Nucleic acid quality and protein expression in sodium alginate FFPE cell blocks prepared under different formalin fixing conditions

Abstract

Objective : We investigated the nucleic acid quality and stability of protein expression in sodium alginate formalin-fixed paraffin-embedded (FFPE) cell blocks (CB) produced under different formalin fixing conditions.

Study Design : Cell lines were fixed in two types of formalin solutions for various lengths of time, and FFPE CBs were prepared using sodium alginate. The DNA integrity number was investigated to assess the DNA quality. The FFPE CBs were then evaluated with regard to stainability.

Results : The DNA quality deteriorated in the samples fixed in both formalin solutions, in a time-dependent manner. The DNA in the cell lines fixed in 10% neutral buffered formalin (NBF) for 3 and 6 hours was of higher quality than that in the cell lines fixed in the same solution for 24 hours or more. In regard to immunostaining for cytokeratin, cell lines fixed in both types of formalin solutions for 3 and 6 hours showed good staining. Furthermore, the Ki-67 labeling index of the cell lines fixed in formalin solution for 24 hours or more was lower than that observed after the cell lines had been fixed for 3 and 6 hours.

Conclusion : Our data show that comparatively higher quality DNA and stable protein expression can be obtained from cytological samples fixed in 10% NBF for 3 to 6 hours in the sodium alginate FFPE CB method.