Objective: Neuromelanin (NM) is different to other melanins in that its ultrastructure includes a lipid component. The objectives of this study were to identify and quantify lipids associated with NM.
Results: Quantification of the lipid component associated with the pigment on electron micrographs demonstrated that this component comprises 35% of the NM granule volume in the normal brain. The irregular ultrastructural appearance of the NM granules was quite different to the round regular boundary of melanin granules. Using reversed phase high performance liquid chromatography (HPLC) coupled with atmospheric pressure chemical ionization (APCI) mass spectrometry we demonstrated that the isoprenoid dolichol accounted for approximately 12% of total NM pigment mass. Low levels of other lipids were detectable (cholesterol, ubiquinone-10 and alpha-tocopherol) and account for <0.05% of NM lipid, in contrast to cholesterol accounting for 35% of total brain lipids.
Conclusion: Unlike other melanins, a substantial proportion of NM volume is comprised of lipid and the major type of lipid associated with NM granules is the isoprenoid dolichol.