Abstract 862: Effects of fixation and antigen retrieval on the RNA integrity number

Abstract

Abstract The effect of fixation and antigen retrieval (AR) on RNA as measured by the RNA integrity number (RIN) has not been adequately explored. RIN is an index (pseudo-measure) used to measure stability of mRNA; however, RIN is an actual measure of the stability of ribosomal RNA and not an actual measure of mRNA. RIN values range from 1 for highly degraded to 10 for intact RNA. Most surgical specimens are fixed in 10% neutral buffered formalin (3.7% formaldehyde) because of its ability to preserve morphological detail and prevent degradation. However, formaldehyde fixation causes changes in proteins through formation of crosslinks, which masks the immunorecognition of some antigens. In immunohistochemical evaluations, antigen retrieval (AR) approaches e.g., boiling of tissue sections under pressure are used to reverse these effects of fixation. It is believed that fresh or snap frozen specimens serve as most the suitable source of intact mRNA, DNA and other macromolecules for molecular analysis. However, more recent studies using rt-Q PCR indicate that RNA and DNA can be measured in formalin fixed paraffin embedded (FFPE) tissue samples which usually have RIN values of 3 or less. The question arises as to what is the usefulness of RIN in FFPE tissues. This study used three cancer cell lines DU145 (prostate), MDA231 (breast) and S2VP10 (pancreas) to examine the relationship between 10% NBF fixation, RIN and AR. The first objective was to analyze whether the duration of fixation of cells in 10% NBF correlated with decreases in RIN. Three fixation times i.e., 5 minutes, 20 minutes and 120 minutes were studied. The second objective was to investigate the effects of two AR approaches on RIN. Two AR conditions at pH 6 and pH 9 were used on the same cell lines and fixation times. For each cell line and treatment i.e., no fixation, or fixation at different times (with and without AR), RNA was extracted and RIN analyzed using the Agilent 2100 Bioanalyzer. RIN values obtained from the Agilent 2100 Bioanalyzer were statistically analyzed. T-tests show that the large decreases to about 3 in RIN values after fixation (5, 20 and 120 minutes) are statistically significant for all cell lines. All p-values are less than 0.0001. This study confirms that fixation of cells in 10% NBF lowers RIN to about 3 the value observed for fixed tissues. RIN did not vary significantly with time of fixation in 10% NBF and RIN did not change from the fixed values after either condition of AR. Thus RIN is not a useful measure of RNA stability in 10% NBF fixed tissue. Citation Format: Dennis Otali, Maitlyn Mullen, He Qinghua, Denise Oelschlager, William E. Grizzle. Effects of fixation and antigen retrieval on the RNA integrity number [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 862.