Antihypertensive medications that cross the blood-brain barrier (BBB) may be linked with less memory decline, compared with other drugs for high blood pressure, suggest the findings of a meta-analysis.
Over a 3-year period, cognitively normal older adults taking BBB-crossing antihypertensives demonstrated superior verbal memory, compared with similar individuals receiving non–BBB-crossing antihypertensives, reported lead author Jean K. Ho, PhD, of the Institute for Memory Impairments and Neurological Disorders at the University of California, Irvine, and colleagues.
According to the investigators, the findings add color to a known link between hypertension and neurologic degeneration, and may aid the search for new therapeutic targets.
“Hypertension is a well-established risk factor for cognitive decline and dementia, possibly through its effects on both cerebrovascular disease and Alzheimer’s disease,” Ho and colleagues wrote in Hypertension. “Studies of antihypertensive treatments have reported possible salutary effects on cognition and cerebrovascular disease, as well as Alzheimer’s disease neuropathology.”
In a previous study, individuals younger than 75 years exposed to antihypertensives had an 8% decreased risk of dementia per year of use, while another trial showed that intensive blood pressure–lowering therapy reduced mild cognitive impairment by 19%.
“Despite these encouraging ﬁndings…larger meta-analytic studies have been hampered by the fact that pharmacokinetic properties are typically not considered in existing studies or routine clinical practice,” wrote Ho and colleagues. “The present study sought to ﬁll this gap [in that it was] a large and longitudinal meta-analytic study of existing data recoded to assess the effects of BBB-crossing potential in renin-angiotensin system [RAS] treatments among hypertensive adults.”
Methods and Results
The meta-analysis included randomized clinical trials, prospective cohort studies, and retrospective observational studies. The researchers assessed data on 12,849 individuals from 14 cohorts that received either BBB-crossing or non–BBB-crossing antihypertensives. Cognition was assessed via the following seven domains: executive function, attention, verbal memory learning, language, mental status, recall, and processing speed.
Compared with individuals taking non–BBB-crossing antihypertensives, those taking BBB-crossing agents had significantly superior verbal memory (recall), with a maximum effect size of 0.07 (P = .03).
According to the investigators, this finding was particularly noteworthy, as the BBB-crossing group had relatively higher vascular risk burden and lower mean education level.
“These differences make it all the more remarkable that the BBB-crossing group displayed better memory ability over time despite these cognitive disadvantages,” the investigators wrote.
Still, not all the findings favored BBB-crossing agents. Individuals in the BBB-crossing group had relatively inferior attention ability, with a minimum effect size of –0.17 (P = .02).
The other cognitive measures were not significantly different between groups.
Clinicians May Consider Findings After Accounting for Other Factors
Principal investigator Daniel A. Nation, PhD, associate professor of psychological science and a faculty member of the Institute for Memory Impairments and Neurological Disorders at the University of California, Irvine, suggested that the small difference in verbal memory between groups could be clinically significant over a longer period of time.
“Although the overall effect size was pretty small, if you look at how long it would take for someone [with dementia] to progress over many years of decline, it would actually end up being a pretty big effect,” Nation said in an interview. “Small effect sizes could actually end up preventing a lot of cases of dementia,” he added.
The conflicting results in the BBB-crossing group — better verbal memory but worse attention ability — were “surprising,” he noted.
“I sort of didn’t believe it at first,” Nation said, “because the memory finding is sort of replication — we’d observed the same exact effect on memory in a smaller sample in another study…The attention [finding], going another way, was a new thing.”
Nation suggested that the intergroup differences in attention ability may stem from idiosyncrasies of the tests used to measure that domain, which can be impacted by cardiovascular or brain vascular disease. Or it could be caused by something else entirely, he said, noting that further investigation is needed.
He added that the improvements in verbal memory within the BBB-crossing group could be caused by direct effects on the brain. He pointed out that certain ACE polymorphisms have been linked with Alzheimer’s disease risk, and those same polymorphisms, in animal models, lead to neurodegeneration, with reversal possible through administration of ACE inhibitors.
“It could be that what we’re observing has nothing really to do with blood pressure,” Nation explained. “This could be a neuronal effect on learning memory systems.”
He went on to suggest that clinicians may consider these findings when selecting antihypertensive agents for their patients, with the caveat that all other prescribing factors have already been taking to account.
“In the event that you’re going to give an ACE inhibitor or an angiotensin receptor blocker anyway, and it ends up being a somewhat arbitrary decision in terms of which specific drug you’re going to give, then perhaps this is a piece of information you would take into account – that one gets in the brain and one doesn’t – in somebody at risk for cognitive decline,” Nation said.
Exact Mechanisms of Action Unknown
Hélène Girouard, PhD, assistant professor of pharmacology and physiology at the University of Montreal, said in an interview that the findings are “of considerable importance, knowing that brain alterations could begin as much as 30 years before manifestation of dementia.”
Since 2003, Girouard has been studying the cognitive effects of antihypertensive medications. She noted that previous studies involving rodents “have shown beneficial effects [of BBB-crossing antihypertensive drugs] on cognition independent of their effects on blood pressure.”
The drugs’ exact mechanisms of action, however, remain elusive, according to Girouard, who offered several possible explanations, including amelioration of BBB disruption, brain inflammation, cerebral blood flow dysregulation, cholinergic dysfunction, and neurologic deficits. “Whether these mechanisms may explain Ho and colleagues’ observations remains to be established,” she added.
Andrea L. Schneider, MD, PhD, assistant professor of neurology at the University of Pennsylvania, Philadelphia, applauded the study, but ultimately suggested that more research is needed to impact clinical decision-making.
“The results of this important and well-done study suggest that further investigation into targeted mechanism-based approaches to selecting hypertension treatment agents, with a specific focus on cognitive outcomes, is warranted,” Schneider said in an interview. “Before changing clinical practice, further work is necessary to disentangle contributions of medication mechanism, comorbid vascular risk factors, and achieved blood pressure reduction, among others.”
The investigators disclosed support from the National Institutes of Health, the Alzheimer’s Association, the Waksman Foundation of Japan, and others. The interviewees reported no relevant conflicts of interest.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.