ABSTRACT
AIMS: Cervical cytology biobanking is a feasible concept in cervical pathology and could be an indispensable tool for fundamental and applied molecular biological research. PCR is a powerful molecular technique that can be performed on a variety of cervical sample types including Pap-stained cervical smears. However, since the quality of DNA from such specimens is inferior to that from fresh tissue, the correct processing methods are required. This study evaluates three commercial isolation methods and one digestion procedure for their ability to obtain DNA suitable for PCR from fixed and stained Pap smears. METHODS: The High Pure PCR Template Preparation kit, the NucliSENS easyMAG system, the QIAamp DNA Mini Kit and crude proteinase K digestion were used to obtain DNA for subsequent PCR applications. Amplification of beta-globin was performed to verify the presence and integrity of target DNA. The influence of PCR inhibitors and extent of DNA fragmentation were analysed. RESULTS: All commercial DNA isolation techniques provided DNA suitable for PCR amplification, and DNA isolated from 10-year-old archival smears yielded amplicons up to 400 base pairs. Conversely, crude proteinase K digestion limited the amplicon size to 300 bp and did not consistently yield amplifiable digests, as these were contaminated with PCR-inhibiting factors and debris. CONCLUSION: The study indicates that commercial DNA isolation techniques are suitable for PCR amplification of DNA isolated from archival smears, yielding amplicons up to 400 base pairs. Proteinase K digestion is not suitable to obtain amplifiable DNA from fixed and stained Pap-stained smears.
Subject(s)
Biological Specimen Banks , DNA/isolation & purification , Papanicolaou Test , Vaginal Smears , Female , Humans , Polymerase Chain Reaction/methods , Reagent Kits, Diagnostic , Specimen Handling/methods , Staining and LabelingABSTRACT
AIMS: Despite many improvements, cervical cancer screening is still subject to shortcomings. Diagnostic accuracy may improve by using molecular biological techniques, requiring RNA of superior quality. This study determined the effect of SurePath fixation on RNA integrity to assess the suitability of clinical samples collected in this medium for RNA-based molecular assays. METHODS: RNA isolation was performed on fresh and fixed HeLa cells and exfoliated cervical cells fixed in SurePath. The RNA integrity was evaluated by analysis of ribosomal RNA as an indicator of quality. The effect of SurePath preservation on PCR amplification was evaluated by real-time reverse transcriptase (RT)-PCR. RESULTS: In contrast to unfixed cells, SurePath-fixed cells yielded less and severely degraded RNA, as shown by the absence of ribosomal RNA bands. RNA derived from SurePath-fixed cells showed poor real-time RT-PCR amplification characteristics, as evidenced by the absent correlation between threshold values and log cDNA concentration. CONCLUSIONS: Implementation of molecular biology in a clinical context is on the rise and may alleviate shortcomings in current screening and diagnostics. This study shows that SurePath fixation gives rise to highly fragmented RNA with insufficient quality for further reliable analysis by standard real-time RT-PCR applications. The increasing prominence of molecular screening stresses the importance of this finding, which must be considered in relation to choice of an appropriate liquid-based cytology system.
Subject(s)
RNA, Neoplasm/isolation & purification , Tissue Fixation/methods , Uterine Cervical Neoplasms/diagnosis , Vaginal Smears , Female , HeLa Cells , Humans , Mass Screening/methods , RNA, Neoplasm/analysis , Reverse Transcriptase Polymerase Chain Reaction/methodsABSTRACT
The causal relationship between persistent infection with high-risk HPV and cervical cancer has resulted in the development of HPV DNA detection systems. The widely used MY09/11 consensus PCR targets a 450bp conserved sequence in the HPV L1 gene, and can therefore amplify a broad spectrum of HPV types. However, limitations of these consensus primers are evident, particularly in regard to the variability in detection sensitivity among different HPV types. This study compared MY09/11 PCR with type-specific PCRs in the detection of oncogenic HPV types. The study population comprised 15, 774 patients. Consensus PCR failed to detect 522 (10.9%) HPV infections indicated by type-specific PCRs. A significant correlation between failure of consensus PCR and HPV type was found. HPV types 51, 68 and 45 were missed most frequently. The clinical relevance of the HPV infections missed by MY09/11 PCR was reflected in the fraction of cases with cytological abnormalities and in follow-up, showing 104 (25.4%) CIN2+ cases. The MY09/11 false negativity could be the result of poor sensitivity, mismatch of MY09/11 primers or disruption of L1 target by HPV integration or DNA degradation. Furthermore, MY09/11 PCR lacked specificity for oncogenic HPVs. Diagnostic accuracy of the PCR systems, in terms of sensitivity (MY09/11 PCR: 87.9%; type-specific PCRs: 98.3%) and specificity (MY09/11 PCR: 38.7%; type-specific PCRs: 76.14%), and predictive values for histologically confirmed CIN2+, suggest that type-specific PCRs could be used in a clinical setting as a reliable screening tool.
