Mercury neurotoxicity: Mechanisms of blood-brain barrier transport

Mercury exists in a wide variety of physical and chemical states, each of which has unique characteristics of target organ toxicity. The classic symptoms associated with exposure to elemental mercury vapor (Hg⁰) and methylmercury (Ch₃Hg⁺; MeHg) involve the central nervous system (CNS), while the kidney is the target organ for the mono- and divalent salts of mercury (Hg⁺ and Hg⁺⁺, respectively). Physical properties and redox potentials determine the qualitative and quantitative differences in toxicity among inorganic mercury compounds, while the ability of MeHg to cross the blood-brain barrier accounts for its accumulation in the CNS and a clinical picture that is dominated by neurological disturbances. This review gives an up-to-date account of mercury's physical and chemical properties and its interaction with biologically active sites pertinent to transport across the blood-brain barrier, a major regulator of the CNS millieu.