5-Aminolevulinic Acid (5-ALA)-Induced Protoporphyrin IX Fluorescence by Glioma Cells—A Fluorescence Microscopy Clinical Study

SIMPLE SUMMARY: 5-aminolevulinic acid (5-ALA)-induced PpIX fluorescence is used in neurosurgery for intraoperative identification of high-grade glioma tissue. In this paper, using a fluorescence microscopy analysis on human tumor specimens, we assessed the actual number of fluorescence-positive tumor cells both in low-grade and high-grade glioma, and the ability of 5-ALA to cross the blood–brain barrier (BBB). We found that in high-grade gliomas, 32.7–75.5 percent of cells display 5-ALA induced PpIX fluorescence, whereas in low-grade gliomas the tumor cells did not fluoresce following 5-ALA. Immunofluorescence for BBB components suggested that 5-ALA does not cross the un-breached BBB. These findings are of crucial importance in planning neurosurgical resection of gliomas. ABSTRACT: 5-aminolevulinic acid (5-ALA)-induced PpIX fluorescence is used by neurosurgeons to identify the tumor cells of high-grade gliomas during operation. However, the issue of whether 5-ALA-induced PpIX fluorescence consistently stains all the tumor cells is still debated. Here, we assessed the cytoplasmatic signal of 5-ALA by fluorescence microscopy in a series of human gliomas. As tumor markers, we used antibodies against collapsin response-mediated protein 5 (CRMP5), alpha thalassemia/mental retardation syndrome X-linked (ATRX), and anti-isocitrate dehydrogenase 1 (IDH1). In grade III–IV gliomas, the signal induced by 5-ALA was detected in 32.7–75.5 percent of CRMP5-expressing tumor cells. In low-grade gliomas (WHO grade II), the CRMP5-expressing tumor cells did not fluoresce following 5-ALA. Immunofluorescence with antibodies that stain various components of the blood–brain barrier (BBB) suggested that 5-ALA does not cross the un-breached BBB, in spite of its small dimension. To conclude, 5-ALA-induced PpIX fluorescence has an established role in high-grade glioma surgery, but it has limited usefulness in surgery for low-grade glioma, especially when the BBB is preserved.