HOPE fixation: a novel fixing method and paraffin-embedding technique for human soft tissues.

We have developed a novel method for tissue fixation, including subsequent paraffin-embedding and sectioning, that allows the complete pathological analysis of all types of human soft tissues. Furthermore, it maintains additional positive features relevant to immunohistochemistry and molecular pathology. The so-called HOPE-technique (Hepes-Glutamic acid buffer mediated Organic solvent Protection Effect) comprises a protection-solution with an organic buffer, acetone as the only dehydrating agent, and pure paraffin of 52-54 degrees C melting temperature. Although the exact mechanism of protection has still to be elucidated, it seems rather unlikely that chemical bindings occur during the whole process of fixation, which is described and compared with the standard formalin-paraffin technique. Essentially, HOPE-fixed sections show formalin-like morphology. However, the sections are somewhat difficult to handle because of their fragility. This is due to the absence of any type of protein cross-linking and the dynamic processes of immersion and outflow of the HOPE protection solution. HOPE-fixed sections provide an excellent preservation of proteins and antigenic structures for differential analysis by immunohistochemical and/or enzyme histochemical techniques. However, their most remarkable feature is the extremely low degradation of nucleic acids (DNA and RNA) combined with good results obtained by in situ hybridization techniques. In conclusion, HOPE fixation may become a valuable additional tool in modern pathology.