Biobanks store many different types of biospecimens, ranging from cells and small tissue samples right through to whole organs, whole limbs or even whole bodies. Cells and small biospecimens can be flash frozen in cryoprotectant solutions and stored in liquid nitrogen to preserve their structure and function. However, it is not currently possible to flash freeze large biospecimens such as whole limbs.
The Old Method of Preserving Large Biospecimens
Whole limbs and organs are valuable biospecimens because they allow researchers to study changes in tissue structure and architecture during disease. This information cannot be gathered by studying cells and smaller biospecimens. Often researchers and clinical pathologists preserve larger biospecimens by fixing them in 10% formalin or other fixatives. Fixatives maintain tissue structure within biological samples by cross-linking proteins. This method of preserving samples is relatively cheap and easy to perform, and fixed biological samples can be stored at room temperature.
The main problem with this process is that it damages RNA and DNA. Therefore, it is difficult to isolate high-quality RNA and DNA from fixed biological samples. Formalin and formaldehyde are also toxic so any researchers using samples fixed with these chemicals must use appropriate protective equipment and take care not to breath in fumes or splash the chemicals onto their skin or eyes.
A New Method to Preserve Large Biospecimens
Researchers from Central South University in China recently published a new method to preserve limbs amputated for surgical reasons (1). They developed a new embalming solution and tested whether it could preserve intact limbs and smaller biospecimens dissected from limb tissue.
Humans have used embalming solutions to preserve bodies for over 5000 years (2). Today, embalming is commonly used to prepare a body for viewing before a funeral or memorial service. It is also possible to preserve biospecimens for research by embalming, however, embalming solutions can damage DNA in samples (3). Many embalming solutions contain the toxic fixative formaldehyde. Moreover, molecules from biospecimens can leach into embalming fluid. This means that embalmed tissues may not have their normal levels of calcium and other chemical elements. Therefore, researchers cannot currently use embalmed tissues to study these molecules. This may be possible in the future if embalming solutions can be designed to minimize leaching.
Embalming Can Preserve Structure in Whole Limbs
Dr JuFang Huang and his research team at Central South University designed and patented a novel embalming fluid and used this fluid to preserve limb samples for up to 24 months. They embedded some of the preserved tissue in paraffin blocks and stained these sections with hematoxylin and eosin (H&E) to look at how the embalming affected tissue structure. The researchers found that embalming preserved the macrostructure of skin, muscle, arteries and nerves within biospecimens.
The researchers then used transmission electron microscopy to look closer at the preserved biospecimens and assess cellular architecture. They found normal ultrastructure in embalmed whole limbs. In contrast, they found degradation of nuclei, mitochondria and muscle fibers in smaller dissected samples.
Chemical Elements Leach into Embalming Solutions
Dr Huang’s team also used plasma atomic emission spectrometry to analyze whether macroelements and trace elements leached from the preserved biospecimens into the embalming solution. Results showed minimal leaching of calcium and sodium, but significant leaching of other elements including magnesium, potassium and zinc. This leaching increased over time and was highest after 24 months of embalming.
Conclusions
This study shows that embalming can preserve the structure of large biospecimens such as whole limbs for up to 24 months. However, it did not look at whether DNA, RNA or proteins could be extracted from embalmed samples and used in molecular studies. Also, significant amounts of metabolically important elements such as potassium leached from biospecimens into the embalming solution.
Overall the data from this study shows that embalming could offer an alternative to formalin fixation, but it does not show whether embalmed tissues can be used for any assays except histology.
References
1. Luo et al. A New Method of Biostorage and Biopreservation for Human Amputated Extremities. Biopreserv Biobank. 2018
2. Brenner. Human body preservation – old and new techniques. J. Anatomy. 2014
3. Gielda and Rigg. Extraction of amplifiable DNA from embalmbed human cadaver tissue. BMC Res Notes. 2017.
