Is L-Norvaline Bad for the Brain?
A 2019 study published in Toxicology in Vitro caused quite the stir in supplement circles when a common pre workout nitric oxide booster was shown to be cytotoxic to brain cells.
The ingredient in question?
The arginase inhibitor, and nitric oxide extender, L-Norvaline.
Let’s take a look beyond the attention-grabbing headlines, dive deep into the study and see what’s really going on here.
What is L-Norvaline?
L-Norvaline is a derivative of the branched-chain amino acid (BCAA) valine that has been noted in research to be a mixed arginase inhibitor.[1,2,6] Arginase is the enzyme in the body that degrades arginine -- the primary substrate used to generate nitric oxide, increase blood flow, and boost muscle pumps. It also plays a role in many inflammatory disorders by reducing nitric oxide synthesis and inducing fibrosis and tissue regeneration.
The theory goes that by limiting the actions of arginase, you’re removing the “governor” plate in your body allowing for unrestricted nitric oxide production, yielding stronger, longer-lasting pumps.
L-Norvaline isn’t the only arginase inhibitor commonly used in pre workout supplements either. Many pre workouts use Agmatine Sulfate
Now, as we mentioned L-Norvaline is a mixed arginase inhibitor, which means that it both degrades arginase in the liver as well as in the lumen of the GI tract and endothelium of blood vessels.
In regards to enhancing blood flow and pumps, arginase inhibition in the endothelium and lumen would be beneficial, in theory as it would lead to greater arginine availability. However, you would only benefit from the increased arginine if there was a subsequent enhancement in eNOS expression -- the enzyme that actually generates nitric oxide.
Furthermore, all studies using L-Norvaline are in unhealthy individuals, there is no substantial body of evidence in otherwise healthy individuals that L-norvaline exerts the same anti-arginase / anti-inflammatory activity.
Continuing on, arginase inhibition in the liver is a bit of a concern, as arginsase is a critical component of nitrogenous waste removal where it catalyzes the final step in the production of urea.
By inhibiting arginase in the liver to a large enough extent, there is the potential for an excess of ammonia in the body (hyperammonemia), which is often seen in individuals with congenital arginase deficiency, and may lead to brain injury and death.
And this brings us to the current study.
L-Norvaline and Cytotoxicity
Researchers took SH-SY5Y brain cells, placed them in petri dishes, and exposed them to 500-2000uM l-norvaline.
FYI, this verges on injecting yourself with upwards of 1g of L-Norvaline. The typical pre workout supplement contains between 100-300mg of L-Norvaline.
Researchers noted that brain cells die when exposed to L-Norvaline, and the longer they were exposed to it, the more toxic it was.
The method in which L-Norvaline caused neuronal cell death may be due to its starving the brain cells of energy, as tests showed it did not reduce the amount of mitochondria, but decreased their size.
Interestingly, researchers found that by increasing the concentration of the three BCAAs (Leucine, Isoleucine, and Valine), it was possible to fully protect against the toxic effects of L-Norvaline. It’s worth mentioning that the BCAAs are also the amino acids most closely related in structure to L-Norvaline. As a result, the BCAAs may limit L-Norvaline’s uptake into the cell by blocking system L transporters, the group responsible for transporting large, neutral amino acids into the cell.
In a follow-up press release to the publication of the study, Kate Samardzic, lead author of the study said:
“Protein requirements are higher in very active individuals and proteins are considered to improve and increase performance. The demand for amino acids in supplements has expanded but in addition to the normal protein-building amino acids other 'non-protein' amino acids are being taken.
Some non-protein amino acids are toxic because they can mimic protein amino acids and deceive the body into making faulty proteins; a property used by some plants to kill predators.
Some plants can even release non-protein amino acids into the soil to kill other plants so that they can have access to all the nutrients. Chemical warfare among plants is a well known phenomenon. Since there was evidence that L-norvaline has antimicrobial and herbicidal activity we examined its toxicity in human cells."
The Plot Thickens…
Shortly after publication, a rebuttal was published in the December 2019 issue of Brain Science aptly titled: “Reports of L-Norvaline Toxicity in Humans May Be Greatly Overstated.”
The authors point out several issues with the study suggesting norvaline’s cytotoxicity to neurons, namely that they used a cell culture model, no in vivo toxicity for norvaline has been established, and a few others I’ll discuss below.
The authors conclude:
“In brief, the conclusions of the study by Samardzic and Rodgers are significantly overstated and omit the fact that L-norvaline toxicity is limited to specific in vitro assays at exceedingly high concentrations… the study at hand does not confirm any human toxicity of L-norvaline; however, it makes claims unsupported by actual data, which resonate in newspaper articles and interviews. For example, they claim that “Bodybuilding supplement could be bad for the brain”, which is a misleading and false statement.“
Could L-Norvaline Be Beneficial for Cognitive Function?
Despite these more recent findings, previous research actually finds that L-Norvaline may support cognitive function and brain health.
As an arginase inhibitor, L-norvaline can boost nitric oxide production as well as reduce urea production.
Other research has shown that L-norvaline can inhibit the activity of ribosomal protein S6 kinase β-1 (S6K1) as well as offer anti-inflammatory properties. Combined, these actions suggest that L-Norvaline could be an effective option for Alzheimer’s Disease extremely effective in AD. Animal models of Alzheimer’s Disease have found that decreasing expression of S6K1 improves spatial memory and synaptic plasticity.
The Takeaway on L-Norvaline and Nitric Oxide
Now, it should be noted that the aforementioned “controversial” study on L-norvaline was conducted using cell cultures. It was not conducted with individuals ingesting L-Norvaline as they would in a pre workout supplement. Still, this does bring a bit of concern to the ingredient especially in regards to the amount and frequency of using it pre workout formulations.
In the end, low doses of L-Norvaline likely aren’t effective in healthy populations, high doses may be dangerous (and potentially toxic), and moderate doses may increase the bioavailability of co-ingested L-arginine.
- Arginase inhibitor in the pharmacological correction of endothelial dysfunction. Int J Hypertens. 2011;2011:515047.
- Ming XF, Rajapakse AG, Carvas JM, Ruffieux J, Yang Z. Inhibition of S6K1 accounts partially for the anti-inflammatory effects of the arginase inhibitor L-norvaline. BMC Cardiovasc Disord. 2009;9:12. Published 2009 Mar 13. doi:10.1186/1471-2261-9-12
- Samardzic, K., & Rodgers, K. J. (2019). Cytotoxicity and mitochondrial dysfunction caused by the dietary supplement l-norvaline. Toxicology in Vitro. https://doi.org/10.1016/j.tiv.2019.01.020
- University of Technology Sydney. "Bodybuilding supplement could be bad for the brain: People taking the protein supplement L-norvaline should be aware of its potential for harm, scientists say." ScienceDaily. ScienceDaily, 7 February 2019. <www.sciencedaily.com/releases/2019/02/190207102627.htm>
- Ivanenkov YA, Chufarova NV. Small-molecule arginase inhibitors. Pharm Pat Anal. 2014 Jan;3(1):65-85. doi: 10.4155/ppa.13.75. PMID: 24354980.
- Chang CI, Liao JC, Kuo L. Arginase modulates nitric oxide production in activated macrophages. Am J Physiol. 1998;274:H342–H348.
- Caccamo A, Branca C, Talboom JS, Shaw DM, Turner D, Ma L, Messina A, Huang Z, Wu J, Oddo S. Reducing Ribosomal Protein S6 Kinase 1 Expression Improves Spatial Memory and Synaptic Plasticity in a Mouse Model of Alzheimer's Disease. J Neurosci. 2015 Oct 14;35(41):14042-56. doi: 10.1523/JNEUROSCI.2781-15.2015. PMID: 26468204; PMCID: PMC4604237.