Liquorice versus SARS

An extract of liquorice root already used to treat HIV could become the first line of defence against a future outbreak of SARS, according to German researchers.

The World Health Organization has declared the present SARS outbreak officially over much to the relief of people around the world, but especially those in the Far East and Canada. Now, medical researchers are working on the first line of defence against the next wave of severe acute respiratory syndrome should it emerge again.

SARS is a highly infectious disease, recently identified as a new coronavirus. While the present outbreak seems to have been controlled there are new concerns that it might be a seasonal disease and could emerge again. Ribavirin is the most commonly used antiviral for treating SARS infection and it is used in combination with anti-inflammatory steroids, although no definitive treatment has yet been identified against the coronavirus that causes the disease. A fast-track research paper in The Lancet suggests that the antiviral agent glycyrrhizin could be more effective than other antiviral drugs in the treatment of SARS.

SARS coronavirus

Jindrich Cinatl and colleagues at the Frankfurt University Medical School, Germany, have tested the antiviral potential of five drugs - ribavirin, 6-azauridine, pyrazofurin, mycophenolic acid, and glycyrrhizin - against two isolates of the SARS coronavirus from patients with SARS admitted to the clinical center at Frankfurt University. Each compound is a commercial product having previously been used in antiviral, antitumor, or as an immunosuppressive.

The researchers found that glycyrrhizin, a triterpene glycoside originally isolated from liquorice root that has proven efficacy against the unrelated viruses HIV-1 and hepatitis C infection, was the most active antiviral in inhibiting replication of the virus. Its mode of action is thought to involve increased nitrous oxide synthesis. "The mechanism of glycyrrhizin's activity against SARS-CV is unclear," explains Cinatl. However, it is known that glycyrrhizin affects cellular signalling pathways such as protein kinase C; casein kinase II; and transcription factors such as activator protein 1 and nuclear factor kappa-B. The researchers point out that glycyrrhizin and its aglycone metabolite 18-beta glycyrrhetinic acid upregulate expression of the enzyme nitrous oxide synthase and production of nitrous oxide in macrophages, which coincides with the inhibition of virus replication and so could be the underlying mechanism.

The German investigators comment that their findings "suggest that glycyrrhizin should be assessed for treatment of SARS."

Lancet, 2003, 361, 2045-2046