Gelatin Zymography Can Be Performed on Fixed Brain Tissue

Gelatin zymography is widely used to detect gelatinase activity, which is performed on unfixed tissue because it is assumed that fixation inactivates enzymes. However, using fixed tissues has several advantages over using fresh tissues for such prevention of tissue decay, thereby preserving the proteins as well as the morphology and structure of the specimens. In this study, we investigated the effects of the four commonly used fixatives (ethanol, acetone, zinc-based fixative (ZBF), and paraformaldehyde (PFA)) on the gelatinolytic activity in mouse brain tissue. Multiple protocols were employed to extract proteins from the fixed brain tissue. Western blotting and in-gel zymography (IGZ) were used to detect the gelatinase proteins and gelatinolytic activity of the extractions, respectively. In situ zymography (ISZ) revealed that ethanol, acetone, ZBF, and short-time PFA fixation did not inhibit gelatinolytic activity. Neither 1% Triton + 1 M NaCl nor 10% DMSO + 1 M NaCl was effective in extracting proteins from ethanol-, acetone-, ZBF-, or PFA-fixed brain tissues. However, 8 M urea + 4% CHAPS effectively extracted gelatinase proteins from ethanol- and acetone-fixed tissues while retaining the gelatinolytic activity. 2% SDS effectively extracted gelatinase proteins from ethanol-, acetone-, and ZBF-fixed tissues while retaining the gelatinolytic activity. Although 2% SDS + heating extracted gelatinase proteins from ethanol-, acetone-, ZBF-, and even long-term PFA-fixed tissues, the gelatinolytic activity was not retained. Our findings suggest that both ISZ and IGZ can be performed on fixed brain tissue, which is anticipated to be an improvement over the conventionally used gelatin zymography methods. (J Histochem Cytochem 71: 481-493, 2023).

Single-cell resolution in high-resolution synchrotron X-ray CT imaging with gold nanoparticles

Gold nanoparticles are excellent intracellular markers in X-ray imaging. Having shown previously the suitability of gold nanoparticles to detect small groups of cells with the synchrotron-based computed tomography (CT) technique both ex vivo and in vivo, it is now demonstrated that even single-cell resolution can be obtained in the brain at least ex vivo. Working in a small animal model of malignant brain tumour, the image quality obtained with different imaging modalities was compared. To generate the brain tumour, 1 × 10(5) C6 glioma cells were loaded with gold nanoparticles and implanted in the right cerebral hemisphere of an adult rat. Raw data were acquired with absorption X-ray CT followed by a local tomography technique based on synchrotron X-ray absorption yielding single-cell resolution. The reconstructed synchrotron X-ray images were compared with images obtained by small animal magnetic resonance imaging. The presence of gold nanoparticles in the tumour tissue was verified in histological sections.