High performance mass spectrometry reveals possible kerogen substructures in persistent ancient human brain

Abstract

The recovery of visually recognizable brain masses from skeletonized human burials is rare; the discovery of an exceptionally well-preserved 2500-year-old brain during excavations at Heslington, Yorkshire, UK, therefore attracted international publicity. Analysis of a lipidic extract of that brain material showed the presence of high molecular weight organic components. To determine whether the presence of such compounds is a common feature of unusually preserved brain specimens, we have carried out high resolution matrix-assisted laser desorption/ionization Fourier transform ion-cyclotron resonance mass spectrometric (MALDI FT-ICR-MS) analyses of lipidic extracts of preserved brain remains from 14 contexts, obtained from four archaeological sites ranging from 200 to 2500 years old. These data allowed elemental formulae for the predominant signals in the resulting spectra to be generated, and a detailed comparison of the resulting very rich dataset was carried out, allowing 38 molecular formulae to be assigned. The components identified across all the sample extracts analysed fell into the same class of large organic molecules as those from the Heslington brain and are generally functionalized with low numbers of heteroatoms (oxygen, nitrogen, or both). These components do not correspond to those identified in adipocere, but instead resemble kerogen substructures, surprisingly formed over historic rather than geological timescales. The presence of such insoluble, inert structures would help explain why brain material in which they are found is persistent. Our results pave the way for further analyses aimed at understanding the processes that take place when brain material is preserved in the archaeological record.