Thimerosal

Abstract: Objective It has been suggested that thimerosal, a mercury-containing preservative in vac- cines, is a risk factor for the development of autism We examined whether discontinuing the use of thimerosal- containing vaccines in Denmark led to a decrease in the incidence of autism Design Analysis of data from the Danish Psychiatric Central Research Register recording all psychiatric ad- missions since 1971, and all outpatient contacts in psy- chiatric departments in Denmark since 1995 Patients All children between 2 and 10 years old who were diagnosed with autism during the period from 1971-2000 Outcome Measures Annual and age-specific inci- dence for first day of first recorded admission with a diagnosis of autism in children between 2 and 10 years old Results A total of 956 children with a male-to-female ratio of 35:1 had been diagnosed with autism during the period from 1971-2000 There was no trend toward an increase in the incidence of autism during that period when thimerosal was used in Denmark, up through 1990 From 1991 until 2000 the incidence increased and contin- ued to rise after the removal of thimerosal from vaccines, including increases among children born after the dis- continuation of thimerosal Conclusions The discontinuation of thimerosal-con- taining vaccines in Denmark in 1992 was followed by an increase in the incidence of autism Our ecological data do not support a correlation between thimerosal-contain- ing vaccines and the incidence of autism Pediatrics 2003; 112:604 - 606; autism, vaccine, thimerosal, mercury, popu- lation, epidemiology

Abstract: Thimerosal is a preservative that has been used in manufacturing vaccines since the 1930s. Reports have indicated that infants can receive ethylmercury (in the form of thimerosal) at or above the U.S. Environmental Protection Agency guidelines for methylmercury exposure, depending on the exact vaccinations, schedule, and size of the infant. In this study we compared the systemic disposition and brain distribution of total and inorganic mercury in infant monkeys after thimerosal exposure with those exposed to MeHg. Monkeys were exposed to MeHg (via oral gavage) or vaccines containing thimerosal (via intramuscular injection) at birth and 1, 2, and 3 weeks of age. Total blood Hg levels were determined 2, 4, and 7 days after each exposure. Total and inorganic brain Hg levels were assessed 2, 4, 7, or 28 days after the last exposure. The initial and terminal half-life of Hg in blood after thimerosal exposure was 2.1 and 8.6 days, respectively, which are significantly shorter than the elimination half-life of Hg after MeHg exposure at 21.5 days. Brain concentrations of total Hg were significantly lower by approximately 3-fold for the thimerosal-exposed monkeys when compared with the MeHg infants, whereas the average brain-to-blood concentration ratio was slightly higher for the thimerosal-exposed monkeys (3.5 +/- 0.5 vs. 2.5 +/- 0.3). A higher percentage of the total Hg in the brain was in the form of inorganic Hg for the thimerosal-exposed monkeys (34% vs. 7%). The results indicate that MeHg is not a suitable reference for risk assessment from exposure to thimerosal-derived Hg. Knowledge of the toxicokinetics and developmental toxicity of thimerosal is needed to afford a meaningful assessment of the developmental effects of thimerosal-containing vaccines.

Abstract: Thimerosol is an antiseptic containing 49.5% ethyl mercury that has been used for years as a preservative in many infant vaccines and in flu vaccines. Environmental methyl mercury has been shown to be highly neurotoxic, especially to the developing brain. Because mercury has a high affinity for thiol (sulfhydryl (–SH)) groups, the thiol-containing antioxidant, glutathione (GSH), provides the major intracellular defense against mercury-induced neurotoxicity. Cultured neuroblastoma cells were found to have lower levels of GSH and increased sensitivity to thimerosol toxicity compared to glioblastoma cells that have higher basal levels of intracellular GSH. Thimerosal-induced cytotoxicity was associated with depletion of intracellular GSH in both cell lines. Pretreatment with 100 mM glutathione ethyl ester or Nacetylcysteine (NAC), but not methionine, resulted in a significant increase in intracellular GSH in both cell types. Further, pretreatment of the cells with glutathione ethyl ester or NAC prevented cytotoxicity with exposure to 15 mM Thimerosal. Although Thimerosal has been recently removed from most children’s vaccines, it is still present in flu vaccines given to pregnant women, the elderly, and to children in developing countries. The potential protective effect of GSH or NAC against mercury toxicity warrants further research as possible adjunct therapy to individuals still receiving Thimerosal-containing vaccinations.