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Pennington Biomedical Research Center scientist Dr. Nikhil Dhurandhar is the first in the world to suggest a virus may cause
obesity in humans, and his phone is now continually ringing with calls from reporters.
It started with a routine conversation some time ago. Dr. S.M. Ajinkya, a renowned veterinary pathologist from Bombay Veterinary College in Bombay, India, had discovered a chicken virus that was sweeping across poultry farms in India,
killing thousands of chickens. At one point, he related his findings to Dr. Dhurandhar. The chickens showed, “Pale and enlarged liver and kidneys, excess fat in the abdomen and a shrunken thymus.”
Dhurandhar
stopped him there.
Something didn‘t
sound right.
Excess fat in the
abdomen? A
bird that withers
away from a viral
infection should be
skinny. Could the
virus be causing the
excess fat?
To find out, Dhurandhar and
Ajinkya subjected a group of
chickens to the virus, called
SMAM-1, and then compared
them with a group of healthy
chickens. All the chickens ate
similar amounts of food, and still,
only the infected ones became
obese. Curiously, cholesterol
- usually in higher amounts in
obesity - was at a lower level in the
infected, obese chickens.
A fat causing virus?
Could it do the same to humans?
One good way to tell if a human has been
infected with a virus is to look for specific
antibodies in the bloodstream. For example,
any human infected by SMAM-1 would likely
have antibodies in his or her blood, naturally
created by the body to fight off the virus.
When Dhurandhar and his colleagues searched
for antibodies in blood samples from obese
persons, they found that 20% of these people
had antibodies to fight off SMAM-1. Those
with the antibodies (and presumably the virus)
were heavier and had lower cholesterol levels
than those without
– the same symptoms as
the SMAM-1 infected
poultry.
“If SMAM-1, an avian
virus, could cause obesity
in humans, could there
be a human virus that
does the same?” wondered
Dhurandhar.
SMAM-1 is an
“adenovirus” that
infects birds, but
other adenoviruses
are known to
infect humans and
other mammals.
There are fifty
such human
adenoviruses,
all associated
with acute upper
respiratory tract
infections, diarrhea
or conjunctivitis (sore-eyes). Dhurandhar started
his studies with adenovirus type 36 (Ad-36).
In several experiments, chicken, mice, and other
animals infected with the human virus Ad-36
showed the same strange symptoms seen with
the SMAM-1 infection; they became obese but
had low cholesterol. Next, Dhurandhar and
his colleagues conducted a study to find the
relationship between this human adenovirus and
obesity in people. They found that only 11% of
lean people but a significant 30% of the obese
people screened had antibodies to Ad-36. As
with the virus SMAM-1, those with antibodies
against Ad-36 had lower cholesterol levels and
were heavier than those without.
Adding to the mounting evidence were the
findings of a study of twins. It is commonly
understood that twins usually weigh the same;
they are both obese or both lean, due to their
similar genetic makeup. Dhurandhar and his
colleagues studied twin pairs where one twin
was antibody-positive to Ad-36 and the other
antibody-negative. The antibody-positive twins
were heavier and fatter.
Through these studies they showed for the
very first time a human virus is associated with
human obesity!
Dhurandhar and his colleagues are trying to
determine how this virus works, a first step
toward a cure or a vaccine to
prevent obesity caused by Ad-36.
Ad-36 seems to act on specialized
“pre-fat” cells that have the
potential to store fat. When the
body’s existing fat cells are storing
as much fat as possible, the prefat
cells are recruited to quickly
become mature fat cells capable
of storing fat. Dhurandhar and
his colleagues have
recently discovered
that Ad-36 greatly
enhances this
process, effectively
increasing the
number of fat cells.
Following
Dhurandhar’s lead,
other researchers
have determined
at least two
other human
adenoviruses, types
37 and 5, are also likely to cause obesity in
humans and two other adenoviruses do not,
leaving about 45 more adenoviruses to study.
Dhurandhar reminds us that like many other
diseases, obesity has many causes, and multiple
causes may be present in an individual.
“Yes,” he says, “It appears certain adenoviruses
may cause obesity in some people. But this is
only one cause. We still don’t know the complete
picture of obesity, its causes or its cures.”
Editor’s note: This story was written
by Rohan Dhurandhar, son of
Dr. Nikhil Dhurandhar, an LSU
student and a science writer.
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