Imaging Mass Spectrometry (IMS) Approach for the Assessment of Degeneration of Meniscus

Aims: Exact assessment of meniscus structure degeneration is not possible because of interobserver variability even if histochemical methods are included in the diagnostic procedure. For this we have applied imaging mass spectrometry to support objectivity of meniscus diagnostics. Methods: 20 FFPE-tissues of meniscus with areas with low degeneration and strong degeneration were included in this study. Additionally, frozen tissue biopsies were collected to identify proteins involved in meniscus degeneration. All patients gave informed consent; the study design was approved by the local ethics committee. The grade of degeneration was assessed by two pathologists. Consent could be obtained only when a two grade system with low grade and high grade degeneration was applied. Trypsin and matrix deposition onto FFPE and matrix deposition onto fresh frozen biopsy specimens was carried out using the ImagePrep device (Bruker, Bremen) followed by subsequent matrix-assisted laser desorption/ionization (MALDI) analysis using a Bruker Autoflex Speed in profiling and imaging mode. Statistical analysis was done using ClinProTools 3.0. Each analysis was performed as an independent experiment to ensure statistical independence. Results: Statistical analysis generated significantly different signals between the two areas of interested in the FFPE-meniscus tissues. 6 peptide ion signals were sufficient to discern low grade (or normal) from high grade degeneration areas. 3 signals were present in normal meniscus and low degeneration areas and 3 signals strongly expressed in areas with high grade degeneration. Conclusion: MALDI MS technology can discriminate between high grade and low grade meniscus degeneration, either in profiling or in imaging mode. Further studies are required to discriminate old and fresh ruptures as an objective measure to answer questions of clinicians and insurances.