New
Service for TodaysSeniorsNetwork.com
readers...roll mouse over, click on
highlighted links in stories to review items
from Amazon
Now, keep up to date
with daily feeds of newly posted stories
about America's Seniors...click on the box
to the left
Protein
transports nutrients believed to protect
against Eye Disease
Newswise — Scientists have
identified the protein responsible for
transporting nutrients to the eye that are
believed to protect against the development
of age-related macular degeneration, a
leading cause of vision loss in elderly
Americans.
The research sought to
illuminate the process by which compounds
called lutein and zeaxanthin move from the
bloodstream to the eye.
Various studies have
suggested that high concentrations of these
two dietary compounds in particular, known
as xanthophylls, have properties that can
prevent macular degeneration.
These two nutrients are not
made by the body and must be obtained
through the diet. They are commonly found in
green, leafy vegetables, such as kale,
spinach, broccoli, zucchini and peas, and in
yellow or orange fruits and vegetables, such
as carrots, papaya, squash and peaches.
According to the study, the
protein SR-B1, or scavenger receptor class
B, type 1, plays a central role in
transporting these nutrients from the
bloodstream to cells in the eye.
“Our research to understand
this mechanism might provide a greater
appreciation for how one could intervene to
possibly slow macular degeneration,” said
senior study author Earl Harrison, Dean’s
Distinguished Professor and chair of human
nutrition at Ohio State University.
An estimated 10 million
Americans have age-related macular
degeneration, which gradually destroys
sharp, central vision.
The macula is located in the
center of the retina, the light-sensitive
tissue at the back of the eye that sends
nerve signals to the brain.
Deterioration of the macula
blurs the central field of vision needed to
drive and read. Treatment can slow vision
loss, but does not restore vision, according
to the National Eye Institute.
The research appears in the
August issue of the Journal of Lipid
Research.
Xanthophylls are a class of
carotenoids, naturally occurring pigments
that absorb blue light and sometimes
function as antioxidants.
Several studies have
suggested that the ability of lutein and
zeaxanthin to filter out damaging blue
light, combined with their antioxidant
properties, might protect against macular
degeneration.
The xanthophylls are known to
accumulate in the macula region of the
retina to form a yellow spot, and are
referred to as macular pigment.
Though this xanthophyll
concentration in the retina has been
observed and associated with a lower risk
for the disease, the cause of macular
degeneration and the precise role these
compounds play in protecting against vision
loss remain a mystery.
But Harrison and colleagues
had observed in their previous work that
SR-B1 was involved when intestinal cells
absorb these nutrients from the diet, and
believed that the same transporter would be
needed to help the nutrients travel to cells
in the eye as well.
Lutein and zeaxanthin
typically represent about 80 percent of the
total carotenoid content of the retina,
while beta-carotene, a major dietary
carotenoid, is found in only trace amounts.
That high concentration of
one type of carotenoid over another also
suggested that a specific binding protein
would be involved in the absorption process,
Harrison said.
The scientists worked with a
line of human retinal pigment epithelial
cells from the lining of the retina, which
served as a model for how macula cells
function.
The researchers introduced to
these cells three types of carotenoids
typically found in eye cells – the
xanthophylls lutein and zeaxanthin, as well
as beta carotene.
As expected, the retinal
pigment epithelial cells absorbed much more
of the xanthophylls than the beta carotene.
To test the role of the SR-B1
transporter, the researchers used two
different methods to block the protein’s
action.
Under both experimental
circumstances, blocking the SR-B1 protein
also blocked the cells’ absorption of the
two xanthophylls by between 41 percent and
87 percent compared to absorption when SR-B1
activity was not inhibited.
“It’s fairly safe to say that
if you inhibit this transporter, you inhibit
the uptake of xanthophylls.
"So
that certainly suggests that this
transporter is involved in that process,”
Harrison said.
Harrison conducted the work
with postdoctoral fellow Alexandrine During,
now at the Université Catholique de Louvain
in Belgium, and Sundari Doraiswamy, a
support scientist in Harrison’s laboratory
when he was at the U.S. Department of
Agriculture’s Human Nutrition Research
Center in Beltsville, Md.
The research was supported by
grants from the National Institutes of
Health.”
...
...
...