Abstract
Objectives: SELDI-TOF and MALDI-TOF mass spectrometry (MS) are laser desorption technologies that allow for proteomic examination of molecular masses in small amounts of samples. In a precedent study, the feasibility of SELDI-TOF MS assessment of proteins in cerebrospinal fluid and tumor cyst fluid had been shown. In the present study, we analyzed whether MALDI-TOF MS examination of these fluids leads to comparable results. Methods: During neurosurgical intervention, cyst fluids from 24 glioblastomas and 15 metastases were collected. As control, cerebrospinal fluid samples from 23 patients were obtained. The samples were prepared using a protocol optimized for MALDI-TOF MS. Mass spectra were recorded and peaks were extracted, characterized by masses and relative intensities. These peaks were analyzed for statistically significant differences between the diagnosis groups and compared to SELDI-TOF MS data. Results: 41 protein peaks known from the SELDI-TOF MS analysis could be confirmed by MALDI-TOF MS, and the cellular expression of the proteins LuzP6 and ApoC1, corresponding to the protein peaks 6433 and 6632, was shown immunohistochemically in glioblas-toma tissue. The MALDI-TOF spectrometry extends the range of analysis down to 1.4 kDa, whereas the upper detection limit lies below 23 kDa. Discussion: The presented proteomic approach yields an inventory of protein masses, found in the tumor cyst at the time of puncture. It does not reveal pathophysiologic, metabolic or secretory pathways that lead to the presence of proteins in the cyst. These have to be assessed immunohistochemically or on mRNA level in the surrounding tumor cells. Conclusion: MALDI-TOF MS of tumor cyst fluid discloses protein sizes, overexpressed or lost in tumor tissue. A thorough proteomic work-up is needed to identify the underlying proteins and metabolic pathways.
Highlights
Tumor cysts occur in a multitude of brain tumors
The heterogeneity of peaks was lowest in cerebrospinal fluid (CSF) from controls (94 bands from samples, ca. 4/sample), average in cyst fluid from glioblastoma (148 from samples, ca. 6/sample) and highest in metastases (125 peaks from 15 samples, ca. 8/sample)
Concerning proteins shown in table 1, this was the case for the peaks at 3513 and 5865, 6025 and 1865
Summary
Tumor cysts occur in a multitude of brain tumors. While in entities such as hemangioblastoma or oligodendroglioma cysts can be considered to be pathognomonic, the most frequent occurrence is in glioblastoma, metastasis or meningioma [1]. Tumor cyst fluid is only available in small amounts with very low concentration of proteins. The surface enhanced laser desorption ionisation mass spectrometry (SELDI-TOF MS), a highly sophisticated variant of matrix assisted laser desorption ionisation (MALDI-TOF MS), allows to assess directly cyst fluid protein content in as few as 2 microliters of specimen [2]. Standard MALDI-TOF mass spectrometry should be applicable to cyst fluid, if samples are desalted and concentrated properly before mass spectrometric analysis
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