A small new study offers proof of concept in treating
boys who have Duchenne Muscular Dystrophy with Viagra and Cialis, which both
inhibit the enzyme phosphodiesterase type 5.
by John
Tyburski
Copyright © Daily Digest News, KPR Media, LLC. All rights reserved.
Researchers
at Cedars-Sinai Medical Center reported Wednesday that in a small group of boys
with Duchenne muscular dystrophy (DMD), the erectile dysfunction treatment
drugs sildenafil (Viagra) and tadalafil (Cialis) helped to normalize the blood
flow in exercising muscle, which is markedly impaired in DMD. The study also
revealed that the ability of DMD patients’ muscles to receive increased blood
flow during exercise by way of reduced sympathetic tone is impaired and not
improved by current standard of care treatments with corticosteroids alone or
in combination with heart-protecting medication.
Duchenne
muscular dystrophy is a genetic disorder that affects boys and young men. The
disease results from the patient’s inability to produce sufficient amounts of a
protein called dystrophin, which is integral in the synthesis of nitric oxide.
Nitric oxide is crucial for signaling blood vessels to open up and allow more
blood to flow through them during exercise so that the working muscle’s energy
and oxygen demands are met and wastes and carbon dioxide are adequately
removed.
“Boys with
Duchenne muscular dystrophy have a blood flow abnormality — delivery of blood
and oxygen to their muscles — that does not increase the way it should during
mild exercise,” said lead researcher Dr. Ronald Victor, the associate director
of the Cedars-Sinai Heart Institute in Los Angeles.
For DMD
patients, the future has for a long time been grim. Boys with DMD historically
did not live beyond their teens. More recently, their lives are extending into
their 30s and in some cases even into their 40s and 50s. Advances in care are
credited. Steroidal treatments can slow muscle degeneration and protect the
heart and lungs. However, there is no cure, and resolving the blood flow
problem has remained elusive.
What is
significant about this new study, which was conducted with 10 boys aged 8 to 13
years with DMD and 10 healthy control boys, is that the authors identified as a
new protein target for DMD therapy the target of both Viagra and
Cialis—phosphodiesterase type 5 (PDE5). Inhibition of PDE5 by either Viagra or
Cialis results in decreased sympathetic tone, which allows blood vessels to
dilate, or open up. Dilation of blood vessels once sympathetic tone is reduced
increases blood flow through the vessels.
“A few boys
in our study had erections after taking these drugs,” Victor noted. “The
erections were not painful and not dangerous and resolved spontaneously without
treatment.”
According to
Victor, the study paved the way for a much larger study to confirm the results
and to determine whether targeting PDE5 can prevent or at least slow the
degeneration associated with DMD.
The report was
published in the May 7 issue of Neurology.
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