A high intake of salt can trigger antitumor immune reactions.
More and more studies have been pointing to the pro-inflammatory effects of excessive salt intake.
However, in the case of cancer, inducing a pro-inflammatory state may be beneficial in the fight against tumors. Recently, immunotherapy has emerged as one of the most promising avenues for treating cancer.
So, in this context, a team of researchers set out to examine the effects of a high-salt intake on tumor growth in cell cultures and two independent mouse models.
Professor Markus Kleinewietfeld — who is the head of the VIB-UHasselt lab, that is, a collaboration between VIB (the Flanders Institute for Biotechnology) and the University of Hasselt in Belgium — led the research team.
Prof. Kleinewietfeld and colleagues published their findings in the journal Frontiers in Immunology.
How a high-salt intake inhibits tumors
The researchers conducted a cell-culture experiment where they replicated a high-salt environment.
They found that excessive salt inhibited the function of a type of immune cell scientists call myeloid-derived suppressor cells (MDSCs) both in mice cells and in human MDSCs taken from cancer patients.
A high-salt environment stopped MDSCs from inhibiting other immune cells almost completely. Previous studies, explain the researchers, have suggested that MDSCs are key in preventing the immune system from effectively attacking tumors.
In this study, depleting MDSCs altogether while keeping the high-salt environment reversed the inhibitory effects on tumor growth, confirming that MDSCs are crucial for anticancer immunotherapy.
Also, in a mouse model of melanoma transplantation, rodents that were fed a diet high in salt "showed a significantly inhibited tumor growth" compared with the control group, explain the authors.
"Delayed tumor outgrowth was evident as early as day 11 post-injection," they write, "leading to significant differences in tumor size between both groups at day 13 [post-injection] and at the day of sacrifice."
Finally, Prof. Kleinewietfeld and team sought to reproduce these results in a different model. So, they used a mouse model of lung cancer.
In this model also, a diet high in salt "significantly delayed [lung cancer] tumor growth," report the researchers.
"Thus," they conclude, "[a high-salt diet] was able to significantly inhibit tumor growth in two independent tumor transplantation models."
"The findings are highly interesting, and we were surprised to see such an effect on tumor growth just by increasing the salt in the diet."
Prof. Markus Kleinewietfeld
"However," continues the lead researcher, "future studies are needed to fully understand the effect and the detailed underlying molecular mechanisms behind to judge its therapeutic potential for anticancer immunotherapies."
According to the American Cancer Society, there will be 1,762,450 new cases of cancer by the end of 2019 in the United States, and 606,880 people will have died, as a result.