Gaëlle Boulet

Importance of Suitable Reference Gene Selection for Quantitative Real-Time PCR: Special Reference to Mouse Myocardial Infarction Studies

Background Quantitative real-time PCR (qPCR) is a widely used technique for gene expression analysis. Its reliability is highly dependent upon selection of the appropriate reference genes for accurate gene expression normalization. In this study, we investigated the expression stability of 10 commonly used reference genes in a mouse myocardial infarction model. Methods & Results The expression stability of the 10 reference genes (Actb, B2m, Eef1a1, Gapdh, Hprt, Polr2a, Ppia, Rpl13a, Tbp, Tpt1) was analyzed using the geNorm software. Overall, the combination of Hprt, Rpl13a and Tpt1 was the most stable reference gene set in our experiments. Gapdh, Polr2a and Actb consistently showed the highest gene expression variability and the expression levels of Gapdh, Polr2a, Actb, B2m and Eef1a1 were found to be selectively up- or downregulated after myocardial infarction. We normalized the expression of Nppb and Vcam1, using different reference gene strategies and demonstrated that their induction after myocardial infarction was most clearly revealed with the optimal reference gene combination. However, the use of suboptimal reference gene combinations resulted in detrimental effects on gene expression levels and variability with a gradual loss of the expression differences and a significant reduction in statistical power. Conclusions Hprt, Rpl13a and Tpt1 are a set of stably expressed reference genes for accurate gene expression normalization in myocardial infarction studies in mice. We found that Gapdh, Polr2a and Actb display high expression variability in mouse myocardial infarction tissues and that loss of statistical power and increase in sample size are the evident consequences of choosing suboptimal combinations of reference genes. We furthermore caution against the use of Gapdh, Polr2a, Actb, B2m and Eef1a1 for gene expression normalization in myocardial infarction studies because of selective up- or downregulation after myocardial infarction, which could potentially lead to biased study outcomes.

High-throughput detection, genotyping and quantification of the human papillomavirus using real-time PCR.

Abstract Background: The establishment of the causal relationship between high-risk human papillomavirus (HR-HPV) infection and cervical cancer and its precursors has resulted in the development of HPV DNA detection systems. Currently, real-time PCR assays for the detection of HPV, such as the RealTime High Risk (HR) HPV assay (Abbott) and the cobas® 4800 HPV Test (Roche Molecular Diagnostics) are commercially available. However, none of them enables the detection and typing of all HR-HPV types in a clinical high-throughput setting. This paper describes the laboratory workflow and the validation of a type-specific real-time quantitative PCR (qPCR) assay for high-throughput HPV detection, genotyping and quantification. This assay is routinely applied in a liquid-based cytology screening setting (700 samples in 24 h) and was used in many epidemiological and clinical studies. Methods: The TaqMan-based qPCR assay enables the detection of 17 HPV genotypes and β-globin in seven multiplex reactions. These HPV types include all 12 high-risk types (HPV16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59), three probably high-risk types (HPV53, 66 and 68), one low-risk type (HPV6) and one undetermined risk type (HPV67). Results: An analytical sensitivity of ≤100 copies was obtained for all the HPV types. The analytical specificity of each primer pair was 100% and an intra- and inter-run variability of <6.4% was observed. Conclusions: The type-specific real-time PCR approach enables detection of 17 HPV types, identification of the HPV type and determination of the viral load in a single sensitive assay suitable for high-throughput screening.

Human Papillomavirus 16 Load and E2/E6 Ratio in HPV16-Positive Women: Biomarkers for Cervical Intraepithelial Neoplasia ≥2 in a Liquid-Based Cytology Setting?

This retrospective case-control study assessed human papillomavirus 16 (HPV16) viral load and E2/E6 ratio as risk markers for cervical intraepithelial neoplasia (CIN) ≥2 lesions in HPV16-positive women in a routine liquid-based cytology setting. Triplex quantitative PCR for HPV16 E6, E2, and β-globin was done to determine the HPV16 load and the E2/E6 ratio, as a surrogate marker for integration, for women with a negative histologic endpoint (200 controls: 83 normal histology and 117 CIN1) and women with a ≥CIN2 endpoint (180 cases: 41 CIN2, 122 CIN3, and 17 invasive carcinoma). Our analysis showed a significantly higher HPV16 load in the case group, which was completely attributable to the high viral load of samples with invasive carcinoma as histologic endpoint. There was no significant difference in viral load between the other histologic groups. The E2/E6 ratio proved to be lower for the cases. However, the E2/E6 ratio indicated the presence of HPV integration in a considerable amount of control samples (44.3%), which suggests that HPV integration occurs early in the development of cancer and undermines the clinical value of viral integration. Overall, the intrinsic heterogeneous nature of the cervical cytology samples caused a substantial overlap of the HPV16 load and the E2/E6 ratio between controls and cases, which precludes the determination of cutoff values for risk prediction and hampers the clinical applicability in a cervical screening setting. (Cancer Epidemiol Biomarkers Prev 2009;18(11):2992–9)

The TRPM6/EGF Pathway Is Downregulated in a Rat Model of Cisplatin Nephrotoxicity

Cisplatin-induced hypomagnesemia is described in humans and rats, but the underlying mechanisms are still unclear. Recent studies have shown that epidermal growth factor (EGF) stimulates Mg2+ re-absorption in the distal convoluted tubule via the Mg2+ channel TRPM6. This study investigates the role of TRPM Mg2+ channels, claudines, and EGF in the Mg2+ homeostasis in a rat model of cisplatin-induced nephrotoxicity. Wistar rats were given 2.5 mg/kg cisplatin per week for 3 weeks and were euthanized 4 or 9 weeks after the first administration. The cisplatin treatment significantly increased the fractional excretion of Mg2+. Real-time RT-PCR and/or Western blots were performed to assess the renal expression TRPM6, TRPM7, claudin-16, claudin-19, EGF, EGF receptor (EGFR) and EGFR-pathway components. The renal mRNA expression of TRPM6 and EGF showed a significant decrease after cisplatin treatment, while the TRPM7, claudin-16 and EGFR expressions remained stable. The claudin-19 mRNA expression was significantly upregulated after cisplatin treatment. Western blotting confirmed the mRNA expression data for the claudins, but an showed upregulation of EGFR only at week 9. The role of the EGFR pathway, involving Pi3-AKT-Rac1, in cisplatin-induced nephropathy, could not be substantiated in further detail. This study shows that cisplatin treatment results in EGF and TRPM6 downregulation in the rat kidney, causing renal Mg2+ loss. Our results are in line with the hypothesis that EGF influences the renal expression or activation of TRPM6 and plays a significant role in Mg2+ loss in medication-induced nephropathy.

Nucleic Acid Sequence-Based Amplification Assay for Human Papillomavirus mRNA Detection and Typing: Evidence for DNA Amplification

ABSTRACT Human papillomavirus (HPV) E6/E7 mRNA has been proposed as a more specific marker for cervical dysplasia and cancer than HPV DNA. This study evaluated the RNA specificity of nucleic acid sequence-based amplification (NASBA)-based HPV detection using HPV DNA plasmids (HPV type 16 [HPV16], HPV18, HPV31, HPV33, and HPV45) and nucleic acid extracts of several cell lines, which were systematically subjected to enzymatic treatments with DNase and RNase. HPV plasmid dilutions (106 to 100 copies/μl) and nucleic acid extracts (total DNA, RNA-free DNA, total RNA, and DNA-free RNA) of unfixed and fixed (PreServCyt and SurePath) HaCaT, HeLa, and CaSki cells were tested with the NucliSENS EasyQ HPV test. The RNA-free DNA extracts of HeLa and CaSki cells could be amplified by HPV18 and -16 NASBA, respectively. Fixation of the cells did not influence NASBA. All HPV plasmids could be detected with NASBA. Based on the plasmid dilution series, a lower detection limit of 5 × 103 HPV DNA copies could be determined. Our study identified viral double-stranded DNA as a possible target for NASBA-based HPV detection. The differences in diagnostic accuracy between the NASBA-based tests and conventional HPV DNA detection assays seem to be attributable not to the more specific amplification of viral mRNA but to the limited type range and the lower analytical sensitivity for HPV DNA.

Longitudinal quantification of radical bursts during pulmonary ischaemia and reperfusion

OBJECTIVESnPulmonary ischaemia-reperfusion injury (IRI) is associated with several life-threatening pulmonary disorders, and may severely compromise the outcome of lung transplantation. Highly reactive molecules such as superoxide, nitric oxide (NO) and peroxynitrite (ONOO(-)) are presumed to contribute to IRI pathogenesis, but this assumption is based on indirect measurements. We use electron spin resonance (ESR) to directly quantify free radical formation after pulmonary ischaemia and reperfusion.nnnMETHODSnFive groups of 10 Swiss mice were subjected to left pulmonary hilum clamping for 1 h of ischaemia followed by 0, 1, 4 and 24 h of reperfusion or to sham thoracotomy alone as control procedure. In five mice per group, ESR was used to measure iron-diethyldithio-carbamate trihydrate-trapped NO in the lung. In the other group of 5, reactive oxygen species generation in the lung and in blood was quantified with ESR by detection of ascorbyl radical and CMH spin probe, respectively. Pulmonary ONOO(-) was monitored with nitrotyrosine Western blotting.nnnRESULTSnAfter 1 h of reperfusion, a pulmonary NO peak (14.69 ± 0.91 × 10(4) Arbitrary Units (A.U.). vs 1.84 ± 0.75 × 10(4) A.U. in sham; P < 0.001) coincided with a significant increase in nitrosated proteins (0.105 ± 0.015 A.U.) compared with sham (0.047 ± 0.006 A.U.); P < 0.005). Peripheral blood showed a significant free radical burst after 1 h of ischaemia (11 774 ± 728 A.U. vs 6660 ± 833 A.U. in sham; P < 0.001).nnnCONCLUSIONSnLongitudinal quantification of free radicals during IRI reveals the occurrence of two major radical bursts. The radical peak in peripheral blood after ischaemia may be related to systemic hypoxia. After 1 h of reperfusion, the lung tissue shows a significant increase of superoxide, NO and their reaction products, which are probably involved in IRI pathogenesis.

Diversity of HPV types in cancerous and pre‐cancerous penile lesions of South African men: Implications for future HPV vaccination strategies

This study reports the detection of HPV types from cancerous and pre‐cancerous penile lesions that were diagnosed histologically. Sixty‐six (22 pre‐cancerous and 44 cancerous lesions) tissue biopsies, received between 2004 and 2011 by the Anatomical Pathology Department at Dr. George Mukhari Hospital were selected for this study. Total DNA was extracted and genotyped using type specific real‐time quantitative polymerase chain reaction (qPCR) for 18 HPV types. Of 66 samples, only 51 were included in the analysis. Overall, HPV 11 (50.9%) and HPV 16 (49.1%) showed almost similar incidence in the study patients. In pre‐cancerous lesions, HPV 11 was more frequent (80.0%), followed by HPV 31 and HPV 16 at 25.0% each and other HPV types included 35 (15.0%), 59 (15.0%), 53 (10.0%), 33 (10.0%), 18 (5.0%), 51 (5.0%), 52 (5.0%), 56 (5.0%), and 67 (5.0%). For cancerous lesions, HPV 16 was the most detected (62.9%), followed by HPV 11 (34.3%), and other HPV types included 18 (11.4%), 33 (5.7%), 39 (5.7%), 45 (5.7%), 66 (5.7%), 52 (2.9%), 58 (2.9%), 6 (2.9%), and 67 (2.9%). Several lesions demonstrated multiple HPV infections, ranging from two to six different types in one lesion. The study showed high diversity of HPV types in cancerous and pre‐cancerous lesions of South African males with the most frequent being HPV types 11 and 16. The data suggest that boys could directly benefit from vaccination as they are exposed to variety of HPV types as early as 10 years of age in Africa. J. Med. Virol. 86:257–265, 2014.

A flow cytometric approach to quantify biofilms.

Since biofilms are important in many clinical, industrial, and environmental settings, reliable methods to quantify these sessile microbial populations are crucial. Most of the currently available techniques do not allow the enumeration of the viable cell fraction within the biofilm and are often time consuming. This paper proposes flow cytometry (FCM) using the single-stain viability dye TO-PRO®-3 iodide as a fast and precise alternative. Mature biofilms of Candida albicans and Escherichia coli were used to optimize biofilm removal and dissociation, as a single-cell suspension is needed for accurate FCM enumeration. To assess the feasibility of FCM quantification of biofilms, E. coli and C. albicans biofilms were analyzed using FCM and crystal violet staining at different time points. A combination of scraping and rinsing proved to be the most efficient technique for biofilm removal. Sonicating for 10xa0min eliminated the remaining aggregates, resulting in a single-cell suspension. Repeated FCM measurements of biofilm samples revealed a good intraday precision of approximately 5xa0%. FCM quantification and the crystal violet assay yielded similar biofilm growth curves for both microorganisms, confirming the applicability of our technique. These results show that FCM using TO-PRO®-3 iodide as a single-stain viability dye is a valid fast alternative for the quantification of viable cells in a biofilm.

Quantification of Candida albicans by flow cytometry using TO-PRO®-3 iodide as a single-stain viability dye

This study investigated a flow cytometric, single-stain approach to quantify Candida albicans as an alternative for the standard viable plate count. TO-PRO(®)-3 iodide allows an excellent distinction between viable and dead cells. Both quantification methods show a high degree of correlation.

Comparison of viable plate count, turbidity measurement and real‐time PCR for quantification of Porphyromonas gingivalis

The viable plate count (VPC) is considered as the reference method for bacterial enumeration in periodontal microbiology but shows some important limitations for anaerobic bacteria. As anaerobes such as Porphyromonas gingivalis are difficult to culture, VPC becomes time‐consuming and less sensitive. Hence, efficient normalization of experimental data to bacterial cell count requires alternative rapid and reliable quantification methods. This study compared the performance of VPC with that of turbidity measurement and real‐time PCR (qPCR) in an experimental context using highly concentrated bacterial suspensions. Our TaqMan‐based qPCR assay for P. gingivalis 16S rRNA proved to be sensitive and specific. Turbidity measurements offer a fast method to assess P. gingivalis growth, but suffer from high variability and a limited dynamic range. VPC was very time‐consuming and less repeatable than qPCR. Our study concludes that qPCR provides the most rapid and precise approach for P. gingivalis quantification. Although our data were gathered in a specific research context, we believe that our conclusions on the inferior performance of VPC and turbidity measurements in comparison to qPCR can be extended to other research and clinical settings and even to other difficult‐to‐culture micro‐organisms.