Ultrasound-accelerated formalin fixation improves the preservation of nucleic acids extraction in histological sections

The aim of the present study was to examine an ultrasound-accelerated fixation technique that reduces the exposure time of the tissue to formaldehyde with respect to the analysis of nucleic acids. We extracted and analysed DNA and RNA from three series of autopsy specimens from five routine cases. Two series were shortly fixed in 4% buffered formalin (15 and 30 min, respectively) whilst being irradiated with high-frequency, high-intensity ultrasound. The last series (control) was routinely fixed in 4% buffered formalin for 24-48 h without irradiation. Although sufficient amounts of DNA of good quality could be extracted and amplified from all three series, the peak heights obtained from conventional fixation were smaller and allele dropout occurred more often, especially for the longer amplicons. RNA yield depended on the fixation procedure, i.e. the shortest fixation time led to the highest RNA yield and quality. No differences were observed with regard to the quality of the histological slides both with conventional and immunohistochemical staining methods. Keeping in mind the increasing need for molecular diagnosis, this fixation technique can be useful to ensure stable quality of nucleic acids in archived autopsy specimens.