(first published on Nature Network May 11th)
One of the
questions I have been investigating is whether a type of anti-hypertensive
drug, angiotensin converting enzyme inhibitors, may inadvertently cause some
people to develop Alzheimer’s disease.
There is
currently no cure for Alzheimer’s disease.
Patients diagnosed with dementia on average survive for 4 years. Alzheimer’s disease was first described in
1906, but scientists do not know exactly what causes the biological changes characteristic
of the disease. We do know Alzheimer’s disease
gets more common as people get older:
Data from MRC CFAS study.1
This hypothesis
around angiotensin converting enzyme inhibitors was motivated by research
suggesting that angiotensin converting enzymes may have a role in clearing
amyloid-β plaques from the brain. So angiotensin
converting enzyme inhibitors which, as their name suggests, inhibit angiotensin
converting enzyme, may increase the build up of amyloid-β, increasing the
likelihood of Alzheimer’s disease.2
The ideal way
to answer this question would be to do an experiment, which randomly allocates
some people to angiotensin converting enzyme inhibitors and others to another
anti-antihypertensive, and then see whether there were differences in the
number of diagnosed with Alzheimer’s. However,
the effects of angiotensin converting enzyme inhibitors are only thought to
build up after long periods of exposure.
So participants would need to be followed in the experiment for a very long
time. Mercifully, Alzheimer’s disease is
relatively rare in younger people, so we would either need to run the experiment
in older people, or in a very large number of people to detect any difference
in diagnosis rates. This could be hugely
expensive.
Some
epidemiologists, Anderson and colleagues, did the next best thing.3
They followed-up an experiment that had already been run, the ONTARGET
study. In which the outcomes of people
given angiotensin converting enzyme inhibitors were compared to those given
another anti-hypertensive drug, angiotensin receptor blockers.
They
investigated whether the participants experienced differences in cognitive
impairments, defined as a diagnosis of dementia, or had a low score in a
cognitive test, the mini-mental state examination depending on the treatment
they were allocated. They found that
people allocated to angiotensin converting enzyme inhibitors were around 10%
more likely to develop cognitive impairments over the four years of the
experiment,(odds-ratio 1.11 95%CI (0.99,1.25) p-value =0.06). However, they found little difference in
another outcome, cognitive decline (a fall in the mini-mental state exam
score).
These
findings are certainly not conclusive.
This might be because the participants of the ONTARGET experiment were
relatively young, average age of 66, so few participants would be expected to
develop Alzheimer’s disease. Also the
ONTARGET trial’s primary outcome was death from cardiovascular causes,
myocardial infarction, stroke, or hospitalization for heart failure. This means it did not necessarily have enough
data to detect an effect of the drugs on cognitive impairments or cognitive
decline.
Another way
to investigate whether angiotensin converting enzyme inhibitors cause
Alzheimer’s disease, is to compare the outcomes of patients prescribed ACE-Is
and other anti-hypertensive drugs as part of their normal medical care. Some more epidemiologists, Li and colleagues,
did this using data from the United States.4
They found
that patients prescribed lisinopril (an angiotensin converting enzyme inhibitor)
were 23% more likely to develop Alzheimer’s disease than those prescribed angiotensin
receptor antagonists, (odds-ratio 1.23 (95%CI:1.04,1.47), p<0.001). Patients prescribed lisinopril were slightly more likely to develop
Alzheimer’s disease than patients given other cardiovascular drugs (such as
statins) odds-ratio 1.04 (95%CI: 0.99,1.11, p=0.15). But this association was relatively small weak
and could be due to chance. Whist Li and
colleagues adjusted their findings for their patients’ characteristics; it is
possible that these differences are due to underlying differences between
patients prescribed lisinopril and angiotensin receptor antagonists in their
sample. For instance patients prescribed
angiotensin receptor antagonists might be richer or younger.
I looked into
this using data from the General Practice Research Database.5
This is contains administrative data on diagnoses and prescriptions from
over 600 general practices in the UK. We
found evidence that fewer patient prescribed angiotensin converting enzymes
were diagnosed with Alzheimer’s than those prescribed other
anti-hypertensives. However, when we
looked at historical exposure to angiotensin converting enzymes we found little
evidence of an association. Again this is frustratingly inconclusive.
The only way
to conclusively prove whether long term exposure to angiotensin converting
enzyme inhibitors is related to Alzheimer’s disease is with a randomised
controlled trial of sufficient size in older people with higher risks for the
disease.
I'd hear your thoughts on this and our other posts, and do pass on any
papers or links.
1.
Neuropathology Group of the Medical Research Council Cognitive Function and
Ageing Study(MRC CFAS). Pathological correlates of late-onset dementia in a
multicentre, community-based population in England and Wales. Neuropathology
Group of the Medical Research Council Cognitive Function and Ageing Study (MRC
CFAS). Lancet. 2001;357(9251):169–175.
2. Kehoe P, Miners S, Love S. Angiotensins in
Alzheimer’s disease-friend or foe? Trends Neurosci. 2009;32(12):619–628.
3. Anderson C, Teo K, Gao P, et al.
Renin-angiotensin system blockade and cognitive function in patients at high
risk of cardiovascular disease: analysis of data from the ONTARGET and
TRANSCEND studies. The Lancet Neurology. 2011;10(1):43–53.
4. Li N, Lee A, Whitmer R, et al. Use of
angiotensin receptor blockers and risk of dementia in a predominantly male
population: prospective cohort analysis. BMJ. 2010;340(jan12 1):b5465.
5. Davies NM, Kehoe PG, Ben-Shlomo Y, Martin
RM. Associations of anti-hypertensive treatments with Alzheimer’s disease,
vascular dementia, and other dementias. J. Alzheimers Dis.
2011;26(4):699–708.