Point-of-care mass spectrometry metabolomic analysis enabling intraoperative brain tumor diagnosis

Rationale: While mass spectrometry (MS) is known for being capable of analyzing a wide range of biomarkers, its usages in clinical settings have been hindered by the stringent requirements for operating the MS analysis system as well as performing the analytical procedure at the point of care (POC). We have developed a miniature MS system and extremely simplified analytical protocols for POC analysis of tumors. It enabled comprehensive metabolite profiling with brain tissue biopsy, which allowed accurate and real-time diagnosis of brain tumors and guiding of surgical resection strategy. Methods: A miniature linear ion trap MS system with direct sampling ionization for tissue biopsy analysis was developed, which is suitable for performing real-time analysis in a surgical room. A segment scan method was developed to allow coverage of a wide range of metabolites while providing adequate sensitivity. An extremely simplified protocol was developed to allow a real-time analysis of the tissue samples taken from patients. The development and validation of this method involved 137 brain tissue samples from 109 patients. The miniature MS system could operate on battery without requiring compressed gas or large amounts of solvents like traditional MS analysis systems in lab. Results: With optimized sampling and scanning method, 183 metabolites in the range of m/z 50 - 500 could be identified from human brain tissues after a 2 min analysis time. Metabolomic features were extracted that allowed distinctions between glioma and normal tissues (at an area under the curve (AUC) of 0.932), isocitrate dehydrogenase (IDH) mutant and wildtype gliomas (at an AUC of 1.000), and IDH mutant gliomas and glioblastoma (at an AUC of 1.000). A comparison study was also carried out between fresh and stored tissue samples and decrease in abundance was observed for metabolites such as glutamate and N-acetylaspartic acid, which indicates the importance of real-time analysis of the biological samples for clinical applications. Conclusions: This study shows the potential of performing intraoperative or bedside MS analysis of a panel of metabolomic biomarkers in real time to facilitate the diagnosis of the disease as well as the decision making for surgery or therapy. Miniature mass spectrometry system with direct sampling ionization method serves as a valid platform for transferring MS analysis from traditional laboratories to clinical settings.