People taking the protein supplement L-norvaline – an ingredient widely used in body building supplements and promoted as a compound that can boost workouts and aid recovery – should be aware of its potential for brain harm, Australian scientists say. Similar compounds have been linked to neuro-degenerative diseases and a study on human cells, by scientists from the University of Technology Sydney, suggests L-norvaline may also cause damage to brain cells.
The study showed that even at relatively low concentrations the amino acid L-norvaline could make cells unhealthy and eventually kill them.
L-norvaline is one of hundreds of amino acids that are not normally used to make proteins in humans. In recent years the popularity of dietary supplements to enhance body strength and muscle performance has meant that many now contain lots of unusual amino acids that can do harm.
Lead author of the study Kate Samardzic said that the highest consumption of amino acids is among athletes and bodybuilders. “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,” the UTS School of Life Sciences PhD candidate said.
“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,” Samardzic said.
This is the first study that investigates the toxicity of L-norvaline in human cells, specifically testing its effect on the health of brain cells arising from its ability to mimic protein amino acids.
Associate professor Ken Rodgers who led the research said the study revealed that L-norvaline while, it might initially allow cells to produce more energy, after a while the machinery of the cell that generates the energy is damaged. People are taking supplements such as this without really knowing much about what the long-term consequences might be.
In addition to the 20 protein amino acids that are encoded for protein synthesis, hundreds of other naturally occurring amino acids, known as non-proteinogenic amino acids (NPAAs) exist. It is well known that some NPAAs are toxic through their ability to mimic protein amino acids, either in protein synthesis or in other metabolic pathways, and this property is utilised by some plants to inhibit the growth of other plants or kill herbivores. L-norvaline is an NPAA readily available for purchase as a dietary supplement. In light of previous evidence of l-norvaline’s antifungal, antimicrobial and herbicidal activity, we examined the toxicity of l-norvaline to mammalian cells in vitro and showed that l-norvaline decreased cell viability at concentrations as low as 125 μM, caused necrotic cell death and significant changes to mitochondrial morphology and function. Furthermore, toxicity was reduced in the presence of structurally similar ‘protein’ amino acids, suggesting l-norvaline’s cytotoxicity could be attributed to protein amino acid mimicry.
Kate Samardzic, Kenneth J Rodgers