A common amino acid reduces brain plaques in animal models of Alzheimer’s disease

A new study suggests that arginine, a common amino acid, may help reduce the brain plaques associated with Alzheimer’s disease. The researchers found that consuming this compound reduced the accumulation of toxic proteins and improved symptoms in both fruit flies and mice. These findings were published in Neurochemistry International.

Alzheimer’s disease is a progressive condition characterized by the decline of memory and cognitive function. One of the primary biological markers of the illness is the buildup of amyloid beta. This protein fragment clumps together in the brain to form sticky plaques. These aggregates are thought to disrupt communication between nerve cells and trigger inflammation. Eventually, this process leads to the death of brain cells and the symptoms of dementia.

Medical researchers have spent decades looking for ways to stop or reverse this accumulation. Recent years have seen the approval of antibody-based therapies that target amyloid beta.

While these drugs represent significant progress, they come with substantial challenges. They are often expensive and require administration through intravenous lines. They also carry the risk of serious side effects, such as swelling or bleeding in the brain. There is a persistent need for treatments that are safer, more affordable, and easier to administer.

A team of researchers from Kindai University in Japan investigated a different approach. The group included Kanako Fujii, Toshihide Takeuchi, and Yoshitaka Nagai. They focused their attention on arginine. This is a naturally occurring amino acid that the body uses for various functions, including building proteins.

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Arginine acts as a chemical chaperone. This means it helps other proteins fold into their correct shapes and prevents them from sticking together inappropriately. The team hypothesized that this property might stop amyloid beta from clumping into harmful plaques.

The investigation began with experiments in a controlled laboratory setting. The researchers mixed amyloid beta peptides with varying concentrations of arginine in test tubes. They used a special dye called Thioflavin T to measure the formation of clumps. This dye glows when it binds to amyloid fibrils.

The results showed that arginine prevented the protein from aggregating. The effect was stronger when higher concentrations of the amino acid were used. The scientists also used electron microscopes to look at the structures directly. They observed that the amyloid fibrils were shorter and less developed in the presence of arginine.

“Our study demonstrates that arginine can suppress Aβ aggregation both in vitro and in vivo,” explains Nagai. “What makes this finding exciting is that arginine is already known to be clinically safe and inexpensive, making it a highly promising candidate for repositioning as a therapeutic option for AD.”

Following the test tube experiments, the team tested their hypothesis on living organisms. They utilized fruit flies that had been genetically modified to produce a specific, highly toxic form of amyloid beta. This genetic variation is known as the Arctic mutation. In these flies, the toxic protein accumulates in the eyes. This causes visible tissue damage and shrinkage. The researchers fed some of these flies a diet supplemented with arginine.

The flies that consumed arginine showed significantly less damage to their eyes. The treatment appeared to protect the tissue from the toxicity of the amyloid protein. The researchers analyzed the tissues and found that the actual amount of accumulated protein had decreased. This suggested that the amino acid was working inside the living body just as it had in the test tube.

The team then moved on to a more complex animal model. They used mice that had been genetically engineered to carry human genes associated with familial Alzheimer’s disease. These mice, known as the AppNL-G-F model, are bred to develop amyloid plaques as they age. They also exhibit behavioral changes similar to the cognitive decline seen in humans. The researchers provided these mice with drinking water containing arginine.

The treatment began when the mice were five weeks old. The researchers monitored the animals over several months. They examined the brains of the mice at six months and nine months of age. The team found that the mice treated with arginine had significantly fewer amyloid plaques in the cortex and hippocampus. These are regions of the brain vital for memory and learning.

The scientists used a specialized staining technique to identify the dense cores of the plaques. This analysis confirmed that the treatment had suppressed the formation of these hardened protein deposits. The total surface area of the brain covered by plaques was reduced in the treated group.

The researchers also measured the levels of insoluble amyloid beta. This is the form of the protein that is hardest for the brain to clear. The treated mice had lower levels of this stubborn material compared to the untreated group.

Beyond looking at brain tissue, the researchers assessed the behavior of the animals. They utilized a standard assessment called the Y-maze test. This test measures a mouse’s willingness to explore new environments. It is a common way to gauge short-term memory and spatial learning in rodents. Mice with cognitive deficits tend to be less active and less likely to alternate between the different arms of the maze.

The untreated mice showed signs of reduced activity and exploration as they aged. In contrast, the mice that drank the arginine solution performed better. Their movement and exploration patterns were closer to those of healthy, wild-type mice. This suggested that the reduction in plaques was translating into preserved brain function.

The study also looked at inflammation in the brain. The accumulation of plaques typically triggers an immune response. This leads to the release of inflammatory signaling molecules called cytokines. Chronic inflammation is believed to worsen the damage caused by Alzheimer’s.

The researchers measured the genetic expression of several inflammatory markers. They found that the levels of these markers were lower in the mice treated with arginine. This indicated that the treatment had dampened the harmful immune response in the brain.

“Our findings open up new possibilities for developing arginine-based strategies for neurodegenerative diseases caused by protein misfolding and aggregation,” notes Nagai. “Given its excellent safety profile and low cost, arginine could be rapidly translated to clinical trials for Alzheimer’s and potentially other related disorders.”

There are important caveats to consider regarding this research. The study relied on animal models rather than human subjects. While the mouse models are sophisticated, they do not perfectly mimic the complexity of human Alzheimer’s disease.

For instance, the mice used in this study do not develop neurofibrillary tangles. Tangles are another major hallmark of the human disease involving a protein called tau. The mice also do not experience the extensive death of neurons that occurs in human patients.

The genetic mutations used in the mouse and fly models are specific to rare, familial forms of Alzheimer’s. Most human cases are sporadic and do not involve these specific mutations. It is not yet guaranteed that the treatment would work effectively for the general population.

Additionally, the dosage of arginine used in the experiments was quite high. It was adjusted for the metabolism of the animals. Determining the correct and safe dosage for humans would require specific clinical trials.

The researchers emphasize that people should not self-medicate with high doses of supplements based on these early results. The formulation used in the study was optimized for research. Commercial supplements may vary in quality and concentration. Excessive intake of any supplement can lead to imbalances in the body.

Future research will need to bridge the gap between these animal studies and human application. Clinical trials are necessary to verify safety and efficacy in people. Scientists will need to determine how arginine affects the progression of the disease in its later stages.

They will also need to see if it can help with other neurodegenerative conditions. Despite these remaining questions, the study provides a proof of concept. It suggests that supporting the body’s ability to fold proteins correctly could be a viable strategy for fighting dementia.

The study, “Oral administration of arginine suppresses Aβ pathology in animal models of Alzheimer’s disease,” was authored by Kanako Fujii, Toshihide Takeuchi, Yuzo Fujino, Noriko Tanaka, Nao Fujino, Akiko Takeda, Eiko N. Minakawa, and Yoshitaka Nagai.