Introduction
The week before last we talked about how pre-analytical variables affect the integrity of human biospecimens, and this week we’ll be following up on this article by discussing the long term storage and retrieval of biospecimens.
The term “storage” comprises of both short and long-term storage of all biospecimens consistent with the study design and planned future use. Depending on the details of their future use, the specimens are either locally or centrally stored. It can also be stored in both locations. The decision will be made depending on the:
Sample size of biospecimens
Complexity of collection
The accrual rate of biospecimens
Processing procedures
Logistics
Cost of storage and retrieval
Quality issues
Biorepository governance factors
If the biospecimens are stored for various uses, biorepositories should have duplicates that are close in proximity to the main laboratory. Samples that are to be stored for more than a year should be stored centrally. Duplicates should also be stored on different power supplies or different locations as insurance against natural disasters or equipment failure. Biorepositories are also recommended to have approximately 10 percent of the total mechanical freezers as empty backup freezers to protect against freezer failure. Different storage conditions may be required based on the downstream analyses. Some of the pre-analytical variables that affect long-term storage include:
The time involved from processing to storage
Duration of storage
Temperature
Facility
Environmental impact (such as moisture, sunlight, dehydration, humidity, oxidation, evaporation, and desiccation)
Freeze-thaw cycles
Some emergencies include: encapsulation of biospecimens in ice after refreezing and microbiological contamination
Destroyed or no labeling
Missing or misplaced aliquots
Since biobank material is valuable and hard to replace, the use of systems such as the laboratory information management system (LIMS) should be utilized as it helps allow traceability, confirm chain of custody, and manage biospecimens to improve data reliability and retrieval. Once the integrity of a biospecimen is compromised, it is no longer valuable and becomes useless. It is therefore important to retrieve only those biospecimens that are required. As previously mentioned, duplicate collections of biospecimens are ideal to prevent the destruction of samples.
Blood Sample
The study of the stability of analytes compared to the fresh sample, taking into account the recovery rates, are vital to determine the effects of long-term storage. After long-term storage, the recovery rates may decrease or increase resulting in increased or attenuated risk ratios. It is recommended that hormone, chemistry, and protein analytes are much more stable and stored at -80⁰C for up to 13 months. However, various studies have shown that there are different patterns of stability based on the analyte, time, and temperature of storage. There has been no systematic influence regarding omics analyses observed in samples collected in citrate, heparin, or ethylenediamine triacetic acid (EDTA) if stored at -80⁰C in liquid nitrogen. Long term storage in room temperature and repeated freeze cycles must be avoided. At room, low, and ultra-low temperatures, the extraction of DNA from whole blood samples using bio stabilization technology yielded samples that are pure and that have integrity. Although live cells are stable at room temperature for as long as 48 hours, it should be cryopreserved or cultured in liquid nitrogen to ensure its viability. The recovery of sufficient DNA or those that are of acceptable quality for microarray studies involves the transfer of thawed buffy coat or EDTA whole blood into RNA preservative. Serum or plasma that will be used for miRNA analysis must be extracted immediately or maintained at -80 in RNA free cryotubes.
Urine Sample Protocol
For urine samples, long term storage at temperatures less than -80⁰C without additives is ideal unless it has been specified for certain downstream analyses. Urine samples have been stored at -22⁰C for 12 to 15 years without the use of preservatives while ensuring the stability and measurement validity. Urine used for metabolome and proteome analyses will go through progressive protein degradation if stored at room temperature. While freeze-thaw cycles have minimal impact on the protein profiles, repeated cycles should ideally be avoided.
Saliva Sample Protocol
The protocols for saliva storage are ultimately dependent on the expected downstream analyses. There seems to be minimal impact of protein profile changes despite freeze-thaw cycles. It is recommended that it is stored at -80⁰C. If the saliva samples were divided into aliquots and frozen immediately at -80⁰C, there does not seem to be any differences in cortisol, C-reactive protein, mRNA, or cytokines.
Extracted DNA Sample protocol
The most common method of storage for DNA is still freezing it at -80⁰C. It should be noted that DNA degradation increases with repeated freeze-thaw cycles, higher storage temperature, dilution, and multiple suspensions. Special technologies allow the minimization of storage space and the reduction of shipping and electrical costs. This can be beneficial especially when cryogenic or mechanical equipment is unavailable. It can also be an alternative method for backup storage. Using this technology, there is no degradation or accelerated aging of DNA at room temperature or higher temperatures (50-70⁰C) throughout the 8-month storage duration.
RNA sample protocol
Some of the pre-analytical storage factors that can affect the quality and quantity of analyte or gene expression include the concentration of RNA, temperature, storage time, and repeated thaws. New technology for the dry storage of RNA at room temperature has been developed. This is a technology comparable to RNA that is cryopreserved for up to a year for downstream analyses such as RNA sequencing and real-time polymerase chain reaction.
References:
Ellervik C, Vaught J. Preanalytical variables affecting the integrity of human biospecimens in biobanking. Clinical Chemistry. 2015; 61(7): 913-934. http://clinchem.aaccjnls.org/content/clinchem/61/7/914.full.pdf
