Mass spectrometry imaging

Mass spectrometry imaging is a technique used to create a molecular map of living tissue in a single shot. Researchers use this technique to determine the exact location of certain molecules and how they are influenced by diseases. 'In a sense, we're creating the Google Maps of tissue,' says researcher Martijn Arts. 'What makes our research so special is that we’ve developed a method that allows us to visualise molecular changes as they are happening and pinpoint their exact location. In the future, this will allow us to determine how, for example, tumour tissue behaves in a patient. This information is important for both diagnostic and prognosis purposes.'

Visualising liver metabolism

To test their research method, the researchers injected a healthy mouse with the amino acid phenylalanine. The liver converts this essential amino acid into tyrosine, a non-essential amino acid that is commonly found in protein-rich foods like cheese, meat and legumes. This conversion is slower in people with liver disease. 'In order to visualise this biochemical process, we also injected a tracer – in this case stable isotopes – along with the phenylalanine,' explains Zita Soons. 'Think of stable isotopes as a kind of GPS tag that we can detect using mass spectrometry imaging. This allows us to see exactly where the labelled phenylalanine goes in the tissue and what happens to it. We took MSI images of the enzymatic conversion at three fixed intervals – 10 minutes, 30 minutes and 60 minutes – and clearly saw the molecular changes. What makes this method so amazing is that it can be used for lots of other metabolites as well.'

Unique collaboration

Researchers from the Maastricht MultiModal Imaging Institute (M41) and the School of Nutrition and Translational Research in Metabolism (NUTRIM) worked in close collaboration within the research team. Oncologists from GROW research school, radiologists from MAASTRO radiation centre and biochemists from the Cardiovascular Research Institute Maastricht (CARIM) were also involved in the research. ‘A collaboration of this size in an area barely spanning one square kilometre is extremely unique,’ says Arts. ‘A follow-up study is already in the works and will focus on tumour tissue.’