Probing Glioblastoma Tissue Heterogeneity with Laser Capture Microdissection

Among various methods now available to isolate distinct cell populations or even single cells for DNA/RNA and proteomic analysis, laser capture microdissection (LCM) offers a unique opportunity to study cells in their topological contexts. This chapter focuses on the preparation of LCM membrane slides, tissue staining and laser microdissection of cells of interest from frozen or formalin-fixed, paraffin-embedded glioblastoma tissue.

Pre-storage centrifugation conditions have significant impact on measured microRNA levels in biobanked EDTA plasma samples

BACKGROUND

In the past few years, an increasing number of studies have reported the potential use of microRNAs (miRNA) as circulating biomarkers for diagnosis or prognosis of a wide variety of diseases. There is, however, a lack of reproducibility between studies. Due to the high miRNA content in platelets this may partly be explained by residual platelets in the plasma samples used. When collecting fresh plasma samples, it is possible to produce cell-free/platelet-poor plasma by centrifugation. In this study, we systematically investigated whether biobanked EDTA plasma samples could be processed to be suitable for miRNA analysis.

MATERIALS AND METHODS

Blood samples were collected from ten healthy volunteers and centrifuged to produce platelet-poor-plasma (PPP) and standard biobank plasma. After one week at -80 °C the biobanked EDTA plasma was re-centrifuged by different steps to remove residual platelets. Using RT-qPCR the levels of 14 miRNAs in the different plasma preparations were compared to that of PPP.

RESULTS

We were able to remove residual platelets from biobanked EDTA plasma by re-centrifugation of the thawed samples. Nevertheless, for most of the investigated miRNAs, the miRNA level was significantly higher in the re-centrifuged biobanked plasma compared to PPP, even when the platelet count was reduced to 0-1×109/L.

CONCLUSION

We found, that pre-storage centrifugation conditions have a significant impact on the measured EDTA plasma level of miRNAs known to be present in platelets. Even for the miRNAs found to be less effected, we showed that a 1.5-3 fold change in plasma levels may possible be caused by or easily overseen due to sample preparation and/or storage.

Which sample tube should be used for routine glucose determination?

BACKGROUND

Glucose is one of the most frequently requested analytes in clinical laboratory. Blood glucose analysis is affected from in vitro glycolysis. In order to determine the most suitable blood collection tube for this purpose we have compared different tubes: sodium fluoride, lithium heparin, sodium fluoride/citrate buffer containing tubes and serum with clot activator tube for the measurement of glucose when the tube has been kept at room temperature (RT) for up to 4h.

METHODS

Venous blood was collected from 49 healthy volunteers into Sarstedt S-Monovettes for glucose analysis. Reference plasma glucose was determined in a lithium heparin tube and immediately placed in an ice/water slurry. Within 10min it was centrifuged at 4°C and plasma was separated from the blood cells. Samples have been preserved at RT for 1, 2 and 4h after drawing. Glucose has been determined using a hexokinase method.

RESULTS

Glucose levels tested in a serum with clot activator tube, in lithium heparin and in sodium fluoride/sodium EDTA tubes when compared with lithium-heparin reference plasma did not meet the desirable bias for glucose (±1.8%) when kept at RT for up to 4h. GlucoEXACT tubes, when corrected by the Sarsted recommended factor of 1.16, showed a mean (95% CI) bias of +0.96% (0.45-1.47) at 1h, +1.40% (0.88-1.93) at 2h and +0.95% (0.44-1.46) at 4h, reaching the analytical goal for the desirable bias.

CONCLUSIONS

Samples collected into GlucoEXACT tubes containing sodium fluoride/citrate buffer liquid mixture are equivalent to those collected in reference plasma tubes avoiding glycolysis completely and within a 4h delay in plasma separation.

The shift from fluoride/oxalate to acid citrate/fluoride blood collection tubes for glucose testing - the impact upon patient results

OBJECTIVES

To ascertain whether or not the change in blood collection tubes for plasma glucose from fluoride/oxalate to citrate/fluoride/EDTA has had an effect upon the glucose results.

METHODS

Plasma glucose results from fasting patients from 2007 to 2012 were extracted from the laboratory information system. The data was evaluated in order to see the potential impact on patient results due to the change in glucose stabilizer implemented in September 2010.

RESULTS

The mean glucose result was increased by approximately 14% (difference: +0.80mmol/L) after the implementation of the citrate-buffered tubes (mean value=6.45mmol/L; n=15125) as compared to fluoride/oxalate tubes (mean value=5.65mmol/L; n=15867).

CONCLUSIONS

An increase in glucose results is seen after changing to citrate-buffered tubes due to the improved stabilizing effect as compared to fluoride. Properly collected blood samples will lead to the patient being correctly diagnosed. However, decision limits and reference intervals for glucose may need to be revised using citrate-tubes.