PROCESSING OF NEUROPEPTIDE-Y AND SOMATOSTATIN IN HUMAN CEREBROSPINAL-FLUID AS MONITORED BY RADIOIMMUNOASSAY AND MASS-SPECTROMETRY

The processing of four neuropeptides, neuropeptide Y (NPY) 1-36, NPY ( 18-36), somatostatin (SOM) 1-28, and SOM (15-28) was studied in human cerebrospinal fluid (CSF) by using a novel combination of methods that included radioimmunoassay (RIA) and mass spectrometry. Untreated CSF samples were chromatographed using reversed-phase high pressure liquid chromatography (RP-HPLC) followed by NPY-RIA or SOM-RIA. These result s were compared with those obtained by incubating CSF with exogenous s ynthetic peptides and directly detecting peptide fragments by matrix-a ssisted laser desorption/ionization time of-flight mass spectrometry ( MALDI-MS). Using this combination of methods, we were able to determin e the probable identities of peptides/peptide fragments recognized in radioimmunoassays. The most important NPY-immunoreactive components in CSF were found to be NPY (1-36) and NPY 3-36). Metabolic products of SOM (15-28) were found to contribute to SOM-like immunoreactivity (SOM -LI) in CSF, but SOM (1-28) only to a lesser degree. Differences in th e rate of neuropeptide processing were observed. These differences dep ended more on the length of the peptide than its sequence. NPY (18-36) and SOM (15-28) were rapidly and extensively processed, whereas NPV ( 1-36) and SOM (1-28) were processed much more slowly in CSF. The produ ction of SOM (15-28) from SOM (1-28) by enzymes in CSF was not observe d. Also, the presence of a disulfide bond in the somatostatins appeare d to stabilize them against enzymatic digestion of the ring structure. The results detailed in this report confirm MALDI-MS important role i n studies of neuropeptide processing in CSF. (C) 1998 Elsevier Science Inc.