Stephen LaVoie at the University of Georgia studies inorganic mercury, which is known to cause neurological, kidney and autoimmune diseases. Credit: Dorothy Kozlowski/University of Georgia
Inorganic mercury, which was previously thought to be a less harmful form of the toxic metal, is very damaging to key cell processes. This study is the first to compare the effects of inorganic and organic mercury compounds at the biochemical, physiological and proteomic levels in any model organism.
Inorganic mercury from the ore cinnabar was used for centuries against infections; in modern times, humans synthesized organic mercurials as antimicrobials, such as merthiolate. “Today, most human exposure to inorganic mercury is from dental fillings, and organic mercury exposure is from methylmercury in fish,” said Prof. Anne Summers.
Organic mercury exposure is associated with neurological disease, LaVoie explained, whereas inorganic mercury is known to cause neuro, kidney and autoimmune diseases. However, the molecular basis for their distinct toxicity profiles was not understood.
Owing to concern about fish consumption, most research has emphasized organic mercury, assuming it was more toxic. But comparing them on key cellular processes, he found that inorganic mercury “caused more damage at lower concentrations than organic mercury.”
For his study, LaVoie used a common lab strain of E. coli bacteria as a model cellular system. He exposed growing cells to mercury compounds and measured their reactive sulfur called thiols – essential metals and proteins that naturally bind essential metals via amino acid thiols. “We used a fluorescent probe to detect thiols,” LaVoie said. After mercury exposure the thiols decreased more with inorganic than organic mercury. Inorganic mercury was much more efficient at removing iron from iron-dependent proteins than the best organic mercury compound tested.
“As fellow oxygen-breathing creatures, it’s important to know that inorganic mercury is more potent than organic mercury in disrupting protein-iron centers such as those we have in our own cells, ” Summers said. “More is being learned about the bacteria in and on our bodies,” LaVoie said. “What we ingest affects them, too, and their health affects our health.”
Future work will examine the mercury resistance genes that many bacteria have and how these genes help spread antibiotic resistance genes. http://news.uga.edu/releases/article/inorganic-mercury-exposure-1215/
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