Biobanking practice: RNA storage at low concentration affects integrity.

A critical issue in defining protocols for biobanking practices is the preservation of total RNA for assessing the whole transcriptome and ensuring that it can be utilized in clinically oriented studies. Storage conditions, such as temperature and the length of time that tissues and purified RNA stay frozen, may directly impact RNA preservation. In this study, we evaluated a) the quality of RNA (as measured by RNA Integrity Number) purified from head and neck tumor tissues stored at -140°C for distinct time intervals of up to 7 years, and b) the quality of their respective RNAs stored for 4 years at -80°C when diluted at either 250 ng/μL or 25 ng/μL, with repeated freezing and thawing. Additionally, we generated a profile of the RNA collection of human tumors from different body sites stored at the AC Camargo Biobank. Our results showed no significant change in RIN values according to length of storage at -140°C. With respect to RNA aliquots stored at -80°C, RNA integrity at 250 ng/μL was preserved, while statistically significant degradation was observed at 25 ng/μL after only 8 months of storage. The RNA collection from most of the human tumors stored at the AC Camargo Biobank exhibited high quality, with average RIN around seven. However, ovary and stomach samples had the greatest RNA degradation. Taken together, the results show that both the temperature of preservation and the concentration of RNA should be strictly controlled by the biobank staff involved in macromolecule purification. Moreover, the RNAs from our biobank can be useful for the most demanding methods of gene expression analysis by virtue of adherence to optimal standard operating procedures for both tissue and macromolecule laboratories.