Washington, Jan 31 : A new mouse study has suggested that a hormone, that has long been known to boost red-blood-cell production, called Erythropoietin, also keeps blood vessels alive and growing in the eye.
However, the findings of the study, which was led by Lois Smith, MD, PhD, an ophthalmologist at Children's Hospital Boston, has suggested that the hormone may worsen the conditions of patients with anaemia.
The results have also raised doubts before prescribing it to patients with diseases affected by abnormal blood-vessel growth, such as retinopathy and cancer. It also found that the hormone's risk or benefit depends on the timing of administration.
For the study, Smith and his colleague Jing Chen, PhD, worked in mice with retinopathy, an eye disease that begins after the death of healthy blood vessels nourishing the retina. Numerous vessels then grow in, but they are deformed. Ultimately, the deformed vessels may pull the retina off the back of the eye, causing blindness.
After measuring erythropoietin produced in the retina as the disease progressed, the researchers found that the production was 3 to 10 times below normal during early-stage retinopathy, when healthy blood vessels died, and 12 to 33 times above normal during late-stage retinopathy, when deformed blood vessels grew into the retina.
It was concluded that erythropoietin helps blood vessels survive and grow in the retina, with effects that may be healthy or harmful.
The next step was to examine whether the administration of erythropoietin could treat retinopathy. For this, erythropoietin was injected into the bloodstream either early, as the mice lost healthy blood vessels, or later, when deformed blood vessels began to invade--then compared them with untreated mice.
Early bolstering of erythropoietin slowed the disease, leading to the mice losing almost half of healthy blood vessels, causing about 30 pct fewer deformed vessels to grow in.
Raising erythropoietin levels later, when deformed blood vessels were present, seemed to accelerate the disease; slightly more deformed blood vessels grew in.
Smith suggested that if similar effects are found in humans, and its use is properly timed, then giving erythropoietin early could slow loss of healthy blood vessels in retinopathy.
"Right now, there is very little out there to treat blood vessel loss in patients with retinopathy. However, further studies on the restoration of normal levels of erythropoietin are needed to translate these results to patients," she said.
She added that in other diseases, like cancer, in which doctors need to slow blood vessel growth, the hormone could be blocked, although clinical trials would need to confirm this idea.
However, she said that administering erythropoietin at the wrong time may make blood vessels grow in an unhealthy way.
For example, because it boosts red blood cells, erythropoietin is often prescribed to premature babies and diabetic adults for anaemia. Some of these patients also have retinopathy.
Administering the hormone at the wrong time might help anaemia, but worsen the eye disease.
"We're not saying, 'don't do it.' We're saying, 'think about it'. Physicians should look at the state of the eye before giving erythropoietin to patients with retinopathy. They should consider not giving it to patients with full-blown retinopathy, in which abnormal vessels are present, because our work suggests it may accelerate the disease. However, if a patient is early on in the disease, then our work suggests erythropoietin may be beneficial," she said.
She also added that Cancer patients, who often take erythropoietin for anemia, face a similar potential risk.
"Since erythropoietin has the potential to make blood vessels in tumors grow, it could make tumors worse, although a clinical trial is required to know if this is true in humans."
The study was published in the recent issue of the Journal of Clinical Investigation.