Mass Spectrometry in Clinical Laboratory

**55**

**Chapter 4**

**Abstract**

*and Simone König*

Protoporphyrin IX Analysis from

Neurosurgery of Glioblastoma

*Anna Walke, Eric Suero Molina, Walter Stummer* 

Blood and Serum in the Context of

Protoporphyrin IX (PPIX) is formed from δ-aminolevulinic acid (ALA) during heme biosynthesis. Due to its cyclic tetrapyrrole core structure, it absorbs in the visible region of the electromagnetic spectrum and is thus colored. Both ALA and PPIX have become of great interest to neurosurgery, because in high-grade glioma, ALA diffuses into the tumor and is converted to PPIX. Fluorescence-guided resection (FGR) takes advantage of both the enrichment of PPIX in the tumor and its fluorescent properties, which enable visualization of tumor tissue. ALA-mediated FGR thus maximizes the extent of resection with better prognosis for patients. Tumor cells are able to produce porphyrins naturally or after administration of ALA, which is also reflected in elevated plasma fluorescence of cancer patients. PPIX might thus serve as a biomarker for monitoring of the tumor burden. A liquid chromatography-mass spectrometry (LC-MS)-based method is presented to quantify PPIX in blood and serum in the context of current fluorescence-based diagnostics. The method is able to distinguish between zinc PPIX, a component of red blood cells of importance in the detection of lead poisoning and iron deficiency anemia, and metal-free PPIX. In a proof-of-principle study, it was used to follow a time course of a glioblastoma patient undergoing surgery and confirmed elevated PPIX blood levels before ALA administration. During surgery, these blood levels increased about four-fold. The here developed 10 min reversed-phase LC-target MS

method now allows patient screening with high specificity and throughput.

Cyclic tetrapyrroles are biologically important molecules as they form the core structure of prosthetic groups such as porphyrins (e.g. heme), natural pigments like chlorophyll, and of vitamers (cobalamins, e.g. vitamin B12). Due to their large conjugated systems, they absorb in the visible region of the electromagnetic spectrum

Porphyrins occur naturally as metal complexes with the red pigment in blood cells, heme, being the best-known example. Hemes (**Figure 1**), the cofactors of

**Keywords:** protoporphyrin IX, zinc protoporphyrin IX, iron deficiency, lead poisoning, porphyria, biomarker, cancer, ion trap mass spectrometry,

brain tumor, glioblastoma, blood

and are thus colored [1, 2].

**1. Introduction**
