Abstract
Technological and methodological advances in molecular biology have enabled the obtainment of DNA from paraffin embedded tissue, thus allowing the use of extensive pathological archive sources and samples of uncommon diseases in retrospective studies. The aim of this work was to carry out a brief review of some factors inherent in the quality of product from paraffin embedded material. The processes involved in the pre-fixation, fixation and post-fixation phases have several aspects that may result in unsatisfactory final products. In the pre-fixation phase, biochemical changes influence the preservation of macromolecules. The molecular changes caused by fixation, an attempt to prevent cell autolysis, may be a limiting factor at the time of DNA extraction. The quality of DNA obtained in the first two phases is regarded important for post-fixation procedures (DNA extraction and purification). In the literature there are several protocols whose steps can be modified to obtain DNA from paraffin embedded material. Therefore, the understanding of reactions at each stage is important in order to solve or minimize problems that interfere in the quality of DNA macromolecules.
Highlights
Technological and methodological advances in molecular biology have enabled the obtainment of DNA from paraffin embedded tissue, allowing the use of extensive pathological archive sources and samples of uncommon diseases in retrospective studies
The aim of this work was to carry out a brief review of some factors inherent in the quality of product from paraffin embedded material
The processes involved in the pre-fixation, fixation and post-fixation phases have several aspects that may result in unsatisfactory final products
Summary
As blocotecas dos setores de patologia, primeiro banco estruturado de tecidos patológicos estabelecido em grande escala, foram e continuarão sendo valiosas fontes de pesquisa de doenças(23, 46). Os avanços tecnológicos e metodológicos dos últimos tempos ampliaram a utilização dos blocos de parafina; além do uso em estudos histomorfológicos, histoquímicos e imuno-histoquímicos, passaram a ser também fonte de material para a pesquisa com métodos da biologia molecular(5, 11, 38). Esses fatores fazem que ocorra grande interesse nos estudos das bases genéticas das doenças, e os acervos de materiais biológicos que foram enviados para exame nas rotinas hospitalares permanecem como fonte de material para diferentes estudos genéticos(34). As amostras dos blocos de parafina podem ser fontes de estudos para a epidemiologia molecular, de caráter retrospectivo, de instabilidades em regiões de microssatélites, de detecção ou diferenciação de microrganismos patogênicos(3, 31, 34, 39). A análise molecular de ácidos nucleicos tem tradicionalmente exigido DNA genômico obtido a partir de tecidos frescos ou congelados; as macromoléculas encontram-se bem preservadas quando extraídas desse tipo de material(32, 44). Grau de fragmentação do DNA, efeito do fixador, tempo de fixação e temperatura utilizada no processamento do material são exemplos de fatores que podem influenciar na amplificação dessas amostras de DNA(20-22)
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