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PARIS, June 13 (AFP) - A major ingredient in licorice has proven remarkably successful at combatting the SARS virus in lab-dish tests, according to a German study reported on Saturday in the British weekly journal The Lancet.
Glycyrrhizin, a compound extracted from licorice roots which has been previously explored in anti-viral research, was highly effective at stopping the SARS virus from reproducing, the authors say.
It easily beat out four standard compounds used to block virus or tumorous cell replication -- ribavirin, 6-azauridine, pyrazofurin and mycophenolic acid.
The research is only a preliminary study and much further work is needed, assessing safety as well as effectiveness, before anyone can call glycyrrhizin a cure for Severe Acute Respiratory Syndrome (SARS).
Even so, the findings are so positive that it should be taken seriously as a potential weapon in the fight against this disease, say the team, led by Jindrich Cinatl from Frankfurt University Medical School.
The experiment involved taking samples of the SARS virus from two patients with SARS who had been admitted to the university's medical centre.
The viruses were then used to infect Vero cells, a tissue culture of monkey kidney cells that are a standard item of lab equipment.
The dishes were exposed to each of the five compounds and examined 72 to 96 hours later to see how many infected cells had reproduced.
Ribavirin -- a drug widely used against SARS but which has had very disappointing results -- did nothing to stop the virus sample from replicating, nor did mycophenolic acid.
Pyrazofurin and 6-azauridine had low and modest effect respectively, but were outclassed by glycyrrhizin, which was more than five times more effective than those two compounds and at high concentrations completely blocked replication.
"Of all the compounds, glycyrrhizin was the most active in inhibiting replication of the SARS-associated virus. Our findings suggest that glycyrrhizin should be assessed for treatment of SARS," Cinatl's team says.
Glycyrrhizin gets its name from Glycyrrhiza glabra, the Latin sobriquet for the licorice plant, which homeopathic medicine has long claimed to be useful in tackling respiratory, urinary and digestive irritations and infections of the mouth and throat. Licorice is especially used in traditional Chinese medicine.
Glycyrrhizin has previously been used experimentally against hepatitis B and C virus and even against the AIDS virus, where small-scale studies have suggested it boosts numbers of T-cells, a key component of the immune system.
The extract is derived from licorice roots and takes the form of a yellow powder with a bittersweet taste.
Why glycyrrhizin apparently works against SARS is unclear, the study says.
It may induce the infected cell to produce nitrous oxide, thus blocking the molecular pathway that helps the virus to replicate. Nitrous oxide has previously been established as an inhibitor of the Japanese encephalitis virus.
Glycyrrhizin is a well-known molecule with relatively few side-effects even at high doses, unlike ribavirin, whose toxic effects include reductions in haemoglobin, the oxygen-carrying substance in the blood, the study says.
Since emerging in China's southern Guangdong province last November, SARS has killed 750 people and infected more than 8,400 worldwide, according to figures from the World Health Organisation.
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