The most common cause of blindness is the explosive growth of blood vessels near the retina, and scientists may have a finger key culprit in this process: growth hormone. The findings, reported in today's issue of Science * could lead to an alternative to drug-based laser surgery, the current treatment of this form of blindness that often strikes people with diabetes and children born prematurely.
There are fifty years, doctors have found that removal of the pituitary gland could restore vision in some blind diabetics. But the loss of the plant hormone - which produced a number of chemicals essential for metabolism, including growth hormone - makes people tired, intolerant of stress, and susceptible to infections. Today, the treatment of choice is laser surgery, but it can partially destroy the retina and decrease peripheral vision, and not always successful in restoring sight.
The search for a less risky treatment, a team led by Lois Smith, a pediatric ophthalmologist at Harvard Medical School and Children's Hospital Boston, hungry mice of oxygen, which induces growth of blood vessels near the retina, the layer of cells that captures light for forming images. Blood leaking from blocks light of new vessels from reaching the retina. "Even more devastating, leaking vessels form scar tissue, which pulls the retina at the back of the eye and leads to total blindness," says Smith.
team induced by the blood of the Smith growth of vessels in normal mice and mice genetically to express a gene for a protein that inhibits the growth hormone. the dwarf transgenic mice had 34% less growth of new blood vessels that checks had. the team Smith then injected normal mice with MK678, a hormone drug growth suppression, and found that reduced blood vessel growth up to 44%. Smith suspect that growth hormone triggers the growth of blood vessels by stimulating another hormone, insulin-like growth factor-I, and indeed, infusing the mice with IGF-I washed the beneficial effects of the drug.
experts applaud the results . "Before, it was only an assumption that hormones did the damage," said David Clemmons, an endocrinologist at the University of North Carolina, Chapel Hill. Now, he says, the study "proves unequivocally" that growth hormone is involved. But Smith and others warn that the development of a drug to fight against this form of blindness will not be easy: the growth of blood vessels is required for processes such as wound healing and repair heart tissue after a heart attack . Thus, any new drug must seek growth in the retina and allow growth hormone to work in peace elsewhere in the body.
* For details, Science Online subscribers can link to the full report.
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