Tannic Acid Solution: A Better Fixative Solution Than Formalin for Elastin and Collagen-Toxic and Morphological Assessment.

Formaldehyde is commonly used worldwide, even though it is classified as carcinogenic to humans by the International Agency for Research on Cancer. This has motivated intensive investigations of formaldehyde substitutes, and recently, some alternative solutions were found, which can potentially replace it. Previous research showed that tannic acid (TA) in glutaraldehyde solution has the ability to stabilize elastin and collagen. This provided a basis for the development of a new alcoholic fixative solution, particularly aimed at extracellular matrix components, with TA as a main component. Heart, brain, and intestinal samples were fixed by immersion in 10% regular formalin solution (RFS), 70% ethanol solution (ES), and tannic acid ethanolic solution (TAES). Next, tissue fragments were prepared for routine histology procedures. The toxicity of TA was analyzed using in silico tests for mutagenicity, as well as for cutaneous and respiratory toxicity. Analyses of photomicrographs demonstrated that all fixative solutions have the ability to preserve the fragments. The quantitative analyses showed that capability of TAES to preserve and stabilize elastin and collagen is superior to that of RFS and ES. We demonstrated that TA is not mutagenic, and it is less toxic for skin and respiratory tract. We therefore conclude that TAES can potentially represent a powerful and feasible alternative solution for fixing extracellular matrix of microscopic examination samples. Anat Rec, 301:1544-1550, 2018. (c) 2018 Wiley Periodicals, Inc.