Early results from a study on a vaccine to treat high blood pressure suggests that one day it might be more effective than drugs because more people would stick to a regime based on a shot in the arm every few months than taking pills every day for the rest of their lives, said the researchers.
The hypertension vaccine has been the subject of a small US study presented this week at a meeting of the American Heart Association’s Scientific Sessions 2007, in Orlando, Florida, by lead author Dr Juerg Nussberger and colleagues. Nussberger is professor of medicine at the University Hospital of the Canton of Vaud, in Lausanne, Switzerland.
The vaccine could be an effective alternative because many patients don’t always take their regular medication when they should, resulting in poor treatment results for the more conventional drug therapies.
Nussberger said that:
“Despite the fact that effective drugs are available, only about one out of four people has their blood pressure successfully controlled.”
Nussberger said many patients are either unable or don’t want to take pills every day for the rest of their lives.
“If we could add or substitute a vaccine that would need to be given just every few months, I think we could achieve better control of high blood pressure,” he added.
All that remains is for larger scale clinical trials to verify the results of the small study that suggest the vaccine is safe and effective.
The vaccine is a non-infectious particle shaped like a virus and chemically combined with angiotensin II, a molecule that occurs naturally in the blood and makes blood vessels narrow, thus causing high blood pressure. The body’s immune system responds by attacking the virus, thereby creating antibodies against angiotensin II.
Drugs that treat high blood pressure also target angiotensin II, but they do so either by inhibiting its conversion from angiotensin I or by stopping it from docking on the receptors that lead to blood vessel constriction. They are only effective if kept to a certain level in the blood stream, hence the need to take them every day.
The vaccine, on the other hand, teaches the body to regard angiotensin II as the “enemy”, thus causing it to make its own anti-angiotensin “agents” in the form of antibodies. The effect of the vaccine lasts much longer than conventional drugs; a person would only need a top up every few months.
The researchers treated 72 patients (65 men and 7 women) with mild to moderate high blood pressure by injecting them three times with 100 or 300 micrograms of vaccine or placebo. The injections were done at the start of the study (week zero), and then at week 4 and again at week 12. They measured the blood pressure changes at week 14. The average age of the patients was 51.5 years.
After the injections, the patients in the vaccine group had a strong antibody response against angiotensin II, and this response was significantly stronger in the patients who had the higher dose.
For the patients who were given the 300 microgram vaccine injections (the higher dose), their daytime systolic blood pressure (the higher of the two readings, taken as the heart constricts) was 5.6 mm of mercury (mm Hg) lower than that of the placebo group. Their diastolic blood pressure (the lower of the two readings, taken when the heart relaxes between beats) was 2.8 mm Hg lower than the placebo group’s.
Senior co-author of the study and chief scientific officer at vaccine developer, Cytos Biotechnology AG in Zurich, Switzerland, Dr Martin Bachmann said:
“Quite unexpectedly, our vaccine had the most striking effect early in the morning, the most dangerous time to have high blood pressure because it raises the risk of heart attack and stroke.”
The researchers found that the 8 am systolic blood pressure was 25 mm Hg lower and the diastolic was 13 mm Hg lower in the 300 microgram vaccine group than the placebo group.
They pointed out another potential advantage of the vaccine compared with medication. The vaccine makes anitbodies behave like a “sponge”, said Bachmann:
“The sponge empties out during the night when little angiotensin II is produced, so it is able to take up all the angiotensin II produced early in the morning,” he explained.
This compares with conventional drug therapies where medication is at its lowest level in the blood stream at this vulnerable time in the morning because it is just before people take their dose for the day.
Another potential advantage the vaccine has over drugs is that they increase levels of the enzyme renin, which causes inflammation and is thought to increase risk of kidney failure, whereas the vaccine only caused a slight increase in renin, said the researchers.
The researchers intend to trial the vaccine in another small study to find out if a different dosage pattern causes a greater antibody response and can further reduce blood pressure.
President of the American Heart Association, Dr Daniel Jones said he was encouraged by the study’s promising findings and novel approach, even if it may be too early to evaluate its clinical usefulness.
Written by: Catharine Paddock