Experts Close in on Diabetic Retinopathy Cause
Researchers have found that a long-suspected molecule helps
cause diabetic retinopathy, one of the leading causes of vision loss in the
US, according to a report in the New England Journal
of Medicine.
Some 700,000 Americans have diabetic retinopathy, with 63,000
new cases and 5,000 cases of diabetes-caused blindness every year, the authors
say.
Diabetic retinopathy is caused by changes in the blood
vessels of the retina. In some people with diabetic retinopathy, retinal blood
vessels may swell and leak fluid, while in others, abnormal new blood vessels
grow on the surface of the retina. These changes may result in vision loss
or blindness.
Diabetic retinopathy cannot be completely avoided, but the
risk can be greatly reduced. Better control of blood sugar level slows the
onset and progression of retinopathy and reduces the need for laser surgery
for severe retinopathy.
A person with an early stage of diabetic retinopathy may
be asymptomatic [without symptoms] and without pain. Vision may not change
until the disease progresses.
A condition called macular edema may occur when the macula,
a part of the retina, swells from the leaking fluid and causes blurred vision.
When new vessels grow on the surface of the retina, they can bleed into the
eye, blocking vision.
The molecule found to be associated with diabetic retinopathy
is erythropoietin, a protein hormone whose main function is to stimulate formation
of red blood cells. The study by researchers at Kyoto University in Japan found
excessively high levels of erythropoietin in the eye fluid of patients with
diabetic retinopathy.
The 73 patients in the study, all of whom had diabetes,
were in the last stages of retinopathy, in which overgrowth of blood vessels
in the eye destroys vision. Levels of erythropoietin were more than 12 times
higher in their eyes than in the eyes of 71 people without diabetes whose levels
were also measured.
But the study also found that erythropoietin is just part
of the molecular conspiracy that destroys vision in the diabetic eye.
The researchers detected extremely elevated levels of vascular
endothelial growth factor (VEGF), another molecule that has long been identified
as a contributor to diabetic retinopathy by stimulating blood vessel growth.
VEGF will occur in 60 percent of persons with diabetes unless
something is done to prevent it, says an accompanying editorial in the journal
by Dr. Lloyd Paul Aiello, who heads the section on eye research at the Joslin
Diabetes Center in Boston.
"This is the first time folks have shown with extensive
human data that erythropoietin is involved in diabetic retinopathy," Dr. Aiello
notes. "Its action is independent of that of VEGF."
Attention has been focused on VEGF. Several medications
designed to block its action are in advanced testing, and one has been approved
by the US Food and Drug Administration (FDA) for
use against a different cause of blindness, age-related macular degeneration,
he says.
"But preclinical data suggests that VEGF might not be totally
responsible, and this work now points out that another molecule is independently
involved," Dr. Aiello says.
The finding opens a new area of research, he says, adding
that "a good deal of work needs to be done to see if inhibiting erythropoietin
can have a beneficial effect."
One issue is the safety of blocking erythropoietin in persons
with diabetes, since there are studies indicating that it also acts to protect
the retina from damage during times of stress, he explains.
"This is groundbreaking work," says Dr. John Loewenstein,
associate chief of ophthalmology at the Massachusetts Eye and Ear Infirmary. "And
like all groundbreaking work, it has to be confirmed by others. First it has
to be confirmed by more experiments, and then we can look for inhibitors of
erythropoietin."
Always consult your physician for more information.
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