Background: The validity of molecular studies using RNA extracted from decades-old formalin-fixed and embedded tissue blocks is well documented. Formalin-fixed samples are, however, known to be poor materials for molecular biological applications. The aim of this study was to investigate the effect of formalin as a preservation agent on RNA quality and relevant molecular applications.
Methods: The quantity and quality of RNA from liver tissues are modified by the fixation time. Rat liver tissues were harvested and fixed for 4, 8, 12, and 24 h in 10% buffer formalin, and only 9% of RNA could be extracted from the formalin-fixed tissue stored for 4 h.
Results: Agarose gel electrophoresis did not show the characteristic pattern of RNA with 18S and 28S in all lanes. Based on the results, it is thought that the RNA was damaged owing to one or more of the following reasons: 1) formalin directly degrades RNA, 2) formalin inactivates RNase, and/or 3) formalin destroys the reagent for extraction of RNA. In this study, it was shown by electrophoresis that very little RNA was extracted by Trizol with 1% formalin.
Conclusions: Formalin has direct and indirect ill effects on RNA during the extraction process.