Activation of methionine synthase by insulin-like growth factor-1 and dopamine: a target for neurodevelopmental toxins and thimerosal. Waly M, Olteanu H, Banerjee R, Choi S-W, Mason J B, Parker B S, Sukumar S, Shim S, Sharma A, Benzecry J M, Power-Charnitsky V-A, and Deth R C. Molecular Psychiatry 2004;(advance online publication 27 January)
Do various chemicals that could affect development affect important processes within nerve cells?
This study examined the capacity of various substances to affect growth factor signaling in neuroblastoma (a form of cancerous nerve) cells—an important step in the development of cells of the central nervous system. The reason that this might be important is that changes in the development of those cells might imply a mechanism wherein exposure to these chemicals could lead to disorders of the developing brain.
The researchers exposed cells in the laboratory (in vitro) to various concentrations of lead, ethylmercury, aluminum, ethanol, and copper. They did not study developing neural (brain) cells but human neuroblastoma cells (a cancer derived from nerve cells), which are easily maintained in the laboratory. They then examined if these substances interrupted the growth factor signaling of these cells.
All the substances used—lead, ethylmercury, monovalent copper, and aluminum— interrupted growth factor signaling, causing adverse effects on the transfer of carbon atoms.
This study shows how these various substances might affect an important growth pathway in a laboratory setting. Exposing neuroblastoma cells directly to these compounds in the laboratory, however, is very different from the possibility of exposure of developing brain cells to them, including ethylmercury contained in thimerosal-containing vaccines. This study defines a way in which these substances could conceivably affect brain development, but does not demonstrate that they do.
Methylmercury, a very different compound than the form of mercury in thimerosal, is a known neurotoxin that accumulates in the body. It is plausible (conceivable) that other mercury compounds could act similarly. While this is an interesting study on possible mechanisms of toxicity, the researchers studied concentrations of thimerosal that are likely to be far higher than would be expected to be found in the brain. Fortunately, excellent well controlled studies in children have examined the relationship between thimerosal in vaccines and found no evidence for an association.