TABLE 5

Solid Tissue Storage and Processing

ParameterMolecule(s)TissuesEffect(s)
TemperatureRNA integrity; Protein stability; Posttranslational modificationsBrain• PMI effects on RNA integrity are dependent on storage temperature269
• Protein stability depends on storage temperature234
• Reduced intensity of phosphorylated-τ occurs when samples were stored at RT for longer periods234
• Dry ice freeze step significantly reduces the PMI effect on tryptophan levels55
Heart• Gene expression profile is maintained at RT for up 24 h78
FixationNucleic acids: DNA degradationIntestine• Fixation of solid tissue causes DNA fragmentation and formation of covalent adducts225
• Incomplete fixation produces greater loss of DNA than complete fixation due to autolytic or bacterial degradation, and may interfere with immunohistochemistry225
• Fixation of solid tissue can be successfully done for pathologic examination and protein detection techniques225
• The use of fixative containing mercury or picric acid, results in DNA that cannot be amplified by PCR225
Brain• Long-term formalin fixation at RT results in DNA degradation due to the progressive acidification of formalin to formic acid229
• Periodical renewal of the buffered fixative solution improves DNA preservation229
Intestine• Long-term storage in formalin fixative alters DNA, thereby reducing the identification of point mutations, deletions, or triple expansions229
• Buffered formalin (4%) is somewhat less DNA damaging than unbuffered (10% formalin)225,229
Freeze/thaw stepsNucleic acids: RNA degradationBrain• Tissue thawed to RT and then refrozen is often usable for biochemical studies234
• RNA quality, estimated by the RIN, is reduced by freeze/thaw, in which the tissue pH remains unchanged233
  • RT, room temperature.