Download Researchers report continued progress in studies of AMD

John W Crabb
Cheryl Guttman
in Fort Lauderdale
PEPTIDOMIC analysis of plasma may allow
early identification of AMD risk as well as a
method for monitoring the efficacy of AMD
therapeutic interventions, according to
researchers from the Cleveland Clinic Cole
Eye Institute.
“Although progress is being made in
identifying AMD susceptibility genes,
environmentally induced oxidative stress is
also thought to play a role in the
development and progression of the
disease.We are hoping that our research to
identify oxidative modifications as AMD
biomarkers will lead to the availability of
diagnostic technology that will allow
detection of persons at risk for AMD
before the disease becomes clinically
evident,” said Jiayin Gu, a graduate student
in the laboratory of Dr John W Crabb,
Cole Eye Institute, Cleveland Clinic,
Cleveland, OH.
Research to discover biomarkers for
AMD is ongoing at the Cole Eye Institute
under the direction of John W Crabb PhD.
The investigators presented their most
recent findings at the annual meeting of the
Association for Research in Vision and
Ophthalmology (ARVO).
In early work, they showed the presence
of carboxyethylpyrrole (CEP) adducts in
drusen, and subsequently, they determined
levels of the CEP oxidative protein
modifications were significantly higher in
various ocular tissues derived from AMD
eyes compared with eyes of normal human
donors (2002 Proc Natl Acad Sci USA 99,
14682). Interest in the CEP adducts as a
potential AMD biomarker was based on
knowledge that these protein modifications
are uniquely generated through oxidative
fragmentation of docosahexaenoatecontaining lipids that are abundant in the
photoreceptor outer segments of the
retina. Further support was derived from
studies showing that CEP adducts were
generated by intense light exposure in
animal models, were elevated in plasma
from AMD patients (2003 J Biol Chem 278,
42027) and stimulated neovascularisation in
vivo (2006 Proc Natl Acad Sci USA 103,
13480).
“These findings led to our hypothesis
that CEP oxidative protein modifications
play a role in the development of choroidal
neovascularisation in late stage AMD and
may be a primary catalyst in triggering
immune responses,” said Dr Crabb, who is
a professor, in the Departments of
Ophthalmology and Molecular Medicine,
Cleveland Clinic Lerner College of
Medicine of Case Western Reserve
University, and in the Department of
Chemistry, Case Western Reserve
University.
At the 2007 ARVO meeting, the
researchers reported on findings from
ELISA analyses of plasma samples from 732
AMD patients (AREDS categories 2, 3, and
4) and 171 unaffected, age-matched
controls that corroborated their previous
work showing elevated CEP
immunoreactivity (~50 per cent) and CEP
autoantibody titres (~30 per cent) in the
AMD patients relative to the normal
controls.They also reported that plasma
samples from 98 AMD patients and 100
age-matched normal donors exhibited
immunoreactivity for nitrotyrosine that was
about ~30 per cent higher in the AMD
specimens compared with the controls.
“Nitrotyrosine is an oxidative stressinduced modification of protein tyrosine
Retina Update
Researchers report continued
progress in studies of AMD biomarkers
that we have also shown is generated in the
retina after intense light exposure in animal
eyes,” said Dr Crabb.
The investigators also presented
encouraging results using peptidomic mass
analysis to discriminate between AMD
plasma and normal control samples.Their
methods use anti-CEP monoclonal
antibodies attached to magnetic beads to
fractionate the plasma samples and recover
CEP adducted peptides.Then, MALDI TOF
mass spectrometry and bioinformatic
methods are applied to characterise
differences between the peptide profiles of
the plasma samples from the AMD patients
and unaffected controls.
The mass spectrometry peptide pattern
analysis was performed using plasma
samples from 90 AMD patients and 80
controls seen at the Cole Eye Institute or
the Louis Stokes Veteran Affairs Medical
Centre in Cleveland.That technique allowed
93 per cent correct classification of the
plasma sample donor with 98 per cent
sensitivity and 88 per cent specificity.
[email protected]
21