From June 23, 2006
University
of Colorado Scientists Find That Pesticides in Mothballs Are Carcinogenic
(Beyond Pesticides, June 23, 2006) A new study spearheaded
by the University of Colorado at Boulder find that chemical compounds
in household products like mothballs and air fresheners can cause cancer
by blocking the normal process of "cell suicide" or apoptosis
in living organisms, reports Science
Daily. Apoptosis is a normal function of certain cell groups that
acts as a "brake" to prevent unchecked cellular proliferation
similar to the process that triggers the formation of cancerous tumors.
Naphthalene, found
in mothballs and para-dichlorobenzene, and PDCB,
found in some air fresheners, were shown to block enzymes that initiate
programmed cell death, or apoptosis, said Associate Professor Ding Xue,
PhD of CU-Boulder's molecular, cellular and developmental Biology department."
While naphthalene and PDCB have been shown to cause cancer in rodents
and are classified by the National Toxicology Program and the International
Association for Research on Carcinogens as potential human carcinogens,
their biochemistry has not been well understood, said Dr. Xue. But using
a common, eyelash-sized worm known as C. elegans, the research team
has shown that naphthalene can cause the inactivation of a group of
enzymes known as caspases -- which control cell suicide -- by oxidizing
them.
The study appears in the June issue of the journal Nature
Chemical Biology. Along with Dr. Xue, the study was authored
by David Kokel of CU-Boulder's MCD biology department and Yehua Li and
Jun Qin, PhD of the Baylor College of Medicine in Houston.
"This study shows why mothballs and some air freshener products
may be harmful to humans," said Dr. Xue. "And, for the first
time, we have developed a systematic way to screen virtually any potential
cancer-causing chemical that may affect humans using these nematodes
as animal models."
In the study, caspase enzymes from both nematodes and from humans were
blocked after exposure to naphthalene, indicating a "comparable
pharmacology" between worms and humans, said Dr. Xue.
Understanding how carcinogenic compounds can trigger tumor growth is
important for federal regulatory agencies that deal with human exposure
to hazardous chemicals, said Dr. Xue. More than 1 million pounds of
naphthalene and PDCB are used by consumers annually, according to the
study.
The nematodes were grown on a culture medium coated with a soybean-based
oil that is harmless to the worms but which can dissolve naphthalene
and PDCBs, said Dr. Xue. When the chemicals were added to the culture,
they deactivated the caspases, resulting in the survival of "extra"
cells in the tiny worms that normally would have been eliminated by
apoptosis, said Dr. Xue.
Apoptosis is an essential process in animal development and occurs in
many tissues, said Dr. Xue. In amphibians it rids frogs of tails as
they develop from larvae to adults, and in humans it removes cells that
make up "webbing" tissue between the fingers and toes of embryos
during development, he said.
"Apoptosis serves as a checking mechanism to ensure that the right
amount of cells are generated in the body," Dr. Xue said. In Alzheimer's
disease and Parkinson's disease, too much apoptosis is occurring, while
in cancer and autoimmune disorders, too little apoptosis is occurring,
he said.