Arginine and Alzheimer's Prevention: Linking Diet, Immunity, and Brain Health

New study on Alzheimer's and arginine, plus circling back to the T cell exhaustion study

A new study published in the journal Neurochemistry International shows that the amino acid arginine may help to prevent amyloid-beta plaque accumulation in animal models of Alzheimer’s disease.

Background on Arginine:
Arginine is a semi-essential amino acid that is used in the body for protein synthesis and nitric oxide synthesis. It is also the precursor for other amino acids, including proline and creatine.

Semi-essential, in amino acid terms, means that most of the time the body can produce enough arginine to meet its needs. For arginine, this means that the body can synthesize it from glutamine via citrulline. In the lining of the small intestine, glutamine (or glutamate) is converted to citrulline, which is then carried in the bloodstream to the kidneys, where it is converted to arginine. In times of physical stress, such as for significant wound healing, sepsis, burns, or trauma, or when in kidney failure, arginine is essential to get from the diet. Arginine is also a key amino acid needed for optimal T cell function in cancer or chronic infections.

The New Study:
The study looked at the interaction of arginine with amyloid-beta plaque. The researchers used cell models and then used animal models of multiple types of familial Alzheimer’s mutations. The animals were treated with arginine added to their water starting at a relatively early age. Compared to a control Alzheimer’s model group, the arginine groups had significantly less amyloid-beta accumulation and a substantial decrease in inflammatory cytokine levels. Wildtype mice (no Alzheimer’s mutations) showed no significant changes from arginine consumption (no changes in weight, no changes in normal inflammation levels, no behavior changes, etc). The researchers note that arginine can help to prevent aggregation of polyglutamine proteins in certain diseases, including spinocerebellar ataxia.¹

What Else Is Known About Arginine and Alzheimer’s?

You may be thinking, “So what?” that the amino acid prevents amyloid beta buildup in mice. A lot of things are effective in mouse models of Alzheimer’s disease (AD)…

There are several reasons that this study stands out: studies showing reduced arginine in Alzheimer’s disease patients, immune system changes, gut microbiome connection, and dietary connections.

First, it’s been known for a while that arginine and the metabolites of arginine are altered in the brain samples of Alzheimer’s patients. One of the downstream metabolites of arginine is spermidine, which is also decreased in AD.² ³

Arginine, Diet, and Mild Cognitive Impairment
A nifty study from 2021 looked at the effect of diet on amino acid composition in the cerebrospinal fluid of people with mild cognitive impairment (MCI) and a normal control (NC) group. The trial involved a diet high in saturated fat and high glycemic index (called the High Diet) compared to a diet low in saturated fat and with a low glycemic index (called the Low Diet). The participants with MCI eating the High Diet had a significant decrease in arginine levels in their cerebrospinal fluid. A couple of other amino acids, including valine and isoleucine, were also altered by diet and only in the MCI group.⁴

This ties together the epidemiological studies showing that a high fat/high glycemic index diet increases the risk of Alzheimer’s disease with decreased arginine in the brain.

Immune System and T Cell Exhaustion:
Arginine is also the limiting factor in powering T cells, and not enough arginine can increase T cell exhaustion.⁵ I wrote about it recently — explaining a study on how sucralose changes the gut microbiome in a way that limits arginine production. The lack of arginine then increases T cell exhaustion in cancer patients undergoing immunotherapy.

The question is: Are T cells plaing a role in Alzheimer’s disease?

T cells are a type of white blood cell, part of the adaptive immune system. They can be activated by antigens, such as those from a virus, bacteria, or cancer, and then act to kill off the bad/infected cells. T cells have surface receptors that can downregulate the response, called checkpoints. When T cells have been stimulated continually by an antigen for a while, they can become exhausted. In the exhausted state, the checkpoint proteins are increased, and the T cells no longer mount the normal immune response.

A number of studies have shown that amyloid beta plaque may form in response to a persistent viral infection in the brain, such a herpes simplex virus (HSV1 or HSV2).⁶ ⁷

T cell activation has been studied in the brain for Alzheimer’s disease for a couple of decades or more, and higher T cell response toward amyloid-beta is found in older adults with Alzheimer’s disease.⁸

Multiple clinical trials are currently going on for several types of vaccines that stimulate the immune system against the amyloid-beta or tau protein in the brain. This isn’t a new idea, with vaccine trials for Alzheimer’s dating back decades. One of the prior clinical trials found that some patients ended up with meningoencephalitis from the vaccine due to an excessive inflammatory response, so the goal is to not overstimulate the immune response. ⁹¹⁰¹¹¹²¹³

T cell exhaustion, in the context of the brain, could mean that a persistent infection is no longer kept in check by the immune system or that persistent antigen stimulation is occurring. One conundrum with Alzheimer’s is that some people with amyloid-beta buildup have no cognitive impairment, while others will have dementia. In a study involving cerebral spinal fluid samples from people with amyloid-positive brains but who were cognitively normal compared with amyloid-positive plus cognitive impairment, the researchers found T cell exhaustion only in those with cognitive impairment.¹⁴

Dietary Sources of Arginine:
Arginine is found in protein-rich foods, such as meat, fish, dairy, nuts, and seeds. It is also made by a healthy gut microbiome. (Again, a connection to AD risk from altered gut microbes.)

Arginine Supplements:
Arginine is also available as a supplement in powdered form* or in capsules. The advantages of powder are that you can vary your dose, starting low and increasing. However, without clinical trials to know how much is effective. Arginine can decrease blood pressure, so talk with your doctor if you have any questions or are on any medications.

Supporting Arginine Production Through the Gut Microbiome
The recent study showing that sucralose (an artificial sweetener) altered the gut microbiome in a manner that reduces arginine production is a good reminder that gut health is important and complex.

Lactobacillus rhamnosus GG is a probiotic that has been shown in clinical trials to both enhance gut barrier function and specifically to stimulate gut arginine metabolism. You can get L. rhamnosus GG as a standalone probiotic or as part of a probiotic multistrain complex. ¹⁵

Conclusion:
Is arginine a key supplement that everyone should take to prevent Alzheimer’s? We really need more studies than just mouse and cell studies to know. I kind of doubt that it is the one single supplement that will cure all, but it makes sense that T cell exhaustion and arginine could be part of the problem. The arginine connection nicely ties in the gut microbiome and the immune system, both of which have decades of studies on them in terms of their connection to AD.

1. https://www.sciencedirect.com/science/article/pii/S019701862500155X

2. https://pubmed.ncbi.nlm.nih.gov/24746363/

3. https://pmc.ncbi.nlm.nih.gov/articles/PMC2600464/

4. https://pmc.ncbi.nlm.nih.gov/articles/PMC8673538/

5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5075284/

6. https://pubmed.ncbi.nlm.nih.gov/39956964/

7. https://link.springer.com/article/10.1186/s12974-024-03166-9

8. https://pmc.ncbi.nlm.nih.gov/articles/PMC166296/

9. https://www.pnas.org/doi/10.1073/pnas.0506209103

10. https://www.sciencedirect.com/science/article/abs/pii/S0264410X06006566

11. https://www.insideprecisionmedicine.com/topics/precision-medicine/nuravax-alzheimers-vaccine-to-amyloid-beta-is-safe-immunogenic-in-phase-1/

12. https://hscnews.unm.edu/news/unm-researchers-plan-clinical-trials-to-test-vaccine-against-alzheimers-promoting-tau-protein-6911889

13. https://www.sciencedirect.com/science/article/abs/pii/S0889159125002089

14. https://pmc.ncbi.nlm.nih.gov/articles/PMC10516910/

15. https://pmc.ncbi.nlm.nih.gov/articles/PMC12282327/

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