Detection and quantification of neurotensin in human brain tissue by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A method was developed for mass spectrometric detection of neurotensin (NT) -like immunoreactivity and quantification of NT in human brain tissue. The method is based on immunoprecipitation followed by analysis using matrix-as sisted laser desorption/ionization time-of-flight mass spectrometry (MALDI- TOF-MS), The identity of the major component of the immunoprecipitates as n eurotensin was confirmed by fragment ion analysis on an electrospray ioniza tion quadrupole time-of-flight instrument. MALDI-TOF-MS quantification of N T was achieved using stableisotope-labeled NT as the internal standard, yie lding an error of less than 5%, The method allowed detection of low-femtomo le amounts of NT, starting from low-milligram amounts of lyophilized brain tissue. In addition to NT, several other peptides were detected in the puri fied samples, most of which, according to their molecular masses, correspon ded to fragments of NT, The method is demonstrated with quantification of N T from human hypothalamus tissue, and a comparison is made with results obt ained from competitive radioimmunoassay.