Often used as an alternative to traditional smoking, e-cigarettes (EC) come with their own health risks. E-cigarettes produce a stress response in neural stem cells, which are critical cells in the brain, finds a study.

The study published in the journal 'iScience' used cultured mouse neural stem cells and identified the mechanism underlying EC-induced stem cell toxicity as 'stress-induced mitochondrial hyperfusion,' or SIMH.

"SIMH is a protective and survival response. Our data show that exposure of stem cells to e-liquids, aerosols, or nicotine produces a response that leads to SIMH," said Prue Talbot, lead researcher of the study.

"Although originally introduced as safer, ECs, such as Vuse and JUUL, are not harmless. Even short-term exposure can stress cells in a manner that may lead, with chronic use, to cell death or disease. Our observations are likely to pertain to any product containing nicotine," said Atena Zahedi, first author of the study.

"The high levels of nicotine in ECs lead to a nicotine flooding of special receptors in the neural stem cell membrane. Nicotine binds to these receptors, causing them to open up. Calcium and other ions begin to enter the cell. Eventually, a calcium overload follows," Zahedi added.

Zahedi explained that too much calcium in the mitochondria is harmful. The mitochondria then swell, changing their morphology and function. They can even rupture and leak molecules that lead to cell death.

"If the nicotine stress persists, SIMH collapses; the neural stem cells get damaged and could eventually die. If that happens, no more specialised cells can be produced from stem cells," Zahedi said.

Zahedi added that damaged stem cell mitochondria could accelerate aging and lead to neurodegenerative diseases. Neural stem cells can get exposed to nicotine through the olfactory route, she explained. Users inhale the fumes, which can travel through the olfactory tracks to reach the brain.

Talbot and Zahedi stressed that youth and pregnant women need to pay especially close attention to their results.

"Their brains are in a critical developmental stage," said Talbot.

"Nicotine exposure during prenatal or adolescent development can affect the brain in multiple ways that may impair memory, learning, and cognition. Furthermore, addiction and dependence on nicotine in youth are pressing concerns. It's worth stressing that it is the nicotine that is doing damage to neural stem cells and their mitochondria. We should be concerned about this, given that nicotine is now widely available in ECs and their refill fluids," Talbot added.

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