Manganese speciation related to neurotoxicity in humans

Abstract

Manganese (Mn) is an essential trace element, exerting important functions in metabolic and redox homeostasis. However, increasing concerns are rising about the Mn exposure of humans and related neurotoxic effects. In this chapter, several aspects about Mn and neurotoxicity are provided for updated information, including chemical speciation of Mn compounds. Evidence on Mn-related Parkinsonism (Parkinson's disease) is presented as well as some chemical aspects of Mn and its compounds, enlighting oxidation states in general and in biological matrices. This is followed by considerations on natural sources of human exposure, occupational sources and anthropogenically caused environmental sources, for example from the use of methylcyclopentadienyl manganese tricarbonyl. This contribution also deals with Mn levels in the human organism, showing normal Mn concentrations in various tissues or body fluids, and continues with the toxicology of Mn. Specifically, the transfer of Mn to the brain is focused on. A short comparison between primary and Mn-dependent Parkinsonism is given, including a risk assessment and a consideration of susceptible groups. An important part highlights recent investigations on Mn speciation. Analytical problems and their solutions for correct identification of relevant Mn compounds in matrices of human origin are discussed. Finally, future needs are discussed, such as further investigations on those Mn species which may overcome neural barrier control, disease-modulated barrier control, susceptibility to certain Mn species and interaction of Mn with Fe homeostasis in brain.