Driving has become a common mode of transportation in our daily lives. However, a hidden health crisis is quietly approaching. A recent study by Southeast University reveals that 6-PPDQ, a byproduct of the tire anti-aging agent 6-PPD, may pose a serious threat to human health, particularly to mitochondria, during tire wear.

6-PPD is a commonly used tire protectant. As an antioxidant, it effectively resists ozone attacks and prevents tire breakage. However, when tires rub against the ground during vehicle operation, producing wear particles, 6-PPD reacts with ozone in the environment to generate the highly toxic 6-PPDQ. This chemical substance not only harms the environment but may also enter the human body through daily activities, shortening our healthy lifespan.

The research team exposed nematodes to an environment containing 6-PPDQ and found that the lifespan of these nematodes was significantly shortened. Nematodes with an expected lifespan of 24 days had their lifespan reduced by 6 days after exposure to 6-PPDQ, equivalent to a 25% reduction. If this is analogous to humans, it means that a person with an expected lifespan of 80 years might only live to 60 years under the influence of 6-PPDQ.

The key factor in 6-PPDQ's impact on lifespan lies in its destructive effect on mitochondria. Mitochondria are the "powerhouses" of cells, responsible for converting oxygen and functional substances into ATP to provide energy for cells. However, the study found that 6-PPDQ can severely damage mitochondrial function. When nematodes are exposed to 6-PPDQ, their mitochondrial membrane potential decreases, oxygen consumption rate increases, but ATP content decreases, leading to severe damage to mitochondrial function.

6-PPDQ damages mitochondria by significantly reducing the activity of mitochondrial complexes. Further experiments showed that as the concentration of 6-PPDQ increased, the expression of genes encoding mitochondrial complexes in nematodes gradually decreased, exacerbating mitochondrial damage.

(A) The activity of mitochondrial complexes I and II and (B) the expression of genes encoding components in mitochondrial complexes I and II (gas-1, nuo-1, nuo-6, and mev-1) were significantly reduced.

The damage of 6-PPDQ to mitochondria is not limited to functional decline. Further research has found that it also interferes with the insulin signaling pathway (IIS pathway), affecting the expression of the daf-2 gene. Under normal circumstances, activation of the IIS pathway leads to a decrease in daf-2 expression and an increase in downstream daf-16 expression, thereby improving cellular antioxidant capacity, DNA repair, and metabolic regulation, and extending lifespan. However, after 6-PPDQ treatment, the expression of daf-2 abnormally increased, activating downstream kinases and inhibiting the expression of daf-16, thus shortening the lifespan of nematodes.

Given the potential hazards of 6-PPDQ, countries have begun to take measures. The United States has legislated to ban the addition of 6-PPD to tires and has screened five tire additives with less environmental impact as alternatives.

In addition, scientists are also studying the use of pre-treated TESPT silane as a rubber substrate to improve the internal structure of rubber and reduce vulcanization, thereby reducing the formation of 6-PPDQ.

Before optimization (left) and after optimization (right) diagrams of the internal structure of rubber-based tires

Driving is a convenient choice, but the hidden health crisis cannot be ignored. The research of Southeast University has sounded an alarm for us, reminding us that while pursuing speed and convenience, we should also pay attention to the health risks that may be caused by the tire anti-aging agent 6-PPDQ. Through scientific research and technological innovation, we are confident that we will find more effective countermeasures in the future to protect our health and the "longevity" of the earth.

References:

[1]Hua X , Liang G , Chao J ,et al.Exposure to 6-PPD quinone causes damage on mitochondrial complex I/II associated with lifespan reduction in Caenorhabditis elegans[J].Journal of Hazardous Materials, 2024, 472.DOI:10.1016/j.jhazmat.2024.134598.

[2]Li C , Zhang Y ,Shiqi YinQin WangYuanyuan LiQiang LiuLiuqingqing LiuXianxiang LuoLingyun ChenHao ZhengFengmin Li.First insights into 6PPD-quinone formation from 6PPD photodegradation in water environment[J].Journal of Hazardous Materials, 2023, 459(Oct.5):132127.1-132127.10.DOI:10.1016/j.jhazmat.2023.132127.

[3]Ansarifar A , Saeed F , Ostad Movahed S ,et al.Using a sulfur-bearing silane to improve rubber formulations for potential use in industrial rubber articles[J].Journal of Adhesion Science & Technology, 2013, 27(4):371-384.DOI:10.1080/01694243.2012.705541.

[4]https://www.ustires.org/largest-global-tire-industry-consortium-releases-preliminary-6ppd-alternatives-analysis-report