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.