Long-term storage of endocrine tissues at - 80°C does not adversely affect RNA quality or overall histomorphology.

Background: Today, no consensus exists regarding how human tissues are best preserved for long-term storage. Very low temperature storage in liquid nitrogen is often advocated as the superlative method for extended periods, but storage in -80 degrees Celsius (-80°C) freezers, while sometimes debated, is a possible alternative. RNA is the most easily degradable component of a biological sample in a molecular biology context and the quality can reliably be measured.

Aim: To investigate to what extent long-term storage of tissues in -80°C affects the RNA quality and overall histomorphology. The tissue storage period represents nearly three decades (1986-2013).

Methods: RNA extraction from 153 tissue samples with different storage periods was performed with the mirVana kit (Invitrogen). RNA integrity was assessed using an Agilent bioanalyzer to obtain RNA integrity numbers (RIN). Further, tissue representative testing using light microscopy was performed by two pathologists to assess tissue composition and morphology.

Results: RIN values were measured in all samples, showing a variability that did not correlate with the storage time of the tissues. Microscopically, all samples displayed acceptable tissue morphology regardless of storage time.

Conclusion: Long-term storage in -80°C does not adversely affect the quality of the RNA extracted from the stored tissues, and the tissue morphology is maintained to a good standard.