The APOE 4/4 genotype (often referred to in literature as “APOE homozygotes” or APOE -/-) carry a significantly increased risk of Alzheimer’s disease and cardiovascular disease. By understanding the deeper science of the APOE gene, it may be possible to procure treatment protocols and support the body where it may be lacking.
Functions of the APOE Protein
- APOE is known as Apolipoprotein E
- APOE is involved in the transport of lipids, fat-soluble vitamins and cholesterol into the blood and lymphatic system
- APOE is produced in the liver and spleen, and is also produced by resident glial cells in the brain and nervous system
- APOE affects the metabolism of Triglycerides in the blood, as well as their levels (R)
- APOE significantly interacts with the LDL (low density lipoprotein) receptor (R)
- The APOE protein is the primary transport of cholesterol in the brain and nervous system (R)
- The APOE protein in the brain is integral in brain repair processes (R)
- The APOE protein significantly influences the immune system:
- APOE proteins are synthesized by numerous immune cell types. APOE inhibits T-cell proliferation through interactions with macrophages (R)
- Your APOE genotype will influence a number of immune activities (see below)
APOE 2 Genotypes
- APOE 2 exists in roughly 5% of the population (R)
- APOE 2 confers multiple protective effects against Alzheimer’s disease and cognitive impairment (R)
- APOE 2 carriers may have reduced risk of preeclampsia, and this may be due to a higher amount of antioxidants and less oxidative stress (R)
- APOE 2 carriers have been found to have less amyloid ß plaque in the neocortex (R)
- APOE 2 carriers show better repair of neuronal cells (R)
- APOE 2 carriers have shown enhanced cognition in aging (R)
- Preliminary research suggests most protective effect of APOE 2 status may be with males but not females (R)
- APOE 2 phenotypes may make more of certain types of collagen and ECM (extracellular matrix) constituents (R)
- APOE 2 has a lower binding affinity for LDL (low density lipoprotein) receptors compared to other APOE genotypes (R). APOE 2 proteins have a higher affinity for HDL (high density lipoprotein) (R)
- APOE 2 genotypes appear to metabolize fat slower than other APOE genotypes, and this appears to account for the higher triglyceride concentrations found among APOE 2 carriers (R)
- APOE 2 genotypes have been found to have Type 3 Hyperlipoproteinemia (characterized by slower metabolism of and higher levels of VLDL and chylomicrons) (R), yet only 2% of APOE 2 carriers develop vascular disease
APOE 3 Genotypes
- APOE 3 is the most common APOE genotype worldwide
- APOE 3/4 carriers are likely to suffer the most from malarial infection (R)
- Research in mice suggest APOE 3 genotypes produce less inflammation and promote repair mechanisms better than APOE 4 genotypes (R)
- APOE 3 carriers show better repair of neuronal cells (R)
- In mice, APOE 3 genotypes produce more microglial cell inflammation than do the APOE 3/4 genotypes but not as much as the APOE 4/4 genotypes (R)
APOE 4 Genotypes (include 3/4 and 4/4)
From a genetics perspective, the APOE genotype is based upon the combination of 2 APOE SNP’s (rs429358 and rs7412). The ApoE 3/4 is the heterozygote, and ApoE 4/4 is the homozygote.
- For infants, APOE 3/4 and 4/4 is associated with increased neuronal development, as measured by MDI (mental developmental index) (R)
- APOE 4/4 homozygotes have a significantly increased risk of Alzheimer’s disease, with as much as 20x the risk (R)
- APOE 4/4 carriers have reduced antioxidant protection, and may be more susceptible to the oxidative effects of Iron toxicity (R), (R)
- The APOE 4/4 protein preferentially binds to lower density lipoproteins such as LDL and VLDL in the blood stream (R)
- The APOE 4/4 protein interacts significantly with ß-amyloid plaque, and this complex relationship plays a significant role in ß-amyloid accumulation, and subsequent Alzheimer’s pathophysiology (R)
- APOE 4/4 and APOE 3/4 carriers are believed to absorb dietary fat more efficiently (Bredesen et, al), and this accounts for the sensitivity to diet-induced rises in triglycerides (R).
- Carriers of APOE 4/4 who have hepatitis C infection, and who are overweight and have higher levels of LDL-C are more likely to have spontaneous clearance of the virus (R).
- This study is one of several lines of evidence that indicates APOE 4 carriers evolved from conditions of pathogen-rich environments, and have a robust ability to resolve or contain certain types of infection.
- The APOE 4/4 genotypes generally have more immune active immune systems and produce more inflammation.
- APOE deficient mice (seen in APOE 4/4) have activated classical pathway including complement C1q. The complement immune system is a central part of the innate immune system (R)
- APOE (4/4 genotype) results in enhanced expression of immuno-stimulatory cell surface molecules by the activated APC (antigen presenting cells) (R)
- APOE deficient mice (APOE 4/4) have shown impaired innate immune response to a number of bacteria (R, R)
- APOE 4/4 genotypes lack sufficient SIRT-1 activity, which is a key metabolic switch that regulates gene expression (epigenetics), stem cell activity and a variety of cellular functions (R), (R)
- In mice, the APOE 4/4 genotypes have been shown to feature reduced Thioredoxin-1 (TRX-1) activities (R). Thioredoxins are sulfur-containing antioxidants that are major regulators of redox equilibrium within cells, and regulate the protective effects of antioxidants against free radicals and aging
- APOE 3/4 and APOE 4/4 appear to have tendencies towards lower thyroid function. A sizable study performed on postmenopausal women in Poland identified that APOE 4 genotypes had higher levels of TSH and lower levels of both free and total T3 (R), compared to non-APOE 4 carriers.
- It’s worth pointing out that an in vitro study found that the thyroid hormone T3 induces a dose-dependent increase in APOE expression in the brain’s astrocytes (R). Astrocytes are the primary brain cell which maintain brain antioxidants, and neurotrophins to counter-regulate any oxidative stress.
- It would make sense that T3 values would be lower among ApoE4 carriers. The hormone T3 is biosynthesized via 5-deiodinase. 5-deiodinases are a group of enzymes that are catalytically dependent upon NADPH redox reactions (R). Because redox systems are impaired among ApoE4 carriers (due to reduced thioredoxin), this would reduce the biosynthesis of T3 from T4.
- The above referenced chain of research may have significant implications for thyroid hormone therapies among APOE 4 genotypes.
- Elevated Nitric Oxide – ApoE4 carriers generate more nitric oxide in numerous cell types. This includes macrophages as well as microglial cells in the brain. It is important to point out that what characterizes ApoE4 is the shift of the amino acid cysteine for arginine. Arginine is the primary amino acid that drives nitric oxide biosynthesis (R), (R). In addition, ApoE4 carriers have deficient S-nitrosylation of the ApoE4 protein. S-nitrosylation is the binding of nitric oxide to a sulfur group. S-nitrosylation of ApoE2 and ApoE3 isoforms leads to conformational changes and the loss of LDL receptor binding. In ApoE4, this doesn’t happen (R). This is potentially a really big deal, because S-nitrosylation is a critical factor that regulates redox homeostasis. Again, to reiterate the phenotypic characteristics of ApoE4, it is characterized by a cysteine to arginine amino acid switch. As such, there are no cysteine residues on which nitric oxide can bind. Why is this important? High nitric oxide with low S-nitrosylation causes multiple disturbances in cells. This includes signal transduction, redox homeostasis, protein modification, ubiquination, apoptosis/cell survival balance, etc. (R).
APOE 4 & Mercury Toxicity
The concept of enhanced mercury toxicity among carriers of APOE 4 was first posited by Haley and Pendergrass in 1995. The novel hypothesis was based on the fact that the different APOE genotypes produce proteins with divergent sulfhydryl-containing cysteine amino acids. APOE 4 genotypes produce proteins with 2 arginine amino acids, and no cysteine, and consequently would be more adversely affected due to mercury toxicity. Subsequent research identified that APOE 4 carriers trend towards higher mercury concentrations, or suffer adverse effects due to mercury, compared to non-APOE 4 carriers (R), (R), (R) (R).
In addition to the Pendergrass and Haley theory regarding the lack of cysteine residues among APOE 4 carriers inducing mercury toxicity, it is also known that APOE 4 genotypes have reduced levels of thioredoxin-1 (R). Because thioredoxin regulates redox signaling, this will necessarily adversely affect glutathione electron transfer.
Insufficient thioredoxin will be exacerbated in the presence of selenium deficiency (R). Moreover, having the ApoE4 genotype appears to affect selenium levels in the brain. ApoE4 is associated with lower selenium levels in the temporal cortex, and increased soluble selenium (R).
Significant Therapeutic Targets for APOE 4/4 Genotypes
Being able to significantly influence patients with complex illness is a not always a linear process, because the pathophysiology of complex illness is not always linear. You will often read on other websites, simple “biohacks for APOE genotypes” or simplistic supplement recommendations to affect complex illness. This is equivalent to a 1+1=2 approach. While these recommendations may look solid on paper because they’re cited with research studies, it doesn’t mean these approaches will actually work clinically. Furthermore, even if these treatments do work, they may not work consistently. To re-emphasize, complex illness is complex, largely because it is highly multi-factorial and non-linear.
When it comes to complex illnesses such as Alzheimer’s disease, the idea of simplistic linearity simply does not exist. There are so many moving variables occurring simultaneously it is profoundly difficult to map these out. And even if you can map out these complex variables, nothing remains constant, everything is in a continual state of flux and change.
What we’re after:
- Identifying the significant influencing variables and how to affect change of these variables
- Pattern recognition – i.e. how the above influencing variables affect other variables. Often you’ll gain hypotheses that influencing variables are affecting multiple physiological systems. For example, the APOE gene does not only influence amyloid plaque and levels of lipo-proteins, it significantly interacts with the immune system, as well as directs intracellular proteins, which regulate redox homeostasis and mitochondrial function. This is only the tip of the iceberg with APOE, but it gives you the appreciation for the highly multi-dimensional complexity of how a single influencing variable can affect dozens, hundreds or thousands of molecular actions downstream
- The appreciation of new system’s biology approaches – This is the idea that we can map all of these things out. That sounds like a great idea, but even this has limitations. Wouldn’t it be great if we could reduce the unfathomable complexity of the human body and disease processes to neatly architected biological frameworks? An impossible task, possibly futile. However, from the clinical angle we need to at least adjust our thinking to this type of lens. The standard laboratory testing is uni-dimensional in the face of multi-dimensional biology-based machine learning algorithms, but we shouldn’t throw the tests out the window either, because they can often provide important insights.
When it comes to heritable genetics such as the APOE status, there are always pros and cons. ApoE genotype is contextually-interactive. From an evolutionary standpoint, this equates to advantages and disadvantages of having a particular genotype, within the context of certain conditions (such as age) and environments. This concept is known as evolutionary antagonistic pleiotropy (R), and it applies greatly to our understanding of the ApoE4 genotype. Paradoxically, ApoE4 produces fitness advantages early in life, including greater cognitive functions, yet later in life these are often impaired with dementia and cognitive decline. However, a much closer examination reveals that not all populations who carry ApoE4 develop Alzheimer’s. The difference has to do with Evolutionary Mismatch.
APOE 4 & PARASITE PROTECTION
- APOE 4 genotypes may have evolved to protect against parasitic infection. Studies find that individuals with the APOE 4 genotype have protection against parasites, including malaria (R), (R).
- Unlike in the industrialized world, carriers of the APOE 4 genotype living in non-industrialized society with a higher parasite burden have greater cognitive performance (R). Remarkably, having a higher burden of parasites protects ApoE4 carriers from developing Alzheimer’s/dementia, which is an inflammatory disease.
- ApoE4 is not, repeat NOT, associated with Alzheimer’s disease in Sub-Saharan Africa nor in New Guinea. These regions are endemic with malaria, and other tropical infections. Therefore, evolutionarily speaking, this further supports the hypothesis that ApoE4 is better adapted for pathogen combat and for survival in pathogen-rich environments.
APOE 4: Helminthic Therapy
Helminthic therapy is the ingestion of parasites to treat inflammatory diseases. While ingesting oral parasitic hookworms seems crazy to most people, this has been a significant therapy for many decades now, with a considerable body of published literature to support the use.
In an article I authored and published in Holistic Primary Care, I made a strong case that the ApoE4 gene evolved specifically due to symbiotic relationships with helminths and parasites. Parasites and helminths inhibit TH1 driven inflammatory responses, and it is clear that the ApoE4 phenotype generates more robust inflammatory immunity. Notably, in malarial and parasitic-endemic regions, geriatric ApoE4 carriers do not develop dementia or Alzheimer’s. Furthermore, An Amazonian, forager-horticulturist study found that increased parasite burden among ApoE4 carriers is associated with improved cognition with age (R). The theory I put out is that the reason ApoE4 carriers develop Alzheimer’s and vascular diseases in modern geographies is due to maladaptive responses, because modern geographies lack parasite diversity. This theory is very significant because it forces a reframing of molecular genetics’ linear cause and effect reductionism. It forces one to view evolution in terms of symbiosis, driven by interactions and cues from the environment.
Helminthic therapy is worth considering as a treatment for ApoE4 genotypes. It is quite surprising to find that there have yet to be published trials on the use of helminthic therapy in Alzheimer’s disease among carriers of ApoE4. Given that parasitic infections confer protective effects in cognition among ApoE4 carriers, and that helminthic therapy is known to reduce inflammatory activity, including in the brain (see research on ‘Helminthic therapy and MS’) this seems like a major therapeutic opportunity.
Helminthic therapy is used to successfully treat inflammatory diseases, including: multiple sclerosis, asthma, dermatitis, Crohn’s disease and other autoimmune diseases (R).
- One study found a greater disease relapse and higher inflammatory activity among MS patients who underwent parasite eradication (R), following helminthic therapy. The authors of this study found in their previous research that MS patients undergoing helminthic therapy had fewer relapses, lower inflammatory activity and reduced disability scores.
- Helminths and parasites are known to induce a TH2, anti-inflammatory response (R)
- Helminthic therapy inhibits colitis by increasing anti-inflammatory TGFß signaling, IL10, and immuno-tolerant TREGs cells (R), (R).
The use of Helminthic Therapy for ApoE4 genotypes makes sense also because APOE 4 carriers produce more inflammation, especially in the brain’s glial cells (R), and helminthic therapy promotes TH2, anti-inflammatory immunity.
Helminthic therapy has shown to reduce brain lesions in multiple sclerosis, largely by shifting the TH1-driven inflammatory signaling towards a TH2, anti-inflammatory response. This TH1 to TH2 shift may be one mechanism to counter the excessive inflammation of ApoE4 genotypes.
APOE 4: SIRT1
One of the primary therapeutic targets for APOE 4 genotypes in the Bredesen protocol for Alzheimer’s is SIRT1 (sirtuin-1). SIRT-1 is also known as NAD-dependent deacetylase.
SIRT-1 is a major intracellular, nuclear protein that has many extensive effects throughout the body. Two of sirtuin’s significant functions is modulating gene expression, and modulating stem cell activities (R), (R).
Sirtuins can protect stem cells from the damaging effects of stress and aging.
- APOE 4/4 genotypes lack sufficient SIRT-1 (R)
- APOE 4/4 genotypes lack the neuroprotective effects of SIRT-1, favoring an imbalance between SIRT-1 (neuroprotective) and SIRT-2 (neuroinflammatory) (R)
Switching on SIRT-1 in spite of APOE 4/4 is a difficult task, and one that to my knowledge has not been proven by research. However, activation of SIRT-1 is known to be modulated by numerous mechanisms. In the Alzheimer’s training taught be Dale Bredesen, MD, the use of resveratrol has been referenced. Possibly the greatest effect on increasing SIRT1 can be induced by fasting.
Therapeutic Targets for SIRT-1
Hormesis is essentially the benefit of something stressful on the body, working by affecting change through some mechanism of adaptation. Simple example of hormesis are: exercise, caloric restriction, cold exposure and fasting.
- In mice, a 24-hour fast was enough to induce expression of SIRT-1 as well as it’s necessary companion NAD+ (R)
- A study performed on 43 men found that 30 days of religious, Ramadan fasting induced a 4.63 fold increase in SIRT-1 mRNA in mononuclear cells, compared to the non-fasting group (R)
- In aging rats, exercise increased SIRT-1 levels (R)
- In a mouse model of Alzheimer’s disease, treadmill exercise increased SIRT-1 activity as well as reduced amyloid ß accumulation (R)
- Resveratrol has shown to be effective at attenuating SIRT-1 deacetylation in vitro (R), even though other research has failed to confirm this.
- In mice the combined, synergistic effect of low dose resveratrol, with ß-hydroxybutyrate and the amino acid Leucine increased SIRT-1 activity and stimulated fatty acid oxidation as well as AMPK stimulation (R). There’s something to be said for nutrient synergy.
Thioredoxin-1 (TRX-1), PGC-1a & APOE 4
APOE 4/4 mice have shown to have reduced expression of Thioredoxin-1 (TRX-1) (R).
Thioredoxin is one of the central thiol-based redox systems in humans. The thioredoxin system is comprised of:
- Thioredoxin reductase
These 3 systems are integral in the removal of reactive oxygen species through electron donation. As such, the thioredoxin system plays a critical role in repairing damaged DNA, reducing one-carbon methylation oxidative reactions, influencing immune signaling, as well as overlapping with glutathione reduction systems (R).
- TRX-1 is a master sulfur-containing redox protein in cells. TRX-1 is able to activate some of the more sought after and critical antioxidant pathways in human cells including:
- NRF1 and NRF2. NRF2 is a rate-limiting factor for glutathione synthesis (R). NRF1 is necessary for neurite growth (R) as well as mitochondrial DNA replication and transcription (R)
- The thioredoxin system overlaps with the glutathione reduction system (R)
- Many of the nuclear transcription factors such as NF kappa ß are dependent upon thioredoxin (R)
- PGC-1a – Regulation of mitochondrial biogenesis, it is induced by cellular stresses, such as free radicals, cold exposure and exercise
THERAPEUTIC TARGETS FOR TRX (THIOREDOXIN)
- Research in mice found that Sulforaphane induces thioredoxin through the ARE (antioxidant response element) system (R). Sulforaphane is an extensively studied compound from cruciferous vegetables with the notable ability to induce Nrf2, an important nuclear target which switches on important antioxidant systems, such as glutathione (R).
- A study in rats found that the trace mineral selenium increased thioredoxin reductase (R)
PGC-1a, ApoE4 & Alzheimer’s
- PGC-1a also known as PPARγ-coactivator-1α (peroxisome proliferator-activated receptor gamma coactivator 1-alpha) is a major therapeutic target for Alzheimer’s.
- ApoE4 mice have lower PGC1-a levels compared to ApoE3 R
- PGC-1a is a major transcriptional regulator of metabolic activities (R)
- PGC-1a is reduced in the Alzheimer’s brain (R)
- PGC-1a has been shown to reduce ß-amyloid plaque, modulate insulin resistance and reduce neuronal loss in a variety of models of Alzheimer’s disease (R)
- Ketogenic diet (a recommendation in the Bredesen protocol for Alzheimer’s) (R). It is worth noting that APOE 4/4 genotypes may not do well with ketogenic diets. This is based upon a few anecdotal reports, but more research is needed. It is suspected that APOE 4/4 genotypes absorb fat better than other APOE genotypes.
- Cold exposure (R)
- Fasting & caloric restriction (R)
- Exercise (R). The referenced study found PGC-1a levels peaked 2 hours following the leg extension exercises
- Acetyl L-carnitine (R) – This notable amino acid bound to an acetyl group may benefit acetylcholine levels (one target in Alzheimer’s), cognition, fat-burning, mitochondria function and a variety of other variables (R).
- Resveratrol (R), in addition it may modulate SIRT-1 as noted above
- PQQ – an in vitro study found PQQ increased PGC-1a (R)
APOE 4 & METALLOTHIONEIN
Metallothionein is a large, cysteine-rich antioxidant protein. It has a high affinity for zinc and is capable of scavenging a variety of toxic metals. Metallothioneins can also capture a variety of free radicals.
- Mice with the APOE 4 genotype were found to have reduced MT1 and MT2 hepatic mRNA, as well as lower metallothionein protein levels (R)
- Zinc administration can increase metallothionein induction (R)
- The redox state, including the ratio of glutathione to glutathione disulfide and selenium combine to affect metallothionein gene expression through complex interactions (R)
ApoE Status: Metabolic Healing Nutrigenomics Report
The Metabolic Healing Nutrigenomics Report allows consumers and healthcare practitioners to evaluate a variety of genetic markers, based upon their 23andme or AncestryDNA raw data files. This includes ApoE genetics.