Presence of Filterable and Nonfilterable mRNA in the Plasma of Cancer Patients and Healthy Individuals

As RNA is labile, we investigated whether circulating RNA in human plasma may be present in a particle-associated form. Blood was collected from 27 healthy individuals and 16 hepatocellular carcinoma (HCC) patients. The plasma from each individual was processed by two means: filtration through filters with different pore sizes (from 5 microm to 0.22 microm) and ultracentrifugation. We assessed plasma RNA content by a real-time quantitative reverse transcription-PCR assay for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) transcripts and plasma DNA by a real-time quantitative PCR assay for the beta-globin gene. The plasma GAPDH mRNA concentrations in the healthy individuals were significantly different in every pair of these filter sizes (P