UC Riverside research on mice focused on biomarkers in a time-dependent manner.

Researchers at the University of California, Riverside have found that thirdhand-smoke (THS) exposure has a significant effect on health as early as one month after initiation of exposure – an effect that worsens with time. THS results when exhaled smoke and smoke emanating from the tip of burning cigarettes gets on surfaces such as clothing, hair, homes, and cars. THS has been shown, in mice, to cause type 2 diabetes, hyperactivity, liver and lung damage, and wound-healing complications.

Using a system in which the exposure of mice to THS mimics that of human exposure in the homes of smokers, the researchers investigated the effects of THS exposure on biological molecular markers – or “biomarkers” – found in serum, and in liver and brain tissues. The liver plays a major role in metabolism and detoxification; the brain plays significant roles in behavior. “Our goal was to determine the minimum amount of time required to cause physiological changes in mice when they are exposed to THS, using an exposure system that mimics human exposure,” said Manuela Martins-Green, professor and chair of the Department of Molecular, Cell and Systems Biology, who led the research. “We found that THS exposure as early as one month resulted in liver damage. THS exposure for two months resulted in further molecular damage, and at four to six months caused even more such damage. We also found that the mice showed insulin resistance after long-term THS exposure.”

Damage to the liver can hinder its capability to detoxify the body, leading to more damage by THS toxins. Martins-Green and her team examined the brains of THS-exposed mice and found that stress hormones, such as epinephrine, increased in one month of exposure. Additional stress hormones are seen at two months, four months, and six months, eventually causing immune fatigue in the mice.

Study results appeared in the journal Clinical Science.

Most people are either unaware they are being exposed to THS, or don’t believe in the damage THS can do, according to Martins-Green. THS toxins, which are invisible but can be smelled, remain on surfaces for many years, and are resistant to even strong cleaning agents. Further, they accumulate and age by reacting with the ambient air, and change into carcinogenic chemicals.

Because THS is absorbed through skin, children are especially vulnerable given their close contact with household surfaces. Children frequently ingest these toxins by putting their hands in their mouths. They also absorb them through the skin. Children living in the homes where smoking has occurred have been known to show tobacco metabolites in their urine as well as tobacco-derived carcinogens called tobacco specific nitrosamines.