Proteinase K treatment improves RNA recovery from thyroid cells fixed with liquid-based cytology solution

• Published in: BMC research notes 2018-11, Vol.11 (1), p.822-822, Article 822
• Main Authors: Jikuzono, Tomoo, Horikawa, Aya, Ishikawa, Tomoko, Hirokawa, Mitsuyoshi, Sugitani, Iwao, Inui, Takashi, Ishibashi, Osamu
• Format: Article
• Language: English
• Subjects: Biopsy; Biopsy, Fine-Needle - methods; Cancer; Cell cycle; Cellular biology; Cost-Benefit Analysis; Cytodiagnosis; Cytological Techniques - methods; Cytology; Diagnosis; Endopeptidase K; Endopeptidase K - chemistry; Fine-needle aspiration biopsy; Fixatives; Gene expression; Humans; Liquid-based cytology; Metastasis; MicroRNAs; Polymerase chain reaction; Proteinase; Reproducibility of Results; Research Note; Reverse transcription; RNA; RNA - isolation & purification; RNA integrity number; snRNA; Thyroid cancer; Thyroid diseases; Thyroid Gland - cytology; Thyroid Neoplasms - genetics; Tumors
• ISSN: 1756-0500; 1756-0500
• DOI: 10.1186/s13104-018-3914-4

Fine-needle aspiration biopsy (FNAB), an important diagnostic tool given its simplicity, safety, and cost-effectiveness, is fast becoming a popular procedure in the diagnosis of thyroid diseases. Generally, cells isolated from biopsies are transferred directly to microscope slides to prepare smears for cytopathological examination; however, the technical difficulties of this procedure often cause poor reproducibility, which limits the accuracy of diagnostic results. Liquid-based cytology (LBC), in which isolated cells are collected in a fixative solution, is advantageous in that it facilitates the preparation of homogenous cytological specimens. However, LBC has not been applied to molecular diagnoses, such as RNA expression-based diagnosis, mainly because of difficulties in cell recovery and RNA isolation. This study was aimed to improve RNA extraction from papillary cancer-derived K1 cells and thyroid FNAB specimens suspended in LBC solutions. K1 cells suspended in CytoRich-Red and CytoRich-Blue, fixatives for LBC, were efficiently recovered by trapping to glass-fiber filters. Importantly, subsequent Proteinase K treatment was essential for efficient RNA extraction from the fixed cells. This finding was also applicable to RNA extraction from CytoRich-Red-fixed thyroid FNAB specimens processed in the same way. Consistently, U6 small nuclear RNA was detected in these RNA samples by reverse transcription-polymerase chain reaction.