The comparative biology of neuromelanin and lipofuscin in the human brain.

Neuromelanin and lipofuscin are two pigments produced within the human brain that, until recently, were considered inert cellular waste products of little interest to neuroscience. Recent research has increased our understanding of the nature and interactions of these pigments with their cellular environment and suggests that these pigments may, indeed, influence cellular function. The physical appearance and distribution of the pigments within the human brain differ, but both accumulate in the aging brain and the pigments share some structural features. Lipofuscin accumulation has been implicated in postmitotic cell aging, while neuromelanin is suggested to function as an iron-regulatory molecule with possible protective functions within the cells which produce this pigment. This review presents comparative aspects of the biology of neuromelanin and lipofuscin, as well as a discussion of their hypothesized functions in brain and their possible roles in aging and neurodegenerative disease.