In an "unexpected" discovery, vitamin C has been found to kill drug-resistant forms of tuberculosis, which could mean existing drugs can be redesigned to combat the disease.
Researchers at Albert Einstein College of Medicine of Yeshiva University, New York have determined that vitamin C kills drug-resistant tuberculosis (TB) bacteria in laboratory culture.
The finding suggests that vitamin C added to existing TB drugs could shorten TB therapy, and it highlights a new area for drug design.
TB is caused by infection with the bacterium M tuberculosis. According to the World Health Organisation (WHO), TB sickened some 8.7 million people and took some 1.4 million lives in 2011, researchers said.
Infections that fail to respond to TB drugs are a growing problem: About 650,000 people worldwide now have multi-drug-resistant TB (MDR-TB), 9 per cent of whom have extensively drug-resistant TB (XDR-TB).
The discovery arose during research into how TB bacteria become resistant to isoniazid, a potent first-line TB drug.
William Jacobs, lead investigator and senior author of the study and his colleagues observed that isoniazid-resistant TB bacteria were deficient in a molecule called mycothiol.
"We hypothesised that TB bacteria that can't make mycothiol might contain more cysteine, an amino acid," said Jacobs.
"So, we predicted that if we added isoniazid and cysteine to isoniazid-sensitive M tuberculosis in culture, the bacteria would develop resistance. Instead, we ended up killing off the culture - something totally unexpected," he said.
Researchers suspected that cysteine was helping to kill TB bacteria by acting as a "reducing agent" that triggers the production of reactive oxygen species, which can damage DNA.
"The combination of isoniazid and vitamin C sterilised the M tuberculosis culture. We were then amazed to discover that vitamin C by itself not only sterilised the drug-susceptible TB, but also sterilised MDR-TB and XDR-TB strains," he said.
Vitamin C induced what is known as a Fenton reaction, causing iron to react with other molecules to create reactive oxygen species that kill the TB bacteria.
"We don't know whether vitamin C will work in humans, but we now have a rational basis for doing a clinical trial," said Jacobs.
The study was published in the journal Nature Communications.
