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Chronic marijuana use by donors tied to poor outcomes in islet transplantation

As more states and countries legalize marijuana, it stands to reason that more people are using the drug for medical and recreational reasons. In fact, a recent Gallup survey found that nearly half of all American adults have tried marijuana, the highest number ever reported to date. But while many advocates tout the potential health benefits of cannabis use, previously unknown negative side effects are also coming to light.   
For example, a recent study by City of Hope researchers found that donor islet cells from chronic marijuana users failed to reverse diabetes at a much higher rate than those from donors who did not use the drug. Islets are clusters of cells found in the pancreas, and one type in particular — beta cells — produce insulin, a hormone essential for maintaining glucose balance and good health. When beta cells become impaired, diabetes develops. For individuals with severe diabetes, islet transplants are one way to provide insulin and hopefully extend life.
“Results in this study highlight the possible negative effects of chronic marijuana usage on pancreatic islets,” said Ismail Al-Abdullah, Ph.D., research professor in the Department of Translational Research & Cellular Therapeutics at City of Hope and lead author of a paper published Oct. 27 in the journal PLOS One outlining the team’s findings.

Ismail Al-Abdullah, Ph.D.

Al-Abdullah and the other researchers compared the islets of deceased individuals who smoked marijuana chronically (defined as a minimum of four times weekly for three years or more) with islets donated from non-users. When transplanted into diabetic mice, islets from heavy marijuana users reversed diabetes only 35% of the time. In the mice that received non-user islets, diabetes was reversed 77% of the time. Furthermore, the islets from marijuana users were of lower quality, displaying reduced insulin secretion and appearing enlarged. Previous studies have shown that smaller islets result in higher rates of transplantation success.

Reassessing Screening Protocols

“As medical and recreational marijuana use continues to increase in the Unites States and worldwide, our study makes a case for thorough assessment of donor lifestyle activities, including marijuana use, when evaluating human islets for transplantation or research,” Al-Abdullah said.
He and the team plan to continue to examine islets from donors with a history of chronic marijuana use. They hope to determine the signaling pathways involved in the deterioration of the islets, with a focus on islet cannabinoid receptor activation.
And while the researchers emphasize that the results of this study show that heavy marijuana use should be added to the screening criteria for islet cell donors, since a clear link was established between use of the drug and islet function deterioration, so far there is no evidence that chronic marijuana increases the risk of developing diabetes in general.
“None of our donors were diabetic, and it was difficult to make a firm conclusion about whether the long-term use of marijuana would [at some point] have severe consequences on normal individuals who are heavy users,” Al-Abdullah said.
However, he does caution that people with type 1 diabetes may want to tread lightly when it comes to marijuana use.
“Previous studies have shown that cannabis use in patients with type 1 diabetes is associated with an increased risk for diabetic ketoacidosis — a potentially life-threatening complication — and emergency admission for this condition has been increasing since the legalization of marijuana in several states.”