A headache of measurement errors: the true concentration of somatostatin in human blood

Abstract

Research in this thesis commenced with the novel hypothesis that the disabling neurological disease migraine is caused by decreased release of the neuropeptide somatostatin (SST) in the brain, affecting signalling in the periaqueductal grey and nucleus raphe magnus regions. However, when work commenced on the development of a method to measure SST concentration in blood it soon became evident that this was a challenging analyte indeed. A reported SST half-life of 2-3 mins, in combination with published innate mammalian blood concentrations at pg/mL levels posed difficulties in terms of sample collection, sample preparation and instrument sensitivity requirements. Consequently, the development of a method to enable measurement of the actual concentration(s) of SST in human blood became the focus of this study. The introduction presents a new hypothesis on the role of SST in the cause of migraine and reasons for its postulation. A review and critique of blood plasma SST concentrations reported in the literature is then provided. The second chapter discusses the development of ultraperformance liquid chromatography (UPLC) and electrospray ionisation tandem mass spectrometry (ESI-MS/MS) methods for somatostatin and its isotopically labelled internal standard, d5-SST, on two different triple quadrupole mass spectrometer platforms. Commercial standards in pure solvents were used for this work. Chapter three details method development for the quantification of SST in plasma. The main objectives were to arrest the degradation and maximise recovery of the analyte through the introduction of sample pre-treatment and sample preparation measures, and to minimise mass spectrometer ion suppression through effective sample clean-up. The fourth chapter tackles method development for SST quantification in whole blood. Failure of inhibitor formulations developed for plasma to translate to whole blood forced a different approach. Chapter five reports on a study initiated by an accidental discovery. In the search for a suitable internal standard for the quantification of SST several cyclic peptides were assessed. Chapter 6 commences with method development for SST concentration determination in human blood using a higher sensitivity LC-MS/MS platform and finishes with the application of the method to a pilot study.

Date of Thesis submission	2022
Original language	English
Awarding Institution	Western Sydney University
Supervisor	David Mahns (Supervisor) & David Harman (Supervisor)