How fine particles can cause lung cancer

THE ESSENTIAL

  • According to the World Health Organization, air pollution accounts for seven million deaths each year.
  • Inhalable fine particles are classified as Type 1 carcinogens.
  • For the authors, peroxidasin could become a target in the prevention of air pollution-related diseases.

In 2018, more than 45,000 new cases of lung cancer were diagnosed in France. Several factors can explain their occurrence: smoking, exposure to carcinogenic substances at work and pollution. In 2013, the World Health Organization, through the International Agency for Research on Cancer, classified air pollution and particulate matter as carcinogenic to humans. However, the causes of this link between cancer and air pollution remain uncertain. In the magazine eLifeA research team from the University of Nanjing (China) provides explanations.

The indirect effects of environmental pollution on cancer cells

They carried out work on fine particles and their effects on human cells. “Recent research suggests that inhalable fine particles do not directly promote – and may even inhibit – lung cancer cell growthstates the lead author, Zhenzhen Wang, Associate Researcher at the University of Nanjing (NJU). This suggests that inhalable fine particles could cause cancer through indirect means that promote tumor growth..” With his team, he worked on a hypothesis that had previously been put forward by other researchers: fine particles could block the movement and action of immune cells. To test this theory, they collected fine particle samples from seven Chinese sites and then tested them on immune cells tasked with fighting tumor growth, cytotoxic T cells (CTLs), in an experiment on mice infected with the fine particles If the particles were not exposed, the CTLs migrated to the lungs to destroy the tumor cells. When the lungs were exposed to the particles, the infiltration of the CTLs was delayed, allowing the tumor cells to colonize the lung tissue.

Cells slowed down by a change in the structure of the lung tissue

Second, the scientific team wanted to understand why the CTLs do not reach the lungs as quickly in the event of exposure to the pollutants. Studying these immune cells, they found that while the CTLs exposed to the fine particles still retained their ability to migrate, the stress of pollution significantly compressed the structure of the lung tissue and the spaces between which the immune cells moved. Further analysis of the tissue showed that the structural changes were caused by an increase in a collagen subtype called collagen IV. Continuing their work, they found that exposure to fine particles causes changes in the action of an enzyme, peroxidasin, responsible for this increase in collagen production. “This means that where fine particles are present in the lungs, increased peroxidasin activity leads to structural changes in lung tissue that can prevent immune cell entry and block tumor cell growth.”, stresses Zhenzhen Wang. According to him, these results could allow the development of new approaches to prevent or treat the initial lung changes that lead to cancer.

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