Adduct formation of Thimerosal with human and rat hemoglobin: a study using liquid chromatography coupled to electrospray time-of-flight mass spectrometry (LC/ESI-TOF-MS).

Thimerosal (THI) is used as a preservative in many vaccines throughout the world. Ethylmercury (EtHg(+)), released from THI in aqueous media, has a high affinity to thiol functions of proteins. In blood, hemoglobin is a likely target protein because of its high abundance and its several free thiol functions. In comparison to hemoglobin of human origin, hemoglobin of rats exhibits almost twice as many free thiol groups, which might lead to different binding behavior and therefore a limited comparability between the situation in man and in rats, which are frequently used as models for mercury species toxicity investigations. Thus, the adduct formation of EtHg(+) with hemoglobin of humans and rats was compared under simulated physiological conditions by using gradient reversed-phase liquid chromatography (LC) with electrospray time-of-flight mass spectrometry (ESI-TOF-MS) detection. The binding stoichiometry correlated with the number of free thiols in the α- and β-chain of hemoglobin. The use of rats to verify the safety of additives in vaccines like Thimerosal is therefore doubtful and should be reevaluated.