New Melanic Pigments in the Human Brain That Accumulate in Aging and Block Environmental Toxic Metals

New neuronal pigments of melanic type were identified in the putamen, cortex, cerebellum, and other major regions of human brain. They consist of granules of 30 nm size contained in organelles together with lipid droplets and accumulate in aging, reaching concentrations as high as 1.5 – 2.6 µg/mg tissue in major brain regions. These pigments which we term neuromelanins, contain melanic, lipid, and peptide components. The melanic component has typical aromatic structure, contains a stable free radical, and the precursor of its synthesis is cysteinyl–3,4-dihydroxyphenylalanine (Cys–DOPA). The precursors of lipid components of the pigments are the polyunsaturated lipids present in the enveloping organelles. The melanic component has chelating ability and accumulates environmental toxic metals (mercury and lead) and other metals, thus providing a protective effect. The synthesis of these neuromelanins is an important protective process as their melanic component is generated by removing reactive/toxic quinones that would otherwise cause neurotoxicity.