Amino acids are the building blocks of the proteins that do much of the work in cells. Changes in amino acid levels can affect how cells function, and recent research suggests that low levels of one amino acid, arginine, can leave aging bodies vulnerable to colon cancer.

Arginine is part of a protein, MHC-1, that sits on the outside of most cells. It helps immune cells mount an appropriate immune response against threats to the cell, such as cancerous cells or a viral or bacterial infection.

The results suggest that increasing arginine intake could help keep one's immune system strong.

A team led by researchers at Rockefeller University has found that low levels of arginine affect the expression of genes that code for MHC-1 in models of colon cancer and respiratory viruses such as influenza and SARS-CoV-2, the virus that causes COVID-19 in mice.

When arginine levels are low, fewer MHC-1 proteins are made, cells grown in the lab showed. The result — fewer T cells are called to destroy the affected and infected cells.

These findings suggest that old age, a time when arginine levels naturally decline, and diet create the perfect environment for colon cancer to develop, Sohail Tavazoie, corresponding author on the study, told TheDoctor in an email.

An age-related decrease in arginine may also be the reason why older people have higher mortality rates when they have respiratory viruses like influenza and SARS-CoV-2.

First author Qiushuang Wu, a postdoctoral fellow at Rockefeller, used mouse models to test the effect of different levels of arginine in the diet on the risk of colon cancer.

Mice with lower levels of dietary arginine developed more tumors than those whose diet contained higher levels of arginine. She got the same results when she repeated these experiments with mouse models of influenza and COVID-19.

Wu also found that mice fed an arginine-rich diet had milder symptoms after viral infection. Giving mice arginine after they were infected with the influenza virus also improved their outcomes.

An age-related decrease in arginine may also contribute to high mortality rates among older persons from respiratory viruses like influenza and SARS-CoV-2.

The results suggest that increasing arginine intake could help keep one's immune system strong. As Tazavoie said, “A well-balanced diet may prevent arginine deficiency.”

For those hoping to strengthen their bodies' immune responses, he noted that many high-protein foods are rich in arginine, including:

  • Nuts, such as walnuts and almonds, and pumpkin seeds
  • Meats, such as chicken and turkey
  • Seafood, such as tuna, salmon, shrimp
  • Legumes, such as chickpeas, lentils and soybeans
  • Grains, such as brown rice and oats

The researchers hope arginine supplementation may offer humans the same benefits as those seen in mice. “Considering arginine is inexpensive and readily available,” Tavazoie, head of the Elizabeth and Vincent Meyer Laboratory of Systems Cancer Biology at Rockefeller, explained, “we hope that therapeutic and preventative studies can be done soon.”

Arginine supplementation could be tested in patients receiving immunotherapies, for example, or given to at-risk patients who have been exposed to viral pathogens like flu or COVID.

The study is published in Cell.