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NSF PR 97-45 - June 18, 1997
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Researcher Closing in on Birth Control Pill for Men
Love May Indeed Be Blind
It's often been said that love is blind. Now a scientist
is hoping that he has found a way to apply that old
saying to a new method of family planning. Joseph
Hall, a biochemist at North Carolina State University
in Raleigh, is unlocking the secrets of sperm, and
closing in on a possible birth control pill for men.
The scientist, whose research is supported by the
National Science Foundation's division of integrative
biology and neuroscience, has taken the next step
in his quest to develop a male contraceptive. Hall
has recently developed a synthetic chemical compound
that "blinds" sperm. "I've worked on this for more
than ten years," he says, "and now I feel that we're
getting close to identifying a beginning point for
sperm-targeted contraceptive development."
Hall found that the compound, a sugary substance,
inhibits 98 percent of the enzymatic activity needed
for sperm maturation and fertility in male rats, without
altering their hormonal balance. He's now testing
the compound on bull and human sperm, with results
thus far "very promising." A patent application has
been filed on the sugar analog, and on two similar
compounds.
"The sugar analog appears to have a short onset of
action, negligible effects on the libido, and no residual
effect on fertility after the dosage has been discontinued,"
says Hall.
His analog works by inhibiting the activity of the
'B' form of the N-acetyl-beta-D-hexosaminidase enzyme,
which is secreted and inserted into sperm cells after
they leave the testis, where they are created. They
then move into a long, tubelike organ called the epididymis.
The analog gives sperm cells the ability to recognize,
bind with and penetrate egg membranes, resulting in
fertilization. The enzyme's two variant forms, 'A'
and 'B,' perform the same physiological function.
But the main difference, explains Hall, is that while
both forms are found in all other cells, sperm cells
contain only the 'B' type.
"The 'B' variant gives sperm its 'eyes,' so to speak,"
he says. "When you inhibit it, you essentially create
blind sperm that cannot recognize eggs. But because
you're not inhibiting the 'A' variant, you're not
preventing the enzyme from performing its necessary
physiological function in the rest of the body."
In addition to in vitro (test tube) experiments on
rat sperm, which show that the analog inhibits 98
percent of the enzymatic activity required for egg
recognition, Hall also has demonstrated that his analog
blocks fertilization by about 90 percent when given
to rats orally, or in vivo.
"However, we do not fully understand if the same mechanism
that occurs in vitro also occurs in vivo, since we
have not yet performed experiments to determine how
the compound is metabolized," he explains.
Additional work will be needed before scientists can
know for sure whether the analog is safe and effective
on humans, but Hall's recent discoveries take researchers
one step closer to a male contraceptive.
Most research, up to this point, has focused on chemical
or endocrinologic manipulation of sperm in the testis,
he says, which studies have shown can cause hormonal
imbalances and other undesirable side effects. "By
targeting sperm after it has reached the epididymis,
we don't have to mess with male hormones at all."
Hall is a father of six. Early in their marriage,
when Hall and his wife discussed contraception as
a young couple, there were relatively few options
available. His wife challenged him to develop a safe,
effective male birth control pill. If current results
are any indication, he's well on his way to meet the
goal.
Broadcasters: For a copy of a video news release
contact Dena Headlee, (703) 306-1070, dheadlee@nsf.gov.
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