Thiomersal (C9H9HgNaO2S) is an exogenous organic compound with an average molecular weight of 404.81 g/mol that exists as a solid at room temperature. Thiomersal belongs to the benzoic acids and derivatives, a subclass of benzene and substituted derivatives within the organic compounds. It is utilized as a fungicide and disinfectant for biological applications, as well as an industrial preservative. Recorded sources of the compound include soap dispensers, antiseptics and disinfectants, and food processing such as the processing of fish and the preparation of vinegar. Exposure routes include ophthalmic and cutaneous contact.
The compound interacts with 32 recorded protein targets. It acts as an antagonist of Toll-like receptor 9 (TLR9) and targets methionine synthase (MTR), the cystine/glutamate transporter (SLC7A11), and sodium/potassium-transporting ATPase subunit gamma (FXYD2). Mercury in the compound inhibits alkaline phosphatase, tissue-nonspecific isozyme (ALPL), which alters the blood-brain barrier and impairs brain microvascular function and formation. Similarly, the inhibition of protein kinase C (including alpha, beta, delta, and epsilon types and two other proteins) impairs brain microvascular formation and function and alters the blood-brain barrier. Mercury also inhibits aquaporins, such as Aquaporin-1 (AQP1) and Lens fiber major intrinsic protein (MIP), resulting in cell death and injury by halting water flow across the cell membrane. Additionally, the inhibition of tyrosine-protein kinase Lck (LCK) causes immune system depression and decreased T-cell signalling. Finally, organic mercury binds to tubulin—including Tubulin alpha-1A, 1B, and 1C chains, Tubulin-like protein alpha-4B, and 14 other proteins—causing mitotic inhibition and preventing microtubule assembly, which exerts developmental effects.
belongs to the class of organic compounds known as o-sulfanylbenzoic acids. These are benzoic acids which bear a sulfanyl group (R-SH) attached to the benzene ring at positions 1 and 2, respectively.
High-affinity binding of the divalent mercuric ion to thiol or sulfhydryl groups of proteins is believed to be the major mechanism for the activity of mercury. Through alterations in intracellular thiol status, mercury can promote oxidative stress, lipid peroxidation, mitochondrial dysfunction, and changes in heme metabolism. Mercury is known to bind to microsomal and mitochondrial enzymes, resulting in cell injury and death. For example, mercury is known to inhibit aquaporins, halting water flow across the cell membrane. It also inhibits the protein LCK, which causes decreased T-cell signalling and immune system depression. Mercury is also believed to inhibit neuronal excitability by acting on the postsynaptic neuronal membrane. It also affects the nervous system by inhibiting protein kinase C and alkaline phosphatase, which impairs brain microvascular formation and function, as well as alters the blood-brain barrier. Organic mercury exerts developmental effects by binding to tubulin, preventing microtubule assembly and causing mitotic inhibition. Mercury also produces an autoimmune response, likely by modification of major histocompatibility complex (MHC) class II molecules, self peptides, T-cell receptors, or cell-surface adhesion molecules. (8, 3, 4, 5)
Metabolism
Organic mercury is absorbed mainly by the gastrointestinal tract, then distributed throughout the body via the bloodstream. Organic mercury complexes with free cysteine and the cysteine and sulfhydryl groups on proteins such as haemoglobin. These complexes are able to mimic methionine and thus be transported throughout the body, including through the blood-brain barrier and placenta. Organic mercury is metabolized into inorganic mercury, which is eventually excreted in the urine and faeces. (13)
Mercury mainly affects the nervous system. Exposure to high levels of metallic, inorganic, or organic mercury can permanently damage the brain, kidneys, and developing fetus. Effects on brain functioning may result in irritability, shyness, tremors, changes in vision or hearing, and memory problems. Acrodynia, a type of mercury poisoning in children, is characterized by pain and pink discoloration of the hands and feet. Mercury poisoning can also cause Hunter-Russell syndrome and Minamata disease. (8)
Symptoms
Common symptoms include peripheral neuropathy (presenting as paresthesia or itching, burning or pain), skin discoloration (pink cheeks, fingertips and toes), edema (swelling), and desquamation (dead skin peels off in layers). (1)
Treatment
Mercury poisoning is treated by immediate decontamination and chelation therapy using DMSA, DMPS, DPCN, or dimercaprol. (2)
