Chronic hypoperfusion due to intracranial large artery stenosis is not associated with cerebral b-amyloid deposition and brain atrophy
Alzheimer’s disease (AD) is the most common cause of age-related dementia, affecting over 55 million people worldwide—and that number is projected to triple by 2050. While beta-amyloid (Aβ) plaques and tau tangles are hallmarks of AD, the factors that trigger these toxic deposits remain poorly understood. One long-debated question is: Does reduced blood flow to the brain (cerebral hypoperfusion) directly drive Aβ deposition and brain shrinkage (atrophy)—key steps in AD progression? A 2022 study from researchers at Daping Hospital and Third Military Medical University in China offers critical new data on this link.
The Study: Unilateral Hypoperfusion as a Natural Experiment
Led by Dongyu Fan, Huiyun Li, and Yanjiang Wang, the team focused on a unique group of cognitively normal adults (10 participants, median age 64) with unilateral chronic cerebral hypoperfusion. This means reduced blood flow in one brain hemisphere—often caused by severe narrowing (stenosis) of large arteries like the middle cerebral artery (MCA) or internal carotid artery (ICA). The other hemisphere had normal perfusion, creating a perfect “internal control” to eliminate variables like genetics, lifestyle, or age that complicate cross-person comparisons.
To qualify, participants had no history of stroke, dementia, or major organ disease. They underwent:
- CT perfusion (CTP): Maps blood flow to identify hypoperfused regions.
- CT angiography (CTA): Checks for artery narrowing.
- 11C-Pittsburgh Compound B PET (PiB-PET): Measures Aβ plaque burden using a radioactive tracer (SUVR, or standard uptake value ratio, compares tracer uptake in brain tissue to the cerebellum—a region rarely affected by Aβ).
- CT scans: Calculates brain atrophy using established indices (e.g., Evans index for ventricle size, Bicaudate index for brain shrinkage).
Key Findings: No Link Between Hypoperfusion and AD Pathology
The results were stark: there was no significant difference in Aβ deposition or brain atrophy between the hypoperfused hemisphere and the normally perfused contralateral side.
- Aβ Deposition: Even in the areas with the most severe hypoperfusion (measured via small 15mm “volume of interest” or larger “region of interest” areas), Aβ levels (SUVR) were nearly identical to the healthy side. To rule out bias from lower tracer delivery (a potential issue with low blood flow), the team checked the grey matter/white matter (GM/WM) ratio—still no difference.
- Brain Atrophy: All atrophy indices (e.g., Bicaudate, Evans, Ventricular) were similar between the hypo and normal hemispheres. Even one participant with pre-existing bilateral Aβ deposits (SUVR >1.42, a marker of AD risk) showed no worsening in the hypoperfused region.
What This Means for Alzheimer’s Research
The study challenges a common assumption from animal studies—where reducing blood flow in mice does increase Aβ plaques and neuron loss. But in humans, the link isn’t direct. Why?
- Human vs. Animal Differences: Animal models use sudden, severe hypoperfusion (e.g., carotid artery ligation), while human hypoperfusion is often milder and chronic.
- Duration Matters: The study couldn’t confirm how long participants had hypoperfusion—short-term low blood flow may not trigger Aβ.
- Vascular Risk vs. Direct Cause: Midlife vascular risks (e.g., high blood pressure, diabetes) still raise AD risk—likely by damaging the brain’s “neurovascular unit” (cells that regulate blood flow and Aβ clearance) over decades, not by hypoperfusion alone.
Strengths and Limitations
The study’s design is a major strength:
- Within-Subject Control: Comparing the same person’s hypo and normal sides eliminates individual variability.
- Excluded Confounders: Participants had no major strokes (which can cause brain damage unrelated to hypoperfusion) or cognitive decline.
- Older Adults: The median age of 64 aligns with when AD-related changes typically begin (15–20 years before dementia).
Limitations include:
- Small Sample: Only 10 participants—larger studies are needed to confirm results.
- Unknown Hypoperfusion Duration: It’s possible longer-term low blood flow could have effects.
- No Small Vessel Disease: The study focused on large artery stenosis; small vessel disease (a common cause of hypoperfusion) may interact differently with Aβ.
Conclusion: Hypoperfusion Isn’t a Direct Driver of AD Pathology
The findings suggest that chronic hypoperfusion from large artery stenosis does not directly cause Aβ deposition or brain atrophy in humans. This doesn’t mean vascular health isn’t important—midlife vascular risks still increase AD risk, likely through indirect pathways (e.g., damaging blood vessels that clear Aβ). But for people with large vessel narrowing and normal cognition, hypoperfusion alone isn’t a direct trigger for AD.
This study was published in the Chinese Medical Journal in 2022 by Dongyu Fan, Huiyun Li, and colleagues from Daping Hospital, Third Military Medical University, Chongqing, China. doi:10.1097/CM9.0000000000001918
Was this helpful?
0 / 0