Cadmium--a heavy metal used in coatings, batteries, and plastics--can cause cancer by disturbing the DNA repair system that cells use to prevent uncontrolled growth. The finding, published in the 8 June Nature Genetics, reveals a novel mechanism by which a toxin can lead to cancer.
Many people are exposed to cadmium by consuming food and drinking water tainted with runoff from factories or discarded batteries in landfills or by inhaling cadmium-containing particles from factory or cigarette smoke. Metal workers are especially at risk. But although researchers had linked cadmium to increased rates of lung and other types of cancer, they knew little about the mechanism.
Many toxins cause cancer by directly causing genetic mutations. Cadmium is even more insidious, according to the new study. In addition to causing mutations, it blocks the repair mechanisms that correct them. Cells must duplicate their DNA in order to reproduce, and this process inevitably creates DNA spelling mistakes. Normally, however, these miscues are corrected by efficient repair mechanisms akin to a computer's spellchecker. Without these mechanisms, mutations would multiply as cells reproduced, potentially leading to cancer.
Geneticist Thomas Kunkel and colleagues at the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, treated yeast and human cells with different concentrations of cadmium chloride--a reactive, hazardous form of the metal. In yeast cells, cadmium increased mutations as much as 2000-fold, and up to 50% of spontaneous mismatches were left unrepaired. In human cells treated with cadmium chloride, 28% of spontaneous mismatches went uncorrected. In both cases, the amount of cadmium needed to inhibit repair and increase mutations was remarkably small. "We saw substantial effect from cadmium exposure from concentrations that may well be environmentally relevant, especially to cadmium-related industry workers and smokers,” says Kunkel.
The study shows a "novel and very unexpected mechanism for elevating mutation rates," says biologist Susan Jinks-Robertson at Emory University in Atlanta. Scientists had generally assumed that cancer-causing toxins target DNA directly, she says. She adds that the work "will certainly provide a stimulus for examining the mechanisms of other environmental carcinogens."
Background on cadmium and human health from the U.S. Centers of Disease Control and Prevention
Detailed information about cadmium from the U.S. Occupational Safety and Health Administration