Evaluation of RNA isolation methods for microRNA quantification in a range of clinical biofluids

Background Extracellular microRNAs (miRNAs), released from cells into biofluids, have emerged as promising biomarkers for diagnostic and prognostic purposes. Several RNA isolation methods are available for the analysis of these cell-free miRNAs by RT-qPCR. Not all methods, however, are equally suitable for different biofluids. Here, we extracted total RNA from four very diverse biofluids: serum, urine, bile, and graft preservation fluid (perfusate). Four different protocols were used: a phenol-chloroform extraction and alcohol precipitation in combination with a precipitation carrier (QP) and three different column-based isolation methods, one with phenol-chloroform extraction (RN) and two without (NG and CU). For this range of clinical biofluid samples, we evaluated the potential of these different RNA isolation methods assessing recovery efficiency and the co-purification of RT-qPCR inhibiting compounds. Results Differences were observed between each of the RNA isolation methods in the recovery of cel-miR-39, a synthetic miRNA spiked in during the workup procedure, and for endogenous miRNAs. Co-purification of heparin, a known RT-qPCR inhibitor, was assessed using heparinase I during cDNA synthesis. RT-qPCR detection of synthetic miRNAs cel-miR-39, spiked in during RNA workup, cel-miR-54, spiked in during cDNA synthesis, and endogenous miRNAs was strongly improved in the presence of heparinase I for some, but not all, isolation methods. Other, co-isolated RT-qPCR inhibitors were not identified, except for biliverdin, which co-isolated from some bile samples with one of the methods. In addition, we observed that serum and urine contain compounds that enhance the binding of heparin to certain solid-phase columns. Conclusions For reliable measurements of miRNA-based biomarkers in biofluids, optimization of RNA isolation procedures is recommended as methods can differ in miRNA detection and in co-purification of RT-qPCR inhibitory compounds. Heparinase I treatment confirmed that heparin appeared to be the major RT-qPCR inhibiting compound, but also biliverdin, co-isolated from bile, could interfere with detection.

Quantification of purified endogenous miRNAs with high sensitivity and specificity

MicroRNAs (miRNAs) are short (19–24 nt) non-coding RNAs that suppress the expression of protein coding genes at the post-transcriptional level. Differential expression profiles of miRNAs across a range of diseases have emerged as powerful biomarkers, making a reliable yet rapid profiling technique for miRNAs potentially essential in clinics. Here, we report an amplification-free multi-color single-molecule imaging technique that can profile purified endogenous miRNAs with high sensitivity, specificity, and reliability. Compared to previously reported techniques, our technique can discriminate single base mismatches and single-nucleotide 3′-tailing with low false positive rates regardless of their positions on miRNA. By preloading probes in Thermus thermophilus Argonaute (TtAgo), miRNAs detection speed is accelerated by more than 20 times. Finally, by utilizing the well-conserved linearity between single-molecule spot numbers and the target miRNA concentrations, the absolute average copy numbers of endogenous miRNA species in a single cell can be estimated. Thus our technique, Ago-FISH (Argonaute-based Fluorescence In Situ Hybridization), provides a reliable way to accurately profile various endogenous miRNAs on a single miRNA sensing chip.

Evaluation of RNA isolation methods for microRNA quantification in a range of clinical biofluids.

BACKGROUND Extracellular microRNAs (miRNAs), released from cells into biofluids, have emerged as promising biomarkers for diagnostic and prognostic purposes. For the analysis of these cell-free miRNAs in various biofluids by RT-qPCR, several RNA isolation methods are available. However, not all methods are equally suitable for different biofluids. The aim of this study is to evaluate the potential of different RNA isolation methods in a range of clinical biofluid samples.METHODS Total RNA was isolated from serum, urine, bile, and graft preservation fluid (perfusate) using four different protocols: phenol-chloroform extraction in combination with a precipitation carrier, and three different column-based isolation methods. Co-purification of heparin, a known RT-qPCR inhibitor, was assessed using heparinase I during cDNA synthesis. Synthetic miRNAs, spiked-in during RNA workup (cel-miR-39) or during cDNA synthesis (cel-miR-54), and endogenous miRNAs were quantified using RT-qPCR.RESULTS Recovery of cel-miR-39 significantly differed between methods with miRNeasy columns providing the best overall recovery in the four biofluids tested, as was also observed for endogenous miRNAs. Contamination of RNA with heparin differed between sample type and isolation method, and could be counteracted using heparinase I. Other co-isolated RT-qPCR inhibitors were not identified, except for biliverdin which co-isolated from some bile samples with one of the methods.CONCLUSIONS For reliable measurements of miRNA-based biomarkers in biofluids, optimization of RNA isolation procedures is recommended as methods can differ in miRNA detection and co-purification of RT-qPCR inhibitory compounds. Heparinase I treatment confirmed that heparin appeared to be the major RT-qPCR-inhibiting compound but also biliverdin, co-isolated from bile, could interfere with detection.

PSVII-13 Effects of corn supplementation on muscle microRNA profiles within horses

The objective of this study was to determine the effect of corn supplementation on muscle microRNA (miRNA) profiles. Twelve mares were blocked by weight and BCS and assigned to one of two treatments (6 hd/treatment): 1) control, (basal diet: 9 Kg/hd/d of chopped mixed grass hay and ad libitum mixed grass hay), 2) basal diet supplemented with 454 g/d steam flaked corn individually using feed bags. All mares were placed on the basal diet and in the same pen 14 days prior to the beginning of corn supplementation. Mares were weighed and BCS on d -7 and 28. Muscle biopsies of the gluteus medius were taken from all horses on d0 and d26. Muscle samples were analyzed using real time RT-qPCR for 277 endogenous miRNAs. Raw CT values were normalized with the geometric mean of three consistently appearing endogenous miRNAs. Sixteen miRNAs that consistently appeared in at least 8 horses including 3 relating to metabolic disorders appearing at d0, d26, or both were analyzed. Differential abundances of miRNAs using log transformed fold change and differences between BW and BCS of treatment groups were determined by ANOVA and LS means analysis. There was no difference between BW (P < .05) and BCS (P < .05) between the two treatment groups. Feeding corn lead to higher quantities (P < .05) of mir 133a, 1515p, 6155p, 770, and 99b within muscle compared to control group. Lower quantities of mir 382 and 433 were found within muscle of horses fed corn compared to the control group (P < .05). Based upon the results of this study corn supplementation appears to influence endogenous miRNA expression profiles within muscle of horses.

A stress-induced response complex (SIRC) shuttles miRNAs, siRNAs, and oligonucleotides to the nucleus

Although some information is available for specific subsets of miRNAs and several factors have been shown to bind oligonucleotides (ONs), no general transport mechanism for these molecules has been identified to date. In this work, we demonstrate that the nuclear transport of ONs, siRNAs, and miRNAs responds to cellular stress. Furthermore, we have identified a stress-induced response complex (SIRC), which includes Ago-1 and Ago-2 in addition to the transcription and splicing regulators YB1, CTCF, FUS, Smad1, Smad3, and Smad4. The SIRC transports endogenous miRNAs, siRNAs, and ONs to the nucleus. We show that cellular stress can significantly increase ON- or siRNA-directed splicing switch events and endogenous miRNA targeting of nuclear RNAs.

Assessment of six commercial plasma small RNA isolation kits using qRT-PCR and electrophoretic separation: higher recovery of microRNA following ultracentrifugation

Growing interest in blood-borne microRNAs (miRNAs) as biomarkers has led to the introduction of a number of commercial kits for isolating small RNAs from plasma/serum. We sought to compare the efficacy of six such kits in isolating miRNAs from either whole plasma or a plasma-derived ultracentrifugation (UC) fraction from 2 healthy volunteers with some of the results being validated in 10 additional subjects. To assess the overall yield and concentration of isolated small RNAs, we measured the levels of one spiked-in and four endogenous miRNAs by quantitative reverse transcription and polymerase chain reaction (qRT-PCR). We also tested the performance of the Agilent Bioanalyzer small RNA assay with these RNA samples. Additionally, we tested the effects of hemolysis on measured miRNA levels in whole plasma and in the UC fraction. Both the efficiency of RNA isolation and the relative levels of specific miRNAs in different samples varied considerably between the tested extraction methods. Of all kits tested, the QIAGEN miRNeasy kits (Mini and Serum/Plasma kits) and the Macherey-Nagel NucleoSpin kit produced the highest RNA yields. The QIAGEN Exo kit produced lesser yields than what could be extracted from the UC fraction using the QIAGEN miRNeasy kits and the Macherey-Nagel NucleoSpin kit. Bioanalyzer results showed an average correlation of R2 = 0.8 with endogenous miRNA qRT-PCR results, for sample concentrations >40 pg/µl. The levels of the endogenous miRNAs measured in the two volunteer samples were compared with those in a larger group of subjects (n = 10) and found to be typical. Our comparison favors the use of the QIAGEN Serum/Plasma kit and the Macherey-Nagel NucleoSpin kit for plasma miRNA applications. Furthermore, extraction of miRNAs from the UC fraction results in higher yield than extraction from whole plasma.