Thiomersal is an organomercuric compound. It is used mainly as an antiseptic and antifungal agent. Thiomersal was developed and registered under the trade name Merthiolate in 1928 by the pharmaceutical corporation Eli Lilly and Company and has been used as a preservative in vaccines, immunoglobulin preparations, skin test antigens, antivenins, ophthalmic and nasal products, and tattoo inks. Mercury is a heavy, silvery d-block metal and one of six elements that are liquid at or near room temperature and pressure. It is a naturally occuring substance, and combines with other elements such as chlorine, sulfur, or oxygen to form inorganic mercury compounds (salts). Mercury also combines with carbon to make organic mercury compounds. (6, 12)
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)
