A paper published in the journal Biosensors and Bioelectronics has caused a stir in the longevity community by showing that nicotinamide riboside (NR), a precursor to NAD+, makes tumors more aggressive in a mouse model [1].
Using a novel diagnostic tool
In this new paper, the researchers employed a well-known technique called bioluminescence imaging [2] to quantify NR uptake by cells and tissues, and they meticulously described how this was done.
The researchers were able to demonstrate that their bespoke bioluminescence probe called BiNR can be used to monitor NR uptake in real time both in vitro and in vivo. The purpose of BiNR is to help scientists gain new insights into the activity and effects of NR, and the researchers used it to assess how NR supplementation affects cancer dynamics.
NAD+ has a complex relationship with cancer. On one hand, cancer cells are highly metabolically active and require a lot of energy to grow and divide. For energy production, most cancers switch from cellular respiration to aerobic glycolysis due to the Warburg effect, which leads to an increased demand for NAD+ [3]. Many types of cancer cells have been shown to depend on metabolic pathways regulated by NAD+ [4]. On the other hand, activated immune cells that fight cancer also consume more NAD+, and there is evidence that NAD+ supplementation fights cancer by boosting the immune system [5].
Sample size affects significance
For their experiments in vitro, the researchers used the BiNR probe to quantify NR uptake in four human breast cancer cell lines. The signal from the probe was four times more intensive in triple negative breast cancer (TNBC) cells than in non-TNBC cells. However, the researchers did not show how this compares to non-cancer cells.
Moving to the in vivo stage, the researchers divided several mice into two groups, putting one on a regular diet and the other one on an NR-rich diet. Two weeks later, both groups were inoculated with cells from the MDA-MB-231 TNBC cancer line. By week 10 of the experiment, 7 out of 10 mice in the NR group and 5 out of 9 mice in the control group had detectable tumors: a 27% difference. However, with such a small sample size, this was not statistically significant data, and even a single mouse could have changed the results.
The next experiment, in which the researchers assessed the effect of NR supplementation on the rate of tumor metastases’ formation by injecting MDA-MB-231 cells directly into the heart, was more clear-cut: 9 out of 11 mice in the study group and only 3 out of 12 in the control group developed metastases. This result easily clears the bar of statistical significance.
Interestingly, the researchers also demonstrated the anti-cancer side of NR by showing that its uptake is sharply increased in T cells upon activation. This suggests that both cancer cells and cancer-fighting cells need NAD+ to fuel their increased energy demands, and scientists might have to figure out the way to strike a good balance here.
Conclusion
Growing evidence suggests that NAD+ supplementation has many health benefits, but this study shows that its universal ability to spur cellular activity needs to be carefully studied and considered when devising treatments. It is possible that prior to cancer emergence, NAD+ supplementation fuels the immune system in ways that help prevent cancer, but after the disease is there, it fuels the cancer cells as well. Of course, more research is needed to either support or disprove this hypothesis.
Under normal circumstances, aggressive cancer cells do not suddenly appear in a living organism, and this study did not attempt to assess whether or not NR increases cancer risk in cancer-free mice. This should serve as a reminder that when it comes to science, we should read beyond the headlines and not rush to conclusions.
Literature
[1] Maric, T., Bazhin, A., Khodakivskyi, P., Mikhaylov, G., Solodnikova, E., Yevtodiyenko, A., … & Goun, E. (2022). A bioluminescent-based probe for in vivo non-invasive monitoring of nicotinamide riboside uptake reveals a link between metastasis and NAD+ metabolism. Biosensors and Bioelectronics, 114826.
[2] Sadikot, R. T., & Blackwell, T. S. (2005). Bioluminescence imaging. Proceedings of the American Thoracic Society, 2(6), 537-540.
[3] Luengo, A., Li, Z., Gui, D. Y., Sullivan, L. B., Zagorulya, M., Do, B. T., … & Vander Heiden, M. G. (2021). Increased demand for NAD+ relative to ATP drives aerobic glycolysis. Molecular cell, 81(4), 691-707.
[4] Gujar, A. D., Le, S., Mao, D. D., Dadey, D. Y., Turski, A., Sasaki, Y., … & Kim, A. H. (2016). An NAD+-dependent transcriptional program governs self-renewal and radiation resistance in glioblastoma. Proceedings of the National Academy of Sciences, 113(51), E8247-E8256.
[5] Morandi, F., Horenstein, A. L., & Malavasi, F. (2021). The key role of NAD+ in anti-tumor immune response: an update. Frontiers in Immunology, 12, 658263.
