Provocative new research suggests that a common virus might play
a role in high blood pressure. The work, by Harvard University scientists, so far is only in mice - and the usually symptomless infection is so widespread that proving an effect in people will be tough.
Still, it's the latest clue that infections may somehow affect a
number of the factors that lead to heart disease, from stiffening
arteries to obesity.
"There's likely to be considerable scepticism about this in the
medical profession," acknowledged lead researcher Dr Clyde
Crumpacker, an infectious disease specialist at Beth Israel
Deaconess Medical Centre in Boston. But, "what we would postulate
is yes, there can be persistent infection of blood vessels that
could be leading to high blood pressure."
At issue is cytomegalovirus, or CMV. More than half of US adults are infected by age 40, according to the Centres for Disease
Control and Prevention. It's a lifelong infection, but the vast majority will never even know they have it.
Yet CMV causes serious problems for select groups: Women
infected during pregnancy sometimes pass the virus to their foetuses, and 8 000 infants a year in the US suffer disabilities including mental impairments, and hearing or vision loss as a result.
Riskier in people with weak immune systems, CMV also causes
a type of blindness in Aids patients, and has been linked to
problems in heart transplant recipients.
How the study was done
For the new study, Crumpacker teamed with cardiologists who
could do a neat trick: thread tiny tubes directly into a vital neck
artery of mice, to measure exactly what happened to their blood
Crumpacker started with healthy mice, some fed a normal rodent
diet and others a high-cholesterol diet for a month. Then he
injected CMV into the abdominal cavities of half of each group. A
few weeks later, blood pressure had jumped among all the
CMV-infected mice, but not among their uninfected counterparts,
Blood pressure jumped the most in mice given a high-cholesterol
diet -and a few even were developing artery plaques, he wrote in
the journal PLoS Pathogens, a publication of the Public Library of Science.
Peering into the rodents' carotid arteries, the researchers
found the CMV was infecting the blood vessels' lining. Heart
disease is linked with a low-level artery inflammation, and three
different inflammatory molecules were found in the infected mice.
Delving deeper, Crumpacker then infected both mouse and human
cells in lab dishes and found that CMV spurred increased production
of an enzyme called renin, known to activate a molecular pathway
that can lead to high blood pressure.
Human testing still far away
Nearly one in three adult Americans, or 72 million people, and
almost 1 billion people worldwide have high blood pressure. It is a
leading cause of heart disease and strokes. Poor diet and lack of
exercise are key risk factors, but doctors don't understand all of
the underlying triggers of hypertension - including why some couch
potatoes never get it and some thin, fit people do.
"It's an intriguing report" that calls for more research into
the possible effect, said Dr Cheryl L. McDonald of the National
Heart, Lung and Blood Institute, which funded the work. But she cautioned that any human testing would be years away.
Because of the inflammation connection, researchers have long
hunted bacteria or viruses in heart disease. A type of adenovirus,
a member of the cold virus family, has been linked to obesity, and
a different respiratory germ has been linked to clogged arteries.
But giving heart patients an antibiotic failed to prevent heart
attacks, and many cardiologists have been sceptical of the
infection theory ever since. "We're not convinced that it's an issue," said American Heart Association spokesman Dr Dan Jones of the University of Mississippi. He called the new study "an incremental step and not a
big one." – (Sapa, May 2009)
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