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Alex Y. Lu, Jack L. Turban, Eyiyemisi C. Damisah, Jie Li, Ahmed K. Alomari, Tore Eid, Alexander O. Vortmeyer and Veronica L. Chiang

OBJECTIVE

Following an initial response of brain metastases to Gamma Knife radiosurgery, regrowth of the enhancing lesion as detected on MRI may represent either radiation necrosis (a treatment-related inflammatory change) or recurrent tumor. Differentiation of radiation necrosis from tumor is vital for management decision making but remains difficult by imaging alone. In this study, gas chromatography with time-of-flight mass spectrometry (GC-TOF) was used to identify differential metabolite profiles of the 2 tissue types obtained by surgical biopsy to find potential targets for noninvasive imaging.

METHODS

Specimens of pure radiation necrosis and pure tumor obtained from patient brain biopsies were flash-frozen and validated histologically. These formalin-free tissue samples were then analyzed using GC-TOF. The metabolite profiles of radiation necrosis and tumor samples were compared using multivariate and univariate statistical analysis. Statistical significance was defined as p ≤ 0.05.

RESULTS

For the metabolic profiling, GC-TOF was performed on 7 samples of radiation necrosis and 7 samples of tumor. Of the 141 metabolites identified, 17 (12.1%) were found to be statistically significantly different between comparison groups. Of these metabolites, 6 were increased in tumor, and 11 were increased in radiation necrosis. An unsupervised hierarchical clustering analysis found that tumor had elevated levels of metabolites associated with energy metabolism, whereas radiation necrosis had elevated levels of metabolites that were fatty acids and antioxidants/cofactors.

CONCLUSIONS

To the authors' knowledge, this is the first tissue-based metabolomics study of radiation necrosis and tumor. Radiation necrosis and recurrent tumor following Gamma Knife radiosurgery for brain metastases have unique metabolite profiles that may be targeted in the future to develop noninvasive metabolic imaging techniques.

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Zhengping Zhuang, Meng Qi, Jie Li, Hiroaki Okamoto, David S. Xu, Rajiv R. Iyer, Jie Lu, Chunzhang Yang, Robert J. Weil, Alexander Vortmeyer and Russell R. Lonser

Object

Astrocytomas and oligodendrogliomas are primary CNS tumors that remain a challenge to differentiate histologically because of their morphological variability and because there is a lack of reliable differential diagnostic markers. To identify proteins that are differentially expressed between astrocytomas and oligodendrogliomas, the authors analyzed the proteomic expression patterns and identified uniquely expressed proteins in these neoplasms.

Methods

Proteomes of astrocytomas and oligodendrogliomas were analyzed using 2D gel electrophoresis and subsequent computerized gel analysis to detect differentially expressed proteins. The proteins were identified using high-performance liquid chromatography accompanied by tandem mass spectrometry. To determine the role of the differentially expressed proteins in astrocytes, undifferentiated glial cell cultures were treated with dibutyryl–cyclic adenosine monophosphate (cAMP).

Results

Two-dimensional gel electrophoresis revealed that glutamine synthetase was differentially expressed in astrocytomas and oligodendrogliomas. Western blot and immunohistochemical analyses confirmed the increased expression of glutamine synthetase in astrocytomas compared with oligodendrogliomas. Whereas glutamine synthetase expression was demonstrated across all grades of astrocytomas (Grade II–IV [15 tumors]) and oligoastrocytomas (4 tumors), it was expressed in only 1 oligodendroglioma (6% [16 tumors]). Treatment of undifferentiated glial cell cultures with dibutyryl-cAMP resulted in astrocyte differentiation that was associated with increased levels of glial fibrillary acidic protein and glutamine synthetase.

Conclusions

These data indicate that glutamine synthetase expression can be used to distinguish astrocytic from oligodendroglial tumors and may play a role in the pathogenesis of astrocytomas.

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Jie Li, Hiroaki Okamoto, Chunyue Yin, Jay Jagannathan, Jun Takizawa, Sadao Aoki, Sven Gläsker, Elisabeth J. Rushing, Alexander O. Vortmeyer, Edward H. Oldfield, Ryuya Yamanaka and Zhengping Zhuang

Object

The lack of primary lymphoid tissue within the central nervous system (CNS) confounds our understanding of the pathogenesis of primary CNS lymphomas (PCNSLs). Comparing the protein expression of PCNSLs and sporadic systemic lymphomas (SSLs) provides a useful strategy for identifying a molecular signature that characterizes disease-associated features and provides information regarding tumor initiation and progression.

Methods

Seven diffuse large B-cell PCNSLs were selected to undergo 2D gel electrophoresis, and profiled proteomes from these PCNSLs were compared with those from 7 diffuse large B-cell SSLs. Distinguishing proteins were sequenced using mass spectrometry.

Results

Two-dimensional gel electrophoresis identified an average of 706 proteins from each specimen. Computerized gel analysis and manual reconfirmation revealed a 96% similarity in the proteomes of PCNSLs and SSLs. Comparative analysis identified 9 proteins significantly overexpressed (p < 0.05) and 16 proteins downregulated in PCNSLs. The proteomic findings were further validated using Western blot and immunohistochemical staining.

Conclusions

The similarities in proteomic patterns between PCNSLs and SSLs suggest that these tumor types share structural similarities, acquired during differentiation. The ultimate fate of lymphomatous cells (CNS vs systemic) may be related to differentially expressed proteins, which function in homing and host processing. Elucidating the roles of these differentially expressed proteins will prove valuable in understanding the pathogenesis of PCNSL.