-Hill, San Francisco, USA). The individual values
were inserted by group on the spreadsheet and were inserted
by a non-parametric ANOVA test and Bonferroni’s t test,
where appropriate. The study of correlation was performed
by the Spearman test. A P value < 0.05 was considered
In the HS plasma, ADM levels ranged from 3.1–19.9
pg/mL, averaging 13.7 T 6.1 pg/mL. Mean plasma ADM
levels in all patients with RP (23.4 T 10.7 pg/mL) were
significantly higher (P < 0.0001) than those of HS (Fig.
1b). Fig. 1a shows the scattered values of plasma ADM
concentrations in all studied groups. ADM levels were
increased in all the RP subgroups: US patients (28.7 T
10.9 pg/mL) and Cone Rod patients (29.1 T 21.2 pg/mL).
The patient with LMBB showed high plasma ADM (26.1
pg/mL). Considering the whole sample for the syndromic
RP, the mean plasma level of ADM was 28.7 T 14.3 pg/
mL, and this value was significantly higher than those of
HS (13.7 T 6.1 pg/mL) and RP patients (23.4 T 10.7 pg/
mL) (P < 0.0017, respectively) (Fig. 1b). The study
correlation between pigmentary grading and ADM plasma
levels did not find a statistically significant correlation (r =
?0.09; P = 0.6). Table 1 shows the medians and
percentiles of ADM of our tapetoretinal degeneration
The current study was designed to assess the behavior of
plasma ADM levels in patients with RP. Our data revealed
an increase of plasma ADM concentrations in patients with
RP compared to HS, in particular in patients with syndromic
RP. These findings suggest that ADM may play a role in the
pathophysiology of the diseases that involve the retinal
pigment epithelial (RPE) cells such as RP.
Whereas ADM was first isolated from pheochromocy-
toma tissue and the concentration of the peptide is high in
the adrenal medulla , current evidence points to vascular
tissue, particularly endothelial cells , as likely being the
major source of circulating ADM in plasma . Moreover,
ADM is expressed in the outer layer of the retina, in
particular in retinal pigment cells .
Udono et al.  have demonstrated that human RPE
cells produce and secrete ADM and revealed that ADM
secreted from RPE cells, after treatment with cytokines
(IFN-g and IL-1h), plays an important role in some
inflammatory or degenerative diseases of the eyes. More-
over, these researchers demonstrated that hypoxia induced
the expression of ADM in human RPE cells  and
exogenously added ADM abolished the decrease in the
number of the hypoxia-induced RPE cells . These
findings suggest that ADM may have a protective effect
against hypoxic damage of the RPE cells.
Our data do not show a relation between pigmentary
grading and ADM plasma levels; in our view, this is
probably because pigmentation is not a parametric
variable so that we need more samples to achieve
significance. Moreover, pigmentation grading may also
depend on other patient characteristics such as iris color,
skin pigmentation, and refraction and consequently might
have variation that is not dependent upon ADM plasma
The increase of plasma ADM levels revealed in our RP
patients may be a response to photoreceptor damage, such
as scarring within the retina or may be due to a protective
effect on photoreceptor cells damaged by an altered photo-
transduction process. Moreover, the ADM production in
response to hypoxic stress may mimic the metabolic damage
secondary to the phototransduction alteration [10,17,18]. In
fact, some authors [15,16,18] demonstrated that the supple-
mentation of oxygen or vitamin A in patients with RP may
slow the degenerative process. The amount of ADM
produced by the eye, in particular by the RPE cells, might
seem to be small compared to the plasma compartment.
According to data presented by Udono et al. , this might
be explained by a secretion proportional to metabolic
damage that retinal tissue receives and in the case of
retinitis pigmentosa, retinal damage reaches 85–90% of the
We thank Mr. Giovanni Clemente for his technical
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