USC Researcher, Medical Marijuana Movement At Odds
Don’t Bogart that joint, my friend — particularly if you’re susceptible to certain cancers, have a compromised immune system and are a mouse.
At first blush, that seems to be the takeaway from a study conducted by Prakash Nagarkatti, a professor of pathology and microbiology at the USC School of Medicine who has been injecting mice with THC (the main psychoactive substance in the cannabis plant) and studying the cannabinoid’s effects on their immune systems for the past two years.
The results of Nagarkatti’s study, which was funded by the National Institute on Drug Abuse (NIDA), appear in the December issue of The European Journal of Immunology and have recently generated something of a buzz — both among the medical marijuana community and the mainstream media.
According to Nagarkatti, marijuana cannabinoids affect the body through two types of receptors. The first, called CB1 receptors, are found in the brain. It is through these that marijuana users experience the psychotropic effects associated with smoking pot. CB2 receptors, however, are present only in our immune systems. It is these receptors that fascinate Nagarkatti and his colleagues.
“We were interested in finding out, basically, what are these receptors doing on the immune cells and what happens to these cells if they are exposed to these cannabinoids,” Nagarkatti explains.
Previously, Nagarkatti had conducted research suggesting that cannabinoids might be effective for fighting cancers of the immune system such as leukemia and lymphoma. He says he was therefore “surprised” to discover that when those same cannabinoids are injected into mice they also trigger the production of immunosuppressive cells of the same type typically triggered by cancer growth and metastasis.
These cells — called myeloid-derived suppressive cells, or MDSCs — are normally produced by the body in very small numbers as a way of regulating the far greater number of infection-fighting immune cells present in a healthy individual, but a sudden flood of such cells could potentially overwhelm the immune systems of cancer patients or of people susceptible to certain cancers. That means cancer patients receiving medical marijuana or marijuana users genetically susceptible to certain cancers could be at an elevated risk, according to Nagarkatti.
Still, Nagarkatti is not completely dismissive of medical marijuana, calling his recent THC findings “a double-edge sword” and noting that there is often a therapeutic benefit to suppressing the immune system.
“There are about 18 different autoimmune diseases like arthritis, lupus, multiple sclerosis, certain types of diabetes, in which our immune system goes haywire and starts killing our own cells and our own tissues,” Nagarkatti says. “In such cases, the only way you can treat those diseases is to suppress the immune system.”
“So, now we have discovered a new method where the cannabinoids might be able to suppress the immune system by inducing these MDSCs,” he continues.
Despite having demonstrated potential therapeutic benefits of THC alongside its possible drawbacks, Nagarkatti has generated some criticism among advocates of medical marijuana, including Donald I. Abrams, president of the Society for Integrative Oncology.
Abrams, who is also chief of Hematology/Oncology at San Francisco General Hospital and a professor of medicine at UCSF, is familiar with Nagarkatti’s study but skeptical of its findings because it was conducted on mice rather than humans, and because it used only THC, which is just one of many chemicals found in marijuana.
“Out of 400 compounds, some are going to be immune-suppressing, some are going to be immune-enhancing,” Abrams contended. “But the overall effect, I think, is that cannabis in people is not immune-suppressive. These things work together in concert. That’s why nature gave it to us this way.”
Abrams went on to cite a number of studies, including a highly publicized, large-scale study conducted in 2006 by Donald Tashkin, a doctor of pulmonary medicine at UCLA, which demonstrated that smoking marijuana, even habitually, does not seem to heighten the risk of developing lung cancer. Abrams also cited his own study on the effects of marijuana on HIV-AIDS patients, the results of which were published in the Annals of Internal Medicine.
“We measured a huge amount of immune parameters in patients with HIV … and we were not able to find that any damage to the immune system had occurred with exposure to cannabis three times a day over the 21 days of our experiment. In fact, if anything, it boosted the immune function in these patients who were immune-compromised.”
“I take issue with mouse studies,” Abrams added. “I think there’s always a risk when doing studies on animals when you’re trying to find out what the impact is on man.”
Abrams is also suspicious of Nagarkatti’s study because it was funded by NIDA, which he says has a “mandate … only to study substances of abuse only as substances of abuse … you can’t get their funds or their marijuana unless you’re trying to prove harm.”
Nagarkatti freely admits that studying mice and isolating THC cannot generate a complete picture. Still, he says his study is an important first step, not leastwise because pure THC is already being prescribed.
“In fact, that’s what we’re saying — that this clearly warrants human studies because THC is used in cancer patients and HIV-AIDS patients and certain glaucoma patients to do different things,” Nagarkatti explains. “How it impacts the immune system is critical to find out.”
Source: Columbia Free Times
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