Protoporphyrin IX purification from blood and serum for mass analysis – Considerations with respect to neurosurgery

Abstract

Protoporphyrin (PPIX) and its precursor 5-aminolevulinic acid (ALA) are routinely used in fluorescence-guided resection (FGR) in neurosurgery of glioblastoma. Orally administered prior to surgery, ALA diffuses preferentially into the tumour-bearing brain region and is there transformed into PPIX as part of the heme biosynthesis.During the resection of high-grade gliomas (HGG), the fluorescent properties of PPIX enable the differentiation of healthy and malignant brain tissueresulting in a more complete tumour resection and, ultimately, a better prognosis for patients. 1,2 Despite the use of ALA-FGR, complete tumour removal is impossibledue to the infiltrative growth of HGG, e.g., glioblastoma multiforme (GBM), tumours often reoccur. Clinical diagnosis of HGG/GBM is furthermore not straightforward and requires expensive imaging technology as well as tissue biopsies. So far, the prognosis for GBM patients remains one of the lowest in modern day oncology. 1,3,4 We thus investigated PPIX as a potential blood biomarker for the diagnosis of primary and recurrent GBM using liquid chromatography/mass spectrometry (LC/MS). 5 Some cancer research studies to that effect using plasma have already been published. [6][7][8] It was also demonstrated that extracellular vesicles originating from glioma cells contained PPIX, 9 but none of these investigations used mass spectrometry (MS) as detector.Whole blood contains the most PPIX, but it is not the best matrix for such studies, because of unspecific contributions from erythrocyte ZnPPIX. For serum or plasma, though, the published PPIX levels,