By NORA SCHULTZ Sept. 12, 2008
Substances harvested from cannabis plants could soon outshine conventional antibiotics in the escalating battle against drug-resistant bacteria. The compounds, called cannabinoids, appear to be unaffected by the mechanism that superbugs like MRSA use to evade existing antibiotics.
Scientists from Italy and the United Kingdom, who published
their research in the Journal of Natural Products last month, say that
cannabis-based creams could also be developed to treat persistent skin
infections.
Cannabis has long been known to have antibacterial properties and was
studied in the 1950s as a treatment for tuberculosis and other
diseases. But research into using cannabis as an antibiotic has been
limited by poor knowledge of the plant’s active ingredients and by the
controversy surrounding its use as a recreational drug.
Now Giovanni Appendino of the Piemonte Orientale University, in
Italy, and Simon Gibbons of the School of Pharmacy at the University of
London, U.K., have revisited the antibiotic power of marijuana by
systematically testing different cannabinoids’ ability to kill MRSA.
MRSA, short for methicillin-resistant Staphylococcus aureus, is a
bacterium that can cause difficult-to-treat infections since it does not
respond to many antibiotics. Many healthy people carry S. aureus on
their skin, but problems arise when multi-drug-resistant strains infect
people with weak immune systems through an open wound. In the worst
cases, the bug spreads throughout the body, causing a life-threatening
infection.
To make matters worse, resistance to antibiotics is rapidly
increasing, and some strains are now even immune to vancomycin, a
powerful antibiotic that is normally used only as a last resort when
other drugs fail.
But when Appendino, Gibbons, and their colleagues applied extracts
from five major cannabinoids to bacterial cultures of six strains of
MRSA, they discovered that the cannabinoids were as effective at killing
the bugs as vancomycin and other antibiotics.
“The cannabinoids even showed exceptional activity against the MRSA
strain that makes extra amounts of the proteins that give the bugs
resistance against many antibiotics,” says Gibbons. These proteins, he
explains, allow the bacteria to “hoover up unwanted things from inside
the cell and spit them out again.”
Conveniently, of the five cannabinoids tested by the researchers, the
two most effective ones also happen to be nonpsychoactive, meaning that
they cannot cause a high. “What this means is, we could use fiber hemp
plants that have no use as recreational drugs to cheaply and easily
produce potent antibiotics,” says Appendino.
In an attempt to discover how the cannabinoids kill MRSA, the team
manipulated several chemical groups within the compounds. Most of the
changes did not affect the antibiotic activity at all, and those that
did seemed to influence only how well the cannabinoid is taken up by the
bacterial cells.
“Everything points towards these compounds having been evolved by the
plants as antimicrobial defenses that specifically target bacterial
cells,” says Gibbons. “But the actual mechanism by which they kill the
bugs is still a mystery. We’ve tested whether the cannabinoids affect
common antibiotic targets like fatty acid synthesis or the [DNA-bending
enzyme] DNA gyrase, but they don’t. I really cannot hazard a guess how
they do it, but their high potency as antibiotics suggests there must be
a very specific mechanism.”
Appendino and Gibbons say that cannabinoids could quickly be
developed as treatments for skin infections, provided the
nonpsychoactive varieties are used. “The most practical application of
cannabinoids would be as topical agents to treat ulcers and wounds in a
hospital environment, decreasing the burden of antibiotics,” says
Appendino.
Whether the cannabinoids could also be delivered in the form of an
injection or in pills is less clear, the pair says, because they may be
inactivated by blood serum.
Frank Bowling of the University of Manchester, who has had success
treating MRSA-infected wounds with maggots, says that “any alternative
treatment that removes MRSA from the wound and prevents it from
spreading into the body is fantastic and preferable to using antibiotics
that have strong side effects and against which resistance is already
developing.” He cautions, however, that the researchers still need to
show that the cannabinoids are safe to use.
This is not something that Appendino is too concerned about: “The
topical use of cannabis preparations has a long tradition in European
medicine, and no allergies have been reported.”
Mark Rogerson of GW Pharmaceuticals, a U.K.-based company that
develops cannabinoid-based drugs to treat severe pain caused by multiple
sclerosis and cancer, says that the discovery that cannabinoids kill
MRSA “really underlines the potentially great diversity of medical
applications that cannabis-based medicine can have. You can almost think
of the cannabis plant as a mini pharma industry in its own right.” But
Rogerson says that it is unlikely that existing cannabis-based medicines
could be used to treat MRSA because the exact effect will depend on the
correct combination and dosage of cannabinoids.
Meanwhile, Appendino and Gibbons hope that antibacterial
effectiveness could also make cannabinoids suitable preservatives for
cosmetics and toiletries. “The golden standards of preservatives are
parabens and chlorinated phenols,” says Appendino, but these compounds
do not degrade well in the environment and are strongly suspected to be
hormonal modifiers. He also argues that, since all major cannabinoids
are similarly effective, complete purification of a single compound
isn’t necessary. So semipurified cannabinoid mixtures extracted from
nonpsychoactive plants could make a cheap and easy alternative to
conventional preservatives.
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