Cannabinoids are potent antibiotics against MRSA: why the neglect?
All the major cannabinoids, which are found in the hemp plant, Cannabis sativa, have been shown to be powerful antibiotics. What is more, they have been shown to be effective against the "superbug" MRSA.
What is MRSA
MRSA is the abbreviation for methicillin-resistant Stapylococcus aureus.
Stapylococcus aureus bacteria are widespread and can live on the skin and in the throat and nose of healthy people without causing any problems. At most, they might cause pimples or the skin disease impetigo.
However, if Stapylococcus aureus succeeds in penetrating into the interior of the body, for example, through a wound or surgical incision, it can cause serious conditions. These include infections of the blood (sepsis), soft tissue (cellulitis), lungs (pneumonia) or heart (endocarditis).
Although these conditions are serious, and can be life-threatening if left untreated, they are usually cured by a course of antibiotics. Methicillin is a potent antibiotic from the penicillin family that can often be used successfully to treat Stapylococcus aureus infections.
MRSA bacteria magnified 9560x
Unfortunately, strains of Stapylococcus aureus have emerged, which are resistant to methicillin.
The immune system of healthy people can deal even with MRSA. However, elderly people, patients subjected to cancer chemotherapy or major surgery, people with AIDS, organ transplant recipients, young children and others with a weaker immune system are unable to fight this superbug.
MRSA infections cause serious problems and many deaths in hospitals and care homes. For this reason, MRSA is classed as a serious risk for public health. According to data published by the Center for Disease Control in 2007, over 18,500 hospital deaths per year in the USA are due to MRSA. The costs of direct healthcare are increased by up to $9.7 billion per year because of MRSA.
Antibiotic activity of Cannabis sativa
Attention is often focused on the traditional religious uses of cannabis, which relate to its psychoactive properties (i.e. the effect on mental processes and mood). However, it also has a long history of medicinal use. This includes a recognition of its antiseptic, antibacterial properties in the ancient cultures of Africa, Greece and the Middle East.
Western scientists started investigating these antiseptic properties in the 1950s. Preparations made from the plant were shown to be very effective antiseptics when applied to the skin or inside the mouth. They were also active against tuberculosis.
At that time, not enough was known about the constituents of the plant to be able to identify which ones were responsible. However, in the 1970s-1980s researchers showed that it is cannabinoids and their precursors, which provide the antimicrobial activity. These include cannabichromene, cannabigerol and cannabidiol, which are not psychoactive, as well as Δ9-tetrahydrocannabinol (THC), which is.
In 2008, scientists from three centres in Italy and the School of Pharmacy at the University of London, UK, published the results of a joint study. This was a structure-activity study, which aimed to find out exactly which chemical structures on the cannabinoids give them their antimicrobial activity.
They found that the cannabinoids Δ9-Tetrahydrocannabinol, cannabidiol, cannabigerol, cannabichromene and cannabinol all have very potent antibiotic activity against various strains of Staphylococcus aureus. The activity was exceptionally high when tested with the multidrug-resistant (MDR) SA-1199B. Another very important result is the potent activity against two strains responsible for MRSA, namely EMRSA-15 and EMRSA-16. These two strains are the main culprits for MRSA epidemics in hospitals in the UK.
Cannabis abusers do not benefit from cannabinoid antibiotic properties
The results of the Italian-UK study have been widely disseminated by campaigners for legalising the use of cannabis. They argue that there is a potential health benefit because the cannabinoids will protect users against bacterial infection.
However, the whole plant contains many other components, some of which may have deleterious effects. In addition, the tars in the inhaled smoke will certainly be injurious.
Cannabis abusers have been found to suffer from infections more frequently than non-users. One study from the School of Medicine at University College Los Angeles showed that lung macrophages from marijuana smokers are less efficient in killing Staphylococcus aureus than macrophages from complete non-smokers or tobacco smokers. The same research group also found that Δ9-tetrahydrocannabinol (THC) inhibits the activity of T cells and thus lowers the immune response.
Cannabinoids remain an unexploited resource in the fight against MRSA
The authors of the Italian-UK study gave a number of reasons why more attention should be given to developing the use of cannabinoids as antibiotics and antiseptics.
- Antibiotic activity is present in cannabinoids such as cannabidiol and cannabigerol which are not psychoactive.
- Cross-resistance between antibiotics obtained from plants and the commonly used antibiotics, which are obtained from microorganisms, is extremely rare.
- Even more importantly, the study showed that cannabinoids would not be affected by the most common ways in which bacteria develop resistance to antibiotics
- The chemical structures responsible for the antibiotic activity are tolerant to being modified. This leads the authors to suggest a further use for cannabinoids as antibacterial agents in cosmetics and toiletries. They would make cheap and biodegradable alternatives to less potent synthetic preservatives, which are not as safe and not as environmentally friendly.
Obviously, further work would be required to confirm these results. In addition, safety and efficacy studies would need to be conducted, first in animals and then in humans before it was possible to register cannabinoid products as antiseptics/antibiotics.
Nevertheless, there is no obvious evidence whatsoever that these findings have been taken up by the pharmaceutical industry, despite the fact that it has developed cannabinoid preparations for other uses. No newer studies on cannabinoids as antibiotics appear to have been published. The US and EU clinical trials registers show a few current trials of the use of cannibinoids in multiple sclerosis and fibromyalgia, but none focusing on their use as antibiotics.
It is a mystery why this potential resource against the huge public health problem of MRSA has not been placed on a fast-track R&D pathway.
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Antibacterial cannabinoids from Cannabis sativa: a structure-activity study
J. Nat. Prod. 2008 71(8): 1427-1430 Full text
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