In vivo Quantification of the Transition of Brain Extracellular Mercury after Thimerosal Administration
Researchers from Taiwan developed a method for the in-vivo determination of the transition of brain extracellular mercury after thimerosal administration.
Monomethylmercury (MMHg) is recognized as one of the most potent neurotoxins. While the chemistry of ethylmercury (EtHg) is not fundamentally different from that of methylmercury, its toxicity has often been discussed as totally different. The ethylmercury moiety is part of thimerosal (TMHg), which is used as a preservative in vaccines to prevent fungal and bacterial growth since the 1930s. After injection into the body, the EtHg moiety is released from TMHg to the surrounding tissues and therefore should follow the same toxicological pathways as other ETHg absorbed into the body from other sources. While numerous studies exist, showing the strong toxic effects produced by EtMg, the use of TMHg in vaccines has not been associated with any clear connections with serious human neurodevelopmental disorders.
While the use of TMHg in vaccines in Europe and the US has been considerably reduced after 1999, especially for children and pregnant women, the worldwide use of TMHg-containing vaccines is still important. While the brain in general is protected against the inflow of many exotic toxic substances by the blood-brain barrier (BBB), mercurial substances can overcome the barrier and cause serious toxic effects. Therefore, the investigation of mercury concentrations between blood and extracellular fluid (ECF) of the brain following the administration of TMHg is important for improving the knowledge of the neurotoxicity of TMHg.
The new study:
Researchers from Taiwan now developed a method for the in-vivo determination of the transition of brain extracellular mercury after thimerosal administration. In order to cope with the extremely low available sample volume, the low Hg concentration and the high salinity of the sample matrix, a microfluidic approach was developed based on microdialysis for sampling and photocatalyst-assisted vaporization for sample introduction to the ICP-MS. Under optimal operation conditions, the developed analytical system provided limits of detection (based on 3s) of 2.7 and 1.7 ng/L for MMHg and TMHg.
Using this system, the transport of mercury to the brain of adult male Sprague-Dawley rats was studied after intraperitoneal administration of MMHg or TMHg in saline solution with a time resolution of about 13 min. The system was able to monitor the rapid change of mercurial concentration appearing in ECF. The results of the animal experiments with the two organomercurials indicated extremely similar transition trends. Thus the researchers concluded, that the BBB penetration behaviour of TMHg is very similar to that of MMHg although the transport mechanism of TMHg remains unclear.
The original publication:
Cheng-Hsing Lin, Cheng-Kuan Su, Yuh-Chang Sun, Development of Online Microdialysis–Microfluidic-Based Photocatalyst-Assisted Vaporization Device–Inductively Coupled Plasma-Mass Spectrometry Hyphenated Analytical System for in vivo Quantification of the Transition of Brain Extracellular Mercury after Thimerosal Administration, Microchem. J., 154 (2020) 104569. DOI: 10.1016/j.microc.2019.104569
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