Biobanks frequently freeze samples to store them for future research use, but maintaining quality of nucleic acids under frozen conditions can be tricky. Following specific quality practices can ensure the preservation of RNA, which is crucial for maintaining samples for clinical studies. Storage conditions, including the temperature and the length of time tissues and purified RNA stay frozen, play a role in RNA preservation. In this post, we’ll explore a recent study by Oliveiri et al. (1), evaluating the optimal freezing temperatures for cryopreservation. Specifically, the study investigated “the quality of RNA purified from head and neck tumor tissues stored at –140°C for distinct time intervals of up to 7 years, and the quality of their respective RNAs stored for 4 years at –80°C when diluted at either 250 ng/ml or 25 ng/ml, with repeated freezing and thawing.”
Storage temperature for tissue samples and the extracted RNA aliquots is critical for preserving RNA integrity, as optimized storage temperatures for tissue samples are required to avoid degradation by endogenous RNases. Additionally, RNA is typically diluted in aqueous solution before cryopreservation. Therefore, optimized storage temperatures for RNA aliquots are also required to avoid degradation by hydrolysis. To assess potential challenges associated with protocols adopted for long-term storage of frozen tissue samples at –140°C and short-term storage at –80°C, this study investigated the quality of total RNA purified from head and neck tumor tissue samples.
The results of the study showed no significant changes in RNA integrity number values in terms of the length of storage at –140°C. RNA aliquots stored at –80°C showed preserved RNA integrity at 250 ng/ml, while significant degradation occurred at 25 ng/ml after 8 months of storage. Researchers found that the temperature of preservation and the concentration of RNA should be “strictly controlled by the biobank staff involved in macromolecule purification.” While the study was limited to evaluation of head and neck tumors within one biobank, their results can serve as a basis for further investigation on the best ways to store RNA in order to maintain integrity.
The full study can be found here.
Olivieri, E.H. et al. (2014) Biobanking practice: RNA storage at low concentration affects integrity. Biopreserv. Biobank. 1, 46.