Although we do not have direct experience in isolating RNA from serum, I am aware that RNA can be routinely isolated using TRIzol for subsequent expression analysis etc. Search in PubMed.

There is a variety of commercial kits out there that is designed for this. I.e. Norgen Biotek offers a wide range (depending on sample volume etc.) of kits. We have successfully sequenced samples that were extracted this way.

http://www.norgenbiotek.com/product-category-list-blood-plasma-serum-sample-preparation-kits.php

I have tried a few different protocols, and the one I like most begins with a Trizol LS isolation then moves to using the mirVANA kit once the phases are seperated (after addition of chloroform) and absolute ethanol has been added to the aqueous phase. There are several procedures in PubMed, Chim et al have publisned one using plasma and Chen et al have published another using serum. I know of colleagues that have also successfully used this same modified procedure but have used the miRNeasy kit instead of the mirVANA kit, with similar success. I have used this successfully with the ABI Rodent MicroRNA TLDA cards (with PreAmp).

Does anyone know the minimal amount of serum that is required to get a reliable profile? We obtained with a first test sample about 80,000 reads that mapped to known miRNAs starting with 0.5ug of serum RNA. For all other non-serum samples this was more than 1 or 2 miljon. Also many reads of the serum sample were shorter than 18 nucleotides suggesting degradation.

If you want to avoid inhibitors for RT-PCR, the silica particles work very well, ref http://www.ncbi.nlm.nih.gov/pubmed/7529243 (like in trizol-Plus from life techno).

If you used the classical phenol/chloroform technique, replace chloroform by isochloropropan for a better separation of the phase.

We used mirvana kits without the enrichment for miRNAs. Will you do the NGS? Majority of the protocols have enrichment step and size selection so it should be ok.

You may want to use an optimized protocols for RNA isolation from samples which have both with high protein content and low amount of RNA (e.g. plasma, serum and other body fluids) . First it is crucial to monitor the efficiency of miRNA isolation (e.g. using synthetic spiked-in miRNA controls). Secondly, you have to ensure an efficient and complete denaturation of nucleoprotein complexes when isolating miRNA from liquid protein-rich samples. Finally and most importantly, you should use co-precipitants which increase miRNA recovery. Our experience indicates that the efficacy of miRNA isolation from plasma and serum is about 5-10 times lower when no co-precipitate is added during isolation and when sub-optimal amount of the denaturing agent (Trizol) is used. Please have a look on our recent paper where the protocol is described more thoroughly - [Turchinovich et al, 2011, Nuc. Acid Res]. Good luck!

I have recently used mirvana kit for total RNA isolation from tissue samples. Previously, I had used TRIZOL and obtained upto 12ug total from 3mg tissue samples when dissolved in 30ul water. Now for some reasons, I have to switch to kit. However, with mirvana kit, I am unable to get more than 5ug from 3mg tissue. Another issue is that when I homogenize tissue in mirvana kit lysis solution, there is lot of foam formation which doesn't' happen in case of TRIZOL. Could anyone kindly explain this? Any possible modification or step for the improvement of RNA yield when using mirvana kit?

The foam formation is just because of detergents that have been employed in lysis solutions to dissociate the proteins from plasma membrane (just to break down the membrane) and concentration can be increased by optimization of the tissue quantity and RNA concentration and can also be increased by simply using a lesser amount of water than usual for final elution.

hey every one! i use TRIzol LS for serum miRNA isolation and it works! but i wonder if a proteinase K treatment could enhance the RNA yield. i know it is a necessary step when working on FFPE samples but i have no idea of PK treatment before starting isolation procedure on serum samples.