#395 - Brain lipidology: understanding APOE, cholesterol homeostasis, Alzheimer's disease risk, and the effects of lipid-lowering therapies on brain health | Tom Dayspring, M.D.

Peter Attia and Dr. Tom Dayspring discuss the complex physiology of cholesterol transport, focusing on how the brain's lipid system operates independently from the rest of the body. They explore the connection between the ApoE genotype, cholesterol homeostasis, and the risk of Alzheimer's disease, as well as the impact of lipid-lowering therapies on brain health.

Dr. Tom Dayspring explains the structure and function of high-density lipoproteins (HDLs) and the apolipoprotein B (ApoB) family, including VLDLs and LDLs. He describes how these particles traffic lipids through the bloodstream and the mechanisms of direct and indirect reverse cholesterol transport back to the liver.

Peter Attia and Dr. Tom Dayspring discuss the transport of lipids and lipoproteins through the plasma, explaining the differences between the ApoA and ApoB families. They clarify the role of LDL and HDL in reverse cholesterol transport and examine where the majority of the body's cholesterol is actually stored.

Dr. Tom Dayspring explains that the brain contains far more cholesterol than the liver, holding onto it securely while the liver acts as a transfer station. They discuss how lowering circulating cholesterol reduces the risk of atherosclerosis, which is driven by ApoB-containing lipoproteins entering and building up in the artery walls.

Dr. Tom Dayspring and Dr. Peter Attia discuss the physiological mechanisms of atherogenesis, emphasizing how ApoB particle concentration drives cholesterol entry into artery walls. They explore why cardiovascular disease risk varies among individuals with similar lipid profiles, pointing to factors like metabolic health, inflammation, and genetics.

Dr. Tom Dayspring explains that the brain's cholesterol levels are independent of circulating blood cholesterol because ApoB-containing lipoproteins cannot cross the blood-brain barrier. The brain synthesizes its own cholesterol de novo, primarily through glial cells like oligodendrocytes and astrocytes, to support myelin production and cell membranes.

Tom Dayspring explains how astrocytes produce cholesterol and package it into ApoE-containing lipoproteins to transport it to neurons via the brain's interstitial tissue. He and Peter Attia discuss the function of the low-density lipoprotein (LDL) receptor, which in the brain primarily interacts with ApoE due to the absence of ApoB.

Dr. Tom Dayspring and Dr. Peter Attia discuss the structural mechanics of lipoprotein clearance, explaining how ApoB conformation affects LDL receptor binding. They detail how neurons utilize LRP1 and scavenger receptors, rather than just LDL receptors, to clear small ApoE-containing lipoproteins in the brain.

Dr. Tom Dayspring and Dr. Peter Attia discuss the two primary pathways of cholesterol synthesis, highlighting desmosterol as a key marker for brain cholesterol. They also explain the distinction between the ApoE protein and the APOE genotype, detailing how different genetic isoforms affect protein structure and function. This genetic variation plays a crucial role in cholesterol transport and its association with Alzheimer's disease risk.

Peter Attia and Tom Dayspring discuss how different ApoE genotypes, particularly the E4 allele, non-linearly influence the risk of developing Alzheimer's disease. They also delve into the complex biology of high-density lipoproteins (HDLs), explaining that their diverse protein cargo is far more critical to human health and immune function than the amount of cholesterol they transport.

Dr. Tom Dayspring explains how ApoA1 traverses the blood-brain barrier to bind with ApoE-containing brain HDLs. He details how the dysfunctional ApoE4 genotype disrupts cholesterol transport in neurons, leading to cholesterol overload and the production of toxic beta-amyloid and tau proteins associated with Alzheimer's disease.

Dr. Tom Dayspring explains how the brain regulates cholesterol levels, specifically focusing on the conversion of excess cholesterol into the oxysterol 24-S-hydroxycholesterol. This water-soluble compound serves as a key biomarker for brain health and Alzheimer's risk, though it remains difficult to measure outside of research settings.

Dr. Tom Dayspring and Dr. Peter Attia discuss how lipid-lowering therapies, specifically statins, interact with the brain. They explain that statins are unique in their ability to cross the blood-brain barrier and regulate brain cholesterol synthesis. The discussion highlights the differences between lipophilic and hydrophilic statins and their potential impact on Alzheimer's disease risk.

Peter Attia and Tom Dayspring discuss the impact of lipid-lowering therapies, particularly statins, on brain cholesterol synthesis and cognitive health. They explore the hypothesis that over-suppressing brain cholesterol can lead to side effects like brain fog, and highlight desmosterol as a potential biomarker for monitoring brain lipid levels.

Dr. Tom Dayspring and Dr. Peter Attia discuss the potential cognitive benefits of the cholesterol-lowering drug ezetimibe, noting its active metabolite can cross the blood-brain barrier. They also explore the roles of omega-3 fatty acids, specifically EPA and DHA, in supporting brain health and how they are absorbed by the body.

Tom Dayspring explains how omega-3 fatty acids like DHA and EPA cross the blood-brain barrier and integrate into brain cell membranes. Peter Attia and Dayspring discuss the strength of the scientific evidence, noting that while randomized controlled trials are limited, observational data strongly supports the benefits of omega-3s for brain structure and function.

Peter Attia and Tom Dayspring discuss the therapeutic potential of CETP inhibitors, focusing on the novel drug obicetrapib. They highlight promising data from the Broadway trial, which demonstrated positive shifts in Alzheimer's-associated biomarkers like p-tau and amyloid ratios. The hosts explain the underlying mechanisms of how CETP inhibition might increase protective proteins in the brain and rescue dysfunctional HDL particles.

Peter Attia and Tom Dayspring discuss the importance of patient selection in clinical trials, referencing the PREDIMED study. They also reflect on their fifteen-year professional relationship and mutual mentorship in the field of lipidology.