Nature lends a helping hand in the fight against parasitic diseases.

Once parasites have found their way inside a host animal, they are very tricky to kill. The problem lies not so much in finding the right biocide as in transporting that agent to the right place. But amino acids could provide the solution, claims a multi-disciplinary team of researchers from Scotland and the US.

They coupled Triclosan, a widely used biocide, to a fragment of arginine, an amino acid. Triclosan is known to inhibit enoyl-ACP-reductase (ENR), a key enzyme that parasites use to synthesise fatty acids; and short oligomers of arginine are known to be capable of entering some parasites.

In in vitro tests, the Triclosan-amino acid (TA) system entered Toxoplasma gondii and disabled the parasite's ENR activity, reports Paul Wender, professor of chemistry at Stanford University and board member of CellGate, a therapeutics company based in Sunnyvale, California.

In mice inoculated with T. gondii , Wender notes how the TA system appeared to reduce the number of parasites by carrying its antimicrobial cargo across a number of obstacles, and even inside cysts containing previously untreatable parasitic forms.

'What merits attention in this area is that many drugs or drug candidates could be improved by either enhancing or enabling their bioactivity,' says Wender, who led the research team. Anti-malarial products could follow, he suggests, because the problem with many drugs is that although they are very effective once they reach their target molecules, they often cannot get access to them.

The work is 'very promising' and could provide 'an excellent way to get around the delivery-of-drugs-across-membranes problem', says Mark Field, a reader in molecular cell biology at Imperial College London. He also predicts that the amino acid carrier system 'could be very important in bacterial and even oncological settings'.

However, Field is not totally convinced by the team's in vivo data. 'The design of the experiment does not mimic a true infection and a good outcome is rather more likely from the protocol used than in a real toxoplasmosis infection,' he notes.

Because Triclosan is used in many antibacterial soap products the researchers are optimistic that the TA system will not have too many nasty side effects. 'This is a new concept and will take some time to move through various stages of testing,' accepts Wender. 'It is however very promising and we feel that if we run into problems we should be able to fix them.'

Emma Davies