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ANAHEIM -- Heat-not-burn tobacco devices are marketed outside the U.S. as a safer alternative to cigarette smoking, but early, animal studies suggested this may not be completely true, researchers said here.

When rats were exposed to vapor produced by the heat-not-burn tobacco product iQOS Heatstick (Philip Morris International), and cigarette smoke from a traditional combustile cigarette (Marlboro), they showed similar, on blood vessel function, according to Matthew L. Springer, PhD, of the University of California San Francisco, and colleagues.

Following 10 15-second exposures to vapor from the heat-not-burn product over 5 minutes, blood vessel function decreased by an average of 58%. Exposure to the cigarette smoke for the same amount of time resulted in a 57% average decline in blood vessel function, they reported at the American Heart Association meeting.

Also, ten 5-second exposures over 5 minutes was associated with a 60% reduction in blood vessel function versus a 62% reduction after equal exposures to cigarette smoke.

Springer told MedPage Today via email that while the products, which may soon be approved for sale in the U.S., are undoubtedly safer than combustible cigarettes in some ways, they may be just as harmful in other ways.

"Our findings suggest that in the case of impairing endothelial function, iQOS 'vapor' (actually aerosol) is as harmful as cigarette smoke," he said. "This means that whether or not these products are less harmful in other ways, they are not harmless and should not be thought of that way."

Blood from the rats showed high levels of nicotine following exposure to both products, with higher levels seen with the heat-not-burn exposures.

Springer said nicotine exposure might explain the short-term impact on blood vessel function, but it may not.

Earlier studies conducted by his group showed that marijuana smoke exposure also impairs endothelial function, even though marijuana smoke does not contain nicotine.

In the current study, Springer's group exposed eight rats via nose cone to 15 seconds of iQOS aerosol, cigarette mainstream smoke, or air. There were 10 separate exposures over a f5-minute period using a syringe pump to generate and deliver aerosol.

Blood vessel flow-mediated dilation (FMD) was quantitated pre- and post-exposure by measuring femoral artery diameter with micro-ultrasound before and after 5 minutes of transient surgically induced ischemia, and expressed as the percent vasodilation.

The study showed FMD was impaired by exposure to iQOS aerosol (10.6% versus 4.5%, P=0.0008) and cigarette smoke (10.6 versus 4.6%, P=0.0004). Also, FMD was not affected in the clean air controls (8.3% versus 8.8%, P=0.82).

Philip Morris International has applied to the FDA for Modified Risk Tobacco Product status for its heat-not-burn products, meaning that if approved for sale in the U.S., iQOS could be marketed as safer than traditional tobacco products. According to 3.7 million smokers outside of the U.S. switched to iQOS.

The heat-not-burn product has proven to be wildly popular in Japan, where it was launched in 2014, and it is now sold throughout Europe and in close to a dozen other countries.

Springer declined to weigh in on whether heat-not-burn devices should be approved as reduced risk products, but he said it would be misleading, at this point, to call the products safe.

"It is important for people to realize that reduced harm is not the same as harmless, or safe, and that even if this product is less harmful than cigarettes in some ways, it may still be every bit as harmful in other ways," he said.

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