Turns out that tub of black licorice you got from Costco, and managed to eat in only a few days (don’t worry, I won’t tell anybody!), might have actually done you some good. A recent publication in NeuroToxicology shows that liquiritigenin, a chemical found in the licorice root, may be a neuroprotecting agent.
So what’s the magic behind this yummy treat? Liquiritigenin may reduce the toxicity of glutamate, a compound naturally found in our brain. Under normal conditions, glutamate acts a signaling molecule, allowing neurons to communicate with one another. Although glutamate is essential for healthy brain activity and regulates important functions like learning and memory, too much of it can be toxic to neurons. As Paracelsus infamously said, “the dose makes the poison.” What is good at one dose is often toxic at another, and glutamate is no different.
While some neurotransmitters are inhibitory, causing neurons to be less likely to fire action potentials, other neurotransmitters such as glutamate are excitatory, and cause neurons to be more likely to fire. Thus, when glutamate reaches high levels in the brain, it overexcites neurons, causing them to fire more frequently. This overexcitation of neurons can lead to excitotoxicity or even neuronal cell death.
Let me give you a brief primer on excitotoxicity. When a neuron is exposed to too much glutamate, it causes more positive ions to enter the cell, including calcium. Small, localized increases in calcium levels are normal and are one of the signals involved in causing a neuron to fire an action potential. Calcium in high levels, however, is very toxic to the cell and can cause an increase in oxidative stress, a breakdown of membranes, and/or the degradation of essential proteins. Taken together, these effects of calcium on the cell cause the cell to no longer be able to function properly, and ultimately results in cell death. To sum it up, too much glutamate can result in too much calcium, which is toxic to neurons and can cause them to die.
Glutamate deregulation and toxicity is thought to play a role in the cell loss responsible for Alzheimer’s disease and Huntington’s disease, among several other neurological disorders. Consequently, finding a way to quench glutamate toxicity could potentially have significant neural health benefits. To test the neuroprotective benefits of liquiritigenin, Yang et al. utilized neural cell cultures and examined the toxic effects of increased glutamate levels. The researchers showed that, under normal conditions, increasing glutamate in the culture media caused neural toxicity and cell death. However, when liquiritigenin was included in the culture media, the neural toxicity/death was greatly reduced! These findings are in line with previous studies, which demonstrated that licorice extracts could protect against heart damage, cancer and inflammation. However, this is the first report looking at glutamate neurotoxicity in particular. Further work will be needed to confirm that these findings extend from the culture dish to the human body.
Written by Ciara Martin
Yang E.J., Park G.H. & Song K.S. (2013). Neuroprotective effects of liquiritigenin isolated from licorice roots on glutamate-induced apoptosis in hippocampal neuronal cells, NeuroToxicology, 39 114-123. DOI: 10.1016/j.neuro.2013.08.012