Table of Contents
ISRN Surgery
Volume 2014, Article ID 405360, 6 pages
http://dx.doi.org/10.1155/2014/405360
Research Article

Quantification of Protoporphyrin IX Accumulation in Glioblastoma Cells: A New Technique

1Upper Michigan Brain Tumor Center, Marquette, MI 49855, USA
2Biology Department, Northern Michigan University, Marquette, MI 49855, USA
3Purdue University, West Lafayette, IN 47906, USA
4Division of Neurosurgery, Marquette General Hospital, Marquette, MI 49855, USA
5School of Clinical Sciences, Northern Michigan University, Marquette, MI 49855, USA

Received 6 December 2013; Accepted 20 January 2014; Published 4 March 2014

Academic Editors: D. Galetta, Y. Kaku, and A. Polydorou

Copyright © 2014 Johnathan E. Lawrence et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Introduction. 5-Aminolevulinic Acid (5-ALA) is a precursor of heme synthesis. A metabolite, protoporphyrin IX (PpIX), selectively accumulates in neoplastic tissue including glioblastoma. Presurgical administration of 5-ALA forms the basis of fluorescence-guided resection (FGR) of glioblastoma (GBM) tumors. However, not all gliomas accumulate sufficient quantities of PpIX to fluoresce, thus limiting the utility of FGR. We therefore developed an assay to determine cellular and pharmacological factors that impact PpIX fluorescence in GBM. This assay takes advantage of a GBM cell line engineered to express yellow fluorescent protein. Methods. The human GBM cell line U87MG was transfected with a YFP expression vector. After treatment with a series of 5-ALA doses, both PpIX and YFP fluorescence were measured. The ratio of PpIX to YFP fluorescence was calculated. Results. YFP fluorescence permitted the quantification of cell numbers and did not interfere with 5-ALA metabolism. The PpIX/YFP fluorescence ratio provided accurate relative PpIX levels, allowing for the assessment of PpIX accumulation in tissue. Conclusion. Constitutive YFP expression strongly correlates with cell number and permits PpIX quantification. Absolute PpIX fluorescence alone does not provide information regarding PpIX accumulation within the cells. Our research indicates that our PpIX/YFP ratio assay may be a promising model for in vitro 5-ALA testing and its interactions with other compounds during FGR surgery.