Study examines whether vaccine ingredient is safe for human beings

• Until the removal of Thimerosal, which contains 49.9% ethyl mercury by weight, from most pediatric vaccines in 2001, the source of the largest human exposure to mercury in the US was in children under 18 months of age undergoing routine childhood immunization schedules.
• Before 2001, a child may have received a cumulative dose of over 200 ¼g/kg (micrograms per kilogram) in the first 18 months of life.
• In the 2005 issue of NeuroToxicology, the authors of a study examine the toxicity of Thimerosal within the body including neurons.
• They examine the neurotoxic mechanisms, how the body detoxifies mercury, and the use of N-Acetylcysteine, or NAC for short, in facilitating the detoxification pathway within the body.
• Glutathione, a tripeptide composed of cysteine, glutamate, and glycine, is manufactured in the liver and also in the brain.
• Normally, the concentrations of glutathione in the cells are quite high providing for detoxification of a variety of heavy metals including mercury.
• However, when this essential antioxidant is depleted the excess mercury can bind to internal cellular proteins leading to toxic damage.
• They found that the higher the concentration of Thimerosal the greater the number of cells that were killed although the nerve cell response occurred with only a 3 hour exposure, whereas the other cell line required a 48 hour exposure demonstrating that nerve cells are more sensitive to Thimerosal toxicity.
• "In both cell lines, a progressive increase in cytotoxicity (decrease in viability) was observed when Thimerosal dose was progressively doubled from 2.5 ¼mol/L [micromoles per liter] to 5, 10, and 20 ¼mol/L.
• They found that, "Thimerosal alone induced more than a 6-fold decrease in viability", and that NAC, "provided significant protection against cell death".
• The authors note, "Thimerosal induces oxidative stress and apoptosis by activating mitochondrial cell death pathways.