TRICLOSAN, THE DIRTY SIDE OF SOAP
Triclosan is an
antimicrobial commonly found in soaps, shampoos, toothpastes and many other
household items. Despite its widespread use, researchers at University of
California, San Diego School of Medicine report potentially serious
consequences of long-term exposure to the chemical. The study, published Nov.
17 by Proceedings of the
National Academy of Sciences, shows that
triclosan causes liver fibrosis and cancer in laboratory mice through molecular
mechanisms that are also relevant in humans.
Triclosan's
increasing detection in environmental samples and its increasingly broad use in
consumer products may overcome its moderate benefit and present a very real
risk of liver toxicity for people, as it does in mice, particularly when
combined with other compounds with similar action," said Robert H. Tukey,
PhD, professor in the departments of Chemistry and Biochemistry and
Pharmacology. Tukey led the study, together with Bruce D. Hammock, PhD,
professor at University of California, Davis. Both Tukey and Hammock are
directors of National Institute of Environmental Health Sciences (NIEHS)
Superfund Programs at their respective campuses.
Tukey, Hammock and
their teams, including Mei-Fei Yueh, PhD, found that triclosan disrupted liver
integrity and compromised liver function in mouse models. Mice exposed to
triclosan for six months (roughly equivalent to 18 human years) were more
susceptible to chemical-induced liver tumors. Their tumors were also larger and
more frequent than in mice not exposed to triclosan.
The study suggests
triclosan may do its damage by interfering with the constitutive androstane
receptor, a protein responsible for detoxifying (clearing away) foreign
chemicals in the body. To compensate for this stress, liver cells proliferate
and turn fibrotic over time. Repeated triclosan exposure and continued liver
fibrosis eventually promote tumor formation.
Triclosan is perhaps
the most ubiquitous consumer antibacterial. Studies have found traces in 97
percent of breast milk samples from lactating women and in the urine of nearly
75 percent of people tested. Triclosan is also common in the environment: It is
one of the seven most frequently detected compounds in streams across the
United States.
"We could
reduce most human and environmental exposures by eliminating uses of triclosan
that are high volume, but of low benefit, such as inclusion in liquid hand
soaps," Hammock said. "Yet we could also for now retain uses shown to
have health value -- as in toothpaste, where the amount used is small."
Triclosan is already
under scrutiny by the FDA, thanks to its widespread use and recent reports that
it can disrupt hormones and impair muscle contraction.
Co-authors include
Koji Taniguchi, Shujuan Chen and Michael Karin, UC San Diego; and Ronald M.
Evans, Salk Institute for Biological Studies.
This research was
funded, in part, by U.S. Public Health Service grants ES010337, GM086713,
GM100481, A1043477, ES002710 and ES004699.
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