In most countries, cigarette packets are accompanied by pictures and texts that warn smokers of risks such as heart attacks, cancer and pregnancy complications. Many of these dangers are associated with inhaling tobacco smoke. However, the focus is less on the effects that the smoke has on the eyes. For example, there is a link with age-related macular degeneration, glaucoma and cataracts – and thus some of the world's most common causes of blindness and severe vision loss. These diseases occur inside the eye: in the retina, optic nerve and lens. Now Japanese researchers have discovered how cigarette smoke and aerosols from tobacco heaters also kill the cells in the most exposed layer of the eye: the cornea.
"It is exposed to the extreme surface of the eye and environmental influences such as chemicals, light and infections," says Wataru Otsu, biomedician at the Gifu Pharmaceutical University in Japan. People who smoke tobacco suffer from dry-eye syndrome twice as often as non-smokers. This manifests itself through a dry, red and itchy eye surface and can lead to visual disturbances, infections or corneal ulcers. According to OTSU, it is important to find out how cigarettes and tobacco heater, which emit only a few centimeters in front of the eye aerosole, affect the most endangered tissue of the sense organ. This is the only way to develop better protection for those affected.
The smoke induces corneal epithelium iron deposits.
In 2006, a clinical study by the Başkent University in Turkey showed that smoking affects the tear film that covers and protects the surface of the cornea. In addition, attempts on rats show that the cigarette smoke damage the cornea and the tear glands. In the new study published in "Scientific Reports" in September, OTSU and his colleagues report that the chemical compounds in tobacco smoke cause iron deposits that kill cells in the corneal epithelium. They found that the cornea can also be damaged if no smoke came directly into the eye: the iron -related cell death also occurred when the visual organ was exposed to other types of tobacco products.
The scientists exposed human corneal epithelial cells to a cigarette smoke extract, which contains most of the ingredients inhaled during smoking. This solution is often used in preclinical studies as a substitute for cigarette smoke. They also tested whether tobacco heaters affect corneal cells in a similar way. These devices heat tobacco leaves strongly, but without burning them and produce aerosols in the process. "Many people use the new devices as an alternative to cigarettes, but we know little about how they affect health," says Otsu.
It turned out that tobacco in the heated or burned form damages the cells in the cornea even if the product used does not contain tar or nicotine. In addition, the eyes of non -smokers could also be damaged by passive smoking if they are constantly exposed to it.
Smoking tobacco causes programmed cell death.
OTSU and his colleagues found that after 24 hours more cells had died that were exposed to the smoke extract or heated tobacco erosols (even if they did not contain nicotine) than those who had not experienced such exposure. On closer inspection, there were signs of damaged cell membranes, iron lumps and a wealth of damaged ferritin, a protein complex that stores the iron required for cellular processes.
Taken together, the findings indicate that the tobacco products trigger a form of programmed cell death in the epithelial cells. This process is driven by iron and called ferroptosis. The process begins with the fact that connections in the smoke come into contact with the corneal cells. This means that ferritin is broken down in the cells and saved iron is released, explains Otsu. Part of this iron accumulates and reacts with naturally occurring hydrogen peroxide to create hydroxyl radicals - highly reactive molecules that damage cells. Usually, the cell's repair mechanisms can be finished with these radicals. However, if too many accumulate, they damage the lipids in the membranes and lead to the death of the cells.
Otsu and his colleagues also discovered that more cells survived when they added substances to them that can bind iron or block ferroptosis. The findings suggest that treatment with ferroptosis inhibitors could help smokers suffering from corneal damage.
Using a ferroptosis inhibitor as a potential therapy
Because the study was conducted on cell cultures rather than living human eyeballs, the researchers can't yet say how quickly tobacco smoke damages a person's cornea. It is also not yet known how effective the ferroptosis inhibitors are in the treatment of smoking-related corneal diseases. The next steps are therefore experiments on animals, says Otsu.
But according to Dilek Altinörs, an ophthalmologist at the Başkent University, the results are already meaningful. She suspects that the tear film, which covers the cornea, is also affected by tobacco products. The lipids in this film prevent the eye from drying out, and it is already known that smokers are more susceptible to damaged tear films and dry eyes. It still has to be found whether the ferroptosis is to blame.
The results encourage the effectiveness of eye drops that contain ferroptosis inhibitors. Thus, smokers could possibly offer long -term relief and protection against dry eyes. “Maybe we can bring these substances into artificial tears. This opens up a completely new way to treat dry eyes, «says Altinörs.
© Springer Nature Limited Scientific American, Cigarette Smoke Kills Eye Cells, 2021
