Scientists tested arginine supplements on mice and found that increasing arginine levels reduced cancer tumors and made viral infections milder, writes Medical News Today.
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Since arginine is relatively inexpensive, scientists hope that in the future it could become an affordable supplement to existing treatments – of course, if these results are confirmed by human studies.
The study was published in the scientific journal “Cell”.
How can arginine affect the immune system?
Arginine is an amino acid abundant in protein-rich foods: meat, fish, dairy products, nuts, and legumes.
Amino acids are often called the “building blocks” of proteins. Arginine is also important for the immune system, circulation, wound healing, and other bodily processes.
The body produces some arginine on its own and obtains some from food. However, in cases of cancer or viral infections, such as COVID-19, its levels in the body may decrease.
Such conditions can activate immune cells that produce the enzyme arginase, which breaks down arginine.
The authors of the new study wanted to find out whether such changes in arginine levels could directly affect the body’s immune response to cancer and viral infections.
First, they analyzed existing data on amino acid levels in cancerous tissues and lung tissues of mice infected with flu or SARS-CoV-2 virus.
The analysis showed that arginine was one of the amino acids whose levels consistently decreased under these conditions.
Then the scientists restricted arginine levels in human and mouse colon cancer cells. They also studied human melanoma, breast, stomach, and pancreatic cancer cell lines.
The team measured the amount of a protein called class I major histocompatibility complex (MHC-I). This protein helps the immune system recognize infected or altered cells.
The scientists evaluated how many antigens cancer cells presented on their surface and how effectively CD8 T lymphocytes destroyed them. They also studied how arginine affects protein production in cells.
Later, the scientists fed mice with induced colon cancer different diets – with higher, normal, or restricted arginine levels.
In separate experiments, mice were infected with flu or a mouse-adapted form of the SARS-CoV-2 virus. Researchers monitored weight loss, survival, virus levels in the body, and lung damage.
Arginine improved cancer and viral infection outcomes in mice
Arginine restriction reduced MHC-I protein levels in human and mouse colon cancer cells. A similar effect was observed in other cancer cell lines.
Providing mice with more arginine reduced colon tumors and also improved the course of flu and SARS-CoV-2 infections.
Cancer cells with less arginine presented fewer antigens on their surface. As a result, CD8 T lymphocytes were less able to recognize and destroy cancer cells.
When arginine levels were restored after 24 hours of restriction, MHC-I protein levels increased again within a few hours.
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Scientists found that at low arginine levels, ribosomes – cell structures responsible for protein production – began to stall when producing MHC-I protein.
In experiments with colon cancer, mice fed more arginine developed fewer and smaller tumors. Meanwhile, mice receiving less arginine developed more tumors.
Arginine supplements also reduced weight loss and mortality in flu-infected mice. Positive effects were observed even when supplements were started one day after infection.
In SARS-CoV-2 infected mice, arginine supplements reduced weight loss, virus levels in the body, and lung damage.
One of the study authors, physician and scientist Sohail Tavazoie, said that the amount of arginine given to mice, when converted to humans, would correspond to about 10 grams of arginine per day.
His team hopes to study the effects of arginine supplements in humans with flu and at high risk of severe disease in the future.
The US National Institutes of Health indicate that doses of 9–30 grams of arginine can cause digestive discomfort and slightly lower blood pressure.
Therefore, human studies are necessary to show whether a dose of about 10 grams of arginine per day is safe and can truly improve health.
Is it worth taking arginine supplements to boost the immune system?
Surgeon oncologist Dr. Anton Bilchikas, who was not involved in the study, said the research reveals an interesting and potentially important role of arginine – an inexpensive and widely available amino acid.
According to the expert, most healthy people can generally tolerate 10 grams of arginine per day, but such a dose may pose risks for people with kidney or liver diseases. Therefore, consulting a healthcare professional before taking arginine to boost immunity is advisable.
“Patients should not start taking supplements like arginine on their own hoping to strengthen immunity or improve cancer treatment outcomes until we have more reliable human studies,” he warned.
Professor of public health at New Mexico State University Jagdish Khubchandani, who also was not involved in the study, agreed that arginine could theoretically improve MHC-I protein production.
However, he emphasized that the study was conducted under highly controlled conditions with animals and examined specific antiviral and anticancer situations.
“Until there are human studies, the practical value of these results is very limited,” he said, adding that it remains to be determined who could benefit from arginine and under what circumstances.
The expert stressed that people with cardiovascular, kidney, or liver diseases, as well as pregnant women, should not take such amounts of arginine without medical supervision.
“We have too many nutrition fads and supplements, most of which are almost worthless,” Khubchandani warned, adding that the next necessary step should be human studies.
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