Root of tooth decay: NMR chews over liquorice

Dental caries inhibited

Dried liquorice root contains substances that apparently stop tooth decay. Research published in the Journal of the American Chemical Society describes the isolation and NMR spectroscopic analysis of key components.

Stefan Gafner of "Tom's of Maine", and colleagues, Chantal Bergeron, Jacquelyn R. Villinski, Markus Godejohann, Pavel Kessler, John H. Cardellina, Daneel Ferreira, Karine Feghali, Daniel Grenier, report that dried root of the liquorice plant (Glycyrrhiza uralensis) has been a common herbal remedy and flavouring for many years. The popular sweet or candy liquorice uses all sorts of flavourings but often has little to do with G uralensis nor its cousin G glabra and others and many sweet products commonly use anise oil instead as it has a similar flavour. The sweet taste of genuine liquorice root is due to the presence of triterpene glycosides. In addition liquorice species are known to contain some 300 flavonoid compounds, including several unusual isoflavans, isoflavenes, and pterocarpans. Regardless, the use of genuine licorice root in traditional medicine for a variety of ailments, including respiratory and digestive problems, has led some researchers to pursue the plant as a potential source of novel and perhaps diverse natural products with physiological activity.

It should be emphasised that there are known contra-indications for liquorice, such as raised blood pressure and interactions with some conventional prescription medications and over-the-counter pharmaceuticals products.

Supercritical extraction

Gafner and colleagues have used a variety of techniques to root out two intriguing substances from liquorice root. A supercritical fluid extract of liquorice root yield the compounds, which they have now shown can kill the major bacteria responsible for tooth decay and gum disease, Streptococcus mutans, S sobrinus, Porphyromonas gingivalis and Prevotella intermedia. Writing in the Journal of Natural Products, they explain that these substances could have a role in the development of agents for treating and preventing tooth decay and gum disease. Previously, the team had identified potent anti-inflammatory properties in a laboratory macrophage model and an ex vivo human whole blood model for supercritical carbon dioxide extracts of liquorice root.

The two liquorice compounds, licoricidin 1 and licorisoflavan A 2, were effective antibacterial substances. Licoricidin was also moderately active against a third gum disease bacterium, Fusobacterium nucleatum at 10 micrograms per millilitre. Pencillin G was shown to be an active control against all bacterial species tested, the team says.

The international collaboration involved researchers from Bruker-Biospin, in Rheinstetten, Germany, Reeves Group, in Walkersville, Maryland, The University of Mississippi, and the Universiteì Laval, Quebec City, Canada. They also found 20 known isoflavonoids and coumarins, and a glycycarpan, and a new pterocarpan the skeleton of which was obtained by proton NMR spectroscopy.

An additional point of interest regarding the isolated compounds is that the team showed that the two antibacterial compounds isolated can undergo suspected metal-catalyzed oxidative degradation.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.