Frozen Tissues

Frozen tissue is a valuable resource for research and diagnostics. Snap freezing helps maintain cellular structure and the integrity of biomolecules, such as DNA, RNA, and proteins, allowing for accurate analysis of disease mechanisms at both histological and molecular levels. Cryostat sections of frozen tissue are used for histological quality control.

Frozen Tissue Storage

Frozen tissue samples are carefully stored by biobanks to preserve their biological integrity for long-term research use. Typically, these tissues are stored at ultra-low temperatures, often in liquid nitrogen tanks (at around -196°C) or in specialized freezers maintained at -80°C. This extreme cold halts cellular processes, preventing degradation and maintaining the tissue’s molecular structure, DNA, RNA, and proteins.

The picture opposite shows a scientist accessing samples from a -80°C freezer.

 

Snap frozen tissue samples are stored in freezers

Notes On Tissue Procurement

A practising pathologist should supervise tissue procurement to safeguard diagnostic requirements. Solid tissues may be very heterogeneous in composition. For example, tumour samples may include a variable mix of different components.

Read more on tissue procurement

  • These components include neoplastic cells, normal cells, necrosis and fibrosis. So, one must examine a histological section from each aliquot under the microscope. In the case of frozen samples, a cryostat section must be cut.

  • The person collecting must keep specimens on wet ice until frozen or fixed.

  • The technologist must also prevent cross-contamination, dehydration and desiccation of samples.

  • Consider all human specimens as potential biohazards (section F6.1).

Snap Freezing Tissues

Snap freezing human tissue is a method used to preserve biological samples quickly by cooling them rapidly, usually in liquid nitrogen or a dry ice-isopropanol bath. This prevents the formation of ice crystals, which can damage cellular structures and degrade important biomolecules like RNA, DNA, and proteins.

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Key points of snap freezing:

  1. Rapid Cooling: The tissue is frozen within seconds to minimize any biochemical changes or degradation.
  2. Minimized Ice Crystal Formation: By freezing quickly, the formation of large ice crystals is reduced, preventing damage to the tissue’s microstructure.
  3. Preservation of Biomolecules: Snap freezing helps to preserve the tissue’s genetic material and proteins, making it suitable for later analysis.
  4. Common Freezing Media: Liquid nitrogen (at -196°C) or a mixture of dry ice and isopropanol (around -78.5°C) are often used for this process.

SOPs

Preparing Cryostat Sections

Cutting cryostat sections involves slicing frozen tissue samples into thin layers, typically using a cryostat, for use in various research and diagnostic applications. These sections are invaluable because they allow for the preservation of cellular and molecular integrity. The ability to maintain tissue morphology and biomolecular content in a near-native state makes cryostat sections essential for studying disease processes, identifying biomarkers, and validating therapeutic targets.

The video opposite from Damien Harkin of the Queensland University of Technology (QUT), shows the preparation of frozen (or cryostat) sections.

References On Snap Freezing And Storage Of Frozen Tissue Blocks

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